THE GEOLOGY OP THE MERCUR GOLD CAMP, UTAH

b y

E d w i n M i c h a e l G u e n t h e r

A t h e s i s s u b m i t t e d t o t h e f a c u l t y o f t h e U n i v e r s i t y o f U t a h i n p a r t i a l f u l f i l l m e n t o f t h e r e q u i r e m e n t s

f o r t h e d e g r e e o f

M a s t e r o f S c i e n c e

i n

E c o n o m i c G e o l o g y

D e p a r t m e n t o f G e o l o g i c a l a n d G e o p h y s i c a l S c i e n c e s

U n i v e r s i t y o f U t a h

J u n e 1 9 7 3

THI! GEOLOGY OF THI! MERCUR GOLD CAMP. UTAH

by

Edwin Michael Guenther

A thesis s ubmitted to the faculty of the Universlty of Utah in partial fulfIllment of the requirements

for the degree of

Master of SOience

in

Economic Geology

Department of GeologIcal and Geophysical SCiences

Univers lty of Utah

June 1973

THE GEOLOGY OF THE MERCUR GOLD CAMP, UTAH

b y

E d w i n M i c h a e l G u e n t h e r

C o p y r i g h t © 1 9 7 3 E d w i n M i c h a e l G u e n t h e r

No p a r t o f t h i s b o o k m a y b e r e p r o d u c e d b y a n y m e c h a n i c a l , p h o t o g r a p h i c , o r e l e c t r o n i c p r o c e s s f o r p u b l i c o r p r i v a t e u s e w i t h o u t w r i t t e n p e r m i s s i o n f r o m t h e a u t h o r .

THE GEOLOGY OF THE MERCUR GOLD CAMP, UTAH

by

Edwin Michael Guenther

cOPyright~1973 Edwin Michael Guenther

No pa rt of this book may be reproduced by any mechan ical , photographic. or electronic process for public or priva te use without written permission from the autho r .

This thesis for the

Master of Scienoe Degree

by

EdN1n n.lchael Guenther

UNIVERSITY OF UTAH LIBRARIES

AC KNO iJU: LG 11E NT S

The fol1cHing thesis �ms originated, researched.

arid I=0.1d for by the author. 1'he author was hindered in

h1s re��8:'cl, effr)Tts by 'i:he lack of availabl1i ty of

instruments and the lack of funds.

I would lite to the.nk Dre M.L. Jensen, Dro .. T . H .

Goodwin, and Prof. M.P. Erickson for critically reading

the manuscript and making suggestions for improving it.

I would also like to thank Dr. M.L • . Jensen for letting

the author conduct som� sulfur isotope analyses and

making constructive criticisMS on ln�erpretatlon of the

sulfur isotope data. I would l�ke to thank the U.S.

Bureau of Mines for some carbon assays of samples. The

author who has worked with Great Northern Re sou rc e

Development would like to thank them for graclcusly

allowlL� the gratuitous publication of information

valued at $275.000 in this thesis at the University of

Utahe Pursuant to the wishes of Great Northern Resource

Development the author is unfortunately restl'1cted

from present1ng all observat1ons or conclusions that

were reached d.uring the investigation of th0 area.

,

CONTENTS

P a g e

A b s t r a c t . . . • . . • • .X

I n t r o d u c t i o n . . 1

A . G e o l o g i c M a p p i n g . . 2

L • I/O C L l u i O » » 4 « * t » f i « « » » « # » » » t « » i » » # # » « » » » « « e » » J ;

C . A n a l y t i c a l P r o c e d u r e s » , . 3

D . B r i e f H i s t o r y o f M i n i n g A c t i v i t i e s

i n t h e A r e a . 5

S t r a t i g r a p h y . *9

S t r u c t u r e

A , B r e c c i a P i p e s . , , . s . . l 6

B . J o i n t P a t t e r n s . . . . 1 9

I n t r u s i v e H o c k s • . . . . . 2 4

A . K e r s a n t i t e . . . . . . . . . . . . . . . . . . 2 4

B . B i r d ' s - e y e P o r p h y r y . . . . . . 2 4

C , E a g l e H i l l R h y o l i t e 0 2 5

1 . S t r u c t u r a l R e l a t i o n s • 2 6

2 . P e t r o l o g y , 2 8

A l t e r a t i o n o f t h e S e d i m e n t a r y R o c k s . . . . . . . . . . . . . . 3 1

A . S i 1 v e r L e d g e • « • • • • • • • • . . . 3 2

B . G o l d L e d g e . 3 6

C • W e a t h e r i n g * . . . . • • • • • • • • • . • • • • . . . . • 4 0

CONTENTS

Page

A bs tr9.c t •. Co •••• A ••••••••••••••••••• ., •••••••••• CII .... x

IntroGuct:lr.n. 1 _ • • • • • • • • • • • • • • • • • e , • • • • • • • • • ~ • • • e ~

A. Geologie • eo. • • • ~ • • ~ • • • ~ • • • • • • ~ • • .2

B. I/oc·9.tlon ••••••••••••• ~ •••••••••• " ••••••••• 3

c. Analytje.al Procedures. . . . . ~ . . . . . . . . . . . . . ~ .3

D. Brief History of Mining Activities

in the i_rea ............•.•....•..........• 5

Stratigra.phy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . •• 9

Structure ••.••••••••••••••••••• < •••••••••••• ~ •••• 12

Breccia Pipes •• . . . . . . . . . . . . . . . . . . . . . . . ~ . .16

D. Joint Patterns. . . . . . . . . . . . . . . . . . . . . . . . . . • 19

Intrusiva Rocks ••• • • • • • • • • • • • ~ • • • • • • • • c • • • • • • • • • • 24

Kersantite • • • • • • • • • • • • ~ • • • • • • • • • • • Q - • • • • .. 24

B. Bird's-eye Porphyry. . ~ . . . . . . . . . . . . . . . . ~ . .. 24

c. Eagle Hill Rhyolite ••••• · . ~ . . . . . . . . . . ~ ~ . 1 • f)truc tural Rela.tions. · . . . . . ~ . . . . . . . . . • 26

2" Pe t 1'0 loe;y •••••••••••• · . . . . . . . . . . . . . . . • 28

Altera.tion of the Sedimentary Rocks. • • • • • • • • • • • 0 • )1

A. Ledge. o « 0 • • • • • • • • • • • • 0 • • • • • • • • • • • .)2

B. Gold Ledge. e _ • • • • • • • • • • • • • • • • • • • ~ • • • • • • • • )6

c. • • ~ • • • • • • • ~ • • • ~ c ~ ~ ~ • • • • _ • . . • 40

P a g e

A l t e r a t i o n o f t h e E a g l e H i l l I n t r u s i v e • . . , . . 4 3

T h e G o l d D s p o s i t s . . . . . . . 4 8

E l e m e n t a l A n a l y s e s o f R o c k S a m p l e s 5 ^

I m p l i c a t i o n s o f C a r b o n a n d O r g a n i c C o m p o u n d s . . . . . 5 6

S u l f u r I s o t o p i c D a t a . . « . > . » • • • . • • • • • • • • • • . 6 3

S u m m a r y a n d R e c o m m e n d a t i o n s , „ . * . . • • 7 3

S e l e c t e d R e f e r e n c e s • • • . • • • • • • • • • • • • • • • • • . • » 7 6

V i t a , . . . . 8 0

v i

PClge

.t.,lt;er::;.tion of the E~Lc;le lUll Intrusi~e •....... ... 4)

Tt~·: Golfl :;3r.l;slts ................... oe~ •• c ••••• 9 ••• 48

Elemental Analyses of Reck Samples ••• o.~ ••• # ••••• 52

IL.pllcations of C8:z.'bon Si.i1G. Organic Co~poun~3 ..... 056

StL!.fur Da.ta- ••• Oq ....

Su:nmary and Reco7!llnend8tions.

• • • • • • h • • • • • • 0 ~ • ~ • • ... 63

.73 ~ . ~ . • • . . . . . . . . . . . .6. Selected References •••••••••••••••••••••••••••••• 76

V 1 ta .... e ........ It •• f' •• 0, •••• & • II , • o!# •••••••• ~ ....... 19 .80

vi

ILLUSTRATIONS

P a g e

F i g u r e 1 . — I n d e x m a p s h o w i n g l o c a t i o n o f

l i s j u i i r j U t a n • • • . • • . • • • . . * • . • • • . • . . , • - • - • • . * • #4

2 , — V i e w o f H e r c u r f r o m E a g l e H i l l . . . . . . . . . 6

3 . . — V i « w o f M e r c u r f r o m S u n r i s e H i l l . , 6

4 . — G e o l o g i c m a p o f M e r c u r , U t a h . . . . 1 3

5 . — C o l l a p s e b r e c c i a G e y s e r - M a r i o n m i n e . , , 1 6

6 , — - S a c r a m e n t o m i n e v i e w . . . . . . . 1 ?

? . — C l o s e - u p o f b r e c c i a . . « , . . . . 1 ?

8 , - - C o n t o u r d i a g r a m o f j o i n t d i s t r i b u t i o n , 2 0

9 . — P l o t o f s t r i k e d i r e c t i o n s * * . , , 2 1

1 0 , — P l o t o f f a u l t s t r i k e d i r e c t i o n s 2 1

1 1 * — I n d e x m a p o f i g n e o u s r o c k s l o c a t i o n . • . 2 5

1 2 . - ~ C l o s e » u p o f M e r c u r j a s p e r o i d t y p e s . . . . 3 4

1 3 . — P h o t o m i c r o g r a p h o f a n h e d r a l j a s p e r o i d , 3 5

1 4 . - - P h o t o m i c r o g r a p h o f t y p i c a l j a s p e r o l d . . 3 5

1 5 . — P h o t o m i c r o g r a p h o f g o l d o r e s e q u e n c e . . 3 9

1 6 . — P h o t o s h o w i n g r e l a t i o n s h i p s b e t w e e n

w e a t h e r e d a n d u n w e a t h e r e d o r e . , . » . , « , . , 4 2

ILLUSTaAT IO~JS

P.s.ge

Figure 1.--In1ez ~ap showing lecation of

1-19j'·8ur:- Uta:l •. ., ........ o. $. (t a" ••• & W 9 •••• 4

2o--View of Mercur from Eagle Hlll ••••••••• 6

3. --V_,~.··.··.T of· ~.A_rcu·.-.~. f-o~ Sun~{~· q4J~1 6 _ • 1 ~ ..1.. ~.AU .... ..4. .. )0 '_ ...... ..l.. ~. .., •••••

4.--Geologlc map of Mercur. Utah •••••••••• 13

5.--Collapsb breccia Geyder-Marion mine ••• 16

6 .. --Sacr&mento mine v~.e~l ••••••••••••••••• e17

7c--Close~up of brece1a •••••••••••••• 9 •••• 17

8.--Contour diagram of Joint distribution.20

9.--Plot of strike dlrec~~ons ••••• Q ••• ~.~.21

10.--Plot of fault strike d1rections ••••••• 21

11~ao~Index map of 19neous rocks lccation .... 25

12.--Close-up of Nereur j3spero1d types~ ••• 34

13~--Photo~lcrograph of anhedral jasperoid.35

14.--Photomlcrograph of typ1cal jasperoid •• 35

15.--Photomlcrcgraph of gold ore sequence •• 39

l6.--·Photo showJ.ng relationshtps between

weathered and unweathered ore ••••••••• 42

P a g e

F i g u r e 1 9 . - - I n f r a r e d s p e c t r a o f NaOH o r g a n i c

e x t r a c t i o n s * • . . . . . . . . . . . • . 6 0

2 0 I n f r a r e d s p e c t r a o f NH^Ac o r g a n i c

e x t r a c t i o n s - 6 1

2 1 . — M a p s h o w i n g s u l f u r i s o t o p e s a m p l e

c o l l e c t i o n s i t e s , t . . . . . . . . 6 5

2 2 . — R e a c t i o n s i n a f u m a r o l i c c o n d u i t . . . . * 6 8

v i i l

Page

Fi gure 19 .--Infra r ed ::;pectra of taOH organ ic

extract1ons • • •• • ••••••• ~ • • • c •••• • •• •• 60

20 .--Infrared spect r a of NH4AC organic

ex t r o.c ti ons •. •••• •• ••••.••• • •••••• ••• 61

21. --Nap showing s ulfur i sotope s umple

collec t1on s1tes • . •• •• •• •• •• 8 • • ••• • •• 6S

22.--Reac tions in a fumarollc conduit ... . .. 68

"1111

TABLES

P a g e

1 . A t o m i c a b s o r p t i o n v a l u e s 4 5

2 . Q u a l i t a t i v e e m i s s i o n s p e c t r o g r a p h s a n a l y s e s . . 5 3

3 * S e m i - q u a n t i t a t i v e e m i s s i o n s p e c t r o g r a p h l c

a n a l y s e s . . A . . . . . . . . . . . . . . . * . . . . . . . . . * . . * . . » . . . » 5^*

4 . S u l f u r i s o t o p i c d a t a . . 6 6

»

TAELES

Page

1. At o51ic llbso rptlon val ues •• • ••••••••••••••••••• 45

2. Qualitative em i ssion spectrogr aphic ar~lyses •• 5J

3. Seml -qu~ntltatlve emission spectrog raphic

a nalyses ......... .. .... . ~ .... .. . ... ... 0 " ..................... . 54

4. Sulfur i s otopic data •••••••. • •• •• •••••••• • •••• 66

ABSTRACT

The g o l d d e p o s i t s a t M e r c u r , U t a h , a r e t y p i c a l

e p i t h e r m a l d e p o s i t s . O r e d e p o s i t i o n p r o b a b l y o c c u r r e d

a t d e p t h s o f 1 , Q 0 0 f e e t o r l e s s w i t h l o w t e m p e r a t u r e s O Q

r a n g i n g f r o m 2 0 0 + t o 1 0 0 0 , T h e m o s t p r o m i n e n t t y p e

o f m e t a s o m a t i s m a s s o c i a t e d w i t h t h e g o l d d e p o s i t s i s

s i l i c i f i c a t l o n a c c o m p a n i e d b y s e r i c i t i z a t l o n . S u l f u r

i s o t o p i c d a t a f o r t h e d e p o s i t s h a v e a m e a n v a l u e o f

o f + 7 . 9 p e r m i l a n d h a v e a s p r e a d o f v a l u e s w h i c h c o r r e l a t e

w i t h s u l f u r i s o t o p i c d a t a f o r h o t s p r i n g d e p o s i t s .

M e r c u r i s o f i n t e r e s t s t r u c t u r a l l y b e c a u s e o f t h e

o c c u r r e n c e o f t w o b r e c c e a p i p e s b e l i e v e d t o h a v e

o r i g i n a t e d a s e x p l o s i v e e v e n t s .

O r g a n i c e x t r a c t i o n a n d a n a l y s i s b y i n f r a r e d

s p e c t r o s c o p y o f c a r b o n - r i c h s a m p l e s f r o m M e r c u r , U t a h ,

a n d C a r l i n a n d G e t c h e l l M i n e , N e v a d a , s h o w t h e p r e s e n c e

o f a l k a n e a n d c a r b o n y l g r o u p s . T h e c a r b o n p r e s e n t i n

a l l t h r e e a r e a s i s b e l i e v e d t o b e t h e r e s u l t o f

r e d u c t i o n o f h y d r o c a r b o n s t o c a r b o n b y t h e c h e m i c a l

c o n d i t i o n s t h a t o n c e e x i s t e d i n t h e h y d r o t h e r m a l a r e a s .

'\

ABSTRACT

The gold teposits at M~rcur, Utah, ar~ typical

epithermal deposits. Ore deposition proba"oly occurred

at d,..;pths 0;.' 1.000 feet or less with low terr:p~ratures

.... 0 0 r ranging fran ~OO + to 100 C. 'he most prominent type

of metasomatism associated with the gold deposits 1s

siliclfic~tion accompanied by sericitization. Sulfur

isotopic d9.t-a fOT the deposits ha.ve a. mean value of <5 s31•

of +7.9 permil and have a spread of values which cOl'relates

with sulfv.r isotopic data for hct; spring deposits.

lJlercur 1s of interest struc{;urally b~cause of the

occurre!me of two breccea pipsE believed to have

originated as explosive events.

Org~nic extraction a.nd analysis by infra.red

spectroscopy of carbon-rich samples from Mercur, Utah,

and Carlirl and Getchell Mine, Nevada, shDw the preset'!ce

of alkane and carbonyl groups. The carbon present in

all three areas is believed to be the result of

reduction of hydrocarbons to carbon by the chemical

conditions that once existed in the hydrot.hermaJ. areas.

INTRODUCTION

T h e f i r s t c o m p r e h e n s i v e w o r k o n t h e M e r c u r a r e a

w a s d o n e b y S p u r r ( 1 8 9 4 - 9 5 ) w h e n t h e d i s t r i c t w a s s t i l l

i n i t s i n f a n c y a s a g o l d p r o d u c e r . T h e a u t h o r i s

i n d e b t e d t o h i s d e s c r i p t i o n s o f t h e m i n e l o c a t i o n s ,

w o r k i n g s , a n d g e o l o g i c s e t t i n g s — e s p e c i a l l y r e g a r d i n g

t h e p r e s e n c e o f c a r b o n , S p u r r a l s o g a v e t h e f i r s t

d e t a i l e d a c c o u n t o f t h e h y d r o t h e r m a l a l t e r a t i o n o f t h e

b e d r o c k a s s o c i a t e d w i t h t h e d e p o s i t s . Some o f h i s

i n t e r p r e t a t i o n s a s t o a l t e r a t i o n w e r e l a t e r d i s c r e d i t e d

b y B u t l e r ( 1 9 2 0 , p , 3 9 0 ) who f o u n d t h a t w h a t S p u r r h a d

c a l l e d a l t e r e d i n t r u s i v e s i l l s w e r e i n r e a l i t y a l t e r e d

l i m e s t o n e o r s h a l e l a y e r s .

T h e f i r s t c o m p r e h e n s i v e s t u d y o f t h e g e o l o g y

a n d o r e d e p o s i t s o f t h e s o u t h e r n O q u i r r h M o u n t a i n s w a s

d o n e b y G i l l u l y ( 1 9 3 2 ) d u r i n g t h e s u m m e r s o f 1 9 2 6

a n d 1 9 2 7 , b u t h e d i d n o t d o a d e t a i l e d s t u d y o f t h e

o r e d e p o s i t s o f t h e M e r c u r a r e a b e c a u s e h e s t a t e s

t h a t t h e m i n e s w e r e i n a c c e s s i b l e a t t h e t i m e o f h i s

I n v e s t i g a t i o n . H i s d i s c u s s i o n o f t h e a l t e r a t i o n o f t h e

i g n e o u s r o c k s a n d o f t h e s e d i m e n t a r y r o c k s o f t h e a r e a

h a s b e e n m o s t h e l p f u l t o t h e a u t h o r i n d e l i n e a t i n g

w h a t h a d b e e n d o n e i n t h i s a r e a .

R i g b y a n d B i s s e l l ( 1 9 5 9 ) o f B r i g h a m Y o u n g U n i v e r s i t y

w e r e t h e n e x t i n v e s t i g a t o r s t o c o n d u c t r e s e a r c h i n t h e

INTRODUCTION

The first comprehensive work on the Mercur area

was done by Spurr (1894-95) when the district was still

in its infancy as a gold producer. The author is

indebted to his descriptions of the mine locations,

workings, and ~eologic settings--especially reg~rding

the presence of carbon. Spurr also gave the first

detailed account of the hydrothermal alteration of the

bedrock associated with the deposits. Some of his

interpretations as to alteration were later discredited

by Butler (1920, p. 390) who found that what Spurr had

called altered intrusive sills were in reality altered

limestone or shale layers.

The first comprehensive study of the geology

and ore deposits of the southern Oquirrh Mountains was

done by Gilluly (1932) during the summers of 1926

qnd 1927. but he did not do a detailed study of the

ore deposits of the Mercur area because he states

that the mines were inaccessible at the time of his

investigation. His discussion of the alteration of the

igneous rocks and of the sedimentary rocks of the area

has been most helpful to the author in delineating

what had been done in this area.

Rigby and Bissell (1959) of Brigham Young University

were the next investigators to conduct research in the

2

a r e a . I n 1 9 5 5 • t h e y s u p e r v i s e d a g e o l o g i c s u m m e r f i e l d

c a m p d u r i n g w h i c h t h e a r e a w a s r e m a p p e d a t a s c a l e o f

1 : 1 2 , 0 0 0 f o r t h e f i r s t t i m e s i n c e G i l l u l y ( 1 9 3 2 ) h a d

m a p p e d t h e a r e a . T h e l a t t e r 1 s m a p w a s m a d e b y p l a n e t a b l e

a n d o p e n - s i g h t a l i d a d e o n a t o p o g r a p h i c b - i s e w i t h a

s c a l e o f 1 : 3 1 , 2 5 0 ( G i l l u l y , 1 9 3 2 , p . 4 ) . T h e a u t h o r ,

d u r i n g a r e c o n n a i s a n c e e x a m i n a t i o n o f t h e a r e a i n t h e

s u m m e r o f 1 9 7 1 » o b s e r v e d s u f f i c i e n t p r e v i o u s l y o v e r l o o k e d

s t r u c t u r a l f e a t u r e s , a l t e r a t i o n p a t t e r n s , a n d s t r a t i g r a p h i c

f i e l d r e l a t i o n s w h i c h , b e c a u s e o f t h e i r i m p o r t a n c e t o t h e

e c o n o m i c g e o l o g y o f t h e a r e a , l e d t h e a u t h o r t o u n d e r t a k e

t h i s s t u d y .

G e o l o g i c M a p p i n g

G e o l o g i c m a p p i n g o f t h e M e r c u r a r e a a t a s c a l e

o f 1 : 6 , 0 0 0 w a s u n d e r t a k e n b y t h e a u t h o r d u r i n g t h e

s u m m e r 1 9 7 2 . T h e g e o l o g y w a s p l o t t e d on. a t o p o g r a p h i c

b a s e m a p w h i c h w a s m a d e b y p h o t o g r a p h i c a l l y e n l a r g i n g

t h e U . S . G e o l o g i c a l S u r v e y ' s M e r c u r , U t a h , 1 5 m i n u t e

t o p o g r a p h i c q u a d r a n g l e . A e r i a l p h o t o g r a p h s w e r e u s e d f o r

p r e l i m i n a r y s t u d y o f t h e a r e a . T h e s c a l e o f t h e i n c l u d e d

g e o l o g i c m a p ( F i g . 4 ) w a s d e c r e a s e d f r o m t h e o r i g i n a l

t o r e d u c e t h e c o s t o f d u p l i c a t i o n ,

S i l i c i f i c a t i o n i n t h e g o l d o r e s e q u e n c e w a s n o t

m a p p e d b e c a u s e o f t h e d i f f i c u l t y o f t r a c i n g t h e

2

~rea. In 1955. they supervised a geologie summer field

c~mp during which the area w~s remapped at a scale of

1:12.000 for the first time since Gilluly (1932) had

mapped the area. The latter's map was made by plane table

qnd open-sight alidade on a topographic b'lse wi th A

scale of 1:31.250 (Gilluly. 1932. p. 4). The author,

during a reconnaisance examination of the ~rea in the

summer of 1971. observed sufficient previously overlooked

structural features, alteration patterns, and stratigraphic

field relations which, because of their importance to the

economic geology of the area. led the author to undertake

this study.

Geologic Mapping

Geologic mapping of the Mercur area at a scale

of 1:6,000 was undertaken by the author during the

summer 1972. The geology was plotted on a topographic

base map which was made by photographically enlarging

the U.S. Geological Survey's Mercur, Ut~h. 15 minute

topographic quadrangle.

preliminary study of the

Aerial photographs were used for

area. The scale of the included

geologic map (Fig. 4) was decreased from the original

to reduce the cost of duplication.

Silicification in the gold ore sequence was not

mapped because of the difficulty of tracing the

3

a l t e r a t i o n z o n e s , J a s p e r o i d w a s m a p p e d b e c a u s e i t

r e p r e s e n t e d e a s i l y m a p a b l e a r e a s .

L o c a t i o n

M e r c u r , U t a h , i s l o c a t e d a t t h e h e a d o f M e r c u r

C a n y o n ( f o r m e r l y L e w i s t o n C a n y o n ) i n t h e s o u t h e r n

p a r t o f t h e O q u i r r h M o u n t a i n s a b o u t 7 0 m i l e s b y r o a d

s o u t h e a s t o f S a l t L a k e C i t y ( F i g . 1 ) .

T h e t e r r a i n o f t h e s u r r o u n d i n g h i l l s i s o n e o f

m o d e r a t e r e l i e f . T h e m a x i m u m r e l i e f b e t w e e n t h e

g h o s t t o w n o f M e r c u r a n d E a g l e H i l l i s a b o u t 1 , 3 0 0 f e e t .

A n a l y t i c a l P r o c e d u r e s

T h e a u t h o r , d u r i n g t h e c o u r s e o f t h e p r e s e n t

i n v e s t i g a t i o n , u s e d s e v e r a l i n s t r u m e n t a l t e c h n i q u e s

t o g a i n i n f o r m a t i o n n e e d e d t o s o l v e t h e g e o l o g i c p r o b l e m s .

X - r a y d i f f r a c t i o n a n d f l u o r e s c e n c e t e c h n i q u e s w e r e u s e d

f o r m i n e r a l d e t e r m i n a t i o n s . A t o m i c a b s o r p t i o n a n d

e m i s s i o n s p e c t r o s c o p y t e c h n i q u e s w e r e u s e d f o r e l e m e n t a l

d e t e r m i n a t i o n s . I n f r a r e d s p e c t r o s c o p i c a n d g a s

c h r o m a t o g r a p h i c t e c h n i q u e s w e r e a p p l i e d t o t h e p r o b l e m

o f o r g a n i c i d e n t i f i c a t i o n o f c a r b o n a c e o u s s a m p l e s .

S e v e r a l p o l i s h e d s e c t i o n s w e r e p r e p a r e d f o r s t u d y

o f t h e o p a q u e m i n e r a l s o f t h e o r e s e q u e n c e . T h i n s e c t i o n

s t u d i e s w e r e u n d e r t a k e n t o e x a m i n e t h e m i n e r a l s u i t e

p r e s e n t , f o r r o c k i d e n t i f i c a t i o n , a n d f o r s t u d y o f

alteration zones. Jasperoid was mapped because it

represented easily mapable areas.

Location

Mercur, Utah, is loc~ted at the head of Mercur

Canyon (formerly Lewiston Canyon) in the southern

part of the Oquirrh Mountains about 70 miles by road

southe'-lst of Salt Lake City (Fig. 1).

The terrain of the surrounding hills is one of

moderate relief. The maximum relief between the

)

ghost town of Mercur and Eagle Hill is about 1,)00 feet.

Analytical Procedures

The author, during the course of the present

investigation, used several instrumental techniques

to gain information needed to solve the geologic problems.

X-ray diffraction and fluorescence techniques were used

for mineral determinations. Atomic absorption and

emission spectroscopy techniques were used for elemental

determinations. Infrared spectroscopic and gas

chromatographic techniques were applied to the problem

of organic identification of carbonaceous samples.

Several polished sections were prepared for study

of the opaque minerals of the ore sequence. Thin section

studies were undertaken to examine the mineral suite

present, for rock identification, and for study of

4

Great Salt Lake U T A H

Scale 0 50 miles I—II—I K3

UTAH

. Solt Lake City

O---:=-:::::::;::;===.-, , \

I

r •

, \

Tooel. Co. \

Stockton

rJ

~~H L.\e :0. , )

Figure 1. Index map s howing the locatlon of Mercur . Ut a h. (small bar 1n inset re pre s ent s one mile)

4

5

m i n e r a l h a b i t s ( t e x t u r e s ) .

B r i e f H i s t o r y o f M i n i n g A c t i v i t i e s i n t h e A r e a

S i l v e r w a s d i s c o v e r e d i n I 8 6 9 a t L e w i s t o n , t h e f o r m e r

n a m e o f M e r c u r , b u t t h e o r e p o c k e t s p r o v e d s p o t t y a n d

w e r e s o o n e x h a u s t e d . T h e d i s t r i c t w a s o r g a n i z e d o n A p r i l

1 6 , 1 8 7 0 , a s t h e Camp F l o y d d i s t r i c t . T h e e a r l y m i n e s

i n c l u d e d t h e C a r r i e S t e e l e , S p a r r o w h a w k , L a s t C h a n c e ,

S i l v e r C l o u d , M a r i o n , a n d M o r m o n C h i e f w i t h t h e C a r r i e

S t e e l e a n d S p a r r o w h a w k m i n e s b e i n g t h e b i g g e s t p r o d u c e r s .

T h e l o c a t i o n o f t h e S p a r r o w h a w k i s s h o w n o n F i g u r e s 2

a n d J, A f t e r s e v e r a l y e a r s o f s i l v e r p r o d u c t i o n , t h e

t o w n w a s d e s e r t e d i n 1 8 8 0 a n d t h e n a m e o f L e w i s t o n w a s

g i v e n t o a n o t h e r t o w n i n C a c h e C o u n t y , U t a h .

I n 1 8 7 9 » A r i e P i n e d o r e n a m e d t h e s i t e M e r c u r a f t e r

h i s d i s c o v e r y o f m e r c u r y i n t h e a r e a , b u t h i s d i s c o v e r y

D r o v e d u n e c o n o m i c a l . W i t h t h e d i s c o v e r y o f g o l d i n t h e

a r e a i n 1 8 8 3 » p r o s p e c t i n g w a s a g a i n r e s u m e d b u t t h e p o o r

e x t r a c t i o n o f t h e g o l d f r o m t h e m i l l e d o r e w a s d i s c o u r a g i n g .

I n I 8 9 O , a c a r l o a d o f o r e w a s s e n t t o D e n v e r , C o l o r a d o ,

f o r t r e a t m e n t b y t h e n e w l y d e v e l o p e d M c A r t h u r - F o r r e s t

c y a n i d e p r o c e s s . T h e r e s u l t s f r o m t h e t e s t p r o v e d

e n c o u r a g i n g a n d t h e f i r s t c y a n i d e p l a n t i n t h e U n i t e d

S t a t e s w a s c o n s t r u c t e d a t M a n n i n g , U t a h , n e a r M e r c u r

( G i l l u l y , 1 9 3 2 , p . 1 2 3 ) .

5

miner81 hqbits (textures).

Brief History of Mining Activities in the Area

Silver W<3.S d.iscovered in 1869 at Lewiston, the for-,er

name of Mercur, but the ore pockets proved spotty and

were soon exhausted. The district was organized on April

16, 1870, as the Camp Floyd district. The early mines

included the Carrie Steele. Sparrowhawk, Last Chance,

Silver Cloud, Marion. and Mormon Chief with the Carrie

Steele and Sparrowhawk mines being the biggest producers.

The loc<3.tion of the Sparrowhawk is shown on Figures 2

and 3. After several years of silver production, the

town was deserted in 1880 and the name of Lewiston was

given to another town in Cache County, Utah.

In 1879, Arie Pinedo renamed the site Mercur after

his discovery of mercury in the area. but his discovery

nroved uneconomical. With the discovery of gold in the

area in 1883. prospecting was again resumed but the poor

extraction of the gold from the milled ore was discouraging.

In 1890. a carload of ore was sent to Denver, Colorado,

for tre~tment by the newly developed McArthur-Forrest

cyanide process. The results from the test proved

encouraging and the first cyanide plant in the United

States was constructed at Manning, Utah, near Mercur

(Gilluly, 1932. p. 123).

6

F i g u r e 2 . P a n o r a m i c v i e w o f M e r c u r , U t a h f r o m E a g l e H i l l . ( 1 ) M e r c u r H i l l , ( 2 ) S p a r r o w h a w k m i n e , ( 3 ) G e y s e r -M a r i o n m i n e , ( 4 ) B r i c k y a r d m i n e , ( 5 ) I n g e r s o l l s h a f t , ( 6 ) G o l d e n G a t e m i n e a n d m i l l s i t e , ( ? ) E d ' s H i l l , ( 8 ) L e w i s t o n P e a k

( 1 ) S p a r r o w h a w k m i n e , ( 2 ) I n g e r s o l l s h a f t , ( 3 ) G e y s e r - M a r i o n m i n e , ( 4 ) M e r c u r H i l l m i n e , ( 5 ) G o l d e n G a t e m i n e a n d m i l l s i t e , ( 6 ) E d ' s H i l l

6

Figure 2. Panoramic view of Mercur, Utah from Eagle Hlli. (1) Mercur H1ll, (2) Sparrowhawk m1ne, () Geyser­Marlon m1ne, (~) Br1ckyard m1ne, (5) Ingersoll shaft, 6) Golden Gate m1ne and m1ll s1te, (7) Ed's H Lew1ston Peak

Pigure). Panoramic view of Mercur. Hlli. (1) Sparrowhawk m1ne, (2) Ingersoll shaft, (3) Geyser- Marlon mine, (4) Mercur Hill mine, ( 5) Golden Gate m1ne and m1ll s1te, (6) Ed's H1ll

7

T h e m a i n g o l d p r o d u c t i o n i n t h e d i s t r i c t c a m e f r o m

o n l y a f e w ^ i n e s . ( G e y s e r - M a r i o n , S a c r a m e n t o , M e r c u r

H i l l , B r i c k y a r d , a n d G o l d e n G a t e ) a l l n e a r t h e t o w n

o f M e r c u r , T h e G e y s e r a n d M a r i o n m i n e s w e r e J o i n e d i n

1 8 9 7 t o f o r m t h e G e y s e r - M a r i o n m i n e . T h e G o l d e n G a t e

m i l l w a s c o n s t r u c t e d i n I 8 9 8 a n d i n 1 8 9 9 t h e M e r c u r

M i n e s G o . c o m b i n e d w i t h t h e M e r c u r G o l d M i n i n g a n d

M i l l i n g C o . w h i c h r e s u l t e d i n t h e o r e s f r o m t h e M e r c u r

H i l l a n d t h e G o l d e n G a t e m i n e s b e i n g m i l l e d a t t h e G o l d e n

G a t e m i l l . I n 1 9 1 3 , t h e C o n s o l i d a t e d M e r c u r G o l d M i n e s

C o . , w h i c h a c c o u n t e d f o r m o s t o f t h e g o l d p r o d u c t i o n i n

t h e d i s t r i c t , c e a s e d m i n i n g o p e r a t i o n s b e c a u s e o f t h e

f a i l i n g o r e g r a d e . T h e t o w n o f M e r c u r s o o n d w i n d l e d a l t h o u g h

t h e G e y s e r - M a r i o n a n d S a c r a m e n t o m i n e s o p e r a t e d f o r s e v e r a l

y e a r s t h e r e a f t e r ( F r a n k l i n a n d M i l l e r , 1 9 3 8 , p . 2 - 4 ) .

T h e S a c r a m e n t o m i n e w a s t h e o n l y m i n e i n t h e a r e a t o y i e l d

c i n n a b a r a n d g o l d a n d p r o d u c e d a r e p o r t e d 3 # 5 3 8 f l a s k s

o f m e r c u r y ( H o w a r d , 1 9 * 3 . P» 1 3 ) -

I n 1 9 3 3 t h e S n y d e r M i n e s C o . b e g a n w o r k i n g t h e

t a i l i n g s d u m p s t o t h e s o u t h o f M e r c u r a t t h e o l d t o w n

s i t e o f M a n n i n g . A t a b o u t t h e s a m e t i m e , t h e m i n e s

a t M e r c u r w e r e r e - o p e n e d b y t h e S n y d e r M i n e s C o . w i t h

t h e o r e s f i r s t b e i n g s h i p p e d t o M a n n i n g f o r m i l l i n g .

L a t e r , i n 1 9 3 7 , t h e m i l l i n g o p e r a t i o n s w e r e s h i f t e d t o

M e r c u r ( F r a n k l i n a n d M i l l e r , 1 9 3 8 , p . 5 ) . T h e y m i n e d t h e

e a s i l y w o r k a b l e l o w - g r a d e s u r f a c e o r e s i n q u a r r i e s o n

?

The main ~old production in the district came from

only a few~ines, (Geyser-Marion, Sacramento, Mercur

Hill, Brickyqrd, and Golden Gate) all neqr the town

of Mercur. The Geyser and Marion mines were joined in

1897 to form the Geyser-Marion mine. The Go1den Gate

mill was constructed in 1898 and in 1899 the Mercur

Mines Co. combined with the Mercur Gold Mining qnd

Milling Co. which resulted in the ores from the Mercur

Hill and the Golden Gate mines being milled at the Golden

Gate mill. In 1913, the Consolidated Mercur Gold Mines

Co., which accounted for most of the gold production in

the district, ceased mining operations because of the

fqiling ore grade. The town of Mercur soon dwindled although

the Geyser-Marinn and Sacramento mines operated for several

yeqrs thereafter (Franklin and Miller, 1938, p. 2-4).

The Sacramento mine was the only mine in the area to yield

cinnabar and gold and produced a reported 3.538 flasks

of mercury (Howqrd, 1913. p. 13).

In 1933 the Snyder Mines Co. began working the

tailings dumps to the south of Mercur at the old town

site of Manning. At about the same time, the mines

at Mercur were re-opened by the Snyder Mines Co. with

the ores first being shipped to Manning for milling.

Later, in 1937, the milling operations were shifted to

Mercur (Franklin and Miller. 1938. p. 5). They mined the

e8sily workable low-grade surface ores in quarries on

8

a l e a s e b a s i s ( F r a n k l i n a n d M i l l e r , 1 9 3 8 , p . 5 ) • T h e y

a l s o w o r k e d t h e r e m a i n i n g o r e i n t h e G o l d e n G a t e m i n e

t h r o u g h t h e I n g e r s o l l s h a f t ( F i g . 2 ) . T h e m i n e s w e r e

a g a i n s h u t d o w n i n 1 9 ^ 2 b e c a u s e o f a g o v e r n m e n t a l d e c r e e

c l o s i n g g o l d m i n e s .

T h e M e r c u r Dome G o l d M i n i n g C o . f o r m e d i n 1 9 3 7

m i n e d f r o m a n a r e a j u s t w e s t o f M e r c u r o f f t h e i n c l u d e d

g e o l o g i c m a p ( F i g , 4 ) . T h e B u r e a u o f M i n e s r e p o r t e d t h e

p r e s e n c e o f v a n a d i u m i n a c a r b o n a c e o u s s h a l e h o r i z o n

i n t h i s m i n e ( K i n g a n d W i l s o n , 1 9 ^ 9 . P . 1 ) .

T h e m i n e s t o t h e s o u t h a t S u n s h i n e i n c l u d e d t h e

O v e r l a n d a n d t h e S u n s h i n e , T h e g o l d o r e m i n e d a t S u n s h i n e

r e p o r t e d l y w a s s i m i l a r t o t h e o r e s f r o m M e r c u r . J a s p e r o i d ,

s i m i l a r t o t h a t a t M e r c u r , i s p r e s e n t .

T h e t w o l a r g e s t m i n e s i n t h e W e s t D i p c a m p w e r e

t h e N o r m a a n d t h e L a C i g a l e . T h e g o l d o r e h e r e a l s o w a s

r e p o r t e d l y s i m i l a r t o t h e o r e s f r o m M e r c u r , b u t t h e c a m p

h a d o n l y l i m i t e d p r o d u c t i o n .

P r o c t o r ( i n B i s s e l l , 1 9 5 9 # P . 2 1 4 ) s t a t e s t h a t

o v e r $ 2 5 * 5 0 0 , 0 0 0 I n m e t a l v a l u e s h a v e b e e n m i n e d a t M e r c u r .

I n I 9 6 9 * N e w m o n t E x p l o r a t i o n L t d . u n d e r t o o k e x p l o r a t o r y

d r i l l i n g f o r g o l d m i n e r a l i z a t i o n a r o u n d t h e o l d m i n e s o f

M e r c u r . T h e r e s u l t s o f t h e d r i l l i n g w e r e v e r y d i s c o u r a g i n g

a n d N e w m o n t h a s g i v e n m o s t o f t h e d r i l l c o r e a n d c u t t i n g s

t o t h e U t a h G e o l o g i c a l a n d M l n e r a l o g i c a l S u r v e y ' s c o r e

l i b r a r y .

8

a lease bqsis (Franklin and Miller. 1938, p. 5). They

also worked the remaining ore in the Golden Gate mine

through the Ingersoll shaft (Fig. 2). The mines were

again shut down in 1942 because of a governmental decree

closing gold mines.

The Mercur Dome Gold Mining Co. formed in 1937

mined from an area just west of Mercur off the included

geologic map (Fig. 4). The Bureau of Mines reported the

presence of vanadium in a carbonaceous shale horizon

in this mine (King and Wilson, 1949. p. 1).

The mines to the south at Sunshine included the

Overland and the Sunshine. The gold ore mined at Sunshine

reportedly was similar to the ores from Mercur. Jasperoid,

similar to that at Mercur. is present.

The two largest mines in the West Dip camp were

the Norma and the La Cigale. The gold ore here also was

reportedly similar to the ores from Mercur, but the camp

had only limited production.

Proctor (lU Bissell. 1959. p. 214) states that

over $25,500,000 in metal values have been mined at Mercur.

In 1969, Newmont Exploration Ltd. undertook exploratory

drilling for gold mineralization around the old mines of

Mercur. The results of the drilling were very discouraging

and Newmont has ~iven most of the drill core and cuttings

to the Utah Geological and Mineralogical Survey's core

library.

STRATIGRAPHY

T h e Humbug F o r m a t i o n a n d t h e G r e a t B l u e L i m e s t o n e

a r e t h e t w o s t r a t i g r a p h i c u n i t s i n t h e m a p a r e a . B o t h

h a v e b e e n d e s c r i b e d p r e v i o u s l y b y G i l l u l y ( 1 9 3 2 ) a n d b y

B l s s e l l ( 1 9 5 9 ) .

T h e c o n t a c t b e t w e e n t h e Humbug a n d t h e o v e r l y i n g

G r e a t B l u e L i m e s t o n e i s a r b i t r a r i l y p l a c e d " a t t h e

t o p o f t h e h i g h e s t o r t h o q u a r t z i t e , q u a r t z i t i c s a n d s t o n e , o r

c a l c a r e n i t e o f s i g n i f i c a n c e i n t h e H u m b u g 1 ' ( B i s s e l l , 1 9 5 9 ,

p . 5 6 ) . G d l l u l y h a s c a l l e d t h e o r t h o q u a r t z i t e s l e n t i c u l a r

a n d t h i s a u t h o r v e r i f i e d t h i s w h e n m a p p i n g t h e c o n t a c t

b e t w e e n t h e Humbug a n d t h e G r e a t B l u e . G i l l u l y e s t i m a t e s

t h a t o r t h o q u a r t z i t e s c o m p r i s e J0% o f t h e Humbug ( 1 9 3 2 ,

p . 2 8 ) . T h e m e a s u r e d t h i c k n e s s o f t h e Humbug v a r i e s f r o m

6 3 5 t o 6 4 5 f e e t f o r t h e u n i t i n t h e i m m e d i a t e a r e a ( G i l l u l y ,

1 9 3 2 , p . 2 8 ; B i s s e l l , 1 9 5 9 . p . 5 * 0 . T h e a g e o f t h e

f o r m a t i o n i s U p p e r M i s s i s s i p p i a n .

T h e G r e a t B l u e L i m e s t o n e , n a m e d b y S p u r r , i s t h e u n i t

f r o m w h i c h a l l t h e g o l d h a s b e e n m i n e d a t M e r c u r , I t

h a s b e e n d i v i d e d i n t o t h r e e m a p a b l e u n i t s : t h e L o w e r

G r e a t B l u e w h i c h i s U p p e r M i s s i s s i p p i a n , t h e L o n g T r a i l

S h a l e , a n d t h e U p p e r G r e a t B l u e w h i c h i s L o w e r

P e n n s y l v a n i a n , T h e " g o l d l e d g e " c o m p r i s e s s o m e o f t h e

b e d s a b o v e t h e L o n g T r a i l S h a l e , t h e L o n g T r a i l S h a l e ,

a n d b e d s o f t h e L o w e r G r e a t B l u e b e l o w t h e L o n g T r a i l

STRATIGRAPHY

The Humbug Formation and the Great Blue Limestone

9re the two stratigraphic units in the map area. Both

hqve been described previously by Gilluly (1932) and by

Bissell (1959).

The contact between the Humbug and the overlying

Great Blue Limestone is arbitrarily placed -at the

top of the highest orthoquartzite, quartzitic sandstone, or

calcarenite of significance in the Humbug- (Bissell, 1959.

p. 56). ~illuly has called the orthoquartzites lenticular

and this author verified this when mapping the contact

between the Humbug and the Great Blue. Gilluly estimates

that orthoquartzites comprise 30% of the Humbug (1932.

p.28). The measured thickness of the Humbug varies from

635 to 645 feet for the unit in the immediate area (Gilluly,

1932, p. 28; Bissell, 1959. p. 54). The age of the

formation is Upper Mississippian.

The Great Blue Limestone, named by Spurr, is the unit

from which all the gold has been mined 3t Mercur. It

has been divided into three mapable units: the Lower

Great Blue which is Upper Mississippian, the Long Trail

Shale, and the Upper Great Blue which is Lower

Pennsylvanian. The -gold ledge- comprises some of the

beds above the Long Trail Shale. the Long Trail Shale,

and beds of the Lower Great Blue below the Long Trail

1 0

S h a l e . T h e " s i l v e r l e d g e * i s I n t h e L o w e r G r e a t B l u e

b e l o w t h e " g o l d l e d g e . " T h e t o t a l t h i c k n e s s o f t h e

f o r m a t i o n i s a b o u t 3 . 6 0 0 f e e t a c c o r d i n g t o G i l l u l y

( 1 9 3 2 , p . 2 9 ) — t h e L o w e r G r e a t B l u e b e i n g a b o u t 5 0 0

f e e t t h i c k a n d t h e Long T r a i l S h a l e b e i n g a b o u t 1 0 0 f e e t

t h i c k . T h e U p p e r G r e a t B l u e h a s b e e n d e s c r i b e d a s

m o n o t o n o u s , t h i c k t o m a s s i v e l i m e s t o n e b e d s . I n t h e

L o w e r G r e a t B l u e , t h i n o r t h o q u a r t z i t e a n d s a n d s t o n e l a y e r s

c a n b e f o u n d a b o v e t h e Humbug c o n t a c t i n t h e M e r c u r a r e a .

A t s e v e r a l l o c a t i o n s i n M e r c u r , o n l y t h i n s a n d s t o n e

l a y e r s w e r e f o u n d w h e r e t h e c o n t a c t s h o u l d h a v e b e e n

b e t w e e n t h e G r e a t B l u e a n d t h e H u m b u g . T h e s e c t i o n

a b o v e t h e L o n g T r a i l S h a l e c o n t a i n s i n t e r b e d d e d s i l t s t o n e ,

s h a l e , a n d l i m e s t o n e b e d s a s d o e s t h e s e c t i o n b e l o w t h e

L o n g T r a i l S h a l e , The L o n g T r a i l S h a l e c a n b e r e c o g n i z e d

b y t h e f a c t t h a t s i l t s t o n e a n d s h a l e b e d s t h i c k e n t o

b e t w e e n 5 - 1 0 f e e t i n t h e u n i t w h e r e a s s h a l e a n d s i l t s t o n e

b e d s a b o v e a n d b e l o w a r e u s u a l l y l e s s t h a n t w o f e e t t h i c k .

B i s s e l l ( 1 9 5 9 . P . 5 7 ) h a s s t a t e d t h a t t h e L o n g T r a i l S h a l e

w a s e s p e c i a l l y h e l p f u l i n d e l i n e a t i n g s t r u c t u r e s i n t h e

m a p p e d a r e a b u t t h e u n i t i s n o t e a s i l y r e c o g n i z a b l e i n

t h e f i e l d b e c a u s e i t i s a n e a s i l y e r o d e d u n i t . On t h e

m a p b y B i s s e l l a n d R i g b y t h e u n i t w a s m a p p e d b e t w e e n

v a l l e y s , g u l l i e s , a n d i o w s p o t s b e t w e e n h i l l s w h i c h o n e

m i g h t e x p e c t t o b e d u e t o t h e w e a t h e r i n g o f a s h a l e

s e q u e n c e b u t c l o s e e x a m i n a t i o n s h o w s t h e u n i t i s n o t

10

Sh9le. The ·silver ledge· is in the Lower Great Blue

below the ·gold ledge.· The total thickness of the

formation is about 3,600 feet according to Gilluly

(1932, p. 29) --the Lower Great B-lue being about 500

feet thick and the Long Trail Shale being about 100 feet

thick. The Upper Great l!1ue has been described as

monotonous, thick to massive limestone beds. In the

Lower Gre~t Blue, thin orthoquartzite and sandstone layers

can be found above the Humbug contact in the Mercur area.

At several locations in Mercur, only thin sandstone

layers were found where the contact should have been

between the Gre~t Blue and the Humbug. The section

above the Long Trail Shale contains interbedded siltstone,

shale, and limestone beds as does the section below the

Long Trail Shale. The Long Trail Shale can be recognized

by the fact that siltstone and shale beds thicken to

between 5-10 feet in the unit whereas shale and siltstone

beds above and below are usually less than two feet thick.

Bissell (1959, p. 57) has stated that the Long Trail Shale

was especially helpful in delineating structures in the

mapped area but the unit is not easily recognizable in

the field because it is an easily eroded unit. On the

map by Bissell and Rigby the unit was mapped between

valleys, gullies, and iow spots between hills which one

might expect to be due to the weathering of a shale

sequence but close examination shows the unit is not

1 1

e x a c t l y w h e r e t h e y m a p p e d i t o r i n s o m e c a s e s i s n o t

p r e s e n t a t a l l .

A l l u v i u m c o n s i s t i n g o f s t r e a m g r a v e l a n d v a l l e y f i l l

c o v e r s a p r e v i o u s l y d e v e l o p e d e r o s i o n s u r f a c e . T h e g r a v e l

t o t h e s o u t h o f t h e B r i c k y a r d m i n e s h o w s s t r a t i f i c a t i o n ,

b u t t h e g r a v e l i n t h e g r a b e n w e s t o f t h e B r i c k y a r d s h o w s

n o s t r a t i f i c a t i o n a n d c o n s i s t s o f J u m b l e d r o c k f r a g m e n t s .

T h e t h i c k n e s s o f t h e a l l u v i u m v a r i e s , b u t i s c o m m o n l y

5 - 3 0 f e e t t h i c k . A w e l l - d e v e l o p e d t h i c k s o i l o c c u r s t o

t h e e a s t a n d s o u t h - e a s t o f t h e M e r c u r H i l l m i n e .

T h e a l l u v i u m i s p r e s e n t l y b e i n g e r o d e d a w a y s l o w l y ,

p o s s i b l y d u e t o u p l i f t o f t h e a r e a a n d / o r t h e c h a n g e o f

c l i m a t i c c o n d i t i o n s s i n c e t h e l a s t g l a c i a l p e r i o d .

exactly where they mapped it or in some cases is not

present at all.

11

Alluvium consisting of stream gravel snd valley fill

cov~rs a previously developed erosion surface. The gravel

to the south of the Brickyard mine shows stratification,

but the gravel in the graben west of the Brickyard shows

no stratification and consists of jumbled rock fragments.

The thickness of the alluvium varies. but is commonly

5-30 feet thick. A well-developed thick soil occurs to

the east and south-east of the Mercur Hill mine.

The alluvium is presently being eroded away slowly.

possibly due to uplift of the area and/or the change of

climatic conditions since the last glacial period.

STRUCTURE

T h e s t r u c t u r a l e l e m e n t s i n t h e M e r c u r a r e a i n c l u d e

f o l d s , f a u l t s , j o i n t s , b r e c c i a p i p e s , a n d a n i g n e o u s

i n t r u s i o n . B o t h r e g i o n a l a n d l o c a l f o l d s o c c u r i n t h e

a r e a w i t h t h e s m a l l f o l d s n e a r t h e i n t r u s i o n a p p a r e n t l y

b e i n g r e l a t e d t o t h e i g n e o u s i n t r u s i o n . M o s t o f t h e

f a u l t s a r e s m a l l w i t h d i s p l a c e m e n t s l e s s t h a n 5 0 f e e t .

M e r c u r i s o n t h e e a s t f l a n k o f t h e O p h i r a n t i c l i n e ,

a b r o a d , a s y m m e t r i c a l s t r u c t u r e o f L a r a m i d e a g e . T h e

g e n e r a l s t r i k e o f t h e e a s t l i m b o f t h e a n t i c l i n e s h o w n

i n t h e n o r t h e r n p a r t o f t h e m a p ( F i g . 4 ) i s a b o u t N 30°W

a n d t h e s t r i k e o f t h e a n t i c l i n a l a x i s , t a k e n f r o m B i s s e l l

a n d R i g b y ' s m a p ( 1 9 5 9 t p l a t e 1 ) , i s a b o u t N 2 0 ° W . I n t h e

s o u t h e r n p a r t o f t h e m a p a r e a a r o u n d t h e E a g l e H i l l

I n t r u s i v e , d i p a n d s t r i k e o f t h e b e d s d e v i a t e f r o m t h e

t r e n d o f t h e O p h i r a n t i c l i n e . T h e s e c h a n g e s , o v e r l o o k e d

b y p r e v i o u s i n v e s t i g a t o r s , s e e m t o i n d i c a t e a f o r c e f u l

e m p l a c e m e n t o f t h e i n t r u s i v e a f t e r r e g i o n a l f o l d i n g .

S e c o n d a r y f o l d i n g o n t h e n o r t h s i d e o f t h e i n t r u s i v e

f o r m s a s m a l l s y n c l i n e . A s m a l l a n t i c l i n e a l s o o c c u r s

t o t h e s o u t h o f t h e m a p a r e a o n t h e s o u t h - w e s t r i d g e o f

E a g l e H i l l . B o t h s t r u c t u r e s d e v i a t e f r o m t h e a x i a l t r e n d

o f t h e O p h i r a n t i c l i n e . One s m a l l s y n c l i n e o c c u r s o n t h e

h i l l t o t h e e a s t o f t h e G o l d e n G a t e m i n e . I t s a x i a l p l a n e

n e a r l y p a r a l l e l s t h e l a r g e r s t r u c t u r a l f e a t u r e o f t h e a r e a

STRUCTURE

The structural elements in the Mercur area include

folds, faults, joints, breccia pipes, and an igneous

intrusion. Both regional and local folds occur in the

area with the small folds near the intrusion apparently

being related to the igneous intrusion. Most of the

faults are small with displacements less than 50 feet.

Mprcur is on the east flank of the Ophir anticline,

a broad, asymmetrical structure of Laramide age. The

general strike of the east limb of the anticline shown

in the northern part of the map (Fig. 4) is about N JOoW

and the strike of the anticlinal axis, taken from Bissell

and Rigby's map (1959, plate 1), is about N 200 W. In the

southern part of the map area around the Eagle Hill

intrusive, dip and strike of the beds deviate from the

trend of the Ophir anticline. These changes, overlooked

by previous investigators, seem to indicate a forceful

emplacement of the intrusive after regional foldingo

Secondary folding on the north side of the intrusive

forms a small sync line. A small anticline also occurs

to the south of the map area on the south-west rldge of

Eagle Hill. Both structures deviate from the axial trend

of the Ophir anticline. One small syncline occurs on the

hill to the east of the Golden Gate mine. Its axial plane

nearly parallels the larger structural feature of the area--

1 3

F i g u r e 4 , G e o l o g i c m a p o f M e r c u r , U t a h , Figure 4.

1)

GEOLOGIC MAP OF MERCUR, UTAH

EXPLANATION

Alluvial deposits Stre-lll !;ravel and vall",! fill

Eagl. Hill Rhyolite rntrulHv ... hiterhyollteWJ.th

50m",o"artz,al'lJll-dine. andbiotitephenocry"tB

Mgbu

~~~t' Mgbl

Great Blue Llm •• lane

Mgbu,uFP"rwember; thick to llmestonebeds

Mgt!:ie~~:!~E:~~3 ~~~ ~e 6~1~;~~~P5, Hgl.1.1" .... r .. elllb<lT; thick to

,""ssivelJ.meston.ebeds

Humbu" Formation

JOlperold

Silicifi.d rock.

Explosive breccia

Geologie map of Mercur, Utah.

.. .. " z ::: c :::> o

Breccia

Kaolinized and Silicified Intrulive

Contad I/;J.shedwttereapproximatelylocaled;

dottecl..h .. reconc""led

~----............ . Fault, shawing dip

Dashed .. bereapproXl:matclylocatedj dotted .. here conc~aled. ~id~pthro- sJ.de; D, do.ntbrQft

~ .. Strike and dip of bed,

.,~

Vertical and Inclined shafts

Portal of adi'

Prospect

(if) Mine dump

Scale

0E"'='=="'='~3::==':;O.OO feet

.~"",=,====="",=,==="",=,===3o.5 km

N

1 Topo!':l'aphic baBe modi tied rrom

tb .. 1968 USGS Mercur, Ut"""

topo!':l'apblcauadraJI..II:1e

14

t h e O p h i r a n t i c l i n e . I t i s b e l i e v e d t o h a v e r e s u l t e d

f r o m f u r t h e r c o m p r e s s i o n o f t h e a r e a f o l l o w i n g t h e

f o r m a t i o n o f t h e O p h i r a n t i c l i n e .

T h e E a g l e H i l l i n t r u s i v e d e f i n i t e l y c u t s t h e G r e a t

B l u e L i m e s t o n e s e q u e n c e a n d a p p a r e n t l y h a s c a u s e d s o m e

d r a g f o l d s n e a r i t . I t a p p e a r s t o b e a l a r g e i n t r u s i v e

d i k e t h a t c o u l d o n c e h a v e s e r v e d a s a c o n d u i t f o r a

f i s s u r e e r u p t i o n . T h e t r e n d o f t h e i n t r u s i v e i s N 75°W

i n t h e m a p a r e a w i t h t h e g e n e r a l t r e n d o f f t h e m a p t o

t h e w e s t b e i n g a b o u t N 9 0 ° W ,

N o r m a l , r e v e r s e , a n d s t r i k e - s l i p f a u l t s o c c u r i n t h e

m a p a r e a . A l l f a u l t s o b s e r v e d i n t h e g o l d o r e s e q u e n c e

d i s p l a c e t h e a l t e r e d r o c k a n d a p p e a r t o h a v e f o r m e d

a f t e r s i l i c i f i c a t i o n , a l t h o u g h t h e r e c o u l d h a v e b e e n

r e n e w e d m o v e m e n t a f t e r s i l i c i f i c a t i o n . M o s t o f t h e

f a u l t s a p p e a r t o b e n o r m a l , b u t s e v e r a l o f t h e l o w - a n g l e

f a u l t s a p p e a r t o b e r e v e r s e , S p u r r ( 1 8 9 4 - 9 5 ) m e n t i o n e d

t h a t s o m e o f t h e g o l d d e p o s i t s o c c u r a l o n g s m a l l f a u l t s .

Some o f t h e f a u l t s s h o w s e v e r a l p e r i o d s o f d i s p l a c e m e n t .

S l i c k e n s i d e s o n a l o w - a n g l e f a u l t a b o v e t h e f a u l t e d

b l o c k o f j a s p e r o i d n e a r t h e c e n t r a l p a r t o f t h e G e y s e r -

M a r i o n m i n e s h o w a p r o m i n e n t r e v e r s e d i r e c t i o n o f m o v e m e n t ,

b u t m o v e m e n t p r o b a b l y o c c u r r e d i n b o t h d i r e c t i o n s . T h i s

l o w - a n g l e f a u l t i s c u t a n d o f f s e t a f e w i n c h e s b y a h i g h

a n g l e f a u l t . Two s m a l l f a u l t s w h i c h o c c u r o n o p p o s i t e

s i d e s o f t h e b r e c c i a i n t h e S a c r a m e n t o m i n e a r e a c l e a r l y

14

the Ophir anticline. It is believed to have resulted

from further compression of the area following the

form~tion of the Ophir anticline.

The Eagle Hill intrusive definitely cuts the Great

Blue Limestone sequence and apparently has caused some

drag folds near it. It appears to be a large intrusive

dike that could once have served as a conduit for a

fissure eruption. The trend of the intrusive is N 750 W

in the map area with the general trend off the map to

o the west being about N 90 w.

Normal, reverse, and strike-slip faults occur in the

map area. All faults observed in the gold ore sequence

displace the altered rock and appear to have formed

after silicification, although there could have been

renewed movement after silicification. Most of the

faults appear to be normal, but several of the low-angle

faults appeqr to be reverse. Spurr (1894-95) mentioned

that some of the gold deposits occur along small faults.

Some of the faults show several periods of displacemento

Slickensides on a low-angle fault above the faulted

block of jasperoid near the central part of the Geyser-

Marion mine show a prominent reverse direction of movement,

but movement probably occurred in both directions. This

low-angle fault is cut and offset a few inches by a high

angle fault. Two small faults which occur on opposite

sides of the breccia in the Sacramento mine area clearly

1 5

e x t e n d a s h o r t d i s t a n c e i n t o t h e i n t r u s i v e . T h e o n e o n

t h e s o u t h s i d e o f t h e p i p e h a s a r e d h e m a t i t e - s t a i n e d

f r a c t u r e z o n e w h i c h i s m o r e s i l i c i f l e d t h a n n o r m a l

f o r t h i s p a r t o f t h e a l t e r e d i n t r u s i v e . T h e f a u l t o n

t h e n o r t h s i d e o f t h e p i p e h a s a l a r g e r v e r t i c a l

d i s p l a c e m e n t t h a n t h e o n e o n t h e s o u t h s i d e .

T h e b r e c c i a t h a t o c c u r s n e a r t h e c e n t e r o f t h e o l d

t o w n o f M e r c u r o n t h e SE s i d e o f t h e G e y s e r - M a r i o n

m i n e o c c u r s a p p r o x i m a t e l y a t t h e i n t e r s e c t i o n o f t w o

f a u l t s ( P i g . 5 ) • One o f t h e f a u l t s a p p e a r s t o e x t e n d

d o w n f r o m t h e g r a b e n w h i c h f o r m s t h e w e s t e r n b o u n d a r y o f

t h e B r i c k y a r d m i n e * T h e b r e c c i a i s n o t s i l i c i f l e d

a n d t h e r e f o r e p r o b a b l y f o r m e d a f t e r t h e h y d r o t h e r m a l

a c t i v i t y i n t h e a r e a . T h e b r e c c i a w a s m i n e d f o r g o l d

b u t t h e u n a l t e r e d s e d i m e n t a r y s e q u e n c e i n c o n t a c t w i t h

t h e b r e c c i a w a s n o t m i n e d w h i c h s u g g e s t s t h a t m i n e r a l i z e d

m a t e r i a l w a s o n t h e d o w n f a u l t e d s i d e o r f e l l i n t o a n

o p e n a r e a . T h e m a t e r i a l a b u t t i n g t h e f a u l t n e a r t h e

B r i c k y a r d m i n e a p p e a r s t o b e u n s o r t e d a l l u v i u m , w h e r e a s

t h e m a t e r i a l b e l o w t h e G e y s e r - M a r i o n m i n e i s a b r e c c i a .

T h e b r e c c i a c o u l d h a v e r e s u l t e d f r o m e x t e n s i o n o f t h e

f a u l t z o n e a n d r e p e a t e d u p a n d d o w n m o v e m e n t o f t h e

f a u l t , o r f r o m t h e f o r m a t i o n o f a s o l u t i o n c a v e i n t h e

f a u l t z o n e a n d c o l l a p s e o f t h e r o o f .

15

extend a short distance into the intrusive. The one on \

the south side of the pipe has a red hematite-stained

fracture zone which is more silicified than normal

for this part of the altered intrusive. The fault on

the north side of the pipe has a larger vertical

displacement than the one on the south side.

The breccia that occurs near the center of the old

town of Mercur on the SE side of the Geyser-Marion

mine occurs approximately at the intersection of two

faults (Fig. 5). One of the faults appears to extend

down from the graben which forms the western boundary of

the Brickyard mine. The breccia is not silicified

and therefore probably formed after the hydrothermal

activity in the area. The breccia was mined for gold

but the unaltered sedimentary sequence in contact with

the breccia was not mined which suggests that mineralized

material was on the down faulted side or fell into an

open area. The material abutting the fault near the

Brickyard mine appears to be unsorted alluvium, whereas

the material below the Geyser-Marion mine is a breccia.

The breccia could have resulted from extension of the

fault zone and repeated up and down movement of the

fault, or from the formation of a solution cave in the

fault zone and collapse of the roof.

16

F i g u r e 5» C o l l a p s e b r e c c i a o n e a s t s i d e o f t h e G e y s e r -M a r i o n m i n e s h o w i n g o l d m i n e w o r k i n g s .

B r e c c i a P i p e s

O n e o f t h e m o s t n o t i c e a b l e b r e c c i a s i n t h e M e r c u r

a r e a o c c u r s a t t h e S a c r a m e n t o m i n e ( F i g . 6 ) . I t a p p e a r s

t o b e a n e x p l o s i v e b r e c c i a p i p e t h a t r e s u l t e d f r o m a

r e l e a s e o f b u i l t - u p g a s p r e s s u r e . T h e p i p e o c c u r s

a t t h e c o n t a c t b e t w e e n t h e i n t r u s i v e a n d t h e G r e a t B l u e

L i m e s t o n e . T h e b r e c c i a s h o w s a c r u d e z o n a t i o n o f b r e c c i a

f r a g m e n t s . On b o t h e d g e s o f t h e e x p o s e d p i p e , t h e

b r e c c i a i s c o m p o s e d o f a n g u l a r f r a g m e n t s o f 1 - 5 c m ,

a v e r a g e s i z e i n a r e d , f i n e - g r a i n e d , s i l i c i f i e d ( q u a r t z

a n d c h a l c e d o n y ) g r o u n d m a s s ( F i g , 7 ) » I n t h e c e n t r a l p o r t i o n

o f t h e p i p e , t h e b r e c c i a i s c o m p o s e d o f m o s t l y a n g u l a r

f r a g m e n t s a n d b l o c k s i n a r e d , f i n e - g r a i n e d s i l i c i f i e d

( q u a r t z a n d c h a l c e d o n y ) g r o u n d m a s s . A l a r g e m a s s o f

s i l i c i f i e d r o c k o c c u r s a t t h e b a s e o f t h e p i p e e x p o s u r e

16

Figure 5. Collapse breccia on east side of the Geyser­Marion mine showing old mine workings.

Brecc ia Pipes

One of the most noticeable breccias in the Mercur

area occurs at the Sacramento mine (Fig. 6). It appears

to be an explosive breccia pipe that resulted from a

release of built-up gas pressure. The pipe occurs

at the contqct between the intrusive and the Great Blue

Limestone. The breccia shows a crude zonation of breccia

frq~ments. On both edges of the exposed pipe, the

breccia is composed of angular fragments of 1-5 cm.

average size in a red, fine-grained, silicified (quartz

and chalcedony) groundmass (Fig. 7). In the central portion

of the pipe, the breccia is composed of mostly angular

fragments and blocks in a red, fine-grained silicified

(quartz and chalcedony) groundmass. A large mass of

silicified rock occurs at the base of the pipe exposure

F i g u r e 6 . V i e w o f S a c r a m e n t o m i n e a r e a M e r c u r , U t a h . ( 1 ) a l t e r e d E a g l e H i l l r h y o l i t e , ( 2 ) S a c r a m e n t o b r e c c i a p i p e , ( 3 ) c a r b o n - r i c h a r e a , ( 4 ) o l d b u i l d i n g s a n d a d i t l o c a t i o n s f o r t h e S a c r a m e n t o m i n e

F i g u r e 7 . C l o s e - u p o f t y p i c a l b r e c c i a f o u n d n e a r t h e e d g e o f t h e S a c r a m e n t o b r e c c i a p i p e .

Figure 6. View of Sacramento mine area Mercur, Utah. (l) altered Eagle HlII rhyollte, (2) Sacramento breccIa pIpe, (J) c .. rbon-rich are .. , (4) old bu ildings a nd adit locations for the Sacramento mine

Flgure 7, edge

Close-up of typical breccia found of the Sac ramento breccia pipe.

nea r the

17

1 8

a n d s i m i l a r f r a g m e n t s o c c u r i n t h e g r o u n d m a s s a b o v e .

T h e m a s s c o n t a i n s r a r e q u a r t z p h e n o c r y s t s w h i c h s u g g e s t

t h a t t h i s r o c k i s a n i n t r u s i v e t h a t i n v a d e d t h e b r e c c i a

a f t e r p i p e f o r m a t i o n . T h e l a r g e m a s s c o u l d a l s o r e p r e s e n t

a l a r g e b l o c k o f a l t e r e d i n t r u s i v e i n c l u d e d i n t h e

b r e c c i a . T h e e n t i r e p i p e h a s b e e n a l t e r e d t o a s i l i c e o u s

s i n t e r w h i c h a d d s t o t h e d i f f i c u l t y o f i d e n t i f y i n g t h e

l l t h o l o g y o f t h e r o c k f r a g m e n t s . A h i g h a n g l e f a u l t

o f s m a l l d i s p l a c e m e n t c u t s t h e p i p e . T h i s f a u l t m i g h t

b e d u e t o s t r e s s e s d i r e c t e d u p w a r d s a n d s i d e w a r d s c a u s e d

b y r e n e w e d p o s t - c o n s o l i d a t i o n m o v e m e n t o f t h e i n t r u s i v e

a f t e r p i p e f o r m a t i o n . A n a r r o w h i g h l y f r a c t u r e d ,

s l l c k e n s i d e d z o n e w a s o b s e r v e d i n t h e m i n e d a r e a a r o u n d

t h e p i p e .

T h e o n l y p r e v i o u s d e s c r i p t i o n o f t h i s a r e a i s g i v e n

b y L e n z l ( 1 9 7 1 , p . 2 ) .

To t h e s o u t h , a b o v e M e r c u r , a r e s e v e r a l o p e n c u t s a l o n g t h e m o u n t a i n w i t h o n e v e r y l a r g e o p e n s l o p e t h a t e x p o s e s t h e c o n t a c t o f i n t r u s i v e r h y o l i t e w i t h t h e l i m e s t o n e c o u n t r y r o c k . T h e l i m e s t o n e h a s b e e n a l t e r e d t o a l i g h t v i o l e t a n d r e d c o l o r n e a r t h e i n t r u s i v e , o t h e r w i s e t h e a l t e r a t i o n a p p e a r s a s l i g h t b u f f , s i l i c i f i e d l i m e s t o n e o r l i g h t - g r a y - t o w h i t e s i l i c i f i e d s h a l e s .

I n c o n t r a s t , t h e e x p o s u r e a p p e a r s t o b e a h i g h l y b r e c c i a t e d

z o n e a n d n o t a c o n t a c t z o n e o f v i o l e t t o r e d a l t e r e d l i m e s t o n e .

O n e o t h e r e x p l o s i v e b r e c c i a p i p e o c c u r s w a s t o f t h e

S a c r a m e n t o b r e c c i a p i p e . T h e M e r c u r S o u t h b r e c c i a p i p e

i s s i m i l a r t o t h e S a c r a m e n t o b r e c c i a p i p e e x c e p t t h a t

1~

and similar fragments occur in the groundmass above.

~he mass contains rare quartz phenocrysts which suggest

that this rock is an intrusive that invaded the breccia

after pipe formation. The large mass could also represent

a lRrge block of altered intrusive included in the

breccia. ~he entire pipe has been altered to a siliceous

sinter which adds to the difficulty of identifying the

lithology of the rock fragments. A high angle fault

of small displacement cuts the pipe. This fault might

be due to stresses directed upwards and sidewards caused

by renewed post-consolidation movement of the intrusive

after pipe formation. A narrow highly fractured,

slickensided zone was observed in the mined area around

the pipe.

The only previous description of this area is given

by Lenzi (1971. p. 2).

To the south. above Mercur, are several open cuts along the mountain with one very large open slope that exposes the contact of intrusive rhyolite with the limestone country rock. The limestone has been altered to a light violet and red color near the intrusive. otherwise the ~lteration appears as light buff, silicified limestone or light-gray-to white silicified shales o

In contrast, the exposure appears to be a highly brecciated

zone and not a contact zone of violet to red altered limestor.e.

One other explosive breccia pipe occurs wast of the

Sacramento breccia pipe. The Mercur South breccia pipe

is similar to the Sacramento breccia pipe except that

1 9

i t l a c k s t h e r e d c o l o r o f t h e g r o u n d m a s s . T h e r e i s a

r a d i a t i n g f a u l t p a t t e r n o n t h e s o u t h s i d e o f t h e p i p e

b u t n o z o n a t i o n o f t h e b r e c c i a i s e v i d e n t f r o m t h e

o u t c r o p e x p o s u r e . T h e r o c k f r a g m e n t s a n d g r o u n d m a s s

i n t h e p i p e a r e s i l i c i f i e d t o a s i l i c e o u s s i n t e r . O n e

r o c k f r a g m e n t f r o m t h i s p i p e w h i c h w a s b e l i e v e d t o b e

a n i n t r u s i v e f r a g m e n t w h e n a n a l y z e d b y X - r a y d i f f r a c t i o n

s h o w e d t h e p r e s e n c e o f q u a r t z a n d s a n i d i n e .

F e a t u r e s s u g g e s t i n g i n c i p i e n t b r e c c i a p i p e f o r m a t i o n

o c c u r t o t h e e a s t o f t h e M e r c u r S o u t h p i p e . H e r e s l i g h t

s i l i c i f i c a t i o n s i m i l a r t o t h a t o f t h e o t h e r t w o p i p e s

o c c u r s a t t h e i n t e r s e c t i o n o f t w o f a u l t s . J u m b l e d

s t r a t a e x p o s e d t o t h e e a s t i n a r o a d c u t ( n o t s h o w n o n

F i g . 4 ) m i g h t b e d u e t o f a u l t i n g , s l u m p , o r p o s s i b l y

b r e c c i a p i p e f o r m a t i o n p r o c e s s e s .

J o i n t P a t t e r n s

To d e t e r m i n e p a s t s t r e s s e s i n t h e a r e a , 1 2 9 j o i n t

a t t i t u d e s w e r e m e a s u r e d i n t h e M e r c u r a r e a p r i m a r i l y

i n t h e G e y s e r - M a r i o n a n d M e r c u r H i l l a r e a s a n d w e r e

c o n t o u r e d t o g i v e F i g u r e 8 . F i g u r e 9 s h o w s t h e p l o t

o f t h e s t r i k e d i r e c t i o n s o f t h e 1 2 9 j o i n t s u s e d f o r

F i g u r e 8 ; F i g u r e 1 0 s h o w s t h e p l o t o f t h e s t r i k e d i r e c t i o n s

o f ? 1 f a u l t s o n t h e i n c l u d e d g e o l o g i c m a p ( F i g . 4 ) .

F i g u r e 1 0 s h o w s a g e n e r a l N 6 0 ° E s t r i k e o f m a n y o f

t h e f a u l t s ; t h e s t r i k e s o f t h e j o i n t s h a v e a c o n c e n t r a t i o n

19

it lacks the red color of the groundmass. There is a

radiating fault pattern on the south side of the pipe

but no zonation of the breccia is evident from the

outcrop exposure. The rock fragments and groundmass

in the pipe are silicified to a siliceous sinter. One

rock fragment from this pipe which was believed to be

an intrusive fragment when analyzed by X-ray diffraction

showed the presence of quartz and sanidine.

Features suggesting incipient breccia pipe formation

occur to the east of the Mercur South pipe. Here slight

silicification similar to that of the other two pipes

occurs at the intersection of two faults. Jumbled

strata exposed to the east in a road cut (not shown on

Fig. 4) might be due to faulting, slump, or possibly

breccia pipe formation processes.

Joint Patterns

To determine past stresses in the area, 129 joint

attitudes were measured in the Mercur area primarily

in the Geyser-Marion and Mercur Hill areas and were

contoured to give Figure 8. Figure 9 shows the plot

of the strike directions of the 129 joints used for

Figure 8; Figure 10 shows the plot of the strike directions

of 71 faults on the included geologic map (Fig. 4). o

Figure 10 shows a general N 60 E strike of many of

the faults; the strikes of the joints have a concentration

F i g u r e 8 . C o n t o u r d i a g r a m ( l o w e r h e m i s p h e r e p r o j e c t i o n ) o f j o i n t d e n s i t y o f 1 2 9 j o i n t s i n t h e M e r c u r , U t a h a r e a .

20

N

w E

s

F1gure 8. Contour dlagram (lower hemisphere project1on) of jo1nt dens1ty of 129 jo1nts 1n the Mercur. Ut ah area.

2 1

N 0

F i g u r e 9 . P l o t o f s t r i k e d i r e c t i o n s o f 1 2 9 j o i n t s .

F i g u r e 1 0 . P l o t o f s t r i k e d i r e c t i o n s o f ?1 f a u l t s a t M e r c u r , U t a h .

N o

W 90 L..-..-----~~~22~:.::.L---_.l90 E

Figure 9. Plot of strike directions of 129 joints.

N o

W 90 L-_____ -=:::::SWI~~~L_ ___ __.J 90 E

Figure 10. Plot of strike directions of 71 faults at Mercur. Utah.

21

2 2

a t a b o u t N 5 0 ° E w h i c h i s i n c o m p a r a t i v e a g r e e m e n t w i t h

t h e f a u l t d i r e c t i o n s . T h i s d i r e c t i o n i s a p p r o x i m a t e l y

p e r p e n d i c u l a r t o t h e a x i a l p l a n e o f t h e O p h i r a n t i c l i n e

w h i c h w o u l d m a k e t h i s t h e p r o b a b l e t e n s i o n d i r e c t i o n .

T h i s d i r e c t i o n i s v e r y s i m i l a r t o t h e t r e n d o f t h e l i n e

c o n n e c t i n g t h e t w o b r e c c i a p i p e s (N 5 5 ° B ) w h i c h m i g h t

I n d i c a t e a s t r u c t u r a l c o n t r o l f o r t h e i r f o r m a t i o n .

Two f a u l t s s h o w e x t e n s i o n in t h e M e r c u r M i l m i n e a r e a

b u t o n l y o n e c o r r e l a t e s w i t h t h e t e n s i o n d i r e c t i o n .

T h i s m i g h t i n d i c a t e t h a t o t h e r s t r e s s f i e l d s e x i s t e d

• o

i n t h e p a s t . T h e N 4 0 W m i n o r c o n c e n t r a t i o n o n t h e

f a u l t p l o t i s b e l i e v e d t o b e t h e r e l e a s e j o i n t a n d f a u l t

d i r e c t i o n . T h e N 2 5 ° E a n d N 8 0 ° B d i r e c t i o n s a r e b e l i e v e d

t o b e t h e s h e a r d i r e c t i o n s . T h e t r e n d o f t h e i n t r u s i v e

i s a b o u t N 7 5 ° W i n t h e m a p a r e a w i t h t h e g e n e r a l t r e n d

t o t h e w e s t o f t h e m a p a r e a b e i n g a b o u t B-W w h i c h i s

s i m i l a r t o o n e o f t h e s h e a r d i r e c t i o n s . H o w e v e r , i t

i s n o t c l e a r t h a t t h e i n t r u s i v e c a m e i n a l o n g t h e s h e a r

d i r e c t i o n .

T h e g e n e r a l s e q u e n c e o f e v e n t s f o r t h i s a r e a i s

b e l i e v e d t o h a v e s t a r t e d w i t h c o m p r e s s i o n t o f o r m t h e

O p h i r a n t i c l i n e w i t h s o m e f a u l t i n g . G i l l u l y ( 1 9 3 2 , p . 9 1 )

b e l i e v e d t h e c o m p r e s s i o n o c c u r r e d i n L a t e C r e t a c e o u s

o r e a r l y T e r t i a r y t i m e . T h e i n t r u s i o n o f t h e E a g l e H i l l

r h y o l i t e f o l l o w e d t h e f o r m a t i o n o f t h e a n t i c l i n e a n d

d i s r u p t e d t h e g e n e r a l a n t i c l i n a l t r e n d s , b u t o c c u r r e d

22

at about N 500 E which is in comparative agreement with

the fault directions. This direction is approximately

perpendicular to the axial plane. of the Ophir anticline

which would make this the probable tension direction.

This direction is verI similar to the trend of the line

connecting the two breccia pipes (5' 550 B) which might

indicate a structural control for their formation.

Two faults show extension in- the Mercur lfill mine area

but only one correlates with the tension direction.

This might indicate that other stress fields existed o in the past. The N 40 V minor concentration on the

fault plot is believed to be the release joint and fault

direction. The N 250 E and N 80°8 directions are believed

to be the shear directions. The trend of the intrusive

is about N 7SoV in the map Iirea with the general trend

to the west of the map area being about B-V which is

similar to one of the shear directions. However, it

is not clear that the intrusive came in along the shear

direction.

The general sequence of events for this area is

believed to have started with compression to form the

Ophir anticline with some faulting. ~illull (1932, p. 91)

believed the compression occurred in Late Cretaceous

or early Tertiary time. The intrusion of the Eagle Hill

rhyolite followed the formation of the anticline and

disrupted the general anticlinal trends, but occurred

2 3

w h i l e t h e a r e a w a s s t i l l i n c o m p r e s s i o n . F u r t h e r

c o m p r e s s i o n o f t h e a r e a c a u s e d n e w a n d r e n e w e d f a u l t i n g .

T h i s s e q u e n c e i s s i m i l a r t o t h a t g i v e n b y G i l l u l y

e x c e p t t h a t t h e a u t h o r b e l i e v e s t h e a r e a w a s i n a

c o n t i n u a l s t a t e o f c o m p r e s s i o n d u r i n g t h e s e q u e n c e o f

e v e n t s . B e c a u s e o n l y o n e s e t o f s t r e s s d i r e c t i o n s i s

r e a d i l y a p p a r e n t t h i s w o u l d t e n d t o i n d i c a t e o n e

m a j o r s t r e s s f i e l d . G i l l u l y ( 1 9 3 2 , p . 9 1 ) b e l i e v e d t h a t

t h e i g n e o u s i n t r u s i o n s o c c u r r e d i n E o c e n e t i m e . M o o r e

( 1 9 7 3 . p . 9 9 ) g i v e s a b i o t i t e K - A r a g e d a t e o f 3 1 . 6 + 0 . 9

m . y . ( O l i g o c e n e ) f o r t h e E a g l e H i l l r h y o l i t e i n t h e

S a c r a m e n t o m i n e a r e a a t M e r c u r .

23

while the area was still in compression. Further

compression of the area caused new and renewed faulting.

This sequence is similar to that given by Gilluly

except that the author believes the area was in a

continual state of compression during the sequence of

events. Because only one set of stress directions is

readily apparent this would tend to indicate one

major stress field. Gilluly (1932, p. 91) believed that

the igneous intrusions occurred in Eocene time. Moore

(1973. p. 99) gives a biotite K-Ar age date of 31.6 ± 0.9

m.y. (Oligocene) for the Eagle Hill rhyolite in the

Sacr~mento mine area at Mercur.

I N T R U S I V E R O C K S

F i g u r e 1 1 s h o w s t h e g e n e r a l d i s t r i b u t i o n o f i n t r u s i v e

I g n e o u s r o c k s i n t h e s o u t h e r n O q u i r r h M o u n t a i n s ( G i l l u l y ,

1 9 3 2 , p l a t e 1 3 , p . 9 7 ) . T h e v a r i e t i e s o f i g n e o u s

r o c k s I n c l u d e r h y o l i t e p o r p h y r y ( E a g l e H i l l r h y o l i t e ) ,

l a m p r o p h y r e ( k e r s a n t i t e ) , a n d g r a n o d i o r i t e p o r p h y r y

( B i r d ' s - e y e p o r p h y r y ) ,

K e r s a n t i t e

G i l l u l y ( 1 9 3 2 , p . 6 3 ) f o u n d f o u r l a m p r o p h y r e

( k e r s a n t i t e ) d i k e s o u t c r o p p i n g i n O p h i r C a n y o n , T h e

a u t h o r h a s c o l l e c t e d s o m e o f t h e l a m p r o p h y r e f r o m t h e

e a s t s i d e o f H a r t m a n n G u l c h a n d h a s f o u n d s m a l l a m o u n t s

o f p y r i t e p r e s e n t i n t h e r o c k . I t i s a l t e r e d a s G i l l u l y

( 1 9 3 2 , p . 6 4 ) h a s s t a t e d .

B i r d ' s - e y e P o r p h y r y

T h e B i r d ' s - e y e p o r p h y r y , n a m e d b y S p u r r ( 1 8 9 4 - 9 5 ,

p . 3 7 9 ) # o u t c r o p s o n P o r p h y r y H i l l , P o r p h y r y K n o b , a n d

L i o n H i l l . G i l l u l y ( 1 9 3 2 , p . 5 0 ) c l a s s i f i e d i t a s a

g r a n o d i o r i t e p o r p h y r y . T h e a u t h o r h a s e x a m i n e d e x p o s u r e s

o f i t o n P o r p h y r y K n o b a n d P o r p h y r y H i l l . T h e g r o u n d m a s s

o f t h e B i r d ' s - e y e p o r p h y r y o n P o r p h y r y K n o b i s n o t i c e a b l y

p r o p y l i t i z e d a n d w e a t h e r e d . G i l l u l y ( 1 9 3 2 , p . 4 9 ) f o u n d

i t t o c o n t a i n p h e n o c r y s t s o f p l a g i o c l a s e ( A b ^ Q - A n ^ Q ) ,

b a r r e l s h a p e d , h e x a g o n a l b l o t l t e t a b l e t s , h o r n b l e n d e ,

iNTRUSIVE ROCKS

Figure 11 shows the general distribution of intrusive

igneous rocks in the southern Oquirrh Mountains (Gilluly,

1932. plate 13. p. 97). The varieties of igneous

rocks include rhyolite porphyry (Eagle Hill rhyolite).

lamprophyre (kersantite), and granodiorite porphyry

(Bird's-eye porphyry).

Kersantite

Gilluly (1932. p. 63) found four lamprophyre

(kers~ntite) dikes outcropping in Ophir Canyon. The

author has collected some of the lamprophyre from the

e'3.st side of Hartmann Gulch and has found small amounts

of pyrite present in the rock. It is altered as Gilluly

(1932. p. 64) has stated.

Bird's-eye Porphyry

The B'ird' s-eye porphyr;r. named by Spurr (1894-95,

p. 379). outcrops on Porphyry Hill, Porphyry Knob, and

Lion Hill. Gllluly (1932, p. 50) classified it as a

granodiorite porphyry. The author has examined exposures

of it on Porphyry Knob and Porphyry Hill. The groundmass

of the Bird's-eye porphyry on Porphyry Knob is noticeably

propylitlzed and weathered. Gilluly (1932, p. 49) found

it to contain phenocrysts of plagioclase (Ab60-An40)'

barrel shaped. hexagonal biotite tablets, hornblende.

2 5

F i g u r e 1 1 . I n d e x m a p s h o w i n g t h e g e n e r a l d i s t r i b u t i o n o f i g n e o u s r o c k s i n t h e s o u t h e r n O q u i r r h M o u n t a i n s .

... O~)I ( .n)lOn

!

N

1 Sel l.

.;..~~~~'===",;2 .. li n

•

! ,,-/

( i ., '

\ \

"-,

I'tinnt

I

Figure 11. Index map showing the general distribution of igneous rocks in the southern Oquirrh Mountains.

2 6

m i n o r o r t h o c l a s e , a n d q u a r t z .

E a g l e H i l l R h y o l i t e

T h e E a g l e H i l l r h y o l i t e w a s n a m e d b y S p u r r ( 1 8 9 4 - 9 5 ,

p . 3 7 7 ) f o r t h e r h y o l i t e p o r p h y r y t h a t c r o p s o u t o n

t h e n o r t h s i d e o f E a g l e H i l l . T h e i n t r u s i v e r h y o l i t e

p o r p h y r i e s a t O p h i r a n d M e r c u r h a v e b e e n g i v e n t h e s a m e

n a m e a n d a r e s o m e w h a t s i m i l a r m i n e r a l o g i c a l l y • A l l

o u t c r o p s o f t h e r h y o l i t e e x a m i n e d w e r e i n t r u s i v e i n

c h a r a c t e r *

S t r u c t u r a l R e l a t i o n s

E x p o s u r e s o f E a g l e H i l l r h y o l i t e w e r e e x a m i n e d i n

t h e O p h i r a r e a i n D r y C a n y o n a n d o n t h e n o r t h s i d e o f

O p h i r C a n y o n . T h e r h y o l i t e p o r p h y r y h a s t h e f o r m o f a

d i k e i n O p h i r C a n y o n a n d h a s a n a r r o w c o n t a c t z o n e . I n

t h e D r y C a n y o n a r e a a b o v e O p h i r s e v e r a l i n t r u s i v e m a s s e s

o f r h y o l i t e o c c u r . G i l l u l y ( 1 9 3 2 , p . 5 8 ) d e s c r i b e d

s e v e r a l o u t c r o p s o f r h y o l i t e b r e c c i a i n t h e D r y C a n y o n

a r e a . T h e a u t h o r e x a m i n e d t h e o n e a b o v e t h e H i d d e n

T r e a s u r e m i n e .

Two s m a l l o u t c r o p s o f r h y o l i t e p o r p h y r y w h i c h h a v e

b e e n p r e v i o u s l y o v e r l o o k e d o c c u r NNE o f t h e o l d

t o w n s i t e o f W e s t M e r c u r . T h e s o u t h e r n m o s t o f t h e s e

o u t c r o p s o f r h y o l i t e e x h i b i t s c h a r a c t e r i s t i c s o f b o t h a

s i l l a n d a d i k e . An a d i t b l a s t e d i n t o t h e i n t r u s i v e

26

minor orthoclase, and quartz.

Eagle Hill Rhyolite

The Eagle Hill rhyolite Was named by Spurr (1894-95.

p. 377) for the rhyolite porphyry that crops out on

the north side of Eagle Hill. The intrusive rhyolite

porphyries at Ophir and Mercur have been given the same

name and are somewhat similar mineralogically. All

outcrops of the rhyolite examined were intrusive in

character.

Structural Relations

Exposures of Eagle Hill rhyolite were examined in

the Ophir area in Dry Canyon and on the north side of

Ophir Canyon. The rhyolite porphyry has the form of a

dike in Ophir Canyon and has a narrow contact zone. In

the Dry Canyon area above Ophir several intrusive masses

of rhyolite occur. Gilluly (1932, p. 58) described .-

several outcrops of rhyolite breccia in the Dry Canyon

area. The author examined the one above the Hidden

Treasure mine.

Two small outcrops of rhyolite porphyry which have

been previously overlooked occur NNE of the old

townsite of West Mercur. The southernmost of these

outcrops of rhyolite exhibits characteristics of both a

sill and a dike. An adit blasted into the intrusive

e x p o s e s a g o u g e z o n e a t t h e c o n t a c t b e t w e e n t h e l i m e s t o n e

a n d t h e i n t r u s i v e . P i e c e s o f b r e c c i a c o n t a i n i n g l i m e s t o n e

a n d i n t r u s i v e c a n b e f o u n d o n t h e o u t c r o p a n d a p p e a r t o

b e a n i n t r u s i v e b r e c c i a . T h e i n t r u s i v e i s b e l i e v e d t o

h a v e b e e n e m p l a c e d a s a v i s c o u s , d r y m a g m a . A l i g n m e n t

o f b i o t i t e f l a k e s i s a p p a r e n t w h i c h s u g g e s t s i n j e c t i o n

o f a v i s c o u s m a g m a .

T h e n o r t h e r n o f t h e t w o o u t c r o p s i s b e s t e x p o s e d

i n a n e x p l o r a t i o n p i t a n d i s a b r e c c i a o f l i m e s t o n e

a n d r h y o l i t e f r a g m e n t s . T h e b r e c c i a I s b e l i e v e d a l s o

t o b e a n i n t r u s i v e b r e c c i a . T h e l a c k o f h y d r o t h e r m a l

a l t e r a t i o n o f t h e l i m e s t o n e o r t h e i n t r u s i v e f r a g m e n t s

a n d t h e s m a l l c o n t a c t z o n e i s i n d i c a t i v e o f a h o t , d r y

m a g m a . T h e s e e x p o s u r e s a r e i m p o r t a n t b e c a u s e t h e y

a r e b e l i e v e d t o r e p r e s e n t a r e l a t i v e l y u n a l t e r e d e x p o s u r e

o f i n t r u s i v e s i m i l a r t o t h a t e x p o s e d o n t h e n o r t h s i d e o f

E a g l e H i l l .

T h e r h y o l i t e t h a t o u t c r o p s a t t h e m o u t h o f M e r c u r

C a n y o n h a s t h e f o r m o f a d i k e .

T h e s t r u c t u r a l c h a r a c t e r f o r t h e E a g l e H i l l r h y o l i t e

o n t h e n o r t h s i d e o f E a g l e H i l l i s a l a r g e d i k e w h i c h

h a s b e e n f o r c i b l y i n j e c t e d . I n m o s t p l a c e s o n l y a

n a r r o w c o n t a c t z o n e e x i s t s b u t i n s e v e r a l p l a c e s

s i l i c i f i e d z o n e s r a n g i n g u p t o s e v e r a l t e n s o f f e e t o c c u r .

I n t h e q u a r r i e d a r e a a t t h e S a c r a m e n t o m i n e , m i n i n g

o p e r a t i o n s e x p o s e d t h e c o n t a c t z o n e w h i c h i s c o n v e x o u t w a r d .

27

exposes a ~ouge zone at the contact between the limestone

and the intrusive. Pieces of breccia containing limestone

and intrusive can be found on the outcrop and appeqr to

be an intrusive breccia. The intrusive is believed to

have been emplaced as a viscous, dry magma. Alignment

of biotite flakes is apparent which suggests injection

of a viscous magma.

The northern of the two outcrops is best exposed

in an exploration pit and is a breccia of limestone

and rhyolite fragments. The breccia is believed also

to be an intrusive breccia. The lack of hydrothermal

alteration of the limestone or the intrusive fragments

and the small contact zone is indicative of a hot, dry

magma. These exposures are important because they

are believed to represent a relatively unaltered exposure

of intrusive similar to that exposed on the north side of

Eagle Hill.

~he rhyolite that outcrops at the mouth of Mercur

Canyon has the form of a dike.

The structural character for the Eagle Hill rhyolite

on the north side of Eagle Hill is a large dike which

has been forcibly injected. In most places only a

narrow contact zone exists but in several places

silicified zones ranging up to several tens of feet occur.

In the quarried area at the Sacramento mine, mining

operations exposed the contact zone which is convex outward.

2 8

P e t r o l o g y

T h e r h y o l i t e e x a m i n e d i n t h e O p h i r a r e a i s a p o r p h y r y

c o n t a i n i n g a b o u t 7 - 1 0 # v i s i b l e q u a r t z p h e n o c r y s t s . Q u a r t z ,

s a n i d i n e , o l i g o c l a s e , s e r i c i t e , a p a t i t e , c a l c i t e , a n d

o p a q u e s a r e v i s i b l e i n t h i n s e c t i o n . T h e g r o u n d m a s s i s

a p h a n i t i c , K - f e l d s p a r s t a i n i n g s h o w e d t h e g r o u n d m a s s t o

c o n s i s t o f s a n i d i n e a n d q u a r t z . T h e s a n i d i n e a n d

p l a g i o c l a s e b l e n d w i t h t h e w h i t e g r o u n d m a s s i n h a n d s p e c i m e n .

No b i o t i t e w a s s e e n i n t h e e x p o s u r e s o r i n t h i n s e c t i o n .

No m a g n e t i t e w a s s e e n b y t h e a u t h o r a l t h o u g h i t w a s

d e s c r i b e d b y G i l l u l y ( 1 9 3 2 , p . 5 9 ) . P y r i t e i s p r e s e n t .

S a n i d i n e o c c u r s a s p h e n o c r y s t s a n d i s t h e d o m i n a n t

f e l d s p a r p r e s e n t . O l i g o c l a s e i s m o r e a b u n d a n t i n t h e

i n t r u s i v e a t O p h i r t h a n i n t h e r h y o l i t e a t M e r c u r ,

a l t h o u g h o n l y a f e w t h i n s e c t i o n s o f t h e r h y o l i t e a t

O p h i r w e r e s t u d i e d .

T h e W e s t M e r c u r i n t r u s i v e c o n t a i n s a b u n d a n t b i o t i t e

a n d q u a r t z p h e n o c r y s t s w h i c h c o m p r i s e a b o u t 7 - 1 0 $ o f t h e

r o c k . Q u a r t z , s a n i d i n e , o l i g o c l a s e , b i o t i t e , s e r i c i t e ,

a n d c a l c i t e a r e v i s i b l e i n t h i n s e c t i o n . Q u a r t z , s a n i d i n e ,

a n d b i o t i t e a r e t h e m o s t a b u n d a n t m i n e r a l s — c a l c i t e i s

a l s o a b u n d a n t . T h e g r o u n d m a s s i s a p h a n i t i c .

I n t h e d i k e a t t h e m o u t h o f M e r c u r C a n y o n , q u a r t z ,

s a n i d i n e , p l a g i o c l a s e , c a l c i t e , a n d s e r i c i t e a r e v i s i b l e

i n t h i n s e c t i o n . T h e g r o u n d m a s s i s a p h a n i t i c . S m a l l

28

Petrology

The rhyolite examined in the Ophir ~rea is a porphyry

cont~inlng about 7-10% visible quartz phenocrysts. Quartz,

s~nidine, oligocl~se, sericite, apatite, calcite, ~nd

opaques qre visible in thin section. The groundmass is

aphanitic. K-feldspar staining showed the groundmass to

consist of sanidine and quartz. The sanidine and

plagioclase blend with the white groundrnass in hand specimen.·

No biotite was seen in the exposures or in thin section.

No m~gnetite was seen by the author although it was

described by Gilluly (1932, p. 59). Pyrite is present.

Sanidine occurs as phenocrysts and is the dominant

feldspar present. Oligoclase is more abundant in the

intrusive at Ophir than in the rhyolite at Mprcur,

although only a few thin sections of the rhyolite at

Ophir were studied.

The West Mercur intrusive contains abundant biotite

and quartz phenocrysts which comprise about 7-10% of the

rock. Quartz, sanidine, oligoclase, biotite, sericite,

and c~lcite are visible in thin section. Quartz, sanidine,

and biotite are the most abundant minerals--calcite is

also abundant. The groundmass is aphgnitic.

In the dike at the mouth of Mercur Canyon, quartz,

sanidine, pla~ioclase, calcite, and sericite are visible

in thin section. The groundmass is aphanitic. Small

2 9

s p h e r u l i t e s o f w h a t a r e e i t h e r q u a r t z o r k a o l i n i t e

a r e p r e s e n t . Q u a r t z a n d s a n i d i n e a r e t h e t w o m o s t

a b u n d a n t m i n e r a l s p r e s e n t — c a l c i t e i s l o c a l l y a b u n d a n t .

K a o l i n i t e w a s i d e n t i f i e d b y X - r a y d i f f r a c t i o n . Some

b i o t i t e w a s f o u n d o n s t u d y o f t h e o u t c r o p e x p o s u r e . S m a l l

a m o u n t s o f p y r i t e a r e v i s i b l e i n p o l i s h e d s e c t i o n .

I n t h e E a g l e H i l l r h y o l i t e a t M e r c u r , q u a r t z , s a n i d i n e ,

o l i g o c l a s e , b i o t i t e , s e r i c i t e , c a l c i t e , a n d o p a q u e s a r e

v i s i b l e i n t h i n s e c t i o n . T h e o p a q u e s i n t h i n s e c t i o n

i n r e f l e c t e d l i g h t a p p e a r t o b e p y r i t e . K a o l i n i t e

i s p r e s e n t i n s m a l l a m o u n t s t h r o u g h o u t t h e i n t r u s i v e

a n d i s a b u n d a n t i n t h e i n t r u s i v e n e a r t h e S a c r a m e n t o

b r e c c i a p i p e . I t w a s i d e n t i f i e d b y X - r a y d i f f r a c t i o n .

S c a t t e r e d s m a l l a m o u n t s o f i l l i t e , a l s o i d e n t i f i e d

b y X - r a y d i f f r a c t i o n , a p p e a r t o b e p r e s e n t i n t h e i n t r u s i v e .

C a l c i t e , w h i c h i s p r o b a b l y h y d r o t h e r m a l , i s a b u n d a n t

l o c a l l y i n t h e i n t r u s i v e w h e r e t h e r e i s a d e c r e a s e i n

p h e n o c r y s t c o n t e n t . C a l c i t e r e p l a c e s s a n i d i n e a n d

p l a g i o c l a s e p h e n o c r y s t s a s i s e v i d e n t i n t h i n s e c t i o n s .

T h e s i z e o f p l a g i o c l a s e c r y s t a l s v a r i e s f r o m p h e n o c r y s t s

t o m i c r o l i t e s . Some o f t h e p h e n o c r y s t s h a v e r i m s o f

q u a r t z . A g g r e g a t e s o f p h e n o c r y s t s - ( g l o m e r o p h y r i t l c

t e x t u r e ) o c c u r r a n d o m l y i n t h e i n t r u s i v e . I n t e r g r o w t h s

o f q u a r t z a n d f e l d s p a r o c c u r i n t h e p h e n o c r y s t a g g r e g a t e s

o r o c c u r a s s i n g l e p h e n o c r y s t s i n t h e g r o u n d m a s s .

T h e E a g l e H i l l r h y o l i t e w h i c h o u t c r o p s a t W e s t

29

spherulites of what ~re either quartz or kaolinite

are present. Quartz and sanidine are the two most

abundant minerals present--calcite is locally abundant.

Kaolinite was identified by X-ray diffraction. Some

biotite was found on study of the outcrop exposure. Small

amounts of pyrite are visible in polished section.

In the Eagle Hill rhyolite at Mercur, quartz. sanidine,

oligoclase, biotite, sericite. calcite, and opaques are

visible in thin section. The opaques in thin section

in reflected light appear to be pyrite. haolinite

is present in small amounts throughout the intrusive

and is abundant in the intrusive near the Sacramento

breccia pipe. It was identified by X-ray diffraction.

Scattered small amounts of illite, also identified

by X-ray diffraction, appear to be present in the intrusive.

Calcite, which is probably hydrothermal, is abundant

locally in the intrusive where there is a decrease in

phenocryst content. Calcite replaces sanidine and

plagioclase phenocrysts as is evident in thin sections.

The size of plagioclase crystals varies from phenocrysts

to microlites. Some of the" phenocrysts have rims of

quartz. A~gregates of phenocrysts. (glomerophyritic

texture) occur randomly in the intrusive. Intergrowths

of quartz and feldspar occur in the phenocryst aggregates

or occur as single phenocrysts in the groundmass.

The Eagle Hill rhyolite which outcrops at West

3 0

M e r c u r , M e r c u r , a n d O p h i r , i f i t d o e s c o m e f r o m o n e l a r g e

p l u t o n , p r o b a b l y u n d e r w e n t d i f f e r e n t i a t i o n . T h e d e p o s i t s

a t O p h i r a r e t y p i c a l m e s o t h e r m a l d e p o s i t s , w h e r e a s

t h e d e p o s i t s a t M e r c u r a r e e p i t h e r m a l . R o c k a l t e r a t i o n ,

r e p r e s e n t e d b y j a s p e r o i d , i s d i s t r i b u t e d b e t w e e n O p h i r

a n d M e r c u r ( G i l l u l y , 1 9 3 2 , p . 9 7 ) . T h i s a l t e r a t i o n c o u l d

r e p r e s e n t s i l i c a f r o m h y d r o t h e r m a l s o l u t i o n s c o m i n g f r o m

a p l u t o n a t d e p t h . O n e o f t h e d i s t i n g u i s h i n g f i e l d

c h a r a c t e r i s t i c s b e t w e e n t h e i n t r u s i v e s a t O p h i r a n d

M e r c u r i s t h a t t h e E a g l e H i l l r h y o l i t e c o n t a i n s m o r e b i o t i t e

a t M e r c u r t h a n a t O p h i r , M o o r e ( 1 9 7 3 t p . 1 0 0 ) s u g g e s t s

t h a t d i f f e r e n t i a t i o n f r o m a l a r g e m o n z o n i t i c p a r e n t m a s s

u n d e r l y i n g t h e O q u i r r h M o u n t a i n s g a v e r i s e t o t h e r h y o l i t e s

a t O p h i r a n d M e r c u r , U t a h .

30

Mercur, Mercur, and Ophir, if it does come from one lqrge

pluton, prob9bly underwent differentiation. The deposits

at Ophir are typic~l mesothermal deposits, whereas

the deposits ~t Mercur are epitherm91. Rock 91terqtion,

represented by jasperoid. is distributed between Ophir

and Mercur (Gilluly, 1932, p. 97). This alteration could

represent silica from hydrothermal solutions coming from

a pluton at depth. One of the distinguishing field

characteristics between the intrusives at Ophir and

Mercur is that the Eagle Hill rhyolite contains more biotite

at Mercur than at Ophir. Moore (1973, p. 100) suggests

that differentiation from a large monzonitic parent mass

underlying the Oquirrh Mountains gave rise to the rhyolites

a.t Ophir and JVlercur, Utah.

ALTERATION OF THE SEDIMENTARY ROCKS

T h e m o s t p r o m i n e n t t y p e o f m e t a m o r p h i s m o f t h e

s e d i m e n t a r y r o c k s i n t h e M e r c u r a r e a i s s i l i c i f i c a t i o n .

T h e s i l v e r l e d g e f r o m w h i c h s i l v e r w a s m i n e d i n t h e

e a r l y d a y s o f t h e c a m p i s a t y p i c a l j a s p e r o i d o f i n t e r g r o w n

q u a r t z g r a i n s a n d w h e r e m a s s i v e h a s l i t t l e a p p a r e n t

p e r m e a b i l i t y . T h e b r e c c i a t i o n o f t h e t y p i c a l j a s p e r o i d

c o u l d h a v e o c c u r r e d a f t e r o r e d e p o s i t i o n . T h e g o l d

l e d g e i s v a r i a b l e i n m a k e - u p a s t o d e g r e e a n d t y p e o f

a l t e r a t i o n . C e r t a i n l a y e r s h a v e b e e n h i g h l y s i l i c i f i e d

a n d o t h e r l a y e r s h a v e q u a r t z , s e r i c i t e , i l l i t e , a n d

c a l c i t e a d d e d , b u t p e r m e a b i l i t y s t i l l e x i s t s i n m o s t o f

t h e g o l d l e d g e w h e r e s i l i c i f i c a t i o n h a s n o t b e e n i n t e n s e .

T h e l a c k o f p e r m e a b i l i t y i n t h e m o r e m a s s i v e p o r t i o n s o f

t h e s i l v e r l e d g e c o u l d e x p l a i n w h y t w o d i f f e r e n t t y p e s

o f e l e m e n t a l d e p o s i t s o c c u r . T h a t i s , t h e g o l d b e a r i n g

s o l u t i o n s d i d n o t h a v e a c c e s s t o t h e s i l v e r l e d g e b e c a u s e

o f l a c k o f p e r m e a b i l i t y . T h u s t h e s i l v e r d e p o s i t e d i n

t h e s i l v e r l e d g e w h i c h h a s a h i g h e r t e m p e r a t u r e m i n e r a l

a s s e m b l a g e t h a n t h e g o l d l e d g e m a y b e e a r l i e r t h a n g o l d

d e p o s i t i o n . S p u r r ( 1 8 9 4 - 9 5 , p . 3 9 3 ) m e n t i o n e d t h a t

s m a l l a m o u n t s o f g o l d o c c u r i n t h e s i l v e r l e d g e ; a n d

l o w c o n c e n t r a t i o n s o f s i l v e r w e r e f o u n d b y t h e a u t h o r

i n t h e g o l d l e d g e .

ALTERATION OF THE SEDIMENTARY HOCKS

The most prominent type of metamorphism of the

sedimentary rocks in the Mercur area is silicification.

The silver ledge from which silver was mined in the

early days of the camp is a typical jasperoid of intergrown

quartz grains and where massive has little apparent

permeability. The brecciation of the typical jasperoid

could h~ve occurred after ore deposition. The gold

ledge is variable in make-up as to degree and type of

alteration. Certain layers have been highly silicified

qnd othpr layers have quartz, sericite, illite, and

calcite added. but permeability still exists inmost of

the gold ledge where silicification has not been intense.

The lack of permeability in the more massive portions of

the silver ledge could explain why two different types

of elemental deposits occur. That is. the gold bearing

solutions did not have access to the silver ledge because

of lack of permeability. Thus the silver deposited in

the silver ledge which has a higher temperature mineral

assemblage than the gold ledge may be earlier tha-n gold

deposition. Spurr (1894-95. p. 393) mentioned that

small amounts of ~old occur in the silver ledge; and

low concentrations of silver were found by the author

in the gold ledge.

32

S i l v e r L e d g e

G i l l u l y ( 1 9 3 2 , p . 9 7 - 1 0 1 ) m a d e a t h o r o u g h i n v e s t i g a t i o n

o f t h e j a s p e r o i d s i n t h e a r e a . He r e p o r t s t h a t a l l t h e

j a s p e r o i d s h a v e a t h o r o u g h l y b r e c c i a t e d c h a r a c t e r a n d i n

p l a c e s c o n t a i n s o m e l a m i n a t e d f r a g m e n t s r e s e m b l i n g b e d d i n g

j u m b l e d a t a l l a n g l e s . I n s o m e a r e a s , t h e j a s p e r o i d

a p p e a r s m a s s i v e a n d n o t t h o r o u g h l y b r e c c i a t e d — t h i s

c o n d i t i o n i s m o r e c o m m o n t h a n o n e i s l e d t o b e l i e v e f r o m

h i s r e p o r t . T h e j a s p e r o i d n e a r t h e o l d C a r r i e S t e e l e

w o r k i n g s c l e a r l y t r a n s g r e s s e s b e d d i n g .

G i l l u l y f o u n d t w o t y p e s o f j a s p e r o i d i n t h e a r e a o f

t h e s o u t h e r n O q u i r r h M o u n t a i n s . O n e t h a t i s :

a n a g g r e g a t e o f a n h e d r a l q u a r t z c r y s t a l s , a l l v e r y m i n u t e , u s u a l l y l e s s t h a n 0 . 0 3 m i l l i m e t e r i n d i a m e t e r , c o n t a i n i n g s m a l l q u a n t i t i e s o f a p a t i t e a n d z i r c o n a n d r a t h e r l a r g e q u a n t i t i e s o f b l u e - g r e e n , s t r o n g l y p l e o c h r o i c t o u r m a l i n e , m u s c o v i t e p l a t e s , a n d c a l o i t e c r y s t a l s . . . A s e c o n d v a r i e t y h a s t h e t e x t u r e k n o w n a s t h e ' t y p i c a l j a s p e r o i d 1 t e x t u r e . I t c o n s i s t s o f i n t e r g r o w n q u a r t z g r a i n s w i t h a s t r o n g t e n d e n c y t o e u h e d r a l f o r m s , s o t h a t i n t h i n s e c t i o n m o s t o f t h e g r a i n s a p p e a r b o u n d e d b y s t r a i g h t l i n e s , a n d n u m e r o u s h e x a g o n a l a n d p r i s m a t i c c r y s t a l o u t l i n e s a r e p r e s e n t . . . T o u r m a l i n e , s e r i c i t e , c a r b o n a t e , c a r b o n , e p i d o t e , a p a t i t e , a n d z i r c o n w e r e a l l r e c o g n i z e d i n t h i s v a r i e t y o f j a s p e r o i d a s w e l l a s i n t h e a n h e d r a l v a r i e t y . T h e s e e u h e d r a l q u a r t z g r a i n s a v e r a g e p r o b a b l y 0 . 1 5 t o 0 . 2 m i l l i m e t e r I n d i a m e t e r , a l t h o u g h l o c a l l y t h e a v e r a g e g r a i n m a y b e a b o u t 0 . 5 t o 0 . 7 m i l l i m e t e r . ( 1 9 3 2 , p . 9 8 )

G i l l u l y ( 1 9 3 2 , p . 9 9 ) d e s c r i b e d p l a c e s w h e r e t h e

t w o t y p e s b l e n d t o g e t h e r a n d r e p o r t s t h e b o u n d a r y

b e t w e e n t h e t w o a s b e i n g w a v y . T h e a u t h o r h a s f o u n d o n e

l o c a t i o n i n t h e G e y s e r - M a r i o n m i n e a r e a w h e r e t h i s i s

32

Silver Ledge

Gl11uly (1932, p. 97-101) made a thorough investigation

of the jasperoids in the area. He reports that all the

jasperoids have a thoroughly brecciated character qnd in

places contc:tin some laminat/!d fragments resembling bedd ing

jumbled at all angles. In some areas, the jasperoid

appears massive and not thoroughly brecciated--this

condition is more common than one is led to believe from

his report. The jasperoid near the old Carrie Steele

workings clearly transgresses bedding.

Gilluly found two types of jasperoid in the 9rea of

the southern Oquirrh Mountalns. One that iSI

an aggregate of anhedral quartz crystals, all very minute, usually less than 0.03 milllmeter in diameter, containing small quantities of apatite and zircon and rather large quantities of blue-green, stron~ly pleochroic tourmaline, muscovite plates, and caloite crystals ••• A second variety has the texture known as the 'typical jasperold' texture. It consists of int~rgrown quartz grains with a strong tendency to euhedral forms, so that in thin section most of the grains appear bounded by straight lines, and numerous hexagonal and prismatic crystal outlines are present ••• Tourmaline, sericite, carbonate, carbon, epidote, apatite, and zircon were all recognized in this variety of jasperoid as well as in the anhedral variety. These euhedral quartz grains average probably 0015 to 0.2 millimeter in diameter, although locally the avprage grain may be about 0.5 to 0.7 millimeter. (1932, p. 98)

Gilluly (1932, p. 99) described places where the

two types blend together and reports the boundary

between the two as being wavy. The author has found one

location in the Geyser-Marlon mine area where this is

3 3

c l e a r l y s h o w n ( F i g . 1 2 ) . F i g u r e 1 3 i s a p h o t o m i c r o g r a p h

o f t h e r o c k t y p e r e p r e s e n t e d b y BM-1 o n F i g u r e 12 w h i c h

i s s i m i l a r t o G i l l u l y 1 s a n h e d r a l v a r i e t y o f j a s p e r o i d

a n d c o u l d b e c a l l e d a s i l i c e o u s s i n t e r . Some o f t h e

q u a r t z g r a i n s a r e l a r g e r t h a n t h e t y p e r e p o r t e d a n d s o m e

s h o w a t e n d e n c y t o e u h e d r a l f o r m . F i g u r e 14 i s a

p h o t o m i c r o g r a p h o f t h e r o c k t y p e r e p r e s e n t e d b y BM-2 o n

F i g u r e 12 w h i c h i s s i m i l a r t o G i l l u l y ' s d e s c r i b e d

" t y p i c a l j a s p e r o i d . " T h e " t y p i c a l j a s p e r o i d " i s t h e

d o m i n a n t v a r i e t y o f j a s p e r o i d p r e s e n t . T h e q u a r t z g r a i n s

i n t h i n s e c t i o n h a v e w a v y e x t i n c t i o n s h o w i n g t h a t t h e y

h a v e b e e n s u b j e c t e d t o a s t r e s s f i e l d . G i l l u l y ( 1 9 3 2 ,

p . 1 0 0 ) b e l i e v e s t h a t t h e b r e c c i a t e d c h a r a c t e r o f t h e

j a s p e r o i d i s d u e t o c o n t r a c t i o n o f t h e c o l l o i d a l - s i l i c a

g e l w h i c h r e p l a c e d t h e o r i g i n a l l i m e s t o n e w h e n i t

c r y s t a l l i z e d . T h e s t r e s s o f c o n t r a c t i o n o f t h e s i l i c a

g e l m a s s c o u l d h a v e c a u s e d t h e d e f o r m a t i o n o f t h e

c r y s t a l l o g r a p h i c e l e m e n t s .

C e l c i t e i s p r e s e n t i n b o t h t y p e s o f J a s p e r o i d b u t

t h e a n h e d r a l v a r i e t y c o n t a i n s m o r e c a l c i t e i n t h e

G e y s e r - M a r i o n m i n e a r e a t h a n t h e " t y p i c a l j a s p e r o i d "

t y p e . T h e c a l c i t e i n t h e a n h e d r a l v a r i e t y m a y b e

u n r e p l a c e d l i m e s t o n e a s i n t h e e u h e d r a l v a r i e t y . Some

c a l c i t e m a y b e h y p o g e n e a s G i l l u l y ( 1 9 3 2 , p . 9 9 ) b e l i e v e s ,

b u t n o t a l l . T h e " t y p i c a l j a s p e r o i d " i s b e l i e v e d t o

r e p r e s e n t a g r e a t e r a m o u n t o f s i l i c i f i c a t i o n t h a n t h e

33

clearly shown (Fig. 12). Figure 13 is a photomicrograph

of the rock type repres~nted by BM-l on Figure 12 which

is similar to Gilluly's anhedral variety of jasperoid

and could be called a siliceous sinter. Some of the

quartz grain~ are larger than the type reported ~nd some

show a tendency to euhedral form. Figure 14 is a

photomicrograph of the rock type represented by BM-2 on

Figure 12 which is similar to Gilluly's described

. "typical jasperoid.- The -typical jasperoid- is the

dominant v8riety of jasperoid present. The quartz grains

in thin section have wavy extinction showing that they

have been subjected to a stress field. Gilluly (1932,

p. 100) believes that the brecciated character of the

jasperoid is due to contraction of the colloidal-silica

gel which replaced the original limestone when it

crystallized. The stress of contraction of the silica

gel mass could have caused the deformation of the

crystallographic elements.

C91cite is present in both types of jasperoid but

the 3nhedral variety contains more calcite in the

Geys~r-Marion mine area than the -typical jasperoid"

type. The calcite in the anhedral variety may be

unreplaced limestone as in the euhedral v~riety. Some

c~lcite may be hypogene as Gilluly (1932, p. 99) believes,

but not all. The "typical jasperoid" is bplieved to

represent a greater amount of silicification than the

3 4

F i g u r e 1 2 . A n h e d r a l v a r i e t y ( B M - 1 ) i n c o n t a c t w i t h t h e " t y p i c a l v a r i e t y * ( B M - 2 ) v a r i e t y o f j a s p e r o i d i n t h e G e y s e r - M a r i o n a r e a ,

o t h e r t y p e a n d t h u s r e p r e s e n t s a f u r t h e r s t a g e o f

c r y s t a l d e v e l o p m e n t ,

G i l l u l y ( 1 9 3 2 , p . 9 9 ) r e f e r s t o t h e c a r b o n f o u n d i n

t h e j a s p e r o i d s a s a h y p o g e n e m i n e r a l . T h i s i s p r o b a b l y

o p e n t o q u e s t i o n s i n c e t h e l i m e s t o n e t h e q u a r t z r e p l a c e d

p r o b a b l y c o n t a i n e d c a r b o n a c e o u s m a t e r i a l a s d o e s s o m e o f

t h e u n r e p l a c e d l i m e s t o n e i n . t h e s e q u e n c e .

T h e d i s t r i b u t i o n o f j a s p e r o i d f r o m L i o n H i l l , w h i c h

i s s o u t h o f O p h i r , t o M e r c u r i s o f i n t e r e s t b e c a u s e i t

m i g h t l e a d t o s o m e u n d e r s t a n d i n g o f t h e i g n e o u s h i s t o r y

o f t h e a r e a . A l t h o u g h G i l l u l y h a s s t a t e d t h a t t h e r e i s

n o d i r e c t r e l a t i o n b e t w e e n t h e j a s p e r o i d s a n d t h e i n t r u s i v e s

i n t h e a r e a b e t w e e n L i o n H i l l a n d M e r c u r ( 1 9 3 2 , p . 9 8 ) .

34

Figure 12. Anhedral variety (BM - i) 1n cont~ct with the -typical variety· (BM- 2) variety of jasperold 1n the Geyser-Marion are~ .

other type and thus represents a further stage of

cryst~ l development.

G111uly (1 932. p. 99) refers to the ca rbon found 1n

the jasperolds ~s a hypogene mineral. Thi s 1s probably

open to question since the limestone the quartz replaced

probably contained carbonaceous matprial as does some of

the unreplaced 11mestone . ln . the sequence.

The dlstrlbutlon of jasperold from Llon H1H, whlch

1s south of Ophir. to Mereur 1s of interest because it

might lead to some understanding of the igneous hi s t ory

of the a res. Al tho ugh Gl11uly has stated that there 1s

no direct relat Io n between the jasperolds and the intrusives

ln the a rea between Llon Hl11 and Mercur (1 932 . p. 98) ,

F i g u r e 1 3 . P h o t o m i c r o g r a p h o f t h e a n h e d r a l v a r i e t y o f j a s p e r o i d ( B M - 1 ) . c r o s s e d - n i c o l s . 4 7 X

Figure 1). Photomicrograph of the anhedral variety of jasperoid (BM-i) . crossed-nicols. 47X

Figure 14. Photomicrograph of (BM-2). crossed-nlcols.

-typical 47X

jasperoid-

35

3 6

G o l d L e d g e

M e t a m o r p h i s m o f t h e g o l d l e d g e v a r i e s a c c o r d i n g

t o t h e p a r t o f t h e s e d i m e n t a r y s e q u e n c e m i n e r a l i z e d

a n d c l o s e n e s s t o t h e S a c r a m e n t o b r e c c i a p i p e . T h e m a i n

t y p e o f a d d i t i v e m e t a m o r p h i s m i s s i l i c i f i c a t i o n a l t h o u g h

l o c a l l y , a l o n g w i t h t h e s i l i c a , s e r i c i t e , i l l i t e , a n d

c a l c i t e h a v e b e e n d e p o s i t e d . I l l i t e i s a b u n d a n t i n t h e

a l t e r e d c l a y a n d c a r b o n r i c h a r e a n e a r t h e S a c r a m e n t o

b r e c c i a p i p e .

M e t a m o r p h i s m o f t h e L o n g T r a i l S h a l e i n t h e M e r c u r

a r e a i s l a r g e l y a s i l i c i f i c a t i o n p r o c e s s . T h e q u a r t z

g r a i n s o f t h e s i l i c i f i e d r o c k s a r e a n h e d r a l , r e s e m b l i n g

t h e a n h e d r a l v a r i e t y o f J a s p e r o i d , y e t t h e r o c k i s

d i f f e r e n t f r o m t h e p r e v i o u s l y d i s c u s s e d t y p e , w h i c h i s

s i m i l a r t o a s i l i c e o u s s i n t e r , a n d c o n t a i n s i l l i t e . T h e

q u a r t z p r e s e n t i s p r o b a b l y r e c r y s t a l l i z e d q u a r t z f r o m

t h e s h a l e a n d s i l t s t o n e s e q u e n c e ; a d d i t i o n o f q u a r t z b y

h y d r o t h e r m a l s o l u t i o n s i s v e r y p r o b a b l e . T h e r o c k h a s t h e

a p p e a r a n c e o f a s i l t s t o n e e x c e p t t h a t i t l a c k s b e d d i n g .

T h e p y r i t e a n d a r s e n o p y r i t e p r e s e n t a r e i n v i s i b l e t o t h e

e y e a n d i m p a r t a d e g r e e o f f a l s e b e d d i n g t o t h e r o c k i n

t h i n s e c t i o n .

A l t e r a t i o n o f t h e L o n g T r a i l S h a l e , i n t h e M e r c u r

H i l l m i n e a r e a i s s i m i l a r t o t h a t i n t h e B r i c k y a r d m i n e

a r e a . C e r t a i n l a y e r s , w h i c h w e r e p r o b a b l y l i m e s t o n e l a y e r

b e f o r e s i l i c i f i c a t i o n , a r e h i g h l y s i l i c i f i e d a n d r e p r e s e n t

Gold Ledge

Metqmorphism of the gold ledge varies according

to the part of the sedimentary sequence mineralized

36

and closeness to the Sacramento breccia pipe. The main

type of additive metamorphism is silicification although

locally, along with the silica, sericite, illite, qnd

calcite have been deposited. Illite is abundant in the

altered clay and carbon rich area near the Sacrgmento

brecc ia pipe.

Metamorphism of the Long Trail Shale in the Mercur

area is largely a silicification process. The quartz

gr8ins of the silicified rocks are anhedral, resembling

the anhedr~l variety of jasperoid, yet the rock is

different from the previously discussed type, which is

similar to a siliceous sinter, and contains illite. The

quartz present is probably recrystallized quartz from

the shale and siltstone sequence; addition of quartz by

hydrothermal solutions is very probable. The rock has the

appearance of a siltstone except that it lacks bedding.

The pyrite and arsenopyrite present are invisible to the

eye and impart a degree of :false bedding to the rock in

thin section.

Alteration of the Long Trail Shale, in the Mercur

Hill mine area is similar to that in the Brickyard mine

area. Certain layers, which were probably limestone layers

before silicification, are highly silicified and represent

3 7

a j a s p e r o i d .

Some o f t h e b e d s b e l o w t h e L o n g T r a i l S h a l e

s e q u e n c e i n t h e G e y s e r - M a r i o n m i n e s h o w g r a i n s i z e

g r a d a t i o n s a n d b e d d i n g s t r o n g l y r e m i n i s c e n t o f a

s i l t s t o n e i n t h i n s e c t i o n . T h e s e b e d s a r e o n l y s l i g h t l y

a l t e r e d a l t h o u g h t h e y a r e a d j a c e n t t o h i g h l y s i l i c i f i e d

u n i t s . T h e b e d s b e l o w t h e L o n g T r a i l S h a l e i n t h e M e r c u r

H i l l m i n e a r e a a r e s i l i c i f i e d a n d i n p l a c e s a r e s e r i c i t i c i z e d .

Wha t i s m o s t n o t i c e a b l e a b o u t t h e o r e s e q u e n c e h e r e i s

t h e i n t e r l a y e r i n g o f a l t e r e d , s l i g h t l y a l t e r e d , a n d

u n a l t e r e d b e d s i n t h e o r e s e q u e n c e . R e m n a n t b e d d i n g i s

v i s i b l e i n t h e a l t e r e d b e d s w h i c h i s o n e c h a r a c t e r i s t i c

t h a t i s l a c k i n g i n t h e s i l v e r l e d g e o r t h e " t y p i c a l

j a s p e r o i d . " T h e h i g h l y a l t e r e d b e d s a r e b e l i e v e d t o

r e p r e s e n t b e d s t h a t o n c e h a d h i g h e r p e r m e a b i l i t y t h a n

t h e o t h e r b e d s a n d t h u s c o u l d s e r v e a s c h a n n e l w a y s

f o r s o l u t i o n s . Some o f t h e f o s s i l s i n t h e a l t e r e d g o l d

s e q u e n c e w h i c h h a s b e e n s i l i c i f i e d a n d s e r i c i t i z e d a p p e a r

t o h a v e b e e n u n a l t e r e d d u r i n g t h e a l t e r a t i o n p r o c e s s e s

a n d c o n t a i n u n r e p l a c e d c a l c i t e .

I n o n e o f t h e q u a r r y a r e a s i n t h e M e r c u r H i l l m i n e

o n e s i d e o f a f a u l t i n t h e a r e a i s h i g h l y s i l i c i f i e d t o

j a s p e r o i d w h e r e a s t h e o t h e r , s i d e h a s b e e n l e s s s i l i c i f i e d

a n d h a s v e i n l e t s o f s e r i c i t e p a r a l l e l t o r e m n a n t b e d d i n g

p l a n e s . V e i n l e t s o f c a l c i t e c r o s s - c u t q u a r t z a n d s e r i c i t e

i n t e r g r o w t h s i n t h i n s e c t i o n w i t h t h e c a l c i t e p r o b a b l y

37

a jasperoid.

Some of the beds below the Long Trail Shale

sequence in the Geyser-Marion mine show grain size

gradations and bedding strongly reminiscent of a

siltstone in thin section. These beds are only slightly

altered although they are adjacent to highly silicified

units. The beds below the Long Trail Shale in the Mercur

Hill mine area are silicified and in places are sericiticized.

What is most noticeable about the ore sequence here is

the interlayering of altered. slightly altered, and

unaltered beds in the ore sequence. Remnant bedding is

visible in the altered beds which is one characteristic

that is lacking in the silver lecig.e or the "typical

jasperoid." The highly altered beds are believed to

represent beds that once had higher permeability than

the other beds and thus could serve as channelways

for solutions. Some of the fossils in the altered gold

sequence which has been silicified and sericitized appear

to have been unaltered during the alteration processes

and cont~in unreplaced calcite.

In one of the quarry areas in the Mercur Hill mine

one side of a fault in the area is highly silicified to

jasperoid whereas the other, side has been less silicified

and has veinlets of sericit(~ parallel to remnant bedding

planes. Veinlets of calcite cross-cut quartz and sericite

intergrowths in thin section with the calcite probably

3 8

b e i n g h y d r o t h e r m a l i n o r i g i n . S e v e r a l g e n e r a t i o n s o f

p y r i t e a r e e v i d e n t w i t h t h e l a t e r p y r i t e m o r e a n h e d r a l

i n f o r m ( P i g . 1 5 ) . T h e d i f f e r i n g a l t e r a t i o n t y p e s o n

e i t h e r s i d e o f t h e f a u l t a r e b e l i e v e d t o b e d u e t o f a u l t

r e l a t i o n s a n d t o t h e e f f e c t o f h y d r o t h e r m a l s o l u t i o n s

o n d i f f e r i n g r o c k t y p e s a n d d i f f e r i n g s e d i m e n t a r y s e q u e n c e s

w h i c h h a d b e d s o f h i g h e r p e r m e a b i l i t y .

Some f l u o r i t e w a s f o u n d i n a c o m p a r a t i v e l y u n a l t e r e d

s e q u e n c e a t t h e t o p o f M e r c u r H i l l .

T h e s e d i m e n t a r y s e q u e n c e n e a r t h e S a c r a m e n t o b r e c c i a

p i p e i s b e l i e v e d t o r e p r e s e n t e i t h e r t h e L o n g T r a i l

S h a l e s e q u e n c e o r b e d s b e l o w i t . a n d i s c h a r a c t e r i z e d

l o c a l l y b y b e d s h a v i n g l a r g e a m o u n t s o f i l l i t e . P y r i t e

i s p r e s e n t i n v a r y i n g a m o u n t s . T h e a r e a a r o u n d t h e b r e c c i a

p i p e i s o f i n t e r e s t b e c a u s e o f t h e d i f f e r e n t

a l t e r a t i o n t y p e s i n w h i c h c a r b o n i s p r e s e n t . O n e s a m p l e

a s s a y e d f o r c a r b o n n e a r n u m b e r 3 o n F i g u r e 6 h a d 4 , 2 $

c a r b o n p r e s e n t . H y d r o c a r b o n s a r e c l e a r l y v i s i b l e i n

t h i n s e c t i o n f r o m r o c k s a m p l e s t h a t s h o w c a r b o n a s s o c i a t e d

w i t h c l a y m i n e r a l s t h a t p r o b a b l y f o r m e d i n s m a l l s o l u t i o n

c h a n n e l w a y s b e t w e e n f r a c t u r e s . I n t h e a r e a o f n u m b e r 3

o n F i g u r e 6 t h e a l t e r a t i o n v a r i e s f r o m a s i l i c e o u s

s i n t e r w i t h i n t e r s t i t i a l c a r b o n t o a n i l l i t e - q u a r t z

r o c k w i t h c a r b o n . I t i s q u e s t i o n a b l e i f a n y o f t h e

c a r b o n - r i c h a r e a i s a l t e r e d i n t r u s i v e , b u t t h e n e a r n e s s

o f t h e i n t r u s i v e t o t h e c a r b o n - r i c h a r e a i s s u g g e s t i v e .

38

being hydrothermal in origin. Several generations of

pyrite are evident with the later pyrite more qnhedrql

in form (Fig. 15). The differing alteration types on

either side of the fault are believed to be due to fault

relations and to the effect of hydrothermal solutions

on differing rock types and differing sedimentary sequences

which had beds of higher permeability.

Some fluorite was found in a comparatively unaltered

sequence at the top of Mercur Hill.

The sedimentary sequence near the Sacramento breccia

pipe is believed to represent either the Long Trail

Sh~le sequence or beds below it, and is characterized

locally by beds having large amounts of illite. Pyrite

is present in varying amounts. The area around the breccia

pipe is of interest because of the different

alteration types in which carbon is present. One sample

assayed for carbon near number J on Figure 6 had 4.2%

carbon present. Hydrocarbons are clearly visible in

thin section from rock samples that show carbon associated

with clay minerals that probably formed in small solution

channelways between fractures. In the area of number 3

on Figure 6 the alteration varies from a siliceous

sinter with interstitial carbon to an illite-quartz

rock with c~rbon. It is questionable if any of the

carbon-rich are~ is altered intrusive, but the nearness

of the intrusive to the carbon-rich area is suggestive.

3 9

F i g u r e 1 5 - P h o t o m i c r o g r a p h o f a l t e r e d g o l d o r e s e q u e n c e f r o m t h e M e r c u r H i l l m i n e s h o w i n g a c a l c i t e v e i n l e t w i t h p y r i t e i n t h e c e n t e r w h i c h w a s d e f o r m e d b y t h e l a t e r g r o w t h o f a p y r i t e c r y s t a l , t r a n s m i t t e d l i g h t , 4 7 X c a , c a l c i t e ; p y , p y r i t e ; q t z + s e r , q u a r t z a n d s e r i c i t e l n t e r g r o w t h ; j , j a r o s i t e s t a i n

S m a l l n o d u l e s t h a t m i g h t b e m o r e s i l i c e o u s t h a n t h e

s u r r o u n d i n g r o c k c a n b e f o u n d i n t h e c a r b o n - r i c h a r e a a n d

c o n t a i n t h i n f i l m s o f p y r i t e a l o n g f r a c t u r e s .

Wavy e x t i n c t i o n o f t h e q u a r t z g r a i n s a n d t h e l a r g e

a m o u n t o f s l i c k e n s i d e d f r a g m e n t s i n t h e c a r b o n - r i c h z o n e

m i g h t r e p r e s e n t t h e s h o c k m e t a m o r p h i c e f f e c t s t o t h e

s u r r o u n d i n g r o c k s w h e n t h e S a c r a m e n t o b r e c c i a p i p e w a s

f o r m e d . Some o f t h e f r a g m e n t s i n t h e c a r b o n - r i c h z o n e

r e s e m b l e p h y l l i t e i n h a n d s p e c i m e n b e c a u s e o f t h e t h o r o u g h l y

s l i c k e n s i d e d n a t u r e o f t h e r o c k a n d t h e h i g h c o n t e n t o f

c l a y m i n e r a l s p r e s e n t .

No n o t i c e a b l e h y d r o t h e r m a l a l t e r a t i o n w a s e v i d e n t i n

t h e l i m e s t o n e b e d s a b o v e t h e g o l d l e d g e o n t h e h i l l b e h i n d

39

Figure 15. Photomicrograph of altered gold ore sequence from the Mercur Hill mine showing a calcite velnlet with pyrite 1n the center which was deformed by the later growth of a pyrite crystal. transm1tted 11ght. 47X ca, calcite; py, pyrite; qtz + ser, quartz and serlctte Intergrowth; j, jaroslte stain

Small nodules that might be more siliceous than the

surrounding rock oan be found 1n the carbon-rich area and

contain thin films of pyrite along fractures.

Wavy extinction of the quartz grains and the large

amount of slickensided fragments 1n the carbon-rich zone

might represent the shock metamorphic effects to the

surrounding rocks when the Sacramento breccia pipe was

formed. Some of the fragments 1n the carbon-rich zone

resemble phyll i te in hand specimen because of the thoroughly

slickens ided nature of the rock and the high content of

clay minerals present.

No noticeable hydrothermal alteration was evident in

the 11mestone beds above the gold ledge on the h111 beh1nd

4 0

t h e G o l d e n G a t e m i l l s i t e . A l t e r a t i o n a s s o c i a t e d w i t h

w i t h t h e g o l d o r e s e q u e n c e s e e m s t o b e r e s t r i c t e d t o

t h e m o r e p e r m e a b l e u n i t s a n d d o e s n o t v e r t i c a l l y

t r a n s c e n d b e d d i n g n o t i c e a b l y . T h i s w o u l d s e e m t o i n d i c a t e

t h a t i f o n e w e r e t o l o o k f o r o t h e r a l t e r a t i o n a s s o c i a t e d

w i t h g o l d m i n e r a l i z a t i o n , o n e m u s t f i n d a n a c t u a l

a l t e r e d o u t c r o p .

W e a t h e r i n g

W e a t h e r i n g o f t h e s i l v e r l e d g e o r m o r e c h a r a c t e r i s t i c a l l y

o f t h e " t y p i c a l j a s p e r o i d " i s t y p i f i e d b y a l t e r a t i o n

o f s u l f i d e m i n e r a l s t o s u l f a t e s , c a r b o n a t e s , o r o x i d e s ,

S t i b n i t e t h a t w a s o n c e p r e s e n t a l t e r s t o s t i b i c o n i t e

a n d s u l f u r . C o p p e r - b e a r i n g s u l f i d e s a l t e r t o a z u r i t e a n d

m a l a c h i t e . A z u r i t e a n d m a l a c h i t e c a n b e f o u n d o n t h e

o l d d u m p s t o t h e w e s t o f t h e o l d C a r r i e S t e e l e m i n e .

Some a z u r i t e a n d m a l a c h i t e w a s f o u n d n e a r t h e o l d S i l v e r

C l o u d m i n e . J a r o s i t e , m a l a c h i t e , a n d a b l u e - g r e e n a l u n i t e

a r e f o u n d i n t h e q u a r r y a r e a s o f t h e o l d S p a r r o w h a w k m i n e .

W e a t h e r i n g o f t h e g o l d l e d g e i s t y p i f i e d b y t h e

a l t e r a t i o n o f s u l f i d e m i n e r a l s t o s u l f a t e s o r o x i d e s .

G y p s u m i s f o u n d i n m a n y o f t h e o x i d i z e d a r e a s . I n t h e

p r o t e c t e d a r e a s u n d e r g r o u n d h a l o t r i c h i t e i s l o c a l l y

a b u n d a n t a n d i s u s u a l l y f o u n d i n t h e o x i d i z e d z o n e s .

I t t a k e s t h e f o r m o f s t a l a c t i t e s , h e l i c t i t e s , n e e d l e s , o r

f i b r o u s m a s s e s . P y r i t e a l t e r s t o j a r o s i t e a n d g o e t h i t e ;

40

the Golden Gate mill site. Alter~tion associated with

with the gold ore sequence seems to be restricted to

the more permeable units and does not vertically

transcend bedding noticeably. This would seem to indicate

that if one were to look for other alteration associated

with gold mineralization, one must find an actual

altered outcrop.

Weathering

WeJ3.thering of the silver ledge or more characteristically

of the Mtypical jasperoid" is typified by alteration

of sulfide minerals to sulfates, carbonates, or oxides.

Stibnite that was once present alters to stibiconite

and sulfur. Copper-bearing sulfides alter to azurite and

malachite. Azurite and malachite can be found on the

old dumps to the west of the old Carrie Steele mine.

Some azurite and malachite was found near the old Silver

Cloud mine. Jarosite, malachite, and a blue-green alunite

are found in the quarry areas of the old Sparrowhawk mine.

Weathering of the gold ledge is typified by the

alteration of sulfide minerals to sulfates or oxides.

Gypsum is found in many of the oxidized areas. In the

protected areas underground halotrichite is locally

abundant and is usually found in the oxidized zones.

It takes the form of stalactites, helictites,needles, or

fibrous masses. Pyrite alters to jarosite and goethite;

j a r o s i t e m a i n l y g i v e s t h e a l t e r e d s e q u e n c e i t s y e l l o w

c o l o r . P i s a n i t e - m e l a n t e r i t e ( s o l i d s o l u t i o n s e r i e s )

i s p r e s e n t i n s e v e r a l l o c a l i t i e s a t M e r c u r a n d i s t h e

m a i n m i n e r a l i n w h i c h c o p p e r i s f o u n d h e r e . P e c u l i a r l y ,

i t i s f o u n d p r e d o m i n a n t l y i n t h e r e l a t i v e l y u n o x i d i z e d

p o r t i o n s o f t h e o r e s e q u e n c e s u g g e s t i n g t h a t t h e d e g r e e

o f o x i d a t i o n o f t h e o r e h a d s o m e i n f l u e n c e a s t o l o c a t i o n o f

f o r m a t i o n . T h e p i s a n i t e - m e l a n t e r i t e u s u a l l y i s f o u n d

t o o c c u r a s f r a c t u r e f i l l i n g s w h i c h m i g h t h a v e r e s u l t e d

e i t h e r f r o m t h e m i n e r a l ' s f o r c e o f c r y s t a l l i z a t i o n o r

t e c t o n i c a c t i v i t y . A y e l l o w v a r i e t y o f s c o r o d i t e w a s

f o u n d i n t h e G e y s e r - M a r i o n m i n e a r e a a n d w a s f o u n d t o

h a v e r e s u l t e d f r o m t h e d i r e c t o x i d a t i o n o f o r p i m e n t w i t h

t h e a d d i t i o n o f i r o n .

T h e w e a t h e r i n g o f t h e L o n g T r a i l S h a l e i n t h e

B r i c k y a r d m i n e i s o f i n t e r e s t b e c a u s e o f t h e l e n s - s h a p e d

n a t u r e o f t h e u n o x i d i z e d p o r t i o n s . C l o s e t o t h e s u r f a c e

t h e o x i d i z e d p o r t i o n s , i n m a n y i n s t a n c e s , s u r r o u n d

t h e u n o x i d i z e d p o r t i o n s . A t d e p t h , t h e u n o x i d i z e d

p o r t i o n s f o r m c o l u m n s s u r r o u n d e d b y o x i d i z e d m a t e r i a l .

F i g u r e 1 6 s h o w s t h e l e n s - s h a p e d n a t u r e o f t h e u n o x i d i z e d

p o r t i o n i n a s t o p e o f t h e B r i c k y a r d m i n e . C a r b o n a s s a y s

s h o w t h a t b o t h t h e o x i d i z e d a n d u n o x i d i z e d p o r t i o n s

h e r e c o n t a i n l e s s t h a n 0.1% c a r b o n s o t h e b l a c k c o l o r

o f t h e u n o x i d i z e d m a t e r i a l i s p r o b a b l y d u e t o t h e p r e s e n c e

o f f i n e l y d i s s e m i n a t e d p y r i t e a n d a r s e n o p y r i t e .

jarosite mainly gives the altered sequence its yellow

color. Pisanite-melanterite (solid solution series)

41

is present in several localities at Mercur and is the

main mineral in which copper is found here. Peculiqrly.

it is found predominantly in the relatively unoxidized

portions of the ore sequence suggesting that the degree

of oxidation of the ore had some influence as to location of

formation. The pisanite-melanterite usually is found

to occur as fracture fillings which might have resulted

either from the mineral's force of crystallization or

tectonic activity. A yellow variety of scorodite was

found in the Geyser-Marion mine area and was found to

have resulted from the direct oxidation of orpiment with

the addition of iron.

The weathering of the Long Trail Shale in the

Brickyard mine is of interest because of the lens-shaped

nature of the unoxidized portions. Close to the surface

the oxidized portions, in many instances, surround

the unoxidized portions. At depth, the unoxidized

portions form columns surrounded by oxidized matprial.

Figure 16 shows the lens-shaped nature of the unoxidized

portion in a stope of the Brickyard mine. Carbon assays

show that both the oxidized and unoxidized portions

here contain less than 0.1% carbon so the black color

of the unoxidized material is probably due to the presence

of finely disseminated pyrite and arsenopyrite.

4 2

S e m i - q u a n t i t a t i v e e m i s s i o n s p e c t r o g r a p h s a n a l y s e s

o f t h e o x i d i z e d a n d u n o x i d i z e d p o r t i o n s s h o w n i n F i g u r e

1 6 a r e p r e s e n t e d i n T a b l e 3.

F i g u r e 1 6 . P h o t o s h o w i n g r e l a t i o n s h i p s o f w e a t h e r e d ( m o t t l e d y e l l o w , w h i t e , a n d b r o w n ) t o u n w e a t h e r e d ( b l a c k ) s t r a t a i n a s t o p e o f t h e B r i c k y a r d m i n e .

42

Semi-quantitative emission spectrographic analyses

of the oXidized and unoxldlzed portions shown 1n Figure

16 are presented 1n Table J.

Figure 16. Photo showing relationships of weathered (mottled yellow. white. and brown) to unweathered (black) strata 1n a stope of the Brickyard mine.

ALTERATION OP THE EAGLE H I L L INTRUSIVE

T h e c h i e f v a r i e t i e s o f a l t e r a t i o n o f t h e i n t r u s i v e

i n c l u d e , k a o l i n i z a t i o n , s e r i c i t i z a t i o n , a n d s i l i c i f i c a t i o n ,

K a o l i n i t e i s p r e s e n t i n s m a l l a m o u n t s t h r o u g h o u t

t h e i n t r u s i v e . T h e a m o u n t o f k a o l i n i t e i n t h e i n t r u s i v e

i n c r e a s e s m a r k e d l y a r o u n d t h e S a c r a m e n t o b r e c c i a p i p e

w h e r e t h e I n t r u s i v e h a s b e e n h i g h l y a l t e r e d . T h e r h y o l i t e

d i k e a t t h e m o u t h o f M e r c u r G a n y o n h a s a l s o b e e n h i g h l y

a l t e r e d a n d k a o l i n i z e d . T h e o c c u r r e n c e o f

k a o l i n i t e p r e s u m a b l y r e s u l t e d f r o m e a r l y h i g h a c i d c o n d i t i o n s

o f t h e h y d r o t h e r m a l s o l u t i o n s , K a o l i n i t e h a s n o t b e e n

r e c o g n i z e d p r e v i o u s l y i n t h e i n t r u s i v e .

S e r i c i t e i s v e r y w i d e s p r e a d i n t h e g r o u n d m a s s o f

t h e i n t r u s i v e a s w e l l a s i n t h e a l t e r e d s e d i m e n t a r y

s e q u e n c e . I t i s d e f i n i t e l y a l a t e m i n e r a l a n d w a s

p r o b a b l y f o r m e d u n d e r l e s s a c i d c o n d i t i o n s t h a n t h e

k a o l i n i t e .

C a l c i t e i s p r e s e n t i n t h e i n t r u s i v e a n d i s p r o b a b l y

t h e r e s u l t o f h y d r o t h e r m a l a c t i v i t y a l t h o u g h s o m e c o u l d

b e t h e r e s u l t o f w e a t h e r i n g . Some o f t h e c a l c i t e r e p l a c e s

p l a g i o c l a s e . b u t m o s t o c c u r s r a n d o m l y d i s t r i b u t e d i n

t h e a l t e r e d g r o u n d m a s s .

S i l i c i f i c a t i o n i s t h e m o s t w i d e s p r e a d o f t h e

a l t e r a t i o n t y p e s a n d h a s c o m p l e t e l y a f f e c t e d t h e i n t r u s i v e .

Q u a r t z h a s b e e n a d d e d t o t h e f i n e - g r a i n e d g r o u n d m a s s

ALTERATION OF THE EAGLE HILL INTRUSIVE

The chief varieties of alteration of the intrusive

include, kaolinization, sericitization, and silicification.

Kaolinite is present in small amounts throughout

the intrusive. The amount of kaolinite in the intrusive

increases markedly around the Sacramento breccia pipe

where the intrusive has been highly altered. The rhyolite

dike at the mouth of Mercur Ganyon has also been highly

altered and kaolinized. The occurrence of

kaolinite presumably resulted from early high acid conditions

of the hydrothermal solutions. Kaolinite has not been

recognized previously in the intrusive.

Sericite is very widespread in the groundmass of

the intrusive as well as in the altered sedimentary

sequence. It is definitely a late mineral and was

probably formed under less acid conditions than the

kaolinite.

Calcite is present in the intrusive and is probably

the result of hydrothermal activity although some could

be the result of weathering. Some of the calcite replaces

plagioclase, but most occurs randomly distributed in

the altered groundmass.

Silicification is the most widespread of the

alteration types and has completely affected the intrusive.

Quartz has been added to the fine-grained groundrnass

4 4

i n a l l t h i n s e c t i o n s s t u d i e d . Some p h e n o c r y s t s h a v e

r i m s o f c o a r s e - g r a i n e d q u a r t z .

T h e a r e a a r o u n d t h e S a c r a m e n t o b r e c c i a p i p e i s

h i g h l y a l t e r e d ( F i g . 4 a n d 1 ? ) . M o s t o f t h e q u a r t z

a n d b i o t i t e p h e n o c r y s t s h a v e b e e n h y d r o t h e r m a l l y r e m o v e d

a n d a l l t h e p l a g i o c l a s e a n d s a n i d i n e p h e n o c r y s t s s e e m

t o h a v e b e e n h y d r o t h e r m a l l y r e m o v e d . T h e a d d i t i o n o f

q u a r t z c o n t a i n i n g n u m e r o u s i n c l u s i o n s i s p r o n o u n c e d i n

t h i s p a r t o f t h e i n t r u s i v e . T h e i n t r u s i v e h a s b e e n v e r y

s i l i c i f i e d h e r e a s h a s t h e s e d i m e n t a r y s e q u e n c e n e x t

t o t h e p i p e . T h e a l t e r e d i n t r u s i v e i n t h i s a r e a , a s

p r e v i o u s l y m e n t i o n e d , c o n t a i n s k a o l i n i t e a n d s e r i c i t e

a n d a l i t t l e c a l c i t e .

T w e n t y - t h r e e s a m p l e s f r o m t h e i n t r u s i v e a n d t h e

a l t e r e d s e d i m e n t a r y s e q u e n c e i n c o n t a c t w i t h i t w e r e

a n a l y z e d f o r Mn , Z n , A g , a n d C u b y a t o m i c a b s o r p t i o n

s p e c t r o p h o t o m e t r y ( F i g . 1 7 a n d T a b l e 1 ) , T h e p u r p o s e

w a s t o s e e i f a n y a n o m a l o u s v a l u e s o c c u r r e d i n t h e

h i g h l y a l t e r e d p o r t i o n s c o m p a r e d t o t h e l e s s a l t e r e d a r e a s .

T h e m e a n p l u s t w o s t a n d a r d d e v i a t i o n v a l u e s w e r e t a k e n t o

b e a n o m a l o u s v a l u e s w h i c h f o r t h e e l e m e n t s t e s t e d w o u l d

b e : Mn ( 1 3 5 * 3 p p m ) , Zn ( 3 ^ . 6 p p m ) , Ag ( 7 . ^ p p m ) , a n d Cu

( 1 3 . 1 p p m ) . S a m p l e s 1 0 2 , 1 0 9 , 1 3 0 , 1 3 2 , a n d 1 3 3 s h o w e d

a n o m a l o u s v a l u e s b u t o n l y 1 0 2 a n d 1 0 9 a r e I n t h e h i g h l y

a l t e r e d a r e a . No t r e n d i s r e a d i l y a p p a r e n t b e t w e e n t h e

h i g h l y a l t e r e d a n d t h e s l i g h t l y a l t e r e d s a m p l e s b u t a t o m i c

in all thin sections studied. Some phenocrysts have

rims of coarse-grained quartz.

The are3 3round the Sacramento breccia pipe is

highly altered (Fig. 4 and 17). Most of the quartz

44

and biotite phenocrysts have been hydrothermally removed

and all the plagioclase and sanidine phenocrysts seem

to have been hydrothermally removed. ~he addition of

quartz containing numerous inclusions is pronounced in

this part of the intrusive. The intrusive has been very

silicified here as has the sedimentary sequence next

to the pipe. The altered intrusive in this area, as

previously mentioned, contains kaolinite and sericite

and a 1ittle calcite.

Twenty-three samples from the intrusive and the

altered sedimentary sequence in contact with it were

analyzed for Mn, Zn, Ag, and Cu by atomic absorption

spectrophotometry (Fig. 17 and Table 1). The purpose

was to see if any anomalous values occurred in the

highly altered portions compared to the less altered areas.

The mean plus two standard deviation values were taken to

be anomalous values which for the elements tested would

be: Mn (1)5.) ppm), Zn ()4.6 ppm), Ag (7.4 ppm), and Cu

(1).1 ppm). Samples 102, 109, 1)0, 1)2, and 1)) showed

~nomalous values but only 102 and 109 are in the highly

altered area. No trend is readily apparent between the

highly altered and the slightly altered samples but atomic

^ 5

y > . t 305

Hob

*«3« _ «4Ci

Mob \ JUBi • 133*

Seal* 0 £ 3

> 131* ,,'

1000 f«*t

Kgb

ieg&nd Mgb Great Flue Llm?ctons ch Eagle Mill rhyolite Altered intrusive *• Silicified country rocK ! * Sample location » fault

N JO5 fcV Hgb

eh th

1

\ Mgb

G e n e r a l g e o l o g y m a p s h o w i n g a t o m i c p t i o n s a m p l e l o c a t i o n s .

T a b l e i .—Atomic A b s o r p t i o n V a l u e s

Sample Mn Zn Ag Cu

H i g h l y A l t e r e d 4 ppm 102 6 ppm 10 ppm 8 ppm 4 ppm

109 45 3 7 . 5 4 14 305 7 7 . 5 1 7 . 5 1 .5 5 404 9 16 k 2 . 5 405 5 9 1 .5 11 406 6 7 2 . 5 5 407 69 9 1 .5 6 702 2 0 4 . 5 2 . 5

S l i g h t l y A l t e r e d 46 130 100 46 6 4

131 101 2 . 5 2 . 5 6 132 1 6 2 . 5 9 4 2 . 5 133 50 10 8 2 . 5 134 35 4 2 . 5 11 301 40 7 . 5 1 .5 6 302 5 2 . 5 7 2 . 5 2 o 303 65 5 . 3 4 4 306 8 6 . 5 14 2 2 . 5 307 90 0 5 2 . 5 309 65 3 2 . 5 11 401 35 5 4 . 5 2 . 5 402 6 2 . 5 8 4 . 5 2 , 5 403 65 2 , 5 5 2 . 5 4 0 § 103 3 2 . 5 1 .5 0

1'------ , 134 •

,

\ \ ,

IlJ - ' ,,....-.~~ "

-"" } .. _---\, ' , ' , , , , .... , , \ , '

45

L~.~&nd ~6b (::rc,t FL.lt' Lim'::'Gton1J ch E.lC~:~ ;!1ll rhyullt.

~::- ~~ t~r("d 1l".t:'US1VC

~. ~11!clC~~d co~ntry rQc~

• ~~:fie lcc~tl~h

... ... "

Mgb , '- ~ " ... - I"

th

, - - .~.I ~ I

" th ,----" " ...

\ \ 11gb '-':

',"\ ,--'

Seale

o 1000 h.t ~=C-::::J , ,

"" '... , "" ..... --,

Figure 17. General geology m~p showing atomic absorption sample locatloDA.

Table 1.--Atomlc Absorption Values

Semple Mn Zn Ag Cu

Highly Altered 102 6ppru 10ppm 8ppro 4ppm 109 45 37.5 4 14 305 77.5 17.5 1.5 5 40lJ 9 16 1~ 2.5 405 5 9 1.5 11 406 6 7 2 &; 5 • .1

407 69 9 1.5 6 702 2 0 4.5 2~5

Slightly Altered 1}0 100 46 6 4 131 101 2.5 2.5 6 132 162.5 9 L~ 2.5 133 50 10 8 2.5 1Jl} )5 4 2.5 11 301 40 7.5 1.5 6 302 52.5 7 2.5 2., 30) 65 5.) 4 4 306 86.5 14 2 2.5 307 90 0 5 2.5 309 65 ) 2.5 11 401 35 5 4.5 2.5 402 62.5 8 4.5 2.5 403 65 2.5 5 2.5 IWq 103 32.5 1.5 0

• • lC~

)O} •

J

4 6

a b s o r p t i o n v a l u e s f o r o t h e r s a m p l e s f r o m t h e a l t e r e d

s e d i m e n t a r y s e q u e n c e s h o w h i g h e r v a l u e s f o r Zn t h a n

i n t h e u n a l t e r e d s e q u e n c e .

S i l i c i f i c a t i o n o f t h e c o u n t r y r o c k a r o u n d t h e

i n t r u s i v e ( P i g . 4 ) i s a p p a r e n t l y r e l a t e d t o f l u i d s w h i c h

e m a n a t e d f r o m t h e i n t r u s i v e . T h e d e g r e e o f a l t e r a t i o n

a r o u n d t h e S a c r a m e n t o b r e c c i a p i p e i s q u i t e p r o n o u n c e d ;

t h e a l t e r e d s e d i m e n t a r y s e q u e n c e s h o w s i n t e n s e s i l i c i f i c a t i o n .

T h e a r e a o f s i l i c i f i c a t i o n a r o u n d s a m p l e s i t e # 3 0 5 a n d

t h e a r e a t o t h e s o u t h a r e p r o b a b l y r e l a t e d t o t h e

d e p o s i t i o n o f q u a r t z b y h y d r o t h e r m a l f l u i d s f r o m t h e

i n t r u s i v e . T h e s e t w o s i l i c i f i e d a r e a s w e r e t h e o n l y a r e a s

w h e r e l a r g e p y r i t e c r y s t a l s a n d p y r i t l z e d f o s s i l s w e r e

f o u n d . S a m p l e # 3 0 5 w a s f o u n d t o c o n t a i n 1 6 ppm g o l d

( 0 . 4 6 o z A u / t o n ) w h i c h s u g g e s t s t h a t g o l d d e p o s i t i o n w a s

r e l a t e d t o h y d r o t h e r m a l a c t i v i t y t h a t a r o s e a s a

c o n s e q u e n c e o f i g n e o u s a c t i v i t y . T h e s i l i c i f i e d a r e a n e a r

s a m p l e s i t e # 3 0 9 i s a l s o e v i d e n t l y r e l a t e d t o h y d r o t h e r m a l

a c t i v i t y . T h e s i l i c i f i c a t i o n t o t h e SB o f t h e SB c o r n e r

o f F i g u r e 4 , n e a r t h e i n t r u s i v e , a l s o i s p r o b a b l y r e l a t e d

t o h y d r o t h e r m a l a c t i v i t y . T h e s e o c c u r r e n c e s s e e m t o

i n d i c a t e t h a t t h e c o n t a c t b e t w e e n t h e i n t r u s i v e a n d t h e

c o u n t r y r o c k w a s f a v o r a b l e f o r t h e p a s s a g e o f s o l u t i o n s

w h i c h r e p l a c e d c a l c i t e a n d d e p o s i t e d q u a r t z i n t h e c o u n t r y

r o c k . T h e t h r e e r o o f p e n d a n t s n o t r e m o v e d b y e r o s i o n f r o m

t h e r o o f o f t h e i n t r u s i v e s h o w n o n o t i c e a b l e a l t e r a t i o n .

absorption values for other samples from the altered

sedimentary sequence show higher values for Zn than

in the unaltered sequence.

46

Silicification of the country rock around the

intrusive (Fig. 4) is apparently related to fluids which

emanated from the intrusive. The degree of alteration

around the Sacramento breccia pipe is quite pronounced;

the altered sedimentary sequence shows intense silicification.

The area of silicification around sample site #305 and

the area to the south are probably related to the

deposition of quartz by hydrothermal fluids from the

intrusive. These two silicified areas were the only areas

where large pyrite crystals and pyritized f~ssils were

found. Sample #305 was found to contain 16 ppm gold

(0.46 oz Au/ton) which suggests that gold deposition was

related to hydrothermal activity that arose as a

consequence of igneous activity. The silicified area near

sample site #309 is also evidently related to hydrothermal

activity. The silicification to the SE of the SE corner

of Figure 4. near the intrusive, also is probably related

to hydrothermal activity. These occurrences seem to

indicate that the contact between the intrusive and the

country rock was favorable for the passage of solutions

which replaced calcite and deposited quartz in the country

rock. The three roof pendants not removed by erosion from

the roof of the intrusive show no noticeable alteration.

T h e c h e m i c a l w e a t h e r i n g o f t h e i n t r u s i v e i s very

s u b t l e . I n p a r t s o f t h e i n t r u s i v e , w e a t h e r i n g h a s r e m o v e d

m o r e o f s p e c i f i c l a y e r s r e s u l t i n g i n l a y e r e d r i d g e s t h a t

g i v e t h e r o c k a f a l s e - f l o w a g e c h a r a c t e r , N e a r t h e S a c r a m e n t o

b r e c c i a p i p e , s m a l l h e m a t i t e s p o t s i n t h e i n t r u s i v e m i g h t

r e p r e s e n t t h e f o r m e r p r e s e n c e o f f i n e l y d i s s e m i n a t e d

p y r i t e . Some o f t h e b i o t i t e f l a k e s a t t h e s u r f a c e a r e

w e a t h e r e d .

T h e E a g l e H i l l i n t r u s i v e s h o w s p r o g r e s s i v e

m e t a m o r p h i s m i n t h e M e r c u r a r e a . T h e g r o u n d m a s s w a s

p r o b a b l y t h e f i r s t t o b e a l t e r e d w i t h s a n i d i n e b e i n g

a l t e r e d t o k a o l i n i t e a n d t h e n t o s e r i c i t e w i t h d e c r e a s i n g

a c i d c o n d i t i o n s . P l a g i o c l a s e p h e n o c r y s t s a r e r a r e i n t h e

i n t r u s i v e a t M e r c u r a n d a p p a r e n t l y w e r e h y d r o t h e r m a l l y

r e m o v e d . T h e a m o u n t o f b i o t i t e p r e s e n t a p p e a r s t o b e a

g o o d i n d i c a t o r o f h y d r o t h e r m a l a l t e r a t i o n . W h e r e b i o t i t e

i s a b s e n t o r s c a r c e h y d r o t h e r m a l a l t e r a t i o n h a s b e e n m o s t

i n t e n s e . T h e i r o n f r o m t h e b i o t i t e i s b e l i e v e d t o h a v e

g o n e t o w a r d t h e f o r m a t i o n o f p y r i t e . S a n i d i n e p h e n o c r y s t s

a l s o a r e l e s s c o m m o n w h e r e h y d r o t h e r m a l a l t e r a t i o n w a s

m o r e i n t e n s e . Q u a r t z p h e n o c r y s t s a l s o s e e m t o b e i n d i c a t i v e

o f t h e i n t e n s i t y o f a l t e r a t i o n a l t h o u g h t o a l e s s e r d e g r e e

t h a n t h e l a c k o f b i o t i t e , p l a g i o c l a s e , a n d s a n i d i n e

p h e n o c r y s t s . Q u a r t z p h e n o c r y s t s a r e n o t c o m m o n i n

t h e i n t r u s i v e n e a r t h e S a c r a m e n t o b r e c c i a p i p e .

47

The chemical weathering of the intrusive is v~ry

subtle. In parts of the intrusive, weathering has removed

more of specific layers resulting in layered ridges that

give the rock a false-flowage character. Near the Sacramento

breccia pipe, small hematite spots in the intrusive might

represent the former presence of finely disseminated

pyrite. Some of the biotite flakes at the surface are

weathered.

The Eagle Hill intrusive shows progressive

metamorphism in the Mercur area. The groundmass was

probably the first to be altered with sanidine being

altered to kaolinite and then to sericite with decreasing

acid conditions. Plagioclase phenocrysts are rare in the

intrusive at Mercur and apparently were hydrothermally

removed. The amount of biotite present appears to be a

good indicator of hydrothermal alteration. Where biotite

is absent or scarce hydrothermal alteration has been most

intense. The iron from the biotite is believed to have

gone toward the formation of pyrite. Sanidine phenocrysts

also are less common where hydrothermal alteration was

more intense. Quartz phenocrysts also seem to be indicative

of the intensity of alteration although to a lesser degree

than the lack of biotite, plagioclase, and sanidine

phenocrysts. Quartz phenocrysts are not common in

the intrusive near the Sacramento breccia pipe.

THE GOLD D E P O S I T S

T h e g o l d d e p o s i t s a r e r e p l a c e m e n t d e p o s i t s t h a t

a r e l a r g e l y s t r a t i g r a p h i c a l l y c o n t r o l l e d . T h e y a r e

c h a r a c t e r i z e d m i n e r a l o g i c a l l y b y t h e p r e s e n c e o f o r p l m e n t ,

r e a l g a r ( F i g , 1 8 ) , a r s e n o p y r l t e , f i n e l y d i s s e m i n a t e d

p y r i t e , a n d l o c a l l y c i n n a b a r . G a l e n a , c i n n a b a r , s p h a l e r i t e ,

s u l v a n i t e , a n d c h a l c o p y r i t e h a v e b e e n r e p o r t e d a l t h o u g h

t h e y w e r e n o t o b s e r v e d b y t h e a u t h o r . S p u r r ( 1 8 9 ^ - 9 5 ,

p . 4 3 0 ) r e p o r t e d t h e p r e s e n c e o f r e a l g a r a s b e i n g a

f a v o r a b l e s i g n o f g o l d m i n e r a l i z a t i o n , b u t n o t a l w a y s .

A l l p r e v i o u s i n v e s t i g a t o r s r e p o r t t h e g o l d a s n o t b e i n g

v i s i b l e i n p o l i s h e d s e c t i o n a l t h o u g h i t w a s r e p o r t e d a s

b e i n g v i s i b l e b y u s e o f t h e r e f l e c t i n g m i c r o s c o p e o n c e

t h e o r e h a d b e e n r o a s t e d . T h e a u t h o r , t h r o u g h s t u d y o f

p o l i s h e d s e c t i o n s f r o m t h e o r e s e q u e n c e , w a s u n a b l e

t o d e t e c t a n y v i s i b l e g o l d .

T h e p r e s e n c e o f o r p l m e n t a n d r e a l g a r i s u s u a l l y

a t t r i b u t e d t o l o w t e m p e r a t u r e h y d r o t h e r m a l e n v i r o n m e n t s ,

s u c h a s h o t s p r i n g s . T h e g o l d d e p o s i t s a t M e r c u r p r o b a b l y

a r e o f t h e e p i t h e r m a l t y p e a n d w e r e p r o b a b l y e m p l a c e d

a t s h a l l o w d e p t h s i n a t y p i c a l h o t s p r i n g e n v i r o n m e n t .

N i c h o l s a n d P e t e r s o n ( 1 9 7 0 ) o f t h e U . S . B u r e a u o f

M i n e s m a d e a s t u d y o f t h e m i l l t a i l i n g s a t M e r c u r a i m e d

a t d e v i s i n g a p r o f i t a b l e m e t h o d f o r e x t r a c t i n g t h e

r e m a i n i n g g o l d f r o m t h e t a i l i n g s . T h e y s t a t e t h a t t h e i r

" q u a l i t a t i v e a n a l y t i c a l m e t h o d s s h o w e d t h a t g o l d i s

THE GOLD DEPOSITS

The gold deposits are replacement deposits that

are largely stratigraphically controlled. They are

characterized mineralogically by the presence of orp1ment,

realgar (Fig. 18), arsenopyrite, finely disseminated

pyrite, and locally cinnabar. Galena. cinnabar, sphalerite,

sulvanite. and chalcopyrite have been reported although

they were not observed by the author. Spurr (1894-95,

p. 4)0) reported the presence of realgar as being a

favorable sign of gold mineralization, but not always.

All previous investigators report the gold as not being

visible in polished section although it was reported as

be1ng visible by use of the reflecting microscope once

the ore had been roasted. The author, through study of

polished sections from the ore sequence. was unable

to detect any visible gold.

The presence of orpiment and realgar is usually

attributed to low temperature hydrothermal environments,

such as hot springs. The gold deposits at Mercur probably

are of the epithermal type and were probably emplaced

at shallow depths in a typical hot spring environment.

Nichols and Peterson (1970) of the U.S. Bureau of

Mines made a study of the mill tailings at Mercur aimed

at devising a profitable method for extracting the

remaining gold from the tailings. They state that the1r

-qualitative analytical methods showed that gold is

4 9

F i g u r e 1 8 . P h o t o s h o w i n g o r p l m e n t ( y e l l o w ) a n d r e a l g a r ( r e d ) i n t h e u n o x i d i z e d z o n e o f t h e B r i c k y a r d m i n e . T h e w h i t e p o r t i o n s a r e t h e s u l f a t e m e l a n t e r i t e - p i s a n i t e w h i c h i s p r e s e n t .

a s s o c i a t e d w i t h a l l m i n e r a l s w i t h a h i g h e r c o n c e n t r a t i o n

i n t h e o r g a n i c a n d m a g n e t i c m i n e r a l s * ( N i c h o l s a n d P e t e r s o n ,

1 9 7 0 , p . 6 ) .

G o l d s e e m i n g l y h a s b e e n m i n e d f r o m t h e a l t e r e d

s e d i m e n t a r y b e d s i n c o n t a c t w i t h o r f r o m t h e b r e c c i a

z o n e s a t M e r c u r . T h e t w o s i l i c i f i e d b r e c c i a p i p e s a c t e d

a s c h a n n e l w a y s f o r h y d r o t h e r m a l s o l u t i o n s , b u t d o n o t

a p p e a r t o h a v e b e e n m i n e d f o r g o l d . T h e z o n e s a r o u n d

t h e b r e c c i a p i p e s h a v e b e e n m i n e d f o r g o l d , w h i c h s u g g e s t s

t h a t g o l d d e p o s i t i o n p r e c e d e d p i p e f o r m a t i o n o r t h a t t h e

z o n e s a r o u n d t h e p i p e s w e r e m o r e f a v o r a b l e f o r g o l d

d e p o s i t i o n t h a n t h e b r e c c i a p i p e s t h e m s e l v e s . T h e

f a u l t b r e c c i a z o n e s a p p e a r t o h a v e f o r m e d l a t e r t h a n t h e

Figure 18. Photo shol<ling orpiment (yellow) and rea lgar (red) 1n the unoxidized zone of the Brickyard mine . The white portions are the s ulfate melanterite -pisanlte which is present.

associated with all minera ls with a higher concentrat ion

in the orga nic and magnetic minerals· (Nichols and Peterson.

1970 . p. 6).

Gold seemingly has been mined from the altered

sedimentary beds in contact with or from the breccia

zones at Mercur. ~he two sIlIcified breccia pipes ac ted

as c hannelways fo r hydrothermal solutions, but do not

appear to have been mined for go ld. The zones around

t he breccia pipes have been mined for gold, which suggests

that go ld deposition preceded pipe formation or that the

zones around the pipes were more favorable for go ld

deposition than the breccia pipes themselves. The

f quIt breccia zones appe~r to have formed later than the

50

h y d r o t h e r m a l a l t e r a t i o n , b u t g o l d e n r i c h m e n t c o u l d h a v e

o c c u r r e d f r o m t h e s o l u t i o n a n d r e m o v a l o f c a l c i t e .

C i n n a b a r w a s m i n e d c o m m e r c i a l l y f o r m e r c u r y

o n l y a t t h e S a c r a m e n t o g o l d m i n e i n t h e M e r c u r c a m p .

M e r c u r y w a s r e p o r t e d t o o c c u r i n t r a c e a m o u n t s a s

c i n n a b a r w i t h t h e g o l d d e p o s i t s i n t h e o t h e r m i n e s o f

t h e c a m p . T h e c o m m e r c i a l c o n c e n t r a t i o n s o f m e r c u r y

a t t h e S a c r a m e n t o m i n e c o u l d b e c a u s e d b y t h e s a m e p r o c e s s e s

t h a t f o r m e d t h e S a c r a m e n t o b r e c c i a p i p e . U n s a f e c o n i t i o n s

f o r e n t r y t o t h e o l d m i n e w o r k i n g s d i d n o t a l l o w

e x a m i n a t i o n o f t h e o r e s e q u e n c e u n d e r g r o u n d a t t h e

S a c r a m e n t o m i n e . E x a m i n a t i o n o f t h e q u a r r y a r e a d i d n o t

r e v e a l t h e p r e s e n c e o f a n y c i n n a b a r .

G e n e r a l p a r a g e n e t i c r e l a t i o n s f o r t h e g o l d d e p o s i t s

c a n b e g i v e n f r o m g e n e r a l f i e l d , p o l i s h e d s e c t i o n , o r

t h i n s e c t i o n o b s e r v a t i o n s . T h e r e p l a c e m e n t o f c a l c i t e

i n t h e l i m e s t o n e b e d s b y q u a r t z p r o b a b l y o c c u r r e d f i r s t .

L o c a l l y s e r i c i t e a n d i l l i t e a c c o m p a n y t h e q u a r t z . P y r i t e

a n d a r s e n o p y r i t e d e p o s i t i o n f o l l o w e d w i t h a n h e d r a l p y r i t e

f o r m i n g b e f o r e t h e e u h e d r a l p y r i t e . A n h e d r a l p y r i t e

a n d a r s e n o p y r i t e v i e w e d i n t h i n s e c t i o n o c c u r b e t w e e n

t h e i n d i v i d u a l q u a r t z g r a i n s i n r o c k s f r o m t h e B r i c k y a r d

m i n e . E u h e d r a l p y r i t e , i n p o l i s h e d s e c t i o n , w a s o b s e r v e d

t o h a v e f o r m e d a r o u n d t h e q u a r t z g r a i n s . O r p i m e n t a n d

r e a l g a r a r e a p p a r e n t l y l a t e m i n e r a l s s i n c e t h e y o c c u r

a s f r a c t u r e a n d v u g f i l l i n g s . Some o f t h e b e s t

50

hydrothermal alteration, but gold enrichment could h~ve

occurred from the solution and removal of calcite.

Cinnabar was mined commercially for mercury

only at the Sacramento gold mine in the Mercur camp.

Mercury was reported to occur in trace amounts as

cinnabar with the gold deposits in the other mines of

the camp. The commercial concentrations of mercury

at the Sacramento mine could be caused by the same processes

that formed the Sacramento breccia pipe. Unsafe conitions

for entry to the old mine workings did not allow

examination of the ore sequence underground at the

Sacramento mine. Examination of the quarry area did not

reveal the presence of any cinnabar.

General paragenetic relations for the gold de~osits

can be given from general field, polished section, or

thin section observations. The replacement of calcite

in the limestone beds by quartz probably occurred first.

Locally sericite and illite accompany the quartz. Pyrite

and arsenopyrite deposition followed with anhedral pyrite

forming before the euhedral pyrite. Anhedral pyrite

and arsenopyrite viewed in thin section occur between

the individual quartz grains in rocks from the Brickyard

mine. Euhedral pyrite, in polished section, was observed

to have formed around the quartz grains. Orpiment and

realgar are apparently late minerals since they occur

as fracture and vug fillings. Some of the best

c r y s t a l l i n e r e a l g a r w a s f o u n d i n l i m e s t o n e v u g s

s u r r o u n d e d b y c a l c i t e c r y s t a l s . T h e t i m e a t w h i c h

g o l d d e p o s i t i o n o c c u r r e d i s u n k n o w n b e c a u s e g o l d c o u

n o t b e s e e n . S i n c e g a l e n a , s p h a l e r i t e , a n d c i n n a b a r

w e r e n o t o b s e r v e d t h e i r p a r a g e n e t i c r e l a t i o n s a l s o

a r e u n k n o w n .

crystalline realgar was found in limestone vugs

surrounded by calcite crystals. The time at which

gold deposition occurred is unknown because gold could

not be seen. Since galena, sphalerite, and cinnabar

were not observed their paragenetic relations also

are unknown.

51

ELEMENTAL ANALYSES OP ROCK SAMPLES

Q u a l i t a t i v e e m i s s i o n s p e c t r o g r a p h s a n a l y s e s o f

r o c k s a m p l e s f r o m t h e g o l d l e d g e s e q u e n c e a r e g i v e n i n

T a b l e 2 . T h e s i m i l a r i t y o f e l e m e n t a l c o m p o s i t i o n b e t w e e n

r o c k s f r o m t h e s l i g h t l y a l t e r e d L o n g T r a i l S h a l e ( C - 1 0 3 ) ,

t h e a l t e r e d L o n g T r a i l S h a l e ( 6 0 2 ) , a n d t h e c a r b o n - r i c h

r o c k ( G - 1 0 1 ) i s o f I n t e r e s t b e c a u s e t h e I n t e n s i t y o f

a l t e r a t i o n a p p a r e n t l y d o e s n o t a f f e c t t h e e l e m e n t s p r e s e n t .

T h e u n a l t e r e d L o w e r G r e a t B l u e L i m e s t o n e s a m p l e ( 5 0 1 )

w a s c o l l e c t e d f r o m t h e s o u t h e r n p a r t o f t h e G e y s e r - M a r i o n

m i n e . T h e a l t e r e d L o w e r G r e a t B l u e L i m e s t o n e ( 3 0 5 )

s a m p l e w a s c o l l e c t e d f r o m a s i l i c i f i e d - p y r i t i z e d z o n e

n e x t t o t h e i n t r u s i v e . T h e d i f f e r e n c e s i n e l e m e n t a l

c o m p o s i t i o n a r e o b v i o u s b e t w e e n t h e s e t w o r o c k s a m p l e s

w i t h t h e a l t e r e d r o c k s a m p l e s h o w i n g t h e p r e s e n c e o f

g o l d . T h e p r e s e n c e o f A s , B , A u . P b , H g , K, S i , A g , T l ,

a n d Zn c h a r a c t e r i z e t h e a l t e r e d s a m p l e s a n d a r e b e l i e v e d

t o r e p r e s e n t e l e m e n t s d e p o s i t e d f r o m h y d r o t h e r m a l s o l u t i o n s .

S e m i - q u a n t l t a t l v e e m i s s i o n s p e c t r o g r a p h l c a n a l y s e s

f o r t h r e e r o c k s a m p l e s a r e g i v e n i n T a b l e 3. T h e v a l u e s

g i v e n s h o u l d n o t b e t a k e n t o r e p r e s e n t e x a c t v a l u e s b u t

o n l y t o r e p r e s e n t a n e l e m e n t ' s p r e s e n c e . T h e d e t e c t i o n

l i m i t f o r t e l l u r i u m i s 0 . 0 1 $ w h i c h i n d i c a t e s t e l l u r i u m

i s n o t p r e s e n t i n s u f f i c i e n t c o n c e n t r a t i o n s i n t h e s e

s a m p l e s t o b e d e t e c t e d . O t h e r u n p u b l i s h e d a n a l y s e s

ELEMENTAL ANALYSES OF ROCK SAMPLES

Qualitative emission spectrographic analyses of

rock samples from the gold ledge sequence are given in

Table 2. The similarity of elemental composition between

rocks from the slightly altered Long Trail Shale (C-l03).

the altered Long Trail Shale (602), and the carbon-rich

rock (~~101) is of interest beoause the intensity of

alteration apparently does not affect the elements present.

The unaltered Lower Great ~ue Limestone sample (501)

was collected from the southern part of the Geyser-Marion

mine. The altered Lower Great Blue Limestone (305)

sample was collected from a silicified-pyritized zone

next to the intrusive. The differences in elemental

composition are obvious between these two rock samples

with the altered rock sample showing the presence of

gold. The presence of As, B, Au, Pb, Hg, K. Si. Ag. TI,

and Zn characterize the altered samples and are believed

to represent elements deposited from hydrothermal solutions.

Semi-quantitative emission spectrographic analyses

for three rock samples are given in Table 3. The values

given should not be taken to represent exact values but

only to represent an element's presence. The detection

limit for tellurium is 0.01% which indicates tellurium

is not present in sufficient concentrations in these

samples to be detected. Other unpublished analyses

T a b l e 2 . — Q u a l i t a t i v e E m i s s i o n S p e c t r o g r a p h s A n a l y s e s o f R o c k S a m p l e s P r o m M e r c u r , U t a h

E l e m e n t C - 1 0 3 C - 1 0 1 6 0 2 5 0 1 3 0 5

Ag X X X A l X X X X X As X X T r X Au X B X X X X C a X X X X X C r X X X X X F e X X X T r X Hg X X X X K X X X T r X Mg X X X X X Mn X X T r T r Na X X X X X P b X X X X S i X X X X X T i X X X X X T l X X Zn X X

c - 1 0 3 - - s l i g h t l y a l t e r e d L o n g T r a i l S h a l e C - 1 0 1 - - c a r b o n - r i c h r o c k , S a c r a m e n t o m i n e 6 0 2 — - g o l d o r e , L o n g T r a i l S h a l e , B r i c k y a r d m i n e 5 0 1 — - u n a l t e r e d L o w e r G r e a t B l u e L i m e s t o n e 3 0 5 — - a l t e r e d L o w e r G r e a t B l u e L i m e s t o n e

X e l e m e n t p r e s e n t T r — t r a c e o f e l e m e n t p r e s e n t

Table 2.--Qualitative Emission Spectrographic Analyses of Rock Samples From Mercur. Utah

Element C'-103 C-10l 602 501 305

Ag X X X Al X X X X As X X Tr Au B X X X Ca X X X X Cr X X X X Fe X X X Tr Hg X X X K X X X Tr Mg X X X X Mn X X Tr Na X X X X Pb X X X Si X X X X Ti X X X X TI X Zn X X

C-103--slightly altered Long Trail Shale C-10l--carbon-rich rock, Sacramento mine 602----gold ore, Long Trail Shale, Brickyard mine 501----unaltered nower Great Blue Limestone 305----altered Lower Great Blue Limestone

X---element present Tr--trace of element present

X X X X X X X X X X Tr X X X X X

53

5 *

T a b l e 3 - — S e m i - q u a n t i t a t i v e E m i s s i o n S p e c t r o g r a p h i c A n a l y s i s o f R o c k S a m p l e s F r o m M e r c u r , U t a h

Unweathered gold ore Weathered gold ore Carbon-rich rock Element Brickyard mine Brickyard mine Sacramento mine

Ag .0001* .0005* .0006* Al ca 4.0 ca 5.0 ca 3.0 As .12 .13 .02 Au N.O. N.D.. N.D.. B .008 .008 .01 Ba .02 .03 .01 Be .0003 .0003 .0002 Bi N.D. N.D.. N.D. Ca .003 .05 .20 Cb N.D. N.D. N.D. Cd N.D. N.D. N.D. Ce N.D. N.D. N.D. Co <.001 <.001 <.001 Cr .005 .004 .006 Cu .80 .20 .15 Pe ca 4.0 ca 4.0 ca 3.0 Ga < .001 <.001 < .001 Ge N.D.. N.D. N.D. Hf N.D. N.D. N.D. Hg N.D.. N.D. N.D. In < .001 <.001 1 .001 La .01 .01 <.01 Mg .15 .15 .15 Mn .001 .003 .0005 Mo <.001 <.001 <.001 Na .03 .07 .30 Ni .000? .0004 .0005 P .04 .06 .03 Pb .0004 .0004 .0005 Pd N.D. N.D. N.D. Pt N.D. N.D.. N.D. Sb .001 .001 .001 Si ca 20.0 ca 20.0 ca 20.0 Sn N.D. .0003 .0003 Ta N.D. N.D.. N.D. Te N.D. N.D. N.D. Th N.D. N.D. N.D. Ti .15 .15 .10 V .003 .004 .006 w N.D.. N.D* N.D. Y .002 .002 .003 Zn ca .1 ca .1 <.01 Zr .008 .013 .005 N.D. not detected ca approximately < less than Analyzed by R. Woods, Kennecott Research Center

Table J.--Semi-quantitative Emission Spectrographic Analysis of Rock Samples From Mercur. Utah

Unweathered gold ore Weathered gold ore Carbon-r1ch rock Element Br1ckyard m1ne Br1ckyard m1ne Sacramento m1ne

Ag .000U .0005% .0006% AI ca 4.0 ca 5.0 ca 3.0 A8 .12 .1) .02 Au N.D. N.D •. N.D •. B .008 .008 .01 BIt .02 .03 .01 Be .0003 .0003 .0002 B1 N.D. N.D •. N.D. Ca .003 .05 .20 Cb N.D. N.D. N.D. Cd N.D. N.D. N.D. Ce N.D. N.D. N.D. Co < .001 <..001 <..001 Cr .005 .004 .006 Cu .BO .20 .15 Fe ca 4.0 ca 4.0 ~a 3.0 Ga < .001 <. .001 .001 Ge N.D •. N.D. N.D. at N.D. N.D. N.D. Bg N.D •. N.D. N.D. In < .001 <.001 .( .001 La .01 .01 <. .01 fig .15 .15 .15

"" .001 .003 .0005

"0 (.001 <.001 (.001 !fa .03 .07 .30 .1 .0007 .0004 .0005 p .04 .06 .03 Pb .0004 .0004 .0005 I'd N.D. N.D. N.D. Pt N.D. N.D •. N.D. 8b .001 .001 .001 81 ca 20.0 ca 20.0 ca 20.0 8n N.D. .0003 .0003 Ta N.D. N.D •. N.D. Te N.D. N.D. N.D. Th N.D. N.D. N.D. '1',. .15 .15 .10 V .003 .004 .006 V N.D •. N.D. N.D. I· .002 .002 .003 ZD ca .1 ca .1 <.01 Zr .008 .01) .005

N.D. not detected ca approx1mately

< less thlln

Analyzed by R. Woods, Kennecott Research Center

5 5

s h o w t e l l u r i u m i s p r e s e n t a s p r e v i o u s l y p u b l i s h e d a n a l y s e

h a v e s h o w n . T h e b o r o n p r e s e n t i s b e l i e v e d t o b e h e l d i n

t h e c r y s t a l s t r u c t u r e o f t h e c l a y m i n e r a l s . T h e s o u r c e

f o r t h e b o r o n w a s p r o b a b l y t h e h y d r o t h e r m a l s o l u t i o n s

t h a t a t o n e t i m e p e r v a d e d t h e s e q u e n c e . T h e h i g h

p e r c e n t a g e o f c o p p e r i s o f i n t e r e s t s i n c e n o p r e v i o u s l y

p u b l i s h e d a n a l y s e s i n d i c a t e a n y m o r e t h a n a t r a c e o f

c o p p e r . T h e h i g h c o p p e r a n a l y s e s c o m e s f r o m a p o r t i o n

o f t h e s e q u e n c e t h a t d o e s c o n t a i n m e l a n t e r i t e - p i s a n i t e

b u t t h e s a m p l e s e l e c t e d d i d n o t h a v e a n y o f t h e s u l f a t e

m i n e r a l v i s i b l e .

A t o m i c a b s o r p t i o n a n a l y s i s v a l u e s f o r Mn, Z n , A g ,

a n d C u f o r o t h e r s e l e c t e d s a m p l e s s h o w e d a h i g h a m o u n t

o f z i n c t o b e p r e s e n t i n t h e a l t e r e d s e q u e n c e c o m p a r e d

t o t h e u n a l t e r e d s e q u e n c e . T h e u n a l t e r e d l i m e s t o n e

( 5 0 1 ) s h o w e d a h i g h a m o u n t o f s i l v e r ( 1 0 p p m ) w h i c h t h e

q u a l i t a t i v e e m i s s i o n s p e c t r o g r a p h i c a n a l y s i s f a i l e d

t o s h o w .

55

show tellurium is present as previously published analyses

have shown. The boron present is believed to be held in

the crystal structure of the clay minerals. The source

for the boron was probably the hydrothermal solutions

that at one time pervaded the sequence. The high

percentage of copper is of intereRt since no previously

published analyses indicate any more than a trace of

copper. The high copper analyses comes from a portion

of the sequence that does contain melanterite-pisanite

but the sample selected did not have any of the sulfate

mineral visible.

Atomic absorption analysis values for Mn, Zn, Ag,

and eu for other selected samples showed a high amount

of zinc to be present in the altered sequence compared

to the unaltered sequence. The unaltered limestone

(501) showed a high amount of silver (10 ppm) which the

qu~litative emission spectrographic analysis failed

to show.

IMPLICATIONS OF CARBON AND ORGANIC COMPOUNDS

T h e a s s o c i a t i o n o f c a r b o n w i t h t h e g o l d d e p o s i t s

o f M e r c u r h a s b e e n k n o w n f o r m a n y y e a r s . Many i n v e s t i g a t o r s

h a v e s t u d i e d t h e a b i l i t y o f c a r b o n a n d o r g a n i c a c i d s

t o p r e c i p i t a t e g o l d f r o m s o l u t i o n . Ong a n d S w a n s o n

( I 9 6 9 ) h a v e f o u n d t h a t c o l l o i d a l g o l d c a n b e p r e c i p i t a t e d

f r o m g o l d c h l o r i d e s o l u t i o n s b y c e r t a i n o r g a n i c a c i d s .

T h e y s t a t e t h a t , * i n a c i d i c s o l u t i o n s , f o r e x a m p l e n e a r

o r e d e p o s i t s w h e r e t h e pH i s o f t e n l e s s t h a n 3 , g o l d c a n

b e t r a n s p o r t e d a s g o l d c h l o r i d e i o n s . H o w e v e r , o r g a n i c

a c i d s a r e n o t s o l u b l e i n t h i s a c i d e n v i r o n m e n t a n d a r e

t h u s i n c a p a b l e o f t r a n s p o r t i n g g o l d . I f o r g a n i c a c i d s

h a v e b e e n p r e c i p i t a t e d n e a r a n o r e d e p o s i t t h e g o l d i t s e l f

w i l l b e p r e c i p i t a t e d f r o m s o l u t i o n a s c o l l o i d s o f m e t a l l i c

g o l d a n d i n c o r p o r a t e d w i t h t h e o r g a n i c m a t t e r * ( O n g

a n d S w a n s o n , I 9 6 9 . P - 4 2 1 ) , T h e y g i v e n o c r i t e r i a f o r

s t a t i n g t h a t o r g a n i c a c i d s a r e n o t s o l u b l e i n a n a c i d

e n v i r o n m e n t o f l e s s t h a n a pH o f 3» R a d t k e a n d S c h e i n e r

( 1 9 7 0 , p , 9 7 ) , who h a v e d o n e w o r k o n t h e C a r l i n g o l d

d e p o s i t , h a v e c o n d u c t e d o r g a n i c e x t r a c t i o n s o n c a r b o n - r i c h

g o l d o r e s a m p l e s f r o m C a r l i n , N e v a d a , a n d h a v e f o u n d

t h e m t o c o n t a i n h u m i c a c i d s , ( I f t h e y m e a n c a r b o x y l i c

a c i d s t h e i n f r a r e d s p e c t r a t h e y p r e s e n t d o n o t c o r r e s p o n d

t o a c a r b o x y l i c a c i d s p e c t r a . ) F r o m t h e f l o w d i a g r a m

f o r a NaOH e x t r a c t i o n g i v e n b y D e g e n s a n d R e u t e r ( 1 9 6 4 ,

IMPLICATIONS OF CARBON AND ORGANIC COMPOUNDS

The association of carbon with the gold deposits

of Mercur has been known for many years. Many investigators

have studied the ability of carbon. and organic acids

to precipitate gold from solution. Ong and Swanson

(1969) have found that colloidal gold can be precipitated

from gold chloride solutions by certain organic acids.

They state that. -in acidic solutions, for example near

ore deposits where the pH is often less than 3, gold can

be transported as gold chloride ions. However, organic

acids are not soluble in this acid environment and are

thus incapable of transporting gold. If organic acids

have been precipitated near an ore deposit the gold itself

will be precipitated from solution as colloids of metallic

gold and incorporated with the organic matter- (Ong

and Swanson. 1969. p. 421). They give no criteria for

stating that organic acids are not soluble in an acid

environment of less than a pH of 3. Radtke and Scheiner

(1970, p. 97), who have done work on the Carlin gold

deposit, have conducted organic extractions on carbon-rich

gold ore samples from Carlin. Nevada. and have found

them to contain humic acids. (If they mean carboxylic

acids the infrared spectra they present do not correspond

to a carboxylic acid spectra.) From the flow diagram

for a NaOH extraction given by Degens and Reuter (1964.

5 ?

p - 3 8 5 ) o n e w o u l d e x p e c t t o e x t r a c t h u m i c a c i d s . T h e y

b e l i e v e m o s t o f t h e g o l d o c c u r s a s a n o r g a n o m e t a l l i c

c o m p l e x i n t h e Au ( I ) v a l e n c e s t a t e a n d t h u s m o s t o f

t h e g o l d I s n o t p r e s e n t i n a f r e e s t a t e i n t h e r o c k s .

V a r i a t i o n s o f t h e o r g a n i c e x t r a c t i o n t e c h n i q u e s

g i v e n b y D e g e n s a n d R e u t e r ( 1 9 6 4 ) w e r e u s e d b y t h e a u t h o r

o n s a m p l e s f r o m M e r c u r , U t a h ; G e t c h e l l M i n e , N e v a d a

( s a m p l e t a k e n f r o m d u m p ) ; a n d t h e N e w m o n t m i n e , C a r l i n ,

N e v a d a ( s a m p l e f r o m t h e e a s t p i t ) , t o d e t e r m i n e i f

h y d r o c a r b o n s w e r e p r e s e n t .

T h r e e m e t h o d s o f e x t r a c t i o n , w h i c h w i l l b e d e s c r i b e d

b r i e f l y b e l o w , w e r e u s e d o n c r u s h e d c a r b o n - r i c h r o c k

s a m p l e s w i t h t h e o r g a n i c e x t r a c t b e i n g d i s s o l v e d i n C C l ^

b e f o r e b e i n g i n j e c t e d i n t o W i l k s c e l l s f o r u s e i n a

B e c k m a n I R * 2 0 s p e c t r o p h o t o m e t e r . T h e i n f r a r e d s p e c t r a

o b t a i n e d w e r e c o m p a r e d a g a i n s t t h e s p e c t r a f o r p u r e

C C l ^ t o d e t e r m i n e w h i c h o r g a n i c s w e r e p r e s e n t . E x t r a c t i o n

t e c h n i q u e s i n v o l v e d u s i n g a m i x t u r e o f b e n e z e n e , m e t h a n o l ,

a n d a c e t o n e ; 0 , 3 N NaOH; o r 0 . 5 N NH/jAc s o l u t i o n s .

I n t h e b e n e z e n e - m e t h a n o l - a c e t o n e m e t h o d ( 7 0 : 1 5 : 1 5

b y v o l u m e ) , t h e B-M-A m i x t u r e w a s f o u n d t o l e a v e a n

i n f r a r e d d e t e c t a b l e r e s i d u e w h i c h w a s d e l e t e r i o u s t o

i n t e r p r e t a t i o n o f t h e M e r c u r , C a r l i n , a n d G e t c h e l l s a m p l e s .

T h e o r g a n i c e x t r a c t i o n t e c h n i q u e u s i n g a 0 . 3 N NaOH

s o l u t i o n w a s f o u n d t o b e m o r e e f f e c t i v e t h a n t h e B-M-A

p. 385) one would expect to extr~ct humic acids. They

believe most of the gold occurs as an organometallic

complex in the Au (I) valence state and thus most of

the gold is not present in a free state in the rocks.

5'1

Variations of the organic extraction techniques

given by Degens and Reuter (1964) were used by the author

on samples from Mercur, Utah; Getchell Mine, Nevada

(sample taken from dump); and the Newmont mine, Carlin,

Nevada (sample from the east pit), to determine if

hydrocarbons were present.

Three methods of extraction, which will be described

briefly below, were used on crushed carbon-rich rock

samples with the organic extract being dissolved in CCl4

before being injected into Wilks cells for use in a

Beckman IR"20 spectrophotometer. The infrared spectra

obtained were compared against the spectra for pure

CCl4 to determine which organics were present. Extraction

techniques involved using a mixture of benezene, methanol.

and acetone: 0.3 N NaOH; or 0.5 N NH4Ac solutions.

In the benezene-methanol-acetone method (70:15:15

by volume), the B-M-A mixture was found to leave an

infrared detectable residue which was deleterious to

interpretation of the Mercur, Carlin, and Getchell samples.

The organic extraction technique using a 0.3 N NaOH

solution was found to be more effective than the B-M-A

5 8

m e t h o d . I n t h i s m e t h o d NaOH w a s a l l o w e d t o p r e c o l a t e

t h r o u g h t h e s a m p l e w h i c h w a s o n a f i b e r g l a s s f i l t e r p a p e r

i n a B u c h n e r f u n n e l w i t h t h e s o l u t i o n b e i n g a l l o w e d t o

c o l l e c t i n a b e a k e r . T h e l e a c h a n t w a s t h e n p l a c e d i n

a p l a s t i c b o t t l e w i t h C C l ^ a n d s h a k e n o n a p a i n t s h a k e r

f o r 3 0 m i n u t e s . T h e C C 1 ^ # w h i c h i s h e a v i e r t h a n t h e

NaOH, w a s d r a w n o f f a n d p a r t i a l l y e v a p o r a t e d t o c o n c e n t r a t e

a n y o r g a n i c s p r e s e n t — t h e s o l u t i o n w a s t h e n i n j e c t e d i n t o

a W i l k s c e l l f o r u s e o n t h e i n f r a r e d s p e c t r o p h o t o m e t e r .

E x t r a c t i o n u s i n g a 0 . 5 N NH^Ac s o l u t i o n o n t h e

M e r c u r , C a r l i n , a n d G e t c h e l l s a m p l e s a l s o w a s f o u n d t o

b e e f f e c t i v e . T h e NH^Ac s o l u t i o n w a s a l l o w e d t o p e r c o l a t e

t h r o u g h t h e s a m p l e o n a f i b e r g l a s s f i l t e r p a p e r i n a

B u c h n e r f u n n e l . T h e s o l u t i o n w a s e v a p o r a t e d i n a b e a k e r

b e l o w 8 0 ° C o n a h o t p l a t e . C C I 4 w a s t h e n a d d e d a n d

s t i r r e d t o d i s s o l v e a n y o r g a n i c s . T h e C C l ^ w a s a l l o w e d

t o p a r t i a l l y e v a p o r a t e t o c o n c e n t r a t e a n y o r g a n i c s a n d

t h e s o l u t i o n w a s t h e n i n j e c t e d i n t o a W i l k s c e l l f o r u s e

o n t h e i n f r a r e d s p e c t r o p h o t o m e t e r . An i o n e x c h a n g e

c o l u m n o f a m b e r l i t e MB-3 w a s t r i e d b e f o r e t h e a b o v e

d e s c r i b e d m e t h o d t o r e m o v e t h e a c e t a t e i o n a n d g a v e t h e

s a m e r e s u l t s .

T h e e x t r a c t i o n s a n d f i l l i n g o f t h e W i l k s c e l l

s h o u l d b e p e r f o r m e d u n d e r a f u m e h o o d w i t h t h e W i l k s

c e l l b e i n g f l u s h e d w i t h CCl/^ s e v e r a l t i m e s b e t w e e n s a m p l e s .

T h e i n f r a r e d s p e c t r a f o r t h e s a m p l e s a r e p r e s e n t e d

58

method. In this method NaOH was allowed to precolate

through the sample which was on a fiberglass filter paper

in a Buchner funnel with the solution being allowed to

collect in a beaker. The leachant was then placed in

a plastic bottle with CC14 and shaken on a paint sh~ker

for )0 minutes. The CCI4. which is heavier than the

NaOH, was drawn off and partially evaporated to concentrate

any organics present--the solution WqS then injected into

a Wilks cell for use on the infrared spectrophotometer.

Extraction using a 0.5 N NH4Ac solution on the

Mercur, Carlin, and Getchell samples also was found to

be effective. The NH4Ac solution was allowed to percolate

through the sample on a fiberglass filter paper in a

BUchner funnel. The solution was evaporated in a beaker

below BOoc on a hotplate. CC14 was then added and

stirred to dissolve any organics. The CCl4 was allowed

to partially evaporate to concentrate any organics and

the solution was then injected into a Wilks cell for use

on the infrared spectrophotometer. An ion exchange

column of amberlite MB-3 was tried before the above

described method to remove the acetate ion and gave the

same results.

The extractions and filling of the Wilks cell

should be performed under a fume hood with the Wilks

cell being flushed with CC14 several times between samples.

The infrared spectra for the samples are presented

59

i n F i g u r e 1 9 a n d 2 0 . T h e 0 , 3 N NaOH e x t r a c t i o n

( F i g . 1 9 ) w a s f o u n d t o c o n t a i n o r g a n i c s o f t h e a l k a n e

g r o u p w h i c h h a v e a c h a r a c t e r i s t i c i n f r a r e d a b s o r p t i o n

b a n d a r o u n d 2 9 0 0 c m " 1 . T h e 0 . 5 N NH^Ac e x t r a c t i o n

( F i g . 2 0 ) w a s f o u n d t o d i s s o l v e c a r b o x y l i c a c i d s ( c a r b o n y l

g r o u p — n o t b e l i e v e d t o b e a c e t i c a c i d ) w h i c h h a v e a

c h a r a c t e r i s t i c i n f r a r e d a b s o r p t i o n b a n d a r o u n d 1 7 0 0 c m ~ *

a n d s o m e o r g a n i c s o f t h e a l k a n e g r o u p . ( A l k a n e s a r e o n e

o f t h e m a i n h y d r o c a r b o n c o n s t i t u e n t s o f p e t r o l e u m . )

O r g a n i c a c i d s a n d m e t h a n e a r e k n o w n p r o d u c t s o f b a c t e r i a l

a c t i o n b u t t h e a u t h o r i s u n c e r t a i n w h e t h e r t h e c a r b o x y l i c

a c i d s a r e b a c t e r i a l p r o d u c t s . T h e c a r b o x y l i c a c i d s

c o u l d a l s o b e o r g a n i c d e c a y p r o d u c t s i n t r o d u c e d b y

g r o u n d w a t e r .

Some m o b i l i z a t i o n o f c a r b o n i n a h y d r o t h e r m a l

e n v i r o n m e n t h a s b e e n s u g g e s t e d b y J o r a l e m o n ( 1 9 5 1 . P - 2 7 3 )

f o r t h e g o l d d e p o s i t a t G e t c h e l l M i n e , N e v a d a , a n d b y

H a u s e n a n d K e r r ( 1 9 6 8 , p , 9 3 0 ) f o r t h e g o l d d e p o s i t

a t C a r l i n , N e v a d a , T h e a u t h o r f o u n d n e a r t h e S a c r a m e n t o

b r e c c i a p i p e a s m a l l v e i n l e t o f i n t e r s t i t i a l c a r b o n

a l o n g w h i c h a s m a l l o f f s e t h a d o c c u r r e d . T h e s m a l l

f r a c t u r e p r o b a b l y s e r v e d a s a c o n d u i t f o r a n o r g a n i c

r i c h s o l u t i o n w i t h t h e c a r b o n d i s p e r s i n g i n t o t h e

s u r r o u n d i n g r o c k . N e a r t h e s a m e l o c a t i o n c a r b o n - r i c h

m a t e r i a l a b u t s a g a i n s t a h i g h l y a l t e r e d o u t c r o p o f r o c k

w h i c h m i g h t b e a l t e r e d i n t r u s i v e a n d w h o s e p h y s i c a l

--,

59

in Figure 19 9nd 20. The 0.3 N NaOH extraction

(Fig. 19) was found to contain organics of the alkane

group which have a characteristic infrared absorption

band around 2900 -1 cm • The 0.5 N NH4Ac extraction

(Fig. 20) was found to dissolve carboxylic acids (carbonyl

group--not believed to be acetic acid) which have a

characteristic infrared absorption band around 1700 cm- 1

and some organics of the alkane group. (Alkanes are one

of the main hydrocarbon constituents of petroleum.)

Organic acids and methane are known products of bacterial

action but the author is uncertain whether the carboxylic

gcids are bacterial products. The carboxylic acids

could also be organic decay products introduced by

ground water.

Some mobilization of carbon in a hydrothermal

environment has been suggested by Joralemon (1951. p. 273)

for the gold deposit at Getchell Mine, Nevada, and by

Hausen and Kerr (1968, p. 930) for the gold deposit

at Carlin, Nevada. The author found near the Sacramento

breccia pipe a small veinlet of interstitial carbon

along which a small offset had occurred. The small

fracture probably served as a conduit for an organic

rich solution with the carbon dispersing into the

surrounding rock. Near the same location carbon-rich

material abuts against a highly altered outcrop of rock

which might be altered intrusive and whose physical

6 0

Wavelength in Micron* 4.1 •

—i r • S T T.I t t to II II 14 1, 10 10 40

—i 1 • i i • i 1 1—H r—i-*"-!—i 1—r CCI4

Sacramento Mi no, Mercur, Utah

Brickyard Mine, Mercur, Utah

long Trail Shale, Ophir, Utah

Carlin. Nevada

Getchell Mine, Nevada

1000 1000 1*00 1400 1100 1000 100 *00 400 Wavenumber Cm"'

F i g u r e 1 9 . I n f r a r e d s p e c t r a o f 0 * 3 N NaOH o r g a n i c e x t r a c t i o n s f r o m r o c k s a m p l e s a s s o c i a t e d w i t h g o l d d e p o s i t s .

Wavelength In Micron.

"I I ••• ••• • ... , U • '0 It II ..,. 20

Sacramento Mine, Mereu" Utah

Brickyard Mine, Mere ur, Utah

long Trail Shale, Ophir, Utah

Carlin, Nevada r-----..,------.......

Getchell Mine, Nevada

.000 JOOO 1000 •••• •• 00 1400 noo .000 .00

Wavenumber Cm-l

Figure 19. Infrared spectra of 0.3 N NaOH organic extractions from rock samples associated with gold deposits.

.00

60

.00

F i g u r e 2 0 . I n f r a r e d s p e c t r a o f 0 . 5 N NHjhAc o r g a n i c e x t r a c t i o n s f r o m r o c k s a m p l e s a s s o c i a t e d w i t h g o l d d e p o s i t s .

l' u '.1 1.1 • ... , , .• e " '0 "11 ,.. '. 20

Sacramenta Mine, Mercur, Utah

Brickyard Mine, Mereur, Utah

long Troll Shale, Ophir, Utah

Carlin, Nevada

Getchell Mine, Nevada

4000 3000 2000 1eoo 1600 1400 1200 tooo eoo

Wavenumber em-'

Figure 20 0 Infrared spectra of 0.5 N NHaAc organic extractions from rock samples assoc1ated with gold deposits.

600

61

10 ...

400

r e l a t i o n m i g h t b e d u e t o f a u l t i n g . Some c a r b o n

s t r e a m i n g i n t o h e a l e d f r a c t u r e s i n t h e a l t e r e d m a s s i s

a p p a r e n t . T h e a l t e r e d m a s s c o n s i s t s o f c a l c i t e ,

k a o l i n i t e , q u a r t z , a n d i l l i t e . T h e c a r b o n i s n o t

r e s t r i c t e d t o o n e r o c k t y p e a t t h e S a c r a m e n t o b r e c c i a

p i p e , w h i c h s u g g e s t s e i t h e r m o v e m e n t o f c a r b o n a n d / o r

h y d r o c a r b o n s o r v a r y i n g d e g r e e s o f a l t e r a t i o n . No

e v i d e n c e f o r s o l u t i o n t h i n n i n g , w h i c h m i g h t h a v e c a u s e d

c a r b o n e n r i c h m e n t , w a s s e e n i n t h e S a c r a m e n t o m i n e a r e a ,

b u t t h i s d o e s n o t m e a n i t d i d n o t h a p p e n .

T h e p r e s e n c e o f c a r b o n i s b e l i e v e d t o b e d u e t o

t h e r e d u c i n g a c t i o n o f p a s t h y d r o t h e r m a l s o l u t i o n s

o n a n y h y d r o c a r b o n s t h a t m i g h t h a v e b e e n p r e s e n t i n

t h e s h a l e s a n d s i l t s t o n e s . T h e q u e s t i o n o f w h e t h e r

h y d r o c a r b o n s a n d / o r c a r b o n a r e m o b i l e i s a n u n a n s w e r e d

q u e s t i o n , b u t f i e l d e v i d e n c e a n d t h i n s e c t i o n s t u d y

s u g g e s t t h a t t h e r e h a s b e e n a n a p p a r e n t m o b i l i t y o f

c a r b o n a n d h y d r o c a r b o n s •

62

relation might be due to faulting. Some carbon

streaming into healed fractures in the altered mass is

apparent. The altered mass consists of calcite,

kaolinite, quartz, and illite. The carbon is not

restricted to one rock type at the Sacramento breccia

pipe, which suggests either movement of carbon and/or

hydrocarbons or varying degrees of alteration. No

evidence for solution thinning, which might have caused

carbon enrichment, was seen in the Sacramento mine area.

but this does not mean it did not happen.

The presence of carbon is believed to be due to

the reducing action of past hydrothermal solutions

on any hydrocarbons that might have been present in

the shales and siltstones. The question of whether

hydrocarbons and/or carbon are mobile is an unanswered

question, but field evidence and thin section study

suggest that there has been an apparent mobility of

carbon and hydrocarbons.

SULFUR I S O T O P I C DATA

T w e n t y s a m p l e s o f s u l f u r b e a r i n g m i n e r a l s w e r e

c o l l e c t e d f r o m v a r i o u s m i n e s a r o u n d t h e g h o s t t o w n o f

M e r c u r , U t a h , f o r a s u l f u r i s o t o p i c s t u d y ( F i g . 2 1 ) .

P r i m a r y b a r i t e o c c u r s i n t h e s i l v e r l e d g e f r o m w h i c h

s i l v e r w a s p r o d u c e d i n t h e e a r l y d a y s o f t h e d i s t r i c t .

S e c o n d a r y s u l f a t e s o c c u r a s j a r o s i t e , a l u n l t e , m e l a n t e r i t e -

p i s a n i t e , h a l o t r l c h i t e , s c o r o d l t e , a n d g y p s u m .

N a t r o a l u n i t e w a s f o u n d i n s e v e r a l p l a c e s o u t s i d e t h e

M e r c u r c a m p ( C l a y C a n y o n a n d W e s t M e r c u r ) . P r i m a r y

s u l f i d e s o c c u r a s p y r i t e , o r p l m e n t , r e a l g a r , c i n n a b a r ,

a r s e n o p y r i t e , s t i b n i t e , c h a l c o p y r i t e , s u l v a n i t e ,

s p h a l e r i t e , a n d g a l e n a . S e c o n d a r y s u l f i d e o c c u r s

s p a r i n g l y a s e l e m e n t a l s u l f u r . P r i m a r y s u l f i d e s a r e n o t

c o m m o n i n t h e d i s t r i c t . P y r i t e i s t h e m o s t c o m m o n s u l f i d e

f o u n d i n t h e o l d q u a r r y a r e a s .

S u l f u r d i o x i d e w a s p r e p a r e d f r o m s u l f i d e s a n d

s u l f a t e s b y m e t h o d s o u t l i n e d , b y M » L . J e n s e n a t t h e

L a b o r a t o r y o f I s o t o p e G e o l o g y , U n i v e r s i t y o f U t a h . T h e

s u l f i d e s w e r e b u r n e d i n a v a c u u m a t 8 5 0 ° G f o r 1 5 m i n u t e s

w i t h c o p p e r o x i d e t o p r o d u c e S 0 2 • T h e SO2 a n d C 0 2

f o r m e d w e r e s e p a r a t e d i n a s e r i e s o f c o l d t r a p s . T h e

S 0 2 a n d G 0 2 w e r e f i r s t c o l l e c t e d i n a l i q u i d n i t r o g e n

t r a p . T h e f r o z e n S 0 2 a n d C 0 2 w e r e a l l o w e d t o s u b l i m a t e

o n c e t h e l i q u i d n i t r o g e n t r a p w a s r e m o v e d a n d c o l l e c t e d

SULFUR ISOTOPIC DATA

Twenty samples of sulfur bearing minerals were

collected from various mines around the ghost town of

Mercur. Utah. for a sulfur isotopic study (Fig. 21).

Primary barite occurs in the silver ledge from which

silver was produced in the early days of the district.

Secondary sulfates occur as jarosite. alunite, melanterite-

pisanite, halotrichite, scorodite. and gypsum.

Natroalunite was found in several places outside the

Mercur camp (Clay Canyon and West Mercur). Primary

sulfides occur as pyrite. orpiment, realgar. cinnabar.

arsenopyrite. stibnite, chalcopyrite. sulvanite,

sphalerite. and galena. Secondary sulfide occurs

sparingly as elemental sulfur. Primary sulfides are not

common in the district. Pyrite is the most common sulfide

found in the old quarry areas.

Sulfur dioxide was prepared from sulfides and

sulfates by methods outlined; by M~L. Jensen at the

Laboratory of Isotope Geology, University of Utah. The

sulfides were burned in a vacuum at 8500 C for 15 minutes

with copper oxide to produce S02. The 502 and CO2

formed were separated in a series of cold traps. The

S02 and CO2 were first collected in a liquid nitrogen

trap. The frozen 502 and CO2 were allowed to sublimate

once the liquid nitrogen trap was removed and collected

6 4

i n a t r a p o f N - p e n t a n e f r o z e n b y l i q u i d n i t r o g e n .

An i n t e r v e n i n g c o l d t r a p o f a c e t o n e a n d d r y i c e r e m o v e d

a n y w a t e r p r e s e n t . A l l o w i n g t h e N - p e n t a n e t o m e l t ,

g a s e o u s C 0 2 i s f i r s t r e l e a s e d l e a v i n g t h e S 0 2 . T h e S 0 2

i s c o l l e c t e d i n a g a s f l a s k f o r m a s s s p e c t r o m e t r i c

a n a l y s i s •

T h e s u l f a t e s a r e p r e p a r e d b y r e a c t i n g t h e m w i t h a

m i x t u r e o f H I , HNO^, a n d HC1 p r o d u c i n g H 2 S w h i c h i s

b u b b l e d t h r o u g h a c a d m i u m a c e t a t e s o l u t i o n t o p r o d u c e

C d S . T h e C d S i s c o n v e r t e d t o A g 2 S b y a d d i n g AgNO^

s o l u t i o n . T h e d r i e d A g 2 S i s b u r n e d b y t h e s a m e p r o c e d u r e

a s t h e s u l f i d e s t o p r o d u c e S 0 2 •

T h e S 0 2 s a m p l e s w e r e a n a l y z e d o n a m a s s s p e c t r o m e t e r

b y J o s e p h J e n s e n w i t h t h e c a l c u l a t i o n s b e i n g m a d e b y t h e

a u t h o r . T a b l e 4 s h o w s t h e r e s u l t s o f t h e a n a l y s e s .

S u l f u r i s o t o p i c c o m p o s i t i o n o f a s u l f u r - b e a r i n g

m i n e r a l i s c o n t r o l l e d b y a n u m b e r o f f a c t o r s i n c l u d i n g ,

a c c o r d i n g t o O h m o t o ( 1 9 7 2 , p . 5 5 3 ) " ( 1 ) t h e r e l a t i v e

i s o t o p i c e n r i c h m e n t f a c t o r s o f a q u e o u s s u l f u r s p e c i e s ,

( 2 ) t h e m o l e f r a c t i o n s o f a q u e o u s s u l f u r s p e c i e s , a n d

( 3 ) t h e m e a n i s o t o p i c c o m p o s i t i o n o f s u l f u r i n t h e

s o l u t i o n s . " O h m o t o ( 1 9 7 2 , p . 5 5 6 ) f u r t h e r s t a t e s t h a t ,

" t h e m o l e f r a c t i o n s o f a q u e o u s s u l f u r s p e c i e s r e l a t i v e

t o t o t a l s u l f u r c o n t e n t a r e d e p e n d e n t o n t h e e q u i l i b r i u m

c o n s t a n t s f o r t h e r e a c t i o n s , t h e a c t i v i t y c o e f f i c i e n t s

o f a q u e o u s s p e c i e s , t h e f u g a c i t y o f o x y g e n , t h e p H ,

64

in a trap of N-pentane frozen by liquid nitrogen.

An intervening cold trap of acetone and dry ice removed

any water present. Allowing the N-pentane to melt,

gaseous CO2 is first released leaving the S02' The S02

is collected in a gas flask for mass spectrometric

analysis.

The sulfates are prepared by reacting them with a

mixture of HI, HNO J , and HCI producing H2S which is

bubbled through a cadmium acetate solution to produce

CdS. The CdS is converted to Ag2S by adding AgNOJ

solution. The dried Ag2S is burned by the same procedure

as the sulfides to produce S02.

The S02 samples were analyzed on a mass spectrometer

by Joseph Jensen with the calculations being made by the

author. Table 4 shows the results of the analyses.

Sulfur isotopic composition of a sulfur-bearing

mineral is controlled by a number of factors including,

according to Ohmoto (1972, p. 55J) -(1) the relative

isotopic enrichment factors of aqueous sulfur species,

(2) the mole fractions of aqueous sulfur species, and

()) the mean isotopic composition of sulfur in the

solutions.- Ohmoto (1972, p. 556) further states that,

-the mole fractions of aqueous sulfur species relative

to total sulfur content are dependent on the equilibrium

constants for the reactions, the activity coefficients

of aqueous species, the fugacity of oxygen, the pH,

CONTOUR INTERVAL 40 FEET DATUM IS MEAN SEA LEVEL

g u r e 2 1 . Map o f p a r t o f t h e M e r c u r . U t a h t o p o g r a p h i c q u a d r a n g l e s h o w i n g c o l l e c t i o n s i t e s a n d s a m p l e n u m b e r s f o r t h e s u l f u r i s o t o p e s a m p l e s .

CONTOUR INTERVAL 40 FEET DATU M IS MEAN SEA Ll VEL

.65

Figure 21~ Map of part of the Mercur~ Utah topographic quadrangle showing collection sites and sample numbers for the sulfur isotope samples.

T a b l e 4 . S u l f u r i s o t o p e d a t a .

S a m p l e 6 ^ s A r e a o f C o l l e c t i o n

1 - - o r p i m e n t + 4 . 8 3 G e y s e r - M a r i o n m i n e

2 - - r e a l g a r 7 . 1 3 M e r c u r H i l l m i n e

3 - - r e a l g a r 6 . 2 8 G e y s e r - M a r i o n m i n e

4 - - o r p l m e n t 4 . 6 3 B r i c k y a r d m i n e

5 - - o r p l m e n t 1 5 * 8 0 B r i c k y a r d m i n e

6 - - r e a l g a r 8 . 9 0 B r i c k y a r d m i n e

7 - - r e a l g a r 6 . 5 7 B r i c k y a r d m i n e

8 - - b a r l t e 1 5 - 2 6 G e y s e r - M a r i o n m i n e

9 - - o r p l m e n t 9 . 5 1 G e y s e r - M a r i o n m i n e

1 0 - - p y r i t e 1 1 . 5 5 S a c r a m e n t o m i n e

1 1 - - p y r i t e 4 . 7 8 M e r c u r H i l l m i n e

1 2 - - b a r i t e 3 . 7 3 G e y s e r - M a r i o n m i n e

1 3 - - p y r i t e 9 . 8 7 S a c r a m e n t o m i n e

1 4 - - s t l b n i t e 1 0 . 1 2 G e y s e r - M a r i o n m i n e

1 5 - - p y r i t e 1 7 . 1 2 S a c r a m e n t o m i n e

1 6 - - b a r i t e 2 . 8 8 M e r c u r H i l l m i n e

1 7 - - a l u n i t e 2 . 6 0 G e y s e r - M a r i o n m i n e

1 8 - - j a r o s i t e 3 . 1 3 G e y s e r - M a r i o n m i n e

1 9 - - a l u n i t e 2 . 6 4 G e y s e r - M a r i o n m i n e

2 0 - - r e a l g a r 1 0 . 2 9 M e r c u r H i l l m i n e

Table 4. Sulfur isotope data.

Sample

1--orpiment

2--realgar

3--realgar

4--orpiment

5--orplment

6--realgar

7--realgar

8--barite

9--orpirnent

10--pyrite

11--pyrite

12--barite

13--pyrlte

14--stibnlte

15--pyrlte

16--barite

17--alunite

18--jarosite

19--alunite

20--realgar

6 34S

+4.83

7.13

6.28

4.63

15.80

8.90

6.57

15.26

9.51

11.55

4.78

3.73

9.87

10.12

17.12

2.88

2.60

3.13

2.64

10.29

Area of Collection

Geyser-Marion mine

Mercur Hill mine

Geyser-Marion mine

Brickyard mine

Brickyard mine

Brickyard mine

Brickyard mine

Geyser-Marion mine

Geyser-Marion mine

Sacramento mine

Mercur Hill mine

Geyser-Marion mine

Sacramento mine

Geyser-Marion mine

Sacramento mine

Mercur Hill mine

Geyser-Marion mine

Geyser-Marion mine

Geyser-Mar1.on mine

Mercur Hill mine

66

6 ?

a n d t h e m o l a l i t i e s o f p o t a s s i u m a n d s o d i u m i o n s i n t h e

s o l u t i o n s . T h e e q u i l i b r i u m c o n s t a n t s a r e m a i n l y a

f u n c t i o n o f t e m p e r a t u r e , a n d t h e a c t i v i t y c o e f f i c i e n t s

o f t e m p e r a t u r e a n d t h e i o n i c s t r e n g t h o f f l u i d s . " M o r e

s p e c i f i c a l l y O h m o t o ( 1 9 7 2 , p . 5 5 1 ) b e l i e v e s t h a t t h e

pH a n d o x y g e n f u g a c i t y o f a h y d r o t h e r m a l s y s t e m c a n

c o n t r o l t h e < S s 3 ^ c o m p o s i t i o n o f t h e m i n e r a l .

J e n s e n e t . a l . ( 1 9 7 1 a , p . 6 2 4 ) p o i n t o u t t h a t

a n d S 0 2 t e n d t o e q u i l i b r a t e b y t h e i s o t o p i c

e x c h a n g e r e a c t i o n :

^ S 3 ^ + s 3 2 o 2 J * H 2 S 3 2 + S 3 ^ 0 2

S i n c e t h e p r e d o m i n a n t g a s p r e s e n t a t h i g h t e m p e r a t u r e s

i s S 0 2 a n d H 2 S a t l o w t e m p e r a t u r e s , H 2 S i s e n r i c h e d

32 3 4 i n S ^ a n d S 0 2 i n S ^ a s t h e t e m p e r a t u r e i s l o w e r e d

( J e n s e n e t . a l . , 1 9 7 1 b , p , 7 6 ) , M g u r e 2 2 i s J e n s e n ' s

d i a g r a m a t i c r e p r e s e n t a t i o n o f t h e c h e m i c a l r e a c t i o n s

t a k i n g p l a c e i n a f l u i d a f t e r i t h a s l e f t i t s s o u r c e .

Some c o n s i d e r a t i o n s t h a t m u s t b e t a k e n i n t o a c c o u n t

i n a n a l y z i n g t h e M e r c u r s u l f u r i s o t o p i c d a t a a r e t h e

a d d i t i o n o f s u l f u r f r o m a u t h i g e n i c p y r i t e , a s u l f u r

b e a r i n g m i n e r a l ' s f o r m a t i o n r a n g e , t h e pH a n d o x y g e n

f u g a c i t y o f t h e h y d r o t h e r m a l s o l u t i o n , t h e t e m p e r a t u r e

o f t h e s o l u t i o n , a n d t h e m i x i n g o f g r o u n d w a t e r s w i t h

j u v e n i l e w a t e r s .

T h e t w o m a i n s o u r c e s o f s u l f u r r e p r e s e n t i n t h e

s u l f u r b e a r i n g m i n e r a l s a r e b e l i e v e d t o h a v e c o m e f r o m

67

and the molalities of potassium and sodium ions in the

solutions. The equilibrium constants are mainly a

function of temperature, and the activity coefficients

of temper~ture and the ionic strength of fluids." More

specifically Ohmoto (1972, p. 551) believes that the

pH and oxygen fugacity of a hydrothermal system can

control the oS34 composition of the mineral.

Jensen et. ale (1971a, p. 624) point out that

H2S and S02 tend to equilibrate by the isotopic

exchange reaction:

H S34 + s32 0 -. H S32 + S34 0 2 2 ~ 2 2

Since the predominant gas present at high temperatures

is S02 and H2 S at low temperatures, H2 S is enriched

in S32 and S02 in S34 as the temperature is lowered

(Jensen et. al., 1971b, p. 76). Figure 22 is Jensen's

diagramatic representation of the chemical reactions

taking place in a fluid after it has left its source.

Some considerations that must be taken into account

in analyzing the Mercur sulfur isotopic data are the

addition of sulfur from authigenic pyrite, a sulfur

bearing mineral's formation range, the pH and oxygen

fugacity of the hydrothermal solution, the temperature

of the solution, and the mixing of ground waters with

juvenile waters.

The two main sources of sulfur represent in the

sulfur bearing minerals are believed to have come from

6 8

34

(Medium T and Low P) Orifice of fumarole

H2 CO

S02—>S04 (with same bS composition as HjS)

rigin of hypogene sulfates, ich are enriched in s34

(derived from h^S-OSO.,-*^), while associated sulfides are comparatively enriched in S 3 2 (derived from H2S)

H,S to S02, H2S03, and H^O^ at 250*C gives s'A enrichments of +16,+25, and +357.o respectively H.T.

(Hi T and Hi P) ^0

Origin of early pyrite which in many cases is later replaced by Cu, Zn, and Pb. Sulfide minerals with little if any change in cS^ composition

Isotopic equilibrium occurring between H2S and SC>2 (aided by catalytic H2 and H?0 agents) results in gradual increase

3 2 in H2S and of S 3 4 in SO2 (H , s 3 4 + s 3 V :> H o s 3 2 + s 3 V)

f Parent magma or Rocks undergoing metamorphism H O-CO -H S in order of abundance

H2S if pH < 7 HS" if pH > 7

F i g u r e 2 2 . C h e m i c a l r e a c t i o n s a n d v a l u e s i n a f u m a r o l i c c o n d u i t . ( f r o m J e n s e n e t . a l . , 1 9 7 1 . P . 7 7 )

3H2S03-->::!2S04 +S+1l20

Origin of SOZ enriched in 534

(InClllence on tS)4 vallle of marine S04 oC +20.21..]

Indigenous ferric iron disseminated through

rock

68

slllfates, which are enriched in SJ4 (derived from H2S-->S02-~OJ)' while associated slllCides are co=paratively enrlched in SJ2 (derived fro~ H25)

t 14 . ~S variation increasing

between 502 and H2S with increasing ti~e of equll ibration

Origin of early pyrite which in many cases 1. later replaced by ell, Zn, and Pb. Sulfide mineral. with little if any change 1n tSJ4 composition

HZS to SOZ' H2S03, and H2S04 at 2~OiC gives SJ4 enrichments of +16,+25, and +357.. respectively H.t. M2S S02

M S+ZH O~->SO +)H 3H2 ~sotoP1C equi l1briulII occllrring bet .. ·een

H2S and 50

2 (aided by catalytic H2 and

H20 agents) reslllt. in gradual increase of SJ2 in H2S and of 534 in S02 2 2 2 2

(Hi T and Hi P) H20

HZS

CO2

(M 534+5320 ~:>H S32+S340 ) 2 2 2 2

~ ":.~- f::::;:o::::;",g ~u="" •• ~02-H25 in order of abundance

"ZS if pH < 7

HS- if pH> 7

Figure 22. Chemical reactions and S14 values in a fuma.rolic conduit. (from Jensen et. al •• 1971, p. 77)

6 9

J u v e n i l e a n d g r o u n d w a t e r s . T h e a d d i t i o n o f s u l f u r

f r o m h y d r o c a r b o n s a n d a u t h i g e n i c p y r i t e w a s p r o b a b l y

m i n o r a n d t h u s h a d v e r y l i t t l e e f f e c t o n t h e i s o t o p i c

c o m p o s i t i o n o f t h e s u l f u r b e a r i n g m i n e r a l s .

T h e a u t h o r b e l i e v e s t h a t t h e s u l f u r i s o t o p i c

c o m p o s i t i o n o f t h e s a m p l e s w a s n o t c o n t r o l l e d b y pH

a n d o x y g e n f u g a c i t y b e c a u s e t h e i s o t o p i c v a l u e s g i v e n

b y O h m o t o ( 1 9 7 2 , p . 5 5 9 , 5 6 0 , 5 7 3 ) d o n o t f i t t h e pH

c o n d i t i o n s b e l i e v e d t o h a v e b e e n p r e s e n t d u r i n g

h y d r o t h e r m a l a l t e r a t i o n . One c a n n o t e x p e c t t h e i s o t o p i c

v a l u e s o f T a b l e 4 t o r e f l e c t d i r e c t c h a n g i n g e q u i l i b r a t i o n

c o n d i t i o n s b e t w e e n H 2 S a n d S 0 2 a s i n F i g u r e 2 2 . S i n c e

i n F i g u r e 2 2 o n e c o n s i d e r s H 2 S e n r i c h e d i n S 3 ^ a n d

32

S 0 2 e n r i c h e d i n S a t h i g h t e m p e r a t u r e s a n d d o e s n o t

c o n s i d e r t h e m i x i n g o f j u v e n i l e a n d g r o u n d w a t e r s a t

m o d e r a t e t o l o w t e m p e r a t u r e s .

M e r c u r , U t a h , r e p r e s e n t s a l o w t e m p e r a t u r e

e p i t h e r m a l d e p o s i t , a l t h o u g h h i g h t e m p e r a t u r e c o n d i t i o n s

a r e b e l i e v e d t o h a v e e x i s t e d i n t h e i n t r u s i v e m a g m a .

A c o n v e c t i v e h y d r o t h e r m a l s y s t e m m a y h a v e e x i s t e d i n a n d

a r o u n d t h e magma w i t h t h e g r o u n d w a t e r b e i n g w a r m e d a n d

m i x e d w i t h j u v e n i l e w a t e r s . I n m o d e r n h o t s p r i n g a r e a s ,

o x y g e n i s o t o p e s i n d i c a t e t h a t m o s t o f t h e w a t e r i s

m e t e o r i c . S i n c e r h y o l i t e s a r e b e l i e v e d t o r e p r e s e n t

r o c k s o f l o w w a t e r c o n t e n t , a n y w a t e r d r a w n t o w a r d s a n d

69

juvenile and ground waters. The addition of sulfur

from hydrocarbons and authigenic pyrite was probably

minor and thus had very little effect on the isotopic

composition of the sulfur bearing minerals.

The author believes that the sulfur isotopic

composition of the samples was not controlled by pH

and oxygen fugacity because the isotopic values given

by Ohmoto (1972, p. 559. 560, 573) do not fit the pH

conditions believed to have been present during

hydrothermal alteration. One cannot expect the isotopic

values of Table 4 to reflect direct changing equilibration

conditions between H2S and S02 as in Figure 22. Since

in Figure 22 one considers H2S enriched in s34 and

S02 enriched in S32 at high temperatures and does not

consider the mixing of juvenile and ground waters at

moderate to low temperatures.

Mercur. Utah, represents a low temperature

epithermal deposit. although high temperature conditions

are believed to have existed in the intrusive magma.

A convective hydrothermal system may have existed in and

around the magma with the ground water being warmed and

mixed with juvenile waters. In modern hot spring areas,

oxygen isotopes indicate that most of the water is

meteoric. Since rhyolites are believed to represent

rocks of low water content, any water drawn towards and

7 0

i n t o t h e i n t r u s i v e w o u l d h e l p l e a c h t h e r o c k a s i t

w a s b e i n g a l t e r e d . T h i s l e a c h i n g a n d m i x i n g o f w a t e r s

w o u l d a d d s u l f u r t o t h e w a t e r s .

S i n c e m o s t o f t h e s u l f u r p r e s e n t i n t h e s u l f i d e s

i s b e l i e v e d t o r e p r e s e n t s u l f u r f r o m m e t e o r i c a n d

j u v e n i l e w a t e r s , a n y h e a t i n g a n d m i x i n g o f m e t e o r i c

w a t e r s w i t h j u v e n i l e w a t e r s w o u l d b e a c c o m p a n i e d

b y t h e e q u i l i b r a t i o n o f H2S a n d S 0 2 r a t i o s a c c o r d i n g

t o e x i s t i n g T a n d P c o n d i t i o n s . A t l o w t e m p e r a t u r e s ,

t h e c o n v e r s i o n o f S 0 2 a n d H 2 S i n e q u i l i b r i u m c o n d i t i o n s

w o u l d , a c c o r d i n g t o J e n s e n e t , a l . ( 1 9 7 1 b t p , 7 7 ) .

3 4 g i v e r i s e t o s u l f i d e s d i f f e r i n g i n S c o m p o s i t i o n :

S 3 4 0 2 + 3 % — * ftgS34 + 2 H 2 0

3 4 T h e H 2 S V f o r m e d b y t h e a b o v e r e a c t i o n s w o u l d a d d t o t h e

32

H 2 S e n r i c h e d i n S p r e s e n t i n s o l u t i o n i n n e a r - s u r f a c e ,

l o w t e m p e r a t u r e c o n d i t i o n s .

T h e d i f f e r i n g d e g r e e s o f a l t e r a t i o n a t M e r c u r

s u g g e s t t h a t d i f f e r e n t p h y s i c a l a n d c h e m i c a l e n v i r o n m e n t s

e x i s t e d t h e r e a t o n e t i m e . T h u s t h e p h y s i c a l a n d c h e m i c a l

c o n d i t i o n s t h a t w e r e p r e s e n t i n o n e l o c a l i t y d i d n o t

n e c e s s a r i l y e x i s t i n a n e a r b y a r e a . T h i s s i t u a t i o n

p r o b a b l y a r o s e o u t o f v a r y i n g p e r m e a b i l i t y c o n d i t i o n s ,

f r a c t u r e p l u m b i n g c o n t r o l , n e a r n e s s t o t h e i n t r u s i v e ,

a n d t h e a v a i l a b i l i t y a n d a b i l i t y o f g r o u n d w a t e r t o

e n t e r t h e s y s t e m . T h e s e v a r y i n g p h y s i c a l a n d c h e m i c a l

c o n d i t i o n s w o u l d c o n t r o l t h e a m o u n t s o f a q u e o u s s u l f u r

into the intrusive would help leach the rock as it

was being altered. This leaching and mixing of waters

would add sulfur to the waters.

Since most of the sulfur present in the sulfides

is believed to represent sulfur from meteoric and

juvenile watprs, any heating and mixing of meteoric

w~ters with juvenile waters would be accompanied

by the equilibration of H2S and S02 ratios according

to existing T and P conditions. At low temperatures,

70

the conversion of S02 and H2S in equilibrium conditions

would, according to Jensen et. ale (1971b, p. 77).

give rise to sulfides differing in S34 composition:

S3402 + 3~ --. ~s34 + 2H20

The H2S34 formed by the above reactions would add to the

H2S enriched in S32 present in solution in near-surface,

low temperature conditions.

The differing degrees of alteration at Mercur

suggest that different physical and chemical environments

existed there at one time. Thus the physical and chemical

conditions that were present in one locality did not

necessarily exist in a nearby area. This situation

probably arose out of varying permeability conditions,

fr~cture plumbing control, nearness to the intrusive.

and the availability and ability of ground water to

enter the system. These varying physical and chemical

conditions would control the amounts of aqueous sulfur

7 1

s p e c i e s t h a t w e r e p r e s e n t a n d t h u s t h e i s o t o p i c

c o m p o s i t i o n o f t h e s u l f u r - b e a r i n g m i n e r a l s .

T h e a l u n i t e a n d j a r o s i t e f o r w h i c h s u l f u r i s o t o p i c

v a l u e s w e r e o b t a i n e d b o t h s h o w 6 S 3 ^ v a l u e s n e a r t h e

34

p r i m a r y <5S^ v a l u e . T h e y a r e b e l i e v e d t o b e s e c o n d a r y

a n d t h e r e s u l t o f t h e w e a t h e r i n g o f p r i m a r y s u l f i d e s ,

s u c h a s p y r i t e a n d s t i b n i t e .

T h e o r p l m e n t a n d r e a l g a r f r o m t h e B r i c k y a r d m i n e 3 4

s h o w a v a r i a t i o n i n 6 S ^ w h i c h c o u l d i n d i c a t e m i n e r a l

f o r m a t i o n o v e r a p e r i o d o f t i m e w i t h c h a n g i n g c h e m i c a l

c o n d i t i o n s o r a c c e p t a n c e b y t h e m i n e r a l o f s u l f u r w h o s e

i s o t o p i c c o m p o s i t i o n w a s d e t e r m i n e d b y pH a n d o x y g e n

f u g a c i t y w h i c h a c c o r d i n g t o O h m o t o 1 s d i a g r a m s ( 1 9 7 2 ,

p . 5 6 0 , 5 5 8 ) i s u n l i k e l y .

B a r i t e s a m p l e s n u m b e r 12 a n d 1 6 h a v e a l o w

p o s i t i v e s S 3 w h i c h c o u l d i n d i c a t e a r e l a t i v e l y h i g h 32

t e m p e r a t u r e o f f o r m a t i o n s i n c e S 0 2 i s e n r i c h e d i n S v

a t h i g h t e m p e r a t u r e s . A l t e r n a t i v e l y , e q u i l i b r i u m

b e t w e e n H 2 S a n d S 0 2 m a y n o t h a v e b e e n r e a c h e d d u r i n g

f o r m a t i o n o f t h e b a r i t e . B a r i t e s a m p l e n u m b e r 8 3 4

h a s a l a r g e p o s i t i v e 6 S ^ w h i c h c o u l d i n d i c a t e a

p r i m a r y o r i g i n i n n e a r - s u r f a c e c o n d i t i o n s .

T h e s t i b n i t e ( s a m p l e # 1 4 ) s a m p l e h a s a + 1 0 . 1 2 #

v a l u e w h i c h c o u l d i n d i c a t e a h o t s p r i n g e n v i r o n m e n t

o r t h a t e q u i l i b r i u m c o n d i t i o n s w e r e n o t a t t a i n e d .

P r a g e n e t i c r e l a t i o n s f o r t h e t w o m i n e r a l s i n h a n d s p e c i m e n

71

species that were present and thus the isotopic

composition of the sulfur-bearing minerals.

The alunite and jarosite for which sulfur isotopic

values were obtained both show 0834 values near the

primary os34 value. They are believed to be secondary

and the result of the weathering of primary sulfides,

such as pyrite and st1bnite.

The orpiment and realgar from the Brickyard mine

show a variation in oS34 which could 1ndicate mineral

formation over a period of time with changing chemical

conditions or acceptance by the mineral of sulfur whose

isotopic composition was determined by pH and oxygen

fugacity which according to Ohmoto's diagrams (1972,

p. 560, 558) is unlikely.

Barite samples number 12 and 16 have a low

positive oS34 which could indicate a relatively high

temperature of formation since 802 is enriched in S32

at high temperatures. Alternatively, equilibrium

between H2 S and S02 may not have been reached during

formation of the barite. Bar1te sample number 8

has a large positive os34 which could indicate a

primary origin in near-surface conditions.

The stibnite (sample #14) sample has a +10.12%

value which could indicate a hot spring environment

or that equilibrium conditions were not attained.

Pragenetic relations for th,! two minerals in hand specimen

i n d i c a t e t h e s t i b n i t e w a s d e p o s i t e d i n t h e l a t e r s t a g e s

o f b a r i t e d e p o s i t i o n o r w a s d e p o s i t e d a f t e r t h e b a r i t e .

P y r i t e s a m p l e s n u m b e r 1 1 , 1 3 $ a n d 1 5 w h i c h c o m e

f r o m o r n e a r t h e S a c r a m e n t o m i n e s h o w a c h a n g e o f

p o s i t i v e v a l u e s w h i c h c o u l d r e f l e c t c h a n g i n g c h e m i c a l

c o n d l t i o n s •

34

T h e d e v i a t i o n s o f <5S^ v a l u e s o b t a i n e d c o u l d b e

e x p l a i n e d b y t h e n o n - e q u i l i b r a t i o n o f S 0 2 a n d H 2 S w h i c h

w a s c a u s e d b y t h e c o n t i n u o u s a d d i t i o n o f s u l f u r f r o m

g r o u n d w a t e r s . A l s o u p w e l l i n g h o t w a t e r s u n d e r g o

c h a n g e s i n s u l f u r g a s s p e c i e s c o n t e n t a s t h e w a t e r s

a r e c o o l e d a n d t h e s u l f u r g a s s p e c i e s a r e o x i d i z e d .

T h u s , t h e s u l f u r i s o t o p i c c o m p o s i t i o n s o f t h e d i s s o l v e d

g a s e s a r e a f f e c t e d . T h e i s o t o p i c c o m p o s i t i o n s f o u n d

a r e b e l i e v e d t o r e p r e s e n t t h e c h e m i c a l c o n d i t i o n s

c o m m o n l y f o u n d i n h o t s p r i n g e n v i r o n m e n t s .

72

indicate the stibnite was deposited in the later stages

of barite deposition or was deposited after the barite.

Pyrite samples number 11. 13. and 15 which come

from or near the Sacramento mine show a change of

positive values which could reflect ohanging chemical

conditions.

The deviations of 6S34 values obtained could be

explained by the non-equilibration of S02 and H2S which

was caused by the continuous addition of sulfur from

ground waters. Also upwelling hot waters undergo

changes in sulfur gas species content as the waters

are cooled and the sulfur gas species are oxidized.

Thus, the sulfur isotopic compositions of the dissolved

gases are affected. The isotopic compositions found

are believed to represent the chemical conditions

commonly found in hot spring environments.

SUMMARY AND RECOMMENDATIONS

T h e t r u e s t r u c t u r a l c h a r a c t e r o f M e r c u r h a s b e e n

o v e r l o o k e d f o r m a n y y e a r s . T h e r h y o l i t e i n t r u s i v e

o n t h e n o r t h s i d e o f E a g l e H i l l a p p e a r s t o h a v e b e e n

f o r c e f u l l y i n t r u d e d a n d t o b e y o u n g e r t h a n f o l d i n g

b e c a u s e o f t h e d r a g f o l d s t h a t o c c u r , n o t i c e a b l y

o n i t s n o r t h s i d e . T h e t w o e x p l o s i v e b r e c c i a p i p e s '

f o r m a t i o n i s b e l i e v e d t o b e r e l a t e d t o t h e h y d r o t h e r m a l

a c t i v i t y w h i c h w a s a p a r t o f e n d - s t a g e m a g m a t l c a c t i v i t y .

T h e c o l l a p s e b r e c c i a n e a r t h e c e n t e r o f t h e g h o s t

t o w n o f M e r c u r f o r m e d a t t h e I n t e r s e c t i o n o f t w o

f a u l t s a n d p r o b a b l y r e s u l t e d f r o m t h e c o l l a p s e o f

t h e r o o f o f a s o l u t i o n c a v e .

A l t e r a t i o n o f t h e G r e a t B l u e L i m e s t o n e a n d t h e

E a g l e H i l l r h y o l i t e i s l o w - g r a d e i n t h e a r e a ,

S l l i c i f i c a t i o n w i t h s o m e s e r i c i t e a n d i l l i t e i s

c h a r a c t e r i s t i c o f t h e g o l d o r e s e q u e n c e . A l t e r a t i o n

o f t h e E a g l e H i l l r h y o l i t e i s v a r i e d a n d i n c l u d e s

k a o l i n i z a t i o n , s e r i c i t i z a t i o n , a n d s l l i c i f i c a t i o n .

K a o l i n i z a t i o n a n d s l l i c i f i c a t i o n a r e m o s t p r o m i n e n t i n

t h e i n t r u s i v e a r o u n d t h e S a c r a m e n t o b r e c c i a p i p e .

S e r i c i t i z a t i o n o f t h e g r o u n d m a s s o f t h e i n t r u s i v e i s

p r o b a b l y l a t e - s t a g e , d e u t e r i c a l t e r a t i o n .

T h e g o l d o r e s e q u e n c e c o n t a i n s m i n e r a l s t h a t a r e

c h a r a c t e r i s t i c o f a n e p i t h e r m a l d e p o s i t . T h e g o l d

SUMMARY AND RECOMMENDATIONS

The true structural character of Mercur has been

overlooked for many ye~rs. The rhyolite intrusive

on the north side of Eagle Hill appears to have been

forcefully intruded and to be younger than folding

because of the drag folds that occur, noticeably

on its north side. The two explosive breccia pipes'

formation is believed to be related to the hydrothermal

activity which was a part of end-stage magmatic activity.

The collapse breccia near the center of the ghost

town of Mercur formed at the intersection of two

faults and probably resulted from the collapse of

the roof of a solution cave.

Alteration of the Great &lue Limestone and the

Eagle Hill rhyolite is low-grade in the area.

Silicification with some sericite and illite is

charqcteristic of the gold ore sequence. Alteration

of the Eagle Hill rhyolite is varied and includes

kaolinization, sericitization, and silicification.

Kaolinization and silicification are most prominent in

the intrusive around the Sacramento breccia pipe.

Sericitization of the groundmass of the intrusive is

probably late-stage, deuteric alteration.

The gold ore sequence contains minerals that are

characteristic of an epithermal deposit. The gold

7 4

m i n e r a l i z a t i o n i s a s s o c i a t e d w i t h o r p l m e n t , r e a l g a r ,

g a l e n a , a r s e n o p y r i t e , s p h a l e r i t e , c h a l c o p y r i t e , a n d

c i n n a b a r . T h e g o l d i s i n v i s i b l e e v e n w i t h t h e a i d

o f a r e f l e c t i n g m i c r o s c o p e , ,

T h e c a r b o n - g o l d - a r s e n i c r e l a t i o n s h i p o b s e r v e d a t

M e r c u r , U t a h ; C a r l i n , N e v a d a ; a n d G e t c h e l l M i n e , N e v a d a ,

i s a n i n t e r e s t i n g l o w t e m p e r a t u r e r e l a t i o n s h i p . T h i s

r e l a t i o n s h i p i s p r o b a b l y d u e t o h y d r o t h e r m a l s o l u t i o n s

e n t e r i n g p e r m e a b l e r e a c t i v e b e d s t h a t c o n t a i n e d

h y d r o c a r b o n s . O r g a n i c e x t r a c t i o n p r o c e d u r e s a p p l i e d

t o c a r b o n - r i c h m a t e r i a l s f r o m t h e t h r e e g o l d c a m p s

s h o w e d b y t h e u s e o f I n f r a r e d s p e c t r o s c o p y t h e p r e s e n c e

o f t h e a l k a n e a n d c a r b o n y l g r o u p s . A l k a n e s a r e o n e

o f t h e m a i n c o n s t i t u e n t s o f p e t r o l e u m . T h e r e f o r e ,

s o m e f o r m o f h y d r o c a r b o n p r o b a b l y s e r v e d a s t h e s o u r c e

f o r t h e c a r b o n .

S u l f u r i s o t o p e d a t a f o r t h e s u l f i d e s a t M e r c u r

3 4

h a v e a m e a n o f + 7 . 8 8 6 S ^ a n d a s p r e a d o f v a l u e s

w h i c h i s c h a r a c t e r i s t i c o f s u l f u r i s o t o p e d a t a f r o m

o t h e r h o t s p r i n g d e p o s i t s . T h e s u l f u r i s o t o p e d a t a

a r e b e l i e v e d t o r e f l e c t n e a r - s u r f a c e c o n d i t i o n s , l o w

t e m p e r a t u r e , a n d t h e c o n t i n u a l m i x i n g o f g r o u n d w a t e r s

w i t h h e a t e d w a t e r s w h i c h r e s u l t e d i n H 2 S - S 0 2 d i s e q u i l i b r i u m .

R e c o m m e n d a t i o n s f o r f u r t h e r s t u d y i n c l u d e K - A r d a t i n g

o f t h e E a g l e H i l l r h y o l i t e i n t r u s i v e s a t O p h i r , M e r c u r ,

W e s t M e r c u r c o m b i n e d w i t h c h e m i c a l d a t a o n t h e i n t r u s i v e s

mineralization is associated with orpiment, realgar,

galena, arsenopyrite, sphalerite, chalcopyrite, and

cinnabar. The gold is invisible even with the aid

of a reflecting microscope.

The carbon-gold-arsenic relationship observed at

74

Mercur, Utah; Carlin, Nevada; and Getchell Mine, Nevada,

is an interesting low temperature relationship. This

relationship is probably due to hydrothermal solutions

entering permeable reactive beds that contained

hydrocarbons. Organic extraction procedures applied

to carbon-rich materials from the three gold camps

showed by the use of infrared spectroscopy the presence

of the alkane and carbonyl groups. Alkanes are one

of the main constituents of petroleum. Therefore,

some form of hydrocarbon probably served as the source

for the carbon.

Sulfur isotope data for the sulfides at Mercur

have a mean of +7.88 8S34 and a spread of values

which is characteristic of sulfur isotope data from

other hot spring deposits. The sulfur isotope data

are believed to reflect near-surface conditions, low

temperature, and the continual mixing of ground waters

•

with heated waters which resulted in H2S-S02 disequilibrium.

Recommend~tions for further study include K-Ar dating

of the Eagle Hill rhyolite intrusives at Ophir, Mercur.

West Mercur combined with chemical data on the intrusives

7 5

a t e a c h l o c a l i t y t o d e t e r m i n e i f t h e y c a m e f r o m t h e

s a m e p l u t o n . C a r b o n i s o t o p e d a t a o f t h e c a r b o n - r i c h

z o n e a t t h e S a c r a m e n t o m i n e m i g h t b e o f i n t e r e s t .

M o r e p r e c i s e i d e n t i f i c a t i o n o f t h e o r g a n i c c o m p o u n d s

m i g h t g i v e s o m e c l u e a s t o t h e c h e m i c a l a n d t e m p e r a t u r e

c o n d i t i o n s t h a t e x i s t e d d u r i n g t h e h y d r o t h e r m a l

a c t i v i t y . M o r e s t u d y o f t h e s t r u c t u r e o u t s i d e t h e

M e r c u r a r e a m i g h t b e o f i n t e r e s t . M o r e p o l i s h e d

s e c t i o n w o r k w i t h t h e u s e o f p r o p e r i n s t r u m e n t a t i o n

m i g h t b e u s e f u l t o t h e i d e n t i f i c a t i o n o f g o l d o c c u r r e n c e s

a n d r e l a t i o n s h i p s w i t h o t h e r m i n e r a l s .

at each locality to determine if they came from the

same pluton. Carbon isotope data of the carbon-rich

zone at the Sacramento mine might be of interest.

75

More precise identification of the organic compounds

might give some clue as to the chemical and temperature

conditions that existed during the hydrothermal

activity. More study of thf! structure outside the

Mercur area might be of interest. More polished

section work with the use of proper instrumentation

might be useful to the identification of gold occurrences

and relationships with other minerals.

SELECTED REFERENCES

A l l e n , R . H . , 1 9 1 0 , M i n e s a n d M i l l o f C o n s o l i d a t e d M e r c u r C o . : E n g . a n d M i n . J o u r . , v . 8 9 , n . 2 5 , p . 1 2 7 3 - 1 2 7 7 .

A n d r e w s , W . B . , 1 9 3 7 . M e r c u r a n d M a n n i n g M i n i n g D i s t r i c t s : C o m p a s s , v . 1 7 . n . 3 , p . 1 4 8 - 1 5 2 .

B i s s e l l , H . J . , 1 9 5 9 . G e o l o g y o f t h e S o u t h e r n O q u i r r h M o u n t a i n s a n d F i v e m i l e P a s s — N o r t h e r n B o u l t e r M o u n t a i n A r e a , T o o e l e a n d U t a h C o u n t i e s , U t a h : U t a h G e o l o g i c a l a n d M i n e r a l o g i c a l S u r v e y G u i d e b o o k N u m b e r 1 4 , 2 6 9 p .

B u t l e r , B . S . , 1 9 2 0 , T h e O r e D e p o s i t s o f U t a h : U . S . G e o . S u r v e y P r o f . P a p e r 1 1 1 , p . 3 8 7 - 3 9 5 .

D e g e n s , E . T . a n d H . R e u t e r , 1 9 6 4 , A n a l y t i c a l T e c h n i q u e s i n t h e F i e l d o f O r g a n i c G e o c h e m i s t r y , i n I n g e r s o n , E . , A d v a n c e s i n O r g a n i c G e o c h e m i s t r y : New Y o r k , P e r g a m o n P r e s s , p . 3 7 7 - 4 1 5 -

E h l m a n n , A . J . , 1 9 5 8 , P y r o p h y l l l t e i n S h a l e s o f N o r t h C e n t r a l U t a h : U n p u b l i s h e d t h e s i s , U n i v , o f U t a h , p . 6 4 - 7 9 .

E m m o n s , S . F . a n d G . F . B e c k e r , 1 8 8 5 . C a m p F l o y d D i s t r i c t , i n S t a t i s t i c s a n d T e c h n o l o g y o f t h e P r e c i o u s M e t a l s : T e n t h C e n s u s o f t h e U n i t e d S t a t e s , v , 1 3 , p . 4 5 4 - 4 5 5 .

E r i c k s o n , R . L . , A . L . . M a r r a z i n o , U . O d a , a n d W.W.. J a n e s . 1 9 6 4 , G e o c h e m i c a l E x p l o r a t i o n N e a r t h e G e t c h e l l M i n e , H u m b o l d t C o u n t y , N e v a d a : U . S . G e o . - S u r v e y B u l l . 1 1 9 8 - A , 2 6 p .

F r a n k l i n , W . J . a n d V . M i l l e r , 1 9 3 8 , M e t a l l u r g i c a l D e v e l o p m e n t s a t M e r c u r , U t a h : U . S . B u r e a u o f M i n e s T e c h . P a p e r 5 8 8 , 4 2 p .

G e m m e l l , B . C . , 1 8 9 7 . T h e C a m p F l o y d M i n i n g D i s t r i c t a n d t h e M e r c u r M i n e s , U t a h : E n g . a n d M i n . J o u r . , v . 6 3 , n . 1 7 . p . 4 0 3 - 4 0 4 ; 4 2 7 - 4 2 8 .

G i l l u l y , J . , 1 9 3 2 , G e o l o g y a n d O r e D e p o s i t s o f t h e S t o c k t o n a n d F a i r f i e l d Q u a d r a n g l e s , U t a h : U . S . G e o . S u r v e y P r o f . P a p e r 1 7 3 , 1 7 1 p -

SELECTED REFERENCES

Allen, R.H., 1910, Mines and Mill of Consolidated Mercur Co.: Eng. and Min. Jour •• v. 89. n. 25, p. 1273-1277.

Andrews. W.B., 1937, Mercur and Manning Mining Districts: Compass. v. 17. n. 3. p. 148-152.

Bissell. H.J •• 1959. Geology of the Southern Oquirrh Mountains and Fivemile Pass--Northern Boulter Mountain Area. Tooele and Utah Counties. Utah: Utah Geological and Mineralogical Survey Guidebook Number 14. 269p.

Butler. B.S., 1920. The Ore Deposits of Utah: U.S. Geo. Survey Prof. Paper 111, p. 387-395.

Degens. E.T. and H. Reuter, 1964. Analytical Techniques in the Field of OrganiC Geochemistry, in Ingerson, E.. Adva.nces in Organic Geochemistry: New York, Pergamon Press. p. 377-415.

Ehlmann, A.J •• 1958, Pyrophyllite in Shales of. North Central Utah: Unpublished thesiS, Univ. of Utah. p. 64-79.

Emmons, S.F. and G.F. Becker. 1885, Camp Floyd District, in Statistics and Technology of the Precious Metals: Tenth Census of the United States. v. 1), p. 454-455.

Erickson, R.L., A.L •. Marrazino, U. Oda, and W.W. Janes, 1964, Geochemical Exploration Near the Getchell Mine, Humboldt County, Nevada: U.S. Geo •. Survey Bull. 1198-A, 26p.

Franklin, W.J. and V. Miller, 1938. Metallurgical Developments at Mercur, Utah: U.S. Bureau of Mines Tech. Paper 588, 42p.

Gemmell, R.C •• 1897. The Camp Floyd Mining District and the Mercur Mines, Utah: Eng. and Min. Jour •• v. 63, n. 17, p. 403-404; 427-428.

Gilluly, J., 1932, Geology and Ore Deposits of the Stockton and Fairfield Quadrangles. Utah: U.S. Geo. Survey Prof. Paper 17). 171p.

7 7

H a u s e n , D . M . a n d P . K . K e r r , 1 9 6 8 , F i n e G o l d O c c u r r e n c e a t C a r l i n , N e v a d a : i n R i d g e , J . D , , O r e D e p o s i t s o f t h e U n i t e d S t a t e s , 1 9 3 3 - 1 9 6 7 : New Y o r k , A I M E , p . 9 0 8 - 9 4 0 .

He i k e s , V . C . , 1 9 2 0 , C a m p F l o y d o r M e r c u r D i s t r i c t , i n B . S , B u t l e r , T h e O r e D e p o s i t s o f U t a h : U . S . G e o . S u r v e y P r o f . P a p e r 1 1 1 , p , 3 8 2 - 3 8 7 .

H e l g e s o n , H . C . a n d R . M . G a r r e l s , I 9 6 8 , H y d r o t h e r m a l T r a n s p o r t a n d D e p o s i t i o n o f G o l d : E c o n . G e o . , v . 6 3 , p . 6 2 2 - 6 3 5 .

H i l l , V . C . , 1 8 9 4 , O r e D e p o s i t s o f C a m p F l o y d D i s t r i c t , T o o e l e C o u n t y , U t a h : P r o c . C o l o . S c i . S o c . , v . 5 , p . 5 ^ - 6 5 .

H o w a r d , L . O . , 1 9 1 3 a , T r e a t m e n t o f M e r c u r D u m p s : S a l t L a k e M i n , R e v . , v . 1 5 , n . 8 , p . 1 7 - 1 9 .

1 9 1 3 b , H i s t o r y o f M i l l i n g a t t h e G e y s e r -M a r i o n a n d t h e S a c r a m e n t o : S a l t L a k e M i n . R e v . , v . 1 5 . n . 9, p , 9 - 1 3 .

1 9 1 3 c , H i s t o r y o f C y a n i d i n g a t S u n s h i n e : S a l t L a k e M i n . R e v . , v . 1 5 , n . 1 0 , p . 1 1 - 1 6 .

1 9 1 3 d , M o d e r n F l o t a t i o n s D e b t t o S u n s h i n e : S a l t L a k e M i n . R e v . , v . 1 5 , n . 1 1 , p . 1 3 - 1 6 .

1 9 1 3 e , C y a n i d i n g o n t h e W e s t D i p , M e r c u r : S a l t L a k e M i n . R e v . , v . 1 5 , n . 1 2 , p . 1 3 - 1 6 .

J e n s e n , M . L . , I 9 6 7 . S u l f u r I s o t o p e s a n d M i n e r a l G e n e s i s , i n B a r n e s , G e o c h e m i s t r y o f H y d r o t h e r m a l O r e D e p o s i t s : New Y o r k , H o l t R i n e h a r t a n d W i n s t o n , I n c . , p . 1 4 3 - 1 6 5 .

R . P . A s h l e y , a n d J . P . A l b e r s , 1 9 7 1 a , P r i m a r y a n d S e c o n d a r y S u l f a t e s a t G o l d f i e l d , N e v a d a : E c o n . G e o . , v . 6 6 , p . 6 1 8 - 6 2 6 .

S . O a n a , N . N a k a i , a n d G . D e s s a u , 1 9 7 1 b , S u l f u r I s o t o p i c G e o c h e m i s t r y o f V o l c a n i c a n d F u m a r o l i c F l u i d s : S o c M i n . G e o . J a p a n , S p e c . I s s u e 2 , p . 7 6 - 7 9 .

J o r a l e m o n , P . , 1 9 5 1 . T h e O c c u r r e n c e o f G o l d a t t h e G e t c h e l l M i n e , N e v a d a : E c o n . G e o . , v . 4 6 , p . 2 6 7 - 3 1 0 .

Hausen, D.M •. and P.K. Kerr, 1968, Fine Gold Occurrence at Carlin, Nevada: in Ridge, J.D., Ore Deposits of the United StateS71933-1967: New York, AlME, p. 908-940.

Heikes, V.C., 1920, Camp Floyd or Mercur District. in B.S. Butler. The Ore Deposits of Utah: U.S. Geo. Survey Prof. Paper 111, p. 382-387.

Helgeson, H.C. and R.M. Garrels, 1968, Hydrothermal Transport and Deposition of Gold: Econ. Geo., v. 63. p. 622-635.

Hill, V.C., 1894, Ore Deposits of Camp Floyd District, Tooele County, Utah: Proc. Colo. Sci. Soc •• v. 5, p. 54-65.

??

Howard, L.O., 1913a, Treatment of Mercur Dumps: Salt Lake Min. Re v ., v. 15 , n. 8, p • 17 -19 •

1913b, History of Milling at the Geyser­Marion and the Sacramento: Salt Lake Min. Hev., v. 15, n. 9, p. 9-13.

1913c, History of Cyaniding at Sunshine: Salt Lake Min. Hev., v. 15, n. 10, p. 11-16.

1913d, Modern Flotations Debt to Sunshine: Sa I t Lake Min. He v " v. 15, n. 11. p. 13 -16 •

1913e, Cyaniding on the West Dip, Mercur: Salt Lake Min. Hev., v. 15. n. 12, p. 13-16.

Jensen, M.L •• 1967, Sulfur Isotopes and Mineral Genesis, in Barnes • Geochemistry of Hydrothermal Ore DeposIts: New York, Holt Rinehart and Winston, Inc •• p. 143-165.

____ ~--_____ R.P. Ashley, and J.P. Albers, 1971a. Primary and Secondary Sulfates at Goldfield, Nevada: Econ. Geo •• v. 66, p. 618-626.

----~~~---e S. Oana. N. Nakai. and G. Dessau. 1971b. Sulfur Isotopic Geochemistry of Volcanic and Fumarolic Fluids: Soc. Min. Geo. Japan, Spec. Issue 2, p. 76-79.

Joralemon. P., 1951, The Occurrence of Gold at the Getchell Mine, Nevada: Hcon. Geo., v. 46, p. 267-310.

7 8

K i n g , W . H . a n d S . R . W i l s o n , 1 9 ^ 9 . D i a m o n d - D r i l l a n A u g e r S a m p l i n g o f V a n a d l f e r o u s S h a l e , M e r c u r Dome M i n e , T o o e l e C o u n t y , U t a h : U . S . B u r e a u o f M i n e s R e p t . o f I n v . 4 5 7 2 , 8 p ,

L e n z i , G . W . , 1 9 7 1 # G e o c h e m i c a l R e c o n n a i s a n c e a t M e r c u r , U t a h : U n p u b l i s h e d M a s t e r ' s t h e s i s , U n i v , o f U t a h , 5 1 p .

M a b e y , D . R . , M . D . C r i t t e n d e n . J r . , H . T . . M o r r i s , R . J . R o b e r t s , a n d E . W . T o o k e r , 1 9 6 4 , A e r o m a g n e t i c a n d G e n e r a l i z e d G e o l o g i c Map o f P a r t o f N o r t h -C e n t r a l U t a h : U . S . G e o . S u r v e y G e o p h y s . I n v . Map G P - 4 2 2 .

M a g u i r e , D , , L . O . H o w a r d , 1 9 1 3 a , T h e R o m a n c e o f a F a m o u s G o l d M i n e : S a l t L a k e M i n , R e v , , v . 1 5 , n . 6 , p . 1 3 - 1 7 .

a n d L . O . H o w a r d , 1 9 1 3 b , T h e R o m a n c e o f a F a m o u s G o l d M i n e , S a l t L a k e M i n . R e v . , v . 1 5 . n . 7 . p . 9 - 1 5 .

M a r t i n , G . , 1 9 3 ^ . M e r c u r H a s New H o p e s : E n g . a n d M i n . J o u r . , v . 1 3 5 . n . 1 0 , p . 4 4 6 - 4 4 7 .

M e r w i n , R . W . , 1 9 6 8 , G o l d R e s o u r c e s i n t h e O x i d i z e d O r e s a n d C a r b o n a c e o u s M a t e r i a l I n t h e S e d i m e n t a r y B e d s o f N o r t h e a s t e r n N e v a d a : U . S . B u r e a u o f M i n e s T e c h . P r o g . R e p t . 1 , 1 6 p .

M o o r e , W . J . , 1 9 7 3 . A S u m m a r y o f R a d i o m e t r i c A g e s o f I g n e o u s R o c k s i n t h e O q u i r r h M o u n t a i n s , N o r t h C e n t r a l U t a h : E c o n . G e o . , v . 6 8 , p . 9 7 - 1 0 1 .

N i c h o l s , I . L . a n d L . P e t e r s o n , 1 9 7 0 , L e a c h i n g G o l d -B e a r i n g M i l l T a i l i n g s F r o m M e r c u r , U t a h : U . S . B u r e a u o f M i n e s R e p t . o f I n v . 7 3 9 5 , l O p .

O h m o t o , H . , 1 9 7 2 , S y s t e m a t i c s o f S u l f u r a n d C a r b o n I s o t o p e s i n H y d r o t h e r m a l O r e D e p o s i t s : E c o n . G e o . , v . 6 7 . n . 5 . P . 5 5 1 - 5 7 8 .

O n g , H . L . . a n d V . W . S w a n s o n , 1 9 ^ 9 , N a t u r a l O r g a n i c A c i d s i n t h e T r a n s p o r t a t i o n , D e p o s i t i o n , a n d C o n c e n t r a t i o n o f G o l d : C o l o . S c h o o l M i n e s Q u a r t , , v . 6 4 , n . 1 , p . 3 9 5 - ^ 2 5 .

King, W.H. and S.R. Wilson, 1949, Diamond-Drill an Auger Sampl1ng of Vanadiferous Shale, Mercur Dome Mine, Tooele County, Utah: U.S. Bureau of Mines Rept. of Inv. 4572, 8p.

78

Lenzi, G.W., 1971, Geochemical Reconnaisance at Mercur, Utah: Unpublished Master's thesis, Univ. of Utah, 51p.

Mabey. D.R ... M.D. Crittenden. Jr., H.T .•. Morris. R.J. Roberts, and E.W. Tooker, 1964, Aeromagnetic and Generalized Geologic Map of Part of North­Central Utah: U.S. Geo. Survey Geophys. Inv. Map GP-422.

Maguire, D., L.O. Howard, 1913a, The Romance of a Famous Gold Mine: Salt Lake Min. Rev., v. 15. n. 6, p. 13-17.

and L.O. Howard. 1913b, The Romance of a ----=Pa-m-o-u-s-Gold lIUne: Salt Lake Min. Rev., v. 15.

n. 7, p. 9-15.

Mart1n. G •• 1934, Mercur Has New HOpes: Eng. and Min. Jour., v. 135. n. 10. p. 446-447.

Merwin. R.W., 1968, Gold Resources in the Oxidized Ores and Carbonaceous Material in the Sedimentary Beds of Northeastern Nevada: U.S. Bureau of Mines Tech. Prog. Rept. 1, 16p.

Moore, W.J., 1973. A Summary of Radiometric Ages of Igneous Rocks in the Oquirrh Mountains, North Central Utah: Rcon. Geo •• v. 68. p. 97-101.

Nichols, I.L. and L. Peterson. 1970. Leach1ng Gold­Bear1ng Mill Tailings From Mercur, Utah: U.S. BUreau of M1nes Rept. 'Df Inv. 7395. lOp.

Ohmoto. H., 1972, Systemat1.cs of Sulfur and Carbon Isotopes in Hydrothermal are Deposits: Econ. Geo., v. 67. n. 5. p. 551-578.

Ong, H.L •. and V.W. Swanson, 1969, Natural Organic Ac1ds 1n the Transportation. Deposition, and Concentrat1on of Gold: Colo. School M1nes Quart., v. 64, n. 1, p. 395-4250

7 9

P a l m e r , L . A . , 1 9 0 9 , M i l l i n g P r a c t i c e a t t h e C o n s o l i d a t e d M e r c u r : S a l t L a k e M i n , R e v , , v . 1 0 , n . 2 3 , p , 1 5 - 1 7 .

R a d t k e , A . S . a n d B . J . S c h e l n e r , 1 9 7 0 , S t u d i e s o f H y d r o t h e r m a l G o l d D e p o s i t i o n ( I ) . C a r l i n G o l d D e p o s i t , N e v a d a : T h e R o l e o f C a r b o n a c e o u s M a t e r i a l s i n G o l d D e p o s i t i o n : E c o n , G e o . , v . 6 5 , p . 8 7 - 1 0 2 .

R o b e r t s , R . J . , A . S . R a d t k e , a n d R . R . C o a t s , 1 9 7 1 , G o l d - B e a r i n g D e p o s i t s i n N o r t h C e n t r a l N e v a d a a n d S o u t h w e s t e r n I d a h o : E c o n . G e o , , v , 6 6 , p . 1 4 - 3 3 *

S c h e i n e r , B . J . , R . E . L i n d s t r o m , a n d T . A . H e n r i e , 1 9 6 8 , I n v e s t i g a t i o n o f O x i d a t i o n S y s t e m s F o r I m p r o v i n g G o l d R e c o v e r y F r o m C a r b o n a c e o u s M a t e r i a l s : U . S . B u r e a u o f M i n e s T e c h . P r o g . R e p t . 2 , 8 p .

R . E . L i n d s t r o m , a n d T . A . H e n r i e , 1 9 6 9 . E l e c t r o l y t i c O x i d a t i o n o f C a r b o n a c e o u s O r e f o r I m p r o v i n g G o l d R e c o v e r y : U . S . B u r e a u o f M i n e s T e c h . P r o g . R e p t . 8 , 1 2 p ,

R . E . . L i n d s t r o m , W . J . . G r a y , a n d D . G . P e t e r s o n , 1 9 7 2 , E x t r a c t i o n o f G o l d F r o m C a r b o n a c e o u s O r e : P i l o t P l a n t S t u d i e s : U . S . B u r e a u o f M i n e s R e p t . o f I n v , 7 5 9 7 . 2 0 p .

S p u r r , J . E . , 1 8 9 4 - 9 5 . E c o n o m i c G e o l o g y o f t h e M e r c u r M i n i n g D i s t r i c t , U t a h : S i x t e e n t h A n n u a l R e p o r t o f t h e U n i t e d S t a t e s G e o l o g i c a l S u r v e y , P a r t I I — P a p e r s o f a n E c o n o m i c C h a r a c t e r , p . 3 ^ 3 - ^ 5 5 •

Z e l l e r , R . P . , 1 9 5 8 , P a l e o c o l o g y o f t h e L o n g T r a i l S h a l e M e m b e r o f t h e G r e a t B l u e L i m e s t o n e , O q u i r r h R a n g e , U t a h : B r i g h a m Y o u n g U n i v . R e s . S t u d . - -G e o . S e r . , v . 5 . n . 8 , 3 6 p .

79

Palmer, L.A., 1909, Milling Practice at the Consolidated Mercur: Salt Lake Min. Rev., v~ 10, n. 23, p. 15-17.

Radtke. A.S. and B.J. Scheiner, 1970, Studies of Hydrothermal Gold Deposition (I). Carlin Gold Deposit. Nevada: The Role of Carbonaceous Materials in Gold Deposition: Bcon. Geo., v. 65. p. 87-102.

Roberts, R.J •• A.S. Radtke, and R.R. Coats. 1971, Gold-Bearing Deposits in North Central Nevada and Southwestern Idaho: Econ. Geo., v. 66, p. 14-33.

Scheiner, B.J., R.E. Lindstrom, and T.A. Henrie, 1968, Investigation of Oxidation Systems For Improving Gold Recovery From Carbonaceous Materials: U.S. Bureau of Mines Tech. Prog. Rept. 2, 8p.

R.E. Lindstrom, and T.A. Henrie, 1969, Electrolytic Oxidation of Carbonaceous Ore for Improving Gold Recovery: U.S. Bureau of Mines Tech. Prog. Rept. 8, 12p.

R.E •. Lindstrom, W.J •. Gray, and D.G. Peterson, 1972, Extraction of Gold From Carbonaceous Ore: Pilot Plant Studies: U.S. Bureau of Mines Rept. of Inv. 7597, 20p.

Spurr, J.E., 1894-95, EconomiC Geology of the Mercur Mining District, Utah: Sixteenth Annual Report of the United States Geological Survey, Part II-­Papers of an Economic Character, p. 343-455.

Zeller, R.P., 1958, Paleocology of the Long Trail Shale Member of the Great Blue Limestone, Oquirrh Range. Utah: Brigham Young Univ. Res. Stud.-­Geo. Ser., v. 5, n. 8, 36p.

VITA

Name

B i r t h p l a c e

B i r t h d a t e

H i g h S c h o o l

C o l l e g e

U n i v e r s i t y

D e g r e e

P r o f e s s i o n a l O r g a n i z a t i o n s

P r o f e s s i o n a l P o s i t i o n s

E d w i n M i c h a e l G u e n t h e r

C h i c a g o . I l l i n o i s

M a r c h 1 9 . 1 9 ^ 8

A u r o r a H i g h S c h o o l A u r o r a , O h i o J u n e 1 9 6 6

B a l d w i n - W a l l a c e C o l l e g e B e r e a , O h i o 1 0 - 6 6 — 3 - 6 8

U n i v e r s i t y o f U t a h S a l t L a k e C i t y , U t a h 3 - 6 8 — 5 - 7 3

B . S . . , U n i v e r s i t y o f U t a h S a l t L a k e C i t y , U t a h 1 9 7 1

AIMS G e o l o g i c a l S o c i e t y o f A m e r i c a

S t u d e n t g e o l o g i s t , U . S . S t e e l C o r p . , Y e r i n g t o n , N e v a d a , s u m m e r I 9 6 8 ; R e s e a r c h a s s i s t a n t , K e n n e c o t t R e s e a r c h C e n t e r , S a l t L a k e C i t y , U t a h 5 - 7 1 — 5 - 7 2

Name

Birthplace

B1rthdate

H1gh School

College

University

Degree

Professional Organizations

Professional Positions

VITA

Edwin Michael Guenther

Chicago, Illin01s

March 19, 1948

Aurora High SChool Aurora, Ohio June 1966

Baldwin-Wallace College Berea, Ohio 10-66--3-68

University of Utah Salt Lake City, Utah 3-68--5-73

B.S •. , University of Utah Salt Lake City, Utah 1971

A 1MB Geological Society of America

Student geologist, U.S.,Steel Corp., Yerington, Nevada, summer 1968; Research assistant, Kennecott Research Center, Salt Lake City, Utah 5-71--5-72