University of Nevada, Reno

A Study of the Adanac Porphyry Molybdenum Deposit and Surrounding Placer Gold Mineralization in Northwest British Columbia With a Comparison to

Porphyry Molybdenum Deposits in the North American Cordillera and Igneous Geochemistry of the Western United States

A thesis submitted in partial fulfillment of the

requirements for the degree of Master of Science in

Geology

by

Jessica Leigh Smith

Dr. Greg B. Arehart/Thesis Advisor

December, 2009

UMI Number: 1478532

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THE GRADUATE SCHOOL University of Nevada, Reno

We recommend that the thesis prepared under our supervision by

JESSICA LEIGH SMITH

entitled

A Study Of The Adanac Porphyry Molybdenum Deposit And Surrounding Placer Gold Mineralization In Northwest British Columbia With A Comparison To

Porphyry Molybdenum Deposits In The North American Cordillera And Igneous Geochemistry Of The Western United States

be accepted in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

Greg B. Arehart, Ph.D., Advisor

John Mccormack, Ph.D., Committee Member

Danny Taylor, Ph.D., Graduate School Representative

Marsha H. Read, Ph. D., Associate Dean, Graduate School

December, 2009

I

Abstract

The Adanac molybdenum deposit has been studied in detail in this thesis in order

to classify the deposit as Climax-type or Endako-type. Placer gold from a nearby Creek

that drains the Adanac deposit was sampled in order to compare initial Os signatures with

that of magnetite from the porphyry deposit, so that it may be determined whether some

of the placer gold is from eroded margins of the porphyry molybdenum deposit.

Characteristics of porphyry molybdenum deposits throughout the North American

Cordillera were summarized and tabulated. Finally, some of the geochemical

characteristics of porphyry molybdenum deposits were used to query igneous rock

databases for the Western United States to identify areas that may be host to more

molybdenum deposits.

The Adanac deposit is hosted in multiple intrusions of alkalic magma with high

silica and K and moderately high Rb/Sr ratios. The Westra and Keith classification of

1981 using the K2O value at 57.5 wt% SiC«2 is 5, meaning the Adanac deposit is classified

as the alkalic, high F, Climax-type molybdenum deposit. The trace element and

alteration patterns conform to this classification as well. Adanac has a high-Mo zone as

disseminated large to medium sized molybdenite rosettes in a smoky quartz vein

stockwork that straddles and blankets at least 2 intrusions. There is a zone of high W

(huebnerite) that is smaller than the molybdenite zone and coincides with it. A high F

zone exists above and peripheral to the Mo and W. Small amounts of Pb and Zn (galena

and sphalerite) occur primarily in faults. No other base metals or trace elements exist in

appreciable amounts in the deposit. Alteration consists of a high silica core and potassic

II

alteration as feldspar floods and potassic envelopes around veins that coincide with

mineralization. QSP alteration and stilbite-calcite alteration is weak and occurs in veins

or fractures that extend outward from Mo mineralization. A weak propylitic overprint

(chlorite, kaolinite) occurs with mineralization but grows stronger outward from

mineralization. Illite and kaolinite occur in the core of the deposit. Montmorillonite

occurs in faults.

Re-Os dating of molybdenite confirmed at least two episodes of mineralization at

70.87 ± 0.36 Ma and 69.66 ± 0.35 Ma, and also confirmed very low Re concentrations (5-

39 ppm) in the molybdenite, which is typical of Climax-type molybdenites. X-ray

diffraction of the molybdenite confirms it is the 2H polytype, which is also typical of

Climax-type molybdenites and may be linked to the low Re concentrations. U-Pb dating

of zircons confines the magmatism at Adanac from 81.6 ± 1.1 Ma to 69 ± 1.2 Ma, giving

the Mount Leonard stock a lifespan of 13.9 Ma. No appropriate age match was found for

an intrusion and mineralization episode using a weighted mean of 30 zircon analyses for

each lithology, which is the standard for reporting U-Pb zircon ages. There are too many

inherited zircons in Adanac lithologies for a mean age to be reliable, and statistical

methods for determining lead loss discredit ages that are most likely valid. It is likely

true that most, if not all, of the lithologies that were dated at Adanac were still

undergoing some crystallization just before (1 Ma) or during mineralization.

The isotopic comparison of the gold sample from Ruby Creek and magnetite from

Adanac does not provide a link between the deposits. The gold has a primitive initial Os

signature (0.1249) that clearly points to an origin associated with mantle rocks such as

Ill

peridotites. The magnetite sample has an initial Os of 1.237 that has been enriched from

terrestrial Os reservoirs. If any placer gold from the Atlin camp is intrusion related it was

not identified in this study, but the possibility that some of the gold is intrusion-related

still exists.

For exploration purposes, the North American Volcanic and Intrusive Database

(NAVDAT) was queried for rock types with high silica (>70 wt%) and high Rb/Sr (>1)

and locations of suitable intrusive lithologies for porphyry molybdenum deposits were

plotted on a map of the western United States, and compared with locations of known

porphyry molybdenum deposits. The resulting areas highlighted numerous potential

porphyry molybdenum camps. Some of these areas could be extensions of known camps,

such as those in Colorado or in Idaho. Other areas, such as in southern Arizona, have no

known porphyry molybdenum deposits but descriptive characteristics of rock types

clearly enumerate potential for new discoveries.

IV

Acknowledgements

The author wishes to thank John Chesley of the University of Arizona at Tucson for his

expertise and guidance concerning the Re-Os study of molybdenite and the Os

comparison of magnetite and gold. Fernando Barra of the University of Arizona at

Tucson also provided guidance in this area and contributed the figure comparing the Os

concentration of gold compared with that of other gold deposits in the world. Much

appreciation is felt for the financial support provided by Geoscience BC of Canada.

Above all, the author wishes to thank both Adanac Molybdenum Corporation for access

to their deposit and data and financial support for this thesis, and Robert Pinsent, Adanac

Molybdenum Corporation's head consulting geologist, for sharing his years of acquired

wisdom and knowledge of the Adanac deposit.

V

Table of Contents

Introduction 1

Geochemistry of Host Rocks 15

Trace Element Zoning 36

Hydrothermal Alteration 65

Molybdenite Polytype Study 84

Geochronology 88

The Relationship of Placer Gold on Ruby Creek with Adanac 108

Characteristics of Porphyry Molybdenum Deposits in The North American Cordillera And Some

Possible Areas That May Be Host To More 115

Conclusions 134

Appendix of Figures and Tables 137

References 178

vi

List of Figures

Figure 1: Plot ofFe content vs. oxidation state 3

Figure 2: Location map for the Adanac molybdenum deposit 7

Figure 3: Regional geologic map of 104N/11W, 12E (Atlin area) 8

Figure 4: Boulder Creek and Ruby Creek area map showing main mineral occurrences 9

Figure 5: Surface geology of the Adanac molybdenum deposit 10

Figure 6: Large molybdenite rosettes in a smoky, ribbon textured quartz vein 12

Figure 7: Molybdenite rosettes on the plane of a quartz vein 12

Figure 8: Relative rock ages based on observed cross cutting relationships 15

Figure 9: CGQM in core sample 17

Figure 10: A typical twinned and perthitic feldspar phenocryst in CGQM, in photomicrograph 17

Figure 11: CGQM-T in core sample 19

Figure 12: CQFP in core sample 19

Figure 13: SQFP grading to CQFP in core sample 19

Figure 14: Graphic intergrowth of quartz and feldspar in photomicrograph 20

Figure 15: MQMP in core sample .....21

Figure 16: SQMP in core sample 22

Figure 17: CQMP in core sample 23

Figure 18: Selective clay alteration on feldspars (photomicrograph) 23

Figure 19: Selective clay alteration of plagioclase (photomicrograph) 24

Figure 20: MEQM in core sample 25

Figure 21: MFP in core sample 26

vii

Figure 22: Finely crystalline quartz and biotite in the matrix of MFP (photomicrograph) 26

Figure 23: Small plagioclase crystal inside a larger alkali feldspar phenocryst (photomicrograph) 27

Figure 24: FGQM in core sample 28

Figure 25:1UGS classification scheme of igneous intrusive rocks showing all Adanac lithologies 29

Figure 26: Alkali lime index for lithologies at Adanac 30

Figure 27: K20 value at 57.5 wt% Si02vs. Rb and Sr for Adanac and other porphyry deposits 34

Figure 28: Example diagram of natural statistical breaks used to calculate geochemical breaks 37

Figure 29: Surface geologic map of Adanac showing the location of cross-sections 38

Figure 30: Geology of cross section A-A' 41

Figure 31: Geology of cross section B-B' 42

Figure 32: Geology of cross section C-C' 43

Figure 33: Geology of cross section D-D' 44

Figure 34: Molybdenum contours overlaid on the geology of cross section A-A' 47

Figure 35: Molybdenum contours overlaid on the geology of cross section B-B' 48

Figure 36: Molybdenum contours overlaid on the geology of cross section C-C 49

Figure 37: Molybdenum contours overlaid on the geology of cross section D-D' 50

Figure 38: Tungsten contours for cross section A-A' 52

Figure 39: Tungsten contours for cross section B-B' 53

Figure 40: Tungsten contours for cross section C-C 54

Figure 41: Tungsten contours for cross section D-D' 55

Figure 42: Fluorine contours for cross section A-A' 59

Figure 43: Fluorine contours for cross section B-B' 60

viii

Figure 44: Fluorine contours for cross section C-C 61

Figure 45: Fluorine contours for cross section D-D' 62

Figure 46: Alteration zoning for an ore body at Climax 66

Figure 47: Silicification in drill core 69

Figure 48: Silicification of biotite in thin section 69

Figure 49: Photomicrograph of opaque minerals in a silicified zone 70

Figure 50: Hydrothermal alteration on cross section A-A' 71

Figure 51: Hydrothermal alteration zones on cross section C-C 72

Figure 52: Hydrothermal alteration zones in cross section D-D' 73

Figure 53: Feldspar flooding in drill core 75

Figure 54: A typical feldspar envelope around a quartz vein (drill core) 75

Figure 55: Primary and secondary feldspar in photomicrograph 76

Figure 56: Secondary biotite in photomicrograph 77

Figure 57: QSP fracture fill (drill core) 78

Figure 58: Appearance common of clay alteration in core 79

Figure 59: Stilbite-calcite alteration (drill core) 80

Figure 60: Stilbite-calcite alteration (photomicrograph) 81

Figure 61: Clay replacement in faults (photomicrograph) 82

Figure 62: Schematic diagram of paragenetic relationships of molybdenite samples 91

Figure 63: Results of U-Pb age dating using the weighted mean 101

Figure 64: Hypothetical diagram of magnetite from Adanac and gold from Ruby Creek that are related. 111

Figure 65: Os and Re concentrations of some gold deposits compared with gold from Ruby Creek 113

ix

Figure 66: Porphyry Deposits of the North American Cordillera 117

Figure 67: Intrusive rocks of the North American Cordillera with Rb/Sr > 1 and silica > 70wt% 127

List of Tables

Table 1: Proposed new names for Adanac lithologies 35

Table 2: Results of molybdenite X-ray diffraction polytype study 87

Table 3: Molybdenite Re-Os samples, and predicted paragenesis 90

Table 4: Re-Os molybdenite mineralization age dates 93

Table 5: K-Ar Ages (Ma) for lithologies as determined by Christopher and Pinsent 96

Table 6: Lowest reported age of all zircons from each lithology 104

Table 7: Average U concentration (ppm) for zircons from each lithology 106

Table 8: Results of the gold and magnetite analyses 112

Table 9: Characteristics of porphyry molybdenum deposits throughout the NA Cordillera 118-123

1

Chapter 1

Introduction

At the beginning of this thesis in 2006, there was a surge of research into and

exploration for molybdenum deposits in Canada and elsewhere because the price of

molybdenum (and other metals) revived from the slump experienced in the 1980s. There

was also renewed economic interest in increasing production (Kitsault) or resuming

production in historic mines (i.e., the proposed reopening of Climax and Endako).

Industrialization in developing nations like China was driving the need for metals like

molybdenum. Because of the current economic downturn it appears that this demand has

ebbed for a while, but because industrialization is still ongoing in other parts of the world

the current decline in demand for metals may reverse itself in the near future. Currently,

there are numerous poorly understood, relatively under-explored molybdenum deposits

and occurrences in the North American Cordillera that may be explored over the next

several years. It would be of great benefit to the exploration community if more was

known about certain high and low-fluorine type molybdenum deposits in British

Columbia and the United States.

In addition, there are geochemical similarities (e.g., redox state of the associated

pluton; trace and major element chemistry of associated plutons; mineral and elemental

assemblages such as high Bi, Te, W and low and peripheral Cu, Pb, Zn) between

porphyry molybdenum deposits and "intrusion-hosted" gold deposits (e.g., Tombstone

Belt) (Stephens et al., 2004) (Fig. 1) suggesting a possible genetic link. The Adanac

molybdenum deposit belongs to an important class of occurrences that lie within the

2

Atlin gold camp. The Adanac deposit contains no gold itself, but placer gold is still being

mined on the lower reaches of Ruby Creek below the deposit. Historically, it has always

been assumed that the molybdenum deposit post-dates gold mineralization, which occurs

in quartz-carbonate-bearing shears in Paleozoic Cache Creek Group volcanic strata and

as placers. However, a study by Mihalynuk et al. (1992) suggests that this may not be the

case. Mihalynuk's work on Feather Creek suggests that at least some of the placer gold

in the Atlin area may have been derived from the Cretaceous Surprise Lake Batholith

because some of the gold nuggets are associated with thorite and cassiterite. This is

consistent with the presence of gold- and tungsten-bearing quartz veins in the Boulder

Creek drainage immediately to the south of the Adanac Molybdenum deposit, because

wolframite is commonly associated with porphyry molybdenum deposits, peripheral to

the molybdenite zone (Wallace et al., 1968). Thus the presence of gold in those

wolframite veins raises the question of a potential linkage between gold-depleted

molybdenum and gold-bearing tungsten "intrusion related" deposits. Understanding the

association (or lack thereof) is an important step toward focusing further exploration in

the North American Cordillera for both of these deposit types.

10

in ro E CD

E Vfc -

O

E 5

a c 8

oxidized. ' •,"***». chalcop.hile NA,<?> ( 1 Au association

reduced, lithophile

Au association

^ V /

XL

C

<3

Sn

Continental arc-rift °-30 -20 -10 relatively reduced log fo 2 relatively oxidized

Figure 1. Plot of Fe content vs. oxidation state for plutons and associated "porphyry" mineral deposits. Note that Au is found in both oxidized (porphyry Cu) and reduced (porphyry Sn-W-Mo) environments. The Surprise Lake pluton plots approximately at the solid triangle. Fields from Thompson et al., 1999.

History of the Adanac Porphyry Molybdenum Deposit and Atlin Gold Camp

Placer gold mining in the area dates back to 1898, and by the turn of the century,

mining camps centered on this activity flourished in the surrounding areas of the Adanac

deposit (See Figure 2). The three most productive creeks were Spruce, Boulder, and Pine

Creek (Ballantyne and Littlejohn, 1982), which are still being actively mined. Some

placers were protected from Quaternary glacial stripping by being buried under older

Quaternary basalts, and so some pay gravels were reached by underground tunneling,

especially on Ruby Creek (also currently being mined for gold). Boulder Creek, which

drains the western side of the Adanac deposit, also produced minor amounts of tungsten

and tin from placer deposits.

4

Searches for lode gold in the area led to the discovery of quartz veins, usually

located at the contacts between ultramafic and volcanic rocks, and these veins contained

carbonate, pyrite, sphalerite, galena, chalcopyrite, and native gold in the form of electrum

and argentiferous gold (Bloodgood, 1988).

The Adanac molybdenum deposit was discovered in 1905 but serious drilling and

exploration did not begin until the 1960s. In 1967-1970, Adanac Mining and Exploration

Limited staked the valley at the head of Ruby Creek and completed 13,000 meters of core

drilling. From 1970-1971, Kerr Addison Mines Limited acquired interest in the property

and completed some drilling and underground exploration. During the period from 1971-

1978, Adanac Mining and Exploration Limited, Noranda Exploration Company Limited,

and Climax Molybdenum Company all further explored the deposit, delineating most of

the major rock units, cross-cutting relationships, and mineralization types. In 1978,

Placer Development Limited optioned the Adanac property and submitted stage 1 and 2

feasibility reports to the Ministry of Energy, Mines, and Petroleum Resources in Canada.

This resulted in defining open pit mineable reserves of 152 million tonnes at 0.063% Mo

at a cut-off of 0.04% Mo. Molybdenum prices plummeted shortly thereafter and the

claims were allowed to lapse after 1980. Adanac Molybdenum Corporation staked

claims at the property in 2000. In 2004, Adanac completed 9,022 m of drilling and in

2005 they completed 4,984 m of drilling. In April of 2005 the property was in National

Instrument 43-101 compliance. In 2006, Adanac completed 2,668 m of drilling in the

proposed main pit area, as well as 1,333 m of drilling in a newly-discovered zone of

mineralization on the southwest end of the property. This newly-discovered zone,

together with the main proposed pit area, resulted in a total resource in 2007 of 218

5

million tonnes at 0.063% Mo. To date, the Adanac property has a total of 49,786 m

(163,300 ft) of drilling in 283 holes completed since exploration commenced in 1969.

Construction of the processing plant and infrastructure also commenced in 2007. In

2008, the company received mining permits, but at the time of this writing is still waiting

for approval of environmental permits. Production was slated to begin in 2010, and

Adanac would have been the world's first large-scale open pit primary molybdenum mine

in 25 years. Due to the current economic slump, the immediate future of the deposit is

uncertain.

Geological Background:

Regional Geology

The Adanac molybdenum deposit is located in the northwestern corner of British

Columbia, near the town of Atlin (Fig. 2). The geology of the Atlin area was mapped by

Aitken (1959), and the regional setting of the deposit is discussed by Christopher and

Pinsent (1982). The Atlin area (Fig. 3) is underlain by deformed and weakly

metamorphosed ophiolitic rocks of the Pennsylvanian and/or Permian-aged Cache Creek

Group (Monger, 1975). These rocks, which include chert, clastic sediments, marble and

limestone, mafic volcanic rocks, peridotite, serpentinites, dunite, and gabbro, have long

been thought to be the source of much of the placer gold found in the Atlin area

(Mihalynuk et al, 1992). The Cache Creek group rocks in the area are typically

metamorphosed to sub-greenschist grade (Kikauka, 2002). In the Atlin area, the

sedimentary and volcanic rocks are cut by two younger batholiths. North of Pine Creek,

they are cut by a Jurassic granodiorite to diorite intrusion (Fourth of July batholith), and

north and south of Surprise Lake they are cut by a Late Cretaceous granitic intrusion

6

(Surprise Lake batholith and Mount Leonard stock). The Surprise Lake batholith is a

highly differentiated, fluorine-rich (0.27% F), uranium-rich (14.6 ppm), peraluminous

granite (Ballantyne and Littlejohn, 1982). The batholith is a known host of quartz vein

stockworks (especially associated with the multi-phased Mount Leonard stock) and skarn

alteration that hosts base and precious metal mineralization including W, Sn, Mo, Cu, Co,

Pb, Zn, U, F, Ag, and Au that occur as both sulfides and oxides (Ballantyne and

Littlejohn, 1982). One skarn, the Silver Diamond, is associated with a marginal quartz-

rich phase of the batholith and is hosted in Paleozoic marble and chert, greenstone, and

ultramafic rocks (Figure 4). The mineralization is largely pyrrhotite and sphalerite with

minor pyrite, chalcopyrite, scheelite, galena, cassiterite, and tetrahedrite. Another

important deposit related to the batholith and occurring within 3 miles of the Adanac

deposit is the Black Diamond tungsten vein (Figure 4). The Black Diamond is a N60°E-

trending and 60°NW-dipping quartz vein containing pyrite, scheelite, wolframite, and

minor chalcopyrite, arsenopyrite, and molybdenite, and anomalous tellurium (Kikauka,

2002). This vein lies mostly within coarse granite of the Mount Leonard Stock, except

for the eastern portion which is in Paleozoic marble. Elevated gold values along with Pb,

As, and Sb anomalies also occur in this eastern portion. A soil sample survey in this area

showed anomalous Cu, Pb, Ag, Sb, Bi, and Au (Kikauka, 2002).

Structures in the area consist of a series of ENE faults, such as the Adera, and

another series of north-trending fault systems such as the Boulder Creek fault (Figure 3).

There have also been periods of intense brittle deformation resulting in crack-seal

textures in plutonic rocks and zones of brecciation. Most of the fault systems are normal

and result in horizontal dilation zones (Kikauka, 2002).

7

Figure 2. Location map for the Adanac molybdenum deposit (from Pinsent and Christopher, 1995). Figure 3 (regional geology map) is an area on this map bounded by Atlin lake and Surprise Lake, which is the curved lake immediately to the east of the Adanac property. The white box (Adanac property) is the approximate location of Figure 4 (local geology map). Inset is a location map of the province of British Columbia.

8

Figure 3. Regional geologic map of 104N/11W, 12E (Atlin area). The drainage and fault cutting the Mount Leonard stock are Boulder Creek and Boulder Creek Fault, respectively. The drainage cutting Ruby Mountain Quaternary volcanic rocks is Ruby Creek. Both creeks have their headwaters on opposite sides of the Adanac molybdenum deposit and drain into Surprise Lake. The Adera Fault bounds the Adanac deposit at surface, and has dropped the mineralization down to the north. From Bloodgood, 1988.

9

,? A " C i ~

i '• ' -' ' *

' ' ,- '0 1 ' . -KX' . •" ' 1/5/ '••

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Southwest Mo Zone^Jg^ }

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. y\^, - .>ti \ Vki •: ..<

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^ ^ • - • ; - t \ \ \ -

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. ' • ' • : • . , ' - ^

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Surprise Lake

Figure 4. Boulder Creek and Ruby Creek area map showing main mineral occurrences discussed throughout this thesis, and faults. The Ruby Creek Mo Main Zone is the approximate location of Figure 5. The base map is a regional aeromagnetic survey from GSC, 2002. Warmer colors (pink, red, orange, and yellow) show higher gravity values while cool colors (green and blue) show lower gravity values. Grid shows UTM Zone 9, NAD 83 coordinates.

Local Geology

The deposit area was described by Sutherland Brown (1970), White et al. (1976),

Christopher and Pinsent (1982), and Pinsent and Christopher (1995). The Adanac

molybdenum deposit underlies the valley floor near the head of Ruby Creek. It is largely

buried and has very little surface expression. There is little outcrop in the lower part of

10

the valley and molybdenite is only rarely found in float and/or veins in outcrop in the bed

of the creek. The geology underlying the valley floor is largely derived from drill data

(Fig. 5). Adanac has a single flat-lying to steeply-dipping "shell" of mineralization as

described by White et al. (1976) and Pinsent and Christopher (1995).

^620750 mil

-ۥ320250 m?l

•A

• s' Jr-zr^i * • . /* CQMP N

MQMP

1

f ! COQM \ 1

. 1 . •• •

. • / s

IK

MFP

\CGQM

N I I 0 I

>)J

0 125

miles

Figure 5. Surface geology of the Adanac molybdenum deposit (Mo main zone in Fig 4). The black dots are drillholes, and the black dashed lines are strong faults that cause displacement, such as the Adera, and the grey dashed lines are weak faults, or faults that cause no discernable displacement. CGQM (crowded quartz monzonite porphyry), CGQM-T (transitional phase), MQMP (mafic quartz monzonite porphyry), and SQFP (sparse quartz feldspar porphyry) are all the first phase of intrusion. The second phase is SQMP and CQMP (sparse and crowded quartz monzonite porphyry). The third phase of intrusion, the fine grained aplite dikes, is not represented on the map, but cuts other lithologies at more localized scales. The grid shows coordinates in UTM Zone 8, WGS 84.

11

The deposit is near the western margin of the Surprise Lake batholith (Ballantyne

and Littlejohn, 1982). It is hosted within the multi-phased Mount Leonard Stock, and

entirely within plutonic rock. There were three stages of intrusion: an early, generally

coarse-grained, stage that was deformed prior to intrusion of second-stage porphyry

domes, and a late fine-grained phase that was injected through the porphyry domes. The

deposit itself is a disrupted blanket-shape deposit that formed late in the development of

the plutonic suite. The deposit is partially controlled by the Adera fault system which

trends approximately NE-SW and defines much of the southern boundary of the pre-ore

Fourth of July batholith. This fault is a normal fault dipping approximately 80 degrees

northwest. The approximately N-S Boulder Creek fault system appears to have localized

emplacement of the late, third stage porphyritic and aplitic plutonic rocks which are

thought to have generated the majority of mineralization (Pinsent and Christopher, 1995).

Mineralization is in the form of 3-4 cm sized molybdenite rosettes in a stockwork of

smoky, ribbon textured quartz veins (Figures 6 and 7). Some late-stage milky white

quartz veins carry smaller and less frequent rosettes, but are typically barren. There is

very little fine molybdenite, and some molybdenite paint on fractures and in faults.

Figure 6. Large molybdenite rosettes in a smoky, ribbon textured quartz vein.

Figure 7. Molybdenite rosettes on the plane of a quartz vein from a boulder at Adanac.

13

Research Objectives

The first goal of this thesis is to refine exploration models for porphyry

molybdenum deposits in the North American Cordillera, both at the deposit level and

regional scale. To accomplish this, the Adanac (Ruby Creek) Molybdenum deposit has

been analyzed in terms of trace element, mineralogical, and alteration zonation, as these

are common considerations for classifying low-fluorine versus high-fluorine

molybdenum deposits (Clark, 1972). Trace elements present were determined by ICP-

MS analysis of drill core. Mineralization and alteration observations were both

determined from megascopic analysis of drill core (core logging). Studies on alteration at

Adanac were further enhanced by petrographic analysis and X-ray diffraction analysis of

clays. Standard whole rock geochemical measurements (ICP-MS) were completed in

order to compare the plutonic suite responsible for mineralization at Adanac (Mount

Leonard stock) to other plutonic suites hosting molybdenum mineralization throughout

the cordillera. Another important aspect of comparing molybdenum deposits in the

Cordillera is their age. To this end, a geochronologic study of mineralization versus

magmatism by using Re-Os isotopic dating of molybdenite and U-Pb zircon dating of

major lithologies in the deposit was completed. This indicates how long the

hydrothermal system at Adanac was active, and also was intended to help determine

which lithologic phase was responsible for mineralization. Molybdenite samples from

the deposit were also analyzed for polytype and Re concentration, as these characteristics

can also shed light on similarities and differences between Mo-bearing porphyry deposits

in the Cordillera.

14

The second goal of the thesis is to determine if there is a connection between

porphyry molybdenum deposits and intrusion-hosted gold deposits. As there is a possible

link between the molybdenite mineralization and gold mineralization in the Ruby Creek

vicinity, the Adanac deposit provides a unique opportunity to investigate a possible

continuum between these deposit types. Trace element and whole rock data at Adanac

was compared with descriptions of chemically-reduced intrusion-hosted gold deposits.

Os isotopic signatures in magnetite have been used from Adanac and from placer gold

samples in Ruby Creek (downstream) to test for a possible genetic link and to see if these

deposits have a common origin.

15

Chapter 2

Geochemistry of Host Rocks at Adanac

Summary of Lithologies at Adanac

Each fresh lithology in the deposit was described according to hand sample and

thin section analyses, and samples of rock that had undergone the least amount of

alteration were chosen. These data complement the whole-rock geochemical data and are

utilized for comparison to other molybdenite deposits. Lithologies are described roughly

in order from oldest to youngest based on observed cross-cutting relationships (Figure 8).

Because cross-cutting relationships were not observed between a few lithologies, some

relationships are uncertain. Isotope geochronological data are presented later in this

document.

FGQM

MFP

MEQM

SQMP

?

7

CQMP

MQMP

CQFP CGQM-T CGQM CGQM-H SQFP

Figure 8: Relative rock ages based on observed cross cutting relationships in the deposit. Question marks are placed by MFP and MEQM because the relative ages of these two lithologies is unknown, as there are no cross-cutting relationships.

16

Coarse-grained quartz monzonite (Figure 9) (CGQM - field term used by

previous workers) is the oldest and most common rock in the Mount Leonard Stock,

comprising roughly 50 percent of the stock in the mine area. It is a weakly to moderately

deformed, pink or grey, equigranular, coarse-grained (0.5-3.0 cm) granite. In hand

specimen, it contains roughly equal amounts of potassium feldspar, plagioclase, and

quartz, with minor biotite. Two samples of fresh CGQM were examined in thin section.

Quartz is the dominant mineral in both sections, at 45-50%, with potassium feldspar and

plagioclase present roughly equal amounts at about 20-25% each. Biotite comprises 3-

10% of the rock. Quartz is generally anhedral and equant in appearance and typically

ranges from 0.5-3 mm in maximum dimension. Feldspars are equant to tabular and up to

5 mm in maximum dimension, and often perthitic (Figure 10). Orthoclase is generally

larger than plagioclase, and may occasionally reach 15 mm in size. Plagioclase is

typically albite twinned, and has an anorthite content of 13 percent, based on CIPW

normative calculations. Larger plagioclase and orthoclase phenocrysts are typically

concentrically zoned, displaying varying extinction angles within a crystal. In a few

instances, myrmekitic textures between quartz and orthoclase were observed. Biotite is

usually brown in uncrossed polars and generally tabular to platy in nature with maximum

long dimensions of 10 mm and short dimensions of about 3 mm. Under crossed polars,

biotite exhibits classic birds-eye extinction in various shades of brown. Typically biotite

is slightly altered to green chlorite on the margins or cleavages. Small (less than 0.1mm),

euhedral apatite is also present within quartz and biotite crystals, comprising less than 1%

of the rock. Other minerals that were observed (probably secondary hydrothermal

alteration) included: fine-grained chlorite replacing biotite; very fine-grained sericite and

17

kaolinite (up to 10% by volume) replacing feldspars; euhedral pyrite replacing or

overprinting chlorite or replacing magnetite; and magnetite (<0.05 mm rounded blebs)

replacing chlorite; and traces of calcite, usually replacing feldspars or surrounding biotite.

Total secondary minerals comprise from 1 to 5% of the rock.

Figure 9. CGQM in core sample. On the right hand side of the core is aFGQM dike. From drill hole A-04-14, 705ft.

• ' 321=142=1

18

Figure 10 (previous page). A typical twinned and perthitic feldspar phenocryst in CGQM, in photomicrograph, crossed polars, from drill hole A-06-321, 142ft.

Transitional and hybrid coarse-grained quartz monzonite (CGQM-T and CGQM-H)

and sparse and crowded quartz feldspar porphyry (SQFP and CQFP) are porphyritic

varieties of CGQM that contain increased groundmass, approximately 25% in transitional

and 50% in the hybrid type (Figure 11 shows CGQM-T, Figure 12 shows CQFP, and

Figure 13 shows a transition between some of these lithologies). Groundmass comprises

the same mineral assemblage and relative percentages as in CGQM, but grains are 2-

4mm in size. CGQM-T and CGQM-H occur at contacts where CGQM grades into

SQFP. All of these phases occur as preore dikes that are cut by mineralized quartz veins,

but also occur as separate and mappable units on the outer margins of the CGQM.

CGQM-T, CGQM-H, SQFP and CQFP all have the same modal mineralogy as CGQM.

In thin section, CGQM-H is 50% quartz, 20% each of alkali feldspar and plagioclase, 5%

biotite, and 5% secondary minerals. Anorthite content of plagioclase is estimated at 13%

based on CIPW normative calculations. Secondary minerals include calcite, pyrite,

magnetite, sericite, and chlorite (alteration product of biotite). Pyrite and calcite are

associated and occur together in the groundmass as 1-3 mm crystals. Pyrite also occurs

replacing chlorite along cleavage planes and replacing magnetite. Magnetite and chlorite

both occur as replacement products of biotite. Sericite and calcite occur as fine crystals

replacing the centers of feldspars. In one sample a 1 mm fluorite grain was noted

alongside calcite inside a plagioclase crystal. CGQM-T and CGQM-H commonly exhibit

graphic intergrowths and myrmekitic textures (Figure 14).

19

• r » . ;

••*-!itoa£^..

Figure 11. CGQM-T in core sample, from drill hole A-04-28, at 463 ft.

Figure 12. CQFP in core sample, from drill hole A-04-26, at 30ft.

.**•

v - » « "*»«' * ..

Figure 13. SQFP (on the left) grading to CQFP (on the right) in core sample, from drill hole A-04-15, at 79ft.

20

Figure 14. Graphic intergrowth of quartz and feldspar is often seen in thin section for Adanac lithologies. The texture seen here is from the rock "Fdiss", discussed in the geochemistry section. This particular lithology is found in float near the tungsten trenches (location of trenches shown in Figure 4 of introduction) and is part of the Mount Leonard stock, but is not found in the Adanac molybdenum deposit. The rock is unique because it has fluorite disseminated in amphibole crystals. Crossed polars.

Mafic quartz monzonite porphyry (MQMP) (Figure 15) is a grey-colored rock

unit distinguished from other rocks in the deposit by an elevated biotite content. This

unit cuts CGQM but is cut by SQMP and CQMP (described below). Biotite crystals are

fine-grained (1mm). Plagioclase and orthoclase phenocrysts are 7mm to 3cm in size.

Plagioclase crystals are chalky-white colored while orthoclase is typically grey. Quartz

phenocrysts are 6mm to 3cm. The matrix comprises a mixture of biotite, quartz, and

feldspar. In thin section, this rock has a slightly higher feldspar content than CGQM.

Quartz is 40%, while plagioclase and alkali feldspar make up 50%, with slightly more

21

plagioclase than alkali feldspar. Plagioclase feldspar has an anorthite content of 19%

based on CIPW calculations. Biotite makes up the other 10% of the rock with other

minerals such as apatite and zircon all comprising less than 1%. Chlorite typically

replaces margins of hiotite, and pyrite and magnetite replace both biotite and chlorite.

Pyrite is euhedral while magnetite is typically anhedral, and both are about 0.4mm in

size. Kaolinite and sericite occur as alteration products within feldspars. Anhedral

calcite was observed locally near the pyrite- and magnetite-altered biotite. Graphic

intergrowth textures were more common in MQMP than in other rocks. These textures

occurred over areas of about 0.2 mm diameter, and consisted of quartz and feldspar

intergrowths (Figure 14).

Figure 15. MQMP in core sample, from drill hole A-04-01, 469ft.

On the basis of cross-cutting relationships, sparse and crowded quartz monzonite

porphyry (SQMP and CQMP) (Figure 16 and 17) are younger than CGQM and MQMP.

They both consist of white plagioclase, pink orthoclase, quartz, and biotite phenocrysts

that are 2-6mm and set in a light brownish to pinkish aphanitic matrix. In the sparse

variety, phenocrysts make up 10-30% of the rock and in the crowded variety phenocryst

22

content increases to between 60-80%. SQMP may be slightly younger as it is seen to

sometimes cut the crowded version. In thin section, quartz makes up about 45% of the

rock with plagioclase and alkali feldspar about 25% each. One small area (0.3mm)

exhibited graphic intergrowth textures as mentioned above in the section for MQMP.

Anorthite content of plagioclase is 9% for SQMP and 11% for CQMP based on CIPW

calculations. Biotite is about 4% in some of the samples, and opaque (secondary)

minerals such as pyrite, magnetite, and molybdenite comprise the rest. One 0.5mm

zircon crystal was observed with a brownish to orange damage halo in the surrounding

rock. Chlorite commonly replaces biotite, and plagioclase feldspars have clays (these

appear to be kaolinite and sericite but are too fine-grained for clear identification)

clustered in the centers of crystals or in outer rings (Figure 18 and 19). In two thin

sections it was observed that molybdenite occurs in cleavage planes of biotite that is

altering to chlorite. Molybdenite crystals were large (1mm) and euhedral. Clustering

around the molybdenite and appearing to post-date it were small amounts of subhedral

0.3 mm sphalerite and galena.

Figure 16. SQMP in core sample, from drill hole A-04-06, 289ft, photo also shows a molybdenite vein.

23

Figure 17. CQMP in core sample, from drill hole A-07-338, 612ft.

Figure 18. Clay alteration is selective in feldspars. It will commonly replace the centers or occur in an outer ring (Figure 19). Photomicrograph, crossed polars, from drill hole A-07-318, 660ft.

24

Figure 19. Clay alteration (dark colored) selectively replacing an outer ring-shaped area of a plagioclase feldspar. Photomicrograph, plane light, from drill hole A-07-324, 863ft.

Medium-grained equigranular quartz monzonite (MEQM) (Figure 20) is a lithology

that apparently is not widespread in the deposit, and occurs as an intrusion only known in

drillholes in the southwest end of the deposit. It intrudes CGQM, but has no observed

cross-cutting relationships with most of the other lithologies in the deposit, except for

FGQM, which cuts the MEQM. It has a mosaic texture that is equigranular, and consists

of equal amounts of quartz, plagioclase, and alkali feldspar that are all about 1 -2 cm.

Biotite is present as well, with crystals being about 5 mm. In thin section, biotite is more

abundant than in CGQM or FGQM, comprising up to 15% of the rock. Quartz,

plagioclase, and alkali feldspar comprise roughly equal amounts at 25-30% each.

Anorthite content of plagioclase is 14%. Other minerals include trace small zircon and

apatite, plus fine-grained secondary minerals such as clay alteration of feldspars, plus

25

calcite, chlorite, pyrite and magnetite that are similar in occurrence to those described for

CGQM.

Figure 20. MEQM in core sample, from drill hole A-06-331, unknown footage.

Megacrystic feldspar porphyry (MFP) (Figure 21) is noticeably different from

other lithologies in the deposit. It consists of a very fine grained (< 0.2mm) dark blue

matrix, and contains small biotite crystals (0.5mm). Phenocrysts are rounded, 6mm

smoky quartz eyes, and larger, 1- to 4-cm euhedral plagioclase and alkali feldspar

crystals. It is not widespread and usually occurs as dikes or sills cutting CGQM and

MQMP at the southwest and south end of the deposit. In thin section, quartz is 40% of

the rock, biotite is 15%, and plagioclase and alkali feldspar are each approximately 20%.

Anorthite content of plagioclase is 22%. The matrix is mostly very small crystals

(0.1mm) of quartz and feldspar (<0.03mm) with intergrown biotite (Figure 22).

Feldspars are moderately altered to kaolinite and/or sericite. Feldspars sometimes exhibit

poikilitic textures, with randomly-oriented plagioclase crystals (1mm) inside larger (3 cm)

alkali feldspars (Figure 23). The rock has a larger percentage of opaque minerals relative

26

to other lithologies in the deposit. Opaque minerals are mostly pyrite and magnetite, with

minor chalcopyrite and pyrrhotite, and comprise up to 1% of the rock. Magnetite

commonly replaces chlorite, while pyrite, chalcopyrite, and pyrrhotite replace magnetite.

Figure 21. MFP in core sample, from drill hole A-06-333, 950ft.

Figure 22. Finely crystalline quartz and biotite in the matrix of MFP, crossed polars, photomicrograph from drill hole A-04-314, 212ft.

27

Figure 23. Small twinned plagioclase crystal inside a larger alkali feldspar phenocryst. Photomicrograph, crossed polars, from drill hole A-04-321, 340ft.

Fine-grained quartz monzonite (FGQM) (Figure 24) is the youngest known

lithology in the deposit as it is seen to cut all other units. This unit occurs as both dikes

and sills throughout the deposit. It also postdates mineralization-related silicification. It

is a brownish to pinkish lithology that is equigranular and is a mixture of white and pink

feldspar, quartz, and trace biotite. The grain size ranges from less than a millimeter to

about 3mm. In thin section, FGQM contains roughly equal amounts of quartz,

plagioclase, and alkali feldspar, the three of which comprise 90% of the rock. Anorthite

content of plagioclase is 11%. Biotite makes up 5-10%, with secondary minerals

comprising the rest. The secondary minerals include chlorite replacing biotite; clays and

calcite replacing feldspars; and small grains (0.2mm) of eu-subhedral pyrite or magnetite,

either in the matrix or replacing biotite or chlorite. In one thin section where the FGQM

28

occurs as a dike cutting CGQM, there are several occurrences of graphic intergrowth

textures of quartz and feldspar.

Figure 24. FGQM in core sample, cut by a smoky quartz vein with a feldspar envelope, from drill hole A-04-26, 333ft.

Whole Rock Geochemistry

Major and trace element composition was determined for nine samples of fresh

rock, one from each major lithology in the deposit. The table showing the results of this

analysis is located in the appendix (Table A-l). The analyses were done at ACME

analytical labs in Vancouver, B.C., using inductively coupled plasma-emission

spectroscopy. The lithologies include CGQM and its transitional variety (CGQM-T); the

feldspar porphyries into which CGQM grades north of the Adera fault (CQFP and

SQFP), and which represent the cap of the system; MQMP; the two porphyry intrusions

in the main pit area (SQMP and CQMP); MFP; and MEQM. Normative mineral amounts

were calculated using the CIPW (Cross et al., 1903) method. According to the IUGS

system of classification (Streckeisen, 1973) all rocks in the suite are granites (Figure 25).

29

The rocks have an average of 35% normative quartz. Alkali-total feldspar ratios in all

lithologies were about 50. An alkali-lime index (Peacock, 1931) (defined as the wt%

silica where Na20 + K2O = CaO) of 50 wt% SiC>2 was calculated (Figure 26), meaning

the rocks are further classified as alkalic. On the basis of the ratio of the mole percent

alumina compared to the added sums of CaO, K2O, and Na20, it was also determined that

the suite is peraluminous (Shand, 1949).

Ouaitz

Granite Field: IUGS Classification

AIIAdanac M* • Lithologies

Alkali Feldspar —K K

Pla.qioclase

Figure 25. IUGS classification scheme of igneous intrusive rocks showing that all Adanac lithologies fall into the category of a granite.

10

50 55 60

Alkali Lime Index

R2 = 0.1324

R2 a 0.9423

30

65 Si02wt%

70 75 80

Figure 26. Alkali lime index (wt% silica where Na20 + K20 = CaO) graphed for lithologies at Adanac. Because of the limited and high silica range, the trends were extrapolated considerably.

A series of Harker diagrams (see Appendix) was also made to evaluate

differentiation trends and the genesis of the various rock units. The Harker diagrams

dealt with the principal fresh lithologies described above, and also with a textural variety

(coarser grained) of MQMP, a sample of FGQM from the west end of the deposit as

opposed to FGQM from the pit area, and another rock called "Fdiss", which stands for

"fluorine disseminated". The sample of Fdiss is a rock found in float west of the main

known mineralized area, where tungsten (wolframite) mineralization is exposed at

surface in a large (1-2 meters wide) quartz vein. The sample is unusual because it has

31

visible fluorite disseminated in amphibole crystals in hand specimen. These samples

were included in separate Harker diagram sets for the sake of consistency. With

increasing silica, AI2O3, FeaCb, and CaO decrease; U, F, Mo, Rb, MgO, Na20, FeO,

MnO, and Ti02 either remain constant or values are too scattered (poor, or less than 0.2

R2, i.e. correlation coefficient of a linear trend line and data points) to see any trend; and

K2O values increase.

Discussion

Although they encompass a limited silica range, the Harker diagrams indicate

Adanac lithologies are consistent with normal differentiation trends with respect to major

oxides. It was hoped that with increasing silica, there would be an increase in U content,

but no clear pattern emerged from the data (Figure A-5). It is highly interesting to note

the negative correlation between F and Mo (Figure A-8). Based on cross-cutting

relationships, it is well established that CGQM is the oldest lithology known in the stock,

and FGQM is the youngest. It might be suspected that since FGQM is the youngest, but

still is cut by mineralized veins, that it may be the source (or generated from the source)

of mineralization. If F is the ligand used for transport of Mo in hydrothermal solutions, it

would not be surprising to find that both elements decreased in content in lithologies that

were losing these elements to hydrothermal solutions. However, this is not what is seen.

F decreases fairly consistently with increasing silica (and decreasing age) and Mo

increases with increasing silica. This behaviour may somehow be related to the relative

abundance of the two elements in the different rocks, coupled with the efficiency of

extraction of the Mo using F as a ligand. Alternatively, it may be that the presence of F is

negatively affecting the compatibility of Mo in the rocks, and they are released into

32

hydrothermal fluids at different times (F first, Mo last). A third (much less likely)

possibility is that these rocks are not all from the same suite. This is not likely because

all of the lithologies (with the exception of "Fdiss") are in close proximity to each other,

and not near any other known intrusive suite and also yield virtually identical ages

(discussed below). It also may be a possibility that, while there is some difference in the

F content between these rocks based on how much of the element has been released in a

hydrothermal fluid, what the Harker diagrams are really reflecting is biotite content.

Fluorine should concentrate in biotite because the mineral allows for water and some

incompatible elements in its structure. Therefore, even if biotite F content is less for

older rocks, these same older rocks have more biotite and this obscures a lower F content

relative to the whole rock analysis. If this is the case, the opposite trend in F should be

seen when just the biotite is analyzed.

Classification of Adanac

Published literature on porphyry molybdenum deposits broadly outlines two basic

types of deposits, the "granite" and "quartz monzonite" types (White et al., 1981,

Sutherland Brown, 1969, Wallace, 1995). Westra and Keith (1981) recognized that these

two basic types can be separated based on the K2O value of unaltered igneous host rocks

at 57.5 weight % Si02. A natural dividing line occurs between those deposits with a K2O

value of less than 2.5% and those with values above that. If the K2O value is less than

2.5, the molybdenum deposits are classified as the "calc-alkaline" quartz-monzonite type,

which typically have low F values (0.1-0.25%). These deposits typically have lower

molybdenite grades (0.25% M0S2), little Sn, and W is present as scheelite. Source

33

(genetically related) plutons have between 100 to 350 ppm Rb, and 100 to 800 ppm Sr.

Those deposits with K2O values above 2.5% are broadly referred to as the Climax-type of

molybdenum deposit. Climax-type deposits are associated with alkali-calcic to alkalic

granites, and are enriched in F (0.5- >5%) and Sn. Rubidium content of the associated

plutons is typically 200-800 ppm, with less than 125 ppm Sr (Figure 27). The

molybdenite grades are typically higher than 0.30% M0S2 and W is present as

wolframite.

Since granite and quartz monzonite molybdenum deposits have these different

and predictable geochemical characteristics, those characteristics should be useful in

delineating the nature of the system at Adanac. Using the Westra and Keith (1981)

criteria for classification of porphyry molybdenum deposits, the K2O value at 57.5 weight

% Si02 (K2O57.5) was calculated to be ~5 for the rocks at Adanac, thus placing them

clearly in the Climax-type group. All of the rocks at Adanac contain between 70 and

76% silica, so the K2O value had to be extrapolated considerably. Even so, the calculated

value of 5% is well above the dividing point of 2.5%. Fresh lithologies at Adanac group

well with other Climax-type deposits based on Rb and Sr content, as well as on the basis

of the K2O57.5 value (Figure 27). It is not surprising that Climax-type and transitional

types of porphyry molybdenum deposits exhibit higher Rb contents than calc-alkaline

type porphyry molybdenum deposits and continental margin and island arc porphyry

copper deposits. The Climax-type and transitional type porphyry molybdenum deposits

are farther inboard of subduction zones than porphyry deposits associated with copper.

Rb content is reflective of the extent of mixing with continental crust. At Climax, the Rb

contents are especially high, and this may be due to flat-slab subduction which was the

34

tectonic environment there at the time of intrusion, unlike Adanac (Westra and Keith,

1981).

900 V

700-

ppmRbV jS

Unaltered igneous rocks

K20575>2.5

500-

300-!

100 A

K2057.5<2.5

o Climax-type molybdenum C "Transitional" molybdenum A Calk-alkaline molybdenum O Mt. Pleasant A Continental margin porphyry Cu O Island arc porphyry Cu ^Adanac

* . ^ - A r A A I s» A A A,

O

A A A

/£& A

A A

on "kR A A

' 200 ' 460 ' 660 860 ' IO'OO ' i2'oo ' i4bo '

ppm Sr Westra & Keith, 1981

Figure 27. Plot showing how the K20 value at 57.5 wt% Si02 is useful in dividing porphyry deposits,along with Rb and Sr content. Mt. Pleasant is a porphyry tungsten deposit. Diagram modified from Westra and Keith, 1981.

Conclusions

On the basis of the data presented here, it is clear that the rocks in the area of the

Adanac deposit should be reclassified as granites. More appropriate nomenclature for

these rocks is listed in Table 1. All of the rocks contain dominantly quartz, orthoclase,

and plagioclase feldspar, with minor amounts of mafic and accessory minerals. Modal

estimates establish that these fall into the granite field of Streckeisen (1973).

Geochemical data, when calculated to CIPW norms, yield similar results, with all rocks

falling into the granite field. On the basis of rock types, style of mineralization, and

whole-rock geochemistry, Adanac appears to

deposits.

Old Adanac Lithology Name

CGQM, -T, -H: coarse-grained quartz monzonite, -transitional, -hybrid

MQMP: mafic quartz monzonite porphyry

SQMP: sparse quartz monzonite porphyry

CQMP: crowded quartz monzonite porphyry

CQFP: crowded quartz feldspar porphyry

SQFP: sparse quartz feldspar porphyry

MFP: megacrystic feldspar porphyry

FGQM: fine-grained quartz monzonite

MEQM: medium-grained equigranular quartz monzonite

35

best be grouped with the Climax-type

Proposed New Name

CGG, -T, -H: coarse grained granite, - transitional, -hybrid

MGP: mafic granite porphyry

SGP: sparse granite porphyry

CGP: crowded granite porphyry

same

same

same

FGG: fine-grained granite

MEG: medium-grained equigranular granite

Table 1. Proposed new names for Adanac lithologies based on whole rock geochemistry study.

36

Chapter 3

Geology and Trace Element Zoning at Adanac

The type, amount, and zoning of trace elements are an important consideration for

understanding porphyry molybdenum deposits. To interpret trace element zonation, drill

core pulps (1835 samples from 22 drillholes) were composited at the lab based on similar

lithologies in intervals of 10-40 feet and analyzed for 41 trace elements plus fluorine by

inductively coupled plasma emission spectrometry (ICPMS) at ACME labs in

Vancouver, British Columbia. Trace element data have been studied for patterns and

anomalies of Mo, Pb, Zn, W, F, Sn, Cu, and Au (no other trace elements were present in

any amount above normal background contents for granites). The ranges of values for

trace elements were grouped based on natural statistical breaks, determined by using the

Geochem application of the GIS program Map Info. Values were distributed in their

respective groups so that the average of each group is as close as possible to each of the

values in that group. An example of how these ranges were broken out is shown in

Figure 28. For most elements analyzed, the bottom range (grey) represents normal

background contents for that element in granites. The exception is fluorine, where the

blue group represents normal background content and the grey group represents

depletion. Any group or range above these two bottom groups is always considered

anomalous or highly anomalous, a relative term applied for how far a statistical group

exists above the background content. There are no quantitative criteria for calling

elements "highly anomalous". This term is used only for fluorine and molybdenum, both

of which have very high contents in this deposit.

37

Four cross sections were chosen in the deposit to represent geology and trace

element zoning. One cross section (A-A') is oriented approximately in a northeast-

southwest direction, while the other three (B-B', C-C, and D-D') are oriented

approximately northwest-southeast (Figure 29). Full-color cross sections depict geology

(Figures 30-33). Black and white cross sections with colored overlays represent selected

trace element zonation (colors) against the backdrop of geology (black and white

patterns) (Figures 34-45).

lum

ppm

•5

1: b

ackg

roun

d

Gro

up

(gre

y c

(A 3 o CD £ o c CO ^ ^

(0 -C P ? .2>S

3 2:

ano

mal

ous

colo

red)

roup

3: a

nom

alc

reen

col

ored

)

• G

roup

4: h

•

(yel

low

col

y an

omal

ous

Gro

u|

(blu

e

^ ^-JHk^**

O 3

, * - * * * « •<• '

• ^

•

y

up 5

: hig

hl

colo

red)

G

ro

(red

Number of Samples

Figure 28. Example diagram of how natural statistical breaks were used to distribute samples into their respective groups. See text for discussion of terms. A change in slope marks the beginning of a new group.

38

- i . 1-

• AD-344

Approximate Proposed Main Pit ^0.345

• AO-346

/LD-34? )

miles

Figure 29. Surface geologic map of Adanac showing the location of cross-sections. The proposed main pit area approximately circles the CGP and SGP intrusion area on the map. The southwest end of the deposit, referred to commonly in this thesis, would begin near hole AD-333 (the far west end of cross section A-A') and continue west and south of this location. This area was being drilled in 2008, and mineralization was continuing to be discovered on this end. Lithologic units are labelled on the map, using the new names proposed in Chapter 2, Table 1. These include coarse-grained granite (CGG - orange), transitional coarse­grained granite (CGG-T - flesh colored), sparse quartz feldspar porphyry (SQFP - yellow), mafic granite porphyry (MGP - pink), megacrystic feldspar porphyry (MFP - purple), crowded granite porphyry (CGP -dark green) and sparse granite porphyry (SGP - light green). Strong faults (ones that cause obvious displacement) are shown as black dashed lines while weak faults (ones that cause no disceraable displacement) are shown in grey. Adanac (AD series) drill holes are labelled, and drill holes that appear in cross sections have a white halo around their label. Unlabelled drill holes are holes drilled by other companies in the past. Map coordinates are in UTM Zone 11, WGS 84.

Geology and Structure

Geology is shown below in Figures 30-33. Geology was determined based on

drill logs and is labelled according to the new terminology proposed at the end of Chapter

2.

CGG is the oldest lithology because all other units cut it or intrude it (Figure 30).

MGP intruded CGG on the east (Figure 30). SGP and CGP intrude CGG and MGP on

39

the eastern and central portions of the deposit (Figure 33). SGP and CGP have

gradational contacts and are therefore regarded as the same intrusion, the difference

between the two being the amount of phenocrysts present. CGP is known to occur as a

lens in SGP based on other numerous surrounding drill holes. CGP also occurs as a

cupola, or as the upper portion of the SGP intrusion on the eastern side of the deposit. On

the south end of the deposit, there is some undrilled fault that drops these- lithologies

(Figure 32).

MEG intruded CGG on the west side of the deposit (Figure 31). MFP is a dike

that occurs above the contact of MEG with CGG (Figure 30 and 31) where the CGG was

probably faulted and structurally weak due to this intrusion of MEG. MFP also occurs as

a dike in drill hole AD-314 (Figure 31). MFP is generally restricted to the west area of

the deposit, south of the Adera Fault. The CGG on this end of the deposit (both drill

holes in Figure 31, the west end) is typically labelled CGG-T because it is not as coarse­

grained as the CGG to the east, and has some fine-grained crystals in between large

grains.

FGG dikes cut all lithologies in the deposit, and are commonly more abundant

stratigraphically above the SGP and CGP intrusions, and disappear with increasing depth

into these intrusions. This may be interpreted to mean that they are following structurally

weak zones in the CGG created by these intrusions. Some of these structurally weak

zones can be seen in Figure 32, where steeply oriented faults occur in the upper part of

the intrusion of SGP/CGP. Large FGG dikes generally have no dip to a slight dip (10

degrees) and can be traced from drill hole to drill hole. Large FGG dikes are considered

to be greater than 5 ft in drill core. Smaller FGG dikes have numerous orientations from

40

vertical to horizontal. Some of these dikes may be the matrix of SGP/CGP that got left

over to the final stages of crystallization, because in some drill holes FGG is seen to

grade into SGP or CGP, even though FGG cuts SGP and CGP most of the time. On the

west end, FGG dikes may be the matrix of CGG-T or -H that got left over in the final

stages of crystallization, as the FGG is sometimes seen to grade into the matrix of these

lithologies (CGG-T and -H). Thus there are several generations of FGG dikes from

different intrusions, and they are seen in drill core to cut each other.

Fault movement at Adanac has displaced some lithologies and disrupted some

trace element patterns. The faults logged in drill core may not have produced significant

movement but they can be coincident with trace element highs or alteration patterns and

are therefore still relevant. The fault between drill holes 323 and 301 (Figure 30) has

moved the MGP and lateral parts of the SGP and CGP intrusions to the north. The fault

between holes 314 and 321 (Figure 31) does not noticeably displace lithologies so much

as trace element patterns (Figure 35), from which the vertical movement direction was

interpreted.

41

Figure 30. Geology of cross section A-A'. Colored backgrounds and associated background grey patterns both depict different lithologies in the deposit. Dashed blue lines indicate faults, with arrows showing inferred direction of movement. The "X" next to the fault represents movement into the page (away from the viewer) and the arrow point on the west side of the fault represents movement out of the page (toward the viewer). If no movement is labeled on a fault, this means that the movement direction is not known and is probably insignificant with regard to dislocation of lithology or trace element patterns.

42

Figure 31. Geology of cross section B-B', symbology as in figure 30. MFP is a dike occurring on the west end of the deposit that probably exploited weak zones in CGG above the MEG intrusion. The dike at the top of drill hole 314 may be following a structurally weak zone related to the Adera fault, which is a regional-scale structure. The Adera fault system exists at surface just to the north of this section.

43

NW

DH323

Geology Cross Section C-C

DH326

SE

1500

1400 :

DH340

%..-? Silicified j

13001

Silicified

DH348 •

Silicified

Silicified ^ , --***

»*** . *****

Silicified

. 100 m |

200 400

Distance (ni> 600 800

Figure 32. Geology of cross section C-C. Drill holes 323 and 340 are consistent with each other and drill the top portion of the SGP and CGP intrusion. Faults in these two drill holes can be traced between holes and have the same dip and orientation as the tops of the SGP intrusion, the silicified zone, and the CGP lens within SGP. Between hole 340 and 326 there has been some movement that down-dropped the SE portion of the deposit.

44

NW

• 1400

—""—

ratio

n (m

l El

e* 1300

-1200

0

DH301 V

CGG

FGG

MGP

. -

• • • • -

Geology Cross Section D-D'

DH 305

^Kz3B&

~^> £BM

^^^K*^^^E*^F^

SGP

^ / '

100 200 Distance (m)

SE

DH 343 ^ n ^ — ^ •

^ S

I

. . ^ • ^ "

, 50 m .

.??p.

Figure 33. Geology of cross section D-D'. MGP intruded CGG which was in turn intruded by SGP and CGP. FGG dikes intruded all of these lithologies after the intrusion of SGP and CGP, and the largest FGG dike in this cross section is shown in yellow. FGG dikes occur less frequently deeper within SGP and CGP intrusions.

Trace Element Zonation

To interpret trace element zonation, drill core pulps (1835 samples from 22

drillholes) were composited at the lab and analyzed for 41 trace elements plus fluorine by

inductively coupled plasma emission spectrometry (ICPMS) at ACME labs in

45

Vancouver, British Columbia. Trace element data have been studied for patterns and

anomalies of Mo, Pb, Zn, W, F, Sn, Cu, and Au (no other trace elements were present in

any amount above normal background contents for granites). The ranges of values for

trace elements were grouped based on natural statistical breaks, described in the

introduction at the beginning of this chapter (Figure 28).

Molybdenum

The general pattern of molybdenite mineralization forms a blanket over and on

the flanks of porphyry intrusions in the deposit. The porphyry intrusions that the

mineralization straddle include CGP and SGP in the central portions of the deposit, and

MEG on the west end. Mineralization decreases within these intrusions.

Molybdenum is highest (670-1430 ppm) in drill holes 333 and 321 on the west

end directly above the MEG intrusion, in CGG (Figure 34 and 35). Molybdenum values

are also high in drill hole 301 in CGG and MGP above the SGP intrusion, and below this

higher grade zone on and within the flanks of the SGP intrusion (Figure 34 and 37). High

values also occur above and within the MGP in drill hole 301. Drill hole 301 may be

penetrating two different molybdenite blankets, one of which occurrs above MGP and the

other occurring on the flanks of the SGP intrusion (Figure 34). The difference in

molybdenum grades between drill holes 318, 304, and 323 is interpreted to represent

some lateral movement as well as vertical on the interpreted faults (Figure 34). It appears

that the block containing drill hole 304 is low-grade compared to drill hole 323 and drill

hole 318, but there has been relatively little displacement of lithology. This also may

46

indicate that the two faults bounding drill hole 304 are pre-mineralization and that

mineralization did not penetrate into this fault-bounded block.

Molybdenite mineralization is somewhat weaker in zones above the SGP and

CGP intrusions in the central part of the deposit (Figure 34). Molybdenum content

decreases within the SGP and CGP intrusions (Figure 37). On the southeast portion of

section C-C (Figure 36) past the fault, the drill hole 326 molybdenum pattern resembles

the top of drill hole 301, i.e., there is a highly anomalous blanket of mineralization above

the MGP intrusion. This may indicate that higher molybdenum grades exist on the flanks

of the SGP and CGP intrusions rather than directly above, as it would be expected to

encounter the flanks of SGP/CGP if one drilled deeper in this area. It may appear as if

the mineralization is post-faulting since the molybdenum shells are at the same elevation

and seem to continue undisrupted across the fault. This seems unlikely because the

faulting would have had to occur only in a very narrow time frame between the SGP and

CGP intrusion (which is clearly offset or affected by the movement) and the

mineralization event. It is much more likely that the mineralization here is pre-fault

movement, and that the portion of the deposit drilled by hole 326 was originally farther

south and has been moved northward.

47

w Molybdenum Cross Section A-A'

1600

1500

1400

i\

DH333 DH321

/ >

Silicified

Silicified

MFP

MEG

t

CGG

DH318

til

Silicified

J. L ^ IT CGP

DH301 DH 304 DH 323

FGG

SGP

xi 08)

MGP

CGP I

1200

<2O0 ppm 209-400 ppm

401-C00 ppm

M1-8M ppm :»®}C ppm

, 100 rn .

588700 589000 589300 UTM Easting (m)

589600

Figure 34. Molybdenum contents of cross section A-A'. High molybdenum values form a blanket over the MEG and SGP porphyries.

48

N W Molybdenum Cross Section on B-B'

DH314 SE

150a

1400

1300

100 Distance (m)

200

< 200 ppm

200-400 ppm

401-600 ppm

601-830 ppm

> 830 ppm

Figure 35. Molybdenum contents of cross section B-B'. Molybdenum is highest over the MEG intrusion.

49

Molybdenum Cross Section C-C

^ ^

t

200-400 ppm

00 Distance ( ™t)

401-600 ppm

600 I

, 100 m •

I 1601-830 I |

I |PP<" I I 800

I I

>830 ppm

Figure 36. Molybdenum contents of cross section C-C. Molybdenum high values occur as a blanket over SGP and CGP intrusions and also form a blanket within CGG towards the southeast, but die out towards the far southeast where drill hole 348 is. Molybdenum mineralization is weak but present over the SGP and CGP intrusions in holes 323 and 340.

50

NW Molybdenum Cross Section D-D' SE

-1200

<200 ppm 200-400 ppm

100

401-600 ppm

200 Distance (m)

601-830 ppm

i 5 0 m i

>830 ppm

300

Figure 37. Molybdenum contents of cross section D-D'. Molybdenum is highest above the SGP and CGP intrusions, but is less anomalous out towards the south (drill hole 343). Some slightly higher values do occur around the faults in drillhole 343. The slightly higher values in drillhole 343 are coincident with fault and fracture zones, likely following the trend of listric type faults on the flanks of SGP and CGP.

Tungsten

Tungsten, manifested as huebnerite, is coincident with the molybdenite

mineralization (Figures 38-41). It is not uncommon to see huebnerite mineralization in

51

drill core in the central part of the deposit where the pit is planned. The highest tungsten

values reported are 200 ppm, because that is the upper detection limit for the analytical

technique. In most of the drill holes, the upper detection limit for tungsten was reached

in at least one composited 10 ft trace element analysis.

Tungsten high values mimic the pattern of molybdenum, except for in drill hole

301 (Figure 38). In drill hole 301, tungsten only has high values above the SGP and

CGP, while molybdenum high values occur above and below this location. Tungsten

high values appear to occur slightly below (closer to the intrusion boundary) than does

molybdenum, for example in drillhole 321 and 318. It is not known whether the W

blanket over SGP/CGP would connect with that of the MEG intrusion, or would hug the

flanks of both. Tungsten high values in cross section B-B' and D-D' (Figure 39 and 41

respectively) show the same pattern as molybdenum. In cross section C-C (Figure 40),

tungsten anomalies do not appear to exist below the molybdenum shell as in A-A'. South

of the fault, tungsten anomalies are present surrounding, along the margins of, and within

silicified zones. It is possible that this is because the same hydrothermal fluids depositing

silica also deposited tungsten, or because the silicification increased brittleness of the

rock thereby allowing paragenetically later fluids to pass through and deposit tungsten.

In drillhole 326, there is a fractured zone (fractures not depicted) below the silicified zone

where the tungsten anomaly reaches >76 ppm. This anomaly is different from others

because there is a clear pattern of tungsten leaching or deficiency from the wallrock.

52

w Tungsten Cross Sect ion A-A'

o;

i\

1200

DH333 DH321

y' A

MFP

MEG

Silicified

Silicified

N>

CGG

DH318

til IT i i CGP

! i i i s i » C

! !

i •

DH301 DH 304 DH 323

eg> C G P l

E

SGP

MGP

< 30 ppm J30-75 ppm

76-150 ppm

>1S0 ppm , 100 m .

589000 689300

UTM Easting (ml

Figure 38. Tungsten contours for cross section A-A'.

53

NW Tungsten Cross Section on B-B'

DH314

1500

n > 1400

1300

100 Distance (m)

200

< 200 ppm

30-75 ppm

76-150 ppm

> 150 ppm

Figure 39. Tungsten contours for cross section B-B'.

54

NW Tungsten Cross Section C-C

DH326

-M500

o 5 a m

1400?

-11300

SE DH348 .

*

Silicifie<i

Silicitlei—t^- -^ "7

^ l O J H t ^ ^ .

k 30 ppm 30-75 ppm

76-150 ppm >150 ppm

200 400 600 Distance (m>

800

Figure 40. Tungsten contours for cross section C-C.

55

NW DH301

\ •

Tungsten Cross Section on D-D' SE

1400"

1300

1200

DH343 •

SGP

, 50 m ,

< 30 ppm

100

30-75 I ppm (

200 Distance (ml

76-150 J ppm

>150 ppm

300

Figure 41. Tungsten contours for cross section D-D'. Tungsten on cross section DD is coincident with molybdenum mineralization (Figure 9).

Other Base Metals (Pb, Zn, Cu, Sn) and Precious Metals (Au)

For low-Ca granitic rocks, the background metal contents are 39 ppm for Zn, 19

ppm for Pb, 10 ppm for Cu, 3 ppm for Sn, and 0.004 ppm for Au (Turekian and

Wedepohl, 1961). High values of Pb and Zn (150-250 ppm) occur in and are controlled

by faults in the areas of cross sections (no areas outside of cross sections were analyzed

for Pb or Zn). High values sometimes occur in silicified zones or above intrusions

56

possibly because increased late stage (post-mineralization) brittleness or fracturing

occurred in these areas. However, not all faults or fractured zones have anomalous Pb

and Zn. The value of 200 ppm was chosen as a "high value" in both cases based on

natural statistical breaks in the data. No visible galena or sphalerite mineralization is

regularly seen within the deposit. There are only trace (background) or slightly

anomalous amounts of Cu and Sn (5-15 ppm each) and Au values are constant throughout

the deposit at below the detection limit (0.1 ppm). Chalcopyrite mineralization is only

rarely seen, usually in a silicified zone alongside huebnerite.

It should be taken into consideration, however, that trace element cross sections

only cover ground within the main areas of molybdenite mineralization. Farther to the

south and west of the main pit, within one kilometer of the southwest Mo zone, and likely

within the same hydrothermal system (based on proximity and similarity of host rocks,

i.e., still the CGG and its associated units), the tungsten trenches exhibit large quartz

veins with visible but minor chalcopyrite, and abundant huebnerite mineralization (see

Figure 4). Within 4 kilometers of the deposit, roughly towards the south along the trace

of the Boulder Creek fault (Figures 3 and 4), another occurrence of molybdenite

mineralization (in large quartz veins still hosted in the Mount Leonard stock) along with a

tin and base metal skarn (the Silver Diamond, partially hosted within the Mount Leonard

stock) is known to occur (see Introduction of thesis). Both gold and silver mineralization

are known to occur as well within these smaller satellite deposits of Adanac. While the

Adanac deposit itself is not anomalous in these elements (except for W) it is clear that the

Mount Leonard stock produced a range of types of mineralization and trace element

anomalies.

57

Fluorine

Average F values are considered to be >800 ppm while high values are considered

to be >1420 ppm based on natural statistical breaks. The average F content of a low-Ca

granitic rock is 850 ppm (Turekian and Wedepohl, 1961). High F contents tend to extend

further out and above the SQMP and CQMP intrusions than does Mo (compare Figures

36 and 44) and are highest north of the Adera fault (not shown on cross sections), which

is the down dropped upper portion of cross section A-A' (Figure 29). At Adanac, there is

a consistent anomalous F content (801-1420 ppm) in certain rock types, such as CGG.

Because the F background is consistent over a certain rock type this would indicate that

the F is located within a common mineral (most likely biotite) rather than being

controlled by an alteration (like greisen) or veining pattern. The highest F located in the

cross sections is in MGP (mafic because of high biotite content), silicified zones, and

some FGG dykes. High values in silicified zones and FGG dykes may be due to

differentiation, or that the last fluids produced by the porphyry intrusions typically

contained the fluorine. Fluorine values are typically depleted (defined as <800 ppm, or

depleted relative to average low-Ca granitic rocks) within and surrounding the SGP,

CGP, and MEG intrusions.

In the cross sections, very high values of F (>1420 ppm) occur as a small shell in

the MGP above the CGP/SGP intrusion in drillhole 301 and in one FGG dyke in drill

hole 318 (Figure 42). The F pattern between drillhole 321 and 314 (Figure 43) has been

affected by vertical movement. Drillhole 314 is mostly low in F except near the surface,

58

while 321 is consistently high. This trace element pattern is the most compelling

evidence for fault movement between these two holes, and is likely part of the Adera

fault system. In cross section C-C (Figure 44) F shows the typical pattern of being

depleted in the SGP and CGP intrusions but being consistently high in CGG. Silicified

zones to the far south of the intrusions have very anomalous F values (>1420 ppm).

Drillhole 326 has some narrow zones of depletion in the same areas that show Mo and W

anomalies. In cross section D-D' (Figure 45), F is depleted towards the core of SGP and

CGP intrusions. There is one zone in drillhole 343 (fractured) that shows a F anomaly.

59

w Fluorine Cross Section on A-A"

1600

15001

1400 ^

1300

1200

OH 333 DH321 DH318

DH 304 DH 323 DH301

j<430 ppm 430-800 | 1801-1420 ppm I I ppm >1420 ppm

S89000 689300

UTM Easting (ml

689600

Figure 42. Fluorine contours for cross section A-A'. Fluorine anomalies may be lithologically controlled, as they tend to be consistently'high in one rock type (CGG) and low in others (any of the intrusions).

60

NW Fluorine Cross Section on B-B'

DH314

MFP

SE

1500.

c g A

> IU

1400

1300

50 m

DH321

HI

j /^ijieifiel;

T t l ! A ^ - " " "

r

\ \ \

100 200 Distance (m)

< 430 ppm

430-800 ppm

801-1420 ppm

> 1420 ppm

Figure 43. Fluorine contours for cross section B-B'. The F pattern between hole 321 and 314 has been affected by vertical movement.

61

NW Fluorine Cross Section C-C

DH 326

SE

JTHP Silicified

CGG

MGP

>1420 ppm 600

Silicified

Silicified

« l o p j n _ -

800 Distance (rnl

Figure 44. Fluorine contours for cross section C - C F has the typical pattern of being depleted in the SGP and CGP intrusions but being consistently high in CGG.

62

Figure 45. Fluorine contours for cross section D-D'. F is depleted towards the core of SGP and CGP intrusions. There is one zone in drillhole 343 (fractured) that has a F anomaly.

Trace element zonation in Climax-type molybdenite deposits

Molybdenite mineralization in Climax-type deposits commonly occurs directly

above and straddles or overlaps with the causative intrusion (Westra and Keith, 1981).

Ore zones do not commonly occur further than 100 meters above the intrusion. Grades

inward of these locations can commonly be in excess of 1800 ppm Mo, or 0.18% Mo.

Close spatial relationships exist between potassic alteration zones and molybdenite

63

mineralization zones. Strongly anomalous fluorine is present within and several hundred

meters peripheral to the molybdenite zone (Clark, 1972). Anomalous tungsten is due to

wolframite or huebnerite (rarely scheelite) mineralization above or coincident with the

molybdenite ore zone. A tin halo may be present with the tungsten halo, or may coincide

with an outer base metal halo. The outer base metal halo (300 - 600 meters above the ore

zone) at Climax has strongly anomalous Zn, Ag, and Mn, and weakly anomalous Pb, Cu,

Bi, and Sn (Westra and Keith, 1981).

Adanac does not have the variety of anomalous trace elements present at Climax

(elements such as Bi, Ag, Mn, and Sn are not anomalous at Adanac). The trace elements

that are anomalous (Pb, Zn, W, F) fit the above descriptions of Climax-type trace element

patterns, and are in similar positions relative to Mo mineralization. The base metal

concentrations of Pb and Zn at Climax are likely located above the main ore zone and

farther away from the causative intrusions because these minerals are deposited at later

paragenetic stages than Mo or W (Clark, 1972). Lead and Zn at Adanac are deposited

almost exclusively in faults or areas of intense fracturing, where it is likely that

paragenetically later and cooler fluids passed through, as evidenced by the abundance of

montmorillonite clays in these locations (see below). In this study which included

observations on 142 thin and polished sections, as well as in all of the field work, there

was no sample where molybdenite and base metal mineralization could be clearly seen to

have a paragenetic relationship, but, it is also likely that the Pb and Zn mineralization in

faults is younger than molybdenite mineralization because these faults always cut

molybdenite mineralization, and no molybdenite is known to have been deposited in

faults.

64

It is also important to note that the cross sections on which these elements were

contoured never really extended past the main ore zone because the deposit was drilled to

define the molybdenum ore body as opposed to the entire hydrothermal alteration zone.

Therefore, there are insufficient data on the potential peripheral zonation of base metals.

65

Chapter 4

Hydrothermal Alteration

Most porphyry molybdenum deposits have a potassic core, a quartz-sericite-pyrite

zone, and outer and upper argillic and propylitic zones (Westra and Keith, 1981). Calc-

alkaline type deposits have poorly-developed potassic zones compared with alkalic or

alkali-calcic type porphyry molybdenum deposits. Alkalic and alkali-calcic deposits are

also more likely to have high silica cores, or silicification zones. At Climax, alteration

zones are more complex and intense, because the deposit formed from multiple intrusions

which caused overprinting of alteration zones (White et al., 1981). Alteration at Climax

does include several high silica zones in the deepest parts of the intrusion, below

mineralized areas (Figure 46). Above silicification and straddling the deepest (and

youngest) intrusion is both the potassic zone and a blanket of tungsten mineralization.

Outward from this core of intrusion and mineralization are the argillic zone (kaolinite and

montmorillonite), QSP zone, and molybdenite ore body (White et al., 1981). The

propylitic zone of alteration is the largest zone of alteration, overprints other alteration

types and also occurs farthest out from the intrusion, and thus provides the exploration

geologist with a large target area to identify when looking for hydrothermal systems.

66

Figure 46. Alteration zoning for an ore body at Climax in relationship to molybdenite and tungsten mineralization, and causative intrusion. Starting at the porphyry intrusion and moving outwards would roughly be a high silica core, a K-feldspar or potassic alteration zone, a sericite-pyrite zone, and an argillic zone. A propylitic alteration assemblage would overprint all of these alteration packages and would also extend furthest out from the porphyry intrusion. Figure from paper by Hall et al., 1974, and originally from Wallace etal., 1968.

Characteristics and Zoning of Hydrothermal Alteration at Adanac

Alteration at Adanac was compared with that at Climax to aid in classification of

the Adanac deposit and to contribute to understanding and characterization of alteration

of these deposit types. The characteristics and spatial relationships of alteration packages

at Adanac are described below. Alteration characteristics were determined from analyses

of 35 polished thin sections, 22 X-ray diffraction analyses of clay altered and fresh rocks,

67

and hand sample (drill core) descriptions. Clay samples were prepared by deflocculation

of clays by grinding and mixing the sample in soapy water and allowing for settling out

of heavy particles for ten minutes. The top portion of the liquid was decanted and

allowed to evaporate, thus leaving behind the clay sample. Quartz impurities from the

original granite were used as an internal standard for X-ray diffraction. Clay samples

were analyzed on a Philips brand XRG 3100 X-ray generator and run for 25 minutes

using CuK radiation at 40 kilovolts and 30 milliamps, and reported at 2-theta. Tabulated

results for clay X-ray diffraction samples are located in the Appendix. Alteration zoning

was determined from drill holes re-logged over summer 2007 with a focus on alteration.

All of the alteration zones are described below in paragenetic order based on cross-

cutting relationships seen in drill core. In general, silicification zones occur closest to the

apices of porphyry intrusions, and potassic alteration zones occur above silicification

zones. Further out from intrusions, the QSP and stilbite-calcite zones occur, along with a

chlorite overprint.

Silicification is characterized by the addition of quartz and opaque minerals,

typically pyrite. Silicification occurs as patchy zones that extend for one foot to several

feet in drill core (Figure 47). Silica replacement is estimated from thin sections to be

anywhere from 70% to 25% of total mineralogy in thin section. Quartz is seen replacing

feldspars and biotite (Figure 48) or chlorite, suggesting there may have been some early

propylitic alteration before silicification. Opaque minerals added during silicification

include, in paragenetic order from oldest to youngest, 1) magnetite 2) pyrite 3)

chalcopyrite, and typically comprise 10% of total minerals in thin section (Figure 49).

There is rarely some pyrrhotite, galena, and sphalerite seen with chalcopyrite. Opaque

68

minerals are found disseminated and in veins. Magnetite commonly replaces biotite or

chlorite and pyrite and chalcopyrite replace the magnetite and biotite or chlorite. Pyrite

and magnetite are the most abundant opaque minerals. About one-third of the biotite is

altered to chlorite or (less commonly) sericite. Sericite also rarely occurs replacing

feldspars. Clay alteration occurs as replacements of feldspars in the center of the crystal,

but does not destroy textures, and clay minerals make up only about 5% of the rock.

XRD analyses of silicification zones indicate most clay alteration products are illite,

kaolinite and chlorite are common, and montmorillonite is absent.

Silicification zones occur at depth on the western end in cross section A-A'

(Figure 50). Zones of silicification in this area are common and may extend for up to 6

feet in drill core. Silicification extends to other areas in the cross sections as smaller

patchy zones that form sill-shaped bodies traceable from one drill hole to the next (Figure

51). They do, however, become less frequent and smaller (one foot) away from the

deeper western end, near hole 333. This likely means that drill hole 333 is approximately

centered over the most intense silicification. Silicification zones appear to drape over and

extend into the MEG intrusion on the west, and drape over the SGP and CGP intrusions

to the east (Figure 50 and 51), but have largely disappeared in the far SE (Figure 52).

69

* * > * . #

• ^ • e ^ f e l • • * - • » ' v. ^ • f c » i HI TT MIIT 1861

Figure 47. Silicification in drill core, drill hole 24, 544ft.

Figure 48. Silicification of biotite in thin section. Crossed polars, From drill hole 326, 132ft.

70

Klagnefflta

.^%i

w n

ommsm

Figure 49. Photomicrograph of opaque minerals in a silicified zone. Reflected light, drill hole 348,488ft.

71

Figure 50. Hydrothermal alteration on cross section A-A'. The colors represent geologic units and are the same as in Chapter 3.

72

NW Alteration Cross Section C-C"

DH326

SE

TTnTTT-T^-T;::^ -T^ -^ IWt i i

: :^i4-':::^+::::^ : : : : : : : : : : • : ' : : : • : • : • • . • . • • • - • . • . • • • • • . • . •

:: :^+::::^::::V " I " » * I ' • * I ' I * • *• " *•"*

j:i:::jii::::i4;:;

••^•'••'•^jiSSSSt

::: r^T+JjSSSSP?^

::-:-::-:-:-; ;i5j!BI

-^+- -B-f-

-3-f- -*-6-

-i- -*->• -«-

- i - i - -i-fr-

rs^TrTop1

• - T - - —

-T-T- ^ +

. J .

••:::^»::::V^: : • : • : • : • : • : • : • : • : •

::::::::::::::::::

lPPP* :::.*+: ^iiilHHiliiH -: = :H^::::*^*:: : • : • : * : • : • : • : • : - : •

4i^;: :^i»:::: i i

pi - - H - ^ « -

- * • + - * - • • •<

-*-+• -i-*- -«

- -»-+• •+-*-

&g£5&^ —r- ^— -i . - _ _ J .

- " - -t . - ^ - .i-L.

Distance (nfiT

Figure 51. Hydrothermal alteration zones on cross section C-C.

73

NW Alteration Cross Section D-D'

0 100 200 300 ' ' 1 Distahce (m> r

Figure 52. Hydrothermal alteration zones in cross section D-D'.

Potassic alteration is characterized by unaltered, pink potassic feldspar that occurs

as replacement of primary feldspars (Figure 53) and biotite in zones (floods) that extend

from 1-3 feet in drill core, or as a high frequency of pink feldspar envelopes around

quartz veins (Figure 54). Figure 55 shows both primary and secondary potassic feldspar

in photomicrograph. Secondary biotite occurs in the feldspar floods (Figure 56), and is

consistently fresh, or not altered to chlorite as in silicified zones or the stilbite-calcite

zone (described below). Secondary biotite is typically 2-3 mm in size. It is characterized

74

by shredded, anhedral crystals. In thin section, pyrite is typically absent, but magnetite

may be present. There is some clay alteration of feldspars which is most likely illite,

based on XRD analysis of several samples of feldspar flood zones. Kaolinite and chlorite

are rare, and montmorillonite is absent. Clay alteration products are least common in

potassic altered rocks, and clay minerals comprise only 2-3% of the total rock. Several

samples contain fluorite that appears to be cogenetic with secondary potassium feldspar,

based on the observation that fluorite has interlocking grain boundaries with these

feldspar crystals. Calcite grains (<0.1 mm) cluster around biotite, or occur with fluorite

grains and have common grain boundaries with fluorite. There are abundant calcite

grains in most samples, which appear to be cogenetic with potassic alteration because,

like fluorite, it was observed to have interlocking grain boundaries with secondary

feldspars.

Potassic zones occur above the main silicification zones on the western end of A-

A' and overlap with the upper sill-shaped bodies of silicification (Figure 50), and extend

towards the east and south (Figure 51). The potassic alteration zone is most pronounced

(largest, and has more intense replacement) on the SW end similar to the silicification,

and occurs coincident with and above the silicification zone here. The character of the

potassic alteration zone on the west end of the cross section (Figure 50, A-A') is distinct

from that of the east end, because on the west side of the deposit there are large zones (up

to 7 feet) of near total pink feldspar replacement of primary mineralogy. On the east and

south end, above the SGP intrusion and within the CGP and the SGP, potassic alteration

consists mostly of pink feldspar vein envelopes or selvages. On the far southeast, zones

of potassic alteration are not present (Figure 52).

75

Figure 53. Feldspar flooding in drill core. The pink area, about 5 cm wide, is a feldspar flood with small dark patches of secondary biotite. The arrows point to molybdenite crystals on either side of the flood. These molybdenite crystals may be cogenetic with feldspar flooding and were tested for a Re-Os mineralization age (see Chapter 6). This type of potassic alteration typically occurs in the western end of the deposit. From drill hole 369, 650ft.

Figure 54. A typical feldspar envelope (white-pink envelope) around a quartz vein (grey). This type of potassic alteration is typically found in the central pit area. From drill hole 351, 671 ft.

76

Figure 55. Primary and secondary feldspar in photomicrograph. Primary feldspar typically has defined and sharp crystal edges, while secondary feldspar has jagged or irregular edges, and replaces other feldspars. Drill hole 305, 343ft, crossed polars.

77

Figure 56. Secondary biotite in thin section. Drill hole 305, 343ft, plane light.

The phyllic. or quartz-sericite-pvrite (OSP) zone is characterized in hand sample

by 1 -3 mm veinlets or hairline fractures filled with minor quartz, abundant sericite, and

pyrite (Figure 57), with sericite and pyrite also extending into 1-6 cm envelopes around

the veins or fractures. In the QSP zone, which is peripheral to the zones containing

abundant silicification and feldspar flooding (for example, drill hole 348 on cross section

C-C, Figure 51), the rocks begin to appear greenish, olive-colored, or have a brown hue

(Figure 58). In thin section there is an increased amount of clay alteration in this zone

compared with silicified and potassic alteration zones, with most feldspars typically

having centers that are texturally destroyed. The total amount of clay alteration is

estimated to destroy 20% of original mineralogy. The alteration of biotite to chlorite is

78

common in the QSP zone. Clay minerals in the QSP zone are dominated by kaolinite and

chlorite, with illite also being common. Montmorillonite is absent.

The quartz-sericite-pyrite alteration zone occurs in the eastern portion of A-A',

and in the southern portions of the deposit, represented in cross sections C-C' on the

southeast side and the entire section D-D' (Figures 51 and 52). The QSP zone is seen in

drill hole 323 above and on the margins of the SGP, and overlapping and overprinting a

smaller zone of silicification (Figure 50). QSP alteration is typically absent in the deeper

portions of the SGP and CGP intrusions, and on the west side of cross section A-A'

where silicification and potassic alteration are most intense.

Figure 57. This core broke along the plane of QSP fracture fill. Most of the surface shown in the photo is sericite, but a small amount is pyrite. From drill hole 338, 105ft.

79

* *

Figure 58. Appearance common of clay alteration outside the potassic and silicification zones. Feldspars in this area are commonly texturally destroyed and altered to kaolinite, and biotite is altered to chlorite. This rock is cut by an open fluorite-filled fracture from the stilbite-calcite alteration phase. From drill hole 18, at 481ft.

The stilbite-calcite zone is characterized in hand sample by 2 mm to 3 cm-sized

fractures that are filled with calcite and stilbite, + fluorite (Figure 58, 59 and 60). These

fractures cut other alteration types including silicified zones and potassic zones.

Fractures may be completely filled with calcite and stilbite or sometimes are open and

contain only vuggy, euhedral stilbite. Wall rocks also have a greenish or bluish hue,

similar to the QSP alteration, probably the result of chlorite. Fluorite is present with this

stage of alteration, occurring as vein fill along with both calcite and stilbite. In thin

section, stilbite is confined to veins and fractures, but both calcite and fluorite are seen in

adjacent wall rock. Clay alteration in this zone is similar to that in the QSP zone. Clay

alteration is more common than in zones of silicification and potassic alteration. Centers

of feldspars are destroyed texturally, and replaced by clay minerals. These clays are

80

primarily kaolinite, with chlorite and illite being common as well. Clay alteration is

estimated from thin section to replace 20% of total primary minerals. The stilbite-calcite

zone overprints the phyllic zone further to the east in cross section A-A', and is entirely

coincident with the phyllic zone in the southern portions of the deposit. Neither the

phyllic or stilbite-calcite zones appear in deeper, fresher portions of the SGP/CGP

intrusion in cross section D-D'.

Figure 59. Stilbite-calcite alteration. The open fracture (horizontal in this photo) is filled with mostly stilbite (the yellow drusy mineral), but these fractures commonly contain a white powdery or yellow crystalline calcite, and more rarely fluorite. The fractures with the stilbite-calcite assemblage cut all other alteration types and mineralized veins. The fracture in the picture was probably an earlier mineralized vein (notice the feldspar envelope and the quartz running up the length of the fracture on the left side) that experienced displacement and dilation, and was later filled with the stilbite. From drill hole 01, at 981ft.

81

Figure 60. Fractures cut through a quartz crystal and are filled with calcite and stilbite. The grainy material in the middle of the calcite-filled fracture is brecciated quartz from faulting, which indicates that the calcite-stilbite alteration post-dates some faulting. From drill hole 314, 636 ft, crossed polars.

Faults, or rock that exhibits gouge or crumbling in the drill core, have a dirty

olive green or brown appearance. In thin section, the feldspars are texturally destroyed

and contain black, white, and dark brown patches (Figure 61). These rocks are always

dominated by montmorillonite and kaolinite, commonly contain chlorite, and less

commonly contain illite. These rocks almost certainly allowed (post-ore) low-

temperature fluids to pass through them, and montmorillonite may be the product of these

fluids based on its presence exclusively in faults.

82

Figure 61. In faults, clay replacement of certain minerals (likely a feldspar) can be complete. X-ray diffraction shows that kaolinite, chlorite, illite, and montmorillonite are all present in faults, montmorillonite being observed only in faults. From drill hole 326, at 618 ft.

Discussion

Based on the trace element patterns at Adanac compared with those of Climax-

type deposits, there are two possible causative intrusions for mineralization and

alteration. The CGP/SGP intrusion is a possible choice when one considers the eastern

end of the deposit at drill hole 301 because mineralization, silicification, and potassic

alteration straddle the outer contacts of the intrusion (Figure 34 an 50). However, drilling

in 2005 discovered a high-grade zone at the western end of the deposit (drill hole 333, for

example) where no SGP or CGP is known to exist, and this high-grade zone sits above

83

the MEG intrusion (Figure 34). It may be that both the CGP/SGP intrusion and MEG

intrusion caused mineralization and alteration at Adanac, and, given the similar

geochemical nature of CGP/SGP and MEG intrusions (see Chapter 2), they may be

different textural phases of the same intrusion. Since the two intrusions are straddled by

halos of mineralization and alteration, it is likely that hydrothermal fluids were generated

during the introduction of both of these intrusions.

The pattern of alteration zoning at Adanac conforms to that of Climax-type

molybdenum deposits, although alteration at Adanac is not as intense. At Climax,

alteration is more intense, and it commonly occurs as total replacement of minerals

except for quartz phenocrysts (Hall et al., 1974). Alteration at Climax is also more

intense than at Adanac because of multiple overlapping intrusions and resulting

overlapping alteration zones. While the trace element pattern at Adanac leaves the

observer to question whether either or both of the CGP/SGP intrusion and MEG intrusion

are the source of mineralization, the alteration pattern more clearly points to MEG as the

causative intrusion, because both silicification and potassic alteration are more

pronounced at the western end above the MEG, and this is evidence of a more intense

hydrothermal system being generated from this intrusion.

Because Adanac has both intense silicification and potassic alteration zones, the

Adanac deposit is more like an alkalic, or Climax-type porphyry molybdenum deposit

than a calc-alkalic molybdenum deposit. The alteration types and patterns seen at

Adanac thus is consistent with what would be expected based on geochemical

information described above from Adanac, such as high Rb and low Sr, high silica

contents, and the K2O value at 55 wt % silica.

84

Chapter 5

Molybdenite Polytype Study

Molybdenite Polytypism

Molybdenite occurs in one of two polytype structures: the common 2H type, or

the exotic 3R type (Newberry, 1979). The 2H polytype is a hexagonal mineral consisting

of two layers per unit cell. The rare 3R type is a rhombohedral mineral consisting of 3

layers per unit cell. Both types are closely stacked planar S-Mo-S layers that differ only

in the length of the c axis. Some studies suggest that the 3R polytype grows by a screw-

dislocation mechanism and is unstable relative to 2H but does not convert readily to the

latter because of kinetic barriers (Newberry, 1979). Screw dislocations occur most

frequently in nature due to internal strains caused by impurities, mainly rhenium when

considering molybdenite. The other more common impurities in molybdenite are tin,

titanium, bismuth, iron, and tungsten. Other authors suggest that the differences in

polytypes are the result of sulfur fugacities, i.e., the 3R polytype forms in exotic low

sulphur-fugacity environments and is sulfur-deficient relative to 2H (Clark, 1970). It has

also been suggested that molybdenite polytype plays a role in Re concentration (Ayres,

1974), and that temperature and depth of ore formation is a controlling factor of

polytypism (Ishihara, 1988).

Whatever the cause of polytypism, porphyry molybdenum deposits, tungsten-

molybdenum skarns, and pegmatites that bear molybdenum are generally associated with

low rhenium concentrations in molybdenite (10-100 ppm, 30-400 ppm, and 0.1 - 100

85

ppm, respectively) while molybdenite from porphyry copper-molybdenum deposits and

copper-molybdenum skarns has higher rhenium concentrations (100-3000 ppm, and 50-

800 ppm, respectively). This may be why molybdenum deposits with no copper have

almost exclusively the 2H type molybdenite. The latter group of copper-bearing

molybdenite systems typically have a mix of 2H and 3R polytype, and have been known

to have up to 95% of molybdenite in a deposit be of the 3R type (Newberry, 1979). The

purpose of testing whether or not molybdenite is exclusively 2H or is a mixture of 2H and

3R is to aid in classifying the deposit. If there is a mixture of the two polytypes at

Adanac, it may mean that there is more copper at Adanac than has been currently drilled.

Sample Analysis

Samples were prepared by extracting molybdenite from host rock using a hammer

and tweezers. Samples were ground and then floated in water to separate molybdenite

from other particles. The floating molybdenite was then scooped off the top of the water

and sprinkled onto a Vaseline-coated slide so that the mineral would be randomly

oriented. Seven samples of molybdenite were analyzed for polytype on a Philips brand

XRG 3100 series X-ray diffractometer for 30 minutes each using CuK alpha radiation at

40 kilovolts and 30 milliamps. Samples were run from 30 to 50 degrees two-theta with a

step of 0.1 degrees and a dwell time of 0.45 seconds. Pure NaCl was used as an internal

standard.

86

Results and Discussion

All molybdenite crystals analyzed on the X-ray diffractometer were of the 2H

type (Table 2), and therefore consistent with other porphyry molybdenum deposits with

no copper. There was no variation of polytype seen with age, location, vein type, or

original (pre-preparation) crystal size. The 2H polytype is easily distinguished from the

3R polytype in XRD scans due to two weak peaks at the start of the scan. The 3R

polytype has these same peaks, but the peaks are strong. One of the scans is shown in the

appendix (A-23) for example.

The Re concentration of molybdenite at Adanac was determined during Re-Os

analysis for dating of mineralization (Table 4 in Chapter 6) and ranges from 5.5 to 39

ppm. The lower end of the Re concentration at Adanac is actually below reported

average values for porphyry molybdenum deposits, which is 10-100 ppm (Newberry,

1979). This may actually mean that there is more molybdenite at Adanac than has been

discovered by drilling. This is because Re concentration in molybdenite may be

reflective of bulk molybdenite deposition: larger deposits like Climax have very low Re

concentrations presumably because the total Re in the hydrothermal system is contained

mostly within the molybdenite, and there is a lot of molybdenite. For a complete

discussion on this topic, refer to the Re-Os isotopic analysis and reported Re

concentrations in Chapter 6.

87

Sample ID:

(drill hole

and footage)

352-413

375-1036

375-1054

375-1125

313-110

314-858

364-501

Location and Description

N of the Adera fault in SQFP. Very fine molybdenite crystals in a smoky quartz vein.

Very fine molybdenite in a wispy, ribbon textured vein within 5 feet of the paragenetically later vein types (milky quartz, brittle and sharp contacts with host rock, not a ribbon textured vein).

Disseminated molybdenite in a feldspar flood

Large rosette molybdenite in a paragenetically late milky white quartz vein with brittle and sharp contact with host rock.

SW end of deposit, N of Adera fault. Coarse molybdenite in quartz vein.

West end of deposit, coarse molybdenite in quartz vein.

Central pit. Coarse molybdenite + other sulfides and oxides chalcopyrite, wolframite, magnetite, pyrite) in white quartz vein.

Polytype

. 2H

2H

2H

2H

2H

2H

2H

Table 2. Results and sample descriptions of molybdenite X-ray diffraction polytype study.

88

Chapter 6

Geochronology of the Adanac Molybdenum Deposit, British Columbia

Re-Os ages of molybdenite and U-Pb ages of various lithologies at Adanac were

determined in order to compare ages of mineralization and magmatism. One goal of this

study was to identify the causative, or mineralizing intrusion by matching a

mineralization age with a magmatic age. Another goal was to constrain the life span of

the hydrothermal system at Adanac. The results of this study can be also be used to

compare Adanac to other porphyry molybdenum deposits. Age and number of

mineralization events (multiple or single) are criteria commonly used to classify porphyry

deposits (Clark, 1970).

Re-Os Mineralization Ages

Four samples of molybdenite were analyzed for Re-Os isotopic age in order to

constrain mineralization ages at Adanac. Samples are listed below in Table 3, with a

description and an inferred relative age based on cross-cutting relationships or known

characteristics of Climax-type porphyry molybdenum deposits (i.e., molybdenite

associated with other base metals in porphyry deposits are usually later mineralization

events). Figure 62 shows a schematic diagram illustrating cross-cutting relationships

seen in drill-core. All samples were hosted in CGG.

The first 3 samples in the table are all from drillhole 375, which was drilled in the

western end of the deposit where the suspected mineralizing intrusion is located (see

Figure 29). They were selected based on differences in vein type (discussed below) or

89

other host (feldspar flood). Their location in one drill hole within 30 feet of each other

adds confidence to the assumption that any differences in ages are not correlated with

distance from each other in the deposit but represent temporal changes in vein type. The

last sample, 364-50, was chosen from the central part of the deposit, in the blanket of

mineralization located above the SGP and the CGP intrusions.

Sample 1: 375-1054. This molybdenite was disseminated in a feldspar flood in the

potassic-altered core of the deposit.

Sample 2: 375-1036. This molybdenite was in a ductile, ribbon-textured vein. The

quartz in these vein types is usually dark and sooty colored, either from fine molybdenite

or because it is smoky quartz. Veins that carry this type of molybdenite and exhibit dark,

sooty coloration are usually small (~ 2 cm) and consistently bear molybdenite. Other

quartz veins bearing molybdenite are commonly seen to cut these vein types.

Sample 3: 375-1125. This molybdenite was in a large, 4-6 cm milky-white quartz vein.

Molybdenite in these veins usually forms large 2-5 cm rosettes. The contact of the vein

with the host rock, in contrast to the previous sample, is sharp. These veins less

frequently carry mineralization and are sometimes barren. This vein type commonly cuts

other vein types.

Sample 4: 364-50. This molybdenite was taken from a vein cutting CGG that had an

abundance of other visible opaque minerals, such as pyrite, chalcopyrite, wolframite, and

magnetite. No distinct temporal relationships with other vein types were observed.

However, it is typical in Climax-type porphyry molybdenite deposits to have

mineralizing events that have specific temporal relationships that can be partially defined

90

by associated sulfides, such as early events that bear molybdenite only, and later events

that bear molybdenite + pyrite (Westra and Keith, 1981). Therefore, this sample was

dated to assess the possibility that this vein represents a separate and distinct late

mineralizing event.

Sample

375-1054

375-1036

375-1125

364-50

Location

southwest end

southwest end

southwest end

central mineralized

blanket

Host Rock

CGG

CGG

CGG

CGG

Vein Type

No vein, feldspar

flood

2cm ductile ribbon

textured vein with

fine molybdenite

large, 5cm milky white quartz vein

with molybdenite

rosettes

4 cm milky white quartz

vein

Associated Minerals

feldspar

none

none

pyrite, chalcopyrite, wolframite, magnetite.

Probable Paragenesis

1

2

3

4

Table 3. Molybdenite Re-Os samples. The sample ID refers to the drillhole and the depth

from which it was taken.

91

/ * / / J? /

/ £/ / f / <? / / / / / f* /

/ / / / / / / w / / O /

/ * /

/ / / / / /

/ / / A i f & A\ s / of AW

Jr / ^Aw 4 / if Aw / fAW / &Aw

/ #W / 4?W

375-1125 brittle, sharp

contact vein,

#3

J ^f^^^^^^r w

SAW^ A^T

AWT AW^

A*r W^ 374-1054

Feldspar Flood #1

Molybdenite Re-Os Samples Host Types and Cross-Cutting

Relationships (ordered oldest-youngest)

Figure 62. Schematic diagram showing paragenetic relationships (seen in drill core) of the four Re-Os molybdenite samples. Sample 364-50 may have no cross-cutting relationships with the other samples, but it is presumed to be last based on a high base metal content. Base metals are usually deposited after main molybdenite mineralization in alkalic porphyry molybdenum deposits.

Samples were prepared by breaking apart the host rock with a hammer on a clean

surface (a sheet of paper) and molybdenite was handpicked with a pair of tweezers. The

molybdenite was ground in a steel mortar and pestle and placed in a small dish of water.

Because molybdenite is a micaceous mineral, surface tension of water held the thin

mineral particles at the top of dish while feldspar, quartz, and other impurities sank to the

bottom of the dish. The water containing the floating molybdenite was decanted and

allowed to evaporate. Samples were then examined under a binocular microscope and

any other impurities were removed with tweezers. Tweezers, hammer, mortar and pestle,

92

and the dish were washed with soap and water between samples. Samples were then sent

to the Re-Os geochronology lab at the University of Arizona at Tucson.

At the lab, samples were handpicked and loaded in a Carius tube and dissolved

with 8 ml of reverse aqua regia. The tube was heated to 240°C overnight, and the

solution later treated in a two-stage distillation process for osmium separation (Nagler

and Frei 1997). Osmium was further purified using a microdistillation technique, similar

to that of Birck et al. (1997), and loaded on platinum filaments with Ba(OH)2 to enhance

ionization. After osmium separation, the remaining acid solution was dried and later

dissolved in 0.1 N HNO3. Rhenium was extracted and purified through a two-stage

column using AG1-X8 (100-200 mesh) resin and loaded on platinum filaments with

Ba(SO)4. Samples were analyzed by negative thermal ion mass spectrometry (NTIMS)

(Creaser et al., 1991) on a VG 54 mass spectrometer. Osmium was measured using a

Daly multiplier collector, and rhenium using a Faraday collector. Isochrons and weighted

means are calculated using Isoplot (Ludwig 2001).

Molybdenite ages are calculated using a Re decay constant of 1.666 x 10 year

(Smoliar et al. 1996). Uncertainties for molybdenite analysis include instrumental

counting statistics and in the 187Re decay constant (0.31%). In this work, uncertainties are

calculated using error propagation, taking in consideration uncertainty in the rhenium

decay constant.

93

Sample ID

375-1054

375-1036

364-50

375-1125

Total Re (ppm)

9.521

8.011

5.572

39.0

187Re (ppm)

5.96

5.015

3.488

24.42

1870s (ppb)

7.036

5.828

4.048

28.38

Age (Ma)

70.87

69.71

69.61

69.72

Error 2o

(0.5%)

0.36

0.35

0.35

0.35

Sample Host

Feldspar flood in

CGG Ductile ribbon vein, in CGG With base

metals, in CGG Large, brittle contact vein, in CGG

Expected Relative

Age (oldest -

youngest)

1

2

4

3

Measured Relative

Age (oldest-youngest)

1

2

2

2

Table 4. Summary of data for Re-Os mineralization dates.

Sample 375-1054 was molybdenite disseminated in a. feldspar flood on the western

end of the deposit and, as expected, was the oldest sample at 70.87 Ma. It was not

surprising that this was the oldest sample because this molybdenite was disseminated in a

feldspar flood, and potassic alteration is commonly early in the sequence of hydrothermal

events. There was no distinction in ages between the other 3 samples (375-1036, 364-50,

and 375-1125) when one considers the error of 0.35 Ma. All three mineralization events

occurred in a relatively restricted time of less than 1 m.y. Besides the calculated isotopic

age, there are other factors to consider when determining paragenetic sequence. First,

cross-cutting relationships cannot be ignored. The molybdenite in smoky quartz veins

with a ribbon texture and a ductile contact with host rock is consistently seen to be cut by

thicker milky white quartz veins that usually bear less molybdenite. Therefore, this vein

94

type (sample 375-1036) is clearly older than veins with milky white quartz, even if they

may be a part of the same mineralization event.

Based on the Re-Os results, 375-1125 should be placed as the last and youngest

sample, based on using the Re concentration as a proxy for fluid evolution. It makes

more geologic sense for molybdenite samples being deposited to maintain a somewhat

consistent Re concentration until there is some change in environment to force deposition

of the element within the molybdenite. In other words, it does NOT make sense for the

hydrothermal system to go from depositing molybdenite with 8 ppm Re, then to 39 ppm,

and then back to molybdenite containing 5.6 ppm Re. It makes more sense for the Re

concentration to jump at the end stages of mineralization because the element has

nowhere else to go, and molybdenite deposition at the end stage of the hydrothermal

system must incorporate all the remaining Re thus increasing the concentration.

It is a possibility that, because no cross-cutting relationships were observed between

the base metal-carrying vein and other samples, that the vein represents the same

paragenetic stage as sample 375-1125, but locally, the Re in the fluid may have been

divided between some of the other minerals: magnetite and chalcopyrite, although there

is no analysis at Adanac for Re content in minerals other than molybdenite. An addition

of Re to other minerals would explain the low Re concentration in sample 364-50. This

scenario puts the paragenetic order of the base metal vein in line with what is observed in

other porphyry molybdenum deposits, namely, that base metal stages usually occur last

(Westra and Keith, 1981).

95

The Re concentrations reported for these samples are among the lowest reported

for porphyry molybdenum deposits. Fleisher (1959) and Riley (1967) report that Climax-

type molybdenite deposits usually have less than 100 ppm Re in molybdenite, and are

more commonly under 20 ppm, while other molybdenite deposits (including low-fluorine

Endako type porphyries) contain hundreds to even thousands of parts per million Re.

The cause of Re concentration variability has been a source of debate. It has been

suggested that 1) molybdenite polytype plays a role in Re concentration (Ayres, 1974), 2)

bulk Re concentration in hydrothermal systems of Mo porphyry versus Cu-Mo

porphyries is a controlling factor (Schindler 1976), 3) temperature and depth of ore

formation is a controlling factor (Ishihara, 1988), and also that 4) oxygen fugacity

controls Re concentration and volatile transport (Bernard et al., 1990). Further discussion

of the true cause of Re concentration variability in porphyry molybdenum deposits is

beyond the scope of this paper, and may be a combination of one or more of the above

factors. As reported by Fleisher (1959) Re concentrations in molybdenite range from 5 -

28 ppm at Climax and 8 - 1 2 ppm at Questa, which are the lowest values reported and

similar to Adanac. Re concentrations for the Jinduicheng Climax - type porphyry

molybdenum deposit in China are reported at around 17 ppm (Stein et al., 1997).

However, recent analyses of the Endako porphyry molybdenum deposit do not

support the observation that Re concentration can always be correlated with porphyry

type (Selby et al., 2001). Eight molybdenite samples tested at Endako range from 9 ppm

to 38 ppm Re, but at the nearby Nithi Mountain molybdenite occurrence (geologically

and geochemically similar to Endako, but subeconomic) the Re concentration is higher

(77 ppm). In the Endako deposit proper, Re concentration could not be correlated with

96

alteration, vein type, polytype, or temperature of formation (Selby et al., 2001). This

suggests that if Re is present in the hydrothermal fluid, the amount of Re deposited in

molybdenite is controlled by bulk molybdenite deposition, regardless of other features of

the deposit.

This also suggests that Adanac, given its somewhat low reported Mo grade, may

actually be higher grade or larger than is currently thought. If bulk Re concentration is

usually high in porphyry deposits bearing molybdenite, then the low Re concentration in

molybdenite may be explained by postulating that there is more molybdenite elsewhere in

the deposit. This is entirely feasible, as the deposit is not fully explored, the mineralizing

intrusion is not identified yet, and the geographic limits and expanse of the deposit have

not been identified or drilled.

U-Th-Pb Magmatic Ages

There has been previous work on magmatic ages of the Mount Leonard Stock and

the Surprise Lake Batholith. Mihalynuk et al. (1992) report a U-Pb age of zircons from

the Surprise Lake Batholith as 83.8 Ma. Christopher and Pinsent (1979) obtained K-Ar

ages of biotites from some lithologies within the Adanac deposit. The average age was

70.6 Ma, and the individual ages of each lithology are shown below in Table 5.

CGG MGP SGP MEG

71.6 + 2.2 70.3 + 2.4 71.6 + 2.1 71.4±2.1

Table 5. K-Ar Ages (Ma) as determined by Christopher and Pinsent, 1979. Lithologies are using new terminology described above.

97

For this study, a total of seven samples from Adanac were analyzed for U-Th-Pb

ages in zircons in order to constrain the duration of magmatism of the Mount Leonard

stock, re-test some of the ages reported by Pinsent et al., determine ages of some new

lithologies not tested previously and for which relative ages were obscure, and to identify

the intrusion responsible for mineralization by comparing the ages of molybdenite to the

ages of lithologies. Predicted ages of lithologies at Adanac are summarized in Figure 8 in

Chapter 2.

Samples were collected on site at Adanac and crushed with a rock crusher before

being bagged. In between samples, the crusher was washed with soap and water and

vacuumed. Samples were then sent to the Arizona LaserChron Center in Tucson,

Arizona. Here, samples were run through a pulverizer to reduce the sample to sand-sized

grains. In between samples, the pulverizer was cleaned with soapy water, a wire brush,

and vacuumed. The samples then went through the first of two gravity separation steps, a

Wilfley table separation, after which a hand magnet was used to remove magnetic grains.

The sample was processed in methylene iodide, and then magnetic grains were removed

with a Franz magnetic separator. The zircons were stored and carefully labeled. Mounts

were made by selecting and arranging zircons and standards on a piece of tape, epoxying

the sample, sanding, labelling, and finally, imaging the sample with enough detail so that

individual grains can be seen.

U-Pb geochronology of zircons was conducted by laser ablation multicollector

inductively coupled plasma mass spectrometry (LA-MC-ICPMS) at the Arizona

98

LaserChron Center under the direction of Victor Valencia, during the month of June

2008. The ablation of zircons was done with a New Wave/Lambda Physik DUV193

Excimer laser operating at a wavelength of 193 nm, using a spot diameter of 25 microns.

Ablated material was carried into a GV Instruments Isoprobe, where U, Th, and Pb

isotopes are measured simultaneously in static mode. Each individual zircon analysis

began with a 20-second integration on peaks with the laser turned off (for backgrounds)

and then 20 one-second integrations were completed on each zircon with the laser firing.

The laser operated at 23 KV with a repetition rate of 8 Hz. The resulting ablation pit was

12 micrometers across. Inter-element fractionation was monitored by analyzing crystals

of SL-1, a large concordant zircon crystal from Sri Lanka with a known (isotope dilution

- thermal ionization mass spectrometry) age of 564 + 4 Ma (2a) (G. Gehrels, unpublished

data). The reported ages for zircons from Adanac are based entirely on 206Pb/238U

ratios. The errors of 207Pb/235U and 206Pb/207Pb analyses were too large for the ages

to be considered reliable because of the low intensity signal (<0.5 mV) of 207Pb from the

young (<lGa) zircons. The 206Pb/238U ratios were corrected for common Pb by using

the measured 206Pb/204Pb, the common Pb composition as reported from Stacey and

Kramers (1975), and an uncertainty of 1.0 unit on the common 206Pb/204Pb.

Zircon crystals that were analyzed by the laser but showed evidence of lead loss

or assumed to be metamictic were ignored. A crystal was determined to have suffered

lead loss if, as the laser analyzed successive layers of zircon crystallization deeper into

the center of the crystal these ages did not plateau or become stable (explained in more

detail below). Also, the crystal could be visually determined to be metamictic by

99

displaying a characteristic honey-brown color, indicating radiation damage to the crystal

and thus a mechanism for lead loss.

The reported age of each sample is the weighted mean of 30 individual zircon

analyses, excluding crystals that were then statistically assumed to have experienced lead

loss or statistically assumed to be inherited. A crystal was statistically identified as being

inherited or suffering lead loss if its reported age was outside of a coherent population of

ages (at the 95% level). The weighted mean of all of the crystals believed to have a

reliable age was calculated according to Ludwig (2003). The mean considers random

errors (i.e., measurement errors). Age of standard, calibration correction from standard,

composition of common Pb, and decay constant uncertainty are contributors to the error

in the final age determination. All of these uncertainties are grouped as the "systematic

error." Rocks at Adanac displayed a range of 0.9 -1.7% in systematic error. The error in

the actual age of the sample is determined by quadratically adding the systematic and

measurement error. All age uncertainties are reported at the 2-sigma (2a) level.

Dated lithologies include CGG, CGG-T, SQFP, MFP, MEQM, and two samples

of FGG. CGG, CGG-T, CGG-H, CQFP, and SQFP are all essentially the same intrusion.

They are certainly the oldest rocks (see Chapter 2). The contacts between them are

gradational, the coarse grained unit (CGG) grades upward and outward into both the

transitional and hybrid varieties with increasing groundmass content, or becomes more of

a porphyritic unit. Considered separately and slightly older than these three lithologies

are CQFP and SQFP, which are basically the porphyritic equivalents of CGG and its

transitional and hybrid varieties. They were at one time the upper margin of the intrusion

based on geographic location but the Adera fault has dropped these units to the north.

100

One sample of CGG, CGG-T, and one sample of SQFP were submitted for U-Pb zircon

dating to get an older limit on magmatic ages at Adanac.

Based on cross-cutting relationships, MGP and then the SGP and CGP intrusions

were emplaced. Like the CGG and -T and -H units, SGP and CGP are essentially the

same intrusion with gradational contacts, and their designation as a separate unit is based

on distinct geographic locations and differing phenocryst content. These three units were

not dated because units both older and younger were tested, and this constrains the ages

of these units to within a relatively small range of geologic time.

The relative ages of MEG and MFP are somewhat less certain than other units.

MEG occurs as an intrusion at depth on the southwest end of the deposit, and cuts both

CGG and CGG-T. The MFP unit is a dike that cuts the CGG, CGG-T, and the SGP and

CGP units. It is not known whether MEG is younger or older than SGP and CGP, nor is

the age relationship between MFP and MEG seen. Because the hydrothermal alteration is

the most intense in the southwest area above MEG, this unit is thought to have been

responsible for mineralization. Mineralizing intrusions in other porphyry deposits are

usually directly under the most intense hydrothermal alteration (Westra and Keith, 1981).

Because mineralization cuts the SGP, CGP and MGP, MEG was, therefore, assumed to

be younger than these units as well. MFP, because it is a dike that must have been

emplaced after most or all of the previous units is considered to be one of the younger

units. Both the MEG and MFP were dated by U-Pb. FGG exists in the deposit as dikes

that are always seen to cut everything else. However, two samples of FGG were dated,

one from the pit area and one from the southwest end, to see if there is more than one

generation of these dikes. It was recognized that if MEG and FGG have similar ages to

101

the mineralization it would mean that these units represented, or were at least

synchronous with, the mineralizing intrusion.

Summary results of the isotopic dating are shown in Figure 63. The complete

results, including element concentrations, isotopic ratios, and concordia diagrams are

included in the Appendix.

Sample Lithology Age Error

333-939 FGG(SW) 77.5 +/-1.0 Ma

364-162 MFP 78.5+/-1.4 Ma

314-367 CGG 79.4+/-1.1 Ma

352-1000 CGG-T 79.5+/-1.6 Ma

315-342 SQFP

333-324 MEG

79.9+/-1.5 Ma

80.2 +/-0.9 Ma

364-342 FGG(PIT) 81.6+/-1.1 Ma

75.0 77.0 79.0 81.0 83.0 85.0 Age (Ma)

Figure 63. Results of U-Pb zircon ages for each lithology tested. The sample IDs are the drill hole, the footage depth, and the rock tested. Uncertainties are reported at 2a.

The ages for lithologies at Adanac span 77.5 to 81.6 Ma, giving the Mount

Leonard stock a minimum lifespan of 1 Ma when factoring in errors. Most of the

lithologies ages are indistinguishable from one another due to uncertainties in the

reported age. However, several relationships are apparrent from these ages. On the basis

of the geochronology, FGG from the pit area is older than CGG. This cannot be the case,

as FGG cuts CGG. Also, FGG from the pit area has an age that is older than FGG from

102

the SW area, and these lithologies represent two different FGG intrusions or injections.

This relationship is uncertain, however, due to the fact that FGG (pit) has an incorrect

age. The U-Pb ages in Figure 63 also indicate that there is no intrusion that matches the

age range for the mineralization. The temporal gap between the oldest possible

mineralization (71.23 Ma) and youngest possible magmatism (74.5 Ma) is 3.3 Ma. From

the earliest possible start of magmatism to the latest (or youngest) close of mineralization

would be 13.4 Ma.

There are three possiblilities that could explain the difference in ages and the

relationship between mineralization and magmatism. One possibility is that all of the

reported magmatism ages are correct, and the mineralizing intrusion has not yet been

dated. This seems unlikely because the FGG (pit) age is incorrect relative to CGG. Also,

in porphyry molybdenum deposits, the mineralizing intrusion is usually directly under

mineralization itself. The bulk of molybdenite mineralization at Adanac forms blankets

directly above both MEG and SGP/CGP, and is therefore likely genetically related to

either or both of them.

The second possibility is that the ages are correct, but that the intrusion stayed hot

enough for long enough to account for the temporal gap between the mineralization and

magmatism. This possibility still seems unlikely because the FGG (pit) age cannot be

correct.

The third possibility is that several aspects of the statistically calculated ages are

not relevant or meaningful in this study. First, there is probably a high incidence of

inherited zircons in each lithology that shift the mean age to what is older than reasonably

103

expected. In any given 1000 ft drillhole at Adanac, there may be up to 5 different

igneous intrusive phases that would be passed through in close spatial relationship to

each other. It is unlikely that each of these lithologies did not inherit a significant amount

of zircons from lithologies older than it, including from the Surprise Lake Batholith.

Second, zircons that probably did not experience lead loss were tossed out as such,

further skewing the ages to what is older than reasonably expected. There were two ways

that a zircon could have been considered to have undergone lead loss. If a zircon age fell

statistically below 95% of the population, it was tossed out as anomalous and therefore

likely experiencing lead loss (for example, see figures A-23 - A-35 in the Appendix).

The other way to determine lead loss was more dependant on measurements taken

directly from the zircon crystal. When each zircon from a rock is analyzed for an age, the

laser fires many times and creates an ablation pit in the zircon. Each firing of the laser

reports an age and analyzes successively deeper layers of the zircon crystal. The outer

layers are expected to show some lead loss, and the ages get progressively older as the

laser analyzes closer to the core. If the ages plateau, then the core is considered to

represent a real crystallization age. If there is no plateau of ages, then the entire zircon is

considered to have experienced lead loss, and the particular zircon is not included in the

30 tallied zircons crystals for the weighted mean. Analyses continue until there are a

total of 30 crystals that show reliable core ages. What this means is that zircon crystals

that did show a diagnostically reliable core age were tossed out from the weighted mean

because they were outside of 95% of the population. However, 95% of the population is

not representative of an age for the rock because there are too many inherited zircons.

104

Table 6 shows the lowest reported age for a zircon from each lithology. All of the

zircons in the table had reliable plateau core ages.

Sample 333-939 333-324 -364-342 314-367

352-1000 315-342 364-162

Lithology FGG (SW)

MEG FGG (PIT)

CGG CGG-T SQFP MFP

Youngest Age (Ma) 72.1 +1.0 71.1 + 1.0 74.6 + 2.3 69.0 + 1,2 71.4 + 2.2 72.5 + 1.3 73.1 ±1.1

Table 6. Lowest reported age for a zircon from each lithology. Because they were the lowest reported, the ages were excluded from the statistical mean. Each zircon had a plateau core age.

Most of the ages in Table 6 are slightly older than the mineralization but

not a single zircon gave an age that is lower or younger than one would expect

considering the mineralization ages. If these zircons had experienced lead loss it would

be reasonable to expect that at least some of them would be younger than the

mineralization. What this probably means is that the ages seen here are real

crystallization ages. The two samples of the FGG dikes did not contain any zircons that

are younger than the other lithologies. This is not surprising because the FGG dikes are

low volume lithologies (not much of the rock exists at Adanac, relative to the volume of

other lithologies in the deposit) and this makes it less likely that a zircon that crystallized

completely within the dike would be sampled. Because the FGG dikes cut accross all

other rocks, they probably had a much higher incidence of inheritance relative to other

lithologies in the deposit.

Based on the fact that every lithology dated has some zircons that show no lead

loss and that closely resemble the age of mineralization, it is likely that all of the

105

lithological units at Adanac were experiencing some crystallization right before

mineralization occurred. Therefore, using U-Pb zircon dating does not reliably identify a

single intrusion that caused mineralization. What this does mean is that magmatism

probably began by 82.7 Ma, during the waning stages of crystallization of the Surprise

Lake Batholith, and continued until at least 69 Ma. This represents a time span of about

13.7 Ma. There were a number of inherited zircons from the Surprise Lake Batholith

spanning from 85 Ma to about 90 Ma. There were no inherited zircons from the Fourth

of July Batholith, which is Jurassic in age. The crystallization ages of biotite using the K-

Ar method from 1979 are likely recording the last hydrothermal event they were affected

by, since the closing temperature of biotite using this method is 300°C.

Heaman and Parrish (1991) report that the average U content for zircons in felsic

igneous rocks is 50 - 300 ppm. Most zircons analyzed from Adanac have U

concentrations well above this value (Table 7), making them very high-U zircons and

hinting at the highly evolved nature of the Surprise Lake Batholith and Mount Leonard

Stock. Uranium content in analyzed zircons from Adanac ranged from 250 ppm to

almost 12,000 ppm. This high U content is not surprising, as it was known beforehand

that the Adanac molybdenum deposit lithologies had above background U content.

Typical whole rock analyses of silicic rocks in general show that they contain on average

2-10 ppm U (Peterman, 1963). Adanac lithologies have an average whole-rock U value

of 18 ppm U, and a range of 7 - 34 ppm. It is well-known that U concentrates in magma

throughout the process of differentiation (Peterman, 1963). The average U concentration

in zircons determined in this study is listed in Table 7 for all the lithologies in order of

106

reported age from oldest to youngest, excluding any zircons that were inherited from the

Surprise Lake Batholith.

Sample

364-342 333-324 315-342 352-1000 314-367 364-162 333-939

Lithology

FGG (pit) MEG SQFP

CGG-T CGG MFP

FGG (SW).

Age (Ma)

81.6 80.2 79.9 79.5 79.4 78.5 77.5

Uncertainty (Ma)

1.1 0.9 1.5 1.6 1.1 1.4 1.0

U concentration (ppm) 3883 3812 3342 1855 2761 893

2811

Table 7. Average U concentration (ppm) for zircons that were used to determine ages.

There does not seem to be any correlation between U content and mean age of the

samples. There is also no correlation between age of a single zircon and U concentration,

as shown for each lithology and its associated zircons in the Appendix (Figures A-23 -

A-35). A correlation would have been expected since each successive phase of

magmatism should have concentrated more U. This may be due to the fact that U content

in zircons does not account for all of the U in the rock. Uranium probably exists in the

lattice of the feldspar crystals and in biotite (Peterman, 1963). Because U does not exist

in just one mineral, it is possible that a better analysis of U content related to age or

crystallization sequence can be made using whole rock geochemistry, discussed in more

detail in Chapter 2. The analysis of U concentration on a Harker diagram may

hypothetically be used as a proxy for age, because as a magma moves through its

successive phases of intrusion and crystallization, it should become more highly evolved,

contain more U, and contain a higher weight percent silica. The R2 value for the U

107

Harker diagram diagram was considerably low at <0.05, and therefore showed no real

linear trend at all (Figure A-14). It is important that rocks at Adanac showed no

correlation between age, silica content, and/or U content. For whatever reason, rocks

within the Adanac deposit cannot be shown to have age-related geochemical trends

concerning U.

108

Chapter 7

The Relationship of Placer Gold on Ruby Creek to the Adanac Deposit

There are many similarities between porphyry molybdenum deposits and

intrusion-hosted gold deposits such as Pogo, Donlin Creek, and Fort Knox. These

similarities include redox states and trace and major element chemistry of the host rocks,

and mineral and elemental assemblages of the deposits themselves. Porphyry

molybdenum deposits and intrusion-hosted gold deposits both are hosted in relatively

reduced and alkalic or felsic magmas, and host rocks typically belong to the S-type

magma series (Thompson et al 1999). The trace elements and mineral assemblages

present in intrusion-hosted gold deposits are characterized by bismuth, tungsten, arsenic,

tin, molybdenum, tellurium and antimony. While the Adanac deposit itself contains no

minerals or trace elements in significant quantities other than molybdenum and tungsten,

within 3 miles of the deposit and clearly related to the Mount Leonard Stock are several

deposits and veins (Figure 4) that have the same trace elements as intrusion-hosted gold

deposits. These include elevated tellurium, arsenic, and bismuth, along with wolframite,

gold (unknown whether its native gold or electrum), cassiterite, molybdenum and stibnite

in quartz veins hosted in the same igneous rocks that host Adanac. Gold in intrusion-

hosted deposits like Fort Knox can be concentrated in locations distal (1-3 km) to an

intrusion, is correlated with bismuth and tellurium, and typically occurs in sheeted veins

(Stephens et al, 2004). Molybdenum and tungsten can occur more closely to the

intrusion. Therefore, the mineral assemblage at and within the vicinity of Adanac is

consistent with that of intrusion-hosted gold deposits. Intrusion-hosted gold deposits are

109

also associated with Phanerozoic arc settings and tungsten-tin provinces (like Fort Knox)

(Thompson et al, 1999). This is consistent with the setting for the Adanac molybdenum

deposit, which is very close to Logtung (a porphyry tungsten deposit) and other tin

deposits such as the Germaine porphyry Sn deposit and the JC Sn skarn (Figure 66).

Sack and Mihalynuk (2004) showed that gold from the Atlin camp may be at least in

part derived from an intrusive source, because cassiterite, thorite, and granitoid clasts

were found to be intimately associated with some gold nuggets in the camp. The Surprise

Lake Batholith is enriched in tin and is known to contain thorite. Because the Adanac

deposit occurs at the head of two creeks (the Ruby and Boulder Creek) that have placer

gold deposits on their lower drainages, Adanac presents a good opportunity to test for a

possible genetic link between porphyry molybdenum deposits and intrusion-hosted gold

deposits.

In order to test this theory, Os isotopic contents of placer gold from Ruby Creek were

compared with Os isotopic contents of magnetite from drill core of the Adanac

molybdenum deposit. The placer gold was taken from the mouth of Ruby Creek, and

was an aggregate of small rounded grains (2-10 mm), and were never analyzed for trace

metal content (copper, silver, etc.). The color varied from rose-colored gold to highly

metallic, pure-appearing gold. The magnetite was a larger crystal (5 cm) taken from a

smoky quartz vein within the main pit area of Adanac, with no other vein minerals

present.

In both of these minerals, Re decays to Os, and the Os content is measured

and recorded in ratio to the stable 1880s isotope. The intended method was to take the

110

measured Re and measured Os concentrations and isotopic ratios and calculate

backwards for both samples. Because the age of the magnetite is known, the measured

Re and Os isotopic contents can be plugged into the age equation and generate what is

known as the inital or chondritic Os ratio, or the Os/ Os at the time of that Os

separating from the mantle. For the gold sample, we would have assumed an age (the age

of mineralization at Adanac), and calculated the initail Os. If the age assumption had

been correct, two lines representing the evolution of the Os isotopic ratio (plotted against

time) in the gold and the magnetite would have crossed at a geologically meaningful age

(the age of Adanac mineralization)(Figure 64).

This equation is possible because, if the gold and magnetite are from the same

hydrothermal system, at the time of their formation in the porphyry deposit their Os

isotopic ratios must be the same (even if they have differing Re and Os amounts), and

also must be greater than chondritic Os. The Os isotopic ratios evolve separately after

formation of the porphyry deposit because the different minerals (gold and magnetite)

187 1R7

incorporate different amounts of Re, and Re decays to Os.

If, in Figure 64, the lines had never intersected, the samples would not have been related

because there was never a time in the past that the Os ratios were the same. If they had

intersected but crossed below chondritic Os at the time the surrounding rocks were

formed, the samples could not possibly be related. If the lines had intersected at a

geologically meaningful age (the age of mineralization at Adanac), it would have been

safe to hypothesize they are from the same source.

Hypothetical Diagram of Magnetite and Gold from the Same Hydrothermal System

Measured Os ratio of magnetic M Assumed initial Os ratio of gold,

based on a geologic age of around 70 Ma, which is the age of molybdenite from Adanac

Measured Os ratio of gold

- Calculated initial Os ratio of magnetite

Evolution of mantle Os

90 60 50 40

Time in the Past, Ma

111

Figure 64. Hypothetical diagram showing magnetite from Adanac and gold from Ruby Creek that are from the same hydrothermal system. The measured 187Os/188Os of the magnetite would have been used to calculate the initial Os ratio, because the age of the sample is known. The measured Os ratio of the gold and an assumed age (that of Adanac) would have been used to calculate an initial Os ratio for the gold. If the assumed age of the gold was correct, the lines of Os evolution would have crossed at around 70 Ma. The line showing evolution of Os in the earth's mantle over time is taken from Chen et al. (1998).

Both the gold and magnetite samples were dissolved and homogenized using the

same Carius tube technique as described in Chapter 5 for the molybdenite ages and

analyzed by thermal ionization mass spectrometry. This was done at the Re-Os

geochronology lab at University of Arizona, Tucson, and the results are summarized in

Table 8.

112

Sample

Ruby Creek-1

Ruby Creek-1*

Adanac 351-957

Phase

Au

Au

Mt

187 188

Os/ Os 0.1249

0.1253

1.237

Error

0.0005

0.0005

0.011

187 188

Re/ Os 0.016

0.001

872.25

Os(ppb)

345

4538

0.015

Re(ppb)

1.16

0.82

2.42

Table 8. Results of the gold (Ruby Creek-1 and -1* ; - 1 * is a duplicate of the same gold sample) and magnetite (Mt, Adanac 351-957) analyses.

The gold analyzed had little Re and a resulting very small Re/Os ratio. No age

regression was possible for the gold. For the magnetite, there was not enough material

submitted for multiple analyses, even though the largest known single magnetite crystal

from Adanac was selected for the analysis. Therefore, no isochron could be made for

magnetite, because multiple analyses are needed for an isochron. Regardless of these

problems, the question of whether the gold is related to the hydrothermal system that

generated the Adanac deposit can still be answered with reasonable certainty. The gold

has a Os/ Os that is very primitive, even lower than the current mantle value of

0.129, and so is likely from the mantle, and not from a porphyry deposit (see Figure 65).

Also, the Os content of the gold sample is very large and variable, suggesting the

presence of osmiridium grains, which would be likely in a source associated with

chromites, or peridotites, and not a porphyry deposit. It is interesting that the Os and Re

concentrations of the gold are very high in relation to other porphyry gold deposits, and

actually quite similar to the mantle-derived Witwatersrand in South Africa (Figure 65).

113

100000 j

I I

10000 |

1000 j

3" a 3 100 ' (A o

10

1 )

0.1 -0.1

Re and Os Concentrations in gold samples

- - - • - • - • • • — • - • - - - - • - • - -

.

* • •

•

1 o

1 10

Re (ppb)

|

•

|

100

• Witwatersrand (WA)

• Witwatersrand (VR)

• Ruby Creek

o Grasberg

Figure 65. Os and Re concentrations of some gold deposits compared with gold from Ruby Creek. The Witwatersrand deposit is historically the largest gold deposit in the world, accounting for about 40% of total world production (Frimmel and Minter, 2002) and is mantle-derived (Kirk et al., 2002). The two Witwatersrand samples are from different formations: WA (Western Area) and VR (Vaal Reef). The Grasberg is a porphyry copper-gold deposit in Indonesia. Figure is modified from Kirk et al., (2002).

Although the results of this study suggest the gold on Ruby Creek is unrelated to the

hydrothermal system at Adanac, this does not mean that none of the gold in the Atlin

Camp is related to Adanac. Wallace et al., (1968) report the presence of gold and

wolframite in veins clearly related to the Mount Leonard hydrothermal system in the

Boulder Creek drainage area. Perhaps it would have been better to sample gold from

placers on Boulder Creek rather than Ruby Creek. Perhaps it would have been better to

get multiple samples as well, because if some of the gold is derived from the Surprise

Lake batholith (and the Mount Leonard stock) then this means that gold in the Atlin camp

114

is from mixed sources. Multiple samples would have increased the likelihood of

identifying at least one sample that is igneous-derived.

115

Chapter 8

Characteristics of Porphyry Molybdenum Deposits in the North American

Cordillera and Some Possible Areas that may be Host to More

Porphyry Molybdenum Deposits of the North American Cordillera

The purpose of the last study completed for this thesis is to list important

characteristics of porphyry molybdenum deposits throughout the North American

Cordillera, and determine areas in British Columbia and the United States that may host

more deposits. Several databases were queried for porphyry deposits to make the map

shown in Figure 66. These include the USGS Mineral Resources Data System, the

British Columbia Minfile Mineral Inventory, the Alaska Resource Data File (USGS), the

Yukon Geological Survey Minfile Mineral Inventory, and the paper of Mutschler et al.

(1999). Porphyry molybdenum deposits of low-F and high-F types, Pogo-type porphyry

Au deposits (Thompson et al., 1999), porphyry Cu (-+ Au and Mo), and porphyry Sn and

W deposits are shown on the map in Figure 66. Only those deposits with reserves (each

database listed whether or not there were proven or probable reserves associated with

each prospect) were included in order to increase some confidence about the level of

exploration completed and thus the level of certainty about their classification. The

important porphyry deposits discussed in this thesis are numbered in the Figure.

Descriptive characteristics of some important porphyry molybdenum deposits in the

North American Cordillera are listed in Table 9. References for these descriptions are

116

listed separately (page 195) from other references for this thesis and are linked to the

numbers at the end of each row in the table.

Figure 66 (next page). Porphyry Deposits of the North American cordillera that have reported reserves. Important deposits discussed in this thesis are numbered.

117

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Table 9 (previous 6 pages). Descriptive characteristics of low-F and high-F type porphyry molybdenum deposits in the North American cordillera, with references for each description in the last column. Abbreviations used are as follows: ccpy -chalcopyrite, po -pyrrhotite, mt -magnetite, ref -references, qtz -quartz, moly or mo -molybdenite, sphal -sphalerite, gal -galena, py -pyrite, fl -fluorite, q-s-p -quartz-sericite-pyrite.

All of the deposits listed are associated with some type of porphyry intrusion,

typically of quartz-monzonitic type for low-F types, but some high-F types are associated

with granites or rhyolites (Adanac, Cave Peak, Hope, Questa, Climax, Mt. Emmons, for

example). All deposits are Mesozoic or younger in age, while those Climax-type or

transitional types, especially in the United States, tend to be Tertiary (Nogal Peak, Pine

Grove, deposits in Colorado, some in Idaho, Cave Peak). Some few deposits in Canada

of stated quartz monzonite-type (or low-F) are probably Tertiary as well, such as Red

Bird and Lucky Ship. This is probably the result of high-F types being more associated

with extensional tectonism rather than subduction (Wallace et al. 1995), because

extensional tectonism is a younger event in North America than is subduction. Deposits

associated with extensional tectonism would be farther inboard from the subduction zone,

would have formed at deeper levels in the crust, and have more time to differentiate (and

become enriched in Mo and F) from parent magmas formed from upper mantle materials

(Westra and Keith, 1981).

Mineralization in Climax-type deposits is commonly molybdenite, rare chalcopyrite

and pyrite, huebnerite or wolframite, fluorite and topaz, galena, magnetite, and sphalerite.

Mineralization in low-F types consists of molybdenite, chalcopyrite, pyrite, rare fluorite,

galena, sphalerite, and scheelite. Most deposit types have stockwork veins, but low-F

types have higher incidence of molybdenite disseminated in breccias bodies, or along

intrusive contacts or faults. This may be the result of a lower silica content in quartz

125

monzonite or quartz diorite magmas, or a higher water content which facilitates

formation of breccia bodies. Climax-type ore bodies also more commonly have inverted

cup shapes, centered on and controlled by the apex of porphyry intrusion.

Porphyry molybdenum deposits of all types typically have propylitic (chlorite) and

phyllic (quartz-sericite-pyrite) zones of alteration. Climax types or high-F types also

more commonly have a high silica, or silicified core, and an increased amount of potassic

alteration compared to low-F types, due to the increased amount of silica and K available

for this type of alteration and an increased temperature due to deeper levels of formation.

An even more uncommon type of alteration associated with Climax-types is greisen

alteration, consisting of muscovite, topaz, quartz, and high-F garnet, which forms at very

high temperatures.

Possible Host Rocks for Porphyry Molybdenum Deposits

The Western North American Volcanic and Intrusive Rock Database (NAVDAT)

was queried for all rock types that have silica contents greater than 70 wt %, and that

have Rb/Sr ratios greater than 1. The states that were included in the query are

Washington, Montana, Wyoming, Idaho, Oregon, California, Nevada, Utah, Colorado,

Texas, New Mexico, and Arizona. British Columbia and Yukon Territory were also

included in the queries but produced few results, probably as a result of the NAVDAT

database being primarily one of the United States. All resulting rock types that met these

criteria are shown in Figure 66, along with porphyry molybdenum deposits of both the

low-F and high-F type. The green diamonds represent plutonic igneous rocks (mostly

126

granites) and the black diamonds represent volcanic igneous rocks (mostly rhyolites).

Areas of obvious interest are numbered and the samples that produced these results are

briefly discussed below. The discussion of prospective samples include any geologic

descriptions available from the NAVDAT database and proper names of plutons from

which the samples came. This information is included here because some descriptive

features, such as alteration, make an area more prospective for a porphyry deposit. Only

samples with intrusive rocks that meet the criteria are numbered as areas of interest

because porphyry molybdenum deposits are associated with some intrusive igneous

component, even though they may have extrusive rocks as well.

127

< * 1

Porphyry Molybdenum Deposits and NAVDAT rocks of Si02 > 70

• and Rb/Sr >1

. < • • • • * 4 » 3 < ^ < * • ; •

# 5 ^ *

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1 4 *

- Climax-type porphyry molybdenum deposits

^ Low-F porphyry molybdenum deposits

^ Intrusive NAVDAT rocks (high silica and high Rb/Sr)

^ Extrusive NAVDAT rocks (high silica and high Rb/Sr)

8

• # * 11

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4$ 12 * • * ••• < a 5

16© _15 " ^ ($13 V

Figure 67. The western United States and associated high and low F porphyry molybdenum deposits, and NAVDAT samples with Si02 contents >70 wt% and Rb/Sr >l. Prospective areas for other undiscovered molybdenum deposits are numbered and discussed below.

Washington:

1. This sample of rocks is located in the Western Cascades magmatic arc (Dubray et al.

2006). The samples are from a series of small intrusions existing in a northeast trend

128

in between Mt. St. Helens and Mt. Rainier. There are several Miocene intrusions that

range from quartz monzonite and quartz diorite in composition, and also an area of

argillic alteration on the ground about a mile in diameter. This intrusion is called the

Spirit Lake Pluton, and samples actually may be close to the Margaret porphyry

copper prospect.

Idaho:

2. Area 2 is part of the Idaho Batholith, more specifically the Bitterroot Lobe. The

Bitterroot Lobe is mostly 85-65 Ma granodiorite, but is known to contain granitic

pegmatite bodies (Alt and Hyndman, 1989).

3. Area 3 is a suite of Eocene granitic intrusions and subvolcanic rhyolite that cut the

Cretaceous Idaho Batholith. The intrusions include the Casto, Sawtooth, Lolo, and

Bungalow stocks (Alt and Hyndman, 1989).

4. Area 4 appears to be a trend of high silica and Rb plutonic rocks following the Trans-

Challis Fault Zone, and located within the Atlanta Lobe of the Idaho Batholith. The

samples are mostly reflective of Eocene stocks of the Challis magmatic episode

(Lewis and Kiilsgaard, 1991). Two stocks that produced a lot of favourable samples

are the Prairie Creek and Boulder Mountain (Reppe, 1997). This area is host to the

Cumo, Thompson Creek, and White Cloud porphyry molybdenum deposits, but there

are apparently several favourable stocks in this area.

Nevada:

129

5. These samples are from the Ruby Mountains of the Basin and Range area of Nevada,

and are located in Lamoille Canyon. These samples are of a Late Cretaceous two-

mica pegmatitic gneiss (Lee, 1991).

6. Area 6 is near the low-F porphyry molybdenum deposit listed as the Jolly Roger

claims. The samples are from granitic rocks in the northern Pine Nut Mountains

(John, 1992).

Utah:

7. These samples are from 11 Ma granitic rocks of the Mineral Mountains Batholith.

Nothing else is known about the samples (Coleman and Walker, 1992).

Colorado:

8. This area is east of the Climax type porphyry molybdenum deposits in central

Colorado, and samples are taken from Laramide age (or younger) intrusive rocks in

the Thirtynine Mile volcanic field (Cambell, 1994).

California:

9. This area in southeast California is mostly within the Sierra Nevada Batholith. Some

of the more interesting samples lie within the McAfee Creek muscovite granite (100

Ma) that cuts the Barcroft pluton in the central White Mountains, Mount Barcroft

Area (Ernst et al., 2003). These samples lie on the western most edge of the basin

and range province in Nevada. Other samples have little information about them

because they are part of a region-wide study of Sr isotope characteristics of the Sierra

Nevada Batholith (Kistler and Ross, 1990), or are not interesting from a mining stand

point because they are close to Yosemite National Park (Gray, 2003). Some other

130

interesting samples in this area include the Golden Bear and Coso K-feldspar

porphyry intrusions (dikes) that cut the Independence and Sardine plutons in the

Sierra Nevada, and the Coso leucogranite in the Coso Range, respectively. These

intrusions occur on opposite sides of the Owens Valley and are offset dextrally by 65

km. They are presumably the same intrusion, both 83 Ma (Kylander-Clark et al.,

2003). These areas in California are unknown for porphyry molybdenum deposits,

but many of the rocks in these samples are geochemically similar to rocks in Idaho,

Nevada, and Colorado that are known for porphyry molybdenum deposits.

Arizona:

10. These samples of granites are located in northwest Arizona, along a trend of basin

and range extension. The samples are from two studies by Lang (1991), and Faulds

et al., (1995). The samples on the northern part of the trend are 16 Ma while those on

the southern end are 78 Ma.

14. Samples here are from the Schultze Granite (Stavast, 2006) and also part of the Lang

(1991) study of Laramide igneous rocks in Arizona.

15. These samples are from the Stavast (2006) thesis, like in area #14. These particular

rocks are from the Schultze and Belmont granites. The Belmont granite is especially

unusual for Arizona because it is high in F, Rb, K, and lithophile elements. The

Schultze granite is associated with porphyry copper mineralization, but the Belmont

may be more of a candidate for molybdenum mineralization.

16. These samples are from a middle Cenozoic plutonic complex that is also reported to

131

be extensively altered (Cox et al., 2006). The area is in Pima County in the Ajo

mining district.

New Mexico:

13. These rocks are from the Organ Needle pluton, which is 36 Ma (Verplanck, 1996).

New Mexico and Texas:

11 and 12. Both of these areas are from a study of subsurface Precambrian igneous

rocks (Barnes et al., 1999). Samples in area 11 are from the Panhandle volcanic

terrane, in which there are undeformed rhyolites and granites. Area 12 is in the

crystalline terrane, which is mildly to strongly deformed intermediate to felsic

intrusive rocks. The age of these rocks makes it likely that any associated mineral

deposits are eroded.

Discussion

Prospective sample identifications and associated latitude and longitude, in decimal

degrees, are listed in the Appendix of this thesis, grouped based on areas numbered in the

map. The sample ID can be used in NAVDAT to look up the original data source. The

samples in NAVDAT are obviously biased to those areas that have geochemical studies

published on them, such as areas that already have productive mines. However, this is

somewhat useful because it can be seen in the map that areas with both low F and high F

molybdenum deposits have rocks that give a positive (i.e., fit the search requirements)

identification for prospective molybdenum deposits. This should raise curiosity in other

132

areas that fit the search requirements on the map but are not associated with known

deposits. Some areas, such as 2, 3, and 4 in Idaho are known camps for molybdenum

deposits but the rocks that are geochemically prospective are not the same ones that host

such deposits as Thompson Creek. Therefore, there are probably other undiscovered

deposits in these areas, and the samples that are positive would warrant a field check or

further research. Area 15 is highly interesting, because it is not near any known

molybdenum deposits, yet the rock sampled is clearly a candidate for this type of deposit.

It is an unusual granite for southern Arizona with high amounts of F and K, like Adanac.

Other areas, like Lamoille Canyon in Nevada (area 5) may have hosted a molybdenum

deposit in the past but are less prospective now because of the high degree of

metamorphism it has undergone. The case of southern California is interesting, because

it seems that there are a high incidence of prospective rocks, but this area is not remote

and has been mapped and prospected extensively for other types of deposits. Perhaps the

rocks here are geochemically, but not tectonically favorable. Molybdenum deposits

typically form at deeper depths in the crust, and also require the presence of crust in order

to scavenge elements like Mo and F. The Sierra Nevada batholith may have been too

shallow or too close to the active tectonic margin. Southern California igneous rocks

may have been at least far enough inboard of subduction to have elevated Rb, unlike

northern California igneous rocks.

Another interesting result of this map is that, even though specifically Climax-type

high F molybdenum deposits are supposed to have high Rb/Sr ratios, this parameter

seems to pick up low-F types as well. This probably means that all or most host rocks of

porphyry molybdenum deposits have somewhat elevated Rb relative to other rocks. Of

133

course, some deposits are likely to be under-explored, and may have characteristics

similar to Climax-types, as was the case for Adanac which was originally classified as a

low F type molybdenum deposit. This elevated Rb content of most porphyry

molybdenum deposits makes them easier to find, as opposed to only singling out a more

rare type of molybdenum deposit while ignoring others that may still be very economic.

134

Chapter 9

Conclusions

The Adanac molybdenum deposit is hosted in multiple intrusions that are

classified as alkalic, peraluminous granites that have normal differentiation trends

relative to major oxides. These host rocks are high in silica and potassium. Using the

Westra and Keith classification (1981) Adanac host rocks have a K2O value at 57.5 wt%

Si02 of 5, placing them in the "Climax-type" category. .

Mineralization at Adanac consists of molybdenite blankets or cupolas that occur

over the MEG and SGP/CGP intrusions. Tungsten mineralization, manifested as

huebnerite, is coincident with molybdenite, and fluorine mineralization occurs over and

outward of molybdenite and huebnerite. Lead (galena) and zinc (sphalerite) occur almost

exclusively within faults overprinting molybdenite mineralization. There is very little to

no copper, tin, or gold within the area of molybdenite mineralization. The patterns of

trace elements and mineralization that occur at Adanac are consistent with descriptions of

other Climax-type deposits.

Alteration at Adanac consists of high-silica and potassic alteration cores that

occur above the MEG and SGP/CGP intrusions, even though silica and potassic alteration

are not as intense as described at Climax. QSP alteration is somewhat weak compared to

other Climax-type deposits, because it does not occur as near complete replacement of

host rock but occurs as primarily fracture-fill. This zone occurs further outward from

porphyry intrusions, along with a zone of stilbite-calcite fracture fill alteration that cross

cuts all other alteration types. Propylitic alteration occurs as patchy spots within the

135

higher-grade zone but is strongest further out from QSP and stilbite-calcite zones. Clay

alteration consists of illite and kaolinite in higher-grade molybdenite zones and in deeper,

fresher-appearing rocks. Clay alteration is primarily chlorite, kaolinite, and minor illite

in QSP, stilbite-calcite, and propylitic alteration zones. Montmorillonite is present only

in faults. Alteration characteristics are similar to Climax-type molybdenite deposits.

Molybdenite at Adanac is all of the 2H polytype, like other porphyry molybdenite

deposits, and unlike porphyry copper-molybdenite deposits. The Re concentrations in

Adanac molybdenite are some of the lowest values reported, which may be the cause of

the exclusive 2H polytype.

Re-Os analysis of molybdenite confirmed at least two generations of

mineralization at 70.87 ± 0.36 Ma and about 69.66 ± 0.35 Ma, with the youngest

mineralization occurring at the southwest end of the deposit above the MEG intrusion

and disseminated in a feldspar flood. U-Pb ages of zircons from Adanac host rocks place

magmatism at 81.6 ± 1.1 Ma to 69 ± 1.2 Ma, giving the Mount Leonard stock a probable

life span of almost 14 Ma. When using the weighted mean of 30 zircon analyses for each

lithology, no appropriate age match was found for an intrusion and mineralization

episode, and the FGG (pit) age is certainly incorrect. There are too many inherited

zircons for a mean age to be reliable, and statistical methods for determining lead loss

discredit ages that are most likely valid. It is likely true that most, if not all, of the

lithologies that were dated at Adanac were still undergoing some crystallization just

before (1 Ma) or during mineralization.

136

The gold from Ruby Creek analyzed in comparison with magnetite from Adanac

is derived from rocks more like peridotites than porphyry deposit host rocks. The

question of whether some of the gold in the Atlin camp is igneous-derived remains

unanswered. The next step in answering this question would be to try to get multiple

samples of magnetite from the Mount Leonard stock or the Surprise Lake batholith to

compare with multiple gold samples from the Boulder Creek placers or gold from sheeted

quartz veins to the southwest of Adanac.

Using Rb/Sr and silica content of intrusive igneous rocks is probably a productive

way to search for other molybdenum deposits of both the Climax- and low-F types.

Particularly interesting areas in the western Cordillera of the United States include stocks

and batholiths in both Colorado and Idaho that are underexplored but in known camps of

other molybdenite deposits. The Schultze and Belmont granites in southern Arizona are

particularly interesting because they are not near other molybdenite deposits, and are

unusual granites for Arizona. The rocks are high in K, F, and Rb, and reported from the

NAVDAT database to be enriched in lithophile elements and therefore represent one of

the better areas that are prospective for future molybdenite deposits

137

Appendix of Figures and Tables

Whole Rock Geochemistry and Selected Trace Elements

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138

Table A-l (previous page). Whole rock analysis of fresh lithologies from the composite Mount Leonard Stock. Table also includes some trace elements.

Harker Diagrams

AI203wt%

0 *

68 74

Si02(vvt%)

Figure A-l. AI2O3 Harker diagram

139

4

3 -

2.5

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•

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SK>2(urt%)

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140

Figure A-3. CaO Harker diagram.

141

I s -

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Figure A-4. K20 Harker diagram.

142

Uranium R1 = 0.0465

6S 70 72 74 76 78 80

Si02(wt%)

Figure A-5. U Harker diagram.

143

Mo

80

I 1

•

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•

Si02 (wtX)

Figure A-6. Mo Harker diagram.

144

3000 T Fluorine

Ft! = 0.1781

0 4—

68 74

Si02(wt%|

Figure A-7. F Harker diagram.

145

Mo vs. F

Figure A-8. Plot showing the negative correlation between Mo and F.

Alteration Study:

Clay X-ray Diffraction Results

Sample ID

343-138-148

373-763

301-718-728

301-378-388

348-708-718

348-418-428

348-488-498

333-268-278

348-148

333-748-758

Alteration Descriptin

fault, clay gouge

competent sheared

rock, some clay

fault, clay gouge

fresh

greenish, clay altered,

fractured

competent, slight

discoloratio n (greenish)

silicified

competent, slight blue hue from sericite?

greenish, clay altered

competent sheared

fault, some gouge

Mite

X

X

X

X

X

X

Kaolinite

X

X

X

X

X

X

X

X

Chlorite

X

X

X

X

X

X

Mont-mor-

illonite

X

X

X

X

147

318-759-769

326-285-298

314-638-648

314-278-288

304-218-228

301-378-388

321-89-99

321-449-459

323-158-168

330-659-669

326-618-628

321-459-469

fresh

silicified, fractured, greenish

fault

silicificified, competent,

bluish

competent but greenish

hue

olive green alteration

dark olive green,

fractured

fresh, but Q-S-P veins

oxidized and faulted, clay

gouge

fault, clay gouge

sheared, competent, no gouge

no apparent clay, but

stilbite veins

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

148

Table A-2(this and previous page). Results of clay X-ray diffraction study.

J313-11 (Mno.MDt] Commenfrmotyixlenlte polylype <Psi=0.0>

I,A

17-0740 Mof/bd«nrt«-3R - McS2,M^v) 37-1492* I M y M v M - I H , «yn - Mo62{Matar)

0SO62S> fWto syn - N«a<M^or)

i - i i • • I

Two-Theta (deg)

rXRD|smith264)<cAOocumart» and Settmgslamah264\My Document»tacans> Tuesday. Apr 22. 2006 11:08a (MD1/JADE6)

Figure A-9. XRD scan for molybdenite polytype study. The red peaks represent the pattern for molybdenite 3R, the blue peaks represent the pattern for molybdenite 2H, and the green peaks represent the

standard (halite).

U-Pb Isotopic Age Dates:

Data for Samples and Concordia Plots

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Table A-3 (two previous pages). Sample 333-324 U-Pb isotopic zircon analysis results.

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85 0

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Figure A-18. Zircons discarded from the age calculation for sample 333-939.

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Table A-8(two previous pages). U-Pb isotopic zircon analysis results for sample 364-342.

Figure A-20. Zircons excluded from the age calculation for sample 364-342.

0.014

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a. %

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0.011

7 N Sample 364-342 Concordia Age =

81.6±1.1Ma V MSWD (of concordance) = 12

data-point error ellipses are 2c

0.03 0.05 0.07 0.09 207Pbl235U

0.11 0.13

Figure A-21. Concordia plot for sample 364-642.

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Table A-9(two previous pages). U-Pb isotopic zircon analysis results for sample 315-342.

93.0- I

8 5 . 0 '

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2000 4003 6000

U (ppm)

5000 10003

31S-342

12033

Figure A-22. Zircons excluded from the age calculation for sample 315-342.

135 +

125 +

115 +

data-point error ellipses are 2c

105

Sample 315-342 Concordia Age =

79.9 ±1.5 Ma MSWD (of concordance) =11.6

0.03 0.05 0.07 0.09 207PW235U

0.11 0.13

Figure A-23. Concordia plot for sample 315-342.

NAVDAT Areas of Interest:

Sample IDs and Locations (Decimal Degrees)

Area 1.

SAMPLE ID 9167

9E58B

9174

9I09A

7N98 9R19B 7N135

LATITUDE

46.3903 46.3742

46.315 46.3586

46.4092

46.3219 46.3825

LONGITUDE

-122.078

-122.151

-122.132

-122.185

-122.059 -122.104 -122.111

Area 2.

SAMPLE ID

90TF032

90TF033

90TF046

90TF051A

90TF096

90TF102B

90TF104

90TF105

90TF108

90TF109

91TF070

BCP258

90TF010

981B-26

90TF102A

90RL002

90TF022

90TF032

90TF033

90TF046

90TF064A

90TF066

90TF095

90TF098

90TF099

90TF100

LATITUDE

46.732

46.7643

46.7665

46.8449

46.5504

46.5685

46.5139

46.5124

46.4978

46.4853

46.4762

46.7895

46.6744

46.6358

46.5685

46.7075

46.6294

46.732

46.7643

46.7665

46.7194

46.7133

46.5616

46.5319

46.5548

46.57

LONGITUDE

-115.551

-115.494

-115.382

-115.619

-114.969

-115.07

-115.109

-115.117

-115.155

-115.155

-115.088

-115.598

-115.058

-115.512

-115.07

-115.092

-115.475

-115.551

-115.494

-115.382

-115.123

-115.108

-114.93

-115.057

-115.072

-115.067

Area 3.

SAMPLE ID

78WM010A

78WM021A

78WM081B

78WM097B

78WM184A

78WM194B

79WM021A1

79WM081

787-21B

787-21C

787-21D

787-25A

981B-19

89RL072

92TF139

92TF120

92TF150

92TF151

92TF155B

92TF113

92TF108

92TF114

92TF118

92TF119

92TF120

92TF150

92TF151

92TF152

92TF153A

92TF154

92TF167

92TF172

92TF174

LATITUDE

45.9698

45.9242

46.034

46.093

46.1405

46.034

46.093

45.7725

45.9833

45.9817

45.9733

46.125

45.7067

45.7614

45.4117

45.5305

45.6976

45.7029

45.6308

45.6242

45.5119

45.6463

45.5301

45.5305

45.5305

45.6976

45.7029

45.733

45.6818

45.6659

45.636

45.6533

45.7278

LONGITUDE

-114.841

-114.883

-115.007

-115.117

-114.97

-115.007

-115.117

-114.674

-114.965

-114.965

-115.002

-114.933

-114.6

-114.782

-114.373

-114.439

-114.54

-114.631

-114.834

-114.854

-115.041

-114.6

-114.437

-114.439

-114.439

-114.54

-114.631

-114.744

-114.81

-114.807

-114.92

-114.948

-115.077

Area 4 (next page).

SAMPLE ID

84-5

84-11

85-56

84-32

CBC87-24

DPI

K47

L81-28

MCR 7 82

MCR 7 83

MCR 7 29 1

MCR 7 29 2

MCR 7 30 2

MCR 7 30 3

MCR 7 30 5

MCR 7 3 1 1

MCR 7 312

MCR 8 13 1

MCR 8 13 2

MCR 8 13 3

MCR788

MCR 7 5 7

MCR744

MCR745

MCR 7 4 6

MCR 6 30-1

MCR 6 30-2

MCR 7 5 3

MCR74 2

MCR 7 1-4

THR 62995-1

THR 62995-2

THR 62995-3

THR 62995-4

THR 62995-5

THR 70395-2A

THR 70395-3A

THR 70595-4B

THR 70595-7

THR 70795-1

THR 70895-1

THR 70895-2

LATITUDE

43.7014

43.7411

43.7

43.6856

44.1736

43.4

44.0729

43.55

43.8269

43.8275

43.8244

43.8236

43.8203

43.8242

43.8283

43.8244

43.8264

43.8319

43.8347

43.8375

43.8261

43.8289

43.8297

43.83

43.8303

43.8303

43.8297

43.8311

43.8258

43.8364

43.7419

43.7414

43.7453

43.7461

43.745

43.7539

43.7533

43.7528

43.7519

43.7569

43.75

43.7497

LONGITUDE

-114.72

-114.669

-114.734

-114.646

-114.944

-115.65

-115.265

-114.9

-114.547

-114.548

-114.553

-114.553

-114.557

-114.555

-114.557

-114.575

-114.574

-114.579

-114.579

-114.579

-114.546

-114.544

-114.537

-114.538

-114.538

-114.538

-114.538

-114.547

-114.534

-114.539

-114.632

-114.633

-114.633

-114.634

-114.635

-114.646

-114.645

-114.646

-114.646

-114.651

-114.647

-114.645

SAMPLEJD

TAM18

TAM5

TAM11

86RL-257

86RL-386

CBC87104B

CBC87-19

CBC87-23

CBC87-42

CBC87-82

L86-33

L86-37

L86-38

73-Tg

78-Tga

83-Tr

107-Tr

65-Tr

KR57T

RR135C

8519K

86135K

8725K

RL374

RL73

981B-59

98IB-61

MCR 6 30-3

MCR 6 30-4

MCR 6 30-5

MCR 6 30-6

MCR 6 30-7

MCR 6 29-4

MCR 6 29-5

MCR 6 29-6

MCR 6 29-7

MCR 6-29-8

MCR 6-29-9

MCR 7 29 4

MCR 31 3

MCR 315

MCR 7 8 5

LATITUDE

43.7

43.7047

43.7056

43.4833

43.5439

44.0597

44.2056

44.1736

43.4

44.3

43.8264

44.2875

44.2875

43.9139

43.9083

43.9175

43.9006

43.9178

44.0098

43.8458

43.6383

43.69

43.7814

43.5533

43.5533

43.655

43.7128

43.8297

43.83

43.8286

43.8286

43.8283

43.8264

43.8269

43.8264

43.8269

43.8258

43.8256

43.8228

43.8264

43.8356

43.8267

LONGITUDE

-114.721

-114.695

-114.692

-114.967

-114.878

-115.731

-115.098

-115.018

-115.857

-115.631

-114.578

-115.158

-115.158

-114.505

-114.512

-114.518

-114.453

-114.498

-115.372

-114.591

-115.828

-115.668

-115.32

-115.83

-115.83

-115.738

-115.628

-114.537

-114.536

-114.538

-114.538

-114.539

-114.537

-114.538

-114.539

-114.539

-114.539

-114.539

-114.553

-114.574

-114.566

-114.547

173

Area 5.

SAMPLE ID

SPI-A

64W66

RM-47-66

RM-11-66

J l

RM-17-66

RM-19-66

RM-1-67

B110

B120

B130

B170

B90

H80RUBY2*

H83RUBY106* H83RUBY108*

IL180

IL20 IL40

IL50

IL70 IL80

ILI-26 LEE-11

LEE-4BB

LEE-4BM

LEE-5

LEE-7

LEE-8

RD-IOC

RD-lOE

RD-13av

RD-19C-analysisl

RD-19C-analysis2

RD-20

RD-21

LATITUDE

40.851

40.5159

40.4125

40.3874

40.3874

40.3942

40.4267

40.3089

40.6048

40.6064

40.605

40.6082

40.6067

40.6175

40.6175 40.6175

40.6199

40.6159

40.622

40.6174

40.6157

40.6224

40.6083 40.6022

40.6481

40.6481

40.6438

40.6481

40.6438

40.585

40.585

40.6146

40.6012

40.6012

40.6012

40.6011

LONGITUDE

-115.237

-115.555

-115.545

-115.499

-115.499

-115.435

-115.432

-115.501

-115.39

-115.389

-115.379

-115.378 -115.39

-115.392

-115.392

-115.392

-115.387

-115.378

-115.375

-115.388

-115.389

-115.375

-115.387

-115.381

-115.407

-115.407

-115.411

-115.407

-115.411

-115.393

-115.393

-115.375

-115.379

-115.379

-115.379

-115.38

SAMPLE ID

RD-23

RD-28

RD-29

RD-32

RD-4

RD-5

RD-57

RD-59

RD-70

RD-73

RD-74

RD-79

RD-7B

RD-81

RD-82

RD-83

RD-84

RD-85

RD-88

RD-89

RL-16A

RL-16B

RM-20

BB-103-94

CB-295

HP-39-95

BB-17-93

BB-102-94

HP-8-95

HP-11-95

BB-99-94

HP-17-95

HP-21-95

HP-28-95 RD-22

LATITUDE

40.6021

40.5942

40.601

40.6008

40.6009 40.5997

40.6065

40.6029

40.606

40.6099

40.6099

40.5959

40.5935

40.6148

40.6147

40.6147

40.6022

40.6022

40.5945

40.5925

40.6672

40.6672

40.778

40.3057

40.3393

40.3681 40.3687

40.3033

40.3405

40.3421

40.3396

40.3018

40.2988

40.3897

40.6011

LONGITUDE

-115.377

-115.387

-115.381

-115.382

-115.38

-115.381

-115.384

-115.381

-115.385

-115.385

-115.385

-115.392

-115.383

-115.377

-115.376

-115.376

-115.387

-115.387

-115.386

-115.385

-115.446

-115.446

-115.311

-115.504

-115.473 -115.557

-115.555

-115.504

-115.563

-115.559

-115.534 -115.521

-115.539

-115.526

-115.38

Area 6.

SAMPLE ID

F16

F17

FI2

FI5

92-DJ-88

90-DJ-19

87-DJ-202

92-DJ-37

91-DJ-41

91-DJ-9

91-DJ-32

88-DJ-118

88-DJ-115

87-DJ-150

87-DJ-76

87-DJ-71

87-DJ-69

87-DJ-68

87-DJ-67

LATITUDE

38.8895

38.8897

38.8896

38.8895

39.625

39.625

39.625

39.625

39.625

39.625

39.625

39.5889

39.59

39.0197

39.8458

39.8458

39.8481

39.8486

39.1578

LONGITUDE

-118.182

-118.182

-118.182

-118.182

-118.25

-118.25

-118.25

-118.25

-118.25

-118.25

-118.25

-118.193

-118.189

-118.315

-118.208

-118.201

-118.207

-118.219

-118.38

Area7.

SAMPLE ID MM88-12

MM88-20

MM88-3 MM88-8 MM89-4

LATITUDE

38.5133

38.3178 38.3631 38.3617

38.3536

LONGITUDE

-112.76 -112.832 -112.844

-112.779 -112.812

Area8.

SAMPLE ID

A LG-1-145 SRMS-1-96

SRMS-2-97

48

50 OIL-16

LATITUDE

38.5636 38.3319

38.327

38.49 38.67

38.283

LONGITUDE

-106.311

-105.793

-105.796 -106.53

-106.25 -106.672

Area 9. SAMPLE ID

MP-192

MP-845

MP-117

MP-156A

HD01-83

MG-2

HL-29

DVB-110

DVB-117

DVB-131

21C

29-0

49C

97A

7A

46B

104A

AB-1011-10

AB-1011-17

AB-1011-31

AB-1011-8

LGC-11

LGC-25

LI-35

M742

1S82

1S128

LATITUDE

37.6333

37.65

37.5667

37.55

37.8449

37.2283

37.1083

35.3153

35.6361

35.1939

37.0567

37.0439

37.1878

37.2117

37.0994

37.1494

37.1972

36.8167

36.7833

36.1667

36.7583

35.7425

35.6874

35.7128

36.9842

37.0883

37.1346

LONGITUDE

-119.317

-119.417

-119.383

-119.367

-119.373

-118.595

-119.145

-115.582

-116.275

-116.143

-118.558

-118.57

-118.614

-118.548

-118.644

-118.617

-118.551

-118.9

-118.625

-118.7

-118.95

-118.411

-118.416

-118.392

-118.744

-119.133

-118.455

SAMPLEJD

68M40

67M46

67M93

68M2

68M1

M794

FC01-03

IP0203

85S74

HD01-78

HD02-96

IP0203

1S23

1S24

1S27

1S28

1S29

1S51

1S52

1S53

1S54

1S58

1S77

1S79

1S80

1S81

LATITUDE

36.8974

36.9081

36.7755

36.7759

36.7795

36.7817

35.6957

36.7602

36.5617

37.8391

37.8311

36.7603

36.7189

36.7191

36.714

36.7147

36.7153

37.104

37.1011

37.0999

37.0986

37.082

37.0993

37.0963

37.0942

37.0901

LONGITUDE

-118.656

-118.679

-118.63

-118.616

-118.615

-118.64

-118.239

-118.262

-118.554

-119.486

-119.349

-118.262

-118.961

-118.962

-118.975

-118.976

-118.977

-119.09

-119.09

-119.094

-119.101

-119.136

-119.109

-119.11

-119.118

-119.126

Area 10.

SAMPLE ID 93-80

93-77

93-91

B21 D42

D51

LATITUDE 35.5428

35.5336

35.5844 34.5944

34.8436 34.8392

LONGITUDE

-114.558 -114.512

-114.482

-113.233

-113.773 -113.76

Area 11.

SAMPLEJD

509

513

620

LATITUDE

36.3996

35.6133 36.7213

LONGITUDE

-102.245

-101.999 -103.333

Area 12.

SAMPLE ID

502

519

520

LATITUDE

33.5356

33.5529

33.4491

LONGITUDE

-100.85

-100.275

-100.133

Area 13.

SAMPLE ID

TmoeDl

SUM

RE1

3591

3491

3691

3791

292

192

1691

3891

LATITUDE

32.3027

32.3454

32.3676

32.4153

32.4153

32.4153

32.2611

32.2611

32.3411

32.3417

32.4153

LONGITUDE

-106.535

-106.564

-106.588

-106.592

-106.592

-106.592

-106.533

-106.54

-106.492

-106.486

-106.592

Area 14.

SAMPLEJD

R34 DM04-564

DM04-633B

DM04-589 BS04-329

BS04-246D

BS03-51 BS05-845

DM04-600

DM04-665 BS04-264

LATITUDE

33.155 33.3417

33.3492 33.3594

33.3436

33.3596

33.3578 33.3693 33.3527

33.3618

33.3531

LONGITUDE

-111.051 -110.892

-110.847

-110.852

-110.898

-110.879 -110.957 -110.983

-110.85

-110.878 -110.85

Area 15.

177

SAMPLE ID

BS05-565

RS028 F2-6694

BS05-564

LATITUDE

31.8867

31.94

31.9167

31.8818

LONGITUDE

-111.24

-111.155

-111.208 -111.239

Area 16.

SAMPLE ID

24

lOlTfg

LATITUDE

32.3667

32.378

LONGITUDE

-112.901

-112.881

178

References

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