6 NENANA BASIN, ALASKA by CIA Merrittdggs.alaska.gov/webpubs/dggs/pdf/text/pdf1985_019.pdf · NENANA BASIN, ALASKA by Roy CIA Merritt ... NENANA BASIN, ALASKA b Y Roy D. Merritt

PDF 85-19

FIELD TRIP GUIDEBOOK: LIGNITE CREEK AND HEAh\6 CREEK COAL FIELDS,

NENANA BASIN, ALASKA

by Roy CIA Merritt

Coal Geologist Alaska Division of Geological and Geophysical Surveys

Fairbanks, Alaska

AAPG-SEPM-SEG Pacific Section, 60th Annual Meeting 'Alaskan and West Coast Geology and Energy and Mineral Resources'

Post-Convention Field Trip, May 27, 1989

FIELD TRIP GUIDEBOOK:

LIGNITE CREEK AND HEALY CREEK COAL FIELDS,

NENANA BASIN, ALASKA

b Y

Roy D. Merritt

THIS REPORT HAS NOT BEEN REVIEWED FOR TECHNICAL CONTENT (EXCEPT AS NOTED IN

TEXT) OR FOR CONFORMITY TO THE EDITORIAL STANDARDS OF DGGS.

AAPG-SEPM-SEG Pacific Section, 60th Annual Meeting

'Alaskan and West Coast Geology and Energy and Mineral Resources'

Post-Convention Field Trip,

May 27, 1985

'Hydraulic pit,' Usibelli Mine, Healy Creek coal field, Nenana basin. Coals (No. 1 M No. 2 Seams shown) hydraulically mined in late 1950's to early 1960's (1981 photo). Stop No. 6.

FIELD TRIP GUIDEBOOK: LIGNITE CREEK AND HEALY CREEK COAL FIELDS. NENANA BASIN. ALASKA

by Roy D . Merritt

CONTENTS

(Page

Field trip itinerary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v i Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Coal production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 3.7 Usibelli Coal Mine. Inc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.20 Synopsis of Nenana basin coal geology . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 . 52

Location and access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-21 General geologic setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-23 Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Physiography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Distribution of coal.bearingrocks ......................... 24-25

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structural geology 25-27 Regional tectonism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 General stratigraphy and lithology of the coal-

bearing group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-36 Healy Creek Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Sanctuary Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Suntrana Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-34 Lignite Creek Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32, 35 Grubstake Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-36 Nenana Gravel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Depositional environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36-40 Healy Creek Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sanctuary Formation 39 Suntrana Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Lignite Creek Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Grubstake Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Nenana Gravel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Coal petrology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-43 Coal quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44-47 Coal resources and reserves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44.4 8-50

Healy Creek field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Lignite Creek field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48. 50

Overburden character and reclamationpotential ............. 50-5 2 References cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53-55 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56-57

ILLUSTRATIONS

Figure Page 1 . . . . .A laska ' s coal basins. fields. and isolated coal

occurrences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 . . . . . Alask a and Nenana coal production . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 . . . . . Suntran a Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 . . . . . 01 d Healy Creek tipple of Usibelli Mine and coal

. . . . . . . . . . . . . . . . beds of Healy Creek and Suntrana Formations 6 . . . . . . . . . . . . . . . . . . 5 I n a c t i v e mine sites. prospects. and facilities 8

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 . . . . . 01 d Healy Creek wash plant 9 7 . . . . . Usibell i Coal Mine. Inc . road and mileage map . . . . . . . . . . . . . 1 0 8 . . . . .Section s of Suntrana Formation at Poker Flats

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . and Two Bull Ridge 11 ........... 9 . . . . . Sequenc e of operation at the Usibelli Coal Mine 1 2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 . . . . . 'Ace-in-the-Hole1 dragline 13 11 . . . ..Poke r Flats pit. Usibelli Coal Mine . . . . . . . . . . . . . . . . . . . . . . . 1 3 12 . . . . . State of Alaska coal-lease areas . . . . . . . . . . . . . . . . . . . . . . . . . . 15 13 . . . . . Gold Run Pass Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 14 . . . . . Cros s and stratigraphic sections for Gold Run

Pass Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 15 . . . . .Generalize d location map of Alaska r a i l b e l t region . . . . . . . . 1 8 1.6 . . . . . Usibell i Coal Mine shop-office-warehouse complex

and tipple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 17 . . . . . Coa I hopper at Usibelli Coal Mine tipple east . . . . . . . . . . . . . 1 9 18 . . . ..Generalize d geologic map of Nenana coal basin . . . . . . . . . . . . . 2 1 19 . . . . . Majo r coal fields of Nenana basin . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 20 . . . . . Cros s section through the western Lignite Creek

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . and Healy Creek fields 27 21 . . . . .Generalize d section of the coal-bearing group

............................................... a t s u n t r a n a 2 9

2 2 . . . . . Stratigraphi c nomenclature. stage. and series for coal-bearing group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

23 . . . . . Ind iv idua 1 cycles of sedimentation and depositional types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

24 . . . . . Basi c lithologic components and depositional types for fining-upward cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2 5 . . . . .Depositions 1 models representing paleoenvironmental conditions during formation of coa l - bearing group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

. . . . . 26 V i t r i n i t e reflectance frequency histogram for Nenana basin coal samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

27 . . . ..Rang e in rank parameters for Nenana basin coal samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

28 . . . . . Ba r graph of total and pyritic sulfur in Nenana basin coals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

29 . . . . . Trace element contents in Nenana basin coal ashes . . . . . . . . . 4 7

Table Page

1 . . . ..Chronology of coal mining history for Nenana coal basin . . . . . . . . . . . . . . . . . . . . . . . * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 . ..Summary of coal petrologic data for Nenana basin samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2

3 . . .Proportions of the three maceral groups in coal samples of the coal-bearing formations of the Nenana basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

4 . . .Summary of proximate and ultimate analysis data for the Nenana coal basin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

5 . ..Summary of the coal resources of Alaska . . . . . . . . . . . . . . . . . . 49

6 . . ..Estimates of potentially minable coal resources in fields of Nenana basin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

7 . . . . .Geochemical and physical characteristics of Nenana basin overburden samples.,. .............................. 52

FIELD TRIP ITINERARY

Time

Depart from Mt. McKinley Park Station Hotel.....................8:00 a.m.

Meet Usibelli Coal Mine representative (Mitch Usibelli) at Stop No. 1

. . . Stop No. 1 ..Golden Valley Electric Association Power ide-bus) Plant at Healy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8:30 a.m.

Roy Merritt---introductory comments Mitch Usibelli---power plantlintertie

Stop No. 2.....Suntrana---Healy Creek tipple; type sec- (de-bus) tion for coal-bearing group ...................... 9 : 0 0 a.m.

Roy Merritt---geology summary Don Triplehorn---comments Mitch Usibelli---facilities

. . . Stop No. 3 ..Suntrana roadcut---Healy Creek Formation, ide-bus) burn rock, plant-fossil collecting ............... 9:30 a.m.

Roy Merritt---comments Don Triplehorn---comments

Stop No. 4. .... Suntrana Mine---underground entrance . . . . . . . . . . . . 10:OO a.m Mitch Usibelli---comments

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stop No. 5 . . . . .Wash plant 10: 10 a.m. Mitch Usibelli---comments

. . . . *Stop No. 6 .Hydraulic pit---reclamation, dall sheep Mitch Usibelli---comments Roy Merritt---comments

Stop No. 7.. .. .Gold Run Pass ----ancillary pit of Usibelli ide-bus) Coal Mine; upper Lignite Creek-Jumbo Dome.......10:30 a.m.

Roy Merritt---geology and resources Don Triplehorn---geology Mitch Usibelli---mine

*Stop No. 8.. . . .Poker Shop Mitch Usibelli---comments

.................... Stop No. 9 . . . . .Poker Flats Pit - - -dragl ine . .I1 : 15 a.m. ide-bus) Roy Merritt---comments

Mitch Usibelli---mining methods

*Stop No. 10 . . .Lignite Creek road construction---Two ~ u l l Ridge area, site of future mining

Mitch Usibelli---comments

Stop No. 11 . . . .Usibelli Coal Mine tipple and shop-warehouse- ide-bus) off ice complex. , , .. , . , . , .... , ................... 12 : 00 Noon

Mitch Usibelli---facilities Roy Merritt---final comments

Lunch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12:15 p.m. Field trip break-up, departure for Anchorage or Fairbanks

*Optional stop depending on schedule

V i

INTRODUCTION

The field trip today will focus on the geology and coal resources of

the Lignite Creek and Healy Creek fields of the Nenana basin, interior

Alaska (Figure 1). These fields contain the largest coal resources of the

region, and they will continue to play a prominent role in Alaskan steam

coal production for both in-State use and export to the Pacific rim. Be-

cause of their strategic location adjacent to the Alaska Railroad and

Parks Highway corridor near the Nenana River, the two fields contain the

most economic coal deposits of the region.

COAL PRODUCTION

Coal production has been relatively continuous in the Nenana basin

since about 1916 (Figure 2). Important events in the development of the

coal basin are listed in table 1. All of Alaska's post-1970 coal produc-

tion and much of the State's production prior to 1970 is accounted for by

that of the Usibelli Coal Mine and other operations in the western Nenana

basin. About one-third of the 32-million-short-ton Alaska production is

estimated to have been mined in the Healy Creek basin. Another third has

been produced on Lignite (Hoseanna) Creek, mainly at Poker Flats. The re-

maining third was produced in the Matanuska Valley (about 7.5 million

short tons) and elsewhere in Alaska.

Early mining in the Nenana basin was mainly by underground methods.

The Suntrana Mine on Healy Creek was in nearly continuous production from

1922 to 1962, when serious fires forced its closure (Figure 3). The mine

has two main underground entrances; one a d i t is observable from the Healy

Creek road (Stop No. 4). Mining in the Nenana basin in the future will

predominantly use open-pit surface methods. Most mining to date in the

Healy Creek and Lignite Creek fields has occurred in the F bed of the

Healy Creek Formation and numbers 1 , 2 , 3 , 4 , and 6 beds of the Suntrana For-

mation (Conwell, 1976). Many of these beds can be seen behind the old

Healy Creek tipple at Suntrana (Figure 4; Stop No. 2). Numerous outcrop-

ping seams near Suntrana have spontaneously combusted over the years form-

ing abundant red burn rock in the canyon walls. These burned seams are of-

ten promising plant-fossil collecting sites (Stop No. 3). The locations

1450- ---- Total coal production - Nenana coal field production

1400- . ****** Total surface-mining production

5

Surface mining

YEAR

Figure 2. Alaskan and Nenana coal production (1915-1985) by underground and surface mining methods.

3

Table 1. Chronology of coal mining history for the Nenana coal basin.

.First geologic reconnaissance of the Nenana coal fields.

. .President Woodrow Wilson and the U.S. Congress pass the Alaska Rail- road Act authorizing the construction of the Alaska Railroad to pass through the Nenana coal basin.

.The Alaska Railroad reaches the Nenana coal fields

..Over 30,000 tons of coal are produced at the Peterson Mine by the Healy River Coal Corporation on the west bank of the Nenana River opposite the mouth of Healy Creek.

. . The Alaska Railroad is completed to Nenana af ter the construction of the Riley Creek Bridge at McKinley Park. A 4.4mile rail spur up Healy Creek is completed and the Suntrana Mine is established.

.The Mt. McKinley Bituminous Coal Company operates the Yanert Mine

..The Suntrana Mine produces nearly half of the total coal mined in Alaska.

..The Suntrana Mine is the largest coal mine in the Alaskan Territory.

..Over 60,000 tons of coal are produced from the Dunkle Mine on Cos- tello Creek west of Broad Pass for use by the Alaska Railroad.

. .T rad i t i ona l underground coal mining in Alaska gives way to surface mining methods with the opening of two strip mines in the Nenana coal basin.

. .Emile Usibelli and T.E. Sanford open a strip mine on Healy Creek east of the Suntrana Mine under a U.S. Army license. This mine was a fore- runner of the Usibelli Coal Company of today.

..The Gold Run Pass Mine on upper Lignite Creek is opened.

. .About 900 tons of coal are produced at a small mine in the Jarvis Creek field.

..Emile Usibelli purchases the Suntrana Mine.

. .The Suntrana Mine is closed because of serious fires.

..A mine-mouth power plant is built at Healy that supplies electricity to the Golden Valley Electric Association of Fairbanks.

..The Usibelli Coal Mine becomes the only significant operating coal mine in the state of Alaska.

. . U s i b e l l i Coal Company's Poker Flats Mine on Lignite Creek is opened.

. . U s i b e l l i Coal Mine signs initial contract with a South Korean consor- tium to provide 880,000 short tons of Alaska coal annually for export to that Far East nation.

. .Delta Coal Company of Fairbanks receives a mining permit from the U.S. Bureau of Land Management on its preference-right lease in the Jarvis Creek field.

. .Alaska1 s first deep-water coal port is developed at Seward. The first shipment of Usibelli Coal Company's coal is made to South Korea under Sun Eel contract.

F i g u r e 3 . The Suntrana Mine, Healy Creek f i e ld , opened i n 1 9 2 2 and closed 40 years l a t e r .

Figure 4. Old C s i b e l i i l Mine tipple at Suntrana with coal beds B,D,F,G (Healy Creek Formation) and 1 and 2 (Suntrana Formation) in the b<irk--l ground. Stop No. 2.

of several inactive mine sites, prospects, and facilities in the western

Nenana coal basin are shown in figure 5. Abandoned mine facilities on

Healy Creek include the old tipple and wash plant (Figure 6; Stop No. 5).

USIBELLI COAL MINE, INC.

The Usibelli Coal Mine, Inc. (UCM) has been the only significant

operating coal mine in Alaska since 1971. In recent years the mine has

produced over 800,000 short tons of subbituminous coal from the Lignite

Creek field of the Nenana basin. UCM's past production has mainly been

used for heating and generation of electricity for the city of Fairbanks

(including four area power plants), interior Alaska military bases (Ft.

Wainwright Army Base, Clear and Eielson Air Force Bases), the Golden

Valley Electric Association's (GVEA) power plant at Healy (Stop No. I ) ,

and the University of Alaska. Of the 803,000 short tons produced in

1983, about 625,000 short tons were transported via the Alaska Railroad

to these consumption points. The 25-megawatt coal-fired plant of the

GVEA used 140,000 tons of UCM coal to produce 200 million kwh of elec-

tricity or about 60 percent of the utilities power requirement in 1980

(Land, 1981). UCM's 1984 production was about 850,000 short tons.

Currently at UCM's Poker Flats pit on the south side of Lignite

Creek (Figure 7; Stop No. 9), numbers 3 , 4 , and 6 seams of the Suntrana

Formation are being mined and contain most of the reserves of the area

(Denton, 1981). The three beds total about 60 ft of coal in a 235-ft sec-

tion (Figure 8). A modified box-cut strip mining (open pit) method is

used. Figure 9 illustrates the general sequence of operation at Poker

Flats. The overburden:coal ratio is less than 5:1, and the poorly indur-

ated overlying sandstones of the coal beds produce favorable stripping

conditions. In 1978, the Bucyrus Erie ' Ace-in-the-Hole ' dragline was

assembled at the Poker Shop warehouse (Stop No. 8) and began overburden

stripping operations (Figures 10 and 11) . The 4.3 million pound machine 3 with a 33-yd' bucket capacity is the largest single piece of equipment

in Alaska. It has stripped some 400 million yd3 of overburden to uncover

the 800,000 short tons of coal produced in recent years. After the over-

burden is stripped, the coal is removed, loaded, and transported by a

loader-truck combination.

After completing the mine cycle at Poker Flats, UCM will move into

E X P L A N A T I O N

Mine,

prospect,

f a c i l i t y

n u m b e r N a m e

Minr,

p r o s p a c t , L o c a t i o n f a c i l i t y

r y p e * L a t i t u d e L o n g i t u d e n u m b e r Name

M o o s e Seam s C a r i b o u Seam S

A r c t i c C o a l C o . M ine s Mi le 3 6 3 Mine U

Gold Run Pass No. 2 s Gold Run Pass No. 1 3 B u r n s M ine (M i l e 3 6 2 ) U

H e e l y C reek A d i t s u U p p e r H e a l y C k . M i n e s R o t h - T a y l o r M ine S

C r l p p l e C r e e k M i n e S

Cripple Creek Wes t S

F r e n c h C reek S

t i e s l y C reek T i p p l e F

S u n t r a n a P e t e r s o n M ine &

New M ine

D i a m o n d C o a l M i n e

M o o d v C reek

M i l e 3 5 3 P r o s p e c t

Sanc tua ry A

Savage River Suahana Tek lan i ka R i ve r

H i n r s C reek

Yan0r t M i n e

Sab le M o u n t a i n

P o l v c h r o m e M o u n t a i n

L o c a t i o n

T y p e w L a t i t u d e L o n g i t u d e

'P : prospect (@), S = surface mining activity (a); U u n d e r g r o u n d m i n e a c t i v i t y (a), U I S - hoth underground and surface mine a c t i v i t y ( + I : F f a c i l i t y (A). Note that 'mine' here connotes generally small-gcalo operations.

Figure 5. Generalized map of the western Nenana coal basin showing the locations of inactive mine sites, prospects, and facilities.

Figure 6. Old wash plant of Usibelli Mine on Healy Creek Stop No. 5.

Figure 7. Road and mileage map of the Healy Creek and Lignite Creek region showing the location of Usi- b e l l i Coal Mine, Inc.'s Poker Flats pit (from U s i b e l l i Coal Mine, 1984).

I Figure 8A.

I Typical section of Suntrana Formation at Poker Flats. From Denton, 1981.

S t o ~ No. 9

Figure 8B. Schematic structural sections of upper part of Suntrana Formaticn of lower Lignite Creek. From Denton, 1981. Stop Nos. 9 & 10

1 Two Bull Ridge

o r i g i n a l s u r f a c e --

P R O F I L E S H O W I N G 3 S E A M M I N E D A N D 4 S E A M H I G H W A L L

o r i g i n a l s u r f a c e i 4 w a s t e e x c a v a t e d \- --

4 seam

3 seam

o r i g i n a l s u r f a c e

P R O F I L E S H O W I N G 4 S E A M W A S T E E X C A V A T E D

. . - - _ \

4 s e a m m l n e d - - ? 3 w a s t e

- - - --- .- - . 3 r e a m ----- - -\

P R O F I L E S H O W I N G 4 S E A M C O A L M I N E D

P R O F I L E S H O W I N G 3 S E A M W A S T E E X C A V A T E D


P R O F I L E S H O W I N G 3 S E A M M I N E D

P R O F I L E


l e v e l i n g f o I I O W e d l e v e l e d b~ y

S H O W I N G N E X T P R O P O S E D S T E P T O S O U T H W I T H R E C L A M A T ' O N F o L 1

s u r f a c e

f a c e

. O W I N G

Fiqure 9. Sequence of operation at the Usibelli Coal Mine (from Usibelli, 1981) stop No. 9.

Figure 10. 'Ace-in-the-Hole' dragline. Stop No. 9.

Figure 11. Poker Flats pit, Usibelli Coal Mine, Inc. Stop N o . 9 .

tl1e'l'woIlu23 Ridge area (Stop No. l o ) , which is about 1.5 miles northeast and has proven reserves of 38 million tons at a stripping ratio of 3.6:1

(Figures 8 and 12; Denton, 1.981) . Lower Lignite Creek holds large resources

of coal and will be an area of increasing future development. Mining will

progress up Lignite Creek to the Arctic Coal Company tract and to the Gold

Run Pass pit area of upper Lignite Creek (Stop No. 7),where mining has

taken place intermittently in the past (Figures 13 and 14) . In 1984, UCM finalized and signed a 15-year contract with the Korean

Electric Power Corporation, Sun Eel Shipping Company, Ltd. and its subsi-

diary Suneel Alaska Corporation for the annual delivery of 880,000 short

tons of coal to South Korea. According to the terms of the agreement,

55,000 tons were shipped in December, 1984; 770,000 tons will be shipped

in1985, and the first full complement of 880,000 tons will be exported

in 1986. The coal is being used in KEPCO's 1000-megawatt Honam Power Plant

located on the southern tip of S o ~ ~ t l i Korea. UCM's 1985 production should

increase to over 1.5 million short tons (Figure 2), essentially doubling

Alaska's recent total coal production and setting an all-time Alaska coal

production record. The co,iL travels from the mine via the Alaska Railroad

to Alaska's first deep-water coal port at Seward (Figure 15) where it is

onloaded to a 60,000 ton (deadweight) ship of Hyundai Merchant Marine of

Korea Lor ocean transport.

UCM has invested $30 million in new equipment and mine facilities over

the past several. years. The systems were necessitated and installed as a

result of the Sun Eel export contract. However, due to the efficiencies

made possible by this ambitious renovation and expansion program, the cost

o f UCM coal W'IS projected to decrease from $30/ ton to $28/ ton. In 1981,

UCM constructed . I new $6-million coal preparation and loading facility (or

tipple) near the current mine site at Poker Flats (Figure 16; Stop No. 11) . Run-of-mine coal. is dumped into a large hopper (Figure 17; Stop No. 11)

with a Strimler feeder-breaker at its base that crushes the coal to less

than eight-inch size. This primary crusher then feeds the coal into a two-

rol.1 secondary crusllcr t tut reduces it to a two-inch top size. The coal is

t l i e n transported across the NencinCl River on , l conveyor belt where it is

stored J r l ,in A-f rame silo aw, i i t inf : subsequent loading on r a i l c a r s (Usibel l i 3

Co,il Mine, 1984). In 1.983, tlic company completed n new 46,000 ft hc. ,~dqu~ir-

tcr:: complex including o t l ices, shop, and warehouse facilities (Stop No. ll),

Figure 12. state of Alaska c.oa 1-lease areas in the Nenana coal basin. The 1-ocations of Poker li'lats, 'Cwo Hu l l Ridge, Arctic Coal Colllpany and old Run Pass are ill so shown.

Figure 13. Gold Run Pass mine pit, upper Lignite Creek

field. Stop No. 7.

o IQO ago SO& In feet

I ' ig i~re 14. Cross ;irld s t rat i g r a p l l i c sec t ions tor t h e G o 1 d l!un I1ass Mine ;Irr;i, r1ppc.r I, i g n i t e ( :reek f i e l t l (Ileal y D-4 qu, l r l rwngle , NK~I, 0 1 SKI,, of' sect ior l i 4 . 1'. 1 1 S . , I ? . h W., I c l t i t t l d e 63.9158' N . , longi ~ i l r l c ' 1 4 8 . 6 8 7 8 ~ ) W. ; , ~ f t c ~ r ( :onwc~l I , 197h,1, 19761,). .';to J N O 7.

Figure 16. Usibelli Coal Mine shop-office-warehouse complex (bottom left) and tipple (center foreground) adjacent to Nenana River. Stop No. 11.

Figure 17. Large coal hopper at Usibelli Coal Mine tipple east with primary crusher at its base. wNn

and purchased :r fleet of 75-ton WABCO haul trucks and a new D-10 caterpil-

lar tractor. Tl lc l l n i t train loading facility (tipple west) at the mine can

fill 45 75-ton hopper cars per hour.

In 1983, IJCM submitted two new surface mining permit applications to

the State Division of Mining under requirements of the Alaska Surface Coal

Mining program. One application covered current operations at Poker Flats

;,nd t h e second was for the Gold Run Pass Mine. UCM has practiced a success-

ful progr:lm 0 r c:oil I n i i r l c land reclamation since about 1970.

SYNOPSIS OF NICNANA COAI, BASIN GHOI,OGY

LOCATION AND ACClCSS

7 ' 1 1 ~ Healy Creek and Lignite Creek coal fields of the Nenana basin fall

mainly in the H e a l y D-4 (1363,360 scale) quadrangle (Figure 1.8) . The Nenana

basin encompasses over 2500 mi2 with outcrops of the coal-bearing group re-

stricted to : ~ n tire;~ less than 1000 mi2. 'The Nenana trend continues 150 to

200 miles s o u t l l w c s ~ of the Nenann b:isin proper and includes coal-bearing

rocks of the Farewell ( 1 , i t t l e Tonzona) field (Figure 1).

l'he Alaska Railroad crosses the Nenana coal basin and generally paral-

lels the Nenana River. Both Anchorage-to-Fairbanks highways (the Parks on

the west and tlic Richardson on the east) transect the region. Numerous haul

roads and trails extend from H e n l y northeastward to Jumbo Dome (Stop No. 7).

However, most of lie Nenana basin is unpopulated, undeveloped, and relative-

ly isolated from existing transportation routes. Several private landing

strips are located at Healy, Suntrana, and other sites in the Nenana region.

Scheduled commercial flights operate between Anchorage and Fairbanks and

McKinley Park.

The historic mining and railroad town at Healy is connected to the

Parks Highway by ,I 2. 5-mile side road. Healy is 112 miles from Fairbanks,

244 miles from Anchorage, 100 miles west of Delta, and 370 miles to coastal

access at Seward's coal port. Delta Junction, which has a population of

about 4000, is located at the intersection of the Alaska and Richardson

Highways.

Some of the workers at the I J s i b c l l i Coal Mine live in the coal-mining

town of U s i b e l li on Healy Creek. Coal mining and railroad communities of

the past include Suntrclna, Lignite, and Ferry. Fort Greely, an army arctic

t ril in in!: cerlLcr, i t ic Ludcs portions of t lie eastern Nenana coal b a s i n .

GENERAL GEOLOGIC SETTING

The Location < ~ n d configuration of the structurally similar series of

disconnected coal fields forming the Nenana basin are shown in figure 19.

The Lignite Creek and Hedly Creek fields are the most important. The wes-

tern Nenana ('l'ek1:lnik;l) field, 1oc; l t ed along the northern boundary of Mt.

McKinley National Park, is the third Largest field of the basin; it con-

tains an es t in i , l ted 250 million tons of coal that mostly fall within the

con£ ines of the park (Watirhiiftig and others, 1951) . Poker Flats (Stop No. 9)

and Gold Run Pass (Stop No. 7 ) pits of the Usibelli Coal Mine are located

in the Lignite Creek field. The H e a l y Creek field has historically been one

of the most important coal-mining areas in Alaska.

Other coal Fields of the Nenana basin include Kex Creek, Tatlanika

Creek, Mystic Creek, Wood River, West Delta, East Delta, and Jarvis Creek.

Tlle Jarvis Creek field, which is situated at the east end of the basin, is

favorably located near the community of Big Delta on the Richardson Highway.

The climate of the Nenana coal basin region is continental with the

average a n n u a l precipitation varying locally from 12 to 20 inches. Precipi-

tation is generally greater than at Fairbanks with moderate to heavy snow-

falls occurring from November to March. Light snows may come as early as

September 1. Over half of the annual precipitation falls from June through

September w i t 1 1 ,Tuly and August typically the wettest months. Cloudbursts

are common on l n t c afternoons during summer and these cause rapid erosion

;lnd dissection of gullies within the relatively soft coal-bearing rocks.

Summers are usually cool in the region with a mean temperature of 5 5 ' ~ ; the

mean July temperature is over 6 0 ' ) ~ . The mean temperature during the coldest

winter months is between 00 to 5' F. The short-term winter temperature may

dip to -60°F (U.S. Department of Commerce, 1968) .

'I'lle Nenana 1)' lsin is underlain by discontinuous permafrost (Ferrians,

1965). Only minor permafrost problems have been encountered by Usibelli

ConLMine. Melting of ice pockets in spoil during the relatively warm sum-

mer months liave resul t e d in 1 oc;l l izerl slumps.

PHYSIOGRAPHY

The Healy Creek and Lignite Creek fields of the Nenana coal basin are

located in the Alaska Range physiographic province (Wahrhaftig, 1965). More

specifically, they lie in the foothills belt of the north-central Alaska

Range south of tlie Tanana Flats. It is a region of diverse physiographic

features. The rugged, generally parallel, alpine ridges of the Alaska Range

trend east-west. Numerous peaks within the range attain altitudes over

10,000 ft. Mt. Hayes has an altitude of 13,800 ft, and Mt. McKinley, the

highest mountain p e , ~ k in North America, has an altitude of 20,300 ft and

Lies southwest ul the main coal fields.

Several other isolated prominences form important landmarks in the

western Nenana basin region. Jumbo Dome (Stop No. 7), a hornblende dacite

intrusion, has an altitude of 4505 ft. Walker Dome, which lies about five

miles west of Jumbo Dome, lias an alltitude of 3900 ft; it is an isolated

mound within rather extensive northward-sloping erosion surface overlain

by the Nenana Gravel. Rex Dome, ;~pproxin ia teLy 12 miles northwest of Jumbo

Dome, has an altitude of 4155 ft and consists of Paleozoic schist.

The main drainage lines of the Nenana basin run northward transverse

to the ridges. The most important drainages from west to east are the Nena-

na and l 'o ta t lani lca Rivers, T a t l a n i k a Creek, and the Wood, Little Delta, and

Delta Rivers, ; i l l tributaries of the Tanana River. Henly and Lignite Creeks

drain westward into the Nenana River. Sanderson Creek (Stop No. 7 ) enters

Lignite Creek from the southwest about 11 miles above its mouth.

Most coal deposits of the region are found at elevations less than

3,000 ft lying between rather dissected valleys. The foothills belt gra-

dually descends down to the broad Tanana Flats, i l lowland of slight relief

about 30 miles wide. The northward extent of the belt of coal-bearing rocks

beneath the Tannna Flats is unknown.

DISTRIBUTION OF COAL-BEARING ROCKS

The Tertiary coal-bearing rocks of the Nenana basin occupy a discon-

tinuous belt extending about 130 miles along the north-central flank of

the. A l;lska I{<~ngc and up to 15 miles wide. The deposits are centered in an

arc,l ( l b o t ~ t 60 miles southwest of Pa i rbanks ancl 200 miles north of Anchor-

'Ige.

Although the coal-bearing rocks are widely distributed along the

northern foothills , they are discontinuous, having been removed by ero-

sion in the intermediate areas, Isolated patches of these rocks near

the tops of certain ridges are indicative of their once more extensive

distribution. 111 addition, their areal distribution is undoubtedly

greater than their surface exposure over the region, with large areas

covered by Nenana Gravel or unconsolidated outwash gravel (sandur plains)

and morainal material. The belt of coal-bearing rocks probably continues

into the s u b s u r f a c e beneath the southern Tanana Flats.

Thin l i g n i t i c and subbituminous coals occur in the Kantishna Hills

( 7 . ' . K. Hundtzen, personal communication, 1983) . The Farewell-Little Ton- ~ o n i i f i c l d , contains one subbituminous coil1 seam over 100-f t thick (Play-

er, 1.976) . Coals of the Western Nenana field are scattered along the

northeast boundary of Mt. McKinley National Park. Coal outcrops are also

found :it several locations within the park itself, and at Yanert near its

eastern margin about 130 miles south of Fairbanks.

STRUCTURAL GEOLOGY

The fold axes of the relatively shallow warped basins of the Nenana

region are generally aligned east-west parallel to the structural trend

of the Eoothil1.s belt and of the Alaska Range. S.W. Hackett and W.G. Gil-

bert (personal communication, 1983) have outlined the existence of several

major tectonic blocks across the north-central portion of the Alaska Range

by gravity and magnetic surveys and structural evidence. These blocks are

bounded on the north by the southern edge of the Tanana basin, on the

south by the McKinley strand of the Denali fault system, on the west by

the Tcklanika River, and on the east by the West Fork of the Little Delta

River and Yanert Glacier. They have evidence for a broad Bouguer gravity

low greater than 12 milligals near HeaLy and for large density contrasts

between the Tertiary coal.-bearing sediments of the Healy Creek and Lig-

nite Creek l i e 1 . d ~ and the denser underlying Precambrian-Paleozoic rocks.

The down-dropped tectonic blocks of Tertiary sedimentary rocks resting

on tlic underlying heavier Paleozoic or older basement result in a low

er:ivity anomaly along the trend of the synclinal axes of the Nenana coal

b a s i n to Lhc' casL .

Both the Healy Creek and Lignite Creek coal fields occur in major

synclinal structures (Figure 20) . The Poker Flats mine site is located

on a smaller-scale a n t i c l i n a l structure south of Lignite Creek and north

of the major fault separating the two fields. This near-vertical fault

displaces the coal-bearing strata on the north upward about 3,000 to

4,000 ft, bringing the coal beds close enough to the surface to create

favorable surface-mining situations.

The Healy Creek section occurs in a westward-plunging syncl ine with

dips off the limbs ranging from 30' to g o 0 . Mining on Healy Creek in the

past woslimited to the south limb which dips on the average at 450.

Near the east end of the Healy Creek field and the axis of the faulted

syncline, beds are near-vertical to slightly overturned, and drag folds

and rolls are present locally (Wahrhaftig and Freedman, 1945; Conwell,

1972).

The geologic structure of the Lignite Creek deposits is dominated

by several synclines and anticlines with fypicdly gentler dips around

20°, but in places with dips 30° to 3 5 O (Wahrhaftig and Birman, 1954).

REGIONAL TECTONISM

The coal-bearing rocks of the Nenana basin lie on Precambrian to

Paleozoic metamorphic rocks. Erosion of the basement surface continued

into the middle Tertiary (late Oligocene) when deposition of the coal.-

bearing group began. Clastics shed from low to moderate highlands in

the general vicinity of the western Yukon-Tanana upland served as a

sediment source for most of the coal-bearing group (Wahrhaftig, 1958).

By Pliocene time when the Nenana Gravel was deposited, the source of

the cl.:istics had shifted from the north to the south following rejuve-

nation in the Alaska Range. These uplifts resulted in the elevation and

tilting of certain structural blocks, and caused faulting and folding

in the codbeds. The late Pliocene-Pleistocene upheaval of Jumbo Dome

(Stop No. 7 ) greatly affected the section adjacent to its flanks and

caused significant structural adjustments and attitude changes in the

' r e r t i c ~ r y rocks of the region.

CI<NEIUI, STRA'I'I(;IIAI'HY AND LITHOLOGY OF THE COAL- BEARING GROUP

'l'llc Tertiary coal-bear Lng group (an informal geo Logic unit name) of

SOUTH

-k

Figure 20. North to south cross section through the western Lignite Creek and Healy Creek fields showing the major geologic structures (modified from Wahrhaftig, 1970) . Horizontal and vertical scales are each about 1 inch to 1 mine. No exaggeration.

the Nennna coal basin was subdivided by Wahrhaftig and others (1969) based

on bio- and l i t h o - s t r a t i g r a p h y and age dating into five new formations (in

ascending order) : the Healy Creek Formation, Sanctuary Formation, Suntriln;)

Formation, Lignite Creek Formation, and Grubstake Formation (Figure 21).

The series may be as much as 3,000-ft thick locally. The coal-bearing group

includes strata characteristic of the Angoonian, Seldovian, and Homerian

stages of Wolfc and others (1980; Figure 22) .

H e d l y - Creek Format ion

The basal unit of the coal-bearing group is the Healy Creek Formation

(Figure 21). Tts type section is on the northeast canyon wall of Healy

Creek a t Suntrana from the top of the Birch Creek Schist to the top of the

1; coal bed (Wnt~r l laf t ig and others, 1969; Stop No. 2). It is of late Oligo-

cene cjnd early Miocene age, and the thickness of the formation varies great-

ly within short distances. One geologic section in t hc Lignite Creek coal

f i e l d reveals 1150 f t of H c a l y Creek strata (Wahrhaftig, 1958).

The Healy Creek Formation is the most widely distributed unit of the

coal-bearing group and has been mapped from the Sushana River of the West-

ern NenanCl coal field to the J a r v i s Creek field east of the Delta River.

Most of the scattered patches of coal-bearing rocks of undecided affinity

nurth of the A l n s k c i Range are probably corre la table with the Healy Creek

Formation (Wahrhaftig and others, 1969, p . D 8 ) .

The HeaLy Creek Formation contains interbedded sandstones, conglome-

rates, claystones, and subbituminous coals. The conglomerntic sandstones

have a clayey matrix, are commonly gray to light reddish brown, and poorly

l i t h i f i e d . The continuity of individual beds vary greatly within a short

distance. Lenticular beds and mixed lithologic components in the same bed

are diagnostic features. Coalified leaves and carbonized plant detritus

are abundant throughout the unit. Considered in its entirety, the Healy

Creek Formation possesses characteristics of a high-energy Eluvia l environ-

ment.

Wahrhaftig (1958) found that paleocurrent indicators pointed to a mul-

ti- source provenancc of sediments. Dickson (1981) has a northerly prove-

nance f o r the formation (most likely the Yukon-Tanann upland) based on the

presence of abundant black c h e r t in the unit.

The Healy Creek Formation contains the second largest resource of coal

w i thin the c o a l - b e c ~ r i n g group.

S E C T I O N OI C O A L B E A R I N 6 GROUP AT SLJNTRANA

GRUISTAKE~ORMATION INTERBEOOEOCLAYSTONE. SHALE MNOSTONE. ANOFINECONGLOMERATE P R C ~ O M I N A N T L Y O A R K GRAY CLAYSTONE. POORLY CONSOLIOATFO. MASSIVE. I ~ L T < A N O O M € € N ~ B H GRAY SHALE. T H l N 8 F 0 0 € 0 . V A R V f O . CONTAINS THlN B f O S l L E S 3 0 N E FOOT1 A N O P A M l I N G S O f COAL A N D B O N E SANDSTONE I T 0 1 0 F l l . DARK GRAY. POORLYCONSOLIOAIEO WITH AIUNOANT OARK ROCK FRAOMENTS. BLACK CHERT A N 0 OTHER DARK M I N E R A L I WEATHERSBROWNlSH RE0 OR LOCALLYSTAINEO ORANGE SY I R O N O X l O f ALONG10INTSANO f M A C T U R F I U R f A C E 6 CONOLOMERATE LENSES CONTAINPEBBLESOf M I L K Y OUARTZ A N 0 DULL SLACK CHERT GENERALLY LESSTHAN ONE H A L F INCH IN OIAMETER PlYO THICK BEOSOf FINE. W H l l E V I l R I C ASHOCCUR L O C A I L Y I N THE LOWEAPART OF THE f O R M A T I O N ILOWER SEO. 14 f T UWLRBEO. I3 F T I LATE MIOCENE

LIGNITE CREE& FORYATIOU I R E 0 0 M I N A N l L Y INTERBEOOEO. ARKOSICSANDSTOYE WITH LENSES OF PESBLE TO C O O B l t COMGLOMERATE *NO PEBBLE BEDS ISLXI. C L A Y S T O N ~ mvn INTERIEOOEO THIN LENSES OF SILTSTONE AND FINE GRAINED SANDSTONE. %I. AND THIN COAL BEDS 15XI THE COAL BEARING FACIES CONSISTS OF REPETlTlVESEOUENCESGENERALLY CAWED BYSEVERAL THlN COAL BEDS WITH CLAYSTONf I k T E A I f O S SANOSTONE. PUOALYCONSOLIOAlE0. CLEAN. CROSSBC00E0. WELLSORTIO. PERMEABLE. BUFF COLOREO. WlTHABUNOANTCOLOREOGIA1NSANO FRESH fE.MG MINERALS COAL BEOS LATERALLY OISCUNTINUOUSANOOREAK UP ONWEATH ERlNG I N r O Y A M L S O F LONO N A I R O W F L A K E S P A R A L L E L T O OEODIHG. THE E O G t S O F THESE FLAKESSHOWTIGHTLY C O M f R E ~ r O ANNUAL GROWTH RINGS A GENERAL N O R I H W A I O INCREQE I N GRAIN SIZE A N 0 PINCHING OUT O f COAL A N 0 CLAYSTONE LITHOLO G I E S I N T H E N O N COAL BEARING FACIES INOICATEAPROVENANCE FOR THECLASTIC COMPONENTS O f THC fORMATlON TO T k T NORTH MIDDLE MIOCENE

SUNTRANA FORMATION R E f E T I l I V E SEOUENCESOF C O N G L O M f I A T f A N 0 COARSE GRAINEO P I B l l l Y SANOSTONEGRAOlNC UPWARD IFROM BASE1 THROUGH UEOlUM A N 0 f l N C G R A I N E O U N O I T O N E TOCLAYSTONCAN0 COAL i ( lTHETOP1. GENERALLY ONETHICK A N 0 R E L A T I V E L Y f E I S I S T E h T C O A L I E O C A A M O B T ~ f O U E N C E S . I U T L O C A L L Y l W O O R T H R E E T H I N N t R SEAUS AM€ lNTERBE00EO WITH CLAYSTONE SANOSTONES, CHALK WHITE TO VERY LIGHT BUFF. P00RLYCONSOLIOAIEO. CRO6SBEOOEO. GENERALLY CLEAN WCLLSOMTEO. O f T E N W I T H "SALT A N O P E U E n " W E A R A N C E . A N O M A Y B E S T A l N t O ORANGE O n RED B Y IRON OKlOE UPTOSEVERAL FEET ABOVCFACHCOAL BEO. PEBILESOF CONGLOMERATESANOSANOSTONESMAlNLYOUARTZ. CHERT OUARTI ITE. AHOARGILLITE I A B O U T O ~ I MINORJASVE~, o a r m r c r c , o n r E N s r a n t . s w l r t . ANO VOLCANIC c r ~ s r s c o ~ r ~ ~ ~ i r ~ r BULK o r r n E COAL mr SOURCES Of THE NENANA FIELO COALSARE C H I E f L Y S U I I I T U M I N O U S . B L A C K W I T H A U A R K BROWNSTREAK. BLOCKY. LOWTO MOO €RATE ASH A N l l EXTREMELY L O W S u L f U R CONTENTS MIDDLE MIOCENE

H E A L ~ C R E E K F O I I M A T I O N INTEMBE00E0?00MLYCONSOLl0ATEOOUAMlZMlCASANOSlONEANOOUAMlZCHERlCONGLOMEMATE CLAYSTONE A N O S U B I I l U M I N O U S C O A L LENIICULAM 810s LITHOLOGlCCOMPONENTSOfTfNMlX€O TOOETHER 1 N l H E U M E I E D R A T H E M T H A N C L t A Y L Y S E P A M A T E O A S I N O V E R L Y l N O f 0 I M A T 1 0 N S M N O S T O N f s C O M M O N L Y H A V t ACLAYBIWOER C L A V I T O N E I WITH P E I I L E S A N O ANGULAR MOCK fMAGMENTSCOMMON E D E C I A L L Y NEAR BASE 0 1 FORMATION COALSAME T H l N I E O O E O A N O LOCALLY BONY LATE I11 OLIGOCENE TO E A M l Y U l O C E N E

L X P L A N I T I O N

Figure 21. Generalized section : , of the coal-bearing group at <EP$S

El Bony . Q ~ ~~kk Slhl.l Suntrana (Hea ly Creek field) l u n * n l l r m l l y O #I l m ~ ~ with the chief l i t h o l o g i c cha r - ! b";s;;;,$fl acteristics of the different

formations and seam i d e n t i f i - ns (after Wahrhaftig and others, 1969).

Sanctuary Formation

The Sanctuary Formation type section lies between the top of the F

coal bed and the base of the coarse conglomerate below the No. 1 and G

coal beds near Suntrana on Healy Creek (Figure 21; Stop No. 2) . The for-

mation was named for exposures on the Sanctuary River near the northern

boundary of Mt. McKinley National Park in the Western Nenana coal field.

The unit is early to middle Miocene in age, and varies from a few feet

to 350 feet in thickness. It is found in most fields of the Nenana coal

basin, and generally conformably overlies the Healy Creek Formation. The

unit forms a useful marker 'bed' in the coal-bearing group.

The Sanctuary Formation is a chocolate-brown to yellowish-brown wea-

thering shale (gray on fresh exposure). Varve-like or lenticular-banded

silts and clays are present. It breaks down rapidly on exposure and forms

brown to gray gleys when saturated. Rounded landforms, landslides, and

slumps are common and particularly characteristic of the Sanctuary Forma-

tion. The fine silts and clays most likely accumulated in a large shallow

lake. The unit also contains coalified wood fragments, and its clay min-

eralogy (high silica, chlorite, and illite and low kaolinite) possibly

suggests a basic igneous rock source, different from clays in the Healy

Creek Formation. Thin coal and bone layers are found in some sections of

the Sanctuary Formation but they are unminable and the unit holds no eco-

nomic coal deposits (Wahrhaftig, 1958).

Suntrana Formation

The Suntrana Formation type section includes strata in the walls of

Suntrana Creek, tributary to Healy Creek between the top of the Sanctuary

Formation and the top of the No. 6 coal bed (Figure 21; Stop No. 2) . The

unit is of middle Miocene age. The maximum thickness of the formation is

1290 ft on the Coal Creek tributary of Healy Creek. The unit is widely ex-

posed in the Henly Creek and Lignite Creek fields. It is conformable with

the overlying Lignite Creek Formation, but locally unconformably overlies

the Sanctuary Formation (Wahrhaf tig, 1958) . The composition of the Suntrana Formation averages 70 percent sand-

stone and 15 percent each of coal and claystone. It is lithologically

similar to the Healy Creek Formation, but its sands are cleaner overall.

The sandstones of the Suntrana Formation are whitish to light-buff co lor -

ed, weakly consolidated, typically well-sorted, and crossbedded. A petro-

logic analysis shows the following average composition: quartz 70-75 per-

cent, orthoclase 5-10 percent, plagioclase 1-5 percent, chert and rock

fragments 5-10 percent, and heavy minerals (predominantly a low-grade

metamorphic suite) 6.5 percent. Pebbles of conglomerates are typically

less than one inch in diameter and consist predominantly of the following

rock types: 1) resistant rock types, 65 percent---quartz, quartzite, chert,

argillite, and jasper; and 2 ) nonresistant rock types, 35 percent---grani-

tic rocks, gabbro, greenstone, graywacke, and volcanic rocks (Wahrhaftig,

1958).

The Suntrana Formation exhibits cyclic sedimentation. The maximum num-

ber of repetitive cycles described by Wahrhaftig (1958) was 10 to 12 in the

Suntrana Formation alone. Buffler and Triplehorn (1976) recognized 23 cy-

cles in the entire coal-bearing group section on Healy Creek (Figure 23).

The typical fining-upward cycle includes a lower coarse-grained unit, a

middle fine-grnined unit, and an upper coal unit (Figure 24).

Coalified stumps, roots, leaves, and twigs are found throughout the

Suntrana Formation. Schlaikjer (1937) found fossil fish of Miocene age in

coal-bearing rocks of the unit near the Suntrana coal mine on Healy Creek.

The Suntrana Formation accumulated in a subsiding basin, but condi-

tions were apparently more uniform in this depositional basin at this time

than during the deposition of the Healy Creek Formation earlier. Paleocur-

rent measurements from crossbeds show predominantly southward directions

in the Healy Creek and Lignite Creek fields. Clas t i c components (particu-

larly black chert and garnet) are thought to have been derived from the

southern Yukon-Tanana upland (Wahrhaftig, 1958).

The Suntrana Formation contains the bulk of the coal resources and

reserves of the Nenana coal basin, including most of the thicker (common-

ly 10 to 60 ft) and laterally more continuous coal beds. These beds can

be correlated better than those in other parts of the coal-bearing group,

and can be traced up to eight miles in some cases. The numbered coal beds

( 3 , 4 , and 6 seams) presently being mined at Poker Flats (Stop No. 9) occur

in the Suntrana Formation.

Lignite Creek Formation - The Lignite Creek Formation type section is found at Suntrnna Creek,

B A S I C LITHOLOGIC C O M P O N E N T (FACES) DEPOSITIONAL TYPE(S)

U P P E R C O A L U N I T S W A M P , F O R E S T , B O G . E T C . , D E P O S I T S

M I D D L E F I N E - G R A I N E D U N I T OVERBANK O R F L O O D P L A I N D E P O S I T S Fine grained s a n d s t o n e , s i l t s tone , m u d s t o n e ,

6 S H A R P E R O S I O N A L B A S E

and c laystone

L O W E R C O A R S E - G R A I N E D U N l T Sands tone andlor Cong lomera te

D I F F E R E N T T Y P E S O F FLUVIAL C H A N N E L D E P O S I T S

1. Grave l l y b ra ided s t reams

2 . Sandy b ra ided s t reams 3. Point bars

Figure 24. Basic 1ithol.ogic: components and depositional types for the common fining-upward cycles in the coal-bearing group (adapted from Buffler and T r i p l e h o r n , 1976) .

Healy Creek field from the top of the No. 6 coal bed to the base of the

distinctive greenish-gray shale near the top of the coal-bearing group

(Figure 21; - S* No. 2). The unit is named for the extensive badland ex-

posures in the hills on the north side of Lignite Creek (Wahrhaftig, 1958).

The formation is of middle Miocene age, and is 630 ft thick at its type

sect ion. It consists of a coal-bearing facies and a noncoal-bearing facies.

The coal-bearing facies varies in thickness from 500 ft in the northwest

part of the Lignite Creek field to 1000 ft at its east end. The noncoal-

bearing facies averages about 250 ft thick. The Lignite Creek Formation is

typically conformable with the underlying Suntrana Formation (Wahrhaftig,

1958; Wahrhaftig and others, 1969) .

The unit consists of interbedded, buff-colored sandstones, greenish-

gray claystones, nrkosic conglomerates, and relatively thinner and more

discontinuous coal beds than in the Suntrana Formation. Repetitive sequen-

ces are also present as in the Suntrnna Formation. In contrast to the

blocky Eracturing coals of the Suntrana Formation upon weathering, the coals

of the Lignite Creek Formation break into long, narrow chips and flakes.

Woody materials from the original coal-forming forest are preserved through-

out the formation (Wahrhaftig, 1958).

'The Lignite Creek Formation was deposited in the same basink) in

which the Suntrana Formation accumulated, but the basin continued to

subside at a faster rate. Most paleocurrent features in cross-bedded

sandstones are for a southern source with a secondary northern source for

the larger c l a s t i c components (Wahrhaftig, 1958).

The Lignite Creek Formation contains the smallest coal resource of

the three significant coal-bearing units of the coal-bearing group in

the Nenana basin.

Grubstake Formation

The Grubstake Formation type section is on Grubstake Creek of the

Lignite Creek field. The unit is of late Miocene to early Pliocene age

and is the youngest formation of the coal-bearing group. It is nearly

1000-ft thick at its type locality, but is of local extent. Exposures

ikre found in the Healy Creek and Lignite Creek fields. The formation

conformably o v c r l i e s the lighter (buff) sandstone beds of the Lignite

Creek Formation, a n d u n d c r l i e s he Nenana Gravel (Wahrhaf tig, 1958) .

The G r ~ b s t ~ l k e I'onnation consists of greenish-gray, thin-bedded shale

and claystone in the l lealy Creek and Lignite Creek fields. Elsewhere,

interbedded dark claystones and sandstones, g r u s (fine conglomerate), and

local reworked ash beds are present. 1, i thol o g i c a l l y , the unit is more similar to the Nenana Gravel than to the coal. --bearing group (Wahrhaftig,

1.958; Wahrhaftig and others, 1969) . The Grubstake Formation probably accumulated in a 1.acustrine environ-

ment. Certain c l a s t i c components as well as crosscurrent directions indicate

.I southerly prc,ven<\ncc-. Only thin heds of insignificant bone coal are found

in the Grubst:tkc: Formation.

Nenana Gravel

The name 'Ne11;in:l Gravel ' was f irs t used by Capps (191 2) to refer to

gravel overlying i t ~ e coal-bearing format ion. This Pliocene-aged unit

is the youngest o i - t h p Tertiary deposits of the Nennna coal basin. Thick

exposures of Nen;in.l ( : r ;~vel a s much as 4,000-f t thick occur between Healy

and 1 , i g n i t e (:reeks (Wahrhnftig ,ind Freeman, 1945) . They are extensively

exposed along the lower s l o p e s of the mountains on the north side of the

Alaska Range and west of the Delta River in the Nenana basin. In most

areas, the Nen.ln,t (;r,lvel unconformably overlies the coal-bearing group.

' The unit contains loose to poorly consolidated, well -rounded and

re l r i t ivc ly uniform, mccl ium to coarse gravel with some large cobbles and

bo~i l d e r s of nong l:tci:i l origin included locally. Pebb Les in the gravel. are

predominantly t ; r - ,~yw.~ckc and conglomerate, but a l s o irlcl ude schist, quart-

zite, granite, dacite, and green ophitic diorite. A few interstratif ied

lenses of cross-bedded sandstone and thin beds of purplish clay and silt

are also locally present. 'l'he deposits are generally oxidized to yellow or

brownish colors. lThe L o r m a t i 0 1 1 was originally deposited as a continuous

sheet that was 1;lter subjected to erosion.

Wnhrhaf t ig ant1 o tliers (1951) state that the pebbles of the formation

were derived from ;I r e juvena ted orogeny in the Alaska Kange and deposited

by north-flowing strcams t11:it formed coalescing gravel deposits.

I)l<l'OSl'T LONAI, 1:NV LWONMlCN'I'S

The 'I'crt i ; l r y c,o;il s of the Nenana basin formed l n I , ~ t e Oligocene and

Miocene I?pochs from ; ~ b o t l ~ 10 to 30 million years ago. These coal-bearing

rocks are a l l similar in age, structure, and sedimentologic character.

They are products of terrestrial (continental) sedimentation, including

fresh-water stream-laid, lacustrine, and poorly-drained swamp deposits.

They accumulated on an irregular, deeply weathered and eroded basement

surface which had been raised above the sea in Cretaceous time (Wahr-

h a f t i g , 1958; Wahrhaftig and others, 1969) .

Healy Creek Formation

The Healy Creek Formation is a Eluvial sequence of conglomeratic

sandstones interbedded with claystones and subbituminous coal. It was

deposited in late Oligocene and early Miocene Epochs (Figure 25A). The

weathered schist basement on which it was deposited was a very irregu-

lar surface with several hundred feet of relief, resulting in a major

unconformity. Densely vegetated coal swamps developed in nearly iso-

topographic lows on this irregular surface. Poorly drained swamps,

ponds, sandy stream channels, Levees, and crevasse splays (overwash

flood deposits) occurred over this forested plain surrounded by forest-

ed uplands of moderate relief. Sediments carried by meandering streams

across the swampy plains were derived mainly from the basement rock of

these nearby hills, particuLar1.y from quartz veins in the weathered

schist. They are characterized by a diversity of source rocks. At cer-

tain intervals, the forests were either destroyed by fires or the hills

laid barren and made susceptible to erosion and large landslides. Clas-

tics washing into the coal swamps eventually closed off each coal-form-

ing episode. Several localized basins of deposition (depocenters) form-

ed across the region.

Conditions in the depositional system have determined the sedimen-

t o l o g i c character of the preserved rocks of the Healy Creek Formation.

Variations in these local. conditions of deposition have resulted in

lenticular and intertonguing beds exhibiting rapid facies changes. Dis-

continuous sand sheets or mudflows often occur as splits in coal seams.

Although coal beds of the Healy Creelc Formation are Locally thick, they

maint3-i.n L i t t l e lateral continuity. Wahrhaftig (1.958) believed that firm

reserve figures could not be calculated due to the thin coal beds and

their marked L e n t i c u l : ~ r i t y .

Paleotopoelraphic low with peat deposits

Alluvial fan Meandering stream

Braided stream

Landslide deposit

I7igure 2 5. (:e~iet::l 1 i ztcl a n d s i nip1 i s t i c t1eposition:l I ~ n o d c l s r e p r e s e n t i n g pt l leoenviron- mcnt ;~ I cond l t . ions tlr~r.ing t l i c I o r:nl;~l.io~l o f t h e T e r t i a r y C O ~ I - b e a r i n g r o c k s of t h e Ne- n;lna b:~sin. Refer t o t - cx t f o r d i s c u s s i o n . N o p ; l r t icuLar scn lc ! o r s p e c i f i c a r e a i s i m p l i e d . 'I'lie : l l l ces t r :~ I m o u n t :liris of (: ailti E r e p r e s e n t po ten t i ; i l solirce ;-Ireas o f c l a s - t i c s n e a r t h e wtLs t c \ r l l e n d ol' 1 Ilc Yuko~i-'l';inan;l up l a n d . '['he i inccls t r ; r I n~ount i l ins t o t h e s o u t h 011 I I r e p r e s e n t u p 1 i f L:; i r k ~ . l ~ c b A l i ~ n k ; ~ R :~nge .

Sanctuary Formation - The Sanctuary Formation is a locally thick claystone of probable

lacustrine origin. It was deposited in early to middle Miocene time

(Figure 2 5 B ) . The silt and clay that washed into this large shallow

lake were derived apparently from sources different than the Healy

Creek, possibly from basic igneous rocks in a fairly distant region.

Prominent lacustrine deltas formed locally. The formation thickens

somewhat to the south and southeast. During most of the period, the

lake was sufficiently deep to prevent the rooting of aquatic vegeta-

tion, but parts of the lake became restricted late in the depositional

cycle and coal swamps began to form. However, very little coa ly mater-

ial has been preserved, and it is near the top of the formation.

Suntrana Format i-on

The Suntrana Formation formed on a subsiding plain with scatter-

ed, fairly extensive coal-swamp development during the middle Miocene

(Figure 25C and 25D). Periods in which streams carried sheets of sand

and gravel from northern source areas, that is, uplift and subsidence

(Figure 25C) alternated with periods in which most of the plain was a

coal-forming swamp (Figure 25D). Important subenvironments include

channels, levees, crevasse splays, forested plains, and al-luvral fans.

Subsidence was greatest to the south, and the formation gradually

thickens in this direction. Chert pebbles indicate a source near the

western margin of the Yukon-Tanana upland, perhaps from the Livengood

Chert (Wahrhaftig, 1958) .

Crosscurrent directions preserved in sandstones show a northerly

provenance for the elastics. Depositional conditions were much more

uniform in the coal-forming periods than during the deposition of the

Healy Creek Formation earlier and resulted in more laterally contin-

uous coal beds in the Suntrana Formation. Several depocenters with

substantial thicknesses of coal developed toward the southern margin

of the basin where subsidence was greatest. As the hills to the north

were gradually lowered, and the sediment supply became more restricted,

silts and clays were deposited. A period of renewed uplift would ini-

tiate another cycle of sedimentation.

Lignite Creek Formation

Sediments of the 1 , i g n i t e Creek Formation were deposited in the same

basin(s) as the Suntrana Formation in middle Miocene time (Figure 25R and

2 5 F ) . The pattern of deposition was similar to that of the Suntrann, and

was to some degree also cyclic. Little or no significant break in deposi-

tion occurred, and sediments derived from the north poured into the sub-

siding basin at an increased rate (Figure 25E). Since the pebble 1.itholo-

gies are less resistant than those of the Suntrana, they may have been

derived from a less distant source area or different source unit, and/or

af ter considerable rejuvenation of the source area (Wahrhaf tig, 1958) .

1,arge alluvi;iL fans developed on the sloping terrain between the subsiding

basin and the highland source areas. The coal swamps that developed during

this time were often inundated by flood waters depositing silts, sands,

and gravel (Figure 25F). Hence, coal seams of the Lignite Creek Formation

are very lenticular and laterally discontinuous. The former highlands to

the north were lowered depleting the supply of clastic materials. Shallow

Lakes formed locally and silts and clay were deposited.

Grubstake Formation

The Grubstake Formation consists mainly of claystone and was deposi-

ted during the transition period in late Miocene to early Pliocene that

separates the derivation of c l a s t i c materials from northerly source areas

and Later on from southerly source areas (Figure 25G). An unconformity

separates the Lignite Creek and Grubstake Formations. This period was re-

latively unstable and depositional conditions shifted between large shal-

low lakes and broad alluvial plains. Local uplifts closed off rivers and

the drainage was 'ponded' in the lowland. Lacustrine deltas locally splayed

into the lakes. The unstable depositional conditions are reflected in the

absence of coal and in the interbedded finer-grained sediments with rela-

tively dark-colored sandstones and conglomerates (Wahrhaftig, 1958).

Nenana Gravel

The Nenana Gravel was derived from southerly source areas in the

P l i o c e n c a n d covers the coal-bearing sediments in a thick Layer of

c-o;~rsc> gr;tvcl w i t l ~ some inc I~ ide t l cobbles ;~n t l bou ltlcrs (Figure 25H) .

COAL PETROLOGY

The petrology of Nenana basin coals is consistent with their inter-

preted origin in continental-fluvial systems and associated subenviron-

ments. It suggests that most of the coal seams formed from tree-vegeta-

tion peats with abundant preservation of woody materials as huminites.

The woody peats accumulated in poorly drained forest-moor swamps filling

nearly isotopographic lows. The thicker and more continuous peats origi-

nated during relatively quiescent periods that alternated with periods

of uplift and the influx of c l a s t i c s that ended each peat-forming cycle.

A forest-terrestrial moor environment is envisloned for certain coals

in the Lignite Creek Formation as indicated by their higher content of

inertinite. They would have formed under drier conditions than the coals

of the forest-moor in the telmatic (or groundwater level) zone, as did

most coals of the Suntrana and Healy Creek Formations.

The coals of the Nenana basin are predominantly huminitic with minor

inertinite and variable liptinite contents. Table 2 summarizes the maceral

compositions for Nenana basin coal samples. The huminite group of macerals

is the most abundant in the coals of the region; the huminite group content

ranges from over 68 percent to about 91 percent (volume, mineral-matter-

free basis), and the mean content is about 83 percent in the 70 samples

analyzed. The mean inertinite content is 2.7 percent, but the samples

exhibit a range to over 20 percent. The mean liptinite content is about

14 percent.

Table 3 shows that certain general trends can be expected in the

maceral compositions of coals sampled from the different coal-bearing

formations in the Nenana basin. Huminite contents are high in coals from

<111 formations. Liptinite contents tend to be somewhat more abundant in

the older formation (Healy Creek Formation and probable equivalent un-

differentiated Tertiary coal-bearing unit) and is typically less abun-

dant in the Lignite Creek Formation and more variable in the Suntrana

Formation. lnertinite shows a trend toward increasing abundance upward

in the coal-bearing formations.

Mean-maximum reflectance values ( L m ) for analyzed coal samples of the Nenana basin are summarized in figure 26. They exhibit a range from

0.21 to 0.53 percent, ;~ntl generally support the rank c Liissif i c a t i o n s

; ~ : ; ~ i g n c t l I,y proximate i ln~l u L t lrn;t~c :111;1! y s c s .

Table 2 . Surnmi~ry of coal petrologic data for coal silmplcs from the Nen;irla basin.

Maceral/maceral type

I J l m i n i t e * / v i t r i n i t e Pseudovitrinite Porigelinite Phlobaphinite Pseudophlobaphinite Humodetrinite

Total huminite

Fusini te Semifusinite Sclerotinite Macrinite Inertodetrinite

Total inertini te

Cutinite Sporinite Resinite**/suberinite/

exsudatinite Alginite Liptodetrinite

Total liptinite

Range Mean

*Almost exclusively ulminite. **Predominantly resinite.

'I.'able 3. Proportions of the three maceral groups in coal samples of the coal.-bearing formations of the Nenana coal basin.

Maceral srouD Format ion Huminite Liptinite Inertinite

Lignite Creek Sunt rana Healy Creek Undifferentiated Tertiary

coal-bearing unl . t*

L-M L-H M-H M-H

M-H L-M L L

Criteria as used here: LOW ( L ) Moderate (M) High (H) Huminite <50% 50-75% >75% Liptinite < 5 % 5-15% >15% Tnertinite <5% 5-15% > 15%

*Most of these samples were taken from stratigraphic sections that probably correlate with the Healy Creek Formation.

Frequency (%)

Fi~gu re 2 6 . V i t r i n i . t e reflectance frequency histogram for Nenana basin coal s a m p I es . Number in brackets indicates total number of grains counted at Lhc given reflectance interval.

COAL QUA1,ITY

Coals of the Healy Creek Formation and lower Suntrana Formation are

typically of better quality than coals higher in the coal-bearing group.

This is reflected in measured values for most rank parameters---particu-

larly calorific value, vitrinite reflectance, fixed carbon and carbon

content. Coals of the Lignite Creek Formation tend generally to have

higher ash and moisture contents, sometimes higher sulfur, and to be

thinner and more discontinuous laterally.

Figure 27 shows the classification for the lower stages of c o a l i f i -

cation Shaded areas represent the general range of values for different

rank parameters ;is measured in Nenana basin coal samples. These include

mean-maximum reflectance values from 0.21 to 0.53 percent, volatile matter

contents from about 8 to 30 percent, and calorific values from 6650 to

11650 B r i t i s l ~ thermal units per pound (moist, ash-free basis). Table 4

gives a brief summary of proximate and ultimate analysis data for Nenana

basin c o a l samples.

Total sulfur values for Nenana basin coal samples are shown in figure

28. The mean pyritic sulfur content is less than 0.02 percent and the mean

total sulfur content is about 0.30 percent. Typically in most Alaskan coals,

the organic sulfur content occurs in the highest proportion.

Figure 29 summarizes the range of trace element contents commonly Found

in all. coals with the range in Nenana basin coal samples. The latter values

were averaged from the results of Rao and Wolff (1981), Conwell (1976a) , and

A f f o l t e r , Simon, and S t r i c k e r (1981). For most elements, Nenana basin Sam-

ples fall toward the Lower end of the range observed in other coals.

COAL RESOURCES AND RESERVES

The formations of the coal-bearing group that contain the greatest re-

sources of minable coal (in decreasing order) are the Suntrana, Healy Creek,

and Lignite Creek Formations. Thus, significant coal deposits occur in three

of the five formations composing the Tertiary sequence. The Suntrana and

Healy Creek Formations, making up the lower half of the coal-bearing group,

contain the majority of the economic deposits with the most numerous and

thickest. beds. 'Tlliuner and more discontinuous seams characterize the Lignite

Creek Format i o ~ i . 'I'11c s u b b i t ~1111111~us c . o : ~ l beds of the Ncn:ln;i basin range from

10- to 60-l t thick.

4 4

I B e d Calorific

(Vitrite) m.a.f. % Btullb.

--- - (kcall -

Peat 88

Apflg~bllity of Different Rank Parameters

F i g u r c 27. Genet-') l r.lngc3 c ~ f v a l lies lor different r a n k par , jmete rs i n N e n a n , ~ b a s i n cocil samples. Classi t i c ; lL ion o f co<l l i f i c a t i o n st ~ l g c s I K O I I I S i , ~ c l i ' ~ n d o t h e r s , 1982, t , ~ l > l r ' 4 , p . 4').

U - 5;

.d e, rn arb

Q

0 0 0 o o o m c o o ~ m

0 0 0 0 o o o m d ' m w o m m - 4

w 4 m m i I 1 1 1

I I - r" r c n 1 I N N I I C\1

The Nenana basin contains the third largest coal-resource base in

Alaska and is surpassed only by the deposits of northwest Alaska and

Cook Inlet-Susitna lowland provinces (Table 5). Measured resources are

about 3.5 billion short tons, identified resources are 7 billion short

tons, and hypothetical resources are estimated at 17 billion short tons

(Schaff and Merritt, 1984). Estimates of potentially minable coal re-

sources of the ten fields of the Nenana basin are listed in table 6.

Three different scenarios are shown based on different levels of assur-

ance---high, moderate, and low. Considering the Nenana basin proper,

there is relative high assurance of at least 1.4 billion short tons of

minable coal resources to a depth of 1000 ft in beds over 2.5-ft thick.

Healv Creek Field 2 The Healy Creek field covers an area less than 25 mi stretching

from the middle reaches of the Healy Creek drainage westward to the Ne-

nana River. I t lies south of the large fault that separates it from the

Lignite Creek field, and north of the central Alaska Range mountain

front.

Nearly complete sections of the coal-bearing group crop out along

Healy Creek. At the east end of the field, 32 different coal beds were

once exposed ranging to 55 ft in thickness, together totaling 375 ft of

coal in 1500 ft of strata (Wahrhaftig and Freedman, 1945). The Healy

Creek syncline is essentially depleted of economically attractive strip-

minable coal, and the stripping ratio of that remaining is relatively

high (COACMAR, 1980). However, undoubtedly substantial amounts of addi-

tional coal can be exploited in the future by underground methods.

Potentially minable coal resources of the area to a projected depth

(overburden limit) of 1000 ft are estimated to be at least 250 million

short tons (Merritt, in press).

U s i b e L l i Coal Company and its predecessors operated mines on Healy

Creek from about 1944 to 1972.

Lignite Creek Field

The Lignite Creek field extends from the upper reaches of Sheep

Creek in the east, to the Nenana River on the west, to Eva, Elsie, and

California Creeks confluence in the north. The western end of the field

Table 5. Summary of the coal resources of Alaska (in millions of short tons) .

Measured Identified Hypothetical Region resources Resources resources Northern Alaska 250 150,000 to 4,000,000

Cook Inlet-Susitna lowland ) 2,500 1.1,000 to 1,600,000 Beluga and Yentna fields 2,500 10,000 to 30,000 Kenai field ( i n c l . offshore) 0.5 320 to 150,000a

t o 1 , 5 0 0 , 0 0 0 ~ Matanuska field 8 0 180 to 500 Broad Pass field 10 5 0 to 500

Nenana trend 4,000 8,000 to 20,000 Nenana basin 3,500 7,000 to 17,000 Farewell-Little Tonzona 500 1,000 to 3,000 Jarvis Creek field 1 7 5 to 175

Other interior coal occurrences - - - - - - to 5,000

Bering River field 6 0 100 to 3,500

Chignik-Herendeen Bay fields 2 0 200 to 3,000

TOTAL 6,300 7168,000 7 5,600,000

a: To 2,000-ft depth. b: To 10,000-ft depth.

'Tab1.e 6. Estimates of Nenann basin, in milli limit) of 1000 ft and

potentially minable coal resources in fields of tlie .ons of short tons projected to a depth (overburden including all beds greater than or equal to 2.5-ft

thick

High Moderate Low Fie 1 d assurance assurance assurance

1) Lignite Creek 2 ) Healy Creek 3 ) Western Nenana 4 ) Tatlanika Creek 5) Wood River 6) Jarvis Creek 7) Rex Creek 8) Mystic Creek 9) West Delta 10) East Delta

Total 1380 2 6 7 0 4090

1 ies about 4 miles north of Healy. Healy and Lignite Creeks are about 5

miles apart and ;Ire separated by schist ridge north of the fault and

thick sections of Nenana Gravel south of the fault. Outcrops of the 1.ig-

nite Creek field are scattered over an area of about 100 mi2.

The field includes n e a r l y complete sections of coal-bearing group

strata from the Healy Creek Formation upward to the Grubstake Formation.

Over 1,000 f t of coal-bearing strata are exposed in steep-sided cuts a-

long typical Lignite Creek valley outcrops. At one location on Lignite

Creek, a coal-bearing section exposes an aggregate 260 ft of coal, while

sections commonly expose up to 200 ft aggregate thickness. The number 1

bed is the thickest of the coal-bearing group extending up to 60 ft local-

ly within the region, and the number 2 and number 3 beds can be over 40

ft thick. The number 6 seam has been found to be continuous along strike

for up to 10 miles (Wahrhaf t ig , 1.958, 1973; Wahrhaftig and others, 1969).

The coal deposits of the Lignite Creek field are the most important

of the Nenana basin. They are concentrated in four areas: 1) Poker Flats

(or lower L i g n i t e Creek; Stop No. 9) ; 2) Two Bull Ridge (Stop No. 10) ;

3) Arctic Coal Company (or middle Lignite Creek) ; and 4) Gold Run Pass

(Stop No. 7) . Sanders (1981) estimates reserves of the Usibelli leases

alone at over 250 million tons. Denton (1981) estimated design reserves

at Poker Flats at 28 million short tons at a stripping ratio of 4 . 5 : 1

and proven reserves of 80 million tons at a stripping ratio less 5 : l .

Meadowlark Farms (AMAX Coal Company, Inc., based in Indianapolis, In-

diana) holds leases with significant coal resources to the north and

east of the Usibelli tracts. These deposits occur mainly in the Mar-

guerite Creek drainage basin of the Jumbo Dome region (Stop No. 7). Mer-

ritt (in press) lias estimated potentially minable coal resources of the

Lignite Creek tield to , I projected depth of 1000 ft at 850 million short

tons.

OVERBUKDEN CHARACTER AND RECLAMATION POTENTIAL

Mitchell and others (1981) analyzed overburden samples from three

sites on Healy and Lignite (:reeks: 1) Healy A site, substratum material

overlying a coal seam; 2) Healy B site, spoil bank sample containing

s i g n i f i c : ~ n t ;imouuts of r -oa l and shale material; and 3 ) overburden sam-

5 0

ples taken down to a relatively shallow coal seam at a Lignite Creek site.

They concluded that a positive growth response could be expected at both

Healy sites A and B with applications of nitrogen, phosphorous, and potas-

sium fertilizer. Both sites were marginal with respect to potassium supply,

but showed adequate calcium and magnesium levels. Healy A site was defi-

cient in both the ammonium ion (NH~') and nitrate (NO ) , while Healy B 3 site demonstrated relatively high ammonium levels and slightly elevated

nitrate levels. Trace-metal concentrations were in the 'adequate' range.

They believe it unlikely that a micronutrient deficiency would present a

major problem in mine spoil revegetation. They also conclude that problems

of metal phytotoxicity or accumulation of metals in plant tissue that

might be toxic to wildlife are not indicated, nor should problems of ex-

cessive soil salinity or adsorbed sodium be anticipated.

The overburden sample from the Lignite Creek site showed soil reac-

tion levels that were higher than that normally associated with aluminum

and manganese toxicity. Saturation extract analysis of these samples re-

vealed no significant potential for the development of high levels of

salt or sodium accumulation. Sodium adsorption ratios were below the range

commonly associated with poor soil structure and its resultant negative

effects on plant growth.

Further overburden characterization analyses by the author (Table 7;

Merritt, in press) generally confirm the conclusions of Mitchell and

others. The levels of trace elements do not suggest the development of a

toxicity or deficiency condition in mine soils developed from these over-

burden materials.

Thus, both field observations and the results of overburden analyses

to date suggest that few environmental problems can be expected with re-

gard to the quality of overburden and interburden materials. Certain a-

mendments, particularly nitrogen and phosphorous, may need to be added

to promote mine spoil revegetation. Reclamat ion programs at the Usibelli

Coal Mine over the past 15 years have generally been very successful.

Table 7. Summary geochemical and physical characteristics of 43 coal-overburden samples from six general areas of the Nenana coal basin.

Overburden parameter Range Mean Units

paste pH Electrical conductivity Saturation percentage Water soluble cations

Calcium Magnesium Sodium

Sodium adsorption ratio Exchangeable sodium

percentage Particle size

Sand Silt Clay

Texture

Bulk density Organic matter Total organic carbon Extractable nutrients

Nitrate nitrogen (NO ) Phosphorous

3

Potassium Ammonium acetate extractable

cat ions Calcium Magnesium Sodium Potassium

Cation exchange capacity Base saturation Total sulfur Lime Acid potential. Neutralization potential

Potential acidity

Trace elements Boron Copper Molybdenum Lead Selenium

6-83 3 8 4-68 3 9 7-42 2 2 LS, L, SL, SCL, SiL, - - S i C L , CL, c, sic* 0.81-1.39 1.10 0.14-11.67 4.58 2.9-50.5 16.2

0.45-6.85 0.31-32.14 0.12-0.76 0.07-68.18

co. 01

ratio 2

meq/100 gms % %

% meq H+/100 gms tons CaCO equivalent

per 1 a00 tons tons CaCO equivalent

per 1 a 00 tons

*LS loamy sand; L = loam; SL = sand loam; SCL = sandy clay loam; S I L = silt loam; SFCL = silty clay loam; CL = clay loam; C = clay; and SIC = silty

c l a y .

REFERENCES CITED

Affolter, R.H., Simon, F.O., and Stricker, G.D., 1981, Chemical analyses of coal from the Healy, Kenai, Seldovia, and Utukok River 1:250,000 quadrangles, Alaska: U.S. Geological Survey Open-file Report 81-654, 88 p.

American Society for Testing and Materials, 1981, Standard specifications for the classification of coals by rank (ASTM designation D-388-77): 1981 annual book ofASTM standards, pt. 26, p. 212-216.

Barnes, F. F., 1.967, Coel resources of Alaska; a summary of information concerning the quantity, quality, and distribution of coal : U. S. Geo- logical Survey Bulletin 1242-B, 36 p., scale 1:2,500,000, 1 sheet.

Buff ler, R. T. , and Triplehorn, D. M., 1976, Depositional environments of continental Tertiary deposits, central Alaska, in - Recent and ancient sedimentary environti!ents in Alaska, symposium proceedings: Alaska Geological Society, Anchorage, p. Hl-H10.

C.C. Hawley and Associates, Inc., 1978, Mineral appraisal of lands adjacent to Mt. McKinley National Park, Alaska: U. S. Bureau of Mines Open- file Report 24-78, p. scattered.

Collier, A.J., 1903a, Coal. resources of the Yukon basin, Alaska: U.S. Geological Survey Bulletin 213, p. 276-283.

- - - - , 1903b, 'l'he coal resources of the Yukon, Alaska: U.S. Geolo- gical Survey Bulletin 218, 71 p .

Committee on Alaskan Coal Mining and Reclamation (COACMAR), 1980, Surface coal. mining in Alaska, an investigation of the Surface Mining Control and Reclamation Act of 1977 in relation to Alaska: National Academy Press, Washington, D . C . , p. 19-21.

Conwell, C.N., 1972, Alsskan coals: Society of Mining Engineers, AIME Transactions, v. 252, no. 3, p. 279-282.

- - , 1976a, S.smples from Healy coal field analyzed, in Mines and Geology Bulletin: Alaska Division of Geological and G e o a s i c a l Surveys, v. 25, no. L , p. 1-4.

, 1.976b, Reclaiming mined lands in Alaska: Society of Mining ----- Engineers, AIIQ Transactions, v. 260, p. 81-84.

1977, Land reclamation is an integral part of the only operating coal mine .in Alaska: The Coal Miner, v. 2, no. 3, p. 21-30

Denton, S.W., 1981, Geology and coal resources of the lower Lignite Creek area, in Rao, I 3 . D . , and Wolff, E.N., eds., Focus on Alaska's coal ' 80 : university of Alaska Mineral Industry Research Laboratory Report SO, p. 138-1413.

Dickson, R.K., 1.981, Uranium mineralization in the Nenana coal field, Alaska, - in Short notes on Alaskan geology: Alaska Division of Geo- logical and Geophysical Surveys Geologic Report 73, p. 37-42.

Ferrians, 0. J. , Jr . , 1965, Permafrost map o t Alaska: U.S. Geological Sur- vey Micce I 1 aneous Ceologic Investigations Map 1-445, scale 1 : 2,500,000.

Gassawny, J. S. , and Abramson, B. S. , 1978, Map and table showing distribution of known coal deposits in central Alaska: U.S. Geological Survey Open-file Report 77-1688, scale 1:1,000,000, 1 sheet.

Land, S.E., 1981, Alaskan coal---another energy option?: Alaska R u r c ~ l i t e , v. 28, no. 5, p. 25.

Mason, Brian, 1966, Principles of geochemistry: John Wiley and Sons, Inc., New York, p. 241-243.

Merritt, R.D., (in press), Coal atlas of the Nenana basin, Alaska: Alaska Division of Geological and Geophysical Surveys Professional Report.

, 1985, .Alaska coal---description of seams, in Keystone Coal Industry Manual: New York, Mining Informational Services, McGraw-Hill (in press).

, 1985, Paleoenvironmental and tectonic controls in major coal basins of Alaska, in Lyons, R.C., and Rice, C.L., eds., Paleoen- vironmental and tectonic controls in major coal-forming basins of the United States: Geological Society of America Special Paper (in press).

Mitchell, G.A., Mitchell, W.W., and McKendrick, J.D., 1981, Soil characterization of Alaskan coal mine spoils, in Rao, P.D., and Wolff, E.N., eds . , Focus on Alaska's coal '80: University of Alaska Mineral Indus- try Research Laboratory Report SO, p. 412-417.

Plangraphics, Inc., 1!)83, Alaska abandoned mined land reclamation plan; prepared for the Alaska Department of Natural Resources, Division of Minerals and Energy Management, Anchorage, 147 p . , 9 appendixes.

Player, Gary, 1976, The Little Tonzona coal bed near Farewell, Alaska; an important extension of the coal field north of the Alaska Range: Gary Player Ventures consultant report, Anchorage, 10 p.

Rao, P. D., and Wolf f , E .N. , 1981, Petrological, mineralogical, and chemical characterizations of certain Alaskan coals and washability products, in Rao, P.D., and Wolff, E.N., eds., Focus on Alaska's coal '80, Pro- ceedings of con£ erence, Znd, Fairbanks : University of Alaska Mineral Industry Research Laboratory Report 50, p. 194-235.

Sanders, R.B., 1981, Coal resources of Alaska, in Rao, P.D., and Wolff, E.N., eds., Focus on Alaska's coal '80, Proceedings of conference, 2nd, Fairbanks : University of Alaska Mineral Industry Research Labora- tory Report No. 50, p. 11-31.

, 1982, Coal resources of Alaska, in Alaska's oil/gas and minerals industry: Alaska Geographic ~ u a r t e r 5 , v. 9, no. 4, P. 146-

Schaf f , R.G., and Merritt, R.D., 1984, Coal resources of Alaska: Alaska Division of Geological and Geophysical Surveys Information Circular 17, 9 p.

Schlaikjer, E.M., 1937, New fishes from the continental Tertiary of Alas- ka: American Museum Natural History Bulletin, v. 74, p. 1-23.

I t

Stach, E. , Ma$Fowsky, M. -7%. , Teichmuller, M. , ' Taylor, C.II. , Chandra, ;. , and Teichmuller, R., 1982, S t a c l l ' s textbook of coal petrology: Gebru- der Borntraeger, Berlin, 535 p .

U. S. Department of Commerce, 1968, Climates of the States---Alaska: En- vironmental Science Services Administration, Climatography of the United States 60-49, 23 p.

Usibelli Coal Mine, 1984, Usibelli coal miner, v. 4, 16 p

U s i b e l l i , Joseph, 1976, Mining constraints and operations at Usibelli coal mine, in Kao, P.D., and Wolff, E.N., eds., Focus on Alaska's coal ' 75, Proceedings of conference, lst, Fairbanks : University of Alaska Mineral. Industry Kesearctl Laboratory Report 37, p. 93-101.

, 1981.a, Mining methods at U s i b e l l i Coal Mine using dragline, in Rao, P.D., and Wolff, E.N., eds., Focus on Alaska's coal '80, Proceedings of conference, 2nd, Fairbanks: University of Alaska Mineral Industry Research Laboratory Report 50, p. 392- 397.

------ , 1981b, Current and future mining activities at Usi- b e l . l i Coal Mine, Kao, P .D., and Wolf f, E.N., eds., Focus on Alaska's coal '80, Proceedings of conference, 2nd, Fairbanks: University of Alaska Mineral Industry Research Laboratory Report 50, p. 491-492.

Wahrhaftig, Clyde, 1958, Lithol.ogy and conditions of deposition of the formations of the coal-bearing group in the Nenana coal field: U.S Geological Survey unpublished draft report, 93 p.

-* 19 6 5 , Physiographic divisions of Alaska: U.S. Geolo-

gical Survey Professional Report 482, 52 p.

----.--- , 1970, Geologic map of the Healy D-4 quadrangle: U.S. Geological Survey G . Q . map 806, scale 1:63,360.

- - - - - , 1973, Coal. reserves of the Healy Creek and Lignite Creek coal b a s i n s , Nenana coal field, Alaska: U.S. Geological Sur- vey Open--file Report 568, 24 sheets, various scales.

Wahrhaftig, Clyde, and Birman, J.H., 1954, Stripping-coal deposits on lower Lignite Creek, Nenana coal field, Alaska: U.S. Geological Survey Circular 310, 11 p.

Wahrhaf t ig , Clyde, and Freedman, Jacob, 1945, Coal deposits in the val- Ley of the Healy River, Alaska: U.S. Geological Survey War Minerals Report, 8 p.

Wahrhnftig, Clyde, Hickcox, C.A., and Freedman, Jacob, 1951, Coal deposits on Healy and Lignite Creeks, Nenana coal field, Alaska; with a section on c l a y deposits of Healy Creek by E.H. Cobb, - in Barnes, F.F., and others, Coal investigations in sou th - cen t r a l Alaska, 1944- 1946 : U. S. Geological Survey Bulletin 963-E, p. 141-168.

Wahrhnftig, Clyde, Wolfe, J.A., Leopold, E.B., and Lanpliere, M.A., 1.969, 'rhe coal-bearing group in the Nenana coal. field, Alaska: U.S. Geolo- gical Survey B u l l e t i n 1274-D, 30 p .

Wol.fe, . J . A . , Hopkins, D.M., I,eopold, F.B., and Tanai, Tanya, 1.980, The Miocene S p l tlovi:l t'oirlt f - l era from the K e n a i Group, Alaska: 11. S. (:c.ologic'i 1 SLI r-vey I'ro t c: ;s lonn 1 Paper 1 1 0 5 , 7H 1).

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