Synopsis of the 

Mineral Resources and 

Geology of Alaska

GEOLOGICAL SURVEY BULLETIN 1307

1

Synopsis of the

Mineral Resources

Geology of Alaska

and

By EDWARD H. COBB

GEOLOGICAL SURVEY BULLETIN 1307

Published under a cooperative agreement with the 

Department of Natural Resources, State of Alaska

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1974
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress Catalog-card No. 74-600019

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington, D. C. 20402 - Price 70 cents (paper cover)

Stock No. 2401-02478
CONTENTS

Page

Introduction _________________________________ 1

Alaska Peninsula region ___________________________ 1

Aleutian Islands region ______________________________ 9

Bering Sea region ___________________________________ 9

Bristol Bay region __________________________________ 10

Cook Inlet-Susitna River region ______________________ 11

Copper River region _____________________________ __ _____ 13

Kenai Peninsula region ____________________________ 15

Kodiak region _____________________________________ 17

Kuskokwim River region ______________________________ 18

Northern Alaska region ____________________________ 19

Northwestern Alaska region _^_______________________ 21

Seward Peninsula region ____________________________________ 22

Southeastern Alaska region __________________________ __ 24

Yukon River region _____________________________________ 26

Anvik district _______________________________ 26

Black district ____________________________________ 26

Bonnifield district ___________________________________ 27

Chandalar district ____________________________________ 28

Chisana district _____________________________________ 29

Circle district _____________________________________ 30

Delta River district __________________________________ 31

Eagle district ____________________________________ 32

Fairbanks district _________________________.___ 33

Fortymile district _______________________________ 35

Goodpaster district________________________________ 36

Hot Springs district ____________________________________ 37

Hughes district ________________________________ 38

Iditarod district _____________________________-.___- 39

Innoko district ______________________________________________ 40

Kaiyuh district _______________________________________ 41

Kantishna district ______________________-_-_-___---___--_ 42

Koyukuk district_____________________________________ 44

Marshall district____________________________________________ 45

Melozitna district ________________________________________________ 46

Rampart district ___________________________________________________ 47

Ruby district ____________________________________________________ 48

Sheenjek district.___________________--__--_-__--__--_-_______ 49

Tok district _____________________________________ 50

Tolovana district_____________________________________ 51

Yukon Flats district ________________________________________________ 52

References cited ________________________________________________ 53

in
IV CONTENTS

ILLUSTRATIONS

Page

FIGUREI. Mining districts and regions in Alaska ______________ 2

2. Physiographic provinces of Alaska____________________ 4

3. Geologic map of Alaska__________________________ 6

4. Graph showing value of minerals produced in Alaska, 1900-1972. 8
SYNOPSIS OF THE

MINERAL RESOURCES AND GEOLOGY 

OF ALASKA

By EDWARD H. COBB

INTRODUCTION

This outline is an outgrowth of preparatory work for reports on the 

lode (Berg and Cobb, 1967) and placer (Cobb, 1972) deposits of Alaska. 

Essentially it summarizes data presented in those reports and in a 

similar report on the coal resources of Alaska prepared by Barnes 

(1967). Data on petroleum and natural gas were gathered from many 

sources, including a summary of potential petroleum resources by 

Gryc (1971) and annual reports of the State of Alaska Division of 

Geological Survey and its predecessor agencies. As the above reports 

contain extensive bibliographies, no reference citations are given in 

the body of this summary. Data are arranged by mining regions and, 

within the Yukon River region, by mining districts because the U.S. 

Geological Survey and U.S. Bureau of Mines historically have listed 

production data by regions or districts.

The mining regions and districts, the physiographic divisions and 

provinces, and the generalized geology of Alaska are shown in figures 

1, 2, and 3 respectively. Figure 4 summarizes the dollar value of the 

mineral production of Alaska from 1900 through 1972.

ALASKA PENINSULA REGION

The Alaska Peninsula region comprises the part of the Alaska 

Peninsula southwest of Becharof Lake, Unimak and Chirikof Islands, 

and other smaller islands southeast of the mainland.

The dominant physiographic feature is the Aleutian Range, made 

up of northeast-trending ridges 1,000-4,000 feet in altitude surmounted locally by volcanoes, some of which are several thousand feet 

higher. Northwestward the range merges with a low sand- and 

gravel-mantled plain that has 50-250 feet of local relief.

Geologically the Alaska Peninsula region consists of two main belts 

that extend for most of its length. The northwestern belt, as much as 35 

miles wide in the northeastern part of the region, is predominantly 

unconsolidated Quaternary silt, sand, and gravel. The southeastern 

belt consists mainly of Mesozoic and Cenozoic sedimentary and vol-
THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

Base from U.S. Geological Survey, 1964

FIGURE 1. Mining regions and districts in
ALASKA PENINSULA REGION

\\\\\\ r\r\r\

ALASKA PENINSULA REGION 

ALEUTIAN ISLANDS REGION 

BERING SEA REGION 

BRISTOL BAY REGION

COOK INLET-SUSITNA REGION

1. Anchorage district .

2. Redoubt district

3. Valdez Creek district

4. Willow Creek district

5. Yentna district 

COPPER RIVER REGION

6. Chistochina district

7. Nelchina district

8. Nizina district

9. Prince William Sound district

10. Yakataga district 

KENAI PENINSULA REGION

11. Homer district

12. Hope district

13. Seward district 

KODIAK REGION 

KUSKOKWIM RIVER REGION

14. Aniak district

15. Bethel district

16. Goodnews Bay district

17. McGrath district 

NORTHERN ALASKA REGION

18. Barrow district

19. Canning district

20. Colville district

21. Lisburne district

22. Wainwright district 

X(46) INORTHWESTERN ALASKA 

>-< \ REGION

\ 23. Kiana district 

24. Noatak district 

125. Selawik district 

6. Shungnak district

SEWARD PENINSULA 

REGION

27. Council district

28. Fairhaven district

29. Kougarok district

30. Koyuk district

31. Nome district

32. Port Clarence district

33. Serpentine district 

SOUTHEASTERN ALASKA 

REGION

34. Admiralty district

35. Chichagof district

36. Hyder district

37. Juneau district

38. Ketchikan district

39. Kupreanof district 64

40. Petersburg district

41. Yakutat district 

YUKON RIVER REGION

42. Anvik district

43. Black district

44. Bonnifield district

45. Chandalar district

46. Chisana district

47. Circle district

48. Delta River district

49. Eagle district

50. Fairbanks district

51. Fortymile district

52. Goodpaster district

53. Hot Springs district

54. Hughes district

55. Iditarod district

56. Innoko district

57. Kaiyuh district ^ 

58: Kantishna district

59. Koyukuk district

60. Marshall district

61. Melozitna district

62. Rampart district

63. Ruby district

64. Sheenjek district

65. Tok district

66. Tolovana district

Alaska. Based on Ransome and Kerns (1954).
THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

MAJOR NORTH AMERICAN PHYSIOGRAPHIC 

DIVISIONS IN ALASKA

Base from U.S. Geological Survey, 1964

FIGURE 2. Physiographic provinces
ALASKA PENINSULA REGION

EXPLANATION

High rugged mountains 

Summits more than 5,000 feet

Low mountains, plateaus, and highlands 

of generally rolling topography

Summits 1,000-5,000 feet

Plains and lowlands

Generally less than 1,000 feel

Boundaries between physiographic units

\v\.\\\\

of Alaska. From Wahrhaftig (1965).
THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

Base from U.S. Geological Survey,1964

FIGURE 3. Geologic map of Alaska. Based
ALASKA PENINSULA REGION

\i\ \\\ r\r\nr\

EXPLANATION

SEDIMENTARY AND

METAMORPHIC ROCKS IGNEOUS ROCKS

Quaternary and Tertiary volcanic 

rocks

Quaternary surficial deposits, alluvium, glacial debris, eolian sand 

and silt

Tertiary and Upper Cretaceous intrusive rocks: mainly granitic; 

includes small ultramafic and 

mafic bodies

Tertiary sandstone, conglomerate, 

shale, mudstone; nonmarine and 

marine

Mesozoic sandstone and shale; Mesozoic intrusive rocks; mainly

marine and nonmarine;includes 

some metamorphic rocks

Mesozoic volcanic rocks

Paleozoic and Precambnan sandstone, shale, limestone; mostly

Paleozoic volcanic rocks

morphic rocks; schist, gneiss, and 

so forth; mainly Paleozoic

Paleozoic intrusive rocks; granitic

Fault

Dashed where inferred

1 1 1 1 1 \ \ ».. 0

^ j^<C=f »-

» ALEUTIAN ADAK Q*t **^

,»% ^ ^ ,» ,». '

1 1 1 1 1 \

^^&1

\.T v \ \ T \

on U.S. Geological Survey (1964, fig. 8).
8 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA 

350

325

300

275

75

50

25

1900 1910 1920 1930 1940 1950 1960 1970

FIGURE 4. Value of minerals produced in Alaska, 1900-1972.

canic rocks intruded and metamorphosed by Tertiary granitic plutons. 

A single exposure of unequivocally dated Permian sedimentary rocks, 

near Puale Bay at the northeast corner of the region, has been reported; some of the volcanic rocks probably are late Paleozoic in age 

also. The entire Alaska Peninsula was glaciated during the Pleistocene Epoch but now is ice free except for some of the highest peaks. 

The region is generally free of permafrost. Several of the volcanoes 

that surmount the Aleutian Range have been active within the last 

few years.

Lodes in the Alaska Peninsula region contain gold, silver, copper, 

lead, and zinc. The only ones that were worked commercially are on 

Unga Island, where about $2 million, chiefly in gold and silver from 

the Apollo mine, was produced between 1891 and 1904. Placer gold, 

probably not much more than 600 ounces in all, was mined from 

beaches on Popof and, possibly, Unga Islands in the early 1900's. 

Titaniferous magnetite and ilmenite are common constituents of 

beach sands along the shores of Bristol Bay, but material that contains 

as much as 100 pounds of iron per cubic yard has been found only in a
ALEUTIAN ISLANDS REGION 9

few places. Every few years interest is revived in almost inaccessible 

sulfur deposits near the head of Stepovak Bay, though no actual work 

has been done there. Significant coal resources are known at Chigriik 

and Herendeen Bays and on Unga Island, but there has been no large 

production. Several unsuccessful test wells have been drilled for petroleum in Mesozoic and Tertiary rocks.

ALEUTIAN ISLANDS REGION

The Aleutian Islands region includes the islands west of Unimak 

Island. It consists of an archipelago surmounting a submarine ridge 

1,400 miles long, 20-60 miles wide, and rising 12,000 feet from the sea 

floor. About 40 volcanoes, 21 of which have been active in historic time, 

form an arcuate line; the highest members rise as much as 6,975 feet 

above sea level.

The region is underlain by Cenozoic basalt and andesite lava flows, 

tuffs, and clastic rocks that were cut by mafic to felsic dikes, sills, and 

stocks. This region is geologically the youngest in Alaska, as all others 

are at least partly underlain by rocks as old as Mesozoic.

Reported and definitely located lodes in the Aleutian Islands region 

are restricted to gold deposits (some of which may have been productive) and metallic sulfide occurrences on Unalaska and neighboring 

Amaknak and Sedanka Islands. Capps reported that natives were said 

to have mined copper on Salt Island, a small island off the north shore 

of Atka; he speculated that the copper might have been from an 

amygdaloidal lava flow. The only placer occurrence reported from the 

Aleutian Islands is a few small grains of gold from a tributary of the 

Makushin River on Unalaska Island. There has been sporadic interest 

in developing sulfur deposits that have long been known on Unalaska 

and Akun Islands, but work never got far beyond the planning stage.

BERING SEA REGION

The Bering Sea region includes St. Lawrence, St. Matthew, and the 

Pribilof Islands and nearby smaller islands and offshore rocks.

The islands of the Bering Sea are mainly rolling uplands and 

emerged marine platforms, generally within a few hundred feet of sea 

level; above which isolated mountain masses rise to altitudes between 

800 or 900 and about 2,000 feet. All the islands rise from the shallow 

Bering Shelf, much of which was emergent at times during the 

Cenozoic Era.

The Pribilof Islands and St. Matthew are composed mainly of 

Cenozoic volcanic rocks and surficial deposits, though periodotite older 

than the volcanic rocks has been found in a small area on St. George 

Island in the Pribilofs. Recent work on St. Lawrence Island, the largest 

in the Bering Sea, indicates that the eastern part of the island is made
10 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

up of a thick section of Paleozoic and Mesozoic sedimentary rocks, 

including limestone, that are generally similar to coeval rocks exposed 

in the Brooks Range of northern Alaska and in the Chukotsk Peninsula of Siberia. The western part of the island is made up of similar 

probably correlative rocks, small areas of coal-bearing Tertiary continental deposits, and Cretaceous and Tertiary volcanic rocks. Tertiary(?) and Quaternary basaltic rocks, some very fresh and young, 

cover the older rocks in central St. Lawrence Island. Permian gabbro 

and diabase, hypabyssal phases related to some of the volcanic rocks, 

and Cretaceous quartz monzonite and olivine monzonite plutons invaded the older rocks in both the eastern and western parts of the 

islands.

The known lode deposits on St. Lawrence Island include disseminated molybdenite in one of the plutons, a small low-grade porphyry 

copper deposit with minor molybdenite in a small satellitic stock, and 

several small sulfide deposits containing lead, zinc, and silver. These 

lode deposits have been little explored. An old report of cassiterite 

having been found near the southwest end of the island did not specify 

if it was a bedrock or placer occurrence. Recent stream-sediment sampling and reconnaissance geologic mapping in the area, however, 

failed to find any indication of tin mineralization. With the possible 

exception of this rumor of cassiterite, no placer deposits have been 

reported from the land area of the Bering Sea region. There has been, 

however, very little prospecting in the region, owing in part to its 

remoteness and in part to governmental restrictions.

Recent investigations in the Bering Sea suggest that local concentrations of gold in bottom sediments, particularly between St. Lawrence Island and the Seward Peninsula, and possibly petroliferous 

Cenozoic basins in the northern and southern parts of the region might 

be attractive exploration targets.

BRISTOL BAY REGION

The Bristol Bay region includes the area drained by streams flowing 

into Bristol Bay from Cape Newenham on the west to Egegik Bay on 

the east, and into Shelikof Strait from Cape Douglas on the north to 

Cape Kekurnoi on the south.

The southeast border of the region is part of the Aleutian Range of 

the Pacific Mountain System; northwest of them are lower mountains, 

plateaus, and basins of the Intermontane Plateaus. The highest peaks 

are mainly Quaternary volcanoes, some active in historic time, with 

summit elevations of 5,000 to 7,500 feet. The Bristol Bay-Nushagak 

Lowland is a lake-dotted area less than 1,000 feet above sea level, 

above which isolated hills rise a few hundred to slightly more than 

2,000 feet. The Ahklun Mountains in the western part of the region are
COOK INLET-SUSITNA RIVER REGION 11

a low but rugged range with many large deep lakes of extraordinary 

scenic grandeur.

The mountains in the eastern part of the Bristol Bay region consist 

of rocks that range in age from possibly Permian metamorphosed 

volcanic rocks (seen only in a few isolated exposures) to Tertiary and 

Quaternary lava flows and fragmental rocks. The bulk of the bedded 

rocks, however, are Mesozoic sandstone, shale, and conglomerate. 

Northwest of a major lineament (Bruin Bay fault) the older rocks were 

invaded and locally metamorphosed by diorite and quartz diorite that 

make up the Aleutian Range batholith of Jurassic age. There are also 

smaller younger felsic and mafic plutons and volcanic necks.

In the western part of the region, bedrock consists mainly of clastic 

and volcanic rocks of Carboniferous to Cretaceous age and Tertiary 

felsic and mafic dikes, sills, and small plutons. Between the eastern 

and western mountains, the region is a lowland underlain by thick 

glacial and alluvial deposits with bedrock exposed only around its 

margins and in a few hills that protrude through the surficial materials. Except for its north-central part, the region was glaciated. It is now 

mainly in zones characterized by isolated masses of permafrost.

Lode deposits containing mercury, gold, silver, copper, lead, zinc, 

antimony, and iron are known in the Bristol Bay region, but little ore 

has been produced from them. The greatest recent interest has been in 

low-grade iron deposits in the eastern part of the region, in a copperiron deposit near Lake Clark, and in a mercury deposit (from which 

there has been small production) at Marsh Mountain north of Dillingham.

The part of the region on the Alaska Peninsula has been the scene of 

considerable exploration for petroleum, but no commercial oil or gas 

field has been discovered. Interest has also been shown in pumice and 

pumicite in the southeastern part of the region for use as a component 

of light-weight concrete aggregate. In 1947 a few tons of this material 

was mined at Geographic Harbor about 15 miles northeast of Katmai 

Bay.

COOK INLET-SUSITNA RIVER REGION

The Cook Inlet-Susitna River region is the area drained by streams 

flowing into Cook Inlet between Cape Douglas on the south and the 

east end of Turnagain Arm. It is divided into the Anchorage, Redoubt, 

Valdez Creek, Willow Creek, and Yentna districts.

The region is entirely within the Pacific Mountain system. Its west 

and north borders are along the east and south slopes of the Alaska 

Range and its southeastern boundary is the crest of the lower, but no 

less rugged, Chugach Mountains. The region includes another highland area, the Talkeetna Mountains, a nearly circular mountain mass 

with most peaks between 6,000 and 8,300 feet in elevation. The east-
12 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

ern boundary of the region is an ill-defined divide in the western part of 

the poorly drained lake-speckled Copper River Lowland. A somewhat 

poorly drained area, the Cook Inlet-Susitna Lowland, is an extension 

of Cook Inlet; it separates the southern Alaska Range from the Talkeetna Mountains. Low mountains and ranges of hills rise from a few 

hundred to a few thousand feet above the lowland, particularly near 

the foothills of the Alaska Range.

The oldest geologic units in the region are Paleozoic clastic and 

carbonate rocks, exposed mainly in the Alaska Range, that are now 

being studied in detail. Mesozoic and early Tertiary volcanic and 

clastic rocks, locally with considerable interbedded limestone, make 

up the bulk of the bedded rocks in the Chugach Mountains, the northern part of the Alaska Peninsula, the hills rising from the Cook 

Inlet-Susitna Lowland, and areas bordering the Copper River Lowland. Large batholiths of Jurassic, Cretaceous, and Tertiary age that 

consist of granodiorite, quartz monzonite, and related rock types invaded the older sedimentary and volcanic rocks in the Talkeetna 

Mountains and Alaska Range. Smaller plutons are in the Chugach 

Mountains and other parts of the region. The middle part of a discontinuous belt of small ultramafic bodies of probable Paleozoic age that 

extends from Kodiak Island to the St. Elias Mountains is in the Anchorage district.

Tertiary continental deposits underlie Cook Inlet and large areas in 

the Susitna Lowland and Matanuska Valley and small areas in the 

northeastern part of the Valdez Creek district. Tertiary and Quaternary volcanic rocks have been found in the Matanuska Valley and 

west of Anchorage, and in the southern Alaska Range, where Augustine Island and some of the highest peaks are active volcanoes. Much of 

the Cook Inlet-Susitna Lowland and the western part of the Copper 

River Lowland are underlain by thick glacial and alluvial deposits. 

Except along Cook Inlet and some of the large rivers, most of the region 

is underlain by permafrost. Ice completely covered this part of Alaska 

during the Pleistocene, spreading from the Alaska Range far out to 

sea. Ice still covers the highest parts of the mountains, and valley 

glaciers, one more than 35 miles long, extend far from their source 

areas.

Gold and silver have been recovered from lodes in many parts of the 

Cook Inlet-Susitna region and a little copper from deposits in the 

Redoubt and Valdez Creek districts. These and other lodes have also 

been investigated as possible sources of antimony, iron, chromite, 

molybdenum, copper, lead, and zinc. In the southern Alaska Range 

metallic sulfide minerals are common in and near granitic plutons. 

Float samples collected in the vicinity of one pluton in the southwestern part of the Yentna district contained as much as 60 parts per
COPPER RIVER REGION 13

million (about 1.7 ounces per ton) of gold associated with chalcopyrite, 

arsenopyrite, and other sulfides. The only large-scale production, however, was from the Willow Creek area north of Palmer where between 

1909 and World War II gold-bearing quartz veins in the southern 

border zone of the Talkeetna batholith were the source of about 

404,425 ounces of gold, 5 percent of Alaska's total lode gold output. 

Minor amounts of gold, silver, and base metals have been produced 

from the upper Chulitna area near the Alaska Railroad. Total metallic 

resources are large and, in the future, might well become important to 

the Alaskan economy.

Placer gold was discovered in the Cook Inlet-Susitna River region in 

the late 19th century, and mining has been carried on continuously 

since the early 1900's. Output was probably about 250,000 ounces, or 

less than 70 percent of the lode-gold production. The bulk of the placer 

gold has come from steams that drain the Dutch Hills and Fairview 

Mountain in the Yentna district, from Valdez Creek in the Valdez 

Creek district, and from Crow Creek in the Anchorage district.

Other mineral resources that have been exploited include pumice 

from Augustine Island, minor amounts of ceramic clay and agricultural lime from near Anchorage, a little gypsum and clay from Sheep 

Mountain in the upper Matanuska Valley, soapstone (for carving) 

from near Palmer, and large amounts of construction materials along 

railroad and highway routes and near Anchorage, the largest metropolitan area in the state. Limestone deposits in the northwestern 

part of the Valdez Creek district and in the Matanuska Valley east of 

Palmer have been investigated as possible sources of raw material for 

Portland cement.

Oil and gas produced from fields in Cook Inlet and southeast of it in 

the Homer and Hope districts of the Kenai Peninsula region have far 

outshadowed all other mineral commodities in value; since 1959 the 

value of this hydrocarbon production has been greater than $1V4 billion and constitutes almost the entire production of the State.

There are large resources (more than 2 l/z billion short tons) of 

bituminous and subbituminous coal in the Matanuska Valley of the 

Willow Creek district, in the Tyonek-Beluga River area of the Redoubt 

district, in the central part of the Yentna district, and near Broad Pass 

in the Valdez Creek district. Extensive mining has been carried on 

only in the Matanuska Valley.

COPPER RIVER REGION

The Copper River region includes the area drained by the Copper River 

and its tributaries, the area east of the divide between Prince William 

Sound and Cook Inlet, the area drained by streams flowing into the 

Gulf of Alaska between the Copper River and 141° west longitude, and
14 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

offshore islands, including Middleton Island. It is divided into five 

districts: Chistochina, Nelchina, Nizina, Prince William Sound, and 

Yakataga.

The region is in the Pacific Mountain System and includes parts of 

the Alaska Range, Wrangell, St. Elias, and Kenai-Chugach Mountains, and Copper River Lowland physiographic provinces. The mountains, which rise to summits more than 16,000 feet in elevation in the 

Wrangells and to more than 18,000 feet at Mount St. Elias, support 

and nourish the largest ice fields and piedmont ice lobes and some of 

the longest valley glaciers in North America; all are remnants of 

Pleistocene ice that covered most of the region. The Copper River 

Lowland and the Chitina Valley are largely mantled by thick accumulations of Pleistocene and Holocene glacial, lacustrine, and fluvial 

deposits that are frozen to depths of several hundred feet. The islands 

and most of the shores of Prince William Sound, the Copper River 

delta, and the lowlands and low mountains bordering the Gulf of 

Alaska in the Yakataga district are generally free of permafrost.

Bedrock in the Copper River region ranges in age from late Paleozoic 

to Quaternary. The bulk of the rocks are of Mesozoic age, and they 

include great thicknesses of graywacke, slate, and greenstone and 

lesser amounts of carbonate rocks. In late Mesozoic and early Tertiary 

time, plutons, some of batholithic dimensions, invaded older rocks in 

many parts of the region. Most are composed of granodiorite, quartz 

diorite, and related rock types. The largest are in the Alaska Range 

and the Chugach and St. Elias Mountains.

In the Yakataga district complexly deformed Tertiary and lower 

Pleistocene marine and continental rocks underlie the area between 

the crest of the Chugach Mountains and the Gulf of Alaska. Some may 

be continuous with similar coeval rocks in Cook Inlet and on Kodiak 

Island. They extend at least as far offshore as Middleton Island, the 

highest part of a broad topographic feature that rises abruptly from the 

continental shelf. The most prominent formation in the Wrangell 

Mountains is the Wrangell Lava, a thick pile of Tertiary and Quaternary andesitic flows and associated rocks. Mount Wrangell (14,005 ft) 

still emits steam and ash.

Lodes in many parts of the Copper River region contain copper, gold, 

silver, molybdenum, antimony, nickel, chromite, iron, lead, and zinc, 

but only copper, gold, and byproduct silver were mined commercially. 

The famous Kennecott mines near McCarthy in the Nizina district and 

mines in the southwestern and northeastern parts of Prince William 

Sound accounted for most of the copper (690,000 short tons) produced 

in Alaska. Two or three million dollars worth of gold and smaller 

amounts of silver came from mineralized quartz and calcite veins in 

graywacke, slate, and granitic rocks and as byproducts of copper min-
KENAI PENINSULA REGION 15

ing in the Prince William Sound district. Similar veins in the southeastern part of the Nelchina district were mined in a small way, but 

the entire region was not a significant contributor to the total lode gold 

production of Alaska.

Placer deposits have been worked in all the districts of the Copper 

River region, but the total production was probably less than 350,000 

ounces of gold and a few ounces of platinum. Placers near the head of 

the Chistochina River (derived from gold-bearing Tertiary continental 

rocks and glacial deposits) and near Slana in the Chistochina district 

probably accounted for 150,000-160,000 ounces of gold and all the 

platinum, deposits in the north-central part of the Nizina district for 

about the same amount of gold, and beach and stream placers in the 

Yakataga and Nelchina districts for almost all the remainder. Production from the Prince William Sound district probably did not exceed 

500 ounces. About 40 tons of native copper was recovered from Dan 

Creek in the Nizina district, and copper is a constituent of concentrates 

from neighboring streams.

The first successful oil well in Alaska was drilled in Tertiary rocks 

near Katalla in the western part of the Yakataga district in 1902. 

Although more wells, all shallow, were drilled during the ensuing 30 

years, total production was only about 150,000 barrels. A few miles to 

the north, Tertiary coal-bearing rocks underlie an area of about 50 

square miles in the Bering River coal field. Prospecting has failed to 

develop a commerical mine, probably because of the great structural 

complexity of the area. Other than road metal and some construction 

materials for local use, no nonmetallic mineral resources have been 

developed in the Copper River region.

KENAI PENINSULA REGION

The Kenai Peninsula region is the Kenai Peninsula south of Turnagain Arm and west of the divide between Cook Inlet and Prince 

William Sound. It is divided into the Homer, Hope, and Seward districts.

The region, which is entirely within the Pacific Mountain System, 

includes parts of two major physiographic provinces. West of a line 

extending from the head of Kachemak Bay to Turnagain Arm is an 

area of subdued relief that is part of the Cook Inlet^Susitna Lowland. 

Most of it is considerably less than 1,000 feet above sea level, but 

rolling hills and a few steep-sided ridges rise to elevations of nearly 

3,000 feet. The rest of the Kenai Peninsula, part of the Kenai-Chugach 

Mountains, is characterized by high relief with many of the summits 

between 4,000 and more than 6,000 feet in altitude. Deep fiords, many 

with glaciers at their heads, embay its southeastern coastline. Remnants of Pleistocene ice that covered the entire peninsula and extended
16 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

far to sea are preserved as alpine glaciers and ice fields. The entire 

region is free of permafrost.

The Kenai Mountains, the highest parts of which are virtually 

unexplored, are made up of limestone, chert, and tuff of Triassic age 

that rest on metamorphosed older volcanic and clastic rocks of possible 

Paleozoic age and are in fault contact with Jurassic volcanic rocks and 

a thick sequence of intensely deformed but only slightly metamorphosed slate and graywacke, mainly of Late Cretaceous age. These 

rocks were intruded by Tertiary(?) granitic dikes, sills, and stocks. The 

Kenai Lowland and adjacent parts of Cook Inlet are underlain by 

many thousand feet of poorly consolidated, mainly continental, rocks 

of Tertiary age that rest on rocks similar to those exposed in the Kenai 

Mountains. These Tertiary rocks are buried by Quaternary deposits 

except along sea cliffs and in isolated inland exposures.

Only gold, alloyed with silver, and chromite have been mined from 

lodes in the Kenai Peninsula region, though copper, lead, zinc, molybdenum, antimony, and nickel minerals also have been found in them. 

Nearly 30,000 long tons of chromite with an average Cr2 O3 content of 

about 45 percent has been mined from two dunite and pyroxenite 

stocks in the southern part of the Homer district. In the eastern part of 

the Hope district and at Nuka Bay in the Homer district, quartz veins 

in graywacke and slate near small quartz diorite stocks and granite 

dikes and in the intrusive bodies themselves are hosts for gold and 

various sulfide minerals. The lode-gold production of the region probably was about 19,000 ounces.

Placer gold was discovered in 1848 on the Kenai River by P. P. 

Doroshin, a mining engineer in the employ of the Russian-American 

Company, but the gold was not in sufficient quantities for profitable 

mining at that time. Later placer mining was concentrated in the part 

of the Hope district where lode deposits were most extensively explored and mined, though a few streams and beaches in other parts of 

the Kenai Peninsula region where potentially valuable lodes have not 

been found were worked on a small scale. Total placer production from 

the Kenai Peninsula region since about 1895 was probably between 

100,000 and 105,000 ounces of gold.

The first major oil discovery in Alaska was in 1957 in the Swanson 

River field near Cook Inlet in the western part of the Hope district. 

This general area, Cook Inlet itself, and the adjoining parts of the Cook 

Inlet-Susitna River region have been the source of almost all of 

Alaska's petroleum production (see section on "Cook Inlet-Susitna 

River Region").

The first coal mine in Alaska was opened by Russians in 1855 at Port 

Graham in the southwestern part of the Homer district, and a few 

years later small-scale mining began near Homer. Total production
KODIAK REGION 17

from the Kenai Peninsula, however, probably did not exceed a few 

thousand tons of subbituminous coal and .lignite, almost all for local 

use. Total resources are estimated to be about 318 million short tons. 

Other than sand and gravel, no nonmetallic mineral resources in the 

Kenai Peninsula have been exploited, though deposits of diatomaceous earth, limestone, clay, and material possibly useful for manufacturing light-weight aggregate have been investigated.

KODIAK REGION

The Kodiak region includes Kodiak, Afognak, and the Trinity Islands and nearby small islands. The region is characterized by mountains with summits 2,000-4,000 feet in altitude and by gently rolling 

uplands. Long narrow inlets extend well into the interiors of Kodiak 

and Afognak Islands.

Most of the region is underlain by Cretaceous graywacke, slate, and 

conglomerate and older Mesozoic and probable Paleozoic marine and 

volcanic rocks containing a few small mafic and ultramafic bodies. 

These units and overlying early Tertiary volcanic and marine 

sedimentary rocks were invaded and locally metamorphosed by quartz 

diorite plutons, some of batholithic dimensions, in early Tertiary time. 

Younger Tertiary marine and continental rocks form the Trinity Islands and a fringe along the southeastern coast of Kodiak Island. 

Quaternary glacial and fluvial deposits mantle bedrock in low areas on 

western Kodiak Island, at the heads of bays, and along some of the 

larger streams. Long faults, some thrust and others steep with predominantly vertical movement, extend the length of the major islands. 

Outcrop and fault patterns give the region a pronounced northeasttrending grain that, if extended, would join generally similar features 

at the southwest end of the Kenai Peninsula. The Kodiak region was 

covered by Pleistocene ice that extended from the crest of the Aleutian 

Range across the islands and several tens of miles into the Pacific 

Ocean. Glaciation removed most unconsolidated material and any 

placer deposits that may have been formed in preglacial valleys. Ice 

remains in a few cirque glaciers on the highest peaks on Kodiak Island.

An unknown, but probably small, amount of gold was mined from 

several lode deposits in the Kodiak region, mainly before World War I 

and in the 1930's. The known lode occurrences of tungsten and copper 

have proved to be too small and too low grade to be mined.

The only placers that have been found in the region are in beach 

deposits where gold was concentrated from glacial outwash and till. 

Most placer mining was on the west coast of Kodiak Island where wave 

action concentrated heavy minerals in a veneer of material in transit 

across a planation surface cut on glacial deposits. Ninety-five percent 

of the concentrates was magnetite. Other heavy minerals in the con-
18 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

centrates include pyrite, chromite, gold, and a little platinum.

The total production of gold probably was not more than a few 

thousand ounces.

Current interest in the mineral resources of the region is mainly in 

the possibility of finding petroleum in Shelikof Strait and on the outer 

continental shelf in the Gulf of Alaska.

KUSKOKWIM RIVER REGION

The Kuskokwim River region includes Nunivak and Nelson Islands 

and the mainland area drained by streams flowing into Baird Inlet, 

Etolin Strait, and Kuskokwim Bay. It is divided into the Aniak, 

Bethel, Goodnews Bay, and McGrath districts.

Most of the Kuskokwim River region is in the Intermontane 

Plateaus physiographic division and is dominated by the Kuskokwim 

Mountains, a succession of rounded northeast-trending ridges 

1,500-2,000 feet in altitude surmounted locally by rugged mountains 

as much as 2,000 feet higher. Other upland areas include the Kilbuck 

Mountains and parts of Nunivak Island. The eastern boundary of the 

region is the crest of the southern Alaska Range, most of which is more 

than 6,000 feet in elevation. About a third of the region consists of 

parts of the Yukon-Kuskokwim and Kuskokwim-Tanana Lowlands 

and all of the Holitna Lowland, areas less than 1,000 feet in altitude.

The oldest rocks, exposed as a narrow belt of gneiss and schist about 

75 miles long in the western part of the region, are certainly older than 

Devonian and may be Precambrian in age. Paleozoic sedimentary 

rocks range in age from Cambrian to Devonian in the Alaska Range 

and from Devonian to Permian in the Kuskokwim Mountains. In the 

western part of the region, sedimentation, interspersed with volcanic 

activity, was virtually continuous through Mesozoic and Tertiary 

time. A great thickness, possibly as much as 5 or 6 miles, of graywacke, 

shale, conglomerate, volcanic rocks, and limestone underlies most of 

the area west of the Alaska Range and its foothills. These rocks were 

displaced along major northeast-trending zones of strike-slip faulting, 

some of which can be traced far beyond the boundaries of the region.

Tertiary and Quaternary basaltic lava flows and associated tuffs 

cover most of Nunivak and Nelson Islands. Upper Cretaceous and 

Tertiary plutons, dikes, and sills intruded the older rocks in nearly all 

parts of the region. The intrusive rocks range in composition from 

ultramafic to felsic, but most are granodiorite, quartz monzonite, and 

similar rock types. Quaternary fluvial and glacial deposits that locally 

have been reworked by wave and wind action floor the lowlands and 

valleys. Most of the surficial deposits are perennially frozen except 

near large bodies of water; many of the mountainous parts of the 

region are in areas underlain by discontinuous or isolated masses of
NORTHERN ALASKA REGION 19

permafrost. Only the Alaska Range, the mountains in the southwestern part of the region, and isolated summits of the Kuskokwim Mountains nourished Pleistocene glaciers, remnants of which are preserved 

in cirques and valleys in the Alaska Range.

Lodes in the Kuskokwim River region have been the source of 

almost all the mercury mined in Alaska, a total of about 40,000 

76-pound flasks since 1902. Some gold and a little byproduct antimony 

ore have also been mined. Other lodes, some of which were fairly 

extensively prospected, contain gold and various copper, lead, zinc, 

molybdenum, arsenic, tungsten, bismuth, antimony, mercury, manganese, and uranium minerals. Many occurrences of base and precious 

metals in the eastern parts of the Aniak and McGrath districts are in 

bedrock, and others consist of mineralized float that cannot have 

travelled far from lode sources in and near contact zones around 

granitic plutons.

Most of the mercury deposits consist of ore bodies that carry cinnabar, with or without stibnite, associated with diabase dikes (now 

altered to rocks composed of silica, carbonate, and clay minerals) that 

cut graywacke and shale. North of Medfra in the McGrath district 

auriferous lodes in recrystallized limestone intruded by quartz monzonite plutons were the source of 40-60 thousand ounces of gold and a 

little silver.

Prospectors looking for gold passed through the Kuskokwim River 

region as early as 1889, but no placer deposits were found until about 

1900. Placer gold production since 1908 has been about 650,000 

ounces, approximately 3.2 percent of the total for the State. The major 

producing area was near Nyac in the Aniak district; significant 

amounts of gold also came from streams in the Bethel, Goodnews Bay, 

and McGrath districts. Platinum or mercury accompanies gold in most 

of these placers. The Salmon River drainage near Platinum in the 

southwestern part of the Goodnews Bay district has been the source of 

well over half a million ounces of platinum-group metals, a major 

portion of the primary production of the United States. These deposits 

are still being actively mined. Scheelite was mined as a byproduct of 

gold from Fortyseven Creek in the central part of the Aniak district.

No occurrences of potentially valuable nonmetallic mineral commodities or mineral fuels have been reported from the region, though 

there are a few thin beds of probably bituminous coal on Nelson and 

Nunivak Islands.

NORTHERN ALASKA REGION

The northern Alaska region is the part of Alaska drained by streams 

flowing into the Arctic Ocean and Chukchi Sea from the AlaskaYukon boundary (141° west longitude) on the east to and including the
20 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

Wulik River on the southwest. The region is divided into the Barrow, 

Canning, Colville, Lisburne, and Wainwright districts.

The region lies wholly within the Interior Plains and Rocky Mountain System physiographic divisions and includes the Arctic Coastal 

Plain, nearly all the Arctic Foothills, and about half of the Brooks 

Range and DeLong Mountains. The lake-dotted coastal plain rises 

gradually from the Arctic Ocean to a maximum altitude of 600 feet at 

its south margin, where it merges with rolling plateaus and uplands. 

The southern part of the region is marked by rugged east-trending 

mountains 4,000-8,000 feet in altitude.

The bedded rocks form two east-trending belts: a southern belt of 

Paleozoic carbonate and clastic rocks and a northern belt of Mesozoic 

mainly clastic rocks. Tertiary conglomerate, sandstone, and siltstone 

underlie parts of the Canning and Colville districts. The Paleozoic and 

Mesozoic rocks were displaced northward along folds, nappes, and 

thrust faults, along some of which there were many miles of movement. In the Romanzof Mountains in the eastern part of the Canning 

district, granitic rocks invaded bedded rocks of pre-Mississippian age. 

In the western Brooks Range and the Arctic Foothills, Jurassic mafic 

intrusive bodies cut the older rocks. The Arctic Coastal Plain is covered by Quaternary silt, sand, and gravel.

In northern Alaska only the Brooks Range and DeLong Mountains 

supported extensive Pleistocene glaciers, small remnants of which 

form isolated cirque glaciers. The entire region is in a zone of continuous permafrost, which reaches thicknesses of many hundreds of feet.

Economic interest in northern Alaska has been focused mainly on 

fossil fuels. In 1968 one of the largest oil discoveries in North America 

was made at Prudhoe Bay near the mouth of the Sagavanirktok River 

in the Canning district. Other smaller oil and gas fields were found 

while exploring Naval Petroleum Reserve No. 4 during and after 

World War II. Total proved reserves of known fields are about 10 

billion barrels of oil and about 26 trillion cubic feet of gas. Oil shale, 

some very rich, is widely distributed along the Brooks Range. Between 

Cape Lisburne and the Colville River, coal occurs in Paleozoic and 

Mesozoic rocks. Very conservative estimates of the total coal resources 

under less than 3,000 feet of overburden are 9,292,000,000 tons of 

bituminQus coal in beds more than 14 inches thick and 

100,905,000,000 tons of subbituminous coal in beds more than 2Vfe feet 

thick. A little gas near Barrow and small tonnages of coal from several 

places near the coast have been produced for local use.

No metallic lode deposits have been reported from northern Alaska 

although from time to time Eskimos have brought to Barrow specimens of galena and sphalerite, the sources of which are not known. 

Small amounts of gold have been found in the drainages of the Firth,
NORTHWESTERN ALASKA REGION 21

Malcolm, and Kongakut Rivers in the eastern part of the Canning 

district, but no valuable placer deposits have been discovered anywhere in the northern Alaska region. Phosphatic materials in 

amounts or concentrations of no commercial importance under present 

economic conditions occurs in Carboniferous and Triassic rocks.

NORTHWESTERN ALASKA REGION

The northwestern Alaska region is the area drained by streams 

flowing into Kotzebue Sound from the Wulik River on the north to (and 

including) the Kauk River on the south. It is divided into the Kiana, 

Noatak, Selawik, and Shungnak districts.

The region includes the Baird Mountains, part of the Brooks Range, 

and diverse parts of lower uplands and lowlands drained mainly by the 

Noatak, Kobuk, and Selawik Rivers. Most of the mountains are in 

rugged eastward-trending groups 3,000-5,000 feet in altitude that are 

separated by lake-dotted tundra-floored lowlands. A few peaks in the 

eastern part of the region reach altitudes of more than 8,000 feet.

In the northern part of the region, which is still incompletely mapped, the bedded rocks include limestone and marble, dolomitic limestone (some reefoid), and metamorphosed clastic and volcanic rocks, 

most of which are of early Paleozoic age, though some of the volcanic 

rocks are as young as Jurassic. These rocks have been complexly folded 

and displaced by thrust and normal faults. Mafic and ultramafic bodies 

of probable Jurassic age cut the older rocks near Misheguk Mountain 

and north of the Kobuk River. Cretaceous clastic rocks overlie the 

older units. In the southern part of the region, the bedded rocks are 

mainly Cretaceous clastic and volcanic rocks that were intruded by 

granitic plutons, some of which are alkalic. The Mesozoic rocks are 

overlain by Tertiary and Quaternary basalt flows. Most of the lowland 

areas are covered by thick deposits of Quaternary fluvial, glacial, 

eolian, and marine sand, silt, and gravel.

Pleistocene ice covered northwestern Alaska except for parts of the 

Baird Mountains and the southern part of the Selawik district. Now, 

however, only a few cirque glaciers remain. The region is underlain by 

continuous permafrost except for an area in the Selawik district and 

along some of the larger streams.

Lodes potentially valuable for copper have been found in the Kiana, 

Noatak, and Shungnak district, but only one, that at Bornite in the 

western part of the Shungnak district, has been extensively explored. 

Galena, silver, and a little gold are constituents of some lodes. Float 

magnetite is common on Iron Mountain near Bornite, but the bedrock 

source has not been found. In 1944 and 1945, 45 tons of tremolite and 1 

ton of chrysotile asbestos were shipped from deposits near Dahl Creek 

in the Shungnak district. Asbestiform minerals are common in veins
22 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

here and elsewhere north of and within a few miles of the Kobuk River. 

Nephrite jade, some of gem quality, occurs with the asbestos.

Placer gold was discovered near Shungnak in 1898, on Klery Creek 

in the central part of the Kiana district in 1909, and much more 

recently near Purcell Mountain in the Selawik district. Data on production, though incomplete, indicate that the total amount of gold 

mined was probably somewhat less than 100,000 ounces, about half of 

which came from the streams near Shungnak and about half from 

Klery Creek and its tributaries. Jade, used for jewelry and objets d'art, 

is picked from streams and old tailings piles near Shungnak.

Coal close to the borderline between bituminous and subbituminous 

in rank occurs in widely scattered localities in Cretaceous rocks near 

the Kobuk River, but none has been mined except for local use in 

nearby placer-gold fields.

SEWARD PENINSULA REGION

The Seward Peninsula region includes the Seward Peninsula and 

the drainage basins of the Buckland, Inglutalik, Ungalik, and Shaktolik Rivers and Egavik Creek. The region is divided into the Council, 

Fairhaven, Kougarok, Koyuk, Nome, Port Clarence, and Serpentine 

districts.

The Seward Peninsula consists mostly of rounded hills and flat 

divides 500-2,000 feet in altitude; there are also isolated groups of 

rugged glaciated mountains 20-60 miles long and 10 miles wide that 

rise to peaks 2,500-4,700 feet in altitude. A relatively small part of the 

region consists of interior lowlands and a coastal plain that fringes 

much of the peninsula.

About half the region is underlain by schist, gneiss, limestone, and 

slate, which is predominantly of Paleozoic age, but locally, as in the 

Kigluaik and Bendeleben Mountains, may be as old as Precambrian. 

Most of the region's lode deposits are in the Paleozoic rocks. Mesozoic 

rocks broadly divisible into two major groups are abundant in the 

eastern part of the region. One group consists chiefly of slightly 

metamorphosed intermediate volcanic rocks, and the other mainly of 

marine sandstone and shale. The youngest stratified rocks are volcanic 

ash and basaltic lava flows, in part perhaps as old as late Tertiary but 

mainly Pleistocene in age. One lava flow near Imuruk Lake is no more 

than a few centuries old. Most of the pre-Tertiary bedded rocks are 

complexly deformed. In Early Cretaceous time they were involved in a 

series of imbricate thrust sheets that were then intricately folded and 

displaced by normal faults, some with displacement measurable in 

thousands of feet and intruded by stocks and batholiths that range in 

age between 100 and 90 million years.

Sand, gravel, and silt thinly mantle bedrock throughout the Seward
SEWARD PENINSULA REGION 23

Peninsula region and form deposits as much as 100 feet thick in the 

lowlands. The Kigluaik, Bendeleben, Darby, and York Mountains and 

highland areas near the Kiwalik River in the eastern part of the region 

were glaciated during the Pleistocene Epoch. Ice extended to the Bering Sea from the Kigluaik Mountains at Nome and from the York 

Mountains in the western part of the peninsula. Only a few small 

cirque glaciers remain in the highest mountains. The entire peninsula 

is generally underlain by permafrost.

Metalliferous lodes that were sources of significant amounts of ore, 

or that contain important resources, include deposits of gold and of tin, 

tungsten, antimony, and beryllium minerals. Other metals have been 

discovered, but no major deposits are known although small amounts 

of copper, lead, and silver, and possibly mercury, have been mined. 

Total gold production from lodes in the region was no more than a few 

tens of thousands of ounces; tin lodes in the western part of the Port 

Clarence district were sources of about 350 tons of tin metal.

The Seward Peninsula has been the source of 30.7 percent, about 

6,260,000 ounces, of the placer gold produced in Alaska. Only the 

Fairbanks district of the Yukon River region has produced more. Data 

are not adequate to apportion the total published production for the 

region among the districts of the Seward Peninsula, but probably half 

the placer gold reported came from beaches, both modern and Pliocene 

and Pleistocene, in the Nome district, and the greater part of the rest 

from stream placers in the Nome, Kougarok, Council, and Fairhaven 

districts. In much of the peninsula the richest stream placers are near 

mineralized contacts (possibly thrust faults) between limestone and 

schist of Paleozoic age. About 2,000 tons of placer tin has been recovered from valleys in the western part of the Seward Peninsula. A little 

byproduct platinum has come from the eastern part of the region, and 

about 1,800 units (36,000 pounds) of WOs (tungstic oxide) from 

streams and residual material near scheelite-bearing lodes in the 

Nome area. An additional unknown, but undoubtedly small, amount 

of scheelite was saved during placer-mining operations for gold in both 

the eastern and western parts of the peninsula. Some wolframite may 

have been recovered during tin-mining operations.

Nonmetallic mineral resources include large fluorite deposits near 

Lost River in the western part of the Port Clarence district. These have 

recently been extensively explored by a private company and may be 

in production soon. Tin, tungsten, and possibly beryllium are potential 

coproducts or byproducts. A little graphite was mined from schist on 

the north flank of the Kigluaik Mountains in the southern part of the 

Port Clarence district. In the same general area a few tons of garnet 

sand was shipped to Nome from a beach of Imuruk Basin.

Lignitic coal occurs in small areas in several parts of the Seward
24 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

Peninsula but has been mined only in the Kugruk valley in the 

Fairhaven district where 60,000-100,000 tons was mined for local use 

between 1908 and 1911. Petroleum possibilities of the region are 

restricted to the continental shelves north and south of the Seward

TJ^-pl -I M O| 1 1 Q

SOUTHEASTERN ALASKA REGION

The southeastern Alaska region is the part of Alaska east of longitude 141°W. It is divided into the Admiralty, Chichagof, Hyder, 

Juneau, Ketchikan, Kupreanof, Petersburg, and Yakutat districts.

The region, part of the Coast Mountains physiographic province, is 

essentially mountainous and is composed of a wide belt of rugged 

islands with summits 2,500-3,500 feet in elevation and a deeply embayed mainland strip with high peaks, many over 10,000 feet in 

elevation, along the Alaska-Canada boundary. Many of the interisland waterways and major fiords and streams occupy long linear 

depressions, the most prominent of which is Chatham Strait, a deep 

trench 4-15 miles wide and at least 200 miles long. In the northwestern part of the district a narrow coastal plain, generally less than 200 

feet above sea level and in part covered by the Malaspina Glacier, 

separates the mountains and the Gulf of Alaska.

Southeastern Alaska was one of the earliest parts of the State to be 

settled, but the geology of much of it is still not well known. The 

outcrop pattern of southeastern Alaska is dominated by two 

northwest-trending belts of Mesozoic sedimentary and volcanic rocks, 

one adjacent to the Coast Range batholith along the Alaska-British 

Columbia boundary and the other along the seaward margin of the 

region. These belts are separated by a band of Paleozoic bedded rocks. 

Lava flows and tuffs of intermediate to mafiic composition and of 

Tertiary and Quaternary age are exposed on Admiralty, Kruzof, Kuiu, 

and Revillagigedo Islands. Mount Edgecumbe on Kruzof Island is a 

volcano that may have been active in historic time. Tertiary marine 

and nonmarine clastic rocks underlie part of the coastal plain and 

foothills near Yakutat. Tertiary nonmarine clastic rocks are exposed 

on central and southern Admiralty Island.

About a third of the region is made up of plutonic rocks ranging in 

composition from felsic to ultramafic and in age from Paleozoic to 

Tertiary. The largest pluton is the Coast Range batholith, a composite 

structurally complex generally felsic mass exposed along the International Boundary for the length of southeastern Alaska. Smaller plutons, dikes, and sills occur throughout the region. All the preQuaternary bedded rocks have been folded and displaced by faults, 

some with estimated displacements measurable in many tens of miles.

Extensive Pleistocene glaciation greatly modified the preexisting 

surface of southeastern Alaska. Valleys and interisland waterways
SOUTHEASTERN ALASKA REGION 25

were scoured and deepened, and most preglacial unconsolidated deposits were removed. Remnants of Pleistocene glaciers and ice fields 

still cover large areas in the high country, and glacial deposits mantle 

the lower slopes. The Malaspina Glacier in the Yakutat district is one 

of the largest piedmont ice lobes in the world. In general the region is 

free of permafrost.

Gold, silver, copper, lead, zinc, platinum-group metals, tungsten, 

and uranium have been mined commercially from lode sources. Exploratory work, some intensive, has been carried on at prospects potentially valuable for the same metals and for nickel, cobalt, chromite, 

iron, molybdenum, antimony, and rare-earth elements. Most of the 

lodes are in metamorphic rocks adjacent to the Coast Range batholith 

and smaller plutons, though some are confined to the plutons, mainly 

in marginal facies. Lode production amounted to 7V6 to 8 million 

ounces of gold (mostly from the Juneau and Chichagof districts), several million ounces of silver (all byproduct or coproduct), about 30 

million pounds of copper (from Prince of Wales Island), and more than 

a quarter of a million pounds of lead (mainly from the Hyder district), 

as well as small amounts of platinum and palladium (from the Salt 

Chuck mine in the Ketchikan district), tungsten, zinc, and uranium. 

Deposits of iron ore near Klukwan in the northern part of the Juneau 

district and at Port Snettisham in the southern part of the district have 

been extensively explored since World War II. One or both may soon be 

developed for the Japanese market.

Compared to the large amount of gold from lode sources in the 

region, the amount recovered from placer deposits (probably less than 

125,000 ounces) is insignificant. Intense alpine glaciation removed 

most placers that might have been formed as a result of the preglacial 

erosion of lodes. Most modern streams have extremely steep gradients 

and discharge into deep fiords, so few gravel deposits are being formed 

today. Streams near Haines and Juneau in the Juneau district and 

near Windham Bay in the Petersburg district were the sources of most 

of the placer gold that has been recovered. Beach sands near Lituya 

and Yakutat Bays in the Yakutat district were mined for many years, 

but the total production was probably less than 4,000 ounces. A little 

platinum occurs with the gold near Lituya Bay.

Nonmetallic mineral resources include large amounts of highcalcium limestone and smaller amounts of marble, gypsum, garnet, 

and barite, all of which have been produced commercially. Asbestos, 

fluorite, and mica occurrences are also known but may not be of 

economic importance.

Sometime before 1929 a little bituminous coal was shipped to 

Juneau from a mine in Tertiary rocks on central Admiralty Island, but 

the beds are thin and contain shale partings, so extensive development
26 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

in the forseeable future is unlikely. Although drilling for oil near 

Yakutat has not been successful, there is great interest in the offshore 

petroleum potential of the Gulf of Alaska.

YUKON RIVER REGION

The Yukon River region is the area drained by the Yukon River and 

its tributaries and by the Unalakleet and Manopiknak Rivers and 

intermediate streams flowing into Norton Sound and the Bering Sea. 

The region is divided into 26 districts, described below in alphabetical 

order.

ANVIK DISTRICT

The Anvik district comprises the western drainage of the Yukon 

River between Koyukuk and (and including) the Koserefsky River and 

the area drained by streams flowing into Norton Sound between Unalakleet and St. Michael Bay.

The district is in the Nulato Hills physiographic province, an area 

characterized by north- to northeast-trending ridges with crests generally between 2,000-4,000 feet in altitude separated by structurally 

controlled valleys with long straight segments. The ridges near Norton Sound are somewhat lower.

The area is underlain largely by Cretaceous and Tertiary (?) volcanic rocks and by mainly Cretaceous clastic marine and nonmarine 

units of the Koyukuk sedimentary basin. An older Paleozoic and 

Mesozoic volcanic unit includes intrusive diabase and serpentinite. A 

large Mesozoic felsic pluton and a line of smaller similar bodies are 

exposed near the Anvik River. The area southeast of St. Michael is 

underlain by Tertiary (?) and Quaternary basalt, some of which is so 

young that primary volcanic features are only slightly modified. The 

district was not glaciated. It is mainly in a zone of thick to thin 

permafrost.

The only lode deposit so far discovered in the Anvik district consists 

of traces of cinnabar and stibnite in hydrothermally altered rhyolite 

about 40 miles northeast of Marshall. The single commercial placer 

deposit was on Flat Creek in the southwest corner of the district. An 

unknown amount of gold, probably less than 25,000 ounces, was mined 

between 1918 and 1940. Concentrates contained a little cinnabar.

Bituminous coal, generally in thin beds, is a common constituent of 

some of the Cretaceous rocks. Many years ago small tonnages were 

mined from several beds exposed at various places along the Yukon 

River for use in river steamboats. Lignitic coal in Tertiary shale about 

10 miles south of Unalakleet has also been mined for local use.

BLACK DISTRICT

The Black district is bounded on the east by the Alaska-Yukon
YUKON RIVER REGION 27

boundary, on the south by the Yukon River, on the west by an arbitrary line between Graphite Point on the Porcupine River and Circle 

on the Yukon River, and on the north by the divide between the Black 

and Porcupine Rivers.

The district is mainly in the Porcupine Plateau and Ogilvie Mountains physiographic provinces. The Porcupine Plateau consists generally of rounded ridges averaging 1,500-2,000 feet in altitude, above 

which isolated summits and a small mountain range project a few 

hundred feet and into which the principal rivers have cut wide, 

flat-floored valleys. The Ogilvie Mountains in the southeastern part of 

the district are somewhat higher; a few peaks reach elevations of over 

4,500 feet. The western boundary of the district roughly follows the 

east edge of the swampy Yukon Flats, most of which is at an altitude of 

less than 800 feet.

Sedimentary and volcanic rocks that range in age from Precambrian 

to Cretaceous underlie most of the Black district. Quaternary fluvial 

deposits and loess floor the major valleys and blanket much of the 

northwestern part of the district. The area was not glaciated but is in 

zones of discontinuous and thick to moderately thick permafrost.

The only metallic mineral resource is hematite in a basalt and 

red-bed unit of the Precambrian Tindir Group in the southeastern part 

of the district.

Bituminous coal occurs in the Nation River Formation of Devonian 

age. About 2,000 tons was mined in 1897.

BONNIFIELD DISTRICT

The Bonnifield district is the area drained by southern tributaries of 

the Tanana River between and including the Teklanika and Little 

Delta Rivers.

The district is in the Alaska Range and Tanana-Kuskokwim Lowland physiographic provinces. The highest peaks in this part of the 

Alaska Range rise over 11,900 feet, but most of the crest is only about 

5,000 feet above sea level and is less than 2,500 feet at Broad Pass, 

which separates major headwater tributaries of the Nenana and 

Chulitna Rivers. The range is flanked on the north by foothills that are 

parallel to the main range and slope northward to lowlands generally 

well below 1,000 feet in altitude.

The Alaska Range is underlain by Precambrian (?) and Paleozoic 

schists of both sedimentary and igneous origin, quartzite, and marble, 

all of which were intruded by Mesozoic and Tertiary stocks and dikes of 

granite, granodiorite, dacite, andesite, and basalt. In the extreme 

southern part of the district, unmetamorphosed Paleozoic and 

Mesozoic rocks similar to those in the northern part of the adjacent 

Cook Inlet-Susitna River region are exposed. Several thousand feet of
28 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

Tertiary clastic rocks, coal, and volcanic rocks crops out along the 

north flank of the Alaska Range. The Nenana Gravel, a still younger 

Tertiary formation that commonly is poorly consolidated, covers wide 

areas between the crest of the Alaska Range and the TananaKuskokwim Lowland. Deposits of several Pleistocene glaciations have 

been identified, particularly in the Nenana River valley. Except for 

several ice tongues that extended well beyond the mountains, the 

lowlands were not glaciated, though thick glaciofluvial deposits and 

loess derived from them cover the bedrock except for a few isolated 

groups of hills in which Precambrian or Paleozoic rocks are exposed. 

The highest mountains are ice covered and are the source of several 

valley glaciers, two of which are more than 15 miles long. The district 

is in zones underlain by discontinuous or isolated masses of permafrost.

Lodes in the Bonnifield district are chiefly sulfide disseminations, 

veins, and lenses in schist and related rocks near the borders of felsic 

intrusive bodies. Small amounts of gold with subordinate silver and a 

few tons of antimony ore constituted the lode production. The district 

has been a small but steady producer of placer gold since 1904; the total 

output was probably only 45,000 or 50,000 fine ounces. Most of the 

deposits are stream placers, though gravel on a few benches also was 

mined. The ultimate source of the gold and accompanying heavy minerals was in quartz veins and mineralized zones in Precambrian (?) and 

Paleozoic schists, but much of the gold was probably reconcentrated 

from the Tertiary Nenana Gravel.

The most important mineral resources are extensive deposits of 

Tertiary coal, mainly subbituminous in rank. Total original resources 

in beds 2Mj feet thick or more and beneath less than 1,000 feet of 

overburden are estimated at 4,789,600,000 short tons. The major current commercial coal mining in Alaska is near Suntrana. Deposits of 

many nonmetallic mineral commodities and of construction materials, 

including limestone and perlite, have been investigated, but none 

have been developed except for road metal and railroad ballast.

CHANDALAR DISTRICT

The Chandalar district is the area drained by the Chandalar River 

and its tributaries above the village of Venetie. Its northern boundary 

is the crest of the Brooks Range.

The district includes parts of the Brooks Range, Porcupine Plateau, 

and Yukon Flats physiographic provinces and an extension of the 

Yukon-Tanana Upland (the Hodzana Highland). The Brooks Range 

slopes southeastward from a crestline 5,000-7,000 feet in altitude to 

less rugged mountains in the uplands where few summits are above 

5,000 feet. Broad valleys of some of the major forks of the Chandalar
YUKON RIVER REGION 29

River merge downstream into the Yukon Flats, a swampy area of low 

relief most of which is at an altitude of less than 1,000 feet.

The bedded rocks are mainly conglomerate and finer clastic 

sedimentary rocks, limestone and calcareous shale, and mafic volcanic 

rocks and chert, all of Paleozoic and early Mesozoic age. Basalt flows 

south of the Chandalar River are of possible Tertiary age. Devonian 

metamorphic rocks, largely of greenschist facies, form an almost continuous belt, in places as much as 25 miles wide, across the southern 

part of the district. Mesozoic granitic plutons, some of batholithic 

dimensions, with well-developed migmatite zones around some borders extend along the southern boundary of the district. Similar plutons intruded sedimentary and metamorphic rocks west and north of 

Chandalar Lake.

Except for some of the lower areas in the southern part, the district 

was covered by Pleistocene glaciers, remnants of which are still on 

some of the high peaks of the Brooks Range. Continuous permafrost 

underlies most of the district, though it may be absent locally.

Lodes in the Chandalar district contain gold and various sulfides, 

including stibnite, galena, and sphalerite. The only production, however, was an undetermined but probably small amount of gold, mainly 

from the Little Squaw mine in the southwestern part of the district. 

The deposits consist of many steeply dipping auriferous quartz veins in 

schist cut by gneissic granite. Since 1906 the district has been the 

source of probably 25,000-30,000 ounces of placer gold, mainly from 

streams that drain the area around the Little Squaw mine.

No nonmetallic mineral resources (other than material suitable for 

road metal) or mineral fuels have been found in the district.

CHISANA DISTRICT

The Chisana district is the Alaskan part of the area drained by the 

upper White River and its tributaries and by southern tributaries of 

the Tanana River above and including the Nabesna River.

From south to north it includes the summit areas and north slopes of 

the Wrangell Mountains, the Nutzotin Mountains and the southeastern part of the Mentasta Mountains (parts of the Alaska Range), and a 

lake-studded lowland above which rises several isolated patches of 

hills. The larger rivers all head in glaciers in the high mountains and 

carry heavy sediment loads. Except for lowlands near the Tanana 

River, the district was covered by ice during at least two Pleistocene 

glaciations. Isolated masses of permafrost occur in most of the area. 

Some of these were penetrated in placer workings.

The Chisana district is underlain mainly by thick sequences of 

Paleozoic and Mesozoic sedimentary and volcanic rocks cut by several 

large plutons composed chiefly of granodiorite and quartz diorite of
30 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

Mesozoic age. There are also a few small intrusive bodies of probable 

Tertiary age. Several isolated remnants of a once more extensive 

Tertiary gravel cover overlie the older rocks. The Wrangell Lava, a 

thick sequence of Tertiary and Quaternary flows, caps the high mountains in the southern part of the district. Unconsolidated glacial and 

fluvial deposits cover most of the lowlands.

Metallic lode deposits are scattered throughout the highland parts of 

the district, except in areas underlain by the Wrangell Lava. Between 

1930 and World War II, production from the Nabesna mine totaled 

$1,870,000 mainly in gold, but with some silver and copper. No production was recorded from any other lode deposit in the district. Of great 

current interest are several porphyry copper-molybdenum deposits 

that are being investigated by private enterprise.

Since 1913, placers in the district, almost all in an area of a few 

square miles near Bonanza Creek, have been the source of about 

45,000-50,000 ounces of gold. The gold was originally derived from 

small veins in the bedded Paleozoic and Mesozoic rocks, but much of it 

was reconcentrated from an extensive cover of Tertiary gravel, a 

remnant of which caps a hill near Bonanza Creek. Native copper, 

probably largely from amygdules in Triassic lava flows, is a common 

constituent of placer concentrates, both in the Bonanza Creek area and 

in other parts of the district.

No potentially valuable nonmetallic mineral resources or mineral 

fuels have been reported from the Chisana district.

CIRCLE DISTRICT

The Circle district is the area drained by north-flowing tributaries of 

the Yukon River from (and including) the Charley River to Circle, 

Birch Creek above the latitude of Circle, and most of Preacher Creek.

The district includes part of the Yukon-Tanana Upland, the northwest end of the Eagle Trough, and a small tip of the Yukon Flats 

physiographic provinces. The upland is an area of nearly accordant 

ridge crests, 3,000-5,000 feet in altitude, above which domes and 

isolated summits, especially in the southeastern part of the district, 

rise as much as 1,400 feet. The gross pattern of the entrenched complex 

drainage system probably was determined by faults and by jointing in 

crystalline rocks. The Eagle Trough, also called the Tintina Valley, is 

a lower area that extends northwestward from the Alaska-Yukon 

boundary parallel to the Yukon River, from which it is separated by a 

line of low hills. At its northwest end, about 25 miles south of Circle, it 

merges with the Yukon Flats, a lake-studded area less than 1,000 feet 

above sea level.

The upland area is a complex metamorphic terrane of Precambrian 

(?) and Paleozoic gneiss, schist, and crystalline limestone that was
YUKON RIVER REGION 31

invaded by mainly Mesozoic felsic, mafic, and ultramafic intrusive 

bodies, the largest of which is the Charley River batholith, which 

underlies much of the southeastern part of the district. Upper Cretaceous and Tertiary continental rocks, including a few thin lignite or 

subbituminous coal beds, floor the Eagle Trough. Between the Eagle 

Trough and the Yukon River bedrock is Paleozoic and Mesozoic unmetamorphosed clastic, carbonate, and volcanic rocks. Quaternary 

deposits include alluvium and terrace gravels along streams, loess in 

many places, and glacial deposits near some of the highest mountains, 

the only parts of the area that were covered by Pleistocene ice. The 

highland parts of the district are in a zone of discontinuous permafrost, 

and the lowlands in zones characterized by generally continuous permafrost.

No productive lodes have been found in the Circle district, though a 

few prospects have been explored for copper, gold, or lead. Since 1894 

nearly 750,000 ounces of placer gold (about 3.6 percent of the total for 

the state) has been mined from streams in the Circle district. The bulk 

of this came from Mammoth and Deadwood Creeks and their 

tributaries near Miller House and from Coal and Woodchopper Creeks, 

which are tributaries of the Yukon River. Near Miller House the heavy 

minerals in the placers were derived from mineralized veins in the 

metamorphic rocks and younger felsic plutons. When the price of tin 

and tungsten was high, small amounts of byproduct cassiterite and 

wolframite were separated from the rest of the concentrates. Some of 

the gold in the placers of Coal and Woodchopper Creeks was probably 

reconcentrated from Tertiary and continental rocks.

No nonmetallic mineral resources other than material suitable for 

road metal and similar uses have been found in the district. As far as it 

is known, there has been no attempt to utilize the coal in the Eagle 

Trough.

DELTA RIVER DISTRICT

The Delta River district is the area drained by northward-flowing 

tributaries of the Tanana River between and including the Johnson 

River on the east and Delta Creek on the west.

The district is mainly in the Alaska Range, where many peaks are 

more than 8,000 feet and a few are more than 13,000 feet in altitude. 

The drainage divide between the Delta and Gulkana Rivers is about 35 

miles south of the highest peaks. From the crest of the Alaska Range 

the land slopes northward to the flats of the Tanana-Kuskokwim 

Lowland where elevations are less than 1,500 feet.

The Denali fault, one of the major tectonic elements of Alaska and 

adjoining parts of Canada, crosses the district just south of the crest of 

the Alaska Range. The area north of the fault is underlain mostly by 

Precambrian and Paleozoic metamorphosed rocks, largely of sedimen-
32 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

tary origin. They were intruded, mainly in the Mesozoic Era, by granitic dikes, sills, and plutons, some of batholithic dimensions. South of 

the fault a few exposures of metamorphic rocks have been reported, but 

most of the area is underlain by Paleozoic and Mesozoic volcanic and 

clastic rocks with discontinuous interbedded Paleozoic limestone 

units. Dikes, sills, and other intrusive bodies that range in composition 

from felsic to ultramafic and are of Paleozoic and Mesozoic age intruded the bedded rocks. Tertiary nonmarine rocks, some coal bearing, 

cover large areas north of the mountain front and smaller areas in the 

Alaska Range. The mountains were glaciated several times during the 

Pleistocene. Large tongues of ice advanced down the valley of the Delta 

River nearly to its confluence with the Tanana. Much of the high 

country is still ice covered, and large valley glaciers extend down to 

elevations well below 3,000 feet. Glacial and glaciofluvial deposits 

cover most of the district, and loess derived from periglacial flood 

plains blankets much of the Tanana valley. Most of the district is in a 

zone of discontinuous permafrost; some areas in the TananaKuskokwim Lowland are underlain by moderately thick to thin permafrost.

Except for a few tons of ore that was mined, but not shipped, from a 

molybdenite deposit about 15 miles north of Mount Hayes, there has 

been no lode mining in the Delta River district, though occurrences of 

sulfide minerals, most associated with ultramafic or volcanic rocks 

south of the Denali fault, have been found. Some of these deposits and a 

quartz vein in schist a few miles north of the Denali fault carry a little 

gold, but not enough to be of current economic interest. Total placergold production was not enough to be of current economic interest. 

Total placer-gold production was not much more than 1,000 ounces 

and was mainly from Rainy Creek south of the Denali fault where 

some of the gold was probably reconcentrated from glacial deposits.

The nonmetallic mineral resources of the district consist of asbestos 

associated with serpentinite near the headwaters of the Delta River 

and granite in a quarry east of the lower Gerstle River.

The Jarvis Creek coal field contains resources of high-ash subbituminous coal in thin beds estimated at 76,500,000 short tons. A few 

thousand tons were mined in 1958 and in 1971-72.

EAGLE DISTRICT

The Eagle district is the area drained by the southern tributaries of 

the Yukon River between (but excluding) the Charley River on the 

west and the Alaska-Yukon boundary on the east.

The district includes parts of the Eagle Trough and Yukon-Tanana 

Upland physiographic provinces. The upland is an area of even-topped 

ridges, 3,000-5,000 feet in elevation, separated by generally narrow 

valleys and, along the southern boundary of the district, surmounted
YUKON RIVER REGION 33

by isolated mountains that rise as much as 1,000 feet above the general 

level. The Eagle Trough, also called the Tintina Valley, is southwest of 

and parallel to the Yukon River, from which it is separated by discontinuous low hills. Ridges within the trough are 2,000-2,500 feet in 

altitude and are separated by valleys 1,000-1,500 feet deep.

The upland areas are mainly Precambrian (?) and Paleozoic 

metamorphic rocks that were invaded by Mesozoic and, to a lesser 

extent, Paleozoic and Tertiary plutons, dikes, and sills of felsic, mafic, 

and ultramafic composition. The Eagle Trough, which generally follows the Tintina fault zone, a major tectonic element in this part of 

Alaska and adjoining Canada, is underlain by Upper Cretaceous and 

Tertiary continental conglomerate, finer grained clastic rocks, and 

thin beds of lignite or subbituminous coal. Between the Tintina fault 

zone and the Yukon River, the pre-Late Cretaceous rocks are sedimentary and volcanic members of the Tindir Group of Precambrian age, 

and clastic and carbonate formations of Paleozoic and Mesozoic age. 

Quaternary deposits in the district are mainly alluvium and terrace 

deposits along streams. Except for cirque glaciers on a mountain in its 

southern part, the district was ice free during the Pleistocene Epoch. 

The area is mainly in a zone of discontinuous permafrost.

No workable lodes have been found in the Eagle district although 

sulfide-bearing material was reported from Eagle Bluff near the 

mouth of Mission Creek. In 1968, sulfide-bearing samples were collected during a geochemical reconnaissance of part of the Seventymile 

River area, but nothing of immediate commercial interest was discovered.

Placer-gold deposits, first discovered in about 1895, have been mined 

consistently since 1900, and have yielded a total of somewhat less than 

50,000 ounces, mainly from tributaries of the Seventymile River. The 

ultimate sources of most of the gold were veins in metamorphic rocks 

and mineralized fault zones, but much of the gold was immediately 

derived from auriferous conglomerate and associated clastic rocks in 

the Eagle Trough. Platinum, either as discrete grains or alloyed with 

gold, is a constituent of some placer concentrates.

Asbestos, associated with serpentinized ultramafic rocks, is the only 

nonmetallic mineral resource other than sand and gravel, in the district. Although none has been mined, there has been considerable 

recent interest in several of the deposits.

A little coal was mined from beds in the Eagle Trough in about 1900.

FAIRBANKS DISTRICT

The Fairbanks district is the area drained by the Chatanika River 

and northern tributaries of the Tanana River from Minto to and 

including Shaw Creek.
34 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

The district is within the Yukon-Tanana Upland except for isolated 

areas along its southwest border that are in the Tanana-Kuskokwim 

Lowland, and it consists of marshy flats along the lower courses of 

major tributaries of the Tanana River. Most of the district is a dissected plateau 2,000-4,500 feet in altitude that rises gently from west to 

east and is characterized by many wide valleys separated by broad 

rolling divides surmounted by rounded domes and a few mountainous 

areas that rise several hundred feet higher.

The oldest rocks in the Fairbanks district are a group of schists, 

crystalline limestone, quartzite, amphibolite, and gneiss of Precambrian and early Paleozoic age. These rocks were intruded by mainly 

Mesozoic plutons and dikes, most of which are granodiorite, quartz 

diorite, or porphyritic granite and quartz monzonite. Nearly all the 

domes and mountains that rise above the general upland surface are 

underlain by such rocks. Many serpentinized ultramafic bodies are in 

the upper valley of the Salcha River in the eastern part of the district. 

Except for a few local cirque glaciers on the highest mountains, the 

district was not ice covered, but the Quaternary history of this periglacial area is complex. The uplands are generally covered by a blanket of loess derived (and still being derived) from the proglacial flood 

plains of streams issuing from the Alaska Range many miles south of 

the Tanana River. Loess mixed with locally derived clastic material 

and vegetation chokes valleys and forms the frozen muck that overlies 

most of the placer-gold deposits. Frozen tissues and skeletal remains of 

Pleistocene mammals are common in this material.

Most of the lodes in the Fairbanks district are concentrated in an 

area within about 25 miles of Fairbanks, though a few, none of which 

have been productive, have been found elsewhere. Total lode production was about 239,250 ounces of gold, 39,000 ounces of silver, 

2,500-3,000 tons of antimony ore, and scheelite ore and concentrates 

containing several thousand units of WO3. In the vicinity of Fairbanks, gold lodes are near granitic plutons at Pedro and Gilmore 

domes northeast of Fairbanks and at Ester dome (where the pluton has 

not yet been unroofed) west of the city. The tungsten deposits (predominantly scheelite) are principally in the Gilmore dome area. Lodes in 

other parts of the district appear to be in similar geologic settings. The 

precious-metal lodes are commonly in fissure veins, composed mainly 

of quartz, that cut schist, usually near contacts with felsic intrusive 

rocks. The antimony deposits occupy the same lodes as the economically more important gold deposits. Sulfide and sulfosalt minerals are 

constitutents of most of the veins. The tungsten deposits are in limestone lenses that were largely replaced by silicate minerals, in granitic 

and pegmatitic dikes, and in auriferous quartz veins.

The Fairbanks district has produced more placer gold than any other
YUKON RIVER REGION 35

in the state, exceeding the total production of the Seward Peninsula 

region by well over a million ounces. About 7,650,000 ounces has been 

produced since 1902, when gold was discovered on Pedro Creek. This 

amount represents 37.2 percent of the total recorded Alaskan placergold production. Large dredges were first used near Fairbanks in 1928. 

Before that time high-grade deposits were worked mainly by drift 

mining and scraper plants after permafrost had been thawed with 

steam. Some of the deposits were very rich; for example, the average 

tenor of the gravel mined in 1908 was about $5.60 (gold at $20.67 per 

ounce) per cubic yard. The dredges worked lean ground that had been 

thawed with cold water and reworked areas that had been mined by 

other methods. Placer mining in parts of the district not close to 

Fairbanks accounted for between 100,000 and 200,000 ounces of gold.

The heavy minerals in the placers were probably derived from local 

lode deposits, as valuable placers were found only where lodes containing the same minerals were mined or prospected. Most of the placers in 

the district were stream placers that had been buried by more recent 

alluvium and loess that choked creek valleys; a few deposits on buried 

bedrock benches, however, were found during drift mining.

The nonmetallic mineral resources (other than material used for 

road metal, railway ballast, and decorative stonework) in the district 

consist of small bodies of limestone and deposits of clay possibly suitable for rough ceramic uses. None have been developed. No occurrences 

of mineral fuels are known in the district.

FORTYMILE DISTRICT

The Fortymile district comprises the Alaskan part of the Fortymile 

River drainage basin, the area drained by streams flowing southwest 

into the Tanana and Chisana Rivers and Scottie Creek from Tanacross 

to the Alaska-Yukon boundary, and the Alaskan parts of the basins of 

western tributaries of the Sixtymile and Ladue Rivers.

The district is almost entirely within the Yukon-Tanana Upland 

physiographic province and consists of discontinuous groups of mountains that rise a few hundred feet above a fairly uniform plateau that is 

3,000-5,000 feet above sea level, except where interrupted by the 

valleys of the Fortymile River and its forks and a few other streams.

Most of the district is a complex terrane of Precambrian(?) and 

Paleozoic gneiss and schist and minor crystalline limestone that was 

intruded at intervals during Paleozoic, Mesozoic, and Tertiary time by 

felsic, mafic, and ultramafic rocks. Some of the felsic intrusive bodies, 

particularly those in the western and northern parts of the district, are 

Mesozoic batholiths of great areal extent. Ultramafic bodies, wholly or 

partially serpentinized, crop out in many parts of the Fortymile and 

neighboring districts and are of Mesozoic age. A small syenite pluton,
36 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

dikes, sills, and other small intrusive masses of granite porphyry, and 

mafic and felsic volcanic rocks were emplaced during the Cenozoic Era. 

Detrital Tertiary rocks were deposited in local basins where they are 

associated with volcanic and volcaniclastic material.

The Yukon-Tanana Upland was not glaciated (except for the summits of some of the highest mountains) but loess, derived largely from 

proglacial floodplains to the south, mantles much of the area. The 

district is in a zone of discontinuous permafrost. Much of the ground 

that was placer mined was permanently frozen.

Only a few lodes have been found in the Fortymile district; a little 

gold was mined from one near Chicken. The lodes consists of quartz 

veins in metamorphic rocks or, less commonly, contact-metamorphic 

deposits carrying gold, silver, lead, copper, zinc, antimony, and iron.

The Fortymile is one of the oldest placer districts in Alaska. The 

discovery of gold in the late 1880's was followed in 1893 by a stampede 

during which claims were staked in most of the valleys. Placers have 

yielded about 470,000 ounces of gold, 2 percent of the total placer-gold 

production from Alaska. The source of the gold was abundant small 

mineralized veins in metamorphic rocks near contacts with felsic 

intrusive bodies. Heavy minerals in concentrates include gold, scheelite, cassiterite, and various sulfide minerals, but none except gold have 

been recovered commercially. Both bench and stream placers were 

mined, with the bulk of the gold coming from bench deposits near 

Chicken and from the Fortymile River and its tributaries where 

dredges were used from 1906 until the end of the 1967 season.

Recently there has been much interest in newly discovered asbestos 

deposits in serpentinized ultramafic bodies, but activity has not progressed beyond the prospecting stage. The only mineral fuel resource 

in the district is subbituminous coal at Chicken where a bed at least 22 

feet thick, but of small areal extent, was once mined for local use.

GOODPASTER DISTRICT

The Goodpaster district is the area drained by northern tributaries 

of the Tanana River between Big Delta and Tanacross. Physiographically and geologically it is an extension of the adjoining Fortymile 

district.

The only lode production consisted of a small quantity of gold ore 

mined from free gold- and sulfide-bearing quartz veins near Tibbs 

Creek in the northern part of the district where antimony and molybdenum minerals have also been found. There has been prospecting for 

placer gold in several parts of the district, and a few minor discoveries 

were reported, but the total production was so small that it was never 

reported separately from that of neighboring districts. No nonmetallic 

or mineral-fuel resources have been discovered.
YUKON RIVER REGION 37 

HOT SPRINGS DISTRICT

The Hot Springs district is the area drained by southern tributaries 

of the Yukon River between Kallands and (but not including) Fish 

Creek and by tributaries of the Tanana River as far upstream as 

Dugan Creek.

The northern part of the district is in the Yukon-Tanana Upland and 

the southern part mainly in the Tanana-Kuskokwim Lowland. The 

northern part consists of several even-topped ridges 1,600-2,500 feet 

in altitude and a few more rugged isolated mountains with summits 

below 5,000 feet. Wide valleys merge with the Tanana-Kuskokwim 

Lowland, much of which is less than 500 feet above sea level. The 

northeast end of the Kuskokwim Mountains is in the extreme southern part of the district and is made up of groups of hills 2,000-3,200 feet 

in altitude that are separated by broad valleys that slope northward 

and northeastward to the lowland.

North of the Tanana River, Paleozoic chert, limestone, and clastic 

rocks, many somewhat sheared and metamorphosed, are the oldest 

units. They are overlain by Cretaceous argillaceous rocks, graywacke, 

and sandstone that were metamorphosed in much of the area to slate, 

phyllite, and quartzite. The youngest consolidated bedded rocks are 

Tertiary continental conglomeratic beds in a small area near the 

Yukon River about 20 miles upstream from Tanana. Bodies of mafic 

rocks, now largely serpentinized, intruded the bedded rocks near 

Tofty. Felsic plutons of probable Tertiary age make up several of the 

mountains and high parts of ridges. South of the Tanana and Yukon 

Rivers clastic, carbonate, and volcanic rocks, of Paleozoic, Mesozoic, 

and Tertiary ages, were intruded by at least two granitic plutons. 

Nearly all major stream valleys and the Tanana-Kuskokwim Lowland 

within the district are covered by Quaternary glaciofluvial material 

derived from the Alaska Range to the south, alluvium of local origin, 

and loess. Much of this material is perennially frozen and has a high 

content of organic material. No part of the Hot Springs district has 

been glaciated.

None of the few lode deposits in the district has been productive. A 

shear zone on the summit of Manley Hot Springs Dome contains 

argentiferous galena and minor amounts of gold, various sulfide minerals and their alteration products, and erythrite, a cobalt mineral. 

Grains of chromite disseminated in a serpentinized mafic rock were 

found on Serpentine Ridge near Tofty.

Since the discovery of gold near Eureka in 1898, placers in the Hot 

Springs district have produced about 450,000 ounces of gold (about 2.2 

percent of the total placer-gold production of Alaska) and several 

hundred tons of cassiterite concentrates from gold mines near Tofty. 

Definite sources of the valuable heavy minerals in the placers have not
38 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

been found. Because of thick frozen silt and moss cover, data on bedrock in much of the district can come only from drill holes, prospect 

shafts, or ephemeral exposures in placer mines. Chromite, a major 

constituent of the concentrates from some creeks, probably came from 

serpentinized ultramafic or mafic rocks such as are exposed on Serpentine Ridge. No valuable placer deposits have been found in the part of 

the district south of the Tanana and Yukon Rivers.

Except for material suitable for road metal, valuable nonmetallic 

mineral deposits have not been found in the district. Subbituminous 

coal occurs in Tertiary continental rocks near the Yukon River, but not 

in currently minable amounts.

HUGHES DISTRICT

The Hughes district includes the area drained by the Koyukuk River 

and its tributaries below the Kanuti River and by northern tributaries 

of the Yukon River between Koyukuk and Melozi.

The central part of the district is made up of the Koyukuk Flats, a 

swampy, lake-studded lowland generally less than 200 feet above sea 

level through which the Koyukuk River and its tributaries meander. 

Low mountains and uplands fringe the lowlands. The crests of the hills 

are commonly 2,000-3,000 feet in altitude though the summit, Indian 

Mountain, east of Hughes, is more than 4,200 feet above sea level, and 

several broad passes and ill-defined drainage divides are below 1,000 

feet.

The mountains surrounding the Koyukuk Flats are underlain 

mainly by Jurassic and Cretaceous marine and nonmarine clastic and 

volcanic rocks that were intruded by large granitic and monzonitic 

plutons and small bodies of latitic hypabyssal rock of Late Cretaceous 

age. The Koyukuk Flats are underlain by thick alluvial and 

glaciofluvial deposits covered by eolian deposits, including large areas 

of active sand dunes. Broad alluviated valleys of the major rivers 

merge downstream into the flats. Pleistocene ice from the Brooks 

Range covered the northern part of the district and parts of the Zane 

Hills, Purcell Mountains, and Indian Mountains, but, in general, the 

area was not glaciated and there are no modern glaciers. Except for the 

Zane Hills, where there are unfrozen areas, the district is in zones of 

continuous permafrost.

The only lode deposits in the district are near Indian Mountain 

where small amounts of zinc and copper sulfides occur in highly altered 

fine-grained pyritiferous intrusive rocks, metavolcanic rocks, and aplite near the borders of a pluton. Molybdenite has been found in 

bedrock exposed during placer mining on Indian River. Near the head 

of Utopia Creek, massive barite boulders, for which no bedrock source 

has been determined, contain tetrahedrite, galena, and sphalerite.
YUKON RIVER REGION 39

Near a slough of the Koyukuk River a float block of altered silicified 

rock containing disseminated cerrusite, galena, and malachite and 3 

ounces of silver per ton was found. This material, numerous dikes, and 

a zone of thermally metamorphosed andesite suggest that a pluton 

may underlie the area at shallow depth.

Placer gold was discovered in about 1890 on bars of the Koyukuk 

River. Most later mining, however, was near Hogatza and on streams 

that drain Indian Mountain east of Hughes. No accurate estimate of 

the amount of gold produced can be made, but it must have been 

several times the 8,500 ounces definitely allocatable to the Hughes 

district on the basis of published data. A large dredge has been operated at Hogatza since 1957; the owner, however, has released no 

pertinent information other than the number of employees.

A thin bituminous coal bed in Upper Cretaceous clastic rocks exposed along the Yukon River may have provided a few tons of fuel for 

river boats in about 1900. Possible resources of minable coal in the 

district are probably small. Cretaceous sedimentary rocks in the 

Koyukuk Basin have been investigated as a possible source of petroleum, but the current outlook is not promising because igneous 

bodies are more common than had been anticipated, and no large 

uncomplicated structures have been discovered. No deposits of potentially valuable nonmetallic mineral commodities have been found in 

the district.

IDITAROD DISTRICT

The Iditarod district comprises the areas drained by eastern 

tributaries of the Yukon River between and including Paimut and 

Shageluk Sloughs, by southern tributaries of the Innoko River between Holikachuk and Dishkakat, and by tributaries of the Innoko 

below Holikachuk.

The district is in the Kuskokwim Mountains and YukonKuskokwim Lowlands physiographic provinces. The southeastern 

part of the area consists of rounded northeast-trending ridges generally less than 1,500 feet in altitude that are surmounted by a few 

isolated rugged mountains, most of which are on the YukonKuskokwim divide and all of which are lower than 3,000 feet. Major 

valleys are generally straight and, except in headwater sections, broad 

and swampy. The rest of the district is low (at most only a few hundred 

feet above sea level), lake speckled, swampy, and crossed by widely 

meandering tributaries and sloughs of the Yukon River.

The upland part of the district is underlain mainly by Cretaceous 

shale (now metamorphosed in places to slate) and coarser clastic rocks 

and basalt, by an upper Paleozoic and lower Mesozoic clastic unit, and 

by older Paleozoic metamorphic rocks. Tertiary mafic and felsic rocks 

form sills and other small intrusive bodies. Near Flat, small Tertiary
40 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

monzonite stocks, possibly apophyses of an incompletely unroofed 

pluton, metamorphosed the surrounding Cretaceous clastic rocks. 

Much of the highland area is mantled by a blanket of weathered 

residual material, colluvium, and silt. The valleys and lowlands near 

the Yukon and Innoko Rivers are covered by thick deposits of alluvium. The mountains are not high enough for Pleistocene cirques to 

have formed, and ice from glaciers in adjoining areas did not invade 

the district. Most of the district is in a zone of moderately thick to thin 

permafrost except the lower Iditarod and Innoko valleys which are 

underlain by isolated masses of perennially frozen ground rather than 

continuous permafrost.

Lodes in the Iditarod district contain cinnabar, stibnite, gold, silver, 

and lead and zinc minerals. The DeCourcy Mountain mine in the 

southern part of the district produced more than 1,200 flasks of mercury and is the major Alaskan mercury mine outside the Kuskokwim 

River region. Near Flat many quartz and calcite veins carrying stibnite, cinnabar, other sulfide minerals, and gold occur in two small 

monzonite stocks and in contact-metamorphic aureoles in the surrounding Cretaceous bedded rocks. Most of the veins are less than 3 

feet thick. Many have been explored on a small scale, and an unrecorded amount of gold is said to have been mined from some of them in 

the early years of activity in the area. One mine that was operated in 

the 1920's and 1930's had a total reported production of 528 tons of ore 

from which 2,706 ounces of gold, 2,620 ounces of silver, 9,336 pounds of 

lead, and 653 pounds of zinc were recovered.

Placer gold was discovered near Flat late in 1908, setting off a 

stampede in 1910. In 1912 more than 130,000 ounces of gold was mined 

from the immediate area. Total production from the Iditarod district 

was more than 1,325,000 ounces, or over 6 percent of the placer gold 

produced in Alaska; almost all was from within 9 miles of Flat. The 

source of the gold is veins in two monzonite stocks and their surrounding contact aureoles. Cinnabar is a common constituent of the concentrates from almost every creek. Some may have been saved and retorted to produce quicksilver for local use.

No valuable nonmetallic mineral resources are known in the district. The only organic-fuel occurrences reported are in Cretaceous 

rocks between Iditarod and Flat where sheared anthracite coal is 

exposed in several places. There has been no significant development 

of this resource.

INNOKO DISTRICT

The Innoko district is, excepting the Poorman area, the area drained 

by the Innoko River and its tributaries above Dishkakat.

Most of the district is in the Kuskokwim Mountains physiographic 

province, but the northwestern and western parts are low country that
YUKON RIVER REGION 41

is continuous with the Koyukuk Flats and the Yukon-Kuskokwim 

Lowland. The mountain area is a rolling upland generally less than 

2,000 feet in elevation above which rise several isolated rugged masses 

with summits from 3,500 to more than 4,200 feet above sea level. The 

lowlands and part of the upper Innoko valley are swampy and dotted 

with small lakes of probable thermokarst origin.

The uplands are underlain mainly by Cretaceous clastic rocks, some 

of which now exhibit slaty cleavage. Older rocks include Paleozoic and 

Mesozoic metasedimentary and metavolcanic rocks and chert. Cretaceous and Tertiary igneous rocks include basaltic lava flows and 

tuffs, dikes and other small intrusive bodies ranging in composition 

from rhyolite to pyroxenite, and monzonite and quartz monzonite 

plutons that in places metamorphosed the enclosing rocks to hornfels. 

The lowlands and major valley floors are covered by surficial deposits 

that are mainly of nonglacial origin. Silt, largely wind deposited, 

mantles many of the slopes, and colluvium and residual weathered 

material hide bedrock in much of the upland part of the district. The 

higher isolated mountain groups supported Pleistocene cirque 

glaciers, but most of the district was ice free. Permafrost, discontinuous beneath parts of the Innoko and Dishna valleys and some of the 

higher hills and mountains, underlies the area.

Lodes in the Innoko district contain stibnite, cinnabar, and gold. The 

only production was a little gold from a quartz vein along the hanging 

wall of a felsic dike about 10 miles southeast of Ophir. Similar lodes are 

probably hidden beneath the overburden.

Placer mining centered around Ganes and Cripple Creeks in the 

eastern part of the district and Boob Creek near the Dishna River. Gold 

was discovered first on Ganes Creek in 1906 and a few years later in 

the other two areas. Production for the district has been about 550,000 

ounces, or 2.7 percent of the total for the State. A small amount of 

platinum was recovered from Boob Creek in the course of gold mining. 

In the Ganes Creek area most of the deposits are on buried bedrock 

benches, although stream placers were also mined. The gold came from 

small gold-bearing quartz veins and, probably, mineralized zones with 

little or no quartz near dacite and andesite dikes that closely follow 

slaty cleavage. Veinlets in and around plutons were the probable 

sources near Cripple and Boob Creeks.

No nonmetallic or mineral-fuels resources have been found in the 

Innoko district.

KAIYUH DISTRICT

The Kaiyuh district is the area drained by streams flowing west and 

north into the Yukon River from Shageluk Slough to (but excluding) 

the Yuko (Yuki) River and by streams flowing south into the Innoko 

River between Holikachuk and Dishkakat.
42 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

The district includes most of the Kaiyuh Hills physiographic province and large low-lying areas continuous with the Koyukuk Flats 

and Yukon-Kuskokwim Lowland. The Kaiyuh Hills is an isolated 

range of northeast-trending mountains generally from 1,000 to 2,250 

feet in elevation with several summits that are a few hundred feet 

higher. The range is broken into three segments by broad valleys 

separated at their heads by divides only a few hundred feet above sea 

level. About two-thirds of the district is made up of low swampy areas 

with many lakes, sloughs of the Yukon and Innoko Rivers, and sluggish streams following tortuous courses.

The Kaiyuh Hills are made up mainly of Precambrian or lower 

Paleozoic schist, quartzite, and recrystallized limestone, and younger 

upper Paleozoic and (or) lower Mesozoic metamorphosed mafic extrusive and intrusive rocks with some interbedded chert, limestone, and 

graywacke. Cretaceous clastic rocks similary to those in the Koyukuk 

sedimentary basin to the north and west form low hills east of the 

lower Khotol River and an isolated peak just south of the Yukon River 

between Nulato and Galena. Several granitic plutons of Mesozoic or 

Tertiary age intruded the older rocks. The highlands are generally 

covered by frost-rived rubble, colluvium, and silt (some of which is 

probably loess) and are generally below tree line, so outcrops are 

scarce. The lowlands are covered with thick alluvium. The district was 

not glaciated. Except for part of the Innoko valley where permafrost is 

discontinuous, the area is in a zone generally underlain by moderately 

thick to thin frozen ground.

Lode deposits have been found in two places in the Kaiyuh district. 

In the northern part of the district near the crest of the Kaiyuh Hills 

argentiferous galena veins in schist were the source of 100-200 tons of 

silver-lead ore. In the southern part of the district a molybdenitebearing quartz vein in rhyelite porphyry was explored in 1942, but no 

ore was mined.

The only placer mining in the district was at Camp Creek at the site 

of the abandoned village of Tlatskokot where an unknown, but undoubtedly small, amount of gold was recovered immediately after 

World War II.

No nonmetallic or mineral-fuels resources have been discovered in 

the district.

KANTISHNA DISTRICT

The Kantishna district is the area drained by the Kantishna River 

and southern tributaries of the Tanana River between the Kantishna 

and the Zitziana Rivers.

The southern boundary of the district follows the crest of the Alaska 

Range. To the north the mountains drop off abruptly to the Tanana-
YUKON RIVER REGION 43

Kuskokwim Lowland, a gently northward-sloping lake-dotted area 

generally less than 2,000 feet above sea level. The Kantishna Hills, a 

group of rugged mountains less than 5,000 feet in altitude, extend 

about 20 miles north of the range.

North of the Denali fault zone, which is about 6 miles north and 

northwest of the crest of the Alaska Range and is hidden beneath the 

Muldrow Glacier for 17 miles, the geology is an extension of that of the 

adjacent Bonnifield district. In the Kantishna district, however, the 

distribution of Tertiary rocks is much more restricted, and most of the 

Mesozoic felsic intrusive bodies are much larger than in the Bonnifield 

district. The rocks south of the Denali fault zone are generally 

Mesozoic sedimentary rocks. They were intruded by a large granitic 

batholith near Mount McKinley and by possibly related stocks. The 

lowlands north of the mountains are covered by Quaternary unconsolidated glaciofluvial and eolian deposits. The Alaska Range and part 

of the piedmont were covered by ice during several Pleistocene glaciations, but the lowlands were ice free. Today most of the high country is 

glacier covered with spectacular ice tongues. Longest is the Muldrow 

Glacier, extending down to elevations of less than 4,000 feet. The 

mountains and the Kantishna Hills are in a zone of discontinuous 

permafrost; the lowlands are largely underlain by moderately thick to 

thin continuous permafrost, though in areas of coarse-grained deposits 

only isolated masses are perennially frozen.

Lodes in the Kantishna district have yielded small amounts of gold, 

silver, antimony, and lead ore. Most of the lodes are quartz veins in 

schistose rocks, and these veins carry gold, argentiferous galena, and 

other sulfide minerals, but one group of prospects from which there has 

been no production is in contact-metamorphic deposits of argentiferous galena and other sul!des in recrystallized limestone. About 1,000 

tons of argentiferous galena ore averaging from $150 to more than 

$250 a ton in silver and carrying a little gold and an unreported 

amount of lead was taken from mines in the Kantishna Hills. In the 

same general area about 3,500 tons of stibnite ore was mined from 

deposits at Stampede and on Slate Creek. Cinnabar is a major constituent of one nonproductive lode high in the mountains.

In 1905, gold in paying quantities was found in several creeks in the 

Kantishna Hills. Mining continued for many years with no more than 

4,000 ounces being recovered in any single year. Total production was 

between 45,000 and 50,000 ounces. The heavy minerals in the placers 

came from nearby lodes.

No occurrences of nonmetallic mineral resources other than material for road metal have been reported. There are coal beds in some of 

the Tertiary rocks in the eastern part of the district, but no one has 

mined them.
44 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

KOYUKUK DISTRICT

The Koyukuk district is the area drained by the Koyukuk River and 

its tributaries above and including the Kanuti River.

Areally one of the largest in the Yukon River region, the district 

extends from the Brooks Range southward to extensions of the 

Yukon-Tanana Upland. Between these highlands are lower uplands 

and broad poorly drained lowlands, of which the Kanuti Flats in the 

southern part of the district is the largest. The crest of the Brooks 

Range, which reaches elevations of 6,000 to more than 7,000 feet, is 

broken by several passes, the lowest of which is below 2,200 feet. The 

Kanuti Flats and similar terrain near the confluence of the South Fork 

of the Koyukuk with the main river are generally less than 600 feet 

above sea level, though a few isolated hills are somewhat higher. The 

southern and southeastern boundaries of the district follow the crests 

of the Ray Mountains and the Hodzana Highlands, with summit elevations generally between 3,000 and 4,000 feet, though there are several 

higher peaks.

Geologically the northern two-thirds of the district is a westward 

extension of the Chandalar district with bedded rocks of Paleozoic age 

underlying much of the area, and a belt of metamorphic rocks, mainly 

of greenschist facies and of Devonian age, extending across the southern foothills of the Brooks Range. Except near Big Lake and west of the 

head of Malamute River, this part of the Koyukuk district was not 

invaded by large granitic plutons, though dikes are fairly common in 

some places. In the Ray Mountains and the highlands at the head of the 

Ball River, however, large late Cretaceous quartz monzonite plutons 

and smaller bodies of hypabyssal rocks intruded metasedimentary 

rocks. The Koyukuk basin is underlain by Cretaceous marine 

graywacke and mudstone and nonmarine clastic and tuffaceous beds. 

Felsic flows and volcaniclastic rocks overlie the older units. Pleistocene ice from the Brooks Range and from cirque glaciers in the Ray 

Mountains covered much of the higher parts of the district. Modern 

glaciers are restricted to cirques in the highest parts of the Brooks 

Range. The lowlands are floored by Pleistocene glaciofluvial and 

Holocene flood-plain deposits. Most of the area is in zones of continuous 

permafrost, except for some of the highlands and a few valleys where 

permafrost is discontinuous.

Lodes containing gold and silver, and antimony, copper, lead, and 

manganese minerals have been discovered in the part of the district 

underlain by metamorphic rocks, but no lode mines have been developed. The lode deposits are mainly quartz and quartz-stibnite veins 

in phyllite and schist and galena in crystalline limestone.

Placer gold was found on bars of the Koyukuk River and on some of
YUKON RIVER REGION 45

its forks between 1885 and 1890, but the first major discoveries were in 

creeks near Wiseman in about 1900. Total production from the district 

was probably not less than 270,000 or more than 295,000 ounces of 

gold, more than 85 percent of which came from streams in a small area 

north of Wiseman. Other mining was near Wild Lake and on 

tributaries of the John and Middle Fork of the Koyukuk Rivers. Heavy 

minerals, which include native silver and copper and stibnite, were 

derived from auriferous quartz and quartz-stibnite veins, many of 

which were uncovered during mining operations. A total of about 5 

tons of stibnite was sluiced from creek gravels and weathered material 

above a lode in the bottom of one creek during World War II.

No nonmetallic mineral resources other than sand and gravel have 

been found in the Koyukuk district. Coal beds in Upper Cretaceous 

rocks have not been sufficiently investigated to determine their 

economic potential.

MARSHALL DISTRICT

The Marshall district is the area drained by the Yukon River and its 

tributaries below Paimiut Slough and by streams flowing into the 

Bering Sea between Hazen and St. Michael Bays. In addition the 

district includes a small area northwest of the Yukon River between 

(but excluding) the Koserefsky River and the lower end of Paimiut 

Slough.

The district includes the northern half of the Yukon-Kuskokwim 

Lowland and the southwest end of the Nulato Hills physiographic 

provinces. The part of the district in the Yukon-Kuskokwim Lowland 

is mainly the delta and old flood plains of the Yukon River, a low 

marshy area studded with lakes and traversed by sluggish streams. 

Small but rugged mountain masses protrude through the alluvial 

cover, reaching elevations greater than 2,000 feet. The southwest end 

of the Nulato Hills consists of a series of northeast-trending ridges 

with crest elevations generally between 1,000 and 2,000 feet.

Mesozoic, mainly Cretaceous, marine and nonmarine clastic rocks 

and andesitic volcanic and volcaniclastic rocks underlie most of the 

Marshall district. Volcanic and sedimentary rocks of Carboniferous (?) 

to Cretaceous age are exposed in the hills north of the Yukon River 

east of Marshall. Younger Cretaceous felsic bodies, including a 

granodiorite batholith, intruded some of the bedded rocks and thermally metamorphosed them near some contacts. The youngest consolidated rocks in the district are horizontal Quaternary basalt flows 

and associated fragmental rocks and their source cones, some of which 

are almost unmodified by erosion. These mafic volcanic rocks are 

exposed in a large area on Stuart Island and on the mainland near St. 

Michael and in several smaller areas in the Yukon Delta. Quaternary
46 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

alluvial, deltaic, and marine sand and silt make up most of the Yukon 

Delta and floor most rivers valleys and a large, low swampy area north 

of Marshall. Deposits in the Askinuk Mountains in the Yukon Delta 

record small Pleistocene cirque glaciers; the rest of the district was ice 

free. The entire area is in a zone generally underlain by moderately 

thick to thin permafrost.

Lodes in the Marshall district contain gold and lead, molybdenum, 

copper, and tungsten minerals, but none have been productive. The 

most thoroughly explored deposit, about 7 miles east of Marshall, is in 

altered volcanic rock and consists of mineralized quartz-calcite veins 

as much as a foot thick.

Since 1914, placer mining on creeks east of Marshall has resulted in 

the recovery of possibly as much as 95,000 ounces of gold and a little 

platinum. The source of most of the heavy minerals probably was 

nearby narrow mineralized quartz-calcite veins in altered volcanic 

rock.

No nonmetallic or minable mineral-fuel resources have been discovered, although there are thin coal beds in some of the Cretaceous 

nonmarine rocks near the Yukon River.

MELOZITNA DISTRICT

The Melozitna district is the area drained by northern tributaries of 

the Yukon River between and including the Melozitna and Ray Rivers.

The district is almost entirely within the Kokrine-Hodzana Highlands, a westward extension of the Yukon-Tanana Upland from which 

it is separated by a narrow trough that is followed for most of its length 

by the Yukon River. The highlands consist of rolling ridges generally 

2,500-4,000 feet in altitude above which a few isolated groups of 

mountains rise as much as 1,500 feet. The upper parts of some of the 

major rivers flow in wide swampy valleys choked with alluvium and 

commonly less than 1,000 feet in elevation.

Bedrock in most of the district is metamorphosed sedimentary and 

volcanic rocks, mainly of probable Paleozoic age, similar to those that 

underlie most of the Yukon-Tanana Upland. In the eastern part of the 

district, a large area northwest of the Yukon River is underlain by the 

principally volcanic Rampart Group of probable Permian age. Much of 

the valley of the Melozitna River is in the Cretaceous marine and 

nonmarine clastic rocks of the southeastern margin of the Koyukuk 

basin. Granitic plutons of Mesozoic age intruded and further 

metamorphosed the older rocks in many parts of the district. Pleistocene cirque glaciers developed in the higher parts of the Kokrines 

Hills and Ray Mountains but have now disappeared. The district is in 

zones of moderately thick to thin permafrost.

Lode deposits have been found at only three places in the Melozitna
YUKON RIVER REGION 47

district. At Gold Hill a gold-quartz vein, discovered in 1890, was the 

site of the first attempt at lode mining in interior Alaska. The amount 

of gold recovered, however, was not significant. The other lodes are 

galena veins about 25 miles up the Yukon River from Tanana and on 

Tozimoran Creek.

Only a few thousand ounces of gold have been mined from placers in 

the district. Cassiterite is a common constituent of many of the deposits, and tin concentrates were saved from time to time but may not 

have been marketed. Although all the placers are within a few miles of 

known or postulated granitic intrusive bodies, no lode sources of the 

gold or cassiterite have been found.

Coal-bearing rocks of Tertiary age are exposed on the west bank of 

the Yukon River opposite the mouth of Hess Creek. At least 1,000 tons 

of bituminous coal was mined for use on river steamers before 1902. 

The economic potential is small, as the coal-bearing rocks are exposed 

only in a 4-square-mile area in a bend in the river. No deposits of 

nonmetallic mineral commodities other than material suitable for 

local use as road metal have been found in the district.

RAMPART DISTRICT

The Rampart district is the area drained by southern tributaries of 

the Yukon River between and including Fish and Hamlin Creeks.

The district, entirely within the Yukon-Tanana Upland, is marked 

by broad ridges 1,500-3,000 feet in elevation separated by wide valleys. The western part of the area is more rugged than the eastern, 

with deeper, narrower valleys and several isolated peaks with altitudes greater than 3,500 feet.

Most of the geologic units in the Rampart district trend northeastward and consist of mainly noncalcareous clastic units and chert of 

Paleozoic age. In the western part of the district and near Livengood, 

limestone is interbedded with some of the other rocks. A mass of 

Devonian limestone is in the extreme eastern corner of the district. 

The probably Permian Rampart Group, which is mainly volcanic but 

includes some interbedded limestone, chert, and clastic rocks, is exposed along the Yukon River and underlies about half of the district. 

Cretaceous clastic rocks extend from the adjoining Hot Springs district 

into the southwestern part of the Rampart district. Tertiary terrestrial 

conglomerate, sandstone, and shale with a few coal beds were deposited in a local basin near the Yukon River north and west of Rampart. 

Unconsolidated auriferous terrace gravels east of Minook Creek are of 

Pliocene age(?). Tertiary granitic plutons were emplaced along the 

southern boundary of the district. Felsic dikes, probably associated 

with the plutons, and small mafic dikes, some possibly associated with 

the volcanic rocks of the Rampart Group, are fairly common in the
48 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

Minook Creek area. From east to west the Paleozoic rocks of the 

district are progressively more metamorphosed; some are now garnet 

schists.

Much of the district is mantled by Quaternary residual deposits, 

alluvium, and loess and, particularly in the Minook Creek area, extensive stream terraces are covered with gravel and finer alluvial material. This part of the Yukon-Tanana Upland was not glaciated. It is in a 

zone of discontinuous permafrost.

No lode mines have been developed in the Rampart district, though 

antimony and manganese minerals have been found in bedrock and in 

float that must be close to its source.

Placer gold was found in 1882 in a northern tributary of the Yukon 

River and in Minook Creek the next year. Total placer-gold production 

from the district was about 80,000-90,000 ounces, mainly before 1920. 

Nearly all the gold came from the basins of Minook and Troublesome 

Creeks in the southwest corner of the district. Well over half of the gold 

mined came from the stream gravels of Little Minook Creek, and much 

of the rest came from high bench deposits along other streams. The 

heavy minerals probably were derived from fairly abundant quartz 

veins and mafic rocks now altered to greenstone although some of the 

richest placers were probably reconcentrated from older gravels.

No nonmetallic mineral resources have been reported from the district. Little if any of the coal in the Tertiary rocks near Rampart was 

mined.

RUBY DISTRICT

The Ruby district comprises the Poorman area and the area drained 

by southern tributaries of the Yukon River from (and including) the 

Yuko (Yuki) River on the west to Kallands on the east.

The district includes the eastern part of the Kaiyuh Mountains, the 

northern part of the Kuskokwim Mountains and a low, poorly drained 

area that connects the Koyukuk Flats and the Tanana-Kuskokwim 

Lowland. Broad ridge crests in the mountain provinces are generally 

less than 2,000 feet in elevation except in the southern part of the 

district where several are more rugged and about 1,000 feet higher. A 

few isolated summits in the northern part of the area are above 3,000 

feet and Von Frank Mountain, on the divide between the Yukon and 

Kuskokwim drainages, is 4,508 feet in elevation. The lowlands are 

poorly drained areas of low relief, mainly less than 500 feet above sea 

level, through which streams meander in wide belts characterized by 

many oxbow lakes.

The district is mainly underlain by Precambrian(?) and Paleozoic 

crystalline limestone, schist, and other metamorphic rocks generally 

similar to those in the Yukon-Tanana Upland and by altered volcanic 

rocks. In the southern part of the district and near Yuki Mountain,
YUKON RIVER REGION 49

early Paleozoic carbonate rocks are exposed. Near Poorman, Cretaceous chert and argillite are interbedded with coarser clastic and 

volcanic rocks. Cretaceous and probable Tertiary granitic plutons 

invaded the older rocks in many parts of the district, but only small 

intrusive bodies have been found in areas with known mineral deposits. The district was not glaciated. Large areas are covered by 

weathered residual material and unconsolidated alluvium and terrace 

deposits, most of which are perennially frozen.

A silver-lead deposit in metamorphic rocks about 10 miles south of 

Ruby is the only described lode in the district. Although an unknown, 

but certainly small, amount of ore was mined, the venture was abandoned in the 1930's. Other mineralized zones are probably hidden by 

the thick mantle of residual debris that generally supports a heavy 

growth of vegetation and effectively hides bedrock even on most 

ridges. Gold nuggets with intergrown quartz, as well as the mineral 

suites in some placer concentrates, suggest that the creeks drain 

mineralized zones around granitic plutons.

Thin beds of subbituminous coal of probable Cretaceous age were 

found in placer prospect holes near Poorman. At most only a few tons 

was mined for local use; it was not good blacksmith coal and slacked 

badly. No nonmetallic mineral resources have been found.

Placer gold was discovered in the district in 1907, but sustained 

production did not begin until several years later. Most of the mining 

was on Long Creek and its tributaries about 25 miles south of Ruby 

and near Poorman in the headwaters of the Innoko River drainage. 

Total production was 390,000-400,000 ounces of gold (1.9 percent of 

Alaska's total placer gold output), about 10 tons of byproduct tin 

concentrate, and a few ounces of platinum separated from the concentrates from one creek. Most of the placer deposits are in buried channels that could be located only by random shaft sinking. Cassiterite is a 

common constituent of many of the placer deposits, but no bedrock 

source for it or for the gold has been found.

SHEENJEK DISTRICT

The Sheenjek district is bounded on the west by the drainage divide 

east of the East Fork of the Chandalar River, on the north by the crest 

of the Brooks Range, and on the east by the Alaska-Yukon boundary. 

Its southern border is an arbitrary line extending eastward from 

Venetie on the Chandalar River to Graphite Point on the Porcupine 

River, beyond which it follows the divide between the Porcupine and 

Black Rivers to the Canadian boundary.

The Sheenjek district is mainly in the Porcupine Plateau and Brooks 

Range physiographic provinces; the lower parts of the valleys of the 

Sheenjek and Christian Rivers are in the Yukon Flats province. Peaks
50 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

marking the crest of the Brooks Range are 4,000-7,000 feet in elevation except near the Alaska-Yukon boundary where they are lower 

and separated by a few passes below 3,000 feet. The Brooks Range 

merges southward with the rounded ridges of the Porcupine Plateau 

and the low (less than 1,000 feet), swampy Yukon Flats.

The bedded rocks in the district are mainly Paleozoic and Mesozoic 

clastic, carbonate, and volcanic rocks. Some of the sedimentary rocks 

may be as old as Precambrian, and some of the volcanic rocks are as 

young as Quaternary. Near the boundary between the Yukon Flats 

and the Brooks Range, many of the rocks have been regionally 

metamorphosed to schist and phyllite. In the eastern part of the district, two Carboniferous granitic plutons intruded Paleozoic rocks. A 

large Jurassic mafic igneous complex intruded Paleozoic rocks in the 

west-central part of the district. The Yukon Flats are composed of 

Quaternary alluvial fan and related terrace deposits, beneath which 

aeromagnetic data suggest large areas underlain by mafic rocks.

Only the northern part of the district was glaciated, though 

glaciofluvial deposits make up much of the Quaternary deposits in the 

lowlands. Some of the peaks at the head of the Sheenjek River still 

support small glaciers. Most of the district is in zones of continuous 

permafrost, though in parts of the northern Yukon Flats perennially 

frozen ground may be locally absent.

No mineral resources have been exploited in the Sheenjek district. 

Copper or lead sulfide minerals have been found in two places, and a 

little placer gold has been reported from the Coleen River drainage 

basin. Oil shale occurs in the Christian River basin but has not been 

thoroughly investigated.

TOK DISTRICT

The Tok district is the area drained by southern tributaries of the 

Tanana River between (and including) Berry Creek and the Tetlin and 

Kalutna Rivers. Most of the district is on the northeast flank of the 

Alaska Range, which slopes from Mount Kimball (10,300 feet) to 

lowlands along the Tanana River that are about 1,500 feet above sea 

level. Ice, remnants of Pleistocene glaciers that covered most of the 

Alaska Range, persists around Mount Kimball and other high mountains and flows several miles down some of the larger valleys. Discontinuous permafrost underlies the district.

Bedrock is mainly Paleozoic and Mesozoic clastic and volcanic rocks, 

large Mesozoic granitic plutons, and smaller bodies of older more mafic 

intrusive rocks. The lowlands are mantled by unconsolidated fluvial 

and glacial deposits largely derived from the Alaska Range. A stibnite 

prospect in a shear zone in schist on a tributary of the Tok River and an 

occurrence of several metallic minerals near the highway between
YUKON RIVER REGION 51

Gulkana and Tok Junction have not been productive, although the 

stibnite prospect was fairly extensively explored. Only two occurrences of placer gold have been reported in the district, and neither 

proved to be of economic interest. A little nephrite jade was found near 

Mentasta Pass; there has been no production from this prospect.

TOLOVANA DISTRICT

The Tolovana district is the area drained by southwest-flowing 

tributaries of the Tanana River from Dugan Creek on the west to the 

Tolovana River on the east. The drainage basin of the Chatanika River 

above the mouth of the Tatalina River is not included. The district is 

bounded on the north by an arbitrary line dividing the lowlands of the 

Yukon Flats from higher ground drained mainly by upper Beaver 

Creek.

Most of the district is in the Yukon-Tanana Upland and is characterized by broad even-topped ridges with an average summit elevation 

of about 2,000 feet above which elongate mountain masses rise 

2,000-3,000 feet. In general the valley floors are wide and occupied by 

widely meandering streams. The lower part of the Tolovana River 

valley is a broad, low, lake-dotted, marshy area through which the 

main stream and the lower parts of its tributaries flow in tortuous 

channels. This part of the district is in the Tanana-Kuskokwim Lowlands province.

The southern part of the district, geologically an extension of the 

adjacent Fairbanks and Circle districts, is a metamorphic terrane of 

schists and related rocks of Precambrian(?) and early Paleozoic age. To 

the northwest these rocks are succeeded by northeastward-trending 

belts of slightly metamorphosed Paleozoic clastic, volcanic, and carbonate rocks and chert. Lower Cretaceous clastic rocks underlie an 

area in the western part of the district. Diorite, quartz monzonite, 

granodiorite, and granite plutons and dikes, mainly of Mesozoic age, 

are common in the district. A belt of serpentinite bodies of Devonian(?) 

age extends northeastward from Livengood for many miles. Evidence 

of more than one Pleistocene glaciation has been found on the higher 

peaks, but all are now ice free. The district is mainly within a zone of 

discontinuous permafrost; many south-facing slopes are not perennially frozen. The flats in the lower valley of the Tolovana River 

generally are underlain by moderately thick to thin permafrost and 

numerous isolated masses of frozen ground.

Lodes in the Tolovana district have been found only in the area 

immediately around Livengood and on Sawtooth Mountain about 30 

miles to the west. They contain gold, silver, antimony, mercury, 

chromium, nickel, and iron. However, only small amounts of antimony 

ore from Livengood and Sawtooth Mountain and a little mercury from
52 THE MINERAL RESOURCES AND GEOLOGY OF ALASKA

Livengood have been recovered from lode sources. One of the serpentinite bodies near the head of the Tolovana River contains abnormally 

large amounts of nickel and detectable platinum and palladium. Many 

of the placer cuts near Livengood have uncovered quartz and calcite 

veins that contain gold and sulfide minerals; similar veins have been 

found in nearby hills.

At least 380,000 ounces of placer gold (1.9 percent of the total for the 

State) has been mined from creeks in the area near Livengood and 

from Nome Creek in the southeast corner of the district. The most 

productive placers near Livengood are old buried stream channels, one 

of which was followed for about 4 miles, and stream placers in which 

gold from old channels was further concentrated. The gold and other 

heavy minerals, which include stibnite and cinnabar, were probably 

derived from the mineralized quartz and calcite veins that are common 

in placer cuts and the nearby hills. The area around Nome Creek is 

similar to the neighboring part of the Fairbanks district.

Asbestos occurs in veinlets in serpentinite near the head of the 

Tolovana River. No mineral fuels are known in the district.

YUKON FLATS DISTRICT

The Yukon Flats district comprises the relatively flat basin of the 

Yukon River from Circle to the site of Fort Hamlin (a few miles 

downstream from Stevens Village), the drainage basin of the Porcupine River below Graphite Point, and the entire drainage basins of 

the Dall, Hodzana, and Hadweenzic Rivers.

Most of the district is in the Yukon Flats physiographic province, a 

swampy area of low relief generally less than 1,000 feet in elevation. It 

is a basin filled with late Tertiary and Quaternary unconsolidated 

continental deposits, including glaciofluvial material from the Brooks 

Range to the north, stream deposits derived from the upper Yukon 

basin, and reworked material forming loess blankets and sand dunes. 

Near the northwest margin of the basin, older rocks similar to those 

exposed north of the Yukon Flats have been uncovered beneath the 

unconsolidated sediments in stream cuts. The Hodzana Highland, an 

extension of the Yukon-Tanana Upland from which it is separated by a 

narrow trough followed by the Yukon River, makes up the northwestern part of the district. The oldest rocks are schist, quartzite, and 

crystalline limestone of early Paleozoic or possibly Precambrian age 

that were cut by granitic plutons. Sedimentary and volcanic and associated mafic intrusive rocks exposed along the Yukon River are 

probably Permian; some of the intrusive rocks are probably as young 

as Triassic. Tertiary continental rocks, including beds of subbituminous coal, were deposited in local basins near the Dall and Hodzana 

Rivers.
REFERENCES CITED 53

The only lode reported is on Trout Creek in the northwest margin of 

the district. Specimens from there contain sphalerite and molybdenite. 

An unknown, but certainly small, amount of placer gold has been 

mined from Slate Creek and a tributary, Trout Creek. There has been 

no other mining in the district.

Some interest has been expressed in the petroleum possibilities of 

the Yukon Flats basin, but aeromagnetic investigations suggest that 

much of the area beneath the surficial deposits is underlain by mafic 

igneous rocks, making the basin a less attractive exploration target 

than had been anticipated. The coal deposits have not been studied in 

any detail, and none have been mined.

REFERENCES CITED

Barnes, F. F., 1967, Coal resources of Alaska: U.S. Geol. Survey Bull. 1242-B, p.

B1-B36. 

Berg, H. C., and Cobb, E. H., 1967, Metalliferous lode deposits of Alaska: U.S. Geol.

Survey Bull. 1246, 254 p.

Cobb, E. H., 1972, Placer deposits of Alaska: U.S. Geol. Survey open-file report, 132 p. 

Gryc, George, 1971, Summary of potential petroleum resources of Region 1 (Alaska and

Hawaii) Alaska, in Future petroleum provinces of the United States their

geology and potential: Am. Assoc. Petroleum Geologists Mem. 15, p. 55-67. 

Ransome, A. L., and Kerns, W. H., 1954, Names and definitions of regions, districts, and

subdistricts in Alaska: U.S. Bur. Mines Inf. Circ. IC-7679, 91 p. 

U.S. Geological Survey (prepared in cooperation with State of Alaska), 1964, Mineral

and water resources of Alaska: U.S. 88th Cong., 2d Sess., Senate Comm. Interior

and Insular Affairs, Comm. Print, 179 p. 

Wahrhaftig, Clyde, 1965, The physiographic divisions of Alaska: U.S. Geol. Survey Prof.

Paper 482, 52 p.

U.S. GOVERNMENT PRINTING OFFICE: 1974 B43 S83/ SB