Preliminary Geologic 

Investigations of 

Western St. Lawrence Island, 

Alaska

GEOLOGICAL SURVEY PROFESSIONAL PAPER 684-C
Preliminary Geologic 

Investigations of 

Western St. Lawrence Island, 

Alaska

By WILLIAM W. PATTON, JR., and BELA CSEJTEY, JR.

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 684-C

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

W. A. Radlinski, Acting Director

Library of Congress catalog-card No. 79-176116

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

Washington, D.C. 20402 - Price 40 cents (paper cover)

Stock Number 2401-1146
CONTENTS

Abstract________.____.____

Introduction. __.________________

Layered rocks._____________________________

Devonian.. ____________________________

Mississippian__ _ ______________________

Mississippian to Cretaceous._____________

Cretaceous _ _ _________________________

Tertiary. ______________________________

Felsic volcanic and hypabyssal rocks.. 

Sandstone, coal, and tuff____________

Tertiary (?) and Quaternary.______ ___ _

Quaternary ____________________________

Page 

Cl 

2 

5 

5 

5 

5

5

6

6

6

6

7

Intrusive rocks___________-______

Permian(?)__ ___________...

Cretaceous... ___-_-----_____.

Quartz monzonite ______

Olivine-bearing monzonite.

Structure _-__---_----_---_-_____.

Mineral occurrences.______________

Molybdenum__ _ ____________

Copper.______--___--___-_._.

Lead, zinc, and silver. ________

References cited__________________

Page 

C7

7

7

7

7

8

8

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13

15

15

ILLUSTRATIONS

FIGURE 1. Index map of Alaska showing location of St. Lawrence Island and area of this report-.

2. Reconnaissance geologic map of western St. Lawrence Island_____________________

3. Exposures of Sevuokuk pluton along west coast of St. Lawrence Island ___._____-_.

4. Location of analyzed bedrock samples listed in table 2________________________

5. Molybdenum distribution in stream-sediment samples of western St. Lawrence Island.

6. Copper distribution in stream-sediment samples of western St. Lawrence Island._____

7. Lead distribution in stream-sediment samples of western St. Lawrence Island _..

8. Zinc distribution in stream-sediment samples of western St. Lawrence Island...... 

9. Silver distribution in stream-sediment samples of western St. Lawrence Island _. 

TABLES

Page

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2

5

9

10

11

12

13

14

TABLE 1. Potassium-argon age determinations_____________________________________---_--____-_----_-------------

2. Semiquantitative spectrographic analyses of selected grab samples of sulfide-bearing rocks from western St. 

Lawrence Island_____________________________________________________________________________

Page 

C6

m

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

PRELIMINARY GEOLOGIC INVESTIGATIONS OF WESTERN 

ST. LAWRENCE ISLAND, ALASKA

By WILLIAM W. PATTON, JR., and BELA CSEJTEY, JR.

ABSTRACT

Reconnaissance geologic mapping indicates that western St. 

Lawrence Island is underlain by a wide variety of volcanic, 

Plutonic, and sedimentary rocks ranging in age from middle 

Paleozoic to late Cenozoic. The oldest rocks are dolomite of 

Devonian age and limestone and chert of Mississippian age; 

these rocks crop out in the northeastern part of the Putgnt 

Plateau. They are overlain by a poorly exposed sequence of 

mudstone, black shale, chert, and limestone a sequence which 

is at least in part, Triassic but which may also include rocks 

as old as Mississippian and as young as Cretaceous. Overlying 

this sequence is a widespread unit of andesitic and latitic flows 

and volcaniclastic rocks of Cretaceous age. Small patches of 

early Tertiary felsic flows occur on the Putgut Plateau, and 

terrigenous coal-bearing deposits of middle Tertiary age crop

out around Niyrakpak Lagoon. Late Tertiary (?) and Quaternary basalt flows of the Kookooligit Mountains sequence crop 

out along the southeast flank of the Poovoot Range. Gabbro 

and diabase of probable Permian age are exposed in a narrow 

belt extending northwestward from Powooiliak Point, and 

quartz monzonite of Cretaceous age underlies about one-third 

of the mapped area in two large plutons, the Sevuokuk and 

Taphook.

Geochemical sampling indicates that disseminated molybdenite is widespread in the Sevuokuk pluton. A small lowgrade porphyry copper deposit was discovered in a satellitic 

stock of quartz monzonite in the Poovoot Range, and five separate deposits of lead-zinc-silver sulfides were found along a 

belt that extends northeastward across the island from Southwest Cape.

180° 170° 160

\

0 100 200 300 400 MILES 

I_____i_____|_____i_____i

FIGURE 1. Location of St. Lawrence Island and area of this report.

Cl
C2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

171°30' 171°00'

63° 40'

30'

63° 20'

Gambellg

Base from U.S. Geological Survey 

1:25,000, 1954

Geology mapped by W. W. Fatten, Jr. 

and T. P. Miller, 1966; W. W. Fatten, Jr. 

and B6la Csejtey, 1968-69

FIGURE 2. Reconnaissance geologic map of western St. Lawrence Island.

INTRODUCTION

St. Lawrence Island, about 2,000 square miles in 

area, is in the northern Bering Sea 130 miles west of 

mainland Alaska and 40 miles southeast of the Chukotsk Peninsula, U.S.S.E. This report covers about 600 

square miles of the western part of the island (fig. 1).

Keconnaissance geologic mapping of this area is part 

of a long-range program to investigate the mineral resources of the Bering Sea shelf. The purpose of these 

investigations is not only to assess the mineral potential 

of the island itself but also to provide basic geologic information needed in the interpretation of offshore geo-
GEOLOGIC INVESTIGATIONS OF ST. LAWRENCE ISLAND, ALASKA C3

EXPLANATION 

LAYERED ROCKS

Undivided rocks

Dolomite 

INTRUSIVE ROCKS

Contact, approximately 

located

Fault, approximately 

located

Location of sample dated by 

potassium-argon method

Number refers to sample 

number in table 1

Fossil locality

physical data. In addition, the geology of St. Lawrence Island is of special interest because it furnishes 

a critical tie-point for regional correlations between 

Alaska and northeastern Siberia.

The western part of St. Lawrence Island is dominated by the Poovoot Range, a group of barren, rubble-covered hills that extend from near Kongkok Bay 

and Boxer Bay on the southwest coast to Taphook 

Mountain on the north coast (fig. 2). The range is 

flanked on the southeast by the Putgut Pleateau, a 

nearly flat, lake-dotted, tundra-covered surface 100-200 

feet above sea level. The west and southwest coasts from 

Gambell to Powooiliak Point are marked by rugged 

cliffed headlands and narrow boulder-strewn beaches 

(fig. 3). The north coast and the south coast east of 

Powooiliak Point are bordered by broad coastal lowlands, tidal lagoons, and barrier beaches.

Bedrock exposures on western St. Lawrence Island 

are limited to sea cliffs and a few scattered cutbanks 

along locally incised streams. Interior parts of the island below 400 feet elevation are almost completely 

blanketed by tundra vegetation and above that elevation by frost-riven rock rubble. Trees and shrubs do 

not grow more than a few feet high anywhere on the 

western part of the island.

The island has no all-weather roads or trails. During 

the summer, overland transportation is limited to 

tracked or other type vehicles capable of traveling over 

water-saturated tundra. The lagoons and the larger 

lakes are suitable for float-plane landings after spring 

breakup, which generally occurs in mid-June. Coastal 

areas can be reached by small boat from Gambell when 

surf and wind allow. Gambell, the only settlement on 

western St. Lawrence Island, is served by scheduled airline from Nome.

The reconnaissance geologic mapping and geochemical 

sampling were conducted by Patton and T. P. Miller 

during the summer of 1966 and by Patton and Csejtey 

during the summers of 1968 and 1969. Transportation on 

the island was by small tracked vehicles and float plane. 

Approximately 250 stream-sediment and rock samples 

were collected and were analyzed by semiquantitative 

spectrographic and atomic-absorption methods. The 

authors were assisted in the field by V. A. Frizzell, M. B. 

Estlund, and A. F. White, geological assistants, W. T. 

Booshu, camphand, and J. K. Patton, volunteer helper.

Previous reports of the geology of St. Lawrence are 

confined to early exploratory surveys along the coast 

(Dawson, 1894; Emerson, 1904, p. 38-42; Collier, 1906), 

an archeological investigation by O. T. Geist and F. G. 

Rainey (1936), and an unpublished geological reconnaissance map compiled by E. H. Muller (Dutro and 

Payne,1957).
C4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

A
GEOLOGIC INVESTIGATIONS OF ST. LAWRENCE ISLAND, ALASKA

LAYERED ROCKS 

DEVONIAN

The oldest rocks on western St. Lawrence Island comprise a sparsely exposed sequence of dolomite and subordinate dolomitic limestone in the northeastern part 

of the Putgut Plateau (fig. 2). Much of the dolomite 

has been recrystallized to a light-tan and gray sugarytextured marble as a result of contact metamorphism 

by the nearby Taphook pluton. A few scattered exposures of unaltered dolomite, however, occur on small incised drainages along the north edge of the plateau. 

Gray massive laminated locally brecciated dolomite and 

dolomitic limestone in the lower part of the sequence 

grade into sooty-black thin-bedded fine-grained dolomite in the upper part.

These dolomitic rocks are believed to be Devonian in 

age and to correlate with the dolomitic sequence along 

the Seknak Kiver in eastern St. Lawrence Island described by Patton and Dutro (1969). A Devonian age 

for these rocks is also suggested by the discovery of 

brachiopods of Devonian age in an isolated patch of 

rubble of silicified coquina on the shore of a lagoon 4 

miles west of Kangee Camp. J. T. Dutro, Jr., who examined this collection, reports

brachiopod shells, predominantly atrypids (both Atrypa and 

Spinatrypa) ; also a few spiriferoids including a possible Kozlowskiellina and a Miicrospirifer? sp. The age is definitely Devonian, no younger than Frasnian on the basis of atrypids. If 

the Koslowskiellina is correctly identified, overlapping ranges 

would suggest an Emsian (late Early Devonian) or possibly 

early Eifelian (early Middle Devonian) age.

MISSISSIPPIAN

Stratigraphically above the Devonian dolomite is an 

estimated 1,500 feet of gray crinoidal limestone containing abundant black nodular chert. These rocks 

crop out on several small incised streams in the northeastern part of the Putgut Plaueau and appear to be 

localized along two narrow northeast-trending bands 

(fig. 2). The limestone contains abundant but poorly 

preserved fragmental debris of crinoids, corals, and 

brachiopods of probable Mississippian age. Both the 

f aunal assemblage and the lithology indicate a strong 

correlation between these limestone and chert beds and 

the Upper Mississippian strata in the Ongoveyuk River

FIGURE 3. Exposures of Sevuokuk pluton along west coast of 

St Lawrence Island. A. Cliffed headlands of quartz monzonite south of Booshu Camp. Cliffs in middle ground are 15-30 

feet high. B. Jointed quartz monzonite in wave-cut bench 

near Booshu Camp. Quartz monzonite contains molybdenite 

in sparsely disseminated grains.

area of eastern St. Lawrence Island (Patton and Dutro, 

1969).

MISSISSIPPIAN TO CRETACEOUS

Overlying the Mississippian limestone and chert is 

a diverse assemblage of rocks including dark pyritiferous mudstone, black shale, chert, thin-bedded dark 

limestone, and subordinate amounts of graywacke, tuff, 

and breccia. Scattered talus banks and rubble patches 

of this rock assemblage were found on the northeastern 

part of the Putgut Plateau and in a small roof pendant 

that lies within the Taphook pluton, 8 miles southwest 

of Taphook Mountain (fig. 2). In addition, a few 

isolated patches of rubble (too small to be shown in 

fig. 2) occur in the belt of gabbro and diabase of Permian ( ?) age that trends northwestward from Powooiliak Point.

The stratigraphic relationships of the various rock 

types included in this assemblage are uncertain owing 

to structural complexities and poor exposures, and the 

age of most of the strata cannot be fixed more closely 

than Mississippian to Cretaceous. Some black-shalechert-limesitone beds, however, appear to correlate with 

Middle and Upper Triassic strata on the eastern part 

of the island (Patton and Dutro, 1969). Fragmentary 

flat clams of probable Triassic age were found in a 

rubble patch of these strata, 6 miles southwest of Taphook Mountain.

CRETACEOUS

Andesitic and latitic volcanic and hypabyssal rocks 

underlie more than 120 square miles of western St. 

Lawrence Island. They occur mainly in two broad 

belts: one just east of the Sevuokuk pluton and the other 

along the southern part of the Putgut Plateau (fig. 2). 

These rocks are best exposed in steep but largely inaccessible sea cliffs in the vicinity of Boxer Bay. Inland 

exposures consist of patches of frost-riven rubble, 

sparse erosional knobs, and a few stream cutbanks, 

chiefly along the south edge of the Putgut Plateau.

The unit includes a wide variety of flows, hypabyssal 

intrusives, and volcaniclastic rocks. The flows and intrusives range in composition from andesites to latites, 

but basalts, quartz latites, and rhyolites are locally 

present. The volcaniclastic rocks include andesitic and 

latitic lithic and crystal tuffs, breccias, and volcanic 

conglomerates and graywackes. Adjacent to the quartz 

monzonite plutons, the volcanic rocks have been metamorphosed to hornblende hornfels and albite-epidote 

hornfels. All the volcanic rocks are devitrified and altered in varying degree to a greenish-gray aggregate of 

chlorite, epidote, sericite, clay minerals, calcite, and 

pyrite.
O6 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

TABLE 1. Potassium-argon age determinations

[Argon analyses and age calculations by J. C. Von Essen and Joan Engels; potassium analyses by L. B. Schlocker. Decay constants for K*°: 

Xe =0.585X10-'° year-i; X/j=4.72X10-«» year-". Atomic abundance of K«=U9X10-*J

Sample Mineral

KiO KsO 

(percent) (average (10~i° moles 

percent) per g) Ar*°«o«»i

Apparent 

age.

1 (69APal87b) __ __._

2 (66APa242) __ ______

3 (69APa229a) ___ _._

4(66AMm211)________

____ Biotite ______ _

-_--___ Sanidine- __ ______

Hornblende _

_ _____ Hornblende _ ___.

____ Biotite. _____ .

J5. 96

1 5. ye 

J6. 24

ID. -55 

J .955

| . «7t7V

J .890

- I .895 

J4.77 ------14.72

} 5.97

j 6.245

} .972

} .892

} 4.745

8.009

5.894

.8837

3.348

7.606

0.76

.92

.52

.87

.95

88. 7±3

62. 8±1. 9

60. 5±1. 8

238 ±7

106 ±3

1. Andesitic crystal tuff, near Powooiliak Point.

2. Trachyte, near VABM Glass.

The volcanic rocks are assigned c» a Cretaceous ageo

on the basis of a potassium-argon age determination of 

88.7±3 m.y. (million years) from a crystal tuff near 

Powooiliak Point (table 1, sample 1). Although this 

age determination dates the sampled rocks as Late 

Cretaceous (Harland and others, 1964), some of the 

volcanic rocks included in this assemblage clearly cannot be younger than Early Cretaceous as they are intruded and altered by mid-Cretaceous (106±3 m.y.) 

quartz monzonite of the Sevuokuk pluton.

TERTIARY 

FELSIC VOLCANIC AND HYPABYSSAL ROCKS

Felsic volcanic and hypabyssal rocks crop out at the 

east edge of the Putgut Plateau near VABM Glass and 

in a small area along the beach about 2 miles north of 

Powooiliak Point (fig. 2). Near VABM Glass the rocks 

are typically light-gray to drab unaltered trachyte flows 

composed of large phenocrysts of'twinned sanidine and 

reddish-brown hornblende in a fine-grained trachytic 

groundmass. Float of lignite, presumably from interbedded coaly layers, was found along a small drainage 

that flows northward from VABM Glass. The rocks 

north of Powooiliak Point include light-gray fine- to 

medium-grained massive quartz latite crystal tuffs, and 

a small hypabyssal intrusive of light-gray fine-grained 

rhyolite. Thin seams and disseminated particles of 

carbonaceous material occur in the fine-grained tuffs.

The trachyte flows at VABM Glass are assigned a 

Paleocene age on the basis of a potassium-argon determination of 62.8±1.9 m.y. and 60.5±1.8 m.y. on the 

mineral pair sanidine and hornblende (table 1, sample 

2). The rocks north of Powooiliak Point have not been 

isotopically dated, but their general lithologic character 

and apparent stratigraphic position above the andesitic 

and latitic volcanic rocks of Cretaceous age suggest that 

they too are probably earlj Tertiary.

3. Qabbro, north of Mamagnak Mountains.

4. Quartz monzonite, east of Qambell.

SANDSTONE, COAL, AND TUFF

Terrigenous coal-bearing deposits of Tertiary age are 

exposed in bluffs along the west shore of Niyrakpak 

Lagoon and in scattered cutbanks on the lower Aghnuk 

Kiver (fig. 2). These deposits are composed of poorly 

consolidated calcareous sandtsone, grit, and conglomerate, carbonaceous mudstone, ashy tuff, volcanic breccia, and seams of lignitic coal as much as 2 feet thick. 

Exposures of these deposits are so badly slumped that 

little can be determined about their thickness and structure. Plant fossils from the Niyrakpak Lagoon exposures, originally assigned an Eocene age by Chaney 

(1930), are now regarded as Oligocene by J. A. Wolfe 

(oral commun., 1968).

TERTIARY (?) AND QUATERNARY

Nearly flat-lying basalt flows of late Cenozoic age, 

which form the main mass of the Kookooligit Mountains, are exposed near the east edge of the mapped area. 

Small patches of these basalts also occur on the northwestern part of the Putgut Plateau and cap upland 

surfaces between Boxer Bay and the Okok Eiver (fig. 2). 

Most of the flows are composed of fresh medium- to 

dark-gray vesicular olivine basalt containing large 

rounded crystals of strained olivine in a fine-grained 

intergranular groundmass of labradorite, augite (probably titanaugite), olivine, and magnetite. Some vesicles 

are filled with zeolites. Pyroclastics, including tuffbreccias and lithic tuffs, are interlayered with the flows 

at the base of the Kookooligit Mountain sequence. Clasts 

in the pyroclastic rocks consist of a dark-gray to black 

fresh fine-grained to cryptocrystalline basalt and range 

in diameter from less than 1 inch to as much as 10 

inches. Olivine is lacking, and only a few clasts are 

vesicular. The matrix of the pyroclastics is cryptocrystalline, probably glass in part, and is partly altered 

to chlorites and possibly chlorophaeite.
GEOLOGIC INVESTIGATIONS OF ST. LAWRENCE ISLAND, ALASKA C7

The fresh, unaltered character of some of the flows 

and volcanic cones in the Kookooligit Mountains suggests that the latest extrusion took place not more than 

a few thousand years ago, and probably most, if not all, 

of the olivine basalt flows are of Quaternary age. The 

basal pyroclastic rocks, however, may be as old as late 

Tertiary.

QUATERNARY

Unconsolidated deposits of gravel, sand, silt, and peat 

underlie the coastal lowlands and are exposed in scattered bluffs along the seashore and around the lagoons. 

Terrace gravels as much as 100 feet thick crop out in 

bluffs near Kangee Camp and on the lagoons that fringe 

the north edge on the Putgut Plateau.

About 30 feet of deformed marine silt and sand 

overlain by scattered patches of glacial drift containing 

striated boulders is exposed on a spit at the east end of 

Niyrakpak Lagoon (D. S. McCulloch, oral commun., 

1970). The source of the drift is uncertain, but two possibilities are suggested: (1) it was derived from a small 

Pleistocene cirque glacier on nearby Taphook Mountain 

or (2) it was deposited by a vast ice sheet which covered 

the Bering Strait region and large parts of the western 

Seward Peninsula during the Pleistocene (Sainsbury, 

1967). Morainal deposits (not mapped on figure 2) also 

were found in two places near Kongkok Bay, but these 

clearly had their source in small Pleistocene cirque 

glaciers on the northwest flank of the Poovoot Range.

INTRUSIVE ROCKS 

PERMIAN (?)

Gabbro and diabase underlie about 40 square miles, 

primarily along a belt that trends northwestward across 

the island from Powooiliak Point (fig. 2). Isolated 

patches of rubble were also found on the southern and 

eastern parts of the Putgut Plateau. Outcrops of the 

gabbro and diabase can be seen in accessible sea cliffs 

along the coast near the mouth of the Okok River and in 

cutbanks along the lower course of the Okok River.

The bulk of this unit is composed of dark-greenishgray rusty-weathering massive gabbro and diabase. 

Also included in this unit are minor amounts of siliceous 

mudstone and .finely laminated tuff, which occur in 

isolated outcrop within the belt of gabbro and diabase.

Thin-section study shows that the gabbro and diabase 

are composed of augite, plagioclase (chiefly sodic labradorite), hornblende, opaque minerals, potash feldspar, and quartz as well as accessory apatite and zircon. 

The texture is intergranular and grades into subophitic 

in the diabase. Hornblende occurs in reaction rims 

around augite; potash feldspar and quartz are interstitial and form graphic intergrowths. Point counts on 

six stained rock slabs (600-900 counts per slab) indicate 

the following modal composition ranges in volume percent: plagioclase, 30-48; mafic minerals, 43-54; magnetite and subordinate ilmenite and chalcopyrite, 3-14; 

potash feldspar, 1-6; quartz, 0-5; and pyrite, < 1-2. All 

the feldspars are altered in varying degree to sericite, 

clay minerals, and calcite, and the mafic minerals are 

altered to chlorites, biotite, and magnetite.

This unit is assigned a tentative Permian age on the 

basis of a potassium-argon age determination of 

238±7 m.y. (table 1, sample 3) from gabbro collected in 

an isolated exposure north of the Mamagnak Mountains.

CRETACEOUS 

QUARTZ MONZONITE

Quartz monzonite underlies about 150 square miles 

of western St. Lawrence Island in two large intrusive 

bodies: the Sevuokuk pluton along the western coast 

and the Taphook pluton in the north-central part of the 

mapped area (fig. 2). The Sevuokuk pluton is well 

exposed in nearly continuous wave-cut cliffs and benches 

along the west coast from Gambell to Boxer Bay 

(fig. 3).

The quartz monzonite is light brownish gray to light 

gray, medium to coarse grained, and commonly porphyritic. A fine-grained dark-brownish-gray phase occurs 

along the borders of the plutons. Aplite dikes and xenoliths of mafic hornf els are locally abundant. Two sets of 

vertical joints striking northeast and northwest are 

conspicuous in every coastline exposure.

Point counts on five stained rock slabs (1,000 counts 

per slab) from the Sevuokuk and Taphook plutons give 

the following modal ranges in volume percent: plagioclase (calcic oligoclase to sodic andesine), 35-43; potash 

feldspar, 26-40; quartz, 10-27; biotite, 4-8; hornblende, 

0-5; accessory minerals (opaque and nonopaque), 0.6-1.

Both the Sevuokuk and Taphook plutons are discordant and are characterized by lack of linear and planar 

structures. No essential lithologic differences were noted 

between the two plutons, and it seems likely that they 

are comagmatic and possibly coextensive at depth. Both 

plutons are assigned a Cretaceous age on the basis of 

a potassium-argon determination of 106 ±3 m.y. on 

biotite from a sample near Gambell (table 1, sample 4).

OLIVINE-BEARING MONZONITE

A small stock of divine-bearing monzonite, less than 

1 square mile in area, crops out along the east shore of 

Boxer Bay. Massive sea-cliff exposures of the stock 

fringe the coastline but are accessible on foot in only a 

few places.
C8 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

The olivine-bearing monzonite is medium to dark 

greenish gray, coarse to medium grained, and granitic 

textured. Hand specimens show crystals of twinned 

plagioclase, as long as 15 mm, dark-greeiiish-gray pyroxene, and flakes of reddish-brown biotite. Point counts 

on four thin sections (2,000 counts per section) and 

one rock slab (1,000 counts) indicate the following 

modal-composition ranges in volume percent: plagioclase, 53-64; potassium feldspar, 22-29; augite, 4-10; 

biotite, 3-7; olivine, 1-3; magnetite, 1-3; and apatite, 

about 1. Most of the plagioclase is sodic labradorite. 

Olivine forms small anhedral crystals, partly altered to 

biotite and magnetite, and occurs poikilitically enclosed 

in feldspars.

The olivine-bearing monzonite is thought to be of 

Cretaceous age and to be related to the intrusion of the 

nearby Sevuokuk pluton. Both bodies intrude the andesitic and latitic volcanic unit of Cretaceous age.

STRUCTURE

Very little structural information is obtainable on 

western St. Lawrence Island owing to the scarcity of 

bedrock exposures. The few outcrops available, chiefly 

along sea cliffs and stream cutbanks, indicate that all 

pre-Tertiary rocks are intensely deformed and faulted. 

Gross distribution of the major rock units seems to suggest that regional trends are N. 40°-50° E. in the eastern part of the mapped area and north to N. 25° W. in 

the western part (fig. 2). Aerial photographs show two 

prominent sets of lineaments, probably faults, trending 

N. 25°Ht5° E. and N. 25° W.

MINERAL OCCURRENCES

Reconnaissance geochemical sampyling of the stream 

sediments and rock units was carried out as a first step 

toward appraising the mineral resources of western St. 

Lawrence Island. All samples were analyzed for 30 elements by semiquantitative spectrographic and atomic 

absorption methods. Analytical results for molybdenum, copper, lead, zinc, and silver are shown in figures 5-9 and table 2. Complete analytical results for 

the stream-sediment samples have been reported in 

open file (Patton and Csejtey, 1970).

The reconnaissance sampling has served to outline 

several broad target areas that appear to warrant further mineral investigations. It should be emphasized, 

however, that the mineral deposits found during this 

survey were not examined in detail and little is known 

about their lateral extent or structural setting.

MOLYBDENUM

The presence of molybdenite near Booshu Camp on 

the west coast of St. Lawrence Island has been known

TABLE 2. Semiquantitative spectrographic analyses of selected grab samples of sulfide-bearing rocks from western St. Lawrence Island.

[Results reported in parts per million in the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, 0.1. N, not detected; G, greater than value shown; L, detected but below limit of determination.

Sample localities shown in figure 4. Analysts: K. J. Curry, C. L. Forn, A. Farley, Jr.]

Sample 

locality

1

2

3 

4

5 

6

7 

8 

9

10 

11

12

13

14

15

16

17 

18 

19

20

Field No.

69APa-38c __

69APa-38e. _

66AMm-239_, 

69APa-49b_.._

69APa-51b _ _ 

69APa-51d __

69APa-514. _ 

69APa-83b.._ 

69APa-84c._._

69APa-84d__ 

69APa-212.

69APa-219b__

69APa-202b__

69APa-203b._

66AMm-227a_

69ACy-212___

69ACy-181___ 

68ACy-75b__. 

69APa-132b.__

69APa-132d

Ag

N

N

N 

1.5

1

N

N 

N 

2

1. 5 

10

1

N

N

1,000

1. 5

L 

10 

15

70

Cu

300

10

30 

1,000

700 

150

15 

20 

150

1,000 

1,500

3,000

700

700

10, 000

30

L 

150 

15

700

Mo

150

700

1,000 

15

7 

500

1,500 

500 

500

7 

30

L

N

N

L

N

N 

N 

N

N

Pb

L

L

30 

30

L

20

10

N 

30

70 

L

70

N

N

G20, 000

2,000

15 

2,000 

G20, 000

G20, 000

Zn

N

L

N 

N

N 

N

N 

N 

N

N 

L

N

L

L

G10, 000

N

700 

3,000 

200

G10, 000

Remarks

Disseminated molybdenite and chalcopyrite in quartz

monzonite.

Molybdenite and vein quartz in altered quartz monzonite.

Molybdenite disseminated in quartz monzonite. 

Disseminated pyrite and chalcopyrite in quartz monzonite.

Pyritiferous quartz monzonite. 

Thin veinlet of molybdenite in pyritiferous quartz

monzonite.

Irregular masses of molybdenite in monzonite. 

Molybdenite and pyrite in drusy quartz vein. 

Pyritiferous and silicified quartz monzonite with veinlets

of molybdenite.

Pyritiferous quartz monzonite. 

Pyritiferous altered volcanic rock.

Disseminated , malachite, chalcopyrite, and pyrite in

quartz monzonite porphyry. 

Disseminated magnetite, ilmenite, pyrite, and chalcopyrite in gabbro. 

Disseminated magnetite, ilmenite, pyrite, and chalcopyrite in gabbro. 

Galena, sphalerite, chalcopyrite, and pyrite in calcite

veinlet in gabbro.

Galena and pyrite in volcanic rock.

Pyritiferous volcanic rock. 

Galena and sphalerite in quartz veins in volcanic rock. 

Galena in contact marble.

Galena and sphalerite in contact marble.
GEOLOGIC INVESTIGATIONS OF ST. LAWRENCE ISLAND, ALASKA C9

by the local inhabitants for many years and was reported by Anderson (1947) and by Berg and Cobb 

(1967). Additional deposits were found during the 

present investigations, and these together with some 

anomalously high stream-sediment sample values, indicate that the distribution of molybdenite in and 

around the Sevuokuk pluton is far more widespread

than formerly recognized. In all occurrences, however, 

the molybdenite is sparsely disseminated, and the deposits appear to be low grade.

The deposit near Booshu Camp (Anderson, 1947) is 

on a wave-cut bench of quartz monzonite half a mile 

south of the outlet of the Moghoweyik River (fig. 3) 

(Iocs. 1, 2, 3 in fig. 4). The molybdenite occurs as dis63 "40' 

63° 20' 

Base from U.S. Geological Survey 

1:25,000, 1954

FIGURE 4. Location of analyzed bedrock samples listed in table 2,
CIO SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

geminated grains and thin scaly fracture fillings, along 

with minor amounts of chalcopyrite and pyrite. Sulfide mineralization appears to have been accompanied 

by addition of small amounts of quartz and partial 

sericitization of feldspars.

Molybdenite was also found on the north bank of the 

Moghoweyik Kiver three-quarters of a mile above the 

mouth (Iocs. 5, 6, 7 in fig. 4). Here thin veinlets of molybdenite occur in highly oxidized pyritiferous quartz 

monzonite which is cut by aplite dikes and quartz veins. 

A pan concentrate from the riverbed gravels at this 

locality yielded 70 ppm (parts per million) molybdenum and 5,000 ppm tungsten.

Another deposit was found on the upper Moghoweyik 

Eiver along the east edge of the Sevuokuk pluton (Iocs. 

8, 9, 10 in fig. 4). In this deposit the molybdenite is

171-30' 171°00'

63 "40'

30'

63° 20'

Gambell

EXPLANATION

Sample localities showing molybdenum 

concentration, in parts per million

Kaghoopalik 

Point

Aghsit 

Point

10 MILES i

Base from U.S. Geological Survey 

1:25,000, 1954

FIOTJBE 5. Molybdenum distribution in stream-sediment samples of western St. Lawrence Island.
GEOLOGIC INVESTIGATIONS OF ST. LAWRENCE ISLAND, ALASKA Cll

sparsely distributed throughout a half-mile-wide zone 

of heavily oxidized limonite-stained pyritiferous quartz 

monzonite near the contact with volcanic rocks of Cretaceous age. The molybdenite occurs as scales and thin 

veinlets along fine fractures in the quartz manzonite 

and as large euhedral crystals in drusy quartz veins.

Anomalous molybdenum contents (15 ppm or greater) were found in sediment samples from several 

streams draining the Sevuokuk pluton and the bordering volcanic rocks (figs. 2, 5). Contents as high as 70 

ppm were found on tributaries of the Kookooliktook 

Eiver which drain a large pyrite gossan and a small

171-30' 171°00'

63°40' 

Sample localities showing copper concentration, 

in parts per million

63° 20' 

Base from U.S. Geological Survey 

1:25,000, 1954

FIGURE 6. Copper distribution in stream-sediment samples of western St. Lawrence Island.
C12 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

63°40' 

Base from U.S. Geological Survey 

1:25,000, 1954

FIGURE 7. Lead distribution in stream-sediment samples of western St. Lawrence Island.

mineralized quartz monzonite porphyry stock. Small 

flecks of molybdenite are visible in the quartz monzonite, but none were seen in the pyrite-rich volcanic rock. 

Stream-sediment samples with molybdenum ranging 

from 15 to 50 ppm were obtained on an eastern tributary of the Boxer River, 2y2 miles north of Boxer Bay.

The source of the molybdenum is believed to be a nearby pyrite gossan in the volcanic rocks (fig. 4).

A single stream-sediment sample from Kitnepaluk 

Creek, which drains the Sevuokuk pluton 14 miles south 

of Gambell, yielded TO ppm molybdenum (fig. 5).
GEOLOGIC INVESTIGATIONS OF ST. LAWRENCE ISLAND, ALASKA

171"30' 171"00'

C13

63°40'

63° 20' 

Gambell

EXPLANATION

mple localities showing zinc concentration, 

in parts per million

Kaghoopalik 

Point

Aghsit 

Point

10 MILES

Base from U.S. Geological Survey 

1:25,000, 1954

FIGUBE 8. Zinc distribution in stream-sediment samples of western St. Lawrence Island.

COPPER

Finely disseminated chalcopyrite, malachite, pyrite, 

and minor molybdenite occur in a small stock of quartz 

monzonite porphyry in the Poovoot Eange near Poovookpuk Mountain (loc. 12 in fig. 4). The stock, which 

is roughly half a mile across, intrudes Cretaceous volcanic rocks. The sulfide minerals, although spread over 

a large part of the stock, are sparsely disseminated. 

Selected grab samples of the mineralized rock yielded 

as much as 3,000 ppm copper, but composite chip samples randomly collected on foot traverses across the 

stock contained TOO ppm copper or less. The Cretaceous
O14 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

171°30' 171°00'

63°40'

30'

63° 20'

Gambell

EXPLANATION

Sample localities showing silver concentration, 

in parts per million

Not detected

Kaghoopalik 

Point

Aghsit 

Point

Poovookpuk" -T 

Mountain *

X

1 MILE

Enlargement of Poovookpuk 

Mountain area

Kangee Camp

XVABM

Kongkok 

Bay

10 MILES

Base from U.S. Geological Survey 

1:25,000, 1954

FKHTBE 9. Silver distribution in stream-sediment samples of western St. Lawrence Island.

volcanic rocks are heavily pyritized and extensively 

oxidized over a broad area in the vicinity of the porphyry stock. No sulfides other than pyrite were identified in the volcanics, but a selected grab sample of 

massive pyritized volcanic rock near the intrusive contact contained 1,500 ppm copper and 10 ppm silver (loc. 

11 in fig. 4). Stream-sediment samples from several

small tributaries of the Kookooliktook Eiver that drain 

the stock and the surrounding altered volcanic rocks 

contained as much as 70 ppm molybdenum, 1,500 ppm 

copper, 500 ppm lead, 700 ppm zinc, and 1.5 ppm silver 

(figs. 5, 6, 7, 8, 9).

Several grab samples of gabbro from the Okok Eiver 

yielded 700 ppm copper (Iocs. 13, 14 in fig. 4). No cop-
GEOLOGIC INVESTIGATIONS OF ST. LAWRENCE ISLAND, ALASKA C15

per sulfides are visible in hand specimens of the gabbro, 

but polished sections reveal finely disseminated blebs of 

chalcopyrite.

A small amount of native copper was found in float 

of a mafic volcanic hornfels 4V& miles northeast of 

Vngyat Point.

LEAD, ZING, AND SILVER

Small sulfide deposits of lead, zinc, and silver were 

found along a belt trending northeastward from the 

Okok Eiver on the south coast to near Kangee Camp 

on the north coast (Iocs. 15 to 20 in fig. 4 and the following table). None of these deposits appear to be of 

economic significance, but their apparent structural 

alinement suggests that a careful search for additional 

deposits along this belt may be warranted.

Locality Minerals 

15_--._- Galena, sphalerite,

chalcopyrite,

pyrite.

16-_____ Pyrite, galena

17. Pyrite.

18------ Galena, sphalerite_

19, 20-.- Galena, sphalerite, 

pyrite.

Remarks

Sulfides in 1- to 2-inch-wide 

calcite vein cutting finegrained gabbro. Vein strikes 

about N. 35°E. Exposed on 

wave-cut bench in tidal zone.

Sulfides in irregular quartz 

veins cutting kaolinized 

limonite-stained lithic tuff. 

Well exposed along bench, at 

base of wave-cut cliff.

Pyrite containing 700 ppm Zn, 

in silicified fine-grained volcanic rock. Exposed in 

streambed.

Sulfides in quartz veins cutting 

altered andesitic volcanic 

rocks.

Irregular stringers in marble 

near contact with Taphook 

pluton. Exposed in streambed.

REFERENCES CITED

Anderson, Eskil, 1947, Mineral occurrences other than gold deposits in northwestern Alaska: Alaska Dept. Mines Pamph. 

5-R, 48 p.

Berg, H. C., and Cobb, E. H., 1967, Metalliferous lode deposits of 

Alaska: U.S. Geol. Survey Bull. 1246, 254 p.

Chancy, R. W., 1980, A Sequoia forest of Tertiary age In St. 

Lawrence Island: Science, n.s., v. 72, p. 653-654.

Collier, A. J., 1906, Geology and coal resources of the Cape Lisburne region, Alaska: U.S. Geol. Survey Bull. 278, 54 p.

Dawson, G. M., 1894, Geological notes on some of the coasts and 

islands of the Bering Sea and vicinity: Geol. Soc. America 

Bull., v. 5, p. 117-146.

Dutro, J. T., Jr., and Payne, T. G., 1957, Geologic map of Alaska: 

U.S. Geol. Survey, scale 1:2,500,000.

Emerson, B. K., 1904, General geology; notes on the stratigraphy 

and igneous rocks [of Alaska] in Harriman Alaska Series, 

v. 4: Washington, D.C., Smithsonian Institution, p. 11-56.

Geist, O. W., and Rainey, F. G., 1936, Archeological investigations at Kukulik, St. Lawrence Island, Alaska: Univ. 

Alaska Misc. Pub., v. 2, 391 p.

Harland, W. B., Smith, A, G., and Wilcock, Bruce, eds., 1964, The 

Phanerozoic time-scale A symposium dedicated to Professor Arthur Holmes: Geol. Soc. London Quart. Jour., supp., 

v. 120, p. 260-262.

Patton, W. W., Jr., and Csejtey, Bela, Jr., 1970. Analyses of 

stream-sediment samples from western St. Lawrence Island, 

Alaska: U.S. Geol. Survey open-file report, 50 p.

Patton, W. W., Jr., and Dutro, J. T., Jr., 1969, Preliminary report on the Paleozoic and Mesozoic sedimentary sequence 

on St. Lawrence Island, Alaska, in Geological Survey research, 1969: U.S. Geol. Survey Prof. Paper 650-D, p. D138- 

D143.

Sainsbury, C. L., 1967, Upper Pleistocene features in the Bering Strait area, in Geological Survey research, 1967: U.S. 

Geol. Survey Prof. Paper 575-D, p. D203-D213.

Shorter Contributions 

to General Geology, 

1970

GEOLOGICAL SURVEY PROFESSIONAL PAPER 684

This volume was published as 

separate chapters A C

CONTENTS

[Letters designate the separately published chapters]

(A) The Pierre Shale near Kremmling, Colorado, and its correlation to the east and the west, by G. A. Izett, W. A. Cobban, and 

J. R. Gill.

(B) Plutonic rocks of the Klamath Mountains, California and Oregon, by Preston E. Hotz.

(C) Preliminary geologic investigations of western St. Lawrence Island, Alaska, by William W. Patton, Jr., and Bela Csejtey, Jr.

O