GEOLOGICAL SURVEY CIRCULAR 759

The Alaska Mineral Resource 

Assessment Program: Guide to 

Information Contained in Folio of 

Geologic and Mineral Resource Maps 

of the Philip Smith Mountains 

Quadrangle, Alaska
The Alaska Mineral Resource 

Assessment Program: Guide to 

Information Contained in Folio of 

Geologic and Mineral Resource Maps 

of the Philip Smith Mountains 

Quadrangle, Alaska

By H. N. Reiser, W. P. Brosge, T. D. Hamilton,

D. A. Singer, W. D. Menzie II, K. J. Bird, J. W. Cady,

J. R. Le Compte, and J. B. Cathrall

GEOLOGICAL SURVEY CIRCULAR 759

7983
United States Department of the Interior 

JAMES G. WATT, Secretary

Geological Survey

Dallas L Peck, Director

Library of Congress Cataloging in Publication Data

The Alaska Mineral Resource Assessment Program: Guide to information 

contained in folio of geologic and mineral resource maps of the Philip 

Smith Mountains quadrangle. Alaska.

(Geological Survey circular 759)

Bibliography: p. 20-22

Supt. of Docs, no.: I 19.4/2:759

1. Geology Alaska Philip Smith Mountains. I. Reiser, Hillard N., 1924-

. II. Series: United States. Geological Survey. Circular 759. 

QE75.C5 no. 759 557.3s 83-600020 

[QE84.P49] [557.98'6]

Free on application to Branch of Distribution, U.S. Geological Survey 

604 South Picket* Street, Alexandria, VA 22304
CONTENTS

Page

Abstract........................................................................................ 1

Introduction ................................................................................ 1

Purpose and scope.............................................................. 1

Geography and access ...................................................... 1

Acknowledgments.............................................................. 4

Mineral exploration and production .................................... 4

Geological investigations.......................................................... 5

Previous investigations .................................................... 5

Recent investigations ........................................................ 5

Geologic summary...................................................................... 6

Stratigraphy........................................................................ 6

Structure.............................................................................. 10

Subsurface basement rocks ............................................ 11

Page

Description of component maps ............................................ 12

Surficial geology ................................................................ 12

Bedrock geology....._.......................................................... 13

Mineral resources other than oil and gas .................... 14

Oil and gas resources ........................................................ 15

Aeromagnetic map and interpretation ........................ 16

Interpretation of Landsat imagery .............................. 16

Reconnaissance geochemistry ........................................ 17

Sample selection, preparation and analysis ....... 17

Usefulness of heavy-mineral concentrates ......... 18

Anomalous areas ......................................................... 19

References .................................................................................. 20

ILLUSTRATIONS

Page

FIGURE 1. Index map of Alaska showing location of Philip Smith Mountains artd Chandalar quadrangles .......................... 2

2. Map of Philip Smith Mountains quadrangle showing location of Arctic Foothills and Brooks Range

physiographic provinces, the James W. Dalton Highway, and large airstrips .................................................... 3

3. Generalized stratigraphic sections............................................................................................................................................ 7

4. Generalized stratigraphic columns .......................................................................................................................................... 8

5. Generalized geologic map of the Philip Smith Mountains quadrangle .......................................................................... 9

6. Cross section across the Philip Smith Mountains quadrangle .......................................................................................... 11

7. Map of the North Slope petroleum basin showing locations of hydrocarbon accumulations, exploratory

wells, and Philip Smith Mountains quadrangle............................................................................................................ 15

8. Flow chart showing preparation of rock and stream-sediment samples and of heavy-mineral concentrates

from stream sediments, Philip Smith Mountains quadrangle.................................................................................. 19

TABLE

TABLE 1. Component maps and reports of the Philip Smith Mountains quadrangle mineral resource assessment.

Page

2
The Alaska Mineral Resource Assessment Program:

Guide to Information Contained in Folio of Geologic

and Mineral Resource Maps of the Philip Smith

Mountains Quadrangle, Alaska

By H. N. Reiser, W. P. Brosge, T. D. Hamilton, D. A. Singer, W. D. Menzie II, K. J. Bird, J. W. Cady,

J. R. Le Compte, and J. B. Cathrall

ABSTRACT

The geology and mineral resources of the Philip Smith 

Mountains quadrangle were virtually unexplored until the 

investigations for oil began in northern Alaska. Construction 

of the Trans-Alaskan Pipeline System has now made the 

quadrangle accessible by road. In 1975 and 1976 a team of 

geologists, geochemists, and geophysicists investigated the 

quadrangle in order to assess its mineral resource potential. 

This report is aguide to the resulting folio of twelve maps that 

describe the geology, stream sediment geochemistry, aeromagnetic features, Landsat imagery, and mineral resources 

of the area.

The bedrock geology and aeromagnetic surveys show that 

mineral deposits associated with intrusive rocks are probably 

absent. However, the geology and geochemical anomalies do 

indicate the possibility of vein and strata-bound deposits of 

copper, lead, and zinc in the Paleozoic shale and carbonate 

rocks in the southern part of the quadrangle and of stratabound deposits of zinc and copper in the Permian and Mesozoic shales along the mountain front. The northwestern part 

of the quadrangle has a low to moderate potential for oil or 

gas; Mississippian carbonate rocks are the most likely reservoir. The only minerals produced to date have been construction materials.

INTRODUCTION 

PURPOSE AND SCOPE

This circular and a separate folio of related 

maps are intended to provide information about 

the mineral resources of the Philip Smith Mountains quadrangle. The set of publications is one of 

a series of individual quadrangle reports prepared under the auspices of the Alaska Mineral 

Resource Assessment Program (AMRAP) in 

order to provide information for use in planning a 

national minerals policy and in making government and private decisions about land-use and 

minerals exploration and development.

The Philip Smith Mountains quadrangle was 

selected for assessment because it lies on the projected trend of areas that were found favorable 

for mineral resources in the adjacent Chandalar

quadrangle (De Young, 1978) and it has been relatively unexplored. The recent completion of the 

Trans-Alaskan pipeline and the James W. Dalton 

Highway has greatly improved access to the 

quadrangle.

The folio comprises twelve individually available quadrangle maps that show the geology and 

telegeology, the geochemical and aeromagnetic 

data, and the areas favorable for mineral resources (see table 1). These are reconnaissance 

maps; the 1:250,000 scale is compatible with the 

low density of the field observations, which were 

designed to provide information rapidly and uniformly over a large and little-known region.

GEOGRAPHY AND ACCESS

The Philip Smith Mountains quadrangle is 

an area of about 13,600 km2 in northern Alaska 

between latitudes 68° N. and 69° N., and longitude 147° W. and 150° W. (fig. 1). The Endicott 

and Philip Smith Mountains of the Brooks Range 

occupy all but the northwestern quarter of the 

quadrangle and include the Continental Divide, 

which crosses the quadrangle diagonally from 

southwest to northeast (fig. 2).

The mountains, which have been glaciated 

recently, are generally steep and narrow crested, 

rising about 1,000 m above the flat valley floors. 

Cirques and small alpine glaciers are common 

near the Continental Divide, particularly near 

the center of the quadrangle where the two 

highest peaks reach an elevation of 2,446 m. 

Along the south edge of the quadrangle, the 

mountains are more subdued and rounded, and at 

the north front of the range, they slope down 

abruptly to the Arctic Foothills, which in this 

area are gently sloping plains covered by glacial 

deposits with only a few bedrock hills.

The Sagavanirktok River and its tributaries 

drain most of the quadrangle north of the divide
TABLE 1. Component maps and reports of the Philip Smith Mountains quadrangle mineral resource assessment.

Report Subject

U.S. Geological Survey Miscellaneous 

Field Studies (MF) Maps:

HF-879A 

MF-879B 

MF-879C 

MF-879D 

MF-879E 

MF-879F 

MF-879G 

MF-879H 

MF-879I 

I1F-87 9J 

MF-879K 

MF-879L

(Hamilton, 1978) Surficlal geology.

(Brosge and others, 1979) Bedrock geology.

(Menzle II and others, 1983) Mineral resources other than oil and gas.

(Bird, 1983) Oil and gas resources.

(Cady, 1978) Aeromagnetlc contours and Interpretation.

(Le Compte, 1979) Interpretation of Landsat imagery.

(Cathrall and othe

(Cathrall and othe

(Cathrall and othe

(Cathrall and othe

(Cathrall and othe

(Cathrall and othe

1978a) Copper in stream sediment.

1978b) Lead in stream sediment.

1978f) Zinc in stream sediment.

1978c) Silver in stream sediment.

1978d) Barium in stream sediment.

1978e) Antimony, arsenic, bismuth, cadmium,

	molybdenum and tin in stream sediment.

U.S. Geological Survey Open-File (OF) Reports:

OF-77-223 (Detra, 1977) - 

OF-77-244 (Cathrall and others, 1977b) 

OF-77-426 (Cathrall and others, 1977a)

OF-78-559 (Dutro and Detra, 1978)

U.S. Geological Survey Circular: 

Clrc. 772-B (Dutro, 1978) -

 Delineation of anomalous lead-zinc area.

 Geocheralcal analyses of stream sediment.

 Geocheraical analyses of heavy mineral 

concentrates from stream sediment.

 Geochemlcal analyses of the Hunt Fork 

Shale.

 Potential strata-bound lead-zinc 

mineralization.

158° Barrow OCA

150° '^V

142°

0 50 100 150 KILOMETERS

i i i

FIGURE 1. Index map of Alaska showing location of Philip Smith Mountains quadrangle (dark shading) and Chandalar

quadrangle (light shading).
and flow into the Arctic Ocean near Prudhoe Bay. 

The northwestern part of the quadrangle is 

drained by the Itkillik River, which heads against 

the Continental Divide west of the quadrangle, 

and by the Kuparuk and Toolik Rivers, which 

head against the mountain front. On the south 

side, the Dietrich River, whose valley is occupied 

by the James W. Dalton Highway, drains a small 

area in the extreme southwest corner of the 

quadrangle. The Dietrich River is a tributary of 

the Koyukuk, but all the other south-flowing

rivers are tributaries of the Chandalar. The 

largest of these tributaries is the Wind River, in 

the southeast part of the quadrangle. None of 

these rivers is easily navigable.

Two low passes in the western part of the 

quadrangle, at an elevation of about 1,450 m, lie 

at the heads of tributaries of the North Fork of the 

Chandalar and the Dietrich Rivers. An unnamed 

pass is at the head of the Wind River in the east. In 

the center of the quadrangle, the Middle Fork of 

the Chandalar and all its tributaries head in

150° 147°

FIGURE 2. Philip Smith Mountains quadrangle showing location of Arctic Foothills and Brooks Range physiographic 

provinces, the James W. Dalton Highway, and large airstrips (airplane symbols). Only the Galbraith Lake airstrip is 

maintained.
glaciers and steep canyons, and there are no 

passes for a distance of about 60 km along the 

divide.

The James W. Dalton Highway, built for the 

Trans-Alaskan pipeline, gives access to the quadrangle by way of the Dietrich River and a tributary of the North Fork of the Chandalar River, 

south of the divide; Atigun Pass; and the Atigun 

and Sagavanirktok Rivers north of the divide. 

The highway connects with Fairbanks to the 

south and with Prudhoe Bay to the north. Adjacent to the road, four private airstrips, 760-1,580 

m in length, are suitable for heavy aircraft. As of 

March 1981, the largest of these, at Galbraith 

Lake, was maintained but access was limited. 

The other airstrips were closed and were not 

maintained (fig. 2). Away from the highway, two 

large lakes at the north front of the range and 

several smaller lakes at and south of the continental divide provide landing places for float planes 

in the summer and wheel or ski planes in the 

winter. In addition, most of the rivers flow 

through gravel bars and terraces that may provide suitable landing places for light airplanes.

ACKNOWLEDGMENTS

Fieldwork in the northern part of the quadrangle in 1949-51 was entirely supported by the 

U.S. Navy as part of the investigation of Naval 

Petroleum Reserve No. 4. Studies of surficial 

geology by Hamilton in 1969-71 were carried out 

during his employment as a consultant to the 

Alyeska Pipeline Service Company. This organization later (1975-76) supplied meals, lodging, 

office space, and helicopter fuel at their Galbraith Lake camp for U.S. Geological Survey 

field crews. Without the facilities provided by the 

pipeline camp, field operations would have been 

far more difficult and costly.

The bedrock geological work for the AMRAP 

investigation was done by R. L. Detterman, J. T. 

Dutro, Jr., N. J. Silberling, and the authors. S, P. 

Marsh lent his experience to help with the geochemical sampling in the adjacent Chandalar 

quadrangle. David E. Detra, Martha MillerHoare, William B. Maze, David M. Orchard, 

Margo I. Toth, and R. M. Thorson gave valued 

assistance in the field and office. Miles L. Silberman made the potassium-argon age determinations. Chemical analyses were done by E. F. Cooley, J. A. Dupree, J. T. Hurrell, R. L. Hutchens, R.

M. O'Leary and P. A. Svendsen, and statistical 

analyses of data were done by T. M. Billings, S. K. 

McDanal, and C. M. Dougal.

MINERAL EXPLORATION AND PRODUCTION

Schrader (1904), in his description of the gold 

resources of the upper Koyukuk River, stated 

that prospectors had reported finding placer gold 

on the Arctic side of the divide and that further 

investigations by the prospectors were contemplated. The area Schrader referred to must have 

been partly in the Philip Smith Mountains quadrangle, but no other mention of early exploration 

or mineral discovery within the quadrangle has 

been found in the literature.

More recently, because of the advent of better 

maps, better airborne capabilities, and more 

sophisticated exploration methods, the region has 

been explored and several mineralized areas 

have been located. Seventy-five claims, staked 

since 1971, were still active in 1978. The claims 

are grouped around four localities. The first 

locality consists of 2 groups of 28 claims, called 

the Beaucoup and the Occasional, which were 

staked by Placid Oil Company in 1971 on occurrences of copper minerals in the southeastern 

part of the quadrangle between the Middle Fork 

of the Chandalar and Wind Rivers. Interest in the 

second locality began with the delineation of an 

anomalous zinc-lead area by the AMRAP investigation (Detra, 1977). Investigations by Noranda 

Exploration Incorporated and Resource Associates of Alaska resulted in the staking of 47 

claims in 2 groups on zinc, lead, and copper minerals in an area between the Middle Fork of the 

Chandalar River and Your Creek. Just outside 

the quadrangle, two small groups of claims, 

about 6, have been located on occurrences of 

copper and silver minerals. One group is 7 km 

south and the other is 7 km northeast of the southeast corner of the quadrangle. Other exploration 

targets suggested by the AMRAP study include 

strata-bound and vein deposits. The presence of 

porphyry and contact metamorphic mineralization to the south (DeYoung, 1978) may also influence mineral exploration in the Philip Smith 

Mountains quadrangle.

No economic deposits of oil, gas, or coal are 

known although the geologic regime of the 

northwestern part of the quadrangle is compatible with the presence of these hydrocarbons.
Eleven wildcat wells have been drilled in similar 

rocks in the adjoining Sagavanirktok quadrangle 

to the north. Ten of these are dry holes, including 

the nearest two wells, which are 12 km and 17 km 

north of the quadrangle boundary (Tailleur, Pessel, and others, 1978). The only success was a gas 

well located 45 km north of the quadrangle. Geophysical exploration related to these wells probably extended into the quadrangle, but the record 

has not been made public.

To date the only minerals produced from 

within the Philip Smith Mountains quadrangle 

have been rock, gravel, sand, and fill. All material quarried was used locally in the construction 

of roads, airstrips, and building sites for the 

Trans-Alaskan pipeline. The volume of quarried 

material as of March 1977 was approximately 7.6 

million cubic meters (Al Alson, written commun., 

1977).

GEOLOGICAL INVESTIGATIONS

PREVIOUS INVESTIGATIONS

The Philip Smith Mountains quadrangle was 

virtually unmapped until military aerial photography of northern Alaska was obtained during 

World War II. In the 1936 edition of the Geological 

Survey map of Alaska (Map E), the ar£a of the 

quadrangle north of the Chandalar River system 

is blank; no northward-flowing streams are 

shown. The first reconnaissance topographic map 

was published in 1951.

Only the extreme southwestern part of the 

quadrangle was explored by early-day geologists 

and topographers. In 1899, during their reconnaissance of the Chandalar and Koyukuk Rivers, 

F. C. Schrader, geologist, and T. G. Gerdine, 

topographer, mapped northward along the present highway route in the Dietrich Valley but did 

not get far enough to recognize Atigun Pass 

(Schrader, 1900, 1904). In 1923, J. B. Mertie, Jr. 

mapped the geology of the Chandalar quadrangle 

and extended his foot-traverse mapping about 10 

km northward into the Philip Smith Mountains 

quadrangle in the area between the highway and 

Your Creek (Mertie, 1925). In 1927, Mertie continued his mapping northeastward, and although 

his route was 25-100 km east of the Philip Smith 

Mountains quadrangle, he traversed across the 

strike of most of the Paleozoic rocks found in the 

quadrangle (Mertie, 1929).

In 1934, Robert Marshall published a geographic sketch map of the northern Koyukuk 

region based on his own compass surveys and on 

information from prospectors and trappers. His 

map (Marshall, 1934), which included a small 

part of the quadrangle west of the North Fork of 

the Chandalar River, improved on the earlier 

maps by recognizing a pass across the continental 

divide from the highway route westward into the 

Itkillik Valley although it did not show the pass 

into the Atigun Valley. North of the divide, the 

quadrangle remained unmapped.

Although only a small part of the quadrangle 

was visited during these early investigations, the 

geologic work by Mertie in the adjacent quadrangles in 1923 and 1927 enabled him to describe 

a stratigraphic succession of the major rock units 

of Silurian, Devonian, and Mississippian age that 

also describes most of the rocks within the Brooks 

Range in the Philip Smith Mountains quadrangle.

RECENT INVESTIGATIONS

Fieldwork used in the present report began 

in 1949, when detailed stratigraphic studies of 

the Lisburne Group carbonate rocks and some 

limited geologic mapping were done at Itkillik 

Lake (Bowsher and Dutro, 1949). This work and 

an earlier geologic reconnaissance boat traverse 

down the Atigun and Sagavanirktok Rivers (Gryc 

and Lathram, 1946) were part of the geologic 

studies related to the determination of the petroleum potential of Naval Petroleum Reserve No. 4. 

From 1950 through 1952, and again in 1965, additional fieldwork pertaining to that program included areas of study within the quadrangle. Geologic mapping in 1950 along the north front of the 

Brooks Range included the northwest edge of the 

quadrangle along the Itkillik River (Patton and 

Tailleur, 1964). That same year, stratigraphic 

studies and some limited mapping were done at 

Galbraith Lake (Brosge and Reiser, 1951; Brosge 

and others, 1962). In 1951 geologic mapping to 

the east along the front of the Brooks Range 

included most of the foothills east of the Sagavanirktok River (Keller and others, 1961). In the 

following years, a number of short traverses were 

made in the quadrangle primarily for stratigraphic studies. These were at: Elusive Lake in 1952 

and Your Creek in 1958 (Brosge and others, 1960), 

Atigun Gorge by Tailleur in 1965 (Imlay, 1967), 

and the Ivishak and Saviukviayak Rivers in the 

northeast part of the quadrangle in 1969 and 1972
(Detterman, 1976). The authors made short helicopter traverses south of the Continental Divide 

in 1960 and along the Dietrich River and the head 

of the Sagavanirktok River in 1974. During 1976 

and 1977, the U.S. Bureau of Mines made field 

reconnaissance studies in the eastern Brooks 

Range which included the eastern part of the 

Philip Smith Mountains quadrangle (Barker, 

1978). The results of these investigations provided background and supplemental data which 

have been used in preparing this circular and the 

folio.

Planning and construction of the TransAlaskan pipeline (1969-77) initiated a number of 

special geologic and hydrologic studies concerned 

with the pipeline and its right-of-way. The areas 

within the Philip Smith Mountains quadrangle 

are discussed in many of the reports. For information regarding these studies, the reader is 

referred to the comprehensive bibliographies of 

the quadrangle compiled by E. H. Cobb of the 

U.S. Geological Survey (Cobb, 1974-79). Field 

studies of surficial geology by T. D. Hamilton 

were begun along the pipeline route in 1969 and 

continued until 1971.

Reconnaissance gravity data were collected 

by the Geological Survey in this part of the 

Brooks Range in the early 1960's. More detailed 

gravity data in the quadrangle were obtained 

during the pipeline leveling (W. E. Strange, 

National Oceanic and Atmospheric Administration, written commun., Sept. 1976) and in conjunction with the 1976 geochemical sampling. All 

available data have been incorporated in a simple 

Bouguer anomaly map (Barnes, 1977), and a terrain corrected map is forthcoming pending the 

availability of digital elevation data.

Regional geologic bedrock mapping for 

AMRAP began in the Philip Smith Mountains 

quadrangle in June 1975 and continued into 

August 1975. In the 1976 field season, an extensive geochemical reconnaissance sampling program was carried out during June and July 

under the direction of S. P. Marsh and J. B. 

Cathrall, and the bedrock mapping program was 

completed in August. During these same field 

seasons, T. D. Hamilton independently mapped 

the quadrangle's surficial deposits. In order to 

complete this fieldwork, the geologists relied 

heavily upon helicopter support. The aeromagnetic survey was flown in 1976 and interpreted by 

J. W. Cady in 1977. Landsat imagery was acquired

in 1974 and interpreted by J. R. Le Compte in 

1978.

GEOLOGIC SUMMARY

STRATIGRAPHY

Almost all the rocks exposed in the Philip 

Smith Mountains quadrangle are sedimentary. 

They form a Silurian to Cretaceous stratigraphic 

sequence about 8 km thick; the sequence is interrupted by several erosional unconformities but 

has no major angular unconformities (see figs. 3 

and 4). Successively older parts of this sequence 

are exposed from north to south across the quadrangle (fig. 5). Jurassic and Cretaceous rocks 

form the Arctic Foothills. Mississippian to Triassic rocks form most of the Brooks Range north of 

the Continental Divide; the Kanayut Conglomerate, the youngest of the Devonian formations, 

crops out along and immediately north of the 

divide, and the Silurian and older Devonian formations form most of the mountains south of the 

divide.

The stratigraphic sequence contains two 

lithologic cycles; each cycle is about 4 km thick 

and each cycle culminates in the coarse clastic 

deposits of a major orogeny. The lower cycle consists of the Silurian and Devonian rocks of the 

Franklinian sequence (Lerand, 1973); the upper 

cycle consists of the Mississippian to Cretaceous 

rocks of the Ellesmerian and Brookian sequences. 

In each cycle, about 600-800 m of carbonate rocks 

are succeeded by 1,700-2,000 m of marine shale 

and siltstone, and these are succeeded by 1,000- 

1,500 m of marine and nonmarine sandstone and 

conglomerate. The thick shale that forms the 

middle of each cycle is mostly dark gray to black. 

The Jurassic and Cretaceous shales in the upper 

cycle are rich enough in organic material to be 

regarded as the probable source rocks for the oil 

in the Prudhoe Bay field (Morgridge and Smith, 

1972). The shales and the thick carbonate units 

that underlie them in each cycle are also important to the mineral resource assessment as potential host rocks for strata-bound metal deposits. In 

both cycles the coarse-grained rocks above the 

shale are mostly cyclically bedded fluvial deposits with a basal marine sandstone. An additional 

thick sequence of coarse-grained rocks comprises 

the southernmost outcrops of the Cretaceous section where, instead of the Cretaceous black shale
Southern 

foothills

Brooks Range

and

northern 

foothills

Fortress Mountain 

Formation

Okpikruak 

Formation

o o o 

o o o o o o o 

ooo o o o

KILOMETERS

Southeast

part of 

quadrangle

Siksikpuk

Formation

Lisburne Group

 <^> <^=> CZ5-

1 1

1 1 1 1 1

1 1

1 1 1 1 1

EXPLANATION

Shale and siltstone

Unconformity or 

disconformity

J_

Marine shoreline 

retreating

Sandstone and 

graywacke

8 -

V

\ 

\ 

\

\

6-

x

4 - 

2 -

o -1

^\y\^^<\y^\

Thickness not known

° . " o . ' o . .0

O O Q O O 0

~~ _ _ _T~ _ r" __ _

j __ _ _; __ _

Z^Z -E ^ -E -E

iii i

 

i i i

i i i

i i i

-z-z-z-z-z0 O O O O

o o o o o

 o o O 

o o o o o

o . o . o. o. o. O 

o o o o o

 . . . . . 

-1-1-1-1-1-

1 I 1 1 1

O o o o o

1

1 1

1

2!

V 

(0

1a

CO

0)

o

c

0) 

3 

tJ 

0)

c

CD

i_

Ellesme

Franklinian Sequence

Colville Group

Chandler 

Formation

Tuktu Formation 

Torok Formation

Kongakut 

Formation

Kingak Shale

Shublik Formation

Sadlerochit 

Group

Lisburne Group

Kayak Shale

Kanayut 

Conglomerate

Hunt Fork Shale

Beaucoup 

Formation

Skajit Limestone

- CRETACEOUS

- JURASSIC

- TRIASSIC

PERMIAN 

PENNSYLVANIAN

- MISSISIPPIAN

- DEVONIAN

- SILURIAN

FIGURE 3. Generalized Stratigraphic sections of Paleozoic and Mesozoic rocks exposed in Philip Smith Mountains 

quadrangle. Stratigraphic sections show name, age, dominant rock types, and approximate thickness of each formation or 

group.
that occurs farther north, there is a thick unit of 

graywacke turbidite overlain by a very coarse 

graywacke conglomerate that contains some 

clasts of igneous rocks (see fig. 3).

Lerand (1973) divided the rocks along the 

Beaufort Sea into the Franklinian and Ellesmerian sequences, whose rocks were derived mainly 

from old land areas to the north, and the Brookian 

sequence, whose rocks in Alaska were derived 

from a new land area that rose in the south during 

the Mesozoic to form the ancestral Brooks Range. 

The rocks exposed in the Philip Smith Mountains 

quadrangle are the deposits of a series of marine 

transgressions and retreats around these land 

areas; the major retreats occurred during the

compressional Ellesmerian and Laramide orogenies and several minor retreats may be related 

in part to periods of extensional block-faulting 

and vertical uplift (Hitzman, 1980).

The Skajit Limestone was deposited in a shallow sea on a stable shelf. Subsequent local uplifts 

at the beginning of the Late Devonian resulted in 

some erosion and silicification of weathered surfaces before the overlying Devonian shale and 

conglomerate of the Beaucoup Formation was 

deposited in deepening water. Where the sea 

remained shallow, small carbonate reefs interfingered in the Beaucoup shales.

The thick Upper Devonian clastic wedge 

composed of the marine Hunt Fork Shale and the

sw 150 km NE

KILOMETERS

\ Mississippian to Permian

limestone, siltstone,

and shale

Ordovician and 

Cambrian(?)

phyllite, metasiltstone, and 

metavolcanic 

rocks

^

\

\

\

\

x \

\ N

\

( \

\

Mississippian

to

Permian

limestone,

siltstone,

and shale

Upper Devonian

shale and

sandstone

Middle Devonian and 

Silurian

limestone, shale.

sandstone.

and conglomerate

o o _^^ 

, /

/// /

Mississippian

to

Permian

limestone,

siltstone,

and shale

- ^_^~ x__-^- ^-/

Ordovician(?) and

Cambrian

chert, phylltte.

metavolcanlc rocks,

and limestone \ /\/\y\/\y ?'/ v ' v '

li 1 1

/ /

iiiiii 1 1

iiii 1 1

i

i

i

- 4

- 3

- 2

- 1

L- 0

FIGURE 4. Generalized stratigraphic columns showing the Paleozoic sequences exposed in the central and southern Philip 

Smith Mountains quadrangle (B) and on the Doonerak Anticline 8 km southwest of the quadrangle (A); and the inferred 

Paleozoic sequence in the northeastern part of the quadrangle (C), where rocks older than Mississippian are not exposed.

8
overlying largely nonmarine Kanayut Conglomrate marks a major retreat of the shoreline 

that was caused by the outpouring of these deltaic 

deposits away from a land area to the northeast 

during the Ellesmerian orogeny. The shoreline 

gradually transgressed northward again during 

the deposition of the Mississippian Kayak Shale 

and the overlying carbonate rocks of the Mississippian and Pennyslvanian Lisburne Group. The 

direction of transgression is demonstrated by the 

fact that each of these marine formations is 

slightly younger to the north. The Lisburne carbonate deposits evidently filled up the basin, so 

that no Upper Pennsylvanian strata were deposited, and the upper surface of the Lisburne was 

exposed locally to erosion, marking a minor

147°

Mostly Jurassic and Cretaceous 

rocks shale, stttstone, sandstone , 

and conglomerate

Mostly Mississippian. Pennsylvanian, 

Permian and Trlassto rocks limestone 

shale, sikstone.and sandstone

Mostly Upper Devonian Kanayut Conglomerate

Mostly Silurian and pre-Kanayut De 

vonian shale and limestone

Location of cross section shown in figure 6

0 5 10 15 20 25 KILOMETERS

FIGURE 5. Generalized geologic map of the Philip Smith Mountains quadrangle. Barbed heavy lines show location of axes of 

anticlines mentioned in the text; arrows show direction of plunge. DA is Doonerak anticline; CA is the anticline in which 

Cambrian rocks are exposed farther east. Dashed line is inferred location of the north edge of the thrust plate that 

contains most of the exposed Kanayut Conglomerate, and it is also the approximate northern limit of the area in which 

large thrust faults are common in the Paleozoic rocks.
regression of the shoreline. Above the Lisburne, 

the Permian shallow marine sandy and limey 

rocks at the base of the Sadlerochit Group also 

become younger northward. The Permian rocks 

thus represent a second northward transgression 

of the marine shoreline across a northern land 

area. At the same time, the Permian chert and 

shale of the Siksikpuk Formation were being 

deposited in deeper water to the south. In contrast, the Triassic shale and siltstone in the upper 

part of the Sadlerochit Group are the southern 

marine facies of a delta system that becomes 

coarser and partly nonmarine north of the quadrangle. The Triassic rocks thus represent another 

retreat of the shoreline caused by deltas growing 

southward from a northern land area.

Above the Sadlerochit Group the deepwater 

limestone and shale of the Triassic Shublik Formation and the black marine shales of the Jurassic Kingak Shale and Lower Cretaceous Kongakut Formation show that the sea again transgressed the northern land. But, at the same time, 

the ancestral Brooks Range was rising to the 

south at the beginning of the Laramide orogeny. 

While the Cretaceous marine black shales of the 

Kongakut and Torok Formations were being deposited in the northern part of the Arctic Foothills, the marine turbidites of the Okpikruak 

Formation and the partly nonmarine conglomerate of the Fortress Mountain Formation were 

being deposited near the mountains that were 

rising to the south. The Torok Formation itself is 

the shaly offshore marine facies of an Early Cretaceous delta system that gradually advanced 

northward and eastward into the area so that 

eventually the marine sandstone of the Tuktu 

Formation and the partly nonmarine conglomerate of the Chandler Formation were deposited 

above the Torok.

In well exposed outcrops west of the quadrangle, the Upper Cretaceous Colville Group 

represents a final marine transgression and then 

another northward retreat of the shoreline, during which marine and nonmarine deltaic deposits 

again prograded northward from the Brooks 

Range. These rocks may be 1,000 m thick in the 

northern part of the quadrangle, but they have 

not been measured because only a few beds of 

sandstone, coaly shale, and tuff are exposed 

beneath the extensive cover of glacial deposits. 

Since Tertiary time the shoreline has remained to 

the north.

The only igneous rocks exposed in the quadrangle are small basaltic flows and sills in the 

Devonian shale in the southeast part of the area, a 

few thin mafic dikes in the Skajit Limestone, and 

a diorite sill in the Lisburne Group at the northeast edge of the quadrangle. The diorite is probably contemporaneous with small andesitic flows 

that occur in the Lisburne 10 km farther north. A 

small granitic pluton at a depth of 1.2-2.5 km may 

be inferred from a magnetic anomaly in the area 

of Mississippian rocks in the northeast (Cady, 

1978), but the nearest known outcrops of granitic 

rocks are 15 km south of the quadrangle.

A wide belt of greenschist and higher grade 

metamorphic rocks surrounds the granitic rocks 

that crop out south of the quadrangle, and the 

zone of low-grade greenschist metamorphism 

extends into the southern part of the quadrangle. 

In that area, the Devonian shale is commonly 

metamorphosed to slate and locally to phyllite, 

and many of the Devonian basalts have been 

altered to greenstone. Devonian and younger 

rocks farther north are unmetamorphosed.

STRUCTURE

Most of the rocks in the Brooks Range and in 

the southern part of the Arctic Foothills are tightly folded and thrust faulted on both a large and a 

small scale (fig. 6). The deformation was caused 

by the Laramide orogeny that probably began in 

the Jurassic or earliest Cretaceous and continued 

into the Tertiary. The intensity of this deformation decreases in the northern quarter of the 

quadrangle. The younger Cretaceous rocks in the 

northwest are exposed in broad, gently-folded 

synclines, and the Mississippian to Triassic rocks 

in the northeast, although compressed into tight 

west-plunging folds, seem not to be broken by 

many thrust faults. The northern limit of the area 

in which large thrust faults are abundant is 

shown on figure 5.

The dip of axial planes of folds ranges from 

vertical to about 30° and is generally to the south. 

However, the axial planes dip northward in the 

two large anticlines in Mississippian rocks that 

are shown on figure 5 just north of the northern 

limit of large thrust faults. This local dip reversal 

may reflect an arch in the basement rocks.

Imbricate thrust faults are the most striking 

style of deformation in the Kanayut Conglomerate and in a 15-20-km-wide zone of younger rocks

10
immediately north of the outcrops of the Kanayut. 

Most of these faults seem to be at the leading 

edges of broken overturned anticlines, and generally the displacement on each fault diminishes 

along strike so that the structure ends as an 

unbroken plunging anticline. However, beddingplane thrusts with displacements of at least 4-8 

km do occur in the Mississippian rocks, particularly at the front of the range in the western part 

of the area (see fig. 6) and directly north of the 

large thrusts and folds in the Kanayut Conglomerate in the eastern part of the area. Bedding 

plane thrusts also probably occur at depth in the 

Mesozoic shales of the Arctic Foothills and 

throughout the Paleozoic rocks of the Brooks 

Range.

The most complex folds are in the Devonian 

shale in a zone just south of the Kanayut Conglomerate belt. In that area, marker beds of the 

Kanayut Conglomerate, and locally of the Skajit 

Limestone, have been infolded in the shale, and 

these beds outline recumbent isoclinal folds with 

amplitudes of about 6 km and with gently dipping to horizontal axial planes (see south end of 

fig. 6). Southeast of this zone the shale may be 

highly deformed, but the underlying Skajit is 

exposed in a series of fairly symmetrical doublyplunging anticlines and small domes whose axes 

are shown on figure 5.

SUBSURFACE BASEMENT ROCKS

The sequence of rocks hidden beneath the 

Mississippian to Triassic rocks in the northeastern part of the quadrangle (fig. 4) is probably 

very different from the sequence of Silurian and 

Devonian rocks that is exposed to the south (fig. 

3). In exposures of pre-Mississippian rocks north 

and east of the quadrangle and throughout the 

northeastern Brooks Range, the Devonian shale 

and conglomerate formations are absent and the 

Mississippian rocks rest with angular unconformity on deformed rocks of Precambrian, Cambrian, and probable Ordovician age. The southernmost-known exposure in which these deformed 

basement rocks lie directly beneath the Mississippian is about 40 km east of the quadrangle on a 

west-plunging anticline whose axis (C A on fig. 5) 

extends into the northeastern corner of the quadrangle. It is likely that the Cambrian and Ordovician(?) chert and volcanic rocks exposed to the 

east on this anticline continue beneath the Mississippian for some distance westward into the 

northern Philip Smith Mountains quadrangle. 

Similarly, the Mississippian in wells 150 km 

north of the quadrangle at Prudhoe Bay rests 

unconformably on deformed Ordovician(?) and 

Silurian argillite (Carter and Laufeld, 1975). 

This unconformity continues southward in the 

subsurface beneath the cover of Mesozoic rocks

5 i

Brooks Range

l»Ms> ^ Dk ,l»Ms ,DSs

Basement

rocks 

{Ordovician 

volcanic rocks)

25 30 KILOMETERS

VERTICAL EXAGGERATION X1.67

FIGURE 6. Cross section across the Philip Smith Mountains quadrangle along line ABC of figure 5 showing the tightly 

folded and thrust-faulted rocks in the southern part of the Arctic Foothills and the Brooks Range. Letter symbols 

for stratigraphic units are as in figure 5. Dashed lines show beds within the larger units. Heavy lines are faults; 

arrows show direction of movement. Structure shown below depth of 1 km is hypothetical.

11
(Tailleur, Bird, and Engwicht, 1978) and may 

extend into the Arctic Foothills within the quadrangle. Thus both jn the Arctic Foothills and in 

the Brooks Range the southern limit of the area in 

which the Mississippian may rest on pre-Devonian 

basement rocks is probably within the quadrangle.

The northern limit of the area in which the 

Devonian Hunt Fork Shale and Kanayut Conglomerate are actually present beneath the Mississippian is also not exactly known. The Devonian rocks that are actually exposed in the 

quadrangle, together with the Mississippian to 

Triassic rocks that immediately overlie them, 

seem to have glided 20-30 km northward on a flat 

thrust plate in the Devonian shale (fig. 6). The 

approximate northern limit of this thrust plate, 

shown on figure 5, is terminated with a question 

mark near the east side of the quadrangle where 

the displacement on this and adjacent thrusts 

seems to die out. The northern terrane that lacks 

Devonian rocks may extend some distance southward beneath this thrust plate.

It is possible that the northern basement terrane may extend beneath the entire quadrangle 

at depth, because the same kind of terrane is 

exposed again just south of the quadrangle on the 

Doonerak anticline (DA on fig. 5) which plunges 

northeastward into the southwest corner of the 

quadrangle. In the core of this anticline, Mississippian rocks rest unconformably on Ordovician 

volcanic rocks and phyllite (Dutro and others, 

1976) and are overlain by a thrust plate composed 

of Devonian shale that is continuous with the 

Devonian shale within the quadrangle. The lower 

part of the cross section in figure 6 was drawn to 

illustrate the hypothesis that all the Devonian 

rocks in the Philip Smith Mountains quadrangle 

are parts of this thrust plate and were moved into 

the quadrangle from an original position south of 

the Doonerak anticline a displacement of at 

least 50 km. The Ordovician or older basement 

rocks inferred for the northern part of the quadrangle and the Mississippian and younger rocks 

that overlie them may extend beneath this thrust 

plate to where they are exposed again on the Doonerak anticline. This hypothesis would explain 

all the observed relations except that no fault of 

such large displacement has been recognized in 

the Mississippian to Triassic rocks in the mountainous eastern part of the quadrangle where the 

leading edge of the thrust plate should be exposed.

DESCRIPTION OF COMPONENT MAPS

SURFICIAL GEOLOGY 

(MAP MF-879A)

The initial fieldwork along the Atigun and 

Sagavanirktok valleys was carried out in connection with trans-Alaska pipeline activities in 1969- 

71, and the entire Philip Smith Mountains quadrangle subsequently was covered by ground and 

helicopter traverses during 1975 and 1976. Able 

assistance during the 1975 and 1976 field seasons 

was provided by Robert M. Thorson.

The surficial geologic map of the Philip 

Smith Mountains quadrangle is based on (1) surface observations of morphology and composition 

of unconsolidated deposits, (2) examination of test 

pits, trenches, road cuts, and other shallow excavations, (3) stratigraphic study of bluff exposures, and (4) analysis of maps and drill logs prepared by U.S. Geological Survey personnel and 

Alyeska consultants for the trans-Alaskan pipeline corridor (see Map MF-879B). Placement of 

glacial deposits within the standard central 

Brooks Range stratigraphic sequence (Detterman and others, 1958; Williams, 1962; Hamilton 

and Porter, 1975) was based on (1) similarities in 

position, extent, and postglacial modification to 

the Anaktuvuk, Sagavanirktok, Itkillik, and 

Echooka drift sheets at type localities designated 

by R. L. Detterman and (2) concordant or crosscutting relationships of drift sheets, valley trains, 

and meltwater channels in neighboring valleys. 

Drift nomenclature has been revised in accordance with the recommendations of Keroher and 

others (1966) and Hamilton and Porter (1975). 

The originally published names Anaktuvuk and 

Sagavanirktok Glaciations have been changed to 

the "Anaktuvuk River Glaciation" and "Sagavanirktok River Glaciation" to avoid conflict with 

previously named rock units (Keroher and others, 

1966, p. 91 and 3379; Sable, 1977, p. 24-30). The 

names Itkillik Glaciation and Echooka or 

Echooka River Glaciation are replaced by "Itkillik I," "Itkillik II," and "late Itkillik"; these names 

correspond to the glacial sequences described 

and illustrated by Hamilton and Porter (1975).

Surficial geology of the Philip Smith Mountains quadrangle is dominated by the effects of 

successive episodes of Pleistocene valley-glacier 

activity. The glaciers deeply scoured mountain 

passes and valleys systems and deposited vast

12
quantities of till, ice-contact stratified drift, and 

outwash at and beyond the margins of the Brooks 

Range. They also eroded the lower slopes of the 

valley walls and created oversteepened, unstable 

rock faces that are subject to falls and slides of 

rock and debris which accumulate as talus and 

landslide rubble. Glacial retreat from massive 

end moraines near the north flank of the range 

left closed and partly closed basins (stippled pattern) which received thick deposits of lacustrine 

sediment, alluvium, fluvial and eolian sand, and 

fan-delta sediments at the mouths of tributary 

streams. The older glacial deposits generally are 

more weathered, more dissected by stream erosion than the younger deposits, and the older deposits often bear relatively thick blankets of icerich frozen silt and muck. The younger deposits 

are less altered by postglacial processes, hence 

they provide more suitable and readily accessible 

construction materials.

Massive overlapping drift sheets were deposited beyond the north flank of the range during 

each Pleistocene glaciation. The oldest drift, of 

Anaktuvuk River age, was formed by coalescing 

piedmont glaciers that spread relatively freely 

over the low terrain north of the range front. 

Younger glacial deposits, of Sagavanirktok River 

age, formed massive lateral moraines 200-300 m 

high that confined the outermost drift of the succeeding Itkillik glaciers. Thick and extensive 

loess, colluvium, and thaw-lake sediments cover 

the older drift and outwash deposits; in contrast, 

blankets of ice-rich organic silt tend to be thin 

and commonly are absent above drift and outwash deposits of Itkillik age. Itkillik II deposits, 

characterized by extensive ice-contact and outwash gravel, provide particularly well drained 

and stable surfaces for transportation routes, 

structures, and borrow materials. Late Itkillik 

deposits locally provide favorable surfaces, but 

elsewhere the drift consists mainly of poorly 

sorted till and fine-grained glaciolacustrine 

sediment.

Holocene glacier and rock-glacier activity 

has been restricted to relatively high altitudes, 

predominantly in a 25-km-wide belt centered on 

the Continental Divide. Older drift of presumed 

Neoglacial age forms bouldery vegetated moraines that terminate at altitudes of 900-1200 m 

3-8 km from cirque headwalls. Younger Neoglacial drift forms fresh unstable moraines that typically occupy cirque floors close to the fronts of

existing glaciers. Rock glaciers are active along 

valley sides at altitudes above about 1,000 m and 

occupy cirque floors and headwalls at higher altitudes. Most rock glaciers were formed from talus, 

but many rock glaciers within cirques have developed from glacial debris. Additional Holocene 

deposits include beaches along lake shores, solifluction sheets and aprons on slopes, earthflows 

where unstable banks of till have been exposed by 

river downcutting, alluvium along valley centers, 

and fans at the mouths of tributary streams. 

Many of these deposits are much more abundant 

than indicated on the map because the scale is too 

small to show alluvium along smaller tributary 

valleys, minor earthflows on moraine surfaces, 

and small or thin sheets of talus and solifluction 

debris.

With the exception of alluvium beneath some 

of the largest rivers and lakes, all surficial deposits of the Philip Smith Mountains quadrangle are 

perennially frozen. Permafrost lies at shallow 

depths (0.1-0.6 m) beneath most surfaces north of 

the Brooks Range; its depth is more variable (0.2- 

2 m) within mountain valleys north of the Continental Divide. South of the Divide, unfrozen alluvium is more widespread than it is north of the 

divide, and permafrost tends to occur at greater 

depths (0.3-3 m).

Radiocarbon dates from the central Brooks 

Range indicate that the Itkillik I glacial phase 

occurred more than 53,000 radiocarbon years ago 

and that glacier advances during the Itkillik II 

phase attained maxima between about 24,000 to 

16,000 yr B.P (Hamilton, 1982). Late Itkillik 

readvances took place about 13,000-12,500 yr 

B.P, and post-Itkillik basin fill ing commenced by 

at least 10,500 yr B.P. in some valleys (Hamilton, 

1979a, b). Middle and late Holocene cycles of 

alluviation and downcutting have been dated in 

the Itkillik, Atigun, Ribdon, and Sagavanirktok 

valleys. At least two of these cycles, which took 

place about 3,800-2,000 yr B.P. and within the 

past 500 years, evidently were caused by accelerated glacial and periglacial sedimentation related 

to expansion of cirque glaciers at valley heads 

(Hamilton and others, 1982).

BEDROCK GEOLOGY 

(MAP MF-879B)

The bedrock geology of the Philip Smith 

Mountains quadrangle is shown in black and

13
white at 1:250,000 scale on map MF-879B. On this 

map, the area shown as bedrock has been expanded at the expense of the area shown as surficial deposits wherever the deposits are thin and 

the character of the bedrock can be inferred readily. A generalized version of this map is used as 

the base for the other component maps of the folio. 

In both of these published geologic maps, the 

Upper Devonian rocks beneath the Hunt Fork 

Shale have been described as members of an 

unnamed unit of "brown calcareous clastic rocks." 

Since these maps were published, the name 

Beaucoup Formation (Dutro and others, 1979) 

has been established to include most of these 

unnamed rocks.

Detailed descriptions of some of the stratigraphic units have been given in separate reports. 

The Sadlerochit Group was described by Detterman (1976); the Lisburne Group by Bowsher 

and Dutro (1949), Brosge and others (1962), Armstrong and others (1970), and Armstrong and 

Mamet (1977, 1978); the Hunt Fork Shale by 

Dutro (1978); and the Beaucoup Formation by 

Dutro and others (1979).

MINERAL RESOURCES OTHER THAN OIL AND GAS 

(MAP MF-879C)

The quadrangle's mineral deposits and occurrences and its potential mineral resources 

other than oil and gas are described in MF-879C. 

Locations of the known deposits are shown on the 

map, and the deposits are classified by type and 

chief commodity in an accompanying table. Mineral production from the quadrangle has consisted solely of sand, gravel, rock, and fill that was 

used locally, primarily for construction of the 

Alyeska pipeline.

Only in the last 10 years has there been active 

interest in the metalbearing deposits of the Philip 

Smith Mountains quadrangle. The interest is 

reflected in several groups of claims on the lead, 

zinc, and copper deposits shown on the map 

(Menzie and others, 1982). The known deposits 

and occurrences have not been drilled, and exploration in the quadrangle has been scant.

Although few metal-bearing deposits are 

known, the information presented in the folio of 

maps that accompany this report suggests that a 

number of vein-type and strata-bound deposits in 

shale and in carbonate rocks may occur in the 

quadrangle. The scarcity of intrusive rocks (which

was interpreted from the aeromagnetic map) was 

used to eliminate from consideration those types 

of deposits that are closely associated with igneous rocks.

Ideally a resource assessment should consist 

of three basic steps (Singer, 1975):

1. Delineation of areas that are geologically 

permissive for various types of mineral 

deposits.

2. Estimation of the number of deposits of each 

type within each delineated tract.

3. Construction of grade-tonnage or contained 

metal models for the deposit types. 

In this quadrangle, this ideal methodology 

had to be modified. Deposits that may exist 

within the Philip Smith Mountains quadrangle 

are likely to be of stratiform or strata-bound 

types. For these deposit types, only a limited 

amount of both geologic and grade/tonnage information is available for model building. Thus it 

was only possible to construct one preliminary 

grade/tonnage model for use in the resource 

assessment. Because only a limited amount of 

exploration has been undertaken in the quadrangle and because an estimate of number of deposits 

has little meaning without an associated grade/ 

tonnage model, no attempt was made to estimate 

numbers of deposits. However, tracts of land that 

potentially contain deposits of different types 

were delineated. The possibility exists that tracts 

designated as permissive may not contain deposits, and also that areas not commented upon may 

contain deposits.

Boundaries of the mineral resource areas 

were determined by the authors of the component 

maps of this study, assisted by J. T. Dutro, Jr., and 

J. A. Briskey, Jr. Final responsibility rests with 

the authors of the mineral resources map. The 

tracts were outlined on the basis of their known 

deposits and their potential for undiscovered 

deposits as interpreted from geologic, geophysical, and geochemical data presented in other 

maps of the folio. The types of deposits that may 

occur in these tracts were inferred from occurrences in similar geologic settings elsewhere. The 

particular criteria used to delineate each tract 

are listed on the map sheet. Tract boundaries 

were not allowed to extend beyond geologic units 

that are permissive for the occurrence of a deposit 

type. Tracts were also restricted in areal extent if 

examination demonstrated absence of mineralization.

14
Of the metal-bearing deposit types delineated, only vein deposits containing copper, lead, 

and(or) zinc are known to occur in the quadrangle. Although locally vein deposits can be rich, 

they are typically low in tonnage. Lead and zincbearing strata-bound deposits of the shale-hosted 

type or the carbonate-hosted Mississippi Valley 

type have not been observed, but they are known 

to occur elsewhere in geologic environments that 

are similar to the delineated tracts in the Philip 

Smith Mountains quadrangle. If strata-bound 

deposits are in the quadrangle, then their tonnages may be large; in northwestern Canada and 

in northwestern Alaska, deposits of this type have 

been discovered that have tonnages ranging from 

10's to 100's of millions of tons. Mississippi Valley 

type deposits, not previously discovered in Alaska, 

probably have tonnages that are slightly lower 

than strata-bound shale-hosted deposits.

OIL AND GAS RESOURCES 

(MAP MF-879D)

The potential for hydrocarbon accumulations 

in the Philip Smith Mountains quadrangle is

estimated, with a large degree of uncertainty, to 

be low to moderate for the northwest third of the 

area, and low for the remaining area. The uncertainty stems primarily from the absence of subsurface data which are necessary in understanding the relation of surface geology to subsurface 

geology a relation most difficult to determine in 

this area because of thrust faulting.

The quadrangle is located on the southeast 

edge of the North Slope petroleum basin. It is 

situated 140 km south of the Prudhoe Bay oil 

field, 48 km south of the nearest hydrocarbon 

accumulation, the Kemik gas field, and 10 km 

from the nearest exploratory well (fig. 7). The 

quadrangle also straddles the western North 

American Thrust Belt province. This province is 

a folded and thrust-faulted belt of sedimentary 

rocks about 150 km wide, and it extends continuously from northern Alaska through Canada to at 

least as far south as Arizona. There is considerable current exploratory interest in this province 

because of numerous significant petroleum discoveries, originally in Canada and, most recently, 

in Wyoming and Utah (Lamb, 1980; Powers, 

1980).

South Barrow^ ~,East Barrow

^__5^^ Kuparuk River

Prudhoe Bay

NPRA

- Pt Thomson 

'Flaxman Island

Meade Ci Fish Creek v\

r

Wolf Creek ^ ^*& 0 ° Q n> s-'o East 

,1 \ /^ Umiat

1 ° .

i

J RANGE

°° 0° °°^

 . /^'

 y 

Philip 

Smith 

 Mountains 

quadrangle

<^tek^^-" T

^> " 'Q

,mi^ ANWR \5

^, \1 

\ ^-H

»

80

I

160 KILOMETERS

I

EXPLANATION \ 

Exploratory well 

Gas field 

Oil field

FIGURE 7. North Slope petroleum basin (mostly north of Brooks Range) showing locations of hydrocarbon accumulations,

exploratory wells, and Philip Smith Mountains quadrangle.

15
Although petroleum reservoir potential in 

the quadrangle is judged low to moderate, relevant data are sparse. Cretaceous sandstones are 

mostly graywackes, and these sandstones in nearby wells exhibit fair porosity (up to 15 percent) in 

the youngest strata and poor porosity (less than 10 

percent) in the older strata. Pre-Cretaceous sandstone, primarily that in the Kanayut Conglomerate, is described as quartzite, and the porosity in 

the Cretaceous sandstone is expected to be less 

than 10 percent. Carbonate reservoirs with 

greater than 5 percent porosity are present in the 

dolomites of the Lisburne Group (Brosge and 

Reiser, 1951). However, the occurrence of dolomite in the Lisburne is erratic and presently 

unpredictable. Dolomite of unknown porosity is 

present in the Skajit Limestone.

The petroleum source rock potential is good, 

and the rocks are mature as indicated by geochemical analyses of outcrop samples and samples from nearby wells. The best source rocks (>1 

percent organic carbon and predominantly amorphous and herbaceous kerogen) are the Kongakut 

Formation, Kingak Shale, and Shublik Formation. The poorest source rocks (<0.5 percent 

organic carbon and predominantly humic and 

inert kerogen) are the Siksikpuk Formation, the 

Sadlerochit Group, and the Hunt Fork Shale. 

Though thermal maturity (>0.65 vitrinite reflectance or >2.5 TAI) is achieved at the stratigraphic 

level of the Torok Formation, a lower level of the 

oil-generation stage (>1.2 vitrinite reflectance or 

>3.5 TAI) occurs at the stratigraphic level of the 

Siksikpuk and the Sadlerochit. Data are insufficient to determine whether maturity was achieved 

before or after tectonism and trap formation.

The most difficult facet of the petroleum 

geology of this area to assess is structure (trap 

occurrence). Folds and faults are abundant, as 

described in the geologic summary, but, except in 

the northwest corner of the quadrangle, most 

folds are breached. The presence of thrust faulting and the absence of subsurface data leave 

unresolved many important questions such as: (1) 

what are the subsurface reservoir characteristics; (2) what is the areal extent of the subsurface 

reservoirs; (3) what is the depth to autochthonous 

reservoirs; and (4) what is the degree of stack-up 

of fault-repeated reservoirs. The petroleum potential of this area could be considered greater if, 

for example, it were known that the Devonian 

reef deposits, the Hunt Fork Shale, and the Skajit

Limestone occurred at drillable depths beneath 

the northern front of the Brooks Range, or that 

the generation and migration of hydrocarbons 

occurred after the structures were formed.

AEROMAGNETIC MAP AND INTERPRETATION 

(MAP MF-879E)

The aeromagnetic survey of the Philip Smith 

Mountains quadrangle was flown in 1976, and the 

map was originally released as an open-file report 

by the U.S. Geological Survey in 1977. The map is 

remarkably featureless, owing to the sparse 

magnetic crystalline rocks within the thick sedimentary sequence of the northern Brooks Range. 

Hence, aeromagnetic data are of little use in delineating the configuration of near-surface rock 

units, and a relation between aeromagnetic features and areas of resource potential has not been 

established.

The only major aeromagnetic highs are in the 

northern part of the quadrangle; these highs are 

caused by deep-seated sources of unknown rock 

type and regional extent. Several of these magnetic highs are associated with gravity highs. The 

probable cause of the anomalies is dense, magnetic mafic or ultramafic basement rocks occurring over a large area north and west of, as well as 

in, the Philip Smith Mountains quadrangle.

INTERPRETATION OF LANDSAT IMAGERY 

(MAP MF-879F)

Interpretations of Landsat data were made 

on (1) a black and white Landsat mosaic (band 7) 

of the state of Alaska compiled by the U.S. 

Department of Agriculture, (2) an unpublished 

black and white Landsat mosaic (band 7) of the 

state of Alaska constructed by R. G. H. Raynolds, 

and (3) computer-enhanced black and white and 

color Landsat imagery processed by the U.S. Geological Survey in Flagstaff, Arizona. Landsat 

scenes selected for computer-enhancement were 

1773-21014 and 1773-21020, both taken September 4, 1974.

The black and white computer-enhanced 

product used in this report is a horizontal first 

derivative image. Color computer-enhanced 

Landsat images include linearly stretched standard false-color, sinusoidally "stretched" falsecolor, and simulated natural color images. Each 

of the computer-enhanced products is a mosaicked

16
composite that was derived from the two images 

noted above. More detailed descriptions of the 

various computer-enhancement techniques used 

in these images are given in Albert and Steele 

(1976a, b) and Condit and Chavez (1978).

As a geologic mapping tool, Landsat imagery 

is probably most effective for reconnaissance 

studies, contributing remotely sensed information about geomorphology, structural features, 

and variations in spectral response of surficial 

materials. This information can be used to plan 

and direct geologic mapping and geochemical 

sampling. However, in the Philip Smith Mountains quadrangle, where reconnaissance geologic 

mapping and geochemical sampling were completed prior to the Landsat study, the Landsat 

interpretation, which itself is an abridged version of similar interpretative investigations previously conducted in other areas of Alaska (Albert, 

1975; Albert and Steele, 1976a, b; Albert and 

others, 1978; Steele and Albert, 1978), augmented 

geological and geophysical observations by identifying: (1) possible extensions of many mapped 

faults; (2) many lineaments that were undetected 

previously; (3) many circular features, some of 

which have diameters of over 200 km; and (4) 

arcuate features.

A unique result of this investigation has been 

the identification of an approximately 700-kmlong, east-trending (structural?) zone located in 

the northern Brooks Range. In the western part 

of the range, the zone coincides with the northfacing range front, approximating the locations 

of major thrusts in the area (King, 1969; Beikman 

and Lathram, 1976; Brosge and others, 1979). In 

the north-central part, which includes the Philip 

Smith Mountains quadrangle, the zone bifurcates to form northern and southern segments, 

coinciding with the approximate location of several major thrusts (King, 1969; Beikman and 

Lathram, 1976; Brosge and others, 1979) and 

coinciding in part with one of the major lineaments. In the eastern part of the northern 

Brooks Range, these two segments rejoin to form 

a single zone that may coincide with the northernmost limit of major thrusting in that region 

(Beikman and Lathram, 1976; Lathram, E. H., 

oral commun., 1978). This zone is not directly 

associated with any of the potential mineral 

tracts mapped in the Philip Smith Mountains 

quadrangle. Instead, it marks the northern limit 

of the tracts believed to be permissive for stratabound deposits of lead, zinc, and copper, and it 

separates them from the tracts in younger rocks 

to the north that are believed to be permissive 

mainly for zinc.

RECONNAISSANCE GEOCHEMISTRY 

(MAPS MF-879G-L)

Reconnaissance geochemical investigations 

were undertaken in the Philip Smith Mountains 

quadrangle, Alaska in 1975 and 1976 to help 

evaluate the mineral resource potential by outlining areas considered to have anomalous metal 

content. During these field seasons, 759 streamsediment samples, 39 rock samples, and 737 samples of heavy-mineral pan concentrates from 

stream sediments were collected and analyzed. 

One other stream sediment sample was collected 

in 1974.

Six maps showing the distribution and 

abundance of copper, lead, zinc, silver, barium, 

molybdenum, arsenic, antimony, bismuth, tin, 

and cadmium for the various sample media are 

presented in the folio. These elements were chosen 

because they are either ore elements or orerelated elements and relevant to a regional mineral resource appraisal of the Philip Smith 

Mountains quadrangle and because they adequately reflect the economic potential of the area 

within the limits of this reconnaissance evaluation. Analytical data for elements normally determined, together with statistical summaries 

and sample locations, are given in the two openfile reports of Cathrall and others (1977a, b).

SAMPLE SELECTION, PREPARATION, AND ANALYSIS

Stream sediments were chosen as the primary sample medium because of the large size of 

the area that influences each sample. The general 

lack of knowledge of the nature or even the existence of mineralization, and the short time available for sample collection dictated regional coverage with widely spaced sample sites. The sites 

were so selected that the material for each sample 

was derived from a drainage basin of approximately 10 square kilometers. The processes of 

weathering, mass transport, and fluvial transport in a drainage basin provide a collecting and 

compositing mechanism such that a small sample 

of stream sediment is representative of the rock 

types in the drainage basin.

17
Two sample media from the stream sediment 

were chosen in order to afford maximum coverage of the major geochemical components of each 

drainage basin. They are (1) the medium to fine 

fraction (-80 mesh (0.18 mm)) of the active sediment in the bedload of the stream, and (2) the 

heavy minerals incorporated in the bedload of the 

stream.

The first type of sample provides a typical 

geochemical cross section of the transported components of the drainage basin. Its chemical composition is controlled predominantly by the major 

rock types in the drainage basin and, to a lesser 

extent, by scavenging materials such as amorphous iron-manganese oxides, clays, and organic 

matter. Geographically small components of the 

drainage basin, such as a deposit of potentially 

economic minerals, are usually reflected in this 

sample medium, but their influence is often small 

because of dilution from the rest of the area.

The second type of sample is actually a concentrate of a particular phase of the first. It is 

used to enhance the detection of less abundant 

heavy components such as ore-related minerals 

and to mitigate the enhancing effect of organic 

material, clays, and, in some instances, iron and 

manganese hydrous oxide. Most of the sediment 

is usually composed of minerals, such as quartz, 

feldspar, and clay, that are of low specific gravity 

and of little or no interest in the search for mineralization. In contrast, elements of importance in 

the exploration of many mineral deposits are 

transported as components of minerals of high 

specific gravity, and these minerals can be concentrated by simple gravity separation. Even soft 

or fragile ore minerals that break down easily to 

small grain sizes, such as galena, sphalerite, cerussite, malachite, and cuprite, can be concentrated by this method.

The stream sediments contain at least 90 

percent light minerals, so panning with a gold 

pan raises the relative amounts of heavy minerals 

by 10 to 100 times. A 5-kilogram sample usually is 

panned to about 100 grams, which is a concentration ratio of 50 to 1. Further separations in the 

laboratory reduce this 100 gram sample to 100 

milligrams, resulting in a total concentration 

ratio of 50,000 to 1 (that is, 1 part per billion 

becomes 50 parts per million if there are no 

losses). These concentration procedures raise the 

relative content of ore- and ore-related elements 

so that they can be detected by spectrographic

analysis. In the laboratory, the heavy-mineral 

concentrates were split into three fractions on the 

basis of the magnetic susceptibility of the minerals, as shown in figure 8. The least magnetic sample split was chosen for analysis for the following 

reasons. Many of the metals that form ores or are 

associated with ores also occur in common rockforming silicate minerals (for example, barium 

and lead in feldspar). Though these minerals are 

abundant, they do not contain economic amounts 

of metals. Their metal content makes up the 

background of the total metal content. Most iron 

and magnesium silicate minerals are removed 

when passed through an electromagnetic separator. The magnetic separation, therefore, further 

reduces the interference from nonore-related 

minerals. Most of the ore minerals are nonmagnetic and are concentrated in a nonmagnetic 

fraction that is analyzed. This concentration 

accentuates the differences in metal content between the samples from drainage basins that contain ore minerals and those that do not.

The rock and stream-sediment samples were 

collected, prepared, and analyzed as illustrated 

in figure 8.

USEFULNESS OF HEAVY-MINERAL CONCENTRATES

There is a higher contrast in metal content 

between samples in the heavy-mineral separates 

than in the fine to medium fraction of the stream 

sediments. Thus, the use of heavy-mineral concentrates from stream-sediments for reconnaissance geochemical evaluation of a logistically difficult and large area like the Philip Smith 

Mountains quadrangle has decided advantages 

over the use of the fine to medium fraction of the 

stream sediments. These advantages are: (1) A 

much lower sample density is sufficient to obtain 

useful results. (2) The problem of hard-to-evaluate 

scattered spot anomalies is largely eliminated. (3) 

Optical mineralogic studies can be made to determine the minerals of possible economic interest and to eliminate spurious anomalies caused by 

buckshot, barbed wire, etc.; thus the minerals 

rather than metal percentages can be used as a 

prospecting guide. (4) Some economic minerals 

(for example: cassiterite, fluorite, and wolframite) can be detected only by this method. Because 

these minerals are resistant to physical and 

chemical weathering, they are transported primarily as mineral grains, not as ions adsorbed on

18
clays or contained in organic matter as are base 

metals derived from sulfides. (5) The values of 

some ore-related elements (arsenic, antimony, 

cadmium, tungsten, molybdenum, bismuth, and 

thorium) in the fine to medium fraction of the 

stream sediment are frequently very close to or 

below the detection limit for spectrographic and 

chemical analysis. In the heavy mineral concentrates, the concentration of these elements is 

raised well above the detection limit. Thus the 

contrast between mineralized and unmineralized 

areas is increased, and the anomalies are enhanced. (6) The variable effect of organic matter, 

which may be present in one drainage basin but 

not in another, is eliminated. (7) The concentrates 

are independent of the variable diluting effects 

caused by variations in sediment transport and 

hydraulic sorting. Heavy-mineral concentrates 

have delineated several areas as worthy of followup studies.

ANOMALOUS AREAS

The anomalous levels shown for the base 

metals on the geochemistry maps were chosen at

Rock sample « 

from outcrop

Crushed to <6 m 

Split ' Discard

 Drainage basin

Active, course stream sediment from 

stream

I

Sieve in field to pass 2 mm into 36 cm - 

gold pan

Stream-sediment sample taken from 

gold pan-

 Dry at temperatures to prevent loss of 

volatile elements

80 mesh (0.18 mm) sieve

I

Vertical pulverizer (ground to <150 

mesh (0.01 mm) on ceramic plates)

I

Analysis

(1) Emission spectrography (Grimes 

and Marranzino, 1968)

(2) Atomic absorption (Ward and 

others, 1969)

Saved for possible 

future analysis

Discard floats

Magnetic fraction" 

Label C-l

intermediate fraction at 0.2 to 0.6 ampere Label C-2

Nonmagnetic fraction split at 0.6 ampere Label C-3

Optical mineroiogy

Plus 2 mm sediment discarded

Any use of trade names is for descriptive purposes only and 

does not imply endorsement by the U.S. Geological Survey.

Remaining stream sediment

\

Rough concentrate in field in gold pan 

to reduce percentage of low specific 

gravity minerals

20-mesh (0.83 mm) sieve

* 

Bromoform separation

Heavy-mineral fraction

Hand magnet separation and Frantz 

separator 1 set at 0.2 ampere (forward 

and side slope 5 and 10 degrees)

Nonmagnetic fraction at 0.2 ampere

Frantz separator set at 0.6 ampere 

(forward and side slope 5 and 10 degrees) --* 

Nonmagnetic fraction at 0.6 ampere

Split -* 

Nonmagnetic split hand grind in mullite mortar

*

Label C-3 

I

Analysis

Emission spectrography (Modified 

from Grimes and Marranzino, 

1968)

FIGURE 8. Flow chart showing preparation of rock and stream-sediment samples and of heavy-mineral concentrates from

stream sediments, Philip Smith Mountains quadrangle, Alaska.

19
the 86th to 96th percentile of the frequency distribution of sample values. In drawing the mineral resource map, the same anomalous levels 

were used for stream-sediment samples, but 

higher values, the 93rd to 96th percentile, were 

used for the heavy concentrates. About 80 percent 

of these anomalous samples are within the potential mineral tracts that were outlined.

Except in the Atigun Pass area, almost all 

the copper, lead, and zinc anomalies in the heavy 

concentrates are south of the Continental Divide 

where most of the exposed rocks are Devonian. 

These anomalies are most abundant in the southeastern part of the quadrangle east of Your 

Creek.

Silver anomalies in the heavy concentrates 

are also common in these areas, but about half of 

the silver anomalies are in a separate belt extending through the mountains from east to west 

across the center of the quadrangle.

Most of the copper, lead, and zinc anomalies 

in the stream sediments are also south of the 

divide and east of Your Creek. However, copper 

and lead are also abundant west of Your Creek, 

and about one-third of the zinc anomalies are in a 

separate linear zone that follows the northern 

mountain front across most of the quadrangle. 

The zinc anomalies are mostly in Permian and 

Mesozoic rocks.

Antimony, arsenic, bismuth, and cadmium 

were not detected in any of the stream-sediment 

samples, and tin was detected only in one sample. 

Detectable quantities of these metals were also 

rare in the heavy concentrates. On the other hand, 

samples with anomalous barium are common 

except in the area of carbonate rocks in the northeastern part of the quadrangle.

The heavy mineral concentrates were 

scanned for thorium in addition to the elements 

reported in the published data (Cathrall and others, 1977a, b). Thorium was detected only in 20 

samples, all of which are clustered around the 

areas of Permian rocks near the mountain front 

in the northeastern part of the quadrangle.

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Tailleur, I. L., Bird, K. J., and Engwicht, S. E., 1978, Maps 

showing depth to basement from drilling and from seismic exploration, eastern North Slope petroleum province, Alaska: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-928U, scale 1:500,000.

Tailleur, I. L., Pessel, G. H., Levorsen, J. A., and Engwicht, S. 

E., 1978, Maps showing land status and well locations and 

tables of well data, eastern North Slope petroleum province, Alaska: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-928A, 5 sheets, scale 1:500,000.

Ward, F. N., Nakagawa, H. M., Harms, T. F., and Van Sickle, 

G. H., 1969, Atomic absorption methods of analysis useful 

in geochemical exploration: U.S. Geological Survey Bulletin 1289, 45 p.

Williams, J. R., 1962, Geologic reconnaissance of the Yukon 

Flats district, Alaska: U.S. Geological Survey Bulletin 

1111-H, p. H289-H331.

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