Preliminary Geologic 

Investigations in the 

Kanuti River Region, 

Alaska

By WILLIAM W. PATTON, JR., and THOMAS P. MILLER

CONTRIBUTIONS TO ECONOMIC GEOLOGY

GEOLOGICAL SURVEY BULLETIN 1312-J

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pccora, Director

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

Washington, D.C. 20402 - Price 15 cents (paper cover)
CONTENTS

Page

Abstract. _---__--_-__-____--_-_-__-____-__-_-___--_-_-__-_______-- Jl

Iritroduction ______________________________________________________ 1

Geologic setting___________________________________________________ 3

Caribou Mountain-Melozitna ultramafic belt________________________ 4

Kanuti Kilolitna Creek area._______________________________________ 7

Upper Kanuti River area_________________________________________ 8

References cited_____-_____-__-__-_--_--__---__------___---____-- 10

ILLUSTRATIONS

Page 

FIGURE 1. Map of Kanuti River region showing location of areas described

in text.______________________________________________ J2

2-4. Reconnaissance geologic maps of:

2. Caribou Mountain-Melozitna ultramafic belt.________ 5

3. Kanuti Kilolitna Creek area______________________ 7

4. Upper Kanuti River area.-__--___-___-__________-_ 9

in

CONTRIBUTIONS TO ECONOMIC GEOLOGY

PRELIMINARY GEOLOGIC INVESTIGATIONS IN THE 

KANUTI RIVER REGION, ALASKA

By WILLIAM W. PATTON, JR., and THOMAS P. MILLER

ABSTRACT

Reconnaissance geologic mapping and geocheinical studies in the Kanuti River 

region of central Alaska indicate three areas worthy of further mineral investigation. Six large previously unreported ultramafic bodies have been mapped in a 

Co-mile-long belt extending from Caribou Mountain to the upper Melozitna River. 

Although no mineral occurrences of economic significance were noted during the 

brief examination of these bodies, additional investigation is warranted, particularly for such related commodities as asbestos, platinum, chromium, and nickel. 

Anomalous amounts of tin were found in stream sediment and pan concentrate 

samples from a tributary of Kanuti Kilolitna Creek draining the Sithylemenkat 

pluton. The presence of placer tin deposits on strike 60 miles to the southwest 

in the Gold Hill district suggests that the granitic terrane in the intervening 

areas as well as in the Kanuti Kilolitna area is favorable for the occurrence of 

tin. Disseminated galena and sphalerite were found in a small Tertiary (?) 

rliyolite body on the upper Kanuti River. The striking similarity to a leadline-silver occurrence previously reported in a rhyolite body on the Indian River 

suggests that such rhyolite bodies may be particularly favorable targets for 

exploration in this part of Alaska.

INTRODUCTION

Reconnaissance geologic mapping and geocheinical studies in the 

Kanuti River region of central Alaska suggest three areas of possible 

interest for mineral prospecting (fig. 1). No mining is being carried 

out in the region at the present time and there is no record of significant 

mining activity in the past. Because of its inaccessibility, the region 

proabably has not been thoroughly prospected.

The Kanuti River region extends over an area of nearly 4,000 square 

miles in the eastern part of the Koyukuk River basin and includes 

parts of the Kanuti Flats and Kokrines-Hodzana Highlands. It is 

covered by parts of the Settles and Tanana 1: 250,000 scale topographic 

maps.

Jl
J2 CONTRIBUTIONS TO ECONOMIC GEOLOGY

150° 00'

INDEX MAP SHOWING LOCATION 

OF REPORT AREA (SHADED)

20 KILOMETERS

EXPLANATION

Caribou Kanuti 

Mountain-Melozitna Kilolitna Creek

Upper 

Kanuti River

Approximate southeastern 

margin of Yukon-Koyukuk basin

FIGURE 1. Map of Kanuti River region showing location of areas described in

text.

The region is not accessible by any type of all-weather road or trail, 

although a winter road constructed in 1968-69 connecting Fairbanks 

with the Arctic Slope passes through the northern part of the region. 

The Kanuti Kiver is navigable by small river boat in high water as 

far as the western edge of the Kokrines-Hodzana Highlands, and several small lakes in the Kanuti Flats and along the western edge of the 

Kokrines-Hodzana Highlands are suitable for float plane landings. 

The villages of Bettles, 50 miles to the north, and Tanana, TO miles to 

the south, are the closest points served by scheduled airlines.

Geologic mapping and geochemical studies were carried out over a 

3-week period during the summer of 1967 and a 2-week period during
PRELIMINARY INVESTIGATIONS, KANUTI RIVER, ALASKA J3

the summer of 1968. A helicopter was used for transportation into the 

region from an operating base at Bettles. Approximately 225 stream 

sediment and rock samples were collected and analyzed by semiquantitative spectrographic and atomic-absorption methods. The authors 

were assisted in the field by R. L. Elliott, geologist, M. B. Estlimd and 

V. D. DeRuyter, field assistants, and R. E. Leonard, camphand.

Very little was known of the geology of this region prior to the 

present investigations. Early exploratory surveys by Mendenhall 

(1902), Maddren (1913), and Eakin (1916) traversed the region, but 

their reports contain only abbreviated accounts of the geology.

GEOLOGIC SETTING

The Kanuti River region straddles the southeastern boundary of 

the Yukon-Koyukuk basin (fig. 1) and includes sedimentary and volcanic rocks of the basin sequence as well as metamorphic and plutonic 

rocks of the adjoining Kokrines-Hodzana Highlands complex. The 

structural grain of the bedrock parallels the margin of the basin, and 

the regional dip is northwestward into the basin.

The oldest bedrock unit in the region is a thick sequence of pelitic 

schist, quartzite, and phyllite which underlies a large part of the Kokrines-Hodzana Highlands. These metasedimentary rocks are extensively intruded and altered by granitic rocks of Cretaceous age. Although the age of the metasedimentary rocks cannot be fixed more 

closely than pre-Late Triassic in the Kanuti River region, they are 

believed to be largely Paleozoic because they appear to interfinger to 

the northeast and southwest with limestone containing mid-Paleozoic 

fossils .(Brosge and Reiser, 1964; Mertie and Harrington, 1924).

Overlying and intruding the metasedimentary rocks along the northwest flank of the Kokrines-Hodzana Highlands is an ophiolitelike 

assemblage including altered pillow basalt, diabase, and gabbro, serpentinized peridotite and dunite, and bedded chert. These rocks appear to be alined along a major structural hinge line which marks the 

edge of the Yukon-Koyukuk basin. There is no proof that all the rocks 

comprising this ophiolitelike assemblage are the same age, but their 

close spatial relationship in the Kanuti River region and elsewhere 

around the rim of the Yukon-Koyukuk basin suggests emplacement 

at roughly the same time, probably in Late Triassic or Jurassic. Similar mafic intrusive rocks on strike to the northeast have been dated 

by potassium-argon methods as Jurassic (Reiser and others, 1965) and 

a possibly equivalent mafic intrusive near Rampart on the Yukon 

River has been dated by the same methods as Late Triassic (Brosge and 

others, 1969).
J4

Both the ophiolite assemblage and the metasedimentary rock unit 

of the Kokrines-Hodzana Highlands are intruded by granitic rocks 

which have been dated as mid-Cretaceous (Albian and Cenomanian) 

by potassium-argon methods. Two large discordant intrusive bodies 

were mapped in the Kanuti River region, the Sithylemenkat pluton on 

the south and the Kanuti pluton on the north. Both bodies are composed 

predominantly of coarsely porphyritic biotite quartz monzonite. Dikes 

of coarse pegmatite occur in local abundance on the perimeters of 

these intrusive bodies.

Bordering the Kokrines-Hodzana Highlands on the northwest are 

sedimentary and volcanic rocks of the Yukon-Koyukuk basin sequence. 

The sedimentary rocks include a highly deformed section of marine 

volcanic gray wacke and mudstone of mid-Cretaceous age and a gently 

deformed succession of nonmarine quartz conglomerate, sandstone, 

shale, thin coal seams, and ash-fall tuffs of probable Late Cretaceous 

age. These sedimentary rocks are overlain by a thick pile of flows and 

volcaniclastic rocks, chiefly of rhyolitic and latitic composition, which 

are mainly early Tertiary in age but may range into Late Cretaceous.

Pleistocene drift, deposited by glaciers fed from the Brooks Range, 

mantles most of the Kanuti Flats and obscures broad areas of the 

underlying bedrock.

CARIBOU MOUNTAIN-MELOZITNA ULTRAMAFIC BELT

Reconnaissance mapping has served to outline six large ultramafic 

bodies extending in a belt along the northwest flank of the KokrinesHodzana Highlands from Caribou Mountain to the upper Melozitna 

River, a distance of 65 miles (fig. 2). These bodies range in size from 

less than a square mile to 22 square miles and have a combined total 

area of about 60 square miles. In addition, numerous smaller bodies 

(too small to be shown in fig. 2) were identified along this belt. Other 

than brief mention of serpentinite along the Kanuti River by Mendenhall (1902), none of these ultramafic bodies has previously been reported and it seems unlikely, in view of their inaccessibility, that any 

of the bodies has been given more than a cursory examination by prospectors. Although no significant mineral occurrences were found during 

the course of our reconnaissance mapping, further investigation of 

these bodies is believed to be warranted particularly for such related 

commodities as asbestos, platinum, chromium, and nickel.

Field and aerial photo studies suggest that these ultramafic rocks 

occur as grossly layered tabular bodies dipping generally northwestward 10° to 60°. Judging from the dip of the layering and the width 

of outcrop, the Holonada body appears to be about 2,500 feet thick. In
PRELIMINARY INVESTIGATIONS, KANUTI RIVER, ALASKA J5

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J 6 CONTRIBUTIONS TO ECONOMIC GEOLOGY

the Kilolitna and lower Ivanuti bodies the layering is less well defined 

but the width of outcrop suggests that these two bodies probably are 

at least as thick. The lower contact of the ultramafic bodies is sharply 

defined, possibly by a fault, and there is little evidence of thermal 

alteration of the underlying rocks. The upper contact is poorly exposed 

but, in the few places where seen in the field, it appears gradational 

from the ultramafics through a zone of interlayered mafic and ultramafic intrusives into the overlying assemblage of mafic volcanics and 

intrusives.

The ultramafic rocks are typical alpine serpentinites, composed 

almost entirely of serpentinized peridotites, chiefly harzburgite, and 

serpentinized dunite. In the field these rocks are recognizable, even 

at a distance, by their characteristic red-brown weathering and sparse 

cover of vegetation. The peridotites are typified by rough "hobnail" 

surfaces due to the relative resistance to weathering of large pyroxene 

pseudomorphs. Exposed surfaces of the dunite, by contrast, are generally smooth except for streaks of resistant chrome spinels. Both 

peridotites and dunites are pervasively cut by veinlets and irregular 

masses of chalcedony and drusy quartz. One small mass of colloform 

magnesite was found in the northern part of the Kilolitna body.

In order to determine the trace content of chromium, nickel, and 

platinum metals in the ultramafic rocks, composite chip samples were 

collected on foot traverses across the Kilolitna and lower Kanuti 

bodies. Nine samples, each weighing approximately 3 pounds, were 

collected and analyzed. Chromium and nickel values were determined 

by atomic absorption methods and platinum group metal values by 

fire assay:

Parts per million

(ppm)

Cr _________ _____________________________ 2400-3000 

Ni ____ __ ___ _____________________ 1900-2400

Pt __________________________________________ <. 010

Rd _________________________________________ <. OOo 

Pd _________________________________________ <. 004-. 008

Chromium values range as high as 9 percent in selected grab samples of dunite streaked with grains of chrome spinel. However, the 

average value of 2,600 ppm for the nine composite chip samples agrees 

closely with the average value of 2,400 ppm given by Goles (1967) for 

ultramafic rocks.

The average value for nickel in the nine composite chip samples is 

2,300 ppm; this is higher than the average of 1,500 ppm given by Goles 

(1967) for ultramafic rocks but is within the range of various published estimates. Although no nickel sulfides were recognized in the
PRELIMINARY INVESTIGATIONS, KANUTI RIVER, ALASKA J7

ultramafics, a careful search should be made for residual deposits enriched in nickel, particularly beneath the overlapping nonmarine Cretaceous and Tertiary rocks along the northwest flank of the KokrinesHodzana Highlands.

KANUTI KILOLITNA CREEK AREA

Anomalous tin values in stream sediment samples collected along 

the upper part of Kanuti Kilolitna Creek suggest that further investigation for placer and lode tin deposits in this area (fig. 3) may be

151'OQ'

EXPLANATION

Surficial deposits

Graywacke, sandstone, Granitic rocks 

conglomerate, and 

mudstone

Geology by W. W. P.itton, Jr., 

and 1. P. Miller, 1967-68

0 5 MILES

O 1/1

ID

O

UJ

O

5 KILOMETERS

Schist, quartzite, and phyllite

Approximate contact

Queried where inferred

Fault, approximately located

FIGURE 3. Reconnaissance geologic map of the Kanuti Kilolitna Creek area.

warranted. Kanuti Kilolitna Creek drains the southwestern part of the 

Sithylemenkat pluton, a 170-square-mile body of biotite quartz monzonite that intrudes the metasedimentary rocks of the Ivokrines-Hodzana Highlands. Eleven samples were collected along the tributary 

stream that heads near VABM Ivan (fig. 3) and were analyzed by 

semiquantitative spectrographic methods. Of these, nine showed tin 

values ranging from 10 to 300 ppm. In addition, six of these samples 

gave anomalous lead values ranging from 70 to 300 ppm, and two samples had anomalous beryllium values of 10 and 20 ppm. (The following values, based on hundreds of analyses of stream sediment samples 

from central and western Alaska, are considered by the authors to be 

anomalous for granitic rock terranes: for tin, 10 ppm or greater; for
J8

lead, TO ppm or greater; and for beryllium, 7 ppm or greater.) A pan 

concentrate from near the head of the tributary yielded values much 

greater than 1,000 ppm (upper limit of determinability) for tin and 

2,000 ppm for tungsten. Some stream sediment samples collected along 

streams draining the north side of the Sithylemenkat pluton also had 

detectable amounts of tin, although none of the values exceeded 15 

ppm. Two pan concentrates from the stream draining Tokusatatquaten 

Lake contained 300 ppm tin.

Two bulk samples of tourmalinized quartz monzonite from near 

Sithylemenkat Lake gave tin values of 20 and 70 ppm. However, five 

bulk samples of the intrusive rock from the central and eastern part 

of the pluton showed no detectable tin.

The Kanuti Kilolitna tin occurrence appears to be roughly on strike 

with the tin placer deposits of the Gold Hill district, 60 miles to the 

southwest (Cobb, 1960). A brief reconnaissance of the intervening 

area shows it to be underlain in large part by porphyritic biotite 

quartz monzonite intrusives of the Sithylemenkat type. This suggests 

that not only the Kanuti Kilolitna Creek area but also the entire belt 

extending southwestward to the Gold Hill district may be worthy of 

investigation for additional tin deposits. Sainsbury and Hamilton 

(1967) have pointed out the nearly universal association of tin deposits with such biotite-bearing granitic rocks and have noted that tin 

deposits commonly are distributed along narrow structurally controlled zones.

UPPER KANUTI RIVER AREA

Galena, sphalerite, and pyrite were found as disseminated fine grains 

in oxidized and silicified rhyolite on the upper Kanuti River (fig. 4). 

The sulfides occur in a gossan about 100 yards long exposed in a bluff 

on the west side of the river. The rhyolite is composed of tuff and tuff 

breccia and is exposed over an oval-shaped area 3 miles long by 1 mile 

wide. It has been silicified and sericitized and is composed of angular 

fragments of quartz and felsic volcanic rock in a fine-grained to 

cryptocrystalline groundmass of quartz and sericite. The rhyolite, 

which is probably early Tertiary in age, rests on and probably intrudes Cretaceous biotite quartz monzonite of the Kanuti pluton. Located nearby are scattered roof pendants of hornfelsic schist.

Galena and sphalerite in grains as much as 5 mm (millimeters) longare disseminated through a pyritiferous zone about 100 yards long in 

the rhyolite. This pyritiferous zone is extensively oxidized and the 

rocks are stained and permeated by limonite. Composite grab samples 

collected along the oxidized part of the bluff contain 700 to 20,000
PRELIMINARY INVESTIGATIONS, KANUTI RIVER, ALASKA J9

150*00'

66-30' -

and T. P. Miller. 1967-68 

1 2 MILES

1 2 KILOMETERS

EXPLANATION

and phyllite

Approximate contact 

Fault, approximately located

X X X X

Gossan

FIGURE 4. Reconnaissance geologic map of upper Kanuti River area.

ppm lead, <200 (trace) to 3,000 ppm zinc, 3 to 30 ppm silver, and 70 

to 500 ppm copper. The north end of the gossan is richer in lead and 

the south end is richer in zinc and copper.

Sediment samples from streams draining the mineralized zone contain anomalous (that is, 70 ppm or greater) concentrations of lead. 

The highest values are from the upstream end of the gossan where 

samples contain as much as 700 ppm lead, 700 ppm zinc, and 3 ppm 

silver., Values drop to 70 ppm or less a short distance downstream from 

the gossan.

The examination of this deposit was brief and, because of poor 

exposure, evaluation of its economic potential is difficult. The sparsely 

disseminated sulfides in the gossan may represent leakage from an 

underlying more extensive mineral deposit. This deposit is also of 

interest because of the similarity to lead-zinc-silver mineralized rhyolite bodies on the Indian River, 75 miles to the southwest (Miller and 

Fenians, 1968). The association of this type of mineralization with 

Tertiary (?) rhyolites suggests that such bodies may be favorable 

targets for exploration in this part of Alaska.
J 10 CONTRIBUTIONS TO ECONOMIC GEOLOGY

REFERENCES CITED

Brosge, W. P., Lanyhere, M. A., Reiser, H. N., and Chapman, R. M., 1969, Probable Permian age of the Rampart Group, central Alaska: U.S. Geol. Survey

Bull. 1294-B. (In press.) 

Brosge, W. P., and Reiser, H. N., 1964, Geologic map and section of the Chandalar quadrangle, Alaska: U.S. Geol. Survey Misc. Geol. Inv. Map 1-375. 

Cobb, E. H., 1960, Molybdenum, tin, and tungsten occurrences in Alaska: U.S.

Geol. Survey Mineral Inv. Resource Map MR-10. 

Eakiu, H. M., 1916, The Yukon-Koyukuk region, Alaska: U.S. Geol. Survey Bull.

631, 88 p. 

Goles, G. G., 1967, Trace elements in ultramafic rocks, in Wyllie, P. J., ed., Ultraniafic and related rocks: New York, John Wiley & Sons, Inc., p. 352-362. 

Maddren, A. G., 1913, The Koyukuk-Chandalar region, Alaska: U.S. Geol. Survey

Bull. 532,119 p. 

Mendenhall, W. C., 1902, Reconnaissance from Fort Hamlin to Kotzebue Sound,

Alaska : U.S. Geol. Survey Prof. Paper 10, 68 p. 

Mertie, J. B., Jr., and Harrington, G. L., 1924, The Ruby-Kuskokwini region,

Alaska : U.S. Geol. Survey Bull. 754,129 p. 

Miller, T. P., and Ferrians, O. J., Jr., 1968, Suggested areas for prospecting in

the central Koyukuk River region, Alaska: U.S. Geol. Survey Circ. 570,12 p. 

Reiser, H. N., Lanphere, M. A., and Brosge, W. P., 1965, Jurassic age of a mafic

igneous complex, Christian quadrangle, Alaska: U.S. Geol. Survey Prof.

Paper 525-C, p. C68-C71. 

Sainsbury, C. L., and Hamilton, J. C., 1967, Geology of lode tin deposits: Tech.

Conf. on Tin, Internat. Tin Council, London, March 1967,35 p.

U.S. iflVERNMENT PRINTING OFFICE: 1969