Asbestos Occurrence in the 

Eagle C-4 Quadrangle 

Alaska 

Asbestos Occurrence in the 

Eagle C-4 Quadrangle 

Alaska 

By Helen l. Foster 

GEOLOGICAL SURVEY CIRCULAR 611 

Washington J 969 
United States Department of the Interior 

STEWART l. UDALL, Secretary 

Geological Survey 

William T. Pecora, Director 

Free on application to the U.S. Geological Survey, Washington, D.C. 20242 
CONTENTS 

Abstract--------------------------------------------------------

Introduction-----------------------------------------------------

Physiographic setting and access--------------------------------

Regional geologic setting ---------------------------------- --- ----

Geology of the asbestos occurrence and vicinity ---------------------

Description of occurrence --------------------------------------

Summary of asbestos occurrences in the Eagle quadrangle and 

suggestions for prospecting------------------------------------

References cited-------------------------------------------------

ILLUSTRATIONS 

Figure 1. Index maps showing location of Eagle quadrangle and 

asbestos occurrence described in this report------------

2. Geologic map of vicinity of asbestos occurrence 

described in this report-------------------------------

3. Map showing asbestos and ultramafic rock occurrences 

in the Eagle quadrangle-------------------------------

Ill 

Page 

1 

1 

3 

3 

3 

6 

6 

7 

Page 

2 

4 

Asbestos Occurrence in the 

Eagle C-4 Quadrangle, Alaska 

By Helen L. Foster 

ABSTRACT 

An asbestos occurrence was discovered in a remote part of the 

Eagle quadrangle, Alaska, in the summer of 1968 during geologic 

r econnaissance in connection with the U.S. Geological Survey's 

Heavy Metals program. The exposed part of the deposit consists of 

large joint blocks of serpentine which are cut by closely spaced 

subparallel veins. Most of the veins are about l( inch thick, and 

they consist of cross-fiber chrysotile asbestos. The asbestos appears to be of commercial quality, but the total quantity is unknown. 

The asbestos occurs in a serpentinized ultramafic mass which 

appears to intrude metamorphic rocks. Many other serpentinized 

ultramafic masses are known in the Eagle quadrangle, but this is 

the first one in which considerable asbestos has been found. The 

deposit is of importance because it shows that geologic conditions 

are locally favorable for the formation of asbestos in the YukonTanana Upland, and hope of finding commercial asbestos deposits 

thus seems possible. 

INTRODUCTION 

An asbestos occurrence was discovered in the Eagle 

quadrangle, Alaska (fig. 1), in August 1968 during geochemical sampling and geologic reconnaissance in 

connection with the U.S. Geological Survey's Heavy 

Metals program. This is the first occurrence of asb2Btos reported in the Eagle quadrangle, although asbestos is being mined 55 miles to the east-southeast 

on Clinton Creek in the Yukon Territory, Canada. The 

asbestos is in a serpentinized ultramafic mass located 

in mountainous terrain about 36)2 miles west of the 

Taylor Highway; it is on the eastern border of the 

Eagle C-4 quadrangle, 42 miles southwest of the village of Eagle. Even though this occurrence is probably 

not large enough to be of commercial interest at 

present, it indicates that geologic conditions necessary 

for the formation of asbestos did occur in this part of 

Alaska, and thus gives hope for finding other serpentinized ultramafic masses with commerical quantities 

of asbestos in the Yukon-Tanana Upland. 

Little detailed geologic information is available on 

the central part of the Eagle quadrangle. The most recent published geologic map of the area (Mertie, 1937) 

is not sufficiently detailed to show small occurrences 

of ultramafic rock. The present report is based on l 

day's fieldwork on foot in the general area covered by 

the geologic map (fig. 2) and is also based on additional fieldwork in the eastern part of the quadrangle. 

1 4 3° 

I 

Eagl e I 

. 1 I quaarang ~ 

Fairbanks'• "WA

1 

I 

Anchorage ~ 

ALASKA 

141° 

Yukon Rw~ 65' 

Eagle 

EAGLE QUAD RANG LE 

Chicken • L-----------~~----------~~L---------~ 64° 

0 50 MILES 

Figure 1.--Index maps showing location of 

Eagle quadrangle and asbestos occurre~ce 

described in this report. Area shown 1n 

figure 2 is crosshatched. 
EXPLANATION 

UNCONSOLIDATED DEPOSITS 

0 

. Colluvium and alluVium 

PLUTONIC ROCKS 

l>r1zh:j 

Hornblende adamellite 

Granodiorite 

~ 

~ 

METAMORPHIC ROCKS 

Serpentinite 

~ 

~ 

with cross- fiber asbestos 

u 

}~ r...l 

u 

)I 

Quartzite, mostly gray- banded; somewhi te or tan ~ 

Quartz - graphite schist 

Includes rocks of 

several lithologies; 

principal subunits 

Marble 

Greensch~st, 

~ 

~ 

mostly 

li{r_y 

relationships 

shown to right; 

unknownl 

age ~ 

~ 

Quartz-muscovite 

Biot i te-bea_ring metamorphic rocks 

0 

N 

0 

r...l 

...:1 

-< p, 

0 l/2 1 2 MILES 

Approximate contact 

Suspected fault 

_.!:7 

Strike and dip of foliation 

_ s 

Bearing and plunge of axis of 

tight minor fold 

Pingo * 

? 

Unmapped area 

Figure 2.--Geologic map of vicinity of asbestos occurrence described in this report. 

2 
Physiographic Setting and Access 

The asbestos occurrence is in the central and eastern parts of the Yukon-Tanana Upland as defined by 

Wahrhaftig (1965, p. 24). The area is unglaciated and 

consists of wooded and brush-covered ridges and 

valleys. The ridges range in elevation from 3,000 to 

nearly 5,000 feet and relief is about 600 to 1,600 feet. 

The deposit is on a northeast-trending ridge, at an 

elevation of about 3,500 feet, between Happy New Year 

and Bryan Creeks (fig. 3), which are tributaries to Slate 

Creek. This ridge extends northeast from the main 

ridge which forms the divide between drainage into the 

mtddle fork of the Fortymile River to the south and 

Slate Creek to the north. 

Access to the area is difficult because the nearest 

road, the Taylor Highway, is 367.! miles to the east. 

The nearest usable landing strip is 23 miles to the 

southwest, on the middle fork of the Fortymile River 

at the site of the former settlement of Joseph (fig. 3 ). 

Although the landing strip is partly overgrown with 

brush, small bush planes (Cessna 180 or smaller) can 

land there. There is also a· short abandoned landing 

strip partly overgrown with brush on the ridge between Gold Run and Jim Creek 8 miles west of the deposit. The outcrop containing asbestos is sufficiently 

clear of trees and brush that, with caution, a small 

helicopter can land there or on quartzite half a mile 

to the southwest. 

REGIONAL GEOLOGIC SETTING 

The eastern part of the Yukon-Tanana Upland is a 

complex metamorphic terrane that has been intruded 

at intervals over a long span of time by felsic, mafic, 

and ultramafic rocks. In places Tertiary sedimentary 

and volcanic rocks lie unconformably on, or are in 

fault contact with, metamorphic rocks or older igneous rocks. The northern boundary of the metamorphic 

terrane is a major zone of faulting called the Tintina 

trench (Roddick, 1967, p. 23). Themetamorphic rocks 

range in grade from greenschist to amphibolite facies 

and are of both sedimentary and igneous origin. Most 

of the metamorphic rocks are of unknown age, but 

some are of Paleozoic age as shown by poorly preserved crinoid columnals in marble. 

Ultramafic rocks crop out in many places throughout 

the Eagle quadrangle. Mapping of the Tintina fa u 1 t 

zone, although incomplete, suggests one or two 

northwest-trending linear zones, parallel to the trend 

of the Tintina trench, along which ultramafic masses 

are exposed. Other ultramafic outcrops appear to have 

a random distribution. Many of the ultramafic bodies 

are associated with greenstones and g r e ens chi s t s. 

Most of the ultramafic rocks have been wholly or 

partly serpentinized; the serpentine has been identified as antigorite in specimens that have been checked 

by X-ray diffraction. The age of the ultramafic rocks 

is unknown, but they are tentatively considered to be 

late Paleozoic or early Mesozoic because they appear 

to intrude the metamorphic rocks and because they 

3 

are probably older than the plutonic rocks of middle 

or late Mesozoic age. The ultramafic rocks may be 

somewhat more abundant than shown in figure 3 because mapping has not been sufficiently detailed to find 

some small outcrops. Ultramafic rock in stream float 

definitely indicates the presence of other occurrences. 

GEOLOGY OF THE ASBESTOS OCCURRENCE 

AND VICINITY 

The serpentinized rock containing asbesto~ crops 

out as an elongate mass apparently cutting greenschist 

facies metamorphic rocks (fig. 2 ). It is the onl:r known 

outcrop of either serpentinite or ultramafic ro-::k in the 

vicinity. The nearest ultramafic rock, also serpentinized and also having some thin bands of asbes':os, occurs 24 miles to the east-southeast (fig. 3). 

Granitic rocks also cut the metamorphic reeks and 

crop out about 214 miles southwest, a little over half a 

mile northeast, and 2 miles west of the asbestos occurrence. The granitic rock to the north e a s t is a 

medium -grained hornblende adamellite. It is part of a 

small pluton that is probably about 1 square mile in 

area. The rock is fairly dark colored becauee of the 

abundance of hornblende. The potassium feldspar is 

microcline and the plagioclase is oligoclase. Sphene 

and apatite are abundant accessories. The granitic 

rock to the southwest, which is part of a pluton several 

square miles in area, is mostly granodiorite. ':'"'he rock 

is fine to fairly coarse grained, and most of it is medium grained. Biotite is the principal mafic mineral, 

but some of the exposures are relatively low in biotite 

and consist dominantly of quartz and f e 1 d spar. The 

granitic rock to the west (outside the area shown in 

fig. 2) is possibly a dike and is coarse grain~d with 

pink feldspar; in places it is green owing to epidote. 

Its extent is not known. 

The metamorphic country rock is mostly gra?, white, 

and tan quartzite, quartz schist, and quartz-m~.1scovite 

schist; gray quartz-graphite schist; arid green chlorite 

schist and limy chlorite schist. Quartz-biotite schist 

and impure quartzite with fine-grained biotite occur in 

one area (fig. 2). The most abundant rock is gray 

quartzite, much of which is banded. It is a type characteristic of greenschist facies metamorphic rocks 

that are abundant to the east and have been mapped as 

a quartz-graphite schist unit (Foster and Keith, 1968). 

Gray quartz-graphite schist is the dominant ~·ock type 

on the east-trending ridge south of the ultramafic mass. 

Thin bands of white quartz-muscovite schis':, interlayered in quartzite, are evident in several p 1 aces 

(fig. 2 ). Greenschist, most of which is limy, crops out 

in four places (fig. 2) and may represent two northor northeast-trending bands. 

The metamorphic rocks are complexly deformed and 

cut by numerous faults, but because good outcrops are 

rare, details of structure are not evident. Rock types 

are determined largely on the basis of rubble, and only 

a few reliable strike and dip measurements were obtained. 
45' 

EXPLANATION 

cz z 

Ultramafic rock, partly serpentinized; 

large outcrops 

)( 

Ultramafic rock, all or partly 

serpentinized; small outcrops 

0 

Asbestos occurrence in serpentinized 

ultramafic rock 

See insets l and 2 and geologic map 

5 0 5 10 MILES 

Base from U.S. Geological Survey 1:250,000 

30' 

+ 

\ ~( 

~~ "" '-'>"-~f/" 0_ ,r1f'' 'r' ~ -f. \ *f~ 

Asbestos occurrence described in this report 

c'~ 

64• Eagle, 1957 

00' ~~--~~~--------------~--~------------L_----~--~--~~--~~~------~~.~~--~~----~ 

Figure 3.--Asbestos and ultramafic rock occurrences in the Eagle quadrangle. 

4 
X 

~~~~~~~n I 

I I l 

Figure 3.--Continued. 

5 
Description of Occurrence 

The asbestos occurrence consists of large joint 

blocks of dark -gray, b 1 a c k, and dark -greenish and 

brownish-black serpentine (antigorite). The approximate extent of the mass, as determined from limited 

ground observations and a study of aerial photographs, 

is shown on the map (fig. 2). Thewell-exposed part of 

the outcrop, all of which is believed to contain asbestos, 

is about 500 feet long and 200 feet wide and rises 30 

feet or more above the main level of the ridge. The 

rock is cut by closely spaced (mostly from one to a few 

inches apart) subparallel veins of cross-fiber chrysotile asbestos that range in width from 1/8 inch to about 

3j 4 inch. Most of the veins are about ~ inch wide and 

m'lny are compound. In the limited exposure examined, 

the asbestos veins cutting the massive serpentine 

would, if the occurrence were large enough, be sufficiently abundant and of good enough quality to have 

commercial value. 

SUMMARY OF ASBESTOS OCCURRENCES IN THE 

EAGLE QUADRANGLE AND SUGGESTIONS FOR 

PROSPECTING 

Because asbestos generally occurs in veins in serpentinized ultramafic rocks, knowledge of the occurrence of ultramafic rocks in an area is useful in the 

search for commercial asbestos deposits. Occurrences of ultramafic rocks that are known in the Eagle 

quadrangle are shown in figure 3 (for more exact location of many localities see Foster and Keith, 1968). 

Chrysotile asbestos has been found in the deposit described in this report, south of Champion Creek in the 

Eagle B-2 quadrangle (fig. 3), Sn miles southeast of 

Mount Harper in the Eagle A-6 quadrangle (fig. 3 ), and 

1n miles east of North Peak in the Eagle D-3 quadrangle (fig. 3 ). At the locality south of Champion Creek 

only pieces of float with a few narrow (1/8 inch) veinlets of asbestos have been found in the vicinity of serpentinized ultramafic rock. The ultramafic rock is 

bounded on the south by greenschist. Southeast of Mount 

Harper; asbestos has been found in float around an outcrop of partially serpentinized peridotite. The peridotite occurs in large blocks 4 feetormore indiameter. From a distance the outcrop can be recognized 

by its pinkish-brown color. The fiber is about 2 inches 

long and is probably slip fiber but none has been found 

in place. Serpentinized ultramafic rock east of North 

Peak contains a few tiny veinlets, almost microscopic 

in size, of asbestos. Some of the other u 1 tram a f i c 

masses, including the one along American Creek and 

the one south of Boundary (fig. 3), locally have fibrous 

serpentine but the fibers are stiff. 

The conditions that have caused the formation of asbestos in some of the serpentinized ultramafic bodies 

but not in others are not known, although some geologists have suggested that faulting is an important 

factor. Most of the Yukon-Tanana Upland is complexly 

faulted, but extensive cover makes it difficult to locate 

and trace faults. Marker beds are not generally present, and in many places small local faults are difficult 

to distinguish from large regional faults. 

6 

Some of the ultramafic bodies, particularly in the 

eastern part of the quadrangle, are associated with 

greenstone of probable andesitic and basaltic composition. Many serpentinized bodies, ho·~,ever, including the one described in this report, are not associated 

with greenstones. Some serpentinization ofgreenstones of probable basaltic or andesitic origin has been 

noted, but no fibrous material has been discovered. 

The serpentinization of greenstones is less common 

and less extensive than that of the ultramafic rocks. 

Most of the ultramafic rocks are in areas of greenschist facies metamorphic rocks. Only a few bodies of 

ultramafic rock have been found in the areas of amphibolite facies metamorphic rocks, and some of them 

are not serpentinized. This observation, however, 

should not preclude further exploration in areas of 

higher grade metamorphic terrane, as its significance, 

if any, is unknown. 

Prospectors searching for asbestos deposits in the 

Eagle quadrangle may find the following criteria useful for recognizing ultramafic rocks, including those 

that have been serpentinized. The fresh ultramafic 

rock commonly is dark gray, black, or greenish black; 

weathered surfaces may be grayish brcwn, pinkish 

brown, or greenish gray. The rock is generally massive and is heavier than the other local rocks. Ultramafic rocks may occur as large or snail irregular 

masses and as dikes and sills. Con c err t r at ions of 

boulders of ultramafic rocks in streams are generally 

not far from their outcrop, and the outcr')p can usually 

be located by following the stream float. Outcrops of 

ultramafic rocks are .characteristicall~· almost bare 

or vegetation is sparse. However, some of the quartzite outcrops in the area also have sparse vegetation. 

No pattern useful for prospecting has been observed 

in known outcrops of ultramafic rocks of the E a g 1 e 

quadrangle (fig. 3). One or two belts of serpentinized 

ultramafic rock occur along faults parallel totheTintina trench, but no asbestos has yet bet~n found. Significant structure related to the occurrence of other 

ultramafic outcrops is unknown. 

Parts of the Yukon-Tanana Upland n':"lt recent 1 y 

m'1pped probably contain several undisc':"lvered ultramafic bodies. These areas include the western part 

of the Eagle quadrangle and much of the Big Delta 

quadrangle, especially the eastern part. The Tanacross (Foster, 1968), Char 1 e y River (Brabb and 

Churkin, 1964), and eastern part of the Eagle (Foster 

and Keith, 1968) quadrangles have recently been 

mapped, but because much of the mapping is only reconnaissance there are some undiscovered ultramafic 

bodies in the these areas. 

The Eagle quadrangle is covered by an aeromagnetic 

survey (Brosge and others, 1968), but the lines of flight 

are too widely spaced (10 miles) to giv~ much aid in 

locating small bodies of ultramafic ro~k. More detailed aeromagnetic surveys would be 'Tery useful in 

searching for asbestos. 
REFERENCES CITED 

Brabb, E. E .• and Churkin, Michael, Jr., 1964, Preliminary geologic map of the Charley River quadrangle, east-central Alaska: U.S. Geol. Survey 

open-file report. 

Brosge, W. P., Brabb, E. E., and King, E. R., 1968, 

Geologic interpretation of reconnaissance aeromagnetic survey of northeastern Alaska: U.S. Geol. 

Survey open-file report. 

Foster, H. L.. 1968. Reconnaissance geologic map of 

the Tanacross quadrangle, Alaska: U.S. Geol. Survey open-file report. 

Foster, H. L., and Keith, T. C., 1968, Preliminary geologic map of the Eagle B-l and C-1 quadrc-ngles, 

Alaska: U.S. Geol. Survey open-file report. 

Mertie, J. B., Jr., 1937, The Yukon-Tanana region, 

Alaska: U.S. Geol. Survey Bull. 872, 276 p. 

Roddick, J. A., 1967, Tintina trench: Jour. Geology, 

v. 75, no. 1, p. 23-32. 

Wahrhaftig, Clyde, 1965, Physiographic divisions of 

Alaska: U.S. Geol. Survey Prof. Paper 482, 52 p. 

7