GEOLOGICAL SURVEY CIRCULAR 195 

RADIOACTIVITY OF SELECTED ROCKS 

AND PLACER CONCENTRATES FROM 

NORTHEASTERN ALASKA 

By Max G. White 

• 
• 
UNITED STATES DEPARTMENT OF THE INTERIOR 

Oscar L. Chapman, Secretary 

GEOLOGICAL SURVEY 

W. E. Wrather, Director 

GEOLOGICAL SURVEY CIRCULAR 195 

RADIOACTIVITY OF SELECTED ROCKS AND PLACER CONCENTRATES 

FROM NORTHEASTERN ALASKA 

By Max G. White 

This report concerns work done on behalf of the 

U. S. Atomic Energy CommiBBion and is published 

with the permiBBion of the Commission. 

Washington, D. C., 1952 

Free on application to the Geological Survey, Washington 25, D. c: 

RADIOACTIVITY OF SELECTED ROCKS AND PLACER CONCENTRATES 

FROM NORTHEASTERN ALASKA 

CONTENTS 

Part 1. Radioactivity in gneissic granite oJ the 

Mount Michelson area, northeastern 

Alaska 

Page 

Abstract . . . . . . . . . . . . . • . . . . . . . JJ 

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

Geology..... . . . . . . . . . . . . . . . . . 3 

Radioactivity and 

mineralogy..... . . . . . . . . . . . . 4 

Conclusions................... 4 

References cited . . . . . . . . . . . . . . 4 

Part 2. Radioactivity and mineralogy of placer 

concentrates from the Wiseman and 

Chandalar districts 

Page 

Abstract.................... 8 

Introduction . . . . . . . . . . . . . . . . 8 

Discussion of data.......... . 8 

Wiseman district . . . . . . . 8 

Chandalar district . . • . . . 8 

Conclusions . . . . . . . . . . . . . . . 12 

References cited . . • . . . . . . . . . 12 

ILLUSTRATIONS 

Page 

Figure 1. Map of northeastern Alaska showing location of the Mount Michelson area . . . . • • • . • . • . . • . . . . . 2 

· 2. Sketch map of the Mount Michelson area, northeastern Alaska. • . • . • . . . . • . . • • . • • • . . . . . • . . . . . 3 

3. Map of northeastern Alaska showing location of parts of the Wiseman and Chandalar districts.. 9 

4. Sketch map of a portion of the Wiseman district, northeastern Alaska . . . . . • • • . . . . • . • • . . . . . . . 9 

5. Sketch map of a portion of the Chandalar district, northeastern Alaska . . . . • . • . . . . . . . . . . . . . . . . 12 

TABLES 

Page 

Table 1. Data on samples from the Mount Michelson area, northeastern Alaska. . • . . • . • . . . . . • . . . . • . . . . . 5 

2. Mineral composition of heavy-mineral fractions containing more than 0. 01 percent equivalent 

uranium, Mount Michelson area, northeastern Alaska . . . . . . . . . • . . . . . . . . . . . . . . . • . . . . . . . .. . 7 

3. Radiometric and mineralogic data on placer concentrates from the Niseman district, northeastern Alaska ..•....................... -, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10 

4. Radiometric and mineralogic data on placer concentrates from the Chandalar district, northeastern Alaska . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . 11 

PART I. --RADIOACTIVITY IN GNEISSIC GRANITE OF THE MOUNT MICHELSON AREA, NORTHEASTERN ALASKA 

ABSTRACT 

Radiometric examination of 13 samples collected 

in the Mount Michelson area, northeastern Alaska, in 

1948, shows that four samples of gneissic granite contain an average of 0. 007 percent equivalent uranium. 

The heavy-mineral fractions from three of these four 

samples contain an average 0. 052 percent equivalent 

uranium and 0. 03 percent uranium. The heavy-mineral fractions of panned concentrates from gravels of 

streams draining relatively large areas of granitic 

rock, contain an average of 0. 028 percent equivalent 

uranium, whereas similar heavy fractions of panned 

concentrates from streams that drain areas other than 

those largely underlain by granitic rock contain an 

average of only 0. 005 percent equivalent uranium. 

Mineralogic study of all heavy-mineral fractions 

having more than 0. 01 percent equivalent uranium 

indicates that the radioactive material apparently is 

confined to biotite, which in one sample contains 

1 

1. 19 percent uranium. Fluorite, hematite, zircon, 

sphene, galena, and molybdenite, commonly associated elsewhere with uranium, apparently are disseminated in the granite with the biotite. 

The presence of uranium in the biotite of the 

granite and, of other minerals associated with uranium 

elsewhere, suggests that this area should be considered 

in relation to others in Alaska as a possible locality to 

search for high-grade uranium deposits. 

INTRODUCTION 

On the latest geologic map of Alaska, compiled 

by Smith (1939, pl. 1)7 three areas of intrusive rocks 

are shown in northeastern Alaska on the north flank 

of the Brooks Range. These areas are as follows: 

1) On the international boundary about 30 miles south 

of the Arctic coast (fig. 1). 1See references cited. 
A R C T 

c I 

50 0 

0 c c 

4 4' 

I 

I 

\ 50 MILES 

Figure 1. --Map of northeastern Alaska showing location of the Mount Michelson area. 

2) In the vicinity of Mount Michelson about 80 miles 

west of the international boundary (figs. 1, 2). 

3) In the vicinity of Mount Chamberlain about 15 miles 

west of Mount Michelson (fig. 2). 

The presence of granite in areas (1) and (3) 

listed above is uncertain. Its presence has been 

confirmed by recent field investigations only in the 

vicinity of Mount Michelson, area (2), (Whittington 

and Sable, 1948, unpublished report, pp. 14-16, 

and fig. 1; Payne and others, 1951) . A. G. Maddren, 

the only Survey geologist to work along the northern 

part of the international boundary, indicates in his 

unpublished notes and maps that the rocks in area (1) 

are tuffs and agglomerates. The area around Mount 

Chamberlain (fig. 2), originally mapped by Leffingwell 

2 

(1919, pl. 2) as granite(?), was found by Whittington 

and Sable (1948, fig. 1) to consist instead of preCambrian(?) schists of the Neruokpuk formation. 

In the Mount Michelson area, however, the work by 

Whittington and Sable corroborated the occurrence of 

intrusive rock as mapped by Leffingwell (1919, pp. 

126-128, and pl. 2). It is thus the only verified 

occurrence of intrusive rock in northeastern Alaska 

on the north flank of the Brooks Range. 

Following the field season of 1948, Whittington 

turned over to the author a collection of 13 samples 

from the Mount Michelson area (fig. 2). The purpose 

of this report is to present the results of the radiometric and mineralogic studies of these samples. 

This work was done on behalf of the Division of Raw 

Materials of the U. S. Atomic Energy Commission. 

/ 
EXPLANATION 

r---J UNDIFFERENTIATED PRE-CAMBRIAN(?), PALEOZOIC 

L___j AND MESOZOIC SEDIMENTARY AND BASLC 

IGNEOUS ROCKS 

~ 

~ 

PRE-CARBONIFEROU!p (PRE-CAMBRIAN)? 

GNEISSIC GRANITE 

• SAMPLE LOCATION 

0 5 10 Miles 

Geology and bose from mops by U.S. Geological Oil Unit 

Figure 2. --Sketch map of the Mount Michelson area, northeastern Alaska. 

GEOLOGY 

The gneissic granite at Mount Michelson is 

commonly gray and coarse-grained. According to 

Whittington and Sable (1948, unpublished report, 

pp. 14-15) the granite 

"seems to be made up of several different 

granites. The granite which is apparently 

most common is gray in color. In general 

the granites are composed of quartz, white 

feldspars, and minor amounts of dark minerals. Quartz probably averages 25 percent with feldspars contributing the bulk 

of the remainder. The feldspars are mostly 

white in color, but pink feldspar was seen 

in float. In a number of hand specimens 

two different white feldspars were tentatively differentiated. Although the dark 

minerals are generally a minor constituent, 

in a few cases they were folllld to comprise 

3 

a considerable percentage, 30 to 50 percent, of the rock. The dark mineral or 

minerals have been mostly altered to 

chlorite. In a few cases biotite was foillld 

with a chlorite outline. Feldspar phenocrysts are present in some of the rock. 

Outcrops of granite containing phenocrysts 

were found near the north edge of the mass. 

Erratics bearing phenocrysts are common, 

and many of them have come from other 

parts of the mass. In general, the phenocrysts are one to one and one-half inches 

long, but some have been seen up to six 

inches in length. The phenocrysts are 

usually fractured, often showing two sets 

of fractures approximately at right angles. 

"Inclusions and segregations were seen 

only in outcrops along a creek which flows 

from the west into the Okpilak River near 
the north edge of the granite mass. The 

inclusions are generally angular, but the 

corners are rounded and the edges minutely 

scalloped, suggesting absorption of some 

of the rock by the including magma. Both 

light and dark colored inclusions were 

found. They are generally finer-grained 

than the including rock and are thought 

to be entirely igneous. One dark colored 

inclusion contained a light colored inclusion. 

Another dark inclusioifcontained feldspar 

phenocrysts. Segregations seen apparently 

consist of small masses of biotite which 

have been concentrated into layers. " 

In places the granite grades into the schist and 

phyllite of the Neruokpuk formation of pre-Cambrian(?) 

age (Payne and others, 1951). A gneissic structure 

is characteristic of the granite, but is not universally 

present and varies considerably in degree of development. Where the granite grades ir.to the schist, 

the gneissic structure becomes more intense and 

passes into the foliation of the Neruokpuk formation. 

On the basis of the gneissic structure, the apparent 

lateral gradation into schist, and the unmetamorphosed 

condition of adjacent Carboniferous limestone, the 

granite of the Mount Michelsor. area is considered to 

be at least pre-Carboniferous(?) (Payne and others, 

1951). If this granite is as old as pre-Cambrian, it 

may be related to the Pelly gneiss of the Yukon-Tanana 

region (Mertie, 1937,_ pp. 201-203). 

RADIOACTIVITY AND MINERALOGY 

The 13 samples frorri. the Mount Michelson area 

co~sisted of four specimens of the granite bedrock 

along the Okpilak River, seven panned concentrates 

from gravels of streams in the immediate vicinity of 

Mount Michelson, and two panned concentrates from 

stream gravels of the Sadlerochit River and one of 

its tributaries west of Mount Michelson (fig. 2). The 

four rock samples were crushed to minus-20 mesh and 

analyzed radiometrically. They were then fractionated 

with bromoform (sp gr 2. 8). The nine panned concentrates from stream gravel also were sized to minus-20 

mesh and fractionated with bromoform. The bromoform-heavy fractions of both the crushed rock samples 

and panned concentrates were then analyzed radiometrically. The bromoform-heavy fractions of three 

of the rock samples were analyzed for uranium 

fluorometrically. Table 1 gives the data on the 13 

samples. Mineralogic studies were made of all the 

heavy-mineral fractions containing more than 0. 01 percent equivalent uranium (eU). Table 2 shows the 

mineral composition of these radioactive heavy-mineral fractions. 

The four samples of gneissic granite bedrock 

contain an average of 0. 007 percent equivalent uranium. 

The heavy-mineral fractions of three of these four 

samples contain an average of 0. 052 percent equivalent 

uranium and 0. 03 percent uranium. Thus by concentrating the heavy minerals of the granite by a ratio of 

4 

about 30:1 approximately a seven-fold increase in 

the equivalent uranium content is obtained, of which 

about 60 percent is uranium. 

On the basis of the radiometric data on the 

panned-concentrate samples, it appears obvious that 

the radioactive material comes from the granite, as 

all samples from gravels of the streams draining 

large sectors of the granitic area have a relatively 

large equivalent uranium content (samples 3248, 

3249, and 3251, fig. 2 and table 1). The equivalent 

uranium content decreases considerably in other sectors 

even where the watershed of the stream contains a 

small amount of granitic rock. 

The radioactivity of all the samples investigated 

mineralogically appears to be entirely in the biotite. 

X-ray studies of selected grains of this mineral from 

sample 3253-L show a mixed pattern with major 

biotite-phlogopite( ?) lines. Spectrographic analysis 

of the biotite indicates the presence of silicon, calcium, 

iron, aluminum, magnesium, lanthanum, zirconium, 

and rare earths. A fluorimetrit test shows that the 

biotite from sample 3253-L contains 1. 19 percent 

uranium. Minerals such as fluorite, hematite, 

molybdenite, galena, zircon, and sphene (table 2), 

commonly associated with radioactive materials 

elsewhere, apparently are disseminated in the gneissic 

granite with the biotite, although the fluorite and 

molybdenite suggest either pegmatitic or hydrothermal 

conditions. 

CONCLUSIONS 

Radiometric and mineralogic study of four 

bedrock samples and nine panned-concentrate samples 

from the Mount Michelson area of northeastern Alaska 

shows that uranium is associated with biotite in the 

pre-Carboniferous(?) gneissic granite of the area. 

Fluorite, hematite, molybdenite, galena, and other 

minerals, associated with uranium elsewhere, also 

occur in the granite. These occurrences suggest that 

this area should be considered in relation to others 

in Alaska as a possible source of high-grade deposits 

of uranium. 

REFERENCES CITED 

Leffingwell, E. de K., 1919, The Canning River region, 

northern Alaska: U. S. Geol. Survey Prof. Paper 

109. 

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

Alaska: U. S. Geol. Survey Bull. 872. 

Payne, T. G., and others, 1951, Geology of the 

Arctic Slope of Alaska: U. S. Geol. Survey Oil 

and Gas Investigations, Map OM 126. 

Smith, P. S., 1939, Areal geology of Alaska: U. S. 

Geol. Survey Prof. Paper 192. 

Whittington, C. L. and Sable E. G., 1948, Preliminary report on the geology of the Sadlerochit 

River area [Alaska]: U. S. Geol. Survey Geological Investigations, Naval Petroleum. Reserve 

no. 4, Alaska, (report in files of U. S. Geol. 

Survey). 
01 

Sample no. 

3253-L 

3254-L 

3255-L 

3256-L 

3244 

3245 

3246 

3247 

3248 

3249 

3250 

I 

I 

I 

I 

I 

I 

I 

Table 1.--Data on samples from the Mount Michelson area, northeastern Alaska 

Location 

(see fig. 2) 

Left limit of Okpilak River about 

midway between northern and 

southern edges of intrusive mass. 

-do-

-doRight limit of Okpilak River at 

northern edge of intrusive mass. 

Sadlerochit River about 7 miles 

southwest of Lake Schrader. 

Tributary of Sadlerochit River 

about 3 miles southeast of Lake 

Schrader. 

East tributary of Hulahula River 

about 5 miles upstream from 

junction with Hulahula River and 

about 10 miles north of Mount 

Michelson. 

Esetuk Creek about 1 mile upstream 

from junction with Hulahula River 

and about 8 miles downstream from 

granite contact. 

Kolotuk Creek about 4 miles upstream from junction with Hulahula River and about 1 mile downstream from granite contact. 

Small tributary on west side of 

Okpilak River just downstream 

from north edge of granite. 

Small tributary on east side of 

Okpilak River at contact of 

granite and limestone. 

Crushed bedrock 

eU (percent) 

Bedrock samples 

0.007 

.007 

.008 

.005 

Panned-concentrate sample 

--

-- I 

I -- I 

I -- I 

I -- I 

I -- I 

I I --

fraction 

u (percent:F 

0.080 0.033 

.034 .010 

.043 .046 

.oo8 --

.006 

I 

--

.004 --

.002 I --

.013 I --

.030 I --

.030 I --

.005 I --

Concentration 

ratio2 

40:1 

18:1 

36:1 

10:1 

12,600:1 

I 5,1oo:1 

14,400:1 

14,000:1 

I 5,300:1 

I 7,5oo: 1 

I 10,000.:1 
Table 1.--Data on samples from the Mount Michelson area, northeastern Alaska--Continued 

Sample Location Crushed bedrock Heavy-mineral fraction ,----- Concentration no. (see fig. 2) eU (percent) eU (percent) f U (percent)l ratio2 

---· ---~----· ------ --·· --·- - -

Panned-concentrate sample--Continued 

3251 West tributary of Okpilak River, -- .040 -- 10,000:1 

about 2 miles upstream from 

junction with Okpilak River; near north edge of granite .. 

3252 West fork of Okpilak River, about -- .007 -- 2,500:1 

3/4 mile upstream from junction 

of forks; near south edge of 

granite where it is in contact 

with the Neruokpuk formation. - - - , __ -

·lnetermined.fluorometrically by the Geological Survey Laboratory. 

2concentration ratio is ratio between original material and heavy-mineral fraction. 

m 
Table 2.--Mineral compositionl of heavy-mineral fractions containing more than 0.01 percent equivalent uranium, Mount Michelson area, northeastern Alaska 

[Minerals are listed in order of decreasing abundance. Asterisk(*) indicates trace only ] 

3247 3248 3249 3251 3253-L 3254-L 3255-L 

Biotite Biotite Biotite Biotite Biotite Biotite Fragments of 

quartz with 

Chlorite Chlorite Hematite Garnet Muscovite Muscovite biotite, 

muscovite, 

Muscovite Muscovite Pyrite Muscovite Pyrite (with Yttrocerite(?) pyrite, and 

hematite magnetite. 

Epidote Yttrocerite(?) Ilmenite Chlorite coating) Fluorite 

Muscovite 

*Fluorite Fluorite Zircon Tourmaline Yttrocerite(?) Chlorite 

Biotite 

*Zircon Magnetite *Zoisite Yttrocerite(?) Fluorite Magnetite 

Pyrite (with 

*Hematite *Magnetite Fluorite *Garnet hematite 

coating) 

*Sphene Pyrite *Chlorite 

Magnetite 

*Brookite *Zircon *Magnetite 

*Scheelite *Hematite *Molybdenite 

*Galena 

1Analyses by K. Onada, Geological Survey Laboratory, 

7 
PART 2. --RADIOACTIVITY AND MINERALOGY OF PLACER CONCENTRATES FROM THE WISEMAN 

AND CHANDALAR DISTRICTS 

ABSTRACT 

Radiometric and mineralogic study of 19 placer 

concentrates revealed the presence of monazite on 

Rye Creek in the Wiseman district and on several 

creeks northeast of Chandalar Lake in the Chandalar 

district, upper Yukon region, northeastern Alaska. 

Uranium-bearing thorianite( ?) occurs on the South 

Fork of the Koyukuk River at Gold Bench and vicinity 

in the Wiseman district. 

The radioactive minerals are almost always 

associated in the placers with hematite and several 

of the metallic sulfides. Such association may indicate the possible occurrence of primary uranium 

ores with hematitic alteration within the drainage 

basins of the streams where the radioactive minerals 

are found. Selected areas in the vicinity of the radio8-ctive mineral occurrences in the Wiseman and 

Chandalar districts might contain primary uraniferous 

deposits. 

INTRODUCTION 

The Wiseman and Chandalar districts, upper 

Yukon region, are located in northeastern Alaska 

north of the Yukon River and south of the Brooks 

Range (fig. 3). The Wiseman district includes all 

the headwater drainage of the Koyukuk River from a 

point about 25 miles downstream from Bettles at the 

confluence of the North and South Forks. The 

Chandalar district includes all the drainage of the 

Chandalar River from a point about 50 miles above 

its junction with the Yukon River {fig. 3). 

The purpose of this report is to present the 

results of the radiometric and mineralogic study of 

19 samples from the Wiseman and Chandalar districts 

which are available in the Geological Survey's Alaskan 

collection. This work was done on behalf of the 

Division of Raw Materials of the U. S. Atomic Energy 

Commission. 

DISCUSSION OF DATA 

Wiseman district 

Only generalized information is available on 

the geology of the Wiseman district (fig. 4), the 

best and most recent being that obtained by Maddren 

(1913). Maddren's report is accompanied by a topographic and geologic map on a scale of 1:500, 000. 

Placer-gold mining has been conducted in many 

areas within this district since the early part of the 

century. The ten samples available from the Wiseman 

district are from several localities within some of 

the mining areas of the district. The data on the 

samples from the Wiseman district are summarized 

in table 3. 

8 

Only three samples from the Wiseman district 

show a significant amount of radioactivity. The 

radioactivity of the sample from Rye Creek (no. 1358, 

table 3 and fig. 4) is attributed to a trace of monazite 

which was not found in the other sample from the 

same creek (no. 1359, table 3 and fig. 4). Traces 

of pyrite, chalcopyrite, galena, scheelite, and gold 

are significant associates of the monazite. 

The radioactivity of the samples from Gold 

Bench and vicinity on the South Fork of the Koyukuk 

River (nos. 1151 and 1548, table 3 and fig. 4) is 

ascribed to traces of uranium-bearing thorianite( ?) 

which occurs as minute cubes and fragments in the 

minus 100-mesh portion of the nonmagnetic fraction 

of the concentrate. Hematite and traces of bismuthinite( ?) , chalcopyr~te, cinnabar, galena, cassiterite, 

and scheelite are associated with the uranium-bearing 

thorianite( ?) • 

Gold Bench, according to Maddren (1913, pp. 105-

107), is a deposit of high-stream gravels situated on 

the northeast side of the South Fork of the Koyukuk 

River with the gold-bearing gravels lying on top of 

thick unconsolidated wash deposits. Ironside Bar, 

possibly the source of sample 1151, is similar to 

. Gold Bench but lies on the south side of the Fork about 

a mile above.Gold Bench. Gold Bench is about 30 miles 

south of the settlement of Wiseman (fig. 4). 

Chandalar district 

The geology of the Chandalar district has been 

discussed briefly by Ma,.ddren (1913) and in some 

detail by Mertie (1925). The placer-mining operations 

in the district are located largely on creeks a short 

distance northeast of Chandalar Lake (fig. 5). Of 

the nine samples available from the Chandalar district 

for study only two (nos. 2253 and 2254, table 4 and 

fig. 5) are probably representative of the heavy sands 

in the placers. The others appear to be splits from 

the heavy sands and carry a concentration of only one 

or two minerals in an amount that is probably not 

representative of the minerals as they occur in the 

placers. The data on the samples from the Chandalar 

district are summarized in table 4. 

Monazite is probably the main radioactive mineral in the samples from the Chandalar district 

(table 4). Hematite, scheelite, gold, and a trace 

of galena are associated with the monazite on Tobin 

Creek. On Big Creek these same minerals and 

arsenopyrite and chalcopyrite are associated with 

the monazite. Mertie (1925, p. 262) reports the 

occurrence of arsenopyrite, pyrite, stibnite, galena, 

sphalerite, and siderite in gold-quartz veins in a 

mineralized area at the head of Little Squaw, Boulder, 

Tobin, and Big Creeks (fig. 5). 
C T I C 

B 

Figure 3. --Map of northeastern Alaska showing location of parts of the Wiseman and Chandalar districts. 

Miles 

EXPLANATION • Concentrates available through 1948 

Bose from US. Geological 6urvey Bull. 844-E 

~·· ·i • northE: .stern :1laska. 
Table 3.--Radiometric and mineralogic data on placer concentrates from the Wiseman district, 

northeastern Alaska 

Sample 

no. 

215 

249 

259 

266 

356 

365 

1151 

1358 

Location 

Nolan Creek, west of 

Wiseman. 

-doVicinity of Bettles and 

John River, exact 

locality unknown. 

-do-

-do-

-doGold Bench (or Ironside 

Bar, about a mile above 

Gold Bench), South Fork, 

Koyukuk River. 

Rye Creek--------------

Equivalent 

uranium 

(percent) 

.010 

.014 

10 

Mineral composition 

Minerals 

Pyrite 

Arsenopyrite 

Galena 

Garnet 

Gold 

Magnetite 

Magnetite 

Pyrite 

Galena 

Hematite 

Spinel 

Garnet 

(Chalcocite fragments 

up to l in. in diameter coated with 

malachite.) 

Galena (coated with 

cerussite). 

Pyrite 

Schist, quartzite, 

and granite fragments. 

Hornblende 

Garnet 

Magnetite 

Pyrite 

Biotite· 

Galena (coated with 

cerussite). 

Magnetite 

Garnet 

Hematite 

Rock minerals 

( olivene, epidote ). 

Sphene 

Zircon 

Pyrite 

Rutile 

Scheelite 

Galena 

Cassiterite 

Thorianite(?) 

Ilmenite 

Schist fragments 

Chlorite 

Andalusite 

Zoisite 

Epidote 

Pyrite 

Zircon 

Chalcopyrite 

Monazite 

Percent 

60 

30 

5 

3 

Tr. 

Tr. 

40 

35 

15 

5 

2 

2 

65 

25 

10 

55 

40 

3 

l 

l 

100 

60 

25 

8 

4 

2 

l 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

35 

25 

20 

7 

5 

5 

3 

Tr. 

Tr. 

Tr. 
Table 3.--Radiometric and mineralogic data on placer concentrates from the Wiseman district, 

northeastern Alaska--Continued 

Equivalent Mineral composition 

Sample 

no. 

1358 

1359 

1548 

uranium 

Location (percent) Minerals 

Rye Creek--Continued .014 Kyanite 

Sphene 

Galena 

Scheelite 

Gold 

Rye Creek-------------- .001 (Mineralogy is similar 

to sample 1358, but 

does not contain 

monazite.) 

Gold Bench, South Fork, .027 Magnetite 

Koyukuk River. Garnet 

Hematite 

Zircon 

Rock minerals 

(olivene, epidote ). 

Sphene 

Pyrite 

Scheelite 

Galena 

Chalcopyrite 

Rutile 

Cinnabar 

Cassiterite 

Bismuthinite(?) 

Thorian+te(?) 

arndicates less than 0.001 percent equivalent uranium. 

Table 4.--Radiometric and mineralogic data on placer concentrates from the Chandalar 

district, northeastern Alaska 

Equivalent Mineral composition 

Sample uranium no. Location (percent) Minerals Percent 

180 Lake Creek------- 0.017 -- -- 460 Little Squaw Creek. .002 -- -- 468 Big Creek-------- .007 -- -- 469 Big Creek-------- .005 -- -- 470 Big Creek-------- .007 -- -- 471 Little Squaw Creek. .003 -- -- 1445 Big Creek-------- .002 -- -- 2253 Tobin Creek------ .020 Hematite 50 

Rock minerals 25 

Monazite 10 

Scheelite 7 

Gold 3 

Pyrite 2 

Magnetite Tr. 

Rutile Tr. 

Galena Tr. 

2254 Big Creek-------- .050 Hematite 20 

Pyrite 20 

Arsenopyrite 20 

Monazite 15 

Rock minerals 15 

Scheelite 10 

Galena Tr. 

Ilmenite Tr. 

Rutile Tr. 

Chalcopyrite Tr. 

11 

Percent 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

--

65 

25 

5 

2 

2 

1 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 

Tr. 
149°2.0' 0 67 

40' 

.. 

0 

&r» 

2.0' 

149 2.0' 

• Concentrates available 

through 19 48 

\-···-. ........ I 

5 

149 oo' 

Base from U.S. Geological Survey Bull. 773, · pl.6. 

40' 

"··. 

\ 

40 

148° oo' 

67 

40' 

67 

2.0' 

148 oo' 

Figure 5. --Sketch map of a portion of the Chandalar district, northeastern Alaska. 

Mertie (1925, p. 263) suggests that the gold 

and monazite in the district may be related genetically 

and that the bedrock source is probably some highly 

felsic granitic, rock, possibly of pegmatitic origin. 

However, the only granitic rocks found in the vicinity 

of the ·placers are small bodies of a Pale'ozoic granitic 

gneiss, which are probably offshoots of a northeasttrending belt of gneiss north of .Chandalar Lake. This 

granite is also exposed in the vicinity of Lake Creek, 

and further search may reveal its presence in the 

valleys of other creeks. 

CONCLUSIONS 

Study of placer concentrates from the Wiseman 

district revealed the· occurrence of uranium-bearing 

thorianite( ?) associated with hematite and various 

metallic sulfides on the South Fork of the Koyukuk 

River. Such association suggests the possible occurrence of primary uranium ores in association with 

metalliferous lodes in the drainage area upstream from 

the point where the uranium-bearing thorianite(?) was 

found. 

Relatively large amounts of hematite are 

associated with galena, chalcopyrite, pyrite, arsenopyrite, and monazite in concentrates from placer 

operations northeast of Chandalar Lake in the Chandalar 

district. Such an assemblage of minerals indicates 

the possibility of hematitic alteration in association 

with the deposition of metallic sulfides. This possible 

alteration and association, along with the occurrence 

of radioactive minerals, such as monazite, suggests 

that the area northeast of Chandalar Lake might 

contain primary uraniferous deposits. 

REFERENCES CITED 

Maddren, A. G., 1913, The Koyukuk-Chandalar 

region, Alaska: U. S. Geol. Survey Bull. 532. 

Mertie, J. B. , Jr. , 1925, Geology and gold placers 

of the Chandalar district [Alaska]: U. S. Geol. 

Survey Bull. 773-E, pp. 215-263.