517 HHI

GEOLOGICAL SURVEY CIRCULAR 317

RECONNAISSANCE FOR RADIOACTIVE 

DEPOSITS IN THE MANLEY HOT 

SPRINGS-RAMPART DISTRICT 

EAST-CENTRAL ALASKA, 1948

This report concerns work done on 

behalf of the U. S. Atomic Energy 

Commission and is published with 

the permission of the Commission.
PROM:
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

GEOLOGICAL SURVEY CIRCULAR 317

RECONNAISSANCE FOR RADIOACTIVE DEPOSITS IN THE MANLEY HOT 

SPRINGS-RAMPART DISTRICT, EAST-CENTRAL ALASKA, 1948

By Robert M. Moxham

This report concerns work done on 

behalf of the U. 8. Atomic Energy 

Commission and is published with 

the permission of the Commission.

Washington, D. C., 1954

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

RECONNAISSANCE FOR RADIOACTIVE DEPOSITS IN THE MANLEY HOT 

SPRINGS-RAMPART DISTRICT, EAST-CENTRAL ALASKA, 1948

By Robert M. Moxham

CONTENTS

Page

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

Introduction............................... *. 1

Geography.................................. 3

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

Radioactivity investigations................... 3

Measurement of radioactivity. ............................. 3

Areas investigated...................... -3

Hot Springs Dome area............. 3

Hot Springs Dome leadsilver deposit.............. 3

Page

Radioactivity investigations Continued 

Areas investigated Continued

Hot Springs Dome area Cont.

Granite at Hot Springs Dome.... 4

Tofty tin belt................. 4

Roughtop Mountain-Boulder

Creek area................. 6

Eureka area....................... 6

Rampart area..................... 6

Conclusions.................. ^............... 6

Literature cited............................. 6

ILLUSTRATIONS

Page

Figure 1. Geologic map of the Manley Hot Springs-Rampart district...................................... 2

2. Geologic map of the Tofty tin belt............................................................ 4

TABLE

Page

Table 1. Radioactivity data on concentrates from the Tofty tin belt...................................... . 5

ABSTRACT

The occurrence of cobalt in lead-silver deposits 

near Manley Hot Springs, Alaska, is mentioned in several of the earlier publications of the Geological Survey; 

additional mineralogic data are sparse. In 1945 and 

1947 radioactivity and mineralogic studies of Alaskan 

placer samples disclosed the presence of five radioactive minerals eschynite, ellsworthite, columbite, 

monazite, and zircon in association with extensive 

gold-tin placer deposits in the Tofty area, a few miles 

north of the lead-silver deposits. On the basis of the 

mineral associations and the geographic relationship 

between the two types of deposits, field studies seemed 

warranted and were undertaken in 1948.

Field work failed to disclose the bedrock source 

of the radioactive minerals in the gold-tin placers. 

None of the material collected from the lead-silver 

deposits showed any radioactivity, although the granite 

country rock has an average equivalent uranium content 

of 0. 003 percent which is attributed mostly to disseminated monazite. No field evidence could be found

to establish a geomorphic relationship between the 

two types of deposits.

A few concentrates from gold-placer mines in 

the -Eureka area northeast of Manley Hot Springs 

contain small amounts of monazite and radioactive 

zircon. Granitic rocks at nearby Elephant Mountain 

are also slightly radioactive due to monazite and are 

probably the ultimate source of the radioactive minerals in the placers of the Eureka area.

INTRODUCTION

The Manley Hot Springs-Rampart district 

(fig. 1) of east-central Alaska is one of the few 

areas in Alaska from which radioactive minerals 

had been reported prior to the initiation in 1944 

of the Trace Elements program of the Geological 

Survey. Waters (1934) had identified monazite, 

eschynite, and xenotime in concentrates from 

the Tofty tin belt of this district. The radioactivity study of the Alaskan placer concentrate
Contact, dashed where 

approximately located

Geology by H.M. Eakin, 1913, J.B. Mertie, 1922, R.G. Woyland, 1941 , R.M. Moxhom, 1948

Figure 1. Geologic map of. the Manley Hot Springs-Rampart district, east-central Alaska.

2
collection, in 1944 and 1945, l revealed the widespread 

occurrence of radioactive materials in the concentrates 

from the Tofty belt. Mineralogic study of the Tofty 

concentrates by the author in 1947 showed that ellsworthite, columbite, and radioactive zircon were 

present in addition to the minerals reported by 

Waters (1934).

The proximity of these radioactive minerals to 

a cobaltiferous lead-silver lode on Hot Springs Dome 

led to the belief that uraniferous lodes might occur in 

the same vicinity either with the lead-silver deposit 

or in its immediate vicinity. A field investigation 

was therefore undertaken in 1948 with the following 

objectives: (1) To investigate the Hot Springs Dome 

lead-silver deposit and other possible bedrock sources 

of the radioactive minerals in the Tofty placers; (2) to 

determine whether the Tofty placers or tailings from 

the mining of these placers contained sufficient radioactive material to warrant recovery as a byproduct of 

placer mining for gold and tin; (3) to carry the investigations to the adjacent Eureka and Rampart mining 

areas which were readily accessible by road, if 

time permitted.

The field party consisted of Robert M. Moxham, 

geologist, and John C. Whitaker, Fred Freitag, and 

Russell j. Wolfgram, camp assistants. This work was 

done on behalf of the Division of Raw Materials of the 

U. S. Atomic Energy Commission.

GEOGRAPHY

The Manley Hot Springs-Rampart district (fig. 1) 

is situated between the Yukon and Tanana Rivers, west 

of the 150th meridian in the Tanana and Kantishna River 

quadrangles (Alaska reconnaissance topographic series, 

scale 1:250, 000). The center of the area is approximately 90 miles west of Fairbanks. The total permanent 

population, concentrated mainly at the villages of Tanana, 

Rampart, and Manley Hot Springs, is about 400. Aircraft are used almost exclusively for the transportation 

of passengers and light freight to the district, whereas 

heavy cargo is transported by barge on the Tanana River. 

Dirt roads, passable most of the year, connect the Tofty 

and Eureka mining areas with Manley Hot'Springs, and 

the Hunter Creek and Little Minook Creek mining areas 

with Rampart.

GEOLOGY

The oldest rocks of the Manley Hot SpringsRampart district (fig. 1) are pre-Middle Ordovician 

strata, chiefly slate. These rocks form the low hills 

in the southeastern part of the district. Successively 

younger formations crop out to the northwest, including the Middle Silurian Tolovana limestone and Devonian slate, graywacke, and greenstone. Three 

Mississippian units have been recognized: (1) Slate, 

shale, schist.and quartzite crop out north of the YukonTanana divide; (2) limestone forms the divide in the 

central part of the area; and (3) the Rampart group, 

comprising bedded volcanic rocks and associated 

sedimentary strata, crops out between the divide and

1 Harder, J. O., and Reed, J. C., 1945, Preliminary report on radioactivity of some Alaskan placer samples: U. S. Geol. Survey Trace 

Elements Inv. Kept. 6. [Unpublished.]

the Yukon River. Cretaceous slate, quartzite, and 

schist crop out between the Tanana River and the 

divide. Tertiary shale, sandstone, conglomerate, 

and coal occur in small isolated areas near the 

Yukon River.

Pliocene gravels are found on the tops of ridges 

at elevations up to 1, 500 feet in the Rampart area. 

A series of regional uplifts between Pliocene and 

Recent time are indicated by the remnants of terraces 

in the major valleys in this area. In some of the valleys and lowlands in the Tofty, Eureka, and Rampart 

areas, there are buried deposits of late Tertiary or 

early Quaternary gravel, ranging from less than 

1 foot to 40 feet in thickness. Boulders and pebbles 

of graywacke, phyllite, sandstone, and quartzite, 

all apparently of local derivation, are the predominant 

constituents. The gravel is overlain by late Pleistocene 

glaciofluvatile and aeolian deposits, from 5 to 90 feet 

thick, which consist of a complex frozen mixture of 

peat, gravel lenses, vegetal debris, silt, and muck.

The principal igneous rocks of the area are the 

granites and monzonites which form Hot Springs Dome, 

Roughtop Mountain, Elephant Mountain, and the. "Ramparts" along the Yukon River. Small bodies of mafic 

intrusive rock are found in the headwaters area of 

Patter son Creek.

Detailed descriptions of the geology of the Manley 

Hot Springs-Rampart district are given by Eakin (1913), 

Mertie (1934), and Wayland. 2

RADIOACTIVITY INVESTIGATIONS 

Measurement of radioactivity

Radioactivity surveys carried out by a jeep and 

on foot were made with a standard portable survey 

meter utilizing a probe of two 1- by 14-inch gamma 

tubes connected in parallel. Semiquantitative tests 

were made with a 6-inch beta tube.

Areas investigated

The radioactivity investigations were confined 

to the three principal mining areas in the Manley 

Hot Springs-Rampart district: the Hot Springs Dome 

area, in the western part of the district; the Eureka 

area, in the east-central part of the district; and the 

Rampart area, in the northeastern part of the district.

Hot Springs Dome area

Hot Springs Dome lead-silver deposit. Leadsilver veins occur on the summit of Hot Springs Dome 

at the Barrett prospect, about 5 miles northwest of 

Manley Hot Springs (fig. 1). Mineralization has taken 

place in a shear zone in the hornfels and schist which 

form the aureole of a biotite granite stock. Metallic 

minerals occur in a zone from 20 to. 3 5 feet wide which 

has been traced horizontally for a distance of 2, 000 feet. 

Ores found in the oxidized zone are chiefly limonite and 

cerussite, with locally abundant side rite and small 

amounts of copper carbonate. Ore found on the dumps

2 Wayland, R. G., the Tofty tin belt [ Alaska J , manuscript report in 

files of Alaskan Geology Branch, U. S. Geol. Survey.
indicates galena to be the most abundant primary sulf ide, 

with lesser amounts of chalcopyrite, pyrrhotite, and 

pyrite. A careful search of the mineralized zone 

yielded only one piece of siderite carrying a thin encrustation of erythrite (cobalt bloom).

All of the accessible test pits and trenches were 

examined and the dump material tested. No underground workings could be entered owing to flooding or 

caving but all dump material was scanned. No radioactive material was found. Eleven representative 

samples of the various types of ore, including the 

erythrite, were tested in the laboratory. All showed 

an equivalent uranium content of less than 0. 001 percent.

Granite at Hot Springs Dome. In conjunction with 

the study of the lead-silver veins which are found in 

the metamorphosed country rock north of the granite 

at Hot Springs Dome, a series of traverses were made 

over parts of the intrusive mass. Anomalous radiation 

was indicated in all areas of the granite outcrop. The 

radiation was noticeably less in the aureole surrounding 

this stock and also in those areas covered by appreciable 

amounts of soil and vegetation. Inasmuch as most of 

the streams draining the granite outcrop area contain 

considerable monazite, the anomalous conditions are 

probably due to this and other disseminated radioactive 

accessory minerals.

Six samples of the granite have an average 

equivalent uranium content of 0, 003 percent.

Toftv tin belt. -Most of the Tofty tin belt (fig. 2) 

lies in the area drained by the headwaters of Patterson 

Creek. The commercial placers are found in a northeast-trending belt extending from Woodchopper Creek 

to Killarney Creek, a distance of about 12 miles. The 

placers comprise a series of subparallel deposits 

oriented normal to the trend of the belt. In general 

the northern limits of the deposits are sharply defined, 

and the definiteness of the boundaries and the concentration of valuable metals gradually decrease southward. 

The gravels are late Tertiary or early Quaternary in 

age and are buried beneath 15 to 80 feet of frozen silt 

and muck of Pleistocene age. Gold and cassiterite are 

the only minerals recovered at present, although considerable chromite occurs at the western end of the 

belt.

Although the exposed country rock along the tin belt 

shows intense shearing and intrusion by numerous quartz 

veins, no metalliferous lodes have been found despite considerable prospecting, nor has cassiterite been found on the sxirface in gravels of the present drainage cycle. The absence oi 

tin lodes has resulted in the formulation of two theories for 

the origin of these placers. The first requires a lode source 

at some distance from the present deposits, presumably associated with the granite mass atHotSprings Dome. It is 

sugge sted that a m aj or stre am flowing westward from this 

area deposited the Tertiary gravel in the general orientation 

of the present tin belt. A change of baselevel followed, resulting in the redistribution of the material to its present po^i 

tion by subsequent southward-flawing streams. The second

Recent and Pleistocene EXPLANATION

Geology by R.G. Woylond, 1941, J.B. Mertie, 1922

Alluvial and glacial deposits 

QUATERNARY

Serpentinized basic intrusive Phyllite and groywacke

TERTIARY CRETACEOUS

Buried gold-tin placer deposits. 

Boundary dashed where approximate

Tailings sample

Figure 2. Geologic map of the Tofty tin belt showing gold-tin placer deposits and sample localities.

4
theory suggests that the tin mineralization originated 

from a local, unexposed magmatic source and was emplaced along the shear zone which parallels the tin belt. 

The cycle of erosion which resulted in the formation of 

the placers continued until the source lodes were completely removed. The placers therefore are eluvial in 

character, having accumulated approximately in place. 

Both theories are discussed in detail by Mertie (1934) 

and Waters (1934).

In 1941, R. G. Wayland3 collected tailings concentrates throughout the tin belt as well as sluice-box 

and drilling concentrates from active mining operations. 

Preliminary scanning of this material for radioactivity 

in 1945 4 gave the following results:

Number of 

samples

58

24

5

Type of concentrate

Tailings--- 

Drill-holeSluice-boxAverage ell1 content 

___(percent)_____

0.063

.003

.011

1 Equivalent uranium.

The most radioactive sample, a concentrate of tailings found on Idaho Gulch, contained 2.3 percent equivalent uranium.

These preliminary results, although indicating 

the tenor of the placer material, gave little information 

relating to the concentration of radioactive minerals 

in the placer gravel either^n place or in the tailings.

During the 1948 investigations the buried placers 

could be tested only at localities where mines were in 

operation. These included the opencut workings of 

Cleary Hill Mines, Inc., on Sullivan Creek and Tofty 

Gulch; and the Dean drift mine on Miller Creek. Representative samples of the tailings were collected over the 

entire^placer belt. As the radioactive material in the 

placer and tailings is confined to the heavy minerals, 

a concentration of the samples was effected to remove 

the light material. The heavy residue obtained would 

approach that recoverable by Humphrey spirals or 

other gravity methods. Results of tests for radioactivity 

in the heavy concentrates are given in table 1. The 

amount of heavy concentrate in both the placer gravels 

and tailings is very small. The Tertiary gravel contains heavy fractions (those greater than 3.3 specific 

gravity) in an average ratio of 19, 425:1. Removal of 

slimes during mining operations results in a higher 

ratio 10,900:1-in the tailings.

Five radioactive minerals have been identified 

in the concentrates from the tin-gold placers in the 

Tofty area:

e llsworthite CaO.Nb205 .2H20

eschynite (Ce, Ca. Fe, Th) (Ti, Nb) 206

columbite (Fe, Mn) (Nb, Ta)206

monazite (Ce, La, Di) P04

zircon Zr Si04

Ellsworthite has been found previously in only one 

other locality near Hybla, Ontario where it is

3Wayland, R. G., op. cit.

*Harder, J. O., and Reed, J. C., op. cit.

associated with a pegmatitic facies of a pre-Cambrian 

granite gneiss complex (Walker and Parson, 1923). 

The mineral is chocolate brown and has a vitreous 

luster. Two chemical analyses of the Canadian specimen averaged 19 percent uranium oxide. The X-ray 

pattern of the Tofty material is identical with that of 

a specimen from Hybla. Spectrographic examination 

of the mineral from Tofty showed uranium to be a 

major constituent. No thorium was found.

Table 1. Radioactivity data on heavy-mineral 

concentrates collected in 1948 from the 

Tofty tin belt.

Location

Dalton Creek 

Harter Creek 

Sullivan CreekTV> - - -

TVi

TV) _____ __ _ _

Do 

Tofty Gulch ~ 

Do 

Do 

TVu __ ..____,__. _______

Do 

T)n ____ ,, ____

TVi ____ _, ____

TVi - --

Do 

Idaho Gulch 

Do 

TV, __ _ _ __

Miller Creek 

Do ________

TV>/7^ TT\ C*1f*fbfb\r mm mm im, _-

Do -

TV, ___________

TV,

TV. -

Sample 

no.

53 

52

^5

46

47i,p

8

36 

37-zP 30

39 

40

41

42

43

44

9 

64

65

49 

50

20

21

23

24

51

eul 

(percent)

0.007 

.030 

.019

.014

.009

.027

-.017

.012 

.015

.013

.011

.014

.012

.011

.016

.017

.035

035

.015 

.026

.017 

.015

.011

.014

.016

/^O^T

Type of 

material

Tailings . 

Do.. 

Tertiary 

gravel. 

Do.

TVi

Tertiary 

gravel. 

Do.

TVi

TV,

Do.

TV

Do.

gravel.

TV)

Tailings . 

Do.

Do.

Tertiary 

gravel.

TQ^ T 3 xirra

Dn

Do.

Do.

Do.

1 Equivalent uranium.

Eschynite is commonly associated with plutonic 

rocks or high-temperature veins. It is reddish brown, 

with a dull to vitreous luster. Spectrographic analyses 

of the Tofty eschynite showed less than 1 percent 

thorium and no uranium.

Columbite usually occurs in pegmatite veins. It 

is black, with a submetallic luster. Sodium fluoride 

bead tests for uranium on the Tofty material were 

negative, although in the presence of a high percentage 

of niobium the tests are not always dependable. Rough 

quantitative radioactivity tests indicate a content of 

approximately 0.1 percent equivalent uranium.

Tests of the monazite show the equivalent uranium 

content probably does not exceed 1 percent.
The average equivalent uranium content of the 

zircon from six samples is 0.072 percent.

A mineralogical examination of the concentrates 

from the Tertiary gravel of the Tofty tin belt shows 

that with the exception of ellsworthite, the radioactive 

minerals have a rather even distribution throughout 

the length of the tin belt. Ellsworthite was found in 

only three samples and the quantity was relatively 

small. The other four radioactive minerals were 

found in all of the samples studied in detail.

In an effort to locate the bedrock source of the 

placer material a radioactivity survey by foot and jeep 

was made along the valley slopes and upland areas adjacent to the lowlands in which the tin placers are found, 

but no radioactivity anomalies were detected. It was 

apparent, however, that the thick cover of tundra and 

soil which was present over a large percentage of the 

area probably would reduce any radiation to a low, 

perhaps undetectable, level.

Although the 1948 field work failed to find direct 

evidence of the source of the heavy minerals found in 

the placer deposits, one occurrence in favor of the 

theory of local origin was disclosed. It will be recalled 

that chromite is found in considerable quantity in the 

bur-ied placers in the western part of the tin belt, particularly in the area between Miller and Woodchopper 

Creeks. Investigation of the region at the head of these 

creeks, on the ridge between Woodchopper and Boulder 

Creeks, revealed an area of serpentinized ultramafic 

rocks. A considerable quantity of chromite float was 

found on the slope south of the ridge and small lenses 

and stringers of chromite were found in place on the 

ridge top. Although it is extremely unlikely that tin 

and radioactive minerals are associated with these 

particular rocks, it does suggest that at least some of 

the source rocks of the placer constituents are present 

in the immediate area of the tin belt.

Roughtop Mountain-Boulder Creek area. The 

Roughtop Mountain-Boulder Creek area (fig. 1) is a 

short distance north of the Tofty tin belt. Roughtop 

Mountain, which has been formed from a quartz monzonite stock, has been unsuccessfully prospected as a 

source of the tin lodes. Many trenches and pits were 

examined, but little evidence of metallization was seen. 

As no radioactivity of significance was detected, no 

samples were collected at Roughtop Mountain.

Placer gold has been mined sporadically for many 

years from the Tertiary gravel on Boulder Creek and its 

tributaries. No radioactivity anomalies were found in 

this area and the only radioactive minerals in the placers 

were zircon and monazite, probably derived from the 

quartz monzonite of Roughtop Mountain.

t

Several samples of stream pebbles, reportedly collected from Boulder Creek, were submitted to the Territorial Department of Mines in 1949 by a resident of Hot 

Springs. The New York laboratory of the Atomic Energy 

Commission reported that one of these samples contained 

0.21 percent equivalent uranium oxide and the other was 

moderately radioactive. Eschynite was tentatively identified as the radioactive mineral. No further information relating to the material is available. However, the occurrence 

of this mineral in the Boulder Creek gravels would seem to 

substantiate the inferences that the ultimate source of the 

tin and radioactive minerals lies north or northeast of the 

Tofty tin belt rather than in the vicinity of Hot Springs Dome.

Eureka area

Slightly anomalous radiation was indicated in 

the outcrop area of granite at Elephant Mountain near 

Eureka (fig. 1), but no concentration of radioactive 

material was found. Three samples of the quartz 

monzonite average 0.004 percent equivalent uranium, 

due chiefly to monazite.

In the course of the investigation in the vicinity of 

Eureka, placer samples were collected from various 

mining operations in the area. The equivalent uranium 

content of the concentrates ranges from 0.004 to 0.042 per - 

cent with an average of 0.019. The radioactivity is due 

almost entirely to monazite.

Rampart area

Placer concentrates were collected from all of the 

operating mines in the Rampart area (fig. 1). The 

equivalent uranium content of the concentrates ranges 

from less than 0.001 to 0.010 percent. A small amount 

of zircon is thought to be responsible for the higher 

radioactivity.

A thin lignite bed cropping out near the mouth of 

Hunter Creek contains 0.001 percent equivalent uraniuir.,

CONCLUSIONS

Radioactivity surveys in the Manley Hot SpringsRampart district were for the most part ineffectual because of the thick tundra and muck cover which concealr 

the bedrock. Although the bedrock source of the radioactive minerals in the Tofty tin placers could not be 

located, the existence of a local bedrock source for bott* 

the radioactive minerals and the cassiterite in the Tofty 

area is suggested by geologic data. The presence of 

the thick tundra cover would necessitate a detailed trenching program to locate the possible source. No radioacf .v< 

material appears to be associated with the cobaltiferous 

lead-silver deposit on Hot Springs Dome, nor could field 

evidence establish a geomorphic relationship between 

this lode deposit and the placers of the Tofty tin belt.

The concentration of radioactive minerals in the 

Tofty placers is probably too low to warrant recovery 

as a byproduct of gold and tin mining under present 

economic conditions.

None of the other mines or prospects in the district seem to hold any commercial possibilities as 

sources of radioactive minerals.

LITERATURE CITED

Eakin, H. M., 1913, A geologic reconnaissance of a 

part of the Rampart quadrangle, Alaska: U. S. Geol. 

Survey Bull. 535.

Mertie, J. B., Jr., 1934, Mineral deposits of the 

Rampart and Hot Springs districts, Alaska: U. S. 

Geol. Survey Bull. 844-D, p. 163-226.

Walker, T. L., and Parson, A. L., 1923, Ellsworthite 

and associated minerals from Hybla, Ontario: Toronto 

Univ. Studies, Geol. ser., no. 16.

Waters, A. E., Jr., 1934, Placer concentrates of the 

Rampart and Hot Springs districts: U. S. Geol. Survey Bull. 844-D, p. 227-246.

IOT.-DUP. SEC., WASH., D.C.-SJS9B