Geochemi~ 1 anO Geological . 

·Reconnaiss. nee in the 

Seventymi[ River Area, 

Alaska 

BULLETIN 1315 

Geochemical and Geological 

Reconnaissance in the 

Seventymile River Area, 

Alaska 

By SANDRA H. B. CLARK and HELEN L. FOSTER 

GEOLOGICAL SURVEY BULLETIN 1315 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971 
UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY 

William T. Pecora, Director 

Library of Congress catalog-card No. 74-608377 

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

Washington, D.C. 20402 - Price 25 cents (paper cover) 
CONTENTS 

Page 

Abstract -------------------------------------------·---------------------------------------------- _________________ 1 

In trod ucti on ----------------------------·-------··------------------------------------------------------------------ 1 

Geologic setting _______________________________ -------------------------------- -------------------------------------- 3 

Geochemical data ______________________________ --------------------------------------------------------------------- 6 

Mineralized areas _ _____ __ _ _______________ ------------------------------------------------------------------------ 6 

Flume Creek-Alder Creek area____________________________________________________________________ 6 

Crooked Creek area__________________________________________________________________ 10 

American Creek area _____________________________________________________________________________________ 11 

Eagle Bluff area _______ -----·--------------------------------------------------------------------------------- 14 

Anomalous samples from other localities ______________________________________________________ 14 

Conclusions ___________________________ _____ ______ ________ _______________ ________________ _ ______ 20 

References cited ______________________________________ -------------------------------------------________________________ 21 

ILLUSTRATIONS 

Page 

FIGURE 1. Index map showing location of the Seventymile River area 2 

2. Generalized geologic map of the Eagle D-2 and D--3 

quadrangles ------·---------·------------------------------------------------------------------------ 4 

3. Map showing rock and soil sample localities in the Flume 

Creek-Alder Creek area________________________________________________________________ 7 

4. Generalized geologic map showing sample localities in the 

American Creek area______________________________________________________________________ 12 

5. Map showing generalized geology and sample localities in 

the Eagle Bluff area______________________________________________________________________ 15 

6-8. Maps showing distribution of anomalous amounts of selected 

elements in stream-sediment samples from the 

Eagle D-2 and D-3 quadrangles: 

6. Silver, molybdenum, and copper ________________________________________ 16 

7. Lead, zinc, and tin_ ------------------------------------------------------------- 17 

8. Nickel and chromium __________________________________________________________ 18 

9. Map showing localities in the Eagle D-2 and D-3 

quadrangles where rock samples contain anomalous 

amounts of selected metals ___________ -------------------------------- _______________ 19 

TABLE 

Page 

TABLE 1. Partial analyses of selected samples from the 

Seventymile River area ______________________________________________________ _ 8 

III 

GEOCHEMICAL AND GEOLOGICAL 

RECONNAISSANCE IN THE 

SEVENTYMILE RIVER AREA, 

A~LASKA 

By SANDRA H. B. CLARK and HELEN L. FOSTER 

ABSTRACT 

Geochemical data were secured from 322 stream-sediment samples, 207 

rock samples, and 76 soil samples collected in the Seventymile River area. 

Geochemical anomalies occur in the Flume Creek-Alder Creek, Crooked Creek, 

American Creek, and Eagle Bluff areas. Gold in the Flume Creek-Alder 

Creek area south of the Seventymile River is believed to be associated with 

ultramafic bodies in a fault zone. Placer gold and other metals in anomalous 

amounts in stream sediments north of the Seventymile River in the Crooked 

Creek area may be related to dikes and faults that cut Tertiary and Tertiary ( ?) sedimentary rocks. Geochemical sampling in the American Creek 

and Eagle Bluff areas did not define any new mineral deposits, but several 

anomalies of unknown origin, particularly in the Eagle D-2 and D-3 quadrangles, are worthy of further investigation. 

INTRODUCTION 

A geochemical and geological reconnaissance of part of the 

Seventymile River area (fig. 1), Eagle quadrangle, Alaska~ was 

conducted during the summer of 1968 as a part of the U.S. Geological Survey's Heavy M:etals Program. The principal investigation was in the Eagle D-2 and D-3 quadrangles, but some sampling 

was done in the American Creek and Eagle Bluff areas and at a 

locality north of Fisher Creek, in the Charley River A-4 quadrangle. 

Gold was first discovered on tributaries of the Seventymile River 

near the end of the 19th century, and placer mining soon became 

an important activity. Gold has come primarily from Flume, Alder, 

Barney, Crooked, and American Creeks; but it has been mined on 

most of the tributaries entering the Seventymile River from the 

south between Last Chance and Flume Creeks and· on tributaries 

entering from the north between Barney and Fox Creeks, as well 

as on the Seventymile River itself (Barney Hansen, oral commun., 

1 
2 SEVENTYMILE RIVER AREA, ALASKA 

141° 

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Base from U.S. Geologica I Su rvey 1:250,000 

Charley River, 1956 ; Eagle, 1957 0 10 20 MILES 

FIGURE 1.-Index map showing location of the Seventymile River area and 

of mineralized areas and localities discussed in text. The Seventymile River 

area is outlined; the area shown in figures 6 to 9 is stippled. Mineralized 

areas and localities discussed in text are: 1, Flume Creek-Alder Creek 

area; 2, Crooked Creek area; 3, American Creek area; 4, Eagle Bluff area; 

6, locality north of Fisher Creek; 6, drainage area of upper Flume Creek, 

Alder Creek, and Deep Creek; 7, headwaters of Suter, Deer, and Sonickson 

Creeks, and 8, North Peak locality. 

1968). Interest in the mining areas led to geologic exploration; 

the primary investigations were conducted by Prindle (1906) and 

Mertie (1930, 1937, 1938) from 1903 to 1936. Part of the area is 

now covered by more recent geological maps by Brabb and Churkin 

(1964, 1965), Foster and Keith (1968), and Clark and Foster 

(1969a). 

The authors were assisted in the field by Ronald Warbelow, 

Sharleen McDonald, and Kathryn Nichols. Charles C. Hawley and 

Allen L. Clark contributed to the geological mapping and sampling. 

Mr. and Mrs. Barney Hansen, longtime residents and miners in 

the Seventymile River area, provided valuable information, particularly about the placer operations on Crooked Creek. Mr. and 

Mrs. Anton Merly, J. R. Layman, and other residents of Eagle 

also assisted the field party in many ways. 
SEVENTYMILE RIVER AREA, ALASKA 3 

GEOLOGIC SETTING 

The geology of the Seventymile River area is complex, partly 

because the Tintina Trench (Roddick, 1967), a major fault zone, 

cuts through the northeastern part of the area. The Tintina fault 

zone trends about N. 55° W. and, in this part of Alaska, separates 

unmetamorphosed Paleozoic and Mesozoic rocks (Brabb and Churkin, 1964) on the northeast from Pre cam brian and (or) Paleozoic 

metamorphic rocks on the southwest. In the Eagle D-·2 quadrangle 

(fig. 2), the Tintina fault zone is buried beneath Quaternary deposits and Tertiary and Tertiary(?) sedimentary rocks, although 

there are some small faults in the sedimentary rocks above, which 

may or may not be related to it. Prominent northwest-trending 

faults occur on the southwest side of the Tintina fault zone. Serpentinized ultramafic rocks, altered basalt and diorite, and, locally, 

orange-stained silica-carbonate rock crop out for at least 13 miles 

along the southwest side of the most continuous of these faults. The 

metamorphic rocks southwest of the Tintina fault zone are intruded by granitic rocks of Mesozoic ( ?) age. Locally, Tertiary and 

Tertiary(?) detrital rocks of subaerial origin unconformably overlie the metamorphic and igneous rocks. 

Metamorphic rocks of Precambrian and (or) Paleozoic age 

south of the Tintina fault zone are divided into three map units 

(fig. 2). These units are (1) a biotite gneiss and schist unit of 

amphibolite facies rocks exposed along the southwest side of the 

Seventymile River; (2) a quartz-graphite schist unit with subordinate greenschist, phyllite, marble, and quartzite; and (3) a 

phyllite unit with subordinate argillite, quartzite, metaconglomerate, and metagraywacke. The latter two units are primarily greenschist facies rocks. 

The granitic rocks are primarily granodiorite but range in 

composition from granite to diorite. The large intrusions are 

probably of Mesozoic age, but some small unmapped hypabyssal 

intrusions must be of Tertiary and Tertiary(?) age because they 

cut sedimentary rocks. 

A few dikes and small masses of serpentinized ultramafic rocks 

of uncertain age, outside of the zone previously described, cut the 

metamorphic rocks. 

The sedimentary rocks consist of conglomerate, sandstone, siltstone, shale, and local seams of coal. Plant fossils indicate that 

at least part of this sedimentary sequence is Tertiary (Mertie, 

1938, p. 237-241). 
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EXPLANAT ION 

UNCONSOLIDATED DEPOSITS 

Surficial deposits 

Flood-plain allul'itntt and terrae£' deposit:; 

SEDIMENTARY ROCKS 

~ 

~ 

Detrital rocks 

Co11glomerute. 8aWI8tOI/e, siltstone. a11d 8hale; include 

('()(1//ocal/y 

IGNEOUS ROCKS 

.. 

Mafic and ultramafic intrusive rocks with associated 

silicic and intermediate rocks in a fault zone 

Undifferentiated granitic rocks 

Chi t7y gm11odicn·ite and <ltlllrtz ttiOnzonitl'. Could include 

rocks younge r than Me sozo-ic a.gl' 

B 

Ultramafic rocks 

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METAMORPHIC ROCKS 

Phyllite unit 

Mainly phyll-ite, argillite, and quartzite 

Quartz-graphite schist unit 

Mainly quartz-graphite schist. q No rtzi t e, quartz p h y ilitP, 

quo rtz- m uscvv'ite s c h-ist, and q u artz- m us co vil e- chlor ite 

schist. Greenstone, greenschist, or marble predom1>nnnt 

locally 

EJ 

Biotite gneiss and schist unit 

Mn·i:nly qunrtz-biot'ite gneiss nnd schist, 

quartz·ite, and nmphiboli te 

Approximate contact 

Probable fault 

Dotted where concenled 

Tintina fault zone 

1-nj'e rred and approrimately locnted ;concenled benenth detri tal 

rock ., n nd unco ru;ol-idated depos·its 

FIGURE 2.-Generalized geologic map of the Eagle D-2 and D-3 quadrangles. 

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6 SEVENTYMILE RIVER AREA, ALASKA 

GEOCHEMICAL DATA 

Three hundred and twenty-two stream-sediment samples, 207 

rock samples, and 76 soil samples from the Seventymile River 

area were analyzed by semiquantitative spectrographic methods. 

Gold was determined by the atomic absorption method. The results, along with a statistical summary which includes histograms, 

are available in an open-file report (Clark and Foster, 1969b). The 

selection of anomalous levels is based largely on inspection of the 

histograms and is subjective and interpretive. The following concentrations are considered anomalous in this report: 

Lower limit of 

anomalous concentrations, 

in parts per million 

Element 

Gold ______________ ___ _______________________________ _ 

Silver ____________________________________________ _ 

Molybdenum _______________ ____________________ _ 

Copper _____________________________________________ _ 

Lead ____________________________________________ _ 

Zinc ____________________________________________________ _ 

Nickel ____________________________________________ _ 

Chromium _________________________________________ _ 

Barium ____________________________________________ _ 

Tin ____________________________________________________ _ 

Stream-sediment 

and soil samples 

0.04 

.5 

5.0 

150 

100 

200 

1 150 

500 

5,000 2 Detected 

1 In the American Creek area, 200 ppm nickel is the lower limit. 2 Less than 10 ppm. 

MINERALIZED AREAS 

Rock samples 

0.06 

.7 

20 

300 

300 

300 

5,000 

5,000 

5,000 

50 

Several areas in the Seventymile River area contain placer 

gold deposits and (or) bedrock prospects and were sampled in more 

detail than the rest of the area. The principal areas are the Flume 

Creek-Alder Creek, Crooked Creek, Eagle Bluff, and American 

Creek areas. The results of the sampling are discussed below. 

FLUME CREEK-ALDER CREEK AREA 

The Flume Creek-Alder Creek area (area 1, fig. 1) includes a 

northwest-trending fault zone (fig. 2) along which altered ultramafic masses and other igneous rocks, including diorite and bas~lt, 

occur. Alteration includes serpentinization, sericitization, silicification, and the formation of silica-carbonate rock. Mineralization is 

associated with this fault zone and particularly with the ultramafic 

masses along it. 
MINERALIZED AREAS 7 

Stream-sediment samples from the fault zone and downstream 

from it contain anomalous amounts of chromium, nickel, and copper. Placer gold has been reported from these streams, but gold was 

not detected in the samples. 

A limonite-stained silica-carbonate (magnesite) zone up to 40 

feet wide associated with serpentinite and altered diorite(?) occurs 

a few hundred yards upstream from the mouth of Flume Creek. 

Locally, rocks in the zone have a green garnierite ( ?) stain. The 

silica-carbonate rocks are cut by numerous small quartz and carbonate veinlets. Euhedral crystals in vugs suggest open-space 

filling. 

Partial analyses of samples from the silica-carbonate zone are 

given in table 1 (samples 1 to 5); these analyses show anomalous 

amounts of arsenic and minor amounts of gold. Sample localities 

are shown in figure 3. 

A few hundred feet upstream from the mineralized silicacarbonate zone, a short adit has been driven into limonite-stained 

altered diorite on the east side of the creek. The diorite is probably 

only a small intrusive body, because serpentinite crops out on 

either side. An irregular quartz vein with a width of about 1 to 3 

feet occurs near the portal, and other quartz veins from a fraction 

of an inch to about 7 inches wide cut the diorite. The diorite is 

silicified adjacent to the larger veins; strongly silicified and 

EXPLANATION 

0 1-5 

Sample locality 

Numbers indicate samples for 

which partial anal11ses are 

given in ta.ble 1 

1,'2 1 MILE L__ __ _;_______________j 

FIGURE 3.-Rock and soil sample localities in the Flume Creek-Alder Creek 

area. 
TABLE 1.-Partial a'fULlyses of selected samples from the Seventymile River area OQ 

[Analyses. except gold, are semiquantitative spectrographic by K. J. Curry. Analyses for gold are atomic absorption by A. L. Meier. W. R. Vaughn. 

and R. L. Miller. Results are in parts per million. Limit of determination given in parentheses in boxhead below element symbol. N. not detected; 

L. detected but below limit o.f determination] 

--

Sample Description Au Ag Mo Cu Ph Zn As Ni Cr 

No. (0.02) (0.5) (5.0) (5.0) (10.0) (200.0) (200.0) (5.0) (5.0) 

Flume Creek silica-carbonate zone 

00 

1 Garnierite (?)-stained silica-carbonate trJ 

rock ------------------------------------------------ 0.2 L N 50 10 L 700 1,500 1,500 ;3 

z 

2 Limonite-stained silica-carbonate rock_ _____ .9 L N 15 L L 7,000 50 50 1-3 

~ 

3 Limonite, garnierite (?)-stained silica- a= 

1-4 carbonate rock_ _______________________________________ .4 0.5 N 15 10 N 1,500 1,000 1,500 t"" 

trJ 

4 Quartz vein_ _________________________________________________ .4 L N 100 10 N 700 150 50 ~ 1-4 

5 Serpentinite from a few inches above ;3 

~ silica-carbonate zone _______________________________ N L N 30 L N N >5,000 5,000 > 

~ 

Flume Creek adit trJ 

? 

6 Quartz vein about 3-7 inches wide ___________ 2.3 N N 50 L N >10,000 50 100 > 

s: 

7 Silicified diorite above quartz vein_ __________ .3 N N 70 15 N 1,500 150 700 00 

~ 

8 Quartz vein about 2-5 inches wide ____________ .7 N N 50 10 N N 50 150 > 

9 Silicified zone below quartz vein _______________ N N N 100 L N N 300 2,000 

10 Quartz vein from outcrop above adit _________ 6.0 N N 15 L N >10,000 10 L 

11 Quartz vein material from dump --------------· 6.0 L N 20 L L >10,000 10 7 

12 Altered diorite host rock from outcrop near adi t ___________________________________________________ N N N 70 10 N N 70 70 
Bonanza Creek prospect 

18 Channel sample, 7 feet, mixed weathered 

bedrock and colluvium _____________________________ .1 N N 30 L L L 1,500 1,500 

14 Channel sample, 7 feet, soil and colluvium 

containing serpentinite and 

silica-carbonate rock_ ________________________________ 7.0 L N 100 L L 500 3,000 5,000 

15 Channel sample, 6 feet, serpentinized 

fine-grained intrusive (diorite?) __ .2 L N 50 100 N N 70 150 

16 Channel sample, 7 feet, same rock type 

as sample 15--------------------------------------------- N N N 1.5 30 N N 5 30 a:: 

1-1 

17 Channel sample, 6 feet, silica carbonate z 

1:;1;1 

rock at contact between serpentinite ~ and intrusive rock __________________________________ .06 N N 70 L N 1,000 2,000 5,000 t"4 

1-1 

N 

18 Channel sample, 5 feet, same rock type 1:;1;1 

1:::::' as sample 17_____________________________________________ 11.0 1.5 N 150 L L 1,000 2,000 3,000 > 

19 Silicified diorite ( ? ) inclusion _____________________ .02 N N 70 L N 700 3,000 2,000 ~ 

1:;1;1 

> rD. 

Crooked Creek area 

-------

Trachyte porphyry _______________________________________ N L 5 100 300 L N L 10 

Andesite _______________ ----------------------------------------- N N N 70 15 L L 50 70 

co 
10 SEVENTYMILE RIVER AREA, ALASKA 

sericitized fragments of wallrock are included in the veins. Arsenopyrite occurs in some of the vein quartz, around the wallrock 

fragments included in the vein quartz, in euhedral crystals disseminated throughout the fragments, and in the silicified zone. 

Samples 6 to 12 (fig. 3) were taken near and in the adit; partial 

analyses of these samples are given in table 1. These analyses 

indicate that gold occurs in the quartz veins which cut the diorite 

and in the silicified zone above the veins. 

Descriptions and partial analyses of rocks from outcrops and 

trenches on a small prospect between Bonanza Creek and Easter 

Creek are given in table 1 (samples 13 to 19). Mineralization 

occurs in a 60-foot-wide limonite-stained contact zone between 

serpentinite and a fine-grained mafic intrusive rock. Siliceous and 

calcareous veinlets cut both the serpentinite and the intrusive rock. 

The highest gold contents in the samples are 11 ppm (parts per 

million) in a channel sample of the silica-carbonate rock (sample 

18) and 7 ppm in a channel sample across the contact zone (sample 

14). 

The analyses suggest that lode gold in the Flume and Bonanza 

Creek area occurs in small amounts in quartz veins and silicacarbonate rock associated with serpentinized ultramafic bodies. 

The ultramafic bodies along the fault zone are discontinuous, and 

reconnaissance sampling along the fault zone to the southeast does 

not indicate a continuation of mineralization. The possibility of 

extension to the northwest was not checked. 

A belt of discontinuous ultramafic masses in association with 

gold here along the Seventymile River has some similarity to a 

discontinuous belt of alpine-type serpentinite bodies that locally 

contain anomalous amounts of nickel, chromium, copper, and gold 

in the central Alaska Range described by Hawley, Clark, Herdrick, 

and Clark (1969). Also, silica-carbonate rocks which were derived 

from serpentinite contain small lode gold deposits in the Livengood 

district (Foster, 1968). 

CROOKED CREEK AREA 

The Crooked Creek area (area 2, fig. 1), one of the principal 

placer mining districts along the Seventymile River, differs from 

the other mineralized areas discussed because the bedrock consists 

of Tertiary and Tertiary(?) sedimentary rocks that are largely 

conglomerate. Gold is found in streams from Barney Creek to Fox 

Creek on the north side of the Seventymile River, and gold from 

Crooked Creek assays the highest of any from the Seventymile 
MINERALIZED AREAS 11 

River area-the mean fineness of three samples is 902 parts per 

thousand (Mertie, 19~~:8, p. 197). The source of the gold is unknown, but fine gold has been panned in very small amounts from 

the conglomerate (Mertie, 1942, p. 249). Silver nuggets, galena, 

and hematite have also been recovered front sluice boxes (Mertie, 

1938, p. 197; Barney Hansen, oral commun., 1968). Arsenic was 

detected in all stream-·sediment samples from Crooked Creek and 

in about 55 percent of all the samples from tributaries entering the 

Seventymile River from the north. Zinc (200 to 500 ppm) was 

found in several stream-sediment samples from Fox Creek and 

Broken Neck Creek but in only one sample from Crooked Creek 

(fig. 7). Anomalous amounts of copper (fig. 6), barium, and 

boron ( > 150 ppm) occur with the zinc on Fox Creek. An anomalous amount of lead oecurs with the zinc on Broken Neck Creek 

(fig. 7). Slightly anomalous amounts of chromium and nickel were 

found, particularly in Fox Creek sediments (fig. 8). 

Trachyte porphyry and other dikes (partial analyses in table 1) 

cut the sedimentary rocks on Crooked Creek. Also, the Tintina 

fault zone is inferred to lie beneath the Crooked Creek area. Thus, 

there are several possible sources of gold and other economic 

minerals. For example, all or part of the gold may be derived from 

the Tertiary and Tertiary ( ?) sedimentary rocks; mineralization 

may be associated with the igneous dikes which cut the sedimentary rocks; or mineralllzation may be associated with the underlying Tintina fault zone and (or) younger faults. One or more of 

these sources may be involved, as well as sources such as Pleistocene terrace gravel. The source of the slightly anomalous chromium 

and nickel is unexplained because no relation to ultramafic rocks, 

such as was found south of the Seventymile River, is known. 

AMERICAN CREEK AREA 

Stream-sediment, soil, and bedrock sampling was carried on in 

the American Creek area (area 3, fig. 1) because mineralization 

is indicated by the occurrence of placer gold. 

The high background concentrations of nickel and chromium in 

stream-sediment, rock, and soil samples from the northern and 

eastern parts of the area (fig. 4) are probably due to the greenschist and scattered small ultramafic masses in the area. One 

sample of ultramafic 1·ock (sample 1, fig. 4) contains more than 

5,000 ppm of both chromium and nickel, and another (sample 2, 

fig. 4) contains more than 5,000 ppm of chromium and 5,000 ppm 

of nickel. 
12 SEVENTYMILE RIVER AREA, ALASKA 

Base from U.S. Geologica l Survey 

1:63,360, Eagle C-1, 1956 

0 2 MILES 

I 

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"' o«- 0 

z ~ 

w .:::'-' ::;) 

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APPROXIMATE MEAN 

DECLINATION, 1970 

FIGURE 4.-Generalized geologic map showing sample localities in the 

American Creek area. 
MINERALIZED AREAS 

EXPLANATION 

~ 

~ 

Detrital rocks 

Conglomerate, snndstone, and shale 

Ultramafic rocks 

Mostly serpentinized 

~ Chiefly greenschist, quartzite, 

and marble 

I~P.~~ Chiefly quartz-graphite schist 

Approximate contact 

Probable fault 

SAMPLE LOCALITIES 

• Stream-sediment sample; no anomalous amounts 

of selected elements 

0 Stream-sediment sample, showing element(s) present 

in anomalous concentration 

Au, gold (0.04-0.08 ppm); 

As, arsenic (detected but less than 200 ppm); 

Cu, copper ( 150 ppm); 

Cr, chromium (500-1000 ppm); 

Ni, nickel (:W0-1500 ppm); 

Mo, molybdenum (5.0-7.0 ppm); 

Sn, tin (detected to 15 ppm); 

Ba,barium (5000 ppm) 

• Soil sample; no anomalous amounts of selected elements 

0 

Soil sample; one or more elements present in anomalous concentration. Symbols for elements given above 

Efl 

Series of five Boil samples; four of the five contain 

detectable arsenic 

b. I 

Location of rock sample discussed in text 

X 

Location of panned concentrate sample; 

a.ll samples contain gold 

13 
14 SEVENTYMILE RIVER AREA, ALASKA 

The arsenic, tin, and barium content of the samples shown in 

figure 4 cannot be directly related to normal bedrock content and 

may indicate mineralized localities. Four out of five soil samples 

taken across a probable fault (fig. 4) on Teddys Fork near Nugget 

Gulch contain detectable arsenic. Arsenic was also detected in 

other samples collected farther upstream on Teddys Fork, on 

Dome Creek, and in the ridge between Teddys Fork and Discovery 

Fork. 

EAGLE BLUFF AREA 

The Eagle Bluff area (area 4, fig. 1) was sampled because of its 

proximity to the Tintina fault zone and because mineralized rock 

has long been recognized there (Saunders, 1967). Eagle Bluff is 

dominantly greenstone on the south and east faces, and argillite 

crops out on the north (fig. 5). Several different rock types from 

Eagle Bluff were analyzed and found to contain locally high but 

sporadic concentrations of copper (7 to > 10,000 ppm), lead ( <10 

to 1,500 ppm), zinc ( <200 to 1,500 ppm), cobalt ( <5 to 2,000 

ppm), silver ( <5 to 1.5 ppm), and tin ( <10 to 500 ppm). Silver is 

present in amounts of 0.7 to 3 ppm in two soil samples, and zinc is 

present in an amount of 700 ppm in one soil sample collected about 

1.2 miles northwest of Eagle Bluff. Zinc (300 to 500 ppm), barium 

(>5,000 ppm), and (or) molybdenum (5 ppm) are present in 

anomalous amounts in four stream-sediment samples from Lost 

Creek (fig. 5). Anomalous values are very irregular in distribution, and not enough data are available to determine their significance. 

ANOMALOUS SAMPLES FROM OTHER LOCALITIES 

Malachite- and azurite ( ?) -stained chalcopyite-bearing quartz 

and carbonate vein material occurs in the Charley River A-4 quadrangle north of Fisher Creek (loc. 5, fig. 1). Small mineralized 

veins cut greenschist, greenstone, and thin carbonate layers. The 

vein material is estimated as less than 3 percent of the rock exposed. No other nearby localities were examined. 

Other anomalous samples that are not related to known mineralized areas are from the Eagle D-2 and D-3 quadrangles. The 

localities of all stream-sediment samples from these quadrangles 

and the localities of samples having anomalous amounts of selected 

metals are given in figures 6 to 8. Localities of rock samples from 

the Eagle D-2 and D-3 quadrangles that have anomalous amounts 

of selected metals are shown in figure 9. 
MINERALIZED AREAS 

EXPLANATION 

[2] 

Flood-plain alluvium and 

terrace deposits 

~ ' ' 

Detrital rocks 

D W § 

Chiefly argillite Chiefly greenstone, includes Chiefly limestone, 

altered vesicular basalt, some argillite 

diorite, and gabbro 

Approximate contact 

<~I 

Base from U.S. Geolog1cal Survey --.___ 

1.63.360 Eagle 0-1, 1956 

15 

FIGURE 5.-Generalized g·eology and sample localities in the Eagle Bluff area. 

Triangles show rock sample localities; squares show soil sample localities; 

and circles show stream-sediment sample localities. Solid symbols indicate 

localities of samples that contain anomalous amounts of gold, silver, copper, 

lead, zinc, molybdenum, tin, or barium. 

In the drainage area of Flume Creek, Alder Creek, and Deep 

Creek (area 6, fig. 1) upstream from the fault zone in the Flume 

Creek-Alder Creek area, anomalous amounts of several metals · 

were found in some stream-sediment and rock samples (figs. 6 to 

9). Stream-sediment samples from all three creeks contain anomalous amounts of chron:tium and nickel. Anomalous amounts of silver 

and molybdenum were found in two samples from Flume Creek; 

anomalous amounts of copper were found in two samples from 

Flume Creek and one from Alder Creek; and anomalous amounts 

of lead and zinc were found in one sample from Flume Creek. 
T. 2 N 

.. T. 1 N. 

T 1 S. 

142°00' R 28 E 141 °30' R· 29 E 

.fi.itte~.. \ - ? 

-:eyGr "'~~·, 

- - 64°45' ~----~---------~----~----~~------~----L---------~----~--------~----~~~~ 

Base from U.S. Geological Survey 

1:250,000,Eagle, 1957 

0 5 10 MILES 

EXPLANATION 

. Stream-sediment sample 

locality 

Copper, molybdenum, and 

silver not present in 

anomalous concentrations 

e 

Copper concentration of 

150 ppm or more 

~ 

Molybdenum concentration of 5 ppm or more 

+ Silver concentration of 

0.5 ppm or more 

FIGURE 6.-Distribution of anomalous amounts of silver, molybdenum, and copper in stream-sediment samples from 

Eagle D-2 and D-3 quadrangles. 

1-4 

0') 

00 

~ z 

~ Is: 

~ ~ 

~ > 

~ 

tzj 

? 

> 

~ 00 

~ 

> 
"142°00' RzgE R30E 0 , "v " • " "' c ,R ;8 E IL • 65 00 ----._ """'-~"--=' ~~- ··~ ,Utte_~ \ 

;:e;;cr Q..,1 \ 

. ..,..,. ) 

~ "-Etil'er ~,/ ,.~ 

T 2 N 

141°30' 

'Or gQj// 

$'~·· 

~ 

[7-.fe J~ c! 

f) 

i'• 

~~-· . ""' '-' ~~'IJ"i I I,. rw "iiii..l ll""' -~~-'::::\ i __;~- " 

T. I N 

T I S 

64°45' 

!~ 

~+ 

-~-

I 

<:)~l J I ' i' "t /· 1//t 

At( 

( -- ~:J;/ e:,~/ -/ 

Base from U.S. Geological Survey 

1:250,000, Eagle, 1957 

I } ' i i / Ali .. 

r 

J' 

-~ 

North 7 Peak~ 

0 

-· , 

. 

5 

"' I ·.jr ~ l ;~-~}l_ 

I '1 I• • J'~ I 

7

/ ~- ,I {;: \ 

·~ -:,; ) ~§ ' "=~·-

/ 

M~/'j 

__ ,/-41 l~--

10 MILES 

\ 

EXPLANATION 

Stream-sediment sample 

locality 

Zinc, lead, and tin rwt 

present ·in anomalous 

rnnrPntrnfiwns 

a Zinc concentrati.on of 

200 ppm or more 

~ 

Lead concentration of 

100 ppm or more 

+ Tin detected in any concentration. Limit of 

detection less than 

10 ppm 

FIGURE 7.-Distribution of anomalous amounts of lead, zinc, and tin in stream-sediment samples from the Eagle 

D-2 and D-3 quadrangles. 

~ 1-1 

z 

trj 

1-1 

~ N 

l:%j 

t::::l 

~ > UJ 

"""' -::J 
141°30' 65°00' n«c we n.<,L "--~ 1-----::1 T. 2 N. 

T I N 

T 1 S 

64°45'~------~--------~----~-----L~------~--~~----------L---__ L_ ________ _L ____ L_~--~ 

Base from U.S. Geological Survey 

1:250,000, Eagle, 195 7 0 5 10 MILES 

EXPLANATION 

• Stream-sediment sample 

locality 

Chromium and nickel not 

present in anomalous 

roncentrations 

t::. Nickel concentration of 

150 ppm 

D Nickel concentration of 

200 ppm or more 

0 Chromium concentration 

of 500 ppm 

Chromium • concentration 

of 700 ppm 

Chromium • concentration 

of 1000 ppm or more 

FIGURE B.-Distribution of anomalous amounts of nickel and chromium in stream-sediment samples from the Eagle 

D-2 and D-3 quadrangles. 

'"""' 00 

00 

tz:l 

;j 

z 

1-3 

~ 

a= 

-t'4 

tz:l 

~ 

~ 

~ tz:l 

r 

> §: 

00 

~ 

> 
T. 1 N 

T 1 5 

R 27 E 

142°00' R 28 F 

I 

~I 

d'" '"'"~ ,:" I Cu :~0111121 / ( 

R 29 E R ,30 E 141°30' 

C{ /!s-A} l/.0113) 

;Y"Pb 300(26) Ag 0 7 C'u ~0111 71~/ i if Ag 0.7, Mo 30(14) i . · · . " I L!'Mo 20(15) Tnangle locates sample; Ag 1.0 Mo 30(10) ___ " .". J~g "·'· mv '"'~o', I ~ I'A"· Lm,r. a no malo us element 

followed by concentration, in parts per 

million 

Number "in parentheses 

refers to sam pie description ill list 

& 

C!Au0.4(221 

1 Au 0.2(23) ""J ' f1 North 

Peak ~-

Two or more samples 

from the same location 

64"45'L Base from U.S. Geolog1cal . Survey ~, 1:250,000,Eagle, 1957 

0 5 10 MILES 

Sample descriptions 

(1) Serpentinite 

(2) Sheared phyllite 

(3) Sericite schist 

(4) Phyllite 

(51 Phyllite 

(61 Basalt 

(7) Fine-grained 

igneous rock 

(8) Quartzite 

(9) Quartzite 

(10) Quartzite 

(11) Phyllite 

(12) Quartzite 

(13) Quartzite 

(14) Phyllite 

( 151 Phyllite 

(16) Hornfels 

(17) Hornfels 

(18) Silicified fine-grained 

igneous rock 

(19) Silicified fine-grained 

igneous rock 

(20) Quartzite 

(21) Andesite 

(22) Greenschist 

(23) Hornfels 

(24) Quartz monzonite (?) 

(25) Mica schist 

(26) Trachyte porphyry 

FIGURE 9.-Localities in the Eagle D-2 and D-3 quadrangles where rocks contain anomalous amounts of selected 

metals. Sample localities in the Flume Creek-Alder Creek area are omitted on this map and shown in figure 3. 

a= 

1-1 

z 

~ 

E= 

1-1 

~ 

t;l:j 

I:' 

> 

~ > 00. 

~ 

(.0 
20 SEVENTYMILE RIVER AREA, ALASKA 

Samples of sheared metamorphic rocks from a fault zone exposed 

near Flume Creek contain anomalous gold, silver, and copper (fig. 

9). Greenstone and ultramafic rocks occur in the drainage basins 

and may be the source of the anomalous nickel, chromium, and 

copper in the stream-sediment samples. 

Anomalous amounts of silver, molybdenum, copper, lead, and 

zinc were found in quartzite and phyllite near the headwaters of 

Suter, Deer, and Sonickson Creeks (area 7, fig. 1). Of 44 grab 

samples analyzed, 16 contain anomalous metals (fig. 9). Limonite-stained outcrops are common in the area, and specks of sulfide 

minerals are abundant in the stained rock. More than half of the 

stream-sediment samples from the headwaters of Suter Creek contain silver but in amounts less than 0.5 ppm. Four of the samples 

contain 0.5 ppm silver, and two contain 150 ppm copper (fig. 6). 

Two rock samples collected near North Peak (loc. 8, fig. 1) 

contain gold (fig. 9). 

A few rock samples from other undiscussed parts of the Eagle 

D-2 and D-3 quadrangles also contain anomalous amounts of 

metals. Likewise, single stream-sediment samples from several 

undiscussed places in these quadrangles (figs. 6, 7) contain anomalous amounts of one or more metals from an unknown source. 

Most of the chromium and nickel anomalies (fig. 8) can be attributed to mapped mafic and ultramafic bodies. Some scattered 

chromium-nickel anomalies, especially in the Eagle D-2 and D-3 

quadrangles, may indicate the presence of unmapped ultramafic 

rocks. 

CONCLUSIONS 

During geochemical reconnaissance in the Seventymile River 

area, no new mineral deposits were detected, although several 

anomalies were found in localities not previously known to be 

mineralized. These anomalies may be worthy of further investigation, particularly the chromium and nickel anomalies that may 

indicate unmapped ultramafic rock bodies. 

Gold in the Flume Creek-Alder Creek area seems to be related 

to ultramafic rock in a fault zone, but studies of analyses of 

samples did not indicate an extension of mineralized rock to the 

southeast, and the possibility of extension to the northwest was 

not investigated. The significance of the zone is not fully understood and deserves further geologic study. 

The origin of the placer gold and anomalous amounts of other 
REFERENCES CITED 21 

metals in stream sediments on the north side of the Seventymile 

River seems to be different from the origin of the gold on the 

south side. The tributaries entering from the north drain an area 

of Tertiary and Tertiary(?) sedimentary rocks, which may be a 

source of the gold; however, all or part of the mineralization may 

be related to dikes and (or) faults which cut the sedimentary rocks. 

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 map, scale l: 250,000. 

---1965, Preliminary geologic map of the Eagle (D-1) quadrangle, east 

central Alaska: U.S. Geol. Survey open-file map, scale 1:63,360. 

Clark, S. H. B., and Foster, H. L., 1969a, Preliminary geologic map of the 

Eagle D-2 and D-3 quadrangles, Alaska: U.S. Geol. Survey open-file 

map, scale 1: 63,360. 

---1969b, Analyses of stream-sediment, rock, and soil samples from a 

part of the Seventymile River area, Eagle quadrangle, Alaska: U.S. 

Geol. Survey open-fHe report, 10 p. 

Foster, H. L., and Keith, T. C., 1968, Preliminary geologic map of the Eagle 

B-1 and C-1 quadrangles, Alaska: U.S. Geol. Survey open-file map, scale 

1:63,360. 

Foster, R. L., 1968, Potential for lode deposits in the Livengood gold placer 

district, east-central Alaska: U.S. Geol. Survey Circ. 590, 18 p. 

Hawley, C. C., Clark, A. L., Herdrick, M. A., and Clark, S. H. B., 1969, Results 

of geological and geochemical investigations in an area northwest of the 

Chulitna River, central Alaska Range: U.S. Geol. Survey Circ. 617, 19 p. 

Mertie, J. B., Jr., 1930, Geology of the Eagle-Circle district, Alaska: U.S. 

Geol. Survey Bull. 816, 168 p. 

---1937, The Yukon-Tanana region, Alaska: U.S. Geol. Survey Bull. 872, 

276 p. 

---1938, Gold placers of the Fortymile, Eagle, and Circie districts, Alaska: 

U.S. Geol. Survey Bull. 897-C, p. 133-261. 

---1942, Tertiary deposits of the Eagle-Circle district, Alaska: U.S. Geol. 

Survey Bull. 917-D, p. 213-264. 

Prindle, L. M., 1906, The Yukon-Tanana region, Alaska-Description of Circle 

quadrangle: U.S. Geol. Survey Bull. 295, 27 p. 

Roddick, J. A., 1967, Tintina trench: Jour. Geology, v. 75, no. 1, p. 23-33. 

Saunders, R. H., 1967, Mineral occurrences in the Yukon-Tanana region, 

Alaska: Alaska Div. Mines and Minerals, 60 p. 

*U.S. GOVERNMENT PRINTING OFFICE: 1970 0-389-680