Some Shorter Mineral 

Resource Investigations 

in Alaska 

Some Shorter Mineral 

Resource Investigations 

in Alaska 

GEOLOGICAL SURVEY CIRCULAR 615 

Washington J 969 
United States Department of the Interior 

WALTER J. HICKEL, Secretary 

Geological Survey 

William T. Pecora, Director 

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

Page 

Introduction ------------------------------- 1 

Nickeliferous serpentinite near Beaver 

Creek, east-central Alaska, by R. L. 

Foster---------------------------------- 2 

Abstract------------------------------ 2 

Introduction--------------------------- 2 

Geologic setting ----------------------- 2 

Serpentinite--------------------------- 2 

Conclusion---------------------------- 2 

Bedrock depth by resistivity soundings, 

Middle Fork of the Koyukuk River, 

by L.A. Anderson and G. R. 

Johnson--------------------------------- 5 

Abstract--...: __ ------------------------- 5 

Introduction--------------------------- 5 

Problems and procedure-------------- 5 

Wiseman area------------------------- 7 

Porcupine Creek area------------------ 9 

Summary and conclusions---------------- 10 

Boundary Creek molybdenum-silver 

occurrence, by David A. Brew and 

A. B. Ford.,------------------------------ 12 

Abstract------------------------------ 12 

Introduction--------------------------- 12 

Location---------------------------- 12 

Geologic setting ----------------------- 12 

Molybdenum-silver occurrence---------- 14 

Conclusions--------------------------- 14 

Geochemical data on the South ore zone, 

White Mountain mine, and on the gold 

content of other mercury ores, southwestern Alaska, by C. C. Hawley, E. E. 

Page 

Martinez, and John Marinenko------------- 16 

Abstract------------------------------ 16 

Introduction--------------------------- 16 

Geologic setting ----------------------- 16 

Sleetmute area ---------------------- 18 

Cinnabar Creek area----------------- 18 

Juninggulra Mountain----------------- 18 

Dillingham area --------------------- 18 

White Mountain mine------------------- 19 

Sampling and trace elements ---------- 20 

Gold content of other mercury ores ------ 20 

Conclusions--------------------------- 20 

Geochemical data in the Sikonsina Pass area, 

by Sandra H. B. Clark, W. H. Condon, 

Helen L. Foster, and J. M. Hoare---------- 21 

Abstract------------------------------ 21 

Introduction ------ - - --- ----------- ----- 21 

Location and access------------------ 21 

Geologic setting----------------------- 21 

Stream-sediment anomalies------------- 21 

Metal concentrations in two bedrock 

samples ----------------------------- 24 

Conclusions--------------------------- 25 

References cited--------------------------- 25 

ILLUSTRATIONS 

Page 

Figure 1. Index map of Alaska showing locations of study areas ---------------------------------- 1 

2. Outcrop map of Beaver Creek serpentinite showing sample locations--------------------- 3 

3. Map of the Middle Fork of the Koyukuk River showing resistivity-sounding locations 

and the generalized geology-------------------------------------------------------- 6 

4-8. Diagrams showing results of resistivity soundings: 

4. Adjacent to main stream channel near Wiseman-------------------------------- 7 

5. Wiseman airstrip----------------------------------------------------------- 8 

6. Comparison of resistivity curves for a horizontally layered section of 

infinite lateral extent------------------------------------------------------ 9 

7. Along winter trail, east bank of the Middle Fork of the Koyukuk River near 

Wiseman ----------------------------------------------------------------- 10 

8. Near Porcupine Creek------------------------------------------------------- 11 

9. Index map showing Juneau and vicinity and the area of figure 10------------------------- 13 

III 
IV CONTENTS 

Page 

Figure 10. Geologic sketch map of the Boundary Creek molybdenum-silver occurrence and 

vicinity-------------------------------------------------------------------------- 14 

11. Map showing locations of some mercury mines and prospects and areas with associated 

cinnabar and gold----------------------------------------------------------------- 17 

12. Geologic map of opencut South ore zone, White Mountain mine--------------------------- 20 

13. Reconnaissance geologic map of the Sikonsina Pass area showing sample localities-------- 22 

14-15. Maps showing mineral concentrations in stream-sediment samples, Sikonsina Pass area: 

14. Lead ---------------------------------------------------------------------- 24 

15. Copper -------------------------------------------------------------------- 24 

TABLES 

Page 

Table 1. Chemical analyses of Beaver Creek serpentinite--------------------------------------- 4 

2. Analyses of molybdenite-bearing and associated rocks, Boundary Creek area------------- 15 

3. Analyses of mercury ores and associated rocks, South ore zone, White Mountain, 

and other localities, southwestern Alaska ------------------------------------------- 18 

4. Analyses of stream-sediment and bedrock samples, Sikonsina Pass area----------------- 23 

5. Maximum metal concentrations in the Sikonsina Pass area compared to crustal 

average and to concentrations considered anomalous along the Taylor Highway 

and in the Slana area ------------------------------------------------------------- 24 
Some Shorter Mineral Resource Investigations 

in Alaska 

INTRODUCTION 

This circular gives the results of several brief geologic studies on mineral resources in Alaska. These 

studies were made in 1967 for the Heavy Metals program of the U.S. Geological Survey during the course 

of more extensive geologic or geophysical research. 

Each article, however, describes an area favorable for 

prospecting or gives background data of interest to a 

prospector or economic geologist. 

The first article describes a nickeliferous serpentinite in the Livengood ultramafic trend. The second 

article is a geophysical study on the depth to bedrock 

in the Wiseman area. The third article describes a 

new molybdenum occurrence in the Coast Range 

batholith near Juneau. This article points out that the 

Coast Range batholith west of Juneau is a very complex body, notahomogeneousrockunitofone age. This 

has an important implication, namely that parts ofthe 

Coast Range batholith in Alaska need more geologic 

evaluation before they cari be considered unfavorable 

for ore deposits. The fourth article shows that anomalous amounts of certain e 1 em en t s could serve as 

geochemical tracers in the area of the White Mountain 

mercury deposit and summarizes the gold contents of 

some Alaskan mer~ury ores. The fifth article describes an area near Sikonsina Pass in the Alaska Range 

characterized by anomalous concentrations of gold, 

copper, and lead. 

The areas reported on here are widely distributed in 

Alaska (fig. 1); they were studied by geologists, geophysicists, and chemists all cooperating in the U.S. 

1 

Geological Survey's Heavy Metals program in Alaska. 

These individuals were greatly aided in their investigations by many Alaskans, and although it w':luld be 

difficult to name all those who gave indirect aid, the 

Geological Survey wishes to acknowledge, specifically, 

assistance from R. F. Lyman, WhiteMountainrr~rcury 

mine, and Andrew Miscovich, Porcupine CreeL 

100 200 300 MILES 

EXPLAN'TION 

Locations of s•ndy areas 

I.Nictclil'erous IIC'_.,tiuitc area 

2-Koyukut River area 

3. Boundary Creel' molybdenumsilvcrarea 

4-.Soudlwcst Alu~o men:ury area 

5.SikoD$ina Pass orca 

Figure 1.--Index map of Alaska showing locations of study areas. 
Nickeliferous Serpentinite Near Beaver Creek 

East-central Alaska 

By R. L. Foster 

ABSTRACT 

The Beaver Creek alpine-type serpentinite body in the northeastern part of the Livengood ultramafic trend, east-central 

Alaska, contains nickel concentrations of as much as 0.51 percent 

and, locally, detectable amounts of platinum and palladium. 

INTRODUCTION 

An irregular mass of nickeliferous s e r p en t i n i t e 

approximately 20 miles long, with maximum width of 

over 1 mile, crops out in the Livengood C-2 and C-3 

quadrangles, east-central Alaska. This northeasterly 

trending alpine-type serpentinite conforms generally 

to the regional structural grain and is flanked on the 

southeast by metamorphosed siliceous graywacke 

clastic rocks and on the northwest mainly by fractured 

and rehealed chert strata (fig. 2). The analytical results from samples of the ultramafic material coiiected 

during reconnaissance g eo I o g i c examinations along 

this northeasternmost segment of the Livengood ultramafic trend (Foster, 1967) indicate that these rocks are 

abnormally nickeliferous as compared to some serpentinites from other parts of the world (table I). 

GEOLOGIC SETTING 

The serpentinite mass forms a conspicuous lightgreen to brown band which consists of o u t crop and 

rubble and is characte;rized by sparse vegetation and 

low rolling hills with isolated pinnacles of more resistant rock. These pinnacles are tectonic inclusions 

or mafic igneous intrusives within the serpentinite 

terrane. Southeast of the serpentinite body are contorted Devonian(?) metagraywackes that contain abun2 

dant clasts of chert and igneous rock frannents. To thE 

northwest are shattered massive and banded cherts. 

The juxtaposition of these divergent metamorphic rock 

types and the nature and geometry of tl' ~ serpentinite 

mass suggest tectonic emplacement of the ultramafic 

material along a major reverse or stJike-slip fault. 

SERPENTINITE 

The ultramafic rock is completely serpentinized, 

has no consistent internal fabric, and varies from a 

massive blocky variety to highly shear?.d slickentite. 

In the massive rocks, serpentine-group minerals occur as fine scaly aggregates in a semiradial distribution as lanieiiar fibrous scales normal to serpophite 

"eyes" or opaque veinlets, and as a E'Bmidecussate 

meshwork. The slickentite rocks have ttese same textures partially or totally modified by s"lear. Bastite, 

minor asbestos-fiber veinlets, and prinary and secondary spinel group minerals are ubiquitous, whereas 

only traces of sulfides were recognized. 

CONCLUSION 

These ultramafic rocks contain concentrations of 

nickel which justify detailed investigatior. Although the 1 

detected amounts of platinum, palladium. and rhodium 

are low, their presence is noteworthy. The possible 

existence of covered bodies on strike with or paraliel 

to the major ultramafic trend could be tested by magnetometer surveys; coincident anomalies derived from 

Alectromagnetic and magnetic surveys could outline 

additional targets for physical exploratic n. 
Bo~ hom US Geolog•col Sur11ev I 63,360 

hwengoodC-2ondC-3 1954 

r·':J 

;~l~ 

EXPLANATION 

L:::._:j 

~ 

Metasedimentary rocks 

EJ 

Scrpentimte 

~ 

~ Bedded~hert 

LtmJtofserpentimte 

outcrop 

Strileandd1poffohat1on lSt,..Sd 

Sample locat1on 

N11rnlwr "f~ 10 table I 

Benchmark 

4MILES 

Figure 2.--0utcrop map of Beaver Creek serpentinite showing sample locations. 

3 
Table 1. -ChemiaaZ anaZyses of Beaver> C:r>eek s.e:r>pentinite 

[Analysts: Spectrographic, Arnold Farley, Jr.; chromium, G. T. Burrow; nickel, E. J. Rowe; 

palladium, platinum, and rhodium, L. B. Riley, W. D. Goss, and Joseph Haffty. Analyses, unless noted, are semiquantitative spectrographic and are reported in the series 0.1, 0.15, 

0.2, 0.3, 0.5, 0.7, 1.0, 1.5, and so on, or by the following symbols: N, not detected; Tr, 

trace. Results are given in parts per million except for Cr, Ni, Fe, Mg, Ca, and Ti, which 

are given in percent. Looked for but not detected, limits of determination given in parentheses: Ag (0.5), As (200), Be (1), Bi (10), Cd (20), La (20), Mo (5), Nb (2), Pb (10), Sn 

(10), Sr (50), W (50), Y (10), Zn (200), and Zr (20); exceptions: Be, 2 ppm in sample ll; 

La, 30 ppm in samples 4 and 20; and Nb, <20 ppm in samples 7 and 13. Not determined because of interferences: Sn in sample 13 and Zn in sample 5. All samples contain <0.02 ppm 

Au and <100 ppm Ba. Sample localities are shown in figure 2] 

Sample Cu B Co Mn Sc v Fe Mg~ ____ c_a ______ T_i_ 

l 

2 

3 

4 

5 

7 

200 

5 

20 

20 

20 

20 

30 

50 

200 

150 

100 

100 

70 

300 

700 

1,000 

1,000 

1,000 

1,000 

<0.010 

<. 010 

Tr 

.011 

<.010 

<0.004 

<.004 

.009 

<.004 

<.004 

<0.005 

<.005 

<.005 

<.005 

<.005 

10 

7 

10 

10 

N 

30 

15 

30 

50 

300 

0.06 

.11 

.10 

.19 

12.8 

0.50 

.35 

.51 

.48 

.33 

15 

15 

10 

7 

15 

<0.05 

.05 

<. 05 

.l 

.07 

0.007 

.01 

.005 

.007 

.07 

6 

7 

8 

9 

10 

20 

10 

7 

100 

i 

70 70 

20 100 

50 100 

30 150 

70 100 

500 

700 

700 

1,000 

700 

<.010 

<.010 

<.010 

.012 

.014 

.011 

<.004 

<.004 

.033 

<.004 

<.005 7 

<.005 15 

<.005 7 

<. 005 10 

<.005 15 

30 

50 

30 

50 

50 

.20 

.16 

.15 

.19 

.13 

.48 

.48 

.49 

.36 

.47 

10 

10 

15 

15 

15 

>10 

>10 

10 

10 

10 

.05 

.07 

<. 05 

.05 

.07 

.015 

.015 

.007 

.03 

<·001 

ll 

12 

13 

14 

15 

30 

5 

15 

50 100 

70 100 

50 150 

50 150 

700 

700 

500 

700 

Tr 

.010 

Tr 

Tr 

.006 

.004 

Tr 

.006 

.005 15 

.005 15 

.005 N 

.005 15 

70 

50 

15 

30 

.13 

.08 

.32 

.12 

.21 

.25 

.24 

.25 

10 

15 

15 

15 

10 

>10 

>10 

10 

.05 

.05 

.05 

<. 05 

.03 

.005 

.007 

.007 

Limits of determination 

----------------

5 10 5 10 0.01 0.004 0.005 5 10 0.05 0.02 0.05 0.001 

1 Specific instrumental or chemical method. 

Sample Desaription 

- - - - - - - - Grab rock sample; blocky dark-green serpentinite (greenish-brown weathered surface). 

2 - - - - - - - - Grab rock sample; blocky dark-green serpentinite with trace amounts of sulfides (reddishbrown lichen on weathered surface). 

3 - - - - - - - - Selected rock sample; slightly sheared block} 

dark-green serpentinite with minor fiber veinlets (light-green on weathered sheared surface). 

4 - - - - - - - - Grab rock sample; blocky dark-green serpentinite (tan on weathered surface). 

5 - - - - - - - - Selected scree rock sample; she a r e d black 

c h r om i t it e (brownish -white on weathttred 

sheared surface). 

6 - - - - - - - - Grab scree rock sample; dark-green slickentite 

(dark-green on weathered sheared surface). 

7 - - - - - - - - Grab scree rock sample; dark-green mottled 

slickentite (olive-green on weathered sheared 

surface). 

4 

Sampl-e Desaription 

8 - - - - - - - - Grab rock sample; blocky dark-green bastitic 

serpentinite (green on weathered surface). 

9 - - - - - - - - Grab rock sample; blocky dark -green serpentinite with parallel elong'l'te bluish-gray 

mottling (greenish-white on weathered 

surface). 

10 - - - - - - - - Selected rock sample; blocky dark-green serpentinite (rusty -brown on weathered surface). 

li - - - - - - - - Grab rock sample; blocky dtrk-green bastitic 

serpentinite (light-gree., on weathered 

surface). 

12 - - - - - - - - Grab rock sample; blocky dFrk -green serpenUnite (light-green on weathered surface). 

13 - - - - - - - - Grab rock sample; blocky dark-green mottled 

serpentinite (olive-green 0"1' weathered surface). 

14 - - - - - - - - Selected rock sample; blo~y dark-green 

serpentinite with- pervasive: metallic veinlets 

(greenish-white on weathered surface). 
Bedrock Depth by Resistivity Soundings, Middle 

Fork of the Koyukuk River 

By L.A. Anderson and G. R. Johnson 

ABSTRACT 

Six resistivity soundings were made near the town of Wiseman 

and Porcupine Creek on the Middle Fork of the Koyukuk River in 

Alaska. The purpose of the soundings was to evaluate this method 

as a means of determining bedrock depths in the vicinity of the 

main stream channel as the first step in appraising the potential 

of the Middle Fork valley for a gold-dredge operation. Considerable 

difficulty was met in interpreting the soundings in the absence of 

detailed geologic control, but a reasonable interpretation of bedrock depth at Porcupine Creek is 60 feetand at Wiseman, 13 

, miles north, 270 feet. The reason for the rather large difference 

in bedrock depths at the two locations is unknown. 

INTRODUCTION 

Placer gold has beenobtainedbydriftmining, caterpillar and dragline operations, hydraulic mining, or 

various combinations of these from many t rib uta r y 

valleys to the Middle Fork of the Koyukuk River since 

about the turn of the century. The contribution of gold 

from the tributaries to the main valley of the Middle 

Fork suggests that, unless other factors such as glaciation have interfered, the main valley itself should 

locally be gold bearing. This possibility further suggests that a large-scale dredging operation in the main 

river channel may be economically feasible, but before 

such an undertaking can be considered, the thickness 

of the stream gravels must be known. 

The nature of the problem and its possible economic 

significance was outlined by H. N. Reiser of the U.S. 

Geological Survey, who accompanied the authors and 

aided in the investigation. The main p u r p o s e of the 

investigation was to test there sis ti vi ty-s o u ndi ng 

method as a practical approach for determining bedrock 

depths at selected locations along the Middle Fork of 

the Koyukuk River. Four days were allotted to the survey, and in the span of time, a thorough investigation 

of the bedrock problem was not possible. The data are 

reported, however, because possibly meaningful depths 

were obtained at two stations and because considerable 

ex p e r i en c e was gained on the a p p li c at ion of the 

resistivity-sounding method in a complex geologic environment. 

5 

The general location of the Middle Fork of the 

Koyukuk River is shown in figure 1; the locations of 

the six electrical-sounding stations and the p:eologic 

setting near Wiseman and Porcupine Creek are shown 

in figure 3. The resistivity surveys were made in these 

areas because of their landing facilities for circraft. 

A river boat rented in Wiseman and a tracked vehicle 

borrowed from Mr. Andrew Miscovich at Porcupine 

Creek were of considerable help in reducing the traveltime between sounding locations. 

Problems and procedure 

The problems met in applying the resistivity method 

in interior Alaska have been discussed by Joesting 

( 1941) and by Barnes and McCarthy ( 1964). One problem 

stems from the fact that permanently frozen ground 

(permafrost) forms a near-surface highly resistive 

layer which is very difficult to penetrate electrically. 

The permafrost can be penet;ated if very large separations between current electrodes are used, but the presence of permafrost reduces the resolving pov•erofthe 

method in determining the electrical conductivity of the 

rock material underlying the permafrost. Thepermafrost is often laterally discontinuous, which adds to the 

complexity of the resistivity-sounding curve and makes 

interpretation more difficult and often unreliable. 

Another serious problem in applying any geophysical 

method in the Middle Fork area is the lack of detailed 

geologic control, which is essential if a definitive interpretation of the geophysical data is to be made. In 

the absence of detailed information, it was assumed that 

the geologic section was relatively simple: sand and 

gravel resting on a schist bedrock. In order to determine the thick n e s s of the sand and grave 1 by the 

resistivity-sounding method, a significant r~~sistivity 

contrast must exist between the resist i v j t y of the 

stream gravel and that of the schist. The r?.sistivity 

ranges of rock materials obtained for interior Alaska 

by Joesting (1941), our own experience with r?.sistivity 
Qa 

Geology from Brosge and Reiser ( 1960) 

I 0 2 3 4 MILES 

L~~-L~------~------~------~----~ 

EXPLAJI.~ATION 

~ Allu,·ium 

Igneous rocks 

Phyllite 

Contact 

>- IX 

}~ :::> 

" 

(2 

2 

<I( 

z 

0 

> w 

0 

Dashed where approximately locate, 

or infe·red 

~-...,-··· .. ······ .. Thrust fault 

Dashed where approximately locatet 

dotted where concealed 

Normal fault 

Dashed where approximately located. 

dotted where concealed 

P-1 

Location of resistivity sounding 

Figure 3.--Map of the Middle Fork of the Koyukuk River showing resistivity-sounding locations 

and the generalized geology. 

6 
soundings in the Fairbanks area, and laboratory measurements on representative samples of the schist from 

Porcupine Creek were helpful in interpreting the 

Wiseman-Porcupine Creek resistivity data. 

The resistivity surveys were made using the Schlumberger array and the resulting data were interpreted 

in two steps. First, the album of three-layer Schlumberger theoretical curves (OrellanaandMooney, 1966) 

was used in conjunction with the auxiliary point diagrams to interpret multilayer curves (Kalenov, 1957; 

Keller and Frischknecht, 1966; Orellana and Mooney, 

1966; and Zohdy, 1965). Second, the geologic section 

constructed on the basis of the geophysical interpretation was modeled by means of an IBM 360/65 computer to approximate the curve described by the field 

data. Good agreement between the theoretically computed curve and the field data lends credibility to the 

original interpretation but does not signify a unique 

solution. 

WISEMAN AREA 

Four resistivity soundings were made in the Wiseman area, with the intention of obtaining a bedrock 

profile starting on the airstrip on the west bank of the 

1000 

en 

0:: 

w 

tw 

~ 

I 

~ 

:I: 

0 

~ 

river and extending across the stream depos'ts to a 

winter trail on the east bank. Two of the soundings (W -1 

and W-2, fig. 3) were made on sand and gravel bars 

in the channel of the Middle Fork. 

Only one (W-1, fig. 3) of the two soundings on the 

river channel deposits was interpreted. Lateral 

inhomogeneities in the near-surface gravel at s-:lUnding 

location W-2 caused data scatter on the resistivitysounding curve, and an i n t e r p ret at ion was not considered feasible. Sounding W-1, made on a srqd lens 

overlying the gravel, gave a relatively smooth s':lunding 

curve (fig. 4). The geologic section interpret<':!d from 

the curve is indicated in figure 4. 

On the basis of laboratory resistivity measur~ments, 

the 140-ohm-meter material comprising the uppermost bedrock layer is assumed to be graphitic. schist. 

The geologic map by Brosg~ and Reiser (1960) 

described the schist at Wiseman and black mica and 

quartz-mica; rocks of this type would be exp~cted to 

have a resistivity sign if i cant 1 y greater than 140 

ohm-m. Joesting (1941) reported a range of 200-800 

ohm-m for schists from various localities in interior 

Alaska, and our work near Fairbanks in 1967 suggests 

a resistivity range of 300-1,000 ohm-m for schist 

-___.-l...L.... .. o_o-o-~ / ~ 100 Vertical geoelectric section and inferred lithologies 

> i= Unconsolidated deposits en 

c:;; 

w 

0:: 

tz 

w 

0:: 

<C( 

a.. 

a.. 350 

<C( n-m 280 0-m 

2 5.5 

DEPTH, IN FEET (Logarithmic scale) 

10 

10 100 1000 

ELECTRODE SPACING (4j-), IN FEET 

Figure 4.---Resistivity sounding (W-1, fig. 3) made adjacent to the main stream channel near 

Wiseman. The circles are the field data from which the vertical geoelectric section was determined. The solid line is a theoretical curve computed using the geoelectric section as a 

model. The electrode-spacing axis is also the depth axis for the inferred geologic column 

in which the values of resistivity are indicated. 

7 
containing little or no graphite. For sections of schist 

near Fair banks suspected to be graphitic, values of 

resistivity as low as 30 ohm-m were obtained. Laboratory measurements on the Porcupine Creek schist 

samples show the resistivity to be less than 200 

ohm-m. To gain some assurance that the low resistivity was caused by graphite, a total-carbon analysis 

and an X-ray pattern were obtained on concentrates 

from one of the samples. Both methods verified the 

existence of graphite, although not any large amount. 

However, a slightly graphitic schist can provide innumerable conduction paths along which current can 

easily flow, thereby reducing the resistivity of the rock 

below that measured on small rock samples. 

The possibility exists that a layer of schist, electrically i ndi s ti ngu ish able from the stream gravel, 

overlies the graphitic schist unit. If this were true, 

the depth to bedrock would obviously be less than the 

270-foot figure determined from the sounding interpretation. On the other hand, if the 140-ohm-m I aye r, 

10000 

en 

0::: 

w 

1-

w 

~ 

I 

~ 

:I: 

0 

~ 

> 1-

> i= 

V) 1000 

v; 

w 

0::: 

1-

z 

w 

0::: 

thought to be graphitic schist, was actually clay-rich 

gravel, the bedrock surface would be at adepth in excess of 500 feet. The valley configuration is not consistent with a gravel thickness of this magnitude, and 

therefore it is felt that 270 feet is the r1aximum depth 

to bedrock. 

The curve of the resistivity soundi1g (W-3) made 

on the airstrip (fig. 5) could not be interpreted in its 

entirety because the second maximum on the curve 

cannot be matched to a curve describing a laterally 

homogeneous layered section. The interpreted part of 

the curve indicates a soil cover less tl !ln 2 feet thick 

underlain by dry gravel which extends down to 12 feet, 

the probable level of the water table. ~.'lle third layer 

is water-saturated sand, clay, and gravel. This unit 

has electrical properties which suggest that the top of 

a lenticular body of permafrost exists at a depth of 

about 88 feet from the surface. The re;;oistivity of the 

permafrost is extremely high and has been assigned 

a value of infinity in the vertical geoe1.ectric section 

1.9' 

12' 

50' 

100' 

INFERRED GEOLOG'C SECTION 

1000 FEET ~ 

s il 

Dry gravel 

Moist gravel 

Frozen gravel 

0 

oo 

0 

00 

<C( 

Q.. Vertical geoelectric section and inferred lithologies Q.. 

<C( Unconsolidated deposits 

Frozen gravel 

6800-m 3000 0-m 280 0-m 

1.9 

100 

DEPTH, IN FEET.(Logarithmic scale) 

10 100 1000 

ELECTRODE SPACING ( A! ), IN FEET 

Figure 5.--Resistivity sounding made on the Wiseman airstrip (W-3, fig. 3). The circles are 

the field data from which the vertical geoelectric section was determined. The solid line 

is a theoretical curve computed using the geoelectric section as a model~ The electrodespacing axis is also the depth axis for the inferred geologic column in which th~ values of 

resistivity are indicated. The vertical geologic section in which a permafrost lens is included is, in part, inferred from the uninterpretable part of the field curve. 

8 
shown in figure 5. The observed rapid decrease in the 

apparent resistivity at AB 12 spacings (half the distance 

of the current-electrode separation) between 400 and 

1,200 feet is apparently a result of the horizontally 

discontinuous nature of the permafrost body. 

To illustrate the effects of a horizontally discontinuous resistive layer at some depth on the shape of 

the sounding curve, two diagrams have been taken from 

Alfano (1959) (fig. 6A and B). The characteristics of 

the modeled structures are indicated in the sketches 

adjacent to the vertical electric-sounding curves. In 

these sketches the midpoint of the sounding is represented by a center line, t., and the sounding direction 

is represented by the arrows. The resistivity contrast, 

P2 : Pl, between the second and first layers is 19 to I; 

the third-layer resistivity is equal to P1. Layers 1 

and 2 are equal in thickness, and layer 3 is infinite in 

thickness. 

In figure 6A, the sounding curve for a horizontally 

homogeneous t h r e e-1 aye r medium (dashed line) is 

compared with the sounding curve obtained when the 

second layer is truncated some distance T from the 

center of the sounding array (solid line). The deviation 

from the standard curve caused by the truncation of 

the second layer can be erroneously interpreted by 

assuming a greater resistivity contrast between the 

second and third layers than actually exists and by interpreting the descending part of the curve in terms of 1 

,..-..... 

~10 ·!-

>- p 2 = 19 ..... 

> pi !!.1..=2 ~ hi rn 

;;; 

w ..!..=7 ~ hi 

..... 

z 

w 

~ 

<( 

~ 

~ 

<( 11 10 

AB 

2hi A 

1'-

~10 >-

..... 

> ~=19 .!!1...=2 ~ pi hi rn 

;;; 

w 

~ 

..... 

z 

w 

~ 

<( 

~ 

11 ~ 

<( 

~ 

2hi B 

Figure 6.--Comparison of resistivity curves 

for a horizontally layered section of infinite lateral extent (dashed lines) with: A, 

The resistivity curve obtained when the 

second layer is semi-infinite in horizontal 

dimension (solid line). B, The resistivity 

curve obtained when the second layer is 

finite in horizontal dimension for the indicated conditions (solid line). Modified 

from Alfano (1959). 

9 

more than one layer decreasing monotonically in resistivity with depth. However, it is not quite possible 

to match theoretical curves describing a layered condition with a field curve in which one layer is c~scontinuous without subjecting the field data to some degree 

of smoothing. In figure 6B, the standard curve for a 

horizontally homo gene o u s three-layer co'ldition 

(dashed line) is compared with the curve obtained when 

the second layer is truncated at both ends (solid line). 

The descending part of the curve falls off so rapidly 

that an interpretation by curve matching with curves 

for horizontally homogeneous media is impossible. 

The decrease in the apparent resistivity (fig. 5) following the second maximum most nearly corresponds 

to the effects noted for the two-dimensional body of 

finite lateral extent. The maximum resistivit? value 

on the solid curve shown in figure 6B occurs at a 

spacing approximately equal toone-halfofthed~stance 

T ; therefore, it may be reasonable to assume that the 

permafrost layer at the Wiseman airstrip pinc'"tes out 

approximately 800 feet from the midpoint of the sounding array. 

The effect of the resistive schist at depth can be 

observed in figure 5 at electrode spacings grea-:er than 

AB/2= 1,000 feet, but the existence of graphitic. schist 

within the section cannot be ascertained. The distortion 

of the sounding curve due to the permafrost lens· makes 

it of little value in determining the depth to bedrock 

except to say that the bedrock surface must be deeper 

than 88 feet. 

The resistivity sounding (W -4) made on the east bank 

of the river is shown in figure 7. The sounding data 

were not interpreted because the curve could not be 

matched with the standard theoretical thre?.-layer 

curves for horizontally homogeneous media. The field 

curve rises rapidly, presumably sensing th ~ nearsurface permafrost, and at AB /2 spacings greater than 

200 feet, the apparent resistivity decreases at a rate 

greater than possible for a horizontally layered condition. The decrease in the resistivity values is probably caused by lateral effects as described by Alfano 

( 1959) and as illustrated in figure 6, although similar 

effects from other lateral conditions arepossfble. 

PORCUPINE CREEK AREA 

Weather conditions and local flooding limited the 

number of soundings to two near Porcupine Creek; one 

on the stream gravel and the other on the west bank of 

the Middle Fork of the Koyukuk River. The f'ounding 

on the west bank proved to be extensively underlain by 

permafrost and was not interpreted. 

The sounding on the stream gravel (P-l)lis shown 

in figure 8. The geologic section interpreted from the 

curve is indicated in figure 8. 

The resistivity change within the upper e-and and 

gravel at 7. 5 feet is probably due to the influence of 

the water table at that level. The 260-ohn:t-rn section 
1000 

{/) 

IX ~ 

w 

~ 

w 

~ 

I 

~ 

:I: 

0 

~ 

>' 

~ 

> i= 

~ 100 w 

IX 

~ 

z 

w 

IX 

< 0.. 

0.. 

< 

0 

0 

0 

0 

0 

0 

0 

0 

0 

000 

0 

0 

0 

0 

0 0 

00 

0 

0 

0 

10~----------------------~--------------------~----------------------.------

10 100 1000 

ELECTRODE SPACING ( ~B ), IN FEET 

Figure ?.--Resistivity sounding (w-4, fig. 3) made along winter trail, east bank cf the Middle Fork of the Koyukuk River near Wiseman. 

from 30 to 60 feet correlates well with the 280-ohm-m 

sand, clay, and gravel detected near Wiseman. The 

bedrock, having a resistivity of130ohm-m and thought 

to be graphitic schist, is very similar to that at Wiseman and is interpreted to be 60 feet below the surface. 

The graphitic schist(?) unit appears to become more 

conductive with depth at this site, whereas, in the Wiseman area it is rather thin and underlain by a resistive 

rock unit. The fact that the supposed graphitic schist 

at Porcupine Creek is almost 1,000 feet thick precludes any identification with a cIa y-r i c h stream deposit and is according I y thought to constitute the 

bedrock layer here ana at Wiseman. 

SUMMARY AND CONCLUSIONS 

In the absence of certain geologic information, the 

assumption was made that graphitic schist with aresistivity of 130-140 ohm-m is the local bedrock in the 

Wiseman and Porcupine Creek sounding areas. If this 

assumption is valid, the resistivity data in d i cat e a 

rather large discrepancy between the bedrock depths 

at sounding W-1 nearWiseman(270feet) andP-1 near 

Porcupine Creek (60 feet). The interpreted 210-foot 

10 

difference in bedrock depths at the two survey locations 

may possibly be explained by the much broader valley 

of the Middle Fork of the Koyukuk River at Porcupine 

Creek. The inferred bedrock depth of 60 f~et at Porcupine Creek is within reach of a large dredge. On the 

other hand, the inferred 270-foot-bedrock depth at 

Wiseman is well beyond reach of any known dredge. 

The sounding on the Wiseman airstrip (V'-3) supports 

the impression that bedrock is deeper in this area than 

at Porcupine Creek. · 

Additional res i s t i vi t y soundings s h o u 1 d provide 

additional information on bedrock depth, especially if 

it is possible to avoid permafrost areas by working on 

the sand and gravel bars adjacent to the: present-day 

stream channel. However, the uncertainties involved 

in correlating the geoelectric section with the geology 

would still be a significant shortcoming in this approach 

to the problem. A series of gravity profiles across the 

valley coupled to bore holes drilled for c.ontrol might 

be more effective because the entire valley configuration could then be established without regard to the 

limitations imposed on the resistivity m~thod by permafrost. 
1000 

(/) 

Q:: 

w 

Iw 

~ ~ 

:I: 

0 

~ 

>-' 

I-

> i= 

(/) 

Vi 100 w 

Q:: 

Iz 

w Vertical geoelectric section and inferred lithologies 

Q:: 

<( 

0.. Unconsolidated deposits Graphitic schist 0.. 

<( 

1900 0-m 1200 0-m 130 0-m 310-m 

60 1000 

DEPTH, IN FEET(logarithmic scale) 10~--------------------.-----------~----~~------~--------~---.------

10 100 

ELECTRODE SPACING ( ~ ), IN FEET 

1000 

Figure a.--Resistivity sounding made near Porcupine Creek (P-1, fig. 3). The circles are the 

field data from which the vertical geoelectric ·section was determined. The solid lin~ is a 

theoretical curve computed using the geoelectric section as a model. The electrode-spacing 

axis is also the depth axis for the inferred geologic column in which the values of resistivity are indicated. 

11 
Boundary Creek Molybdenum-silver Occurre. :e 

By David A. Brew and A. B. Ford 

ABSTRACT 

Two molybdenite occurrences with local an om a 1 o u s concen 

trations of silver were found in a dikelike body of iron-stained 

granodiorite and aplite; the body is more than 2 miles long and 

at least 2,000 feet thick. The Tertiary(?) granodiorite-aplite body 

cuts tonalite and related rocks of Cretaceous(?) age approximately 10 miles north of the Taku River and 5 miles west of the 

United States-Canadian border. 

INTRODUCTION 

A previously unreported occurrence of mineralized 

rock with unusually high molybdenum and silver content was found during geologic f i e 1 d studies in the 

Juneau Icefield area on August 5, 1967. The mineralized 

rock is well exposed in a recently deglaciated cirque 

at the headwaters of Boundary Creek and consists of 

intensely iron-stained aplite with locally visible molybdenite. The complete extent of the mineralized area 

is not known, but the dikelike granodiorite and aplite 

host unit is at least 2 miles long, is exposed for 2,000 

vertical feet, and has several prominent iron-stained 

zones within and near it. Two samples contain 1,000 

ppm (parts per million) molybdenum each, 300 ppm and 

7 ppm copper, and 9.6 ppm and 0.9 ppm silver, respectively. 

Location 

The Boundary Creek molybdenum-silver occurrence 

is on the eastern periphery of the Juneau Icefield (figs. 

-9 and 10) about 31.5 miles northeast of Juneau in southeastern Alaska (fig. 9). The sampled occurrence is 

4,450 feet above sea level near the north end of the 

crest of the southeast-facing cirque that contains the 

headwaters of Boundary Creek, a stream that joins 

the Taku River about h a 1 f a mile west of the United 

States-Canadian border. The cirque face is partly 

covered by an icefall which is a remnant of the glacier 

that once filled the valley of Boundary Creek. Northwest of the crest the glacier joins the Hades Highway 

Glacier of the Juneau Icefield. 

12 

The icefall has receded in recent years and is not 

as extensive as shown on the Taku Ri,T-7.r C-6 quadrangle (U.S. Geol. Survey, 1:63,360 tor0graphic map 

series) which provided the contours and glacier limits 

shown in figure 10. The deglaciation has exposedbedrock for at least 2,000 vertical feet on the north side 

of the cirque. Although steep, the cirqu~ wall is quite 

easily accessible from the top and the bottom. 

The area is most easily reached by air. Helicopters 

can land easily on the cirque crest, cirque floor, and 

elsewhere in the vicinity. Ski-wheel aircraft can land 

on the gently sloping glacier surface northwest of the 

crest. The area can be reached on foot from either the 

icefield side or via Boundary Creek. Th~ latter would 

involve a laborious hike of about 11 miles up the brushy 

valley of the creek from Taku River. The former would 

involve a glacier traverse of much greater length. 

GEOLOGIC SETTING 

The oldest r o c k s in the vicinity of the Boundary 

Creek molybdenum-silver occurrence are schistose 

biotite hornfels, hornblende hornfels, calcsilicate 

hornfels, and minor marble (fig. 10). Th~se metamorphic rocks are folded about north- to west-trending 

axes and are locally cut by abundant small dikes of 

fine-grained leucocratic granodiorite. These rocks 

are tentatively correlated with rocks of Mesozoic age 

just across the United States-Canadian border (Kerr, 

1948; Forbes, 1959). 

The hornfelses are cut by two grou'Js of igneous 

rocks-an older group dominated by tcnalite (quartz 

diorite), and a younger group dominated by granodiorite. The molybdenum-silver occurrences are in 

aplite or altered granodiorite of the Y''Junger group. 

The tonalite group is composed of hornb ~nde tonalite, 

hornblende tonalite gneiss, and intrusion breccia with 
IOMilES 

Figure 9.--Index map showing Juneau and vicinity and the area of figure 10. 

a matrix of hornblende tonalite. The tonalite and tonalite gneiss, mapped as a separate unit from the breccia 

(fig. 10), consists of foliated sphene-bearing hornblende tonalite and local zones of migmatitic gneiss. 

The intrusion breccia unit is similar in that it also 

contains homogeneous tonalite gneiss but in small 

amounts. It is dominatly a complex breccia of dark 

fine-grained mafic-rich fragments in a matrix of foliated tonalite. To the south beyond the map area this 

unit becomes more uniform and more like the tonalite and tonalite gneiss unit. These rocks are inferred 

to be Cretaceous in age on the basis of their similarity 

to Cretaceous igneous units elsewhere in northern 

southeastern Alaska (Brew and others, 1966; Loney and 

others, 1967). 

The tonalite-rich sequence is intruded by leucocratic hornblende-biotite gran o diorite, biotitehornblende granodiorite, and aplite. These rocks are 

shown in figure 10 as two separate units on the basis 

of the presence or absence of alteration and of aplite, 

but they probably are part of the same intrusive complex and thus connect beneath the glaciers and to the 

southwest of the area shown in the figure. 

13 

In the northwestern part of the mapped area the unit 

is a locally foliated, light-yellowish-gray-weathering 

hornblende-biotite granodiorite which grades imperceptibly into biotite-hornblende granodiorite. It is part 

of the large granodiorite batholith which underlies 

much of the eastern Juneau Icefield. The dikelike unit 

which trends north-northeast through the center of 

figure 10 is the host rock for the Boundary Creek molybdenum-silver occurrence. Where exposed on the 

east side of East Twin Glacier the unit is medium- to 

coarse-grained biotite-hornblende granodiorite with 

less than 10 percent ovoid inclusions of hornblende 

tonalite. Northeast-striking joints there are locally 

intensely iron stained. On the crest of Boundary Creek 

cirque the unit consists of intense 1 y iron-stained, 

creamy-weathering aplite. The relationship between 

the aplite and the granodiorite to the south is not known, 

but the aplite is inferred to be nearthe top of the dikelike body. These lucocratic bodies are correlated with 

the granodiorite at Turner Lake near Taku Inlet, which 

is Tertiary in age (M. A. Lanphere, oral commun., 

1965). 
EXPLANATION 

Alluvium and colluvium 

Hornblende-biotite and 

biotite-hornblende 

granodiorite 

Hornblende tonalite and hornblende tonalite gneiss 

Hornblende tonalite gneiss 

and intrusion breech 

Biotite hornfels, calcsilicate 

hornfels, and marble 

•ACF 462 XX -----

Sample location Iron stain Ice contact Contact 

Dashed where approximately 

located; dotted where concealed 

Figure 10.--Geologic sketch map of the Boundary Creek molybdenum--silver occurrenc~ and 

vicinity. 

14 

MOLYBDENUM-SILVER OCCURRENCE 

The intensely iron-stained altered aplite exposed 

near the cirque crest (fig. 10), samples ACF459 and 

ACF460) contains local concentrations of visible pyrite and molybdenite. Analysis of sam p 1 e ACF459 

(table 2) represents a composite chip sample of ironstained rock with little visible molybdenite. Sample 

ACF460 is a grab sample of rock with readily visible molybdenite. The intensely iron-stained area is 

at least 100 feet wide and is exposed over a slope 

distance of at least 300 feet. Distant observations indicate that this area probably extends well down the 

cirque wall. The sampled area with readily visible 

molybdenite is at least 6 feet wide and is exposed for 

a vertical distance of at least 12 feet. 

Apophyses of the dikelike mass of aplite and granodiorite extend into the overlying metamorphic rocks. 

Sample ACF461 (table 2) is of iron-stained hornfels 

from an area of abundant aplite dikelets 500 vertical 

feet above the main aplite body. Other iron-stained 

zones noted in the north and south are shown in figure 

10. One of these zones in recently deglaciated (s t i 11 

shown on base map as glacier-covered) granodiorite 

near the East Twin Glacier, is represented by sample 

ACF458 (table 2). Another, in sulfide-bearing dike 

rock which cuts hornfels near the Bacon Glacier, is 

represented by sample ACF462 (table 2). 

The analyses show that molybdenum, silver, and 

copper are present in markedly anomalous amounts 

in the intensely iron-stained aplite near the crest of 

the cirque. Other elements which are also anomalously 

high in some samples include manganese, beryllium, 

bismuth, niobium, lead, mercury, and tin. Anomalously 

low elements are barium, strontium, and vanadium. 

These comparisons are based not only on the analyses 

given in table 2 but also on analyses of similar rocks 

beyond the limits of figure 10. 

CONCLUSIONS 

The available data are insufficient to adequately appraise the economic potential of the Boundary Creek 

molybdenum-silver occurrence. The potential size of 

the occurrence and the anomalously high analytical 

values of molybdenum, mercury, and copper suggest 

that further, more detailed, study is warranted, including mapping and sampling of the iron-stained and 

visibly molybdenite-bearing zones on the cirque wall. 
Table 2.--Analyses of molybdenite-bearing and assoaiated roaks, Boundary Creek area 

[Analyses by semiquantitative spectrographic methods except analyses for Ag and Au, which are 

by atomic absorption and for As, Hg, and Sb, which are special analyses by a quantitctive 

or semiquantitative method. Results are reported in parts per million, except for Mg, Fe, 

Ca, and Ti, which are reported in percent. Analyses by G. W. Sears, Jr., G. T. Burrow, 

E. J. Fennelly, and W. W. Janes. N, not detected; L, detected but below limit of determination; ---, not looked for; elements looked for but not detected: Cd, Pd, Pt, Ta, Te, W, and 

Zn, with the exceptions that Pd, Pt, Ta, Te, and W were not looked for in sample ACF462] 

Sample No.------------------ ACF458 ACF459 ACF460 ACF46l PCF462 

Field No.------------------- 67ABdl26 67ABdl38B 67ABdl38D 67ABdl39B 67AFd206 

Ag-------------------------- <0.2 9.6 0.9 0.6 1.5 

As-------------------------- <10 <10 <10 <10 

Au-------------------------- <.02 <.02 <.02 <.02 <.02 

Ba-------------------------- 1,500 150 30 2,000 1,000 

Be-------------------------- N 3 3 N 1 

Bi-------------------------- N 300 10 N L 

Co-------------------------- N N N 30 L 

Cr-------------------------- 2 l 1 10 L 

Cu-------------------------- 1.5 300 7 150 30 

Hg-------------------------- <.01 <.01 <.01 <.01 .13 

La-------------------------- N N N N 30 

Mo-------------------------- N 1,000 1,000 3 N 

Mn-------------------------- 100 15,000 1,000 1,500 150 

Nb-------------------------- N 15 20 N 10 

Ni-------------------------- N N N 7 L 

Pb-------------------------- 30 150 70 30 15 

Sb-------------------------- 2 4 2 2 

Sn-------------------------- N 15 N N N 

Sr-------------------------- 100 30 15 1,500 500 

V--------------------------- 15 15. 7 150 20 

Y--------------------------- N 70 20 20 20 

Zr-------------------------- 150 200 10 100 150 

Mg--------------------~----- .07 .07 .02 3.0 .15 

Fe-------------------------- 1.5 5 .7 7 l 

Ca-------------------------- .07 . 5 . 5 7 . 7 

Ti-------------------------- .l .07 .07 . 7 .15 

15 
Geochemical Data on the South Ore Zone, White Mountain Mine 

and on the Gold Content of Other Mercury Ores 

Southwestern Alaska 

By C. C. Hawley, E. E. Martinez 

and John Marinenko 

ABSTRACT 

Mercury ores of southwestern Alaska generally contain only 

trace amounts of gold or they are gold free. Gold was detected 

(0.03 ppm) in one new sample from the South ore zone, White 

Mountain mercury mine, and it exists in near crustal-backgroun(' 

amounts to anomalous amounts in at least six other prospect£-

widely scattered in southwestern Alaska that had been sampled 

previously. Only one sample (Cinnabar Creek mine) contained 

m or e than 0.10 ppm gold, and gold was absent or below detectior: 

in three samples from the Red Devil mine, the most productive 

mercury deposit of the region. 

Although ore at the White Mountain mine is characterized by a 

sparsity of trace elements except mercury, the fault gouge in the 

main vein, South ore zone, is characterized by anomalous amounts 

of Ti, As, Sb, B, Cr, and Zr. Similar compositions of fault gouge 

elsewhere in the region may be a guide to miner a 1 i zed areas. 

INTRODUCTION 

Mercury is widespread in southwestern Alaska and 

has been mined at several localities (Sainsbury and 

MacKevett, 1965). Cinnabar is associated with southwestern Alaska gold deposits in the Flat district and 

at Donlon and Little Creeks (fig. 11 ). Mercury is also 

associated with some gold deposits elsewhere, notably 

at the Getchell mine in Nevada (Erickson and others 

1964) where trace amounts of mercury, arsenic, and 

tungsten characterize the gold ore. Therefore, it seems 

worthwhile to gather data on the gold content of mercur~ ores in conjunction with the search for gold deposits. As an in it i a 1 step in the accumulation data 

samples were collected at one part of the White Moun~ tain mine by C. C. Hawley during a brief visit in 1967. 

The results for gold atthe South ore zone, White Moun-

~ain mine, were almost negative as gold was detected 

m only one of six samples. The same general sparsity 

of gold appears to characterize other southwestern 

Alaska mercury deposits. At the suggestion of c. L. 

Sainsbury, samples collected earlier and reported by 

Sainsbury and MacKevett (1965, table 1) were resubmitted for gold analysis. Of the 13 samples with adequate splits available, gold was detected only in eight. 

At the White Mountain mine, however, significant 

amounts of several other trace elements which may 

serve as tracers for mercury ore were detected in 

fault gouge in the South ore zone. 

The White Mountain mercury mine is about 60 miles 

south-southeast of Me Grath, approximately on the 

physiographic boundary between the Alaska Range and 

the Tanana-Kuskokwim Lowland (Wahrhtftig, 1965). 

The mine is best reached by air, and a good gravel 

airstrip is just west of the mine working~. 

The other mines or prospects repref'<:!nted by the 

older samples are: (1) North ore zone, White Mountain, (2) Alice and Bessie mine, Willis Froperty, and 

Red Devil mine, Sleetmute area, (3) Red Top mine 

north of Dillingham, (4) Rhyolite prospe,~t on Juninggulra Mountain, and (5) the Cinnabar Creek and Lucky 

Day prospects in the Cinnabar Creek area. 

GEOLOGIC SETTING 

The main deposits at the White Mountain mine are 

in a northeasterly t r ending zone about 1, 600 f e e t 

west-northwest of the main break of the Farewell fault 

(Sainsbury and MacKevett, 1965, pl. 3). The zone of 

deposits coincides with a subsidiary fault system which 

places shales and limestones, or different limestones, 

all of Ordovician age, in juxtaposition. At the South 

ore zone, the subsidiary faults dip much steeper than 

the strata, but generally both dip steeply. Dolomitized 

or silicified limestones were recognized in the three 

main productive areas of the mineralized zone (Sainsbury and MacKevett, 1965). 

The other prospects represented by th'?. older samples are dominantly in graywacke and siltstone oraltered diabasic(?) rocks as shown by the following information abstracted from Sainsbury and MacKevett 

(1965; pages given in parentheses refer to their report). 

16 
B R I s T 0 L B A y 

~~ ~· 

___ __L_ I ___________ L_ ~t __ 

50 

EXPLANATION 

~ )I( 

Mercury mine Mercury prospect 

156 

50 MILES 

® 

Cinnabar associated 

with gold 

\ 

I 

I 

I 

\ 

! 

j 

Figure 11.--Map showing locations of some mercury mines and prospects and areas with associated cinnabar and gold. 

17 
Sleetmute Area 

Red De vi~ mine. -Mercury ores occur as pencilshaped shoots along intersections between altered diabase(?) dikes and graywacke and slate of the Kuskokwim 

Group of Cretaceous age (p. 9-11). 

A~iae and Bessie prospeat. -Mercury Ores 

occur in and near altered sills intruded into graywacke 

and slate of the Kuskokwim Group (p. 11-12, pl. 1). 

Wi ~tis property. -Rocks are similar to the Alice 

and Bessie prospect (p. 15-18). 

Cinnabar Creek Area 

cinnabar Creek mine.-Ore occurs in and near a 

northwesterly striking fault zone cutting graywacke 

and siltstone of the Gemuk Group of Mississippian(?) 

to Cretaceous age and an altered d:.abase(?) dike 

(p. 36-39, pl. 4). 

Luaky Day prospeat.-Massive siltstoneofthe 

Gemuk Group cut by dikes (p. 41-42 ). 

Juninggulra Mountain 

Rhyolite prospeat. -Ore occurs in altered dike 

rocks and in graywacke of the Kuskokwim Group near 

a large mass of rhyolite porphyry (p. 46-4 7, pl. 6 ). 

Dillingham Area 

Red Top mine.-Graywacke and silt stone of the 

Gemuk Group, locally calcareous; one minette dike 

noted (p. 59-60, pl. 7). 

Table 3.--Ana~yses of meraury ores and assoaiated roaks, South ore 

[Gold samples 1-7 analyzed by atomic absorption and arsenic, antimony, and tungsten, by 

by John Marinenko and Floyd Brown by rhodamine B fluorometric method following aqua regia 

method; other mercury analyses by atomic absorption. Results are given in parts per million, 

except for those indicated above, are semiquantitative spectrographic by E. E. Martinez and 

on, or by the following symbols: N, not detected; L, detected but below limits of 

limits of determination given in parentheses: Ag(0.5), Be(l), Bi(lO), Cd(20), La(20), and 

in sample 5; La, detected but below limit of determination in samples 1 and 4] 

Sample 

No. 

Lab. 

No. As Au B Ba Co Cr Cu Hg Mn Nb Ni Pb 

South ore zone, White Mountain 

1 

2 

3 

4 

5 

300 

20 

60 

300 

80 

N 

N 

0.03 

N 

N 

300 

L 

N 

200 

N 

200 10 100 

L 

N 

100 

N 

15 > 6 

1 > 6 

200 10 30 

100 rr N 

150 rr N 

20 

L 

L 

10 

L 

N N 

N N 2 > 6 

200 100 2 > 6 20 10 10 

N N 2 > 6 200 rr 7 

6 

7 278244 

30 

N 

N 

.03 

N 

N 

N 

7 

N 

3 

N 

3 

2 > 6 

3 45.69 

150 

30 

N 

tT 

N L 

N Trace 

Other localities, southwest Alaska 

8 

9 

10 

11 

12 

278243 

245 

246 

248 

249 

13 251 

14 252 

15 253 

16 254 

17 257 

18 260 

19 261 

Limits of 

determination---

Sampl.e 

N 

3,000 

N 

N 

N 

3,000 

N 

7,000 

3,000 

7,000 

3,000 

15,000 

200 

0.02 

.02 

<.01 

<.006 

.03 

.14 

.008 

.05 

.01 

<.005 

<.05 

<.006 

0.005-

.02 

Descr-iption 

N 

N 

N 

N 

N 

L 

N 

N 

N 

70 

N 

L 

10 

30 

300 

15 

70 

700 

300 

7 

30 

700 

700 

30 

1,500 

5 

- - - - - - - - 1.0-foot channel sample; dark-brown clay 

gouge, footwall on breccia zone. 

2 - - - - - - - - 7 .0-foot channel sample; silicified limestone 

breccia, veinlike cinnabar near footwall, 

disseminated cinnabar throughout breccia. 

3 - - - - - - - - 0.5-foot channel sample; high-grade_ cinnabar 

on hanging wall. 

4 - - - - - - - - 1.5-foot channel sample; dark-brown clay 

gouge, central to breccia zone. 

18 

N 

N 

N 

N 

N 

N 

N 

7 

7 

7 

N 

7 

5 

Sampl.e 

7 

3 

3 

30 

30 

3 

7 

30 

30 

30 

1.5 

70 

5 

7 60.31 

70 10.6 

30 57.68 

30 38.74 

70 54.10 

30 

30 

70 

150 

70 

15 

30 

5 

6.53 

70.10 

35.87 

34.53 

5.16 

30.31 

20.97 

150 

30 

70 

300 

30 

70 

7 

15 

15 

300 

N 

150 

10 

Descr-iption 

1(' 

7 

7 

N 

N 

7 

7 

N 

30 

7 

30 

N 

30 

5 

30 

30 

N 

N 

L 

L 

N 

30 

15 

N 

N 

N 

10 

5 - - - - - - - - 5.0-foot channel sample; silicified limestone 

breccia. 

6 ------- - Grab sample of veinlike and disseminated 

cinnabar ore in thin-beddM limestone. 

7 - - - - - - - - Sample reported by Sainsbur:r and MacKevett 

(1965, table 1). 
WHITE MOUNTAIN MINE 

The White Mountain mine was discovered in 1958; 

mining started in 1964, and since then the mine has 

been operated during the summer seasons by R. F. 

Lyman. Mercury ore has been produced from three 

recognized zones at the mine, which were called the 

South, Center, and North ore zones by Sainsbury and 

MacKevett (1965). The data recorded here show the 

results of mining at the South ore zone and were collected in 1-day visit to the mine in 1967 by C. C. 

Hawley. 

Most of the mercury produced from the South ore 

zone has come from a shallow open pit (fig. 12). From 

southeast to northwest the pit cuts interlayered shale 

and siltstone, a complex shear zone, and thin-bedded 

limestone. The fault zone strikes approxirrately N. 

40° E. and dips 60°-80° NW. It is mainly corrposed of 

a silicified limestone breccia, but it also hss cinnabar vein material and two prominent clay gouge zones, 

one on the footwall, and the second in the approximate 

center of the zone. Cinnabar is disseminated in the 

breccia, but it is especially concentrated next to the 

hanging wall of the footwall gouge zone anc on both 

walls of the central gouge zone. Cinnabar alsc is found 

in the hanging-wall limestone, both in vein~ and in 

disseminations. According to R. F. Lym')n (oral 

commun., 1967), very rich cinnabar also occurred in 

a nearly vertical pipelike body in limeston~ on the 

hanging wall of the fault zone, as shown in figure 12. 

zone, White Mountain, and other loaalities, southwestern Alaska 

special analyses by A. L. Meier, R. L. Miller, and T. A. Roemer. Gold samples 8-19 analyzed 

leaching. Mercury in samples 7-19 was determined by D. L. Skinner by the Whitton distillation 

except for Hg-in samples 7-19 and Fe, Mg, Ca, and Ti, which are given in percent. Analyses, 

N. M. Conklin and are reported in the series 0.1, 0.15, 0.2, 0.3, 0.5, 0.7, 1.0, 1.5, and so 

determination; ---, not looked for. The following elements were looked for but not detected, 

Mo(l5); exceptions are: Ag, 15 ppm in sample 12; Be, detected but below limit of determination 

Sample 

Sb Sc Sn Sr v w y Zn Zr Fe Mg Ca Ti No. 

South ore zone, White Mountain--Continued 

5,000 15 L N 100 <20 15 N 100 0.5 7 0.2 3 1 

1,000 N L N L --do-- N N N >10 . 7 >20 .02 2 

300 N N N L --do-- N N N >10 1 20 .015 3 

100 N L N 100 --do-- 15 N 100 . 5 5 . 5 . 5 4 

100 10 L N L --do-- N N N >10 1 20 .005 5 

100 N 10 N N --do-- N N N >10 1 20 .002 6 

N N N 150 15 N N N N 7 .07 >10 .015 7 

Other localities, southwest Alaska--Continued 

N N N 300 30 N N N N 0.7 3 3 0.015 8 

>100,000 N N 70 N N N N N .07 .03 1.5 .0007 9 

7,000 N N 30 150 N N N N . 7 • 7 1.5 .015 10 

150 N N 150 15 N N N N . 7 3 3 . 0 3 11 

300 N N 70 15 N N 700 N 1.5 .0015 .003 .07 12 

>10,000 N N 30 15 N 15 N 15 • 7 .015 .07 .07 13 

300 N N N N N N 1,500 N .15 <.001 <.002 N 14 

>10,000 N N 30 15 N N 700 N . 3 .007 . 03 .03 15 

>100,000 N N 30 30 N N 700 N .15 .003 . 3 N 16 

700 7 N 150 30 N 15 N 30 • 7 . 3 . 3 .15 17 

>100,000 N N N N N N N N .015 .0015 <.002 .0015 18 

--do-- N N 300 15 N N N 30 .07 3 .03 .07 19 

100 5 10 50 10 50 10 200 20 0.05 0.02 0.05 0.001 

Sample Location and description ,Sample Location and description 

8 - - - - - - - - North Ore zone, White Mountain mine; cinna- 14 -------- Lucky Day prospect; cinnabar ore. 

bar ore. 15 -------- Lucky Day prospect; cinnabar orefromcinna9 - - - - - - - - Alice and Bessie prospect; stibnite-cinnabar bar-quartz vein. 

ore. 16 - - - - - - - - Willis property; cinnabar-stibnite ore. 

10 - - - - - - - - Red Top mine, ore pile; cinnabar ore. 17 - - - - - - - - Red Devil mine, 300-foot level; ci.,nabar ore. 

11 - - - - - - - - Red Top mine, lower adit; cinnabar ore. 18 - - - - - - - - Red Devil mine, surface; cinnaba: ore. 

12 - - - - - - - - Rhyolite prospect; cfnnabar ore. 19 - - - - - - - - Red Devil mine, Mary Jane stope above 200-

13 - - - - - - - - Cinnabar Creek mine; cinnabar ore. foot level; cinnabar ore. 

19 
N 

1 

Base and geology from pace and compass 

survey by C. C. Hawley, 1967 

20 20 40 FHT 

EXPLANATION 

Limestone in 

1- to 3-inch beds 

Interlayered shale 

and siltstone 

Silicified limestone breccia, 

tBO 

Contact, showing dip 

t60 

Fault, showina dip 

Locally mineralized 

1 ,l; £Z7 

Cinnabar vein, 

Showing dip 

@ 

Cinnabar pipe 

Nearly vertical 

Disseminated cinnabar 

1 

1 to4 

T 

Sample localities 

Refer to text 

table 3 

Figure 12.--Geologic map of opencut South ore 

~one, White Mountain mine. 

No other sulfides were observed in the ore, but limonite seems relatively abundant in vein 1 e t s near the 

cinnabar occurrences which suggests either the former 

presence of pyrite or the hypogene deposition of iron 

oxides with cinnabar. 

Sampling and Trace Elements 

Results of analyses of seven samples from the South 

ore zone open pit, including five from the main fault, 

zone, one from mineralized limestone, and one re- 1 

ported by Sainsbury and MacK evett (1965, table 1,, 

p. 80) are given in table 3. 1 

Trace elements other than mercury are not abun-, 

dant in samples of ore taken from the South ore zone! 

(table 3, samples 2, 3, and 5-7). These samples con-; 

tain small amounts of As, Mn, Sb, Cu, Ph, V, and i 

i 

possibly W. Elements detected in one o1· more samples of the mercury oreincludeB, Ba, Be, Cr, Ni, Sn, 

and Sr. Gold values of approximately 0.03 ppm were 

found in high-grade mercury ore, but gold is absent 

or less than 0.02 porn in the other sample;:;o an a 1 y zed. 

In contrast to the ore, the clay gouge on the footwall and in the center of the main breccia zone has a 

rather abundant and unusual trace-eleme:-1t suite (table 

3, samples 1 and 4), characterized by titanium, arsenic, boron, chromium, antimony, and zirconium as 

well as mercury. 

This trace -element suite· is similar to that in a sampie of-mud from a nearby sulfur spring that also contains anomalous Ti, Sb, Ba, and Cr. (~'linsbury and 

MacKevett, 1965, table 1). 

GOLD CONTENT OF OTHER MERCURY ORES 

Gold in the samples collected earlier by Sainsbury 

and MacKevett (1965) ranged from 0.008 to about 0.14 

ppm, but it was absent or less than the limit of sensitivity in five of the 12 samples (tab 1 e 3). The limit 

of sensitivity varies with the sample size. Samples 11, 

17, and 19 contain less than 0. 005 or 0. 006 ppm gold, 

or less than the abundance of gold in seYeral common 

rock types-including carbonates, sandstones, and 

shales-which has been estimated by Turekian and 

Wedepohl (1961) to be O.OOX ppm. Go~d was most 

abundant in the ore from the Cinnabar Creek mine, 

where two splits of one sample showed, respectively, 

0.11 and 0.16 ppm gold. Perhaps significant is the 

association of this ore with abundant nstive mercury 

(Sainsbury and MacKevett, 1965, p. 39), which could 

trap gold by amalgamation. 

CONCLUSIONS 

The mercury ore in the South ore zone of the White 

Mountain mine has a very small gold content and a 

general sparsity of trace elements. Its associated clay 

gouge is more strongly metalliferous and is mainly 

characterized by its Ti, As, B, Cr, Sb, and Zr content. This trace -element suite is similar to mercurybearing mud from a spring in the same area. Although 

data from other areas are lacking, it seems possible 

that muds and clay gouges near mercury deposits may 

trap or otherwise contain anomalous amo·mts of metals 

and consequently may be an indirect guid~ to mercury 

deposits. 

Other mercury ores sampled contain less than detectable amounts of gold to amounts meaE'ured in tenths 

of a part per million. The present data suggest, but 

do not conclusively prove, that gold is a very minor 

constituent of typical mercury ores in southwestern 

Alaska. The sparsity of gold in the typical ores, together with the occurrence of cinnabar and gt>ld in some 

i other deposits of the region and with tte occurrence 

of mercury in some types of gold deposits elsewhere, 

suggests that much more study is needed to explain 

.the geochemical cycle of mercury in relation to that of 

,gold. 

20 
Geochemic.al Data in the Sikonsina Pass Area 

By Sandra H. B. Clark, ,W. H. Condon 

Helen L. Foster, and J. M. Hoare 

ABSTRACT 

Anomalous concentrations of lead, gold, copper, and molybenum 

were detected locally in analyses of stream-sediment samples from 

the Sikonsina Pass area. Only two bedrock samples were analyzed; 

one sample contained about 1 percent copper, and the other contained 3 ppm ·silver. The area is mainly underlain by metasedimentary rocks of Paleozoic(?) age. 

INTRODUCTION 

Reconnaissance geochemical sampling in part of the 

Tanacross quadrangle of east-central Alaska in conjunction with the Heavy Metals program of the U.S. 

Geological Survey indicated weakly anomalous concentrations of lead, molybdenum, gold, and copper near 

Sikonsina Pass. The cause or causes of the anomalous 

concentrations have not been investigated. Although the 

metal concentrations are low, they indicate possible 

mineralization in the southwestern part of the Tanacross quadrangle. 

Location and access 

The Sikonsina Pass area is in the eastern A 1 ask a 

Range in the southwestern part of the Tanacross A-6 

quadrangle (U.S. Geol. Survey, 1:63,360 topographic 

map series). Sikonsina Pass itself is in a conspicuous 

glaciated valley occupied by Timber Creek, Burnt 

Lake, Burnt Creek, and lower Bone Creek. Relief in 

the map area is approximately 4,000 feet. 

The Sikonsina Pass area is accessible by floatplane, 

by foot, or possibly by tracked vehicle from Mentasta 

Lake. 

GEOLOGIC SETTING 

The Sikonsina Pass area is predominantly underlain 

by a sequence of quartz-mica schists, phyllites, quartzites, marbles, and some metaconglomerates. These 

rocks are part of Moffit's (1954) unit of undifferentiated early P a 1 eo zoic or Precambrian rocks and 

21 

Foster's (1968) phyllite and schist unit of Paleozoic(?) 

age. Richter ( 1967) mapped the continuation of this 

metamorphic sequence to the southeast as part of a 

unit of quartz-mica schist, phyllite, and slate of Devonian(?) age. Several distinctive marble la~·ers are 

shown on thegeologicmap(fig. 13), and locally, other 

calcareous layers occur in the phyllite and scl-tist unit. 

The metaigneous rocks include a metadiorite and 

Devonian(?) greenstone. Devonian(?) greenstcn.e is in a 

layer probably as much as 5,000 feet thick (Richter, 

1967, p. 4) and in other small bodies. 

Rocks of the phyllite and schist unit commonly contain small-scale structures that indicate inte.nse folding. The Denali fault(fig. 13), amajorstrike-slip fault, 

separates the metamorphic sequence from sedimentary and volcanic rocks to the south (Richter, 1967, 

p. 1). A second fault, which may also be a strike-slip 

fault, has been mapped in the area, and other faults 

are likely. 

STREAM-SEDIMENT ANOMALIES 

Stream-sediment samples collected near tre mouths 

of t r i b u tar i e s to Burnt and Timber C r e e k s near 

Sikonsina Pass and above some of the upstream forks 

of the tributaries were analyzed for gold l::r atomic 

absorption and for other elements by semiquantitative 

spectrographic analysis (table 4). Sample density is 

only one to two samples per square mile bu<: is much 

higher than in other parts of the Alaska Ra:rq:e in the 

Tanacross quadrangle. The regional sparsity of samples precludes the calculation of significant background 

values, but comparison of metal concentrations from 

the Sikonsina Pass area (table 5; fig. 13)witl· concentrations of the other samples from the AlaFka Range 

in the Tanacross quadrangle, with concentrations considered average or anomalous in nearby areas (table 
• I 1/2 

~ 

~ ... 6'CJ 

.t 

~ .. APPROXIMATE MEAN 

DECLINATION. 1969 

143"50' 

EXPLANAT 

UNCONSOLIDATED D_EPOSITS 

. ~ r-::1 }~ ~ Alluvium, colluvium, glacial depos- ~ 

its, landslide deposits, and rock ~ 

glaciers o 

SEDIMENTARY ROCKS IGNEOUS ROCKS 

--

Argillite Diorite • 

...... S ...... M 

Silicit: dike Mafic dike 

METAMORPHIC ROCKS 

Greenstone Metadiorite 

j:~:~ Phyllite and schist unit 

F\m. marble. shown locally 

u 

0 

N 

0 

w 

--' c( 

ll.. 

0 N 

Geology by J. M Hoare, W H .. Condon, Helen l. Foster, and 

Sondra H B. Clark, 1967. Geology 1n southwest mop area 

from R1chter ( 1967) 

Contact, approximately loc<ted 

--~?·--·-··· Fault Dashed where inferred; dotted where 

concealed. Probable relative move- ment shown by queried arrows 

~5 

Strike and dip of foliation and (or) 

schistosity 

20 

Direction and plunge of lineation 

os 

Stream-sediment sample 

tP 

Rock sample 

Sample data are given in table 4 

Figure 13.--Reconnaissance geologic map of the Sikonsina Pass area showing sample localities. 
Table 4.--AnaLyses of stream-sediment and bedrock sampLes~ Sikonsina Pass area 

[Gold analyses by atomic absorption by A. L. Meier, R. L. Miller, and T. A. Roemer. Other analyses by J. C. Hamilton and 

J. L. Finley are semiquantitative spectrographic and are reported in the series 0.1, 0.15, 0.2, 0.3, 0.5, 0.7, 1.0, 1.5, 

and so on, or by the following symbols: N, not detected; L, detected but below limit of determination; ---, not looked for. 

Results given in parts per million. Looked for but not detected, limits of determination given in parentheses: Ag(O.OS), 

As(200), Bi(lO), Cd(20), Sb(lOO), Sn(lO), W(SO), and Zn(200); exception, Ag, 3 ppm in sample 16] 

Sample Lab. Field 

No. No. No. Au B Ba Be Co Cr Cu La Mo Mn Nb Ni Pb Sc Sr v y Zr 

STREAM-SEDIMENT SAMPLES 

1 ACD-834 67AFrl048s <0.02 100 700 1.5 20 70 30 70 N 700 15 30 70 15 100 70 70 200 

2 833 47s <.02 70 700 1.5 15 70 70 100 N 700 15 50 30 15 150 70 30 200 

3 830 37s <.02 100 700 1.5 15 70 30 70 N 700 10 30 100 15 100 70 70 150 

4 832 38s <. 02 70 1000 1.5 15 70 50 100 N 700 15 50- 20 15 100 70 30 200 

5 ACC-949 32s <.02 70 700 2 15 70 100 70 N 700 15 30 20 15 100 100 30 300 

t-.J 

""' 6 935 75s <.02 70 1500 1.5 15 70 100 70 N 700 15 30 70 15 100 70 30 300 

7 936 74s <.02 70 1000 2 15 70 50 70 N 700 15 30 15 15 100 70 30 300 

8 937 72s <.02 100 1500 3 15 70 30 70 3 700 15 30 20 30 150 150 so 200 

9 938 7ls <.02 70 700 2 15 70 50 70 N 700 15 30 30 15 150 70 30 200 

10 ACD-823 69s .02 70 700 1.5 15 70 50 50 3 700 15 30 20 15 150 150 30 150 

11 940 66s .04 70 700 2 15 70 50 70 N 700 15 30 30 15 150 70 30 200 

12 835 Sls <.02 70 500 1.5 15 70 30 70 N 700 15 30 30 15 100 70 70 300 

13 836 52s <,02 70 1000 N 20 150 100 N 3 700 L so 15 30 200 300 30 100 

14 838 64s <.02 70 700 N 20 70 100 N 3 700 L so 10 30 150 200 30 100 

15 837 54s <.02 100 1000 3 15 70 30 100 N 500 15 30 30 30 150 150 70 200 

BEDROCK SAMPLES 

16 ACD-872 67AFr3124 <0.02 N 3000 N N 5 15 N N 50 L N 20 10 150 15 15 150 

17 873 13 <.02 N 1000 1 15 50 10,000 30 10 500 L 50 30 10 150 50 15 200 

Limits of determination 0.02 10 5 1 5 5 5 20 3 10 10 2 10 5 50 10 10 20 
Table 5.--Maximum metal concentrations in the Sikonsina Pass area compared to crustal average and to concentrations considered anomalous along the Taylor Highway and in the Slana area 

[Results given in parts per million] 

Crustal average Sikonsina 

Pass area 

(Taylor, 1964) 

Maximum 

concentrations 

Lead---------- 12.5 100 

Copper-------- 55 100 

Molybdenum---- 1.5 3 

Gold---------- .004 .04 

5), and with average crustal abundances (table 5) suggests that the contents of lead, gold, molybdenum, and 

copper in the area are weakly anomalous. The large 

percentage of the samples which are anomalous in at 

least one metal and the large area of anomalous concentrations may be significant, even though metal enrichment is only two or three times the apparent 

background. 

The highest concentrations of lead occur northwest 

and northeast of Burnt Lake (fig. 14), whereas anomalous copper values were found throughout the sampled 

area (fig. 15). Molybdenum was detected in 4 samples 

(table 4 and fig. 13, samples 8, 10, 13, 14), and gold 

in two (samples 10, 11). The distribution of metals 

suggests that more sampling might result in recognition of zonal pattern, and the association of copper, 

molybdenum, lead, and gold suggests a possibility that 

any mineral occurrences in the area could be polymetallic. 

JMILES 

LEAD CONCENTRATION 

Stream-sediment samples 

• >50 ppm 

4il 30pj)m 

0 dO ppm 

Figure 14.--Lead concentrations in streamsediment samples, Sikonsina Pass area. 

24 

Stream-sediment samples 

Slana area (Richter, 1967; 

Richter and Matson, 1968) 

Anomalous 

concenMode trations 

10 >55 

40-50 ~15o 2.5 ~8 

<.02 ~.02 

3MILES 

Taylor Highway 

(Saurders, 1966) 

>20 

>40 

>3 

COPPER CONCENTRATION 

Stream-sediment samples 

>50 • ppm 

Q 

SO ppm 

0 

:<::30ppm 

l

-3o~_ 

~ ;;~ ~ ~ 

~ 

APPROXIMATE MEAN 

DECUNA1't0N, 1969 

Figure 15.--Copper concentrations in stream~ 

sediment samples, Sikonsina Pass area. 

METAL CONCENTRATIONS IN TWO BEDROCK 

SAMPLES 

Two bedrock samples which contained some metalbearing minerals were also analyzed. Sample 17 (fig . 

13; table 4) represents a calcareous phyllite and was 

coiiected a few inches below the base of a metadiorite 

sill, about 200 feet of which is exposed ca:"Jping a knob 

on the ridge. Rock surfaces near the contac<: are stained 

with malachite and azurite, and the meta'liorite contains smaii amounts of sulfides. Sample 1 7 contained 

about 1 percent ( 10,000 ppm) copper and 7,000 ppm 

of barium. Because most of the slope just below the 

metadiorite is covered with talus, the thickness ofthe 

copper-bearing rock is not known, but the exposed 

copper-bearing zone is less than a foot w:'de. 

Sample 16 (fig. 13), from a limonite-stained gray 

quartzite layer not known to be near any intrusive 

rocks, contained 3 ppm silver. The layer from which 
the sample was collected is several feet thick, and 

much more detailed sampling and mapping would be 

necessary to determine the significance of the silver 

value. 

CONCLUSIONS 

R e conn a i s s an c e geochemical sampling in the 

Sikonsina Pass area shows weakly anomalous concentrations for lead, gold, molybdenum, and copper widely scattered throughout about 20 square miles. Some 

mineralization is associated with a metadiorite sill 

which may be one possible source of anomalous values. 

Proximity to the Denali fault, the existence of other 

faults in the anomalous area, and the presence of favorable host rocks such as marbles and calc-phyllites as 

well as rocks of igneous origin are geologic features 

which seem to make the area attractive for prospecting. Because of the sparsity of samples in adjacent 

areas, it cannot yet be concluded that the Sikonsina 

Pass area is, however, any more favorable than elsewhere in the A 1 ask a Range parts of the Tanacross 

quadrangle. 

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ivnoi 

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25 

GPO 873·861