GEOLOGICAL SURVEY CIRCULAR 559

Lead, Zinc, and Silver 

Deposits at Bowser Creek 

McGrath A-2 Quadrangle 

Alaska
Lead, Zinc, and Silver 

Deposits at Bowser Creek 

McGrath A-2 Quadrangle 

Alaska

By Bruce L. Reed and Raymond L. Elliott 

GEOLOGICAL SURVEY CIRCULAR 559

Woih'mgtan 1968
United States Department of the Interior

WALTER J. HICKEL, Secretary

Geological Survey

William T. Pecora, Director

First printing 1968 

Second printing 1970

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

Page

Abstract- ----------------------------- 1

Introduction ---------------------------- l

Geology -------------------------- -_- 4

Bedded rocks -------------------------- 4

Intrusive rocks ------------------------- 4

Metamorphism ------------------------- 4

Structure ---------------------------- 5

Mineral deposits ------------------------- 5

Deposits in limestone- --------------------- 5

Area southwest of Bowser Creek -------------- 6

Area northeast of Bowser Creek -------------- 7

Deposits in breccia ----------------------- 8

Area at head of Bowser Creek ---------------- 8

Other deposits- ------------------------- 8

Summary and suggestions for prospecting ------------ 9

Reference cited -------------------------- 10

ILLUSTRATIONS

Figure 1. Index map showing location of Bowser Creek area

and McGrath A-2 and B-2 quadrangles ------- 1

2. Reconnaissance map showing generalized geology 

and sample locations at Bowser Creek, McGrath 

A-2 quadrangle ------------------- 2

3. Sketch map showing geology and location of samples

on southwest side of Bowser Creek --------- 5

4. Generalized sketch of cliff face showing sulfide 

vein adjacent to felsite dike in area southwest 

of Bowser Creek ------------------- 6

5. Sketch map showing geology and location of

samples on northeast side of Bowser Creek - - - - 7

6. Generalized sketch of sulfide bodies at sample

location 41-42 -------------------- 8

7. Sketch map showing geology and location of samples

at the headwaters of Bowser Creek --------- 9

TABLES

Page

Table 1. Analyses of bedrock samples from the southwest 

side of Bowser Creek for gold, silver, copper, 

lead, and zinc --------------------- 13

2. Semiquantitative spectrographic analyses and gold 

analyses of soil and bedrock samples from the 

southwest side of Bowser Creek ----------- 14

3 Analyses of bedrock samples from the northeast 

side of Bowser Creek for gold, silver, copper, 

lead, and zinc --------------------- 15

4. Semiquantitative spectrographic analyses and gold 

analyses of bedrock samples near the headwaters 

of Bowser Creek ------------------- 16

III

Lead, Zinc, and Silver Deposits at Bowser Creek 

McGrath A-2 Quadrangle, Alaska

By Bruce L. Reed and Raymond L. Elliott

Abstract

New occurrences of lead, zinc, and silver of potential economic 

significance were identified during a heavy metals investigation of 

the southern Alaska Range in 1967. The deposits, approximately 

23 miles south of Farewell, are replacement bodies and fissure 

veins in limestone and fracture fillings in igneous breccia. Deposits in limestone show a close spatial relation to igneous breccia 

and granodiorite porphyry aswellastofelsitedikes. Ore minerals 

are argentiferous galena and sphalerite. Deposits in breccia consist of pyrrhotite and sphalerite and may represent only part of a 

more extensively mineralized breccia mass. Although most of the 

deposits that crop out are sporadic and discontinuous, the number 

of occurrences with locally high silver content, their possible continuity beneath surficial deposits, and a favorable geologic environment suggest that the area has an economic potential for base 

and precious metals.

INTRODUCTION

New occurrences of argentiferous galena-sphalerite 

and sphalerite-pyrrhotite were identified in the summer of 1967 during a field geologic evaluation of the 

southern Alaska Range as part of the U.S. Geological 

Survey's Heavy Metals program. The deposits occur 

in limestone as replacement bodies and fissure veins 

adjacent to granodiorite, igneous breccia, and felsite 

dikes, and in the breccia as fracture fillings. The deposits appear to be sporadic and discontinuous but 

locally are quite rich.

The Bowser Creek area is approximately 23 miles 

south of Farewell, a Federal Aviation Agency station 

that maintains a 5,000-foot gravel runway (fig. 1). 

McGrath, about 62 air miles northwest of Farewell, 

is the nearest source of gasoline and supplies. No roads 

or trails lead to the area. The deposits can best be 

reached by helicopter. Small, properly equipped aircraft can land on gravel bars along the Post River; the 

deposits can then be reached by walking westward about 

3 miles up Bowser Creek (fig. 2).

Bowser Creek basin is in rugged terrain, with relief 

of about 3,000 feet. The valley floor is mantled by surficial deposits. Talus covers the lower part of the surrounding slopes. There is virtually no vegetative cover 

in the basin; the nearest trees are along the Post River.

Little geologic information is available about this 

remote rugged sector of Alaska, the only previous work 

being that of Brooks (1911) who traversed the Alaska

Range via the south fork of the Kuskokwim River in 

1902. The present report is based on 2 days of examination and sampling. The area shown in figure 2 was 

mapped with the aid of a helicopter in about 5 hours, 

supplemented by aerial photointerpretation. The contacts and structural interpretations must be considered 

tentative; additional mapping of this and surrounding 

areas will be necessary before the geology and significance of the deposits can be fully understood.

10 20 MILES

Figure ]. Location of Bowser Creek area (fig. 2) and McGrath 

A-2 and B-2 quadrangles.

1
L...

Base from U.S. Geological Survey, 

McGrath A-2, 1958

Geology by R. L. Elliott, C. P. Buckley and 

B. L. Reed, 1967

2 MILES

____________I

Contour Interval 100 Feet 

Figure 2. Generalized geology and sample locations at Bowser Creek, McGrath A-2 quadrangle.

2
EXPLANATION

Surficial deposits

Includes alluvium, talus, rock glaciers, and various morainal deposits. Occasional bedrock outcrops may be found 

in ravines and on steep slopes

IGNEOUS ROCKS

Igneous breccia Granodiorite porphyry 

SEDIMENTARY ROCKS

Siltstone with interbedded shale and gray limestone

Is, limestone unit, shown locally

Limestone 

Gray, thin to thick bedded

Argillite

_? 7 .

'Contact

Dashed where approximately located, queried where doubtful, 

dotted where concealed. Concealed contacts shown only for 

igneous bodies

U

Fault

Dashed where approximately located; queried where doubtful, dotted where concealed U, upthrown side; D, downthrown side

Anticline

Showing approximate trace of axial plane,queried where 

doubtful; dotted where concealed

Overturned anticline

Showing approximate trace of axial plane,queried where 

doubtful; dotted where concealed

Syncline 

Showing approximate trace of axial plane

Inclined Vertical Overturned Crumpled, crenulated or

undulatory Strike and dip of beds

Dashed symbol indicates attitude estimated from distant 

field observations

Sample location 

Number refers to table 4

ci

Figure 2. Continued.
GEOLOGY

The Bowser Creek area is underlain by a folded sequence of limestone, siltstone and shale, and argillite 

cut by small intrusive bodies that locally have developed narrow contact aureoles. Mineral deposits are 

spatially related to the igneous rocks and occur both 

in limestone and in the igneous rocks themselves.

Bedded Rocks

Limestone, and siltstone with interbedded shale and 

limestone, are the predominant rocks in the Bowser 

Creek area. Dark-gray argillite appears to underlie 

the limestone in a northern tributary to Bowser Creek. 

Thus the apparent stratigraphic succession, from oldest to youngest, is argillite, limestone, and the predominantly siltstone unit. Rocks in this part of the 

Alaska Range are probably Paleozoic (Brooks, 1911). 

Graptolites, including species of Glyptograptus and 

Climacograptus, which indicate a Middle or Late Ordovician age (Michael Churkin, Jr., oral commun., 

1968) were found in carbonaceous shale of the siltstone 

unit on the west fork of Jay Creek approximately half 

a mile west of the edge of the area shown in figure 2.

Intrusive Rocks

The sedimentary rocks of the Bowser Creek area 

are cut by two igneous breccia bodies, each about 1 

mile across, and a small granodiorite porphyry body 

about 800 feet across. Many felsite and mafic dikes, 

too small to be shown on figure 2, are present throughout the mapped area. Some felsite dikes cut mafic 

dikes.

The southernmost igneous body forms a prominent 

chimneylike mass on the southwest side of Bowser 

Creek. It is a light-gray breccia that consists of angular to subangular rock fragments in a light-gray aphanitic matrix. The rock fragments range from microscopic particles, which form part of the matrix itself, 

to blocks a foot or more across. Silicated limestone, 

quartz-feldspar rock, and cognate inclusions make up 

a large part of these fragments, but many fragments 

are so extensively altered to quartz, epidote, leucoxene, sericite, chlorite, calcite, and opaque minerals 

that their original nature cannot be determined. Many 

fragments show corrosion of their borders. The matrix 

is a micro- to cryptocrystalline paste of plagioclase, 

quartz, and subordinate potassium feldspar and contains abundant fragments of quartz and plagioclase. 

The center of the breccia mass was not examined, but 

the rock glacier which heads near its center consists 

of boulders similar in composition to the outcrops examined near the edge.

The northernmost intrusive, also a breccia, underlies the basin at the headwaters of Bowser Creek. Its 

contacts with the enclosing rocks are largely concealed 

by surficial deposits. This intrusive was examined only 

along Bowser Creek, where it is a light-greenish-gray 

intrusive breccia similar in composition to the southern intrusive body. Near the southern contact, breccia

fragments 0.25-2 inches in diameter make up 60percent or more of the rock and are sharply angular, but 

away from the contact the fragments become more 

widely separated, the amount of matrix increases, and 

the fragments become more rounded. Specks and clots 

of a sulfide mineral (pyrrhotite?) are disseminated 

throughout the breccia, and veins filled with pyrrhotite 

and sphalerite locally fill fractures in the breccia.

A small body of granodiorite porphyry occur son the 

north side of Bowser Creek (fig. 2). The contact of the 

porphyry with the enclosing limestone is covered, but 

the dimensions of the igneous body are approximately 

delineated by granodiorite porphyry rubble. The porphyry is yellowish gray with small (0.2 5-3 mm), partly 

corroded phenocrysts of plagioclase and subordinate 

subrounded quartz crystals in a microcrystalline aggregate of plagioclase, quartz, and potassium feldspar. 

Scattered prismatic crystals of hornblende are now 

altered to iron-rich chlorite and epidote. The plagioclase is usually turbid from incipient alteration.

Light-gray to white felsite dikes, from 1 to 50 feet 

thick, occur throughout the Bowser Creek basin. They 

vary in texture from an aphanitic equigranular aggregate of quartz, plagioclase, and potassium feldspar to 

porphyritic dikes withphenocrysts of plagioclase (partially altered to sericite, calcite or epidote) and 

rounded quartz crystals embedded in a very fine 

grained crystalline groundmass of feldspar and quartz. 

The felsite dikes intrude the bedded rocks, and along 

the upper reaches of Bowser Creek they cut igneous 

breccia.

Fine-grained dark-greenish-gray porphyritic mafic 

dike rocks locally are present. In thin section, altered 

phenocrysts of plagioclase and hornblende occur in a 

felted groundmass of altered plagioclase and femic 

alteration products. The plagioclase phenocrysts are 

extensively saussuritized, chiefly to albite and epidote. 

The original hornblende phenocrysts have retained 

their prismatic form but now are wholly altered to actinolite, epidote, chlorite, and opaque minerals, as are 

the primary groundmass mafic minerals. Irregular 

grains of potassium feldspar in the groundmass make 

up less than 5 percent of the rock. Originally these 

dike rocks were probably hornblende andesite.

Metamorphism

Rocks of the Bowser Creek area show little or no 

effects of regional metamorphism. However, within a 

hundred feet or so of the contact with intrusive bodies, 

limestone and pelitic country rock may be converted 

to hornfels. Contacts for the most part are poorly exposed because of extensive talus cover, but where field 

examination was possible, normally gray limestone is 

in many places bleached and recrystallized to a hard 

fine-grained silicated marble or calc-silicate hornfels. The pelitic rocks are baked and converted to a 

hard fine-grained hornfels. Such effects are evident 

adjacent to the northern intrusive breccia exposed in 

the headwaters of Bowser Creek.
The most conspicuous metamorphic effects, and 

those which appear to have the greatest potential economic significance, are skarn zones developed near 

felsite dikes and granodiorite porphyry. Ore minerals 

in the skarn are pyrrhotite and sphalerite (marmatite) 

with associated calc-silicate minerals,chieflyepidote 

and clinopyroxene. The skarn replaces silicated limestone. Generally within 10 feet of the sulfide-rich skarn 

bodies, the rock is altered to light-greenish-gray dense 

silicated marble composed of quartz, epidote, clinopyroxene, calcite, and chlorite.

Structure

The sedimentary strata have been deformed into 

folds which trend north-northeast and plunge to the 

south-southwest and north-northeast. The folds are 

locally overturned; axial planes are vertical or dip 

steeply to the east-southeast. Subsidiary asymmetric 

and disharmonic folds with wavelengths of a few inches 

to tens of feet were noted on the limbs of the larger 

folds. Faults, mapped from aerial photographs, are of 

two generations. The north-trending fault exposed 

south of Bowser Creek apparently accompanied the 

main period of folding. Cross faults of small apparent 

displacement (not shown in fig. 2) border the southern 

intrusive breccia.

500

_I

Approximate scale 

Contour Interval 100 Feet

1000 FEET 

I

The northeast-trending structural features are cut 

by intrusions of igneous breccia and associated felsite 

and subordinate mafic dikes. The southern breccia body 

shown near the center of figure 2 cuts the southwest 

end of an elongate locally overturned anticline. The 

northern breccia body cuts subparallel folds.

MINERAL DEPOSITS

The mineral deposits are of two main types: (1) 

galena-sphalerite or sphalerite-phrrhotite deposits in 

limestone and (2) narrow pyrrhotite-sphalerite fracture fillings in igneous breccia. The deposits in limestone are in two areas, one southwest and the second 

northeast of Bowser Creek. The deposits in igneous 

breccia are near the headwaters of Bowser Creek. The 

locations of all three areas are indicated in figure 2. 

All deposits are closely associated with intrusive igneous bodies.

Deposits in Limestone

The galena-sphalerite or sphalerite-pyrrhotite deposits in limestone consist of replacement bodies and 

fissure veins. Sphalerite (marmatite) and pyrrhotite 

are the ore minerals in the replacement bodies; argentiferous galena, with or without other sulfide minEXPLANAT1ON

Limestone 

(partly covered)

Contact 

Dashed where approximately located

80\y ^ 40

/ f . S**)^r\

Inclined Vertical Undulatory 

Strike and dip of beds

Sample location 

Number refers to tables 1 and 2

Figure 3. Geology and location of samples on southwest side of Bowser Creek.

5
erals (chiefly marmatite), characterizes the fissure 

veins. Pyrite and minor chalcopyrite are locally present. The replacement bodies range from a few inches 

to 10 feet in width. They are generally tabular or podlike and replace silicated limestone. Individual podlike 

bodies may consist of as much as 85 percent combined 

sphalerite and pyrrhotite. The long axes of the pods 

are generally parallel to the bedding of the limestone. 

Many bodies were observed to pinch out within a few 

feet.

Area southwest of Bowser Creek. Deposits of 

sphalerite-pyrrhotite and argentiferous galena are 

concentrated in an area on the southwest side of Bowser 

Creek (figs. 2, 3). Analyses for gold, silver, copper, 

lead, and zinc, and semiquantitative spectrographic 

analyses for the samples collected in this area are 

given in tables 1 and 2.

The largest replacement body examined (table 1, 

samples 3-5) has a vertical dip and an apparent width 

of 10 feet. Chip samples across this body indicate as 

much as 14.7 percent zinc and 6.1 ounces of silver per 

ton. Only the south side of the body is exposed; the 

contact is parallel to the limestone beds. Outcrops in 

talus downslope indicate a vertical extent of about 50 

feet.

About 1,200 feet north of the limestone-breccia 

contact a group of tabular or veinlike bodies occurs 

in altered limestone and shows a close spatial relationship to felsite dikes (fig. 3). One vein (fig. 4), 

consisting of pyrite, galena, sphalerite (marmatite), 

and minor pyrrhotite inagangueofwhitemilky quartz, 

minor calcite, and unreplaced limestone fragments, 

follows the contact between limestone and a felsite 

dike. This vein is irregularly massive without marked 

banding and is oxidized to a dark chocolate brown. 

The vein pinches out upward into silicated limestone; 

the lower extension is covered by talus.

A few narrow discontinuous fissure veins consist 

of nearly solid argentiferous galena. These veins, 

however, pinch and swell irregularly and do not appear to have great continuity. The maximum width 

of massive galena in these veins is 10 inches, but 

most are between 2 and 6 inches across. A 20-foot 

chip sample (table 1, sample 10) across oxidized 

skarn (see fig. 3) containing narrow veins of galena 

assayed slightly more than 52 ounces of silver per 

ton. The walls of some of these veins are marked by 

brownish-yellow gouge. Preliminary examination of 

a polished section of sample 11 (see fig. 3; tables 

1, 2), which contains 309.8 ounces of silver per ton,

3-6 in. of galena 

in 18 in. shear zone

EXPLANATION

Felsite dike

Oxidized vein

Sulfide minerals

Galena vein

(Chiefly galena, sphalerite and pyrite) 

Chip sample ([[IP

Iron-stained silicated limestone

Gray limestone 

(Partly covered)

i " 

Brecciated limestone

Sample location 

Number refers to tables 1 and 2

Approximate scale

Figure 4. Cliff face showing sulfide vein adjacent to felsite dike in area southwest of Bowser Creek.

6
shows that approximately 85-90 percent of the sample 

is galena. Other primary minerals include sphalerite, 

pyrite, and minor amounts of tetrahedrite. Small 

grains of other minerals, perhaps members of the 

copper-arsenic sulfide group of sulfo-salts (Arthur 

Radtke, oral commun., 1968), also are present. Secondary minerals developed along galena cleavages 

include cerussite, hematite, and mimetite(?).

Area northeast of Bowser Creek. The deposits 

northeast of Bowser Creek (figs. 2, 5) show a close 

spatial association with the small granodiorite porphyry body or with felsite dikes. A description of the 

deposits examined and analyses for gold, silver, copper, lead, and zinc of samples collected from them 

are given in table 3.

500

\

Approximate scale 

Contour Interval 200 Feet

1000 FEET 

_I

Much of the area shown as limestone in figure 5 

is covered by talus. However, mineralized skarn 

which appears to have potential economic significance locally crops out near the granodiorite porphyry 

and felsite dikes. The skarn typically consists of 

pyrrhotite and sphalerite (marmatite), associated with 

a variety of silicate minerals including epidote, clinopyroxene, quartz, and chlorite. The iron-bearing 

sulfide minerals weather to a deep reddish brown. 

There are scattered exposures of skarn in talus along 

the east side of the granodiorite porphyry. The skarn 

zones are as much as 25 feet across, and if they prove 

continuous beneath talus cover, then a north-trending 

skarn zone at least 1,000 feet long is indicated (fig. 5, 

samples 34-40).

EXPLANATION

Surficial deposits

Argillite

Approximate contact 

(Short dashed where inferred)

Vertical Undulatory 

Strike and dip of beds

Shear zone 

(Queried where doubtful)

Sample location 

Number refers to table 3

Figure 5. Geology and location of samples on northeast side of Bowser Creek.
Other deposits in this area occur along shear zones 

which border felsite dikes (table 3, samples 27-33). 

The sulfide minerals replace limestone, and locally 

the dikes are partly replaced. Most deposits are 

narrow and discontinuous and pinch out within a few 

feet (fig. 6).

- Deposits in Breccia

Small fractures filled with pyrrhotite and sphalerite occur in the northern igneous breccia body. 

Individual deposits appear to be small, but poor exposures prevent delineation of their true extent. The 

fracture fillings may represent only part of a more 

extensively mineralized breccia mass.

Area at head of Bowser Creek. Deposits in igneous 

breccia were examined only along the headwaters of 

Bowser Creek (fig. 7). Descriptions of the individual 

localities and analyses of samples from these localities are given in table 4 (samples 43-58). The deposits consist of small sulfide veins largely controlled by northwest-trending fractures in igneous 

breccia (fig. 7). Specks and clots of a sulfide mineral 

(pyrrhotite?) also are disseminated in the breccia. 

The veins have steep to vertical dips and strike N.

40°-60° W. Significant replacement of the breccia 

does not appear to have occurred, because in many 

places vein walls match. None of the veins exceed 

2 feet in width, and some veins end abruptly. Surficial deposits prevent tracing the veins for more 

than 10 feet. The veins consist of pyrrhotite with 

minor sphalerite (marmatite), chalcopyrite, and a 

trace of galena. One 4- to 6-inch vein (table 4, sample 54) contains 85 percent of sphalerite. Although 

the pyrrhotite has little current economic value, 

further exploration in this area may find significant 

concentrations of sphalerite.

Other Deposits

The locations of other scattered occurrences north 

and west of Bowser Creek are shown in figure 2. Semiquantitative~spectrographic analyses of samples from 

these localities and a brief description of the samples 

are given in table 4 (samples 59-64). Of particular interest are samples 63 and 64 from the ridge west of 

Bowser Creek. Although the outcrops are small, and 

deposits are consequently of unknown extent, they do 

suggest that lead-zinc-silver mineralization extends 

for at least one-half mile southwest of the area shown 

in figure 3.

EXPLANATION

Sulfide minerals

(Chiefly sphalerite and pyrrhotice; crosshatched where highly oxidized)

Chip sample

 o

Limestone

Sample location 

Number refers to table 3

Approximate scale

Figure 6.-Sulfide bodies at sample location 41-42 (fig. 5); looking northeast at small cliff.
N

EXPLANATION

Locally covers at least 50 percent of areas

shown as bedrock outcrop

Felsite dikes

Limestone and argillite

Contact 

Dashed where approximately located

Strike of vertical bed

m 4Sm

Vertical Inclined 

Strike and dip of joints

=*= =£5 

Vertical Inclined 

Vein showing dip

Stream

200 FEET

Approximate scale

Sample location 

Number refers to table 4

Figure 7, Geology and location of samples at the headwaters of Bowser Creek,

SUMMARY AND SUGGESTIONS 

FOR PROSPECTING

Metalliferous deposits in the Bowser Creek area 

occur as replacement bodies (skarn) and fissure veins 

in limestone and as fracture fillings in igneous breccia.

Ore minerals in the replacement bodies and fissure 

veins are sphalerite and argentiferous galena. These 

deposits occur near igneous breccia and granodiorite 

porphyry. In many places the sulfide deposits are 

adjacent to felsite dikes.

Table 1. Analyses of bedrock samples from the southwest side of Bowser Creek

[Analysts: W. D. Goss, Claude Huffman, Jr., J. A. Thomas, L. B. Riley, and V. E. Shaw. Gold determined by 

fire assay, silver by atomic absorption and gravimetric fire assay, lead and copper by atomic absorption, and 

zinc by atomic absorption and gravimetric analysis]

Sample 

No.

3

k

5

6

7

8

9

10

11

13

Ik

18

22

Lab. 

No.

ACG85^

ACJ015

016

017

018

019

ACG853

852 698

850

ACJ051*

ACG851

ACJOll*

Field No.

67AMa251

R353A

R353B

R35 1*A

R35to

R35^C

Ma250

Ma2l*9

R3UI

Ma2WA

R311D

Ma2l*8B

R351

Au 

(ppm)

0.03

.k

.05

.06

<.02

.03

.02

<.02

.2

.05

<.02

.03

.k

Ag 

(oz per ton)

2.k

6.1

3.9

2.k

.k

.9

3 ' 2

^ 52.2

J 309.8

1.9

I 56.3

J 20.5

2.k

Cu

0.11

A9

.32

.Ok

.01

.08

.01

.11 .Ik

.19

.25

.07

.15

Pb

(percent)

0.09

.78

.Ik

.09

.03

.03

.02

27.2

60.0

.2

39.0

16.0

.17

Zn

5.95

1U.7

7.^2

2.55

.61

o - W

2 .22

1.59

2.17

3.18

5.70

3.72

k.3

1 

Sample type

8-1. Includes 3 ft of limestone.

5-1. Continuation of sample 3.

Selected.

5-1

5-1. Continuation of sample 6.

8-1. Continuation of sample 7.

30-1. Includes 5 ft of limestone.

20-1

Selected.

12-1. Includes 2 ft of dike.

Selected.

20-1

5-1

"TJnless noted, samples are chip samples. First number is length in feet and second number is interval 

between chips in feet; that is, 8-1 is an 8-ft-chip sample with chips collected every foot. 

Analyses by atomic absorption, 

-gravimetric fire assay.

DESCRIPTION OF SAMPLES

Samples 3-5. 10-ft-wide massive skarn zone adjacent to limestone. Skarn consists of brecciated silicated 

limestone (quartz, clinopyroxene, minor epidote) replaced by sphalerite and pyrrhotite. Sulfide minerals 

make up 50-90 percent of zone. Outcrops in talus downslope indicate a vertical extent of about 50 ft. 

Samples 6-8. Silicated limestone with discontinuous stringers and pods of sulfide minerals (sphalerite, pyrrhotite); highly oxidized. 

Sample 9. Taken across oxidized skarn (quartz, clinopyroxene, epidote); no fresh sulfide minerals visible in

outcrop.

Sample 10. Taken about 50 ft below sample 9 across oxidized skarn adjacent to felsite dike (quartz, plagioclase, 

potassium feldspar). Shear zones in skarn locally contain thin stringers and lenses of galena from 1 to 10 

in. thick. Lenses of pyrite, galena, and minor sphalerite as much as 2 ft wide also occur sporadically in 

skarn; pinch out to thin stringers over a vertical distance cf a few feet. 

Sample 11. A selected sample of galena from shear zone.

Sample 13. Highly oxidized vein of pyrite, galena, sphalerite, and minor pyrrhotite 3-5 ft wide between felsite dike and limestone; oxidized capping of vein exposed over a vertical distance of about MD ft, lower 

extension covered by talus, pinches out upward (fig. k). Location of samples about 75 ft below sample 10. 

Sample Ik. A selected sample of pyrite and galena with minor sphalerite, quartz, and calcite from widest part

of vein.

Sample 18. Taken across silicated limestone (quartz, clinopyroxene, calcite): Replacement by galena occurs 

along small shear zones in limestone; lenses of pyrite, galena, and minor sphalerite also occur sporadically in limestone.

Sample 22. Stringers and lenses of oxidized sulfide minerals (pyrite, galena, and sphalerite) in skarn adjacent to felsite dike; mineralized zone pinches out upward, lower part covered by talus.

13
Table 2. Semiquantitative spectrographic analyses and gold analyses of soil and bedrock samples

from the southwest side of Bowser Creek

[Analysts: A. L. Button, Jr., Arnold Farley, Jr., spectrographic; A. L. Meier, R. L. Miller, 

and T. A. Roemer, gold-atomic absorption. Spectrographic analyses reported in parts per 

million to the nearest number in the series 0.5, 0.7, 1.0, 1.5, 3.0, 5.0, 7.0, 10, 15, 

and so on, which represent approximate midpoints in a geometric scale. The precision of 

a reported value is approximately plus 100 percent or minus 50 percent. See figure 3 for 

location of samples. Symbols used; >=greater than; <=detected, but below limit o^ determination; A=not detected; I=interference; ND=not determined; M=>10 percent]

Sample 

No.

1

2

11

12

Ik

15

16

17

19

20

21

Lab 

No.

ACJ072

073

ACG687

686

682

683

68^

685

680

681

679

Field 

No.

67AR352

353

R31H

311H

311D

311E

3HF

311G

311B

3HC

311A

Ag

20

70

> 1,000

> 1,000

> 1,000

700 150

30

70

200

As

A <

A

> 10, 000

300

700

> 10, 000

200

200

200

200

7 200

Au

0.02

.02

.05

.06

Qh

Q]I

.05

.06

1.0

.0^

.02

B

ND

ND

70

10

<10

50

70

100

50

30

Ba

15

7

100

<100

<100

100

<100

<100

<100

<100

<100

Be Co

2 200

2 150

< 1 < 10

<1 < 10

<1 <10

<1 20

<1 100

<1 100

<1 150

<1 10

<1 <10

Cr

3

15

A

A

A

A

A

A

10

A

A

Cu

10,000

10,000

1,500

2,000

2,000

700

2,000

1,500

3,000

50

150

La

A

A

<20

<20

<20

<20

<20

<20

<20

<20

<20

Mn

50,000

10,000

1,500

300

1,500

700

1,000

700

2,000

2,000

1,000

Mo

A

A

7

<5

<5

I

I

I

7

<5

<5

Nb

A

A

<20

<20

<20

<20

<20

<20

<20

<20

<20

Limit of detectibility: 

Samples 1 and 2 

Samples 11-20

1 2,000 .02 ND 

.5 200 .02 10

2

20

3

10

30

20

1

20

10

10

Sample 

No.

1

2

11

12

1^

15

16

17

19

20

21

Ni

50

30

<2

<2

<2

<2

10

10

<2

2

<2

Pb

7,000

15,000

>5,000

>5,ooo

>5,ooo

>5,000

3,000

1,500

300

>5,ooo

30

Sc

ND

ND

<5

<5

<5

<5

<5

<5

<5

<5

<5

Sr

10

30

< 10

< 10

<10

<10

10

15

30

20

10

V

A

20

<10

<10

<10

<10

10

15

30

20

10

Y

A

A

15

<5

<5

<5

7

7

5

5

15

zn

M

100,000

> 10, 000

> 10, 000

> 10, 000

>10,000

>10,000

>10,000

> 10, 000

>10,000

500

Zr

A

15

<20

<20

<20

<20

<20

<20

70

70

<20

Ca Fe Mg Ti

(percent)

1.0

1.0

.7

<.05

.5

.07

.15

.3

10

15

7

1.5

1.0

15

7

7

20

>20

>20

15

7

5

0.7

.7

.03

<.02

<.02

<.02

< .02

.03

.7

.3

.2

0.02

.05

.015

.001

.02

.007

.02

.03

.07

.03

.02

Sample 

type

Soil

Soil

Selected.

Selected.

Selected.

Selected.

Selected.

Selected.

Grab.

Selected.

Grab.

Limit of detectibility:

Samples 1 and 2 3 10 ND 5 7 10 200 10 .005 .001 .005 .0002 

Samples 11-20 2 10 5 50 5 5 200 10 .05 .05 .02 .002

DESCRIPTION OF SAMPLES

Sample 1. From brown horizon 12 in. below surface.

Sample 2. From 2-in. greenish-gray hori?on below 

sample 1.

Samples 11, 12. Galena from shear zone in silicated limestone. For assay and description see 

samples 10 and 11 in table 1.

Samples lit-, 15. Pyrite and galena with minor sphalerite, quartz, and calcite. For assay and further description see sample lit- in table 1.

Samples 16, 17. Sphalerite with minor galena and 

pyrrhotite. For description of vein see sample 13 in table 1.

Sample 19. Oxidized skarn.

Sample 20. Skarn containing galena and sphalerite. 

For further description see sample 18 in table 1.

Sample 21. Felsite dike that cuts silicated limestone.
Table 3 Analyses of bedrock samples from the northeast side of^Bowser Creek

[Analysts: W. D. Goss, Claude Huffman, Jr., J. A. Thomas, L. B. Riley, and V. E. Shaw. Gold 

determined by fire assay; silver by atomic absorption, lead and copper by atomic absorption, 

and zinc by atomic absorption and gravimetric analysis]

Sample Lab. 

No. No.

23

2k

25

26

27

28

29

30

31

32

33

3^

35

36

37

38

394o

41

42

ACG595

596

597

700

ACJOOl

002

003

004

005

006

007

008

009

010

Oil

012

013

ACG856

855

ACJ020

Field No.

67AEr245

Er246

Er247

R327

R328

R329A

R329B

R330A

R330B

R33M

R331B

R333A

R334A

R334B

R335

R336A

R336B

Ma254

Ma252

R356

Au 

(ppm) 1

0.3

.07

.2

<.02

.02

.5

.7

<.02

.03

<.02

.2

1.1

3.4

.8

.7

2.0

1.6

.2.

.02

.03

' ^ H- ,oz per tor

3.

1.

5.

11.

1.

3.

3.

2.

1.

.

f

1.

3.

10.

5

9

6

5

2

5

0

9

7

1

2

6

5

6

5

5

4

6

7

1

Cu l)

2.44

.65

1.10

.02

.07

.03

.55

.02

.07

.03

.96

.08

.02

.05

.02

.ok

.02

.06

.13

.33

Pb Zn Sample type

(percent)

0.02

.02

.05

24.0

.15

.04

.26

1.55

11.5

.01

.06

.48

.02

.03

.04

.02

.17

.08

.24

2.1

4.

1.

4.

,

5.

4.

22.

2.

lO.

12.

7.

2.

4.

4.

14.

4.

7.

4.

8.

02

04

72

16

95

83

1

96

7

03

2

44

88

76

55

5

3

46

97

55

3 -.5. Includes 18 in. to 2 ft of

3-. 5. Includes 18 in. to 2 ft of

3-. 5. Includes 18 in. to 2 ft of

Selected.

Selected.

3-. 5

Selected.

5-. 5

Selected.

5-. 05.

Selected.

5-1

5-1

8-1. Continuation of sample 35.

5-1

10-1

15-1. Continuation of sample 38.

15-1

25-1. Includes 2 ft of limestone

of dike.

Selected.

limestone.

limestone.

limestone.

and 2 ft

Unless noted samples are chip samples. First number is length of chip in feet, and second number is interval 

between chips in feet; that is, 8-1 is an 8-ft-chip sample with chips collected every foot. 

Analyses by atomic absorption

DESCRIPTION OF SAMPLES

Samples 23-25. Irregular lensatic sulfide bodies (sphalerite with minor chalcopyrite, pyrite) in Silicate'1 

limestone (clinopyroxene with subordinate epidote, quartz, and calcite) along discontinuous fractures. Limestone cut by felsic and mafic dikes.

Sample 26. Sporadic 2- to 3-in.-wide lenses of galena as much as 1 ft long in skarn adjacent to felsite dike. 

Mineralized within 1 ft of dike.

Samples 27-31. Shear zone (strike F. 55° W., dip 75° NW.) adjacent to felsite dike that cuts limestone. Sphalerite, galena, and minor chalcopyrite localized along shear as small pods and stringers; sulfide minerals replace both skarn (epidote, calcite, quartz, and chlorite) and dike. Maximum width of pods is 20 in.; most 

pods pinch out within 10 ft along dip of shear.

Samples 32, 33- l8-in.-wide.lens of sphalerite in skarn along shear zone; shear exposed for 6 ft along dip.

Sample 34. Silicated limestone with veins of sphalerite and pyrrhotite 4-5 in. wide in limestone (strike

N. 10° E., dip 90°). Outcrop is 8 ft wide, 25 ft long; extensions covered by talus. About 100 ft downslope 

to south a similar small outcrop with minor content of sulfide minerals.

Samples 35> 36. Poorly.exposed outcrop of oxidized skarn isolated by talus.

Sample 37. Small outcrop of skarn with sphalerite and pyrrhotite; isolated by talus.

Samples 38, 39. Poorly exposed small outcrops of skarn (chiefly sphalerite, pyrrhotite, quartz, clinopyroxene, 

and epidote); pods of sphalerite and pyrrhotite as much as 10 in. wide.

Sample 40. Body containing 40-80 percent sulfide minerals (chiefly sphalerite and pyrrhotite) about 4 ft by 

20 ft in skarn; body pinches out downward; may extend upward to sample 38.

Samples 4l, 42. Zone of sulfides 10 in. to 4 ft wide in skarn adjacent to felsite dike. A 5-ft-wide vein of 

sphalerite and pyrrhotite extends upward from sulfide-rich skarn zone for about 30 ft pinches out (fig. 6). 

Lower part of skarn zone and dike covered. Mineralized skarn zone contains about 75 percent sphalerite and 

pyrrhotite in a ratio of about 1:1. Silicated limestone contains quartz, epidote, calcite, and minor chlorite (sample taken 5 ft from sulfides). Chip sample taken across mineralized skarn zone and dike.

15
Table k. Semiquantitative spectrographic analyses and gold analyses

[Analysts: A. L. Sutton, Jr., Arnold Parley, Jr., spectrographic ; A. L. Meier, R. L. Miller, and 

the nearest number in the series 0.5, 0.7, 1.0, 1.5, 3.0, 5-0, 7.0, 10, 15, and so on, which 

proximately plus 100 percent or minus 50 percent. See figures 2, 7 for location of samples. 

I=interference; M=>10 percent]

Sample 

No.

1+3

1+1+

1+5

1+6

1+7

1+8

1+9

50

51

52

53

5»+

55

56

57

58

59

60

6l

62

63

6k

Lab.

No.

ACG587

588 589

590

569

591

592

568

567

566

593

565

561+

562

563

591+

966

570

571

572

901+

905

Field No.

67AEr232

233A

233B

23U

210

231+B

235

208

207

206

238

205

203

202A

202B

21+1+

67ABul95

67AEr215

67AEr217

67AEr2l8

67ABul31

67ABul32

Ag

10

20

70

20

100

100

7

300

100

10

5

200

200

A

A

A

50

30

100

100

300

5,000

As

A

A

A

A

A

100,000

A

A

A

A

A

A

7,000

A

A

A

A

A

A

A

1,500

30,000

Au

0.07

.02

.0^

.02

.1

.03

<.02

.08

.08

.06

< .02

.1

.05

.01+

.ok

.03

<.02

<.02

.05

.05

.06 .08

Ba

3,000

2,000

500

3,000

200

500

3,000

50

150

500

3,000

20

3,000

1,500

1,000

1,500

700

100

7

20

30

50

Be

A

A

A

A

A

A

A

A

A

A

A

A

A

1

1.5

A

A

A

1.5

1.5

A

A

Co

50

50

150

50

200

200

30

100

150

200

7

500 150

7

10

20

15

7

100

50

7

A

Cr

5

3

1

10

A

1

5

A

A

1-5

7

1.5

5

7

30

70

50

5

70

7

2

15

Cu

500

1,500

10,000

1,500

3,000

3,000

500

20,000

3,000

2,000

200

30,000

15,000

15

50

200

150

200

30,000

20,000

1,500

1,500

La

A

A

A

30

A

A

30

A

A

A

20

A

20

20

30

30

20

A

50

A

A

A

Mn

100

300

1,000

300

200

3,000

200

2,000

200

50

3,000

2,000

2,000

300

700

3,000

2,000

15,000

5,000

5,000

50,000

1,000

"TJnless noted samples are chip samples. First number is length of chip in feet, and second number is

DESCRIPTION OF SAMPLES

Samples 1+3-1+9. Veins of pyrrhotite with minor chalcopyrite and sphalerite in igneous breccia. Veins show 

strong localization along N. 1+0°-60° W. fractures. There is no replacement of wallrock in many places 

opposite sides of vein match. Lack of continuous exposure prevents tracing of veins for more than 10 ft, 

and except where noted, lengths of veins are defined by surficial cover. Some veins pinch and swell and 

may end abruptly. Sample 1+3: 2-3 in. wide and k ft long; pinches out on one end. 

wide and 8 ft long. Samples 1+6-1+8: 2 ft wide and 10 ft long; probably 

Sample 1+9: 3-5 in. wide and 8 ft long.

Samples 50-52. Narrow northwest-trending veinlets of pyrrhotite, sphalerite, and minor chalcopyrite in igneous breccia. Sample 50: 2 in. wide; 1+0 percent pyrrhotite, 30 percent sphalerite, 10 percent chalcopyrite, trace of galena, 20 percent quartz. Sample 51: 8 in. wide; pyrrhotite with subordinate chalcopyrite and sphalerite. Sample 52: 3-8 in^ wide; chiefly pyrrhotite.

Sample 53. Narrow (1 in. wide) northwest-trerfdarig. veinlets of pyrrhotite in igneous breccia.

Sample $k. k- to 6-in.-wide northwest-trending vein of sulfides in igneous breccia; 85 percent sphalerite, 

5 percent chalcopyrite, 5 percent pyrrhotite, 5 percent gangue.

Samples 1+1+-1+5: 

continuation of vein 1+8.

2 ft

16
of bedrock samples near_the headwaters of Bowser Creek

T. A. Roemer, gold-atomic absorption. Spectrographic analyses reported in parts per million to 

represent approximate midpoints in a geometric scale. The precision of a reported value is apSymbols used: >=greater than; <=detected, but below limit of determination; A=not detected;

Mo

<5

<5

<5

<5

<5

< 5

<5

<5

<5

<5

3

<5

< 5

A

A

A

<5

A

< 5

< 5

<5

<5

Nb

A

A

A

A

A

A

A

A

A

A

A

A

A

10

10

A

10

A

A

A

A

A

Ni

5

5

10

7

10

15

7

7

7

50

5

15

5

7

15

20

100

15

50

100

15

7

Pb

200

200

1,000

150

700

3,000

100

3,000

1,000

30

150

50

700

20

50

15

10,000

7,000

500

30

M

M

Sr

500

200

20

500

7

20

500

10

7

30

500

A

500

500

700

500

20

1,000

70

100

70

30

V

50

30

A

50

A

A

50

A

A

10

50

A

30

70

100

70

50

A

70

100

A

15

I

15

10

A

15

A

A

10

A

A

A

15

A

A

30

20

20

10

10

30

10

A

A

Zn

A

A

30,000

1,000

3,000

M

500

100,000

2,000

5,000

2,000

M

M

A

1,000

A

5,000

20,000

5,000

2,000

50,000

30,000

Zr

100

70

15

100

A

20

100

A

A

A

150

A

50

100

150

200

100

A

100

A

A

10

Ca

0.15

.2

.15

.2

.01

.03

.3

.5

.02

.15

2

.1

.7

3

5

5

.05

M

3

5

.07

.15

Fe

(percent)

7

M

M

10

M

M

5

M

M

M

2

M

M

1.5

1.5

3

M

5

10

10

M

10

Mg

0.1

.1

.03

.15

.01

.02

.3

.02

.01

.01

.7

.2

.07

.7

1.5

2

1

3

5

2

.05

.07

Ti

0.15

.15

.01

.2

.015

.03

.2

.002

.005

.01

.2

.001

.15

.15

.15

.5

.2

.01

.2

.015

.015

.05

Sample 

type

3-. 5

5-. 5

Selected.

5-. 5

Selected.

Selected.

3-. 5

Grab.

Grab.

Grab.

3-. 5

Grab.

Selected.

Grab.

Grab.

3-. 5

Selected.

Selected.

Selected.

Selected.

Selected.

Selected.

interval between chips in feet; that is, 5-. 5 is a 5-ft-chip sample with chips collected every one-half foot.

DESCRIPTION OF SAMPLES

Sample 55. Small breccia zone 3-^- in. wide consisting of angular fragments of silicated limestone and felsite 

cemented by sphalerite with minor chalcopyrite and pyrrhotite. Sulfides make up about 30 percent of rock.

Samples 56, 57. Igneous breccia containing less than 5 percent of disseminated specks and clots of sulfide 

minerals. Samples taken within 50 ft of breccia-limestone contact.

Sample 58. Discontinuous narrow (8-10 in, wide) oxidized zone of pyrrhotite and sphalerite in silicated limestone.

Sample 59. Pyritized mafic dike.

Sample 60. Narrow mineralized shear zone; highly oxidized.

Sample 6l. 3-ft-wide mineralized shear(?) in altered, highly oxidized argillite (pyrite with minor chalcopyrite),

Sample 62. Small outcrop of mafic rock with disseminated -pyrite, pyrrhotite, and sphalerite.

Sample 63. Iron oxide-stained shear zone in limestone.

Sample 6k. Narrow vein of galena (2-6 in. wide) in limestone poorly exposed, extent unknown.

17

* U. S. GOVERNMENT PRINTING OFFICE : 1970 O - 375-784