Tertiary Mineralization and 

Hydrothermal Alteration in the 

Stinkingwater Mining Region, 

Park County, Wyoming

GEOLOGICAL SURVEY BULLETIN 1332-C

Tertiary Mineralization and 

Hydrothermal Alteration in the 

Stinkingwater Mining Region, 

Park County, Wyoming

By FREDERICK S. FISHER

CONTRIBUTIONS TO ECONOMIC GEOLOGY

GEOLOGICAL SURVEY BULLETIN 1332-C

A study of a porphyry copper deposit 

in the Absaroka Range, its altered 

volcanic rocks and metal distributions

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 74-189825

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

Washington, D.C. 20402 - Price 30 cents (paper cover)

Stock Number 2401-2086
CONTENTS

Page

Abstract............................................................................................................. Cl

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

Acknowledgments.............. .................................. ....... .. . 4

General geology of the Stinkingwater region....................................... .... 5

Layered rocks............................................................................................ 5

Intrusive rocks.......................................................................................... 8

Needle Mountain Granodiorite ................................................ 8

Crater Mountain Dacite... .................................................... 8

Dikes................................................................................................... 9

Structural geology.................................................................................... 9

Economic geology............................................................................................. 13

General nature.......................................................................................... 13

Primary sulfide minerals and mineralized rock.................................. 13

Disseminated types .................................................................... 13

Vein types........ ............................................................................ 15

Secondary minerals and mineralized rock........................................... 16

Oxidized rocks................................................................................... 16

Supergene copper-enriched rocks.................................................. 16

Altered rock............................................................................................... 17

Geochemical sampling............................................................................. 18

Metal distributions........................................................................... . 28

Prospecting guides................................................................................... 30

Local................................................................................................. 30

Regional............................................................................................. 31

References cited................................................................................................ 32

ILLUSTRATIONS

Page

FIGURE 1. Photograph showing part of the Stinkingwater mining

region from top of Needle Mountain................................... C2

2. Index map of the Absaroka volcanic field ........................... 3

3. Geologic map of the Stinkingwater mining region . . . 7

4. Lineament map of Stinkingwater mining region

and vicinity. ........................................................................ 10

5. Photograph of the South Fork of the Shoshone River

and canyon that reflects northwest-trending fracture set 12

6. Photograph showing part of the zone of disseminated

sulfide minerals on Crater Mountain................................... 14

7. Photograph showing part of the zone of disseminated

sulfide minerals on Needle Mountain................................... 15

8-11. Histograms showing concentrations of selected elements

in samples from the Stinkingwater mining region: 

8. Silver, arsenic, and gold.............................................. 21

ill
IV CONTENTS

FIGURES 8-11. Histograms Continued Page

9.. Barium, copper, and mercury.................................... C23

10. Manganese, molybdenum, lead, and zinc................... 25

11. Calcium, iron, magnesium, and titanium.................. 27
CONTRIBUTIONS TO ECONOMIC GEOLOGY

TERTIARY MINERALIZATION AND HYDROTHERMAL

ALTERATION IN THE STINKINGWATER MINING

REGION, PARK COUNTY, WYOMING

By FREDERICK S. FISHER

ABSTRACT

Disseminated copper-molybdenum mineralization was associated with multiple intrusions of Tertiary granodioritic to dacitic stocks in the Stinkingwater 

mining region, Wyoming. In the mineralized zone, which covers about 1 square 

mile, rock outcrops are highly fractured, bleached, and silicified, and they are 

commonly stained with iron oxide. Chalcopyrite, molybdenite, and pyrite 

occur as disseminated grains and also as coatings on fracture surfaces within 

the main area of mineralized rock. Crudely clustered around this area are 

narrow, steeply dipping veins and stringers that contain pyrite, galena, 

sphalerite, and chalcopyrite, along with the major gangue minerals quartz, 

calcite, and some dolomite. Gold occurs sporadically along the veins, and silver 

is present in galena-rich parts of the veins.

An oxidized and supergene copper-enriched zone formed during Miocene (?) 

and Pliocene (?) time across the area of primary disseminated sulfide minerals. Parts of this zone were removed by glaciation and erosion during 

Quaternary time, and therefore only remnants of the original leached mineralized cap and underlying supergene-enriched zones are present.

Hydrothermal alteration in the region resulted in a central quartz-sericitepyrite zone which contains irregular potassium-rich areas and which is surrounded by a fringe of propylitically altered rock. The intensity of alteration 

was extremely variable; however, in general it increased toward the center 

of the zone of disseminated-sulfide mineralization. Metal distributions indicate a central zone of copper-molybdenum minerals surrounded by a fringe 

area of veins that contain minerals of silver, gold, lead, zinc, arsenic, and 

possibly mercury. The elements of the fringe zone are important in prospecting for similar but "blind" disseminated-sulfide deposits elsewhere in the 

Absaroka Range.

INTRODUCTION

The Stinkingwater mining region (fig. 1) is about 50 miles 

southwest of Cody, Wyo., in the southern Absaroka Range. It lies 

in the southeast corner of the Ishawooa quadrangle (Hague, 

1899b) and within the South Absaroka Wilderness area (fig 2). 

The region is about 8 miles from the nearest road and is accessible 

on the ground only by foot or horseback.

Cl
C2 CONTRIBUTIONS TO ECONOMIC GEOLOGY

FIGURE 1. View from the top of Needle Mountain upstream (south) along 

the South Fork of the Shoshone River valley, showing the Stinkingwater 

mining region. The main area of disseminated sulfide minerals is on the 

lower slopes of Crater Mountain, in the approximate center of the area 

shown in the photograph. Landslide debris at the base of Crater Mountain 

partly covers the western side of the mineralized area. Linear features in 

the left-center of the photograph are rock masses in the Crater Mountain 

Dacite that have slumped because of gravity.

The exact time when mineralized rock in the Stinkingwater 

region was first discovered is not known. Hague (1899b) reported 

that some adits and prospect pits were present in the region in 

1893 but that they were not being worked at that time. The entire 

known history of the region involves mainly sporadic prospecting. 

Several adits and numerous prospect pits were dug at various 

times; however, there have been no known shipments of ore. In 

recent years prospecting in the region has been relatively intense, 

and some diamond drilling has been done in the area. Early prospecting in the region was undoubtedly directed at gold-silver 

minerals in veins, whereas recent work has been concentrated on 

the occurrence of disseminated copper and molybdenum of the 

porphyry type.

The present study is one of several on the Stinkingwater mining 

region on which I have reported as a result of my field investigations during 1963 and 1964. The genesis of recent gypsum in the 

region has been briefly discussed (Fisher, 1965), and the geology 

has been mapped and discussed in detail, with emphasis on the
STINKINGWATER MINING REGION, WYOMING C3

111° 110° 109°

*Cooke City MONTANA

FIGURE 2. Index map of the Absaroka volcanic field (stippled). Solid 

black, intrusive bodies. Axes and plunges of major folds shown by arrows.

petrology of the intrusive bodies in the region (Fisher, 1967). 

More recently, geochemical data and sample locality maps of the 

region have been released (Fisher, 1971).

Previous geological studies of the Stinkingwater region were 

limited to reconnaissance. Hague (1899a, p. 16) briefly discussed 

in general terms the broad geological features of the region. 

Rouse (1934, 1935) studied the volcanic rocks, physiography, and 

glacial geology in the Valley area, about 10 miles north of the 

Stinkingwater region (fig. 2). His main discussion centered on 

the extrusive rocks; however, he also presented a map showing 

the intrusive body in the Stinkingwater region. W. H. Wilson (in 

Osterwald and others, 1959, p. 121) did geological reconnaissance 

and briefly discussed the mineralized rock in the Stinkingwater 

region.

The Absaroka volcanic field is a dissected volcanic plateau composed primarily of andesitic volcanoclastic rocks, lava flows, and
C4 CONTRIBUTIONS TO ECONOMIC GEOLOGY

flow breccias that unconformably overlie folded Paleozoic and 

Mesozoic rocks (Wilson, 1964a, b; Parsons, 1958; Keefer, 1957; 

Rouse, 1940, 1937; Love, 1939; Hague, 1899b; Hague and others, 

1899). Numerous intrusive bodies, which range in composition 

from gabbro to rhyolite and in size from thin dikes to stocks a 

few square miles in area, cut the entire layered volcanic sequence 

(Ketner and others, 1966; Wilson, 1964b; Parsons, 1960; Rouse, 

1940; Larsen, 1940 ; Love, 1939; Hague, 1899b). Sulfide minerals 

are associated with several of the intrusive centers which are 

characterized by a complex igneous history and several episodes 

of intrusive activity. Chadwick (1970) suggested that the intrusive rocks in the Absaroka volcanic field could be divided into two 

northwestward-trending belts. He further suggested that the 

"igneous rocks of the Eastern Absaroka Belt are more potassic 

than those of the Western Absaroka Belt." The Stinkingwater 

region is near the south end of the western Absaroka belt.

The layered rocks of the southern Absaroka Range are flat 

lying to gently inclined. Local areas of faulting and folding, many 

of which are related to igneous activity, have been described 

(Fisher, 1967; Wilson, 1964a, b; and Love, 1939). On a regional 

scale the layered volcanic rocks of the southern Absaroka Range 

are folded into a broad shallow westward-trending syncline 

(Fisher and Ketner, 1968). The Stinkingwater region is on the 

axis and approximately in the center of the syncline.

ACKNOWLEDGMENTS

I gratefully acknowledge the assistance received during this 

study. The Wyoming Geological Survey underwrote part of the 

research expense. William H. Wilson provided considerable help 

and criticism throughout the study. The Bear Creek Mining Co. 

and Mrs. Grace Wight cooperated in many ways and released the 

diamond-drill core to me for the research. All the drill cores 

discussed in this report were from diamond drilling done by the 

Bear Creek Mining Co.

All analyses were done in U.S. Geological Survey laboratories. 

Semiquantitative spectrographic analyses were by E. E. Martinez 

and J. M. Motooka. Gold analyses were made by atomic-absorption 

spectrometry by W. L. Campbell, W. H. Ficklin, W. D. Goss, R. F. 

Hansen, Claude Huffman, Jr., H. D. King, R. W. Leinz, H. G. 

Mandeville, E. E. Martinez, S. K. McDanal, R. L. Miller, D. K. 

Parker, M. S. Rickard, T. A. Roemer, and A. J. Toevs. Mercury 

analyses were made by the vapor detector method by J. V. Desmond, R. F. Hansen, H. D. King, S. K. McDanal, and R. L. Miller.
STINKINGWATER MINING REGION, WYOMING C5 

GENERAL GEOLOGY OF THE STINKINGWATER REGION

LAYERED ROCKS

The exposed stratigraphic sequence in the Stinkingwater region 

comprises rocks that range in age from Eocene to Holocene. The 

Eocene formations are flat lying to gently dipping and consist of 

middle Eocene early basic breccia, named the Wapiti Formation 

by Nelson and Pierce (1968) ; the middle Eocene early basalt 

flows, named the Trout Peak Trachyandesite by Nelson and 

Pierce (1968); and the middle and upper Eocene Wiggins Formation. These three formations are composed primarily of andesitic 

to basaltic material and in the Stinkingwater region are mainly 

lava flows, breccias, and flow breccias with some volcanic sediments.

The Wapiti Formation is about 300-400 feet thick in the Stinkingwater region, where it is exposed in only two relatively small 

areas (fig. 3). It is flat lying and consists mainly of dark-brown 

to grayish-brown flow breccias and volcanic breccias. The fragments in the breccias are angular to subrounded, make up about 

40-65 percent of the rock, and are composed of pyroxene andesite, 

hornblende-pyroxene andesite, and andesite. Most of the fragments 

are about 1-6 inches in diameter. The groundmass of the breccias 

is composed of the same material as the fragments. It consists 

of small rock fragments, sand- and silt-sized particles, some 

tuffaceous material, and minor feldspar and pyroxene phenocrysts.

The Trout Peak Trachyandesite is well exposed in the Stinkingwater region. Individual flows within the unit commonly display 

columnar jointing, and locally the tops of some of the flows are 

vesicular. The unit is characterized by lava flows with minor 

amounts of interbedded breccia. The flows and breccias are composed of pyroxene and plagioclase basalt, andesite, and some 

hornblende andesite. In the flows, phenocrysts of plagioclase, 

pyroxene, some olivine, and, in places, hornblende are set in a 

pilotaxitic to hyalopilitic matrix which is composed of feldspar 

and ferromagnesian minerals. In hand specimen the flows appear 

as dark-gray to black aphanitic to porphyritic rock.

The Wiggins Formation comprises the bulk of the layered rock 

in the Stinkingwater region. In this report all rocks in the region 

that overlie the Trout Peak Trachyandesite are assigned to the 

Wiggins. The Wiggins Formation is extremely varied lithologically. Andesitic volcanic breccias, flow breccias, and lava flows 

are the most common rock types; however, some conglomerates 

and sandstones are also present in the sequence.

456-042 O- 72 - 2
C6 CONTRIBUTIONS TO ECONOMIC GEOLOGY

109°36'50"

Tn Needle

Mountain 

12,130
STINKINGWATER MINING REGION, WYOMING

b EXPLANATION

C7

| S

ll

Alluvium Landslide and

rock glacier

deposits

Wapiti Formation

Contact, showing dip

Dashed where approximately located,

dotted where concealed

______T______

Inferred fault 

Bar and ball on downthrown side

Fracture set

Strike and dip of beds 

Veins and stringers

Approximate area of mineralized and 

altered zone

Prospect pit

Sample locality

.S-2 

Diamond-drill hole

FIGURE 3. Geologic map of the Stinkingwater mining region, Park County, 

Wyo. Fault showing lateral movement, in section: T, toward observer; A, 

away from observer. Geology mapped in 1963-64. Base from aerial photographs taken in 1954.
C8 CONTRIBUTIONS TO ECONOMIC GEOLOGY

INTRUSIVE ROCKS

Intrusive rocks which are exposed in the Stinkingwater miningregion, and which cut all the layered rocks in the region, consist 

of two stocks, named the Needle Mountain Granodiorite and the 

Crater Mountain Dacite by Fisher (1967), and numerous dikes 

and some sills (fig. 3). At least three periods of emplacement of 

intrusive material can be demonstrated by crosscutting relationships among stocks and dikes.

Needle Mountain Granodiorite

The Needle Mountain Granodiorite, the oldest and largest intrusive body in the Stinkingwater region, is well exposed on both 

Needle and Crater Mountains (fig. 3). The contacts of the stock 

with the country rocks range from relatively narrow zones a few 

feet wide where the stock intrudes the Trout Peak Trachyandesite 

to broad zones several hundred feet wide where it cuts the Wiggins Formation. The layered rocks in the contact aureole of the 

Needle Mountain Granodiorite have been metamorphosed to the 

hornblende-hornfels facies (Fisher, 1967, p. 80).

The Needle Mountain Granodiorite is composed primarily of 

fine- to medium-grained light- to dark-gray phaneritic rocks that 

range in composition from diorite to granodiorite. The various 

rock types are similar in mineral composition, but they are different in the concentration, size, and distribution of various mineral 

components (Fisher, 1967, p. 78). Plagioclase (An35-An48 ) makes 

up about 45-60 percent of the minerals in the stock. Potassium 

feldspar (10-15 percent), quartz (10-15 percent), biotite (9-15 

percent), hornblende (7-12 percent), and minor pyroxene (<1 

percent) are the remaining principal minerals. Magnetite, apatite, 

sphene, zircon, and epidote are the common accessory minerals. 

With the exception of the area of altered and mineralized rock, 

which is discussed in a later section, the rocks of the stock are 

generally unaltered.

Crater Mountain Dacite

The Crater Mountain Dacite is exposed in two separate stocks, 

on Needle and Crater Mountains. Both stocks have been emplaced 

largely within the Needle Mountain Granodiorite. The contact 

with the granodiorite is very sharp, and the Crater Mountain 

Dacite has a well-defined fine-grained border zone about 3-15 

feet wide.

The rocks of the Crater Mountain Dacite are porphyritic lightto medium-gray rhyodacite and dacite. Phenocrysts, as much as 

10 mm (millimeters) in diameter and set in a light-gray aphanitic matrix, in most places make up 40-45 percent of the rock but
STINKINGWATER MINING REGION, WYOMING C9

in a few localities make up as much as 80-90 percent. In the finer 

grained border zones of the stocks they compose only about 10 

percent. The phenocrystic minerals consist of about 50-60 percent 

plagioclase (An40-An48 ), 20-25 percent biotite, 10 percent quartz, 

5-10 percent hornblende, and minor amounts of augite. Magnetite, 

apatite, zircon, and epidote are the common accessory minerals, 

and rutile is present in minor amounts as individual grains and as 

sagenitic inclusions in biotite.

The matrix material of the Crater Mountain Dacite is composed 

of an aggregate of small subhedral crystals of plagioclase and 

anhedral potassium feldspar and quartz. The matrix is nearly 

cryptocrystalline in the chilled border zones of the stocks. Some 

of the plagioclase microlites commonly display a preferred orientation due to flow in the border zones.

Dikes

Many dikes are related to, form a radial pattern around, and 

are apophyses of the Needle Mountain Granodiorite. Most of the 

dikes of this group are andesitic to dacitic in composition. Other 

dikes in the area, probably related to the Crater Mountain Dacite, 

are more restricted in extent and have more or less random 

trends. These dikes range in composition from porphyritic andesite to rhyodacite. A third but smaller group of dikes, mainly 

hornblende andesite and pyroxene andesite, crosscut all the other 

intrusive rocks and represent the youngest intrusive sequence 

in the region.

STRUCTURAL GEOLOGY

The layered rocks in the Stinkingwater region are flat lying to 

gently dipping. They have been domed slightly by the emplacement of the Needle Mountain Granodiorite, and the flanks of the 

dome dip from a few degrees to 10°. A few high-angle normal 

faults are in the region, and these are probably related to emplacement of the stocks and consequent readjustment of the host rocks. 

Exact displacements on these faults are difficult to determine; 

however, in some places movement of a few tens to a few hundreds of feet can be demonstrated.

Structurally the most important features involved in interpretation of the mineralizing and intrusive activity in the area 

are two fracture sets which crosscut the intrusive and layered 

rocks with generally northwest and east to northeast trends (figs. 

3, 4). These fracture sets are expressed in a variety of ways. 

Generally, the sets are represented by steeply dipping well-defined 

joints or fractures. Displacement along these fractures is unknown, but in some places movement is suggested by slickensides.
CIO CONTRIBUTIONS TO ECONOMIC GEOLOGY

Locally the fracture sets are represented by topographic depressions and (or) scarps, and the rocks in the vicinity of the scarps 

are highly fractured and in places slickensided. The fracture sets 

have controlled the drainage patterns in several places on the 

South Fork of the Shoshone River, Needle Creek, and Saddle 

Creek. Bends of 90° in streambeds are common, and in these

AREA OF FIGURE 3

FIGURE 4. Lineament map of Stinkingwater mining region and 

vicinity. Data from aerial photographs.
STINKINGWATER MINING REGION, WYOMING Cll

places the streams follow the trends of the major fracture sets 

northwest and east to northeast (fig. 4).

Drill hole S-6 (fig. 3) penetrated a fault zone along Needle 

Creek, as indicated by considerable amounts of fault gouge and 

breccia in the core between 157 feet and the bottom of the hole 

at 838 feet. The hole probably was drilled down the dip of the 

fault zone. Slickensides in the core suggest both strike-slip and 

dip-slip components of movement. This fault is probably part of 

the east- to northeast-trending set of fractures. The fault breccia 

contains some mineralized fragments and also is cut by some thin 

pyrite veins and stringers, indicating movement during a period 

of mineralization. In the Cody adit and the D-adit (fig. 3) on 

Crater Mountain, faults with strikes of about N. 55° W. are 

present. These fault zones contain mineralized rock fragments in 

the gouge and are also cut by pyrite and pyrite-quartz veinlets, 

again suggesting movement during mineralization.

On a broader scale, aerial photographs show the two major 

fracture sets in the district as well-developed lineaments that 

trend northwest and east to northeast through the district 

(fig-4).

The northwest-trending fracture set is well developed in the 

vicinity of the junction of Fall Creek with the South Fork of the 

Shoshone River. The deep canyon (fig. 5) through which the 

South Fork of the Shoshone River flows is an expression of the 

northwest fracture set. The fracture set extends northwestward 

from the canyon, out of the area of detailed mapping (fig. 4). 

Southeastward this fracture set can be traced in the field approximately to the middle of the mapped area. The northwest fracture 

set is also expressed in the area of Saddle Creek, mainly as local 

zones of stream control. The overall trends of Saddle Creek and of 

the upper part of Needle Creek probably also reflect the northwest-trending fracture set.

The east- to northeast-trending fracture set can be traced 

entirely across the mapped area. It is well developed in the southwest corner of the area (fig. 3), along the South Fork of the 

Shoshone River, and is traced eastward to an area of intensely 

shattered rock on the northwest side of Crater Mountain. Past 

the shattered zone the fracture set is traced upstream on Needle 

Creek beyond the mapped area (figs. 3, 4).

The two fracture sets represent major zones of weakness that 

probably controlled the location of the intrusive complex, which 

lies near their intersection. The intersection of these zones of 

fracturing in the underlying basement rocks probably allowed 

easier access for intrusive magmas, and the continued fault
C12 CONTRIBUTIONS TO ECONOMIC GEOLOGY

activity of these zones favored longer periods of intrusion and 

thus a more complex igneous history. The intersection of the zones 

also allowed access to higher parts of the crust for hydrothermal 

solutions.

FIGURE 5. Low-altitude oblique aerial photograph looking north down the 

South Fork of the Shoshone River. Canyon in left center of photograph is 

result of stream control by northwest-trending fracture system in the region.
STINKINGWATER MINING REGION, WYOMING C13

An area of intensely shattered rocks is present on the northwest 

side of Crater Mountain and extends to the base of the southwest 

side of Needle Mountain along Needle Creek. The area also lies 

within the main zone of mineralized rock. The shattered zone 

may be related to shrinkage of solidified parts of the intrusive 

bodies after their emplacement, as suggested by Hulin (1945). 

It is also possible that the shattered zone resulted from the intersection of the two major fracture sets.

ECONOMIC GEOLOGY

GENERAL NATURE

Disseminated copper-molybdenum mineralization occurred in an 

area, about 1 mile long by one-half mile wide in plan view, that 

extends from the northwest side of Crater Mountain (fig. 6) to 

the base of the southwest side of Needle Mountain along Needle 

Creek (figs. 3, 7). Rocks within this area consist of the Needle 

Mountain Granodiorite and the Crater Mountain Dacite. Outcrops 

of these rocks are fairly abundant; however, the lower parts of 

the mineralized area are obscured in places by landslide debris, 

soil, talus, and alluvium (figs. 1, 6, 7; Fisher, 1965, 1967). All the 

outcrops in the mineralized area are highly fractured and bleached 

and are altered to varying degrees; most of the outcrops are 

stained with iron oxide. Narrow, steeply dipping veins occur 

crudely clustered near, and in places as much as a mile away 

from, the mineralized area.

Remnants of a leached mineralized cap and an underlying 

supergene enriched zone are present on the northwest side of 

Crater Mountain. Parts of these zones were removed by Quaternary glaciation and erosion.

PRIMARY SULFIDE MINERALS AND MINERALIZED ROCK 

Disseminated Types

Chalcopyrite is the major sulfide ore mineral present in the 

area of disseminated sulfide minerals, followed in order of abundance by molybdenite and minor bornite. Pyrite occurs throughout and is much more abundant than the other sulfides. The total 

sulfide content is as much as about 10 percent. The chalcopyrite 

and molybdenite are present as disseminations throughout the host 

rocks and also as thin coatings on fracture surfaces. They also 

occur in very narrow (1-4 mm) quartz veinlets. Molybdenite coats 

fractures and occurs in veinlets more commonly than do the copper minerals.

The narrow quartz-molybdenite veinlets that occur in the area 

of disseminated sulfide minerals are very different in mineralogy

456-042 O - 72 - 3
C14 CONTRIBUTIONS TO ECONOMIC GEOLOGY

FIGURE 6. Main zone of disseminated sulfide minerals on Crater Mountain 

shown by light-colored scars in approximate center of area shown in photograph. Linear aspect of trees in center of photograph is reflection of break 

in slope near top of landslide material; below this line is landslide debris. 

View looking east.
STINKINGWATER MINING REGION, WYOMING

VTt i :w«nim "i it '

FIGURE 7. Edge of main zone of disseminated sulfide minerals on Needle 

Mountain is light area (arrow) shown in right-center of photograph. Rocks 

exposed in the mineralized area shown in the photograph are the Needle 

Mountain Granodiorite, which has been bleached a white to yellow color. 

View looking northeast.

and nature of occurrence from other veins in the region. The 

quartz-molybdenite veinlets are irregular and anastomosing, and 

they may represent some type of local replacement feature rather 

than a true fracture filling. Only locally do these veinlets appear 

to follow a definite fracture. They are composed primarily of 

quartz, but they also contain molybdenite, pyrite, and minor 

chalcopyrite.

The disseminated sulfide minerals are generally very fine 

grained. Chalcopyrite, bornite, and molybdenite grains are commonly 1 mm or less in size; pyrite grains are commonly about 

1-2 mm but are as large as 10 mm.

Vein Types

The second type of primary mineralized rock occurs as narrow, 

steeply dipping veins that are mainly in relatively unaltered 

country rocks a few hundred yards from the area of disseminated 

sulfide minerals, although in some places they occur almost a mile 

from the disseminated zone, and locally they are within the disseminated zone. In most places the veins are only 1-2 inches wide, 

but in a very few places they are as much as 1 foot wide. Most 

of the veins can be traced along strike for only very short distances, and in general the veins are poorly exposed. Galena, chalcopyrite, sphalerite, pyrite, and minor amounts of arsenopyrite 

and tetrahedrite are the major sulfide minerals in the veins.
C16 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Quartz, calcite, dolomite, and some siderite are the major gangue 

minerals. The veins are commonly composed of crustiform and 

banded material within well-defined wallrocks. In several places 

the vein material is distinctly vuggy. Little structural displacement is apparent along the veins, and most veins are considered 

to be simple fracture fillings. Very little wallrock alteration was 

associated with the veins.

SECONDARY MINERALS AND MINERALIZED ROCK 

Oxidized Rocks

A leached and oxidized cap was formed during Miocene (?) and 

Pliocene (?) time across the area of primary disseminated sulfide 

minerals. Parts of this leached cap were removed by glaciation 

and erosion during Pleistocene and Holocene time. The original 

thickness of the cap is unknown, but drill hole S-4 (fig. 3) penetrated about 109 feet of oxidized material. The area of disseminated sulfide minerals extends southeastward from drill hole S-4 

beneath Crater Mountain for an unknown distance. Rock outcrops 

on the side of Crater Mountain above drill hole S-4 are oxidized 

in places, indicating that the remaining parts of the oxidized zone 

may be a few tens of feet to several hundred feet thicker than the 

zone penetrated in drill hole S-4. The primary ore exposed by 

glaciation has undergone oxidation; however, the effects of this 

oxidation are apparently only superficial. Rocks in the oxidized 

zone are leached, silicified, and stained with iron oxides. Voids 

relict from oxidized sulfides are very common. Only minor amounts 

of chalcopyrite are still present, as well as some pyrite and molybdenite. Limonite and jarosite are relatively abundant, and minor 

amounts of malachite, azurite, and ferrimolybdite occur in a few 

localities.

Supergene Copper-Enriched Rocks

A zone of supergene copper-enriched rocks was penetrated in 

drill holes S-4 and S-7. In drill hole S-4 this zone is about 200 

feet thick, and in drill hole S-7 it is about 100 feet thick. The 

supergene copper-enriched zone probably extends southeastward 

from drill holes S-4 and S-7 beneath Crater Mountain, but its 

extent beneath Crater Mountain is unknown. This zone was probably more extensive prior to Pleistocene glaciation.

Rocks within the supergene-enriched zone are Crater Mountain 

Dacite. These rocks are altered, but relict porphyritic texture is 

commonly present. Chalcopyrite, molybdenite, and pyrite are the 

major sulfides in the rock. Sooty chalcocite is present as very small 

disseminations and as rims around grains of chalcopyrite, indicating somewhat incomplete replacement. Occasionally chalcocite 

rims and replaces pyrite.
STINKINGWATER MINING REGION, WYOMING C17

ALTERED ROCK

Several types of hydrothermally altered rock are present in the 

district. They may be broadly grouped, following Creasey (1959, 

and in Titley and Hicks, 1966), as propylitic, potassic, and quartzsericite types. Many of the altered rocks, however, do not conveniently fit into these groupings because of the presence of 

metastable or unstable mineral phases or because of the lack of 

diagnostic minerals in the sampled rocks.

Propylitization of both the intrusive rocks and the layered volcanic rocks was common throughout the district. The intensity of 

propylitization was extremely variable, but in general it increased 

toward the main area of disseminated sulfide minerals; and 

intensely propylitized rock forms a fringe around the area of disseminated sulfide minerals. Where propylitic alteration was intense, several mineralogical changes from the fresh granodiorite 

and dacite are evident in thin section. Hornblende and biotite were 

altered to chlorite, sericite, magnetite, and some calcite. Plagioclase was altered to sericite, calcite, epidote, and some albite (?). 

Some of the larger plagioclase crystals were altered to quartz, 

calcite, and epidote. Chlorite, pyrite, calcite, and epidote are generally abundant in the propylitized rocks, scattered through the 

matrix in small grains (1-2 mm) and occasionally in larger clots. 

Sericite, quartz, rutile, and leucoxene are also present in variable 

amounts. The presence of sagenitic rutile in chlorite and of sericitic pseudomorphs in altered rocks is indicative of the former 

presence of biotite in the rock. In weakly altered dacite, sagenitic 

rutile, generally altered to leucoxene, is common in biotite phenocrysts. Quartz phenocrysts and the potassium feldspar in the rock 

were relatively unaffected by the propylitization.

The quartz-sericite-pyrite alteration-mineral assemblage, the 

most characteristic of the region, is widespread in the central 

part of the main mineralized area on the northwest side of Crater 

Mountain and along Needle Creek at the base of the southwest 

side of Needle Mountain. Rocks within this area were highly 

altered, bleached, and silicified. In most places the original porphyritic texture is preserved by sericitic pseudomorphs; however, in 

some places the rocks were totally recrystallized, and all original 

texture was erased. The sericite is present both as very fine 

grained flakes in the matrix and as irregular clots depicting former phenocrysts. Quartz is very abundant as small ragged grains 

in the matrix. Secondary quartz rims some original quartz phenocrysts, and quartz veinlets are common. Pyrite is present as fine 

disseminations in the matrix and also as larger grains (10 mm) 

scattered through the rock. It also occurs with quartz in thin
CIS CONTRIBUTIONS TO ECONOMIC GEOLOGY

irregular veinlets. Commonly the wallrock next to the veinlets 

shows abundant sericite. Anhydrite in quartz veinlets and as scattered grains occurs in the lower parts of the drill core from the 

main zone of mineralized rock. Higher in the holes the anhydrite 

was altered to gypsum.

Potassic alteration in irregular ill-defined zones took place 

within the quartz-sericite-pyrite areas on the northwest side of 

Crater Mountain. This type of alteration was characterized by 

the development of secondary biotite. In general the rocks in the 

potassic assemblage are highly altered; however, in most places 

the original texture of the rocks is preserved by sericitic pseudomorphs after plagioclase and by the original quartz phenocrysts. 

Sericite, quartz, biotite, and remnant plagioclase are the most 

abundant minerals in the areas where potassic alteration occurred. 

The plagioclase phenocrysts have all undergone some degree of 

alteration to sericite. Quartz phenocrysts are commonly rimmed 

by secondary quartz, and secondary quartz along with flakes of 

sericite and secondary biotite compose the matrix material of 

these rocks.

Within areas of supergene enrichment some clay minerals are 

present in the rocks. These may be the product of supergene 

processes, for they are apparently restricted to the zone of supergene enrichment and thus possibly represent some form of supergene argillic alteration. The clay minerals are relatively sparse in 

the sampled rocks, and they normally occur as cloudy brown areas 

in the vicinity of plagioclase phenocrysts.

In general there appears to be much overlap between the different alteration zones in the region. The presence of chlorite 

and carbonates in scattered localities within rocks of the quartzsericite assemblage indicates superposition of the propylitic and 

quartz-sericite assemblages. This relationship also suggests that 

the rocks failed to reach equilibrium during the quartz-sericite 

phase of alteration. In total aspect, the pattern of altered rock 

in the region is a central quartz-sericite-pyrite zone with included 

irregular areas of potassium-rich rock. Surrounding the central 

quartz-sericite-pyrite zone is a fringe of propylitically altered 

rock. The intensity of alteration in the region was extremely 

variable, although generally it increased toward the center of 

disseminated sulfide minerals.

GEOCHEMICAL SAMPLING

To determine the chemical character of mineralized rock in the 

Stinkingwater region, 650 rock samples were analyzed by semi-
STINKINGWATER MINING REGION, WYOMING C19

quantitative spectrographic methods. Most of the samples were 

taken from outcrops and from 3,503 feet of diamond-drill core; 

a few were taken from adits in the area. Geochemical summaries 

of selected elements are presented in figures 8-11; the raw data 

for all samples used in figures 8-11 were reported previously 

(Fisher, 1971). The rocks were classified as unaltered, altered, 

mineralized, vein material, oxidized, supergene, and protore. The 

unaltered rocks were collected chiefly from outcrops outside the 

main area of mineralized rock. These rocks contain little or no 

disseminated pyrite or other sulfides and no sulfide veinlets. They 

appear fresh in hand specimen and microscopically show no minerals that may be attributed to the effects of hydrothermal alteration. The unaltered rocks are composed mainly of the Needle 

Mountain Granodiorite and the Crater Mountain Dacite, but they 

also include some layered rocks. The unaltered rocks were collected not only for comparison with altered or mineralized rocks, 

but also to help determine the background content of selected 

elements in the Stinkingwater region.

The altered rocks represent any rock material which has been 

affected by one or more types of alteration. These rocks commonly 

contain considerable amounts of pyrite and in some places minor 

amounts of other ore minerals. They were collected from outcrops, 

drill cores, and mine dumps, primarily in and near the main area 

of mineralized rock, and they consist of the Needle Mountain 

Granodiorite, Crater Mountain Dacite, and a few specimens of 

layered rock. The altered rocks provide information regarding the 

distribution of selected elements and the zonational characteristics 

of the alteration and mineralization that took place in the region.

The mineralized rocks contain visible ore minerals in significant 

amounts; samples collected from vein deposits were excluded from 

this classification. The division between mineralized samples and 

altered samples is somewhat arbitrary (based primarily on visual 

estimates of ore minerals, excluding pyrite) ; however, some broad 

differences between the two groups can be seen for selected elements. Rocks in the mineralized group were collected from outcrops, drill cores, and mine dumps in the main area of mineralized 

rock and are composed of the Needle Mountain Granodiorite and 

the Crater Mountain Dacite. Though they provide data as to the 

character and intensity of mineralization that took place, and help 

to show the extent of mineralized material, the data are not 

adequate for calculating possible ore reserves.

The vein-material rock samples consist of both gangue and ore 

minerals which occur primarily as fracture-filling veins in and
C20 CONTRIBUTIONS TO ECONOMIC GEOLOGY

11

8 -

« E

- "S

(t-S) 3H010Hd Ufr) 3N39H3dflS 

IN30M3d Nl '

(U) Q3ZIQIXO
Looked for but not detected 

in 6 percent of samples

Looked for but not detected 

in 94 percent of samples

Looked for but not detected 

in 98 percent of samples

Looked for but not detected 

in 100 percent of samples

ToTsl ooloololoool 

o ooooooo

 I r-t CM CO

LOG CONCENTRATION, IN PARTS PER M

FIGURE 8. Histograms showing concentrations of silver, arsenic, and gold 

region. Arrow indicates geometric mean. Type of samples indicated a

samples analyzed.
C22 CONTRIBUTIONS TO ECONOMIC GEOLOGY

3H010ad (Ifr) 3N39H3dflS

!N30N3d Nl '

(ID Q3ZIQIXO (ZW NI3A
LOG CONCENTRATION, IN PARTS PER MIL

FIGURE 9. Histograms showing concentrations of barium, copper, and 

water mining region. Arrow indicates geometric mean. Type of sam

theses is number of samples analyzed.
C24 CONTRIBUTIONS TO ECONOMIC GEOLOGY

o o o o o oo o o o ooo o o ooo o o o o 

(t-5) 3H010Hd (It) 3N39H3dflS (II) 03ZIOIXO (Zfr) NI3A 

!N30H3d Nl 'AON3n03Hd
LOG CONCENTRATION, IN PARTS PER MI

FIGURE 10. Histograms showing concentrations of manganese, molybdenum, 

mining region. Arrow indicates geometric mean. Type of samples indica

samples analyzed.
C26 CONTRIBUTIONS TO ECONOMIC GEOLOGY

(W

iN30a3d Nl 'A
o o o o o o o

LOG CONCENTRATION, IN PARTS PER MI

FIGURE 11. Histograms showing concentrations of calcium, iron, magnesium

mining region. Arrow indicates geometric mean. Type of samples indica

samples analyzed.
C28 CONTRIBUTIONS TO ECONOMIC GEOLOGY

near the main area of mineralized rock. These samples, taken from 

outcrops and mine dumps, were collected to examine metal distributions in the area and to compare vein-type material with the 

disseminated sulfides in the region. They, too, are inadequate for 

estimating possible ore reserves.

The oxidized-, supergene-, and protore-classified samples are all 

Crater Mountain Dacite from drill cores S-4 and S-7 (fig. 3) and 

were taken to examine altered and mineralized rock at depth in 

the area of disseminated sulfides on Crater Mountain. The classification is based on the presence or absence of chalcocite, together 

with the position of the samples in the drill core.

The oxidized rocks are bleached, stained, and devoid of chalcocite. Most of the chalcopyrite and some of the pyrite have been 

removed by leaching. Some open spaces and voids relict from oxidized sulfides are lined with iron oxide. These rocks are from the 

upper 109 feet of drill core S-4.

The supergene rocks were collected from 109 to 310 feet in 

drill core S-4 and from 130 to 227 feet in drill core S-7. These 

rocks all contain some very fine grained chalcocite, which is the 

main criterion for classifying them in the supergene group.

The protore rocks are from 310 to 501 feet in drill core S-4 

and from 227 to 500 feet in drill core S-7. These samples are 

from below the zone of supergene enrichment and are devoid of 

chalcocite.

METAL DISTRIBUTIONS

The intensity of primary mineralization that occurred in the 

region is readily seen by comparing histograms and geometric 

means of unaltered rocks, veins, and protore (figs. 8-11). Geometric means were calculated by using a method developed by 

Cohen (1959, 1961) for censored distributions. The geometric 

mean is an estimate of central tendency of a frequency distribution that is roughly symmetrical on a log scale, and it is therefore 

useful to describe and characterize the abundance of a given element in an individual sample group (Miesch, 1963, 1967).

The following elements were looked for and either were not 

found or were found in amounts normal for the rock type sampled 

and thus were not included in the statistical summary: B, Be, Co, 

Cr, La, Nb, Ni, Sc, Sn, Sr, V, W, Y, Zr.

The character of metal distributions between the veins and the 

area of disseminated-mineralized rock is indicated by histograms 

and geometric means for the vein and protore groups. These show 

that the samples from veins are enriched in silver, arsenic, gold, 

mercury, lead, and zinc as compared with the samples of protore. 

Bismuth, cadmium, and antimony, which are not shown in figures
STINKINGWATER MINING REGION, WYOMING C29

8-11, are restricted to the veins. The bismuth is generally found 

in samples from galena-rich parts of the veins, and the cadmium 

values are invariably associated with sphalerite. Copper and molybdenum are more abundant in the protore group of samples 

than in the vein group. The distribution of the veins around the 

area of disseminated sulfide minerals and the relative enrichment 

of the previously mentioned elements in the veins give a broad 

zonational pattern to the metal distribution in the region.

The behavior of selected metals and other elements in the oxidized and supergene zones is shown by figures 8-11. Copper, as 

expected, shows the most marked enrichment in samples from the 

supergene zone. Some copper, however, is still present in the 

oxidized zone. Gold and silver may have been slightly enriched 

by the oxidation-supergene process, but more samples are needed 

to provide a better basis for comparison. Barium, molybdenum, 

iron, titanium, mercury, and magnesium show no apparent enrichment as a result of oxidation and supergene processes. The slight 

depletion of mercury in oxidized rocks probably represents a loss 

of mercury vapor to the atmosphere. Calcium and manganese both 

apparently are progressively depleted by the weathering process 

and show a continued decrease in abundance from protore to 

supergene to oxidized material. Lead appears to be slightly enriched in the oxidized rocks, which may be reflecting the development of some lead oxide minerals. It should be reemphasized that 

the small number of samples of oxidized material could bias the 

results.

Broad gains and losses of various elements in unaltered and 

altered rocks, indicating the overall characteristics of the alteration in the region, can be seen in figures 8-11. The mineralized 

group of samples should also be considered here for comparative 

purposes, because all the mineralized samples are normally more 

altered than even the altered group. No attempt has been made to 

compare chemical changes among the different alteration assemblages. Silver, copper, and molybdenum all show slight increases, 

and arsenic and zinc may have increased some with progressive 

alteration. Calcium, iron, and manganese are all depleted to some 

extent in the altered and mineralized groups. Magnesium, titanium, and barium show slight depletion with increasing alteration. 

The concentration of lead appears to have been unchanged by the 

alteration process. Potassium was not analyzed for; however, it 

probably would show some increase with progressive alteration as 

suggested mineralogically by the development of secondary biotite 

and-by sodium cobaltinitrite staining, which indicates potassium 

enrichment next to quartz-pyrite veinlets.
C30 CONTRIBUTIONS TO ECONOMIC GEOLOGY

The metal zonation in the region is characterized by a central 

copper-molybdenum zone surrounded by a fringe of silver, gold, 

lead, zinc, arsenic, and possibly mercury. In terms of actual tonnage present, probably more gold and silver are concentrated in 

the lower grade disseminated-sulfide zone than in the higher grade 

border-zone veins. Thus, gold and silver could also be grouped in 

the assemblage that resulted from central-zone mineralization. In 

terms of prospecting, however, it is more desirable to group the 

gold and silver in the assemblage that resulted from the fringe 

mineralization because their higher grade in the fringe veins 

makes them more amenable to discovery. In addition, the wider 

distribution of the veins provides a somewhat larger target for 

prospecting, even though the veins aggregate a much 'smaller 

volume than does the disseminated-mineralized rock.

PROSPECTING GUIDES 

Local

Metal zonation in terms of areal occurrence now known provides 

only a framework for prospecting. Several additional guides 

should be made available for further prospecting in the Stinkingwater region. First, a detailed outcrop map should be prepared 

of the main area of altered and disseminated-mineralized rock to 

provide more information on the distribution of and relation 

between the hydrothermal alteration types and mineralization. 

Particular attention should be paid to both mineral and metal 

zonations, because these may further define the most favorable 

targets for prospecting within the region.

Second, additional diamond drilling should be done in the area 

southeast of drill holes S-4 and S-7, higher on the side of Crater 

Mountain. The detailed mapping suggested in the preceding paragraph should be a help in locating the best positions for holes 

that will delineate the extent of mineralized rock beneath Crater 

Mountain. Some diamond drilling in this area has already been 

completed, but the results of this work are not available.

Third, the possible presence of replacement mineral deposits in 

sedimentary rocks at depth should be investigated. Replacement 

ores have been found in sedimentary rocks in the Cooke City district farther north in the Absaroka Range (Levering, 1930). That 

sedimentary rocks may occur relatively close to the surface in the 

Stinkingwater region is suggested by the fact that Paleozoic sandstone and limestone crop out in an area about 4 miles southwest 

of the region, along the east side of the South Fork of the Shoshone River. Regional mapping and structural interpretations
STINKINGWATER MINING REGION, WYOMING C31

should provide estimates of the depths of sedimentary rocks in 

the Stinkingwater region. If the depths are reasonable, then diamond drilling for replacement mineral deposits may be feasible.

Regional

The mineralized rocks in the Stinkingwater region are intimately associated with an igneous center which had a relatively 

long and intense history of intrusive and probably extrusive activity. Examination of other intrusive bodies in the Absaroka Range 

suggests that plutons with only one phase of emplacement of 

intrusive material are devoid of mineralized rock, whereas all the 

known mineral deposits in the Absaroka Range are associated 

with areas of complex multiple intrusive and probably extrusive 

activity (Pedersen, 1968; Fisher, 1967; Dreier, 1967; Wilson, 

1964a; Rubel, 1964; Parsons, 1937; Levering, 1930).

The Stinkingwater region is located on a roughly defined northwest-trending belt of intrusive bodies. This belt probably represents a zone of weakness or fracturing in the underlying basement 

rocks. In the Stinkingwater region, northwest-trending fracture 

zones are intersected by other fracture zones which trend northeast to east. Similar relations may be observed in other mineralized districts in the Absaroka Range. The mineral deposits in the 

Absaroka Range thus may be situated above areas where a northwest-trending basement weakness is intersected by northeast- to 

east-trending fracture zones. Regional mapping of lineaments on 

aerial photographs may outline broad structural patterns from 

which favorable targets for further study may be located.

The streams in the vicinity of the Stinkingwater region are 

transporting small amounts of gold (1/2-1 part per million in pan 

concentrates of stream alluvium) that was probably derived from 

the vein system clustered around the area of disseminated sulfide 

minerals. The veins extend several hundred to a few thousand feet 

outward and upward from the area of disseminated sulfide minerals. Effects of wallrock alteration near the veins are generally 

lacking, and the veins are very inconspicuous in outcrop. Similar 

vein systems are associated with other mineralized areas in the 

Absaroka Range. The location of the noneconomic veins may suggest potential target areas for further exploration for blind porphyry copper-type deposits in the Absaroka Range. The areas of 

vein outcrop can probably be located by chemical analyses for gold 

in pan concentrates taken from stream sediments.

Some mercury is present in the Stinkingwater region, both in 

the disseminated-mineralized rock and in the surrounding border-
C32 CONTRIBUTIONS TO ECONOMIC GEOLOGY

zone veins. Selected target areas for mercury could be further 

investigated by methods suggested by McCarthy, Vaughn, Learned, 

and Meuschke (1969).

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STINKINGWATER MINING REGION, WYOMING C33

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V. S. GOVERNMENT PRINTING OFFICE : 1972 O - 456-042