Geology of the Vienna Mineralized Area, 

Blaine and Camas Counties, Idaho 

By J. Brian Mahoney and Michael C. Horn 

Prepared in cooperation with the Idaho Geological Survey, 

Idaho State University, and the University of Idaho 

Bulletin 2064-DD 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior

Gale A. Norton, Secretary 

U.S. Geological Survey

Charles G. Groat, Director 

U.S. Geological Survey, Reston, Virginia: 2005 

Posted online April 2005, version 1.0

This publication is only available online at:

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endorsement by the U.S. Government.

Although this report is in the public domain, it contains copyrighted materials that are noted in the text. 

Permission to reproduce those items must be secured from the individual copyright owners.

Suggested citation:

Mahoney, J.B., and Horn, M.C., 2005, Geology of the Vienna mineralized area, Blaine and Camas Counties, Idaho: U.S. 

Geology Survey Bulletin 2064–DD, 9 p.
iii 

Contents

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

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

Historical Perspective .................................................................................... 2 

Previous Work ............................................................................................. 2 

Geologic Setting .......................................................................................... 2 

Lithology ............................................................................................. 2 

Structure ............................................................................................. 4 

Mineral Deposits .......................................................................................... 4 

Quartz-Silver-Sulfide Ribbon Veins ............................................................... 6 

Quartz-Sericite-Pyrite-Galena Veins ............................................................ 6 

Genesis of Mineral Deposits ..................................................................... 7 

Acknowledgments ....................................................................................... 8 

References Cited .......................................................................................... 8 

Figures

1. Map showing location of Vienna mineralized area, Blaine and Camas Counties, 

Idaho .......................................................................................... 1 

2. Generalized geologic map of the Vienna mineralized area, Blaine and Camas 

Counties, Idaho .............................................................................. 3 

3. Photograph of silver-sulfide ribbon ore, Vienna mineralized area ..................... 6 

4. Schematic diagram of mineralized shear zone typical of Vienna mineralized area ... 6 

5. Photograph of mineralized shear zone in the Pilgrim mine, Vienna mineralized area 7 

6. Photograph of brecciated quartz and silver-sulfide ribbon veins in an 

oxidized quartz-sericite-pyrite-galena matrix ............................................. 7 

Table

1. Analytical data from selected samples of the Vienna mineralized area, Blaine 

and Camas Counties, Idaho .................................................................. 5 
iv 

Metric Conversion Factors

Multiply By To obtain 

tons 1.016 metric tons

short tons 0.907 metric tons

troy ounces 31.103 grams

ounces 28.35 grams
Geology of the Vienna Mineralized Area, Blaine and

Camas Counties, Idaho

By J. Brian Mahoney and Michael C. Horn 

Abstract 

The Vienna mineralized area of south-central Idaho was 

an important silver-lead-producing district in the late 1800s 

and has intermittently produced lead, silver, zinc, copper, 

and gold since that time. The district is underlain by biotite 

granodiorite of the Cretaceous Idaho batholith, and all mineral 

deposits are hosted by the biotite granodiorite. The granodiorite intrudes Paleozoic sedimentary rocks of the Sun Valley 

Group, is overlain by rocks of the Eocene Challis Volcanic 

Group, and is cut by numerous northeast-trending Eocene 

faults and dikes. 

Two mineralogically and texturally distinct vein types are 

Federspiel and others, 1987, 1992). The majority of mining 

activity and ore production has been from the headwaters of 

Smiley and Beaver Creeks, in the Vienna and Sawtooth mining 

districts, although a number of small mines and prospects are 

in the surrounding drainages (Umpleby, 1915; Van Noy and 

others, 1986; Federspiel and others, 1987). The level of erosion may be an important factor to the discovery of economic 

deposits because most successful workings are in deep glacial 

cirques that face northeast.

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present in a northwest- and east-trending conjugate shear-zone 

system. The shear zones postdate granodiorite emplacement 

and joint formation, but predate Eocene fault and dike forma- ���

tion. Ribbon veins consist of alternating bands of massive 

vein quartz and silver-sulfide (proustite and pyrargyrite) 

mineral stringers. The ribbon veins were sheared and brecciated during multiple phases of injection of mineralizing fluids. 

A quartz-sericite-pyrite-galena vein system was subsequently 

emplaced in the brecciated shear zones. Both vein systems are ������

believed to be the product of mesothermal, multiphase miner- ����������������

alization. K-Ar dating of shear-zone sericite indicates that sericitization occurred at 80.7±2.8 Ma; thus mineralization in the 

Vienna mineralized area probably is Late Cretaceous in age. 

Introduction 

The Vienna mineralized area of south-central Idaho is at 

the southwest end of the Stanley Basin, approximately 60 km 

north of Ketchum, Idaho (fig. 1). The area is in the northern 

Smoky Mountains, at the south end of the Sawtooth Mountains, in Blaine and Camas Counties, Idaho. It includes the 

drainages of Smiley, Frenchman, Johnson, Emma, and Beaver 

Creeks and part of the headwaters of Alturas Lake Creek (Jake 

and Eureka Gulches). 

The Vienna mineralized area, as described in this paper, 

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encompasses parts of the Vienna, Sawtooth, Skeleton Creek, Figure 1. Location of Vienna mineralized area, Blaine and 

and Big Smoky mining districts (Van Noy and others, 1986; Camas Counties, Idaho. 
2 Geology of the Vienna Mineralized Area, Idaho 

Historical Perspective 

The Vienna and Sawtooth mining districts were discovered in 1879, and the majority of mining activity occurred 

between 1880 and 1888. The largest producers were the Webfoot, Vienna, Silver King, and Pilgrim mines (fig. 2). Approximately two million dollars (historical prices) of silver ore was 

removed from the districts during this initial period of activity 

(Umpleby, 1915); significant production has not occurred 

since that time. Exploration has been intermittent since the 

late 1800s, including brief flurries of activity in the 1930s 

and early 1940s and in the late 1960s to early 1970s, when 79 

claims were filed in the Vienna mining district (Van Noy and 

others, 1986). A small amount of production occurred in the 

early 1980s when material from existing mine dumps was processed by a custom mill along Warm Springs Creek, approximately 70 km south of the Vienna mining district. The Vienna 

and Sawtooth mining districts currently (1992) contain 55 

patented claims and 170 current claims (Federspiel and others, 

1992). Exploration, including a drilling program, was being 

conducted in 1992 at the Webfoot property in the headwaters 

of Smiley Creek; production is anticipated but is contingent on 

precious-metal prices.

Previous Work 

The Vienna mining district and adjoining districts were

important metal-producing areas in south-central Idaho during

the late 1800s and have been the subject of numerous geologic

investigations. Umpleby (1915) compiled a brief reconnaissance report of the district during mapping of the Sawtooth

30-minute quadrangle. Ballard (1922) discussed the district in

a detailed report on the ore deposits of the Alturas 30-minute

quadrangle. Ross (1927) conducted a detailed investigation

of the surficial and subsurface geology of the Vienna mining

district. Shannon (1971) mapped the district in detail, and

conducted an extensive geochemical survey (stream sediment)

in order to evaluate the use of geochemistry as an exploration

tool. There are also numerous unpublished mining company

reports of the area. The Vienna mineralized area was discussed

as part of the northern addition to the South BoiseYuba study

area (Federspiel and others, 1987). Mahoney and Horn (1989)

reviewed the geologic setting and mineral deposits of the Vienna

mineralized area, and the present report is a reevaluation of

findings presented in that report. Federspiel and others (1992)

evaluated mines and prospects in the area during a mineral

resource investigation of the Smoky Mountains.

Geologic Setting 

Lithology 

The Vienna mineralized area is on the southeast edge of

the Atlanta lobe of the Cretaceous Idaho batholith (Kiilsgaard, Lewis, and Bennett, 2001). Biotite granodiorite to

quartz monzonite of the batholith underlies most of the area.

Mineral deposits in the area, with the exception of two small

sediment-hosted skarn deposits west of Smiley Creek (Ura

group and P&D claims) and one sediment-hosted replacement and polymetallic vein deposit (Mountain King claim),

are hosted by the biotite granodiorite (fig. 2).

The biotite granodiorite is medium to coarse grained and 

composed of quartz, plagioclase, microcline, and biotite, and 

accessory magnetite, zircon and sphene. It is locally porphyritic, containing alkali feldspar phenocrysts as long as 8 cm; 

the porphyritic nature of the biotite granodiorite is believed to 

be the result of potassium metasomatism (Johnson and others, 

1988). Cataclastic textures are visible in thin section, and in 

outcrop the biotite granodiorite locally displays an incipient 

gneissic texture, particularly northwest of Beaver Creek (fig. 

2). Thin (2–20 cm), randomly oriented aplite and pegmatite 

dikes locally cut the granodiorite. The origin of the aplite and 

pegmatite dikes is uncertain: they may be a late-stage differentiate of the Cretaceous batholith. It is also possible that they 

are related to the Tertiary biotite (pink) granite of the Sawtooth batholith, exposed 8 km to the north, or to the Prairie 

Creek stock, a smaller Tertiary biotite (pink) granite intrusion, 

exposed 5 km to the south. 

The biotite granodiorite intrudes micritic sandstone,

siltstone, and sandy limestone of the Middle Pennsylvanian

to Lower Permian Grand Prize Formation of the Sun Valley

Group in the east half of the Vienna mineralized area (Mahoney

and others, 1991) (fig. 2). The Grand Prize Formation in this

area has been contact metamorphosed to calc-silicate hornfels and locally contains abundant wollastonite, diopside, and

tremolite. The metamorphosed Grand Prize Formation hosts

antimony-, silver-, and tungsten-rich skarn deposits (Ura group

and P&D claims) on the north edge of the Vienna mineralized

area, west of Smiley Creek, and silver-lead polymetallic veins

and replacement deposits on Mule Creek, in the southern part

of the area (fig. 2). Small roof pendants of sedimentary rock

are exposed along ridges in the northeastern part of the mineralized area.

Andesitic to dacitic lavas and associated volcaniclastic

sedimentary rocks of the Eocene Challis Volcanic Group

unconformably overlie both the Cretaceous granodiorite and

the Pennsylvanian-Permian Grand Prize Formation in the

eastern part of the mineralized area (fig. 2). The volcanic

rocks comprise a section more than 500 m thick of andesitic to dacitic flow rocks, tuff breccias, and volcanogenic

Figure 2 (following page). Generalized geology of the Vienna 

mineralized area, Blaine and Camas Counties, Idaho. 
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4 Geology of the Vienna Mineralized Area, Idaho 

sandstone and siltstone. The volcanic rocks are locally in

fault contact with the granodiorite where they are preserved

in downthrown fault blocks adjacent to north- and northeasttrending normal faults.

Northeast-trending Eocene dacite porphyry dikes cut the 

biotite granodiorite throughout the Vienna mineralized area. 

The pervasive northeast trend and the spatial relationship 

between northeast-trending faults and dacite porphyry dikes 

suggest that dike emplacement was structurally controlled. 

Chilled contacts within the dikes and minor alteration zones in 

the country rock characterize the intrusive contact between the 

dike rocks and the granodiorite, but no evidence of mineralization associated with Eocene dike emplacement was identified. 

Eocene dacite porphyry dikes reportedly cut mineralized veins 

at depth, although we could not confirm this.

Thin (0.2–0.4 m) lamprophyric dikes of uncertain age 

locally cut the biotite granodiorite. These dikes are inferred 

to be Cretaceous in age elsewhere in the region, although 

no absolute dates exist. Lamprophyric dikes apparently cut 

mineralized veins in the Webfoot mine (“diabase” of Ballard, 

1922; Ross, 1927), but on the surface the highly altered nature 

of the dikes makes the exact relationship between these dikes 

and mineralized structures ambiguous.

Structure 

The Cretaceous biotite granodiorite contains a prominent joint system that is exposed in the headwaters of Beaver 

Creek. The dominant joint set strikes N. 35°–50° W. and 

dips steeply to the north. This orientation roughly parallels 

the east edge of the batholith, suggesting that the dominant 

joint system represents contraction joints parallel with the 

batholith margin. The geometry of the joint set varies markedly, however, from planar, parallel joint sets to curvilinear 

joint patterns. Previous workers have suggested that mineral 

veins in the Vienna mineralized area are confined to the joint 

sets (for example, Ballard, 1922), but it is now recognized that 

the vein system is subparallel with the joint sets and clearly 

postdates them. Joint sets are locally mineralized adjacent to 

crosscutting subparallel mineralized shear zones.

Mineralized rock in the Vienna mineralized area occurs 

along shear zones that cut the granodiorite. The shear zones 

approximate a conjugate fracture set in which one set trends 

about N. 60° W. and the second set trends east-west. The 

shear zones are generally near vertical or dip steeply to the 

north. On the surface, the shear zones are iron oxide stained 

(limonite) and locally brecciated; below ground, breccia is 

common within shear zones, and intense chloritic and sericitic 

alteration extends for 1–3 m from the shear zones. Evidence 

of shearing and brecciation is more pronounced along the easttrending shear zones (Ballard, 1922). Both sets of shear zones 

are mineralized, although the east-trending set is normally of 

higher grade. Ore shoots are present locally at shear zonejoint and shear zone–shear zone intersections. Vein material is 

commonly sheared and brecciated, and small offsets from one 

to tens of meters of veins attest to syntectonic vein emplacement (figs. 4, 5).

The most pronounced structures in the Vienna mineralized area are northeast-trending (N. 50°–75° E.) normal

faults that have displacements ranging from tens to hundreds

of meters. These high-angle normal faults cut the Paleozoic

Grand Prize Formation, the Cretaceous biotite granodiorite, and the Eocene Challis Volcanic Group (fig. 2) and are

believed to be associated with the Eocene trans-Challis fault

system (Bennett, 1986). The faults apparently controlled

emplacement of the Eocene dacite porphyry dikes and must

therefore be coeval with or slightly older than the Eocene

dikes. The brittle nature, prominent surficial expression, large

offset, lack of hydrothermal alteration, and lateral extent of

these normal faults make them different from the more subdued mineralized shear zones previously discussed. There

is a strong correlation between the trend of the normal faults

and the location of mines and prospects in the Vienna mineralized area, and the faults may structurally control the location

of mineral deposits. Three large economic deposits in the

Vienna mineralized area (Webfoot, Solace, and Vienna mines)

are apparently in a horst block bounded by Eocene normal

faults at the head of Smiley Creek; deeper, more highly mineralized levels of the biotite granodiorite may have been uplifted

along these Eocene structures. The relationship at depth

between the northeast-trending Eocene faults and mineralized

structures is unknown.

A prominent north-trending normal fault downdrops 

andesitic flow rocks of the Challis Volcanic Group against 

Cretaceous biotite granodiorite west of Smiley Creek (fig. 

2). The fault is almost vertical and has an offset of least 500 

m, based on the thickness of the volcanic rocks on the downthrown eastern block of the fault. The fault apparently cuts 

shear zones in the granodiorite and is believed to be associated 

with basin and range extension. This north-trending normal 

fault is subparallel with the Sawtooth fault to the north, which 

is the eastern bounding fault of the Sawtooth batholith horst 

block, and may be an extension or splay to the Sawtooth fault 

(Tschanz and others, 1986).

Mineral Deposits 

Two distinct types of mineralized veins are present in the 

Vienna mineralized area: shear-zone-hosted silver-sulfide ribbon veins and shear-zone-hosted quartz-sericite-pyrite-galena 

veins. The veins are spatially associated but are mineralogically and texturally distinct. Crosscutting relations indicate 

that formation of the ribbon veins preceded emplacement of 

the quartz-sericite-pyrite-galena veins. Samples obtained from 

the principal mines in the mineralized area (Pilgrim, Webfoot, 

Solace, Vienna) were assayed; results are listed in table 1.

Both types of veins in the Vienna mineralized area are

classified in the regional descriptive model of Worl and

Johnson (1995) as polymetallic quartz veins and lodes; the
Table 1. Analytical data from selected samples of the Vienna mineralized area, Blaine and Camas Counties, Idaho.[Selected assay results from numerous mines and prospects throughout the Vienna mineralized area are listed. Samples are grouped by property and listed by Proprietary restrictions prevent the disclosure of individual sample locations. Assays were selected specifically to provide a representative description of minin the area. Sample types: Rock samples were fire assayed for gold and silver and analyzed for a 15-element or 12-element geochemical suite using atomic or inductively coupled plasma (ICP) spectrometry. Gold analysis by fire assay with atomic absorption finish or by ICP of one assay ton of material; silver anassay; copper, lead, zinc analysis by ICP. All samples analyzed by the U.S. Bureau of Mines. Samples stored at U.S. Bureau of Mines, Western Field OperatSpokane, Wash.]

Sample Gold Silver Copper Lead Zinc Sample Drainage De

Number (ounces per ton) (ounces per ton) (percent) (percent) (percent) type 

30363744374630332997371824742475249824902497165716762469168916962472

 0.365

0.1350.1160.142

0.050.1270.1270.1180.8610.1690.0890.2820.1110.080.0540.0790.115

 0.10

7.6

1.520.29

12.83

7.62

29.656.1

0.65

47.5

9.05

18.1

9.356.213.223.823.95

 0.0002

0.0460.002

0.00130.0095

0.0170.052

0.0585

0.0030.0510.001

0.0285

0.1280.002

0.0067

0.008

0.0053

0.0007

0.220

0.00360.0012

0.0610.115

1.05

0.2460

0.0150.086

1.10

0.0315

0.2550.211

0.03950.1625

0.026

 0.028

0.800.01

0.0060.0780.0650.120

0.1

0.0060.2260.3950.048

0.24

0.0050.0140.0220.015

ChipSelectChipChipSelectSelectChipChipSelectChipChipGrabGrabSelectGrabGrabSelect

Beaver CreekBeaver CreekBeaver CreekBeaver Creek Beaver Creek Beaver CreekSmiley CreekSmiley CreekSmiley CreekSmiley CreekSmiley CreekSmiley CreekSmiley CreekSmiley CreekSmiley CreekSmiley CreekSmiley Creek

Vein

StocBandBandMill SheaBandBandSheaSheaSheaDumDum

Quar

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Quar
6 Geology of the Vienna Mineralized Area, Idaho 

silver-sulfide ribbon veins belong to the silver variety and

the quartz-sericite-pyrite-galena veins to the base-metal

variety. Similar crosscutting relationships between these two

varieties are documented elsewhere in the region (Worl and

Johnson, 1995).

Quartz-Silver-Sulfide Ribbon Veins 

The quartz-silver-sulfide ribbon veins consist of roughly

defined bands of massive white vein quartz and aphanitic

dark-gray silver-sulfide minerals, primarily pyrargyrite and

proustite (figs. 3, 4). Aphanitic minerals are present as thin

(<0.5 cm) stringers in thicker (≈0.7–2 cm) white quartz

veinlets, which are present as anastomosing ribbons separated

by elongate blebs of highly altered wallrock. Tetrahedrite,

ruby silver, argentian stibnite, and argentite (“black metal”)

are locally abundant (Ballard, 1922; Shannon, 1971). The

arsenic and antimony contents of the deposits vary considerably across the district (Shannon, 1971; Federspiel and

others, 1992) but are highest in the Silver King mine, which

represents the deepest level of exposure in the district (fig. 2).

Pyrite and arsenopyrite are common in the altered wallrock

and in the gangue of shear zones but are notably absent in the

competent ribbon veins.

The ribbon veins pinch and swell along strike and locally 

form tabular ore lenses. Veins range in width from 0.1 to 2 m, 

and alteration zones extend from 1 to 3 m from the veins. The 

ribbon vein system is parallel to subparallel with shear zones; 

wallrock fractures are commonly parallel with the ribbon 

veins and are best developed in the east-trending shear zones. 

Brecciation and folding of the ribbon veins are common (fig. 

5). Alteration adjacent to the veins consists of intense sericitization close to the veins and chloritization and kaolinitization 

near the outer edges of the altered zones to a distance of 1–3 m 

from the veins. 

Figure 3. Photograph of silver-sulfide ribbon ore, Vienna 

mineralized area, Idaho. Note sericitic and chloritic alteration 

surrounding silver sulfide and quartz veinlets. 

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Figure 4. Schematic diagram of mineralized shear zone typical 

of Vienna mineralized area, Idaho. Note brecciated ribbon veins 

overprinted by quartz-sericite-pyrite-galena veins and alteration 

halos surrounding shear zone. Host rock is biotite granodiorite 

country rock. 

The ribbon veins represent a hypogene mineralization 

event characterized by repeated pulses of quartz deposition 

and deposition of aphanitic sulfide minerals, as indicated 

by the development of ribbon structures and the presence of 

vein-parallel inclusions of intensely altered wallrock (J.S. Lee, 

unpub. data). Sulfide mineral paragenesis and the primary 

alteration features associated with the ribbon veins are difficult 

to determine because of subsequent shearing and brecciation 

during late-stage and post-mineralization tectonism.

Quartz-Sericite-Pyrite-Galena Veins 

The quartz-sericite-pyrite-galena vein system consists 

of galena, sphalerite, and arsenopyrite and minor stibnite 

and argentite in a quartz, sericite, siderite, and pyrite gangue 

(fig. 6). The arsenopyrite contains minor amounts of gold 

(Shannon, 1971), and disseminated gold is presented in the 

alteration zones (J.S. Lee, unpub. data). Pyrite, and to a lesser 

extent, arsenopyrite are disseminated throughout the shear 

zone and surrounding altered wallrock. The sulfide minerals 

are present as irregular patches within the intensely sheared 

gouge zone, and open-space-filling textures are locally evident. Sulfide minerals locally form massive lenses as long as 

3 m, particularly near shear zone–joint and shear zone–shear 

zone intersections. The gangue material consists primarily of 

irregular, elongated grains of quartz and abundant sericite and 

siderite. Andorite and other sulfosalts are locally important 

(J.S. Lee, unpub. data).

Sericite from a northwest-trending shear zone in the

headwaters of Beaver Creek yielded a K-Ar date of 80.7±2.8

Ma that indicates mineralization in the Vienna mineralized area
7 

Figure 5. Photograph of mineralized shear zone in the Pilgrim 

mine, Vienna mineralized area, Idaho. Note folded and brecciated 

ribbon veins. Hammer head shown for scale. 

to be Late Cretaceous (D. Runkle and J. Herckel, University

of British Columbia Geochronology Lab, unpub. data). This

date agrees with field relations, which indicate that mineralization occurred following emplacement of the Cretaceous biotite

granodiorite and development of the joint system, yet prior

to intrusion of the crosscutting Eocene dacite porphyry dikes.

This age of mineralization corresponds with the earliest Late

Cretaceous–Paleocene mineralization episode suggested by

Snee and Kunk (1989).

Quartz-sericite-pyrite-galena veins are present in the 

same shear zones as the ribbon veins and significantly overprint the early phase of mineralization. The ribbon veins are 

strongly sheared and brecciated, although small unsheared 

segments of the ribbon veins are present as inclusions within 

the intensely sheared and mineralized gouge zone (figs. 4, 5). 

The gouge zone contains abundant sericite and minor chlorite, 

and the wallrock is chloritized and sericitized as far as 1–3 m 

from the shear zone. Quartz-sericite-pyrite-galena mineralized 

rock is present along both shear-zone systems in the Vienna 

mineralized area, and ore shoots of this assemblage locally 

are present at shear-zone intersections. Minor mineralized 

rock also is present along joint planes near joint–shear zone 

intersections.

Genesis of Mineral Deposits 

The two vein types in the Vienna mineralized area are

mineralogically and texturally distinct but are spatially and

genetically related. The quartz-sericite-pyrite-galena veins postdate the ribbon veins, as shown by (1) brecciation and shearing

of the ribbon ore within the highly sericitized and mineralized

shear zones and (2) dissemination of pyrite and arsenopyrite

throughout the gouge and alteration zones but absence of those

minerals in the more competent (impermeable) ribbon veins.

Ribbon veins are concentrated near the center of shear zones,

whereas the quartz-sericite-pyrite-galena veins are present

Mineral Deposits 

throughout the gouge and alteration zones, as well as in ore

shoots at shear zone and shear zone–joint intersections.

Mineralization in the Vienna mineralized area is believed 

to be the result of multiphase injection of mineralizing fluids 

along a conjugate shear system during the Late Cretaceous. 

Structural control on the conjugate shear set is unclear; the 

shear zones may be the result of hydrostatic stress associated 

with the late-stage hydrothermal system or may have formed 

from post-intrusion, pre-mineralization tectonic stress. 

The two vein systems probably formed as the result 

of changes in hydrostatic pressure, temperature, and fluid 

composition during a mesothermal mineralization event of 

multiple phases. This event was characterized by emplacement and continued brecciation of the ribbon ore, followed by 

deposition of the quartz-sericite-pyrite-galena system along 

the same shear zones. The ribbon vein system is mesothermal 

in origin and was emplaced during several stages of quartz 

injection, sericitization, and mineralization, as suggested by 

the ribbon nature of the veins, alternating brecciation and ribbon vein formation, and inclusion of altered wallrock within 

the shear zones. The quartz-sericite-pyrite-galena system was 

subsequently deposited along the sheared and brecciated shear 

zones. This vein system displays open-space textures characteristic of an epithermal origin, but such textures also develop 

in mesothermal systems in void spaces created by brecciation 

and at the intersections of shear zones and shear zone and 

joints (C. Godwin, consulting geologist, oral commun., 1990). 

The paragenetic sequence is believed to progress from 

deposition of silver-sulfide minerals to deposition of galena, 

sphalerite, arsenopyrite, and pyrite, and probably is the result 

of changes in ore fluid composition related to depletion and 

the interaction between evolving ore fluid and granodiorite 

wallrock. The metal-bearing fluids are probably a late-stage 

hydrothermal system associated with Cretaceous biotite 

granodiorite; however, lead-isotope analysis suggests that the 

Figure 6. Photograph of brecciated quartz and silver sulfide 

ribbon veins in an oxidized quartz-sericite-pyrite-galena matrix, 

Vienna mineralized area, Idaho. 
8 Geology of the Vienna Mineralized Area, Idaho 

ultimate source of the metals may be related to Precambrian 

upper crustal rocks (Sanford and Wooden, 1995).

Crosscutting field relations (dikes and faults cutting 

veins), a lack of associated silver-lead deposits in adjacent 

Eocene rocks, the mesothermal nature of the ribbon veins, 

and K-Ar dating of shear-zone sericite suggest that mineralized rock in the Vienna mineralized area is primarily hosted 

by biotite granodiorite of the Cretaceous Idaho batholith and 

is of Late Cretaceous age. Eocene emplacement of northeasttrending faults and dacite porphyry dikes may have caused 

minor remobilization of the Cretaceous ore minerals but did 

not contribute new ore material. Mines and prospects of the 

mineralized area are in uplifted fault blocks and in deeply 

eroded glacial cirques, suggesting that mineralization is more 

prevalent at depth. Mineralogical zonation of the deposits of 

the Vienna mineralized area is suggested by a higher proportion of argentian stibnite and galena in deeper workings (such 

as Silver King). Additional mineral deposits may be present 

at depth in the Vienna mineralized area, particularly in areas 

characterized by higher level surficial exposures, such as the 

headwaters of Johnson Creek and Emma Gulch.

Acknowledgments 

We thank Earl Waite, Jr., and the Rothschild Corporation 

for access to the Webfoot mine and for the numerous discussions about the area. Frank Federspiel of the U.S. Bureau of 

Mines provided the sericite sample and is greatly appreciated 

for his discussions and a review of the manuscript. The assistance of Jody Robb and the ladies at the Smiley Creek Lodge 

is gratefully acknowledged. We thank Dita Runkle and Joe 

Herckel of the University of British Columbia Geochronology 

Laboratory for providing the critical sericite age date. This 

manuscript benefited from reviews by Frank Federspiel, Gary 

Winkler, Jeff Jones, Ron Statelmayer, and Ron Worl.

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