U.S. GEOLOGICAL SURVEY CIRCULAR 1077 

Mineral Resource Assessment of the 

Dillon 1 ox 2° Quadrangle, 

Idaho and Montana 
AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY 

Instructions on ordering publications of the U.S. Geological Survey, along with the last offerings, are given in the current-year issues of 

the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior 

to the cmTent year are listed in the most recent annual "Price and Availability List." Publications that are listed in various U.S. Geological 

Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. 

Prices of repm1s released to the open files are given in the listing "U.S. Geological Survey Open-File Reports," updated monthly, which 

is for sale in microfiche from the U.S. Geological Survey Books and Open-File Reports Sales, Box 25425, Denver, CO 80225. 

Order U.S. Geological Survey publications by mail or over the counter from the offices given below. 

BY MAIL 

Books 

Professional Papers, Bulletins, Water-Supply Papers, Techniques of Water-Resources Investigations, Circulars, publications 

of general interest (such as leaflets, pamphlets, booklets), single 

copies of periodicals (Earthquakes & Volcanoes, Preliminary Determination of Epicenters), and some miscellaneous reports, including some of the foregoing series that have gone out of print at the 

Superintendent of Documents, are obtainable by mail from 

U.S. Geological Survey, Books and Open-File Report Sales 

Box 25425 

Denver, CO 80225 

Subscriptions to periodicals (Earthquakes & Volcanoes and 

Preliminary Determination of Epicenters) can be obtained ONLY 

from 

Superintendent of Documents 

U.S. Government Printing Office 

Washington, DC 20402 

(Check or money order must be payable to Superintendent of 

Documents.) 

Maps 

For maps, address mail order to 

U.S. Geological Survey, Map Sales 

Box 25286 

Denver, CO 80225 

Residents of Alaska may order maps from 

U.S. Geological Survey, Map Sales 

101 Twelfth Ave., Box 12 

Fairbanks, AK 99701 

OVER THE COUNTER 

Books 

Books of the U.S. Geological Survey are available over the 

counter at the following U.S. Geological Survey offices, all of 

which are authorized agents of the Superintendent of Documents. 

• ANCHORAGE, Alaska-4230 University Dr., Rm. 101 

• ANCHORAGE, Alaska-605 West 4th Ave., Rm G-84 

• DENVER, Colorado-Federal Bldg., Rm. 169, 1961 Stout St. 

• LAKEWOOD, Colorado-Federal Center, Bldg. 810 

• MENLO PARK, California-Bldg. 3, Rm. 3128,345 

Middlefield Rd. · 

• RESTON, Virginia-National Center, Rm. 1C402, 12201 

Sunrise Valley Dr. 

• SALT LAKE CITY, Utah-Federal Bldg., Rm. 8105, 125 South 

State St. 

• SAN FRANCISCO, California-Customhouse, Rm. 504, 555 

Battery St. 

• SPOKANE, Washington-U.S. Courthouse, Rm. 678, West 

920 Riverside Ave. 

• WASHINGTON, D.C.-U.S. Department of the Interior Bldg., 

Rm. 2650, 1849 C St., NW. 

Maps 

Maps may be purchased over the counter at the U.S. Geological Survey offices where books are sold (all addresses in above list) 

and at the following Geological Survey offices: 

• ROLLA, Missouri-1400 Independence Rd. 

• FAIRBANKS, Alaska-New Federal Building, 101 Twelfth 

Ave. 
Mineral Resource Assessment of the 

Dillon 1 o x 2° Quadrangle, 

Idaho and Montana 

By ROBERT C. PEARSON, CHARLES M. TRAUTWEIN, 

EDWARD T. RUPPEL, WILLIAM F. HANNA, 

LAWRENCE C. ROWAN, JEFFREY 5. LOEN, 

and BYRON R. BERGER 

Background information to accompany a folio of 

geological, geophysical, remote sensing, and 

mineral resource maps-a part of the Conterminious 

United States Mineral Assessment Program (CUSMAP) 

U.S. GEOLOGICAL SURVEY CIRCULAR 1077 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1992 

Free on application to 

Book and Open-File Report Sales 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Mineral resource assessment of the Dillon 1 <?<2° quadrangle, Idaho and Montana I 

by Robert C. Pearson ... [et al.]. 

p. em.- (U.S. Geological Survey Circular 1077) 

Includes bibliographical references. 

Supt. of Docs. no.: 119.4/2:1077 

1. Mines and mineral resources-Idaho. 2. Mines and mineral resourcesMontana. I. Pearson, Robert Carl, 1926- . II. Series. 

TN24.12M53 199291-46339 

553'.09786-dc20CIP 

91-46339 

CIP 
CONTENTS 

Abstract 1 

Purpose of the study 1 

Location and geography 1 

Previous studies 3 

Present investigations 3 

Acknowledgments 3 

Products and results of the Dillon CUSMAP project 3 

Geology 3 

Aeromagnetic and gravity studies 4 

Remote sensing 7 

Limonite and hydrothermally altered rocks 7 

Lineaments and linear features 7 

Geochemistry 7 

Mines and prospects 8 

Mineral resource assessment 8 

Assessment of deposits of Precambrian age 9 

Assessment of vein and replacement deposits of base and precious 

metals 10 

Assessment of placer gold and silver deposits 10 

Assessment of porphyry deposits of copper, molybdenum, and gold and skarn 

deposits of tungsten, copper, silver, and gold 10 

Conclusions 11 

Selected bibliography 11 

FIGURES 

1. Index map showing location of Dillon 1 °X2° quadrangle 1 

2. Index map of Dillon 1 °X2° quadrangle showing geographic features 2 

3. Tectonic province map of Dillon 1 °X2° quadrangle 5 

4. Generalized geologic map of the Dillon 1 °X2° quadrangle 6 

TABLES 

1. Maps of the Dillon quadrangle CUSMAP folio 4 

2. Mineral-deposit types in the Dillon 1 °X2° quadrangle 8 

Content' Ill 

Mineral Resource Assessment of the 

Dillon 1 o x 2° Quadrangle, Idaho and Montana 

By Robert C. Pearson, Charles M. Trautwein, Edward T. Ruppel, 

William F. Hanna, Lawrence C. Rowan, JeffreyS. Loen, and Byron R. Berger 

ABSTRACT 

The Dillon 1 "x2° quadrangle in southwestern Montana 

and east-central Idaho was investigated as part of the U.S. Geological Survey's Conterminous United States Mineral Assessment Program (CUSMAP) to determine its mineral resource 

potential. An interdisciplinary study was made of geology, 

geochemistry, geophysics (gravity and aeromagnetics), remote 

sensing, and mineral deposits. The results of those studies, as 

well as mineral resource assessment of numerous mineraldeposit types, are published separately as a folio of maps. This 

report summarizes the studies, provides background information on them, and presents a selected bibliography relevant to 

the geology and mineral resources of the quadrangle. 

The quadrangle contains large resources of gold and substantial resources of talc and chlorite, all of which were being 

mined in the 1980's and early 1990's. Submarginal resources 

of molybdenum, copper, tungsten, and iron range from moderately large to large. Other commodities that may be present in 

significant amounts are chromite, lead, zinc, silver, barite, zeolite minerals, and various nonmetallic metamorphic minerals. 

PURPOSE OF THE STUDY 

The studies of geology and mineral resources that are 

summarized in this report were made largely under the Conterminous United States Mineral Assessment Program 

(CUSMAP), the chief purpose of which is to determine the 

mineral resource potential of selected quadrangles by means 

of a multidisciplinary approach. CUSMAP is intended to 

provide information on mineral resources to assist Federal, 

State, and local governments in formulating minerals policy 

and land-use policy and to provide information to the general 

public for use in mineral exploration and development. This 

report gives general information on the Dillon quadrangle 

and describes and summarizes a series of reports that present 

pertinent features of geology, geochemistry, geophysics, and 

mineral resources. These reports are mainly in the form of 

maps at a scale of 1:250,000. Mineral commodities 

Manuscript approved for publication November 26, 1991. 

considered to be beyond the scope of this project are coal, oil 

and gas, thorium, uranium, phosphate, and geothermal 

energy. 

LOCATION AND GEOGRAPHY 

The studies described herein were made within the Dillon 

1 °X2° quadrangle in southwestern Montana and east-central 

Idaho, a region that encompasses about 6,820 mi2 (fig. 1). 

The quadrangle is bounded by latitude 45° and 46° north and 

longitude 112° and 114 o west. The Montana part of the quadrangle is drained largely by the Jefferson River and its tributaries, most notably the Big Hole, the Beaverhead, and the 

Ruby Rivers (fig. 2). Small areas along the northern edge of 

the quadrangle are drained by tributaries of the Clark Fork 

River, and the northwestern comer is drained by the Bitterroot River-both of these rivers are on the western side of 

the Continental Divide. The Idaho part of the quadrangle is 

in the Salmon River drainage, which is also west of the 

Divide. 

Figure 1. Index map showing location of Dillon 1 "x2° quadrangle and nearby quadrangles. CUSMAP quadrangles patterned. 

Location and Geography 
11 4' 00' 

46'00' 

a: 

w 

> 

a: 

50 MILES 

50 KILOMETERS 

8 

QUADRANGLE LOCATION 

11 2'00' 

:ll 

)> 

z 

Gl 

m 

Figure 2. Index map of Dillon 1 °X2° quadrangle showing geographic features. 

The Montana part of the quadrangle contains many small 

mountain ranges-the Tobacco Root Mountains, Ruby 

Range, Blacktail Mountains, Highland Mountains, Pioneer 

Mountains, and Anaconda Range. The Continental Divide, 

on the crest of the Beaverhead Mountains in the western part 

of the quadrangle, forms the boundary between Idaho and 

Montana. In Idaho, parts of the Lemhi Range and Salmon 

River Mountains are present. The mountain ranges, especially in Montana, are separated by broad valleys that are 

used mostly as irrigated crop or pasture land. 

The lowest altitude within the quadrangle is about 3,600 

ft, where the Salmon River leaves the quadrangle at its westem edge, and the highest point is 11,154 ft, on Mt. Tweedy 

in the Pioneer Mountains, very near the center of the quadrangle. 

The northern boundary of the quadrangle passes through 

Butte, Montana, the largest city in the immediate area. 

Salmon, Idaho, and Dillon, Montana, are other small cities, 

and ten or so other communities are scattered through the 

quadrangle. The largest of these other towns are Whitehall, 

Twin Bridges, Sheridan, and Wisdom, all in Montana 

Much of the mountainous terrain is National Forest. 

Together, the Beaverhead, Deer Lodge, Bitterroot, and 

Salmon National Forests occupy more than 50 percent of the 

area of the quadrangle. Lands administered by U.S. Bureau 

of Land Management or owned by the two States comprise 

additional sizable tracts, leaving about one-quarter of the 

land of the quadrangle under private ownership. 

The principal industry in the area is agriculture. Cattle 

ranching and growing of forage and small-grain crops predominate. Tourism is a significant industry that has grown 

steadily just as logging has steadily declined. The mining 

industry increased appreciably in importance during the 

1980's as a result of an increase in gold mining. 

Mining of talc in the Ruby and Greenhorn Ranges was 

the principal mineral industry activity in the Dillon 

2 Mineral Resource Assessment, Dillon 1 •x2• Quad., Idaho and Montana 
quadrangle in the 1970's and early 1980's, but as the price of 

gold rose, more emphasis was placed on its exploration and 

development. In 1990, the largest mining operation in the 

quadrangle, as well as the largest gold mine in the State of 

Montana, was the Golden Sunlight mine near Whitehall (fig. 

2). The Beal mine, in the north-central part of the quadrangle (fig. 2), is also a large-tonnage gold mine that began 

operations in 1988. In addition, several smaller mining operations have produced ore in recent years, and exploration 

continues, chiefly for precious metals and talc. 

PREVIOUS STUDIES 

Geologic studies in the Dillon quadrangle began in the 

early part of the twentieth century. Umpleby (1913) prepared a geologic map of the Idaho part of the quadrangle and 

reported on its mining districts. Winchell (1914) made a cursory but extremely valuable investigation of all mining districts in the eastern half of the quadrangle and adjacent areas 

and commented on their geologic setting. Those early studies were followed by more detailed studies of individual 

mining districts: Shenon (1931) in the Bannack, Blue Wing, 

and Argenta districts; Karlstrom (1948) in the Hecla district; 

Sahinen (1939, 1950) in the Rochester, Silver Star, and several other districts in the Highland Mountains; Johns (1961) 

in the southern Tidal Wave district; Burger (1967) in the 

Sheridan district; and Alexander (1955) and Lindquist 

(1966) in the Whitehall district. Important compilations of 

information on mines and geology are those by Geach 

(1972), Roby and others (1960), and Tansley and others 

(1933). A very significant report on the history of mining in 

Beaverhead County, Montana, is by Sassman (1941). 

A selected bibliography, which is applicable to the geology and mineral deposits of the quadrangle, is at the end of 

this report, and a more extensive bibliography is given in 

Loen and Pearson (1989). 

PRESENT INVESTIGATIONS 

Geologic mapping in connection with the Dillon CUSMAP project began in 1977 in the southwestern part of the 

quadrangle by E.T. Ruppel and D.A. Lopez. New geologic 

mapping and field checking continued intermittently 

through 1988. In 1978, a series of mineral resource assessments of Wilderness Study Areas was begun by the U.S. 

Geological Survey (O'Neill, 1983a, 1983b; O'Neill and others, 1983; Berger and others, 1983; Elliott and others, 1985; 

Pearson and Zen, 1985; Pearson and others, 1987; Pearson 

and others, 1988; Smedes and others, 1980; and Tysdal and 

others, 1987a, 1987b). These studies, which continued 

through much of the 1980's, provided information important 

to the objectives of the CUSMAP project. The wilderness 

studies produced critical new geologic mapping, stream-sediment and rock geochemical data, and aeromagnetic and 

ground gravity measurements. Examination and sampling 

of mining districts and individual mineral deposits and prospects began in 1981 by R.C. Pearson and B.R. Berger. A literature search and a compilation of information on mines 

and prospects was made by J.S. Loen and R.C. Pearson; data 

were compiled through 1984. Aeromagnetic coverage of the 

quadrangle was completed in 1981 (U.S. Geological Survey, 

1975, 1979, 1981a, 1981b), and gravity measurements were 

completed in 1986 (Hassemer and others, 1986; Kaufmann 

and others, 1983). Results of analysis of remote-sensing 

data to locate hydrothermally altered rocks and linear features in rocks (Segal and Rowan, 1989; Purdy and Rowan, 

1990) were field checked to a limited extent by D.B. Segal 

and L.C. Rowan. Digitizing and computer analysis of the 

data and maps were done at the U.S. Geological Survey's 

EROS Data Center, Sioux Falls, South Dakota, under the 

direction of C.M. Trautwein. 

ACKNOWLEDGMENTS 

Of the many persons who contributed significantly to this 

project, the authors of several of the principal reports-in 

addition to those of the present report-should be mentioned 

expressly: J.H. Hassemer, H.L. James, S.K. Jenson, H.E. 

Kaufmann, D.A. Lopez, S.H. Moll, J.M. O'Neill, T. L. 

Purdy, B.D. Ruppel, and D.B. Segal. Others who have contributed directly to the completion of the project are N .R. 

Desmarais, J.L. Dwyer, D.L. Hanneman, W.C. Pecora, L.W. 

Snee, and E-an Zen. 

PRODUCTS AND RESULTS OF THE 

DILLON CUSMAP PROJECT 

The principal reports resulting from the Dillon CUSMAP 

project are listed in table 1 and discussed below, together 

with a summary of their contents. 

Geology 

(Open-File Report 83-168; Map 1-1803-H} 

The geologic map of the Dillon quadrangle includes earlier mapping that was field checked and compiled from 

many sources and much new mapping in the central and 

western parts of the quadrangle. A preliminary version of 

the map, U.S. Geological Survey Open-File Report 83-168 

(Ruppel and others, 1983), was used in interpreting and 

depicting the remote sensing and geophysical data and as a 

source of data for mineral resource assessment. A 

Products and Results of the Dillon CUSMAP Project 3 
Table 1. Maps of the Dillon quadrangle CUSMAP folio 

[See Selected Bibliography for complete references. OF, U.S. Geological Survey Open-File Report; I, U.S. 

Geological Survey Miscellaneous Investigations Series Map] 

Map No. Subject Authors 

OF-83-168 Preliminary geologic map Ruppel, O'Neill, and Lopez 

I-1803-A Limonite and hydrothermal alteration Segal and Rowan 

I-1803-B Analysis of linear features Purdy and Rowan 

I-1803-C Mines and prospects Loen and Pearson 

I-1803-D Mineral assessment of Precambrian deposits Pearson and others 

I-1803-E Mineral assessment of vein and replacement deposits Pearson and others 

I-1803-F Mineral assessment of placer deposits Pearson and others 

I-1803-G Mineral assessment of skarn and porphyry deposits Pearson and others 

I-1803-H Final geologic map Ruppel, O'Neill, and Lopez 

I-1803-I Aeromagnetics and Bouguer gravity Hanna and others 

generalized version of the map has been used as a geologic 

base for other maps in the Dillon quadrangle folio. The 

Open-File map is superseded by U.S. Geological Survey 

Miscellaneous Investigations Series Map I-1803-H (Ruppel 

and others, in press), which is the final geologic map, printed 

in color. 

The rocks of the Dillon region differ in each of the tectonic provinces shown on figure 3. Those in the eastern, foreland part of the quadrangle include a sequence about 11 ,500 

ft thick of marine and nonmarine sedimentary rocks of Paleozoic and Mesozoic age that were deposited on the Archean 

and Early Proterozoic crystalline metamorphic rocks of the 

North American craton (fig. 4). Sedimentary rocks in the 

frontal fold and thrust zone and in the Grasshopper thrust 

plate (fig. 3) are similar to those on the craton, except that the 

Grasshopper plate includes a sequence of Middle Proterozoic sandstone and quartzite more than 23,000 ft thick. The 

Medicine Lodge thrust plate, in the western part of the quadrangle (fig. 3), is made up of sedimentary rocks of Middle 

Proterozoic age, mainly quartzite and siltite that differ radically and abruptly from those on the Grasshopper plate. The 

Medicine Lodge plate is above the Middle Proterozoic Y ellowjacket Formation, which is inferred to be autochthonous. 

The thrust faulting that defines the different tectonic 

provinces probably began, perhaps some distance west of the 

quadrangle, about 90-100 Ma (mid Cretaceous) and was 

completed by about 65 Ma (latest Cretaceous to early Paleocene). Most of the thrusting had ended when the first of the 

widespread complex bodies of granitic rocks, many of 

batholithic dimensions, were intruded at about 80 Ma. 

Thrusting, probably minor, also took place at about 77 Ma 

and at about 65-70 Ma. The earliest thrust faulting was 

accompanied by foreland deformation that formed a synclinal moat in front of the thrust belt and, farther east, a broad, 

anticlinal foreland uplift (Blacktail-Snowcrest uplift). The 

moat was partly filled with clastic sediments derived both 

from the advancing thrust plates and from erosion that 

exposed Archean rocks in the core of the foreland uplift. 

Volcanic rocks, also of Late Cretaceous age, were erupted in 

the northeastern and south-central parts of the quadrangle. 

In Eocene and Oligocene time, broad blankets of tuffaceous sediments were deposited in shallow basins, and 

volcanic rocks were erupted from many local centers. The 

present deep basins of the region started to form in the late 

Oligocene, and tuffaceous sedimentary deposits continued to 

accumulate in them throughout Miocene and Pliocene time. 

These basins and their flanking mountain blocks are 

bounded by steeply dipping faults, many of Archean ancestry, that have moved recurrently throughout the Cenozoic 

and continue today to control the rhombic pattern of faults in 

the region. 

Thus, the present basins and ranges are products of faulting and mountain building that have been almost continuous 

through much of the Cenozoic. The ranges have been steepened and their height accentuated through sculpturing by 

repeated alpine glaciation, and mountain valleys commonly 

are choked with moraines. Glacial outwash gravels are 

widespread in the Big Hole, a Tertiary basin in the western 

and north-central parts of the quadrangle (fig. 2). In other 

parts of the region, glaciers contributed gravels to broad alluvial fans and to the alluvial fill that continues to accumulate 

along most stream valleys. 

Aeromagnetic and Gravity Studies 

(Map 1-1803-0 

Aeromagnetic and gravity maps were prepared from data 

gathered in several separate surveys that range widely in 

scale, age, and quality. These interpretations are being 

released as map 1-1803-1 (Hanna and others, in press). 

The interpretation of aeromagnetic and gravity data was 

enhanced by laboratory measurement of rock density and 

magnetization on 291 samples. 

4 Mineral Resource Assessment, Dillon 1 °x2° Quad., Idaho and Montana 
114°00' 

46°00' 

45°00' 

o. 10 

10 20 

113°00' 112°00' 

20 30 MILES 

30 40 KILOMETERS 

EXPlANATION 

Craton 

Frontal fold and thrust zone 

Grasshopper thrust plate 

Medicine lodge thrust plate 

Autochthonous Yellowjacket Formation 

Steep fault 

........___.... Thrust fault-Dash.ed where inferred; 

queried where doubtful 

Figure 3. Tectonic province map of Dillon 1 "x2° quadrangle, Idaho and Montana; modified from Ruppel and Lopez (1984). 

Igneous rocks and surficial deposits not shown. 

The aeromagnetic maps were derived from data collected 

in five surveys flown at different times, flight heights, flightline spacings, and other specifications (Johnson and others, 

1965; U.S. Geological Survey, 1975, 1979, 198la, 1981b). 

The individual surveys were combined photographically to 

produce a single map that contained all of the detail of the 

original surveys. The data of the original surveys were also 

merged mathematically to produce another map with uniform parameters. Both maps, as well as other derivative 

maps, were used to interpret the distribution and magnetization of various rock bodies and structures that, in tum, were 

used in the interpretation of mineral resource potential. 

Gravity measurements were made at about 2,500 stations 

in the quadrangle. About 2,050 of these were made by 

Harold E. Kaufmann, Scott B. Sorensen, and Kelley J. 

O'Neill (Kaufmann and others, 1983). Additional measureProducts and Results of the Dillon CUSMAP Project S 
~ 

"' = 

~ 

~ ~ 

9 = 

~ ;;;; 

~ 

6 Mineral Resource Assessment, Dillon 1 •x2• Quad., Idaho and Montana 
EXPlANATION 

Quaternary and Tertiary surficial deposits 

Tertiary basin·fill 

Tertiary sedimentary rocks 

Tertiary and Cretaceous volcanic rocks 

Tertiary and Cretaceous intrusive rocks 

Mesozoic sedimentary rocks 

Paleozoic sedimentary rocks 

Proterozoic sedimentary rocks 

Archean metamorphic rocks 

---Contact 

---·· ··Fault-Dashed where inferred: dotted 

where concealed 

• • • Thrust fault-Sawteeth on upper plate 

Figure 4 (above and facing page). Generalized geologic map of the Dillon 1 °X2° quadrangle, Idaho and Montana (adapted from 

Ruppel and others, 1983, by Purdy and Rowan, 1990). 

ments were made by Jerry H. Hassemer (Hassemer and 

others, 1986) and Byron D. Ruppel (unpub. data). 

Remote Sensing 

Measurements of reflected and emitted electromagnetic 

radiation from the surface of the earth were recorded by 

means of satellite and airplane. These measurements are 

referred to as remote-sensing data. Interpretation of these 

data is presented in maps I-1803-A and I-1803-B. 

Limonite and Hydrothermally Altered Rocks 

(Map 1-1803-A) 

Map I-1803-A portrays the areal distribution of iron 

hydroxides (commonly called limonite) that stain the surface 

of certain rocks. Limonite in some environments is significant in mineral resource investigations because it is a common product of weathering of minerals, typically iron 

sulfides, that are associated with metallic mineral deposits. 

The sulfides break down to form limonite, whose existence 

can be recognized by combining measurements of certain 

spectral wavelength bands obtained from satellite imagery. 

Limonite can form in ways other than weathering of ironbearing sulfides associated with mineral deposits, and therefore, many limonite anomalies were examined on the ground 

to attempt to determine those which might have mineraldeposit significance. Coniferous forests and other types of 

vegetation, which are extensive in the Dillon quadrangle, 

conceal the limonite to a variable degree. 

The presence of limonite, based on its characteristic 

spectral reflectance, can be approximated by determining 

ratios of spectral bands using Landsat multispectral scanner 

(MSS) images. Bands used are 4, 5, 6, and 7, which correspond, respectively, to wavelengths of 0.5-0.6 ~m. 0.6-0.7 

~m. 0.7-0.8 ~m. and 0.8-1. wm. The ratios of bands 4:5 and 

6:7 and the compound ratio (4:5):(6:7) were found to be useful in identifying limonite in the Dillon quadrangle. In part, 

map I-1803-A distinguishes between anomalies that are 

thought to be caused by mineralization from those of other 

origins. 

Lineaments and Linear Features 

(Map 1-1803-B) 

Map I-1803-B reports the results of analysis of linear 

features observed on digitally processed MSS images; both 

color-infrared composite images and black-and-white 

images of MSS bands 5 and 7 are analyzed. In addition, linear features were mapped on synthetic-aperture radar 

images. Digitizing and statistical analysis of this data 

revealed clusters of linear features and certain azimuthal 

maxima. The clusters; some of which are aligned, are 

defined here as lineaments. 

The linear features and lineaments derived from them are 

regarded as having structural significance and, as such, many 

of them represent faults, joints, and other geologic features. 

A statistical analysis of the association oflimonite anomalies, certain linear features, and lineaments with areas of 

mineralization in the Dillon quadrangle indicates a positive 

correlation. 

Geochemistry 

Several geochemical studies within the Dillon quadrangle were used in the mineral resource assessment (Berger, 

Breit, and others, 1979; Berger, VanderVoort, and others, 

1979; Broxton, 1979; Elliott and others, 1985; LeathamGoldfarb and others, 1986; O'Neill, 1983b; O'Neill and 

others, 1983; Pearson and others, 1987, 1988). Geochemical 

data on mineralized rock samples were interpreted by statistical techniques in order to relate suites of elements to various mineral-deposit types. Using the suites of elements thus 

determined, the database of Broxton (1979kdited and 

augmented by additional geochemical analyses by the U.S. 

Geological Survey-was utilized in the mineral resource 

assessment. The samples of Broxton (1979) were streamserument samples that broadly covered the entire 

quadrangle. 

Products and Results of the Dillon CUSMAP Project 7 
Mines and Prospects 

(Map 1-1803-C) 

The Dillon quadrangle occupies a part of the northern 

Rocky Mountains long known for its abundance and variety 

of mineral deposits. The locations of mines and prospects, 

their classification into mineral-deposit types, and various 

aspects of their geology are presented in map 1-1803-C 

(Loen and Pearson, 1989). Mineral production of mining 

districts is also given, although the amount of this production 

is poorly known and, hence, largely estimated. The information in map 1-1803-C was compiled from several earlier 

compilations, chiefly the U.S. Geological Survey's Mineral 

Resource Data System (MRDS) and also from numerous 

other compilations (Bentley and Mowatt, 1967; Geach, 

1972; Roby and others, 1960; Sassman, 1941; Strowd and 

others, 1981; Tansley and others, 1933; Umpleby, 1913; and 

Winchell, 1914). A large number of other sources that provide detailed information about individual mines and prospects were used (see Loen and Pearson, 1989, for a list of 

these sources). A table that accompanies map I-1803-C 

gives information on 821 mines, prospects, claims, and 

claim groups. 

More than 500 of the localities are classified as vein and 

replacement deposits of base and precious metals. These 

deposits include virtually all deposits that were mined and 

prospected, other than placer deposits, during the early days 

of mining (1862 until about 1900). These were, and continue 

to be, valuable mainly for gold or silver and lead; the ores 

from some have appreciable copper or zinc as well. The 

remaining mines and prospects have been classified into a 

variety of deposit types. Placer deposits of gold are abundant. Skarn tungsten deposits have been significant in the 

past. Porphyry, stockwork, or disseminated deposits and 

prospects of molybdenum and copper are numerous, but they 

have not yet been exploited, owing to subeconomic grades. 

Belt copper-silver (named for the Middle Proterozoic Belt 

Supergroup) and Sullivan-type massive sulfide deposits 

(named for the Sullivan mine in British Columbia) are 

known but, likewise, have not been mined, except where 

iron-rich gossan that had formed by weathering of the sulfides was used as smelter flux. Among the nonmetallic minerals, talc is of major significance; chlorite has been mined 

in recent years from one deposit; and deposits and prospects 

are known for barite, graphite, manganese, garnet, chromite, 

and several metamorphic minerals. 

. ~he mines and prospects tend to be clustered in mining 

distncts. As they are recognized in this study, all or parts of 

44 districts are in the quadrangle, and some mines and prospects are scattered outside recognized mining districts. 

Mineral Resource Assessment 

The mineral resource assessment of the Dillon quadrangle attempted to locate those parts of the quadrangle that are 

potentially favorable for various types of mineral deposits 

and to determine, if possible, the amount of mineral commodities that they contain in mineable concentrations. Mineral deposits that are known to exist (or that are susi>ected to 

exist from a knpwledge of the geologic setting) have been 

grouped into 30 deposit types based on mineralogy, mineral 

commodity, or structural or depositional setting (table 2). 

These 30 deposit types may be combined in various ways. A 

separate assessment was undertaken for several of the 

deposit types listed in table 2. The deposit types have been 

divided into four groups whose similarities make them amenable to being treated together. Metallic minerals were 

emphasized, but some important nonmetallic minerals were 

also considered. Fossil fuels are beyond the scope of this 

Table 2. Mineral-deposit types in the Dillon 1 °X2° 

quadrangle 

[*,deposit types assessed in CUSMAP folio reports] 

Deposits associated with Archean crystalline rocks 

*Bedded iron-formation 

*Talc 

*Chlorite 

*Exhalative gold 

*Chromite 

*Nickel 

*Graphite 

Manganese 

Metamorphic minerals (corundum, sillimanite, asbestos) 

Deposits associated with Middle Proterozoic sedimentary rocks 

*Exhalative Sullivan-type massive sulfide (base metals) 

*Belt copper-silver 

*Exhalative Blackbird-type cobalt-copper-gold 

Hydrothennal and other epigenetic deposits 

*Skarn (W, Cu, Ag, Au, Fe) 

*Stockwork, porphyry, or disseminated (Mo, Cu, Au) 

*Vein and replacement deposits (base and precious metals) 

*Vein barite 

*Vein fluorspar 

Vein thorium 

Vein manganese 

Vein uranium 

Syngenetic, diagenetic, and other deposits in sedimentary rocks 

Manganese 

Phosphate 

Oil shale 

Clay (bentonite and other clay) 

Coal 

Uranium 

*Placer gold and silver 

Zeolites 

Building stone 

Sand and gravel 

8 Mineral Resource Assessment, Dillon 1 °X2° Quad., Idaho and Montana 
investigation, and other minerals, such as phosphate, uranium, and thorium, have been investigated previously. Certain nonmetallic commodities, such as sand and gravel, are 

in very large supply, and the deposits of other commodities, 

such as clay, bentonite, and zeolites, are not sufficiently well 

known to permit an assessment. 

An assessment of the quadrangle for uranium was made 

under the National Uranium Resource Exploration Program 

(NURE) (Wodzicki and Krason, 1981). This study was 

largely a compilation of existing data and included only minimal field studies. The results of this investigation indicate 

that the Dillon quadrangle probably does not contain substantial resources of uranium. No uranium has been mined, 

and the few places that exhibit abnormally high radioactivity 

do not have geologic characteristics that indicate a high 

potential. The geologic environments with the highest 

potential for uranium are the Tertiary basins that contain 

abundant pyroclastic debris that may have provided a source 

of uranium. The basins also have permeable aquifers that 

could serve as host rocks. 

Thorium resources are present in the Lemhi Pass thorium 

district, which is mostly south of the Dillon quadrangle. The 

deposits in the Lemhi Pass district are in veins that cut Proterozoic sedimentary rocks. Moderately large resources are 

present in these deposits (Staatz, 1979). The few veins that 

extend from the main part of the district into the Dillon quadrangle probably contain only very small resources of thorium. 

Phosphate resources were studied by Popoff and Service 

(1965) and Swanson (1970). Phosphate rock was mined for 

many years from deposits in the central part of the quadrangle near Melrose. Large resources remain, but they are considered to be subeconomic at the present time. The Permian 

Phosphoria Formation, which contains the phosphate 

resources, also contains subeconomic resources of oil shale, 

fluorine, uranium, vanadium, and other minor metals either 

within the phosphate rock or in associated strata (Swanson, 

1970). 

Mineral resources in the quadrangle were assessed using 

a procedure that relied on the development of deposit models 

for each deposit type. The models used here are basically a 

description of the deposits' physical characteristics and of 

their spatial relationships to local and regional geological, 

geochemical, and geophysical features. Once a model was 

constructed for each deposit type, the quadrangle was examined throughout to determine the distribution of all pertinent 

characteristics or attributes, and, from that, the favorability 

for deposits of each type was estimated. 

A computer-based geographic information system (GIS) 

was used to develop each deposit model, to assist in the mineral resource assessment, and to prepare the mineral resource 

assessment maps. The GIS provides a means of comparing 

and interrelating the various kinds of data that can be referenced geographically. The data sets described above (geology, geochemistry, gravity, aeromagnetics, linear features, 

hydrothermal alteration, and mines and prospects) we~ digitized and entered into the GIS, where they could be compared quantitatively throughout the quadrangle. B :· this 

technique, the effects of any two or more data sets at any 

geographic point can be considered simultaneously. ['"'tails 

of the technique-what it consists of and . how i• was 

used-are presented in the discussion that acco~anies 

maps 1-1803-E, 1-1803-F, and 1-1803-G. This is til~ first 

comprehensive application of GIS technology to asses" mineral resources of large areas. 

For some deposit types, the important characte~stics 

(favorability criteria) that are relevant to the formaf 'ln or 

localization of a deposit are both few and simple or s re not 

available at the scale of this study (1:250,000). The sssessment for those types was made almost entirely subjecively. 

In some cases, the only available pertinent criteria we-~ the 

kind and age of host rock. Talc deposits in Archean do~'>mite 

units are an example. Other deposit types were treated by the 

more sophisticated GIS procedure, in which all favor( .. bility 

criteria were examined for the entire quadrangle. 

Assessment of Deposits of Precambrian Age 

(MAP 1-1803-D) 

Map 1-1803-D deals with mineral deposits that f"rmed 

in the Precambrian and that are hosted by Precambrian rocks. 

The Precambrian rocks can be divided into crystalline. rocks 

of Archean and Early Proterozoic age and unmetamorr~osed 

to weakly metamorphosed sedimentary rocks of MiddT ·~Proterozoic age. Each of these groups of rocks is favorahle for 

a separate group of mineral deposits. 

Archean metamorphic rocks in the southeastern part of 

the Dillon quadrangle are hosts for deposits and prosp~cts of 

talc, iron, chlorite, chromium, and other mineral coiPn.odities. Archean dolomite marble units host economical':· significant talc deposits in the Ruby Range and adj~n~ areas 

in the southeastern part of the quadrangle. Bedded ironformation is also present in that part of the quadrangle. 

Although these deposits contain substantial amounts of iron 

of adequate grade for mining, the aggregate tonnage available cannot justify co~truction of ore processing facil ~ies in 

the foreseeable future. Deposits of high-grade mag"'lesian 

chlorite, formed by replacement of granitic gneiss, have been 

mined, beginning in 1977 and continuing throughc'tt the 

1980's, at one mine near Silver Star (Berg, 1979). Small 

bodies of chromitite have been prospected; trace amounts of 

nickel minerals are present; and vein-type graphite d~posits 

have been mined. These and numerous concentrati 'lDS of 

metamorphic minerals that may have some future ecc .-.oniic 

importance are present in the crystalline rocks. 

Mineral deposits in the Middle Proterozoic Belt Supergroup, Lemhi Group, and Yellowjacket Formation i~dude 

types of deposits that are known widely in the sam~ rock 

groups outside the Dillon quadrangle. Stratabound C'lpperProducts and Results of the Dillon CUSMAP Proj~ 9 
silver deposits are present in the Belt Supergroup and have 

been explored but not mined. Base-metal sulfide deposits of 

the exhalative Sullivan type are known in the Highland 

Mountains and have been explored extensively but, likewise, 

have not been mined. Minor amounts of cobalt in the Yellowjacket Formation at one small mine in the Salmon, Idaho, 

area suggest a low probability of cobalt deposits in the Dillon 

quadrangle, although the main Idaho cobalt belt is west of 

the quadrangle. 

Assessment of Vein and Replacement Deposits of Base and 

Precious Metals 

(MAP 1-1803-E) 

The vein and replacement deposits of base and precious 

metals in the quadrangle are discussed in map 1-1803-E. Of 

the several hundred deposits, mines, and prospects of this 

deposit type, only a few (about 15) have been moderately 

large producers (about $1 million to $20 million worth of 

metals at the time of production). Of these, most are gold 

mines, but in addition, silver and lead have been the main 

commodities from mines in the Argenta, Blue Wing, and 

Hecla districts, and copper has been predominant at the Pope 

Shenon and Harmony mines near Salmon, Idaho (Ross, 

1925). 

This deposit type combines many sorts of deposits that 

might have been classified differently and assessed separately. Other investigators perhaps would have done so. A 

lack of diagnostic criteria to make such separate assessments 

meaningful, however, prompted us to be "lumpers" rather 

than "splitters." 

The Golden Sunlight deposit, near the northeast comer of 

the quadrangle, for example, in earlier decades produced 

substantial gold from high-grade veins, but it has recently 

been developed into a large bulk-tonnage mine. The Golden 

Sunlight deposit is considered to be a vein and replacement 

deposit for the purpose of this study, although it could, per· 

haps, be more properly classified as a breccia-pipe or disseminated type. Similarly, the Beal deposit, which was the 

lode source of one of the largest placer deposits in the quad· 

rangle (German Gulch), is a disseminated deposit, similar in 

some respects to the Golden Sunlight, and it too might have 

been classified differently. 

Vein barite and replacement and vein fluorspar also are 

similar to the vein and replacement deposits, and they are 

included in the discussion in map 1-1803-E, although they 

are not base or precious metals. 

Assessment of Placer Gold and Silver Deposits 

(MAP 1-1803-F) 

Placer gold and silver deposits in the Dillon quadrangle 

are-assessed in map 1-1803-F. Placer deposits have been the 

main source of gold, and they are numerous in the quadrangle. Placer mining in the quadrangle began in 1862, and it 

continues in the 1990's. Most of the placering has taken 

place along small to medium-sized stream~, either in 

Holocene alluvium on the present flood plains or in bench 

placers that are locally more than 100ft above present stream 

levels. In addition, some eluvial deposits have been mined 

from slopes directly below lode deposits. 

Other sedimentary deposits that are consid ~red in map 

1-1803-F are the Tertiary deposits in basins. Dnring the late 

Tertiary, uplift of mountainous parts of the qur1rangle was 

rapid. The resulting rapid erosion caused debris to be moved 

from the uplands out into the developing basin~ Wherever 

gold-bearing lodes were eroded during this period, gold 

might have been transported to a site in the basir (most probably a site along the edge of the basin and not far from the 

lodes) and concentrated into placer deposits. p·111~er mining 

of such deposits has taken place only to a limiterl degree, but 

the possible existence of such deposits is infe"Ted, and an 

attempt is made to delineate areas where such deposits may 

occur. 

Assessment of Porphyry Deposits of Copper, 

Molybdenum, and Gold and Skarn Deposits of 

Tungsten, Copper, Silver, and Gold 

(MAP 1-1803-G) 

Porphyry deposits of copper, molybdenum, and gold and 

skarn deposits of tungsten, copper, silver, a"'fi gold are 

assessed in map 1-1803-G. The largest tungs~~n mines in 

Montana are in the Dillon quadrangle. These mines have 

produced very little since the 1950's, but exploration during 

the 1970's and 1980's has indicated that large .tungsten 

resources remain. 

Porphyry deposits were sought extensive!:' by mining 

companies in the 1960's and 1970's. One deposit was delineated by drilling, and others were drilled sufficiently to 

determine that they have high economic potentiru. The porphyry deposits are mostly in the Pioneer M<''mtains and 

occur in the Highland Mountains, Tobacco Roo~ Mountains, 

Salmon River Mountains, and Anaconda Rru"~e as well. 

None of the porphyry deposits have been Qlinerl. Copper is 

the principal metal sought in two of the prospect~: the Bobcat 

Gulch prospect near North Fork, Idaho, and the Grasshopper 

prospect east of Bannack. The Grasshopper r,..ospect was 

initially explored for copper and molybdenum, but in 1989, 

exploration was conducted in the same locati 'ln for gold. 

Molybdenum is the principal metal in the Can""~,van Gulch 

deposit, which has been developed by drilling to an extent 

that size and grade are known. All known porpt'vry deposits 

are within or adjacent to granitic plutons of Lab~ Cretaceous 

or earliest Tertiary age. 

1 0 Mineral Resource Assessment, Dillon 1 o,ao Quad., Idaho and Montana 
CONCLUSIONS 

The Dillon quadrangle is part of a mineral-rich region 

where mining has been continuous since 1862. A wide variety of mineral commodities is present. Mining has always 

been sporadic, waxing and waning with fluctuations in 

prices of commodities and costs of production; some 

deposits have become exhausted and new deposits have been 

discovered. It will probably continue to be a mining region 

indefinitely. Many deposits are known that have not been 

mined because their small size or low grade render them 

uneconomic. As of 1991, gold production is at an all-time 

high. The Golden Sunlight mine is producing more than 

90,000 ounces of gold per year, and the Beal mine is producing at a rate of more than 35,000 ounces per year. It seems 

likely that additional deposits of a wide variety of mineral 

commodities will continue to be discovered. 

SELECTED BIBLIOGRAPHY 

[Includes references cited in this report and other selected references to 

geology and mineral deposits in the Dillon quadrangle. •, principal reports 

of the Dillon CUSMAP folio] 

Alden, W.C., 1953, Physiography and glacial geology of western 

Montana and adjacent areas: U.S. Geological Survey Professional Paper 231, 200 p. 

Alexander, R.G., Jr .• 1955, Geology of the Whitehall area, Montana: Yellowstone-Bighorn Research Association Contribution 195, 106 p. 

Anderson, A.L., 1956, Geology and mineral resources of the 

Salmon quadrangle, Lemhi County, Idaho: Idaho Bureau of 

Mines and Geology Pamphlet 60, 15 p. 

__ 1957, Geology and mineral resources of the Baker quadrangle, Lemhi County, Idaho: Idaho Bureau of Mines and Geology Pamphlet 112,71 p. 

__ 1959, Geology and mineral resources of the North Fork 

quadrangle, Lemhi County, Idaho: Idaho Bureau of Mines 

and Geology Pamphlet 118, 92 p. 

Armstrong, F.C., and Full, R.P., 1950, Geologic maps of Crystal 

graphite mine, Beaverhead County, Montana: U.S. Geological Survey Open-File Report 50-26. 

Armstrong, R.L., and Hollister, V.F., 1978, K-Ar dates for mineralization in the White Cloud--Cannivan porphyry belt of 

Idaho and Montana-A reply: Economic Geology, v. 73, p. 

1,368. 

Armstrong, R.L., Hollister, V.F., and Harakel, J.E., 1978, K-Ar 

dates for mineralization in the White Cloud--Cannivan 

porphyry molybdenum belt of Idaho and Montana: Economic Geology, v. 73, p. 94-108. 

Bayley, R.W., and James, H.L., 1973, Precambrian iron formations 

of the U.S.: Economic Geology, v. 68, no. 7, p. 934-959. 

Bentley, C.B., and Mowatt, G.D., 1967, Reported occurrences of 

selected minerals in Montana: U.S. Geological Survey Mineral Investigations Resource Map MR-50, scale 1:500,000. 

Berg, R.B., 1979, Talc and chlorite deposits in Montana: Montana 

Bureau of Mines and Geology Memoir 45, 66 p. 

__ 1987, Potential for talc deposits within the BLM Wilderness 

Study Area of the northern part of the Ruby Range, Madison 

County, Montana: U.S. Geological Survey Open-File Report 

87-1, scale 1:24,000. 

__ 1988, Barite in Montana: Montana Bureau of Mines and 

Geology Memoir 61, 100 p. 

Berger, B.R., Breit, G.N., Siems, D.F., Welsch, E.P., and Speckman, W.S., 1979, A geochemical survey of mineral deposits 

and stream deposits in the Eastern Pioneer Wildemer~ Study 

Area, Beaverhead County, Montana: U.S. Geologbal Survey Open-File Report 79-1079, 128 p. 

Berger, B.R., Snee L.W., Hanna, W.F., and Benham, I.R., 1983, 

Mineral resource potential of the West Pioneer Wf·ierness 

Study Area, Beaverhead County, Montana: U.S. Ge'llogical 

Survey Miscellaneous Field Studies Map MF-1585-A, scale 

1:50,000. 

Berger, B.R., Van der Voort, J.L., Siems, D.F., and Welsch, E.P., 

1979, Geochemical exploration studies in the Dillo,., Montana-Idaho 1 OX2° quadrangle: Geochemical reconn:Ussance 

of mining districts in the southern Pioneer Mountr~ns and 

vicinity, Beaverhead County, Montana: U.S. Ge'llogical 

Survey Open-File Report 79-1426,45 p. 

Breit, G.N., 1980, Geochemical exploration study of the Polaris 

mining district and vicinity, Beaverhead County, Montana: 

Golden, Colorado School of Mines, M.S. thesis, 265 p. 

Broxton, D.E., 1979, Uranium hydrogeochemical and strerm-sediment reconnaissance of the Dillon NTMS quadrangl ~. Montana/Idaho, including concentrations of forty-three 

additional elements: U.S. Department of Energy Q~n-File 

Report GJBX-38(79), 228 p. 

Bunning, B.B., and Burnet, F.W., 1981, Copper-molybdenum mineralization in the Bobcat Gulch porphyry system., Lemhi 

County, Idaho: Reprint of paper presented at t'-e 87th 

Annual Northwest Mining Association Con"ention, 

Spokane, Washington, December 5, 1981. 

Burger, H.R., ill, 1967, Bedrock geology of the Sheridan district, 

Madison County, Montana: Montana Bureau of Mines and 

Geology Memoir 41, 22 p. 

Chadwick, K.E.W., 1941, Some chromite deposits-l ~adison 

County, Montana: Butte, Montana School of Mina.s, B.S. 

thesis. 

Desmarais, N.J., 1981, Metamorphosed ultramafic rock~ in the 

Ruby Range, Montana: Precambrian Research, v. 16, p. 

67-101. 

__ 1983, Geochronology and structure of the Chief Jos~ph plutonic-metamorphic complex, Idaho-Montana: Seattle, University of Washington, Ph.D. thesis, 150 p. 

Elliott, J.E., Wallace, C.A., O'Neill, J.M., Hanna, W.F., Rowan, 

L.C., Segal, D.B., Zimbelman, D.R., Pearson, R.C., Close, 

T.J., Federspiel, F.E., Causey, J.D., Willett, S.L., Morris, 

R.W., and Huffsmith, I.R., 1985, Mineral resource f'>tential 

map of the Anaconda-Pin tier Wilderness and contigu"us roadless area, Granite, Deer Lodge, Beaverhead, and Ravalli 

Counties, Montana: U.S. Geological Survey Misce~Janeous 

Field Studies Map MF-1622-A, scale 1:50,000. 

Evans, K.V., and Zartman, R.E., 1988, Early Paleozoic alkalic plutonism in east-central Idaho: Geological Society of America 

Bulletin, v. 100, p. 1,981-1,987. 

__ 1990, U-Th-Pb and Rb-Sr geochronology of Midc'1e Proterozoic granite and augen gneiss, Salmon River Mo·~utains, 

east-central Idaho: Geological Society of America p~,uetin, 

v. 102, p. 63-73. 

Fields, R.W., Rasmussen, D.L., Tabrum, A.R., and Nichols, Ralph, 

1985, Cenozoic rocks of the intermontane basins of western 

Montana and eastern Idaho: A summary, in Flore~- R.M. 

and Kaplan, S.S., eds, Cenozoic paleogeography of westSelected Bibliograpf.y 11 
central United States: Rocky Mountain Section, Society of 

Economic Paleontologists and Mineralogists Symposium 3, 

p. 9-36. 

Filipek, L.H., and Berger, B.R., 1981, Effects of bedrock geology 

and geomorphology on the partitioning of Fe, Mn, Cu, and 

Zn in stream sediments and soils [abs.]: Geological Society 

of America Abstracts with Programs, v. 13, no. 7, p. 450. 

Ford, R.B., 1954, Occurrence and origin of the graphite deposits 

near Dillon, Montana: Economic Geology, v. 49, p. 31-43. 

Fraser, G.D., and Waldrop, H.A., 1972, Geologic map of the Wise 

River quadrangle, Silver Bow and Beaverhead Counties, 

Montana: U.S. Geological Survey Quadrangle Map 

GQ-988, scale 1:24,000. 

Garihan, J.M., 1973, Geology and talc deposits of the central Ruby 

Range, Madison County, Montana: University Park, Pennsylvania State University, Ph.D. thesis, 209 p. 

Geach, R.D., 1972, Mines and mineral deposits (except fuels), Beaverhead County, Montana: Montana Bureau of Mines and 

Geology Bulletin 85, 193 p. 

Giletti, B.J., 1966, Isotopic ages from southwestern Montana: Journal of Geophysical Research, v. 71, p. 4,029-4,036. 

Hammitt, R.W., and Schmidt, E.A., 1982, Geology and mineralization of the Cannivan Gulch deposit, Beaverhead County, 

Montana: Guidebook of the Seventh Annual Tobacco Root 

Geological Society Field Conference, p. 15--20. 

*Hanna, W .F., Kaufmann, H. E., Hassemer, J.H., Ruppel, B.D., Pearson, R.C., and Ruppel, E.T., in press, Interpretation of gravity and magnetic anomalies, Dillon 1 Ox2° CUSMAP 

quadrangle, Montana and Idaho: U.S. Geological Survey 

Miscellaneous Investigations Map 1-1803--1, scale 

1 :250,000, 1:500,000. 

Hassemer, J.H., Kaufmann, H.E., and Hanna, W.F., 1986, Description of magnetic tape containing the principal facts for the 

gravity stations in and adjacent to the Dillon 1 Ox2° quadrangle, Montana and Idaho: National Technical Information 

Service PB 86-197407/AS, 6 p. 

Heinrich, E.W., 1949, Pegmatite mineral deposits in Montana: 

Montana Bureau of Mines and Geology Memoir 28, 56 p. 

Heinrich, E.W., and Rabbitt, J.C., 1960, Pre-Beltian geology of the 

Cherry Creek and Ruby Mountains areas, southwestern 

Montana: Montana Bureau of Mines and Geology Memoir 

38, 40p. 

Hum, C.K.W., 1943, Geology and occurrence of graphite at the 

Crystal graphite mine near Dillon, Montana: Butte, Montana 

College of Mineral Science and Technology, B.S. thesis. 

James, H.L., 1981, Bedded Precambrian iron deposits of the Tobacco Root Mountains, southwestern Montana: U.S. Geological 

Survey Professional Paper 1187, 16 p. 

__ 1990, Precambrian geology and bedded iron deposits of the 

southwestern Ruby Range, Montana: U.S. Geological Survey Professional Paper 1495,39 p. 

James, H.L., and Hedge, C.E., 1980, Age of basement rocks of 

southwestern Montana: Geological Society of America Bulletin, v. 91, pt. l, p. 11-15. 

James, H.L., and Wier, K.L., 1972a, Geologic map of the Carter 

Creek iron deposit, sec. 3, 9, and 10, T. 8 S., R. 7 W., Madison and Beaverhead Counties, Montana: U.S. Geological 

Survey Miscellaneous Field Studies Map MF-359, scale 

1:3,600. 

__ 1972b, Geologic map of the Kelly iron deposit, sec. 25, T. 

6 S., R. 5 W., Madison County, Montana: U.S. Geological 

Survey Miscellaneous Field Studies Map MF-349, scale 

1:2,400. 

James, H.L., Wier, K.L., and Shaw, K.W., 1969, Map showing 

lithology of Precambrian rocks in the Christensen Ranch and 

adjacent quadrangles, Madison and Beavei'Mad Counties, 

Montana: U.S. Geological Survey OpeiT .. file Report 

69-132, scale 1:20,000. 

Jerome, S.E., and Cook, D.R., 1967, Relation of some metal mining 

districts in the western United States to reg::'>nal tectonic 

environments and igneous activity: Nevada Bureau of Mines 

Bulletin 69, 35 p. 

Johnson, R.W., Jr., Henderson, J.R., and Tyson, N.S ~ 1965, Aeromagnetic map of the Boulder batholith area, southwestern 

Montana: U.S. Geological Survey Geophysi~al Investigations Map GP-528, scale 1:250,000. 

Johns, W.M., 1961, Geology and ore deposits of the routhern Tidal 

Wave mining district, Madison County, MontMa: Montana 

Bureau of Mines and Geology Bulletin 24, 53 p. 

Jones, V.E., 1931, Chromite deposits of Sheridan, Montana: Economic Geology, v. 26, no. 6, p. 625-629. 

Karasevich, R.P., 1981, Structural history of the pre·,Beltian metamorphic rocks of the northern Ruby Range, southwestern 

Montana [abs.]: Geological Society of Amer~.a, Abstracts 

with Programs, v. 13, no. 4, p. 200. 

__ 1981, Geologic map of the northern Ruby Range, Madison 

County, Montana: Montana Bureau of Mines and Geology 

MapGM25. 

Karlstrom, T.N.V., 1948, Geology and ore deposits of the Hecla 

mining district, Beaverhead County, MontaJ~q: Montana 

Bureau of Mines and Geology Memoir 25, 87 p. 

Kaufmann, H.E., Sorensen, S.B., and O'Neill, K.J., 1983, Principal 

facts and complete Bouguer gravity anomaly map for the 

Dillon 1 Ox2° quadrangle, Montana and Idaho: U.S. Geological Survey Miscellaneous Field Studies Map MF-1354-E, 

scale 1 :250,000. 

Kirkemo, Harold, Anderson, C.A., and Creasey, S.C., 1965, Investigations of molybdenum deposits in the conte~inous United States: U.S. Geological Survey Bulletin 1183--E, 90 p. 

Koschmann, A.H., and Bergendahl, M.H., 1968, Prindpal gold districts in the United States: U.S. Geological s~"rvey Professional Paper 610, 283 p. 

Kuenzi, W.D. and Fields, R.W., 1971, Tertiary strati~raphy, structure, and geologic history, Jefferson basin, M "'lntana: Geological Society of America Bulletin, v. 82, no. 12, p. 

3,373--3,394. 

Lambe, R.N., 1981, Crystallization and petrogenesi~ of the southem portion of the Boulder batholith, Montar~: Berkeley, 

University of California, Ph.D. thesis, 171 p. 

Leatham-Goldfarb, S., Siems, D.P., Welsch, E.P., and Berger, B.R., 

1986, Analytical results and sample locality map of skarn, 

porphyry, and vein samples from the Dillo.,., Butte, and 

Dubois 1 OX2° quadrangles, Idaho-Montana: U.S. Geological 

Survey Open-File Report 86-37, 83 p. 

Levandowski, D.W., 1956, Geology and mineral d~~sits of the 

Sheridan-Alder area, Madison County, Mcntana: Ann 

Arbor, University of Michigan, Ph.D. thesis, 318 p. 

Lindquist, AE., 1966, Structure and mineralization of the Whitehall mining district, Jefferson County, MoiTtma: Butte, 

Montana College of Mineral Science and Technology, M.S. 

thesis. 

*Loen, J.S., and Pearson, R.C., 1989, Map showin .. location of 

mines and prospects in the Dillon 1 Ox2° qua~rangle, Idaho 

and Montana: U. S. Geological Survey Miscell "neous Investigations Series Map 1-1803-C, scale 1:250,()('1. 

Lopez, D.A., 1981, Stratigraphy of the Yellowjacket Formation of 

east-central Idaho: Golden, Colorado Schc()l of Mines, 

Ph.D. thesis, 252 p. 

12 Mineral Resource Assessment, Dillon 1 OX2° Quad., Idaho and Montana 
Lorain, S.H., 1937, Gold lode mining in the Tobacco Root Mountains, Madison County, Montana: U.S. Bureau of Mines 

Infonnation Circular 6972, 72 p. 

Lorain, S.H., and Metzger, O.H., 1939, Reconnaissance of placermining districts in Lemhi County, Idaho: U.S. Bureau of 

Mines lnfonnation Circular 7082, 81 p. 

Lowell, W.R., 1965, Geologic map of the Bannack-Grayling area, 

Beaverhead County, Montana: U.S. Geological Survey Miscellaneous Investigations Series Map 1433, scale 1:31,680. 

Lyden, C.A., 1948, The gold placers of Montana: Montana Bureau 

of Mines and Geology Memoir 26, 152 p. 

McMannis, W.J., 1963, LaHood Fonnation-a coarse facies of the 

Belt Series in southwestern Montana: Geological Society of 

America Bulletin, v. 74, no. 4, p. 407-436. 

Meyer, J.W., 1980, Alteration and mineralization of the Grasshopper prospect, Beaverhead County, Montana: Tucson, University of Arizona, M.S. thesis, 90 p. 

Moore, G.T., 1956, The geology of the Mount Fleecer area, Montana: Bloomington, Indiana University, Ph.D. thesis, 88 p. 

Myers, W.B., 1952, Geology and mineral deposits of the northwest 

quarter Willis quadrangle and adjacent Browns Lake area, 

Beaverhead County, Montana: U.S. Geological Survey 

Open-File Report, 46 p. 

Newcomb, R.C., 1941, Gray quartz breccia ore body of the Highland mine, Butte, Montana: Economic Geology, v. 36, p. 

185-198. 

Noel, J.A., 1956, The geology of the east end of the Anaconda 

Range and adjacent areas, Montana: Bloomington, Indiana 

University, Ph.D. thesis, 74 p. 

Okuma, A.F.,1971, Structure of the southwestern Ruby Range near 

Dillon, Montana: University Park, Pennsylvania State University, Ph.D. thesis, 122 p. 

Olson, R.H., 1976, The geology of Montana talc deposits, in Eleventh Industrial Minerals Forum Proceedings: Montana 

Bureau of Mines and Geology Special Publication 74, p. 

99-143. 

O'Neill, J.M., 1983a, Geologic map of the Middle 

Mountain-Tobacco Root Roadless Area, Madison County, 

Montana: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-1590-A, scale 1:50,000. 

__ 1983b, Geochemical map of the Middle Mountain-Tobacco 

Root Roadless Area, Madison County, Montana: U. S. Geological Survey Miscellaneous Field Studies Map 

MF-1590-B, scale 1:50,000. 

O'Neill, J.M., Cather, Eric, and Cinne, J.M., 1983, Mineral 

resource potential map of the Middle Mountain-Tobacco 

Root Roadless Area, Madison County, Montana: U.S. Geological Survey Miscellaneous Field Investigations Map 

MF-1590-C, scale 1:50,000. 

O'Neill, J.M., and Lopez, D.A., 1985, Character and regional significance of Great Falls tectonic zone, east-central Idaho and 

west-central Montana: American Association of Petroleum 

Geologists Bulletin, v. 69, no. 3, p. 437-447. 

Pardee, J.T., 1950, Late Cenozoic block faulting in western Montana: Geological Society of America Bulletin, v. 61, p. 

359-406. 

Pattee, E.C., 1960, Tungsten resources of Montana-deposits of 

the Mount Torry batholith, Beaverhead County: U.S. Bureau 

of Mines Report of Investigations 5552, 41 p. 

Pearson, R.C., and Berger, B.R., 1980, Geology and geochemistry 

of some hydrothennally altered rocks, Pioneer Mountains, 

Beaverhead County, Montana: U.S. Geological Survey 

Open-File Report 80-706, 24 p. 

Pearson, R.C., Berger, B.R., Kaufmann, H.E., Hanna, W.F., and 

Zen, E-an, 1988, Mineral resources of the eastern Pioneer 

Mountains, Beaverhead County, Montana: U.S. Ge:ological 

Survey Bulletin 1766, 34 p. 

•Pearson, R.C., Hanna, W.F., James, H.L., Loen, J.S., MC'H, S.H., 

Ruppel, E.T., and Trautwein, C.M., 1990, Map showing mineral resource assessment for silver, cobalt, and base r"etals in 

Proterozoic sedimentary rocks and for iron, chromiu""• nickel, talc, chlorite, gold, and graphite in Archean a;·stalline 

rocks, Dillon 10X2° quadrangle, Idaho and Montar~: U.S. 

Geological Survey Miscellaneous Investigations Series Map 

1-1803-D, scale 1:250,000. 

Pearson, R.C., Hassemer, J.H., Hanna, W.F., Hoover, D.B., Pierce, 

H.A., and Schmauch, S.W., 1987, Mineral resou~w.s of the 

Parlin Creek Wilderness Study Area, Beaverhead County, 

Montana: U.S. Geological Survey Bulletin 1724-C, 13 p. 

*Pearson, R.C., Loen, J.S., Trautwein, C.M., Ruppel, E.T., a~d Moll, 

S.H., 1991, Mineral resource assessment of placer gold and 

silver, Dillon 10X2° quadrangle, Idaho and Montar~: U.S. 

Geological Survey Miscellaneous Investigations Series Map 

1-1803-F, scale 1:250,000. 

•Pearson, R.C., Trautwein, C.M., Berger, B.R., Hanna, W.F., Jenson, S.K., Loen, J.S., Moll, S.H., Purdy, T.L., Rowr~n. L.C., 

Ruppel, E.T., and Segal, D.B., in press, Mineral resource 

assessment of vein and replacement deposits of base and precious metals, barite, and fluorspar, Dillon 1 o,ao quz(jrangle, 

Idaho and Montana: U.S. Geological Survey Miscellaneous 

Investigations Series Map 1-1803-E, scale 1:250,000, 

1:500,000. 

*Pearson, R.C., Trautwein, C.M., Moll, S.H., Berger, B.R., Hanna, 

W.F., Loen, J.S., Rowan, L.C., Ruppel, E.T., ani Segal, 

D.B., in press, Mineral resource assessment of copper and 

molybdenum in porphyry and stockwork deposits a~d tungsten, iron, gold, copper, and silver in skarn deposit~ Dillon 

1 o,ao quadrangle, Idaho and Montana: U.S. Geo1og•~al Survey Miscellaneous Investigations Series Map 1-1803-G, 

scale 1:250,000, 1:500,000. 

Pearson, R.C., and Zen, E-an, 1985, Geologic map of thr. eastern 

Pioneer Mountains, Beaverhead County, Montan:l: U.S. 

Geological Survey Miscellaneous Field Studi~s Map 

MF-1806-A, scale 1:50,000. 

Pecora, W.C., 1987, Geologic map of the central part of th~ Blacktail Mountains, Beaverhead County, Montana: U.S. Geological Survey Open-File Report 87-79. 

Perry, E.S., 1948, Talc, graphite, vermiculite and asbestos in Montana: Montana Bureau of Mines and Geology Mel""()ir 27, 

44p. 

Popoff, C.G., and Service, A.L., 1965, An evaluation of the: western 

phosphate industry and its resources; Part 2, Montar1a: U.S. 

Bureau of Mines Report of Investigations 6611, 14( p. 

Porter, E.W, and Ripley, E.M., 1985, Petrologic and stablr~isotope 

study of the gold-bearing breccia pipe at the Golden Sunlight 

deposit, Montana: Economic Geology, v. 80, 11'(). 6, p. 

1,689-1 '706. 

*Purdy, T.L. and Rowan, L.C., 1990, Analysis of linear fe~tures in 

the Dillon, Idaho-Montana, 1 Ox2° quadrangle for mineral 

appraisal: U.S. Geological Survey Miscellaneous Irvestigations Series Map 1-1803-B, scale 1:250,000. 

Rasmussen, D.L., 1973, Extension of the middle Tertiary U"~onformity into western Montana: Northwest Geology, v. 2, p. 

27-35. 

Reid, R.R., 1957, Bedrock geology of the north end of the Tobacco 

Root Mountains, Madison County, Montana: Montana 

Bureau of Mines and Geology Memoir 36, 26 p. 

Roby, R.N., Ackennan, W.C., Fulkerson, F.B., and Crowby, F.A, 

1960, Mines and mineral deposits, except fuels, Jefferson 

Selected Bibliograar~y 13 
County, Montana: Montana Bureau of Mines and Geology 

Bulletin 16, 120 p. 

Ross, C.P., 1925, The copper deposits near Salmon, Idaho: U.S. 

Geological Survey Bulletin 774, 44 p. 

Rostad, O.H., 1978, K-Ar dates for mineralization in the White 

Cloud-Cannivan porphyry molybdenum belt of Idaho and 

Montana-a discussion: Economic Geology, v. 73, p. 

1,366-1,368. 

Ruppel E.T., 1967, Late Cenozoic drainage reversal, east-central 

Idaho, and its relation to possible undiscovered placer deposits: Economic Geology, v. 62, p. 648-663. 

__ 1978, Medicine Lodge thrust system, east-central Idaho and 

southwest Montana: U.S. Geological Survey Professional 

Paper 1031,23 p. 

__ 1985, The association of Middle Cambrian rocks and gold 

deposits in southwest Montana: U.S. Geological Survey 

Open-File Report 85-207, 26 p. 

Ruppel, E.T., and Lopez, D.A., 1984, The thrust belt in southwest 

Montana and east-central Idaho: U.S. Geological Survey 

Professional Paper 1278,41 p. 

*Ruppel, E.T., O'Neill, J.M., and Lopez, D.A., 1983, Geologic map 

of the Dillon 1 o,ao quadrangle, Montana and Idaho: U. S. 

Geological Survey Open-File Report 83-168, scale 

1:250,000. 

* __ in press, Geologic map of the Dillon 1 °X2°quadrangle, Idaho and Montana: U.S. Geological Survey Miscellaneous 

Investigations Series Map 1-1803-H, scale 1:250,000. 

Sahinen, U .M., 1939, Geology and ore deposits of the Rochester 

and adjoining mining districts, Madison County, Montana: 

Montana Bureau of Mines and Geology Memoir 19, 53 p. 

__ 1950, Geology and ore deposits of the Highland Mountains, 

southwestern Montana: Montana Bureau of Mines and Geology Memoir 32, 63 p. 

Sassman, Oren, 1941, Metal mining in historic Beaverhead: Missoula, University of Montana, M.A. thesis, 310 p. 

Schmidt, E.A., and Worthington, J.E., 1979, Geology and mineralization of the Cannivan Gulch molybdenum deposit, Beaverhead County, Montana [abs.]: Geological Association of 

Canada, Program with Abstracts, v. 2, p. 46. 

*Segal, D,B., and Rowan, L.C., 1989, Map showing exposures of 

limonitic rocks and hydrothermally altered rocks in the Dillon, Montana-Idaho, 1 °X2° quadrangle: U.S. Geological 

Survey Miscellaneous Investigations Series Map 1-1803-A, 

scale 1 :250,000. 

Shenon, P.J., 1931, Geology and ore deposits of Bannack and 

Argenta, Montana: Montana Bureau of Mines and Geology 

Bulletin 6, 77 p. 

Sinkler, Helen, 1942, Geology and ore deposits of the Dillon nickel 

prospect, southwestern Montana: Economic Geology, v. 37, 

no. 2, p. 136-152. 

Smedes, H.W., Hanna, W.F., and Hamilton, Michael, 1980, Mineral resources of the Humbug Spires Instant Study Area, Silver 

Bow County, Montana: U.S. Geological Survey Open-File 

Report 80-836, 25 p. 

Smedes, H.W., Klepper, M.R., and Tilling, R.I., 1968, Boulder 

batholith-a description of geology and road log: Geological Society of America (Rocky Mountain Section, Bozeman, 

Montana), Field trip 3, 21 p. 

Smith, J.L., 1970, Petrology, mineralogy, and chemistry of the 

Tobacco Root batholith, Madison County, Montana: Bloomington, Indiana University, Ph.D. thesis, 198 p. 

Snee, L.W., 1978, Petrography, K-Ar ages, and field relations of 

the igneous rocks of part of the Pioneer batholith, southwestem Montana: Columbus, Ohio State University, M.S. thesis, 

llOp. 

__ 1982, Emplacement and cooling of the Pion~-er batholith, 

southwestern Montana: Columbus, Ohio Stat~ University, 

Ph.D. thesis, 320 p. 

Staatz, M.H., 1979, Geology and mineral resources of the Lemhi 

Pass thorium district, Idaho and Montana: U.S. Geological 

Survey Professional Paper 1049-A, 90 p. 

Stroud, W.B., Mitchell, V.E., Hestedde, G.S., and E~nnett, E.H., 

1981, Mines and prospects of the Dillon quadrangle, Idaho: 

Idaho Bureau of Mines and Geology Mines and Prospects 

Map Series, 9 p., scale 1:250,000. 

Swanson, R.W ., 1970, Mineral resources in Permian rocks in southwest Montana: U.S. Geological Survey Profe~~ional Paper 

313-E, p. 661-777. 

Tansley, Wilfred, Schafer, P.A., and Hart, L.H., 1933, A geological 

reconnaissance of the Tobacco Root Mounta:'ls, Madison 

County, Montana: Montana Bureau of Mines and Geology 

Memoir 9, 57 p. 

Taylor, A.V., 1942, Quartz Hill district near Divide, Montana, in 

Newhouse, W. H., ed., Ore deposits as related to structural 

features: Princeton University Press, p. 215-216. 

Thorson, J.P., 1984, Suggested revisions of the lowe .. Belt Supergroup stratigraphy of the Highland Mountains, southwestern 

Montana: Montana Bureau of Mines and Geology Special 

Publication 90, p. 10-12. 

Tilling, R.I., 1973, The Boulder batholith, Montana-a product of 

two contemporaneous but chemically distinct magma series: 

Geological Society of America Bulletin, v. 84, p. 

3,879-3,900. 

Tysdal, R.G., 1976, Geologic map of the northern part of the Ruby 

Range, Madison County, Montana: U.S. Geological Survey 

Miscellaneous Investigations Series Map 1-951, scale 

1:24,000. 

__ 1988, Geologic map of the northeast flank of the Blacktail 

Mountains, Beaverhead County, Montana: U.S. Geological 

Survey Miscellaneous Field Studies Map MF-2041, scale, 

1:24,000. 

Tysdal, R.G., Lee, G.K., Hassemer, J.H., Hanna, W.F., and Benham, J.R., 1987a, Mineral resources of the Blccktail Mountains Wilderness Study Area, Beaverhead Court.y, Montana: 

U.S. Geological Survey Bulletin 1724-B, 21 p, 

Tysdal, R.G., Lee, G.K., Hassemer, J.H., Hannr" W.F., and 

Schmauch, S.W., 1987b, Mineral resources of the Ruby 

Mountains Wilderness Study Area, Madison County, Montana: U.S. Geological Survey Bulletin 1724-A. 22 p. 

Umpleby, J.B., 1913, Geology and ore deposits of Lemhi County, 

Idaho: U.S. Geological Survey Bulletin 528, 182 p. 

U.S. Geological Survey, 1975, Aeromagnetic map of southwestern 

Montana and east-central Idaho: U.S. Geok~ical Survey 

Open-File Report 75-655, scale 1:250,000. 

__ 1979, Aeromagnetic map of the Pioneer-Beaverhead area, 

Montana: U.S. Geological Survey Open·File Report 

79-758, scale 1:250,000. 

__ 1981a, Aeromagnetic map of the Tobacco RoNs area, Montana: U.S. Geological Survey Open-File Re.port 81-777, 

scale 1 :50,000. 

__ 1981b, Aeromagnetic map of the Sapph'~Anaconda 

Mountains area, Montana: U.S. Geological f•Jrvey OpenFile Report 81;-1160, scale 1:62,500. 

14 Mineral Resource Assessment, Dillon 1 <>x2° Quad., Idaho and Montana 
Vitaliano, C.J., and Cordua, W.S., 1979, Geologic map of the 

southern Tobacco Root Mountains, Madison County Montana: Geological Society of America Map and Chart Series 

MC-31, scale 1:62,500. 

Wardlaw, B.R., and Pecora, W.C., 1985, New Mississippian-Pennsylvanian stratigraphic units in southwest Montana and adjacent Idaho, in Sando, W .J ., ed, Mississippian and 

Pennsylvanian stratigraphy in southwest Montana and adjacent Idaho: U.S. Geological Survey Bulletin 1656, p. 

B1-B9. 

Weis, P.L., 1973, Graphite, in United States Mineral Resources: 

U.S. Geological Survey Professional Paper 820, p. 277-283. 

Willis, G.F., 1978, Geology of the Birch Creek molybdenum prospect, Beaverhead County, Montana: Missoula, University of 

Montana, M.S. thesis, 74 p. 

~U.S. GOVERNMENT PRINTING OFFICE: 1992·673-049146047 

Winchell, A.N., 1914, Mining districts of the Dillon quadrangle, 

Montana, and adjacent areas: U.S. Geological Survey Bulletin 575, 191 p. 

Wodzicki, Antoni, and Krason, Jan, 1981, National u~nium 

resource evaluation, Dillon quadrangle, Montana and Idaho: 

U.S. Department of Energy GJQ-007(81), 81 p. 

Wooden, J.L., Vitaliano, C.J., Koehler, S.W., and Ragland P.C., 

1978, The late Precambrian mafic dikes of the so·,them 

Tobacco Root Mountains, Montana: Geochemistry, Rb-Sr 

geochronology, and relationship to Belt tectonics: Ca~adian 

Journal of Earth Sciences, v. 15, p. 467-479. 

Zen, E-an, 1988, Geology of the Vipond Park quadrangle, 1341\averhead County, Montana: U.S. Geological Survey B·•lletin 

1625, 49p. 

Zimbelman, D.R., 1984, Geology of the Polaris 1 SE quadtangle, 

Beaverhead County, Montana: Boulder, University of Colorado, M.S. thesis, 154 p. 

Selected Bibliograp~y 1 S