Torshab Mine Stone

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standards.
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Open File Report 2004-1005

Mineral deposit data for epigenetic base- and precious-metal and uranium-thorium
deposits in south-central and southwestern Montana and southern and central
Idaho
By T.L. Klein
Introduction
Metal deposits spatially associated with the Cretaceous Boulder and Idaho
batholiths of southwestern Montana and southern and central Idaho have been exploited
since the early 1860’s. Au was first discovered in placer deposits; exploitation of vein
deposits in bedrock soon followed. In 1865, high-grade Ag vein deposits were
discovered and remained economically important until the 1890’s. Early high-grade
deposits of Au, Ag and Pb were found in the weathered portions of the veins systems. As
mining progressed to deeper levels, Ag and Pb grades diminished. Exploration for and
development of these vein deposits in this area have continued until the present. A
majority of these base- and precious-metal vein deposits are classified as polymetallic
veins (PMV) and polymetallic carbonate-replacement (PMR) deposits in this
compilation. Porphyry Cu and Mo, epithermal (Au, Ag, Hg and Sb), base- and precious-
metal and W skarn, W vein, and U and Th vein deposits are also common in this area.
The world-class Butte Cu porphyry and the Butte high-sulfidation Cu vein deposits are in
this study area. PMV and PMR deposits are the most numerous in the region and
constitute about 85% of the deposit records compiled. Several types of
syngenetic/diagenetic sulfide mineral deposits in rocks of the Belt Supergroup or their
equivalents are common in the region and they have been the source of a substantial
metal production over the last century. These syngenetic deposits and their
metamorphosed/structurally remobilized equivalents were not included in this database;
therefore, deposits in the Idaho portion of the Coeur d’Alene district and the Idaho Cobalt
belt, for example, have not been included because many of them are believed to be of this
type.

More than 3,300 epigenetic mineral deposits are included in this compilation (fig.
1). More than 1600 of these deposits either have produced metal or have unexploited
resources. Mineral deposit information in this database is summarized in 39 fields and is
presented in an Excel spreadsheet file format. This database was compiled for
metallogenic studies, grade and tonnage model development, and mineral resource
assessments for metal deposits in the region. This information was compiled as part of a
USGS study of central and western Montana and Idaho (Headwaters Project), which was
undertaken, in part, to provide geologic and mineral resource information and geologic
interpretations for the Department of Agriculture-Forest Service for use in land
management.
Data Sources
The information contained in this database was primarily derived from mineral
resource information extracted from the Mineral Resource Data System (MRDS) of the
U.S. Geological Survey. This information was supplemented from several primary data
sources that are listed in Table 1. Many of these reports listed in Table 1 contain
information from the Conterminous United States Mineral Assessment Program
(CUSMAP). The purpose of the CUSMAP studies was to assess the mineral resource
potential at a scale of 1:250,000 for areas covered in the U.S. Geological Survey 1° x 2°
3

topographic quadrangles series conducted in the 1970’s and 1980’s. The Butte, Challis,
Dillon, Hailey, and Idaho Falls 1° x 2° topographic quadrangles were assessed under this
program. Location, geologic, and production information from mineral resources
assessments for the Challis, Gallatin, Helena, Payette, Salmon and Targhee National
Forests were also used to supplement original MRDS data. Additional mineral
production and geologic information were obtained from reports of the Montana Bureau
of Mines and Geology and the Idaho Bureau of Mines and Geology, the Securities and
Exchange Commission EDGAR database website
(http://www.sec.gov/edgar/edgarsearch/webusers.htm), and the many National Forest
Wilderness area reports (Table 1) that were completed in the area by the USGS and
Mineral Land Assessments (MLA) completed by the U.S. Bureau of Mines in the 1970’s
and 1980’s. Production data from Bliss (1994), Long and others (1998), and Spanski
(2004) were used extensively for the economically significant deposits in the study area.





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