The Butte 1?x2 ? quadrangle in west-central Montana was investigated as part of the U.S. Geological Survey's Conterminous United States Mineral Assessment Program (CUSMAP). These investigations included geologic mapping, geochemical surveys, gravity and aeromagnetic surveys, examinations of mineral deposits, and specialized geochronologic and remote-sensing studies. The data collected during these studies were compiled, combined with available published and unpublished data, analyzed, and used in a mineral-resource assessment of the quadrangle. The results, including data, interpretations, and mineral-resource assessments for nine types of mineral deposits, are published separately as a folio of maps. These maps are accompanied by figures, tables, and explanatory text. This circular provides background information on the Butte quadrangle, summarizes the studies and published maps, and lists a selected bibliography of references pertinent to the geology, geochemistry, geophysics, and mineral resources of the quadrangle. The Butte quadrangle, which includes the world-famous Butte mining district, has a long history of mineral production. Many mining districts within the quadrangle have produced large quantities of many commodities; the most important in dollar value of production were copper, gold, silver, lead, zinc, manganese, molybdenum, and phosphate. At present, mines at several locations produce copper, molybdenum, gold, silver, lead, zinc, and phosphate. Exploration, mainly for gold, has indicated the presence of other mineral deposits that may be exploited in the future. The results of the investigations by the U.S. Geological Survey indicate that many areas of the quadrangle are highly favorable for the occurrence of additional undiscovered resources of gold, silver, copper, molybdenum, tungsten, and other metals in several deposit types.

Circular↗

USGS1993

Maps showing mineral resource assessment for porphyry and stockwork deposits of copper, molybdenum, and tungsten and for stockwork and disseminated deposits of gold and silver in the Butte 1° x 2° quadrangle, Montana

This report documents the assessment for potential occurrences of undiscovered porphyry and stockwork deposits of copper, molybdenum, and tungsten (porphyry Cu-Mo-W) and stockwork and disseminated deposits of gold and silver (disseminated Au-Ag) in the Butte 1 °X2° quadrangle. The Butte quadrangle, in west-central Montana, is one of the best known mineral producing regions in the U.S. Mining districts in the quadrangle, including the world famous Butte or Summit Valley district, have produced a variety of metallic and nonmetallic mineral commodities valued at more than $6.4 billion (at the time of production). Because of its importance as a mineral producing region, the Butte quadrangle was selected for study by the U.S. Geological Survey under the Conterminous United States Mineral Assessment Program (CUSMAP). Under this program, new data on geology, geochemistry, geophysics, geochronology, mineral resources, and remote sensing were collected and synthesized. The field and laboratory studies were supported, in part, by funding from the Geologic Framework and Synthesis Program and the Wilderness Program. The methods used in this resource assessment for porphyry Cu-Mo-W and disseminated Au-Ag deposits in the quadrangle include a compilation of all data, the development of descriptive occurrence models, and the analysis of data using techniques provided by a Geographic Information System (GIS). This map is one of several maps on the Butte 1 °X2° quadrangle. Other deposit types have been assessed for the Butte quadrangle, and maps (U.S. Geological Survey (USGS) Miscellaneous Investigation Series Maps) for each of the following have been prepared: Vein and replacement deposits of gold, silver, copper, lead, zinc, manganese, and tungsten (Elliott, Wallace, and others, 1992a) and skarn deposits of gold, silver, copper, tungsten, and iron (Elliott and others, 1992b ). Other publications resulting from this study include linear features map (Rowan and others, 1991 ); limonite and hydrothermal alteration map (Rowan and Segal, 1989); mineral occurrence maps (Elliott and others, 1986; Elliott, Loen, and others, 1992); and geologic maps (Wallace, 1987; Wallace and others, 1987).

Montana↗

USGS1992

Map showing mineral resource assessment for vein and replacement deposits of gold, silver, copper, lead, zinc, manganese, and tungsten in the Butte 1° x 2° quadrangle, Montana

The purpose of this report is to assess the potential for undiscovered vein and replacement deposits of gold, silver, copper, lead, zinc, manganese, and tungsten in the Butte 1° x 2° quadrangle. This quadrangle, in west-central Montana, is one of the most mineralized and productive regions in the United States. Its mining districts, including the world famous Butte or Summit Valley district, have produced a variety of metallic and nonmetallic mineral commodities valued at more than $6.4 billion. Because of its importance as a mineral producing region, the Butte quadrangle was selected for study by the U.S. Geological Survey under the Conterminous United States Mineral Assessment Program (CUSMAP). Under this program, new data on geology, geochemistry, geophysics, geochronology, mineral resources, and remote sensing were collected and synthesized. The field and laboratory studies were also supported by funding from the Geologic Framework and Synthesis Program and the Wilderness Program. The methods used in resource assessment include a compilation of all data into data sets, the development of a descriptive model for vein and replacement deposits in the quadrangle, and the analysis of data using techniques provided by the Geographic Information System (GIS). This map is one of a number of reports and maps on the Butte 1 °X2° quadrangle. Other publications resulting from this study include U.S. Geological Survey Miscellaneous Investigations Series Maps 1-2050-A (Rowan and Segal, in press) and I-2050-B (Purdy and Rowan, in press); Miscellaneous Field Studies Map MF-1925 (Wallace, 1987); and Open-File Reports 86-292 (Wallace and others, 1986) and 86--0632 (Elliott and others, 1986). Reports on mineral resource assessment for several other types of deposits in the Butte quadrangle are in preparation.

Montana↗

USGS1992

Maps showing mineral resource assessment for skarn deposits of gold, silver, copper, tungsten, and iron in the Butte 1 degree by 2 degrees Quadrangle, Montana

The purpose of this report is to assess the potential for undiscovered skarn deposits of gold, silver, copper, tungsten, and iron in the Butte 1 °X2° quadrangle. Other deposit types have been assessed and reports for each of the following have been prepared: Vein and replacement deposits of gold, silver, copper, lead, zinc, ·manganese, and tungsten; porphyry-stockwork deposits of copper, molybdenum, and tungsten; stockwork-disseminated deposits of gold and silver; placer deposits of gold; and miscellaneous deposit types including strata-bound deposits of copper and silver in rocks of the Middle Proterozoic Belt Supergroup, phosphate deposits in the Permian Phosporia Formation, and deposits of barite and fluorite. The Butte quadrangle, in west-central Montana, is one of the most mineralized and productive mining regions in the U.S. Its mining districts, including the world famous Butte or Summit Valley district, have produced a variety of metallic and nonmetallic mineral commodities valued at more than $6.4 billion (at the time of production). Because of its importance as a mineral producing region, the Butte quadrangle was selected for study by the U.S. Geological Survey under the Conterminous United States Mineral Assessment Program (CUSMAP). Under this program, new data on geology, geochemistry, geophysics, geochronology, mineral resources, and remote sensing were collected and synthesized. The field and laboratory studies were supported, in part, by funding from the Geologic Framework and Synthesis Program and the Wilderness Program. The methods used in resource assessment include a compilation of all data into data sets, the development of an occurrence model for skarn deposits in the quadrangle, and the analysis of data using techniques provided by a Geographic Information System (GIS). This map is one of a number of reports and maps on the Butte 1 °X2° quadrangle. Other publications resulting from this study include U.S. Geological Survey (USGS) Miscellaneous Investigations Series Maps 1-2050-A (Rowan and Segal, 1989), 1-2050-B (Rowan and others, 1991), 1-2050-D (Elliott and others, in press); Miscellaneous Field Studies Map MF-1925 (Wallace, 1987a); and Open-File Reports OF-86-292 (Wallace and others, 1986) and OF-86-0632 (Elliott and others, 1986).

IMAP↗

USGS1992

Geologic map of the Anaconda-Pintlar wilderness and contiguous roadless area, Granite, Deer Lodge, Beaverhead, and Ravalli counties, western Montana

Explore the source record for details and available documents.

Miscellaneous Field Studies Map↗

USGS1990

Faults of the central part of the Lewis and Clark line and fragmentation of the Late Cretaceous foreland basin in west-central Montana

The Lewis and Clark line is a prominent zone of strike-slip, dip-slip, and oblique-slip faults that extends from near Wallace, Idaho, to east of Helena, Montana. Faults of this zone have been intermittently active from Middle Proterozoic to Holocene time, and because of numerous tectonic overprints, controversy continues about displacement directions and times of displacement along specific faults. Geologic mapping shows evidence that many principal faults of the Lewis and Clark line, such as the St. Marys-Helena Valley, Bald Butte, Ninemile, and Osburn faults, had right separation or slip that ranged between 28 and 11 km, and this displacement probably occurred during Late Cretaceous time. Other faults, such as the Elevation Mountain, Placer Creek, and Ranch Creek faults, have Late Cretaceous right separations that range between 8 and 3.2 km, and the Mount Sentinel fault zone has between 6.5 and 3 km of right separation of probable Late Cretaceous age. Subsidiary structures of the Lewis and Clark line postdate Paleozoic and Lower Cretaceous rocks and predate Late Cretaceous stocks at some places; subsidiary faults and folds that have age constraints have slip directions compatible with right slip along adjacent, principal faults. Sedimentation patterns of Lower and Upper Cretaceous rocks indicate that faults of the Lewis and Clark line fragmented the foredeep region of the foreland basin into separate northern and southern basins in Late Cretaceous time. The Lower and Upper Cretaceous Blackleaf Formation (Albian and lower Cenomanian) was deposited in a continuous foredeep basin that extended across the Lewis and Clark line from north of the Canadian border to southwestern Montana, a distance of about 450 km. North of the Lewis and Clark line, middle and upper Cenomanian rocks are absent, and a thin sequence of uppermost Cenomanian to Campanian rocks was deposited in a marine environment that changed to a strand-line and continental environment in early Campanian time. South of the Lewis and Clark line, middle and upper Cenomanian deposits are also absent, but a thick sequence of Turonian-to-Campanian rocks was deposited in brackish water and strand-line environments, and during later Campanian time, in a continental environment. In the region between the St. Marys-Helena Valley and Bald Butte faults, a barrier may have formed that served as a local sediment source between foredeep regions in the northern and southern foreland basin during the period 91 to 75 Ma. South of the Bald Butte fault, an extensional tectonic regime contributed to a higher sediment-accumulation rate in the foredeep region along the north border of the southern basin (30 cm/1,000 yr), as compared to lower sediment-accumulation rates (6.9 and 7.8 cm/ 1,000 yr) in the foredeep region of the south part of the northern basin.

Montana↗

USGS1989