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Research about Montana

Source-linked reports with geographic coverage including Montana.

At least 559 records · Page 31Linked to original sources
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.

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USGS1991

Large-scale distribution of metal contamination in the fine-grained sediments of the Clark Fork River, Montana, U.S.A.

Historic discharges from the mining and smelting complex at the head-waters of the Clark Fork River have resulted in elevated Ag, Cd, Cu, Pb and Zn concentrations in the <60 μm fraction of both bed and flood-plain sediments of the river. Processes affecting the trends in longitudinal distributions of these metals were investigated by repeated sampling over a 380 km river reach between August 1986 and July 1989. At the most upstream site, bed-sediment metal concentrations were enriched 18–115 times above least enriched tributaries, depending on the metal. All metals decreased exponentially with distance downstream away from mining. The exponential model predicts that elevated metal concentrations should occur over 550 km downstream, in Lake Pend Oreille. Longitudinal trends, obvious on a scale of hundreds of kilometers, were obscured by small-scale spatial variability when shorter stretches of the river were considered. Longitudinal dispersion appeared to be controlled largely by physical dilution with less-contaminated sediments. Evidence suggests that erosion of contaminated flood-plains contributes to metal contamination in the bed sediments. Tributary input appeared to have little influence on the large-scale, downstream distribution of metals; however, it did contribute to local variability in bed-sediment metal concentrations. Association of metals with specific mineral grains, as well as variability in total organic C and Fe concentration, appeared also to contribute to variability. Some year-to-year variability in bed-sediment metal concentrations was observed, however, trends in longitudinal dispersion were not significantly different between at least two of the years sampled.

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USGS1991

Map showing the association of linear features with metallic mines and prospects in the Butte 1° x 2° quadrangle, Montana

This study was undertaken as part of the Conterminous U.S. Mineral Assessment Program (CUSMAP). The purpose of the study was to map linear features on Landsat Multispectral Scanner (MSS) images and a proprietary side-looking airborne radar (SLAR) image mosaic and to determine the spatial relationship between these linear features and the locations of metallic mineral occurrE-nces. The results show a close spatial association of linear features with metallic mineral occurrences in parts of the quadrangle, but in other areas the association is less well defined. Linear features are defined as distinct linear and slightly curvilinear elements mappable on MSS and SLAR images. The features generally represent linear segments of streams, ridges, and terminations of topographic features; however, they may also represent tonal patterns that are related to variations in lithology and vegetation. Most linear features in the Butte quadrangle probably represent underlying structural elements, such as fractures (with and without displacement), dikes, and alignment of fold axes. However, in areas underlain by sedimentary rocks, some of the linear features may reflect bedding traces. This report describes the geologic setting of the Butte quadrangle, the procedures used in mapping and analyzing the linear features, and the results of the study. Relationship of these features to placer and non-metal deposits were not analyzed in this study and are not discussed in this report.

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USGS1991

Lead poisoning of a marbled godwit

A thin adult female marbled godwit ( Limosa fedoa ) found dead at Benton Lake National Wildlife Refuge, Montana, was found to have 17 ingested lead shot in its gizzard. Its liver contained 51.7 ppm lead (wet weight). Based on these necropsy findings a diagnosis of lead poisoning was made.

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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.

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USGS1990

Survival of Mallard broods in Benton Lake National Wildlife Refuge in north central Montana

We estimated duckling survival in broods of 31 radio-marked female mallards ( Anas platyrhynchos ) on Benton Lake National Wildlife Refuge (NWR) in northcentral Montana in 1985 and 1986. Overall survival for the 60-day prefledging period was 0.3951, and 87% of all duckling losses occurred within the first 18 days. Survival through the Class I interval (0.4664) was lower (P < 0.05) than through Class II (0.8887) and Class III (0.9531). Total brood loss occurred among 37% of the females and accounted for 60% of all duckling losses. Broods that survived to fledging averaged 5.0 ducklings. The 60-day survival probability (0.4417) of ducklings in broods that hatched early (on or before 10 Jun) was higher (P < 0.05) than survival of late broods (0.3324). Apparent brood size did not differ (P > 0.05) between marked and unmarked adult females.

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USGS1990

Mineral resources of the Elkhorn Wilderness Study Area, Broadwater and Jefferson Counties, Montana

The Elkhorn Wilderness Study Area in west-central Montana has a moderate to high potential for resources of porphyry-type copper and molybdenum in the western part of the area, and a moderate to high potential for resources of gold, silver, lead, and zinc in replacement and vein deposits in the eastern part of the area. No evidence of potential oil, gas, and geothermal resources was identified in this study.

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