A report about gold mineralization at the Golden Sunlight breccia pipe, southwestern Montana, is related to emplacement of Late Cretaceous alkali-calcic rhyolite and subsequent collapse of the Belt Supergroup wallrock and rhyolite in the pipe.

The following report presents measured sections and lithostratigraphic correlations of the units in the order to document a syntectonic unconformity in order to understand the tectonic history of the area.

From abstract: This report contains complete Bouguer anomaly, isostatic residual anomaly, and horizontal gradient anomaly gravity maps of the Powder River Basin and surrounding areas in southeastern Montana, northeastern Wyoming, and western South Dakota were compiled using gravity data from 21,528 stations. A total-intensity anomaly aeromagnetic map with 3 mile spaced east-west flight-lines is also presented. Also included is an analysis of these maps and data, focusing on gravity and aeromagnetic studies.

From abstract: This report describes Cambrian through Mississippian rocks in the Powder River Basin representing five depositional sequences that reflect both the biological evolution and the tectonic development of western North America.

From abstract: This report is a study on the history of sedimentology and deposition of the lower Paleocene Tullock Member of the Fort Union Formation, Powder River Basin, Wyoming and Montana while looking at the geometry and sedimentary structures.

From abstract: The uppermost Cretaceous Lance Formation was studied in the Powder River Basin and nearby basins of Wyoming and Montana. The Lance Formation is overlain by the continental Paleocene Fort Union Formation. This report is a petrography and stratigraphy study on these basins.

From abstract: A mineral resource survey was conducted in 1987 by the U.S. Geological Survey and the U.S. Bureau of Mines to evaluate mineral resources (known) and mineral resource potential (undiscovered) of the Sleeping Giant Wilderness Study Area (MT-075-111) in Lewis and Clark County, Montana. The only economic resource in the study area is an inferred 1.35-million-ton reserve of decorative stone (slate); a small gold placer resource is subeconomic. A high resource potential for decorative slate exists directly adjacent to the area of identified slate resource and in the northeastern part of the study area. The rest of the study area has a low potential for decorative slate. The westernmost part of the study area has a moderate resource potential for copper and associated silver in strata-bound deposits in green beds and limestone; potential is low in the rest of the study area.

The following report analyzes geological studies on surficial deposits in the Sheridan quadrangle of Wyoming and Montana.

From summary:A mineral resource survey of a 10,610-acre part of the Blacktail Mountains Wilderness Study Area (MT-076- 002) was conducted in 1984-85. Identified subeconomic resources of barite exist in the area at the northernmost boundary, and a zone partly within the area along the northeastern boundary has a moderate mineral resource potential for silver and barite, and associated gold, copper, lead, and zinc. No producing mines occur in or adjacent to the area. The area lies within a region that is rated as having moderate energy resource potential for oil and for gas.

Abstract: The Farlin Creek Wilderness Study Area (MT-076-034) is in the south-central Pioneer Mountains about 24 miles west-northwest of Dillon, Beaverhead County, southwestern Montana. At the request of the U.S. Bureau of Land Management, an area of 610 acres (less than 1 square mile) was investigated by the U.S. Geological Survey and the U.S. Bureau of Mines in 1984. The area contains no mines or prospects, no visible evidence of mineralization, and no identified mineral resources. Geophysical evidence suggests that three parts of the area have moderate mineral resource potential for undiscovered resources of molybdenum. The entire area has a low resource potential for all other metals and for all nonmetals, fuels, and geothermal energy.

From abstract: A mineral resource survey of the Ruby Mountains Wilderness Study Area (MT-076-001) was made in 1984- 85. Thirty-two million tons of subeconomic mineral resources that average 21 percent iron occur in the Kelly iron deposit and constitute an identified resource adjacent to the southeasternmost edge of the study area. Moderate and high mineral resource potential for talc deposits occur within a large body of Archean (see geologic time chart in appendix) marble in the central part of the study area (fig. 1). The study area has a low mineral resource potential for uranium and for oil and gas sources. No phosphate deposits exist in the study area.

From purpose and scope: The purpose of this study was to describe existing hydrologic systems, to obtain data on the water quality in the area, and to assess potential impacts of surface coal mining on local water resources.

From purpose and scope: The purpose of this report is to summarize and evaluate water-quality data acquired from streams within the study area from October 1975 through September 1981. This report updates data collected at 9 stations during the initial study and provides new data for 14 stations.

From purpose and scope: The purpose of this report is to describe the existing hydrologic and water-quality conditions of the shallow ground-water system above the Bearpaw Shale and to describe the surface-water resources in the Fort Union coal region of east-central Montana. The objective of this study was to provide premining data that would be useful for water-resources planning.

From purpose and scope: The purpose of this report is (1) to describe the flow system within the Kootenai Formation, which is the principal aquifer, and (2) to describe the interaction between the Kootenai and overlying and underlying Mesozoic aquifers.

From introduction: The purpose of this report is to provide estimates of 100-year flood discharges at selected sites in Glacier and Yellowstone National Parks. Estimates for streams with contributing drainage areas outside Glacier National Park were determined using only the contributing drainage area in the park.

From introduction: The purpose of this report is to provide methods for estimating mean annual runoff and peak discharges for ungaged streams in northeastern and western Montana.

From introduction: The purpose of this report is to describe the channel-geometry technique and to present equations for estimating mean annual runoff and peak flows for ungaged streams in southeastern Montana.

From purpose and scope: The purpose of this report is to present biological data and to compare the physical, chemical, and biological data to water-quality criteria that are desirable for the proposed reservoir uses.

From purpose and scope: The purpose of this report is to summarize and evaluate fluvial-sediment data collected in the study area by the U.S. Geological Survey. The principal products of this report are sediment concentration and load statistics, sediment-transport curves, calculated mean annual sediment yields at selected stations, and an areal sediment-yield map. A secondary purpose is to describe sediment relationships between stations and basins and to identify environmental factors that are important in determining sediment yield.

From purpose and scope: The purpose of this study was to describe existing hydrologic systems, to obtain data on the water quality in the area, and to assess potential impacts of surface coal mining on local water resources. Specific objectives of the study were to: (1) Identify ground-water resources and use; (2) identify surface-water resources and runoff characteristics; (3) determine chemical quality of the ground-water resources; (4) identify probable impacts on existing water resources by mining operations; and (5) evaluate the potential for reclamation of local water resources.

From abstract: The Snider Creek area of the Rosebud and Ashland coal fiends contains strippable reserves of Federal coal that have been identified for potential lease sale. A hydrologic study has been conducted in the potential lease area to describe the existing hydrologic systems and to assess potential impacts of surface coal mining on local water resources.

From abstract: During fiscal years 1978 through 1981, the U.S. Geological Survey contracted for the acquisition and analysis of hydrologic data from 104 surface water stations, 26 ground water stations, and 15 precipitation gages as well as for several hundred miscellaneous surface water measurements of flow and water quality. The work was performed in Montana, North Dakota, Wyoming, Utah, New Mexico, and Oklahoma, terminating at the end of the fiscal year 1981. This report is an assessment of this contracting effort from the standpoint of cost and of quality control measures employed to ensure an acceptable product.

From objectives and scope: This study was undertaken in response to U.S. Bureau of Land Management concerns for the water resources of the Wibaux-Beach area in the event of lignite mining. The objectives of the study were to: (1) Define the stratigraphic sequence within a few hundred feet above and below the minable lignite; (2) define the premining hydrologic and geochemical regime of the Wibaux-Beach deposit area; and (3) describe some of the hydrologic implications of the strip-mining process. A fourth objective, the establishment of historical data base with which to access any modifications to the system attributable to future mining, was accomplished as a byproduct of the other three.