Geology topics
Publications and source records attributed to Margaret Hinkle.
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The measurement of concentrations of volatile species in soil gases has potential for use in geochemical exploration for concealed ore deposits and for monitoring of subsurface contaminants. However, the interpretation of anomalies in surficial gases can be difficult because soil-gas concentrations are dependent on both meteorological and environmental conditions. For this study, concentrations of He, CO 2 , O 2 and N 2 and meteorological conditions were monitored for 10–14 months at eight nonmineralized sites in both humid and dry environments. Gases were collected at 0.6–0.7-m depth at seven sites. At one site, gases were collected from 0.3-, 0.6-, 1.2-, and 2.0-m depths; diurnal monitoring studies were conducted at this site also. Rain and snowfall, soil and air temperatures, barometric pressure, and relative humidity were monitored at all the sites. The sand, silt and clay content, and the organic carbon content of surficial soil were measured at each site. Meteorological conditions generally affected He and CO 2 concentrations in the same way at all the sites; however, these effects were modified by local environmental conditions. Both seasonal and diurnal concentration changes occurred. The most important seasonal concentration changes were related to rain and snowfall and soil and air temperatures. Seasonal changes tended to be larger then the diurnal changes, but both could be related to the same processes. Local conditions of soil type and organic content affected the amount of pore space and moisture present in the soil and therefore the soil-gas concentrations.
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The U.S. Geological Survey (USGS) is responsible for the geochemical evaluations used for mineral resource assessments of large tracts of public lands in the Western United States. Many of these lands are administered by the Bureau of Land Management (BLM) and are studied to determine their suitability or nonsuitability for wilderness designation. Much of the Western United States is arid or semiarid. This report discusses various geochemical sample media that have been used for evaluating areas in arid environments and describes case histories in BLM wilderness study areas in which stream-sediment and heavy-mineral-concentrate sample media were compared. As a result of these case history studies, the nonmagnetic fraction of panned heavy-mineral concentrates was selected as the most effective medium for reconnaissance geochemical sampling for resources other than gold, in arid areas. Nonmagnetic heavy-mineral-concentrate samples provide the primary analytical information currently used in geochemical interpretations of mineral resource potential assessment of BLM lands.
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The Federal Land Policy and Management Act of 1976 instructed the Bureau of Land Management (BLM) to review all public lands under its jurisdiction and to determine their suitability or nonsuitability for wilderness designation. As part of this process, the Geological Survey and the Bureau of Mines conduct mineral surveys of areas for which a preliminary determination of wilderness suitability has been made. The BLM has completed its wilderness inventory phase and has found that 23.2 million acres deserve further study for wilderness consideration. These 23.2 million acres of wilderness study areas include 1 million acres of natural and primitive areas (Instant Study Areas), 5.7 million acres in the California Desert Conservation Area, and 16.5 million acres in other wilderness study areas. Mineral surveys on all areas recommended for wilderness will be completed by 1990.
Geological, geochemical, and geophysical evidence, together with a 'review of historical mining and prospecting activities, suggests that most of the Whitewater Wilderness Study Area has low potential for all types of mineral and energy resources- including precious and base metals, building stone and aggregate, fossil fuels, radioactive-mineral resources, and geothermal resources. One small area in the southern part of the study area shows evidence of gold and silver mineralization, and this locality has a low to moderate potential for the discovery of low-grade gold and silver resources.
Geological, geochemical, and geophysical evidence, together with a review of historical mining and prospecting activities, suggests that most of the Bighorn Mountains Wilderness Study Area has low potential for the discovery of all types of mineral and energy resources-including precious and base metals, building stone and aggregate, fossil fuels, radioactive-mineral resources, and geothermal resources. Low-grade mineralization has been documented in one small area near Rattlesnake Canyon, and this area has low to moderate potential for future small-scale exploration and development of precious and base metals. Thorium and uranium enrichment have been documented in two small areas in the eastern part of the wilderness study area; these two areas have low to moderate potential for future small-scale exploration and development of radioactive-mineral resources.
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The U.S. Geological Survey and the U.S. Bureau of Mines have conducted a mineral-resource assessment of the Pusch Ridge Wilderness Area, in Pima County near Tucson Arizona. The study consisted of coordinated geological, geochemical, and mineral resource studies with the objective of evaluating the potential for mineral deposits in the 200 km area. The geochemical survey consisted of the collection of stream-sediment samples, stream-sediment samples taken for panning to produce heavy-mineral concentrates, and rock and water samples. The samples were analyzed by both wet chemical and semiquantita-tive emission spectrographic techniques. The sampling procedures, and methods of sample preparation and analysis were reported by Hinkle and others (1981).
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Measurements of the helium concentration of soil samples collected and stored in Vacutainer-brand evacuated glass tubes show that Vacutainers are reliable containers for soil collection. Within the limits of reproducibility, helium content of soils appears to be independent of variations in soil temperature, barometric pressure, and quantity of soil moisture present in the sample.