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Research about Colorado

Source-linked reports with geographic coverage including Colorado.

At least 1,261 records · Page 70Linked to original sources
USGS1993

Mineralogy, mineral chemistry, and paragenesis of gold, silver, and base-metal ores of the North Amethyst vein system, San Juan Mountains, Mineral County, Colorado

Gold-rich adularia-sericite-type mineralization occurs near the southern margin of the San Luis caldera, at the intersection of the Equity fault and the northern extension of the Amethyst fault system. Mineralized rock is confined primarily to steeply dipping structures in silicified rhyolite and dacite. Intense sericitic alteration occurs at higher levels in the vein system, and wall rock adjacent to some veins is bleached. The ores are multiply brecciated, and vein filling locally shows sedimentary textures. Textural, mineralogical, and chemical criteria indicate that there are at least two partially coextensive associations of mineral assemblages separated by periods of brecciation and sedimentation. An older gold-bearing association consists of two fine-grained ore stages, both of which contain electrum, uytenbogaardtite, tetrahedrite, silver sulfosalts, silver sulfides and base-metal sulfides, and a manganese-rich stage containing the assemblages (1) manganese silicate + manganese carbonate minerals + quartz and (2) magnetite + hematite + pyrite + quartz. A younger crosscutting association contains calcite, adularia, fluorite, and quartz, plus the assemblages (1) coarse-grained basemetal sulfides and (2) hematite + chlorite + quartz. Quartz, manganese-rich calcite, and trace pyrite line late-stage vugs. Mineralogic, lead-isotopic, and fluid-inclusion characteristics of the younger association are similar to those of ores of the southern and central parts of the Creede mining district. In contrast, the gold and manganese-silicate assemblages of the older association are rare to absent in the southern and central parts of the district. The local and early occurrence of the manganese and gold assemblages may indicate that they formed in a small hydrothermal cell that predated the extensive hydrothermal system from which ores of the central and southern parts of the Creede district are proposed to have been deposited (Bethke, 1988). If similar early-stage cells were present in the southern and central parts of the district, they may have been replaced or overprinted by later assemblages, and they may remain to be discovered. In the latter case, mineral assemblages that formed at early stages in the paragenesis hold the most promise for gold exploration.

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USGS1993

Geomorphic, hydrologic, and erosion data for selected reclaimed hillslopes, the Seneca II mine, Routt County, Colorado, October 1988-July 1990

Geomorphic, hydrologic, and erosion data were collected from five reclaimed hillslopes at the Seneca II mine near Hayden, Colorado. Hillslope surveys were used to determine hillslope lengths, which range from 670 to 1,280 ft, and hillslope gradients, which range from 0.17 to 0.23 ft/ft (17 to 23 percent). Elevations in the study area range from 6,890 to 7,140 feet and hillslope aspect generally is west or south. Mean total vegetation cover ranges from 74 to 91 percent. Total monthly precipitation for December 1988 through May 1990 was computed from daily measurements made with weighing-bucket precipitation gages. Several snowpack measurements were made during 2 winters. Volumetric soil-water content was determined at incremental depths using a neutron probe and in the upper 11.8 in of soil using a time-domain reflectometer. Active and recent soil erosion was indicated by the presence of rills. Rill density (the sum of rill lengths/unit area) was computed at 50-feet intervals along each hillslope study area. Differences in soil-surface elevations between September or October 1989 and June 1990 were determined with an erosion frame and replicate soil-surface surveys at 16 erosion-study plots.

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USGS1993

Reconnaissance investigation of water quality, bottom sediment, and biota associated with irrigation drainage in the Pine River Project area, Southern Ute Indian Reservation, southwestern Colorado and northwestern New Mexico, 1988-89

During 1988-89, water, bottom sediment, biota, soil, and plants were sampled for a reconnaissance investigation of the Pine River Project area in southwestern Colorado. Irrigation drainage does not seem to be a major source of dissolved solids in streams. Concentrations of manganese, mercury, and selenium exceeded drinking-water regulations in some streams. The maximum selenium concentration in a stream sample was 94 microg/L in Rock Creek. Irrigation drainage and natural groundwater are sources of some trace elements to streams. Water from a well in a nonirrigated area had 4,800 microg/L of selenium. Selenium concentrations in soil on the Oxford Tract were greater in areas previously or presently irrigated than in areas never irrigated. Some forage plants on the Oxford Tract had large selenium concentrations, including 180 mg/km in alfalfa. Most fish samples had selenium concentrations greater than the National Contaminant Biomonitoring Program 85th percentile. Selenium concentrations in aquatic plants, aquatic inverte- brates, and small mammals may be of concern to fish and wildlife because of possible food-chain bioconcentration. Selenium concentrations in bird samples indicate selenium contamination of biota on the Oxford Tract. Mallard breasts had selenium concentrations exceeding a guideline for human consumption. The maximum selenium concentration in biota was 50 microg/g dry weight in a bird liver from the Oxford Tract. In some fish samples, arsenic, cadmium, copper, and zinc exceeded background concentrations, but concentrations were not toxic. Mercury concentrations in 16 fish samples exceeded the background concentration. Ten mercury concentrations in fish exceeded a guideline for mercury in food for consumption by pregnant women.

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USGS1993

Landfill mapping using multi-disciplinary geophysical techniques at the U.S. Air Force Academy, Colorado Springs, CO

This paper describes a multi-disciplinary geophysical survey conducted over a landfill on the U.S. Air Force Academy grounds near Colorado Springs, Colorado. The landfill is known to contain waste generated during the construction of the Academy and reportedly contains buried steel drums. The purpose of the geophysical surveys was to determine the subsurface distribution of buried metallic objects within the landfill. Different geophysical techniques were evaluated along a test line to determine their relative effectiveness at this site. The geophysical methods included total magnetic field, vertical magnetic gradient, VLF, horizontal and vertical coplanar electromagnetic, GPR and seismic refraction. Magnetic and coplanar electromagnetic (EM) methods were chosen to survey the entire landfill because they easily detected magnetic and conductive sources and have better anomaly resolution than other methods evaluated, as demonstrated by the test line results. In addition, these methods are rapid and cost effective for surveys involving a large number of measurements. Surveys of the landfill identified numerous magnetic and conductive anomalies indicating the presence of buried metallic objects. The vertical gradient and EM measurements indicate that several of the large total field anomalies are produced by groups of smaller objects rather than by single, large buried sources. Many of the smaller anomalies are associated with the position of a recently dismantled railroad track and result from iron and steel parts buried along the abandoned grade. Two long, narrow conductive anomalies were identified by the electromagnetic surveys. These conductive features have no surface expression and apparently run the length of the landfill. The EM data indicates these conductors are narrow and relatively shallow. One conductor is relatively magnetic, the other conductor has no magnetic signature suggesting a different composition. The geophysical surveys determined that large areas of the landfill are relatively free of buried metal due to the lack of observed magnetic or conductive anomalies. The geophysical data also suggests the landfill may be larger than originally thought. Numerous magnetic and conductive responses were observed beyond the eastern edge of the present landfill in an area thought to be natural terrain.

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USGS1993

Slumgullion; Colorado’s natural landslide laboratory

The mammoth Slumgullion landslide in southwestern Colorado is the largest actively moving landslide in Colorado and, perhaps, the entire country. To learn more about how and why landslides move the way they do, scientists at the U.S Geological Survey (USGS) have observed and monitored the remarkably regular movement of this landslide for more than 30 years. Located near Lake City in the San Juan Mountains, Slumgullion was chosen for a comprehensive study of landslide processes because part of the landslide appears to have been moving continuously for the past 300 years, transporting material hundreds of meters downslope, and because the slide has the potential to threaten life and property. Surface features of the landslide, such as folds and faults within the sliding mass, are constantly changing, either being created or destroyed by the continuous movement of the landslide. Current evaluation of hazards includes possible landslide. Current evaluation of hazards includes possible landslide damage to State Highway 149 and recreational areas in the vicinity of Lake San Cristobal. The mountains of Colorado, and the Rocky Mountains in general, have one of the highest levels of landslide hazard in the nation. In a typical year, landslides hazard in the nation. In a typical year, landslides cause several fatalities and millions of dollars in damage to highways, pipelines, buildings, and forests in Colorado. To reduce such losses we need to understand why landslides occur and how they behave once they form. The Slumgullion landslide, an ideal natural laboratory, offers a unique opportunity to carefully observe and monitor the movement of a large, active landslide. In 1990, soon after the State of Colorado assigned high priority to hazard evaluation of the Slumgullion landslide, the USGS began an intensive study as part of its Landslide Hazards Reduction Program.

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USGS1993

The Golden bypass landslide, Golden, Colorado

Slope instability along a new highway bypass in Golden, Colorado, became a major concern in 1993. Rains and snowmelt accelerated movement of a landslide that had begun to develop before the bypass was opened to traffic in July of 1991. The downslope movement of earth materials increased significantly in 1993. During the first few months of the year, the landslide pushed onto the west shoulder of the road and crumpled the pavement beneath the south-bound lane. As we prepare this article (September, 1993), the slide continues to encroach onto the highway, posing a persistent problem despite repeated efforts to slow or stop its movement. As this article will show, permanent solutions to landslide problems of this kind are difficult to obtain.

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USGS1992

Pliocene and Pleistocene geologic and climatic evolution in the San Luis Valley of south-central Colorado

Sediments of the Alamosa Formation spanning the upper part of the Gauss and most of the Matuyama Chrons were recovered by coring in the high (2300 m) San Luis Valley of south-central Colorado. The study site is located at the northern end of the Rio Grande rift. Lithologic changes in the core sediments provide evidence of events leading to integration of the San Luis drainage basin into the Rio Grande. The section, which includes the Huckleberry Ridge Ash (2.02 Ma) and spans the entire Matuyama Chron, contains pollen, and invertebrate and vertebrate fossils. Stable isotope analyses of inorganic and biogenic carbonate taken over most of the core indicate substantially warmer temperatures than occur today in the San Luis Valley. At the end of the Olduvai Subchron, summer precipitation decreased, summer pan evaporation increased, and temperatures increased slightly compared to the earlier climate represented in the core. By the end of the Jaramillo Subchron, however, cold/wet and warm/dry cycles become evident and continue into the cold/wet regime associated with the deep-sea oxygen-isotope Stage 22 glaciation previously determined from outcrops at the same locality. Correspondence between the Hansen Bluff climatic record and the deep-sea oxygen-isotope record (oxygen-isotope stages from about 110-18) is apparent, indicating that climate at Hansen Bluff was responding to global climatic changes.

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