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Research about Colorado

Source-linked reports with geographic coverage including Colorado.

At least 1,567 records · Page 87Linked to original sources
USGS1979

K-Ar age of alunite alteration at Red Mountain, Lake City area, western San Juan Mountains, Colorado

The San Juan Mountains of southwestern Colorado are famous for rich vein deposits of base and precious metals and for patterns of conspicuous hydrothermal alteration. Areas of acid-sulfate alteration, characterized by extensive base leaching of volcanic rocks or hypabyssal plutons, are of current interest because of their local association with Au, Ag, and, in some cases, U mineralization (Lipman and others, 1976; Cunningham and others, 1978; Steven and others, 1979). Potential may also exist for recovery of aluminum from altered rocks rich in alunite (Hall, 1978). Alunite has been shown to be suitable for K-Ar dating in other mining districts (Mehnert and others, 1973b; Ashley and Silberman, 1976). We report here two concordant K-Ar ages determined on hydrothermal alunite from Red Mountain, in the Lake City area of the western San Juan Mountains.

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USGS1979

Stratigraphic sections of Jurassic San Rafael Group and adjacent rocks in Routt, Park, Pitkin, and Gunnison counties, Colorado

These sections were measured prior to 1960, before adoption of the metric system. Publication was delayed by other assignments of the authors and later by the untimely death of J. C. Wright. They are being released at this time because of the increased interest in the uranium potential of Jurassic rocks. The Curtis and Entrada are the only formations of the San Rafael Group that are present in these sections.

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USGS1979

Water-resources investigations of the U.S. Geological Survey in Colorado; fiscal year 1979

Water-resources investigations of the U.S. Geological Survey in Colorado consist of collecting water-resources data and conducting interpretive hydrologic investigations. The water-resources data and the results of the investigations are published or released by either the U.S. Geological Survey or by cooperating agen-cies. This report describes the water-resources investigations in Colorado for the 1979 fiscal year (October 1, 1978, to September 30, 1979). The U.S. Geological Survey's investigations of the water resources of Colo-rado are under the direction of James F. Blakey, District Chief. The Colorado District office is located in Building 53, Denver Federal Center, Lakewood, Colo. (fig. 1). The Colorado District has four subdistrict offices located in Grand Junction, Lakewood, Meeker, and Pueblo (fig. 1).

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USGS1979

Reconnaissance evaluation of surface-water quality in Eagle, Grand, Jackson, Pitkin, Routt, and Summit Counties, Colorado

Water-quality data were collected from streams in a six-county area to determine if the streams were polluted and, if so, to determine the sources of the pollution. Eighty-three stream sites were selected for sampling in Eagle, Grand, Jackson, Pitkin, Routt, and Summit Counties. Also included are data from 28 sites in Routt County collected for a U.S. Geological Survey cooperative study on the Yampa River basin. A summary of data collected prior to this study, results of current chemical and biological sampling, and needs for future water-quality monitoring are reported for each county. The kinds of data collected were site specific depending upon land-use activities. Data collected at selected sites included temperature, pH, specific conductance, dissolved oxygen, and stream discharge. Chemical data collected included nutrients, inorganics, organics, and trace elements. Biological data collected included counts and species composition of total and fecal-coliform bacteria, fecal-streptococcus bacteria, benthic invertebrates, and phytoplankton. Most of the sites were sampled three times: in April-June 1976, August 1976, and January 1977. The major water-quality problems at the 17 sites sampled in Eagle County are related to mining, recreation, and geology. The Eagle River and Cross Creek in the vicinity of Minturn have concentrations of trace elements that exceed water-quality standards. Gore Creek is influenced by winter recreational use and the water during the winter has total bacteria counts as great as 72,000 per 100 milliliters and concentrations of un-ionized ammonia greater than 0.02 milligrams per liter downstream from the sewage-treatment plant. Mineralized water in the downstream reaches of the Eagle River results from natural chemical processes. The water-quality problems in Grand County, especially on the Fraser River, are related to recreation and urban activities. Chemical and biological indications of water-quality degradation exist for the Fraser River downstream from Winter Park.

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USGS1979

Abundance and distribution of thorium in the carbonatite stock at Iron Hill, Powderhorn District, Gunnison County, Colorado

The carbonatite stock at Iron Hill is part of an alkalic complex of Cambrian or latest Precambrian age containing pyroxenite, uncompahgrite, ijolite, nepheline syenite, and related rocks characterized by their subsilicic composition and by their lack of calcic plagioclase. Thorium averages 36.2 parts per million (ppm) Th (0.0041 percent Th0 2 ) in the carbonatite, which also contains considerably more Ba, Ce, Nd, La, Nb, P, Mn, Mo, Sr, U, and rare-earth elements than average igneous rocks. Thorium content of the carbonatite ranges from 6 ppm Th (0.0007 percent Th0 2 ) 150 ppm Th (0.017 percent Th0 2 ), and several areas of anomalous concentration are apparent. The distribution of thorium is not the same as the distribution of niobium and rare-earth elements. Thorium abundances of the level found in the carbonatite at Iron Hill are of little economic interest unless considered as a byproduct of potential niobium, rare-earth, and uranium exploitation.

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USGS1979

Digital-transport model study of Diisopropylmethylphosphonate (DIMP) ground-water contamination at the Rocky Mountain Arsenal, Colorado

Diisopropylmethylphosphonate (DIMP) is an organic compound produced as a byproduct of the manufacture and detoxification of GB nerve gas. Ground-water contamination by DIMP from the disposal of wastes into unlined surface ponds at the Rocky Mountain Arsenal occurred from 1952 to 1956. A digital-transport model was used to determine the effects on ground-water movement and on DIMP concentrations in the ground water of a bentonite barrier in the aquifer near the northern boundary of the arsenal. The transport model is based on an iterative-alternating- direction-implicit mathematical solution of the ground-water-flow equation coupled with a method-of-characteristics solution of the solute-transport equation. The model assumes conservative (nonreactive) transient transport of DIMP and steady-state ground-water flow. In the model simulations, a bentonite barrier was assumed that was impermeable and penetrated the entire saturated thickness of the aquifer. Ground water intercepted by the barrier was assumed to be pumped by wells located south (upgra-dient) of the barrier, to be treated to remove DIMP, and to be recharged by pits or wells to the aquifer north (downgradient) of the barrier. The amount of DIMP transported across the northern boundary of the arsenal was substantially reduced by a ground-water-barrier system of this type. For a 1,500-foot-long bentonite barrier located along the northern boundary of the arsenal near D Street, about 50 percent of the DIMP that would otherwise cross the boundary would be intercepted by the barrier. This barrier configuration and location were proposed by the U.S. Army. Of the ground water with DIMP concentrations greater than 500 micro- grams per liter, the safe DIMP-concentration level determined by the U.S. Army, about 72 percent would be intercepted by the barrier system. The amount of DIMP underflow intercepted may be increased to 65 percent by doubling the pumpage, or to 73 percent by doubling the length of the barrier.

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USGS1979

Hexavalent chromium in the ground and surface waters near Telluride, Colorado; preliminary data report

Data showing results of 38 groundwater and 25 surface-water samples analyzed for hexavalent chromium are presented. Most samples were taken within the Telluride, Colo., city limits during October 1978. Twenty-four of the 38 groundwater samples (63%) contained more than 50 micrograms per liter of hexavalent chromium. Excluding the mill tailings pond 6 of the 23 surface-water samples (26%) contained more than 50 micrograms per liter of hexavalent chromium. Hexavalent chromium concentrations in groundwaters ranged from 0 to 2700 micrograms per liter and in surface waters from 0 to 160 micrograms per liter.

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