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Research about Gunnison County, Colorado

Source-linked reports with geographic coverage including Gunnison County, Colorado.

13 recordsLinked to original sources
USGS2025

Remote sensing of chlorophyll a and temperature to support algal bloom monitoring in Blue Mesa Reservoir, Colorado

We present methods to reconstruct historical chlorophyll a and surface water temperatures from satellite-based remote sensing products for Blue Mesa Reservoir, Colorado, to support algal bloom monitoring. A machine learning model was trained to construct chlorophyll a concentrations from Sentinel-2 satellite imagery and in situ measurements of chlorophyll a concentrations (out of bag RMSE = 1.9 μg/L, R 2 = 0.63) and reconstruct summertime chlorophyll a concentrations over the entire reservoir from 2016 through 2023. Concurrently, we developed an approach to retrieve remotely sensed water temperatures from the Landsat collection 2 provisional surface temperature product (MAE = 0.6°C) and reconstructed summertime surface water temperature records from 2000 through 2023. Finally, we demonstrate how the reconstructed chlorophyll a and temperature records can yield insight on reservoir dynamics. The chlorophyll a records indicate that algal blooms have a consistent spatial pattern across multiple years, initiating in the eastern end of the reservoir and spreading to the west over time. Water temperatures increased at a linearized rate of 0.3°C per decade from 2000 through 2023 and were inversely proportional to reservoir water surface elevation. Finally, mean summer remotely sensed chlorophyll a concentration had a moderately positive correlation with mean summer remotely sensed water temperature.

Colorado↗
USGS2019

Heterogeneity in hyporheic flow, pore water chemistry, and microbial community composition in an alpine streambed

The hyporheic zone, where surface water and groundwater mix, is an important microbial habitat where biogeochemical reactions influence water quality. We show that spatial variability in hyporheic flow in the East River near Crested Butte, Colorado, drives heterogeneity in streambed geochemical conditions and microbial community assemblages, but the diversity of assemblages remains nearly constant throughout the reach. In July 2018, we collected approximately 100 pore water samples at 20 cm depth and analyzed them for anions, cations, dissolved organic carbon, dissolved organic matter (DOM) quality, and basic water quality parameters. Vertical hydraulic head gradients were also measured to assess the potential for upward or downward flow, and heat tracing was used to quantify vertical flux rates at a subset of locations. We found that regions of the streambed that are more groundwater-dominated contain less dissolved oxygen, higher concentrations of reduced metals, and more microbially-processed, recalcitrant DOM, while more surface water-dominated locations contain higher dissolved oxygen concentrations and terrestrially-derived, labile DOM. 16S rRNA gene sequencing of extracted DNA revealed that microbial community composition varies with geochemical gradients related to hyporheic flow. These findings provide a better understanding of hyporheic controls on streambed biogeochemistry during the baseflow season, which is expected to lengthen with climate change in alpine watersheds due to earlier snowmelt onset and reduced snowpack.

Colorado↗
USGS2009

The Iron Hill (Powderhorn) carbonatite complex, Gunnison County, Colorado — A potential source of several uncommon mineral resources

A similar version of this slide show was presented on three occasions during 2008: two times to local chapters of the Society for Mining, Metallurgy, and Exploration (SME), as part of SME's Henry Krumb lecture series, and the third time at the Northwest Mining Association's 114th Annual Meeting, held December 1-5, 2008, in Sparks (Reno), Nevada. In 2006, the U.S. Geological Survey (USGS) initiated a study of the diverse and uncommon mineral resources associated with carbonatites and associated alkaline igneous rocks. Most of these deposit types have not been studied by the USGS during the last 25 years, and many of these mineral resources have important applications in modern technology. The author chose to begin this study at Iron Hill in southwestern Colorado because it is the site of a classic carbonatite complex, which is thought to host the largest known resources of titanium and niobium in the United States.

Colorado↗
USGS2009

Geochemistry of standard mine waters, Gunnison County, Colorado, July 2009

In many hard-rock-mining districts water flowing from abandoned mine adits is a primary source of metals to receiving streams. Understanding the generation of adit discharge is an important step in developing remediation plans. In 2006, the U.S. Environmental Protection Agency listed the Standard Mine in the Elk Creek drainage basin near Crested Butte, Colorado as a superfund site because drainage from the Standard Mine enters Elk Creek, contributing dissolved and suspended loads of zinc, cadmium, copper, and other metals to the stream. Elk Creek flows into Coal Creek, which is a source of drinking water for the town of Crested Butte. In 2006 and 2007, the U.S. Geological Survey undertook a hydrogeologic investigation of the Standard Mine and vicinity and identified areas of the underground workings for additional work. Mine drainage, underground-water samples, and selected spring water samples were collected in July 2009 for analysis of inorganic solutes as part of a follow-up study. Water analyses are reported for mine-effluent samples from Levels 1 and 5 of the Standard Mine, underground samples from Levels 2 and 3 of the Standard Mine, two spring samples, and an Elk Creek sample. Reported analyses include field measurements (pH, specific conductance, water temperature, dissolved oxygen, and redox potential), major constituents and trace elements, and oxygen and hydrogen isotopic determinations. Overall, water samples collected in 2009 at the same sites as were collected in 2006 have similar chemical compositions. Similar to 2006, water in Level 3 did not flow out the portal but was observed to flow into open workings to lower parts of the mine. Many dissolved constituent concentrations, including calcium, magnesium, sulfate, manganese, zinc, and cadmium, in Level 3 waters substantially are lower than in Level 1 effluent. Concentrations of these dissolved constituents in water samples collected from Level 2 approach or exceed concentrations of Level 1 effluent suggesting that water-rock interaction between Levels 3 and 1 can account for the elevated concentration of metals and other constituents in Level 1 portal effluent. Ore minerals (sphalerite, argentiferous galena, and chalcopyrite) are the likely sources of zinc, cadmium, lead, and copper and are present within the mine in unmined portions of the vein system, within plugged ore chutes, and in muck piles.

Colorado↗
USGS1985

Mineral resource potential map of the Fossil Ridge Wilderness Study Area, Gunnison County, Colorado

Parts of the Fossil Ridge Wilderness Study Area have a high resource potential for gold and silver in small deposits, uranium in medium-size deposits, and high-calcium limestone in large deposits. Parts have a moderate to high potential for uranium, thorium, and light rare-earth elements in small- to medium-size deposits, a moderate potential for copper, lead, and zinc in small deposits, a low potential for molybdenum in small deposits, and an unknown potential for molybdenum in deposits of unknown size. Parts of the area have a low potential for cobalt, chromium, tungsten, beryllium, boron, and tin in small deposits. And, depending on the extraction of precious metals, parts of the area could have a low potential for arsenic in small deposits. Tungsten, rare-earth elements, and tin could not be considered resources except for coexisting base metals, thorium, and uranium. Areas that immediately adjoin the Fossil Ridge Wilderness Study Area have a high potential for molybdenum in large deposits, lead in medium-size deposits, and zinc -in small- to medium-size deposits. Depending on the extraction of base metals, parts of the adjoining areas could have a low resource potential for bismuth and cadmium as byproducts in medium-size deposits.

Colorado↗
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.

Colorado↗
USGS1954

Thorium and rare earth minerals in the Powderhorn district, Gunnison County, Colorado

Thorium has been found since 1949 in at least 33 deposits in an area 6 miles wide and 20 miles long in the Powderhorn district, Gunnison County, Colo. The district is composed largely of pre-Jurassic metamorphic and igneous rocks, which are chiefly if not entirely pre-Cambrian in age. The metamorphic and igneous rocks are overlain by sandstone of the Morrison formation of Jurassic age, and by volcanic rocks of the Alboroto group and Hinsdale formation of Miocene and Pliocene (?) age, respectively. The thorium deposits occur in or near alkalic igneous rocks in which such elements as titanium, rare earths, barium, strontium, and niobium occur in greater-than-average amounts. The greatest mass of the alkalic igneous rocks the Iron Hill composite stoc,- occupies an area of 12 square miles in the southeastern part of the district. The age of the thorium deposits, like that of the alkalic igneous rocks, is not known other than pre-Jurassic. The thorium veins and mineralized shear zones range from a few inches to 18 feet in thickness and from a few feet to 3,500 feet in length. The veins are composed of calcite,.dolomite, siderite, ankerite, quartz, barite, pyrite, sphalerite, galena, goethite,. apatite, alkali feldspar, and many other minerals. The thorium occurs at least partly in thorite or hydrothorite. Sparse xenotime has been tentatively identified in one deposit. Several minerals containing rare earths of the cerium group as major constituents are found in carbonate veins near Iron Hill. Bastnaesite has been identified by X-ray methods, and cerite and synchisite are probably present also.The fluorapatite in some veins and in parts of the carbonate rock mass that occupies 2 square miles in the central part of the Iron Hill complex contains rare earths of the cerium group, generally in amounts of a fraction of a percent of the rock. The radioactivity of the deposits appears to be due almost entirely to thorium and its daughter products The ThO 2 content of selected highgrade samples from the Little Johnnie vein is as much as 4 percent. The ThO 2 content of the veins is generally less than 1 percent, however, and is only 0.05 to 0.1 percent in many of the veins studied. The little Johnnie vein, which was mapped in detail, can be traced discontinuously for a distance of more than 3,500 feet. The thoriumbearing material occurs as irregular veinlets and thin films introduced into the fault zone. The mineralized shear zone ranges from less than 6 inches to 5 feet in thickness. Near its west end the vein is broken by many faults in a zone that marks the edge of a roughly circular fault block, 1 1/2. miles in diameter, that has dropped 1,000 feet or more since the deposition of Miocene volcanic-rocks that now floor the Milkranch basin.

Colorado↗
USGS1952

Geology of the Quartz Creek Pegmatite District, Gunnison County Colorado

The Quartz Creek pegmatite district includes an area about 29 square miles in the vicinity of Quartz Creek in Gunnison County,. Colo. This area contains 1,803 pegmatites that are intruded into pre-Cambrian rocks. The rocks exposed in the district range in age from pre-Cambrian to Recent. The oldest pre-Cambrian rocks are chiefly quartzites interbedded with a few arkoses and conglomerates. These rocks are surrounded by more abundant hornblende gneiss and tonalite. A small body of biotite tonalite was intruded and two thin layers of dacitic pillow lava were extruded into this series. The hornblende gneiss and tonalite have the same composition and differ only in texture. The older material (hornblende gneiss) has a well-marked lineation, whereas the younger (tonalite) is equigranular. Subsequently, a large body of quartz monzonite was intruded along the northern boundary of the mapped area. Later, coarse-grained granite was intruded into the southern part of the area. Dikes of fine-grained granite cut the coarse-grained variety. The last period of intrusive activity in pre-Cambrian time is marked by a large number of pegmatites. The pre-Cambrian rocks were tilted and eroded, and the flatlying Jurassic Morrison formation was deposited on the irregular surface. This formation is conformably overlain by the Cretaceous Dakota sandstone. Faulting produced a vertical offset of 410 feet in the Mesozoic sediments along the only large fault in the area. At the end of Mesozoic time there was another period of erosion. Tertiary (?) tuff is exposed in small, scattered areas in the southern part of the district. It overlies both the Dakota sandstone and pre-Cambrian formations. Glacial till occurs along the edges of Quartz Creek and Wood Gulch. Quaternary alluvium fills the valley bottoms. Although the composition of the country rock has little effect on the shape of the pegmatites, the foliation imposed on this rock has a localizing effect and in part controls the ultimate shape of pegmatites. Zoned and related internal structures are not well developed in the pegmatites of this region. Many of the pegmatites are homogeneous and those that are zoned usually contain a large wall zone and small discontinuous cores. In addition to the more common homogeneous and zoned pegmatites, 7 percent of the pegmatites show a layered structure of textural and mineralogical units not repeated on the opposite side of the pegmatite. Other internal structural units include pegmatites which vary in composition along strike, multiple or “line-rock pegmatites” and fracture fillings. The mineralogy of the pegmatites is described in detail. Specific attention was given to most of the 27 observed minerals. A study of the index of refraction of 439 specimens of plagioclase showed that the variation from zone to zone and layer to layer is minor and that there is no systematic variation in respect to the entire district. No correlation could be found between the refractive index of plagioclase in the pegmatites and the type country rock, or the presence of various accessory minerals. Index of refraction determinations on 95 specimens of muscovite showed no constant variation from wall zone to core or from layer to layer. Curved muscovite has identical optical properties with the flat variety. The index of refraction was determined for 189 beryl specimens. The beryl in the pegmatites containing only a wall zone and a core showed no difference between zones, but in pegmatites that have intermediate zones, the indices of refraction of the beryl showed an inward increase in the alkali content from the contact. Beryl occurs with almost all of the pegmatite minerals and is not restricted in its mineral associations. Tourmaline, except the black variety, is associated with lepidolite. Dark green and blue tourmaline is found in the outer zones of pegmatites containing lepidolite, and the pink and light green varieties are found in direct contact with lepidolite. Lepidolite occurs in aggregates of fine grains, in flat plates, and in curved plates; the three varieties are optically identical. The lighter-colored varieties have higher indices of refraction and contain less lithia than the darker varieties. In addition, the occurrence of the following minerals is described in detail: perthite, quartz, martite, biotite, garnet, columbite-tantalite, monazite, microlite, topaz, gahnite, allanite, and an unidentified mineral. The lack of alteration in the wall rocks adjacent to the pegmatites is interpreted as indicating that the original pegmatite magma did not have an excess of materials such as B, OH-, and P that are needed to form alteration minerals. Because of their low concentration, the above materials were available only in the pegmatitic magma during its crystallization. Pegmatites that contain the rare minerals such as beryl, tourmaline, curved muscovite, biotite, magnetite, monazite, columbite-tantalite, cleavelandite, topaz, lepidolite, and microlite show a grouping in clusters within the district. Beryl-bearing pegmatites occur most abundantly in hornblende gneiss and are only rarely found in either granite or quartz monzonite. The types of minerals that form in a pegmatite appear to be determined by the character of the material segregated from the original magma and the period in which it segregated. The elements escape at one period and may be from only-a specific pocket in the magma. These liquids tend to form groups of pegmatites in which the later bodies contain a high proportion of volatiles. Inferred reserves of the district are estimated for beryl, scrap mica, both hand-cobbing and milling feldspar, lepidolite, columbite-tantalite, topaz, monazite, and microlite. No sheet mica was found. Reserves are small and transportation costs are high so substantial production of low-priced feldspar and scrap mica will depend on the adoption of economica milling techniques for recovering the large quantities of feldspar available. Beryl is irregularly distributed and its recovery as a byproduct will depend on the establishment of a stable market for feldspar and scrap mica. Lepidolite reserves are small low grade.

Colorado↗