Geology topics
Research about Colorado
Source-linked reports with geographic coverage including Colorado.
Geology and mineral deposits of the Needle Mountains District, Southwestern Colorado
The Needle Mountains district is set in highly fractured Precambrian granitic rocks that have intruded and metamorphosed older Precambrian metasedimentary rocks. The Precambrian rocks are overlain by outliers of Paleozoic strata and intruded by a late Tertiary stock. Past mineral production reportedly was limited to silver and gold ores presumably taken from small fissure veins. Although the economic potential of the district has not been adequately explored, some evidence indicates potential for base metal deposits.
Leasable mineral and waterpower land classification map, Leadville quadrangle, Colorado
No abstract available.
Simulated effects of the proposed Narrows Reservoir on the water-table aquifer, along the South Platte River, Morgan County, Colorado
A computer model was used to estimate the effects of the proposed Narrows Reservoir on the alluvial aquifer adjacent to the South Platte River near Fort Morgan, Colo. Changes in ground-water discharge to the river caused by the proposed reservoir were estimated assuming steady-state conditions. The pro-posed reservoir was simulated for two different reservoir pool altitudes. For the conditions simulated, the principal effects of the proposed reservoir on the ground-water system would be an increase in water-table altitude in the aquifer and a redistribution of ground-water discharge to the South Platte River. The proposed reservoir would cause water-level changes in the aquifer between Fort Morgan and the proposed dam. The change in water level at Fort Morgan was less than 1 foot (0.3 metre) for the two reservoir conditions simulated. No significant change in the ground-water system would occur downstream from Fort Morgan. Ground-water discharge to the South Platte River would be decreased at the reservoir site and increased downstream from the proposed reservoir. The model study indicates that ground-water discharge would decrease by 24 cubic feet per second (0.68 cubic metre per second) above the proposed dam and increase by 24 cubic feet per second (0.68 cubic metre per second) below the proposed dam for steady-state conditions with the reservoir pool at 4,404 feet (1,342 metres). Ground-water discharge would decrease by 11 cubic feet per second (0.31 cubic metre per second) above the proposed dam and increase by 15 cubic feet per second (0.42 cubic metre per second) below the proposed dam for steady-state conditions with the reservoir pool at 4,383 feet (1,336 metres).
Leasable mineral and waterpower land classification map, Denver quadrangle, Colorado, showing lands withdrawn, classified, and prospectively valuable for leasable minerals, occurrences of other selected minerals, and lands withdrawn or classified for waterpower and reservoir sites
No abstract available.
Leasable mineral and waterpower land classification map, Durango quadrangle, Colorado, showing lands withdrawn, classified, and prospectively valuable for leasable minerals, occurrences of other selected minerals, and lands withdrawn or classified for waterpower and reservoir sites
No abstract available.
Hydrologic studies of the U.S. Geological Survey related to coal development in Colorado
The coal resources of Colorado are extremely valuable. Viewed in the perspective of the existing energy crisis, coal is the sole energy resource for which the United States is completely self-sufficient. The productive life of known oil and gas fields is measured in decades, whereas the productive life of coal resources, based on present rates of production, is measured in centuries. Twenty-eight percent of the State of Colorado is underlain by coal (fig. 1). The U.S. Bureau of Mines estimates that total coal resources that can be strip mined are approximately 18 billion tons (16.3 billion t). Development of coal resources and associated activities will impact water resources.
Leasable mineral and waterpower land classification map of the Pueblo quadrangle, Colorado
No abstract available.
Analytical data from geologic sampling in the eastern San Juan Mountains, Colorado 1966 to 1968
No abstract available.
Leasable mineral and waterpower land classification map of the Trinidad quadrangle, Colorado: Lands withdrawn, classified, and prospectively valuable for leasable minerals, occurrences of other selected minerals, and lands withdrawn or classified for waterpower and reservoir sites
No abstract available.
Waterlogging in an alluvial aquifer near Lake Minnequa, Pueblo, Colorado
The Lake Minnequa area, located immediately south of the Arkansas River near Pueblo, Colo., is mantled with as much as 46 feet (14 meters) of alluvium covering bedrock of Pierre Shale and Niobrara Formation. Surface water enters the area by the Minnequa Canal and the St. Charles Flood Ditch. The water is stored in Lake Minnequa and other reservoirs. Seepage from St. Charles Reservoirs No. 2 and No. 3 is the major source of water to the alluvial aquifer. The depth of the water table ranges from 0 to 40 feet (0 to 12.2 meters). An 0.5-square-mile (1.3-square-kilometer) area immediately south of Lake Minnequa has a water table less than 6 feet (1.8 meters) below land surface. Lake Minnequa is the principal cause of the shallow water table and resulting waterlogged soil. The bedrock hill east of Lake Minnequa and ground-water flow also contribute to the problem. To eliminate the waterlogging problem, the water table would have to be at least 6 feet (1.8 meters) below land surface. Possible alternatives for eliminating the problem include lowering the water level in Lake Minnequa, placing a network of dewatering wells, or constructing a drainage system in the waterlogged area. (Woodard-USGS)
A geochemical study of oil in metalliferous veins, Idarado Mine, San Juan Mountains, Colorado
A tarry, benzene-soluble material is present in metal-rich veins in the Idarado mine, Ouray County, Colo., in an area not known to have petroleum resources. The material was compared chemically, spectometrically, and chromatographically with oils from four fields in the nearby Paradox basin. Each of these oil fields contains reservoir rocks equivalent to rock units known to extend beneath volcanic rocks near the mine. Carbon and sulfur isotope data and gas chromatographic data indicate a similarity between the oil from the nearby Sierra field and the oil from the mine. Thus, it seems both geologically and chemically possible that oil in the mine originated in Cretaceous sediments. Variations in the composition of oil from the mine and differences between the mine oil and Sierra oil, notably in the distributions of hydrocarbons, are attributed to bacterial degradation.
Brown, yellow, orange, and greenish-black thorites from the Seerie pegmatite, Colorado
Four types of thorite - brown, yellow, orange, and greenish-black - occur together in narrow fracture fillings rich in brown fluorite near the outer edge of the Seerie pegmatite. The brown thorite is by far the most abundant. The thorites are remarkably similar in composition except for their Fe 2 O 3 and UO 2 contents. The common brown thorite contains about 5 percent Fe 2 O 3 , but the other types have only about 0.3 percent. The greenish-black thorite contains about 15 percent UO 2 ; the yellow and orange, about 7 percent; and the brown, about 3 percent. All four thorites have high total rare-earth oxide contents, which vary from 17.3 to 20 percent. The rare-earth assemblage is unusual in that the heavy rare earths predominate, ytterbium being the most abundant lanthanide. Unheated brown and yellow thorites gave thorite X-ray patterns, but the orange and greenish-black types are metamict. All the thorites gave a ThO 2 -UO 2 X-ray pattern as well as a thorite pattern after heating in air for 1- and 2-hour periods at 1,000°C. In addition, the pattern of the greenish-black thorite contained peaks which we ascribe to a second UO 2 compound. Minute black inclusions present in the greenish-black thorite were identified as uraninite by microprobe analysis.
Mapping of mountain soils west of Denver, Colorado, for landuse planning
No abstract available.
Bog stratigraphy, radiocarbon dates, and Pinedale to Holocene glacial history in the Front Range, Colorado
Radiocarbon dates and stratigraphic cores from bogs, kettle ponds, and former ice-marginal lakes on the east and west sides of the Front Range, Colo., between lat 40°00' and 40°24' N. suggest that (1) valley glaciers of Pinedale age began to recede from their terminal positions between about 14,600 and 13,000 yr ago, (2) revegetation of glaciated areas at altitudes of 2,600-2,900 m (8,600-9,500 ft) was complete by 11,000-10,000 yr ago, (3) at one site, 3,500±1,000 yr elapsed before peat began to form after deglaciation, (4) the formation of bogs within the glaciated areas kept pace with glacier recession in a general way, beginning at progressively later times as deglaciation proceeded upward, (5) Pinedale glaciers had disappeared or were reduced to small remnants by about 8,000 yr ago, (6) moraines that have been mapped as belonging to the early stade of Pinedale Glaciation are no younger than 13,000 yr B.P. and may be older than 14,600 yr, and those delimiting what has been mapped as late stade are no younger than about 7,600 yr B.P. and are probably older than 7,800 yr, and (7) most of the till mapped as Pinedale was deposited between about 14,600 and 8,000 yr ago.
Ocher as a prospecting medium in the Montezuma district of central Colorado
Ocher occurs widely In the Montezuma district as small sinters and as bedded deposits of bog iron and ocher-cemented conglomerates. The iron of the ochers is derived from pyrite-rich veins and from pyritic hydrothermally altered rocks. Trace amounts of ore metals in the ocher and its admixed detritus are partly from the pyritic source rocks but also include contributions from other rocks and ores in the watershed, both during and after formation of the ocher deposit. Ocher is evidence for the presence and character of the generally ill exposed pyritic rocks, which are important, in evaluating the porphyry-metal system of ore deposits. The trace-element composition of the ocher is at best a qualitative guide to the ore metals present in the provenance of the ocher deposit but not to their abundance or necessarily to their mode of occurrence.
Fluid inclusion studies of vein, pipe, and replacement deposits, northwestern San Juan Mountains, Colorado
Base and precious metal ores valued in excess of $300 million have been mined from vein, pipe, and replacement deposits located on the northwest side of, and structurally related to, the middle Tertiary Silverton caldera. A belt of normal faults radial to the caldera contains veins which have been mined for as much as 15,000 feet (4,600 m) along strike and 3,700 feet (1,100 m) downdip. Structural relations, metal distributions, and fluid inclusion data suggest that many of the veins were open at the same general time and received the same mineralization. Fluid inclusions in quartz and sphalerite of the main ore stage of the Argentine and adjoining veins have filling temperatures ranging from 315 degrees to 249 degrees C and salinities from 7.9 to 0.1 wt percent NaCl equivalent. However, the majority of inclusions from base metal and gold stages are in a relatively narrow range near 280 degrees to 290 degrees C and salinities are unusually low (less than 2 wt %). Filling temperatures in postsulfide quartz and fluorite are as low as 153 degrees C and salinities are generally less than 0.5 wt percent. A pressure correction of about +25 degrees C should be added to the filling temperatures. Ore fluids were physically homogeneous liquids over the 3,700-foot (1,100 m) vertical and 11,200-foot (3,400 m) lateral range studied and no systematic variations in filling temperatures or salinity in this space are noted, but significant fluctuations are evident locally. Recently developed base metal replacement deposits occur in the Eocene Telluride Conglomerate adjacent to many metal-bearing veins. Calc-silicate alteration of the conglomerate host was probably by moderately saline fluids that ranged in temperature from 320 degrees to about 400 degrees C. Quartz-bearing clasts in altered zones contain secondary halitebearing inclusions with filling temperatures of about 250 degrees C and salinities about 34 wt percent; such inclusions are not known from the base metal stage and are interpreted to have been preore. Hydrothermal quartz, sphalerite, and calcite from replacement pods contain inclusions with filling temperatures ranging from 204 degrees to 309 degrees C and salinities from 11.2 to 0.2 wt percent. That the replacement zones and throughgoing veins are genetically related is suggested by the similarity of filling temperatures and compositions of base metal-stage fluid inclusions and by structural evidence. Small high-grade pipe deposits of base and precious metals occur along the ring-fault zone of the Silverton caldera. Filling temperatures for inclusions in quartz, sphalerite, and barite of the main ore stage of these deposits range from 216 degrees to 308 degrees C and salinities range from 1.6 to 0.2 wt percent NaCl. Quartz in altered wall rocks and silicified capping contains moderately saline secondary inclusions with relatively uniform liquid: vapor ratios that suggest filling temperatures of about 225 degrees to 300 degrees C. From the available samples there is no fluid inclusion evidence for boiling. Throttling, which had been hypothesized to explain the telescoped nature of the pipe ores, is neither substantiated nor discredited by the inclusion data.
The Pikes Peak batholith, Colorado front range, and a model for the origin of the gabbro-anorthosite-syenite-potassic granite suite
This study of the Pikes Peak batholith includes the mineralogy and petrology of quartz syenite at West Creek and of fayalite-bearing and fayalite-free biotite granite near Mount Rosa; major element chemistry of the batholith; comparisons with similar postorogenic, intracratonic, sodic to potassic intrusives; and genesis of the batholith. The batholith is elongate in plan, 50 by 100 km, composite, and generally subalkalic. It was emplaced at shallow depth 1,040 m. y. ago, sharply transects its walls and may have breached its roof. Biotite granite and biotite—hornblende granite are predominant; quartz syenite, fayalite granite and riebeckite granite are present in minor amounts. Fayalite-bearing and fayalite-free quartz syenite, fayalite-biotite granite and riebeckite granite show a well-defined sodic differentiation trend; the less sodic fayalite-free granites exhibit a broader compositional range and no sharp trends. Crystallization was largely at P H2O < P total ; P H2O approached P total only at late stages. Aplite residual to fayalite-free biotite granite in the north formed at about 1,500 bars, or 5 km depth. Feldspar assemblages indicate late stages of crystallization at about 720°C. In the south ilmenite and manganian fayalite indicate f O2 of 10 −17 or 10 −18 bars. Biotite and fayalite compositions and the ‘granite minimum’ imply completion of crystallization at about 700°C and 1,500 bars. Nearby fayalite-free biotite granite crystallized at higher water fugacity. All types of syenite and granite contain 5–6% K 2 O through a range of SiO 2 of 63–76%. Average Na 2 O percentages in quartz syenite are 6.2, fayalite granite 4.2, and fayalite-free granite 3.3 MgO contents are low, 0.03–0.4%; FeO averages 1.9–2.5%. FeO/Fe 2 O 3 ratios are high. Fluorine ranges from 0.3 to 0.6%. The Pikes Peak intrusives are similar in mode of emplacement, composition, and probably genesis to rapakivi intrusives of Finland, the Younger Granites of Nigeria, Cape Ann Granite and Beverly Syenite, Mass., and syenite of Kungnat, Greenland, among others — allowing for different levels of erosion. A suite that includes gabbro or basalt, anorthosite, quartz syenite, fayalite granite, riebeckite granite, and biotite and/or hornblende granites is of worldwide occurrence. A model is proposed in which mantle-derived, convecting alkali olivine basaltic magma first reacts with K 2 O-poor lower crust of granulite facies to produce magma of quartz syenitic composition. The syenitic liquid in turn reacts with granodioritic to granitic intermediate crust of amphibolite facies to produce the predominant fayalite-free biotite and biotite-hornblende granites of the batholith. This reaction of magma and roof involves both partial melting and the reconstitution and precipitation of refractory phases, as Bowen proposed. Intermediate liquids include MgO-depleted and Na 2 O-enriched gabbro, which precipitated anorthosite, and alkali diorite. The heat source is the basaltic magma; the heat required for partial melting of the roof is supplied largely by heats of crystallization of phases that settle out of the liquid — mostly olivine, clinopyroxene and plagioclase.