Hydrogeology of the Great Basin region of Nevada, Utah, and adjacent states

Book · January 1988with3 Reads
The many geologic formations and rock types found in the Great Basin can be grouped into 12 major hydrogeologic units on the basis of lithology, areal extent, and water-bearing characteristics. The units range in age from Precambrian through Holocene, and represent metamorphic rocks, carbonate and clastic sedimentary rocks of both marine and continental origin, and plutonic and volcanic rocks. Regional aquifers are comprised of basin-fill deposits in all parts of the Great Basin, Paleozoic carbonate rocks (limestone and dolomite) in the eastern Great Basin, and possibly Tertiary and Quaternary volcanic rocks in some parts of the Great Basin.
    • "Carbonate-rock aquifers underlie most of eastern Nevada, including the Spring Valley area, and often form deep regional flow systems that encompass several valleys (Thomas et al., 1986; Plume, 1996; Hershey et al., 2007; Welch et al., 2007). The carbonate rock aquifers are thousands of feet thick and provide a connection for groundwater flow from mountain block recharge areas to valleys (Plume, 1996; Thomas et al., 1996; Mankinen et al., 2006; Lundmark et al., 2007; Welch et al., 2007). "
    Full-text · Article · Nov 2015
    • "The Paleozoic carbonate aquifer is composed of upper and lower permeable members separated by a Mississippian–Devonian confi ning unit (Plume and Carlton, 1988; Dettinger et al., 1995). Aquifer tests within carbonate rocks (Plume and Carlton, 1988; Dettinger et al., 1995 ) yield hydraulic conductivity values between 0.03–10 m/day (10 −11.1 –10 −9.1 m 2 ). This is comparable to values reported by Winograd and Doty (1980) in southwestern Nevada in the vicinity of the Nevada Test Site. "
    [Show abstract] [Hide abstract] ABSTRACT: The Great Basin region in the western United States contains active geothermal systems, large epithermal Au-Ag deposits, and world-class Carlin-type gold deposits. Temperature profiles, fluid inclusion studies, and isotopic evidence suggest that modern and fossil hydrothermal systems associated with gold mineralization share many common features, including the absence of a clear magmatic fluid source, discharge areas restricted to fault zones, and remarkably high temperatures (>200 °C) at shallow depths (200-1500 m). While the plumbing of these systems varies, geochemical and isotopic data collected at the Dixie Valley and Beowawe geothermal systems suggest that fluid circulation along fault zones was relatively deep (>5 km) and comprised of relatively unexchanged Pleistocene meteoric water with small (<2.5%) shifts from the meteoric water line (MWL). Many fossil ore-forming systems were also dominated by meteoric water, but usually exhibit δ18O fluid-rock interactions with larger shifts of 5‰-20‰ from the MWL. Here we present a suite of two-dimensional regional (100 km) and local (40-50 km) scale hydrologic models that we have used to study the plumbing of modern and Tertiary hydrothermal systems of the Great Basin. Geologically and geophysically consistent cross sections were used to generate somewhat idealized hydrogeologic models for these systems that include the most important faults, aquifers, and confining units in their approximate configurations. Multiple constraints were used, including enthalpy, δ18O, silica compositions of fluids and/or rocks, groundwater residence times, fluid inclusion homogenization temperatures, and apatite fission track anomalies. Our results suggest that these hydrothermal systems were driven by natural thermal convection along anisotropic, subvertical faults connected in many cases at depth by permeable aquifers within favorable lithostratigraphic horizons. Those with minimal fluid δ 18O shifts are restricted to high-permeability fault zones and relatively small-scale (∼5 km), single-pass flow systems (e.g., Beowawe). Those with intermediate to large isotopic shifts (e.g., epithermal and Carlin-type Au) had larger-scale (∼15 km) loop convection cells with a greater component of flow through marine sedimentary rocks at lower water/rock ratios and greater endowments of gold. Enthalpy calculations constrain the duration of Carlin-type gold systems to probably <200 k.y. Shallow heat flow gradients and fluid silica concentrations suggest that the duration of the modern Beowawe system is <5 k.y. However, fluid flow at Beowawe during the Quaternary must have been episodic with a net duration of ∼200 k.y. to account for the amount of silica in the sinter deposits. In the Carlin trend, fluid circulation extended down into Paleozoic siliciclastic rocks, which afforded more mixing with isotopically enriched higher enthalpy fluids. Computed fission track ages along the Carlin trend included the convective effects, and ranged between 91.6 and 35.3 Ma. Older fission track ages occurred in zones of groundwater recharge, and the younger ages occurred in discharge areas. This is largely consistent with fission track ages reported in recent studies. We found that either an amagmatic system with more permeable faults (10-11 m2) or a magmatic system with less permeable faults (10-13 m2) could account for the published isotopic and thermal data along the Carlin trend systems. Localized high heat flow beneath the Muleshoe fault was needed to match fl uid inclusion temperatures at Mule Canyon. However, both magmatic and amagmatic scenarios require the existence of deep, permeable faults to bring hot fluids to the near surface.
    Full-text · Article · Jan 2008
    • "Here, ground water is organized into extensive regional systems (Harrill and Prudic, 1998) where it can flow between adjacent topographic ranges and basins. Primary aquifer units include Paleozoic carbonate rocks and Tertiary volcanics that occur regionally, in addition to Cenozoic basin-fill units (Plume and Carlton, 1988; Dettinger and others, 1995; Harrill and Prudic, 1998). Because much of the structure that controls the hydrogeology of the valleys in eastern Nevada is obscured by sediments, geophysical investigations are underway to characterize the subsurface structures and framework influencing ground-water resources. "
    [Show abstract] [Hide abstract] ABSTRACT: Inversion of audiomagnetotelluric (AMT) sounding data collected in eastern Nevada shows significant structure within the upper kilometer of the subsurface that defines the geologic framework from which hydrologic models will be developed. We collected AMT data along two profiles in Spring and Cave valleys in 2004-2005, using the Geometrics StrataGem EH4 system, a four-channel, natural and controlled-source tensor system recording in the range of 10-92,000 Hz. Profiles were 12 and 3 km in length with station spacing of 200-400 m. Two-dimensional inverse models show detailed structure within the alluvial basin including clear transitions between unsaturated and saturated alluvium/volcanic rocks, highly-resistive (>1000 ohm-m) carbonate rocks, and the locations of range-front and intra-basin faults. In addition, our results define the shape of and the depth to the basement surface, which correlates well with depth to basement estimates derived from the inversion of gravity data.
    Full-text · Article · Jan 2006 · Geosphere
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