New Geologic Maps – in Elko and Clark Counties
Open-File Report 13-5
Preliminary Geologic Map of the Tuscarora Geothermal Area, Elko County, Nevada, by Gregory M. Dering and James E. Faulds, 2013
Tuscarora is an amagmatic geothermal system that lies in the northern part of the Basin and Range province, ~15 km southeast of the Snake River Plain and ~90 km northwest of Elko, Nevada. The Tuscarora area is dominated by late Eocene to middle Miocene volcanic and sedimentary rocks, all overlying Paleozoic metasedimentary rocks. A geothermal power plant was constructed in 2011 and currently produces 18 MWe from an ~170°C reservoir in metasedimentary rocks at a depth of 1740 m. Two distinct structural settings at different scales appear to control the geothermal field. The regional structural setting is a 10-km wide complexly faulted left step or relay ramp in the west-dipping range-bounding Independence–Bull Run Mountains normal fault system. Geothermal activity occurs within the step-over where sets of east- and west-dipping normal faults overlap in a northerly trending accommodation zone. The distribution of hot wells and hydrothermal surface features, including boiling springs, fumaroles, and siliceous sinter, indicate that the geothermal system is restricted to the narrow (< 1 km) axial part of the accommodation zone, where permeability is maintained at depth around complex fault intersections. Shallow up-flow appears to be focused along several closely spaced steeply west-dipping north-northeast-striking normal faults within the axial part of the accommodation zone. The recognition of the axial part of an accommodation zone as a favorable structural setting for geothermal activity may be a useful exploration tool for development of drilling targets in extensional terranes, as well as for developing geologic models of known geothermal fields. In addition, the presence of several high-temperature systems in northeastern Nevada demonstrates the viability of electrical-grade geothermal activity in this region despite low present-day strain rates as indicated by GPS geodetic data. Geothermal exploration potential in northeastern Nevada may therefore be higher than previously recognized.
1:24,000; two plates including cross sections, available on the Web:
Open-File Report 13-6
Preliminary Geologic Map of the Valley of Fire East Quadrangle, Clark County, Nevada, by Thomas W. Muntean (Geology Department, Adrian College, Adrian, MI), 2013
The Valley of Fire East quadrangle geologic map is a compilation of previous maps (1:62,500- to 1:250,000-scale maps) from the region and new mapping. New geologic mapping was primarily conducted to resolve the local stratigraphy of, and structural features affecting, the late Neogene Muddy Creek Formation (MCF) at the 1:24,000 scale. Compilation mapping was predominantly used to improve the resolution of pre-MCF unit contacts and exposures within the map area.
1:24,000; plate and text, available on the Web: