Subsurface Stratigraphy, Structure, and Alteration in the Senator Thermal Area, Northern Dixie Valley Geothermal Field, Nevada-Initial Results from Injection Well 38-32, and a New Structural Scenario for the Stillwater Escarpment

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Conference Paper: Subsurface Stratigraphy, Structure, and Alteration in the Senator Thermal Area, Northern Dixie Valley Geothermal Field, Nevada-Initial Results from Injection Well 38-32, and a New Structural Scenario for the Stillwater Escarpment

Abstract
Two injection wells (DV 38-32 and DV 27-32) in the Senator thermal area of the northern Dixie Valley geothermal field supply all the injectate reaching the field's northernmost group of production wells. These injectors are also the only wells in the field drilled between the surface trace of the northeast-trending Dixie Valley fault zone, at the base of the Stillwater Range escarpment, and the surface projection of the main geothermal reservoir centered on the fault zone 2-2.5 km to the southeast in Dixie Valley. As such, the Senator injection wells provide new insight into the field's structural geometry, alteration, hydrothermal history, and present-day thermohydrology and injection characteristics. The shallower (301 m) of the two injection wells, 27-32, penetrated alluvium encapsulating an apparently intact block of Jurassic Boyer Ranch Formation quartzite. The deeper (1 168 m) injector encountered the following lithologies, in sequence: alluvium ( I 01-412 m; no samples above the shallower depth); Boyer Ranch quartzite (412-800 m); a mix of the quartzite and Jurassic granodiorite to quartz diorite (granitoid) of the Humboldt igneous complex (800-900 m); essentially all granitoid (900-1055 m); cataclasite (900-1055 m); a massive calcite- fluorite-quartz-adularia vein (1055- 1079 m); total lost-circulation (no sample, 1079- 1082 m); and Triassic phyllite (1082- 1168 m). The cataclasite, mostly derived from a granitoid protolith, contains a downward-increasing component (up to at least 15 vol.%) of brick-red, Tertiary tuffaceous volcanic rock and its comminuted equivalent. The alluvium is intensely silicified below 167 m depth; the quartzite is weakly silicified and sericitized; the granitoid is moderately calcite-chloritesericite- albite altered; the cataclasite is intensely calcite-chlorite- sericite-altered and locally silicified; and the phyllite beneath the thick vein underlying the cataclasite is essentially unaltered.

Authors 
Stuart D. Johnson and Jeffrey B. Hulen






Conference 
GRC Annual Meeting; Reno, NV; 2002/09/22


Published 
Geothermal Resources Council, 2002





DOI 
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Online 
Internet link for Subsurface Stratigraphy, Structure, and Alteration in the Senator Thermal Area, Northern Dixie Valley Geothermal Field, Nevada-Initial Results from Injection Well 38-32, and a New Structural Scenario for the Stillwater Escarpment

Citation

Stuart D. Johnson,Jeffrey B. Hulen. 2002. Subsurface Stratigraphy, Structure, and Alteration in the Senator Thermal Area, Northern Dixie Valley Geothermal Field, Nevada-Initial Results from Injection Well 38-32, and a New Structural Scenario for the Stillwater Escarpment. In: Transactions. GRC Annual Meeting; 2002/09/22; Reno, NV. Davis, CA: Geothermal Resources Council; p. 533-542