Conceptual Models of Geothermal Resources in the Eastern Great Basin

Abstract

Producing geothermal fields in the eastern Great Basin include Beowawe, Cove Fort, Dixie Valley, Raft River, Roosevelt, Thermo, and Tuscarora. In these, fault-fracture systems, typically associated with range fronts and basin margins, localize hydrothermal fluid flow from the surface down to more than 2-3 kms depth. Additional types of geothermal resources include hot sedimentary aquifers, which are inferred to exist in the Steptoe and Elko basins in Nevada and beneath the Black Rock desert in Utah. An EGS type resource (FORGE Utah DOE site) has been identified in the north Milford valley, Utah, where a broad area of conductive heat flow occurs within a very large volume of crystalline rock made of granodiorite and gneiss. The diversity of geothermal resources is simply an expression of the elevated heat flow and local geology, which controls the storage and flow of hot fluids. The geothermal resource at Beowawe appears to be a hybrid model where a strong connection exists between a deep hot carbonate aquifer, which is laterally extensive, and a narrow fault fracture mesh, which focusses hydrothermal upflow to the surface. This model is supported by the chemical composition of the produced fluid, which is dominated by aqueous bicarbonate despite producing from a siliciclastic rock formation, and the very large sinter sheet, which required more than 200 km^3 of hot water to account for all the silica. Beowawe appears to hold much greater geothermal potential than what could have been predicted from the exploration and production drilling, showing the promise of other large resources in the region.