Preliminary Geological and Geophysical Evaluation of the Castle Dome HDR Geothermal Prospect, Southwestern Arizona

Abstract

The Castle Dome HDR geothermal prospect is located in Yuma County, Arizona, in a region centered about 80km north of Yuma along U.S. Rte. 95. The area of interest is broadly defined by a negative residual Bouguer gravity anomaly which is about 45 km across, steep sided in many places, and as much as 30 mgals in magnitude. The geology of this Basin and Range area is poorly known, but the few published reports and current Los Alamos Scientific Laboratory (LASL) field studies indicate that the Castle Dome Mountains and adjacent ranges are chiefly a thick pile of welded ash-flow tuffs of probable mid-Tertiary age. The tuffs rest uncomfortably on Mesozoic metasedimentary rocks exposed only outside steep edges of the gravity low. This gravity anomaly may reflect the presence of a large caldera. A regional magnetotelluric study now in progress will define the depths to electrical conductors within the crust and upper mantle and contribute to understanding of crustal structure, the gravity anomaly, and the Hot Dry Rock (HDR) geothermal potential of the Castel Dome area.