Surficial Alteration and Spring Deposits of the Wheeler Mercury Prospect, with Initial Results from Wheeler Corehole 64-16, Coso Geothermal Area, California

Abstract

The Wheeler prospect is centered on the only know siliceous sinter in the Coso geothermal field. Active, acid sulfate kaolization affects the sinter and nearby bedrock and alluvism. Silicified felsite and quartz latite at the prospect are probably subsurface equivalents of sinter; associated carbone stockworks and travertine appear to be similarly affiliated. Corehole 64-16 penetrates pre-Cretaceous metadiorite intruded by Cretaceous granitic rocks, felsites and quartz latites. Alteration consists of widespread chloritization and sericitization (illite and mixed layer illite smectite), development of a smectite cap, and selective siliicifcation of felsites and quartz latites. Chlorite and epidote veinlets are widespread; late stage calcite appears above 158 m. The illite smectite was probably developed at 175°C-200°C, perhaps contemporaneously with sinter depositions. Fluid inclusions in subsequently deposited calcite homogenize at 150°-170°C, suggesting a post sinter cooling trend.