Characterization of past hydrothermal fluids in the Humboldt House Geothermal Area, Pershing County, Nevada: Geochemical and paragenetic studies of core samples

The project purpose was to characterize reservoir rock and to develop a fluid-event history of the Humboldt House Geothermal Area (HHGA) using standard petrographic and geochemical methods. SEM revealed multiple silica phases present in P32-2 core in addition to pyrite, plagioclase feldspar, kaolinite, and barite. Petrographic and geochemical evidence from the P10-1 core points to a somewhat simple alteration of alluvial sediments by moderate to high temperature, dilute, silica-rich fluids. Alluvial sediments in P10-1 were altered by reduced, moderate temperature fluids (∼150-200°C) in the pH range of 4.5 to 8.0. Multiple fluid events were evident by optically continuous properties in silica, and mineral phase relationships between silica, sulfides, and clay. P10-1 core was altered by hydrothermal fluids in a reducing environment generally associated with pyrite-rich, propylitic alteration. Minerals typically found in higher temperature 392-572°F (200-300°C) geothermal systems such as I-S, illite and chlorite were found in the P10-1 core.