The Fluid Inclusion And Mineralogic Record Of The Transition From Liquid- To Vapor-Dominated Conditions In The Geysers Geothermal System, California

Fluid-inclusion measurements and textural relationships demonstrate that coarse-grained quartz and calcite from the upper part of The Geysers thermal system formed during the transition from liquid-dominated conditions to the modern vapor-dominated regime. The most diagnostic characteristics of these transition assemblages are: 1) evidence of quartz dissolution; 2) contemporaneous trapping of high-and low-salinity waters representing liquids dominated by boiled reservoir fluid and condensate respectively; 3) the presence of solid inclusions in quartz of bladed, but commonly corroded, calcite; and 4) the common occurrence of multiple generations of primary, C02bearing vapor-rich inclusions. Corrosion of the quartz and calcite occurred as condensate, generated at the top of the developing heat pipe, percolated downward. These minerals were subsequently precipitated when the descending fluids boiled.