THE ROLE OF FAULTS IN THE PLUMBING OF THE GREAT BASIN GEOTHERMAL SYSTEMS AND GOLD MINERALIZATION

The Great Basin groundwater flow system is remarkable in many respects. Despite the complex basin and range tectonics and associated topographic features a deep, regional-groundwater flow system exists within the thick Paleozoic carbonate aquifer system at depth. The Great Basin also hosts both world class geothermal systems and gold deposits. Temperature profiles and fluid inclusion studies suggest that both modern day and fossil geothermal systems associated with gold mineralization share many common features including the absence of a magmatic source, fault controlled up-flow zones restricted to range bounding faults and remarkably high temperatures ( 200 oC <) at shallow depths (< 500m). While the plumbing of these systems is not well understood, recent geochemical data collected at the Dixie Valley and Beowawe geothermal systems suggest that fluid circulation along fault zones is relatively deep (< 5 km) and meteoric in origin.

Here we use two- and three-dimensional mathematical models to study the plumbing of modern and ancient geothermal systems within the Great Basin. Multiple tracers are used in our model including oxygen- and carbon-isotope composition of the fluid/rocks, groundwater residence times, silica transport/precipitation, and temperature anomalies to constrain the plumbing of these systems. Our preliminary results suggest that both fossil and modern geothermal systems were probably driven by natural convection cells restricted to high permeable fault zones. The geothermal systems that formed Carlin gold deposits and modern geothermal systems such as Dixie Valley were probably transient in nature.