138-12 Effects of Fault Zone Permeability on Fault Controlled Fluid Circulation in Active and Fossil Hydrothermal Systems in the Great Basin

See more from this Division: Topical Sessions
See more from this Session: Fault Seals or Conduits? Insights from Hydrologic and Petroleum Systems

Sunday, 5 October 2008: 11:00 AM
George R. Brown Convention Center, 330A

Amlan Banerjee, Geology, Indiana University, Bloomington, IN, Mark Austin Person, Geological Sciences, Indiana University, Bloomington, IN, Albert Hofstra, CR Minerals Team, US Geol Survey, Lakewood and Donald Sweetkind, USGS, Denver, CO
Abstract:
Faults play a critical role in fluid circulation along modern hot springs and in the formation of Eocene Carlin-type gold deposits in the Great Basin. Here we present a suite of numerical models that asses the conduit/barrier behavior of the faults at Beowawe and Carlin trend, Nevada. In order to match the published fluid homogenization temperature, fluid-rock isotope exchange and silica precipitation data along the Carlin trend and Beowawe geothermal system, a vertical fault permeability between 10-11 to 10-13 m2, a fault zone anisotropy of 100 (Kz/Kx), and a permeability contrast on the order of 103 to 104 between lithostratigraphic units and faults are needed. Carlin trend the fault segments that cut the low permeability (10-17 m2) upper plate rocks were found to have a lower vertical permeability and resulted in the formation of a loop style fluid circulation through the underlying carbonate rocks which host the gold mineralization. This resulted in significant fluid-rock isotopic exchange. On the other hand, the absence of low permeability cap rocks at Beowawe produces a single-pass hydrothermal flow cell with relatively little fluid-rock isotope exchange. Field observation of fault gauge and damage zone formations along the ore feeder faults at the Post-Betze and Gold Quarry mines supported the numerical model parameter selection.

Key words: Great basin, fault, fluid circulation, permeability, anisotropy

See more from this Division: Topical Sessions
See more from this Session: Fault Seals or Conduits? Insights from Hydrologic and Petroleum Systems