2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 12
Presentation Time: 11:00 AM

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

BANERJEE, Amlan, Geology, Indiana University, 1001 East 10th Street, Bloomington, IN 47405, PERSON, Mark, Geological Sciences, Indiana University, 1001 E. 10th Street, Bloomington, IN 47405, HOFSTRA, Albert, CR Minerals Team, US Geol Survey, Denver Federal Center, Lakewood, 80225 and SWEETKIND, Donald, USGS, U.S Geological Survey, Mail Stop 973, Box 25046, Denver Federal Center, Denver, Denver, CO 80225, ambanerj@indiana.edu

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