Age of Mineralization at the Twin Creeks SHMG Deposit, Nevada
Chris M. Hall, Grigore Simon, Stephen E. Kesler, 1997. "Age of Mineralization at the Twin Creeks SHMG Deposit, Nevada", Carlin-Type Gold Deposits Field Conference, Peter Vikre, Tommy B. Thompson, Keith Bettles, Odin Christensen, Ron Parratt
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This paper will explore the significance of thermochemical sulfate reduction (TSR) to the origin of sedimenthosted disseminated gold (SHDG) deposits. TSR provides a means of generating abnormally high concentrations of H2S at moderate temperatures (e.g., 100 to 200°C). A high H2S content is a prerequisite for mobilizing gold and other metals associated with SHDG deposits (Ag, Hg, Sb, As), and is also necessary to form ore bodies with a high Au/Ag ratio. Field and sulfur-isotopic evidence supporting the TSR hypothesis will be reviewed. The discussion will focus on SHDG deposits in the Carlin Trend and similar deposits in China, as well as the Hemlo gold deposit, Ontario, a possible Archean analog of this deposit type. If valid, the TSR hypothesis has significance to the minerals exploration industry as a means to discriminate between favorable vs. unfavorable source rocks.
Mineralization at Twin Creeks mine is hosted by rocks of the Ordovician Comus Formation, which consists of dolomitic to calcareous black shales with tuffaceous interbeds and interlayered basalt flows and sills. These rocks have been deformed into a northwest-trending fold system with a known length of about 4.5 km (3 miles). Gold mineralization post -dates this folding, and is concentrated in the nose of this fold and in favorable stratigraphic horizons in the limbs of the fold. In the most intensely mineralized part of the deposit, the Megapit, the fold is cut into three sections by right-lateral the TC (northern) and DZ (southern) faults trending NE-SW (Fig. 1) and dipping steeply to