Relation Between Pyrite and Gold at the Twin Creeks SHMG Deposit, Nevada
Grigore Simon, Stephen E. Kesler, Dean R. Peltonen, Stephen L. Chryssoulis, Hui Huang, James E. Penner-Hahn, 1997. "Relation Between Pyrite and Gold 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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Most gold in sediment-hosted micron gold (SHMG) deposits cannot be imaged by conventional reflected light, secondary electron (SEM), or transmitted electron (TEM) microscopy. Gold particles with a diameter of about 200 Å were observed by Bakken et al. (1989) as inclusions in pyrite, cinnabar, quartz and illite from the Carlin mine, although considerable gold could not be accounted for. Arehart et al. (1993) showed that much of this “invisible” gold at Post/Betze and Gold Quarry is in As-rich growth zones in pyrite, possibly in solid solution. At Twin Creeks, we have observed mat the gold content of ores appears to vary with the texture of pyrite. We report here results of a preliminary study on the relation between gold values and pyrite textures at the Twin Creeks SHMG deposit, based in part on ion probe measurements of gold concentrations in pyrite and X-ray Absorption Near-Edge Spectroscopy (XANES) measurements to determine the oxidation state of gold in the pyrite.
SHMG mineralization in the Megapit (see Fig. 1 of Hallet al., this volume) area of the Twin Creeks deposit, where our work was concentrated, is hosted by calcareous black shales and interlayered volcanic rocks of the Ordovician Comus Formation, which form a large fold. Gold mineralization is concentrated in the nose of this fold and in favorable stratigraphic horizons in the limbs of the fold. Gold is associated with arsenic-bearing pyrite (arsenian pyrite) that was deposited along with various combinations of quartz, adularia, sericite, realgar, orpiment, and stibnite. The Megapit deposit is