USGS1990
Organic tissues and metallic minerals were studied in acid residues and thin section of the Jerritt Canyon (Bell Mine) gold deposit. The purpose was to compare gold-bearing and gold-free rocks, characterize their differences, and assess a possible relationship between the invisible gold and the organic tissues in these early Paleozoic, carbonaceous limestones, dolomites, and claystones. The most visually abundant acid-resistant component in the sooty, unoxidized, gold-bearing rocks is a black, rectangular, carbon-bearing mineraloid. In X-ray diffraction, it is poorly crystalline; in nuclear magnetic resonance, it is a highly aromatized structure. The increase in gold content that accompanies the increase in content of this protographite suggests that it may be the major gold-bearing compound. Less abundant among the acid-resistant residues are uncarbonized organic tissues that are typical of marine settings. The tissues not in the vicinity of silicified veins are medium to dark brown. The dominant tissues are the amorphous remains of algae and their zooplankton predators. These uncarbonized indigenous tissues indicate that temperatures were lower than those determined by geochemical and fluid inclusion methods. The presence of different kinds of carbon-bearing compounds could account for the discrepancy between the palynological and geochemical data. The uncarbonized organic tissues comprise such a small percentage of these rocks that they could be easily missed by bulk analytical methods. The presence of uncarbonized tissues helps to constrain the duration of the high heat flow that is shown by the fluid inclusion data. The presence of mixed signals suggests that the protographite may be the product of chemical rather than thermal reactions.