Carlin-type mineralization and alteration of late Cambrian and Ordovician carbonate rocks at Long Canyon, Pequop Mountains, Nevada

This study examines local carbonate-hosted disseminated gold deposits near Long Canyon in the northern part of the Pequop Mountains located in northeastern Nevada. Several features typical of Carlin-type mineralization can be observed at the Long Canyon prospect. Gold is primarily hosted in Cambro-Ordovician limestone units, with mineralization commonly focused along structural features such as the lithologic contacts between the Cambrian Notch Peak limestone, the overlying Notch Peak dolostone and Ordovician aged Pogonip group limestone units. Like other Carlin-type deposits in Nevada, gold mineralization at Long Canyon is strongly associated with decarbonatization and silicification of carbonate host rocks. Geochemical and petrographic observations reveal silica introduction to be significant despite the fact that silicified limestones or jasperoids are volumetrically insignificant at Long Canyon. Rims of arsenian pyrite which are characteristic of Carlin-type deposits, around preexisting non-arsenian pyrite have been observed in the samples studied here. Typical of Carlin-type deposits, As, Fe, Si, Sb and Hg show a clear and strong chemical correlation to Au. Additionally, there is some evidence that elements Cd, Se, P, Sn, Tl, Be, Li, Pb, Ti, V, and Zr may also be associated with Au at Long Canyon. In high-grade samples, gold is commonly observed as discrete 2-5mum blebs of pure [native] gold. The deposits at Long Canyon are highly oxidized. Ore-grade material is strongly hematitic with locally observable jarosite and scorodite. Surviving gold-stage sulfide minerals such as arsenian pyrite are only observed where encapsulated in quartz. Despite the generally oxidizing conditions in the system, it is not uncommon for unmineralized samples to contain trace amounts of very fine diagenetic pyrite surviving due to encapsulation in both quartz and calcite grains. Intrusive rocks are locally observable on the site as swarms of (or individual) dikes and sills. These can serve as a favorable host for gold mineralization however, they appear to be volumetrically insignificant.