Abstract

The Black Hills gold province has produced almost 40 million ounces of gold and 13.7 million ounces of silver since 1875. Although dominated by the Homestake deposit at Lead, production has come from a wide variety of gold deposits. Precambrian deposits include uranium-gold paleoplacers in quartz-pebble conglomerate, stratabound gold associated with iron formation (e.g. Homestake mine), gold-quartz veins in fault zones, metagraywacke and amphibolite, and polymetallic gold-quartz veins. Phanerozoic deposits include gold paleoplacers (Cambrian) in the basal Deadwood Formation, Tertiary epithermal intrusion-hosted and breccia-hosted gold deposits, Tertiary epithermal Precambrian-hosted deposits, Tertiary epithermal sediment-hosted Au-Ag-(Pb)-(W) vein and replacement deposits, and Oligocene-Holocene placer gold. Currently, the iron formation-hosted and epithermal deposits are the favored exploration targets.

The iron formation-hosted deposits (early Proterozoic), which may have originated from submarine hot springs, comprise the dominant gold resource in the Black Hills. Precambrian quartz-gold veins may have been formed by regional metamorphic processes or granite-related hydrothermal systems. The Tertiary epithermal deposits were generated by alkalic magmatism. Isotopic compositions of Pb, C, and S in the Tertiary epithermal gold-silver deposits suggest element sources in the Precambrian rocks and Tertiary intrusive rocks. However, the iron formation-hosted and other Precambrian gold deposits were not essential precursors for the Tertiary deposits. Some recycling of gold is indicated by Deadwood Formation paleoplacer deposits derived from erosion of iron formation-hosted gold deposits and Precambrian gold-quartz veins. Oligocene-Holocene placers derived gold from all of the earlier deposits. The Tertiary magmatism led to the doming of the northern Black Hills and the consequent unroofing of the Homestake deposit.