Gold Deposits In The Black Hills, South Dakota
Colin J. Paterson, Alvis L. Lisenbee, Jack A. Redden, 1990. "Gold Deposits In The Black Hills, South Dakota", Metallogeny of Gold in the Black Hills, South Dakota, Colin J. Paterson, Alvis L. Lisenbee, Tommy B. Thompson
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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)-CW) 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
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Metallogeny of Gold in the Black Hills, South Dakota
Since the discovery of gold in 1874, the Black Hills has been well-known as a gold metallogenic province. In fact it is one of the richest areas in the world, having produced approximately 354 kg/km2 (31,750 oz/mile2). The premier mine in this province, theHomestake mine, is one of the oldest and longest -operating in the world, having been in production since 1876. Furthermore, the variety of gold deposit types in such a small area is unique. These include Au-U quartz pebble conglomerate deposits of early Proterozoic age, iron-formation-hosted and quartz vein gold deposits of middle Proterozoic age, paleoplacer Au in basal conglomerates of Cambrian age, epithermal igneous-hosted and sediment-hosted Au-Ag deposits of early Tertiary age, and recent gold placer deposits (see summary of gold deposits in Paterson et al., 1988; reprinted in this volume).
Although the history of mining here is a long one, the origins of the Homestake and other gold deposits in the Black Hills are yet to be fully explained. This is not a result of lack of interest or investigation. Significant studies regarding these deposits were conducted as long ago as 1904 by Irving, and subsequently by Connolly (1927) and Connolly and O'Harra (1929), and by Noble (1950) and Noble and Harder (1948). Then as now, there were opposing schools of thought regarding the origins of the various deposit types. For example, for the Tertiary sediment-hosted replacement deposits, Irving (1904) favored ore deposition from meteoric waters heated by the Tertiary igneous intrusions, whereas Connolly (1927) was a proponent of the magmatic-hydrothermal origin for the sediment-hosted replacement gold-silver deposits. Simultaneously, it was recognized that there were important structural and stratigraphic controls on ore localization, and that the mechanics of the sill and laccolith emplacement influenced the continuity and distribution of ores.
There remain many important questions to be answered regarding the origin and distribution of the gold deposits in the Black Hills. We summarize here some of the more important ones for your consideration during this field conference.
Is the Homestake deposit epigenetic (Noble, 1950; Slaughter, 1968; Bachman and Caddey*; Kath and Redden) or syngenetic but later remobilized (Rye and Rye, 1974; Rogers)? There is no consensus here, even among geologists working directly or indirectly with the Homestake Mining Company. There is general agreement however, that the mineralization is Proterozoic in age (Bachman and Caddey), and not Tertiary as reported inadvertently in the introduction to the