The Homestake Mine, Lead, South Dakota: An Overview
R. L. Bachman, S. W. Caddey, 1990. "The Homestake Mine, Lead, South Dakota: An Overview", Metallogeny of Gold in the Black Hills, South Dakota, Colin J. Paterson, Alvis L. Lisenbee, Tommy B. Thompson
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The Homestake mine in the northern Black Hills, South Dakota is the largest iron-formation-hosted gold deposit known (Fig. 1), and has produced 1,113 tonnes (35.8 million oz.) of gold from 128 million tonnes of ore milled. In 1989 the mine produced 11.9 tonnes of gold. The deposit was discovered in 1876, and the mine has operated continuously to the present day (Fig. 2). Ore is currently mined from depths to 2,438 meters. Gold is the major commodity produced along with a minor silver by-product. The gold/silver ratio averages 5:1; base metal content is negligible.
The Homestake gold deposit is hosted within quartz-veined, sulfide-rich segments of an early Proterozoic, carbonate-facies iron-formation in a sequence of originally calcareous, pelitic, and quartzose rocks (Fig. 3). Strata that contain the Homestake deposit were complexly deformed by a series of tight isoclinal and sheath fold events, and synchronous, extensive ductile and ductile-brittle shearing. Mine area rocks have been subjected to upper greenschist-lower amphibolite facies metamorphism. Early-stage ductile shearing appears to have controlled fluid movement in the system thereby controlling thermal energy and metamorphic processes. Observed prograde metamorphism in the district is therefore characterized as dynamothermal. Intrusion of a 1.72 Ga Harney Peak-type granite in an area northeast of the mine post -dated regional prograde metamorphism, and appears to be contemporaneous with later stages of semi-brittle deformation (Bachman et al., 1990).