Day Two The Homestake Iron-Formation-Hosted Gold Deposit: An Introduction
Colin J. Paterson, 1990. "Day Two The Homestake Iron-Formation-Hosted Gold Deposit: An Introduction", Metallogeny of Gold in the Black Hills, South Dakota, Colin J. Paterson, Alvis L. Lisenbee, Tommy B. Thompson
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This day's venture involves the Homestake mine and its environs. The morning trip is an underground tour of the Homestake mine to examine the styles of mineralization. In the afternoon we will examine the surface geology of the Lead area in order to provide a general overview of the stratigraphic, metamorphic, and structural features in the Lead area. An attempt will be made to provide a three dimensional perspective of the gold deposit on each of the stops by referencing to the underground mine.
The Homestake mine has been operating continuously since 1876. Over 126 million tonnes of ore have been mined, and during the summer of 1990, the 36 millionth ounce (1116 tonnes) of gold was poured. The Homestake deposit is an iron-formation-hosted gold deposit of epigenetic origin and Early Proterozoic age (see Bachman and Caddey, 1990, this volume). Gold occurs within a folded and sheared iron-formation known as the Homestake Formation, which has an approximate age of 1.97 Ga. The Homestake Formation is typically a carbonate-facies iron formation, dominated by siderite. Locally, pyrrhotite blebs and bands parallel the bedding. Above the garnet isograd (east of a line approximately along the axis of the open cut), the iron formation is manifested as a cummingtonite- grunerite schist. This transition is very erratic, however, and cummingtonite can even be found in biotite zone rocks in the west wall of the Open Cut. Quartz veins and associated arsenopyrite (Fig. 1), chlorite, and pyrrhotite in the Homestake Formation are direct indicators of gold