Petrogenesis Of The Homestake Iron Formation, Lead, South Dakota: Assemblages Of Metamorphism
Randy L. Kath, Jack A. Redden, 1990. "Petrogenesis Of The Homestake Iron Formation, Lead, South Dakota: Assemblages Of Metamorphism", Metallogeny of Gold in the Black Hills, South Dakota, Colin J. Paterson, Alvis L. Lisenbee, Tommy B. Thompson
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The core of the Black Hills consists of approximately 99% Proterozoic metasedimentary rocks deposited in the interval2.2 - 1.9 Ga, and about 1% Archean granite (2.5 Ga) and older metasedimentary rocks (Redden et al., 1990). The lower Proterozoic stratigraphy consists chiefly of metamorphosed graywacke, quartzite, shale, basalt, gabbro, and iron formation. Carbonate and silicate type iron formations occur in five major districts in the Black Hills. These numerous metamorphosed iron formations host many minor gold, arsenic, and iron deposits as well as the Homestake gold mine, which is one of the largest producing gold deposits in the western world.
The strong association of gold deposits with these iron formations in the Black Hills has led several investigators to propose a syngenetic origin for the gold with subsequent remobilization during metamorphism (Nelson, 1987). Rye and Rye (1974) presented isotopic data from the Homestake mine that indicate a hot springs hydrothermal source for the Homestake Formation and presumably gold mineralization. However, more recent data, mainly structural, by Caddey et al. (1990) and Bachman et al. (1990) suggest a shear-controlled, epigenetic origin for gold mineralization in the Homestake mine.
Because of the debate of a possible syngenetic origin with subsequent metamorphic reconstitution or an externally-derived, shear-controlled epigenetic origin, it is important to evaluate the metamorphic reactions, geothermometry, geobarometry, and textural data within the Homestake Formation. These data are necessary to establish whether the metamorphic conditions were important in influencing migration of fluids which may have been important in localizing gold. To assess the metamorphic evolution of the Homestake