Ore Paragenesis And Fluids In The Gilt Edge Deposit, South Dakota
J. Groff, C. J. Paterson, 1990. "Ore Paragenesis And Fluids In The Gilt Edge Deposit, 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 Gilt Edge Au-Ag porphyry-related deposit is located in the northern Black Hills of South Dakota, approximately 8 km southeast of Lead (Fig. 1). The deposit is part of a larger east-west trending belt of Tertiary (38.8-60.5 Ma) alkalic intrusions (Shapiro, 1971). Intrusions at the Gilt Edge deposit include hornblende trachyte, trachyte, and quartz trachyte porphyry (MacLeod, 1986). Fracture zones trending NW-SE, NE-SW, and N-S traverse the deposit and may represent pre-existing structures in the Precambrian basement that were reactivated during the Tertiary igneous activity in the Gilt Edge area (MacLeod and Barron, 1990, this volume).
Gold mineralization is contained in breccias, along lithologic contacts, and in fracture zones. Intermittent mining from the late 1800's to the 1940's produced 2675 kg (86,000 oz) of gold (Norton, 1974) from breccias and fracture zones in trachyte and quartz trachyte porphyry. Active mining of the deposit resumed in 1988, with current reserves of 49.0 million tonnes at 1.28 g/t (0.041 oz/t) gold (Barron, 1990).
The origin of ore-forming fluids in the Tertiary hydrothermal systems in the Black Hills has been proposed to be either largely meteoric water (Irving, 1904) or magmatic fluids derived from the intrusions (Connolly, 1927). Paterson et al. (1989) suggested that the ore-forming fluids contained a large component of magmatic fluid, but mixing with meteoric waters above the Precambrian unconformity is suggested by isotopic and fluid inclusion data. The source of gold at the Gilt Edge deposit has been proposed to be the quartz trachyte stocks (Mukherjee, 1968), or magmatic