Day Two - Road Logs
Gold in the Open Cut area was first discovered by two Frenchmen, Moses and Frederick Manuel, on April 9, 1876 (Irving, 1904). A quartz outcrop located somewhere near the center of the current Open Cut (see frontispiece) was the site of the original Homestake lode discovery in 1876 (see Frontispiece for this volume). By the following year the numerous claims filed in the area had been consolidated into four large companies. Irving further states: "Not long after the mines opened it was found advisable to work them under a single management, and as time went on the Homestake Company came either into control or into actual possession of the other properties...”
The gold ore was free-milling, and by the summer of 1878, 80 stamps were in operation in mills near large open cuts on the steep hillside. By 1880, a total of 740 stamps were crushing 2 to 3 tons of ore each per day. The old headframe of the B & M No. 2 underground mine, one of the early underground operations on the Homestake gold deposit, remains beneath the hill crest. Mining in the Open Cut was renewed as a supplemental surface operation in 1984, with 1989 gold production at 2678 kg (86,400 oz).
Figures & Tables
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