Day Four - Papers
Hundreds of dikes, sills, laccoliths, and stocks were emplaced within the crystalline Precambrian basement and the overlying Phanerozoic strata of the Black Hills uplift during the Paleocene and early Eocene. The great volume of plutons was sufficient to swell the basement forming the Bear Lodge, Tinton, and Lead-Deadwood domes (Fig. 1) and produced laccolithic clusters in the Phanerozoic section, such as those of the Black Buttes, Vanocker, Gilt Edge, and Theodore Roosevelt complexes. Individual plutons, such as Bear Butte and Devils Tower, are abundant outside the larger complexes. The alkalic igneous rock suite includes rhyolite, quartz latite, trachyte, and phonolite. Associated with the plutons are numerous bodies of breccia including diatremes, breccia pipes and intrusion breccias. These fragmental rocks are the theme of this paper.
There appear to be distinguishing internal features as well as differing spatial distribution between the intrusion breccias, breccia pipes and diatremes. For the purposes of distinguishing amongst them the following criteria are proposed.
Figures & Tables
Metallogeny of Gold in the Black Hills, South Dakota
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