Carbonate-Hosted Au-Ag-Pb Deposits, Northern Black Hills
Montri Wimonrat, Colin J. Paterson, 1990. "Carbonate-Hosted Au-Ag-Pb Deposits, Northern Black Hills", Metallogeny of Gold in the Black Hills, South Dakota, Colin J. Paterson, Alvis L. Lisenbee, Tommy B. Thompson
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The Carbonate and Ragged Top mining districts, located about 5 miles northwest and west of Lead respectively, are the only two areas in the northern Black Hills where significant replacement deposits of silver-lead and gold-silver occur in the Mississippian Pahasapa Limestone (Fig. 1). There is an additional occurrence of weakly- mineralized Pahasapa Limestone in the Vanocker area, SE of Lead (Fig. 1). Following discovery of high grade silver- lead ores in 1881, Carbonate became a flourishing mining camp from 1885 to 1891 with a total production of at least 2.6 kg (83 oz) of gold; 525 kg (18,511 oz) of silver; and 5,193 kg (183,191 lbs) of lead (Shapiro and Gries, 1970). At Ragged Top (Fig. 1), after gold was discovered in 1896, mining operations were continuous until 1917, producing a total of 1,879 kg (60,598 oz) of gold (Shapiro and Gries, 1970). From 1937 to 1958, the deposit was sporadically exploited and was finally abandoned. Current mining and heap-leach processes make the Carbonate and Ragged Top areas favorable for renewed exploration.
In the Carbonate district, the Pahasapa Limestone has been intruded extensively by early Tertiary sills and dikes. The principal ore bodies are of two types: fissure veins and solution cavity-filling. Fissure veins consist of Au- bearing ferruginous gouge in the center and Pb-Ag rich (galena, cerussite, and cerargyrite) jasperoids along the margins (Irving, 1904). The solution cavity-filling ores are usually close to igneous intrusions, are less siliceous than jasperoid and are rich in lead, silver with minor gold
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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