Recent and paleokarst systems and their relation to ore mineralization in the Iberg-reef-complex, Harz Mountains

In the SW Harz Mountains (F.R.G.) the dome-shaped Devonian Iberg-Winterberg reef limestone emerges from the surrounding Carboniferous graywackes. The small limestone outcrop (km2) consists of two atoll-like structures, the Iberg in the SE and the Winterberg in the NW. The original reef shape is suppressed by boundary faults, separating the limestone from the clastic rocks. Its total extension may have amounted to 12.5 km2, with a thickness of 600 m (FRANKE, 1973). More than 80 cavities are known within the complex descending a few to 50 m belwo the surface. Most of them are closely associated with iron-manganese ore bodies, which gave rise to intensive mining activity during the last centuries. The natural caves served as shafts for bost descending into the mines and hauling the iron ores in the eralier periods of mining. In the middle of the 19th centruy a gallery (Eisensteinstollen) was driven into the IBerg, but already in 1887 the last mine was abondoned. In 1986 the gallery and the system of natural caves and mines was made accessible again exceeding a total length of 5 km (Fig. 1,2).