Eocene Iron Ore Deposits at the Northern Welt of the Bavarian Alps

Summary

The iron ore deposits of Achtal-Kressenberg consists of 5 separated, seam-bearing wedges dipping about 78° to SE. The wedges are successively staggered. Their apparent length of outcrop is somewhat more than 2 km, their width about 500 m. The thickness of the ore layers varies from 1 to 3 m. Their average iron content is 25% to 30% Fe.

The stratigraphic sequence comprises Upper Cretaceous strata (Upper Maastricht), Paleocene and Eocene. The ore formation is generally restricted to 2 seam groups: the Illerdian (Paleocene) “Schmalflöz” group, the Cuisian (Lower Eocene) “Roterz” group, the Lutetian (Middle Eocene) “Schwarzerz” group.

The ore formation occurred in the epicontinental Mesoeuropean shelf inundated by waters from the adjacent subtropical Tethys. The iron was oxidized in the weak-alkaline seawater on the shelf and deposited from sea floor currents. Iron-rich weathering solutions originated from already uplifted Alpine chains.

In contrast to earlier interpretations the block patterns and the hook-shaped outcrop of the seams, which are characteristic for the Achtal-Kressenberg mining area, can be explained by subaquatic gravitational gliding during Upper Eocene. Uplifting and arrangement of the wedge units from SW to NE, however, are assumed to be connected with the superposition of the Ultra-Helveticum and Helveticum by flysch during Upper Oligocene.