Abstract
The Upper Proterozoic (?) metamorphic rocks on the western edge of the Bohemian Massif are subdivided into two distinct groups (Variegated Group, Monotonous Group) which sharply differ from each other with respect to their lithology and metallogenic significance. The somewhat older Monotonous Group metamorphics originated from arenaceous and argillaceous clastic rocks which were laid down in a shallow marine rift basin (1-st order basin). There is some evidence for placer-like gold concentrations to have been re-mobilized by subsequent LP/HT regional metamorphism. The 2-nd order basin opened during advanced stages of rifting and received the various volcanic and sedimentary rocks of the ‘Variegated Group’. Chemical discrimination allows assigning the bimodal volcanic rocks to within plate volcanism. There is no argument for collission-related volcanic activity. Sedimentary rocks consisted of limestones, marls and graywackes that reflect rapid subsidence of the basin. Except for graphite this series is of little economic importance. Most of the concentrations of U, W, and Sn present, have to be classified as “protore” rather than “ore”. By contrast, the 3-rd order basin gains metallogenetic significance, for it hosts the massive sulfides of Bodenmais Kies Belt. These sediment-hosted FeZnCuPb sulfides show a rough zonation into proximal FeZnCu and distal PbBa mineralization. Zn concentration in these stratabound ores involved precipitation of Fe-rich sphalerite, zincian spinel and Zn staurolite. Silver was enriched during retrograde metamorphism, when Ag-rich fahlores, schapbachite, and native silver were formed. By analogy to sediment-hosted deposits elsewhere in the world and especially in view of the “barite fringe” these stratiform ore deposits are classified as Sullivan-type or Meggen-type deposits. Moreover, this interpretation is supported by Pb and S isotopes.
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