Antimoniferous mineralization from the Mid-European Saxothuringian Zone: mineralogy,geology, geochemistry and ensialic origin |
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| Authors: | Dr Harald Dill |
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| Institution: | 1. Federal Institute for Geosciences and Natural Resources, P.O. Box 5101 53, D-3000, Hannover 51, FR Germany
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| Abstract: | In the North Bavarian Basement (FR Germany) as well as in the Thuringian Forest (GDR) both of which belonging to the Saxothuringian Zone antimony mineralizations have been worked up to the early fifties. Mineralogical and geological investigations led to the following classification of antimony ore deposits and -concentrations: - Stratabound and stratiform fahlore (Fahlerz) mineralization in Silurian and Lower Devonian black shales.
- Sulphosalt- and stibnite-bearing veins (partly associated with native gold) in wall rocks of the Late Variscan granites.
- Monometallic and monomineralic antimony lodes along anticlinal structures.
- Sulphosalt-bearing lead-zinc veins.
Antimony in the black shales was concentrated during late diagenetic cementation along with copper. The sulpho-salt-bearing stibnite veins in the metamorphic country rocks of the granites are genetically associated with the granitic intrusions nearby. This is proved by trace element chemistry and structural as well as mineralogical features of those veins. U/Pb age dating of contemporaneous pitchblende from the »polymetallic uranium paragenesis« from Hoehensteinweg uranium deposit yielded a late Variscan age of formation for these veins of type 2. Early Paleozoic rocks (metavolcanics) are suggested to have been the parent material for these granite-related Sb concentrations. However the monotonous Sb veins are more akin to the basic protore in deeper crustal sections. The thermal aureole of a deep-seated heat source is preserved by the Ag/Sb ratio of galena in Pb-Zn veins (type 4), which shows a marked variation along the SW plunging Berga Anticline from increased Ag/Sb ratios near the core of the anticline towards reduced values in mining sites more peripheral to this fold structure. Pb isotopes of stibnite as well as Pb sulphides point to a crustal derivation of both elements. An in-situ re-deposition and leaching of Sb from the wall rocks as well as antimoniferous black shales may be ruled out. It has to be emphasized that intra-crustal mass movements (A subduction) and the late Vanscan igneous activity are the major factors controling release of Sb from the Early Paleozoic low metal concentrations within metavolcanic rocks and subsequent discharge of Sb-bearing fluids within joints and fractures related to late Variscan tectonic movements. A schematic exploration concept is outlined. |
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