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    STUDIA GEOLOGIA - Issue no. 1 / 2007  
         
  Article:   ISOTOPIC STUDY OF LATE DIAGENETIC ORE MINERALIZATION IN THE BLEIBERG LEAD-ZINC DEPOSIT (EASTERN ALPS, AUSTRIA).

Authors:  ERICH SCHROLL, STAN HALAS, HENRYK KUCHA. 		 
       
         
  Abstract:  The strata-bound Pb-Zn deposit of Bleiberg (Carinthia, Austria) is hosted by Triassic platform carbonates of Carnian age. Today, the mining activities are finished. Bleiberg is the largest deposit in the Alps. So far 2.2 million tons (Pb:Zn = 1:1) have been mined. The age of the deposit is synchronous with these Carnian rocks. Brigo et al. (1972) supposed a Triassic (Carnian) age of the mineralization in the Bleiberg Pb-Zn deposit and his affiliated deposits. Sulphur isotope data (Schroll & Rantitsch, 2005), lead isotopes and rubidium/strontium ages (Schroll et al., 2006) and the detection of fossil sulfate-reducing bacteria (Kucha et al., 2005) support this supposition. The pre-burial deposed ores were heated up to ca. 130°C during the Jurassic and Cretaceous (Rantitsch, 2001, 2003). Re-mineralization processes during this interval depend on the availability of fluids. The dewatering of gypsum that contains 20% H2O is an important source of diagenetic fluids. Gypsum is transformed into anhydrite at temperatures around 55°C (Bilo, 1986). Blue anhydrite of diagenetic origin is common in evaporitic limestones. This also happened in the lagoonal Wetterstein formation in the Antoni mine (Bleiberg). According to the thermal model (Rantitsch, 2001, 2003) this diagenetic process lasted during Jurassic times. Irregular metasomatic bodies of blue anhydrite are hosted by the lagoonal Wetterstein limestone. Locally the anhydrite intruded into pre-existing ore bodies. The border anhydrite - limestone is rimed by a coarse-grained brownish sphalerite and/or calcite. The sphalerite is intimately associated with pyrite, marcasite, fluorite and quartz. The pre-existing sphalerite - galenite ores partly show re-crystallization.  
         
     
         
         
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