Structural controlled ore mineralisation in the Graz Paleozoic (Eastern Alps, Austria): a mineralogical, petrological and geological study

摘要

The mineralisations in the Graz Paleozoic are the gold-arsenopyrite in Strassegg, the Pb-Zn-baryte in Arzberg and the pyrrhotite in Naintsch. The petrology, mineralogy and structural aspects of the mineralisations have been studied on a local and regional scale. Although the three areas show different mineralisation types, they belong to the same tectonic unit and contain primary and secondary structurally controlled mineralising phases. The Strassegg gold and arsenopyrite mineralisation is associated with mineralized quartz-carbonate extensional veins and has precipitated in situ from a metamorphic fluid. The lead-zinc and baryte deposits at Arzberg are also found in greenschist facies metamorphosed chlorite- and carbonate-rich schists. Arzberg contains primary, metasedimentary and secondary structurally controlled mineralising phases. The pyrrhotite in Naintsch is found as a disseminated, primary mineralisation within folded black shales. The chemistries of the possible mineralising fluids extracted from quartz extensional gashes vary from fluid mixing of CO_2-H_2O and H_2O-NaCl at Strassegg to subordinate CO_2-N_2-H_2O and H_2O-NaCl-CaCl_2+-MgCl_2 at Arzberg and to dominant H_2O-NaCl-CaCl_2-MgCl_2 at Naintsch. P-T-conditions of the secondary mineralisation are as follows: T = 450-500°C and P = 3-5 kbar at Strassegg; T = 300-350°C and ca. P = 2 kbar at Arzberg.