To reach Europe’s ambitious goals for the “Green Deal”, the supply of resources to build the Green Energy Infrastructure needs to be assured. At this moment, recycling is not able to handle the exponential increase in demand for precious and critical raw materials. Therefore, it is still necessary to explore new and alternative sources of these metals. At Straßegg (Styria, Austria) an abandoned medieval As-Ag-Au mining district contains several mine waste dumps with up to 14,000 tonnes of material. The main sulfide minerals in the deposit are arsenopyrite, chalcopyrite, and pyrite as well as several sulfosalts such as boulangerite, bournonite, and galena. Due to the limited ore processing ability in previous centuries, the deposit and its waste still contain abundant precious metals and critical raw materials.
The potential of sulfide minerals to host critical and precious metals is already known from Carlin-type Au-deposits, orogenic gold and epithermal deposits. These elements are incorporated as inclusions, nanoparticles, or in the crystal structures of the sulfide mineral. Pyrite is especially known for its ability to incorporate Au, Ag, As Co, Cu, Ga, Ge and Ni into the crystal structure by the substitution of S2- or Fe2+ with As2+/2-. A distortion of the lattice as well as partial charge imbalances allow the incorporation of metals. Arsenopyrite is also capable of incorporating various metals, when the ratio of Fe:As:S is disturbed and Au, Co, Mn, Ni, Sb, Se and Te might be incorporated. Chalcopyrite is a potential host for Ag, Bi, Cd, Co, Ga, Hg, In, Mn, Pb, Se, Sb, Sn, Tl and Zn.
This thesis applies a combination of whole rock geochemistry and trace element mapping to identify element correlations and zonation patterns to better understand the evolution of the deposit and its potential as a source of critical metals. Arsenopyrite appears to be a host for Au, Co, Ni, Pb and Sb. Pyrite contains appreciable Au, As, Co and Ni. The trace metal content is generally related to an elevated amount of As in arsenopyrite and pyrite. Chalcopyrite is enriched in Ag, In, Pb and Zn.
The thesis highlights several ore stages for Straßegg, beginning with an Fe-rich fluid, followed by an As-rich fluid, and finally a Pb-Sb-Ag rich one. Each of these main stages has been subdivided into a series of substages depending on the element correlations noted in the element maps.
Additionally, U/Pb age dating was conducted on calcite veins from Straßegg and Flatschach, another historical mining district in the Eastern Alps, to compare the temporal evolution of mineralization in the Eastern Alps. Due to the high content of common Pb in Straßegg calcite, the age dating was unsuccessful, while those from Flatschach provided ages spanning from the Oligocene to the Pliocene.