Hydrothermal alteration footprint of the Chelopech high-sulfidation Cu-Au epithermal deposit, Bulgaria

The Chelopech high-sulfidation Cu-Au epithermal deposit is a part of Apuseni-Banat-Timok-Srednogorie Metallogenic Belt. The mineralization is related to a Upper Cretaceous magmatic complex, represented as transition from shallow intrusive-related phreatomagmatic environment to an underwater hydrothermal vent system. It is characterized by sulfide-sulphosalts-rich replacement with well-defined metal and alteration zonation. The core of the ore bodies is characterized by intense acid-sulfate alteration, including vuggy silica and APS minerals, laterally grading into silica-dickite-kaolinite alteration associated with Cu-Au-As-Ag-Te-Bi mineralisation. Kaolinite forms diffuse envelope surrounding high sulfidation mineralisation, transiting at depth into a diaspore-pyrophyllite dominated facies that marks the lower extent of Cu mineralization. A large phyllic halo surrounds the Cu-Au ore bodies, extending laterally and below, with relative Pb-Zn-Mn-Tl-Ag enrichment. Specific short-wave infrared spectral features provide a vectoring within a wide range of illite-sericite assemblages. The distal parts are presented by phengite-chlorite-smectite propilitic assemblage. Sr-K-Rb-Na-Ca-Mg-Fe data provides additional vector within this alteration footprint.