Geological characteristics of the newly outlined Cu-Au deposits at the Sharlo Dere and Krasta prospects, northeast of the Chelopech Mine, Bulgaria

The Sharlo Dere and Krasta prospects, located on the northeastern flank of the Chelopech hydrothermal system, contain newly identified high-sulfidation (HS) Cu-Au mineralization zones, which are potential future resources for the Chelopech mine. This deposit is part of an Upper Cretaceous magmatic complex in a back-arc basin. The HS mineralization formed in a transition from a shallow intrusive epithermal environment to an underwater hydrothermal vent system, featuring sulfide- and sulfosalt-rich zones. It is associated with advanced argillic alteration and hosted by a 91.9±0.2 Ma dioritic intrusive system. The mineralization occurs in various settings, including structurally controlled feeders, breccia injections, and hydro-magmatic vent flows. It consists of minerals mostly like pyrite, chalcopyrite, and bornite, with two main chalcophile associations: Cu-Au-As-Sb-Bi-rich and Au-Mo-Tl-rich. Two main sulfosalt assemblages, enargite-luzonite and tennantite-tetrahedrite, are distinguished. As the first one is forming richer in Au central ore zone, and the latter is characterized more peripheral one.