Late Cretaceous Cu-Au epithermal deposits of the Panagyurishte district, Srednogorie zone, Bulgaria

Abstract

This review compiles geological, mineralogical, and isotopic data from the four largest Cu-Au epithermal deposits of the Late Cretaceous Panagyurishte mineral district, Bulgaria, including from north to south: the producing Chelopech, and the past-producing Krassen, Radka and Elshitsa deposits. Epithermal Cu-Au deposits of the northern and older part of this district are mainly hosted by andésites, whereas those from the southern and younger district are hosted by dacites. Advanced argillic alteration is described in the majority of the deposits, with the most complex alteration assemblage occurring at Chelopech. In all deposits, mineralization is the result of replacement and openspace deposition producing massive sulphide lenses surrounded by disseminated mineralization. Additionally at Chelopech, stockwork vein zones are also an important ore type.At Elshitsa. Radka and Krassen, the mineralized zones are controlled by WNW-oriented faults, and at Chelopech there is a supplementary control by NE-oriented faults.A three-stage paragenesis is recognized in all deposits, including an early disseminated to massive pyrite stage; an intermediate, Au-bearing Cu-As-S stage, which forms the economic ore; and a late Zn-Pb-Ba stage. Sulphur isotopic compositions of sulphide and gangue minerals are consistent with similar data sets from other highsulphidation deposits. Variations in Sr and Pb isotope data among the deposits are interpreted in terms of fluid interaction with different host-rocks, additionally variability in Pb isotopic compositions can be attributed to differences in composition of the associated magmatism. Throughout the Panagyurishte district, there is a coherent and continuous sequence of events displayed by the epithermal Cu-Au deposits indicating that they result from similar ore forming processes. However, latitudinal differences in ore deposit characteristics are likely related to emplacements at different depths, differences in degrees of preservation as a function of post-ore tectonics and/or sedimentary processes, efficiency of ore formation, and/or modifications of regional controls during the 14 Ma-long geological evolution of the Panagyurishte district, such as magma pedogenesis and/or tectonic regimes.