THE PALEA KAVALA REDUCED INTRUSION-RELATED BI-TE-PB-SB±AU SYSTEM, NORTHEASTERN GREECE: MINERALOGICAL, FLUID INCLUSION, AND SULFUR ISOTOPE STUDIES

Reduced intrusion-related gold systems (RIRGS) are generally characterized by a Au-Bi-Te-W metal assemblage genetically linked to the emplacement of granitoids. The Palea Kavala ore system, Greece, consists of ~150 minor Fe-Mn (Pb±Zn±Ag), Fe-Mn-Au, Fe-As-Au, Fe-Cu-Au, and Bi-Te-Au occurrences that are found in overlapping zones centered on the ~21 Ma granodioritic Kavala pluton, which intrudes metamorphic rocks of the Paleozoic Rhodope metamorphic core complex. The so-called Kavala vein is a newly discovered E-W trending, ~4 km long, sheeted quartz vein system of Bi-Te-Pb-Sb±Au mineralization that crosscuts the Kavala pluton, and schists and gneisses of the Rhodope massif. The pluton consists mostly of granodiorite, with minor amounts of diorite, tonalite and monzodiorite, which was emplaced along the regional E-W trending Kavala-Komotini fault.

The Kavala vein system is comprised of quartz with lesser amounts of K-feldspar, plagioclase and muscovite. Quartz-sericite-pyrite alteration is pervasive but minor kaolinite is also present. Pyrite (~5% of vein volume) contains inclusions of tetradymite (some gold-bearing), bismuthinite, and cosalite. Sulfur isotope values (n = 27) of pyrite from the Kavala and Chalkero veins, as well as pyrite and galena from the Garizo Hill Fe-Mn-Pb vein range from -4.7 to 1‰ and suggest a magmatic sulfur source. Homogenization temperatures (T_h) of type I (two-phase aqueous liquid-vapor) and type II (three-phase, H₂O-CO₂-rich) fluid inclusions that homogenize into the liquid phase in quartz from the Kavala and Chalkero veins range from 216.0º to 420.0ºC (n = 216) and 255.7 º to 414.0 ºC (n = 112), respectively. The T_h of type III (two-phase aqueous liquid-vapor), which homogenize into the vapor phase, range from 210.4^o to 323.4^oC (n = 28). The salinities of type I and type II inclusions range from 15.9 to 22.6 wt. % NaCl equiv. and 5.5 to 11.2 wt. % NaCl equiv., respectively. Eutectic temperatures of -58.5^o to -44.3^oC for type I inclusions suggest the presence of appreciable CaCl₂ in addition to NaCl. The occurrence of a zoned metallogenetic district centered on Bi-Te-Pb-Sb±Au mineralization within the Kavala pluton, and the two high-temperature, high-salinity, immiscible carbonic and aqueous fluids associated with the Kavala and Chalkero veins are consistent with them being part of an RIRGS.