Is the Palea Kavala Bi–Te–Pb–Sb ± Au district, northeastern Greece, an intrusion-related system?

Abstract

Intrusion-related gold systems are generally characterized by a Au–Bi–Te ± Sn–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 occur primarily in quartz–calcite–sulfide veins (hypogene mineralization), or as supergene bodies, in overlapping zones centered on the ~ 21–22 Ma granodioritic Kavala pluton, which intrudes metamorphic rocks of the Paleozoic Rhodope metamorphic core complex. The pluton consists mostly of granodiorite with lesser amounts of diorite, tonalite and monzodiorite, which was emplaced along the regional E–W trending Kavala–Komotini fault. The recently discovered, ~ 4 km long, E–W trending so-called Kavala vein is a sheeted quartz vein system of Bi–Te–Pb–Sb ± Au mineralization that crosscuts the Kavala pluton and the schists and gneisses of the Rhodope Massif. 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 Garizo Hill Fe–Mn–Pb vein range from − 1.9 to 1.0‰ (with one outlier of − 4.6‰) and suggest a magmatic sulfur source. Homogenization temperatures (T h) of type I (two-phase aqueous liquid–vapor) and type II (three-phase, H 2O–CO 2-rich) fluid inclusions that homogenize into the liquid phase in quartz from the Kavala and Chalkero veins range from 216.0° to 420.0 °C (n = 216) and 255.7° to 414.0 °C (n = 112), respectively. The T h of type III (two-phase aqueous liquid–vapor), which homogenize into the vapor phase, ranges from 210.4° to 323.4 °C (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° to − 44.3 °C for type I inclusions suggest the presence of appreciable CaCl 2 in addition to NaCl. Clathrate melting temperatures for type II inclusions of ~−56.7 °C indicate that CO 2 is the major component of the gaseous phase, however up to ~ 6% CH 4 is present in some inclusions. The presence of a zoned metallogenetic district centered on Bi–Te–Pb–Sb ± Au mineralization within the Kavala pluton, the presence of both magnetite and ilmenite in 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 intrusion-related gold system that formed along the ilmenite–magnetite buffer.