Metallogeny and distribution of critical and strategic metals in the polymetallic vein mineralization at Kolchiko, Vertiskos Unit, northern Greece

Abstract

The Kolchiko polymetallic vein-hosted mineralization is part of a broad mineralization system in the Vertiskos crustal unit in northern Greece, which includes several gneiss- and mica-schist-hosted gold, copper and antimony bearing quartz veins. Mineralization includes gold-bearing arsenopyrite and pyrite, chalcopyrite, sphalerite occurring in massive to disseminated forms in quartz-veins, as well as quartz-pyrite veins. The mineralized veins are enveloped by hydrothermal halos related to sericitization of the mica-schist host rocks. Arsenopyrite and pyrite are the most abundant ore minerals, while enrichment in bismuth (<992 ppm) and tellurium (<3 ppm) are related to the variable occurrence of galenobismuthinite, hessite, tellurobismuthite and native bismuth. Particularly gold is enriched (<9.2 ppm) in the massive veins. The ore parageneses, the mineral chemistry analysis and the fluid inclusions imply that the mineralization formation was characterized by two stages of magmatic-hydrothermal activity: 1) an early higher temperature (T = 300 to 444 °C) Fe-As-sulfide rich stage that produced the arsenopyrite- and pyrite-dominated polymetallic massive veins, and 2) a later lower temperature stage (T = 160 to 300 °C) characterized by the formation of Bi-sulfosalts and tellurides in the polymetallic quartz and quartz-pyrite veins. It is suggested that the gold-polymetallic mineralization at Kolchiko was developed under regional retrograde greenschist facies metamorphism and was structurally controlled by the onset of the late Oligocene to early Miocene dextral strike-slip fault zone, which is documented along the western edge of the Vertiskos Unit.