Efemcukuru B-rich epithermal gold deposit (Izmir, Turkey)

摘要

Efemcukuru, located in the Aegean Region, Turkey, is an example of vein-type epithermal gold deposit with related stockwork and replacement mineralisation. The veins are hosted by Late Cretaceous-Paleogene flysch facies rocks of the Izmir-Ankara zone, which were intruded by rhyolites from of Neogene volcanism. Gold mineralisation is associated with late pulses of magmatic hydrothermal activity and is present in zones of hydraulic brecciation adjacent to veins or stockwork zones around a dome-shaped small intrusion. The intrusion and later epithermal mineralisation are both controlled by NW-SE-trending faults, and mineral deposits occur along strike with dips 60 deg to 80 deg to the northeast. Individual quartz veins associated with sulphide minerals and mineralised hornblende facies hornfels are other important ore-bearing formations. The alteration associated with mineralisation is represented mainly by rhodonite, rhodochrosite, axinite, quartz, calcite and adularia in veins and stockwork zone and chlorite, sericite, illite and kaolinite in the wall rock. Homogenisation temperatures of 200-300 deg C reflect emplacement of ore distant from inferred magmatic heat in epithermal environment. Due to wide range in salinity of the fluids (0-9 eq.wt. percent NaCl), sulphide diversity in the deposit is rather rich than the low-sulphidation epithermal systems. The fluid inclusion data indicate that a complicated geothermal system existed. Both the gas data and the microthermometry data indicate that there was fluid mixing. Each type of mineralisation has been studied with the aim of clarifying the paragenetic relationships among the different minerals. Arsenopyrite, pyrite (marcasite), sphalerite, galena and chalcopyrite are the main minerals with pyrrhotite, fahlore group, sphene, rutile and gold occurring as accessories. Pyrolusite, limonite (goethite, lepidocrocite), covellite - chalcocite, malachite and azurite are of secondary origin.