INSIGHTS INTO THE EVOLUTION OF A MAGMATIC-HYDROTHERMAL SYSTEM: THE ÇÖPLER AU-CU DEPOSIT, EAST CENTRAL TURKEY

The 7.5 Moz Çöpler Au-Cu deposit, located in the Tauride mountain range of east central Turkey, represents a sub-economic porphyry-style vein stockwork system that is overprinted by intermediate-sulfidation state veins. The fluid evolution at the deposit was reconstructed through detailed paragenetic studies on vein samples using a combination of optical petrography, fluid inclusion petrography, optical CL microscopy, and scanning electron microscopy. The research demonstrates that repeated reopening and reactivation of veins occurred throughout the evolution of the magmatic-hydrothermal system. The earliest quartz generation present in porphyry veins formed under lithostatic and super-lithostatic pressure conditions at temperatures above 400°C. Early quartz veining was associated with potassic alteration of the surrounding wall rocks. The second generation of quartz present in porphyry veins records a pressure transition from lithostatic to hydrostatic conditions at a minimum paleodepth of 1.4 km. Both quartz types contain abundant hypersaline liquid and vapor inclusions. Coarse chalcopyrite and pyrite present in porphyry veins are associated with chlorite and sericite alteration, respectively. Coarse chalcopyrite, accounting for the bulk of the copper resource, precipitated at temperatures near or below 400°C under hydrostatic pressure conditions. Minerals formed later in the paragenetic sequence are present within reopened porphyry veins or intermediate-sulfidation state veins. Base metal Zn-Cu-Pb-Sb mineralization at Çöpler occurred between 300−250°C from a low-salinity liquid. Backscattered electron imaging and trace element analysis of pyrite showed that Au enrichment at Çöpler can be related to the hydrothermal alteration of earlier formed coarse pyrite and the formation of euhedral pyrite crystals late in the paragenesis at temperatures below 250°C. No evidence for boiling of the mineralizing low-salinity liquid was observed. The results suggest that the Çöpler deposit formed from a single cooling magmatic-hydrothermal system and represents a rare example of the transition from an early porphyry system to a porphyry-related intermediate-sulfidation state hydrothermal system. The research also permits the development of new exploration guidelines.