Hydrothermal evolution of the Sar-Kuh porphyry copper deposit, Kerman, Iran: A fluid inclusion and sulfur isotope investigation

Sar-Kuh porphyry copper deposit is located 6 km southwest of the Sar-Cheshmeh copper mine, Kerman Province, Iran. Based on field geology, petrography and fluid inclusions studies, four alteration types have been identified in the Sar-Kuh area. Early hydrothermal alteration formed a potassic zone in the central parts of Mamzar granite/grano-diorite stock and propylitic alteration in its peripheral parts. The late hydrothermal activity caused a limited phyllic and argillic alteration zones. The mineralized quartz veins are classified into four groups, on the basis of mineralogy and cross-cutting relationships. Group I and II veins are concentrated mainly in the potassic alteration zone, while group III and IV are most abundant in the phyllic and propylitic alteration zones, respectively. Fluid inclusion studies on group I and II quartz veins show that potassic alteration has originated from a dominantly magmatic fluid with high salinity (30-50 wt % NaCl equiv) and temperature ( > 300oC). The ?34S values of separated pyrite and chalcopyrite from samples range between +1.29‰ to +4.72‰ (mean value of +2.68‰), consistent with a magmatic origin for sulfur. Consequently, the meteoric water penetrated into peripheral and internal parts of stock along a network of late fractures mixed with magmatic water and produced a hydrothermal fluid with salinity ranging from 10 to 20 wt % NaCl equiv. This fluid produced propylitic as well as limited phyllic and argillic alterations in the peripheral of stock and volcanic rocks. Fluid inclusions are trapped at pressure of 300 to 3500 bar, but most of them are trapped at pressure of > 1000 bar. The low grade of Cu (0.4 % Cu) and relatively high pressure of fluid entrapment at Sar-Kuh can be attributed to the emplacement of Mamzar stock at moderate to great depths. As the result of over-pressuring and thus low-density development of vein stockworks, the mineralizing fluids failed to provide sites for concentrating high grades of copper. Therefore, Sar-Kuh is considered a sub-economic porphyry copper deposit.