Gold Distribution in Porphyry Copper Deposits of Kerman Region, Southeastern Iran

Gold contents of the Kerman porphyry copper deposits are generally low, ranging from 0.010 to 0.190 g/t. The copper ores exhibit Cu/Au atomic ratios much greater than 40000, and Au/Mo ratios below 30, which signifies them as gold-poor porphyry copper deposits. The gold-poor signature of the Kerman deposits complies with features such as higher contents of chalcopyrite and pyrite over bornite and magnetite in the hypogene ores, widespread phyllic and argillic alterations, weak correlations between Au and Cu, poor correlations between Au and Mo, and their association with adakitic-like intrusions derived from partial melting of the lower crustal rocks at a thickened continental arc. These features reflect r ather low temperature (less than 600°C) and l ow oxygen fugacity of the primary ore-forming fluids involved in the formation of the Kerman porphyry copper deposits, indicating the low solubility of gold in low temperature fluids in comparison with higher temperature (~700°C) and more oxidized fluids responsible for the formation of gold-rich porphyry copper deposits. Present study indicates that a strong positive correlation exists between the gold and the magnetite contents of the porphyry copper deposits. These relationships indicate that deposits with higher gold and magnetite contents (e.g. Sar Kuh, Meiduk and Abdar), were emplaced at higher crustal levels and formed from more oxidized fluids in comparison to the gold-poor deposits (e.g. Sar Cheshmeh). These features can be used as exploration tools for identification of the gold-rich porphyry copper deposits in the porphyry copper metallogenic provinces.

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