Sulfide Rb-Sr, Re-Os And In Situ S Isotopic Constraints On Two Mineralization Events At The Large Hongnipo Cu Deposit, Sw China

The Hongnipo deposit, a newly discovered large copper deposit in the Kangdian copper belt, SW China, is hosted in the Paleoproterozoic Hekou Group. This deposit contains similar to 4200 Mt of Cu ores, with an average grade of 1.42 wt.% Cu. Orebodies occur mainly as stratiform, stratoid and lenticular forms. Mineralization consists predominantly of high grade vein-type ores and low grade laminated ores. Field relationships indicate vein-type mineralization crosscuts laminated mineralization and host rocks, indicating that there were at least two mineralization events during the formation of the deposit. Pyrite separates from the laminated ores yield a Rb-Sr isochron age of 1552 +/- 80 Ma, with a highly radiogenic initial Sr-87/Sr-86 ratio of 0.71214 +/- 0.00081, indicating a major contribution from the ore-hosting rocks. Sulfides from the laminated ores have delta S-34 values ranging from -1.8 parts per thousand to 11.4 parts per thousand, with the vast majority in the range of 5.3 parts per thousand to 11.4 parts per thousand, suggesting the mixed derivation of sulfur from seawater sulfates and magmatic fluids. Chalcopyrite separates from the vein-type ores have a Re-Os isochron age of 794.8 +/- 7.9 Ma. The initial Os-187/Os-188 (2.8 +/- 1.2) and gamma(Os) (+2202) values are slightly lower than the average values of continental crust, indicating a major metal source of the Hekou Group with minor mantle input. Sulfides from the vein-type ores have delta S-34 values that range from -10.3 parts per thousand to 4.0 parts per thousand and cluster between 0 parts per thousand to 2.2 parts per thousand, which implies a significant contribution of magmatic-sourced sulfur with minor biogenic sulfur. Two major mineralization events have been identified. The Rb-Sr age of the laminated ores likely records a VMS mineralization event at similar to 1.6 Ga. The much younger Re-Os age is considered to represent the timing of an important mineralization event, which is likely related to the Neoproterozoic magmatism and/or metamorphism and represents a newly documented mineralization event to be targeted by exploration.