Pyrite Re-Os isotope systematics at the Zijinshan deposit of SW Fujian, China: Constraints on the timing and source of Cu-Au mineralization

Zijinsh an is the largest high-sulfidation epithermal Cu-Au deposit on mainland China. The primary mineralization at the deposit is characterized by pyrite, digenite and covellite. Although some Rb-Sr isochron ages of the fluid inclusions in quartz and the apparent K-Ar age of the Cu-bearing alunite alteration zone have been previously interpreted as the ore-forming age, the Rb-Sr and K-Ar dating systems are usually readily reset due to their closure temperature, and thus document the latest thermal event. In order to precisely determine the age of the Cu mineralization, eight-pyrite separates were Re-Os dated, and seven yielded an isochron age of 103 +/- 4 Ma with an initial Os-187/Os-188 ratio of 0.45 +/- 0.14. This date is interpreted as the age of Cu mineralization, which is in agreement with geochronological data from molybdenite and the porphyritic granodiorite that hosts Cu-Mo mineralization at Luoboling (located 2 km NE of Zijinshan), suggesting that these two deposits were formed during the same metallogenic event. The relatively low initial Os-187/Os-188 ratio indicates that the source of the Cu at Zijinshan is predominantly the crust with input from the mantle. (C) 2016 Elsevier B.V. All rights reserved.