Abstract

The Kangdian Copper Belt is one of the most important Cu-, Au-, and Fe-producing areas in China. Although there are numerous iron oxide-copper-gold (IOCG) deposits in the Kangdian Copper Belt, their genesis remains controversial because of a lack of direct Cu mineralization age constraints. We report Re-Os isotope data of chalcopyrite from the Lala IOCG deposit, one of the largest IOCG deposits in the Kangdian Copper Belt, southwest China. Six samples show a large range in Re and Os abundance, and Re-Os isotope compositions. These samples contain high Re abundances (27.1–1,477 ppb) and predominately high radiogenic Os compositions, so we define these samples as low level highly radiogenic (LLHR). These data yield a seven-point isochron age of 1290 ± 38 Ma. Since chalcopyrite is the primary copper mineral and Au-bearing mineral, we interpret this isochron age as the timing of Cu-Au mineralization, based on field geology and petrographic evidence. Using 187Re/188Os versus 187Os/188Os to yield a typical Re-Os age with initial 187Os/188Os ratio of 8.3 ± 4.0, which suggests the source of ore-forming metal (i.e., Os with referred Cu-Au) is crustal. Our new data demonstrate that chalcopyrite can yield a robust age that constrains the direct timing of IOCG deposits, which even suffered from greenschist facies metamorphism with temperatures up to 500°C.

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