矿床地球化学国家重点实验室知识库

Giant sedimentary rock-hosted stratiform copper (SSC) deposits commonly occur in rift environments, temporally coincident with the breakup of the Rodinia and Pangea supercontinents. However, whether or not such deposits have also formed during the breakup of the Paleoproterozoic Columbia supercontinent is not well known. A group of dolostone-hosted Cu deposits in late Paleoproterozoic rift-related sedimentary sequences of the Dongchuan Group, South China, form one of the largest SSC districts in the world. Being one of the largest SSC deposits in the region, the Yinmin deposit has stratiform Cu orebodies intruded by dolerite dykes. One dyke has a SIMS zircon U–Pb age of 1,701±28 Ma, slightly younger than the orehosting strata with a zircon U–Pb age of 1,742±13 Ma for a tuff unit. Six chalcopyrite and bornite separates from stratiform orebodies contain highly radiogenic Os and extremely low common Os and yield a weighted mean Re–Os model age of 1,666±82 Ma and a 187Os–187Re errorchron age of 1,585±100 Ma. The present zircon U–Pb and sulfide Re–Os ages thus constrain the timing of the mineralization at ~1,700 Ma. The Yinmin deposit and, by inference, other SSC deposits in the region, arguably represent a large-scale SSC mineralization event during the late Paleoproterozoic. The formation of these deposits was coeval with the initial breakup/fragmentation of the Columbia supercontinent. This study highlights the temporal and likely genetic links between large-sized SSC deposits and the supercontinent cycle.