Detrital zircon constraint on the timing of amalgamation between Alxa and Ordos, with exploration implications for Jinchuan-type Ni–Cu ore deposit in China

Abstract

The Jinchuan Ni–Cu deposit, which is the largest single magmatic sulfide ore deposit in the world, is hosted by a mafic-ultramafic intrusion in the Alxa block, northwestern China. The timing of amalgamation between the Alxa block and the adjacent Ordos block, which is important for Precambrian reconstruction of North China Craton and the search for another Jinchuan-type ore deposit, is contentious. The age distribution patterns of detrital zircon crystals with Precambrian ages from the Devonian and older sedimentary rocks of the Alxa and Ordos blocks are similar. This supports the traditional view that the Alxa and Ordos blocks were amalgamated in the Paleoproterozoic along the 1.95Ga Khondalite Belt, long before the emplacement of the ∼830Ma Jinchuan intrusion. The U–Pb–Lu–Hf isotope data of comagmatic zircon crystals from the Jinchuan intrusion, together with its whole-rock Sm–Nd isotopes and trace element compositions given previously by other researchers, indicate that the Jinchuan ore-bearing intrusion is the product of continental rift-related basaltic magmatism which took place during the early stage of Rodinia breakup. Based on these observations, we conclude that in addition to the Alxa block, the adjacent regions in the North China Craton such as the Ordos basin, the Khondalite belt and the Yinshan terrane are most promising for new discoveries of Jinchuan-type Ni–Cu ore deposits.