中国西部典型岩浆铂族元素矿床超常富集成矿机制

Extreme enrichment and ore-forming mechanism of main mafic magma-related platinum group element deposits in western China

中国西部探明了一系列与新元古代以来幔源岩浆有关的镍铜铂族元素(platinum group elements,PGE)岩浆矿床,华北克拉通新元古代金川镍铜铂族硫化物矿床、峨眉山二叠纪大火成岩省金宝山铂族元素矿床等记录了不同构造环境幔源岩浆PGE超常富集成矿过程。亲铁性的铂族元素高度富集于地核,深部地幔起源、高程度部分熔融形成的镁铁质岩浆中PGE含量较高,地幔岩浆系统不同条件下铂族元素以纳米态元素簇、合金、硫化物熔体或超临界流体运移-聚集成矿,在阶段性岩浆房多阶段、多途径富集,成矿作用类型丰富。华北-华南克拉通岩石圈地幔PGE含量均略高于原始地幔值;华北克拉通岩石圈地幔PGE含量从古生代到中新生代略有降低,表明存在PGE抽取岩浆事件。中国西部新元古代以来的幔源岩浆源区PGE不亏损、岩浆活动时间长、岩浆-硫化物相互作用PGE多阶段富集及地幔柱岩浆动力学背景是PGE超常富集成矿的有利地质条件,其控制因素及动力学背景的认识对查明PGE成矿潜力和拓展资源储量具有重要意义。

Neoproterozoic mafic magmatism in western China produced a number of platinum group element(PGE)deposits in different geological time and tectonic geodynamic settings,including the Neoproterozoic Jinchuan Ni-Cu-PGE sulfide deposit located in southwestern margin of the North China Craton,and the Jinbaoshan PGE deposit,a member of the Permian Emeishan large igneous province(LIP)in southwestern China.PGEs as siderophiles are more enriched in the Earth’s core than in the mantle and crust.Therefore,they can be transported into the crust by mantle-derived magma as elemental nanoclusters,alloy or immiscible sulfide melt,and their concentration in the magma tends to increase with the depth and degree of partial melting in the mantle source.PGE-bearing sulfide and other minerals in the magma can be concentrated gradually in the magma chambers and associated conduits through a multi-stage process,and form economically valuable multi-type PGE deposits.The subcontinental lithospheric mantle(SCLM)beneath the North and South China Cratons has higher PGE contents than the primitive mantle.The concentration of PGEs in the SCLM of the North China Craton may also decrease from the Palaeozoic to Cenozoic,indicating some PGE extraction magmatisms.Neoproterozoic mafic magmatism in western China is a plausible mechanism of PGE mineralization,as inferred from PGE-rich mantle(plume)source,high PGE content in mantle-derived magma,long-lived magmatic activity as well as multi-stage PGE extreme enrichment by magma-sulfide interaction.A better understanding of the geodynamic settings and mineralization processes in PGE deposits is important for assessing PGE mineralization potential in the region and finding more PGE resources in China.