新疆黄山-镜儿泉成矿带对俯冲-碰撞过程中镁铁-超镁铁岩浆活动与铜镍硫化物成矿作用的启示

Continental rift and mantle plume are considered the most important background for Cu-Ni sulfide deposit and the exploration potential of the mafic-ultramafic intrusion in orogenic belt have been underestimated. In contrast, discovery of large- and medium-sized Cu-Ni sulfide deposits in orogenic belt over the world (for enstance the Xiarihamu superlarge Cu-Ni-Co deposit in the East Kunlun Orogenic Belt) indicated a well ore-forming condition and large exploration potential. However, it is still debated what tectonic stage is the best for the formation of the Ni-Cu sulfide mineralization. The southern margin of the Central Asian Orogenic Belt hosts the second largest nickel resources, with larger than 200 Mt Ni metal reserves, following the Jinchuan deposit in China and the largest region for Cu-Ni sulfide deposit in the world. This project will focus on the key issues for the formation of Cu-Ni sulfide deposit in orogenic belt and the Huangshan-Jingerquan Ni-Cu deposit belt, the largest and most representative one in the southern margin of the Central Asian Orogenic Belt. The aims are to understand the linkage between the formation of the Huangshan-Jingerquan Ni-Cu deposit belt and subduction-collision process, the nature of the mantle source and the role of asthenosphere upwelling on the generation and nature of original magma, relationship between sulfide immiscibility and magma evolution, and mechanism and key factors dominating sulfide segregation, and build the formation model for the deposits and the hosting intrusions. We will also probe into the formation of the Cu-Ni sulfide deposits in different tectonic stages at the southern margin of the Central Asian Orogenic Belt on the bases of comparison with the other Cu-Ni sulfide deposits in the adjacent tectonic units. This study is significant for our understanding on the mantle derived magmatism and formation of Cu-Ni sulfide deposit in orogenic belt.

现有理论认为大陆裂谷和地幔柱是铜镍硫化物成矿最有利的地质背景，然而，国内外若干造山带大型铜镍硫化物矿床的发现（如东昆仑夏日哈木超大型镍钴矿床）说明造山带也具有很好的成矿条件和找矿前景，然而，造山作用的哪个阶段更有利于成矿尚有争议。中亚造山带南缘是我国仅次于金川的第二大镍资源基地和世界上发现铜镍矿床最多的造山带，镍金属储量超过200万吨。本项目选择规模最大、最为典型的黄山-镜儿泉成矿带，针对造山带铜镍硫化物成矿的关键问题开展系统研究，从多个角度深入分析该成矿带与俯冲-碰撞过程的耦合关系；探讨地幔源区特征以及软流圈上涌构造机制对原始岩浆起源和性质的控制作用；阐明硫化物熔离与岩浆演化的关系，揭示硫化物聚集成矿的机制和关键因素，建立成岩成矿模式；通过与相邻构造单元其它同类矿床对比，探讨中亚造山带南缘不同构造演化阶段的铜镍硫化物成矿作用规律，切实加深对造山带幔源岩浆作用和铜镍硫化物成矿规律的认识。

现有理论认为大陆裂谷和地幔柱是铜镍硫化物成矿最有利的地质背景，然而，国内外若干造山带大型铜镍硫化物矿床的发现（如东昆仑夏日哈木超大型镍钴矿床）说明造山带也具有很好的成矿条件和找矿前景，然而，造山作用的哪个阶段更有利于成矿尚有争议，岩浆通道成矿模式及成矿关键控制因素也不十分清楚。中亚造山带南缘是我国仅次于金川的第二大镍资源基地和世界上发现铜镍矿床最多的造山带，镍金属储量超过200万吨。本项目对规模最大、最为典型的黄山-镜儿泉成矿带，针对造山带铜镍硫化物成矿的关键问题开展系统研究，取得的主要创新认识包括：1）系统揭示出康古尔-雅满苏岛弧岩浆作用分为俯冲阶段 (390-300Ma)，碰撞阶段 (300-285Ma)，碰撞后早期阶段 (285-280Ma)和碰撞后阶段 (280-260Ma)； 2）确定了黄山-镜儿泉成矿带铜镍硫化物成矿发生在碰撞后早期阶段(285-280Ma)，区域走滑背景下，使得俯冲洋壳在较浅深度断离，并导致上涌软流圈强烈的“爆发式”熔融，产生巨量玄武岩浆，从而为大规模岩浆硫化物成矿提供了充分的物质基础；3）建立了黄山-镜儿泉成矿带岩浆通道系统硫化物熔离-运移-沉降-堆积的成矿新模式，在成矿带尺度上揭示了造山带岩浆硫化物成矿的条件、过程和机制；4）根据碎屑锆石U-Pb年龄，纠正了甘墩组和梧桐窝子组地层的沉积年龄，从而理顺了黄山-镜儿泉成矿带岩浆通道成矿系统，阐明了“中泥盆统梧桐窝子组中岩墙状镁铁-超镁铁含矿岩体为深部通道相，晚石炭统甘墩组中的大岩体为岩浆通道上部的岩浆房”的新观点，为区域找矿方向提供了新的理论基础；5）指出岩浆通道系统上部的大岩体有利于形成大矿床，甘墩断裂以南大黄山与红柳沟岩体之间的戈壁覆盖区有进一步找矿潜力，含矿岩体直接围岩是否富硫化物不能作为找矿标志；6）东昆仑造山带的对比研究表明，俯冲的挥发份越多，越有利于发生大规模的与成矿有关的较高程度的部分熔融，而且允许部分熔融深度较大。