东天山黄山东铜镍硫化物矿床的岩浆期后韧性变形特征与成矿元素再活化机制研究

It is generally accepted that the Ni-Cu sulfide deposits are typical magmatic segregation deposits resulting from immiscibility between mafic - ultramafic magmatic and sulfide melt. Actually, the Ni-Cu sulfide deposits are usually experienced postmagmatic hydrothermal overprinting and the late-hydrothermal metamorphism reworking. Recently, many studies focus on mechanism of postmagmatic hydrothermal overprinting on Ni-Cu sulfide deposits and metallogenic element remobilization in the deposits. However, seldom detailed studies have been conducted to reveal the process of postmagmatic hydrothermal overprinting and related ore-forming mechanism for Ni-Cu sulfide deposits companied by coeval regional ductile shearing..The Huangshandong magmatic Ni-Cu sulfide deposits located in the Huangshan - Jinerquang area of the eastern Tianshan Mountains, Central Asia Orogenic Belt. The Ni-Cu sulfide deposits and ore-bearing mafic - ultramafic pluton had underwent dramatic post-magmatic hydrothermal overprinting, while regional ductile shearing run throughout with the process of magmatic crystallization and Ni-Cu mineralization. This project will conduct detailed studies on fabric, mineralogy and geochemistry on the mainly two type of orebody, that is,ore mylonite related to postmagmatic hydrothermal within the ductile shearing zone and sprongs sideronitic orebody related to magmatic Ni-Cu sulfide mineralizaion. Combined with the studies on the characteristics of fluid inclusions related to different type of mineralization, the project should reveal the enrichment process of nickel and copper under the postmagmatic hydrothermal overprinting with coeval regional ductile shearing, discuss remobilization mechanism of some metallogenic elements. Our research will be hopeful to further improve the metallogenic theory of Ni-Cu sulfide deposits, and be helpful to provide new ideas on hydrothermal bonanza prospecting in mafic - ultramafic pluton which experienced a coeval ductile shearing with magmatic Ni-Cu sulfide mineralzation and magmatic crystallization.

铜镍硫化物矿床是镁铁-超镁铁质岩浆与硫化物熔体发生液态不混溶的产物，是典型岩浆熔离矿床。铜镍硫化物矿床常受岩浆期后的热液叠加和后期热液-变质作用的改造。目前，对铜镍硫化物矿床岩浆期后热液叠加及成矿元素的再活化机制研究较多，尚无对受区域韧性剪控制的岩浆期后热液的叠加过程和成矿机制的详细研究。位于东天山的黄山东铜镍硫化物矿床经历了区域韧性剪带控制的岩浆期后热液叠加和韧性变形，且韧性剪切贯穿于岩浆结晶和成矿过程。本项目将开民展对黄山东铜镍矿床中具韧性变形特征的矿石糜棱岩和具海绵陨铁结构的铜镍硫化物矿石的对比研究，结合对伴生脉石矿物中流体包裹体的详细分析，阐明岩浆铜镍硫化矿床在岩浆侵位过程中，受区域韧性剪带控制的岩浆期后热液叠加作用所产生铜镍富集过程及和成矿元素活化机制，进一步完善铜镍硫化物矿床成矿理论，并为周边地区同样经历了同岩浆韧性剪切的铜镍硫化物矿床中热液叠加型富矿体的找矿工作提供新的思路。

黄山东铜镍硫化物矿床产于东天山地区的黄山-镜儿泉韧性剪切带中，大地构造上属中亚造山带东天山觉罗塔格岛弧带。该铜镍矿所在的黄山东镁铁-超镁铁岩体呈纺锤状侵位于晚石炭纪火山岩中，其边部发生了与区域剪切带总体走向一致的强烈片理化作用。矿床中的部分矿体发生强烈韧性变形，其中17号矿体完全产于韧性变形带内，岩石和矿石都发生了强烈的破碎和蚀变而形成矿石糜棱岩。在上述韧性变形带内，还发育一定规模的网脉状和细脉状富铜碳酸盐-硫化物脉。本项目在详细野外地质和构造形迹观察的基础上，对黄山东铜镍矿床不同类型的矿石开展了细致的显微岩相和矿相学观察，识别出三种类型矿石：原生矿石、强烈变形矿石和热液叠加矿石。海绵陨铁结构的原生矿石中，脉石矿物几乎不发生蚀变和变形，矿石矿物仅发生脆性破裂；强烈变形矿石中，脉石矿物和矿石矿物均发生强烈变形，主要以纤闪石的波状消光和膝折、金云母的书斜构造、磁黄铁矿的定向拉长为特征；热液叠加矿石中的磁黄铁矿普遍发育颗粒的扁平化、重结晶，局部可见磁黄铁矿的退火平衡结构。此外，矿床中还发育一系列以上三类矿石的过渡类型。.黄山东铜镍硫化物矿床的侵位与变形时间与区域黄山-镜儿泉剪切带的韧性剪切作用时间相一致。岩体冷却过程经历的强烈韧性剪切变形作用不但造成矿石矿物的强烈韧性变形而形成矿石糜棱岩，还使伴生脉石矿物发生细粒化和热液蚀变，释放出流体和成矿元素，并叠加于变形的矿石和岩石之上，从而形成了网脉状和细脉状矿体。磁黄铁矿、镍黄铁矿和黄铜矿的激光原位微量元素分析表明热液叠加矿石中的磁黄铁矿具有较高的Ni和Co含量，镍黄铁矿具有较高的Ni含量，黄铜矿具有较高的Ag和Cd含量。我们推断热液叠加矿石的Ni和Co主来来源于橄榄石蚀变过程中释放的Ni和Co，而富黄铜矿的热液叠加矿石的Cu主要来源于原生黄铜矿的分解。.黄山东铜镍矿的原生硫化物固熔体铁含量较高，因而在硫化物熔体结晶过程只形成六方磁黄铁矿而无伴生单斜磁黄铁矿和黄铁矿。在热液叠加过程中，流体沿边缘和裂隙面交代早期六方磁黄铁矿，形成单斜磁黄铁矿反应边。论文还发现六方磁黄铁矿形成的新机制：即在高硫逸度和高氧逸度的条件下，随后体系温度的降低，单斜磁黄铁矿可从热液六方磁黄铁矿中出溶形成呈叶片状单斜-六方磁黄铁矿交生体。