东昆仑东段地区那更康切尔沟独立银矿床成因机制研究

Silver ore exploration has been made a breakthrough in the east section of the East Kunlun in recent years. Especially the discoverey of Nagengkangqieergou independent silver deposit has filled the exploratory void of such type of deposit in Qinghai province. The existing geological work indicates that the deposit is produced in the collisional orogenic setting, and the distribution of the ore bodies is controlled by the fault, which is the typical representative of the domestic vein independent silver deposit. However, its genetic mechanism, such as metallogenic fluid properties and source, source of ore-forming materials, ore-forming process, etc are not clear due to the late discovery and exploration. This project takes the Nagengkangqieergou independent silver deposit as the research object, and the source - transport- storage of the deposit formation as the main idea, applies large scale tectonic lithofacies - mineralization - alteration mapping, fluid physical and chemical properties analysis, geochemical tracing and metallogenetic age determination to elucidate sources, migration and concentration of ore-forming fluids, and sources and precipitation mechanism of ore-forming materials. These originally researches can not only further enriching and perfecting the vein independent silver mineralization theory,but also guide the prospecting exploration.

近年来东昆仑东段地区银矿勘探取得了重大突破，尤其是那更康切尔沟脉状独立银矿的发现填补了青海省独立银矿床的空白。已有的基础地质工作表明，该矿床产于碰撞造山环境，矿体空间分布受断裂构造控制，是国内脉状独立银矿的典型代表。然而，由于发现较晚，其成因机制如成矿流体性质和来源、成矿物质来源、成矿过程等还不明确。已有的对脉状独立银矿的认识已不能解碰撞造山背景下该类型矿床的成因。本项目以那更康切尔沟独立银矿为研究对象，以矿床形成的源-运-储研究为主体思路，通过矿区大比例尺构造-岩相-矿化-蚀变填图、流体物理化学性质分析、地球化学示踪、成矿年龄测定等技术，查明矿区内成矿流体和成矿物质来源、迁移与沉淀作用，再塑矿床成矿过程，揭示其成矿机理。上述研究特色显著，原创性强，其研究成果既可进一步丰富和完善脉状独立银矿成矿理论，又能直接指导找矿勘探。

围绕脉状独立银矿床成因这一关键科学问题，按成矿的“源-运-储”系统为主线，对东昆仑东段那更康切尔沟独立银矿床进行了系统研究。结果表明，该独立银矿床成矿流体显示低温、低盐度、低密度的特点，成矿流体早期可能与岩浆作用密切相关，而随着流体的不断演化，受大气降水的影响逐渐变大；成矿物质S和Pb来自岩浆作用，三叠纪强烈的岩浆活动也为金属元素的运移提供了热量；矿体严格受构造控制，北西向逆冲推覆构造在推覆结束的松弛阶段转变为张性属性，为成矿流体运移提供了通道和成矿空间；绢云母40Ar-39Ar加权平均年龄为212.52±0.78Ma，含矿石英脉中获得220±0.62Ma的岩浆锆石U-Pb年龄，代表了鄂拉山组流纹岩的形成年龄，明确了银矿成矿时限在212Ma-220Ma之间，为晚三叠世晚期；综合上述研究，结合黄铁矿LA-ICP-MS原位微量元素测试判断矿床成因为低温热液脉型，是印支晚期东昆仑造山带发生强烈的岩石圈拆沉和软流圈上涌后，形成的成矿作用大爆发的产物。