辉钼矿Sr-Nd-S-Pb、Mo同位素地球化学对东秦岭多时代钼成矿作用的约束

The East Qinling Mo Belt is the most important Mo ore belt in the world. Numerous, diverse types of Mo deposits in the East Qinling Mo Belt have high Mo reserve and experienced multistage of mineralization so that the East Qinling Mo belt is an ideal place to study the origins of diverse Mo metallogeny. Two important questions remain unclear in the belt, first, what is the specific background for individual stage of Mo mineralization? Second, is the multistage pre-Jurassic Mo mineralization responsible to the "explosive" Mo mineralization in the Late Jurassic-Early Cretaceous? The project is planned to investigate five different ore-types and/or periods of deposits, including Neoproterozoic fluorite-vein type Tumen, Silurian quartz-vein type Yindonggou, Triassic carbonatite-hosted type Huanglongpu, Jurassic porphyry-skarn Nannihu and Cretaceous porphyry Donggou deposits. Molybdenite and other sulfides will be analyzed for major and trace elements and Sr-Nd-S-Pb isotopic compositions. The new dataset will enable us to trace the sources of fluids and metals for the Mo deposits and discuss the possible inheritance of Mo in young Mo deposits. Mo isotopic compositions of molybdenite from five different types of Mo deposits will be analyzed to demonstrate Mo isotopic characteristics of each deposit so that a criteria on Mo isotopes will be yield to discriminate between differernt types of Mo deposits. The results may help us to better understanding the mechanisms of massive Mo accumulation in the late Jurassic to early Cretaceous and guide future exploration projects in the region.

东秦岭是世界第一大钼矿带，具有规模大、成矿类型多样、多时代成矿三大特点，是研究钼成矿作用的极佳地区。其关键科学问题是不同时代的钼成矿背景如何？以及多时代钼成矿作用是否具有累积效应，而促成晚侏罗世-早白垩世钼"爆发式"成矿？本项目拟选择新元古代土门萤石脉型、志留纪银洞沟石英脉型、三叠纪黄龙铺碳酸盐脉型、侏罗纪南泥湖斑岩-矽卡岩型和白垩纪东沟斑岩型5个钼矿床，以辉钼矿为主线，查明辉钼矿及其它硫化物的微量、稀土元素和Sr-Nd-S-Pb同位素组成，示踪各钼矿床成矿流体和成矿物质来源，探索其可能存在的继承性；系统查明各矿床辉钼矿的Mo同位素组成，对比分析Mo同位素组成与矿床类型、成矿期次等因素之间的关系，探讨不同类型钼矿床Mo同位素组成差异的原因和机理。这不仅可理解东秦岭晚侏罗世-早白垩世钼 "爆发式"成矿的形成机理，拓宽钼勘查找矿思路；也可为建立不同类型钼矿床的Mo同位素示踪模式提供重要约束。

东秦岭是世界上最大的钼矿带，拥有从元古代到白垩纪多期次钼成矿作用，形成了多种不同类型钼矿床。本项目对东沟超大型斑岩型钼矿床、南泥湖-三道庄超大型斑岩钼矿床、上房沟斑岩-矽卡岩型钼矿床、金堆城大型斑岩型钼矿床、黄龙铺碳酸盐脉型钼矿床、龙门店钼矿和寨凹钼矿开展了钼同位素研究。同时，项目还开展了外方山石英脉型钼矿田的流体地球化学特征研究、新元古代土门钼矿床的同位素地球化学特征研究、熊耳山地区西南缘香炉沟铜成矿作用的黄铜矿Re-Os等时线定年工作、熊耳山地区西南缘辉绿岩的岩石地球化学和年代学地球化学研究，以及利用同步辐射X射线光刻技术研究了闪锌矿中的单个流体包裹体的三维成像。同时，项目对美国科罗拉多州钼矿带和印度尼西亚Grasberg矿床进行了钼同位素研究，经与伊朗科尔曼地区和华南大湖塘超大型钨铜钼矿床的钼同位素对比后发现，地幔来源的辉钼矿富集轻钼同位素，地壳来源的辉钼矿富集重钼同位素，显示钼同位素具有成矿物质来源的示踪潜力。