石英脉型黑钨矿床"五层楼"垂直形态分带形成的动力学机制

Our goal is to explore the dynamic mechanism of five-storey vertical morphological zonation in vein-type wolframite deposits by vein morphology, structural analysis, cathodoluminescence and fluid inclusion analysis, and numerical simulation. Three vein-type wolframite deposits with five-storey morphological zonation will be studied: Taoxikeng wolframite deposit, Piaotang wolframite deposit, and Huangsha wolframite deposit in Jiangxi Province. First, geometry of their morphological zonation will be measured to clarify filling mechanism of hydrothermal fluids and fractal propagation of ore-bearing quartz veins and to put a constraint on fluid overpressure. Second, occurrences of quartz veins, conjugated joints, and micro-fractures of quartz will be measured to determine ancient stress fields, and differential stresses in quartz will be estimated according to dislocation densities in quartz; these constraints on stress fields will be used to analyze how structure controlled fluid immigration and filling mechanism. Third, cathodoluminescence textures, race element concentration, and fluid inclusion experiments will be combined to detect hydrothermal fluids in different times and to unravel physical and chemical history of ore-forming fluids. Forth, three physical processes will numerically simulated: regional stresses and fluid flow, fluid flow and thermal stresses from magma, and mass and heat transfer with silica precipitation, which is to quantitatively analyze how regional stresses, thermal stresses from magma, and ore-forming fluids lead to formation of five-storey vertical morphological zonation. Finally, formation mechanism of five-storey vertical morphological zonation will be reached from these four mechanical and chemical analysis, and metallogenic model of vein-type tungsten deposits will be developed further.

研究拟从矿脉形态、构造分析、阴极发光与包裹体研究和定量模拟四种途径探索脉型黑钨矿床"五层楼"垂直形态分带形成的动力学机制。选择我国几个典型脉型黑钨矿床，包括赣南漂塘、黄沙和淘锡坑等，测量矿脉几何形态，分析成矿流体充填和矿脉分形生长机制,对流体压力做出约束；测量矿脉、节理和石英显微裂隙产状，利用石英位错密度估算差应力值，对比三种方法所反演的应力场，探索构造对流体充填的约束；进行石英阴极发光、微量元素和流体包裹体研究，探索不同期次石英的阴极发光和微量元素特征，约束不同期次流体温度、压力条件，深化对成矿流体演化过程的认识；定量模拟在区域应力与岩浆热应力作用下成矿流体流动规律，阐明流体充填的动力学过程；定量模拟流体传热传质与二氧化硅等沉淀过程，分析渗透率变化规律，探究流体流动在"五层楼"形态分带形成中的作用。综合上述研究，阐明"五层楼"形态分带形成的动力学机制，完善石英脉型黑钨矿床的成矿模式。

石英脉型黑钨矿床“五层楼”分带是石英脉体系统在近1公里垂直空间内表现的形态学特征，是由我国地质工作者提炼出的经验成矿模式，在钨矿找矿中发挥了重要作用，在世界矿床模式中也占有一席之地。那么，为什么我国南岭地区会形成这种独有的现象？经过脉体分形几何、构造、流体包裹体和有限元数值模拟分析，项目组认为“五层楼”垂直形态分带是受构造-流体-多期成矿耦合控制。首先，构造是控制“五层楼”分带的第一变量。南岭石英脉型钨矿床在相对较深的应力环境下（4-5公里），形成一套具有优选方位的垂直裂隙系统。作为热液输运通道和主要成矿定位构造，垂直裂隙系统的几何特征对成矿流体聚焦流动的位置和强度有重要影响。石英脉型钨矿的容矿裂隙几何特征有利于成矿流体在深部聚焦，从而为深部形成宽脉提供物质基础。高压成矿流体对围岩的压缩作用抑制成矿流体与围岩的水岩反应，促进成矿流体在节理区聚焦流动。这种物理过程有利于成矿元素从源区向成矿就位场所的高效率输运，但造成浅部围岩蚀变强于深部的围岩蚀变。另外，深部多期次裂隙张开和成矿充填过程是深部宽脉比浅部多的重要原因之一。岩浆热液过渡阶段的高压流体、应力场、构造、围岩的岩性等多因素耦合作用是南岭地区石英脉型钨矿床形成 “五层楼”垂直形态分带的关键。近年来国内学者将“五层楼”模式发展为“五层楼+地下室”。经细致地研究发现，大吉山“地下室”（69号岩体浸染型矿体）的浸染型黑钨矿为热液成因，可能与石英脉型钨矿体同源，为统一“五层楼”矿脉和“地下室”矿体的成矿理论提供重要证据。