江西朱溪特大矽卡岩型W-Cu矿床流体成矿作用研究

Skarn scheelite deposit is one of the most significant types of Tungsten Deposit in the world. Its metallogenesis is seriously restricted by geochemical features of granites, composition of wall rocks, forming depth of mineralization and alteration, and redox condition and temperature variation of metallogenic system. However, effect of hydrothermal components on tungsten precipitation is unclear. The newly discovered Zhuxi deposit is a giant skarn scheelite deposit related with granites. All its ore bodies are restricted above the contact zone of Neoproterozoic metasedimentary rocks and Paleozoic carbonate rocks and many F-rich minerals such as vesuvianite, fluorite and muscovite could be observed in the skarn mineral assemblages. What's more, lots of chalcopyrite grows altogether in the Zhuxi deposit so that the copper resource adds up to over 10 Wt. All of the above characteristics made the Zhuxi deposit very suitable to carry out genesis research so as to find out the ore-forming mechanism of the skarn scheelite deposit and its significane on precipitation of tungsten and copper. Additionally, the Zhuxi tungsten deposit was located in the northeastern Jiangxi Province, where tungsten deposit had never been discovered and all geological research and mineral exploration had been completely focused on the metal including Cu, Mo, An and Pb-Zn before. It is unclear how the tectonics, regional sedimentary rocks and magmatism influence the tungsten mineralization. Therefore, a typical metallogenesis research on the fluid inclusions and its significance on tungsten and copper precipitation stable isotopes, as well with comparative analysis of different sorts of tungsten deposits in the Nanling area and typical scheelite Skarn-type depsosits in other countries, will be carried out in this paper, to make clear the mechanism of skarn scheelite deposits, the factors affected the precipitation of scheelite and chalcopyrite, and regional metallogenic regularity in South China.

矽卡岩型白钨矿床是最重要的钨矿床之一，岩浆热液是W迁移、沉淀的重要控制因素。然而，关于热液组分（F-、Cl-、Na/Ca金属阳离子、CO2-等）对矽卡岩型白钨矿床W-Cu沉淀的控制作用存在争议，阻碍了人们对矽卡岩型白钨矿床成因的理解。朱溪W-Cu矿床是华南新发现的与区内燕山期花岗岩有关的特大矽卡岩型白钨矿床，其成因研究处于起步阶段，与典型的矽卡岩型白钨矿床成矿地质特征类似，而且该矿床以钨铜为组合特征，明显区别于南岭地区以钨锡、钨钼组合为主的钨矿床，另外，朱溪钨铜矿床的发现与赣东北地区以铜钼金为成矿特点相悖，需要重新认识赣东北及相邻区域地质背景、区域成矿规律及其对钨矿的控矿作用。为此，本课题拟选取朱溪W-Cu矿床开展流体成矿作用研究，理清流体组分特征及其对W、Cu沉淀的控制机制，确定W、Cu来源及沉淀机制，并结合已有的成因模式和解释，解析矽卡岩型白钨矿床成因，为钨矿床勘查找矿提供理论依据。

朱溪W-Cu矿床是华南新发现的与区内燕山期花岗岩有关的特大矽卡岩型白钨矿矿床，其成因研究处于起步阶段。而且该矿床以钨铜为组合特征，明显区别于南岭地区以钨锡、钨钼组合为主的钨矿床。为此，本课题对朱溪W-Cu矿床开展了系统的地质踏勘工作和地质填图、矿石镜下鉴定、流体包裹体显微测温计算、流体包裹体气体成分分析、以及稳定同位素地球化学分析工作等。确定了早期白钨矿、晚期黄铜矿阶段分别形成于153-150Ma和146-148Ma，表明朱溪矿床成矿过程至少经历了3-5Ma，矿化事件与成矿岩体侵位年龄近乎一致。厘定了朱溪矿床的钨铜矿化、蚀变特征，确定朱溪矿床至少经历了三期成矿作用：进矽卡岩阶段、退矽卡岩阶段和晚期石英硫化物阶段。不同阶段酸碱度、氧逸度变化情况：成矿岩体氧逸度较低，在矽卡岩阶段为弱氧化，中酸性条件，到后期氧逸度略有降低；直到退化蚀变阶段受角闪石、绿泥石等矿物影响，氧逸度升高，pH升高。对不同期次蚀变-矿化矿物开展了详细的流体包裹体测试分析及H-O-S-Pb同位素示踪，厘定了成矿温度-压力条件：从进矽卡岩期、退矽卡岩期至热液石英硫化物期，压力从0.97–1.38 kbars、1.24kbars降低到静水压力75–252 bar之间，温度从450–>500℃降低到280–320℃和160–240℃，流体成分从H2O-NaCl/KCl/CaCl2±CH4/C2H4体系、H2O-NaCl/KCl/CaCl2体系又变为H2O-NaCl/KCl/CaCl2±CH4/C2H4体系。而H-和O同位素值表明矽卡岩阶段和退矽卡岩阶段成矿流体主要来源于岩浆水，石英硫化物热液期成矿流体主要为岩浆水、大气水和少量围岩贡献的混合流体，硫、铅同位素分析表明，朱溪矿床的硫、铅、铜、锌、铁等成矿物质主要来源于当地的岩浆和沉积源。地质、流体包裹体和同位素资料支持朱溪矿床是一个典型的矽卡岩型钨(铜)矿床，与钛铁矿系花岗质岩有关，形成于挤压构造环境。总之，朱溪钨(铜)矿床流体包裹体研究表明，沸腾、温度下降和氧化作用增强可能是退变质期钨、铜大量沉积的因素；在石英硫化物热液阶段，压力、fO2和温度的降低可能是金属沉淀的主要因素。