江西岩背锡矿床流体包裹体特征与成矿作用研究

Characteristics of fluid inclusions and mineralization in Yanbei tin deposit,in Jiangxi Province

岩背锡矿床位于武夷山南段江西会昌县境内,是一个大型独立斑岩锡矿床。矿床产于花岗斑岩和流纹斑岩的接触带内,矿体以富含原生黄玉为特征。矿石构造以浸染状、细脉浸染状和脉状为主。矿石矿物主要有锡石、黄铁矿、黄铜矿和辉钼矿等;脉石矿物主要有石英、黄玉、萤石、绿泥石、绢云母等。对岩背锡矿各阶段石英流体包裹体进行了岩相学观察、显微测温和激光拉曼探针分析。结果表明,流体包裹体的类型主要为富液相气液两相包裹体,其次为富气相气液两相包裹体、含CO2三相包裹体和含石盐子矿物多相包裹体。成矿前期和成矿后期以富液相气液两相包裹体为主,均一温度分别为228～433℃、147～195℃,w(NaCleq)分别为4.34%～17.26%、1.91%～6.3%。成矿期4类包裹体均发育,以富液相气液两相包裹体为主,均一温度为180～349℃,w(NaCleq)为3.87%～15.47%。激光拉曼分析显示,流体包裹体的气相成分主要是H2O、CO2、SO2、HCl和HF。已有的氢、氧同位素研究表明,成矿流体主要来自岩浆水,晚期有大气降水的混入。矿床的初始流体来源于岩浆水,低温度、低盐度大气水的混入,导致流体温度、盐度降低和锡石的沉淀。

Located in Wuyi Mountain within Huichang county of Jiangxi Province, the Yanbei tin deposit with rich original topaz is a large-sized tin deposit in the study area. Its major tin orebodies are mainly hosted in the contact zones of granite porphyry and rhyolitic porphyry. The ore mainly has disseminated, veinlet-disseminated and nervation. Ore minerals consist simply of cassiterite, pyrite, chalcopyrite, molybdenite etc; gangue minerals are mainly quartz, topaz, fluorite, chlorite, sericite etc; and the ores occur in disseminated and veinlet forms. Fluid inclusions in quartz from Yanbeitin deposit were studied by such means as petrography, microthermometry and Laser Raman Spectrometer analysis. Some conclusions have been reached through results： there are mainly liquid rich two-phase vapor-liquid inclusions, gas rich two-phase vapor-liquid inclusions, CO2-bearing three-phase inclusions and minor daughter minerals-bearing polyphase inclusions. Fluid inclusions in quartz in the pre-ore stage and post-ore stage are mainly liquid rich two-phase vapor-liquid inclusions. The homogenization temperatures and salinities of the former stage vary from 228~433℃ and from 4.34%~17.26% respectively, and those of the latter stage vary from 147~195℃ and from 1.91%~6.3% respectively. During the mineralization stage, all the four types of fluid inclusions were formed in ores, their homogenization temperatures and salinities range from 180~349℃ and from 3.87%~15.47% respectively. The analytic results through Laser Raman Spectroscopy suggest that the fluids are rich in H2O, CO2, SO2, HCl and HF. According to previously analyses of the isotopic composition of hydrogen and oxygen of the ores, it was suggested that the ore-forming fluid was mainly derived from the magmatic water and meteoric water mixing in the later. Combined with previous researches on Yanbei tin deposit, this paper maintains that the ore-forming fluid derived from magmatic water, meteoric water mixed in the later, resulted in the fell of temperature and salinities of the fluid, and made the depo sition of cassiterite.