湖南双峰包金山矿区白钨矿流体包裹体特征

Inclusion Characteristics of Scheelite at Baojinshan Mining Area in Shuangfeng County of Hunan Province

包金山矿区位于湘中成矿区的北东部白马山-龙山东西向构造带和紫云山-沩山北西向复背斜带的重合位置.文章通过系统的野外地质调查、岩相学和白钨矿流体包裹体的研究,发现矿区内白钨矿为热液石英脉型,钨(金)矿化从构造结合部位向外逐渐减弱,主要形成于乳白色石英脉阶段(A)和烟灰色石英脉阶段(B).矿床内白钨矿中的研究显示流体包裹体为气液两相.在乳白色石英脉阶段均一温度介于272~377℃,峰值为291~380℃,盐度为4.55~9.19(wt%),密度为0.62~0.83 g/cm^3;在烟灰色石英脉阶段均一温度介于267~417℃,盐度为5.01~7.68(wt%),密度为0.54~0.82 g/cm^3;两个阶段的包裹体温度和盐度相差较小,为中高温、低盐度流体系统.早期流体密度和盐度略大于晚期,推测成矿后期大气降水混入岩浆热液,引起成矿的温度降低和成矿流体的稀释.矿区大多数包裹体密度与大多数岩浆热液流体密度相当,推测钨矿可能来源于岩浆热液.

Baojinshan mining area is located in the antielinorium rendezvous of Baimashan-Longshan east-west tectonic belt and Weishan-Ziyunshan north west direction, Central Hunan. Based on the detailed field study on petrography and scheelite fluid inclusions, it is recognized that the hydrothermal quartz vein is the only type of the scheelite mine, and scheelite mineralization is evidently controlled by the conjunction of several geotectonic. The deposit was mainly formed in two phases of the ivory-white quartz vein stage （ stage A） and grey quartz vein stage （ stage B）. The research of the fluid inclusions from scheelite reveals that vapor-rich and liquid-rich inclusions are coexisting. At the stage A, with the homogenization temperatures range of 272 -377 ℃ and peak of 291 - 380 ℃, with salinity of 4. 55 -9. 19%（ wt%NaCl equiv）and density of 0. 62 = 0. 83/cm3 ; at the stage B, homogenization temperatures range of 267 - 417 ℃, with salinity of 5.01 - 7.68 % （wt %NaCl equiv）and density of 0. 54 -0. 82 g/cm3. Homogenization temperature and salinity of inclusions in both phases are similar, featuring high-medium temperature and low saltness. Salinity and density in early mineralization fluids are slightly higher than that of the later fluids, for magmatic fluids evolved in the later stage which mixed with meteoric water, causing temperature dropping and fluid dilution. In mining area,the density of most inclusions is similar with magmatic hy- drothermal fluid, suggesting that scheelite deposit source is from magmatic hydrothermal.