摘要:
湘东南地区位于南岭多金属成矿带中段,邓阜仙钨矿是湘东南地区一个重要的钨矿床。本文通过对邓埠仙矿区主要矿化阶段含矿石英及萤石脉中的流体包裹体进行初步岩相学观测并结合显微测温及拉曼探针分析,发现邓埠仙钨矿中流体包裹体类型较为简单,成分主要为H2O-NaCl(I型),对其进行进一步的研究及测试,我们发现即使成分相同,包裹体的均一温度及盐度仍显示出了较大的差异性,其中I型包裹体的均一温度从100~350℃均有分布,且大致可以划分为三个温度区间,分别为①240~290℃的高温区②170~240℃的中温区③120~170℃的低温区,盐度整体<12wB%NaCleq.,峰值为5wB%NaCleq.,这些都说明研究区成矿具有多期次性,反映出多阶段矿化的特征。结合前人研究,我们认为邓埠仙钨矿成矿流体的捕获压力约为100Mpa,按照静岩压力换算,成矿的最小深度约为3.7km。同时对邓埠仙钨矿的I型包裹体的拉曼探针测试显示,萤石中的包裹体发育宽泛的H2O包络峰,而石英中发育的包裹体除宽泛的H2O包络峰另可见少量N2,综合分析我们认为流体在演化过程中所经历的混合作用导致以H2O为主的气相溢出使得流体压力改变,同时流体温度降低或许才是邓埠仙钨矿的主要沉淀机制。邓埠仙钨矿产于花岗岩体中,其中中粒二云母花岗岩与成矿关系最为密切,其成岩年龄有助于我们更详细的了解及推测邓埠仙矿区的成矿年龄,通过LA-ICP-MS锆石U-Pb年龄测定,中粒二云母花岗岩的加权平均年龄为158.6±0.7 Ma,属燕山早期。
Abstract:
The southeast of Hunan Province is in the middle of Nanling Range polymetallic metallogenic belt. Dengbuxian tungsten deposit is one of the most important in this area. In this paper, we selected the fluid in-clusions from quartz and fluorite veins in the main mineralization stages of mining ore from this deposit, through preliminary petrographic observations, microthermometry research and Raman microprobe analysis, we found the type of fluid inclusions in the deposit is relatively simple, the main chemical compositions is H2O-NaCl (type I). After further research and testing, we discovered that even inclusions with the same composition, their uniform temperatures and salinities are still showed a larger difference, the inclusion's homogenization temperature dis-tribute from 100~350℃ (without pressure correction) with multi-peak characteristics. We can identify three distinct temperature ranges:①The high temperature of 240~290℃;②The medium temperature of 170~240℃;③The low temperature of 120~170℃,and all of the inclusions salinity are below 12 wt%NaCleq, with a peak of 5 wt%NaCleq. All of these show that the ore-forming has multiple periods, and reflects the characteristics of the multi-stage mineralization in research area. Combined with previous studies, we figured out trapping pressure about 100 Mpa, according to lithostatic pressure conversion, the minimum depth of mineralization is about 3.7 km. The type I inclusions laser Raman probe test results show that both of the inclusions in quartz and fluorite veins were detected broad H2O envelope peak, while only a small number of N2 envelope peak was detected in quartz inclusions. Comprehensive analysis, we think the fluid migmatization lead to gaseous phase (mainly H2O) overflow which occurred in the evolution process, then fluid pressure changed. Meanwhile, temperature reduction is the main factor of Dengbuxian tungsten mineralization. Dengbuxian tungsten deposit is in the granitic pluton, its dige-netic age can help us to understand more details about this metallogenic ages and speculate it. Through LA-ICP-MS zircon U-Pb dating, the weighted average age of medium grain two-mica granites is 158.6 ± 0.7 Ma, belongs to the early Yanshanian.
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