大兴安岭南段西坡拜仁达坝-维拉斯托矿床成矿流体特征及其演化

Ore-Forming Fluid and Its Evolution of Bairendaba-Weilasituo Deposits in West Slope of Southern Great Xing'an Range

拜仁达坝-维拉斯托矿床是大兴安岭南段西坡最大的2个热液脉型银矿床,对这两个矿床各阶段矿物（如黑钨矿、浅色闪锌矿、石英和萤石）中的流体包裹体进行研究,并对硫化物进行了硫同位素分析.结果表明,拜仁达坝矿床的流体从早阶段到晚阶段（Ⅰ→Ⅱ→Ⅲ）均一温度和盐度逐渐降低.维拉斯托矿床热液成矿期第Ⅰ、Ⅱ成矿阶段具有高温高盐度的流体；第Ⅲ成矿阶段具有不混溶流体,即中温中盐度的流体（均一温度为208~294℃,盐度含量为4.65%~12.39%）和高温低盐度的流体（均一温度为333~406℃,盐度含量为3.55%~6.88%）；第Ⅳ成矿阶段具有低温较低盐度的流体.两个矿床的流体包裹体气相成分表明成矿流体均为 CO2-H2O-NaCl 体系.拜仁达坝矿床的均一温度和盐度随着成矿阶段逐渐降低和氢氧同位素证据均表明,早阶段的流体主要为岩浆水来源,晚阶段的流体混入了大气降水.维拉斯托矿床氢氧同位素证据和流体中的成分（CH 4/C2 H 6为39.271%~101.438%）均表明其成矿流体主要为岩浆水来源.拜仁达坝-维拉斯托矿床的硫具有深源特征,拜仁达坝矿床的成矿机制主要与不同来源的成矿流体混合有关；维拉斯托矿床的成矿机制主要与降温和成矿流体不混溶有关.

The Bairendaba-Weilasituo deposits are the two of the largest hydrothermal vein-type silver deposits at the southern Great Xing？？an Range.This paper presents the studies of the fluid inclusions from wolframite,light sphalerite,quartz and fluo-rite and the sulfur isotope of sulfides.Results show that the homogenization temperatures and salinities decrease gradually from stages Ⅰ to Ⅲ in the Bairendaba deposit.During the mineralization periods of the Weilasituo deposit,fluid of stages Ⅰ and Ⅱis featured with higher temperature and salinity.The stage Ⅲ has immiscible fluid,which is of medium temperature and salini-ty （homogenization temperature is 208 to 294 ℃,salinity is 4.65% to 12.39%）,and the higher temperature and lower salinity （homogenization temperature is 333 to 406 ℃,salinity is 3.55% to 6.88%）respectively.The fluid of the stage Ⅳ is character-ized by lower temperature and salinity.The gas phase compositions of the fluid inclusion show that ore-forming fluids are CO 2-H 2 O-NaCl system in the two deposits.In the Bairendaba deposit,the temperature and salinity decreased from stagesⅠ to Ⅲand H-O isotopes show that the earlier stage fluid is magmatic and the later stage fluid is meteoric water.In the Weilasituo de-posit,H-O isotopes and fluid composition （CH 4/C2 H 6 varies from 39.271% to 101.438%）,showing that the fluid is magmat-ic.Sulfur isotopes demonstrate that the sulfur is from the deep source in Bairendaba-Weilasituo deposits.It is concluded that metallogenic mechanism of the Bairendaba deposit is the fluid mixing with different origins,metallogenic mechanism of the Weilasituo deposit is cooling and fluid immiscibility.