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

Mei Wei; LXinbiao; Tang Rankun; Wang Xiangdong; Zhao Yan

doi:10.3799/dqkx.2015.010

Abstract：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.