Study On The Fluid Inclusions From Nuri Cu-W-Mo Deposit In Tibet

Nuri Cu-W-Mo deposit located in the north rim of Yarlung Zangbo suture zone and the east section of yanshan-Himalayan epicontinental magmatic arc is a typical skarn deposit.The deposit occurred in contact belt within late Cretaceous diorite,Eocene granodiorite and the formation of Bi Ma group went through two periods of skarn activity at least,which is dominated by formation,magmatite and structure.Joints and fissures formed by uplifting provide a good ore-hosted place.The fluid petrographic study of garnet,quartz and calcite formed in multiperiodic hydrothermal activities shows that inclusion are mainly consist of gas-liquid inclusions??-type?and containing mineral polyphase inclusions??-type?.The homogenization temperature is 163.0?⁵64?,and with the salinity range of 3.1⁵2.8 wt%.The hydrothermal temperature in skarn stage of garnet is 560?⁵64?,and with the salinity range of 49.7⁵5.8 wt%.The hydrothermal temperature during the period of magnetite and quartz is 340.1?³40.1?,and with the salinity range of 7.1⁷.5 wt%.The hydrothermal temperature in the stage of Quartz and sulfide is 217.7?³10.6?,and with salinity range of 3.1⁸.0 wt%;The hydrothermal temperature in the stage calcite is 166.9?¹76.4?,and with salinity of 6.88 wt%.Hydrothermal experienced a complex evolutionary process from the high temperature and high salinity of fluid in garnet period to low temperature and low salinity in calcite period,which is the result of hydrothermal overlapping reconstruction.The result estimated by empirical formula shows that Nuri Cu-W-Mo deposit formed in shallow environment with the pressure of 52.5 Mpa and depth of 1.9 km.The gas compositions of are mainly CO₂,CH₄ and H₂O.And the liquid composition is H₂O.The hydrothermal gas composition in Garnet skarn stage is mainly composed of CO₂ and H₂O.The hydrothermal gas composition during the period of magnetite and quartz is composed of CH₄,CO₂ and H₂O.The hydrothermal gas composition in Quartz and hydrothermal sulfide phase is composed of CH₄ and H₂O.And a small amount is given priority to with CO₂ and H₂O vapor,but CH₄ and CO₂ are none.The hydrothermal gas composition in calcite stage is composed of H₂Owith no CH₄ nor CO₂.This phenomenon shows that CO₂ escape a lot after the formation of magnetite which is advantageous to the sulfide precipitation with the decrease of oxygen fugacity and increase of sulfur fugacity.With the pressure and temperature reduced,CH₄ and CO₂ gas escape in the calcite hydrothermal period.The overlap within homogenization temperature,salinity and composition of fluid inclusions formed in multiperiodic hydrothermal activities shows that the earlier temperature and salinity of fluid inclusions affected by the later hydrothermal activities.