Ore-forming fluid and evolution of Luming molybdenum deposit,Heilongjiang Province

The Luming molybdenum deposit,located in the Lesser Xing'an Range-Zhangguangcai Range polymetallic ore-forming belt,is mainly hosted in monzogranite. According to mineral assemblages,alteration and crosscutting relationships of the veins,the mineralizing stages of the Luming molybdenum deposit can be divided into three: 1) potassium silicification disseminated mineralization stage; 2) silicified stockwork mineralization stage; 3) chlorite-carbonate stage. Aqueous,gaseous,CH4( CO2)-bearing and daughter mineral-bearing inclusions coexist in molybdenite quartz veins of Luming molybdenum deposit. The homogenization temperatures of aqueous inclusions are from 133 to 425℃,salinities of 1. 6% ~ 16. 1% Na Cleqv. Gaseous inclusions with homogenization temperatures of 243 ~ 500℃,salinities of 1. 2% ~ 14. 1% Na Cleqv. Daughter mineral-bearing inclusions with homogenization temperatures of 297 ~449℃,salinities of 38. 2% ~ 53. 1% Na Cleqv. CH4( CO2)-bearing fluid inclusions by laser Raman spectroscopic analysis confirmed that the components of bubble phase are dominated by CH4,a few containing a small amount of CO2,with homogenization temperatures of 334 to 437℃. δ34S range of 4. 5‰ ~ 5. 7‰,shows the sulfur comes mainly from magmatic hydrothermal ore-forming fluid. The hydrogen and oxygen isotope data fall near the magmatic water and drift to the meteoric water in the δD-δ18OH2Odiagram,indicating that ore-forming fluids in main mineralizing stages were magmatic water and mixed with a small amount of meteoric water. The trapping pressures of fluid inclusions are estimated to be 30 ~ 90 MPa,and consequently corresponding to a depth of 3 to 9km. The ore-forming fluid was initially a single H2O-Na Cl-CH4( CO2) supercritical fluid system with high temperature and medium salinity separated from the magma chamber. The ore-forming fluid boiling happened and multiple types of fluid inclusions captured due to reduced pressure and mixed with different fluids. With the continuous evolution of the fluid and the ore-forming temperature gradually reduced,the metallic minerals constantly precipitate and mineralization. From fluid inclusion study on the Luming molybdenum deposit,the ore-forming fluid may not originate from a single magmatic differentiation,but large-scale mixed fluids as well. The complex tectonic backgrounds also control the molybdenum mineralization.