Fluid inclusion and stable isotopes study of Liancheng Cu-Mo polymetallic deposit in Lanping basin, Yunan Province
兰坪盆地连城Cu-Mo多金属矿床流体包裹体和稳定同位素地球化学研究

The sediments-hosted base metal deposits controlled by Cenozoic thrust-nappe structural system in Lanping basin,Southwest China,apparently differ from the sediments-hosted base metal deposits in other parts of the world.The Liancheng Cu-Mo polymetallic deposit is one of these deposits in Lanping basin.The ore-forming process can be divided into early,middle and late stages,which is characterized by quartz-molybdenites veins,quartz-sulfides veins and carbonates veins,respectively.Three types of fluid inclusions are distinguished including aqueous water(A-type) inclusions,CO2-H2O(B-type) inclusions and pure CO2(C-type) inclusions.The homogenization temperatures of the primary A-type and B-type fluid inclusions in the early and middle-stage quartz range from 177 to 346℃,with salinities ranging from 1% to 22% NaCl equivalent.Gases in fluid inclusions are CO2 and small quantities of CH4.The late-stage quartz veins contain only aqueous fluid inclusions with homogenization temperatures between 121 and 185℃,and salinities ranging from 1% to 9% NaCl equivalent.The trapping pressure is up to 50 ～ 160Mpa,corresponding to the depth of 5 ～ 5.9km.The δ13 C values obtained from fluid inclusions in calcite and quartz range from-3.4‰ to-8.1‰.The Liancheng deposit yield δ18 O values of 5.5‰ to 8.6‰ and corresponding δD values of-56‰ to-109‰,suggesting that the mineralizing fluids originated mainly from magmatic water and accompanied participation of meteoric water.It was concluded from synthetical analyses that the buried magma hydrothermalism in the area induced by the Indo-Asian collision at about 65Ma might eventually led to the formation of the Liancheng Cu-Mo polymetallic deposit.Temperature decrease and fluid immiscibility are the important mechanism for deposition and enrichment of molybdenum and other mineralizing elements.