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

Fluid inclusion and stable isotopes study of Liancheng Cu-Mo polymetallic deposit in Lanping basin,Yunan Province

兰坪盆地贱金属矿床是一套独特的受逆冲推覆构造系统控制的矿床类型,连城Cu-Mo多金属矿床是其重要组成部分。成矿过程包括早、中、晚三个阶段,分别以石英-辉钼矿、石英-多金属硫化物和石英-碳酸盐组合为标志。矿区不同阶段石英中广泛发育流体包裹体,可分为水溶液包裹体(A型)、纯CO2包裹体(C型)、CO2-H2O包裹体(B型)三类。早、中阶段主要发育B型和A型包裹体,均一温度集中在177～346℃,流体盐度介于1%～22%NaCleqv之间,密度介于0.67～1.04g/cm3;晚阶段主要发育A型包裹体,均一温度为121～185℃,流体盐度介于1%～9%NaCleqv之间。发育在早、中阶段的B型和C型流体包裹体气相成分主要为CO2,含有少量的CH4。成矿压力为50～160MPa,成矿深度为5～5.9km。矿区不同阶段矿石氧同位素组成总体变化较小(5.5‰～8.6‰),氢同位素变化较大(-56‰～-109‰),碳同位素组成变化为-3.4‰～-8.1‰,表明成矿流体可能以岩浆源为主,并伴有大气降水的参与。综合对比研究认为,65Ma左右印度-亚洲大陆发生对接碰撞,由此诱发的岩浆热液作用可能导致了连城Cu-Mo多金属矿床形成。温度的降低和流体的不混溶是导致钼等成矿元素沉淀和富集的重要机制。

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.