内蒙古西拉沐伦成矿带碾子沟钼矿床成矿流体地球化学特征  

Ore-forming fluid geochemistry of Nianzigou molybdenum deposit in Xilamulun molybdenum metallogenic belt,Inner Mongolia

作　　者：张作伦[1,2] 刘建明[1] 段晓侠[1,2] 陈伟军[1,2] 

机构地区：[1]中国科学院地质与地球物理研究所中国科学院矿产资源研究重点实验室,北京100029 [2]中国科学院研究生院,北京100049

出　　处：《岩石学报》2010年第5期1375-1385,共11页Acta Petrologica Sinica

基　　金：国家自然科学基金面上项目(40972065);国家重点基础研究项目(2006CB403507)联合资助

摘　　要：碾子沟钼矿床是内蒙古西拉沐伦钼多金属成矿带中石英脉型钼矿床的典型代表,矿体以石英大脉形式产于燕山期中粗粒黑云母二长花岗岩内,受断裂构造控制。流体包裹体研究发现包裹体均为气液两相,按照相比不同,可进一步分为WL型(5%～20%)和WV型(20%～50%)。Ⅰ阶段流体为低温(89.3～245.2℃)、中低盐度(2.07%～17.96%NaCleqv)流体;Ⅱ阶段流体具有中低温(134.4～458.8℃,峰值170℃～240℃)、中低盐度(0.53%～19.92%NaCleqv)特征;Ⅲ阶段流体为低温(134.9～202.4℃)、中低盐度(4.96%～14.97%NaCleqv)流体。流体成分均以H2O为主(>96.1mol%),含少量挥发份CO2、N2、CH4、C2H6、Ar、H2S,阳离子以Na+为主,阴离子以SO42-、Cl-为主,属NaCl-H2O体系。各阶段成矿热液氢、氧同位素特征为:δ18OH2O介于-5.75‰～-1.90‰、δD介于-128.821‰～-109.234‰,说明成矿流体是岩浆热液与古大气降水混合而成。开放的断裂体系为流体混合创造了条件,流体的混合作用是造成碾子沟辉钼矿沉淀成矿的主要原因。这与斑岩型钼矿床的高盐度流体以及以沸腾为主的矿石沉淀机制具有显著区别。Nianzigou Mo deposit is a typical quartz vein deposit in Xilamulun molybdenum metallogenic belt,Inner Mongolia.Its major molybdenite ore bodies are controlled by fault structures within the Yanshanian medium-coarse biotite monzogranite.Fluid inclusion studies show that WL(5% ～ 20%) type and WV(20% ～ 50%) type liquid-vapor inclusions are hosted in vein quartz.Fluid of the early stage is characterized by low temperature(89.3 ～ 245.2℃),middle-low salinities(2.07% ～ 17.96% NaCleqv).The ore-forming fluid in the main mineralization stage is characterized by epithermal(134.4 ～ 458.8℃,most values in the range of 170 ～ 240℃),middle-low salinities(0.53% ～ 19.92% NaCleqv).The late mineralization fluid is characterized by low temperature(134.9 ～ 202.4℃),middle-low salinities(4.96% ～ 14.97% NaCleqv).The molecule composition includes H2O(> 96.1 mol%),CO2,N2,CH4,C2H6,Ar,H2S,and the ion composition are mainly Na +,SO42-,Cl-.These indicate the ore-forming fluids have the composition of NaCl-H2O system.Hydrogen and oxygen isotopes of fluid inclusions in various mineralization stages are-128.821‰ ～-109.234‰ and-5.75‰ ～-1.90‰,and these indicate that the solutions were originated from magmatic water and meteoric water.Open fracture system created conditions for fluid mixing which caused the deposition of Mo.These characters are different from the high salinity porphyry deposit,and the mechanism for ore-metals precipitation is fluid-boiling in porphyry deposit.

关 键 词：钼矿床 流体包裹体 氢、氧同位素 碾子沟 西拉沐伦 

分 类 号：P618.65[天文地球—矿床学]