胶东胡八庄金矿成矿流体、稳定同位素及成矿时代研究

Ore-forming fluids,stable isotope and mineralizing age of the Hubazhuang gold deposit,Jiaodong Peninsula of eastern China

胡八庄金矿是胶东牟平-乳山金成矿带内典型的黄铁矿、多金属硫化物-石英脉型金矿,金主要产出于黄铁矿和多金属硫化物石英脉中。流体包裹体研究表明,不同蚀变带岩石和各成矿阶段金矿石中的流体包裹体主要有三种类型:富CO2包裹体、CO2-H2O包裹体和H2O溶液包裹体。成矿早期(第Ⅰ阶段)主要为富CO2包裹体,主成矿期(第Ⅱ阶段)CO2-H2O包裹体和H2O溶液包裹体,成矿后期(第Ⅲ阶段)H2O溶液包裹体。包裹体显微测温结果表明,成矿早期(第Ⅰ阶段)包裹体均一温度范围为260～360℃,盐度1.0%～7.4%NaCleqv;主成矿期(第Ⅱ阶段)包裹体均一温度范围为180～269℃,盐度1.7%～13.1%NaCleqv;成矿后期(第Ⅲ阶段)包裹体均一温度范围为104～189℃,盐度0.9%～8.8%NaCleqv。成矿早期为中-高温、富含挥发份、低盐度的流体,到主成矿期演化为中低温、含少量挥发份、盐度变化范围大的CO2-H2O-NaCl流体体系,成矿后期流体的温度、盐度和挥发份含量均降低。对各成矿阶段石英的H-O同位素研究表明,胡八庄金矿成矿早期既有岩浆水又有大气降水参与,大气降水较少地参与了成矿,到了主成矿期成矿流体为以大气降水为主的混合流体。成矿阶段S同位素研究表明胡八庄金矿成矿物质可能主要来源于大气降水循环淋滤的围岩。温度降低和流体不混溶可能是胡八庄金矿金沉淀的主要原因。蚀变岩石中绢云母Rb-Sr等时线获得的胡八庄金矿的成矿时代为126.5±5.6Ma。

Hubazhuang gold deposit is a typical pyrite-and polymetallic sulfide-quartz lode deposit in the Muping-Rushan gold belt of Jiaodong Peninsula and gold occurs mainly in pyrite-and polymetallic sulfide-quartz vein.Fluid inclusion studies show that in the different altered wall rocks and gold ores of different mineralization stages there are three major types of fluid inclusions：CO2-rich fluid inclusions,CO2-H2O fluid inclusions and aqueous fluid inclusions.CO2-rich fluid inclusions occur mainly in the early mineralizing stage（stage Ⅰ）;the main mineralizing stage（stage Ⅱ）contains CO2-H2O fluid inclusions and aqueous fluid inclusions;there are only the aqueous fluid inclusions in the late mineralizing stage（stage Ⅲ）.Microthermometric study shows that in stage Ⅰ the homogenization temperatures and salinities range respectively from 260℃ to 360℃ and 1.0% to 7.4% NaCleqv,and stage Ⅱ the range is 180℃ to 269℃ and 1.7 to 13.1% NaCleqv,then stage Ⅲ is 104℃ to 189℃ and 0.9% to 8.8% NaCleqv.The fluids in stage Ⅰ were medium-high temperature,volatile-rich and low salinity fluid system.During stage Ⅱ the fluids evolved to a CO2-H2O-NaCl fluid system with medium-low temperature,low volatile and wide range of salinity.Finally in stage Ⅲ the temperature,salinity and volatile content all decreased.The study of hydrogen and oxygen stable isotope indicates that in stage Ⅰ the mineralizing fluids were mainly magmatic water,but during stage Ⅱ the mineralizing fluids were mixed fluids which originated mainly from meteoric water.Sulfur isotope of the main mineralizing stage reveals that ore-forming materials may mainly come from the wall rocks which were leached by the meteoric water.Temperature decline and fluid immiscibility are the main reason of the gold precipitation.Rb-Sr isochron of sericite in altered rocks shows that the mineralizing age of Hubazhuang gold deposit is 126.5±5.6Ma.