海南土外山金矿床流体包裹体特征及其地质意义

Characteristics of Fluid Inclusion in the Tuwaishan Gold Deposit,Hainan Province and Their Geological Significances

土外山金矿位于海南西部戈枕含金剪切带的北东端,属于破碎蚀变岩型金矿,矿体主要分布在剪切带下盘的混合岩中。流体包裹体的研究表明,该矿床的原生包裹体主要以气液包裹体为主,含CO2包裹体较少,成矿流体属于NaCl-H2O型热液体系;早、中、晚三个成矿阶段的均一温度范围分别为240～320℃,210～260℃,180～240℃,盐度分别范围为8%～10%,4%～8%,3%～8%,具有中低温、低盐度特点。氢氧同位素测试表明成矿流体主要是岩浆水、大气降水的混合。成矿流体在演化过程中不断有大气降水的加入,导致成矿温度和盐度呈规律下降。

The Tuwaishan gold deposit is located in the North-East part of the Gezhen auriferous shear zone in western Hainan province. It belongs to fragmentary altered rock gold deposit. The ore bodies occur mainly in migmatite in the hanging wall of shear zone. The study of fluid inclusion shows that quartz contains a great deal of primary fluid inclusions, i. e. , pure aqueous phase inclusion（Ⅰ）, aqueous two-phase inclusion （Ⅱ）, CO2-bearing three phase inclusion（ Ⅲ ） and pure CO2 inclusion（Ⅳ） , with more than 70 % of the fluid inclusion belonging to type（Ⅱ）. The ore-forming fluid belongs to NaCl- H2O type charactered by lowmoderate temperature, low salinity and low density. The homogenization temperature of the three mineralization stages are240-320℃, 210-260℃, 180-240℃; the salinity are 8%-10%, 4%-8%, 3%-8%, respectively, suggesting characteristics of low-meso temperatures and low salinity. The study of hydrogen and oxygen isotopic shows that the ore-forming fluid of Tuwaishan gold deposit were mainly derived from magmatic water and mixed with meteoric water. The increasing involvement of meteoric water resulted in falling of ore-forming temperature and salinity gradually.