右江盆地微细浸染型金矿成矿流体特征与来源

THE CHARACTERISTIC AND ORIGIN OF ORE-FORMING FLIUD FROM MICRO-DISSEMINATED GOLD DEPOSITS IN YOUJIANG BASIN

右江盆地金矿床原生包裹体中液体包裹体占包裹体总数的90%以上,包裹体的均一温度和盐度均较低,化学组成富Na+低K+、富Cl-低F-,2<Na+/K+<10,1.5<Na+/(Ca2++Mg2+)<4,不具有岩浆水和热卤水的特点。氢氧同位素组成表现为氢同位素变化不大,氧同位素变化范围大,但在δD-δ18O图解上具有大致沿华南中生代大气降水δD=-70‰的直线上下分布的规律。流体包裹体中36Ar属大气成因,Sr同位素具有壳源的特点。上述证据表明,右江盆地微细浸染型金矿成矿流体中的水主要来源于大气降水。并指出大气降水在金矿成矿过程中不是矿区范围内的直线下渗,而是作盆地规模的由南向北的渗流。

Fluid inclusions from micro-disseminated gold deposits in Youjiang basin area are mainly liquid inclusions which are more than 90% in all inclusions in quantity. The physical and chemical features of the inclusions are as follow: low homogenization temperature, low salinity, high Na^+, low K^+, high Cl^- , low F^-, and 2<Na^+/K^+<10,1.5<Na^+/(Ca^(2+)+Mg^(2+))<4 which are not character of magmatic fluid and hot brine. Hydrogen isotope of samples vary in little range, whereas Oxygen isotopes vary in large range. On the figure of δD-δ^(18)O, the data distribute approximately along the line δD = -70‰ which represents evolving line of Mesozoic meteoric water in Southchina. In fluid inclusions,^(36)Ar came from atmosphere and Sr derived from crust. An above evidence indicates that the water in ore-forming fluids is mainly from meteoric water. In the process of mineralization of gold, meteoric water didn't infiltrate downward vertically in ore district, but infiltrated from south to north on basin scale.