热液体系中Si的络合作用

COMPLEXATION OF SiO_2 IN HYDROTHERMAL SYSTEMS

在不同温度、p H和硅浓度条件下 ,实验标定了 Au- Si O2 以及 Sn- Si O2 之间的络合反应 :Au+ +H3 Si O-4 =Au H3 Si O4 lg K=- 1.6 5436 +96 11.2 1/TSn4 + +4H3 Si O-4 =Sn(H3 Si O4 ) 4 lg K2 0 0℃ =4 2 .73通过与 Au- Cl、Au- HS以及 Sn- OH络合物迁移能力的比较 ,表明在具地质意义的 p H和 Eh条件下 ,Au H3 Si O4 和 Sn(H3 Si O4 ) 4络合物可成为含硅热液中 Au、Sn的主要迁移形式。热液中硅浓度和氧逸度的降低导致溶解反应逆向进行 ,析出 Au和 Si O2 以及 Sn O2 与 Si O2 的沉淀。研究阐明了热液中 Si的络合作用对 Au、Sn等金属成矿具有普遍的重要意义。

The Au SiO 2 and Sn SiO 2 complexes have been experimentally calibrated at varying temperature, silica concentration and pH values: Au ++H 3SiO - 4=AuH 3SiO 4 lg K =-1.654 36+9 611.21/ T Sn 4+ +4H 3SiO - 4=Sn(H 3SiO 4) 4 lg K 200℃ =42.73 Compared with Au Cl, Au HS and Sn OH complexes, AuH 3SiO 4 and Sn(H 3SiO 4) 4 complexes can be recognized as the dominant transport forms in Si bearing solutions under pH and Eh conditions of geological interest. The decrease of SiO 2 concentration and oxygen fugacity would reverse the direction of dissolution complexing reactions, resulting in the precipitation of gold and silica, as well as cassiterite and silica. This study illustrated the significance of SiO 2 complexation in hydrothermal solutions for gold, tin and other metallization.