长江中下游中性－中酸性岩浆岩的母岩浆来源及铜的成矿作用──实验研究

STUDY ON GENESIS OF MAGMA FORMING INTERMEDIATE AND INTERMEDIATE-ACID MAGMATIC ROCKS FROM MIDDLE-LOWER REACHES OF CHANGJIANG RIVER AND COPPER MINERALIZATION

针对长江中下游形成中性和中酸性岩浆岩的岩浆成因和Ｆｅ、Ｃｕ成矿作用问题，完成了一系列壳幔物质混合物、下地壳物质混合物及中性－中酸性岩浆岩在１０００－２０００ＭＰａ和９００－１５５０℃的水不饱和条件下熔融实验研究。实验结果表明，本地区中性和中酸性岩浆岩可能主要由适当比例的壳幔物质混合物熔化而得的岩浆结晶而成。硅酸盐玻璃的电子探针分析数据没有显示出Ｋ与Ｃｕ和Ｆｅ与Ｎａ的相关关系。在含硫体系中，铜在中性－中酸性硅酸盐熔体中的溶解度介于０．０２％－０．２３％之间，但多数铜分析值在０．１％以上（大致相当于初始物中１５％的铜溶解在硅酸盐熔体中）。余下的部分铜则以Ｃｕ、Ｆｅ、Ｓ组成的小球粒形式不均匀地散布在硅酸盐熔体中。实验结果还表明，中性－中酸性硅酸盐熔体的不混溶性普遍存在。

To counter the genesis of the magma forming intermediate and intermediate-acid magmatic rocks from middle-lower reaches of Changjiang River and Fe, Cu mineralization,a series of melting experiments have been carried out on the mixture of lower crust and upper mantle, mixture of materials of lower crust,and intermediate and intermediate-acid rocks under the conditions of the unsaturated water and at 900-1550°C and 1000-2000MPa. The results show that intermediate and intermediate-acid magmatic rocks possibly crystallized from the magma derived from the melting of the mixture of lower crust and upper mantle with suitable proportion. The data of electron probing analyses for silicate do not show any interrelation between K and Cu as well as Fe and Na. In S-bearing system, the solubilities of Cu in the intermediate and intermediate-acid silicate melts are between 0.02% and 0.23%,but most of the analytical values are above 0.l%, corresponding to a dissolution of about 15% starting material Cu in the silicate melts. The remaining parts of copper are inhomogeneously distributed as small spherulites in the silicate melts. The results also show that the immiscibility of the intermediate and intermediate-acid silicate melts exists widespreadly.