钨、锡流-熔分配实验结果及其矿床成因意义

THE EXPERIMENTAL RESULTS OF W AND Sn PARTITIONING BETWEEN FLUID AND MELT AND THEIR SIGNIFICANCE FOR THE ORIGIN OF W AND Sn ORE DEPOSITS

本文用实验确定了钨、锡在成分不同的花岗质熔体相与共存水热流体相的流-熔分配系数(D_(Me)^(V/L))及其与介质溶液(NaF,KF,HF,NaCl等水溶液)摩尔浓度间的函数关系。实验结果表明,钨、锡的分配行为明显不同。在相同条件下,随体系的不同,D_W^(V/L)比D_(Sn)^(V/L)大几倍至二十倍。钠和钾对钨、锡的流-熔分配行为的影响基本相同,而氟和氯对钨、锡的分配行为的影响相差甚远,花岗质熔体的主成分对D_W^(V/L)和D_(Sn)^(V/L)有复杂的影响。利用这些结果探讨与花岗岩有关的钨、锡矿床的成矿机理,得出了一些与前人不同的新认识。

A series of experiments have been carried out for determining partitioning coefficients of tungsten and tin between various types of hydrothermal fluids and granitic melt (Dwv/L and Dsv/Ln) at 850℃ and 150 MPa. Results of the experiments indicate that the partitioning behaviors of tungsten and tin are different from each other in the same system, at the same conditions and that the values of Dvw/L are several times to twenty times higher than those of DVS/Ln in different systems. DVW/L and DVS/Ln respectively passess the following function relations with the molar concentration of the starting medium solution:ln DSnV/L=0.784 lnmNaF-6.427(0≤mNaF≤1.0);ln DSnV/L=0.7846 lnmKF-6.283(0≤mKF≤2.0);ln DWV/L=1.957 mNaF-3.427(0≤mNaF≤0.5);ln DWV/L=0.62 mNaF-4.70(0.5<mNaF≤1.0);ln DWV/L=-1.732 mKF-3.504(0≤mKF≤0.5);ln DWV/L=1.382 mKF-5.069 (0.5<mKF<2.0); DW/VL = 0.0757 mNaCl + 0.0084 (0≤mNaCl≤4.0); Dwv/l=-0.0103mKF+ 0.0318 (0≤mHF≤2.0);DWV/L = 0.014 mHF-0.0115(2.0≤mHF≤3.0);lnDWV/L=-0.28 -2.405(1.0<mLiF≤3.0mol/kg);DWV/L = 0.0833mNaCl + 0.071(0≤mNaCl≤4.0;for glass D)Na and K affect the fluid-melt partitioning behaviors of tungsten and tin in a similar way. However, F and Cl excert very different influences on the partitioning behaviors of tungsten and tin in the system. The values of DWv/ L and DSNv/l change with the main composition of the graintic melt, and at the same conditions DWv/ L and DSnV/L in the melt-fluid system with relatively high contents of SiO2 and K2O are respectively higher than those in the system with relatively low contents of SiO2 and K2O.Based on the DSnV/L, determined by the experiments, it is concluded that under the conditions of the parameters of granitic magmas F and Cl (especially F) can not make considerable tungsten and tin migrate from granitic magmas to hydro-thermal fluids to form W and Sn ore deposits.