100MPa、800℃下磷对铌锰矿和钽锰矿在简单花岗质熔体中溶解度影响的实验研究

Influence of phosphorus on the solubility of manganocolumbite (MnNb_2O_6) and manganotantalite (MnTa_2O_6) in haplogranite melts-An experimental study

选取人工合成的简单花岗岩玻璃以及铌锰矿和钽锰矿晶质矿物作为实验初始物,实验研究了100MPa、800℃条件下铌锰矿和钽锰矿在水饱和(或近水饱和)的无磷和含磷简单花岗质熔体中的溶解度。实验结果显示,在过碱质熔体中铌锰矿和钽锰矿的溶解度远高于它们在准铝质和过铝质熔体中的溶解度,但两者之间的溶解度相差不大;在准铝质和过铝质熔体中,铌锰矿的溶解度要明显低于钽锰矿。在过碱质熔体中,铌锰矿、钽锰矿的溶解度与体系中P2O5的含量存在负的线性相关性,即lgKspNb=-0.29×P2O5-2.05(R2=0.96)和1gKspTa=-0.29×P2O5-1.79(R22=0.98);在准铝质熔体中,铌锰矿、钽锰矿的溶解度则随体系中P2O5含量的增大呈逐渐升高趋势;在过铝质熔体中,铌锰矿、钽锰矿的溶解度随体系中P205的含量增大,先表现为降低的趋势,但是当P2O5的含量大于约3%时铌锰矿、钽锰矿的溶解度在误差范围内随P205含量的升高基本保持恒定。上述实验结果产生的主要原因很可能与铌、钽在硅酸盐熔体中的溶解机制以及磷在不同化学组成的硅酸盐熔体中不同的结构作用有关。

Solubility experiments of manganocolumbite （MnNb2O6） and manganotantalite （MnTa206） in the haplogranite-P2O5 system were conducted under H/O-saturated condition at 800 ℃ and 100 MPa. The results show： 1） solubilities of MnNb206 and MnTa2O6 in peralkaline melts are significantly higher than those in subaluminous and peraluminous melts, furthermore, solubilities of MnNbzO6 and MnTazO6 are almost identical in hydrous peralkaline melt, but solubilities of MnNbzO6 are much less than those of MnTa206 in H20-saturated subaluminous and peraluminous melts; 2~solubilities of MnNb206 and MnTa206 in peralkaline melts are functions of P205 content, which is given as： lgKsp= -0.29~P205-2.05 （RZ=0.96） and lgKsp= -0.29~P205-1.79 （R2=0.98）, that is, solubilities of MnNb206 and MnTa206 decrease with increasing PzO5 contents. For subaluminous melt, solubilities of MnNb206 and MnTa2O6 increase with increasing P2Os contents As P2O5 contents increases in peraluminous system, solubilities of MnNb206 and MnTa2O6 decrease at first in relatively low P205 system （〈3 wt% P205）, and then keep constantly in relatively high P2O5 system （〉3 wt% P205）. The main causes of the above experiment results may be related to the mechanism of Nb, and Ta dissolved in the granitic melt and phosphorus show different structural effect in different chemical composition of silicate melts.