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Methodology is described in this paper for investigating biotite reactions in pneumatolyto-hydrothermalsolutions rich in Na,F and Li by using tow buffer systems,NNO and CFG.The results show:(1)Under theexperimental conditions biotite is unstable and different new stable phases will be formed,depending uponthe fugacity of oxygen.Na-rich minerals,such as aegirine and albite,will be produced at low oxygen fugacity.while Li-rich micas are found stable at high oxygen fugacity.This agrees with the field observation thatalbitization occurs in general at a lower position than that of Li-rich micas,suggesting that alkali-metasomatism of biotite may provide the necessary components for subsequent reactions.(2)The stability ofLi-rich micas is dependent on Mg~(2+) concentration in the medium,which in turn is determined by Mg~(2+)content in the starting biotite.Li-rich micas are favored by metasomatism of only those biotites that are poorin Mg~(2+).(3)Unstability of biotite would favor the incorporation of ore-forming elements contained in it asisomorphous impurities into solutions.
Methodology is described in this paper for investigating biotite reactions in pneumatolyto-hydrothermal heatsolutions rich in Na, F and Li by using tow buffer systems, NNO and CFG. The results show: (1) Under the experimental conditions biotite is unstable and different new stable phases will be formed, depending uponthe fugacity of oxygen. Na-rich minerals, such as aegirine and albite, will be produced at low oxygen fugacity. while Li-rich micas are found stable at high oxygen fugacity. this agrees with the field observation thatalbitization occurs in general at a lower position than that of Li-rich micas, suggesting that alkali-metasomatism of biotite may provide the necessary components for subsequent reactions. (2) The stability of Li-rich micas is dependent on Mg ~ (2+) concentration in the medium, which in turn is determined by Mg ~ (2+) content in the starting biotite. Li-rich micas are favored by metasomatism of only those biotites that are poorin Mg ~ (2 +). (3) Unstability of biotite would favor the incorpor ation of ore-forming elements contained in it asisomorphous impurities into solutions.