黑钨矿、锡石、铌铁矿、细晶石、铌钽铁矿生成条件及黑钨矿和锡石中钽、铌含量变化的实验研究

CONDITIONS OF FORMATION OF WOLFRAMITE, CASSITERITE,COLUMBITE, MICROLITE AND TAPIOLITE AND EXPERIMENTALSTUDIES ON THE VARIATION OF Nb AND Ta INWOLFRAMITE AND CASSITERITE

Physicochemical conditions of formation for wolframite, cassiterite and columbite and the principal factors which contribute to the Nb^-, Ta^- variation in wolframite and cassiterite were experimentally studied under hydrothermal environments. It has been shown that wolframite, cassiterite, columbite, mierolite, tapiolite can be synthesized under wide ranges of temperature and pressure (300-600℃, 500---2,000 bars). Wolframite and cassiterite can be crystallized under either alkaline or acid conditions. Columbite may be formed in solution with a pH of 2--4, while columbite and microlite crystallize within a pH range of 3-8. In the presence of Ta and Nb, the variation of Ta and Nb in wolframite and cassiterite is found to be controlled largely by solution pH, oxidation-reduction potentials and reaction dynamics.Wolframite crystallizing from acid solution is rich in Ta, while eassiterite in Ta and Nb. On the other hand, Nb, is strongly concentrated in wolframite formed from weakly alkaline selutions, while cassiterite formed under the same condition carries higher content of Ta. Oxidation favors the entry of Ta and Nb into wolframite. Ta and Mb occur as isomorphous impurity or inclusions in wolframite and cassiterite. The maximum content of Ta2O5 in wolframite as isomorphous constituents can be as high as 6.10 percent under the experimental conditions.

Physicochemical conditions of formation for wolframite, cassiterite and columbite and the principal factors which contribute to the Nb-, Ta- variation in wolframite and cassiterite were experimentally studied under hydrothermal environments. It has been shown that wolframite, cassiterite, columbite, microlite, tapiolite can be synthesized under wide ranges of temperature and pressure (300-600℃, 500-2,000 bars). Wolframite and cassiterite can be crystallized under either alkaline ' or acid conditions. Columbite may be formed in solution with a pH of 2-4, while columbite and microlite crystallize within a pH range of 3-8. In the presence of Ta and Nb, the variation of Ta and Nb in wolframite and cassiterite is found to be controlled largely by solution pH, oxidation-reduction potentials and reaction dynamics. Wolframite crystallizing from acid solution is rich in Ta, while cassiterite in Ta and Nb. On the other hand, Nb, is strongly concentrated in wolframite formed from weakly alkaline solutions, while cassiterite formed under the same condition carries higher content of Ta. Oxidation favors the entry of Ta and Nb into wolframite. Ta and Nb occur as isomorphous impurity or inclusions in wolframite and cassiterite. The maximum content of Ta2O5 in wolframite as isomorphous constituents can be as high as 6.10 percent under the experimental conditions.