钾交代的热力学计算及其与铀成矿关系讨论

结合薄片镜下鉴定特征,探讨不同温度及埋深条件下斜长石钾长石化、黑云母绿泥石化以及[UO2（CO3）3]4-还原成沥青铀矿的ΔrG变化及其相互关系。结果表明：钾长石交代斜长石在无深部热流体作用的情况下不能进行;黑云母绿泥石化具有最低的ΔrG,且随埋深的加大ΔrG表现出先降低后增加直至为正值,表明该反应在相对低温条件下更容易进行;[UO2（CO3）3]4-在碱性环境下被磁铁矿还原时的ΔrG始终为负值,说明其可以在任何温度压力条件下进行;在无外来钾源流体作用下,黑云母绿泥石化可以为钾交代提供稳定的钾源,当两者反应交集温度越宽,则该深度越有利于钾交代的进行,并且钾交代主要发生在埋深2500 m以上;在钾交代区域内出现代表酸性流体的特征矿物,则表明沥青铀矿富集程度愈高。

Thermodynamic calculation of feldsparzation and its relationship with uranium mineralization

Combined with the microscope characteristic of thin section,This paper discussed the variety of ΔrG and its interrelation with temperatures and burried depth for the feldsparzation of plagioclase,chloritization of biotite and reduction of [UO2（CO3）3]4-.The result indicates that the feldsparzation of plagioclase can not be proceed without the presence of deep hydrothermal fluid.The reaction of chloritization of biotite owns the least ΔrG value,it falls at the firstly and then increases subsequently to positive value which suggest that the reaction can proceed easily under lower temperature.The ΔrG value for the reduction of [UO2（CO3）3]4-is negative in condition with alkaline and magnetite which shows that the reaction can proceed with any temperatures and pressures.The chloritization of biotite can provide potassium steadily in case of no external potassium source.The wider the intersectional temperature area of two reacitonis,the easier for feldsparzation of plagioclase in that deepness.And the feldsparzation of plagioclase takes place mostly beneth 2500 m depth.The appearance of typical mineral for acid fluid will indicate the rich uraninite in the area of potash metasomatism.