风化壳稀土成矿作用——一种不平衡过程

RARE EARTH MINERALIZATION IN WEATHERING CRUST——A NONEQUILIBRIUM PROCESS

华南风化壳离子吸附型稀土矿床的形成取决于风化壳渐进发育过程中REE自上而下的淋滤作用。实验测定REE在粘土与介质溶液之间的分配系数(Kd)变化于1.9—24.1ml/g,与天然环境获得的实际值(10~4-10~5)相差悬殊。对交换反应动力学方程的线性稳定性分析可以证明其热力学定态解是不稳定的,从而表明REE的成矿作用是一种不平衡过程。

The downward leaching process of REE is responsible for ion-adsorbed type rare earth mineralization during the gradual development of weathering crust in South China. The experimental results show that cation exchange capacities(CEC) of clays are not the control of the process; instead, the strong dependence between adsorption and pH values is a key factor. The measured distribution coefficients(Kd) of REE between clays and solutions, ranging from 1.9 to 24.1ml/g, are significantly lower than those(10~4-10~5) obtained from the natural environment. The stability analysis for kinetic equations of exchange reaction after linearization proves that its thermodynamical steady-state solution is not stable. It can therefore be concluded that the REE metallogenesis is caused by a nonequilibrium process.