EXCESS FREE-ENERGIES OF MIXING OF SR,BA-BEARING BINARY FELDSPAR SOLID-SOLUTIONS (EXPERIMENTAL-DATA)

The distribution of potassium and strontium, potassium and barium betw een feldspars and aqueous chloride solutions was studied at 700 degree s C, 2 kbar and 800 degrees C, 2 kbar respectively. The distribution o f Sr and Ba between coexisting feldspar and chloride solutions is not ideal; Sr and Ba are enriched in feldspar relative to solution. In ord er to estimate the phase state of the chloride solutions, special expe riments were conducted using the synthetic fluid-inclusion method in t he systems KCl-BaCl2-H2O and KCl-SrCl2-H2O at 700-800 degrees C, 2 kba r. It was shown that (0.5M KCl+0.5M SrCl2) aqueous solution is homogen eous at 800 degrees C, 2 kbar. The 0.25-0.5M SrCl2 solutions are homog eneous at 700 degrees C, 2 kbar. The (0.5M KCl+0.5M BaCl2) solution is homogeneous at 700 degrees C, 2 kbar and heterogeneous at 800 degrees C, 2 kbar. Margules parameters for describing the excess energy of mi xing of the (K,Sr)- and (K,Ba)-feldspar solid solutions were calculate d. The integrated values of excess energy of mixing (G(int)(ex)) were estimated for the different binary feldspar solid solutions, and a cor relation of G(int)(ex) with the crystallochemical parameter rho = (R(A )-R(B))/D(Me-O) was observed. Feldspar solid solutions can be subdivid ed into three groups based on the relationship between G(int)(ex), rho and the stability of the solid solution.