THE EFFECT OF PRESSURE ON MINERAL SOLUBIL ITY IN AQUEOUS CHLORIDE SOLUTIONS UNDER SUPERCRITICAL CONDITIONS

In the context of the investigation of fluid phases as an environment for ore (mineral) material mobilization and transport, the solubilitie s of fluorite and scheelite were studied by the monocrystal weight-los s technique. Solubility in a 2 M NaCl solution was measured at 600 deg rees C and at 0.5, 0.7, 1.0, 1.5, and 2.0 kbar. A maximum solubility o f 3 S CaF2/kg H2O and 2.9 g CaWO4/kg H2O was reached at 0.5-0.7 kbar. The solubility decreases approximately by an order of magnitude as the pressure is increased to 1 kbar, and only slightly increases at 1.5 a nd 2.0 kbar. This kind of relationship is caused by the NaCl-H2O fluid heterogenization at a pressure less than 1 kbar with the formation of a concentrated phase that has a high capacity for dissolving minerals . The results of an independent calculation of solubility in the heter ogeneous system carried out by the lever rule are in good agreement wi th the experiment. The observed relatively small effect of pressure on mineral solubility in homogenous fluid indirectly supports our previo us proposal that charge-free particles of complex composition are prod uced by fluorite and scheelite dissolution. As opposed to the generall y accepted concept, the results obtained show that a decrease in press ure does not always stimulate ore (mineral) deposition. On the contrar y, the heterogenization of natural fluid solutions, induced by a press ure drop or by gaseous components, may occasionally serve as an additi onal agent of ore (mineral) mobilization and ore stabilization in solu tions.