EXPERIMENTAL AND MATHEMATICAL-MODELING OF GREISENISATION IN A SYSTEM GRANITE-SNO2-H2O-HF-NAF

Experimental and mathematical modeling of the interaction of fluorineb earing aqueous fluid with granite in a system: granite + SnO2 + HF + H 2O at H2-fugacity of Ni - NiO buffer at 500-degrees-C and 1 kbar is ca rried out. Tin concentration in the aqueous fluid is determined by flu orine content and pH value of the equilibrium aqueous phase. The value of Sn concentration is just suitable (2 . 10(-3) - 4 . 10(-2) m) for the mobilisation of Sn by acidic fluorinebearing solutions (specifical ly in the systems with low rock/water ratio much-less-than0.1) and its deposition at successive migration of aqueous fluid to the zone where the fluid acquires the low alkaline pH values (specifically the migra tion is directed to the field of enhanced rock/water ratio). The equil ibrium composition of the aqueous fluid is varying not so significantl y: SIGMAK = (1 - 4.5) . . 10(-2); SIGMANa = (0.4 - 1.6) . 10(-1); SIGM ASi = 4.5 . 10(-2); SIGMAAl = (0.25 - 1.9) . 10(-1). The total fluorin e concentrations practically are equal to the initial values. It is sh own that the equilibrium quantitative ratios of greizen typomorphic mi nerals [(quartz + microcline + albite + biotite + + (topaz)] depend on the pH value of the initial fluids and water/rock ratio. Along with t he increase of aqueous fluid acidity the quartz fraction is increasing while that of albite is decreasing. The interaction with alkaline sol utions leads to the decrease of the topaz and biotite up to complete e limination of these minerals. The presence of topazbearing assemblage is concerned as a reason and indicator of cassiterite preferential dep osition.