Аннотация:Mass exchange in hydrothermal systems was analyzed using computer modeling. These systems are characterized by subparallel flows of initially single solutions infiltrating through metamorphic rocks with contrast compositions: graphite and pyrite-bearing black schists and leucocratic carbonless metamorphites. Two areas of such systems have been considered. In the first one mass exchange between one and the same solution (CO2-bearing or chloride) and one of the rocks separately resulted in formation at 150-degrees-C and saturated vapor pressure two different pore solutions - oreless H2S- and CH4-bearing (equilibrated with black schists), and ore-bearing one (contaming up to 10(-5) mol U and 10(-4) mol Pb extracting from the rock) in equilibrium with leucocratic metamorphites. In the second one mixing two of such solutions under favorable conditions (within regional discordance zones or cross breaks interrupted subparallel flow filtration through different geochemical environment) resulted in mineral precipitation with strong ore mineral predominance: nasturane (uraninite) alone or nasturane together with galenite. The systems considered look like natural ones and their analogs are probably responsible for uranium deposits formation.