COMPARATIVE ANALYSIS OF TECHNIQUES USED IN THE EQUILIBRIUM-DYNAMIC SIMULATIONS OF INFILTRATION METASOMATIC ZONING

Abstract

Thermodynamic simulation techniques of infiltration-controlled metasomatic columns based on the local equilibrium principle are analyzed. The validity criteria of the results were corollaries from D.S. Korzhinskii's theory of metasomatic zoning. For a situation with phases of constant compositions, these corollaries are formulated as follows: (1) the column is formed instantaneously in its final and complete form and can only grow with time; (2) individual zones grow linearly with time; (3) the concentrations of minerals do not vary across the zones; and (4) the solution composition varies discontinuously at zone boundaries and remains unchanging within zones. It is demonstrated that the reaction progress technique (Helgeson, 1968) does not allow the fulfillment of any of these corollaries, because it is applicable only to systems closed with respect to the solution and does not provide for a mass transfer. The results of calculations in compliance with this technique pertain net to an infiltration column but to associations that replace one another with time, for example, in an autoclave. The technique of a system with a flow corresponds to the start-up regime of a flow-through reactor, in which corollaries (1) and (2) cannot be valid in principle. The results of calculations by this technique are inconsistent with corollaries (3) and (4), because both the proportions of minerals and the composition of the solution vary within zones. The method of multiwave flow-through step reactor (MFSR) utilizes the idea to simulate metasomatic processes by passing several portions of solution through an array of cells containing certain rock amounts. This technique makes it possible to reproduce corollary (2) and, roughly, also corollaries (3) and (4) but is not efficient enough when utilized in calculations. The features of infiltration columns described by Korzhinskii can be directly applied to a simulation algorithm, as is done in the proposed boundary-reaction method, which automatically ensures the fulfillment of alt four corollaries from Korzhinskii's theory.