Contemporary understanding of metasomatic zoning is based on fundamental works by Korzhinskii (1959, 1970), who considered a metasomatic process as a transfer of matter with chemical interaction in natural heterophase systems. Korzhinskii summarized geological data on metasomatic processes and formulated the principle of mosaic or local chemical equilibrium (LCE). In particular, thermodynamic ordering of metasomatic zones follows from the principle of LCE and corresponds to their ordering on equilibrium phase diagrams.
The studies of Korzhinskii have given impetus to a great number of geological, theoretical and experimental investigations in metasomatism. Extensive experimental studies conducted by Zaraisky et al. (1981, 1986) under hydrothermal conditions in a temperature range of 300°–700°C have confirmed the equilibrium metasomatic theory. Some principal results of the experimental investigations are given by Zharikov and Zaraisky (Chapter 9 in this volume).
In the seventies the LCE-theory of metasomatism was further developed by Frantz & Mao (1975, 1976, 1979). They have dealt with a joint system of differential mass transfer equations and algebraic equations corresponding to the law of mass action under conditions of constant porosity and small ratio of component concentration in pore solution to its concentration in solid phases. Solid phases were considered as constant composition minerals. In these works possibilities of inner-zone mineral production and inhomogeneity of mineral composition in a polymineralic zone were discussed.