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This study of the formational nature ot melaso matites from the zones of acid leaching in the Western Srednogorie is based on an integral zonal metasomatic column and on composition-paragenesis diagrams of each zone constructed to follow out the thermodynamic behaviour of components and the reactions between mineralpar ageneses at the zone boundaries. The propylite type of rocks forming aureoles around proper secondary quartzites is not a separate formational unit but belongs to the outermost zone of the secondary quartzite formation. The physico-chemical analysis of mineral parageneses in the propylite type of rocks shows the equilibria between actinolite, epidote, chlorite, sericite, calcite and magnesite as dependent on temperature and potassium oxide chemical potential. Epidote-chlorite, actinolite-epidote-chlorite and epidote-actinolite parageneses are distinguished as a function of temperature. The physico-chemical analysis of mineral parageneses in the rocks of inner zones gives the equilibria between quartz, kaolinite, alunite, illite and pyrophyllite as dependent on two of the intensive parameters, namely the chemical potentials of K+, SO42- and H2O, and pH of the mineral-forming environment.

It is carried out ore parageneses digital study of the iron and copper sulphides and oxides and native copper in the Fe-Cu-S-O system, open for the sulphur and oxygen at T = 400"C and P = I kbar. The system includes 10 minerals: pyrrhotite (Po), pyrite (Py), magnetite (Mt), hematite (Hem), chalcopyrite (Ccp), bornite (Bn), native copper (Cop), chalcocite (Cc), covellite (Cv) and cuprite (Cup). For the calculations is used Shvarov's (1992) database for the thermodynamical properties of the minerals and the sulphur and oxygen fugacities. Paragenetic incompatible are the minerals: Po - Hem, Po - Ce, Po - Cv, Po - Cup, Py - Cop, Py - Cup, Py - Cc, Mt - Cv, Mt - Cup, Cop - Bn, Cop - Ccp, Cop - Cv, Cup - Bn, Cup - Ccp, Cup - Cv, Cv - Ccp H Cc - Ccp. The simultaneous occur of some of these minerals indicates metastable state of the system. It is estimated the values of the sulphur and oxygen fugacity in the gas phase, that is in the equilibrium with the association of the ore mineral parageneses at T = 400ºC and P = I kbar. These values enable to draw monovariant lines, setting landmarks between the fields of the different ore mineral parageneses stability and chemical transform reactions. The results of the calculations are presented on the plot with coordinates IgfS2 - IgfO2.

The study of mineral equilibria in the K2O-Al2O3-SiO2-H2O-SO3 system permits to propose thermodynamic basis for distinguishing the acid-sulphate and adularia-sericite alteration types of volcanic rokcs and frequently associated subvolcanic intrusive rocks in the epithermal deposits. The fields of the acid-sulphate and adularia-sericite types of alteration are divided by the fields of the advanced argillic alteration without sulphatebearing minerals and the sericitiztion in the prognostic paragenetic diagram of the mineral equilibria in the system studied. This study presents theoritical arguments for the existence of the two end paragenetic incompatible types of wall rock alteration in epithermal deposits. The advanced argillc alteration of the rocks is subdivided of the acid-sulphate and acid-chlorine types of alteration. The mineralogical synonyms of the acide-sulphate type are kaolinite-alunite and alunite alteration types and of the acid-chlorine type are kaolinite, pyrophyllite and dickite-pyrophyllite types wallrock alteration. The study of the system is basis for genetic interpretations of the advanced argillic, sericitic, greisen, K-silicate and adularia-sericite alteration.