Metasomatic Rocks

rocks formed as the result of metasomatism. Depending on the mode of occurrence, formation temperature, and stages of the hydrothermal process at which they formed, metasomatic rocks are divided into different groups.

Among the high-temperature products of the early alkaline stage are magnesian and calcareous skarns, which usually form at the contacts of granites and syenites with carbonate rocks. Magnetite, borate, borosilicate, and phlogopite ores are associated with magnesian and calcareous skarns. The formation of greisens (with tin, tungsten, and beryllium mineralization) and secondary quartzites (with copper and molybdenum mineralization) occurs during the acid stage. The products of metasomatism developing near ore veins—beresite, listvenite, and chlorite-carbonate rocks—are from the late alkaline stage and the stage that is transitional to it. In volcanic regions propylites are widely distributed. Fenites form at contacts with intrusive alkaline rock, and albitite and albite-spodumene rocks with rare-earth mineralization develop in association with pegmatites. In eugeosynclinal ophiolitic belts, chlorite-albite, glaucophane, aegirine, and jadeite rocks and spilites form as a result of sodic metasomatism. Serpentinites, steatites, and anthophyllitic and quartz-magnesite rocks develop by replacement of dunites and peridotites.