the metasomatic transformation of the primary minerals of basic and intermediate igneous rocks with the formation in them of chlorite, albite, adularia, actinolite, sericite, pyrite, and zeolites. Propylitization is associated with the action of postmagmatic, sometimes ore-bearing, solutions in the cracks of country rocks in areas of active volcanism.

Three mineral facies of propylitization are distinguished by temperature of formation: high-temperature (actinolite-epi-dote-albite), medium-temperature (epidote-chlorite-albite),

Figure 1

and low-temperature (chlorite-albite-calcite and adularia-zeolite or nonalbite). The processes of propylitization are frequently related to zones of hydrothermal change in rocks that accompany the formation of sulfide ores of Cu, Au, Ag, Zn, Pb, Mo, As, Sb, and Hg. Manifestations of propylitization are an important sign in searching for ore.