mineral deposits formed in the process of metamorphism under conditions of high pressure and temperature. The deposits are subdivided into metamorphosed and metamorphic deposits.
Metamorphosed deposits form as a result of the processes of regional and local metamorphism of minerals. The bodies of minerals are deformed and acquire features characteristic of metamorphic rocks; they develop schistose and fibrous structures and granoblastic textures. Low-density minerals are replaced by minerals of high volumetric mass. Hydrous minerals are replaced by anhydrous ones, and amorphous matter crystallizes. The largest number of metamorphosed deposits are found in Precambrian formations (for example, the graphite deposits in Krasnoiarsk Krai, the iron ore deposits in the Krivoi Rog basin and the Kursk magnetic anomaly in the USSR; the manganese deposits in Brazil and India, and the deposits of gold and uranium ores in South Africa).
Metamorphic deposits form anew in the process of metamorphism. Limestones are converted to marbles, sandstones to quartzites, and clay rocks to roofing slates (and with a high degree of metamorphism to deposits of andalusite, kyanite, and sillimanite); emory forms in place of bauxite deposits.
REFERENCESmirnov, V. I. Geologiia poleznykh iskopaemykh, 2nd ed. Moscow, 1969.
V. I. SMIRNOV