deposits of minerals formed deep in the earth’s crust during the solidification and crystallization of basic or alkaline magma containing high concentrations of valuable minerals. These deposits vary in shape and occur in igneous rocks that are related to them in origin.
The formation of valuable minerals in magma that is cooling is the result of three factors. First, when cooling, magma may separate into two immiscible liquids, one of which consists of a mineral substance. This process is called liquation and deposits that are formed in this way are called magmatic liquation deposits (for example, sulfide copper-nickel ores containing cobalt and platinoids in the deposits of Noril’sk, Talnakh, and Pechenga in the USSR and Sudbury in Canada). Second, during the crystallization of magma valuable minerals may form earlier than others and sink to the bottom of the magma reservoir, forming early magmatic deposits. These deposits are also called segregation or accumulative deposits (chromium, titanium, and iron deposits). The kimberlite diamond pipes of Eastern Siberia and South Africa are original early magmatic deposits. Third, when gas-rich magma crystallizes the mineral substance may concentrate in the easily fusible residual melt and during the ensuing solidification form late magmatic or hysteromagmatic deposits (the titanomagnetite deposits of Mount Kachkanar in the Urals, chromites in the Southern Urals, apatites of the Kola Peninsula, tantalum, niobium, and rare earths). Much less frequently magmatic deposits may occur in the form of flows that issue from volcanic vents (for example, volcanic sulfur flows).
The most important beds in magmatic deposits are those of iron, titanium, vanadium, chromium, platinum, copper, nickel, cobalt, apatite, diamonds, niobium-tantalum, zirconium, and hafnium.
REFERENCESGodlevskii, M. N. “Magmaticheskie mestorozhdeniia.” In Genezis endogennykh rudnykh mestorozhdenii. Moscow, 1968.
Smirnov, V. I. Geologiia poleznykh iskopaemykh, 2nd ed. Moscow, 1969.
V. I. SMIRNOV