Essential features of porphyry copper/molybdenum and rare-metal (Sn, W, Mo, Be, Li) ore deposits
published: Jan 1, 1996
ArtNo. ESP136000503007, Price: 19.00 €
Porphyry copper-molybdenum deposits and Sn-W-Mo-Be-Li granitoid deposits represent two economically important groups of ore deposits genetically related to felsic magmatism. The majority of the world's prophyry copper-molybdenum deposits are located in the Circum-Pacific region and in central parts of Alpine orogenic belts. In addition most of tin and tin-tungsten granitoid deposits occur in the Circum-Pacific orogenic belt, in continent or island-arc-continent collisional settings, or intracontinental rifts. Both groups of deposits are formed by processes of magma generation which ultimately lead to the origin of felsic magma. This magma does not differ substantionally in the content of major element oxides like SiO2, Na2O and K2O. The magma of the both groups of igneous rocks belongs to the calc-alkaline, or more rarely to the alkaline magmatic series. In recent years, the differences in origin of these two groups of deposits have been proposed as due to: (1) their different position over subduction zones at active continental margins, (2) melting of continental or oceanic crust by continent-continent collision, (3) depth of intrusion of felsic magmas, (4) level of exposure, (5) time and location of magma generation, (6) quantity of metals incorporated into the magma, (7) conditions leading to metal and volatile concentration, and (8) by provincial inhomogeneities of the crust or the mantle. Present definition of genetic models indicates that many genetic features are common to both groups of deposits. Both can be produced by orthomagmatic or mixed orthomagmatic and meteoric fluids related to felsic magmatism. However, contrasting geochemical association with dominant Sn and W combination in rare - metal deposits or Cu and Mo combination in porphyry copper deposits have been explained by metal behaviour in silicate melts whether the metals were retained in the melt (U, Sn, W) or released in hydrothermal fluids in the early development of magmatic systems.