Geochemistry and origin of the intrusive hosts of Noril'sk-Talnakh Cu-Ni-PGE deposits

摘要

The large, rich deposits of Cu, Ni and platinum-group elements of the Noril'sk-Talnakh district in Russia are hosted by small, complex mafic-ultramafic bodies that intrude Permian sedimentary rocks just beneath the Siberian continental flood basalts. The ore-bearing intrusions immediately overlie, and probably are penecontemporaneous with, a set of weakly mineralized intrusions that have similar petrological features, but contrasting chemical compositions.To clarify the relations between the various types of igneous bodies (ore-bearing intrusions, weakly mineralized intrusions and overlying volcanic rocks) and to help to understand the formation of the ore deposits a detailed geochemical and Nd, Sr and Os isotope study of four of the more important intrusions has been undertaken. The results show that these intrusions formed through the input of a series of magma pulses, each of which had a distinctive petrological character and chemical composition. These compositions are interpreted as mixtures of mantle-derived magmas with different types of crustal rocks that were encountered during passage to the surface.