BASIC PEGMATOIDS AND NORILSK-TYPE PGE MIN ERALIZATION

The Norilsk layered mineralized, platinoid-associated ultrabasic-basic intrusions typically contain lower and upper endocontact horizons com posed of basic pegmatoids (taxitic gabbro-dolerites and pegmatoid gabb ros). In their absence no ore mineralization occurs there. It is shown that abundant ore mineralization only owed to the interaction between high-temperature metasomatized fluids and sub-ultrabasic rocks of par ent intrusive to form first an isomorphous admixture of platinoids in sulfide solid solutions and then independent platinoid phases (Pt and Pd). There are two possible ways for high-temperature ore-forming sulf ides with an isomorphous admixture of platinoids to form. They crystal lize either from a homogeneous sulfide melt or by the interaction of h igh-temperature metasomatizing fluids with sub-ultrabasic rocks of the parent intrusive, which are the source of ore components recovered, t ransported, and precipitated by fluids related to the main pegmatoids of this intrusive. The concept of metasomatic-sulfurization genesis of the Norilsk Cu-Ni platinum-associated ores is useful in solving the p roblem of the existing disbanance between high content of platinoids i n the ores and non-correlatable very low volume of magma in the ore-be aring intrusives as well as in overcoming some other compositional con straints on the genesis of the ores.