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The Talnakh deposit is one of the largest PGE-Cu-Ni deposits in the world. It is located inside the NorthWestern part of the Siberian Trap province and consists of three branches. The problem of massive ore origins has been discussed for several decades. The structure of the SouthWestern branch and the mineralogy of related its Cu-rich ore are discussed in this article. The Southern 2 orebody has a deep inclination (45 •) inside the intrusive body, close to its wall, in contrary to the horizontal orebodies of the NorthEastern branch. Mineral composition of the Southern 2 orebody differs from the composition the other orebodies of the Talnakh intrusion as well. It consists ofchalcopyrite, pentlandite with subordinate cubanite, and pyrrhotite. Its specific feature is a large amount of bornite and chalcocite. These minerals occur in disseminated and massive ores. The ores of the other branches of the Talnakh intrusion have chalcopyrite-pyrrhotite compositions whilethe Southern 2 massive ore is enriched in Cu (19.03-25.8 wt %; Cu/Ni = 3.8-8.6) and PGE: ΣPGE changes from 39.1 to 279 ppm, Pd/Pt = 1.3-32. Twelve minerals of the systems Pd-Sn-Cu, Pd-Pb-Bi, Pd-Ni-As, Au-Ag-Pd-Cu, and intermetallics of the Pt-Fe-Cu-Ni types were discovered in ores, but are also widespread in other orebodies. Isoferroplatinum, sperrilite and cooperitewere not found. The unusual structure and composition of the Southern 2 orebody suggest its origin from a separate magma impulse. The correlation between disseminated and massive ores of the Southern 2 orebody in term of chemical and mineralogical composition is evidence of the formation of massive oresin situ, without displacement along the bottom of the massif.

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