Genesis and Platinmineralization of the Guli Massif

The Guli Massif, situated in the northern part of the Siberian Platform, represents the worlds largest dunite- clinopyroxenite complex. It is composed of an ultramafic rock portion, consisting of chromitite-bearing dunites and clinopyroxenites, and is spatially associated with ultramafic (i.e. meymechites) and mafic volcanics. The massif is further cut by stock-like bodies of carbonatites. The economic potential of the Guli Massif is remarkable: apart of apatite, phlogopite, iron, and rare earth element deposits, related to the carbonatites, economic platinum-group mineral (PGM) and Au placer deposits occur in close vicinity. The majority of the PGM in the placers of the Guli Massif are Os-(Ir-Ru) alloys and subordinate Pt-Fe alloys. Preliminary studies on the placer PGM indicate derivation from chromitites hosted in the dunites, although no significant primary platinum-group element (PGE) mineralisation has been found so far. The Guli Massif shows similarities to typical zoned-massifs, although size , shape and not strictly concentrically rock suite are at variance, if compared with other zoned massifs. Furthermore, the dominance of Os-(Ir, Ru) over Pt-Fe alloys is striking and unusual. The application of an array of new methods, such as special separation and concentration techniques and determination of the Os-isotope composition of single PGM, in a combined geological, mineralogical, petrological, geochemical, and isotope study on the Massif, should provide new insights into the genesis and petrological evolution of the Guli Massif and associated PGE mineralisation. Particular emphasis is put onto the PGE-containing ultramafic rocks, that are of rather small size (i.e. 450Km2), if compared to PGE-bearing ultramafic sequences of layered intrusions (e.g. Bushveld Complex), but have concentrated a huge amount of predominantly Os and Pt. This obvious concentration and fractionation of PGE is striking and diserves detailed investigation. The results of this project will make a significant contribution to the understanding of the origin and formation of zoned massifs, as well as the fractionation, transport, and deposition of PGE in this special geological environment.

The Guli Massif, situated in the northern part of the Siberian Platform, represents the world`s largest dunite- clinopyroxenite complex. It is composed of an ultramafic rock portion, consisting of chromitite-bearing dunites and clinopyroxenites, and is spatially associated with ultramafic (i.e. meymechites) and mafic volcanics. The massif is further cut by stock-like bodies of carbonatites. The economic potential of the Guli Massif is remarkable: apart of apatite, phlogopite, iron, and rare earth element deposits, related to the carbonatites, economic platinum-group mineral (PGM) and Au placer deposits occur in close vicinity. The majority of the PGM in the placers of the Guli Massif are Os-(Ir-Ru) alloys and subordinate Pt-Fe alloys. Preliminary studies on the placer PGM indicate derivation from chromitites hosted in the dunites, although no significant primary platinum-group element (PGE) mineralisation has been found so far. The Guli Massif shows similarities to typical zoned-massifs, although size , shape and not strictly concentrically rock suite are at variance, if compared with other zoned massifs. Furthermore, the dominance of Os-(Ir, Ru) over Pt-Fe alloys is striking and unusual. The application of an array of new methods, such as special separation and concentration techniques and determination of the Os-isotope composition of single PGM, in a combined geological, mineralogical, petrological, geochemical, and isotope study on the Massif, should provide new insights into the genesis and petrological evolution of the Guli Massif and associated PGE mineralisation. Particular emphasis is put onto the PGE-containing ultramafic rocks, that are of rather small size (i.e. 450Km2), if compared to PGE-bearing ultramafic sequences of layered intrusions (e.g. Bushveld Complex), but have concentrated a huge amount of predominantly Os and Pt. This obvious concentration and fractionation of PGE is striking and diserves detailed investigation. The results of this project will make a significant contribution to the understanding of the origin and formation of zoned massifs, as well as the fractionation, transport, and deposition of PGE in this special geological environment.