Ontogeny of ore Cr-spinel and composition of inclusions as indicators of the pneumatolytic-hydrothermal origin of PGM-bearing chromitites from Kondyor massif, the Aldan Shield

摘要

The thoroughly studied ontogeny and chemical composition of ore Cr-spinel from PGM-bearing chromitites of the Kondyor clinopyroxenite-dunite massif in the Aldan Shield show that this mineral crystallizes jointly with relatively low-temperature minerals: Cr-diopside, amphiboles, phlogopite, chlorite, serpentine, apatite, etc. Induction surfaces between Cr-spinel and silicates of the ore matrix are established. The ore Cr-spinel contains a great number of octahedral carbonic fluid and silicate inclusions, as well as octahedral gold and serpentine aggregates. These data, along with the relationships of Cr-spinel with low-temperature silicates, are evidence for the pneumatolytic-hydrothermal origin of Cr-spinel in Cr-PGE ore. Chromitite is a contrasting and nonequilibrium system with respect to host dunite in both chemical compositions of minerals and formation conditions in agreement with the concept of the epigenetic nature of chromitite stated more a century ago by A.N. Zavaritsky and A.G. Betekhtin.