Mineralogical variation in platinum group element within altered chromitite of the Kondapalli layered igneous complex (Southern India): Implication on magmatic evolution and its petrogenetic significance

摘要

The Kondapalli Layered Igneous Complex (KLIC) is deformed and dismembered stratiform type of mafic-ultramafic complex emplaced into high-grade metamorphic rocks of Eastern Ghat Belt (EGB). Which contains chromite with relatively oxidized compositions that occur as bands, pockets, pods, stringer, and dissemination. This chromite hosts traces of PGM eg. laurite, irarsite [(Ir, Ru, Rh, Pt)AsS], Os-Ir-Ru alloys and Fe-Ni-As-S minerals. The present study helps to understand the changes and/or reworking of chromite and PGM due to the effect of alteration. Petrographic observations and EPMA study indicate that the chromite core is still consistent with magmatic fractionation processes, whereas sequential alteration of the chromite rim suggests upper greenschist to lower amphibolite facies of metamorphism (500 degrees to 550 degrees C). The platinum-group minerals (PGM), however, display evidence of partial hydrothermal/metamorphic reworking. Especially, laurite and irarsite which occur near the chromite grain boundary. In contrast, the primary ones which probably formed at high-T and low fs(2) and occur in the chromite cores are relatively less affected by alteration.