Akademik Veri Yönetim Sistemi
CHEMICAL GEOLOGY, cilt.674, 2025 (SCI-Expanded, Scopus)
Platinum-group minerals (PGMs) in podiform chromitites usually occur in the interior and/or edge of chromite. However, the origin of PGMs in podiform chromitites has long been a matter of debate. Here we examined sub-micro to nanoscale textural features, morphologies, and compositions of PGMs from the disseminated, banded, massive and nodular chromitites in the Kizildag ophiolite in southern Turkiye, and found both primary and secondary PGMs. The aim of this study is to reveal the transformation processes from primary to secondary PGMs, thereby taking a thorough examination of the origin of these PGMs. Primary PGMs include laurite and Os-Ir alloy, which are prevalent in all samples. They are typically enclosed within or located at the edge of chromite, and formed either prior to or contemporaneously with the crystallization of chromite at temperature of 1100-1200 degrees C and logfS(2) values of -2 to -1. In contrast, PGE-bearing pentlandite are commonly present at the edge of chromite, corresponding to an increase of fS(2) with the progressive crystallization of chromite. These primary PGMs and PGE-bearing pentlandite in the intergranular space of chromite are susceptible to alter and transform into secondary PGMs and base metal mineral assemblages, which include Os-Ru nanophases (Os-Ru nanoparticle and OsRu3 nanoalloy) + awaruite (FeNi3) + trevorite (Fe2NiO4) in nodular chromitite, Os-rich laurite + Os-Ir(Ru) alloy/oxide + pentlandite + millerite (NiS) in banded and massive chromitite, and Ru(Ir) oxide + heazlewoodite (Ni3S2) in disseminated chromitite. The development of these diverse assemblages can be attributed to the degrees of serpentinization of chromitites. The nodular chromitite underwent weak serpentinization and had low water/rock ratios (