Platinum–Rhenium–Osmium Isotope Systematics of Chromitites and Native Osmium of the Guli Massif, Maimecha–Kotui Province, Russia

To gain insight into the source of ore material, this study presents new Re–Os and Pt–Os isotopic and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance data for chromitite and native osmium from the Guli massif of ultramafic alkaline rocks and carbonatites located in the Maimecha–Kotui province, Polar Siberia. The study utilized a number of analytical techniques, including electron probe microanalysis (EPMA), negative thermal ionization mass spectrometry (N-TIMS), and high pressure asher digestion and isotope dilution inductively-coupled plasma mass-spectrometry (ID ICP-MS). The HSE concentrations in chromitite samples range from 191 to 866 ppb with a predominance of Ir-group platinum-group elements (PGE) (Os, Ir, and Ru) over Pt-group PGE (Rh, Pt, and Pd) and Re, which is consistent with the platinum-group mineral control (i.e., Os–Ir alloys and laurite, RuS2) within the chromitite. The Re–Os and Pt–Os isotope data indicate that the HSE budget of the chromitite and native osmium from the Guli massif was largely controlled by that of their mantle source, which evolved with long-term near-chondritic Re/Os and Pt/Os ratios; this source had time-integrated Re/Os and Pt/Os within the range of those for the majority of komatiites and abyssal peridotites worldwide.