GRAINS OF Pt–Fe ALLOY AND INCLUSIONS IN A Pt–Fe ALLOY FROM FLORENCE CREEK, YUKON, CANADA: EVIDENCE FOR MOBILITY OF Os IN A Na–H2O–Cl-RICH FLUID

摘要: We report results of detailed electron-microprobe analyses (EMP) fourteen grains Pt–Fe alloy, ca. 0.4 to 1 mm, principally droplet-shaped or roundish, from Florence Creek, Yukon. also describe new occurrences Pt–(Pd)–Fe alloy Arch Creek (up 11 wt.% Pd) and Canadian An extensive compositional series is observed at Florence, in which values ∑PGE/(Fe + Cu Ni) vary 2.2 5.4. Minor Ir Os display a contrasting behavior this series. The levels are generally greater than those Os. correlates negatively with Pt (the correlation coefficient, R, −0.81; 140 EMP point-analyses); contrast, the between slightly positive (R = 0.64). Probably, higher temperature crystallization, readily replaces structure alloy. As result, did not attain its maximum, inclusions exsolution-induced Ir-dominant hosted by moderately enriched (52–54 at.%). inclusion erlichmanite (4.2 Rh) partial rim Au–Ag (Au 0.80 Ag 0.18 ) were observed. Droplet-like highly aluminous silicate minerals, rich Na, K Cl 2 wt.%). Veinlets micrograins an Os-rich (86–92 Os) intimately associated nearly pure albite, Ab 97.8 1.7 Or 0.5 , intermediate member chamosite–clinochlore association chamosite albite native osmium, infilling cavity host grain was likely deposited late Na–H O–(Cl)-bearing fluid phase postmagmatic–hydrothermal stage, less 700°C. Na possibly mobilized transported as Na–(Os)-rich complexes related sodium hydroxy- oxo-osmates. precipitation metallic could be change physicochemical conditions, e.g., pressure redox potential, leading instability these oxo-osmate complexes. suggest that mineralized zone chromite–magnesiochromite Alaskan–Uralian-type complex provenance for recovered Creek.