PLATINUM-GROUP MINERALS FROM A PLACER DEPOSIT IN BURWASH CREEK, KLUANE AREA, YUKON TERRITORY, CANADA

Five placer grains of Pt-Fe alloy, ca. 0.5 to 2 mm, roundish in shape, and hitherto unconfirmed from this locality, were recovered from a placer deposit in Burwash Creek, Kluane area, Yukon. Our results of multiple electron-microprobe analyses (EMP) display the presence of elevated levels of Pd (0.49-5.84, mean 2.38 wt.%), Rh (1.05-1.94, mean 1.50 wt.%), Ir (<0.2 to 6.91, mean 1.33 wt.%), and Cu (0.17-1.19, mean 0.62 wt.%) in these alloy grains; a compositional series is observed, in which values of Sigma PGE/(Fe + Cu + Ni) vary from 3.0 to 5.7. Concentrations of Ru are invariably low (<0.03 to 0.11 wt.%) in this series. These grains of Pt-Fe alloy host micro-inclusions of various species of platinum-group minerals, PGM, diopside [Ca45.7-47.5Mg37.5-48.0Fe4.9-16.8, mg# = 100Mg/(Mg + Fe2+) in the range 69.0-90.7], plagioclase (Ab(57.5-60)An(35.1-39.9)Or(2.6-4.8)), and sodic-calcic amphiboles (0.6 and 1.1 Na apfu), some of which are rich in Cl (0.72 and 1.17 wt.%, or 0.17 and 0.36 Cl apfu, respectively). The analyzed inclusions of PGM are members of the bowieite Rh2S3 - kashinite Ir2S3 solid-solution series, miassite (Rh,Pt,Pd)(17)S-15, cooperite PtS, isoferroplatinum Pt3Fe (or Fe-rich platinum), vasilite (Pd,Cu,Pt)(16)S-7, keithconnite Pd20Te7, an unusual Pt-Pd-Ni-Cu alloy (i.e., Pd-rich platinum: Pt47.7-52.8Pd29.3-37.9Ni6.3-8.0Cu6.1-7.5), and a sulfotelluride of Pd, Pd11Te2S2 (?), which may represent a new isomertieite-type compound. The trace-element composition of the silicate melt inclusions determined using laser-ablation ICP-MS shows a notable enrichment in large-ion lithophile elements. We infer that the reported association of PGM and the trace-element composition of silicate melt inclusions observed at Burwash Creek probably correspond to an Alaskan-Uralian-type mineralization; considered less likely is a relation with a Triassic ultramafic-mafic complex (sill-like) of so-called Kluane-type, also developed in the placer area.