Platinum-Group Minerals From a Placer Deposit in Burwash Creek, Kluane Area, Yukon Territory, Canada

Abstract

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 SPGE/(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 Mg 37.5-48.0 Fe 4.9-16.8 , mg# = 100Mg/(Mg + Fe 2+ ) 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 Rh 2 S 3 -kashinite Ir 2 S 3 solid-solution series, miassite (Rh,Pt,Pd) 17 S 15 , cooperite PtS, isoferroplatinum Pt 3 Fe (or Fe-rich platinum), vasilite (Pd,Cu,Pt) 16 S 7 , keithconnite Pd 20 Te 7 , an unusual Pt-Pd-Ni-Cu alloy (i.e., Pd-rich platinum: Pt 47.7-52.8 Pd 29.3-37.9 Ni 6.3-8.0 Cu 6.1-7.5 ), and a sulfotelluride of Pd, Pd 11 Te 2 S 2 (?), 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.

Multi-Analytical Characterization of Minerals of the Bowieite–Kashinite Series From the Svetly Bor Complex, Urals, Russia, and Comparison With Worldwide Occurrences

“…5A, B). The bowieite from the Svetly Bor dunite has a composition comparable with those reported from placer deposits in the Yukon Territory, Canada (Fedortchouk et al 2010); eastern Madagascar ; Kamchatka (Podlipskii et al 1999, Sidorov et al 2004; and far East Russian (Gornostayev et al 1999), as well as with those described from the Austrian chromitite of Kraubath ( 2003) (Figs. 5A, C).…”

“…The type locality of bowieite is Goodnews Bay in Alaska, where the new mineral was found included in Pt-Fe nuggets. Since its official discovery, more than 20 occurrences of bowieite have been documented and in most of them bowieite occurs as inclusions in Pt-Fe nuggets associated with placer deposits (Atanasov 1990, Hagen et al 1990, Weiser & Schmidt-Thomé 1993, Gornostayev et al 1999, Podlipskii et al 1999, Britvin et al 2001, Sidorov et al 2004, Barkov et al 2005, Melcher et al 2005, Stanley et al 2005, Oyunchimeg et al 2009, Fedortchouk et al 2010, Zaccarini et al 2013, Airiyants et al 2014. Bowieite has also been reported to occur in banded chromitite associated with ophiolites from Canada and Austria (Corrivaux & Laflamme 1990, Malitch et al 2001.…”

Petrogenesis of the Platinum-Group Minerals

“…Intrusions hosted in orogenic belts in Russia are referred to as Uraliantype (cf. Noble and Taylor 1960;Taylor 1967;Foley et al 1997;Garuti et al , 2003Augé et al 2005a), whereas those located in similar tectonic settings in southeastern Alaska (and more generally the North American Cordillera) are termed Alaskan-type (Findlay 1969;Himmelberg et al 1986;Patton et al 1994;Himmelberg and Loney 1995;Fedortchouk et al 2010). Examples of CUAAC have also been reported from all over the world (e.g., Australia, Colombia, Ecuador, Egypt, Madagascar, and Papua New Guinea), and can collectively be termed Uralian-Alaskan-type complexes (see and Supplementary Table 3).…”