RHENIUM AND OSMIUM ISOTOPES IN BLACK SHALES AND NI-MO-PGE-RICH SULFIDE LAYERS, YUKON-TERRITORY, CANADA, AND HUNAN AND GUIZHOU PROVINCES, CHINA

Rhenium and osmium abundances and osmium isotopic compositions were de termined by negative thermal ionization mass spectrometry for samples of Devonian black shale and an associated Ni-enriched sulfide layer fr om the Yukon Territory, Canada. The same composition information was a lso obtained for samples of early Cambrian Ni-Mo-rich sulfide layers h osted in black shale in Guizhou and Hunan provinces, China. This study was undertaken to constrain the origin of the PGE enrichment in the s ulfide layers. Samples of the Ni sulfide layer from the Yukon Territor y are highly enriched in Re, Os, and other PGE, with distinctly higher Re/Os-192 but similar Pt/Re, compared to the black shale host. Re-Os isotopic data of the black shale and the sulfide layer are approximate ly isochronous, and the data plot close to reference isochrons which b racket the depositional age of the enclosing shales. Samples of the Ch inese sulfide layers are also highly enriched in Re, Os, and the other PGE. Re/Os-192 are lower than in the Yukon sulfide layer. Re-Os isoto pic data for the sulfide layers lie near a reference isochron with an age of 560 Ma, similar to the depositional age of the black shale host . The osmium isotopic data suggest that Re and PGE enrichment of the b recciated sulfide layers in both the Yukon Territory and in southern C hina may have occurred near the time of sediment deposition or during early diagenesis, during the middle to late Devonian and early Cambria n, respectively.