EXTREME PGE CONCENTRATIONS IN LOWER CAMBRIAN ACID TUFF LAYER FROM THE KUNYANG PHOSPHATE DEPOSIT, YUNNAN PROVINCE, SOUTH CHINA--POSSIBLE PGE SOURCE FOR LOWER CAMBRIAN Mo-Ni-POLYELEMENT ORE BEDS

• DOI: 10.2113/econgeo.105.6.1047
• Publication Date: 2010-12-14T16:54:25Z
• Authors: J. Pasava; H. Frimmel; L. Taiyi; M. Koubova; K. Martinek
• Keywords: Illite

A study of the platinum group element (PGE) distribution in various lowermost Cambrian rock types Kunyang phosphate deposit south China revealed unusually high PGE concentrations (434 ppb Pt, 142 Pd, 57.97 Rh, <1 Ru, and 0.14 Ir) a whole-rock sample acid tuff that is interbedded with phosphorite. Stratigraphically above this unit an Mo-Ni–polyelement (including Au) phosphatic sulfidic black shale. The consists clastic glass fragments matrix clay minerals (dominantly mixed-layer illite-smectite) cryptocrystalline quartz minor dolomite, nodules, rare pyrite. clay-quartz fraction elevated Ru (11 ppb) Ir (1.4 concentrations, but depletion Pt (6.8 ppb), Pd (25 Rh (0.35 relative to whole rock. LA-ICPMS analyses pyrite yielded Ni values (up 1,243 ppm) some grains also Re 576 190 concentrations. No were detected nodules. It very likely are part bound submicroscopic inclusions and/or intermetallic phases fraction. Petrographic observations isotope data obtained on paragenetically late dolomite veinlets, which C O ratios correspond those contemporaneous seawater ( δ 13C ranges −2.32 −2.44‰ V-PDB, 18O −10.07 −9.94‰ V-PDB), do not indicate any hydrothermal overprint. Instead, formation ascribed diagenesis reduced environment shales, as supported by 34S for between 6.31 7.54 per mil CDT If other tuffs region have similar anomalous PGE, they could played important role origin slightly younger shales Yangtze platform.