Re-Os Dating of Polymetallic Ni-Mo-PGE-Au Mineralization in Lower Cambrian Black Shales of South China and Its Geologic Significance

• DOI: 10.2113/gsecongeo.97.5.1051
• Publication Date: 2011-12-21T20:55:29Z
• Authors: J. Mao; B. Lehmann; A. Du; G. Zhang; D. Ma; Y. Wang; M. Zeng; R. Kerrich
• Keywords: 13. Climate action; 01 natural sciences; 0105 earth and related environmental sciences

Black shales of the basal Lower Cambrian Niutitang Formation, southeast China, host a regionally distributed concordant, several centimeter-thick, sulfide layer which displays extreme metal enrichment, i.e., Mo-NiSe-Re-Os-As-Hg-Sb >1,000 times enriched and Ag-Au-Pt-Pd >100 over bulk continental crust. Mineable portions have about 5.5 wt percent Mo, 3.5 Ni, 1 g/t PGE + Au. A six-point 187 Os/ 188 Os versus Re/ isochron on molybdenum-nickel ore samples defines an age 541 ± 16 Ma (2σ) with initial ratio 0.78 0.19. This is in agreement depositional black shale host; close to present-day seawater. The layer/average seawater order 10 6 8 , 100 higher than that for average metalliferous shale. Synsedimentary enrichment from under anoxic (sulfate-reducing) conditions appears likely but requires unusually low sedimentation rate and/or high replenishment fresh marine basin. paleogeographic setting margin Yangtze craton indicates local basins controlled by synsedimentary rifting. Stagnant water episodically replenished upwelling oxidized thought be responsible formation polymetallic phosphorite, barite, sapropelic “stone coal” (combustible shale) beds.