Origin and Enrichment of Vanadium in the Lower Cambrian Black Shales, South China.

ABSTRACT

The Lower Cambrian black shales of the Sansui vanadium deposits, located in South China, host a thin accumulation of Ni, Mo, V, and platinum group of elements (PGE). However, among them, the origin of V-bearing deposits remains controversial. To characterize the enrichment process of V-bearing deposits, samples of the mineralized layer and surrounding rocks from the Sansui area, South China, were investigated through bulk geochemical analysis and scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analyses. There is a consistency in the change curves of Mo, Ni, and V from the Sansui V deposits, but the contents of elements show a great difference. This means the strong similarities in the metal sources but a difference in enrichment factors of Mo, Ni, and V. The presence of the tuff and the barite layer in the Sansui V deposits indicates that the formation of the associated V deposits was closely related to either a volcanic or hydrothermal activity. Analysis of geochemistry and sedimentation suggests a hydrothermal source of the metals, where the mineralization of V is related to clay and organic matter. Phosphorus nodules were observed at all sites of black shale V deposits in early Cambrian and were most likely related to the upwelling currents during the depositional period. The comparison with the Ni-Mo deposits highlights a stronger enrichment of clay in the V deposits. The V deposits are located in the lower part of the continental slope. Both organic matter and clay minerals are abundant in the Sansui deposits. However, the isomorphism of V-Al is promoted by the hydrothermal activity and suggests that the origin of V deposits is a multistage process.