Paleo-sedimentary-tectonic environment and vanadium enrichment mechanism of the Lijiawan black rock series in the northern margin of the Yangtze Platform

Lijiawan is a representative vanadium deposit hosted in black rock series of the Niutitang Formation. In order to identify the geochemical characteristics and depositional environments of the black rock series, and to reveal the enrichment mechanism of vanadium in this deposit, a comprehensive study has been conducted, including field investigation, microlithological analysis, whole-rock X-ray diffraction (XRD) for mineralogical composition, as well as major and trace element geochemical analysis of various lithological units. Furthermore, micro-XRF surface scanning was employed for selected representative samples. The black rock series of the Niutitang Formation is subdivided into three distinct lithological units, primarily composed of quartz, clay minerals, dolomite, and organic matter. This sequence exhibits a notable enrichment in V, Mo, Ni, Se, and Sb, while being relatively depleted in Mn, Co, and Sn. Vanadium is primarily enriched in the first lithological unit, where its concentration is positively correlated with the concentrations of Mo, Ni, and Se, suggesting a common origin and enrichment process. The formation of black rock series in the Lijiawan deposit is attributed to a shallow marine setting characterized by medium to high salinity, anoxic conditions, and weak sediment retention. The sedimentary and ore-forming materials are derived from seafloor hydrothermal solutions, with vanadium predominantly incorporated into clay minerals in the form of isomorphism.