Genesis of Early-Cambrian barite deposits in the southeastern margin of the Yangtze Platform

Abstract

The Tianzhu barite deposit in Guizhou, South China, is the world’s largest barite deposit, hosted within the chert of the Lower Cambrian Liuchapo Formation. Its genesis has long been debated, with proposed models suggesting either submarine hydrothermal or cold-seep origins. To clarify its formation process, comprehensive mineralogical, sedimentological, paleontological, and geochemical analyses were conducted. The deposit exhibits distinct vertical zoning, including columnar and pie-like barite at the base, massive and granophyric barite in the middle, laminar and banded barite at the top, associated with barite nodules, hyalophane and small-shell fossils. Trace element data, along with sulfur, carbon, oxygen, and silicon isotope compositions, suggest that the Tianzhu barite deposit is unlikely to have formed through submarine hydrothermal processes. Instead, it primarily precipitated in confined basins in a shallow-water, oxidizing environment. Ba-rich fluids erupted along faults near ancient islands and accumulated in these basins. During transgressions, deep-sea sulfate ions mixed with Ba-rich fluids, triggering extensive barite precipitation. In later stages, sulfate depletion in seawater facilitated hyalophane formation at the uppermost layers. These findings provide new insights into the genesis of the Tianzhu barite deposit and suggest that large-scale barite precipitation played a significant role in reducing toxic Ba concentrations in Cambrian oceans, potentially contributing to the Cambrian explosion.