Trace element geochemistry and genetic implications of sphalerite and pyrite from the Lower Cambrian Dahebian stratiform barite deposit and its associated deep-seated sulfide mineralization, South China

Abstract

The southeastern margin of the Yangtze Block hosts significant stratiform barite deposits within the early Cambrian black shales. Various models, including submarine exhalative hydrothermal activity, cold seep, and biological enrichment, have been proposed to explain their genetic types. Recently, substantial Zn-Pb-Fe sulfide ores mainly hosted by the Doushantuo Formation were discovered beneath the early Cambrian stratiform barite ores. The sulfide and barite ores along this belt demonstrated a common characteristic of close spatial relationship; however, it remains unclear whether a genetic relationship also exists. Nevertheless, this shed newly light on to decoding the genetic mechanism of massive barite deposition during this period. The mineralogy and trace element concentrations of sphalerite and pyrite in both deep-seated sulfide ores and stratiform barite ores at the Dahebian region were determined in this study. Hyalophane intergrown with apatite was frequently observed in both types of ores. This association contrasts with the Mississippi Valley Type (MVT) zinc-lead mineralization hosted in the Qinxudong Formation within this region, where apatite is predominantly surrounded by hydrothermal calcite. Furthermore, a covariant trend of minor concentrations of sphalerite and/or pyrite has been observed between sulfide ores and barite ores, indicating their precipitation within evolving hydrothermal fluids. This observation is corroborated by the decreasing temperatures of sphalerite during precipitation: the early-stage sulfide mineralization, late-stage mineralization, and stratiform barite deposit have recorded hydrothermal fluid temperatures in the ranges of 109 °C to 235 °C, 99 °C to 231 °C, and 38 °C to 199 °C, respectively. Furthermore, a comparable decreasing trend in sulfur fugacities was observed during the transition from sulfide to barite ore mineralization. The elevated concentrations of Ni, Cu, Se, and V in the late-stage pyrite of deep-seated sulfide deposits suggest that anoxic-euxinic bottom seawater infiltration along extensional faults likely facilitated mineralization. The enhanced influx of infiltrating seawater into mineralization zones significantly reduced the temperature of hydrothermal fluids, leading to a decrease in the rates of thermochemical sulfate reduction. Therefore, it can be reasonably inferred that the sulfide ore underlying the stratiform barite ores likely originated from sedimentary exhalative hydrothermal fluids. The Zn-Pb-Fe sulfide ores, which are deeply seated, underwent mineralization within the feeder zone at depth. Conversely, the stratiform barite deposits represent the uppermost expression of sedimentary-exhalative mineralization. These findings collectively suggest intense venting of Zn-Pb-Fe-Ba-bearing hydrothermal fluids into the rift basin along the southeastern margin of the Yangtze Block during the early Cambrian period.