Sources of rare earth elements and yttrium in late Devonian svanbergite from the Shifang phosphorite deposit

Abstract

The Devonian Shifang phosphorite deposit in the South China Craton (SCC) contains a significant amount of aluminum phosphate-sulphate (APS) minerals, particularly in svanbergite, with rare earth elements and yttrium (REY) concentrations ranging from 1060 to 3257 ppm, with an average of 2259 ppm. Notably, the svanbergite ore body within the Shifang phosphorite deposit exhibits higher REY concentrations than the underlying phosphorite ore body. Despite this, the REY sources in the svanbergite from this unique deposit remain ambiguous. In this study, we carried out major and trace element analysis, as well as whole rock Sr and Nd isotopes analysis, on svanbergite from Shifang and phosphorite from Qingping. Furthermore, we also present Nd isotopic data from granodiorite samples collected from Dashuizha anticline. Additionally, UPb dating and trace element analysis of detrital zircons hosted within Shifang svanbergite were performed to better elucidate the material sources of REY in the svanbergite. Our results indicate that REY enrichment in the Shifang svanbergite was primarily driven by primary marine sedimentation and weathering. Major and trace element data, especially Y/Ho ratios and REY concentrations, along with ⁸⁷Sr/⁸⁶Sr ratios, suggest that both seawater and terrestrial sources contributed to the REY enrichment. The εNd(t) values and T_2DM ages of Shifang svanbergite align with certain Neoproterozoic granites (Tonian granite, 750–875 Ma) and Cambrian granites (498–536 Ma) in the SCC continental crust. Combined with the trace element analysis as well as zircon UPb ages of the svanbergite, we conclude that these Cambrian and Tonian granites were likely significant contributors to the REY in the Shifang svanbergite. Furthermore, the Cambrian Qingping phosphorite deposit may have also contributed to the REY content in the Shifang svanbergite.