Geochemical evolution of the Doushantuo economic phosphorite in Central Guizhou, South China: Quantified multi-stage metallogenic process
Liang Qi, Yaguan Zhang, Liangxuan Jiao, Jianzhong Liu, Yuansheng Du, Zepeng Wang, Wenchao Yu, Huaming Guo, Qun Chen, W. D. Wu
Abstract
Economic phosphorite from Ediacaran Doushantuo Formation is the first true phosphorite giant and represents the onset of the Precambrian-Cambrian global phosphogenic event. The Doushantuo phosphorite may have deposited during the early-middle Ediacaran (ca. 632-574 Ma) according to the latest radiochronological data. Petrographically, in central Guizhou, it can be subdivided into two types of lithofacies: pristine phosphorite (micritic phosphorite, phosphatic shale, banded phosphorites) and reworked phosphorite (intraclastic phosphorite, vuggy intraclastic phosphorite, unconsolidated phosphorite). Geochemical data show that chemical/biochemical enrichment is the most effective process to condense the phosphatic sediments and obviously improve the grade of P2O5 (can reach 38.8 wt%). Hydrodynamic reworking may not play an important role in the further enrichment of P2O5 content but effectively got rid of SiO2 and Al2O3 components in phosphorite by the removal of lighter terrigenous particles and clays. Mass change calculation shows that Ca and Mg are heavily depleted in the chemical leaching process, implying it is a key process to upgrading the quality of phosphorite by separating the carbonate constituents from phosphorite. Therefore, a multi-stage metallogenic model of chemical/biochemical enrichment, hydrodynamic reworking, and chemical leaching is proposed, quantified the composition changes and elucidated the constrained factors in the formation of high-graded phosphorite. Such a metallogenic process effectively produced high-quality phosphorite deposits and bring great benefits to metallurgy.