Study on the Weathering Process and Re-enrichment Mechanism of the Ediacaran Phosphorus Deposits in Central Guizhou, China

Phosphorus deposits in central Guizhou are typical of global phosphorogenic events after the Neoproterozoic Ice Age. These deposits exhibit a high correlation between weathering characteristics and the ore grade level. To investigate the mechanisms of the process in which phosphate is partially dissolved, phosphorus weathering migration, precipitation, and re-enrichment in the supergene environment, this study uses X-ray diffraction analysis, scanning electron microscopy, energy spectrum analysis, elemental geochemical tests, saturation method rock porosity experiments, and dissolution experiments to compare the primary ore and weathered ore of phosphorus deposits in central Guizhou. It is considered that the weathered phosphate ore is lighter in color and is highly porous. The main gangue mineral, dolomite, is mostly dissolved, and characteristic weathering fabrics are widely observed. The P₂O₅ content in primary phosphate ore is not strongly correlated with porosity. However, in weathered ores, when the weathering indexes reach the weathering thresholds, there is a strong correlation between the P₂O₅ content and porosity, with a significant increase in P₂O₅ content. When the grade reaches around 35%, the correlation between porosity and P₂O₅ content deteriorates again, and the impact of weathering and leaching on phosphorus enrichment is significantly reduced. REEs may be adsorbed, migrated, and lost by clay minerals, especially the LREEs, which are more prone to loss. The δCe negative anomaly becomes weaker, indicating that the weathering of phosphate ore occurs in a weakly acidic environment. The weathering and enrichment process of phosphorus deposits includes three stages: superimposed weathering conditions, carbonate mineral leaching, and phosphate mineral recrystallization. This study can further enrich the ore-forming theory of weathering-type phosphorus deposits and provide geological evidence of mineral exploration practices.