Study On The Enrichment Mechanism Of Phosphorous In The Epigenetic Environment Of Tongren, Guizhou

The average P₂O₅ content of marine phosphorite deposit is 17.74%,which occurs at the top of Liuchapo Formation and the bottom of Jiumenchong Formation in the early Cambrian in Tongren,Guizhou Province.It also rich in rare earth elements and associated with many beneficial elements,such as Ni,Mo,V,Ba,U and so on.In recent years,it is found that in the epigenetic environment,the P₂O₅ content can reach28.94%,which phosphorous is obviously enriched,but the migration and enrichment mechanism under oxidative condition is still lack systemic research.In this paper,the mechanism of phosphorous migration and enrichment under epigenetic conditions is explored by analyzing,comparing and summarizing the features of minerals,structures and geochemistry of weathering profile.The main conclusions are as follows:(1)The weathered phosphate ores are mainly clastic phosphate rock and nodular phosphate rock,and the ore minerals are mainly cellophane,followed by pseudocrystal apatite.There is a large number of sasaites were distributed on the ore surface and fissures,which is a sign of weathering of phosphorous-rich sediments;the content of kaolinite increased obviourley,and most carbonate mineral are dissolved,The structure of weathered phosphate ore is mainly recrystallized structure,pea-like structure,pseudocrystal structure,and typical weathering texture such as nodular texture,directional texture and metacolloidal structure are developed.(2)The CaO,MgO,K₂O,Fe₂O₃ and other elements of weathered ore is relatively active,which are dissolved at first,the activity of P₂O₅is weak,so it is enriched in situ.The high field-strength elementit such as Zr,Pb,Th,Nb,Ta are strongly or moderately carried out,resulting in more loss of these elements in weathered ores.The REEs are generally stable,and the total amount increases significantly,indicating that the REEs existing in apatite lattice by isomorphism,which are residual and enriched with phosphate minerals under epigenetic conditions.But the LREEs are slightly carried out,resulting in more relative enrichment of HREEs in weathered ores.And?Ce shows obvious negative anomaly,indicating a high degree of oxidation;?Eu changes from positive anomaly to weak negative anomaly,indicating that the geochemical features in reponse to hydrothermal sedimentation are weakened under epigenetic conditions.(3)The weathering of primary ores is affected by ore composition,structure,climatic conditions,topography,geomorphology,geological structure,overburden conditions,hydrogeological conditions.The water-rock interaction makes the soluble components such as carbonate and silicate minerals dissolve and separate out,and forms secondary oxidation minarals such as sasaite,limonite and kaolinite.(4)The chemical weathering indexes show that the weathering degree of the broken metal-rich layer is the highest,followed by the weathered phosphate ore,and the primary profile has undergone moderate chemical weathering in the temperate climate.The epigenetic enrichment process of phosphorous has gone through three stages:the original rock/ore mechanical crushing,the carbonate mineral dissolution and the secondary phosphate mineral formation stage.