Geological Characteristics and Sedimentary Environment of Chengqiangyan Phosphate Deposit in Mianzhu Area, Sichuan Province

The chengqiangyan phosphate deposit in Mianzhu area of Sichuan province is one of the famous Shifang-type phosphate deposits. The ore bearing strata are Shawozi Formation of Lower Devonian, and the occurrence of ore body is basically consistent with the stratum, being layered or quasi-bedded. The grade of P₂O₅ is 18.29%~35.57%, having a positive correlation with the thickness of phosphorus bearing layer. Its lithofacies assemblage is "kaolinite clay rock-aluminophosphate rock-phosphorite rock". The natural type of ore is clayey or sandy gravel phosphorite, and the industrial type is siliceous and silicate phosphorite.The correlation and cluster analysis of main components of ores show that P₂O₅, CaO and F are closely related; Fe₂O₃ and Al₂O₃, MgO and CO₂ are also closely related; Fe₂O₃, Al₂O₃ and RE₂O₃ are significantly correlated.Combined with the analysis of regional metallogenic geological conditions,it is held that Sinian Mianzhu type phosphate deposit was weathered and eroded in the early Devonian, and the ore was transported to the coastal shallow sea, forming the Shifang type phosphate deposit.The values of trace elements indicate that the Chengqiangyan phosphate deposit formed in an arid oxygen-rich marginal marine environment.