四川绵竹地区城墙岩磷矿床地质特征及沉积环境

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

四川绵竹地区城墙岩磷矿床属著名的“什邡式”磷矿产地之一。赋矿地层为下泥盆统沙窝子组,其中矿体与地层产状基本一致,呈层状、似层状产出,P_(2)O_(5)品位为18.29%~35.57%,品位高低变化与含磷层的厚度具正相关性。其岩相组合为“高岭石黏土岩铝磷酸盐岩磷块岩”。矿石自然类型为黏土质或砂砾屑磷块岩矿石,工业类型为硅质及硅酸盐型磷块岩矿石。矿石主要成分相关性和聚类分析表明,P_(2)O_(5)、CaO、F密切相关;Fe_(2)O_(3)和Al_(2)O_(3)、MgO和CO_(2)紧密相关;Fe_(2)O_(3)、Al 2 O 3和RE_(2)O_(3)明显相关。结合区域成矿地质条件分析认为,在早泥盆世,震旦系“绵竹式”磷矿遭受风化剥蚀,矿质搬运至滨浅海沉积形成“什邡式”磷矿床。微量元素特征值指示,城墙岩磷矿床形成于干旱、富氧的边缘海相环境。

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 P_(2)O_(5) 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 P_(2)O_(5),CaO and F are closely related;Fe_(2)O_(3) and Al_(2)O_(3),MgO and CO_(2) are also closely related;Fe_(2)O_(3),Al_(2)O_(3) and RE_(2)O_(3) 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.