四川绵竹红岩什邡式磷矿地质特征及找矿标志

Geological characteristics and prospecting criteria of Shifang type phosphate deposit in Hongyan,Mianzhu,Sichuan Province

绵竹是中国四大磷矿基地之一,区内磷矿分布集中,但对其成因认识、找矿标志还存在不同认识。为此,选择在地质工作程度较高的绵竹红岩地区,对磷矿矿层、矿体特征及变化规律进行总结,以期为绵竹地区下一步找矿工作提供借鉴。工程揭露显示下泥盆统沙窝子组一段(D3s1)为赋矿地层,矿体与地层产状基本一致,呈层状、似层状产出,走向北东-南西,倾角16°~68°,沿走向约5.8 km,倾向延伸大于1000 m。其岩相组合为"高岭石粘土质岩—铝磷酸盐岩—磷块岩"。矿石的自然类型为粘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。矿体厚度1.26~14.69 m,平均4.71 m;P2O5品位15.01%~35.37%,平均23.72%。磷矿是以风化淋滤沉积作用为主,后期经历滨浅海化学沉积而形成,属典型的"什邡式"磷矿。其找矿标志为震旦系灯影组"花斑"白云岩古岩溶侵蚀面、泥盆系沙窝子组白云岩→含磷白云岩、含磷粘土岩→粘土质或砂砾屑磷块岩。

Mianzhu is one of the four major phosphorite bases in China. The distribution of phosphorite is concentrated in Mianzhu,but there are different understandings on its genesis and prospecting criteria. In order to provide reference for the next prospecting work in Mianzhu Hongyan area,the characteristics and variation law of phosphate ore bed and orebody are summarized. The project revealed that the first member of Shawozi Formation( D3 s1) of Lower Devonian is the ore bearing stratum. The ore body is basically the same as the occurrence of the stratum,which is layered and stratoid. It strikes from northeast to southwest with an angle of 16 °-68 °.Along the strike,it is about 5.8 km and tends to extend more than 1000 m. The lithofacies assemblage is"kaolinite claystone aluminophosphatite phosphorite". The natural type of ore is clayey or sandy gravel Phosphorite Ore,and the industrial type is siliceous and silicate phosphorite ore.The thickness of ore body is 1.26-14.69 m,with an average of 4.71 m. P2 O5 grade is 15.01%-35.37%,and the average is 23.72%. Phosphorite is mainly formed by weathering and leaching sedimentation,and later by chemical deposition in coastal shallow sea,it is typical Shifang type phosphate rock. The exploration criteria are summarized as follows: Sinian Dengying Formation"flower spot"dolomite paleokarst erosion surface,Devonian shawozi formation dolomite→phosphorous dolomite,phosphorous clay rock→clayey soil or sand gravel phosphorite.