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Xuanlong-type iron Formation distributes in Xuanhua and Longguan area of Hebei province, northern China. As the oldest depositional iron deposit, it is characterized by oolitic and stromatolitic ironstone. SEM (scanning electron microscope) and EMPA (electron microprobe analysis) show that most ferruginous colds are composed of continuous and concentric sheaths (cortices) Which are made up of dark and light layers. These layers are made of flakes, platelets, and granules of hematite or siderite and show large variation in major oxide compositions, especially in FeO and SiO2,contents. The average of FeO and SiO2, in the dark layers is 94.982% and 1.723%, respectively, Whereas in the light ones are 78.533% and 29.969%. SiO2, Al2O3, K2O and CaO are concentrated in the light layers but depleted in the dark ones. Compared their internal fabric with recent and ancient carbonate colds, combined with environmental characteristics and plentiful microfossil found in the colds, it is likely that both microorganism and fluctuation setting are helpful for the generation of oolitic ironstone.
Xuanlong-type iron Formation distributes in Xuanhua and Longguan area of Hebei province, northern China. As the oldest depositional iron deposit, it is characterized by oolitic and stromatolitic ironstone. SEM (scanning electron microscope) and EMPA (electron microprobe analysis) show that most ferruginous colds are composed of continuous and concentric sheaths (cortices) Which are made up of dark and light layers. These layers are made of flakes, platelets, and granules of hematite or siderite and show large variation in major oxide compositions, especially in FeO and SiO2, contents. The average of FeO and SiO2, in the dark layers is 94.982% and 1.723%, respectively, Whereas in the light ones are 78.533% and 29.969%. SiO2, Al2O3, K2O and CaO are concentrated in the light layers but depleted in the dark ones. Compared their internal fabric with recent and ancient carbonate colds, combined with environmental characteristics and plentiful microfossil found in the colds, it is likely that both microorganism and fluctuation setting are helpful for the generation of oolitic ironstone.