As part of the Archean greenstone belt, the Qian'an iron deposit is a typical banded iron formation (BIF)‐hosted iron deposit in the North China Craton. The BIF iron orebodies, together with Archean host rocks, have experienced multiphase metamorphism and plastic deformation. Folds, especially large‐scale synclines, played the most important role in the enrichment and preservation of the Qian'an BIF iron deposit. Exploration and mining reveal that orebodies in the deposit are located in the cores of folds. Structural analysis of the BIF ores suggests that rocks and minerals show obvious plasticity and tend to form types II and III folds of the Ramsay fold classification in the early stage of high temperature deformations (granulite facies), whereas type Ib parallel folds and sometimes type Ic folds are widely developed in the late stage of relatively low temperature deformations (e.g., amphibolite facies). Hand specimens of different types of folded iron ores are investigated with respect to their thickening coefficients, dimensional fabrics and lattice‐preferred orientation fabrics, to find out the characteristics and variation of folded layers, and the importance of iron enrichment during formation of different types of folds. Our studies prove that folding in Qian'an ore deposit occurred under different deformation conditions and thus led to various degrees of enrichment of magnetite. Among them, the type III folds have the most important significance to the enrichment of magnetite. Thickening coefficient analysis shows that the thicknesses of the quartz layers remain relatively constant, and those of the magnetite layers vary evidently during folding. It is concluded that the quartz‐rich layers dominate the deformation as competent layers, and magnetite‐rich layers as relatively weak and passive layers. In addition, the EBSD (Electron Back‐Scattered Diffraction) technique is applied to analyze the dimensional and crystallographic fabrics of both quartz and magnetite grains in folded BIF ores. The quartz <0001> and magnetite <001> fabrics of samples from the cores and limbs of the different types of folds show complex orientation patterns related to plastic deformation superposition. It is shown that the EBSD analysis is a very effective technique analyzing dimensional and crystallographic fabrics of deformed iron ores.
