Characteristics And Genesis Of Nanminghe Iron Deposit In Wuan,Hebei Province

HanXing-type iron deposit,located in Wuan city of southern Hebei province,is one of the most important large-scale iron ore concentration areas which is characterized by its large reserve and high-grade ores.A lot of research about the genesis of Hanxing-type deposit has been done in this area,but controversy also reminds.The mainstream viewpoint ascribed the formation of the deposit to contact metasomatism,while others attributed it to hydrothermal process.Concerning the different understanding about HanXing-type iron deposit,we focus our research on Nanminghe iron deposit in this area to make clear its texture and structure characteristics and the genesis of HanXing-type iron deposit,and to provide theoretical instructions for the future prospecting in the area.The Carbonates of middle Ordovician Majiagou deformation is the main strata in the Nanminghe iron ore district,The iron ore bodies yield in the contact zone between the carbonate rocks and diorite intrusions mainly,but some of them are found in carbonate rocks and the cracks of intrusions in the shape of veins.The intrusions related to the iron ore mineralization includes Fushan complex cock,Wuan complex rock and Hongshan complex rock,and belong to mafic-neutral alkaline intrusive complex bodies.Through the study of the Nanminghe deposit,We can discover obvious and straight boundaries between ore bodies and magma,the harbor-like structure and flow structure on the surface of the iron ore body occasionally.The iron ore in Nanminghe deposit shows euhedral-subhedral structure under the microscope,and the crystallization characteristics are obvious,So it can be testified preliminary of magmatic relating genesis by these phenomena above.Under the polarizing microscope,It shows that the andradite garnet and magnetite ore coexiste,and the garnet crystallographic particles and the zonal struture are well developed.The result of major elements of electron microprobe analysis shows that there is some regular changes from the center to the edge in the garnet ring.It shows a relatively small difference(<0.2%)in CaO contents,but a considerable large range of variation(mostly>1%)in A1203 and FeO with a negative correlation.The phenomenon above is caused by the chemical oscillation of the ring belt in the garnet during the magmatic crystallizing process.From the features described above,we can draw conclusion that the formation of garnet is related to the crystallization of magma.The center part of garnet ring is characterized by high LREE,low HREE,positive Eu anomalies distribution patterns,positive Eu anomalies distribution patterns.This kind garnet is usually regarded as iron-rich andradite,with similar REE patterns to intrusive rock,and indicated the magmatic origin of Nanminghe ore deposit.