Geological Characteristics, Metallogenic Epoch Of The Zhaoanzhuang Iron Deposit In Wuyang Area Of Henan Province，and Their Implication For Genesis

Wuyang area of Henan province is located in the southern margin of the NorthChina plate, and this area is the mainly producing area of iron ore of Henan province.Identified reserves of iron ore accounted for46%of the total. There is two types ofiron ore deposit: such as the type of BIF iron deposit existed in Tieshanmiao group ofProterozoic era and the type of late magmatic iron deposit which is related toultrabasic rock store in Zhaoanzhuang formation in Archaeozoic era.The super basic intrusion which is related to metallization and layered like andlenticular intrude into the diopside-hornblende plagioclase gneiss in Zhaoanzhuanggroup, and it mainly contain three types of rock as olive, pyroxenite and hornblenderocks. Zhaoanzhuang iron deposit is slowly inclined blind deposit and formed at thebottom of ultrabasic rocks. The orebody sharp is basically consistent with the basicrock mass, and the thickness of the orebody is positively correlated with rock mass.Microscopic features of the orebody shows typical sideronitic texture. Due to themetamorphism of late magmatism, olivine has been occurrence of serpentinization.All of the above features indicate that the deposit is a late magmatic ore deposit.The ore composition of the Zhaoanzhuang ore iron deposit is mainly magnetite. There are a large number of apatite and a little of ilmenite, retile and zircon which aresymbiosis with magnetite, beside serpentine. The data of EMPA show that thecomposition of magnetite are greater different from the area’s of Damiao of Hebeiprovince. In this deposit, the oxide contents are less than1%and are pure, besideFeOT.Veined diopsidite in the late period of evolution of the ultrabasic rock cut the ironore deposit of BIF type of Tieshanmiao group and the marble, beside the ultrabasicrock which are stratiform-like in early evolution intrude into the gneiss ofZhaoanzhuang group. It shows they are comagmatic evolution that the trace elementanalysis of pyroxenite who cut the BIF and the Zhaoanzhuang iron ore body. Theanalysis of trace elements show that they have the negative correlation of P, Ti andother elements. The characteristic of distribution of element can be explained by themacro-vice-mineral content. There are a large number of apatite and magnetite, so thechemistry result show the content of P, Ti and other elements positive anomaly. Alarge number of apatite and ilmenite are crystallization differentiation during earlystage of magmatic evolution. Pyroxenite are the result of late magma fractional, so thecontent of P, Ti are low.Zircon which are gaind from serpentine-magnetite are determined byLA-MC-ICP-MS. Through the analysis of zircon CL images, the zircons suffer fromthe late metamorphism. It upper intercept age of1943±5Ma imply metamorphic age.The age is the upper limit of the ore deposit formation age. Diopsidite vein which arelate differentiation by ore body intrusion cut the BIF iron ore deposit of Tieshanmiaogroup. Palaeoproterozoic erawhen Tieshanmiao group have been formation in can bethe lower limit of the formation age of ore body. So the deposit has been formationduring1943Ma–2500Ma.Through studying the factors of ore-forming material sources, metallogenicdynamics, metallogenic characteristics and metallogenic epoch, we suggest ametallogenic model. Zhaoanzhuang iron ore deposit which has been stored inultrabasic rock in Palaeoproterozoic era is a late fractional crystallization magmaticdeposit. It is known as the oldest magmatic iron deposit in China.