Geochronology And Genesis Of The Tieshanmiao BIF-Hosted Iron Deposit,Wuyang Area

The Wuyang Tieshanmiao area located in the south margin of the North China Craton is a typical BIF-hosted Fe deposit.This study focuses on studies of the Tieshanmiao Fe deposit.Based on the detailed field geological survey,mineralography,petrographical,geochemical,geochronological,and Lu-Hf isotopic data,material source,metallogenic age and genesis of the Tieshanmiao Fe deposit are discussed.Major achievements of this research are as follows:(1)The Tieshanmiao Fe deposit is hosted in the Neoarchean metamorphic rocks of the Tieshanmiao Formation.Orebody is layered and lenticular.There are two ore types,including massive pyroxene magnetite and banded quartz pyroxene magnetite.(2)REE distribution curves of the wall rocks are characterized by La/La*positive anomaly(0.91-2.31),Ce weak negative anomaly(Ce/Ce* = 0.87-10.94),Eu positive anomaly(Eu/Eu* =0.81-1.65),indicating that the mainly sourced from mixed volcanic hydrothermal fluid and seawater.The deposit is formed in anoxic environment as product of the Precambrian marine chemical deposition.(3)LA-ICP-MS zircon U-Pb geochronological analysis of the wall rocks in the Tieshanmiao Fe deposit shows that the inherited zircon,magmatic crystallization,and metamorphic ages of the garnet-bearing biotite-plagioclase gneiss with 2736 ± 23 Ma,2363 ± 23 Ma,and 2220 ± 70 Ma.The crystallization and metamorphic ages of the plagioclase gneiss are 2406 ± 24 Ma and 2073 ± 60 Ma.On the basis of analysis of the two samples' ages,the metallogenic age of this deposit ranges from 2406 to 2363 Ma,and the metamorphic events are between 2073 and 2220 Ma.(4)Zircon Lu-Hf isotopic results show that the garnet-bearing biotite-bearing plagioclase gneiss and plagioclase gneiss are derived from the melting of ancient crustal materials contaminated by depleted mantle.(5)The Tieshanmiao Fe deposit is volcanic sedimentary-metamorphic iron deposit and belongs to the Algoma-type.