Formation Age and Tectonic Setting of Iron-Bearing Formation in Huai'an Complex, North China Craton

Tian Hui; Zhang Jiahui; Wang Huichu; Ren Yunwei; Wang Quan

Abstract：Iron-bearing formations (BIFs) in lumpy, lenticular or stratified forms frequently occur in the Huaian Complex, North China Craton.Compared with BIFs in greenstone belts on North China Craton, the iron-bearing formation with characteristics of small scale, complicated lithology, and high-grade metamorphism-deformation in the study area has rarely been studied.Petrology, geochronology and geochemical studies on the basis of field survey have been conducted, and it is concluded: (1) The iron-bearing formations in Tianzhen-Huaian area are comprised of banded (perilla/amphibole) magnetic quartzite, metamorphic basic volcanic rock (two-pyroxene granulite/plagioclase amphibolites/high-pressure granulite) , garnetbiotite-plagiogneiss, and a few garnet-quartzite strips or lumps, and these rocks are intercalated or symbiotic with each other.Characteristics of being small in scale, closely symbiotic with metamorphic volcanic rocks suggesting BIF ore in TianzhenHuaian area belongs to Algoma type. (2) The age (2 489±19Ma) of residual intermediate-basic igneous zircons in banded (perilla/amphibole) magnetic quartzite may represent the formation age of the BIFs in Tianzhen-Huaian area, which afterwards underwent the 1 800-1 850Ma metamorphism. (3) The geochemical characteristics of metamorphic volcanic rocks of iron-bearing formations show enrichment in elements Rb, Ba, U, Pb, and depletion in elements Nb and Ta.It is concluded the iron-bearing formations are closely related to seabed hydrothermal activity formed in back-arc basin according to the patterns of trace elements and rare earth distribution of metamorphic volcanic rocks and positive anomality of Eu in PAAS normalized rare earth elements distribution pattern of iron ore.