Genesis of the Hanwang Fe deposit in Neoarchean granite-greenstone succession of the eastern North China Craton

Abstract

Research on history of the Earth’s continents and the genesis of mineral deposits has been one of the hotspots in geology. But only limited studies have been completed on iron deposits hosted by banded iron-formations (BIFs), such as the large Hanwang iron deposit located in the eastern North China Craton (NCC). In this contribution, we present the petrology, zircon U–Pb geochronology, Lu–Hf isotopes and whole-rock geochemistry on Hanwang iron deposit hosted by the metamorphosed Neoarchean to early Paleoproterozoic Taishan Group and orthogneiss derived from tonalite–trondhjemite–granodiorite (TTGs). Magnetite-bearing amphibolite, magnetite-bearing quartz amphibolite, and gneiss host the Hanwang iron deposit, which is characterised by subhedral to euhedral magnetite, pyrite with minor galena and BIF laminations. Gangue minerals include hornblende, plagioclase and quartz with minor amounts of biotite, chlorite, epidote and microcline. This mineral assemblage is indicative of amphibolite-facies metamorphism with regression to greenschist-facies. The deposit is located in a transition zone between metamorphosed mafic to felsic volcanic rocks. The age of the Hanwang BIF-hosted iron deposit is late Neoarchean. Lu–Hf isotope systematics indicate that the protolith for the biotite amphibolite is derived from a Neoarchean mantle contaminated by the crust, and orthogneiss is derived from the Neoarchean crust. The biotite amphibolite is characterised by high Na, Fe and low K assays, enrichment in light rare earth elements (LREE), and relatively depletion in heavy REEs (HREE) without an obvious Ce anomaly. The geochemistry of the orthogneiss is characteristic of a volcanic–arc granite, although this must be accepted with caution given that the orthogneiss is metamorphosed and deformed at amphibolite-facies.It is proposed that Hanwang iron deposit was deposited in a marine volcanic–arc environment and derived from hydrothermally leached volcanic units, and similar to the Algoma-type iron deposit. Most BIFs occurring in Neoarchean granite-greenstone succession of the eastern NCC belong to the Algoma-type iron deposits. Globally, this sequence appears to be coeval with the Yilgarn Craton in Western Australia.