Geological characteristics and zircon U-Pb age of the Wudaoyangcha Neoarchaean vanadic titanomagnetite deposit in Baishan, Jilin Province

Located in Baishan City of southern Jilin Province, the Wudaoyangcha vanadic titanomagnetite deposit is a large- size magma type iron deposit lying in amphibolite layered intrusions in Archaean strata, founded for the first time in the world. The discovery of the deposit has important implications for mineral resource exploration in areas with similar geological conditions. The deposit is located in northern Banshigou greenstone belt on the southern margin of Longgang paleo-continental nucleus of the Liao- Ji paleocontinent. No. Ⅰ, Ⅱ and Ⅵ orebodies lie in Wudaoyangcha amphibolite layered intrusions, and vanadic titanomagnetite mineralization is closely related to the layered intrusions. The protolith of the layered intrusions belongs to orthometamorphite, and its tectonic environment belongs to the island arc basalts in the convergent margin of the plate. Orebodies are mainly in layered form. Ore textures include mainly crystallization texture, solid solution separation texture and sideronitic texture. Ore structures are dominated by massive structure, disseminated structure, spongy- meteoritic structure and layered structure. Magnetite- ilmenitepyrite makes up most metallic mineral association of the ore. The magnetite and ilmenite of the vanadic titanomagnetite ore was investigated by means of EPMA. The magnetite is genetically magmatic liquation titanomagnetite. The chemical composition of the ilmenite is generally consistent with the theoretical constituents of ilmenite. The authors carried out U-Pb dating and micro-scale in situ trace elements and REE research on zircons separated from the Wudaoyangcha amphibolite layered intrusions. The characteristics of trace elements and REE show that these zircons are magmatic zircons. Zircon LA-ICP-MS U-Pb dating yielded a discordant age, with the discordant upper intercept age for 28 spots of sample WCD1 being (2 526±35) Ma. This age represents the crystallization age of layered intrusions.