Genesis of the Bailingshan Iron Deposit in Eastern Tianshan, NW China: Constraints From Geology, Geochemistry and Isotopic Compositions

Abstract

The Bailingshan deposit is located in the Yamansu arc in eastern Tianshan, NW China. As an economically significant iron deposit in the region, Bailingshan is spatially and temporally associated with volcanism and is hosted in the submarine volcanic and volcaniclastic rocks of the Middle Carboniferous Matoutan Formation, suggesting a potential genetic relationship. The trace element compositions of the major ore mineral (magnetite) from iron ores show lower Ga (1.99–10.80 ppm), Zn (10.0–42.8 ppm), V (9.8–17.3 ppm), Ti (21.2–77.8 ppm) and Cr (10.6–31.3 ppm), but higher Ni (21.0–92.8) and Ni/Cr (1.39–5.89). Together with an evaluation of the morphology of orebody, ore fabrics and petrology, we correlate the iron mineralisation at the Bailingshan area with the hydrothermal process. The δ¹⁸O values of magnetite span from −1.5‰ to 3.5‰, while the δ³⁴S values of pyrite sulphides range from 1.7‰ to 7.6‰, demonstrating a wide variation, which suggests that the source components of the ore-forming materials originated from a mixture of magma and seawater. In addition, the Pb isotopic compositions of pyrite are similar to those of igneous rocks (e.g., dacitic tuff and granodiorite) at Bailingshan, suggesting a common Pb isotope origin. Based on the results of this study, it is proposed that primary magmatic-hydrothermal fluids, which interacted with infiltrating seawater, played a crucial role in the significant iron mineralisation observed at Balingshan.