Ore-forming age and mineralization mechanism of the Biyushan submarine volcanic-hosted iron deposit in the Beishan orogenic belt: insights from zircon U-Pb dating, Hf isotopes, and magnetite texture and chemistry

In the Late Paleozoic, subduction-accretion processes in the Beishan and Tianshan orogenic belts of the Central Asian Orogenic Belt led to significant submarine volcanic-hosted iron mineralization. The origins of these deposits remain debated, with proposed models involving magmatic and magmatic-hydrothermal processes. This study examines the Biyushan iron deposit in the Beishan orogenic belt to investigate its metallogenic characteristics and its spatial–temporal connection with the Tianshan belt during Late Paleozoic iron (and copper) mineralization. Zircon U-Pb dating and Hf isotopic analysis of ore-hosting volcanic-subvolcanic rocks were conducted using LA-ICP-MS to determine the time of mineralization and the sources of materials. The formation ages of the mineralized host rock, propylitized plagioclase rhyolite, and the post-mineralization propylitized plagioclase rhyolite are 324.1 ± 0.95 Ma and 317.2 ± 1.2 Ma, respectively. Their respective zircon εHf(t) values range from 4.62 to 7.69 and −0.99 to 7.90. This indicates that the parental magma was likely derived from partial melting of either the depleted mantle or juvenile lower crust. In-situ LA-ICP-MS analysis of Biyushan magnetite from mineralization Stages I and II reveals high and widely varying Ti and V concentrations, indicating formation through magmatic and hydrothermal processes. These involved multiple medium- to high-temperature phases with significant fluid-rock interaction. Subsequent magnetite transformation occurred via fluid-induced dissolution-reprecipitation, oxidation-exsolution, dissolution reequilibration, and later hydrothermal metasomatism and alteration. A comparison of the Beishan and Tianshan metallogenic belts reveals shared geological settings, formation ages, and tectonic evolution. The Biyushan iron deposit is classified as a submarine volcanic-hosted iron deposit, formed in a southward subduction magmatic arc setting during the Late Carboniferous