Genesis of the Erik Iron Ore Deposit in the Taxkorgan Area of the West Kunlun, Xinjiang: Constraints from Ore Deposit Geology and In Situ LA-ICP-MS Analysis of Magnetite

The Erik iron deposit is one of the biggest deposits in the Taxkorgan iron deposit belt in Xinjiang, an important high-grade one recently discovered in West China, which has been rarely studied. To identify the genesis of the Erik iron deposit, ore deposit geology survey and in situ LA-ICP-MS analysis of magnetite have been conducted in this study. It is found that mineralization occurs at the Bulunkuole meta-volcano-sedimentary sucession. Ore occurrences are basically coordinated with those of host rocks, and exhibit obviously stratabound characteristics. Two main mineral associations of magnetite+anhydrite and magnetite+calcite in variable proportions commonly occurred in the high-grade iron bodies and formed dense disseminations and massive ores. Both magnetite grains from these two associations show constant contents of many elements including Mg (119×10-6-313×10-6), Al (692×10-6-1 034×10-6), Ti (540×10-6-840×10-6), V (3 340×10-6-3 971×10-6), Mn (950×10-6-1 160×10-6), Co (4×10-6-5×10-6), Ni (52×10-6-64×10-6), Zn (84×10-6-143×10-6), and Ga (26×10-6-31×10-6) and similar to those of in high-temperature hydrothermal environment. It is interpreted that the high Al, Ti, V contents, with high Ni/Cr and low Ti/V ratios in magnetites result from relatively reduced, Al-Ti-rich seafloor hydrothermal activities under a stable sedimentary environment. The (Al+Mn)-(Ti+V) feature of the Erik magnetites implies a high-temperature crystallization (300-500 ℃). The magnetites coexisting with anhydrite have higher Ti (690×10-6), P (27×10-6) concentrations in average, and lower Ca (36×10-6) than those coexisting with calcites (Ti=574×10-6, P=7×10-6, Ca=203×10-6). Moreover, the former are more depleted in high field strength elements of Zr, Hf, Sc, Ta, suggestting them have suffered more severely hydrothermal activities and Ca contents in magnetites are reduced with Ca2+ entering into crystal lattice of anhydrites. Integrating obtained evidences, including regional geology, ore deposit geology, magnetite composition, and we conclude that the Erik iron deposit was formed from an Early Cambrian seafloor high-temprature hydrothermal system. The development of the Erik iron deposit is related with a volcanic arc caused by southward subduction of Proto-Tethyan Plate. The Erik iron deposit is classified into a marine volcanic-sedimentary hosted Fe oxide deposit formed at or near the seafloor in submarine volcanic settings. © 2018, Editorial Department of Earth Science. All right reserved.