An Erratum to this paper has been published: https://doi.org/10.1134/S0016702925230016

The Aksu River region, located in East Kunlun, Xinjiang, is part of the Qin-Qi-Kun Orogenic System and the North Kunlun magmatic arc. The region hosts Late Triassic volcanic rocks of the Elashan Formation, primarily composed of andesite, dacite, and rhyolite. Geochemical analyses of these volcanic rocks are essential to deciphering the tectonic evolution of the region. This study investigates the geological characteristics, petrology, and geochemistry of the Elashan Formation to elucidate its tectonic setting and significance. The rocks display SiO ₂ contents of 53.65–76.16%, total alkali contents of 4.77–6.05%, Rittmann index values of 0.86–3.2, and aluminum saturation indices (ASI) of 1.39–1.84, classifying them as predominantly calc-alkaline, ranging from metaluminous to peraluminous, and intermediate to acidic in composition. The total rare earth element (REE) content ranges from 101.05 to 215.77 ppm, with light-to-heavy REE ratios of 6.44–19.24, indicating significant REE fractionation and light REE enrichment (δEu = 0.53–1.05). The REE distribution patterns exhibit a rightward incline. Large-ion lithophile elements (LILEs) such as Rb, U, and K exhibit significant enrichment, while Nb, Ta, Sr, P, and Ti are relatively depleted, forming troughs in trace element distribution diagrams indicative of enrichment in strongly incompatible elements. Based on Rittmann, Pearce, and Harris diagrams, along with regional tectonic evolution and petrographic characteristics, the Elashan Formation volcanic rocks are interpreted to have formed in an active continental margin continental arc environment.

The North China Craton hosts abundant skarn iron resources, yet the regional large-scale mineralization mechanism remains incompletely understood. The Litun deposit is a newly discovered skarn iron deposit in the North China Craton. Integrated field geological investigations, petrographic observations, fluid inclusion microthermometry and stable isotope geochemistry are applied to constrain evaporite contributions to metallogenic processes. Four mineralization stages are identified: skarn, oxide, sulfide, and carbonate. Early skarn-stage fluids are iron-rich magmatic hydrothermal fluids with high temperatures (498 to >550 °C), high salinities (18.6 to 59.4 wt% NaCl eqv.), and magmatic δ¹⁸O values of 8.3 to 10.8‰. Subsequent oxide to late carbonate stages record continuous infiltration of meteoric water, supported by H–O isotopic trends of rising meteoric water proportions. Pyrite from the magnetite ores has δ³⁴S_V-CDT values between 12.0 and 15.0‰, significantly higher than those of pyrite in the Litun diorite (−0.8 to 1.1‰), indicating the contributions of sulfur from evaporites (δ³⁴S_V-CDT 26.9 to 28.6‰) in the mineralization process. Moreover, vein pyrite formed in later stages displays even higher δ³⁴S values (17.3 to 20.9‰), demonstrating progressive enrichment of evaporite-derived sulfur as hydrothermal activity evolves. Synchronous rises in meteoric water fraction and evaporite sulfur proportion indicate evaporites are delivered into the ore-forming system via meteoric water mixing. The mixing of meteoric water containing dissolved evaporites and iron-rich magmatic-hydrothermal fluids may be the major mechanism of magnetite precipitation in the Litun deposit.