LAUSR

Abstract The Jia'erbasidao deposit is a Fe skarn deposit discovered in the South Altay, Northwest China. Fe orebodies occur at the contact zone between the biotite monzogranite of Keziergui intrusion and marble of Altay Formation. The petrography of Keziergui intrusion mainly composes of granodiorite, tonalite, and porphyritic biotite monzogranite. Zircon U Pb dating indicates that the granodiorite and porphyritic biotite monzogranite formed in 389.8 Ma and 276.1 Ma, respectively. The granodiorite and tonalite spatially show a gradual contact relationship, they are weakly peraluminous, enriched in light rare earth elements (LREE), and depleted in high field strength elements (HFSE). These samples yield moderate Mg# values (33–39), and show negative to positive but near-zero eNd(t) values (−1.0 to +0.5). In addition, granodiorite displays variable positive eHf(t) values (mainly from +3.21 to +8.84), and show clear negative Eu anomalies (δEu = 0.39–0.52) and low Zr/Hf ratios (whole rocks: 30–32; zircons: 37–42). The granodiorite and tonalite are both I-type granites, and granodiorite underwent moderately fractionated. They are most likely derived from the partial melting of mantle components and mixed with some lower crust. In comparison, the porphyritic biotite monzogranite has geochemical characteristics of moderately fractionated I-type granites, which have relatively low Zr + Nb + Y + Ce (310–377 ppm) and 10,000*Ga/Al (2.6–2.7) values in whole rocks, and Zr/Hf ratios in whole rocks (33–35) and zircons (39–51). The porphyritic biotite monzogranite yields low Mg# values (17–22), and shows positive but near-zero eNd(t) values (+0.5 to +1.2) and variable positive eHf(t) values (+5.49 to +10.97). The geochemical characteristics of the porphyritic biotite monzogranite indicate that it was mainly sourced from partial melting of mantle materials and less significant mixing with ancient lower crust. Zircon grains of the granodiorite show variable Ce4+/Ce3+ ratios (103–350, avg. 259), which are consistent with related values from Fe-enriched magmas (moderate- to high- oxygen fugacity). Based on a comprehensive analysis of geochronological, geochemical, and Sr-Nd-Hf isotopic data of intrusions in Chinese Altay, we consider that Early Devonian intrusions formed in a continental arc setting, while Early Permian intrusions formed in an extensional environment influenced by a post-collisional setting. Finally, the Early Devonian magmatism is benefit for forming significant Fe skarn in Chinese AOB based on the researches of magma properties, magma sources, and tectonic setting.