Geochemical characteristics of granites in the Suonaga Pb-Zn-Ag deposit of Dong Ujimqin Banner, Inner Mongolia, and their tectonic and ore-forming implications

Abstract：The ore-bearing pluton in the Suonaga Pb-Zn-Ag deposit is composed of medium-coarse-grained granite, fine-grained biotite granite and pseudoporphyritic K-feldspar granite. The zircon U-Pb dating results show that the medium-coarse-grained granite was formed at 319.6±4.1 Ma, the fine-grained biotite granite was formed at 172.5±1.4 Ma, and the pseudoporphyritic K-feldspar granite was formed at 165.5±1.8 Ma. The petrogeochemistry of the three rock bodies is characterized by high K, rich alkali and poor magnesium, so they all belong to calcium-basic, quasi-aluminous to weakly peraluminous and highly-differentiated rocks. All of the granites have high REE and negative Eu anomalies, exhibiting relative enrichment of LREE. These rock bodies belong to S-type granites, because they are enriched in U and Th and their Rb/Sr ratios are higher than those of the crustal source. Regional geology and granite geochemistry indicate that the medium-coarse-grained granite was formed in a post-collisional extensional environment in Late Carboniferous; the Middle Jurassic fine-grained biotite granite and pseudoporphyritic K-feldspar granite were formed in an intraplate extensional environment, and they were products of different evolutionary stages of a comagmatic region. The pseudoporphyritic K-feldspar granite was probably the ore-forming parent rock, because its diagenetic age is consistent with the molybdenite Re-Os ages (163.4±2.4Ma to 166.6±2.4Ma) and the rocks are enriched in metallogenic elements Pb and Zn.