New constraints on genesis of the Jiudian gold deposit, Jiaodong Peninsula, Eastern North China Craton: Evidence from monazite u-pb dating and H-O-S-Pb-He-Ar isotopes

Numerous large to giant-size gold deposits cluster in the northern and central part of the Zhao-Ping fault zone, forming a world-class gold metallogenic belt (∼1500 t Au). By contrast, only small to medium-sized gold deposits are present in the southern segment, and their genesis remains unclear, making it challenging to investigate potential relationships among the gold mineralization systems along the Zhao-Ping belt. This contribution presents integrated geochronological and isotopic studies on the Jiudian Au deposit, the largest one (∼30 t Au) in the southern Zhao-Ping belt, to address above issues. The Jiudian gold deposit comprises quartz-sulfide veins that are hosted in Linglong suites which are intruded into Paleoproterozoic Jingshan Group. The gold mineralizations exhibits a five-phase paragenetic sequence: (I) sericitization-pyritization-sillification-potassic alteration, (II) quartz veins with coarse-grained pyrite, (III) quartz veins containing fine-grained pyrite, (IV) polymetallic sulfide-quartz veins, and (V) late-stage carbonate-quartz veinlets with minor pyrite, with stages II, III, and IV being main ore stage. Monazite has been identified in stage III, where it is found enclosing pyrite and quartz grains along with primary fluid inclusions. These observations coupled with low Y, U, and Th contents, elevated REE contents, as well as pronounced LREE/HREE fractionation of monazites demonstrate they may co-precipitate with gold mineralization from ore-forming fluids. In situ monazite U-Pb geochronology precisely constrains the Jiudian Au mineralization at 116 ± 3 Ma (2σ), coinciding with the main stage of Au mineralization and wide-spread mantle-derived magmas in the Zhao-Ping belt, but significantly post-dating metamorphism of the Jingshan group (∼1.8 Ga) and intrusion of the crust-derived Linglong suite (∼160 to 152 Ma). Auriferous quartz oxygen and enclosed fluid inclusions hydrogen isotope are 9.4 to 12.0 and −88.3 to −79.2‰, respectively. Pyrites from main ore stage show consistent δ 34 S CDT values (2.9 to 9.6‰) and Pb isotopic compositions ( 206 Pb/ 204 Pb of 17.022–17.579, 207 Pb/ 204 Pb of 15.543–15.550, and 208 Pb/ 204 Pb of 38.548–38.088). Fluid inclusions extracted from these pyrites show high 3 He/ 4 He ratios (1.10 − 1.33 Ra) and 36 Ar/ 40 Ar (1053 to 2293). The present study, by integrating geochronological and geochemical results, indicates that the ore-forming fluids and metals had primarily derived from deep-seated subduction modified mantle-derived magmas under the context of the North China Craton destruction. The similarities of formation ages, mineral assemblages, and geochemical characteristics between the Jiudian Au deposit and equivalents in the northern and central Zhao-Ping belt reveal a consistent gold mineralization event. Additional implication of present study is emphasizing a critical role of magmatism in the lode gold mineralization.