Geochronological and petrochemical constraints on Paleoproterozoic granites in the Liaoshang gold deposit, Jiaodong Peninsula: Implications for geological setting and ore sources

Abstract

The Liaoshang gold deposit in the Jiaodong Peninsula is a tectonically controlled pyrite-carbonate vein-type system, genetically distinct from the Jiaojia-type altered rock-hosted and Linglong-type quartz-vein gold deposits in the region. Due to the considerable resource potential of Jiaodong gold deposits, extensive research has been conducted on their temporal and metal sources, yet the geological framework of individual mining districts such as the Liaoshang deposit remains poorly constrained. This study integrated petrography, geochemistry, and U − Pb geochronology of zircon, apatite and monazite from local granitiods to elucidate the tectonic history and mineralization processes. Two granite types were identified: plagioclase granites emplaced at 2.14–2.09 Ga, which underwent regional metamorphism at 1.98–1.83 Ga, and monzogranite dykes intruding the meta-sedimentary rocks of the Paleoproterozoic Jingshan Group crystallized at 1.85–1.84 Ga. Apatite from the dykes records a metamorphic age of 248 ± 15 Ma, indicating involvement in the Triassic Sulu ultrahigh-pressure orogeny. Hydrothermal monazite from the monzogranite yields a lower intercept U-Pb age of 140 ± 5.7 Ma, predating the main mineralization event at Liaoshang (∼116 Ma) and other Jiaodong deposits (∼120 Ma) by approximately 20  Ma. Petrographic and microstructural evidence further suggest an early hydrothermal event, implying that ore formation was a prolonged, multi-stage process lasting at least ∼ 20 Ma. Whole-rock geochemistry shows that, compared to those of weakly altered granites, mineralized plagioclase granites are significantly enriched in Ag, Pb, As, Te, Sb and Bi. These elements also correlate strongly with Au and total Fe₂O₃, indicating co-precipitation with polymetallic sulfides and native gold. In addition, As-rich zonation also exists in pyrite formed during the main mining period. Combined with the elevated arsenic content and the obvious Au − As correlation, these findings highlight the important contribution of Precambrian basement rocks, particularly the Jingshan Group metasediments, to the metal endowment of the Liaoshang gold system.