Dating and geochemical constraints on the origin and regional exploration of the Dayinshan deposit, east China

• First report of garnet U–Pb age (137.2 ± 3.3 Ma) representing the mineralization timing of the Dayinshan mining district. • Integrated geochronologic and geochemical data affirm the deposit’s affiliation with the Middle-Lower Yangtze River Belt and define its transitional southeastern margin. • A novel exploration indicator is proposed: >135 Ma intrusions with ΔFMQ ≈ +1.34, guiding future targeting in the region. The Dayinshan porphyry–skarn gold-polymetallic deposit, located within the Northern Zhejiang Metallogenic District, is situated at the tectonic junction between the Middle-lower Yangtze River metallogenic belt (MLYB) and the Qin-Hang metallogenic belt (Q-HB). However, the metallogenic age, genetic mechanism, and regional tectonic significance of this deposit are still poorly constrained. Based on detailed field investigations, this study conducted U–Pb dating of zircon and garnet from drill core ZKH101, combined with in situ trace element analyses of pyrite, zircon, and garnet, together with whole-rock major and trace element geochemical analyses and Isocon-based mass balance calculations on altered rocks. The results reveal two magmatic episodes at 144–136 Ma and 133–129 Ma, with the mineralization age constrained to ∼ 137 Ma, consistent with the Early Cretaceous Cu–Au metallogenic event in the MLYB. The geochemical characteristics of the mineralized intrusions are transitional between normal arc rocks and adakitic rocks, formed in a setting of partial melting of a thickened lower crust. This indicates thatthe Dayinshan deposit shows a closer affinity to the MLYB than to the Q-HB, and should be regarded as part of the transitional zone at the southeastern margin of the MLYB. Isocon analysis further reveals significant mobilization and re-enrichment of ore-forming elements in the alteration system: strong influx of Mo (mass gain up to + 872.38 %) in the potassic zone, and systematic enrichment of ore-forming elements in the sericitic + propylitic alteration zones, indicating a typical porphyry–skarn mineralization mechanism. Future exploration should focus on intrusions older than 135 Ma with ΔFMQ > +1 in the mining area and the southern volcanic-covered region.