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Mercury (Hg) isotopes display unique mass-independent isotope fractionation (MIF, reported as Δ199Hg), which is primarily generated via Hg photochemical processes in the land-ocean-atmosphere system. Magmatic and hydrothermal processes do not trigger MIF of Hg isotopes, therefore, Hg-MIF signals detected in deep reservoirs (mantle and crust) are theoretically sourced from recycled surface materials. Here, we observed positive Δ199Hg signals (0.10 ± 0.07‰, SD) in Mesozoic porphyry Mo deposits of NE China. These values correspond to the recently reported Δ199Hg signature of Mesozoic epithermal Au Ag systems in NE China (Δ199Hg: 0.11 ± 0.07‰, SD), suggesting that both mineral systems receive large amounts of Hg from subducted marine materials, given that marine Hg has positive Δ199Hg composition. Our study thus provides novel geochemical evidence on the linkage between oceanic plate subduction and metallogeny of various hydrothermal systems at convergent margins. Subduction contributes large amounts of volatiles to arc magmas, which then release metal-rich magmatic-hydrothermal fluids of the porphyry to epithermal ore deposit spectrum. [ABSTRACT FROM AUTHOR]

• A Late Jurassic porphyry Cu-Mo deposit in the Erguna Block is reported. • Ore-bearing rocks were derived from the partial melting of the oceanic slab. • Petrogenesis of ore-related rocks related to a flat-slab subduction. The genesis of igneous rocks associated with the newly discovered Xiaokele porphyry Cu-Mo deposit, located in the eastern Erguna Block, NE China, can give insights into the regional geodynamic evolution during the Late Mesozoic. Several ore-bodies have been identified in a granodiorite porphyry stock, which intruded the rhyolite and was subsequently intruded by diorite porphyry and granite porphyry. The U–Pb ages of zircons from rhyolite, mineralized granodiorite porphyry, diorite porphyry and granite porphyry associated with the Xiaokele deposit are 152.5 ± 1.7, 150.0 ± 1.6, 147.9 ± 1.3, and 123.2 ± 1.7 Ma, respectively. The rhyolite and granite porphyry have high SiO 2 and low MgO, Cr, Co, and Ni contents. Their isotopic data show negative ε Nd (t) values of −4.76 to −0.87, initial 87Sr/86Sr ratios of 0.7066 to 0.7134 and positive zircon ε Hf (t) values of 0.33–5.56, indicating that they were derived from a basaltic lower continental crust. The mineralized granodiorite porphyry is characterized by high Sr/Y values and low Y (3.7–8.0) contents, showing adakite affinity. The low K 2 O/Na 2 O (0.51–0.7) ratios, high CaO contents, weakly negative ε Nd (t) (−1.17 to −0.27), and low zircon ε Hf (t) (1.49–5.4) values from the adakitic samples indicate that they were derived from the partial melting of an altered oceanic slab together with assimilation of mantle peridotite and crustal materials. The 148 Ma diorite porphyry has high Mg# (51–58), weakly negative and positive ε Nd (t) (−0.09 to 0.01) values, and lower (87Sr/86Sr) i (0.7055–0.7057) ratios, suggesting an enriched mantle wedge source. Considering the late Mesozoic regional tectonic evolution of the Erguna Block and adjacent area, we propose that the formation of the Xiaokele deposit is linked to the southward flat-slab subduction of the Mongol–Okhotsk oceanic plate during the Later Jurassic-Early Cretaceous. [ABSTRACT FROM AUTHOR]

Abstract Multistage igneous rocks identified in the newly discovered Fukeshan porphyry Cu Mo deposit, NE China give new insights into the late-stage southwards subduction of the Mongol-Okhotsk oceanic slab (MOOS) and Cu Mo mineralization during the late Mesozoic. The U Pb ages of zircons from medium-grained monzogranite, coarse-grained monzogranite, ore-related quartz diorite porphyry, quartz monzonite, ganodiorite porphyry, diorite porphyry and andesitic porphyry associated with the Fukeshan deposit are 192.7 ± 1.9, 192.2 ± 2.7, 148.7 ± 0.8, 148.8 ± 0.9, 144.1 ± 1.1, 144.9 ± 0.9, and 144.8 ± 1.3 Ma, respectively. The Early Jurassic coarse-grained monzogranite, Late Jurassic quartz monzonite and quartz diorite porphyry, and Early Cretaceous granodiorite porphyry are characterized by low Yb and Y contents, and high Sr/Y ratios, indicating adakite affinities. The whole-rock geochemistry, and Sr Nd and zircon Hf isotopic features of the coarse-grained monzogranite and granodiorite porphyry indicate they were derived from the partial melting of a thickened basaltic lower crust. On the other hand, the quartz monzonite and quartz diorite porphyry probably originated from the melting of oceanic crust together with assimilation of enriched mantle and continental crust. The medium-grained monzogranites were possibly derived from a basaltic lower crust at shallower depths, and the diorite porphyry and andesitic porphyry probably originated from a metasomatized mantle source. Considering the Early Jurassic–Early Cretaceous magmatism and regional tectonic evolution of the Erguna Block, we propose that the MOOS was subducted towards the south during the Early Jurassic (195–170 Ma), slab retreat occurred during the early Late Jurassic (165–155 Ma), oceanic ridge subduction took place during the Late Jurassic (150–147 Ma). The final closure of the Mongol-Okhotsk Ocean occurred during the Early Cretaceous (145–143 Ma). The southwards subduction of a ridge on the MOOS provided a favorable tectonic setting for Cu Mo mineralization, and this is accordance with the discovery of many Late Jurassic–Early Cretaceous porphyry Cu Mo deposits in the eastern part of the Erguna Block. Highlights • Multiple episodes of magmatism during Mesozoic indicated by zircon geochronology • The rocks show different sources: oceanic slab, lower crust and enriched mantle. • The slab-derived rocks indicate a Late Jurassic ridge subduction of the MOOS. • The ridge subduction dominated the generation of porphyry Cu Mo deposits. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spatial differences of Cu and Mo mineralization were observed. • Both Cu and Mo were extracted from a same magmatic source. • F and Cl variation in hydrothermal fluids causes the Cu and Mo separation. The Late Jurassic large Xiaokele porphyry Cu-Mo deposit is newly discovered in the northern Great Xing'an Range, NE China. Both Cu and Mo mineralizations have occurred in the potassic stage and are present in the potassic zone, but only Mo (Cu negligible) mineralization has been developed in the phyllic stage and is present in the phyllic zone. The cause for such temporal and spatial difference of Cu and Mo mineralization at Xiaokele remains unclear. In this study, biotite major element compositions were studied to reveal the magmatic-hydrothermal processes, and the temporal and spatial difference of Cu and Mo mineralization at Xiaokele. Biotite geochemical data show that the magmatic biotites (Bi-I), and the potassic-stage (Bi-II) and phyllic-stage (Bi-III) hydrothermal biotite are Mg-biotites, and that mineralization at Xiaokele occurred under 52–86 MPa (equivalent to 1.95–3.32 km depth). Calculated oxygen fugacity of Bi-I, Bi-II, and Bi-III biotites are all above nickel-nickel oxide (NNO) oxygen buffer, suggesting that these biotites were formed under oxidizing conditions. The decreasing Cl and largely constant F content from Bi-I, Bi-II to Bi-III result in an increasing trend of IV(F/Cl), indicating different elemental behavior between F and Cl during the magmatic-hydrothermal fluid evolution. Given that Cl content is a key Cu-transporting ligand in porphyry type mineral systems, the decreasing Cl content in Bi-III indicates lower Cu transporting capacity in the phyllic stage, resulting in the negligible Cu mineralization in the phyllic zone. Since F is important for Mo transport in hydrothermal systems, we conclude that the constant F content reflects stable Mo transporting capacity in the fluids, resulting in significant Mo mineralization in both the potassic and phyllic zones. Our results show that biotite geochemistry can be used to explain the temporal and spatial distribution of Cu and Mo mineralization in porphyry Cu-Mo systems. [ABSTRACT FROM AUTHOR]