The Dongjun Pb-Zn-Ag deposit in the northern part of the Great Xing'an Range (NE China) consists of quartzsulfide vein-type and breccia-type mineralization, related to granite porphyry. Hydrothermal alteration is well-developed and includes potassic-silicic-sericitic alteration, phyllic alteration and propylitic alteration. Three stages of mineralization are recognized on the basis of field evidence and petrographic observation, demarcated by assemblages of quartz-pyritearsenopyrite (early stage), quartz-polymetallic sulfide (intermediate stage) and quartz-carbonate-pyrite (late stage). Zircon LA-ICP-MS U-Pb dating indicates that the granite porphyry was emplaced at 146.7 ± 1.2 Ma (Late Jurassic). Microthermometry and laser Raman spectroscopy shows that ore minerals were deposited in conditions of intermediate temperatures (175-359°C), low salinity (0.5-9.3 wt% NaCl eqv.) and low density (0.60-0.91 g/cm 3 ). Ore-forming fluids were derived largely from magmatic hydrothermal processes, with late-stage addition of meteoric water, belonging to a H 2 O -NaCl-CO 2 ± CH 4 system. The δ 34 S V-CDT values range from 0.75‰ to 4.

In the northern and central Great Xing'an Range, there exist widespread Late Mesozoic volcanic rocks, of which the petrogenesis and geodynamic setting remain controversial. These rocks are composed of andesite, trachyandesite, basaltic andesite, and rhyolite. This study presents new data of zircon U-Pb dating, Hf isotopic composition, and whole-rock geochemistry of the Late Jurassic intermediate-mafic volcanic rocks within the northern Great Xing'an Range. In addition, the geochronological and geochemical data for the Late Mesozoic intermediate-mafic rocks within the northern and central Great Xing'an Range are summarized for constraining the geochronological framework, petrogenesis, and geodynamic setting of the large-scale Late Mesozoic volcanism in this region. The intermediate-mafic volcanic rocks are enriched in large-ion lithophiles and light rare earth elements and are depleted in high-fieldstrength elements such as Nb, Ta, and Ti, with positive ε Hf (t) values (+0.7 to +15.4). The data indicate that the volcanic rocks were derived from the partial melting of a mantle wedge that was modified by previously subducted slab-derived fluids. These Late Mesozoic intermediate-mafic volcanic rocks record a post-collisional lithospheric extensional setting resulting from the closure of the Mongol-Okhotsk Ocean.

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