Age and Tectonic Setting of Mesothermal Magmatic Hydrothermal Vein‐Type Pb–Zn–(Ag) Mineralization in the Xiaohongshilazi Deposit, Central Jilin Province, Northeast China

The Xiaohongshilazi deposit located in central Jilin Province, Northeast China, is a newly discovered and medium-scale Pb-Zn-(Ag) deposit with ore reserves of 34,968 t Pb, 100,150 t Zn, and 158 t Ag. Two-stage mineralization has been identified in this deposit. Stratiform volcanic-associated massive sulfide (VMS) Pb-Zn mineralization interbedding with the marine volcanic rocks of the Late Carboniferous-Early Permian Daheshen Formation was controlled by the premineralization E-W-trending faults. Vein-type Pb-Zn-(Ag) mineralization occurs within or parallel to the granodiorite and diorite porphyries controlled by the major-mineralization N-S-trending faults that cut the stratiform mineralization and volcanic rocks. To constrain the age of vein-type Pb-Zn-(Ag) mineralization and determine the relationship between mineralization and magmatism, we conducted LA-ICP-MS U-Pb dating on zircon from the ore-bearing granodiorite and diorite porphyries and Rb-Sr dating on metal sulfide. Granodiorite and diorite porphyries yield zircon U-Pb weighted-mean Pb-206/U-238 ages of 203.6 +/- 1.8 Ma (Mean Standard Weighted Deviation [MSWD] = 1.8) and 225.6 +/- 5.1 Ma (MSWD = 2.3), respectively. Sulfides from four vein-type ore samples yield a Rb-Sr isochron age of 195 +/- 17 Ma (MSWD = 4.0). These results indicate a temporal relationship between the granodiorite porphyry and vein-type Pb-Zn-(Ag) mineralization. The granodiorite associated with vein-type mineralization has high SiO2 (68.99-70.49 wt.%) and Na2O (3.9-4.2 wt.%; Na2O/K2O = 1.07-1.10) concentrations, and A/CNK values of 0.95-1.04; consequently, the intrusion is classified as a high-K, calc-alkaline, metaluminous I-type granite. The granodiorite porphyry is enriched in large-ion lithophile elements (e.g. Rb, Th, U, and K) and light REE and is depleted in high-field-strength elements (e.g. Nb, Ta, P, and Ti) and heavy REE, indicating that it represents a subduction-related rock that formed at an active continental margin. Furthermore, the granodiorite porphyry has Mg# values of 31-34, indicating a lower crustal source. Based on petrological and geochemical features, we infer that the ore-bearing granodiorite porphyry was derived from the partial melting of the lower crust. In summary, mineralization characteristics, cross-cutting relationships, geochronological data, and regional tectonic evolution indicate that the region was the site of VMS Pb-Zn mineralization that produced stratiform orebodies within the Late Carboniferous-Early Permian marine volcanic rocks of the Daheshen Formation, followed by mesothermal magmatic hydrothermal vein-type Pb-Zn-(Ag) mineralization associated with granodiorite porphyry induced by the initial subduction of the Paleo-Pacific Plate beneath the Eurasia Plate during the Late Triassic-Early Jurassic.