The Middle Jurassic Sanhe Pb–Zn–Ag deposit in NE China: Constraints from Geochronology, Geochemistry, Fluid Inclusion and Multi-Isotope (S–Pb–He–Hf) Systematics

The Sanhe is a typical medium-size Pb-Zn-Ag deposit in the Argun Massif, NE China. Its Pb-Zn-Ag orebodies are mainly hosted in the Jurassic Tamulangou Formation volcanic rocks. The orebodies occur as quartz vein clusters. The ore-forming quartz porphyry is LA-ICP-MS zircon U-Pb dated to be 165.2 +/- 1.2 Ma, and the ore sphalerite yielded a Rb-Sr age of 162.5 +/- 4.3 Ma. These ages indicate that the Sanhe represents the oldest Pb-Zn-Ag mineralization in the Argun Massif. Combined with published age data, the Pb-Zn-Ag mineralization of the Argun Massif occurred in three phases at ca. 160 Ma, 140 Ma and 130 Ma. The quartz porphyry shows right-inclining REE ((La/Yb)(N) = 22.92-40.69) patterns and negative Eu anomalies (delta Eu = 0.68-0.81), together with enrichments in K, La, Ce, Nd, Zr and Hf but depletions in Ba, Ta, Nb, Sr, P and Ti. Whole-rock geochemistry and Hf isotopes suggest that the quartz porphyry was derived from partial melting of juvenile lower crustal materials during the post-collision extension of the Mongol-Okhotsk orogenic belt. Sulfide S-Pb isotope compositions indicate that the ore-forming materials were derived from the deep magma, whilst He isotopes indicate that the ore fluids were dominantly crustal-derived. Fluid chemical compositions obtained from LA-ICP-MS single fluid inclusion analyses support that mixing of magmatic fluids with meteoric water was an important mineralization trigger at Sanhe. Our new data show that the involvement of unusually metal-rich fluids is a prerequisite to form abundant Pb-Zn-Ag mineralization at Sanhe.