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

Abstract

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 (δEu = 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.