Diagenesis and metallogenetic mechanisms of the Tuanjiegou gold deposit from the Lesser Xing’an Range, NE China: Zircon U–Pb geochronology and Lu–Hf isotopic constraints

Abstract

The Tuanjiegou gold deposit is a large-sized breccia-hosted epithermal gold deposit in Heilongjiang Province, eastern China, and was discovered in the late 1950s. The scale and unusual metallogenic setting of this gold deposit have made it the focus of many previous studies. We systematically analyzed ore samples, and volcanic and granitic rocks that are associated with the formation of the deposit by single zircon U–Pb dating, obtaining three distinct concordant groups of U–Pb ages from dacitic pyroclastic rocks and lavas: 119.3±3.3 (n=2), 113.2±1.1 (n=13), and 109.1±1.4Ma (n=8); four groups of concordant U–Pb ages from an ore-bearing granite porphyry: 112.5±2.2 (n=2), 107.0±1.2 (n=4), 103.0±0.70 (n=10), and 99.9±1.1Ma (n=4); two groups of concordant U–Pb ages from a pyrite-rich, quartz vein-cemented, brecciated and silicified granite porphyry: 104.23±0.51 (n=16) and 101.3±1.3Ma (n=2); and five groups of concordant U–Pb ages from pyrite-rich, quartz vein-cemented, brecciated or chunky ore samples: 139±4 to 144±3 (n=2), 127±4 (n=1), 113.8±2.1 (n=8), 101.3±3.4 (n=3), and 91±3Ma (n=1). Combining the whole-rock and Lu–Hf isotope geochemistry with the geology of the mining area and these new U–Pb dates, we have redefined the ore deposit-related temporal history of the area, with formation age of the magma associated with the Ningyuancun Stage volcanics being 119±1.4Ma and eruption of the volcanics at 113±1.1Ma. The granodiorite-porphyry and granite porphyry were emplaced at 107.0±1.2Ma and 103–102Ma, respectively, with ore deposit formation at 102–100Ma. The magmato–hydrothermal interaction that formed the deposit was closely related to Late Mesozoic crust–mantle interaction, with the early stage calc-alkaline and high-K calc-alkaline magmatism in this area potentially being derived from interaction between asthenospheric mantle material and the underplated lower crust. However, the magmas associated with late-stage intrusive calc-alkaline and high-K calc-alkaline magmatism may have been generated during interaction between adakite-like magmas derived from the subduction of an oceanic plate and lower crustal material. Here, we suggest that the fluids that formed this deposit formed by interaction with both early- and late-stage mantle-derived magmas and the lower crust, with subsequent aggregation after significant igneous differentiation. During ore formation, the area was in a back-arc initial (passive) rift and continental margin island arc tectonic environment associated with Late Mesozoic subduction of the Pacific Plate, with metallogenesis occurring during a change in the tectonic environment between the latest Early Cretaceous and the Late Cretaceous.