Late Mesozoic magmatism and metallogeny in NE China: The Sandaowanzi–Beidagou example

The Sandaowanzi (>22t Au) and Beidagou (>5t Au) tellurium–gold deposits are located in the northeastern Central Asian Orogenic Belt (Heilongjiang Province, NE China). The ore-hosting volcanic rocks unconformably overly monzogranite and were intruded by adakitic granodiorite. In this study, we report new-age, geochemical, and Sr–Nd–Pb isotopic data to elucidate the genetic link between the igneous rocks and the Te–Au mineralization. New-age data indicate that local magmatism occurred in the Early Jurassic (ca. 177.2 Ma) and Early Cretaceous (ca. 118.7 − 122.0 Ma). Geochemically, the igneous rocks are enriched in LREEs, Pb, K, and U, and depleted in Nb, P, and Ti, showing calc-alkaline affinity. The Early Jurassic monzogranite rocks are featured by ⁸⁷Sr/⁸⁶Sr = 0.7111−0.7118; ε_Nd(t) = −4.6 to −4.7; ²⁰⁶Pb/²⁰⁴Pb = 18.098−18.102, ²⁰⁷Pb/²⁰⁴Pb = 15.558−15.580, and ²⁰⁸Pb/²⁰⁴Pb = 37.781−37.928, whereas the Early Cretaceous adakitic granodiorite contains: ⁸⁷Sr/⁸⁶Sr = 0.7071−0.7073; ε_Nd(t) = − 3.4 to −3.2; ²⁰⁶Pb/²⁰⁴Pb = 17.991−18.080, ²⁰⁷Pb/²⁰⁴Pb = 15.483−15.508, and ²⁰⁸Pb/²⁰⁴Pb = 37.938−37.985. Initial isotopic ratios for the Early Cretaceous volcanic rocks: ⁸⁷Sr/⁸⁶Sr = 0.7061−0.7087; ε_Nd(t) = − 3.6 to −2.9; ²⁰⁶Pb/²⁰⁴Pb = 18.136−18.199, ²⁰⁷Pb/²⁰⁴Pb = 15.512−15.628, and ²⁰⁸Pb/²⁰⁴Pb = 38.064−38.155. The pyrite, chalcopyrite, and telluride grains yielded δ³⁴S of −6.52 ‰ to 2.13 ‰ (mean = − 0.82 ‰) and δ¹³C_PDB of the calcite samples are in the range of −6.64 ‰ to −5.24 ‰, implying the ore materials were derived from mantle. The geochemical and isotopic results indicate that primary melts of Late Mesozoic magmatic rocks have features by partial melting of the continental crust. The adakitic rocks may have been the products of the thickened lower crustal delamination and the subsequent asthenospheric upwelling during the intra-continental extension in NE China. Regionally, intrusive activity and molybdenum mineralization during the Jurassic was affected by subduction setting, whereas gold mineralization was controlled by the Early Cretaceous tectonothermal events associated with a superposition extension.