Guangwei Wang’s research while affiliated with China Geological Survey and other places

The Zhaojinggou Nb–Ta deposit is one of large rare metal deposits newly discovered in the northern margin of the North China Craton in recent years. This paper reports petrography, petrochemistry, columbite‐group minerals U–Pb chronology study of the amazonite granitic pegmatite (AGP) exposed in this deposit, and composition of columbite‐group minerals and biotite are obtained by electron probe microanalyzer and LA‐ICP‐MS. Eighteen analyses of columbite‐group minerals yielded weighted mean 206Pb/238U age of 116.9 ± 1.4 Ma. The crystallization temperature of biotite is 630–650°C, and the oxygen fugacity is 10−17–10−18 bars. The biotite has low MgO contents and high Rb, Rb/Sr, and FeOT/(FeOT + MgO) ratios. The AGP has extremely low MgO, Cr, Co and Ni contents, with Nb/Ta ratios range from 1.63 to 9.05 and Rb/Sr ratios range from 303.30 to 648.90, and obvious ‘M’ type tetrad effect of rare earth element indicating that the formation of the AGP is related to crust‐derived magma. The contents of Nb2O5 and FeO decrease, while the Ta2O5 and WO3 contents, Mn# and Ta# values increase gradually from the core to the rim of columbite‐group minerals. Some columbite‐group minerals have unobvious oscillatory zoning, and some have a clear bright zoing with high Ta contents on the rim, indicating that the genesis of Zhaojinggou Nb–Ta deposit is mainly magmatic crystallization differentiation, accompanied by hydrothermal autometasomatism in the late stage. The deposit was formed in an extensional tectonic background in the late Yanshanian, magma was formed by partial melting of Nb–Ta‐rich lower crust, undergoing high evolution. Mineralization is crystallization differentiation and hydrothermal self‐metasomatism

The timings of subduction of the Palaeo-Pacific Plate beneath the North China Craton and of associated mineralisation remain unresolved. We studied a granodiorite porphyry in the Banmiaozi gold mining area, located along the northeastern margin of North China Craton, to shed light on these timings. Using zircon U–Pb geochronology, major- and trace-element geochemistry, Sr–Nd isotopes, and biotite compositions, we show that the granodiorite porphyry formed during the early Middle Jurassic and has a composition similar to those of ‘C-type adakites’ from eastern China. The granodiorite rocks have initial Sr isotopic compositions of 0.713418–0.713694, εNd(t) values of −15.9 to −16.69, and depleted-mantle single-stage model ages of 2.70–2.49 Ga, implying that the parental magma originated via subduction of the Palaeo-Pacific Plate beneath the North China Craton and resulted also in the generation of basaltic magmas and partial melting of thickened lower crust. As the Archaean basement rocks were rich in Au and magnetite, the magma was characterized by high Au contents and oxygen fugacity (fO2 = 10−13 bar). Subsequent mixing with, or contamination by, partially melted Proterozoic marine strata, such as the marble-bearing Laoling Group, played an important role in mineralisation. These country rocks provided large quantities of Cl−, CO32−, and SO42− to the magma, which formed soluble complexes with ore-forming elements such as Au, allowing enrichment and migration of the metals. Our data show that the Banmiaozi gold deposit is an orogenic gold deposit associated with subduction-related adakitic magmatism.