Implications for Metallogenesis and Tectonic Evolution of Ore-Hosting Granodiorite Porphyry in the Tongkuangyu Cu Deposit, North China Craton: Evidence from Geochemistry, Zircon U-Pb Chronology, and Hf Isotopes

Abstract

The Tongkuangyu copper deposit in Zhongtiaoshan at the southern margin of the North China Craton is one of the oldest porphyry Cu deposits in the world and its metallogenesis and tectonic evolution have been debated. Here, porphyritic intrusion geochemical and geochronological data are reported to identify the diagenetic age, mineralization, tectonic setting, and evolution of the deposit. Geochemical data show that granodiorite porphyry is a peraluminous rock, with low concentrations of Fe (~3.99%) and Ti (~0.29%) and high concentrations of alkali (~6.13%) and high Al (~15.42%) and Mg numbers (~51). The rocks show comparative enrichment of Na, K, and Mg; higher La/Yb ratios, no significant Eu anomaly, and obvious Nb–Ta–Ti negative anomaly, showing similar geochemical characteristics to Archean TTG and sanukitoid. ΣREE vary greatly, ranging from 33.47 × 10−6 to 277.81 × 10−6 (average 137.09 × 10−6). The characteristics of REE show obvious fractionation of LREE and HREE, enrichment of LREE, and depletion of HREE. Some of the LREE (La and Ce) and LILE (K, Rb, and Ba) are enriched, but some of the LILE (Th and U) are depleted. In addition, some of the HFSE (Nb, Ta, P, and Ti) are depleted while some (Zr and Hf) are enriched. High precision LA–MC–ICP MS zircon U–Pb dating yield concordant ages of 2159 ± 19 Ma, which is broadly coeval with ore formation (~2.1 Ga) in the area. Zircon εHf(t) values range from −3.8 to 1.13, with a model age of 2778 to 2959 Ma, indicating that the formation of porphyry is related to the partial melting of Archean crust (~2.7 Ga) with a minor amount of mantle material added. Tongkuangyu granodiorite porphyry formed in the tectonic setting of the post-orogenic extension in the Paleoproterozoic, and Tongkuangyu Cu deposit may be related to the extension of the North China Craton in the Paleoproterozoic.