Using apatite to differentiate metallogenic potential and environment of granitic rocks: A case study from the Tongshanling W-Sn-Cu-Pb-Zn ore field, Nanling Range (South China)

Abstract

The Tongshanling ore field is one of the most representative W–Sn–Cu–Pb–Zn polymetallic deposits in the central-western Nanling Ore Belt, which developed multiple mineralization types, including Cu–Pb–Zn (Tongshanling), W–Sn (Weijia), Pb–Zn (Jiangyong), and Mo (Yulong) deposits. Here, we analyzed apatite from the Tongshanling granodiorite and the Weijia granite porphyry, integrating major and trace elements, U–Pb dating, and Nd isotopic analyses to compare the difference in geochronology, magma source, redox environment, and evolution between the Tongshanling and Weijia deposit. The U–Pb dating of the Tongshanling and Weijia apatite samples yield a lower intercept age of 166.2 ± 11.3 Ma (1σ, MSWD = 0.22) and 160.87 ± 8.92 Ma (1σ, MSWD = 0.44) on Tera-Wasserburg diagrams, respectively. The 147Sm/144Nd and 143Nd/144Nd ratios of the Tongshanling apatite samples are 0.136769–0.182878 and 0.512159–0.512246, respectively, with corresponding εNd (t = 166 Ma) ranging from −8.32 to −6.60, suggesting that the Tongshanling granodiorite was produced by partial melting of metaigneous rocks in the deep crust. The Tongshanling apatite shows a right-inclined REE pattern, while the Weijia apatite displays a “V” type REE pattern. The Tongshanling apatite shows higher Eu/Eu* values, and lower Mn and Ce/Ce* values than the Weijia apatite, indicating that the former formed in higher magmatic oxidation state while the latter formed in more reduced conditions. The granodiorite in the Tongshanling deposit is characterized by a lower degree of fractionation than the granite porphyry in the Weijia deposit, of which the Weijia apatite has lower Sr, Mg contents, and higher Y contents. Furthermore, apatite from Cu-bearing granites exhibits lower F/Cl ratios compared to those from W-bearing granites in the South China Block. In the Tongshanling area, apatite from the Tongshanling granodiorite has higher Cl contents than the Weijia apatite, indicating that the crustal basement of the Tongshanling area was affected by the high Cl fluid derived from the Proterozoic oceanic subduction and remelted to form granite in the Mesozoic, while the Weijia granite porphyry formed from remelting of a sedimentary source. The Tongshanling granodiorite and Weijia granite porphyry with different degrees of fractionation, magma source, and halogens contents can be effectively distinguished by the geochemistry of apatite. The difference in trace elements (Sr, Y, Mg, and REE) and isotopes of apatite can be applied to the identification of different types of ore-bearing granites in the Nanling Range.