幕府山 (MFS) 和连云山 (LYS) 花岗岩杂岩位于湖南东北部（华南），拥有重要的 Nb-Ta 矿化带。细粒白云母花岗岩 (FGMGs) 以侵入体形式出现在冷家溪群内，并与含矿伟晶岩呈空间关系。在这里，对 MFS 和 LYS 复合体的 FGMG 进行了地球化学、地质年代学和同位素研究，以比较它们的岩浆来源和成矿潜力。MFS 和 LYS FGMG 是强过铝质 (A/CNK > 1.5) 和高度分异的 S 型花岗岩。相比之下，MFS FGMGs 具有更多负 Eu (Eu/Eu* = 0.19–0.60)、Ba (3.3–360 ppm)、Sr (6.2–156 ppm) 和 Zr (4–26 ppm) 异常，以及更多正 Ta (1.1–15.8 ppm) 异常比 LYS FGMGs，表明岩浆分异更强。此外，来自 MFS FGMG 的锆石显示出较高含量的 Hf（MFS = 34336 至 60010 ppm，LYS = 6795 至 28937 ppm），Nb（MFS = 16.49 至 401.56 ppm，LYS = 1.12 至 20.22 ppm），Ta（MFS = 33.45 至 20.22 ppm） 138.65 ppm，LYS = 1.11 至 7.19 ppm），Th（MFS = 458 至 3630 ppm，LYS = 11 至 710 ppm）和 U（MFS = 8400 至 30100 ppm，LYS = 1285 至 5220 ppm） FGMGs，表明 MFS FGMGs 的分馏程度更高，其锆石经历了热液蚀变。MFS 和 LYS FGMG 的锆石 U-Pb 测年结果分别为 140.6 ± 0.5 Ma 和 139.9 ± 0.7 Ma 的一致年龄，这意味着早白垩世岩浆-热液事件。此外，与 LYS FGMG 相比，地球化学和同位素（全岩 Sm-Nd 和锆石 Lu-Hf）成分显示 MFS FGMG 的来源更年轻，它们源自古元古代基岩在碰撞后伸展环境中与富含粘土物质的部分熔化。我们的结果，结合以前的研究，表明所研究的 FGMGs 是广泛 Nb-Ta 矿化的母岩，高度分馏的 MFS FGMGs 比 LYS FGMGs 更有利于承载 Nb-Ta 矿化。强过铝和高分馏的 S 型 FGMGs 可以作为进一步勘探华南和其他地区 Nb-Ta 矿床的良好目标。和高度分馏的 MFS FGMGs 比 LYS FGMGs 更有利于承载 Nb-Ta 矿化。强过铝和高分馏的 S 型 FGMGs 可以作为进一步勘探华南和其他地区 Nb-Ta 矿床的良好目标。和高度分馏的 MFS FGMGs 比 LYS FGMGs 更有利于承载 Nb-Ta 矿化。强过铝和高分馏的 S 型 FGMGs 可以作为进一步勘探华南和其他地区 Nb-Ta 矿床的良好目标。
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Contrasting Nb-Ta mineralization between the Mufushan and Lianyunshan granites, South China: Evidence from whole-rock and zircon geochemistry and geochronology
The Mufushan (MFS) and Lianyunshan (LYS) granitic complexes are located in northeastern Hunan (South China) and host important Nb-Ta mineralization. Fine-grained muscovite granites (FGMGs) occur as intrusions within the Lengjiaxi Group and show a spatial relationship with the ore-bearing pegmatites. Here, geochemical, geochronological, and isotopic investigations were carried out on the FGMGs of the MFS and LYS complexes to compare their magma sources and metallogenic potential. The MFS and LYS FGMGs are strongly peraluminous (A/CNK > 1.5) and highly fractionated S-type granites. Comparatively, the MFS FGMGs possess more negative Eu (Eu/Eu* = 0.19–0.60), Ba (3.3–360 ppm), Sr (6.2–156 ppm), and Zr (4–26 ppm) anomalies, and more positive Ta (1.1–15.8 ppm) anomalies than the LYS FGMGs, suggesting a stronger magma differentiation. In addition, the zircons from the MFS FGMGs exhibit higher contents of Hf (MFS = 34336 to 60010 ppm, LYS = 6795 to 28937 ppm), Nb (MFS = 16.49 to 401.56 ppm, LYS = 1.12 to 20.22 ppm), Ta (MFS = 33.45 to 138.65 ppm, LYS = 1.11 to 7.19 ppm), Th (MFS = 458 to 3630 ppm, LYS = 11 to 710 ppm), and U (MFS = 8400 to 30100 ppm, LYS = 1285 to 5220 ppm) than those from the LYS FGMGs, suggesting that the MFS FGMGs are more fractionated and their zircons have undergone hydrothermal alteration. Zircon U-Pb dating yielded concordant ages of 140.6 ± 0.5 Ma and 139.9 ± 0.7 Ma for the MFS and LYS FGMGs, respectively, implying an Early Cretaceous magmatic-hydrothermal event. Moreover, the geochemical and isotopic (whole-rock Sm-Nd and zircon Lu-Hf) compositions show younger sources for the MFS FGMGs compared to the LYS FGMGs, which were derived from the partial melting of Paleoproterozoic basement rocks with clay-rich material in a post-collision extensional setting. Our results, combined with previous studies, indicate that the studied FGMGs are the parental rocks of extensive Nb-Ta mineralization, and the highly fractionated MFS FGMGs are more conducive to hosting Nb-Ta mineralization than the LYS FGMGs. The strongly peraluminous and highly-fractionated S-type FGMGs can be used as good targets for further exploration of Nb-Ta deposits in South China and elsewhere.
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