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<p>The Early Paleozoic porphyry-epithermal Au system of the Songshunangou district sits in the central segment of the North Qilian orogenic belt (NQOB). The porphyry Au mineralization is centered on the quartz diorite porphyry (QDP), which is constrained to the Late Ordovician period. However, the geochemical signatures, the origin, and the tectonic setting of the QDP are not yet known and understood and are thus in the focus here. The QDP is a high-K calc-alkaline metaluminous rocks (K<sub>2</sub>O + Na<sub>2</sub>O: 6.90–8.13; Al<sub>2</sub>O<sub>3</sub>/(CaO + Na<sub>2</sub>O + K<sub>2</sub>O): 0.69–0.90) characterized by high (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub><i>t</i></sub> values (0.709 3–0.710 1) and low <i>ε</i><sub>Nd</sub>(<i>t</i>) values (−2.9 to −2.7) with corresponding <i>T</i><sub>DM2</sub> (Nd) ages of 1 408 to 1 430 Ma. Zircon <i>ε</i><sub>Hf</sub>(<i>t</i>) values are low (−1.51 to +2.76) with corresponding <i>T</i><sub>DM2</sub> (Hf) ages of 1 262 to 1 533 Ma. The lead isotope values are 17.695–18.476 for (<sup>206</sup>Pb/<sup>204</sup>Pb)<sub><i>t</i></sub>, 15.585–15.629 for (<sup>207</sup>Pb/<sup>204</sup>Pb)<sub><i>t</i></sub>, and 37.214–37.948 for (<sup>208</sup>Pb/<sup>204</sup>Pb)<sub><i>t</i></sub>. These data indicate that the QDP formed by the mixing of mantle-derived magmas (50%–70%) with lower crustal melts. The QDP is enriched in LREEs and LILE (Rb, Th, K) and is depleted in HFSE (Nb, Ta, Ti), expressing a clear volcanic arc affinity. High La and Th contents, and Zr/Y and Hf/Yb values suggest that the QDP formed in an Andean-type continental margin arc setting related to the northward subduction of the North Qilian oceanic slab. The Early Paleozoic subduction-related intermediate-acidic intrusions in NQOB have arc magma affinity, indicating that these rocks bear a great potential to discover further fertile porphyry deposits.</p>

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Origin and Tectonic Setting of the Ore-Related Late Ordovician Porphyry in the Songshunangou District, North Qilian, Northwest China: Whole-Rock Geochemical, Sr-Nd-Pb Isotopes and Zircon Hf Isotopes Constraints

  • 期刊论文

  • 发表日期：

    2025年3月8日

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  • Zuopeng Xiang,
  • Xinghai Lang,
  • Xuhui Wang,
  • Stephanie Lohmeier,
  • Bernd Lehmann,
  • Yulin Deng,
  • Weicai Dong,
  • Chao Luo

摘要

The Early Paleozoic porphyry-epithermal Au system of the Songshunangou district sits in the central segment of the North Qilian orogenic belt (NQOB). The porphyry Au mineralization is centered on the quartz diorite porphyry (QDP), which is constrained to the Late Ordovician period. However, the geochemical signatures, the origin, and the tectonic setting of the QDP are not yet known and understood and are thus in the focus here. The QDP is a high-K calc-alkaline metaluminous rocks (K2O + Na2O: 6.90–8.13; Al2O3/(CaO + Na2O + K2O): 0.69–0.90) characterized by high (87Sr/86Sr)t values (0.709 3–0.710 1) and low εNd(t) values (−2.9 to −2.7) with corresponding TDM2 (Nd) ages of 1 408 to 1 430 Ma. Zircon εHf(t) values are low (−1.51 to +2.76) with corresponding TDM2 (Hf) ages of 1 262 to 1 533 Ma. The lead isotope values are 17.695–18.476 for (206Pb/204Pb)t, 15.585–15.629 for (207Pb/204Pb)t, and 37.214–37.948 for (208Pb/204Pb)t. These data indicate that the QDP formed by the mixing of mantle-derived magmas (50%–70%) with lower crustal melts. The QDP is enriched in LREEs and LILE (Rb, Th, K) and is depleted in HFSE (Nb, Ta, Ti), expressing a clear volcanic arc affinity. High La and Th contents, and Zr/Y and Hf/Yb values suggest that the QDP formed in an Andean-type continental margin arc setting related to the northward subduction of the North Qilian oceanic slab. The Early Paleozoic subduction-related intermediate-acidic intrusions in NQOB have arc magma affinity, indicating that these rocks bear a great potential to discover further fertile porphyry deposits.