Formation of the Qiyugou porphyry gold system in East Qinling, China: insights from timing and source characteristics of Late Mesozoic magmatism

  • Xin-Kai Hu
    Key Laboratory of Submarine Geosciences, Ministry of Natural Resources & Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China
  • Li Tang
    School of Earth Sciences and Resources & State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
  • Shou-Ting Zhang
    School of Earth Sciences and Resources & State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
  • Toshiaki Tsunogae
    Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan
  • M. Santosh
    School of Earth Sciences and Resources & State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
  • Li Sun
    MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
  • Christopher J. Spencer
    School of Earth and Planetary Sciences, The Institute of Geoscience Research, Curtin University, Perth, WA 6845, Australia
  • Heejin Jeon
    Centre for Microscopy, Characterisation and Analysis, University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia
  • Liang Wang
    School of Earth Sciences and Resources & State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China

抄録

<jats:p> The Qiyugou gold deposit, located in the East Qinling Orogen, is characterized by porphyry, breccia pipe-hosted and fracture-controlled hydrothermal mineralization. Four intrusive phases are identified in this deposit: pre-mineralization quartz porphyry, syn-mineralization granite porphyry associated with breccia pipe-hosted mineralization, syn-mineralization hornblende monzogranite associated with porphyry mineralization and post-mineralization monzogranite porphyry. These granitoids are metaluminous, alkalic to calc-alkalic, shoshonitic to high-K series, and belong to highly fractionated I-type granitoids. Most of the Qiyugou granitoids show relatively lower Sr/Y (<40) and (La/Yb) <jats:sub>N</jats:sub> (average = 12.0) than the typical adakite-like rocks. The granitoids are strongly enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) and depleted in heavy rare earth elements (HREE) with slightly negative europium anomalies (except for hornblende monzogranite) and moderate depletion of high field strength elements (HFSE), mostly plotting in the range of the basement Taihua Group rocks. Zircon U–Pb ages of granite porphyry, hornblende monzogranite and monzogranite porphyry from the Qi189 pluton, and hornblende monzogranite beneath the J4 breccia pipe are 133.4 ± 0.8, 131.3 ± 0.9, 128.0 ± 0.7 and 129.9 ± 0.9 Ma, respectively. The <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ε</mml:mi> </mml:math> </jats:inline-formula> Hf <jats:sub> ( <jats:italic>t</jats:italic> ) </jats:sub> values and T <jats:sub>DM2</jats:sub> ages show a variation trend from −37.4 to −11.4 and from 3530 to 1912 Ma, consistent with Hf isotopic features of the Taihua Group. The <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ε</mml:mi> </mml:math> </jats:inline-formula> Hf <jats:sub> ( <jats:italic>t</jats:italic> ) </jats:sub> values have a positive correlation with MgO and negative correlation with SiO <jats:sub>2</jats:sub> , indicating sustained involvement of mantle-derived materials. Notably, these granitoids have comparable <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> </jats:inline-formula> <jats:sup>18</jats:sup> O <jats:sub>zircon</jats:sub> values ranging from 5.7 to 5.9‰. The covariations of geochemical and isotopic data indicate that these granitoids were produced by mixing of the partially melted Taihua Group basement with mantle-derived components. The Qiyugou granitoids were generated at different crustal levels by a lithospheric thinning process linked to the tectonic transition from compression to extension at 133–128 Ma. The hornblende monzogranite from the Qi189 pluton was probably more hydrous and resulted from a highly evolved magma after hornblende fractionation, which was favourable for porphyry mineralization. Our study provides insights into the formation of a porphyry gold system associated with a prolonged and active magmatic–hydrothermal system, upwelling of hot asthenosphere and intense mantle–crust interaction. </jats:p> <jats:p content-type="supplementary-material"> <jats:bold>Supplementary material</jats:bold> : Tables giving compositions of the granitoids are available at <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" specific-use="dataset is-supplemented-by" xlink:href="https://doi.org/10.6084/m9.figshare.c.5835494">https://doi.org/10.6084/m9.figshare.c.5835494</jats:ext-link> </jats:p>

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