A Textural and Mineralogical Study of the Shanzhuang Banded Iron Formation, Southeastern Margin of the North China Craton: Implications for the Overprint History of Hydrothermal Alteration and Supergenesis after Mineralization
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We would like to thank Chen Wentao and Wu Kanglin on the field work, as well as Liu Huanan for his drawing. This study was financially supported by the National Natural Science Foundation of China (Grants No. 41503038, 41140025, 41672084, 41372086), Special fund for “Taishan scholars” project in Shandong Province, Key R&D Program of Shandong Province (Grant No. 2019GSF109101), Key R&D Program of China (Grants No. 2016YFC0600105-04, 2016YFC0600606), Shandong Provincial Natural Science Foundation (Grant No. ZR2019PD005), and Shandong Key Laboratory of Mineralization Geological Processes and Resources Utilization in Metallic Minerals (Grant No. kfkt201809).

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    Abstract:

    The newly discovered Shanzhuang BIF is hosted in the Shancaoyu Formation of the Taishan Group within the Eastern Block, southeastern margin of the North China Craton. The ores can be subdivided into three types in terms of mineral assemblages, corresponding to three types (I, II, III). The element concentration of the type I magnetite is similar to that of the type II magnetite, while the type III magnetite is similar to that of the schist. In general, magnetite and hematite grains from the ores show high concentrations of Mn (1317, 1162 ppm), Co (787, 1023 ppm), Al (2224, 2435 ppm) and Ti (540, 300 ppm), Whereas magnetite is depleted in Si (420 ppm) and hematite enriched in Si (1690 ppm). Detailed petrographic and mineral chemical analysis of magnetite, hematite, amphibole/hornblende and pyroxene, reveals that almost all the minerals occur as subhedral-anhedral grains with pits and fractures, and the BIF is recrystallized to metamorphic assemblages of high amphibolite facies. Hornblende is highly enriched in Fe, Mg and Ca, but depleted in K and Na, mostly belonging to magnesiohornblende. In addition, the ratios of Mg/(Mg+Fe2+), Fe3+/(Fe3++Fe2+), Si/(Si+Ti+Al) and Al/Si are 0.48–0.64, 0.17–0.36, 0.79–0.88 and 0.14–0.27, respectively. It is suggested that hornblende is neither a typical magmatic origin nor a typical metamorphic. Pyroxene has the characteristics of high Ca and Fe, but low Ti and Al, with end-member components En, Wo and Fs in the ranges of 25.22–28.64 wt%, 43.71–46.40 wt% and 24.51–27.62 wt%, respectively, belonging to clinopyroxene, and mostly diopside, might be formed during the prograde metamorphism in the absence of H2O. The carbonate such as dolomite-ankerite series is probably a precursor mineral of the BIF deposit. Mass mineral chemical and structural characteristics indicate that the Shanzhuang iron deposit has been subjected to varying degrees of oxidized hydrothermal superimposed reformation, metamorphism, and supergenesis after mineralization, during which some elements have been migrated in some degree.

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ZHANG Yan, YU Xuefeng, PENG Qiming, LI Dapeng, LI Xiaowei, SHEN Kun, ZHANG Shangkun, SHAN Wei.2020. A Textural and Mineralogical Study of the Shanzhuang Banded Iron Formation, Southeastern Margin of the North China Craton: Implications for the Overprint History of Hydrothermal Alteration and Supergenesis after Mineralization[J]. Acta Geologica Sinica(),94(6):2134-2151

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History
  • Received:June 11,2019
  • Revised:December 24,2019
  • Adopted:
  • Online: December 25,2020
  • Published: