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<p>At the Rudnogorskoe iron deposit (Tunguska Basin, East Siberia), the textures and structures of oolitic ironstones show sedimentological features, such as asymmetric gradational layering, load casts and the presence of banded ore fragments and iron ooids. Iron and trace elements were sourced from volcanic glass and accessory titanomagnetite–ilmenite, which were altered to Fe-rich smectites as a result of halmyrolysis in bottom conditions. It is suggested that particulate clay material precipitated on the surface of magnetite ore or skarn fragments to form a coating of ooids close to gas seeps. The clay particles were periodically replaced by magnetite, hematite or chlorite. The lumpy mineral layers alternate with radial magnetite incrustations. The primary minerals are partly replaced by next-stage skarn minerals. The geochemical zoning of the ooids is consistent with the mineral evolution. In addition to Mg, smectite scavenged V, Mn, Na, K, Li, Pb, U, Ba, Zn, Sr, Pb, B, Cu and Au from metalliferous brines. During recrystallization to chlorite, smectitelost most trace elements except for Li, Al, Ga, Ge, Zn and Cr. After the dissolution of titanomagnetite and ilmenite, crichtonite group minerals were deposited with elevated concentrations of some trace elements (Ti, Sr, Ca, Mn, Zr, Pb, V, Nb, U, Ba Th, U, LREE, Y). Iron oxides are depleted in many elements except for V, Zn, Mn, Co, Ni and Ga. Later skarn minerals such as garnet (Ti, V, Mn, Zr, REE, U), diopside (Ca, Mg, Si, Na, LREEs) and titanite (Ca, Ti, REEs) inherited elements probably from hot groundwater brines. This new sedimentary and halmyrolytic–diagenetic chemical model of the ooid growth contradicts previous magmatic and hydrothermal hypotheses of the iron deposit formation as a lode in a diatreme.</p>

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Mineral and trace element zoning of magnetite–hematite ooids of the Rudnogorskoe iron-oxide deposit at the Tunguska Basin, East Siberia: the development of sedimentary accretion and halmyrolysis–diagenesis model

  • 期刊论文

  • 发表日期：

    2025年10月11日

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  • V. V. Maslennikov,
  • A. S. Tseluyko,
  • N. R. Ayupova,
  • D. A. Artemyev

摘要

At the Rudnogorskoe iron deposit (Tunguska Basin, East Siberia), the textures and structures of oolitic ironstones show sedimentological features, such as asymmetric gradational layering, load casts and the presence of banded ore fragments and iron ooids. Iron and trace elements were sourced from volcanic glass and accessory titanomagnetite–ilmenite, which were altered to Fe-rich smectites as a result of halmyrolysis in bottom conditions. It is suggested that particulate clay material precipitated on the surface of magnetite ore or skarn fragments to form a coating of ooids close to gas seeps. The clay particles were periodically replaced by magnetite, hematite or chlorite. The lumpy mineral layers alternate with radial magnetite incrustations. The primary minerals are partly replaced by next-stage skarn minerals. The geochemical zoning of the ooids is consistent with the mineral evolution. In addition to Mg, smectite scavenged V, Mn, Na, K, Li, Pb, U, Ba, Zn, Sr, Pb, B, Cu and Au from metalliferous brines. During recrystallization to chlorite, smectitelost most trace elements except for Li, Al, Ga, Ge, Zn and Cr. After the dissolution of titanomagnetite and ilmenite, crichtonite group minerals were deposited with elevated concentrations of some trace elements (Ti, Sr, Ca, Mn, Zr, Pb, V, Nb, U, Ba Th, U, LREE, Y). Iron oxides are depleted in many elements except for V, Zn, Mn, Co, Ni and Ga. Later skarn minerals such as garnet (Ti, V, Mn, Zr, REE, U), diopside (Ca, Mg, Si, Na, LREEs) and titanite (Ca, Ti, REEs) inherited elements probably from hot groundwater brines. This new sedimentary and halmyrolytic–diagenetic chemical model of the ooid growth contradicts previous magmatic and hydrothermal hypotheses of the iron deposit formation as a lode in a diatreme.