The magnetite-series and ilmenite-series granitic rocks.

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  • 磁鉄鉱系花崗岩類とチタン鉄鉱系花崗岩類
  • 磁鉄鉱系花崗岩類とチタン鉄鉱系花崗岩類〔英文〕
  • ジテッコウケイ カコウガンルイ ト チタン テッコウケイ カコウガンルイ エイ

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Abstract

Opaque minerals of common granitic rocks were studied microscopically. The granitoids were divided into (i) a magnetite-bearing magnetite-series and (ii) a magnetite-free ilmenite-series. Each series has the following characteristic assemblages of accessary minerals:<BR>Magnetite-series: Magnetite (0.1-2 vol.%), ilmenite, hematite, pyrite, sphene, epidote, high ferric/ferrous (and high Mg/Fe) biotite;<BR>Ilmenite-series: Ilmenite (less than 0.1 vol.%), pyrrhotite, graphite, muscovite, low ferric/ferrous (and low Mg/Fe) biotite.<BR>The mineral assemblages imply a higher oxygen fugacity in the magnetite-series granitoids than in the ilmenite-series granitoids during solidification of the granitic magmas. The boundary separating the two series is probably near the Ni-NiO buffer.<BR>The magnetite-series granitoids are considered to have been generated in a deep level (upper mantle and lowest crust) and not to have interacted with C-bearing materials; whereas the ilmenite-series granitoids were generated in the middle to lower continental crust and mixed with C-bearing metamorphic and sedimentary rocks at various stages in their igneous history. The former carries porphyry copper-molybdenum deposits and the latter accompanies greisen-type tin-wolframite deposits. Lack of porphyry copper deposits in the Mesozoic orogeny belts in East Asia is related to a general paucity of the magnetite-series granitoids in this terrane.

Journal

  • Mining Geology

    Mining Geology 27 (145), 293-305, 1977

    The Society of Resource Geology

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