Mineralogical composition of the Ashibetsu coals in the Ishikari coalfield. 3. Carbonate and phosphate minerals, and boemite

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  • 石狩炭田芦別炭の鉱物組成3.炭酸塩鉱物,リン酸塩鉱物,ベーマイト
  • イシカリ タンデン アシベツタン ノ コウブツ ソセイ 3 タンサンエン コウ

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Abstract

Carbonate and phosphate minerals, and boemite in the seven Paleogene coal seams of the Ashibetsu colliery in the Ishikari coalfield, Hokkaido, were investigated by X-ray diffraction for low temperature ash, shale, and tuff. A scanning electron microscope (SEM) equipped with an electron probe X-ray microanalyzer (XMA) was used to observe the morphology of carbonate minerals and apatite.<BR>Calcite is the most abundant among the minerals studied, and is contained in 83% of the seventy five coal samples containing less than 40% ash. Ankerite is also abundant, and was found in 71% of the coal samples. Both calcite and ankerite appear as cleat and fracture fillings in the Ashibetsu coals. Aragonite is rare, and is thought to appear as a part of cleat and fracture fillings. Carbonate minerals are rare in shale. The Ca, Mg, and Fe content in the low ash and pyrite free coals, rich in calcite and/or ankerite, is estimated to be nearly the same as in plants or peats. This indicates that these minerals may have been formed in cleats and fractures by interaction of Ca, Mg, and Fe, and CO2, released from organic material during the second stage of coalification.<BR>Siderite is found in 20% of the coal samples, and is rare in shale. Siderite occurs as aggregates composed of fine grains or nodules of different sizes from less than 1 μm to 10 μm. Dolomite (ferroan dolomite) appears in only 4% of the coal samples, and also occurs as aggregates of nodules of irregular shape, up to 100 μm. Both siderite and dolomite are syngenetic minerals in the Ashibetsu coals.<BR>Apatite are found in 63% of the coal samples containing less than 40% ash. All of the apatites found in the Ashibetsu coals are thought to be fluorapatite. Detrital apatite appears in the mineral band or mineral rich part of the high ash coal seams, and epigenetic apatite appaers as fracture fillings in the low ash coal seams. Apatite is rare in shale. Goyazite was detected in the samples that were relatively rich in apatite. Goyazite coexists with both detrital and epigenetic apatite. As P correlates well with Sr, these two phosphate minerals are thought to be closely related in origin.<BR>Boemite is detected in 32% of the coal samples, most of low ash content. Organic Al may be the source of boemite.

Journal

  • Shigen-Chishitsu

    Shigen-Chishitsu 45 (250), 99-109, 1995

    The Society of Resource Geology

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