栃木県今市市猪倉産アルミニウム燐酸塩鉱物

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Turquoise and planerite from a clay deposit at Inokura, Imaichi City, Tochigi Prefecture, occur in veins in argillized dacite and acidic tuff partially stained by goethite. Their chemical analyses indicate the former to be differentiated into two variants, Fe-free Cu-deficient and Fe^<3+>-rich Cu-deficient ones, and the latter to be a Zn-and Ba-bearing one. Their average figures are, respectively; CuO 5.54,5.72,3.35; ZnO -, -, 1.21; BaO -, -, 0.36; Al_2O_3 37.77,29.95,37.76; Fe_2O_3 -, 9.52,0.70; P_2O_5 33.69,33.41,35.52; totals 78.42,78.60,78.90 wt%. Their empirical formulae taking the rests as due to water are : (Cu_<0.56>□_<0.44>)Al_<5.99>(PO_4)_3(PO_3OH)(OH)_<8.09>・5.14H_2O, (Cu_<0.61>□_<0.39>)(Al_<4.99>Fe_<1.01>)_<Σ6.00>(PO_4)_3(PO_3OH)(OH)_<8.22>・5.48H_2O, and(Cu_<0.34>Zn_<0.15>Ba_<0.02>□_<0.49>)(Al_<5.92>Fe_<0.07>)_<Σ5.99>(PO_4)_3(PO_3OH)(OH)_<7.99>・4.87H_2O, respectively, calculated on the basis, of P=4,where the half-empty formula is taken as the basis. Preferential incorporation of Zn into planerite rather than turquoise is demonstrated. The Ferich tur-quoise veins are developed in goethite-stained parts. Wavellite and cacoxenite are found as coatings on fracture walls. Turquoise of both types and planerite will be precipitates from hydrothermal solutions containing Cu^<2+> and PO_4^<3->, where Al^<3+> might have been supplied from the clay minerals in wall rocks due to the loss of Al^<3+> in kaolinite to form quartz. Diminishing Cu^<2+> content in the solution favoured the precipitation of planerite rather than turquoise. Fragments of altered wallrocks enclosed within the veins of Fe^<3+>-rich turquoise consist of pyrophyllite, kaolinite, quartz, and wavellite, indicating prolonged mineralization of phosphates. Also, altered wallrocks involve minor aggregates of chalcopyrite and sphalerite, bornite, covelline, and djurleite, but it seems that they are not direct sources of copper in turquoise and planerite and of zinc in the latter.
国立科学博物館の論文
1994-09-22

栃木県今市市猪倉産アルミニウム燐酸塩鉱物

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