栃木県足尾町久良沢鉱山大滝坑産鉄マンガン鉱石中の含バナジン満礬石榴および含バナジン褐廉石

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Vanadium-bearing spessartine and allanite occur as idiomorphic inclusions in coarse tephroite-fayalite grains forming manganese-iron ore together with minor rhodonite and manganpyrosmalite from the Odaki orebody of the Kyurazawa mine. They are compositionally zoned. The empirical formula of the core of the former is : (Mn_<2.66>Ca_<0.38>)_<Σ3.04>(Al_<1.45>V_<0.56>)_<Σ2.01>Si_<2.97>O_<12> and that of the margin is : (Mn_<2.28>Ca_<0.51>Fe^<2+>_<0.19>Mg_<0.04>)_<Σ3.00>(Al_<1.73>V_<0.17>Fe^<3+>_<0.12>)_<Σ2.02>Si_<2.98>O_<11.99>. The outward decrease of V_2O_3 contents is clearer than that in allanite. The formula of the core of allanite is : (Ca_<0.99>Ce_<0.50>La_<0.22>Nd_<0.03>Mn_<0.22>^<2+>)_<Σ1.96>(Al_<1.24>V_<0.73>Fe^<2+>_<0.45>Fe^<3+>_<0.36>Mn_<0.22>^<2+>)_<Σ3.00>Si_<3.00>O_<12>OH and that of the margin is : (Ca_<0.90>Ce_<0.49>La_<0.19>Nd_<0.08>Mn^<2+>_<0.33>)_<Σ1.99>(Al_<1.12>V_<0.69>Fe^<2+>_<0.48>Fe^<3+>_<0.45>Mn^<2+>_<0.21>Mg_<0.05>)_<Σ3.00>Si_<3.00>O_<12>OH, Tiny blebs of allanite also occur in spessartine grains. The sequence of formation is : allanite, spessartine, fayalite-tephoroite, rhodonite and manganpyrosmalite. The occurrences of vanadium or rare earths minerals are not uncommon in contact metamorphosed bedded manganese or manganese-iron ore deposits in Japan. The predominance of Fe^<2+>-bearing minerals at the Kyurazawa mine suggests the condition of formation to be relatively reducing. This is conformable with the existence of these V^<3+>-bearing minearls, but Fe^<3+> is bound to be involved in both of them after the interpretation of microprobe analyses. The coexistence of V^<3+> and Fe^<3+> reflective of two conflicting conditions in a single mineral is considered to be due to the presence of these ions not in their single forms but in combined forms with oxygen.
国立科学博物館の論文
1994-03-22

栃木県足尾町久良沢鉱山大滝坑産鉄マンガン鉱石中の含バナジン満礬石榴および含バナジン褐廉石

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