On the mode of occurrence and mineral paragenesis of iron-wollastonite skarn in the Sampo mine, Okayama Prefecture

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  • 岡山県山宝鉱山における鉄珪灰石スカルンの産状と鉱物共生について
  • オカヤマケンサン ホウ コウザン ニ オケル テツケイカイセキ スカルン ノ サンジョウ ト コウブツ キョウセイ ニ ツイテ

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Remarkable zonal arrangement of magnetite ore and skarn is observed in the Sampo mine, Okayama Prefecture. Zonal arrangement in Yoshiki No. 1 ore bodies at 9L is summarized from granite-side to marble-side as follows: granite→hornfels→banded Pyroxene skarn→iron -wollastoni te skarn→green pyroxene skarn→iron-wollastonite skarn→white skarn →garnet skarn→magnetite ore→“Ashinaga”→marble. Iron-wollastonite is accompanied intimately with hedenbergite, and both the minerals occur as monomineralic seam and/or monomineralic zone in the skarn. Iron-wollastonite and clino-pyroxene skarns have been intensely folded concordantly with marble which shows a complicated folding structure, and both extensions are cut by granite intrusives. A close paragenetic relation between iron-wollastonite and hedenbergite is observed in the field as well as under the microscope. Although wollastonite is associated with ferrosalite-hedenbergite series of wide compositional range, iron-wollastonite with 17～19 mol. % (Fe, Mn)SiO_3 is associated with pure hedenbergite exclusively. On the other hand, by comparison of three pairs in Skye, Hijikuzu and Sampo mine, it is inferred that there is a certain rule for Mn partition between iron-wollastonite and hedenbergite judging from the parallel tie-lines. The occurrence of iron-wollastonite and clino-pyroxene skarns suggests that both the minerals were primalily formed by the thermal metamorphism of granite intrusion. The iron-wollastonite and clino-pyroxene skarns were altered to white skarn, which consists of andradite and wollastonite, under the effect of magnetite-andradite-fluorite mineralization.

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