Iron-copper deposits of the Sampo mine, Okayama Prefecture are of contact-metaso-matic type, and the iron-oxide(magnetite)ores have been known to contain tin with up to 0.5 percent by weight. In these ores, tin appears to occur as minute grains of cassiterite, varying in size up to 100μ across, and they are embedded in calcite immediately adjacent to magnetite.
In this paper, malayaite from clinopyroxene skarn lying between crystalline limestone and leucocratic biotite-granite through magnetite ore on the Yoshiki 9th adit-level of the mine is examined by use of electron-probe X-ray microanalyzer and micro-beam X-ray diffractometer.
The present malayaite occurs as a microvolume mineral up to 300μ across, euhedral to subhedral in form, and is developed sparsely in the mosaic aggregates of clinopyroxene, actinolitic hornblende and fluorspar. The chemical analyses of Grain#(A)by electron microprobe method gave the following chemical composition on the average; SiO
2 22.22, TiO
2 0.60, SnO
2 56.72, Fe
2O
3 0.05, CaO 20.61, Total 100.20 (all in weight percent). From this, the chemical formula on the basis of five oxygen atoms may be calculated as, Ca
0.98(Sn
1.00Fe3+0.00Ti
0.02)
1.02O
1Si
0.99O
4, which corresponds closely to CaSnOSiO
4, the stoichiometric composition of malayaite. The principal reflections appearing on the X-ray diffraction patterns are, 5.03Å(35)(011), 3.29Å(20)(200), 3.06Å(35)(002), 2.668Å(>100)(122, 031)and 2.415Å(25)(211).
As far as the present malayaite is concerned, it might be formed by the reaction of calcium, tin and silica at the frontal zone of skarnization, where tin and other volatile constituents might have been concentrated(TAKENOUCHI and SHOJI, 1969; TAKENOUCHI, 1971).
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