Welinite in the bedded manganese ore deposits of Japan

Abstract

The mode of occurrence, mineral assemblage, and chemical composition of welinites from the Taguchi, Fukumaki and the Ioi manganese mines were described.
Welinite from the Taguchi mine in the Ryoke metamorphic belt, occurs in rhodochrosite-tephroite-alabandite ore associated with small amounts of galaxite and pyrophanite. The mineral occurs as fine-grained crystals about 0.3-0.7mm in diameter. Under the microscope, the welinite is weakly pleochroic in shades of yellowih brown to pale yellow. No cleavage is observed. A parting is developed which is similar to that of tephroite. X-ray powder diffraction data for welinite are agreement with those of welinite from the Langban mine.
Welinite from the Fukumaki mine in the Ryoke metamorphic belt, occurs in rhodochrosite-alabandite ore. In thin section, it is associated intimately with tephroite and alabandite. Small amount of rhodochrosite, galaxite and pyrophanite coexist with the welinite. The mineral is rarely, occurs as very fine grains up to 0.2mm in diameter. Under the microscope, it is colorless or has slight yellowish tint, therefore it is difficult to distinguish it from tephroite.
Welinite from the Ioi mine in Paleozoic Chichibu formation, occurs in tephroite-alabandite ore. The mineral is associated with tephroite, rhodochrosite, alabandite and small amounts of galaxite and pyrophanite. The mineral is yellow to yellowish brown in color, and 0.05-0.10mm in diameter.
Microprobe analyses of welinites from the Taguchi, Fukumaki, and Ioi mines yield the empirical formula Mn ₆WSi₂ (O, OH) ₁₄ on the basis of (O, OH)=14. Welinite in the bedded manganese ore deposits is interpreted as a product due to the reaction of manganese ores and hydrothermal solutions cotaining WO₃, H₂O, and CO₂ probably sup-plied from granitic bodies near the ore deposits.