1977 Volume 27 Issue 141 Pages 31-37
Wolframite has been found from the contact-metasomatic scheelite deposits of the Kiwada, Fujigatani and Kuga mines. Wolframite in the Kiwada deposit occurs in porous, relatively low-grade ores composed mainly of quartz, albite, muscovite, chlorite and siderite, and is intimately associated with pyrite. The mineral assemblage is unique in its Ca-poor chemistry which contrasts with Ca-rich ordinary ores from the deposit. The mineral occurs as pseudomorph after scheelite (<1 mm in diameter). The pseudomorph is composed of fine-grained (0.02-0.04 mm) wolframite crystals.
Wolframite from the Fujigatani and Kuga deposits examined here are obtained from mill products. Although their modes of occurrence in field have not been clarified yet, microscopic observation indicates that these wolframites are also pseudomorphic products after scheelite. Sporadic and minor occurrence of wolframite in all of the deposits suggests that the favorable condition for wolframite in place of scheelite may have been attained only in limited portions of the deposits towards the last stage of mineralization.
Mineralogical data obtained by X-ray diffraction, wet chemical analysis and EPMA analysis are summarized in Table 1 and Fig. 4. It is likely that Fe/Mn ratio of pseudomorphic wolframite can be variable widely, though Fe-rich species seem to be most common.
Fe/Mn ratios in the specimens collected from two ore bodies of the Kiwada deposit show large difference: 0-12 mol.% MnWO4 in the Oogiri No. 5 ore body and about 44% MnWO4 in the Shin-ei ore body. Mn-content in coexisting chlorite is found to be correspondingly higher in the Shin-ei ore, suggesting that the mineralization environment has been more manganiferous in this ore body than the Oogiri No. 5. Wolframite from the Fujigatani and Kuga deposits seem to be generally close to the Fe end-member. However, some of the grains from the mill product of Kuga are rich in Mn up to 80% MnWO4. The observation is in accord with the fact that common constituent minerals in the two deposits such as clinopyroxene, garnet and calcite are occasionally more manganiferous in the Kuga deposit.
