Geochemical Characteristics of Tungsten in Miyako Granitoid and Scheelite-bearing Aplitic Veins at the Yamaguchi Cu-W Skarn Deposit, Iwate, Japan

Tungsten analyses were made on 16 samples collected from the North Miyako granitic body in Northeast Japan. Petrographic facies of the North granitic body vary from quartz diorite in the marginal zone (zone A), to tonalite and granodiorite (zone B), and to granite in the central zone (zone C). A large number of barren and scheelite-bearing aplitic veins are distributed around the Yamaguchi deposit which occurs in the contact aureole of zone C granite. The tungsten content of zone C granite is lower than that of the granitic rocks in zones A, B and the aplitic veins. It appears that tungsten in the differentiated granitic magma, which was associated with ore mineralization, was transported out of the magma chamber by magmatic fluids. The tungsten content is generally low in the North Miyako granitic rocks but high in granitic rocks of Okinoshima zoned pluton, as well as in Otani granite and Busetsu granite from the Southwest Japan. In the case of magnetite-series, however, the behavior of tungsten in the Miyako granitic body from the tungsten metallogenic province is similar to that of the Okinoshima zoned pluton from molybdenum metallogenic province in Southwest Japan. Behavior of tungsten in granitic magma is affected by magmatic evolution during the process of saturation of granitic melt with magmatic fluid.