The Cretaceous Takatori tin-tungsten deposit, Ibaraki Prefecture, Japan, is characterized by wolframite-bearing quartz veins. While tin-tungsten type deposits are usually considered to be produced by hydrothermal fluids from granitic magma, no granitic rocks have previously been described around the mine. Aplite veins are found in a diamond-drill hole located 350m west of No. 7 vein of the Takatori deposit. The drill hole is situated within the area of the mineralization. The aplite, composed of quartz (30-40%), K-feldspar (25-35%), plagioclase (25-40%) and muscovite (2-4%), characteristically contains small amounts of fluorite and topaz. The aplite samples are peraluminous and have high SiO2 contents (76.4 to 76.9%), and high Ga contents. Judging from mode of occurrence and petrological characteristics, the aplite is intimately related to the formation of the tin-tungsten deposit. The presence of this aplite implies that the granitoid body that produced the aplite could be present at depth.
While the Takatori deposit was formed at about 71 Ma, ages of the Younger granitoids of the Yamizo mountains are slightly younger, ranging from 66 to 69 Ma. The mineralization also predates the intrusion of granitoids in the Tsukuba mountains, that have ages between 58 and 66 Ma. Therefore, the Takatori deposit was formed by granitic plutonism that is slightly older than these granitoids intrusions.
