1977 Volume 27 Issue 142 Pages 119-132
The Matsumine is the largest Kuroko deposit in Japan, situated in western margin of the Hokuroku district, Akita Prefecture. In October 1966, the first production was started at the rate of 20, 000 tons of crude ore per month and the rate was increased in the following years up to 50, 000 tons per month. Total production of crude ore since the beginning of operation amounts to more than 5 million tons. The stratabound ore deposits in the Matsumine lie 200m to 400m below the surface, and extend horizontally in the area N-S 800m and E-W 600m.They are all distributed in definite stratigraphical horizons of Hanaoka formation of the Miocene Tertiary and divided into three units, which are called lower, middle, and upper ore beds. In each of these units, the zoning according to the mineral assemblage are observed such as pyrite ore, yellow ore, and black ore in ascending order. Generally the lower ore is rich in yellow ore and poor in black ore, the middle one consists of black ore and yellow ore, and upper one is dominant in black ore. A recent prospecting in this mine has performed from the center of mineralized area to the outward and the downward. A new method of upward drilling has investigated the black ore of the upper ore bed. As the results of these works, the following objects have been made clear.
1) Mode of occurrence on three ore beds (upper, middle, and lower), and the mineral composition of ore in each bed.
2) Existence of four lava domes of rhyolite and the form of each dome, which are closely related to the genesis of the ore deposits.
3) Mineralization in the footwall under the stratabound deposits.
4) Internal structures in the ore deposits.
