Internal Structure of Black-Ore Deposit of the Yokota Mine

• Published in: Mining Geology Vol. 16; no. 76-77; pp. 106 - 115
• Main Author: HIRABAYASHI, Takeo
• Format: Journal Article
• Language: English; Japanese
• Published: The Society of Resource Geology 1966; 資源地質学会
• ISSN: 0026-5209
• DOI: 10.11456/shigenchishitsu1951.16.106

The Yokota Mine is located at about 44km west of Aizu-wakamatsu City, Fukushima Prefecture. The Neogene Tertiary formation in this area are divided into four stratigraphic units as follows : 1) Sodeyama Formation, 2) Oshio Formation, 3) Takizawagawa Formation, and 4) Yokota rhyolite. The first three formations are characterized by rocks of the so-called "green tuff" facies. Black ore deposits of the Yokota mine comprise two types from the viewpoint of their internal structure. Banded black ore deposit occurs under black mudstone of the Oshio Formation, and massive disseminated or network deposit is found mainly in the Takizawagawa Formation and Yokota rhyolite. Zonal arrangement of these to types of ore deposits are shown below. Oshio Formation Banded black ore deposit Massive disseminated or network deposit Takizawagawa Form. and Yokota rhyolite mudstone soapstone (roof) quartz-hematite zone compact black ore zone drusy black ore zone chalcopyrite rich zone siliceous yellow ore zone siliceous ore of stockwork type zone rhyolite and tuff breccia (bottom) Motoyama mine lot, situated in the southeastern part of the Yokota mine, forms the center of silicified zone and banded black ore deposit developed along an anticlinal axis. Massive disseminated or network ore deposit are associated with many sand dykes in the anticilinal structure. By these facts, the hydrothermal solution might have ascended continuously along these sand dykes during Takizawagawa and earlier Oshio stages.