1981 Volume 31 Issue 166 Pages 99-114
The Toyoha mine is located in the geothermal area of Southwest Hokkaido, Japan. The geothermal surveys revealed the presence of very high heat flow areas widely spread over the ore deposit in the Neogene system. The heat flow amounts to 25.7 HFU (heat flow unit), about ten times higher than we expect generally in the Green-tuff region of Japan. Notwithstanding, few hot springs and vapor fumaroles are found around the area and neither prospect tunnels nor drillings have ever disclosed any conspicuous underground hot-water reservoirs.On the basis of the geothermal data obtained from the borehole temperature measurements, it is proved that the temperature distribution has a clear tendency to increase southeastwards and vertically downwards. The source of the high heat flow concerned is presumed as a kind of hot dry rock.
The mining operation will be concentrated on the conspicuously high heat flow areas in the future. Thus it is an important problem how to lower the temperature at the underground working site. For the purpose of obtaining the basic data for the future exploration and development in hot areas, the present study aims to draw a possible limit of exploitation by computing the heat balance in tunnel.
