Abstract: Water, air, other fluid flows downwardly through a tube which extends from the surface of an underground mine to a number of conduits arranged in loops which extend into bore holes at or near the bottom of the shaft. The fluid in the conduits remains isolated from the walls of the bore holes to prevent contamination by minerals in the walls. The fluid remains in the conduits while its temperature rises by geothermal action. The heated fluid is then pumped through a second tube to a station at which the ambient temperature is lower than that of the fluid. Thermal energy is extracted from the heated fluid at the station.