Temperature Phenomena and Meat Flow Estimates in Two Precambrian Ore-bearing Areas in North Sweden

Temperature measurements in 17 drillholes reaching vertical depths between 365 and 780m below ground surface in the Skellefte area (lat. 65 " 52 ' N, long. 20 " 20 ' E Gr) and Aitik area (lat. 67 " 5 ' N, long. 21 " E Gr) in the Swedish Precambrian are reported. The absolute accuracy of the measurements was about 0.03 "C and the relative one about 0.005 "C. A large number of thermal diffusivity measurements were made on rock samples from the two areas in order to estimate the correction to the observed steady geothermal gradients due to climatic amelioration at the end of the Pleistocene. The corrected gradients are between 0.01266 "C m- ' and 0.01485 "C m- ' (Skellefte) and between 0-01684°C m-l and 0.02268 "C m- ' (Aitik). The diffusivity measurements were supplemented by thermal conductivity determinations on 265 drillcore samples from the different rock formations in the holes. The undisturbed heat flow in the Skellefte area is found to be 48.7 mW m- ' and that in the Aitik area to be 49.8 mW m-'. Distortion of the heat flow due to a sulphide ore in the Skellefte area is demonstrated. The heat flow through the Lingsele ore in this area is of the order of 70 mW m-'