Thermal Conductivity of Altered Granitic Rocks

Abstract

Recently, geothermal resources or hot springs have been developed in granitic bodies at some areas. A wide alteration zone occurred in these areas. To make clear the thermal history of the body, it is important to examine how the alteration effects on thermal properties of the rock. In order to investigate a thermal conductivity variation with the alteration of granitic rocks, we carried out mode mineral analyses and thermal conductivity measurements for 16 rock samples. These samples consisted of 8 samples collected from outcrops on the middle reaches of the Kurobe River in the Northern Japan Alps, and 8 samples from borehole cores at the Western part of Omachi City near the Northern Japan Alps, and at Kumihama in Kyoto Prefecture. 10 samples include alteration minerals such as Chlorite, Sericite, Calcite and some other clay minerals. Bulk density was measured for all samples, but thermal conductivity did not depend on density. The Hashin-Strickman's Formula was adoped on the calculation for thermal conductivity of rocks using that of rock-forming minerals to describe the relation between thermal conductivity of rocks and mode of minerals. These results showed that the Quartz content dominates thermal conductivity of granitic rocks, because Quartz has very high thermal conductivity. And also showed that as contents of alteration minerals, such as Chlorite and Calcite, altered from Feldspar and Mica increased, thermal conductivity of the rock increased, because the thermal conductivity of Chlorite and Calcite are higher than that of Feldspar and Mica.