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Electrical resistivity of quartzite obtained from the gold-belt of the Tarkwaian rock formation in South-Western Ghana
The variation of the electrical resistivity between room temperature (300 K) and elevated temperature (500 K) has been investigated for quartzite obtained from the Gold Belt of the Tarkwaian rock formation in the south-western part of Ghana. The resistivity was measured for the passage of current through the samples in two orthogonal directions, parallel and perpendicular to the rock foliation. The average value of the room temperature resistivity for electrical conduction in the two directions were respectively, 9.02 x 105 W m and 1.95 x 108 W m. These values indicate that the ease with which current flows in the direction of foliation is about 200 times greater than in the perpendicular direction which confirms the general anisotropic behaviour of rocks. The average anisotropic coefficient was found to be 14.7. It was observed that generally, the resistivity increased with increase in temperature, attaining a maximum value at about 430 K, above which the resistivity decayed exponentially. This trend in conductivity is suggestive that two types of conduction take place in the quartzite within the temperature range studied. Between 300 K and the maximum temperature, it appears, that conduction is due to ions within the electrolytes filling the pores of the rock samples. Above the maximum temperature, the pores become dry and most probably charge carriers are responsible for the conduction as it occurs in a semiconductor. The average activation energies obtained for conduction above the maximum temperatures, in the parallel and perpendicular directions were respectively, 0.20 ± 0.03 eV and 0.83 ± 0.04 eV. These values compare favourably with the activation energies of other rock samples and are also similar to the values for some semiconductor materials.
JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 2 No. 2 (2000) pp. 114-120