b'Chalcocite conductivityFeatureand perhaps anilite Cu 7 S 4(77.6% Cu). Digenite may have aPp743-752 (The Australasian Institute of Mining and conductivity two orders of magnitude greater than chalcocite,Metallurgy: Melbourne).and djurleite one order of magnitude greater (Shuey, 1975).Read, H.H., 1970. Rutleys elements of mineralogy, George Allen & These two minerals dominate the economic mineralogy of theUnwin.Esperanza copper deposit in the Mt Isa Inlier (Richardson and Moy,Shuey, R.T., 1975. Semiconducting ore minerals, Elsevier.1998). Chalcocite is black cuprous sulphide, a closely associatedTelkes, M., 1950. Thermoelectric power and electrical resistivity mineral is the indigo-blue cupric sulphide, CuS, covellite (66.4%of minerals, American Mineralogist, 35, 536-555.Cu), which acts as a p-type metal with a conductivity exceedingYang, Y.P., and Emerson, D.W., 1997. Electromagnetic 1000 000 S/m. Covellite usually does not occur in abundance, butconductivities of rock cores, theory and analog results, as inclusions in, or coatings on, other copper sulphides. It doesGeophysics, 62, 1779-1793. doi: 10.1190/1.1444278.not match its associated sulphides in copper content, but it surely could affect their electrical properties. Although known to occur sometimes as primary sulphides, e.g., in hydrothermal veins, all these minerals are mainly encountered in the supergene zoneDon Emerson is a geophysical consultant specialising in and, to better to target an important metal resource, they warrantthe physics of minerals and rocks, he also has an interest in further petrophysical studies. Any such investigations shouldancient and medieval geoscience.be tied tightly to chemistry and mineralogy, as work carried out on synthetic copper sulphides (e.g. Okamoto and Kawai, 1973) has shown that conductivity is highly sensitive to variations in stoichiometry.AcknowledgementsThanks are due to David and Lainie Kalnins for suggestions, and for the preparation of the manuscript and figures.ReferencesBlanchard, R., 1968. Interpretation of leached outcrops, Bulletin 66, University of Nevada.Emerson, D.W., 1990. Notes on mass properties of rocksdensity, porosity, permeability, Exploration Geophysics, 21, 209-216. doi: 10.1071/EG990209.Emerson, D.W., 2019. Pyrite, Preview 203, 52-64.Harvey, R.D., 1928. Electrical conductivity and polished mineral surfaces, Economic Geology and the Bulletin of the Society of Economic Geologists, 23, 778-803. doi: 10.2113/gsecongeo.23.7.778.Jones, N., 2016. The copper sulphides, Rock & Gem., 46/5, 10-15.Jones, N., 2018. Copper minerals of Bristol, Rock & Gem., 48/6, 16-21.Lindgren, W., 1933. Mineral deposits, McGraw-Hill Book Company Inc.Okamoto, K., and Kawai, S., 1973. Electrical conduction and phase transition of copper sulphides. Japan Journal of Applied Physics. 12, 1130-1138.Pelletier, R.A., 1964. Mineral resources of South-central Africa, Oxford Uni Press.Richardson, S.M. and Moy, A.D., 1998. Gunpowder copper deposits, in Geology of Australian and Papua New Guinean Mineral Deposits (Eds: D.A. Berkman and H.H. Mackenzie). 51 PREVIEW JUNE 2021'