b'Chalcocite conductivityFeatureThe conductivity of chalcocite, the richest copper sulphideFigure 1.Chalcocite crystals exhibiting platy habit and metallic lustre (lateral dimensions ~30 mm) from (left) Mammoth Mine northwest Queensland and Don Emerson(right) Cornwall, England. Chalcocite crystals or crystal aggregates can display emersondw@yahoo.com a bluish tarnish (left) and striations (right). Good crystals are not common, and collectors pay high prices (hundreds to thousands of dollars) for nice specimens. Most chalcocite, however, occurs as unattractive duller, dark, fine grained granular aggregates, or as porphyry style disseminations. Source: Chalcocite / Introduction Rob Lavinsky, iRocks.comCC-BY-SA-3.0Exploration for copper has long been a focus for humankind. Developments in modern technologies have generatedandeven more demand for this most useful metal. The cuprous5FeS 2 +14CuSO 4 +12H 2 O = 7Cu 2 S +5FeSO 4 +12H 2 SO 4sulphide, chalcocite (CuS) with a 79.8% Cu content is the 2richest and most valuable sulphide of copper (compare chalcopyrite, CuFeS 2 , 34.5% Cu), but its conductivity hasThus, a very desirable secondary ore of copper is produced in been little investigated. This article aims to contribute to thesecondary, messy, acidic reactions resulting in a highly altered, limited database with some inductive electromagnetic (EM)porous environment. The chalcocite, Cu 2 S, is dark, sometimes measurements. sooty, soft (Mohs hardness3), imperfectly sectile, dense (5.55.6 g/cc, t/m3). It is a p-type semiconductor (Shuey, Chalcocite can occur as a primary crystalline sulphide e.g., in1975), crystallising in the monoclinic system, but readily the hydrothermal veins of granite in Cornwall, but most of itpseudomorphs e.g. after pyrite. Usually, it is found as tabular forms as fine-grained dark blankets under the water table incrystals, mainly fine to very fine grained; rarely coarse.the supergene enrichment zone above primary chalcopyrite ore, in metasediments. This zone of enrichment is fed by copper sulphate solutions descending through the weathered zones. MeasurementsThe old CSA Mine, Cobar NSW, had a nine metre supergeneMass property (Emerson, 1990) and EM conductivity (Yang and zone. The Mt Isa Inlier, northwest Queensland, hosts severalEmerson, 1997) measurements were carried out at mesoscale deposits of supergene chalcocite. Much chalcocite occurson 21 samples from the USA, D R Congo, and Australia. The as disseminations in low grade porphyry coppers. Furthersamples, categorised in Groups I to VII, ranged from high information on occurrences, genesis, and mines in Australiaconductivity, collector grade, crystal aggregates through fine and overseas can be found in Blanchard (1968), Lindgrengrained massive ores varying in chalcocite, chalcopyrite, pyrite (1933), Read (1970), Richardson and Moy (1998), Jones (2016,and graphite content, to a low conductivity carbonaceous 2018), and will not be repeated here. An instructive summarysiltstone host rock containing minor amounts of chalcocite of chalcocite and its structure may be found at https://www. and pyrite. Samples were examined under the microscope mindat.org/min-962.html. Figure 1 shows two examples ofto estimate mineralogy. In Table 1, for Groups I to V, the collector grade chalcocite. samples have been listed in decreasing order of chalcocite content, so for Group V #11 has the most chalcocite and #14 has the least. Group VI is dominantly pyritic with only minor Ore genesis chalcocite, some of these samples show signs of decomposition and disaggregation. The various mineral assemblages were Consider a primary chalcopyrite body, usually associatedgalvanically micro-probed to investigate, qualitatively, relative with pyrite, which undergoes weathering and develops anconductivities. This established that conductivity diminished enrichment cap. In the weathered zone, oxidation generatesin the order: graphitechalcopyritechalcocitepyrite. The iron sulphate (which, when hydrated, is green vitriol) andsamples and results are given in Table 1 along with relevant very mobile copper sulphate. The copper sulphate descendsinformation and measurement techniques discussed in other in solution to interact with chalcopyrite and pyrite, possibleprevious articles (e.g. Preview 203, 52-64, on pyrite).reactions are:CuFeS 2 + CuSO 4 = 2CuS +FeSO 4 (covellite + vitriol) ResultsthenThe results given in Table 1 are plotted against density in 5CuS +3CuSO 4 + 4H 2 O = 4Cu 2 S + 4H 2 SO 4 (chalcocite + acid) Figure2. A feature of the results is the extraordinary values JUNE 2021 PREVIEW 48'