b'FeatureBornite conductivityThe conductivity of bornite, peacock ore, a copper-iron sulphideDon Emerson emersondw@yahoo.comIntroductionCopper is a prominent member of the green metal suitemost bornite occurs in unappealing, granular, massive forms (Cu, Ni, Li, rare earths) essential to the worlds embracemanifesting dark purplish or black hues Such were the of decarbonisation which entails a need for ever moreappearances of the bornites (from Zambia, Mexico and Victoria) electric cabling Coppers value has increased substantiallyavailable for this study These samples were checked for softness (currently ~ $10 000 per tonne) and so has exploration(Mohs hardness 3) and visually inspected for other sulphides that, interest in a metal mined for millennia and still keenly soughtwhen present, were in minor/trace amounts only The absence In exploration geophysics, applied to copper provinces,of pyrrhotite was attested by low magnetic susceptibilities the conductivities of copper sulphides are a significantSome samples were pyrrhotitic but were discarded from consideration It is interesting to note that graphite, ironically,testing as pyrrhotite would have dominated the conductivity is also in demand for green technologies It sells for ~ $1000measurements The bornite mineralogy was checked by noting / tonne Graphite is semi-metal (electronically) and verysoftness and checking the brownish bronze colour of fresh conductive in concentrated form (see my article in Preview 72) fracture surfacesa characteristic of bornite Bornite samples were difficult to obtain Several samples purporting to be bornite The three commercially significant Cu sulphides are:were found on examination to be mainly chalcopyrite, pyrite, and chalcopyrite, a primary mineral, lowest grade; chalcocite,pyrrhotite mixes and, accordingly, discardedhighest grade, usually found in secondary enrichments; and bornite (erubescent peacock ore), intermediate grade occurringFor interest and for comparison some chalcopyrite samples in both primary and secondary modes Associated sulphides(pyrrhotite free) were measured and included in the studyinclude digenite and covellite (usually minor constituents ofI have already discussed the mesoscale conductivities of a deposit) and the iron sulphides; pyrite and pyrrhotite Thesechalcocite (Preview 212), pyrite (Preview 203), and pyrrhotite sulphides are soft (except for pyrite) and form part of the(Preview 92, 188)Cu-Fe-S system (Klein & Hurlbut, 1993) as listed in Table 1 and depicted in Figure 1 Bornite seems to have been little studied MeasurementsMaterials Mesoscale electrical conductivities of suitable bornites were measured to show how these compare with other sulphides Attractive types of bornite are shown in Figure 2 where prettyMesoscale means core or hand sample usually comprising crystal colours and tints are evident The striking iridescencecrystal or granular aggregates; it is intermediate between the of some bornite gives it the name of peacock ore However,microscale (small single crystal) and the macroscale (regional Table 1.Some sulphides in the Cu-Fe-S systemMineral Type of Formula Cu Fe S Density Magnetic Hardness Electricalconductivity (approx.) g/cc susceptibility (Mohs scale) conductivity(Shuey, 1975)wt. %SI x 1010Chalcocite p type semiconductor Cu 2 S 798 0 202 570 3 moderateDigenite p type metal Cu 69 Fe 01 S 4 766 trace 224 560 3 extremely highCovellite p type metal CuS 664 0 336 470 2 extremely highBornite p type semiconductor Cu 5 FeS 4 633 112 255 507 ~ 55 3 see textChalcopyrite n type semiconductor CuFeS 2 346 304 350 42 ~ 35 4 highPyrite p,n type semiconductor FeS 2 0 466 534 502 4 61/2 moderatePyrrhotite, mon low mobility metal Fe 7 S 8 0 604 396 46 35000 4 very highPyrrhotite, hex low mobility metal Fe 9 S 10 0 611 389 47 144 4 very high41 PREVIEW OCTOBER 2022'