b'Pyritethe firestoneFeaturefor pure pyrite. The cube specimen #3 has a low grain density for pyrite, 4.86 g/cc, which is assumed to be due to internal occluded voids inaccessible to the vacuum saturant.Porosities are very low (0.1%) for eight samples, low (0.20.8%) for twelve samples, moderate (12.9%) for ten samples, high (5.612.1%) for five Peruvian samples (very voidy, visually), and very high (22.9%) for an extremely weathered massive (now skeletal) sulphide (#19).Magnetic volume susceptibilities (k) are generally low (50 10-5SI) except for four samples (#2023) containing minor pyrrhotite (416820 10-5SI). Pyrites mag k was thought to be 4 10-5SI, but 16 samples have mag k values below this. Sample mag ks up to 50 10-5SI can be ascribed to the presence of minor amounts of Fe paramagnetic silicates, Fe carbonate etc.The conductivity data are best viewed in the perspective of a density crossplot which is presented in Figure 11 where the sample conductivities from low (0.5 S/m) to high (4250 S/m) are clearly seen to increase, broadly with density.InterpretationThe data have been grouped and trended as follows:Figure 10.Coarse grained Gumeracha pyrite from South Australia provided I.massive single crystal pyrite, #1, 2, 3, 4; the core for testing in an induction coil of type used in the conductivityII.massive variably porous pyrite, polycrystalline aggregate,measurements. The wire winding is 70 mm long x 30 mm internal diameter. #515; A conductive core inserted in the coil causes a change in its resistance, R, III.massive pyrite + minor silicate and sphalerite in siltstone,which is measured on an LCR meter. If the core is magnetic it also causes a #16, 17; change in the coil inductance, L. From these quantities electromagnetic IV.pyrite altered-minor alt. #36, moderate alt. #19; conductivity and magnetic susceptibility are derived (Yang and Emerson 1997). The measurements are usually run in the kHz range (below the onset of skin V.pyritic banded metasediment, moderately pyritic to semieffect). An air gap correction would be necessary if this method is used for a massive, #2733; mag k measurement. For low susceptibility pyrite the change in inductance VI.veinlet, blebby pyrite in black shale, #25, and quartz #26; is quite small so a high sensitivity meter is required. The 45 mm long, 25 mmVII.banded, #34, semi massive, #35, and massive, #24, pyrite alldiameter Gumeracha pyrite test core shown here is sample 10 with a 28 S/m EM with minor chalcopyrite; conductivity and 2 x 10-5 SI mag k. This pyrite is porous and has a minor silicate VIII. massive pyrite with minor pyrrhotite, #2023 (note thecontent.elevated mag k values in Table 3).Also shown are chalcopyrite ore with metasedimentary gangue,Adding minor chalcopyrite to the pyrite boosts conductivity C, Cobar NSW; and nickeliferous pyrrhotite, K, from Kambalda(vii), as does minor pyrrhotite (viii) which is even more effective.WA. These two massive sulphide samples contain minor pyriteThe remaining pyritic categories (v), (vi) have quite low and are not in Table 3, they are included for comparison only, toconductivities around the 1 S/m level. These conductivities are contrast with the lower conductivity of massive polycrystallineapparent as they are due to bands in the core not to the whole pyrite. core.The pyrite single crystal conductivities (i) are high by anyTypical massive chalcopyrite ore (C) has a conductivity standard, 1000s S/m. However, pyrite of interest in the fieldcomparable to single crystal pyrite; the massive nickeliferous occurs massively aggregated and the conductivities of thepyrrhotite (K) is an order of magnitude better.samples (ii, iii) in this group are two orders of magnitude below that of the single crystals. Conductivities in the 10s to lowThe groupings are based on mineralogy and texture, but the 100s S/m increase, more or less, with density and diminishingsuperimposed trends are subjective. No claims whatsoever porosity. Voids, microcracking, intercrystalline alterationare made for the data being generally definitive of pyrite, products, and grain boundary replacement (surface film) ofbut the data are indicative of at least some types of pyrite presumably Fe sulphate and/or marcasite (Deer, Howie, andconductivity and pyrites frequent inferiority to chalcopyrite Zussman 1992) can be seen or presumed in the samples. Alland pyrrhotite.serve to reduce conductivity and this tendency is exacerbated by pyrites cubic blocky crystallinity. So texture, overall, impedesMarcasiteaggregated pyrite attaining its single crystal conductivity, at least in the samples tested here. Contrast this with theMarcasite is the low temperature, chemically unstable, pervasive, threading, connecting, dendritic habit of chalcopyriteorthorhombic dimorph of pyrite. It can be difficult to distinguish and pyrrhotite, much better for electrical continuity thanfrom pyrite, sometimes Xray diffraction is required. It has a pale sutured pyrite polyhedra. yellow colour, its density, 4.89 g/cc, is less than that of pyrite, 5.02 g/cc. It deteriorates rapidly in moist air and many a mineral Minor amounts of insulating minerals diminish conductivitycollection cabinet has been ruined by its ferrous sulphate and (iii); alteration of the pyrite lowers conductivity yet further (iv).sulphuric acid alteration products. Usually the presence of white DECEMBER 2019 PREVIEW 62'