b'CommentaryMinerals geophysicsstacked layers of graphene. Graphite Minerals geophysics is strongly electrically conductive, much more so parallel to the graphene layers than perpendicular to them. In mineral exploration, apart from Terry Harveydirect detection in the search for Associate Editor for Minerals geophysics massive graphite deposits, the value E terry.v.harvey@glencore.com.au of graphite detection comes from its presence in metamorphosed sedimentary sequences which may, Form and substance plate can generate the same responsefor example, host strata-bound zinc magnitude as a thick plate ofdeposits, and from its occurrence Whenever Im discussing geophysicalmoderateconductivity. in disruptive structures. Systematic interpretation with geologists mymapping of both these features will aid emphasis is on the petrophysicalPyrrhotite geologicalunderstanding.property involved: magneticIn electromagnetic exploration, the susceptibility for magnetics, densityPyrrhotite is a common iron sulphideimpact of graphite, too, can go beyond for gravity, electrical conductivity formineral of variable composition its strong electrical conductivity. In electromagnetics, etc. Our approachFe (1-x) S where x = 0 - 0.17. The variablemetamorphosed sedimentary units, then is to try and relate geology to thedeficiency in iron is responsible for itsboth layering and associated pyrite interpreted geophysically-derived valuesvariable magnetic properties, but that(particularly in the case of units and distribution of the petrophysicalis not our concern here. Unlike most ofassociated with strata-bound zinc property in the sub-surface. Thisthe common metallic sulphide mineralsdeposits) contribute to enhanced typically involves questions like What(pyrite, chalcopyrite, galena, etc.) whichelectrical connectivity and conductivity. likely rock types are both dense andare semi-conductors, pyrrhotite is aConductance comes into play too, magnetic? and, perhaps more hopefullymetallic conductor with significantlyin that a lower conductivity due to Could this relatively shallow flat-lyinghigher electrical conductivity (seethe somewhat disseminated nature conductor be mineralisation related Pearce et al. 2006 for backgroundof the conductive minerals can be perhaps enhanced weathering or even adetail). In mineral exploration,compensatedfor by unit thickness. secondary enrichment blanket?. the value of pyrrhotite detectionSystematic detailed mapping of these In this piece Id like to take a closercomes from its association with oreunits at a sub-regional scale is feasible look at electromagnetics and electricalminerals, as for example in some VMSwith airborne electromagnetics; conductivity; in particular, two stronglypolymetallic, SEDEX zinc and magmaticfavourable sites for mineralisation, conductive minerals the propertiesnickeldeposits. notably fold closures, may thus be of which and their distribution inIn electromagnetic exploration, thehighlighted. In disruptive structures, geology (respectively the substanceimpact of pyrrhotite can go beyond itsthe distribution and platy nature of and form of my title) impact on thestrong electrical conductivity. In manygraphite can enhance the electrical use of electromagnetics in mineralcases the nature of the distribution ofconnectivity within the structures, exploration. For the most part, neitherpyrrhotite within the mineralisationrendering them more amenable to mineral is an exploration target in itsenhances the electrical connectivity,electromagnetic detection. Again, own right, but both have associations ofrendering the body more amenablemapping of these structures with economicsignificance. to electromagnetic detection. Stories,electromagnetics can contribute to the In very simplistic terms, thein some cases perhaps apocryphal,overall explorationprogramme.electromagnetic geophysical techniqueof drilling a strongly conductiveSo there you have it. In mineral utilises electromagnetic generation, thenelectromagnetic target only to findexploration the electromagnetic subsequent electromagnetic detection,20cmof massive pyrrhotite as thetechnique targets the petrophysical of transient electrical currents flowingpotential source, are commonplace.property electrical conductivity within a conductive target body. Plate- Certainly, in my experience the first(substance). And the very nature of the like target bodies have the optimumchoice of the possible source mineralgeological distribution (form) of two shape. Key properties of the target bodyfor a particularly conductive targetminerals of high electrical conductivity are the conductivities of constituentis pyrrhotite. And in exploration forenhances the effectiveness of that minerals, electrical connectivity, andmagmatic nickel deposits, there aretechnique. Substance and form - theres size, more specifically for plate-likethe additional bonuses of the layeredanice symmetry there.targets, areal extent and thickness. Thenature of the deposits and the presence generated transient electrical currentsof metallically conductive pentlandite must be of sufficient strength, duration(FeNi) 9 S 8 . No wonder electromagneticsReferencesand extent to create a quantifiableis the go-to geophysical explorationPearce, C.I., R. A. D. Pattrick, D. J. Vaughan, secondary electromagnetic field. As atechnique there! 2006.Electrical and Magnetic Properties of further consideration the strength of theGraphite Sulphides, Reviews in Mineralogy & Geochemistry. electromagnetic response is proportional61: 127-180to conductance (conductivity xGraphite is a naturally occurringWikipedia https://en.wikipedia.org.wiki thickness). A thin extremely conductivecrystalline form of carbon comprisinggraphite, pentlandite, pyrrhotite36 PREVIEWFEBRUARY 2024'