b'Mineral geophysics Minerals geophysicsthe conductive carbonaceous shalesmovement of material such as occurs in themselves may allow you to focus yourglaciated terrain. In areas of no outcrop, efforts in particular areas. Your targetradiometrics may also have mapping may then be a specific environmentapplications. Where there is residual considered favourable for mineralisationcover, will radiometric mapping of the rather than a discrete conductor. surficial material reflect the distribution of underlying rock types? Where there Silicification and carbonate floodingis transported cover, will radiometric associated with mineralisation can rendermapping of the surficial materials have the adjacent country rock more resistantapplication in the normalisation of to weathering and erosion, resulting inmobile metal geochemistry results?mineralisation being associated with topographic highs. In one prospectiveA greater depth of burial may put the Terry Harvey region with negligible outcrop andtarget beyond the reach of your preferred Associate Editor subdued topographic relief we seriouslygeophysical technique. Time domain EM for Minerals geophysics considered using detailed elevationis the conventional choice for conductive firstname.lastname@example.org maps as an initial targeting tool. Wheretargets, but there are depth of younger transported sediments coverinvestigation limitations. It could be that the old land surface, geophysicalone of the deeper penetrating frequency techniques that estimate depth todomain EM techniques such as CSAMT, Horses for courses bedrock (e.g. EM and refraction or passiveAMT or MT may merit consideration. Or seismics) may be used to map out theperhaps you will have to resort to indirect palaeo-topography. As a bonus, thesedetectionwould magnetics (magnetite In mineral exploration is the selection oftechniques could provide information onassociation) or gravity (density contrast) an appropriate geophysical techniquethe properties of the bedrock as well. work for you?as straight-forward as it first seems? EM for massive sulphides (VMS), IP-resistivityWeathering processes can provideThe presence of man-made features can for disseminated sulphides (porphyryopportunities to vary your explorationlimit the application of an otherwise copper), magnetics for magnetite (ironmethod. IP-resistivity is the go-toappropriate geophysical technique. This ore), gravity for massive iron oxidesexploration method for disseminatedis particularly relevant on mine sites, (IOCG), and radiometrics for uraniumsulphides, but circumstances such aswhere unwanted responses from mine minerals and monazite (beach sands)restricted surface access or unfavourableinfra-structure can interfere with the all seem pretty straightforward. But,ground conditions can confound its use.results of geophysical surveys. Attention in the real world, things can get a bitDisseminated sulphide mineralisationto detail in planning and executing the complicated. There may be factorsmay show little electrical conductivitysurvey will be required. Perhaps you will at work that can generate difficultiesor density contrast with the countryhave to resort to less than ideal survey or provide opportunitiesa bit ofrock, but preferential weathering andparameters and coverage, or even try a innovative thinking might be calledsupergene enrichment will renderdifferent method. Gravity, which arguably for. The geological environment,this section of the mineralisationis less affected by man-made structures geological processes associated with themore conductive and, in some parts,than magnetics, EM and electrical mineralisation, the weathering regime,less dense. Both EM and gravity maytechniques, may be worth considering if depth of burial and nature of overlyingthen have application in locating themeasurable and recognisable responses materials, presence of man-made featuresnear-surface weathered expressionsfrom your targets could reasonably be and even site access considerations canof these targets where conditionsexpected in the survey results.all play a part. You may have to resortare unfavourable for IP-resistivity. to indirect detection using associatedWidespread and rapid geophysicalSo, the mantra that mineral geophysical features rather than direct detection ofexploration for disseminated sulphidesexploration can only be successful if the mineralisation itself. from the air with EM, or detailedthere is a physical property contrast exploration in an electrically challengingbetween the target and its environment Consider EM surveying for massiveenvironment with gravity may bewhich produces a measurable and base metal sulphides in an electricallypossible. recognisable response in the geophysical conductive environment such assurvey holds in most cases, but carbonaceous pyritic shales. It may notThe depth of burial and nature of thesometimes a bit of lateral thinking may be possible to discriminate an otherwisecover materials can influence yourbe needed.recognisable target conductor responsechoice of geophysical technique and in this highly electrically anomalousthe way that you apply it. Less than aI look forward to catching up with you environment, but the disposition ofmetre of cover will effectively obscureat the upcoming AEGC 2019 Data to the conductive shales themselvesradioactivity, but other processes mayDiscovery Conference in Perthif you are might provide clues. Are your targetscome to your aid to get radioactiveplanning to attend. As always feedback structurally controlled, say in foldmaterials to the surface: radon gason past Preview articles and suggestions hinges, or associated with disruptivediffusion, ground water movementfor topics for future issues would be very features? Mapping the distribution ofof dissolved salts, even physicalwelcome.37 PREVIEW AUGUST 2019'