b'Education matters These included cultural influences,Five inversion methods were used andThe results achieved by the 2D seismic a mechanical setup issue that wascompared for a 2D seismic section. Themethod do not provide reliable mapping enhanced by prevailing weathermethods used were: Coloured Inversion,of the deposits on its own. However, the conditions and an effect introducedModel-Included Coloured Inversion,combination of different geophysical during processing. Three workflowsBand-limited Inversion, Soft-Constraintsmethods increases the confidence in were used to investigate the effect andModel-Based Inversion and Hard- targeting of pegmatite formations and magnitude of this noise, two focusing onConstraints Model-Based Inversion. Inthe overall understanding of the geology.filtering gridded data, and one focusingthe coloured inversion section, structuresJake Tomlinson, Curtin University: on filtering line data prior to gridding.could be identified as breaks in lithology.A practical comparison of transient The workflows were then successfullyIn the model-based techniques, itelectromagnetic sensors over a conductive applied to a second drone-based surveybecame clear that the starting model wastarget in regional Western Australia.over a different geological target toof paramount importance as this model observe their effectiveness in removingdominated the final inversion. ThelowestTime domain electromagnetic noise whilst leaving signal intact. error between borehole log and thesurveys are the primary geophysical Timothy Hill, Curtin University:inverted log was achieved with themethodemployed to locate Comparative analysis of seismic inversionHard-Constraints Model-Based Inversioneconomic base-metal deposits. Such techniques for hard rock environments. method (1054.88 (m/s)*(g/cc)) howeverexploration surveys utilise a transient the best balance between model inputelectromagnetic sensor to record the The Nova-Bollinger ore deposit is one ofand seismic data was qualitativelysecondary magnetic field produced by the most significant discoveries of recentachieved using the Band-limited inversiontargets of interest. This thesis presents years. Initially discovered in 2012, themethod. In most cases, the known Novaa comprehensive analysis of the high orebody contains 13.1 Mt of ore (2.03%and Bollinger orebodies were not abletemperature SQUID and fluxgate Ni, 0.83% Cu, 0.07% Co) constitutingto be located, however discriminationmagnetometer which are commonly a multi-billion-dollar resource, ownedbetween intrusive zones and meta- used in time domain electromagnetic and operated by Independence Groupsediments was found to be possible. surveys. The fluxgate magnetometer NL (IGO). Extensive effort in the formJames Regan, Curtin University: Locatinghas a long and extensive history in of drilling and geophysical surveyinglithium-bearing pegmatites using thegeophysical exploration, but with limited has been undertaken in recent years inseismic reflection method in Tabba Tabba,near surface deposits left undiscovered order to further characterise the existingPilbara, Western Australia. exploration companies have turned orebodies and to determine structuralto a more advanced receiver antenna. controls on orebody deposition. The demand for lithium has increased inSuperconducting quantum interference the previous years due to its many usesmagnetometers are regarded as the most In 2017, a 2D seismic survey wasand extensive applications. In Westerncapable readily available sensor.undertaken by HiSeis Pty. Ltd. on behalfAustralia the element is found in theThe quality of data recorded by a of IGO, which revealed two super- mineralised form and is commonly heldtransient electromagnetic sensor in domains separated by the Nova Fault, aswithin pegmatites. Most of the productiona practical setting is dependent on well as several fault systems and intrusiveof lithium within WA comes from theinternal and external factors. The bodies. Based on the results of the 2DGreenbushes Province in the southdominant internal factors influencing the survey, a 58 square-kilometre 3D seismicwest, but can also be found in sufficientreceivers ability to accurately record the survey was commissioned in 2018,quantities in the Pilbara, where the regionsecondary electromagnetic field decay is revealing possible relationships betweenpresents major shear zone structures.sensitivity, intrinsic noise level and sensor structural and stratigraphic controls andExploration for pegmatites can belimitations. These factors are unique to the ore deposits, as well as identifyingproblematic as the structural formationsindividual magnetometers and often several prospective targets, promptingare characteristically complex and varyspecific to the magnetic effect used to further drilling. in orientation and thickness. This meansmeasure the magnetic field variations. The primary objectives of this study werethat straight forward interpretation of drillDominant external factors include to form a robust link between the seismicholes can be misguiding. geological noise sources, geomagnetic data and available borehole data, produceThe question then lies with, whethervariations and survey design.and compare seismic inversion techniquesor not we are able to get a betterAnalysis of time domain electromagnetic for efficacy and to determine whetherunderstanding of how these depositsdata acquired from two separately seismic inversion techniques could helptrend within the subsurface? Aconducted surveys permitted the discriminate prospective lithology inpossible solution to this may beassessment of the internal and external the form of mafic intrusives from non- achieved by applying geophysicalfactors listed above.prospective lithology. The overall purposemethods. In the past, geophysical for this research was to determineexploration over these deposits hasKey outcomes of the research saw the applicability and methodologystruggled even though contrasts invariations in receiver sensitivities and of Quantitative Interpretation (QI)the physical properties of pegmatitesintrinsic noise levels dictating the techniques in hard-rock environments.and the surrounding host are present.abilities of the magnetometers to Current methods are qualitative in nature,However, imaging the structuresaccurately identify known subsurface and if seismic inversion is successful aremains difficult. The regions in whichtargets. In survey 1 the Phoenix coil failed more robust approach to stratigraphicthey are formed are commonly quiteto illuminate three confined conductors drill targeting could potentially lead tocomplex geological settings, resultingimaged by the B-field magnetometers. significant cost and time savings in thein additional complications in theIn survey 2 the fluxgate magnetometer hunt for the next Nova-Bollinger. accuracy of the geophysical data. misidentified two known parallel 39 PREVIEW DECEMBER 2019'