b'AEGC 2021Short abstractsInterpretation of the nature and extent of basement rocks inIgneous rocks are important sources of rare earth elements many regions is hampered by lack of exposure and because(REE) and other rare or critical metals. Demand for such potential field data tend to reflect the signatures of overlyingelements is currently met by few deposits but is expected upper crustal units, highlighting the need for tools thatto continue to rise as their importance for technological image deeper. In Northwest Queensland (NWQ) numerousdevelopment is realised. Of the igneous rocks, carbonatites crustal-scale seismic lines were collected from 1994 to 2019and peralkaline rocks are considered the most prospective within the eastern North Australia Craton. Although multiplefor high field strength elements, including REE. Many of interpretations have been published for some lines, definitionthese rocks host known resources, including in Australia. of the underlying basement terranes has remained elusive. ThisResources can be hosted in the primary igneous rocks project presents a new understanding of the basement terranesor within the products of hydrothermal alteration or that form the fundamental building blocks of the Mount Isaweathering. Peralkaline igneous rocks are considered region based on crustal-scale interpretation of all the majorfavourable sources due to their relative enrichment in the seismic lines, integrated with magnetotellurics and tomography,more valuable heavy REE.in the mid to lower crust. Surface geology and potential field data helped constrain the upper crustal interpretation. Peralkaline rocks predominantly result from extensive fractional crystallisation (i.e. 85%) of very low degree The major lower crustal blocks beneath the outcropping Mountpartial melts of enriched or metasomatised mantle. Such Isa region include a broad, trapezoidal, N-S trending basementcircumstances are commonly associated with rifting or terrane (Pitta Pitta) that reaches its shallowest level beneath themantle plumes in intracontinental environments. Eastern Kalkadoon-Leichhardt Belt, and a 24-30 km thick terrane (CentralQueensland has experienced episodes of rifting and plume Isa) that overlies Pitta Pitta and extends east beneath the Easternmagmatism since the late Triassic. Felsic rocks resulting Fold Belt. The wedge-shaped, eastern margin of these two terranesfrom this activity stretch between Mackay in the north has been thrust over Numil crust along the Gidyea Structure. Theand the southern border ranges. They include large A- and large Pitta Pitta terrane has been overthrust from the west byI-type plutons as well as clusters of smaller rhyolitic to the Altjawarra crustal block, and, the Central Isa terrane was latertrachytic domes, lavas and shallow intrusions. Some are thrust west across the Pitta Pitta and Altjawarra basement terrane.well-known but the majority have very little geochemistry, The seismic data indicates that the Tennant basement terranegeochronology or detailed mapping available for study. underlying the Tennant Creek region has limited depth extent as itDespite this, the few rocks investigated as potential sources forms an E-W trending, bivergent block overlying the Altjawarra toof REE have shown considerable promise.the south and Murphy basement terranes to the north.REE and other rare or critical metals are non-traditional commodities and our current knowledge of the distribution 231: The Do-It-Yourself geophysicist of favourable lithologies and potential for economic deposits Dr Anton Kepic 1 is limited. We now require a better understanding of these factors to aid both mineral exploration and land use planning. 1 RoqSense The inventory of peralkaline rocks in Queensland is a compilation of all known information and is an important first Today we are spoilt for choice when it comes to the ability tostep in evaluating the potential for primary or secondary REE make our own measuring instruments and analysis of data.enrichment.This is not obvious to most of us who have mostly lived in a production environment in our professional careers. There are many occasions where a bit of customisation makes a huge235: How deep does ground EM see?difference in capability and marketability for the entrepreneurial. An example is the migration to drone platforms with strap onDr Andrew Fitzpatrick 1, Mr Mike Whitford1 and Mr Anthony instruments. The proliferation of open software and hardware,Huizi1such as Micropython and other GNU-based licensing of generic embedded computing platforms provides a data acquisition1 IGO Limitedand data fusion platform that allow many geophysicists toNickel exploration routinely utilises electromagnetic make the measurements they need to transform themselvestechniques as a direct detection tool. In the Australian to new markets or reinvent old practices. In addition, the freecontext, conductive regolith dominated terrains reduces availability of production-ready CAD software such as KiCad andthe depth of penetration of electromagnetic techniques. FreeCad allows even the novice to create complex electronic/ Modelling is typically performed to determine the depth mechanical devices in 3D by sending a CAD file for manufactureof investigation for basement conductors. These can be directly. These CAD filesmay be slight variants of designs openlymodelled as plates of various geometries, size, dip and published. Thus, a new cottage industry of DIY geophysicists.conductance, leading to an infinite number of scenarios. The open-source hardware and software revolution also altersIGO Limited has been exploring for nickel deposits in the the ability to educate the next generation of geophysicists as itAlbany Fraser Orogeny in Western Australia at belt scale. This facilitates and empowers self-directed learning. has generated a large number of ground electromagnetic targets to form a significant database. This paper presents 234: An inventory of peralkaline rocks in Queenslandan empirical approach of depth of investigation using this for evaluation of REE enrichment potential comprehensive EM plate database, in conjunction with a conductance grid derived from a belt-scale AEM survey. The Mr David Purdy 1, Mr Dominic Brown1 and Mr Bob Bultitude1 results provide a more practical tool for depth of investigation approach that can assist geologists determine effectiveness of 1 Geological Survey of Queensland EM in their given project area.AUGUST 2021 PREVIEW 102'