With the increasing need to extend mineral exploration under cover, new approaches are required to better understand concealed geology, and to narrow the mineral prospectivity search-space. Hydrogeochemistry is a non-invasive exploration technique based on the premise that groundwater interacting with a deposit or supergene alteration can cause anomalous elemental and isotopic signatures down-gradient. Water chemistry can reflect mineralisation directly, but can also reveal other key components of a mineral system, including fluid-flow pathways (e.g. fault/fracture zones), evidence for mineral system traps (e.g. evaporites, shales), or metal sources (e.g. mafic rocks). The Northern Australia Hydrogeochemical Survey (NAHS) was a multiyear regional groundwater sampling program that aimed to understand the regional mineral potential within the Tennant Creek to Mt Isa area (Schroder et al. 2020). This presentation will explore the application of NAHS for investigating mineral potential of a region and present a workflow for establishing spatial or lithological baselines to evaluate hydrogeochemical anomalies. The Georgina Basin is well known for its phosphate potential, with several >1Mt deposits discovered in recent years such as Amaroo and Wonarah; however, the basin has been largely unmapped in terms of phosphate distribution under cover. This work focuses on a subset of 160 NAHS samples collected within two predominant aquifers of the Cambrian Georgina Basin (and time equivalents in the Wiso Basin). This focus restricts us to samples which experience a similar climate, recharge conditions, and aquifer compositions, reducing the hydrogeochemical variation that can mask intra-aquifer anomalies. Elevated dissolved phosphate, PO43- (normalised to HCO3- or Cl-), is observed in the groundwater on the eastern margin of the Georgina Basin. This region is known for Cambrian phosphorite deposits, with sampled bores proximal to a number of near-surface Georgina Basin phosphate deposits. We tested trace element (i.e. U, V and REEs) concentrations as a tool for discriminating phosphate dissolution, however at this regional scale of sampling, possible anomalies were only seen in few bores, thus it is difficult to conclude if this is a consistent relationship robust enough for exploration. More promising may be the use of REE ratios as another indicator of proximity to a phosphate deposit. Emsbo et al. (2015) note that REE compositions of phosphates are relatively consistent globally within a geological period. REE spidergrams of the high PO43- waters are similar to the average REE spidergram of Cambrian phosphates, which contrasts to the REE spidergram of low PO43- groundwaters. Cerium and Europium deviations make this relationship less diagnostic, thus we explore a series of REE ratios (i.e. Er/Dy, Er/Gd, Sm/Nd) for characterising PO43- relationships in groundwater, and use this to suggest other regions of the Georgina Basin with potential for subsurface phosphate deposits. References: Emsbo, P., McLaughlin, P.I., Breit, et al., 2015. Rare earth elements in sedimentary phosphate deposits: solution to the global REE crisis? Gondwana Research, 27(2), 776-785. Schroder, I.F., Caritat, P. de, Wallace, L., et al., 2020. Northern Australia Hydrogeochemical Survey: Final Data Release and Hydrogeochemical Atlas for EFTF. Geoscience Australia, Canberra. http://dx.doi.org/10.11636/Record.2020.015 Abstract presented at the 2021 Australian Earth Sciences Convention (AESC)

The Mesozoic alkaline and related igneous rocks of Australia web map service depicts the spatial representation of the alkaline and related rocks of Mesozoic age.

Alkaline and related rocks are a relatively rare class of igneous rocks worldwide. Alkaline rocks encompass a wide range of rock types and are mineralogically and geochemically diverse. They are typically though to have been derived by generally small to very small degrees of partial melting of a wide range of mantle compositions. As such these rocks have the potential to convey considerable information on the evolution of the Earth’s mantle (asthenosphere and lithosphere), particularly the role of metasomatism which may have been important in their generation or to which such rocks may themselves have contributed. Such rocks, by their unique compositions and or enriched source protoliths, also have considerable metallogenic potential, e.g., diamonds, Th, U, Zr, Hf, Nb, Ta, REEs. It is evident that the geographic occurrences of many of these rock types are also important, and may relate to presence of old cratons, craton margins or major lithospheric breaks. Finally, many alkaline rocks also carry with them mantle xenoliths providing a snapshot of the lithospheric mantle composition at the time of their emplacement. Accordingly, although alkaline and related rocks comprise only a volumetrically minor component of the geology of Australia, they are of considerable importance to studies of lithospheric composition, evolution and architecture and to helping constrain the temporal evolution of the lithosphere, as well as more directly to metallogenesis and mineralisation. This contribution presents data on the distribution and geology of Australian alkaline and related rocks of Mesozoic age. The report and accompanying GIS document the distribution, age, lithology, mineralogy and other characteristics of these rocks (e.g., extrusive/intrusive, presence of mantle xenoliths, presence of diamonds), as well as references for data sources and descriptions. The report also reviews the nomenclature of alkaline rocks and classification procedures. GIS metadata are documented in the appendices.

As part of the first phase of the Exploring for the Future (EFTF) program, depth estimates have been compiled across the North Australian Craton (NAC) in the Estimates of Geological and Geophysical Surfaces (EGGS) database. These depth estimates are ultimately intended to be used to build national-scale models of Australia’s geological cover sequences. EGGS contains depth estimate points of chronostratigraphic era boundaries derived from multiple geological and geophysical datasets. This includes points from the interpretation of airborne electromagnetic (AEM) and magnetotelluric (MT) datasets, as well as from magnetic modelling. Surface and solid geology maps, and formation tops data for groundwater, petroleum and mineral boreholes are linked with the Australian Stratigraphic Units Database (ASUD) to provide chronostratigraphic context for the depth estimates. Following on from work completed across the NAC, the structure of the EGGS database has been re-designed to better enable users to extract additional key information required to build 3D models, and abide by the FAIR (Findable, Accessible, Interoperable, Reusable) data principles. For example, EGGS now identifies points associated with a significant (era-scale) chronostratigraphic unconformity – such as where the Cenozoic overlies Paleozoic or older rocks – enabling better interpolation between points in gridded cover surfaces. We are extending our EGGS coverage to the south, along the Eastern Resources Corridor, including over the Cooper Basin. Newly added data from this area includes magnetic depth estimates from targeted magnetic inversion modelling, interpretation of the AusAEM Eastern Resources Corridor survey data, and compilation of well formation tops across South Australia, Victoria and New South Wales. These data will be used to generate a 3D depth to cover model over the Eastern Resources Corridor and contribute towards building a national-scale geological architecture model. This Abstract was submitted/presented to the 2022 Central Australian Basins Symposium IV 29-30 August (https://agentur.eventsair.com/cabsiv/).

The Archean alkaline and related igneous rocks of Australia web map service depicts the spatial representation of the alkaline and related rocks of Archean age. All are from the Pilbara and Yilgarn Cratons of Western Australia.

The Archean alkaline and related igneous rocks of Australia web map service depicts the spatial representation of the alkaline and related rocks of Archean age. All are from the Pilbara and Yilgarn Cratons of Western Australia.

The Cenozoic alkaline and related igneous rocks of Australia web map service depicts the spatial representation of the alkaline and related rocks of Cenozoic age.

The Mesozoic alkaline and related igneous rocks of Australia web map service depicts the spatial representation of the alkaline and related rocks of Mesozoic age.

The Proterozoic alkaline and related igneous rocks of Australia web map service depicts the spatial representation of the alkaline and related rocks of Proterozoic age.

The Paleozoic alkaline and related igneous rocks of Australia web map service depicts the spatial representation of the alkaline and related rocks of Paleozoic age.