Mapping landscape domains in Western Australia: Developing a tool to link geology, geochemistry and landscape variability at large scales

I González-Álvarez1,2, T Albrecht3, J Klump1, S Pernreiter4, K Heilbronn5, T Ibrahimi1

1CSIRO, Mineral Resources, Discovery Program, Perth, Australia; 2University of Western Australia, Centre for Exploration Targeting, Perth, Australia; 3Department of Mechanical and Aerospace Engineering, Monash University, Melbourne, Australia; 4Institute of Geology, University of Innsbruck, Innsbruck, Austria; 5Geosciences, College of Science and Engineering, James Cook University, Townsville, Australia

Landscapes contain essential information related to the geochemical footprint of ore deposits at depth. Variable surface topographical features can be grouped to define and classify unique landscape domains. Climatic conditions, tectonic activity, geological features, biological activity, and sedimentary dynamics are fundamentally linked to landscape variability. Consequently, the study of landscapes can reveal the link between surface features and geological processes at depth. Ore deposits and mineral systems can have dispersed or enhanced geochemical footprints, depending on how the landscape evolved. Geochemical dispersion halos penetrating through cover can be detected by selecting suitable landscape regimes and appropriate sampling media. Cataloguing landscape variability and understanding their evolution at a regional scale can be challenging. The primary difficulty is associated with the selection of the geographic extension of surficial features. In the past, landscape variability mapping relied on field observations along transects. However, a constraint on this approach lies in the uncertainty related to the extrapolation of field observations, especially when attempting to extrapolate them to regional scales. Such extrapolation can be unreliable due to the complexity and variability of landforms, the paucity of data availability, and the difficulty in defining quantitative criteria that discriminate diverse landscape types. Modern data analytics technology and advanced satellite data provide access to large data sets that can assist in characterizing landscape features and their distribution at regional scales. The ability to accurately map landscape variability domains may reveal a vector that links the geochemistry and geology at depth with the architecture of the cover. Such an approach will result in more efficient means to detect and constrain geochemical footprints and dispersion processes at large scales.


Biography

Ignacio is currently Principal Geochemist at CSIRO in Perth. Ignacio worked in Industry in Europe and Australia, and in Academia.
At present, Ignacio’s leading research is focussed on various aspects of landscape evolution and sedimentary systems, weathering processes, chemical element mobility in the continents, and mineral exploration.

Airborne electromagnetics for regional cover thickness mapping

Roach, Ian C.1, Wong, Sebastian1, Ley-Cooper, Yusen1, Brodie, Ross C.1, Wilford, John1

 1Geoscience Australia, GPO Box 378, Canberra

Geoscience Australia applies airborne electromagnetic (AEM) surveying to map regional geology and the architecture of mineral, energy and groundwater systems. Most recently, Geoscience Australia has engaged in very large area, very wide line spacing AEM data acquisition as part of the AusAEM program. In this, we acquire ~20 km line spacing data to broadly characterise the electrical conductivity of wide swathes of Australia in the world’s largest (by area) AEM surveys.

Results from regional AEM surveys demonstrate the efficacy of the AEM method for mapping regolith and sedimentary cover over basement rocks, as well as for mapping large hydrostratigraphic systems. Data commonly also reveal conductivity features associated with potential ore host rocks and alteration systems. Airborne electromagnetic data are especially effective when interpreted in combination with other datasets including boreholes and potential fields. The AusAEM data are being combined with other data to develop 3D cover thickness and stratigraphic surface models either by manual interpretation or by using a machine learning approach.

As an example, in the Paterson Province of Western Australia, 2 km and 6 km spaced AEM lines and industry boreholes were used to develop a 3D depth to Proterozoic basement model. This, together with newer, more detailed AEM acquired by explorers, is now being used by industry as a first-pass risk reduction dataset for locating new Au, Cu and base metal resources in Neoproterozoic rocks of the Anketell Shelf under the Canning Basin. The AEM data have also been used in this area to map groundwater systems within the palaeodrainage systems, which can be used to model the sources and sinks of potash-bearing brinesa ACT 2601, Australia


Biography

Ian Roach is a senior geoscientist at Geoscience Australia. Ian’s interests are many and varied.

Regional Cover Characterisation of the Central Gawler – Clipping regolith-plant associations to better constrain geology and prospectivity

Petts, Anna1; Noble, Ryan2; and Reid, Nathan2

1Geological Survey of South Australia, Department for Energy and Mining, Adelaide, Australia; 2CSIRO, Mineral Resources, Discovery Program, Perth, Western Australia, Australia

Basement rocks and basin sediments seem far detached from surface features such as soils, landform features and plant assemblages. Regolith research in the last 50 years in Australia and abroad has proven many times that the types of assemblages of plants seen across a landscape is in fact well connected to the underlying geology, however, and therefore may be used to demarcate different regolith and landform features for mapping and for cover charactering. Also, these same plants will be linked to the geochemistry of the cover and underlying geological units through plant-nutrient cycling and groundwater uptake and therefore present a suitable, available and sometimes widespread sampling media for exploration geochemistry surveys and mining rehabilitation studies.

This concept has been tested in a regional survey across the Central Gawler Craton, of South Australia.  The Geological Survey of South Australia (GSSA) has collected 212 native plant samples as part of a wider collaboration with CSIRO Minerals. The biogeochemical analysis will be used in conjunction with over 150 CSIRO UltraFine+ (UF) soil results to constrain complex plant-soil chemical relationship as well as test exploration geochemistry applications for plants as regional sampling media. Biogeochemical surveys are becoming increasingly popular first-pass techniques for mineral exploration companies and the GSSA has identified the need to provide relevant regional datasets to assist with identification, analysis and interpretation of plant major and trace element levels. This will enable better confidence when using similar techniques as well as provide improved data reporting standards.

The the availability of select plant species (including Bladder Saltbush Atriplex vesicaria, Pearl bluebush Maireana sedifolia, Black bluebush Maireana pyramidata, Mulga Acacia aneura and Mallee) for sampling and mapping purposes has not been widely recorded analysed. Also the regolith-plant associations of the Central Gawler region, utilising current statewide and newly available regional regolith-landform map products, shows useful relationships and will contribute to accurate promotion of best biogeochemical practice in this region . The most widespread plant assemblage in the Central Gawler Craton UF survey area is chenopod shrubland, with the top two plant species sampled being Pearl Bluebush (47%) followed by Bladder Saltbush (39%) – based on data collected during fieldwork.


Biography

Anna has a keen interest in applying innovative exploration techniques for geochemistry and mineral exploration, as well as understanding fundamental regolith and landform processes. She completed her PhD in 2009 on using termite mounds as a sampling media, and has worked in exploration and mining as well as government.

Anomalous high REE content in clay sediments linked with coastal progradation in the SW Murray Basin: source of REE and role of regolith processes

Keeling, John1, Pobjoy, Rick2, Raven, Mark3, Self, Peter4

1Geological Survey of South Australia (retired); 2Tawel Exploration, Adelaide, Australia; 3CSIRO Mineral Resources, Adelaide, Australia; 3CSIRO Land and Water, Adelaide, Australia

Reconnaissance geochemistry of Pliocene sedimentary deposits of the Murray Basin by McLennan (2016) recorded sites with anomalous levels of rare earth elements (REE). These were followed up subsequently to identify broad zones of clayey sediments, east of the Kanawinka fault zone, containing between 500 to 2800 ppm total rare earth oxides (TREO) + Y, over 1-3 m-thick depth intervals. The sediments occupy depositional environments of estuary, lagoon and interdunal swamps developed behind stranded coastal barrier sands during Late Miocene – Early Pliocene marine regression across the Murray Basin. The clayey sediments are 2-22 m thick and unconformably overlie Oligo-Miocene Murray Group shallow marine, bryozoan limestone. The REE are mostly concentrated within a few metres of the contact with underlying limestone. A broad exploration target extending from Comaum in the south to Frances in the north, bordered to the west by the Kanawinka Fault and extending beyond Apsley (Vic) to the east, outlines the Koppamurra REE project (~2000 km2) – the focus of current investigations.

Analyses of selected drill cuttings showed dominantly light REE (Ce, La and Nd) plus Y, with ~50% of REE recoverable using acid leach (pH 1) and repeated washing with NaCl solution. XRD and XRF analyses of a representative drill sample, from east of Wrattonbully, confirmed high clay content (78%) composed of co-dominant kaolin and smectite, with ~10% goethite. Electron microscopy of the clay fraction identified minor secondary REE minerals cerianite (CeO2) and Ce-monazite ((Ce,La,Nd) PO4) with trace of zircon, all with no detectable Th or U. Results are consistent with surficial mobilisation and concentration of REE, where a high proportion of REE are adsorbed on clay and iron (hydr)oxide surfaces.

The source of REE in this region of the Murray Basin is most likely mafic igneous rocks, including:

  • Cambrian mafic volcanics within metamorphosed basement underlying basin sediments at >30 m depth, and in weathered outcrop on the Western Dundas Tableland, ~20 km to the east-southeast,
  • Newer Volcanics (<4.5 Ma), as basalt flows capping weathered basement on the Dundas Tableland and as volcanic ash from explosive volcanic centres, in particular, early-Middle Pleistocene offshore eruptions that formed the Mt Burr archipelago, 35-44 km southwest of the Kanawinka escarpment.

Fluvial or groundwater transport of REE possibly was directed to the site of deposition by uplift along the Western Highlands-Gambier axis and defeat of drainage towards the south. REE deposition was affected by salinity change at the coast. Any windblown glassy volcanic ash deposited and concentrated in lagoonal depressions, was subsequently altered to smectite and kaolin. Lowering of the water table, in response to drier climate and retreat of the sea from Middle Pleistocene time, resulted in remobilisation of iron and REE and concentration deeper in the profile.

McLennan SM 2016. Sedimentation and geochemistry of the Loxton-Parilla Sands in the Murray Basin, southeastern Australia. PhD Thesis, University of Adelaide.


Biography

John Keeling was formerly Senior Principle Geologist and Program Coordinator of the Mineral Systems Team at the Geological Survey of South Australia. Since retirement in 2019 he has collaborated with colleagues Mark Raven and Peter Self at CSIRO to assist with progressing mineral industry exploration projects, including REE exploration.

Application of indicator minerals in mineral exploration

Salama, Walid1; Le Vaillant, Margaux1; Schoneveld, Louise1; Schlegel, Tobias1; Anand, Ravi1

1CSIRO Mineral Resources, Kensington, Perth, Western Australia

Mineral exploration in weathered and covered terrains has given preference to geophysical and geochemical methods over mineralogical analyses. Airborne and ground geophysical surveys identify magnetic, electromagnetic and gravitational anomalies and allow the rapid delineation of exploration targets. However, the methods don’t indicate whether a target is mineralised or not. Geochemical surveying, based on the analysis of soils, vegetation, termites or calcrete are well-established techniques for locating and identifying variable types of mineralisation. However, their application in areas of deep cover is limited. Indicator minerals, useful for exploration in the weathered and covered terranes, are those that 1) resist chemical weathering in weathered profiles; 2) undergo chemical changes to form secondary minerals in the weathering profile; 3) precipitate within organic-rich sediments during diagenesis; and 4) resist physical weathering during erosion, transportation and deposition.

Mineral explorers are interested in knowing the fertility of a mineral system, in minerals indicating the presence or absence of mineralisation and in vectors towards mineralisation. Within the CSIRO Discovery Program, research projects continue to focus on the identification and characterisation of indicator minerals. Examples of such studies are the potential use of trace element zoning patterns in pyroxenes as fertility indicators for magmatic Ni-Cu-Co-(PGE) deposits, white mica composition in hydrothermal alteration halo as a vector toward Au mineralisation, trace element composition of chromite and arsenide as exploration tools for Ni and Au deposits, and the REE composition of fluorite which reflect the fluid type involved in IOCG mineralisation.

In weathered terrains, rutile, gahnite and cassiterite with base metal sulfide inclusions are residually enriched in the leached and lateritic zone over the Scuddles massive sulfides forming Bi, Sb and Pb anomalies. The use of heavy indicator minerals is also a practical exploration tool in areas of Quaternary glacial till in Canada and Fennoscandia and in the Permian glacial diamictites in Australia. In Australia, the diamictites deposited immediately above the Permian unconformity are largely unweathered and contain detrital sulfides. The distance that indicator minerals disperse from the source depends mainly on the topography of the unconformity between the cover and the bedrock. In northeast Yilgarn Craton, the Permian diamictites were deposited on a rough topography and indicator minerals are expected to be derived from proximal source rocks. Iron, Cu, Zn, As, Ni and Co sulfides were identified at the base of the Permian cover above mafic-ultramafic rocks and used as vectors toward Au mineralisation at Agnew and Lancefield in Western Australia.

In summary, trace element contents of indicator minerals are used to vector toward mineralisation and the source fluids involved in its formation. Residual and supergene indicator minerals in weathered profiles can indicate mineralised bedrock underneath the cover. Detrital and diagenetic indicator minerals in transported cover are a potential vectoring tool for various types of mineral deposits.    


Biography

Walid Salama is a senior research scientist working for CSIRO Mineral Resources. He joined the regolith geoscience group as a postdoc fellow in 2012. His research focused on geochemical exploration of Au, base metals, Ni and Fe in the weathered and covered terrains in Western Australia, Queensland and Botswana.

About the GSA

The Geological Society of Australia was established as a non-profit organisation in 1952 to promote, advance and support Earth sciences in Australia.

As a broadly based professional society that aims to represent all Earth Science disciplines, the GSA attracts a wide diversity of members working in a similarly broad range of industries.