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  • The calcrete dataset, compiled from 23 sources by PIRSA, was assessed to determine whether such a dataset could be used for baseline geochemical studies. The database has 162,524 entries and lacks important information on calcrete type, sample location, analytical methods. It has a limited suite of geochemical analyses (Ag, As, Au, Ca, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb & Zn) such that mass balances cannot be done to determine the integrity of the data. Only 80% of the data have Ca geochemistry and it appears as though high Au does not necessarily correspond to high Ca suggesting that some of the samples unlikely to be pure calcrete by definition and probably contain other components such as lithic fragments, gypsum, dolomite or gangue materials. There are significant issues with detection limits relating to the gold assay results and although reported as ppb it is difficult to determine whether those samples below 0.2 are ppb or in fact ppm. Some of the Ca values reported have more Ca than pure calcite which is improbable given the sampling conditions. For the reasons stated above and calcretes limited distribution within Australia this dataset, and calcrete sampling in general, is unsuitable for baseline geochemical purposes. Before it is used for any other purposes, the dataset needs to be reassessed and time spent on quality control. If a unified approach to sampling was adopted then its suitability as a sampling medium for mineral exploration would improve.

  • Geoscience Australia and the Cooperative Research Centre for Landscape Environments and Mineral Exploration (CRC LEME), in collaboration with State agencies are conducting a series of pilot baseline geochemical surveys (BGS). These surveys are intended to characterise regional geochemical patterns and are contributing to what is presently a limited research direction in Australia. BGS provide valuable information about the state of the environment and can assist in (1) establishing baselines to monitor future change; (2) targeting mineral exploration; (3) developing informed environmental policies; and (4) geomedical studies on plant and animal well-being. In 2004-05, sampling at an average sampling density of one sample per 1100 km2,was conducted in the Gawler Craton, South Australia. In contrast to our first pilot region in the Riverina of New South W ales and Victoria, the Gawler region lacks well developed drainage systems, with the western portion being dominated by aeolian dunes. One of the key aims of the Gawler study is to determine whether element excesses or deficiencies exist in the regolith, and the implications of these for plant, animal and human health. Top (0-10 cm depth) and bottom (10 cm from ~55-90 cm depth) sediment samples were collected in the lower parts of 42 catchments. The composition of the <75 um and <180 um fractions were analysed for total major and trace elements using XRF (major and some trace elements), ICP-MS (most trace elements) and ISE (F) methods. Preliminary results show that F, Cr and V are locally elevated above national and international guideline concentrations, raising concerns that these elements may pose potential health issues. Heavy mineral fractions (density >2.95) in 6 samples (3 sites) are dominated by iron oxides (hematite, magnetite, goethite), spinels (ilmenite, spinel), rutile, zircon and barite. Some Cr and V may be associated with heavy minerals such as spinels, limiting their bioavailability. Cu, Se and Zn are potentially deficient in parts of the region, but once identified in agricultural areas can easily be remedied through the application of appropriate fertilizers. Dispersion of elements in the region appear to be at the catchment scale. The pilot studies conducted highlight the need for more comprehensive national guidelines for the assessment of elements in the natural environment. Results from this study are based on total elemental concentrations, and do not account for bioavailability, which plays an important role in assessment of geochemical hazards. However, assessment of baseline regional geochemical trends greatly assists in focusing more detailed research.

  • The National Geochemical Survey of Australia (NGSA) project was launched in 2007 as part of the Australian Government's Energy Security Initiative. Knowledge of the concentrations and distributions of chemical elements in the near-surface environment, used in combination with other datasets, can contribute to making exploration for energy and mineral resources more cost-effective and less risky. As a spin-off, the multi-element dataset can also have applications in environmental fields. During precursor pilot projects, various sampling media, grain-size fractions and analytical methods were tested. It emerged that catchment outlet sediments (from either overbank or floodplain landforms, or from similar low-lying settings) were an ideal sampling medium found across Australia. These sediments are well-mixed composites of the dominant rock and soil types of a catchment, and are typically fine-grained. Results from the pilot projects indicated that catchment outlet sediments could reflect geochemical signatures from basement and mineralisation, even through thick transported overburden. Building on these methods, the NGSA project targeted catchment outlet sediments as a uniform sampling medium. A shallow (0-10 cm) and a deeper (~60-80 cm) sediment sample was collected at the outlet of 1186 catchments covering ~80% of the country. Sampling was carried out by State and Northern Territory geoscience agencies following protocols described in the Field Manual and practiced during in-field training with Geoscience Australia project staff. All sampling equipment (augers, shovels, etc.) and consumables (bags, labels, etc.) were provided centrally. Dry and moist Munsell colours, soil pH, digital photographs, site information and GPS coordinates were recorded in the field. .../...

  • ,,,/,,, Censored data (<Lower Limit of Detection) was imputed using a neural networks-based analysis. The compositional data was transformed using centred logratios (clr) to circumvent closure issues. A Principal Component Analysis (PCA) was then performed on the dataset. The four first PCs account for 59 % of the variance in the dataset. Both negative and positive loadings of each of these PCs relate to geological processes consistent with the element associations they represent as well as the spatial distribution patterns they produce. For instance, the positive loadings of PC1 represent the accumulation of resistant minerals rich in Rare Earth Elements (REEs) that results from intense weathering. Negative PC1 loadings represent secondary minerals formed during weathering (carbonates, sulfates, Fe-oxihydroxides). Negative PC2 loadings are a mixture of elements (e.g., Co, Mn, Zn, V) characterising mafic and ultramafic minerals; conversely negative PC3 loadings (e.g., K, Rb, Na, Sr, Ca) represent more felsic minerals. Spatial distributions of the PCs are compared with independent spatial dataset such as geological maps, airborne radiometric and spaceborne spectroscopic datasets and the implied processes (e.g., lithological control, weathering, transport, secondary mineral precipitation) overall match well with this new geochemical evidence. Future work directions with this dataset include lithological prediction and mineral prospectivity analysis.

  • We describe a model to predict soil-regolith thickness in a 128,000 ha study area in the central Mt Lofty Ranges in South Australia. The term soil-regolith includes the A, B, and C soil horizons to the lower boundary of the highly weathered bedrock zone (R horizon). The thickness of the soil-regolith has a major control on water holding capacity for plant growth and movement of water through the landscape, and as such, it is important in hydropedological modelling and in evaluating land suitability, e.g. for forestry and agriculture. Thickness estimates also have direct application in mineral exploration and seismic risk assessment. Geology and landscape evolution within the area is complex, reflecting the variable nature of bedrock materials, and the partial preservation of deeply weathered profiles as a consequence of weathering processes dating to the Cenozoic, or possibly older. These characteristics, together with strong climatic gradients across the area, make the study area an ideal location to understand the environmental and landscape evolution controls on weathering depth. The area also features weathered landscape analogues to many parts of southern Australia. We use a digital soil mapping piecewise linear decision tree approach to develop the model to predict soil-regolith thickness. This model is based on relationships established between 714 soil-regolith thickness measurements and 28 environmental covariates (e.g. rainfall, slope, gamma-ray spectrometry). The results establish a correlation R2 of 0.64, based on a 75:25% training:test data split. These results are encouraging, and are a significant advance over soil depth mapping by traditional soil-landscape mapping methods.

  • Surface geology of Australia 1:1,000,000 scale, South Australia The 1:1 million-scale "Geology of South Australia" dataset has been compiled from the latest published 1:250 000-scale and some 1:100 000-scale geological maps, modified to incorporate results of recent research by PIRSA in the Olary Domain. Much of South Australia is covered by Cenozoic regolith, mainly sand plains, dunes, playas and colluvium, with lesser silcrete, calcrete and laterite. Six main Precambrian provinces have been recognised: the Gawler and Curnamona Cratons, Musgrave Block, Officer Basin, Adelaide Fold Belt (Geosyncline) and Coompana Block (concealed). The Gawler Craton outcrops in the centre and south. Neoarchaean igneous and sedimentary rocks of the Mulgathing and Sleaford Complexes form the basement of the Craton and were metamorphosed to granulite facies during the period 2.7 to 2.4 Ga. Clastic and chemical sediments of the Hutchison Group were deposited along the eastern margin of the Craton during the Palaeoproterozoic, and were subsequently deformed during the Kimban Orogeny (1850 to 1700 Ma). Little deformed Mesoproterozoic sediments and the Gawler Range Volcanics were deposited unconformably over the older rocks, mainly in the east of the Craton. Coeval granites of the Hiltaba Suite are distributed throughout the Craton. Three domains of the Curnamona Craton - the Olary Domain, and Mt Babbage and Mt Painter Inliers - outcrop in the central east. They consist of Palaeoproterozoic schist and gneiss, metamorphosed and disrupted during the Olarian Orogeny (1700-1580Ma), and intruded by Palaeo- to Mesoproterozoic granite. The inliers were further disrupted by the Delamerian Orogeny (~500Ma) and are surrounded by Neoproterozoic to Cenozoic sediments. The Musgrave Block in the northwest of the State comprises quartzofeldspathic orthogneiss and granite, and minor pelitic, siliceous and calcareous metasediments. Widespread metamorphism at about 1600 Ma was followed by extensive granite intrusion at about 1500 Ma. Emplacement of the mafic-ultramafic Giles Complex at about 1080 Ma occurred towards the end of metamorphism and granite emplacement of the Musgravian Orogeny (1225-1075 Ma). During the Petermann Orogeny (~540 Ma), granulite of the southern Musgrave Block overthrust amphibolite facies gneiss north of the Woodroffe Thrust. Tectonic disruption on regional scale shear zones continued to the end of the Alice Springs Orogeny (400-350 Ma). During Neoproterozoic to Cambrian times, sedimentation occurred in shelf and trough settings in the Officer Basin (south of the Musgrave Block), and in the Adelaide Fold Belt. At times these basins were linked, yielding similar sedimentary sequences. The Adelaide Fold Belt was folded and disrupted during the Delamerian Orogeny (~500 Ma) and locally intruded by granite. Many of the intrusions are concealed by Murray Basin sediments, but coeval granites are exposed in the Padthaway Ridge inboard of the southeast coast. Small Precambrian inliers are exposed elsewhere in the state. They include: the Ammaroodinna and Yoolperlunna Inliers southeast of the Musgrave Block; Peake, Denison and Mount Woods inliers north of the Gawler Craton; and Houghton, Warren, Aldgate, Oakbank, and Myponga Inliers within the Adelaide Fold Belt. Carboniferous to Permian glaciation affected much of the state, and was followed by deposition of mixed marine and terrestrial sediments in the Mesozoic Eromanga Basin and Cenozoic Eyre, Murray, and Eucla Basins.

  • This interactive training module is an introduction to the theory, application and interpretation of gamma-ray spectrometry for regolith science. It uses descriptions, diagrams and three dimensional models to describe gamma-ray spectrometry for regolith science. The tutorial was created by Geoscience Australia and the Cooperative Research Centre for Landscape Environments and Mineral Exploration.

  • The Granites-Tanami induration styles 1:500,000 map illustrates the distribution of regolith cemented regolith materials and the landforms on which they occur, described using the RTMAP scheme developed by Geoscience Australia