Data gathered in the field during the sample collection phase of the National Geochemical Survey of Australia (NGSA) has been used to compile the Preliminary Soil pH map of Australia. The map, which was completed in late 2009, offers a first-order estimate of where acid or alkaline soil conditions are likely to be expected. It provides fundamental datasets that can be used for mineral exploration and resource potential evaluation, environmental monitoring, landuse policy development, and geomedical studies into the health of humans, animals and plants.

The Northern Australian Development Committee nominated the region of the Ord and Victoria rivers to be surveyed by the Northern Australian Regional Survey, when the Barkly Region had been completed. The immediate objectives of the Survey are "to accurately record the nature of the country, to establish a sound basis upon which the production possibilities of the Region may be appraised and to make general recommendations concerning development and further investigations." It was decided that the region should include the Army Four Mile Map Sheets of Delamere, Victoria River Downs, Wave Hill, Birrundudu, Limbunya, Waterloo, Auvergne, Port Keats, Medusa Banks, Cambridge Gulf, Lissadell, Dixon Range, and Gordon Downs, and that the field work would be commenced during the 1949 dry season. The techniques and methods used to complete this survey work are noted. The stratigraphy, pedology, and economic geology of the area are described in some detail.

Analytical data for 10 major oxides (Al2O3, CaO, Fe2O3, K2O, MgO, MnO, Na2O, P2O5, SiO2 and TiO2), 16 total trace elements (As, Ba, Ce, Co, Cr, Ga, Nb, Ni, Pb, Rb, Sr, Th, V, Y, Zn and Zr), 14 aqua regia extractable elements (Ag, As, Bi, Cd, Ce, Co, Cs, Cu, Fe, La, Li, Mn, Mo and Pb), Loss On Ignition (LOI) and pH from >3500 soil samples from two continents (Australia and Europe) are presented and compared to (1) the composition of the upper crust, (2) published world soil average values, and (3) data from other continental-scale soil surveys. It is demonstrated that average upper continental crust values do not provide reliable estimates for natural concentrations of elements in soils. For many elements there exist substantial differences between published world soil averages and the median concentrations observed on two continents. Direct comparison with other continental datasets is hampered by the fact that often mean, instead of the statistically more correct median, is reported. Using a database of the worldwide distribution of lithological units, it can be demonstrated that lithology is a poor predictor of soil chemistry. Climate-related processes such as glaciation and weathering are strong modifiers of the geochemical signature inherited from bedrock during pedogenesis. To overcome existing shortcomings of predicted global or world soil geochemical reference values, we propose Preliminary Empirical Global Soil reference values based on analytical results of a representative number of soil samples from two continents (PEGS2).

Global-scale mapping of surface mineralogy is now becoming possible using remote hyperspectral sensing technologies. Global-scale mineral maps have now been generated for Mars using thermal infrared hyperspectral data collected from the Mars-orbiting Thermal Emission Spectrometer (TES- http://jmars.asu.edu/data/), including maps of feldspar, pyroxene, olivine and quartz contents. Other mineral maps of Mars are now being assembled using the recently launched Compact Reconnaissance Imaging Spectrometer (CRISM - http://crism.jhuapl.edu/), including sulphates, kaolinite, illite/muscovite, chlorites, carbonate and water (www.lpi.usra.edu/meetings/7thmars2007/pdf/3270.pdf). In contrast, even though mapping the mineralogy of the Earth's land surface can improve understanding and management of Earth's resources, including: - monitoring of soils (acid sulphate soils, salinity, soils loss and soil carbon); - better characterisation of regolith materials (e.g. transported versus in situ); - discovery of new mineral deposits using alteration vectors; and - more accurate environmental assessments during resource exploitation (baseline mapping, monitoring and closure)

The ability of thermal and shortwave infrared spectroscopy to characterise composition and textural was evaluated using both particle size separated soil samples and raw soils. Particle size analysis and separation into clay, silt and sand sized soil fractions was undertaken to examine possible relationships between quartz and clay mineral spectral signatures, and soil texture. Spectral indices, based on thermal infrared specular and volume scattering features, were found to discriminate clay mineral-rich soil from mostly coarser quartz-rich sandy soil, and to a lesser extent, from the silty quartz-rich soil. Further investigations were undertaken using spectra and information on 51 USDA and other soils within the ASTER Spectral Library to test the application of shortwave, mid- and thermal infrared spectral indices for the derivation of clay mineral, quartz and organic carbon content. A non linear correlation between quartz content and a TIR spectral index based on the 8.62 im was observed. Preliminary efforts at deriving a spectral index for the soil organic carbon content, based on 3.4 - 3.5 im fundamental H-C stretching vibration bands were also undertaken with limited results.

A weathering intensity index (WII) over the Australian continent has been developed at 100 m resolution using regression models based on airborne gamma-ray spectrometry imagery and the Shuttle Radar Topography Mission (SRTM) elevation data. Airborne gamma-ray spectrometry measures the concentration of three radioelements - potassium (K), thorium (Th) and uranium (U) at the Earth's surface. The total gamma-ray flux (dose) is also calculated based on the weighted additions of the three radioelements. Regolith accounts for over 85% of the Australian land area and has a major influence in determining the composition of surface materials and in controlling hydrological and geomorphological processes. The weathering intensity prediction is based on the integration of two regression models. The first uses relief over landscapes with low gamma-ray emissions and the second incorporates radioelement distributions and relief. The application of a stepwise forward multiple regression for the second model generated a weathering intensity index equation of: WII = 6.751 + -0.851*K + -1.319* Relief + 2.682 * Th/K + -2.590 * Dose. The WII has been developed for erosional landscapes but also has the potential to inform on deposition processes and materials. The WII correlates well with site based geochemical indices and existing regolith mapping. Interpretation of the WII from regional to local scales and its application in providing more reliable and spatially explicit information on regolith properties is described.

pH is one of the more fundamental soil properties governing nutrient availability, metal mobility, elemental toxicity, microbial activity and plant growth. The field pH of topsoil (0-10 cm depth) and subsoil (~60-80 cm depth) was measured on floodplain soils collected near the outlet of 1186 catchments covering over 6 M km2 or ~80% of Australia. Field pH duplicate data, obtained at 124 randomly selected sites, indicates a precision of 0.5 pH unit (or 7%) and mapped pH patterns are consistent and meaningful. The median topsoil pH is 6.5, while the subsoil pH has a median pH of 7 but is strongly bimodal (6-6.5 and 8-8.5). In most cases (64%) the topsoil and subsoil pH values are similar, whilst, among the sites exhibiting a pH contrast, those with more acidic topsoils are more common (28%) than those with more alkaline topsoils (7%). The distribution of soil pH at the national scale indicates the strong controls exerted by precipitation and ensuing leaching (e.g., low pH along the coastal fringe, high pH in the dry centre), aridity (e.g., high pH where calcrete is common in the regolith), vegetation (e.g., low pH reflecting abundant soil organic matter), and subsurface lithology (e.g., high pH over limestone bedrock). The new data, together with existing soil pH datasets, can support regional-scale decision-making relating to agricultural, environmental, infrastructural and mineral exploration decisions.

The present report is a compilation of 531 geochemical maps that result from the National Geochemical Survey of Australia. These constitute the first continental-scale series of geochemical maps based on internally consistent, state-of-the-art data pertaining to the same sampling medium collected, prepared and analysed in a uniform and well documented manner and over a short time period (four years). Interpretations of the data and maps will be published separately. The geochemical maps can be used for better understanding the accumulation, mobility and significance of chemical elements in the near-surface environment of Australia. It is expected that they will provide a new, additional pre-competitive dataset for the energy and mineral resource exploration industry, which should help prioritise areas for further exploration investment and thus reduce risk. Further, it is also likely that some of the geochemical maps will find use in other disciplines related to natural resource management and environmental monitoring.

Our planet provides everything we need for our lives, including the food we eat. As the human population increases and expectations for lifestyle quality increases, so too do the pressures placed on our planet to provide that food. We therefore need to be better at producing food and understanding how that links to our scientific understanding of our planet. For National Science Week 2021, the Geoscience Australia public seminar (co-sponsored by the ACT Division of the Geological Society of Australia and the ACT Branch of the Australian Marine Sciences Association) will present four speakers to demonstrate how geoscience is integral to the provision of our food. Steve Hill – The Long View: Across many disciplines of geoscience and different spatial scales, geology, soils and even plate tectonics influence our food (and wine). Andrew Carroll – Finding Important Seabed Habitat (FISH): Did you know that seabed mapping data directly contributes $9 billion to the Australian economy each year and employs over 56,000 people? For the fishing and aquaculture sectors, seabed mapping is valued at $3 billion. However, only one quarter of Australia’s seabed is mapped! Learn how GA is addressing this challenge to support the rapid growth of Australia's Blue Economy. Claire Krause – Food at Scale: In a country as big and dynamic as Australia, producing food is no small task. Satellite imagery is being leveraged to map, monitor and understand Australia’s food production regions and to identify and manage challenges in the sector. Anna Riddell – From Paddock to Plate with Positioning: Have you ever wondered how your food arrives on your plate and the role that navigation satellites play? Positioning is becoming ubiquitous in everyday life and even has a part in enabling our food to be grown, harvested and transported.

A fundamental component of soils is its mineralogy which is a key driver/indicator of important soil properties/processes such as soil pH (acidity), metal availability (e.g. Al, K, Fe, Si, Ca, Mg) and water content/permeability/runoff. However, soil mineralogy is not routinely measured as part of current soil mapping programs at the paddock-, catchment- or continental-scales mainly because currently deployed measurement technologies are not able to deliver soil mineralogy directly, though remote radiometric and microwave sensing technologies do provide useful soil information. In contrast, mineralogy is now being efficiently delivered to the Australian minerals exploration industry through a new generation of field, airborne and spaceborne hyperspectral technologies (www.hyvista.com; nvcl.csiro.au/). This mineral information includes two of the three major soil mineral components, namely: clays (e.g. kaolinite, illite, smectite); and iron/aluminium oxyhydroxides (e.g. hematite. goethite, gibbsite), with specific information being delivered on their composition, abundances and physicochemistries (disorder and chemistry). The third dominant soil mineral component, quartz, is also spectrally measurable but has diagnostic features at wavelengths longer than current "operational" hyperspectral systems. These hyperspectral technologies thus provide an excellent opportunity to transfer mineral mapping capabilities being developed for the minerals industry into the soil mapping application, especially for establishing baseline inventories of soil mineral composition and providing a possible mechanism for quantitative monitoring of change in soil properties related to its mineralogy (e.g. pH, soil loss, water effects, metal activities and possibly soil carbon and salinity). This opportunity is explored using results from a collaborative geological remote sensing project between the CSIRO, the Geological Survey of Queensland and Geoscience Australia (www.em.csiro.au/NGMM, www.nrw.qld.gov.au/science/geoscience/projects/hyperspectral.html) which involves the collection and processing of 25,000 km2 of airborne HyMap imagery (~300 flight-lines at 5m pixel resolution and totalling >1 Terabyte of raw data) from across Queensland, including areas covered by airborne radiometrics and published geology at 1:100 000 scale around the Mount Isa region. The processed hyperspectral data show that lateritic materials in the Tick Hill area comprise relatively abundant iron oxides and kaolinite (poorly ordered) whereas the radiometrics shows these areas as being relatively high Th and U counts. This kaolinite is presumably developed in response to more acid conditions and/or better (downward percolating) drainage. The hyperspectral data also maps extensive areas of Al-smectite (montmorillonite) associated with the weathering of carbonate (calcite and dolomite) parent rocks or as "pedogenic" occurrences in alluvium/colluvium, with the latter sometimes associated with abundant opaline silica (also mapped using the hyperspectral data). These Al-rich smectites are formed in more alkaline conditions where there is sufficient Ca or Mg and water at the near surface and typically show in the radiometric as being poor in K and Th. Muscovite (water-poor, K-bearing white mica) is mapped over exposed parent rocks whereas illite (water-rich, K-bearing white mica) is typically mapped in weathered materials, including many soils and dried lake beds where there is sufficient available K. The radiometric data typically shows these areas as being K-rich. Note that the accuracy of the hyperspectral clay mineral maps was also validated by field sampling and associated laboratory spectral and X-Ray diffraction analyses.