In a land management context, conductivity can be related to quantities such as salt store, ground water salinity, clay content, hydraulic permeability, degree of groundwater saturation or more generally to definition of regolith and bedrock units. These relationships open the way for the use of electromagnetic methods to measure subsurface conductivity. From the very early trials, efforts have been made to transform the measurements to conductivity. The real world presents a myriad of difficulties, that translate into errors and artifacts in 2D sections or 3D volumes produced from individual 1D conductivity transformation solutions. Reconciliation of AEM conductivity predictions with other spatial information presents a deceptively difficult challenge. A variety of improvements in the future will lead to a more accurate portrayal of conductivity in 3D.

This report documents the findings of the 'Northern Territory Coastal Plain: Mapping Seawater Intrusion (SWI) in Coastal Plain Aquifers Using Airborne Electromagnetic (AEM) Data' project. The principal objective of this project is to carry out an assessment of the potential for SWI to impact on aquifers within the Darwin Rural Water Control District (DRWCD). The project was funded by the National Water Commission (NWC), with significant in-kind resources and funding provided by Geoscience Australia (GA) and the Northern Territory Department of Resources, Environment, Tourism, Arts and Sports (NRETAS). The project entailed acquisition of regional AEM data over the priority areas within the DRWCD, small sonic and rotary mud drilling programs, borehole geophysical logging, groundwater sampling, laboratory analysis of pore fluids and groundwater samples, and integration, analysis and interpretation of results.

The role of palaeovalley evolution in the manifestation of salinity across the Australian continent P.M. English1 & J.W. Magee1, 2 1Geospatial & Earth Monitoring Division, Geoscience Australia, GPO Box 378, Canberra, ACT 2601 Pauline.English@ga.gov.au 2Department of Earth & Marine Sciences, Australian National University, Canberra, ACT 0200 jwmagee@ems.anu.edu.au Networks of palaeovalleys characterise much of arid, semi-arid and sub-humid Australia, including widespread rangelands and agriculturally important regions. These ancient river valley systems are very commonly the focus of salinity across our landscape, both primary salinity (Quaternary salt lakes and associated saline landforms), and secondary salinity in regions that have been cleared for agricultural development in the last 150 years. The preservation of palaeovalleys is a legacy of the continents tectonic stability, low relief and slow erosion and sedimentation rates. Palaeovalleys drain all the cratonic blocks and extend from Precambrian basement uplands across Palaeozoic, Mesozoic and Cainozoic sedimentary basins. They are now largely filled with Tertiary, or older, sediments and are commonly blanketed with Quaternary lacustrine, alluvial or aeolian sediments, including saline sediments and salts. While the palaeovalleys and their sedimentary infill are relatively ancient (early to mid Tertiary) the groundwater systems they host have evolved during latest Tertiary and Quaternary times. Salt began to concentrate in these palaeovalley networks and surrounding hinterlands from as long as 350 000 years ago, in response to glacial-interglacial cyclicity driven by global climate regimes. More recent salt accumulation in the historic period is the consequence of hydrologic disequilibrium wrought by land clearing which has caused broad-scale mobilisation of ancient salt stores into topographic lower areas and waterways in agricultural regions. Sodium chloride (NaCl) is the dominant salt in the Australian terrestrial environment, in both the arrays of ancient salt lakes and in secondary salinised agricultural regions. This reflects the dominance of marine aerosol source of salts in our rainfall and the longevity of salt accumulation in the near-surface environment. The marine signature is further pronounced in the case of primary salinity occurrences, where calcium sulphate, or gypsum (CaSO4.2H2O), is prevalent across the inland landscape. The ubiquity and solubility of NaCl and its mobility in shallow groundwater systems accounts for the recurrence and concentration of salinity in palaeovalley systems in particular. The persistence of ancient palaeovalley networks and of marine-derived salts in the salinised Australian landscape forms the basis of comparisons with southern Africa, for example, where tectonism and a significantly higher proportion of terrestrially-derived salts predispose contrasting manifestations of salinity. Such comparisons provide some insight and a broad perspective relevant to Australias contemporary salinity issues.

This study reports the findings of salt store and salinity hazard mapping for a 20-km wide swath of the Lindsay - Wallpolla reach of the River Murray floodplain in SE Australia. The study integrated remote sensing data, an airborne electromagnetics (AEM) survey (RESOLVE frequency domain system), and lithological and hydrogeochemical data obtained from a field mapping and drilling program. Maps of surface salinity, and surface salinity hazard identified Lindsay and Wallpolla Islands, and the lower Darling Floodplain as areas of high to extreme surface salinity hazard. In the sub-surface, salt stores were found in general to increase away from drainage lines in both the unsaturated and saturated zones. Beneath the Murray River floodplain, salt stores in both unsaturated and saturated zones are high to very high (100 to 300t/ha/m) across most of the floodplain. Sub-surface salinity hazard maps (incorporating mapped salt stores and lithologies, depth to water table and the hydraulic connectivity between the aquifers), identify Lindsay and Wallpolla Islands; the northern floodplain between Lock 8 and Lock 7; and northern bank of Frenchman's Creek as areas of greatest hazard. Overall, the new data and knowledge obtained in this study has filled important knowledge gaps particularly with respect to the distribution of key elements of the hydrostratigraphy and salinity extent across the Murray River and lower Darling floodplain. These data are being used to parameterise groundwater models for salinity risk predictions, to recalculate estimates of evapotranspiration for salt load predictions, address specific salinity management questions, and refine monitoring and management strategies.

The map shows salt lake regions favourable for potash deposits. For a more detailed description of selection method see Jaireth et al (2013)

No abstract available

The map shows salt lake regions favourable for boron deposits. For a more detailed description of the selection method see Jaireth et al. (2013).

Salinity of groundwater directly affects its suitability for different uses, from human consumption, agricultural use, to mineral and energy extraction. Traditionally, direct measurements of groundwater salinity at monitoring bores have been used to create salinity maps. However, drilling is expensive and logistically challenging, while leaving us with a small set of salinity measurements over large areas. Airborne electromagnetic (AEM) surveying provides a cost effective solution to this problem. We have developed a scripted geostatistical methodology, which can be repeated on a computer cluster as new AEM data are acquired or boreholes are drilled. We also provide uncertainties on the knowledge gained, allowing remote communities to manage their land and water resources effectively.

An inventory of saline water disposal basins, Murray Basin : volume 3 additional basins in South Australia, Victoria and New South Wales 1998.

The GILMORE Project (Geoscience In Land Management and Ore System Research for Exploration) is a pilot study designed to assess methodologies and technologies for identifying mineral prospectivity and dryland salinity in areas of complex regolith cover (Lawrie et al., 2000). The project area (100 x 150 km) lies in the eastern part of the Murray-Darling Basin in central-west NSW and straddles the Gilmore Fault Zone, a major NNW-trending crustal structure that separates the Wagga-Omeo and the Junee-Narromine Volcanic Belts in the Lachlan Fold Belt. Included in the project area are tributaries of the Lachlan and the Murrumbidgee Rivers. A critical aspect of this research was to develop databases and a GIS to enable researchers to view and analyse complex datasets and their inter-relationships in both two and three dimensions. The GILMORE Project GIS consists of 11 CDs in 2 volumes. Volume 1 is comprised of 5 CDs and contains airborne electromagnetic (AEM), magnetic and gamma-ray spectrometric geophysical datasets. These are included in point located (line) form as ASCII column format files, and in gridded form as ERMapper format grids. These data have already been released. Volume 2 comprises of 6 CDs containing data in ESRI\222s ArcInfo and ArcView for mat. Each CD has an ArcView Project accessing colour geophysical images (created in ERMapper), ArcInfo polygon, point and line coverages, ArcView shape files, with links to gif images, photos and .dbf files. The GIS will also be released in MapInfo format.