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  • We collected 38 groundwater and two surface water samples in the semi-arid Lake Woods region of the Northern Territory to better understand the hydrogeochemistry of this system, which straddles the Wiso, Tennant Creek and Georgina geological regions. Lake Woods is presently a losing waterbody feeding the underlying groundwater system. The main aquifers comprise mainly carbonate (limestone and dolostone), siliciclastic (sandstone and siltstone) and evaporitic units. The water composition was determined in terms of bulk properties (pH, electrical conductivity, temperature, dissolved oxygen, redox potential), 40 major, minor and trace elements as well as six isotopes (δ18Owater, δ2Hwater, δ13CDIC, δ34SSO4=, δ18OSO4=, 87Sr/86Sr). The groundwater is recharged through infiltration in the catchment from monsoonal rainfall (annual average rainfall ~600 mm) and runoff. It evolves geochemically mainly through evapotranspiration and water–mineral interaction (dissolution of carbonates, silicates, and to a lesser extent sulfates). The two surface waters (one from the main creek feeding the lake, the other from the lake itself) are extraordinarily enriched in 18O and 2H isotopes (δ18O of +10.9 and +16.4 ‰ VSMOW, and δ2H of +41 and +93 ‰ VSMOW, respectively), which is interpreted to reflect evaporation during the dry season (annual average evaporation ~3000 mm) under low humidity conditions (annual average relative humidity ~40 %). This interpretation is supported by modelling results. The potassium (K) relative enrichment (K/Cl mass ratio over 50 times that of sea water) is similar to that observed in salt-lake systems worldwide that are prospective for potash resources. Potassium enrichment is believed to derive partly from dust during atmospheric transport/deposition, but mostly from weathering of K-silicates in the aquifer materials (and possibly underlying formations). Further studies of Australian salt-lake systems are required to reach evidence-based conclusions on their mineral potential for potash, lithium, boron and other low-temperature mineral system commodities such as uranium. <b>Citation:</b> P. de Caritat, E. N. Bastrakov, S. Jaireth, P. M. English, J. D. A. Clarke, T. P. Mernagh, A. S. Wygralak, H. E. Dulfer & J. Trafford (2019) Groundwater geochemistry, hydrogeology and potash mineral potential of the Lake Woods region, Northern Territory, Australia, <i>Australian Journal of Earth Sciences</i>, 66:3, 411-430, DOI: 10.1080/08120099.2018.1543208

  • Legacy product - no abstract available

  • The use of airborne electromagnetics (AEM) for hydrogeological investigations often requires high resolution data. Optimisation of AEM data therefore requires careful consideration of AEM system suitability, calibration, validation and inversion methods. In the Broken Hill managed Aquifer Recharge (BHMAR) project, the helicopter-borne SkyTEM transient EM system was selected after forward modeling of system responses and assessment of test line data over potential targets. The survey involved acquisition of 31,834 line km of data over an area of 7,500 km2 of the River Darling Floodplain, and was acquired by two systems over a 9-week period.. Initial Fast Approximate Inversions (FAI) provided within 48 hours of acquisition were used to target 100 sonic and rotary mud holes for calibration and validation. A number of different (Laterally and Spatially Constrained) inversions of the AEM data were carried out, with refinements made as additional information on vertical and lateral constraints became available. Finally, a Wave Number Domain Approximate Inversion procedure with a 1D multi-layer model and constraints in 3D, was used to produce a 3D conductivity model. This inversion procedure only takes days to run, enabling the rapid trialing to select the most appropriate vertical and horizontal constraints. Comparison of borehole induction logs with adjacent AEM fiduciary points confirms high confidence levels in the final inversion. Using this approach has produced quantitative estimates of the 3D conductivity structure that provide a reliable platform for identifying new groundwater resources and a range of MAR options, and developing new geological and hydrogeological conceptual models. Integration of the AEM data with borehole lithology, textural, mineralogical, groundwater and pore fluid hydrochemical and borehole NMR data has enabled maps of hydrostratigraphy, hydraulic conductivity, groundwater salinity, salt store and neotectonics to be produced.

  • Legacy product - no abstract available

  • The 'River Murray Corridor (RMC) Salinity Mapping Project', provides important new information in relation to salinity hazard and management along in a 20 km-wide swath along a 450 km reach of the River Murray. The project area contains iconic wetlands, national and state forest parks, irrigation and dryland farming assets and the Murray River, significant areas of which are at risk from increasing salinisation of the River, the floodplain, and underlying groundwater resources. The project utilised a hydrogeological systems approach to integrate and analyse data obtained from a large regional airborne electromagnetic (AEM) survey (24,000 line km @ 150m line-spacing in a 20 km-wide swath along the Murray River), field mapping, and lithological and hydrogeochemical data obtained from drilling. New holistic inversions of the AEM data have been used to map key elements of the hydrogeological system and salinity extent in the shallow sub-surface (top 20-50 m). The Murray River is known to display great complexity in surface-groundwater interactions along its course. Electrical geophysical methods (such as AEM) are able to map surface-groundwater interaction due to the contrast between (electrically resistive) fresh water in the river, and (electrically conductive) brackish to saline groundwater in adjacent sediments. The location of significant river flush zones is influenced both by underlying geology and the location of locks, weirs and irrigation districts. The study has also identified significant areas of high salinity hazard in the floodplain and river, and quantified the salt store and salt load across the floodplain. The study has also identified sub-surface factors (including saline groundwater, shrinking flush zones, declining water tables) linked to vegetation health declines.

  • Legacy product - no abstract available