This report presents key results from hydrogeological investigations at Alice Springs, completed as part of Exploring for the Future (EFTF)—an eight year, $225 million Australian Government funded geoscience data and information acquisition program focused on better understanding the potential mineral, energy and groundwater resources across Australia. The Southern Stuart Corridor (SSC) project area within the Northern Territory extends in a north–south corridor from Tennant Creek to Alice Springs, encompassing four water control districts and a number of remote communities. Water allocation planning and agricultural expansion in the SSC is currently limited by a paucity of data and information regarding the volume and extent of groundwater resources and groundwater systems more generally. This includes recharge rates, surface water –groundwater connectivity, and the dependency of ecosystems on groundwater. Outside the proposed agricultural areas, the project includes numerous remote communities where there is a need to secure water supplies. Geoscience Australia, in partnership with the Northern Territory Department of Environment and Natural Resources and the Power and Water Corporation, undertook an extensive program of hydrogeological investigations between 2017 and 2019. Data acquisition included helicopter airborne electromagnetic (AEM) and magnetic data, investigative groundwater bore drilling, ground-based and downhole geophysical data (including nuclear magnetic resonance for mapping water content and induction conductivity/gamma for defining geological formations), and hydrochemistry for characterising groundwater systems. This report investigates the hydrogeology across the Alice Springs focus area, which includes the Roe Creek and proposed Rocky Hill borefields, where five hydrostratigraphic units were mapped based on AEM interpretation and borehole geophysical information. The mapping supports the presence of a syncline, with a gentle parabolic fold axis that plunges westward, and demonstrates that the main Siluro-Devonian Mereenie Sandstone and Ordovician Pacoota Sandstone aquifers are continuous from Roe Creek borefield to the Rocky Hill area. Areas with the highest potential for recharge to the Paleozoic strata are where Roe Creek or the Todd River directly overlie shallow subcrop of the aquifer units. Three potential recharge areas are identified: (1) Roe Creek borefield, (2) a 3 km stretch of Roe Creek immediately west of the proposed Rocky Hill borefield, and (3) the viticulture block to the east of Rocky Hill. Analysis of groundwater chemistry and regional hydrology suggests that the rainfall threshold for recharge of the Paleozoic aquifers is ~125 mm/month, and groundwater isotope data indicate that recharge occurs rapidly. The groundwaters have similar major ion chemistry, reflecting similar geology and suggesting that all of the Paleozoic aquifers in the focus area are connected to some degree. Groundwater extraction at Roe Creek borefield since the 1960s has led to the development of a cone of depression and a groundwater divide, which has gradually moved eastward and is now east of the proposed Rocky Hill borefield. The majority of the groundwater within the focus area is of good quality, with <1000 mg/L total dissolved salts (TDS). The brackish water (7000 mg/L TDS) further to the east of the proposed Rocky Hill borefield warrants further investigation to determine the potential risk of it being captured by the cone of depression following the development of this borefield. This study provides new insight to the hydrogeological understanding of the Alice Springs focus area. Specifically, this investigation demonstrates that the Roe Creek and proposed Rocky Hill borefields, and a nearby viticulture area are all extracting from the same aquifer system. This finding will inform the future management and security of the Alice Springs community water supply. New groundwater resource estimates and a water level monitoring scheme can be developed to support the management of this vital groundwater resource.

The Exploring for the Future Southern Stuart Corridor Groundwater Project undertook extensive multidisciplinary geoscientific investigations across four study areas and six Indigenous communities in central Australia to better understand and characterise groundwater resources. The project was developed to support improvements in water resilience for communities and future agricultural developments in the region. Geoscience Australia collected 9800 line kilometres of airborne electromagnetic data, drilled and installed 15 new monitoring bores, acquired 78 surface nuclear magnetic resonance soundings, recorded downhole geophysical data and groundwater level measurements from >50 bores, and completed hydrochemical analysis of 75 samples. Integration of these datasets provided insights into recharge areas and rates, and potential for managed aquifer recharge. The project also improved our understanding of the geological systems hosting groundwater and interconnections between systems. Potential new groundwater supplies, enhanced understanding of groundwater processes and improved geological models will assist water agencies to better manage groundwater resources across the region. <b>Citation:</b> Hostetler, S., Slatter, E., McPherson, A.A., Tan, K.P., McInnes, D. J., Wischusen, J.D.H. and Ellis, J.H., 2020. A multidisciplinary geoscientific approach to support water resilience in communities in Central Australia. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

The hyperspectral HyLoggerTM instrument for collecting high resolution spectra data of drill core and drilling chips is a widely used and powerful in mineral and energy exploration, including sediment hosted mineralisation and hydrocarbons. It enables mapping of hydrothermal, diagenetic, and weathering assemblages, clarification of stratigraphy, and determination of primary mineralogy. This report presents key results of hyperspectral data from the HyLogger-3TM instrument collected from drilling in the Southern Stuart Corridor (SSC) project area in the Northern Territory conducted as part of Exploring for the Future (EFTF)—an eight year, $225 million Australian Government funded geoscience data and information acquisition program focused on better understanding the potential mineral, energy and groundwater resources across Australia. The results show that HyLogger plots are in most cases in the most effective means of identification of stratigraphic contacts. HyLogger plots are also especially effective and determining the depth and mineralogy of weathering and distinguishing provenance in shallow transported material such as palaeovalley fill and alluvium. Geological observations are however still crucial, especially in determining texture, which cannot be determined by the HyLogger scans or from photographs of chips and core, and in cases where contamination obscures or confuses the spectral signals. Weathering in the SSC can be determined by the appearance of dickite and poorly crystalline kaolinite. This allows a better determination of base of weathering than visual means: generally based of the presence of oxidised iron phases such as goethite and haematite (which are not definitive where the rocks already contained these prior to weathering), or where oxidised iron deposition has not occurred. This aids in depth of weathering mapping from regional AEM data. The ability of the HyLogger to discriminate between swelling (montmorillonite) and non-swelling (kaolinite, dickite) clays is potentially significant in the prediction of aquifer properties and the validation of borehole MR methods. The detection of zones of potential dolomitisation and dedolomisation through mineralogy (presence of dolomite and possible secondary calcite and magnesite, respectively) in carbonate units has the potential to similarly predict properties in carbonate units, through the potential increase in porosity/permeability of the first and decreased porosity/permeability of the second.

This report presents a summary of the groundwater hydrochemistry data release from the Alice Springs project conducted as part of Exploring for the Future (EFTF). This data release records the groundwater sample collection methods and hydrochemistry and isotope data from monitoring bores in the Alice Springs project area, Northern Territory (NT). The Alice Springs project is a collaborative study between Geoscience Australia and the NT Government. Hydrochemistry and isotope data were collected from existing and newly drilled bores in the Alice Springs area.