This report presents a summary of the groundwater hydrochemistry data release from the Western Davenport 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 Western Davenport project area, Northern Territory (NT). The Western Davenport 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 Western Davenport area.

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 key results from the Western Davenport study conducted as part of Exploring for the Future (EFTF), an Australian Government-funded geoscience data and information acquisition program. The Western Davenport (WD) investigation used existing geological and hydrogeological data and new AEM data to develop a 3D hydrostratigraphic model of the central part of the study area. This was augmented by existing and newly acquired hydrogeological and hydrochemistry data to improve the understanding of groundwater in the area. The collection and interpretation of these datasets have enabled a correlation between hydrostratigraphic units in the Wiso and Georgina basins in the WD area. The hydrochemistry data shows that the central zone of the WD is characterised by good-quality groundwater (<1000 mg/L total dissolved solids), with the newly drilled bores identifying areas of low-salinity groundwater. These initial hydrochemistry results suggest groundwater in the WD could support irrigated agriculture. The hydrochemistry data has identified three zones of potentially higher recharge. The groundwater stable isotope dataset suggests that there is minimal evaporation of water prior to recharge and that groundwater recharge only occurs following heavy rainfall events. This preliminary information suggests recharge to groundwater is dominated by episodic recharge from floodouts and creeks rather than direct infiltration across the WD area from large rainfall events. However, more data are needed to better define the role of floodouts in recharge to the groundwater system and to determine the contribution of creek beds versus floodouts to recharge. Given the aridity of the area and the variable nature of recharge events, managed aquifer recharge could increase the security of groundwater resources in the area. The regolith mapping presented can assist in better understanding the surface and near-surface environments, and their influence on hydrogeological processes. This provides a tool with which to begin identifying potential areas for enhancing natural recharge processes to supplement existing groundwater resources. This mapping was possible because of the increasing availability of higher resolution digital elevation, airborne radiometric and Landsat satellite remotely sensed data. The improved understanding of geology and hydrogeology, coupled with managed aquifer recharge mapping undertaken as part of the EFTF program, provides new information to support groundwater management in the WD area.

The Western Davenport region has been identified as an area of interest for future agricultural development. However, realisation of this potential depends on access to a reliable supply of groundwater, underpinned by rigorous geological and groundwater information. A three-dimensional stratigraphic model has been created for the Western Davenport area of the Southern Stuart Corridor project under the Exploring for the Future program. Our interpretation integrates airborne electromagnetic data with historical drillhole and outcrop data to improve geological and hydrogeological understanding. Results show that stratigraphies of the Wiso and Georgina basins are equivalent and laterally continuous in this area. This enables a more complete hydrostratigraphy to be defined and underpins improved hydrogeological conceptualisation. New hydrochemical data support the conceptual model that the aquifers of the Wiso and Georgina basins are interconnected at a regional scale. The initial assessment of water quality indicates that groundwater may support further agricultural development. Analysis of new water chemistry data has improved understanding of groundwater processes and potential areas of recharge. This work will inform management decisions to enhance the economic and social opportunities in the Western Davenport area, while protecting the environmental and cultural value of water resources. <b>Citation:</b> Northey, J.E., Clark, A.D., Smith, M.L. and Hostetler, S., 2020. Delineation of geology and groundwater resources in a frontier region: Western Davenport, Northern Territory. 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.