Groundwater geochemistry, hydrogeology and potash mineral potential of the Lake Woods region, Northern Territory, Australia

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

Second report on the possibilities of underground water at Piney Creek, Block 10, Stromlo district, ACT

On 21st November, 1944, a visit was made to the above block at the request of the lessee (Mr. G.D.C. Tanner) who had asked for advice regarding water supply. The report following this visit recommended the testing of an alluvium-filled basin which occupies part of the southeastern quarter of the block. Subsequently Mr. Tanner sank a well at a site about 1,000 feet south of the point indicated as most favourable. For all practical purposes it may be considered that the well has proved that the alluvium is not capable of yielding a useful supply of water at the end of a dry period, and it became necessary to consider the possibility of obtaining water from the bedrock. The present report embodies results of a further examination with this end in view. The location, topography, geology, and possibility of underground water at Block 10 are discussed in this report. A geological sketch map of Block 10 is included.

Convection or conduction? Interpreting temperature data from sedimentary basins

The economic viability of geothermal energy depends on the depth that must be drilled to reach the required temperature. This depends on the geothermal gradient, which varies vertically and horizontally in the Earth's crust. Traditionally these variations in geothermal gradient have been interpreted in terms of thermal conduction. However, advection and convection influence the temperature distribution in some sedimentary basins. Convection can cause the temperature gradient to vary significantly with depth, such that temperature estimates derived from extrapolation of shallow temperature gradients could be misleading. We use borehole temperature measurements in the Perth Basin (Western Australia) and the Cooper Basin (South Australia and Queensland) to reveal spatial variations in the geothermal gradient, and consider whether these patterns are indicative of convection.

Groundwater resources of Niue Island