A multi-disciplinary systems mapping approach, utilising airborne electromagnetics (AEM), and validated by a 7.5 km drilling program (100 sonic and rotary mud holes), and complementary hydrogeological and hydrogeochemical investigations, has identified potential groundwater resources stored within Pliocene aquifers (Calivil Formation (CFm) and Loxton Parilla Sands (LPS)) to depths of ~100m beneath the Darling River floodplain. The Pliocene aquifers are sandwiched between thick clay aquitards, and vary from confined to 'leaky confined' systems. The CFm, which extends over the north and central parts of the study area, varies significantly in thickness (0-70 m). This variability results from (1) in-filling of broad (structurally-controlled) palaeovalleys in an undulating palaeo-landscape, with relief of up to 40m from valley bottoms to hill tops; and (2) post-depositional tectonic effects that include structural inversion on faults, as well as warping and tilting. The lower bounding surface of the CFm is marked by an erosional contact (10 m year hiatus) with Renmark Group sediments. Facies analysis indicates that the CFm was deposited in deep braided streams across a dissected sedimentary landscape. Overall, the sequence is fining-upwards, with evidence for transgression over the LPS. Channel fill materials comprise gravels and sands, and local fine-grained units represent abandoned channels and local floodplain sediments. The upper surface of the CFm is irregular, with up to 16 m of relief evident, due to a combination of tectonics and depositional filling of channel and bar topography in the upper CFm. Integration of textural and hydraulic testing data has revealed there are five hydraulic classes within the CFm, ranging from clays to gravels. At a regional scale (kms), sands and gravels are widely distributed with particularly good aquifers developed in palaeochannels and at the confluence of palaeo-river systems. In these strategic locations, the CFm has high storage capacity, very high transmissivities (up to 50 l/s), and significant volumes of fresh groundwater. At a local scale, there is considerable lithological heterogeneity (10s to 100s of metres) within the palaeochannels. The use of AEM was critical to the targeting of premium aquifer sites and detailed hydrogeological investigations.

Langbien's Bore is situated about 12 miles south-east of W.R. Johnston's Bore previously reported upon. The samples examined are from a depth of 50 feet down to 450 feet.

Surface-groundwater interactions are often poorly understood. This is particularly true of many floodplain landscapes in Australia, where there is limited mapping of recharge and discharge zones along the major river systems, and only generalised quantification of hydrological fluxes based on widely spaced surface gauging stations. This is compounded by a lack of temporal data, with poor understanding of how surface-groundwater interactions change under different rainfall, river flow and flood regimes. In this study, high resolution LiDAR, in-river sonar, and airborne electromagnetic (AEM) datasets (validated by drilling) have been integrated to produce detailed 3-dimensional mapping that combines surface geomorphology and hydrogeology. This mapping enables potential recharge zones in the river and adjacent landscape to be identified and assessed under different flow regimes. These potential recharge zones and groundwater flow pathways were then compared against the spatial distribution of discontinuities in near-surface and deeper aquitard layers derived from the AEM interpretation. These 3D mapping constructs provide a framework for considering groundwater processes. Hydrochemistry data, allied with hydraulic data from a bore monitoring network, demonstrate the importance of recharge during significant flood events. In many places, the AEM data also affirm the spatial association between fresher groundwater resources and sites of river and floodplain leakage. At a more localised scale, hydrogeochemical data allows discrimination of lateral and vertical fluxes. Overall, this integrated approach provides an important conceptual framework to constrain hydrogeological modelling, and assessments of sustainable yield. The constructs are also invaluable in targeting and assessing managed aquifer recharge (MAR) options.

The available reef exposures were examined under ultra-violet light on September 28th-29th by N.H. Fisher and C.L. Knight, together with Mr. F.N. Hanlon of the New South Wales Geological Survey. A description of the scheelite follows in the report.

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