Until recently, the development of better constrained models for gold mineralisation in the western Lachlan Fold Belt has been hindered by the paucity of data on the chemistry of the ore-bearing fluids, the temperatures and pressures at the time of mineralisation, and the extent and nature of wallrock alteration. Newly available data, however, has allowed us to use thermodynamic mass transfer modelling to test some of the models proposed for gold mineralisation in the western Lachlan Fold Belt and to investigate whether the results of the modelling correlate with the styles of mineralisation and alteration assemblages observed in these turbidite-hosted gold deposits. The first model (cf. Keays, 1987) invokes initial seawater alteration of tholeiitic rocks, followed by leaching of gold from these rocks by a metamorphic fluid. This fluid then ascends into the overlying turbidite succession where fault-valve behaviour leads to phase separation and progressive water-rock interaction. Phase separation results in gold precipitation but the associated mineral assemblage contains significant amounts of feldspar, epidote and prehnite, which is not in accord with observed vein and alteration mineralogies. The third model (cf. Gray et al., 1991; and Cox et al.,1995) proposes that the ore-bearing fluids originated from metamorphic devolatilisation process occurring in deep level crustal rocks. This fluid then ascends to upper crustal levels as before. Phase separation leads to a relatively large decrease in the activity of sulfur in the fluid, resulting in gold precipitation and the precipitation of quartz, muscovite, arsenopyrite with chlorite, feldspar and pyrite forming at lower water-rock ratios. Therefore, this model is the one that best reproduces the vein and alteration assemblages commonly observed in the western Lachlan Fold Belt.

No abstract available

A model to study Fire Weather Potential has been developed at Geoscience Australia (GA). Fire Weather Potential refers to the set of climatic conditions which can lead to bushfires if the other two elements of the bushfire development process are present: fuel load and ignition. Detecting high fire weather danger would allow emergency authorities warn the population concerned and ban the lit of fires in the open. They can also be better prepared to mitigate the consequences of a bushfire if such an event occurs. FWP is assessed by calculating Return Periods (RP) of the McArthur Forest Fire Danger Index (FFDI). The RP is an indicator of the frequency and intensity of extreme values and hence it is calculated by fitting an Extreme Value Distribution to the tail of the FFDI data distribution. The FFDI depends on four variables: Drought Factor, Relative Humidity, Air Temperature and Wind Speed. We are particularly interested in studying the impact of climate change on FWP and hence our model calculates FFDI based on climate model simulations. Comparison of climate model based results and observations show that the model tends to underestimate the FFDI in the regions of high FFDI. In the regions of medium FFDI the reverse can be observed: the simulations overestimate the FFDI. Our results show that it is necessary to develop a bias correction procedure for RP calculation if we want to have confidence in our simulation based model to study Fire Weather Potential in Australia. This paper discusses the characteristic of the problem and proposes an algorithm suitable for bias correction of extreme values, the values of interest in the calculation of RP. To illustrate the algorithm an example based on the calculation of FFDI in south-eastern Australia is discussed.

The AuScope geodetic Very Long Baseline Interferometry (VLBI) array consisting of three new 12 m radio telescopes Hobart (Tasmania), Katherine (Northern Territory) and Yarragadee (Western Australia) and a correlation facility in Perth (Western Australia) has started operations in 2010. The daily station positions of the AuScope array are estimated with a precision of a few millimetres, whereas the daily positions vary within a range of 20-30 mm on the annual scale. The most recent analysis of the geodetic VLBI sessions reveals small linear trends in the times series of baseline length between the Australian and New Zealand stations. In addition, a seasonal signal of about 10 millimetres was detected for baseline Hobart12-Katherine. This signal is consistent with collocated GPS data. It should be incorporated to the fitting model to improve the estimates of positions and linear velocities. More details on the geodetic results are discussed in this paper.

This study reports the findings of salt store and salinity hazard mapping for a 20-km wide swath of the Lindsay - Wallpolla reach of the River Murray floodplain in SE Australia. The study integrated remote sensing data, an airborne electromagnetics (AEM) survey (RESOLVE frequency domain system), and lithological and hydrogeochemical data obtained from a field mapping and drilling program. Maps of surface salinity, and surface salinity hazard identified Lindsay and Wallpolla Islands, and the lower Darling Floodplain as areas of high to extreme surface salinity hazard. In the sub-surface, salt stores were found in general to increase away from drainage lines in both the unsaturated and saturated zones. Beneath the Murray River floodplain, salt stores in both unsaturated and saturated zones are high to very high (100 to 300t/ha/m) across most of the floodplain. Sub-surface salinity hazard maps (incorporating mapped salt stores and lithologies, depth to water table and the hydraulic connectivity between the aquifers), identify Lindsay and Wallpolla Islands; the northern floodplain between Lock 8 and Lock 7; and northern bank of Frenchman's Creek as areas of greatest hazard. Overall, the new data and knowledge obtained in this study has filled important knowledge gaps particularly with respect to the distribution of key elements of the hydrostratigraphy and salinity extent across the Murray River and lower Darling floodplain. These data are being used to parameterise groundwater models for salinity risk predictions, to recalculate estimates of evapotranspiration for salt load predictions, address specific salinity management questions, and refine monitoring and management strategies.

In this study, AEM mapping validated by drilling has enabled the lateral extents and thickness of the Pliocene aquifers to be identified. The Pliocene in this area dominantly comprises the fluvial Calivil Formation, with the shallow marine Loxton-Parilla Sands restricted to the southernmost part of the area. Post-depositional warping, tilting and discrete offsets associated with neotoectonics are also recognised. Facies analysis indicates the Calivil was deposited in deep braided streams across a dissected sedimentary landscape. Overall, the sequence is fining-upwards, with evidence for progradation over the Loxton-Parilla. Channel fill materials comprise gravels and sands, and local fine-grained units represent abandoned channels and local floodplain sediments. Integration of textural and hydraulic testing data has revealed there are five hydraulic classes within the Calivil,. At a local scale (10s to 100s of metres), there is considerable lithological heterogeneity, however 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. Aquifer testing has revealed Calivil to be an excellent aquifer, with high storage capacity, and locally very high transmissivities (up to 50 l/s). Integration of the AEM data with borehole geophysical data (gamma, induction and NMR) and textural and pore fluid data has enabled maps of aquifer properties including groundwater salinity, porosity, storage and hydraulic conductivity to be derived. Overall, the multi-disciplinary approach adopted has enabled rapid delineation of new groundwater resources, and facilitated assessment of the Pliocene aquifers for managed aquifer recharge.

The potential for geochemical reactions to cause aquifer clogging or detrimental water quality changes was assessed for an aquifer storage and recovery (ASR) target in the Darling River floodplain. The assessment used ambient groundwater quality from the target Calivil Formation aquifer, as well as from the shallow unconfined aquifers; Darling River source water quality; and mineralogy and geochemistry of sonic-cored aquifer samples. PHREEQC was used to examine the impact of mixing and interaction between these end-members. There is considerable variability in the redox state within the Calivil Formation aquifer, with groundwater pe values ranging from -6 to 8. PHREEQC simulations using the median pe value of 3 resulted in super-saturation with respect to Fe(OH)3. Hence, injection of an oxygenated source water into anoxic zones within the target aquifer can result in iron clogging due to precipitation of any source water dissolved iron and any Fe(II) oxidation in the sediments (in pyrite or displaced from exchange sites). The amount of Fe(II) within the storage zone available to be oxidised is unknown and may be limited given that Fe(III) oxides were present in the core material. The aquifer material contains species that may be released during ASR, including aluminium, arsenic, fluoride, iron, manganese, molybdenum, nickel, selenium and uranium. Injection of source water with elevated dissolved organic carbon (DOC) could enhance metal and metalloid release through reductive dissolution of iron oxides within the storage zone. The fate of any mobilised trace species would be dictated by storage zone redox conditions. Arsenic and molybdenum are likely to be adsorbed to any iron oxide surfaces under oxic conditions. Uranium and selenium are likely to re-precipitate in anoxic zones. This provides the opportunity for natural treatment within the storage zone to control mobilised trace metal species. The use of separate injection and recovery wells (ASTR) may enhance this treatment capacity. This evaluation has provided insights into source water pre-treatment requirements, the potential use of redox mapping to optimise MAR bore-field design, appropriate monitoring for assessing aquifer clogging and water quality changes, and the appropriate contingency plans for treatment of recovered water if required.

High-resolution hydrogeophysical data are increasingly acquired as part of investigations to underpin groundwater mapping and management (such as locating borefields and managed aquifer recharge (MAR) sites, mapping contamination plumes etc). Airborne electromagnetic (AEM) surveys provide a rapid cost-effective means of mapping relatively large, hydrogeologically complex areas. However, optimization of AEM data requires careful consideration of AEM system suitability, calibration, validation and inversion methods. In modern laterally-correlated inversion of AEM data, the usefulness of the resulting inversion models depends critically on an optimal choice of the vertical and horizontal regularization of the inversion. Set the constraints too tight, and the resulting models will become overly smooth and potential resolution is lost. Set the constraints too loose, and spurious model details will appear that have no bearing on the hydrogeology. There are several approaches to an automatic choice of the regularization level in AEM inversion based predominantly on obtaining a certain pre-defined data misfit with the smoothest possible model. However, we advocate a pragmatic approach to optimizing the constraints by an iterative procedure involving all available geological, hydrogeological, geochemical, hydraulic and morphological data and understanding. In this approach, in a process of both confirming and negating established interpretations and underlying assumptions, the inversion results are judged by their ability to support a coherent conceptual model based on all available information. This approach is dependent on integrating a team of scientists, where all facets of data and interpretation are considered and questioned in a transdisciplinary analysis of the hydrogeological system. Necessary elements for this approach to succeed are the experience and professional insights of the scientists involved and a willingness and ability of scientists from diverse areas to establish a dialogue that will question and refine the inversion constraints and the quality of the final hydrogeological conceptual model. This approach has been essential to the identification and assessment of MAR and groundwater extraction options in the Broken Hill Managed Aquifer Recharge project.

Crustal deformation in Fennoscandia is associated with the Glacial Isostatic Adjustment (GIA) process that is caused by ongoing stress release of the mantle after removal of the Late Pleistocene ice sheet by ~10 cal ka BP. With an earth model of defined structure and rheology and an ice-sheet model of known melting history, the GIA process can be simulated by geophysical models, and the surface deformation rates can be calculated and used to compare with GPS observations. Therefore, the crustal deformation rates observed by GPS in Fennoscandia provide constraints on the geophysical models. On the basis of two ice sheet models (ANU-ICE and ICE-5G) reconstructed independently by the Australian National University (ANU) and University of Toronto, we use the GPS derived deformation rates to invert for lithosphere thickness and mantle viscosity in Fennoscandia. The results show that only a three-layer earth model can be resolved from current GPS data, providing robust estimates of effective lithosphere thickness, upper and lower mantle viscosity. The earth models estimated from inversion of GPS data with two different ice sheet models define a narrow range of parameter space: the lithosphere thickness between 93~110 km, upper mantle viscosity between 3.4~5.0 × 1020 Pa s, and lower mantle viscosity between 7~13 × 1021 Pa s. The estimates are consistent with those inverted from relative sea-level indicators (Lambeck et al., 2010).

The aim of this project was to assess the potential for seawater intrusion (SWI) to impact on the principle water supply aquifer within the Darwin Rural Water Control District. In 2008-2009, an airborne electromagnetic (AEM) survey (3,875 line km) was acquired to map the SWI interface. Limited sonic and rotary mud drilling and hydrochemical analysis were used to calibrate and validate the survey. Drilling confirmed that the AEM data mapped the SWI interface that extends a 50 km inland beneath the Adelaide and Mary Rivers, and 10 km inland at Howard Springs. A potential SWI hazard to the Koolpinyah Dolomite Aquifer has been identified in four areas: north-west of Lambells Lagoon, Howard Springs, Gunn Point and Middle Point. In each case, highly saline groundwater, interpreted as SWI ingress, is facilitated by higher transmissivity structural corridors, and/or potential preferential recharge pathways in the overlying aquifer system. The greatest concern is the area north-west of Lambells Lagoon, where highly saline groundwater is present at depth within an area earmarked for possible water supply development. At Howard Springs, an increase in salinity, albeit still relatively low, has been observed in advance of the mapped SWI wedge. Limited age dating and chemical characterisation suggests there is an important distinction between 'older' deeper saline water bodies and more recent saline ingress from the coastal areas and floodplains. However, the apparent continuity of the mapped SWI wedge requires further work to establish if there are separate groundwater systems. In the confined aquifer system, the connectivity of the groundwater system and pressure responses in that system, both in terms of natural recharge and extraction from the Koolpinyah Dolomite Aquifer may be more important than the age of the groundwater itself in determining the dynamics of the saline ingress, and the salinity hazard to the Koolpinyah Dolomite Aquifer. Further investigations in 2012 established a strategic monitoring network and groundwater modelling is being carried out to understand the groundwater and salinity processes and dynamics in each of these hazard areas. Project data and products been used to subdivide the Koolpinyah Dolomite Aquifer into a number of groundwater zones based on water quality and other aquifer characteristics.