<p>Lu-Hf isotopic analysis of zircon is becoming a common way to characterise the source signature of granite. The data are collected by MC-LA-ICP-MS (multi-collector laser ablation inductively coupled plasma mass spectrometry) as a series of spot analyses on a number of zircons from a single sample. These data are often plotted as spot analyses, and variable significance is attributed to extreme values, and amount of scatter. <p>Lu-Hf data is used to understand the origin of granites, and often a distribution of εHf values is interpreted to derive from heterogeneity in the source or from mixing processes. As with any physical measurement, however, before the data are used to describe geologic processes, care ought to be taken to account for sources of analytical variability. The null hypothesis of any dataset is that there is no difference between measurements that cannot be explained by analytical uncertainty. This null hypothesis must then be disproven using common statistical methods. <p>There are many sources of uncertainty in any analytical method. First is the uncertainty associated with the counting statistics of each analysis. This uncertainty is usually recorded as the SE (standard error) uncertainty attributed to each spot. This uncertainty commonly underestimates the total uncertainty of the population, as it only contains information about the consistency of the measurement within a single analysis. The other source of uncertainty that needs to be characterised is similarity over multiple analyses. This is very difficult to assess in an unknown material, but can be assessed by measuring well-understood reference zircons. <p>Reference materials are characterised by homogeneity in the isotope of interest, and multiple analyses of this material should produce a single statistical population. Where these populations display significant excess scatter, manifested as a MSWD value that far exceeds 1, this means that counting statistics are not the sole source of uncertainty. This can be addressed by expanding the uncertainty on the analyses until the standard zircons form a coherent statistical population. This expansion should then be applied to the unknown zircons to accommodate this ‘spot-to-spot-uncertainty’ or ‘repeatability’ factor. This approach is routinely applied to SHRIMP U-Pb data, and here is similarly applied to Lu-Hf data from granites of the northeast Lachlan Orogen. <p>By applying these uncertainty factors appropriately, it is then possible to assess the homogeneity of unknown materials by calculating weighted means and MSWD factors. The MSWD is a measure of scatter away from a single population (McIntyre et al., 1966; Wendt and Carl, 1991). Where the MSWD is 1, the scatter in data points can be explained solely by analytical means. The higher the MSWD, the less likely it is that the data can be described as a single population. Data which disperses over several εHf units can still be attributed to a single population if the uncertainty envelopes of analyses largely overlap each other. These concepts are illustrated using the data presented in Figure 1. Four out of five of the εHf datasets on zircons from granites form statistically coherent populations (MSWD = 0.69 to 2.4). <p>A high MSWD does not necessarily imply that variation is due to processes occurring during granite formation. Although zircon is a robust mineral, isotopic disturbances are still possible. In the U-Pb system, there is often evidence of post-crystallisation ‘Pb-loss’ which leads to erroneously young apparent U-Pb ages. The Lu-Hf system in zircon is generally thought to be more robust than the U-Pb system, but that does not mean that it is impervious to such effects. In the data set presented in Figure 1, the sample with the most scatter in Lu-Hf (Glenariff Granite, εHf = -0.2 ± 1.5, MSWD = 7.20) is also the sample which had the most rejections in the SHRIMP U-Pb data due to Pb-loss. The subsequent Hf analyses targeted only those grains which fell within the magmatic population (i.e., no observed Pb-loss), but the larger volume excavated by laser Hf analysis means that it is likely that disturbed regions of these grains were incorporated into the measurement. This gives an explanation for the scatter that has nothing to do with geological source characteristics. <p>This line of logic can similarly be applied to all types of multi-spot analyses, including O-isotope analyses. While most of the εHf datasets presented here form coherent populations, the O-isotope data are significantly more scattered (MSWD = 2.8 to 9.4). The analyses on the unknowns scatter much more than on the co-analysed TEMORA2 reference zircon. This implies a source of scatter additional to those described above. In addition to the above described sources of uncertainty, O-isotope analysis by SIMS is also extremely sensitive to topography on the surface of the epoxy into which zircons are mounted (Ickert et al., 2008). O isotopes may also be susceptible to post-formation disturbance and so care should also be taken when interpreting O data, before assigning geological meaning. <p>While it is possible for Lu-Hf and O analyses of zircons in granites to reflect heterogeneous sources and/or complex formation processes, it is important to first exclude other sources of heterogeneity such as analytical sources of uncertainty, and post-formation isotopic disturbances.

The Kingoonya Palaeovalley is one of the largest arid zone palaeovalley systems in South Australia. Situated in the remote central-western Gawler Craton this relict drainage network, now buried and obscured by surficial Quaternary sediments, is characterised by multiple headwater tributaries which flowed predominantly westwards towards the Eucla Basin. Fluvial and lacustrine sediments infilling the incised palaeovalley, in places forming stacked sequences >100 metres thick, were sporadically deposited from the Mid Eocene to the Early Pliocene. Previous drilling transects indicated a variety of channel shapes and heterogeneous sediment packages, with favourable aquifer sequences (sand-rich) common in deeper parts. In 2010 detailed groundwater sampling from existing bores was conducted in the Kingoonya Palaeovalley for the National Water Commission-funded Palaeovalley Groundwater Project. Analysis of these samples indicates that most Kingoonya groundwaters are moderately to highly saline and dominated by Na and Cl ions. Trace element enrichments are uncommon, although locally elevated levels of some metals (e.g., Fe and Mn) likely reflect groundwater interactions with the heterogenous sediments. The Kingoonya groundwaters also have near-neutral to slightly acidic pH, low alkalinity and are mostly oxidising. Stable water isotopes define a distinct trend away from the LMWL, interpreted as multiple stages of evaporative recycling and relative enrichment from the original isotopic signatures (precipitation derived from nearby Southern Ocean). Radiocarbon ages indicate a spectrum of groundwater residence times, ranging from modern recharge to groundwater signatures >20,000 years in deeper parts of the basal palaeovalley aquifer.

The Victoria and Birrindudu Basins of the Victoria River region, NW Northern Territory, represent a pair of stacked unmetamorphosed Palaeoproterozoic to Neoproterozoic basins unconformably overlying low-grade metamorphic basement. SHRIMP U-Pb analysis of detrital zircons provide a basis for lithostratigraphic correlations with other Proterozoic Basins across northern Australia. The Palaeoproterozoic Stirling Sandstone (basal Limbunya Group) is tentatively correlated with the Mount Charles Formation in the Tanami region. The Jasper Gorge Sandstone (basal Auvergne Group) correlates with basal units of the lower Cryogenian Supersequence 1 of the Centralian Superbasin (Heavitree Quartzite and its correlatives). A third correlation, previously proposed elsewhere and further explored here, suggests that the Duerdin Group may correlate with the upper Cryogenian ca. 635 Ma 'Marinoan' glacigenic units of Supersequence 3 of Centralian Superbasin. In particular, the Cryogenian pre-glacigenic Black Point Sandstone Member (basal Duerdin Group) is dominated by detrital zircons with age components characteristic of the Musgrave Complex, implying significant exhumation and erosion of the Musgrave Complex occurred, at least partially, prior to the end of the Cryogenian (<ca. 635 Ma) far earlier than generally thought. The latter two correlations suggest that the Victoria Basin in the Victoria River region represents yet another relic component of the extensive former Centralian Superbasin, at least during Cryogenian time. Sm-Nd whole rock determinations overwhelmingly, and unsurprisingly, are consistent with clastic derivation from the evolved North Australian Craton and, for the Black Point Sandstone Member, from the Musgrave Complex. A relatively juvenile signature ('Ndt ' +1) is observed coincident with aerial volcanism within the Birrindudu Basin at ca. 1640 Ma as has been recently noted in other Australian Palaeoproterozoic terrains.

The Nolans Bore deposit, located in the Aileron Province of south-central Northern Territory, is an emerging Australian rare earth development. It consists of steeply northwest dipping apatite veins hosted by ~1806 Ma granite gneiss. A preliminary ~1240 Ma U-Pb age for apatite may correspond to a major global period of alkalic magmatism between 1300 and 1130 Ma, including emplacement of the Bayan Obo deposit in China. Low ?Nd and 87Sr/86Sr in the mineralisation is reminiscent of modern EM-1 ocean island basalts and may indicate a link to carbonatitic magmatism. Oxygen isotope thermometry indicates a mineralisation temperature of 410°C, with '18Ofluid of ~8.0'. Fertilisation of the mantle to produce the EM-1 source may relate to subduction associated with convergence along the southern margin of the North Australian Craton.

The Brattstrand Paragneiss, a highly deformed Neoproterozoic granulite-facies metasedimentary sequence, is cut by three generations of ~500 Ma pegmatite. The earliest recognizable pegmatite generation, synchronous with D2-3, forms irregular pods and veins up to a meter thick, which are either roughly concordant or crosscut S2 and S3 fabrics and are locally folded. Pegmatites of the second generation, D4, form planar, discordant veins up to 20-30 cm thick, whereas the youngest generation, post-D4, form discordant veins and pods. The D2-3 and D4 pegmatites are abyssal class (BBe subclass) characterized by tourmaline + quartz intergrowths and boralsilite (Al16B6Si2O37); the borosilicates prismatine, grandidierite, werdingite and dumortierite are locally present. In contrast, post-D4 pegmatites host tourmaline (no symplectite), beryl and primary muscovite and are assigned to the beryl subclass of the rare-element class. Spatial correlations between B-bearing pegmatites and B-rich units in the host Brattstrand Paragneiss are strongest for the D2-3 pegmatites and weakest for the post-D4 pegmatites, suggesting that D2-3 pegmatites may be closer to their source. Initial 87Sr/86Sr (at 500 Ma) is high and variable (0.7479-0.7870), while -Nd500 tends to be least evolved in the D2-3 pegmatites (-8.1 to -10.7) and most evolved in the post-D4 pegmatites (-11.8 to -13.0). Initial 206Pb/204Pb and 207Pb/204Pb and 208Pb/204Pb ratios, measured in acid-leached alkali feldspar separates with low U/Pb and Th/Pb ratios, vary considerably (17.71-19.97, 15.67-15.91, 38.63-42.84), forming broadly linear arrays well above global Pb growth curves. The D2-3 pegmatites contain the most radiogenic Pb while the post-D4 pegmatites have the least radiogenic Pb; data for D4 pegmatites overlap with both groups. Broad positive correlations for Pb and Nd isotope ratios could reflect source rock compositions controlled two components. Component 1 (206Pb/204Pb-20, 208Pb/204-43, Nd -8) most likely represents old upper crust with high U/Pb and very high Th/Pb. Component 2 (206Pb/204Pb -18, 208Pb/204Pb~38.5, -Nd500 -12 to -14) has a distinctive high-207Pb/206Pb signature which evolved through dramatic lowering of U/Pb in crustal protoliths during the Neoproterozoic granulite-facies metamorphism. Component 1, represented in the locally-derived D2-3 pegmatites, could reside within the Brattstrand Paragneiss, which contains detrital zircons up to 2.1 Ga old and has a wide range of U/Pb and Th/Pb ratios. The Pb isotope signature of component 2, represented in the 'far-from-source' post-D4 pegmatites, resembles feldspar Pb isotope ratios in Cambrian granites intrusive into the Brattstrand Paragneiss. However, given their much higher 87Sr/86Sr, the post-D4 pegmatite melts are unlikely to be direct magmatic differentiates of the granites, although they may have broadly similar crustal sources. Correlation of structural timing with isotopic signatures, with a general sense of deeper sources in the younger pegmatite generations, may reflect cooling of the crust after Cambrian metamorphism.

The carbon and hydrogen isotopic data of natural gases provide a crucial tool to interpret the origin, occurrence and inter-relationships of natural gases. The CF-GC-IRMS is a convenient system to separate gas mixture and obtain continuous, on-line isotopic data of individual compounds. With CF-GC-IRMS system, the abundance of target components is crucial. For an accurate result, there should be enough target compound going through the furnace to be measured as CO2 using isotopic ratio mass spectrometry. For carbon isotopes, a m/z 44 response below 0.3 V (or over 7V) is regarded as unreliable. For high abundant compounds, there is no difficulty in attaining a voltage over 0.3V with a normal injection of under 100ul with adjusted split flow. However, the acquisition for the low concentration component is problematic since "normal" injection would not produce a strong enough signal. In this presentation, we demonstrated the techniques used to obtain low concentration components occurring in the Australian natural gases and how we apply the results in gas comparison studies. Cryogenics (liquid nitrogen trap) is applied to trap and concentrate low amount of compounds other than methane (C1), including CO2, C2 and above. With this method, extreme low concentration of C2 from very dry gases was obtained with large volume injection of 10ml. Back-flash is used together with cryogenics. For analyses for only C4 and C5 compounds, cryogenics was not needed, since they focus at the front of the column at 40oC and elute from the column under oven temperature programming as single peaks. Neo-pentane (neo-C5) is generally the least abundant wet gas component. Its concentration is enhanced in the gases which are biodegraded, wherein the other gas components have been selectively removed by microbial activity. Neo-pentane is extremely resistant to biodegradation and shows no isotopic alteration even in severely biodegraded gas. In such cases, neo-C5 is the only gas component that can be confidently used in gas-gas correlation. Neo-pentane is an example where we employ injection of a large volume (e.g. to 40ml for hydrogen isotopes), combining a back-flashing technique for compounds eluting before C4 (inclusive) and C5 compounds. The neo-C5 elutes between nC4 and i-C5. Under the current GC conditions, there is a time "window" of less than 40 seconds to capture neo-C5. A manual operation to set back-flash to straight flow to allow capture neo-C5 just after n-C4 elutes and then back to back-flush to eliminate interference of C5's compounds. Mass balance estimation indicates that there is no loss of neo-C5 during the large volume injection and repeatability is excellent.

The New England Orogen (NEO) forms the easternmost part of continental Australia, being one of a number of identified orogenic belts within the Tasman Orogenic Zone of eastern Australia. The NEO borders parts of the Lachlan, Thomson and North Queensland Orogens (see Fig. 1), though actual contacts are largely obscured by the Sydney-Gunnedah-Bowen basin system and other cover rocks. The NEO consists of a collage of terranes and has a complex history that stretches from the Neoproterozoic to the Late Mesozoic, although most of the exposed geology is Devonian and younger. A major characteristic of the NEO in this convergent margin setting is the voluminous Carboniferous to Triassic magmatism, which forms a major component of the orogen. Importantly, this magmatism is not confined to the NEO. Carboniferous to mid Triassic felsic magmatism (ca. 350-220 Ma) (Post-Kanimblan Orogeny to Hunter-Bowen Orogeny) forms a major part of the Tasman Orogenic Zone, extending in a wide belt from central New South Wales (the Bathurst region) to islands within the Torres Straits, straddling the Lachlan, Thomson, New England and North Queensland Orogens (Fig. 1), as well as extending into the Proterozoic basement west of the Tasman Orogenic Zone in northern Queensland (Fig. 1). As such, the geochemical and isotopic characteristics of these magmatic rocks, and their regional variations, have the potential to provide significant information regarding the nature and age of the crust in these orogens, as well as to provide constraints on the relationship of the development of the NEO to the neighbouring orogens.

<div>Komatiites are extinct volcanic rocks that formed by partial melting of 20-50% of their mantle source – a unique feature that allows us to understand the composition of the mantle in the early Earth. Due to their high temperature, komatiites incorporate proximal rock types on their way to, and on, the Earth’s surface. In this craton-scale study, we looked to use this property of komatiite magmas to track their interaction with the crust of the Yilgarn Craton. The results yielded Hf and Nd isotope arrays (Figure 1), that potentially have three components. The first likely represents the depleted mantle source of the magmas, and most plot in the region between +2 and +6 εHfi and 0 to +3.3 εNdi. The second source represents a more unradiogenic component, most likely 3.5-3.3 Ga continental crust (minimum). This component is more notable in the 2.8 and 2.9 Ga events with values trending to CHUR and negative εNd. The 2.8 Ga dataset, and particularly the komatiitic basalts from the Marda region, appear to show the most contamination with old crust. This is likely due to this area representing the old nucleus of the craton, as shown in Hf-isotope mapping. The final component represents an ultra-depleted source. Data from Ravensthorpe, Mt Clifford, and Wiluna show trends towards this source referred to as the Early Refractory Reservoir (ERR)(Nebel et al. 2014). We suggest that the 2.7 and 2.9 Ga plumes interacted with refractory Hadean plume residues, which constitute the ERR, within the Yilgarn lithosphere. Isotopic data on crustal rocks suggests the Yilgarn may have formed in the Hadean to Eoarchean, and hence the ERR could represent the residue of the Hadean crust generation process that formed the low Lu/Hf Jack Hills zircons. If correct, this suggests that the ERR survived for much longer than previously thought, as a rare component within the Earth’s oldest cratons.</div> This Abstract was submitted/presented to the 2023 6th International Archean Symposium (6IAS) 25 - 27 July (https://6ias.org/)

<div>Poster for the Specialist Group in Geochemistry, Mineralogy & Petrology (SGGMP) conference in Yallingup WA in November 2022.</div><div><br></div>This Poster was presented to the 2022 Specialist Group in Geochemistry, Mineralogy and Petrology (SGGMP) Conference 7-11 November (https://gsasggmp.wixsite.com/home/biennial-conference-2021)

<div>This report presents key results from the Upper Darling River Floodplain groundwater study conducted as part of the Exploring for the Future (EFTF) program in north-western New South Wales. The Australian Government funded EFTF program aimed to improve understanding of potential mineral, energy, and groundwater resources in priority areas for each resource.</div><div><br></div><div>The Upper Darling River Floodplain study area is located in semi-arid zone northwest New South Wales is characterised by communities facing critical water shortages and water quality issues, along with ecosystem degradation. As such, there is an imperative to improve our understanding of groundwater systems including the processes of inter-aquifer and groundwater-surface water connectivity. The key interest is in the fresh and saline groundwater systems within alluvium deposited by the Darling River (the Darling alluvium - DA) which comprises sediment sequences from 30 m to 140 m thick beneath the present-day floodplain.</div><div><br></div><div>The study acquired airborne, surface and borehole geophysical data plus hydrochemical data, and compiled geological, hydrometric, and remote sensing datasets. The integration of airborne electromagnetic (AEM) data with supporting datasets including surface and borehole magnetic resonance, borehole induction conductivity and gamma, and hydrochemistry data has allowed unprecedented, high resolution delineation of interpreted low salinity groundwater resources within the alluvium and highly saline aquifers which pose salination risk to both the river and fresher groundwater. Improved delineation of the palaeovalley architecture using AEM, seismic, and borehole datasets has permitted interpretation of the bedrock topography forming the base of the palaeovalley, and which has influenced sediment deposition and the present-day groundwater system pathways and gradients.</div><div><br></div><div>The integrated assessment demonstrates that the alluvial groundwater systems within the study area can be sub-divided on the basis of groundwater system characteristics relevant to water resource availability and management. Broadly, the northern part of the study area has low permeability stratigraphy underlying the river and a generally upward groundwater gradient resulting in limited zone of freshwater ingress into the alluvium around the river. A bedrock high south of Bourke partially restricts groundwater flow and forces saline groundwater from deeper in the alluvium to the surface in the vicinity of the Upper Darling salt interception scheme. From approximately Tilpa to Wilcannia, sufficiently permeable stratigraphy in hydraulic connection with the river and a negligible upward groundwater gradient allows recharge from the river, creating significant freshwater zones around the river within the alluvium.</div><div><br></div><div>Hydrometric and hydrochemical tracer data demonstrate that the alluvial groundwater systems are highly coupled with the rivers. Results support the conceptual understanding that bank-exchange processes and overbank floods associated with higher river flows are the primary recharge mechanism for the lower salinity groundwater within the alluvium. When river levels drop, tracers indicative of groundwater discharge confirm that groundwater contributes significant baseflow to the river. Analysis of groundwater levels and surface water discharge indicates that the previously identified declining trends in river discharge are likely to produce the significant decline in groundwater pressure observed across the unconfined aquifer within the alluvium. Improved quantification and prediction of groundwater-surface water connectivity, water level and flux is considered a high priority for both the Darling River and the wider Murray–Darling Basin. This information will assist in understanding and managing water resource availability in these highly connected systems, and enhance knowledge regarding cultural values and groundwater dependent ecosystems (GDEs).</div><div><br></div><div>This study identifies several aquifers containing groundwater of potentially suitable quality for a range of applications in the south of the study area between Wilcannia and Tilpa and assessed the geological and hydrological processes controlling their distribution and occurrence. Potential risks associated with the use of this groundwater, such as unsustainable extraction, impacts on GDEs, and saline intrusion into aquifers or the river, are outside the scope of this work and have not been quantified.</div>