Inland sulfidic soils have recently formed throughout wetlands of the Murray River floodplain associated with increased salinity and river regulation (Lamontagne et al., 2006). Sulfides have the potential to cause widespread environmental degradation both within sulfidic soils and down stream depending on the amount of carbonate available to neutralise acidity (Dent, 1986). Sulfate reduction is facilitated by organic carbon decomposition, however, little is known about the sources of sedimentary organic carbon and carbonate or the process of sulfide accumulation within inland sulfidic wetlands. This investigation uses stable isotopes from organic carbon (13C and 15N), inorganic sulfur (34S) and carbonate (13C and 18O) to elucidate the sources and cycling of sulfur and carbon within sulfidic soils of the Loveday Disposal Basin.

Initial lead isotope ratios from Archean volcanic-hosted massive sulfide (VHMS) and lode gold deposits and neodymium isotope model ages from igneous rocks from the geological provinces that host these deposits identify systematic spatial and temporal patterns, both within and between the provinces. The Abitibi-Wawa Subprovince of the Superior Province is characterized by highly juvenile lead and neodymium. Most other Archean provinces, however, are characterized by more evolved isotopes, although domains within them can be characterized by juvenile isotope ratios. Metal endowment (measured as the quantity of metal contained in geological resources per unit surface area) of VHMS and komatiite-associated nickel sulfide (KANS) deposits is related to the isotopic character, and therefore the tectonic history, of provinces that host these deposits. Provinces with extensive juvenile crust have significantly higher endowment of VHMS deposits, possibly as a consequence of higher heat flow and extension-related faults. Provinces with evolved crust have higher endowment of KANS deposits, possibly because such crust provided either a source of sulfur or a stable substrate for komatiite emplacement. In any case, initial radiogenic isotope ratios can be useful in predicting the endowment of Archean terranes for VHMS and KANS deposits. Limited data suggest similar relationships may hold in younger terranes.

<div>A groundwater chemistry, regolith chemistry and metadata record for legacy geochemical studies over the southern Curnamona Province done by GA and partners as part of CRC LEME from 1999 to 2005, that was never fully released. This includes comprehensive groundwater chemistry from more than 250 bores in the Broken Hill region, containing physicochemical parameters, major and trace elements, and a suite of isotopes (34S, Pb, Sr, 18O, D). Recent work on this dataset (in 2021) has added hydrostratigraphic information for these groundwater samples. Also included is a regolith geochemistry dataset collected adjacent to some of the groundwater bores which tests the geochemical response of a range of different size fractions, depths and digests.</div>

The Nolans Bore deposit, located in the Aileron Province of south-central Northern Territory, is a developing Australian rare earth element (REE) deposit. The deposit currently has a defined global resource of 30.2 Mt grading 2.8% rare earth oxides, 12.9% P2O5 and 200 ppm U3O8 (ASX:ARU 11/11/08). It consists of massive and brecciated fluorapatite veins that are up to 75-m-thick and hosted by ~1806 Ma granitic and metasedimentry units. Although initial drilling indicated that these veins dipped steeply to the NNW, more recent drilling has indicated a more complex 3D-vein configuration across the deposit. Even though apatite is the dominant mineral in the veins, the paragenesis is complex, with a massive zone of apatite-allanite-amphibole breccia, and numerous cross-cutting veins. The apatite hosts REE but it also typically contains abundant inclusions of other REE-bearing minerals, such as monazite and allanite along with other REE 'bearing phosphates, silicates and carbonates. Localised zones of higher grade REE mineralisation occur as intensely kaolinitised and clay altered rocks dominated by fine grained monazite and crandallite group minerals. A preliminary ~1240 Ma U-Pb age for apatite, which is interpreted as a minimum age, corresponds to a major period of global alkalic magmatism between 1300 and 1130 Ma. Low ?Nd and 87Sr/86Sr in the mineralisation are suggestive of EM-1 sources. The deposit is interpreted to be a carbonatite-related hydrothermal deposit. Fertilisation of the mantle to produce the EM-1 source may relate to subduction associated with older convergence along the southern margin of the North Australian Craton.

Natural gas is Australia's third largest energy resource after coal and uranium but despite this economic importance, the gas origin is not always recognized. To address this, isotope and geochemistry data have been collated on 850 natural gases from all of Australia's major gas provinces with proposed source ages spanning the earliest Paleozoic to the Cenozoic. Unaltered natural gases have a thermogenic origin ('13C methane ranges between -49 and -27'; 'D methane ranges between -290 and -125'). Microbially altered natural gases were identified primarily on the basis of 13C and D enrichments in propane and/or 13C depletion in methane and/or 13C enrichment in CO2. The carbon isotopic composition of the gas source has been estimated using '13C iso-butane as a surrogate for '13C kerogen while for gases where biodegradation is moderate to severe, '13C neo-pentane provides an alternative measure. The '13C kerogen of gas source rocks range from -47 to -22' with the older Paleozoic sources and marine kerogen amongst the most depleted in 13C. The '13C CO2 also provides an insight into crustal- and mantle-derived components while '15N N2 (-6.0 to 2.3' for N2 up to 47 %) distinguish between organic and inorganic (groundwater) inputs. This dataset provides a better understanding on the source and preservation history of Australian gas accumulations with direct implications on improving exploration success.

Intrusive and extrusive, predominantly felsic, magmatism of Carboniferous to Permian age occurs throughout the north Queensland region (Figure kennedy), and comprises the most widespread and voluminous magmatic event in the region. The great bulk of the exposed KIA is concentrated in the Townsville-Cairns-Cooktown-Georgetown-Charters Towers-Burdekin Falls regions (Figure Kennedy)-within the early-mid-Palaeozoic Hodgkinson and Broken River Provinces, the Etheridge Province and associated Proterozoic provinces, and in the northern part of the Thomson Orogen including the Greenvale, Charters Towers, and Barnard Provinces, and the northern Drummond Basin. The boundary between the northern Drummond Basin and Connors (nNEO) Subprovince is taken to be the Millaroo Fault Zone (MFZ). Geophysical data (and limited geochronology) show that Carboniferous-Permian granites also form a westerly trending belt-the Townsville-Mornington Island Belt (TMIB; originally Townsville-Mornington Island Igneous Belt), which extends under cover from north of Mount Surprise, at least as far as Mornington Island in the Gulf of Carpentaria, transecting regional trends (Wellman, 1992, 1995; Wellman et al., 1994). There is also recent geochronological evidence for KIA magmatism in the environs of the Millungera Basin (Neumann & Kositcin, 2011). Outcrop is discontinuous in the belt extending northwards from Cairns up Cape York Peninsula, to the islands of Torres Strait (and beyond) but geophysical evidence implies there is more extensive magmatism under cover.

New provenance data from Palaeoproterozoic and possible Archaean sedimentary units in the central eastern Gawler Craton forms part of a growing dataset suggesting that the Gawler Craton shares important basin formation and tectonic time lines with the adjacent Curnamona Province and the Isan Inlier in northern Australia. U-Pb dating of detrital zircons from the Eba Formation (previously mapped as Tarcoola Formation), yield exclusively Archaean ages (~2530-3300 Ma). This is consistent with whole rock Nd and zircon Hf isotopic data for the Eba Formation which have evolved compositions. Elsewhere in the eastern Gawler Craton, cover sequences historically considered to be Palaeoproterozoic in age also contain exclusively Neo and Meso Archaean aged detrital zircons (Reid et al, 2009 Econ. Geol.; Szpunar et al, 2007, SGTSG). The absence of Palaeoproterozoic detrital grains in several differently mapped sequences (including the Eba Formation) despite the proximity of voluminous Palaeoproterozoic rock units, suggests that the Eba Formation may be part of a Neo-Archaean or early Palaeoproterozoic cover sequence derived from erosion of a complex Archaean aged source region. The Labyrinth Formation unconformably overlies the Eba Quartzite, and contains rhyolitic units that constrain deposition to 1715 ± 9 Ma (Fanning et al., 2007; PIRSA Bulletin 55). This age is identical to the timing of deposition of the lower Willyama Supergroup in the adjacent Curnamona Province. Detrital zircon ages in the Labyrinth Formation range from NeoArchaean to Palaeoproterozoic, and are consistent with derivation from > 1715 Ma components of the Gawler Craton. Isotopic zircon Hf data and whole rock Nd data also suggest a source region with a mixed crustal evolution (-Nd -4.5 to -6), consistent with what is known about the Gawler Craton. Compared to the Lower Willyama Supergroup, the Labyrinth Formation has a source more obviously reconcilable with the Gawler Craton.

Amino acid racemization (AAR) dating of the eolianite on Lord Howe Island is used to correlate several disparate successions and provides a geochronological framework that ranges from Holocene to Middle Pleistocene time. The reliability of the AAR data is assessed by analysing multiple samples from individual lithostratigraphic units, checking the stratigraphic order of the D/L ratios and the consistency of the relative extents of racemization for a suite of seven amino acids. Three aminozones are defined on the basis of the extent of racemization of amino acids in land snails (Placostylus bivaricosus) and 'whole-rock' eolianite samples. Aminozone A includes Placostylus from modern soil horizons (e.g. mean D/L-leucine ratio of 0.03±0.01) and whole-rock samples from unconsolidated lagoonal and beach deposits (0.10±0.01-0.07±0.03). Aminozone B includes Placostylus (0.45±0.03) and whole-rock samples from beach (0.48±0.01) and dune (0.45±0.02-0.30±0.02) units of the Neds Beach Formation, deposited during OIS 5. The oldest, Aminozone C, comprises Placostylus recovered from paleosols (0.76±0.02) and whole-rock eolianite samples (0.62±0.00) from the Searles Point Formation, which indicate the formation was likely deposited over several Oxygen Isotope Stages (OIS), during and prior to OIS 7. These data support independent lithostratigraphic interpretations and are in broad agreement with U/Th ages of speleothems from the Searles Point Formation and corals from the Neds Beach Formation, and with several TL ages of dune units in both formations. The AAR data reveal that eolianite deposition extends over a significantly longer time interval than previously appreciated and indicate that the deposition of the large dune units is linked to periods of relatively high sea level.

Australia as it exists today is a product of geological processes that have occurred over its 4.5 billion year history. Isotopic studies are one approach to understanding the history and evolution of the Australian continent. Isotope geochronology tells us about the timing of a wide range of geological processes like crystallisation, deformation and cooling of rocks. Isotope geochemistry informs on the precursor components from which the rocks formed, and can act as 'paleogeophysical' sensors to tell us more about the subsurface. The Isotopic Atlas of Australia brings together five of the most widely used isotopic systems in geology and delivers publicly available maps and datasets in a consistent format. This work is unlocking the collective value of decades of investment in data collection, and facilitating qualitative and quantitative comparison and integration with other datasets such as geophysical images. This talk will be an introduction to the world of isotopes as applied to understand geology, and an overview of the Isotopic Atlas recently produced as part of the Exploring for the Future Program.

This is a collection of conference program and abstracts presented at AOGC 2010, Canberra.