The Arthurs Seat Igneous Complex, on the Mornington Peninsula, has been assumed to be Late Devonian in age, in common with the vast majority of Devonian silicic igneous rocks in central Victoria. New zircon U-Pb isotope data show that the volcanic part of the complex is Middle Devonian, with a sample of a biotite-hornblende rhyolite ignimbrite (AS2) yielding a model 1 discordia upper intercept age of 389.7 +/- 4.3 Ma (2 sigma, MSWD = 1.1). Compared with other I-type rocks in the region, the zircon population contains an unusually low proportion of inherited grains-just 15%. This inherited zircon is not derived from the Paleozoic metasedimentary rocks in the Melbourne Zone and is inferred to have been inherited from the source rocks of the rhyolitic magma. Given that previous work has shown that the initial Sr and Nd isotope ratios indicate magma derivation through partial melting of relatively unevolved rocks, the most likely source of the Arthurs Seat magmas is Cambrian andesitic to dacitic metavolcanic rocks in the Selwyn Block, similar to those that crop out on Phillip Island and at Cape Liptrap. The high-K chemistry of some Arthurs Seat rocks, most particularly the Dromana Granite, indicates the presence of metasedimentary rocks accompanying the meta-igneous source materials. In common with all the Devonian silicic igneous rocks of the region, the main population of inherited zircon in sample AS2 has an age of ca 400 Ma. This shows that there was a widespread episode of deep-crustal, high-grade metamorphism and partial melting during the Tabberabberan Orogeny. However, the absence of Early Devonian silicic magmatic rocks in the Melbourne Zone suggests that magma ascent to upper-crustal levels was hampered by the overall compressive tectonic regime at this time.
Through systematic studies of zircon U-Pb dating, petrogeochemistry and Lu-Hf isotopes of two episodes of early Paleozoic volcanic rocks in the Kunlunhe area, Qinghai Province, this paper reveals their genetic mechanisms and tectonic evolution significance. The results indicate that the pillow basalt within the ophiolite in the Kunlunhe area formed in the late Cambrian (488.4 +/- 1.4 Ma) and represents the residual oceanic crust of the early Paleozoic Proto-Tethys Ocean. The massive basalt in the Nachitai Group formed in the late Silurian (425.7 +/- 3.6 Ma), contemporaneous with the continental rift bimodal volcanic rocks in the region. Geochemical characteristics and positive epsilon Hf(t) values (average values of 4.0 and 1.95, respectively) demonstrate that the two episodes of basalts exhibit the geochemical signatures of enriched mid-ocean ridge basalt (E-MORB) and ocean island basalt (OIB), respectively, with low degrees of crustal contamination and derivation from the asthenospheric mantle. Tectonic evolution analysis shows that the late Cambrian ophiolite formed in a mid-ocean ridge setting, while the late Silurian basalt originated in an intraplate rift environment. The bimodal volcanic rocks are typical products of this rift setting, recording the tectonic transition process of the Eastern Kunlun Orogenic Belt from Proto-Tethys Ocean collisional orogeny to continental rift development during the initial stage of the Paleo-Tethys Ocean. Stratigraphic attribution determination confirms that as the residual oceanic crust in the late Cambrian tectonic m & eacute;lange, the ophiolite has essential differences in formation age and tectonic setting from the Silurian Nachitai Group and should not be classified into this group.
The Bosumtwi crater, a 10.5 km-diameter meteoritic impact structure formed 1.07 Ma ago, formed on a target dominated by Paleoproterozoic metasedimentary rocks (ca 2.1 Ga) and intrusive bodies covered by a thick lateritic regolith. Airborne radiometric data and field observations reveal that new lateritic profiles have developed on the crater ejecta, which consists primarily of brecciated metasedimentary rocks and granitoids. The objective of this study is to determine whether airborne radiometric data can discriminate between mature lateritic profiles outside the crater and its ejecta and more recent lateritic profiles that have developed on the crater rim and ejecta. This study demonstrates that the log(10)(K/Th) values are negatively correlated with the Chemical Alteration Index, and that the distributions of log(10)(K/Th) values of lateritic profiles inside and outside the ejecta are clearly distinct. A map of log(10)(K/Th) derived from airborne radiometric data allows spatial differentiation between mature and recent regolith profiles. This map also led to the discovery of an outer ejecta layer, extending a few kilometres beyond the distal ridge, that shares alteration characteristics similar to those of the inner ejecta layer. The Bosumtwi impact crater, previously recognised as a rampart crater analogous to those observed on Mars, appears to be comparable with double-layered-ejecta rampart craters. On Mars, this subtype is less common than 'single-layered-ejecta rampart craters' but is preferentially concentrated in topography lows likely associated with volatile-rich sedimentary deposits. From a methodological perspective, this study demonstrates that log(10)(K/Th) maps derived from airborne radiometric data offer a robust tool for exploration geology, particularly for revealing subtle variations in low-K regions (<1 wt%) and mapping variations in regolith development and surface rock alteration.
The Paleocene second member, Funing Formation, in the Jinhu Depression, Subei Basin of East China contains lacustrine carbonate successions with exquisitely preserved caddisfly case-bearing microbialites. These understudied deposits provide a unique opportunity to establish diagnostic criteria and elucidate the physico-chemical and biological controls on their formation. The study shows that the fossil caddisfly cases are single-walled or nested tubes, appearing curved and tapered, and ranging from agglutinated to non-agglutinated. They occur in concentrated clusters alternating with micro-laminated carbonate layers. Two facies associations (FA1 and FA2) comprising six discrete facies (F1-F6) are defined. FA1, representing wave-dominated, high-energy carbonate shorelines, is widespread along the western depression. It includes littoral-zone mixed carbonate shoals (F1), caddisfly case-dominated spring mounds (F2) and sandstone (F5), alongside littoral-to-profundal, low-energy carbonate microbial mounds (F3), sediment-gravity flow deposits (F4) and shale (F6). FA2, found in localised eastern areas, corresponds to sheltered, low-energy shorelines dominated by littoral microbial mounds overlying sublittoral-to-profundal facies similar to FA1. These successions are interpreted as deposits of a hydrologically open, freshwater to brackish-water lake. The western margin was influenced by spring/groundwater discharge, evidenced by gregarious caddisfly case accumulations, a dominant freshwater fauna with subordinate brackish-water indicators, absence of evaporites, negative delta(1)& sup3;C and delta O-18 values with poor covariance and crystalline dendritic to fan-shaped calcite fabrics. Microbial mound growth was primarily controlled by microbial processes (e.g. calcification, metabolism and extracellular polymeric substances/cell surface functions). In contrast, the distribution of caddisfly case-dominated spring mounds reflects the larval habit of annually attaching pupal cases to substrates in photic, high-energy littoral zones with concomitant spring discharge.
Pegmatites are a major source of lithium (Li), a critical metal enabling the transition from a fossil fuel-based energy sector to a sustainable, renewable energy future. The Greenbushes Li deposit in Western Australia is the world's largest single source of Li, and many other geological environments across Australia are highly prospective for pegmatite-hosted Li deposits. The recent Li rush has highlighted that downstream industries underestimate the complexity of pegmatite-hosted Li deposits, particularly regarding the wide range of Li-bearing minerals present in a single pegmatite. This paper presents an overview of Li-pegmatite mineral assemblages from various regions across Australia, including the southwestern part of Western Australia (WA), hosting Greenbushes, the Eastern Yilgarn Craton (Londonderry), the Pilbara Craton (Pilgangoora, King Col), Queensland's Georgetown Inlier (Buchanan's Creek) and the Dorchap Pegmatite Swarm in Victoria. Mineral assemblages from said localities are examined using publicly available hyperspectral drill core analyses (HyLogger3 (TM)). These findings are compared with those of Greenbushes drill core C3DD0024, supported by whole-rock geochemistry, Fourier transform infrared (FTIR) spectroscopy and X-ray diffractometry (XRD). Reflectance spectral characteristics of Li-bearing, gangue and alteration minerals are evaluated across the visible near-infrared (VNIR), shortwave infrared (SWIR) and thermal infrared (TIR) wavelength ranges to identify suitable unmixing and feature extraction algorithms for inferring relative mineral abundances and mineral chemistry. Newly developed algorithms-most notably the spodumene abundance index, show a significant correlation with XRD validation and whole-rock geochemistry, demonstrating their effectiveness for mineral detection. Furthermore, the distribution of other Li-bearing minerals, such as petalite and eucryptite, was mapped across the study sites using reference library spectra. The applied hyperspectral mineral abundance and composition indices provide key insights into mineral assemblages and their variations by (1) tracing variations of mineral assemblages within pegmatites and country rocks at centimetre scale, (2) showing that spodumene is predominantly associated with quartz +/- plagioclase (without K-feldspar), whereas petalite is mostly associated with quartz and K-feldspar in the absence of plagioclase, (3) confirming that most white mica in pegmatites exhibits an Al-rich composition, (4) demonstrating that phengitic alteration halos around pegmatites are narrow and (5) indicating that chlorite +/- biotite +/- epidote alteration is common in mafic-ultramafic and metasedimentary wallrocks. The algorithms and workflows provided in this study offer significant potential for expanding applications to large-scale hyperspectral drill core datasets, furthering the understanding of pegmatite genesis, supporting Li-exploration and guiding metallurgical processes by characterising Li-host minerals.
This study incorporates background correction and dilution correction methods for delineating Au geochemical anomalies using data of catchment outlet sediments from two horizons: top outlet sediments (TOS, 0-10 cm) and bottom outlet sediments (BOS, 60-90 cm), collected across the entire Queensland region as part of the National Geochemical Survey of Australia (NGSA) project. The dataset comprises Au concentrations from catchments covering numerous lithological units, which were merged into seven dominant lithologies for analysis. Multiple regression analysis was applied to estimate background Au values owing to lithology, enabling separation of background signals from mineralisation-related anomalies. Results show that dilution-corrected Au residuals improve anomaly detection, with BOS samples outperforming TOS in spatial alignment with 26 of 30 known gold deposit clusters, compared with 14 clusters identified by raw TOS data. The BOS horizon benefits from enrichment in fine sediment fractions (<75 & micro;m) and reduced effects of surface weathering, providing a more stable and representative geochemical signal. Elevated Au levels associated with dominant lithologies may mask true anomalies, underscoring the importance of background correction.
The geochemistry of In, Ga and Ge of muscovite and topaz was investigated from magmatic-hydrothermal systems related to tin and polymetallic vein mineralisation associated with Carboniferous-Permian granites from the Herberton Mineral Field (HMF) in northeast Queensland. Muscovite and topaz from the Baal Gammon and Isabel deposits were sampled and analysed. Each deposit shows two stages of hypogene mineralisation. The first stage is related to tin mineralisation associated with reduced intrusive rocks including the Jumna Granite, the Herberton Hill Granite and the UNA Porphyry. The second stage is related to Cu mineralisation associated with oxidised magmas that formed during the emplacement of the Slaughter Yard Creek Volcanics. Muscovite and topaz associated with the reduced intrusive rocks mainly occur in the greisen derived from the UNA Porphyry, whereas the muscovite associated with the oxidised phase occur with the massive sulfide mineral assemblage hosted by the Slaughter Yard Creek Volcanics and the Hodgkinson Formation. In general, the topaz grains have higher concentrations of Ga and Ge (average 196 ppm and 68 ppm, respectively) than the muscovite grains (average Ga = 8.4 ppm and Ge = 2 ppm). In contrast, muscovite grains have higher In concentrations (up to 60 ppm) than the topaz grains (below limit of detection). The normalised trace-element pattern of muscovite grains from different tin deposits indicates that Ga and Ge have a negative anomaly in oxidised granites and a positive anomaly in reduced granites. In contrast, the In anomaly is not sensitive to the oxidation state of the magmas. Geochemical modelling indicates that In forms stable complexes in acidic conditions, whereas Ga and Ge form stable complexes with oxide and hydroxide ions in near-neutral to weakly basic and reduced conditions. Thus, the geochemistry of In is decoupled from that of Ga and Ge owing to the redox conditions of the magmatic-hydrothermal systems.
Identifying geothermal resources typically requires time-consuming extensive geophysical surveys and deep drilling, which are costly and logistically challenging. This study illustrates the use of readily available shallow groundwater temperature data combined with surface air temperature records as a fast, low-cost, exploration screening tool for geothermal anomalies in deep sedimentary basins. The data were collated from existing piezometers used to monitor water-table fluctuations in groundwater monitoring wells, which are far more common than the bores typically used for geothermal temperature measurements. Geothermal anomalies can be identified by spatial analysis of the difference between the phreatic surface temperature and long-term averaged air temperature data. The study evaluates the workflow using known deep geothermal anomalies in two geologically distinct sedimentary basins: the onshore Perth Basin in Western Australia and the Hunter Valley in New South Wales. The analysis demonstrates that the widely available and commonly acquired hydrogeological data, along with average surface air temperature data, can be used for exploration for deeper geothermal anomalies. While the data are commonly measured to provide information about subsurface water levels, collating a more comprehensive national database of borehole temperature data would further facilitate geothermal exploration programs that are seeking deep sources of heat for electricity generation or shallow sources of heat for ground-source heat pumps.
Hyperspectral drill-core sensors provide a fast and non-destructive technique for collecting reflectance spectral data from drilling products. The spectral response allows proportions of a wide range of minerals to be estimated. This information can be used for supporting accurate drill-core logging and alterations mapping that are essential components of reporting the geology of a drill hole. The AuScope National Virtual Core Library (NVCL) contains more than 5900 drill cores from across Australia with HyLogger3 (TM) hyperspectral data collected by the Australian geological surveys. These data include the visible to near infrared, shortwave infrared and thermal infrared wavelength ranges. HyLogger3 (TM) data can be pre-processed using various algorithms in The Spectral Geologist software (TSG (TM)), and the results are available to the public through NVCL.In this paper, we present a workflow for HyLogger3 (TM) data, called MyLogger, that translates the thermal infrared hyperspectral drill-core data into a first-pass geological log using the main rock-forming mineral groups. The workflow requires a few simple decisions by the user, and decisions are facilitated by the provision of interactive plots. The workflow is provided as a web app using Python (TM) and Streamlit, and uses the wavelet tessellation method for multiscale drill-core analysis as well as using Scikit-learn machine learning. This workflow is demonstrated using HyLogger3 (TM) data from drill hole from South Australia's Mineral Systems Drilling Program as a case study for the generation of a geologically meaningful and depth accurate first-pass geological log. The ability to automatically extract a geological log from hyperspectral drill-core data alleviates the time-consuming process of manual interpretation of spectra by subject-matter experts to allow a rapid assessment of drill-hole geology. This will make the geological information contained in the NVCL database as well as other hyperspectral drill-core data more accessible to a broader range of geoscientists.
The Cooalinga Member of the Talisker Formation is the basal unit of the Bollaparudda Subgroup, the upper subgroup of the lower Cambrian Kanmantoo Group, in the southern part of the Adelaide Superbasin. Where present, the Cooalinga Member rests disconformably on the Backstairs Passage Formation. The sandstones of the Cooalinga Member are greywackes, in contrast to the relatively clean quartz-rich sands of the Backstairs Passage Formation. The Cooalinga Member is up to 1000 m thick in the central Mount Lofty Ranges and occupies deep erosional valleys and channels in the top of the Backstairs Passage Formation. However, in the Karinya Syncline, the Cooalinga Member has a maximum thickness of approximately 50 m and is absent in some places. Following a fall in sea-level that led to the incision of the Backstairs Passage Formation, most of the Cooalinga Member was deposited as high-density turbidity currents during a time of rapidly rising relative sea-level. It is suggested that the turbidites were derived from the south, as were the turbidites of the higher units of the Kanmantoo Group, with the source area probably in Antarctica. In the central Mount Lofty Ranges there are several conglomerates containing clasts up to 15 cm across within channels in the bottom part of the Cooalinga Member. The clasts are dominated by well-rounded quartzite with subordinate granite, gneiss, pegmatite, siltstone and calc-silicates set in a calc-silicate matrix. One of the granite clasts has a SHRIMP age of 1780 +/- 4 Ma and may have been derived from the Gawler Craton to the west.
The Tomkinson Province is a poorly understood component of the extensive Proterozoic basin system in northern Australia, spanning the Paleoproterozoic to Mesoproterozoic. These include the greater McArthur Basin, the South Nicholson Basin and the Lawn Hill Platform. The basins are broadly coeval and were deposited under comparable environmental conditions, resulting in similar stratigraphic successions. However, thick overlying sedimentary sequences obscure and separate individual basin components, complicating regional correlation and hindering reconstructions of their tectonic and depositional histories. The Tomkinson Province comprises three major stratigraphic packages-in ascending order, the Tomkinson Creek Group, Namerinni Group and the Renner Group-and is interpreted to be contiguous in the subsurface with the McArthur and Birrindudu basins. The Renner Group is a siliciclastic succession that has been historically correlated with the Roper Group of the McArthur Basin and the Tijunna Group of the Birrindudu Basin. However, there are few geochronological data to constrain the depositional age of the group and refine the correlations between these basins. Data here show that the Renner Group has major detrital zircon age peaks at ca 1850 Ma and 1750 Ma with minor peaks at ca 2200-1900 Ma and 2500 Ma. Large zircon epsilon Hf(t) arrays (-8 to +10) occur at ca 2500 Ma and ca 1850 Ma, with the most radiogenic values associated with older zircons-interpreted to reflect crustal thickening and orogenic activity. Importantly, the data suggest that the Renner Group is best correlated with the lower Roper Group (Collara Subgroup) of the McArthur Basin sensu stricto. If the Maiwok Subgroup (upper Roper Group) has equivalents within the Tomkinson Province, they appear to be restricted to the poorly exposed Lake Woods beds. Moreover, the detrital zircon age spectra from this study and others support previous seismic interpretations that the upper Roper Group is absent in the western Birrindudu Basin, with limited preservation west of the Daly Waters Fault Zone.
Paleoproterozoic granitoids of the Mount Isa Inlier record a prolonged history of crustal magmatism linked to the tectonic evolution of the North Australian Craton during assembly of the Nuna supercontinent. This study presents a lithogeochemical investigation of intrusions from the Dajarra region, in the southern Western Fold Belt, to constrain their geochemical characteristics, petrogenesis, and tectonic setting. The intrusions were emplaced at ca 1850-1650 Ma and correspond to four major magmatic episodes: the Kalkadoon, Argylla, Wonga-Burstall and Sybella igneous events. Thirty-three representative samples of plutons and associated dykes were analysed for whole-rock major and trace elements. The granitoids are dominantly felsic (SiO2, 62.6-76.7 wt%), with low MgO and TiO2 contents, high total alkalis and coherent fractionation trends consistent with extreme magmatic differentiation. Most samples are ferroan, alkalic-calcic to calc-alkalic and strongly peraluminous, whereas the Kalkadoon (KIE) sample is metaluminous. Trace-element patterns are characterised by enrichment in large ion lithophile elements and high-field-strength elements (HFSEs), pronounced negative Nb, Ti, Sr and Eu anomalies, and moderately to strongly fractionated rare earth element patterns. Distinct geochemical differences are observed between granitoid suites and across major structural boundaries, notably between Argylla intrusions east (AIE-E) and west (AIE-W) of the Rufus Fault. Many AIE-E, Wonga-Burstall and Sybella samples display elevated HFSE abundances and high zircon saturation temperatures, whereas AIE-W samples are HFSE-poor and exhibit lower temperatures, consistent with S-type affinities. On granite discrimination diagrams, most samples plot near the I- and A-type boundary and mainly within the A2 field, indicating derivation from reworked continental crust. This suggests that granitoid magmatism in the Dajarra region was dominated by partial melting of continental crust, with episodic mantle input required to achieve high melt temperatures. The magmatism occurred within a long-lived convergent margin system characterised by tectonic switching between contractional and extensional regimes during the Paleoproterozoic evolution of the Mount Isa Inlier.
The Qinshui Basin is one of the key basins for coal-bed methane exploration and development in China. In the southern S Block of the basin, the No. 3 coal seam of the Permian Shanxi Formation has demonstrated significant gas production potential. However, overall recovery rates remain low, and development results are suboptimal. There are many factors that affect the productivity of coal-bed methane, among which the conditions of the coal seam itself are the basis. The unclear sedimentary evolution and coal-accumulation patterns of coal-bearing rocks restrict the understanding of the basic conditions of coal seams. This study focuses on the No. 3 coal seam of the Shanxi Formation in the S area of the Qinshui Basin. Integrating core data, well logs and 3D seismic data, we investigate the characteristics and evolution of sedimentary facies to establish a coal-accumulation model. The findings indicate: (1) The Shanxi Formation comprises delta-plain deposits, which can be subdivided into three fourth-order sequences. From sequence S1 to S3, the depositional environment transitioned from lacustrine-swamp settings to distributary channel and natural levee systems. (2) The S1 sedimentary period is most conducive to the development of large-scale high-quality coal seams. We have identified five sedimentary stacking patterns and proposed that type I (lake-swamp-lake) is the most favourable. (3) We have established a delta-plain coal-accumulation model based on sedimentary stacking patterns. High-quality coal seams in the Shanxi Formation formed primarily where specific depositional microfacies associations developed consistently, which required a stable, sustained sedimentary environment. The proposal of the coal-accumulation model in the delta plain not only elucidates the relationship between sedimentary microfacies combination and coal reservoir development but also enriches the theory of coal-formation models in the delta plain. It is also significant for the selection of coal-bed methane exploration and development targets and can provide reference for similar blocks.
Estimates of the frequency of hydroclimatic extremes from stream gauging, meteorological observations and satellite imagery are not sufficiently robust for estimation of event frequencies because of the shortness of the records. Accordingly, a 1400-year record of extreme hydroclimatic events, both floods and coast-crossing cyclones (TCs), is presented for the Top End of monsoonal Australia. From this record, event frequencies have been estimated, along with peak flows for some floods, and the relationships of the events to climate states explored. The paleorecords documented in this paper are based on radiometrically dated sedimentary archives from beach ridges and ch & eacute;nier ridges for TCs and mainly from paleoflood deposits for large floods. Large floods in the region are a result of either TCs or intense tropical lows that commonly begin as TCs. This hydrological connection is apparent in episodes of co-occurring TCs and floods, both in the recent past and over the entire 1400-year record. Both the El Ni & ntilde;o-Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO) have influenced the occurrence of the extreme events. Flood frequency has varied through time with evidence for long periods with few events. The Modern Warm Period from ca 1850 CE is a time of high-flood and TC frequency, consistent with an increase in high stream flows from an independent study of the Katherine/Daly River and rainfall in monsoonal Australia more widely. The results presented here should be part of flood mitigation strategies, and assessments of the role of climate change.
The coastal strata of the Port Campbell region in southeast Australia host several 40-70 m-high limestone sea stacks called the 'Twelve Apostles' and over 40 km of near continuous sea cliffs. Despite their 'iconic' status, their geology is not well known. Mapping using photographic and digital imagery, with field mapping, stratigraphic and microfossil analyses, reveals their geology spans 15 million years of Earth history. The cliffs and sea stack preserve middle to late Miocene Heytesbury Group carbonates overlain by Pliocene to Quaternary ferruginous clay and calcareous siliciclastic units. The oldest unit east of the Twelve Apostles is the unconsolidated outer shelf middle Miocene Gellibrand Marl (15-14 Ma). The overlying shallow shelf Port Campbell Limestone is a brittle unit that forms most cliffs and sea stacks. Two Port Campbell Limestone units are present. A grey clay-rich unit in the lower half of cliffs and sea stacks deposited in deeper and shallower marine conditions from 14 to 11.6 Ma. Overlain by a yellow limestone unit in the upper half of the cliffs and stacks deposited in shallow shelf conditions from 11.6 to 8.6 Ma. Late Miocene uplift, accompanied by karstification and erosion, terminated limestone deposition after 8.6 Ma. This was accompanied by northwest-southeast compression causing 1-5 degrees tilting, creating folds and thrust faults. Subsequently, early Pliocene (ca 5 Ma) Hanson Plains Sands were deposited in terrestrial to shallow marine conditions accompanied by ongoing Pliocene weathering, creating ferricrete laterite soils and the Hesse Clay 'buckshot' gravel. This is the youngest red brown unit at the top of cliff sections and sea stacks. In the last million years, coastal Bridgewater Formation siliciclastics were deposited as a series of dunes and soils during high sea-level periods. Holocene flooding since the Last Glacial Maximum 23 000-20 000 years ago created 'modern' estuaries, sea stacks and cliffs.
