This record presents new zircon U-Pb geochronological data, obtained via Sensitive High Resolution Ion Microprobe (SHRIMP) for eleven samples of plutonic and volcanic rocks from the Lachlan Orogen, and the New England Orogen. The work is part of an ongoing Geochronology Project (Metals in Time), conducted by the Geological Survey of New South Wales (GSNSW) and Geoscience Australia (GA) under a National Collaborative Framework (NCF) agreement, to better understand the geological evolution of New South Wales. The results herein (summarised in Table 1.1 and Table 1.2) correspond to zircon U-Pb SHRIMP analysis undertaken on GSNSW mineral systems projects for the reporting period July 2015-June 2016. Lachlan Orogen In the Lachlan Orogen, the age of 418.9 ± 2.5 Ma for the Babinda Volcanics is consistent with the accepted stratigraphy of its parent Kopyje Group, agrees with the ages of other I-type volcanic rocks within the Canbelego-Mineral Hill Volcanic Belt and indicates eruption and emplacement of this belt during a single event. The age of the Shuttleton Rhyolite Member (421.9 ± 2.7 Ma) of the Amphitheatre Group is compatible with recent U-Pb dating of the Mount Halfway Volcanics, which interfingers with the Amphitheatre Group (MacRae, 1987). The age is also similar to nearby S-type granite intrusions, which suggests that the limited eruptive volcanic activity in the region was accompanied by local coeval plutonism. The results for the Babinda Volcanics and Shuttleton Rhyolite Member, in conjunction with previous GA dating and other dating and studies (summarised in Downes et al., 2016) establishes that significant igneous activity occurred between ~423 and ~418 Ma within the Cobar region but comprised two compositionally distinct but broadly contemporaneous belts of volcanics and comagmatic granite intrusions. The new age for the unnamed quartz monzonite at Hobbs Pipe constrains the maximum age of the hosted gold mineralisation to 414.7 ± 2.6 Ma. The wide range in ages for granites along the Gilmore Suture suggests that mineralisation in this region is not necessarily constrained to a single short-lived event. The new age of 413.5 ± 2.3 Ma for volcanics at Yerranderie indicates that that the Bindook Volcanic Complex was erupted over a relatively short period, and also indicates that the epithermal mineralisation at Yerranderie was not genetically related to the host volcanics but probably to a younger rifting event in the east Lachlan. New England Orogen Four units were dated from the Clarence River Supersuite in the New England Orogen. All four are between 255 and 256 Ma, demonstrating that these granites are related chemically, spatially, and temporally. While these four ages are indistinguishable, the current age span for Clarence River Supersuite is more than 40 million years. This wide age range indicates that classification of granites into the Clarence River Supersuite needs further refinement. The new age for the Newton Boyd Granodiorite (252.8 ± 1.0 Ma) is similar to some previously dated units within the Herries Supersuite, but both the Herries Supersuite and Stanthorpe Supersuite (into which the Herries Supersuite was reclassified by Donchak, 2013) incorporate units with a broad range of ages: the age distribution for the Stanthorpe Supersuite spans 50 million years. Classification of granites in the New England Orogen in New South Wales is worth revisiting. Two units were dated from the Drake Volcanics, nominally in the Wandsworth Volcanic Group and indicate that the middle to upper section of the Drake Volcanics, including the mineralising intrusions, were emplaced within the space of 1-2 million years. These results support a genetic and temporal link between the Au-Ag epithermal mineralisation at White Rock and Red Rock and their host Drake Volcanic packages rather than to younger regional plutonism (i.e., Stanthorpe Supersuite) or volcanism (i.e., Wandsworth Volcanics). The almost 10 Ma gap between the Drake Volcanics and the next lowest units of the Wandsworth Volcanic Group supports the argument for considering the Drake Volcanics a distinct unit.

This Record presents new zircon U-Pb geochronological data, obtained using a Sensitive High Resolution Ion MicroProbe (SHRIMP), and thin section descriptions for four samples of plutonic and sedimentary rocks from the Captains Flat 1:50, 000 special map sheet, Eastern Lachlan Orogen, New South Wales. The work was carried out under the auspices of the National Geoscience Accord, as a component of the collaborative Geochronology Project between the Geological Survey of New South Wales (GSNSW) and Geoscience Australia (GA) during the reporting periods 2012 and 2013. The four samples (Table 1.1 and Figure 1.1) were collected from CANBERRA (small and large capitals refer to map sheet names in the 1:100 000 and 1:250 000 Topographic Series respectively); one sample from CANBERRA (northcentral CANBERRA), two from MICHELAGO (southcentral CANBERRA) and one from ARALUEN (southcentral CANBERRA).

New SHRIMP U-Pb zircon ages from the New England Orogen, New South Wales July 2014-June 2015

The late Permian Wandsworth Volcanic Group (WVG) in the southern New England Orogen (SNEO) is dominated by a monotonous series of amalgamated rhyodacitic to felsic eruptives, with minor interbedded flows, intrusives and sediments. The area enclosing known exposures of the WVG cover more than 30,000 km2, with a minimum thickness of 2 km. The top of the succession, as well as the vast majority of the pile representing non-welded material, has not been preserved. Field relationships indicate a broadly contemporaneous (though not necessarily genetic) relationship with late Permian granite magmatism, while Triassic plutons (typically in the range 246-243 Ma) intrude the WVG. SHRIMP U-Pb zircon dating indicates ages around 256.4 ± 1.6 Ma for basal units of the WVG, and 254.1 ± 2.2 Ma for the youngest preserved member of the WVG (Dundee Rhyodacite), defining a short period of substantial intermediate to acid eruptive volcanism. The compositionally unevolved Drake Volcanics to the northeast are older (264.4 ± 2.5 Ma) while those at Halls Peak are older still (Early Permian). Granites of the I-type Moonbi and Uralla Supersuites are dominantly 256-251 Ma and thus overlap in timing (and space) with the WVG event. Interestingly, many mineralized leucogranites (e.g. Parlour Mountain, Oban River, Gilgai) which were formerly regarded as Triassic are now established as synchronous with the Moonbi and Uralla Supersuites and the WVG. The age range of eruption of the WVG permitted by the SHRIMP results (~6 Ma) has been further constrained by CA-ID-TIMS U-Pb zircon analysis which yielded oldest and youngest ages of 255.54 ± 0.16 Ma and 253.26 ± 0.15 Ma respectively, indicating a maximum eruptive time range of ~2 Ma for the preserved pile. Our new results coincide with those determined from CA-ID-TIMS dating of tuffs in the Sydney and Gunnedah Basins. WVG exposures at Attunga are exactly (within ~0.1 Ma) coincident with the age of tuffs within the Trinkey Formation located in the Gunnedah Basin to the west, and the Dundee Rhyodacite is similarly closely matched to the thick Awaba Tuff in the Sydney Basin. Notably, much of the late Permian volcanic and plutonic magmatism in the SNEO is restricted to a remarkably small time range, which coincides exactly with the range of ash fall events in the Sydney and Gunnedah Basins, and possibly further afield. This suggests the SNEO, and the WVG in particular, was the dominant source of volcanic material erupted into these adjacent basins. Further, the adjacent basins may provide a more complete record of Permo-Triassic magmatism in the SNEO than currently preserved within the orogen itself.

Xenotime (YPO4) occurs in a wide range of geological environments, but its potential to establish the timing of mineralisation and sediment diagenesis has been the focus of most recent studies. Xenotime in these settings usually has a low uranium content (typically < 1000 ppm) and occurs as microscopic crystals (< 20 μm diameter), either individually or as outgrowths on a zircon substrate. Large radius ion microprobes, such as the SHRIMP or Cameca 1270/1280, that have high sensitivity and spatial resolution, are well suited for the U–Pb–Th analysis of xenotime from such environments. SIMS U–Pb–Th analyses of xenotime, however, are prone to significant U–Pb–Th matrix effects (ME) that are related to the wide natural range of U (0–6 wt%) and rare earth element (REE) (ΣREE: 12–22 wt%) concentrations in this mineral. For SHRIMP U–Pb–Th xenotime analyses, a 1 wt% increase in U concentration, relative to the U–Pb–Th calibration reference material (RM), will on average cause a corresponding increase in the measured 206Pb/238U and 208Pb/232Th of approximately 15% and 14% respectively. Similarly, a 1 wt% contrast in ΣREE causes an increase of about 1.2% in 206Pb/238U and about 1.7% in 208Pb/232Th. Correction for these chemically-induced matrix effects requires the concurrent analysis of three xenotime reference materials (RMs) which have known ages and a range of U and ΣREE contents that have been determined accurately by electron probe microanalysis (EPMA). A least squares methodology is used to derive correction coefficients that relate the SHRIMP U–Pb–Th ME to the U and ΣREE concentrations for the RMs. Crucial to the success of this technique is the use of one dimensional (1-D) calibrations using 206Pb+/270[UO2]+ and 208Pb+/248[ThO]+. Processing is carried out in two steps: the first derives the correction coefficients to matrix correct the 206Pb+/270[UO2]+ and 208Pb+/248[ThO]+ ratios, the second processes the matrix corrected ratios to determine 206Pb/238U and 208Pb/232Th. <b>Citation:</b> A.J. Cross, I.S. Williams, SHRIMP U–Pb–Th xenotime (YPO4) geochronology: A novel approach for the correction of SIMS matrix effects, <i>Chemical Geology</i>, Volume 484, 2018, Pages 81-108, ISSN 0009-2541, https://doi.org/10.1016/j.chemgeo.2017.12.017.

This Record presents new zircon U-Pb geochronological data, obtained using a Sensitive High Resolution Ion MicroProbe (SHRIMP) for thirty-five samples of plutonic rocks from the New England Orogen, New South Wales. The work was carried out under the auspices of the National Geoscience Accord, as a component of the collaborative Geochronology Project between the Geological Survey of New South Wales (GSNSW) and Geoscience Australia (GA) during the reporting periods 2012-2014.

<p>The Mesoproterozoic Roper Group of the McArthur Basin has excellent petroleum potential, but its poorly constrained post-depositional history has hampered resource exploration and management. The Derim Derim Dolerite occupies an important position in the regional event chronology, having intruded the Roper Group prior to deformation associated with the ‘Post-Roper Inversion’ event. It was assigned a magmatic crystallisation age of 1324 ± 4 Ma (uncertainties are 95% confidence unless otherwise indicated) in 1997, based on unpublished Sensitive High Resolution Ion Micro Probe (SHRIMP) U-Pb analyses of dolerite-hosted baddeleyite from sample 97106010, collected from the Derim Derim Dolerite type locality in outcrop within the northwestern McArthur Basin. Herein, we refine these data via Isotope Dilution-Thermal Ionisation Mass Spectrometry (ID-TIMS) analysis of baddeleyites plucked from the SHRIMP grain-mounts, which yielded a precise mean 207Pb/206Pb date of 1327.5 ± 0.6 Ma. This date is significantly older than a baddeleyite U-Pb ID-TIMS date of 1313.8 ± 1.3 Ma recently obtained from dolerite ALT-05, sampled in Pacific Oil and Gas Ltd drillhole Altree 2, near the northern margin of the Beetaloo Sub-basin, and 200 km south of 97106010. This pair of results indicates that Derim Derim Dolerite magmatism spanned at least 10-15 Ma. Previously documented geochemical variation in Mesoproterozoic mafic rocks across the Northern Territory (such as the 1325 ± 36 Ma (2σ) Galiwinku Dolerite in the northern McArthur Basin, 1316 ± 40 Ma phonolites intruding the eastern Pine Creek Orogen, and 1295 ± 14 Ma gabbro in the Tomkinson Province) may reflect episodic pulses of magmatism hitherto obscured by the low precision of the available isotopic dates. <p><b>Citation:</b> Bodorkos, S., Yang, B., Collins, A.S., Crowley, J., Denyszyn, S.W., Claoue-Long, J.C., Anderson, J.R. and Magee, C., 2020 Precise U–Pb baddeleyite dating of the Derim Derim Dolerite: evidence for episodic mafic magmatism in the greater McArthur Basin. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

This Record contains new zircon U-Pb geochronological data, obtained via Sensitive High-Resolution Ion Micro Probe (SHRIMP), from two samples of metamorphosed felsic igneous rocks of the Proterozoic Pinjarra Orogen (Western Australia), intersected in diamond drillcore at the base of deep petroleum exploration wells penetrating the Paleozoic sedimentary successions of the Perth Basin. In the southern Perth Basin, petroleum exploration well Sue 1 was terminated at depth 3074.2 m, in crystalline basement rocks of the southern Pinjarra Orogen. Abundant zircon from a biotite-bearing felsic orthogneiss at depth 3073.2-3073.7 m yielded a complex array of U-Pb isotopic data, indicative of significant post-crystallisation disturbance of the isotopic system. A Discordia regression fitted to the array yielded an upper intercept date of 1076 ± 35 Ma (all quoted uncertainties are 95% confidence intervals unless specified otherwise) interpreted to represent magmatic crystallisation of the igneous precursor to the orthogneiss, and a lower intercept date of 680 ± 110 Ma which is our best estimate of the age of the tectonothermal event responsible for post-crystallisation disturbance of the U-Pb system. Crust of known Mesoproterozoic age is rare in the southern Pinjarra Orogen: pre-1000 Ma igneous crystallisation ages in the Leeuwin Complex were previously known only from two c. 1090 Ma garnet-bearing orthogneisses at Redgate Beach (Nelson, 1999), 30 km west of Sue 1. All other dated outcrops have revealed Neoproterozoic (780-680 Ma) granitic protoliths reworked by Early Cambrian (540-520 Ma) magmatism, deformation and metamorphism (Nelson, 1996, 2002; Collins, 2003). In the northern Perth Basin, petroleum exploration well Beagle Ridge 10A was terminated at depth 1482 m, in crystalline basement rocks of the northern Pinjarra Orogen. A leucocratic orthogneiss sampled within the interval 1464.0-1467.0 m yielded only sparse zircon, but four of the seven grains analysed yielded a weighted mean 207Pb/206Pb date of 1092 ± 27 Ma, interpreted to represent magmatic crystallisation of the igneous precursor to the orthogneiss. Our data show no evidence for Neoproterozoic U-Pb resetting of the c. 1090 Ma zircons: where present, post-crystallisation isotopic disturbance is predominantly geologically recent. The two newly dated samples are located at opposite ends of the Perth Basin (about 470 km apart), and although the two magmatic crystallisation ages are imprecise, the date of 1092 ± 27 Ma from the Beagle Ridge 10A leucocratic orthogneiss is indistinguishable from the date of 1076 ± 35 Ma from the Sue 1 felsic orthogneiss. Furthermore, both rocks contain inherited zircon of Mesoproterozoic age (1620-1180 Ma in Sue 1; 1290-1210 Ma in Beagle Ridge 10A), indicating the presence of pre-1100 Ma crustal components in their parent magmas. This is consistent with a suite of Paleoproterozoic Sm-Nd model ages determined by Fletcher et al. (1985) on buried Pinjarra Orogen orthogneisses, which span 2.01 ± 0.06 Ga to 1.78 ± 0.04 Ga in the north (near BMR Beagle Ridge 10A), and including a model age of 1.80 ± 0.04 Ga from a sample of granitic gneiss obtained from Sue 1. Fletcher et al. (1985) argued that the consistency of 2.1-1.8 Ga Nd model ages obtained from crystalline basement in drillcore beneath the southern and northern Perth Basin, and from outcrop in the Northampton Complex and Mullingarra Complex of the northern Pinjarra Orogen, indicated a similar or shared crustal evolution. Our new U-Pb zircon data support this model, expanding the known extent of 1100-1050 Ma felsic magmatism in both the southern and northern Pinjarra Orogen, and indicating that Neoproterozoic tectonothermal overprinting appears to be restricted to the Leeuwin Complex, with no corresponding event discernible in the northern Pinjarra Orogen.

This Record presents new U-Pb geochronological data, obtained via Sensitive High Resolution Ion Micro Probe (SHRIMP), from six samples of igneous rocks and four samples of sedimentary rocks, collected from south-central New South Wales. The work is part of an ongoing Geochronology Project, conducted by the Geological Survey of New South Wales (GSNSW) and Geoscience Australia (GA) under a National Collaborative Framework (NCF) agreement, to better understand the geological evolution of the central Lachlan Orogen in the East Riverina region. The results presented herein correspond to the reporting period July 2015-June 2016.

<div>This Record presents data collected in March 2022–February 2023 as part of the ongoing Northern Territory Geological Survey–Geoscience Australia SHRIMP geochronology project under the National Collaborative Framework agreement and Geoscience Australia’s <em>Exploring for the Future Program</em>. New U–Pb SHRIMP zircon geochronological results were derived from sedimentary rock chip samples of the Warburton Basin collected from four petroleum exploration wells (Beachcomber 1, Thomas 1, Simpson 1, Colson 1) in the southeastern corner of the Northern Territory. Geologically, this is a region in the Simpson Desert that encompasses several superimposed intracratonic sedimentary basins that are separated by regional unconformities that extend over areas of adjoining Queensland, South Australia and New South Wales. The exposed Mesozoic Eromanga Basin overlies the late Palaeozoic Pedirka Basin, which is largely restricted to the subsurface. The Warburton Basin is an early Palaeozoic pericratonic basin containing an early Cambrian and Ordovician succession (Edgoose and Munson, 2013), with possible Devonian rocks observed in some areas (Radke, 2009). As the Warburton Basin is entirely concealed beneath the Pedirka and Eromanga basins, our current understanding of the geology of the western Warburton Basin is constrained by the lack of surface exposures, the small number of well penetrations, limited biostratigraphic age control, and relatively sparse seismic data coverage. </div><div> The samples analysed herein were collected to aid in understanding the chronostratigraphy and provenance characteristics of the concealed Warburton Basin. All four sedimentary samples are dominated by Mesoproterozoic detritus (ca 1000–1300 Ma), have fewer zircons of Paleozoic age, and generally have sparse older Palaeoproterozoic–Archaean aged zircons. Samples from the two westernmost wells yielded 238U/206Pb maximum depositional ages of 469&nbsp;±&nbsp;9&nbsp;Ma (Colson 1) and 394&nbsp;±&nbsp;6&nbsp;Ma (Simpson 1). Samples from the two easternmost wells yielded older 238U/206Pb maximum depositional ages of 569&nbsp;±&nbsp;10&nbsp;Ma (Thomas 1) and 506&nbsp;±&nbsp;5&nbsp;Ma (Beachcomber 1). These data imply that known Devonian stratigraphy extends at least as far as the Simpson 1 well, but may not extend further east.</div><div><br></div><div>BIBLIOGRAPHIC REFERENCE: Kositcin N, Verdel C and Edgoose C, 2023. Summary of results. Joint NTGS–GA geochronology project: western Warburton Basin, March 2022–February 2023. <em>Northern Territory Geological Survey, Record </em>2023-006.</div><div><br></div><div><br></div>