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 Sensitive High Resolution Ion Microprobe (SHRIMP) U–Pb geochronological results for samples collected from the Mount Isa Inlier and covered areas to the east. The Mary Kathleen Domain is the focus of this work and 11 metasedimentary and igneous samples were analysed from across the distribution of the domain. An additional two metasedimentary samples and one igneous sample from drill cores located east of the outcropping Mount Isa Province were also analysed. <b>Bibliographic Reference: </b>Kositcin, N., Purdy, D.J., Bultitude, R.J., Brown, D.D. & Hoy, D. Summary of Results. Joint GSQ–GA Geochronology Project: Mary Kathleen Domain and rocks under younger cover east of the Mount Isa Inlier, 2019–2020. <i>Queensland Geological Record</i><b> 2021/01</b>.

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.

<div>This Record presents data collected as part of the ongoing Northern Territory Geological Survey–Geoscience Australia SHRIMP geochronology project under the National Collaboration Framework agreement. New U-Pb SHRIMP zircon geochronological results were derived from six samples of sedimentary rocks collected from two petroleum exploration drillholes (CBM 107-001 and CBM 107-002) that intersect the Pedirka Basin in the southeastern corner of the Northern Territory.</div><div><br></div><div>Geologically, this is a region in the Simpson Desert that encompasses several superimposed intracratonic sedimentary basins, which are separated by regional unconformities extending over areas of adjoining Queensland, South Australia and New South Wales. In the southeastern corner of the Northern Territory, the Pedirka Basin is one of three stacked basins. The exposed Mesozoic Eromanga Basin overlies the late Palaeozoic to Triassic Pedirka Basin, which is largely restricted to the subsurface, and in turn overlies the Palaeozoic pericratonic Warburton Basin (Munson and Ahmad 2013).</div><div><br></div><div>As the Pedirka Basin is almost entirely concealed beneath the Eromanga Basin, our current understanding of the geology in this southeastern corner of the Northern Territory is constrained by a limited number of exploration drillholes and 2D seismic coverage (Doig 2022). The samples described herein were collected to aid in defining the chronostratigraphy and sedimentary provenance characteristics of the Pedirka Basin.</div><div><br></div><div>BIBLIOGRAPHIC REFERENCE: Jones S.L., Jarrett A.J., Verdel C.S. and Bodorkos S. 2024. Summary of results. Joint NTGS–GA geochronology project: Pedirka Basin. Northern Territory Geological Survey, Record 2024-003.</div>

The South Nicholson Basin sits between the Mount Isa Province to the east and southern McArthur Basin to the northwest. The McArthur Basin and Mount Isa Province are well studied and highly prospective for both mineral and energy resources. In contrast, the South Nicholson region is mostly undercover, little studied and consequently relatively poorly understood. A comprehensive U–Pb SHRIMP zircon and xenotime geochronology program was undertaken to better understand the stratigraphy of the South Nicholson region and its relationship to the more overtly prospective adjacent Mount Isa Province and McArthur Basin. The age data indicate South Nicholson Basin deposition commenced ca 1483 Ma, with cessation at least by ca 1266 Ma. The latter age, based on U–Pb xenotime, is currently interpreted as the timing of post-diagenetic regional fluid flow. The geochronology presented here provides the first direct age data confirming the South Nicholson Group is broadly contemporaneous with the Roper Group of the McArthur Basin. Some rocks, mapped previously as Mesoproterozoic South Nicholson Group and comprised of proximal, immature lithofacies, have detrital spectra consistent with that of the late Paleoproterozoic McNamara Group of the western Mount Isa Province which necessitates a revision of existing regional stratigraphic relationships. The stratigraphic revisions and correlations proposed here significantly expands the extent of highly prospective late Paleoproterozoic stratigraphy across the South Nicholson region and possibly, further west beneath the Georgina Basin. The data and conclusions presented here allow for improved regional stratigraphic correlations between Proterozoic basins, improved commodity prospectivity and targeted exploration strategies across central northern Australia. Presented at the 2020 Annual Geoscience Exploration Seminar (AGES)

<div>This Record is the fourth of a series of reports detailing the results of U–Pb dating of samples collected during investigations of the Mary Kathleen Domain and adjacent areas of the Mount Isa Inlier in 2018–19 by the Geological Survey of Queensland and co-workers (Kositcin <em>et al</em>., 2019, 2021, Bodorkos <em>et al</em>., 2020). It presents new Sensitive High Resolution Ion Microprobe (SHRIMP) U–Pb geochronological results for five samples collected from the inlier. Two of the samples are from units in the Kalkadoon–Leichhardt Domain and the remaining three from units in the adjacent Mary Kathleen Domain (Figure i). The ages of these units are poorly constrained and various ages have been proposed for most of them by different investigators.</div><div> <b>Bibliographic Reference:</b> Kositcin, N., Bultitude, R. J., Purdy, D. J. 2023. <i>Summary of results. Joint GSQ–GA Geochronology Project: Kalkadoon–Leichhardt and Mary Kathleen Domains, 2018–2020. </i>GSQ Record 2023/04, Geological Survey of Queensland. GA Record 2023/41, Geoscience Australia, Canberra. http://dx.doi.org/10.26186/148600 https://geoscience.data.qld.gov.au/data/report/cr141810

<div>This Queensland Geological Record presents ten new Sensitive High Resolution Ion MicroProbe (SHRIMP) U–Pb zircon and monazite results obtained under the auspices of the Geological Survey of Queensland–Geoscience Australia (GSQ–GA) National Collaborative Framework (NCF) geochronology project between July 2017 and June 2018. These data were collected in support of ongoing regional mapping and geoscientific programs led by the GSQ in the Mount Isa region.&nbsp;</div><div><br></div><div><br></div><div><br></div><div><br></div><div><strong>Bibliographic reference:</strong></div><div>Kositcin, N., Lewis, C. J. Withnall, I. W., Slade, A. P., Sargent, S. and Hutton, L. J. 2023. Summary of results. Joint GSQ–GA Geochronology Project: Mount Isa region, 2017–2018. GSQ Record 2023/03. Geoscience Australia, Canberra. Record 2023/32, Geological Survey of Queensland. http://dx.doi.org/10.26186/147793</div>

This Record presents new Sensitive High Resolution Ion Micro Probe (SHRIMP) U–Pb geochronological results for six drill core samples from the Rover mineral field, an area of prospective Palaeoproterozoic rocks southwest of Tennant Creek that is entirely concealed below younger sedimentary cover rocks. The work is part of an ongoing collaborative effort between Geoscience Australia (GA) and the Northern Territory Geological Survey (NTGS) that aims to better understand the geological evolution and mineral potential of this region. SHRIMP U–Pb detrital zircon results from two samples, a meta-siltstone/mudstone from the Au–Cu–Bi Rover 1 deposit (drillhole WGR1D011; sample BW20PGF090) and a volcaniclastic sandstone from the Explorer 142 prospect (drillhole NR142D001; sample BW20PGF156) gave near identical maximum depositional ages of 1849.1 ± 3.1 Ma and 1848.9 ± 3.0 Ma respectively. The euhedral nature of the zircons in both samples and their unimodal age distributions, support the interpretation that the maximum depositional ages of these samples are good approximations for their true age of deposition. These results are a very close match with U–Pb zircon geochronology of some other drill core samples from the Rover mineral field. Two magmatic rocks from drillhole RVDD0002 (located in the East of the Rover field), gave ages of ca 1851–1850 Ma, while a volcaniclastic sandstone from RVDD0002 gave a maximum depositional age of 1854.0 ± 2.9 Ma (Cross et al 2021). Our new results from drillholes WGR1D011 and NR142D001 confirm the widespread presence of detrital zircons at ca 1854–1849 Ma across much of the Rover mineral field. SHRIMP U–Pb detrital zircon analysis was undertaken on four samples from the base metal Curiosity prospect drillhole, MXCURD002. The first sample analysed GS20PGF058 [520.0–525.7 m], has a maxima at ca 1842 Ma but youngest statistical grouping at 1729 ± 17 Ma (n = 6). This is in stark contrast with a previous sample from this drillhole (GS19DLH0056 [437.63–438.18 m]) that is 82 metres above GS20PGF058, and gave a MDA of 1854.0 ± 2.9 Ma (Cross et al 2021). In an effort to further investigate the ca 1729 Ma date given by GS20PGF058, three further samples were collected from drillhole MXCURD002, one sample below, GS20PGF190 [525.7–531.5 m] and two samples above, GS20PGF085 [515.0–520.0 m] and GS20PGF084 [468.1–473.45 m]. Additionally, samples GS20PGF190 and GS20PGF085 are continuations of the same meta-siltstone/mudstone unit sampled by GS20PGF058. These three samples returned maximum depositional ages of 1851.7 ± 3.9 Ma (GS20PGF085), 1846.6 ± 3.2 Ma (GS20PGF190) and 1841 ± 12 Ma (GS20PGF084). They are also indistinguishable within their uncertainties (MSWD = 0.71, POF = 0.49) and have an average date of ca 1848 Ma. Therefore, the evidence from SHRIMP U–Pb detrital zircon studies of four rocks from drillhole MXCURD002 (this study and that of Cross et al 2021), indicates that the metasedimentary rocks in MXCURD002 were probably deposited at ca 1850 Ma, similar to other metasedimentary units within the Rover mineral field. We suggest that the relatively younger statistical grouping in sample GS20PGF058 at ca 1730 Ma is possibly the result of isotopic re-setting due to a thermal and/or fluid event associated with lead–zinc–copper mineralisation at a similar time which has been recently reported by Farias et al (2022). Although other explanations to explain the ca 1730 Ma grains in this sample such as laboratory contamination or that the zircons have in fact preserved their original crystallisation age, cannot be ruled out. <b>Bibliographic Reference:</b> Cross AJ, Farias PG and Huston DL, 2022. Summary of results. Joint NTGS–GA geochronology project: Rover mineral field, Warramunga Province, July–December 2020. <i>Northern Territory Geological Survey</i>, <b>Record 2022-005</b>.

<p>The Mesoproterozoic South Nicholson Basin (SNB) in northern Australia extends across an area approximately the size of Tasmania. It is flanked by the resource rich Mt Isa Orogen and McArthur Basin. Limited outcrop and a dearth of drilling has hampered understanding of the evolution of the Basin, its relationship to other tectonic elements in northern Australia and its resource potential. The lack of any identified interbedded volcanic rocks within the studied sections has led us to concentrate on an extensive SHRIMP U-Pb detrital zircon geochronology program that so far exceeds 40 samples. In addition, we have undertaken SHRIMP U-Pb geochronology of authigenic xenotime. <p>Detrital zircon U–Pb maximum depositional ages (MDA) for the South Nicholson Group (SNG) are up to 100 My younger than previously reported [1]. The new MDA for the Constance Sandstone is ~1470 Ma and is the youngest so far recorded in the SNB. Additionally, it accords with an MDA for the underlying Crow Formation of ~1483 Ma. SHRIMP U–Pb xenotime analyses of authigenic overgrowths on detrital zircons from the Constance Sandstone gave an age of ~1266 Ma. This new data brackets the deposition of the SNG to between 1470 Ma and ~1266 Ma and provides the first evidence that the SNG is broadly contemporaneous with the 1500–1320 Ma Roper Group of the McArthur Basin. Using Multidimensional Scaling of the detrital age distributions has also added an extra dimension to our evolving understanding of the development of the SNB. <p>[1] Carson (2011) Queensland Geological Record 2011/03.

This Record presents new U–Pb geochronological data, obtained via Sensitive High Resolution Ion Micro Probe (SHRIMP), from 43 samples of predominantly igneous rocks collected from the East Riverina region of the central Lachlan Orogen, New South Wales. The results presented herein correspond to the reporting period July 2016–June 2020. This 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 agreement, to better understand the geological evolution and mineral prospectivity of the central Lachlan Orogen in southern NSW (Bodorkos et al., 2013; 2015; 2016, 2018; Waltenberg et al., 2019).