<div>This Record presents 16 new Sensitive High Resolution Ion Micro Probe (SHRIMP) U-Pb zircon results obtained under the auspices of the Geological Survey of Queensland-Geoscience Australia (GSQ-GA) National Collaborative Framework (NCF) geochronology project in 2023-2024. These data were collected in support of the Peralkaline Magmatic Systems Project and the Northeast Queensland Deposits Project led by the GSQ. Cenozoic felsic igneous rocks in Queensland occur in scattered localities between Mackay and the southern Border Ranges and as far west as areas around Emerald. These rocks are primarily associated with eroded central volcanoes and exhibit well-defined age progression resulting from movement of the Australian plate over a mantle plume during the Cenozoic (see Cohen et al., 2013a, b). The location and existing K-Ar and Ar-Ar age data for the central volcanoes show a strong younging to the south, extending from Cape Hillsborough (ca. 33 Ma) through Nebo, Peak Range and Springsure to Buckland (ca. 27 Ma), forming the northernmost part of the Cosgrove Hotspot Track (Davies et al., 2015). Existing geochronology for units along this track is dominated by K-Ar and Ar-Ar data with only a few units having reconnaissance-quality U-Pb zircon ages. Our study aimed to produce new, high-quality emplacement ages to compare with existing data, constrain the ages of undated units and test correlations, and to identify any inheritance that could help to understand their origin.</div><div><br></div>

<div>This record presents nine new zircon and titanite U–Pb geochronological data, obtained via Sensitive High Resolution Ion Microprobe (SHRIMP) for seven samples of plutonic rocks from the Lachlan Orogen and the Cobar Basin, plus one garnet-bearing skarn vein from the Cobar region. Many of these new ages improve existing constraints on the timing of mineralisation in the Cobar Basin, as 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 Collaboration Framework (NCF) agreement. The results herein (summarised in Table 1.1) correspond to zircon and titanite U–Pb SHRIMP analysis undertaken on GSNSW Mineral Systems projects over July 2017–June 2019.</div><div><br></div><div>Our new data establish an episode of c. 427–425 Ma I-type plutonism, coeval with regional S-type granites, which marginally predated opening of the Cobar Basin. Widespread S-type and high-level I-type magmatism accompanied 423–417 Ma basin development. At least two episodes of skarn-related mineralisation are recognised in the southern Cobar Basin: c. 387 Ma (from pre-mineralisation skarn veins) at Kershaws prospect, and c. 403 Ma at the adjacent Hera mine (Fitzherbert et al., 2021).</div><div><br></div><div>Three intrusive rocks were dated at the Norma Vale prospect in the southwestern Cobar Basin, where calcic iron-copper skarn mineralisation is thought to have been caused by I-type but compositionally complex high-level intrusive rocks emplaced along a northeast-oriented fault related to the nearby Rookery Fault (Fitzherbert et al., 2017). A 423 ± 8 Ma I-type quartz diorite potentially constrains the timing of skarn mineralisation, but is indistinguishable in age from a 421.3 ± 3.0 Ma S-type cordierite-biotite granite and a 417.5 ± 3.3 Ma coarse-grained S-type granite, both from deeper in the same drillhole. These results suggest that at least some of the coeval S-type and high-level I-type magmatic activity accompanying opening of the Cobar Basin was associated with early mineralisation, although skarn-forming processes regionally are complex and episodic (Fitzherbert et al., 2021).</div><div><br></div><div>In the Cobar mining belt, our new date of 422.8 ± 2.8 Ma for I-type rhyolitic porphyry at Carissa Shaft (which is one of the southernmost high-level intrusions associated with the Perseverance and Queen Bee orebodies) is coeval with the 423.2 ± 3.5 Ma ‘Peak rhyolite’ (Black, 2007), but marginally older than the 417.6 ± 3.0 Ma Queen Bee Porphyry (Black, 2005). At Gindoono, a 423.0&nbsp;±&nbsp;2.6&nbsp;Ma unnamed dacitic porphyry intruded and hornfelsed the undated I-type Majuba Volcanics, thereby establishing a minimum age for that unit.</div><div><br></div><div>East of Cobar, the I-type Wild Wave Granodiorite intruded the Ordovician Girilambone Group, but was exhumed and eroded to form clasts within pebble conglomerates of the lowermost Cobar Basin. Its new U–Pb SHRIMP zircon age of 424.1 ± 2.8 Ma constrains the timing of I-type plutonism which marginally predated formation of the Cobar Basin. A similar zircon age of 426.7 ± 2.3 Ma was obtained from the concealed Fountaindale Granodiorite north of Condoblin, indicating that this I-type pluton is coeval with the nearby and much larger c. 427 Ma S-type Erimeran Granite. Titanite from the same sample of Fountaindale Granodiorite yielded an age of 421.6 ± 2.7 Ma, which is significantly younger than the zircon age, and is interpreted to constrain the timing of ‘deuteric’ (chlorite-albite-epidote-titanite-sericite-carbonate) alteration during post-magmatic hydrothermal activity (e.g. Blevin, 2003b).</div><div><br></div><div>A garnet-bearing skarn vein at Kershaws prospect, adjacent to the Hera orebody (Fitzherbert et al., 2021), predates the main phase of mineralisation, and yielded a titanite age of 387.2 ±&nbsp;6.2&nbsp;Ma. This indicates that the skarn-forming hydrothermal event at Kershaws prospect is significantly younger than the c. 403 Ma age for the main mineralising event at Hera mine (Fitzherbert et al., 2021).</div>

<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>

<div>This Record presents new zircon U-Pb geochronological data, obtained via Sensitive High Resolution Ion Microprobe (SHRIMP), for 12 samples of igneous rocks from central and southern New South Wales, as 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. Eight samples were selected to better understand the geological evolution and mineralisation history of areas prioritised for investigation by the MinEx Co-operative Research Centre (MinEx CRC) under its National Drilling Initiative (NDI) program. Three samples are from the northern Molong Volcanic Belt east of Dubbo (‘MXDU’), and five are from the eastern Lachlan Orogen near Forbes (‘MXFO’). The remaining four samples are from the central Lachlan Orogen in southern NSW, in support of GSNSW’s East Riverina mapping program (‘ERIV’). The results herein correspond to U-Pb SHRIMP zircon analyses undertaken by the GSNSW-GA Geochronology Project during the July 2020–June 2021 reporting period. All quoted uncertainties are 95% confidence intervals.</div> <b>Bibliographic reference: </b> Jones, S.L., Bodorkos, S., Eastlake, M.A.S., Campbell, L.M., Hughes, K.S., Blevin, P.L. and Fitzherbert, J.A., 2023. <i>New SHRIMP U-Pb zircon ages from the Lachlan Orogen, NSW: Dubbo, Forbes and East Riverina areas, July 2020–June 2021. </i>Record 2023/36, Geoscience Australia, Canberra. Report GS2023/0017, Geological Survey of New South Wales, Maitland. https://doi.org/10.26186/147971