Orogenic gold deposits provide a significant source of the world’s gold, but their depth of formation is contentious. One hypothesis is that orogenic gold deposits formed along crustal faults over a wide range of depths spanning sub-greenschist to granulite facies. Other authors suggest that the source is restricted to a smaller range of crustal depths (~20-30 km) and temperatures (~550⁰C) that correspond to the transition from greenschist to amphibolite metamorphic facies. Rapid burial of C and S-rich oceanic sediments and amphibolite-grade metamorphism leads to the production of large amounts of fluid in a short amount of time. In order to help discriminate between these competing hypotheses, we compiled thirty years of magnetotelluric (MT) and geomagnetic depth sounding (GDS) data across western Victoria and south-eastern South Australia. This region contains one of the world’s foremost and largest orogenic gold regions that has produced 2% of historic worldwide gold production. Three-dimensional inversion of the MT and GDS data shows a remarkable correlation between orogenic gold deposits with >1 t production and a <20 ohm.m low-resistivity region at crustal depths >20 km. Such depths are at the pressures and temperatures of greenschist to amphibolite-grade metamorphism that releases HS- ligands for Au from C and pyrite (FeS2) rich sediment interbedded with mafic oceanic rocks. Carbon is then precipitated through retrograde hydration reactions with CO2 precipitating as conductive flake graphite. Thus, our model indicates that orogenic gold in western Victoria is most likely sourced from C and FeS2 rich oceanic sediments at amphibolite-grade facies. Citation: Heinson, G., Duan, J., Kirkby, A. et al. Lower crustal resistivity signature of an orogenic gold system. Sci Rep 11, 15807 (2021). https://doi.org/10.1038/s41598-021-94531-8

<p>Exploring for the Future (EFTF, <a href="http://www.ga.gov.au/eftf">http://www.ga.gov.au/eftf</a>) is a four-year (2016–2020) $100.5 million program investigating the mineral, energy and groundwater resource potential in northern Australia and parts of South Australia. The program is delivering new geoscience data, knowledge and decision support tools that support increased industry investment and sustainable economic development. <p>Geoscience Australia commissioned ACIL Allen Consulting to independently quantify the return on investment from selected EFTF projects that are representative of the nature of the work done under the program. The objective was to develop a plausible and economically robust estimate of the returns to government through increased government revenue as a result of the case study projects. Geoscience Australia would like to acknowledge the organisations that have contributed to or supported these EFTF case study projects. <p>The results of this independent analysis can be used to estimate the impact and value of the EFTF program as a whole relative to the funds invested in these activities. The evaluation framework used by ACIL Allen Consulting to assess the impact and value of Geoscience Australia’s pre-competitive geoscience under EFTF is one that has been used for similar assessments of similar organisations in the past. <p>The analysis shows that the benefits that could potentially flow to the Commonwealth as a result of the EFTF projects examined at least match what has been spent on the program, and the returns can be as much as an order of magnitude higher than the cost of the entire program.

Herein we present the results of a national compilation of mineral deposits (available in Excel or CSV format) for Australia. The deposits were selected as they have substantial endowment (i.e. pre-mining mineral resource) and/or detailed geological information is available. For each deposit (or, in some cases, district) the dataset includes information on: 1. Name (including synonyms), location and GA identifying numbers; 2. Tectonic province that hosts the deposit; 3. Type(s) and age(s) of mineralising events that produced/affected the deposit (including metadata on ages); 4. The metal/mineral endowment of the deposit; 5. Host rocks to the deposit; 6. Spatially and/or temporally associated magmatic rocks; 7. Spatially and temporally associated alteration assemblages (mostly proximal, but, in some cases, regional assemblages); 8. The Fe-S-O minerals present in the deposit and relative abundances where known; 9. Sulfate minerals present; 10. Peak metamorphic grade; 11. Data sources; and 12. Comments. This document presents more detailed descriptions of the metadata presented in the compilation. The dataset is presented in Appendix A. Appendix B presents a national classification of geological provinces based mostly on existing State survey classifications; Appendix C presents a deposit classification based on the classification proposed by Hofstra et al. (2021); and Appendix D presents mineral abbreviations used in the dataset.

Geoscience Australia commissioned ACIL Allen Consulting (ACIL Allen) to independently quantify the return on investment from six pre-competitive geoscience projects. These projects include three from the first phase of the $225 million Exploring for the Future (EFTF) program (2016-2024) and three pre-EFTF projects that were undertaken within the last two decades: the Mineral Potential Mapper Project (2012-2016), the Salt Lakes Study (2012-2014), and the Northeast Yilgarn Project (2001-2004). ACIL Allen has shown that the net benefits that have been estimated to flow as a result of Geoscience Australia’s spending on each of the projects are all positive, and in many cases, quite large. The return on investment analysis for the three EFTF case studies is published separately (https://pid.geoscience.gov.au/dataset/ga/132897) and the analysis of the three pre-EFTF case studies is available here in three standalone reports. An additional overview report synthesises the findings from all six case studies to assess the broader impact and value of pre-competitive geoscience projects. This synthesis includes projects undertaken by Geoscience Australia alone or in collaboration with state/territory geological surveys and other research organisations. ACIL Allen estimated that the net present value of benefits to Australia attributed to Geoscience Australia’s contribution to the three pre-EFTF projects are between $962 million and $2.4 billion, depending on the scenario considered. ACIL Allen also estimated that for every dollar invested by Geoscience Australia in these pre-EFTF projects, the Australian Government could gain a net benefit of at least $15 and potentially as much as $157. The analysis also shows that direct jobs associated with mining operations potentially arising from GA’s work on the six projects could number in the thousands. The ACIL Allen analysis also demonstrates that considerable time may elapse between the completion of a Geoscience Australia project and commencement of the mining of any resources that are identified. The three pre-EFTF projects examined suggest that it is around 10 years between the publication of Geoscience Australia’s results and the development of a mine. Therefore, If the development of any resources based on the findings of the EFTF projects follow similar timelines, then we could potentially expect to see new mines in operation sometime between 2026 and 2030.

The importance of critical minerals and the need to expand and diversify critical mineral supply chains has been endorsed by the Federal governments of Australia, Canada, and the United States. The geoscience organizations of Geoscience Australia, the Geological Survey of Canada and the U.S. Geological Survey have created the Critical Minerals Mapping Initiative to build a diversified critical minerals industry in Australia, Canada, and the United States by developing a better understanding of known critical mineral resources, determining geologic controls on critical mineral distribution for deposits currently producing byproducts, identifying new sources of supply through critical mineral potential mapping and quantitative mineral assessments, and promoting critical mineral discovery in all three countries.

The Hera Au–Pb–Zn–Ag deposit in the southeastern Cobar Basin of central New South Wales preserves calc-silicate veins/skarn and remnant carbonate/sandstone-hosted skarn within a reduced anchizonal Siluro-Devonian turbidite sequence. The skarn orebody distribution is controlled by a long-lived, basin margin fault system, that has intersected a sedimentary horizon dominated by siliciclastic turbidite, with lesser gritstone and thick sandstone intervals, and rare carbonate-bearing stratigraphy. Foliation (S1) envelopes the orebody and is crosscut by a series of late-stage east–west and north–south trending faults. Skarn at Hera displays mineralogical zonation along strike, from southern spessartine–grossular–biotite–actinolite-rich associations, to central diopside-rich–zoisite–actinolite/tremolite–grossular-bearing associations, through to the northern most tremolite–anorthite-rich (garnet-absent) association in remnant carbonate-rich lithologies and sandstone horizons; the northern lodes also display zonation down dip to garnet present associations at depth. High-T skarn assemblages are pervasively retrogressed to actinolite/tremolite–biotite-rich skarn and this retrograde phase is associated with the main pulse of sulfide mineralisation. The dominant sulfides are high-Fe-Mn sphalerite–galena–non-magnetic high-Fe pyrrhotite–chalcopyrite; pyrite, arsenopyrite and scheelite are locally abundant. The distribution of metals in part mimics the changing gangue mineralogy, with Au concentrated in the southern and lower northern lode systems and broadly inverse concentrations for Ag–Pb–Zn. Stable isotope data (O–H–S) from skarn amphiboles and associated sulfides are consistent with magmatic/basinal water and magmatic sulfur inputs, while hydrosilicates and sulfides from the wall rocks display elevated δD and mixed δ34S consistent with progressive mixing or dilution of original basinal/magmatic waters within the Hera deposit by unexchanged waters typical of low latitude (tropical) meteoritic waters. High precision titanite (U–Pb) and biotite (Ar–Ar) geochronology reveals a manifold orebody commencing with high-T skarn and retrograde Pb–Zn-rich skarn formation at ≥403 Ma, Au–low-Fe sphalerite mineralisation at 403.4 ± 1.1 Ma, foliation development remobilisation or new mineralisation at 390 ± 0.2 Ma followed by thrusting, orebody dismemberment at (384.8 ± 1.1 Ma) and remobilization or new mineralisation at 381.0 ± 2.2 Ma. The polymetallic nature of the Hera orebody is a result of multiple mineralizing events during extension and compression and involving both magmatic and likely basinal fluid/metal sources. <b>Citation:</b> Fitzherbert, Joel A., McKinnon, Adam R., Blevin, Phillip L., Waltenberg, Kathryn., Downes, Peter M., Wall, Corey., Matchan, Erin., Huang Huiqin., The Hera orebody: A complex distal (Au–Zn–Pb–Ag–Cu) skarn in the Cobar Basin of central New South Wales, Australia <i>Resource Geology,</i> Vol 71, Iss 4, pp296-319 <b>2021</b>. DOI: https://doi.org/10.1111/rge.12262

<p>This record presents new zircon and titanite U–Pb geochronological data, obtained via Sensitive High Resolution Ion Microprobe (SHRIMP) for twelve samples of plutonic and volcanic rocks from the Lachlan Orogen and the New England Orogen, and two samples of hydrothermal quartz veins from the Cobar region. Many of these new ages improve existing constraints on the timing of mineralisation in New South Wales, 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 Collaborative Framework (NCF) agreement. The results herein (summarised in Table 1.1 and Table 1.2) correspond to zircon and titanite U–Pb SHRIMP analysis undertaken on GSNSW mineral systems projects for the reporting period July 2016–June 2017. Lachlan Orogen <p>The Lachlan Orogen samples reported herein are sourced from operating mines, active prospects, or regions with historical workings. The new dates constrain timing of mineralisation by dating the units which host or crosscut mineralisation, thereby improving understanding of the mineralising systems, and provide stronger constraints for mineralisation models. <p>In the eastern Lachlan Orogen, the new dates of 403.9 ± 2.6 Ma for the Whipstick Monzogranite south of Bega, and 413.3 ± 1.8 Ma for the Banshea Granite north of Goulburn both provide maximum age constraints for the mineralisation they host (Whipstick gold prospect and Ruby Creek silver prospect, respectively). At the Paupong prospect south of Jindabyne, gold mineralisation is cut by a dyke with a magmatic crystallisation age of 430.9 ± 2.1 Ma, establishing a minimum age for the system. <p>The 431.1 ± 1.8 Ma unnamed andesite and the 428.4 ± 1.9 Ma unnamed felsic dyke at the Dobroyde prospect 10 km north of Junee are just barely distinguishable in age, in the order that is supported by field relationships. The andesite is the same age as the c. 432 Ma Junawarra Volcanics but has different geochemical composition, and is younger than the c. 437 Ma Gidginbung Volcanics. The two unnamed units pre-date mineralisation, and are consistent with Pb-dating indicating a Tabberaberran age for mineralisation at the Dobroyde gold deposit. <p>Similarly, the 430.5 ± 3.4 Ma leucogranite from Hickory Hill prospect (north of Albury) clarifies that this unit originally logged as Jindera Granite (since dated at 403.4 ± 2.6 Ma) is instead affiliated with the nearby Mount Royal Granite, which has implications for the extent of mineralisation hosted within this unit. <p>Cobar Basin <p>Titanite ages of 382.5 ± 2.6 Ma and 383.4 ± 2.9 Ma from hydrothermal quartz veins that crosscut and postdate the main phase of mineralisation at the Hera mine in the Cobar region constrain the minimum age for mineralisation. These ages are indistinguishable from a muscovite age of 381.9 ± 2.2 Ma interpreted to be related to late- or post-Tabberaberan deformation event, and these results indicate that mineralisation occurred at or prior to this deformation event. <p>New England Orogen <p>The new ages from granites of the New England Orogen presented in this record aid in classification of these plutons into various Suites and Supersuites, and these new or confirmed relationships are described in detail in Bryant (2017). Many of these plutons host mineralisation, so the new ages also provide maximum age constraints in the timing of that mineralisation. <p>The 256.1 ± 1.3 Ma age of the Deepwater Syenogranite 40 km north of Glen Innes indicates that it is coeval with the 256.4 ± 1.6 Ma (Black, 2006) Arranmor Ignimbrite Member (Emmaville Volcanics) that it intrudes, demonstrating that both intrusive and extrusive magmatism was occurring in the Deepwater region at the same time. The 252.0 ± 1.2 Ma age for the Black Snake Creek Granite northeast of Tenterfield is consistent with its intrusive relationship with the Dundee Rhyodacite (254.34 ± 0.34 Ma; Brownlow et al., 2010). Similarly, the 251.2 ± 1.3 Ma age for the Malara Quartz Monzodiorite southeast of Tenterfield is consistent with field relationships that demonstrate that it intrudes the Drake Volcanics (265.3 ± 1.4 Ma–264.4 ± 2.5 Ma, Cross and Blevin, 2010; Waltenberg et al., 2016). <p>The 246.7 ± 1.5 Ma Cullens Creek Granite north of Drake was dated in an attempt to provide a stronger age constraint on mineral deposits that also cut the Rivertree and Koreelan Creek plutons (249.1 ± 1.3 Ma and 246.3 ± 1.4 Ma respectively, Chisholm et al., 2014a). However, the new age is indistinguishable from the Koreelan Creek Granodiorite, and timing of mineralisation is not further constrained, but the new age demonstrates a temporal association between the Cullens Creek and Koreelan Creek plutons. <p>The 239.1 ± 1.2 Ma age for the Mann River Leucogranite west of Grafton is indistinguishable in age from plutons in the Dandahra Suite and supports its inclusion in this grouping. The new age also constrains the timing of the distal part of the Dalmorton Gold Field, and implies that the gold vein system postdates the Hunter-Bowen orogeny. <p>The 232.7 ± 1.0 Ma Botumburra Range Monzogranite east of Armidale is younger than most southern New England granites, but this age is very consistent with the Coastal Granite Association (CGA), and the new age, along with the previously noted petrographic similarities (Leitch and McDougall, 1979) supports incorporation of the Botumburra Range Monzogranite into the Carrai Supersuite of the CGA (Bryant, 2017).