LoopStructural 1.0: Time aware geological modelling

Grose, Lachlan1, Ailleres, Laurent1, Laurent, Gautier2, Jessell, Mark3

1School of Earth Atmosphere and Environment, Monash University, Melbourne 3800, Australia, 2 Université d’Orléans, CNRS, BRGM, ISTO, UMR 7327, Orleans France, 3 Mineral Exploration Cooperative Research Centre, School of Earth Sciences, UWA, Perth, Australia

LoopStructural is a new open source 3D geological modelling python package (www.github.com/Loop3d/LoopStructural). Geological features are encoded into the geological model using a time aware approach where the relative timing of different deformation features is used to help construct complicated geometries. We use structural frames which are curvilinear coordinate systems based around the major structural feature (e.g. fold axial surfaces, fault surfaces), structural direction (e.g. fold axis, fault slip direction) and where necessary an intermediate direction (e.g. fault extent). This allows for folds and faults to be integrated into the description of the geological features in the implicit models. In this contribution we will use map2loop to automatically extract and augment input data from open access geological datasets from Geological Survey of Western Australia from the Hamersley Basin. The model area will include consists of upright refolded folds of Archean and Proterozoic stratigraphy overlying an Archean basement. The folded stratigraphy is overprinted by NW-SE trending faults. In the model the fault network is modelled first using observations of the fault trace using the estimated displacements from the geological map. The folded stratigraphy is then modelled by building a fold frame that characterises the geometry of the axial surface and the fold axis direction. The fold geometry is modelled by fitting curves representing the fold axis geometry in the axial surface and the fold geometry looking down plunge. We show that by using the fold constraints the geometry of the modelled folds are consistent with the geometries drawn in cross sections.


Biography

Lachlan is a research fellow at Monash University working on the Loop project. His research interests are encoding structural geology in 3D geological modelling algorithms.

Controls on gold endowments of porphyry deposits

 Massimo, Chiaradia1

1Department of Earth Sciences, University of Geneva, Geneva, Switzerland

Porphyry deposits are natural suppliers of ~75% copper and ~20% gold to our society. Nonetheless, gold endowments of porphyry deposits are characterized by a wide range going from a few tons to >2500 tons of gold. Here, I propose a model to explain the reasons of the large variations in metal endowments of porphyry Cu-Au deposits.

Porphyry Cu-Au deposits define two distinct trends in Au versus Cu tonnage plots: Cu-rich (Au/Cu ~4*10-6) or Au-rich (Au/Cu ~80*10-6). Cu-rich porphyry deposits are related to Andean-type subduction and typical calc-alkaline magmatism in thick continental arcs. In contrast, Au-rich porphyry deposits are associated with high-K calc-alkaline to alkaline magmatism in late to post-subduction or post-collision and extensional settings, and also with calc-alkaline magmatism. The largest Au-rich porphyry deposits are associated with high-K calc-alkaline to alkaline magmatism. Geochronological data at individual porphyry deposits suggest that gold endowments for both trends grow larger the longer the mineralization process is. However, Au is precipitated at much higher rates in Au-rich (~4500 tons Au/Ma) than in Cu-rich porphyry deposits (~100 tons Au/Ma).

Monte Carlo modelling of petrologic processes suggests that the different rates of gold precipitation in Cu-rich and Au-rich porphyry deposits most likely result from a 5-12 times better efficiency of gold precipitation in Au-rich than in Cu-rich deposits. The reason of the different efficiencies of gold precipitation is the different depths of formation of Cu-rich and Au-rich porphyry deposits which favour (deep level) or not (shallow level) a decoupling of Au and Cu precipitated from the magmatic-hydrothermal fluids. Interestingly, Au-rich porphyry deposits formed at shallower levels are also associated with magmatic rocks that have evolved at average shallower levels than Cu-rich deposits, as suggested by systematically lower Sr/Y values of the former (Au-rich systems) with respect to the latter (Cu-rich systems). Monte Carlo modelling shows that the higher gold endowments of Au-rich porphyry deposits associated with alkaline magmas require higher gold contents in the parental magmas such as those that are typical of alkaline magmas but not of calc-alkaline ones. This suggests an additional petrogenetic control in the formation of the Au-richest porphyry deposits associated with variably alkaline magmas.

Whereas depth of porphyry formation and chemistry of magmas (alkaline versus typical calc-alkaline) seem to control the Au-rich versus Cu-rich nature of porphyry Cu-Au deposits, the correlation of the Cu and Au endowments with ore deposition duration suggests that the final Cu and Au endowments of these deposits are determined by the cumulative number of mineralizing steps that are ultimately controlled by magma volume and ore process duration. The difference is that variably alkaline systems and shallow crustal calc-alkaline systems are inherently associated with magmas, whose fluids are tectonically (i.e., shallow emplacement) and chemically (alkaline magmas) optimized for high gold precipitation efficiency. In contrast, typical calc-alkaline (high Sr/Y) magmas form in a geodynamic context that favours enormous magma accumulations, which are necessary to produce behemothian Cu-rich deposits, but are emplaced at depths at which the exsolved fluids are less efficient for gold precipitation.


Biography

Massimo Chiaradia obtained a MSc at Padova University (Italy) and a PhD at Fribourg University (Switzerland). After post-docs in Sydney (CSIRO), Geneva and Leeds he became Senior Lecturer at Geneva University. His main research focus is the petrogenesis of convergent margin magmas and their association with porphyry Cu-Au deposits.

Bayesian inversion of 3D groundwater flow within the Sydney-Gunnedah-Bowen Basin

Ben Mather1, Dietmar Müller1, Craig O’Neill2, Louis Moresi3

1EarthByte Group, School of Geoscience, The University of Sydney, Camperdown, NSW, Australia, 2Department of Earth and Environmental Sciences, Macquarie University, North Ryde, NSW, Australia, 3Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia

In the driest inhabited continent on Earth, aquifers of the Sydney-Gunnedah-Bowen Basin are essential for Australian agriculture production, yet they experience progressively declining water level trends. In addition, groundwater discharge from the basin into the coastal ocean, a process now widely recognised as being important for providing significant inputs of nutrients and solutes to the oceans, has never been modelled. We have constructed a 3D Bayesian numerical groundwater flow model spanning the entire width and depth of this continent-scale basin. Our model assimilates groundwater recharge rates from water chloride concentrations, and borehole temperature measurements to constrain hydrothermal flow within the basin. We show that inland aquifers exhibit slow flow rates of 0.5 cm/day, resulting in a groundwater residence time of approximately 383 thousand years. In contrast, coastal aquifers have flow rates of approximately 30 cm/day, and a groundwater residence time of just 182 years. Our open-source modelling approach can be extended to any basin and help inform policies on the sustainable management of groundwater. In the future, our approach will enable time-dependent modelling of groundwater flow in response to uplift, erosion and climate change.


Biography

Ben is a postdoc with the EarthByte Group at the University of Sydney. He is interested in coupling geophysical and geochemical observations with numerical solid Earth models to constrain crustal evolution. Ben is aiming to apply for a DECRA in 2021.

Three decades of geoconservation in retrospection

Díaz-Martínez, Enrique1,2,3, Brocx, Margaret3,4,5

1 Geological Survey of Spain (IGME), Madrid, Spain, 2 Geological Society of Spain (SGE), 3 European Association for the Conservation of Geological Heritage (ProGEO), 4 Murdoch University, Perth, Australia, 5 Geological Society of Australia (GSA)

During the last 30 years, geoconservation has seen an accelerated evolution and advancements, but there are also a few steps backwards. We herein provide a summary from the perspective of three points of view: Spain, The United Kingdom, and globally. Both the United Kingdom and Spain had an active geological survey by the mid-19th century and began work on geoconservation in the 1970s, but an acceleration of achievements began in the 1990s with The European Association for the Conservation of Geological Heritage (ProGEO) as a catalyser for inventories, legislation, conferences, publications, and later on (2009) a peer reviewed journal (Geoheritage). ProGEO promoted the Global Geosites Programme (GGP) with support from IUGS and UNESCO, starting a list of geological sites of international relevance.  After the establishment of World Heritage criterion viii for geological heritage (1972), the first international conference on geoheritage was held in Digne, France (with the Declaration of the Memory of the Earth in 1991), followed by the Global Geoparks Programme (2004), the definition of the scope and scale of geoheritage including indigenous heritage (2007), and the first inclusion of geoheritage within IUCN resolutions (2008, 2012 and 2016).  This was followed by the establishment of a Geoheritage Specialist Group within IUCN’s World Commission on Protected Areas, the inclusion for the first time of geoconservation in a World Parks Congress (2014), and of a specific chapter on geoconservation in the 2015revised edition of IUCN’s book on Protected Area Governance and Management

Currently, the United Kingdom, Spain, and Portugal are the only countries in the world having fulfilled the GGP, and after China, Spain has the second highest number of UNESCO Global Geoparks (15 in 2020). The withdrawal of official support for the GGP by IUGS and UNESCO in 2003, left the programme orphaned. In its quest for an international standard that would force the Spanish government to inventory and protect its geoheritage, the Geological Society of Spain (SGE) became a member of IUCN in 2008, and that same year managed to pass resolution WCC-2008-RES-040 obliging to include geoconservation in the IUCN agenda and for all its members. ProGEO joined IUCN in 2011 and, for the first time in the history of IUCN, the 5th WCC (2012) saw many geoconservation-related activities, including resolution WCC-2012-RES-048 recommending the use of inclusive terms to refer to nature, natural heritage and natural diversity (it’s not all biodiversity!), as well as IUCN’s support to the GGP.

This presentation will further explore nodal points in the history of geoconservation on the global platform, lessons learnt, and Spain as a case study of a country that has worked towards establishing a national inventory of sites of geoheritage significance for the purpose of geoconservation.


Biography

PhD Geology from University of Idaho (USA, 1994) and MSc Management of Protected Areas from University of Madrid (Spain, 2006). Researcher with Spanish National Research Council (1998 to 2003) and with Geological Survey of Spain (IGME) since 2004, working on geoconservation projects including inventories, legislation, management and public outreach.

Mapping and modelling a future passive margin in Afar, East Africa

Zwaan, Frank1,2; Corti, Giacomo3, Keir, Derek1,4, Sani, Federico1, Muluneh, Ameha5, Illsley-Kemp, Finnigan6, Papini, Mauro1.

1University of Florence, Florence, Italy; 2University of Bern, Bern, Switzerland; 3National Italian Research Council, Florence, Italy; 4University of Southampton, Southampton, United Kingdom;         5Addis Ababa University, Addis Ababa, Ethiopia; 6Victoria University Wellington, Wellington, New Zealand (email: frank.zwaan@geo.unibe.ch)

This multidisciplinary research project (Zwaan et al. 2020a, b) focuses on the tectonics of the Western Afar Margin (WAM), which is situated between the Ethiopian Plateau and Afar Depression in East Africa. The WAM represents a developing passive margin in a highly volcanic setting, thus offering unique opportunities for the study of rifting and (magma-rich) continental break-up so that our results have both regional and global implications.

We show by means of earthquake analysis that the margin is still deforming under a ca. E-W extension regime (a result also obtained by analysis on fault measurements from recent field campaigns), whereas Afar itself undergoes a more SW-NE extension (Zwaan et al. 2020a). Together with GPS data, we see Afar currently opening in a rotational fashion. This opening is however a relatively recent and local phenomenon, due to the rotation of the Danakil microcontinent modifying the regional stress field (since 11 Ma). Regional tectonics is otherwise dominated by the rotation of Arabia since 25 Ma and should cause SW-NE (oblique) extension along the WAM. This oblique motion is indeed recorded in the large-scale en echelon fault patterns along the margin, which were reactivated in the current E-W extension regime. We thus have good evidence of a multiphase rotational history of the WAM and Afar.

Furthermore, analysis of the margin’s structural architecture reveals large-scale flexure towards Afar, likely representing the developing seaward-dipping reflectors that are typical for magma-rich margins. Detailed fault mapping and earthquake analysis show that recent faulting is dominantly antithetic (dipping away from the rift), bounding remarkable marginal grabens, although a large but older synthetic escarpment fault system is present as well.

By means of analogue modelling efforts (Zwaan et al. 2020b) we find that marginal flexure indeed initially develops a large escarpment, whereas the currently active structures only form after significant flexure. Moreover, these models show that marginal grabens do not develop under oblique extension conditions. Instead, the latter model boundary conditions create the large-scale en echelon fault arrangement typical of the WAM. We derive that the recent structures of the margin could have developed only after a shift to local orthogonal extension. These modeling results support the multiphase extension scenario as described above.

Altogether, our findings are highly relevant for our understanding of the structural evolution of (magma-rich) passive margins. Indeed, seismic sections of such margins show very similar structures to those of the WAM. However, the general lack of marginal grabens, which are so obvious along the WAM, can be explained by the fact that most rift systems undergo or have undergone oblique extension, often in multiple phases during which structures from older phases affect subsequent deformation.

References

Zwaan, F., Corti, G., Sani, F., Keir, D., Muluneh, A., Illsley-Kemp, F., Papini, M. 2020(a): Structural analysis of the Western Afar Margin, East Africa: evidence for multiphase rotational rifting. Tectonics. http://doi.org/10.1029/2019TC006043

Zwaan, F., Corti, G., Keir, D., Sani, F. 2020(b). An analogue modeling study of marginal flexure in Afar, East Africa: implications for passive margin formation. Tectonophysics. https://doi.org/10.1016/j.tecto.2020.228595


Biography

Frank Zwaan is a structural geologist and analogue modeller specialized in rift tectonics. He studied earth sciences in the Netherlands and France, finished his PhD in Switzerland, did a Postdoc in Italy and is currently working at the University of Bern in Switzerland

Thermochronology Frontiers in Australia 

McInnes, Brent I.A.

1John de Laeter Centre, Curtin University, Perth, Australia

The field of thermochronology in Australia has seen a significant increase in both capability and capacity development over the last decade. New labs have sprung up at University of Adelaide, the University of Queensland and Curtin University, which augment the University of Melbourne lab which has been a research powerhouse for almost half a century. These lab developments are one of many positive outcomes of informal meetings organised by geochemistry labs around the country via TANG3O (Thermochronology and Noble Gas Geochronology and Geochemistry Organisation).

Most labs now take an integrative approach using multiple radiometric dating techniques (e.g., U-Pb, Ar-Ar, U-He, fission-track) to generate geothermochronology data sets which provide a complete cooling history for any given rock sample. Repeating this process for multiple samples at scale allows researchers to detect differences in thermal history models that reflect major tectonic events in crustal evolution (e.g., continental breakup and collision, mountain-building and basin formation). Computational inversion of geothermochronology datasets are also becoming more sophisticated and allow the 4D thermal evolution of the crust to be imaged, providing a more detailed understanding of tectonic processes as well as predictive capability in the search for mineral and energy resources.

Another promising development is the increasing collaboration between research labs and geological surveys across Australia to address significant geoscience questions, such as: (1) mapping out thermal events across the continent (e.g., National Argon Map project led by Geoscience Australia), (2) demarcation of the end of orogenic events (Hall et al., 2016; Quentin de Gromard et al., 2020), and (3) regolith geochronology (Wells et al., 2019). Continued cooperation will lead to the training of a cadre of young geoscientists skilled in being able to provide a “biography” of a geological unit rather than just its “birth date”.   

Challenges remain however in understanding the crystal chemistry factors that produce inaccurate or irreproducible thermochronology ages in Archean and Proterozoic lithologies. The in situ U-Th/Pb-He microanalysis approach (Danisik et al., 2017), which generates grain-scale zircon He maps and quantifies intragrain He distribution, can be used by researchers to exclude problem areas in grains with anomalous He concentrations due to crystal defects or inclusions. The potential adoption of in situ microanalysis in thermochronology can be viewed similarly to the paradigm shift experienced by the geoscience community when SHRIMP became available in the 1990’s, an event which led to orders of magnitude increase in zircon U-Pb data production and fundamental changes to the design of geological maps and our understanding of the planet.

References

Danišík, M et al (2017) Seeing is believing: Visualization of He distribution in zircon and implications for thermal history reconstruction on single crystals. Science Advances 3:2, e1601121. DOI: 10.1126/sciadv.1601121.

Hall, JW et al (2016) Exhumation history of the Peake and Denison Inliers: insights from low-temperature thermochronology. AJES 63:7, 805-820. DOI: 10.1080/08120099.2016.1253615

Quentin de Gromard, R et al (2019) When will it end? Long-lived intracontinental reactivation in central Australia. Geoscience Frontiers, 10, 149-164. DOI: 10.1016/j.gsf.2018.09.003 

Wells, MA et al (2019) (U-Th)/He-dating of ferruginous duricrust: Insight into laterite formation at Boddington, WA. Chemical Geology 522, 148-161. DOI: 10.1016/j.chemgeo.2019.05.030


Biography

Professor Brent McInnes is a Research Professor at Curtin University and Director of the John De Laeter Centre, WA. Previous to this he was a Chief Research Scientist at CSIRO. Educated in Canada and trained at Caltech, he has 28 years of experience in the geoscience and resources research sector. 

Thermodynamic modelling of ore transport and deposition: The good, the bad, and the ugly

Brugger, Joël1; Etschmann, Barbara1; Gonzalez, Christropher1; Liu, Weihua2; Yuan, Mei2; Guan, Qiushi1; Raiteri, Paolo3; Testemale, Denis4; and Xing, Yanlu5

1Monash University, Clayton, Australia, 2 CSIRO Mineral Resources Flagship, Clayton, Australia, 3Curtin University, Perth, Australia, 4Université Grenoble Alpes, Grenoble, France, 5University of Minnesota, Minneapolis, USA

Ore deposit formation and the associated fluid-induced alteration require effective advective mass transfer of fluids, volatiles, and metals over length scales of meters to hundreds of kilometres. Over the past 20 years, our understanding of the geochemical aspects of ore transport and deposition has seen major advances driven by revolutions in theoretical, experimental, and characterization capabilities. This has improved our ability to predict metal behaviour at scales ranging from the ore system to the hand specimen, but this new knowledge raises also important new challenges.

  1. Thermodynamic modelling enables prediction of the metal-carrying capacity of geological fluids, and mapping the distribution and efficiency of metal-precipitating processes through time and space. In the past 20 years a large amount of in situ spectroscopic data complemented by increasingly accurate first principle molecular dynamic simulations have dramatically improved our understanding of the molecular-level nature of the hydrothermal reactions that are responsible for metal transport in the mid-to upper-crust. This underpins the development of more accurate models of reactive transport over wide ranges in pressure, temperature, fluid composition, and physical states.
  2. Supercritical aqueous fluids link subducting plates and the return of water, carbon, sulfur, and metals to the Earth’s surface. Innovative theoretical thermodynamic extrapolations have extended our capacity to model the role of aqueous fluids in the deep Earth. These new predictions suggest a rather more profound role for deep fluids than originally thought: for example, dissolved organic carbon species stable at high pressure recycle large amounts of carbon out of the subduction zone and into the atmosphere; and polysulfide species, stable at high pressure, may form Au deposits rather than the reduced sulfur species stable at lower pressure. With regard to metal complexes, these extrapolations are ultimately based on a large body of experimental studies; the vast majority were conducted at near ambiant temperature and pressure; a reasonable number investigated solutions to ~300 ˚C, P ≤ 300 bar; but few experimental data are available at pressures above 1 kbar, and hardly any reliable data is available beyond 10 kbar for any metal complex. Molecular dynamics can be used to address this fundamental limitation. The data produced by MD provide realistic properties in PT space that underpin accurate simulations of element transfer by fluids expelled from subducting slabs and their contributions to the deep Earth’s volatile, redox and metal budgets.
  3. Finally, the role of fluids in controlling both the kinetics and pathways of mineral replacement reactions is now firmly established. The positive feedback between these reactions and porosity creation is one of the key mechanisms that explains the pervasive nature of many alteration reactions. On-going experiments demonstrate the important role of trace elments in controlling the fate of fluid-driven reactions. For example, we discovered that the presence of trace amounts of dissolved cerium (Ce) increases the porosity of hematite (Fe2O3) formed via fluid-induced replacement of magnetite (Fe3O4), thereby increasing the efficiency of coupled magnetite replacement, fluid flow, and element mass transfer.

Biography

Joël Brugger obtained his PhD in Basel, Switzerland. Following 12 years  in a joint role at the South Australian Museum and the University of Adelaide, he took up the chair in Synchrotron Geosciences at Monash University. Joël uses state-of-the-art experimental techniques to study the transport and deposition of metals.

Immersive virtual reality in geotourism

Raimondo, A/Prof. Tom1

1UniSA STEM, University Of South Australia, GPO Box 2471, Adelaide, Australia

Project LIVE (Learning through Immersive Virtual Environments) is a cross-disciplinary initiative at the University of South Australia to embed immersive virtual and mixed reality experiences across the entire teaching program of UniSA STEM. This is achieved using techniques such as Remotely Piloted Aircraft (drone) surveying, 3D photogrammetry, gigapixel photography, terrestrial laser scanning (LiDAR), 360-degree panoramic photos and videos, and location-based mobile learning apps. The Project LIVE team has recently developed a flexible template for the efficient production of high-quality virtual tours, where users can easily substitute images, videos, 3D models and narrative components such as voiceovers and text descriptions to adapt the experience to new field locations. Our platform opens up significant opportunities for the creation of a suite of engaging, authentic and impactful VR geotourism experiences. This presentation will demonstrate a proof of concept using the Hallett Cove Geological Heritage Site in Adelaide, South Australia. Entitled Beyond the Ice, the virtual tour incorporates several complementary elements including an immersive VR experience, web-based geotour, mobile learning game and 360 street view walking trail, all of which are freely available at: https://www.projectlive.org.au/beyond-the-ice. Further examples from other major geosites across Australia will be shown, concluding with a discussion of the future geotourism opportunities to be explored.


Biography

Tom Raimondo is Associate Professor of Geology and Geochemistry and Professorial Lead for STEM at the University of South Australia. He is also the Director of Project LIVE (Learning through Immersive Virtual Environments).

Geoelectric Structure of Tasmania from Multi-Scale Magnetotelluric Data

Ostersen, Thomas1,2, Reading, Anya2, Cracknell, Matthew2, Roach, Michael2, McNeill, Andrew3, Duffett, Mark3, Bombardieri, Daniel3, Thiel, Stephan4, Robertson, Kate4, Duan, Jingming5, Heinson, Graham6

1Solve Geosolutions, Hobart, Australia, 2University of Tasmania, Hobart, Australia, 3Mineral Resources Tasmania, Hobart, Australia, 4Geological Survey of South Australia, Adelaide, Australia, 5Geoscience Australia, Canberra, Australia, 6University of Adelaide, Adelaide, Australia

The current understanding of Tasmania’s enigmatic tectonic history has been informed by geological information observed or sampled at the Earth’s surface coupled with geophysical data sets sensitive to magnetic, density and seismic properties of the rocks forming the crust and mantle beneath. With the completion of the Tasmanian portion of the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP), new 3D and 2D geophysical models describing the electrical properties of the Tasmanian lithosphere at different spatial scales have been derived to compliment these data.

At the whole-of-state scale, 3D inverse models of the long period magnetotelluric (MT) data have illuminated the electrical structure of the mid-crustal to lithospheric mantle depths. This model images the full extent of the Tamar Conductivity Anomaly, a crustal-scale conductor extending from northern to southern Tasmania along the boundary between eastern and western Tasmanian geologic terrains.

In the west of the state, a 2D inverse model transecting the Cambrian Mount Reid Volcanics brings the electrical structure of the upper- to mid-crustal depth range in this economically important part of the state into sharper focus. The model images west-dipping conductive structures spatially coincident with major faults and associated copper mineralisation near Queenstown.

Finally, in the central east of Tasmania, a joint inversion incorporating legacy broadband MT data with newer AusLAMP MT data using the whole-of-state scale model as a priori geoelectric structure was conducted. Inversion results demonstrate a potential use case for regional scale AusLAMP models to improve higher resolution geoelectric structure modelling, with the joint inverse model imaging the Lemont geothermal field at higher resolution while simultaneously mapping geologically feasible 3D resistivity structures.


Biography

Thomas is a geophysicist and PhD candidate at the University of Tasmania studying the geoelectric structure of the Tasmanian lithosphere. He is now applying his geophysical and scientific programming skills to a consultant role with Solve Geosolutions.

Uncovering the Cobar Basin – new results from the NSW MinEx NDI areas

Folkes, Chris1; Deyssing, Liann2; Trigg, Steven2; Carlton, Astrid1; Schifano, Joe3

1Mineral Exploration Cooperative Research Centre, Geological Survey of New South Wales, Department of Regional NSW, Maitland, NSW, Australia, 2Mineral Exploration Cooperative Research Centre, Geological Survey of New South Wales, Department of Regional NSW, Orange, NSW, Australia, 3Mineral Exploration Cooperative Research Centre, University of New South Wales, Sydney, NSW, Australia

The Cobar region of central-western New South Wales hosts numerous precious and base metal mineral systems, many exploited by active and historical mine workings. These are mostly located around rock outcrops and under shallow cover sequences of the Cobar Basin. The North Cobar and South Cobar MinEx CRC National Drilling Initiative (NDI) areas were selected by the Geological Survey of New South Wales (GSNSW) to improve the understanding of the geology, mineral systems and groundwater in basement and regolith profiles that extend away from the margins of these known mineralised areas.

Understanding the prospective basement geology in the Cobar region is complicated by variations in the depth and nature of the weathering profiles through the region. A mix of transported and in situ weathering reflects a complex palaeo-landscape.

Recent activities by the GSNSW are designed to map the thickness and character of the weathering profile and increase our knowledge of basement geology. This work will inform and complement proposed drilling in the NDI areas to further investigate the geochemical and petrophysical signatures of basement geology and mineral systems. The activities also have implications in understanding groundwater resources.

Comprehensive audit and gaps reports were published in 2020 for the North Cobar and South Cobar NDI areas. These reports reviewed existing data, provided recommendations for new sampling and data capture, and prioritised the scientific questions that should be addressed. Recent mineral potential mapping and mineral-systems studies identified new prospective areas and provided a better understanding of the main controls on, and timing of mineralisation for the Cobar region.

An airborne electromagnetic (AEM) survey was flown in the region in 2019, comprising 116 east‒west lines spaced at 2.5 km and 5 km, totalling approximately 11,000 line km. Ongoing modelling and interpretation of the data have enhanced knowledge of depth and nature of the cover, groundwater systems, structural geology (e.g. fault locations and geometry), mineral systems and stratigraphy. The AEM data, with other datasets such as fault attribution, NSW Seamless Geology, and crustal-scale fault models, are being integrated into a new 3D model of the region that will benefit mineral explorers and hydrogeologists.

The AEM data have also been integrated with drilling, hydrogeochemical, biogeochemical and spectral surveys. Downhole lithology and assay information from legacy drilling has been imported into 3D viewable datasets. Hydrogeochemical analyses from waterbores in the Cobar region were completed by CSIRO and GSNSW and highlighted new areas for potential exploration. Researchers from UNSW analysed Cypress Pine needles to provide a regional biogeochemical dataset with focus areas over known mineralisation. Spectral scanning of legacy drillcore using the HyLoggerTM has provided useful constraints on the depth and nature of weathering, and alteration of basement rocks.

These activities build on recent mineral system studies to advance the understanding of the geology, and mineral and groundwater resources in the North Cobar and South Cobar NDI areas. This has greatly helped to inform the site selection and scientific questions to be answered with future MinEx CRC drilling in these NDI areas.


Biography

Chris Folkes is a senior geoscientist in the Regional Mapping team at the Geological Survey of NSW. He completed his undergraduate studies at the University of Bristol in the UK, and a PhD at Monash University in volcanology, igneous geochemistry and geochronology.

About the GSA

The Geological Society of Australia was established as a non-profit organisation in 1952 to promote, advance and support Earth sciences in Australia.

As a broadly based professional society that aims to represent all Earth Science disciplines, the GSA attracts a wide diversity of members working in a similarly broad range of industries.

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