Zircon Chemistry as an Exploration Tool for Iron Oxide-Copper-Gold Deposits

Brotodewo, Adrienne1,2,, Tiddy, Caroline1,2, Zivak, Diana3, Fabris, Adrian4, Giles, David1,2

1Future Industries Institute, University of South Australia, Adelaide, Australia, 2Mineral Exploration Cooperative Research Centre (MinEx CRC), Adelaide, Australia, 3Department of Earth and Environmental Sciences, The University of Adelaide, Adelaide, Australia, 4Geological Survey of South Australia, Adelaide, Australia

Zircon preserves chemical signatures that reflect crystallisation environments and post-crystallisation modification (e.g. Belousova et al., 2002). Typically, zircon is used to study petrogenesis and evolution of rocks due to its robustness during surficial, metamorphic and igneous processes, as well as its affinity for rare earth elements (REE), U and Th. Recent research has focused on understanding and characterising the geochemical composition of zircon. However, this has been met with many challenges as REE and trace element compositions can be highly variable in zircon from the same lithological unit, and within a single grain itself as a result of micro inclusions, metamictisation, strong differences in compositional zoning and recrystallisation (Nardi et al., 2003). Despite this, zircon has successfully been used as a provenance tool to discriminate between igneous, metamorphic and sedimentary source rocks (Belousova et al., 2002). Zircon has also been demonstrated to preserve a geochemical signature that can be related to porphyry Cu mineralisation (Lu et al., 2016). However, the use of zircon as a pathfinder for other commodities, such as iron oxide-copper-gold (IOCG) deposits, is limited (Courtney-Davies et al., 2019).

The Gawler Craton, South Australia, preserves a complex geological history dating back to the late Archean. The craton preserves multiple igneous units that each have their own unique geochemical characteristics and some of which are associated with IOCG mineralisation. IOCG mineralisation occurred during a major period of mineral genesis, magmatism, deformation and metamorphism at ca. 1600-1580 Ma (e.g. Tiddy & Giles, 2020) and includes the Olympic Dam, Prominent Hill and Carrapateena deposits along the eastern Gawler Craton. Within the Gawler Craton, zircon has commonly been used for dating or isotopic purposes. However, limited research has focused on the geochemistry of zircon, its variability between igneous suites and its use as a pathfinder mineral towards IOCG deposits.

In this study, new zircon geochemical data is presented on samples from the ca. 1850 Ma Donington Suite, ca. 1600-1575 Ma Hiltaba Suite and ca. 1594-1587 Ma Gawler Range Volcanics. Samples from all three suites preserve evidence of variable potassic and hematite alteration associated with hydrothermal activity during IOCG mineralisation at ca. 1600-1580 Ma. Assessment of zircon chemistry within each of the three igneous units shows that there are characteristic enrichments and depletions in trace and REE chemistry in samples that have undergone variable degrees of alteration. The variations in zircon chemistry between unaltered and altered samples is attributed to chemical modification by F-rich hydrothermal fluids that altered the host rocks and was associated with IOCG mineralisation. These distinct geochemical characteristics recognized in zircon suggests the potential of zircon as a pathfinder for IOCG deposits in the Gawler Craton.

References

Belousova et al. 2002: Contrib. Min. Pet. 143, 602-622

Courtney-Davies et al. 2019: Min. 2019, 9, 364

Lu et al. 2016: Soc. Eco. Geo. Vol 19

Nardi et al. 2013: Chem. Geo. 335, 1-7

Tiddy & Giles, 2020: Ore Geo. Rev. 122, 103-483.


Biography

Adrienne Brotodewo is a PhD candidate at the Future Industries Institute, University of South Australia, and is undertaking her research as part of MinEx CRC.

Adrienne is focusing on establishing a geochemical exploration criteria using zircon within basement and cover sequences in the Gawler Craton, South Australia.

Optimization of sequential drilling locations to reduce geological uncertainty

Pirot, Guillaume1 and Lindsay, Mark1 and Jessell, Mark1

1Centre for Exploration Targeting, The University of Western Australia, Crawley, Australia

In a context of early stage exploration, geological modelling relies heavily on sparse surface and drillhole geological observations. These data allow us to develop interpretations of the stratigraphy, organizing identified lithological formations. Though the data may provide local estimations about the thickness and depth of some formations, geological uncertainty away from the observations may be huge. One way to reduce this geological uncertainty is to acquire more data by drilling. However, given the associated costs and risk to the project, the next drilling location is carefully selected. This is difficult as the next location for drilling is often decided under uncertainty due to a dearth of supporting information and knowledge.

Here, we explore different strategies to optimize the selection of successive drilling locations. The first strategy relies on the volume of influence around the borehole design, acting as a moving window filter, and on the value of new information, that is assumed proportional to the current state of geological uncertainty. The second exploration strategy aims at reducing the geological misfit with a Bayesian Global Optimizer.

We test the different strategies on a synthetic case based on a Precambrian basin setting. The initial geological knowledge is composed of surface data and five initial boreholes, whose locations are determined by Latin Hypercube Sampling. At each iteration, an ensemble of geological realizations is generated by stochastic perturbation of the current geological knowledge. Geological uncertainty is summarized from different indicators based on the cardinality, entropy, connectivity, topology and geostatistics of both lithological formations and their underlying scalar-fields.

Preliminary results show that the first strategy allows a decrease of both the mean and ninetieth percentile of the geological uncertainty. The Bayesian Global Optimisation approach reduces locally the geological misfit. A third strategy combining the first two approaches gives a good compromise to reduce both the geological uncertainty and the geological misfit and shows promise to support decision-making in practical regional geological exploration scenarios.

Acknowledgement

This work is supported by the ARC-funded Loop: Enabling Stochastic 3D Geological Modelling consortia (LP170100985) and DECRA (DE190100431) and by the Mineral Exploration Cooperative Research Centre whose activities are funded by the Australian Government’s Cooperative Research Centre Programme. This is MinEx CRC Document 2020/45.


Biography

Guillaume joined the Centre for Exploration Targeting in September 2019. He is involved in the ‘Automated 3D Modelling’ MinEx CRC project and as Work-Package 5 leader in the LOOP consortium (loop3d.org), where he develop tools to improve the characterization, the propagation and the reduction of prediction uncertainties.

Characterising fluid composition and source in a greenfields terrane: west Arunta Orogen, Western Australia

Finch, Emily G.1,2,3, Kelsey, David E.1,3

1Mineral Exploration Cooperative Research Centre, Perth, Australia, 2University of South Australia, Adelaide, Australia, 3Geological Survey of Western Australia, Perth, Australia

Discovering major mineral deposits is increasingly difficult because easily findable deposits located at Earth’s surface have already been discovered. Exploration focus has now consequently shifted to relatively unexplored regions where basement rocks are commonly obscured by sedimentary cover. Exploration success in covered regions requires understanding of whole mineral systems. Fluids are crucial to understanding hydrothermal mineral systems, because fluids are present during all stages of ore formation: in the source region, throughout transport, and in deposition of metals.

The Arunta Orogen is one such underexplored and largely covered terrane, and is a key focus for the Geological Survey of Western Australia in the National Drilling Initiative. It is comprised of two Paleoproterozoic provinces overlain by sedimentary basins, and spans east–west across the Northern Territory, with the westernmost extent crossing into Western Australia. The Northern Territory component of the Arunta Orogen contains several mineral prospects and deposits, but the Western Australian component (the west Arunta) is one of the continent’s least explored regions for mineral deposits due to its remoteness, paucity of outcrop, and lack of detailed study aimed at constraining key geological factors such as lithostratigraphy and age. Limited work on the west Arunta indicates the region is prospective for copper, gold, uranium, and sedimentary-exhalative base metal deposits, but little to no analysis of alteration signatures or fluid source has been undertaken there to date.

Basement rocks of the west Arunta have undergone multiple high-temperature metamorphic and deformation events, most of which appear to postdate fluid infiltration events of interest, making these rocks unsuitable for fluid inclusion studies. Instead, minerals such as apatite can preserve information about fluids they have formed from or interacted with, and can be used to infer fluid characteristics such as composition and potential source. Additionally, apatite can be used as an exploration tool because it is an indicator mineral for different rock types and mineralisation styles.


Biography

Dr Emily Finch is UniSA’s MinEx CRC Embedded Researcher, working within the Geological Survey of Western Australia and forming a collaborative link between GSWA and UniSA. The focus of her research is on mineralising systems, with a particular interest in fluid chemistry and sources in under-explored regions of Western Australia.

Multicommodity mineral systems analysis for the National Drilling Initiative: The TISA and Delamerian case study

Metelka, Vasek1; Schofield, Anthony2; Wise, Tom3; Cole, David4; Otto, Alex1; Fabris, Adrian3; Hong, Wei5; Murr, James2

1CSIRO Mineral Resources, Perth, Australia; 2Geoscience Australia, Canberra, Australia; 3Geological Survey of South Australia, Adelaide, Australia; 4CSIRO Data 61, Melbourne, Australia; 5Univeristy of Adelaide, Adelaide, Australia

The National Drilling Initiative (NDI) and MinEx CRC research activities aim at providing new data that will drive our understanding of geological processes and mineral systems in key underexplored areas of the Australian continent. Ultimately, the newly acquired knowledge will underpin the future of the exploration industry as we push for discoveries under deeper cover.

Prospectivity analyses were conducted to aid with drill targeting for the NDI. These analyses were performed for two regions of interest: The East Tennant Creek – Mount Isa Area (TISA) of Northern Territory and Queensland and the Delamerian Orogen (Delamerian) Area of South Australia. Both regions, albeit with a different geological setting, were primarily omitted from substantive exploration efforts either due to thick regolith or younger sedimentary cover or lacking knowledge and missing significant discoveries. On paper; however, the geological settings and the proximity to known mineralisation suggest a high potential for discovery of new deposits under younger sedimentary/ regolith cover or deposits that formed mineral systems that were not considered previously.

We employed a multicommodity knowledge-based mineral systems analysis approach to identify critical components and model the overall propensity to mineralisation. Theoretical gold and copper-gold mineral systems models were established first. The models were then converted to geospatial representations, and quantitative prospectivity maps were created utilising fuzzy logic inference and compared to weighted overlay as well as data-driven methods (logistic regression, random forest), where training data could be applied from adjacent uncovered regions.

The results show several zones of interest that can serve the researchers and stakeholders as first-pass information for drill targeting. The approach also highlighted the importance of primary input data. It helped focus on areas where data quality or discrepancies existed as well as identified data sets that were crucial for mapping the components of a mineral system more accurately. When compared to the data-driven methods, which showed good classification accuracy metrics, the knowledge-driven results open up more space and enable conceptual, regional targeting.


Biography

Dr Vasek Metelka is a Senior Research Geologist with CSIRO Mineral Resources in Perth. He has over 15 years of R&D experience from research organisations in Australia and the Czech Republic. Throughout his career, Vasek focuses on interdisciplinary projects bridging geology, geochemistry, geophysics and remote sensing.

The MinEx CRC National Drilling Initiative

Budd, Anthony 1,2

1 Geoscience Australia, Canberra, Australia; 2 MinEx CRC, Canberra, Australia

Approximately 80% of Australia has some form of cover rocks obscuring potentially mineralised geological regions. In order to remain internationally competitive for exploration investment, government geoscience agencies around Australia provide precompetitive geoscience data to lower exploration risk. Mostly this has been geophysical data to see through cover – MinEx CRC is developing new tools and opportunities to sample bedrock directly by drilling.

MinEx CRC was established in 2018 under the Australian Government’s Cooperative Research Centre program (www.minexcrc.com.au). MinEx CRC has three Programs: Program 1 is developing new drilling technologies; Program 2 is developing new ways of gaining data from drilling; and Program 3 is the National Drilling Initiative (NDI).

The NDI is conducting drilling campaigns in selected areas as determined by each sponsoring geological survey. During September-November 2020, two campaigns are underway on behalf of Geoscience Australia (GA) with the Northern Territory Geological Survey in the Barkly region of the Northern Territory. A program of 10 holes of depths between ~300-500 m is designed test a range of stratigraphic and mineral system targets in the East Tennant region. The East Tennant area was selected during GA’s Exploring for the Future Program (https://www.ga.gov.au/eftf) as a possible extension to the Tennant Creek mineralised region. A single deep stratigraphic borehole (~2000 m) is underway to test the Carrara Sub-basin recently identified in the Barkly Seismic Program of the EFTF (https://www.ga.gov.au/eftf/energy/barkly-seismic-survey) in the South Nicholson area. Both of these campaigns are being conducted using conventional drilling methods.

In 2021 two campaigns are expected to be conducted utilising the RoXplorer Coiled Tube drilling rig undergoing further development by MinEx CRC Program 1 (https://minexcrc.com.au/program-one-drilling-technologies/project-2-coiled-tubing-drilling-for-definition-of-mineral-deposits/). MinEx CRC will conduct drilling on behalf of the GSWA in the East Yilgarn, and in two areas of the Delamerian for the GSSA. Further campaigns are planned for the North and South Cobar, Mundi, Dubbo and Forbes areas for the GSNSW, and the Tabberabberan for the GSV. Additional drilling campaigns are likely to be undertaken in other areas later in the life of the MinEx CRC.

MinEx CRC picks up from three previous CRCs: DET CRC for the RoXplorer and associated technologies; CRC LEME for exploration through cover using cover materials; and the pmd*CRC for mineral systems analysis. Taking a mineral systems approach, the Geological Architecture and Evolution project provides new data and interpretations in the drilled areas to underpin mineral systems analysis, and develops new technologies and methodologies for acquiring and interpreting this data.

The Targeting Mineral Systems in Covered Terranes project deploys fit-for-purpose data and geoscience analytical techniques designed to identify and map mineral system footprints within cover and underlying basement and apply a suite of mineral systems mapping tools designed to identify and prioritise areas of high prospectivity.

The Maximising the Value of Data and Drilling Through Cover project provides the tools and data infrastructure to facilitate upload and management of legacy and NDI drilling data delivered to stakeholders and researchers in near real-time, and to the broader geoscience community in efficient time frames.


Biography

Anthony is the Program 3/National Drilling Initiative Leader for the MinEx CRC, a joint appointment with Geoscience Australia. Anthony has worked at Geoscience Australia for 25 years in Minerals, Geothermal and Unconventional Gas, as well as Advice, Assessment and Promotions

Mineral and petroleum potential in the South Nicholson region, and the NDI Carrara 1 stratigraphic drill hole

Jarrett, Amber1,2, Bailey, Adam1, Carr, Lidena1, Henson, Paul1, Schofield, Anthony1,2, O’Rouke, Angela1,2, Roach, Ian1,2, Budd, Anthony1,2, Munson, Tim3, Williams, Ben3, Symmons, Jack3, Close, Dorothy3

1Geoscience Australia, Canberra, Australia, 2MinEx CRC, Canberra, Australia, 3Northern Territory Geological Survey, Darwin, Australia

The MinEx CRC-led National Drilling Initiative (NDI) is the world’s largest mineral exploration collaboration designed to undertake precompetitive geoscience research in underexplored, but potentially prospective regions. One of the first NDI projects is being undertaken in the South Nicholson region of the Northern Territory (NT) as a collaboration with Geoscience Australia and the Northern Territory Geological Survey.

The South Nicholson Basin, and underlying Lawn Hill Platform region, have the potential for sediment‑hosted base metal mineral deposits including critical minerals and hydrocarbons. The region is poorly understood compared with the neighbouring resource‑rich areas of the McArthur Basin and the Mount Isa Province. Providing baseline data in frontier basins is essential as legacy data coverage can often be inadequate for making investment decisions, particularly with new commodities where exploration may not yet have provided the required information.

In 2017, Geoscience Australia acquired the L210 South Nicholson Deep Crustal Seismic Reflection Survey. This survey demonstrated the existence of an approximately 1550 km2 sedimentary depocentre underlying the surface sedimentary rocks of the Georgina Basin, and coincident with a prominent gravity low. This depocentre has been termed the ‘Carrara Sub‑basin’ and its successions may host a continuation of the resource-rich rocks located on the northern Lawn Hill Platform of northwest Queensland, in addition to South Nicholson stratigraphy that has never been sampled by drill core.

MinEx CRC and its partners seek to better understand the geology and resource potential of the Carrara Sub‑basin through the drilling of the first deep vertical stratigraphic borehole in the region –the NDI Carrara 1 stratigraphic borehole. This borehole has been designed to answer key scientific questions suggested by Geoscience Australia and the Northern Territory Geological Survey including determining geological and geochemical characteristics of sedimentary units from fresh drill core, identifying any evidence of alteration or fluid flow, and finally determining whether there are favourable indicators for the presence of mineral or petroleum systems. To address these questions, both physical samples (e.g. drill core and cuttings) and downhole data (e.g. wireline geophysical data) will be acquired over the entire borehole interval, to a depth of about 2000 m.

Drilling of NDI Carrara 1 is set to be completed by the end of 2020. This presentation will provide a rationale for drilling the NDI Carrara 1 stratigraphic borehole and will present preliminary data generated through drilling.

The South Nicholson NDI has already provided and integrated new geoscience data and knowledge in the region, and NDI Carrara 1 will allow for direct testing of resource potential. This precompetitive data is fundamental to underpinning increased industry investment and sustainable economic development in this greenfield region of northern Australia.


Biography

Amber Jarrett is a Geochemist in the Minerals, Energy and Groundwater Division, Geoscience Australia. Her research interests include petroleum geochemistry, basin hosted resource potential, isotopes, biomarkers and early life. Amber graduated with a BSc (Hons) in 2008, majoring in both Geology and Biology, and a PhD in 2014 from ANU.

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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