Brief description
Geoscience Australia’s Exploring for the Future program provides precompetitive information to inform decision-making by government, community and industry on the sustainable development of Australia's mineral, energy and groundwater resources. By gathering, analysing and interpreting new and existing precompetitive geoscience data and knowledge, we are building a national picture of Australia’s geology and resource potential. This leads to a strong economy, resilient society and sustainable environment for the benefit of all Australians. This includes supporting Australia’s transition to net zero emissions, strong, sustainable resources and agriculture sectors, and economic opportunities and social benefits for Australia’s regional and remote communities. The Exploring for the Future program, which commenced in 2016, is an eight year, $225m investment by the Australian Government. This work contributes to building a better understanding of the Australian continent, whilst giving the Australian public the tools they need to help them make informed decisions in their areas of interest.
As part of the Australia's Resources Framework Project, in the Exploring for the Future Program, Geoscience Australia and CSIRO undertook a magnetic source depth study across four areas, with the objectives of generating cover model constraints from magnetic modelling to expand national coverage, and to improve our subsurface understanding of these areas. During this study, 2005 magnetic estimates of depth to the top of magnetization were generated, with solutions derived using a consistent methodology (targeted magnetic inversion modelling, or TMIM; also known as ‘sweet-spot’ modelling). The methodology for these estimates are detailed in a summary report by Foss et al (2024), and is available for download through Geoscience Australia’s enterprise catalogue (https://pid.geoscience.gov.au/dataset/ga/149239).
The new points were generated over four areas: 1) the western part of Tasmania that is the southernmost extension of the Darling-Curnamona-Delamerian (DCD) project area; 2) northeastern Queensland; 3) the Officer Basin area of western South Australia and southeastern West Australia; and 4) the Eastern Resources Corridor (ERC), covering eastern South Australia, southwest Queensland, western New South Wales and western Victoria. These depth estimates have been released, together with a summary report detailing the data and methodology used to generate the results, through Geoscience Australia's product catalogue (ecat) at https://pid.geoscience.gov.au/dataset/ga/149239.
This supplementary data release contains the chronostratigraphic attribution of the new TMIM magnetic depth estimates, which range in depth from at surface to 13,294 m below ground. To ensure that the interpretations took into account the local geological features, the magnetic depth estimates were integrated and interpreted with other geological and geophysical datasets, including borehole stratigraphic logs, potential fields images, surface and solid geology maps, and airborne electromagnetic interpretations (where available).
Each depth-solution is interpretively ascribed to either a chronostratigraphic boundary with the stratigraphic units above and below the depth estimate, or the stratigraphic unit that the depth estimate occurs within, populated from the Australian Stratigraphic Units Database (ASUD). Stratigraphic attribution adds value and informs users of the depth to certain stratigraphic units in their areas of interest. Each solution is accompanied by confidence estimates. The depth estimate points are formatted for compliance with Geoscience Australia’s (GA) Estimates of Geological and Geophysical Surfaces (EGGS) database, the national repository for standardised depth estimate points.
Results from these interpretations provided some support to stratigraphic drillhole targeting, as part of the Delamerian Margins NSW National Drilling Initiative campaign, a collaboration between GA’s EFTF program, the MinEx CRC National Drilling Initiative and the Geological Survey of New South Wales. The magnetic depth-estimate solutions produced within this study provide important depth constraints in data-poor areas. These data help to construct a better understanding of the 3D geometry of the Australian continent and aid in cover thickness modelling activities. The availability of the depth-estimate solutions via the EGGS database through Geoscience Australia’s Portal creates enduring value to the public.
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Maintenance and Update Frequency: asNeeded
Statement:
This study interpreted 2005 new magnetic TMIM depth estimates generated by Foss et al (2024) across four study areas: ERC, Tasmania, northeast Queensland and Officer Basin. The depth to top magnetisation points were generated as part of ARF, and were generated using targeted magnetic inversion modelling, also known as sweet-spot modelling. The top magnetisation depths range from at surface (0.1 m) to 13,294 m.
This interpretation was undertaken in 2023-24 as part of GA’s EFTF Australian Resources Framework Officer Basin and Darling-Curnamona-Delamerian projects. The interpretations were in-part made to support stratigraphic drillhole targeting, as part of the Delamerian Margin's NSW National Drilling Initiative campaign, a collaboration between GA’s EFTF program, the MinEx CRC National Drilling Initiative and the Geological Survey of New South Wales. The estimates also provide valuable input for cover modelling activities.
A preliminary workflow to assist with semi-automatic stratigraphic attribution of points used the point location intersections with the solid geology chronostratigraphic layers. Each intersection was assigned values of ‘Yes’, ‘No’ and “Maybe’ based on whether interpreters knew of any magnetic sources within the era layers. In most instances, while a chronostratigraphic era may contain a magnetic source, the solid geology did not intersect the magnetic unit, and interpreters were ultimately forced to integrate the magnetic depth estimates with other available supporting geological and geophysical datasets.
All stratigraphic unit information is consistent with GA’s Australian Stratigraphic Units Database (https://asud.ga.gov.au), and the spreadsheets included as part of this digital release meet the data standards for the Estimates of Geological and Geophysical Surfaces (EGGS) database (Mathews et al., 2020; accessible through GA’s Data Delivery Portal https://portal.ga.gov.au).
These points are formatted for and intended to be uploaded to GA’s EGGS database. This interpretation, alongside other multidisciplinary depth estimate available from the EGGS database, have applications in a wide range of investigative, modelling and analytical uses
Notes
Purpose
The interpretation of magnetic depth estimates in the four key study areas provides information about both the chronostratigraphic meaning of and depth to top of magnetisation sources across Australia. This information is useful for mapping both the horizontal and vertical distribution of magnetic stratigraphic units that are dated as Cenozoic, Mesozoic, Paleozoic, Neoproterozoic, Mesoproterozoic and Paleoproterozoic in age. In some instances, these boundaries denote post-depositional intrusive units, for example the Cenozoic, Mesozoic and Paleozoic dolerites in Tasmania, which intrude into older rocks or where aging relationships have been inverted as a result of structure. The regional interpretation of the magnetic depth estimates was made to support GA’s Exploring for the Future (EFTF) Australian Resources Framework (ARF) project. The four regional interpretations also contribute to national coverage of TMIM estimates, complimenting work carried out in the North Australian Craton (Matthews et al, 2020), in the Thomson Orogen (Goodwin et al., 2017), and over the Murray Basin in southeast Australia. The magnetic depth estimates also provided a preliminary estimate of cover thickness to support stratigraphic drill hole targeting in the Loch Lilly-Kars Belt area as part of the Delamerian Margins NSW National Drilling Initiative campaign. This stratigraphic drilling campaign was conducted as a collaboration between Geoscience Australia’s EFTF program’s Darling-Curnamona-Delamerian (DCD) project, the MinEx CRC National Drilling Initiative and the Geological Survey of New South Wales.Each interpretation point is attributed with interpretation-specific metadata, including location, depth, elevation or height of the magnetometer and elevation of ground level, chronostratigraphic relationship, stratigraphy, confidence in both the stratigraphic interpretation and 3D location of the point, the basis of interpretation, any further supporting comments regarding the interpretation, and the interpreter’s details. Chronostratigraphic relationships are captured by the eras of the units above and below the interpretations, which identify if the high-level chronostratigraphic order is continuous or discontinuous. The stratigraphic unit fields capture the stratigraphic unit names and numbers for the units above and below the depth estimate (if the interpreted depth estimate occurs at an era boundary) or the stratigraphic unit name and number of the unit within which the depth estimate is located (if the estimate sits entirely within one unit). The interpreter’s confidence in the point depth and in stratigraphic units occurring in the locations in which they are interpreted, are also provided. All stratigraphic names and numbers are consistent with GA’s Australian Stratigraphic Unit Database (ASUD), with all interpreted stratigraphic units being current at the time of the interpretation.The interpretations were performed by integrating the magnetic depth estimates generated by CSIRO with supporting multidisciplinary datasets. The types of datasets that support the interpretation are captured in the attributes of each point, in the basis of interpretation field. In addition to this, the reference field includes a link to the magnetic depth estimates data package and summary report. The comments field provides further information about the interpretation (if required). The names of the interpreter(s) for each point are also provided.Interpretation of the magnetic depth estimates was made by integrating the modelled estimates with additional information and supporting datasets including interpreter local area knowledge, literature, surface and subsurface (basement geology, solid geology) geological maps, boreholes, magnetics, airborne electromagnetic interpretation, and other geophysical datasets (including gravity and seismic). Generating depth to magnetic sources is a non-invasive and cost-effective way to quickly estimate the thickness of largely non-magnetic sedimentary cover over magnetic rocks. The attribution of these depth estimates with stratigraphic unit information, consistent with the Australian Stratigraphic Units Database (ASUD), adds value and utility to the depth estimates. In addition to the data in this release, this interpretation is also available for visualisation on Geoscience Australia’s Data Delivery Portal and is stored in, and retrievable from, the Estimates of Geological and Geophysical Surfaces (EGGS) database, also accessible through the Portal. Delivery through the EGGS database means that these depth estimate will have enduring value to a wide range of users in academia, government and industry.