Automated subsampling of geological maps as inputs of 3D geological multiscale modelling: Yalgoo–Singleton Greenstone Belt example

Joshi, Ranee1,2, Jessell, Mark1,2, Lindsay, Mark1,2 and Ivanic, Tim, J.3

 1 Centre of Exploration Targeting, School of Earth Sciences, University of Western Australia, 35 Stirling Highway, Crawley 6009 Western Australia; 2 Mineral Exploration Cooperative Research Centre (MinEx CRC), School of Earth Sciences, University of Western Australia, 35 Stirling Highway, Crawley 6009 Western Australia; 3 Geological Survey of Western Australia, Mineral House, 100 Plain Street, East Perth 6004 Western Australia

To maximize the meaningful geological information provided by three-dimensional (3D) geological models, we propose producing dynamic geological models that allow data to be subsampled and dynamically visualized to better answer specific scale-dependent geological questions. Given that most geological questions are scale-dependent, building a multiscale geological model would seem to be desirable. Achieving this aim requires developing workflows that properly subsample various forms of geoscientific data (e.g. lithology, stratigraphy, structure, geophysics) and dimensionalities (0D: point observations, 1D: drilling data, 2D: lines and polygons on maps and sections) to be able to use them appropriately as inputs for 3D geological modelling.

In this contribution, we present the preliminary results of subsampling 1:500 000 knowledge-rich geological data and their resulting multiscale models. The geological data, in the form of geological maps and structural measurements, were generated from recent regional geologic mapping of the western Youanmi Terrane, Yilgarn Craton, Western Australia by the Geological Survey of Western Australia (GSWA). The case study area for this work covers the Yalgoo–Singleton Greenstone Belt (YSGB), a mineralized, lithologically diverse and structurally complex area with regions of sparse and clustered data. The multiscale models are built through systematically subsampling the geological maps (ESRI shapefile format), to ensure 3D samples were representative and preserved heterogeneity. The geological maps are subsampled based on a combination of the stratigraphic hierarchy (derived from the GSWA Explanatory Notes System), prospective units and petrophysical contrasts. The polygonal features are upscaled by simplifying the geometry however, preserving the crucial vertices critical to preserving the shape and topology. The structural measurements (GSWA WAROX database) are subsampled depending on the scale of interest.

The resulting subsampled data is used as inputs into modelling applications. Multiple 3D geological models were built; 1:2 500 000 using craton/terrane information; 1:500 000 using rock group and suite levels and at 1:100 000 using rock units. These models show that stratigraphic filters maintain meaningful information at most scales. However, we show that particular combinations of filters is desirable. The suite of scaled models show that vertex simplification with a point reduction of up to 86% on the polygons maintains the geometric and geological constraints of the greenstone belts and plutons. The scaled geological models were built with minimal user-provided input, and stayed true to the digital geoscientific inputs that describe the geology at all three scales. Our results from the 1:2 500 000 scale model indicate a need for additional depth constraints in the southwestern Youanmi Terrane (e.g. deep-reflection seismic data).

Preliminary results show the proof-of-concept that this workflow of subsampling geological vector maps effectively selects and identifies relevant geological features, aggregates features into hierarchical stratigraphic groups, simplifies 2D vectors by vertex reduction and extracts topological information, basal and intrusive contacts. The tools developed to subsample geological inputs for multiscale modelling are compiled as a part of the Python package map2loop.

Keywords: 3D geological modelling, multiscale analysis, subsampling, Yalgoo–Singleton Greenstone Belt, Youanmi Terrane, stratigraphy

We acknowledge the support of the MinEx CRC and the Loop: Enabling Stochastic 3D Geological Modelling (LP170100985) consortia. The work has been supported 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 2020/42.


Biography

Ranee is a PhD candidate in the Centre for Exploration Targeting working with Mark Jessell, Mark Lindsay, Nicolas Thebaud and Tim Ivanic. She works on developing subsampling workflows to be able to automate multiscale 3D geological modelling. This project is a collaboration between the Loop and MinEx CRC consortium.

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.

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