Authors / CoAuthors
Williams, N.C. | Lyons, P. | Lane, R. | Peljo, M.
Abstract
Knowledge of the spatial and temporal relationships between fluid flow, the generation of structures, and crustal architecture is essential to understanding a mineral system. In regions dominated by cover, such knowledge strongly depends on interpretation of potential field data. Forward modelling and inversion of cross-sections, based on solid geology maps, provide valid approximations of 3D crustal geometries but reliability of interpolation decreases away from section planes. Models of crustal architecture are more rigorously produced by 3D inversion. Inversion programs derive physical property distributions that reproduce potential field observations consistent with a set of model parameters and geological constraints. The inversion techniques used in this study are based on the potential field inversion software, MAG3D and GRAV3D, developed at the University of British Columbia-Geophysical Inversion Facility (UBC-GIF). These programs have largely been used at the deposit-scale, but we modified the approach and settings for use at a regional-scale. The volume of crust chosen for study, centred on the Olympic Dam deposit, is 150 kmx 150 kmy 10 kmz. It comprises Archaean granulites, Palaeoproterozoic orthogneiss and metasediments (including BIFs), and early Mesoproterozoic felsic and mafic intrusives and extrusives. Zones of Fe oxide alteration are distributed throughout the upper parts of the crustal volume. Because a buffer is required to minimise edge effects, the volume for inversion is expanded to 198 kmx 198 kmy 18 kmz, discretised into 1 kmx 1 kmy 0.5 kmz cells. A series of trial inversions were run on a desktop PC with a 2.0 GHz processor and 2 GB of RAM. The initial trials were designed to investigate the feasibility of doing regional-scale inversions and to show where development of methods and support software were needed. For tractable computation, it is necessary to split each volume into a number of overlapping tiles that can be processed independently then rejoined. Even so, runs took up to 40 hours. The time elapsed can be substantially reduced if processing is performed as a distributed application across a network with each PC dedicated to a single tile. The inherent non-uniqueness of potential field inversion means that, even after some models have been rejected on 'geo-logical' grounds, a number of models consistent with the solid geology and 2D cross-section forward modelling, inter alia, will remain. Tests that prove or disprove the models may be devised, but actual physical testing may not be practical. However, we can make probabilistic determinations of the distribution of Fe oxide alteration, which may be used to map likely fluid pathways and guides to Fe oxide Cu-Au ore. Such predictions are amenable to testing through current exploration practice.
Product Type
nonGeographicDataset
eCat Id
68350
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
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Keywords
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- PowerPoint
- ( Theme )
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- geochemistry
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- AU-SA
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_External
Publication Date
2004-01-01T00:00:00
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geoscientificInformation
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[-31.0, -30.0, 136.5, 137.25]
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