Regional dome evolution and its control on ore-grade distribution: Insights from 3D implicit modelling of the Navachab gold deposit,Namibia |
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| Institution: | 1. School of Earth, Atmosphere and Environment, Monash University, Australia;2. Orefind Pty Ltd, Fremantle, Australia;1. Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves, 9500, Bairro Agronomia, 91501-970 Porto Alegre, Rio Grande do Sul, Brazil;2. Departamento Nacional de Produção Mineral, Superintendência do Mato Grosso do Sul, Rua General Odorico Quadros, 123, 79020-260 Campo Grande, Mato Grosso do Sul, Brazil;3. Geological Survey of Brazil (CPRM), SUREG-GO, Rua 148, 485, Setor Marista, 74170-110 Goiânia, Goiás, Brazil;1. Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Science, Peking University, Beijing 100871, China;2. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi''an 710069, China;3. ARC Centre of Excellence in Ore Deposits (CODES), School of Physical Sciences, University of Tasmania, Hobart 7001, Australia;1. School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia;2. Phillipsgold Pty Ltd, PO Box 3, Central Park, Victoria 3145, Australia;3. Department of Earth Sciences, University of Stellenbosch, Stellenbosch, South Africa |
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| Abstract: | We introduce a novel approach to analyse and assess the structural framework of ore deposits that fully integrates 3D implicit modelling in data-rich environments with field observations. We apply this approach to the early Palaeozoic Navachab gold deposit which is located in the Damara orogenic belt, Namibia. Compared to traditional modelling methods, 3D implicit modelling reduces user-based modelling bias by generating open or closed surfaces from geochemical, lithological or structural data without manual digitisation and linkage of sections or level plans. Instead, a mathematically defined spatial interpolation is used to generate 3D models that show trends and patterns that are embedded in large drillhole datasets. In our 3D implicit model of the Navachab gold deposit, distinctive high-grade mineralisation trends were identified and directly related to structures observed in the field. The 3D implicit model and field data suggest that auriferous semi-massive sulphide ore shoots formed near the inflection line of the steep limb of a regional scale dome, where shear strain reached peak values during fold amplification. This setting generated efficient conduits and traps for hydrothermal fluids and associated mineralisation that led to the formation of the main ore shoots in the deposit. Both bedding-parallel and highly discordant sets of auriferous quartz-sulphide veins are interpreted to have formed during the later lock-up stage of the regional scale dome. Additionally, pegmatite dykes crosscut and remobilise gold mineralisation at the deposit scale and appear to be related to a younger joint set. We propose that kilometre-scale active folding is an important deformation mechanism that influences the spatial distribution and orientation of mineralisation in ore deposits by forming structures (traps and pathways for fluids) at different preferred sites and orientations. We also propose that areas that experience high shear strain, located along the inflection lines of folds can act as preferred sites for syn-deformational hydrothermal mineralisation and should be targeted for regional scale exploration in fold and thrust belts. Our research also suggests that examination of existing drillhole datasets using 3D implicit modelling is a powerful tool for spatial analysis of mineralisation patterns. When combined with fieldwork, this approach has the potential to improve structural understanding of a variety of ore deposits. |
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