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Eevaliisa Laine, Geological Survey of Finland (Finland)
Kerstin Saalmann, Geological Survey of Finland (Finland)
Gabriel Courrioux, BRGM (France)
Esko Koistinen, Geological Survey of Finland (Finland)
Jouni Lerssi, Geological Survey of Finland (Finland)
Juhani Ojala, Geological Survey of Finland (Finland)
Nicole Patison, Southern Cross Group (Finland)
Noora Salminen, Helsinki University of Technology (Finland)
Timo Tervo, Geological Survey of Finland (Finland)
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The Keretti and Vuonos Cu-Co-Zn-Ni sulfide ores in eastern Finland are hosted by the distinctive Outokumpu assemblage, which comprises serpentinized peridotite massifs that have been altered and metamorphosed to quartz rocks, Cr-silicate skarns and carbonate rocks. The Outokumpu assemblage, and the enclosing metamorphosed black shales and turbidites belong to an allochthonous nappe complex emplaced onto the Karelian Craton margin during the early stages of the Svecofennian Orogeny. The Keretti orebody, which was discovered in 1910, contained 28 Mt of ore, of which 23 Mt was mined before closure in 1989. The Vuonos orebody, discovered in 1965, some10km NE of Keretti, contained 6 Mt of ore of which 4 Mt was extracted.
The 3D visualization of the Keretti and Vuonos orebodies has been undertaken as part of a 3D/4D development project, the aim of which is to study 3D/4D modelling methods and principles, especially in visualizing and modeling complicated geological structures . The Outokumpu ore was chosen as a case study because of a long history of research, and hence, availability of data from several sources.
The visualization has been done at three different scales. (1) The orebodies, which are only several meters thick, were modeled using drillhole data (from the GEOMEX-project at GTK) and the traditional section-by-section interpretation method. This seems to be the best way to delineate these thin and irregularly shaped orebodies, which were found to be rather continuous, though locally truncated by vertical faults. The triangulation into solid models was made using Surpac mining software. (2) The Outokumpu assemblage enclosing the ore bodies, typically about 100 m thick, was visualized from georeferenced maps and sections, based on structural geological interpretations published by Koistinen in 1981. The software used in this case was Geomodeller, which enabled the use of constraints from structural observations, even though it was not possible to define a reliable stratigraphy within these complexly deformed rocks. The stratigraphy was therefore defined using the present sequence of rock layers. The resultinig model appears structurally realistic. (3) The ore and Outokumpu assemblage models were then combined (together) with the seismic reflection sections from the Outokumpu region, to a depth of 3000 m, using Gocad software; results illustrate the structural position the Outokumpu ore zone within its wider geological context.
We conclude that the use of different approaches and softwars are needed in a comprehensive data capture and 3D visualization of complex geology, such as present in the Outokumpu district. It is also evident that purely technical visualization without involving geological ideas and interpretations is impossible. The Outokumpu 3D model for example, depends on interpretations of the regional deformation and alteration history; a different interpretation of the geological history could lead to a quite different 3D model.
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