| The Outokumpu mining district - a metallogenic province about 100 km long x 60 km wide - hosts a Palaeoproterozoic sulfide deposit characterized by an unusual lithological association. It is located in the North Karelia Schist Belt , which was thrust on the late Archaean gneissic–granitoid basement of the Karelian craton during the early stages of the Svecofennian Orogeny between 1.92 and 1.87 Ga (Koistinen 1981). Two major tectono-stratigraphic units can be distinguished, a lower, parautochthonous ‘Lower Kaleva’ unit and an upper, allochthonous ‘upper Kaleva’ unit or ‘Outokumpu allochthon’. The latter consists of tightly-folded deep marine turbiditic mica schists and metagraywackes containing intercalations of black schist, and the Outo¬kumpu assemblage, which comprises ca. 1950 Ma old, serpentinized peridotites surrounded by carbonate–calc-silicate (‘skarn’)–quartz rocks. The ore body is enclosed in the Outokumpu assemblage, which is thought to be part of a disrupted and incomplete ophiolite complex (Vuollo & Piirainen 1989) that can be traced to the Kainuu schist belt further north where the well-preserved Jormua ophiolite is ex¬posed (Kontinen 1987, Peltonen & Kontinen 2004). Outokumpu can be divided into blocks divided by faults and shear zones (Saalmann and Laine, 2014). The aim of this study was to make a 3D lithological model of a small part of the Outokumpu association rocks in the Vuonos area honoring the 3D fault model built by Saalmann and Laine (2014). The Vuonos study area is also a part of the Outokumpu mining camp area (Aatos et al. 2013, 2014). Fault and shear structures was used in geostatistical gridding and simulation of the lithologies. Several possible realizations of the structural grids, conforming the main lithological trends were built. Accordingly, it was possible to build a 3D structural grid containing information of the distribution of the possible lithologies and an estimation the associated uncertainties.
References:
Aatos, S., Jokinen, J., Koistinen, E., Kontinen, A., Korhonen, J., Korpisalo, J., Kurimo, M.,Lahti, I., Laine, E., Levaniemi, H., Sorjonen-Ward, P. & Torppa, J. 2014. Developing deep exploration methods in the Outokumpu Mining Camp area. In: Lauri, L. S., Heilimo, E., Levaniemi, H., Tuusjarvi, M., Lahtinen, R. & Holtta, P. (eds) Current Research: 2nd GTK Mineral Potential Workshop, Kuopio, Finland, May 2014. Geological Survey of Finland,Report of Investigation 207.
Koistinen, T. J., 1981. Structural evolution of an early Proterozoic strata-bound Cu-Co-Zn deposit, Outokumpu, Finland. Transactions of the Royal Society of Edinburgh: Earth Sciences, 72, pp. 115-158.
Kontinen,A., 1987.An early Proterozoic ophiolite—the Jormuamafic–ultramafic complex, northern Finland. Precambrian Research 35, 313–341.
Peltonen, P. & Kontinen, A. 2004. The Jormua Ophiolite: a mafic-ultramafic complex from an ancient ocean-continent transition zone. In: Precambrian ophiolites and related rocks. Developments in Precambrian geology 13. Amsterdam: Elsevier, 35–71.
Saalmann, K.; Laine, E.L, 2014. Structure of the Outokumpu ore district and ophiolite-hosted Cu-Co-Zn-Ni-Ag-Au sulfide deposits revealed from 3D modeling and 2D high-resolution seismic reflection data. Ore Geology Reviews, Volume 62, October 2014, Pages 156-180.
Vuollo, J., and Piirainen, T., 1989. Mineralogical evidence for an ophiolite from the Outokumpu serpentinites in North Karelia, Finland. Bulletin of the Geological Society of Finland 61, 95-112. |