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Cadre géologique des indices sulfurés à Zn, Pb, Cu, Fe du secteur de Gouézec-St-Thois : Dévono-Carbonifère du flanc Sud du bassin de Châteaulin (Finistère).

Abstract : Systematic surveying perfomed during the sixties, in the armorican Massifhas evidenced numerous mineralized occurences and economic deposits (Pb, Zn, Cu, Fe, Ag) in Brioverian and Paleozoic formations. Portes-aux-Moines and Bodennec deposits are early Devonian and are older than the Grès de Landevennec Forma-: tion. Following the discovery of geochimical and geophysical anomalies, the B.R.G.M. decided to set up bore hole on the Torhoat area. Many of them have crossed the mineralized formations. The aim of the present study proposed by the B.R.G.M. is the definition of the mineralization. Mapping and study of drill cores allowed one to identify six formations of which ages vary from Silurian to Carboniferous. Volcanics rocks are of two types : tholeitic rocks of intraplate type, acid rocks of ignimbrite type. The study of geophysical data gives evidences for the presence of heavy axes and allows one to make more exact the boundaries of formations * . The regional tectonometamorphic evolution can be summarized as follows : - The first tectonic phase in contemporaneous with a metamorphic event and with development of schistosity This phase is attributed to the hercynian "phase bretonne". The second phase attributed to the "namuro-westphalienne" phase resulted in strike-slips thrusts. Two stratabound ore bodies are present in two different formations -One is of sedimentary type * -One is linked to acid volcanic rocks and sphalerite dominated. Mapping, study of drill cores and micropaleontologiCal data give evidences for middle to late devonian ages. Following the study of Bodennec and Porte-aux-Moines areas the main conclusion was the presence of only one mineralized level in lower Devonian formations of the Olâteaulin Bassin. The discovery of middle and late Devonian mineralized occurences in the Gouezec-St This area could be a starting point for a new surveying.
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Submitted on : Friday, March 2, 2012 - 10:17:16 AM
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E. Taillebois. Cadre géologique des indices sulfurés à Zn, Pb, Cu, Fe du secteur de Gouézec-St-Thois : Dévono-Carbonifère du flanc Sud du bassin de Châteaulin (Finistère).. Sciences de la Terre. Université Rennes 1, 1987. Français. ⟨tel-00675859⟩

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