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Salsigne - Peyrebrune, Fontaine de Sante, Ramele |
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France |
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Au As Bi Ag Cu
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Super Porphyry Cu and Au
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The Salsigne mesothermal Au-As-Bi-Ag-Cu deposit is located in the southern part of the French Massif Central, 15 km north of Carcassone and 100 km east of Toulouse in France.
The Salsigne mine has been one of the most important gold producers in Western Europe. The Salsigne district includes about 20 deposits and showings distributed over an area of about 12 x 8 km. The deposits of the district show have a zonal distribution, with some in the outer part having been mined for Pb, Zn, Cu and F. From the Roman period to the end of the 19th century, Fe, Cu, Pb, Ag and As weresporadically exploited. Gold was first discovered in 1892 in the Roc des Cors showing and later in the pyrite-arsenopyrite ore of the old Salsigne iron mine. Between 1960 and 1981 Salsigne has produced 104 tonnes of Au, 249 t of Ag, 30 200 t of Cu, 1706 t of Bi, 397 000 t of As and 454 000 t of sulphuric acid (from 1961 to 1991). The gold production of the other deposits in the district has not exceeded a few hundred kilograms.
The Salsigne deposit lies within the Montagne Noire, part of the southern external zones of the French Variscan orogen, which consists of a pile of thrust nappes stacked on the autochthonous Axial zone of the Montagne Noire.
The deposit is located within and close to the lowest unit, the Fournes nappe which is less than 500 m thick and intercalated between more
competent terranes, with the large Minervois nappe above and the autochthonous Axial zone below. The host rocks have been intensely deformed by several stages of folding, shearing, and brittle faulting.
The host to the deposit comprises siliciclastic and carbonate rock. The main deposits of the Salsigne district have been classified into four morphological types: i). vein-type orebodies in NNWSSE and WSWENE fractures, ii). stockworks in some beds of the Marcory sandstones, iii). replacement of carbonates by massive sulphides, and iv). orebodies along thrust planes, at the base of the Minervois nappe, in minor thrusts within the Fournes unit, at the base of the Fournes nappe, and in the shear zone at the base of Combe Bour-rel thrust slice.
Most gold occurrences in the Salsigne district occur as two belts of veins hosted in north-south faults. The first is located within an 8 km long belt of folds, while a second 12 km long WSWENE belt of small mines and showings occurs near the contact between the Axial zone and the Fournes nappe, hosted in both autochthonous and allochthonous units. The alluvial gold showing of Galinié and several gossans extend this belt for a further 50 km ENE from Salsigne. The most productive veins are located at the intersection of these two belts, hosted in the lower Cambrian formations of the Fournes nappe. From west to east, they are the 700 m long Peyrebrune, the >1200 m long x 350 m up dip Fontaine de Santé and the 900 x 300 m Raméle vein. These orebodies, which have have grades in the range of 10 to 50 g/t Au, have accounted for about half of the gold from Salsigne. Veins are wide in sandstone and dolomite and pinch out rapidly upward in the green pelites and downward into the Devonian limestone. The Fontaine de Santé and Ramčle ore-bodies, hosted in strongly silicified and mineralised country rocks, have a complex structure consisting of veins that are tens to a few hundreds of metres in length and a few tens to 100 m vertical extent, forming an en echelon network, both vertically and laterally. The total thickness of these complex structures varies from a few to tens of metres.
Nine hydrothermal events, commonly separated by tectonic events, have been recognised within the deposit. The first four stages, which were responsible for stockwork, massive, and disseminated mineralisation, were controlled by ductile to ductile-brittle structures synchronous with the emplacement of the nappes. These included: i). arsenopy-rite-pyrrhotite-gold associated with biotite, ii). quartz-muscovite alteration, iii). massive sulphides (arsenopyrite-pyrrhotite-pyrite) and gold associated with chlorite, and iv). feldspathization.
The succeeding five stages were controlled by brittle tectonics that frequently reactivated earlier structures, and include barren silicification and quartz veins followed by four stages of sulphide precipitation separated by fracturing.
The hydrothermal system, which was probably related to late Variscan magmatism, was initiated when the tectonic regime changed from ductile-brittle to brittle conditions and from a compressional to an extensional regime. Fluids were channeled by a shear mesh created at the base of the nappe pile and in the upper part of the autochthonous terranes by the nappe development. The Salsigne deposit is located along a major (>100 km) shear zone at its intersection with transverse brittle structures and sheared fold structures.
The most recent source geological information used to prepare this decription was dated: 2006.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Demange M, Pascal M L, Raimbault L, Armand J, Forette M C, Serment R and Touil A, 2006 - The Salsigne Au-As-Bi-Ag-Cu Deposit, France : in Econ. Geol. v101 pp 199-234
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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