Abstract
A field study combined with a laboratory study and 3D modeling have been performed in order to decipher the genesis of the Salau deposit W-Au mineralization (Pyrenees, France), one of the most important for tungsten in Europe. Results show the existence of two superimposed ore types, emplaced ca. 10 km depth and within decreasing temperature conditions: a calcic silicates skarn with rare scheelite and disseminated sulphides followed by a mineralized breccia with massive sulphides (pyrrhotite and chalcopyrite dominant), coarse-grained scheelite and gold, representing the main part of the ore mined in the past. This breccia is localized in ductile-brittle shear-zones which crosscut the granodiorite. U/Pb dating on zircon, apatite and scheelite, previously realized, confirmed this polyphase evolution. These two types of mineralization, linked to the emplacement of two successive intrusions as confirmed by sulphur isotopic analysis, granodioritic then leucogranitic, can be classified as belonging to the Intrusion-Related Gold Deposit type (IRGD). The emplacement of the high-grade gold and scheelite breccia was initiated by the progressive localization of the regional deformation in the Axial Zone of the Pyrenees during the Permian within E-W dextral-reverse faults.
Highlights
Results show the existence of two superimposed ore types, emplaced ca. 10 km depth and within decreasing temperature conditions: a calcic silicates skarn with rare scheelite and disseminated sulphides followed by a mineralized breccia with massive sulphides, coarse-grained scheelite and gold, representing the main part of the ore mined in the past
Main results of our work show that: 1 two different types of mineralization coexist at Salau (Fig. 10), a skarn with calcic silicates, fine-grained scheelite and disseminated sulphides developed around La Fourque intrusion emplaced at 800 °C and 3.3 kbar at 295 ± 2 Ma, as well as a vein breccia with massive sulphide, coarse-grained scheelite and gold hosted by the Veronique fault, emplaced at 450 °C and 3.2 to 5.9 kbar at 289 ± 2 Ma
These two mineralizations have mineralogical characteristics, peri-intrusion locations, morphology and emplacement in decreasing temperature conditions which link them to an Intrusion-Related Gold Deposit type (IRGD) model; 2 the coexistence of two types of mineralization results from a magmatic polyphase, like the copper porphyry systems, the source of the vein breccia mineralization with high tungsten and gold content being linked to the emplacement of an evolved leucogranite which ascent in the upper crust through regional EW faults; 3 the evolution of mineralizing phenomenon in the Salau deposit reflects the dynamics of the differentiation at depth of late Variscan magmatism in the axial zone of the Pyrenees
Summary
The origin of fluids involved in the formation of gold-bearing skarns of the Andorra Granite (central Pyrenees, Spain); sulphur isotope data. Fonteilles M, Soler P, Demange M, Derré C, Krier-Schellen AD, Verkaeren J, et al 1989. The scheelite skarn deposit of Salau (Ariège, French Pyrenees). Transpressional tectonic setting during the main Variscan deformation: evidence from four structural levels in the Bossòst and Aston-Hospitalet mantled gneiss domes, central Axial Zone, Pyrenees. Mineralization, stable isotope, and fluid inclusion characteristics of the Vostok-2 reduced W-Cu skarn and Au-W-Bi-As stockwork deposit, Sikhote-Alin, Russia. Pétrographie, minéralogie et géochimie des cornéennes calciques et des skarns dans le gisement de scheelite de Salau (Ariège, France). The perigranitic W-Au Salau deposit (Pyrenees, France): polyphase genesis of a late Variscan intrusion related deposit, BSGF - Earth Sciences Bulletin 192: 22
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