Geological, mineralogical and geochemical constraints on the genesis of the Chinipi arsenopyrite-pyrite-invisible gold vein (Canfranc, Central Spanish Pyrenees)
Mateo, Ester; Fanlo, Isabel; Subías, Ignacio; Recio, Clemente; Billström, Kjell
published: Sep 1, 2010
ArtNo. ESP154018703006, Price: 29.00 €
The sulphidic ore deposit of Chinipí, hosted by early Carboniferous limestones, is related to a Variscan thrust affecting Devonian siltstones and Carboniferous limestones. Locally, the geology is marked by late Variscan to early Alpine tectono-magmatic episodes that gave rise to calc-alkaline granites and their extrusive equivalents and subsequent alkaline volcanics. No regional metamorphism has affected these rock suites. Two mineral assemblages have been distinguished: the main one consisting of pyrite, arsenopyrite, with minor chalcopyrite and pyrrhotite and rare native bismuth, bismuthinite, galenobismutite, kobellite, argentite and sphalerite and a second one consisting of chalcopyrite, tennantite and proustite. Trace contents of invisible gold are also present in the first assemblage. The ores show cataclastic textures, reflecting intense deformation. The host rocks exhibit an alteration halo consisting of carbonates at the hanging wall and chlorite at the footwall. According to arsenopyrite geothermometry, vein formation occurred at around 405 °C. Invisible gold along with the absence of regional metamorphism, and a spatial connection with magmatic episodes make this ore deposit different to other Au-bearing deposits in the Pyrenees.The available isotopic data hint to a strong magmatic component of the mineralizing fluids, which likely gained their mineralizing components from the Variscan basement. In the preferred model the Chinipí vein formation was favoured by a transtensional regime during the late-Variscan times, which also promoted magmatic episodes. Hence, this ore-forming process may be considered as an integral part of the transition from late Variscan to Alpine tectonics.