Ore metamorphism in sulfide mineralizations from the Cinco Villas Massif (Western Pyrenees, Spain)

Abstract

Massive stratiform and vein-type Zn-Pb-Fe-F-Ba mineralizations, associated with Namuro-Westfalian metasediments, occur in the Cinco Villas Paleozoic massif. These mineralizations were previously considered to be the result of the precipitation of hydrothermal fluids liberated by the Aya granitic intrusion. However, the orebodies show several metamorphic features typical of similar mineralizations described in the geologic literature, suggesting a preintrusive genesis of probably exhalative sedimentary nature.The sedimentary sequence consists of two formations: (1) the Aranaz limestones, dated as Namurian, and (2) a Westphalian schistose formation, composed of pelitic, semipelitic, and psammitic rocks, with some conglomeratic tuffs, albite-rich laminae, tourmalinites, and interlayered basic sills. These materials have been affected by the Hercynian deformation and a low-pressure regional metamorphism ranging from anchizone to biotite zone. Mesoscale structural data and microscopical observations suggest three periods (D 1 , D 2 , and D 3 ) of progressive deformation, accompanied by fracturing and shearing phenomena. D 2 , the main deformation, developed isoclinal to recumbent folds and a regional foliation (S (sub 0-2) ). The more important metamorphic traits are produced during this deformation, and at the same time, the Aya granitoid intrusion was emplaced.The orebodies exhibit a lenticular to tabular morphology concordant with host rocks or forming a variable angle with S . Sphalerite, galena, and different proportions of pyrite, pyrrhotite, and chalcopyrite represent the major sulfide minerals. Quartz, carbonates, fluorite, and barite are the main gangue minerals. Regional deformation and metamorphism have caused uneven but important effects on the geometry and primary textures of the orebodies. However, there is evidence of some premetamorphic textures, such as debris-flow breccias, slump folds, and particularly in pyrite, framboidal relicts and colloform textures. Folding, foliation, transposition, shearing, durchbewegung, and vein-type ores are common metamorphic features in ore layers where the sulfides and gangue minerals have responded differently to deformation. Thus, textures in pyrite denote a fundamentally brittle behavior, but in some cases there is evidence of cataclastic flow, kinking, deformation bands, and recrystallization. In contrast, sphalerite, galena, chalcopyrite, and pyrrhotite exhibit different textures indicating that dislocation glide and creep, mechanical twinning, and recrystallization have generally been important mechanisms. These processes suggest deformation under temperatures <400 degrees C which is consistent with the degree of metamorphismon in the host rocks. Micro- and mesoscale remobilization of gangue and ductile sulfides due to a mixture of both mechanical and chemical processes is a generalized phenomenon in all deposits; probably a major-scale remobilization has been operative. This would explain the existence of important vein-type mineralizations in this region.