Controles structuraux de la mineralisation aurifere de la veine consuelo, Pataz, La Libertad, Perou

This MSc. project, sponsored by Poderosa Mining S.A., had for objective to identify the various geological features associated with the early stages of vein formation and to characterize the deformation along the evolution of the hydrothermal system. The ultimate goal was to provide a better understanding of structural controls and mecanisms for vein formation as well as to propose a comprehensive emplacement model.;The Poderosa mines are located along the eastern Andean Cordillera within the Pataz Province of northern Peru. The lodes are structurally-controlled and display characteristics previously interpreted as typical to those of orogenic-type. The gold-bearing veins (312 Ma 40Ar/ 39Ar) are located along the western margin of the early-carboniferous Pataz Batholith (329 Ma). This calc-alkalic intrusion forms a 90 km long N-S striking dioritic to monzogranitic elongated body. The veins are typically associated with brittle-ductile shear zones oriented parallel to the NNW lithospheric thrust-fault of the Maranon valley. The veins commonly exhibit km-scale vertical and lateral continuity with m-scale thicknesses.;The Consuelo vein is a N-striking planar structure dipping roughly 45° to the east that can be followed over 1km in length and 600m in depth. Thickness varies from a few cm up to 5 m in the centre of the oreshoot. The vein generally fills one or several parallel fracture zones which are also noted away from the main stopes. The lode (15-20 g/t Au) displays a multi-stage sulphide-rich mineral assemblage (Py, Sp, Ga, Aspy, Cp) with quartz, carbonates, electrum and gold.;Crack-and-seal laminations, hydrothermal breccias, open-space filling comb and void textures typically characterized weakly deformed veins. Despite strike and dip variations, these textures are ubiquitous suggesting multiple opening vectors. Strongly deformed veins display ribbon-textures, shear bands and foliated host rocks. Features such as unfoliated rock fragments and asymmetric shear intensity along the vein margins are compatible with "pre-deformation" veins overprinted by late-deformational events.;The proposed model to explain vein emplacement comprises extensional veins formed along pre-existing fracture sets in a high-fluid pressure environment. Additionally to vein-parallel fractures, the lithological contact between the dioritic host and a hornblendite unit may also represent an important structural control. Several dip-parallel oreshoots exist at Consuelo and their long axis, along with the preferential orientation of high-grade Au samples, corresponds to the intersection of the vein with subvertical east-trending conjugate faults. Additional factors including pervasive chloritic alteration, hydrothermal-filling and anomalous gold values suggest the faults may have provided an important pathway for fluid transport.