The boundary between the Central Iberian and the Ossa-Morena zones of the Iberian peninsula is marked by the Badajoz shear zone along which movements were focused during the Hercynian orogeny. To the north of the shear zone, in the La Codosera area, auriferous veins are located in a series of late Hercynian north-south- to northeast-southwest-trending faults which are antithetic to the main shear zone. The passage of dilute CO 2 -rich fluids at 350 degrees to 400 degrees C and 2,800 to 3,300 bars along these faults resulted in mineralization where dilatant structures, for example, offsets, intersections, or fault terminations developed within black slate lithologies. By combining geological and geochemical systematics, including vein orientation, lithology, and fluid chemistry, with remotely sensed fracture data, a testable exploration model for the region has been developed.

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