Dissolution-precipitation processes induced by hot water in a fractured granite; Part 1, Wall-rock alteration and vein deposition processes

Petrographic observations in zoned alteration haloes around hydrothermal veins cutting the La Peyratte granite, SE Armorican Massif, allowed the determination of time-space relationsbetween dissolution of primary minerals (biotite, oligoclase) and crystallization of secondary ores (chlorite, albite, phengite, fluorite, pyrite and illite-smectite). The change in bulk composition of the rock is relatively weak. During the alteration process, the open space of the fracture is progressively sealed while a newly formed porosity appears inside the wall-rock. The development of the alteration zoning around the vein is a time- dependent process controlled by a sequence of interrelated mineral reactions.