Le batholite composite du Veynazes (Cantal, France); petrographie, geologie et geochimie; relations avec le gisement tungstifere de Leucamp

Abstract

F. Abstract. - The Veynazes granite is a late Variscan batholith that intrudes the epimetamorphic rocks of the Chataigneraie series. In the NE part of the batholith, near the Leucamp tungsten ore deposit, the batholith is characterized by a complex series of pluton : the (( black granite )) appears as small bell-shaped bodies, frequently exhibiting chilled margins; its peraluminous character (garnet destabilized in biotite - corundum - sillimanite) suggests a crustal contamination at a deep level. This first unit is disrupted by the (( main granite D, a common porphyritic granite which constitutes the greater part of the massif and seems to be buried as a strip beneath the schists to the North. Finally, the (( granite n, a porphyritic, microgranular granite, appears as twisted, more or less concentric veins; the existence of a hidden granitic apex is suggested. Geochemical data are consistent with the hypothesis of consanguinious magmatism for these different units. The detailed discussion of these level by fractional crystallization and crystal accumulation, with later hydrothermal alterations (greisenization and sericitization). The economic metallic elements are concentrated during these different stages; the available geochemical data are not sufficient to define unambiguously the formation stage of the mineralizing fluids. The most likely hypothesis is that this phenomenon took place during the last evolution of the ochre granite. I data indicates that the granitic suite has evolved at two levels : (1) at depth by a differentiation process binding the different units; (2) at the emplacement