Bull. Minéral.
(1987), 110, 249-259
U-Th-REE mobility during albitization and quartz dissolution in granitoids : evidence from south-east French Massif Central
by Michel CATHELINEAU CREGU and GS.C.N.R.S.-CREGU, B.P. 23, 54501 Vandœuvre-les-Nancy Cedex, France.
Mobilité de U, Th et des Terres Rares lors de /’ albitisation et de la dissolution du quartz dans les granitoïdes : l’exemple du Sud-Est du Massif Central français.
Introduction
Most of the hydrothermal uranium deposits located within the Hercynian belt are spatially associated with peraluminous granites (Figure 1). Among these deposits, two types are com¬ monly distinguished : the vein-type deposits re¬ presented by intra to perigranitic veins of South Britanny, Vendée (Cathelineau, 1981, 1984), Forez (Cuney, 1978) and Limousin (Leroy, 1978) and the deposits related to strong sub¬ solidus alterations of granitoids. Such alterations
consist mainly in total leaching of quartz. This causes a significant increase in the rock permea¬ bility (Leroy, 1978 ; Cathelineau, 1986) ; the altered rocks, so-called “episyenites” in french mining terminology, subsequently play an im¬ portant rôle as reservoir rocks for ores and may be considered as preferential circulation pipes for hydrothermal to supergene fluids.
Fundamental questions with respect to these episyenitic pipe deposits may be formulated as follows :
@ Société française de Minéralogie et de Cristallographie, Paris, 1987.
