HRTEM STUDY OF THE CHLORITIZATION OF MICAS IN THE TALC-CHLORITE DEPOSIT AT TRIMOUNS (PYRENEES, FRANCE)

We have studied by high-resolution transmission electron microscopy (H RTEM) four rock samples resulting from the metasomatic alteration of p egmatite in the Trimouns talc-chlorite deposit. Two co-existing ways o f mica chloritization can be distinguished: dissolution-recrystallizat ion for muscovites and phlogopites, and ''solid-state'' transformation for other phlogopites. The latter occurs according to the two transfo rmation mechanisms usually described in chloritization phenomena. Chem ical microanalyses reveal the presence of potassium, probably associat ed with the ''brucite-like'' layer, in chlorites resulting directly fr om the transformation of micas. Little or none of this potassium is fo und in the later-formed chlorites constituting the ore, it is therefor e considered as a probable geochemical tracer of older micas.