Geochemical aspects of the uranium occurrences of Macusani, Puno (Peru)

The ignimbrites of the Quenamari formation, of Mio-Pliocene age, are found in graben-type tectonic depressions in the south-east of Peru, and their uraniferous potential is promising. They are peraluminous, occur in an unusual mineralogical association with andalusite, sillimanite and muscovite; and are enriched in volatile, trace and metallic elements. The uraniferous mineralization is mainly uranium with sulphides (pitchblende); phosphuranylite-renardite, autunite, meta-autunite and gummite have also been identified, and the presence of phosphorus in the uranium oxide (pitchblende) has been detected with the microprobe. These rocks are the result of partial fusion of the crust material in back-arch position in the Andean geotectonic structure. (author)