¹Dept. Minas, Universidad de Atacama, Avda. John Kennedy 485, Cas. 240, Copiapo Chile

²Institut für Angewandte Geologie, Freie Universität Berlin, Wichernstr. 16, D-1000 Berlin 33B.R.D.

³Hahn-Meitner-Institut für Kernforschung GmbH, Arge Geochemie, Glienicker Str. 100, D-1000 Berlin 39B.R.D.

The hydrothermal alteration of the early and middle stages affected basaltic fragments of a breccia pipe. La and Ce were leached from the rock fragments located at the bottom and at the middle part of the breccia pipe and partly redeposited at the top during alteration. Sm, Eu and Tb were released selectively and the heavy REE behaved as relatively immobile elements. Sericite is the most important alteration mineral for fixing the REE during this stage. The incoming fluids had low REE contents.

The late stage of hydrothermal alteration happened simultaneously with the intrusion of a gabbroic volcanic neck, affecting mainly these subvolcanic rocks. REE patterns of samples from the top and bottom of the alteration zone exhibit roughly parallel trends, but are systematically enriched in REE in comparison to unaltered samples. This enrichment seems to be more intensive at the top of the altered area coinciding with the enrichment of Rb, K and Cu in these rocks. Epidote plays the most important role for fixing this hydrothermal input of REE during the latest stage of alteration.