This award supports the dissertation of Milka A. Skewes, a Chilean graduate student who is studying for her Ph.D. under James L. Munoz at the University of Colorado. They will study the fluid transport and deposition of metals in the early stages of development of the porphyry Cu deposits of Los Pelambres, Chile which are similar to those in Butte, Montana. Samples from Los Pelambres with hydrothermal deposition in veins will be collected and the mica minerals from the veins chemically analyzed for the halogens, F and Cl. The vein density at Los Pelambres is low and therefore there is little alteration by later events on the early veins. Halites reside in the mica in these veins and the study of the F/Cl ratio gives a record of the changes in halogen composition of the hydrothermal fluids during formation. The veins are associated with biotitic breccia which forms a link between the host rock and early magmatic fluids. Samples of this breccia available at the University allow a study of the transition from the magmatic to the hydrothermal stage in this deposit. The results of this research on a unique ore deposit which makes an important contribution to the economy of Chile will significantly add to the understanding of mineral ore genesis. This research is particularly relevant to the SDC Program objective of supporting projects related to a developing-country problem and in this case a similar one in the U.S. Munoz has developed the techniques of using biotitic mineral chemistry and has facilities for petrographic studies, fluid inclusion measurements and electron microprobe analysis. Work is underway on samples provided by W. Atkinson. The requested funds will be used for field studies, thin section preparation and microprobe analysis. The breccia zone will be mapped and sampled by Skewes over three-four weeks this winter and sample analysis carried out at Colorado. The results will be valuable to the copper industries in both Chile and the U.S. and there should be a significant contribution to international science and the training of the Chilean student.
