Trace element analyses of melt inclusions as probes for the evolution of Bolivian tin porphyry deposits

Micron-sized melt inclusions (MI), trapped in host quartz crystals from roc ks of magmatic systems, probe the evolution of ore deposits. PIXE in combin ation with NRA of light element concentrations provide a nearly complete da tabase for geochemical characterisation. Tin deposits are usually associate d with highly fractionated granitic magmatism. The tin porphyry deposits of Bolivia however have only a moderately fractionated bulk rock geochemistry . The investigation of MI revealed high degrees of fractionation with compo sitions similar to tin granites. It is supposed that the bulk rock geochemi stry must be interpreted as the product of magma mixing. Unexposed granitic portions, represented by MI, provide magmatic vapour phases for hydrotherm al alteration and mineralisation. (C) 1999 Published by Elsevier Science B. V. All rights reserved.