Saturation versus undersaturation of granitic melts in tin, tungsten and molybdenum oxides is discussed on the basis of experimental data. Results of dry and hydrothermal experiments are evaluated under the assumption of ideal solubility of Sn, W and Mo oxides in granitic melts. A conservative interpretation arrives at concentration levels of _>1000ppm SnO2, WO 3 and MoO 3 respectively, considered as the maximum solubility of these components in granitic melts at 750~ -800 ~ Such values are never reached in natural granites unaffected by hydrothermal alteration and therefore even highly evolved granites are expected to be undersaturated in these metals. Consequently cassiterite and scheelite are neither common liquidus minerals of ore-bearing granites nor restite minerals from partial melting events.
Highly evolved granites of specialized composition (high Si02, low alkaline earth and iron oxide contents) are parental rocks of some tin, tungsten and molybdenum deposits of magmatic affiliation. Recent advances in the knowledge of their chemistry raised the question whether such specialized granites or rhyolites caused the concentration of metals into ore deposits. Among the principal questions which remain unanswered are whether orebearing granites became saturated or undersaturated in tin, tungsten and molybdenum, and if the data on Sn, W and Mo contents in granites are comparable with the results of experimental studies.
Recent experimental studies, however, indicate considerable problems in attaining equilibria in even long lasting runs at P-T conditions of the upper crust. The present study compares the results of runs carried out by different techniques to estimate the ranges of tin, tungsten and molybdenum oxides' saturation in granites under geologically realistic conditions. 206 Rb Cs