The evolution of an aqueous vapor phase from a simplified tonalite (quartz diorite) magma during intrusion and crystallization has been quantitatively modeled for a stock of square cross-section using the procedure developed for a quartz monzonite composition by Whitney (1975b). Vapor generation from tonalitic compositions may continue from a significant portion of the body to greater depths than was encountered in the quartz monzonite model. In addition, higher initial temperatures in tonalites may allow intrusion and vapor generation at shallower depths than previously determined. This model suggests vapor fractionation may be a viable method of separating economic elements from tonalitic magmas over a greater pressure and depth range than was found for quartz monzonite compositions.

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