Isocon analysis: A brief review of the method and applications

Isocon analysis [Grant, J.A., 1986. The isocon diagram-a simple solution to Gresens’ equation for metasomatic alteration. Economic Geology 81, 1976-1982.] is a simple and effective means of quantitatively estimating changes in mass or volume or concentrations in mass transfer. It may be accomplished graphically by plotting an altered composition against an original composition with no significant manipulation of the data. Species that have remained immobile in the process define the isocon, which is a straight line through the origin. The paper reviews suggested means of identifying immobile species, graphical, statistical or by computation, and suggests that whatever the means, the geochemical characteristics of the species and of the process should be considered. It is shown that scaling of data need not affect the choice of immobile species or the slope of the isocon. Applications of the method to hydrothermal alteration, replacement, migmatites, shear zones, paleosols, silcretes, sedimentary exhalative deposits and fumarolic deposits are briefly reviewed.