Abstract

This study complements the isocon method of Grant (1986) for describing mass transfer during metasomatic alteration by introducing a normalization solution to illustrate sequential mass transfers among multiple progressively altered geologic samples. The principle of the normalization solution involves adjusting all the isocons (defined by unaltered and altered sample pairs) to a single unified isocon without modifying the relative concentration changes of the corresponding components. When the normalization solution is applied to a sequence of progressively altered samples, an immobile component is defined or assumed, and the measured concentrations of all components in all altered samples are normalized by multiplying the corresponding normalizing factors; these factors are calculated using the concentration data for the immobile component. The normalized compositions of the altered samples are then plotted against the original measured composition of the unaltered sample in a single normalized isocon diagram that illustrates all the mass changes for a series of progressively altered samples.

This study applies the above approach to a set of progressively altered hydrothermal quartz-feldspar-porphyries at the Millenbach Cu-Zn mine (Riverin and Hodgson, 1980). The graphically displayed result indicates that the normalized isocon diagram can illustrate not only the mass changes of any component between any two altered zones, but also mass transfer trends of all components in the entire alteration zone. The normalization solution can be applied to any group of progressively altered geologic samples.

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