Composition-volume relationships of metasomatism

Abstract

The actual gains and losses that take place in metasomatic alterations cannot be obtained without a knowledge of the relationship between composition changes and volume changes that accompany the process. A general set of equations is derived that allows calculations of gains and losses in terms of the chemical analyses and the specific gravities of the unaltered and metasomatized rocks or minerals. When comparing two rocks, it is necessary to know or assume knowledge of either the volume change or the geochemical behavior of one component in order to solve the problem. When N minerals are compared in a single alteration equation, N-1 additional facts or assumptions with respect to volume change or geochemical behavior are necessary. It is not necessary to calculate the structural formulas for the minerals. Examples are given of various techniques for solving composition-volume relationships.

Trace elements should be evaluated in terms of composition-volume relationships because released trace elements are potential ore sources. Trace element data from individual minerals involved in a suspected reaction may be utilized quantitatively as supporting evidence for the reaction.