An attempt to correlate non-predicted variations of distribution coefficients with mineral grain internal inhomogeneity using a field example studied near Sudbury, Ontario

Abstract

This study is an attempt to understand anomalous distribution coefficient values in the light of the fact that many metamorphic minerals are internally inhomogeneous. A number of models are proposed to show how the non-sytematic variation of distribution coefficient values may be produced by partial re-equilibration (and/or reaction) of ions between minerals and which samples would give the values most closely corresponding to those expected from the index minerals. It is suggested that the irregularity of the distribution coefficients is due to chemical variations of the bulk chemistry, both from handspecimen to handspecimen and in different parts of a single handspecimen. Samples from a field area containing the Staurolite-Quartz, Kyanite-Muscovite and Sillimanite-K feldspar subfacies of the Almandine Amphibolite facies, located near Sudbury, Canada, were submitted to mineral separation and analysis as well as electronmicroprobe analysis. Despite the fact that much scatter occurs between distribution coefficients due to partial re-equilibration, the values of Mg and Fe+2 of D biotite/Garnet decrease and Mn and Ca increase recognizably across the area. Generally, the model(s) proposed seem applicable to the field data presented.