Ion-probe determination of rare earths in allanite

Abstract

The epidote-group mineral allanite is characterised by a total RE content in the region of 20 wt.%, with light RE much more abundant than heavy. Only a few of the RE in allanite are within the range of electron-probe analysis, hence the determination of the complete abundance pattern has hitherto required physical separation and bulk analysis by a technique such as INAA. An alternative possibility is ion-probe analysis, which has been applied here to the determination of all 14 RE in single allanite grains in polished thin sections. Satisfactory agreement with the limited electron-probe data for RE is obtained and chondrite-normalised plots of ion-probe data are reasonably smooth. Ion-probe analysis thus appears to have considerable potential for determining RE in allanite and other RE-containing phases, with significant advantages over other available methods.