The significance of europium anomalies in the REE spectra of granites and pegmatites,Mont Laurier,Quebec

Negative Eu anomalies in the REE spectra of granitic rocks are usually interpreted as evidence of earlier separation of a mineral phase such as plagioclase. Our study of the behaviour of the REE, and of U and Th, during late stage alteration of granites and the formation of pegmatites, suggests an alternative means for producing Eu anomalies. Albitization of earlier-formed plagioclase has depleted the granites in Eu and enriched the pegmatites in this element. This process is linked to the mobilization of U in the granites which is dependent on the oxidation state of the fluids. A systematic correlation between the ratios $\text{Eu}\text{Ce}$ and $\text{U}\text{Th}$ leads us to suggest a similar explanation for irregularities in the abundances of Ce and other rare-earths in the REE spectra of these rocks.We suggest that anomalous behavior of Eu in other environments or processes such as the alteration of basalt and the formation of certain ore deposit types may be caused partly by this mechanism.