Archean metavolcanics from the Rouyn - Noranda district, Abitibi greenstone belt, Quebec. 2. Mobility of trace elements and petrogenetic constraints.

Qualitative evaluation of altered mafic pillows from this district shows that for low-grade metamorphism the high field strength elements (HFS) Zr, Y, Ti and REE are immobile. Where alteration is extreme, REE are leached and redeposited by carbonate-rich and K-rich metasomatic fluids whilst Zr/Y and Zr/Ti remain unchanged. Rb, Ba, and, to a lesser extent, Sr are mobile at all levels of alteration, but provided certain filters are applied, the original geochemical values of the lavas for the alkaline elements, HFS and REE can be defined. The geochemical variations thus identified for the volcanic series of Rouyn-Noranda district are ascribed to the combination of contamination and fractional crystallization of a primitive tholeiitic magma.