Chemical and Petrographic Variations In Rhyolitic Zones in the Noranda Area, Quebec

CIM Bulletin, Vol. 70, No. 784, 1977

L. Larson, now at Thompson, Manitoba, and G. R Webber, Associate Professor, Department of Geological Sciences, McGill University, Montreal, Quebec

Rock samples were taken, away from zones of mineralization, from seven sections of five rhyolitic zones as defined by Spence (1967) in the Noranda area. The purpose of the investigation was to test whether there were intrinsic differences between the zones which would differentiate between non-productive zones and productive zones. For the elements sought (major elements, Cu, Pb, Zn and S), no clear chemical difference between the zones was found. Thus, identification of a favourable zone from the over-all composition of the zone does not appear promising. Within sampled sections, there is no clear gradual compositional change up through the sections. A capping of highly siliceous massive rhyolite is present in five of the sections sampled. A layer of relatively basic material occurs near the base of individual units. The third (mine zone) and later zones contain abundant pyroclastic material, whereas the non-productive zones do not.

Mots Clés: Sulphide deposits, Volcanogenic deposits, Rhyolite, Noranda area, Sampling, Alteration, Chemical composition.