A Petrochemical Study of the Abitibi Volcanic Belt and Its Bearing on the Occurrences of Massive Sulphide Ores

CIM Bulletin, 1973

JEAN DESCARREAUX. Consulting Geologist, Val d'Or, Quebec

The Abitibi volcanic belt was sampled along a cross section extending from Matagami to a point east of Rouyn. A few samples were also collected in Louvicourt township, Quebec. The major elements were determined for 344 samples, and rock names were defined using normative minerals. The analytical data were studied by means of variation diagrams. The Abitibi volcanic belt is characterized by rocks belonging to both the tholeiitic and calc-alkaline magmatic series, but t hey show some differences as compared to some typical reference series, particularly those from Japan. Basalt is the predominant rock type and accounts for 44 percent of the sampled outcrops. The volcanic rocks are relatively poor in K20 and Ti02. Regionally, the volcanogenic copper-zinc mineralization is associated with the calc-alkaline volcanic sequences. Locally, within such sequences, some types of abnormal deviations from the averages are recognized only in association with the copper-zinc mineralization. The anomalies are ascribed to hydrothermal alteration consisting of the introduction of MgO and removal of N a20; enrichment in K20 is also observed where zinc mineralization predominates. Examples of such anomalous zones show that, in places, this alteration phenomenon can be quite extensive. Petrochemical characteristics can be used as geochemical ore guides in exploration programs.
Keywords: Abitibi, Abitibi Volcanic Belt, calc-alkaline, Japan, Nickel and Zinc, tholeiitic, Basalts, flow, Rock, Rocks, Value, Volcanic, Volcanic rocks, Volcanics