Trace-element geochemistry of ore-associated and barren, felsic metavolcanic rocks in the Superior Province, Canada.

Abstract

Archaean felsic metavolcanic rocks in the Superior Province of the Canadian Shield may be divided into three groups on the basis of trace-element abundances and ratios: 1) dacites and rhyodacites characterized by steep REE with weakly negative to moderately positive Eu anomalies, high Zr/Y, low abundances of high-field-strength (HFS) elements and high Sr; 2) rhyodacites and rhyolites characterized by sloping REE patterns with variable Eu anomalies, moderate Zr/Y, and intermediate abundances of HFS and Sr; 3) rhyolites and high-silica rhyolite characterized by flat REE which may be subdivided into two types. These geochemical variations are interpreted to reflect differences in the petrogenesis of the felsic magmas, specifically, their formation or degree of modification in high-level magma chambers, which also influenced the formation of massive base-metal sulphide deposits, most of which are underlain by subvolcanic magma chambers, which supplied heat to drive ore-forming hydrothermal systems. Within certain limitations, the geochemistry of felsic metavolcanic rocks may be used as a guide to prospective horizons for massive base-metal sulphide exploration in the Superior Province. The trace-element geochemistry of the felsic metavolcanic rocks of the Province is summarized in tabular form with 24 whole-rock geochemical analyses.-P.Br. Show more