SAMPLING METHODS AND GEOCHEMICAL COMPOSITION OF ARCHEAN ROCKS IN SOUTHEASTERN MANITOBA, CANADA

A 13,000 km2 area of Archean rocks in southeastern Manitoba has been sampled using a multi-stage statistical model. Some 256 outcrop composite samples were analysed in duplicate for Si, Al, Fe, Mn, Mg, Ca, Na, K, Ti and P. The six levels of the model are: geological regions (domains), rock units, traverse line intersections of rock units, sampling locations (stations) within intersections, outcrops within stations, and duplicate analyses within outcrops. The data provide an estimate of the overall composition of this portion of the Canadian Shield. The major components of geochemical variation are at the intersection, station, and outcrop levels. There is significantly less variation between geological domains and between the geological units, as defined by field mapping. The smallest component of variation is generally at the analysis level. These data suggest that in the Canadian Shield, or similar geological terrane, extensive subsampling will be required to detect regional geochemical trends or to characterize the composition of rock units. The relatively low variability between rock units is attributed to the homogenizing effect of high levels of metamorphism, including anatexis, that affected the region. © 1979.