Regional geochemical data compilation and map preparation, Labrador, Canada

Abstract

Abstract Procedures used to compile geochemical data for some 20,000 lake sediment and stream sediment samples from 292,000 km 2 in Labrador, Canada, are described. A methodology for integrating the lake and stream sediment data is developed which compensates for the varying organic component in the matrix of the two sample media. It is shown that this procedure is effective in reducing the variability of the Zn and Ni data due to the organic matrix effect and for normalizing the data for regionalscale comparisons. No compensation was required for U data. In order to generate geochemical maps of the broad-scale patterns in the data, reflecting such features as structural provinces, litho-tectonic packages and metallogenic provinces, the use of medians for the data falling within square cells with a side varying from 10 to 50 km was investigated. An Analysis of Variance procedure is described which was used to select an optimal cell size. For the Labrador data 25×25 km cells were selected, resulting in a 97% reduction in the volume of data to be managed. The reduced data contained approximately 35%, 70% and 55% of the information for Zn, Ni and U, respectively. The final maps appear to reflect major features of the regional geochemistry related to the geological history of Labrador. It is proposed that the procedures developed should be further evaluated to determine their suitability in fulfilling the objectives of IGCP Project 259 on International Geochemical Mapping.