TRACE ELEMENT CHEMISTRY OF APATITE PHENOCRYSTS FROM ALTERED VOLCANIC ASH LAYERS: LOCAL VARIATIONS BETWEEN K-BENTONITES FROM GASPÉ, P.Q. AND REGIONAL VARIATIONS IN THE TIOGA B K-BENTONITE FROM NEW YORK AND PENNSYLVANIA

Trace element analyses of groups of single apatite microphenocrysts separated from K-bentonites define the intralayer homogeneity and interlayer variability of apatites in a set of K-bentonites from the Gaspé Peninsula. Similar analyses show the regional-scale homogeneity of the Tioga B K-bentonite. By analyzing many single grains from each layer it is possible to quantify the homogeneity of layers for statistical comparisons of similarity and differences. This approach leads directly to tests that can be used to chemically correlate (or distinguish) K-bentonite layers. The results from multiple K-bentonite layers from Gaspé demonstrate that many of them may be distinguished from one another. The results from the Tioga B K-bentonite demonstrate that there is little variation in apatite chemistry over distances of several hundred kilometers. This technique is advantageous for use in K-bentonite correlation because it provides a direct test of sample contamination as well as the necessary data on variance of each sample, allowing for robust statistical analysis.