Summary

The mineralogy and chemistry of the amphibolitic matrix of a metamorphosed Precambrian conglomerate throw light on the derivation of the deposit from eroded basic and acid igneous parent rocks. Chemical analyses for 31 elements in 25 samples illustrate the mafic nature of the conglomerate matrix and show the influence of both basic and acid source types. Indicative of basic source rocks are high Mg, Fe, Cr, Ni, and low Si. Acid rock contributions are recognized by high K and Rb (present in K-feldspar and biotite).

The conglomerate is a peculiar type of metasedimentary amphibolite quite unlike ‘normal’ hornblende-plagioclase amphibolites of meta-igneous origin or the para-amphibolites from Ontario and Scotland previously described. It does not however have a unique composition amongst coarse clastic rocks and similar examples from other locations are cited. Such clastic rocks are probably all first cycle alluvial or fluvial deposits from source areas rich in mafic rocks.

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