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

Abstract

Lesher et al. claim that, with certain limitations, prospective horizons for base-metal sulfide deposits in the Superior Province of Canada can be identified from the trace-element characteristics of felsic metavolcanic host rocks. This claim has far-reaching and profound implications for understanding ore genesis and for mineral exploration. Our comments are directed not so much at the apparent correlation between geochemistry and fertility, which may well be correct, but at some of the important underlying assumptions and interpretations. We suggest that it may be premature to develop exploration strategies based on a petrogenetic model that, although it can explain the geochemical observations, is not necessarily unique. The validity of the geochemical groupings established by Lesher et al. is not seriously questioned. However, whether or not the groupings reflect primary or secondary processes or some combination of both is perhaps not quite so clear. We wish to argue that at least some of the elements claimed to be immobile could have been mobile during alteration and that elemental immobility requires demonstration rather than mere assertion. Furthermore, from the data presented, we wish to show that the groups can be distinguished by elements widely regarded as mobile almost as well as by immobile elements.