Genesis of native copper deposits in the Keweenawan rocks is related to the low-T metamorphism of their host basalts. The Keweenawan North Shore Volcanic Group is located in north-eastern Minnesota, on the western shore of Lake Superior. The effects of low-grade metamorphism have been studied from three perspectives:

Geological setting Sampling Regional scale Lava flow scale Mineral scale Summary

1) low-grade metamorphism at the scale of the 8000 m thick North Shore Volcanic Group (i.e. its vertical stratigraphic zonation);

2) low-grade metamorphism at the local scale, observed in individual lava flows, with alteration depending on the morphology and permeability of the lava flow (i.e. textures and structures), and the mineralogical composition of the individual lava flow;

3) variation in composition of the newly formed alteration minerals, mainly albite and mafic phyllosilicates in relation to the flow morphology.