EXPLORING THE COUNTRY ROCK: FOOTWALL MINERALIZATION MECHANISM AND RESOURCE TARGETING

Global demand for base metals is projected to increase significantly as technologies become more available around the globe. To meet demand, it is essential to maximize the resource potential of mineral deposits by efficiently examining all possible mineralization. In the case of magmatic Cu-Ni-PGE deposits, mineralization within the intrusion is often well constrained, but the country rock which hosts the intrusion is neglected. Given that many deposits have modest mineralization in the country rock, constraining the mechanism by which mineralization forms can guide exploration. The Maturi Cu-Ni-PGE deposit is an opportunity to explore the mechanism of country-rock mineralization. At Maturi, typical mineralization occurs as disseminated Cu-Ni-PGE-enriched sulfides within the 50-150m thick multiply-intruded Basal Mineralized Zone. This zone rests on the contact of the South Kawishiwi Intrusion and the granitic rocks of the Giants Range Batholith. Extensive drilling by Twin Metals Minnesota has shown that discontinuous disseminated to massively textured magmatic sulfide may extend 100m into the footwall. This study focuses on three drill cores intersecting separate intrusive sequences above the footwall were relogged and sampled. Subsequent petrographic observations of mylonitic textures, pockets of polygonal quartz-feldspar aggregates, and sieve textures in plagioclase evidence partial melting of the GRB. Moreover, melting textures were more intense in regions interpreted to have greater flow of magma. Melt regions were commonly observed to contain massive to semi-massive sulfide suggesting a relationship between partial melts and sulfide liquid. Isocon mass balance calculations indicate refractory behavior of Cr-Mn and an inverse relationship between chalcophile components and those which are compatible in silicate melt. This behavior suggests removal of melt, addition of sulfide liquid, and retention of refractory mafic phases. This study proposes a mineralization model by which the increased porosity/permeability of the partially melted footwall allows high density sulfide liquid to displace low-density siliceous melt. Regions of high heat flow have the greatest potential for melting and, therefore, have the highest potential to boost resource.