Project: Trace element geochemistry of hornblende from the Bonanza arc, Vancouver Island, Canada
This project is the second part of my PhD dissertation, in which I study crustal differentiation and the evolution of island arcs and related Cu enrichments in space and time.
Porphyry Cu deposits (PCDs) are the world’s primary source of Cu and Mo, and an important source of other elements like Au, Ag etc. PCDs are formed in association with subduction-related magmas and are found in magmatic arcs of all ages worldwide, although they are best preserved in Tertiary arcs. British Columbia is known to host several PCDs that are economically feasible to mine.
It has been long been recognized that there is an intimate link between tectonic and magmatic cycles in arcs and porphyry formation. However the source of the Cu enrichment is unclear as the sub-arc mantle shows no comprably elevated Cu concentrations. My project will test recent hyptheses that Cu enrichment in arcs is a two step process involving, a) the ‘pre-concentration’ of Cu and other chalcophile elements in the lower crust of arcs, and b) the subsequent melting of these lower crustal rocks to liberate the Cu into magmas that go on to form PCDs. I will test various aspects of this hypothesis using natural ultramafic samples from the Bonanza arc on Vancouver Island. This Jurassic island arc is well exposed and also hosted the Island Copper mine in years past, making it an ideal candidate for this study.