Continental-root control on the genesis of magmatic ore deposits

Giant magma-related ore systems are prime targets for modern mineral exploration, yet it is unclear what controls their formation. The magmas originate in Earth's convecting mantle. To reach the surface, they must pass through the stagnant sub-continental lithospheric mantle, but the role of this mantle in ore genesis is vigorously debated. In one view, the ascending magmas are already metal-rich and the sub-continental lithospheric mantle acts only as a passive, buoyant raft on which the continental crust-the final store for the ore deposits-rides. Here we argue that the sub-continental lithospheric mantle may actually contain ore-forming elements that could be entrained by ascending magmas, and that it therefore plays a significant role in the genesis of magmatic ore. Specifically, we suggest that some types of magma pick up ore-forming components, such as diamonds and gold, and possibly platinum-group elements, during their passage through the mantle lithosphere, and that the three-dimensional structure of the lithosphere helps to focus deposition of the ore. We therefore suggest that models for ore genesis and exploration need to incorporate the entire lithosphere to be effective.