On the sustainability of metal supplies: A response to Tilton and Lagos

The sustainability of metal supplies can be discussed from a physical perspective, as done here, as well as from an economic one. The physical approach involves the concept of limits to virgin supplies, either absolute or arising from external constraints, as well as the sometimes-overlooked additional supply provided by recycling and reuse. At present, economic geology data are too sparse to accurately quantify many of these issues, but current trends imply increased emphasis on recycling and the use of alternative materials for some of the metals widely employed in modern technology.