The processes that lead to the formation of some large ore deposits are explored in three review papers published online this week in Nature Geoscience. Such ore giants supply many of the metals humans use - such as copper and gold - and are therefore priority targets for mining companies. However, the processes that control the formation and location of these deposits have remained unclear.

In two related pieces, Jamie Wilkinson and Jeremy Richards review the processes that generate ore deposits in regions where one tectonic plate subducts beneath another. Richards argues that the largest deposits form from a series of ordinary ore-forming processes that fortuitously occur at the same time, while operating at optimum efficiency. Wilkinson, however, suggests that four distinct trigger processes lead to the formation of ore giants above subduction zones, and that the key ingredient is the presence of sulphide-saturated magmas.

William Griffin and colleagues review the worldwide distribution of diamond, gold and metal (such as platinum) deposits. They argue that the structure and composition of the mantle beneath the continents could help to guide upwelling magmas that ultimately form such ore deposits, as well as enrich them with metals. Thus the mantle beneath the continents could influence the location and concentration of metal deposits closer to Earth’s surface.

The three reviews are part of a collection of articles on economic geology, and stress that the search for giant deposits could potentially be made more efficient if the geochemical fingerprints of the above processes are considered during geological exploration.