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Exploration for world-class Ni-Cu-(PGE) deposits in mafic and/or ultramafic igneous rocks has focused on extensional environments where high degrees of mantle melting have occurred in association with mantle plumes. Where continental rifting has been involved, the interaction between large volumes of mafic magma and crustal rocks in either intrusive or extrusive settings may have resulted in contamination that triggered sulfide saturation or melting of sulfides within country rocks. Staging chambers and conduits in the subvolcanic environment and embayments associated with channels in the volcanic environment are localities where immiscible sulfide liquid may accumulate. The large-tonnage, high-grade deposits in conduit and magma chamber environments, such as those at Noril’sk, Siberia, remain high priorities for greenfields exploration, and it is now clear that intrusions with even small footprints may be important exploration targets. Examples of small footprint deposits include the large-tonnage ore systems at Voisey’s Bay in the Nain plutonic suite, Labrador, and the low-tonnage, high-grade mineralization at the Eagle deposit in the Keweenawan of northern Michigan. The high-grade mineralization in small deposits is particularly attractive as incremental feed if smelters are located nearby and transportation routes are available. Low-tonnage, high-grade deposits can also be mined using underground methods, and having lesser environmental impact and remediation is typically more straightforward.

Although convergent margin environments have not been universally viewed as viable target areas for magmatic sulfide-rich Ni-Cu-(PGE) deposits, suprasubduction zone environments have high degrees of mantle melting, and they provide locations for crust-magma interaction and conduit geometries where sulfides may collect. Deposits such as Kalatongke in China, Aquablanca in Spain, and the Turnagain and Duke Island Ural-Alaskan intrusions illustrate that convergent margins should not be dismissed as targets for magmatic Ni-Cu-(PGE) ores.

New advances in hydrometallurgical techniques, particularly pressure leach methods, are making the extraction of Cu, Ni, and PGEs from large-tonnage but low-grade deposits economically promising. The large disseminated sulfide-rich Ni-Cu-(PGE) resources of the Duluth Complex are an example where advances in process technology may permit future development of low-grade occurrences that have traditionally been considered to be of marginal economic value.

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