Abstract Copper production from magmatic Ni-Cu-PGE deposits represents a relatively small (∼ 4.5%) but important contribution to worldwide Cu production. Noril'sk (Russia), Sudbury (Ontario), Voisey's Bay (Labrador), and Jinchuan (China) are all significant producers with annual production > 50,000 metric tons (t) of copper. The larger Cu-Ni-PGE magmatic deposits occur throughout geologic time, formed in a range of tectonic settings but predominantly at craton margins or marginal basins and in a range of volcanic-subvolcanic-intrusive settings, and are associated with most mafic-ultramafic magma types. A few examples (Aguablanca, Karatungk) are located in arc settings, but it is possible that mafic magmas are generated through asthenosphere upwelling and partial melting in nonsubduction processes. In general, Cu-rich mineralization is favored by Cu-rich (metasomatized) mantle sources, lower degrees of partial melting of mantle (but high enough to consume all of the sulfides in the source), higher degrees of fractional crystallization-assimilation (but not high enough to reach sulfide saturation), upgrading of metal contents through reaction with relatively large amounts of magma (R factors), and/or, in particular, higher degrees of subsequent fractional crystallization of monosulfide solid solution (MSS). In broad terms, Cu-rich varieties tend to be younger (fewer Archean examples) and associated with gabbroic to ferropicritic intrusions, perhaps reflecting an increased component of melting of metasomatized subcontinental lithospheric mantle (SCLM) with time.

Abstract Magmatic sulfide deposits fall into two major groups when considered on the basis of the value of their contained metals, one group in which Ni, and, to a lesser extent, Cu, are the most valuable products and a second in which the PGE are the most important. The first group includes komatiite- (both Archean and Paleoproterozoic), flood basalt-, ferropicrite-, and anorthosite complex-related deposits, a miscellaneous group related to high Mg basalts, Sudbury, which is the only example related to a meteorite impact melt, and a group of hitherto uneconomic deposits related to Ural-Alaskan–type intrusions. PGE deposits are mostly related to large intrusions comprising both an early MgO- and SiO 2 -rich magma and a later Al 2 O 3 -rich, tholeiitic magma, although several other intrusive types contain PGE in lesser, mostly uneconomic quantities. Most Ni-rich deposits occur in rocks ranging from the Late Archean to the Mesozoic. PGE deposits tend to predominate in Late Archean to Paleoproterozoic intrusions, although the limited number of occurrences casts doubt on the statistical validity of this observation. A number of key events mark the development of a magmatic sulfide deposit, partial melting of the mantle, ascent into the crust, development of sulfide immisciblity as a result of crustal interaction, ascent of magma + sulfides to higher crustal levels, concentration of the sulfides, their enrichment through interaction with fresh magma (not always the case), cooling and crystallization. Factors governing this development include (1) the solubility of sulfur in silicate melts and how this varies as a function of partial mantle melting and subsequent fractional crystallization, (2) the partitioning of chalcophile metals between sulfide and silicate liquids, and how the results of this vary during mantle melting and subsequent crystallization and sulfide immiscibility (degree of melting and crystallization, R factor and subsequent enrichment), (3) how effectively the sulfides become concentrated and the factors controlling this, and (4) processes that occur during the cooling of the sulfide liquid that govern aspects of exploration and mineral beneficiation. These topics are discussed first in general terms and then with specific reference to deposits at Noril’sk, Kambalda, and Voisey's Bay. With regard to Voisey's Bay, quantitative modeling is consistent with the very low PGE concentrations in this deposit being the result of some sulfide having been left behind in the mantle during partial melting. Both the Noril'sk and Voisey's Bay deposits are shown to be economic because of subsequent upgrading of the ores, which are located in magma conduits, through interaction with fresh, sulfide-unsaturated magma passing along the conduits.

Abstract Thermal decay of Earth resulted in decreased mantle-plume intensity and temperature and consequently a gradual reduction of abundant komatiitic basalt ocean plateaus at ~2.6 Ga. In the Neoarchean, ocean crust was ~11 km thick at spreading centers, and abundant bimodal arc basalt-dacite magmatic edifices were constructed at convergent margins. Neoarchean greenstone belt orogenesis stemmed from multiple terrane accretion in Cordilleran-style external orogens with multiple sutures, where oceanic plateaus captured arcs by jamming subduction zones, and plateau crust melted to generate high thorium tonalite-trondhjemite-granodiorite suites. Archean cratons have a distinctive ~250- to 350-km-thick continental lithospheric mantle keel with buoyant refractory properties, resulting from coupling of the buoyant residue of deep plume melting to imbricated plateau-arc crust. In contrast, Proterozoic and younger continental lithospheric mantle is <150 km thick, denser, and less refractory and therefore easily reworked in younger orogens. The supercontinent cycle has operated since ~2.8 Ga: Kenorland assembled at ~2.7 Ga, Columbia ~1.8 Ga, Rodinia ~1 Ga, and Pangea ~0.3 Ga. Dispersal may have been triggered by superplumes. Komatiite-hosted Ni deposits are related to plumes, where sulfide saturation resulted from crustal contamination. Base metal-rich volcanic rock-associated massive sulfide (VMS) deposits accumulated on thinned, fractured lithosphere within extensional oceanic suprasubduction environments, or back arcs, which were intruded by anomalously hot subvolcanic sills; hence, their abundance in the Superior province of Canada (thick continental lithosphere), contrasting with few in the Yilgarn craton of Australia (thick lithosphere).Orogenic gold deposits formed in sutures between accreted terranes associated with assembly of Kenorland. Diamonds were created by reaction of carbonate-rich asthenospheric liquids with continental lithospheric mantle at >240-km depth, mostly pre-2.7 Ga. They were entrained in kimberlitic to lamproitic melts related to superplume events at 480, 280, and ~100 Ma. Preservation of resulting mineral provinces stems from their location on stable Archean continental lithospheric mantle. Decreased plume activity after 2.6 Ga caused sea level to fall, leading to the first extensive passive-margin sequences, including deposition of phosphorites, iron formations, and hydrocarbons, during dispersal of Kenorland from 2.4 to 2.2 Ga. Deposits of Cr -Ni-Cu-PGE were generated where plumes impinged on failed rifts at the transition from thick Archean to thinner Proterozoic continental lithospheric mantle, e.g., the Great Dyke, Zimbabwe, and later at Norilsk, Russia. Paleoproterozoic orogenic belts, for example, the Trans-Hudson orogen in North America and the Barramundi orogen in Australia, welded together the new continent of Columbia. Foreland basins associated with these orogens, containing reductants (graphitic schists) in the basement, led to the formation of unconformity U deposits, with multiple stages of mineralization generated from diagenetic brines for as much as 600 m.y after sedimentation. Plume dispersal of Columbia at 1.6 to 1.4 Ga led to SEDEX Pb-Zn deposits in intracontinental rifts of North America and Australia, extensive belts of Rapakivi A-type granites on all continents, with associated Sn veins, and Fe oxide-Cu-Au-REE deposits. All were controlled by rifts at the transition from thick to thin continental lithospheric mantle. Plume impingement on Rodinia at ~1 Ga formed extensive belts of anorogenic anorthosites and Rapakivi granites in Laurentia and Baltica, the former hosting Fe-Ti-V deposits. Sedimentary rock-hosted Cu deposits formed in intracontinental basins from plume dispersal of Rodinia at ~800 Ma. Iron formations and mantle plumes have common time series: Algoman type occur from 3.8 Ga to 40 Ma, granular iron formations precipitated on the passive margins of Kenorland at ~2.4 Ga, Superior-type formed on the passive margins of Laurentia, and Rapitan iron formations were created in rifts during latter stages of dispersal of Rodinia at ~700 Ma. Accordingly, such deposits are not proxies for the activity of atmospheric O 2 . Rich Tertiary placer deposits of Ti-Zr-Hf, located on the passive margins of Australia and Southern Africa, reflect multiple cannibalistic cycles from orogens that welded Rodinia and Pangea. Orogenic Au deposits formed during Cordilleran-type orogens characterized by clockwise pressure-temperature-time paths from ~2.7 Ga to the Tertiary; Au-As-W and Hg-Sb deposits reflect the same ore fluids at progressively shallower levels of terrane sutures. The MVT -type Pb-Zn deposits formed in foreland basins, with Phanerozoic Pb-Zn SEDEX ores localized in rifted passive continental margins containing evaporites at low latitudes. Porphyry Cu and epithermal Au-Ag deposits occur in both intraoceanic and continental margin arcs; ore fluids were related to slab dehydration, peridotite fusion, and hybridization with upper-plate crust. Deposits exposed today are largely <200 m.y.-old, given their low preservation potential in topographically elevated ranges.