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.

Abstract Magadiite and cherts from the Magadi basin in southern Kenya and four other localities in the East African Rift all share distinctive compositional systematics: (1) negatively fractionated REE patterns; (2) high absolute concentrations of U, Nb, and Zr (up to 1,500 ppm versus a crustal average of 190 ppm); (3) normalized enrichments of U, Nb, and Zr relative to REE; (4) extreme fractionations of U-Th, Nb-Ta, and Zr-Hf; (5) positive Ce but negative Eu anomalies; and (6) normalized peaks at Mo, Ag, and Sb. Alkaline lake cherts composed of secondary quartz retain the trace-element patterns of the precursor, albeit at lower absolute element contents. Sublacustrine sinters at Lake Bogoria share some of the compositional features of the cherts from Magadi but lack the Ce and Eu anomalies and U-Th, Nb-Ta, and Zr-Hf fractionations. Cherts from ocean-ridge, pelagic, and continental-shelf settings are characterized by progressively larger Zr contents (≤ 170 ppm), but all are distinctly lower than in the alkaline-lake cherts, where micron-scale Zr-rich phases were identified as possible authigenic zircons. Both marine and alkaline-lake cherts share positive Ce anomalies. These result from scavenging of Ce by Fe-Mn oxyhydroxides in seawater, but from the solubility of Ce (IV) in oxidized alkaline brines for the lacustrine cherts. Europium anomalies range from small negative to positive in marine cherts, whereas alkaline-lake cherts feature large negative anomalies. These compositional systematics, which reflect the aqueous environment in which the chert precursor formed, confer a tool for interpreting the paleoenvironment of cherts in the geological record.

Abstract There are six distinct classes of gold deposits, each represented by metallogenic provinces having hundreds to more than 1,000 tonnes (t) gold production. These deposit classes are as follows: (1) orogenic gold; (2) Carlin and Carlin-like gold deposits; (3) epithermal gold-silver deposits; (4) copper-gold porphyry deposits; (5) iron oxide copper-gold deposits; and (6) gold-rich volcanic-hosted massive sulfide to sedimentary-exhalative (sedex) deposits. This classification is based on ore and alteration mineral assemblages, ore and alteration metal budgets, ore fluid pressure(s) and compositions, crustal depth or depth ranges of formation, relationship to structures and/or magmatic intrusions at a variety of scales, and relationship to the P-T-t evolution of the host terrane. The classes reflect distinct geodynamic settings. Orogenic gold deposits are generated at midcrustal (4–16 km) levels proximal to terrane boundaries, in transpressional subduction-accretion complexes of cordilleran-style orogenic belts; other orogenic gold provinces form inboard by delamination of mantle lithosphere or by plume impingement. Carlin and Carlin-like gold deposits develop at shallow crustal levels (<4 km) in extensional convergent margin continental arcs or back arcs; some provinces may involve asthenosphere plume impingement on the base of the lithosphere. Epithermal gold and copper-gold porphyry deposits are sited at shallow crustal levels in continental margin or intraoceanic arcs. Iron oxide copper-gold deposits form at middle to shallow crustal levels; they are associated with extensional intracratonic anorogenic magmatism. Proterozoic examples are sited at the transition from thick refractory Archean mantle lithosphere to thinner Proterozoic mantle lithosphere. Gold-rich volcanic-hosted massive sulfide deposits are hydrothermal accumulations on or near the sea floor in continental or intraoceanic back arcs. The compressional tectonics of orogenic gold deposits are generated by terrane accretion; high heat flow stems from crustal thickening, delamination of overthickened mantle lithosphere inducing advection of hot asthenosphere, or asthenosphere plume impingement. Ore fluids advect at lithostatic pressures. The extensional settings of Carlin, epithermal, and copper-gold porphyry deposits result from slab rollback driven by negative buoyancy of the subducting plate, and associated induced convection in asthenosphere below the overriding lithospheric plate. Extension thins the lithosphere, advecting asthenosphere heat; promotes advection of mantle lithosphere and crustal magmas to shallow crustal levels; and enhances hydraulic conductivity. Siting of some copper-gold porphyry deposits is controlled by arc-parallel or orthogonal structures that in turn reflect deflections or windows in the slab. Ore fluids in Carlin and epithermal deposits were at near-hydrostatic pressures, with unconstrained magmatic fluid input, whereas ore fluids generating porphyry copper-gold deposits were initially magmatic and lithostatic, evolving to hydrostatic pressures. Fertilization of previously depleted subarc mantle lithosphere by fluids or melts from the subducting plate, or incompatible element-enriched asthenosphere plumes, is likely a factor in generation of these gold deposits. Iron oxide copper-gold deposits involve prior fertilization of Archean mantle lithosphere by incompatible element enriched asthenospheric plume liquids, and subsequent intracontinental anorogenic magmatism driven by decompressional extension from far-field plate forces. Halogen-rich mantle lithosphere and crustal magmas form, and likely are the causative intrusions for the deposits, with a deep crustal proximal to shallow crustal distal association. Gold-rich volcanic-hosted massive sulfide deposits develop in extensional geodynamic settings, where thinned lithosphere extension drives high heat flow and enhanced hydraulic conductivity, as for epithermal deposits. Ore fluids induced hydrostatic convection of modified seawater, with unconstrained magmatic input. Some gold-rich volcanic-hosted massive sulfide deposits with an epithermal metal budget may be submarine counterparts of terrestrial epithermal gold deposits. Real-time analogues for all of these gold deposit classes are known in the geodynamic settings described, excepting iron oxide copper-gold deposits.

Abstract A high-precision trace element study of ultramafic, mafic, and felsic rocks of the Kidd Creek Volcanic Complex reveals abundant compositional variety, which in turn indicates a previously unsuspected complexity of geodynamic processes. The stratigraphically lowest part of the Kidd Creek Volcanic Complex comprises mantle plume-related komatiites and komatiitic basalts. The komatiites exhibit light rare earth element (REE) depletion, near-chondritic Al 2 O 3 /TiO 2 ratios, and other features characteristic of Munro-type komatiites. A suite of low Ti tholeiitic basalt flows (TiO 2 typically <0.4 wt %; Al 2 O 3 = 11–22 wt %, MgO = 12–18 wt % in primitive examples), not previously documented in Archean terranes, is intercalated with the komatiites and rhyolitic sequences in the Kidd Creek Volcanic Complex. The low Ti tholei-ites are characterized by very high Al 2 O 3 /TiO 2 ratios (>50), high compatible element abundances (Ni = 300–500 ppm; Cr = 600–1,200 ppm), low incompatible element abundances, low Zr/Y ratios (1.3–2.0), and depleted light REE combined with fractionated heavy rare earth element (REE) ratios (La/Sm N = 0.4–0.7; Gd/Yb N = 0.4–0.5). The low Ti tholeiites and coexisting rhyolites are overlain by a zone of basalts with diverse trace element compositions, ranging from midocean ridge basalt (MORB)-like to arclike. Above the diverse zone, trace element compositions are more uniform over short stratigraphic intervals and two suites of arc-related basalts are identified. The lowermost suite consists of aphyric, primitive arc tholeiites with relatively high Ti contents (TiO 2 = 1.5–2.7 wt %), moderate light REE enrichment (La/Sm N = 1.2–1.5), unfrac-tionated heavy REE, Zr/Y ratios greater than primitive mantle (3.0–3.5), and small negative Nb anomalies (Nb/Nb* = 0.60–0.75). The upper portion of the Kidd Creek Volcanic Complex consists of weakly feldspar-phyric evolved arc tholeiites which are distinguished from the primitive arc basalts by greater LREE enrichment and Nb depletion (La/Sm N = 1.5–2.1; Nb/Nb* = 0.3–0.7) and systematic depletions of Zr and Hf (Zr/Zr* = 0.61; Hf/Hf* = 0.58). Petrographic and geochemical characteristics of the low Ti suite closely resemble post- Archean tholei-ites found in a restricted association with boninites and proto-arcs in extensional settings, involving high-temperature melting of depleted refractory mantle. Combined with the progressively more pronounced arc-type signatures in basalts upward in the Kidd Creek Volcanic Complex, the stratigraphic location of the low Ti tholeiites provides strong evidence that these Archean examples reflect 2.7 Ga arc initiation processes, similar to those now envisioned for Phanerozoic proto-arcs. Geochronological data and stratigraphic evidence indicate that plume activity did not cease with the onset of arc magmatism in the Kidd Creek Volcanic Complex. Instead, interaction of the plume with a trench system probably resulted in plate rearrangements and the local development of a new arc in the Kidd Creek Volcanic Complex. Accordingly, the Kidd Creek deposit is the product of an extensional sub-duction zone geodynamic setting.