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The Ni-Cu-platinum group element (PGE) sulfide mineralization in the 1.85 Ga Sudbury impact structure occurs in two discrete environments: (1) mineralization along or near the basal contact, including disseminated to semimassive mineralization in an inclusion-rich sublayer, semimassive to fragmental mineralization in the underlying anatectic footwall breccia, and veins and disseminations in the underlying pseudotachylitic Sudbury breccia, and (2) disseminated to semimassive mineralization in the inclusion-bearing quartz diorite phase of radial and concentric offset dikes that extend up to 20 km from the basal contact. The sublayer, inclusion quartz diorite, and footwall breccia all contain abundant mafic-ultramafic inclusions—local xenoliths derived from nearby country rocks, exotic xenoliths derived from unexposed upper-middle crustal target rocks and, locally, anteliths derived from an olivine melanoritic early border phase of the Sudbury Igneous Complex—but the quartz diorite margins of offset dikes contain very few local inclusions and no exotic ultramafic inclusions. The similar inclusion populations indicate a genetic relationship between the sublayer and inclusion quartz diorite and interaction between the sublayer and footwall breccia. But the sublayer is characterized by a cumulate noritic matrix, the inclusion quartz diorite by a noncumulate quartz dioritic matrix, and the footwall breccia by an anatectic felsic-intermediate matrix. The overlying main mass norite is very homogeneous in terms of Hf isotopes, indicating that the impact melt sheet was well mixed, but ores, sublayer, inclusion quartz diorite, and to a lesser degree overlying main mass norites vary widely in their Pb-S-(Os) isotope compositions. The majority of mafic-ultramafic inclusions, except for anteliths, contain no sulfide and exhibit no signature of Ni-Cu-PGE depletion caused by prior sulfide saturation, which indicates that the association between mafic-ultramafic inclusions and Ni-Cu-PGE mineralization is attributable primarily to the refractory nature of the inclusions and to a lesser degree their similar hydrodynamic behavior as the sulfide melt and, secondarily, to derivation of sulfides from the same sources as the inclusions. The very large Sudbury impact event volatilized much of the Pb-S-Zn-Cd-Se-Bi and significant amounts of Sb-Ag-Cu-Au-As from the target rocks. It generated large amounts of superheated impact melt and only minor fragmental debris during the compression and excavation stage, which is when the inclusion- and sulfide-poor marginal phase of the offset dikes was emplaced. Large amounts of debris, including sulfide-bearing Huronian basalts, Nipissing and East Bull Lake intrusions, and Archean mafic gneisses, were generated during isostatic rebound, formation of a central uplift, and collapse of the central uplift and crater walls, which is when the inclusion- and sulfide-bearing internal phase of the offset dikes was emplaced. Convective and gravity flow aided horizontal transport of residual exotic inclusions, local inclusions, and sulfide xenomelts into embayments and funnels to form the protosublayer. Olivine-saturated melts, generated by thermomechanical erosion of local olivine-bearing country rocks, locally crystallized an olivine melanoritic early border phase of the main mass, which was disrupted and preserved in the funnels of some North Range offset dikes. Continued thermomechanical erosion of country rocks enlarged dike funnels and exploited other fractures to generate footwall embayments and significant geochemical and Pb-S-(Os) isotope heterogeneities. As the rate of thermomechanical erosion decreased and the rate of heat conducted into the footwall rocks increased, contact ores and some offset ores fractionally crystallized to form residual melts that generated footwall vein systems.

The Jinbaoshan platinum group element-(Cu)-(Ni) deposit in southwest China is a sulfide-poor magmatic platinum-group element deposit that experienced multiple phases of post-magmatic modification. The sulfide assemblages of most magmatic Ni-Cu-platinum-group element deposits in China and elsewhere in the world are dominated by pentlandite-pyrrhotite-chalcopyrite with lesser magnetite and minor platinum-group minerals. However, Jinbaoshan is characterized by (1) hypogene violarite-pyrite 1-millerite-chalcopyrite and (2) supergene violarite-(polydymite)-pyrite 2-chalcopyrite assemblages. The platinum-group minerals are small (0.5–10 μm diameter) and include moncheite Pt(Te,Bi)2, mertieite-I Pd11(Sb,As)4, the atokite Pd3Sn – rustenburgite Pt3Sn solid solution, irarsite IrAsS, and sperrylite PtAs2 hosted mainly by violarite, silicates (primarily serpentine), and millerite. The platinum-group minerals occur in two sulfide assemblages: (1) mertieite-I-dominant (with irarsite, palladium, and Pd-alloy) in the hypogene assemblage and (2) moncheite-dominant (with irarsite, sperrylite, and atokite) in the supergene assemblage. Palladium and intermediate platinum-group elements (Os, Ir, Ru) are concentrated mainly in violarite, polydymite, and pyrite 2. Platinum is seldom hosted by base metal sulfides and occurs mainly as discrete platinum-group minerals, such as moncheite, sperrylite, and merenskyite. Violarite and polydymite in the Jinbaoshan deposit contain more Pb-Ag than pentlandite and pyrrhotite in the Great Dyke and Lac des Iles deposit. The formation of the sulfide assemblages in Jinbaoshan can be interpreted to have occurred in three stages: (1) a magmatic Fe-Ni-Cu sulfide melt crystallized Fe-Ni monosulfide and Cu-rich intermediate solid solutions, which inverted to a primary pyrrhotite-pentlandite-chalcopyrite-magnetite assemblage; (2) an early-secondary hypogene voilarite-millterite-pyrite 1-chalcopyrite assemblage formed by interaction with a lower-temperature magmatic-hydrothermal deuteric fluid; and (3) a late-secondary supergene violarite-polydymite-pyrite 2-chalcopyrite assemblage formed during weathering. Late-magmatic-hydrothermal fluids enriched the mineralization in Pb-Ag-Cd-Zn, which are incompatible in monosulfide solid solution, added Co-Pt into violarite, and expelled Pd to the margins of hypogene violarite and millerite, which caused Pd depletion in the hypogene violarite and the formation of mertieite-I. Supergene violarite inherited Pd and intermediate platinum-group elements from primary pentlandite. Thus, the unusual sulfide assemblages in the Jinbaoshan platinum-group element-(Cu)-(Ni) deposit results from multiple overprinted post-magmatic processes, but they did not significantly change the chalcophile element contents of the mineralization, which is interpreted to have formed at high magma:sulfide ratios (R factors) through interaction of crustally derived sulfide and a hybrid picritic-ferropicritic magma derived from subduction-metasomatized pyroxenitic mantle during impingement of the Emeishan plume on the Paleo-Tethyan oceanic subduction system.

The ∼259 Ma Baimazhai Ni-Cu-(platinum-group element) deposit is located in the Ailaoshan-Red River fault zone on the southwest margin of the Yangtze Plate in the Jinping area of southeastern Yunnan Province. The intrusion is lenticular (∼530 m long × 190 m wide × 24–64 m thick) and concentrically zoned (margin to core) from gabbro through pyroxenite to peridotite. It contains ∼50 kt of Ni-Cu-(platinum-group element) mineralization, concentrically zoned (margin to core) from disseminated through net-textured to massive sulfides with an average grade of 1.03 wt.% Ni, 0.81 wt.% Cu, and 0.02∼0.69 ppm Pd+Pt. The sulfide assemblage comprises pyrrhotite, chalcopyrite, and pentlandite, with lesser magnetite, violarite, galena, and cobaltite. The mineralization is enriched in Ni-Cu-Co relative to the platinum-group elements and the host rocks are enriched in highly incompatible lithophile elements relative to moderately incompatible lithophile elements with high Th/Yb and intermediate Nb/Yb ratios. These host rocks, and those at most other Ni-Cu-platinum-group element deposits in the Emeishan Large Igneous Province, have high γOs and intermediate εNd values, indicating that they crystallized from a magma derived from a subduction-modified pyroxenite mantle source and modified by crustal contamination. The initial concentrations of metals in the primary magma are estimated to have been on the order of 200 ppm Ni and 100 ppm Cu, but only 0.4 ppb Pd, 0.2 ppb Pt, 0.005 ppb Rh, 0.02 ppb Ru, and 0.01 ppb Ir. The δ34S values of ores and separated sulfides range from 5.8‰ to 8.6‰, between the ∼10‰ value of sulfides in the metasedimentary country rocks and the 0 ± 0.5‰ value expected for magmas derived from MORB-type mantle, or the –2.5 ± 0.3‰ value expected for subduction-modified mantle, consistent with equilibration at magma:sulfide mass ratios (R factors) of 100–1000. Variations in Ir100 and Pd100 (metals in 100% sulfide) are consistent with 40–60% fractional crystallization of monosulfide solid solution to form Ni-Co-intermediate platinum-group element (Ru, Os, Ir)-rich massive ores and Cu-palladium/platinum-group elements (Pt, Pd, Rh)-Au-rich residual sulfide liquids. This process is also recorded by magnetite: Type I (early magmatic), type II (late magmatic), and type III (secondary) magnetites exhibit progressively lower Cr-Ti-V concentrations. The platinum-group element contents in base-metal minerals are low, and only pentlandite, violarite, and cobaltite contain detectable concentrations of Pd, Rh, and Ru. There is abundant textural evidence for metamorphic-hydrothermal alteration of sulfides in the Baimazhai intrusion, with secondary violarite, chalcopyrite, and pentlandite being enriched (Ag, Sb, Au, Pb) or depleted (Sn) in more mobile chalcophile elements. The different tectonic and petrogenetic settings of the Baimazhai and other deposits in China highlight the potential of Ni-Cu-platinum-group element deposits to occur in subduction or post-subduction settings and demonstrate that the key controls are magma flux and access to crustal S. Exploration potential remains for the Ailaoshan orogenic belt to host additional magmatic Ni-Cu deposits.

The c. 1·85 Ga Sudbury Igneous Complex (SIC) is the igneous remnant of one of the oldest, largest and best-preserved impact structures on Earth and contains some of the world’s largest magmatic Ni–Cu–PGE sulfide deposits. Most of the mineralization occurs in Sublayer, Footwall Breccia and inclusion-bearing quartz diorite (IQD), all of which contain significant (Sublayer and IQD) to minor (Footwall Breccia) amounts of olivine-bearing mafic–ultramafic inclusions. These inclusions have only rare equivalents in the country rocks and are closely associated with the Ni–Cu–PGE sulfide mineralization. They can be divided into three groups on the basis of petrography and geochemical characteristics. Group I (n = 47) includes igneous-textured olivine melanorite and olivine melagabbronorite inclusions in the Whistle and Levack embayments on the North Range with Zr/Y, Zr/Nb, Nb/U and Zr/Hf similar to igneous-textured Sublayer matrix. Group I inclusions are interpreted to be anteliths that crystallized from a mixture of SIC impact melt and a more mafic melt, probably derived by melting of ultramafic footwall rocks. Group II includes Group IIA (n = 17) shock metamorphosed wehrlite and olivine clinopyroxenite inclusions in the Levack embayment and Group IIB (n = 2) shock metamorphosed olivine melanorite inclusions in the Foy Offset on the North Range. Group II inclusions have similar trace element patterns [e.g. negative Th–U, Nb–Ta–(Ti), Sr and Zr–Hf anomalies] and overlapping Nb/U to a layered mafic–ultramafic intrusion in the footwall of the Levack and Fraser deposits, which together with their limited distribution suggests that Group II inclusions are locally-derived xenoliths. Group III (n = 21) includes phlogopite lherzolite and feldspar lherzolite inclusions with igneous, recrystallized and shock-metamorphic textures in the Trill, Levack and Bowell embayments, and the Foy Offset dike on the North Range. They have no equivalents in the exposed country rocks. The calculated parental magma is similar to continental arc basalt formed by approximately 5% partial melting of garnet peridotite. Ol–Cpx–Pl thermobarometry of several Group III inclusions indicate equilibration at 900–1120 ºC and 210 ± 166 MPa to 300 ± 178 MPa, suggesting crystallization in the upper-middle crust (7·7 ± 6·6 to 10·9 ± 6·5 km), prior to being incorporated into the lower parts of the impact melt sheet during impact excavation. The exotic xenoliths provide information about the depth of impact and composition of upper-middle crust in the Sudbury region at 1850 Ma, the local xenoliths provide information about the thermomechanical erosion process that followed generation of the impact melt, the anteliths provide information about the early crystallization history of the SIC, and all of the inclusions provide constraints on the genesis of Sublayer, IQD, footwall breccia, and associated Ni–Cu–PGE mineralization.

Ore-forming hydrothermal fluids react differently with different country rocks, but few studies have applied this knowledge with the specific goal of expanding the size of hydrothermal footprints in mineral exploration. To develop this concept, 122 metamorphosed mafic dykes from the world-class Canadian Malartic gold district (18.6 Moz Au) were sampled and analyzed for mineralogy, physical properties, and lithogeochemistry (partial and total digestion). The mafic dykes intrude mainly metasedimentary rocks, post-date D1 deformation, and cross-cut early-D2 quartz monzodiorite intrusions, but they were deformed and altered during D2 deformation, mineralization, and metamorphism. They can be subdivided into three groups: Group 1 dykes are least-altered, characterized by amphibole-rich regional metamorphic assemblages and distributed throughout the Pontiac Subprovince. Group 2 and 3 dykes underwent ore-related hydrothermal biotite–calcite–pyrite alteration and are associated with density- and volume-adjusted concentration gains of over 100% in Au–W–Te–C–S–Ag–Cs–Mo–Cu–K–Rb–Se–U–Pb–Ba–F–Bi–Sn. They define a metasomatic footprint up to 6 km away from the deposit toward the SE and up to 2 km away from the deposit toward the SW. Fifty-eight variables that define halos around the Canadian Malartic deposit have been identified and integrated using principal component analysis. PC1 explains 30% of the variance, separates least-mobile elements from ore-related elements, and is interpreted to reflect the ore-forming alteration process. PC2 and PC3 represent igneous processes. PC4 highlights the calcite–pyrite and biotite alteration. Spatial variations of the modal abundances of amphibole, biotite, calcite, and pyrite are the simplest expression of the metasomatic footprint, and they can easily be documented during exploration at the camp scale.

The Sudbury Igneous Complex is the preserved remnant of a 1.85 Ga impact-induced crustal melt sheet that eventually crystallized into a coherent magmatic stratigraphy. At its base, the complex hosts world-class Ni-Cu- platinum group element (PGE) sulfide mineralization, distributed around the basin. Previous studies have shown strong Pb and Sr isotope contrasts between the North and South ranges of the Sudbury Igneous Complex. This study presents an extensive dataset of Pb isotopes and trace elements of hand-picked feldspars and sulfides from the complex, Ni-Cu-PGE mineralization, and underlying country rocks that reveals the finer details of isotopic decoupling between the North and South ranges. In terms of mean Pb isotope compositions, the new data confirm the previously established picture that North Range Main Mass rocks and associated Ni-Cu-PGE sulfide deposits are more juvenile than South Range Main Mass and associated mineralization, but there are several findings that point to a more complex evolution, with considerable implications for the source of sulfide in the Sudbury Igneous Complex. First, North Range sulfide ores and Main Mass silicates are more radiogenic than local footwall rocks. When expressed as per mil deviation in Pb-207/Pb-204 from a model contemporaneous mantle isochron (Delta Pb-207/Pb-204), the North Range Main Mass ores range from + 130 to + 421 and North Range ores range from + 160 to + 518 (primarily + 160 to + 260). This indicates that the Huronian Supergroup cover constituted a significant target rock type also in the North Range of the Sudbury Igneous Complex. Second, there is significant variability in the Pb isotope compositions between Ni-Cu-PGE sulfide deposits in both the North and South ranges and systematic differences between the average silicate compositions and sulfide compositions of Ni-Cu-PGE deposits. In the South Range Main Mass rocks, the Delta Pb-207/Pb-204 values range from + 360 to + 494, and associated ores range from + 150 to + 481 (primarily + 400 to + 480). Third, North Range mafic norite is much less radiogenic than North Range Main Mass, indicating that it may be contaminated by or derived from less radiogenic Ni-Cu-PGE-bearing mafic-ultramafic rocks. Finally, the Pb isotope variations between Sudbury Igneous Complex ores are corroborated by similar systematic variations in rare earth element patterns likely inherited by assimilation of local footwall rocks. Importantly, the considerable variations in the Pb isotope compositions of the ores between different deposits and the intermediate compositions between overlying Main Mass and footwall rocks suggest that the sulfides originally equilibrated with Main Mass, but acquired significant amounts of Pb (and therefore likely S and other metals) from local footwall rocks, most likely during thermomechanical erosion of the footwall rocks by dense molten sulfides. Potential S and metal sources are the Nipissing gabbros and the East Bull Lake intrusions, both of which are mineralized and whose Pb isotope compositions help to explain the variability in Sudbury Igneous Complex Ni-Cu-PGE sulfide ores. Small-scale lateral variations in Pb isotopes previously identified in the South Range of the Sudbury Igneous Complex are also present in the North Range. This indicates that the laterally extensive (200-km wide x 2.5-km thick) superheated Sudbury Igneous Complex melt sheet developed multiple chemically and isotopically isolated convection cells that continued to assimilate isotopically distinctive footwall rocks after impact. Lateral variations are much greater at lower levels in the magmatic stratigraphy than in the upper part of the stratigraphy. This resulted from a combination of three factors: (1) the overall depletion in Pb of the proto-Sudbury Igneous Complex (likely due to volatile element loss upon impact) made it more susceptible to contamination in this element than in more refractory elements; (2) assimilation of heterogeneous footwall into the base vs. incorporation of more homogeneous fallback breccias into the roof of the Sudbury Igneous Complex; and (3) possible hydrothermal roof alteration. Lead isotopes and trace element data for samples of the footwall collected and analyzed as part of this study used in tandem with data from previous work confirm that the Sudbury Igneous Complex can be reproduced by mixing the currently exposed target lithologies and indicate that no mantle or lower crustal component is required.

A large proportion of ores in magmatic sulfide deposits consist of mixtures of cumulus silicate minerals, sulfide liquid, and silicate melt, with characteristic textural relationships that provide essential clues to their origin. Within silicate-sulfide cumulates, there is a range of sulfide abundance in magmatic-textured silicate-sulfide ores between ores with up to about five modal percent sulfides, called "disseminated ores," and "net-textured" (or "matrix") ores containing about 30 to 70 modal percent sulfide forming continuous networks enclosing cumulus silicates. Disseminated ores in cumulates have various textural types relating to the presence or absence of trapped interstitial silicate melt and (rarely) vapor bubbles. Spherical or oblate spherical globules with smooth menisci, as in the Black Swan disseminated ores, are associated with silicate-filled cavities interpreted as amygdales or segregation vesicles. More irregular globules lacking internal differentiation and having partially facetted margins are interpreted as entrainment of previously segregated, partially solidified sulfide. There is a textural continuum between various types of disseminated and net-textured ores, intermediate types commonly taking the form of "patchy net-textured ores" containing sulfide-rich and sulfide-poor domains at centimeter to decimeter scale. These textures are ascribed primarily to the process of sulfide percolation, itself triggered by the process of competitive wetting whereby the silicate melt preferentially wets silicate crystal surfaces. The process is self-reinforcing as sulfide migration causes sulfide networks to grow by coalescence, with a larger rise height and hence a greater gravitational driving force for percolation and silicate melt displacement. Many of the textural variants catalogued here, including poikilitic or leopard-textured ores, can be explained in these terms. Additional complexity is added by factors such as the presence of oikocrysts and segregation of sulfide liquid during strain-rate dependent thixotropic behavior of partially consolidated cumulates. Integrated textural and geochemical studies are critical to full understanding of ore-forming systems.

The Garson Ni-Cu-platinum group element (PGE) deposit is a deformed, overturned, contact-type deposit along the contact between the Sudbury Igneous Complex and underlying rocks of the Huronian Supergroup in the South Range of the 1850 Ma Sudbury structure. The main Garson orebodies occur along steeply S dipping ductile shear zones, which formed as D1 north-over-south amphibolite facies thrust zones that were rotated and overturned during buckling of the Sudbury Igneous Complex. The shear zones were reactivated as south-over-north greenschist facies reverse shear zones during D2. The mineralization is primarily composed of pyrrhotite-pentlandite-chalcopyrite-magnetite, occurring as four main types: (1) disseminated to matrix-textured sulfides in Main Mass norite and slivers of norite within shear zones, (2) semimassive breccia ore within the shear zones, (3) quartz-calcite-sulfide veins spatially associated with breccia ores, and (4) Cu-Pd-Pt-Au–rich “footwall-type” mineralization in the nearby Garson Ramp deposit. Garson disseminated sulfides and breccia ores have relatively low Pd/Ir ratios and restricted ranges of Ni tenors and Fe/Ni ratios, very similar to those of undeformed disseminated sulfides and contact-type massive ores at the less deformed Creighton deposit. This suggests that the mobilization of the breccia ores by ductile plastic flow during D1 and D2 did not significantly alter their original magmatic geochemical signatures. Garson breccia ores are slightly depleted in Cu-Pt-Pd-Au and slightly enriched in Rh-Ru-Ir relative to disseminated sulfides, similar to other contact-type deposits at Sudbury. In contrast, quartz-calcite-sulfide veins at Garson are characterized by very low Rh-Ru-Ir abundances and very high Pd/Ir ratios, consistent with their mobilization and deposition from metamorphic-hydrothermal fluids. Despite being strongly enriched in Cu-Pd-Pt-Au, there are too few of these veins to account for the broad depletion in Cu-Pd-Pt-Au from the main mass of breccia ores, suggesting that the breccia ores are monosulfide solid solution cumulates that left a residual sulfide melt represented by the Cu-Pd-Pt-Au–rich ores in the Garson Ramp deposit.

The Garson Ni–Cu–platinum group element deposit is a deformed, overturned, low Ni tenor contact-type deposit along the contact between the Sudbury Igneous Complex (SIC) and stratigraphically underlying rocks of the Huronian Supergroup in the South Range of the 1.85-Ga Sudbury structure. The ore bodies are coincident with steeply south-dipping, north-over-south D1 shear zones, which imbricated the SIC, its ore zones, and underlying Huronian rocks during mid-amphibolite facies metamorphism. The shear zones were reactivated as south-over-north, reverse shear zones during D2 at mid-greenschist facies metamorphism. Syn-D2 metamorphic titanite yields an age of 1,849 ± 6 Ma, suggesting that D1 and D2 occurred immediately after crystallization of the SIC during the Penokean Orogeny. The ore bodies plunge steeply to the south parallel to colinear L1 and L2 mineral lineations, indicating that the geometry of the ore bodies are strongly controlled by D1 and D2. Sulfide mineralization consists of breccia ores, with minor disseminated sulfides hosted in norite, and syn-D2 quartz–calcite–sulfide veins. Mobilization by ductile plastic flow was the dominant mechanism of sulfide/metal mobilization during D1 and D2, with additional minor hydrothermal mobilization of Cu, Fe, and Ni by hydrothermal fluids during D2. Metamorphic pentlandite overgrows a S1 ferrotschermakite foliation in D1 deformed ore zones. Pentlandite was exsolved from recrystallized polygonal pyrrhotite grains after cessation of D1, which resulted in randomly distributed large pentlandite grains and randomly oriented pentlandite loops along the grain boundaries of polygonal pyrrhotite within the breccia ore. It also overgrows a S2 chlorite foliation in D2 shear zones. Pyrrhotite recrystallized and was flattened during D2 deformation of breccia ore along narrow shear zones. Exsolution of pentlandite loops along the grain boundaries of these flattened grains produced a pyrrhotite–pentlandite layering that is not observed in D1 deformed ore zones. The overprinting of the two foliations by pentlandite and exsolution of pentlandite along the grain boundaries of flattened pyrrhotite grains suggest that the Garson ores reverted to a metamorphic monosulfide solid solution at temperatures ranging between 550 and 600 °C during D1 and continued to deform as a monosulfide solid solution during D2.

The Garson deposit is one of several deformed magmatic Ni–Cu–platinum group element (PGE) deposits in the South Range of the 1.85 Ga Sudbury structure. The deposits occur along the southeast limb of the folded Sudbury Igneous Complex (SIC), at the contact between the SIC basal norite and underlying Paleoproterozoic metabasalt and metasedimentary rocks of the Huronian Supergroup. At the Garson deposit inclusion-rich breccia and disseminated Ni–Cu–PGE sulfide ores are hosted by steeply south-dipping shear zones and splays that underwent two major ductile deformation events (D1 and D2). D1 is characterized by a steeply, south-dipping, S1 foliation and a down-dip L1 mineral stretching lineation defined by ferrotschermakite in metabasalt and by magnesiohornblende in norite. Coexisting ferrotschermakite and oligoclase in metabasalt indicate amphibolite facies conditions during D1. The shear zones formed along or near the SIC-Huronian contact during the 1.7–1.6 Ga Mazatzal–Labradorian Orogeny. They formed as layer-parallel, north-dipping, north-over-south thrusts in response to flexural slip during buckling of the SIC. As the general transport direction was from south to north during the Mazatzal–Labradorian Orogeny, the D1 shear zones are back-thrusts with opposite transport direction. The thrusts imbricated the SIC, underlying Huronian rocks, and ore zones, and emplaced slivers of Huronian rocks and metabreccia into the overlying norite. In contrast to the D1 shear zones at Garson, the Thayer Lindsley and the regional South Range shear zones, which transgress the SIC-Huronian contact at a high angle, formed as moderately SE-dipping reverse shear zones as a result of localization of folding-induced strain near the hinge zone in order to accommodate further flattening and tightening of the SIC with progressive D1 shortening. Together with the southeast limb of the SIC, the D1 shear zones were overturned into their present steep southerly dips and were reactivated as south-over-north shear zones either later during the Mazatzal–Labradorian Orogeny or during the 1.5–1.45 Ga Chieflakian event, which was coeval with accretion of juvenile Andean-style, calc–alkaline magmatic arcs along the entire southeastern margin of Laurentia. During this D2 reactivation event, S1 was transposed and locally preserved in crenulations bounded by a S2 chloritic shear foliation, which has a strong down-dip L2 mineral chlorite lineation and parallel L2 ductile slickenlines.

The archetypical komatiite-hosted Alexo Ni–Cu–(PGE) deposit occurs in the 2,720–2,710-Ma Kidd-Munro Assemblage of the western Abitibi greenstone belt in Dundonald Township, Ontario. Detailed mapping of a 200-m long glacially polished outcrop provides unequivocal evidence that the host komatiite flow thermomechanically eroded footwall andesites: (1) the contact between komatiite and andesite is very sharp but delicately scalloped, marked by a

Virtually all of the economic Ni–Cu–(platinum group element (PGE)) mineralization in the central part of the Cape Smith Belt of New Quebec is hosted by thick olivine cumulate units in the Katinniq Member of the Raglan Formation at the base of the 1.9 Ga Chukotat Group. These units transgress underlying gabbros and pelitic metasediments, forming 50–200-m deep and 300–1,000-m wide V-shaped embayments and have been interpreted on the basis of surface geology, deep diamond core drilling, and magnetic inversion models to represent the remnants of one or more large, long (at least 20 km, possibly ≥50 km), sinuous, komatiitic basalt lava channels that formed by thermomechanical erosion of their substrates. We have used a mathematical model to test these hypotheses regarding komatiitic lava emplacement and erosion by lava. Our modeling predicts that an initially 10-m thick komatiitic basalt flow should have flowed turbulently near the vent and should have thermomechanically eroded unconsolidated pelitic sediment during emplacement to reach the observed degree of contamination of ≤10% at distances of ~30–60 km downstream from the source. Furthermore, our models predict that, at these distances downstream, a fully inflated 100-m thick komatiitic basalt flow would have had thermal erosion rates over consolidated gabbroic substrate of ~0.7–1.5 m/day, requiring ~70–140 days to incise a 100-m deep channel, depending on the initial temperature of the lava, the paleoslope, and the initial temperature and solidus temperature of the gabbro. These erosion rates would have been associated with volumetric flow rates of >105–106 m3/s and eruption volumes of >103–104 km3. Although these flow rates are orders of magnitude larger than those of most modern terrestrial basaltic flows, they are of the same order as those estimated for the largest terrestrial flood basalt flows and with those inferred for some of the largest extraterrestrial flows. Our predicted flow volumes are also of the same order as those of the largest terrestrial flood basalt units, consistent with the great thickness and widespread distribution of the Chukotat Group. Our modeling of thermomechanical erosion of gabbro by komatiitic basalt results in negligible contamination ( Middle REE–Heavy REE > Nb–Ta–Ti represent contamination by underlying Povungnituk semipelites. This result is consistent with present models for the genesis of the Ni–Cu–(PGE) mineralization in the Raglan Formation that involve thermomechanical erosion of unconsolidated, sulfidic semipelitic sediments, and decoupling of the miscible silicate and immiscible sulfide components.

The Wengeqi complex in Guyang County, Inner Mongolia, is one of several Pd–Pt-mineralized Paleozoic mafic–ultramafic complexes along the north-central margin of the North China. The complex comprises pyroxenites, biotite pyroxenites, amphibole pyroxenites, gabbros, and amphibolites. Zircons extracted from a pyroxenite yield a U–Pb SHRIMP age of 399 ± 4 Ma. Several 2–6-m wide syngenetic websterite dikes contain 1–3 ppm Pd + Pd and are dominated by pyrite–chalcopyrite–pyrrhotite–magnetite–(pentlandite) assemblages with minor sperrylite, sudburyite, and kotuskite. Textural relationships indicate that pyrite has replaced magmatic chalcopyrite and that magnetite has replaced magmatic pyrrhotite. The mineralization is enriched in Pd–Pt–Cu > Au >> Rh–Ir–Os–Ni > Ru, similar to other occurrences of hydrothermally modified magmatic mineralization, but very different from the much less fractionated compositions of magmatic PGE mineralization. Textural, mineralogical, and geochemical relationships are consistent with alteration of an original magmatic Fe–Ni–Cu sulfide assemblage by a S-rich oxidizing high-temperature (deuteric) hydrothermal fluid.

Platinum-group elements (PGE) are strongly chalcophile and are therefore potentially sensitive indicators of processes involving segregation and accumulation of sulfide melts from silicate magmas. Over 500 new high-precision PGE data for komatiites and komatiitic basalts, spanning a wide range of emplacement and crystallization histories, have been combined with literature data on PGE in magmatic systems from other barren and variably mineralized environments, to test the effectiveness of PGE geochemistry as an indicator of processes forming magmatic sulfide ores. Results show that PGE depletion in S-poor komatiites and komatiite basalts spatially and genetically associated with Fe-Ni-Cu sulfide mineralization is not as common or as strong as expected: samples displaying orders of magnitude depletion in PGE represent less than 10 percent of any given data set from any location. The data confirm that most, if not all, komatiites were sulfide undersaturated when they separated from their sources and remained undersaturated on eruption. Some ore-bearing komatiite sequences display no detectable depletion, and the degree of PGE depletion is commonly less than expected based on modeling using experimentally determined partition coefficients. PGE enrichment is more common and spatially widespread than PGE depletion, commonly representing a better approach to lithogeochemical exploration, even where samples containing anomalous Ni or S contents are absent. PGE enrichment and/or depletion associated with sulfide enrichment and/or segregation can be discriminated from secondary hydrothermal and/or metamorphic processes by covariance of all PGE, with the exceptions in some cases of Ir, Ru, and Os whose abundances may be complicated by the presence of saturation in and accumulation of Ir-Os-rich liquidus phases. Variations attributable to other magmatic processes, such as olivine accumulation and fractionation, can be distinguished by variations in PGE/Ti ratios and strong correlations between Pt/Ti, Pd/Ti, and Rh/Ti ratios in mineralized systems. The degree of PGE depletion is consistent with the relatively low R factor estimated for many komatiite-hosted deposits, which fall in the range of 20 to 200 for Thompson, 100 to 500 for Kambalda, and 300 to 1,100 for Raglan, implying that the volume of silicate magma that interacted with sulfide liquid was relatively small. This is also consistent with the relatively small proportion of komatiites displaying PGE depletion within ore-bearing flow sequences, as only magmas in ore-forming channels or conduits will interact with sulfides. False negatives, i.e., mineralized komatiite sequences with no detectable PGE depletion, are associated with systems characterized by high R factors. Basalts and komatiitic basalts show more complex patterns of variation, which can broadly be divided into three categories: (1) systematic PGE depletion over a range of Mg numbers, as in MORB suites, consistent with retention of sulfide in the mantle during partial melting; (2) increasing PGE depletion with decreasing Mg numbers in large igneous province (LIP)-associated basalts, interpreted to reflect attainment of sulfide saturation during fractionation with subsequent cotectic olivine-sulfide segregation; and (3) variable PGE depletion over a range of Mg numbers in komatiitic basalts (e.g., Raglan) interpreted to reflect ore-forming sulfide incorporation and segregation processes. The results of this study confirm that the PGE geochemistry of komatiites and basalts is a powerful indicator of sulfide saturation and ore-forming processes, but that it must be interpreted with the context of physical volcanologic and fluid dynamic processes.

Osmium isotopic compositions, and Re and Os concentrations have been examined in one komatiite unit and two komatiitic basalt units at Dundonald Beach, part of the 2.7 Ga Kidd-Munro volcanic assemblage in the Abitibi greenstone belt, Ontario, Canada. The komatiitic rocks in this locality record at least three episodes of alteration of Re-Os elemental and isotope systematics. First, an average of 40% and as much as 75% Re may have been lost due to shallow degassing during eruption and/or hydrothermal leaching during or immediately after emplacement. Second, the Re-Os isotope systematics of whole rock samples with 187Re/188Os ratios >1 were reset at ∼2.5 Ga, possibly due to a regional metamorphic event. Third, there is evidence for relatively recent gain and loss of Re in some rocks. Despite the open-system behavior, some aspects of the Re-Os systematics of these rocks can be deciphered. The bulk distribution coefficient for Os (DOssolid/liquid) for the Dundonald rocks is ∼3 ± 1 and is well within the estimated D values obtained for komatiites from the nearby Alexo area and stratigraphically-equivalent komatiites from Munro Township. This suggests that Os was moderately compatible during crystal-liquid fractionation of the magmas parental to the Kidd-Munro komatiitic rocks. Whole-rock samples and chromite separates with low 187Re/188Os ratios (

The Panzhihua gabbroic layered intrusion is associated with the 260Ma Emeishan Large Igneous Province in SW China. This sill-like body hosts a giant Fe–Ti–V oxide deposit with 1333 million ton ore reserves, which makes China a major producer of these metals. The intrusion has a Marginal zone of fine-grained hornblende-bearing gabbro and olivine gabbro, followed upward by Lower, Middle, and Upper zones. The Lower and Middle zones consist of layered melanogabbro and gabbro composed of cumulate clinopyroxene, plagioclase, and olivine. These zones also contain magnetite layers. The Upper zone consists chiefly of leucogabbro composed of plagioclase and clinopyroxene with minor olivine. Most rocks in the body show variable-scale rhythmic modal layering in which dark minerals, primarily clinopyroxene, dominate in the lower parts of each layer, and lighter minerals, primarily plagioclase, dominate in the upper parts. The oxide ores occur as layers and lenses within the gabbros and are concentrated in the lower parts of the intrusion. Ore textures and associated mineral assemblages indicate that the ore bodies formed by very late-stage crystallization of V-rich titanomagnetite from an immiscible oxide liquid in a fluidrich environment. The rocks of the Panzhihua intrusion become more evolved in chemistry upward and follow a tholeiitic differentiation trend with enrichment in Fe, Ti, and V. They are enriched in light rare earth elements relative to heavy rare earth elements, and exhibit positive Nb, Ta, and Ti anomalies and negative Zr and Hf anomalies. The silicate rocks and oxide ores of the Panzhihua intrusion formed from highly evolved Fe–Ti–V-rich ferrobasaltic or ferropicritic magmas. The textures of the ores and the abundance of minor hydrous phases indicate that addition of fluids from upper crustal wall-rocks induced the separation of the immiscible oxide melts from which the Fe–Ti–V oxide ore bodies in the lower part of the intrusion crystallized.

The Central Asian orogenic belt (CAOB) is composed of remnants of microcontinents, island arcs and ophiolites. The presence of voluminous Phanerozoic A-type granites suggest that continental growth occurred through addition of juvenile crust, and the presence of mafic–ultramafic intrusions provides direct evidence for a mantle contribution. The origin of the mafic–ultramafic intrusions in the Huangshan area, Eastern Xinjiang, has been debated because of the lack of precise age data or trace element and isotopic analyses. We have studied the geology, petrology, geochemistry and geochronology of two of the intrusions: the Huangshanxi and Huangshandong intrusions. Both are typical layered mafic–ultramafic intrusions composed of diorite, troctolite,norite, gabbronorite, gabbro wehrlite, websterite and lherzolite with systematic geochemical variations that are consistent with the following crystallization sequence: Ol–(Chr), Ol–Pyx–(Chr), Cpx–Pl and Hbl–(Bt). Igneous zircons separated from a diorite in the Huangshanxi intrusion yield a 269±2 Ma SHRIMP U–Pb age. The rocks are enriched in Rb–Ba–U–K–Sr relative to Th and LREE, depleted in Nb–Ta relative to Th and exhibit positive eNd values (+6.7 to +9.3). Ni–Cu–(PGE) sulfide mineralization occurs in the lower parts of the intrusions, primarily strata-bound within wehrlite or lherzolite and locally stratiform along the margins of the intrusions. The parental magmas appear to have been derived from a mantle source that was previously contaminated by subduction of oceanic crust and to have been variably contaminated by upper continental crustal components. The intrusions appear to have formed by plume-related activity within a continental setting, likely related to post-orogenic extension following Carboniferous amalgamation of arc-related terranes in the CAOB. This plume activity was most likely also responsible for providing heat sources to generate large amounts of A-type granites across the CAOB.

Thirty-three whole-rock drill core samples and thirteen olivine, chromite, and sulfide separates from three differentiated komatiite lava flows at Alexo and Pyke Hill, Canada, were analyzed for PGEs using the Carius tube digestion ID-ICP-MS technique. The emplaced lavas are Al-undepleted komatiites with 27% MgO derived by50% partial melting of LILE-depleted Archean mantle. Major and minor element variations during and after emplacement were controlled by 30 to 50% fractionation of olivine Fo93-94. The emplaced lavas are characterized by (Pd/Ir)N 4.0 to 4.6, (Os/Ir)N 1.07, and Os abundances of 2.3 ppb. Variations in PGE abundances within individual flows indicate that Os and Ir were compatible (bulk DOs,Ir 2.4 -7.1) and that Pt and Pd were incompatible (bulk DPt,Pd 0.2) during lava differentiation, whereas bulk DRu was close to unity. Analyses of cumulus olivine separates indicate that PGEs were incompatible in olivine ( DPGEs 0.04 - 0.7). The bulk fractionation trends cannot be accounted for by fractionation of olivine alone, and require an unidentified Os-Ir-rich phase. The composition of the mantle source (Os 3.9 ppb, Ir 3.6 ppb, Ru 5.4 ppb, Pt and Pd 5.7 ppb) was constrained empirically for Ru, Pt, and Pd; the Os/Ir ratio was taken to be identical to that in the emplaced melt, and the Ru/Ir ratio was taken to be chondritic, so that the absolute IPGE abundances of the source were determined by Ru. This is the first estimate of the PGE composition of a mantle source derived from analyses of erupted lavas. The suprachondritic Pd/Ir and Os/Ir of the inferred Abitibi komatiite mantle source are similar to those in off-craton spinel lherzolites, orogenic massif lherzolites, and enstatite chondrites, and are considered to be an intrinsic mantle feature. Bulk partition coefficients for use in komatiite melting models derived from the source and emplaced melt compositions are: DOs,Ir 2.3, DRu 1.0, DPt,Pd 0.07. Ruthenium abundances are good indicators of absolute IPGE abundances in the mantle sources of komatiite melts with 26 to 29% MgO, as Ru fractionates very little during both high degrees of partial melting and lava differentiation. Copyright © 2004 Elsevier Ltd

We sampled basaltic lava flows and underlying dacitic tuff deposits in or near lava tubes of the Cave Basalt, Mount St. Helens, Washington to determine whether the Cave Basalt lavas contain geochemical evidence of substrate contamination by lava erosion. The samples were analyzed using a combination of wavelength-dispersive X-ray fluorescence spectrometry and inductively-coupled plasma mass spectrometry. The results indicate that the oldest, outer lava tube linings in direct contact with the dacitic substrate are contaminated, whereas the younger, inner lava tube linings are uncontaminated and apparently either more evolved or enriched in residual liquid. The most heavily contaminated lavas occur closer to the vent and in steeper parts of the tube system, and the amount of contamination decreases with increasing distance downstream. These results suggest that erosion by lava and contamination were limited to only the initially emplaced flows and that erosion was localized and enhanced by vigorous laminar flow over steeper slopes. After cooling, the initial Cave Basalt lava flows formed an insulating lining within the tubes that prevented further erosion by later flows. This interpretation is consistent with models of lava erosion that predict higher erosion rates closer to sources and over steeper slopes. A greater abundance of xenoliths and xenocrysts relative to xenomelts in hand samples indicates that mechanical erosion rather than thermal erosion was the dominant erosional process in the Cave Basalt, but further sampling and petrographic analyses must be performed to verify this hypothesis.

South China has been considered as part of the Rodinian supercontinent during Neoproterozoic time, although its paleogeographic position within this supercontinent is still a matter of debate. The Wangjiangshan and Bijigou complexes along the northern margin of South China are among the largest mafic intrusions in China. New SHRIMP zircon U‐Pb results indicate that these two intrusions have crystallization ages of 820 Ma and 780 Ma, respectively. Enrichment of large ion lithophile and light rare earth elements and depletion of high field‐strength elements in these intrusions suggest derivation from an active arc along a continental margin. This interpretation of these intrusions as part of a continental arc assemblage is in contrast with the previous view that they were products of a Neoproterozoic mantle plume that initiated the breakup of Rodinia. The presence of a Neoproterozoic magmatic arc suggests that Rodinian oceanic lithosphere was subducted beneath the (present) northern margin of South...

Previous studies have suggested that there were two mass extinction events in the Late Permian: one that occurred at the Permo-Triassic (P/T) boundary (251 Ma) and a second, smaller mass extinction that occurred 5–8 Myr earlier at the end of the Guadalupian. Many workers have argued that there is a causal relationship between large-scale volcanic activity and mass extinctions. The major mass extinction event at the P/T boundary coincides with the outpouring of huge quantities of lava that formed the Siberian flood basalt province in Russia. Courtillot et al. [Earth Planet. Sci. Lett. 166 (1999) 177–195] and Wignall [Earth Sci. Rev. 53 (2001) 1–33] suggested that the earlier Late Permian mass extinction coincided with the eruption of the lavas that formed the Emeishan flood basalt (EFB) province in SW China. However, the age of eruption of the EFB lavas is poorly constrained. Using the Sensitive High-Resolution Ion Microprobe to analyze zircons, we have established the age of the Xinjie intrusion, believed to be a feeder to the main phase of EFB volcanism, to be 259±3 Ma. Hence, the formation of the EFB is coincident with a proposed extinction event at 256–259 Ma. This result supports a temporal link between the Emeishan large igneous province and the end-Guadalupian mass extinction.

We have applied a thermal–fluid dynamic-geochemical model to investigate the emplacement and erosional potential of Archean komatiite flows at Perseverance, Western Australia. Perseverance has been proposed as a site of large-scale thermal erosion by large-volume komatiite eruption(s), resulting in a 100–150-m-deep lava channel containing one of the world's largest komatiite-hosted Fe–Ni–Cu–(PGE) sulfide deposits. Using constraints based on field, theoretical, and geochemical data, we have modeled the emplacement of a range of flow thicknesses over felsic tuffaceous substrates with various degrees of consolidation and water contents. Thermo-mechanical erosion becomes more effective for substrates that are increasingly unconsolidated and water rich. For thermo-mechanical erosion to be responsible for the formation of the ~100-m-deep, concave Perseverance embayment and the highly-contaminated (~10–20%) Perseverance komatiites, the most likely scenarios require emplacement of thick (e.g. ≥10–30 m), turbulent, channelized liquidus or superheated komatiite lavas over a welded or unconsolidated submarine tuff. Flow distances must have been long (tens to hundreds of kilometers) and flow volumes must have been very high (hundreds to thousands of km 3 ). Lava channels and tubes >110 km long have not been observed on Earth, but are consistent with those formed by low-viscosity lavas on Venus, the Moon, Mars and Io. Flow volumes are consistent with those in continental flood basalt eruptions and oceanic plateau Large Igneous Provinces, and may represent the initial outpourings of komatiite lavas from Archean mantle plume activity.

Most magmatic Ni–Cu–(PGE) deposits are considered to have formed from sulfide-undersaturated silicate magmas and to contain a significant component of crustal sulfur that was derived via wholesale melting, partial melting, or devolatilization of wall rocks. Under such circumstances, the system may comprise a silicate magma and a sulfide magma, with or without crystalline solids, undissolved wallrock-derived xenoliths, an unmixed silicate xenomelt, or an undissolved xenovolatile phase, each of which may contain distinct chalcophile and lithophile components. Because traditional two-component (silicate magma – sulfide magma) mass-balance models do not accurately model such systems, we have developed a series of multicomponent elemental and isotopic mass-balance equations to model batch equilibration in magmatic Ni–Cu–(PGE) systems. We have applied them to the type examples of komatiite-associated Ni–Cu–(PGE) deposits at Kambalda, Western Australia. The calculations indicate that the elemental and isotopic compositions of the various components in a multicomponent system will vary considerably as a function of the relative abundances of the components, and that different metals and isotopic systems may decouple from each other, yielding apparently conflicting information regarding the sources of the components. The results suggest that the S isotopic and Zn compositions of the ores are more sensitive indicators of contamination than the Os isotopes, and support a sediment-melting model for Kambalda.

We have developed a mathematical model to evaluate the flow and erosional potential of submarine, channelized komatiite lavas at Kambalda, Western Australia. Field data from Kambalda were used to constrain the choice of important input parameters, and model results were compared with data from field studies and geochemical analyses. Our results suggest that thermal erosion is strongly dependent upon the nature and behavior of the substrate. If the substrate is treated as an unconsolidated, hydrous sediment that can be fluidized by vaporized seawater, then our model predicts that an initially 10-m-thick basal Kambalda komatiite lava could have produced very high thermo-mechanical erosion rates (∼23–10 m/day), crustal thicknesses of ∼5–20 cm at distances of ∼5–35 km from the source, and a high degree of lava contamination (∼3–12%). In contrast, if the substrate is treated as a more consolidated, anhydrous sediment that could not be fluidized, then our model predicts that a Kambalda komatiite flow would have had much lower thermal erosion rates (∼1.2–0.4 m/day) and degrees of contamination (∼1–3%), and would have had crustal thicknesses of ∼5–20 cm at longer flow distances of ∼30–165 km. Field constraints are generally consistent with our predictions for a non-fluidized substrate. The reentrant embayments at Kambalda are thought to form from either erosion of deep channels in a flat basaltic seafioor [Huppert et al., 1984], or erosion of a thin (

This paper uses large sets of whole-rock geochemical data to make comparisons between the komatiitic rocks of Abitibi (AGB) and Norseman-Wiluna (NWGB) greenstone terranes. The NWGB komatiite suite has a much higher proportion of highly olivine-enriched cumulates than the AGB suite, as indicated by data-density distributions on plots of MgO vs FeO and MgO vs Cr, although average compositions of the komatiite magmas in the two belts were not significantly different. NWGB komatiites appear generally more contaminated, on the basis of various ratios of strongly to moderately incompatible low-mobility trace elements. Both factors which are likely contributors to the much higher Ni sulfide resource endowment of the NWGB. The combination of high degrees of contamination and presence of olivine adcumulates in the NWGB attests to the presence of exceptionally high-intensity, prolonged eruptions, capable of forming long-lived entrenched magma pathways, represented by highly olivine-enriched cumulates, and capable of melting substrates to form orebodies. This is in contrast with more episodic, lower volume eruptions in the AGB. The contrast is interpreted as the result of crustal structure and tectonic setting, rather then the size and intensity of mantle plume sources.

The Namew Lake Fe-Ni-Cu sulfide deposit, 60 km south of Flin Flon, Manitoba, is hosted by an undifferentiated metapyroxenite sill enclosed within Early Proterozoic orthogneisses and covered by Paleozoic sedimentary rocks. The Namew Lake pyroxenite contains a relict igneous mineral assemblage of olivine + orthopyroxene + clinopyroxene + or - spinel + or - sulfides, suggesting derivation from a low Mg komatiitic or high Mg basaltic magma.Sulfide ore in the Namew Lake pyroxenite occurs as 3- to 10-mm blebs of disseminated Fe-Ni-Cu sulfides that accumulated during crystallization of olivine and pyroxene. A 0.5- to 5-m-thick layer of massive sulfide at the hanging-wall contact may represent a gravitationally segregated basal layer of a sill and suggests that the mine stratigraphy is inverted. Although the massive sulfides were compositionally modified during metamorphism and supergene alteration, the disseminated sulfides exhibit coherent geochemical trends and may preserve the average composition of the sulfide melt (recalculated to 100% sulfide: ca. 36% S, 42% Fe, 16% Ni, 6.1% Cu, 0.23% Zn, 148 ppm Pb, 5,300 ppb Pd, and 88 ppb Ir). Assuming a silicate/sulfide mass ratio of ca. 560 calculated from the platinum-group element (PGE) contents, the Ni content of a parental magma that would be in equilibrium with sulfides of that composition is similar to that of typical komatiites, but the Cu, Zn, and Pb concentrations are much higher. Thus, a komatiitic magma with ordinary Ni and PGE contents may have partially assimilated volcanogenic Cu-Zn-Pb sulfides, resulting in a high Mg basaltic magma from which the silicates and sulfides subsequently crystallized and equilibrated.The Namew Lake pyroxenite and associated sulfides were affected by five phases of deformation and three phases of metamorphism. The first deformational event in the area, D 1 , involved migmatization and isoclinal folding at upper amphibolite facies conditions. In addition, sheeted tonalites and diorites intruded prior to or during D 1 . D 2 folded the gneisses into domes, synforms, and antiforms. D 3 involved minor boudinage of the pyroxenite, intrusion of dikes, and displacement of the sulfides updip. D 4 shearing locally increased the thickness of the pyroxenite. D 5 and subsequent deformations produced brittle faulting with minor displacement, open folds of the ore horizon, and large-scale domain-bounding faults.The Namew Lake pyroxenite was metamorphosed at upper amphibolite facies (M 1 ), at lower amphibolite facies (M 3 ), and at greenschist facies (M 5 ). M 1 metamorphism of the pyroxenite produced partial replacement of the host pyroxenite by pargasitic amphibole. M 3 produced successive partial replacement by talc + dolomite, tremolite, and biotite, with greatest alteration at the edges of the pyroxenite and near crosscutting dikes. M 5 produced minor serpentine and cummingtonite. Most or all elements, including rare earth elements (REE), were mobile to varying degrees during M 1 , M 3 , and M 5 , resulting in the observed compositional variability of the Namew Lake pyroxenite.

Fe-Zn-Cu sulfide mineralization in the Stone Hill district of the northern Alabama Piedmont is hosted by zones of felsic schist and garnet schist within the Ketchepedrakee Amphibolite. The felsic schist is characterized by quartz-pyrrhotite-biotite-muscovite-plagioclase-rutilesphalerite _ chalcopyrite _ pyrite _ hornblende _ epidote assemblages and the garnet schist is characterized by garnet-hornblende-quartz-biotite-pyrrhotite-chalcopyrite _ sphalerite _ pyrite _ chlorite _ actinolite _ calcite assemblages. Both schists are well banded and highly deformed. The felsic schist locally contains ellipsoidal, polycrystalline aggregates of quartzfeldspar-biotite that superficially resemble sedimentary clasts but clearly formed tectonically by boudinage of felsic bands. The following petrographic and geochemical data and field relationships suggest that both schists are hydrothermally altered basalt (the precursor of the Ketchepedrakee Amphibolite): (1) the felsic and garnet schist units are very localized lenses (