The Beattie syenite is composed of a series of lenticular bodies of syenitic rocks, situated immediately north of the Porcupine-Destor fault zone in the town of Duparquet, approximately 32 km north of Rouyn-Noranda in the Abitibi Subprovince. The principal body is 3.3 km long and 470 m in width and is flanked by a series of smaller lenses to the south and northeast. The intrusion has been zircon dated at 2682±1Ma and 2682.9±1.1 Ma and hosted the major part of the Au-mineralization of the now defunct Beattie mine, which was an important producer of gold in the area from 1933 to 1956 (9.66 Mt at 4.88 g/t Au). A total of 5 petrographic units are defined here, on the basis of field relationships, macroscopic textures, petrology and mineralogy: 1- The porphyritic Beattie syenite unit is composed of 2% to 10% of tabular sub- to anhedral feldspar phenocrysts about 2 mm to 10 mm in size, set in a red feldspathic and aphanitic matrix. This unit can be strongly cataclastic with abundant hydrothermal minerals. 2- The equigranular magnetite-bearing syenite unit includes few feldspar phenocrysts, about 2 mm to 10 mm in a fine-grained matrix. It is characterized by unaltered titanite, epidote, hornblende porphyroblasts and is the only unit with actinolite replacing clinopyroxene. 3- The porphyritic Central Duparquet syenite unit contains between 2% - 25% of coarse equant euhedral feldspar phenocrysts, about 5 mm to 16 mm in size, in a red or sometimes grey aphanitic matrix. 4- The megaporphyritic syenite unit is composed of very coarse alkali feldspar phenocrysts, typically 1 cm to 6 cm across, in a red aphanitic matrix. The phenocrysts often form a glomeroporphyritic texture. 5- The lath syenite unit occurs as numerous ~m-width thin dykes, which cross-cut all other petrographic units. These dykes display a characteristic trachytic texture, as defined by the preferential alignment of alkali feldspar laths, which are typically 1 cm to 3 cm in a grey or red aphanitic matrix. Petrology and geochemistry investigations revealed that the syenite intruded into the older 2720-2718 Ma volcanic Deguisier Formation and the <2687±2 Ma sediments of the Porcupine Group. Detailed geochemical analysis revealed that the Deguisier Formation is composed of three units, forming a complete tholeiitic suite. The Deguisier Formation is proposed here to have been produced in a volcanic arc setting. Detailed petrological, mineralogical and geochemical studies indicate that, the syenite is part of the alkaline series and is metaluminous to peraluminous. The syenite intruded at shallow depths through a sequence of injections, yielding the five comagmatic units. The syenite and country rocks were then subjected to a series of hydrothermal alterations and brittle deformation events, combined with metamorphism to the greenschist facies. The Au-mineralization in this region is attributed to the hydrothermal alteration with brittle deformation.

The Beattie syenite is composed of a series of lenticular bodies of syenitic rocks, situated immediately north of the Porcupine-Destor fault zone in the town of Duparquet, approximately 32 km north of Rouyn-Noranda in the Abitibi Subprovince. The principal body is 3.3 km long and 470 m in width and is flanked by a series of smaller lenses to the south and northeast. The intrusion has been zircon dated at 2682±1Ma and 2682.9±1.1 Ma and hosted the major part of the Au-mineralization of the now defunct Beattie mine, which was an important producer of gold in the area from 1933 to 1956 (9.66 Mt at 4.88 g/t Au). A total of 5 petrographic units are defined here, on the basis of field relationships, macroscopic textures, petrology and mineralogy: 1- The porphyritic Beattie syenite unit is composed of 2% to 10% of tabular sub- to anhedral feldspar phenocrysts about 2 mm to 10 mm in size, set in a red feldspathic and aphanitic matrix. This unit can be strongly cataclastic with abundant hydrothermal minerals. 2- The equigranular magnetite-bearing syenite unit includes few feldspar phenocrysts, about 2 mm to 10 mm in a fine-grained matrix. It is characterized by unaltered titanite, epidote, hornblende porphyroblasts and is the only unit with actinolite replacing clinopyroxene. 3- The porphyritic Central Duparquet syenite unit contains between 2% - 25% of coarse equant euhedral feldspar phenocrysts, about 5 mm to 16 mm in size, in a red or sometimes grey aphanitic matrix. 4- The megaporphyritic syenite unit is composed of very coarse alkali feldspar phenocrysts, typically 1 cm to 6 cm across, in a red aphanitic matrix. The phenocrysts often form a glomeroporphyritic texture. 5- The lath syenite unit occurs as numerous ~m-width thin dykes, which cross-cut all other petrographic units. These dykes display a characteristic trachytic texture, as defined by the preferential alignment of alkali feldspar laths, which are typically 1 cm to 3 cm in a grey or red aphanitic matrix. Petrology and geochemistry investigations revealed that the syenite intruded into the older 2720-2718 Ma volcanic Deguisier Formation and the <2687±2 Ma sediments of the Porcupine Group. Detailed geochemical analysis revealed that the Deguisier Formation is composed of three units, forming a complete tholeiitic suite. The Deguisier Formation is proposed here to have been produced in a volcanic arc setting. Detailed petrological, mineralogical and geochemical studies indicate that, the syenite is part of the alkaline series and is metaluminous to peraluminous. The syenite intruded at shallow depths through a sequence of injections, yielding the five comagmatic units. The syenite and country rocks were then subjected to a series of hydrothermal alterations and brittle deformation events, combined with metamorphism to the greenschist facies. The Au-mineralization in this region is attributed to the hydrothermal alteration with brittle deformation.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This study presents results of a detailed geological mapping and structural analysis of auriferous quartz-vein sets of the nine current open-pit operations, of the Siguiri Mining Complex in the northeastern parts of Guinea. The Siguiri Mining Complex is hosted by a low-grade metamorphic, turbiditic succession within the larger Siguiri Basin, which forms part of the Palaeoproterozoic Birimian Supergroup of the Boualé-Mossi domain on the West African Craton. The Siguiri Mining Complex is located in a deeply weathered saprolite profile developed over the monotonous succession of interlayered metapelites and -psammites. In fresh bedrock and core samples, the host succession is mainly made up of quartz-muscovite schists, muscovite-chlorite schists and metagreywackes, with isolated occurrences of intraformational breccias. The main deformation to have affected the metasedimentary succession of the Siguiri Mining Complex can be assigned to a D2 deformational event. D2 structures comprise of north-south trending strike-slip and reverse faults anastomosing around and enveloping open- to tightly folded domains exposed over an area of 12 by 3 km. The geometry, orientation and kinematics of faults and folds suggest that D2 structures formed during progressive deformation in an overall dextral transpressive brittle-ductile shear zone. Structures within the D2 corridor record east-northeast subhorizontal shortening and north-northwest subhorizontal extension. An omnipresent carbonate alteration in form of carbonate-alteration spots testifies to the pervasive, syn-D2 hydrothermal fluid-flow within the sediments. A structurally- and fracture-controlled fluid-flow is evidenced by the abundance of auriferous quartz veins throughout the Siguiri Mining Complex. These quartz veins host the bulk of the gold mineralization. One main and, at least, three minor sets of auriferous quartz veins can be distinguished. The main quartz-vein set shows very consistent easterly to northeasterly trends and steep southerly dips throughout the Siguiri Mining Complex. This orientation is consistent with the dextral transpressive kinematics and strain within the D2 host structure and illustrates the significance of D2 strains for the mineralization. The volumetrically minor vein sets can be shown to be related to different stages of F2 folding and fold amplification. Zones of economic-grade mineralization occur in areas where competent, psammitic units are developed in structural sites of increased dilatancy. Areas of dilatancy are represented by either dilational jog geometries within the overall transpressive structure or zones of pronounced shear-zone subparallel stretch. Jog geometries could be identified in the larger Bidini-Toubani-Sanu Tinti Complex having formed as a result of the anastomosing geometry of the bounding D2 shear zones. In the large Kami Complex, F2 axial culminations and depressions correspond to zones of increased stretch within the D2 transpression zone, delineated by closer vein spacing and the formation of D2 normal faults parallel to the main vein set and normal to F2 fold hinges. The size and extent of the Siguiri Mining Complex suggests that the host D2 transpressive corridor must be assumed to have a significantly larger along-strike continuation, being part of a larger shear zone system related to the accretionary history of Palaeoproterozoic basins and arcs onto the Archaean Man Shield in West Africa. / AFRIKAANSE OPSOMMING: Hierdie studie lewer die resultate voor van 'n gedetailleerde geologiese kartering en strukturele analise van die gouddraende kwarts-aar stelle in die huidige nege oop-groef operasies van die Siguiri Myn Kompleks, in die noordoostelike deel van Guinea. Die Siguiri Myn Kompleks is geherberg deur 'n lae metamorfiese graad turbidiet suksessie in die groter Siguiri Kom, wat deel form van die Paleo-Proterosoïkum Birimian Supergroep van die Boualé-Mossi streek op die Wes Afrika Kraton. Die Siguiri Myn Kompleks is geleë in die diep veweerde saproliet profiel, wat onwikkel het oor die eentonige suksessie van metapeliete en -psammiete. In vars bodemrots en kern monsters is die herberg-gesteente opgemaak uit kwarts-muskoviet skiste, muskoviet-chloriet skiste en metagrouwakte, as ook afgesonderde voorvalle van intraformasie breksies. Die hoof deformasie fase wat die metasedimentêre suksessie van die Siguiri Myn Kompleks geaffekteer het, kan toegeken word aan 'n D2 deformasie gebeurtenis. D2 strukture bestaan uit noord-suid neigende strekkingwaartse verskuiwings en opskuiwings, wat anastomoserend oop- en steil geplooide gebiede omsluit en is oor 'n area van 12 by 3 km ontbloot. Die geometrie, oriëntasie en kinematika van verskuiwings en plooie stel voor dat D2 strukture gevorm het tydens progressiewe deformasie in 'n algemene regse transpressie skuifskeursone, onder brosheid-duktiliteit toestande. Strukture in die D2 gang wys 'n oos-noordoos subhorisontale verkorting en 'n noord-noordwes subhorisontale verlenging. Die alomteenwoordigheid van karbonaat alterasie, in die vorm van karbonaat-alterasie spikkels, getuig van die deurdringende, sin-D2 hidrotermiese vloeistof vloei in die sedimente. Die strukturele- en breuk-beheerde vloeistof vloei is ook duidelik, as gevolg van die oorvloed van gouddraende kwarts-are reg deur die Siguiri Myn Kompleks. Die kwarts-are bevat die grootmaat van die goud mineralisasie. Een hoof, en te minste drie minder belangrike stele van gouddraende kwarts-aar stelle kan uitgeken word. Die hoof kwarts-aar stel wys konstante oostelike to noordoostelike neigings en steil suidelike hellings, reg deur die Siguiri Myn Kompleks. Die oriëntasie is konstant met regse transpressie kinematika en vervorming in die D2 strukture en illustreer die belangrikheid van D2 vervorming vir mineralisasie. Die minder-belangrike aar stelle is verwant aan die verskillende staduims van F2 plooiing en plooi amplifikasie. Sones van ekonomiese graad mineralisasie kom voor in areas waar bevoegde eenhede van psammiete ontwikkel het in strukturele terreine van verhoogde dilatasie. Areas van dilatasie word verteenwoordig deur dilatasie uitwykings in die transpressie strukture of sones van skuifskeur subparalelle verlenging. Uitwykings geometrië kan geidentifiseer word in die groter Bidini-Toubani-Sanu Tinti Kompleks, waar dit gevorm het asgevolg van die anastomoserende geometrie van die D2 skuifskeur sones. In die groter Kami Kompleks kom F2 aksiale kulminerings en depressies voor in sones van verhoogde strekking binne-in die D2 transpressie sone en word uitgebeeld deur nader aar-spasiëring en die formasie van D2 afskuiwings, parallel aan die hoof kwarts-aar stel en normaal met betrekking tot die F2 plooi-skarniere. Die groote en omvang van die Siguiri Myn Kompleks stel voor dat die D2 transpressiewe gang nog n groter voorsetting het, en vorm deel van 'n groter skuifskeur sisteem en is verwant aan die anngroeings geskiedenis van die Paleo-Proterosoïese komme en boë aan die Argeïese Man Skild in Wes Afrika.

L’hydrodynamique et la probabilité de minéralisation (R²AI) autour des intrusions magmatiques ont été étudiées par modélisation numérique couplant transfert de chaleur et circulation de fluide. L’objectif principal de ce travail est de tester la nature du lien génétique entre l’intrusion et le processus de minéralisation. La première série de résultats s’appuie sur une comparaison avec des exemples naturels de gisements bien connus : i) L’hydrodynamique et la localisation des zones probables de minéralisation sont fortement dépendantes de la profondeur de mise en place du pluton. Au-dessus de 4.5km de profondeur de mise en place, le seuil de perméabilité de 10-16 m² est atteint et les cellules convectives peuvent créer des zones de décharge additionnelles où des minéralisations peuvent avoir lieu ; ii) Pour toutes les profondeurs d’emplacement, la zone en dessous du pluton n'est pas favorable à la précipitation minérale ; iii) Les apophyses focalisent les fluides convectifs et les zones de minéralisation autour d’elles ; iv) La phase de refroidissement n'est pas la phase majeure de convection. La zone advective principale et celle de haute favorabilité peuvent se produire avant et pendant la phase la plus chaude d’emplacement, avant que le magma ne cristallise complètement; v) Les détachements sont capables de fortement modifier et de re-localiser les flux convectifs déclenchés par une intrusion syn-tectonique; vi) Les conditions physiques favorables à la minéraliser sont produites pendant une durée courte autour de la phase la plus chaude de l'intrusion. Même si les arguments chimiques sont absents, la circulation de fluide (induite par la mise en place de magma) joue un rôle principal dans la genèse des gisements d'or associés aux intrusions. De plus, la formation de ce type de gisement est favorisée par l'occurrence d'une auréole thermique fracturée autour de l'intrusion. La seconde série de résultats concerne l’étude du cas naturel de la minéralisation W-Au de Tighza (Jebel Aouam) au Maroc Central. Une campagne d’acquisition de données gravimétriques, l’inversion données et l’utilisation de logiciel 3D, ont permis d’obtenir la géométrie 3D complexe du pluton de Tighza. Les résultats sont les suivants : i) la zone probable de la minéralisation apparaît au début de la mise en place du magma dans la zone perméable (veine W1) et s'étend pour remplir W1 et couvrir la région autour du pluton pendant la phase la plus chaude de mise en place; ii) lors du refroidissement, la zone probable est réduite et limitée à la zone perméable (W1) pendant 0,6 Ma; iii) L’application de la température de fermeture isotopique de la muscovite et de la biotite avec la distribution du R²AI montre que les âges de refroidissement entre la minéralisation au niveau de la veine W1 et l'intrusion ne sont pas séparés de plus de 0,10 Ma. Ceci est confirmé par la datation absolue de la minéralisation de Tighza et permet de discuter la fiabilité des âges obtenus pour la minéralisation dans la veine W1. / Coupled hydro-thermal numerical modeling has been used to simulate the hydrothermal fluid flow regime and the mineralization probability (R²AI) around plutons. The main objective behind this work is to test the nature of the genetic link between mineralization and intrusions. The first series of results comes from comparison with well-constrained mineral deposits: i) Fluid circulation and mineralization patterns are strongly dependent of the emplacement depth of the pluton. Deep seated plutons emplaced below 10 km do not induce an advective heat dissipation. For emplacement depth less than 4.5 km, the permeability threshold of 10-16 m2 is reached and second order convection cells may create additional discharge zones where mineralization are expected; ii) For all emplacement depths, the pluton floor zone is not favorable for mineral deposition; iii) The apexes strongly modified the fluid flow patterns by focusing convective fluids and mineralization zones around them; iv) The cooling phase is not the main phase of convection for large pluton often associated with long-lived magma emplacement. Major advective heat dissipation and mineral deposition zone may also occur sometime before and during the hottest phase of emplacement; v) Extensional detachments faults are able to delocalize and strongly modify classical fluid flow patterns induced by coeval intrusion; vi) Favorable physical conditions for mineral deposition are encountered around middle crust pluton, during a short time span bracketing the hottest phase of intrusion. We conclude that, even if chemical arguments are absent, fluid circulation induced by granite emplacement plays a key role in the genesis of granite-related Au deposits. Moreover, formation of this type of deposit is promoted and controlled by the occurrence of a fractured thermal aureole around the intrusion. The second series of results deals with the W-Au granite related Tighza deposits (Jebel Aouam, Morocco). Based on gravimetric data, inversion, and 3D modeling software, we were able to construct the most probable complex geometry of the Tighza pluton. The 3D geometries of the pluton and major fractures (W1 vein) were injected in the hydro-thermal modeling procedure. The results are: i) the probable zone of mineralization appears at the beginning of magma emplacement within the permeable zone (W1 vein) and extends to fill up W1 and covers the area around pluton at the hottest phase; ii) During the cooling phase, the story was reversed; the probable zone was reduced and restricted in the permeable zone (W1) during 0.6 Myr of cooling; iii) Application of isotopic closure temperature of muscovite and biotite coupled with R²AI distribution shows that the cooling ages between mineralization in W1 veins and the intrusion are not separated by more than 0.10 Myr. This is confirmed by the absolute dating obtained for Tighza Au mineralization and allows discussing the significance of older ages obtained for the mineralization in W1 veins.

Samli Fe-oxide (+Cu&plusmn / Au) deposit is hosted by Samli pluton and rocks of Karakaya Complex in western Anatolia. The pluton consists of both mafic and felsic phases showing magma mixing textures. 40Ar/39Ar geochronology yielded an age range of 23.2&plusmn / 0.5 to 22.42&plusmn / 0.11 Ma for the Samli pluton, overlapping with 40Ar/39Ar age of 22.33&plusmn / 0.59 Ma and U-Pb age of 23.34&plusmn / 0.19 Ma from alterations. Sr-Nd isotope data are suggestive of a metasomatized subcontinental lithospheric mantle (SCLM) source for the magma. Alteration-mineralization pattern is defined by a series of overlapping halos characterized by sodic-calcic (plagioclase-pyroxene&plusmn / scapolite), calcic (garnet-pyroxene&plusmn / epidote), potassic (biotite+magnetite+chalcopyrite), hematite-limonite, and late stage (chalcedony-calcite+native Cu) alterations. Stable (&delta / 18O, &delta / 34S) and radiogenic (87Sr/86Sr,143Nd/144Nd) isotope compositions suggest a magmatic source for the fluids responsible for alteration-mineralization. Given the spatial-temporal association of alteration- mineralization with magmatic rocks, the hydrothermal system that controls mineralization in Samli appears to be linked with emplacement and cooling of Samli pluton. Samli Fe-oxide (+Cu&plusmn / Au) deposit has features characteristic for both skarn- and Iron-Oxide-Copper-Gold (IOCG) type deposits. The spatial and temporal association with a porphyritic intrusion, widespread calc-silicate assemblage, metal content (abundant Fe-oxide with high copper content) are similar to calcic Fe-Cu skarns, whereas low-Ti (&le / 0.05% TiO2) magnetite/hematite, low-S sulfides (chalcopyrite&gt / pyrite), high Cu (up to 6.78%) and moderate Au (up to 8.82 ppm) grades, local structural control in alteration-mineralization, and the derivation of the causative magma from a SCLM resembles the features pertinent to IOCG type mineralization. Therefore, Samli deposit is defined as a skarn type Fe-Cu mineralization with a potential for IOCG type deposit.

La plupart des gisements de Ni-Cu sont issus de magmas komatiitique ou tholéiitique associés à des panaches mantelliques. Leur genèse fait intervenir l’exsolution d’un liquide sulfuré immiscible, l’interaction entre les liquides silicaté et sulfuré afin de concentrer ce-dernier en éléments chalcophiles, et l’accumulation du liquide sulfuré en quantités économiques. La saturation en sulfure est généralement atteinte en réduisant la solubilité des sulfures. Celle-ci se fait par assimilation de roches encaissantes siliceuses et/ou sulfurés.Le dyke d’Älgliden de la ceinture de Skellefte, en Suède, contient des sulfures de Cu et Ni dont les quantités ne sont actuellement pas économiques. La minéralisation d’Älgliden est atypique dans la mesure où elle contient d’importantes teneurs en Au, elle a un faible rapport Ni/Cu et enfin est formé dans un contexte de subduction. Le dyke recoupe un gisement porphyrique à Cu-Au contenant des sulfures ce qui laisse suggérer que la minéralisation d’Älgliden est formée par assimilation.Les objectifs de ce projet de recherche étaient d’examiner les processus de formation de la minéralisation d’Älgliden et son potentiel minier ainsi que de mieux comprendre la formation des gisements à Ni-Cu en contexte de subduction. Ce travail inclut l’étude pétrologique du minerai et de ses roches hôtes, la détermination de compositions minérales, l’analyse des éléments majeurs et traces sur roche totale et enfin des analyses des isotopes du soufre. Ce projet a été financé par la compagnie Boliden qui détient le gisement d’Älgliden.Le dyke est composé en majeure partie de norite à olivines, et minoritairement de leucogabbros. Les compositions sur roches totales, les textures magmatiques et les compositions minérales suggèrent que les norites à olivine se sont formées par accumulation d’olivine tandis que les leucogabbros représentent des liquides résiduels avec ou sans cristaux cumulus de plagioclase ± orthopyroxene. Les norites sont interprétées comme étant formées par une ou deux injections de bouillie cristalline suivie de cristallisation fractionnée. Le magma parent des roches d’Älgliden était un basalte hydraté et évolué dont la teneur en MgO est estimé à 6%.Le minerai sulfuré est principalement disséminé à travers l’ensemble de l’intrusion d’Älgliden. Quelques concentrations modérées de minerai se présentent sous la forme de sulfures en réseaux, de veines de sulfures et de sulfures massifs, lesquelles sont spatialement associées aux leucogabbros et aux xénolites de l’encaissant. L’association entre les leucogabbros et les concentrations en sulfures, leur faible teneur en métaux et leur faible rapport Ni/Cu suggèrent que la phase sulfuré s’est exsolvée tardivement au cours de la différentiation magmatique. Ce timing semble défavorable pour la minéralisation d’Älgliden puisqu’il inhibe à la fois l’interaction entre les liquides silicaté et sulfuré et l’accumulation du liquide sulfuré.La contamination du magma d’Älgliden par son encaissant n’est pas corroboré par les concentrations en élément trace et les compositions isotopiques du soufre. En revanche, ces données indiquent que le magma d’Älgliden s’est mis en place dans une zone de subduction où l’on pense que la saturation en sulfure a été atteinte par réduction d’un magma oxydé et riche en élément volatiles, via la cristallisation de magnétite et/ou dégazage. Les valeurs positives de δ34S suggèrent que l’apport de matériel dérivé du slab est responsable du caractère oxydé du magma d’Älgliden.L’état d’oxydation des magmas d’arc leur permet de dissoudre de grandes quantités de S et d’Au. Leur caractère évolué est responsable de leur fortes concentrations relatives en Au et leur faible rapport Ni/Cu. Ainsi, en contexte subduction les sulfures magmatiques sont susceptibles d’avoir ces caractéristiques, et si l’exsolution du liquide sulfuré a lieu plus tôt que dans le cas d’Älgliden cela pourrait conduire à la formation de gisements économiques. / Most major sulfide Ni-Cu deposits originated from komatiitic or tholeiitic magmas that formed in association with mantle plumes. Their genesis involves the segregation of a immiscible sulfide liquid, reaction of the sulfide liquid with silicate melt to upgrade the sulfide in chalcophile elements, and the concentration of the sulfide liquid in economic amounts. Saturation in sulfide is commonly achieved by lowering the sulfide solubility via assimilation of siliceous wall rock or by increasing the S content by adding S-bearing materials.The Älgliden dike in the Skellefte Belt in Sweden contains currently uneconomic Ni-Cu sulfide mineralization. The Älgliden mineralization is atypical insofar as it contains a significant amount of Au, has a low Ni/Cu ratio and formed in a subduction-related geodynamic setting. The host intrusion intrudes sulfide-bearing Cu-Au porphyry mineralization which led to the suggestion that the Älgliden Ni-Cu-Au mineralization was linked to the assimilation of sulfide-bearing wall rocks.The goals of this research project were to investigate the ore forming processes of the Älgliden mineralization and its ore potential, as well as to improve our understanding of the genesis of Ni-Cu deposits in subduction zones. The work is based on a petrological study of the ore and its host rocks, determination of mineral compositions, analyses of major and trace elements in bulk rocks, and sulfur isotope analyses. This was supported by the Boliden company which owns the deposit.The dike is composed mainly of olivine norites with minor leucogabbros. Bulk rock compositions, magmatic textures and mineral compositions suggest that the olivine norites formed by accumulation of olivine and that the leucogabbros represent residual melts with or without cumulus plagioclase ± orthopyroxene. The norites are interpreted to form by one or two injections of an olivine-rich crystal mush and subsequent fractional crystallization. The parental melt of the Älgliden rocks was a hydrous and evolved basalt estimated to contain ≈6 wt.% MgO.The sulfide ore is mainly disseminated throughout the whole Älgliden intrusion. Some weak ore concentrations occur as network to vein and massive sulfides that are spatially associated with the leucogabbros and wallrock xenoliths. The association between the leucogabbros and the concentrations of sulfide, their low ore grade and Ni/Cu ratio suggest that the sulfide segregated late in the differentiation process. This timing appears unfavorable for the Älgliden mineralization because it inhibited both sulfide-silicate liquid interaction and the accumulation of sulfide.Contamination of the Älgliden magma by its wall rocks is not supported by trace element data and S isotope compositions. Instead these data indicate that the Älgliden magma was emplaced above a subduction zone where the sulfide saturation is thought to occur by reduction of the oxidized and volatile-rich magma by magnetite fractionation and/or by degassing. Positive δ34S values suggest addition of slab-derived material which is thought to be responsible for the oxidized character of the Älgliden magma.The oxidation state of arc magmas allows them to carry large amounts of S and Au. Their evolved character is also responsible for their relatively high Au contents and low Ni/Cu. Such characteristics are likely to occur in magmatic sulfide mineralization in subduction zone settings, and if sulfide liquid segregation had occurred earlier than at Älgliden the process may have produced economic sulfide deposits.