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The greenstone belts along the northern margin of the Wawa subprovince of the Superior Province (Vermilion, Shebandowan, Winston Lake, Manitouwadge) formed at ca. 2720 Ma and have been interpreted to be representative of a rifted-arc to back-arc tectonic setting. Despite a common inferred tectonic setting and broad similarities, these greenstone belts have a significantly different metallogeny as evidenced by different endowments in volcanogenic massive sulphide (VMS), magmatic sulphide, and orogenic gold deposits. In this paper, we examine differences in geodynamic setting and crustal architecture as they pertain to the metallogeny of each greenstone belt by characterizing the regional-scale trace-element and isotopic (Nd and Pb) geochemistry of each belt. The trace-element geochemistry of the Vermilion greenstone belt (VGB) shows evidence for a transition from arc-like to back-arc mafic rocks in the Soudan belt to plume-driven rifted arcs in the ultramafic-bearing Newton belt. The Shebandowan greenstone belt (SGB) has a significant proportion of calc-alkalic, arc-like basalts, intermediate lithofacies, and high-Mg andesites, which are characteristic of low-angle, 'hot' subduction. Extensional settings within the SGB are plume-driven and associated with komatiitic ultramafic and mid-ocean ridge basalt (MORB)-like basalts. The Winston Lake greenstone belt (WGB) is characterized by a transition from calc-alkalic, arc-like basalts to back-arc basalts upward in the strata and is capped by alkalic ocean-island basalt (OIB)-like basalts. This association is consistent with plume-driven rifting of a mature arc setting. Each of the VGB, SGB, and WGB show some isotopic evidence for the interaction with a juvenile or slightly older differentiated crust. The Manitouwadge greenstone belt (MGB) is characterized by isotopically juvenile, bimodal, tholeiitic to transitional volcanic lithofacies in a back-arc setting. The MGB is the most isotopically juvenile belt and is also the most productive in terms of VMS mineralization. The Zn-rich VMS mineralization within the WGB suggests a relatively lower-temperature hydrothermal system, possibly within a relatively shallow-water environment. The Zn-dominated and locally Au-enriched VMS mineralization, as well as mafic lithofacies and alteration assemblages, are characteristic of relatively shallower-water deposition in the VGB and SGB, and indicate that the ideal VMS-forming tectonic condition may have been compromised by a shallower-water depositional setting. However, the thickened arc crust and compressional tectonics of the SGB suprasubduction zone during hot subduction may have provided a crustal setting more favourable for the magmatic NiCu sulphide and relative gold endowment of this belt. Les ceintures de roches vertes le long de la bordure nord de la sous-province de Wawa de la Province du Superieur (Vermilion, Shebandowan, Winston Lake, Manitouwadge) ont ete formees il y a environ 2720 Ma et elles ont ete interpretees comme representant un environnement tectonique d'arc distendu a arriere-arc. Malgre un environnement tectonique commun infere et de grandes similarites, ces ceintures de roches vertes ont des metallogenies tres differentes, tel que mis en evidence par differents enrichissements dans les gisements de sulfures massifs volcanogenes (SMV), de sulfures magmatiques et d'or orogenique. Dans le present article, nous examinons les differences dans les environnements geodynamiques et l'architecture de la croute, soit la maniere dont ces differences concernent la metallogenie de chaque ceinture de roches vertes, en caracterisant les elements traces, a l'echelle regionale, et la geochimie des isotopes (Nd et Pb) de chaque ceinture. La geochimie des elements traces de la ceinture de roches vertes Vermillon (VGB) montre des evidences d'une transition de roches mafiques de style arc a arriere-arc dans la ceinture Soudan, a des arcs distendus par des panaches dans la ceinture de roches ultramafiques de Newton. La ceinture de roches vertes Shebandowan (SGB) contient une proportion significative de basaltes calco-alcalins de type arc, de lithofacies intermediaires et d'andesites a forte teneur en Mg, lesquels sont caracteristiques d'une subduction << chaude >> a angle faible. Les environnements d'extension dans la SGB sont entraines par un panache et ils sont associes a des basaltes ultramafiques komatiitiques et de type dorsale mediooceanique (MORB). La ceinture de roches vertes de Winston Lake (WGB) est caracterisee par une transition de basaltes calco-alcalins de type arc a des basaltes d'arriere-arc vers le haut des strates; elle est coiffee de basaltes alcalin de type basalte d'iles oceaniques (OIB). Cette association concorde avec la distension d'un environnement d'arc mature par un panache. Chacune des ceintures VGB, SGB et WGB montre une certaine evidence pour une interaction avec une croute differenciee juvenile ou legerement plus agee. La ceinture de roches vertes Manitouwadge (MGB) est caracterisee par des lithofacies volcaniques a jeunes isotopes, bimodales, tholeiitiques a transitionnels dans un environnement d'arriere-arc. La MGB comporte les isotopes les plus jeunes et elle est aussi la plus productive en termes de mineralisation en SMV. La mineralisation en SMV riches en zinc dans la WGB suggere un systeme hydrothermal a temperature relativement basse, possiblement dans un environnement d'eau relativement peu profonde. La mineralisation en SMV, dominee par Zn et par endroits enrichie en Au ainsi que les lithofacies mafiques et les assemblages d'alteration sont caracteristiques d'une deposition en eau relativement moins profonde dans la VGB et la SGB; cela indique que la condition tectonique de formation ideale pour la SMV pourrait avoir ete compromise par une deposition dans un environnement aquatique moins profond. Toutefois, l'arc crustal epaissi et la tectonique de compression de la zone de suprasubduction de la SGB durant la subduction chaude pourraient avoir fourni un environnement crustal plus favorable pour l'enrichissement magmatique en sulfures de Ni-Cu et relatif d'or de cette ceinture. [Traduit par la Redaction], Introduction The Wawa subprovince is part of the Wawa-Abitibi terrane, which is the youngest accreted granite-greenstone terrane of the Superior Province (Stott 2011). The Neoarchean greenstone belts of the Wawa [...]

Abstract: The ca. 1110-1120 Ma diabase sills of the Nipigon Embayment represent the oldest phase of the Midcontinent Rift recognized to date. The sills can be subdivided into five geochemically [...]

Abstract: The Seagull and Kitto intrusions in the Nipigon Embayment of northwestern Ontario were studied to gain an understanding of the processes involved in sulfur saturation of the mafic to [...]

Abstract: A variety of metallic and non-metallic mineral deposit types occur within Archean and Proterozoic rocks in the area encompassing the Lake Nipigon Region Geoscience Initiative. Archean deposit types include [...]

Geoscience has been important in Canada's economic and social development, and during the 1980s geoscience funding was robust. However in 1994 target budget reductions were required, with some as large as 50%. All government departments had to assess the need for their programs and priority-setting exercises were undertaken. The Geological Survey of Canada (GSC) had reduced it staff to around 700 by 1998 and its budget was reduced to about 60 million Canadian dollars. New cooperative programs with industry have been initiated, with fund sharing and 'in kind' support.

The ca. 2720 Ma Winston Lake greenstone belt of the Wawa-Abitibi terrane, Superior province, is located on the northern margin of the Wawa subprovince and has important regional tectonostratigraphic implications for the development of the Neoarchean Superior province. The metallogenic importance of the belt is evident from the presence of the Winston Lake, Pick Lake, and Zenith volcanogenic massive sulfide (VMS) deposits. However, the chemostratigraphic evolution has not been fully examined at the greenstone belt scale, nor have the VMS deposits been examined from the perspective of the belt-scale petrogenesis and volcanic reconstruction. This study (1) reviews the geology and VMS mineralization in the Winston Lake greenstone belt, and (2) reconstructs its geodynamic setting, and its magmatic and metallogenetic history using new geological, trace element, and Nd isotope data constrained by new U-Pb geochronology. The belt is subdivided into two main lithotectonic assemblages: the Winston Lake Assemblage composed of tholeiitic to calc-alkalic bimodal volcanic lithofacies, and the Big Duck Lake Assemblage composed of alkalic to tholeiitic mafic flows and sills. The contact between the Winston Lake and Big Duck Lake Assemblages is intruded by the differentiated Zenith gabbro, which hosts the 0.16 Mt Zenith VMS orebody as a series of xenoliths. The variably altered felsic lithofacies of the Winston Lake Assemblage host the 3.1 Mt Winston Lake Main and 1.3 Mt Pick Lake Zn-rich VMS deposits. The felsic volcanic lithofacies of the Winston Lake Assemblage are FIII-type rhyolites and have a bimodal distribution of Zr/Ti indicating two distinct magmas formed by different temperatures of partial melting. Mafic lithofacies of the Winston Lake Assemblage are typically calc-alkalic to transitional between calc-alkalic and tholeiitic in composition. They have arc to back-arc trace element contents with distinctive negative Nb and Ti anomalies, enrichment in the light rare earth elements (LREE), and higher Tb/Nb ratios than the mafic rocks from the Big Duck Lake Assemblage. Mafic strata from the Big Duck Lake Assemblage have trace element characteristics similar to mature back-arc tholeiitic basalts, and OIB-like or oceanic plateau alkalic basalts with high Nb/Th and Ti/V ratios. The chemostratigraphy of the Winston Lake greenstone belt is consistent with a geodynamic model where arc rifting is followed by back-arc development. Nd isotope data indicate that strata from the Winston Lake and Big Duck Lake Assemblages are juvenile and show no evidence of contamination by significantly older crust. Therefore, crustal contamination signatures in the mafic flows from the Winston Lake Assemblage must have formed by contamination from crust that is of similar age and supports a comagmatic relationship between the mafic and felsic strata. The mafic flows of the Big Duck Lake Assemblage represent a mature back-arc setting with evidence for enriched plume-generated basalts in the upper mafic unit. The Winston VMS deposit formed during the early rifting of the arc and the timing is tightly constrained by the hydrothermally altered 2721.2 ± 0.9 Ma VMS-hosting felsic strata and younger, postmineralization, 2719 ± 4 Ma Zenith gabbro. The Zn-dominated VMS mineralization suggests that temperature of the hydrothermal fluid during discharge was relatively cool (<300°C) and did not maintain sufficiently high temperatures to precipitate significant amounts of copper relative to zinc. This is likely due to adiabatic cooling of the fluid because of a low-pressure (<0.5 kb) sea-floor environment and/or permeable volcaniclastic strata. A U-Pb age of emplacement of 2692.1 ± 0.7 Ma from the syndeformation quartz-feldspar porphyry in the Big Duck Lake Assemblage indicate it is comagmatic with syndeformation magmatic events typical of other greenstone belts along the northern margin of the Wawa-Abitibi terrane. This event is interpreted to represent the timing of terrane accretion of the Wawa-Abitibi terrane to the Superior province. [ABSTRACT FROM AUTHOR]

A ~10-km-thick sequence of basaltic to rhyolitic volcanic rocks forms the are component of the Cretaceous Lancones basin in northwestern Peru and underlies part of the Huancabamba deflection. The marine volcanic successions show markedly different compositional features and depositional facies consistent with a maturing arc within a shallowing marine basin. The earliest volcanism accompanying rifting was dominated by basaltic pillow lava and breccia with lesser aphyric to feldspar-quartz porphyritic felsic volcanic rocks. These volcanic successions filled the lowest exposed portion of the basin and were accompanied by volcanogenic massive sulfide (VMS) deposits, which are inferred to have formed in a localized but relatively deep marine setting. U-Pb zircon dating of felsic volcanic rocks associated with VMS deposits at Tambogrande indicates ages from 104.8 ± 1.3 to 100.2 ± 0.5 Ma for the ore-bearing volcanic sequence. The timing of onset of rift-related volcanism is not well constrained but is therefore of middle Albian age or older. Subsequent latest Albian to Turonian volcanism is composed of successions of relatively more felsic rich volcaniclastic rocks and yields U-Pb zircon ages of 99.3 ± 0.3 to 91.1 ± 1.0 Ma. These later volcanic successions are intercalated and overlain by siliciclastic and carbonate sedimentary sequences prevalent in the western forearc section of the Lancones basin. Finally, the basin was intruded by Late Cretaceous to Tertiary granitoids of the Coastal batholith. The genesis of the Cretaceous Lancones basin and other equivalent volcanic rift-related, marginal basins in western South America, including the western Peruvian trough, is related tectonically to the break-up of Gondwana. Early volcanism and associated VMS deposits formed in the Lancones basin during the Albian coincided with the initial rifting stage, prior to active oceanic spreading, between South America and Africa. During this time the relatively stationary western margin of continental South America was undergoing extension and rifting due to a westward and oceanward retreating are, resembling a Mariana arc-type setting. The Mochica orogeny marks the termination of rifting, subsidence, and related volcanism along the western margin of South America. This orogenic event also broadly coincides with the onset of spreading of the South Atlantic and westward drift of the South American continent. Subsequent volcanism in the Lancones basin was more continental arc-like under an Andean-type scenario. [ABSTRACT FROM AUTHOR]