Volcanic belts developed along the southeastern continental margin of Laurentia between 1.70 and 1.30 Ga and subsequently metamorphosed at high grade are today largely concealed among gneiss complexes of the Grenville Province. At the eastern end of the Wakeham Group and in the La Romaine Supracrustal Belt to the east, four 1.50 Ga volcanic centres were found among gneissic synvolcanic intrusions typical of the 1.52–1.46 Ga Pinwarian continental magmatic arc. Upper amphibolite- to granulite-facies rhyolitic to dacitic lavas and coarse lapillistone overlie or are intimately associated with arenites typical of the Wakeham Group. Garnetite, ironstone, carbonate rock, calc-silicate rock, and sillimanite-bearing nodules, veins, and gneiss, locally preserving lapilli, are also present. The distribution, paragenesis, and modes of most of these latter units differ from those of normal metasediments but are diagnostic of metamorphosed exhalites and hydrothermal alteration zones. In the La Romaine Supracrustal Belt, they are associated with pyroclastic horizons and a mineralized composite amphibolite unit. Volcanic textures include flow banding, wispy lapilli moulding fragmented lapilli and rounded lapilli with quartz-feldspar mosaics (filled vesicles), and in situ shattering of lapilli. These textures and the presence of advanced argillic alteration point to vesicular volcanism and hydrothermal activity in a subaerial to shallow submarine environment. Rare mafic lapilli attest to coeval mafic magmatism. The pervasive calc-alkaline signature of the eruptive and intrusive felsic to mafic rocks and their distribution are compatible with the development of 1.50 Ga intra-arc volcano-sedimentary belts stemming from the Wakeham Group basin and extending eastward within the Pinwarian continental magmatic arc.

The La Romaine Supracrustal Belt and the southeastern end of the Wakeham Group in the eastern Grenville Province, Canada, host a series of Pinwarian, 1.50 Ga felsic-dominated volcanic centres metamorphosed at amphibolite to granulite facies during the Grenville orogeny. The centres are interpreted as being related to the emergence of rhyolitic domes in shallow-marine intra-arc basins within the active Pinwarian continental magmatic arc. High-grade metamorphosed hydrothermal alteration zones are intimately associated with pyroclastic deposits composing these volcanic centres and an overlying composite amphibolite unit. They comprise layers of rhyolitic metatuff bearing networks of aluminous nodules and veins, migmatized garnet–biotite–sillimanite gneiss with well-preserved volcanic fragments, and mottled quartz–cordierite gneiss with textures similar to those of vuggy silica facies. Alteration zones of ironstone, carbonate and calc-silicate rocks, garnetite, diopsidite, epidosite, and sulphide mineralization collectively cut across the internal contacts of a composite amphibolite unit inferred to be a mafic lava and sill complex. Lithogeochemical analysis of inferred metamorphosed altered rocks and precursors highlights chemical changes typical of metamorphosed sericitic zones, advanced argillic and silicic zones, and discharge zones characterized by calcic alterations and copper mineralizations. Such zones involve the interaction of hot, very acidic to neutral fluids. Medium to heavy rare-earth elements (REE) and Zr behave as mobile elements in the hydrothermal system as a result of the presence of F-rich fluids. The chemical changes recorded by the various alteration zones share similarities with those observed in high-sulphidation, volcanic-hosted massive sulphide deposits occurring in proximal, shallow-marine, volcanic sequences.

The last field season of the Targeted Geoscience Initiative Eastern Grenville Transect in Quebec unveiled a < 10 km wide by 50 km long southeastern extension of the Wakeham Group, host to an extensive cupriferous hydrothermal system. The supracrustal rocks consist of granulite-facies metasandstone, 1.5 Ga lapillistone, amphibolite, marble, and calc-silicate rock enclosed within a metamorphosed, 1.5 Ga Pinwarian subvolcanic batholith. High-grade metamorphism in this belt would traditionally be seen as an impediment to mineral exploration. However, we have recognized and traced an extensive zone of aluminous gneiss that records strong hydrothermal leaching of metavolcanic units. Amphibolite occuring structurally above and likely serving as a caprock contains garnetite, diopsidite, and hornblendite and provides an effective guide to the site of fluid discharge and mineralization.Anumber of showings were discovered; their systematic occurrence, in a structural and stratigraphic sense, suggests that, although this supracrustal belt is of modest size, it should be explored.

A geological transect centered on La Romaine village in the eastern Grenville Province reveals a significant eastward extension of the Wakeham Group. A lithological assemblage of lapillistone, amphibolite, marble, and aluminous gneiss is locally mineralized and bears similarities with the 1.5 Ga supracrustal units newly recognized northwest of Musquaro Lake. These rocks are surrounded by granitic gneiss with recrystallized anorthosite enclaves. A practically undeformed 1 kmthick layered intrusion contains subvertical layers of peridotite, troctolite, and gabbro, with local Cu mineralization as well as various intrusive breccias. In the study area, two units record polyphase deformation with spectacular interference fold patterns: the eastern margin of the layered intrusion and a tonalitic gneiss of regional extent. Along with the anorthosite enclaves in the granitic gneiss, these units could be the expression of mafic magmatism and orogenesis of Labradorian age such as those found to the east in the Pinware terrane of Labrador.