Recent advances in the characterization of metasomatic iron and alkali-calcic (MIAC) systems with associated iron-oxide apatite (IOA) prospects and iron-oxide–copper–gold (IOCG) and metasomatic cobalt deposits of the Great Bear magmatic zone were used to determine if the geochemistry of glacial sediments can unveil pathfinder elements indicative of mineralization and associated alteration. Analysis of variance within bedrock lithogeochemical (n = 707 samples) and till geochemical datasets (n = 92 samples) are compared. Results show that Fe, Co, Ni, Cu, As, Mo, Bi, La, Th, U, and W were identified as potential vectoring elements in different fractions of till due to their anomalous concentrations down-ice of various mineralized outcrops within the study area. For instance, Fe, Co, Cu, and Mo were established as the most useful vectoring elements in the locally derived till (<2 km down-ice) near the Sue Dianne IOCG deposit, and Fe, Co, Ni, Cu, Mo, W, Bi, and U near the Fab IOCG prospect. At the Sue Dianne deposit, the ratios of near-total (4-acid digestion) versus partial (modified aqua regia digestion) concentrations in the silt + clay-sized till fraction (<0.063 mm) for both La and Th reflect the mineralization alteration signature and define a more consistent dispersal train from mineralization compared to element concentrations mapped alone. Additional testing in an area of continuous till cover near an isolated point source is recommended to further develop the elemental ratio method for exploration of MIAC systems.
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.
The Chevreuil intrusive suite (1.17-1.16 Ga) represents a chronological field marker of regional extent that intruded the Central Metasedimentary Belt in the western Grenville Province of Quebec after peak metamorphism. Style and site of magma emplacement, and extent of deformation of Chevreuil plutons and dykes permit unravelling of the early Grenvillian evolution of the belt with respect to cratonal North America. The suite comprises a series of vertically layered gabbro stocks and monzonite-diorite-gabbro sheet intrusions, and a swarm of microdiorite dykes that cut across gneisses. The dykes display systematic variations in extent of deformation across the belt. We targeted U-Pb geochronology on gneisses within the identified strain windows; they preserve the record of a ca. 1.20 Ga high pressure-temperature (P-T) metamorphic event. The sheet intrusions define magmatic corridors all along, and concordant with, the western, northern, and eastern tectonic boundaries of the belt. The concordant and elongate shape of these bodies results from emplacement, not deformation. Chevreuil magmas thus sealed the belt boundaries largely in their current positions, with the implication that docking of Elzevirian and pre-Elzevirian terranes with cratonal North America predates 1.17 Ga. We interpret the 1.20 Ga metamorphism as evidence for the initiation of Grenvillian continent-continent collision during the culmination of the Elzevirian orogeny at ca. 1.22 Ga. Emplacement-related fabrics indicate that the Chevreuil suite and the coeval Morin anorthosite suite intruded during renewed orogenesis. This orogenic pulse (Shawinigan) is not accretionary, but represents a strongly partitioned, compressive, intraplate reactivation event.
Models of the three-dimensional physical property variation of the NICO Au-Co-Bi-Cu deposit, Northwest Territories, and the Southern Breccia albitite-hosted uranium occurrences and their iron oxide-alkali alteration envelopes, were derived from inversion of high-resolution aeromagnetic, gravity, and magnetotelluric (MT) data at deposit to regional scales. In turn, integration of the geophysical results with physical property measurements and geologic observations leads to a new understanding of the geometry of the deposit, adjacent mineralized and altered zones, and potential cogenetic links within the host metasomatic system. NICO, which is a variant of the magnetite group iron oxide copper-gold (IOCG) class of deposit, is spatially associated with a discrete zone of lower electrical resistivity occurring within a broader, NE-dipping zone of higher density. The high-density zone overlaps a NE-dipping zone of higher magnetic susceptibility and is truncated to the southwest by a NW-striking geophysical discontinuity interpreted as a major fault zone. This inferred fault divides the magnetite-altered metasedimentary rocks hosting the NICO deposit from the albite-altered rocks within the Southern Breccia corridor to the southwest that host the uranium mineralization. Having been active during development of the metasomatic system, this fault influenced the formation of these distinct but complementary deposit types.
The Southern Breccia metasomatic uranium (U) showings are located 1 km south of the NICO deposit, an iron oxide-copper-gold (IOCG) deposit, in the Great Bear magmatic zone of Canada. The timing of both occurrences is tightly constrained to 1873–1868 Ma, linking formation of the albitite-hosted U to development of IOCG mineralization. During this period, regional iron oxide and alkali-calcic metasomatism formed: Na (albite), high-temperature Ca-Fe (amphibole + magnetite), high-temperature Ca-K-Fe (amphibole + magnetite + biotite ± K-feldspar), high-temperature K-Fe (K-feldspar/biotite + magnetite), K (K-feldspar ± biotite), and low-temperature K-Fe-Mg (K-feldspar + hematite + chlorite) assemblages. Primary uraninite and brannerite occur within high-temperature K-Fe alteration composed of magnetite + K-feldspar ± biotite-cemented breccias developed in earlier albitite. The chemistry of primary uraninite supports precipitation from high-temperature, magmatic-derived fluids, as previously proposed for the NICO deposit. Field relationships, petrography, whole-rock geochemistry, and geochronology indicate that alteration of the Southern Breccia corridor host rocks was coeval with early alteration at NICO, whereas U mineralization postdated Au-Co-Bi at NICO. The linkage of the Southern Breccia to the regional iron-oxide and alkali-calcic alteration system that generated the NICO deposit presents a new driver for formation of albitite-hosted U deposits and highlights an exploration target in IOCG districts globally.
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 1.521.46 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.
