CSM in the Grenville: Discoveries and Progress in Understanding their Enrichment Process (Case of Copper, Nb-REE and Graphite Mineralization)

Jacques Martignole (1939–2025) was an internationally renowned geologist whose work profoundly marked our understanding of the Grenville geological province. Originally from Carcassonne, France, he arrived in Québec in 1964 to undertake a Doctorat d’État (state doctorate) on the Morin Anorthositic Complex, marking the starting point of an exceptional career at the Université de Montréal. Spanning over four decades (1968–2012), his scientific journey was distinguished by an integrative approach combining petrology, geochronology, structural geology and metamorphism aimed at understanding the orogenic processes of the Grenville Province.

Jacques Martignole represented the archetype of the field geologist combined with the rigour of a petrologist and the depth of a tectonic thinker. He made a major contribution to the Lithoprobe Program and to the understanding of the geology of the Grenville Province, particularly in three areas: (1) the petrogenesis of anorthosites and anorthosite–mangerite–charnockite–granite (AMCG) suites; (2) the tectonic architecture of the Grenville Province and (3) the structural, thermal and chronological evolution of the Grenvillian Orogeny. His approach was integrative, combining field observations, detailed petrographic analyses, geochronological data and large-scale tectonic reasoning.

Over the years, Jacques Martignole trained several generations of geologists in structural geology, supervised numerous master’s and doctoral students and collaborated with a vast network of researchers. A rigorous and reserved scientist, Professor Martignole was distinguished by his keen sense of humor. He was passionate about mountains, skiing, classical music and Persian rugs.

The Central Metasedimentary Belt (CMB) is part of the monocyclic Allochthon of the Grenville Province in Quebec. It developed in a back-arc volcano-sedimentary basin setting along the margin of Laurentia before being incorporated into the Grenvillian orogen. It represents a remarkable metallogenic domain for critical and strategic metals, hosting graphite, base-metal (Cu, Zn, Ni), precious-metal (Au, Ag), and strategic-metal (Nb, REE, U) mineralization, which to date has been investigated only to a limited extent.

North of Mont-Laurier, two major sediment-dominated basins can be distinguished on either side of the Baskatong antiformal promontory, marked by the Beauregard Lineament. In the Ducarny-Napigon basin, the Ascension Formation (1.28 Ga) comprises evaporitic, carbonate, and pelitic units indicative of a shallow-platform environment. Rhyolites, together with block and lapilli tuffs, also record felsic explosive volcanic activity. Their geochemical signature suggests an arc or back-arc setting.

The basin hosts numerous copper concentrations in volcano-sedimentary, sedimentary, and magmatic settings. The Ducarny and Leroy massive-sulfide showings extend along a trend of more than 10 km along the basin margin and display similarities to Kuroko‑type mineralization. Copper mineralization also occurs in sedimentary and plutonic environments in the northeastern part of the basin. Taken together, these observations highlight the metallogenic potential of the Ducarny-Napigon area and warrant further investigation.

This presentation outlines the results of geological mapping campaigns carried out during the summers of 2024 and 2025 in the Musquanousse Lake (NTS sheet 12K06) and D’Auteuil Lake (NTS sheet 12K11) areas. This area consists mainly of an intrusive rock suite, including Wakeham-age basement (1582 Ma), which corresponds to the Aigle Complex. The latter is overlain by the volcano-sedimentary sequence of the Coude Complex (~1519 to 1491 Ma). The entire sequence is intruded by Pinwarian intermediate to felsic plutons, including the Marie-Claire (~1505 to 1479 Ma), Grand Priant (~1502 Ma) and D’Auteuil (~1494 Ma) intrusive suites, as well as the Grand Portage Granodiorite (~1500 Ma), to which are added the mafic intrusions of the Lillian Intrusive Suite. Later intrusions, including the Dabin Intrusion (~1276 Ma), the Mantuh Intrusive Suite (~1088 Ma) and the Musquaro Gabbroic Intrusion (~1069 Ma), predate the emplacement of weakly deformed intrusions of the Washicoutai Intrusive Suite (~1043 to 1031 Ma) and late granites of the Bouin Intrusive Suite (~1027 Ma), which represent the last recognized magmatic episodes in the area. A few mineralized zones have been identified in the area, including one rare earth element (REE) showing, as well as Zn and Cu zones. The region is characterized by four major types of hydrothermal alteration (sodic, aluminous, ferrous-magnesian and potassic), mainly associated with rocks of the Coude Complex and the Grand Priant Intrusive Suite. Metamorphosed to the amphibolite facies, these alteration zones are interpreted as the expression of a zoned hydrothermal system.

Carbonatites are one of the primary natural hosts for the mineralization of rare earth elements (REE) and niobium (Nb), which are critical metals for modern technologies. While the metallogenic potential of these rocks is widely recognized, the precise processes leading to economic enrichment in Nb and REE remain complex and multifactorial. Among these, the combination and interaction between carbonatitic magmas and host silicate lithologies (syenite, gneiss, pyroxenite, etc.) play a role in the genesis, concentration and redistribution of these elements. These interactions, both magmatic and hydrothermal, manifest as physical (brecciation, assimilation), chemical (fenitization, metasomatism, hydrothermal activity) and mineralogical phenomena that strongly influence the geometry and nature of mineralized zones. This presentation focuses on carbonatites and proposes to evaluate Nb and REE mineralization processes by examining the lithologies of five representative mineralized alkaline complexes in the Grenville Province: Crevier, Grand Lac Brochet, Saint-Honoré, Terres Rompues and Girardville. This approach relies on a combination of field observations, petrographic and geochemical analyses (major and trace elements) and mineral microanalyses, notably by LA-ICP-MS on biotite, to better characterize the signatures of these mineralizations and understand the processes enabling the mobility of Nb and REEs.

Metasedimentary sequences of the Grenville Province have significant potential for a variety of critical and strategic mineral deposits, including graphite, high-purity silica, copper, and zinc. Many of these mineralizations are syngenetic, meaning that they formed contemporaneously with their host rocks. Therefore, understanding the geological environments in which these metasedimentary sequences developed is essential for explaining and predicting the distribution of critical and strategic mineral deposits.

However, the metamorphism and deformation associated with the multiple orogenic events that affected the Grenville Province have greatly complicated the interpretation of these rock successions. Across the province, the original sedimentary rocks are primarily preserved as discontinuous and tectonically dismembered fragments, which may have experienced distinct metamorphic histories. Current classifications of these sequences rely on a limited number of geochronological constraints and are based largely on lithological characteristics and metamorphic grade.

Recent work conducted by our research group has highlighted the limitations of this approach and underscores the need for a comprehensive reassessment of the subdivision of metasedimentary sequences. Such a re-evaluation is essential to improve our understanding of their geological evolution and to enhance the exploration and development of the critical and strategic mineral resources they contain.

Shear zones exert a major influence on the distribution of tectonic domains in the Grenville Province and, by extension, on the distribution of mineral resources. The Central Grenville Province contains a network of syn- to late-Ottawan shear zones, whereas early-Ottawan (>1080 Ma) crustal thickening structures are relatively rare. The NE-striking dextral (± oblique-reverse) St-Fulgence shear zone in Lac-Saint-Jean shows evidence of high-temperature deformation (650–800 °C) around 1060 Ma, following the metamorphic peak. It may have played a role in the emplacement of granitic dykes, locally rich in Th-U-REE, that are parallel and synchronous with this shear zone. In the Mauricie region, the N-S Eastern Taureau and Tawachiche shear zones instead show normal movement at high temperature (675–775 °C) at 1065 Ma and at moderate temperature at 1065–1035 Ma, respectively. These shear zones exhumed the deep crust and juxtaposed it with the Montauban volcano-sedimentary sequences, which contain Zn-Cu-Au-Ag mineralization in the form of massive sulfides. Taken together, these structures record most of the crustal evolution of the Central Grenville Province after the peak of the collision.

Graphite, a critical and strategic mineral, forms through either the metamorphic graphitization of organic matter or the precipitation of carbon from hydrothermal fluids. The Lac-des-Îles Mine, located in the Central Metasedimentary Belt of the Grenville Province (Québec, Canada), is traditionally interpreted as an orogenic graphite deposit formed in a metamorphic-hydrothermal environment. However, the source of carbon, the role of CO₂-rich fluids, and the influence of regional structures remain poorly constrained.

Field investigations completed in 2025 included mapping 88 outcrops, examining six graphite occurrences, and conducting petrographic, geochemical, structural, and geochronological studies. Graphite is present as disseminated flakes within metasedimentary host rocks throughout the study area.

The highest concentrations occur at the Lac-des-Îles Mine and the Lac aux Bouleaux occurrence, where graphite is associated with nodular graphite-bearing marbles and graphite-rich calc-silicate rocks. These units display abundant calcite- and graphite-replacement textures, calcite-graphite veins, and local graphite concentrations reaching up to 50%.

Preliminary results suggest that the nodular graphite-bearing marbles may represent metasomatized calc-silicate rocks formed through interaction with CO₂-rich fluids. Secondary graphite enrichment likely occurred during Grenvillian metamorphism and deformation, controlled by lithological and structural traps. Regional NE-SW-trending structures may have acted as pathways for fluid flow and carbon remobilization, leading to graphite concentration and providing the basis for a revised metallogenic model for southwestern Grenville graphite deposits.

Carbonatites and their associated alkaline intrusions are major hosts of rare earth elements (REE). A notable example is the Neoproterozoic Saint-Honoré complex in the Saguenay Graben, a concentrically zoned alkaline–carbonatite system that host the Niobec Nb–REE deposit. Although previous studies have proposed a hybrid magmatic–hydrothermal origin for REE mineralization in this system, quantitative mineralogical characterization at depth has remained limited.

In this study, an integrated QXRD–XRF workflow is applied to investigate mineralogical and geochemical variability across a 113–1,254 m depth profile from the deepest borehole in the Niobec REE-mineralized zone. Results reveal changes in major and minor phases, including dominant dolomite–ankerite, siderite (0–23%), minor calcite, and REE bearing minerals, including baryte (up to ~34%), fluorapatite (≤25%), monazite (≤10%), and bastnäsite (≤6%). Elemental analyses corroborate these compositions (CaO 15–28%; MgO 4.5–16%; Fe₂O₃ 6–21%) and reveal REE enriched profiles (≤9%) and low Nb₂O₅ contents (<0.3%).

Hierarchical clustering of the QXRD dataset defines three mineralogical facies: (1) carbonate dominated ferrocarbonatite rich in dolomite–ankerite; (2) baryte carbonate assemblages; and (3) REE enriched facies with elevated monazite and fluorapatite. These facies reflect primary magmatic variability, with hydrothermal minerals (kaolinite, annite, quartz, calcite) forming a superimposed overprint rather than a discrete alteration zone. REE rich facies occur preferentially at depth (≈968–1,254 m), suggesting localized preservation or development of REE enrichment.

Rietveld refined QXRD data combined with XRF provides a robust, and reliable analytical strategy for quantifying mineralogical heterogeneity in carbonatite systems, which supports exploration models and resource characterization for REE critical deposits.