Mistinibi-Raude Domain, Southeastern Churchill Province, Nunavik, Quebec, Canada: Geological Synthesis

Featured

Rare metal mineralization in hyperalkaline rocks

 

 

Mineralization associated with volcano-sedimentary rocks

 

 

Cu-Ni magmatic or hydrothermal mineralization in mafic and ultramafic intrusions

 

 

 

 

The Southeastern Churchill Province (SECP) synthesis allowed for the determination of boundaries of the Mistinibi-Raude Lithotectonic Domain. A geological map and stratigraphic diagram of this domain are presented in this bulletin. The Mistinibi-Raude Domain is dominated by the Mistinibi Complex, a sequence of migmatized paragneisses and diatexites, but is also characterized by numerous intermediate to mafic intrusions. The majority of these intrusions were emplaced in the Paleoproterozoic from 2344 Ma to 2312 Ma. In addition, several potassic intrusions were emplaced in this domain in the Mesoproterozoic from 1482 Ma to 1409 Ma. The Mistinibi-Raude Domain has a tectonometamorphic evolution distinct from the rest of the SECP, marked by a major partial melting event between 2145 Ma and 2070 Ma, and by the absence of a Trans-Hudsonian Orogenesis imprint (1.9-1.8 Ga).

This geological context represents an exceptional environment for the development of rare metal mineralization associated with the numerous peralkaline intrusive suites, but also with pegmatites, granites and migmatites resulting from partial melting of paragneiss of the Mistinibi Complex. Numerous mineralized zones in rare earth elements and other strategic metals are actually listed in the Mistinibi-Raude Domain. The presence of two large-scale volcano-sedimentary complexes and the numerous mafic-ultramafic intrusion units, some of which include anorthosite, also indicate potential for exhalative sulphide (Zn-Cu-Au) and magmatic (Ni-Cu and Fe-Ti-V) mineralization.

Methodology

Previous Work

The table below lists the work that has been done in the study area since 1896. It also includes the references cited in the report.

Lithostratigraphy

The Mistinibi-Raude Lithotectonic Domain is located in the SE portion of the Southeastern Churchill Province (SECP). This domain differs from other SECP lithotectonic domains in that it has a small proportion of Archean units and no crystallization ages greater than 2.68 Ga. It is also distinguished by the fact that geological units were preserved from metamorphism associated with the Paleoproterozoic Trans-Hudsonian deformation (1.9-1.8 Ga) in the Torngat and New Quebec orogeneses. Instead, it preserves evidence of a partial melting event prior to the Trans-Hudsonian Orogen (see Metamorphism section below).

The oldest ages (2678-2571 Ma; Nunn et al., 1990; James et al., 2003) were all obtained south of the Zeni Shear Zone (ZCzen). In fact, this area has been recognized as representing a distinct lithotectonic domain by various authors, the Orma Domain (Nunn and Noel, 1982; Nunn et al., 1990; Wardle et al., 1990a; James et al., 2003; Hammouche et al., 2011, 2012; Corrigan et al., 2018). The Orma Domain was introduced in Labrador by Nunn et al. (1990) to define a package of volcano-sedimentary rocks cut by gneiss emplaced in the Neoarchean. Its northern boundary, however, was determined in Quebec by Hammouche et al. (2012), namely the Zeni Shear Zone (ZCzen). Since the Orma Domain shares the same characteristics as the rest of the Mistinibi-Raude Domain, that is the area north of the ZCzen, it is preferable to unify them into one domain as part of the SECP synthesis. Although it is uncertain whether their origin is common, at least they were previously amalgamated with the Trans-Hudsonian Orogen. It is not excluded, however, that these two areas separated by the ZCzen represented distinct entities that merged together before the orogen. 

The Mistinibi-Raude Domain is dominated by paragneiss and diatexite of the Mistinibi Complex (pPmis) and is characterized by the presence of numerous units of intermediate to mafic intrusive rocks, both Paleoproterozoic (2581-2312 Ma) and Mesoproterozoic (1481-1409 Ma). These include the Mistastin Batholith (mPmit), which represents the largest intrusive massif of the Mistinibi-Raude Domain. This section provides a summary description of the domain’s lithostratigraphic units based on the type of lithology and their relative chronology to regional deformation. A more detailed description of these units is available in the Stratigraphic Lexicon.

The simplified stratigraphic opposite diagram presents the relationships between the domain’s lithostratigraphic units to help the reader better understand their spatial and chronological arrangement. It is accompanied by a timescale listing the units’ ages. The size of units on this diagram approximates the surface areas mapped. References associated with dating of units are found in the legend of the Mistinibi-Raude Domain map and in records of the Stratigraphic Lexicon. Unless otherwise stipulated, the ages mentioned in the timescale were obtained by zircon U-Pb analyses. Units prior to the probable sedimentation period of the Mistinibi Complex are presented below a discordance that is no longer observable in the field. In the southern Mistinibi-Raude Domain, the rate of deformation, the lack of geochronological data and the lack of work carried out during the Ministère’s recent mapping make it impossible to determine relationships between units located on either side of the ZCzen. For this reason, contacts between units in this area have been represented as shear zones, as they are currently.

Gneissic Rocks

Gneissic rocks cover a limited area within the Mistinibi-Raude Domain; they are concentrated in the SW and southern portions. The Elson Complex (Aelo) consists of highly deformed and folded tonalitic and granitic gneiss. The Advance Complex (ApPadv) differs from the Elson Complex by its intermediate composition and a greater association with similarly deformed intrusive rock sequences. The Jannière Complex (ApPjai) is characterized by the presence of large zones of tonalite alternating with gneissic areas. These three units, forming the Neoarchean basement of the Mistinibi-Raude Domain, are also differentiated by their geographical distribution. The Advance Complex is located north of Zeni Shear Zone (ZCzen), while the Elson and Jannière complexes are located south and west of this deformation zone. The Adelaide Fault forms an N-S branch ending at the ZCzen and also separates the Elson Complex in the west from the Jannière Complex in the east. The Jannière and Elson complexes are locally migmatized. 

Supracrustal Rocks

The Mistinibi-Raude Domain consists of two different-age volcano-sedimentary sequences, the Zeni (ApPzen) and Ntshuku (pPnts) complexes. Zeni Complex rocks, mostly within the ZCzen, are highly mylonitized, making it difficult to identify protoliths or interpret relationships with gneissic units. However, the Zeni Complex appears to contain a significant proportion of volcano-sedimentary rocks. Amphibolites of this complex have a basaltic to andesic or trachy-andesitic composition and their affinity varies from tholeiitic to calc-alkaline. Rocks of the Ntshuku Complex are also deformed, but include many preserved zones where primary structures can still be observed. They consist of a majority of felsic to intermediate metavolcaniclastics and a lower proportion of amphibolite.

The Mistinibi Complex (pPmis) consists of migmatized paragneiss, diatexite and anatectic granite. This complex is interpreted as a sedimentary basin unconformably deposited on gneiss and intrusions emplaced in the Archean and early Paleoproterozoic. In metasedimentary rocks, inherited zircon cores provide information on the possible source, while metamorphic overgrowth reveals an approximation of the peak temperature. Godet et al. (2018) indicate that the primary detrital source of these metasediments is the Pelland Suite and that their maximum deposition age is ~2220 Ma. The end of the sedimentation process is also constrained by the crystallization age of the first monazites to ~2148 Ma. Paragneiss units may have residual composition, locally influenced by the accumulation of leucosome (see Lithogeochemistry).

The Hutte Sauvage Group (pPht), located in the west-central portion of the Mistinibi-Raude Domain, represents a well-preserved Paleoproterozoic metasedimentary sequence with little deformation and metamorphism. This sequence is interpreted as a basin unconformably overlying the Mistinibi Complex (Girard, 1992; van der Leeden, 1994). However, the exposed contacts are now tectonized. Detrital ages obtained for this unit (2570-1973 Ma) indicate a proximal source within the domain, without significant input from adjacent lithotectonic domains. These ages are similar to those of many intrusive units characteristic of the Mistinibi-Raude Domain, as well as diatexites of the Mistinibi Complex. The maximum sedimentation age around 1980 Ma, and the absence of detrital age coincident with crystallization of the De Pas Supersuite (1861-1805 Ma) also indicate that the Hutte Sauvage Group cannot be derived from the erosion of the former, as suggested by Girard (1992).

Neoarchean Intrusive Rocks

Three Neoarchean intrusive units are known in the Mistinibi-Raude Domain. Two of them are south of the ZCzen. Porphyroclastic rocks of the La Pinaudière Granite (nAlai) cut gneiss and tonalites of the Jannière Complex (ApPjai). The Brass Intrusion (nAbrs), consisting of hypersthene felsic intrusive rocks, is located just north of the Michikamau Suite, a Mesoproterozoic intrusion. The third unit, the Nekuashu Suite (nApPnek), is on the north side of the ZCzen. It consists mostly of monzodiorite, leucogabbro and monzogabbro. The geochemistry of unit nApPnek1 illustrates its compositional diversity. This package of mafic and intermediate rocks seems to have intruded following a polyphase process involving successive intrusions and injections of magmas of different compositions.

The Terriault Complex (ApPter) is a very complex package of several lithologies. It is dominated by felsic intrusive rocks containing 5 to 25% centimetric to metric enclaves of deformed rocks (diorite, quartz diorite, leucogabbro, tonalite and monzodiorite). The SE part of the complex is more homogeneous and composed of enderbite, indicating high metamorphic conditions or lower crust emplacement. Although this unit has not been dated, the presence of layers and masses of diatexite and paragneiss of the Mistinibi Complex in felsic rocks of the Terriault Complex suggests a synmigmatization to post-migmatization emplacement, that is, younger than 2145 Ma. However, uncertainties remain as to its position in the lithostratigraphic column.

Paleoproterozoic Intrusive Rocks

The Mistinibi-Raude Domain consists of several intrusive units, mostly of intermediate to mafic composition, which were emplaced between 2344 Ma and 2312 Ma. The Pelland Suite (pPped) consists mainly of gabbro, gabbronorite, jotunite and opdalite. Field observations suggest polyphase intrusion of mafic to intermediate magmas subsequently intruded by felsic magmas. It is possible that unit pPped3 intrusions are contemporary to those of the Terriault Complex. These two units could have been emplaced during high-grade metamorphism that affected the Mistinibi-Raude Domain between 2145 Ma and 2070 Ma (see Metamorphism section below).

The Raude (pPrae), Lac Cabot (pPcab) and Résolution (pPrso) suites are distinguished from surrounding units by their very strong magnetic signature. These units, which form well-circumscribed intrusions of small dimensions, are generally massive to foliated, but mylonitic zones are observed locally. The Raude Suite includes gabbronorite, diorite and quartz monzonite. The Lac Cabot Suite consists mainly of monzonite and granite, while the Résolution Suite consists of gabbronorite and mangerite. The Pallatin Intrusive Suite (pPpal) consists of metawebsterite and metagabbro units, as well as a porphyraceous quartz monzodiorite and granodiorite unit having a volcanic arc signature. Pallatin Intrusive Suite rocks are commonly interstratified in metric to decametric layers with those of the Ntshuku Complex, suggesting synchronous hypabyssal emplacement with the latter, at least in part. As van der Leeden (1995) noted, due to the high degree of deformation, alternating facies may also be tectonic in origin. Some layers of fine-grained matrix and quartzofeldspathic porphyritic rocks, previously assigned to the Pallatin Intrusive Suite, are now interpreted as quartz-feldspar porphyries (QFP) and are therefore reassigned to the Ntshuku Complex. Unit pPpal3 is generally much coarser grained, but the distinction between this unit and QFP becomes virtually impossible in the most deformed zones where grain size is reduced.

The Déat Suite (pPdea) consists mostly of porphyraceous felsic to intermediate intrusions, alkaline-calcic in affinity and metaluminous to peraluminous. The Déat Suite has not yet been dated, but the geochemical signature suggesting a within-plate granite tectonic setting, it is highly likely to be of the same age as other Paleoproterozoic intrusions described above. However, it is not excluded that paragneiss and diatexite layers of the Mistinibi Complex observed within the Déat Suite are in fact enclaves, which would imply that the Déat Suite would be younger, that is, of the same age as the Dumans Suite (pPdmn). The latter differs from other Neoarchean to Paleoproterozoic intrusive rocks of the Mistinibi-Raude Domain in that it is the only unit to have been emplaced ~1.8 Ga. It includes granite and granoriotite and contains enclaves of the Advance and Mistinibi complexes.

Mesoproterozoic Intrusive Rocks

The Mistinibi-Raude Domain is also characterized by a large amount of Mesoproterozoic intrusive rocks that have been emplaced between 1482 Ma and 1409 Ma, with the exception of the Lac Brisson Pluton, which is younger (1240 Ma). These units are classified as within-plate granites and are generally massive, homogeneous and minimally altered. There are, however, a few facies that are slightly affected at the edges of some intrusions, possibly in connection with their emplacement in a solidified host. These units intruded along the Quebec-Labrador border, forming circumscribed intrusions 5 to 25 km in diameter, roughly circular, and with a magnetic susceptibility, negative or positive, that is easily distinguished from that of host units. From north to south, there are the Lac Brisson Pluton, Napeu Kainut Suite, Mistastin Batholith, Misery Syenite, Ramusio Granite, the Juillet Syenite and Michikamau Suite.

The Mistastin Batholith (mPmit) differs from other intrusions in that it is much larger, forming a >100 km-long continuous mass along an N-S axis. It consists mostly of porphyraceous quartz syenite and syenogranite. Geochemistry indicates that these are type-A granitoids of alkaline-calcic to alkaline affinity. The Ramusio Granite (mPram) consists of even-grained granite that locally contains K-feldspar phenocrystals. The Juillet Syenite (mPjui) includes alkali feldspar syenite of alkaline affinity, and gabbro. The Michikamau Suite (mPmic) is a mafic stratiform intrusion consisting of leucotroctolite, anorthosite, gabbro, gabbronorite and leuconorite, the different facies being in diffuse contact. The Napeu Kainut Suite (mPnak) consists of mangerite, quartz monzonite and granite. The Misery Syenite (mPmsy) consists of fayalite-hedenbergite quartz syenite whose geochemical analyses indicate a type-A magma of alkaline affinity. The Lac Brisson Pluton (mPbri) includes a variety of granite facies, including hypersolvus granite, subsolvus granite and breccia zones, which have not been differentiated at the scale of mapping. These rocks are metaluminous and alkaline in affinity.

All Mesoproterozoic units intrude into surrounding rocks present in their respective areas. North of the ZCzen, the Lac Brisson Pluton and Napeu Kainut Suite cut rocks of the Pelland Suite and Mistinibi Complex. In addition to these same units, the Mistastin Batholith intrudes into all gneiss and intrusions of the Advance Complex. The Ramusio Granite cuts the ZCzen and Archean to Palaoproterozoic rocks of the area, namely those of the Advance, Jannière, Zeni and Mistinibi complexes. On the south side of the ZCzen, the Michikamau Suite and Juillet Syenite cut Neoarchean units of the Brass Intrusion, La Pinaudière Granite and Jannière Complex. Metric to decametric enclaves of older units are also observed in Mesoproterozoic units. Finally, crosscutting relationships have been described between some Mesoproterozoic units, such as the Lac Brisson Pluton intruding into the Napeu Kainut Suite, and the Misery Syenite cutting the Mistastin Batholith.

Mesoproterozoic Dykes

The entire SECP is cut by various swarms of mafic dykes, either ophitic or subophitic, grouped according to their emplacement orientation. Because of their Mesoproterozoic age, these dykes cut all other SECP units, with the exception of the younger Lac Brisson Pluton, and transcend the boundaries of lithotectonic domains. Four hectometre to kilometre-wide dyke swarms were observed in the Mistinibi-Raude Lithotectonic Domain.

The Harp Dykes (mPhar) include NE-SW to ENE-WSW oriented olivine gabbros of the SECP. A total of 14 dykes, ranging from 2 to 85 km in length, were recognized in the southern part of the Mistinibi-Raude Domain. The Slippery Dykes (mPsip) consist of E-W to ENE-WSW oriented olivine gabbros and olivine gabbronorites of the SEPC. Only one ~25 km-long dyke cuts the northern part of the domain. Given their respective orientations, it is possible that the Harp and Slippery dykes belong to the same dyke swarm. However, because few samples were collected and geochemical analyses failed to distinguish Slippery rocks as were those of the Harp Dykes (three groups depending on certain geochemical characteristics), these two units are kept separate for the time being.

The Falcoz Swarm (mPfal) groups NNW-SSE oriented olivine gabbro dykes of the SECP. The 11 dykes assigned to this unit in the Mistinibi-Raude Domain range from 0.5 to 16 km in length. Finally, four <1 km-long gabbro intrusions were assigned to the Slanting Dykes (mPsla). These dykes, oriented mainly NE-SW to N-S, were observed only in the Nekuashu Suite area in the NW of the domain. Given their emplacement context and the fact that they have not been dated, they may also represent a late phase associated with the emplacement of the Nekuashu Suite. However, the absence of foliation, even on the edge of the Rivière George Shear Zone (ZCrge), instead suggests that these dykes are much more recent.

Metamorphism

The Mistinibi-Raude Domain metamorphism was studied by Godet et al. (2018) as part of a doctoral thesis. Metamorphic parageneses observed are biotite ± garnet ± sillimanite ± amphibole ± orthopyroxene. The thermodynamic modelling work carried out in this study indicates granulite facies metamorphic conditions, from 775°C to 815°C and 8.0 kbar to 8.3 kbar. Structural relationships indicate that the deformation responsible for the main foliation is late compared to the peak of metamorphism. Partial retrogressive metamorphism of these parageneses is noted by the presence of chlorite, either in fractures or surrounding garnet crystals, and by large retrogressive muscovite flakes near leucosomes. Prograding metamorphism has been dated on zircon, monazite and garnet from 2150 Ma to 2120 Ma (Godet et al., 2018). Retrogressive zircons and monazites force the end of high temperature conditions (suprasolidus) at ~2070 Ma. Based on this data, Godet et al. (2018) suggest that anatectic conditions would have persisted in the Mistinibi-Raude Domain for over ~75 Ma, from 2145 Ma to 2070 Ma.

Metamorphism identified in the Mistinibi-Raude Domain differs from metamorphic events recognized elsewhere in the SECP, which are generally related to the Trans-Hudsonian Orogen (1.9-1.8 Ga). Anatectic conditions that were identified from paragneiss and mafic gneiss of the Mistinibi Complex likely also affected gneiss and intrusions emplaced in the Archean and early Paleoproterozoic. However, little evidence of this imprint has been identified by zircon U-Pb analyses, with the exception of zircon overgrowth in the Pelland Suite which gave ages between 2090 Ma and 2050 Ma.

Contact metamorphism is recognized near the Mistastin Batholith and was studied by Owen (1991). This metamorphism overprints high-grade metamorphic parageneses detailed above. Through the metamorphic aureole, cordierite and locally spinel replace garnet, biotite and sillimanite. Locally, orthopyroxene forms a coronitic symplectite around garnet with plagioclase and fine biotite flakes. Andalusite, muscovite and chlorite occur locally. Thermal conditions reached in the aureole range from ~700°C to 750°C.

Lithogeochemistry

The lithogeochemistry of Mistinibi-Raude Domain units is presented separately in tabular form.

Structural Geology

Structures of the Mistinibi-Raude Domain can be divided into two groups depending on their development period. First, the ZCzen and structures located more in the centre of the domain, mainly in the Mistinibi Complex and Pelland Suite, belong to a group of structures that predate the Trans-Hudsonian Orogen (D_n) and are probably related to the tectonometamorphic event that produced partial melting conditions from 2145 Ma to 2070 Ma. Then, rocks at the edges of the domain were sheared by the Rivière George and Moonbase shear zones during the Trans-Hudsonian Orogen (D_n+1), whose tectonic and metamorphic imprint is widespread throughout the rest of the SECP between 1.9 Ga and 1.8 Ga.

The schematic structural section shown opposite illustrates the interpretation of the regional structural grain and relationships between units of the Mistinibi-Raude Lithotectonic Domain. On the western and northern periphery, units are mylonitized in shear zones related to the Trans-Hudsonian Orogen (D_n+1). Thus, the western edge of the domain has a type of deformation similar to that of the George Lithotectonic Domain. Units are highly transposed to the N-S foliation of the Rivière George Shear Zone (ZCrge). The northern portion of the Mistinibi-Raude Domain is characterized by the partitioning of the D_n+1 deformation around Neoarchean and Paleoproterozoic intrusions partially affected by the Moonbase Shear Zone (ZCmob). Intrusions form competent sigmoidal lenses that are free of mylonitic deformation but have undergone metamorphic recrystallization as shown by granoblastic textures. Similarly, the competence contrast due to the restite nature of the domain would have led the Trans-Hudsonian shear zones to develop at the edge and confer a roughly lenticular shape to the Mistinibi-Raude Domain.

Along the structural section to the east of the ZCrge are the Ntshuku Complex and Pallatin Intrusive Suite. These are affected by complex folding whose main regional fold consists of a synform inclined eastward. The folding geometry of this area was studied in more detail by Girard (1990a) and van der Leeden (1994). It is proposed that the complexity of these folds is the result of prolonged heterogeneous deformation. Sheath folds were also observed and it is conceivable that regional folding would have a sheath geometry. The existence of type-two polyphase folds is also mentioned. This section provides an interpretation of the possible geometry for this area, but its understanding remains incomplete and is likely the result of the combination of D_n and D_n+1 deformation phases.

The central portion of the section runs through the Mistinibi Complex, in which stromatic banding and tectonometamorphic foliations have similar orientations. Both are subvertical and oriented N-S to NNW-SSE. These structures form the Mistinibi Anticlinorium (van der Leeden, 1995). Correlation between foliations, gneissosities and migmatitic textures suggests that they are contemporary and thus associated with the metamorphic event ranging from 2145 to 2070 Ma. The presence of stretch lineations with shallow to subvertical diving contrasts with the regularity of ZCrge subhorizontal lineations. The cause of this contrast may be a time lag between the Mistinibi Complex deformation and the ZCrge, or partitioning of deformation between two domains, resulting in different structural styles.

In the southern portion of the domain, foliations bend into a WNW-ESE orientation and parallel with the Zeni Shear Zone (ZCzen), a dextral strike-slip ductile shear zone (Hammouche et al., 2012). Interpretation of geophysical maps indicates that the ZCzen is truncated by the ZCrge, thus prior to trans-Hudsonian deformation and likely associated with the D_n phase. The eastern part of the domain consists essentially of Mesoproterozoic intrusions characterized by the absence of deformation.

Regional Tectonics

Structural duality and metamorphic ages obtained in the Mistinibi Complex imply a polyphase tectonic history. First, Neoarchean gneiss and early Paleoproterozoic intrusions representing the source of the Mistinibi Complex sediments had to be exhumed, either tectonically or by erosion, before the peak sedimentary deposition age of ~2220 Ma. These sediments were later buried and reached the granulite facies between 2160 Ma and 2070 Ma. P-T-t paths of Godet et al. (2018) suggest slow exhumation of migmatites by erosion between 2070 Ma and 1980 Ma. According to detrital zircon populations, the sedimentary material of the Hutte Sauvage Group originates from the Mistinibi-Raude Domain (Corrigan et al., 2018). Thus, erosion of migmatites may have contributed in part to sedimentation of the Hutte Sauvage Group. Recent petrochronology work by Godet et al. (2018) supports previous work (Nunn et al., 1990; James et al., 2003) that highlights the absence of a metamorphic imprint in the southern portion of the ZCzen. At ~1825 Ma, combined kinematics of the ZCrge and ZCmob results in horizontal extrusion towards the SE of the Mistinibi-Raude Domain (Vanier et al., 2018). This kinematics, and the previous restite character of the domain, may explain the absence of a Trans-Hudsonian metamorphic imprint in the latter. This extrusion occurs in the context of a network of transpressive shear zones at medium crust depth describing an anastomosed general pattern that has accommodated SW-NE shortening (Vanier et al., 2018). Thus, on a large scale, the geometry of shear zones indicates that they do not occur during exhumation of the Mistinibi-Raude Domain, but rather during its lateral extrusion. The tectonic evolution of this domain ends with the intrusion of the Mesoproterozoic Mistastin Batholith and plutonic suites in an anorogenic setting.

The available information on pre-Trans-Hudsonian structures is incomplete and makes it difficult to detect tectonic implications. The ZCzen is the boundary between what was previously defined as the Orma Domain and Mistinibi-Raude Domain (Hammouche et al., 2012). This shear zone may have contributed to the juxtaposition of rocks formerly associated with the Orma Domain to the rest of the Mistinibi-Raude Domain. However, as mentioned earlier, current data cannot completely exclude a common origin for these two domains.

Economic Geology

The Mistinibi-Raude Lithotectonic Domain is prospective for several types of mineralization:

• rare metal mineralization in hyperalkaline rocks;
• rare metal mineralization in granitic pegmatites;
• mineralization associated with volcano-sedimentary rocks;
• Cu-Ni magmatic or hydrothermal mineralization in mafic and ultramafic intrusions;
• Fe-Ti-V mineralization in mafic intrusions.

The table of mineralized zones below presents the results of analyses for the one hundred three (103) mineralized zones listed in the Mistinibi-Raude Domain.

The table of lithogeochemical analyses of metals of economic interest provides the location, description and analytical results for sixty-six (66) samples selected to assess the economic potential of the region during the Ministère‘s mapping campaign.

Rare Metal Mineralization in Hyperalkaline Rocks

The Mistinibi-Raude Domain is characterized by the presence of numerous Mesoproterozoic hyperalkaline intrusions at its eastern border. The concentration of mineralized zones in this area, many of which have high rare metal contents, highlights the enormous potential of these intrusions. In addition to rare earth elements (heavy and light), these occurrences are also enriched in zirconium, niobium and locally in beryllium, yttrium, thorium and tantalum.

The Lac Brisson Pluton and Misery Syenite are known to contain large-scale rare metal mineralization zones. The Lac Brisson Pluton contains two deposits, namely Strange Lake, for which there are historical resources, and Strange Lake–Zone B, which contains indicated resources (see table above). This area also includes about 10 other rare metal mineralized zones. The Misery Syenite and surrounding area have nearly 30 mineralized zones and numerous anomalous contents. This unit forms an annular intrusion that is clearly visible on the aeromagnetic gradient map. The edges appear to represent the most promising areas where a majority of mineralized zones are concentrated, but more work is required. Similar magnetic signatures are visible at other locations, including directly SE of the Misery Syenite, in the Mistastin Batholith (Aismery and Middle Lakes area) and in the eastern and southern portions of the Napeu Kainut Suite (Ytterby-1 area).

In the Moyen Lake area, the magnetic anomaly is associated with subunit mPmit3a of the Mistastin Batholith, while in the Ytterby-1 area it is largely associated with unit mPmit2 of the Napeu Kainut Suite. Two other circular anomalies are also visible south of the ZCzen; the contours of these correspond to those of the Ramusio Granite and Juillet Syenite. These areas are still poorly explored and represent prospective zones for rare metal mineralization. The Ministère’s mapping campaigns and exploration work conducted by Quest Rares Minerals and Midland Exploration between 2010 and 2014 led to the discovery of many other similar mineralized sites within the Mistastin Batholith (nearly 30 mineralized zones), Napeu Kainut Suite (3 mineralized zones) and Juillet Syenite (1 mineralized zone and several anomalous contents in Zr-Nb). Like the Lac Brisson Pluton and Misery Syenite, these units also consist of clinopyroxene-sodic amphibole intermediate potassic intrusions, alkaline in affinity.

Mesoproterozoic intrusive rocks of the Mistinibi-Raude Domain consist of A-type anorogenic granitoids. These are the product of partial melting of a deep residual crust enriched in incompatible and volatile elements through interactions with magmatic fluids (Petrella et al., 2014). These hyperalkaline rocks are emplaced in intra-continental settings that are generally in extension and bordered by major crustal structures. Although fractionated crystallization allows for the concentration of rare elements in late intrusive phases (pegmatite), remobilization by hydrothermal processes seems essential to the formation of economic mineralization (Sappin and Beaudoin, 2015 and references included). Late fluids alter hyperalkaline rocks (albitization, hematitization and silicification) and allow for the precipitation of minerals rich in variable rare metals (silicates, carbonates, oxides and phosphates). Metallurgical studies conducted on samples from the Strange Lake area also indicate an ease of extraction and recovery of ore (Kerr, 2011).

In the Misery Lake area, a comprehensive study (Petrella, 2012; Petrella et al., 2014) identified lithological facies that carry mineralization. Rare metals are concentrated in clusters and layers within ferrosyenite and in the coarse-grained phases of syenite, which are locally metasomatized (sodic alteration). The mineralization consists mainly of hydroxyapatite and britholite-(Ce) highly enriched in rare earth elements. Disseminated fergusonite-(Y) is also observed near quartz-fayalite dykes cutting ferrosyenite and syenite. Ferrosyenite is mostly composed of fayalite, hedenbergite, ferropargasite and iron oxides in a microperthitic feldspar matrix. It appears in amoeboid enclaves of a few centimetres to several metres within syenite.

In the Brisson Lake area, the mineralization is essentially located within irregular dykes, lenses or pegmatite clusters intruding into the various alkali granite facies of the Lac Brisson Pluton. Metasomatism of these late phases involves significant calcium and magnesium enrichment. In addition, the majority of mineralized zones are associated with strong diffuse hematitization and aegirinization of arfvedsonite in pegmatites and granites. The mineralogy varies from one mineralized zone to another, but the main phases observed are gittinsite, kainaosite, gadolinite, gagarinite, dickgerenite, pyrochlore, elpidite and fluorite. In other areas, the current state of knowledge does not describe the types of alteration or mineralization of mineralized zones. Biotite enrichments are mentioned locally.

In addition to Mesoproterozoic intrusions, anomalous rare metal contents were obtained in Paleoproterozoic intrusive units. These anomalous contents (locally up to showing values) are associated with late and potassic phases of the Nekuashu (nApPnek3) and Pelland (pPped3) suites, as well as granitoids of the Lac Cabot, Dumans and Déat suites. Minerals containing rare metals are diverse and uncommon, therefore exploration with specialized measuring devices would be required to properly identify these mineralized zones.

Rare Metal Mineralization in Granitic Pegmatites

Rare metal mineralization zones have also been recognized in migmatitic rocks of the Mistinibi Complex. These migmatites, as well as pegmatitic granite dykes and clusters that cut them, are prospective for Rössing-type mineralization linked to deep pegmatite migmatization fronts (Jébrak and Marcoux, 2008). Granitic intrusions (especially pegmatitic phases), migmatites and paragneiss (bordering intrusions) of the Mistinibi Complex are locally mineralized in uranium ± thorium with point anomalies in lead or rare earth elements (19 mineralized zones). Little information is available regarding these mineralized zones. The majority are located in the same area ~17 km SE of the Ntshuku Complex. The mineralization appears to be commonly associated with biotite, although biotite-poor and quartz or hematite-rich zones are also carriers. The only economic mineral identified locally is carnotite.

Mineralization Associated with Volcano-Sedimentary Rocks

The Mistinibi-Raude Domain includes two large supracrustal rock complexes: the Ntshuku and Zeni complexes. Therefore, a potential for the development of different types of mineralization exists, such as volcanogenic massive sulphides and orogenic gold.

The Ntshuku Complex includes a volcano-sedimentary sequence of ~20 km by 7 km in the west-central part of the domain. Despite the presence of bimodal volcanics of tholeiitic to calc-alkaline affinity, the geochemistry of felsic volcanics suggests that this is an non-prospective environment for volcanogenic massive sulphides (opposite figure) using trace element methods (Lesher et al., 1986). However, the majority of analyzed samples are volcaniclastics and not rhyolite flows, significantly influencing the rare earth element fractionation process. In the diagram of Pearson (2007), which uses major elements (not influenced by this fractionation), the majority of samples fall in the indeterminate field. Further work would be required to determine the fertility of the complex. A few decimetric to metric rusty zones were observed within amphibolite and crystal tuff. The mineralization is disseminated and mainly composed of pyrite and pyrrhotite. Ananomalous or significant contents of copper (<730 ppm Cu), zinc (<1820 ppm Zn) and nickel (<340 ppm Ni) were obtained.

The Van der Leeden mineralized zone, where gold contents (up to 8.1 g/t Au) are associated with very strong arsenic anomalies (up to 26%), forms a 2 m by 20 m lens rich in arsenopyrite (10-90%) with siliceous walls extending ~10 m by 50 m. This zone is hosted in a sequence of crystal metatuffs interstratified with decimetric layers of metabasalt and arkosic metawacke. The mineralization is rich in volatile elements, depleted in transition metals and has a siliceous metasomatic alteration aureole. This site is interpreted by Girard (1990) as mesothermal mineralization in a sedimentary environment affected by sheared tectonics. This author proposes that the mineralization is secondary and deposited during the percolation of mineralizing fluids along fracture planes. However, field checks conducted in the summer of 2016 did not confirm this hypothesis. Instead, the mineralization host appears to be felsic crystal tuff (dated 2373 Ma by Davis and Sutcliffe, 2018), as mentioned by Bélanger and van der Leeden (1987).

Paragneiss and amphibolite of the Zeni Complex contain discontinuous, decimetric to decametric layers of silicate-oxide facies iron formation. These clinopyroxene-garnet-quartz-magnetite-carbonate-apatite layers contain disseminated to massive sulphides (pyrrhotite, pyrite and trace chalcopyrite). This setting (metasedimentary and mafic metavolcanic rock environment) could be similar to a variant of Besshi-type deposits in Japan (Jébrak and Marcoux, 2008). Ananomalous or significant contents of copper (<1429 ppm Cu), gold (<127 ppb Au) and nickel (<1035 ppm Ni) were obtained in these iron formations.

The abundance of metasedimentary rocks in the Mistinibi-Raude Domain also raises the possibility of finding SEDEX sulphide mineralization, since these can be preserved at the amphibolite and granulite facies. However, no anomalous lead-zinc content has been obtained to date. Paragneiss samples of the Mistinibi Complex, on the other hand, yielded anomalous or significant contents of copper (<850 ppm Cu), gold (<71 ppb Au), arsenic (<400 ppm As), zinc (<280 ppm Zn) and nickel (<480 ppm Ni). Disseminated sulphides (pyrrhotite, secondary pyrite and trace chalcopyrite), with or without graphite, are found in decimetric to metric zones of locally silicified, rusty paragneiss.

Cu-Ni Magmatic or Hydrothermal Mineralization in Mafic and Ultramafic Intrusions

The Mistinibi-Raude Domain includes several units of mafic and ultramafic intrusive rocks that are prospective for Cu-Ni ± Cr ± PGE or Fe-Ti-V (below) mineralization. The main units are attached to the Brass Intrusion and the Michikamau, Pallatin, Résolution and Raude suites. In the Fraser Lake area of Labrador, Ni-Cu mineralization located at the contact between the Michikamau Intrusion and host paragneiss was of interest following the discovery of the Voisey’s Bay deposit in the 1990s. However, on the Quebec side, the nature of host rocks (Brass Intrusion enderbite) diminishes the potential for this type of mineralization, since there does not appear to be a source of sulphur essential for their formation. Anomalous contents of copper (951 ppm Cu) and nickel (620 ppm Ni) were still obtained within a metric gabbronorite layer containing ~10% disseminated sulphides (pyrite, pyrrhotite and trace chalcopyrite) and 5% graphite.

Anomalous Cu-Ni-Cr contents were also obtained in clinopyroxenite and gabbro respectively associated with the Pallatin and Nekuashu suites. The mineralization is in decimetric to metric rusty zones containing disseminated sulphides (pyrite, pyrrhotite and chalcopyrite). The Muriel mineralized zone, however, has a larger rusty zone, in the order of 280 m long by 1 to 10 m wide. Part of the mineralization (chalcopyrite, pyrite and malachite) is disseminated in gabbro of the Pallatin Intrusive Suite and appears to be of magmatic origin. However, sulphide remobilization within quartz or carbonate veinlets is also observed. Vein-type mineralization is also enriched in gold and silver. Samples analyzed yielded up to 2.4% Cu, 1800 ppb Au and 8.8 g/t Ag.

Fe-Ti-V Mineralization in Mafic Intrusions

The best Fe-Ti-V contents were obtained in the Lacasse mineralized zone, where a deformed and metamorphosed boudinaged gabbro sill, decametric to metric in width, contains massive to semi-massive centimetric beds of vanadiferous magnetite and ilmenite. The gabbro sill is fine to medium grained, contains coronitic garnet and is imbricated in the Zeni Complex. Ilmenite contains 10% hematite exsolutions. Hematite is also altering magnetite. The presence of 3 to 4% pyrrhotite-pyrite and trace chalcopyrite causes this mineralized zone to rust on the surface. A sample collected at this location yielded approximately 38% Fe₂O₃, 4.6% TiO₂, 1645 ppm V and 428 ppm Cu. Zeni Complex amphibolite is closely associated with stratiform layers of metamorphosed gabbroic rocks, also assigned to the Zeni Complex, which could therefore carry similar mineralization.

The Nekuashu and Michikamau suites should also be further explored as they include anorthosite. Finally, anomalous vanadium contents were obtained in gabbronorite of the Pallatin Intrusive Suite (pPpal2) and gabbro of the Brass Intrusion (nPbrs2), which hosts the Michakamau Suite.

Contributors

Acknowledgements:

This Geological Bulletin was made possible through the cooperation of many people who have been actively involved in the various stages of the project. We would like to thank all geologists, students and support staff who participated in the Ministère’s mapping work during the summers of 2014 and 2016. Discussions with geologist Fabien Solgadi were very beneficial.

References

Publications Available Trough Sigéom Examine

Other Publications