Geology of the Amos area, Abitibi Subprovince, Abitibi-Témiscamingue Region, Quebec, Canada

In Essence

The 2019 field campaign consisted of mapping and compilation at scale 1:20 000 of the area east of Amos (sheet 32C05-200-0102). The geology of this area consists of Neoarchean units such as 1) mafic to felsic volcanic lithologies (Landrienne and Deguisier formations, and Figuery, Amos, Lac Arthur and La Morandière groups); and 2) intrusive rocks (Laflamme Pluton and various other intermediate to felsic intrusions).

This area is affected by a series of ESE-WNW oriented synclinal and anticlinal folds, all overturned southward. Together, these folds represent the northern part of the Manneville Thrust Zone (Daigneault et al., 2002; Pilote et  al., 2017, 2018), which continues northward to sedimentary rocks of the Chicobi Group. This thrust zone overlies the La Corne Batholith on the south side and extends west and east over several tens of kilometres (Pilote et al., 2009, 2017, 2018). It is bordered and cut by several E-W to ESE-WNW oriented longitudinal faults that dip moderately to steeply northward (Abcourt, Lyndhurst, Beauchamp, Lapaix and Champneuf faults). These faults, some of which could be associated with the development of the “Destor-Porcupine Fault Zone” (Daigneault et al., 2002; Legault et al., 2005; Pilote et al., 2009, 2017, 2018), converge towards the east and are ultimately cut by or imbricate with the Castagnier Fault. Some of these faults, or particular segments thereof, may have been reactivated during regional deformation and are associated with orogenic-type gold mineralization.

Methodology

Previous Work

The table below lists the work that has been done in the study area since 1910. It also includes references cited in the report.

Lithostratigraphy

The Amos-Barraute area is located in the southern part of the Abitibi Subprovince of the Superior Province (Dimroth et al., 1982; Card and Ciesielski, 1986; Calvert and Ludden, 1999; Percival et al., 2012; Thurston et al., 2008). The geology of this area consists of an Archean volcano-sedimentary pile including mafic, intermediate and felsic volcanic and volcaniclastic rocks (2727 ±2 Ma to 2716 ±2 Ma; Pilote et al., 2009). A compilation of the main U-Pb dating on zircons is presented in the opposite figure.

In the Amos-Barraute area (sheet 32C12-SE ), one finds from south to north : 1) the Landrienne Formation (nAla); 2) the Deguisier Formation (nAdg); 3) the Figuery Group (nAfg); 4) the Amos Group (nAam); 5) the Lac Arthur Group (nAur); 6) the La Morandière Group (nAmr); and 7) Neoarchean volcanic rocks (since no group is assigned to any of these, we suggest the“Senneterre Block” as a temporary informal name). Numerous pretectonic to post-tectonic intrusions and dykes, ranging in composition from dioritic-tonalitic to monzonitic and monzogranitic, cut the volcanic sequence (e.g. the Laflamme Pluton).

Volcano-Sedimentary Units

The geological and stratigraphic settings of theAmos-Barraute area are well defined on the adjacent chronostratigraphic column thanks to the work of Weber and Latulippe (1964), Imreh (1979, 1984, 1991), Labbé (1995 and 1999), Otis and Béland (1986) and Pilote et al. (2018, 2019). Stratigraphic units in this area are described below from the oldest to the youngest. The relative chronology of the emplacement of these units is illustrated in this stratigraphic diagram, which takes into account crosscutting relationships observed in the field, as well as the geochronological data. This diagram represents a highly idealized section of the geology of the study area, indicating the age and/or contemporaneity relationships between units as well as their relative positions, taking into account the numerous faults and folding.

The Landrienne Formation (nAla) consists of basalt, gabbro sills, volcaniclastics and felsic volcanic rocks. The significant apparent thickness of this formation can be explained by the successive repetition of units caused by a series of overturned folds, including at least two synclines (Barraute and Figuery synclines, well visible in the NW quarter of sheet 32C05), and anticlines (NE and NW quarters of sheet 32C05). This formation is not assigned to any group. It is bordered by the longitudinal Abcourt (northern flank) and Aiguebelle (southern flank) faults. The Landrienne Formation includes a rhyolitic unit (2727 +/-2 Ma; Labbé, 1999) that is significantly older than adjacent volcanic rocks, located both to the north (Deguisier Formation) and south (Lanaudière Formation), and belonging to the Kinojevis Group (age range: 2716-2720 Ma; Pilote et al., 2009). This arrangement can likely be explained by the presence of a vast anticlinorium, the Manneville Thrust Zone, the central part of which is occupied by the Landrienne Formation and which is truncated by numerous faults, notably the Aiguebelle and Landome faults, as well as the Uniacke Deformation Corridor (Moorhead, 1988; 1989).

The Figuery Group (nAfg) consists of plagioclase porphyritic andesitic flows, intermediate to felsic volcaniclastics and felsic volcanic rocks. The Figuery Group is bordered by the Amos Group (Imreh, 1979; Labbé, 1999) and the Beauchamp Fault (Labbé, 1995; sheet 32C12) to the north, and by the Lyndhurst Fault and the Deguisier Formation to the south. The average age of Figuery Group volcanic rocks should be comparable to or slightly older than that attributed to the Taschereau Batholith (2718.3 +2.3/-2.2 Ma; Frarey and Krogh, 1986), a tonalitic to granodioritic intrusion interpreted as synvolcanic by Doucet (2001).

The Kinojévis Group (nAki) was divided into two formations by Goutier (1997), namely the Deguisier (nAdg) Formation at the base and the Lanaudière (nAln) Formation at the top. The Lanaudière Formation does not outcrop in sheet 32C12-SE; however, it is present in the sheet located immediately to the south (sheet 32C05-NE). The Deguisier Formation (nAdg) consists of tholeiitic basalt, thin chert layers between flows, tholeiitic rhyolite (2719.4 ±1 Ma and 2718.1 ±1.3 Ma; McNicoll, cited in Pilote et al., 2009) and intermediate to felsic volcaniclastic rocks. The Deguisier Formation is in fault contact with the Figuery Group to the north and the Landrienne Formation to the south. The Lanaudière Formation (nAln) consists of mafic to felsic volcanic rocks. The close spatial association observed between extrusive ultramafic rocks and rhyolitic complexes of this formation, dated at 2718.7 ±0.7 Ma and 2716.2 ±0.8 Ma (McNicoll, cited in Pilote et al., 2009) suggests several similarities with the Kidd-Munro assemblage (Bleeker, 1999; Berger, 2002; Ayer et al., 2002). On the other hand, the Lanaudière Formation is bounded to the south by the La Corne Batholith and to the north by the Aiguebelle Fault. This fault, which dips slightly northward (Mueller et al., 1996; Daigneault et al., 2002), may be one of the subsidiary faults of the Destor-Porcupine Fault Zone recognized further west (Goutier, 1997; Legault et al., 2005). Goutier (1997) and Pilote et al. (2009) have proposed that the Deguisier and Lanaudière formations were originally joint and subsequently separated by faults.

The Amos Group (nAam) cuts the study area from east to west (central part of sheet 32C12-SE). This group consists mainly of a monotonous suite of basalt commonly pillowed, locally interstratified with differentiated mafic-ultramafic sills, which include peridotite and gabbro (see Weeks, 1935; Tremblay, 1950; Webber and Latulippe, 1964; Imreh, 1979, 1984; Vogel and Keating, 1979; Ciesielski, 1980; Hébert, 1981, 1982; Otis and Béland, 1986; Labbé, 1994, 1995, 1999, and our work). All these sills represent multiple magma intrusions. The stratigraphic polarity of these rocks is regularly northward. The thickness of this group is ~3 km and proves to be very regular, except in an easterly direction where the Castagnier Fault gradually truncates the volcanic units. This group continues westward (sheet 32D09-32D10) and eastward (sheet 32C011-32C06). Metamorphism reaches the greenschist facies. The contact between the Amos and Figuery groups, on the south side, is interpreted as a fault. The northern contact, between the Amos and Lac Arthur groups, is occupied by the Lapaix Fault. There are no geochronological data for volcanic rocks of this group.

The Lac Arthur Group (nAur) consists of intermediate to felsic volcanic rocks and intrusions of gabbroic, dioritic, tonalitic and granodioritic compositions (see Cooke et al., 1933; Weeks, 1935; Tremblay, 1950; Webber and Latulippe, 1964; Imreh, 1979, 1984; Vogel and Keating, 1979; Ciesielski, 1980; Hébert, 1981, 1982; Otis and Béland, 1986; Labbé, 1994, 1995, 1999; Doucet and Dion, 1998a, 1998b; Doucet, 2001, and our work). Regional metamorphism reaches the greenschist facies. This group mainly occupies the central parts of sheets 32C12-SE and 32D09. It is found in smaller parts of sheets 32C06, 32D11, 32D15 and 32D16. Labbé (1999) revealed an age of 2714 +/-2 Ma for a rhyolitic tuff belonging to this group. This age corresponds to that assigned to the La Motte-Vassan Formation (2714 +/-2 Ma; Pilote et al., 1998, 1999, 2014; Pilote, 2000), located at the base of the Malartic Group. Felsic units of similar age (2713 +/-2 Ma; Corfu et al., 1989; Ayer et al., 2002) are recognized in Ontario, south of Abitibi Lake and in the Timmins area, and occupy the top of the Kidd Munro assemblage at these locations (Thurston et al., 2008).

The La Morandière Group (nAmr) consists of basaltic flows of tholeiitic affinity, felsic to intermediate volcaniclastic rocks, terrigenous and chemical sedimentary rocks, interstratified with subconformable, differentiated intrusive rocks of ultramafic-mafic to dioritic composition (see Cooke et al., 1933; Weeks, 1935; Tremblay, 1956; Webber and Latulippe, 1964; Imreh, 1979, 1984; Vogel and Keating, 1979; Ciesielski, 1980; Hébert, 1981, 1982; Otis and Béland, 1986; Labbé, 1994, 1995, 1999, and our work). The La Morandière Group is generally oriented WNW-ESE. Regional metamorphism reaches the greenschist facies. Volcanic units of the La Morandière Group are interpreted to be bordered and overlain along their northern and southern contacts by andesite of the Lac Arthur Group (Labbé, 1995, 1999). Although the contacts between La Morandière basalts and Lac Arthur Group andesites are not outcropping, Labbé (1995, 1999) interprets them as likely normal, due to the similarity between the attitudes of rocks of these two groups. The southern contact of the La Morandière Group is cut by the Champneuf Fault, while the NE part is gradually truncated by the Castagnier Fault. There are currently no geochronological data for volcanic rocks belonging to this group.

Pre-Kinematic to Late-Kinematic Intrusive Rocks

The Laflamme Pluton consists of varying proportions of monzonite, quartz monzonite and monzodiorite, commonly plagioclase and K-feldspar (pinkish white, millimetric) porphyritic. The granodioritic phase is only observed in very rare places. These lithologies, whitish grey in altered surface and greenish in fresh exposure, are massive and in places intensely fractured. The fine to medium-grained matrix is composed of feldspar, chloritized hornblende and quartz. Our work indicates that this pluton has a monzonite composition and a calc-alkaline affinity. Although there is an absence of penetrative fabric in this intrusion, there is nevertheless a magmatic foliation indicated by the preferential E-W orientation of plagioclase rods. The pluton contains enclaves of volcanic and volcaniclastic rocks at its southern and NW edges (see Damascus mineralized zone). The potassic nature of this pluton gives it a possible syntectonic to late-tectonic relative age. No lithology of syenitic composition was observed, however, contrary to the first interpretations made by Weber and Latulippe (1964). This interpretation of a syntectonic to late-tectonic age gives it a certain gold potential (Legault and Lalonde, 2009; Legault and Goutier, 2014). This intrusion is anomalous in gold and molybdenum associated with quartz-chlorite-carbonate-magnetite veins (Barraute Vll-56 mineralized zone; see Bérubé, 1978; Tremblay, 2007; Pelletier, 2016). The contacts of this intrusion were traced from aeromagnetic surveys (Geological Survey of Canada et al., 2009). They could not be observed on outcrops, although some have been intersected by drilling in its half-south part. Our mapping did not reveal any significant metamorphic aureole around this pluton. The latter is secant to stratification and regional schistosity.

A voluminous intrusion of granodioritic-tonalitic composition, without apparent outcrops, is located in the Figuery Group, SW of the Laflamme Pluton (central part of sheet 32C12-SE). This composition comes from the work of Weber and Latulippe (1964) and drilling descriptions (Trenholme, 1951; Le Mouel, 1983). This intrusion contains the Matico mineralized zone. There is no estimated age for this intrusion.

Proterozoic Diabase Dykes

The area west of Barraute is cut by three dyke swarms, two of which are Paleoproterozoic, the Senneterre and Biscotasing dykes, and the third is Mesoproterozoic, the Abitibi Dykes.

Senneterre Dykes (pPsen): diabase

Biscotasing Dykes (pPbis): diabase

Abitibi Dykes (mPabi): olivine diabase

The Biscotasing and Senneterre dykes consist of subophitic gabbro seams oriented ENE-WSW to NE-SW. Diabase has a characteristic brown patina and a fresh green surface. It is composed of plagioclase, pyroxene, olivine, chlorite and epidote. Hematite is locally very abundant. As for the Abitibi Dykes, oriented NE-SW to NNE, they consist of non-metamorphosed and weakly altered olivine diabase. These three swarms cut all volcanic rocks in the area. The various positions and orientations of these dykes as well as their interpreted trajectories were first plotted on the geological map of the work of Fahrig et al. (1986), Krogh et al. (1987) and Ernst and Buchan (1993). These are based on the orientation of paleomagnetism as well as the age derived from U-Pb dating of the dykes. Subsequently, the trajectories of these dykes were extrapolated in the peripheral areas using aeromagnetic surveys (see aeromagnetic maps and Geological Survey of Canada et al., 2009).

A particularly distinct generation of diabase dykes with a N-S orientation was also observed in the southern and NE parts of the map. These are highly magnetic subophitic gabbro dykes, displaying no evidence of metamorphism. These diabase dykes were also traced from their strong magnetic signature. This N-S oriented network is not assigned to any specific family of dykes at the moment.

Lithogeochemistry

The lithogeochemistry of units of the Amos area is presented separately in tabular form.

Structural Geology

The following nomenclature has been applied to the description of the main structural elements of the Amos-Barraute area. The oldest schistosity has been designated S₁. This schistosity contains observed stretch lineation. The S₁ fabric therefore corresponds to regional schistosity.

This schistosity commonly has a small angle or is subparallel to stratification S₀, except near the hinges of large synclinal and anticlinal P₁ folds (see the geological map, aeromagnetic gradient map, schematic N-S composite section and equi-area projections shown on stereonets opposite). The axial plane traces of these folds were defined by combining our field work, regional aeromagnetic surveys and adjacent geological maps. For example, the trace of the Duverny Syncline corresponds to the eastward extension of the same fold highlighted by the mapping campaigns of Weber and Latulippe (1964) and Labbé (1995). Planar elements S₀ and S₁ are oriented E-W to WNW and dip moderately (55°-75°) northward. The intensity of S₁ is more pronounced in the vicinity of large regional faults. The stretch lineation Ls associated with this schistosity is commonly steeply dipping northward and towards the NNE, generally subparallel to the fabric S₁‘s dip.

Thrust Zone and Axial Planes of Folds

The most remarkable structural element in the Amos-Barraute area (sheet 32C12-SE) is the abundance of synclinal and anticlinal folds, distributed in practically all groups and formations. These folds are oriented ESE-WNW and all overturned southward. Nowhere else in the Val-d’Or-Rouyn axis is such a high number of fold axes observed. For this reason, we suggest interpreting all of these folds as representing the northern part of the Manneville Thrust Zone (MTZ; Daigneault et al., 2002; Pilote et al., 2017, 2018), which likely continues northward to sedimentary rocks of the Chicobi Group. This thrust zone is underlain on the south side by the La Corne Batholith and extends west and east over several tens of kilometres (Pilote et al., 2009, 2017, 2018).

In the Amos-Barraute area, the distribution of structural elements and the traces of fold’s axial planes were defined by combining our field observations, regional aeromagnetic surveys and the various geological maps available from mining companies. For the Landrienne Formation (Domain V), data from the field campaigns of 2018 (Pilote et al., 2019) and 2019 were combined. The poles of S₀ surfaces are distributed on a great circle whose theoretical fold axis (341°/55°) lies more or less close to the maximum concentration of stretch lineations Ls (015°/60°). The mean lineation has a moderate plunge (40-50°) towards the NNE. For the Deguisier Formation (domain IV), the poles of S₀ surfaces are distributed on a great circle whose theoretical fold axis (116°/49°) is relatively close to the maximum concentration of stretch lineations Ls (099°/61). This is the domain having a mean stretch lineation with the best dominant eastward orientation. For the Figuery Group (domain III), the poles of S₀ surfaces are distributed on a great circle whose theoretical fold axis (073°/60°) displays a good collinearity with the maximum concentration of stretch lineations Ls (080°/77°). For the Lac Arthur Group (domain II), the poles of S₀ surfaces are distributed on a great circle whose theoretical fold axis (052°/82°) is relatively close to the maximum concentration of observed stretch lineations Ls (026°/84°). For the Amos Group (domaine I), the poles of S₀ surfaces are distributed on a great circle whose theoretical fold axis (029°/76°) displays a very strong collinearity with the maximum concentration of stretch lineations Ls (023°/81°).

In more detail, for domains I to V, the observations of S₀ and S₁ planes on the same outcrop allowed calculating intersections defining fold axes (L₀/L₁). These axes are distributed on a great circle corresponding to the average schistosity of each domain. This distribution indicates that rocks in these domains are possibly slightly to severely affected by double-dipping folds. These are oriented towards the NW (domain V), east (domain IV) and NE (domains III, II and I). It is important to note that L₀/L₁ measurements are distributed over a mean great circle S₁ with the mean lineation near the theoretical fold axis indicated by the combination of S₀ measurements. Domains I to V thus present the same deformation style overall, but with Ls oriented slightly differently for each domain. The development of double-dipping folds is probably part of the continuity of regional deformation in the absence of a regional cleavage S₂; this mechanism is probably part of the development of the MTZ (Daigneault et al., 2002; Pilote et al., 2018, 2019).

More generally, the Manneville Thrust Zone (Daigneault et al., 2002) affects in its half-south the entire Kinojevis Group, sedimentary rocks of the Fiedmont Formation, the Landrienne Formation (sheet 32C05-NE; Pilote et al., 2019), and in its half-north the Deguisier Formation as well as the Figuery, Amos and La Morandière groups. Finally, the MTZ is underlain by sedimentary rocks of the Chicobi Group to the north. The MTZ would thus have a possible N-S width of ~30 km (dashed line on the aeromagnetic map). This regional-scale thrust can be interpreted as a vast folded sequence, materialized in the Amos-Barraute area by a series of synclinal and anticlinal folds (Trinity, Soma, Duverny, Laflamme), all overturned southward and cut by faults. The most common indicators of polarity come from the arrangement of pillows observed in mafic to intermediate volcanic rocks.

Faults

The MTZ is bordered and cut by several longitudinal faults oriented E-W to ESE-WNW and moderately to steeply dipping northward (Abcourt, Lyndhurst, Beauchamp, Lapaix and Champneuf faults). These faults, some of which could be associated with the development of the « Destor-Porcupine Fault Zone » (Daigneault et al., 2002; Legault et al., 2005; Pilote et al., 2009, 2017, 2018), converge eastward and are ultimately cut by or imbricate with the Castagnier Fault. Some of these faults (or particular segments of them) may have been reactivated during regional deformation. They are associated with orogenic gold mineralization. Maps of the aeromagnetic gradient and distribution of INPUT-type anomalies illustrate this convergence.

The borders and boundaries between formations and groups correspond mainly to shear zones and faults, or to areas with more intense planar deformation. Moreover, these faults truncate the extension of the axial planes of large folds. They are not very exposed and are poorly documented. In a westerly direction, these faults continue along a general E-W orientation over more than a hundred kilometres (up to sheets 32D10 and 32D15). In an easterly direction, the Castagnier Fault follows its trajectory or cuts all of the above-mentioned faults. Because of this crosscutting relationship, the Castagnier Fault does not seem to be included in this network and probably originates from another process, which could be linked to the amalgamation of the series of intrusions associated with the Montgay Batholith to volcanic piling.

The Destor-Porcupine Fault Zone (DPZ) represents a late structure compared to the development of the MTZ. The DPZ is marked in this area (sheet 32C12-SE) by the following regional faults, from south to north: Abcourt, Lyndhurst, Beauchamp, Lapaix and Champneuf faults. All of these E-W to NW-SE oriented structures play major roles as they: 1) affect the continuity of stratigraphic units; 2) form the edge of younger sedimentary units; 3) accommodate successive increments of regional deformation; and 4) materialize the potential for gold mineralization of a specific orogenic type, as demonstrated for example by a higher density of dykes and intrusions along or along the edge of their paths.

Smaller and later faults oriented NW, N-S and NE cut the large E-W faults described above. Apparent horizontal throws vary in amplitude from ~100 m to ~500 m maximum. Oriented NNE, the Rivière Laflamme Fault is a good example of these intersecting faults. Faults have been recognized or interpreted during mapping, drilling or through the numerous aeromagnetic and electromagnetic surveys conducted at different scales in this region.

Metamorphism

The degree of regional metamorphism observed in the Amos-Barraute area is very homogeneous and regular. It corresponds to the greenschist facies. The mineralogical assemblage typical of massive and pillowed mafic volcanic rocks consists of albite-chlorite-carbonate-quartz (Beullac, 1983; Imreh, 1984; Daigneault et al., 2002 ; Pilote et al., 2009, 2017, 2018). Ultramafic units (intrusions and sills) present a chlorite-actinolite-carbonate-serpentine-talc assemblage.

Economic Geology

The Barraute area comprises 11 prospective zones and four types of mineralization:

• Gold mineralization associated with orogenic-type veins hosted in shear zones;
• Massive sulphide mineralization of common metals associated with volcanic rocks;
• Cu-Au-Mo mineralization associated with alkaline porphyry intrusions;
• Gold mineralization associated with porphyry intrusions.

The table of mineralized zones below presents the compilation and analytical results for the 21 metallic and one non-metallic mineralized zones identified in the Amos-Barraute area.

Table of Mineralized Zones in the Amos-Barraute Area

(D): Diamond drilling; (G): Selected sample; (R): Groove – chip sample

Acknowledgements:

This Geological Bulletin was made possible through the cooperation of many people who actively took part in the various stages of the project. We would like to warmly thank students Aube Gourdeau and Miguel St-Denis for their enthusiasm and the quality of their work. James Moorhead (MERN) and Pierre Lacoste (MERN) are also thanked for the exhaustive reading of this document and the many comments made at the various stages of the project. The staff of Mines Abcourt (Mr. Eugène Gauthier) and Corp. Aurifère Monarques (Mr. Ron Lieber) were of great assistance in the evaluation and compilation work of the Bar-Manitou, Mine Barvue, Abcourt (Pershcourt), Abcourt (Frebert), Frebert Extension Ouest and Swanson deposits.

References

Publications of the Government of Québec