Geology and Mineral Potential of the Cadieux Lake Area, Opatica and Opinaca Subprovinces, Eeyou Istchee James Bay, Quebec, Canada

FEATURED

Cu-Mo-Ag mineralized system in contact with the MacLeod Batholith and Laguiche Complex paragneiss
The prospective zone includes several Cu-Mo± Ag±Au mineralized zones: Lac MacLeod, Lac MacLeod-NE, Pointe Rocky, Pointe Richard, ML-06-128, ML-06-123 and Windy Cible 4-3…

 

 

 

 

 

Identification of prospective stratiform exhalative horizons following lithological and structural revision of the UEGB western branch
Work done by the MERN in summer 2018 strengthened the area’s potential for this type of metallogenic context by identifying thin stratiform exhalative horizons…

 

 

 

 

 

New klippes of supracrustal rocks found in the northern portion of NTS sheet 33A02
New klippes of supracrustal rocks were mapped in the northern portion of sheet 33A02. These klippes of limited lateral extension are part of the Mabill Complex…

 

 

 

 

 

Spodumene discovered in a pegmatite of the Wahemen Suite
The presence of pegmatitic, peraluminous and undeformed granites of the Wahemen Suite on the northern edge of the UEGB provides a prospective context for rare element mineralization…

 

 

 

 

 

 

 

 

A new preliminary geological map of the Cadieux Lake area was produced following a survey conducted in the summer of 2018. Mapping helped clarify the boundary between the Opatica and Opinaca subprovinces located north of the Misasque Suite and south of the Cadieux Suite. Field observations, combined with interpretation of a detailed magnetic survey, led to a lithological and structural revision of the western branch of the Upper Eastmain Greenstone Belt (UEGB). Polarities measured in pillow basalts indicate an overturned sequence. The basal unit of the Dolent Formation is overlain, in fault contact, by polymictic conglomerates of the Bohier Group. The western end of the UEGB culminates in the closure of a regional synform that plunges to the NE.

Metasedimentary rocks of the Laguiche Complex, which represent the bulk of Opinaca rocks, are separated into two tectonometamorphic domains by a large dextral strike-slip corridor. The northwestern portion of the map shows highly migmatitized rocks (diatexite, metatexite and paragneiss in lesser amounts) having formed at a deeper structural level than those south of the sheared corridor. Metasedimentary rocks south of the Eastmain Shear Zone are wacke and arenite paragneiss containing up to 10% mobilisate. In the centre portion of sheet 33A02, new klippes of supracrustal rocks were identified within the Mabille Complex. Most of the rocks consist of tonalite and correspond to a structural window of Opatica rocks in the Opinaca Basin.

Fieldwork identified several prospective geological environments from a metallogenic perspective. Detailed geological mapping of UEGB units highlights the presence of orogenic quartz veins and stratiform exhalative horizons near volcanics and ultramafic sills of the Dolent Formation. The MacLeod Batholith, which forms an intrusive mass of 25 km by 15 km, occupies the central part of the map. The contact zone between the MacLeod Batholith and paragneiss of the Laguiche Complex is a first-order metallotect for Cu-Mo±Ag±Au mineralization. Moreover, the Sorbier Mafic-Ultramafic Suite and Dominique Ultramafic Suite, recognized during our work, are prospective lithologies for Ni-Cu (± Cr±EGP) mineralization. Spodumene was observed in a pegmatite of the Wahemen Suite. Finally, greisened granitoids of the Digne Intrusive Suite could be interesting targets for Sn and W mineralization.

Methodology

Stratigraphy

Economic Geology

The Cadieux Lake area has prospective zones for eight (8) types of mineralization. They are listed in order of importance:

• Cu-Mo (±Ag, ±Au) mineralization associated with porphyry intrusions and skarns;
• Stratiform mineralization of exhalative origin;
• Orogenic-type lode gold mineralization;
• Lode gold mineralization in iron formations;
• Magmatic or hydrothermal Ni-Cu (±Cr±EGP) mineralization associated with mafic to ultramafic intrusions;
• Li, Be and Ta mineralization in granitic pegmatites;
• Sn-W stringer mineralization;
• Undetermined-type zinc mineralization.

The table of mineralized zones below presents the results of analyses for the thirteen (13) known mineralized zones in the area:

The table of lithogeochemical analyses of metals of economic interest provides the location, description, and analytical results for forty-five (45) samples selected to assess the economic potential of the area.

Prospective zones identified on the geological map are ranked in order of importance and described in the following sections:

Cu-Mo-Ag Mineralized System in Contact with the MacLeod Batholith and Laguiche Complex Paragneiss 

The “MacLeod” prospective zone includes several Cu-Mo±Ag±Au mineralized zones: Lac MacLeod, Lac MacLeod-NE, Pointe Rocky, Pointe Richard, ML-06-128, ML-06-123 and Windy Cible 4-3. During definition work of the MacLeod project, two main copper-bearing bodies were defined: the Main Zone and the South Zone (Winter, 2008). The Main Zone, which is 1200 m long by 50 m thick, is a mineralized body located on the flank of an antiform. It contains reported resources of 18.18 Mt at 0.60% Cu, 0.094% Mo, 4.48 g/t Ag and 0.06 g/t Au (Cook et al., 2008). Mineralization appear as veinlet, dissemination, cluster and stockwerk of chalcopyrite with lesser amounts of molybdenite, pyrite, pyrrhotite, bornite and chalcocite. The majority of sulphides are located on the edge of the MacLeod Batholith, in migmatitized paragneiss of the Laguiche Complex. However, some of the mineralization is also contained in the intrusion. The highest contents are localized in a biotite-actinolite-chlorite schist located 25 m from contact with the batholith.

 

The work achieved by the Ministère has revealed some characteristics of the mineralization found in this prospective zone:

• The MacLeod Batholith consists of foliated hornblende-biotite-sphene intermediate to felsic rocks (quartz monzodiorite, granodiorite and monzodiorite);
• Chalcopyrite is disseminated, in small cluster, in fine veinlet or in stockwerk in several lithologies: in the biotite-actinolite-chlorite schist, in intrusive rocks of the MacLeod Batholith, and in migmatitized paragneiss of the Laguiche Complex. Molybdenite occurs as disseminated flakes or clusters in these same lithologies and in different types of granitoids;
• Drill cores have higher proportions of chalcopyrite and molybdenite near injections or boudinaged and dismembered quartzo-feldspathic mobilisate;
• Alteration in the MacLeod Batholith is zoned. Potassic alteration (biotite, magnetite and K-feldspar in variable proportions) is present at the centre of the intrusion. Propylitic alteration (quartz, chlorite and epidote) and silicification are located at the edge of the intrusion;
• Mineralization is associated with zones of intense silicification (silica flooding). The Lac MacLeod deposit’s discovery outcrop (18-FM-2074) exhibits a 10 to 15 m silicification zone rich in chalcopyrite and molybdenite. This zone is in contact with a white pegmatite to the north and a paragneiss derived from a wacke to the south. Chalcopyrite forms a cement around quartz grains, giving the rock a granoblastic texture, suggesting that a significant portion of mineralization predates the regional metamorphism and migmatitizion episode. Sulphides melted during migmatization and were remobilized during subsequent deformation episodes;
• Deformation played a major role in the emplacement of mineralization. Indeed, the principal lithology hosting mineralization is a heavily deformed and crenulated schist located in the nose or flanks of regional folds;
• Locally, chalcopyrite is associated with late hematite and epidote veinlets that cut regional foliation sharply. Some of the mineralization was remobilized by a late brittle fracturation episode;
• Finally, a few sterile or very weakly mineralized hydrothermal breccias were documented along the edge of the MacLeod Batholith.

The Cu-Ag-(Mo-Au) metal association in an intrusive rock, mineralization styles and alteration zoning may indicate that some are porphyry-type mineralizations. However, several characteristics typical of porphyry deposits were not observed, including the presence of porphyritic dykes, the zonality of mineralization and the presence of breccia pipes. The mineralization that occurs in the biotite-actinolite-chlorite schist may correspond to metasomatic skarn-type enrichment. In general, copper-bearing exoskarns are developed at the contact or in the vicinity of an intrusion and are genetically linked to the latter. Actinolite may have crystallized during the retrograde hydrothermal phase of skarn development (Jébrak and Marcoux, 2008).

Identification of Prospective Stratiform Exhalative Horizons Following Lithological and Structural Revision of the UEGB Western Branch

The “UEGB Western Branch” zone is prospective for at least three types of mineralization: 1) volcanogenic stratiform exhalative, 2) orogenic lode gold, and 3) lode gold in iron formations.

1) Volcanogenic stratifrom exhalative mineralization: Mineralized zones Dejour-NE (up to 3.4 g/t Au) and lac Dolent (up to 4096 ppm Zn), which are at the same stratigraphic level, are described as disseminated, semi-massive or volcanogenic sulphide mineralization associated with conductive exhalative horizons. The Dejour-NE mineralized zone (outcrop 18-FM-2111) exhibits sulphidic chert horizons oriented parallel to regional foliation. Mineralized horizons are hosted in silicified basalt and contain up to 15% pyrite, pyrrhotite and trace chalcopyrite. Work by the Ministère in the summer of 2018 strengthened the area’s potential for this type of metallogenic context by identifying thin stratiform exhalative horizons of semi-massive to massive sulphides (outcrops 18-AB-1026, 18-MP-5036, 18-MP-5121 and 18-PG-4088). These horizons conformable to stratigraphy are mostly associated with ultramafic rocks of the Dolent Formation. They are locally in contact with a thin strip of felsic tuff and are composed of 30-80% sulphides (pyrrhotite-pyrite±sphalerite±chalcopyrite).

2) Orogenic lode gold mineralization: Mineralized zones Exko Showing, Exko Extension-NE and Dejour-SW are described as orogenic gold mineralization. At Exko Showing, mineralization is hosted in a quartz-pyrrhotite-pyrite vein, in an actinolite schist. The schist horizon is in contact between basalt and ultramafic rocks of the Dolent Formation. Contents of up to 3.55 g/t Au were obtained from selected samples (Beesley, 1989) and 5.25 g/t Au in a drill core (Tremblay, 1994). A conductive zone, which is also expressed by a strong EM anomaly, passes through the Exko zone and extends in an ENE direction up to approximately 2.5 km to the NE of the mineralized zone. Anomalous gold values were obtained in outcrop over approximately 200 m along the axis containing the Exko mineralized zone (Tremblay, 1994). The Exko Extension-NE and Dejour-SW sites were discovered by drilling (Tremblay, 1995) and gold mineralization described are in quartz-carbonate veins that cut altered and sheared pyroxenite or fractured basalt. The proportion of sulphides (pyrite-pyrrhotite) ranges from 15 to 25% in veins of these zones (Tremblay, 1995).

3) Lode gold mineralization in iron formations: Mineralized zone Éch. Q17029 (up to 1.57 g/t Au) is described as mineralization hosted in silicate iron formation beds that are in contact between mafic and ultramafic volcanics of the Dolent Formation (Dobbelsteyn and Frappier-Rivard, 2015). This zone was not visited during MERN work.

Although gold mineralization of the UEGB are associated with different types of mineralization, one common feature is that they are all close to contact with an ultramafic sill or flow. For example, within the Dolent Formation, the two main horizons of ultramafic rocks associated with shear zones are important exploration guides. The first horizon, north of the UEGB, consists of a differentiated mafic-ultramafic sill (nAdln3) and can be tracked over more than 20 km laterally. Further south, unit nAdln4 which consists of a horizon of volcanics and ultramafic sill was also mapped. The latter is in sheared contact with highly deformed polymictic conglomerates of the Bohier Group.

The superposition of two mineralized systems (syngenetic volcanogenic and orogenic lode) appears to contribute to the gold potential of this prospective zone, as described in the former Eastmain Mine area (Beauchamp and Massei, 2017). Indeed, in the study area, emplacement of exhalative horizons and iron formations occurred near ultramafic rocks of the UEGB. These stratiform horizons that mark a pause in volcanism are prospective for volcanogenic mineralization rich in Cu, Zn, Pb, Ag and Au. Subsequently, emplacement of structurally controlled epigenetic gold mineralization was superimposed on the exhalative systems. Orogenic-type lode gold developed in the UEGB, preferably in shear zones and in silicified lithological contacts. This spatial association between gold mineralization and sheared ultramafic horizons in the UEGB was also documented at the Timmins Mine camp (Fyon et al., 1983; Pyke, 1975). Finally, identification of demagnetized zones in ultramafic horizons is of particular interest since they are interpreted as areas where magnetite has been destroyed by alteration (Dobbelsteyn and Frappier-Rivard, 2015).

Spodumene Discovered in a Pegmatite of the Wahemen Suite

The presence of pegmatitic, peraluminous and undeformed granites of the Wahemen Suite at the northern edge of the UEGB provides a prospective context for rare element mineralization (Li, Be, Ta, Nb and Cs). In the Cadieux Lake area, white biotite-muscovite-beryl pegmatic granite of outcrop 18-SG-7072 also contains spodumene, a lithium-bearing alkaline pyroxene. The mineral is concentrated in clusters of centimetric crystals and locally accounts for 20 to 30% of the observed surface. The rock also contains masutomilite, a lithium-bearing mica. This type of mineralogical assemblage is typical of LCT pegmatites (with Li-Cs-Ta) of intermediate depth (emplacement between 3.5 and 7 km). According to Cerny (1991), the presence of a conformable assemblage of gabbroic and mafic volcanic host rocks provides a prospective context for lithium pegmatite within 2 km of anorogenic granitic massifs. In the Léran Lake area (sheet 23D12), a pegmatite block (outcrop 16-AB-1220) belonging to the Wahemen Suite contains accessory mica, tourmaline, beryl, garnet and spodumene. This block had already suggested that the Wahemen Suite was prospective for lithium mineralization. Sample 2016054398 yielded showing values of 1.21% Li (2.6% LiO₂) and anomalous values in Be (247 ppm), Ta (101 ppm), Nb (92.4 ppm), Cs (261 ppm), and Sn (54 ppm).

Iron Formation Identified Near La Corne Lake

The « Lac de la Corne » prospective zone highlights an iron formation horizon that had already been examined (Prior, 1991) and described during the Ministère’s mapping campaign in 2018. The unit was drawn with the total magnetic field detailed survey (GM 64110, Saint-Hilaire, 2008). Outcrop 18-WM-3113 shows a banded and folded iron formation of metric thickness (5-10 m wide) that contains 15 to 20% sulphides (pyrrhotite, pyrite and trace chalcopyrite) as laminae. Centimetric chert horizons are separated by horizons of oxide, sulphide or both iron formation. The iron formation is in contact with amphibolitized basalt. To the ESE, an ultramafic rock unit that is at least 40 m thick was observed (outcrop 18-WM-3112). It should be noted that iron formations can act a chemical and lithological trap for gold mineralization.

Mafic-Ultramafic Rocks of the Cadieux Lake Project: Prospective Lithologies for Ni-Cu-Cr±EGP Mineralization

Several mafic-ultramafic intrusions were observed in the field, while others were interpreted using geophysical data. These lithologies are prospective for Ni-Cu-Cr±EGP mineralization. The Sorbier Ultramafic Suite consists of a string of differentiated intrusive rocks (peridotite, pyroxenite, hornblendite and gabbro) that contains traces of pyrrhotite and pyrite. It consists of several folded and dismembered kilometric bodies, oriented ENE-WSW, that have intruded along the Sorbier and Eastmain shear zones. Further south, the Dominique Ultramafic Suite consists of rounded intrusive bodies (diameter <1.2 km) marked by positive magnetic anomalies that cut sedimentary rocks of the Laguiche Complex. Finally, komatiites and mafic-ultramafic sills of the Dolent Formation (UEGB), and those belonging to the Maingault and Mabille complexes, could also be prospective for this type of mineralization.

Greisened Zones in the Lac Digne Suite

Within the Digne Intrusive Suite, several outcrops have shown a high level of greisenization, particularly outcrops 18-PG-4044, 18-PG-4045 and 18-PG-4046. Greisenization is an intense hydrothermal alteration that transforms feldspar into an assemblage dominated by quartz and muscovite. When the degree of alteration is lower, the rock corresponds to an albitized quartz porphyritic leucocratic granitoid cut by an anastomosed network of muscovite veins and by quartz veins. This type of alteration occurs in the sommital part of very evolved granitic intrusive bodies and is regularly associated with Sn, W, Mo, Bi and Be mineralization that appear as stringers or stockwerks of tin (cassiterite) or tungsten (wolframite) minerals. The most altered zones of the Digne Intrusive Suite are therefore prospective for zones enriched in these elements. However, no mineralization was observed on the surface.

New Klippes of Supracrustal Rocks Found in the Northern Portion of NTS Sheet 33A02

New klippes of supracrustal rocks were mapped on the northern portion of sheet 33A02. These klippes of limited lateral extension are part of the Mabille Complex. This complex includes a basalt unit (outcrops 18-PG-4125 and 18-PG-4126) and an iron formation unit (outcrop 18-SG-7041). Lake-bottom sediment anomalies were identified in the vicinity of these units (DP-2017-09) and delimited the Mabille-1 and Mabille-2 prospective zones. In the Mabille-1 zone, the highest value is 68.1 ppm Cu. The residual value calculated from the multiple spatial regression method is 28.5 ppm Cu, which places it in the 99^th percentile rank of the survey. In the Mabille-2 zone, the most significant anomalous values are 223 ppm Cu, 38.9 ppm Ni and 188 ppm Zn. Residual values calculated from the multiple spatial regression method are 164 ppm Cu, 7.81 ppm Ni and 10.9 ppm Zn, respectively, which place them between 90^th and 100^th percentile in the survey. These new klippes of supracrustal rocks associated with lake bottom anomalies may indicate the proximity of base metal mineralization. However, no mineralization was identified during the mapping campaign of 2018.

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 thank geologists William Chartier-Montreuil, Sarah Galloway, Pierre-Arthur Groulier, Lynda Paquette and Martin Parent, as well as geological assistants Nicolas Benoit, Laurence Bourque, Ève Gosselin, Ola Grignon, Alexandra Harvey, Simon Hector, Guillaume Thériault. We would like to acknowledge the excellent work of camp man Daniel Gosselin. We thank the Mistay company for camp rental. Field transportation was provided by Heli-express. Discussions with geologists Stéphane de Souza (UQAM) and Jean Goutier (MERN) were also very beneficial.

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