Volcanic stratigraphy and mineralisation of the Archean Colomb-Chaboullie greenstone belt, James Bay, Quebec, Canada.

References

Agrawal S, Guevara M, Verma S (2008) Tectonic Discrimination of Basic and Ultrabasic Volcanic Rocks through Log-Transformed Ratios of Immobile Trace Elements. International Geology Reviews 50:1057-1079.

Bandyayera D, Daoudene Y (in preparation) Géologie de la région du lac Nemiscau, secteur du lac Royayer (SNRC 32K13, 32K14, 32N03 et 32N04-SE). MERN report.

Bandyayera D, Daoudene Y (2015) Géologie de la région du lac Nemiscau, secteur du lac Royayer, MERN. CG-2015-05. Carte 1:50,000

Pearce JA (2008) Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust. Lithos 100:14-48. Ross P-S, Bédard JH (2009) Magmatic affinity of modern and ancient subalkaline volcanic rocks determined from trace-element discriminant diagrams. Canadian

Journal of Earth Sciences 46:823-839.

Sun S-S, McDonough WF (1989) Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes, in Saunders AD, and Norry MJ eds, Magmatism in the ocean basins. Geological Society Special Publication 42:313-345.

Winchester JA, Floyd PA (1977) Geochemical Discrimination of Different Magma Series and their Differentiation Products using Immobile Elements. Chemical Geology 20:325-343.

Wood DA (1980) The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary volcanic province. Earth and Planetary Science Letters 50:11-30.

Conclusions

The amphibolised basalt and andesite flows were deposited in a submarine setting which is evident by the presence of the pillowed facies in both of these lithologies (Figs. 2 and 4).

Disseminated sulphides were identified in both massive and pillowed basalt facies. In the pillowed flows, these sulphides were dominantly present in the interpillow material, often associated with chlorite and garnet (<5 mm) in the pillow margins (Fig. 9). This suggests that hydrothermal alteration and mineralisation occurred early on in the primary porosity between the pillows, before diagenesis, and is therefore synvolcanic. In the massive flows, the disseminated sulphides are facture-controlled and form a network of infilling fractures (Fig. 10). This stockwork fracture pattern of sulphides with chloritisation is typical of VMS-type mineralisation which also indicates that these sulphides are synvolcanic.

The geochemistry shows that these volcanic rocks span a range from sub-alkaline basalts to rhyodacite/rhyolite (Fig. 17a-b). The mafic groups (Acch1, Acch1a and Acch1b) are tholeiitic to transitional and plot in the MORB/IAB field (Fig. 17d-e). The intermediate units are calc-alkaline in composition and plot in the IAB field (Fig. 17d-e). The basalts originate from depleted magmas (N-MORB) and follow the AFC trend (Fig. 17f). The Archean crust interacts with these rocks during their evolution, however subduction enrichment may also play a part in the evolution of these rocks (Fig. 17g).

The basalts have a relatively flat REE profile with generally weak negative anomalies of Nb-Ta and Ti (Fig. 17h-j). The intermediate to felsic units are LREE enriched, with more pronounced Nb-Ta and Ti anomalies, suggesting magmatic differentiation and crustal contamination of the parent melt (Fig. 17k-l).

Phonolite Trachyte Com/Pant Rhyolite Trachy And Bsn/ Neph Alk Bas

Sub Alk Bas And/Bas Andesite RhyoDac/Dac Nb/Y Zr/T iO 2

b Winchester & Floyd (1977) Fig. 6

1 0.1 0.01 0.1 0.2 1 2 3 4 5 10 0.001 0.01 0.1 1 10 40 50 80 70 60 SiO (wt. %) 2

Winchester & Floyd (1977) Fig. 2

Phonolite Trachyte Com/Pant Tr/An RhyoDac/ Dac AB Bsn/ TrachyBsn/ Neph And/ Bas And Rhyolite Sub Alk Bas Zr/TiO2 a AC c Zr (ppm) T iO (%) ₂ 25 100 175 250 0.25 1 1.75 2.50

Ross & Bedard (2009)

Tholeiitic Transitional Calc-alkaline Zr/Y Th/Yb d 1 10 20 20 10 1 0.1 0.01 AC MORB IAB CRB + IOB Agrawal (2008) DF1 DF2 0 2 4 6 8 -2 -4 -6 -8 0 2 4 6 -2 -4 -6 -8 AC e

Volcanic arc array

MORB-OIB array OIB N-MORB E-MORB Nb/Yb Th/Yb AC Pearce (2008) 1 0.1 10 100 0.01 0.1 1 10 f depleted magma AFC LEGEND ∞

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Mafic Pillowed Acch1 High Zr Acch1 Acch1 Acch1a Acch1b Intermediate Acch2 Acch2a Intermediate to Felsic Acch3 Acch3a Symbology AC _{Archean crust} SE Subduction enrichement AFC Assimilation-fractional crystallisation Hf / 3 Th Ta A B C D Hf /

Th = 3Primitive arc tholeiites

A=N-MORB B=E-MORB + tholeiitic WPB C=Alkaline WPB D=VAB Calc-alkaline Wood (1980) Fig. 1 SE 90 80 70 60 50 40 30 20 10 10 20 30 40 50 60 70 80 90 90 80 70 60 50 40 30 20 10 g AC 1 10 100 Th Ta Ce Nb La Nd Zr Eu Pr Sm Hf Gd Dy _{Er Lu} Ti Tb Y Yb

rock/ primitive mantle

h 1 10 100 Th Ta Ce Nb La Nd Zr Eu Pr Sm Hf Gd Dy Er Lu Ti Tb Y Yb

rock/ primitive mantle

i ₁₀₀ Gd Hf 10 1 Th Ta Ce Nb La Nd Zr Eu Pr Sm Dy Er Lu Ti Tb Y Yb

rock/ primitive mantle

j 100 Gd Hf 10 1 Th Ta Ce Nb La Nd Zr Eu Pr Sm Dy _{Er Lu} Ti Tb Y Yb

rock/ primitive mantle

k 100 Gd Hf 10 1 Th Ta Ce Nb La Pr SmNd Zr Eu Dy _{Er Lu} Ti Tb Y Yb

rock/ primitive mantle

l

Fig. 17. Geochemical plots for the mafic to felsic volcanic rocks of the Colomb-Chaboullié greenstone belt. The amphibolised basalt has been divided into 3 main units (Acch1, Acch1a and Acch1b), with two smaller geochemical groups that define a basaltic unit in the

east of the belt with well developed pillows, and the other unit defined by high Zr values. The Acch2 and Acch2a units are intermediate in nature, with Acch3 also showing similar characteristics to these intermediate groups. Acch3a represents the true felsic volcanic rocks within the Colomb-Chaboullié belt. The normalisation values for rare earth elements for the spider diagrams are after Sun and McDonough (1989).

Geochemistry of the Colomb-Chaboullié Volcanic Units

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Schistosity Symbology Covered Mineralisation Lithology Acch1 Acch1a LEGEND Rusty patches Massive to disseminated sulphides Deformed pillowed basalt Schist Sample locations Disseminated interpillow sulphides Sampling channel

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62 50 64 58 60 16-SG-3521-A 16-SG-3521-C 16-SG-3535-A 16-SG-3521-B 316606 5662095 ± 2 56621 10 ± 2 316640 N 2.5m 5m 0m 1m 0m trench

Fig. 16. This map illustrates the principle facies and the location of the disseminated and massive sulphide showings within this

outcrop. Fig. 11 shows the sulphide lens in this outcrop orientated SW-NE, with the schistosity of the host rock cross cutting the sulphide lens.

Detailed Map of Outcrop 16-SG-3521

Fig. 15. Zoomed map of the main N-S transect through the volcanic units of the Colomb-Chaboullié belt, carried out by the

first and second authors, showing the geochemical units. See legend below in Geochemistry of the Colomb-Chaboullié Volcanic Units for details.

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5660000 5670000 316000 318000 320000 322000 324000 326000 328000 5662000 5664000 5666000 5668000 314000 47 31 47 58 56 80 57 35 87 45 55 75 75 45 48 45 63 68 50 43 45 70 40 40 %

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Beryl Silver Gold Prospects Lake Geological contact

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2016 outcrops 2016 geochemistry sites 2015 outcrops 2015 geochemistry sites Symbology 2km 0 1 2

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55 43 73 85

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∞∞ _∞ Lac Colomb Route de la Baie-James 296000 304000 312000 320000 328000 336000 344000 352000 5644000 5648000 5652000 5656000 5660000 5664000 5668000 5672000

N

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Fig. 15 Colomb-Chaboullié Group Stratigraphic Legend Colomb-Chaboullié Group Nemiscau Subprovince Opatica Subprovince Paragneiss (bi ± hbl)

Peridotite and pyroxenite Gabbro

Felsic to intermediate volcaniclastics

Porphyritic andesite

Pillowed porphyritic andesite Amphibolised basalt Undifferentiated Nemiscau Subprovince lithologies Undifferentiated Opatica Subprovince lithologies cch8 cch7 cch6 cch5 cch4 cch3 cch2 cch2a cch1 Polymict conglomerate Quartzite/iron formation Gold Gold Gold Gold Regional Faults

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Thrust fault Shear zone Strike-slip shear zone

%

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Structure

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Schistosity Proterozoic Proterozoic dyke

%%%%%%%

Fig. 14. Geological map of the Colomb-Chaboullié greenstone belt (after Bandyayera and Daoudene, 2015) showing the location of the outcrops mapped in 2016 by the first author, the outcrops mapped in 2015 by the MERN,

the location of the 2016 and 2015 lithogeochemical samples, the locations of previously recorded mineralisation in the study area, and the stratigraphic placement of the geochemical units. See legend below in Geochemistry of the Colomb-Chaboullié Volcanic Units for details.

3521

Geological Map of the Colomb-Chaboullié Greenstone Belt

Broadback River

Massive Sulphides

Fig. 12. Rounded siliceous fragments containing pyrite

(Py) embedded in a pyrrhotite (Po) matrix.

Fig. 13. Reflected light photomicrograph of massive

sulphides from the Lac Marcaut outcrop.

Py Po Cpy Py Po Po Bird’s-eye texture 1cm 500 μm

Mineralisation

Fig. 8. Deformed pillows in basalt with rusted

inter-pillow material.

Fig. 9. Synvolcanic alteration of chlorite (Chl) and

garnet (Gr) in the basalt pillow margins.

Fig. 10. Stockwork-style veins of sulphides (V) in the

amphibolised basalt (BaAm).

Fig. 11. Massive sulphide lens from the Lac Marcaut

outcrop (16-SG-3521) containing gold values.

V BaAm _V Chl Gr Chl

Petrography

Fig. 2. Deformed pillows in basalt.

Fig. 3. Basalt photomicrograph, dominantly made up

of amphiboles with plagioclase crystals.

Fig. 4. Pillowed andesite.

Fig. 5. Andesite with plagioclase and amphibole

phenocrysts in a plagioclase-quartz rich matrix.

Fig. 6. Laminations or schistosity in the felsic

volcaniclastic unit.

Fig. 7. Thin section of felsic volcaniclastic unit, with

lamination/schistosity. Pl Pl Act-Tr Qtz-Fsp Am 1mm 1mm 1mm

Location Map

Fig. 1. Simplified geological map of the Superior Province in

the James Bay region of Québec, showing the location of the Colomb-Chaboullié greenstone belt, after Bandyayera and Daoudene (in preparation).

Undetermined ~2,7 Ga

~2,8 Ga

Archean volcano-sedimentary sequences

Paleozoic sequence Paleoproterozoic sequence Fagnant Frotet-Evans Opinaca Nemiscau Opatica Abitibi Opatica La Grande Minto Ashuanipi La Grande Grenville d’Hudson Baie Waskaganish On tario 50 km Bay James Opatica Route du Nord Route Transtaïga Route de la Baie-James Caniapiscau Radisson Wemindji Chisasibi Chibougamau Matagami Waskaganish Eastmain Nemaska 51° 50° 53° 52° 54° 55° 56° 57°80° 78° 76° 74° 72° 70° Superior Province 400 km_80°W 70°W 90°W 45°N 55°N 80°W 70°W 90°W 45°N 55°N Colomb-Chaboullié

Abstract

T h e s m a l l A r c h e a n C o l o m b -Chaboullié greenstone belt, contains a series of base and precious metal-bearing sulphide prospects that indicate exploration potential in the a r e a . W i t h i n t h i s b e l t , s u l p h i d e mineralisation occurs as massive and semi-massive bodies dominantly located in the volcanic units, and as disseminated sulphide zones infilling the inter-pillow basalt material of the pillowed facies. Sulphide veins also occur in massive basalt flows, infilling fractures. Geochemical analysis will h e l p i n c r e a s e t h e s t r a t i g r a p h i c knowledge of this study area and perhaps help link the mineralisation with specific chemo-stratigraphic units. This study will help future exploration of greenstone belts in the northern region of the Superior Province that are underexplored in comparison to the Abitibi greenstone belt.

Volcanic stratigraphy and mineralisation of the Archean Colomb-Chaboullié greenstone belt,

James Bay, Québec, Canada

Sarah Galloway, Pierre-Simon Ross (INRS-Centre Eau Terre et Environnement, Québec), Daniel Bandyayera and Yannick

Daoudene (Ministère de l’Énergie et des Ressources naturelles, Québec)