metallogenie de la zone marco, gite canada
Transcription
metallogenie de la zone marco, gite canada
MARTIN AUCOIN " A METALLOGENIE DE LA ZONE MARCO, GITE , , AURIFERE CORVET EST, BAIE-JAMES, QUEBEC, CANADA Mémoire présenté à la Faculté des études supérieures de l' Université Laval dans le cadre du programme de maîtrise interuniversitaire en sciences de la Terre pour l' obtention du grade de maître ès sciences (M .Sc.) DÉPARTEMENT DE GÉOLOGIE ET DE GÉNIE GÉOLOGIQUE FACULTÉ DES SCIENCES ET DE GÉNIE UNIVERSITÉ LAV AL QUÉBEC 2008 © Martin Aucoin, 2008 Résumé Le gîte aurifère Corvet Est est encaissé par les roches Archéennes de la Province du lac Supérieur dans la région de la Baie-James. La zone Marco est encaissée dans une lentille de dacite de la séquence volcano-sédimentaire du Groupe de Guyer, à proximité du contact, au sud, avec les roches métasédimentaires du Groupe de Laguiche. Les roches sont métamorphisées au faciès des amphibolites et intensément déformées. La zone Marco comprend de l' or disséminé, de la pyrite, de l'arsénopyrite, de la pyrrhotite et de la chalcopyrite. La minéralisation est pré-métamorphique avec un age Re/Os sur arsénopyrite de 2663 Ma. La dacite est faiblement altérée et le basalte est non-altéré. La séquence d'altération est postérieure à la minéralisation et comprend la chloritisation et la tourmalinisation, l'albitisation, la séricitisation suivie d ' une chloritisation tardive. L' environnement tectonique de terranes accrétées, la minéralisation pré-metamorphique en magnétite, ilménite, pyrite et pyrrhotite avec l'or disséminé dans des zones de cisaillement, et la composition isotopique du soufre (0 34S) et de l'oxygène (0 18 0 ) indiquent que le gîte Corvet Est ressemble aux gîtes d'or orogéniques au faciès des amphibolites. Abstract The Corvet'Est gold deposit is in Archean rocks of the Superior Province in the James Bay region. The Marco zone is hosted by a Jens of dacite in the Guyer Group voJcanosedimentary sequence near the contact with the Laguiche Group metasedimentary rocks to the south. The rocks are metamorphosed to the amphibolite grade and highJy deformed. The Marco zone comprises disseminated gold, pyrite, arsenopyrite, pyrrhotite and chalcopyrite. Mineralization is pre-metamorphic, with a Re/Os age on arsenopyrite of 2663 Ma. Dacite displays weakaiteration whereas basait is unaitered. The alteration sequence is post-mineralization and comprises chloritisation and tourmalinisation, aJbitization, sericitization and Jate chloritization.- An accreted terranes tectonic setting, premetamorphism mineralization composed of magnetite, i1menite, pyrite and pyrrhotite with gold disseminated in shear zones, and the isotopic composition of sulfur (8 34 S) and oxygen (8 18 0) indicate that the Corvet Est deposit has similarities with amphibolite-grade orogenic gold deposits. Avant-Propos Ce projet de maîtrise n'aurait pu être réalisé sans les conseils et critiques constructives de mon directeur de recherche Georges Beaudoin, véritable porte-lanterne qui, parmi brumes et noirceurs, m'a appris à porter ma propre lanterne. Je le remercie grandement pour sa patience et son professionnalisme. Robert Creaser est remercié pour son travail de datation isotopique et ses suggestions. Je remercie la compagnie Mines Virginia, spécialement Paul Archer, qui a mis ses ressources et sa confiance entre mes mains. Michel Gauthier et Benoît Dubé sont remerciés pour leurs commentaires et suggestions. Les travaux de terrain furent rendus possibles grâce au support de la compagnie Services Techniques Géonordic. Merci à Charles Perry et Robert Oswald qui m'ont appris les secrets de la propriété Corvet Est, à Denis Chénard et Alain Cayer pour m' avoir initié à l'exploration et à Louis Bisson pour m'avoir transmis sa passion pour la géologie. Sont aussi remerciés les technologues avec qui j'ai fait équipe sur le terrain, en particulier l' érudit Paul Sawyer, dont l' adresse au travail n'a d'égal que sa grande sagesse. Merci à Jean Goutier pour ses conseils à propos de la géologie régionale, ainsi qu 'à Marc Constantin, Louise Corriveau, Carl Guilmette, Alan D' Hulst et Céline Dupuis pour leur aide par rapport à la géochimie. Je suis également très reconnaissant envers la fondation SEG et le Consorem pour m'avoir octroyé des bourses. Je tiens à remercier le personnel du département de Géologie et de Génie Géologique pour leur aide tout au long de ce projet de maîtrise, plus particulièrement Martin Plante, Pierre Therrien, Marc Choquette et Éric David qui ont fait preuve d' implication et d'intérêt pour ma progression. Danielle Pichette et les dames du secrétariat, ainsi que Marcel Langlois sont aussi remerciés pour leur disponibilité et leur gentillesse. Merci à mes amis et à ma famille pour m'avoir supporté moralement tout au long de ce projet. Finalement, un merci tout spécial à ma mère, à feu mon père, et à ma conjointe Catherine pour leur amour inconditionnel. L'auteur de ce mémoire a écrit en totalité l'article qui constitue le chapitre 2. Les coauteurs sont MM. Georges Beaudoin, Robert Creaser, et Paul Archer. Georges Beaudoin est le directeur de mon projet de maîtrise, Robert Creaser a effectué les datations isotopiques sur des échantillons d'arsénopyrite et Paul Archer est vice-président exploration et acquisitions chez Mines Virginia. À mes parents Table des matières Résumé ......................................................................•.............•...........•....•.............................. i Abstract ................................................................................................................................. ii Avant-Propos ...........................•.............••.•.............•....•....................................................... iii Table des matières ................................................................................................................ v Liste des tableaux ................................................................................................................. vi Liste des figu res .................................................................................................................. vii Chapitre 1. Introduction ...................................................................................................... 1 1.1 Généralités ..................... .. .................. .. .... .. .. .... .. .... .. ... .. .... ..... .... .. .... ...................... 1 1.2 Objectifs ........ ... ............... .. ............. ..... .................... .. .. ... ........... .. ..... ...................... 2 1.3 Présentation de l'article ............................................. ...................... .. .......... ......... .3 1.4 Description des annexes .. ..... ............. .. .. ,.............. .................................. ....... .... .. ... 4 Chapitre 2. Metallogeny of the Marco zone, Corvet Est auriferous deposit, James Bay, Québec, Canada ..•..................•.................•...................................................................•........ 5 2.1 Abstract ... .. .......... .. ..... ... ................ .......... ...................... ... ......... ........ .... .... ......... .... 5 2.2 Introduction ........ .. ..... .... .... ......... .... .......... ............ .. .......................... ........ .. ......... ... 7 2;3 Regional geology ............. :......................... ............... ...... .. ... ........ .......... ......... ....... 9 2.3.1 Regional metallogeny .............................. ........ ........ .. ....... ................ .. ............. 11 2.4 Corvet Est deposit geology .. ........... ............ .... .................. ............ ............. .. .... .. .. 13 2.4.1 Poste-Lemoyne pluton .. ......... ........ .. .... .... ........... .. .. ... ......... .... .. .... ................ ... 13 2.4.2 Guyer Group volcano-sedimentary belt.. .. .... .. .. .. .. ... .. ....................... ........ .. ..... 13 2.4.3 Laguiche Group paragneiss ........................... .................. ............. ...... ............. 15 2.4.4 Mineralization ................ .... ......... .. .... ............... ..................................... ......... .. 16 2.5 Mineralogy and paragenetic sequence .................. ............................................... 20 2.5.1 Gold textures .. ..... .. .......... ... .............. :.................. ............. .. .............................. 27 2.6 Analytical methods ................. .......................... ....... ........ .. ......... ...... .. .. ... ...... .. .. .. 29 2.7 Results ........................................................ .. .............. .......................................... 31 2.7.1 Mineral compositions ........... .................................. ...................................... ... 31 2.7.2 Major and trace elements lithogeochemistry., ............... ..... ............................. 37 2.7.3 Alteration geochemistry ..................................... ... ..... .. .. ............... .... ............... 46 2.7.4 Re-Os Geochronology ................... .............. .................................................... 48 2.7.5 Stable isotopes geochemistry .......... .. ............. .................................................. 52 2.8 Discussion ....... .. .................................... ..... ................................................ .......... 57 2.8.1 Geodynamic setting ...................... ............ ......... .............................................. 57 2.8.2 Metamorphic conditions .... .............................................................................. 58 2.8.3 Age ofmineralization ......... .. ... .. .......................... ........ .... ....... ................... ...... 58 2.8.4 Source of sulfur, osmium and fluids ................................................................ 59 2.8.5 Comparison of the Corvet Est deposit with amphibolite grade orogenie, amphibolite grade epithermal, and the Hemlo deposits ............................. ................... 62 2.9 Conclusions .................... .. ................. .................................. ................................. 66 Chapitre 3. Conclusion ....................................................................................................... 67 Bibliographie ..................•.•................................••...••........................................................... 70 Annexe 1: Analyses à la microsonde de minéraux du gîte Corvet Est, Canada ........... 81 Annexe 2: Descriptions de forages et tranchées (en pochette) ........................................ 85 Liste des tableaux Table 2.1: Representative microprobe composition of mineraIs from the Corvet Est deposit, Québec, Canada ............. ... ... ... .......... .. .................................... ........ .. ...... ..... ........... .. .......... 33 . Table 2.2: Major and trace element composition of rocks from the Corvet Est deposit, Québec, Canada ....... ........ .................... .................................................................. ..... ........ 40 Table 2.3: Re-Os geochronology data for arsenopyrite from the Corvet Est deposit, Québec, Canada ......... ..... .. .. ..... .............................................................. ...... ........ ........... ........ ....... ... 51 Table 2.4: Stable isotope data from the Corvet Est deposit, Québec, Canada .................... 55 Table 2.5: Temperature of isotope equilibrium of quartz-plagioclase pairs from the Corvet Est deposit, Québec, Canada ......... ........................... ............................. .... ......... ........ ......... 56 Table 2.6: Comparison of the Corvet Est deposit and other amphibolite grade gold deposits ......... ................... .......................................................... ............................ .. ......... ...... .. ....... 65 Liste des figures Figure 2.1: Geology of the James Bay region, Québec, northeastem Superior province, with location of gold deposits: (1) Corvet Est, (2) Poste-Lemoyne, (3) Auclair, (4) Eleonore, (5) Eastmain and (6) Clearwater deposits (modified from Houle 2006) .. 8 Figure 2.2: Regional geology of the Corvet Est gold deposit, at the boundary between the Opinaca (south) and LaGrande (north) sub-provinces, with location of the PosteLemoyne deposit (modified from Goutier et al. 2002) .......... ... .......... .. ...... ... ......... Il Figure 2.3: Detailed geology of the Corvet Est gold deposit, with location of the Marco and . the Contact zones, driIIholes and trenches with number referred to in text (modified from Perry 2006) ................ .. ..... .......... ..... ... ............ .... .. .... ......... ........ ..................... 15 Figure 2.4: Simplified trench or driIIhole logs from the Marco zone, with lithology, sample location, gold grade, intensity of deformation and gamet, pyrite, arsenopyrite and titanite approximative volume percent. a) Trench 5. b) DDH 2. c) DDH 23. *The gold grades over 5 ppm exceed the chart scale but are indicated by numbers. Apy arsenopyrite; De! deformation; Gt gamet; Litho lithology; Py pyrite; TIn titanite ..... .. ......... .. .. ... ......... .. .. ......... ..... .. ................. ................. ... .. .. ...... .... .. .... ........ 17 Figure 2.5: a) Typical deformed dacite with heterogeneous and stretched blocks of andesite in a felsic matrix (Trench IR, Fig. 2.4). b) Highly mineralized and deformed rusty dacite (Trench 5, Fig. 2.4). c) ·Centimeter-scale, discontinuous, tourmaline layers at the dacite-amphibolite contact (Trench 5, Fig. 2.4) ............ ........ ............ ...... ...... .... 19 Figure 2.6: Paragenetic sequence for the Corvet Est deposit ...... .......... ........ ............ .. ....... 20 Figure 2.7: Stage 1 a) Subhedral cataclased poeciloblastic gamet, subhedral amphibole, subhedral nematoblastic to lepidoblastic biotite and subhedral granoblastic quartz (plane polarized light). b) Euhedral pyrite, arsenopyrite and tourmaline overprinting subhedral sericitized plagioclase, with subhedral titanite, subhedral deformed chlorite and quartz (cross-polarized light). c) Euhedral arsenopyrite interstitial to euhedral pyrite and anhedral pyrrhotite (reflected plane polarized light). d) Xenomorphic pyrite with coronitic subhedral magnetite, granoblastic quartz, euhedral ilmenite and anhedral biotite (reflected plane polarized light). e) Granoblastic euhedral to subhedral quartz, K-feldspar, plagioclase and biotite (cross-polarized light). f) Euhedfal tourmaline overprinting euhedral pyrite, anhedral amphibole and subhedral quartz (plane polarized light). Apy arsenopyrite; Am amphibole; Bt biotite; Chi chlorite; Fk potassic feldspar; Grt gamet; Iim iImenite; Mag magnetite; PI plagioclase; Po pyrrhotite; Py pyrite; Qtz quartz; Tl tourmaline; TIn titanite .............. .. ................ ... ......................................... .. ... .. ..... .... 22 Figure 2.8: Stage 2 a) Photomicrograph of gold interstitial to anhedral titanite and polygonized quartz, with subhedral arsenopyrite and anhedral calcite (reflected plane polarized light). b) Photomicrograph of deformed gold-bearing quartz vein V III with sericitization of plagioclase-rich host rock (cross-polarized light) with location of gold shown in a) indicated by red arrow. c) Photomicrograph of a quartz veinlet (white arrow) surrounded by fine-grained sericite alteration (outlined by red dotted lines) of plagioclase (plane polarized light). d) Photomicrograph of biotite replaced by sericite, then by chlorite (plane polarized light). e) Photograph of postmetamorphic deformed quartz vein with microcline alteration overprinting the SI foliation. f) Photomicrograph of post-metamorphic deformed quartz vein and microcline alteration crosscutting the SI foliation shown in e) (plane polarized light). Apy arsenopyrite; Bt biotite; Cc calcite; Chi chlorite; Mc microcline; PI plagioclase; Qtz quartz; S} foliation; Ser sericite; Ttn titanite .................... .. ... .. ...... 24 Figure 2.9: Stage 3 a) Photomicrograph ofundeformed pyrite breccia vein (reflected plane polarized light). b) Photomicrograph of an undeformed calcite - K-feldspar epidote vein with epidote and K-feldspar alteration of the host rock (plane polarized light). c) Photograph of an undeformed epidote - quartz - calcite breccia with Kfeldspar - epidote - calcite alteration of the host rock. d) Photomicrograph of poeciloblastic calcite with quartz, plagioclase and biotite inclusions (plane polarized light). Bt biotite; Cc calcite; Ep epidote; Fk potassic feldspar; Pl plagioclase; Py pyrite; Qtz quartz .................................................................................................... 26 Figure 2.10: Photomicrographs of gold textures. a) Gold included in pyrite, interstitial to chalcopyrite and tourmaline (reflected plane polarized light). b) Gold inchided in euhedral arsenopyrite (reflected plane polarized light). c) Gold inclusions at the edge of pyrrhotite (reflected plane polarized light). d) Gold inclusions in quartz, sericitized plagioclase, K-feldspar and epidote, and gold interstitial to arsenopyrite and silicates (cross-polarized light). The inset shows the gold in reflected plane polarized light. e) Gold inclusions in epidote and biotite, and gold interstitial to sulfides and silicates (plane polarized light) whereas the inset shows the same area in cross-polarized light. f) Gold, arsenopyrite and pyrrhotite inclusions in gamet, gold interstitial to gamet, quartz and pyrrhotite, and filling garnet fractures (reflected plane polarized light). Apy arsenopyrite; Bt biotite; Cpy chalcopyrite; Ep epidote; Grt gamet; Py pyrite; Po pyrrhotite; Qtz quartz; Pl plagioclase; Tl tourmaline ............ .......................................................................... ......... ................ 28 Figure 2.11: Au/(Ag+Au) ratios for gold grains from the Corvet Est deposit. The average with ± 1s standard deviation is shown by arrows .................................................... 32 Figure 2.12: Whole rock geochemistry from the Corvet Est deposit. a) Winchester and Floyd (1977) Zr/Ti vs Nb/Y diagram with field boundaries revised by Pearce (1996). b) Magmatic affinity diagram for Corvet Est igneous rocks using the Y vs Zr diagram of Barrett and MacLean (1994). c) Geodynamic environment bfCorvet ·Est igneous rocks in the Th vs Hf/3 vs Ta diagram (Wood 1980). d) Geodynamic environment of Corvet Est igneous rocks in the Zr/Y vs Ti/Y diagram (Pearce and Gale 1977) ........... ,................... ....... .................. ............. .......................... ................ 38 Figure 2.13 : a) Rare earth element composition of rocks from the Corvet Est deposit normalized to primitive mantle values from Palme and O'Neill (2004). b) Trace - ----------------------------------------------------------~ IX element Spidergram of Corvet Est deposit rocks normalized to primitive mande values from Palme and O ' Neill (2004) ................ .... ....... ..................................... ... 39 Figure 2.14: Alteration geochemistry of the Corvet Est deposit. a) Ah03 vs Zr diagram (MacLean and Kranidiotis 1987) showing fractionation from amphibolite to dacite and alteration of dacite along a mass gain trend. b) Isocon diagram (Grant 1986) of mineralized (# 55026, 1.7 ppm Au) vs protolith composition from least altered samples average (# 55345 and # 31556) ...................................................... ....... .... 47 Figure 2.15: Photomicrographs of arsenopyrite dated by Re-Os geochronology. a) Mylonitized and mineralized dacite (sample no. 136665) with idiomorphic finegrained arsenopyrite (plane polarized light). b) Barren dacite (sample no. 31567) with subhedral arsenopyrite in medium-grained leucosome (left: reflected plane polarized light, right: cross-polarized light). Am amphibole; Apy arsenopyrite; Bt biotite; Pl plagioclase; Po pyrrhotite; Py pyrite; Qtz quartz; Ser sericite; Ttn titanite . ... .............. ......... .. ......... ........ ............... .. .... .... .......... .. .... .... .. ...... .. ... .. ....... ... .. ..... .. .. .. 49 Figure 2.16: Re-Os geochronology of arsenopyrite from the Corvet Est deposit. a) Model 1 isochron diagram for sample # 136665. b) Weighted average model diagram for sample # 31567 .......... .. ........ ...... .... .. ........ .. .......... ...... ....... .... ............................. .... . 50 Figure 2.17: Histograms of sulfur and oxygen isotope composition from the Corvet Est deposit (Table 2). a) 834 S values for Ryrite and arsenopyrite with average values and range for 1s standard deviation. b) 8 80 values for quartz, plagioclase and tourmaline with average values and range for 1s standard deviation, excluding the quartz leucosome sample ............. ... ............... ........................... ....... .... ... ... ........... .. 53 Figure 2.18: Quartz vs plagioclase 8 18 0 diagram with isotherms according to Bottinga and Javoy (1973) and Matsuhisa et al. (1979) .................................... .. .... .. ................ ... 54 Figure 2.19: Comparison of Corvet Est 834 S values with that from different sources for S . (Sakai et al. 1982, Ueda and Sakai 1984, Kerridge et al. 1983, Coleman 1977, Chaussidon et al. 1989 Lusk et al. 1975, MacLean and Hoy 1991, Kerr and Gibson 1993, Strauss 1986, 1989, Bleeker 1994 in Huston 1999, Franklin et al. 1981 , Zalesky and Peterson 1995, Seccombe 1977, Nunes and Thurston 1980, Papunen et al. 1989, Seccombe and Frater 1981, Yeats 1996, Beaudoin and Pitre 2005) ........ 60 Figure 2.20: Comparison of oxygen isotopic compositions between Corvet Est fluid and that of natural waters from various environments (Taylor 1986, Giggenbachs 1992, Sheppard et al. 1977, Sheppard 1986) .................................................................... 62 - - - - - - - --- ----~--~-~~-------- 1 Chapitre 1. Introduction 1.1 Généralités Le gîte Corvet Est est encaissé dans les roches Archéennes de la Province du lac Supérieur (Eade 1966; Sharma 1977), près du contact entre les sous-provinces de LaGrande et d ' Opinaca. La propriété comprend deux zones minéralisées: 1) la zone Contact est située près du contact faillé entre les roches volcano-sédimentaires du Groupe de Guyer (2820 Ma) et les roches métasédimentaires du Groupe de Laguiche «2650 Ma); 2) la zone Marco est encaissée dans une lentille de dacite de la séquence vol cano-sédimentaire du Groupe de Guyer, à environ 1 km au nord du contact de faille avec le Groupe de Laguiche. Les roches sont métamorphisées au faciès des amphibolites et sont intensément déformées. La zone Marco du gîte Corvet Est présente plusieurs caractéristiques suggérant qu' il s' agit d' un gîte d' or orogénique Archéen au faciès des amphibolites, notamment son environnement de terranes accrétées à proximité d' une zone de faille crustale majeure et la prés"ence 4' or disséminé microscopique dans une zone de cisaillement. La zone Marco se distingue des autres gîtes d' or orogéniques de l'Abitibi car ceux-ci sont mis en place au faciès des . schistes verts dans un contexte mésozonal (Gebre-Mariam et al. 1995), où l' or précipite principalement dans des filons de quartz-carbonates accompagnés d' une forte altération. La rareté des veines et la position stratigraphique de la zone Marco suggèrent aussi une minéralisation syn-volcanique. La propriété Corvet Est est située dans la municipalité de la Baie-James (Fig. 2.1), 240 km à l'est de Radisson et 50 km au sud-ouest du complexe hydroélectrique LG-4 (SNRC. 33G/07, 33G/08, 33H/04 et 33H105). Les prospecteurs de Mines Virginia ont découvert l'indice « Virginal » (Gauthier, comm. pers. 2008), un tuf à bloc felsique zincifère dans la région de Corvet Est en 1997, ce qui mena à l'acquisition de la propriété. Les résultats négatifs de la première phase d'exploration provoquèrent un désintérêt pour la propriété, mais les mêmes prospecteurs y trouvèrent un indice d'or en 2002, menant à la reprise de 13 claims sur Corvet Est (Perry 2007). Le suivi de 2003 (Oswald 2004), incluant des travaux de prospection et de forage, délimita la zone Contact sur une distance de 1.2 km. Le suivi 2 mena également à la découverte de la zone Marco, et l' ajout de 75 c1aims à la propriété. En · 2004, des levés géophysiques magnétométrique et de polarisation provoquée, pétrographique, de reconnaissance géologique, et de prospection, l' excavation de tranchée et des forages (Perry 2005) eurent lieu sur la propriété, avec l' acquisition de 383 c1aims le long de la bande volcano-sédimentaire de Guyer. En 2005 , un levé MAG aéroporté de haute définition (Mouge et Paul 2005) précéda une campagne de prospection et de forage ainsi qu'un levé géochimique de till (Perry 2006). En 2006, des levés de cartographie, prospection, excavation de tranchée et des forages ont permis de prouver la continuité de la zone Marco vers l' ouest (Perry 2007). La cartographie, la description d' affleurements et de carottes de forage, et la récolte d'échantillons ont été effectués lors des travaux de terrain de 2005 et 2006. L ' échantillonnage s' est fait sur des forages et tranchées effectués. de 2003 à 2005. 1.2 Objectifs Cette étude a pour objectif général de mieux comprendre la métallogénie du gîte Corvet Est, en déterminant la nature et les contrôles de la minéralisation en or. Les objectifs spécifiques sont les suivants: 1) Caractériser la minéralogie, la géochimie, la minéralisation aurifère et l'altération hydrothermale. 2) Établir les relations temporelles entre le métamorphisme, la déformation, l'altération hydrothermale et la minéralisation afin de construire une paragénèse. 3) Établir l'origine de l'altération hydrothermale et de la minéralisation aurifère. 3 4) Définir un modèle génétique pour le gîte Corvet Est et comparer la minéralisation aurifère avec d' autres gîtes d' or. La description détaillée des tranchées et forages du gîte Corvet Est a été effectuée afin d' établir des liens entre la minéralisation, le métamorphisme, la déformation et l'altération hydrothermale. L'environnement géodynamique du gîte Corvet Est est précisé à l'aide d' une étude géochimique des roches extrusives et intrusives. La minéralogie, la séquence paragénétique, l'altération et la géochimie isotopique permettent de comparer la zone Marco du gîte Corvet Est avec d'autres gîtes d' or au faciès amphibolite. L' interprétation des processus hydrothermaux ayant contribué à la formation du gîte aidera à mieux cerner l'origine des fluides minéralisateurs, du soufre et des métaux, et les conditions dans lesquelles la minéralisation s'est formée. La comparaison du gîte Corvet Est avec les gîtes d' or orogéniques et épithermaux métamorphisés au faciès amphibolite ainsi qu' avec le gîte Hemlo apportera un intérêt certain pour la communauté scientifique et industrielle en prouvant un potentiel de gîte d'or orogénique dans un nouveau secteur et en corroborant certaines caractéristiques déjà connues. Ce mémoire est divisé en trois parties. La première partie est une introduction, la deuxième partie comprend un article écrit en anglais résumant mes travaux de maîtrise, qui sera soumis pour publication dans une revue scientifique spécialisée en géologie économique, en version anglaise. La troisième partie est une conclusion générale. Le mémoire comprend des annexes contenant tous les résultats d'analyse de l'étude. 1.3 Présentation de l'article L' article intitulé: « Metallogeny of the Marco zone, Corvet Est auriferous deposit, James Bay, Q~ébec, Canada» sera soumis à la revue Mineralium Deposita pour publication. 4 Dans l'article, la problématique du projet est d' abord présentée. La géologie régionale, incluant un survol de la métallogénie du Groupe de Guyer et du Groupe de Laguiche est ensuite abordée. La géologie de la propriété suit, décrivant les différentes lithologies, la minéralisation et son altération. Une description de la minéralogie et de la séquence paragénétique, incluant une description texturale de l' or est ensuite présentée. La description des différentes méthodes analytiques utilisées lors de l'étude précède la présentation des résultats, incluant la composition des minéraux, la litho géochimie des éléments majeurs et traces, la géochimie de l' altération, la géochronologie par la méthode Re-Os, ainsi que la géochimie des isotopes stables du soufre et de l' oxygène. Finalement, une discussion sur l' environnement géodynamique, les conditions du métamorphisme, l' âge de la minéralisation, la source du soufre, de l'osmium et des fluides, ainsi qu' une comparaison du gîte Corvet Est avec différents gîtes au grade amphibolite (orogéniques, épithermaux et Hemlo) est présentée. Une conclusion résume les points importants des résultats et de la discussion. 1.4 Description des annexes Les annexes sont présentées dans l' ordre suivant les différents sujets abordés dans le mémoire. Elles contiennent les résultats d' analyse à la microsonde des carbonates, tourmalines, amphiboles, épidotes, ilmenites, et chlorites, ainsi que les descriptions de tranchées et forages des sections Marco Ouest et Marco Est. 5 Chapitre 2. Metallogeny of the Marco zone, Corvet Est auriferous deposit, James Bay, Québec, Canada 2.1 Abstract Abstract The Corvet Est gold deposit is hosted by Archean rocks of the Superior Province in the James Bay region, Québec, Canada. It comprises two mineralized zones: 1) the Contact zone is close to the fauIted contact between the Guyer Group volcano-sedimentary (2820 Ma), and Laguiche Group metasedimentary «2650 Ma) rocks; 2) the Marco zone is hosted by a lens of dacite near the southern boundary of the Guyer Group rocks. The rocks are metamorphosed to the amphibolite grade and show intense deformation. The Marco zone comprises disseminated gold with an apparent thickness ranging from 1.8 to 39.5 m, and gold grades up to 23 g/t over 1 m, and which is larerally continuous along strike for approximately 1.3 km. The lithotectonic sequence comprises, from south to north, footwall basaItic amphibolite overlain by a lenticular unit of extrusive and volcanoclastic andesite/dacite and then by hangingwall basaltic amphibolite. Footwall basaltic amphibolite and dacite are intruded by quartz-feldspar porphyry dykes. The contacts between basal tic amphibolite and dacite are abrupt to . graduaI. Dacite, basaltic amphibolite and quartzfeldspar porphyry show a calc-alkaline to transitionnal affinity and plot in the plate margin arc basalts field. Spidergrams show typical volcanic arc trace element patterns, with Nb, Ta and Ti depletions. High La/Lu (83) in dacite indicates strong magmatic differentiation. Mineralization consists of up to 4% pyrite, 7% arsenopyrite, 3% pyrrhotite, traces of chalcopyrite and gold, disseminated in deformed dacite, basaltic amphibolite and in quartzfeldspar porphyry dykes. The dacite and basaltic amphibolite contain <50% quartzfeldspar-biotite leucosome and <10% gamet. Dacite displays weak alteration whereas basaIt is unaltered. The alteration sequence of dacite starts with chloritization and tourmalinization, followed by albite alteration, overprinted by sericitization of metamorphic plagioclase and late chloritization. 6 Gold forms inclusions in metamorphic quartz, feldspar and pyrite, or free grains interstitial to quartz, feldspar, pyrite, chalcopyrite and arsenopyrite. Sorne free gold is in late quartz veins cutting the sericitized metamorphic fabric. Inclusion and interstitial gold within metamorphically annealed minerais shows that gold mineralization is pre- to synmetamorphism, with sorne gold remobilized in later veins. Re-Os dating of arsencipyrite yields an isochron age of 2663 ± 13 Ma for mineralization and a weighted average model age of 2632 ± 7 Ma for arsenopyrite formed during peak metamorphism. The ca. 2663 Ma arsenopyrite has a low initial 1870S/1880s of 0.19 ± 0.10, suggesting a juvenile crust or a mande Os source with limited input of older crustal Os. The isotopic composition of sulfur in pyrite and arsenopyrite shows that the Marco zone sulfur could have been leached from its volcanic ho st rocks or come from reduction of Archean seawater. Ôl8 0 values of Corvet Est fluid derived from late vein and met~orphic quartz and metamorphic plagioclase plot within the range of values for fluids in equilibrium with andesitic, S-type magmatie, and metamorphie environments. The Corvet Est deposit displays several eharaeteristics similar to those of amphibolitegrade orogeniç gold deposits, such as pre- to post-metamorphic mineralization, wall rock alteration dominated by calcite and seri cite/muscovite, and opaque mineralogy including magnetite, ilmenite, pyrite and pyrrhotite. Disseminated gold in shear zones, a deformed accretionary prism environment of formation, and the isotopie composition of sulfur (Ô34 S) and oxygen (Ô I8 0) also indicate that the Corvet Est deposit has similarities with amphibolite-grade orogenie gold deposits. Keywords: Orogenic Gold • James Bay • Arehean • Amphibolite • Voleano-sedimentary • Isotopes 7 2.2 Introduction Since the discovery of the Eleonore gold deposit by Virginia Gold Mines (Fig. 2.1 ; Robertson 2005), the Archean rocks of the Superior Province, in the James Bay region, Québec, Canada, have been the focus of a major exploration effort. Although Low (1897) discovered gold along the Eastmain River long before the gold discoveries in the Abitibi sub-province in 1910, the James Bay region has been considered unfavourable for go Id prospectivity for nearly a century. Its narrow, amphibolite facies, green stone belts were underrated compared to the wide, greenschist facies, green stone belts of the Abitibi subprovince. Greenstone belts in the James Bay region contain rare quartz-carbonate Iodes, and the gold mineralization found to date is commonly associated with disseminated sulfides, ail of which did not appeal the mineraI exploration industry. The Eastmain Mine (Couture and Guha 1990), the Auclair deposit (Lanthier and Ouellette 1996) and the Clearwater deposit (Cadieux 2000) are examples of gold deposits hosted by narrow amphibolite facies green stone belts in the James Bay area. Application of traditional orogenic gold vein exploration criteria such as spatial association with crustal scale fault zones along major lithological boundaries, intersection or contact of subsidiary faults with favourable host rocks such as dykes, felsic intrusions, banded iron formations and Fe-rich igneous rocks, or changes of shear zone strike is difficult in the James Bay region because of lack of detailed geological mapping. A strong, regional-scale, metamorphic gradient was proposed by Gauthier et al. (2007) as an exploration criterion for frontier regions such as the James Bay region. This was part of the exploration strategy that led to the discovery of the Eleonore gold deposit by Virginia Gold Mines. A sharp metamorphic gradient occurs along most of the boundary between the La Grande and Opinaca sub-provinces of the Superior Province (Gauthier et al. 2007). The Corvet Est deposit, located about one kilometre north from the La Grande-Opinaca contact, also plots within a strong metamorphic gradient, and so are the Poste Lemoyne, La Grande Sud and the Eastmain deposits (Fig. 2.1). 8 N t Paleozoïc D Archean Sedimentary rocks Granite and paragneiss Proterozoic Clastic and dok>mitic sedimenlary rocks [2] Diabase dykes Il Il Vokarxrsedimentary sequence Paragneiss o Tonalite. monzodiorite and monzonite D Gabbro and diorite • Granulite Tonalitic basement (gneiss and lonalite) * Gold deposit Town Figure 2.1: Geology of the James Bay region, Québec, northeastern Superior province, with location of gold deposits: (l) Corvet Est, (2) Poste-Lemoyne, (3) Auclair, (4) Eleonore, (5) Eastmain and (6) Clearwater deposits (modified from Houle 2006) Epizonal orogenie gold deposits (Gebre-Mariam et al. 1995) are characterized by vein gold mineralization hosted in prehnite-pumpellyite to greenshist facies metamorphic rocks, and display dominant brittle ore-hosting structures and open-space filling vein textures, such as plumose, colloform, cockade, crustiform, comb and rosette. Meso~onal orogenie gold deposits (Gebre-Mariam et al. 1995) contain vein and disseminated gold mineralization in greenshist to lower amphibolite facies metamorphic rocks, and display brittle to ductile orehosting structures. Typical mesozonal orogenie gold deposits of the Abitibi sub-province comprise quartz-carbonate-tourmaline veins in deformation zones near crustal-scale faults (Robert 1996), that typically occur in rocks at the greenschist metamorphic facies but also occur in rocks from pumpellyite to lower amphibolite facies. Carbonatation, sulfidation, alkaline metasomatism, chloritisation and silicification are the main alteration types (Boyle 1979). Hypozonal orogenie gold deposits (Gebre-Mariam et al. 1995) are characterized by 9 microscopic, disseminated, gold in volcanic rocks spatially associated with deformation zones. Disseminated orogenic gold mineralization is characteristic in rocks at the upper greenschist to granulite metamorphic facies with calcite, amphibole, biotite, muscovite and diopside alteration (Groves 1993). This paper presents the geology and geochemistry of host rocks, hydrothermal alteration, paragenetic sequence, geothermometry, geochronology and stable isotope geochemistry of the Marco zone, Corvet Est gold deposit, Québec, Canada. These data are used to interpret the relationships between the tectonic setting, age, fluid origin and alteration, and to compare the Marco zone mineralization with that of other types of gold deposits. A better understanding of the Marco zone of the Corvet Est gold deposit will pro vide improved guidelines for disseminated orogenic gold deposit exploration in amphibolite grade greenstone belts. 2.3 Regional geology The Corvet Est gold deposit is Iocated in the Superior Province, in the James Bay area of northem Québec, Canada, at the boundary between the northem La Grande and the southem Opinaca sub-provinces (Figs. 2.1 , 2.2). The La Grande sub-province comprises an ancient tonalitic basement (2.79 - 3.36 Ga), overlain by volcano-sedimentary belts and ultramafic to felsic intrusions (Goutier et al. 2002). It is bounded to the east by the high metamorphic grade Ashuanipi sub-province, to the west by the James Bay and to the north by the Bienville plutonic sub-province (Fig. 2.1). Plutonic rocks of the Bienville subprovince intrude the northem margin of the La Grande belt and mark a transition to dominantly granitic rocks to the north (Percival 2006). The oldest rocks of the La Grande sub-province (Fig. 2.2) are the Langelier Complex biotite tonalite, tonalitic gneiss, granodiorite and diorite (2.79 - 3.36 Ga; Goutier et al. 1999b, 2000) and the Poste-Lemoyne hornblende-biotite tonalite and quartz-biotite diorite 10 (2.88 Ga; Goutier et al. 2002). The basement rocks are overlain by the volcano-sedimentary sequence of the Guyer Group (Fig. 2.2). U-Pb geochronology indicates that the Langelier Complex rocks are in part younger than Guyer Group rocks (2.82 Ga; Goutier et al. 2002). The Langelier Complex, the Guyer Group and the Radisson plutonic rocks (2.71 Ga; Mortenson and Ciesielsky 1987), are intruded by the Duncan tonalite and diorite (2.71 2.72 Ga; Goutier et al. 1998, 1999a). Early Proterozoic rocks of the La Grande subprovince comprise the Senneterre (2.21 - 2.22 Ga; Buchan et al. 1996) and Lac Esprit (2.07 Ga; Hamilton et al. 2001) gabbro dykes, the Mistassini gabbro and diabase dyke swarm (2.51 Ga; Goutier et al. 2000) and the Sakami sedimentary rocks (2.22 - 2.51 Ga; Goutier et al. 2001). Rocks of the La Grande sub-province bear similarities with rocks of the Sachigo, Ucrn and Wabigoon sub-provinces in northwestem Ontario (Goutier et al. 2002). The metasedimentary and plutonic Opinaca sub-province comprises widespread biotite paragneiss of the Laguiche Group (Fig. 2.2). Primary textures and structures are obliterated in the Laguiche Group, which is intruded by white to pink granite and pegmatitic granite. U-Pb geochronology of detrital zircon indicates that rocks of the Laguiche Group « 2.65 ± 0.5 Ga; Goutier et al. 2002) are younger than those of the La Grande sub-province. The Bezier pluton (2.67 Ga; St. Seymour et al. 1989) and the Vieux Comptoir granite (2.62 Ga; Goutier et al. 1999b; 2000) intruded both the LaGrande and Opinaca sub-provinces and constitute the youngest Archean intrusions of the region (Goutier et al. 2002). Il - ga- Proterozoic LKEsprit dyk.. Senne.". gahb'" dyk.. ".t.. _ ain! dyk• • _ diabase Q8bbro s.Jumi FormI;Ion _ qualtZarrie Archesn vt.ull CompCoir _ gl8nÎt8.t biotite .t biotite palagneis, inclusions Beziw pluton _ quartz monzodiorie '" K.feldspar1*!Yric granociorite Opinac. s ub-provinc. L..PheGroup - biotite :1: magne~1e plragrwns .t granite intrusions. rhgn'I9:tized paragneiss >Mth ~Ie rdIsions ....,<io<it, ba... tanalila _ Sl.b-proYincecontact Figure 2.2: Regional geology of the Corvet Est gold deposit, at the boundary between the Opinaca (south) and LaGrande (north) sub-provinces, with location of the Poste-Lemoyne deposit (modified from Goutier et al. 2002) 2.3.1 Regional metallogeny The Guyer Group volcano-sedimentary belt that hosts the Corvet Est gold deposit contains 3 types of mineralization: 1) Algoma-type banded iron formation; 2) volcanogenic Cu-ZnAg-Au massive sulfides; 3) Au associated with deformation zones, such as Corvet Est (Gauthier et al. 1997, Gauthier 2000, Goutier et al. 2002). Guyer Group banded iron formations comprise oxide and silicate facies Algoma-type with discontinuous decimeterscale layers of disseminated to semi-massive pyrrhotite and pyrite (Gross 1996). A few showings of banded iron formation have low base (Cu ± Pb ± Ni) and precious (Ag ± Au) metal contents (MacFarlane 1973, Osborne 1995, De Chavigny 1998). Stratabound Au associated with banded iron formations such as the Poste LeMoyne Extension and Orfée showings of the Poste LeMoyne deposit are associated to a silicate-oxide facies banded iron formation with local sulfide facies lenses comprising pyrrhotite ± pyrite ± chalcopyrite ± arsenopyrite and visible gold (Fig. 2.2; Chénard 1999, Goutier et al. 2002). The best gold 12 values are obtained in lenses where sulfides are massive to semi-massive in thickened fold hinges, typical of gold deposits in banded iron formations (Kerswill 1996). Volcanogenic Cu-Zn-Ag-Au maSSIve sulfides are characterized by a semi-concordant sericite schist alteration zone, with accessory sillimanite, gamet and cordierite, which, combined with Na leaching, suggests volcanogenic hydrothermal systems. The sericite schist is strongly deformed where rocks were affected by an intense pre-metamorphic aluminous alteration. The sericite schist contains up to 10 % disseminated pyrite, and minor amounts of disseminated or vein chalcopyrite and sphalerite (L ' Heureux and Chénard 1999). Occurrences of volcanogenic massive sulfide rnineralization include the Lac Damn (Eckstrom 1960), and Sericite Schist showings in the Poste Lemoyne deposit area (L' Heureux and Chénard 1999). Au mineralization associated with deformation zones compnses deformed and folded quartz ± carbonate ± tourmaline veins with pyrite, chalcopyrite or pyrrhotite, ± arsenopyrite, or disseminated pyrite, pyrrhotite, chalcopyrite and arsenopyrite. The deformation zones are characterized by chlorite-ankerite ± muscovite alteration in greenschist or by muscovite-biotite alteration in amphibolite grade metamorphic rocks. Gold deposits associated with deformation zones are dominantly hosted by mafic volcanic rocks, although a few deposits are hosted by felsic volcaniclastic rocks or tonalite. The gold deposits associated with deformation zones in Guyer Group rocks show many similarities with orogenic gold veins (Groves et al. 1998). The Laguiche group paragneiss is intruded by migmatite and white pegmatitic dykes with microcline-quartz ± plagioclase-biotite-tourmaline-muscovite ~ gamet ± beryl. Uranium mineralization occurs in intrusions or at the contact with paragneiss but present a marginal economic interest due to low grades, erratic occurrence, and sharp U/Th variations. The UTh relation suggests a magmatic origin (Fouques 1977). 13 2.4 Corvet Est deposit geology The Corvet Est deposit geology comprises the tonalitic basement of the Poste-Lemoyne pluton to the northeast, the Guyer Group volcano-sedimentary sequence and Laguiche Group paragneisses in the south (Fig. 2.3). Regional bedding and foliation strike westnorth-west (Fig. 2.3). 2.4.1 Poste-Lemoyne pluton The Poste-Lemoyne pluton is mostly fine grained tonalite but also compnses granite, granodiorite, monzonite and quartz monzonite. Tonalite contains 5 to 15 % biotite in a feldspar-quartz matrix. Granite contains 20 to 25 % quartz, 70 to 75 % plagioclase, and 2 to 5 % potassic feldspar. Basement rocks foliation and contact with the volcano-sedimentary sequence trends northwest-southeast (Fig. 2.3). 2.4.2 Guyer Group volcano-sedimentary belt Guyer Group volcanic rocks are dominated by basaltic amphibolite. Amphibolite is dark gray to black and composed of 60 % foliated, fine grained, black amphibole, 30 % granoblastic plagioclase, < 8 % quartz, < 5 % purple to pink red, milimeter- to centimeterscale gamet, < 3 % biotite, < 3 % chlorite, < 2 % sulfides (pyrite, pyrrhotite) and < 1 % oxides (ilmenite, magnetite) . Primary volcanic structures such as pillow basalts and flow breccias are rarely preserved, as basaltic amphibolite is generally strongly deformed. The amphibolite contains up to 20 % leucosomes composed of plagioclase, quartz, amphibole and biotite, with a weak to moderate foliation. Andesitic flows and clastic rocks are fine-grained with about 70 % plagioclase and 30 % amphibole, with local porphyritic texture with up to 5 % 1-3 mm feldspar phenocrysts (Fig. 14 2.3). Biotite, muscovite and gamet occur from traces to 5 %. Andesites have a strong to moderate foliation. The andesitic clastic rocks range from ash tuff to pyroclastic breccia, have a polymict composition with microgranular, intermediate to felsic fragments containing feldspar phenocrysts. Ash tuff and lapiIlistone show compositional banding. The andesite contaiA.s up to 15 % leucosome composed of plagioclase, quartz, amphibole and biotite, with a medium foliation. Dacite forms a lenticular body structurally between basaIts or between andesite and basaIt (Fig. 2.3). Dacite is fine-grained to aphanitic, and composed of 60 % plagioclase, 15 % quartz, 10-20 % biotite and amphibole, and up to 5 % gamet, in a felsic matrix. Dacite is strongly deformed to mylonitized, with rare moderate deformation occurences. The dacite contains up to 25 % leucosomes containing plagioclase, quartz, biotite and accessory calcite, with a weak to medium foliation. Guyer Group quartz-feldspar-biotite paragnelsses are fine grained, have equigranular granoblastic textures, are weIl foliated and contain less than 5 % leucosome. Biotite content in the feldspar-quartz matrix ranges from 5 to 30 %, and pink to purple millimeter- to centimeter-scale gamet form up to 5 % of the rock. Gabbro sills intrude the basaItic amphibolite (Fig. 2.3). The gabbro is medium-grained, weakly deformed, and composed of amphibole and plagioclase. Quartz-feldspar porphyry (QFP) dykes intrude amphibolite, andesite and paragneiss. The QFP dykes are less than 1 m thick, weakly foliated and fine- to medium-grained with traces of pyrite and arsenopyrite. Pegmatite dykes occur commonly in the Laguiche Group paragneiss, reaching up to 120 m in thickness (Fig. 2.3; Perry 2007) and locally in the Guyer Group volcanosedimentary sequence. Pegmatite dykes are medium- to coarse-grained, with up to 65 % idiomorphic feldspar crystals, 25-30 % quartz, muscovite, tourmaline, and accessory gamet, biotite and apatite. Pegmatite dykes cut the foliation and are undeformed. 15 2.4.3 Laguiche Group paragneiss Laguiche Group paragneiss is fine- to medium-grained, equigranular and foliated, with saccharoidal, granoblastic and lepidoblastic textures (Fig. 2.3). It contains 5 to 30 % biotite in a feldspar-quartz matrix, and locally contains up to 5 % millimeter- to centimeter-scale pink to purple euhedral gamet. Foliation is weIl developed, emphasized by biotite. The paragneiss contains up to 25 % weakly foliated quartz-feldspar-biotite leucosomes. _ CJ '"V'V Tonalite Dacite Fault _ _ • Pegmatite Basaltic amphibolite DDH (with number) _ _ - Gabbro CJ Para gneiss ~ Foliation Andesite Trench (with number) o 200 --=~ meters Figure 2.3: Detailed geology of the Corvet Est gold deposit, with location of the Marco and the Contact zones, driIlholes and trenches with number referred to in text (modified from Perry 2006) 16 2.4.4 Mineralization The Corvet Est deposit comprises 2 mineralized zones: 1) The Contact zone is located at or near the faulted contact between Laguiche Group paragneiss and Guyer Group volcanosedimentary rocks. Disseminated, microscopic gold mineralization occurs in shear zone and QFP dykes, whereas coarse gold mineralization occurs in late quartz-calcite veins. Mineralized rocks contain pyrite, pyrrhotite, arsenopyrite, and titanite. 2) The Marco zone is located near the structural base of the lenticular dacite unit of the Guyer Group and is continuous along strike for 1.3 km. The Contact zone and the Marco zone follow structural grain, which is W -NW - E-SE (Fig. 2.3). Although detailed mapping of the Contact zone has been carried out, this paper contribution presents data only for the Marco zone. The Marco zone is dominated by disseminated gold and sulfides with minor quartzcarbonate veins in deformed dacite. The Marco zone is up to 39.6 m wide and is located at the highly deformed structural base of a lenticular dacite unit (Fig. 2.4a), although gold can be found across the width of the dacite (Fig. 2.4). Disseminated mineralization is characterized by interstitial gold or gold as inclusions in silicate and sulfide minerais forming the host rocks. Mineralization of the Marco zone comprises pyrite, arsenopyrite, pyrrhotite, traces of chalcopyrite and microscopic gold in dacite and amphibolite, or in QFP dykes. Vein mineralization is characterized by free gold and gold inclusions in deformed quartz veins with rare calcite. The Marco zone comprises numerous mineralized sections: trench 9 graded 7.8 ppm/3 m, DDH 18 graded 4.5 ppm/15 m, and DDH 44 graded 10.1 ppm/5.2 m (Fig. 2.3), with gold grades up to 23 ppm over 1 m (DDH 2; Fig. 2.4b). Gold is located in dacite and in rare andesite (DDH 2; Fig. 2.4b) and amphibolitic basait (DDH 23; Fig. 2.4c) layers in the dacite. Gold is mostly correlated to a high index of deformation (>70; Figs. 2.4a, 2.4b) but not strictly (Fig. 2.4c). Deformation index is based on a scale ranging from 0 to 100, 0 being undeformed and 100 being ultra-mylonitized. Gold is associated with pyrite and arsenopyrite, and locally with gamet and titanite (Figs. 2.4a, 2.4b, 2.4c). 17 c::J Dacite _ _ Basaltic amphibolite Andesite E::J QFP Sam pie • 31 Figure 2.4: Simplified trench or drillhole logs from the Marco zone, with lithology, sample location, gold grade, intensity of deformation and gamet, pyrite, arsenopyrite and titanite approximative volume percent. a) Trench 5. b) DDH 2. c) DDH 23. 18 Figure 2.4: (continued)*The gold grades over 5 ppm exceed the chart scale but are indicated by numbers. Apy arsenopyrite; De! deformation; Gt gamet; Litho lithology; Py pyrite; Ttn titanite Mineralization is hosted by sheared dacite, andesite and basaltic amphibolite and in rare QFP dykes. Trench 18, in the north-western part of the zone, is a rare location where dacite primary textures are preserved, showing stretched layers of ash tuff to pyroclastic breccia containing biotitized amphibolite blocks and/or bombs in a felsic matrix (Figure 2.5a). Meter-scale layers of ash tuff to pyroclastic breccia are cut by QFP dykes. Gold mineralization in trench 18 occurs within a meter-wide foliated QFP dyke containing pyrite, pyrrhotite and arsenopyrite. In trenches # 5, and # 9 in the central part of the map (Fig. 2.3), the tuff unit is thinner (2: 6 m) and deformation is more intense (Fig. 2.5b). Mineralization near the southern contact with amphibolite is in rusty and mylonitized dacite. The disseminated mineralization comprises up to 4 % pyrite, 7 % arsenopyrite, 3 % pyrrhotite and traces of chalcopyrite. Centimeter-scale discontinuous tourmaline layers are common at the dacite - basaltic amphibolite contact (Fig. 2.5c). Rare quartz-carbonate veins are up to 3 cm wide, contain pyrhotite, pyrite, arsenopyrite and titanite, and are foliated. Gold mineralization is generally directly correlated with the index of deformation and the occurence of pyrite and arsenopyrite (Fig. 2.4). 19 Figure 2.5: a) Typical deformed dacite with heterogeneous and stretched blocks of andesite in a felsic matrix (Trench 18, Fig. 2.4). b) Highly mineralized and deformed rusty dacite (Trench 5, Fig. 2.4). c) Centimeter-scale, discontinuous, tourmaline layers at the daciteamphibolite contact (Trench 5, Fig. 2.4) 20 2.5 Mineralogy and paragenetic sequence The dacite consists of 60 % plagioclase, 10 - 15 % quartz, 10 - 20 % biotite and amphibole, < 5 % K-feldspar, < 5 % gamet, < 5 % sericite, < 2 % chlorite, < 1 % epidote, < 1 % calcite, < 4 % pyrite, < 3 % pyrrhotite, < 7 % arsenopyrite, < 1% oxides (ilmenite, magnetite), < 1 % titanite and traces of chalcopyrite, sphalerite and stibnite. Amphibolite consists of 60 % amphibole, 30 % plagioclase, < 8 % quartz, < 5 % gamet, < 3 % biotite, < 3 % chlorite, < 2 % sulfides (pyrite, pyrrhotite) and < 1 % oxides (ilmenite, magnetite). The generalized paragenetic sequence is divided into three stages (Fig. 2.6): (1) metamorphic reequilibration of sulfides, disseminated gold, oxides and silicates, (2) quartzfeldspar-gold-sulfide and garnet post-metamorphic vein surrounded by K-feldspar, sericite and chlorite alteration, (3) late pyrite-quartz-calcite-epidote-K-feldspar vein and breccia vein with K-feldspar, calcite and epidote alteration. Stage 1 Stage 2 Stage 3 garnet pyrite -< arsenopyrite -< >- - chalcopyrite -- >- ~ ~ ~ pyrrhotlte ~ magnetlte i1menite titanite gold ~ - ~ ~ quartz ~ k-feldspar -< plagioclase -< >- ,- -- -> ~ <=> sericite biotite hornblende chlorite tourmaline - epidote calcite Figure 2.6: Paragenetic sequence for the Corvet Est deposit ~ ~ ~ 21 Stage 1 consists of subhedral to cataclased poeciloblastic gamet (0.5 - 10 mm; Fig. 2.7a) with silicate, sulfide, oxide, calcite and gold inclusions, euhedral to subhedral pyrite (0.0013 mm; Figs. 2.7b, 2.7c), euhedral to subhedral arsenopyrite fractured (Figs. 2.7b , 2.7c), anhedral chalcopyrite 2.7c), euhedral to subhedral magnetite « « 3 mm) locally twinned and 20 !lm) and pyrrhotite « 1 mm; Fig. « 0.5 mm), locally displaying coronitic textures around pyrite (Fig. 2.7d), euhedral to subhedral ilmenite « 0.1 mm; Fig. 2.7d) and titanite « 0.2 mm; Fig. 2.7b) , locally displaying fracturation, disseminated in dacite and amphibolite, interstitial to groundmass granoblastic quartz (0.01 - 0.5 mm; Fig. 2.7e), polysynthetic twinned groundmass granoblastic plagioclase (0.01 - 0.5 mm; Fig. 2.7e) and rare granoblastic K-feldspar (0.01 - 0.5 mm; Fig. 2.7e), subhedral nematoblastic to lepidoblastic biotite (0.01 - 1 mm; Figs. 2.7a, 2.7d), and euhedral to anhedral amphibole (0.05 - 0.5 mm; Figs. 2.7a, 2.7f). Anhedral to subhedral chlorite (0.05 - 0.5 mm; Fig. 2.7b) and euhedral tourmaline (0.05 - 0.3 mm; Figs. 2.7b, 2.7f) overgrow amphibole, pyrite, quartz and plagioclase. 22 Qtz ., ., : IIm- ~ ! '1 ....:.: '. 1 ,< Figure 2.7: Stage 1 a) Subhedral cataclased poeciloblastic gamet, subhedral amphibole, subhedral nematoblastic to lepidoblastic biotite and subhedral granoblastic quartz (plane polarized light). b) Euhedral pyrite, arsenopyrite and tourmaline overprintirig subhedral sericitized plagioclase, with subhedral titanite, subhedral deformed chlorite and quartz (cross-polarized light). c) Euhedral arsenopyrite interstitial to euhedral pyrite and anhedral pyrrhotite (reflected plane polarized light). d) Xenomorphic pyrite with coronitic subhedral magnetite, granoblastic quartz, euhedral ilmenite and anhedral biotite (reflected plane 23 Figure 2.7: (continued) polarized light). e) Granoblastic euhedral to subhedral quartz, Kfeldspar, plagioclase and biotite (cross-polarized light). f) Euhedral tourmaline overprinting . euhedral pyrite, anhedral amphibole and subhedral quartz (plane polarized light). Apy arsenopyrite; Am amphibole; Bt biotite; ChI chlorite; Fk potassic feldspar; Grt gamet; Ilm ilmenite; Mag magnetite; PI plagioclase; Po pyrrhotite; Py pyrite; Qtz quartz; Tl tourmaline; Ttn titanite Stage 2 · consists of polygonized anhedral quartz - K-feldspar - plagioclase veins with accessory euhedral arsenopyrite, subhedral calcite, anhedral titanite, anhedral interstitial « 300 flm; Fig. 2.8a), euhedral to subhedral pyrite (0.01 - 3 mm) tourmaline (0.05 - 0.3 mm) and gamet « 1 cm) and anhedral pyrrhotite (0.01 . . :. 1 mm). Alteration consists of euhedral to xenomorphic sericite « 200 flm) replacing plagioclase (Figs. 2.8b, gold grains 2.8c) and biotite along cleavage (Fig. 2.8d), xenomorphic chlorite replacing sericite and biotite along fractures (Fig. 2.8d), and subhedral to anhedral K-feldspar replacing quartz, plagioclase and biotite, crosscutting the foliation (Figs. 2.8e, 2.8f). Sericite alteration is controlled by microfracture permeability (Fig. 2.8c). The chlorite micro fracture cuts stage 2 sericite lenses, causing medium-grained chloritization of stage 1 biotite (Fig. 2.8d). 24 Figure 2.8: Stage 2 a) Photomicrograph of gold interstitial to anhedral titanite and polygonized quartz, with subhedral arsenopyrite and anhedral calcite (reflected plane 25 Figure 2.8: (continued) polarized light). b) Photomicrograph of deformed gold-bearing quartz vein with sericitization of plagioclase-rich host rock (cross-polarized light) with location of gold shown in a) indicated by red arrow. c) Photomicrograph of a quartz veinlet (white arrow) surrounded by fine-grained seri cite alteration (outlined by red dotted lines) of plagioclase (plane polarized light). d) Photomicrograph of biotite replaced by sericite, then by chlorite (plane polarized light). e) Photograph of post-metamorphic deformed quartz vein with microcline alteration overprinting the SI foliation. f) Photomicrograph of postmetamorphic deformed quartz vein and microcline alteration crosscutting the SI foliation shown in e) (plane polarized light). Apy arsenopyrite; Bt biotite; Cc calcite; Chi chlorite; Mc microcline; PI plagioclase; Qtz quartz; SI foliation; Ser sericite; Ttn titanite Stage 3 consists ofxenomorphic pyrite « 1 mm; Fig. 2.9a) and euhedral calcite « 0.5 mm; Fig. 2.9b), anhedral to subhedral epidote 2.lOc) and K-feldspar « « 0.3 mm; Figs. 2.9b, 2.9c) quartz « 1 mm; Fig. 1 mm; Fig. 2.1 Ob) undeformed vein and breccia crosscutting stage 2 veins, with anhedral epidote, K-feldspar (Fig. 2.9c) and subhedral poeciloblastic calcite alteration (Figs. 2.9c, 2.9d) of dacite or amphibolite host rocks. Calcite contains quartz, plagioclase and biotite inclusions. - ------ - -- ~~~~~~~ - - -- - - -- - -- - - -- 26 Figure 2.9: Stage 3 a) Photomicrograph of undeformed pyrite breccia vein (reflected plane polarized light). b) Photomicrograph of an undeformed calcite - K-feldspar - epidote vein with epidote and K-feldspar alteration of the ho st rock (plane polarized light). c) Photograph of an undeformed epidote - quartz - calcite breccia with K-feldspar - epidotecalcite alteration of the host rock. d) Photomicrograph of poeciloblastic calcite with quartz, plagioclase and biotite inclusions (plane polarized light). Bt biotite; Cc calcite; Ep epidote; Fk potassic feldspar; Pl plagioclase; Py pyrite; Qtz quartz -- - - - - - - - - -- -- - - -- -- - - - - - - - - - - - - 27 2.5.1 Gold textures Gold forms anhedral grains « 300 !-lm) disseminated in dacite and amphibolite and in veins. Gold occurs in groundmass with quartz, K-feldspar, plagioclase, epidote, pyrite, arsenopyrite, pyrrhotite, chalcopyrite and tourmaline, whereas gold in veins or near selvages is associated with calcite, titanite (Fig. 2.8a), pyrite, arsenopyrite, pyrrhotite, gamet and epidote. Gold forms inclusions in pyrite (Fig. 2.10a), arsenopyrite (Fig. 2.1 Ob), pyrrhotite (Fig . . 2.1 Oc), quartz, feldspars (Fig. 2.1 Od), epidote (Figs. 2.1 Od, 2.1 Oe) biotite, (Fig. 2.1 Oe) and gamet (Fig. 2.10f). It is also interstitial to sulfides and silicates (Figs. 2.10a, 2.10c, 2.10d, 2.10e, 2.10f). In rare occurrences, go Id fills garnet fractures with pyrrhotite (Fig. 2.10f) or forms coronitic texture around stibnite. 28 Figure 2.10: Photomicrographs of gold textures. a) Gold included in pyrite, interstitial to chalcopyrite and tourmaline (reflected plane polarized light). b) Gold included in euhedral arsenopyrite (reflected plane polarized light). c) Gold inclusions at the edge of pyrrhotite (reflected plane polarized light). d) Gold inclusions in quartz, sericitized plagioclase, Kfeldspar and epidote, and gold interstitial to arsenopyrite and silicates (cross-polarized light) The inset shows the gold in reflected plane polarized light. e) Gold inclusions in epidote and biotite, and gold interstitial to sulfides and silicates (plane polarized light) 29 Figure 2.10: (continued) whereas the inset shows the same area in cross-polarized light. f) Gold, arsenopyrite and pyrrhotite inclusions in gamet, gold interstitial to gamet, quartz and pyrrhotite, and filling gamet fractures (reflected plane polarized light). Apy arsenopyrite; Bt biotite; Cpy chalcopyrite; Ep epidote; Grt garnet; Py pyrite; Po pyrrhotite; Qtz quartz; Pl plagioclase; Tl tourmaline 2.6 Analytical methods Forty-eight samples (13 basait, 28 dacite, 3 dacite leucosome, 2 porphyritic andesite and 2 quartz-feldspar porphyry) were selected from trenches and diamond drill holes from the Marco zone. Whole rock major elements and Cu, Zn, Sr, Zr, Y, Nb concentrations were determined by inductively coupled plasma emission spectrometry (lCP - ES) and by inductively coupled plasma mass spectrometry (ICP - MS) following lithium metaborate/tetraborate fusion and dilute nitric acid digestion, at ACME Laboratories, Vancouver, British-Columbia, Canada. Ag, As, Au, Ba, Br, Cd, Ce, Co, Cr, Cf, Eu, Fe, Hf, Hg, Ir, K, La, Lu, Na, Nd, Ni, Rb, Sb, Sc, Se, Sm, Ta, Tb, Th, U, W and Yb were measured by instrumental neutron activation analysis (INAA) at Université Laval (Constantin, in press). Analysis of SGR - 1 geochemical reference material shows that the analyses are within analytical uncertainty compared to recommended values. Chlorite, amphibole, calcite, feldspar, gamet, biotite, sericite, tourmaline, gold, pyrite, chalcopyrite, pyrrhotite and arsenopyrite mineraI composition were determined using the 5 WDS CAMECA SX - 100 electron microprobe at Université Laval. Analytical conditions for gold were 15 kV and 40 nA, with counting times of 20 s on peak and 10 s on background. Analytical conditions for sulfides were 15 kV and 20 nA, with counting times of 20 s on peak and lOs on background. Analytical conditions for the other minerais were 15 kV and 20 nA, with counting times of 10 to 30 s on peak and 0 to 10 s on background. 30 Sulfur isotope analyses of pure concentrates of pyrite and arsenopyrite hand picked under a binocular were performed by the G.G. Hatch Isotope Laboratory, University of Ottawa, Canada. The sulfur isotope composition was determined by continuous flow isotope ratio mass spectrometry (CF - IRMS). S02 was produced by flash combustion with vanadium pentoxide at l ,800°C in an elemental analyzer, followed by gas chromatography before injection in a Finnigan MAT Delta + mass spectrometer. Quartz, feldspar, garnet, sericite tourmaline and biotite were reacted with BrF 5 according to the method of Clayton and Mayeda (1963) at the Stable Isotope Laboratory, Université Laval. For each analysis, about 15 mg of mineraI concentrates were hand picked under a binocular microscope. The evolved CO2 was analyzed by IRMS at the G.G. Hatch Laboratory, University of Ottawa. Isotope ratios are reported in 8- notation relative to V -SMOW (oxygen) and V -CDT (sul fur) with a precision of ± 0.2 %0. Re-Os isotope analysis were obtained on arsenopyrite mineraI concentrates, (approximately 1 g) prepared by a combination of gravitational and electro-magnetic methods, followed by a selection of grains under a binocular microscope. Re-Os analyses were performed at the Radiogenic Isotope Facility, University of Alberta, Canada. Sample fractions (up to 400 mg) were precisely weighed with a known amount of either a mixed 185Re + 1900S spike or a "mixed double spike" of 185Re' + 1880s_1900s, depending on the amount of common Os present, and were digested by the Carius tube method (Shirey and Walker 1995), using a combination of 6 ml of 16 N nitric acid and 2 ml of ION hydrochloric acid.Re and Os were . separated and purified using a combination of solvent extraction, microdistillation, and chromatographic techniques, following the procedure described by Morelli et al. (2005). The isotopic composition of Re and Os was determined using negative thermal ion mass spectrometry (NTIMS; Creaser et al. 1991; Volkening et al. 1991) on a Micromass Sector 54 mass spectrometer, using Faraday collectors or ETP collectors in a pulse-counting mode. Procedural blanks were monitored throughout the analysis period and aIl data are . corrected for Re and Os blanks of 2.9 ± l.2 pg, and 0.32 ± 0.16 pg, respectively, with a 1870s/1880s ratio of 0.24 ± 0.10. 31 2.7 ResuUs 2.7.1 Mineral compositions In aIl 3 stages, pyrite has low As (0.01 - 0.48 wt %) and Co contents (0 - 0.23 wt%; Table 2.1a). Gold has high Au/(Ag+Au) ratio (0.78 - 0.99 at %; Table 2.1b, Fig. 2.11). Stage 1 groundmass plagioclase composition ranges from Ab 54 to Ab 76, with an average andesine composition (Ab62 ; Table 2.1c). Rare stage 2 vein plagioclase range from pure albite (Ab 100; sample # 55050) to pure anorthite (Ab o; sample # 31596). One plagioclase inclusion in gamet has oligoclase composition (Ab ss ; Table 2.lc). Gamet composition, computed using the method of M. Gaspar (pers. comm. 2005), ranges from almandine to grossular with a significant spessartine cümponent (AI°.4°GR029Spo.27pyo.04 to Al062GR025Spo09AN003pyo.ol ; Table 2.1d), except for one sample (31571) which has an almandine-spessartine composition (SP°.43 Alo.29GRoISpyOI0). Biotite composition, calculated according to Sack and Ghiorso (1989), lies in between the annite and phlogopite end-members (ANo.ssPHo.12 to AN°.35PHo.65 ; Table 2.le) . . 32 0.91 ± 0.06 • 12 • 1 .---- 14 · ~ U 10 C r--- Q) :::J 0- 8 · 6 · 4 · 2 · a> L- u.. o ~ 0.70 0.74 .....- n0.86 . 0.90 . . Au/(Ag+Au) (AtO/o) . 0.78 0.82 0.94 . 0.98 Figure 2.11: Au/(Ag+Au) ratios for gold grains from the Corvet Est deposit. The average with ± 1s standard deviation is shown by arrows The temperature of metamorphic equilibrium of rocks from the Marco zone is estimated using the gamet-biotite Fe - Mg exchange. The gamet - biotite thermobarometer relies on the mixing properties of gamets (Berman 1990) and the equation of state of CO2 at high pressure and temperature (Mader and Berman 1991). Thermobarometry is evaluated with the TWEEQU software package (Berman 2006) using multi-equilibrium ca1culations on gamet - biotite pairs (Tables 2.ld, 2.le) and yield peak temperatures ranging from 585°C to 604°C (sample # 55304), and from 615°C to 633°C (sample # 55039) at pressures ranging from 2 to 6 Kbars (Berman 1991). 33 Table 2.1 Representative microprobe composition of mineraIs from the Corvet Est deposit, Québec, Canada A) Pyrite Sample no. 31571 31596 55016 55026 55123 55131 55305 55308 55313 S (wt%) Pb Au Fe Co Ni Zn Cu As Total 52.33 0.37 0.01 45.90 0.04 0.01 0.05 0.02 0.04 98.78 52.35 0.36 0.02 46.04 0.00 0.11 0.01 0.03 0.21 99.14 52.05 0.41 0.03 46.69 0.00 0.00 0.06 0.49 0.01 99.73 50.72 0.36 0.00 45.97 0.08 0.00 0.06 0.07 0.01 . 97.27 51.63 0.36 0.01 45.66 0.00 0.01 0.02 0.06 0.02 97.77 51.26 0.41 0.00 45.98 0.04 0.01 0.04 0.01 0.45 98.20 52.73 0.35 0.02 46.40 0.00 0.00 0.00 0.00 0.24 99.73 52.18 0.39 0.00 46.17 0.19 0.00 0.07 0.00 0.48 99.47 52.01 0.37 0.03 46.15 0.23 0.04 0.10 0.07 0.33 99.32 B) Gold Samp1e no. 31596 55016 55026 55039 55123 55131 55308 55313 Sb (at%) Ag Au Te Bi Cu Hg Ag/Au 0.04 17.61 82.21 0.01 BDL 0.13 NA 0.22 BDL 22.25 77.51 0.01 BDL 0.23 NA 0.29 0.07 4.61 95.11 0.01 BDL 0.19 NA 0.05 0.05 3.27 96.64 0.01 0.04 0.00 0.00 0.03 0.07 2.81 96.49 0.01 BDL 0.17 0.46 0.03 0.02 4.42 95.53 BDL BDL 0.02 NA 0.05 0.04 5.02 93.79 0.02 BDL 0.12 1.02 0.05 0.04 13 .09 86.35 0.03 BDL 0.16 0.33 0.16 NA Not analysed, BDL Below detection limit 34 Table 2.1 (continued) C) Plagioclase Location Sample no. 55050 55026 55131 55305 55123 31571 55050 31596 55305 55305 58.03 0.03 26.47 0.00 7.83 0.11 0.06 0.00 7.11 0.10 99.73 62 56.26 0.01 26.43 0.00 9.35 0.04 0.06 0.00 6.08 0.09 98.31 54 61.63 0.01 23.61 0.01 5.12 0.17 0.08 0.03 8.72 0.13 99.49 76 57.53 0.02 25.57 0.00 8.26 0.09 0.06 0.01 7.26 0.34 99.13 62 58.37 0.03 26.39 0.01 7.67 0.02 0.06 0.00 7.17 0.20 99.92 63 69. 10 0.01 20.15 0.00 0.05 0.04 0.04 0.07 Il.46 0.27 101.20 100 42.95 0.15 22.97 0.00 26.45 1.04 0.01 0.05 0.02 0.00 93.62 0 67.47 0.00 20.00 0.02 0.42 0.00 0.05 0.00 11.15 0.04 99.14 98 65.11 0.04 22.21 0.01 2.52 0.88 0.02 0.01 10.05 0.16 101.00 88 SiOz TiOz A}z03 MgO CaO FeO* SrO BaO Na10 K10 Total %Ab *Total Fe as FeO 56.45 0.03 25.55 0.00 9.23 0.03 0.06 0.00 6.04 0.16 97.54 54 in groundmass mvem in gamet ~ 35 Table 2.1 (continued) D) Gamet Sample 55026 31571 55313 55039 55304 55305 55031 Si02 Ti02 Zr02 Ah0 3 Cr203 Fe203* MgO CaO MnO FeO Na20 Total Spessartine Pyrope Almandine Grossular Andradite 35.31 0.07 0.02 20.13 0.00 0.84 0.42 13.49 3.64 23.56 0.02 97.51 0.17 0.03 1.01 0.63 0.16 37.27 0.07 0.04 20.65 0.00 0.00 2.29 5.65 17.79 Il.97 0.02 95.75 0.84 0.19 0.55 0.34 0.00 37.32 0.02 0.00 20.76 0.00 0.04 1.74 8.20 9.66 19.92 0.01 97.68 0.44 0.14 0.91 0.48 0.00 36.48 0.11 0.01 20.79 0.00 0.00 1.05 9.65 11.50 17.45 0.02 . 97.06 0.53 0.09 0.80 0.57 0.00 36.32 0.12 0.01 20.63 0.01 0.18 0.43 9.36 3.86 27.89 0.02 98.82 0.18 0.03 1.24 0.49 0.06 36.47 0.06 0.02 20.34 0.01 0.64 0.38 8.79 5.98 26.23 0.02 98.93 0.28 0.03 1.18 0.45 0.06 36.77 0.13 0.02 20.48 0.00 0.52 0.67 1l.76 8.35 19.62 0.02 98.32 0.38 0.05 0.88 0.63 0.05 *Total Fe as Fe203 36 Table 2.1 (continued) E) Biotite Sample no. 31571 55026 55031 55039 55050 55123 55131 55304 55305 Si0 2 Ti0 2 Ah 0 3 Cr20 3 MgO CaO MnO FeO* NiO Na20 K 20 H20 F Cl Total Annite Phlogopite 30.19 3.32 17.13 BDL 2.44 0.65 0.22 32.55 BDL 0.02 7.34 3.54 0.13 BDL 97.53 0.88 0.12 35.93 1.57 17.61 0.01 9.76 0.07 0.43 20.26 0.01 0.11 8.76 3.57 0.69 0.02 98.79 0.54 0.46 26.86 7.95 15.56 0.06 5.92 7.00 0.39 29.62 0.01 0.02 0.17 3.56 0.23 0.01 97.36 0.74 0.26 35.29 1.99 16.87 0.01 12.48 0.06 0.55 17.07 BDL 0.08 8.62 3.65 0.48 0.01 97.14 0.43 0.57 27.94 1.58 18.07 BDL 4.02 0.29 0.42 35 .27 BDL 0.11 2.84 3.45 0.08 0.02 94.10 0.83 0.17 37.5 1 3.20 16.48 0.04 13.84 0.11 0.98 13.41 BDL 0.09 8.65 3.75 0.57 BDL 98.62 0.35 0.65 * Total Fe as FeO BDL Below detection limit 31.36 2.59 16.00 0.01 4.65 1.17 0.33 30.90 0.01 0.04 5.91 3.53 0.21 0.01 96.72 0.79 0.21 35.95 1.70 17.68 BDL 8.28 0.20 0.38 21.42 0.03 0.09 8.54 3.81 0.1 2 BDL 98.20 0.59 0.41 38.90 1.38 18.58 0.02 1.98 5.39 0.38 22 .57 BDL 0.66 5.49 3.88 0.15 0.01 99.38 0.86 0,14 37 2.7.2 Major and trace elements Iithogeochemistry The major and trace elements lithogeochemical data is reported in Table 2.2. The dacitic tuff has a rhyolite/dacite composition in the Nb/Y vs Zr/Ti diagram and overlaps the andesite/basalt field boundary (Fig. 2.12a; Winchester and Floyd 1977; Pearce 1996). The basaItic amphibolite, including plagioclase-phyric andesite has an andesite/basaIt composition whereas quartz-feldspar porphyries (QFP) plot in the field of trachy-andesite (Fig. 2.12a). Leucosome in dacite has a composition that plots in the rhyolite/dacite and andesite/basalt fields (Fig. 2.12a). The dacite and amphibolite have a calc-alkaline to transitional affinity (Fig. 2.12b; Barrett and MacLean 1994). Dacite, amphibolite and QFP plot in the arc-basaIt field (Fig. 2.12e; Wood 1980), and in the field of plate margin basaIt (Fig. 2.12d; Pearee and Gale 1977). 38 A) B) 10 Ê RhyolitelDacite c. .e, 50 >- t N 150 200 250 300 Zr (ppm) .01 0) NblY 8~~--~--~------~ Hf/3 C) 6 A= N-MORB B = E-MORB ~ N C = OIB (Rift) + 4 Plate-margin basait o =Arc basait Intra-plate basait 2 "" oL------------A----------~ D o Ta Th Dacite .Â. Dacite leucosome + 500 1000 Ti/Y Basaltic amphibolite * Porphyric andesite • QFP Figure 2.12: Whole rock geochemistry from the Corvet Est deposit. a) Winchester and Floyd (1977) Zr/Ti vs Nb/Y diagram with field boundaries revised by Pearce (1996). b) Magmatic affinity diagram for Corvet Est igneous rocks using the y vs Zr diagram of Barrett and MacLean (1994). c) Geodynamic environment of Corvet Est igneous rocks in the Th vs Hf/3 vs Ta diagram (Wood 1980). d) Geodynamic environment of Corvet Est igneous rocks in the Zr/Y vs Ti/Y diagram (Pearce and Gale 1977) Dacite and amphibolite REE (Fig. 2.13a; Palme and O'Neill 2004) show a typical volcanic arc rock pattern with an average La/Lu of 101 for amphibolite and 83 for dacite. QFP have fractionated patterns and show a stronger depletion in Y, Yb and Lu than dacite and amphibolite. Leucosomes have HREE-enriched patterns whereas QFP have HREE-depleted patterns. BasaIt and dacite have similar La/Lu ratios and enrichment in REEs. Trace- --~ -~---------- 39 element spidergram (Fig. 2.13b; Palme and O'Neill 2004) also shows a typical volcanic arc pattern for alliithologies, with depletions in Nb, Ta and Ti. A) 100 (1) ;:; C CO E (1) .> 10 :t::: E ·C . - Cl. (1) 1 Cl. E CO Cf) .1 La ho Ce Dacite Nd ... Sm Dacite leucosome Eu + y Tb Basaltic amphibolite * Yb Porphyric andesite Lu [] QFP B)~ooo~~~~~~~~~~~~~~~~~ ;:; C CO E 100 (1) .> ~ E ·C - 10 Cl. (1) Cl. E 1 CO Cf) CsRbBa Th U Ta K La Ce Sr Nd Hf ZrSmEu TI Tb Y Yb Lu Figure 2.13: a) Rare earth element composition of rocks from the Corvet Est deposit normalized to primitive mande values from Palme and O'Neill (2004). b) Trace element Spidergram of Corvet Est deposit rocks normalized to primitive mande values from Palme and O'Neill (2004) 40 . Table 2.2 Major and trace element composition of rocks from the Corvet Est deposit, Québec, Canada 55314a 55314b 31556 31559 55301 55306a 55306b 55307 Sample po andesite . dacite dacite qfp dacite Lithology basait dacite dacite Is DDH2 DDH2 Trench 5 Trench 5 Trench 5 Trench 5 Location Trench 5 Trench 5 70.18 58.43 67.96 65.79 67.86 66.03 69.85 Si02 (wt%) 58.14 15.87 15.94 15.34 16.27 13.98 15.37 16.15 15.42 Ah 0 3 2.15 6.01 5.12 5.07 4.76 6.26 2.81 8.38 Fe203* 0.62 0.33 0.83 7.00 0.56 0.71 0.58 MgO 5.12 2. 58 2.85 2.55 6.48 3.50 3.64 3.41 5.50 CaO 4.66 4.23 5.02 2.92 3.92 4.39 4.34 3.17 Na20 1.84 2.06 2.02 3.79 1.32 1.85 1.59 1.85 K20 0.32 0.55 0.49 0.51 0.52 0.50 0.52 0.88 Ti0 2 0.12 0.30 0.15 0.15 0.16 0.24 0.16 0.15 P20S 0.07 ,0.08 0.03 0.02 0.10 0.09 0.12 0.08 MnO 99.31 98.32 99.30 97.83 98.98 98.53 98.82 99.59 Total 5 17 13 5 5 5 Cu (ppm) Il 5 52 53 47 37 51 61 39 Zn 61 151 252 491 595 213 211 152 228 Sr 128 249 258 242 120 250 157 253 Zr 34 33 15 19 5 31 141 22 Y 7 16 5 5 16 13 9 Nb Il <. 093 <.39 <.14 <.34 <. 18 0.1110 <. 10 <.11 Ag 3.49 1085.74 18.68 8.84 149.81 1201.77 5523.09 35.26 As 0.0018 10.3180 ,0.0029 0.0014 0.0033 0.0281 3.6020 0.0045 Au 818 537 399 1110 145 167 274 Ba 459 <.13 <.30 0.1830 0.3350 <.29 0.4000 0.1613 Br 0.2138 <2 .0 . <1.4 <1.1 <.77 < 1.2 <.87 1.2606 < 1.3 Cd 71.3 69.8 48.4 86.8 64.0 61.0 76.0 Ce 47.7 6.63 7.91 26.25 5.73 4.63 7.56 27.44 5.58 Co 7.3 14.0 20.3 472.4 10.2 11.5 15.3 181.0 Cr 2.2971 1.4355 1.8112 0.9394 1.4249 2.4936 2.1523 3.1981 Cs 1.5347 1.5448 1.6187 1.4033 0.8513 1.5762 2.0724 1.2699 Eu 6.5983 6.8908 3.5180 3.6063 6.7267 6.9114 6.9487 4.0495 Hf <.52 <.16 <. 29 <.21 <.19 <.30 <.20 <.27 Hg <.0004 <.0008 <.0006 <.0007 <.0012 <.0005 <.0005 <.0005 Ir 33 .3891 36.6710 . 43.5714 35.2063 25.1261 30.8057 31.5918 22.3400 La 0.1530 0.4950 0.4736 0.0207 0.1596 2.2460 0.4383 0.2989 Lu 33.3238 30.1494 38.5398 27.4094 21.7836 28.2596 21.6017 32.0802 Nd <2.0 <4.6 4.7 109.3 <6.0 <2.7 <7.9 94.7 Ni 83.0181 56.7646 64.3129 52.1876 47.1239 62.1002 57.2748 53.6698 Rb 4.5167 11.5373 6.3834 23.7943 4.6226 7.1515 1.5125 4.8595 Sb 11.02 10.78 2.89 15.11 22.23 8.29 10.75 19.50 Sc <.14 <.36 <.27 <.16 <. 19 <.57 <. 17 <. 13 Se 6.3835 5.9964 7.0763 3.4840 8.0165 5.3937 6.0551 4.6382 Sm 0.974 0.894 0.421 0.316 0.869 1.143 1.482 0.703 Ta 0.2232 0.5913 0.9517 0.8848 0.6482 0.8213 2.7400 0.6998 Tb . 3.2982 5.1297 7.0707 6.4353 6.0600 5.8139 7.0888 6.1191 Th 1.2194 1.9318 1.4744 1.3945 1.4171 0.7894 1.1719 6.0736 U 2.4234 28.3162 33.6915 4.1998 0.4619 9.8661 W 0.6517 0.5783 1.0214 0.2577 0.9790 3.1678 2.9675 Yb 1.9751 2.7150 15.4600 41 Table 2.2 (continued) Major and trace element composition of rocks from the Corvet Est deposit, Québec, Canada 31562 31564 31568 31571 31573 31575 31579 31581 31582 dacite dacite Is basait basalt basaIt dacite dacite basaIt dacite Is DDH 18 DDH 18 DDH 18 DDH 18 DDH 18 DDH 18 DDH 18 DDH2 DDH2 59.28 68.77 68.78 52.44 73.60 66.55 59.72 67.85 51 .66 14.22 14.82 12.66 15.40 15.97 14.30 14.29 12.99 16.44 11.25 3.87 4.92 9.94 7.50 5.02 3.07 5.47 8.06 6.20 4.58 0.72 0.52 5.06 0.83 0.77 2.46 1.68 2.77 7.24 3.28 0.86 7.80 0.48 5.60 3.35 7.11 2.29 4.66 2.59 3.26 1.73 1.22 3.87 1.42 1.79 1.55 1.44 1.82 8.06 2.17 3.13 2.36 1.09 4.51 0.87 0.41 0.46 0.54 0.83 0.70 0.44 0.43 0.72 0.10 0.13 0.14 0.22 0.15 0.13 0.18 0.29 0.13 0.28 0.04 0.36 0.23 0.11 0.06 0.03 0.07 0.13 96.01 97.44 98.13 98.29 96.61 97.52 97.84 97.99 97.46 12 5 5 29 15 6 87 27 5 62 149 85 45 67 29 79 52 64 196 143 119 62 199 171 175 121 142 229 106 220 260 182 110 227 173 138 24 27 57 68 24 20 18 20 30 14 17 13 8 12 7 13 5 6 0.9551 <. 19 <.20 <.25 0.2813 0.3100 0.9522 0.5960 23194.9 9418.97 8872.21 2121.91 3451.46 2695.85 308.72 12833.5 24.4070 8.1610 1.8163 0.0409 2.0612 3.5016 0.0088 0.0000 Il .6676 218 465 217 257 172 248 300 357 303 < 1.2 <.24 0.3354 0.6259 0.8932 0.6775 0.1503 <.28 <2.5 <1.5 <6.7 <1.8 < 1.1 < 1.7 <.95 2.2060 40.6 61.6 59 57.1 67.3 59.6 40.6 33.8 57.2 23 .32 37.31 6.77 6.00 27.29 7.05 4.96 12.59 33.57 20.6 21.4 412.1 24.4 615.8 153.5 13.4 53.7 191.9 1.3293 0.9167 1.8172 0.8618 1.6823 0.5594 0.8580 1.5003 1.2595 1.1983 1.5983 1.5172 0.9313 0.8602 1.3181 1.2285 4.7964 2.8582 5.7355 6.0662 5.9230 2.9856 4.4631 3.5931 <.30 <.41 <.19 <.20 <1.3 <.41 <.34 <.17 <.0008 <.0006 0.0015 0.0008 <. 0007 <.0013 <.0006 0.0013 <.0017 32.3579 26.5028 16.7478 30.5973 33.6273 28.4140 28.7106 20.4817 0.3237 2.1981 1.0595 0.3656 0.1928 0.4579 0.3060 0.3209 29.7044 22.5100 25.2381 28.1014 19.8108 28.9529 24.9365 17.6889 <1.9 5.0 63.9 <4.7 152.1 <3.9 81.9 101.0 21.0 50.4943 55.2275 84.1727 162.430 104.420 60.5356 64.0948 27.9328 110.809 6.6479 7.1862 5.6890 3.2548 22.4687 3.2931 8.4357 13.5543 7.5389 13.94 31.04 23 .29 9.43 10.56 7.28 24.18 19.78 Il.25 <.15 <.3 <.28 <.31 <.31 <.28 <.35 <.19 <. 50 5.1878 5.8588 5.4788 5.4373 4.2155 5.1510 5.0029 3.6035 0.936 0.402 0.826 1.042 0.677 0.389 0.446 0.666 0.5132 0.7904 0.6015 0.7922 l.2995 0.6555 0.47375 0.6705 3.4287 2.9096 2.1014 5.7063 4.1910 8.9206 7.6931 6.1728 1.4963 0.6353 1.7321 1.7434 1.7056 1.4924 1.6444 1.1264 13.3340 2.6168 19.2575 42.2186 <37 20.0834 11.3806 7.7646 2.0495 1.8391 1.1837 2.7403 2.0743 2.0676 11.9570 7.0672 42 Table 2.2 (continued) Major and trace element comEosition of rocks from the Corvet Est deEosit, Québec, Canada 31585 31589 31590 31594 55006 55012 55014 55017 55025 dacite dacite basaIt dacite basaIt dacite dacite basaIt dacite DDH 18 DDH 18 DDH 18 DDH23 DDH23 DDH23 DDH23 DDH23 DDH36 70.26 57.59 56.22 57.43 66.47 66.32 67.55 61.28 67.19 15.69 16.28 15 .34 13.01 14.72 14.90 15.40 15.48 15.03 4.82 4.37 8.74 6.13 7.12 5.16 5.37 6.57 4.55 0.93 0.29 5.53 8.09 4.48 1.46 0.91 3.69 0.31 2.37 3.95 5.73 6.41 5.94 3.41 1.77 4.10 3.28 4.84 3.16 4.08 3.03 2.54 4.37 2.93 4.42 3.23 2.34 0.48 1.83 2.50 1.14 1.62 5.58 1.51 3.61 0.43 0.83 0.64 0.77 0.46 0.45 0.66 0.47 0.46 . 0.13 0.24 0.16 0.14 0.14 0.15 0.16 0.13 0.15 0.12 0.14 0.10 0.10 0.08 0.07 0.08 0.07 0.06 97.32 98.44 97.84 97.84 98.06 98.08 98.29 98.05 98.32 5 5 65 32 5 20 Il 7 15 41 48 51 37 48 70 60 53 53 151 419 254 251 180 135 246 190 150 101 151 254 250 135 257 215 155 250 17 32 23 17 19 37 38 31 31 6 10 12 10 13 6 8 7 9 <. 11 <.13 <.18 <.22 <.11 <.088 <.36 <.11 <.13 6133.83 10.67 43.19 22.64 18.87 23.07 608.58 36.16 4.7486 3.8258 0.0055 0.0143 <0.0006 0.0030 0.0000 0.1356 0.0024 487 314 482 161 319 368 203 269 300 0.1099 0.2421 0.3825 0.2962 0.1985 0.6539 0.6451 0.6797 <1.4 <. 74 <2.9 <.53 <.52 <.70 <.65 <.46 37.6 71.6 40.7 72.2 41.1 72.0 67.7 70.0 66.0 6.74 5.90 22.81 4.70 5.42 28.47 6.39 22.24 6.10 10.7 97.3 8.8 11.9 84.6 8.5 14.1 239.8 13.4 0.8057 2.4243 3.4467 1.4763 2.9876 1.1165 2.208 2.1302 1.2369 1.4441 1.54385 0.9978 1.5413 0.9021 1.4752 1.3995 1.0791 1.4865 3.7725 6.7277 6.4379 3.6058 6.8854 6.6922 5.5886 3.6594 6.8337 <.44 <.23 <.12 <.14 <.22 <.12 <.094 <.098 <.0004 <.0009 <.0008 0.0006 0.0014 <.0005 <.0007 <. 0005 <.0004 33.1616 19.0231 36.0122 20.7982 34.3928 33 .5499 19.2971 35.0170 0.4131 0.2402 0.2610 0.5409 0.4500 0.3077 0.4664 0.4901 32.5027 28.6016 13.1066 31.9753 20.5990 17.7857 31.1295 30.2116 <3.1 <4.5 54.5 <2.7 <9.3 <1.8 118.6 58.1 <2.7 121.603 45.5939 97.9762 35.7274 15.6408 76.9757 73 .8606 63.3915 42.5685 1.8102 12.8583 1.9504 10.7464 2.0459 1.2955 2.3417 1.7944 3.8370 15.80 10.47 9.44 10.91 16.71 18.40 10.68 10.21 9.46 <.43 <.20 <. 29 <.16 <.31 <.19 <.13 <.35 <. 15 6.2347 3.0732 6.4180 '6.1858 3.4364 5.7207 4.2024 5.6783 0.945 0.945 0.849 0.600 0,970 0.562 0.615 0.911 0.761 0.6287 0.8817 0.7964 0.95075 0.4779 0.8626 0.9731 0.4752 0.9311 5.2369 2.8197 6.4104 3.5854 6.1577 6.2815 6.4499 4.2108 6.3901 1.4928 1.2099 0.7278 0.7713 1.5075 2.1070 0.9795 1.5693 2.1865 <.60 1.1048 7.6652 14.8940 21.8660 1.3335 1.9365 2.8997 2.9966 1.8761 1.5589 3.3116 2.7242 1.4221 2.7894 43 Table 2.2 {continued2 Major and trace element com~osition of rocks from the Corvet Est de~osit, Québec, Canada 55340 55345 55349 55052 55054 55068 55089 55279 55026 basaIt dacite po andesite dacite basaIt dacite basaIt basaIt dacite Trench 18 Trench 18 Trench 18 DDH36 DDH 17 DDH 17 DDH 17 DDH 17 DDH36 59.31 66.11 58.59 58.08 65.08 63 .95 68.11 68.11 66.97 15.22 . 15.50 15.35 15.72 14.34 17.07 11.34 14.64 15.68 5.20 5.91 5.15 4.13 8.08 5.16 7.68 5.05 9.45 0.92 6.62 1.93 0.91 4.36 1.01 5.11 1.13 0.43 6.24 3.52 2.98 3.14 5.23 6.36 3.88 4.66 3.49 4.18 4.62 5.15 4.61 3.89 4.06 4.72 2.87 1.49 2.04 1.28 1.91 1.43 0.93 1.54 1.95 1.41 2.43 0.54 0.53 0.76 0.49 0.58 0.63 0.33 0.45 0.69 0.18 0.20 0.15 0.30 0.19 0.21 0.21 0.13 0.11 0.15 0.11 0.08 0.06 0.13 0.13 0.09 0.23 0.08 99.25 98.48 96.98 99.06 98.60 97.70 97.73 98.58 98.77 21 5 21 23 9 55 Il 10 32 46 56 57 51 37 65 58 59 38 247 197 558 200 273 324 446 387 107 238 124 145 178 159 252 148 159 185 12 20 22 30 23 22 20 29 33 5 9 5 8 6 Il 7 13 6 <.18 <.44 <.31 <.21 <.11 0.1899 <.11 <.22 0.1899 15.71 83.06 1.51 98.80 8.87 7.53 15.98 5220.56 0.0014 0.0186 1.8977 0.0038 0.0010 0.0056 0.0091 1.5534 0.0000 334 244 406 226 227 950 442 263 621 <.15 1.0708 0.9150 <.10 0.5723 <.16 <.36 <.22 <2.8 <. 81 <.94 <.87 <.67 <. 74 <.68 <2.4 52.3 70.7 80.7 46.8 39.7 46.3 39.5 39.7 52.5 5.21 24.88 7.26 27.98 11.01 27.43 9.55 7.26 6.41 447.7 11.5 12.2 178.0 12.6 6.5 159.1 18.2 11.0 2.6418 2.9420 1.0336 1.3489 1.7274 3.3826 1.3489 4.9352 2.2573 1.5141 1.1757 1.5900 1.2083 1.0307 1.0877 1.0307 1.1268 1.0963 . 3.8738 6.6529 4.2454 4.0926 4.7528 4.2653 4.2454 3.8889 4.9574 <.14 <.21 <.30 <.16 <.16 <.16 <. 074 <.32 <.0010 <.0004 <.0006 <.0010 <.0005 <.0005 <.0006 <.0005 0.0036 26.7984 34.6377 36.7612 20.0881 22.8339 22.3423 20.0738 25.5430 0.1291 0.3363 0.4500 0.3372 0.3155 0.3117 0.3098 0.4423 31.3042 34.7634 18.1543 21.9537 20.8123 18.0847 21.6873 21.2878 <5.8 120.7 <4.7 108.1 <5.5 <2.1 <4.7 94.2 <3.4 40.2306 61.9673 33.4611 28.2772 60.3606 33.8140 32.149 62.3137 66.1013 24.7155 2.9861 3.6718 0.9484 0.3575 2.6989 1.7692 0.9776 51.7313 14.77 19.22 9.58 4.16 7.68 6.92 4.16 18.99 8.31 <.14 <.34 <.46 <.20 <.17 <.14 0.1958 <.20 <.22 6.0327 4.5283 6.2467 3.6341 4.1702 4.2471 3.6729 4.6793 0.924 0.400 0.672 0.568 0.668 0.594 0.665 0.568 0.627 0.6542 0.8456 0.5125 0.5941 0.5300 0.7721 0.52995 0.5946 0.5071 3.5214 3.6742 4.0603 5.5569 6.2798 7.0418 5.5569 3.6006 4.7441 0.7331 1.2074 1.8488 0.8737 1.0887 1.0773 0.9175 1.0210 <7.7 4.4216 9.7375 3.0447 0.9661 3.3349 6.0280 0.8809 1.9644 2.0267 2.8114 0.8545 2.5091 1.8417 1.9152 2.1477 44 Table 2.2 (continued) Major and trace element composition of rocks from the Corvet Est deposit, Québec, Canada 55093 55111 55119 55123 55128 55130 55131 55350 55090 dacite basait dacite dacite dacite dacite dacite dacite dacite DDH 16 DDH 16 DDH34 DDH34 DDH34 Trench 18 DDH 16 DDH 16 DDH 16 60.51 64.21 66.42 64.28 65.72 66.63 67.31 61.53 58.13 14.88 14.56 15.37 14.54 15.03 13.92 15.10 15.66 16.01 7.82 6.79 4.80 7.26 6.01 6.58 3.83 8.71 6.82 1.01 1.22 0.83 1.03 0.89 0.65 1.66 3.35 0.98 7.74 3.84 3.12 4.59 3.69 4.16 4.06 1.98 6.90 2.46 3.14 4.00 2.33 3.25 3.20 1.96 3.45 3.77 1.81 2.47 4.09 2.47 2.98 2.65 3.66 3.56 1.06 0.45 0.81 0.48 0.46 0.49 0.47 0.48 0.49 0.52 0.15 0.14 0.26 0.15 0.14 0.16 0.15 0.15 0.16 0.21 0.20 0.12 0.14 0.48 0.19 0.13 0.16 0.15 97.94 98.02 98.13 97.52 97.14 97.51 98.75 98.14 97.18 23 5 5 12 20 30 46 5 9 67 57 61 30 64 64 53 53 97 182 201 201 193 181 348 119 217 203 250 238 248 247 243 242 239 267 165 32 35 32 34 31 35 34 26 38 10 12 14 16 15 14 9 8 8 <.40 <.22 <.30 0.1639 <.27 <.20 0.2590 <.25 <.20 19.03 107.76 13.38 88.22 4810.52 278.53 76.92 0.0014 0.0000 5.2385 0.0396 0.0008 0.0000 0.0038 0.0050 0.2953 468 346 409 540 352 373 287 417 726 0.2918 0.2413 0.1851 <.38 0.2529 <.75 0.2249 <.98 <.67 <1.1 <.26 <1.4 2.6749 <1.4 68.4 70.6 70.0 69.4 77.6 65.9 70.4 77.3 55 .5 3.81 5.67 5.69 5.14 5.80 5.61 21.74 5.05 8.32 11.6 7.4 8.7 11.5 11.9 208.1 6.3 9.3 10.9 2.2774 3.7153 2.4848 5.2075 3.8914 3.1844 1.3426 2.0638 1.8508 1.4040 1.4825 1.4625 1.4879 1.4830 1.25495 1.6504 1.4347 1.6011 6.1278 6.4488 6.3899 6.4646 6.2367 6.4842 4.0871 6.4283 7.2737 <.24 <.13 <.099 <.14 <.54 <.068 <.20 <.0008 <.0006 <.0008 <.0006 0.0013 <.0008 <.0006 <.0005 <.0007 33.4355 33 .7954 35.2550 33.9599 39.2582 32.3890 38.6449 0.5563 0.4489 0.5135 0.4597 0.5408 0.4440 0.5367 30.0520 30.8908 31.0870 33.5596 35.1954 30.1377 36.5457 <4.6 <5.2 <2.7 <2.0 <6.0 <5.0 <3.6 <9.2 82.9 48.6061 79.8167 104.203 70.3231 77.5525 30.5644 76.0259 68.7765 82.8485 1.2512 2.6674 2.9284 1.1545 2.1365 1.4489 0.7409 8.5933 0.3378 9.26 10.24 10.75 9.38 10.16 10.06 11.96 14.54 21.09 <.40 <.27 <.36 <.30 0.1780 <.27 <.19 <. 21 <.31 5.9145 5.8041 6.2278 5.8042 6.1966 6.6850 7.1568 0.873 0.963 0.838 0.934 0.847 0.903 0.943 1.025 0.8741 1.0532 0.6633 1.0139 0.8492 0.8381 0.8758 0.7963 0.82695 7.5206 5.9153 5.9253 5.9015 6.3192 6.7566 3.4572 6.1888 6.0147 1.3325 1.2954 1.6580 1.5088 1.4891 1.6786 1.4358 2.2651 0.2623 1.6662 6.7673 0.6049 1.4313 17.8360 3.2903 3.3706 2.7718 2.7393 3.1157 2.8428 3.3203 - - ---- - -- - - -- -- - -- - -- - -- - -- - - -- - - - - - - - - - 45 Table 2.2 (continued) Major and trace element composition of rocks from the Corvet Est deposit, Québec, Canada 55137 55150 55203 55208 dacite dacite qfp dacite DDH34 DDH34 DDH~4 . DDH34 64.71 64.38 69.90 66.80 16.35 14.73 14.70 15.38 5.35 5.95 2.32 4.56 1.11 0.80 0.89 1.46 2.26 3.62 3.02 1.00 4.62 4.16 4.73 4.24 2.91 3.03 4.08 2.59 0.54 0.48 0.31 0.46 0.14 0.15 0.15 0.16 0.10 0.13 0.03 0.08 98.07 98.01 98.17 98.13 5 14 14 5 41 54 56 57 201 162 230 185 275 249 123 258 32 34 32 5 15 12 5 Il <.26 · <.080 0.2122 <.11 14.61 13.32 5877.88 325.26 0.0026 0.0034 2.2301 0.5535 882 462 476 493 1.0404 <.20 1.7011 0.4624 < 1.4 <.61 <.53 <2.0 43.8 72.0 73.0 67.5 7.25 4.64 5.06 8.10 13 .2 7.3 18.6 8.7 4.3545 2.3935 1.2851 0.8803 1.4563 1.5279 1.5181 0.7305 7.2268 6.3925 3.4337 6.7828 <. 16 <.31 <.088 <.32 <.0005 <.0006 <.0005 <.0008 21.2682 35.5017 35 .7278 32.3020 0.4624 0.4261 0.4414 0.0506 32.7413 27.5051 14.9195 33.8187 <2.8 <4.7 4.4 <3.7 64.3150 81.5371 75.2774 52.2790 4.2244 1.5431 1.2529 1.4752 2.88 10.49 10.94 10.66 <.19 <.16 <.24 <.35 2.9330 6.3590 6.3816 5.8585 . 0.902 0.272 0.997 0.905 0.9180 0.9021 0.1945 0.9025 6.7095 6.1 067 4.5979 6.3993 1.4912 1.6679 1.4917 1.5294 0.7692 7.1529 1.7707 1.4304 2.7615 2.7239 0.2432 2.8897 *Total Fe as Fe2ü3; DDH drillhole; ls leucosome ;po porphyric; qfjJ quartz-feldspar porphyry 46 2.7.3 Alteration geochemistry Alteration geochemistry shows that amphibolite from the Corvet Est deposit is unaltered whereas dacite is weakly altered. On Fig. 2.14a, the trend from matic to felsic rocks is subhorizontal, typical of magmatic fractionation. Dacite samples, however, plot along a line towards the origin, indicating up to 25% in mass gain (MacLean and Kranidiotis 1987). Figure 2.14b is an isocon diagram comparing the protolith composition based on least altered samples (# 55345 , trench 18; Fig. 2.3 and # 31556, DDH 2; Fig~. 2.3, 2.4) with the most altered sample (# 55026, DDH 36; Fig. 2.3), which grades 1.7 ppm Au. Aline formed by immobile elements Zr, Nb, Ce, P20S, Yb and Ti0 2 has a slope of 0.75 indicating a mass gain of25 %. The mineralized and altered sample is enriched in Au (86 200 %), As (54 278 %), Sb (1164 %), Cu (540 %), Mn (109 %), Ca (46 %), and K (20 %). The altered sample (# 55026) is depleted in Fe (54 %), Sr (52 %) and Na (66 %). Elements systematically enriched in other altered samples are Au, As, Sb, Cu, which is the metal assemblage of mineralization. Geochemical data shows weak alteration which does not correlate weIl with mineralization, because most of the mineralized sampI es cluster near the protolith composition (Fig. 2.14a). This is consistent with texturaI and structural evidence that indicates that gold is included in metamorphically annealed mineraIs, whereas alteration overprints the metamorphic fabric (Figs. 2.8c, 2.8d, 2.1 Ob). 47 A) 18 17 E!:.actionation + • . + + 16 + + + + + .; ++ '* 15 14 13 + 12 C"l 0 11 10 N 9 « 8 7 6 5 6 4 + Dacite 3 Basaltic amphibolite 2 0 50 0 300 250 200 150 100 Zr SiO,l2 + Cu <D N + 30 125 MnO + Sb/2 o + L{) L{) Q) 0.. 20 E 4 Ca<2.L -,- 15 Eu + CU ,+b/5 As/600 10 -t3 Au -1- 5~u + + / 'Yt"4 Sm 20 T~ 3 T~o P,O, + CO NV /La zr/ta / AI,O'~O+T 10 11 f t la y */Z');/4 +:.r ~ Nd / 9Cs 'i'V '/ +4e/2 10+Yb / ~f +45 TiO, Cf) 1.<=> y + Fe 2 0 3 ~ lS r/8 +Ba/20 ~ J6 Na 0 2 / W/'2/ a+MgO ~r/16 O~~~----~--------~--------~I---------+ o 10 20 30 40 Protolith Figure 2.14: Alteration geochemistry of the Corvet Est deposit. a) Ah03 vs Zr diagram (MacLean and Kranidiotis 1987) showing fractionation from amphibolite to dacite and alteration of dacite along a mass gain trend. b) Isocon diagram (Grant 1986) of mineralized (# 55026, 1.7 ppm Au) vs protolith composition from least altered samples average (# 55345 and # 31556) 48 2.7.4 Re-Os Geochronology Two arsenopyrite samples were dated by the Re-Os method. Sample 136665 is a mylonitized dacite with millimeter-scale layers dominated by either quartz, sericitized biotite or hornblende (Fig. 2.15a). Sample 136665 contains approxirnatively 37 % plagioclase, 25 % quartz, 15 % biotite, 10 % sericite, 5 % hornblende, 2 % titanite, 2 % pyrrhotite, 1 % gamet, 1 % calcite, 1 % arsenopyrite, 1 % pyrite and traces of chlorite, hematite, and chalcopyrite. Sulfides and oxides are fine-grained and disseminated in a granoblastic matrix. Arsenopyrite forms fine-grained, euhedral to subhedral, locally twinned crystals, typical of pre-peak metamorphism of stage 1 in the paragenetic sequence. Biotite has a lepidoblastic texture. Sericite replaces biotite and plagioclase. Arsenopyrite and pyrite àre idiomorphic to sub-idiomorphic grains up to 0.5 mm whereas pyrrhotite and chalcopyrite are hypidiomorphic and up to 1 mm. Titanite forms sub-idiomorphic to hypidiomorphic grains up to 0.6 mm. Sample 136665 is from a mineralized zone grading 23.1 ppm gold over 1 m in DDH # 2 (Figs. 2.3, 2.4), but no gold was found under the microscope in that sample. Sample 31567 is a dacite containing 10 % volume medium-grained leucosome (Fig. 2.15b). The sample is composed of 40 % plagioclase, 30 % quartz, 15 % biotite, 7 % sericite, 3 % calcite, 2 % arsenopyrite, 1 % pyrite, 1 % pyrrhotite, 1 % ilmenite, with traces of titanite, magnetite and chalcopyrite. Sulfides and oxides are fine- to medium-grained and disseminated in a granoblastic matrix (Fig. 2.15b). Biotite displays a nematoblastic texture. Arsenopyrite forms fine- to medium-grained idiomorphic crystals up to 2 mm in the leucosome, typical of peak metamorphism of stage 1 in the paragenetic sequence. Sample 31567 is located in between two mineralized zones in DDH # 2 (Figs. 2.3, 2.4). 49 Figure 2.15: Photomicrographs of arsenopyrite dated by Re-Os geochrQnology a) Mylonitized and mineralized dacite (sample no. 136665) with idiomorphic fine-grained arsenopyrite (plane polarized light). b) Barren dacite (sample no. 31567) with subhedral arsenopyrite in medium-grained leucosome (Jeft: reflected plane polarized light, right: cross-polarized light). Am amphibole; Apy arsenopyrite; Rt biotite; Pl plagioclase; Po pyrrhotite; Py pyrite; Qtz quartz; Ser seri cite; Ttn titanite Re-Os isotope analyses of arsenopyrite are reported in Table 2.3. For sample 136665, the error correlation function (rho) is used for plotting as the low amount of 1880S in the sample leads to highly correlated errors in conventional isochron plots. AlI age calculations were made using ISOPLOT version 3.0 (Ludwig 2003). Total Re content in disseminated, finegrained, stage 1, arsenopyrite (136665) ranges from 9.5 to 11.5 ppb, total Os content ranges from 283 to 874 ppt (Table 2.3a), and % radiogenic 1870S of > 81 % for aIl samples. Consequently, the 187Re/1880s isotope ratios show a very large range from ~90 to > 3900. Regression of the Re-Os data (n = 5) yields a Model 1 isochron age of 2663 ± 13 Ma (Fig. 2.16a) with an initial 1870S/1880S of 0.19 ± 0.10. For sample 31567, a mixed double spike was used because amount of common Os present in this sample was extremely low or absent, and as such, only a model age results for each analysis. Total Re contents in disseminated, medium-grained, arsenopyrite from sample 31567 ranges from 9.3 to 9.7 ppb and common Os content ranges from 0.37 to 0.78 pg (Table 2.3b). Re-Os data (n = 4) yields a weighted average model age of2632 ± 7 Ma with a 95 % confidence degree (Fig. 2.16b). 50 A) 240 136665 Apy 200 oCIJ 160 --o 120 co co ..- CIJ t-- co ..- 80 40 Age = 2663 ± 13 Ma (2cr, Model 1) Initial 1S70srSOs = 0.19 ± 0.10 MSWD = 0.83 o ~------------------------------------------~ O. 1000 2000 3000 4000 5000 6000 2660 8) 31567 Apy box heights are 2cr 2650 2640 Q) C> CO 2630 Q) "'C 0 ~ 2620 2610 Mean = 2632 ± 8 Ma [0.32%1 95% conf. MSWD 0.26, probability 0.85 ( error bars are 2cr) = 2600 = 31567-C 2590 Figure 2.16: Re-Os geochronology of arsenopyrite from the Corvet Est deposit. a) Model 1 isochron diagram for sample # 136665. b) Weighted average model diagram for sample # 31567 51 Table 2.3 Re-Os geochronology data for arsenopyrite from the Corvet Est deposit, Québec, Canada A) Conventional 1900s+ 185Re mixed spike Sample Re (Ppb)± 2a Os (ppt) ± 2a 187Re ± 2a 1880S 1870S 1880S 136665-A 136665-B 136665-C 136665-D 136665-E 9.504 9.947 10.624 10.466 11 .509 282.8 302.9 873 .9 317.5 343.7 3882 2299 90.43 2822 3902 176.3 103 .8 4.296 128.7 177.9 0.040 0.045 0.047 0.047 0.051 49.4 51.4 9.8 59.0 83.6 500 295 1.20 392 699 ± 2a 22.7 13.4 0.113 17.9 31.9 Rho 0.998 0.997 0.448 0.998 0.998 B) Mixed 1900S + 1880S + 185Re double spike Sample Re (Ppb) ± 2a 1870S (Ppb) ± 2a . Total common Os (pg) Model ± 2a age (Ma) (includes "uncertainty) 31567-B 31567-C 31567-D 31567-E 9.351 9.325 9.695 9.304 0.033 0.033 0.034 0.033 0.2635 0.2619 0.2730 0.2626 0.00 15 0.0023 0.0007 0.0007 0.78 0.37 FALSE FALSE 2632.7 2623 .5 2630.4 2636.2 20.1 26.7 14.3 14.5 52 2.7.5 Stable isotopes geochemistry The sulfur and oxygen stable isotope data is reported in Table 2.4. 834 S values for pyrite range from 1.0 to 2.3 %0 (n=4, average = 1.6 ± 0.4 %0) whereas 834 S values for arsenopyrite range from 1.8 to 2.9 %0 (n=8, average = 2.4 ± 0.4 %0; Fig. 2.17a, Table 2.4). 8 18 0 values for vein quartz range from 11.6 to 15.8 %0 (n = 5, average = 13.5 ± 1.0 %0). The 8 180 value for quartz in leucosome is 20.2 %0, whereas 8 180 value for quartz in dacite granoblastic matrix is 13.6 %0. Ôl 80 values for plagioclase range from 10.5 to 13.4 %0 (n = 6, average = 12.4 ± 0.7 %0). Vein tourmaline 8 180 values are 7.1 and 8.0 %0 (average = 7.6 ± 0.5 %0; Fig. 2.17b, Table 2.4). A quartz - plagioclase pair from the dacite granoblastic matrix (sample # 31552; Table 2.4, 2.5, Fig. 2.18) yields isotope equilibrium at temperatures ranging from 517°C to 627°C (Table 2.5 ; Matthews et al. 1983, Bottinga and Javoy 1973, Matsuhisa et al. 1979, Sharp and Kerschner 1994), whereas a quartz plagioclase pair from a dacite leucosome (sample # 55123; Table 2.4, 2.5, Fig. 2.18) yields isotope equilibrium at temperatures ranging from 56°C to 245°C (Table 2.5; Clayton and Keiffer 1991, Chiba et al. 1989, Bottinga and Javoy 1975, Matsuhisa et al. 1979). Quartztourmaline pairs from veins (sampi es # 31585 and 55304; Table 2.4, 2.5) yield isotope equilibrium at temperatures ranging from 74°C to 269°C (Table 2.5; Kotzer et al. 1993, Blamart 1991 , Zheng 1993). 53 A) • 1 • _----III---_.Arsenopyrite 1.6 ± 0.4 Pyrite 1.6 ± 0.4 ~ (,) 3 C Q) :::J 2 0- Q) 'u. 1 0 0.2 0.6 1.4 B) 6 1.8 2.2 2.6 Quartz' 13.5 ± 1 • 1 1 1 1 Plagioclase 12.4 ± 0.7 -+-- 3 3.4 3.8 4.2 - Matrix Leucosome Vein Quartz Plagioclase _ Tourmaline 7.6 ± 0.5 Tourmaline 5 ~ (,) 4 C Q) :::J 3 0Q) '- u. 2 o 9 10 11 12 13 14 15 16 17 18 19 20 Figure 2.17: Histograms of sulfur and oxygen isotope composition from the Corvet Est deposit (Table 2.2). a) 834 S values for pyrite and arsenopyrite with average values and range for Is standard deviation. b) 8 18 0 values for quartz, plagioclase and tourmaline with average values and range for 1s standard deviation, excluding the quartz leucosome sample 54 20 N ~ ~ 15 o ro ro ok Leucosome (55123) + Granoblastic matrix (31552) 10 ~--~~--~----------~~~~~--~ 20 15 10 818 0 plagioclase Figure 2.18: Quartz vs plagioclase 8 180 diagram with isotherms according to Bottinga and Javoy (1973) and Matsuhisa et al. (1979) 55 Table 2.4 Stable isotope data from the Corvet Est deposit, Québec, Canada Location Sample no. Description DDH2 31552 31555 31559 31561 31567 DDH 18 DDH 16 DDH34 136665 31576 31585 31586 55105 55123 55134 55144 55150 Trench 5 55304 55306 55307 55313 Trench 18 55345 55350 dacite, granoblastic matrix vein in dacite dacite, granoblastic matrix disseminated in dacite dacite, granoblastic matrix disseminated in dacite dacite, granoblastic matrix disseminated in dacite disseminated in dacite vein in dacite disseminated in dacite vein in dacile vein in dacite dacite leucosome dacite leucosome disseminated in dacite disseminated in dacite disseminated in dacite vein in dacite disseminated in dacite vein in dacite disseminated in dacite dacite leucosome dissemimited in dacite Ô34 S (%0, V -CDT) ÔI8 0 (%0, V-SMOW) Pyrite Arsenopyrite Quartz Plagioclase Tourmaline 13.6 12.8 13.0 12.2 2.6 10.4 1.9 12.8 2.1 2.9 8.0 15.8 1.3 13.3 2.3 13.4 20.2 1.0 2.1 1.8 7.1 13.6 2.8 11.6 2.7 12.9 1.7 56 Table 2.5 Temperature of isotope equilibrium of quartz-plagioclase pairs from the Corvet Est deposit, Québec, Canada Sample no. Mineral pair Temperature Reference 31552 55123 31585 quartz-plagioclase quartz-plagioclase quartz-tourmaline 517°C Matthews et al. 1983 593°C Bottinga and Javoy 1973, Matsuhisa et al. 1979 627°C Sharp and Kerschner 1994, Matsuhisa et al. 1979 56°C Clayton and Keiffer 1991 98°C Chiba et al. 1989 104°C Bottinga and Javoy 1975 245°C Bottinga and Javoy 1973; Matsuhisa et al. 1979 96°C Kotzer et al. 1993 Blamart 1991 Zheng 1993 55304 quartz-tourmaline Kotzer et al. 1993 Blamart 1991 Zheng 1993 57 2.8 Discussion 2.8.1 Geodynamic setting In trace-element spidergrams, the strong Ta and Ti depletions are usually related to subduction settings (Briqueu et al. 1984) but these characteristics have also been found in felsic rocks derived from melting of the continental crust (Arculus 1987; Van Wagoner et al. 2002). Lithogeochemistry shows that the Marco zone is composed of dacite interlayered with basalts of calc-alkaline to transitional affinity interpreted to have erupted in a plate margin volcanic arc subduction environment (Fig. 2.13; Winchester and Floyd 1977, Pearce 1996, Barrett and MacLean 1994, Wood 1980, Pearce and Gale 1977, Briqueu et al. 1984), which is consistent with the position of the Guyer Group rocks, at the southem li mit of the La Grande sub-province. The Guyer Group rocks are in faulted contact with the Laguiche Group metasediments to the south, and Percival et al. (1994) interpreted the LaGrande sub-province green stone belts as being comprised of progressively amalgamated terranes along south-facing subduction zones. This indicates that the Guyer Group volcanosedimentary sequence is the southem margin of the LaGrande sub-province. The dacite and basal tic amphibolite compositions plot along a fractionation line in the Y vs Zr diagram (Fig. 2.12b; Barrett and MacLean 1994), and in the Ab03 vs Zr diagram (Fig. 2.14a; MacLean and Kranidiotis 1987), suggesting they evolved by crystal fractionation from the same magma. Similar La/Lu and enrichment in REEs also suggest that dacite and basaltic amphibolite are . cogenetic. However, lack of samples with intermediate composition between basaltic amphibolite and dacite cou Id suggest that the volcanic rocks did not evolve from the same magma, or that intermediate rock composition between basal tic amphibolite and dacite has not been sampled. 58 2.8.2 Metamorphic conditions According to gamet-biotite thermobarometric calculations, the peak metamorphic temperature at the Corvet Est deposit is between 585°C and 633°C at pressures ranging from 2 to 6 Kbars, whereas a quartz - plagioclase pair from the dacite granoblastic matrix yield oxygen isotope equilibrium temperatures ranging from 517°C to 627°C. The consistent temperatures from gamet-biotite thermobarometer and oxygen isotope geothermometer suggests mineraIs crystallized in a state of equilibrium near 600°C. These thermobarometric conditions correspond to the lower- to mid-amphibolite metamorphic facies and this is consistent with the Corvet Est rocks mineraI assemblage, containing plagioclase, hornblende, garnet and biotite. These metamorphic conditions are similar to those of amphibolite facies gold deposits of the Yilgarn Block, Australia (Groves 1993). The temperatures yielded by a quartz - plagioclase pair from the dacite leucosome, ranging from 56°C to 245°C indicates that the leucosome crystallized in a state of isotope disequilibrium, supported by the similar matrix and leucosome plagioclase 8180 values but different quartz 8180 values (Fig. 2.18): if coexisting quartz and plagioclase had crystallized at such low temperature in equilibrium in a closed system, quartz and plagioclase 8 180 would have shifted towards higher and lower 8180 values, respectively. Dacite leucosomes have LREE patterns similar to those of dacite, with HREE-enriched patterns suggesting they were formed by low degree of partial fusion of dacite during amphibolite-grade metamorphism. Using Blamart (1991), quartz-tourmaline pairs from post-metamorphic veins in dacite yield oxygen isotope equilibrium temperatures ranging from 230°C to 269°C, which is consistent with post-metamorphic cooling of the dacite. 2.8.3 Age of mineralization The occurence of gold inclusions in metamorphically annealed mineraIs is evidence that gold mineralization is pre- to syn-metamorphic, with sorne gold remobilized in later veins. The low value of initial 1870s/1880S (0.19 ± 0.10) in arsenopyrite sample # 316665 suggests that this arsenopyrite dates formation rather than resetting of preexisting arsenopyrite, 'in 59 which case the osmium would be more radiogenic. The age of mineralization from Re-Os dating of the low 1870S/1880S fine grained arsenopyrite sample # 316665 is 2663 ± 13 Ma. The age obtained from sample # 31567 (2632 ± 7 Ma) is interpreted as the age of leucosome crystallization and peak metamorprusm, and is slightly older than the age for peak regional metamorphism for the La Grande subprovince (2620 Ma; David and Parent 1997). These Re-Os ages on arsenopyrite indicate that mineralization is pre-metamorphic. 2.8.4 Source of sulfur, osmium and fluids Sulfur in arsenopyrite has 834S values slightly higher than values for pyrite and both mineraIs are in texturaI equilibrium. The low variability of 834 S values (1 to 2.9 %0; Table 2.4, Fig. 2.17a) indicates a homogeneous source for sulfur. Figure 2.19 compares sulfides 834 S values from the Marco zone with those of various volcanic and plutonic rocks, meteorites and volcanic S02 (Sakai et al. 1982, Ueda and Sakai 1984, Kerridge et al. 1983, Coleman 1977, Chaussidon et al. 1989). The 834 S values for Corvet Est plot witrun the range of values typical for island-arc basalts and andesites. This suggests that the Marco zone sulfur was likely leached from its volcanic ho st rocks. Figure 2.19 shows that another possible source for sulfur is reduction of aqueous sulfate in Archean seawater, su ch as that in Archean VMS deposits. The 834 S composition of the Marco zone sulfides are very similar to that of pyrite from orogenic gold deposits in the Laverton greenstone belt, in the northeast of the Eastern Goldfields province of the Yilgarn craton, Australia: the range of median 834 S values of the Kerringal, Red October, Mount Morgans, Jubilee and Wallaby deposits cluster from 1.3 to 2.7 %0 (Fig. 2.19; Salier et al. 2005). The 834 S composition of the Marco zone sulfides are also within the range of values of pyrite samples from quartz - tourmaline - carbonate veins of the Val-d'Or vein field in Abitibi, Québec, Canada (0.6 to 6 %0, Fig. 2.19; Beaudoin and Pitre 2005). 60 Primitive mantle val Island-arc basalts + andesites Voleanie H2 S • Granites 2.6 - 3.0 Ga VMS deposits L....-r----' Val d'Or orogenie deposits, Canada Laverton belt orogenie deposits, Australia -50 -40 -30 -20 -10 o 0 10 20 30 40 034 8 of sulfides (0/00) Figure 2.19: Comparison of Corvet Est 834 S values with that from different sources for S (Sakai et al. 1982, Ueda and Sakai 1984, Kerridge et al. 1983, Coleman 1977, Chaussidon et al. 1989, Lusk et al. 1975, MacLean and Hoy 1991, Kerr and Gibson 1993, Strauss 1986, 1989, Bleeker 1994 in Huston 1999, Franklin et al. 1981, Zalesky and Peterson 1995, Seccombe 1977, Nunes and Thurston 1980, Papunen et al. 1989, Seccombe and Frater 1981 , Yeats 1996, Beaudoin and Pitre 2005) Osmium can be used as a powerful tracer of petrogenetic and ore-forming processes of noble-metal deposits because of the strong fractionation between Re and Os in crustforming processes, wherein crustal rocks evolve to a more radiogenic 1870S/1880S signature compared to the mande (Walker et al. 1989), which is presendy about 0.13 (Meisel et al. 1996). The low initial 1870s/1880s of 0.19 ± 0.10 in arsenopyrite sample # 136665 suggests a juvenile cru st or a mande metal source with limited crustal contamination for the source of Os in 2663 Ma arsenopyrite (Dickin 2005). The Ovens and the Dufferin orogenic gold 61 deposits of the Meguma terrane, Appalachian provInce, Canada, have higher initial IS70S/ISSOS In arsenopyrite than the Corvet Est deposit. The Ovens deposit initial IS70S/ ISSOS In arsenopyrite (0.83 ± 0.16) indicates a crustal derivation, whereas the Dufferin deposit initial IS70S/ISSOS in arsenopyrite (0.38 ± 0.16) suggests a mixture between two components - a principal one with high IS70S/18S0S (older crust) and a subordinate one with a much lower IS70S/ISSOS Guvenile crust or mantle; Morelli et al. 2005). The Central Deborah orogenic gold mine, Bendigo Goldfields, central Victoria, Australia, also have higher initial IS70S/ ISSOS in arsenopyrite (1.04 ± 0.16) than the Corvet Est deposit, indicating a crustal derivation of ore fluids (Arne et al. 2001). Oxygen isotope values in plagioclase are slightly higher than values for quartz and both mineraIs are interpreted to have reached equilibrium near 600°(:. A metamorphic fluid in equilibrium with the dacite at 600°C would have had a 8 1S 0 value of 11.9 %0 (Fig. 2.20). The low variance of 8 1S 0 values indicates a homogeneous source for oxygen, except for the leucosome quartz sample (20.2 %0), suggesting precipitation from a high 8 ISO fluid such as metamorphic water. In post-metamorphic veins, oxygen isotope values in tourmaline are slightly lower than values for qùartz and both mineraIs are interpreted to have reached equilibrium near 250°C (Blamart 1991). The post-metamorphic fluid in equilibrium with vein quartz has 8 1S 0 values ranging from 2.9 to 3.8 %0 (Fig. 2.20), similar to the Val-d' Or orogenic gold vein field supracrustal fluid 8 1S 0 value « 3.9 %0) ca1culated by Beaudoin and Pitre (2005). The Figure 2.20 compares the Corvet Est fluid oxygen isotopic compositions with that of natural waters from various environments (Taylor 1986, Giggenbachs 1992, Sheppard et al. 1977, Sheppard 1986, Bottinga and Javoy 1973, Friedman and O'Neil 1977). The values for Corvet Est fluids plot within the range of values for fluids from andesitic, S-type magmatic and metamorphic environments. Ca1culated oxygen isotope compositions of the hydrothermal ore-forming fluids for Archean and Proterozoic Iode gold deposits range from 6 to Il %0 8 1S 0 (McCuaig and Kerrich 1998, Kerrich 1989), suggesting . that metamorphic hydrothermal fluids formed the Corvet Est deposit. The 8 1S0 values of vein quartz from the Charlotte (11.3 ± 0.3 %0) and Reward (11.4 ± 0.5 %0) orebodies in the Mt Charlotte orogenic gold deposit, Yilgam craton, Australia (Golding et al. 1990a, 1990b), and the Archean Val-d' Or orogenic gold vein field (9.2 to 14.4 %0), Superior 62 province, Canada (Beaudoin and Pitre 2005) are very similar to 8 180 values of quartz from the CorvetEst deposit. Corvet Est (post metamorphic) 1 Corvet Est (metamorphic) MORS Andesitic D S-type magmatic D Primary magmatic Metamorphic -5 o 5 10 0180VSMOW 15 20 (%0) Figure 2.20: Comparison of oxygen isotopie compositions between Corvet Est fluid and that of natural waters from various environments (Taylor 1986, Giggenbaehs 1992, Sheppard et al. 1977, Sheppard 1986) 2.8.5 Comparison of the Corvet Est deposit with amphibolite grade orogenie, amphibolite grade epithermal, and the Hemlo deposits The Corvet Est deposit displays several charaeteristies similar to those of other amphibolite grade gold deposits, whereas other eharacteristies are atypieal of amphibolite grade gold deposits. The Corvet Est deposit is eompared to amphibolite grade orogenie deposits, amphibolite grade epithermal deposits, and to the Hemlo deposit (Table 2.6). Orogenie gold deposits are hosted in deformed allochthonous terranes accreted to continental margins (Groves et al. 2003), and according to Groves et al. (1998), protoliths 63 for the auriferous Archean green stone beIts are predominantly volcano-plutonic terranes of oceanic back-arc basaIt and felsic to matic arc rocks. The Corvet Est deposit resembles amphibolite 'grade orogenic gold deposits because (1) the Corvet Est deposit is hosted in plate margin arc basalts of the La Grande sub-province accreted to the Opinaca subprovince margin; (2) mineralization at Corvet Est is pre-metamorphic with late remobilization whereas orogenic gold mineralization is pre- to post-metamorphic (McCuaig et al. 1993); (3) opaque mineralogy comprises magnetite, ilmenite, pyrite and pyrrhotite; (4) gold is mostly disseminated in shear zones; and (5) the isotopic composition of sulfur (034S) and oxygen (0 180) at Corvet Est is similar to that of amphibolite-grade orogenic gold deposits (Groves et al. 1998). Amphibolite grade orogenic gold deposits differ from Corvet Est by a strong carbonate alteration correlated to mineralization and a metal signature characterized by Ag, Bi and Te (Groves 1993). Epithermal deposits metamorphosed to amphibolite grade such as the Hope brook mine (Dubé et al. 1998) differ from Corvet Est by their strong argilic aIteration metamorphosed to quartz-sericite-pyrite-pyrophyllite schists and o.ccurrence of bomite, tennantite and enargite. Epithermal deposits are typically younger than 65 Ma (Taylor 1996). Epithermal deposits have poor preservation potential, given their shallow depth of formation (Cooke and Simmons 2000), except if they are tilted and buried soon after their deposition (Gauthier, pers.comm. 2008). Corvet Est resembles amphibolite grade epithermal deposits for its felsic volcaniclastic ho st rocks in a calc-alkaline volcanic arc environment, its premetamorphic mineralization and for its metal assemblage, except for lack of Bi, Pb and Ag that are typical of amphibolite grade epithermal deposits (Dubé et al. 1998, Hallberg 1994). The Hemlo gold deposit is interpreted as an atypical, mesozonal-orogenic, disseminatedreplacement-stockwork deposit (Muir 2002), and its genesis remains a subject of debate. Unlike Corvet Est, the Hemlo deposit displays a wide range of 034 S values (-17.5 to 8.7 %0; Cameron and Hattori 1985; Thode et al. 1991), suggesting a more heterogeneous sulfur source compared to Corvet Est. According to Cameron and Hattori (1985), both sulphate and sulphide from the Hemlo deposit may have come from an oxidized magmatic- 64 hydrothermal fluid. Alternatively, the sulphate may be of exogenous origin, which was drawn down into a volcanic-geothermal system and partially reduced to sulphide. The metal assemblage at Hemlo contains Mo, Hg, Tl , Ba, V and B (Harris 1989) which are not present at Corvet Est. Similar to Corvet Est, the Hemlo deposit consists of disseminated pre-metamorphic mineralization in felsic rocks that contains the pyrite-pyrrhotitearsenopyrite-chalcopyrite-stibnite sulfide assemblage. The range of oxygen isotopie composition of the Hemlo fluids (9.2 to 11. 7 %0; Kuhns 1988) is very close to the composition of the Corvet Est metamorphic fluids (11.9 %0). An important difference between Corvet Est and ail these other deposits is that go Id and alteration are not correlated because at Corvet Est, the dominant alteration is post-mineralization and metamorphism. 65 Table 2.6 Comparison of the Corvet Est deposit and other amphibolite grade gold deposits Host rocks Corvet Est deposit Amphibolite grade orogenie deposit Dacite, basaltic amphibolite Paragneiss, felsic to Felsic volcaniclastic, ultramafic volcanic rocks QFP, orthogneiss Amphibolite grade epithermal deposit Hemlo deposit Felsic to mafic volcanic rocks 2880 - 2663 Ma Age of mineralization Archean to Cretaceous 574 - 578 Ma (Hope Brook), 1880 Ma (Enasen) 2677 - 2685 Ma Timing of Pre-metamorphic mineralization late remobilisation Pre- to postmetan:wrphic Syn-volcanic, pre-metamorphic Pre- to synmetamorphic Environment Deformed accreted terranes Calc-alkaline volcanic arc Volcanosedimentary arc Style of Disseminated, shear, mineralization vem Disseminated, shear, vem Disseminated, shear Disseminated, shear, paraconcordant Fluid 8180 . 11.9 %oa 6 to Il %ob ? 9.2 to 11.7 %0 Sulfide 834 S 1.0 to 2.9 %0 oto 9 %0 ? -1 7.5 to 8.7 %0 Po, Apy, Py, Cpy, Ilm, Sp, Lo, Stb Py, Po, Cpy, Bn, Tn, En, Ttr, Bis Py, Mo, Sp, St Re, Ci, Ttn, Tn, Po, Apy Au, Ag, W, As, Bi, Sb, Te Au, Cu, Sb, Bi, Pb, As Ag Au, Mo, Sb, As, Hg, Tl, Ba, V, B Plate margin volcanic arc Ore mineralogy Apy, Py, Po, Cpy, Stb, Ilm Metal assemblage Au, As, Cu, Sb Prl, KIn, And, AIn, Si, K, ·Ser, AISi, ChI, Tur, (pre- to Am, Bt, Grt, Cc, ChI, K-Fp, Pl, Ms AISi CId syn-mx) Ser, K-Fp, Cc (post-mx) Ain alunite; AISi alumino-silicates; Am amphibole; And andalusite; Apy arsenopyrite; Bis bismuthinite Bn bomite; Bt biotite; Ce calcite; Chi chlorite; Ci cinnabar; Cid chloritoid; Cpy chalcopyrite; En enargite; Grt gamet; /lm ilmenite; K-Fp potassic feldspar; Kin kaolinite; Lo loellingite; Ms muscovite; mx mineralization; PI plagioclase; Po pyrrhotite; Prl pyrophyllite; Py pyrite; Re realgar; Ser sericite; Sp sphalerite; St staurolite; Stb stibnite; Tn tennantite; Ttn titanite; Ttr tetrahedrite; Tur tourmaline Amphibolite grade orogenie deposit (Groves et al. 1993; McCuaig et al. 1993; McCuaig and Kerrich 1998; Groves et al. 2003) Amphibolite grade epithermal deposit (Dubé et al. 1998, Hallberg 1994) Hemlo deposit (Harris 1989, J ohnston 1996, Powell and Pattison 1997, Powell et al. 1999, Bodycomb et al. 2000, Lin 200 1, Muir 2002, Davis and Lin 2003 , Muir 2003 , Cameron and Hattori 1985; Kuhns 1988) a excluding the leucosome and vein samples b not restricted to amphibolite-grade deposits Alteration 66 2.9 Conclusions The Marco zone of the Corvet Est deposit is hosted in dacite of calc-alkaline to transitional affinity which plot in the plate margin arc basalts field. The dacite host rocks display weak alteration which does not correlate weil with mineralization. Gold in the Marco zone is premetamorphic and in late veins. Sulfur from the Marco zone is from Archean sea water or leached from volcanic ho st rocks. The very low initia11870s/1880s of 0.19 ± 0.10, suggests a juvenile crust, or a mande, metal source with limited crustal contamination. The Corvet Est fluids plot within the range of values for fluids from andesitic, S-type magmatic, and metamorphic environrnents. The age of the gold mineralization at Corvet Est is 2663 Ma and peak metamorphism occurred at 2632 Ma. The Corvet Est deposit shows resemblances with amphibolite-grade orogenie deposits, amphibolite grade epithermal deposits and the Hemlo deposit. The Corvet Est deposit lacks the metamorphosed argilic alteration of amphibolite grade epithermal gold deposits. The Hemlo deposit contains significant Mo and Hg in the metal assemblage and a wide range of 834S values compared to Corvet Est. An important difference between Corvet Est and the compared deposits is that gold and alteration are not correlated because the main alteration at Corvet Est is post-metamorphic. Many of the features of the Corvet Est deposit are consistent with deep seated amphibolite grade orogenic gold deposits, as they were described in the crustal continuum model proposed by Groves et al (1993): (1) the Corvet Est deposit is hosted in plate margin arc basalts accreted to a continental margin; (2) mineralization at Corvet Est is premetamorphic with late remobilization; (3) opaque mineralogy comprises magnetite, ilmenite, pyrite and pyrrhotite; (4) gold is mostly disseminated in shear zones; and (5) the isotopie composition of sulfur (8 34 S) and oxygen (8 IS 0), indicate that the Corvet Est deposit has similarities with amphibolite-grade orogenie gold deposits (Groves et al. 1993). Chapitre 3. Conclusion La minéralisation en or de la zone Marco du gîte Corvet Est est disséminée dans des zones cisaillantes accompagnées de pyrite, d'arsénopyrite, de pyrrhotite, et de chalcopyrite. La caractérisation des assemblages minéralogiques, des altérations et des fluides hydrothermaux a permis d'établir une séquence paragénétique et un modèle génétique pour la minéralisation du gîte Corvet Est. La lithogéochimie montre que la zone Marco du gîte Corvet Est est encaissée dans une dacite en contact avec des basaltes et andésites d' affinité calco-alcaline à transitionnelle se positionnant dans le champ des basaltes d'arc en marge de plaque, dans un contexte de subduction (Winchester et Floyd 1977, Pearce 1996, Barrert et MacLean 1994, Wood 1980, Pearce et Gale 1977, Briqueu et al. 1984). Ces déductions lithogéochimiques sont compatibles avec la position de la séquence volcano-sédimentaire du Groupe de Guyer, à la limite sud de la sous-province de LaGrande. Les compositions de la dacite et de l'amphibolite basaltique se positionnent le long d' une ligne de fractionnement dans le diagramme Y vs Zr (Barrert et MacLean 1994) et dans le diagramme Ah03 vs Zr (MacLean et Kranidiotis 1987), suggérant qu'ils proviennent de la cristallisation fractionnée d'un même magma. Les rapports La/Lu similaires et un enrichissement en éléments des terres rares suggèrent aussi la nature cogénétique de la dacite et l'amphibolite basaltique. Selon des calculs thermo-barométriques par la methode grenat-biotite, la temperature du plus haut degree de métamorphisme de la zone Marco, est entre 585 et 633 °C à des pressions allant de 2 à 6 Kbars (Berman 1990, Macler and Berman 1991, Berman 2006, Berman 1991) tandis qu'une paire de quartz - plagioclase de la matrice granoblastique dacitique rend une température d'équilibre isotopique de 517°C (Marthews et al. 1983), 593°C (Bortinga et Javoy 1973; Matsuhisa et al. 1979) et 627°C (Sharp et Kerschner 1994; Matsuhisa et al. 1979). Ces conditions thermo-barométriques correspondent au faciès 68 métamorphique amphibolite inférieur à m.oyen et sont compatibles avec l' assemblage minéralogique plagioclase - hornblende - grenat - biotite des roches de Corvet Est. Les inclusions d' or dans des minéraux à texture de rééquilibrage métamorphique prouvent que la minéralisation peut être pre- à syn-metamorphique, avec de l'.or remobilisé dans des veines tardives. L' âge de la minéralisation, obtenu de la datation radiogénique par la méth.ode Re-Os d' arsénopyrite finement grenue est de 2663 ± 13 Ma. L' âge du pic métamorphique est de 2632 Ma. La minéralisation est donc pré-métamorphisme. La faible variabilité des valeurs de 834 S (1.0 à 2.9 %0) d' échantillons de pyrite et d' arsénopyrite du gîte C.orvet Est indique une s.ource hom.ogène pour le soufre. Ces valeurs se positi.onnent dans le champ des valeurs de basaltes et d' andésites d' îles en arc, suggérant que le soufre de la zone Marco a vraisemblablement été lessivé de ses r.oches encaissantes volcaniques. Une autre source possible pour le soufre est l'eau de mer Archéenne. Les sulfures se seraient formés à partir de la réduction du S04 par le H2 S. Le faible 1870S/1880S initial de 0.19 ± 0.l0 dans l' échantillon d' arsénopyrite finement grenue # 136665 suggère que les métaux proviennent d' une croûte juvénile, ou qu' ils sont de source mantélique avec une faible contamination crustale. La faible variabilité des valeurs de 8 18 0 (10.4 à 13.6 %0 excluant l'échantillon provenant d' un leuc.osome) du quartz et du plagi.oclase du gîte Corvet Est indique une s.ource homogène pour l'oxygène, qui s\lggère une précipitation à partir d' un fluide enrichi en 18 0 comme un fluide métamorphique. La composition iS.otopique des fluides de Corvet Est se positionne dans le champ des valeurs pour des fluides d' environnements andésitique, magmatique de type S et métamorphique. Le gîte Corvet Est montre des similitudes avec les gîtes d'.or orogéniques au faciès des amphibolites, les gîtes d' or épithermaux au faciès des amphibolites, et le gîte Hemlo, également métamorphisé au faciès des amphib.olites. Le gîte C.orvet Est est exempt de l' altération argilique métamorphisée des gîtes d'or épithermaux au grade amphibolite. Le gîte HernIo c.ontient des concentrati.ons n.otables de Mo et Hg dans l'assemblage métallique, ainsi qu ' une grande variation des valeurs de 834 S par rapport à Corvet Est. Une différence 69 importante entre Corvet Est et les gîtes comparés est l'absence de corrélation entre l'or et l' altération, puisque l'altération principale à Corvet Est est post-métamorphique. Plusieurs caractéristiques du gîte Corvet Est sont compatibles avec les gîtes d' or orogéniques au grade amphibolite tels qu' ils sont décrits dans le modèle de continuum crustal proposé par Groves et al. 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Earth Planet Sci Lett 120: 247 - 263 Annexe 1 : Analyses à la microsonde de mineraux du gîte Corvet Est, Canada A} , Carbonates Echantillon Mg(C03) (wt%) Ca(C03) Mn(C03) Fe(C03) Sr(C03) Total 550162Si BDL 100.001 0.017 0.141 BOL 100.159 B) , Tourmaline Echantillon 55016 1e FeO (wt%) 10.539 0.012 Cr203 NiO BDL 1.359 Ti02 MnO 0.063 0.057 K20 34.935 Si02 MgO 7.541 1.371 Na20 27.536 Ah 0 3 2.668 CaO B20 3 13.913 Total 99.999 550268a BOL 100.824 0.303 BOL BOL 101.127 55016 If 10.381 0.047 BDL 1.354 0.03 0.058 34.748 7.528 1.379 27.712 2.719 14.042 100.001 550268b 0.269 96.837 0.67 1.433 0.073 99.282 55305 C4 0.22 93.808 2.898 2.383 0.013 99.322 550163iib 11.044 0.044 BDL 1.434 0.066 0.053 30.001 7.669 1.293 28.016 2.716 17.658 100.000 550164c 10.934 0.127 0.028 1.384 0.037 0.047 34.748 7.654 1.38 27.648 2.594 13.414 100.000 B) Tourmaline (suite) 5501610c 10.649 0.044 BDL 1.386 0.058 0.067 34.631 7.451 1.324 27.727 2.734 13.923 100.000 55308 C3 a 9.481 BDL '0.014 1.356 0.118 0.049 35.217 7.566 1.596 29.154 2.165 13 .279 100.000 55308 C3 b 9.12 0.016 BOL 1.029 0.102 0.049 35.24 7.204 1.64 29.968 1.924 13.704 100.002 g 550165id 10.882 0.044 0.033 1.419 0.028 0.06 34.866 7.611 1.359 27.886 2.689 13.118 100.001 55016 lOb 11.105 0.025 0.043 1.323 0.043 0.052 34.569 7.41 1.33 27.703 2.772 13.62 100.000 82 C) Amphibole Échantillon 55026 C8 id 55016 Cl id 55016 C5 ii a Si02 (wt%) 35.46 42.523 42.861 0.646 Ti0 2 0.907 0.949 14.598 10.076 AhO) 9.675 V20 ) 0.183 0.356 BOL BDL 0.043 0.074 Cr20 3 2.413 10.032 10.276 MgO 9.68 Il.889 11.838 CaO MnO 0.377 0.631 0.668 FeO 29.557 17.843 16.74 BOL 0.011 0.01 NiO 0.698 0.894 0.977 Na20 1.18 0.896 0.975 K20 1.844 H20 1.766 1.89 F 0.075 0.197 0.094 0.006 Cl 0.036 0.006 Total 96.639 98.178 97.033 55016 C5 ii b 55016 C5 ii c 55016 C8 i a 43.518 47.877 42.89 0.661 0.283 1.038 9.704 6.21 10.605 0.237 BDL 0.2 0.031 0.056 0.037 10.747 12.84 9.223 12.002 12.208 11.69 0.602 0.63 0.586 17.594 15.437 18.896 0.015 0.031 BOL 0.794 0.423 1.045 0.852 0.386 1.125 1.966 1.951 1.962 0.106 · BOL BDL 0.005 0.004 0.01 98.442 98.728 99.307 C) Amphibole (suite) 55016 C8 i b 43 .613 1.025 9.626 0.191 0.018 9.425 11.722 0.516 19.138 0.012 0.967 1.012 1.885 0.16 0.012 99.322 55016 CIO i a 43.093 0.677 10.236 BDL BOL 10.135 12.082 0.64 17.497 0.015 0.747 0.887 1.952 BDL 0.006 97.967 55016 CIO i d 42.836 0.679 10.507 0.107 BOL 9.937 11.52 0.551 18.418 BOL 0.601 0.702 1.913 0.069 0.009 97.849 55131C3id 42.578 0.812 9.385 0.26 0.105 11.021 11.733 0.952 15.347 0.012 0.92 0.956 1.787 0.286 0.003 96.157 55313 C2 d 43 .807 0.707 11.031 0.025 0.006 9.772 Il .573 0.598 17.854 55131C13g 43 .997 ·0.682 9.846 BDL 0.061 10.562 11.717 0.95 16.96 BDL BDL 0.986 0.844 1.862 0.252 0.008 99.325 0.86 0.975 1.794 0.371 0.006 98.781 83 D) Épidote Échantillon Si02 (wt%) Ti0 2 Ab03 MgO CaO MnO FeO Na20 K20 H20 Total 55123 Cl h 38.196 0.091 25.869 BDL 23.45 0.205 8.745 0.004 0.007 1.858 98.425 31571 C2 a 37.884 BDL 26.135 3.287 22.807 0.432 2.856 BDL BDL 1.848 95.249 55305 C2 b 49.605 0.028 BDL BDL 6.223 0.143 0.01 4.46 40.09 100.559 55031 C4 c 50.595 0.012 BDL 0.008 3.56 0.016 0.023 4.496 40.912 99.622 E) Ilménite Échantillon Ti0 2 (wt%) Ab 0 3 V20 3 Cr20 3 Fe203 Nb20 3 MgO MnO FeO Total 84 F) Chlorite Échantillon Si02 (wt%) Ti0 2 Ah 0 3 Cr203 MgO CaO MnO FeO NiO ZnO Na20 K20 H 20 Total 12.327 0.649 0.623 29.086 55016 C9 i a 31596C5i~ 27.626 25.978 BOL 0.084 15.895 17.99 0.004 BOL 12.967 10.568 0.043 0.066 0.495 0.483 31.063 33.347 BDL BOL BOL 55016 C8 i c 25.785 0.772 18.549 BDL 0.253 BOL 0.003 Il.106 99.153 0.055 0.033 0.012 11.071 99.287 BOL 0.016 0.016 BDL 10.966 99.491 31596 C6 i d 25.087 0.053 19.517 31596ClOia 25.111 0.028 18.761 BOL BOL 10.047 0.013 0.412 33.012 9.891 0.019 0.549 32.387 0.018 0.111 0.017 0.001 10.782 97.675 0.032 0.015 0.026 10.945 99.159 55308 C4 c 25.705 0.037 21.086 0.039 14.672 0.028 0.861 24.969 0.029 0.278 BDL 0.01 Il .354 99.068 F) Chlorite (suite) 55313Clg 37.772 0.151 26.344 0.039 2.926 22.654 0.06 3.417 55313 Cl h 26.397 0.171 19.685 0.004 13.976 0.078 0.503 26.12 BDL BOL BOL 0.12 0.009 0.005 13.195 106.692 0.034 0.049 11.232 98.249 55313 C2 c 26.842 0.026 19.765 0.039 14.189 0.191 0.523 26.631 0.007 0.087 0.094 0.041 11.391 99.826 55313 C3 e 25.71 0.099 21.111 0.043 14.554 0.019 0.3 26.418 BDL 0.016 0.005 0.005 11.396 99.676 55123 C3 f 23.662 0.013 19.455 BDL 4.95 0.014 0.55 40.261 0.011 BDL 0.006 0.009 10.562 99.493 31571Clb 23.176 0.04 . 23.247 BDL 8.994 BDL 1.498 30.974 0.001 0.047 BDL 0.009 10.977 98.963 55313 C4 b 23.782 0.073 21.714 BOL 9.001 0.023 1.77 32.067 BDL BDL 0.01 0.012 10.952 99.404 85 Annexe 2 : Descriptions de forages et tranchées (en pochette)