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. (1993): (1) le gîte Corvet Est est encaissé dans des
basaltes d' arc en marge de plaque accrétés à une marge continentale; (2) la minéralisation
à Corvet Est est pré-métamorphisme avec des remobilisations tardives ; (3) les minéraux
opaques comprennent la magnétite, l' ilménite, la pyrite et la pyrrhotite; (4) l'or est
principalement disséminé dans des zones de cisaillement ; (5) la composition isotopique du
soufre et de l' oxygène est similaire.
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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)