Nicolas Gaillard
email: nicolas.gaillard@mail.mcgill.ca

Anthony E Williams-Jones

James R Clark

Philip Lypaczewski

Stefano Salvi

Stephane Perrouty

Nicolas Piette-Lauzière

Carl Guilmette

Robert L Linnen

Stéphane Perrouty

Affiliations

Mica composition as a vector to gold mineralization: Deciphering hydrothermal and metamorphic effects in the Malartic district, Quebec

Keywords: Canadian Malartic gold deposit, Mica mineral chemistry, Sulfidation-oxidation halo, Metamorphism, Exploration vectors

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Introduction

Canadian Malartic, in the southeastern Superior Province of Canada, is a world-class example of a low-grade, large-tonnage Archean gold deposit. It is located within, and immediately south of the Cadillac-Larder Lake fault zone, which marks the boundary between the Abitibi and Pontiac subprovinces. The Abitibi greenstone belt hosts many well-studied deposits that have been used to develop genetic and exploration models for Archean gold deposits worldwide. Most of the gold deposits are located along two major structures, the Porcupine-Destor fault zone to the north and the Cadillac-Larder Lake fault zone to the south (Fig. 1). Most of these deposits comprise relatively high gold grade quartz-carbonate±tourmaline veins (e.g., McIntyre-Hollinger, Sigma-Lamaque, Kirkland Lake) associated with carbonate-sericite±albite alteration (orogenic-type deposits; [START_REF] Robert | World-class Archaean gold deposits in Canada: An overview[END_REF][START_REF] Goldfarb | Distribution, character, and genesis of gold deposits in metamorphic terranes, Economic Geology and the bulletin of the Society of Economic Geologists, 100th Anniversary[END_REF], but also include gold-rich volcanogenic massive sulfide (VMS) deposits such as Horne, Bousquet and La Ronde-Penna [START_REF] Franklin | Volcanogenic massive sulfide deposits[END_REF]. Canadian Malartic contrasts with these vein-and VMS-related deposits in that the gold is mainly disseminated, and is associated with microveinlet stockworks and microcline-albite-biotite-carbonate-pyrite±white mica alteration. The gold mineralization is also spatially associated with quartz monzodiorite to granodiorite porphyritic intrusions that crosscut the Pontiac Group metaturbidites and Piché Group mafic-ultramafic metavolcanics. On the basis of these features, as well as the inferred nature of the ore fluid, Canadian Malartic has been classified as an oxidized intrusion-related deposit [START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF], a definition that incorporates many of the characteristics of the syenite-associated disseminated gold deposit model of [START_REF] Robert | Syenite-associated disseminated gold deposits in the Abitibi greenstone belt, Canada[END_REF].

Epigenetic gold-dominated deposits formed at different stages during the tectonic evolution of the Abitibi greenstone belt. The syenite-associated deposits are genetically related to Timiskaming-age alkaline magmatism, and are commonly overprinted by a penetrative foliation associated with regional metamorphism [START_REF] Robert | Syenite-associated disseminated gold deposits in the Abitibi greenstone belt, Canada[END_REF]. Quartz-carbonate vein systems, in contrast, generally formed during the main phase of crustal shortening (post-Timiskaming) under conditions close to peak metamorphism [START_REF] Mccuaig | P-T-t-deformation -fluid characteristics of lode gold deposits: evidence from alteration systematics[END_REF][START_REF] Groves | Gold Deposits in Metamorphic Belts: Overview of Current Understanding, Outstanding Problems, Future Research, and Exploration Significance[END_REF][START_REF] Robert | Gold Metallogeny of the Superior and Yilgarn Cratons[END_REF]. The study of these Archean deposits thus represents a major challenge because of the superposition of deformation, hydrothermal and metamorphic events, and common overprinting of primary geological features. Canadian Malartic is such an example, as mineralogical, textural, as well as structural lines of evidence collectively suggest a syn-kinematic, early-to syn-peak metamorphic timing for the gold mineralization.

Because mineral compositions record physico-chemical parameters of fluid-rock interaction (including temperature, pressure, pH, fO2 and ∑aS) and metasomatic processes (e.g., halogen partitioning in micas) associated with the mineralization (Munoz, 1984, Mikucki and[START_REF] Mikucki | The hydrothermal fluid of Archean lode-gold deposits at different metamorphic grades: compositional constraints from ore and wallrock alteration assemblages[END_REF][START_REF] Selby | Chemical composition of biotite from the Casino porphyry Cu-Au-Mo mineralization, Yukon, Canada: evaluation of magmatic and hydrothermal fluid chemistry[END_REF][START_REF] Neumayr | Oxidized and reduced mineral assemblages in greenstone belt rocks of the St. Ives gold camp, Western Australia: vectors to high-grade ore bodies in Archaean gold deposits?[END_REF][START_REF] Ayati | Chemical characteristics and composition of hydrothermal biotite from the Dalli porphyry copper prospect, Arak, central province of Iran[END_REF][START_REF] Bath | Biotite and Apatite as Tools for Tracking Pathways of Oxidized Fluids in the Archean East Repulse Gold Deposit, Australia[END_REF][START_REF] Pearce | Gold deposition caused by carbonation of biotite during late-stage fluid flow[END_REF], this information can be used to develop vectors toward ore zones. In the case of Canadian Malartic, however, extracting such vectors poses a challenge because of the complex patterns that result from superposed hydrothermal, tectonic and metamorphic events.

In this paper, we report results of an investigation of mica mineral chemistry in hydrothermally altered metasedimentary rocks in order to provide insights into the ore-forming conditions at Canadian Malartic.

Silicate-oxide-sulfide thermodynamic calculations have been conducted to assess the effects of sulfidation (∑aS), oxidation (fO2) and activity of K + , Fe 2+ and H + on biotite and white mica composition (cf. [START_REF] Froese | The graphical representation of sulfide-silicate phase equilibria[END_REF]Nesbitt, 1986a,b;[START_REF] Zaleski | Metamorphic petrology of Fe-Zn-Mg-Al alteration at the Linda volcanogenic massive sulfide deposit, Snow Lake, Manitoba[END_REF][START_REF] Hezarkhani | Factors controlling copper solubility and chalcopyrite deposition in the Sungun porphyry copper deposit, Iran[END_REF][START_REF] Spry | Sulfidation and oxidation haloes as guides in the exploration for metamorphosed massive sulfide ores[END_REF][START_REF] Rosenberg | The effects of sulfidation and oxidation during metamorphism on compositionally varied rocks adjacent to the Bleikvassli Zn-Pb-(Cu) deposit, Nordland, Norway[END_REF][START_REF] Heiligmann | The Role of Sulfate-Sulfide-Oxide-Silicate Equilibria in the Metamorphism of Hydrothermal Alteration at the Hemlo Gold Deposit, Ontario[END_REF]. In addition, the composition of biotite and white mica in non-mineralized metasedimentary country-rock around the deposit was determined to assess the effect of metamorphism on the composition of these minerals and evaluate their potential utility as vectors toward mineralization.

Multicomponent phase equilibria diagrams (pseudosections), constrained for specified bulk rock compositions typical of the metasedimentary host rocks, were calculated to model the expected composition of mica solid solutions under varying metamorphic P-T conditions. Our results demonstrate that biotite and white mica compositions provide a valuable tool to define fluid pathways in the hydrothermal system responsible for the formation of the Canadian Malartic deposit, and that it is possible to use these factors to map the distribution of alteration that defines the deposit footprint.

Geological Background

Regional geology

The Abitibi greenstone belt consists of a succession of volcano-stratigraphic units formed from multiple episodes of tholeiitic to calc-alkaline, mafic-ultramafic to felsic volcanism and coeval plutonism, ranging in age from 2750 to 2697 Ma (Figs.1-2; [START_REF] Ayer | Evolution of the southern Abitibi greenstone belt based on U-Pb geochronology: autochthonous volcanic construction followed by plutonism, regional deformation and sedimentation[END_REF][START_REF] Thurston | Depositional Gaps in Abitibi Greenstone Belt Stratigraphy: A Key to Exploration for Syngenetic Mineralization[END_REF]. These volcanic units are overlain by early turbidite-dominated metasedimentary sequences, including the Porcupine assemblage, as well as Kewagama and Cadillac equivalents [START_REF] Ayer | Evolution of the southern Abitibi greenstone belt based on U-Pb geochronology: autochthonous volcanic construction followed by plutonism, regional deformation and sedimentation[END_REF][START_REF] Thurston | Depositional Gaps in Abitibi Greenstone Belt Stratigraphy: A Key to Exploration for Syngenetic Mineralization[END_REF], which were deposited between 2690 and 2685 Ma (Fig. 1; [START_REF] Ayer | Overview of results from the Greenstone Architecture Project: Discover Abitibi Initiative, Ontario Geological Survey[END_REF]. Greywackes and mudstones of the Pontiac Group (~2682 Ma; [START_REF] Davis | U-Pb geochronology of Archean metasedimentary rocks in the Pontiac and Abitibi subprovinces, Quebec, constraints on timing, provenance and regional tectonics[END_REF][START_REF] Frieman | Constraints on the geodynamic evolution of the southern Superior Province: U-Pb LA-ICP-MS analysis of detrital zircon in successor basins of the Archean Abitibi and Pontiac subprovinces of Ontario and Quebec, Canada[END_REF] to the south, and of the Quetico Group (2690-2687 Ma; [START_REF] Zaleski | Geological evolution of the Manitouwadge greenstone belt and Wawa-Quetico subprovince boundary, Superior Province, Ontario, constrained by U-Pb zircon dates of supracrustal and plutonic rocks[END_REF] to the north, formed extensive flyschoid belts that were broadly coeval with Porcupine-type sedimentation. Alluvial-fluvial Timiskaming-type sediments (2677 to 2670 Ma; [START_REF] Corfu | U-Pb ages and tectonic significance of late Archean alkalic magmatism and nonmarine sedimentation: Timiskaming Group, southern Abitibi belt, Ontario[END_REF][START_REF] Ayer | Overview of results from the Greenstone Architecture Project: Discover Abitibi Initiative, Ontario Geological Survey[END_REF] were deposited unconformably on volcanic rocks or older sedimentary assemblages, and are mostly confined to the Porcupine-Destor and Cadillac-Larder Lake fault zones. The Timiskaming rocks constitute the youngest supracrustal assemblage in the southern Abitibi belt (Fig. 3; [START_REF] Thurston | Depositional Gaps in Abitibi Greenstone Belt Stratigraphy: A Key to Exploration for Syngenetic Mineralization[END_REF]. Syntectonic, pre-Timiskaming tonalite and granodiorite batholiths, as well as smaller porphyry plutons of calc-alkaline affinity, were emplaced from 2697 to 2685 Ma (Fig.3;[START_REF] Corfu | The evolution of the southern Abitibi greenstone belt in light of precise U-Pb geochronology[END_REF][START_REF] Sutcliffe | Plutonism in the southern Abitibi Subprovince; a tectonic and petrogenetic framework[END_REF][START_REF] Davis | Geochronology and radiogenic isotope geochemistry of plutonic rocks from the central Abitibi subprovince: significance to the internal subdivision and plutono-tectonic evolution of the Abitibi belt[END_REF], during the first episode of contractional deformation (D1; [START_REF] Robert | Syenite-associated disseminated gold deposits in the Abitibi greenstone belt, Canada[END_REF]. Late syntectonic intrusions and local extrusive equivalents were emplaced between 2681 and 2676 Ma, and display a close spatial and temporal association with Timiskaming sedimentation [START_REF] Davis | Geochronology and radiogenic isotope geochemistry of plutonic rocks from the central Abitibi subprovince: significance to the internal subdivision and plutono-tectonic evolution of the Abitibi belt[END_REF][START_REF] Ayer | Overview of results from the Greenstone Architecture Project: Discover Abitibi Initiative, Ontario Geological Survey[END_REF]. They include high-level plutons of sub-alkaline to alkaline magmatic affinity, ranging in composition from monzodiorite and quartz monzonite to syenite [START_REF] Feng | Geodynamic evolution of the southern Abitibi and Pontiac terranes: evidence from geochemistry of granitoid magma series (2700-2630Ma)[END_REF][START_REF] Sutcliffe | Plutonism in the southern Abitibi Subprovince; a tectonic and petrogenetic framework[END_REF], some of which are genetically related to gold mineralization [START_REF] Robert | Syenite-associated disseminated gold deposits in the Abitibi greenstone belt, Canada[END_REF]. Late-tectonic igneous activity is represented by biotite-muscovite S-type granite intrusions (e.g., Lamotte and Preissac-Lacorne monzogranite) and pegmatite, between 2670 and 2645 Ma [START_REF] Ducharme | Sm-Nd geochemistry and U-Pb geochronology of the Preissac and Lamotte leucogranites, Abitibi Subprovince[END_REF][START_REF] Davis | Geochronology and radiogenic isotope geochemistry of plutonic rocks from the central Abitibi subprovince: significance to the internal subdivision and plutono-tectonic evolution of the Abitibi belt[END_REF][START_REF] Ayer | Evolution of the southern Abitibi greenstone belt based on U-Pb geochronology: autochthonous volcanic construction followed by plutonism, regional deformation and sedimentation[END_REF].

A regional, post-Timiskaming, sub-greenschist (prehnite-pumpellyite) to amphibolite-facies metamorphic event affected all supracrustal units in the southern Abitibi and northern Pontiac subprovinces (Fig.3;Jolly, 1980;Dimroth et al., 1983b). This metamorphic event occurred between 2677 and 2643 Ma [START_REF] Powell | Conditions and timing of metamorphism in the southern Abitibi greenstone belt, Quebec[END_REF], and corresponds broadly to a major phase of deformation [START_REF] Wilkinson | Timing and kinematics of Timiskaming deformation within the Larder Lake -Cadillac deformation zone, southwest Abitibi greenstone belt, Ontario, Canada[END_REF]) that involved regional north-south compression and local strike-slip transpression (D2; [START_REF] Daigneault | Oblique Archean subduction: accretion and exhumation of an oceanic arc during dextral transpression, Southern Volcanic Zone, Abitibi Subprovince Canada[END_REF], and later dextral transcurrent deformation along major fault zones (D3). The main deformation event (D2) produced upright folds (F2), with concurrent development of an axial-planar penetrative schistosity, local thrusts and the overall east-west trending architecture of the Abitibi greenstone belt [START_REF] Robert | Syenite-associated disseminated gold deposits in the Abitibi greenstone belt, Canada[END_REF]. Contact metamorphic aureoles, which consist mainly of lower amphibolite facies assemblages, occur adjacent to syn-volcanic and syn-to late-tectonic intrusions; they are interpreted to have formed pre-to post-regional metamorphism [START_REF] Thompson | A New Metamorphic Framework for Gold Exploration in the Timmins-Kirkland Lake Area, Western Abitibi Greenstone Belt: Discover Abitibi Initiative[END_REF][START_REF] Robert | Gold Metallogeny of the Superior and Yilgarn Cratons[END_REF].

There were several gold mineralization events during the evolution of the Abitibi greenstone belt, the chronological distribution of which is correlated to the complex succession of volcano-magmatic, tectonic and metamorphic events (Fig. 3). Gold-rich VMS deposits formed during the late stages of bimodal volcanism (e.g., La Ronde-Penna, at 2698 Ma; [START_REF] Mercier-Langevin | The LaRonde Penna Au-Rich Volcanogenic Massive Sulfide Deposit, Abitibi Greenstone Belt, Quebec[END_REF] and pre-date regional episodes of deformation. Many intrusion-associated disseminated-stockwork gold deposits (e.g., syeniteassociated deposits; [START_REF] Robert | Syenite-associated disseminated gold deposits in the Abitibi greenstone belt, Canada[END_REF] are genetically related to Timiskaming-age (2677 to 2670 Ma; [START_REF] Ayer | Overview of results from the Greenstone Architecture Project: Discover Abitibi Initiative, Ontario Geological Survey[END_REF] alkaline magmatism. By contrast, mineralization usually characterized as 'orogenic' occurred during two distinct events. Most of this mineralization, represented by the quartz-carbonate vein systems of the Timmins-Val d'Or gold belt, formed during regional D2 deformation and is post-Timiskaming in age [START_REF] Robert | Gold Metallogeny of the Superior and Yilgarn Cratons[END_REF]. However, an early gold mineralization event [START_REF] Couture | Timing of gold mineralization in the Val-d'Or District, southern Abitibi Belt; evidence for two distinct mineralizing events[END_REF], interpreted to be associated with pre-metamorphic magmatic-hydrothermal activity, has been documented for the Norlartic (>2692 Ma) and Kiena (>2686 Ma) deposits of the Val d'Or camp [START_REF] Pilote | Minéralisations aurifères multiphasées dans la région de Val d 'Or : l'exemple de la mine Norlartic[END_REF][START_REF] Morasse | A pre-2686 Ma intrusion-related gold deposit at the Kiena Mine, Val d'Or, Quebec, southern Abitibi Subprovince[END_REF].

District-scale geology

Lithological units

The Canadian Malartic deposit is hosted mainly by three lithologies (Fig. 2), namely metaturbidites of the Pontiac Group (Sladen, Canadian Malartic and Gouldie orebodies), mafic to ultramafic metavolcanic rocks of the Piché Group (Barnat and East Malartic orebodies), and porphyritic quartz monzodiorite to granodiorite intrusions that crosscut all these lithologies [START_REF] Trudel | Synthèse des caractéristiques géologiques des gisements d'or du district de Malartic[END_REF]Helt el al., 2014). The Pontiac Group forms the northernmost domain of the Pontiac Subprovince, and consists of flyschoid sequences of greywacke to mudstone interlayered with minor, local mafic-ultramafic volcanic flows and rare iron formation (Fig. 2; Camiré and Burg, 1993;Camiré et al., 1993a;[START_REF] Benn | Crustal structure and kinematic framework of the northwestern Pontiac Subprovince, Quebec: an integrated structural and geophysical study[END_REF][START_REF] Ghassemi | Tectonic evolution of the Late Archean Pontiac Subprovince, Superior Province, Canada: Structural, metamorphic and geochronological studies[END_REF]. The pelitic wackes of the Pontiac Group display well-preserved primary sedimentary textures, including erosional bases, graded-bedding, as well as load casts and flame structures. Cyclical alternations of mudstone to greywacke beds, ranging in thickness from a few millimetres to about one metre, define partial Bouma sequences, typical of turbiditic sedimentation [START_REF] Card | Geology and mineral deposits of the Superior province of the Canadian Shield, Geology of Canada Series no. 7; in, Geology of the Precambrian Superior and Grenville provinces and Precambrian fossils in North America (Lucas, S. B; St-Onge[END_REF]. These sequences are interpreted to have developed in the context of a fore-arc accretionary wedge complex (Dimroth et al., 1983a;[START_REF] Card | A review of the Superior Province of the Canadian Shield, a product of Archean accretion[END_REF] or as a syn-orogenic foreland basin formed during uplift related to collision or shallow-angle subduction [START_REF] Kimura | A model of ocean-crust accretion for the Superior province, Canada[END_REF]Camiré and Burg, 1993).

The Piché Group consists of a narrow band (generally <1 km wide) of schistose volcanics that are spatially restricted to the Cadillac-Larder Lake fault zone [START_REF] Gunning | Région de Malartic, Québec[END_REF][START_REF] Simard | Multistage gold mineralization at the Lapa mine, Abitibi Subprovince: insights into auriferous hydrothermal and metasomatic processes in the Cadillac-Larder Lake Fault Zone[END_REF]. In the Malartic district, these rocks include variably strained blue-grey komatiites and tholeiitic basalts, as well as their talc-chlorite-carbonate altered equivalents [START_REF] Sansfaçon | The Malartic district[END_REF].

Felsic, borderline sub-alkaline (calc-alkaline) to alkaline feldspar-phyric intrusions, ranging from quartz monzodiorite (Sladen, Barnat, East Malartic zones) to granodiorite (Gouldie zone), crosscut the Pontiac and Piché group rocks [START_REF] Trudel | Synthèse des caractéristiques géologiques des gisements d'or du district de Malartic[END_REF]Helt el al., 2014). Quartz monzodiorite in the Sladen Zone (Fig. 4) is characterized by plagioclase and minor orthoclase phenocrysts (typically <6 mm in length) in a groundmass of quartz, plagioclase, biotite and chlorite with minor epidote, apatite, magnetite, titanite and zircon. These intrusions were emplaced at 2677-2679 Ma [START_REF] De Souza | Geology and hydrothermal alteration of the world-class Canadian Malartic gold deposit: genesis of an Archean stockwork-disseminated gold deposit in the Abitibi Greenstone Belt, Québec[END_REF]Clark et al., in prep.), synchronous with Timiskaming sedimentation to the north of the Cadillac-Larder Lake fault zone (2677.7±0.8 Ma; [START_REF] Pilote | L'architecture des groupes de Malartic, de Piché et de Cadillac et de la Faille de Cadillac[END_REF]. In the Malartic camp, these intrusions occur as structurallycontrolled, elongated stocks and dykes of limited width (usually <100 meters). Numerous mafic dykes and sills (<1 meter wide) intruded the Pontiac Group rocks and are interpreted by Camiré et al. (1993b) to be metamorphosed Mg-rich lamprophyres.

The Pontiac Group is bounded to the south by a granitoid-gneiss plutonic domain, which includes a pre-to syn-tectonic tonalitic suite (e.g., the Lac des Quinze batholith; [START_REF] Card | Geology and mineral deposits of the Superior province of the Canadian Shield, Geology of Canada Series no. 7; in, Geology of the Precambrian Superior and Grenville provinces and Precambrian fossils in North America (Lucas, S. B; St-Onge[END_REF], a syn-to late-tectonic (2685-2671 Ma) I-type monzodiorite-monzonite-granodiorite suite (e.g., the Lac Fréchette complex, the Lac Fournière pluton; [START_REF] Davis | U-Pb geochronology of Archean metasedimentary rocks in the Pontiac and Abitibi subprovinces, Quebec, constraints on timing, provenance and regional tectonics[END_REF] and a late-tectonic (2670-2645 Ma) S-type garnetmuscovite granitic suite (e.g., the Decelles batholith; [START_REF] Feng | Noble metal abundances and characteristics of six granitic magma series, Archean Abitibi Belt, Pontiac Subprovince; relationships to metallogeny and overprinting of mesothermal gold deposits[END_REF][START_REF] Mortensen | U-Pb age constraints for the magmatic and tectonic evolution of the Pontiac Subprovince, Quebec[END_REF]. The last of these is interpreted to have formed from the partial melting of Pontiac Group metasedimentary rocks [START_REF] Feng | Geodynamic evolution of the southern Abitibi and Pontiac terranes: evidence from geochemistry of granitoid magma series (2700-2630Ma)[END_REF].

Structural and metamorphic setting

The Pontiac Group displays a complex south-to southeast-vergent fold and thrust architecture that results from polyphase compressive deformation (Fig.3;[START_REF] Goulet | Stratigraphy and structural relationships across the Cadillac-Larder lake fault, Rouyn-Beauchastel area, Québec[END_REF][START_REF] Sansfaçon | The Malartic Gold District, Abitibi greenstone belt, Québec: Geological setting, structure and timing of gold emplacement Barnat, East-Malartic, Canadian Malartic and Sladen Mines. In: The northwestern Quebec polymetallic belt: a summary of 60 years of mining exploration[END_REF]Camiré and Burg;1993;[START_REF] Benn | Crustal structure and kinematic framework of the northwestern Pontiac Subprovince, Quebec: an integrated structural and geophysical study[END_REF][START_REF] Ghassemi | Tectonic evolution of the Late Archean Pontiac Subprovince, Superior Province, Canada: Structural, metamorphic and geochronological studies[END_REF][START_REF] Perrouty | Structural setting for Canadian Malartic style of gold mineralization in the Pontiac Subprovince, south of the Cadillac Larder Lake Deformation Zone, Québec, Canada[END_REF]. The first deformation event (D1) is represented by a series of NE-SW trending isoclinal anticlines and synclines (F1) and a weak penetrative axial planar schistosity (S1) (Fig. 5A-B; [START_REF] Sansfaçon | The Malartic district[END_REF]. The F1 folds are usually obscured by subsequent deformation (namely D2) and are rarely observed in the vicinity of the deposit, though they are inferred from local polarity inversions [START_REF] Perrouty | Structural setting for Canadian Malartic style of gold mineralization in the Pontiac Subprovince, south of the Cadillac Larder Lake Deformation Zone, Québec, Canada[END_REF]. The S1 foliation is a poorly-preserved, discrete fabric defined by preferential alignment of relict biotite crystals, which is most evident in F2 fold hinges where it occurs at a high angle to the S2 foliation (Fig. 5B; [START_REF] Fallara | Caractérisation géochimique, pétrographique et structurale : nouveau modèle métallogénique du camp minier de Malartic[END_REF]. The second deformation event (D2) is manifested by a series of NW-SE oriented (N115 to N135), upright S-shaped folds (F2) with fold axes plunging to the SE (Fig. 5C). The long limbs of the F2 folds strike approximately E-W and dip steeply to the north, whereas their short limbs strike approximately N-S [START_REF] Sansfaçon | The Malartic Gold District, Abitibi greenstone belt, Québec: Geological setting, structure and timing of gold emplacement Barnat, East-Malartic, Canadian Malartic and Sladen Mines. In: The northwestern Quebec polymetallic belt: a summary of 60 years of mining exploration[END_REF][START_REF] Trudel | Synthèse des caractéristiques géologiques des gisements d'or du district de Malartic[END_REF]. Folding was associated with a regionally pervasive axial-planar S2 foliation (Fig. 5D) defined by the preferential alignment of biotite, white mica, chlorite and elongated pyrrhotite-pyrite aggregates. The S2 foliation is the most prominent structural feature of the Pontiac Group in the Malartic area and strikes roughly parallel to the Cadillac-Larder Lake fault zone. It is interpreted to have developed early during the M2 regional tectono-metamorphic event (prior to peak metamorphic conditions, as discussed below).

The M2 metamorphic assemblages are typical of a Barrovian sequence [START_REF] Jolly | Metamorphic history of the Archean Abitibi belt, Metamorphism in the Canadian Shield[END_REF]Camiré and Burg, 1993;[START_REF] Piette-Lauzière | Métamorphisme régional du nord-est de la Sous-province de Pontiac, Abitibi, Québec[END_REF]. The metamorphic grade increases southward from upper greenschist (at the contact with the Cadillac-Larder Lake fault zone) to mid-amphibolite facies; the garnet isograd is crossed 1.5 kilometers south of the deposit and the staurolite isograd occurs about one kilometer further south (Fig. 2). These isograds are essentially parallel to the S2 fabric and to the Cadillac-Larder Lake fault zone, which further indicates that D2 deformation and prograde metamorphic recrystallization were broadly contemporaneous (Fig. 2). Peak metamorphic conditions in the metasedimentary rocks are indicated by the occurrence of almandine-rich garnet and staurolite (Fig. 5E-F). Cordierite may occur locally in the Malartic district as subhexagonal porphyroblasts that have been pseudomorphed by white mica (Fig. 5G).

Garnet occurs as euhedral (dodecahedral) to rounded crystals, some of which can be found as inclusions in randomly oriented staurolite poikiloblasts (Fig. 5E). The latter host linear trails of quartz and minor biotite inclusions that define an internal foliation (Si), which is identical to and continuous with the main S2 foliation, indicating their late-to post-kinematic formation with respect to D2. Peak metamorphism is thus considered to have been late-to post-D2 (Fig. 3; Piette-Lauzière, 2017). A late, N100-trending cleavage (S2') is observed locally in finer-grained, more aluminous metasedimentary rocks [START_REF] Trudel | Synthèse des caractéristiques géologiques des gisements d'or du district de Malartic[END_REF][START_REF] Desrochers | Structural evolution and early accretion of the Archean Malartic Composite Block, southern Abitibi greenstone belt, Quebec, Canada[END_REF][START_REF] Piette-Lauzière | Métamorphisme régional du nord-est de la Sous-province de Pontiac, Abitibi, Québec[END_REF], and is characterized by crenulation and micro-folding of previous fabrics, and locally by the rotation of syn-kinematic staurolite poikiloblasts containing spiral inclusion trails (Fig. 5E), which may indicate a shear component for late D2 deformation.

Late stage deformation (D3) is expressed through minor chevron folds as well as N045-and N330oriented kink bands [START_REF] Trudel | Synthèse des caractéristiques géologiques des gisements d'or du district de Malartic[END_REF][START_REF] Fallara | Caractérisation géochimique, pétrographique et structurale : nouveau modèle métallogénique du camp minier de Malartic[END_REF], and does not significantly overprint earlier fabrics. Retrograde metamorphism was recorded by local chloritization of biotite, and by white mica pseudomorphs after staurolite.

Distribution and structural controls of gold mineralization

The Canadian Malartic deposit is currently the largest operating gold mine in Canada with an annual production of ~ 585,000 oz Au (in 2016) from an open pit that was commissioned in 2011. Since then, mining operations have produced a total of 2.75 Moz Au (and 2.6 Moz Ag) with estimated total proven and probable reserves of 204 Mt @ 1.08 g/t Au or a total of 7.1 Moz Au (as of December 31, 2016;

Agnico-Eagle 2016 annual report). Between 1935 and 1983, the area produced 5.1 Moz Au at an average grade of 4.5 g/t, from four underground mines. The orebodies exploited by these mines collectively define a >3.5 kilometer long mineralized system including, from west to east, the Canadian Malartic (9.93 Mt @ 3.37 g/t Au historic production), Sladen (3.90 Mt @ 2.43 g/t Au), Barnat (4.55 Mt @ 6.20 g/t Au) and East Malartic (17.95 Mt @ 4.92 g/t Au) deposits (Fig. 4; Sansfaçon et al., 1987a,b;[START_REF] Trudel | Géologie de la Mine East Malartic -Région de Val d'Or[END_REF][START_REF] Trudel | Synthèse des caractéristiques géologiques des gisements d'or du district de Malartic[END_REF]. The overall endowment of the deposit is estimated at 16.3 Moz Au, based on proven and probable reserves, measured and indicated resources, plus historic and recent production.

Gold mineralization in the current Canadian Malartic mine area is associated with a broad zone of disseminated pyrite defining a semi-continuous halo of low-grade gold (0.3-1 g/t Au) enveloping variably developed, higher-grade (generally >1 g/t Au) stockworks, replacement zones and local breccias. Elongated, lens-shaped orebodies are controlled by second-order structures (Fig. 4) that are interpreted to have been the main pathways for hydrothermal fluids. These structures include the E-W trending Sladen Fault, a >3 kilometer-long subvertical to south-dipping ductile-brittle shear zone, which marks the contact between the metasedimentary rocks and the main porphyry stock in the western part of the deposit, and delineates the Piché-Pontiac contact in the east. It is usually defined by a narrow zone of mylonite (<5 meters thick) variably overprinted by brittle faulting characterized by local brecciation, cataclasite and gouge [START_REF] De Souza | Geology and hydrothermal alteration of the world-class Canadian Malartic gold deposit: genesis of an Archean stockwork-disseminated gold deposit in the Abitibi Greenstone Belt, Québec[END_REF]. Controlling structures also include NW-SE trending, north-dipping deformation zones that comprise faulted asymmetric S-shaped F2 folds, the axial planes of which are parallel to the S2 foliation (~N110). The fold hinges consist locally of high-strain zones that contain faultfill (shear) quartz-dominated veins, sub-orthogonal to the sedimentary bedding (e.g., in the Gilbert and Gouldie zones; De [START_REF] De Souza | Geology and hydrothermal alteration of the world-class Canadian Malartic gold deposit: genesis of an Archean stockwork-disseminated gold deposit in the Abitibi Greenstone Belt, Québec[END_REF]. In addition, the WNW-ESE trending Barnat Fault, a ~200 meter wide anastomosed deformation corridor within the Cadillac-Larder Lake fault zone marks the contact between the Piché (to the northeast) and Pontiac (to the southwest) groups [START_REF] Derry | The geology of the Canadian Malartic gold mine, N. Quebec[END_REF][START_REF] Sansfaçon | The Malartic district[END_REF][START_REF] Trudel | Synthèse des caractéristiques géologiques des gisements d'or du district de Malartic[END_REF]. This fault is manifested by intense shearing of ultramafic to mafic talc-chloritecarbonate schists and fracturing of more competent porphyritic quartz monzodiorite and diorite intrusions (Sansfaçon et al., 1987b).

Analytical Methods

Whole-rock analysis

A suite of 596 metasedimentary rock samples was analyzed for whole-rock major and trace element compositions. The samples were prepared using a combination of crushing, splitting and pulverizing (with mild steel). Major element concentrations were determined using XRF analysis on lithium metaborate-tetraborate fused glass by Actlabs, Ontario. Minor and trace element concentrations were measured using a combination of ICP-AES and -MS after sodium peroxide fusion by SGS, British Columbia. Trace element concentrations, including gold, were also measured by ALS, British Columbia, using ICP-MS after digestion by aqua regia. Carbon and sulfur concentrations were determined by SGS using IR combustion. Quality control involved systematic analysis (every 20 samples) of internal standards and blanks, as well as certified reference material USGS SDC-1 (Flanagan, 1976).

Fluoride and chloride concentrations were determined by ion-selective electrode analysis using a Mandel Scientific PC-Titrate automated titration system (Geoscience Laboratories, Ontario Geological Survey). Sample preparation utilized fusion of ~1.0 g of pulverized material mixed with sodium carbonate [START_REF] Pamer | Determination of Fluoride and Chloride Concentrations in Geological Materials by Ion Selective Electrode[END_REF]. The resulting glass was dissolved in deionized water and the pH of the solution was adjusted to 5.5 for the fluoride analysis and to less than 4 for the chloride analysis, using citric and nitric acids, respectively. The ionic strength of the solution was buffered using a mixture of organic compounds for the fluoride analysis, and sodium nitrate for the chloride analysis. Concentrations of fluoride and chloride were measured after diffusion of the analytes through an electrode ion-selective membrane.

Electron microprobe analysis

The chemical compositions of micas were determined using a JEOL JXA-8900L Electron Probe Microanalyzer at the Department of Earth and Planetary Sciences, McGill University. The analyses were carried out using wavelength-dispersive spectrometry with a 5 µm beam diameter, a 15kV accelerating voltage and a 20 nA beam current. Standard reference materials, including albite (Na), orthoclase (K, Al), diopside (Si, Mg, Ca), hematite (Fe), rutile (Ti), spessartine (Mn), chromite (Cr), zircon (Zr), Baorthoclase (Ba), fluorite (F) and vanadinite (Cl) were systematically measured for calibration and internal consistency between analytical sessions. Peak counting times during quantitative analyses were 20 s for Si, Al, Fe, Mg, K, Na, Ti and Mn; 40 s for Cl and Ca; 80 s for Ba and Zr; and 100 s for F. Average lower limits of detections were 0.13 wt% for fluorine and 0.01 wt.% for chlorine.

Hyperspectral imaging

Shortwave infrared (SWIR: 1000-2500 nm) reflectance spectra were acquired on drill-core samples using a Specim SisuROCK TM hyperspectral imaging system (Lypaczewski et al, in prep.). The hyperspectral camera resolution for drill core imaging was 1 mm per pixel, with each pixel attributed an infrared reflectance spectrum. In the SWIR domain, phyllosilicates display characteristic absorption features that are mainly affected by the interactions between the octahedrally-coordinated cations and the hydroxyl (OH -) group [START_REF] Hunt | Spectral signatures of particulate minerals in the visible and near infrared[END_REF][START_REF] Clark | High spectral resolution reflectance spectroscopy of minerals[END_REF]. For example, the Al-OH bond of white mica produces an absorption around ~2200 nm, and the Al(Mg,Fe)-OH bond of biotite produces an absorption around 2250 nm. Substitutions involving octahedral site cations are thus responsible for subtle shifts in the position of the absorption wavelength of phyllosilicates [START_REF] Mcleod | Chlorite infrared spectral data as proximity indicators of volcanic massive sulphide mineralisation[END_REF][START_REF] Duke | Near infrared spectra of muscovite, Tschermak substitution, and metamorphic reaction progress: Implications for remote sensing[END_REF]. The biotite Mg# (i.e., atomic Mg/[Mg+Fe]) and the white mica Al VI content were estimated by calibrating the spectral data (wavelength position of the cation-OH band) with quantitative electron microprobe analyses (Lypaczewski and Rivard, in prep.).

Hydrothermal Alteration and Gold Mineralization

Vein paragenesis

It is evident from the superposition of multiple episodes of veining that Canadian Malartic has had a complex hydrothermal history [START_REF] Derry | The geology of the Canadian Malartic gold mine, N. Quebec[END_REF][START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF][START_REF] De Souza | Geology and hydrothermal alteration of the world-class Canadian Malartic gold deposit: genesis of an Archean stockwork-disseminated gold deposit in the Abitibi Greenstone Belt, Québec[END_REF]. In this section, we use a simplification of the vein nomenclature introduced by De Souza et al. (2016). The earliest veins (v1) pre-date gold mineralization, are a few centimeters wide (commonly <5 cm) and consist mainly of quartz with lesser albite and traces of pyrite±galena. These veins are cut by thin (<1 cm) ore-stage quartz-biotite-calcite±(Fe-carbonate)-microcline-pyrite veinlets (v2) with narrow (<5 mm) biotite±(calcite-microclinepyrite) selvages . Native gold and Au-bearing tellurides occur within v2 veinlets and alteration envelopes in associated stockworks and pervasive alteration zones. In the NW-SE deformation zones (e.g., the Gilbert and Gouldie zones), quartz-dominated fault-fill sheeted veins (up to 1 meter in width) typically occur at a high angle to the sedimentary bedding in sheared F2 fold hinges [START_REF] De Souza | Geology and hydrothermal alteration of the world-class Canadian Malartic gold deposit: genesis of an Archean stockwork-disseminated gold deposit in the Abitibi Greenstone Belt, Québec[END_REF]. These veins contain the same mineral assemblage and are associated with similar alteration features as the v2 veinlets; they are interpreted to be part of the same hydrothermal event. Main-stage stockwork veinlets (v2) and fault-fill veins preferentially occur parallel to the S2 foliation (e.g., in F2 fold hinges; Fig. 7B-C) but are locally deformed and transposed by the D2 event; we interpret these veins to have formed early-to syn-D2 (Fig. 3). Coarse-grained veins (v3), historically referred to as 'pegmatitic' [START_REF] Derry | The geology of the Canadian Malartic gold mine, N. Quebec[END_REF], cut the v2 veinlets and related alteration and represent a marginal type of mineralization.

They are, for the most part, restricted to the porphyritic quartz monzodiorite intrusions along the Sladen Fault. The v3 veins consist of quartz, albite, white mica, orthoclase, carbonate minerals, tourmaline, rutile, pyrite and native gold [START_REF] Derry | The geology of the Canadian Malartic gold mine, N. Quebec[END_REF][START_REF] De Souza | Geology and hydrothermal alteration of the world-class Canadian Malartic gold deposit: genesis of an Archean stockwork-disseminated gold deposit in the Abitibi Greenstone Belt, Québec[END_REF]. In the porphyritic intrusions, v3 veins have a pink alteration halo (up to one meter wide) associated with the replacement of biotite by microcline-white mica-quartz-carbonates-pyrite-rutile±hematite. Shallow-dipping extensional quartz veins (v4) are inferred to have been associated with late movement along the Sladen Fault and postdated gold mineralization. Barren chlorite-calcite veinlets (<1 mm) are associated with D3 kink-bands (v5) and crosscut all earlier sets of veins.

Hydrothermal alteration

Disseminated gold mineralization at Canadian Malartic occurs within stockworks of quartz-biotitemicrocline-carbonate±pyrite veinlets (v2) and associated microcline-albite-biotite±(white mica)carbonate-pyrite pervasively altered wall-rocks (Figs.6-10;[START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF]. A lateral zonation adjacent to the main fluid pathways (e.g., Sladen and Barnat faults, NW-SE deformation zones) is evident from systematic variations in the hydrothermal alteration assemblage (Fig.8;[START_REF] De Souza | Geology and hydrothermal alteration of the world-class Canadian Malartic gold deposit: genesis of an Archean stockwork-disseminated gold deposit in the Abitibi Greenstone Belt, Québec[END_REF]. This alteration sequence is typified by proximal potassic (microcline±albite-phlogopite) and distal potassicsericitic (biotite-phengite-microcline±albite) assemblages (Fig. 11). Extensive pyritization, carbonatization (from proximal calcite-ankerite to distal calcite-only) and albitization, as well as local silicification and retrograde chloritization are prominent features of the alteration.

Proximal alteration is characterized by a yellowish/brown (in metasedimentary rocks) to beige/pinkish-colored (in quartz monzodiorite) replacement assemblage that obliterates primary host-rock textures (Fig. 6). It extends a few meters to a few tens of meters in width and is generally asymmetrical around the main hydrothermal corridors. Proximal alteration is typically associated with dense stockwork veining where it forms a halo adjacent to ore-stage quartz-biotite-carbonate-microcline±pyrite (v2) veinlets (Fig. 6A-B). These veinlets locally crosscut (Fig. 6E), but spatially coincide with zones of pervasive microcline-albite±quartz replacement. A hydrothermally-cemented, open-space filled stockwork breccia is commonly associated with zones of intense ore-stage veining (Fig. 6A; [START_REF] Beaulieu | Perigranitic gold deposit of Canadian Malartic (Québec): 3D modeling contribution to metallogenic interpretation Mémoire de Maîtrise en Sciences de la Terre[END_REF][START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF]. The innermost proximal alteration facies is dominated by a narrow zone (<5 m) of highly strained pervasively altered rocks (replacement-type), which typically delineates the structures that acted as pathways for hydrothermal fluids. In the Sladen Fault zone, the latter is defined by a strongly foliated mylonitic fabric, which suggests a syn-kinematic timing of hydrothermal alteration with respect to ductile deformation (Fig. 6-C; [START_REF] Fallara | Caractérisation géochimique, pétrographique et structurale : nouveau modèle métallogénique du camp minier de Malartic[END_REF][START_REF] De Souza | Geology and hydrothermal alteration of the world-class Canadian Malartic gold deposit: genesis of an Archean stockwork-disseminated gold deposit in the Abitibi Greenstone Belt, Québec[END_REF]. In metasedimentary rocks and quartz monzodiorite, the mineralogy of the proximal alteration assemblage is dominated by very fine-grained (<10 µm) microcline-albite±quartz with variable proportions of phlogopite (±white mica), carbonate minerals (calcite-ankerite±Fe-dolomite), quartz, pyrite and rutile (Fig. 6D-I). Phlogopite, carbonate minerals and quartz occur mainly within ore-stage veinlet (v2) alteration envelopes, and as stringers that formed interstitially between patches of microcrystalline microcline-albite replacement (Fig. 6E-H). Pyrite occurs as coarse euhedra (usually <2 mm) in these stringers as well as fine disseminations in the groundmass. Hematite is restricted to the quartz monzodiorite intrusions where it is closely associated with pyrite (Figs. 9B and11).

The proximal alteration grades outwards into a distal alteration envelope dominated by biotitephengite-microcline±albite-calcite-pyrite (Fig. 7), typically tens to hundreds of meters in width. The intensity of the distal alteration correlates with the density of ore-stage quartz-biotite-microcline-carbonate±pyrite stockwork veinlets (v2) and decreases progressively away from the hydrothermal fluid pathways. Distal alteration in metasedimentary rocks is characteristically blue/grey in color, which is attributed to abundant phengitic white mica and Mg-rich biotite (Fig. 7A-C), and also includes microcline, albite, quartz, calcite, pyrite, rutile and apatite. Increasing proximity to v2 veinlets is associated with progressive replacement of the host-rock plagioclase (An25-30) by fine-grained microcline and albite (Fig. 7C-E). Distal alteration was partly controlled by variations in grain-size and protolith composition.

Sericitization was best developed in mudstone layers because of the more aluminous composition of the latter relative to the coarser-grained greywacke (Fig. 7H-J). In quartz monzodiorite, distally-altered rock is medium grey (Fig. 7D) and changes progressively to a light-pink/beige color in the vicinity of v2 and v3 veins. This alteration consists of a biotite-albite-microcline-white mica-quartz-calcite-pyrite-rutile±hematite±barite assemblage, which typically occurs as patchy aggregates and stringers interstitially to albite-, microcline-, and sericite-altered feldspar phenocrysts.

Distribution of sulfide-oxide minerals

The zonal distribution of alteration was associated with a decrease in the total activity of sulfur species (∑aS) and oxygen fugacity (fO2) away from the main hydrothermal corridors. These variations are manifested by systematic changes in Fe-sulfide and (Fe-Ti)-oxide mineralogy (Figs.9 and 11), which were used as a framework for monitoring changes in physico-chemical conditions and ore-forming processes (cf. [START_REF] Nesbitt | Metamorphic zonation of sulfides, oxides, and graphite in and around the orebodies at Ducktown, Tennessee[END_REF]Nesbitt, 1986a,b;[START_REF] Spry | Sulfidation and oxidation haloes as guides in the exploration for metamorphosed massive sulfide ores[END_REF][START_REF] Neumayr | Oxidized and reduced mineral assemblages in greenstone belt rocks of the St. Ives gold camp, Western Australia: vectors to high-grade ore bodies in Archaean gold deposits?[END_REF][START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF]. Altered rocks within the ore shell contain pyrite and rutile as the main Fe-sulfide and oxide phases, indicating relatively elevated sulfidation and oxidation conditions for mineralization (Fig. 9A; [START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF]. In contrast, metasedimentary rocks beyond the ore shell are characterized by the assemblage pyrite-pyrrhotite-ilmenite±magnetite±(graphite), which is interpreted to have formed under relatively reduced conditions during the prograde metamorphism (Figs.9, 11;[START_REF] Pitcairn | Sources of Metals and Fluids in Orogenic Gold Deposits: Insights from the Otago and Alpine Schists, New Zealand[END_REF]. The appearance of fine-grained, subhedral to euhedral pyrite represents the most distal apparent mineralogical indicator of alteration associated with gold mineralization and delineates the outermost extent of the sulfidationoxidation halo (Fig. 12A). Pyrite in metasedimentary rocks beyond the ore shell is commonly aligned in the main foliation (S2) and shows increasing degrees of replacement by pyrrhotite±(chalcopyritepentlandite) with increasing metamorphic grade southwards (Fig. 9C-D). Rutile (and titanite) replace ilmenite in hydrothermally-altered metasedimentary rocks and its distribution coincides with the pyriteonly side of the pyrite-pyrrhotite transition at the edge of the ore shell (Fig. 11).

In the quartz monzodiorite, the oxidation-sulfidation gradient is manifested by the progressive replacement and overgrowth of magnetite by pyrite+hematite towards the ore zone (Fig. 9B). Igneous titanite was pseudomorphed by rutile±(calcite-hematite-pyrite) in hydrothermally-altered rocks (Fig. 9E), which is interpreted to have been controlled mainly by an increase in X(CO2) towards the hydrothermal fluid pathways [START_REF] Clark | Wall-rock alteration, Victory Gold Mine, Kambalda, Western Australia: processes and P-T-X(CO2) conditions of metasomatism[END_REF]. The fact that hematite and sulfate minerals are restricted to quartz monzodiorite (pyrite-rutile-hematite±barite/celestite) suggests that oxygen fugacity was internally (rock) buffered and that values of fO2 were higher (above the magnetite-hematite buffer) in the intrusions than in the adjacent metasediments (Fig. 11; [START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF]. This observation raises the possibility that the intrusions played a pivotal role in channelling oxidized hydrothermal fluids throughout the mineralized system (e.g., [START_REF] Bath | Biotite and Apatite as Tools for Tracking Pathways of Oxidized Fluids in the Archean East Repulse Gold Deposit, Australia[END_REF].

Gold mineralization and relationship with pyrite

Gold mineralization at Canadian Malartic occurs mainly in the form of native gold grains (generally <10 µm in diameter) and minor Au-(Ag-Bi-Pb)-bearing tellurides, including petzite (Ag3AuTe2), hessite (Ag2Te), calaverite (AuTe2) and altaite (PbTe) (Fig. 10; [START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF]. These minerals are associated with pyrite in ore-stage veinlets (v2), in alteration envelopes surrounding these veinlets and in zones of pervasive alteration. Native gold and the telluride minerals occur as inclusions and fracture-fillings in pyrite, along pyrite-pyrite grain boundaries, and with silicates and carbonates close to pyrite grains (Fig. 10A-E). Hydrothermal pyrite in the ore shell is characteristically zoned (Fig. 10A-B; [START_REF] Gao | Genesis of the Canadian Malartic, Côté Gold, and Musselwhite gold deposits: insights from LA-ICP-MS element mapping of pyrite, Targeted Geoscience Initiative 4: Contributions to the Understanding of Precambrian Lode Gold Deposits and implications for exploration B[END_REF] and, for simplicity, can be subdivided texturally into two generations. Early pyrite (H1) is rich in inclusions (including biotite, microcline, albite, carbonates, rutile) and forms the cores of crystals; it is typically overgrown by late, inclusion-free pyrite (H2). Pyrite H1 is characterized by higher Au-Ag-Bi-Te-Sb-Pb-Zn concentrations than H2, and displays complex oscillatory zonations that are manifested by rhythmic variations in Ni concentrations (Gaillard et al., in prep.). Inclusions of native gold and Au-(Ag)bearing tellurides occur mainly within pyrite H1, together with inclusions of ore-stage sulfides (e.g., chalcopyrite, galena and sphalerite). Gold along healed pyrite fractures is found in both pyrite subtypes (H1 and H2).

The textural association between native gold and pyrite (H1), together with the positive correlation of gold and whole-rock sulfur concentrations (r 2 =0.47 in metasediments), indicates that pyrite and gold mineralization are genetically related. Previous work [START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF] suggested that replacement of ferromagnesian silicates and iron oxides (including magnetite and ilmenite) by pyrite destabilized goldbisulfide complexes (Au(HS)2 -) in the mineralizing fluid and was responsible for the deposition of gold-bearing minerals at a temperature of ~475°C, under relatively oxidizing (just above the magnetitehematite buffer) conditions.

Textural and Compositional Characteristics of the Micas

Nature and distribution of the micas

Gold mineralization at Canadian Malartic is associated with widespread microcline-biotite±white mica potassic alteration that affected most lithotypes. In the proximal alteration zone, biotite generally forms small clusters of fine-to medium-grained crystals (<0.5 mm) and also occurs as biotite-quartz-carbonatespyrite stringers that develop interstitially between patches of microcline-albite±quartz replacement (Fig. 6E-J). In metasedimentary rocks, proximal biotite has a pale yellow to light brown/green color (typically attributed to a high Mg# and/or a high Fe oxidation state) and yellowish to greenish pleochroism (Fig. 6E,H). White mica is generally absent in proximal metasedimentary rocks (see Fig. 11); it is typically restricted to highly aluminous mudstone facies, where white mica occurs within and adjacent to biotite-quartz-carbonate-pyrite stringers as finely disseminated grains (<0.02 mm). In the quartz monzodiorite, white mica consists of unoriented laths (<0.3 mm) associated with biotite, quartz, carbonate minerals and pyrite, and as a partial replacement of feldspar phenocrysts.

Metasedimentary rocks that underwent distal alteration have a higher modal proportion of micas than in the proximal zone. Distal biotite is medium-brown in color and displays a subtle greenish pleochroism.

It commonly occurs within alteration envelopes of ore-stage v2 veinlets, and as elongated grains (<1 mm long) that collectively form braided stringers interstitial to detrital grains in the matrix (Fig. 7E-J). Distal white mica is finer-grained than the biotite (<0.1 mm), and consists of disseminated grains in the matrix.

Elongate prisms of biotite and white mica define a pseudo-foliation (Fig. 7F-G) that resulted from their preferential orientation orthogonal to stress during D2 deformation. Syn-deformation crystallization of alteration minerals is also evident from biotite (together with quartz, microcline and carbonates) in pyrite pressure shadows that consistently extend parallel to the pseudo-foliation (Fig. 7F-G, I-J).

The metamorphic grade in the Malartic district exceeded the biotite zone of the upper greenschist facies (south of the Cadillac-Larder Lake fault), and biotite and white mica are therefore common constituents of the pelitic metamorphic assemblage. Two generations of metamorphic biotite have been distinguished in the metasedimentary rocks beyond the ore shell (Fig. 5B). The main metamorphic foliation (S2) is defined by the preferential alignment of biotite flakes (generally >0.03 mm long) that are locally associated with white mica (developed preferentially in finer-grained metasedimentary layers), chlorite and sulfide minerals (ellipsoidal aggregates of pyrrhotite-pyrite-pentlandite; see Fig. 5F). An earlier metamorphic foliation (S1) is usually poorly preserved and is characterized by relict (corroded) crystals of biotite at a high angle to S2 in quartzo-feldspathic microlithons. Both metamorphic fabrics are best identified in F2 fold hinges (Fig. 5D), whereas S1 biotite has been rotated parallel to S2 elsewhere (F2 fold limbs). The S1 and S2 biotite have comparable optical properties; they are orange to dark brown colored and display a strong pleochroism (Fig. 5B). A late generation of retrograde chlorite occurs commonly as non-oriented flakes (cutting across the S2 foliation), as well as a partial replacement of biotite within and beyond the ore shell.

Mica composition

The major and minor element composition of biotite (79 samples; n=821; Table 1) and white mica (47 samples; n=485, Table 2) was analyzed (electron microprobe) in the metasedimentary rocks along a ~3.5 km north-south cross-section (P2) extending from the ore shell towards the Lac Fournière pluton (Fig. 12A). The mica stoichiometry was calculated on the basis of 20 O + 4 (OH,F,Cl) atoms according to the crystallochemical formula [X2Y4-6Z8O20(OH,F,Cl)4], with the site-specific occupancy determined following Pauling's rules (1929). Partition coefficients between coexisting biotite and white mica were calculated for a total of 47 metasedimentary rock samples and are presented in Appendix 1.

Biotite chemistry

The composition of biotite from hydrothermally-altered zones was distinguished from that of metamorphic biotite beyond the ore shell on the basis of the octahedral, tetrahedral and hydroxyl anion site chemistry. Figures 13 to 16 illustrate compositional changes as a function of distance from the Canadian Malartic deposit and emphasize the zonal distribution of the alteration, which is evident in the systematic decrease in biotite Mg# [molar Mg/(Fetotal+Mg)] away from hydrothermal fluid pathways (Figs. 11 and14A). Biotite is phlogopitic in composition within the proximal alteration zone (biotite Mg end-member; 0.72<Mg#<0.92) and is also enriched in Mg relative to Fe in the distal alteration zone (0.52<Mg#<0.72). By contrast, metamorphic biotite consistently has intermediate Mg# compositions (0.45<Mg#<0.58), which display a weak increasing trend southwards. There is no correlation between the whole-rock compositions of the metasedimentary precursors and biotite Mg#, indicating that the protolith did not exercise a control on the biotite chemistry. Microprobe analyses of coexisting metamorphic S1 and S2 biotite yield similar compositions (Table 1), which suggest that S1 biotite likely re-equilibrated during the M2 metamorphic event.

The mechanisms of element incorporation in biotite were evaluated by determining ratios of cations (or sum of cations) involved in potential substitution reactions from binary plots. A linear distribution and near-unity negative slope of -0.79 (r 2 =0.97) for Fe versus Mg (Fig. 14B) indicates that variations in the biotite Mg# in the octahedral site are accounted for mainly by the substitution Fe 2+ ⇔ Mg (annitephlogopite solid solution). The small deviation from unity suggests the presence of Fe 3+ in the crystal structure and/or participation of other substitution reactions, likely involving Ti 4+ , in determining the composition of the octahedral site. Our observations show that the Mg-rich biotite tends to incorporate a smaller proportion of Ti (Table 1), consistent with the observations of [START_REF] Henry | The Ti-saturation surface for low-to-medium pressure metapelitic biotites: Implications for geothermometry and Ti-substitution mechanisms[END_REF].

Increasing proximity to hydrothermal fluid pathways in altered rocks is manifested by a gradual decrease in the total Al concentration of the biotite, coincident with increases in Si and Fe+Mg contents (Fig. 13A-D). Significantly, Al concentrations in biotite of the proximal alteration zone range between 2.28 and 3.05 apfu (mean=2.69 apfu), and for the distal alteration between 2.70 and 3.09 apfu (mean=2.94 apfu). Metamorphic biotite beyond the ore shell is characterized by consistently higher Al concentrations, ranging from 3.08 to 3.48 apfu (mean=3.26 apfu). In addition, metamorphic biotite displays a progressive increase in the proportion of Al with increasing distance southwards, which is matched by a corresponding decrease in Si (tetrahedrally-coordinated) and Fe+Mg (octahedrally-coordinated) contents.

The overall charge associated with the substitution of Al IV for tetravalent Si was balanced through a coupled Tschermak exchange of Al VI for divalent Fe and Mg cations in the octahedral site: [(Fe 2+ , Mg 2+ ) VI + (Si 4+ ) IV ⇔ (Al 3+ ) VI + (Al 3+ ) IV ], as shown by a plot of Fe+Mg+Si vs. total Al (slope of -0.97; r 2 =0.90; Fig. 14D). This plot illustrates the decrease in the extent of the Si1(Fe,Mg)1Al IV -1Al VI -1 Tschermak exchange in biotite towards more aluminous compositions (in the direction of the siderophyllite-eastonite join) with increasing distance southwards (i.e., towards higher metamorphic grade; Fig. 14C).

Compositional variation in the biotite interlayer site consists of a general decrease in the K content (from 1.97 to 1.70 apfu), coincident with a progressive increase in Na content (from 0.00 to 0.09 apfu)

along the north-south P2 section southwards (Fig. 13E-F). The biotite anion site underwent significant substitution of fluorine (F -) for hydroxyl (OH -), which increased with increasing proximity to hydrothermal fluid pathways (Fig. 15A; Table 1); generally, chlorine (Cl-) concentrations are below the lower limit of detection. The fluorine concentration of biotite outside the ore shell is generally low (0.05-0.20 apfu; mean=0.09 apfu) and is nearly three times higher in the distal (0.12-0.77 apfu; mean=0.25 apfu), and proximal (0.04-0.89 apfu; mean=0.26 apfu) alteration zones. Fluorine incorporation into the hydroxyl site has been demonstrated experimentally and thermodynamically to be dependent on the octahedral site composition, halogen activity and temperature [START_REF] Zhu | F-Cl-OH partitioning between biotite and apatite[END_REF][START_REF] Munoz | F and Cl contents of hydrothermal biotites: a reevaluation[END_REF].

At Canadian Malartic, the fluorine content of biotite covaries with Mg# (Fig. 15D), in good agreement with the crystal-chemical Fe-F avoidance principle [START_REF] Munoz | F-OH and Cl-OH exchange in micas with applications to hydrothermal ore deposits[END_REF].

White mica chemistry

The zonal distribution of alteration features at Canadian Malartic is associated with systematic variations in white mica composition (Fig. 11). In altered metasedimentary rocks, white mica is characteristically phengitic in composition (Fe+Mg>0.6 apfu), as indicated by higher Si and Fe+Mg contents, as well as lower Al concentrations than metamorphic white mica (Fig. 17; Table 2). A trend toward muscovite end-member compositions is indicated by a progressive increase in total Al concentration and decreases in Si and (Fe+Mg) contents southwards (Fig. 17A-D). These relationships are largely controlled by a Tschermak exchange reaction (Fig. 18A), as demonstrated by the correlation (r 2 =0.99) and near-unity negative slope (m=-0.99) for (Fe+Mg+Si) vs. total Al (Fig. 18B). However, substitution mechanisms involving Fe 3+ (e.g., ferrimuscovite substitution, [(Fe 3+ ) VI ⇔ (Al 3+ ) VI ]) may have played a role in controlling the white mica composition, as evidenced by the deviation from the ideal Tschermak substitution line on a plot of (Fe+Mg) vs. total Al (slope of -0.64, r 2 =0.94 ; ideal slope of -0.5). Deviations from ideality might also be related to the contribution of Ti, which is more abundant in white mica from the altered zones (0.05-0.12 apfu) than from the unaltered rocks (0.03-0.06 apfu). In contrast to biotite, hydrothermal and metamorphic white mica cannot be distinguished on the basis of their Mg numbers and there is no evidence of systematic Fe-Mg substitution associated with alteration (Fe vs. Mg display a positive relationship with a r 2 value of 0.41).

The white mica interlayer site composition varies considerably (K=1.54-1.92, Na=0.03-0.30 apfu)

with increasing distance southwards from the deposit (Table 1). There is a general decrease in the white mica K content (Fig. 17E-F), coincident with increases in Na and Ba (towards a paragonitic muscovite composition). A substitution of Na and Ba for K is inferred from the correlation between (Na+Ba) and K (slope of -0.72, r 2 =0.82). The halogen content of white mica (F, Cl) is generally below the lower detection limit; F was detectable in only 47 out of 567 analytical points, reaching a maximum of 0.14 apfu.

Whole-Rock Geochemistry

The distribution and extent of alteration-related mass changes document a lithogeochemical zonation that reflects changes in the fluid-rock ratio and the strength of gold mineralization [START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF][START_REF] Pilote | Géologie Malartic[END_REF]. Mass change calculations (e.g., [START_REF] Maclean | Lithogeochemical techniques using immobile elements[END_REF], involving a comparison of the average composition of altered (n=576) and least-altered metasedimentary rocks (n=20), show that hydrothermal alteration was associated with enrichments in K2O, Na2O, S, C and loss on ignition (Fig. 12B-C; [START_REF] Gaillard | Mineralogical and geochemical vectors to ore: the alteration halo of the Canadian Malartic gold deposit[END_REF]. This observation is consistent with the mineralogical nature of the alteration assemblage (microcline-albite-biotite±white mica-carbonates-pyrite). Distal and proximal alteration in metasedimentary rocks are characterized by significant gains in potassium (average +66% and +161% compared to least altered equivalents, respectively), which define a lithogeochemical zoning with respect to gold mineralization (Fig. 12C). Progressive sulfidation around hydrothermal pathways was manifested by increasing mass gains in sulfur from unaltered Pontiac metasedimentary rocks through distal (average 0.75 wt.% S, corresponding to +384% compared to least altered equivalents) to proximal (average 2.69 wt.% S; i.e. +1740%) alteration zones (Fig. 12B). Most significantly, trace elements associated with hostrock sulfidation (Ag-Te-W-Bi-Mo-As-Sb-Pb) underwent steadily increasing mass gains towards gold mineralization, reaching concentrations several orders of magnitude higher in altered metasedimentary rocks than the least altered equivalents [START_REF] Gaillard | Mineralogical and geochemical vectors to ore: the alteration halo of the Canadian Malartic gold deposit[END_REF]. In general, ratios involving Fe, Mg, Ti and Al are essentially constant, suggesting that these elements were relatively immobile during alteration.

A subset of 79 samples collected along the P2 north-south cross-section (Fig. 2) was used to assess variations in the whole-rock fluorine content in hydrothermally altered metasedimentary rocks (Fig. 15B).

Unaltered metasedimentary rocks are characterized by low fluorine contents, ranging between 300 and 750 ppm (mean=485 ppm; n=34). Distal alteration in the metasedimentary rocks was associated with significant increases in fluorine content (325-2350 ppm; mean=809 ppm). Fluorine content in the proximal alteration zone is highly variable, ranging from 84 to 2825 ppm (mean=733 ppm; n=9). The lowest whole-rock and biotite fluorine contents are from the proximal alteration zone in drillhole DDH-1578 and correspond to strongly brecciated samples, suggesting that halogen devolatilization might have been facilitated by late fluid circulation in a permeable medium.

Hydrothermal Effects on Mica Composition

Physico-chemical controls on biotite composition

Steep gradients of sulfidation (∑aS) and oxidation (fO2) are indicated by systematic variations in the sulfide-oxide mineral assemblage outwards from the hydrothermal fluid pathways (Section 4.3; Figs.9 and 11). These variations coincide spatially with changes in the composition of ferromagnesian silicates (Figs.11,(13)(14). A strong positive correlation between the biotite Mg# and the whole-rock sulfur content (Fig. 16) suggests that increases in ∑aS-fO2 conditions affected biotite composition. Similar trends of magnesium enrichment in (Fe-Mg)-silicates have been documented for the sulfidation-oxidation haloes of many ore deposit types, including Cu- [START_REF] Hezarkhani | Factors controlling copper solubility and chalcopyrite deposition in the Sungun porphyry copper deposit, Iran[END_REF][START_REF] Boomeri | The Miduk porphyry Cu deposit, Kerman, Iran: A geochemical analysis of the potassic zone including halogen element systematics related to Cu mineralization processes[END_REF][START_REF] Wilkinson | The chlorite proximitor: A new tool for detecting porphyry ore deposits[END_REF] and Mo- [START_REF] Gunow | Fluorine in micas from the Henderson molybdenite deposit[END_REF] porphyry deposits, Archean Au deposits [START_REF] Heiligmann | The Role of Sulfate-Sulfide-Oxide-Silicate Equilibria in the Metamorphism of Hydrothermal Alteration at the Hemlo Gold Deposit, Ontario[END_REF][START_REF] Bath | Biotite and Apatite as Tools for Tracking Pathways of Oxidized Fluids in the Archean East Repulse Gold Deposit, Australia[END_REF], as well as metamorphosed VMS (Nesbitt, 1986a,b;[START_REF] Zaleski | Metamorphic petrology of Fe-Zn-Mg-Al alteration at the Linda volcanogenic massive sulfide deposit, Snow Lake, Manitoba[END_REF][START_REF] Spry | Sulfidation and oxidation haloes as guides in the exploration for metamorphosed massive sulfide ores[END_REF] and carbonate-hosted Pb-Zn deposits [START_REF] Chabu | The geochemistry of phlogopite and chlorite from the Kipushi Zn-Pb-Cu deposit, Shaba, Zaire[END_REF].

Thermodynamic modelling

Thermodynamic modelling of silicate-oxide-sulfide equilibria was conducted to assess the effects of varying ∑aS-fO2 on the stability and composition of biotite in altered rocks of the Canadian Malartic deposit. Phase relationships among the main alteration minerals and aqueous sulfur species were evaluated for the system Fe-O-H-S through a series of fO2-pH binary diagrams (Fig. 19) constructed for the inferred ore-forming conditions (475°C and 3kbars; [START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF]. The HCh Unitherm software [START_REF] Shvarov | HCh: a software package for geochemical equilibrium modelling, User's guide[END_REF] was used to derive thermodynamic data (log K) for reactions that define predominance fields and phase boundaries [START_REF] Johnson | SUPCRT92: A software package for calculating the standard molal thermodynamic properties of minerals, gases, aqueous species, and reactions from 1 to 5000 bar and 0 to 1000°C[END_REF][START_REF] Robie | Thermodynamic properties of minerals and related substances at 298.15 K and 1 bar (10^5 pascals) pressure and at higher temperatures[END_REF][START_REF] Shock | Inorganic species in geologic fluids: Correlations among standard molal thermodynamic properties of aqueous ions and hydroxide complexes[END_REF][START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF]. Given the absence of fluid inclusion constraints, the activity of potassium (aK + ) was set at 0.08 molal, as calculated by [START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF] from the equilibration of a low salinity fluid (NaCl=6 wt.%) with microcline and albite. The a-x relationships of biotite (a annite biotite ) and white mica (a muscovite white mica ) solid solutions were calculated from the thermodynamic properties of the endmembers using ideal on-site mixing models [START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF] for both the Fe-Mg and Tschermak substitutions (see Fig. 14). However, the two parameters make an antithetic contribution to the calculated activity of annite in the biotite solid solution. Increasing proximity to hydrothermal fluid pathways was indeed associated with biotite compositional trends away from the annite pole towards the phlogopite-eastonite join (Fe-Mg substitution; Fig. 14A) as well as towards the annite pole away from the siderophyllite-eastonite join (Tschermak substitution; Fig. 14C). The decrease in the calculated activity of the annite end-member with increasing proximity to hydrothermal corridors from metamorphic biotite outside the ore shell (log a annite biotite =-1.27) to distal and proximal biotite (log a annite biotite =-1.62 and -2.25, respectively) demonstrates that the biotite activity calculations were influenced mainly by variations in the Mg# of the biotite.

∑aS -fO2 controls on biotite composition

A series of fO2-pH diagrams (Fig. 19) illustrates the evolution of silicate-oxide-sulfide equilibria for increasing total activity of aqueous sulfur species (∑aS=0.1; 0.3; and 1 m), covering the range of ∑aS values commonly estimated for intrusion-related and orogenic-type gold mineralization in subamphibolite facies systems (e.g., [START_REF] Mikucki | Hydrothermal transport and depositional processes in Archean lode-gold systems: A review[END_REF]. At a low total activity of sulfur species (∑aS=0.1 m), the stability of ilmenite and the replacement of pyrite by pyrrhotite in metasedimentary rocks outside the ore shell constrain the metamorphic fluids to relatively reducing apparent conditions (log fO2 below -26, i.e., ~3.5 log fO2 units below the magnetite-hematite buffer). The occurrence of intermediate Mg# biotite and the common association with white mica in the metamorphic assemblage suggest weakly acidic conditions (pH ~ 4, with neutral pH at 475ºC and 3 kbars calculated to be ~4.8) for metamorphism beyond the ore shell (purple star in Fig. 19A). In the hydrothermal alteration assemblage, the presence of high-Mg# biotite, microcline, phengitic white mica (in the distal assemblage), pyrite and rutile, together with the absence of pyrrhotite indicate that oxygen fugacity was higher during ore formation (constrained to log fO2 ~ -21 at ∑aS=0.1 m, i.e., 1.5 log fO2 units above the magnetite-hematite buffer). In altered quartz monzodiorite, replacement of magnetite by hematite and the occurrence of sulfates support a relatively elevated oxidation state for the mineralizing fluid, close to the H2S-HSO4 -predominance field boundary. Stability relationships among K-silicates in hydrothermally-altered metasediments, including intense microclinization (Fig. 8) and paucity or absence of white mica (Figs.6 and 11) in the proximal alteration zone, suggest that pH evolved to higher values (≥5.2) upon interaction with a mildly alkaline ore-forming fluid, although increasing values of aK + could also account for the expansion of the stability field of microcline at the expense of that of white mica at constant pH, as will be discussed in the following section (see 7.2.1).

An increase in the activity of sulfur species associated with hydrothermal alteration results in the expansion of the pyrite stability field at the expense of pyrrhotite, hematite and magnetite (Fig. 19B-C).

Most importantly, higher ∑aS values cause a shift in the equilibria of sulfidation reactions that involve Fe-sulfides and silicates (biotite, white mica and microcline). As such, progressive sulfidation favors the stability of pyrite (together with microcline and/or white mica) over biotite as the dominant Fe-bearing mineral phase at the conditions of gold mineralization. In proximal alteration zones, these reactions are manifested by textures documenting the replacement of biotite by microcline and by an increase in the modal proportion of microcline and pyrite at the expense of biotite and white mica (Fig. 6E-J, Fig. 8). Iron sequestration by pyrite, in turn, affects the stability of (Fe-Mg)-silicates and promotes the stability of more magnesian biotite compositions [START_REF] Heiligmann | The Role of Sulfate-Sulfide-Oxide-Silicate Equilibria in the Metamorphism of Hydrothermal Alteration at the Hemlo Gold Deposit, Ontario[END_REF]. At ∑aS=0.3 m, intermediate Mg# metamorphic biotite would not be stable at the inferred ore-forming fO2-pH conditions (green star in Fig. 19B), and biotite stability would be restricted to magnesian compositions typical of distal and proximal alteration zones. At ∑aS=1 m, the stability of the annite end-member in biotite is further reduced at the expense of sulfides, and distal alteration zone biotite is superseded by proximal phlogopitic biotite in the ore assemblage, which would be the only stable biotite at these specific conditions (orange star in Fig. 19C).

Physico-chemical controls on white mica composition

The investigation of the major element chemistry of white mica (EPMA) and its spectral characteristics (Lypaczewski et al., in prep.) revealed systematic variations from near end-member muscovite in the metasedimentary rocks beyond the ore shell to more phengitic compositions in hydrothermally-altered rocks (Figs.11,(17)(18). In addition, the mineralogical zoning from proximal potassic (microcline-phlogopite-dominated) to distal potassic-sericitic (high-Mg# biotite-microclinephengite) alteration zones indicates subtle changes in the stability relationships among K-bearing hydrothermal alteration minerals. These variations are interpreted to reflect changes in physico-chemical parameters, and were used to map the spatial distribution and intensity of fluid-rock interactions, and to define activity gradients towards hydrothermal fluid pathways [START_REF] Halley | Footprints: hydrothermal alteration and geochemical dispersion around porphyry copper deposits[END_REF]. Calculations of equilibria involving microcline, biotite and white mica were achieved by balancing individual reactions using K + , Fe 2+ and H + , so that phase relationships within this system could be adequately described as a function of aFe 2+ /a 2 H + and aK + /aH + activity ratios [START_REF] Seedorff | Henderson Porphyry Molybdenum System, Colorado: I. Sequence and Abundance of Hydrothermal Mineral Assemblages, Flow Paths of Evolving Fluids, and Evolutionary Style[END_REF]. The relative effects of these parameters on the composition and stability of K-silicates were evaluated by computing phase relationships in a subset of the K-Fe-O-H system using the Unitherm HcH software, following the same methodology described in section 7.1.1.

The white mica compositional trends associated with increasing proximity to hydrothermal fluid pathways (Fig. 17) were shown to be controlled essentially by a Tschermak exchange reaction (Fig. 18). In contrast to biotite, the activity of the muscovite component in white mica (a muscovite white mica ) was therefore determined entirely by the Al VI content of the octahedral site [START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF]. As discussed in the previous section (see 7.1.1), the magnitude of the Fe-Mg substitution in distal and proximal alteration biotite (increase in Mg# towards hydrothermal fluid pathways) essentially masked the effects of the Tschermak exchange in the biotite activity calculations, preventing any assessment of the physicochemical controls on the Tschermak substitution. Therefore, the geochemical effects on the Tschermak exchange in white mica, modelled in this section, could serve as a proxy for understanding the controls on analogous trends in biotite (e.g., compositional variations towards the annite-phlogopite join).

Effects of K + , Fe 2+ and H + activities on white mica composition

Physico-chemical effects on the composition of white mica were investigated through the construction of a binary diagram illustrating phase equilibria among K-silicates as a function of aFe 2+ /a 2 H + and aK + /aH + activity ratios (Fig. 20). Equilibrium textures between metamorphic biotite and white mica of muscovitic composition (log a muscovite white mica =-0.11), the occurrence of ilmenite, and the absence of microcline in the metasedimentary rocks beyond the ore shell constrained geochemical conditions to relatively low values of aK + /aH + , with aFe 2+ /a 2 H + values buffered along the univariant boundary between the muscovite and biotite stability fields (purple star in Fig. 20). The presence of microcline in the distal alteration assemblage is consistent with an evolution towards higher values of aK + /aH + , concurrent with a decrease in aFe 2+ /a 2 H + in the direction of the invariant point defined by the coexistence of microcline, phengite (log a muscovite white mica =-0.25) and high-Mg# biotite (green star in Fig. 20). The absence or paucity of white mica from the proximal alteration assemblage in the metasedimentary rocks is further evidence for aK + /aH + conditions having increased towards hydrothermal fluid pathways with decreasing values of aFe 2+ /a 2 H + , which were buffered along the univariant boundary between microcline and phlogopitic biotite (orange star in Fig. 20).

In the modelled system, the compositional trend towards a more phengitic composition with increasing proximity to hydrothermal corridors was determined entirely by the aK + /aH + ratio, and is consistent with an increase in aK + and/or pH (Fig. 20). The overall decreasing trend in aFe 2+ /a 2 H + towards hydrothermal fluid pathways was mainly due to sequestration of Fe 2+ by pyrite. The contribution of the Tschermak substitution in biotite, however, is manifested by an increase in the activity of the annite end-member with increasing proximity to hydrothermal corridors, which effectively causes less aluminous biotite to be stabilized at the expense of microcline at higher pH and/or aFe 2+ (higher aFe 2+ /a 2 H + ). The spatial variation in the composition of white mica and biotite, the decline in the intensity of microcline alteration (Cf. Fig. 8) and the decrease in calculated potassium mass gains (Fig. 12C) are all consistent with progressive rock-buffering (decrease in the fluid-rock ratio) of a mildly alkaline, potassium-rich oreforming fluid away from the hydrothermal corridors [START_REF] Oliver | Modeling the Role of Sodic Alteration in the Genesis of Iron Oxide-Copper-Gold Deposits, Eastern Mount Isa Block, Australia[END_REF][START_REF] Cleverley | Comparing closed system, flow-through and fluid infiltration geochemical modelling: examples from K-alteration in the Ernest Henry Fe-oxide-Cu-Au system[END_REF]. The transition from proximal potassic to distal potassic-sericitic alteration is interpreted to record the passage of a metasomatic front along the fluid diffusion path [START_REF] Korzhinskii | The theory of metasomatic zoning[END_REF], as white mica stabilized in response to gradual equilibration of the fluid with the host-rock (progressive decrease in aK + and/or pH away from the hydrothermal centers).

Thermodynamic Modelling of Metamorphism

The well-constrained positive gradient of metamorphic pressure-temperature (P-T) conditions southwards of the Canadian Malartic deposit (Piette-Lauzière, 2017) was used as a framework in which to investigate the district-scale effects of metamorphism on the composition of biotite and white mica.

Multicomponent phase diagrams (pseudosections) were calculated for two representative samples of Pontiac metasedimentary rocks in order to model the composition of mica solid solutions under varying P-T conditions.

Mineral equilibria calculations

Metamorphic phase diagrams were computed for P-T conditions ranging from 425 to 675ºC and 2 to 10 kbar using the Perple_X software [START_REF] Connolly | An automated strategy for calculation of phase diagram sections and retrieval of rock properties as a function of physical conditions[END_REF][START_REF] Connolly | Computation of phase equilibria by linear programming: A tool for geodynamic modeling and its application to subduction zone decarbonation[END_REF] in conjunction with a recently updated version (ds6.2) of the internally consistent thermodynamic dataset of [START_REF] Holland | An improved and extended internally consistent thermodynamic dataset for phases of petrological interest, involving a new equation of state for solids[END_REF]. Mineral equilibria were calculated in the system MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3 (MnNCKFMASHTO), which enabled integration of a comprehensive range of mineral solutions for metasedimentary rock assemblages. Activity-composition (a-x) thermodynamic models used for the calculations included those for biotite, white mica, chlorite, garnet, orthopyroxene, staurolite, cordierite and melt from White et al. (2014a,b), epidote from [START_REF] Holland | An improved and extended internally consistent thermodynamic dataset for phases of petrological interest, involving a new equation of state for solids[END_REF], ilmenite from [START_REF] White | The effect of TiO2 and Fe2O3 on metapelitic assemblages at greenschist and amphibolite facies conditions: mineral equilibria calculations in the system K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3[END_REF] and feldspar from [START_REF] Fuhrman | Ternary-feldspar modeling and thermometry[END_REF]. As a first approximation, the system was considered to be CO2-free and saturated with respect to H2O. Bulk compositions used to constrain the calculations were determined from whole-rock XRF analysis. Ferric iron (Fe 3+ ) was fixed to Fe 3+ /Fe total=0.05 based on the average value for metasedimentary rock from drillhole CD08-D6 (as determined by FeO titration). The latter reflects the overall reducing nature of the protolith, although erratic occurrences of magnetite in the pelitic assemblage suggest local variations in the Fe 3+ content of the metasedimentary rocks.

Petrography and mineral chemistry

Calculations of metamorphic phase equilibria (P-T pseudosections) were constrained by bulk-rock compositions of two samples of non-altered, non-mineralized Pontiac Group metasedimentary rocks . These samples span the range from greywacke (sample K389136) to mudstone (K389232), and display distinct metamorphic assemblages. They are located 1.5 and 2.5 kilometers south of the southern edge of the Canadian Malartic open-pit, respectively (Fig. 2).

Sample K389136 displays a well-developed S2 fabric defined by the alignment of elongated biotitechlorite aggregates in a matrix of poorly-sorted medium-grained quartz and feldspar (Fig. 5F). The metamorphic assemblage includes garnet, and delineates the garnet-in isograd along the P2 section southwards (Fig. 12A). The garnet occurs as porphyroblastic dodecahedrons (~0.2 mm in diameter), and together with biotite, chlorite, plagioclase, quartz and ilmenite, corresponds to the peak metamorphic Sample K389232 is dominated by a higher-grade metamorphic assemblage that includes staurolite, garnet, white mica, biotite, chlorite, plagioclase, quartz and ilmenite (Fig. 5E). The main fabric (S2) consists of a zonal schistosity defined by the preferential orientation of phyllosilicates.

Pseudosection modelling

The stability relationships among metamorphic minerals in samples K389136 and K389232 were established through the construction of the P-T pseudosections presented in Figures 21 and22, respectively. The peak metamorphic conditions for mudstone sample K389136 (garnet-biotite-chloriteplagioclase-quartz-ilmenite assemblage) are reproduced in the pseudosection at lower amphibolite facies conditions, from 565 to 585ºC and 2.8 to 5.0 kbar (Fig. 21A). Field evidence indicates a general lack of cordierite in the metasedimentary rocks south of the deposit; considering the variability due to protolith composition, it is therefore likely that peak metamorphic conditions were in the higher pressure range, away from the cordierite-in iso-reaction line. These conditions were further constrained by calculating compositional isopleths for the garnet core composition (XCa=0.05 and Mg#=0.12), the intersection of which indicates metamorphism reached ~570ºC, 4.4-5.0 kbar. The calculated stability field of the peak assemblage closely coincides with the garnet-in iso-reaction line, in good agreement with the spatial proximity of sample K389136 relative to the garnet-in isograd (Fig. 2). The modelled compositions of plagioclase (An29) and chlorite (Mg#=0.57, Altot=5.61 apfu and Si=5.04 apfu) at the inferred peak conditions match almost perfectly the measured compositions. The textural evidence of replacement of ilmenite by rutile is consistent with a retrograde evolution of conditions through the stability field of rutile at a temperature below 500 ºC.

The peak metamorphic assemblage of greywacke sample K389232 consists of staurolite-garnet-white mica-biotite-chlorite-plagioclase-quartz-ilmenite, which is reproduced in the pseudosection at midamphibolite facies conditions, corresponding to a P-T range from 575 to 615ºC and 5 to 9 kbar (Fig. 22A).

These constraints were further refined by calculating compositional isopleths for garnet core composition (XCa=0.06 and Mg#=0.16) and staurolite (Mg#=0.19), which suggest that the peak metamorphic conditions reached ~585ºC, 5.2-6.4 kbar. This is consistent with the close spatial proximity of sample K389232 to the staurolite-in isograd line (Fig. 2). The compositions of plagioclase (An32) and chlorite (Mg#=0.61, Altot=5.44 apfu and Si=5.13 apfu) modelled for the sample at the above metamorphic conditions closely match those of plagioclase and chlorite as determined from electron microprobe analyses. Curved chlorite aggregates within rotated staurolite strain shadows suggests that shearing (interpreted as late D2) took place during the retrograde path, immediately after peak metamorphism (in the field of chlorite stability). The topology of the muscovite-out iso-reaction lines in samples K389136 (Fig. 21A) and K389232 (Fig. 22A) underlines the compositional controls of the sedimentary protolith composition on the white mica occurrence. In particular, the field of muscovite stability expands to higher temperature in the more aluminous mudstone (e.g., K389232).

The constraints on peak metamorphic conditions provided by samples K389136 and K389232, together with the locations of the garnet and staurolite isograds (Piette-Lauzière, 2017) permitted an evaluation of the metamorphic field gradient in the Malartic district . The absence of high grade metamorphic phases (e.g., garnet or staurolite) prevented an accurate estimate of metamorphic conditions in the upper greenschist environment immediately adjacent to the deposit. The surficial gradient was therefore extrapolated on the basis of a gradual increase in P-T conditions southwards, from upper greenschist facies (450-500ºC) in the vicinity of the Cadillac Larder Lake Fault Zone to midamphibolite facies (>550ºC) a few kilometers to the south (sample K389232). This metamorphic evolution is typical of Barrovian metamorphism, which is characterized by an intermediate P/T gradient;

the gradient for the Malartic district is estimated to be ~30°C/km.

Predictive evolution of metamorphic mica composition

Variations in the equilibrium metamorphic assemblage, including modal abundance and mineral chemistry, are determined entirely by the temperature, pressure and bulk composition of the system.

Systematic and progressive variations in the composition of biotite and white mica with increasing metamorphic grade have been documented for a number of metamorphic sequences in metasedimentary rocks and attributed to both continuous (e.g., Mg-Fe and Tschermak substitutions) and discontinuous, isograd-related reactions [START_REF] Thompson | The Tschermak substitution and reactions in pelitic schists, Problems in Physicochemical Petrology[END_REF][START_REF] Guidotti | Micas in metamorphic rocks[END_REF][START_REF] Miyashiro | Tschermak Substitution in Low-and Middle-grade Pelitic Schists[END_REF][START_REF] Pattison | Variations in Mg/(Mg+Fe), F, and (Fe,Mg)Si=2Al in pelitic minerals in the Ballachulish thermal aureole, Scotland[END_REF][START_REF] Dempster | Zoning and recrystallization of phengitic micas: implications for metamorphic equilibration[END_REF][START_REF] Ikeda | Progressive sequence of reactions of the Ryoke metamorphism in the Yanai district, southwest Japan: the formation of cordierite[END_REF].

Compositional isopleths were computed for biotite and white mica in samples K389136 and K389232

to model the effects of increasing metamorphic pressure and temperature conditions . In both samples, the results of the compositional modelling for the estimated peak metamorphic conditions are in good agreement with the measured compositions of the micas. In sample K389136, the model composition of peak metamorphic biotite (Fig. 21B-C) is predicted to have the characteristics (the analyzed values, in apfu, are indicated in the brackets): Si=5.28 (5.42), Altot=3.19 (3.41),Fe+Mg=5.36 (4.65) and Mg#=0.48 (0.53). The composition of the model biotite in sample K389232 (Fig. 22B-C) at peak metamorphic conditions is estimated to be (in apfu): Si=5.32 (5.36), Altot=3.14 (3.48), Fe+Mg=5.41 (4.76) and Mg#=0.53 (0.54). The corresponding model composition (in apfu) for the white mica is Si=6.05 (6.13), Altot=5.86 (5.64), Fe+Mg=0.09 (0.23) (Fig. 22D) and Na=0.46 (0.30) (Fig. 22E) (the analyzed values are indicated in the brackets).

The thermodynamic modelling results (Figs. 2122) portray the main compositional variations observed in biotite and white mica outside the ore shell along the P2 section (Figs. [13][14][17][18], including the progression of the Tschermak substitution towards more aluminous compositions with increasing P-T conditions southwards. The latter was likely controlled by continuous prograde reactions between coexisting phyllosilicate phases, with biotite (and biotite+garnet at higher grade) progressively forming at the expense of white mica and/or chlorite (Cf. [START_REF] Miyashiro | Tschermak Substitution in Low-and Middle-grade Pelitic Schists[END_REF][START_REF] Simpson | Phase relations, singularities and thermobarometry of metamorphic assemblages containing phengite, chlorite, biotite, K-feldspar, quartz and H2O[END_REF]. The Tschermak vector isopleth modelling in biotite (Figs. 21B and22B) and white mica (Figs. 21D and22D) shows comparable results in samples K389136 and K389232, which only diverge past the P-T limits of chlorite and muscovite stability. Minor discrepancies in the absolute estimate of the Tschermak vector in biotite and white mica are accounted for mainly by differences between the calculated Al and Fe+Mg contents compared to the measured compositions. These inconsistencies coincide with disparities between the observed and calculated chlorite and white mica modal abundances, which appear to be slightly, but consistently overestimated in the output model (Piette-Lauzière, 2017). Given that the extent of the Tschermak substitution in biotite and white mica is dictated entirely by exchange reactions with the coexisting phyllosilicate phases, we expect the disparities in the modeled mineral modes to affect the calculated magnitude of the cation exchange vectors. Such difference likely reflect inaccurate calibration of the thermodynamic parameters used to constrain the phyllosilicate activity-composition models [START_REF] Powell | On parameterizing thermodynamic descriptions of minerals for petrological calculations[END_REF]White et al., 2014a).

Isopleth modelling successfully depicts the progression of other important compositional gradients observed in micas beyond the ore shell, including the steady to weakly increasing trend in biotite Mg# composition (Fig. 14A) with increasing P-T conditions southwards (Figs. 21C and22C). In white mica, the modelled trend toward paragonitic muscovite along the P2 field gradient (Figs. 21E and22E) closely matches the measured increase in Na content (Fig. 17F). The thermodynamic modelling results therefore demonstrate that the district-scale compositional trends documented for biotite and white mica along the metamorphic gradient in non-altered metasedimentary rocks were most likely the product of the increasing P-T conditions southwards.

Discussion

Timing relationships

The precise timing of gold mineralization in metamorphosed terranes has long been a source of debate and remains controversial in the case of many Archean deposits due to the interplay of deformation, hydrothermal and metamorphic events [START_REF] Marshall | Discriminating between regional metamorphic remobilization and syntectonic emplacement in the genesis of massive sulfide ores[END_REF][START_REF] Ridley | Gold deposits in amphibolite and granulite facies terranes of the Archean Yilgarn Craton, Western Australia: evidence and implications of synmetamorphic mineralization[END_REF][START_REF] Groves | Gold Deposits in Metamorphic Belts: Overview of Current Understanding, Outstanding Problems, Future Research, and Exploration Significance[END_REF][START_REF] Goldfarb | Distribution, character, and genesis of gold deposits in metamorphic terranes, Economic Geology and the bulletin of the Society of Economic Geologists, 100th Anniversary[END_REF]. Deciphering the temporal relationships of ore-forming processes with respect to deformation and metamorphism is nonetheless critical to the interpretation of the complex mineralogical patterns that result from the superposition of these events.

The geometry of the Canadian Malartic deposit consists of elongate, lenticular ore zones hosted by second-order structures associated with D2 deformation. The NW-SE deformation zones are manifested by a series of faulted S-shaped F2 folds, with an axial-planar cleavage oriented parallel to the regional foliation S2 (Fig. 4). High-strain zones in sheared F2 fold hinge zones locally host fault-fill quartzdominated auriferous veins (e.g., in the Gilbert and Gouldie zones), which occur orthogonal to bedding (S0) and subparallel to S2 [START_REF] De Souza | Geology and hydrothermal alteration of the world-class Canadian Malartic gold deposit: genesis of an Archean stockwork-disseminated gold deposit in the Abitibi Greenstone Belt, Québec[END_REF]. Ore-stage (v2) stockwork veinlets are typically axialplanar to F2 folds, as they were preferentially emplaced and locally transposed by the S2 fabric; they were also locally folded and dismembered by D2 deformation. Hydrothermal alteration occurred synchronously with deformation, as demonstrated by the preferential alignment of alteration biotite and white mica parallel to the S2 foliation, and crystallization of alteration phases (including biotite, microcline and carbonates) in pyrite pressure shadows.

A broad synchronicity of the M2 metamorphic event with respect to the D2 deformation is indicated by the axial-planar setting of the S2 foliation in F2 folds. Textural relationships of garnet and staurolite porphyroblasts in the lower amphibolite facies further suggest that peak metamorphism was coeval with, or closely followed D2 deformation (Piette-Lauzière, 2017). In addition, hydrothermal alteration at Canadian Malartic occurred under thermal conditions that were broadly compatible with those of metamorphism, as suggested by the overlap between ore formation temperature constraints (~475°C; [START_REF] Helt | Constraints on the Genesis of the Archean Oxidized, Intrusion-Related Canadian Malartic Gold Deposit, Quebec, Canada[END_REF] and the P-T conditions for upper greenschist metamorphism inferred from pseudosection modelling. Mineralogical, textural and structural observations are thus consistent with a syn-kinematic (D2), early-to syn-peak metamorphic (M2) timing for the main ore-forming event at Canadian Malartic.

This interpretation is supported by geochronological data (Fig. 3), suggesting a gold mineralization event at 2664±11 Ma (Re-Os on molybdenite; De [START_REF] De Souza | Geology and hydrothermal alteration of the world-class Canadian Malartic gold deposit: genesis of an Archean stockwork-disseminated gold deposit in the Abitibi Greenstone Belt, Québec[END_REF] and peak metamorphism at 2657±7 Ma in the amphibolite facies immediately south of the deposit (Lu-Hf on garnet; Piette-Lauzière, 2017). The time gap between the inferred ore-stage event and quartz monzodiorite emplacement (2677-2679 Ma;

Clark et al., in prep.) seems to rule out a direct genetic relationship between gold mineralization and the host intrusions. The geochronological data therefore suggest a metamorphic overprint of the main oreforming event, but the errors associated with the age determinations also allow for a broad overlap between peak metamorphism and mineralization (Fig. 3).

Expression and preservation of a hydrothermal signature in the micas

The broad alteration halo around the Canadian Malartic deposit is delineated by steep sulfidation and oxidation gradients that decrease outwards from the ore zones. These variations are manifested by abrupt transitions in sulfide and Fe-Ti oxide mineralogy away from the hydrothermal fluid pathways. Within the ore shell, the sulfide-oxide mineralogy in the altered metasedimentary rocks is dominated by pyrite and rutile, indicating relatively oxidizing ore-forming conditions. Rutile in altered rocks is enriched in W (Clark et al., in prep.) and was stabilized at the expense of ilmenite under high ∑aS-fO2 conditions through the reaction FeTiO3 + 2H2S + 0.5O2=FeS2 + TiO2 + 2H2O (e.g., Nesbitt, 1986a,b). In contrast, ilmenite is the dominant oxide in metasedimentary rocks beyond the ore shell, and sulfides are characterized by variable degrees of replacement of pyrite by pyrrhotite±(chalcopyrite-pentlandite). This latter texture reflects the breakdown of pyrite to pyrrhotite with progressive metamorphic dehydration under reducing conditions, e.g., FeS2 + H2O=FeS + H2S + 0.5O2 [START_REF] Pitcairn | Sources of Metals and Fluids in Orogenic Gold Deposits: Insights from the Otago and Alpine Schists, New Zealand[END_REF][START_REF] Thomas | Pyrite and Pyrrhotite Textures and Composition in Sediments, Laminated Quartz Veins, and Reefs at Bendigo Gold Mine, Australia: Insights for Ore Genesis[END_REF]. In the altered rocks, the physico-chemical conditions were buffered to relatively high values of ∑aS-fO2, which inhibited the conversion of pyrite to pyrrhotite during metamorphism (e.g., [START_REF] Heiligmann | The Role of Sulfate-Sulfide-Oxide-Silicate Equilibria in the Metamorphism of Hydrothermal Alteration at the Hemlo Gold Deposit, Ontario[END_REF].

The preservation of a sulfidation-oxidation halo around the Canadian Malartic deposit greatly affected the equilibria among sulfides, oxides and silicates during coeval and/or subsequent metamorphism.

Increasing ∑aS-fO2 conditions, as well as high fluid-rock ratios proximal to the hydrothermal fluid pathways were the main factors controlling sulfur metasomatism (Fig. 12B), and caused pyrite to be gradually stabilized over biotite as the dominant Fe-bearing mineral phase. The strong positive correlation between whole-rock sulfur content and biotite Mg# (Fig. 16) indicates that iron sequestration in pyrite promoted the stability of magnesian biotite compositions in altered rocks (e.g., [START_REF] Hezarkhani | Factors controlling copper solubility and chalcopyrite deposition in the Sungun porphyry copper deposit, Iran[END_REF][START_REF] Spry | Sulfidation and oxidation haloes as guides in the exploration for metamorphosed massive sulfide ores[END_REF]. The broad covariation between fluorine and Mg# in biotite (Fig. 15D) further suggests that fluorine incorporation was facilitated in biotite of magnesian composition (Fig. 15A), consistent with the Fe-F avoidance feature as described by [START_REF] Munoz | F-OH and Cl-OH exchange in micas with applications to hydrothermal ore deposits[END_REF]. Furthermore, the positive correlation between bulk-rock and biotite fluorine contents (Fig. 15C) demonstrates that Fe-F avoidance in biotite was key to the preservation of a fluorine metasomatic halo around the deposit, which was presumably associated with the circulation of a fluorine-rich oxidized ore-forming fluid (Fig. 15B).

Metamorphic pseudosection modelling indicates that the district-scale compositional trends documented along the metamorphic gradient for biotite and white mica in non-altered metasedimentary rocks, including the progression of the Tschermak substitution towards more aluminous compositions, were most likely the product of increasing metamorphic P-T conditions southwards . The continuity of these trends along the P2 section from unaltered metasedimentary rocks through to distal and proximal hydrothermally-altered zones further supports a late-timing for peak metamorphism with respect to alteration (17)(18). Increasing proximity to hydrothermal fluid pathways, however, was manifested at the drill-hole scale by a Tschermak-controlled decrease in the total Al concentration of biotite and white mica (see Fig. 11), coincident with increases in Si and Fe+Mg contents. Equilibrium relationships among K-silicates in hydrothermally-altered zones (e.g., progressive microclinization towards hydrothermal fluid corridors) likely buffered physico-chemical conditions during metamorphism, which preserved the original alteration zonation pattern from proximal potassic to distal potassic-sericitic zones. Decreasing activity gradients of aK + and/or pH away from the mineralizing fluid pathways were the main controls on the Tschermak-exchange compositional trends and potassium metasomatism in altered metasedimentary rocks, and are attributed to progressive rock-buffering of a mildly alkaline, potassium-rich ore-forming fluid.

Mica mineral chemistry is therefore a sensitive indicator of hydrothermal and metamorphic processes in the Malartic district. On the basis of the compositional characteristics presented in this study, districtscale hyperspectral investigations of biotite and white mica (Lypaczewski et al., in prep.) permitted the delineation of a >10 km hydrothermal footprint extending laterally parallel to the main S2 foliation, which could be efficiently discriminated from the regional metamorphic signal. These results demonstrate that micas provide a powerful and cost-efficient exploration tool, which should prove particularly useful for defining mineral-chemical vectors to ore and mapping the zonation of alteration features that characterize the footprint of other major gold systems hosted in metamorphic terranes.

Conclusions

Biotite and white mica mineral compositions in altered metasedimentary rocks provide insights into the mineralizing conditions at Canadian Malartic and can be used to develop vectors toward ore zones.

Micas record the evolution of physico-chemical conditions associated with fluid-rock interactions, as well as metasomatic processes (e.g., sulfur and halogen additions). A systematic increase in biotite Mg# was associated with increasing ∑aS-fO2 conditions, reflecting greater degrees of sulfur metasomatism adjacent to fluid pathways. The Mg-rich biotite composition associated with alteration, in turn, facilitated the incorporation of fluorine (Fe-F avoidance feature), thus permitting the preservation of a fluorine metasomatic halo through coeval and/or subsequent peak metamorphism. Hydrothermal alteration was also manifested in biotite and white mica compositions by a Tschermak-controlled decrease in Al content, which resulted from decreases in aK + and/or pH upon gradual buffering of the ore-forming fluid with the metasedimentary host-rock.

The delineation of vectors that are useful for exploration for Canadian Malartic-type and related deposits is complicated by the mineralogical interference patterns resulting from the overlap and/or overprint of peak metamorphism with respect to gold mineralization. Thermodynamic modelling demonstrates that the district-scale compositional trends documented along the metamorphic gradient for biotite and white mica in non-altered metasedimentary rocks, including the progression of a Tschermak exchange reaction towards more aluminous compositions, were most likely the product of the increasing P-T conditions southwards.

This study shows that biotite and white mica compositions provide a valuable tool with which to define fluid pathways in the Canadian Malartic hydrothermal system. These parameters are particularly useful, in metamorphic terranes, for mapping the zonation of alteration features that characterize the footprint of major gold deposits, as they typically offer an excellent means for defining mineral-chemical vectors to ore. preferentially distributed along these two structures. Modified from [START_REF] Robert | Gold Metallogeny of the Superior and Yilgarn Cratons[END_REF](Compiled from MERQ-OGS 1983[START_REF] Robert | World-class Archaean gold deposits in Canada: An overview[END_REF][START_REF] Ayer | Evolution of the southern Abitibi greenstone belt based on U-Pb geochronology: autochthonous volcanic construction followed by plutonism, regional deformation and sedimentation[END_REF][START_REF] Thurston | Depositional Gaps in Abitibi Greenstone Belt Stratigraphy: A Key to Exploration for Syngenetic Mineralization[END_REF]. [START_REF] Perrouty | Structural setting for Canadian Malartic style of gold mineralization in the Pontiac Subprovince, south of the Cadillac Larder Lake Deformation Zone, Québec, Canada[END_REF]compiled after Derry, 1939;[START_REF] Gunning | Région de Malartic, Québec[END_REF]Minerais Lac Limited, unpublished reports and maps;Sansfaçon et al., 1987a,b;[START_REF] Fallara | Caractérisation géochimique, pétrographique et structurale : nouveau modèle métallogénique du camp minier de Malartic[END_REF]MERNQ airborne magnetic and outcrop data, SIGEOM Database, 2016). The forming events in the Pontiac and Southern Abitibi Subprovinces (modified from [START_REF] Bateman | The Timmins-Porcupine gold camp, northern Ontario: the anatomy of an Archaean greenstone belt and its gold mineralization: Discover Abitibi Initiative Ontario Geological Survey[END_REF][START_REF] Robert | Gold Metallogeny of the Superior and Yilgarn Cratons[END_REF][START_REF] Pilote | L'architecture des groupes de Malartic, de Piché et de Cadillac et de la Faille de Cadillac[END_REF]. General geochronological constraints are derived from [START_REF] Mortensen | U-Pb age constraints for the magmatic and tectonic evolution of the Pontiac Subprovince, Quebec[END_REF][START_REF] Ayer | Evolution of the southern Abitibi greenstone belt based on U-Pb geochronology: autochthonous volcanic construction followed by plutonism, regional deformation and sedimentation[END_REF][START_REF] Scott | Physical volcanology, stratigraphy, and lithogeochemistry of an Archean volcanic arc: evolution from plume-related volcanism to arc rifting of SE Abitibi Greenstone Belt, Val d'Or, Canada[END_REF][START_REF] Davis | U-Pb geochronology of Archean metasedimentary rocks in the Pontiac and Abitibi subprovinces, Quebec, constraints on timing, provenance and regional tectonics[END_REF][START_REF] Ayer | Overview of results from the Greenstone Architecture Project: Discover Abitibi Initiative, Ontario Geological Survey[END_REF]Frieman et al., 2017 and references therein. Numbers represent geochronological data for specific magmatic and metamorphic events, with associated errors indicated as brackets. 1: Lac Flavrian pluton [START_REF] Galley | Timing of synvolcanic magmatism in relation to base-metal mineralization, Rouyn-Noranda, Abitibi volcanic belt, Quebec, Radiogenic Age and Isotopic Studies: Report 15[END_REF]; 2:

Bourlamaque batholith [START_REF] Wong | U-Pb zircon and rutile chronology of Archean greenstone formation and gold mineralization in the Val d'Or region, Quebec[END_REF]; 3: Round Lake hornblende-granodiorite [START_REF] Mortensen | U-Pb geochronology of the eastern Abitibi Subprovince. Part 2: Noranda -Kirkland Lake area[END_REF]1993); 4: Lac Dufault pluton [START_REF] Mortensen | U-Pb geochronology of the eastern Abitibi Subprovince. Part 2: Noranda -Kirkland Lake area[END_REF]1993); 5: Lac Fournière pluton [START_REF] Davis | U-Pb geochronology of Archean metasedimentary rocks in the Pontiac and Abitibi subprovinces, Quebec, constraints on timing, provenance and regional tectonics[END_REF]; 6: Lac Fréchette pluton [START_REF] Mortensen | U-Pb age constraints for the magmatic and tectonic evolution of the Pontiac Subprovince, Quebec[END_REF]; 7: Canadian Malartic quartz monzodiorite (Clark et al., in prep.); 8a-b: Preissac pluton, muscovite-garnet monzogranite [START_REF] Ducharme | Sm-Nd geochemistry and U-Pb geochronology of the Preissac and Lamotte leucogranites, Abitibi Subprovince[END_REF]; 9a-b: Decelles complex, pegmatite units [START_REF] Mortensen | U-Pb age constraints for the magmatic and tectonic evolution of the Pontiac Subprovince, Quebec[END_REF]; 10: Lu-Hf on garnet (Pontiac Group), Malartic area (Piette-Lauzière, 2017); 11: U-Pb on monazite, Kidd Creek mine [START_REF] Davis | U-Pb dating of minerals in alteration halos of Superior Province massive sulfide deposits: syngenesis versus metamorphism[END_REF]; 12: 40 Ar/ 39 Ar on biotite, Destor area [START_REF] Powell | Conditions and timing of metamorphism in the southern Abitibi greenstone belt, Quebec[END_REF]; 13: U-Pb on titanite, Lac Opasatica orthogneiss [START_REF] Machado | U-Pb geochronology of granitoids from the Pontiac Subprovince: preliminary results[END_REF]. Abbreviations (lithostratigraphic formations): . 12A). A total of 47 samples were investigated and segregated into three categories according to their alteration characteristics, from least altered (purple), through distally altered (green) to proximally altered (orange) metasedimentary rocks. White mica from the proximal and distal alteration zones has higher Mg, Fe and Si concentrations (phengitic muscovite) than white mica beyond the ore-shell (A and B, respectively). There is a steady trend toward end-member muscovite composition southwards, indicated by a progressive increase in Al (D) and decreases in Si (C) and Fe+Mg. The interlayer site composition is strongly correlated with increasing distance away from the deposit; there is a general decrease in K concentration southwards (E), coincident with an increase in Na (F). Mineral abbreviations: ab: albite; bio: biotite; chl: chlorite; crd: cordierite; ep: epidote; gt: garnet; ilm: ilmenite; mu: muscovite; opx: orthopyroxene; pa: paragonite; pl: plagioclase; qz: quartz; ru: rutile; sph: titanite; st

  assemblage. It displays a very subtle concentric zoning (Piette-Lauzière, 2017), with a narrow range of Alm63→62, Prp9→8, Grs5, Sps22→24 (from core to rim). The biotite has the following compositional characteristics: Mg#=0.53, Altot=3.41 apfu and Si=5.42 apfu and the chlorite, which is in textural equilibrium with the biotite, classifies compositionally as ferroan clinochlore (ripidolite) with Mg#=0.57, Altot=5.58 apfu and Si=5.26 apfu. The plagioclase has an average composition of An29 (oligoclase), which varies little at the thin section scale, suggesting complete re-equilibration. Retrograde features are restricted to the rare partial replacement of ilmenite by fine-grained rutile and titanite. Sulfides are present in minor proportions and consist of aggregates of pyrrhotite±(chalcopyrite-pentlandite) that are aligned parallel to the S2 foliation.

  Fig.5E). They contain trails of quartz, biotite, white mica and ilmenite inclusions that define an internal foliation, continuous with the main S2 fabric. Chlorite occurs as a replacement of staurolite and as rare rosettes that crosscut the main foliation. The chlorite is compositionally homogeneous and consists of ferroan clinochlore (ripidolite), with Mg#=0.59, Altot=5.71 apfu and Si=5.16 apfu. Minor proportions of pyrite and pyrrhotite are distributed parallel to the main S2 fabric.

Figure 1 :

 1 Figure 1: Geological map of the Val d'Or-Timmins gold belt displaying the major lithostratigraphic units of the southern Abitibi and Pontiac subprovinces. The Cadillac-Larder Lake Fault Zone (CLLFZ) delineates the contact between the Pontiac and Abitibi subprovinces. The Porcupine-Destor Fault Zone (PDFZ) separates the Northern (NVZ) and Southern (SVZ) volcanic zones of the Abitibi. The most significantly endowed gold deposits are

Figure 2 :

 2 Figure 2: Geological map of the Canadian Malartic district (modified from[START_REF] Perrouty | Structural setting for Canadian Malartic style of gold mineralization in the Pontiac Subprovince, south of the Cadillac Larder Lake Deformation Zone, Québec, Canada[END_REF] compiled after

  map displays the main metamorphic features, including garnet-and staurolite-in isograds, as well as S0-1 and S2 foliations. The outline of the Canadian Malartic open-pit mine is represented as a yellow line. The locations of historic gold mines and occurrences are also shown. Coordinates are in UTM (NAD83-17N).

Figure 3 :

 3 Figure 3: Chronological sequence of volcanic, sedimentary, magmatic, deformation, metamorphic and ore-

  Figure 4: A. Lithological/structural map of the Canadian Malartic gold deposit (adapted from Pilote, 2014; and field mapping). The structures that acted as the main hydrothermal pathways for mineralizing fluids are highlighted as bold black lines (i.e., Sladen and Barnat Faults, NW-SE deformation zones). The trace of the sedimentary bedding (S0-1) and the main S2 foliation are from Perrouty et al., 2017; B. Distribution of gold grades in the Canadian Malartic deposit (all lithologies combined). Note the close spatial association of gold mineralization with the main hydrothermal fluid pathways (interpolated from Canadian Malartic Corporation gold assay data).

Figure 6 :

 6 Figure 6: Representative textural and mineralogical features of the proximal alteration assemblage. A: Hydrothermally-cemented, open-space filled stockwork breccia associated with intense ore-stage quartz-biotitecarbonate-microcline±pyrite (v2) veining in greywacke. Proximal yellowish/brown replacement occurs as an alteration envelope around v2 veinlets, and transitions outwards to a distal alteration assemblage; B: Proximal alteration in quartz monzodiorite consists of a beige/pinkish-colored replacement assemblage that obliterates the host-rock porphyritic texture. It is associated with dense stockwork veining and occurs an alteration halo adjacent to ore-stage (v2) veinlets; C: Innermost proximal alteration at the contact between greywacke and quartz monzodiorite porphyry (Sladen Fault zone). This facies is characterized by a mylonitic fabric (ductile deformation) associated with intense replacement-type alteration; D-F: Pervasive proximal alteration in greywacke, from thin-section (D) to microscopic scale (E: plane light; F: cross-polarized light). Stringers and fracture zones of phlogopite-carbonates-quartz-pyrite-rutile (v2 stage) develop interstitially between patches of microcrystalline (<10µm) microcline-albite±quartz; G-I: Beige/brown replacement-type alteration in greywacke, from thin-section (G) to microscopic scale (H-I, plane light). Ore-stage quartz-biotite-calcite-ankerite-microcline-

Figure 9 :

 9 Figure 9: Representative textural relationships for sulfide-oxide associations in the Malartic district. Systematic transitions in Fe-sulfide and (Fe-Ti)-oxide mineralogy are used as a framework for monitoring changes in physico-chemical parameters (e.g., ∑aS and/or fO2). A: Disseminated pyrite associated with rutile in distallyaltered greywacke (reflected light); B: Euhedral magnetite and titanite in igneous rocks are overgrown and partially replaced by pyrite-hematite-rutile in proximally-altered quartz monzodiorite (reflected light); C:

Figure 10 :

 10 Figure 10: Representative ore textures from the Canadian Malartic deposit. A-B: Backscattered electron images of zoned subhedral pyrite grains, which consist of an inclusion-rich core (H1) overgrown by an inclusion-free rim (H2). Inclusions of native gold and Au-(Ag-Pb)-bearing tellurides (petzite, sylvanite, calaverite), as well as biotite and ankerite are restricted to the pyrite core; C: Photomicrograph (reflected light) of native gold and (Ag-Pb)bearing tellurides, in close proximity to pyrite; D: Photomicrograph (reflected light) of native gold and tellurides (hessite and altaite) within silicates (microcline and biotite), adjacent to rutile (yellow internal reflections) ; E:

Figure 13 :

 13 Figure13: Average biotite composition (atoms per formula unit) in Pontiac Group metasedimentary rocks as a function of distance from the Canadian Malartic ore zone (pink-colored) along the north-south P2 section (see map in Fig.12A). A total of 78 samples were investigated and segregated into three categories according to alteration characteristics, from least altered (purple), through distally-altered (green) to proximally-altered metasedimentary rocks (orange). Biotite from the proximal and distal alteration zones has higher Mg and lower Fe concentrations than metamorphic biotite beyond the ore-shell (A and B, respectively). There is a broad decrease in biotite Si (C) and Fe+Mg contents, matched by a progressive increase in Al (D) with increasing distance southwards (towards higher metamorphic grade). Compositional variations in the interlayer site consist of a general decrease in the K content (E), coincident with a progressive increase in Na (F) along the north-south P2 section southwards.

Figure 14 :

 14 Figure 14: Compositional variations of biotite (Fe-Mg and Tschermak exchanges) in Pontiac Group metasedimentary rocks as a function of distance from the Canadian Malartic deposit (pink-colored) along the P2 section (see map in Fig.12A). Alteration characteristics are indicated from least altered (purple), to distally altered (green) and proximally altered metasedimentary rocks (orange). A: Biotite is phlogopitic within the proximal alteration zone (0.72<Mg#<0.92) and is also enriched in Mg relative to Fe in the distal alteration zone (0.52<Mg#<0.72). By contrast, metamorphic biotite consistently has intermediate Mg# compositions (0.45<Mg#<0.58), which display a weak trend increasing southwards. B: A linear distribution and near-unity negative slope of -0.79 (r 2 = 0.97) for Fe versus Mg indicates that variations in the biotite Mg# are due mainly to the substitution Fe 2+ ⇔ Mg (annite-phlogopite solid solution). C: Hydrothermal alteration is reflected by a decrease in biotite Al content away from the siderophyllite-eastonite join, associated with an increase in Si and Fe+Mg. Metamorphic biotite beyond the ore zone displays a progressive decrease in the extent of Tschermak exchange (towards more aluminous compositions) with increasing distance southwards (corresponding with increasing metamorphic grade). D: Correlation (r 2 =0.90) and near-unity negative slope (m = -0.97) for (Fe+Mg+Si) vs. total Al indicates that variations in biotite Al, Si and Fe+Mg concentrations are mainly controlled by Tschermak substitution [Si1(Fe,Mg)1Al IV -1Al VI -1]. Mineral abbreviations: Ann.: annite; East.: Eastonite; Phl.: phlogopite; Sid.: siderophyllite.

Figure 15 :

 15 Figure 15: Variations of biotite and whole-rock fluorine compositions in Pontiac Group metasedimentary rocks. Samples were segregated into three categories according to their alteration characteristics, from least altered (purple), through distally altered (green) to proximally altered (orange) metasedimentary rocks A: The fluorine concentration of biotite outside the ore zone is generally low (0.05-0.20 apfu) and is nearly three times higher in the distal (0.12-0.77 apfu), and proximal (0.04-0.89 apfu) alteration zones. The latter is characterized by a greater degree of scattering due to unusually low fluorine contents for proximally-altered samples from the DDH-1578 drill-hole (see location in Fig.12A). B: Whole-rock fluorine composition (n = 79) as a function of distance along the P2 section. Unaltered metasedimentary rocks are characterized by low fluorine contents, ranging between 300 and 750 ppm (mean=485 ppm; n=34). Distal alteration in the metasedimentary rocks was associated with significant increases in fluorine content (325-2350 ppm; mean=809 ppm). Fluorine in the proximal alteration zone is highly variable, ranging from 84 to 2825 ppm (mean=733 ppm; n=9). C: Average fluorine in biotite (in apfu) as a function of whole-rock fluorine concentration (in ppm). A broad covariation between these variables suggests that incorporation of fluorine in biotite was an important factor controlling the whole-rock fluorine budget. D: Average fluorine concentration (in apfu) against Mg# in biotite showing a broad covariation that is consistent with the crystal-chemical Fe-F avoidance principle.

Figure 16 :

 16 Figure 16: Average Mg# in biotite as a function of whole-rock sulfur concentration (a proxy for hostrock pyritization) in Pontiac Group metasedimentary rocks. A strong positive linear relationship between these variables (r 2 =0.80) indicates that increasing sulfur metasomatism towards hydrothermal fluid pathways was associated with progressively more magnesian biotite compositions. Alteration characteristics are indicated for least altered (purple), distally altered (green) and proximally altered (orange) metasedimentary rocks.

Figure 17 :

 17 Figure17: Average white mica composition (atoms per formula unit) in Pontiac Group metasedimentary rocks as a function of distance from the Canadian Malartic deposit (pink-colored) along the north-south P2 section (see map in Fig.12A). A total of 47 samples were investigated and segregated into three categories according to their

Figure 18 :

 18 Figure 18: A: Compositional variation of white mica (Tschermak exchange, in atoms per formula unit) in Pontiac Group metasedimentary rocks as a function of distance from the Canadian Malartic ore zone (pink-colored)along the north-south P2 section (see location in Fig.12A). The alteration color code is the same as in Fig.13. B:A linear distribution and near-unity negative slope of -0.99 (r 2 = 0.99) for (Fe+Mg+Si) vs. total Al indicate that variations in white mica Al, Si and Fe+Mg are mainly controlled by Tschermak substitution [Si1(Fe,Mg)1Al IV -

Figure 19 :

 19 Figure 19: Log(fO2)-pH diagrams illustrating silicateoxide-sulfide equilibria under increasing total activities of sulfur species (∑aS = 0.1; 0.3; and 1 m) at the inferred conditions of ore formation (475°C and 3kbar; Helt et al. 2014). The activity of potassium (aK + ) was fixed at 0.08 m (op. cit.). The activity of the annite component in biotite was determined for characteristic compositions of metamorphic biotite in metasedimentary rocks outside the ore shell and of hydrothermal biotite in the distal and proximal alteration zones (see text for calculation details).Corresponding iso-reaction contours (phase boundaries) for specific biotite compositions are represented using the same colour-code as in Fig.13. Inferred physico-chemical conditions are schematically symbolized as stars for the non-altered metamorphic assemblage (purple), and for the distal (green) and proximal (orange) alteration zones.

Figure 21 :

 21 Figure 21: A: P-T Pseudosection constructed for a typical Pontiac Group greywacke (sample K389136) in the MnNCKFMASHTO system. The plain ellipse corresponds to the inferred peak metamorphic conditions (the dotted ellipse refers to the inferred peak conditions in sample K389232; see Fig.22). The arrow represents the proposed surficial metamorphic gradient along the P2 section southwards (see location in Fig.12A). B-C: Calculated isopleths for the Tschermak exchange [Si1(Fe,Mg)1Al IV -1Al VI -1] and Mg# composition of biotite; D-E: Compositional isopleths for the Tschermak exchange and Na content of white mica. Mineral abbreviations: ab:

  . The activity of the annite component in biotite was determined for characteristic compositions of metamorphic biotite in the metasedimentary Consideration of the Mg# and Al VI compositional variables in the biotite activity calculations made it possible to account accurately

rocks outside the ore shell (Mg#=0.57; Al VI =0.56 apfu), and of biotite in the distal (Mg#=0.68; Al VI =0.46 apfu) and proximal (Mg#=0.81; Al VI =0.35 apfu) hydrothermal alteration zones.

  The quartz was recrystallized and, together with the plagioclase (An32), forms an equigranular mosaic of interlocked crystals with characteristic 120° triple junctions (granoblastic texture). Biotite in the matrix has the compositional characteristics, Mg#=0.54, Altot=3.48 apfu and Si=5.36 apfu; the white mica is muscovitic, with a substantial paragonite component (Na=0.30 apfu), Altot=5.64 apfu and Si=6.13 apfu. The garnet is subhedral in habit and displays weak core to rim zoning, with a compositional range of Alm67→69,

	Prp13→12, Grs6→5, Sps13. Staurolite (Mg#=0.19) occurs as homogeneously distributed poikiloblasts up to 5

mm in diameter, which consistently record a syn-kinematic rotation (

  Representative textural and mineralogical features of the distal hydrothermal alteration assemblage. A:

	Figure 8: Thin section blocks of metasedimentary rocks (n=98) from drillholes DDH 1578, 1216, 1705, 1205 and Figure 7: Quartz-biotite-carbonate-microcline±albite-pyrite ore-stage stockwork veining (v2) in a metasedimentary D1 (see Fig.12A for locations) were stained using sodium cobaltrinite to identify and evaluate K-feldspar
	mudstone-siltstone sequence. Proximal beige (microcline/albite-dominated) replacement occurs locally as an alteration (in yellow). The blocks are displayed with increasing depth down-hole. Gold grades (>20 ppb) are
	alteration envelope around v2 veinlets, and transitions outwards to a blue/grey (sericitic) distal alteration color-coded as a function of the alteration characteristics (proximal alteration in orange, distal alteration in
	assemblage. Sericitization was preferentially developed in the fine-grained mudstone facies; B-C: Distal green). Potassic alteration (in the form of pervasive microclinization) displays a close association with gold
	alteration in siltstone (B -from the Gouldie Zone) and greywacke (C -from the Gilbert Zone). Main-stage mineralization and intensifies with increasing proximity to the main hydrothermal fluid pathways.
	stockwork veinlets (v2) and associated alteration features preferentially occur parallel to the main foliation (S2)
	and are axial planar with respect to F2 folding (arrows represent the apparent D2 shortening direction); D:
	Medium-grey distal alteration in quartz monzodiorite occurs as a network of coalesced biotite±chlorite-
	carbonate-quartz-microcline-pyrite (v2) stringers interstitial to igneous feldspar phenocrysts. E-G: Stockwork-
	associated distal alteration in siltstone, from thin-section (E) to microscopic scale (F: plane light; G: cross-
	polarized light). Alteration phases (including quartz, biotite, microcline and carbonates) systematically crystallize
	). Ore-stage quartz-biotite-calcite-ankerite-microcline-in pyrite pressure shadows, which are preferentially oriented parallel to the pseudo-foliation defined by main-
	pyrite veinlets (v2) with narrow biotite-calcite±pyrite selvages. Mineral abbreviations: ab: albite; ank: ankerite;
	bt: biotite; cal: calcite; mic: microcline; py: pyrite; qz: quartz.

stage white mica and biotite; H-J: Protolith-controlled transition from proximal to distal alteration facies, from thin-section (H) to microscopic scale (I: plane light; J: cross-polarized light). Biotite forms stringers oriented orthogonally to the D2 principal stress and crystallizes in pyrite pressure shadows. Mineral abbreviations: ab: albite; bt: biotite; cal: calcite; mic: microcline; ph: phengite; py: pyrite; qz: quartz.

  Mineralogical, geochemical and hyperspectral variations down DDH-1578 (see location in Fig.12A) typify the zonation of alteration adjacent to the Sladen Fault. Hydrothermally-altered metasedimentary rocks contain pyrite and rutile as the main Fe-sulfide and (Fe-Ti)-oxide phases. In contrast, metasedimentary rocks beyond the alteration zone are characterized by a pyrite-pyrrhotite-ilmenite assemblage. Hydrothermal alteration

	associated with gold mineralization is characterized by increasing concentrations of S and K2O from unaltered
	metasedimentary rocks through distal to proximal alteration zones, which coincide spatially with changes in a ~3.5km north-south cross-section (P2) extending
	oxide-sulfide mineralogy. The TiO2/Al2O3 ratio of immobile elements was used to discriminate between the from the ore shell towards the Lac Fournière pluton
	to the south. The extent of the hydrothermal different host-rock lithologies. Mineralogical and geochemical variations are correlated with changes in biotite sulfidation/oxidation halo in metasedimentary rocks Mg# and white mica Al VI content. The hyperspectral profiles emphasize the zonal distribution of alteration, which is outlined by the outermost distribution of pyrite-
	is evident in the systematic increase in biotite Mg# [molar Mg/(Fetotal+Mg)] (2250 nm absorption) and in the only (as the only Fe-sulfide) samples (see text). The
	phengitic component of white mica (2250 nm absorption) towards hydrothermal fluid pathways (decrease in Al VI blue line delineates an envelope that contains <50 %
	of the investigated surficial samples (grey dots), but
	includes >75% of the pyrite-only samples; B-C:
	Maps illustrating sulfur (B) and potassium (C) mass
	changes in metasedimentary rocks from the
	Canadian Malartic district (in %, relative to least
	altered rocks). A lithogeochemical zoning with
	respect to gold mineralization is evident from
	increasing S and K2O mass gains towards the
	deposit.

Backscattered electron image (inset from D) detailing the textures of native

gold, hessite and altaite. Mineral abbreviations: alt: altaite; ank: ankerite; Au: gold; bt: biotite; ccp: chalcopyrite; hes: hessite; pet: petzite; mic: microcline; ph: phengite; py: pyrite; rut: rutile; syl: sylvanite. Figure 11: content)

. The width of the color bar represents the standard error associated with the regression. The oxidesulfide mineralogy was determined through thin section optical microscopy and scanning electron analysis.

Concentrations of Al2O3, TiO2, K2O and S were measured by pXRF analysis at the Memorial University of Newfoundland (analytical procedure as in

[START_REF] Piercey | Analysis of powdered reference materials and known samples with a benchtop, field portable X-ray fluorescence (pXRF) spectrometer: evaluation of performance and potential applications for exploration lithogeochemistry[END_REF]

and cross-calibrated using whole-rock analyses determined from conventional methods. Mineral abbreviations: brt: barite; hem: hematite; ilm: ilmenite; mag: magnetite; po: pyrrhotite; py: pyrite; rut: rutile; tit: titanite. Figure 12. A: Lithological/structural map (A) of the Canadian Malartic gold district (adapted from

[START_REF] Perrouty | Structural setting for Canadian Malartic style of gold mineralization in the Pontiac Subprovince, south of the Cadillac Larder Lake Deformation Zone, Québec, Canada[END_REF]

. Samples investigated for mica mineral chemistry were collected from a series of drillholes (represented as colored circles) that define

  : staurolite.

		0.00	0.01	0.06	0.03	0.00	0.06	0.00	0.04	0.05	0.00
	Total Total	96.20 95.56	95.99 97.05	95.64 96.47	95.44 96.97	94.63 95.32	94.98 95.70	95.43 95.10	96.03 95.42	95.67 95.75	96.33 96.26
	Atoms per formula unit calculated on the basis of 20 O + 4 (OH, F, Cl) Atoms per formula unit calculated on the basis of 20 O + 4 (OH, F, Cl)
	Si Al IV Si Al IV	5.72 2.28 6.36 1.64	5.67 2.33 6.40 1.60	5.59 2.41 6.39 1.61	5.61 2.39 6.29 1.71	5.47 2.53 6.08 1.92	5.46 2.54 6.14 1.86	5.37 2.63 6.21 1.79	5.37 2.63 6.21 1.79	5.40 2.60 6.13 1.87	5.41 6.08 2.59 1.92
	Al VI Fe Al VI Mg Fe Ti Mg Mn Ti Cr Mn Cr	0.17 0.48 3.22 4.81 0.33 0.11 0.45 0.01 0.10 0.02 -0.01	0.37 1.04 3.23 4.10 0.22 0.16 0.50 0.01 0.11 0.01 -0.05	0.49 1.65 3.19 3.34 0.35 0.18 0.45 0.03 0.10 ---	0.44 1.57 3.27 3.37 0.34 0.23 0.39 0.03 0.11 0.02 -0.03	0.70 2.22 3.68 2.62 0.25 0.18 0.13 0.02 0.03 0.01 --	0.67 2.23 3.62 2.64 0.23 0.19 0.18 0.02 0.04 0.01 --	0.83 2.21 3.69 2.59 0.13 0.16 0.18 0.02 0.04 ---	0.80 2.23 3.68 2.55 0.12 0.17 0.19 0.02 0.05 0.01 --	0.87 2.14 3.76 2.51 0.10 0.19 0.14 0.01 0.04 ---	0.87 3.76 2.02 0.10 2.60 0.13 0.17 0.04 0.01 ---
	K Na K Ca Na Ba Ca Ba	1.84 0.01 1.91 -0.05 --0.01	1.94 0.01 1.83 0.02 0.04 -0.01 0.00	1.95 -1.91 -0.05 --0.01	1.85 0.01 1.81 -0.05 0.00 -0.01	1.81 0.03 1.76 -0.16 0.01 0.01 0.04	1.83 -1.71 -0.15 0.01 0.00 0.04	1.67 0.05 1.66 -0.21 0.01 -0.02	1.73 0.05 1.69 -0.20 0.01 -0.02	1.72 0.06 1.57 -0.32 0.01 -0.03	1.86 1.61 0.09 0.37 --0.01 0.04
	OH** F OH** Cl F Cl	3.12 0.88 4.00 ---	3.77 0.23 4.00 ---	3.75 0.25 3.94 -0.06 -	3.70 0.30 4.00 ---	3.91 0.09 4.00 ---	3.90 0.10 3.94 -0.06 -	3.90 0.10 4.00 ---	3.87 0.13 4.00 ---	3.90 0.10 4.00 ---	3.91 4.00 0.09 ---
	XMg XMg	0.91 0.58	0.80 0.70	0.67 0.57	0.68 0.53	0.54 0.37	0.54 0.43	0.54 0.59	0.53 0.60	0.54 0.57	0.56 0.56
	log (fH2O)/(fHF)	5.41	5.88	5.64	5.56	5.91	5.88	5.83	5.73	5.83	5.89
	* Total iron expressed as FeO
	** OH is calculated assuming full site occupancy

* Total iron expressed as FeO ** OH is calculated assuming full site occupancy

Acknowledgements

Financial support for this study was provided by grants from the Natural Sciences and Engineering Council of Canada (NSERC) and the Canada Mining Innovation Council through the NSERC Collaborative Research and Development Program. The SEG is acknowledged for providing a research grant to the first author. We are grateful to Canadian Malartic Corporation for offering logistical support, and for providing access to the drillcore database, and to François Bouchard, Kayla Helt, Carl Corriveau, Pierre de Chavigny, Johan Bergé, Matthieu Dessureault, Alain Hébert, René de Carufel, Antoine Sweet, Christian Tessier and Donald Gervais for assistance and advice during field work. Thomas Raskevicius and Guillaume Clouette-Gauthier are acknowledged for helping with fieldwork and drillcore sampling. Lang Shi is thanked for assistance with microprobe analyses. Steve Piercey and Matthew Crocker provided pXRF whole-rock analyses. We thank our fellow researchers of the Mineral Exploration Footprints Research Network (http://www.cmic-footprints.ca/) and industry sponsors for fruitful discussions throughout the course of this project: Gema Olivo, Robert Wares, Howard Poulsen, Marc Bardoux, Benoit Rivard, François Robert, Didier Béziat, Georges Beaudoin, Kurt Kyser, Jean-François Couture, Alan Galley, Michael Lesher and Charles Lafrenière-Bérubé provided continuous support and feedback. We are also indebted to John Walshe for a very thorough and constructive review. Finally, we acknowledge researchers of the Targeted Geoscience Initiative (TGI-4), Stéphane De Souza, Benoit Dubé, Patrick Mercier-Langevin, and geologists of the Ministère de l'Énergie et des Ressources Naturelles du Québec, Pierre Pilote and Patrice Roy, for constructive discussions. NSERC-CMIC Mineral Exploration Footprints Project Contribution 155.

Figure 5: Metamorphic and textural characteristics of unaltered Pontiac Group metasedimentary rocks from the Malartic district. A: isoclinal F1 fold overprinted by penetrative regional S2 foliation; B-D: relationship between S2 and S0-1 fabrics in a F2 fold hinge, from outcrop (C) to thin-section (D) to microscopic scale (B). The S1 foliation is a poorly-preserved fabric defined by oriented relict biotite at a high angle to the S2 foliation; E: photomicrograph of mudstone sample K389232 (see location in Fig. 2). The main fabric (S2) is defined by the preferential orientation of phyllosilicates (biotite, muscovite and chlorite). The peak metamorphic assemblage is representative of mid-amphibolite facies P-T conditions, as defined by the occurrence of staurolite and almandine garnet. Staurolite poikiloblasts record syn-kinematic rotation (interpreted as late D2); F: photomicrograph of lower-amphibolite facies greywacke sample K389136 (see location in Fig. 2). The S2 foliation is defined by elongated biotite and chlorite, which together with garnet, plagioclase and ilmenite reflect the peak metamorphic assemblage; G: randomly oriented aggregates of muscovite in pseudomorphs after an unidentified prograde metamorphic mineral (cordierite?) in garnet-staurolite bearing siltstone. Mineral abbreviations: bt: biotite; chl: chlorite; gt: garnet; ilm: ilmenite; ms: muscovite; pl: plagioclase; qz: quartz; st: staurolite.