Alteration and Cu-Zn Mineralization of the Turgeon Volcanogenic Massive Sulfide Deposit (New Brunswick, Canada)

Transcription

1 Alteration and Cu-Zn Mineralization of the Turgeon Volcanogenic Massive Sulfide Deposit (New Brunswick, Canada) Mémoire Erik Lalonde Maîtrise interuniversitaire en sciences de la Terre Maître ès sciences (M.Sc.) Québec, Canada Erik Lalonde, 2014

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3 Résumé Le gîte Turgeon est un sulfure massif volcanogène (SMV) riche en Cu-Zn, encaissé dans les roches volcano-sédimentaires ordoviciennes du Groupe de Fournier dans la Boutonnière Elmtree-Belledune, au Nouveau-Brunswick (Canada). Le Groupe de Fournier comprend les formations Devereaux et Pointe Verte, qui sont tous les deux composées de gabbros et de basaltes cousinés. Le gîte Turgeon est composé de deux lentilles de sulfures massifs Cu-Zn avec des stockwerks chalcopyrite-pyrite sous-jacents aux deux lentilles. La géochimie indique que les roches encaissantes sont des basaltes et des andésites d affinité tholéiitique de type MORB. Les roches encaissantes proximales aux lentilles de sulfures massifs sont composées de chlorite + quartz dans les zones stockwerks, tandis que les zones adjacentes aux lentilles de sulfures massifs sont altérées en calcite + sidérite + pyrite + talc. Les sulfures à Turgeon ont une valeur δ 34 S moyenne de 6.9 ( ), indiquant que le soufre est principalement dérivé de la réduction thermochimique de sulfate d eau de mer ordovicienne. iii

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5 Abstract The Turgeon deposit is a mafic-type Cu-Zn volcanogenic massive sulfide (VMS) deposit hosted in the Middle Ordovician gabbros, sheeted dykes, and pillow basalts of the Devereaux Formation of the Fournier Group in the Elmtree-Belledune Inlier, northern New Brunswick (Canada). The Turgeon deposit consists of two lensed-shaped Cu-Zn massive sulfide zones ( 100m Zinc, ) composed of pyrite, chalcopyrite, pyrrhotite, and sphalerite, underlain by chalcopyrite-pyrite stockworks. Trace element geochemistry indicates that the host rocks are composed primarily of tholeiitic basalts and andesites with mid-ocean ridge basalt (MORB) signatures. Alteration mineral assemblages of the footwall basalts proximal to mineralization are dominantly chlorite ± quartz in the stockwork zone, and calcite ± siderite ± pyrite ± talc near the massive sulfide lenses. Sulfides at Turgeon have an average δ 34 S of 6.9 ( ), indicating that sulfur was derived from thermochemical reduction of Ordovician seawater sulfate. v

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7 Table of contents RÉSUMÉ... III ABSTRACT... V LIST OF FIGURES... IX FOREWORD... XI CHAPTER 1 INTRODUCTION Generalities Objectives and methods Presentation of the article... 3 CHAPTER 2: ALTERATION AND CU-ZN MINERALIZATION OF THE TURGEON VOLCANOGENIC MASSIVE SULFIDE DEPOSIT (NEW BRUNSWICK, CANADA) INTRODUCTION REGIONAL GEOLOGY OF THE BMC Northern Miramichi Highlands Elmtree-Belledune Inlier (EBI) ANALYTICAL METHODS GEOLOGY OF THE TURGEON DEPOSIT Least altered basalt, andesite, and rhyolite Basalt and andesite epidote alteration Basalt and andesite chlorite alteration Lithogeochemistry CU-ZN VMS MINERALIZATION OF THE TURGEON DEPOSIT HYDROTHERMAL SULFIDE FACIES Chalcopyrite-pyrite stockwork Massive chalcopyrite-pyrrhotite ± pyrite Massive pyrite Pyrite-chalcopyrite-sphalerite breccia SULFIDE CHEMISTRY AND TEXTURES Pyrite Chalcopyrite Pyrrhotite Sphalerite ALTERATION GEOCHEMISTRY Chlorite geothermometry SULFUR ISOTOPE GEOCHEMISTRY COMPARISON TO VMS DEPOSITS OF THE BMC Tectonic setting Source of sulfur Sulfide mineralization Hydrothermal alteration COMPARISON TO OTHER APPALACHIAN VMS DEPOSITS The Buchans Camp VMS deposits, Newfoundland (Canada) The VMS deposits of the Rambler Camp and Wild Bight Group, Newfoundland (Canada) The Betts Cove and Tilt Cove VMS deposits, Newfoundland (Canada) CONCLUSION CHAPTER 3: GENERAL CONCLUSION BIBLIOGRAPHY APPENDIX 1: ANDESITE GEOCHEMISTRY, TURGEON APPENDIX 2: BASALT GEOCHEMISTRY, TURGEON vii

8 APPENDIX 3: RHYOLITE GEOCHEMISTRY, TURGEON APPENDIX 4: SULFIDE GEOCHEMISTRY, TURGEON APPENDIX 5: ELECTRON MICROPROBE DATA FOR PYRITE APPENDIX 6: ELECTRON MICROPROBE DATA FOR CHALCOPYRITE APPENDIX 7: ELECTRON MICROPROBE DATA FOR PYRRHOTITE APPENDIX 8: ELECTRON MICROPROBE DATA FOR SPHLERITE APPENDIX 9: ELECTRON MICROPROBE DATA FOR CHLORITE APPENDIX 10: SULFUR ISOTOPE DATA FOR SULFIDES, TURGEON APPENDIX 11: COMPARATIVE TRACE ELEMENT CONCENTRATIONS BETWEEN TURGEON AND THE VMS DEPOSITS OF THE BMC viii

9 List of figures Figure 1: Geologic map of the northeastern Appalachian Orogen Figure 2 : Regional geological map of the BMC and EBI Figure 3 : Geologic map of the EBI Figure 4 : Geologic map of the Turgeon deposit Figure 5 : Least and most altered rocks at Turgeon Figure 6 : Cross-section through A Figure 7 : Geochemistry of the volcanic rocks of the Turgeon deposit Figure 8 : Trace element composition of the Turgeon volcanic rocks Figure 9 : Tectonic affinity discrimination diagrams for Turgeon volcanic rocks Figure 10 : Schematic cross-section through FT Figure 11 : Geologic map of the Powerline showing Figure 12 : Photographs of the Powerline showing Figure 13 : Cu Zn Pb ternary diagrams Figure 14 : Photographs of different ore types at Turgeon Figure 15 : Photomicrographs of the four main sulfide facies at Turgeon Figure 16 : Cu, Zn, and trace element binary diagrams of sulfide mineralization Figure 17 : Zr TiO2 diagram of Turgeon volcanic rocks Figure 18 : Elemental mass changes of footwall volcanics, Turgeon deposit Figure 19 : Alteration box plot of the Turgeon volcanic rocks Figure 20 : Grant isocon diagrams of basalt and andesite Figure 21 : Chlorite classification diagram Figure 22 : Chlorite geothermometer, Turgeon deposit Figure 23 : δ34s values for pyrite, chalcopyrite, sphalerite, and pyrrhotite Figure 24 : Secular variations of sulfide and sulfate δ34s values of worldwide VMS deposits through geological time ix

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11 Foreword All of the chapters in this memoir, including the article in the second chapter, were entirely written by this author. The co-author of the article is Georges Beaudoin (Université Laval). Georges Beaudoin is also the research supervisor of this authors Master s project. This project has benefited from the support and collaboration of several people. I would firstly like to thank my research supervisor, Georges Beaudoin, for his geological expertise and guidance over the course of this study. I would also like to thank Éric David, Pierre Therrien, Martin Plante, and Marc Choquette of Université Laval for their help in acquiring quality data for this research project. The administrative aid of Guylaine Gaumond was also much appreciated. This research project was further made possible with the collaboration and financial support of Puma Exploration. I would like to thank Marcel Robillard, as well as Dominique Gagné, Sacha Marie-Boston, and Simon Bernier of Puma Exploration for both their geological insight and help in providing data for this research project. The geological expertise of Jim Walker of the Department of Natural Resources of New-Brunswick was also greatly appreciated. I would finally like to thank my family and friends (Émilie, Marion, Sheida, Antoine) for their moral support. xi

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13 Chapter 1 Introduction 1.1 Generalities The Turgeon Cu-Zn deposit is located 3 km south-west of the city of Belledune in northern New Brunswick, Canada. The deposit is part of the Bathurst mining camp (BMC), which was once considered to be one of Canada s most prominent base metal mining districts. In 2001, the BMC was responsible for producing 30%, 53% and 17% of Canada s total production of Zn, Pb and Ag, respectively (Goodfellow and McCutcheon, 2003). The Turgeon deposit consists of 15 claims that extend over an area of 218 hectares. Several exploration projects were undertaken at the Turgeon prospect since the early 1950s. In the early 1980 s, Esso Minerals undertook an exploration campaign that helped identify the Powerline and Beaver Pond Cu-Zn showings. Extensive drill core logging showed that the Turgeon deposit shared several geological characteristics similar to those that characterize volcanogenic massive sulfide (VMS) deposits. Kettles (1987) completed an MSc thesis and concluded that the mineralization at Turgeon showcased replacement textures and was synvolcanic in origin. Diamond drilling campaigns conducted in 1988 by Heron Mines confirmed the presence of two massive sulfide lenses on the property. In the early 1990s, existing drill holes were re-logged in order to better understand the geological architecture of the deposit. Based on drill core logging and whole rock geochemistry, Thurlow (1993) provided a revised geological map of the Turgeon prospect. He also classified and described the main geological units on the property, and came to the conclusion that Turgeon shared many characteristics with Cyprus-type VMS deposits based on its predominantly mafic volcanic host rocks and Cu-Zn rich massive sulfide lenses. In 2007, Puma Exploration acquired 100% of the Turgeon deposits property. Diamond drilling was undertaken in 2009 through 2011 in order to better constrain geologic 1

14 resources. This Master s research project has been undertaken in coordination with Puma Exploration. 1.2 Objectives and methods The Turgeon deposit is geologically different from the VMS deposits of the BMC. The different tectonic blocks of the BMC represent different portions of the Ordovician Tetagouche-Exploits back-arc basin (van Staal et al., 2003). The majority of the VMS deposits of the BMC are hosted in the middle Ordovician calc-alkaline felsic volcanic rocks and accompanying sedimentary rocks of the Tetagouche and California Lake groups, whereas the Turgeon VMS deposit is hosted in the slightly younger middle to late Ordovician tholeiitic mafic volcanic rocks of the Fournier Group (Goodfellow and McCutcheon, 2003). As a result, the VMS deposits of the BMC are classified in the felsicsilliciclastic group of Franklin et al. s (2005) lithotectonic VMS deposit classification, whereas the Turgeon deposit is classified in the mafic group. The Turgeon deposit and the VMS deposits of the BMC also feature contrasting types of sulfide mineralization as shown by their different Cu, Zn and Pb grades. The Turgeon deposit is characterized by massive pyrite-chalcopyrite along with brecciated sphalerite, whereas VMS deposits of the BMC are characterized by bedded pyrite-sphalerite-galena. This study therefore aims to place the Turgeon deposit within the regional geological framework of the BMC. In order to achieve this goal, the objectives of this study are the following: 1) Determining the geologic and tectonic setting of the Turgeon deposit by: Performing detailed geological mapping of rock outcrops coupled with extensive drill core logging. 2

15 Performing trace element lithogeochemical analyses on the host rocks to mineralization in order to geochemically classify them. 2) Characterizing the Cu-Zn mineralization and hydrothermal alteration by: Performing detailed petrographic studies on mineralization and alteration. Performing alteration lithogeochemical analyses in order to quantify element mobility. Performing microprobe analysis on sulfides and hydrothermal alteration minerals. Performing isotope studies on sulfides in order to identify the sources of sulfur. 3) Interpreting the paleoenvironment by: Comparing the geological characteristics of the Turgeon deposit to those of the VMS deposits of the BMC. Comparing the Turgeon deposit to similar Appalachian VMS deposits. 1.3 Presentation of the article The second chapter of this memoir consists of the article Alteration and Cu-Zn mineralization of the Turgeon volcanogenic massive sulfide (VMS) deposit (New Brunswick, Canada). The article will be submitted for scientific publication in Mineralium Deposita. The article has been entirely written by this author. The co-author of the article is Georges Beaudoin (Université Laval). The article begins by briefly describing the geological characteristics of the VMS deposits of the BMC and how they contrast to those of the Turgeon deposit. The regional geology of the BMC is then described in detail in order to characterize the tectono-stratigraphy of the Northern Miramichi Highlands (NMH) and Elmtree-Belledune inlier (EBI). A brief description of the analytical methods used in the study follows. The local geology of the 3

16 Turgeon deposit is then described, followed by petrographic and lithogeochemical descriptions of fresh and altered rocks. Petrographic and geochemical characteristics of different mineralization types are then described in detail. Hydrothermal alteration lithogeochemistry is then used to quantify major and trace element mobility. Sulfur isotopic data is used to determine the source of sulfur of the Turgeon deposit sulfides. The discussion compares the geological characteristics of the Turgeon deposit with those of the VMS deposits of the BMC, followed by a comparison to the Buchans, Rambler, Wild Bight Group and Tilt Cove/Betts Cove VMS deposits in Newfoundland, Canada. 4

17 Chapter 2: Alteration and Cu-Zn Mineralization of the Turgeon Volcanogenic Massive Sulfide Deposit (New Brunswick, Canada) 2.1 Introduction The Turgeon Cu-Zn volcanogenic massive sulfide (VMS) deposit is located in Belledune, New Brunswick, Canada, within the Bathurst Mining Camp (BMC). The BMC is located in the northeastern portion of the Appalachian Orogen, which is divided into several tectonic zones reflecting different paleogeographic settings within and marginal to the early Paleozoic Iapetus Ocean (Figure 1). The terrains were deformed and accreted to the Laurentian continental margin during the closure of the Iapetus Ocean in the Ordovician and Silurian. The BMC is located in the Dunnage zone of New Brunswick (Figure 1), which represents Cambro-Ordovician portions of the Iapetan ocean floor, along with island-arc, back-arc basin, and continental margin strata. Discovered in the early 1950s, the BMC has been one of Canada s most prominent base metal mining districts, hosting 25 VMS deposits with resources of 1 Mt or more (Goodfellow and McCutcheon, 2003). The camp hosts the world-class Brunswick 12 deposit that has produced 229 Mt grading 7.66 wt% Zn, 3.01 wt% Pb, 0.46 wt% Cu, and 91 g/t Ag (Goodfellow and McCutcheon, 2003). Other notable VMS deposits in the camp include the Brunswick 6 (18.6 Mt; 1.59% Pb, 4.08% Zn, 0.45% Cu), Caribou (69.5 Mt; 1.60% Pb, 4.29% Zn, 0.51% Cu), and Heath Steele (69.9 Mt; 0.89% Pb, 2.69% Zn, 0.98% Cu) deposits. The VMS deposits of the BMC are hosted in the Lower to Middle Ordovician bimodal volcanic and sedimentary rocks of the Tetagouche-Exploits continental back-arc basin. They belong to the felsic-siliciclastic group of Barrie and Hannington (1999) s, as modified by Franklin et al. (2005), lithotectonic VMS classification. The significant VMS deposits of the BMC are spatially and temporally associated with calc-alkalic felsic volcanic rocks, interpreted to have formed by melting of continental crust during the early stages of continental back-arc rifting (Lentz, 2001). The deposits of the BMC are characterized by bedded Zn-Pb-Cu sulfide facies and chlorite-phengite hydrothermal 5

18 alteration (Goodfellow and McCutcheon, 2003). In contrast, the Turgeon Cu-Zn VMS deposit is hosted in tholeiitic MORB pillow basalts, and is a mafic type deposit (Barrie and Hannington, 1999; Franklin et al., 2005). Turgeon is slightly younger than the rocks hosting the neighboring VMS deposits of the BMC, and is characterized by chlorite-pyrite hydrothermal alteration minerals and massive to brecciated Cu-Zn mineralization. The objective of this study is to characterize the mineralization, hydrothermal alteration, sulfur source, and tectonic setting of the Turgeon deposit, with the goal of placing it in context within the geological evolution of the BMC, and comparing it to other similar Appalachian VMS deposits. Figure 1: Geologic map of the northeastern Appalachian Orogen illustrating the location of the Turgeon deposit relative to the VMS deposits of the Buchans Camp, Rambler Camp, Wild Bight Group, and Betts Cove and Tilt Cove Ophiolite (modified from Zagorevski et al., 2012; after Hibbard et al., 2006). 6

19 2.2 Regional geology of the BMC The Northern Miramichi Highlands (NMH) consists of four different tectonic blocks: Fournier, California Lake, Tetagouche, and Sheephouse Brook, all of which host the felsic-silisiclastic VMS deposits of the BMC (Figure 2; van Staal et al., 2003). The blocks, each having their own volcano-sedimentary stratigraphy, represent widely separated ensialic to ensimatic portions of the Tetagouche-Exploits back-arc basin, formed during the Arenig-Caradoc (van Staal et al., 2003). The present spatial distribution of the tectonic blocks is known as the Brunswick subduction complex and is the product of the Ashgill- Ludlow closure of the Tetagouche-Exploits back-arc basin (Goodfellow and McCutcheon, 2003). The Elmtree-Belledune inlier (EBI), located to the north-east of the NMH, exposes small portions of the Ordovician Fournier block through a Silurian sedimentary cover. It is separated to the south from the extensively mineralized rocks of the NMH by a strip of fault-bound Silurian turbidites and molasse along the Rocky Brook Millstream fault zone (van Staal et al., 1990) Northern Miramichi Highlands The California Lake block consists of the rocks of the California Lake and the Miramichi groups. The Miramichi Group consists mostly of passive margin sediments, and forms the stratigraphic basement of each of the blocks in the NMH. The California Lake Group consists of Middle to Upper Arenig rhyolitic to dacitic porphyritic tuffs and flows of the Mount Brittain and Spruce Lake formations (Gower, 1995), as well as pillow basalts of the Canoe Landing Lake Formation (Rogers and van Staal, 2003). All three are overlain by the Boucher Brook Formation, which consists of aklalic basalts, cherts, shales, and siltstones (van Staal and Rogers, 2000). The Mount Britain Formation hosts the Murray Brook and Restigouche VMS deposits, whereas the Spruce Lake Formation hosts the Caribou VMS deposit. 7

20 The Tetagouche block is composed of the rocks of the Tetagouche and Miramichi groups (van Staal et al., 2003). From base to top, the Tetagouche Group consists of the Nepisiguit Falls, Flat Landing Brook, Little River, and Tomogonops formations. The Nepisiguit Falls Formation is characterized by porphyritic dacitic to rhyolitic tuffs, sandstones, and shales. It hosts the largest massive sulfide deposits of the BMC (Brunswick 12, Heath Steele, Half Mile Lake), as well as spatially associated semi-continuous iron formations that are thought to have formed during a period of volcanic quiescence (Peter and Goodfellow, 1996). The Nepisiguit Falls Formation is overlain by the Flat Landing Brook Formation, which is characterized by feldspar-porphyritic dacitic to rhyolitic flows and pyroclastic rocks interlayered with tholeiitic pillow basalts (van Staal et al., 2003). Aside from the Stratmat and Taylor Brook VMS deposits, the Flat Landing Brook Formation is not known to host significant massive sulfides. The Flat Landing Brook Formation is overlain by the Little River Formation, which is composed of shales, siltstones, and cherts with interlayered transitional to alkalic pillow basalts. The Little River Formation is in turn overlain by the Tomogonops Formation, composed of calcareous shales, lithic wackes, and conglomerates. The Sheephouse Brook block forms the southern portion of the BMC. It consists mostly of sedimentary rocks of the Miramichi Group and less abundant volcanic rocks of the Sheephouse Brook Group (van Staal et al., 2003). The Sheephouse Brook Group is subdivided, in stratigraphic order, into the Clearwater Stream, Sevogle River, and Slacks Lake formations. The Clearwater Stream Formation is composed of feldspar-porphyritic dacitic tuffs, and hosts the Chester VMS deposit (Fyffe, 1995). The Sevogle River Formation consists of felsic volcanic rocks and hosts small semi-massive sulfide deposits (Wilson and Fyffe, 1996). The Slacks Lake Formation is characterized by transitional to alkalic pillow basalts and Fe-Mn rich shales. Stratigraphic correlations can be established in certain intervals between the volcanic rocks of the Sheephouse Brook Group and those of the Tetagouche and California Lake Groups (van Staal et al., 2003). 8

21 The Fournier block of the NMH is comprised of the Upper Proterozoic to Lower Cambrian Upsalquitch gabbro and of sedimentary and mafic igneous rocks of the Fournier Group (van Staal et al, 1996). The Fournier Group is subdivided into the Sormany and Millstream Formations. The Sormany Formation is characterized by pillow basalts with mid-ocean ridge basalt (MORB) to island-arc basalt (IAB) affinities, as well as by synvolcanic gabbros and serpentinites. The Sormany basalts are overlain by the shales and sandstones of the Millstream Formation. The Millstream Formation hosts the Nicholas- Denys Zn-Pb-Ag massive sulfide deposit, interpreted to be a SEDEX deposit by Deakin (2011). The Fournier Group preserved in the NMH represents a transitional crust compared to the Fournier Group in the EBI, which is interpreted to represent remnants of back-arc oceanic crust (van Staal et al., 2003; Winchester et al., 1992) Elmtree-Belledune Inlier (EBI) The Turgeon VMS deposit is hosted by the volcano-sedimentary rocks of the EBI (Figures 2, 3). The rocks of the EBI belong to the Fournier Group and Elmtree Formation (Figure 3; van Staal et al., 1990; van Staal and Fyffe, 1991b). The volcanic and sedimentary rocks of the Elmtree Formation are compositionally and lithologically similar to those of the Boucher Brook Formation of the California Lake Group (van Staal et al. 1990). The tectonic contact between the Fournier Group and Elmtree Formation is marked by a 1-2 km wide black shale melange (Figure 3; Winchester et al. 1992). The Fournier Group in the EBI consists of the Pointe Verte and Devereaux formations. The Pointe Verte Formation, which is divided into a lower sedimentary unit (Prairie Brook Member) and an upper volcanic-dominated unit (Madran Member; Winchester et al. 1992), is overlain by the Devereaux Formation (Winchester et al. 1992). The Devereaux Formation consists of tholeiitic basalts, andesites, wackes and shales, all of which are intruded by the Black Point gabbro (Winchester et al. 1992). The Sormany Formation in the NMH correlates with the Devereaux and Pointe Verte formations of the Fournier Group in the EBI (Winchester et al., 1992) 9

22 Figure 2 : Regional geological map of the BMC and EBI illustrating the main tectonic blocks and ore deposits of the area (Deakin, 2011; Modified from van Staal et al., 2003). 10

23 The Turgeon Cu-Zn VMS deposit is hosted in the Belledune tholeiite suite of the Devereaux Formation, which is subdivided into the Duncans Brook, Belledune, and Devereaux tholeiitic suites (Figure 3; Winchester et al., 1992). The Devereaux Formation is intruded by the Black Point gabbro; a subalkalic, high-field strength element (HFSE) depleted unit with an island-arc tholeiite (IAT) affinity (Winchester et al,. 1992). The Devereaux and Belledune tholeiites are composed of primitive Cr-rich pillow basalts and andesites that share MORB-like and IAT affinities. The Belledune tholeiites can be distinguished from the Devereaux tholeiites by their lower Mg, Cr, and Ni and higher Fe, Ti and V contents (Winchester et al., 1992). The Devereaux and Belledune tholeiites have similar Zr/Y and Nb/Y ratios, MORB affinities, as well as similar REE and multi-element profiles, indicating that they are cogenetic (Winchester et al., 1992). The Duncan s Brook tholeiites occur at the highest stratigraphic level directly above the Belledune suite and are considered the youngest unit in the Fournier Group based on the fact that it intrudes underlying lithologies (Winchester et al., 1992). The rocks of the Duncan s Brook tholeiite have MORB and IAT affinities (Winchester et al., 1992). Figure 3 : Geologic map of the Elmtree-Belledune inlier (EBI). Modified after Winchester et al., (1992). 11

24 2.3 Analytical methods Whole rock major and trace elements of 42 fresh and altered igneous rocks were analysed at Activation Laboratories, Ancaster, Ontario. Samples were analyzed by inductively coupled plasma emission spectroscopy (ICP-ES) and inductively coupled plasma mass spectrometry (ICP-MS), and were prepared with a lithium metaborate/tetraborate fusion. The fused material was dissolved in nitric acid. The solution was then analyzed for major, trace, REE, and other metals using a combination of ICP-ES and ICP-MS. Whole rock major and trace elements of 11 sulfide samples were measured using instrumental neutron activation analysis (INAA), total digestion inductively coupled plasma (TD-ICP-OES), and total digestion inductively coupled plasma-mass spectrometry (TD-MS) at Activation Laboratories, Ancaster, Ontario. Chlorite and sulfide mineral compositions were measured using a 5 WDS CAMECA SX-100 electron microprobe at Université Laval, Québec, Canada. The microprobe operating conditions were 15 kv and 20 na with counting times of 20 s on peak and 10 s on background. Natural and synthetic standards were used for calibration. Sulfur isotope analyses of pyrite, chalcopyrite, pyrrhotite and sphalerite were conducted at the G.G. Hatch Isotope Laboratory, University of Ottawa, Canada. For each analysis, 30 mg of sulfide concentrates were prepared under a binocular microscope. Samples were mixed with tungstic oxide and flash combusted at 1800 C in an elemental analyser. SO 2 gas was analysed using the Thermo Finnigan Delta XP isotope ratio mass spectrometer. Analytical precision is ± 0.2. Sulfur isotope ratios are presented in δ- notation relative to Vienna-Canyon Diablo Troilite (V-CDT). 12

25 2.4 Geology of the Turgeon deposit The Turgeon deposit area is divided into three blocks that are separated by steeply dipping, east-west striking faults that post-date all lithological units in the area. The faults are interpreted to be post-volcanic and related to Devonian wrench faulting attributed to the Rocky-Brook Millstream Fault zone (Figure 4; Thurlow, 1993). The North block and the western portion of the Powerline block are composed of a rhyolitic unit characterized by pink perlitic fractures with interstitial chlorite (Figure 4). The rhyolite unit is interpreted to overlie the sheeted dykes and pillow basalts. The Powerline block is characterized by postmineralization gabbros that intrude all of the units in the block. The gabbro is geochemically similar to the sheeted dykes and pillow basalts, and is included in the Belledune tholeiite suite (Winchester et al., 1992; Figure 3). Numerous, east-west striking, late gabbro dykes of the Duncan s Brook tholeiite (Figure 3) intrude all lithologies. The rocks in the south-west portion of the deposit consist of an east-west trending sheeted-dyke complex (Figure 4). The sheeted-dyke complex is overlain by steeply dipping westward facing pillow basalts interlayered with thin horizons of normally graded quartzrich sandstones and interpillow quartz-jasper-pyrite veins (Thurlow, 1993). The pillow basalts contain abundant varioles, quench fractures, and inter-pillow breccia along pillow margins. Basalts are characterized by a medium-dark grey colour with minor quartz-calciteepidote veining, and variable amounts of magnetite. Hyaloclastic and amygdular basalt commonly occur in the pillow basalt unit. The sheeted dykes and pillow basalts are part of the Belledune tholeiite suite of Winchester et al. (1992) (Figures 3 and 4). 13

26 Figure 4 : Geologic map of the Turgeon deposit. Schematic cross-section through FT is shown in Figure 10. Cross section through A2 is shown in Figure 6. This study and Thurlow (1992) Least altered basalt, andesite, and rhyolite The footwall basalts and andesites of the Turgeon deposit, distal to mineralization, have generally undergone lower-greenschist metamorphism (van Staal et al., 1991). Least altered basalt and andesite at Turgeon have preserved primary volcanic textures, and are composed of plagioclase and quartz microcrystals in a matrix of volcanic glass with minor epidote quartz carbonate veins (Figure 5A). Quartz, chlorite, and calcite commonly infill amygdules or form pseudomorphs after primary clinopyroxene phenocrysts. In the basalts, plagioclase microcrystals account for 60% of the rock whereas quartz microcrystals account for 5%. Both are found in a matrix of volcanic glass, which forms 25% of the rock. In the andesitic rocks, quartz microcrystals account for 25% of the rock, whereas plagioclase occupies 65% of the rock in a matrix of volcanic glass (10%). In both the basaltic and andesitic least altered rocks, plagioclase micro-crystals commonly display patches of sericite. Macroscopically, rhyolite is light pink in color and is characterized by flow banding outlined by perlitic fractures. Quartz microcrystals account for 80% of the rock, whereas plagioclase microcrystals form 10% of the rock. Both are cemented by a matrix of volcanic glass altered to chlorite, which occupies the remaining 10% of the rock. 14

27 2.4.2 Basalt and andesite epidote alteration Some of the basaltic and andesitic rocks hosting the deposit have undergone pervasive epidote alteration. The rocks affected by epidote alteration have preserved primary volcanic textures, and contain on average 60% plagioclase microcrystals, 20% epidote, 10% calcite, 5% chlorite, and 5% quartz (Figure 5B). The volcanic glass matrix is altered to epidote and minor chlorite, and is cut by coarse-grained epidote calcite veins. The epidote alteration facies is distal to mineralization. Figure 5 : Least and most altered rocks at Turgeon. Pl = plagioclase, Qz = quartz, Ep = epidote, Cal = calcite, Chl = chlorite, Py = pyrite, Ccp = chalcopyrite A. Photomicrograph of least altered andesite. B. Photomicrograph of epidote altered basalt. C. Photomicrograph of chlorite-pyrite altered basalt. D. Chlorite altered basalt with chalcopyrite veins in the stockwork zone. 15

28 2.4.3 Basalt and andesite chlorite alteration With increasing proximity of mineralization, the volcanic rocks display a progressively more intense chlorite alteration. Macroscopically, basalt and andesite affected by intense chlorite alteration are soft and black in color (Figure 5C). The most altered rocks of the Turgeon deposit have a mineral assemblage composed of 65% chlorite, 20% quartz, 10% chalcopyrite, and 5% pyrite (Figure 5D), and are found proximal to mineralization (Figure 6). When compared to least altered basalt and andesite, the intense chlorite alteration zone displays partial to total replacement of plagioclase and volcanic glass by chlorite and quartz. Primary volcanic textures are not preserved. Quartz forms phenocrysts, veins, and pseudomorphs for primary pyroxene phenocrysts. Pyrite is disseminated in the matrix or forms veins. Chalcopyrite forms veins that can reach thicknesses of up to 5 cm. Chalcopyrite veins increase in abundance stratigraphically below massive sulfide lenses, in the stockwork zone in chlorite altered basalt and andesite (Figure 6). Figure 6 : Cross-section through A2 from Figure 4. The massive sulfide lens is located in the Southern block, near the contact between the pillow basalts and sheeted dykes (Figure 4). The massive sulfide and stockwork zones occur in amygdaloidal and hyaloclastic volcanic rocks. 16

29 2.4.4 Lithogeochemistry On a Zr/Ti - Nb/Y diagram, the footwall volcanic rocks of the Turgeon deposit plot into the fields of subalkaline basalt and andesite (Figure 7A). The hanging wall rhyolite flows of the North block plot in the subalkaline rhyolite field. On a Y-Zr diagram (Figure 7B), basalt and andesite show a tholeiitic affinity, whereas rhyolite plots in the tholeiitic and transitional fields at high Zr content. Rare earth element (REE) patterns for basalt and andesite are flat, similar to those typical of MORBs (Figure 8A). Footwall volcanic rocks that have undergone intense chloritization show pronounced negative Eu anomalies, and are enriched in REE relative to least-altered rocks (Figure 8B). The hanging wall rhyolites have slightly fractionated REE patterns, display negative Eu anomalies, and are enriched in REE relative to least-altered basalt and andesite (Figure 8C). Multi-element plots show that least altered basalt, andesite, and rhyolite have weak negative Nb Ta anomalies, suggesting a volcanic-arc signature (Figure 8D). Rhyolite from the Flat Landing Brook (FLB) Formation of the BMC displays a fractionated REE pattern and pronounced Nb Ta anomaly (Figure 8D). On a Zr/Y - Zr diagram (Pearce and Norry, 1979), footwall volcanic rocks plot dominantly in the MORB field (Figure 9A). On a ternary Nb-Zr-Y diagram (Meschede, 1986), least-altered and altered volcanic rocks plot mainly in the N-MORB field, with some samples plotting in the within-plate tholeiite field (WP thol; Figure 9B). The trend of within-plate tholeiite to N-MORB suggests that the most likely tectonic environment was that of volcanic-arc basalts (VAB). On a ternary La-Nb-Y diagram (Cabanis and Lecolle, 1989), volcanic rocks plot in the back-arc basin and volcanic-arc tholeiite (VAT) fields (Figure 9C). On a (La/Yb) cn Yb diagram (Lesher et al., 1986; revised by Hart et al., 2004), Turgeon s hanging wall rhyolite plots in the field for FIIIa type rhyolites, whereas the Flat Landing Brook (FLB) rhyolite of the NMH plots in the FII field. (Figure 9D). FIIIa type rhyolites are commonly associated to VMS deposits, whereas most FII type rhyolites are not (Lesher et al., 1986; revised by Hart et al., 2004). 17

30 Figure 7 : Geochemistry of the volcanic rocks of the Turgeon deposit. A. Zr/Ti - Nb/Y diagram (Winchester and Floyd, 1977; as modified by Pearce, 1996). B. Zr-Y diagram (Ross and Bédard, 2009; as modified by Barrett and MacLean, 1999). 18

31 Figure 8 : Trace element composition of the Turgeon volcanic rocks normalized to chondrite (McDonough and Sun, 1995). A. REE in least-altered basalt and andesite. B. REE in chlorite altered basalt and andesite. C. REE in rhyolite. D. Multi-element spider diagram of Turgeon least-altered basalt, andesite, and rhyolite, as well as rhyolite from the Flat Landing Brook (FLB) Formation of the BMC (Mean values of 34 samples; Lentz, 1999) normalized to chondrite (Thompson, 1982). 19

32 Figure 9 : Tectonic affinity discrimination diagrams for the Turgeon mafic and felsic volcanic rocks. A. Zr/Y - Zr diagram (Pearce and Norry, 1979). B. Nb*2 - Zr/4 - Y ternary diagram (Meschede, 1986). C. La/10- Nb/8 - Y/15 ternary diagram (Cabanis and Lecolle, 1989). D. (La/Yb) cn Yb cn (Lesher et al., 1986; as modified by Hart et al., 2004). BMC Rhyolite (FLB) values from Lentz, 1999 (Mean values of 34 samples). Chondrite values from Nakamura (1974). 2.5 Cu-Zn VMS mineralization of the Turgeon deposit Mineralization at the Turgeon deposit consists of two sulfide stockwork zones stratigraphically underlying two massive sulfide lenses (Figure 10). The Powerline and Beaver Pond zones crop out whereas the 100m Zinc and massive sulfide lenses are found exclusively in drill core. The Powerline and 100m Zinc zones are in the Powerline block, whereas the and Beaver Pond zones are located in the Southern block (Figure 4). The sulfide lenses are at the contact between the sheeted dykes and pillow basalt units. Massive sulfides are hosted in hyaloclastic basalt flows, interstitial to chlorite altered volcanic glass fragments. Amygdules in the pillow basalts directly overlying mineralization are commonly filled by quartz, calcite, pyrite, and chalcopyrite. 20

33 The Beaver Pond zone consists of variolitic pillow lavas with abundant interpillow jasper-epidote-pyrite veins and hyaloclastite breccia. Mineralization forms quartz-pyrite veins with minor chalcopyrite, chalcocite, bornite, and sphalerite, which cross cut a 4 m by 7 m massive, saucer-shaped body of jasper. Drilling indicates that mineralization does not extend at depth (Thurlow, 1993). Figure 10 : Schematic cross-section through FT illustrating the distribution of mineralization and hydrothermal alteration. The Powerline stockwork zone grades abruptly into the 100m Zinc massive sulfide lens. The massive sulfide lens is stratigraphically underlain by the pyrite-chalcopyrite stockwork zone. The Powerline zone crops out in the Powerline block (Figures 4, 10, 11) and consists of a network of chalcopyrite-pyrite veins cutting intensely chloritized basalt and andesite (Figure 5D). On surface, the Powerline zone is manifested by east-west oriented 21

34 elongated pyrite-chlorite sulfide lenses bordered by basalt (Figure 12A). A distinctive massive sulfide breccia unit at the north of the outcrop consists of angular to sub-rounded, poorly sorted, sulfide (Figure 12B) and amygdular basalt fragments (Figure 12C) up to 20 cm in diameter, cemented in a pyrite-chlorite-silica matrix (Figure 12D). Sulfide fragments consist of pyrite, chalcopyrite, and sphalerite. An east-west trending gabbro truncates the sulfide breccia at the north side of the block (Figure 11). East-west trending gabbroic dykes that intrude basalts in the area are not mineralized or significantly altered. Figure 11 : Geologic map of the Powerline showing. The 100m Zn massive sulfide lens is in the Powerline block (Figures 4, 10). The lens strikes east-west and is considerably sheared and dismembered by the 100m Zinc fault (Figure 10; Thurlow, 1993). The lens has a maximum thickness of 50 m and extends 150 m along strike. The chalcopyrite-pyrite stockwork zone partially exposed on the Powerline block grades abruptly into a massive sulfide lens at depth (Figure 10). The zone is found in the southern block (Figure 4, 10), at the contact between the sheeted dyke complex and the overlying pillow basalts (Figure 6). The massive sulfide lens strikes N-S, and dips steeply to the west. The "48-49 zone consists of chalcopyrite-pyrite veins in 22

35 a stockwork zone that comes in abrupt contact with a massive sulfide lens (Figure 10). The lens has a maximum thickness of 40 m. Figure 12 : A. Elongated north-south striking massive sulfide lenses bordered by moderately silicified basalts containing disseminated pyrite. B. Large pyrite fragment cemented by a matrix of fragmental massive sulfide. C. Large amygdular basalt fragment cemented by a matrix of fragmental massive sulfide. D. Poorly sorted, angular to rounded pyrite fragments cemented by a chlorite silica matrix. 23

36 A historic resource (not NI compliant) at Turgeon has been estimated at 2.5 Mt grading 1.5% Cu and 4.0% Zn (Kettles, 1987). Massive sulfides at Turgeon have low concentrations of Pb (30.1 ± 23.8 ppm; Appendix 4), Au (<2 ppb; Appendix 4), Ag (3.67 ± 3.43 ppm; Appendix 4), and Cd (5 ± 5 ppm; Appendix 4), but are enriched in Co (295 ± 255 ppm) and Se (156 ± 92 ppm). On a ternary Cu Zn - Pb diagram, Turgeon massive and stockwork sulfides plot dominantly along the Cu - Zn axis. The massive sulfides of the BMC plot along the Zn-Pb axis, whereas stockwork sulfides plot near the Cu pole (Figure 13). Figure 13 : Cu Zn Pb ternary diagram of massive sulfides from: a. Turgeon deposit. b. deposits of the BMC (Modified after Goodfellow and McCutcheon, 2003). Contour values are number of samples. 24

37 2.6 Hydrothermal sulfide facies Chalcopyrite-pyrite stockwork The chalcopyrite-pyrite stockwork is characterized by an assemblage of chalcopyrite, pyrite, chlorite, quartz, and calcite. Quartz, pyrite, and chalcopyrite form cmsized veins cutting black, chloritized basalt (Figure 14A). Pyrite is brecciated; it forms rounded to sub-angular fragments of various sizes, and is partially replaced by chalcopyrite (Figure 15A). Pyrite and chalcopyrite vary in abundance with increasing proximity of massive sulfide lenses. Stockworks immediately underlying massive sulfide lenses are dominated by chalcopyrite, whereas adjacent zones are richer in pyrite. Pyrite distal to massive sulfide lenses is not brecciated. Rather, it forms mm-sized euhedral cubes in veins or disseminated in the host rock. Bulk rock analysis shows that the chalcopyrite-pyrite stockwork has high concentrations of Co (up to 705 ppm), Se (up to 325 ppm), and In (up to 53.6 ppm; Appendix 4), all of which display a covariation with Cu (Figures 16A, 16B, 16C) Massive chalcopyrite-pyrrhotite ± pyrite The massive chalcopyrite-pyrrhotite zone is characterized by an assemblage of chalcopyrite, pyrrhotite, chlorite, and pyrite, with minor quartz and magnetite (Figures 14B, 15B). Massive chalcopyrite-pyrrhotite is found at the base of the massive sulfide lens (Figure 10). Similarly to stockwork ore, pyrite in this sulfide facies is brecciated and forms rounded to sub-angular fragments. Pyrite fragments are cemented by chalcopyrite and pyrrhotite, with minor magnetite. The gangue minerals include chlorite, with minor quartz and magnetite. Bulk rock analysis shows that the massive chalcopyrite-pyrrhotite has high concentrations in Se (up to 245 ppm) and Co (up to 788 ppm; Appendix 4). 25

38 2.6.3 Massive pyrite The massive pyrite zone is characterized by pyrite with minor amounts of siderite, calcite, and magnetite (Figures 14D and 15C). Massive pyrite is found exclusively in the central and upper part of the massive sulfide lens. Pyrite is typically coarse grained and euhedral, forming cm-scale cubes. Pyrite is most commonly cemented by calcite, siderite, and talc, with minor magnetite and chlorite. Bulk rock analysis shows that the massive pyrite has low concentrations of Co (up to 162 ppm), Se (up to 117 ppm), and In (up to 2.7 ppm; Appendix 4) Pyrite-chalcopyrite-sphalerite breccia The breccia zone is composed of 70% fragments and 30% matrix. Brecciated fragments are rounded to sub-angular, and consist of 65% pyrite, 20% basalt, 5% chalcopyrite, and 10% sphalerite (Figure 14C). Basalt fragments include amygdular basalt (Figure 12C) and intensely chlorite-altered basalt. The matrix consists of quartz, chlorite, calcite, siderite, talc, chalcopyrite and sphalerite. The chalcopyrite and sphalerite in the matrix are anhedral and are commonly found within fractures in pyrite fragments. Sphalerite contains small chalcopyrite inclusions. The pyrite-chalcopyrite-sphalerite breccia is located at the base of the 100m Zinc lens (Figure 10), as well as on the northern portion of the Powerline showing (Figure 11). Bulk rock analysis shows that the the pyritechalcopyrite-sphalerite breccia ore has the highest concentrations of Cd (up to 16.4 ppm; Appendix 4), which displays a covariation with Zn (Figure 16D). 26

39 Figure 14 : Drill core samples of different ore types at Turgeon. Py = pyrite, Ccp = chalcopyrite, Sp = sphalerite, Chl = chlorite, Qz = quartz, Po = pyrrhotite A. Chalcopyrite-pyrite stockwork ore. B. Massive chalcopyrite-pyrrhotite ore. C. Sphalerite-pyrite. D. Massive pyrite. E. Pyrite stockwork. F. Massive chalcopyrite-pyrite. 27

40 Figure 15 : Photomicrographs of the four main sulfide facies at Turgeon. Py = pyrite, Ccp = chalcopyrite, Po = pyrrhotite, Mag = magnetite, Cb = carbonate, Sp = sphalerite, Tlc = talc. A. Rounded pyrite breccia cemented by a matrix of chalcopyrite, stockwork zone. B. Coexisting pyrrhotite and chalcopyrite in the massive Cpy-Po ore at the bottom of massive aulfide lenses. C. Coarse euhedral to subhedral pyrite cemented by a matrix of calcite, siderite, and magnetite, massive pyrite ore zone located at the top of massive sulfide lens. D. Fragmental ore comprised of sphalerite and pyrite breccia cemented by a matrix of talc. 2.7 Sulfide chemistry and textures The four principal sulfide minerals at Turgeon are pyrite, chalcopyrite, pyrrhotite, and sphalerite. Electron microprobe analyses were performed on 16 polished sections. Sulfide microprobe data are presented in appendices 5, 6, 7 and Pyrite Pyrite at the Turgeon deposit varies in grain size and morphology from fine-grained ( µm), brecciated, sub-rounded to angular fragments in the stockwork zones (Figures 14A and 15A), to coarsely crystalline (up to 1 cm) euhedral cubes in the massive pyrite zones (Figures 14D and 15C). Coarse grained pyrite in pyrite-chalcopyrite-sphalerite breccia is also fragmented and is 5 mm 5 cm in size (Figure 14C). Euhedral pyrite in 28

41 massive pyrite zones contain chalcopyrite, sphalerite, and magnetite inclusions <1 µm in size, whereas fragmental pyrite in the pyrite-chalcopyrite-sphalerite breccia zone is devoid of inclusions. Pyrite in massive pyrite contains up to 0.14 wt% Pb (Appendix 5). Pyrite in stockwork and massive chalcopyrite zones contains up to 0.8 wt% Co, 0.14 wt% Se, and 0.34 wt% Cu (Appendix 5). Pyrite yields concentrations below the detection limits for As, Ag, and Ni (Appendix 5) Chalcopyrite Chalcopyrite mainly occurs as very fine (<100 µm) anhedral aggregates in veins cementing and replacing pyrite (Figure 15A), and is commonly intergrown with pyrrhotite (Figure 15B), quartz and chlorite. Rounded chalcopyrite fragments (<0.5 mm), although rare, are found in the fragmental sulfide facies. Chalcopyrite also occurs as sub-rounded inclusions (<20 µm) within sphalerite fragments in pyrite-chalcopyrite-sphalerite breccia. Chalcopyrite is stoichiometric, and contains very few detectable trace elements. In the stockwork zone, chalcopyrite contains up to 0.1 wt% Se, 0.16 wt% Zn, and 0.1 wt% Pb (Appendix 6). In massive chalcopyrite-pyrrhotite, chalcopyrite contains up to 0.1 wt% Pb, and yields concentrations below the detection limits for Co, Mn, Ni, Ag, and Se (Appendix 6) Pyrrhotite Pyrrhotite is found exclusively at the base of the massive sulfide lens. It mainly forms anhedral aggregates and is intergrown with chalcopyrite (Figures 14B, 15B). With chalcopyrite, pyrrhotite cements and replaces pyrite in breccia. Pyrrhotite is intergrown with magnetite, and forms veins that cut chlorite and quartz veins. Inclusions of chalcopyrite and magnetite in pyrrhotite are <1 µm in diameter and are irregular in form. Pyrrhotite contains up to 0.15 wt% Co, 0.09 wt% Se, 0.15 wt% Zn, 0.12 wt% Cu, and 0.15 wt% Pb, and yields concentrations below the detection limits for Mn, Ni, and Ag (Appendix 7). 29

42 2.7.4 Sphalerite Sphalerite forms massive anhedral aggregates and massive sub-rounded fragments in pyrite-chalcopyrite-sphalerite breccia. Sphalerite is intergrown with chalcopyrite in the massive pyrite ore, where it cements pyrite cubes and fractures. In the pyrite-chalcopyritesphalerite breccia, it forms mm- to cm- scale, sub-rounded fragments (Figure 14C), and small anhedral aggregates cementing pyrite. Sphalerite fragments occasinally contain irregular inclusions of chalcopyrite (<20 µm) typical of the chalcopyrite disease texture. Sphalerite has a range in Fe content between 2-6 wt%, and contains up to 0.2 wt% Cd and 0.15 wt% Bi (Appendix 8). Figure 16 : Cu, Zn, and trace element binary diagrams by type of sulfide mineralization. A. Cu (ppm) vs. In (ppm). B. Cu (ppm) vs. Se (ppm). C. Cu (ppm) vs. Co (ppm). D. Zn (ppm) vs. Cd (ppm). 30

43 2.8 Alteration geochemistry Fresh and altered samples in this section were selected based on their macroscopic characteristics, such as colour and hardness. Petrographic thin sections were also made for each sample in order to verify their respective classification. A TiO 2 -Zr diagram for the Turgeon footwall volcanic rocks shows two alteration arrays that project through the origin (Figure 17). The alteration arrays intersect the tholeiitic fractionation trend at a composition typical for basalt and andesite. Samples that plot near the tholeiitic fractionation trend are least altered. Samples plotting above the tholeiitic fractionation trend have undergone mass loss, whereas those that plot beneath have undergone mass gain. The majority of the volcanic rocks from the Turgeon deposit plot above the tholeiitic fractionation trend, indicating mass loss in most samples. Chlorite altered samples tend to plot at higher Zr and TiO 2 values above the trend, indicating they have lost the most mass during alteration. The hanging wall rhyolite has high Zr and low Ti values, plotting along the unaltered tholeiitic trend. Figure 17 : Zr TiO 2 diagram showing Turgeon deposit rock composition with reference to the fractionation trend of normal volcanic rocks. Alteration lines (dashed) pass through the origin (after MacLean and Barrett, 1993). Highlighted samples are those used in figure

44 Mass changes in mobile elements are illustrated in figure 18 following MacLean and Barrett s (1993) multiple precursor method. Mass changes for one element are calculated based on the respective basaltic or andesitic precursor. Least altered basalt and andesite show minor depletions in both CaO + Na 2 O (0 and -3 wt%) and FeO + MgO, (0 and -5 wt%; Figure 18). Epidote altered basalt and andesite are characterized by CaO gains (up to 4 wt%) and FeO + MgO depletion (Figure 18). Samples affected by intense chloritepyrite alteration show a different pattern, where Na 2 O + CaO is more depleted (between -5 wt% and -7 wt%), whereas FeO + MgO is enriched (0 and +12 wt%; Figure 18). Gradual replacement of feldspar by chlorite is shown by mass losses in CaO and Na 2 O, and mass gains in FeO and MgO (Figure 18). Figure 18 : Elemental mass changes in the footwall volcanics of the Turgeon deposit. Rocks distal from mineralization that exhibit epidote alteration have gains in Na and Ca, and losses in Fe and Mg. Rocks proximal to mineralization that have undergone chlorite alteration have lost Na and Ca, and gained Fe and Mg (after MacLean and Barrett, 1993). The alteration box plot (Figure 19) is a diagram that uses two geochemical alteration indices, the Ishikawa alteration index (AI) and the chlorite-carbonate-pyrite index (CCPI), in order to characterize the nature and degree of alteration in VMS deposits (Large et al., 2001). Least altered rocks plot in the center of the diagram, whereas hydrothermally altered 32