THE GEOLOGICAL EXPLORATION OF KIMBERLITIC ROCKS IN QUÉBEC

J oy R. Hartzler

February, 2007

A thesis submitted to McGill University in partial fulfillment of the requirements of the degree of Master of Science

Department of Barth and Planetary Science McGill University Montreal, Québec Canada

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Abstract

Diamonds have been discovered in a variety of potassic ultramafic rocks including group-1 and group-II kimberlites, olivine lamproites and aillikites, aU of which are macroscopically similar and can be difficult to differentiate when viewed under the microscope. However, group-I kimberlites, and to a much lesser extent group-II kimberlites and olivine lamproites, are known to contain economic concentrations of diamonds. This study addresses the problem of distinguishing among different types of kimberlitic and related rocks by developing a geochemically-based method for classifying them.

Geochemical methods have been largely ignored in the classification of kimberlites and related rock types due to high concentrations ofxenoliths. However, this problem can be largely overcome by only selecting matrix material for analysis. An evolving kimberlitic magma will become enriched or improvished in Si due to the fractionation of olivine and phlogopite, depending on the initial Si concentration of the magma. As they have low Si concentrations, group-1 kimberlites and aillikites can be separated from group-II kimberlites and meimechites, which have higher Si concentrations for any Mg content. Furthermore, since aillikites and meimechites are relatively rich in Fe compared to group-I and group-II kimberlites, these rock types form four separate fields on a Si vs. Fe discrimination diagram. Similar rock-type separation is observed when the ratio of La to Yb is plotted against the ratio of Sm to Yb. Kimberlite and other potassic ultramafic rocks were sampled from nine are as in Québec: the Otish

Mountains, Wemindji, Tomgat Mountains, Desmaraisville, Temiscamingue, Île Bizard,

Lac Leclair, Baie James and Ayer's Cliffregions. Major and selected trace element III concentrations were detennined by XRF analysis for an samples, while a subset of representative samples was selected for trace element analysis by lep-MS. Electron microprobe analyses ofunaltered olivine and phlogopite were also conducted.

Of the 37 samples that were classified both mineralogically and chemically, 23 or

62% were correctly classified using Fe and Si. This number increases to 84%, if the REE are used in conjunction with Si and Fe. The Si vs. Fe discrimination diagram separates group-I kimberlite from most aillikite and meimechite rocks and group-II kimberlite/olivine lamproite rocks from most aillikite and meimechite rocks. Therefore, major and trace element geochemistry offers an important tool for the classification of kimberlitic rocks.

Vasilenko et al. (2002) and Francis (2003) both suggested that diamond grades can be correlated with the major element compositions of the kimberlites. The data collected in this study confinn the inverse relationship between Ti02 concentration and diamond grade. The lowest Ti02 values were obtained on samples from the Otish

Mountains and Renard samples in particular. Other areas of Québec are characterized by higher Ti02 contents with most samples containing greater than 2 wt% Ti02. Therefore, the kimberlitic rocks from the Renard locality have the greatest potential for an economic diamond deposit. The origin ofthis correlation needs to be explored, however, because it is unclear whether this is a feature of the mantle source, or reflects the survivability of diamonds within the kimberlites. IV

Résumé

Des diamants ont été découverts dans divers types de roches ultramafiques potassiques, notamment des kimberlites des groupes l et II, des lamproïtes à olivine et des aillikites, qui sont toutes semblables d'un point de vue macroscopique et qui peuvent être difficiles à distinguer l'une de l'autre au microscope. Cependant, il est généralement reconnu que les kimberlites du groupe l, et de façon beaucoup moins importante, les kimberlites du groupe II et les lamproïtes à olivine, peuvent renfermer des concentrations

économiques de diamants. Cette étude vise à pallier à cette difficulté, en développant une méthode de classification géochimique qui permet de distinguer les différents types de kimberlites et autres roches associées.

Les méthodes géochimiques ont été largement ignorées pour la classification des kimberlites et des autres roches associées, en raison de leur contenu élevé en xénolithes.

Cependant, ce problème peut être résolu principalement en sélectionnant uniquement du matériel de la matrice pour analyse. Au cours de son évolution, un magma kimberlitique s'enrichira ou s'appauvrira en Si lors du fractionnement d'olivine et de phlogopite, selon la concentration initiale en Si du magma. De par leur faible teneur en Si, les kimberlites du groupe l et les aillikites peuvent être distinguées des kimberlites du groupe II et des meiméchites, dont les teneurs en Si sont plus élevées à une teneur donnée en Mg. De plus, puisque les aillikites et les meiméchites sont relativement riches en Fe comparativement aux kimberlites des groupes l et II, ces types de roches forment quatre champs distincts sur le diagramme discriminant Si versus Fe. Des distinctions similaires entres les différents types de roches sont également observées lorsque le rapport La/Yb est présenté versus le rapport Sm/Yb. Des kimberlites et d'autres types de roches ultramafiques v potassiques ont été échantillonnées dans neuf régions du Québec : dans les monts Otish, à

Wemindji, dans les monts Tomgat, à Desmaraisville, au Témiscamingue, à 1'île Bizard, au lac Leclair, à la baie James, et dans la région d'Ayer's Cliff. Les concentrations en

éléments majeurs et quelques éléments traces de tous les échantillons ont été déterminées par fluorescence X (XRF), et un sous-ensemble d'échantillons représentatifs a été sélectionné pour déterminer les concentrations en éléments traces par ICP-MS. Des grains non altérés d'olivine et de phlogopite ont également été analysés par microsonde

électronique.

Parmi les 37 échantillons qui ont été classifiés à la fois par des méthodes minéralogiques et chimiques, 23 ou 62 % ont été correctement classifiés à l'aide du diagramme Fe versus Si. Cette proportion s'élève à 84 % si les terres rares sont utilisés en plus du Si et du Fe. Le diagramme discriminant Si versus Fe permet de distinguer les kimberlites du groupe 1 de la plupart des roches aillikitiques et meiméchitiques, et les kimberlites du groupe II et les lamproïtes à olivine de la plupart des aillikites et des meiméchites. Ainsi, la géochimie des éléments majeurs et des éléments traces représente un important outil de classification des roches kimberlitiques.

Vasilenko et al. (2002) et Francis (2003) ont tous deux suggéré une corrélation entre la teneur en diamant et la composition en éléments majeurs des kimberlites. Les données de cette étude confirment l'existence d'une corrélation inverse entre la teneur en

Ti02 et la teneur en diamant. Les plus faibles teneurs en Ti02 ont été obtenues d'échantillons provenant des monts Otish et de Renard en particulier. D'autres régions du

Québec sont caractérisées par des teneurs plus élevées en Ti02 ; la plupart des échantillons contiennent plus de 2 % poids Ti02. Par ailleurs, les roches kimberlitiques du secteur

Renard présentent le plus grand potentiel d'être associées à un gisement économique de VI diamants. L'origine de cette corrélation doit cependant être examinée, puisqu'il n'est pas clair s'il s'agit d'une caractéristique de la source mantellique ou un reflet du potentiel de survie des diamants à l'intérieur des kimberlites. vu

Acknowledgements

First, many thanks go to Dr. AE. Williams-Jones for the impetus to start this thesis and for his boundless enthusiasm and encouragement. Thanks also go to Dr. D.

Francis for his extensive knowledge of aH things kimberlitic and for his thoughtful and needed critiques.

1 would also like to thank J.R. Clark for sharing his insights into the world of exploration and his helpful input about my research. For technical help and analytical work, thanks go to T. Ahmedali, G. Keating and B. Dionne. 1 would like to thank D.

Savage for his patience in picking rock samples, and A Harlap for his help in the field.

Thanks go to aH that have made my time at McGiH memorable, inc1uding G.

Bernier, K. Rempel, K. Ault, c.P. Mann, L.M. Dolansky and S. Neilson. Sincerest gratitude goes to A Kosowski, who can answer any question and solve any problem.

Lastly, thanks go to D. Hartzler, M.K. Hartzler and S. Hartzler for being so patient and to

R. Lyen for helping me to finally finish.

This project was funded by DIVEX grant awarded to AE. Williams-Jones, D.

Francis, R. Stevenson and N. Machado. Rock samples were donated by Ashton Mining of Canada, Dianor Resources Inc., Ditem Exploration Inc., Dr. D. Francis, Dr. L. Hamois,

Majescor Resources Inc., J. Moorhead and Dr. R. Stevenson. Vlll

Table of contents

Abstract ...... ii

Résumé ...... iv

Acknowledgements ...... vii

Table of contents ...... viii

List of figures ...... x

List of tables ...... xii

List of appendices ...... xii

Preface: Contributions of authors ...... xiii

Chapter 1: General Introduction ...... 1

1.1. Introduction ...... 2

1.2. Review ofknowledge ...... 3

1.3. Mineralogy ...... 4

1.4. Macroscopic F eatures of kimberlites ...... 7

1.5. Geochemistry ...... 8

1.6. Objectives of the study ...... 9

1.7. Thesis organization ...... 10

1.8. References ...... 10

Chapter 2: The geochemical exploration ofkimberlitic rocks in Québec ...... 14

2.1. Abstract ...... 15

2.2. Introduction ...... 17

2.3. Sample Preparation and Analytical Techniques ...... 20

2.4. Mineralogy ofkimberlitic and related ultramafic rocks in Québec ...... 23 IX

2.4.1. Otish Mountains ...... 23

2.4.2. Tomgat Mountains ...... 26

2.4.3. Wemindji ...... 31

2.4.4. Desmaraisville ...... 32

2.4.5. Temiscamingue ...... 33

2.4.6. Île Bizard ...... 35

2.4.7. Other Occurrences ...... 35

2.5. Geochemistry ...... 38

2.5.1. Major Elements ...... 38

2.5.2. Trace Elements ...... 58

2.5.3. Diamond Grade vs. Ti02 ...... 71

2.6. Discussion ...... 77

2.6.1. Classification Schemes ...... 77

2.6.2. Classification of Group-I Kimberlite Samples ...... 79

2.6.3. Classification of Aillikite Samples ...... 81

2.6.4. Classification ofNon-Kimberlitic Samples ...... 83

2.6.5. Evaluation of Si vs. Fe Discrimination Diagram ...... 85

2.7. Conclusions ...... 87

2.8. References ...... 89

Chapter 3: Extended Conclusions ...... 97

3.1. Conclusions ...... 98

3.2 Recommendations for Future Work ...... 99 x

List of figures

Figure 2-1: Map of Québec with kimberlitic and related ultramafic rock occurrences ..... 22

Figure 2-2a: A plot of Si cations versus Mg cations for kimberlitic rocks taken from the

published literature ...... 40

Figure 2-2b: A plot of Fe cations versus Mg cations for kimberlitic rocks taken from the

published literature ...... 41

Figure 2-3a: A plot of Si cations versus Fe cations for published analyses ...... 42

Figure 2-3b: A plot of Si cations versus Fe cations for rocks from Québec ...... 43

Figure 2-4: A plot of Si cations versus Fe cations for Otish Mountain rocks ...... 44

Figure 2-5: A plot of Si cations versus Fe cations for Tomgat Mountain rocks ...... 46

Figure 2-6: A plot of Si cations versus Fe cations for Desmaraisville area rocks ...... 55

Figure 2-7: A plot of Si cations versus Fe cations for Temiscamingue area rocks ...... 56

Figure 2-8: A plot of Si cations versus Fe cations for Ile Bizard rocks ...... 57

Figure 2-9a: A plot of Si cations versus Fe cations for Lac Leclair and Ayer's Cliff rocks

...... 59

Figure 2-9b: A plot of Si cations versus Fe cations for Lac Castignon rocks ...... 60

Figure 2-10: A plot of chondrite normalized REE for rocks from Québec ...... 61

Figure 2-11: A plot of chondrite normalized grouped REE for Québec kimberlitic rocks62

Figure 2-12: A plot oflog La (ppm)/ Yb (ppm) versus log Sm (ppm)/ Yb (ppm) from

published geochemical analyses ofmineralogically classified kimberlitic rocks ...... 64

Figure 2-13: A plot oflog La (ppm)/ Yb (ppm) versus log Sm (ppm)/ Yb (ppm) from

Otish Mountain rocks ...... 65 Xl

Figure 2-14: A plot oflog La (ppm)/ Yb (ppm) versus log Sm (ppm)/ Yb (ppm) from

Tomgat Mountain rocks and Wemindji rocks ...... 66

Figure 2-15: A plot oflog La (ppm)/ Yb (ppm) versus log Sm (ppm)/ Yb (ppm) from Lac

Leclair, Ayer's Cliff and Baie James rocks ...... 68

Figure 2-16a: A spider diagram of primitive mantle normalized incompatible elements for

rocks from the Otish Mountains, Tomgat Mountains, Desmaraisville and Wemindji

...... 69

Figure 2-16b: A spider diagram of primitive mantle normalized incompatible elements for

rocks from Temiscamingue, Ile Bizard, Lac Leclair, Ayer' s Cliff and Baie James .. 70

Figure 2-17: A plot of Ti O2 oxide wt% versus Diamond Grade for most Québec rocks .. 73

Figure 2-18: A plot ofTi02 oxide wt% versus Diamond Grade for Otish Mountain rocks

...... 76 xu

List of tables

Table 2-1: List of mica compositions detennined by electron microprobe from selected

samples with unaltered mica ...... 27

Table 2-2: List of olivine compositions detennined by electron microprobe analysis from

selected samples ...... 30

Table 2-3: Major (wt%) and trace element (ppm) content of Québec kimberlitic rocks .. .47

Table 2-4: Summary of diamonds found at different areas in Québec ...... 74

List of appendices

Appendix 1: List of samples and what region they are from ...... 100

Appendix 2: List ofreferences from which published whole rock geochemistry analyses

were taken ...... 101 Xlll

Preface: Contributions of authors

The research presented in this thesis is a result of collaboration between the author,

Dr. D. Francis, Dr. A.E. Williams-Jones, and J.R. Clark. The thesis is comprised ofthree chapters: a general introduction, a manuscript which has not been submitted yet, and an extended conclusion. Dr. D. Francis, the second author of the manuscript, acted as thesis supervisor, providing research guidance and assistance with data interpretation, along with doing critical reviews of the text. The third author of the manuscript, Dr. A.E.

Williams-Jones, also acted as thesis supervisor and provided general research guidance and critical reviews of the text. J.R. Clark, the fourth author of the manuscript, performed electron microprobe analyses and provided research guidance. XRF analyses ofmajor and trace elements were performed by T. Ahmedali and G. Keating. ICP-MS analyses of forty-three trace elements were performed by C.D. Reid of Activation Laboratories,

Ancaster, Ontario. AlI research work, data analysis, and writing was done by the author. CHAPTERI

GENERAL INTRODUCTION 2

1.1. Introduction

Diamonds have been discovered in a variety ofultramafic rocks, e.g., kimberlites, lamproites, aillikites and minettes, and in a variety of countries, e.g., South Africa,

Botswana, India, Russia, Australia and most recently Canada. Of these discoveries, greater than fort Yhave been in group-I kimberlites, Il have been in group-II kimberlites

(e.g., Finsch pipe, Swartruggens dykes, Roberts Victor pipe, New Elands pipe) and one has been in olivine lamproite (i.e. the Argyle pipe). For this reason the preferred targets for diamond exploration are group-I and group-II kimberlites. However, as group-I and group-II kimberlites, olivine lamproites, aillikites and other lamprophyres all have similar textures and mineralogy, distinguishing among them can be problematic. Though volumetrically insignificant compared to other igneous rock types, kimberlites have been subjected to intense petrological study because oftheir potential to host economic concentrations of diamonds. Despite this, there is still no clear and uncomplicated method which geologists can use to easily differentiate between group-I kimberlites and other uneconomic ultramafic rocks.

The widely held view that kimberlite composition is unrelated to diamond grade is due to a large proportion of diamonds being either much older than or containing inclusions that are unrelated to their kimberlite host. Consequently, the only role generally attributed to kimberlitic magmas in the formation of economic concentrations of diamonds is as a medium for their transport from the mantle to the surface (Meyer,

1985). Recently, however, Vasilenko et al. (2002) reported data which suggest that diamond grades ofkimberlitic pipes in Yakutia, Russia correlate with the major element composition of the host rock, and proposed a complex algorithm for predicting diamond 3 grade based on the major element geochemistry. Using their data, Francis (2003) showed that there is a relatively simple inverse correlation between Ti and Fe concentrations and diamond grade. If these correlations are valid, they would indicate that diamonds are not just accidentaI passengers in kimberlite magmas, but are generally related to the latter.

Previously, kimberlites, lamproites and lamprophyres have been classified according to their mineraI composition. This thesis will present an alternative approach for differentiating potentially economic kimberlites from other ultramafic rocks, based on their bulk rock chemistry, and will evaluate the proposaIs ofVasilenko et al. (2002) and

Francis (2003) that diamond grade can be correlated with the major element chemistry.

Finally, the thesis will describe the mineralogy and petrography of Québec kimberlitic rocks.

1.2. Review of knowledge

A complete review of the history of the nomenclature ofkimberlitic rocks and lamprophyres can be found in Mitchell (1986, 1995) and Rock (1991). The term kimberlite was first used by Lewis (1887, 1888) to describe diamond-bearing rocks exploited in the Kimberley and De Beers mines located in the town of Kimberly, South

Africa. Other kimberlites had been found previously in North America (Syracuse, New

York, and Elliott County, Kentucky; Lewis, 1888) but they were treated as interesting geological anomalies as they did not contain diamonds. Wagner (1914) described kimberlites petrographically and separated them, based on macroscopic phlogopite content, into micaeous (lamprophyric) and basaltic (minimal phlogopite megacrysts) kimberlites. Smith (1983) used Sr, Nd, and Pb isotope ratios to distinguish between 4 basaltic and micaceous kimberlites of different age and mande source. Basaltic kimberlites generally have lower 87 Sr/86Sr ratios and higher 206pbp04Pb ratios than micaceous kimberlites. Smith (1983) also coined the terms group-I and group-II kimberlites, which are still in use today. However, the isotopic and petrological divisions are not always consistent as there are micaceous kimberlites that have a group-1 isotopic signature (e.g. Jagersfontein, Aries, Frank Smith; Taylor and Kingdom, 1999; Edwards et al., 1992; Sharp et al., 1990). The definition ofkimberlite used today was proposed by

Mitchell (1986) based on petrographic and mineralogical criteria taken from Mitchell

(1970, 1979), Skinner and Clement (1979), Clement et al. (1984) and Scott Smith and

Skinner (1984). Recently Rock (1991) classified kimberlites in which they are related to other lamprophyres and are members of a lamprophyric rock clan.

1.3. Mineralogy

Group-I kimberlites are now generally considered to represent a class of volatile­ rich potassic ultrabasic rocks containing macrocrysts (0.5-10 mm diameter crystals) and in sorne cases megacrysts (1-20 cm diameter crystals) of olivine, ilmenite, gamet, diopside, phlogopite, enstatite, and chromite set in a fine grained matrix of second generation olivine, monticellite, phlogopite, perovskite, spinel, apatite, rutile, calcite, and serpentine. Evolved members may contain few to no macrocrysts, and may be composed only of olivine, calcite, serpentine, and magnetite plus minor proportions of phlogopite, apatite, and perovskite (Le Maitre et al., 2002, based on Mitchell, 1986, 1994). Group­

II kimberlites are defined as volatile-rich (generally H20) ultrapotassic peralkaline rocks in which the principal macrocrysts and microphenocrysts are olivine and phlogopite. 5

Accessory mineraIs include diopside, spinel, perovskite, apatite, REE-rich phosphates, titanites, rutile, and ilmenite. Evolved members contain groundmass sanidine and potassium richterite, and in sorne cases late crystallizing zirconium silicates (Le Maitre et al., 2002). It should be cautioned, however, that "[A] definition of Group II kimberlites has not yet been agreed to as they have been insufficiently studied" (Le Maitre et al.,

2002).

The only economic group-II kimberlites that have been found are located in southem Africa; other micaceous kimberlites like the Aries pipe in Australia have group-l isotopic signatures (Edwards et al., 1992). However, micaceous kimberlites have strong affinities with olivine lamproites, and not with group-I kimberlites. Olivine lamproites, like group-II kimberlites, contain 30-40% modal olivine with phlogopite phenocrysts in a groundmass containing diopside, perovskite, and spinel (Mitchell and Bergman, 1991; Le

Maitre et al., 2002). An example of one is the Prairie Creek olivine lamproite in

Arkansas, U.S.A., which was once considered to be a kimberlite due to the fact that it is mineralogically similar to the micaceous kimberlites of South Africa, and contains diamonds (Scott-Smith and Skinner, 1984).

Another rock type that can be easily confused with group-I kimberlites is aillikite, a carbonate-rich lamprophyre. This rock type usually contains phenocrysts of olivine, diopside, amphibole, and phlogopite in a groundmass ofthese mineraIs, plus perovskite, rutile, spinel, calcite, dolomite, and apatite (Le Maitre et al., 2002). Although aillikites have been found only as dykes and sills, they can contain small numbers of diamonds.

Lastly, meimechites are ultramafic lavas similar mineralogically to kimberlites, i.e., they contain olivine phenocrysts, and have a groundmass of olivine, clinopyroxene, magnetite, and glass (Le Maitre et al., 2002). The report by Arndt et al. (1995) of biotite and spinel 6 within meimechite samples from the Meimecha-Kotuj Anabar shield in northem Siberia, further emphasizes the similarity to kimberlite, as does the report that meimechite lavas are regionally associated with the kimberlites of the Yakutian province (Fedorenko et al.,

2000). Other ultramafic rocks, such as komatiite, dunite and picrite, are too different mineralogically to be confused with group-I kimberlites.

There are five different ultramafic rock types that can occur as dykes or sills and are potassic in nature, which contain olivine, clinopyroxene, spinel and mica, thereby making hand sample identification difficult. In princip le, these rock types can be distinguished mineralogically. For example, group-I kimberlites and aillikites generally contain appreciable primary calcite or dolomite, whereas group-II kimberlites, olivine lamproites and meimechites do not contain these mineraIs. Only group-I kimberlites contain monticellite and rarely contain clinopyroxene. Group-II kimberlites do not contain leucite, whereas this mineraI is rarely present in olivine lamproite, but is characteristic of other lamproites. Aillikites contain biotite (or Fe-phlogopite), not phlogopite, whereas meimechites also contain biotite plus volcanic glass. However, most of these distinguishing mineraIs are in minor or trace proportions, and are difficult to see in hand specimen. Moreover, they are commonly altered making it impossible to identify them even in thin section. One tool used extensively for classification is the comparison of specific mineraI compositions of an unknown rock with the minerai compositions from known kimberlites, but this entails expensive and time-consuming electron microprobe analyses.

Most kimberlites contain abundant country rock and mantle xenoliths. Country rock or crustal xenoliths can range from "floating reefs", 50 to 300 m in diameter, to small particles < 100 )..lm in diameter (Mitchell, 1986). Mantle xenoliths, aithough quite 7 numerous, are more difficult to distinguish as they are composed of gamet, olivine, and other ultramafic mineraIs, and blend in with the primary kimberlite mineraIs. As kimberlitic rocks usually have high volatile contents compared to other igneous rocks, there can be interaction between the fluids and the country rock. Thus, during, or after emplacement, primary mineraIs may be replaced by secondary calcite and/or serpentine, obscuring the original nature of the rock.

1.4. Macroscopic Features of kimberlites

Diamondiferous kimberlites occur as dykes and sills, but those mined are generally carrot-shaped intrusions termed pipes. Kimberlite pipes consist ideally of a hypabyssal facies root, a middle diatreme facies, and an upper crater facies. The hypabyssal facies is fine-grained, and contains minor proportions ofmantle and country rock xenoliths. In the diatreme facies, the kimberlite is coarse-grained, and contains higher proportions of macrocrysts and megacrysts than the hypabyssal facies. The mantle xenoliths are larger, and there are abundant lithic fragments ofvarying sizes, plus reworked kimberlite fragments from previous phases of intrusion. The crater facies is characterized by low rims (15-50 m high) made ofhighly altered vesicular tuffs. Few examples of the crater facies have been found as most pipes and the surrounding country rock have been eroded to the level of the diatreme or even the hypabyssal facies of the pipe (Mitchell, 1986). Kimberlites commonly occur in fields (~50 km diameter) containing up to 100 individual intrusions, within which there may be c1usters of up to 20 intrusions located <1 km from each other (Mitchell, 1986). 8

Kimberlite intrusions that are closely spaced and chronologically associated can be markedly different in composition. For example, ten petrologically distinct varieties of kimberlite have been recognized within a single diatreme (Wesselton district of

Kimberley, South Africa) (Shee, 1984). Similarly, although the Newlands and Frank

Smith kimberlites, South Africa, have the same age (114 Ma, Smith, 1983), and only 12 km separate them, the Frank Smith Pipe is isotopically a (micaceous) group-I kimberlite, whereas Newlands is a group-II kimberlite. They are part of the larger Barkley West field ofmicaceous kimberlites, which overlaps the Kimberley field of group-I kimberlites.

1.5. Geochemistry

Geochemical methods have been largely ignored in the classification of kimberlitic and related rock types due to high concentrations of xenoliths and alteration effects. Whole rock analyses are mainly used to compare major element oxide proportions with those of standard analyses, and to determine variation within a study area or between study areas. They have also been used to identify contamination from outside sources (c.f. contamination index (C.I.) = (Si02 + Ah03 + Na20)/(MgO + 2K20);

Clement 1982). Trace element compositions have been used more frequently (as ratios to chondritic or primitive mantle values) to compare kimberlitic rocks from different study areas, and to draw conclusions about the source regions in the mantle for kimberlitic magmas. One notable exception is the study of Rock (1991) who used major oxides to separate the lamprophyric clan into five branches. However, a preliminary survey of published chemical analyses of diamond-bearing hypabyssal facies intrusive rocks suggests that kimberlitic and related rocks can be reliably distinguished on the basis of 9 their Mg, Si, and Fe contents (Francis, 2003). Thus it may be possible to use whole-rock analyses to classify these ultramafic rocks, and thereby provide a preliminary assessment of diamond potential by establishing whether or not they represent group-I or group-II kimberlite.

1.6. Objectives of the study

The overall objectives of the study were:

(1) To determine the mineralogy and petrography ofa selection of Québec

kimberlitic rocks and correlate this to the major and trace element

geochemistry;

(2) To use this correlation to develop a chemically-based classification scheme for

kimberlitic rocks;

(3) To correlate diamond grade to major element chemistry in kimberlitic material.

Since most economic diamond mines are sited on group-l kimberlites and a correlation appears to exist between diamond grade and kimberlite composition, analyzing the major and trace element geochemistry ofkimberlites and other ultramafic rocks provides another way of determining rock type and estimating diamond potential.

An important contribution ofthis thesis has been to assess the reliability of geochemistry as an exploration tool for diamonds. This was done through a survey of diamondiferous and non-diamondiferous ultramafic rocks in Québec. 10

1.7. Thesis organization

This thesis is divided into three chapters: a general introduction, followed by a stand-alone manuscript, and a general conclusion. In the second chapter, l report the results ofa geochemical, mineralogical, and petrological examination of rock samples from occurrences of kimberlitic rock in Québec.

Using the objectives stated previously, the following chapter discusses data analyzed from the kimberlitic and ultramafic occurrences and uses these data to develop a geochemical-based classification scheme. This scheme is then evaluated using the mineralogy-based classification scheme of Le Maitre et al. (2002). Previous suggestions that diamond grade correlates with kimberlitic chemistry, specifically Ti02 contents, are tested using the whole rock geochemistry data.

1.8. References

Arndt, N., Lehnert, K., Vasil'ev, Y., (1995): Meimechites: highly magnesian lithosphere­

contaminated alkaline magmas from deep subcontinental mantle. Lithos, 34: 41-

59.

Clement, c.R., (1982): A comparative geological study ofsome major kimberlite pipes in

the northem Cape and Orange Free State. Unpublished Ph.D. thesis, University of

Cape Town, South Africa.

Clement, c.R., Skinner, E.M.W., Scott Smith, B.H., (1984): Kimberlite redefined. J.

GeaI., 32: 223-228. 11

Edwards, D., Ramsay, RR, Rock, N.M.S., Taylor, W.R, Griffin, B.J., (1992):

Mineralogy and petrology ofthe Aries diamondiferous kimberlite pipe, central

Kimberley Block, Western Australia. J. Petral., 33: 1157-1191.

Fedorenko, V., Czamanske, G., Zen'ko, T., Budahn, J., Siems, D., (2000): Field and

geochemical studies of the melilite-bearing Arydzhangsky Suite, and an overall

perspective on the Siberian alkaline-ultramafic flood-volcanic rocks. Inter. GeaI.

Review, 42: 769-804.

Francis, D., (2003): Implications ofmajor element composition for the mantle sources of

kimberlite, aillikite, olivine lamproite, and meimechite. 8th Inter. Kimberlite

Confer. Extended Abstracts, FLA_0248, 5 p.

Le Maitre, RW., Streckeisen, A., Zanettin, B., Le Bas, M.J., Bonin, B., Bateman, P.,

Bellieni, G., Dudek, A., Efremova, S., Keller, J., Lameyre, J., Sabine, P.A.,

Schmid, R., Sorensen, H., Woolley, A.R. (2002): Igneous rocks: a classification

and glossary ofterms: recommendations of the International Union of Geological

Sciences, Subcommission on the Systematics of Igneous Rocks. Cambridge

University Press, New York.

Lewis, H.C., (1887): On diamantiferous peridotite and the genesis of diamond. GeaI.

Mag., 4: 22-24.

Lewis, H.C., (1888): The matrix ofdiamond. GeaI. Mag., 5: 129-131.

Meyer, H.O.A., (1985): Genesis of diamond: a mantle saga. Am. Mineral., 70: 344-355.

Mitchell, R.H., (1970): Kimberlite and related rocks - a critical reappraisal. J GeaI., 78:

686-704. 12

Mitchell, R.H., (1979): The alleged kimberlite-carbonatite relationship: Additional

contrary mineralogical evidence. Am. J. Science, 279: 570-589.

Mitchell, R.H., (1986): Kimberlites: Mineralogy, Geochemistry and Petrology. Plenum

Press, New York.

Mitchell, R.H., (1994): The lamprophyre facies. Mineral. Petrol., 51: 137-146.

Mitchell, R.H., (1995): Kimberlites, Orangeites and Related Rocks. Plenum Press, New

York.

Mitchell, R.H., Bergman, S.c., (1991): Petrology oflamproites. Plenum Publishing, New

York.

Rock, N.M.S. (1991): Lamprophyres. Blackie, GlasgowNan Nostrand Reinhold, New

York.

Scott-Smith, B.H., Skinner, E.M.W., (1984): A new look at Prairie Creek, Arkansas.

Kimberlites and Related Rocks, Proceed. 3rd Inter. Kimberlite Confer. Elsevier

Science Publishing Company Inc., New York, 255-284.

Sharp, T.G., Otten, M.T., Buseck, P.R., (1990): Serpentinization ofphlogopite

phenocrysts from a micaceous kimberlite. Contrib. Mineral. Petrol., 104: 530-

539.

Shee, S.R., (1984): The oxide mineraIs of the Wesselton Mine kimberlite, Kimberley,

South Africa. Kimberlites and Related Rocks, Proceed. 3rd Inter. Kimberlite

Confer. Elsevier Science Publishing Company Inc., New York, 59-74.

Skinner, E.M.W., Clement, C.R., (1979) : Mineralogical classification of South Africa

kimberlites. Kimberlites, Diatremes, and Diamonds: Their Geology, Petrology 13

and Geochemistry, Proceed. 2nd Inter. Kimberlite Confer. American Geophysics

Union, Washington, 1: 129-139.

Smith, C.B., (1983): Pb, Sr and Nd isotopic evidence for sources ofsouthem African

Cretaceous kimberlites. Nature, 304: 51-54.

Taylor, W.R., Kingdom, L., (1999): Mineralogy of the Jagersfontein Kimberlite; an

unusual group 1 micaceous kimberlite; and a comment on the robustness of the

mineralogical definition of "orangeite". Proceed. 7th Inter. Kimberlite Confer., 2:

861-866.

Vasilenko, V.B., Zinchuk, N.N., Krasavchikov, V.O., Kuznetsova, L.G., Khlestov, V.V.

Volkova, N.I., (2002): Diamond potential estimation based on kimberlite major

element chemistry. J Geochem. Exp/or., 76: 93-112.

Wagner, P.A. (1914): The Diamond Fields of South Africa. Transvaal Leader,

Johannesburg. 14

CHAPTER2

THE GEOCHEMICAL EXPLORATION OF KIMBERLITIC ROCKS IN

QUÉBEC

J.R. Hartzler!, D. Francis!, A.E. Williams-Jones!, and J.R. Clark!

1McGill University, 3450 University St., Montreal, Québec H3A 2A 7 15 .- 2.1. Abstract

In the past, geochemical methods have not been favoured in the classification of

kimberlitic rocks due to the problem associated with the high concentrations of xenoliths.

However, by only selecting matrix material for analysis this problem can be largely

overcome. The fractionation of olivine and phlogopite will cause an evolving kimberlitic

magma to become enriched or improvished in Si depending on the initial Si concentration

of the magma, separating group-l kimberlites and aillikites (low Si concentration) from

group-II kimberlites and meimechites (high Si concentration) at any Mg content. These

rock types form four separate fields in a Si vs. Fe discrimination diagram since group-l

and group-II kimberlites are relatively deficient in Fe compared to aillikites and

meimechites. Similar groupings are discemed when the ratios of La to Yb and Sm to Yb

are plotted against each other for kimberlitic rocks. By determining the mineralogy and

petrography of samples ofkimberlitic rocks, and correlating these data with their whole

rock geochemistry, we have evaluated the success of a chemically-based classification

scheme and used this scheme to assess the economic potential of the various districts in

Québec.

Kimberlitic and related ultramafic rocks were sampled from nine areas in Québec:

the Otish Mountains, Wemindji, Tomgat Mountains, Desmaraisville, Temiscamingue, Île

Bizard, Lac Leclair, Baie James and Ayer's Cliffregions. Major and selected trace

element concentrations in aIl samples were determined by XRF analysis and a

representative subset of samples were analyzed for trace element composition by lCP-MS.

Unaltered olivine and phlogopite were analyzed using the electron microprobe. 16

Mineralogically, the Otish Mountain rocks and the Guigues pipe of the

Temiscamingue area are group-I kimberlites and chemically range in composition between group-I and group-II kimberlite. The Tomgat Mountain dykes and the

Desmaraisville area rocks are best described as aillikites on the basis oftheir mineralogy, with chemical compositions ranging between aillikite and meimechite. Wemindji sills are composed of either group-I kimberlites or carbonatites mineralogically and chemically are considered to be carbonatites, but their REE concentrations plot with those of group-I kimberlites. The ultramafic intrusion in Temiscamingue may be classified mineralogically as olivine lamproite, but the very low REE concentrations do not support this classification. The rocks from Île Bizard are classified as alnoite and chemically are aillikite. Dykes from the Baie James and Ayer's Cliff areas are lamprophyres and chemically are possible ca1c-alkaline lamprophyres. Finally, the Lac Leclair rocks are highly altered and could not be mineralogically classified, but are classified as meimechite chemically.

Of the 37 samples that were classified both mineralogically and chemically, 23 or

62% were correctly classified using the Si vs. Fe discrimination diagram. This number increased to 84%, ifREE are used in conjunction with Si vs. Fe discrimination diagram.

The Si vs. Fe discrimination diagram separates group-I kimberlite from most aillikite and meimechite rocks and group-II kimberlite/olivine lamproite rocks from most aillikite and meimechite rocks.

Diamond grades are generally assumed to be independent ofkimberlite composition. However, Vasilenko et al. (2002) suggested that diamond grades can be correlated with the major element compositions of the kimberlites and Francis (2003) demonstrated that there is a strong inverse relationship between Ti02 and diamond grade. 17

Significantly, the only rocks with consistently low TiOz values were samples from the

Otish Mountains and Renard samples in particular, and these are from pipes which contain the highest concentrations of diamonds discovered in Québec. Most samples from aIl the other areas contained greater than 2 wt% TiOz. The results ofthis study support the suggestion that the diamond potential of a kimberlite can be predicted using its whole rock chemistry.

2.2. Introduction

Diamonds occur in a variety of ultramafic rocks inc1uding lamproites and lamprophyres such as aillikites and minettes. However, the majority of the 50 to 60 primary (versus secondary alluvial) diamond mines in the world (Levinson et al., 1992) exploit group-I kimberlites. Only a few diamond mines exploit group-II kimberlites (e.g. the Finsch pipe, Swartruggens dykes, Roberts Victor pipe, New Elands pipe; Mitchell,

1995), and one large mine (Argyle) in Western Australia exploits an olivine lamproite.

As group-I and group-II kimberlites have similar textures and mineralogy compared to mostly uneconomic lamproites and lamprophyres, distinguishing among them can be problematic. Though volumetrically insignificant compared to other igneous rocks, kimberlites have been the subject of intense scientific scrutiny because of their economic importance as hosts for diamonds. Nevertheless, there is still no c1ear and uncomplicated geochemical definition with which to differentiate between group-I and group-II kimberlites, and between them and other alkaline ultramafic rocks with lesser potential to host economic concentrations of diamonds. 18

Kimberlitic magmas are generally assumed to be the transport media by which diamonds from the upper mantle reach the Earth's surface (Meyer, 1985), implying that diamond grades should be independent ofkimberlite composition. Recently, however,

Vasilenko et al. (2002) reported data which suggest that diamond grades ofkimberlites in the Yakutia region of Russia correlate with the major element compositions of the kimberlites, and proposed a complex algorithm for predicting diamond grade based on major element geochemistry. Using their data, Francis (2003) showed that there is a simple inverse correlation between Ti and Fe concentrations and diamond grades. If these correlations are valid, it would suggest that for sorne kimberlites at least, diamonds are not simply accidentaI passengers, but are somehow related to the origin of these rocks.

In general, group-I kimberlites are a c1ass ofvolatile-rich (generally CO2) potassic ultrabasic rocks containing macrocrysts (0.5-10 mm diameter crystals) and locally megacrysts (1-20 cm diameter crystals) of olivine, ilmenite, gamet, diopside, phlogopite, enstatite and chromite set in a fine-grained matrix of second generation olivine, monticellite, phlogopite, perovskite, spinel, apatite, rutile, calcite and serpentine. Group­

II kimberlites are also volatile-rich (dominantly H20 rather than CO2), but differ from group-I kimberlites as they are mica-ri ch ultrapotassic peralkaline rocks with olivine and phlogopite as the principal macrocrysts and megacrysts in a groundmass of tetraferriphlogopite to phlogopite. Accessory mineraIs inc1ude diopside, spinel, perovskite, apatite, REE-rich phosphates, titanites, rutile and ilmenite. Most group-I and group-II kimberlites contain abundant country rock (crustal) and mantle xenoliths, ranging in size from small partic1es <100 /lm in diameter to "floating reefs" 50 to 300 m in diameter (Mitchell, 1986). Although kimberlites may occur as dykes and sills, most of 19 those mined are carrot-shaped intrusions tenned pipes, which consist ideally of a hypabyssal facies root, a middle diatreme facies, and an upper crater facies. These pipes commonly occur in fields (~ 50 km diameter) containing up to 100 individual intrusions, within which there may be clusters of up to 20 intrusions located less than 1 km from each other (Mitchell, 1986).

Historically, kimberlite classification has been based largely on mineralogical criteria. Lewis (1887, 1888) first used the tenn kimberlite to describe the rocks exploited in the Kimberley and De Beers mines located in the town ofKimberly, South Africa.

Wagner (1914) later described these kimberlites petrographically and separated them, based on macroscopic phlogopite content, into micaceous (lamprophyric) and basaltic kimberlites (minimal phlogopite megacrysts). Smith (1983) used Sr, Nd and Pb isotope ratios to distinguish between basaltic and micaceous kimberlites by age and mantle source.

Group-I (basaltic) kimberlites generally have lower 87Sr/86Sr ratios and higher 206Pbp04Pb ratios than group-II (micaceous) kimberlites. However, such distinctions are not always consistent, as sorne micaceous kimberlites have group-1 kimberlite isotopic signatures

(e.g. Jagersfontein, Aries, Frank Smith; Taylor and Kingdom, 1999; Edwards et al., 1992;

Sharp et al., 1990). Mitchell (1986) proposed a petrographic and mineralogical classification based on earlier research by Mitchell (1970, 1979), Skinner and Clement's

(1979), Clement et al. (1984) and Scott Smith and Skinner (1984), which is now used as the definition ofkimberlite. Rock (1991) subsequently classified kimberlites within a framework in which these rocks are related to lamprophyres, and proposed that they are members of a lamprophyric rock clan. However, these classifications suffer from the practicallimitations that kimberlite mineralogy can vary drastically among different 20 intrusions, or even within one intrusion, and that post-emplacement alteration obscures primary features.

Geochemical methods have not been favoured in the classification ofkimberlite and related rocks due to the problems associated with the high concentrations in them of xenoliths and the effects of alteration (Francis, 2003). However, a preliminary survey of published chemical analyses of diamond-bearing hypabyssal facies rocks suggests that kimberlitic and related lithologies can be reliably distinguished on the basis oftheir Mg,

Si and Fe contents (Francis, 2003). Thus it may be possible to use whole-rock analyses to evaluate these ultramafic rocks. Since most economic diamond deposits occur in group-I and group-II kimberlites, and there is an apparent correlation between diamond grade and kimberlite composition, the major and trace element geochemistry ofkimberlitic rocks could pro vide a simple, direct way of classifying kimberlitic rock types and estimating diamond potential. To test this idea, we have determined the mineralogy and petrography of samples of Québec kimberlitic rocks, and correlated these data with their major and trace element geochemistry to develop a chemically based classification scheme. In addition, we have correlated diamond grades with lithogeochemical data in order to assess the economic potential of various ultramafic rock types in Québec.

2.3. Sample Preparation and Analytical Techniques

Samples from twenty-seven occurrences of kimberlitic rocks in Québec, namely from the Otish Mountains, Wemindji, Tomgat Mountains, Desmaraisville, and

Temiscamingue regions were used in this study (Fig. 2-1). Non-kimberlitic ultramafic rocks from seven occurrences in the Île Bizard, Baie James, Lac Leclair, and Ayre's Cliff 21 regions, sorne ofwhich are reported to contain diamonds, were also sampled (Fig. 2-1).

From these thirty-four occurrences, fifty-seven samples (mainly ofhypabyssal facies rocks) were selected for analysis. Where hypabyssal rocks were not available, samples with minimal proportions of crustal xenoliths were used instead. In general, samples were cut using a rock saw, and then crushed in a mild steel, case hardened BICO jaw crusher. Fragments without visible xenolithic material, veining or external weathering were handpicked from the crushed material using a binocular microscope and ground.

This material was then powdered in an aluminum puck grinding barrel and divided into aliquots of 25 g.

Major (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P) and selected trace element (Ba, Cr,

Ni, Zn) compositions of 32mm diameter fused beads prepared from a 1:5 sample:lithium tetraborate mixture were determined by X-ray fluorescence analysis (XRF) using a

Philips PW 2400 4 kW automated spectrometer. Calibration involved the use of 15 to 40

International Standard Reference Materials (Govindaraju, 1994). The analytical precision is within 0.5% relative to the oxide wt.% measured. Total Fe is reported as Fe203. As aIl samples were not run in a single batch, sample LCR-3 was re-analyzed in each batch to test analytical reproducibility. Another four samples were run as duplicates in a second

XRF batch and two other samples were run as duplicates in the third XRF batch. The

C02 content was analyzed using an Eltra CS-800, which is functionally identical to a

Leco furnace.

Fort y-four of the fifty-seven samples analyzed by XRF were selected for trace element analysis by inductively coupled plasma mass spectrometry (lCP-MS; Actlabs,

Ancaster, Ontario) using a Perkin Elmer SCIEX ELAN 6000. A suite of 43 trace elements (V, Cr, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Cs, 22

Î 0

,..1. Lac Aignea~ . .., * . Lac Castignon

*OtiShMtn.

Desmaraisville *

Figure 2-1: Map of Québec with kimberlitic and related ultramafic rock occurrences.

Black stars indicate areas containing kimberlitic rocks and have had significant diamond exploration occurring there. Grey stars indicate areas containing non-kimberlitic but significant to this study ultramafic rocks. 23

Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Tl, Pb, Bi, Th, U) was analyzed using a 1 g split of each from the original rock powders, which was digested with aqua regia and diluted to 250 ml. Appropriate international reference standards were digested in the same way and at the same time; both samples and standards were then analyzed on a Thermo Jarrell Ash ENVlRO II simultaneous and sequential Perkin Elmer Optima 3000 lCP-MS.

Electron microprobe analyses of olivine and phlogopite were conducted with a

Jeol JXA-8900L Superprobe. Data reduction was preformed using a ZAF correction procedure. Olivine analyses were performed with an accelerating voltage of20 kV, a beam current of 40 nA, a beam diameter of 2 Ilm and a 20 s peak count using olivine­ based standards for major elements. Phlogopite analyses were performed with an accelerating voltage of 15 kV, a beam current of 20 nA, a beam diameter of 5 Ilm and a

20 s peak count except for Ba for which the peak count was 45 s. Orthoc1ase, almandine and diopside were used as a standard for the major elements.

2.4. Mineralogy of kimberlitic and related ultramafic rocks in Québec

2.4.1. Otish Mountains

The Otish Mountain kimberlite field is located in the Otish Mountains in north­ central Québec. This area is in the north east part of the Opatica and Opinaca subprovinces, northwest of the Proterozoic Otish basin along the Archean/ Aphebian unconformity (Moorhead and Beaumier, 2002). The Lac Beaver kimberlite, the first such 24 body to be found in this area, was discovered in 1978 (Jenkins, 1979). More recently,

Ashton Mining of Canada Ltd., in collaboration with SOQUEM, discovered nine potentially economic kimberlite pipes (Renard 1,2,3,4,65, 7, 8, 9, 10) and several kimberlitic dykes ~100 km to the north of Lac Beaver. Four other kimberlitic bodies (H­ l, H-2, H-3, H-4) also occur near Lac Beaver (~20 km to the north), and several other dykes have been found in the Otish area. Lac Beaver has been dated at 550.9 ± 3.5 Ma

(U-Pb on perovskite; Moorhead et al., 2002) and Renard 1 has been dated at 631.6 ± 3.5

Ma (U-Pb on perovskite; Birkett et al., 2004).

Renard rocks from this area are oftwo types; olivine macrocrystic rocks and kimberlitic breccia. The olivine macrocrystic material is a hypabyssal rock with olivine macrocrysts (0.5 to 10 mm) in a groundmass of ilmenite, spinel, perovskite, ulvospinel, phlogopite, monticellite, and apatite in a mesostasis (a very fine-grained to optically umesolvable primary matrix; Mitchell, 1995) dominated by calcite (Birkett et al., 2004).

Samples analyzed in our study consisted of olivine macrocrystic material from the Renard

1 and 4 pipes. The kimberlitic breccias are more complex, comprising macrocrystic and commonly serpentinised olivine locally rimmed by groundmass diopside in a mesostasis ofphlogopite, serpentine and minor calcite (Birkett et al., 2004). Crustal xenoliths of gneiss, tonalite and granite are rare within the hypabyssal olivine macrocrystic rocks but comprise from 15% to 90% rock volume of the kimberlitic breccias (Birkett et al., 2004).

Mica compositions range from Ba-phlogopite-kinoshitalite to tetraferriphlogopite, whereas olivine compositions range from F090 to F094 (Birkett et al., 2004).

Mineralogically, the hypabyssal rock would be classified as group-I kimberlite based on the presence ofmonticellite, kinoshitalite and the highly fosteritic nature of the olivine.

However, Birkett et al. (2004) disagreed with this classification because of the presence 25 oftetraferriphlogopite, the rarity ofnecklace spinel and the very aluminous nature of the other mineraIs. Instead, the y suggested that the Renard rocks are intermediate in composition between group-I kimberlite and melnoite, a name proposed for rocks from the lamprophyric facies of the melilitite clan like alnoite, aillikite, and melilitite (Mitchell,

1991, 1994).

The Lac Beaver rocks contain olivine and ilmenite macrocrysts in a groundmass of olivine, phlogopite, ilmenite, spinel and perovskite, with inters titi al calcite and serpentine. Olivine has large1y been replaced by serpentine, and phlogopite grain margins have been replaced by chlorite. The abundance of crustal xenoliths (which are of granite) ranges between 0 and 5 vol. %, and sorne rocks contain minor ilmenite veinlets. Mica compositions range from almost pure phlogopite to kinoshitalite but olivine composition could not be determined due to the extent of serpentinization. The rocks of the H pipes contain olivine, ilmenite and phlogopite macrocrysts in a groundmass of olivine, phlogopite, perovskite, ilmenite, spinel, and apatite, with interstitial serpentine and calcite.

Olivine is generally only partially serpentinised, although locally sorne olivine is completely serpentinised. Most rocks contain between 0 and 5 vol. % granite crustal xenoliths, but this figure can range up to 20 vol.%. Mica compositions range from phlogopite to kinoshitalite, and olivine compositions range from FOn to FOs5 and average

Fos! (Tables 2-1 and 2-2). Mineralogically, these rocks would be classified as group-I kimberlite based on the presence ofkinoshitalite. 26

2.4.2. Torngat Mountains

The Tomgat Mountains ofnortheastem Québec contain several dyke swanns of ultramafic rocks, the first ofwhich were discovered in 1994 (Digonnet, 1997). The mountains are part of the Tomgat orogenic belt, comprising the eastem part of the

Paleoproterozoic southeastem Churchill Province (Tappe et al., 2004). Two main dyke swanns have been described: the Abloviak dykes (Digonnet, 1997; Digonnet et al., 2000), and the Tomgat dykes (Tappe et al., 2004). The Q39 Tomgat dyke has been dated at

584.0 ± 3.6 Ma (U-Pb on perovskite; Tappe et al., 2004), whereas the Abloviak dykes 4 39 have been dated at 550 Ma (Ar 0_Ar on phlogopite; Digonnet et al., 2000).

Tomgat rocks examined in this study contain biotite and olivine macrocrysts in a matrix of biotite, ilmenite, spinel, olivine, c1inopyroxene, perovskite, apatite, and calcite with serpentine or calcite replacing most olivine and chIo rite replacing minor amounts of phlogopite. Most rocks contain between 0 and 5 vol. % crustal xenoliths of gneiss but the

Peter Pipe contains 10-15 vol.% crustal xenoliths. Mica compositions are mostly Ti-rich biotite (Table 2-1), whereas olivine compositions range from F061 to F084 and average

FOn (Table 2-2). Samples from the Tomgat dykes studied by Tappe et al. (2004) also contain primary gamet, whereas the Abloviak rocks studied by Digonnet et al. (2000) contain gamet and ilmenite macrocrysts and large multicrystalline c1inopyroxene masses that they considered to be xenocrystic. The only crustal contribution takes the fonn of secondary calcite veins; dykes from neither area contain crustal xenoliths. Although the composition ofmatrix mica (biotite) in the Abloviak dykes is different from that of the

Tomgat dykes mica (almost pure phlogopite), both have tetraferriphlogopite rims

(Digonnet et al., 2000). Tomgat dyke rocks also contain biotite megacrysts with 27

Table 2-1: List of mica compositions determined by electron microprobe from selected samples with unaltered mica. Sample 4,5, 10 and 13, - Otish Mountains. Sample 16, 17 and 22 - Tomgat Mountains. Sample 26,29,31 and 34 - Desmaraisville. Sample 37 and

38 - Temiscamingue. Sample 43 - Île Bizard. Sample 53 - Ayer's Cliff. ) ..:.8

4 5 5 10 10 10 13 16 16 17 17 22 22 26 26 29 29 29 31 core core nm core nm core core nm core nm core nm core nm core nm core Si02 37.88 40.67 39.91 41.62 41.70 38.74 37.17 41.99 37.94 38.46 41.06 37.23 37.55 39.53 39.94 39.96 40.84 40.78 39.44 Ti02 0.55 0.51 0.78 1.05 1.00 0.38 1.18 0.39 0.49 4.90 0.69 5.67 5.57 2.85 2.07 1.73 1.44 1.04 4.89 AhO, 15.40 13.49 12.69 11.79 11.92 14.67 17.32 9.34 16.03 12.99 0.66 13.74 13.90 11.51 10.16 11.69 10.89 Il.49 11.52 Cr20 , 0.01 0.00 0.00 0.24 0.34 0.02 0.00 0.00 0.00 0.27 0.01 0.15 0.04 0.01 0.01 0.00 0.00 0.00 0.01 FeO 3.23 2.69 3.63 5.04 4.41 2.19 3.50 7.50 2.46 7.22 17.53 7.20 7.02 6.78 7.59 6.15 6.36 6.01 10.54 MnO 0.03 0.03 0.05 0.04 0.02 0.03 0.05 0.03 0.02 0.04 0.11 0.05 0.05 0.07 0.07 0.08 0.06 0.06 0.08 MgO 25.71 27.14 26.95 24.04 24.79 25.97 24.20 24.52 25.69 21.00 23.82 20.16 20.33 23.21 23.93 24.40 24.79 25.12 18.86 CaO 0.06 0.04 0.04 0.04 0.05 0.02 0.34 0.05 0.06 0.02 0.06 0.02 0.03 0.04 0.06 0.02 0.03 0.07 0.04 BaO 1.04 0.25 0.91 0.04 0.05 2.61 1.92 0.03 2.62 0.36 0.01 0.64 0.63 0.56 0.37 0.48 0.43 0.14 0.55 Na20 0.04 0.05 0.04 0.16 0.10 0.03 0.03 0.14 0.10 0.32 0.40 0.52 0.82 0.24 0.21 0.65 1.23 0.80 0.87 K20 10.24 10.99 10.36 10.99 10.99 10.19 10.44 10.86 10.18 10.49 10.18 9.64 9.45 10.14 10.13 9.66 8.99 9.67 9.24 Total 94.19 95.86 95.36 95.04 95.36 94.85 96.16 94.83 95.58 96.08 94.54 95.03 95.40 94.95 94.53 94.83 95.06 95.18 96.03

Structure fonnulas based on 22 oxygens Si 5.49 5.74 5.71 5.97 5.95 5.60 5.32 6.11 5.45 5.56 6.37 5.43 5.44 5.76 5.86 5.78 5.87 5.85 5.75 Ti 0.06 0.05 0.08 0.11 0.11 0.04 0.13 0.04 0.05 0.53 0.08 0.62 0.61 0.31 0.23 0.19 0.16 0.11 0.54 Al 2.63 2.24 2.14 1.99 2.00 2.50 2.92 \.60 2.72 2.21 0.12 2.36 2.37 1.98 1.76 1.99 1.84 1.94 1.98 Cr 0.00 0.00 0.00 0.03 0.04 0.00 0.00 0.00 0.00 0.03 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe 0.39 0.32 0.43 0.60 0.53 0.26 0.42 0.91 0.30 0.87 2.28 0.88 0.85 0.83 0.93 0.74 0.76 0.72 1.29 Mn 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Mg 5.55 5.71 5.75 5.14 5.27 5.60 5.17 5.32 5.50 4.52 5.51 4.39 4.39 5.04 5.23 5.26 5.31 5.37 4.10 Ca 0.01 0.01 0.01 0.01 0.01 0.00 0.05 0.01 0.01 0.00 0.01 0.00 0.00 0.01 0.01 0.00 0.01 0.01 0.01 Ba 0.06 0.01 0.05 0.00 0.00 0.15 0.11 0.00 0.15 0.02 0.00 0.04 0.04 0.03 0.02 0.03 0.02 0.01 0.03 Na 0.02 0.02 0.02 0.06 0.04 0.01 0.01 0.05 0.04 0.13 0.17 0.21 0.33 0.09 0.09 0.26 0.48 0.31 0.35 K 1.89 1.98 1.89 2.01 2.00 1.88 1.91 2.02 1.87 1.93 2.02 1.80 1.75 1.88 1.90 1.78 1.65 1.77 1.72 Total Cations 16.09 16.08 16.09 15.94 15.94 16.05 16.05 16.08 16.09 15.82 16.58 15.75 15.80 15.93 16.03 16.05 16.12 16.11 15.76 (continued on next page) _J

Table 2-1 (continued)

33 33 34 37 37 38 38 43 53 core nm core core nm core nm core core Si0 2 39.63 39.99 38.27 40.68 40.49 40.82 40.68 35.44 35.26 Ti0 2 1.96 1.78 1.68 0.47 0.49 0.56 0.58 2.72 5.57 Ah03 13.43 13.58 14.08 15.33 15.54 14.66 14.88 16.98 17.40 Cr203 0.02 0.02 0.01 0.31 0.30 0.34 0.35 0.01 0.01 FeO 5.26 5.04 6.61 3.68 3.62 3.14 3.20 5.52 10.54 MnO 0.05 0.05 0.11 0.03 0.03 0.05 0.03 0.07 0.12 MgO 24.11 24.43 23.22 24.40 24.46 24.98 24.87 21.84 16.42 CaO 0.03 0.03 0.13 0.05 0.07 0.03 0.03 0.15 0.11 BaO 0.35 0.33 0.53 0.18 0.17 0.22 0.24 3.65 1.84 Na20 1.08 1.59 0.26 0.32 0.32 0.35 0.38 0.21 0.92 K20 9.23 8.54 10.22 9.61 9.48 9.34 9.31 9.51 8.36 Total 95.16 95.38 95.11 95.05 94.96 94.50 94.55 96.09 96.56

Structure formulas based on 22 oxygens Si 5.66 5.67 5.56 5.75 5.72 5.78 5.76 5.19 5.15 Ti 0.21 0.19 0.18 0.05 0.05 0.06 0.06 0.30 0.61 AI 2.26 2.27 2.41 2.55 2.59 2.45 2.48 2.93 3.00 Cr 0.00 0.00 0.00 0.03 0.03 0.04 0.04 0.00 0.00 Fe 0.63 0.60 0.80 0.43 0.43 0.37 0.38 0.68 \.29 Mn 0.01 0.01 0.01 0.00 0.00 0.01 0.00 0.01 0.01 Mg 5.14 5.16 5.03 5.14 5.15 5.28 5.25 4.77 3.58 Ca 0.00 0.01 0.02 0.01 0.01 0.00 0.00 0.02 0.02 Ba 0.02 0.02 0.03 0.01 0.01 0.01 0.01 0.21 0.11 Na 0.42 0.61 0.10 0.12 0.12 0.14 0.15 0.08 0.37 K 1.69 1.55 1.89 1.73 1.71 1.69 1.68 1.78 1.56 Total Cations 16.04 16.08 16.05 15.84 15.83 15.82 15.83 15.97 15.70 30

Table 2-2: List of olivine compositions determined by electron microprobe analysis from

selected samples. Fosterite composition was determined by MglMg+Fe*100. Sample 10,

Il and 13, - Otish Mountains. Sample 16 and 22 - Tomgat Mountains. Sample 34-

Desmaraisville. Sample 37 and 38 - Temiscamingue. Sample 53 - Ayer's Cliff.

10 11 13 16 22 34 37 38 53 Si02 40.61 40.64 40.64 39.97 39.88 39.66 40.10 40.46 40.53 Ti02 0.02 0.01 0.02 0.01 0.02 0.02 0.00 0.00 0.00 A120 3 0.02 0.01 0.01 0.00 0.02 0.02 0.02 0.01 0.04 Cr203 0.05 0.05 0.04 0.00 0.03 0.02 0.01 0.01 0.02 FeO 9.34 9.40 8.99 13.59 14.28 14.88 12.71 10.40 10.66 MnO 0.12 0.11 0.11 0.17 0.15 0.19 0.30 0.28 0.14 MgO 49.34 49.17 49.50 46.04 45.59 45.10 46.80 48.47 48.26 CaO 0.07 0.05 0.04 0.02 0.05 0.09 0.01 0.00 0.14 NiO 0.31 0.32 0.30 0.24 0.38 0.23 0.24 0.26 0.23 Total 99.89 99.77 99.67 100.04 100.41 100.22 100.18 99.89 100.04

Si 1.01 1.01 1.01 0.98 0.97 0.96 0.98 1.00 1.00 Ti 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Al 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Cr 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe 0.39 0.39 0.37 0.55 0.58 0.60 0.52 0.43 0.44 Mn 0.01 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01 Mg 1.58 1.58 1.59 1.46 1.43 1.41 1.48 1.55 1.54 Ca 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 Ni 0.01 0.01 0.01 0.01 0.02 0.01 0.01 0.01 0.01

Fo ComEosition 80.40 80.30 81.12 72.90 71.32 70.25 74.07 78.33 77.86 31 tetraferriphlogopite rims (Tappe et al., 2004). The presence of biotite, c1inopyroxene and fosterite-poor olivine suggests that these dykes are aillikites (ultramafic lamprophyres)

(Tappe et al., 2004 and Digonnet et al., 2000).

The Tomgat dykes are also contain two other rock types mineralogically different from the aillikites. One ofthem contains olivine and phlogopite macrocrysts in a groundmass of dolomite crystals, breunnerite ([Mgo.95-o.5 FeO.05-0.5] C03), gamet, spinel, ilmenite, rutile and perovskite with the carbonates making up over 50% of the volume of the rock (Tappe et al., 2004). Owing to the amount of carbonate, Tappe et al. (2004) c1assified this rock as carbonatite. The other rock type, a grey inter-granular rock, contains olivine and phlogopite macrocrysts in a groundmass of diopside, amphibole, gamet, spinel, ilmenite, perovskite, rutile, apatite, dolomite, pyrite and chalcopyrite, with phlogopite crystals being rimmed by serpentine and chlorite (Tappe et al., 2004). As there is minimal carbonate in this rock type, which is made up of more than 70 vol. % mafic silicate mineraIs, Tappe et al. (2004) followed the criteria of Rock (1986) and c1assified these rocks as mela-aillikites.

2.4.3. Wemindji

Several sub-horizontal kimberlite sills occur along the east coast of Baie James

(Letendre et al., 2003). These occurrences are 30 to 60 km east of the Cree village,

Wemindji, in the La Grande Subprovince of the Wemindji-Caniapiscau structural zone

(Moorhead et al., 1999). The sills have been dated at 629 ± 29 Ma (Rb-Sr on phlogopite;

Letendre et al., 2003). 32

Wemindji sill rocks from our survey contain olivine, ilmenite, phlogopite and gamet macrocrysts in a groundmass of calcite, dolomite, olivine, ilmenite, spinel, perovskite, diopside, phlogopite and pyrite, with serpentine replacing olivine. No crustal xenoliths were seen, although sorne samples contain numerous thin secondary calcite veinlets. Wemindji rocks studied by Mitchell and Letendre (2003) were also reported to contain rutile, apatite and baddeleyite (Zr02) in the groundmass. Granite crustal xenoliths were mentioned as being present in the sills, but their abundances were not reported

(Mitchell and Letendre, 2003). Mica compositions range from phlogopite to kinoshitalite and olivine compositions from FOS9 to F093 (Mitchell and Letendre, 2003). Owing to the presence ofkinoshitalite, the high proportion of fosterite in the olivine and the high content of calcite, these sills are composed of either group-I kimberlites or carbonatites.

Mitchell and Letendre (2003) classified them as hypabyssal spinel-ilmenite-apatite­ phlogopite-dolomite kimberlite.

2.4.4. Desmaraisville

The first kimberlitic rocks to be described in the Desmaraisville area were a dyke swarm at Bachelor Lake (Watson, 1955). Subsequently, an ultramafic and calc-alkaline lamprophyre dyke swarm was described by Boume and Bossé (1991), and five kimberlite pipes and several other dykes were also discovered. These intrusions are located in the

Lac Shortt region, and are part of the Abitibi greenstone belt, in the Waswanipi-Saguenay structural corridor (Moorhead and Beaumier, 2002). The Bachelor Lake dykes have been dated at 1100 Ma (no error given, K-Ar on phlogopite; Watson, 1967), 1104 ± 17 Ma 33

(Rb-Sr on phlogopite; Alibert and Albarede, 1988) and 1079 ± 10 Ma (U-Pb on perovskite; Machado, N., pers. comm., cited in Heaman et al., 2004).

Rocks from the Ailly Township kimberlitic occurrence, Le Tac occurrence and

Certac dyke examined in our study contain biotite and olivine macrocrysts in a groundmass of biotite, clinopyroxene, calcite, spinel, ilmenite, orthopyroxene, olivine, perovskite and apatite with interstitial serpentine and chlorite. Most olivine has been replaced by serpentine and the mica composition is biotite (Table 2-1). Granite crustal xenoliths are rare, but sorne samples contain secondary calcite veins. The Bachelor Lake dykes also contain calcite and ilmenite macrocrysts (Watson, 1955). There are no crustal xenoliths in these rocks (Watson, 1955) or the ultramafic dykes from Lac Shortt (Boume and Bossé, 1991). Based on the presence of clinopyroxene, orthopyroxene and biotite, the rocks from Ailly, Le Tac and Certac wou Id be classified as aillikite (ultramafic lamprophyre). The Bachelor Lake dykes, though very similar to compositionally to the rocks analyzed in this study, were classified as kimberlites by Watson (1955), whereas the dykes from Lac Shortt were classified as ultramafic lamprophyres by Boume and

Bossé (1991).

2.4.5. Temiscamingue

The Guigues kimberlite pipe is located ~ 12 km from the Québec/Ontario border, west of the village ofNotre-Dame-du-Nord. Two other kimberlite bodies (N.D.N. #1 and

#2) occur ~5 km north of Notre-Dame-du-Nord, and straddle the Québec/Ontario border.

These bodies were intruded into Huronian Supergroup metasediments (Bennet et al.,

1993). An ultramafic intrusion and a lamprophyre dyke swarm are also known in this 34 area, and were emplaced in the Temiscamingue structural (rift) zone (Grenville Sub­

Province; Moorhead and Beaumier, 2002). The Guigues pipe has been dated at 142.3 ±

6.6 Ma (U-Pb on perovskite; Heaman and Kjarsgaard, 2000), the N.D.N. #2 pipe at 126.6

± 1.0 Ma (Rb-Sr on phlogopite; Heaman et al., 2004), and the ultramafic intrusion at

4 1320 Ma (Ar 0_Ar39 on phlogopite; Tom Hashimoto, pers. comm. cited in Moorhead et al.,

1999).

Rocks from the Guigues pipe contain olivine, ilmenite and phlogopite macrocrysts in a groundmass of olivine, perovskite, phlogopite, ilmenite, spinel and calcite, with serpentine having completely replaced olivine. The proportion of limestone crustal xenoliths ranges between 10 and 20 vol.%. N.D.N. #1 and #2 rocks are composed of the same mineraIs as the Guigues pipe and contain 5 to 20 vol. % of limestone or metasiltstone crustal xenoliths (Sage, 1996). Rocks from all three pipes contain more olivine than phlogopite, indicating that they are group-I kimberlites (Sage, 1996). The older ultramafic intrusion contains olivine, phlogopite, amphibole and orthopyroxene phenocrysts in a groundmass of serpentine, chlorite, ilmenite and spine1; crustal xenoliths are absent. The mica is almost pure phlogopite (Table 2-1), whereas the olivine composition ranges from F074 to F078 (Table 2-2). Based on the presence of amphibole, near end member phlogopite and fosteritic olivine, these rocks may be classified as olivine lamproites but do not satisfy the chemical criteria set out in Le Maitre et al. (2002) for lamproite. Therefore, the mineralogical classification for these rocks is suspect. 35

2.4.6. Île Bizard

The Île Bizard intrusion is located just west of Montréal, and was first described by Harvie (1910), but was not considered to be kimberlitic until the 1960's, when 10 microdiamonds were extracted from a bulk sample (Raeside and Helmstaedt, 1982). The intrusion has been dated at 126 ± 6 Ma (K-Ar on whole rock; Clark, 1972), and is part of the Cretaceous Monteregian igneous province (Raeside and Helmstaedt, 1982).

Île Bizard rocks analyzed in this study contain olivine, biotite, clinopyroxene and ilmenite macrocrysts in a groundmass of biotite, clinopyroxene, ilmenite, spinel, calcite, melilite, perovskite, apatite and serpentine. Raeside and Helmstaedt (1982) estimated that xenoliths and xenocrysts make up 5 to 50 vo1.% of the intrusion, and that 5 to 40 vo1.% of them are dolostone or basement gneiss, i.e., of crustal origin. Rare crustal xenoliths were seen in the samples analyzed in the CUITant study. Rather than classify these rocks as kimberlite, as Raeside and Helmstaedt (1982) have done, these rocks are classified here as alnoite (ultramafic lamprophyre) due to the presence of biotite, clinopyroxene and melilite, and lack of groundmass olivine.

2.4. 7. Other Occurrences

Ultrabasic rocks have also been characterized in several other regions in Québec, including Lac Leclair, Baie James, Ayer's Cliff, Lac Aigneau and Lac Castignon. At Lac

Leclair, an ultramafic volcanic 1ens occurs 60 km east of Ak:ulivik village on Hudson's

Bay. This lens lies above the unconformable base of the Proterozoic Cape Smith Belt with underlying Achaean granitoid basement (Baragar et al., 2001). The rocks contain megacrysts of olivine in a groundmass of calcite, dolomite, serpentine, and chlorite with 36 minor amounts of olivine, phlogopite, ilmenite, and spinel. No crustal xenoliths were seen, but as these rocks are highly altered, crustal xenoliths could be altered beyond recognition. Chemical analyses indicate that the mica is pure phlogopite (Baragar et al.,

2001). Owing to the highly altered state of the rocks, neither we nor Baragar et al. (2001) could classify these rocks mineralogically.

The Lac de l'Astrée dyke swarm near Baie James is located ~100 km east­ northeast ofWemindji in the La Grande Subprovince (Yasinski Group) of the Wemidji­

th Caniapiscau structural zone (Dianor Press Release, June 5 , 2001). Lac de l'Astée dykes contain amphibole and ilmenite phenocrysts in a matrix of serpentine, plagioclase, ilmenite, spinel, calcite and pyrite with numerous secondary quartz veins. Crustal xenoliths are rare except for the Bear 1 dyke which contains 10 vol. % of granitic xenoliths. Based on the presence of amphibole and ilmenite, we classify these dykes as lamprophyres.

Near Ayer's Cliff in southern Québec, three Monteregian-related lamprophyric dykes cross-cut Cambrio-Ordovician and Silurio-Devonian rocks (Trzcienski and

Marchildon, 1989). Two of the dykes have been dated by an unspecified K-Ar method at

104 and 106 Ma (J.G. McHone, 1988, pers. commun. cited in Trzcienski and Marchildon,

1989). These dykes contain olivine, clinopyroxene, and hornblende phenocrysts in a matrix of olivine, hornblende, clinopyroxene, plagioclase, spine1, calcite, serpentine and chlorite with serpentine replacing olivine. Trzcienski and Marchildon (1989) also found apatite and glass within the dykes, plus an unspecified proportion of metasedimentary crustal xenoliths. Very few crustal xenoliths were seen in our rocks, with only one sample containing 5 vol.% ofmetasedimentary material. Chemical analyses indicate that 37

the mica is biotite (Table 2-1). Based on the presence of biotite, clinopyroxene and

hornblende, these rocks are classified as lamprophyres (Trzcienski and Marchildon, 1989).

In the Lac Aigneau region, west of the New Québec orogenic belt and 140 km

west-southwest of Kuujjuaq (Lemieux et al., 2002), ultramafic and carbonate dykes were

described by Berclaz et al. (2001). The ultramafic dykes contain phenocrysts of olivine,

Cr-rich diopside, Ti-rich phlogopite and spinel in a fine-grain to aphanitic groundmass of

diopside and phlogopite (Berclaz et al., 2001; Lemieux et al., 2002). Most olivine

crystals have been altered or replaced first by an unspecified carbonate, then by

serpentine, chlorite, talc and magnetite, whereas phlogopite phenocrysts are rimmed by

amphibole (Lemieux et al., 2002). The carbonate dykes contain greater than 90 vol.%

coarse- to fine-grained unspecified carbonates, with apatite and rutile as accessory

mineraIs (Lemieux et al., 2002). Strongly altered ultramafic dykes intennediate in

composition between the ultramafic dykes and the carbonate dykes described above are

also present. In them, the dominant mineraI is an unspecified secondary carbonate and

only rare relicts of olivine, clinopyroxene, phlogopite and spinel remain (Lemieux et al.,

2002). Berclaz et al. (2001) classified the ultramafic dykes as lamprophyres (due to their mafic mineraI content and lack of quartz and plagioclase) and the carbonate dykes as

carbonatites (due to their high carbonate content).

The Lac Castignon pipes and dyke swann, discovered on the western margin of

the Labrador trough ~150 km south of Kuujjuaq, intrude into Early Proterozoic sediments

(Dimroth, 1970). A lamprophyre dyke from the area has been dated at 1873 ± 53 Ma (K­

Ar on whole rock; Dressler, 1975) and a carbonatite dyke has been dated at 1880 ± 2 Ma

(U-Pb on zircon; Chevé and Machado, 1988); both are synchronous with the early stages

of the Hudsonian Orogeny in the Labrador Trough area (Chevé, 1993). Lamprophyre 38 dykes described by Dressler (1975) contain olivine and pyroxene phenocrysts in a fine­ grained groundmass of gamet, phlogopite, apatite, magnetite, pyrrhotite and pyrite.

Olivine has been completely replaced by serpentine and talc while pyroxene has been replaced by chIo rite (Dressler, 1975). Carbonatite dykes, classified as such on the grounds that they contain greater than 50% modal ankerite (Le Maitre et al., 2002), contain biotite, ankerite, olivine, magnetite, apatite and perovskite phenocrysts in an extremely fine-grained groundmass of biotite, ankerite, serpentine, talc and magnetite

(Dimroth, 1970). Olivine has been complete1y replaced by serpentine and biotite has been commonly chloritized. Dimroth (1970) c1assified several of the dykes and breccia heteroliths as meimechites as they contain serpentinised olivine with or without biotite and carbonatized augite in a matrix of serpentine, talc and magnetite with minor amounts of carbonate, but the same rock types were c1assified as a massive serpentinised ultramafic breccia and a micaceous massive ultramafic dyke (Chevé, 1993). Another meimechite described by Dimroth (1970) was thought to be a small gabbroic intrusion by

Chevé (1993). Several other pipe-shaped occurrences are brecciated carbonatites with varying proportions of crustal xenoliths.

2.5. Geochemistry

2.5.1. Major Elements

Potassic ultramafic magmas evolving by fractionation of olivine and phlogopite phenocrysts become enriched or improvished in Si according to whether their initial Si 39 concentration is greater or less than the fractionating mineraIs, respectively. This effectively separates group-I kimberlites and aillikites from group-II kimberlites and meimechites, which can be illustrated by plots of Mg vs. Si for mineralogically classified rocks described in the literature (Fig. 2-2a). Published whole rock geochemical analyses of samples containing greater than 15 wt% MgO, less than 45 wt% Si02 and less than 8 wt% Ab03 can be used for this purpose. In addition, Fe concentration can be used to further discriminate between these rocks. For example, aillikite and meimechite magmas are relatively rich in Fe at any given Mg content compared to group-I and group-II kimberlite magmas (Fig. 2-2b). Consequently these rock types form separate fields on Fe vs. Si plots (Fig. 2-3a) using olivine composition as a field boundary. Kimberlitic and related rocks from Québec classify variably as group-I kimberlite (Kl), group-II kimberlite and olivine lamproite (KIl), aillikite (A), and meimechite (M) (Fig. 2-3b).

Wemindji samples are not plotted on Figure 2-3b as they represent highly evolved carbonate-rich kimberlites and no similar samples were used from pub li shed literature to create the classification scheme. Baie James and Ayer' s Cliff samples also cannot be represented on Figure 2-3b as they are too silica- and/or aluminum-rich to be considered kimberlitic (Table 2-3).

Kimberlitic rocks from the Otish Mountains plot generally in the KI and Kil fields, with one exception plotting in the A field (Fig. 2-4). Renard samples from this study and

Birkett et al. (2004) have large variations in Si concentrations and small variations in Fe.

Birkett et al. has classified these rocks, based on hypabyssal material that contained few or no crustal xenoliths, as intermediate between melnoites and kimberlites. However, melnoites are comprised of aillikites, alnoites and other lamprophyres (Mitchell, 1991,

1994), which plot in the A field at a higher Fe concentration than group-I kimberlite. 40

• Group 1 Kimbcrlit~s o, OIh'ine • Group Il Kimbt:rlitcs , Olivine Lamproitt:s 1 1 1 ~ Aillikilt:s , 1 o Mt:imechitcs , 50 ,

Où ~ 30 • • •

20 30 40 .S "'l' (-catIons• )

Figure 2-2a: A plot of Si cations versus Mg cations for kimberlitic rocks taken from the pub li shed literature. The olivine and mica points describe olivine and mica compositions in cation units of Si and Mg. Aline drawn through these two points separates group-l kimberlites and aillikites from group-II kimberlites/olivine lamproites and meimechites.

References are listed in Appendix 2. 41

• Group 1 Kimbcrlîtcs Group Il Kimbcrlitcs • Olivine Lamproitcs

~ Aillikitcs o Meimcchitcs

5 10 15 Fe (cations)

Figure 2-2b: A plot of Fe cations versus Mg cations for kimberlitic rocks taken from the published literature. Opposite to the previous diagram, group-I kimberlites and group-II kimberlites/olivine lamproites are grouped together while aillikites and meimechites are grouped together. References are listed in Appendix 2. 42

• Group 1 Kimberlitcs Olivine ---1...... o Biotite Group II Kimberlites Aillikites • Olivine Lamproites (A) 1:::.. Aillikitcs 15 Meimechites o Meimechites (M) ~ t/1 t:: ...... 0 ro 10 0 "'-1 0 ~

5

.. Group 1/ Kimberlites .Groùp 1Kimberlites· . Olivine Lamproites (K 1) (K Il)

30 Si (cations)

Figure 2-3a: A plot of Si cations versus Fe cations for published analyses. The Olivine

Line is the compositional variation of olivine in cation units of Fe and Si. The Phlogopite point is showing ideal phlogopite composition in terms of Si and Fe cation units. The

Biotite point is the composition ofK2(Fe, Mg)6[Si6Ah02o](OH)4 in cation units.

References are listed in Appendix 2. 43

1 1 • Group 1 Kimberlites ...... 1--- Olivine • Group II Kimhcrlitcs Olivine Lamproiles 1:::,. Aillikitcs 15 ~ .. - ,-.\ rJj ~ L:::. 0 .~..... Cà 10 ~ - U '-'

1 1 30 40 Si (cations)

Figure 2-3b: A plot of Si cations versus Fe cations for rocks from Québec. The Olivine

Line is the compositional variation of olivine in cation units of Fe and Si. Samples are from most areas within Québec with exception ofWemindji, Baie James and Ayer's Cliff. 44

• Lac Bea.er -c Olivine. H Pipes ... Renard this sludy \l Renard (Birkett el a/.. 2(j04) 15 M

r"- I/':; ~ 0 ~' / ~ 10 ~ / ü ~ / ~ / .~ 5 V'• Kil

30 40 Si (cations)

Figure 2-4: A plot of Si cations versus Fe cations for Otish Mountain rocks. The Olivine

Line is the compositional variation of olivine in cation units of Fe and Si. Renard samples have a large variation in Si concentration while having a very sm aIl variation in

Fe concentration. Lac Beaver sarnples cluster in the KI field with one outlier in both the

A and KIl fields. 45

The large variation in Si concentration and not Fe suggests the possibility that the former is due to Si contamination instead of reflecting a mixture of melnoite and kimberlite as suggested by Birkett et al. Beaver Lake rocks generally plot in the KI field, with the exception of one outlier in the A field (sample 5). This latter sample contains less Si and much more Fe than most Beaver Lake rocks, and is likely related to ilmenite veining and/or related alteration. Similarly, rocks from the H-2, H-3 and H-4 pipes plot in the KI field, except for sample 8; this sample has a higher Si concentration and a slightly lower

Fe than most H rocks, and is probably due to a greater abundance of crust al xenoliths in this sample.

Most kimberlitic rocks from the Tomgat region plot in the A field, with a few samples plotting in the M field and in or near the boundary between the KI and A fields

(Fig. 2-5). Although the rocks are aIl from one geographic area, a large range in both Si and Fe concentrations is found. Rocks categorized by Tappe et al. (2004) as aillikites and mela-aillikites plot as expected, in the A field, but show significant variability in Si concentration coinciding with category names. The aillikites plot mainly in the middle of the A field (lower Si), while the mela-aillikites plot in both the A and M fields (higher Si).

The spread in data would not be attributed to crustal contamination, as most samples had few to no crustal xenoliths.

Si and Fe concentrations in Wemindji samples are very low compared to other

Québec samples. Due to their high CO2 content, they are more similar to carbonatites than kimberlites. As carbonatites were not used in the creation of the Si versus Fe diagram, they cannot be categorized by using the latter. 46

1 1 • Tomgats this sludy Olivine --... ÂDigonnef et a/.. ]O()() \l Mcla-aillikitc ... <> Aillikitc 15 >

1 1 30 40 Si (cations)

Figure 2-5: A plot of Si cations versus Fe cations for Tomgat Mountain rocks. The

Olivine Line is the compositional variation of olivine in cation units of Fe and Si.

Tomgat samples have a large variation in both Si and Fe concentrations. 47

Table 2-3: Major (wt%) and trace element (ppm) content of Québec kimberlitic rocks.

Samples areas described in Appendix 1. 48

Sam~le 2 3 4 5 6 7 8 9 10 SiO, 34.95 39.56 31.38 29.08 27.10 29.67 31.64 42.85 29.38 30.07 TiO, 0.845 0.895 2.499 2.863 2.686 2.741 3.555 2.164 3.536 3.344 Ab0 3 3.11 5.36 2.69 2.69 2.62 3.02 3.48 6.49 3.07 2.81 Fe,03 8.97 8.09 8.74 11.10 18.32 10.14 11.76 7.86 1l.30 11.32 MnO 0.156 0.147 0.132 0.195 0.177 0.158 0.257 0.138 0.176 0.193 MgO 33.84 25.33 29.66 27.59 26.56 29.06 28.29 18.83 27.56 31.49 CaO 7.89 10.35 8.40 8.99 7.78 8.24 5.94 10.51 11.19 6.53 Na,O 0.28 0.74 0.07 0.12 0.09 0.11 0.07 1.26 0.28 0.14 K,O 1.59 1.93 1.17 0.97 1.14 1.27 1.89 2.89 0.5 0.88 P,Os 0.362 0.515 0.396 0.614 0.601 0.588 0.732 0.568 0.129 0.574 BaO 1588 1555 1038 1358 1552 1432 2293 1548 764 1593 Cr,03 2672 2026 2228 2426 2349 2229 3026 1418 2300 2519 Ni 1453 878 993 773 864 958 797 462 738 982 Zn 12 8 16 24

CO, (%) 1.21 1.17 5.15 6.42 4.56 5.74 3.63 0.35 2.25 3.54

Ag

Table 2-3 (continued)

SamEle II 12 13 14 15 16 17 18 19 20 Si02 30.97 35.16 28.51 29.36 29.70 24.18 32.28 36.28 35.72 27.69 Ti02 3.453 2.728 3.118 2.762 3.916 0.734 6.180 4.634 8.892 8.137 Ah0 3 3.03 4.70 2.71 2.51 2.90 0.72 4.04 3.61 5.02 5.51 Fe203 11.68 10.00 10.77 10.31 12.76 10.72 15.13 14.13 14.61 11.65 MnO 0.190 0.167 0.177 0.151 0.223 0.169 0.203 0.199 0.324 0.253 MgO 33.20 27.45 30.75 29.24 26.10 29.12 14.55 22.51 15.79 9.63 CaO 4.76 6.24 8.82 8.84 8.82 13.36 13.45 9.07 10.53 20.22 Na20 0.18 0.18 0.07 0.08 0.13 0.08 0.72 0.86 1.35 0.41 KlO 1.6 3.68 1.19 0.74 2.87 0.46 3.05 2.57 0.62 1.87 P20 5 0.292 0.468 0.619 0.460 0.732 2.887 0.853 0.560 1.294 l.l61 BaO 846 1417 1804 1011 3689 811 1378 2087 699 1083 Cr203 2605 2250 2469 2328 2085 1422 1540 1773 943 878 Ni 999 837 938 981 939 1162 512 1040 499 446 Zn 7

COl (%) 0.76 1.98 5.27 5.95 4.39 10.63 8.37 1.35 0.70 10.43

Ag

Table 2-3 (continued)

Sam21e 21 22 23 24 25 26 27 28 29 30 Si02 33.48 35.72 10.54 19.94 35.59 37.22 36.83 30.96 34.85 27.54 Ti02 7.113 4.016 3.447 1.920 4.948 4.547 3.982 3.080 4.946 5.188 Ah0 3 4.54 3.91 2.17 1.08 4.35 5.67 5.35 2.88 4.57 5.25 Fe203 11.40 14.92 6.61 3.88 16.46 15.12 14.45 14.01 16.34 13.35 MnO 0.215 0.192 0.240 0.112 0.275 0.266 0.268 0.227 0.392 0.445 MgO 14.51 23.56 2J.71 24.27 19.66 20.47 14.98 16.71 23.67 12.00 CaO 13.07 7.57 21.08 17.38 8.09 6.14 13.68 14.14 4.97 17.51 Na20 1.51 0.82 0.11 0.21 0.29 0.32 0.95 0.17 0.31 0.24 K20 2.82 1.91 0.04 0.3 1.91 1.56 1.74 1.48 1.93 2.04 P20 S 1.477 0.612 0.761 0.826 0.784 0.263 0.588 0.472 0.435 0.747 BaO 1842 1084 10ll 1920 1014 908 738 627 923 1280 Cr203 765 2362 1768 1478 lI32 1281 1086 1721 1364 883 Ni 435 1060 449 910 605 668 653 939 767 384 Zn 238 int LOI 9.24 6.15 32.45 29.41 7.44 8.26 6.78 15.32 7.81 15.16 Total 99.68 99.83 99.50 99.76 100.08 100.12 99.85 99.78 100.52 99.71

C0 2 (%) 6.14 1.54 28.46 24.42 3.14 1.04 4.30 10.95 0.34 12.38

Ag

Table 2-3 (continued)

Sample 31 32 33 34 35 36 37 38 39 40 SiO, 37.50 32.88 38.87 24.09 35.50 32.49 42.50 41.82 46.58 43.22 Ti02 4.121 4.233 2.509 5.039 1.121 1.079 0.219 0.249 0.242 0.253 AI,03 4.23 5.19 12.71 3.09 2.15 1.57 5.17 5.00 5.92 5.87 Fe203 17.91 14.33 9.52 16.47 8.44 8.38 10.97 Il.33 8.30 10.20 MnO 0.275 0.284 0.162 0.249 0.131 0.135 0.165 0.174 0.143 0.165 MgO 15.11 16.71 9.97 20.30 36.53 35.36 29.30 32.94 23.34 24.27 CaO 10.43 13.60 Il.59 15.13 2.05 4.89 4.12 2.98 8.72 6.53 Na20 0.59 0.92 3.01 0.17 0.20 0.26 0.29 0.15 0.27 0.43 K20 2.97 2.76 1.77 \.53 1.53 0.78 1.84 1.39 2.86 2.48 P,O, 0.450 0.822 0.900 0.720 0.291 0.505 0.093 0.100 0.055 0.124 BaO 589 1349 3126 1287 533 837 355 356 700 291 Cr20 3 1299 757 408 947 2436 2341 5173 6650 3708 4269 Ni 956 383 161 428 1616 1494 1137 1289 745 817 Zn LOI 5.90 7.60 9.11 12.73 12.44 14.71 5.47 4.33 3.27 5.86 Total 99.77 99.59 100.49 99.78 100.85 100.62 100.80 101.28 100.22 99.94

CO2 (%) 3.63 5.43 3.05 8.50 0.71 2.98 0.53 0.20 0.09 4.69

Ag

Table 2-3 (continued)

SamQle 41 42 43 44 45 46 47 48 49 50 Si02 28.77 3\.75 25.27 26.80 33.77 39.43 5\.10 52.07 54.74 50.95 Ti02 2.113 2.402 2.105 2.134 3.369 2.425 0.711 0.648 0.415 0.623 Ah0 3 6.15 6.38 5.69 5.60 2.68 3.72 Il.32 10.99 10.82 Il.05 Fe203 11.92 13.18 10.69 11.66 14.73 13.68 9.22 8.86 7.04 9.15 MnO 0.169 0.179 0.203 0.202 0.175 0.\17 0.245 0.158 0.136 0.148 MgO 17.07 19.97 15.11 18.55 27.34 28.94 13.52 13.62 14.48 13.79 CaO 18.89 13.77 17.55 17.16 3.38 1.54 7.07 6.97 6.14 6.60 Na20 0.16 0.20 0.21 0.15

CO2 (%) 5.53 2.62 16.04 8.55 10.08 3.53 0.37 0.35 0.11 1.29

Ag

Table 2-3 (continued)

SamEle 51 52 53 54 55 56 57 Si02 51.61 52.69 41.42 41.80 40.58 41.45 31.28 Ti02 0.646 0.610 2.176 2.620 2.674 1.935 5.293 Ah0 3 10.74 14.39 Il.46 15.47 13.95 10.35 3.19 Fe203 8.94 12.49 10.06 9.29 10.05 9.98 16.87 MnO 0.184 0.206 0.167 0.169 0.169 0.163 0.203 MgO 14.30 5.67 16.06 8.08 9.34 18.11 25.04 CaO 7.07 6.78 Il.31 13.03 13.61 10.99 9.91 Na20 2.53 2.51 2.40 \.70 1.88 1.89 0.41 K20 0.83 2.61 1.56 2.29 1.99 1.25 1.5 P20j 0.299 0.446 0.552 0.714 0.765 0.458 0.328 BaO 453 835 662 1497 1024 586 745 Cr20, 1530 281 930 325 427 1179 1613 Ni 506 14 411 46 140 500 795 Zn 77 60 LOI 3.12 2.18 3.43 4.59 4.88 3.64 5.84 Total 100.53 100.70 100.80 99.94 100.05 100.44 100.18

CO2 (%) 0.35 0.10 2.16 1.16 1.77 1.83 3.82

Ag

Desmaraisville area rocks plot mostly in the A field with a few rocks plotting in the M field and one outlier in each of the KI and Kil fields. There is a larger range in Si concentration than there is in Fe (Fig. 2-6). Samples collected by Watson (1955) plot within the A field, near other Desmaraisville rocks, raising the possibility that they are not group-I kimberlites as suggested by him. Somewhat surprisingly, sample 33 plots at the highest Si concentration and in the Kil field, rather than sample 27, which contains visible crustal xenoliths.

Most of the Temiscamingue area samples plot within the KIl field, with one plotting in the KI field (Fig. 2-7). The Guigues pipe samples plot either in the KI field or near the KI/KIl border. Sample 35, which plots on the border between the KI and KIl fields, has more visible crustal xenoliths than the other sample. The ultramafic samples all plot within the KIl field, with one sample plotting on the border between the M and

KIl fields. These samples have a large range in Si concentration and a small range in Fe concentration.

Île Bizard samples plot mostly within KI field with a few plotting on the KI/A border and one plotting in the M field (Fig. 2-8). There is a large range in Si concentration while the range in Fe concentration is small. This study's samples have a greater range in Si concentration compared to the pub li shed analyses, which have a small

Si range. Raeside and Helmstaedt (1982) suggested that rocks from this region were kimberlites, and geochemically their samples plot in the KI field. However, this study's rocks plot mostly in the A field and support Mitchell's (1983) suggestion that they are not kimberlite. Therefore the debate about whether these rocks are group-l kimberlites or alnoites (Raeside and Helmstaedt, 1982, 1983; Mitchell, 1983) can not be settled with this diagram. 55

1 1 Dcsmaraisvillc, lhis study "'4t---Olivine • Ccrtac Dykç + Ailly 'f'LeTac A.. BOl/me & Bossé. 1991 _ 15 1- M o Wa/so/l. /955

~ rJi C 0 .-..... ~ 10 r- - U '-' () ~ 5 - - 'KI Kil

1 1 30 40 Si (cations)

Figure 2-6: A plot of Si cations versus Fe cations for Desmaraisville area rocks. The

Olivine Line is the compositional variation of olivine in cation units of Fe and Si.

Desmaraisville samples have a large variation in both Si and Fe concentrations with both samples from Watson (1955) and Boume and Bossé (1991) plotting in the aillikite field. 56

1 1 • Guigues Pipe ...... --Olivine .À. Ultramatic Intrusion

15 - A M -

~ Vi ...1"" 0 ,...... / ('j 10 - - u ,.. / ,.11;" / (.) ,," . _._.~~ --- .. . ' ~ . T I)(),. 5 - - 'KI- Kil

1 1 30 40 Si (cations)

Figure 2-7: A plot of Si cations versus Fe cations for Temiscamingue area rocks. The

Olivine Line is the compositional variation of olivine in cation units of Fe and Si.

Temiscamingue samples have a large variation in Fe concentrations and a small variation in Si concentrations. 57

1 1 • Ile BizanL this sludv ...... I--Olivine OlJarnois el al., lYY'; \l'Alibel'! & .'J/hart;de. 1Y88 L::..A4archalld. lY7fJ 15 o Rues/de & lIelll/s{lIed!, - - 'A M 1982

/*"" cr./) 0 ...... C\l 10 - - u '-' ~ ~ 5 - - KI' Kil

1 1 30 40 Si (cations)

Figure 2-8: A plot of Si cations versus Fe cations for Ile Bizard rocks. The Olivine Line is the compositional variation of olivine in cation units of Fe and Si. Ile Bizard samples have a large variation in Si concentrations and a smaller variation in Fe concentrations.

Samples from this study plot on the border or in the aillikite field while samples from

Raeside and Helmstaedt (1982), Alibert and Albarède (1988) and Hamois et al. (1990) plot in the group-I kimberlite field. Marchand (1970) sample plots in the meimechite field. 58

Lac Leclair samples have a large range in Si concentration and a small range in Fe compared to Si and mostly plot in the A field with one sample (sample 46) plotting in the

M field (Fig. 2-9a). A possible explanation for the major geochemical differences between the two studies is that in this study samples were handpicked before grinding whereas this was not the case for the samples analyzed by Baragar et al. (2001). Lac de l'Astée's dykes (Baie James region) have greater than 8 wt% Alz03, less than 15 wt%

MgO and the highest Si concentration of the Québec rocks analyzed for this survey, preventing them from being classified in this diagram. Ayer's Cliff area samples are from two different dykes, one of which also contains greater than 8 wt% Alz03 and is not plotted in Figure 2-9a. Sample 57, which represents the other dyke, has lower Alz03 and plots within the A field. No published geochemical analyses of the Lac Aigneau area rocks are known to the author. Lac Castignon rocks plot in both the A and M fields and have a larger range in Si concentration than in Fe (Fig. 2-9b). Meimechites described by

Dimroth (1970) plot in the M field and the A field as do lamprophyres described by

Dressler (1975).

2.5.2. Trace Elements

The chondrite-normalized rare earth element (REE) profiles of Québec kimberlitic rocks from this study are aIl characterized by smooth profiles with strong light REE

(LREE) enrichment (Fig. 2-10). When grouped according to their Si vs. Fe classification, the different rock types can be broadly distinguished based on their absolute REE abundances and the slopes oftheir REE profiles (Fig. 2-11). To further evaluate the feasibility of using the REE to discriminate between kimberlitic rocks, the ratio of La to

Yb was plotted against the ratio of Sm to Yb for rocks described and classified on 59

1 l ,. Lac Leclair titis study ...... 1--- Olivine o Lac Leclair (Saragar el al.• ]()() 1) * Ayer's CIiI!' 15 r- .. 'A' - >:) M ~. (f'; ;::: 0 .-+-' C\! 10 f0- ~oo * - () ~ >:) .. ' .- ". ' 0 ,.- ' ~ ," ... ' ' ':JO

5 "'"" - Kil

1 1 30 40 Si (cations)

Figure 2-9a: A plot of Si cations versus Fe cations for Lac Leclair and Ayer's Cliffrocks.

The Olivine Line is the compositional variation of olivine in cation units of Fe and Si.

Lac Leclair samples from this study do not plot with samples from Baragar et al. (2001). 60

1 1 .. ~ Lamprophyre J ...... I--Ohvme ~ Lmnprophyre :: (l)resslcl; IY75j <> \lCarbomnizcù Mcimcdütc <> ~ Meimechite TujT ' , 15 - 'A '~ M (Dimrolh. 19ïO) -

~ \l rj; 't3 ::: t .....0 <>, -+-J 85 / C\l 10 - "1',, - ,0' / U ," .. ' '-" ' o' / C) 0' ' / 1---"-" ,", ' .' !l.. 90 5 - - K'I" 'Kil

1 1 30 40 Si (cations)

Figure 2-9b: A plot of Si cations versus Fe cations for Lac Castignon rocks. The Olivine

Line is the compositional variation of olivine in cation units of Fe and Si. Lamprophyre 1 dykes from Dressler (1975) plot with meimechite tuff samples from Dimroth (1970). 61

III Otish Mountains • l'omgat Mountains .. Desmuraisville • I,.\'emindji  Temiscamingue # Ile Bizard *' Lac Leclair * Ayer's Cliff + Baie James

0.1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Figure 2-10: A plot of chondrite nonnalized REE for rocks from Québec. The profiles are smooth and have a variety of slopes. 62

_Group 1 Kimbcrlitcs

_Group 11 Kimbcrlili.:~ 1.000 Olivine Lamproîtc~ o Aillikitcs o Mcîmcchitcs

0.1 La Cc Pr Nd Sm Eu Gd Tb Dy 110 Er Tm Yb Lu

Figure 2-11: A plot of chondrite nonnalized grouped REE for Québec kimberlitic rocks.

The profiles have been grouped into their classification categories based on where they plotted in Figure 2-3b. 63

.~ mineralogical grounds in the literature (Fig. 2-12). La, Sm and Yb were chosen as they

represent the light, middle and heavy elements respectively within the Lanthanide series.

Generally, group-I kimberlites plot at higher La/Yb and Sm/Yb values than both group-II

kimberlites and meimechites. For similar values of SmIYb, group-II kimberlites plot at

higher La/Yb values than meimechites. The field of aillikite values overlaps those of the

other kimberlitic rocks, except for the most LREE enriched group-l kimberlite field.

The data for rocks from the Otish Mountains plot mostly within the group-I

kimberlite field and have high values for both La/Yb and Sm/Yb (Fig. 2-13). However,

rocks from the Renard pipes have a broader range in values than do rocks from the Lac

Beaver and H pipes, which spread linearly toward the group-II kimberlite field. The two

samples analyzed from the Wemindji area plot within the group-I kimberlite field and

have high values for both La/Yb and SmIYb (Fig. 2-13), but because oftheir very low

silica content, can not be classified conclusively as kimberlitic (see Section 2.5.1.). The

La/Yb and SmIYb values for the Guigues pipe sample from Temiscamingue place it at the

lower limit of the group-I kimberlite field, consistent with its SilFe classification as a

group-I kimberlite (Fig. 2-13, Section 2.5.1.).

Values for Torngat Mountain rocks plot in the aillikite field but also partially

overlap the group-I kimberlite and group-II kimberlite/olivine lamproite fields (Fig. 2-14).

The compositions of aillikites and mela-aillikites reported by Tappe et al. (2004) plot in

the same area as those of rocks from this study, although the mela-aillikites have a larger

range of La/Yb and Sm/Yb values. It should be noted, however, that based on Si/Fe

discrimination several of these samples would be classified as meimechite. Rocks from

the Desmaraisville area have a wide range of La/Yb and Sm/Yb values, which define a

linear array (Fig. 2-14). These values plot mostly in the aillikite and meimechite fields 64

• Group 1 Kimberlites Group Il Kimbcrlites • Olivine Lamproites ,6. Aillikitcs o Meimcchitcs

1.0 10 [00 [OO(l La/Yb

Figure 2-12: A plot oflog La (ppm)/ Yb (ppm) versus log Sm (ppm)/ Yb (ppm) from published geochemical analyses of mineralogically classified kimberlitic rocks. Tentative groupings have been delineated in darkest grey for group-I kimberlites, medium grey for group-II kimberlites and olivine lamproites, light grey for aillikites and white for meimechites in order to simplify comparison between samples collected in this study to those from published geochemical analyses. References are listed in Appendix 2. 65

• Bcavcr Lake ell Pipes T Renard this study V Renard (Birket! el aL., 20(4) la Wemindji "fi Guigues Pipe \.0 10 100 1000 LaIYb

Figure 2-13: A plot oflog La (ppm)/ Yb (ppm) versus log Sm (ppm)/ Yb (ppm) from

Otish Mountain rocks. Tentative groupings have been delineated as in Figure 2-12. The

Otish samples plot mostly within the group-1 kimberlite area with five samples plotting lower than this group and two plotting higher than this group. The Wemindji sample and

Guigue Pipe sample also plot in this same area. 66

• Tomgats this study \l Mcla-aillikitc <> Aillikitc Tappe t'l al., 20()4 • Cenac Dykc +Aillv TLeTac 1:::.. Boume <~ Bos.\l:, 1991 • lie Bizard 1.0 10 100 1000 La/Yb

Figure 2-14: A plot oflog La (ppm)/ Yb (ppm) versus log Sm (ppm)/ Yb (ppm) from

Tomgat Mountain rocks and Wemindji rocks. Tentative groupings have been delineated as in Figure 2-12. The Tomgat samples plot mostly in the aillikite area with a few in the group-I kimberlite and group-II kimberlite/olivine lamproite area. The Desmaraisville samples also plot in the aillikite field with sorne over-Iap into the meimechite and group-I kimberlite field. The Ile Bizard samples plot on the border between the aillikite and group-II kimberlite field. 67 where the two fields overlap, consistent with their Si/Fe values which classify them as aillikite and meimechite (Section 2.5.1.). The kimberlitic rocks from Île Bizard have compositions overlapping the fields of aillikite and group-II kimberlitel olivine lamproite, whereas on the basis of the Si/Fe determination they would be classified as transitional between aillikite and group-I kimberlite (Fig. 2-14).

The ultramafic samples from the Temiscamingue area have very low La/Yb and

SmIYb ratios and only one sample plots within the meimechite field. The Lac Leclair rocks display a large range in La/Yb values, a small range in SmIYb values and plot within or near the aillikite and group-II kimberlite/olivine lamproite fields (Fig. 2-15).

By contrast, based on their Si/Fe values, all the samples from Baragar et al. (2001) are aillikites and those from this study range from aillikite to meimechite. Despite the wide range in the major element compositions reported by Baragar et al. (2001) and in this study, all samples share similar REE enrichment. The Lac de l'Astrée rocks of the Baie

James region have the lowest SmIYb values of all samples analyzed in this study, very low La/Yb values and do not plot within any of the fields ofkimberlitic rocks (Fig. 2-15) confirming that they are not kimberlitic. The rocks from the Ayer's Cliff area also plot at low values of La/Yb and Sm/Yb, with two samples interpreted to be group-II kimberlites on the basis of Si/Fe composition plotting within the meimechite field.

AlI Québec kimberlitic rocks are enriched in incompatible elements compared to primitive mantle (Fig. 2-l6a and b). Rocks from the Otish Mountains, Tomgat

Mountains, Wemindji and Desmaraisville are as exhibit negative K anomalies and small negative Sr anomalies (Fig. 2-l6a). Two Desmaraisville samples exhibit large positive

Pb anomalies, while one Wemindji sample has a large negative Rb anomaly. Rocks from

Île Bizard, Lac Leclair, Ayer's Cliff and the Guigue Pipe in Temiscamingue also exhibit 68

100 r----.----,--.--,-,-,...... ,r-r-.,-----.,----,--.--.--,--,-,.,..,

..0 <:E 10 Vl

• Lac Lcclair this sludy >::): Lac Lcclair (Bm'agar el al.. .20(1) * Aycr's Cliff + Baic Jamcs .... Ultramafic Intrusion

1.0 ...... ___.L-_--'-_-'----'----'---L...... L-.L....l.. ___ ...... L __-'--...... J'-----'--....L--'--.I...-l....J 10 100 1000 La/Yb

Figure 2-15: A plot oflog La (ppm)/ Yb (ppm) versus log Sm (ppm)/ Yb (ppm) from Lac

Leclair, Ayer's Cliff and Baie James rocks. Tentative groupings have been delineated as in Figure 2-12. Lac Leclair samples plot mostly in the aillikite field with two plotting in the group-II kimberlite/olivine lamproite field. Ayer's Cliff and Baie James samples plot at low La/Yb and Sm/Yb values with two samples from Ayer's Cliffplotting in the meimechite field. The ultramafic intrusion samples from Temiscamingue also plot in this same area. 69

" II1II Otish Ivlountains • Tomgat Mountains • D.:smaruÎsùllc 1.(1)0 • Wemindji

~..... ;:: <':! ~ 100 v ;;- .... ";:::: "C= :;.;:0- !O u 0 '"'

0.1 Rb Ba Th K Ta Nb La Ce Pb Sr Nd P Sm Zr Eu Ti Dy Er Yb Lu

Figure 2-16a: A spider diagram of primitive mantle normalized incompatible elements for

rocks from the Otish Mountains, Tomgat Mountains, Desmaraisville and Wemindji. All

samples have a prominent negative K anomaly. 70

lO.OOIlc:---r-,---,r--r-.-----.,--,.---r-,---,r--r-.-----.,--,.---r-,---,r--r---::l

... T.:mi:;caminguc • Ile Bizard • Lac Leclair 1.000 * Ayer's Cliff • Baie James

10

0.1 Rb Ba Th K Ta Nb La Ce Pb Sr Nd P Sm Zr Eu Ti Dy Er Yb Lu

Figure 2-16b: A spider diagram of primitive mande normalized incompatible elements for rocks from Temiscamingue, Ile Bizard, Lac Leclair, Ayer's Cliff and Baie James. Each area has different anomalies. 71

negative K anomalies (Fig. 2-16b). Lac Leclair rocks, however, are depleted in K when

compared to primitive mantle and exhibit a negative Sr anomaly. The Lac de l'Astrée

dykes of Baie James and the ultramafic intrusion from Temiscamingue have low values

of almost aIl incompatible elements. In contrast to the other rocks analyzed from the

other areas, they have anomalously low Ta and Nb contents.

2.5.3. Diamond Grade vs. n02

Conventional wisdom ho Ids that kimberlites serve only to transport diamonds

from the mantle to the crust (i.e., diamonds and kimberlite are genetically unrelated), and

thus there should be no dependency of diamond concentration on kimberlite composition.

However, Vasilenko et al. (2002) showed that there is a correlation between diamond

grade and kimberlite composition in the Yakutia region of Russia. Using non-linear pairwise regressions, Vasilenko et al. (1982) showed that Ti02, Na20, K20 and P20S

concentrations correlate significantly with diamond content and that Ti02 has the highest

determination coefficient at -0.52 (it is negative as Ti02 is inversely related to diamond

content, Vasilenko et al., 2002). In a subsequent study they developed a ten parameter

(Si02, Ab03, Fe203(tot), Ti02, MgO, CaO, P20s, Na20, K20, LOI) non-linear

multivariate regression algorithm which successfully correlated diamond content with

major oxide composition. Building on Vasilenko et al. (1982,2002), Francis (2003) used

these data to show that diamond grades appear to be inversely related to Ti and Fe

concentrations. Vasilenko et al. (2002) made no distinction between group-I and group-II

kimberlites in developing their algorithm or data set and the mineralogy of the Yakutia

rocks is not discussed in their paper. However, Francis (2003) used their Si and Mg data 72 to detennine which samples represented group-1 kimberlite and which represented group­

II kimberlite. Both groups exhibit a negative correlation of Ti content with diamond grade and are indistinguishable on the basis ofthese parameters.

The Tomgat rocks from this study, Tappe et al. (2004) and Digonnet et al. (2000) have a large range in Ti concentrations, from 0.7 to 9.4 wt% Ti02 (Fig. 2-17). Onlyone sample contains less than 1 wt% Ti02, whereas there is a c1uster of samples with Ti02 concentrations between 2.0 and 2.5 wt% and the rest contain greater than 3 wt% Ti02.

The two samples collected from the Wemindji area contain 1.9 and 3.4 wt% Ti02, whereas rocks from the Desmaraisville region contain between 3.0 to 5.2 wt% Ti02. Île

Bizard rocks have a very narrow range ofTi02 contents between 2.1 and 2.4 wt%.

Although bulk samples have not been analyzed for diamond grades in any ofthese areas, a few small diamonds were found in drill core and/or hand samples (Table 2-4); in each case the estimated diamond grade is less than 0.5 cpht (carats per hundred tons). Yakutia samples with high diamond grades (i.e., > 100 cpht, detennined by sampling prospecting drill holes in 10 m core intervals with samples weighing > 300 kg; Vasilenko et al., 2002) typically have Ti02 concentrations of 0 to 2 wt%, while samples with extremely high diamond grades (i.e., > 300 cpht) have Ti02 concentrations between 0 and 1 wt%.

However, diamond grades as high as those of the Yakutia samples are not commonly reported. The Premier pipe, the Wesselton pipe (both from South Africa), the Dokolwayo pipe in Swaziland and the Orapa pipe in Botswana all have diamond grades in the range offrom 27 to 68 cpht (Jennings, 1995). Pipes with higher diamond grades inc1ude the

Kimberley Mine pipe with 100 cpht (Jennings, 1995) and the Ekati Mine pipes with 109 cpht (Rylatt and Popplewell, 1999). Samples from the Premier pipe have Ti02 concentrations of 1.96 to 2.0 wt% (Maier et al., 2005) as do samples from the Wesselton 73

500~~0~------~• Torngat - this study o Torngat - Tappe et al.. 2004 Digon net el al.. 2()()() • Dcsmaraisvillc • Wcmindji o • Ile Bizard o o ~'llsilellko et al.. ~()()~ IJJ cPtJo 0 o

o

011:1

1 2 3 4 5 6

Ti01 (wt%)

Figure 2-17: A plot ofTi02 oxide wt% versus Diamond Grade for most Québec rocks.

Sorne Tomgat Mountain rocks and the Ile Bizard rocks plot at lower Ti concentrations than other samples from Desmaraisville. 74

Table 2-4: Summary of diamonds found at different areas in Québec. Sites within the

Otish Mountains have produced the most diamonds. Renard diamond grades and

diamonds found are from Ashton of Canada website, December 2005. Lac Beaver, H-2,

H-3 and Temiscamingue ultramafic intrusion diamonds are from Ditem Exploration Inc.

Tomgat 1 diamond grade is from Twin Mining website, December 2005. Wemindji

diamonds found is from Letendre et al. (2003). Diatac diamonds found is from William

Resources/Diabor Inc (Husson, 1994). Île Bizard diamonds found is from Raeside and

Helmstaedt (1982) and Lac de l'Astée diamonds found is from Dianor Resources Ine. website, December 2005.

Area Specifie Site Diamond Grade Diamonds F ound (cpht) Otish Mountains Renard 1 59 diamonds Otish Mountains Renard 2 92 Otish Mountains Renard 3 124 Otish Mountains Renard 4 46 Otish Mountains Renard 65 22 Otish Mountains Renard 7 2.3 Otish Mountains Renard 8 7.7 Otish Mountains Renard 9 97 Otish Mountains Renard 10 127 diamonds Otish Mountains Lac Beaver 3 rnicrodiamonds Otish Mountains H-2 1 rnicrodiamond Otish Mountains H-3 1 rnicrodiamond Tomgat Mountains Tomgat 1 30 Wemindji Wemindji sill 2 rnicrodiamonds Desmaraisville Diatac pipe and dykes 1 rnicrodiamond Terniscamingue Ultramafic Intrusion 22 diamonds Île Bizard Île Bizard Intrusion 10 microdiamonds Baie James Lac de l'Astrée 4 microdiamonds 75 pipe (1.94 to 2.25 wt%; le Roex et al., 2003), while samples from the Kimberley Mine pipe have Ti02 concentrations of2.21 to 2.41 wt% (le Roex et al., 2003). Samples from the Ekati Mine pipes have lower Ti02 concentrations but the range is wider than for the

South African samples, i.e., from 0.11 - 0.47 wt% (Panda pipe) to 1.70 wt% (Rattier pipe;

Nowicki et al., 2004). As aH the examples of economic deposits of diamonds considered above all occur in kimberlitic rocks containing less than 2.5 wt% Ti02, it is reasonable to conc1ude that Québec kimberlitic samples having greater than 2.5 wt% Ti02 are unlikely to contain economic concentrations of diamonds.

Kimberlitic rocks from the Otish region have consistentIy lower Ti02 contents than rocks from the other areas considered in this study (Fig. 2-18). The estimated diamond content from the Renard 1 pipe is 9 cpht, the Renard 2 pipe is 67 cpht, the

Renard 3 pipe is 134 cpht, the Renard 4 pipe is 50 cpht and the Renard 65 pipe is 54 cpht

(Birkett et al., 2004). As with the Yakutia samples, these high diamond grades are consistent with the low Ti02 concentrations found in samples from the Renard pipes, ranging from 0.5 to 1.8 wt% (Birkett et al., 2004, this study). Samples from Lac Beaver,

H-2, H-3, and H-4 pipe rocks have higher Ti02 contents, between 2.1 and 3.5 wt%.

Diamond grades of the Renard rocks have been estimated from bulk samples, but are not available for the Lac Beaver and the H pipes. However, the reports of only smaH numbers ofmicrodiamonds (Table 2-4) suggest that the latter have grades less than 0.5 cpht. Therefore, based on their Ti02 contents, the kimberlitic rocks of the Otish area in general and the Renard locality in particular have the greatest potential for an economic diamond deposit of aH sites sampled in Québec. 76

500 0 • Lac Beaver • H Pipes -400 Id;lo .... Renard this studv ...c:+-> \l Renard (Birketr et al.. 0.. 1(04) ü 0 '-' DO D Vasilenko et al.. 2002 Ij) 0 '"0ro $-< CD cPt:JO 0 0 0 '"0 C 0 roE ...... 0 0 100 D[[J

0 0 2 3 4 5 6 TiO:; (wt%)

Figure 2-18: A plot ofTi02 oxide wt% versus Diamond Grade for Otish Mountain rocks.

Renard samples plot at lower Ti concentrations and higher diamond grades than the other rocks from the Otish Mountains. 77

2.6. Discussion

2.6.1. Classification Schemes

As discussed in the introduction, the classification of group-I kimberlite, group-II kimberlite, olivine larnproite and other ultrarnafic rocks is based primarily on mineralogy and petrography. However, problems arise in classification when primary mineraIs are unidentifiable due to replacement by serpentine or chlorite. Moreover, as group-I kimberlite, group-II kimberlite/olivine lamproite, aillikite and other ultramafic rocks contain similar dominant mineraIs, they are distinguished by the presence of rare mineraIs such as monticellite in the case of group-l kimberlite, or leucite in the case of lamproite, which may only be found after studying a number ofthin sections. Other more common mineraIs like phlogopite, spinel and diopside can be used to identify kimberlitic rocks, but for this to be possible their compositions must be analyzed. With the addition of crustal and/or mantle xenoliths and xenocrysts, the mineralogy of a kimberlitic body may vary considerably even though the composition of the kimberlitic magma is invariant.

The whole rock geochemistry ofkimberlitic samples can potentially provide more information about the rock analyzed and how it should be classified than is possible using just the mineralogy. Using the Si vs. Fe discrimination diagram and REE classification described earlier in this chapter, we have classified aIl the samples in this study and compared the results with the mineralogical classification.

Meimechite and lamproite are the only kimberlitic rocks singled out for geochemical classification by the IUGS (Le Maitre et al., 2002). The composition of meimechite, when calculated anhydrously using the TAS (Total Alkali - Silica) 78 classification, is characterized by between 30 and 52% Si02, greater than 18% MgO, less than 2% (Na20 + K20) and greater than 1 % Ti02 (Le Maitre et al., 2002). Lamproites are ultrapotassic (molar K20 / Na20 > 3), peralkaline (molar [K20 + Na20] / Alz03 > 1) rocks and have molar K20 / Alz03 > 0.8, FeO and CaO contents that are both less than 10 wt%, a Ti02 content ranging from 1 to 7 wt% and high Ba, Sr, Zr and La contents (Le

Maitre et al., 2002). The bulk rock compositions were screened using the ab ove criteria but were only deemed relevant in two cases that are mentioned later in the study.

As reliable mineralogical classification is dependent in part on knowing the proportions of mineraIs, the latter was established using a combination of optical point­ counting and calculated modal mineralogy based on the suite of mineraIs identified in each sample. In princip le, the two methods should yield the same result. The calculation of the modal mineralogy involved relating a vector ofbulk rock oxide compositions to a matrix of mineraI compositions multiplied by a vector containing the proportions of each mineraI: A . X = B, where A is the matrix of mineraI compositions, X the vector containing the proportions of each mineraI to be determined and B, the bulk composition vector (Bohlke, 1989; Mountain, 1992). If the primary mineraIs of a particular sample are destroyed due to the effects of serpentinization and/or chloritization, the sample was assumed to have the same primary mineralogy as associated with kimberlite samples with similar composition. Once the normative mineralogy was determined, the rock was classified according to the mineralogical criteria outlined in Le Maitre et al. (2002). 79

2.6.2. Classification of Group-I Kimberlite Samples

Most samples from the Otish Mountains have been c1assified mineralogically as group-I kimberlites. Renard samples were c1assified by Birkett et al. (2004) as being intermediate between group-I kimberlite and melnoite. The mica ranges from Ba­ phlogopite and kinoshitalite, which is indicative of group-I kimberlite, to tetraferriphlogopite which is indicative of either aillikite or group-II kimberlite/olivine lamproite. The modal mineralogy of the two Renard samples provided for this study by

Ashton Mining of Canada Ltd. was calculated using the mineraIs found in the Lac Beaver and H pipe samples as the Renard samples had been previously cru shed and corresponding thin sections were not supplied. One sample is c1assified as group-I kimberlite using calculated modal mineralogy while the other sample is c1assified as group-II kimberlite. The group-II kimberlite sample contains a large volume of serpentine (73 modal %) and no olivine. It could therefore possibly be misc1assified by the modal mineralogy scheme. Sample 1 plotted in the group-I kimberlite field on the Si vs. Fe diagram, while sample 2 plotted in the group-II kimberlite/olivine lamproite field

(Fig. 2-4). Based on its REE composition, sample 1 again plotted in the group-I kimberlite field, while sample 2 plotted at lower values of La/Yb and SmlYb than either the group-I and group-II kimberlite fields (Fig. 2-13). The amount of normative serpentine in sample 2 implies it has undergone more alteration than sample 1.

Most Lac Beaver and H pipe samples would be c1assified as group-1 kimberlite based on mineralogical criteria, although four samples could not be c1assified mineralogically due to the extent oftheir alteration. Compositions ofmica analyzed in the four samples ranged from pure phlogopite to kinoshitalite, all supporting a group-I 80 kimberlite classification. Based on their calculated modal mineralogy, nine samples from the Lac Beaver and H pipes would be classified as group-I kimberlite and three samples as group-II kimberlite. The samples that have been classified as group-II kimberlite have large proportions of normative serpentine, invariably greater than 50%, little to no olivine

(olivine pseudomorphs are common) and a larger proportion of phlogopite than olivine.

It is quite possible that the classification of the three samples as group-II kimberlite is an artifact of alteration. Nine samples plot within the group-l kimberlite field on the Si vs.

Fe diagram, two plot within the group-II kimberlite/olivine lamproite field and one plots within the aillikite field (Fig. 2-4). The two samples that plot in the group-II kimberlite/olivine lamproite field also would be classified as group-II kimberlite based on their calculated mode mineralogy. AH samples plotted in the group-I kimberlite field on the basis oftheir REE chemistry (Fig. 2-13).

In general, the Si - Fe classification scheme identified 75% of the samples as group-I kimberlite and the REE classification scheme identified aH samples as group-I kimberlite. As the samples which mineraiogically (calculated modal mineralogy) are group-II kimberlite were also the most altered, we conclude that aIl the samples from the

Lac Beaver and H pipes are group-l kimberlite.

The two samples from the Wemindji area contain greater than 50% calcite, and are mineraiogically carbonatite. The calculated modal mineralogy confirms that the samples are calcite-rich (45% calcite), but these samples would be classified as group-I kimberlite because they are calculated to contain olivine, ilmenite, minor amounts of phlogopite and tetraferriphlogopite and less than 50% calcite. Neither sample could be classified using the Si vs. Fe diagram as they contain too little Si, and carbonatites were not considered in the development of the diagram. Their REE profiles (La/Yb and 81

SmlYb ratios) are similar to those of group-I kimberlites (Fig. 2-13). Thus, the samples would be classified as carbonatite in one classification scheme, but as group-I kimberlite in another, creating uncertainty about the true nature of these rocks.

The Temiscamingue Guigue pipe samples would be mineraiogically classified as group-I kimberlite. Only trace amounts ofmica were found in the two samples comprising this group and therefore the mica composition could not analyzed. The calculated modal minerai ogy is similar to the mineralogy observed in thin section and confirms the group-I kimberlite classification. Based on their Si and Fe contents, one sample is a group-I kimberlite, while the other sample is a group-II kimberlite/olivine lamproite (Fig. 2-7). The sample that is group-I kimberlite according to its Si-Fe composition also would be classified as group-I kimberlite in terms ofits LaIYb and

SmIYb ratios (Fig. 2-13).

2.6.3. Classification ofAillikite Samples

Samples from the Tomgat Mountains would aIl be classified as aillikite based on their mineralogy. The Ti-rich biotite and tetraferriphlogopite ofthese rocks are compositionally similar to mica reported for ultramafic rocks found in Aillik Bay area

(Malpas et al., 1986) and recorded in samples studied by Digonnet et al. (2000) and

Tappe et al. (2004). The calculated modal mineralogy confirms the aillikite classification.

Sample 15 was the only sample that could be c1assified chemically as lamproite according to the criteria of Le Maitre et al. (2002) but does not satisfy the mineralogical criteria for lamproite outlined by Le Maitre et al. (2002) as it does not contain leucite, sanidine, or amphibole. Four samples would be classified as aillikite based on their Si-Fe 82 compositions, three samples as meimechite and one as a group-I kimberlite (Fig. 2-5).

The Si-Fe classification scheme correctly classified 50% of the samples. Five samples plot within the aillikite field using the REE discrimination diagram, while one sample plots with the group-I kimberlite field. However, as the aillikite field overlaps the fields of group-l kimberlite and group-II kimberlite/olivine lamproite (Fig. 2-14) one of the aillikite samples would also fall within the field of group-l kimberlite and another within the field of group-II kimberlite/olivine lamproite.

The samples from the Desmaraisville area are all aillikite mineralogically. The mica composition in these rocks is biotite in composition and similar to that of mica found in lamprophyres at AiUik Bay (Malpas et al., 1986). Their calculated modal mineralogy confirrns them to be aillikite. Four samples would be classified as aillikite using the Si vs. Fe discrimination diagram (Fig. 2-6), while five samples would be classified as meimechite and one sample as group-II kimberlite/olivine lamproite. Thus

40% of the samples plot in the aiUikite field of the Si-Fe discrimination diagram. AU six samples plot within the aillikite field using the REE discrimination diagram, only two of which were so classified using the Si-Fe diagram.

Samples from the Île Bizard area are mineraiogically alnoite (or melilite-bearing lamprophyre; Le Maitre et al., 2002). The ca1culated mode mineralogy also yields this classification. The mica in this suite is biotite. AlI samples plot close to the group-I kimberlite/aillikite field boundary on the Si vs. Fe discrimination diagram; three samples plot in the aillikite field and one sample with less Fe plot in the group-I kimberlite field

(Fig. 2-8). Only two samples were analyzed for the REE; based on its La/Yb and SmNb ratios, one ofthese samples classifies as aillikite and the other as transitional between aillikite and group-II kimberlite/olivine lamproite (Fig. 2-14). Therefore these rocks are 83 aillikites when based on the Si vs. Fe discrimination diagram and REE analyses but are alnoite when based on mineralogy.

2.6.4. Classification ofNon-Kimberlitic Samples

The Temiscamingue ultramafic intrusion was classified mineraiogically as a possible olivine lamproite. The mica was determined to be phlogopite and, based on the calculated modal mineralogy, two of the samples would be classified as olivine lamproite and the other two samples as enstatite lamproite (as they were calculated to contain more enstatite than olivine). Based on their Si-Fe compositions, aIl of the samples are group-II kimberlite/olivine lamproite (Fig. 2-7). However, their ratios of LaIYb and Sm/Yb are substantially lower than those for other olivine lamproites and one sample plots within the meimechite field (Fig. 2-15). The classification of these rocks based on the REE discrimination diagram doe not agree with classification based on mineralogy or Si-Fe concentrations. As there is doubt that the mineralogical classification is correct, classification based on REE concentrations would confirm that these rocks are not group­

II kimberlite or olivine lamproite.

The two samples comprising the Lac Leclair suite could not be classified mineralogically as they have been intensely altered. There was not enough calcite to classify them as carbonatite and insufficient concentration of primary mineraIs to classify the samples as any kind ofkimberlitic rock. The calculated modal mineralogy is similar to the observed modal mineralogy and does not shed new light on the nature of the rock prior to alteration. Both samples, however, fulfilled the chemical criteria described by Le

Maitre et al. (2002) for meimechite classification. On the basis of its Si-Fe composition, 84 one sample from this study and all samples from Baragar et al. (2001) would be classified as aillikite and the other sample from this study as meimechite (Fig. 2-9a). However, their REE compositions classify both samples from this study as group-II kimberlite/olivine lamproite (Fig. 2-15); samples from Baragar et al. (2001) plot within the aillikite field (and all except one plot within in the group-II kimberlite/olivine lamproite field). In summary, these samples are too altered to be reliably classified by any method but due to the fact that they fulfill the IUGS meimechite criteria and the fact that at least one sample plots within the meimechite field on the Si vs. Fe discrimination diagram we believe that they should be called meimechite.

Samples from the Baie James suite are classified mineralogically and on the basis of normative calculation as lamprophyres. They could not be classified using the Si vs.

Fe discrimination diagram either as they contain too much Ah03 and Si02 and not enough MgO. Moreover, these samples have very low concentrations ofREE and their

La/Yb and Sm/Yb ratios do not correspond to those of any of the types of kimberlitic rocks considered (Fig. 2-15). Samples from this suite have similar spider diagram profiles and negative Nb anomalies that are typical of minettes (Fig. 2-16b). However the samples cannot be classified mineralogically as minettes as they do not contain biotite, leaving the possibility that they are calc-alkaline lamprophyres instead.

The mineralogy and calculated modal mineralogy ofsamples from the Ayer's

Cliff dykes indicate that these rocks are lamprophyres. Samples from one dyke could not be classified using the Si vs. Fe discrimination diagram as they contain too much Ah03; the other dyke classifies as aillikite (Fig. 2-9a). The low slopes of the chondrite­ normalized REE profiles of the first dyke as seen by the low La/Yb and SmIYb ratios 85 confirms that these samples are of a lamprophyre of an intermediate composition between aillikite and the other calc-alkaline lamprophyre (Fig. 2-15).

2.6.5. Evaluation of Si vs. Fe Discrimination Diagram

Of the 37 samples that were classified both mineralogically and chemically, 23 or

62% were correctly classified using Fe and Si. This number increases to 84%, if the REE are used in conjunction with Si and Fe. A significant number of samples could not be classified mineralogically because of alteration. In these cases, it was necessary to depend on whole-rock calculated modal mineralogy for classification. However, even when the rocks are fresh, geochemistry offers a number of advantages. Kimberlitic rocks from different areas can be compared with relative ease using their whole rock geochemistry without the need for expensive mineralogical studies followed by expensive electron microprobe analysis. The only limitation ofusing whole rock geochemistry for classification purposes is that it is essential to remove aIl crustal xenoliths before analysis, which requires careful examination of the coarse cru shed material before grinding.

Crustal xenoliths must be avoided as they are commonly Si-rich and will affect the application of the Si-Fe discrimination diagram. Contamination by mantle xenoliths is more difficult to prevent as they contain many of the same mineraIs that are found in kimberlitic rocks. Mantle xenoliths may have disintegrated into individual mineraI xenocrysts which cannot be reliably identified microscopically.

The mineralogy of the kimberlitic rocks is a reflection of the whole rock geochemistry. Group-I kimberlite and aillikite are carbonate-rich and therefore plot at a lower Si concentration than olivine, represented by the olivine line (Fig. 2-3). The 86 composition of mica in group-I kimberlite, group-II kimberlite and olivine lamproite is phlogopite, whereas in aillikite it is biotite due to the higher concentration of Fe.

Therefore, the crystallization ofkimberlitic magmas would cause the remaining liquid compositions to move away from the olivine-phlogopite line, either to lower Si and increasing carbonate content or towards higher Si concentrations. The olivine line on the

Si vs. Fe discrimination diagram corresponds to a thermal divide (Francis, 2003).

The Si vs. Fe discrimination diagram is not entirely effective in discriminating among kimberlitic rocks. It does separate group-I kimberlite from most aillikite rocks and aIl meimechite rocks and group-II kimberlite/olivine lamproite rocks from all aillikite rocks and most meimechite rocks. However, not all rocks classified on mineralogical grounds as group-I kimberlite plot within the group-I kimberlite field and not aU mineralogically classified aiUikites plot within the aillikite field. The rocks of each kimberlite field exhibit a relatively large range in Si concentration compared to the smaU range in Fe concentration; each field appears to have its own mean Fe content.

Kimberlitic rocks from the Otish Mountains, Temiscamingue and Île Bizard aU have low mean concentrations of Fe, whereas rocks from the Tomgat Mountains, Desmaraisville,

Lac Leclair and Ayer's Cliff all have high concentrations of Fe. The variation in Si concentration results in both group-I kimberlites and group-II kimberlites/olivine lamproites commonly occurring in the same kimberlite field (e.g. Otish Mountains, Fig.

2-4) and aiUikites and meimechites occurring together in other fields. Either the composition of the kimberlitic source material is heterogeneous in terms of carbonate or a process, such as the separation of a CO2-rich phase, genetically connects the dyke rocks in any given field. 87

2.7. Conclusions

In the past, mineralogical constraints were the basis for kimberlite classification.

Geochemical methods for classification were not highly regarded due to problems of contamination associated with the abundance ofxenoliths and hydrothermal alteration.

However, a preliminary survey of published chemical analyses of diamond-bearing hypabyssal facies rocks suggests that these problems may not be as serious as previously thought and that kimberlitic rock types can be reliably distinguished on the basis oftheir

Mg, Si and Fe contents (Francis, 2003). The objectives of the present study were to determine the mineralogy and petrography of samples of Québec kimberlitic rocks, develop a chemically based classification scheme, correlate the minerai ogy ofthese rocks with their major and trace element geochemistry, then correlate diamond grade with lithogeochemical data and assess the economic potential of various ultramafic rock types in Québec.

This study included kimberlitic samples from six areas within Québec, i.e., the

Otish Mountains, Tomgat Mountains, Wemindji, Desmaraisville, Temiscamingue and Île

Bizard. Other occurrences were sampled because of the ultramafic nature of the rocks

(Lac Leclair, Ayer's Cliff) and/or the occurrence of diamonds (Baie James).

Mineralogically, rocks from the Otish Mountians are variably altered group-I kimberlite.

Rocks from the Tomgat Mountains and Desmaraisville range from aillikite to lamprophyre in composition. The Guigue pipe in Temiscamingue is also a group-I kimberlite, whereas a large, nearby ultramafic intrusion is compositionally similar to olivine lamproite. Based on their mineralogy, the rocks from Île Bizard are aln6ites (an ultramafic lamprophyre). Dykes from the Baie James and Ayer's Cliffregions are also 88 considered to be lamprophyres, whereas rocks from the Lac Leclair region could not be classified mineraiogically due to the extent of alteration they have experienced, but have been classified previously as meimechites by Baragar et al. (2001).

The Si vs. Fe discrimination diagram successfully separates group-I kimberlites from aillikites and meimechites and group-II kimberlites/olivine lamproites from aillikites and meimechites. However, a few group-I kimberlites and aillikites plot within the group-II kimberlite field and meimechite field, respectively. REE concentrations clearly separate kimberlitic rocks from non-kimberlitic rocks and roughly separate kimberlitic rock types. Group-I kimberlites have higher La/Yb and SmIYb ratios than group-II kimberlites/olivine lamproites and meimechites. These three rock types have similar

SmIYb ratios, but group-II kimberlites/olivine lamproites have higher LalYb ratios than meimechites. Aillikites overlap aIl other rock types except for the most LREE enriched group-I kimberlites. Non-kimberlitic ultramafic rocks like minettes and ca1c-alkaline lamprophyres have lower La/Yb ratios than kimberlites and fiat HREE and plot within the least enriched meimechite field and lower.

Of the kimberlitic rocks considered in this study, those from the Otish Mountians had the lowest Ti02 contents with samples from the Renard pipes containing from 0.5 to

1.8 wt% Ti02, and samples from Lac Beaver and H pipes containing from 2.1 to 3.5 wt%

Ti02• In comparison, the aillikites of the Tomgat Mountains exhibit a large range in Ti concentration, from 0.7 to 9.4 wt% Ti02. With the exception of the Otish Mountains kimberlites, kimberlitic rocks in aIl other are as studied contain only a few smaIl diamonds.

The Renard kimberlitic rocks have the highest diamond grades of aIl rocks analyzed, consistent with their low Ti02 contents. 89

2.8. References

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isotopic properties of sorne North American kimberlites. J Geophys. Res., 93:

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Baragar, W.R.A., Mader, u., Lecheminant, G.M., (2001): Paleoproterozoic carbonatitic

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Earth Sei., 38: 1313-1334.

Bennet, G., Dressler, B.O., Robertson, J.A., (1993): The Huronian Supergroup and

associated intrusive rocks. Geology of Ontario, Ministry of Northem

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Berclaz, A., Cadieux, A.M., Sharma, K.N.M., David, J., Parent, M., Leclair, A., (2001):

Géologie de la region du lac Aigneau (24E et 24F/04). Ministère des Ressources

naturelles, Québec, RG 2001-01: 49p.

Birkett, T.C., McCandless, T.E., Hood, C.T., (2004): Petrology of the Renard igneous

bodies: host rocks for diamond in the northem Otish Mountains region, Québec.

Lithos, 76: 475-490.

Boh1ke, J.H., (1989): Comparison ofmetasomatic reactions between a common C02-rich

vein fluid and diverse wall rocks; intensive variables, mass transfers, and Au

mineralization at Alleghany, Califomia. Econ. Geol., 84: 291-327.

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CHAPTER3

EXTENDED CONCLUSIONS 98

3.1. Conclusions

Most economic diamond deposits originate from group-I kimberlites. However, group-I kimberlites are difficult to distinguish from group-II kimberlites, olivine lamproites and lamprophyres like aillikites due to their relatively similar mineralogy.

Classification ofthese rock types is usually based on mineralogy and petrology, particularly the presence or absence of minor or trace mineraIs. Geochemical methods of classification have been largely ignored due in large part to the nature ofkimberlitic rocks; they may have high concentrations of cru st al and mantle xenoliths. These magmas are rich in volatiles (C02 and H20) which commonly interact with the primary igneous mineraIs (olivine, mica and spinel) altering them to serpentine, chlorite or carbonate, and making mineralogical classification even more difficult.

We have assessed the ability of geochemical classification based on Fe and Si to distinguish group-I kimberlites, group-II kimberlites and olivine lamproites, aillikites and meimechites. This classification scheme was tested on twenty-seven kimberlitic and diamondiferous rock occurrences in Québec. AH Québec samples displayed smooth REE profiles and were highly enriched in the LREE when compared to chondritic values.

Group-I kimberlites, group-II kimberlites/olivine lamproite and meimechites from the literature separate into different areas of a La/Yb vs. SrnIYb diagram. AiHikites however, have a large range of values, from those similar to group-I kimberlites to those similar to meimechites. A diagram based on REE was constructed and compared to the classification diagram based on the Si and Fe.

The Si vs. Fe discrimination diagram predicts the mineralogical classification for most samples. When this is not the case it is because rocks from the same field 99 commonly exhibit a wide range of Si contents crossing the olivine thermal divide between aillikites and meimechites and between group-I and group-II kimberlites at a relatively constant Fe. One possible explanation for this is that this there is a differential loss of CO2, either by the separation of an immiscible, carbonate magma or a volatile phase which serves to variably concentrate Si.

3.2 Recommendations for Future Work

This study has shown that major and trace element geochemistry offers an important tool for the classification ofkimberlitic rocks. The applicability ofthe proposed scheme might be enhanced if carbonatites were included in the data base. A compilation of analyses of carbonatites associated with aillikites and kimberlites would define and constrain the width of the immiscibility gap between carbonatite and kimberlitic magmas.

The negative correlation between Ti02 and diamond grade has been generally documented but not explained. The origin ofthis correlation needs to be explored because it is unclear whether this is a feature of the mantle source, or reflects the survivability of diamonds within the kimberlites. A clearer understanding ofthis correlation requires the support of diamond companies willing to give more open access to diamond grades. 100

Appendix 1: List of samples and what region they are from.

Sample # Sample name Area Sample supplied by 1 Renard1 Otish Mountains Ashton Mining of Canada Inc. 2 Renard4 Otish Mountains Ashton Mining of Canada Inc. 3 OH-61-15 Otish Mountains Ditem Explorations Inc. 4 OH97-01-40 Otish Mountains Ditem Explorations Inc. 5 OH98-064-22 Otish Mountains Ditem Explorations Inc. 6 OH98-064-37 Otish Mountains Ditem Explorations Inc. 7 OH98-06B-118 Otish Mountains Ditem Explorations Inc. 8 H2-50 Otish Mountains Ditem Explorations Inc. 9 H2-135 Otish Mountains Ditem Explorations Inc. 10 H3-54 Otish Mountains Ditem Explorations Inc. 11 H3-72 Otish Mountains Ditem Explorations Inc. 12 H3-108 Otish Mountains Ditem Explorations Inc. 13 H4-15 Otish Mountains Ditem Explorations Inc. 14 H4-108 Otish Mountains Ditem Explorations Inc. 15 T-1 Torngat Mountains J. Moorhead, MRNQ 16 T-2 Torngat Mountains J. Moorhead, MRNQ 17 1 Dyke Torngat Mountains J. Moorhead, MRNQ 18 New Dyke Torngat Mountains J. Moorhead, MRNQ 19 Johnny Blow Torngat Mountains J. Moorhead, MRNQ 20 Triangle Pipe Torngat Mountains J. Moorhead, MRNQ 21 Peter Pipe Torngat Mountains J. Moorhead, MRNQ 22 Bella Dyke Torngat Mountains J. Moorhead, MRNQ 23 Maj-W-1 Wemindji Majescor Resources Inc. 24 Maj-W-2 Wemindji Majescor Resources Inc. 25 A93-1-57 Desmaraisville J. Moorhead, MRNQ 26 A93-1-87 Desmaraisville J. Moorhead, MRNQ 27 A94-1-407 Desmaraisville J. Moorhead, MRNQ 28 A94-1-606 Desmaraisville J. Moorhead, MRNQ 29 A94-1-828 Desmaraisville J. Moorhead, MRNQ 30 A94-1-866 Desmaraisville J. Moorhead, MRNQ 31 A94-2-209 Desmaraisville J. Moorhead, MRNQ 32 LT-02-93-46 Desmaraisville J. Moorhead, MRNQ 33 LT-02-93-130 Desmaraisville J. Moorhead, MRNQ 34 Cerlac Dyke Desmaraisville J. Moorhead, MRNQ 35 DB-G-2-321 Temiscamingue De Beers Canada Inc. 36 DB-G-2-432 Temiscamingue De Beers Canada Inc. 37 T96-12-52 Temiscamingue Ditem Explorations Inc. 38 T97-22-209 Temiscamingue Ditem Explorations Inc. 39 T97-23-3.8 Temiscamingue Ditem Explorations Inc. 40 T97-24-172 Temiscamingue Ditem Explorations Inc. 41 761B-23 Ile Bizard L. Harnois, UQAM 42 761B-28A Ile Bizard L. Harnois, UQAM 43 761B-35A Ile Bizard L. Harnois, UQAM 44 761B-37C Ile Bizard L. Harnois, UQAM 45 LCR-1 Lac Leclair D. Francis, McGili University 46 LCR-3 Lac Leclair D. Francis, McGiII University 47 Dian-D-1 Lac de l'Astree Dianor Resources Inc. 48 Dian-D-2 Lac de l'Astree Dianor Resources Inc. 49 Dian-D-3 Lac de l'Astree Dianor Resources Inc. 50 Dian-D-5 Lac de l'Astree Dianor Resources Inc. 51 Dian-D-9 Lac de l'Astree Dianor Resources Inc. 52 Dian-Bear-1 Lac de l'Astree Dianor Resources Inc. 53 2002-AC-02-01 Ayer's Cliff R. Stevenson, UQAM 54 2002-AC-02-02 Ayer's Cliff R. Stevenson, UQAM 55 2002-AC-02-03 Ayer's Cliff R. Stevenson, UQAM 56 2002-AC-02-04 Ayer's Cliff R. Stevenson, UQAM 57 2002-AC-03-05 Ayer's Cliff R. Stevenson, UQAM 101

Appendix 2: List ofreferences from which pub1ished whole rock geochemistry analyses were taken. These analyses were used in Figures 2-2a, 2-2b, 2-3a and 2-12.

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