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The Renard 4 kimberlite : implications for ascent of kimberlites in the shallow crust Gofton, Emma Lindsay 2007

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THE RENARD 4 KIMBERLITE: IMPLICATIONS FOR ASCENT OF KIMBERLITES IN THE SHALLOW CRUST by E M M A L I N D S A Y G O F T O N BSc (Honours), Queen's University, 2002 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Geological Sciences) THE UNIVERSITY OF BRITISH COLUMBIA October 2007 © Emma Lindsay Gofton, 2007 A B S T R A C T Kimberlite rock types that compose the Renard 4 kimberlite in northern Quebec, Canada, record the transition between the root and diatreme zones of a Class 1 kimberlite pipe. Analysis of lithologic textures and the componentry (clasts, macrocrysts and groundmass) of these rock types provides information pertinent to describing the evolution of the kimberlite pipe as well as to understanding the dynamics of its emplacement. This study defines six rock types present in the Renard 4 kimberlite. Five of these are kimberlitic. The rock types include two volcaniclastic facies, coherent kimberlite, transitional kimberlite and country rock breccia. The two volcaniclastic facies are: 1) a tufiisitic kimberlite breccia facies which is further subdivided into four phases and 2) an 'accretionary' magmaclastic facies. Coherent kimberlite is divided into two subfacies: 1) massive coherent macrocrystic kimberlite and 2) macrocrystic kimberlite breccia. The coherent breccia is a contact zone of the massive coherent kimberlite with the rock it intrudes and comprises non-kimberlitic clasts in a matrix of coherent kimberlite. A multi-stage emplacement process is invoked to account for the presence and the geometries of the Renard 4 rock units. Prior to the kimberlite eruption, coherent kimberlite dykes were emplaced. The eruption and filling of the diatreme were succeeded by emplacement of late-stage coherent kimberlite dykes and the emplacement of a late-stage volcaniclastic facies. Textures in the volcaniclastic facies as well as the juxtaposition of volcaniclastic, transitional and coherent rock types indicates that the present day surface of the Renard 4 kimberlite represents a level between the lower diatreme and the root zone of a Class 1 kimberlite pipe. It is proposed that concentration of country rock clasts occurred in areas of highest ascent velocity in the volcanic conduit. The presence of each of the Renard 4 rock types and their spatial distribution has important implications for the emplacement model of this kimberlite and provide important insight for general models pertaining to the formation of the root/diatreme transitional zone in other kimberlite pipes. The accretionary magmaclastic textures seen in some volcaniclastic rock types in Renard 4 indicates that fragmentation of the kimberlite magma occurs as deep as 2 kilometres below the earth surface and that during emplacement these magmas are inflated to many times the volume they currently occupy. It is furthermore suggested that the kimberlite magma is inflated, and the fragmental textures are formed in systems which may never have breached the surface. i i TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS iii LIST OF TABLES vi LIST OF FIGURES vii ACKNOWLEDGEMENTS ix CHAPTER 1: INTRODUCTION AND OVERVIEW 1 CHAPTER 2: GEOLOGICAL SETTING AND DEFINITIONS 3 2.1 BACKGROUND 3 2.2 TECTONIC SETTING AND REGIONAL GEOLOGY 5 2.3 AGE OF THE RENARD KIMBERLITES 8 2.4 DEPTH OF EROSION OF THE RENARD KIMBERLITES 8 2.5 DEFINITION OF KIMBERLITE 10 2.6 CLASSIFICATION OF THE RENARD BODIES AS GROUP 1 KIMBERLITES 11 2.7 KIMBERLITE CLASSES AND MORPHOLOGY OF THE RENARD KIMBERLITES 14 2.8 ROCK TYPE DEFINITIONS 18 2.8.1 HYPABYSSAL KIMBERLITE 18 2.8.2 TUFFISITIC KIMBERLITE 19 2.8.3 TRANSITIONAL KIMBERLITE 22 2.8.4 VOLCANICLASTIC KIMBERLITE 22 2.8.5 COUNTRY ROCK BRECCIA 23 2.9 NOMENCLATURE 23 CHAPTER 3: PETROGRAPHIC UNITS OF THE RENARD 4 KIMBERLITE 25 3.1 INTRODUCTION 25 3.2 METHODOLOGY 29 3.3 COHERENT ROCKS 34 3.3.1 SUBFACIES 1: MASSIVE COHERENT MACROCRYSTIC KIMBERLITE 34 3.3.2 SUBFACIES 2:COHERENT MACROCRYSTIC KIMBERLITE BRECCIA 37 3.4 VOLCANICLASTIC ROCKS 40 iii 3.4.1 V O L C A N I C L A S T I C FACIES 1 43 PHASE 1: G R E Y TUFFISITIC KIMBERLITE BRECCIA 43 PHASE 2: G R E E N TUFFISITIC KIMBERLITE BRECCIA 49 PHASE 3: B R O W N TUFFISITIC KIMBERLITEBRECCIA 52 PHASE 4: B L U E TUFFISITIC KIMBERLITE BRECCIA 54 3.4.2 V O L C A N I C L A S T I C FACIES 2: ' A C C R E T I O N A R Y M A G M A C L A S T I C KIMBERLITE 59 3.5 TRANSITIONAL ROCKS OF T H E R E N A R D 4 KIMBERLITE 61 3.4.1 M A G M A C L A S T I C KIMBERLITE BRECCIA WITH CHARACTERISTICS TRANSITIONAL T O C O H E R E N T KIMBERLITE 61 3.6 C O U N T R Y R O C K BRECCIA 66 3.7 O V E R V I E W A N D DISTRIBUTION OF T H E R O C K TYPES 68 3.7.1 DIFFERENTIATING B E T W E E N PHASES OF V O L C A N I C L A S T I C FACIES 1.... 68 PHASES 2 A N D 4 68 PHASES 3 A N D 4 68 3.7.2 SPATIAL DISTRIBUTION OF T H E R E N A R D 4 R O C K TYPES 68 CHAPTER 4: IMPLICATIONS FOR KIMBERLITE EMPLACEMENT 75 4.0 O V E R V I E W 75 4.1 INTRODUCTION 75 4.2 R E N A R D 4 V O L C A N I C FACIES 77 4.2.1 V O L C A N I C L A S T I C FACIES 79 V O L C A N I C L A S T I C FACIES 1: TUFFISITIC KIMBERLITE B R E C C I A 79 PHASE 1:GREY TUFFISITIC KIMBERLITE BRECCIA 79 PHASE 2: G R E E N TUFFISITIC KIMBERLITE BRECCIA 79 PHASE 3: B R O W N TUFFISITIC KIMBERLITE BRECCIA 81 PHASE 4: B L U E TUFFISITIC KIMBERLITE BRECCIA 81 V O L C A N I C L A S I C FACIES 2: ' A C C R E T I O N A R Y M A G M A C L A S T I C KIMBERLITE 81 4.2.2 C O H E R E N T KIMBERLITE 82 C O H E R E N T SUBFACIES 1: MASSIVE C O H E R E N T KIMBERLITE 82 C O H E R E N T SUBFACIES 2: C O H E R E N T KIMBERLITE BRECCIA 82 iv 4.2.3 TRANSITIONAL KIMBERLITE 84 TRANSITIONAL KIMBERLITE BRECCIA 84 4.2.4 NON-KIMBERLITIC F R A G M E N T A L ROCKS 84 4.3 SPATIAL A N D T E M P O R A L RELATIONSHIPS OF T H E R E N A R D 4 R O C K TYPES 86 4.3.1 V O L C A N I C L A S T I C FACIES 1 86 PHASE 1 86 PHASE 2 88 PHASE 3 88 PHASE 4 88 4.3.2 V O L C A N I C L A S T I C FACIES 2 89 4.3.3 C O H E R E N T SUBFACIES 1 89 4.3.4 C O H E R E N T SUBFACIES 2 92 4.3.5 TRANSITIONAL KIMBERLITE 92 4.3.6 C O U N T R Y R O C K BRECCIA 95 4.4 E M P L A C E M E N T O F T H E R E N A R D 4 KIMBERLITE 95 4.4.1 PHASES OF V O L C A N I C L A S T I C FACIES 1 95 4.4.2 V O L C A N I C L A S T I C FACIES 2 99 4.4.3 E M P L A C M E N T M O D E L 102 M A G M A A S C E N T 102 D Y K E FORMATION 103 ERUPTION A N D FORMATION OF T H E D I A T R E M E 103 E M P L A C E M E N T OF C O H E R E N T SUBFACIES 1 A N D 2 A N D V O L C A N I C L A S T I C FACIES 2 105 A L T E R A T I O N 106 EROSION 106 CHAPTER 5: CONCLUSIONS 108 REFERENCES 110 APPENDIX A: LIST OF SLABS AND THIN SECTIONS 114 v LIST OF TABLES TABLE 2.1: SUMMARY OF KIMBERLITE NOMENCLATURE IN LITERATURE AND IN THE CURRENT STUDY, TABLE 3.1: ROCK UNITS FACIES AND PHASES OF THE RENARD 4 KIMBERLITE TABLE 3.2: NUMBER OF SAMPLES OF EACH RENARD 4 ROCK TYPE EXAMINED TABLE 3.3: COMPARISON OF GROUNDMASS COMPONENTS OF THE RENARD 4 ROCK TYPES TABLE 3.4: COMPARISON OF THE MACROCRYST AND MAGMACLAST POPULATIONS TABLE 3.5: COMPARISON OF COUNTRY ROCK XENOLITH POPULATIONS TABLE 3.6: SUMMARY OF COMPONENTS OF EACH RENARD 4 ROCK TYPE TABLE 4.1: ROCK UNITS FACIES AND PHASES OF THE RENARD 4 KIMBERLITE vi LIST OF FIGURES FIGURE 1.1: MODEL OF A TYPICAL CLASS 1 KIMBERLITE PIPE FIGURE 2.1: LOCATION OF THE RENARD KIMBERLITE FIELD AND THE RENARD 4 KIMBERLITE FIGURE 2.2: LOCATION OF THE RENARD AND LAC BEAVER KIMBERLITES IN THE SUPERIOR CRATON FIGURE 2.3: GEOLOGICAL MAP OF QUEBEC FIGURE 2.4: GLACIAL MAP OF NORTH EASTERN QUEBEC FIGURE 2.S: PETROGRAPHIC RANGES OF ROCK TYPES COMMONLY ENCOUNTERED IN DIAMOND EXPLORATION. FIGURE 2.6: SCHEMATIC COMPARISON OF PIPE MORPHOLOGIES OF CLASS 1, 2 AND 3 KIMBERLITE PIPES FIGURE 2.7: SCHEMATIC OF THE MAJOR FEATURES OF NORTH AMERICAN CLASS 1 KIMBERLITE PIPES FIGURE 3.1: MAP SHOWING THE OUTLINE OF RENARD 4 AND SELECTED DRILL COLLAR LOCATIONS FIGURE 3.2: SCHEMATIC OF A TYPICAL CLASS 1 KIMBERLITE PIPE SHOWING LEVEL EXPOSED AT RENARD 4 , FIGURE 3.3: COHERENT ROCKS OF THE RENARD 4 KIMBERLITE FIGURE 3.4: COHERENT SUBFACIES 1 PHOTOMICROGRAPHS AND MESOSCOPIC IMAGES FIGURE 3.5: IMAGES OF COHERENT SUBFACIES 1 FIGURE 3.6: PHOTOMICROGRAPHS AND MESOSCOPIC IMAGES OF COHERENT SUBFACIES 1 FIGURE 3.7: SCHEMATIC REPRESENTATION OF THE SPATIAL RELATIONSHIP OF COHERENT SUBFACIES 1 AND 2.. FIGURE 3.8: SPATIAL DISTRIBUTION OF THE FOUR PHASES OF VOLCANICLASTIC FACIES 1 FIGURE 3.9: VOLCANICLASTIC FACIES OF THE RENARD 4 KIMBERLITE FIGURE 3.10: PHOTOMICROGRAPHS OF VOLCANICLASTIC FACIES 1 PHASE 1 FIGURE 3.11: PELLETAL LAPILLI AND INCIPIENT PELLETAL LAPILLI IN VOLCANICLASTIC FACIES 1 PHASE 1 FIGURE 3.12: COUNTRY ROCK XENOLITHS IN VOLCANICLASTIC FACIES 1 PHASE 1 FIGURE 3.13: MESOSCOPIC IMAGES OF VOLCANICLASTIC FACIES 1 PHASE 2 FIGURE 3.14: MESOSCOPIC IMAGES AND PHOTOMICROGRAPHS OF VOLCANICLASTIC FACIES 1 PHASE 3 FIGURE 3.15: ALTERATION OF COUNTRY ROCK XENOLITHS IN THE 4 PHASES OF VOLCANICLASTIC FACIES 1.... FIGURE 3.16: MESOSCOPIC IMAGES AND PHOTOMICROGRAPHS OF VOLCANICLASTIC FACIES 1 PHASE 4 FIGURE 3.17: MESOSCOPIC IMAGES AND PHOTOMICROGRAPHS OF VOLCANICLASTIC FACIES 1 PHASE 4 FIGURE 3.18: CONTACTS OF PHASES 3 AND 4 OF VOLCANICLASTIC FACIES 1 FIGURE 3.19: IMAGES OF VOLCANICLASTIC FACIES 2: 'ACCRETIONARY' MAGMACLASTIC KIMBERLITE FIGURE 3.20: IMAGES OF TRANSITIONAL KIMBERLITE vii FIGURE 3.21: PHOTOMICROGRAPHS OF TRANSITIONAL KIMBERLITE FIGURE 3.22: IMAGES OF COUNTRY ROCK BRECCIA FIGURE 3.23: COMPARISON OF THE COMPONENTS OF THE RENARD 4 ROCK TYPES FIGURE 3.24: COMPARISON OF THE COUNTRY ROCK XENOLITHS AND MACROCRYSTS IN PHASES 3 AND 4 FIGURE 3.25: PHOTOMICROGRAPHS COMPARISON OF VOLCANICLASTIC FACIES 1 PHASES 3 AND 4 FIGURE 3.26: SCHEMATIC MODEL OF THE RENARD 4 KIMBERLITE FIGURE 4.1: LOCATION OF THE RENARD KIMBERLITE CLUSTER AND THE RENARD 4 KIMBERLITE FIGURE 4.2: MAP SHOWING THE SURFACE OUTLINE OF RENARD 4 AND DRILL COLLAR LOCATIONS FIGURE 4.3: COMPARISON OF THE COMPONENTS OF THE PHASES OF VOLCANICLASTIC FACIES 1 FIGURE 4.4: COHERENT SUBFACIES OF THE RENARD 4 KIMBERLITE FIGURE 4.5: TRANSITIONAL KIMBERLITE AND COUNTRY ROCK BRECCIA FIGURE 4.6: SCHEMATIC REPRESENTATION OF THE RENARD 4 KIMBERLITE FIGURE 4.7: MAP OF THE SURFACE EXPOSURE OF RENARD 4 FIGURE 4.8: SCHEMATIC REPRESENTATION OF KIMBERLrTE DYKE SHOWING FLOW CONCENTATION FIGURE 4.9: PRESERVATION OF EARLY COHERENT DYKES AS CLASTS IN VOLCANICLASTIC FACIES 1 FIGURE 4.10: TRANSITIONAL ZONE OF A CLASS 1 KIMBERLITE PIPE FIGURE 4.11: ENVELOPES OF COUNTRY ROCK BRECCIA AND FRACTURED COUNTRY ROCK FIGURE 4.12: THE BAGNOLD EFFECT FIGURE 4.13: VARIATION IN ABUNDANCE OF COUNTRY ROCK XENOLITHS AND VELOCITY FIGURE 4.14: EMPLACEMENT OF THE RENARD 4 KIMBERLITE (FIRST STAGES) FIGURE 4.15: FINAL STAGES OF EMPLACEMENT OF RENARD 4 AND POST-EMPLACEMENT PROCESSES viii ACKNOWLEDGEMENTS Financial support for this project was provided by a grant set up by the Mineral Deposit Research Unit that included contributions from the NSERC and Ashton Mining of Canada Inc. (now Stornoway Diamond Corp.) with their joint venture partner SOQUEM. I would like to thank my supervisor Dick Tosdal and co-supervisors Kelly Russell and Tom McCandless. I am grateful to many of the employees of both Ashton and S O Q U E M for support with various aspects of this project. I would also like to thank Tyson Birkett formerly of SOQUEM for numerous helpful emails over the course of the last two years. Finally, I would like to thank my great friend Patrick Smillie whose thoughtful and expeditious reviews improved the quality of this manuscript, and my great co-zookeeper Alan Wainwright whose wise council keep me from throwing in the towel on more occasions than I care to acknowledge, and without whom this document would still be missing an abstract! ix CHAPTER 1: INTRODUCTION AND OVERVIEW The Renard 4 kimberlite provides an unusual opportunity to examine the deeper levels of a volcanic structure. The kimberlite is eroded to 1 km below the paleo-surface (Birkett, personal communication, March 1, 2007) thus exposing the lower diatreme and allowing the transitional zone between the diatreme and the hypabyssal zone of the kimberlite to be mapped and sampled (Figure 1.1). The purpose of this study is to define the lithologic units present in the Renard 4 kimberlite and to describe their distribution and textural/facies variations. Improved constraints on the geology of the Renard 4 kimberlite contributes to the understanding of the root/diatreme transition zone in kimberlites and more generally to the understanding of magma ascent in the shallow crust. This thesis includes a petrographic study of the volcanic facies of the Renard 4 kimberlite, a schematic geologic model of the Renard 4 kimberlite generated from the available data, and a model for the emplacement of the kimberlite. In addition, a model for the formation of an accretionary texture present in one of the facies of the Renard 4 kimberlite is also presented herein. Background information including the regional geology of northeastern Quebec and a summary of the work done on the Renard kimberlites prior to this study are provided in Chapter 2 as well as a discussion of kimberlite nomenclature, kimberlite classes and the classification of the Renard kimberlites as Group 1 kimberlites. Following this, petrographic descriptions of the volcanic facies of the Renard 4 kimberlite are presented in Chapter 3. This study involves the characterization of six distinct rock types, and the classification of the kimberlitic rock types as facies, subfacies and phases of volcaniclastic or coherent kimberlite. A schematic model of Renard 4 is presented at the end of Chapter 3 in order to provide a spatial context for the rock units. Finally, in chapter 4, the geometry of the Renard 4 kimberlite and the contact relationships of the rock units are discussed. An emplacement model for the Renard 4 kimberlite which draws from both descriptions in the kimberlite literature as well as observations of the Renard 4 rock types is presented in addition to a model for the formation of an accretionary texture in the lower diatreme of a kimberlite pipe. 1 Figure 1.1: Model of a typical Class 1 kimberlite pipe. The model shows the vertical extent of each zone of the kimberlite (after Hawthorne, 1975). 2 CHAPTER 2: GEOLOGICAL SETTING AND DEFINITIONS 2.1 Background The Renard kimberlite cluster is located north of the Otish Mountains, approximately 250 km north east of Chibougamau in north eastern Quebec (Figure 2.1). The kimberlite cluster is situated on the Ashton Mining of Canada Inc. - SOQUEM joint venture's 154,000 ha Foxtrot property. The nearest kimberlite occurrences are located approximately 100 km to the southwest at Lac Beaver. The Renard kimberlites are hosted by the Archean rocks of the eastern Superior Province. The kimberlites were discovered by the Ashton Mining - SOQUEM joint venture in 2001 as part of a regional diamond exploration program (Birkett et al., 2004). Airborne and ground magnetic surveys were conducted up-ice of kimberlite indicator mineral anomalies and kimberlite float found by the joint venture. Four anomalies identified by these surveys were targeted for drilling resulting in the discovery of Renard 1 and Renard 2. To date, nine kimberlites pipes have been found (Figure 2.1). A l l nine kimberlites are diamondiferous. The kimberlites range in size from 0.3 to 1.5 ha in area. Renard 4 is the third largest of the Renard kimberlites having an area of approximately 12, 600 m 2 . This portion of the Superior craton is covered in many areas by expanses of Quaternary glacial deposits (Hocq, 1985). The glacial deposits include undifferentiated tills and boulders of granite and gneiss up to tens of meters in their longest dimension. The Renard kimberlites were discovered by drilling of geophysical anomalies as the kimberlites lie under lakes or between 6 and 20 m of glacial deposits. After the discovery of the Renard 4 kimberlite, a road was built to provide easier access to drill sites. During road construction, a small subcrop of the Renard 4 kimberlite was discovered. After the discovery of the subcrop, an area approximately 25 m 2 was cleared, exposing the surface of the Renard 4 kimberlite. This exposed surface was mapped as part of this study. In 2006, an open pit was excavated as part of the bulk sampling program currently being undertaken by the joint venture. Renard 4 is estimated to contain 6.1 million tonnes of kimberlite at an approximate grade of 46 carats per hundred tonnes (Ashton Mining of Canada Inc., 2005). 3 689500 mE mm mt 589506*1 Figure 2.1: Location of the Renard kimberlite field. The map shows the location of the Renard kimberlite field in Canada and the locations of the kimberlites within the field. 4 2.2 Tectonic Setting and Regional Geology Diamondiferous kimberlites are associated with ancient Archean cratons where diamonds are preserved in the deep mantle due to the long-term stability of these lithospheric regions (Mitchell, 1993). The Archean Canadian Shield encompasses a large expanse of rock that has been geologically stable for billions of years. It is the relatively cool, stable rocks or crustal keels that exist beneath ancient cratons and can extend into the diamond stability field which are thought to be the reason for the association of diamondiferous kimberlites with Archean cratons. The Renard kimberlites on the Foxtrot property were emplaced through the Archean metamorphic rocks of the eastern Superior Craton (Figure 2.2). The Foxtrot property is surrounded by Proterozoic rocks of the Labrador Fold Belt to the east, the Cape Smith Fold Belt to the north and the Grenville Province to the south (Figure 2.3). The northern portion of the property is underlain by north-northwest trending, plutonic and gneissic terranes which based on metamorphic grade, mineralogy, lithology and aeromagnetics each appear to vary in width from 70 to 150 km (Clements and O'Connor, 2002). The basement gneiss in the vicinity of the Renard kimberlites has been metamorphosed at upper amphibolite to lower granulite facies in the late Archean (Hocq, 1985). Contained within the gneiss are relict metasedimentary and metavolcanic rock assemblages along with associated mafic and ultramafic intrusives (Clements and O'Connor, 2002). Northwest trending, Proterozoic diabase and gabbro dykes, up to 30 m wide, crosscut all terranes. Isolated outliers of Proterozoic clastic metasedimentary rocks are present in the region. The late Archean Wahamen greenstone belt is located approximately 30 km south of the kimberlite pipes. The greenstone belt includes mafic to ultramafic and minor felsic volcanic and intrusive rocks and associated metasediments. This supracrustal sequence was metamorphosed to a lower metamorphic grade than the nearby basement gneiss. Diabase dykes of the Mistissini Dyke swarm (2.5 Ga) intrude both of these rock types. Nearly 100 km south of the Renard kimberlites, marginal to the Grenville Province, the unmetamorphosed clastic sedimentary rocks of the Proterozoic Otish Mountain and Mistissini Groups rest unconformably on the Archean basement rocks. 5 Figure 2.2: Location of the Renard and Lac Beaver kimberlites in the Superior craton. The margin of the Superior craton is indicated by the blue line. 6 Figure 2.3: Geological map of Quebec. The locations of the Cape Smith Fold Belt, the Labrador Fold Belt, the Grenville Province and the approximate location of the Foxtrot property are shown. The area north of the Grenville Province, south of the Cape Smith Fold Belt and west of the Labrador Fold Belt is the Superior craton. (Modified after Clements and O'Connor, 2002). 7 Pleistocene glaciation of the Foxtrot property left thick glacial till deposits, lag deposits of glacially transported boulders, and large glacial erratics. Among the glacial erratics are a large number of kimberlite boulders, which provide an exploration tool to locate kimberlite dykes on the property. A large feature known as the New Quebec Ice Divide controlled Quaternary glacial cover over this area (Figure 2.4). From this centre, ice flowed north and northeast toward Ungava Bay and west to southwest toward Hudson Bay. Near Hudson Bay, marine sediments of the Tyrell Sea are common. Eskers can be traced for over 100 km and are generally oriented parallel to ice flow direction. In the central portion of the area (nearest to the Renards) hurnmocky and discontinuous unmoulded ground moraines are more prevalent. 2.3 Age of the Renard Kimberlites A single U-Pb age of 631.6 ± 3.5 Ma has been obtained for the Renard kimberlites for groundmass perovskite in coherent kimberlite (Birkett et al., 2004). The nearest confirmed kimberlites at Lac Beaver are significantly younger (551 ± 3 Ma) as are Gaucho Kue, Northwest Territories (542 ± 6 Ma) and Aviat, Nunavut (~ 600 Ma) where rocks similar to those present in the Renard kimberlites have been described (Birkett et al., 2004; Hetman, et al., 2004; Kjarsgaard, 2005). 2.4 Depth of Erosion of the Renard Kimberlites The current depth of erosion of the Renard kimberlites is not known for certain. However, rare fragments of siltstone and carbonate presumed to be derived from the Proterozoic cover rocks of the Otish Group or the approximately time equivalent Sakami Formation have been found in volcaniclastic breccia units of Renard 65 (Clements and O'Connor, 2002). The Otish Group has a stratigraphic thickness of approximately 2 km and a real thickness, after block faulting associated with dyke emplacement at approximately 1.8 Ga and erosion of roughly 1 km (Birkett, 2007 personal communication, March 1, 2007). The presence of these rare sedimentary xenoliths indicates that at the time of the kimberlite emplacement the gneissic basement was covered by the Otish Supergroup. If this 8 0 Renard Kimberlites \ Esker ^ New Quebec Ice Divide ^ Striation Interpreted Ice Direction Figure 2.4: Glacial map of north eastern Quebec. Location of the New Quebec Ice Divide is indicated by the black oval (modified after Clements and O'Connor, 2002). 9 reconstruction is correct, the current surface of the kimberlite represents a level at least than one kilometre below the surface at the time of emplacement. The rock types present in Renard 4 support this reconstruction as their textures suggest that they are part of the lower diatreme or the transitional zone between the root zone and the diatreme of a kimberlite pipe. General models of Class 1 kimberlite pipes indicate that this transitional zone is at depths between 800 m and 1.3 km below the crater of an uneroded kimberlite (Hawthorne, 1975). 2.5 Definition of Kimberlite The term kimberlite was initially used to name the primary host rock of diamond in the type locale in Kimberly, South Africa. Kimberlites are hybrid rocks consisting of minerals derived from the fragmentation of upper mantle xenoliths, country rock xenoliths and the crystallization products of kimberlite magma (Clement, 1982; Mitchell, 1993). The complex nature of these rocks led to many inaccurate, incomplete and/or misleading definitions of kimberlite. The commonly accepted definition of kimberlite is after Clement, (1982): "Kimberlite is a volatile-rich, potassic, ultra-basic igneous rock which contains abundant olivine and generally has a distinctively inequigranular texture resulting from the presence of macrocrysts set in a fine-grained matrix. This matrix contains as prominent primary phenocrystal and/or groundmass constituents, olivine and several of the following minerals: phlogopite, calcite, serpentine, diopside, monticellite, apatite, spinels, perovskite and ilmenite. Other primary minerals may be present in accessory amounts. The macrocrysts belong almost exclusively to a suite of anhedral, cryptogenic, ferromagnesian minerals which include olivine, phlogopite, picroilmenite, magnesian garnet, chromian diopside and enstatite. Olivine is extremely abundant relative to the other macrocrysts all of which are not necessarily present. In addition to macrocrysts smaller grains belonging to the same suite of minerals occur. Kimberlite may contain diamond but only as a very rare constituent. Kimberlite commonly contains inclusions of mantle-derived ultra-mafic rocks. Variable quantities of country rock xenoliths and xenocrysts may also be present. Kimberlite is often altered by deuteric processes mainly involving serpentinization and carbonatization. " 10 This definition has been upheld in many subsequent publications with few changes. It should be noted that diopside is not considered to be a primary groundmass mineral by other authors (Mitchell, 1995; Scott Smith, 1995). Kimberlites were initially divided into group 1 ("basaltic" or olivine-rich, monticellite, serpentine, calcite,) kimberlites and group 2 (micaceous) kimberlites (Wagner, 1914; Mitchell, 1993). The two groups of kimberlites are derived from different parental magmas and should be considered as separate rock types (Scott Smith, 1995). It is important to note that the vast majority of diamond mines in the world exploit group 1 kimberlites. Group 2 kimberlites are not as well described as group 1 kimberlites, but are characterized by the presence of common phlogopite (macrocrysts, phenocrysts and groundmass), common xenocrysts and phenocrysts of olivine together with groundmass diopside and some spinel (Scott Smith, 1995). Clement's (1982) definition given above is most pertinent to Group 1 kimberlites. 2.6 Classification of the Renard Bodies as Group 1 Kimberlites Classification of kimberlite rock types should be based on well crystallized uncontaminated material. Ideally classification should be based on samples of hypabyssal kimberlite as the nature of the minerals in these rocks is a direct reflection of the parental magma from which they are derived (Scott Smith, 1995). Where only volcaniclastic material is available, the mineralogy of juvenile pyroclasts in combination with composition of various mineral constituents may be used to classify kimberlite (Clement, 1982; Scott Smith, 2004; Boyer, 2005). The distinction of rock types is based on characteristic mineral assemblages which reflect the nature of the magma and the composition of the constituent minerals which give further indications about the nature of the parental magmas and therefore, rock type (Mitchell, 1986; Scott Smith, 1995). Hypabyssal kimberlite is generally defined as the "normal crystallization product of kimberlite magma" (Clement, 1982). Hypabyssal kimberlite has not been violently disrupted by fluidization or pyroclastic eruption processes (Field and Scott Smith, 1999). In much of the kimberlite literature, southern African Group 1 kimberlites are divided into three zones based on depth and the dominant rock types at these levels. The three zones are: (1) the Crater Zone, (2) the Diatreme Zone and (3) the Hypabyssal Zone (Figure 1.1). Hypabyssal 11 kimberlite is not necessarily confined to the Hypabyssal Zone of a kimberlite and can occur as dykes or sheets intruding country rock or a kimberlite body at any level. Birkett et al. (2004), using a suite of hypabyssal kimberlite samples from Renard 1, 2, 3, 4, 5 and 7 provide a mineralogical and geochemical classification of the Renard kimberlites. Many of the phlogopite analyses fall in the specified compositional range for Group 1 kimberlites. However, some phlogopite chemically zoned to aluminous biotite is present. Aluminous biotite is typical of melnoites and should not be present in Group 1 kimberlites. They further show that many of the spinel compositions deviate from the Mg-Cr rich compositions typical of Group 1 kimberlites and are more aluminous than are generally accepted for kimberlite, orangite, melnoite or lamprophyre. The variable mineral compositions indicate that the Renard bodies share features with both kimberlites and melnoites and are considered intermediate members of a spectrum of magma compositions (Birkett et al., 2004). No mineral chemistry was obtained as part of this MSc thesis. However, extensive petrographic study of hypabyssal rocks from Renard 4 show that they are composed of the two generations of olivine (macrocrysts and phenocrysts), rare mantle xenoliths and xenocrysts, set in a fine grained groundmass consisting of carbonate, phlogopite, spinel, serpentine, monticellite, perovskite and apatite. These features indicate that texturally, the Renard bodies can be classified as group 1 kimberlite. Although the mineral chemistry for some Renard kimberlites do not classify the rocks as group 1 kimberlite, it has been shown that kimberlite provinces dominated by bodies, or rocks that are typical group 1 kimberlites, they commonly also contain a low proportion of other varieties of volatile-rich, ultrabasic rocks (O'Brien and Tyni, 1999; Mitchell, et al., 1999; Scott Smith, 2004). Such rocks typically fall into the area of overlap between the petrolographic definitions of these different rock types (Figure 2.5). 12 Figure 2.5: Petrographic ranges of rock types commonly encountered in diamond exploration. The horizontal axis is a schematic representation of the petrographic variation within each rock type. The dashed line in the centre of the diagram divides rock types with high CO2 from those with low CO2. The vertical axis represents the relative global abundances of each rock type (not to scale). The width of the base of each curve represents the relative ranges of petrographic variation for each rock type (not to scale). The majority, but not all, rocks will fall definitively within a particular rock type. Extreme varieties of each rock type may fall outside the defined parameters or may show petrographic gradations or overlaps with the adjacent rock types (modified after Scott Smith, 1995). 13 2.7 Kimberlite Classes and Morphology of the Renard Kimberlites The first model of a kimberlite was proposed by Hawthorne (1975). This model consisting of a deep, steep-sided, cone-shaped body composed of three zones is now recognized as only one of three distinct classes of kimberlite pipes (Figure 2.6). Class 1 kimberlite pipes are typified by the southern African pipes used by Hawthorne (1975) to construct his generalized model of a kimberlite (Figure 1.1). These kimberlite pipes consist of a root zone, a diatreme zone and a crater zone. Class 2 pipes are shallow, champagne glass-shaped bodies found in the Canadian prairies, Angola and Siberia (Skinner and Marsh, 2004; Field and Scott Smith, 1999). Class 3 pipes, found in Canada, Africa and Siberia, have steep-sided craters usually greater than 500 m deep and are filled mainly with resedimented volcaniclastic kimberlite with minor pyroclastic kimberlite present (Skinner and Marsh, 2004). Class 3 pipes differ from Class 1 pipes by the great depth of their craters and by the absence of diatreme zones. Class 2 and Class 3 kimberlite pipes are both more common in North America than Class 1 pipes. Class 1 kimberlites are deep, steep-sided pipes with approximately circular or elliptical surface expressions at current erosional levels of approximately 300 m (Mitchell, 1993). Although a completely uneroded kimberlite is not known, the full volcanic structure of Class 1 pipes can be greater than 2 km in vertical extent (Field and Scott Smith, 1999). Class 1 kimberlites are found in southern Africa and northern Canada. This class of kimberlite pipe can be divided into three distinct vertical zones which from the top down are: (1) the crater zone, (2) the diatreme zone, and (3) the root zone. The shallow crater zone commonly with flared walls contains a variety of volcaniclastic rocks. The intermediate diatreme zone, which composes approximately 80% of the total length of the kimberlite pipe, has relatively smooth sides which are consistently at a slope of approximately 82 degrees (Skinner and Marsh, 2006). Tuffisitic kimberlite breccia, a rock composed of mixed country rock xenoliths and pelletal lapilli set in a fine-grained, serpentine-rich matrix containing microlitic clinopyroxene and no primary carbonate, is the typical infilling of the diatreme zone of a kimberlite pipe (Field and Scott Smith, 1999). The presence of a diatreme zone is believed to be unique to Class 1 kimberlite pipes (Field and Scott Smith, 1999; Skinner and Marsh, 2004). The diatreme zone grades with increasing depth into the root zone. The root 14 Figure 2.6: Schematic comparison of pipe morphologies of Class 1, 2 and 3 kimberlite pipes. Note that champagne and wine-glass shaped Class 2 and 3 pipes flare out into incompetent sedimentary rocks while carrot-shaped, Class 1 pipes occur in more competent sedimentary or crystalline basement rocks. Class 2 and 3 pipes tend to flare when crossing the contact between more competent host rock and less competent rock (modified from Field and Scott Smith, 2004). 15 zone is the lowermost zone of the kimberlite pipe and is characterized by irregular contacts with the wall rock and an infilling of coherent kimberlite. Diatremes and root zones of class 1 kimberlites are typically filled with multiple volcaniclastic (diatreme zone) and coherent (root zone) rock types. Kimberlite rock types with transitional coherent to fragmental textures are described in the lower diatreme zones of some Class 1 kimberlite pipes in southern Africa and North America (Skinner and Marsh, 2004; Hetman, et al., 2004, Skinner and Marsh, 2006) (Figure 2.7). A purely magmatic emplacement model with explosive breakthrough occurring when the volatile pressure of the kimberlite magma exceeds the confining pressure of the country rock is invoked for Class 1 kimberlites (Field and Scott Smith, 1999; Skinner and Marsh, 2006). Class 2 kimberlites are distinguished from Class 1 kimberlites by their shallow, champagne-glass cross sections. These pipes have diameters ranging up to 1300m and crater depths mostly less than 200m from the present sub-glacial surface (Field and Scott Smith, 1999). The pipes are not known to have diatremes or root zones but appear to be only shallow craters filled with volcaniclastic kimberlite. Volcaniclastic kimberlite describes fragmental kimberlite deposits for which there is evidence of direct deposition by explosive volcanism (pyroclastic kimberlite) or for which the mode of deposition can be recognized and ascribed to "normal" sedimentary processes (resedimented volcaniclastic kimberlite) (Field and Scott Smith, 1999). Class 2 kimberlites are similar in morphology to maar diatremes and a phreatomagmatic emplacement mechanism is indicated by their geometry, the presence of accretionary lapilli, and the common presence of aquifers at the depths from which the craters flare (Lorenz, 1975, 1987; Field and Scott-Smith, 1999; Boyer, 2005). Class 3 kimberlites include many of the pipes in the Lac de Gras area, North West Territories. Most Class 3 pipes have steep-sided craters extending to greater than 500 m below surface and are filled mainly with reworked volcaniclastic kimberlite and minor pyroclastic kimberlite (Skinner and Marsh, 2004). The shape of these pipes is similar to Class 1 pipes but the absence of diatreme facies rocks distinguishes them although a root zone filled with hypabyssal kimberlite can be present. Rare Class 3 pipes composed predominantly of hypabyssal kimberlite have been described (Graham et al., 1998; Kirkley et al., 1998). The smaller size of Class 3 pipes relative to Class 1 pipes suggests that less energetic eruptions 16 L l H-Tuffisitic Kimberlite Breccia 1 Tuffisitic Kimberlite Breccia 2 Transitional Kimberlite Coherent Kimberlite Flow Zone Contact Breccia Country Rock Breccia Country Rock Figure 2.7: Schematic of the major features of North American Class 1 kimberlite pipes. Tuffisitic Kimberlite Breccia 1 and Tuffisitic Kimberlite Breccia 2 are two distinct tuffisitic kimberlite breccia units. Transitional Kimberlite units are typical of the lower diatreme to root transitional zone in many Class 1 kimberlites, and have characteristics transitional from coherent kimberlite to tuffisitic kimberlite breccia (modified from Hetman, 2006). 17 formed them. An emplacement model for Class 3 kimberlite pipes invokes an initial explosion due to volatile pressure of the kimberlite magma exceeding the lithostatic pressure of the granitic basement, supplemented by phreatomagmatic explosions resulting from magma-wet sediment interaction as the magma intruded Cretaceous unconsolidated sediments overlying the basement (Field and Scott Smith, 1999). 2.8 Rock Type Definitions Kimberlite can most broadly be divided into fragmental (or volcaniclastic) and coherent varieties. Coherent varieties are the product of crystallization of kimberlite magma which has not been disrupted by fluidization or pyroclastic eruption and fragmental varieties are the product of kimberlite magma which has (Clement, 1982; Cas and Wright, 1988; Field and Scott Smith, 1999). Section 2.8 defines kimberlite rock types using the terminology and definitions derived from published descriptions. These definitions are followed by a section defining the terminology used in the current study. 2.8.1 Hypabyssal Kimberlite Hypabyssal kimberlite is the normal crystallization product of kimberlite magma (Clement, 1982). These rocks have not been disrupted by fluidization or pyroclastic eruption mechanisms (Field and Scott Smith, 1999). Hypabyssal kimberlite occurs as the infill of the root zone of the kimberlite and as dykes, sheets and sills cutting kimberlite pipes at any stratigraphic level or in the country rock (Figure 2.5). Hypabyssal kimberlite can have uniform or segregationary, fine-grained, crystalline groundmass. However, uniformly textured, coherent kimberlite is much more common than segregationary textured kimberlite (Skinner and Marsh, 2004). Segregationary textures are the result of the crystallization of certain minerals or groups of minerals in discrete areas of the rock (Clement and Skinner, 1985). The groundmass of hypabyssal kimberlite contains abundant calcite and serpentine which are late-stage crystallization products. Primary clinopyroxene is absent or rare as a groundmass phase in hypabyssal group 1 kimberlites (Skinner and Marsh, 2004). Hypabyssal kimberlite is characterized by an inequigranular texture that results from the presence of anhedral, upper mantle derived minerals in a fine grained groundmass. The 18 most common mantle phase is olivine, but phlogopite, picroilmenite, chromian spinel, magnesian garnet, chrome diopside and orthopyroxene may also be present (Clement and Skinner, 1985). The texture imposed on kimberlites by these anhedral mineral grains is termed 'macrocrystic' (Clement, 1982). Although it is volumetrically rare, aphanitic hypabyssal kimberlite is not uncommon. The absence of macrocrysts in aphanitic kimberlite may result from near-surface flow differentiation or, at greater depths, from other crystal fractionation processes (Clement and Skinner, 1985). Hypabyssal kimberlite can be subdivided into two categories: (1) hypabyssal kimberlite and (2) hypabyssal kimberlite breccia. These two rock types are distinguished on the basis of percent country rock xenoliths in the rock. Hypabyssal kimberlite must contain less than 15% crustal xenolithic material whereas hypabyssal kimberlite breccia must have more than 15% country rock xenoliths (Clement and Skinner, 1985). Country rock xenoliths in hypabyssal kimberlite breccias are commonly strongly altered by the kimberlite magma. Secondary clinopyroxene forms as reaction haloes around quartz-rich xenoliths (Skinner and Marsh, 2004). The extensive metasomatization of the country rock clasts in hypabyssal kimberlite breccias reflects incorporation into a relatively hot, volatile-rich, reactive kimberlite magma (Clement and Skinner, 1985). The lesser degree of alteration of xenoliths in diatreme facies breccias is partially due to the fact that these xenoliths were entrained into degassed kimberlite magma much poorer in volatile components. 2.8.2 Tuffisitic Kimberlite Tuffisitic kimberlite breccia is the most volumetrically abundant textural variety of kimberlite in southern African pipes and was first described by Clement (1982). This rock type is the typical infill of the diatreme zone of Class 1 kimberlites as defined by Skinner (2004) and is characterized by distinct macroscopic and microscopic features which differ from those of volcaniclastic Class 2 and Class 3 rocks. However, in recent years, tuffisitic kimberlite has been recognized in a few North American kimberlites including; Gaucho Kue, North West Territories (DeBeers), Aviat, Nunavut (Storaoway Diamond Corporation), Qilalugaq, Northwest Territories (BHP Billiton Diamond Corporation), Camsell Lake, North West Territories (Field and Scott Smith, 1998) 19 and the Renard kimberlites (Hetman, 2006). Hetman (2006) summarizes the examples of tuffisitic kimberlite in Canadian kimberlites. Tuffisitic kimberlite breccias (TKBs) are soft to moderately hard, brownish-, greenish-, or bluish-grey rocks. They have fragmental textures imposed primarily by the presence of abundant, angular to sub-rounded, country rock xenoliths (Clement, 1982). Olivine macrocrysts are completely pseudomorphed by serpentine and occasionally carbonate. Country rock xenoliths compose a significant volume of tuffisitic kimberlite breccias. There can be significant variation in size of the country rock xenoliths, but most are small (less than 15 cm). Typically, country rock xenoliths in T K B units are fresh relative to those in coherent, macrocrystic (hypabyssal) breccias (Clement, 1982; Clement and Skinner, 1985; Wooley, et al., 1996; Field and Scott Smith, 1999). However, inclusions of country rock in TKBs showing alteration rims are noted in some southern African kimberlites. Alteration is believed to be the result of incorporation of the xenoliths prior to fluidization when the volatile content of the kimberlite magma was still extremely high (Clement, 1982). Tuffisitic kimberlite breccias have a homogeneous appearance on a large scale despite their smaller scale heterogeneity. Clement (1982) suggests that this large scale homogeneity reflects considerable mixing of the components of the country rock xenoliths and other components resulting in an 'ordering' effect reflecting fairly even distribution and spacing of megascopic components. Tuffisitic kimberlite breccia is commonly magmaclastic. The term 'magmaclastic' refers to kimberlite containing clasts of kimberlite magma visually distinct from the kimberlitic groundmass. The term is a general one and refers to any clast of kimberlite regardless of size, morphology or textural variety. Microscopically, tuffisitic kimberlite breccia is characterized by pelletal lapilli. In the kimberlite terminology, lapillus is commonly used to describe a particular texture rather than to define a size range of clasts (Clement, 1982; Clement and Reid, 1988; Field and Scott Smith, 1999). It is thus different from volcanological terms where lapillus refers to a pyroclast between 2 mm and 64 mm in diameter (Cas and Wright, 1988). According to Clement (1982), pelletal lapilli are generally spherical or spheroidal kimberlite clasts with sharp, curviplanar margins. Many pelletal lapilli contain a nucleus of a large serpentinized olivine macrocryst or fragment of country rock with a thin mantle of fine-grained, to 20 cryptocrystalline kimberlitic material. The lapillus nucleus is usually centrally located but may be located off-centre. Lapilli with no kernel and broken lapilli are also noted in many locations. The thin kimberlitic rims of pelletal lapilli are generally of turbid, brown cryptocrystalline material. Larger rims also contain phenocrysts of olivine in a cryptocrystalline or very fine-grained groundmass consisting of several kimberlite groundmass minerals such as phlogopite, serpentine and spinel (Clement, 1982). Pelletal lapilli are thought to form by the fluidization process which is integral to the formation of tuffisitic kimberlite breccias. The term fluidization describes the mixing of a particle (or clast) rich system by the passing of gas or liquid through a "bed" of solid particles such that the entire system behaves as a fluid (McCallum, 1985). When fluid velocity is such that the drag force exerted by the fluid on the particles is sufficient to lift or suspend them against the force of gravity, a fluidized state is attained (McCallum, 1985). In a fluidized state, larger particles will be affected by the drag of the fluid on the particle and by gravity more strongly than smaller particles. Small particles will therefore become fluidized more efficiently than larger particles and will stream past them. In a turbulently fluidized system, accretion of smaller particles around larger particles is easily envisioned. Thus, pelletal lapilli composed of large cores surrounded by rims of very fine kimberlite are formed. Pelletal lapilli differ from some other magmaclasts in that they do not derive from pre-existing kimberlite units but are the result of the fragmentation and fluidization of the kimberlite melt. Inclusions of kimberlite in tuffisitic kimberlite breccias vary considerably in abundance and size but it is uncommon for magmaclasts or autoliths to exceed 10 cm in diameter (Clement, 1982). The majority of kimberlite inclusions are composed of hypabyssal kimberlite and are commonly microscopic. Clement (1982) suggests that these clasts are derived from hypabyssal kimberlite emplaced prior to the formation of a diatreme. As they are soft and incompetent, clasts of tuffisitic kimberlite breccia distinct from the host T K B are rarely preserved. Inclusions of one tuffisitic kimberlite unit in another are most common near the contact of two tuffisitic kimberlite units (Herman, 2006). Several mineralogical varieties of kimberlite inclusions are commonly found within a single tuffisitic unit. Rare units of tuffisitic kimberlite (as opposed to tuffisitic kimberlite breccia) are noted in many of the southern African kimberlites (Clement, 1982) and in Canadian kimberlite pipes (Hetman, 2006). These units have few to no country rock xenoliths greater 21 than 4 mm in size and commonly are only locally developed, narrow (<1 m), discontinuous zones separating tuffisitic kimberlite breccias (Clement, 1982). Clement (1982) attributes these features to flow differentiation within intrusions during intrusion of the fluidized kimberlite magma. 2.8.3 Transitional Kimberlite In a Class 1 kimberlite pipe, tuffisitic kimberlite may grade texturally into coherent kimberlite with depth (Hetman, 2006) (Figure 2.7). The textural rock type transitional between tuffisitic (fragmental) kimberlite and coherent kimberlite has been described in many of the southern African kimberlite pipes as well as in some North American kimberlites (Clement, 1982; Field and Scott Smith, 1999; Hetman et al., 2004, Skinner and Marsh, 2004 and 2006b). Transitional rocks are characterized by irregular areas with coherent textures juxtaposed with areas exhibiting fragmental textures. Areas with fragmental textures contain pelletal lapilli and microlitic textures while those with coherent textures contain macrocrysts in a coherent groundmass of carbonate and/or phlogopite and/or spinel. Areas with more intermediate textures displaying incipient development of pelletal lapilli are also present (Hetman, et al., 2004). With increasing depth, coherent kimberlite become much more abundant than tuffisitic kimberlite. Hetman et al (2004) distinguish between the two end members of transitional kimberlite referring to them as TKt (transitional kimberlite with more features in common with tuffisitic kimberlite), and HKt (transitional kimberlite with more features in common with coherent, magmatic kimberlite). 2.8.4 Volcaniclastic Kimberlite Volcaniclastic kimberlite is the term used to describe extrusively formed fragmental kimberlite deposits (Field and Scott Smith, 1999; Webb et al., 2004). Where the mode of deposition can be recognized and ascribed to normal sedimentary processes, the rock is termed resedimented volcaniclastic kimberlite. If direct deposition by explosive volcanism is indicated, the rock is termed pyroclastic kimberlite. Both resedimented volcaniclastic kimberlite and pyroclastic kimberlite are rock types typical of crater infill. Pyroclastic kimberlite in particular may also be found in crater rim or extra-crater deposits. The absence 22 of a crater and therefore any crater facies kimberlite rock types in the Renard 4 kimberlite preclude the presence or preservation of volcaniclastic kimberlite in the body. 2.8.5 Country Rock Breccia Country rock breccias are breccias associated with a kimberlite pipe which contain less than 5% kimberlitic material. Country rock breccias are dominated by angular, to sub-rounded clasts of country rock. The breccias are differentiated from tuffisitic kimberlite breccia or hypabyssal kimberlite breccia by the absence of a kimberlitic groundmass, olivine macrocrysts, and juvenile fragments. Voids filled with euhedral, late-stage minerals such as calcite and pyrite are commonly present (Clement, 1982). Country rock breccias lie peripheral to a kimberlite pipe or dyke. Commonly at the extreme edge of the brecciated zones surrounding many of the southern African pipes, zones of fractured country rock showing little to no displacement along the fractures are common (Clement, 1982). These fractured zones are generally narrow (<1 to 3 m). Between the strongly brecciated country rock and the fractured zones there is a zone with minor displacement but little to no separation of the country rock blocks (Clement, 1982). Country rock clasts may be locally derived and show little to no displacement (Clement, 1982) or they may include clasts of country rock derived from a variety of stratigraphic levels and show a high degree of mixing (Barnett, 2004). Barnett (2004) suggests that the high degree of mixing of the components seen in some country rock breccias as well as the sharp contacts with the kimberlite facies in those kimberlite pipes is indicative of large mass failures in the country rock sometime before the final stage of volcanism. 2.9 Nomenclature Table 2.1 summarizes the above terms for kimberlite rock types as derived from published descriptions and which have been used in this thesis. For the purposes of this thesis, rocks have been broadly divided into four groups: 1- coherent rocks, 2- volcaniclastic rocks, 3- transitional rocks and 4- country rock breccia. These are further divided into multiple facies of coherent and volcaniclastic rocks. 23 A 'facies' is a body or interval of rock or sediment which has a unique definable character that distinguishes it from other 'facies', or intervals of rock or sediment (Cas and Wright, 1988). In the textural-genetic classification schemes for kimberlite proposed by Clement (1982), Clement and Skinner (1985) and Wooley, et al. (1996), and used by many subsequent authors, kimberlite is subdivided into three broad groups: hypabyssal-facies, diatreme-facies and crater-facies. In these classification schemes the term 'facies' is used to describe rocks confined to particular zones of the pipe, i.e. hypabyssal-facies rocks are confined to the root (or hypabyssal) zone the kimberlite pipe. In this thesis, kimberlite has been broadly divided into coherent and volcaniclastic varieties. The terms 'facies' and 'subfacies' have been used to subdivide the coherent and volcaniclastic units into groups with distinct features believed to result from unique conditions during their emplacement. Table 2.1: Summary of kimberlite nomenclature in literature and in the current study. Kimberlite Literature Current Study Hypabyssal Kimberlite (HK) Coherent Kimberlite Magmatic Kimberlite Tuffisitic Kimberlite Breccia (TKB) Volcaniclastic Kimberlite Volcaniclastic Kimberlite (VK) TKt Transitional Kimberlite HKt Country Rock Breccia Country Rock Breccia 24 C H A P T E R 3: P E T R O G R A P H I C U N I T S O F T H E R E N A R D 4 K I M B E R L I T E 3.1 Introduction This chapter provides detailed descriptions of each of the rock types present in Renard 4. Samples for this thesis were collected from fifteen diamond drill holes in the Renard 4 kimberlite (Figure 3.1). The Renard 4 kimberlite has an irregular, elongate form and is filled with a variety of coherent and volcaniclastic kimberlite rock types. The geometry of the kimberlite in cross-section and dominace of tuffisitic kimberlite breccia indicate that Renard 4 is a Class 1, kimberlite with many features in common with the typical southern African kimberlite pipes. The irregular shape of the pipe and the fact that it is believed that the current level of erosion is approximately 1 km below the paleosurface, suggest that presently, the Renard 4 kimberlite comprises only the lower diatreme and root zone of the original kimberlite pipe (Birkett, et al., 2004) (Figure 3.2). Renard 4 is composed of six rock types which can be grouped into four major rock units: coherent kimberlite, volcaniclastic kimberlite, transitional kimberlite and country rock breccia. There are two subfacies of coherent kimberlite and two facies of volcaniclastic kimberlite. The facies and subfacies of coherent and volcaniclastic kimberlite are summarized in Table 3.1. Table 3.2 shows the number of samples of each rock type used to derive the data presented in this chapter. Table 3.3 summarizes the groundmass mineralogy of each rock type. The colour of the groundmass of each rock type in hand sample is also provided as groundmass colour is used as a primary means of distinguishing the four phases of tuffisitic kimberlite breccia. Table 3.4 lists abundance and size distribution of olivine macrocrysts and number and abundance of magmaclast populations in each rock type. The data presented in Table 3.5 represent the kimberlitic components (additional to the groundmass) present in each rock type. Abundance and volume of country rock xenoliths in each rock type are presented in Table 3.6. The coherent facies are described first as classification of the rocks as Group 1 kimberlite is based on the composition of the coherent kimberlite. The four phases of 25 Renard 4 R4-45 i N Drill hole collar with surface trace Surface trace of kimberlite body metres Figure 3.1: Map showing the surface outline of Renard 4 and selected drill collar locations. The surface outline of the kimberlite as it appears in this figure is based in part on geophysical data. The drill collar locations which appear in this figure are those which were used to obtain data for this thesis. 26 Tuff Ring Crater Diatreme Root Lower Diatreme Diatreme-root transitional zone Figure 3.2: Schematic of a typical Class 1 kimberlite showing level exposed at Renard 4. A . Model of a typical Class 1 kimberlite pipe (modified after Hawthorne, 1975) with the zone encompassing the lower diatreme and the zone transitional between the diatreme and the root expanded (B). B. At the current level of erosion it is this zone of the kimberlite that is exposed in Renard 4. The darkest material represents kimberlite transitional between the volcaniclastic rocks of the diatreme and the coherent rocks of the root. The lightest material represents tuffisitic kimberlite breccia infilling the diatreme. The solid grey areas represent dykes and sills cutting the pipe. 27 Volcaniclastic Facies 1 are described from the periphery to the core of the kimberlite. The second volcaniclastic facies, 'accretionary' magmaclastic kimberlite, is the last volcaniclastic rock type to be described as it is the least volumetrically abundant volcaniclastic facies and the last volcaniclastic facies to have been emplaced. A rock type with characteristics transitional from coherent to volcaniclastic kimberlite is also described in the Renard 4 kimberlite. As this rock type has features in common with both coherent and volcaniclastic kimberlite it is described last. The final rock type present in Renard 4 is a non-kimberlitic fragmental unit in the country rock at the margins of the kimberlite pipe. It is described last as it is most distal to the core of the kimberlite. Furthermore, it is the only unit which is a part of the kimberlite pipe but contains no kimberlite. Table 3.1: Rock units, facies and phases of the Renard 4 kimberlite. Rock Unit Facies Phase Coherent Subfacies 1: Massive coherent, Macrocrystic Kimberlite Subfacies 2: Coherent, Macrocrystic Kimberlite Breccia Volcaniclastic Facies 1: Tuffisitic Kimberlite Breccia Facies 2: 'Accretionary' Magmaclastic Kimberlite Phase 1: Grey tuffisitic kimberlite breccia Phase 2: Green tuffisitic kimberlite breccia Phase 3: Brown tuffisitic kimberlite breccia Phase 4: Blue tuffisitic kimberlite breccia Transitional Transitional Kimberlite Breccia Country Rock Country Rock Breccia Breccia 28 Table 3.2: Number of samples of each Renard 4 rock type examined. Rock Type # Samples #Slab # Thin Section Coherent: Massive 42 32 10 Coherent: Breccia 3 3 0 Volcaniclastic Facies 1: Phase 1 36 21 15 Volcaniclastic Facies 1: Phase 2 34 26 8 Volcaniclastic Facies 1: Phase 3 18 13 5 Volcaniclastic Facies 1: Phase 4 39 34 5 Volcaniclastic Facies 2 5 3 2 Transitional 18 11 7 Country Rock Breccia 8 6 2 3.2 Methodology Componentry data was obtained by point counting of slab and thin section samples. For each slab sample of Coherent Subfacies 2, Volcaniclastic Facies 1 (all phases) and transitional kimberlite, five areas of 5 cm by 3 cm were marked on the samples. In each area the number of country rock xenoliths in each of four size categories was recorded. The size ranges used were: 0.5 to 2 mm, 2 to 5 mm, 5 mm to 2 cm, and greater than 2 cm. The rounding of the country rock xenoliths was recorded as the number of round, the number of subround, the number of subangular and the number of angular xenoliths. Size categories were not considered separately for degree of rounding of the xenoliths. The number of olivine macrocrysts greater and less than 5 mm and the number of rounded versus elongate macrocrysts was recorded for each area. For each area, the point counts were converted to percentages and averaged over the five areas to give a single set of data per sample. The number of magmaclasts per sample was obtained slightly differently due to the lower abundance of these clasts relative to either country rock xenoliths or olivine macrocrysts. For each sample, magmaclasts were counted over a single 20 cm 2 area per sample and the number of distinct magmaclast populations was also recorded. For each slab sample of Coherent Subfacies 1, Volcaniclastic Facies 2 and country rock breccia the point counts were executed in the same manner as for samples of Coherent Subfacies 2, Volcaniclastic Facies 1 and transitional kimberlite except that only three 5 cm 29 by 3 cm areas were counted per sample. This is because the former three rock types are much more homogeneous by nature than the latter two. For every thin section point counts were done on seven randomly selected fields of view at both 20 times and 50 times magnification. In each field of view, the percentage of carbonate, serpentine, phlogopite, spinel and cryptocrystalline material was recorded. The number of olivine phenocrysts and olivine macrocrysts was recorded in each field of view. The values for the seven areas were then averaged to give a single set of data per sample. The data presented in Tables 3.3, 3.4 and 3.5 are the averages of all analysed samples of each rock type. 30 Table 3.3: Comparison of groundmass components of the Renard 4 rock types. Modal abundance, colour and mineralogy of groundmass components in each rock type is presented. Rocks are classified by type as coherent or volcaniclastic and then by facies, subfacies or phase. Transitional rocks have been subdivided into types with more coherent or more volcaniclastic appearance as the nature of the groundmass varies significantly between the two. Groundmass components carbonate (Carb.), phlogopite (Phi.), serpentine (Serp.), spinel, and cryptocrystalline material (Cryp.) do not compose 100% of the groundmass in all samples, but are the major constituents of the groundmass of all samples. For Volcaniclastic Facies 2, the percent groundmass refers to material between 'accretionary' magmaclasts and does not include any material which is part of a rim around a macrocryst. Rock Type Groundmass Colour Vol % Groundmass Vol % Olivine Phenocrysts Groundmass Mineralogy (modal abundance) Carb. Phi. Serp. Spinel Cryp. Coherent: Massive Dark grey 70-98 5-15 5-50 5-50 5-50 1-3 0 Coherent: Breccia Dark grey 1-15 <l-2 5-50 5-50 5-50 1-3 0 Volcaniclastic Facies 1 Grey 15-50 1-5 0 2-5 80-100 1-5 1-5 (Phase 1: Grey TKB) Volcaniclastic Facies 1 Green 45-65 0 0 0 5-25 1-2 75-95 (Phase 2: Green TKB) Volcaniclastic Facies 1 Brown 60-75 1-5 25-45 10-20 5-15 2-7 5-10 (Phase 3: Brown TKB) Volcaniclastic Facies 1 Blue 40-60 0 0 0 0 1-2 98-100 (Phase 4: Blue TKB) Volcaniclastic Facies 2 Dark grey 10-50 1-10 0 5-10 60-90 5-15 0 ('Accretionary') Transitional Coherent patches Mottled dark 65-85 15 35 5 50 10 0 and medium 0 0 0 48 2 50 Volcaniclastic patches grey Country Rock Breccia Grey 3 0 Rock flour - dominantly composed of quartz, Table 3.5: Comparison of country rock xenolith populations. For each rock type the average percentage of country rock xenoliths (by volume) is given and a break-down of the size ranges of xenoliths is given as a percentage of the total number (not total volume) of country rock xenoliths. Note is also made of the rounding and degree of alteration of the xenoliths. The percentages for the rounding of the xenoliths are given as percentages of the total number of xenoliths rather than as percentage of the total volume, and include all sizes collectively. The degree of alteration is defined by the percentage of xenoliths which are altered from a normal granitic assemblage of feldspars, quartz and biotite or hornblende to an assemblage rich in chlorite and serpentine. Rock Type % Country Rock Clasts Size Range Rounding Alteration % % % % % % 0.5-2mm 2-5mm 0.5-2cm <2cm % Rounded Sub-rounded % Sub-angular Angular Coherent: 2 0 0 25 75 25 70 5 0 Extreme Massive Coherent: 90 1 1 3 95 0 0 2 98 Moderate-Breccia strong Volcaniclastic 56 72 13 12 3 0 9 88 3 Weak Facies 1 (Phase 1) (Phase 2) 42 90 5 4 1 1 3 73 23 Weak-moderate (Phase 3) 22 51 17 30 4 2 77 32 1 Strong (Phase 4) 52 70 14 13 3 2 12 77 7 Moderate-strong Volcaniclastic 0 0 0 0 0 0 0 0 0 na Facies 2 Transitional 18 54 27 18 1 0 88 11 1 Extreme Country Rock 98 3 2 5 90 0 25 25 50 Weak to Breccia none Table 3.4: Comparison of the macrocryst and magmaclast populations. For each rock type the percentage of macrocrysts as a function of the total rock volume, the rounding of the macrocrysts and their average size are given. The percentage of magmaclasts as a function of the total rock volume, the number of magmaclasts per 20 cm 2 area and the number of distinct magmaclast populations are also given. A special category for Volcaniclastic Facies 1: Phase 4 within 50 cm of contacts with Volcaniclastic Facies 1: Phase 3 is made as the volume of magmaclasts over these intervals is extremely high. Note that for Volcaniclastic Facies 2, macrocrysts are within magmaclasts and the two components are not considered independently. Rock Type Macrocrysts Magmaclasts Coherent: Massive % Macrocrysts 25 Avg. Size (mm) 3 % Rounded 85 % Magmaclasts 0 #of Magmaclasts per 20 cm2 na Avg. Magmaclast Size (mm) na #of Magmaclast Varieties na Coherent: Breccia <1 <1 90 0 na na na Volcaniclastic Facies 1 <1 <1 100 2 3 25 1 (Phase 1: Grey TKB) (Phase 2: Green TKB) 2 1 100 2 10 10 4 (Phase 3: Brown TKB) 10 7 83 <1 5 3 2 (Phase 4: Blue TKB) 2 3 100 1 15 5 3 (Phase 4: Blue TKB) 2 5 100 30 25 35 3 (but >90% within 50 cm of contacts are clasts of with (Phase 3: Brown Brown TKB) TKB) Volcaniclastic Facies 2 25 5 90 45 <25 10 1 Transitional 7 3 90 <1 2 0.5 1 Country Rock Breccia 0 0 na 0 na na 0 3.3 Coherent Rocks There are two subfacies of coherent kimberlite (Figure 3.3). The first is coherent, macrocrystic kimberlite with less than 5% entrained country rock xenoliths. The second is a coherent, macrocrystic kimberlite breccia. The breccia facies is composed of more than 85% country rock xenoliths cemented by macrocrystic kimberlite. The breccia is not fragmental but rather occurs as zones peripheral to coherent, macrocrystic units where the coherent, macrocrystic kimberlite has intruded along fractures in the wall rock creating a matrix with large country rock clasts. It is the nature and texture of the kimberlite matrix which defines this rock type as a subfacies of coherent kimberlite rather than a volcaniclastic kimberlite breccia. 3.3.1 Subfacies 1: Massive coherent, macrocrystic kimberlite Massive coherent, macrocrystic kimberlite forms steeply dipping dykes intruding the kimberlite pipe. These units have sharp contacts with the host rock. Coherent, macrocrystic kimberlite units cutting tuffisitic kimberlite breccias or country rock breccias generally have sharp but irregular contacts whereas those units cutting the gneissic country rock commonly have sharp, straight margins. Coherent Subfacies 1 contains between 5 and 60% serpentinized, partially serpentinized or fresh olivine macrocrysts, 5 to 15% serpentinized olivine phenocrysts, rare xenocrysts of pyrope garnet, chrome diopside, ilmenite and chromite, and less than 15% strongly altered country rock xenoliths in a fine grained, dark grey to dark grey green matrix (Figure 3.3 a, b and c). The matrix is composed primarily of carbonate, phlogopite, serpentine and spinel (Figure 3.4 a and b). The groundmass of the coherent, macrocrystic kimberlite units is either uniform or contains segregations of carbonate (Figure 3.4 c). Where present, carbonate segregations are rarely greater than 3 mm in their longest dimension. Olivine macrocrysts in Coherent Subfacies 1 range in size from 1 mm to 2 cm but are on average 2-4 mm. Macrocrysts are generally rounded but elongate and most are completely serpentinized (Figure 3.4 d). Partially serpentinized, or fresh olivine macrocrysts are rare (Figure 3.4 e and f). Fractures in serpentinized olivine macrocrysts are commonly filled with calcite. Magnetite or hematite after magnetite is noted locally. These minerals occur most 34 Figure 3.3: Coherent rocks of the Renard 4 kimberlite. A . Mesoscopic image of Coherent Subfacies 1. Serpentinized olivine macrocrysts are dark grey. Small white areas in the macrocrysts are areas of carbonitization. B. Mesoscopic image of Coherent Subfacies 1. In this sample, serpentinized olivine macrocrysts are light green rather than dark grey. C. Hand sample of Coherent Facies 2. Scale bar is 8 cm long. Country rock clasts of various dimensions are cemented by a dark grey coherent kimberlite matrix. 35 Figure 3.4: Coherent subfacies 1 photomicrographs and mesoscopic images. A . Typical groundmass assemblage of Coherent Subfacies 1: serpentine (Serp), phlogopite (Phi), Carbonate (Carb) and spinel (Sp). B . Typical groundmass assemblage viewed through crossed polars. C. Segregationary groundmass in Coherent Subfacies 1. OP = olivine phenocryst. Segregations are of carbonate. D . Typical macroscopic appearance of Coherent Subfacies 1. Note the bright green, entirely serpentinized olivine macrocrysts (OM). E . Fresh core remnants of olivine macrocrysts. Serpentine is present at the rims of the grains and along internal fractures. F. Same field of view as in E but viewed though crossed polars. 36 commonly along fractures in the macrocrysts but are rarely present as rims around macrocrysts (Figure 3.5 a and b). Flow alignment of olivine macrocrysts is common in massive coherent, macrocrystic kimberlite (Figure 3.5 c and e). Locally, flow is marked by bands of coarser serpentinized olivine macrocrysts and aphanitic kimberlite or finer olivine macrocrysts or phenocrysts. Orientation of flow textures in many coherent, macrocrystic kimberlite samples is parallel to the margins of the dyke. Carbonate, phlogopite and serpentine dominate the groundmass assemblage of Coherent kimberlite samples. These minerals occur in one of two textures: 1- evenly mixed together or 2- forming distinct clots. Where the groundmass minerals form distinct clots the carbonate, phlogopite or serpentine may be more abundant than the other minerals or the three minerals may occur in equal proportions. Accessory groundmass minerals include spinel and perovskite (Figure 3.5 d). Locally monticellite is a dominant groundmass mineral (Figure 3.6 a). Spinel generally composes <2% of the groundmass assemblage and is evenly distributed throughout it. Necklace textures with spinel grains concentrated in rings around olivine macrocrysts are noted locally (Figure 3.6 b). Olivine phenocrysts are ubiquitous in facies 1 and compose approximately 15% of the rock. Country rock xenoliths in Coherent Subfacies 1 are rare, but where present, they are extremely strongly altered. Bleaching and chloritization of the granitic and gneissic xenoliths is common (Figure 3.6 c). Alteration products of granite including pectolite are present locally (Figure 3.6 d). The contact relationships of the Coherent Subfacies 1 with Volcaniclastic and country rocks suggest that these dykes intruded along weaknesses in the rocks. In the breccia units, the dykes are irregular and intruded along clast margins while in the gneiss the dykes intruded along joint and foliation surfaces resulting in straight sided dykes. 3.3.2 Subfacies 2: Coherent, macrocrystic kimberlite breccia Coherent Subfacies 2 is composed of 85 to 99% moderately altered, angular country rock xenoliths and 0.5 to 1% olivine macrocrysts in a dark grey, fine-grained, carbonate-rich kimberlite groundmass (Figure 3.3 d). This rock type is classified as coherent instead of fragmental as would be expected of a breccia unit because of the coherent nature of its 37 Figure 3.5: Images of Coherent Facies 1. A . Photomicrograph showing magnetite (MAG) along fractures in an olivine macrocryst (OM). B. Photomicrograph showing hematite (Hem) around the rim and along fractures in an olivine macrocryst (OM). C. Photomicrograph showing flow alignment of olivine macrocrysts (OM). Arrow indicates flow direction. D. Photomicrograph showing perovskite (P) occurring as a minor groundmass phase. E . Flow alignment of olivine macrocrysts in a hand sample of Coherent Subfacies 1. The sample is cut by a series of fine carbonate veins at approximately 35 degrees (centre to left hand side of photo). 38 Figure 3.6: Photomicrographs and mesoscopic images of Coherent Subfacies 1. A . Example of monticellite (light green) as a locally dominant groundmass phase. The opaque mineral is spinel (Sp) and the white mineral is carbonate. B. Necklace texture with spinel (Sp) grains ringing an olivine macrocryst (OM). Other groundmass phases are carbonate (white), and serpentine (grey-green). C. Bleached granite xenolith showing replacement of some mineral phases by chlorite (Chi). D. Highly altered country rock xenolith (outlined with dashed black line) showing alteration to pectolite (Pect). 39 kimberlite matrix. The kimberlite matrix of this breccia unit rarely composes more than 3% of the total rock volume. The rare olivine macrocrysts in this unit are commonly fresh or partially serpentinized. Coherent Subfacies 2 is situated at the margins of coherent, macrocrystic dykes and sheets (Coherent Subfacies 1) cutting the country rock breccias or fractured country rock. In Coherent Subfacies 2 kimberlite from Coherent Subfacies 1 units has seeped into spaces between clasts in country rock breccias or fractures in country rock forming a kimberlite stockwork (Figure 3.7). There is no evidence of fragmentation of the kimberlite matrix and country rock clasts appear to be in situ. Rare examples of Coherent Subfacies 2 units occurring at the margins of Coherent Subfacies 1 dykes which intrude volcaniclastic kimberlite breccias are present in Renard 4. These examples of Coherent Subfacies 2 contain only 10 to 15% xenoliths, far less than those which occur at the margins of dykes cutting country rock breccias or fractured country rock. There are no microscopic observations for this rock unit because the available samples were extremely delicate and proved impossible to cut and make into thin sections. 3.4 Volcaniclastic Rocks There are two facies of volcaniclastic rocks present in the Renard 4 kimberlite: tuffisitic kimberlite breccia and 'accretionary' magmaclastic kiniberlite. Four phases of tuffisitic kimberlite (Volcaniclastic Facies 1) are described. These phases are differentiated by the abundance and alteration of country rock xenoliths, abundance and size of olivine macrocrysts and by the abundance and varieties of magmaclasts present in each. Both volcaniclastic facies are magmaclastic although the abundance and the morphology of the magmaclasts vary between facies. It is the presence of magmaclasts in the volcaniclastic facies and their absence in Coherent Subfacies 2 (coherent, macrocrystic kimberlite breccia) that distinguishes the coherent breccia from the volcaniclastic breccia facies described below. The four phases of Volcaniclastic Facies 1 are described in order from the most peripheral to the most central to the kimberlite core (Figure 3.8). Volcaniclastic Facies 1 is the most volumetrically significant of the volcaniclastic phases and was emplaced before Volcaniclastic Facies 2. Phases 3 and 4 which form the core of the kimberlite pipe are the most volumetrically significant phases of Volcaniclastic Facies 1. 40 Macrocrystic Figure 3.7: Schematic representation of the spatial relationship of Coherent Subfacies 1 and 2. A . Coherent Subfacies 1. This rock type occurs as dykes with sharp contacts with the host rock. B. Coherent Subfacies 2. This rock type occurs at the margins of Coherent Subfacies 1 where the coherent kimberlite intrudes fractures in the host rock forming a stockwork of kimberlite in slightly fractured rock. 41 Figure 3.8: Spatial distribution of the four phases of Volcaniclastic Facies 1. 42 3.4.1 Volcaniclastic Facies 1 Phase 1: Grey Tuffisitic Kimberlite Breccia Volcaniclastic Facies 1 - Phase 1 is the most diluted tufiisitic phase of the Renard 4 kimberlite, with country rock clasts composing between 45 and 85% by volume (Figure 3.9 a). Olivine macrocrysts are rare composing only 1 to 3% of the rock. Magmaclasts compose on average 2% of the rock but vary locally in abundance from less than 1% to greater than 5% of the total volume (Figure 3.10 a). Rare examples of mantle xenocrysts, which are most commonly kelyphite-rimmed pyrope garnets, compose less than 1% of the rock. Phase 1 units occur in the deepest sections of drill holes and at the extreme margins of the kimberlite pipe (Figure 3.8). These units become more dilute (i.e. the abundance of country rock xenoliths increases) the more distally they occur to the centre of the kimberlite. In many instances, there is no clear contact between Phase 1 and country rock breccia. Instead there is a gradual decline in the percentage of magmaclasts and a concurrent increase in the percentage of country rock xenoliths until the kimberlitic component of the rock is too low for it to be considered a kimberlite breccia. Fresh olivine macrocrysts are not present in this rock type. Macrocrysts are most commonly serpentinized. Locally magnetite is present along fractures in some macrocrysts (Figure 3.10 c). Macrocrysts in Phase 1 units are rarely larger than 2 mm. Macroscopically, they are dark grey-green and rounded and compose generally less than 1% of the total volume of the rock. Magmaclasts in this phase range in size from 1 mm to 15 cm and are commonly autolithic clasts of Coherent Subfacies 1 (Figure 3.10 e). These clasts commonly have sub-angular shapes with sharp margins. The groundmass of the magmaclasts is light-grey to chalky green and is dominated by serpentine. The olivine macrocryst population of the magmaclasts is dominated by grains showing replacement of secondary serpentine by carbonate. Clasts of other tufiisitic kimberlite phases are not noted in Phase 1 rocks. Pelletal lapilli are locally well developed in Phase 1 rocks (Figure 3.11 a). These magmaclasts have rounded forms with sharp, curviplanar margins and groundmass rich in spinel and serpentine. Where pelletal lapilli are most abundant lapilli are set in a groundmass of serpentine. Acicular diopside in the inter-lapilli matrix is present. Commonly, pelletal 43 R4--!J4_293.3m 2 c m j : \ ;2 c m R4-U4 145.6m -to c -37.2m 2 c m Figure 3.9: Volcaniclastic Facies of the Renard 4 kimberlite. A . Volcaniclastic Facies 1, Phase 1: Grey Tuffisitic Kimberlite. B. Volcaniclastic Facies 1, Phase 2: Green Tuffisitic Kimberlite. C. Volcaniclastic Facies 1, Phase 3: Brown Tuffisitic Kimberlite. D. Volcaniclastic Facies 1, Phase 4: Blue Tuffisitic Kimberlite. E . Volcaniclastic Facies 2: 'Accretionary' Magmaclastic Kimberlite. 44 Figure 3.10: Photomicrographs of Volcaniclastic Facies 1 Phase 1. A . Field of view containing all components of Phase 1. B. Sketch of A showing locations of crustal xenoliths (X), magmaclasts (MC) and an olivine macrocryst (OM). The margins of the magmaclasts are marked with dotted lines. Note that all of the magmaclasts have kernels of country rock. C. Magnetite along fractures in a strongly altered olivine macrocryst. D. Sketch of C showing locations of country rock xenoliths (X) and the olivine macrocryst (OM). E . Clast of Coherent Subfacies 1 containing olivine macrocrysts. F. Sketch of E showing location of country rock xenoliths (X), the magmaclast (MC) and olivine macrocrysts (OM). The margin of the magmaclast is marked by a dotted line. 4 5 Figure 3.11: Pelletal lapilli and incipient pelletal lapilli in Volcaniclastic Facies 1 Phase 1. A . Area of well developed pelletal texture. Pelletal lapilli have cores of country rock xenoliths and serpentinized olivine macrocrysts. Patches of serpentine (Serp) are present between lapilli. B. Sketch of A showing pelletal lapilli (PL) outlined with dotted lines, areas of serpentine (serp) and locations of country rock xenoliths (X). C. Incipient pelletal lapillus with a country rock kernel. Note the absence of a rim around some sections of the country rock kernel. D. Sketch of C showing the margin of the pelletal lapillus (dotted line) and locations of country rock xenoliths (X). E . Incipient pelletal texture. Serpentine (Serp) is present between the lapilli. F. Sketch of E showing the locations of the pelletal lapilli (PL) marked with dotted black lines, olivine macrocrysts (OM) and country rock xenoliths (X). 4 6 lapilli lie in a matrix of serpentine and spinel and are distinguished from the matrix by an increased abundance of spinel in the lapilli. Pelletal lapilli have kernels of serpentinized olivine macrocrysts or country rock fragments and also occur as rounded clasts with no nucleus. Poorly developed pelletal lapilli with large cores, most commonly of country rock xenoliths are much more abundant than the well formed examples described above. These poorly developed pelletal lapilli are commonly slightly irregular in shape or form only partial rims around the country rock kernels (Figure 3.11b and c). Country rock xenoliths are sub-angular to angular and range in size from less than 1 mm to greater than 15 cm (Figure 3.9 a). The majority of country rock xenoliths are between 5 mm and 4 cm in size. Xenoliths of gneiss are more abundant that granite in this facies. Monomineralic xenoliths (primarily of quartz and feldspar) are the most abundant xenoliths in the 0.5 to 2 mm size range but are less volumetrically significant than larger xenoliths (Figure 3.12 a and b). Country rock xenoliths are weakly to moderately altered. Some xenoliths of gneiss have pale bleached rims approximately 1 mm wide where they are in contact with kimberlitic groundmass (Figure 3.12 c). These bleached xenoliths are concentrated over discrete horizons and are not typical of the facies overall. Although there is a wide range in the abundance of country rock xenoliths in this tuffisitic phase, typically the xenoliths compose between 55 and 70% of the rock. Xenoliths less than 5 mm in diameter compose approximately 85% of the total number of xenoliths, but only approximately 40% by volume. Subangular xenoliths greater than 2 cm compose approximately 1% of the total number of xenoliths in any area, but more than 25% of the xenolithic material by volume. Gneissic xenoliths tend to be subrounded to rounded while single mineral fragments of feldspar or quartz or granitic xenoliths tend to be sub-angular to angular. On a meter to tens of meters scale, there are zones of relatively concentrated country rock xenoliths and zones with fewer and on average smaller country rock xenoliths. Short intervals (less than 20 cm) of tuffisitic kimberlite (as opposed to tuffisitic kimberlite breccia - tuffisitic kimberlite units contain no country rock xenoliths greater than 4 mm) are present in this facies. Small scale (centimetre to tens of centimetres) intervals of this facies have crustal xenolith populations composed of 90 to 100% angular fragments of granite (Figure 3.12 d). Within these zones, country rock xenoliths are locally concentrated and oriented 47 Figure 3.12: Country rock xenoliths in Volcaniclastic Facies 1 Phase 1. A . Photomicrograph showing abundance of country rock xenoliths in the less than 0.5 mm to 2 mm size range. One magmaclast (MC) is present in the field of view. B. Photomicrograph showing lack of alteration of country rock xenoliths. Note presence of fresh feldspars and quartz in the xenoliths. Three magmaclasts (MC) also present in the field of view. C. Mesoscopic image showing a bleached rim on a gneissic xenolith. D. Zone of fragmented country rock xenoliths. 48 parallel to the elongate axis of the fragmented xenoliths. A similar morphology and orientation of country rock xenoliths is noted by Clement (1982) in many of the southern African pipes. Clement (1982) notes that these features are oriented in an approximately vertical sense and occur over distances varying from a few centimetres to a few meters. Because these structures have only been observed in unoriented drill core in Renard 4 it is impossible to define a directionality to the parallel xenoliths. Phase 2: Green Tuffisitic Kimberlite Breccia Phase 2 differs from Phase 1 in that it contains fewer country rock xenoliths, more olivine macrocrysts and have distinctly green groundmass (Figure 3.9 b). In Phase 2, country rock xenoliths compose 35 to 50% of the rock, serpentinized olivine macrocrysts compose 1 to 5% and magmaclasts compose 1 to 5% of the rock. Serpentinized olivine macrocrysts in Phase 2 are always rounded and dark green-grey in colour. They range in size from 1 mm to 8 mm but are on average 2 to 3 mm and are commonly fractured. Macrocrysts compose on average, 2% of the rock by volume. Magmaclasts compose on average 2% of Phase 2 but are locally concentrated up to greater than 5% of the rock. Phase 2 units contain at least four distinct magmaclast populations all of which may occur within a small area (Figure 3.13 a). The four populations are: 1- pelletal lapilli, 2- clasts of volcaniclastic kimberlite, 3- clasts of massive, coherent kimberlite, and 4- clasts of another volcaniclastic kimberlite breccia with different groundmass composition to magmaclast population 2. The first magmaclast population is a population of pelletal lapilli. Pelletal lapilli compose overall less than 1% of Phase 2 but in some areas compose up to 3% of the rock (Figure 3.13 a and b). These clasts range in size from 2 mm to 1 cm and always consist of a large kernel with a fine (<0.5 mm) wide kimberlitic rim. Some of the pelletal lapilli have slightly thicker porphyritic kimberlitic mantles. Pelletal lapilli nucleated on olivine macrocrysts are rare while those nucleated on fragments of country rock are common. The majority of the pelletal lapilli in Phase 2 are associated spatially with another population of magmaclasts. Many are located within clasts of dark grey-brown volcaniclastic kimberlite. 49 Figure 3.13: Mesoscopic images of Volcaniclastic Facies 1 Phase 2. A . Area with examples of all four magmaclast populations. B. Sketch of A showing locations of the magmaclasts (dotted outlines), and country rock xenoliths. Pelletal lapilli (PL) are present only within the clast of grey-brown volcaniclastic kimberlite (MC 2). The smallest magmaclast in this field of view is a clast of coherent, macrocrystic kimberlite (MC 3). A clast of volcaniclastic kimberlite with bright green matrix (MC 4) is a representative of the fourth magmaclast population. C. Grey-brown volcaniclastic kimberlite magmaclast containing pelletal lapilli and with pelletal lapilli occurring immediately outside of the clast. D. Sketch of C. showing locations of pelletal lapilli (PL) and the margin of the large clast (dotted line). The area to the left of the line is the magmaclast. E . Hand sample showing hematite staining of country rock xenoliths. 50 The second population of magmaclasts is the population of dark grey-brown volcaniclastic kimberlite clasts which commonly contain pelletal lapilli or are spatially associated with them (Figure 3.13 b). The groundmass of these magmaclasts is rich in phlogopite, carbonate and spinel. The clasts contain up to 30% entirely serpentinized, highly fractured, olivine macrocrysts. These magmaclasts are the largest of all the magmaclast populations and are commonly greater than 2 cm in diameter. This magmaclast population composes approximately 60% of the total number of magmaclasts present in Phase 2. The third population of magmaclasts in Phase 2 are clasts of massive coherent, macrocrystic kimberlite. This magmaclast population has light green-grey groundmass rich in serpentine and they contain approximately 15% serpentinized olivine macrocrysts. The magmaclasts have sharp margins and sub-rounded to sub-angular forms suggesting that they may be autoliths entrained in the tuffisitic kimberlite unit after they were fully lithified. The fourth population of magmaclasts in Phase 2 are fragments of another tuffisitic kimberlite breccia unit. They contain approximately 20% country rock xenoliths and approximately 5% serpentinized olivine macrocrysts. These magmaclasts have light green groundmass dominated by serpentine. These magmaclasts are the least abundant volumetrically comprising less than 1% of Phase 2. The magmaclasts have sharp margins and subangular forms. Country rock xenoliths in Phase 2 on average compose 40% of the rock. Xenoliths of granite and gneiss occur in roughly equal proportions. In many samples, more than 50% of xenoliths of both lithologies are stained pink by hematite (Figure 3.13 e). The overwhelming majority of the xenoliths in Phase 2 are in the 0.5 to 2 mm size range; however, it is the less abundant larger xenoliths which account for the majority of the volume of xenoliths in this rock type. The xenolith population in the greater than 5 mm size range is dominated by rounded to sub-rounded clasts of granite or gneiss while the population less than 5 mm is dominated by sub-angular, single mineral grains of quartz and feldspar derived from broken country rock clasts. Intervals with no xenoliths greater than 2 mm in size are present in Phase 2. Observations of these intervals are limited to drill core where they are always less than 40 cm long down the core axis and are usually no more than 15 cm long down the core axis. These zones of tuffisitic kimberlite (as opposed to tuffisitic kimberlite breccia) occur in the middle 51 of Phase 2 intervals. Contacts between the tuffisitic kimberlite breccia and the tuffisitic kimberlite are gradational over approximately 10 cm with xenolith size and distribution grading from that described above for the average Phase 2 rock to less than 15% country rock fragments all less than 2 mm in size. Over the intervals of tuffisitic kimberlite, the groundmass remains the same colour and texture as in the surrounding tuffisitic kimberlite breccia. In thin section, the same groundmass assemblage noted in the Phase 2 tuffisitic kimberlite breccia dominated by a cryptocrystalline assemblage is observed. Serpentinized olivine macrocrysts are present in the intervals of tuffisitic kimberlite but are less abundant and on average smaller in size (1 to 2 mm) than in the adjacent tuffisitic kimberlite breccia units. Magmaclasts are not present in the tuffisitic kimberlite intervals. The green-grey matrix of Phase 2 contains minor serpentine but is dominated by a dark brown opaque cryptocrystalline assemblage. Phase 3: Brown Tuffisitic Kimberlite Breccia Phase 3 has the most 'magmatic' appearance of all the tuffisitic kimberlite breccia phases present in Renard 4 (Figure 3.9 c). The country rock xenoliths in this phase are more strongly altered and the abundance of olivine macrocrysts is greater than in any other tuffisitic kimberlite breccia phase. The matrix of Phase 3 is light grey-brown. Phase 3 is magmaclastic. Serpentinized olivine macrocrysts compose on average 10% of Phase 3 by volume but over some intervals, locally up to 10s of meters thick, macrocrysts compose up to 20% of the rock. Serpentinized olivine macrocrysts are dark green to dark grey and range in size from 1 mm to 1.5 cm but are generally 5 to 7 mm in diameter. The majority of macrocrysts are rounded but approximately 15% are elongate (Figure 3.14 a). Phase 3 contains two magmaclast populations, one of pelletal lapilli and the other of angular clasts of coherent, macrocrystic kimberlite. Together, the magmaclast populations account for less than 1% of the rock by volume. The pelletal lapilli, composing approximately 50% of the total magmaclast population, have kernels of either serpentinized olivine macrocrysts or country rock xenoliths (Figure 3.14 b). The size of the lapilli is dependent on the size of the nucleus but the rims are never more than 1 mm thick. The clasts of coherent, macrocrystic kimberlite have dark-grey groundmasses and contain approximately 5% serpentinized 52 Figure 3.14: Mesoscopic images and photomicrographs of Volcaniclastic Facies 1 Phase 3. A . Serpentinized olivine macrocrysts (OM). Note the elongate nature of some of the macrocrysts and the large average size of the grains. Here macrocrysts are concentrated around a strongly altered country rock xenolith (X). B. Pelletal lapillus (in red circle) with a country rock kernel. C. Strongly altered country rock xenoliths (black dotted outlines). D. Phlogopite (Phi) and carbonate (Carb) with minor spinel (Sp) and patches of clay dominate the groundmass of Phase 3. Macrocrysts are outlined with dotted black lines. 53 olivine macrocrysts. These magmaclasts also contain approximately 1% country rock xenoliths. This population of magmaclasts range in size from 2 to 15 mm. Commonly, the edges of these magmaclasts are altered so that they are more serpentine-rich than the centres of the clasts. Country rock xenoliths compose approximately 20% of Phase 3 by volume and range in size from 0.5 to 10 cm but are on average only 2 cm. Country rock fragments less than 2 mm in size compose approximately 50% of the total number of xenoliths, but account for less than 5% by volume of the total xenolithic material. Larger xenoliths (those in the 0.5 to >2 cm range) are more numerous in this phase than in other the other tuffisitic kimberlite breccia phases and are also more volumetrically significant than in other phases. The large xenoliths account for approximately 35% of the total number of xenoliths and approximately 90% of the volume of xenolithic material. Xenoliths of granite and gneiss occur in approximately equal proportions. Country rock xenoliths, especially those less than 5 mm, are strongly altered (Figure 3.14 c). Replacement of individual mineral grains within xenoliths by serpentine and chlorite is common (Figure 3.14 a). Granitic xenoliths tend to be on average slightly larger than gneissic xenoliths. Fragments of quartz and feldspar derived from broken granitic xenoliths are less abundant in this unit than in all the other T K B units. The grey-brown groundmass of Phase 3 is rich in phlogopite, carbonate and contains minor spinel. Patches of opaque cryptocrystalline material are also present (Figure 3.14 d). Phase 4: Blue Tuffisitic Kimberlite Breccia Phase 4 is easily distinguished from the other tuffisitic kimberlite breccia phases by its bright to light blue-grey matrix (Figure 3.9 d). It is further distinguished from other volcaniclastic facies by the abundance and degree of alteration of the country rock xenoliths present and by the abundance of serpentinized olivine macrocrysts. Phase 4 contains 35 to 50% strongly altered country rock xenoliths, 1 to 4% serpentinized olivine macrocrysts and approximately 1% magmaclasts. The degree of alteration of the country rock xenoliths is greater than in Phase 1 or Phase 2 but not as intense as in Phase 3 (Figure 3.15). Serpentinized olivine macrocrysts compose on average 2% of Phase 4 by volume. The macrocrysts are dark grey to dark green, soft and easily eroded. Macrocrysts range in 54 Figure 3.15: Alteration of country rock xenoliths in the 4 phases of Volcaniclastic Facies 1. A . Phase 1. Note the sharp margins and fresh appearance of the country rock xenoliths. B . Phase 2. Note the sharp margins of the country rock xenoliths and the alteration along grain margins (arrows) in the large gneiss xenolith at the upper edge of the photo. C. Phase 3. Note the blurred margins of the country rock xenoliths and the strong degree of alteration at the margins and between mineral grains in the xenoliths. Two examples of country rock xenoliths are marked with dotted black outlines for easier recognition. D. Phase 4. Note the alteration along grain boundaries (arrows) but the sharp edges of most country rock xenoliths. 55 size from 1 mm to 1.5 cm and are on average 5 mm (Figure 3.16 a and b). The abundance of macrocrysts is greater than in Phase 1 and Phase 2 but less than in Phase 3. The average size of the macrocrysts in Phase 4 is greater than in Phase 1 or Phase 2 but less than in Phase 3. Three magmaclast populations are present in Phase 4. These are: 1- clasts of Coherent Subfacies 1, 2- clasts of Phase 3, and 3- clasts of another tuffisitic kimberlite breccia phase not observed anywhere other than in these clasts. Clasts of Coherent Subfacies 1 range in size from 0.2 mm to 4 cm (Figure 3.16 c and d). The clasts contain approximately 10% serpentinized or carbonatized olivine macrocrysts in a carbonate-rich groundmass. The magmaclast margins are sharp and the clasts are subangular to subrounded. The second and third populations of magmaclasts in Phase 4 are differentiated from one another by their groundmass mineralogy, their macrocryst populations and the population of country rock xenoliths present in one. The first group of magmaclasts have brown-grey, phlogopite-rich matrix material and appear to be clasts of Phase 3 (Figure 3.17 a). The magmaclasts contain approximately 5% serpentinized olivine macrocrysts and approximately 10% strongly altered country rock xenoliths. These magmaclasts have sharp, curviplanar margins and rounded shapes and range in size from 1 to 15 cm. Proximal to contacts of Phase 3 and Phase 4, the size and abundance of these magmaclasts increases dramatically. The third population of magmaclasts have medium grey, carbonate-rich matrix material and contain fragments of altered country rock and very small grains of serpentinized olivine (Figure 3.17 b). These magmaclasts have sharp, curviplanar margins and rounded forms. They range in size from 2 mm to 2 cm and compose less than 1% of the rock by volume. The country rock xenolith population of Phase 4 is dominated by granitic xenoliths many of which have a bleached appearance with some phases replaced by a chalky, light green mineral or mineral assemblage (dominated by chlorite) (Figure 3.17 c). Fragments of quartz and feldspar derived from broken granitic clasts are also present. Although the alteration of individual mineral grains within the country rock xenoliths is strong, reactions rims are not noted on any xenoliths in this unit. Gneissic xenoliths compose approximately 10% of the total xenolith population. As in some intervals of Phase 2, there are intervals of 56 Figure 3.16: Mesoscopic images and photomicrographs of Volcaniclastic Facies 1 Phase 4. A . Mesoscopic image showing dark grey serpentinized olivine macrocrysts (OM). B. Photomicrograph showing serpentinized olivine macrocrysts (OM) in Phase 4. C. Photomicrograph showing clast of Coherent Subfacies 1 (dotted black outline). D. Mesoscopic image of a clast of Coherent Subfacies 1 (dotted black outline). 57 Figure 3.17: Mesoscopic images and photomicrographs of Volcaniclastic Facies 1 Phase 4. A . Mesoscopic image of a clast of Phase 3 (black dotted outline). Note the curviplanar margins of the clast. B. Example of the third variety of magmaclast in Phase 4. These magmaclasts have carbonate-rich groundmass and always contain fragments of altered country rock. C. Mesoscopic image showing bleached xenoliths and alteration of some phases in the xenoliths to chlorite and clay (green patches in the xenolith on the centre right of the image). D. Pink hematite staining of country rock xenoliths in Phase 4. E. Photomicrograph showing the abundance of country rock xenoliths in the 0.5 to 2 mm size range (all white, angular fragments in the photo are country rock xenoliths). F. Photomicrograph showing opaque cryptocrystalline groundmass of Phase 4. 58 Phase 4 over which the majority of the country rock xenoliths are stained pink by hematite (Figure 3.17 d). Country rock xenoliths in the 0.5 to 2 mm size range account for approximately 70% of the total number of xenoliths but it is the less numerous xenoliths in the 1 to 10 cm range which account for the greatest volume of xenolithic material (Figure 3.17 e). In all size ranges, xenoliths are dominantly subangular to subrounded. The bright blue groundmass of Phase 4 is dominated by an opaque cryptocrystalline assemblage. No unaltered groundmass phases remain (Figure 3.17 f). Contacts between Phase 3 and Phase 4 are the most frequently observed contacts between tuffisitic kimberlite breccia phases. This is due at least in part to the fact that these two phases are the most commonly encountered tuffisitic kimberlite breccia phases in Renard 4. The contacts are sharp in some instances, but more commonly consist of zones of up to 1 m where there is mixing of the two phases (Figure 3.18 a and b). Large rounded clasts of Phase 3 are included in Phase 4 over these zones. Commonly, the magmaclasts compose 50% or more of the rock over these intervals. The clasts of Phase 3 in these zones have fluidal, amoeboid or rounded forms. Broken macrocrysts, magmaclasts or country rock xenoliths are never observed at the 'contact' between Phases 3 and 4. Rather, the blue groundmass of Phase 4 appears to wrap itself around individual components of Phase 3 suggesting that the 'contacts' are actually alteration fronts (Figure 3.18 c). The 'clasts' of Phase 3 present in Phase 4 are then simply areas unaffected by the alteration. 3.4.2 Volcaniclastic Facies 2: 'Accretionary' magmaclastic kimberlite Volcaniclastic Facies 2 is a kimberlitic unit which is superficially more similar to massive coherent, macrocrystic kimberlite in appearance than it is to Volcaniclastic Facies 1 (Figure 3.9 e). This facies contains few to no country rock xenoliths and is rich in serpentinized olivine macrocrysts similar to the coherent facies. However, the rock is volcaniclastic, being composed primarily of olivine macrocrysts surrounded by rims of fine-grained kimberlitic material similar in appearance to the groundmass of the rock. The 59 Figure 3.18: Contacts of Phases 3 and 4 of Volcaniclastic Facies 1. A . Contact of Phase 3 (left) and Phase 4 (right). Note that the contact is not sharp and does not cut across clasts or macrocrysts but rather wraps around them. B. Contact zone of Phases 3 and 4. Note that the two phases are mixed together giving the interval a patchy appearance. C. Close-up view of the contact shown in A . Note the blue (Phase 4) groundmass wrapping around macrocrysts and forming embayments in the brown (Phase 3). 60 magmaclasts are distinguished from the groundmass by slight differences in colour which reflect slightly different groundmass mineralogy. Serpentinized olivine macrocrysts compose 10 to 35% of Volcaniclastic Facies 2. Macrocrysts range in size from 0.5 mm to 2 cm but are on average 4-5 mm. Macrocrysts greater than 7 mm in size are rare outside of magmaclasts. Fresh olivine macrocrysts or fresh cores of macrocrysts are never present. Because the majority of the macrocrysts in this facies form cores of magmaclasts, it is difficult to consider the population of macrocrysts separately from the population of magmaclasts (Figure 3.19 a). None the less, the two populations can be distinguished. Magmaclasts compose between 15 and 50% of this rock type but most commonly compose >40% of the rock by volume. In many cases, there are so many magmaclasts, the margin of any given magmaclast is in contact with the margin of the neighbours. Magmaclasts range in size from 3 mm to 3 cm but they are on average 5 mm. In rare cases, large magmaclasts have more than one distinct rim (Figure 3.19 c). In large magmaclasts, olivine phenocrysts are concentrically aligned around the clast nucleus. The groundmass of Volcaniclastic Facies 2 rocks is dominated by serpentine and carbonate with accessory spinel present. Magmaclast rims are slightly richer in both carbonate and spinel than the groundmass. 3.5 Transitional Rocks of the Renard 4 Kimberlite Rocks with characteristics transitional between coherent and volcaniclastic rock types are present in the Renard 4 kimberlite. Macroscopically these rocks have a coherent appearance with dark grey, fine-grained matrix very similar in appearance to the groundmass of Facies 1 samples. However, microscopically these rocks are characterized by clots of volcaniclastic material. 3.5.1 Magmaclastic Kimberlite Breccia with Characteristics Transitional to Coherent Kimberlite Transitional kimberlite is characterized by a dark grey groundmass with a macroscopically coherent appearance but displaying magmaclastic textures in thin section 61 Figure 3.19: Images of Volcaniclastic Facies 2: 'accretionary' magmaclastic kimberlite. A . Hand sample. Note the light-grey rims surrounding the dark grey serpentinized olivine macrocrysts. B. Sketch of A showing outlines of the magmaclasts. C. Multiple rims on an accretionary clast (far left hand side of the photograph). Note the concentric alignment of the dark grey phenocrysts in the outer rim. Photo C is of a sample from R65. It is shown here because the texture is exceptionally well developed in this sample. 62 (Figure 3.20 a). This rock type contains 5 to 10% olivine macrocrysts, less than 1% rounded magmaclasts and between 15 and 25% country rock xenoliths. The groundmass is composed of approximately 40% serpentine, 40% carbonate, 20% spinel and 5% phlogopite (Figure 3.20 b and c). Around many country rock xenoliths, carbonate is more abundant and occurs with a mat of very fine, commonly acicular clinopyroxene (Figure 3.20 d). Olivine macrocrysts in Transitional kimberlite are commonly fresh or partially serpentinized although examples of entirely serpentinized macrocrysts are present (Figure 3.20 d and e). Macrocrysts range in size from less than 1 mm to approximately 1 cm and are anhedral and rounded. Approximately 90% of the total macrocrysts population contain relict unaltered olivine. The most strongly serpentinized olivine macrocrysts are concentrated around country rock xenoliths. Magmaclasts have sharp curviplanar margins (Figure 3.21 a and b). The groundmass of the magmaclasts is dominated by phlogopite but contains approximately 10% carbonate and 10% spinel. Magmaclasts are always clasts of massive coherent, macrocrystic kimberlite (Coherent Subfacies 1) and never of tuffisitic kimberlite breccia units. Magmaclasts range in size from 0.25 to 1 mm and are very rarely observed in hand sample due to a combination of their small size and the similarity of the colour of the groundmass of the magmaclasts and the matrix of the host. Country rock xenoliths are most commonly sub-angular and range in size from approximately 0.5 mm to 10 cm but are on average 0.5 to 3 cm in diameter. Xenoliths in the 0.5 to 2 mm size range account for approximately 50% of the total country rock xenoliths but only approximately 5% of the total volume of xenoliths. Gneissic and granitic xenoliths appear in approximately equal proportions but the degree of alteration makes it difficult to determine the protolith of many xenoliths (Figure 3.21 c). Country rock xenoliths are more strongly altered than in any of the phases of Volcaniclastic Facies 1 and equally altered to the rare xenoliths present in Coherent Subfacies 1. Country rock xenoliths are commonly surrounded by areas of lighter grey matrix. These are not magmaclasts but appear to reflect a reaction of the xenoliths with the kimberlite groundmass. 63 Figure 3.20: Images of Transitional Kimberlite. A. Transitional Kimberlite in hand sample. Note the strong alteration of country rock xenoliths and the dark grey, coherent appearance of the groundmass. B . Photomicrograph of Transitional Kimberlite showing groundmass dominated by phlogopite and carbonate with minor spinel (Sp). C. Same field of view as in C. but under crossed polars. The mat of beige fine material that is the groundmass is composed primarily of carbonate and phlogopite. D . Photomicrograph showing alteration assemblage surrounding a country rock xenolith (X) The assemblage is of carbonate (Carb) and clinopyroxene (CPX). Note the fresh olivine macrocrysts (OM). Image is taken through crossed polars. E. Fresh olivine macrocrysts (OM) and strongly altered country rock xenolith (X) in plain light. 64 Figure 3.21: Photomicrographs of Transitional Kimberlite. A . Magmaclast (MC) containing a large, unserpentinized olivine macrocryst (OM). The magmaclast groundmass is the light brown material (phlogopite + carbonate + spinel). B. Magmaclast (MC) of coherent kimberlite (black dotted outline). Country rock xenoliths are marked with black Xs. C. Extreme alteration of a country rock xenolith (X). Alteration assemblage of this xenolith includes pectolite. 65 3.6 Country Rock Breccia The final rock unit of the Renard 4 kimberlite is country rock breccia. These rocks have no kimberlitic component but were formed during the emplacement of the kimberlite (Barnett, 2004). Country rock breccias lie at the periphery of the kimberlite. Although this is where they are preserved, models for kimberlite emplacement suggest that as the kimberlite magma intruded the country rock prior to eruption, country rock breccia formed around the intruding magma. These country rock breccias may then be destroyed as the kimberlite erupts. The Renard 4 kimberlite is not entirely surrounded by an envelope of country rock breccia. The country rock breccia units occur as pockets with varying lateral and vertical extent. Country rock breccias in the Renard 4 kimberlite are not identical in character. They vary in the nature of the country rock clasts, in the abundance of clasts, and in the amount of displacement of the clasts (Figure 3.22 a and b). Clasts vary in abundance from 45 to 99%. The matrix of the breccias consists of country rock fragments and rock flour composed of fragments of quartz, plagioclase, K-feldspar, orthopyroxene and biotite. Feldspar grains in the granite and gneiss country rock are commonly replaced by serpentine reflecting the close association of the country rock breccia with the kimberlite magma and its volatile phases. Void spaces in the matrix material are common in samples with a relatively large ratio of matrix to clasts. The voids are commonly lined with euhedral crystals of calcite and pyrite. Country rock breccias adjacent to the kimberlite pipe show the greatest degree of alteration and rotation of the breccia clasts. These country rock breccias also have the greatest amount of interclast matrix present. As distance from the core of the kimberlite increases, country rock breccia units show less displacement of clasts and less rock flour matrix is present. This change in breccia morphology is gradational. Most distally, country rocks are fractured but there is no displacement and no interclast matrix. Clasts in country rock breccia are dominantly larger than 2 cm and angular. Approximately 2% of all the clasts are less than 2 cm and of these, approximately 50% are in the 5 mm to 2 cm range and 50% are less than 5 mm. Clasts less than 2 cm are sub-angular, angular or rarely sub-rounded. 66 Figure 3.22: Images of country rock breccia. A. Country rock breccia showing little displacement or rotation of country rock clasts and very little rock flour matrix. B. Country rock breccia with rotated and displaced clasts in a rock flour matrix. C. Photomicrograph of country rock breccia showing rock flour matrix. D. Country rock breccia with voids. Many voids like these are filled with euhedral crystals of calcite or pyrite. 67 3.7 Overview and Distribution of the Rock Types 3.7.1 Differentiating between the phases of Volcaniclastic Facies 1 Each of the rock types in Renard 4 is visually distinct and varies in the abundance of macrocrysts, magmaclasts and country rock xenoliths (Figure 3.23). Each of the four phases of Volcaniclastic Facies 1 are visually distinct, but when compared component by component, some are strikingly similar. Table 3.6 summarizes the abundance of each component of each rock type. Phases 2 and 4 The similarity of Phase 2 and Phase 4 in macrocryst content, xenolith content and groundmass mineralogy suggest that these two phases may in fact be the same (Figure 3.23). The two populations have been considered separately due to the presence of different magmaclast populations in each. The opaque cryptocrystalline groundmass assemblage of Phase 2 is very similar to that of Phase 4. Possibly, phases 2 and 4 are the result of alteration of two different phases of tuffisitic kimberlite breccia by the same fluid. Phases 3 and 4 Phases 3 and 4 are distinguished by the abundance of macrocrysts present, the abundance of country rock xenoliths in each, and by the colour and composition of their groundmass (Figures 3.24 and 3.25). It is suggested that the concentration of xenoliths in Phase 4 relative to Phase 3 is a reflection of the position of the phases relative to the centre of the pipe. The differences in alteration of the groundmass and the country rock xenoliths are explained by two distinct alteration events. The former and the latter are discussed at length in Chapter 4. 3.6.2 Spatial distribution of the Renard 4 rock types The phases of Volcaniclastic Facies 1 compose the majority of the Renard 4 kimberlite. Phase 1 occurs at the margins of the kimberlite pipe with Phases 3 and 4 composing the bulk of the central portion of the pipe (Figure 3.26). Phase 2 was observed only on the southern side of the kimberlite pipe. Coherent Subfacies 1 occurs primarily dykes 68 Groundmass Country Rock Xenoliths Olivine Macrocrysts Olivine Phenocrysts Magmaclasts E. Transitional Kimberlite F. Coherent Figure 3.23: Comparison of the components of the Renard 4 rock types. Proportions of groundmass, country rock xenoliths, olivine macrocrysts, olivine phenocrysts and magmaclasts in the four phases of Volcaniclastic Facies 1, in Transitional kimberlite, and in Coherent Subfacies 1 are denoted by different coloured fields in the pie charts. A . Volcaniclastic Facies 1 Phase 1. B . Volcaniclastic Facies 1 Phase 2. C. Volcaniclastic Facies 1 Phase 3. D . Volcaniclastic Facies 1 Phase 4. E. Transitional Kimberlite. F. Coherent Subfacies 1. The colour of the groundmass colour of each phase of Volcaniclastic Facies 1 is given under each pie. 69 Table 3.6: Summary of the components of each Renard 4 rock type. The dominant groundmass minerals are abbreviated as follows: carbonate (Carb), serpentine (Serp), phlogopite (Phi) and cryptocrystalline material (Cryp). Rock Type Vol . % Olivine Macrocrysts Vo l . % Olivine Phenocrysts Vo l . % Country Rock Xenoliths Vol . % Magmaclasts Dominant Groundmass Mineral(s) Groundmass Co lour Coherent: Massive 25 5-15 2 0 Carb, Serp, or Phi Dark grey Coherent: Breccia <1 <l-2 90 0 Carb, Serp, or Phi Dark grey Volcaniclastic Facies 1: Phase 1 <1 1-5 56 2 Serp Grey Volcaniclastic Facies 1: Phase 2 2 0 42 2 Cryp Green Volcaniclastic Facies 1: Phase 3 10 1-5 22 <1 Carb Brown Volcaniclastic Facies 1: Phase 4 2 0 52 1 Cryp Blue Volcaniclastic Facies 2 25 1-10 0 45 Serp Dark grey Transitional 7 15 18 <1 Serp Mottled dark grey and medium grey Country Rock Breccia 0 0 98 0 Rock Flour Grey 71 Figure 3.25: Photomicrographic comparison of Volcaniclastic Facies 1 Phases 3 and 4. These images illustrate the differences in the alteration of country rock xenoliths, macrocrysts and groundmass in the two phases. A.Strongly altered country rock xenoliths (dotted black outline) in Phase 3. B. Relatively fresh country rock xenoliths (X) in Phase 4. One macrocryst (OM) and a magmaclast (MC) are also present in the field of view. C. Phlogopite-rich groundmass with minor spinel (Sp) in Phase 3. Serpentinized olivine macrocrysts are marked by dotted black outlines. D. Opaque cryptocrystalline groundmass in Phase 4. Country rock xenoliths (X) and macrocrysts (OM) are also marked. 72 Figure 3.26: Schematic model of the Renard 4 kimberlite. This figure illustrates the locations of each rock type within the kimberlite pipe. 73 which intrude the phases of Volcaniclastic Facies 1 (Figure 3.26). Clasts of massive coherent kimberlite present in all of the tuffisitic kimberlite phases indicate that some Coherent Subfacies 1 dykes also predate the formation of the tuffisitic kimberlite breccias. These early dykes would have been destroyed as a consequence of the kimberlite eruption and diatreme formation. Coherent Subfacies 2 occurs at the margins of Coherent Subfacies 1 dykes (Figure 3.26). Volcaniclastic Facies 2 has geometry reminiscent of Coherent Subfacies 1 and also intrudes the phases of Volcaniclastic Facies 1 (Figure 3.26). Country rock breccias lie at the periphery of the kimberlite pipe (Figure 3.26). Implications of each of the rock types present in Renard 4 for the emplacement of the kimberlite and the contact relationships of the rock types are discussed in Chapter 4. 74 CHAPTER 4: IMPLICATIONS FOR KIMBERLITE EMPLACEMENT 4.0 Overview This chapter is prepared as a manuscript to be submitted for publication and as such contains some background material and data presented in the earlier chapters of this thesis. 4.1 Introduction The Renard 4 kimberlite is one in a cluster of nine kimberlites on the Foxtrot property located in northern Quebec approximately 250 km north east of Chibougamau (Figure 4.1). The Renard 4 kimberlite has an ovoid surface expression with an approximate surface area of 16,160 m . Evidence from rare sedimentary country rock xenoliths and the rock types and their textures in the Renard 4 kimberlite suggest that the current surface of the kimberlite represents a level no less than 1 km below the paleosurface (Birkett, March 1, 2007, personal communication). The kimberlite is internally complex and is filled with four major rock types two of which are further divided into facies and phases (Table 4.1). Volcaniclastic facies are more volumetrically significant than coherent facies in the Renard 4 kimberlite. The volcaniclastic facies compose the majority of the infill of the kimberlite pipe with coherent facies occurring as late-stage dykes and sheets intruding them. However, the ubiquitous presence of clasts of massive, coherent kimberlite in the phases of the volcaniclastic tuffisitic kimberlite breccia facies (Volcaniclastic Facies 1) indicates that dykes of coherent, macrocrystic kimberlite were emplaced prior to the volcaniclastic facies but destroyed by the kimberlite eruption. A unit of transitional kimberlite which shares characteristics with both coherent and volcaniclastic rock types is also present. Transitional units have been described in deep portions of Class 1 kimberlite pipes lying between the root and the lower diatreme of the kimberlite (Hetman, 2004; Skinner and Marsh, 2004; Hetman, 2006; Skinner and Marsh 2006a and b) This chapter provides brief descriptions of each of the Renard 4 lithofacies, describes their spatial relationships and provides a model for the emplacement of a single kimberlite pipe within the Renard kimberlite field. The bulk of the data used herein was obtained from 75 QUEBEC f v ••—<.« • Renard Kimberlites • Lac Beaver > •» \ U (,••'"'*• / ' ' . i f v ~ * W / 4 • Chlbougarriau , 689000 mE ^ 6895' UTMZone: 18 NAD 27 Figure 4.1: Location of the Renard kimberlite cluster and the Renard 4 kimberlite. The inset shows the location of the kimberlite cluster in the province of Quebec. Kimberlite outlines are based on geophysics and drilling. 76 detailed observation of kimberlite drill core (Figure 4.2) with some additional constraint gained from mapping of a small surface exposure of the kimberlite (see Chapter 3). Volume percentages of each component of each rock type are derived from point counting of slab and thin sections of each rock type. 4.2 Renard 4 Volcanic Facies The volcaniclastic facies are described first as these are volumetrically the most significant of the Renard 4 rock types and were the first of the units to be emplaced. The volcaniclastic facies are described from the periphery of the kimberlite body to the centre. The coherent kimberlite units preserved in the Renard 4 kimberlite cross-cut Volcaniclastic Facies 1 and are described following the descriptions of the volcaniclastic facies. The transitional facies has characteristics in common with both volcaniclastic and coherent facies is described after these units. Country rock breccias are described last as these rocks do not have a kimberlitic component to their clast populations or their matrix. Table 4.1: Rock units, facies and phases of the Renard 4 kimberlite. Rock Unit Facies Phase Volcaniclastic Facies 1: Tuffisitic Kimberlite Breccia Facies 2: 'Accretionary' Magmaclastic Kimberlite Phase 1: Grey tuffisitic kimberlite breccia Phase 2: Green tuffisitic kimberlite breccia Phase 3: Brown tuffisitic kimberlite breccia Phase 4: Blue tuffisitic kimberlite breccia Coherent Subfacies 1: Massive coherent, Macrocrystic Kimberlite Subfacies 2: Coherent, Macrocrystic Kimberlite Breccia Transitional Transitional Kimberlite Breccia Country Rock Country Rock Breccia Breccia 77 Surface trace of kimberlite body 0 50 100 metres Figure 4.2: Map showing the surface outline Renard 4 and drill collar locations. Drill collars which appear in this figure are those from which data was used in this paper. The surface outline is based in part on geophysics. • N 78 4.2.1 Volcaniclastic Facies Two facies compose the volcaniclastic rocks of the Renard 4 kimberlite. These are: Volcaniclastic Facies 1 which is tuffisitic kimberlite breccia and Volcaniclastic Facies 2 which is accretionary magmaclastic kimberlite. Volcaniclastic Facies 1 is further divided into four distinct phases. These phases are distinguished primarily by groundmass colour and composition as well as the abundance of olivine macrocrysts, country rock xenoliths and magmaclast populations (Figure 4.3). Volcaniclastic Facies 1: Tuffisitic Kimberlite Breccia Phase 1: Grey Tuffisitic Kimberlite Breccia Phase 1 is characterized by light grey, serpentine-rich groundmass. Phase 1 is composed of 1-2% serpentinized olivine macrocrysts, 45-85% weakly altered, sub-angular country rock xenoliths and 1-5% magmaclasts (Figure 4.3 a). Pelletal lapilli are locally well developed. Country rock xenoliths range in size from less than 1 mm to greater than 10 cm. Xenoliths less than 1 mm are numerous but less significant volumetrically than those in the 2 mm to 2 cm size range. The dominant magmaclast population in Volcaniclastic Facies 1 is a population of sub-angular to sub-rounded clasts of massive coherent, macrocrystic kimberlite (Coherent Subfacies 1). Phase 2: Green tuffisitic kimberlite breccia Phase 2 is characterized by a grey-green groundmass dominated by an opaque cryptocrystalline assemblage. Moderately altered, sub-angular country rock xenoliths compose 35-50% of the rock (Figure 4.3 b). Serpentinized olivine macrocrysts compose 1-5% of the rock and rounded magmaclasts compose 1-5% of the rock. Country rock xenoliths range in size from less than 1 mm to greater than 10 cm. Xenoliths under 1 mm are extremely abundant but are volumetrically less significant than xenoliths in the >lcm size range. Four distinct magmaclast populations are present in Phase 2. These include: pelletal lapilli, a population of massive coherent, macrocrystic kimberlite, and two distinct populations of clasts of tuffisitic kimberlite breccia with different groundmass compositions and xenolith abundances. 79 Phase 3: Brown tuffisitic kimberlite breccia Phase 3 is characterized by light grey-brown groundmass dominated by carbonate and phlogopite with subordinate spinel (Figure 4.3 c). Patches of opaque cryptocrystalline groundmass are present. Serpentinized olivine macrocrysts compose 5-10% of the rock. Macrocrysts are on average larger in size than those in any other tuffisitic kimberlite breccia unit with macrocrysts in the 0.5 to 1 cm range composing approximately 45% of the total macrocryst population. Strongly altered country rock xenoliths compose 20-30% of the rock. Country rock xenoliths less than 1 mm are rarely present. Zones of light blue-grey cryptocrystalline mineral assemblage surround large country rock xenoliths. Two populations of magmaclasts are present. These compose 2-4% of the rock. The first magmaclast population is of pelletal lapilli and the second is of sub-angular to sub-rounded clasts of massive coherent, macrocrystic kimberlite with groundmass mineralogy dominated by phlogopite. Phase 4: Blue tuffisitic kimberlite breccia Phase 4 is characterized by light blue-grey groundmass with all mineral phases replaced by an opaque cryptocrystalline assemblage. Serpentinized olivine macrocrysts compose 2-7% of the rock. Macrocrysts are more abundant and on average larger in Phase 4 than in Phase 1 or Phase 2 but smaller and less abundant than in Phase 3 (Figure 4.3 d). Moderately to strongly altered, subangular to subrounded country rock xenoliths compose 40-50%o of the rock. Magmaclasts compose <l-5% of the rock. Three distinct magmaclast populations are present. The most abundant magmaclasts are sub-rounded clasts of tuffisitic kimberlite breccia with brown grey groundmass. These appear to be clasts of Phase 3. This magmaclast population is most abundant within tens of centimetres of the contacts of Phase 3 and Phase 4. The second magmaclast population is one of clasts of massive coherent, macrocrystic kimberlite. The third magmaclast population is of a medium-grey, carbonate-rich kimberlite breccia. These clasts have sharp margins and rounded forms. Volcaniclastic Facies 2: 'Accretionary' magmaclastic kimberlite Volcaniclastic Facies 2 is initially more similar in appearance to Coherent Subfacies 1 than to the volcaniclastic facies. Volcaniclastic Facies 2 intrudes the tuffisitic kimberlite 81 breccia phases of Volcaniclastic Facies 1. Volcaniclastic Facies 2 is characterized by extremely abundant serpentinized olivine macrocrysts (up to 55%), the majority of which form the cores of 'accretionary' magmaclasts. The rims of the magmaclasts commonly contain olivine phenocrysts concentrically arranged around the core. Magmaclasts compose on average, more than 70% of the rock by volume. The groundmass of Volcaniclastic Facies 2 is dominated by serpentine with spinel occurring as a minor, but ubiquitous phase. Xenoliths of country rock are absent in these rocks. 4.2.2 Coherent Kimberlite There are two subfacies of coherent kimberlite in the Renard 4 kimberlite: massive coherent, macrocrystic kimberlite and coherent, macrocrystic kimberlite breccia (Figure 4.4). The breccia unit is considered coherent rather than volcaniclastic because country rock xenoliths are cemented by a coherent, macrocrystic kimberlite matrix showing no signs of fragmentation. Coherent Subfacies 1: Massive coherent kimberlite Coherent Subfacies 1 is composed of 5-30% serpentinized olivine macrocrysts, 5-15% olivine phenocrysts and less than 10% country rock xenoliths in a fine-grained, dark grey coherent groundmass (Figure 4.4 a and c). The groundmass mineralogy of Coherent Subfacies 1 is dominated by any of carbonate, phlogopite or serpentine with minor spinel. Monticellite and perovskite are commonly present but are not ubiquitous to Coherent Subfacies 1. Carbonate or serpentine segregations are commonly present in Coherent Subfacies 1. Coherent Subfacies 2: Coherent kimberlite breccia Coherent Subfacies 2 is composed of 85-99% angular or sub-angular country rock clasts in a matrix of unffagmented kimberlite (Figure 4.4 b and c). The matrix material is dark-grey and rich in carbonate and contains small serpentinized olivine macrocrysts. Although it has a volcaniclastic texture, the matrix of this unit is coherent, macrocrystic kimberlite. Coherent Subfacies 2 is likened to a kimberlite stockwork where coherent kimberlite has intruded pre-developed fractures in country rock (Figure 4.4 b). 82 Coherent Subfacies 1 Coherent Subfacies 2 C Figure 4.4: Coherent Subfacies of the Renard 4 kimberlite. A . Coherent Subfacies 1. Coherent Subfacies 1 occurs as dykes that intrude the country rock surrounding the kimberlite and the kimberlite itself. The rock has dark grey groundmass and contains 10 to 40% green or grey serpentinized olivine macrocrysts. B. Coherent Subfacies 2. Coherent Subfacies 2 occurs where coherent kimberlite (M) intrudes fractures in the country rock (CR) forming a kimberlite stockwork. C. Pie charts showing the abundances of country rock xenoliths, olivine macrocrysts, olivine phenocrysts and groundmass in the coherent subfacies. 83 4.2.3 Transitional Kimberlite Rocks with characteristics transitional between coherent and volcaniclastic rock types are present. These rocks have a macroscopically coherent appearance with dark grey, fine-grained matrix with a slightly mottled appearance but otherwise similar to coherent samples. However, microscopically, these rocks have a patchy groundmass with some areas having a coherent appearance and others a volcaniclastic appearance imposed by the presence of small magmaclasts and groundmass rich in opaque cryptocrystalline material. Transitional Kimberlite Breccia Transitional kimberlite is characterized by a mottled light and dark grey groundmass rich in carbonate, serpentine and spinel with minor phlogopite (Figure 4.5 a). The rock is composed of 5-10% olivine macrocrysts, 15-25% country rock xenoliths and less than 1% magmaclasts. Olivine macrocrysts are commonly fresh or have fresh cores and serpentinized rims. Country rock xenoliths are very strongly altered and are most commonly greater than 1 cm in size. The magmaclasts in Transitional Kimberlite units have sharp margins and rounded shapes. The magmaclasts are always clasts of Coherent Subfacies 1 with groundmass material dominated by phlogopite with minor carbonate and spinel present. 4.2.4 Non-Kimberlitic Fragmental Rocks Country rock breccia composed primarily of angular to sub-angular, monolithic clasts of gneissic country rock in a comminuted country rock flour matrix is common at the periphery of the Renard 4 kimberlite (Figure 4.5 b). Despite the absence of a kimberlitic component to either the clast population or the matrix, these rocks are a part of the kimberlite as they were formed as a direct result of the intrusion of the kimberlite magma and the subsequent kimberlite eruption. The matrix material composes between 1 and 10% of the total volume of the rock. Country rock clasts vary in size from less than 0.5 cm to greater than 1 m. 84 Groundmass Olivine Macrocrysts Olivine Phenocrysts Rock Flour Country Rock Xenoliths Magmaclasts Figure 4.5: Transitional Kimberlite and Country Rock Breccia. A . Transitional Kimberlite. On the left is a photograph of a hand sample of Transitional Kimberlite. On the right is a pie chart showing the abundances of each component of the rock. B. Country Rock Breccia. On the left is a photograph of a hand sample of Country Rock Breccia. On the left is a pie chart showing the composition of Country Rock Breccia. 85 4.3 Spatial and Temporal Relationships of the Renard 4 Rock Types Spatial and temporal relationships and the observed contacts of the Renard 4 rock types are discussed below. Contacts of coherent and volcaniclastic units, contacts of the two coherent subfacies, and contacts of Volcaniclastic Facies 1 with country rock breccia are commonly observed in Renard 4. However, contacts of the four phases of tuffisitic kimberlite breccia are rarely observed. This complicates the temporal and spatial interpretations for these phases, and some relationships are inferred. Where possible, the relationships of the rocks are discussed in the same order as they are believed to have been emplaced. 4.3.1 Volcaniclastic Facies 1 The geometry of the phases of Volcaniclastic Facies 1 indicates that although the tuffisitic breccias are distinct from each other, they are all phases of the same volcaniclastic facies. Examples of contacts between the units are rarely observed. Most commonly, phases of Volcaniclastic Facies 1 are separated by Coherent Subfacies 1 dykes. The massive coherent dykes were emplaced late in the formation of the kimberlite and intrude Volcaniclastic Facies 1. The sharp but irregular contacts of the massive coherent dykes with the tuffisitic breccias suggest that they did so by exploiting existing weaknesses in the breccia. The tuffisitic kimberlite breccias have many weaknesses imposed by the presence of abundant and irregularly shaped country rock xenoliths. However, the frequency with which dykes have intruded along the margins of the different phases indicates that these were particularly weak zones in the kimberlite diatreme. Phase 1 Phase 1 is the most peripheral of the phases of Volcaniclastic Facies 1 (Figure 4.6). This phase has entrained a greater volume of country rock xenoliths than any of the other phases of Volcaniclastic Facies 1 (Figure 4.3 a). This is likely the result of the proximity of the phase to the walls of the pipe. The formation of a diatreme is not a static process. Rather, during an eruption, the diatreme is constantly being expanded downward and outward. At the margins of the diatreme, fragmented country rock is being entrained by the magma or fluid in the diatreme. Hence, the phase that is located most proximal to the pipe margins entrains the greatest volume of country rock. 86 Coherent Subfacies 1 Coherent Subfacies 2 Volcaniclastic Facies 2 Volcaniclastic Facies 1 k7~oj Phase 4 Volcaniclastic Facies 1 . 1 Phase 3 Figure 4.6: Schematic representation of the Renard 4 kimberlite. A l l rock types and their spatial distribution are shown. 87 Phase 1 grades into country rock breccia with increased distance from the centre of the kimberlite. This gradational contact indicates that as distance from the centre of the diatreme increases, the amount of broken country rock relative to kimberlite magma becomes so great that the kimberlite component can no longer be detected. Contacts of Phase 1 with other phases of Volcaniclastic Facies 1 are not observed. However, contacts with Coherent Subfacies 1 units are commonly observed. These contacts are always sharp and irregular suggesting that the massive coherent dykes intruded along planes of weakness in the breccia unit imposed by the presence of abundant country rock xenoliths. Phase 1 and other phases of Volcaniclastic Facies 1 are commonly separated by massive coherent dykes. Again, this suggests that the dykes intruded exploiting planes of weakness in the kimberlite. Phase 2 Phase 2 is only observed on the southern side of Renard 4 (Figure 4.2). Data from other drill holes indicate that Phase 1 occurs farther to the south (closer to the kimberlite margin), and Phases 3 and 4 occur to the north (closer to the kimberlite centre), of Phase 2. The only contacts of Phase 2 with other rock types are sharp, irregular contacts with massive coherent dykes. Phase 3 Phase 3 occurs in the central portion of Renard 4 but peripherally to Phase 4 (Figure 4.6). Contacts between Phase 3 and Phase 4 are commonly observed. No broken grains or chill margins are ever observed at these 'contacts'. Rather, they are undulating and irregular and appear to be alteration fronts rather than true contacts. Contacts with massive coherent dykes are commonly observed. These contacts are sharp and irregular as in other phases of Volcaniclastic Facies 1. Contacts of Phase 3 with Transitional Kimberlite units are also observed. These are also sharp. Phase 4 Phase 4 occurs in the most central portion of Renard 4 and is the most volumetrically abundant of the four phases (Figure 4.6). 'Contacts' of Phase 3 and Phase 4 are commonly 88 observed and are described above. Contacts of Phase 4 with Transitional kimberlite and with massive coherent kimberlite dykes are also commonly observed. Contacts with both of these rock types are sharp. 4.3.2 Volcaniclastic Facies 2 Volcaniclastic Facies 2 units are volumetrically rare in the Renard 4 kimberlite. These units have geometry more similar to massive coherent kimberlite dykes than to Volcaniclastic Facies 1 (Figure 4.6). This facies was emplaced subsequent to Volcaniclastic Facies 1. Contacts between Volcaniclastic Facies 2 and Phases 1, 3 and 4 of Volcaniclastic Facies 1 are observed. Contacts are always sharp and are usually irregular. 4.3.3 Coherent Subfacies 1 Coherent Subfacies 1 occurs as steeply dipping dykes with sharp parallel margins where they intrude the country rock peripheral to Renard 4 or as steeply dipping dykes with irregular sharp margins where they intrude the phases of Volcaniclastic Facies 1 or the country rock breccia at the periphery of the kimberlite pipe (Figure 4.6). Coherent Subfacies 1 also occurs as large (1-5 m in diameter) pods or lenses with irregular margins and as small (0.2 mm to 20 cm) subangular to subrounded clasts in the phases of volcaniclastic kimberlite breccia. Because the majority of the observations of the contacts of Coherent Subfacies 1 with the phases of Volcaniclastic Facies 1 are from drill holes the nature of the contact relationships is difficult to establish. The most outstanding feature of the contacts is their irregularity. Dykes between 1 and 50 cm which intrude phases of Volcaniclastic Facies 1 commonly have sharp parallel margins while larger dykes have sharp irregular margins. Both drill core data and outcrop of Renard 4 show that Coherent Subfacies 1 occurs as irregularly shaped undulating bands cross-cutting the volcaniclastic kimberlite breccias (Figure 4.7). Flow alignment of mineral constituents (particularly olivine macrocrysts) and/or flow differentiation marked by concentration of larger constituents over a particular interval is commonly observed in Coherent Subfacies 1. In these cases, it is likely that the orientation of the dyke or sheet could be determined using the alignment of the mineral constituents. In a 89 Figure 4.7: A . Map of the surface exposure of Renard 4. B. Photograph, looking south, of the exposure mapped in A with position where image was taken from marked by an ' X ' . Massive coherent kimberlite units are dark grey (left and centre of photo) and volcaniclastic kimberlite units are light brown. The photograph is taken looking approximately south. Note the A T V on the road for scale. 90 . • • ^ ' r ^ • • • . Olivine macrocrysts Flow direction Dyke margin Macrocryst Size Figure 4.8: Schematic representation of a kimberlite dyke showing flow concentration. Larger constituents are concentrated in the centre of the dyke where the shear effects of the dyke walls on the kimberlite magma are at a minimum. 91 flowing system, coarser constituents will be concentrated in the area where flow is highest (ie where drag is at a minimum). In a dyke, this is in the centre where the drag imposed by the wall rocks is at a minimum (Figure 4.8). In intersections of Coherent Subfacies 1 where the apparent contacts cause confusion, concentrations of coarser constituents may be used to find the centre of the dyke and determine the relative orientation of the dyke margins. The presence of clasts of Coherent Subfacies 1 in all the phases of Volcaniclastic Facies 1 indicates that some Coherent Subfacies 1 dykes must predate the tuffisitic kimberlite breccias. The kimberlite eruption would have removed the bulk of these dykes, preserving evidence of their presence only as clasts in the tuffisitic kimberlite breccias (Figure 4.9). 4.3.4 Coherent Subfacies 2 Contacts between the two coherent subfacies are gradational and commonly observed. Coherent Subfacies 2 occurs at the margins of Coherent Subfacies 1 dykes (Figure 4.4 b). It is important to note that Coherent Subfacies 2 is simply a contact zone of Coherent Subfacies 1 with whatever rock type it is intruding and although the contact zone is manifest as a breccia this is not a volcaniclastic breccia. Clement and Reid (1989) describe this variety of kimberlite breccia as a kimberlite stockwork produced by the intrusion of coherent kimberlite stringers along pre-existing fractures in the rock. 4.3.5 Transitional Kimberlite Transitional kimberlite units are commonly observed as short intersections within Phases 3 and 4 of Volcaniclastic Facies 1 especially proximal to large massive coherent kimberlite units. The lower diatreme to the root zone of Class 1 kimberlites is a complex zone containing large areas of transitional kimberlite, and coherent kimberlite mixed in with tuffisitic kimberlite breccia (Herman et al., 2004; Skinner and Marsh, 2006b). With increasing depth transitional kimberlite becomes a more dominant rock type and deeper still, coherent kimberlite dominates (Figure 4.10). Some authors suggest that transitional kimberlite preserves the degassing front between coherent and fragmental kimberlite (Hetman, et al., 2004). However, it has also been suggested that transitional kimberlite is not a preserved 'snap-frozen' degassing front, but rather a post-emplacement alteration of tuffisitic kimberlite units by late fluids (Cas, 2006). The intersections of transitional 92 A B C Figure 4.9: Preservation of early coherent dykes as clasts in Volcaniclastic Facies 1. A . Kimberlite dykes intrude country rock. B. Kimberlite eruption displaces most of the coherent material preserving the portions of the dykes peripheral to the diatreme. Some of the material is ejected, but most is simply moved some distance from its source. C. After cessation of the kimberlite eruption clasts of coherent material derived from the precursor dykes are preserved in the breccia facies of the kimberlite diatreme. 93 Figure 4.10: The transitional zone of a Class 1 kimberlite pipe. The likely level of the pipe exposed at Renard 4 is enlarged in the box on the right hand side of the figure. Note that at this level in the pipe, blocks of Transitional Kimberlite are present within the Tuffisitic Kimberlite and blocks of coherent kimberlite are present in the Transitional Kimberlite (modified after Hetman, 2006). 94 kimberlite seen in Renard 4 are generally less than 10 m in extent suggesting that the drill holes are sampling the upper portion of the transitional zone. 4.3.6 Country Rock Breccia Country rock breccias form at the periphery of the Renard 4 kimberlite outside of the volcaniclastic kimberlite units in the central portion of the pipe. Coherent Subfacies 1 intrude into country rock breccias locally forming zones of Coherent Subfacies 2 at their margins. In drill holes collared outside of the Renard 4 kimberlite, intervals of fractured country rock with no pulverized country rock matrix are commonly encountered peripheral to the country rock breccia (Figure 4.11). These zones of fractured country rock rarely extend more than 1 m beyond the country rock breccia. Country rock breccias with larger, more angular clasts that appear to be in situ, and less matrix material occur between the fractured country rock and the country rock breccia units with smaller, more abraded clasts and a larger matrix component. 4.4 Emplacement of the Renard 4 kimberlite 4.4.1 Phases of Volcaniclastic Facies 1 The four phases of Volcaniclastic Facies 1 are differentiated by their groundmass composition and by the volume of country rock xenoliths and kimberlitic components (macrocrysts and magmaclasts) that they contain. To explain the presence of at least three of the phases a model for flow of suspended solids in a conduit is invoked. Phase 2 (Green tuffisitic kimberlite breccia) is not considered in this model as it is poorly constrained spatially being only observed in a single drill hole. The Bagnold effect is an effect of flowage differentiation which causes a concentration of suspended particles in the centre of a conduit where the least amount of shear is exerted on the flowing suspension (Bhattacharji and Smith, 1964; Barriere, 1976). The rate of concentration of suspended particles toward the centre of a conduit increases with increased velocity (Bhattacharji and Smith, 1964) (Figure 4.12). The Bagnold effect applies specifically to Newtonian fluids containing at minimum 8% crystals flowing in a conduit bounded by two parallel planes (Barriere, 1976). In nature, such a situation is rare; however, 95 the spatial distribution of country rock xenoliths in the phases of Volcaniclastic Facies 1 in the diatreme of Renard 4 indicate that similar processes may be at work here. In Renard 4 the greatest concentration of country rock xenoliths is the phase farthest from the centre of the diatreme: Phase 1 (Figure 4.6). During formation of the diatreme country rock material from the pipe walls was constantly fracturing and breaking off. At the margins of the diatreme, shear force is highest and the velocity of the magma or fluid is consequently lowest. In the zones nearest the margins of the diatreme the upward force of the kimberlite magma was not great enough to carry all the country rock clasts. Thus, a dilute zone of tuffisitic kimberlite breccia extremely rich in country rock xenoliths is formed and becomes increasingly dilute as distance from the centre of the diatreme increases. From the margins of the Renard 4 diatreme to the centre, there is a decrease in the abundance of country rock xenoliths from Phase 1 to Phase 3 and an increase from Phase 3 to Phase 4 (Figure 4.13). Phase 4 is located in the centre of the kimberlite pipe where shear forces imposed by the walls of the conduit on the fluid are minimized and consequently the flow velocity is maximized (Figure 4.12). In this central portion of the kimberlite where the velocity of the ascending kimberlite magma was greatest, the volume of country rock xenoliths that the magma was able to carry would have been greatest. Superimposed on Phases 3 and 4 are different styles of alteration of the xenoliths and of the groundmass. The country rock xenoliths in Phase 3 are much more strongly altered than those in Phase 4. In contrast, the groundmass minerals of Phase 4 are highly altered to an opaque cryptocrystalline assemblage whereas those in Phase 3 remain unaltered. As the more altered xenoliths are present in the rock with the fresher groundmass (Phase 3) more than one alteration event is required for the alteration of both the xenoliths and the groundmass. Phase 3 occurs between Phases 1 and 4 closer to the centre of the kimberlite than Phase 4 but farther from it than Phase 1 (Figure 4.6). In this zone of the kimberlite, the velocity of the kimberlite magma would have been greater than in the zone most proximal to the conduit walls (Phase 1), but less than in the centre of the pipe (Phase 4). Because the upward flow velocity in this zone was lower than that in the centre of the pipe, xenoliths being carried by the kimberlite magma would have remained in contact with it for longer than those in the centre of the pipe. The very strong alteration of country rock xenoliths in 96 J Tuffisitic kimberlite breccia ^ r ^ « Country rock breccia F Fractured country rock Country rock Figure 4.11: Envelopes of country rock breccia and fractured country rock. These occur at the periphery of the Renard 4 kimberlite pipe (not to scale). 97 |— —| Velocity gradient profile Shear stress profile Tmin Vmax Tmin Tmin Vmax Tmin Tmin Vmax Tmin Vmax Figure 4.12: The Bagnold Effect. A . Illustration of the velocity profile (V) and the shear stress profile (T) over the width of a conduit (modified after Barriere, 1976). B. The effect of increased velocity on the concentration of particles in the centre of the conduit (modified after Bhattacharji and Smith, 1964). 98 coherent kimberlite units in Renard 4 speaks to the extremely reactive nature of the kimberlite magma and indicates that the longer the residence time of a xenolith in the kimberlite magma, the greater the degree of alteration that that xenolith will exhibit. Thus, the strong alteration of the country rock xenoliths in Phase 3 supports the hypothesis that the flow velocity in this zone of the kimberlite was less than that in the centre of the pipe. The alteration of the groundmass of Phase 4 with little to no associated alteration of the country rock xenoliths suggests that the fluid responsible for this alteration was much less reactive than the kimberlite magma responsible for altering the xenoliths in Phase 3. The large number of country rock xenoliths present in Phase 4 cause this phase to have a higher permeability than Phase 3 which contains far fewer xenoliths. This increased permeability creates the means for a fluid to pass easily through Phase 4 altering the groundmass of the rock. Possible sources of this fluid include a late, deuteric fluid, or meteoric fluids percolating down from the surface. The depth of the alteration (1 to 1.5 km minimum) suggests that a magmatic fluid is the more likely of the two to have altered the groundmass of Phase 4. 4.4.2 Volcaniclastic Facies 2 Accretionary Magmaclastic Kimberlite (Volcaniclastic Facies 2) intrudes the phases of Volcaniclastic Facies 1 in a similar manner to the massive coherent kimberlite dykes. This facies is volumetrically minor, but is interesting because of its distinctive accretionary magmaclastic texture. The magmaclasts in this facies of volcaniclastic kimberlite are similar in appearance to accretionary lapilli from crater facies kimberlite. However, these textures in Renard 4 were formed at depths greater than 1 km below the paleosurface and must, therefore, have been formed by different mechanisms. True accretionary lapilli are defined as spheroidal lapilli-sized aggregates of ash which are usually formed in moist environments when suspended ash particles begin to aggregate as a result of electrostatic attraction and particle collision and are held together by surface tension of condensed moisture, electrostatic forces, particle interlocking and growth of new minerals as the condensed moisture evaporates (McPhie, et al., 1993). Accretionary lapilli are commonly described in pyroclastic flow and surge deposits, in co-ignimbrite and 99 Figure 4.13: Variation in abundance of country rock xenoliths and velocity. Both abundance of country rock and velocity vary from the centre of Renard 4 to the margins of the kimberlite pipe. A . Country rock xenolith abundance plotted versus distance from the centre of the pipe. The greatest concentration of country rock xenoliths is in the country rock breccia (CBx) at the margins of the kimberlite pipe. The most country rock xenolith-rich phase of Volcaniclastic Facies 1 is Phase 1 which is the most marginal of the phases. There is an increase in the percentage of country rock xenoliths present from Phase 3 to Phase 4. Phase 4 is the most central of the phases of Volcaniclastic Facies 1 and is therefore located where the upward velocity of the kimberlite magma was maximized allowing transport of the maximum volume of country rock xenoliths (see B.). B . Velocity plotted versus distance from the centre of the pipe. Velocity is maximized in the centre of the pipe and minimized at the pipe walls. 100 co-surge ash falls and ash falls out of eruption plumes and their lateral equivalents (Schumacher and Schmincke, 1995). Structurally different types of accretionary lapilli formed by different modes of tephra transport and aggregate formation are recognized (Schumacher and Schmincke, 1995). The first type (rim-type) has coarser cores surrounded by finer particles of ash. In this type of lapilli, the rims may be graded with grain size decreasing toward the margin, or may consist of alternating layers of fine- and very fine-grained ash. In some cases the lapilli have multiple rims but lack well-defined cores. The second type (core-type) is aggregates of relatively coarse ash without finer grained rims (McPhie et al., 1993). In the rim-type accretionary lapilli, rims are either internally graded with grain size decreasing towards the periphery, or made up of several layers of alternating grain size (Gilbert and Lane, 1994). Most of the 'accretionary' magmaclasts in the Volcaniclastic Facies 2 of the Renard 4 kimberlite are armoured lapilli rather than accretionary lapilli having cores of lapilli sized (2-64 mm) olivine macrocrysts surrounded by ash rims. These 'accretionary' magmaclasts did not form in the same manner as accretionary lapilli in crater facies rocks as the units containing them were emplaced deep below the surface. The formation of rims of ash-sized material on macrocrysts requires that the textures were formed in a gas-rich environment and that the volume of the Volcaniclastic Facies 2 units was much greater during emplacement relative to their preserved volumes. Accretionary textures form in gas-rich environments when suspended fine particles are attracted to larger particles such as olivine macrocrysts via electrostatic forces (Schumacher and Schminke, 1995). In an idealized situation, where a fluid carrying suspended spherical solids is flowing through a smooth, parallel walled conduit, the lateral force exerted by the walls of the conduit sometimes exceeds the longitudinal force exerted by the flow of the fluid or vice versa, causing rotation of the large, spherical grains (Bhattacharji and Smith, 1964). In a natural system, the same forces are exerted on the macrocrysts but the parameters are less controlled and thus the rotation is less predictable. The rotation in combination with the electrostatic attraction of fine material to larger grains may result in the formation of the accretionary textures seen in Volcaniclastic Facies 2. In order to form the accretionary textures observed in Renard 4, the macrocrysts which now form the nuclei of the accretionary magmaclasts must have been moving freely in 101 either a fluid. This requires that the kimberlite magma must have been inflated to many times its current volume and the close packing of the accretionary clasts and macrocrysts that is seen in Volcaniclastic Facies 2 reflects a deflated, and compacted kimberlite magma. Volcaniclastic Facies 2 is observed at depths as widely varied as 19 m and 230 m bellow the present surface of the kimberlite. Assuming that the modern surface of the kimberlite represents a level greater than 1 km below the paleosurface, these rocks were emplaced at considerable depth. This means that at depths as great, or greater than a kilometre below the surface the volatile phases of the kimberlite magma exerted enough pressure on their surroundings to create a large volume for the magma to move through. 4.4.3 Emplacement Model The variety of rocks and textures present in the Renard 4 kimberlite necessitate a multi-stage emplacement process. The following section describes the ascent of the kimberlite magma from the deep mantle to the shallow crust with reference to prior publications and describes the emplacement in the shallow crust with reference to the specific rock types and textures present in the Renard 4 kimberlite. M a g m a ascent Clement and Reid (1989) suggest that kimberlite eruptions are initiated by intermittently active processes including: hydraulic fracturing and wedging, magmatic stoping and intrusion brecciation, and vapour phase-related explosive brecciation (Figure 4.14 a and b). Some of these processes presuppose that juvenile volatiles have separated from the rising kimberlite magma. The depth at which volatiles exsolve from kimberlite magma is not well constrained. At pressures greater than 100 MPa, magmatic volatile phases are relatively incompressible and so the volatile content of the magma cannot play a major role in magma ascent (Spera, 1984). At depths below approximately 3 km where pressure is greater than 100 MPa (Wilson, 1989) the main role of volatiles is in controlling the initial magma flux and the magma pressure during ascent. Once magmatic volatiles exsolve, they may aid in propelling the kimberlite magma to the surface. At these depths, the juvenile volatiles may migrate to the head of the intruding magma and form a gas cap aiding in migration of the kimberlite 102 magma into and along discontinuities in the country rock. Where barriers are encountered, temporary halting of the ascent will cause pressure to build eventually resulting in explosive brecciation in an envelope around the head of the magma column. Once breakthrough of the barrier occurs, further degassing of the magma will occur re-establishing the upward migration of the magma (Field and Scott Smith, 1999). Dyke formation Once the kimberlite magma has ascended as far as the shallow crust (0 to 5 km below surface), one of two things can happen: magma ascent can cease, or it can continue eventually resulting in a kimberlite eruption. The presence of clasts of coherent kimberlite in all the phases of Volcaniclastic Facies 1 in Renard 4 indicate that prior to the emplacement of the kimberlite pipe, coherent kimberlite dykes were emplaced (Figure 4.9). Many of the coherent kimberlite clasts, especially those in Phase 1, are sub-angular to sub-rounded indicating that the coherent kimberlite was fully lithified before it was entrained in the volcaniclastic breccia. Although there is no way to determine the time that elapsed between emplacement of the coherent dykes and the eruption and formation of the Renard 4 kimberlite, it is unlikely that it was very long. A period of hours or days seems the most likely. Eruption and formation of the diatreme When the magma reaches a depth less than 1 km below the surface, the gas overpressures generated by the exsolution of volatiles from the kimberlite magma are believed to cause cracking through of the overlying country rock and breach of the surface (Figure 4.14 c) (Skinner and Marsh, 2006a). Surface breach causes an instantaneous depressurization and accompanying exsolution of all remaining volatiles, cooling, explosion, and shock wave (Skinner and Marsh, 2006a). This depressurization allows the kimberlite diatreme to propagate downward and outward and the level at which the pressure of the magma is greater than the confining pressure of the rocks it is intruding moves downward. At the margins of the diatreme, country rock breccia is formed as the pressure of the magma exceeds the overpressure of the rock causing it to fail. In the presence of sufficient volatiles, the broken country rock is displaced and the clasts are rotated. The farther from the 103 • + 41 + + 4-+ + + + + i f -r + j ! + + 4 1 + t + + Figure 4.14: Emplacement of the Renard 4 kimberlite (first stages). A . Intrusion of the kimberlite magma into the country rock causing fracturing. B . Crack propagation and further advancement of the kimberlite magma. C. Eruption and consequent formation of a diatreme and excavation of a crater and formation of tuff ring. During eruption, the diatreme is expanded downward and outward as the degassing front moves downward. D. Infilling of the diatreme and crater. 104 centre of the diatreme the breccias are, the less exsolved gases from the kimberlite magma they will have been in contact with. Thus, the most distal country rock breccias have clasts which are in situ. The velocity of the ascending kimberlite magma is greatest in the centre of the kimberlite diatreme and least at the margins of the pipe. In Renard 4, this variation in velocity across the kimberlite diatreme resulted in the formation of distinct phases of tuffisitic kimberlite breccia. At the margins of the pipe the fracturing and breaking off of country rock from the pipe walls resulting in expansion of the kimberlite diatreme results in the presence of an increased volume of country rock xenoliths relative to the centre of the pipe. In Renard 4, Phase 1, the most country rock xenolith-rich phase formed as a result of the inability of the kimberlite magma to carry the large volume of broken country rock present in this zone. In the centre of the pipe (Phase 4) where the velocity of the magma is highest there is a concentration of country rock xenoliths relative to the zone between the centre of the pipe and the zone at the pipe margin (Phase 3). However, the concentration of xenoliths in the centre of the pipe is less that that in the most peripheral phase of tuffisitic kimberlite breccia (Phase 1). As the kimberlite eruption waned, the flow sorted material in the kimberlite diatreme (Phases 1-4) became the diatreme infill. After cessation of the eruption, the material in the diatreme relaxed and compacted resulting in the formation of the competent tuffisitic kimberlite breccia which composes the majority of Renard 4 today. Emplacement of Coherent Subfacies 1 and 2 and Volcaniclastic Facies 2 After the emplacement of Volcaniclastic Facies 1, the diatreme of the Renard 4 kimberlite and the surrounding country rock was intruded by many steeply dipping coherent kimberlite dykes (Coherent Subfacies 1) (Figure 4.15 b). These dykes frequently intruded along the margins of the phases of Volcaniclastic Facies 1 taking advantage of the structural weakness of these zones. Coherent Subfacies 2 was formed contemporaneously with Coherent Subfacies 1 when the kimberlite filtered into cracks in the country rock or in the volcaniclastic kimberlite breccia forming very small and localized kimberlite stockworks. Volcaniclastic Facies 2 was also emplaced after Volcaniclastic Facies 1 and intrudes them in a manner very similar to the steeply dipping coherent kimberlite dykes. 105 Alteration Alteration of country rock xenoliths occurred during the emplacement of Renard 4 as a result of the interaction of the kimberlite magma with the granite and gneiss country rock. The country rock xenoliths in Phase 3 were exposed to the kimberlite magma for longer than those in Phase 4 because the velocity of the ascending kimberlite magma was lower in the portion of the pipe peripheral to the centre. The longer residence time of the country rock xenoliths in the highly reactive kimberlite magma accounts for the high degree of alteration of these xenoliths. Alteration of the groundmass of Phase 4 likely occurred after the kimberlite eruption. The large number of country rock xenoliths present in the core of the kimberlite pipe increased the porosity of this zone and made it more susceptible to intrusion of a late, relatively cool magmatic fluid, or to meteoric fluid percolating down through the kimberlite (Figure 4.15 c). It is assumed that this late fluid was less volatile-rich than the kimberlite magma responsible for altering the country rock xenoliths in Phase 3 because the country rock xenoliths in Phase 4 are much fresher than those in Phase 3. Erosion Finally, after the emplacement of the volcaniclastic and coherent kimberlite units and the alteration of these units, the kimberlite was subjected to erosion by weathering and glaciation. Today, the Renard 4 kimberlite is exposed at a level in the transitional zone between the lower diatreme and the root zone (Figure 4.15 d). 106 Figure 4.15: Final stages of emplacement of Renard 4 and post-emplacement processes. A . Settling and compaction of crater and diatreme infill. B. Intrusion of late-stage Coherent Subfacies 1 dykes and consequent formation of Coherent Subfacies 2. Intrusion of Volcaniclastic Facies 2. C. Fluids move through diatreme infill preferentially altering Volcaniclastic Facies 1 Phase 4. D. Erosion of the kimberlite by weathering and glaciation to a level approximately 1 km below the paleosurface. 107 CHAPTER 5: CONCLUSIONS The Renard 4 kimberlite is a Group 1, Class 1 kimberlite exposed by erosion at a level in the transitional zone between the lower diatreme and the root zone of the kimberlite pipe. The kimberlite is composed of six rock types, five of which are kimberlitic. The five kimberlitic rock types include two subfacies of coherent kimberlite, two facies of volcaniclastic kimberlite and Transitional Kimberlite which shares characteristics with both coherent and volcaniclastic rock types. Volcaniclastic Facies 1 comprises four phases distinguished by their groundmass composition and the abundance of country rock xenoliths and kimberlitic components. Phase 1 occurs most proximally to the pipe walls, Phase 3 occurs in the zone between Phase one and the centre of the pipe, and Phase 4 occurs in the pipe centre. Phase 2 is not well constrained spatially. At least three of the phases are the result of several inter-related processes. Firstly, the variation in the abundance of country rock xenoliths is dependent on the velocity of the ascending kimberlite magma at any given location in the volcanic conduit (here the kimberlite diatreme). In the centre of the conduit where the ascent velocity of the magma is greatest, the largest volume of xenoliths can be transported. Thus, country rock xenoliths are concentrated in Phase 4 relative to Phase 3. Phase 1, located immediately adjacent to the wall of the diatreme, is the richest in country rock xenoliths. This is the result of two factors: 1- at the diatreme margins wallrock is being shattered and included in the kimberlite and is thus more abundant than at any other location in the diatreme, and 2- shear force imposed by the walls on the ascending magma results in low magma velocity and limited ability of the magma to transport the broken country rock. Secondly, the lower velocity of magma in the zone between the conduit walls and the centre of the conduit increased the residence time of the country rock xenoliths in Phase 3. The increased residence time in the highly reactive kimberlite magma caused the country rock xenoliths in this phase of kimberlite to be more altered than those in the central portion of the pipe. Thirdly, Phase 4 had a higher porosity than Phase 3 as a result of the larger number of country rock xenoliths present in it. This increased porosity made Phase 4 more susceptible to groundmass alteration by a relatively cool fluid than Phase 3. 108 The contact relationships between rock types in the Renard 4 kimberlite indicate that the emplacement of the kimberlite involved a multi-stage process. Prior to the emplacement of Volcaniclastic Facies 1 (the most volumetrically significant diatreme-filling unit), coherent kimberlite dykes were emplaced. The kimberlite eruption and filling of the diatreme were succeeded by emplacement of late-stage coherent kimberlite dykes and the emplacement of Volcaniclastic Facies 2. Finally, alteration and erosion altered the appearance, texture and mineralogy of the kimberlite and removed the upper 1 kilometre of the pipe. The presence of each of the Renard 4 rock types and their spatial distribution has important implications for the emplacement model of this kimberlite and provide important insight for general models pertaining to the formation of the root/diatreme transitional zone in other kimberlite pipes. The accretionary magmaclastic textures seen in some volcaniclastic rock types in Renard 4 indicates that fragmentation of the kimberlite magma occurs as deep as 2 kilometres below the earth surface and that during emplacement these magmas are inflated to many times the volume they currently occupy. It is furthermore suggested that the kimberlite magma is inflated, and the fragmental textures are formed in systems which may never have breached the surface. Future work on Renard 4 kimberlite should include a geochemical study on the early-and late-stage coherent kimberlite dykes to determine i f the two can be distinguished. This could provide insight as to the evolution of the kimberlite source over the course of the emplacement of the kimberlite. Modeling of the proposed concentration of country rock clasts to the areas of highest velocity in the volcanic conduit would prove whether or not this is a viable method of creating the distribution of phases observed in Renard 4. Furthermore, determination of the chemistry of the fluids responsible for altering the kimberlite could provide insight to the nature and chemistry of the primary mineralogy of the kimberlite and thereby into the nature of the kimberlite magma. 109 REFERENCES Ashton Mining of Canada Inc., News Release, November 8, 2005. Barnett, W., 2004. Subsidence breccias in kimberlite pipes - an application of fractal analysis. Lithos, vol 76, pp. 200-316. Barriere, M . , 1976. Flowage differentiation: limitation of the "Bagnold Effect" to the narrow instrusions. Contributions to Mineralogy and Petrology, vol. 55, pp. 139-145. Bhattacharji, S. and Smith, C.H., 1964. Flowage differentiation. Science, vol. 145, no. 3628, pp. 150-153. Birkett, T.C., McCandless, T.E. and Hood, C.T., 2004. Petrology of the Renard igneous bodies: host rocks for diamond in the northern Otish Mountains region, Quebec. Lithos, vol. 76, pp. 475-490. Birkett, T.C., March 1, 2007. Personal communication regarding the thickness of the Otish Formation. Boyer, L.P., 2005. Kimberlite Volcanic Facies and Eruption in the Buffalo Head Hills, Alberta (Canada). Unpublished MSc. Thesis, University of British Columbia, Canada. 156 pp. Cas, R.A.F. and Wright, J.V. 1988. Volcanic Successions: Modern and Ancient. Chapman and Hall, London. 1s t Edition. 528 pp. Cas, R.A.F., Hayman, P.C., Pittari, A . and Porrit, L .A. , 2006. Terminology for kimberlite pipes. Extended Abstracts of the Kimberlite Emplacement Workshop, Saskatoon, Canada, September, 2006 Clements, B. and O'Connor, A. , 2002. Quebec technical report May 17, 2002. Ashton Mining of Canada Annual Technical Report. Clement, C.R., 1982. A comparative geological study of some major kimberlite pipes in the northern Cape and Orange Free State. Unpublished PhD thesis, University of Cape Town, South Africa. 431 pp. Clement, C.R., and Reid, A . M . , 1989. The origin of kimberlite pipes: an interpretation based on a synthesis of geological features displayed by southern African occurrences. In: Ross, J., et al. (Eds.), Proceedings of the 4 t h International Kimberlite Conference. Kimberlites and Related Rocks, vol. 1, pp. 632-646. 110 Clement, C.R. and Skinner, E.M.W., 1985. A textural-genetic classification of kimberlites. Trasactions of the Geological Society of South Africa, vol. 88, pp. 403-409. Field, M . , and Scott Smith, B.H. , 1999. Contrasting geology and Near-surface emplacement of kimberlite pipes in southern Africa and Canada. In: Gurney, J.J., et al. (Eds.), Proceedings of tht 7 International Kimberlite Conference, vol. 1, pp. 214-237. Gilbert, J.S. and Lane, S.J., 1994. The origin of accretionary lapilli. Bulletin of Volcanology, vol. 56, pp. 398-411. Graham, I., Burgess, J.L., Bryan, D., Ravenscroft, P.J., Thomas, E., Doyle, B.J., Hopkins, R., and Armstrong, K . A . , 1998. The Diavik kimberlites - Lac de Gras, Northwest Territories, Canada. Extended Abstracts of the Seventh International Kimberlite Conference, Cape Town, South Africa, 1998. Hawthorne, J.B., 1975. Model of a kimberlite pipe. Physics and Chemistry of the Earth. In: Ahrens, L. , et al. (Eds), Proc. 1st Int. Kimb. Conf. Physics and Chemistry of the Earth, vol. 9, pp. 1-15. Hetman, C M . , Scott Smith, B.H. , Paul, J.L., and Winter, F., 2004. Geology of the Gahcho Kue kimberlite pipes, NWT, Canada: root to diatreme magmatic transition zones. Lithos 76:51-74. Hetman, C M . , 2006. Tuffisitic kimberlite : A Canadian perspective on a distinctive textural variety of kimberlite. Extended Abstracts of the Kimberlite Emplacement Workshop, Saskatoon, Canada, September, 2006. Hocq, M . , 1985. Geologie de la Region des lacs Campan et Cadieux - Territoire-du-nouveau-Quebec. Ministere de l'energie et les Ressources. Direction General de l'Exploration Gelogique et Mineral. Kirkley, M.B. , Kolebaba, M.R., Carlson, J.A., Gonzales, A . M . , Dyck, D.R., and Dierker, C , 1998. Kimberlite emplacement and processes interpreted from Lac do Gras examples. Extended Abstract of the 7 t h International Kimberlite Conference, pp 429-431. Kjarsgaard, B.A. , 2005. Western Churchill metallogeny project: Speculations on crust/mantle kimberlite relations, Churchill Province. <http://ess.mcan.gc.ca/2002_2006/nrd/wchurchill/project_8_4_pres_15_e.php> Lorenz, V . , 1987. Phreatomagmatism and its relevance. Chemical Geology, 62, pp. 149-156. I l l Lorenz., V. , 1975. Formation and phreatomagmatic maar-diatreme volcanoes and its relevance to kimberlite diatremes. In: Ahrens, L. , et al. (Eds), Proc. 1s t Int. Kimb. Conf. Physics and Chemistry of the Earth, vol. 9, pp. 17-27. McCallum, M.E. , 1985. Experimental evidence for fluidization processes in breccia pipe formation. Economic Geology, vol. 80, pp. 1523-1543. McPhie, J., Doyle, M . , and Allen, R., 1993. Volcanic Textures: A Guide to the Interpretation of Textures in Volcanic Rocks: Hobart, Centre for Ore Deposit and Exploration Studies, University of Tasmania, 196 p. Mitchell, R. H . 1993. Kimberlites and Lamproites: Primary Sources of Diamond. Ore Deposit Models Volume 2. pp. 13- 28. Mitchell, R.H., Scott Smith, B.H. and Larsen, L . M . , 1999. Mineralogy of ultramafic dikes from the Sarfartoq, Sisimiut and Maniitsoq areas, West Greenland. In: Gurney, J.J., Gurney, J.L., Pascoe, M.D. , Richardson, S.H. (Eds.), Proceedings of the 7 t h International Kimberlite Conference. Red Roof Design cc, Cape Town, South Africa, pp. 574-583. O'Brien, H.E. and Tyni, M . , 1999. Mineralogy and geochemistry of kimberlites and related rocks from Finland. In: Gumey, J.J., Gurney, J.L., Pascoe, M.D. , Richardson, S.H. (Eds.), Proceedings of the 7 t h International Kimberlite Conference. Red Roof Design cc, Cape Town, South Africa, pp. 625-636. O'Connor, A . and Lepine, I., 2006. Technical Report and Recommendations: The Otish Mountains, Quebec Project. Ashton Mining of Canada Inc. February 24, 2006. Scott Smith, B.H. 1995. Petrology and Diamonds. Exploration Mining Geology, vol. 4, no. 2, pp.127-140. Scott Smith, B.H. , 2004. Geology of the Renard 09 kimberlite, Quebec. Ashton Mining of Canada Inc., Internal report: SSP-04-1/3. Schumacher, R., and Schminke, H.U., 1995. Models for the origin of accretionary lapilli. Bulletin of Volcanology, vol. 56, pp. 626-639. Skinner, E.M.W. and Marsh, J.S., 2004. Distinct kimberlite pipe classes with contrasting eruption processes. Proceedings of the 8 t h International Kimberlite Conference. Lithos, vol. 76, pp. 183-200. 112 Skinner, E .M.W and Marsh, J.S., 2006a. The emplacement of classl kimberlites - part 1, evidence of geological features. Extended Abstracts of the Kimberlite Emplacement Workshop, Saskatoon, Canada, September, 2006. Skinner, E .M.W and Marsh, J.S., 2006b. The emplacement of classl kimberlites - part 2, evidence of geological features. Extended Abstracts of the Kimberlite Emplacement Workshop, Saskatoon, Canada, September, 2006. Spera, F.J., 1984. Carbon Dioxide in Pedogenesis HI: role of volatiles in the ascent of alkaline magma with special reference to xenolith-bearing mafic lavas. Contributions to Mineralogy and Petrology, vol. 88, pp. 217-232. Wagner, P.A., 1914. The diamond fields of southern Africa. Transvaal Leader. Webb, K. , Scott Smith, B.H. , Paul, J. and Hetman, C , 2004. Geology of the Victor kimberlite, Attawapiskat, Northern Ontario, Canada: cross-cutting and nested craters. Proceedings of the 8 t h International Kimberlite Conference. Lithos, vol. 76, pp. 29-50. Wilson, M . , 1989. Igneous Petrogenesis: A Global Tectonic Approach: London, Chapman and Hi l l . pp. 465. Wooley, A.R., Bergman, S.C., Edgar, A.D. , LeBas, M.J. , Mitchell, R.H., Rock, N.M.S. , and Scott Smith, B.H. , 1996. Classification of Lamprophyres, Lamproites, Kimberlites, and the Kalsilitic, Melilitic, and Leucitic Rocks. The Canadian Mineralogist, vol. 34, pp. 175-186. 113 APPENDIX A: LIST OF SLABS AND THIN SECTIONS Drill Hole From (m) To(m) Thin Section or Slab Rock Type R4-06 23.7 23.82 Slab Coherent Subfacies 1 R4-06 23.7 23.72 Slab Coherent Subfacies 1 R4-06 39.9 40 Slab Coherent Subfacies 1 R4-06 60.7 60.76 Slab Coherent Subfacies 1 R4-06 98.96 99.13 Slab Coherent Subfacies 1 R4-06 98.96 98.98 Thin section Coherent Subfacies 1 R4-07 39.6 39.77 Slab Coherent Subfacies 1 R4-07 39.6 39.62 Thin section Coherent Subfacies 1 R4-07 89.7 89.81 Slab Coherent Subfacies 1 R4-34 29.8 30 Slab Volcaniclastic Facies 1 - Phase 2 R4-34 51.7 52 Slab Volcaniclastic Facies 1 - Phase 2 and Coherent Subfacies 1 -CONTACT R4-34 56.1 56.23 Slab Volcaniclastic Facies 1 - Phase 2 and Coherent Subfacies 1 -CONTACT R4-34 58.9 59.3 Slab Volcaniclastic Facies 1 - Phase 2 R4-34 81.6 81.78 Slab Volcaniclastic Facies 1 - Phase 2 R4-34 83.3 83.5 Slab Coherent Subfacies 1 R4-34 89.25 89.4 Slab Coherent Subfacies 1 R4-34 103.9 104 Slab Coherent Subfacies 1 R4-34 114 114.15 Slab Volcaniclastic Facies 1 - Phase 4 R4-34 138 138.23 Slab Volcaniclastic Facies 1 - Phase 4 R4-34 140.8 141 Slab Volcaniclastic Facies 1 - Phase 4 -contains 20 cm clast of coherent subfacies 1 R4-34 142.95 143.3 Slab Coherent Subfacies 1 R4-34 189 189.12 Slab Volcaniclastic Facies 1 - Phase 2 R4-34 202.4 202.54 Slab Volcaniclastic Facies 1 - Phase 2 R4-35 90 90.23 Slab Volcaniclastic Facies 1 - Phase 2 R4-35 126 126.3 Slab Volcaniclastic Facies 1 - Phase 2 R4-35 145.5 145.67 Slab Volcaniclastic Facies 1 - Phase 2 R4-35 176.2 176.4 Slab Volcaniclastic Facies 1 - Phase 4 R4-35 177 177.15 Slab Volcaniclastic Facies 1 - Phase 3 R4-35 177.5 177.7 Slab Volcaniclastic Facies 1 - Phase 4 R4-35 179.3 179.43 Slab Volcaniclastic Facies 1 - Phase 4 R4-35 181.5 181.6 Slab Coherent Subfacies 1 R4-35 194.1 . 194.27 Slab Volcaniclastic Facies 1 - Phase 1 R4-36 12.6 12.82 Slab Coherent Subfacies 1 R4-36 30 30.3 Slab Volcaniclastic Facies 1 - Phase 2 R4-36 44.05 44.28 Slab Volcaniclastic Facies 1 - Phase 2 R4-36 48.75 48.9 Slab Transitional 114 R4-36 71.08 71.98 Slab Volcaniclastic Facies 1 - Phase 4 R4-36 71.1 71.12 Thin section Volcaniclastic Facies 1 - Phase 4 R4-36 82.8 82.85 Slab Volcaniclastic Facies 1 - Phase 3 R4-36 82.8 82.82 Thin section Volcaniclastic Facies 1 - Phase 3 R4-36 96.7 96.85 Slab Coherent Subfacies 1 R4-36 123.4 123.6 Slab Volcaniclastic Facies 1 - Phase 2 R4-36 151.2 151.27 Slab Transitional R4-36 173.2 173.38 Slab Volcaniclastic Facies 1 - Phase 3 R4-36 173.2 173.22 Thin section Volcaniclastic Facies 1 - Phase 3 R4-37 8 8.11 Slab Volcaniclastic Facies 1 - Phase 2 R4-37 19.95 20.11 Slab Volcaniclastic Facies 1 - Phase 2 R4-37 19.99 20.01 Thin section Volcaniclastic Facies 1 - Phase 2 R4-37 20.06 20.08 Thin section Volcaniclastic Facies 1 - Phase 2 R4-37 20.55 20.71 Slab Volcaniclastic Facies 1 - Phase 2 R4-37 20.69 20.76 XL Thin section Volcaniclastic Facies 1 - Phase 2 R4-37 26.85 26.99 Slab Volcaniclastic Facies 1 - Phase 2 R4-37 26.85 26.87 Thin section Volcaniclastic Facies 1 - Phase 2 R4-37 26.96 26.98 Thin section Volcaniclastic Facies 1 - Phase 2 R4-37 40.1 40.26 Slab Volcaniclastic Facies 1 - Phase 2 R4-37 44.75 44.87 Slab Volcaniclastic Facies 1 - Phase 2 R4-37 48.1 48.25 Slab Volcaniclastic Facies 1 - Phase 2 R4-37 53.65 53.87 Slab Coherent Subfacies 1 R4-37 53.65 53.67 Thin section Coherent Subfacies 1 R4-37 59 59.2 Slab Volcaniclastic Facies 1 - Phase 2 R4-37 59.02 59.07 XL Thin section Volcaniclastic Facies 1 - Phase 2 R4-37 63.45 63.57 Slab Coherent Subfacies 1 R4-37 63.5 63.52 Thin section Coherent Subfacies 1 R4-37 63.53 63.55 Thin section Coherent Subfacies 1 R4-37 85.55 85.68 Slab Volcaniclastic Facies 1 - Phase 2 R4-37 85.51 85.53 Thin section Volcaniclastic Facies 1 - Phase 2 R4-37 105.55 105.7 Slab Volcaniclastic Facies 1 - Phase 1 R4-37 105.62 105.64 Thin section Volcaniclastic Facies 1 - Phase 1 R4-37 107.85 107.99 Slab Volcaniclastic Facies 1 - Phase 1 R4-39 7 7.17 Slab Volcaniclastic Facies 1 - Phase 2 R4-39 18 18.11 Slab Volcaniclastic Facies 1 - Phase 2 R4-39 18.65 18.75 Slab Volcaniclastic Facies 1 - Phase 2 (very dilute) R4-39 20.3 20.46 Slab Coherent Subfacies 1 - cut by late carbonate-flooded corridoor R4-39 21.65 21.85 Slab Transitional R4-39 27 27.13 Slab Coherent Subfacies 1 R4-39 29.5 29.63 Slab Volcaniclastic Facies 1 - Phase 2 (very dilute) R4-39 30.6 30.78 Slab Transitional R4-39 31.65 31.73 Slab Coherent Subfacies 1 R4-39 34.7 34.9 Slab Coherent Subfacies 1 - cut by late carbonate-flooded corridoor R4-39 38.74 38.89 Slab Coherent Subfacies 1 R4-39 47.4 47.57 Slab Volcaniclastic Facies 1 - Phase 1 R4-39 62.75 62.88 Slab Volcaniclastic Facies 1 - Phase 1 115 R4-39 77.45 77.59 Slab Coherent Subfacies 1 R4-39 84.8 85.02 Slab Coherent Subfacies 1 R4-39 94.75 95.02 Slab Coherent Subfacies 1 R4-39 118.3 118.36 Slab Coherent Subfacies 1 - carbonate flooded R4-40 44.7 44.9 Slab Volcaniclastic Facies 1 - Phase 4 R4-40 44.75 44.77 Thin section Volcaniclastic Facies 1 - Phase 4 R4-40 52.9 53.15 Slab Volcaniclastic Facies 1 - Phase 3 R4-40 52.93 52.95 Thin section Volcaniclastic Facies 1 - Phase 3 R4-40 91.95 92.2 Slab Volcaniclastic Facies 1 - Phase 1 R4-41 7.3 7.45 Slab Transitional R4-41 7.39 7.44 XL Thin section Transitional R4-41 13.5 13.65 Slab Coherent - Subfacies 1 R4-41 18.35 18.5 Slab Transitional R4-41 18.42 18.49 XL Thin section Transitional R4-41 21.1 21.3 Slab Coherent - Subfacies 1 R4-41 21.26 21.28 Thin section Coherent - Subfacies 1 R4-41 24.95 25.15 Slab Transitional R4-41 25.04 25.06 Thin section Transitional R4-41 27.7 27.8 Slab Volcaniclastic Facies 1 - Phase 1 R4-42 111.2 111.37 Slab Volcaniclastic Facies 1 - Phase 3 and 4 - CONTACT ZONE R4-42 159.5 159.73 Slab Volcaniclastic Facies 1 - Phase 3 R4-42 159.6 159.62 Thin section Volcaniclastic Facies 1 - Phase 3 R4-43 169.4 169.6 Slab Volcaniclastic Facies 1 - Phase 4 R4-43 169.6 169.9 Slab Volcaniclastic Facies 1 - Phase 4 R4-43 169.65 169.67 Thin section Volcaniclastic Facies 1 - Phase 4 R4-44 7.93 8.11 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 19.4 19.63 Slab Volcaniclastic Facies 2 R4-44 19.5 19.52 Thin section Volcaniclastic Facies 2 R4-44 25.4 25.57 Slab Coherent Subfacies 2 R4-44 30.4 30.57 Slab GNEISS R4-44 34.9 35.09 Slab Vocaniclastic Facies 1 - Phase 1 R4-44 37.95 38.1 Slab Vocaniclastic Facies 1 - Phase 1 R4-44 45.5 45.75 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 49.78 49.91 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 50.85 51 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 57.38 57.58 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 63 63.2 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 80.54 80.99 Slab Volcaniclastic Facies 1 - Phase 3 and Phase 4 - CONTACT R4-44 87.93 88.12 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 89.25 89.45 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 96.37 96.75 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 105.65 106.09 Slab Volcaniclastic Facies 1 - Phase 3 and Phase 4 - CONTACT R4-44 119.08 119.28 Slab Volcaniclastic Facies 1 - Phase 3 and Phase 4 - CONTACT R4-44 127.23 127.49 Slab Transitional R4-44 127.23 127.25 Thin section Transitional 116 R4-44 134.45 134.81 Slab Volcaniclastic Facies 1 - Phase 3 and Phase 4 - CONTACT R4-44 135 135.25 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 137.2 137.66 Slab Volcaniclastic Facies 1 - Phase 3 and Phase 4 - CONTACT R4-44 137.2 137.22 Thin section Volcaniclastic Facies 1 - Phase 4 R4-44 137.6 137.62 Thin section Volcaniclastic Facies 1 - Phase 3 R4-44 140.52 140.79 Slab Transitional R4-44 140.52 140.54 Thin section Transitional R4-44 145.61 145.87 Slab Volcaniclastic Facies 1 - Phase 3 R4-44 150 150.26 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 153.83 154.22 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 160.3 160.5 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 165 165.45 Slab Volcaniclastic Facies 1 - Phase 4 with 5 cm of Phase 3 - CONTACT R4-44 169.29 169.63 Slab Volcaniclastic Facies 1 - Phase 4 (contains 15 cm 'clast' of Phase 3 R4-44 171 171.4 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 179.46 179.8 Slab Volcaniclastic Facies 1 - Phase 4 R4-44 201.33 201.6 Slab Volcaniclastic Facies 1 - Phase 1 R4-44 284.7 284.9 Slab Coherent - Subfacies 1 R4-44 284.71 284.73 Thin section Coherent - Subfacies 1 R4-44 284.87 284.89 Thin section Coherent - Subfacies 1 R4-44 293.3 Slab Volcaniclastic Facies 1 - Phase 1 R4-44 315 315.2 Slab Volcaniclastic Facies 1 - Phase 1 R4-44 315.11 315.13 Thin section Volcaniclastic Facies 1 - Phase 1 R4-44 320.1 Slab Volcaniclastic Facies 1 - Phase 1 R4-44 333.2 333.37 Slab Volcaniclastic Facies 1 - Phase 1 R4-44 348 Slab Volcaniclastic Facies 1 - Phase 1 R4-44 348.05 348.1 XL Thin section Volcaniclastic Facies 1 - Phase 1 R4-44 356.8 357 Slab Volcaniclastic Facies 1 - Phase 1 R4-44 356.87 356.94 XL Thin section Volcaniclastic Facies 1 - Phase 1 R4-44 360.21 360.53 Slab Country Rock Breccia R4-44 370.9 Slab Volcaniclastic Facies 1 - Phase 2 R4-44 371.06 371.08 Thin section Volcaniclastic Facies 1 - Phase 2 R4-44 385.8 386 Slab Country Rock Breccia R4-44 386.7 Slab Country Rock Breccia R4-44 386.7 386.72 Thin section Country Rock Breccia R4-44 394.9 Slab Country Rock Breccia R4-44 394.99 395.01 Thin section Country Rock Breccia R4-44 407.13 407.53 Slab Country. Rock Breccia R4-44 414.71 415.1 Slab Country Rock Breccia R4-45 143.05 143.6 Slab Volcaniclastic Facies 1 - Phase 3 and 4 - CONTACT ZONE R4-45 322.12 322.38 Slab Volcaniclastic Facies 1 - Phase 1 R4-45 322.2 322.22 Thin section Volcaniclastic Facies 1 - Phase 1 R4-45 339.35 339.55 Slab Volcaniclastic Facies 1 - Phase 1 R4-45 339.46 339.48 Thin section Volcaniclastic Facies 1 - Phase 1 R4-45 350.37 350.64 Slab Coherent Subfacies 1 (small dyke cutting gneiss) R4-45 350.5 350.57 XL Thin section Coherent Subfacies 1 (small dyke cutting gneiss) 117 R4-45 359.41 359.65 Slab Volcaniclastic Facies 1 - Phase 1 R4-45 359.46 359.48 Thin section Volcaniclastic Facies 1 - Phase 1 R4-45 359.54 359.56 Thin section Volcaniclastic Facies 1 - Phase 1 R4-45 359.6 359.62 Thin section Volcaniclastic Facies 1 - Phase 1 R4-45 369.17 369.44 Slab Volcaniclastic Facies 1 - Phase 1 R4-45 369.26 369.28 Thin section Volcaniclastic Facies 1 - Phase 1 R4-45 369.31 369.33 Thin section Volcaniclastic Facies 1 - Phase 1 R4-45 369.36 369.38 Thin section Volcaniclastic Facies 1 - Phase 1 R4-45 390.48 390.76 Slab Volcaniclastic Facies 1 - Phase 1 R4-45 390.56 390.58 Thin section Volcaniclastic Facies 1 - Phase 1 R4-45 390.6 390.62 Thin section Volcaniclastic Facies 1 - Phase 1 R4-45 390.64 390.7 XL Thin section Volcaniclastic Facies 1 - Phase 1 R4-45 411.7 411.99 Slab Transitional R4-45 411.77 411.79 Thin section Transitional R4-45 411.87 411.92 XL Thin section Transitional R4-45 423.26 423.56 Slab Volcaniclastic Facies 1 - Phase 1 and Coherent Subfacies 1 -CONTACT R4-45 423.34 423.39 XL Thin section Volcaniclastic Facies 1 - Phase 1 and Coherent Subfacies 1 -CONTACT R4-45 437.34 437.57 Slab Transitional R4-45 437.45 437.47 Thin section Transitional R4-45 437.49 437.51 Thin section Transitional R4-47 11.92 12.23 Slab Volcaniclastic Facies 1 - Phase 4 R4-47 12.0 12.02 Thin section Volcaniclastic Facies 1 - Phase 4 R4-48 33 33.2 Slab Volcaniclastic Facies 1 - Phase 4 and Coherent Subfacies 1 -CONTACT R65-23 236.3 236.4 Slab Volcaniclastic Facies 2 R65-23 236.5 236.6 Slab Volcaniclastic Facies 2 118 

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