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The petrology and petrogenesis of the Ren carbonatite sill and fenites, southeastern British Columbia,… Ya'acoby, Avee 2014

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The Petrology and Petrogenesis of the Ren Carbonatite Sill and Fenites, Southeastern British Columbia, Canada  by  Avee Ya'acoby   B.Sc. (Honours), University of British Columbia, 2011   A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF SCIENCE  in   The Faculty of Graduate and Postdoctoral Studies  (Geological Sciences)   THE UNIVERSITY OF BRITISH COLUMBIA   (Vancouver)  April 2014   © Avee Ya'acoby 2014   ii ABSTRACT  This thesis explores in detail the petrology and petrogenesis of the Ren carbonatite sill and associated fenites, located in the Monashee mountain range of British Columbia. The carbonatite body and fenites have been significantly deformed and metamorphosed, which has provided a unique petrological research opportunity, since only a few other carbonatite occurrences worldwide have been described from highly metamorphosed orogenic settings. This work aims to address knowledge gaps pertaining to the petrology, petrogenesis and economic exploration of comparable carbonatites in similar geotectonic settings.  The effects of amphibolite facies regional metamorphism and progressive deformation are apparent throughout the carbonatite body and adjacent fenites. Many of the rocks display remobilized, passively mixed components, boudinaged structures, and rheomorphic bands, as well as foliation and porphyroblastic textures. Recrystallization of minerals at peak metamorphic conditions (580–730 °C) is indicated primarily in undifferentiated calcite for which metamorphic solvus temperatures (~690 °C) were derived. Other minerals related to metamorphic recrystallization include rims of monazite-(Ce) around earlier fluorapatite, interstitial REE-silicates, and Ca- and Mg-amphibole forming late in the paragenetic sequence, after primary silicates.   Despite the metamorphic overprint and alteration, many petrological features pertaining to the igneous paragenetic record have been preserved, such as textures of primary minerals, compositional trends in phlogopite, clinopyroxene and amphibole, and whole-rock geochemistry of rock units. Solvus temperatures (~760 °C) of calcite, higher than peak metamorphic conditions, highlight preservation of the igneous component. The carbonatite is inferred to be a product of primitive mantle melts(s) that did not undergo significant fractionation processes, and intruded the crustal environment relatively undifferentiated. The whole-rock compositional trend of the fenites and partially fenitized host rocks suggests sodic-potassic alteration of the country rock during emplacement of the carbonatite sill.   The Nb-Ta and REE mineralizations of the Ren occurrence are both insufficient for economic extraction. Nevertheless, rare and new mineral candidates, (Fe,OH)-analogue to västmanlandite-(Ce) and (Mg)-analogue to biraite-(Ce), discovered in the deposit by the author, emphasize its petrological and mineralogical significance.   iii PREFACE  This thesis is original, unpublished, independent work by the author, Avee Ya’acoby, with assistance in data interpretation in Chapter 4 by Dr. Thomas Chudy, and Chapters 5 and 6 by Dr. Jan Cempírek.                               iv TABLE OF CONTENTS   Abstract .......................................................................................................................... ii Preface ............................................................................................................................ iii Table of Contents ........................................................................................................... iv List of Tables .................................................................................................................. ix List of Figures ................................................................................................................ xi Acknowledgments .......................................................................................................... xix 1 The petrology of carbonatites: An introductory survey ............................... 1 1.1 Introduction ........................................................................................................ 1 1.2 Definition and classification of carbonatites ...................................................... 1 1.3 The spatial and temporal distribution of carbonatites ........................................ 5 1.4 Field relations of carbonatites ............................................................................ 6 1.4.1 Carbonatite-igneous rock associations ............................................................... 6 1.4.2 Intrusive carbonatites ......................................................................................... 7 1.4.3 Mineralization, weathering and metamorphism ................................................. 13 1.5 Geochemical characteristics of carbonatites ...................................................... 13 1.6 Mineralogical and textural characteristics of carbonatites ................................. 20 1.7 Petrogenesis of carbonatites ............................................................................... 21 1.7.1 Modes of origin: An ongoing debate ................................................................. 21 1.8 Thesis objectives and scope ............................................................................... 29 1.8.1 Justification ........................................................................................................ 29 1.8.2 Outline of research techniques ........................................................................... 30 2 Mineral exploration and prior characterization of the Ren carbonatite .... 32 2.1 Introduction ........................................................................................................ 32 2.1.1 Location of the Ren carbonatite ......................................................................... 31 2.2 Mineral exploration of the Ren carbonatite ....................................................... 34     v  2.2.1 Historical work ................................................................................................... 34 2.2.2 Recent Work ...................................................................................................... 35 2.3 Prior characterization of the Ren carbonatite sill ............................................... 39 2.3.1 Lithology and mineralogy .................................................................................. 39 2.3.2 General distribution of REE’s, Nb and Ta ......................................................... 40 2.3.3 Geochronology ................................................................................................... 43 3 The geotectonic environment of the Ren carbonatite within the Frenchman Cap Dome ..................................................................................... 44 3.1 Introduction ........................................................................................................ 44 3.2 Monashee Complex ............................................................................................ 54 3.2.1 Basement gneissic rocks .................................................................................... 54 3.2.2 Autochthonous metasedimentary cover sequence ............................................. 55 3.3 Selkirk Allochthon ............................................................................................. 55 3.4 Alkaline and carbonatitic magmatism in the Frenchman Cap Dome area ......... 56 3.4.1 Neoproterozoic alkaline and carbonatitic magmatism ....................................... 56 3.4.2 Devonian to carboniferous alkaline and carbonatitic magmatism ..................... 57 3.5 Metamorphism of the Frenchman Cap Dome area ............................................ 57 4 Lithology and petrography of rock units ....................................................... 59 4.1 Overview ............................................................................................................ 59 4.2 Schematic profiles of lithological units across the Ren carbonatite sill and host rocks ........................................................................................................... 59 4.3 Metamorphic country rocks ............................................................................... 62 4.3.1 Quartzite ............................................................................................................. 63 4.3.2 Calcareous biotite-feldspar paragneiss ............................................................... 63 4.3.3 Biotite-feldspar-quartz (semipelitic) paragneiss (and schist) ............................. 66 4.3.4 Garnet-biotite amphibolite ................................................................................. 69 4.3.5 K-feldspar-quartz augen orthogneiss ................................................................. 69 4.4 Metafenites ......................................................................................................... 72 4.4.1 Fenitized calcareous biotite-feldspar paragneiss ................................................ 74  vi    4.4.2 Plagioclase-phlogopite fenite ............................................................................. 74 4.3.3 Phlogopite-richterite fenite ................................................................................ 77 4.4.4 Calcic-amphibole-K-feldspar-pyroxene fenite ................................................... 77 4.4.5 Richterite-K-feldspar fenite ............................................................................... 78 4.4.6 Albite fenite ........................................................................................................ 79 4.4.7 Contact and vein phlogopite fenites ................................................................... 84 4.5 Metacarbonatites ................................................................................................ 85 4.5.1 Dolomite carbonatite .......................................................................................... 88 4.5.2 Calcite carbonatite .............................................................................................. 88 4.5.3 Dolomite-calcite (and calcite-dolomite) carbonatite .......................................... 92 4.5.4 Richterite-rich, dolomite-norsethite-calcite carbonatite ..................................... 92 4.5.5 Winchite-rich, calcite-dolomite porphyroblastic carbonatite ............................. 96 4.5.6 Wallrock xenoliths and rheomorphic fabrics ..................................................... 99 4.6 Late pegmatites .................................................................................................. 105 4.6.1 Granitic pegmatites ............................................................................................ 106 4.6.2 Calcite-rich pegmatites ...................................................................................... 106 5 Mineralogy ........................................................................................................ 110 5.1 Methodology ...................................................................................................... 110 5.1.1 Analytical conditions for microprobe analysis of mineral compositions ......... 110 5.1.2 Calcite-dolomite geothermometry calculations ................................................. 112 5.2 Rock-forming minerals ...................................................................................... 110 5.2.1 Feldspar .............................................................................................................. 113 5.2.2 Mica ................................................................................................................... 115 5.2.3 Clinopyroxene .................................................................................................... 117 5.2.4 Amphibole .......................................................................................................... 120 5.2.5 Carbonates and calcite-dolomite geothermometry ............................................. 125 5.2.6 Barite .................................................................................................................. 134 5.3 Ore and accessory minerals ................................................................................ 136  vii  5.3.1 Monazite-(Ce) and fluorapatite .......................................................................... 136 5.3.2 Ferriallanite-(Ce) + chevkinite-(Ce) + fergusonite-(Nd) assemblage ................ 141 5.3.3 (Fe,OH)-analogue to västmanlandite-(Ce) + biraite-(Ce) [including (Mg)-analogue to biraite-(Ce)] assemblage ................................................................. 147 5.3.4 Ilmenite + niobian rutile + ferrocolumbite symplectite (± pyrochlore) assemblage ......................................................................................................... 153 5.3.5 Pyrochlore and bariopyrochlore ......................................................................... 160 5.3.6 Thorite ................................................................................................................ 166 5.3.7 Niobian titanite ................................................................................................... 168 5.3.8 Carbocernaite ..................................................................................................... 170 5.3.9 Other minerals .................................................................................................... 172 5.3.10 Chondrite-normalized REE compositional patterns in economic minerals ....... 172 5.3.11 Niobium and Tantalum contents in economic minerals ..................................... 174 5.4 Mineralogical evolution ..................................................................................... 175 6 Whole-rock geochemistry ................................................................................ 179 6.1 Introduction ........................................................................................................ 179 6.2 Methodology ...................................................................................................... 179 6.2.1 Analytical conditions for whole rock analysis of major and trace elements 179 6.3 Major and trace element contents ...................................................................... 182 6.4 Compositional differentiation of carbonatites and fenites ................................. 187 6.5 Chemical classification of Ren Carbonatites ..................................................... 187 6.6 Spatial variations of REE+Y and Ta-Nb contents in relation to the local stratigraphy ......................................................................................................... 191 6.7 Trace element compositions and chemical comparisons with other magnesiocarbonatite ........................................................................................... 193 7 Petrogenetic model ........................................................................................... 200 7.1 Petrogenesis and magmatic evolution ................................................................ 200  viii            7.2 Fenitization ......................................................................................................... 203  7.3 Late stage mineralization ................................................................................... 204 7.4 Effects of metamorphism ................................................................................... 205 8 Other occurrence of västmanlandite-(Ce) and biraite-(Ce) ......................... 207 8.1 Västmanlandite-(Ce) .......................................................................................... 207 8.2 Biraite-(Ce) ........................................................................................................ 208 9 Economic Implications .................................................................................... 210 10 Concluding remarks ........................................................................................ 212 References ....................................................................................................................... 214 Appendices  A The petrology of carbonatites: An introductory survey ............................... 248 B The geotectonic environment of the Ren carbonatite within the              Frenchman Cap Dome ..................................................................................... 310 C Microprobe analyses of minerals .................................................................... 355 D Whole rock geochemical analyses .................................................................. 420  ix LIST OF TABLES   1.1 Average chemical compositions of carbonatites. .............................................. 14 1.2 Average trace element ratios for carbonatites, mantle reservoirs and continental crust. ............................................................................................... 18 2.1 Summary of Ren carbonatite diamond drilling in 2011 (Gibson, 2012). ......... 37 4.1 Modal mineral assemblages (vol. %) of metamorphic country rocks. .............. 62 4.2 Modal mineral assemblages (vol. %) of metafenites. ....................................... 73 4.3 Modal mineral assemblages (vol. %) of metacarbonatites. .............................. 86 4.4 Modal mineral assemblages (vol. %) of pegmatites. ........................................ 105 5.1 Calculated temperatures inferred from calcites comprising exsolved dolomite. ........................................................................................................... 131 5.2 Integrated temperature values (°C) above and within syn-peak metamorphic thermal range. .................................................................................................... 131 5.3 Average and representative chemical compositions of monazite-(Ce). ............ 139 5.4 Average and representative chemical compositions of fluorapatite. ................ 140 5.5 Average and representative chemical compositions of ferriallanite-(Ce). ........ 144 5.6 Chemical compositions of chevkinite-(Ce). ...................................................... 145 5.7 Chemical composition of fergusonite-(Nd). .................................................... 146 5.8 Chemical composition (Fe,OH)-analogue to västmanlandite-(Ce). .................. 151 5.9 Chemical compositions of biraite-(Ce). ............................................................ 152 5.10 Chemical compositions of ilmenite and niobian rutile. .................................... 158 5.11 Chemical compositions of ferrocolumbite. ....................................................... 159 5.12 Chemical compositions of Type 1 (metamict) bariopyrochlore. ...................... 164 5.13 Chemical compositions of Type 2 (non-metamict) pyrochlores. ...................... 165 5.14 Chemical composition of thorite. ...................................................................... 167 5.15 Average and representative chemical compositions of niobian titanite. ........... 169 5.16 Chemical composition of carbocernaite. ........................................................... 171  x  6.1 Fusion ICP oxide detection limits. .................................................................... 180 6.2 Trace elements and detection limits. ................................................................. 181                              xi LIST OF FIGURES     1.1 Chemical classification scheme of carbonatites in terms of CaO–MgO–(FeO + MnO), reproduced from Gittins & Harmer (1997). ............................................. 3 1.2 Geological map of the Khibina massif, reproduced from Arzamastsev et al. (2008). .................................................................................................................. 9 1.3 Hypothetic scheme and explanation of formation of the Khibina massif, reproduced from Arzamastsev et al. (2008). ........................................................ 10 1.4 Idealized cross section of subvolcanic carbonatites and associated nephelinites, representative of such occurrences in East Africa (modified from Le Bas, 1987). ................................................................................................................... 12 1.5 Diagram of (Sr + Ba) vs. (REE + Y) in ppm for carbonatites, other carbonate-rich igneous rocks, sedimentary and metamorphic rocks, reproduced from Samoilov (1991). ................................................................................................. 17 1.6 Primitive mantle-normalized trace element plot of the 1993 lavas from Oldoinyo Lengai, and chondrite-normalized REE plot of the same lavas. .......... 19 1.7 Generalized diagram of the system peridotite (lherzoloite) CO2–H2O (C–H–O).  24 1.8 Univariant reaction boundaries for carbonated peridotite represented by the system CaO–MgO–SiO2–CO2. ............................................................................ 25 1.9 Generalized phase diagram projected from CO2 at 2.5 GPa, and illustrated in the composition tetrahedron CaO–(MgO + FeO)–(Na2O + K2O)–(SiO2 + Al2O3 + TiO2). ...................................................................................................... 26 1.10 Liquidus fields intersected by the join Na2CO3–CaMg(CO3)2, at 0.1 GPa. ........ 28 2.1 The Ren carbonatite and locally associated geological features near Ratchford Creek (Myoff Creek property), adapted from Gibson (2010). ............................ 33 2.2 Summary of Ren carbonatite diamond drilling in 2011 (Myoff Creek property), reproduced from Gibson (2012). ......................................................... 38 2.3 Boudinaged layer of amphibole-rich fenite within the Ren carbonatite. Image reproduced from Höy (1988). .............................................................................. 40  xii   2.4 Drill hole sections through the Ren carbonatite, showing total values of LREE’s (La + Ce + Pr + Nd), MREE’s (Sm + Eu + Gd + Tb + Dy + Ho) and HREE’s (Er + Tm + Yb + Lu) plus Y, Nb and Ta, in parts per million (ppm). .. 41 2.5 Carbonatite occurrences and their emplacement ages in the Canadian Cordillera. ............................................................................................................ 43 3.1 Tectonic belts and geological terranes of British Columbia. ............................... 46 3.2 Regional geology and Minfile mineral deposits of the Frenchman Cap Dome area. ...................................................................................................................... 47 3.3 Geological map and cross sections of the Mount Grace-Blais Creek areas. ....... 50 3.4 Geology of the Ratchford Creek-Perry River areas, adapted from Journeay (1986). .................................................................................................................. 51 4.1 Schematic sections across the Ren carbonatite sill (drill hole MC-11-04) .......... 60 4.2 Schematic sections across the Ren carbonatite sill (drill hole MC-11-08) .......... 61 4.3 Quartzite. Core sample and photomicrographs. ................................................... 64 4.4 Calcareous biotite-feldspar paragneiss. Core sample and photomicrographs. .... 65 4.5 Biotite-feldspar-quartz paragneiss.  Core sample and photomicrographs. .......... 67 4.6 Boudinaged structure in biotite-feldspar-quartz paragneiss. Core sample and photomicrograph. ................................................................................................. 68 4.7 Garnet-biotite amphibolite. Core sample and photomicrographs. ....................... 70 4.8 K-feldspar-quartz augen orthogneiss. Core and photomicrographs. ................... 71 4.9 K-feldspar-quartz augen orthogneiss. Photomicrograph showing albite exsolution lamella (perthite texture) in K-feldspar, myrmekite and very fine-grained, recrystallized quartz and feldspar grains at the centre of the image. ..... 72 4.10 Fenitized calcareous biotite-feldspar paragneiss.  Core sample and photomicrographs. ............................................................................................... 75 4.11 Plagioclase-phlogopite fenite. Core sample and photomicrographs. ................... 76 4.12 Phlogopite-richterite fenite. Core sample and photomicrographs........................ 80 4.13 Calcic amphibole-K-feldspar-pyroxene fenite. Core sample and photomicrographs. ............................................................................................... 81  xiii     4.14 Calcic amphibole- K-feldspar-pyroxene fenite. Photomicrographs. ................... 82 4.15 Richterite-K-feldspar fenite. Core sample and photomicrographs. ..................... 83 4.16 Contact and vein phlogopite fenite. Core sample and photomicrograph. ............ 84 4.17 Images of the Ren carbonatite in the field. .......................................................... 87 4.18 Dolomite carbonatite. Core sample and photomicrograph. ................................. 89 4.19 Calcite carbonatite. Core and field samples. ........................................................ 90 4.20 Calcite carbonatite. Photomicrographs. ............................................................... 91 4.21 Dolomite-calcite carbonatite. Core samples and photomicrograph. .................... 93 4.22 Dolomite-calcite carbonatite. Photomicrographs. ............................................... 94 4.23 Richterite-rich, norsethite-calcite carbonatite. Core sample and photomicrographs. ............................................................................................... 95 4.24 Winchite-rich, calcite-dolomite porphyroblastic carbonatite. Core sample and photomicrograph. ................................................................................................. 97 4.25 Winchite-rich, calcite-dolomite porphyroblastic carbonatite. Photomicrographs. ............................................................................................... 98 4.26 Exposed margins of the Ren carbonatite sill in the field. .................................... 100 4.27 Distorted carbonatite (buff) with rheomorphic fenite comprising feldspathic (white) and mafic (dark) ribbons. ........................................................................ 101 4.28 Carbonatites containing boudinaged wallrock xenoliths and rheomorphic fabrics. Core samples. .......................................................................................... 102 4.29 Carbonatite containing wallrock xenoliths. Photomicrographs. .......................... 103 4.30 Backscattered electron images showing replacement of phlogopite and richterite by clinopyroxene, Na-Fe amphibole and quartz. ................................. 104 4.31 Rehomorphic flow in a dolomite-calcite carbonatite comprising wallrock xenoliths. Photomicrograph. ................................................................................ 104 4.32 Granitic pegmatite. Core sample and photomicrograph. ..................................... 107 4.33 Granitic pegmatite. Photomicrographs. ............................................................... 108 4.34 Calcite-rich pegmatite. Core sample and photomicrograph. ............................... 109  xiv     5.1 Composition of feldspar in terms of albite (Na), orthoclase (K) and anorthite (Ca) components. ................................................................................................. 114 5.2 Chemical variations in K-feldspar, in terms of Na and Ba vs. K. ....................... 114 5.3 Richterite-K-feldspar fenite. Backscattered electron image showing porous rims of K-feldspar crystals replaced by metasomatic albite. ...............................  115 5.4 (A) Classification of biotite in terms of Mg/((Mg+Fe) vs. Al. (B) Classifications of biotite in terms of Al, Fe and Mg. (C) Chemical variations of biotite in terms of Mg vs. F. ................................................................................ 116 5.5 Compositional variations in clinopyroxenes in terms of end-member components. ......................................................................................................... 118 5.6 Dolomite-calcite carbonatite with xenoliths. Photomicrograph in transmitted, plane-polarized light showing secondary clinopyroxene and quartz after richterite. .............................................................................................................. 119 5.7 Photomicrographs of amphiboles in transmitted, cross-polarized light. ............. 121 5.8 Compositional variation diagrams for amphiboles. ............................................. 122 5.9 Classification diagrams of amphiboles after Leake et al. (1997). ....................... 123 5.10 Chemical variations in sodic, sodic-calcic and calcic amphiboles. ..................... 124 5.11 Chemical compositions of carbonates in terms of end-member components. .... 126 5.12 Photomicrographs of carbonates in transmitted, cross-polarized light. ............... 127 5.13 Dolomite-calcite carbonatite. Backscattered electron images showing dolomite exsolution ‘clouds’ (i.e., tiny specks), larger blebs and unidirectional lamella, in calcite. .............................................................................................................. 128 5.14 Backscattered electron images. (A) Carbonate vein in fenitized paragneiss. Strontianite exsolution from calcite. (B) Richterite-rich, dolomite-norsethite-calcite carbonatite. Exsolution of strontianite and carbocernaite from calcite. ... 129 5.15 Backscattered electron images of homogeneously exsolved dolomite in calcite, from dolomite-calcite carbonatite units. Also given are the calculated fraction values for the exsolved dolomite in the calcite grains (Table 5.1). .....................    132  xv     5.16 (A) Frequency distribution diagram of non-integrated temperatures inferred from the composition of analyzed calcite in 28 grains comprising homogenously exsolved dolomite (Table 5.1). (B) Frequency distribution diagram of temperatures from the integrated composition of analyzed homogenously exsolved dolomite (Table 5.1), from dolomite-calcite carbonatite samples only. ..................................................................................... 133 5.17 Chemical variations of Ba vs. Sr in barite. .......................................................... 134 5.18 Backscatter electron images of barite. ................................................................. 135 5.19 Calcareous biotite-feldspar paragneiss. Backscattered electron image of anhedral monazite-(Ce) (white) associated with and surrounding apatite (medium grey). Both minerals are enclosed by K-feldspar (dark grey). ............. 137 5.20 Dolomite-calcite carbonatite. Backscattered electron image showing a monazite-(Ce) ring enclosing fluorapatite. Both monazites, apatite are enclosed by carbonates. ...................................................................................................... 137 5.21 Phlogopite-richterite fenite. Backscattered electron image of anhedral monazite-(Ce) (white) in fluorapatite (medium grey). Both minerals are enclosed by richterite (dark grey). ....................................................................... 138 5.22 Dolomite-calcite carbonatite. Photomicrographs in transmitted plane-polarized light (left) and cross-polarized light (right) showing monazite-(Ce) with inclusions of columbite. ....................................................................................... 138 5.23 Dolomite-calcite carbonatite. Backscattered electron image of fluorapatite (light grey) displaying inclusions of barite (white blebs). The fluorapatite grain is enclosed by dolomite (darker grey). ................................................................. 139 5.24 Calcic amphibole-K-feldspar-pyroxene fenite. Photomicrograph in transmitted cross-polarized light (top) and a corresponding backscattered electron image (bottom) showing paragenetic ferriallanite-(Ce) + chevkinite-(Ce) + fergusonite-(Nd). .................................................................................................. 142 5.25 Chemical compositions of ferriallanite-(Ce) in terms of Al vs. Y+REE. ............ 143  xvi     5.26 Winchite-rich, calcite-dolomite porphyroblastic carbonatite. Photomicrograph in transmitted, plane-polarized light (top), and reflected light plus transmitted, cross-polarized light (bottom) showing REE-minerals (and rock forming minerals). .............................................................................................................    148 5.27 Winchite-rich, calcite-dolomite porphyroblastic carbonatite. Photomicrograph in transmitted, plane-polarized showing translucent brown (Fe,OH)-analogue to västmanlandite-(Ce) and (Mg)-analogue to biraite-(Ce) with inclusions of the former. ............................................................................................................ 149 5.28 Chemical compositions of Biraite-(Ce) in terms of Fe vs. Mg. ........................... 150 5.29 Photomicrographs in transmitted, plane-polarized light and reflected light. (A) Dolomite-calcite carbonatite. Early anhedral ilmenite enclosed in anhedral magnetite that is overgrown by anhedral pyrite. (B) Phlogopite-richterite fenite. Anhedral ilmenite enclosing subhedral pyrite, carbonates and richterite.  154 5.30 Dolomite-calcite carbonatite. Backscattered electron images. (A) Corresponding image to Figure 5.29A. (B) Enlarged ilmenite grain from the same sample with exsolved ferrocolumbite. ........................................................ 154 5.31 Richterite-rich, dolomite-norsethite-calcite carbonatite. Photomicrograph (A) and corresponding backscattered electron image (B) showing paragenetic association of ilmenite with other minerals. ........................................................ 155 5.32 Phlogopite-richterite fenite. Backscattered electron images showing paragenetic association of Nb-minerals. Note the brilliant symplectite texture of ferrocolumbite within ilmenite. ....................................................................... 156 5.33 Solid solution of ferrocolumbite with ilmenite, and ferrocolumbite with niobian rutile. ....................................................................................................... 157 5.34 Calcite carbonatite. Photomicrograph in transmitted, plane-polarized light showing anhedral pyrochlore grain (reddish brown) surrounded by carbonates (clear) and phlogopite (light brown). ................................................................... 161     xvii     5.35 Dolomite calcite carbonatite. Backscattered electron image showing metamict microscopic grain of pyrochlore with zones of bariopyrochlore. Also observed is porous hydrated Fe-oxide with thorite inclusions occurring away from the pyrochlore. ........................................................................................................... 161 5.36 Chemical variations of pyrochlore in terms of Nb, Ta and Ti. ............................ 162 5.37 Chemical variations in pyrochlore. ...................................................................... 163 5.38 Photomicrographs of niobian titanite and associated minerals, in transmitted, plane-polarized light. ........................................................................................... 168 5.39 Dolomite-calcite carbonatite. Backscattered electron image showing crystallographically oriented exsolution lamellae, blebs and microcrack infilling of carbocernaite (white) in calcite. ......................................................... 170 5.40 REE compositional patterns in prospective economic minerals. ......................... 173 5.41 Nb and Ta contents in prospective economic minerals. ...................................... 174 6.1 Harker diagrams for all lithological units. ........................................................... 185 6.2 Chemical variations diagrams in terms of CaO and P2O5 vs. REET+Y and REET+Y vs. Sr+Ba, for all lithological units. ...................................................... 186 6.3 AFM and K2O-Na2O-MgO diagrams for carbonatites and fenites. ..................... 189 6.4 (A) Ren carbonatites classified using the carbonatite classification diagram of Gittins and Harmer (1997). (B) Carbonatite occurrences in the Canadian Cordillera classified using the same diagram. .................................................... 190 6.5 Element variation diagrams for carbonatite and fenite units in relation to the local stratigraphy. ................................................................................................. 192 6.6 Primitive mantle-normalized trace element spidergram for Ren carbonatites and other magnesiocarbonatites for comparison. ................................................ 195 6.7 Primitive mantle-normalized rare earth element ratio spidergrams for Ren carbonatites, compared with other magnesiocarbonatites as in Figure 6.6. ......... 196 6.8 Primitive mantle-normalized rare earth element spidergram for xenolith-free Ren carbonatites, compared with other magnesiocarbonatites as in Figure 6.6. . 197  xviii                                6.9 Primitive mantle-normalized rare earth element spidergrams for Ren carbonatites comprising xenoliths or rheomorphic fenites, compared with other magnesiocarbonatites as in Figure 6.6. ................................................................ 198 6.10 Primitive mantle-normalized rare earth element spidergrams for Ren fenites, compared with magnesiocarbonatites as in Figure 6.6. ....................................... 199 7.1 Petrological models for the genesis of carbonatites. ............................................ 201  xix ACKNOWLEDGMENTS  I would like to express my gratitude to my supervisors, Lee Groat, for providing me with this project and his support, including in matters concerning academia-industry liaison, and, Jan Cempírek, for his invaluable guidance, coaching and encouragement, especially towards the end of my thesis. A very special thanks goes out to Thomas Chudy for his helpful advice and feedback in the course of this research, and to Mati Raudsepp and Craig Hart for their constructive comments at our committee meetings. I would like to sincerely thank Ravinder Sidhu for her assistance in collecting EPMA data at the University of Manitoba. I must also acknowledge Mati Raudsepp, Edith Czech, Elisabetta Pani and Jenny Lai for their help and support while collecting SEM data at UBC. Appreciation also goes out to Waterfront Mining Group and International Bethlehem Mining Corporation for providing access to their Myoff Creek property, logistical support, drill-cores and 1-year sponsorship for this thesis, in 2011. A thanks also goes to Gordon Gibson at International Bethlehem for providing preliminary consultation and information in 2011. I would also like to thank Gold Fields, the Society of Economic Geologists Foundation Inc., Geoscience BC and Endeavour Silver for the grants I received in 2011 and 2012. I would also like to thank Leo Millonig, Jim Evans, Andrea Dixon and the rest of the mineralogy group under Lee Groat’s supervision, for their help and support. Last but not least, I wish to thank my dear family and friends. I am especially grateful to my loving parents, Nily and Yoave Jacobovich (Ya’acoby) for encouraging me in all of my pursuits, believing in me, and being there for me when I need you the most. A special thanks also goes out to Andrew Laird, the Laird’s and Ariane Behrend for their encouragement and helpfulness during this experience.             1 CHAPTER 1 THE PETROLOGY OF CARBONATITES: AN INTRODUCTORY SURVEY   1.1 INTRODUCTION  This chapter provides general information pertaining to the petrology of carbonatites, on the basis of carbonatite research in the last decades. The complete version of this chapter can be found in Appendix A. It should be noted, however, that a comprehensive discussion addressing knowledge gaps and debate concerning the petrogenesis of carbonatites is beyond the scope of this thesis.     1.2 DEFINITION AND CLASSIFICATION OF CARBONATITES  The term carbonatite was first introduced by Brögger (1921) in reference to magmatic carbonate rocks from the Fen alkaline complex in Norway. According to the IUGS Subcommission on the Systematics of Igneous Rocks, carbonatites are igneous rocks containing more than 50% by volume of carbonate minerals (Streckeisen, 1980), with subordinate amounts of mafic silicate minerals, alkali feldspars, apatite and other minerals. These rocks can be categorized according to the dominant carbonate mineral. However, because carbonate species commonly display similar physical properties (i.e. colour, crystal shape, crystal habit, hardness, etc.) and may be complexly intergrown and fine-grained, they are often not resolved in the field, and thus different carbonatite types are often misidentified and incorrectly named (Woolley & Kempe, 1989). According to Woolley & Kempe (1989), a reliable identification and classification of carbonatites can be achieved either from whole-rock chemistry, or, preferably, from the modal carbonate mineralogy—if the carbonate species are properly identified by an electron microprobe. The following paragraphs describe  2 the classification scheme of carbonatites, for the purpose of this study, which is adapted from Gittins & Harmer (1997), as well as from Woolley (1982) and Woolley & Kempe (1989), and is also modified from Streckeisen (1980) and Kresten (1983), and is thus the most consistent system at present.   On the basis of their modal mineralogy, carbonatites (>50% carbonate minerals) can be classified into four distinct end-member classes or “genera”: 1. Calciocarbonatites. Carbonatites in which the dominant constituents are calcium carbonate species. 2. Magnesiocarbonatite. Carbonatites in which the dominant constituents are magnesium carbonate species. 3. Ferrocarbonatite. Carbonatites in which the dominant constituents are iron and manganese carbonate species. 4. Natrocarbonatites (alkali-rich carbonatites). Carbonatites in which the dominant constituents are sodium–potassium–calcium carbonate species.   Excluding natrocarbonatites (typically, <0.3 weight% SiO2 + Al2O2; >25 wt.% NaO2 + KO2; see Dawson et al., 1995a; Keller & Spettel, 1995; Simonetti et al., 1997), if the carbonate mineral constituents of a carbonatite have not been determined, the average molar proportions of CaO, MgO, and (FeO + MnO) should be used as the chemical classification criteria (see Gittins & Harmer, 1997; Fig. 1.1). According to these authors, calciocarbonatites are carbonatites in which the molar proportion of CaO/(CaO + MgO +FeO + MnO) is greater than 0.75. If this proportion is less than 0.75 and MgO/(FeO + MnO) > 1.0, the carbonatites are classified as magnesiocarbonatites. If CaO/(CaO + MgO +FeO + MnO) is less than 0.5 and MgO/(FeO + MnO) < 1.0, the rocks are ferrocarbonatites. In cases where the molar proportion CaO/(CaO + MgO +FeO + MnO) falls between 0.5 and 0.75, with MgO/(FeO + MnO) < 1.0, the rocks are designated as ferruginous calciocarbonatites. In the latter, Fe may be predominantly contained in oxides (i.e., magnetite, hematite), and also in Fe-rich silicates (e.g., biotite, phlogopite) or Na-Fe amphiboles (e.g., riebeckite, ferro-richterite). Gittins & Harmer (1997) note that only ferrous iron (Fe2+) is contained within carbonate minerals, and thus ferric iron (Fe3+) is excluded from this classification scheme.   3  More specifically, however, if the dominant carbonate species is identified, the naming calcite carbonatite, dolomite carbonatite, magnesite carbonatite, etc. is used to designate the carbonatite type or species (e.g., Woolley & Kempe, 1989). Hence this classification scheme implies that calcite carbonatite and aragonite carbonatite (rare) are types of calciocarbonatite; dolomite carbonatite and magnesite carbonatite are types of magnesiocarbonatite; and ankerite or siderite carbonatites are types of ferrocarbonatite.           Figure 1.1 Chemical classification scheme of carbonatites in terms of CaO–MgO–(FeO + MnO), reproduced from Gittins & Harmer (1997) with permission from Elsevier. Oxides in molar proportions. CCMF = CaO/(CaO + MgO + FeO + MnO). Also plotted are the positions of the principal carbonate phases: calcite (CaCO3), magnesite (MgCO3), siderite (FeCO3), dolomite [CaMg(CO3)2] and ferroan-dolomite to ankerite solid solutions [Ca(Mg,Fe)(CO3)2].      4   Once the carbonatite type is established, additional petrological specifications may be considered. If a carbonatite also contains a high proportion of silicate minerals (typically, >20 wt.% avg. SiO2; e.g., see Woolley & Kempe, 1989), the prefix silico is used. Thus dolomite silicocarbonatite and magnesio-silicocarbonatite are adequate terms (the former designates a silicate-rich carbonatite species; the latter designates a silicate-rich carbonatite class or subclass). However, the standalone designation ‘silicocarbonatites’ is avoided as it can be incorrectly interpreted as representing a fifth end-member class. It should therefore only be used as an accessory term alongside the already established carbonatite classes in the nomenclature. Certain silica-rich carbonatites are rheomorphic carbonatites. They are produced by remobilization and incorporation of wall rock material into pre-existing carbonatite fabrics, as opposed to the silicocarbonatites which crystallized from silica-rich melts in the mantle. Since carbonatites commonly contain a mixture of various carbonate phases, they are indicated by prefixes according to the established rules for quantitative composition of rocks at the 10%–50%–90% boundaries (see Streckeisen, 1980; p. 205 and Figure 4 therein). For example, the designation ankerite-dolomite carbonatite is used when the rock contains a secondary carbonate constituent (10%–50% avg.), in this case—ankerite. If three carbonate constituents (10%–50% avg.) are present, additional prefixes are used with the secondary carbonate prefix preceding the tertiary carbonate prefix, e.g. ankerite-calcite-dolomite carbonatite. In other cases, where a minor (5–10% avg.) secondary or tertiary constituent needs to be emphasized, the designation strontianite-bearing, etc. is used. If the constituent is less than 5% avg., the designation ±strontianite is appropriate. Other characteristic non-carbonate minerals may be indicated by prefixes, in order of decreasing modal abundances [e.g., winchite-rich (>10% avg.), pyrochlore-bearing (5–10% avg)], so that the proper designation of a carbonatite type is fully established, e.g. pyrochlore- and magnesite-bearing, dolomite-calcite silicocarbonatite. For all other igneous rocks (including pegmatites) containing only 10%–50% carbonate minerals, the qualification carbonatitic or calcitic or calcite-rich, etc. is used; and those with less than 10% avg. carbonate minerals are qualified as carbonate-bearing or calcite-bearing, etc.   Additionally, on the basis of igneous textures and nature of emplacement, it is essential to indicate whether a carbonatite is magmatic-intrusive, magmatic-extrusive, or  5 carbohydrothermal. Magmatic intrusive and extrusive carbonatites are segregation products of carbonatitic magmas and lavas. Carbohydrothermal carbonatites are indirect magmatic derivatives. They are predominately carbonate-rich veins, forming via precipitation of minerals at subsolidus temperatures from a mixed CO2–H2O fluid (Woolley & Kjarsgaard, 2008a). Furthermore, a very coarse-grained, typically late-stage, high-silica carbonatite vein or dike may be designated as a pegmatitic calcite silico-carbonatite, for example.  The terms melanocratic and leucocratic are rather ambiguous when describing carbonatites (as opposed to surrounding country rock, for example), and thus may not apply when describing these rocks (Streckeisn, 1980). Also, it should be noted that in many field studies carbonatites have been historically and conventionally subdivided, according to Kresten (1980), into ‘sövites’ (coarse-grained calcite carbonatites), ‘alvikites’ (medium- to fine-grained calcite carbonatites), ‘rauhaugites’ (coarse-grained dolomite–ankerite carbonatites), ‘beforsites’ (medium- to fine-grained dolomite–ankerite carbonatites), and ‘lengaites’ (alkali-rich carbonatites). This classification scheme may be convenient for designating carbonatites in the field, but is overly generalized and inadequate for modern petrological studies (Woolley & Kempe, 1989). Therefore, the use of these terms is not recommended, and they will not be applied to carbonatites with this work.  Lastly, high Sr, Ba and REE contents clearly differentiate metamorphosed carbonatites from metamorphosed carbonate rocks of sedimentary origin (e.g., Samoilov, 1991; see Section 1.5). Therefore, metamorphosed carbonatites cannot be qualified as marbles, whereas metamorphic terms such as metacarbonatite, schistous carbonatite or carbonatite schist, and gneissic (gneissose) carbonatite or carbonatite gneiss are applicable.    1.3 THE SPATIAL AND TEMPORAL DISTRIBUTION OF CARBONATITES    To date, there are 527 known carbonatite occurrences covering only a very small total global area (perhaps ~0.1 Mkm2; see Woolley, 1989; Woolley & Kjarsgaard, 2008a; 2008b). Carbonatites are found on all continents, including Antarctica, and the vast majority (~86%)  6 are concentrated in Precambrian cratons, including occurrences of Phanerozoic age (Woolley & Kjarsgaard 2008b). There are few carbonatites in oceanic areas, most of which lie close to continental margins (Woolley, 2009). Additionally, almost one third of carbonatite occurrences are described from Africa, many of which are intimately associated with the East African Rift system, and are younger than 200 Ma (Woolley, 1989; Woolley & Kjarsgaard, 2008a; 2008b). Field studies and isotopic data have shown that many geological provinces experienced repeated carbonatitic magmatism lasting 10 to >100 Ma (e.g., Woolley, 1989), and that many carbonatites are linked both spatially and temporally with mantle plumes and large igneous provinces (LIPs; Ernst & Bell, 2010).  Carbonatitic magmatism extends back to at least 3 Ga, and the oldest known carbonatite to date occurs in Greenland (Tupertalik, U–Pb age of 3.0 Ga; Bizzarro et al., 2002). Other Archean carbonatites include, Carb Lake and Lac Castignon in Canada, Mountain Pass in the USA, Phalaborwa in South Africa, Newania in India, and Silliinjarvi in Finland (e.g., Woolley, 1989; Bell & Simonetti, 2010). Nonetheless, carbonatites of Archean age are relatively uncommon, and the majority of known carbonatites worldwide are younger than 750 Ma (Woolley, 1989; Woolley & Bailey, 2012). The youngest and the only presently active carbonatite volcano on Earth is Oldoinyo Lengai in Tanzania, situated on the floor of the East African Rift Valley (Bell & Keller 1995).    1.4 FIELD RELATIONS OF CARBONATITES  1.4.1 Carbonatite-igneous rock associations   Nearly 90% of known carbonatite occurrences are intrusive and 10% are extrusive (see Woolley & Church, 2005), and both are commonly (but not always) associated with a wide variety of alkaline silicate rocks (Woolley & Kjarsgaard, 2008a). According to these authors, these associations are (in decreasing order of abundance): nephelinite–ijolite (~28%), phonolite–feldspathoidal syenite (~14%), trachyte–syenite (~8%), melilitite–melilitolite (~7%), lamprophyre (~5%), kimberlite (~1%) and basanite–alkali gabbro (~1%). However,  7 nearly 24% of carbonatites are not associated with silicate rocks, and 2.5% of carbonatites are associated with only minor fractions (<0.01%) of silicate rocks (Woolley & Kjarsgaard, 2008a). Additionally, the association of carbonatite with the olivinite, peridotite and pyroxenite suites characterizes 4.7% of carbonatite occurrences, and associations of carbonatites with these ultramafic rocks plus syenite, another 5% (Woolley & Kjarsgaard, 2008a). The accompanying ultramafic rocks are interpreted by these authors as cumulates, and therefore these rocks are not representative of the primary carbonatitic melt compositions.    1.4.2 Intrusive carbonatites    Intrusive carbonatites commonly occur in plutonic (or volcano-plutonic) complexes (e.g., Barker, 1989). Although it is difficult to make generalizations about intrusive carbonatitic complexes, the majority are small- to medium-sized (<50–500 km2) composite plutons emplaced in Precambrian basement rocks (e.g., Barker, 1989). According to Barker (1989) the carbonatites in these concentrically zoned bodies are found with coeval silica-undersaturated, mafic to ultramafic, and feldspathoidal rocks, such as nepheline syenites (e.g., ijolite, urtite, foyaite, etc.), melilitolites, picrites, and pyroxenites (Figs. 1.2, 1.3). Brecciation is widespread and the constituent rock units commonly form breccia pipes and plugs (diatremes), arcuate ring dikes, and cone sheets, which may or may not share a common centre (e.g., Barker, 1989; Arzamastsev et al., 2008 and references therein). Relative to the associated rock units, the carbonatites are typically volumetrically minor and emplaced late in the sequence (Fig. 1.3). They can take several forms, including plugs in the middle sections of a pluton (e.g., Araxá in Brazil, Isaa Filho et al., 1984), a sheet surrounding the older alkaline silicate rocks (e.g., Lueshe in the Democratic Republic of Congo; Maravic and Morteani, 1980), stocks with no clear structural relation to other intrusive units (e.g., Kovdor and Sokli complexes in the Kola Peninsula; Krasnova et al., 2004; Lee et al., 2004) or dikes cutting across the associated alkaline lithologies and the surrounding country rock (e.g., Kovdor complex; Krasnova et al., 2004). Arzamastsev et al. (2001) ascertained that the proportion of carbonatite components and the diversity of carbonatite types are highly  8 variable among plutonic complexes, depending on the extent of erosion. Relatively weakly eroded and better-preserved plutons generally show a higher proportion and greater modal and lithological diversity among the rocks exposed, whereas deeply eroded plutons largely contain ultramafic cumulate rocks, and therefore show the opposite trends (Arzamastsev et al., 2001).  The alkaline-carbonatite complexes are commonly surrounded by fenite aureoles. Fenite is an alkali-rich metasomatic rock, the product of fenitization (i.e., solid-state transformation of older wallrocks by penetration of alkaline hydrothermal solutions that originated from the carbonatitic or nephelinitic magma; Le Bas, 2008). The nature of fenitization varies among different carbonatite intrusions. Potassic fenites are commonly found at the margins of the younger carbonatite complexes, whereas sodic fenites are mostly observed surrounding the older intrusions (e.g., McKie, 1966; Heinrich, 1985). This spatiotemporal disparity is perhaps a product of the earlier depletion of Na relative to K in the evolving carbonatitic magma, resulting in Na-rich fenites at greater depths, which only become exposed in more progressively eroded, older complexes (e.g., Woolley, 1982; Rubie & Gunter, 1983; Le Bas, 2008).  In addition to composite plutons, other forms of intrusive carbonatites are small hypabyssal (subvolcanic) bodies (Fig. 1.4; also see Barker, 1989) including parallel and radial dike swarms (e.g., Maimecha-Kotui region, north Siberia), cone sheets (e.g., Alnö, Sweden), diatremes (e.g., Napak, east Uganda), sills (e.g., near Amba Dongar complex, India), and tabular bodies emplaced along faults (e.g., Pollen, Norway). Many shallow carbonatite intrusions occur with no associated igneous alkaline-silicate rocks (e.g., Abyan province, Yemen; Le Bas et al., 2004; Central Italy; Stoppa & Woolley, 1997). The evidence from hypabyssal intrusions indicate that carbonatites can be emplaced as liquids, nearly solid slurries, or gas–solid suspensions, and that carbonatitic magma can be passive, entering pre-existing gaps and cracks resulting from stress fields independent of the ascending magma, or can be intruded forcefully with vigorous release of volatiles (Barker, 1989).  9     Figure 1.2 Geological map of the Khibina massif, reproduced from Arzamastsev et al. (2008), with permission form Andrey A. Arzamastsev. Pr - Proterozoic, Ar - Archean.  10       Legend    1 - carbonatite     2 - pulaskite     3 - foyaite     4 - urtite–juvite–kalsilite, with apatite ore (dark)     5 - melteigite–ijolite–urtite layered complex     6 - Agpaitic nepheline syenites     7 - alkaline–ultrabasic rocks     8 - alkaline volcanics     9 - Precambrian basement     10 - olivine melanephelinite and picrite dikes  Figure 1.3 Hypothetic scheme and explanation of formation of the Khibina massif, reproduced from Arzamastsev et al. (2008) with permission from the author.   11 Figure 1.3: Explanation a) Caldera collapse originates at the contact between Late Archean tonalite, trondhjemite–granodiorite complex and Early Proterozoic Pechenga–Imandra–Varzuga paleo-riftogenic complex; development of melanephelinite and picrite dikes results in volcanic activity in the peripheral parts of the newly formed structure. b) Alkaline–ultrabasic melts are then intruded forming olivine pyroxenite, melilitolite, and olivine melteigite bodies.  c) Subsequent agpaitic (peralkaline) nepheline syenites (‘khibinites’) are emplaced along outer conical faults.  d) Further collapse of the caldera is associated with the development of a layered melteigite–ijolite–urtite complex in the central portion of the caldera.  e) The melteigite–ijolite–urtite complex is cut by a series of conical faults, along which a phosphate-bearing urtite–juvite–kalsilite (K-nepheline syenite) intrusion is emplaced.  f) A later series of conical faults develops in the central part of the melteigite–ijolite–urtite complex, followed by intrusion of foyaite melts.  g) Lastly, the pulaskite and carbonatite stocks intrude the foyaite.                   12  Figure 1.4 Idealized cross section of subvolcanic carbonatites and associated nephelinites, representative of such occurrences in East Africa (modified from Le Bas, 1987). Intrusion of silica undersaturated alkali magma (ijolite) is accompanied by early fenitization of wall rocks (light pink shaded). Eruption of magma to the surface forms a nephelinitic stratovolcano that subsequently experiences caldera collapse. The early ijolite is intruded by more evolved urtite (member of the ijolite series). Carbonatite magma (most commonly calcitic) is intruded into the ijolite and older country rocks, which results in doming of the roof rocks, plus fenitization and brecciation (green shaded). Later resurgence of magma locally breaches its fenite envelope, and a swarm of carbonatite cone sheets is then emplaced, followed by still later breccia-filled carbonatite dikes (pipes).     13 1.4.3 Mineralization, weathering and metamorphism    Notably a number of intrusive carbonatites contain large mineral deposits that are magmatically and hydrothermally enriched in high-field-strength elements (HFSE’s; i.e., Ti, Nb, Ta, Zr and Hf) rare earth elements (REE’s; lanthanides plus Y and Sc), Fe, P, and even Cu. Many of these elements occur in minerals such as baddeleyite, bastnäsite, perovskite, pyrochlore, monazite, magnetite, apatite, and chalcopyrite (Mariano, 1989; Petrov, 2004; Biondi, 2005), as well as platinum-group minerals (e.g., Rudashevsky et al., 2004) and, potentially, diamonds (Djuraev & Divaev, 1999; Shumilova, 2008). Hydrothermally altered carbonatites are particularly known to have REE-mineralization confined to veinlets and interstices (e.g., Mariano, 1989). Additionally, weathering of carbonatites produces laterites rich in REE- and Nb-bearing apatite (Mariano, 1989). Magmatic, hydrothermal and supergene mineralizations are all of economical importance as a source of phosphate for agricultural applications, as well as metals and special magnets for advanced technological applications (Tolstov & Tyan, 1999; Biondi, 2005).  In addition to alteration by hydrothermal solutions and weathering, carbonatites are subjected to metamorphism. Metamorphosed carbonatites commonly form sill-like or banded structures with preserved magmatic mineral assemblages and fenite aureoles (Barker, 1989). However, in metamorphosed plutonic carbonatites, erasure of primary calcite morphology is common (Zhabin, 1971; 1978). Remobilized carbonatites often contain boudinaged dikes of associated igneous rocks that underwent coeval deformation and metamorphism (Garson 1955; Gold & Vallée, 1969), or display grain comminution and foliation reminiscent of tectonically induced flow (Chakhmouradian et al., 2008; this thesis).    1.5 GEOCHEMICAL CHARACTERISTICS OF CARBONATITES    The geochemical composition of carbonatites is rather unusual compared with most other igneous rocks, and carbonatites can be easily separated from other carbonate-rich rocks, especially marbles, by their anomalous and distinctive trace element contents. Representative geochemical averages for carbonatites are given in Table 1.1.   14  Table 1.1 Average chemical compositions of carbonatites.  Calciocarbonatite Magnesiocarbonatite Ferrocarbonatite Natrocarbonatite  Avg. No. Avg. No. Avg. No. Avg. No. SiO2 Wt.% 2.72 116 3.63 50           4.7 57 0.16 19 TiO2 0.15 115 0.33 49 0.42 57 0.02 21 Al2O3 1.06 116 0.99 53 1.46 53 0.01 21 Fe2O3 2.25 97 2.41 48 7.44 53 0.05 21 FeO 1.01 91 3.93 47 5.28 50 0.23 21 MnO 0.52 119 0.96 54 1.65 57 0.38 23 MgO 1.80 122 15.06 54 6.05 58 0.38 23 CaO           49.1 118          30.1 53          32.8 58         14.0 24 Na2O 0.29 102 0.29 44 0.39 46          32.2 24 K2O 0.26 105 0.28 44 0.39 51            8.38    24 P2O5 2.10 119 1.90 51 1.97 54 0.85 24 H2O+ 0.76 78 1.20 36 1.25 35 0.56 13 CO2         36.6 104 36.8 49         30.7 53          31.6 13 BaO 0.34 74 0.64 32 3.25 38 1.66 24 SrO 0.86 66 0.69 29 0.88 34 1.42 24 F 0.29 31 0.31 21 0.45 20 2.50 13 Cl 0.08 8 0.07 1 0.02 3 3.40 7 S 0.41 23 0.35 12 0.96 12 nd  SO3 0.88 15 1.08 13 4.14 21 3.72 7 Li ppm           0.1 1 nd        10 1     270 11 Be         2 5         <5 1       12 1 nd  Sc          7 7         14 2       10 2 nd  V        80 31         89 9      191 16     116 19 Cr        13 10         55 9        62 8          <3.0 13 Co        11 12         17 9        26 7             1.8 11 Ni        18 11         33 5        26 7          1 13 Cu        24 25         27 12       16 14 nd  Zn      188 16       251 10     606 9          88 13 Ga        <5 1           5 1       12 1        <20 11 Rb        14 6         31 4 nd         178 13 Y          119 16         61 13      204 9            7 19 Zr          189 33       165 14      127 13            2 17 Nb    1204 43        569 18    1292 17           28 19 Mo nd           12 1         71 3         125 11 Ag nd             3 2           3 2 bd 11 Cs        20 1            1 1           1 1              6 11 Hf nd             3 1 nd         <0.4 11 Ta          5 1          21 6           1 1           0.3 11 W nd           10 1         20 1      49 11 Au nd                nd          12 2     18 11 Pb         56 6          89 7       217 4           22 14 Th         52 13          93 11       276 13        4 13 U           9 10          13 13           7 16      11 13 La        608 31        764 19      2666 15    545 17 Ce     1687 18      2183 14      5125 8    645 17 Pr      219 2        560 1        550 4      19 11 Nd      883 8        634 6      1618 4     102 11 Sm      130 2          45 6        128 4         8 11 Eu        39 2          12 6          34 4         2 11 Gd      105 2 nd         130 4         2 11 Tb         9 2             5 6          16 4            0.1 11 Dy       34 2 nd           52 4         2 11 Ho         6 2 nd             6 4            0.1 11 Er         4 1 nd           17 4            0.3 11 Tm         1 1 nd             2 4            0.3 11 Yb         5 10          10 10          16 4 bd 11 Lu         1 1 0.1 1      nd  0.01 11 nd - not determined; bd - below detection Data from Woolley & Kempe (1989), Dawson et al. (1995a), Keller & Spettel (1995) and Simonetti et al. (1997). Excluding natrocarbonatites, it should be noted that many of the data compiled by Woolley & Kempe (1989) came from carbonatite samples that may have been initially treated as representing  15 a carbonatite class using wt.% CaO, MgO, and (FeO + Fe2O3 + MnO) as the classification criteria. Consequently as shown with this table, ‘calciocarbonatite’ represents samples in which the proportion of CaO/(CaO + MgO +FeO + Fe2O3 + MnO) is greater than 80%. Both ‘Magnesiocarbonatite’ and ‘ferrocarbonaite’ represent samples in which this proportion is less than 80%, but samples belong to the former have MgO > (FeO + Fe2O3 + MnO) and those of the latter have MgO < (FeO + Fe2O3 + MnO). The most significant and unfavourable outcome of this classification is that the averages for ‘ferrocarbonatite’ may be based on data from ferruginous calciocarbonatites in addition to ferrocarbonatites (see section 1.2).     Silica (SiO2) content is usually less than 10–15 wt.%, but varies considerably depending on the type of carbonatite, and the nature and proportion of accessory minerals. It generally increases through the series calciocarbonatite–magnesiocarbonatite–ferrocarbonatite, and levels exceeding 30 wt.% have been reported in silica-rich (i.e., silicocarbonatite) varieties (Woolley & Kempe, 1989; Gittins et al., 2005; Wolley & Church, 2005).   The alumina (Al2O3) content shows little variation in the series calciocarbonatite–magnesiocarbonatite–ferrocarbonatite, but fluctuates considerably in the silicocarbonatite varieties (not shown) owing to variable amounts of amphibole-group minerals and mica (Woolley & Kempe, 1989).   Levels of titania (TiO2), iron oxide (ferric oxide, Fe2O3 and ferrous oxide, FeO), Mn, Ba, Co, Cr, and V also generally increase through the series calciocarbonatite–magnesiocarbonatite–ferrocarbonatite (Woolley & Kempe, 1989), but Ni shows a slight decrease in the ferrocarbonatites, which, according to these authors, is likely a statistical artefact due to the few available data. The iron in carbonatites (especially calciocarbonatites) is contained primarily in the mineral magnetite (Woolley & Kempe, 1989).   High Ba values are one of the chemical characteristics of carbonatites, and rocks rich in BaO are usually also rich in sulphite (SO3), indicating the presence of the mineral barite (Woolley & Kempe, 1989). Alkali (Na, K) contents are generally very low and show similar proportions in all intrusive carbonatites, but significantly higher levels are characteristic of natrocarbonatites (Woolley & Kempe, 1989; Dawson et al., 1995a, Keller & Spettel, 1995; Simonetti et al., 1997). Phosphorous, mostly held in apatite, is equally abundant on average, but highly variable among individual carbonatite occurrences (Woolley & Kempe, 1989). Largely contained in fluorapatite but also present in fluorite, F is much more abundant than  16 Cl in carbonatites; but both, as with P and other elements, show significant variation between individual occurrences (Woolley & Kempe, 1989).   Carbon dioxide (CO2) is abundant, but relatively low in ferrocarbonatites because CO2 is lower in FeCO3 than CaCO3, and the greater proportion of non-carbonate minerals in these rocks (Woolley & Kempe, 1989).   In general, Cu values are not particularly high in carbonatites, but one occurrence, Phalaborwa in South Africa, is anomalously rich in Cu for which it is famous (not included in the data shown in Table 1.1; Woolley & Kempe, 1989).   Relative to intrusive carbonatites (and essentially all other rock types), natrocarbonatite lavas are virtually devoid of the commonest rock-forming oxides, SiO2 and Al2O2, but contain extremely high abundances of Na2O and K2O. Carbon dioxide and SO3 levels are most similar to those of ferrocarbonatites, but P2O2 levels are the lowest among the other carbonatites. Natrocarbonatites are also rich in Sr, Ba, and the halogens, which are normally present only as minor constituent elements in most igneous rocks (Dawson, 1989).  In terms of trace elements, intrusive carbonatites are characteristically enriched in REE’s, particularly light REE’s (LREE; typically >500 ppm per element). Average total REE concentrations are 3600 ppm but can reach up to 42000 ppm in some carbonatites; these values are the highest among all rock types (Fig. 1.5; Woolley & Kempe 1989, Samoilov, 1991). Relative to primitive mantle, both intrusive and extrusive carbonatites are enriched in P, Ba, Th, U, Nb, Ta, REE, Y and Sr, but depleted in Cs, Rb, K, Zr, Hf and Ti (Woolley & Kempe, 1989; Mariano, 1989; Dawson, 1989). For natrocarbonatites, the Th/U ratio is ≤1, and the La/Sm ratio is >40, both unusual features for igneous rocks (Simonetti et al, 1997). Some typical trace element ratios for carbonatites are given in Table 1.2. On normalized trace element diagrams (Fig. 1.6), carbonatite lavas commonly display a negative slope indicative of their enrichment in light REE’s relative to heavy REE’s, which results in the highest light-REE/heavy-REE (La/Lu) ratios of any rocks (Cullers & Graf, 1984; Woolley & Kempe, 1989). Comparatively, the HFSE contents display extreme variability—even within the same petrographic unit. However, according to Chakhmouradian (2006), a “typical” HFSE behaviour is enrichment in HFSE5+ relative to HFSE4+, and depletion in heavy HSFE (Ta and Hf) relative to light HSFE (Nb and Zr). Both signatures are attributed to  17 metasomatism-driven fractionation processes during the generation and evolution of carbonate-rich magmas (Chakhmouradian, 2006).           Figure 1.5 Diagram of (Sr + Ba) vs. (REE + Y) in ppm for carbonatites, other carbonate-rich igneous rocks, sedimentary and metamorphic rocks, reproduced from Samoilov (1991), with permission from Elsevier.        18 Table 1.2 Average trace element ratios for carbonatites, mantle reservoirs and continental crust.  Calcio-carbonatite Magnesio-carbonatite Ferro- carbonatite Natro- carbonatite HIMU EM1 EM2 MORB PM BCC Rb/Nb 0.01 0.05*  6.33 0.3–0.4 0.9–1.2 0.6–0.9 4×10-4 0.91 6.1 Rb/Sr 0.012 0.05*  0.018 0.03 0.08 0.10e 0.012 0.03 0.15 Ba/Nb 2.49 10 22.4 65.6 5–6.5 11–18 7–11 4.83 9.0 57 Ba/La 4.93 7.46 7.46 50.3 7–9 13–17 8–11 4.40 9.6 22.8 Ba/Sr 0.41 0.97 3.85 1.44 0.47 0.96  128 0.33 1.4 Th/U 5.8 7.2 39 1.0 3.5 4.3  2.87 4.05 4.3 Th/Nb 0.04 0.16 0.21 0.08 0.08–0.10 0.10–0.12 0.11–0.16 0.064 0.117 0.70 Th/La 0.10 0.75 0.1 0.1 0.11–0.13 0.11–0.13 0.12–0.16 0.058 0.125 0.28 U/Pb 0.16 0.15 0.03 0.11 0.41 0.27  0.14 0.46 0.12 Nb/U 133 44 185 14.4 43–48 41–43 40 45.0 34 6.2 La/Nb 0.50 1.3 2.1 12 3–5 0.9–1.1 0.9–1.1 1.10 0.94 2.5 La/Sm 5* 17 21 45.1 5 5 5e 1.16 1.6 5.1 Ce/Pb 30 25 24 12.6 29–38 15–25 25–31 22.2 9.6 3.9 Zr/Nb 0.16 0.29 0.1 0.1 4–5 4–12 4.5–7.5 0.026 14.8 16.5 Sm/Nd 0.1* 0.07* 0.08* 0.078 0.21 0.20 0.20e 0.33 0.33 0.20 * - insufficient data; e - estimated value  HIMU: High-mu (238U/204Pb). Mantle reservoir characterized by a high U/Pb ratio. EM1: Enriched mantle 1. High Rb/Sr with low U/Pb and Sm/Nd ratios. EM2: Enriched mantle 2. High Rb/Sr (>EM1) and U/Pb, with low Sm/Nd ratios. MORB: Mid ocean ridge basalt. Low Rb/Sr and U/Pb with high Sm/Nd ratios. PM: Primitive mantle. BCC: Bulk continental crust.  Data from Natrocarbonatite of June, 1993 eruption of Oldoinyo Lengai with <0.3% silica, from Simmonetti et al. (1997). HIMU, EM1 and EM2 elemental ratios from Weaver (1991). PM values from Hofmann et al. (1986), Sun & McDonough (1989) and Weaver (1991). MORB values from Arevalo Jr. & McDonough (2010) and others therein. BCC, from Rudnick & Gao (2003).              19            A            B   Figure 1.6 (A) Primitive mantle-normalized trace element plot of the 1993 lavas from Oldoinyo Lengai. Note the peaks for Ba and Sr, and the depletions for Ta, Hf, and Ti. (B) Chondrite-normalized REE plot of the same lavas. Also plotted are average values for OIB (ocean island basalt). Both plots are reproduced from Simonetti et al. (1997) with permission from Elsevier. Primitive mantle values and representative analysis for OIB both taken from Sun & McDonough (1989).     20 1.6 MINERALOGICAL AND TEXTURAL CHARACTERISTICS OF CARBONATITES   Notable carbonates found in carbonatites are REE-rich phases such as bastnäsite (REE,Th)(F,OH)(CO3), burbankite (Na,Ca)3(Sr,Ba,Ce)3(CO3)5, parisite Ca(Ce,La)2(CO3)3F2 and ancylite Sr(La,Ce)(CO3)2(OH)•H2O subgroup minerals (e.g., Mariano, 1989; Zaitsev et al., 2008). Gregoryite Na2(CO3) and nyerereite Na2Ca(CO3)2 are the primary phases in natrocarbonatites at Oldoinyo Lengai, but these are readily subjected to alteration, forming a mixture of low-temperature subsolidus minerals such as calcite Ca(CO3), pirssonite Na2Ca(CO3)2 •2(H2O) and shortite Na2Ca2(CO3)3 (Keller, 1989; Zaitsev et al., 2008).   In addition to carbonates, more than 200 minerals have been described in carbonatites. The majority are species belonging to the pyrochlore, apatite and amphibole groups, many of which containing essential REE, HFSE, Sr and/or Ba (see Hogarth, 1989; Chakhmouradian & Williams, 2004; Wall & Zaitsev, 2004; Chakhmouradian, 2006; Reguir et al., 2012). According to these authors, a prominent pyrochlore-group mineral is uranpyrochlore (U,Ca,Ce)2(Nb, Ta)2O6(OH,F), which is commonly associated with pronounced positive Ce anomalies. Apatite species include fluorapatite Ca5(PO4)3F, hydroxylapatite Ca5(PO4)3(OH), carbonate-rich fluorapatite Ca5(PO4, CO3)3(F,O) and carbonate-rich hydroxylapatite Ca5(PO4, CO3)3(OH,O). These minerals are generally associated with increasing F and Sr during carbonatite development and high REE contents reaching 8.3 wt.% (Hogarth, 1989). Upon weathering of apatite species, Sr and light REEs are worn away; F increases; and the minerals become carbonated with 2–4 wt.% CO2 (Hogarth, 1989). Amphibole group minerals in carbonatites include early calcic species such as magnesiohastingsite NaCa2(Mg4Fe3+)Al2Si6O22(OH)2 and edenite NaCa2Mg5Si7AlO22(OH)2, as well as late alkalic species such as magnesioarfvedsonite Na3Mg4Fe3+(Si8O22)(OH)2, richterite Na2CaMgFe2+2(Si8O22)(OH)2, winchite [ ](CaNa)Mg4(Al,Fe3+)Si8O22)(OH)2 and magnesioriebeckite [ ]Na2[(Mg,Fe2+)3Fe3+2]Si8O22(OH)2 (e.g., Hogarth, 1989).   Apatite crystals from both carbonatites and fenites commonly show two types of zonation: normal and reverse. Normal zoning progresses from a magnesium- and calcium-rich core to an iron- and alkali-rich rim (e.g., Sarfartôq carbonatite, Greenland; Secher &  21 Larsen, 1980). According to these authors, not only does this chemical trend reflect increasing levels of Na and Fe in later amphiboles [i.e., Ca2+ + (Mg2+, Fe2+) ➝ Na+ + Fe3+], but also the progression of crystallization from reduction to oxidation. On the other hand, amphiboles consisting of iron-rich cores and magnesium-rich rims (e.g., carbonatite of west central Arkansas; McCormick & Heathcote, 1987) are regarded by these authors as having reversed zonation.   Carbonatites commonly contain other minerals, such as phlogopite KMg3(AlSi3O10)(F,OH)2, olivine (Mg,Fe)2(SiO4), monticellite CaMgSiO4, melilite (Ca,Na)2(Al,Mg,Fe2+)(Si,Al)2O7, magnetite Fe2+Fe3+2O4, complex Ti-Nb-Zr oxides, Ca-Ti-Zr garnets, , zircon ZrSiO4  and titanite CaTiSiO5 (e.g., Mariano, 1989; Chakhmouradian, 2006).   Carbonatites are texturally diverse and marked textural differences distinguish extrusive from intrusive rocks (e.g., Gittins et al., 2005). Intrusive carbonatites vary from essentially anchinomonomineralic varieties, in which coarse-grained and tabular carbonates are arranged in a mosaic texture, to rhythmically-layered carbonate varieties (Barker, 1989). In the latter arrangement, carbonates are developed interstitially with respect to grains of non-carbonate minerals, whereby the proportions of non-carbonates to the carbonates vary between the layers (Barker, 1989). Occasionally, intrusive carbonatites show flow structures formed by a subparallel orientation of xenoliths and elongated crystals of apatite, oxides and mafic silicates (e.g., Garson, 1955), and/or by a comb-like texture resulting from skeletal branching of calcite crystals (e.g, Katz and Keller, 1981).   1.7 PETROGENESIS OF CARBONATITES   1.7.1 Modes of origin: An ongoing debate  There has been a great debate on the origin of carbonatites for several decades. Initially, the two fundamental models for the petrogenesis of carbonatite were limestone assimilation (Shand, 1945), and metasomatic reworking of clinopyroxenites and other silicate rocks found in association with carbonatites (Kukharenko et al., 1965). However, the discovery of  22 carbonate-rich lavas (Knorring & du Bois, 1961; Dawson, 1962) and preliminary experimental work (Wyllie & Tuttle, 1960; 1962) demonstrated that carbonatites could precipitate from relatively low-temperature magmas. By 1990, further experimental and isotopic studies (e.g., Bailey, 1989; Wyllie, 1989) firmly established the igneous origin of carbonatites and their genesis in the upper mantle. Nevertheless, the mechanism by which carbonatitic magmas are generated remains a matter of ongoing concern to this date.  Significant evidence from phase equilibrium experiments show that carbonatites can be generated by primary mantle melting, and by differentiation of carbonated silicate melts, via liquid immiscibility and crystal fractionation (Figs. 1.7, 1.8, 1.9). Experiments have shown that carbonate-rich magmas can be produced by direct partial melting of a mantle comprising carbonate-bearing peridotite (lherzolite) at depths >70 km (Wylie & Huang, 1975), and that near-solidus melting of the carbonated peridotite can occur at 3 GPa with temperatures of 1250–1475 °C (Moore & Wood, 1998), and at 6 GPa with temperatures of 1380–1505 °C (Dalton & Presnall, 1997). Reactions that can occur within the mantle are   2Mg2SiO4 + CaMgSi2O6 + 2CO2 = 4MgSiO3 + CaMg(CO3)2   (1.1)     forsterite     diopside      fluid      enstatite     dolomite and  (at higher pressures)   CaMg(CO3)2 + 2MgSiO3 = 2MgCO3 + CaMgSi2O6     (1.2)   dolomite      enstatite      magnesite   diopside  producing dolomite and magnesite (respectively) as the stable carbonate phases within lherzolite (Fig. 1.6; Moore & Wood, 1998). Thus, the composition of carbonatitic melts, coexisting in equilibrium with lherzolite mineral assemblages, at pressures from 2 GPa to at least 7 GPa, will invariably be dolomitic with Ca/(Ca+Mg) ratios of 0.3–0.7 and silica content of 4–7.5 wt.% (Dalton & Presnall, 1997; Moore & Wood, 1998). Dalton & Presnall (1997) observes that liquids in equilibrium with a model lherzolite containing 0.15 wt.% CO2 at 6 GPa have a systematic compositional variation with increasing temperatures, and indicate that rock compositions ranging from near-solidus dolomite carbonatites through  23 ultramafic lamprophyre or kimberlite were produced in a continuum over the melting range 0–1%.  The main effect of rising temperatures (above 750 °C) on carbonate liquids derived from the mantle is increasing SiO2 content and decreasing CO2 content. Therefore at higher temperatures, silicate-rich melts are produced rather than carbonatitic. Remarkably, at over 50 °C heating-interval and lower pressure (2.5–3 GPa decreasing to <1.0 GPa ), an abrupt compositional transition (immiscibility) occurs from carbonatite to carbonated silicate liquid (Moore & Wood, 1998; Wyllie & Lee, 1998), which provides significant insights into the production of both carbonatites and the frequently associated carbon-rich silicate rocks (Fig. 1.7). In that context, the immiscibility between silicate and carbonate liquids at crustal pressure (<1.0 GPa) has been the focus of several experimental studies. Most important are 0.2 GPa experiments on the sub-liquidus phase assemblages of an evolved carbonated high-CO2 nephelinite showing two-liquid and melilite phase assemblages, and, thus, signifying a potential genetic association between calciocarbonatites and coexisting melilite nephelinites (Kjarsgaard, 1998). Also, although arguments against the generation of immiscible carbonate and silicate magmas at mantle depths have been proposed by a few petrologists (e.g., Wyllie & Lee, 1998), a wide two-liquid field can exist at mantle pressures (2.5 GPa), implying that immiscibility is not limited to shallow levels (Brooker, 1998).            24  Figure 1.7 Generalized diagram of the system peridotite (lherzoloite) CO2–H2O (C–H–O). Note the position of the mantle ledge at a depth of about 70 km. Melts are generated between A and B where the craton geotherm (dashed line) intersects the mantle solidus (solid line). The solidus will shift to higher temperatures with reduced oxygen fugacity (Taylor & Green, 1988). If CO2 is well in excess of H2O, melts at relatively low temperatures (dashed arrow) will intersect the mantle ledge producing metasomatism and potentially explosive activity. The phase relationships for this system, involving phlogopite (Phlog), dolomite (Do), hornblende (Hbl), magnesite (Mgs) and vapour (V), provide the framework for upper mantle petrology. Reproduced and modified from Wyllie et al. (1990), and references therein, with permission from Elsevier.      25               Figure 1.8 Univariant reaction boundaries for carbonated peridotite represented by the system CaO–MgO–SiO2–CO2. Q is the invariant point (intersection of decarbonation reactions which denotes a prominent ledge in the solidus) involving forsterite (Fo), orthopyroxene (Opx), clinopyroxene (Cpx), dolomite/magnesian calcite (Do/Cc), magnesite (Mc), liquid (L) and vapour (V). Curve A represents decarbonation reaction of dolomite–lherzolite, Do + Opx = Cpx + Fo +V. Curves B–B’, C, E, and F represent respectively vapour-saturates solidi of CO2–lherzoloite, dolomite–harzburgite, dolomite–websterite, and (dolomite–magnesian calcite)–wehrlite. Curve D signifies vapour-absent solidus for dolomite–lherzolite, and G, conversion reaction between dolomite– and magnesite–(lherzolite/websterite), Mc + Cpx = Do + Opx (Fo can be present as non-reacting phase). Reproduced from Wyllie & Lee (1998) and Lee & Wyllie (2000), with permission from Springer.     26   Figure 1.9 Generalized phase diagram projected from CO2 at 2.5 GPa, and illustrated in the composition tetrahedron CaO–(MgO + FeO)–(Na2O + K2O)–(SiO2 + Al2O3 + TiO2), showing dark- and light-shaded liquidus surfaces for the silicate–carbonate field boundary and liquid miscibility gap. The silicate–carbonate field boundary separates liquidus volumes for silicates (on the left) from liquidus volumes for carbonates (on the right). There is also a small area above the dark surface for the silicate–oxide field boundary. Contours indicate wt.% (MgO + FeO) of the two surfaces. The small stippled volumes (groups 1–4) demarcate the experimentally measured liquid compositions from carbonated peridotites. Selected rock compositions are also shown, situated within the silicate volume. These rocks contain low alkalis and magma, and over ~25% (MgO + FeO) (recalculated CO2 free), as shown by their projections down onto the base of the tetrahedron. These rock compositions are well removed from both the silicate–carbonate liquidus boundary and the immiscibility volume. NEPH: magnesian nephelinite field. Reproduced from Wyllie & Lee (1998) with permission from Oxford University Press.       27  Furthermore, assessments of carbonate-silicate melt differentiation in a number of papers (e.g., Lee & Wyllie, 1998; Wyllie & Lee, 1998; Lee et al., 2000) suggest that one potential residual liquid path involves reaching the silicate-carbonate liquidus field boundary, where the conditions for the precipitation of silicate and Ca-rich carbonate mineral phases can result in the formation of calciocarbonatites. The latter, however, cannot equilibrate with harzburgite or lherzolite and must evolve (i.e., Q on Fig. 1.7) from a primary mantle melt by fractional crystallization or wallrock reaction (Moore and Wood, 1998), such as     5MgSiO3 + 2CaMg(CO3)2 = 3Mg2SiO4 + CaMgSi2O6 + CaCO3 + 3CO2.  (1.3)                     enstatite   dolomitic melt     forsterite   diopside    Ca-rich melt    fluid  Because carbonatitic magmas display extremely low viscosities, early liquidus precipitation of calcite from dolomitic melts can occur over a wide temperature range (Fig. 1.8) via kinetic or gravity-induced differentiation of cumulates (Minarik and Watson, 1995). Calciocarbonatite forming as cumulates may therefore account for the majority of carbonatite occurrences (Gittins, 1989), even if the parental melts derived from carbonated lherzolite at high pressures are dolomitic in composition (e.g., Bailey, 1989; Dalton & Presnall, 1997).   There is no reason, however, to assume that direct partial melting of carbonated peridotitic mantle produces only one type the of parental melt composition. Magmatic trace element signatures (i.e., high enrichments of light REE’s and Sr) in Ca-rich carbonates from mantle-derived xenoliths point to the existence of primary calciocarbonatitic melts originating in the mantle (e.g., Gittins, 1989; Bailey, 1993). Figure 1.9 does not support formation of primary calciocarbonatitic melts under mantle conditions by liquid immiscibility, as there is a miscibility gap between the carbonate and silicate liquidi.  According to Gittins et al. (2005), this gap impedes the progression of carbonate-rich melts through the silicate-carbonate liquidus field boundary, so that CaCO3 levels in the exsolved carbonatitic melts are maintained at <85 wt.%, not sufficiently high to be classified as calciocarbonatitic. Similarly, according to Wyllie & Lee (1998), kimberlitic and melititic melt compositions shown on Figure 1.9 are well removed from both the silicate-carbonate field boundary and the immiscibility volume, thus indicating that they were not exsolved from primary silicate melts by liquid immiscibility.  28     Figure 1.10 Liquidus fields intersected by the join Na2CO3–CaMg(CO3)2, at 0.1 GPa where Do=dolomite, Cc=calcite, Ny=nyerereite, L=liquid. Calcite is the liquidus phase beginning from a peritectic at 810 °C in dolomitic liquids with <23 wt.% Na2CO3. At this temperature and under equilibrium conditions, calcite reacts with the remaining liquid to generate dolomite, which remains the liquidus phase with further cooling. Dolomitic liquids can therefore crystallize calcite, with the latter settling out of the liquid as cumulates or a crystal mush (thereby generating disequilibrium conditions), and producing calciocarbonatite. Reproduced from Gittins et al. (2005) with permission from Elsevier.          29  Regardless of the exact igneous process by which carbonatites are produced, the parental calcitic or dolomitic carbonatite melts generally contain >5 wt.% SiO2 in solution (e.g., Lee & Wyllie, 2000). Most carbonatites contain silicate phases, including olivine, pyroxene, mica, amphibole and feldspathoids, as described earlier, indicating that sufficient silica must be present in the parental liquids to precipitate such silicate phases. Cooper & Reid (1998) observe that at Dicker Willem (Namibia), an Eocene age subvolcanic intrusion, the parental melt was a nepheline-bearing calciocarbonatite with between 10–20 wt.% SiO2. The fine-to-medium grained calcite carbonatites and late-stage ferroan dolomite carbonatites are interpreted to have been produced by fractionation of sodic diopside, melanite, nepheline, magnetite, pyrochlore, apatite and Sr-calcite (Cooper & Reid, 1998). Additionally, silicate-bearing natrocarbonatites erupted from Oldoinyo Lengai have been used to model fractional crystallization of nepheline + sodic pyroxene + melanite, resulting in the production of silicate-free natrocarbonatites (Petibon et al., 1998). Noticeably, although single and multiple carbonated parental melts can be found within individual complexes (e.g., Hornig-Kjarsgaard, 1998), the role of silica activity in an evolving carbonatitic liquid is an important feature of carbonatite petrogenesis.   1.8 THESIS OBJECTIVES AND SCOPE  1.8.1 Justification   A number of outstanding problems pertaining to the distribution, petrology and origin of carbonatites and associated alkaline rocks worldwide are discussed above (and more extensively in Appendix A). Perhaps one of the most fascinating areas of carbonatite research involves the number of unusual metamorphosed carbonatite occurrences within orogenic settings, such as those discovered in the Canadian Cordillera (e.g., Pell & Höy, 1989). Only a few studies to date address the petrology and mineralogy of carbonatites within high-grade metamorphosed orogenic settings (e.g., Currie et al., 1992; Moecher et al., 1997; Chudy, 2013) and relatively limited work has been done to understand in detail their origin and evolution. The main challenge for studying the petrogenesis of high-grade  30 metamorphosed carbonatites (and other igneous rocks) stems from resetting of the magmatic isotopic systems (e.g., Millonig et al., 2013), and offsetting of the igneous paragenetic record by the metamorphic overprint and deformation.    Given these circumstances, this thesis examines the petrology of the high-grade metamorphosed Ren carbonatite in the Canadian Cordillera. The main objectives are: (1) to infer and constrain the igneous paragenetic record as opposed to the metamorphic; (2) establish a petrogenetic model on the basis of petrographical and mineralogical record, and geochemical trends; and (3) evaluate the influence of high-grade metamorphism, in the context of carbonatite evolution and economic potential. Addressing these objectives will therefore allow for a deeper understanding of what makes carbonatites in high-grade metamorphosed orogenic settings unique, both petrologically and economically.     1.8.2 Outline of research techniques   The research techniques used to study the petrology and origin of the Ren carbonatite include:  1.  Exploratory fieldwork and first ever diamond drilling of the Ren carbonatite, plus extraction of samples, core logging, and gathering of field data. 2.  Acquisition of a large whole-rock geochemical data set from extensive sections across the carbonatite body and the associated rock units.  3.  Optical petrography and mineralogical techniques to obtain detailed descriptions of mineral assemblages, abundances, textures and paragenesis. 4.  Scanning electron microscope (SEM) and electron-probe microanalyses (EPMA) to examine the chemistry and microtextures of major and accessory minerals. 5.  Processing of the analytical data, including: calculation of mineral formulae from the major-element compositions obtained by EPMA; construction of element distribution diagrams; geochemical relationships between elements; and calcite-dolomite geothermometry. 6.  Petrogenetic modelling, including compilation of the relevant published data and identification of petrologically significant major and trace-element characteristics,  31 and interpretation of these data in the context of carbonatite petrogenesis, metamorphism and evolution.                     32 CHAPTER 2 MINERAL EXPLORATION AND PRIOR CHARACTERIZATION OF THE REN CARBONATITE   2.1 INTRODUCTION    2.1.1 Location of the Ren carbonatite  The Ren carbonatite, named after the historical claims in southeastern British Columbia on which it occurs, is also known as the Ratchford Creek carbonatite (e.g., Pell, 1987). The carbonatite is located in the Monashee Mountain range, 45 km to the northwest of Revelstoke. Rock face exposures on the southern slopes of Ratchford Creek (UTM coordinates: NAD 83, zone 11, 378658 E/ 5691116 N) reveal a semi-concordant carbonatite sill with fenitized margins 3 km long and 20–150 metres wide, striking at 330–335° and dipping at 25–45° to the southwest (Fig. 2.1). The unit is variably enriched in REE’s and HFSE’s (primarily Nb) at generally low-to-medium grades. Mapping (McMillan, 1973; Höy, 1979; Journey, 1982), augmented by recent work (Gruenwald, 2011; Millonig et al., 2012), indicates that the Ren carbonatite comprises additional but discontinuous carbonatite segments approximately 7 km to the south-southeast, in the vicinity of Chilly Lake (see Figs 3.2, 3.4 in Chapter 3). The carbonatite may further extend several km southerly in the alpine and subalpine terrains, west of Perry River, based on airborne field observations by this author. This carbonatite occurrence therefore encompasses a total large unknown tonnage of mostly unknown REE and HFSE grades, which warrants considerable exploration. A summary report on the Ren carbonatite-hosted deposit appears in British Columbia Minfile number: 082M 199 (Meredith-Jones, 2010).     33            376,000E               377,000E              378,000E               379,000E                380,000E                    5,692,000N            5,691,000N        5,690,000N                5,689,000N           5,688,000N  Figure 2.1 The Ren carbonatite and locally associated structural features near Ratchford Creek (Myoff Creek property), adapted from Gibson (2010), with permission from the author.       34 2.2 MINERAL EXPLORATION OF THE REN CARBONATITE   2.2.1 Historical work    Mineral exploration activities in the Ratchford Creek area began in the early 1980s, which led to the discovery of the Ren carbonatite (Pilcher, 1983). In 1983 Duval International Corporation (see Pilcher, 1983) carried out geological mapping, prospecting and sampling over a three-km strike-length of the Ren carbonatite within their claim area. Duval’s exploration program that year produced 469 soil, 72 rock and 15 stream sediment samples. Pilcher (1983) stated that the analytical results were indicative of several highly chemically anomalous areas within the carbonatite, and that the rock samples gave maximum values of 2,400 ppm Nb, 72 ppm Ta, 9,890 ppm Ce, 6,965 ppm La, and 330 ppm Nd. Also mentioned were 21 rock samples analyzed for uranium and thorium, which gave respective averages of 0.00013% and 0.0022%, well below the provincial moratorium thresholds (0.05% U, 0.15% Th; Pilcher, 1983).   In 1988 Teck Explorations Limited (see Gudmund & Betmanis, 1988) conducted stream silt sampling (89 samples) from four drainages, 17.85 line-km of magnetometer surveying, 15.35 line-km of spectrometer-scintillometer surveying and 749 metres of trenching. The trenches were mapped and subsequently sampled from 282 rock channels. The best Nb values were obtained from trench ATR–2, at 0.19% over a width of 55 metres. Carbonatite that was excavated in all trenches averaged 0.13% Nb. Cerium and La were all significantly anomalous, but the values were not plotted. The rock samples were not analyzed for Ta or Nd.   In 2001 Cross Lake Minerals Ltd. (see Miller-Tait, 2001) completed 346 metres of trenching and obtained 73 rock channel samples. Geological mapping and prospecting were subsequently carried out over a 1,500-hectare area, and 15 samples of intrusive Ren carbonatite and 21 samples of nearby extrusive Mount Grace carbonatite were collected and analyzed. According to Miller-Tait’s (2001) report, the intrusive carbonatite has a relatively uniform distribution of Ta, elevated Nb in the central core, and elevated REEs on the west side or hanging wall. It was also noted that where the carbonatite is widest, Ta, Nb, and REE values are highest. In contrast, the extrusive carbonatite was described as “virtually barren of  35 minerals of economic importance” (Miller-Tait, 2001). In an attempt to further investigate the highest Ta value (123 ppm) returned by the mapping and rock sampling (Miller-Tait, 2001), a 35-metre continuous rock channel was sawn in natural exposures of the carbonatite north of trench MT-01-1, where it crosses a fast-flowing creek, on the steep southern slopes of Ratchford Creek. Seven 5-metre samples were collected from that channel for analysis, and the analytical results showed similar values to those obtained by trenching, emphasizing relatively consistent grades in the intrusive carbonatite (Miller-Tait, 2001).   Despite considerable exploration of the Ren carbonatite in the years 1983–2001, only limited petrographical and mineralogical work has been carried out (e.g., Höy, 1988; Miller-Tait, 2001), and thus the mode of occurrence of the REE minerals has not been determined. Similarly, the minerals containing the niobium and tantalum were not positively identified, and the only conclusion made was that these two elements are occurring in iron and iron-titanium oxides (Miller-Tait, 2001).   2.2.2 Recent work    In 2010, structural features associated with Ren carbonatite were mapped in detail by geologist Gordon Gibson (Gibson, 2010; Fig. 2.1). The northernmost trench (MT-01-1) of previous exploration programs by Duval, Teck and Cross Lake was re-visited and sampled in detail by personnel of International Bethlehem Corporation (Myoff Creek property; Gibson, 2010). A total of 7 rock channel and grab samples were taken and submitted for 38 element fusion ICP-MS and whole rock analyses. In general the weighted averages of Nb, Ta, Ce, La, and Nd (when converted to their oxides) are comparable with the results from previous sampling programs (Gibson, 2010). In contrast to Miller-Tait’s (2001) report, the 2010 analytical results show generally erratic distribution of the elements of economic interest in the host carbonatite. These results confirm enrichment of Nb, Ta, and to some extent Ce, La and Nd, in the central and hanging wall portions of the carbonatite across the trench. Gibson (2010) indicated that Sample I021217 (2.96 kg) returned 904 ppm Nd, which, up to that year, is believed to be the highest neodymium value recorded on International Bethlehem’s Myoff Creek property.   36  Preliminary exploration work was also carried out in 2010 in the vicinity of Chilly Lake (Chilly Lake property) by geologist and property owner, W. Gruenwald (see Gruenwald, 2011). This work consisted of several rock, stream and silt sample analyses, re-analysis of two historical silt samples, and a limited petrographical description from one thin section. According to Gruenwald (2011), both of the re-analyzed samples returned significantly anomalous REE concentrations, with a maximum value of 27.50% for the total REE oxides (TREO). The rest of the samples gave generally weak to moderate REE and Nb-Ta contents. The petrographical report provides inconclusive results regarding the species of carbonate and REE-bearing mineral phases (Gruenwald, 2011).      In August–September 2011, International Bethlehem personnel, including the author (as part of undertaking the project as his thesis topic), conducted exploration and first ever diamond drilling of the Ren carbonatite (see also Gibson, 2012). International Bethlehem’s primary objective of the core drilling was to test the grade and thickness of the carbonatite at depths well below the zone of surface weathering. The Company completed a total of 1,134 metres of NQ core from 8 holes at 6 locations, over a 1-km strike length (Table 2.1; Fig. 2.2). The carbonatite intersection range in true thickness was 31–95 metres, and core recovery of the carbonatite was close to 100%. The element fusion Inductively Coupled Plasma Emission Mass Spectrometry (ICP-MS) and whole-rock analytical results from the drilling program are used in this work.  Other fieldwork pertaining to this thesis consisted mostly of core logging in conjunction with geologist Mr. Gordon Gibson at International Bethlehem, in the spring and summer months of 2012. In late 2012, work and resources pertaining to the Ren carbonatite project were discontinued by International Bethlehem, but the author continued investigating the carbonatite for his M.Sc. thesis.          37 Table 2.1 Summary of Ren carbonatite diamond drilling in 2011* (Gibson, 2012).               *Myoff Creek property           Drill Hole No.  Elevation (metres) Azimuth Dip (degress) Depth (metres) MC11-01 1390 073 -55 93.27 MC11-02 1390  vertical 96.93 MC11-03 1470 073 -55 142.34 MC11-04 1490 073 -55 151.18 MC11-05 1500 073 -55 138.99 MC11-06 1490 073 -55 181.97 MC-11-07 1490  vertical 185.32 MC-11-08 1510 073 -55 148.44  38  Figure 2.2 Summary of Ren carbonatite diamond drilling in 2011 (Myoff Creek property), reproduced from Gibson (2012), with permission from the author.    39 2.3 PRIOR CHARACTERIZATION OF THE REN CARBONATITE SILL   2.3.1 Lithology and Mineralogy    Prior to this project, only limited lithological and mineralogical information was available with respect to the Ren carbonatite. Field observations (Höy, 1988; this author) indicated that the Ren is a massive to well-layered sill. The carbonatite displays orange-brown weathering, and has dark mafic fenite margins and zones within it (e.g., Fig. 2.3). The zone of fenitization is intense, extending 10’s of metres into the footwall and up to several 100’s of metres into the hanging wall. The fenite comprises thin discontinuous carbonatite lenses, minor quartzite layers and remnant paragneiss layers that are cut by biotite/phlogopite-amphibole-carbonate veins (Höy, 1988). Limited petrographic studies (Höy, 1988; Miller-Tait, 2001), resulting from mineral exploration work, gave 60–80% calcite, 10–30% apatite, accessory biotite, amphibole, pyroxene and titanite, with minor pyrrhotite, pyrite, chalcopyrite, magnetite, ilmenite and sphalerite. A magnesiocarbonatite component has been also noted (Höy, 1988), which required further investigation and confirmation by this thesis project.    Two samples from the Ren carbonatite, REN-075-1 (51°20′40.12″ N/118°43′54.33″ W; i.e., near Ratchford Creek) and REN-079-3 (51°18′18.85″ N/118°43′49.45″ W; i.e., in the vicinity of Chilly Lake) were analyzed as part of a recent work that investigates geochronologies of carbonatites and alkaline rocks in the Canadian Cordillera (see Millonig et al., 2012; 2013). According to these authors, both carbonatite samples are composed of calcite (70–80 vol.%), amphibole (5–10 vol.%), apatite (5–10 vol.%), biotite (~1–2 vol.%) and zircon, and accessory pyrochlore. Accessory titanite and columbite (REN-079-3), and monazite (REN-075-1) have been also verified (Millonig et al., 2012; 2013). The pyrochlore in both samples is up to ~0.3 mm across, subidioblastic to idioblastic, and black in colour. In contrast, monazite is up to ~0.3 mm across, anhedral, mostly transparent pale yellow and rarely murky yellow-orange (Millonig et al., 2012; 2013). Chapters 4, 5 and 6 provide in-depth descriptions of various aspects pertaining to the lithology, mineralogy and chemistry of the carbonatite and the associated fenites.     40   Figure 2.3 Boudinaged layer of amphibole-rich fenite within the Ren carbonatite. Image reproduced from Höy (1988), with permission British Columbia Geological Survey.    2.3.2 General distribution of REE’s, Nb and Ta   Based on the 2011 drill results and subsequent chemical assay analyses completed in 2012, Nb is present throughout the thickness of the carbonatite (except for zones of pegmatite and gneissic country rock) with the best grades obtained near the middle of the deposit (Fig. 2.4). The best overall grades of Nb occur in the central 250 metres of the drilled strike length, where the carbonatite was found to be the thickest (in drill holes MC-11-03, 04, 05 and 06). It appears that the higher Nb content is spatially associated with disseminations, pods and bands of magnetite and possible ilmenite and other oxides within the carbonatite. Tantalum contents are significantly lower than Nb contents throughout the carbonatite. In addition to the Nb enrichment, the analytical results indicate that the REE’s are strongly zoned into the hanging wall (southwest side) of the carbonatite over the entire drilled strike length (Fig. 2.5).       41 MC-11-01   MC-11-03  MC-11-04  MC-11-05  MC-11-06  MC-11-08   Figure 2.4 Drill hole sections through the Ren carbonatite, showing total values of LREE’s (La + Ce + Pr + Nd), MREE’s (Sm + Eu + Gd + Tb + Dy + Ho) and HREE’s (Er + Tm + Yb + Lu) plus Y, Nb and Ta, in parts per million (ppm).  42 2.3.3 Geochronology  According to Millonig et al. (2012), U–Th–Pb (zircon) analyses of REN-075-1 gave a weighted average intrusion age of 691 ±21 Ma, and U–Pb (zircon) analyses of REN-079-3 defined an estimated intrusion age of 704 ±88 Ma. Despite the large error for sample REN-079-3, the similar stratigraphic relationships and intrusion ages of ~700 Ma denote the same magmatic event. Figure 2.5 shows the location and emplacement age of the Ren carbonatite in relation to other carbonatite occurrence in the Canadian Cordillera.   Based on U–Th–Pb dating of pyrochlore and monazite from the samples, Millonig et al. (2013) conclude that the Ren carbonatite was affected by amphibolite-facies metamorphism at ~51–50 Ma (sample REN-075-1: 51.6 ±1.1 Ma; U–Pb, pyrochlore; 51.87 ±0.90 Ma; U–Pb–Th, monazite; and sample REN-079-3: 49.9 ±1.0 Ma; U–Pb, pyrochlore), with almost complete resetting of the U–Pb system of magmatic pyrochlore as opposed to metamorphic pyrochlore growth. This conclusion is in agreement with results obtained previously by Crowley & Parrish (1999), as indicated by Millonig et al. (2013).                   43   Figure 2.5 Carbonatite occurrences and their emplacement ages in the Canadian Cordillera. Sources: Ren, Millonig et al. (2012); Wicheeda Lake, Dalsin (2013); all other occurrences, Woolley & Kjarsgaard (2008b).                  44 CHAPTER 3 THE GEOTECTONIC ENVIRONMENT OF THE REN CARBONATITE WITHIN THE FRENCHMAN CAP DOME    3.1 INTRODUCTION   The geotectonic settings and geological history of the Ren carbonatite within the Frenchman Cap Dome are summarized in this chapter. The complete version of this chapter can be found in Appendix B.       The Ren carbonatite occurs in the southern Omineca belt, the metamorphic and plutonic hinterland to the Rocky Mountain Foreland Belt of the Canadian Cordillera, which formed subsequent to collision between accreted terranes and the western edge of the North American craton (Monger et al., 1982). The carbonatite lies within the Monashee Metamorphic Complex, on the west margin of the Frenchman Cap Dome (Figs. 3.1, 3.2). The Monashee Complex, also known as the Monashee Terrane (Read & Brown, 1981), is separated from the overlying Kootenay Terrane of the Selkirk Allochthon by the Monashee Décollement on the northwest and south, and by the Columbia River Fault on the northeast (Lane, 1984; Brown et al., 1992). The Monashee Décollement is a west-dipping Middle Jurassic reverse fault (Read & Brown, 1981; Brown et al., 1986; Brown and Journeay, 1987; Parrish, 1995). The Columbia River Fault is an east-dipping Eocene normal-sense shear zone that is superposed on the Monashee Décollement (Lane, 1984 and references therein) and is partly responsible for the tectonic unloading of the complex (Journeay & Brown, 1986; Parrish et al., 1988; Carr, 1991; Johnson and Brown, 1996). Frenchman Cap Dome, a second order structural culmination along the axis of antiformal duplex within the Monashee Complex, is exposed through a tectonic window (Brown et al., 1992), and is interpreted as a regional interference structure produced by the superposition of at least three generations of  45 non-coaxial folding, similar to the Thor Odin Dome to the south (Read, 1979; 1980; Journeay 1981; Read & Klepacki, 1981; Duncan 1984).   Regional geological mapping (Fig. 3.2) of the Frenchman Cap Dome is based on results from a number of mapping projects (Wheeler, 1965; Fyles, 1970; McMillan, 1969; 1970; 1973; Psutka, 1978; Brown, 1980; Brown & Psutka, 1979; Höy, 1979; 1980; Höy & McMillan, 1979; Read & Brown, 1981; Brown & Read, 1983; Okulitch, 1984; Journeay, 1986; Journeay & Brown, 1986). Figure 3.3 is a geological map (1:25,000) of the Mount Grace and Blais Creek areas adapted from Höy (1988). Journeay (1986) provides detailed description and mapping (1:25,000) of the stratigraphy, internal strain, and thermo-tectonic evolution of the north-central Frenchman Cap Dome. The base map in Figure 3.4 is adapted from Journeay’s (1986) original tectonostratigraphic map.   The stratigraphic succession along the northwestern margin of the Frenchman Cap Dome comprises three heterogeneous and distinct tectonostratigraphic assemblages, as shown in Figure 3.2 (also refer to Figs. 3.3 and 3.4). The lower plate of the Monashee Décollement comprises a basement of migmatitic paragneiss and granitoid orthogneiss, unconformably overlain by a sequence of shallow-marine metasedimentary rocks, referred to as the Autochthonous Cover Sequence (Brown, 1980). These two assemblages, the basement gneiss and the autochthonous cover sequence, constitute together the basement fold and thrust nappes system of the Monashee Complex (Read & Brown, 1981; Journeay, 1986). A third assemblage exposed within the upper plate of the Monashee Décollement envelops this duplex system. It is an overthrust package of coarse, clastic, semi-pelitic and calcareous rocks intertwined with anatectically derived migmatites and intrusive sheets of gneissic granite and pegmatite (Wheeler, 1965; Brown & Read, 1983; Journeay, 1986). This assemblage represents the deep-level metamorphic and plutonic framework of the Selkirk Allochthon that was thrust onto the Monashee Complex in Middle Jurassic and Late Cretaceous time (Read & Brown, 1981; Brown & Read, 1983; Journeay, 1986; Brown et al., 1986; Parrish, 1995).      46    Figure 3.1 Tectonic belts and geological terranes of British Columbia. The Ren carbonatite occurs in the Frenchman Cap Dome, a structural culmination with the Monashee Complex.                47  Figure 3.2 Regional geology and Minfile mineral deposits of the Frenchman Cap Dome area. The locations of the Ren carbonatite sill units are shown in stars. The smaller rectangle corresponds to Figure 3.3; the larger rectangle corresponds to Figure 3.4.  48 FIGURE 3.2: LEGEND   QUATERNARY (<1.64 Ma)       Additional symbols       Glacial and/or fluvial deposits        Fault               Extension fault  SELKIRK ALLOCHTHON           Thrust fault             CRETACEOUS (145.6–65 Ma)                 Mineral deposit       Anstey Pluton; meta-granodioritic intrusive rocks              Locations of the                        Ren carbonatite TRIASSIC TO CRETACEOUS (245–65 Ma)                    Metagranite and alkali feldspar granite intrusive rocks   Alpine ice  JURASSIC (178–157.1 Ma)   Adamant Pluton; metagranodioritic intrusive rocks            Selkirk Stocks; metagranodioritic intrusive rocks    CAMBRIAN TO DEVONIAN (570–362.5 Ma)   Lardeau Group–Index Formation; mudstone, siltstone, shale, fine clastic                        metasedimentary rocks  CAMBRIAN (570–536 Ma)     Badshot Formation; limestone, marble, calcareous metasedimentary rocks  UPPER PROTEROZOIC (1,000–570 Ma)         Horsethief Creek Group; mudstone, siltstone, shale, fine clastic metasedimentary rocks   MIDDLE PROTEROZOIC TO DEVONIAN (1,600–352.5 Ma)    Moyie or Mount Ida Plutonic Suite; metadioritic intrusive rocks   MONASHEE COMPLEX  Metasedimentary Cover Rocks  LOWER PROTEROZOIC TO DEVONIAN (2,500–408 Ma)          mc: Marble and calcsilicate metamorphic rocks                pg: Paragneiss metamorphic rocks                    qz: Quartzite, quartz arenite metamorphic rocks   Basement Rocks  LOWER PROTEROZOIC (2,500–1,600 Ma)   Core (basement) orthogneiss metamorphic rocks         Core (basement) paragneiss metamorphic rocks  49        A        50 B    Figure 3.3 Geological map (A) and cross sections (B) of the Mount Grace-Blais Creek areas, showing the main stratigraphic units along the northwestern margin of Frenchman Cap Dome. Adapted from Höy (1988) with permission from BC Geological Survey.   51     Figure 3.4 Geology of the Ratchford Creek-Perry River areas. Adapted from Journeay (1986) with permission from the author.   52 FIGURE 3.4: LEGEND (REFINED FROM THE ORIGINAL MAP)   Quaternary alluvium.  SELKIRK ALLOCHTHON (Upper Proterozoic)   Quartzite–biotite-quartz-feldspar paragneiss unit: quartz-arenite, arkosic and sub-arkosic quartzite, bt-qz-fsp paragneiss, minor pelitic and semipelitic schist, marble.   Quartzofeldspathic paragneiss–amphibolite– pelitic schist unit: heterogeneously interlayered qz-fsp paragneiss, grt-hbl-cpx amphibolite, pyroxene boudins, pelitic and semi-pelitic schist; migmatite and pegmatite.   Quartzofeldspathic paragneiss–quartzose schist unit: quartzofeldspathic gneiss, migmatized quartzose schist; variable pelitic and semipelitic schist; minor arkosic and sub-arkosic quartzite.  MONASHEE COMPLEX  Metasedimentary Cover (Lower Proterozoic to Devonian)  Upper Assemblage   Grt-hbl amphibolite–calcsilicate gneiss unit: interlayered amphibolite, calcsilicate gneiss and feldspathic quartzite;  impure marble in sections.  Massive quartzite unit: fine-grained massive and sub-arkosic quartzite, calcsilicate gneiss and bt-qz-fsp paragneiss in sections.   Upper basal quartzite–pelitic schist unit: feldspathic and micaceous quartzite, pelitic and semipelitic schist; interlayers of calcsilicate gneiss, sil-ky paragneiss; amphibolite in sections.  Middle Assemblage   Calcsilicate gneiss–calcareous schist unit: interlayered calcsilicate gneiss, calcareous schist, pelitic and semipelitic schist, pure and impure marble, stratabound carbonatite tuff.   iii Pelitic and semipelitic schist, calcareous schist, calcsilicate gneiss, pure and impure marble, stratabound oxide-sulphide mineralization.   ii Grey weathering, white crystalline marble.   i Calcsilicate gneiss, calcareous schist, stratabound volcanoclastic carbonatite, minor pelitic and semipelitic schist.   Middle basal quartzite–pelitic schist unit: massive, thin-bedded or blocky feldspathic quartzite, micaceous quartzites and orthoquartzite, interlayered with pelitic and semipelitic schist..  Lower Assemblage   Calcsilicate gneiss–pelitic schist unit: interlayered calcsilicate gneiss and pelitic schist; thin interlayers of feldspathic and sub-arkosic micaceous quartzites, bt-qz-fsp paragneiss, impure marble; amphibolites in sections.   Lower basal quartzite unit: quartz meta-arenite, micaceous quartzite; minor calcsilicate gneiss, pelitic and semipelitic   schist.    qu Well sorted meta-arenite.  c Calcareous schist, calcsilicate gneiss.  p Pelitic and semipelitic schist.  qL Quartz arenite, sub-arkosic quartzite, qz-pebble conglomerate.     3  4  5  6  7  8  9 10 11 12 Qa  53 FIGURE 3.4: LEGEND (cont.)  Basement Terrane (Lower Proterozoic)      Orthogneiss unit: undifferentiated monzogranitic and granodioritic orthogneiss, migmatite, amphibolitic gneiss.    2d Coarse-grained monzogranitic to granodioritic augen gneiss.    2c Tonalitic and trondhjemitic gneiss gt-hbl-cpx monzogranitic orthogneiss, migmatite.   2b Tonalitic orthogneiss, gt-hbl mafic gneiss, migmatite.   2a Grt-bt-hbl granitic gneiss, migmatite.   Paragneiss unit: bt-hbl gneiss, migmatitic, bt-qz-fsp paragneiss, minor pelitic and semipelitic schist, grt-hbl amphibolite    Folds  Overturned anticline–syncline axial surface track; observed, inferred, assumed. Arrows indicate dip direction of axial surface.    Inclined to reclined antiform–synform axial surface trace; observed, inferred, assumed. Arrows indicate plunge direction of fold hinge.     Upright to overturned asymmetric antiform–synform axial surface trace; observed, inferred, assumed.     Monashee Antiform axial surface trace.    D1  KA – Kirbyville Anticline   GMS – Grace Mountain Syncline   MCA – Myoff Creek Anticline   MCS – Myoff Creek Syncline  D2  ARA – Anstey Range Antiform    ARS – Anstey Range Synform  Faults  D1; Pre-to early-metamorphic thrust fault; observed, inferred.     D2; Syn-metamorphic high pressure thrust faults; observed inferred.    D3; Syn- or late-metamorphic low-pressure thrust fault.    Post-metamorphic normal fault.        D1 RCF – Ratchford Creek Fault  D2  ARF – Anstey Range Fault       1  2  54  Journeay (1986) notes that the northwest portion of the Monashee Complex also involves regional-scale, alpine-style recumbent folds (F1, F2), and low-angle imbricate thrust faults of the Monashee Décollement (MD1, MD2). Axial surfaces of the folds dip moderately away from the complex toward the northwest and southwest (Brown, 1980; Höy & Brown, 1980). Both the basement and especially the cover gneiss sequences of the complex are involved in these first-generation deformation (D1) structures which form km-scale, eastward verging isoclinal nappes (Gibson et al., 1999). From west to east and in order of increasingly deeper tectonic levels, these structures include (see Fig. 3.4): the Kibyville Anticline, Anstey Range Fault, Grace Mountain Syncline, Ratchford Creek Fault, Myoff Creek Anticline-Syncline, Anstey Range Antiform, Jordan Range Synform and second order structures along the NW-trending axis of the Frenchman Cap Dome (Journeay, 1986). These structures are inferred to be coeval primarily with the early stages of Cordilleran deformation (D1) recorded in the complex (e.g., Journeay, 1986; Scammell, 1986).  The following paragraphs describe the main lithological characteristics of rock units within the stratigraphic succession in the Ratchford Creek-Perry River areas, as shown in Figures 3.2, 3.3 and 3.4 (for complete descriptions, see Journeay, 1986; Höy, 1988 and references therein,). It should be noted that sharp changes in rock facies, deformation of units, and offsetting due to layer-parallel faults, considerably obstruct the tracing and correlation of units throughout the area (e.g., Höy, 1988).      3.2 MONASHEE COMPLEX  3.2.1 Basement gneissic rocks   Lower Proterozoic (Aphebian) basement (core) gneissic rocks in the north-central Frenchman Cap Dome are very similar in both composition and geochronology to those found in the Thor-Odin Dome (e.g., Reesor & Moore, 1971) and the Malton Gneiss Complex (Morrison, 1982). These gneiss complexes are the oldest known exposures of continental crust within the southern Canadian Cordillera (e.g., Journeay, 1986; Crowley, 1997a; 1997b).   55 3.2.2 Autochthonous metasedimentary cover sequence   Overlying the gneissic rocks of the basement is a cover sequence of clastic and shallow-water metasedimentary rocks (Reesor, 1965; Wheeler, 1965; McMillan, 1969; Fyles, 1970; McMillan, 1973; Psutka 1978; Höy, 1979; Höy & McMillan 1979; Brown, 1980; Höy, 1982, Journeay, 1986; Höy, 1988; Unit PrPzM on Fig 2.4). The stratigraphic break between the basement and cover rocks delineates an erosional unconformity, which is inferred by Höy (1982) largely from the presence of lithic paragneiss fragments within the basal quartz-pebble conglomerate.   The upper portion of the autochthonous cover sequence, which occurs immediately below the Monashee Décollement, comprises two fold nappes and has a structural thickness of nearly 3 km. It is characterized by east-verging, penetrative ductile deformation and kyanite–K-feldspar grade metamorphism dated between 60 and 55 Ma (Parrish, 1995; Crowley and Parrish, 1999; Gibson et al., 1999; Crowley et al., 2001; Foster et al., 2004). Crowley & Parrish (1999) and Crowley et al. (2001) observe that the lower portion of the cover sequence has a structural thickness comprising the upright, lower limb of the lower fold nappe, with a structural thickness of nearly 1.5 km thick. According to these authors, it is also characterized by sillimanite-grade metamorphism and high-temperature, east-verging deformation until ~50 Ma, which is ~5 Ma later than the upper portion.    3.3 SELKIRK ALLOCHTHON   Hanging wall rocks of the Monashee Décollement along the north and west flanks of the Frenchman Cap Dome are known as the Allochthonous Cover Rocks (Brown, 1980). These rocks, which are of sedimentary origin, belong to the Horsethief Creek Group (Wheeler, 1965; Brown, 1981; Read & Brown 1981; Journeay, 1986; Unit uPrHsc on Fig. 3.2) or the Windermere Supergroup (e.g., Poulton & Simony, 1980). They constitute a portion of the miogeocline of the Selkirk Allochthon and the Kootenay Arc (e.g., Smith & Gehrels, 1991 and references therein). Zircons from a granite intrusion, non-conformably overlain by Windermere basal strata within the Deserters Range (north-central BC), give a U–Pb  56 crystallization age of 728 +9/ –7 Ma (Evenchick et al., 1984). Also, the Old Fort Point Formation, which represents the termination of clastic sediment deposition throughout the Windermere basin resulting from a eustatic sea level rise (Ross & Murphy, 1998), has a depositional age of 607.8 ± 4.7 Ma (Kendall et al., 2004; Re–Os, whole rock). Deposition of the Horsethief Creek Group is therefore loosely constrained to between 730 Ma and 600 Ma.    3.4 ALKALINE AND CARBONATITIC MAGMATISM IN THE FRENCHMAN CAP DOME AREA  3.4.1 Neoproterozoic alkaline and carbonatitic magmatism   The initial breakup of Rodinia in the Neoproterozoic (Whitmeyer & Karlstrom, 2007; Li et al., 2008) leading up to the final separation of Laurentia and presumably Siberia (Sears & Price, 2000; Piper, 2011) signifies a prolonged period of episodic extension along the western Laurentian margin (Millonig et al., 2012). Tracing of Neoproterozoic and early Paleozoic rift margins of western Laurentia points to a subsiding, margin-long basin (or a system of basins), having established by ~700–685 Ma and lasting until ~570 Ma (Lund et al., 2010 and references therein). This rifting period is also characterized by alkaline and carbonatitic magmatism (Armstrong et al., 1981; Evenchick et al., 1984; McDonough & Parrish, 1991; Park et al., 1995; Ross et al., 1995; Crowley, 1997a; Harlan et al., 2003; Whitmeyer & Karlstrom, 2007; Lund et al., 2010). In the Monashee Complex, it is highlighted by ~800 Ma intrusion of the Perry River syenites and carbonatite, and subsequent intrusion of the Ren carbonatite at ~700 Ma (Millonig et al., 2012). According to Millonig et al. (2012), intrusions of the Mount Copeland syenite at ~740 Ma (south flank, Frenchman Cap Dome; Parrish and Scammell, 1988) and the protolith of the Mount Grace syenite gneiss at ~724 Ma (Crowley, 1997a) also correspond to this period.     57 3.4.2 Devonian to Carboniferous alkaline and carbonatitic magmatism   The Middle Devonian (~390 Ma) is considered to be a period of major tectonic shift along the western continental margin of Laurentia, from an extensional intraplate basin (or a system of basins) to convergent interplate settings and arc magmatism (Monger & Price, 2002). Subsequently, slab rollback during Late Devonian to Early Carboniferous (e.g., Roback et al., 1994; Smith & Lambert, 1995; Colpron et al., 2007; Nelson & Colpron, 2007; Lund, 2008) prompted reactivation of extensional tectonics and back arc basin formation (Lund et al., 2010) along the newly formed active margin, as indicated by Millonig et al., (2012). Geochronological assessments of syenites and carbonatites from the Canadian Cordillera (e.g., Mäder, 1986; Pell, 1994; Parrish, 1995; Heaman, 2009; Rukhlov & Bell, 2010; Millonig et al., 2012) provide evidence for prevalent alkaline and carbonatitic magmatism contemporaneous with back arc formation in that region. An example from the Frenchman Cap Dome is the intrusive carbonatite dated at ~360 Ma (Parrish, 1995), which, according to Millonig et al. (2012), might be the intrusive counterpart of the coeval Mount Grace volcaniclastic carbonatite.  The back-arc rifting and spreading along the west margin of Laurentia, coupled with subduction and offshore arc extension, continued through Permo-Triassic (~250 Ma; e.g., Gabrielse & Yorath, 1991), which may have also facilitated limited compressional deformation of the Monashee Complex during those times.     3.5 METAMORPHISM OF THE FRENCHMAN CAP DOME AREA  By the Late Paleocene and Early Eocene (~64–49 Ma), the Monashee Complex reached maximum burial and tectonic loading to depths of approximately 25 km beneath the foreland fold-thrust belt (i.e., Selkirk Allochthon), while undergoing rapid uplift, which resulted in syn-peak-metamorphic deformation, with a brief but sharp thermal peak of 580°–730°C at pressures of ~5.5–8.5 kbar (Parrish, 1995; Crowley & Parrish, 1999; Milloning et al., 2013). This high temperature-intermediate pressure deformation has east–northeast-verging shear, penetrative, ductile and anatectic components (e.g., Journeay, 1986). In the Frenchman Cap  58 Dome, it is also recognized by high grade metamorphic rocks (sillimanite–K-feldspar assemblage) at the structurally highest levels of the dome, and by lower grade rocks (sillimanite–kyanite–staurolite–muscovite assemblage) at intermediate levels, overlying higher grade rocks (sillimanite–kyanite–muscovite assemblage) found at the lowest levels (Gibson et al., 1999; Crowley & Parrish, 1999; Crowley et al., 2001; Foster et al., 2004). These observations have been interpreted as resulting from progressive northeastward emplacement of deeply buried hot rocks of the Selkirk Allochthon onto cooler higher level rocks of the Monashee Complex  (Gibson et al., 1999; Crowley et al., 2001). This relatively simple Barrovian-type tectonometamorphism of the Monashee Complex shows progressively younger peak metamorphic ages, which are inferred to correlate with increasing structural depth (Crowley & Parrish, 1999). In contrast to the Monashee Complex, the Selkirk Allochthon is inferred to have undergone several high-grade metamorphic events, from the Middle Jurassic to the Paleocene (e.g., Parrish, 1995).                          59 CHAPTER 4 LITHOLOGY AND PETROGRAPHY OF ROCK UNITS    4.1 OVERVIEW  The Ren carbonatite sill is hosted in metasedimentary cover rocks of the Shuswap Complex, and is exposed on the west side of the Mount Grace synform axial surface (see Chapter 3, Figure 3.4). The metasedimentary rock units were initially recognized and described by Journeay (1986) and subsequently Höy (1988). These units constitute the garnet-amphibolite–calcsilicate paragneiss unit of the upper depositional assemblage summarized in Appendix B. The primary objectives of this chapter are to refine the historical lithological and petrographical descriptions of rock types in the Ren locality and, on the basis of SEM and electron microprobe work, properly designate rock units that are associated with or constitute the carbonatite sill. The lithological units are organized in this chapter into metamorphic country rocks, metafenites, metacarbonatites and late pegmatites. Additional information on the mineral phases is given in Chapter 5.   4.2 SCHEMATIC PROFILES OF LITHOLOGICAL UNITS ACROSS THE REN CARBONATITE SILL AND HOST ROCKS  Figures 4.1 and 4.2 are schematic profiles through the Ren carbonatite sill and host rocks, based on drill core observations and charachterization of the lithological units. The top–bottom of the profiles corresponds to west–east or stratigraphic hanging wall–footwall.      60  Figure 4.1 Schematic sections across the Ren carbonatite sill (drill hole MC-11-04; see Chapter 2, Section 2.3.2), showing the position and relation of lithological units described in the text.      61  Figure 4.2 Schematic sections across the Ren carbonatite sill (drill hole MC-11-08; see Chapter 2, Section 2.3.2), showing the position and relation of lithological units described in the text.        62 4.3 METAMORPHIC COUNTRY ROCKS    Local metamorphic rock units accompanying the Ren carbonatite are: (1) quartzite, (2) calcareous biotite-feldspar paragneiss (and schist), (3) biotite-feldspar-quartz (semipelitic) paragneiss (and schist), (4) garnet-biotite amphibolite and (5) K-feldspar-quartz augen orthogneiss. The modal mineral assemblages of representative rock samples are given in Table 4.1.      Table 4.1 Modal mineral assemblages (vol. %) of metamorphic country rocks. Lithology Quartzite Calcareous biotite-feldspar paragneiss Biotite-feldspar-quartz (semipelitic) paragneiss Garnet-biotite amphibolite K-feldspar-quartz augen orthogneiss n 1 1 2 1 2    avg  avg Quartz 73 4 45 8 77 Plagioclase tr 26 9 10 tr Albite 2 3  2 2 K-feldspar 15 35 24 21 21 Muscovite tr    tr Biotite 1 19 16 25  Pyroxene 4  4  tr Hornblende 1 tr tr 20  Richterite      Tourmaline tr     Garnet  tr  12  Titanite   tr  tr Zircon  tr   tr Calcite 1 9 2 2  Strontianite      Barite 3     Apatite  tr    Monazite  tr tr   Pyrite tr 1 tr tr tr Pyrrhotite tr 2  tr tr Ilmenite      Rutile tr     Magnetite  tr  tr tr tr: trace (<0.5 vol.%). The modal mineralogy was determined directly by counting up to nearly 300 points in thin section.    63 4.3.1 Quartzite   Deformed quartzite occurs in limited horizons or sections in the Ren locality. It is pale buff-grey, and characteristically overprinted by a network of dark green, reticulate and fracture-filling veinlets and veins, 1–3 mm wide (Fig. 4.3A). These veins consist primarily of amphibole (hornblende) and pyroxene, with grains reaching 3 mm in diameter (Fig. 4.3C). The matrix is quartzofeldspathic, consisting primarily of xenoblastic quartz and feldspar (0.5–1 mm), and comprising up to 20% of subangular, coarse-grained and feldspar-rich lithic clasts (Fig. 4.3B). In thin section (Fig 4.3C), quartz shows intense deformation as indicated by numerous centres of nucleation resulting in a fine grain size (>0.25 mm). Many of the quartz grains are bounded by faces that intersect at 120° (triple junctions). Most grains of quartz and feldspar are xenoblastic and elongated, and define a weak foliation seen with zonal changes in grain size (Fig. 4.3B). Many of the pyroxenes display poikiloblastic or subpoikiloblastic texture comprising inclusions of quartz. Late, interstitial barite (<0.5 mm), reaching 3 vol. % in modal abundance, signifies the presence of the nearby carbonatite.   4.3.2 Calcareous biotite-feldspar paragneiss (and schist)    Calcareous biotite-feldspar paragneiss occurs throughout the Ren locality, and is the main host rock for the Ren carbonatite sill. It is medium grained and when fresh cut appears in shades of white-grey and dark brown (Fig. 4.4A). In thin section, biotite schistosity is pronounced and enhanced by segregation layers of quartz and feldspars (Fig 4.4B, C). The aligned sheets of biotite, sandwiched between the xenoblastic quartz and feldspar grains, also define planer foliation bands that are spaced every 1–3 mm in schist, to 0.5–2 cm in gneiss. Similarly, thin layers (1–3 mm) of calcite, sulphides (pyrite and pyrrhotite) and magnetite are also apparent throughout the rock, and are oriented according to the schistosity and/or foliation, except for pressure solution cracks (Fig. 4.4 C). Trace amounts of ovoid apatite and REE-bearing monazite are also present throughout the rock (Fig. 4.4 C, D).    64    Figure 4.3 Quartzite. (A) Core sample showing dark coloured mafic veins overprinting the lighter coloured matrix. Scale unit is in cm. (B) Photomicrograph showing the matrix, veinlet (left) and a coarse-grained lithic clast (right). Transmitted, cross-polarized light. (C) Photomicrograph showing veinlet minerals (mainly hornblende and pyroxene), surrounded by matrix minerals (mainly quartz and feldspars). Transmitted, cross-polarized light.  65     Figure 4.4 Calcareous biotite-feldspar paragneiss. (A) Core sample showing alternating bands primarily of biotite (dark) feldspar and quartz (grey) and calcite (white). Scale unit is in cm. (B) Photomicrograph showing characteristic minerals, schistosity and foliation. Transmitted, cross-polarized light. (C) Photomicrograph showing minerals, including monazite, biotite schistosity and magnetite occupying a pressure solution crack. Reflected light and transmitted, cross-polarized light. (D) Photomicrograph showing minerals, including well-formed calcite and apatite. Reflected light and transmitted, cross-polarized light.    66 4.3.3 Biotite-feldspar-quartz (semipelitic) paragneiss (and schist)   This paragneiss interlayers portions (several meters in thickness) of the calcareous biotite-feldspar paragneiss, and the resulting rock contacts are sharp and conformable. The rock displays white and dark-grey foliation bands, mylonites, pegmatite veins and boudinaged structures (Figs. 4.5A, 4.6). The matrix is fine- to medium-grained, semipelitic in composition, with alternating biotite, quartz and feldspar bands, spaced at 1–5 mm intervals (schistous to gneissose rock texture). Quartz (0.25–3 mm) commonly occurs as recrystallized mortar bands symmetric about the foliation, and in pressure shadows, or forms a granoblastic-polygonal texture with the feldspar (Fig. 4.5B, C). The feldspar (0.25–2 mm) includes xenoblastic, perthitic K-feldspar and minor antiperthitic plagioclase. Subidioblastic pyroxene (0.25–3 mm) occurs in pressure solution cracks and veinlets (0.25–2 mm wide) that cut across foliation (Fig 4.5A, B). Potassic-feldspar, pyroxene and other minerals form coarser augen porphyroblasts (typically 5–10 mm). Minor calcite (>1 mm) occurs as subidioblastic to xenoblastic grains, as intergrowths within poikiloblastic pyroxene porphyroblasts, and around the porphyroblasts in pressure shadows (Fig. 4.5D). The pegmatites in the rock are late veins consisting of quartz and/or K-feldspar, and can reach several cm in thickness. The boudinaged structures (2–10 cm) in the vicinity of the Ren carbonatite display a core of clinopyroxene (1–5 mm), surrounded by prisms of richterite (1–3 mm), with a subsequent increasing in finer quartz and feldspar grains outward from the boudin core (Fig. 4.6).      67     Figure 4.5 Biotite-feldspar-quartz paragneiss. (A) Core sample showing clinopyroxene (green), scapolite (red-brown) and K-feldspar (white-cream) augen porphyroblasts (centre), pressure solution crack (horizontal, curved line) and a K-feldspar pegmatite vein (left). Scale unit is in cm. (B) Photomicrographs showing characteristic minerals, schistosity, foliation, mortar quartz bands, and pressure solution crack (horizontal vein). Transmitted, cross-polarized light. (C) Photomicrograph showing minerals in pressure-shadow formed at the tail  68 of a K-feldspar augen porphyroblast. Transmitted, cross-polarized light. (D) Photomicrograph showing arrangement of biotite and calcite grains associated with a poikiloblastic, clinopyroxene porphyroblast. Transmitted, cross-polarized light.       Figure 4.6 Boudinaged structure in biotite-feldspar-quartz paragneiss. (A) Core sample showing the boudin (centre). Scale unit in cm. (B) Photomicrograph showing coarse-grained clinopyroxene and richterite comprising the centre of boudin. Transmitted, plane-polarized light.       69 4.3.4 Garnet-biotite amphibolite   The amphibolite unit is generally limited to the footwall (eastern side) of the Ren carbonatite sill and may resemble biotite schist in appearance. The matrix is fine to medium grained and consists primarily of biotite, hornblende, K-feldspar and albite (Fig. 4.7). It is highly deformed and many of the minerals are fragmented (Fig. 4.7B). Subidioblastic to xenoblastic garnet (almandine?) forms eye-catching pink-coloured porphyroblasts (4–10 mm), displaying in thin section small cracks and inclusions that commonly host quartz (Fig. 4.7D). These inclusions define a complex internal schistosity (Si) presumably from the garnet overgrowing a pre-existing crenulation fabric (Se). The dominant schistosity of the rock (Se) is defined by the alignment of biotite (Fig. 4.5C) This rock grades into both the calcareous biotite-feldspar and semipelitic paragneisses and schists, and conforms to the metasedimentary stratigraphic succession of the locality.    4.3.5 K-feldspar-quartz augen orthogneiss  Diamond drilling of the Ren carbonatite encountered metamorphosed and moderately mylonitized, granitic pegmatite dikes (0.2–5 m in thickness) that crosscut the carbonatite. In this rock, the original igneous perthitic K-feldspar forms subidioblastic and xenoblastic augen porphyroblasts (0.5–1 cm or larger), about which the rest of the rock has been deformed (Fig. 4.8A, B). Subidioblastic titanite (2–4 mm) forms smaller porphyroblasts (Fig. 4.8D). The matrix is fine-grained, consisting almost entirely of quartz, with minor K-feldspar, clinopyroxene, interstitial muscovite, sulphides and magnetite. Quartz fills pressure shadows around the augen and forms a strongly aligned ribbon texture in the same direction as foliation (Fig. 4.8C, D). Also, both the quartz and K-feldspar appear to have undergone syntectonic recrystallization, forming, in parts, very fine, granular masses (Fig. 4.9). Vermicular quartz and feldspar intergrowths (myrmekitic texture) are common (Fig. 4.9).    70     Figure 4.7 Garnet-biotite amphibolite. (A) Core sample showing pink garnet porphyroblasts. Scale unit in cm. (B) Photomicrograph showing crenulation fabric with fragmented minerals. Transmitted, cross-polarized light. (C) Photomicrograph showing biotite schistosity. Transmitted, cross-polarized light. (D) Photomicrograph showing quartz inclusion and internal deformation in a garnet porphyroblast.   71     Figure 4.8 K-feldspar-quartz augen orthogneiss. (A) Core sample displaying coarse K-feldspar augen porphyroblasts. Scale unit in cm. (B) Photomicrograph showing quartz-rich matrix that has deformed about the K-feldspar porphyroblasts. Transmitted, cross-polarized light. (C) Photomicrograph showing deformed pyrite, and recrystallized quartz and K- 72 feldspar forming a mortar texture in the pressure shadow of a large K-feldspar porphyroblast. Reflected light and transmitted cross-polarized light. (D) Photomicrograph showing a titanite porphyroblast. Transmitted, cross-polarized light.            Figure 4.9 K-feldspar-quartz augen orthogneiss. Photomicrograph showing albite exsolution lamella (perthite texture) in K-feldspar, myrmekite and very fine-grained, recrystallized quartz and feldspar grains at the centre of the image. Transmitted, cross-polarized light.        4.4 METAFENITES  Several metamorphosed fenite units occur in association with the Ren carbonatite: (1) fenitized calcareous biotite-feldspar paragneiss, (2) plagioclase-phlogopite fenite, (3) phlogopite-richterite fenite, (4) calcic amphibole-K-feldspar-pyroxene fenite, (5) richterite-K-feldspar fenite, (6) albite fenite (Höy, 1988) and (7) contact and vein phlogopite fenites. The modal mineral assemblages of representative fenite samples are given in Table 4.2.    73 Table 4.2 Modal mineral assemblages (vol. %) of metafenites. Litholog  Fenitized calcareous biotite-feldspar paragneiss Plagioclase-phlogopite fenite Phlogopite-richterite fenite Calcic amphibole- K-feldspar- pyroxene fenite Richterite- K-feldspar fenite Contact and vein phlogopite fenite  n 1 1 2 2 1 1    avg avg   Quartz 1      Plagioclase  18  tr   Albite 16 tr tr 2 2  K-feldspar 41 6 2 20 81  Phlogopite 22 55 13 12 tr 93 Clinopyroxene  8  34 tr  Tremolite    4   Actinolite    4   Richterite 2  54  4  Winchite    tr   Cummingtonite    1   Titanite    tr   Zircon    tr tr  Chevkinite-(Ce)    tr   Biraite-(Ce)    tr   Ferriallanite-(Ce)    1   “Västmanlandite-(Ce)”    tr   Calcite 12 12 18 10 13 4 Dolomite   4 4  2 Strontianite tr      Carbocernaite   1    Barite 3 tr 2 6   Apatite tr 1 2 1 tr 1 Monazite-(Ce) tr  tr 1 tr  Pyrite tr tr tr tr tr  Pyrrhotite tr  tr tr   Ilmenite tr  2    Nb-rutile  tr tr    Magnetite tr tr  tr   Columbite   1    Fergusonite-(Nd)    tr   Pyrochlore   tr    tr: trace (<0.5 vol.%). The modal mineralogy was determined directly by counting up to nearly 300  points in thin section.          74 4.4.1 Fenitized calcareous biotite-feldspar paragneiss   In the vicinity of the carbonatite, calcareous biotite-feldspar paragneiss displays localized rheomorphic folds and a widespread bluish tint (Fig. 4.10A), resulting from the presence of richterite (typically poikiloblastic, 2–4 mm) and disaggregation of feldspar grains (Fig. 4.10B, C). This altered rock also comprises calcite veinlets (0.5–1 mm wide) that cut across the original biotite schistosity and foliation (Fig. 4.10D). Rich in Sr, this calcite comprises exsolved strontianite (see next chapter) and has likely originated in the carbonatite. Isolated barite grains (0.5–2 mm) are also present throughout this altered paragneiss.   4.4.2 Plagioclase-phlogopite fenite   Plagioclase-phlogopite fenite is commonly associated with the Ren carbonatite. The rock is medium-grained, black to dark green with white patches (Fig. 4.11A). It may appear massive, but more commonly this fenite displays foliation or layering, with phlogopite–plagioclase–calcite compositional bands at 0.5–20 mm intervals. Phlogopite (0.5–4 mm) is the main mineral constituent (~50 vol. %), and compositional zones rich in phlogopite commonly define crenulation or turbidity patterns in the matrix (Fig 4.11 A, B). Well-twinned, xenoblastic plagioclase (0.25–3 mm) is the dominant feldspar phase, and commonly associated with minor K-feldspar (0.5–3 mm). These feldspar minerals occur mainly as granular aggregates that are surrounded by subhedral, poikiloblastic clinopyroxene (1–5 mm) and platy phlogopite (Fig. 4.11B, C). Calcite (0.5–2 mm) displays well-formed subhedral crystals. Apatite (0.5–2 mm), barite, pyrite, magnetite and rutile occur in small amounts (trace–1 vol. %) throughout the unit. Pyrite, phlogopite and calcite are commonly contained within poikilitic clinopyroxene.      75     Figure 4.10 Fenitized calcareous biotite-feldspar paragneiss. (A) Core sample showing a bluish alteration colour and a rheomorphic fold. Scale unit in cm. (B) Photomicrographs showing matrix minerals and disaggregation of K-feldspar. Transmitted, cross-polarized light. (C) Photomicrographs showing poikiloblastic richterite. Transmitted, plane-polarized light. (D) Sr-rich calcite veinlet, with tiny inclusions of exsolved strontianite (pores) seen in the calcite grains. Transmitted, cross-polarized light.  76     Figure 4.11 Plagioclase-phlogopite fenite. (A) Core sample showing characteristic alternating dark and light coloured compositional banding. Scale unit in cm. (B) Photomicrograph showing mineral assemblages associated with the compositional banding. Transmitted cross-polarized light. (C) Photomicrograph showing poikiloblastic clinopyroxene with mineral inclusions.   77 4.4.3 Phlogopite-richterite fenite  Phlogopite-richterite fenite displays swirl patterns that are defined by compositional bands rich in richterite (>50 vol. %), with only minor phlogopite (Fig. 4.12). This fenite commonly grades into the Ren carbonatite, and, in parts, it appears to have been remobilized into the carbonatite, forming a ‘turbulent’ rheomorphic fenite (Fig. 4.12A), whereas in other parts the fenite appears merely massive (Fig. 4.12B). Richterite (1–4 mm) commonly occurs as both rounded anhedral grains and euhedral prisms (Fig. 4.12B, E) giving the rock a greenish-grey colour. The carbonate grains commonly have sutured grain boundaries, but they also display, in parts, a granoblastic-polygonal texture. Small amounts of sulphides (trace–1 vol. %), oxides (trace–4 vol. %), including columbite (SEM), and a trace of pyrochlore (SEM) are also present in the rock. Ilmenite appears to be the most abundant oxide, occurring as medium to coarse poikilitic grains, with inclusions primarily of pyrite, richterite and carbonates.   4.4.4 Calcic amphibole-K-feldspar-pyroxene fenite  This moss-green fenite has a skarn-like appearance in hand samples and cores (Fig. 4.13A). In this rock, both clinopyroxene (30–35 vol. %) and K-feldspar (20–30 vol. %) show bimodality in grain size (0.1–1 mm and 2–5 mm) and occur in paragenesis, forming granoblastic-polysuture textures (Figs. 4.13B, 4.14A). Minor albite occurs primarily in exsolution lamellae in perthitic K-feldspar and subidiomorphic plagioclase (~1mm; 1–3 vol.%) is also present. The K-feldspar, clinopyroxene and also phlogopite (0.25–1 mm; 5–12 vol. %), with or without amphibole, constitute compositional layers (1–10 mm in thickness) that approximate foliation (Fig. 4.13A, B). Crenulation or wave patterns are most prominent in the phlogopite bands. Fine- to medium-grained, anhedral calcite (4–15 vol. %), containing exsolved dolomite (SEM results), occurs sporadically in small clusters (Fig. 4.14B). Calcite may also occur in association with xenoblastic dolomite (3–7 vol. %) and/or barite (2–11 vol. %) in carbonatitic bands (3–10 mm in thickness). Sodic amphibole is virtually absent, with  78 only trace amounts of winchite (Na-Ca amphibole) occurring in the fenite rocks that flank a winchite-rich carbonatite unit. Variable amounts (1–7 vol. %) of fine-grained Ca-amphiboles (actinolite and tremolite) and traces of poorly formed Mg-amphibole (cummingtonite) occur throughout the fenite (Figs. 4.13C, 4.14B, C). The Ca-amphiboles are associated with calcite, and the tremolite grains commonly contain exsolved calcite (Fig. 4.13C). These amphiboles are essentially metamorphic products, but their presence may be indicative of the compositional character of this fenite unit. Monazite (Fig. 4.14C) and allanite (Fig. 4.13D) appear to be the main REE minerals (1–2 vol.%). However, SEM results also indicate trace amounts of chevkinite-(Ce), fergusonite-(Nd) and, in places, biraite-(Ce) and an (Fe,OH)- analogue to västmanlandite-(Ce). These REE-minerals are concentrated in the fenite portions near the eastern edges (hanging wall) of the Ren carbonatite sill.    4.4.5 Richterite-K-feldspar fenite   This pink fenite (Fig. 4.15A, B), found in a large (~ 30 cm) xenolith pod within the carbonatite, is composed primarily of xenoblastic K-feldspar (2–5 mm; 70–90 vol. %), with minor subidioblastic calcite (1–10 mm) and richterite (1–4 mm), and interstitial albite (<1 mm). Interlocking grains of K-feldspar, calcite and richterite form a characteristic granoblastic-polygonal texture with triple- and quadruple-point junctions. (Fig. 4.15C, D). The K-feldspar is microperthitic and has been subjected to intense albitization, primarily along the grain boundaries (Fig. 4.15E). Calcite grains are generally well-formed and both calcite and richterite are concentrated in distorted compositional layer, 0.3–2 cm in thickness (Fig. 4.15A). Phlogopite and subpoikiloblastic clinopyroxene (Fig. 4.15C) are interstitial phases (0.25–1 mm), found in trace amounts. Apatite, monazite and pyrite occur sporadically. This fenite resembles syenite in composition but lacks nepheline.        79 4.4.6 Albite fenite  Höy (1988) obtained one rock sample (Ren-5-H) from an albite fenite pod he had encountered in the Ren carbonatite. According to this author, this type of fenite is associated with other carbonatites in the area and resembles albitite in composition (~90 vol. % albite, plus variable amounts of clinopyroxene, K-feldspar, titanite, apatite, epidote?, magnetite and sulphides). Although this type of fenite has not been identified in all the rock samples and cores available for this thesis, the whole-rock geochemistry analysis from Höy’s (1988) sample Ren-5-H are included in the whole-rock geochemistry chapter (Chapter 6) for the purpose of this study.                  80      Figure 4.12 Phlogopite-richterite fenite. (A) Core sample of a rheomorphic fabric. (B) Core sample of a massive fabric. Scale unit is in cm. (C) Photomicrograph showing richterite-rich and carbonate-rich compositional bands. Transmitted, cross-polarized light. (D) Photomicrograph showing poikilitic ilmenite. Reflected light. (E) Photomicrograph showing characteristic minerals, including both rounded and tabular richterite. Reflected light and transmitted, cross-polarized light.    81    Figure 4.13 Calcic amphibole-K-feldspar-pyroxene fenite. (A) Core sample showing compositional layers of clinopyroxene (green), feldspar (white), phlogopite (dark) and carbonates (pink layer on the right side of image). Scale unit is in cm. (B) and (C) Photomicrographs showing mineral assemblages of the compositional layers. Transmitted, cross-polarized light.  82     Figure 4.14 Calcic amphibole-K-feldspar-pyroxene fenite (photomicrographs). (A) Recrystallized K-feldspar occurring with clinopyroxene. Transmitted, cross-polarized light. (B) Actinolite and cummingtonite occurring with calcite. Transmitted, cross-polarized light. (C) Tremolite displaying exsolution blebs of calcite (centre of image). Transmitted, cross-polarized light. (D) Allanite. Reflected light and plane polarized light.             83      Figure 4.15 Richterite-K-feldspar fenite. (A) and (B) Core samples showing aggregations of K-feldspar (pink and white) associated with richterite-rich (dark) and calcite-rich (grey), distorted layers. (C) Photomicrograph showing a granoblastic-polygonal texture (transmitted, cross-polarized light. (D) Photomicrograph showing calcite, richterite, K-feldspar and albite. Transmitted, plane light. (E) Photomicrograph showing albite forming between K-feldspar grains. A few zircon crystals are also visible. Transmitted, cross-polarized light.    84 4.4.7 Contact and vein phlogopite fenites  The contact zones between wallrock and carbonatite (commonly carbonatite veins) display dark margins and veins, 0.5–4 cm in thickness (Fig. 4.16). Consisting almost entirely of phlogopite, these small-scale and compositionally simple features can be designated collectively as contact and vein phlogopite fenites.       Figure 4.16 Contact and vein phlogopite fenite. (A) Core sample showing a carbonatite vein with phlogopite margins, hosted in calcareous biotite-feldspar paragneiss. Scale unit in cm. (B) Photomicrograph of the carbonatite vein shown in (A). Transmitted, cross-polarized light.  85 4.5 METACARBONATITES  The Ren carbonatite comprises several metamorphosed carbonatite units: (1) dolomite carbonatite, (2) calcite carbonatite, (3) dolomite-calcite carbonatite, (4) richterite-rich, norsethite-calcite carbonatite and (5) winchite-rich, calcite-dolomite porphyroblastic carbonatite. Portions of these carbonatite matrices commonly host wallrock xenoliths and rheomorphic fabrics. The modal mineral assemblages of the carbonatite matrices show noticeable differences (Table 4.3). Images of the Ren carbonatite observed in the field are given in Figure 4.17.                        86 Table 4.3 Modal mineral assemblages (vol. %) of metacarbonatites. Lithology Dolomite carbonatite Calcite carbonatite Dolomite-calcite carbonatite Richterite-rich, dolomite- norsethite-calcite carbonatite Winchite-rich, calcite-dolomite porphyroblastic carbonatite  n 1 2 10 1 1   avg avg   Plagioclase   X   Albite   X   K-feldspar   X   Phlogopite 1 12 8 9 4 Clinopyroxene  tr 1  2 Tremolite      Actinolite      Richterite  1 7 21  Winchite tr    16 Nyböite-eckermannite  1    Cummingtonite     2 Zircon  tr tr tr tr Thorite   tr   Biraite-(Ce)     1 Ferriallanite-(Ce)     1 “Västmanlandite-(Ce)”     1 Calcite tr 79 49 32 23 Dolomite 97 2 22 4 30 Strontianite tr  tr tr tr Carbocernaite tr tr tr tr tr Norsethite   1 19  Barite   2 8 14 Apatite 2 6 5 4 3 Monazite-(Ce)  tr tr 1 3 Pyrite tr 1 tr tr tr Pyrrhotite tr tr tr  tr Ilmenite  tr 1 1  Magnetite  tr 1 1 tr Columbite   tr tr  Pyrochlore  tr tr   tr: trace (<0.5 vol.%). X: occurring in xenoliths (Pl=68%, Ab=20%, Kfs=8% Phl=4%; average, n=5). The modal mineralogy was determined directly by counting up to nearly 300 points in thin section.   87      Figure 4.17 Images of the Ren carbonatite in the field. (A) A 30-metre wide section of carbonatite near Chilly Lake displaying rhomorphic mafic fenite layers. (B) Carbonatite near Ratchford Creek displaying layers and pods of carbonate and mafic minerals (top to bottom of image = ~1 m). (C) Dolomite-calcite carbonatite gneiss near Ratchford Creek. (D) Carbonatite near Chilly Lake comprising xenoliths. (E) Core of niobium-rich, dolomite-A B C D E  88 calcite carbonatite gneiss, displaying dark concentric bands of primarily phlogopite, magnetite, ilmenite and columbite.    4.5.1 Dolomite carbonatite   Occupying mainly the middle portions of the sill, this pink carbonatite (Fig. 4.18A) may be mistaken for marble. The carbonatite comprises almost entirely dolomite (Table 4.3; Fig. 4.18A, B), and is commonly anchimonomineralic. Apatite (1–2 mm), calcite (1–3 mm), interstitial pyrite and winchite (1–3 mm) occur in small amounts. Trace amounts of strontianite and carbocernaite are indicated by SEM results. Dolomite occurs as coarse (2–6 mm), interlocking xenoblastic grains, with relatively equal dimensions (equigranular), and displays a granoblastic texture (Fig. 4.18). Apatite and phlogopite tend to concentrate in contorted compositional bands (2–5 mm thick) that approximate foliation (gneissose texture). Although the studied sample is deficient in monazite and zircon, the minerals may be present in trace amounts throughout the unit.   4.5.2 Calcite carbonatite   Other sections of the sill consist of calcite carbonatite. In contrast to the dolomite carbonatite, this carbonatite comprises primarily calcite (Table 4.3), in places forming nearly anchimonomineralic fabrics that appear pure white when fresh cut (Fig. 4.19A, C). Phlogopite (1–5 mm) and apatite (0.5–2 mm) occur as accessory minerals. Texturally the matrix can be fine-grained, comprising coarse phlogopite porphyroblasts (Figs. 4.19A, B and 4.20A, B), or medium- to coarse-grained displaying a gneissic texture (Figs. 4.19C, D) and 4.20C). The calcite grains are generally undifferentiated and strained, displaying highly sutured boundaries (Fig. 20B).      89    Figure 4.18 Dolomite carbonatite. (A) Core sample in daylight showing phlogopite (dark) and apatite (grey) compositional bands, set in a dolomite-rich matrix (pink). (B) Section of the sample in A, in shortwave UV light, depicting the apatite bands (pink) from the dolomite (dark purple). Scales unit in cm. (C) Photomicrograph showing the dolomite-rich matrix. Transmitted, cross-polarized light.              90      Figure 4.19 Calcite carbonatite. (A) Core sample of a porphyroblastic carbonatite in daylight, displaying subrounded phlogopite porphyroblasts (dark). (B) Section of the sample in A, in shortwave UV light, showing the porphyroblasts (black) set in a calcite-rich matrix (red). Scale unit in cm. (D) Sample of a slightly weathered, calcite carbonatite in daylight, displaying gneissic texture. (E) Section of the sample in D, in shortwave UV light, showing calcite (red) apatite (violet), and phlogopite (black).          91    Figure 4.20 Calcite carbonatite (photomicrographs). (A) Phlogopite porphyroblasts (brown) and apatite (white spheres) set in a fine-grained, calcite-rich matrix (grey). Transmitted, plane-polarized light. (B) The same area in A, in transmitted, cross-polarized light, showing bending and undulose extinction in the phlogopite porphyroblasts (pre-kinematic), about which matrix has been deformed (bottom of image). (C) Matrix of a foliated carbonatite. Transmitted, cross-polarized light. Horizontal colour streaks are an artifact resulting from unevenness in thickness of the thin section.       92 4.5.3 Dolomite-calcite (and calcite-dolomite) carbonatite    The dolomite carbonatite and calcite carbonatite described above are interlayered between dolomite-calcite (mixed) carbonatite. This banded, white and pink carbonatite (Fig. 4.21) constitutes large portions of the Ren carbonatite sill. The main minerals are calcite (0.5–3 mm) and dolomite (1–4 mm), with calcite more commonly occurring in higher concentrations than dolomite (Table. 4.3). Many of the calcite grains have highly sutured boundaries (Fig 4.22A, C). Other types of textures observed for the carbonates include fine and medium-grained granoblastic dolomite displaying triple-point junctions (Fig 4.22A), and dolomite exsolution lamellae and blebs in calcite (Fig. 4.22C). Foliation, defined by alternating calcite, dolomite and phlogopite segregation bands (0.5–4 cm intervals), is recognizable in shortwave UV light (Fig. 4.21B, D) and thin sections (e.g., Fig. 4.22A). Apart from calcite and dolomite, other carbonates include minor strontianite (Fig. 4.21D), carbocernaite and norsethite (SEM results). Non-carbonate phases, in addition to phlogopite (2–15 vol.%), include richterite (0–23 vol. %), apatite (3–12 vol. %) and barite (trace–11 vol. %). Oxides and sulphides (Fig. 4.22B) occur in varying amounts (trace–4 vol. %), as interstices, stout pods or segregation layers. The oxides are also concentrated in fold closure structures (Fig. 4.17E). Additional sulphides observed only in hand samples are molybdenite (trace; Fig. 4.22E) and chalcopyrite (rare). In addition to carbocernaite, another, more common (trace–4 vol.%) REE mineral is monazite. The latter commonly forms rings around apatite. Niobium-bearing minerals are pyrochlore (rare) and columbite (trace).        4.5.4 Richterite-rich, dolomite-norsethite-calcite carbonatite   Occurring near the hanging wall of the sill, this white-grey carbonatite comprises appreciable amounts (10–15 vol. %) of norsethite (1–4 mm) in addition to dolomite and calcite (Fig. 4.23). Fine- to medium-grained subhedral richterite (0.5–3 mm) constitutes about 20% of the rock or more. The carbonates commonly form a granoblastic-polygonal texture (Fig. 4.23C).     93       Figure 4.21 Dolomite-calcite carbonatite. Core samples in daylight (A, C) and shortwave UV light (B, D), showing a gneissic texture. Scale unit is in cm. (E) Characteristic foliated fabric, showing granoblastic-polygonal and granoblastic polysuture textures in the dolomite and calcite bands, respectively. Transmitted, cross-polarized light.   E  94       Figure 4.22 Dolomite-calcite carbonatite (photomicrographs). (A) Sulphide and oxide minerals occurring in paragenesis. Reflected light, and transmitted, plane-polarized light. (B) Dolomite exsolution in calcite. Transmitted, cross-polarized light. (C) Characteristic minerals including strontianite (grainy texture) and a monazite ring around an apatite grain. Transmitted, cross-polarized light. (D) Magnified hand sample in daylight showing characteristic minerals, including molybdenite.    C A  B  D   95      Figure 4.23 Richterite-rich, norsethite-calcite carbonatite. (A) Core sample in daylight. (B) Section of the core in shortwave UV light. Scale unit in cm. (C) Photomicrograph showing characteristic minerals including norsethite. Transmitted, cross-polarized light. (D) Corresponding backscattered electron image of a section in C.     96 4.5.5 Winchite-rich, calcite-dolomite porphyroblastic carbonatite   This massive, blue-spotted, pink and white carbonatite occurs in pockets in the most REE enriched portion of the sill. It consists of blue winchite porphyroblasts (3–10 mm), which are set in a fine-grained matrix comprising a mixture of dolomite and calcite (Fig. 4.24A, B). These carbonates have nearly similar modal abundances, and commonly form a granoblastic texture (Figs. 4.24C, 4.25A). Poorly developed cummingtonite (<0.2 mm) is associated with coronas of winchite around clinopyroxene (Fig. 4.25B). Also present are barite (1–3 mm), magnetite and sulphide masses and numerous grains of monazite (0.5–2 mm), apatite (>1 mm), allanite (0.5–2 mm), biraite (0.5–1 mm), a västmanlandite analogue (<1 mm) and zircon (<0.25 mm). Many of these minerals are shown in Figure 4.25.   97      Figure 4.24 Winchite-rich, calcite-dolomite porphyroblastic carbonatite. (A) Core sample in daylight showing deformed winchite porphyroblasts. (B) Section of the sample in A, in shortwave UV light. Scale unit in cm. (C) Photomicrograph showing main minerals and texture of rock.    B  98     Figure 4.25 Winchite-rich, calcite-dolomite porphyroblastic carbonatite (photomicrographs). (A) Well-formed granoblastic dolomite. Reflected light and transmitted, cross-polarized light. (B) Corona texture of winchite and cummingtonite around clinopyroxene. Barite and allanite are also shown. Reflected light, and transmitted, cross-polarized light. (C) Biraite and a västmanlandite analogue. Reflected light. (D) Section rich in REE phases. Reflected light and transmitted cross-polarized light.          C D A B  99 4.5.6 Wallrock xenoliths and rheomorphic fabrics  Large sections of the sill are essentially carbonate- and silicate-rich mixed rocks, which appear to have been largely produced by remobilization and incorporation of metamorphosed wallrock material into the carbonatite matrices. These silica-contaminated carbonatites cannot be regarded as true silicocarbonatites which originate from silica-rich melts in the mantle, and commonly approach kimberlite in composition and mineralogy. The most striking evidence for rheomorphism to have been affecting the Ren carbonatite comes from field observations, showing: (1) exposed margins of the carbonatite engulfing other rocks (Fig. 4.26A); (2) carbonatite displaying mafic boudinaged structures comprising feldspathic xenoliths (Fig. 4.26B, C); and (3) rheomorphic flow fabrics (Fig. 4.27).   Remobilized wallrock xenoliths (in parts, making up to 70 vol. % of carbonatite units, and typically 0.5–30 cm in diameter), seen in Ren carbonatite drill cores, commonly consist of microperthitic K-feldspar, plagioclase and phlogopite. They appear to have undergone rotation, deformation, disaggregation and assimilation into the resulting silicate-rich carbonatite (Fig. 4.28). The twisted rheomorphic textures of the xenoliths effectively overprint the texture of the carbonatite matrix (Fig. 4.28A, E). In parts of the sill, plagioclase-rich fenite xenoliths have been reduced to long wisps of mafic bands, forming rheomorphic fenites (Fig. 4.28C, F). The rheomorphic reaction occurring between their outlines and the feldspar produce phlogopite, which is replaced by richterite and clinopyroxene (Fig. 4.28F, 4.29A, B). The amphibole increasingly forms a granoblastic texture away from the xenoliths (Fig. 4.29C). The rheomorphic fenite xenoliths therefore appear to ‘stain’ the surrounding carbonatite matrix in green-grey richterite-rich patches or zones, in contrast to the non-fenite xenoliths. The richterite zones commonly comprise poikilitic aegirine-augite with fine-grained richterite and sulphide inclusions, plus residual xenoblastic plagioclase and K-feldspar from the remobilized xenoliths (Fig. 4.29C). Backscattered electron images from the areas adjacent to the xenoliths (Fig. 2.30), show replacement of phlogopite and richterite by clinopyroxene, Na-Fe amphibole and quartz. Figure 4.31 illustrates rheomorphic flow in a carbonatite matrix comprising xenoliths.   100    Figure 4.26 Exposed margins of the Ren carbonatite sill in the field. (A) Carbonatite engulfing metamorphosed wallrocks: 1. Phlogopite-rich fenite, 2. Carbonatite, 3. Calcareous paragneiss, 4. Rheomorphic carbonate-silicate mixed rock. (B) Carbonatite (buff-weathering) comprising remobilized paragneiss xenoliths (white and grey) and phlogopite segregation layers and pods (dark). (C) Boudinaged structure of a remobilized paragneiss xenolith with an S-shaped rheomorphic fold, embedded in carbonatite.   A B C  101   Figure 4.27 Distorted carbonatite (buff) with rheomorphic fenite comprising feldspathic (white) and mafic (dark) ribbons.             102          Figure 4.28 Carbonatites containing boudinaged wallrock xenoliths and rheomorphic fabrics. (A) Core sample in daylight showing feldspar-rich xenoliths set in a calcite carbonatite matrix. (B) Section of the sample in A, in shortwave UV light. (C) Core sample in daylight showing rheomorphic fenites set in a dolomite-calcite carbonatite matrix. (D) Section of the sample in C, in shortwave UV light. (E) Section of the sample in A in longwave UV light, showing various stages of xenolith disaggregation. (F) Section of the sample in C in longwave UV light, showing mineral assemblage associated with rheomorphic reaction.      103    Figure 4.29 Carbonatite containing wallrock xenoliths (photomicrographs). (A) Feldspar xenoliths. Transmitted, plane light. (B) Alteration of phlogopite to richterite. Transmitted, plane polarized light. (C) Well-developed, interlocking richterite grains, associated with poikiloblastic aegirine-augite and barite. Transmitted, cross-polarized light.          104    Figure 4.30 Backscattered electron images of the minerals shown in Figure 4.27B, showing replacement of phlogopite and richterite by clinopyroxene, Na-Fe amphibole and quartz.     Figure 4.31 Rheomorphic flow in a dolomite-calcite carbonatite comprising wallrock xenoliths. Dashed arrows illustrate the relative direction of flow. Note the large twinned calcite grain located at the centre of rotation and the wrapping of phlogopite around it, indicated by the short dashed arrow. Transmitted, cross-polarized light.    105 4.6 LATE PEGMATITES  Late pegmatite dikes, displaying simple mineral assemblages (Table 4.4), cut across portions of the Ren carbonatite. The resulting contacts are sharp and are easily delineated by segregation or reaction bands composed primarily of phlogopite and clinopyroxene. Similar pegmatites have been described from the area by Wheeler (1965), Fyles (1970), Journeay (1986) and Höy (1988).          Table 4.4 Modal mineral assemblages (vol. %) of pegmatites. Lithology  Granitic pegmatite Calcite-rich pegmatite n 3 1  avg   Quartz 28 25 Plagioclase 1 tr Albite 5 2 K-feldspar 51 48 Biotite 3 tr Muscovite tr tr Clinopyroxene 10 13 Actinolite 1  Titanite tr  Calcite tr 11 Apatite tr  Pyrite tr tr Magnetite tr  Graphite tr  tr: trace (<0.5 vol.%). The modal mineralogy was determined directly by  counting up to nearly 150 points in thin section.       106 4.6.1 Granitic pegmatite  This coarse-grained rock displays typical graphic and myrmekitic textures (Figs. 4.32, 4.33A). The primary minerals are quartz and perthitic orthoclase, with accessory albite, clinopyroxene (prismatic and poikilitic), biotite, muscovite, actinolite, calcite, titanite, graphite, apatite, pyrite and magnetite. Several of these minerals are shown in Figure 4.33. Quartz occurs primarily as medium- to coarse-grained crystals, but also as fine recrystallized grains displaying a mortar texture. Muscovite grains are very fine, subhedral to euhedral, located primarily between and within larger grains of feldspar. Rare calcite occurs as isolated grains. The feldspars display sericitic alteration.   4.6.2 Calcite-rich pegmatite  In this pegmatite unit, unidirectional solidification textures and especially graphic intergrowths are generally absent (Fig. 4.34). In addition to the common pegmatite minerals described for the granitic pegmatite, it comprises 8–15 vol. % anhedral calcite (3–5 mm), occurring as scattered grains and veins (0.5–2 cm in thickness). The calcite may be contamination from the carbonatite, during the formation or emplacement of this pegmatite.                 107    Figure 4.32 Granitic pegmatite. (A) and (B) Core samples in daylight. Unit scale in cm. (C) Photomicrograph showing characteristic minerals and a graphic texture. Transmitted, cross-polarized light.          108       Figure 4.33 Granitic pegmatite. Photomicrographs showing characteristic minerals. Transmitted, cross polarized light.            109   Figure 4.34 Calcite-rich pegmatite. (A) Core sample. Unit scale in cm. (B) Photomicrograph showing zones of calcite and a simple texture. Transmitted, cross-polarized light.             110 CHAPTER 5 MINERALOGY   5.1 METHODOLOGY  5.1.1 Analytical conditions for microprobe analysis of mineral compositions   Electron-probe microanalyses of minerals were carried out by the author of this thesis at the microbeam laboratories in the Department of Earth Sciences, University of Manitoba, on a fully automated CAMECA SX-100 instrument, operating in wavelength-dispersion mode.   Carbonates   The Following operating conditions were applied to the electron-probe microanalyses of carbonates: excitation voltage, 15 kV; beam current, 10 nA; peak count time 20 s; background count time, 10 s; spot diameter 10 µm. Data reduction was done using the 'PAP' φ(ρZ) method (Pouchou & Pichoir 1985). Oxygen was determined by stoichiometry and C by difference. For the elements considered, the following standards, X-ray lines and crystals were used: diopside, SiKα TAP and CaKα, LPET; LaPO4, LaLα, LLIF; CePO4, CeLα, LLIF; PrPO4, PrLβ, LLIF; NdPO4, NdLβ, LLIF; SmPO4, SmLβ, LLIF; andalusite, AlKα, TAP; fayalite FeKα, LLIF; spessartine, MnKα, LLIF; olivine, MgKα, LTAP; SrTiO3, SrKα, LPET; barite, BaLα, LLIF; albite, NaKα TAP; apatite, FKα, LTAP.    Silicates  The following operating conditions were applied to the electron-probe microanalyses of silicates: excitation voltage, 15 kV; beam current, 20 nA; peak count time 20 s; background  111 count time, 10 s; spot diameter 10 and 1 µm. Data reduction was done using the 'PAP' φ(ρZ) method (Pouchou & Pichoir 1985). Oxygen and H were determined by stoichiometry and C (where applicable) by difference. For the elements considered, the following standards, X-ray lines and crystals were used: Ba2NaNb5O15, NbLα, LLIF; apatite, PKα, LPET and FKα, LTAP; pyrite SKα, LPET; diopside, SiKα, TAP and CaKα, LPET; titanite, TiKα, LPET; ZrO2, ZrLα, LPET; SnO2, SnLα, LPET; HfSiO4, HfLα, LLIF; ThO2, ThMα, LPET; UO2, UMβ, LPET; VP2O7, VKα, LLIF; andalusite, AlKα, TAP; YPO4, YLα, LPET; LaPO4, LaLα, LLIF; CePO4, CeLα, LLIF; PrPO4, PrLβ, LLIF; NdPO4, NdLβ, LLIF; SmPO4, SmLβ, LLIF; EuPO4, EuLβ, LLIF; GdPO4, GdLβ, LLIF; TbPO4 TbLα, LLIF; DyPO4, DyLβ, LLIF; fayalite FeKα, LLIF; spessartine, MnKα, LTAP; gahnite, ZnKα, , LLIF; olivine, MgKα, LTAP; SrTiO3, SrKα, LPET; barite, BaLα, LLIF; albite, NaKα, TAP; orthoclase, KKα, LPET; tugtuphite, ClKα, LPET.    Oxides and pyrochlore  The following operating conditions: excitation voltage, 15 kV; beam current, 20 nA; peak count time 20 s; background count time, 10 s; spot diameter 10 µm. Data reduction was done using the 'PAP' φ(ρZ) method (Pouchou & Pichoir 1985). Oxygen and H (where applicable) were determined by stoichiometry. For the elements considered, the following standards, X-ray lines and crystals were used: CaWO4, WMα, LPET; Ba2NaNb5O15, NbLα, LLIF; MnNb2Ta2O9, TaMα, TAP; ZrO2, ZrLα, LPET; ThO2, ThMα, LPET; UO2, UMβ, LPET; titanite, TiKα, LPET; VP2O7, VKα, LLIF; Chromite, CrKα, LLIF; YPO4, YLα, LPET; LaPO4, LaLα, LLIF; CePO4, CeLα, LLIF; PrPO4, PrLβ, LLIF; NdPO4, NdLβ, LLIF; SmPO4, SmLβ, LLIF; EuPO4, EuLβ, LLIF; GdPO4, GdLβ, LLIF; TbPO4 TbLα, LLIF; DyPO4, DyLβ, LLIF; TmPO4, TmLα, LLIF; YbPO4; YbMα, TAP; Fayalite; FeKα, LLIF; spessartine, MnKα, LTAP; gahnite, ZnKα, , LLIF; olivine, MgKα, LTAP; SrTiO3, SrKα, LPET; barite, BaLα, LLIF; albite, NaKα, TAP; apatite, FKα, LTAP.       112 Phosphates and barite  The following operating conditions: excitation voltage, 15 kV; beam current, 20 nA; peak count time 20 s; background count time, 10 s; spot diameter 10 µm. Data reduction was done using the 'PAP' φ(ρZ) method (Pouchou & Pichoir 1985). Oxygen and H (where applicable) were determined by stoichiometry. For the elements considered, the following standards, X-ray lines and crystals were used: apatite, PKα LPET; pyrite, SKα, LPET; diopside, SiKα, TAP and CaKα, LPET; ThMα, LPET; UO2, UMβ, LPET; YPO4, YLα, LPET; LaPO4, LaLα, LLIF; CePO4, CeLα, LLIF; PrPO4, PrLβ, LLIF; NdPO4, NdLβ, LLIF; SmPO4, SmLβ, LLIF; EuPO4, EuLβ, LLIF; GdPO4, GdLβ, LLIF; TbPO4 TbLα, LLIF; DyPO4, DyLβ, LLIF; Fayalite; FeKα, LLIF; spessartine, MnKα, LTAP; olivine, MgKα, LTA; SrTiO3, SrKα, LPE; barite, BaLα, LLIF; albite, NaKα, TAP; apatite, FKα, LTAP; ; tugtuphite, ClKα, LPET.     5.1.2 Calcite-dolomite geothermometry calculations   Calcite–dolomite solvus geothermometry in (Section 5.35) was calculated using similar methods described in Mizuochi et al. (2010) and the formulation of Anovitz & Essene (1987):  € TMg= A × (XMg) + B /(XMg)2+C × (XMg)2+ D × (XMg)1/ 2+ E    (5.1)  where A, B, C, D and E are coefficients with values -2360.0, -0.01345, 2620.0, 2608.0 and 334.0, respectively, XMg is the Mg content [Mg ⁄(Ca+Mg) apfu] of calcite, and TMg is the solvus temperature in Kelvin.   The correction for the Fe content requires the additional formula of Anovitz & Essene (1987):     113 € TMg,Fe= TMg+ a × (XCalFeCO3) + b × (XCalFeCO3)2+ c × [(XCalFeCO3) /(XCalMgCO3)]+   (5.2)    € d(XCalFeCO3) + (XCalMgCO3) + e × [(XCalFeCO3) /(XCalMgCO3)]2+ f × [(XCalFeCO3) × (XCalMgCO3)]2   where a, b, c, d, e and f are coefficients with values 1718.0, -10610, 22.49, -262600, 1.33, 0.32837€ ×107, respectively, and the standard error for T is 7.93 K.   Reintegration was carried out by estimating the composition prior to unmixing, from the present compositional data, by estimating the area of calcite and exsolved dolomite using digital BSE images and the image analysis software ImageJ (Abramoff et al., 2004).    5.2 ROCK-FORMING MINERALS  5.2.1 Feldspar  Feldspar minerals are common throughout the Ren carbonatite sill, the accompanying fenites, host rocks and late pegmatites. Potassic feldspar (typically orthoclase) is considerably more abundant than plagioclase in the host rocks, richterite-K-feldspar fenite and late pegmatites. The K-feldspar/plagioclase ratio decreases in the phlogopite-plagioclase fenite and feldspathic xenoliths in carbonatite units. The majority of feldspar compositions plot close to the Ab-Or joint (Fig 5.1). Potassic feldspar (Or55–97) compositions are in the range of sanidine, and the Na contents in the mineral can reach up to 0.45 apfu (Fig. 5.2). Potassic feldspar commonly displays replacement textures (albitization) and disaggregation in and around the carbonatite sill (e.g., Fig. 5.3). The Ba contents in the K-feldspar can reach 0.04 apfu (i.e., 2 wt. % BaO or higher) in the feldspathic, Na-rich fenites (richterite-K-feldspar fenite and Ca-amphibole-K-feldspar-clinopyroxene fenite; Fig 5.2). Plagioclase is oligoclase (An10-15) and commonly occurs as xenoblastic crystal aggregates with minor orthoclase, in plagioclase-rich fenites and xenoliths. High albite (An0–5) forms metasomatic rims and exsolution lamellae in K-feldspar, in xenoliths and late pegmatites.        114     Figure 5.1 Composition of feldspar in terms of albite (Na), orthoclase (K) and anorthite (Ca) components (apfu).              Figure 5.2 Chemical variations in K-feldspar, in terms of Na and Ba vs. K.      115  Figure 5.3 Richterite-K-feldspar fenite. Backscattered electron image showing porous rims of K-feldspar crystals replaced by metasomatic albite.   5.2.2 Mica  Biotite (sensu lato) and muscovite are common mica group minerals throughout the Ren locality. Biotite is a major mineral constituent in almost all the lithological units covered, whereas muscovite (after K-feldspar) occurs in low abundances and is generally limited to the feldspar- and quartz-rich units (e.g., quartzite, orthogneiss, pegmatites). Biotite compositions for the Ren carbonatite and fenite units plot close to the Mg-rich end member, phlogopite (Fig. 5.4A, B), which is a characteristic fenitization mineral in carbonatite and alkaline occurrences. Variations in Fe vs. Mg contents of phlogopite from different fenite units most probably reflect initial compositional heterogeneity of the protoliths. Variations in the Fe vs. Mg contents in phlogopites from dolomite carbonatite and dolomite-calcite carbonatite possibly result from the fractionation of Fe during the evolution of the carbonatite system, but more data may be required to verify this assertion. Phlogopites in the phlogopite-richterite fenite units contain the highest Mg contents and are also most enriched in F ( >1 apfu; Fig. 5.4C), which designates them as fluorophlogopites.     116           A      B   C       Figure 5.4 (A) Classification of biotite in terms of Mg/((Mg+Fe) vs. Al. (B) Classifications of biotite in terms of Al, Fe and Mg. Fe = total iron calculated as Fe2+; TFP = tetra-ferriphlogopite. Values are in apfu. (C) Chemical variations of biotite in terms of Mg vs. F.         117  5.2.3 Clinopyroxene  Clinopyroxene is variably abundant in many of the lithological units in and around the Ren carbonatite sill. It is most common in the green, skarn-like Ca-amphibole-K-feldspar-pyroxene fenite. Clinopyroxene compositions from fenites and late pegmatites plot within the Ca-pyroxene component (Fig. 5.5A) and range between diopside to near hedenbergite (Fig. 5.5B). Clinopyroxenes from carbonatite units have a greater compositional range (Figs. 5.5B, C), from diopside-hedenbergite (near the fenite contacts) toward aegirine (in the middle portion of the carbonatite sill). In thin sections under transmitted, plane-polarised light, the Ca-clinopyroxenes appear colourless, whereas the Na- and Fe-rich varieties appear in more pronounced shades of green.   Excluding the late pegmatites, the apparent compositional trend in the clinopyroxenes, from fenites to carbonatites, shows decreasing in Ca and Mg contents with increasing Fe and Na contents. This trend reflects increasing alkalinity in the carbonatite-fenite system. The Fe-Mg variations in the fenites alone likely reflect compositional heterogeneity of host rock protoliths or the intensity of fenitization, or both. It should be noted that a secondary clinopyroxene (as opposed to the primary magmatic clinopyroxenes), forming together with Na-Fe amphibole and after richterite, was observed near feldspathic xenoliths in carbonatite units (see Chapter 4 and Fig. 5.6). Similar replacements of amphibole by clinopyroxenes have been described from the Larvik Plutonic Complex, Norway (Piilonen et al., 2013). The origin of this secondary clinopyroxene (and the associated Na-Fe amphibole) is not clear.            118 A       B       C                     Figure 5.5 Compositional variations in clinopyroxenes in terms of end-member components (apfu).   119      Figure 5.6 Dolomite-calcite carbonatite with xenoliths. Photomicrograph in transmitted, plane-polarized light showing secondary clinopyroxene and quartz after richterite.             120 5.2.4 Amphibole  The general formula for amphiboles may be written as A0–1B2VIC5IVT8O22(OH, F, CI)2 where roman superscripts represents coordination number of the C and T sites, respectively. The nomenclature and cation distribution used herein follow the recommendations of the International Mineralogical Association (IMA) (Leake 1978; Leake et al., 1997; 2004).   Amphiboles occur throughout most of the studied rocks (Chapter 4; Fig. 5.7). The non-fenitized metasedimentary host rocks around the carbonatite and fenite units commonly comprise variable amounts of hornblende. However, the majority of amphibole compositions (microprobe data) in the carbonatite and fenite units belong to the sodic-calcic group, and include winchite, richterite and fluororichterite (Fig. 5.8A, B; Fig. 5.9). Sodic group amphiboles, ferri-nyböite and ferro-eckermannite were observed only in the calcite carbonatite unit. Calcic amphiboles, tremolite and actinolite, and Fe-Mg amphibole, cummingtonite, commonly occur as replacement minerals for clinopyroxene in the pyroxene fenite and, to less extent, in the neighbouring winchite-rich carbonatite. Tremolite is also present as a primary mineral in these rocks.  The compositions of tremolite and actinolite from the fenite units show an increase in Na+K towards carbonatite units (Fig. 5.8C). The Na-K amphiboles exhibit variable compositions within and across lithological units (Fig. 5.8C). The compositional change from winchite to richterite and katophorite (Fig. 5.9C) shows a general light increase of F, Mg/Mg+Fe, K/(Na+K) and a decrease of Fe3++Al and Fetotal (Fig. 5.10).             121       Figure 5.7 Photomicrographs of amphiboles in transmitted, cross-polarized light. (A) Ca-amphibole-K-feldspar-pyroxene fenite. Actinolite after clinopyroxene and tremolite in actinoite and cummingtonite after clinopyroxene. (B) Ca-amphibole-K-feldspar-pyroxene fenite. Actinolite and cummingtonite after clinopyroxene. (C) Winchite-rich, calcite-dolomite porphyroblastic carbonatite. Corona textures associated with clinopyroxene, resulting from the replacement of cummingtonite (after clinopyroxene) by tremolite, which is also replaced by winchite. (D) Winchite-rich, calcite-dolomite porphyroblastic carbonatite. Euhedral winchite. (E) Dolomite-calcite carbonatite with xenoliths. Euhedral to subhedral  122 fluororichterite. (F) Calcite carbonatite. Subhedral ferric-nyböite comprising inclusions of ferro-eckermannite.            A      B       C    Figure 5.8 Compositional variation diagrams for amphiboles.     123 A B  C    D  Figure 5.9 Classification diagrams of amphiboles after Leake et al. (1997).     124         Figure 5.10 Chemical variations in sodic, sodic-calcic and calcic amphiboles.    125 5.2.5 Carbonates and calcite-dolomite geothermometry  Carbonates (Figs. 5.11, 5.12) occur in variable amounts in all the studies rock units, and they are increasingly more abundant toward the carbonatite sill. Dolomite is present as either well-formed crystals or exsolution microstructures (‘clouds’, blebs, and unidirectional lamellae; Figs. 5.13, 5.15) in calcite, in most carbonatites and intermixing carbonate-rich fenites. Dolomite carbonatite occupies primarily the middle sections the sill, but dolomite-calcite mixed carbonatite is the most prevailing rock. Calcite forms differentiated and undifferentiated crystals, with or without dolomite exsolution features. A nearly “pure” calcite carbonatite was observed in the middle portions of the sill. Lesser amounts of strontianite are characteristic in calcite- and barite-rich veins and units. In thin sections strontianite appears as ‘cloudy’ anhedral grains, and it commonly forms exsolution blebs or symplectite in Sr-rich calcite. Norsethite, BaMg(CO3)2, was observed only near the hanging wall of the sill, in the richterite-rich, dolomite-norsethite-calcite carbonatite unit. In thin sections, norsethite has a generally smoother relief than the other carbonates, and it lacks the typical micropores observed in barite. An accessory REE-carbonate, carbocernaite, occurs as an exsolution component in ‘cloudy’ calcites and is described in Section 5.2.                126 A            B   C  Figure 5.11 Chemical compositions of carbonates in terms of end-member components. Units are in apfu.   127       Figure 5.12 Photomicrographs of carbonates in transmitted, cross-polarized light. (A) Dolomite carbonatite. Xenoblastic dolomite. (B) Dolomite-calcite carbonatite. Anhedral calcite comprising exsolved dolomite. (C) Winchite-rich, calcite-dolomite porphyroblastic carbonatite. ‘Cloudy’ grains of strontianite associated with barite. (D) Richterite-rich, dolomite-norsethite-calcite carbonatite. Anhedral paragenetic assemblage of norsethite, dolomite and ‘cloudy’ calcite comprising carbocernaite.           128     Figure 5.13 Dolomite-calcite carbonatite. Backscattered electron images showing dolomite exsolution ‘clouds’ (i.e., tiny specks), larger blebs and unidirectional lamella, in calcite.           129      Figure 5.14 Backscattered electron images. (A) Carbonate vein in fenitized paragneiss. Strontianite exsolution from calcite. (B) Richterite-rich, dolomite-norsethite-calcite carbonatite. Exsolution of strontianite and carbocernaite from calcite.          A B  130  Calcite-dolomite solvus geothermometry    Calcite-dolomite solvus geothermometry (Anovitz & Essene, 1987) was applied to infer the crystallization temperatures of calcite (Table 5.1). Analyses of 28 grains of non-reintegrated calcite gave temperatures of 420–680 °C (Fig. 5.16A). However, temperatures estimated for 15 calcite grains, reintegrating measured domains comprising homogeneously exsolved dolomite (Table 5.1, Figs. Fig. 5.15, 5.16B), lie in the range of 620–820 °C. On the basis of the established syn-peak metamorphic thermal conditions of 580–730 °C for the Frenchman Cap Dome (Parrish, 1995; Crowley & Parrish, 1999; Millonig et al., 2013 and references therein), the values for the earlier magmatic calcites, which crystallized at temperatures above 730 °C, can be differentiated (thermally) from the later, metamorphic calcites forming at lower temperatures (Table 5.2). The estimated average magmatic calcite-dolomite solvus temperature is around 760 °C, whereas the estimated average metamorphic solvus temperature is around 690 °C. It should be noted that values which fall in the range of 720–740 °C may represent either magmatic or metamorphic solvi. Also, the distribution temperature values in Figure 5.16 may reflect two or more calcite generations in each of the magmatic and metamorphic groups. Further work (e.g., detailed textural characterization using cathodoluminescence) may be required to differentiate between the magmatic and metamorphic calcites and between different generations of calcite in each group.              131  Table 5.1 Calculated temperatures inferred from calcites comprising exsolved dolomite.  Lithology Sample- EMPA point Calcite  T (°C) Dolomite fraction (%) Integrated dolomite  T (°C) Winchite-rich, cal-dol carbonatite 0091A1-5 605   Winchite-rich, cal-dol carbonatite 0091A1-9 597   Winchite-rich, cal-dol carbonatite 0091A1-10 616   Dolomite-calcite carbonatite  0141A1-2 420 25.5 672 Dolomite-calcite carbonatite  0141A1-4 423 19.1 633 Dolomite-calcite carbonatite  0141A1-8 659 18.2 737 Dolomite-calcite carbonatite  0141A1-10 535 11.6 628 Dolomite-calcite carbonatite  0141A1-14 635 19.7 728 Dolomite-calcite carbonatite  0141A1-15 621 8.1 665 Dolomite-calcite carbonatite  0241A2-2 641 17.1 764 Dolomite-calcite carbonatite  0241A3-4 645 13.1 740 Dolomite-calcite carbonatite  0241A3-6 665 20.4 803 Dolomite-calcite carbonatite  0241A3-7 623 17.8 758 Dolomite-calcite carbonatite  0391A1-1 455 26.5 745 Dolomite-calcite carbonatite  0391A1-3 530 21.0 729 Dolomite-calcite carbonatite  0521A1-1 613 14.2 722 Dolomite-calcite carbonatite  0521A1-7 575 14.8 716 Dolomite-calcite carbonatite  0521A1-8 582 13.6 699 Rct-rich, dol-nor-cal carbonatite 2131A1-7 611   Rct-rich, dol-nor-cal carbonatite 2131A1-8 585   Rct-rich, dol-nor-cal carbonatite 2131A1-9 562   Calcite carbonatite  R1181A1-4 638   Calcite carbonatite  R1181A1-5 627   Calcite carbonatite  R1181A1-6 626   Carbonate vein in pyroxene fenite  0081A1-2 638   Carbonate vein in pyroxene fenite 0081A5-2 449   Carbonate vein in pyroxene fenite 0081A5-3 565   Carbonate matrix in phl-rct fenite 0121A4-3 468     Table 5.2 Integrated temperature values (°C) above and within syn-peak metamorphic thermal range*. Within syn-peak metamorphic T range  (T≤730°C); n=9 Above syn-peak metamorphic T range (T>730°C); n=6 avg  median stdv avg  median  stdv 688 699 39.8 758 751 24.5 *(Parrish, 1995; Crowley & Parrish, 1999; Millonig et al., 2013 and references therein)   132  0141A1-2, 25.5%  0141A1-4, 19.1%  0141A1-8, 18.2%  0141A1-10, 11.6%  0141A1-14, 19.7%  0141A1-15, 8.1%  0241A2-2, 17.1%  0241A3-4, 13.1%  0241A3-6, 20.4%  0241A3-7, 17.8%  0391A1-1, 26.5%  0391A1-3, 21.0%  0521A1-1, 14.2%  0521A1-7, 14.8%  0521A1-8, 13.6% Figure 5.15 Backscattered electron images of homogeneously exsolved dolomite in calcite, from dolomite-calcite carbonatite units. Also given are the calculated fraction values for the exsolved dolomite in the calcite grains (Table 5.1).    133     A      B   Figure 5.16 (A) Frequency distribution diagram of non-integrated temperatures inferred from the composition of analyzed calcite in 28 grains including homogenously exsolved dolomite (Table 5.1). (B) Frequency distribution diagram of temperatures from the integrated composition of analyzed homogenously exsolved dolomite (Table 5.1), from dolomite-calcite carbonatite samples only. The magmatic calcites are thermally differentiated from metamorphic calcites (Table 5.2), on the basis of the established syn-peak metamorphic thermal conditions of 580–730 °C for the Frenchman Cap Dome (Parrish, 1995; Crowley & Parrish, 1999; Millonig et al., 2013 and references therein).   134 5.2.6 Barite  Barite concentrations increase across the lithological units, from zero or trace to about 5 vol. %, towards the hanging wall of the carbonatite sill, where concentrations of 8–14 vol. % were noted locally (i.e., in richterite-rich, dolomite-norsethite-calcite carbonatite and winchite-rich, dolomite-calcite carbonatite). Barite occurs as a late mineral, set between grains of primary minerals, in interstices and micro-fractures, and, in places, enclosing corroded strontianite (Fig. 5.18). Microprobe analyses of barite from different locations show variations in Sr contents between 0–0.10 apfu (Fig. 5.17), resulting from substitution or Ba with Sr, and depending primarily on the abundance of strontianite in the rock.     Figure 5.17 Chemical variations of Ba vs. Sr in barite.       135    Figure 5.18 Backscatter electron images of barite. (A) Winchite-rich, dolomite calcite porphyroblastic carbonatite. Late, interstitial barite. (B) Richterite-rich, dolomite-norsethite-calcite carbonatite. Microcrack infilling of barite in northesite. (C) Winchite-rich, dolomite calcite porphyroblastic carbonatite. Paragenetic association of calcite, strontianite and barite.   A B C  136 5.3 ORE AND ACCESSORY MINERALS  5.4.1 Monazite-(Ce) and fluorapatite  Monazite and apatite commonly occur in association throughout the Ren occurrence. They are found primarily in the dolomite-calcite carbonatites, but also in the carbonate-rich fenites and the calcareous paragneiss host rocks. The highest concentrations of monazite (1–3 vol. %) are generally limited to the carbonatite and fenite units observed within 15 metres or less of the hanging wall of carbonatite sill. Other sections of the carbonatite and fenite units, closer to the footwall of the sill, are virtually deficient in monazite or have less monazite than the paragneiss host rock. Apatite concentrations of 2–6 vol. % occur throughout the carbonatite units, with lower amounts observed in the fenite and host rock units.   In thin sections, monazite commonly forms anhedral to amorphous grains in and around apatite (Figs. 5.19, 5.20), and also subhedral, round or elongated grains that are not in direct contact with apatite (Figs. 5.19, 5.22) In places, monazite grains display inclusions of other minerals such as ferrocolumbite and carbonates (Fig. 5.22). In contrast to monazite, apatite is generally more uniform in its ovoid grain shape, but it may also occur as intergrowths with monazite (Fig. 5.21). Apatite grains in carbonatite units may contain small inclusions of barite, which appear to be produced by exsolution from initially Ba-rich apatite (Fig. 5.23). Both monazite and apatite occur together with a wide variety of paragenetically later minerals: carbonates, phlogopite, barite, clinopyroxenes and amphiboles.  Microprobe analyses of monazite (Table 5.3) show depletion in U and Th and enrichment in LREE, which designates the mineral as monazite-(Ce). Apatite is always fluorapatite with F contents between 0.733 and 2.091 apfu (average 0.992 apfu; Table 5.4). It should be noted that the excessively high values of F, above 1.0 apfu, result from the operating and/or specimen surface conditions during microprobe analysis (e.g., apatite grain orientation parallel to c-axis; see Stormer et al.,1993). In comparison to monazite, fluorapatite is poor in REE, with only slight enrichment in LREE (up to 2.66 wt. % Ce2O3 and 1.03 wt. % La2O3). The mineral also exhibits elevated Sr (up to 0.195 apfu, 3.91 wt. %  137 SrO) and Ba (up to 0.019 apfu, 0.56 wt. % BaO). The reader may refer to the tables of mineral compositions in the Appendix.        Figure 5.19 Calcareous biotite-feldspar paragneiss. Backscattered electron image of anhedral monazite-(Ce) (white) associated with and surrounding fluorapatite (medium grey). Both minerals are enclosed by K-feldspar (dark grey).    Figure 5.20 Dolomite-calcite carbonatite. Backscattered electron image showing a monazite-(Ce) corona enclosing fluorapatite. Both monazites and apatite are enclosed by carbonates.     138   Figure 5.21 Phlogopite-richterite fenite. Backscattered electron image of anhedral monazite-(Ce) (white) in fluorapatite (medium grey). Both minerals are enclosed by richterite (dark grey).         Figure 5.22 Dolomite-calcite carbonatite. Photomicrographs in transmitted plane-polarized light (left) and cross-polarized light (right) showing monazite-(Ce) with inclusions of columbite.        139   Figure 5.23 Dolomite-calcite carbonatite. Backscattered electron image of fluorapatite (light grey) displaying inclusions of barite (white blebs). The fluorapatite grain is enclosed by dolomite (darker grey).   Table 5.3 Average and representative chemical compositions of monazite-(Ce).  avg stdev  avg stdev n 8  0091A1-8 0141A1-16  8  0091A1-8 0141A1-16 P2O5 wt. % 28.29 3.24 26.98 30.14 P5+ apfu 0.951 0.085 0.925 0.992 SiO2 0.89 1.51 1.42 0.28 Si4+ 0.037 0.064 0.058 0.011 SO2 0.29 0.30 0.86 0.33 S4+ 0.011 0.012 0.033 0.012 ThO2 0.41 0.66 0.06 0.05 Th4+ 0.004 0.006 0.001 0.000 UO2 0.01 0.01 0.00 0.00 U4+ 0.000 0.000 0.000 0.000 Y2O3 0.05 0.02 0.05 0.03 Y3+ 0.001 0.000 0.001 0.001 La2O3 24.83 1.78 23.79 25.26 La3+ 0.365 0.037 0.355 0.362 Ce2O3 35.61 1.26 35.29 34.80 Ce3+ 0.519 0.027 0.523 0.496 Pr2O3 2.59 0.27 2.65 2.76 Pr3+ 0.038 0.003 0.039 0.039 Nd2O3 6.75 0.83 6.40 6.56 Nd3+ 0.096 0.011 0.093 0.091 SmO 0.35 0.18 0.49 0.56 Sm3+ 0.005 0.003 0.007 0.008 EuO 0.02 0.01 0.02 0.03 Eu2+ 0.000 0.000 0.000 0.000 Gd2O3 0.12 0.09 0.29 0.20 Gd3+ 0.002 0.001 0.004 0.003 Tb2O3 0.13 0.05 0.14 0.06 Tb3+ 0.002 0.001 0.002 0.001 Dy2O3 0.05 0.04 0.07 0.02 Dy3+ 0.001 0.001 0.001 0.000 FeO 0.01 0.02 0.01 0.00 Fe2+ 0.000 0.001 0.000 0.000 MnO 0.00 0.01 0.00 0.00 Mn2+ 0.000 0.000 0.000 0.000 CaO 0.20 0.19 0.09 0.25 Ca2+ 0.009 0.009 0.004 0.010 SrO 0.08 0.06 0.00 0.19 Sr2+ 0.002 0.001 0.000 0.004 BaO 0.42 0.30 0.77 0.04 Ba2+ 0.007 0.005 0.012 0.001 F 0.51 0.25 0.68 0.64 F- 0.064 0.032 0.087 0.079 Cl 0.02 0.01 0.03 0.02 Cl- 0.001 0.000 0.002 0.001 -(O=F, Cl) -0.22 0.11 -0.29 -0.27      Total 101.40 11.21 99.80 101.95      Formulae are normalized on 4 anions; all other analyzed elements are below detection limits.  140 Table 5.4 Average and representative chemical compositions of fluorapatite.  avg stdev  avg stdev n 17  2131A1-2 0141B2-3    2131A1-2 0141B2-3 P2O5 wt. % 41.46 1.04 40.09 39.41 P5+ apfu 2.995 0.049 2.987 2.865 SO2 0.10 0.12 0.03 0.20 S4+ 0.009 0.010 0.003 0.017 SiO2 0.14 0.17 0.04 0.64 Si4+ 0.011 0.013 0.003 0.052 ThO2 0.01 0.01 0.00 0.00 Th4+ 0.000 0.000 0.000 0.000 UO2 0.02 0.02 0.00 0.06 U4+ 0.000 0.000 0.000 0.001 Y2O3 0.03 0.03 0.00 0.01 Y3+ 0.001 0.001 0.000 0.000 La2O3 0.38 0.36 1.03 0.81 La3+ 0.012 0.011 0.033 0.026 Ce2O3 0.97 0.85 2.62 1.76 Ce3+ 0.031 0.027 0.084 0.055 Pr2O3 0.17 0.11 0.44 0.30 Pr3+ 0.005 0.003 0.014 0.009 Nd2O3 0.44 0.37 1.03 0.69 Nd3+ 0.014 0.012 0.032 0.021 SmO 0.17 0.15 0.04 0.17 Sm3+ 0.005 0.005 0.001 0.005 EuO 0.02 0.02 0.04 0.01 Eu2+ 0.001 0.001 0.001 0.000 Gd2O3 0.03 0.05 0.00 0.01 Gd3+ 0.001 0.001 0.000 0.000 Tb2O3 0.05 0.05 0.07 0.08 Tb3+ 0.001 0.001 0.002 0.002 Dy2O3 0.07 0.06 0.13 0.06 Dy3+ 0.002 0.002 0.004 0.002 FeO 0.02 0.03 0.03 0.00 Fe2+ 0.002 0.002 0.002 0.000 MnO 0.10 0.08 0.30 0.10 Mn2+ 0.007 0.006 0.022 0.007 CaO 52.05 2.26 47.33 50.29 Ca2+ 4.758 0.157 4.463 4.628 SrO 1.57 1.19 3.65 2.80 Sr2+ 0.078 0.060 0.186 0.139 BaO 0.11 0.18 0.08 0.56 Ba2+ 0.004 0.006 0.003 0.019 Na2O 0.38 0.33 0.93 0.90 Na+ 0.063 0.055 0.159 0.150 F 3.67 1.12 3.26 3.74 F- 0.992 0.312 0.907 1.016 Cl 0.02 0.01 0.05 0.02 Cl- 0.002 0.002 0.007 0.003 H2O* 0.17 0.18 0.15 0.00 OH- 0.094 0.100 0.085 0.000 -(O=F, Cl) -1.55 0.47 -1.38 -1.58 O- 11.971 0.169 11.992 11.842 Total 100.59 9.27 99.95 101.04 F mol.% 90.4 9.9 90.7 99.7      Cl 0.2 0.2 0.7 0.3      OH 9.4 10.0 8.5 0.0 Formulae are normalized on 8 cations; * determined by stoichiometry; all other analyzed elements are below detection limits. Fluorine contents are above 2 apfu due to diffusion during microprobe analysis.         141 5.3.2 Ferriallanite-(Ce) + chevkinite-(Ce) + fergusonite-(Nd) assemblage   Ferriallanite-(Ce), chevkinite-(Ce) and fergusonite-(Nd) occur together (up to 1 vol. %) close to the hanging wall of the sill, in Ca-amphibole-K-feldspar-pyroxene fenite at the contact zone with the carbonatite. Isolated anhedral ferriallanite grains (i.e., not associated with chevkinite and fergusonite) also occur (<1 vol. %) in winchite-rich, calcite-dolomite porphyroblastic carbonatite next to the pyroxene fenite. The assemblage in the pyroxene fenite displays anhedral allanite overgrowing anhedral chevkinite and subhedral titanite (Fig. 5.24). The titanite is also generally enclosed in the chevkinite. A number of small euhedral crystals of rare fergusonite appear to have formed on top of the titanite crystals. This paragenetic assemblage of ferriallanite, chevkinite and fergusonite occurs together with carbonates, clinopyroxenes, barite and monazite.  Another type of ferriallanite is found as anhedral grains in association with monazite, phlogopite carbonates and, in places, near the biraite and västmanlandite assemblage (Fig. 5.26), in the winchite-rich carbonatite.    Ferriallanite is the iron-rich allanite end-member of the classification diagram for epidote-group minerals (Fig. 5.25). According to the EPMA data, the dominant REE for the mineral is Ce, which designates it as ferriallanite-(Ce), and whose ideal formula is CaCe(Fe3+,Fe2+,Al)3[SiO4][Si2O7]O(OH). In certain analytical spots from two different thin sections, ferriallanite has very low contents of Al, most probably resulting from substitution of Fe3+ for Al. This observation suggests either an analytical error or the existence of a new Al-free species (Fig. 5.25 and Table 5.5). Similarly, chevkinite is chevkinite-(Ce), whose ideal chemical formula is (Nd,Ce)(Nb,Ti)O4, but with higher contents of both La and Ce. In contrast to ferriallanite and chevkinite, fergusonite shows enrichment in Nd and is therefore designated as fergusonite-(Nd). This mineral exhibits high contents of Y and Ce, and the simplified formula is: (Nd0.29Y0.21Ce0.15Sm0.1Gd0.07Pr0.04)(Nb1.0Ta0.02)O4.0.        142   Figure 5.24 Calcic amphibole-K-feldspar-pyroxene fenite. Photomicrograph in transmitted cross-polarized light (top) and a corresponding backscattered electron image (bottom) showing paragenetic ferriallanite-(Ce) + chevkinite-(Ce) + fergusonite-(Nd).          143   Figure 5.25 Chemical compositions of ferriallanite-(Ce) in terms of Al vs. Y+REE (after Petríck et al., 1995).                           144 Table 5.5 Average and representative chemical compositions of ferriallanite-(Ce). Lithology   Calcic amphibole-K-feldspar-pyroxene fenite  Winchite-rich, calcite-dolomite porphyroblastic carbonatite    Calcic amphibole-K-feldspar-pyroxene fenite  Winchite-rich, calcite-dolomite porphyroblastic carbonatite  avg stdev  avg stdev n 53  0081B2-2 0091B4-4   53  0081B2-2 0091B4-4  SiO2 wt.% 31.26 0.58 29.78 30.30 Si4+ apfu 3.021 0.018 2.981 2.966 TiO2 0.76 0.50 2.87 0.43 Ti4+ 0.055 0.038 0.216 0.032 ZrO2 0.00 0.00 0.00 0.00 Zr4+ 0.000 0.000 0.000 0.000 SnO2 0.01 0.01 0.01 0.02 Sn4+ 0.000 0.000 0.000 0.001 HfO2 0.03 0.05 0.06 0.00 Hf4+ 0.000 0.000 0.002 0.000 ThO2 0.02 0.02 0.00 0.00 Th4+ 0.000 0.000 0.000 0.000 UO2 0.01 0.02 0.00 0.02 U4+ 0.000 0.000 0.000 0.000 Al2O3 11.76 2.48 5.09 8.11 Al3+ 1.335 0.264 0.600 0.936 V2O3 0.07 0.05 0.13 0.02 V3+ 0.001 0.002 0.010 0.002 Y2O3 0.02 0.02 0.02 0.03 Y3+ 0.001 0.001 0.001 0.002 La2O3 8.81 1.16 8.29 12.16 La3+ 0.314 0.045 0.306 0.439 Ce2O3 13.51 0.33 13.38 14.12 Ce3+ 0.478 0.017 0.490 0.506 Pr2O3 1.06 0.15 0.96 0.96 Pr3+ 0.037 0.005 0.035 0.034 Nd2O3 2.84 0.53 3.08 1.77 Nd3+ 0.098 0.018 0.110 0.062 SmO 0.21 0.10 0.23 0.09 Sm3+ 0.007 0.003 0.008 0.003 EuO 0.02 0.04 0.00 0.00 Eu2+ 0.001 0.002 0.000 0.000 Gd2O3 0.01 0.03 0.00 0.00 Gd3+ 0.000 0.001 0.000 0.000 Tb2O3 0.09 0.06 0.10 0.13 Tb3+ 0.003 0.002 0.003 0.004 Dy2O3 0.01 0.03 0.11 0.02 Dy3+ 0.000 0.001 0.004 0.001 Fe2O3* 8.23 3.20 15.79 17.35 Fe3+ 0.602 0.244 1.189 1.278 FeO* 8.70 1.64 8.55 2.78 Fe2+ 0.704 0.138 0.716 0.228 (FeOT)** 16.10 2.80 22.76 18.39      MnO 0.93 0.09 1.14 0.89 Mn2+ 0.076 0.008 0.097 0.074 ZnO 0.07 0.03 0.08 0.05 Zn2+ 0.001 0.002 0.006 0.004 MgO 1.79 0.63 1.00 3.11 Mg2+ 0.258 0.092 0.149 0.454 CaO 9.57 0.56 8.97 8.05 Ca2+ 0.990 0.045 0.962 0.844 SrO 0.06 0.15 0.69 0.00 Sr2+ 0.004 0.009 0.040 0.000 BaO 0.00 0.00 0.00 0.00 Ba2+ 0.000 0.000 0.000 0.000 Na2O 0.03 0.03 0.00 0.00 Na+ 0.001 0.003 0.000 0.000 K2O 0.00 0.01 0.01 0.01 K+ 0.000 0.000 0.001 0.001 F 0.04 0.10 0.23 0.42 F- 0.040 0.100 0.073 0.130 H2O 0.75 0.03 0.66 0.63 OH- 0.988 0.031 0.927 0.870 -(O=F) -0.03 0.08 -0.19 -0.35 O- 12    Total 100.43 0.52 101.04 101.11      Formulae are normalized on 8 cations; * determined by stoichiometry; ** EPMA measured value; all other analyzed elements  are below detection limits.       145 Table 5.6 Chemical compositions of chevkinite-(Ce) Lithology Calcic amphibole-K-feldspar-pyroxene fenite  Calcic amphibole-K-feldspar-augite fenite     Calcic amphibole-K-feldspar-augite fenite  Calcic amphibole-K-feldspar-pyroxene fenite   EPMA point   0081B2-12 0081B2-3  avg  0081B2-12 0081B2-3 avg Nb2O5 wt.% 3.42 2.49 2.95 Nb5+ apfu 0.322 0.236 0.279 P2O5 0.00 0.00 0.00 P5+ 0.000 0.000 0.000 SiO2 18.50 18.43 18.46 Si4+ 3.859 3.863 3.861 TiO2 13.17 13.98 13.57 Ti4+ 2.066 2.205 2.135 ZrO2 0.11 0.00 0.06 Zr4+ 0.011 0.000 0.006 SnO2 0.10 0.15 0.12 Sn4+ 0.008 0.012 0.010 HfO2 0.09 0.00 0.05 Hf4+ 0.006 0.000 0.003 ThO2 5.46 5.34 5.40 Th4+ 0.259 0.255 0.257 UO2 0.06 0.03 0.04 U4+ 0.003 0.001 0.002 V2O3 0.19 0.11 0.15 V3+ 0.031 0.019 0.025 Al2O3 0.61 0.30 0.45 Al3+ 0.150 0.073 0.112 Y2O3 0.17 0.13 0.15 Y3+ 0.019 0.014 0.016 La2O3 11.90 11.92 11.91 La3+ 0.915 0.921 0.918 Ce2O3 22.12 21.74 21.93 Ce3+ 1.689 1.669 1.679 Pr2O3 2.14 1.87 2.00 Pr3+ 0.163 0.143 0.153 Nd2O3 6.04 6.00 6.02 Nd3+ 0.450 0.449 0.449 SmO 0.48 0.64 0.56 Sm3+ 0.036 0.048 0.042 EuO 0.08 0.06 0.07 Eu2+ 0.006 0.005 0.006 Gd2O3 0.20 0.16 0.18 Gd3+ 0.014 0.011 0.013 Tb2O3 0.18 0.13 0.15 Tb3+ 0.012 0.009 0.010 Dy2O3 0.04 0.12 0.08 Dy3+ 0.002 0.008 0.005 FeO 10.60 11.04 10.82 Fe2+ 1.850 1.935 1.892 MnO 0.52 0.63 0.57 Mn2+ 0.092 0.112 0.102 ZnO 0.04 0.04 0.04 Zn2+ 0.006 0.006 0.006 MgO 0.56 0.41 0.49 Mg2+ 0.176 0.127 0.151 CaO 2.69 2.57 2.63 Ca2+ 0.600 0.578 0.589 SrO 0.19 0.31 0.25 Sr2+ 0.022 0.038 0.030 BaO 0.00 0.00 0.00 Ba2+ 0.000 0.000 0.000 Na2O 0.00 0.00 0.00 Na+ 0.000 0.000 0.000 K2O 0.00 0.01 0.00 K+ 0.000 0.002 0.001 F 0.35 0.40 0.37 F- 0.232 0.264 0.248 H2O* 0.46 0.44 0.45 OH- 0.768 0.736 0.752 -(O=F) -0.30 -0.34 -0.32 O- 20.686 20.580 20.633 Total 100.16 99.05 99.60     Formulae are normalized on 13 cations; * determined by stoichiometry; all other analyzed elements  are below detection limits.      146 Table 5.7 Chemical composition of fergusonite-(Nd). Lithology Calcic amphibole- K-feldspar-augite fenite    Calcic amphibole- K-feldspar-augite fenite  EPMA point   0081B2-1  0081B2-1 WO3 wt.% 1.08 W6+ apfu 0.014 Nb2O5  45.42 Nb5+  1.025 Ta2O5 1.71 Ta5+ 0.023 TiO2 0.17 Ti4+ 0.006 ThO2 0.00 Th4+ 0.000 UO2 0.07 U4+ 0.001 V2O3 0.00 V3+ 0.000 Cr2O3 0.00 Cr3+ 0.000 Y2O3 8.17 Y3+ 0.217 La2O3 1.31 La3+ 0.024 Ce2O3 8.39 Ce3+ 0.153 Pr2O3 2.30 Pr3+ 0.042 Nd2O3 16.48 Nd3+ 0.294 SmO 5.35 Sm3+ 0.096 EuO 0.03 Eu2+ 0.001 Gd2O3 4.15 Gd3+ 0.069 Tb2O3 0.47 Tb3+ 0.008 Dy2O3 2.03 Dy3+ 0.033 Tm2O3 0.36 Tm3+ 0.006 Yb2O3 0.71 Yb3+ 0.011 Lu2O3 0.00 Lu3+ 0.000 FeO 0.00 Fe2+ 0.000 MnO 0.00 Mn2+ 0.000 ZnO 0.04 Zn2+ 0.001 MgO 0.00 Mg2+ 0.000 CaO 0.55 Ca2+ 0.029 SrO 0.00 Sr2+ 0.000 BaO 0.00 Ba2+ 0.000 Na2O 0.00 Na+ 0.000 F 0.18 F- 0.028 Total 98.97 O- 4.016 Formulae are normalized on 2 cations. All other  analyzed elements are below detection.        147 5.3.3 (Fe,OH)-analogue to västmanlandite-(Ce) + biraite-(Ce) [including (Mg)-analogue to biraite-(Ce)] assemblage  Discove