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Petrology, volcanology, and diamonds of archean calc-alkaline lamprophyres, Wawa, Ontario, Canada Lefebvre, Nathalie Suzanne 2004

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PETROLOGY, V O L C A N O L O G Y , A N D DIAMONDS OF A R C H E A N C A L C - A L K A L I N E LAMPROPHYRES, WAWA, ONTARIO, C A N A D A By NATHALIE SUZANNE LEFEBVRE B.Sc. ( H o n s ) , The U n i v e r s i t y o f W e s t e r n O n t a r i o , 1998  A THESIS S U B M I T T E D I N P A R T I A L F U L F I L L M E N T OF T H E REQUIREMENTS FOR T H E DEGREE OF M A S T E R OF SCIENCE in T H E F A C U L T Y OF G R A D U A T E STUDIES ( D e p a r t m e n t o f Earth and Ocean Sciences; G e o l o g y P r o g r a m m e ) W e accept this thesis as c o n f o r m i n g to the required standard  T H E U N I V E R S I T Y OF B R I T I S H C O L U M B I A M a r c h , 2004 © N a t h a l i e Suzanne L e f e b v r e , 2004  UBCL  mm  THE UNIVERSITY OF BRITISH COLUMBIA  FACULTY OF GRADUATE STUDIES  Library Authorization  In presenting this thesis in partial fulfillment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.  Nathalie Lefebvre  16/08/2004  Name of Author (please print)  Date (dd/mm/yyyy)  Title of Thesis:  Petrology, Volcanology, and Diamonds of Archean Calc-Alkaline Lamprophyres, Wawa, Ontario, Canada  Degree:  Master of Science  Department of  Earth and Ocean Science  Year:  2004  The University of British Columbia Vancouver, BC Canada  grad.ubc.ca/forms/?formlD=THS  page 1 of 1  last updated: 16-Aug-04  ABSTRACT A t y p i c a l diamondiferous p o l y m i c t volcaniclastic breccias and lamprophyre dikes have been recently discovered w i t h i n the W a w a subprovince o f the Superior craton. These rocks comprise part o f a subduction-related volcanic sequence o f the M i c h i p i c o t e n greenstone belt. Dated at 2.67 Ga, they are the oldest k n o w n p r i m a r y diamondiferous rocks. Detailed m a p p i n g o f 9 trenches and 7 outcrops showed that the rocks comprise both dikes and t h i c k continuous units o f p o l y m i c t volcaniclastic breccia. B o t h are m a f i c , metamorphosed to greenschist facies and deformed, w i t h little p r i m a r y magmatic texture preserved.  Magmatic  predecessors, determined f r o m detailed mineralogical and petrographic observations, are calcalkaline lamprophyres. The only preserved magmatic phenocryst is coarse, oscillatory-zoned edenitic and pargasitic amphibole. The parent magmas may have contained phenocrysts o f clinopyroxene  and phlogopite,  and are  similar  in  bulk  composition  to  that  of  Abitibi  lamprophyres and other Archean calc-alkaline lamprophyres. The breccias are interpreted to be volcaniclastic debris f l o w deposits based on the stratigraphy, w i d e range i n fragment lithologies ( w h i c h include pyroclastic material), poor sorting, and paucity o f sedimentary structures.  The explosive eruption style o f the W a w a calc-  alkaline l a m p r o p h y r i c magma is, however, atypical for lamprophyres. The calc-alkaline lamprophyric m a g m a f o r m e d i n the mantle at depths o f - 1 5 0 k m i n a convergent tectonic regime, thus sampling the cool diamondiferous subducting slab. The m a g m a was emplaced very rapidly ensuring preservation o f diamonds d u r i n g ascent. The metavolcanic rocks represent the first c o n f i r m e d occurrence o f diamonds i n  Wawa  calc-alkaline  lamprophyric rocks. The W a w a metavolcanic rocks host a d i a m o n d suite dominated b y microdiamonds. E i g h t y diamonds less than 1 m m i n one d i m e n s i o n were studied b y a variety o f mineralogical  ii  methods. M o r p h o l o g i c a l studies show that the m a j o r i t y o f the diamonds are colourless, w e a k l y resorbed, octahedral single crystals and aggregates. A variety o f d i a m o n d colours, as w e l l as cubic and cubo-octaheral single crystals and aggregates were also observed. I n f r a r e d spectroscopy determined that the diamonds have nitrogen contents ranging f r o m 0 to 740 p p m and t w o modes o f nitrogen aggregation at 0 - 3 0 % B and 6 0 - 9 5 % B-centers. These states o f nitrogen aggregation suggest h i g h (1050 - 1300°C) temperatures o f residence in the mantle. The diamonds exhibit a w i d e range o f mineralogical characteristics and therefore must have f o r m e d under v a r y i n g physical and chemical conditions. The m o r p h o l o g y and nitrogen characteristics o f the W a w a diamonds are comparable to those o f xenocrystal cratonic diamonds and are u n l i k e those o f orogenic diamonds f o r m e d i n subduction zones. It is enigmatic that the W a w a diamonds were emplaced into a subducted-related setting but show characteristics typical o f xenocrystal cratonic diamonds.  iii  TABLE OF CONTENTS  Abstract  ii  L i s t o f Figures  vii  L i s t o f Tables  xiii  Acknowledgements  xvi  Chapter 1: I N T R O D U C T I O N  1  Chapter 2: P E T R O L O G Y O F T H E M E T A V O L C A N I C D I A M O N D I F E R O U S R O C K S  4  2.1  Geologic Setting  4  2.2  Analytical Methods  7  2.3  F i e l d Observations  8  2.3.1  P o l y m i c t Volcaniclastic Breccia  8  2.3.2  Lamprophyre  2.5  2.6  19  Petrography  23  2.5.1  P o l y m i c t Volcaniclastic Breccia  23  2.5.2  Juvenile M a g m a t i c M a t e r i a l  24  2.5.3  Lamprophyre  26  M i n e r a l Compositions  28  2.6.1  Amphiboles  28  2.6.2  Micas  35  2.6.3  Other M i n e r a l s  38  2.7  W h o l e R o c k Geochemistry  40  2.8  Interpretation and Discussion  47  2.8.1  Igneous Protoliths for the Metavolcanic Rocks  2.8.2  V o l c a n o l o g y o f the C a l c - A l k a l i n e L a m p r o p h y r i c Rocks  52  2.8.3  O r i g i n o f the C a l c - A l k a l i n e L a m p r o p h y r i c M a g m a  57  iv  :  47  Chapter 3: P H Y S I C A L A N D C H E M I C A L C H A R A C T E R I S T I C S O F T H E W A W A DIAMONDS  60  3.1  Analytical Methods  60  3.2  Physical Characteristics o f d i a m o n d  61  3.2.1  Introduction  61  3.2.1.1  Size  62  3.2.1.2  Primary Crystal Habit  62  3.2.1.3  Body Colour  68  3.2.1.4  Degree o f Resorption  70  3.2.1.5  Surface Features  72  3.2.2 3.3  Physical Characteristics o f the W a w a D i a m o n d s  79  Infrared A b s o r p t i o n Properties o f D i a m o n d  86  3.3.1  86  3.3.2  Introduction 3.3.1.1  Sequence o f N i t r o g e n Aggregation  90  3.3.1.2  Classification o f Diamonds U s i n g Infrared Spectra  93  3.3.1.3  H y d r o g e n Defects W i t h i n D i a m o n d  95  3.3.1.4  Quantitative Analysis o f I R A b s o r p t i o n Spectra  96  Classification, N i t r o g e n Content and A g g r e g a t i o n State o f the W a w a Diamonds  3.4 Discussion  99 106  3.4.1  Morphology  106  3.4.2  N i t r o g e n Content and Aggregation State  109  3.4.3  O r i g i n o f the W a w a Diamonds  115  3.4.4  Tectonic environment o f D i a m o n d F o r m a t i o n  119  3.4.5  D i a m o n d s o f C a l c - A l k a l i n e Lamprophyres  122  Chapter 4: C O N C L U S I O N S  124  References  126  Appendix A  L o c a t i o n and Trench M a p s  145  Appendix B  R o c k and Fragment Sample Data C o l l e c t i o n I n f o r m a t i o n  163  Appendix C  Photoplates o f C o u n t r y R o c k and Fragment Population  172  Appendix D  Detailed Petrography o f the W a w a Metavolcanic D i a m o n d i f e r o u s Rocks  Appendix E  Structural Data  Appendix F  Precision and M e a n Detection L i m i t s o f Electron M i c r o p r o b e M i n e r a l  ... 181  /.  C o m p o s i t i o n Analyses  Appendix G  208  Electron M i c r o p r o b e M i n e r a l C o m p o s i t i o n Data f o r the W a w a Metavolcanic Rocks  Appendix H  206  209  M a j o r and Trace Element B u l k Geochemistry o f the W a w a D i a m o n d i f e r o u s  Metavolcanic Rocks  225  Appendix I  Sample Statistical Evaluation f o r W h o l e R o c k Geochemical Data  229  Appendix J  Plots o f Compositional V a r i a t i o n i n O s c i l l a t o r y - Z o n e d Hornblende  232  Appendix K  Physical Characteristic o f the W a w a D i a m o n d s  239  Appendix L  I R Spectra and Results o f Spectral D e c o n v o l u t i o n  256  vi  LIST OF FIGURES  Figure 2.1  L o c a t i o n o f calc-alkaline lamprophyres i n the Superior Craton, i n c l u d i n g locations o f the Band-Ore G Q Property, the Pele M o u n t a i n Resources Festival Property, and the Spider Resources, K W G Sandor Occurrence  Figure 2.2  5  S i m p l i f i e d local geology map, a n d location o f trenches and outcrops on the Band-Ore G Q Property  9  j  Figure 2.3  Detailed structure and l i t h o l o g y m a p o f trench B R - 1 , and clast population  map o f trench B Z  10  Figure 2.4  F i e l d photographs o f p o l y m i c t volcaniclastic breccia  16  Figure 2.5  L a m p r o p h y r e f i e l d photos  21  Figure 2.6  Photomicrographs o f the p o l y m i c t volcaniclastic breccia  25  Figure 2.7  Photomicrographs o f the j u v e n i l e magmatic material and lamprophyre  27  Figure 2.8  Classification o f amphiboles  31  Figure 2.9  D i s t r i b u t i o n o f amphibole populations w i t h i n the volcaniclastic breccia,  j u v e n i l e material, and lamprophyre  32  Figure 2.10 Plots o f compositional z o n i n g i n oscillatory-zoned hornblende  Figure 2.11  A 1 0 vs T i 0  w t % and A 1 0 vs F e O w t % plot o f biotites f r o m the W a w a vii metavolcanic rocks 2  3  2  2  3  33  T  36  Figure 2.12  Geochemical discrimination diagrams applied to the W a w a diamondiferous metavolcanic rocks  41  Figure 2.13 Harker variation diagrams f o r the W a w a metavolcanic diamondiferous rocks  43  Figure 2.14 M g O variation diagrams f o r the W a w a metavolcanic diamondiferous rocks  44  Figure 2.15 M g O - A h d V 10 K 0 ( w t . % ) ternary plot f o r whole r o c k compositions o f 2  the W a w a metavolcanic rocks  Figure 2.16  48  Plot o f Si i n the T site versus A l i n the C site o f calcic-amphiboles f r o m the W a w a metavolcanic rocks  Figure 2.17  AI2O3  50  vs TiCh and M g O vs Si02 plots f o r whole rock compositions o f the  W a w a calc-alkaline lamprophyric rocks  51  Figure 3.1  Photograph o f typical diamonds f r o m the W a w a d i a m o n d populations  63  Figure 3.2  Structure o f diamond  63  Figure 3.3  Primary f o r m s o f diamond and their s y m m e t r y  65  Figure 3.4  H i s t o g r a m s h o w i n g frequency o f occurrence o f different crystal f o r m s i n  diamond  80  Figure 3.5  V a r y i n g p r i m a r y morphologies o f the W a w a d i a m o n d population  80  Figure 3.6  A pie-diagram showing crystal regularity o f the W a w a diamonds  81  viii  Figure 3.7  Classification scheme o f M c C a l l u m et al. (1994)  81  Figure 3.8  H i s t o g r a m s h o w i n g the degree o f resorption o f the W a w a d i a m o n d population  83  Figure 3.9  Photomicrographs o f typical diamond g r o w t h , resorption and o x i d a t i o n features  o f the W a w a d i a m o n d population  Figure 3.10  84  I R spectra o f d i a m o n d  88  Figure 3.11 Classification o f d i a m o n d based on I R absorption  94  Figure 3.12 I R absorption spectra f o r the different types o f W a w a diamonds  94  Figure 3.13 Pie diagrams c o m p a r i n g the W a w a d i a m o n d types w i t h colour and  morphology  100  Figure 3.14 D i s c r i m i n a t i o n plots o f regular and irregular diamonds  101  Figure 3.15 Histograms o f nitrogen content and aggregation o f the W a w a diamonds  102  Figure 3.16 Histograms s h o w i n g the distribution o f mantle residence temperatures f o r the W a w a diamonds  107  Figure 3.17 Plots o f nitrogen concentration versus % B f o r 1.8 G a and 10 M a residence times  Figure 3.18  108  Plots o f nitrogen concentration versus % B c o m p a r i n g the W a w a diamonds to other d i a m o n d populations w o r l d w i d e  110  Figure 3.19 H i s t o g r a m comparing the W a w a diamonds w i t h other d i a m o n d suites worldwide  112  ix  Figure 3.20 M o d e l o f a diamondiferous lithospheric root  120  Figure 3.21  Subduction m o d e l f o r the f o r m a t i o n o f diamonds  120  Figure A l  L o c a t i o n o f the Band-Ore Resources, Pele M o u n t a i n Resources, and S p i d e r / K W G Resources w i t h respect to the t o w n o f W a w a , O N  Figure A2  146  Detailed map o f trench B R - 1 indicating l i t h o l o g y and l i t h o l o g y , size, angularity  and distribution o f the fragment population  147  Figure A3  Detailed map o f trench B Z showing l i t h o l o g y and structure  148  Figure A4  Detailed map o f trench D E - 1 showing l i t h o l o g y and structure  149  Figure A5  Detailed map o f trench D E - 1 indicating l i t h o l o g y and l i t h o l o g y , size, angularity  and distribution o f the fragment population  150  Figure A6  Detailed map o f trench D E - 2 showing l i t h o l o g y and structure  151  Figure A7  Detailed map o f trench D E - 2 indicating l i t h o l o g y and l i t h o l o g y , size, angularity  and distribution o f the fragment population  152  Figure A8  Detailed map o f trench D E - 3 showing l i t h o l o g y and structure  153  Figure A9  Detailed map o f trench D E - 3 indicating l i t h o l o g y and l i t h o l o g y , size, angularity  and distribution o f the fragment population  154  Figure A10  Detailed map o f trench E - l showing l i t h o l o g y and structure  155  Figure A l l  Detailed map o f trench E-2 showing l i t h o l o g y and structure x  156  Figure A12  Detailed map o f trench JR-14-1 s h o w i n g l i t h o l o g y and structure  157  Figure A13 Detailed map o f trench JR.-14-1 indicating l i t h o l o g y and lithology, size, angularity  Figure A14  and distribution o f the fragment population  158  Detailed map o f trench JR-14-2 showing l i t h o l o g y and structure  159  Figure A15 Detailed map o f trench JR-14-2 indicating l i t h o l o g y and l i t h o l o g y , size, angularity  Figure A l 6  and distribution o f the fragment population  160  Detailed map o f trench SE-F s h o w i n g l i t h o l o g y and structure  161  Figure A17 Detailed map o f trench SE-F indicating lithology and l i t h o l o g y , size, angularity and distribution o f the fragment population  162  Figure C l  Photoplates o f felsic metavolcanic country rock  173  Figure C2  Photoplates o f mafic metavolcanic country rock  174  Figure C3  Photoplates o f intermediate to mafic intrusive country r o c k  175  Figure C4  Photoplates o f felsic and mafic intrusive fragments  176  Figure C5  Photoplates o f intermediate to m a f i c intrusive r o c k and biotite-rich  greenstone fragments  177  Figure C6  Photoplates o f greenstone and hornblende-rich fragments  178  Figure C7  Photoplates o f gneiss and actinolite-rich fragments  179  Figure C8  Photoplate o f a greenschist fragment  180  Figure DI  Photomicrographs o f the p o l y m i c t volcaniclastic breccia  193  Figure D2  xi Photomicrographs o f the p o l y m i c t volcaniclastic breccia  202  Figure D3  Paragenetic sequence based o n t i m i n g o f m a i n S2 fabric  Figure E l  Plane to pole stereonets o f the  Figure J l  Compositional zoning i n amphibole f o r sample N L - 1 - 1 3 F  233  Figure J2  Compositional zoning i n amphibole f o r sample N L - 1 - 1 9 A  234  Figure J3  Compositional zoning i n amphibole f o r sample N L - 1 - 2 7 A  235  Figure J4  Compositional zoning i n amphibole f o r sample N L - 1 - 2 8 A  236  Figure J5  Compositional zoning i n amphibole f o r sample N L - 1 - 4 3 A  237  Figure J6  Compositional zoning i n amphibole f o r sample N L - 1 - 4 5 A  238  Figure LI  Infrared absorption spectrum o f the T y p e I I W a w a diamonds  257  Figure L2  Infrared absorption spectrum o f the T y p e I a A W a w a diamonds  260  Figure L3  I n f r a r e d absorption spectrum o f the T y p e I a A B w i t h < 5 0 % B-defects W a w a  S2 and S 4 cleavage  diamonds  Figure L4  205  207  261  Infrared absorption spectrum o f the T y p e I a A B w i t h > 5 0 % B-defects W a w a diamonds  263  xii  LIST OF TABLES  Table 2.1  L i t h o l o g i c a l and mineralogical data f o r the p o l y m i c t volcaniclastic breccia, l a m p r o p h y r e , and j u v e n i l e material  Table 2.2  12  Abundance, shape, angularity, size, and texture o f clasts present i n the  p o l y m i c t volcaniclastic breccia and lamprophyre  Table 2.3  Representative electron microprobe analyses o f amphibole compositions  Table 2.4  Representative electron microprobe analyses o f m i c a compositions  Table 2.5  Representative electron microprobe analyses o f epidote, plagioclase and  13  ....  c h r o m i t e compositions  Table 2.6  A v e r a g e abundance o f major element oxides and some trace elements p o l y m i c t  Table 3.2  Table B l  Table B2  46  A comparison o f the W a w a Volcaniclastic Breccia w i t h k n o w n volcaniclastic  deposit types  Table 3.1  37  39  i n the volcaniclastic breccia, lamprophyre and j u v e n i l e material  Table 2.7  29  54  I n f r a r e d characteristics o f the W a w a diamonds  104  C o m p a r i s o n o f m o r p h o l o g y , colour, nitrogen type, and resorption category  o f the W a w a diamonds  113  R o c k sample data collection i n f o r m a t i o n  163  Fragment sample i n f o r m a t i o n f r o m trenches E - l and E-2 xiii  169  Table E l  Structural measurements  Table F l  M e a n detection l i m i t and analytical precision f o r the elements analyzed b y the  206  electron microprobe  208  Table GI  Electron microprobe analyses o f amphibole compositions  209  Table G2  Electron microprobe analyses o f m i c a compositions  217  Table G3  Electron microprobe analyses o f epidote and titanite compositions  221  Table G4  Electron microprobe analyses o f plagioclase compositions  223  Table G5  Electron microprobe analyses o f chromite compositions  224  Table HI  M a j o r and trace element w h o l e rock geochemistry f o r the W a w a lamprophyres M a j o r and trace element w h o l e rock geochemistry f o r the W a w a  225  Table H2  matrix-supported p o l y m i c t volcaniclastic breccia  226  Table H3  M a j o r and trace element w h o l e rock geochemistry f o r the W a w a clast-supported p o l y m i c t volcaniclastic breccia  Table H4  227  M a j o r and trace element w h o l e rock geochemistry f o r the W a w a  j u v e n i l e magmatic material and xenoliths  228  Table II  Standard deviations f o r lamprophyre w h o l e rock analyses  230  Table 12  Standard deviations f o r matrix-supported p o l y m i c t volcaniclastic breccia w h o l e r o c k analyses  230  xiv  Table 13  Standard deviations f o r clast-supported p o l y m i c t volcaniclastic breccia w h o l e  rock analyses  231  Table 14  Standard deviations f o r j u v e n i l e magmatic w h o l e rock analyses  231  Table K l  W a w a d i a m o n d sample locations, dimensions and weights  239  Table K 2  Classification scheme f o r the W a w a d i a m o n d population  245  Table K 3  The physical characteristics o f the W a w a d i a m o n d population and p r e l i m i n a r y  Table L I  appraisal o f the mineral inclusions  248  Results o f W a w a d i a m o n d I R spectral deconvolution  265  xv  ACKNOWLEDGEMENTS  I a m indebted to W a y n e O ' C o n n o r and B o b Duess o f B a n d - O r e Resources L t d . f o r the o p p o r t u n i t y to study the W a w a d i a m o n d i f e r o u s rocks and d i a m o n d s . I a m also indebted f o r t h e i r generous f i n a n c i a l contributions.  I a m grateful to N S E R C and B a n d - O r e Resources L t d . f o r  s u p p o r t i n g m y M S c . t h r o u g h an Industrial Post-Graduate Scholarship.  A s w e l l , I w o u l d l i k e to  t h a n k K e n n e c o t t E x p l o r a t i o n f o r p a r t l y f u n d i n g the f i e l d w o r k . W i t h o u t the m e n t o r i n g b y , and countless discussions w i t h M a y a K o p y l o v a , K e n H i c k e y , K e l l y Russell, M a t t i Raudsepp, G r e g D i p p l e , Stuart Sutherland, K e v i n K i v i , Casey H e t m a n and m y f e l l o w grad students I w o u l d not have been able to w r i t e this thesis. I a m also appreciative o f M a y a , M a t t i , G r e g and K e n f o r r e v i e w i n g earlier drafts o f m y thesis. F i e l d w o r k was carried out w i t h the i n v a l u a b l e assistance o f B o b Duess, K e v i n K i v i and D a v e S m i t h s o n . M a n y thanks to H e r m a n Grutter f o r his tremendous guidance i n setting-up this e x c i t i n g project and h e l p i n g m e t h r o u g h o u t the project. I a m e x t r e m e l y appreciative f o r the u n c o n d i t i o n a l l o v e and support f r o m m y parents, A a r o n , M i c h e l , L i s a , C o d y , L e a h , and L i n d a . I a m also v e r y grateful f o r the f r i e n d s h i p , help and support o f m y f e l l o w grad students especially Dave, L i a n e , K a t h i , M e l a n i e , M a g g i e , S i m o n , K e n and Trevor.  xvi  Chapter 1 INTRODUCTION A suite o f diamond-bearing p o l y m i c t volcanic breccias and lamprophyre dikes have recently been discovered i n the western section o f the M i c h i p i c o t e n greenstone belt, i n the W a w a subprovince o f the Superior craton ( F i g . 2.1). The rocks are remarkable f o r their diamondiferous character, and are n o w a target f o r exploration by m i n i n g companies. T o date thousands o f diamonds have been recovered (Press-Release o f A p r i l 23, 2002, Band-Ore Resources L t d ) , 9 5 % o f w h i c h are microdiamonds (<0.5 m m i n one dimension). The diamondiferous metavolcanic rocks i n the W a w a subprovince are unique i n several aspects. Dated at 2674±8 M a (Stott et al., 2002), they are the oldest p r i m a r y diamondiferous rocks currently k n o w n , as other reported volcanic hosts o f d i a m o n d are Proterozoic to Cenozoic i n age (Gurney, 1989; K i r k l e y et al., 1991). T h e y f o r m e d as a result o f Late Archean subductionrelated m a g m a t i s m (Sage, 1994).  The tectonic setting o f the W a w a diamond-bearing volcanic  rocks is atypical for conventional p r i m a r y diamond sources w h i c h are restricted to A r c h e a n cratons and surrounding Proterozoic m o b i l e belts (Helmstaedt and Gurney, 1995; Capdeliva et al., 1999). The W a w a diamond-bearing rocks have been metamorphosed and deformed, and little evidence o f their p r i m a r y magmatic nature has been preserved. One o f the aims o f this study was to determine i f these A r c h e a n diamondiferous rocks are metamorphic  equivalents o f k n o w n diamondiferous occurrences or are a new,  previously  unrecognized, deposit type. The most c o m m o n rocks to host d i a m o n d are kimberlites and lamproites ( M i t c h e l l , 1995a, b; Scott-Smith, 1995).  Other rarer volcanic rocks that contain  d i a m o n d are ultramafic lamprophyres ( U M L ) , alkali lamprophyres, and komatiites ( M i t c h e l l , 1995a, b; Scott-Smith, 1995; Janse, 1 9 9 1 ; Capdeliva et al., 1999). I used geological, petrological  1  and m i n e r a l o g i c a l methods to classify the volcanic rocks w h i c h host the W a w a diamonds. I also studied v o l c a n o l o g y o f the W a w a calc-alkaline lamprophyres and described the style o f eruption. P r i m a r y diamondiferous deposits occur i n several tectonic settings. The most c o m m o n deposits are associated w i t h Precambrian (Helmstaedt and Gurney, 1995) cratons where diamonds originate w i t h i n the cool, lithospheric cratonic root. These diamonds are brought to the surface i n ascending k i m b e r l i t i c and lamproitic magmas ( K i r k l e y et al., 1991). These diamonds are f o u n d as xenocrysts w i t h i n the volcanic hosts and as primary minerals w i t h i n xenoliths o f peridotite and eclogite, the t w o most c o m m o n upper mantle rocks. H e n c e f o r t h , I w i l l refer to diamonds o r i g i n a t i n g f r o m w i t h i n a Precambrian craton as cratonic xenocrystal diamonds. A s c e n d i n g k i m b e r l i t i c magma can also precipitate diamonds i f it is r i c h i n C-bearing volatiles (Pattison and L e v i n s o n , 1995). K i m b e r l i t e s are the only magmatic type w i t h documented d i a m o n d phenocrysts ( L e u n g et al., 1990; Schrauder et al., 1994; Pattison and L e v i n s o n , 1995). Such diamonds, w h i c h I w i l l call phenocrystal, have some distinct characteristics compared to cratonic xenocrystal diamonds. F i n a l l y , diamonds can also be f o u n d i n orogenic settings ( G r i f f i n et al., 2000). The diamonds originate w i t h i n a cold, subducting slab w h i c h is either r a p i d l y brought to the surface b y u p l i f t i n a metamorphic terrane (Harris, 1992; Shatsky et al., 1998) or sampled b y an ascending m a g m a coeval w i t h the subduction ( G r i f f i n et al., 2000). D i a m o n d s occurring i n such metamorphic terranes have been identified w i t h i n obducted u l t r a - h i g h pressure pyroxenites ( S l o d k e v i c h , 1980, 1983), eclogites ( G r i f f i n et al., 1985, 1987; W a n g et al., 1992), gneisses (Shatsky et al., 1995), and associated peridotites ( K a m i n s k y , 1984; S l o d k e v i c h , 1980, 1983; N i x o n , 1995). Examples o f d i a m o n d suites related to volcanic rocks contemporaneous w i t h subduction are a l l u v i a l diamonds f r o m N e w South Wales ( G r i f f i n et al., 2 0 0 0 ; Davies et al., 2003), and diamonds f r o m volcaniclastic komatiites i n French Guiana (Capdeliva et al., 1999). Henceforth, subducted-related diamonds w i l l be referred to as orogenic diamonds. 2  This w o r k examines diamonds f r o m the p o l y m i c t volcaniclastic breccia and calcalkaline lamprophyre dikes i n the M i c h i p i c o t e n Greenstone belt, western Superior Craton, and compares t h e m w i t h w o r l d w i d e occurrences o f cratonic xenocrystal diamonds, phenocrystal diamonds, and orogenic diamonds. I used m o r p h o l o g i c a l studies and infrared ( I R ) spectroscopy to fingerprint the W a w a diamonds and show that they resemble cratonic xenocrystal diamonds. Further research is needed to determine w h y this d i a m o n d suite apparently f o r m e d i n a subduction-related setting but has similar characteristics to diamonds o f cratonic xenocrystal origin.  3  Chapter 2 PETROLOGY AND VOLCANOLOGY OF THE METAVOLCANIC DIAMONDIFEROUS ROCKS 2.1 GEOLOGICAL SETTING The diamondiferous p o l y m i c t volcaniclastic breccia and lamprophyre are f o u n d i n the western section o f the M i c h i p i c o t e n greenstone belt w i t h i n the W a w a subprovince o f the Superior  craton (Fig.2.1). The  Superior craton comprises  a collage o f Archean  terranes  representing several prominent orogenic, magmatic, and deformational episodes resulting f r o m the subduction and accretion o f numerous volcano-sedimentary arc complexes (Percival, 1996; Stott, 1997). The accreted terranes have been subdivided into subprovinces based on distinct l i t h o l o g y , structure, metamorphism and geophysical patterns ( C a r d , 1990; Stott, 1997).  The  assembly o f these subprovinces to f o r m the Superior craton is believed to have been completed b y 2688 M a ( W i l l i a m s et al., 1991). The M i c h i p i c o t e n greenstone belt preserves evidence f o r three m a i n cycles o f volcanic a c t i v i t y at 2.89 Ga, 2.75 Ga and 2.70 Ga ( T u r e k et al., 1982, 1988, 1992). The 2.89 Ga and 2.75 G a v o l c a n i c units are overlain by i r o n f o r m a t i o n and the 2.70 G a volcanic units are intercalated w i t h clastic sedimentary units ( W i l l i a m s et al., 1991; Sage, 1994). A l l three volcanic cycles are o v e r l a i n b y clastic sedimentary units representing post-2682 M a erosional events ( C o r f u and Sage, 1992). The supracrustal rocks are interpreted to represent an island arc or a c o n v e r g i n g plate environment (Card, 1990; W i l l i a m s et al., 1 9 9 1 ; Sage, 1994).  The diamondiferous  p o l y m i c t volcaniclastic breccia and lamprophyre occur w i t h i n the t h i r d cycle o f volcanism. This t h i r d cycle o f volcanic activity, like the t w o earlier cycles, was b i m o d a l ; w i t h massive and 4  90"W  A  y  56"N  Sachigo 52"NBerene River Bird River)  —  —  •.  —  Uchi •  .—  ^  . y  English River'  Winnipeg River'  /Opatica^f  Wabigoon 94°W  Quetico ^Wawa 2  ti<3>.--  ' ~  0  200km  Scale 1:5 000 000 Late Superior Abitibi Legend: I Superior Craton  TO  Subprovince boundary Michipicoten greenstone belt  I  84"\ 44"N ^  as I  _44"N  J  Abitibi greenstone belt .JL. Archean diamondiferous volcaniclastic breccia and lamprophyre •  ^' V 42"N v  r  80°W  Archean lamprophyres  Figure 2.1 Location of the diamond-bearing polymict volaniclastic breccia and lamporphyre dikes within the Michipicoten greenstone belt, Wawa subpropvince, of the shoshonitic diamondiferous lamprophyres within the Abitibi greenstone belt, Abitibi subprovince (Wyman and Kerrich, 1993; Williams, 2002), and of calc-alkaline lamprophyres within the Uchi and Wabigoon subprovinces (Wyman and Kerrich, 1989). Symbols: 1- Band-Ore Resources GQ Property, 2 - Pele Mountain Resources Festival Property, 3 - Spider Resources and KWG Resources Sandor Occurrence.  5  p i l l o w e d intermediate to mafic, tholeiitic f l o w s , c o n f o r m a b l y overlain b y intermediate to felsic t u f f and breccia and clastic sedimentary rocks ( W i l l i a m s et al., 1 9 9 1 ; Sage, 1994).  The t h i r d  volcanic cycle also produced gabbro to quartz diorite sill-like and d i k e - l i k e intrusions (Sage, 1994). The M i c h i p i c o t e n  greenstone belt  assemblages  experienced polyphase  deformation  resulting f r o m the accretion o f volcanic arcs to f o r m the M i c h i p i c o t e n greenstone belt and the accretion o f the W a w a subprovince to the Superior Craton nucleus (Arias, 1996).  The t i m i n g  o f accretion o f greenstone assemblages w i t h i n the W a w a subprovince is interpreted to predate the coalescence o f the subprovinces to f o r m the Superior craton ( W i l l i a m et al., 1991).  The  deformational events produced large scale recumbent f o l d i n g and thrusting f o l l o w e d b y upright f o l d i n g and h i g h angle reverse faulting (Arias and Helmstaedt, 1990; M c G i l l , 1992) and resulted i n local repetition o f 2.7 Ga stratigraphy ( W i l l i a m s et al., 1991). A f o u r stage deformational history has been recognized by Arias (1990); these deformational events caused regional m e t a m o r p h i s m o f the greenstone belt.  I n the present study area evidence f o r t w o o f these  deformation events is preserved as S2 and S4 foliations. Intermediate to felsic plutonic rocks intruded approximately 2660 - 2690 M a ago during the final stages o f greenstone belt deformation and were responsible f o r contact m e t a m o r p h i s m o f the nearby volcanic rock (Ayres, 1978; Sage, 1994). Late Archean to early Proterozoic diabase and lamprophyre dikes intruded the volcanic rocks (Sage, 1994) d u r i n g the w a n i n g stages o f magmatic activity and transpressional accretionary tectonics ( W y m a n and K e r r i c h , 1989). A r c h e a n lamprophyre dikes w i t h i n the Superior craton have been dated at 2.67 - 2.7 Ga (Barrie, 1990; Stern and Hanson, 1992). The area has remained tectonically stable since diabase dike emplacement ( G o o d w i n , 1964; W i l l i a m s et al., 1991).  6  2.2 ANALYTICAL METHODS Over one hundred samples collected d u r i n g f i e l d m a p p i n g o f the Band-Ore Resources property were the basis for thorough petrographic and mineralogical studies ( A p p e n d i x B ) . R o c k samples included the least altered, and most diagnostic samples o f p o l y m i c t volcaniclastic breccia, lamprophyre, fragments and country rock.  Due to the fine-grained nature o f the  groundmass, the minerals were identified b y energy-dispersion X - r a y spectrometry using a Philips X L - 3 0 scanning electron microscope equipped w i t h a Princeton G a m m a - T e c h I m i x energy-dispersion X - r a y spectrometer. M i n e r a l s were analyzed for chemical c o m p o s i t i o n using an automated C A M E C A  S X - 5 0 wavelength-dispersive electron microprobe (Department  of  Earth and Ocean Sciences, U n i v e r s i t y o f B r i t i s h C o l u m b i a ) . Data reduction was done w i t h the ' P A P ' <))(pZ) on-line correction program. Silicates and oxides were analyzed at an accelerating voltage o f 15 k V and 20 n A beam current except f o r a f e w samples o f fine-grained plagioclase w h i c h were analyzed at a beam current o f 10 n A . Precision ( 2 a ) and m i n i m u m detection l i m i t s f r o m counting statistics are given in Table H I , A p p e n d i x H . On-peak counting times f o r most elements i n mica, amphibole, chromite and epidote were 20 s, except K i n m i c a and amphiboles was counted for 80 s, and V i n amphiboles f o r 40 s. On-peak counting times f o r most elements i n plagioclase was 10 s except for Fe, w h i c h was counted for 30 s.  Analyses w i t h poor  stoichiometry  were  and  totals  were  excluded  and  mineral  compositions  averaged  for  homogeneous phases or presented as i n d i v i d u a l analyses f o r inhomogeneous minerals (Tables 2.3-2.5). Estimation o f ferric i r o n in amphibole was calculated using the m e t h o d o f Schumacher (1997). Fragment-poor volcaniclastic breccia, clast-supported volcaniclastic breccia, cognate magmatic material, lamprophyre and fragments that m a y be mantle xenoliths were chosen for w h o l e rock geochemistry. The analysis was done at the M c G i l l  7  University  Geochemical  Laboratories ( M o n t r e a l , Canada). T h e samples (80-120 g) were reduced i n a j a w crusher and then ground i n a tungsten-carbide r i n g m i l l . A l l major elements, Cr, C o , B a and N i contents were determined b y X - r a y fluorescence ( X R F ) spectrometry using a Philips P W 2 4 0 0 spectrometer and fused pellets. Silica was determined w i t h standard accuracy o f 0.5 relative abs. % , a l l other m a j o r elements w i t h the 1 relative abs. % accuracy, and trace elements w i t h 5 relative abs. % . The general precision o f the X R F spectrometry is better than 0.5 relative abs. % .  2.3 FIELD OBSERVATIONS Seven outcrops and nine trenches were mapped o n the Band-Ore Resources property ( F i g . 2.2) using a m o d i f i e d version o f the Anaconda m a p p i n g m e t h o d (Eianudi, 2000) at a scale o f 1:100 ( A p p e n d i x A ) . A n example o f such a map f o r trenches B Z and B R - 1 is p r o v i d e d i n F i g . 2.3. T h e data o n structure, l i t h o l o g y , and fragment population and distribution w i t h i n the breccia are summarized i n Tables 2.1 and 2.2. Outcrops o f similar r o c k types f r o m the nearby Pele M o u n t a i n Resources and Spider Resources properties were also examined f o r comparison but not i n detail. T w o m a i n types o f diamondiferous metavolcanic rocks were recognised i n the f i e l d . Based on lithological and mineralogical data presented b e l o w , these were interpreted as metamorphosed p o l y m i c t volcaniclastic breccia ( P V B ) and lamprophyre (Table 2.1).  2.3.1  Polymict Volcaniclastic Breccia Discontinuous regions o f the p o l y m i c t volcaniclastic breccia occur over at least 50 k m  w i t h i n the Musquash, M e n z i e s , Lalibert and Leclaire townships o f north-western Ontario. The largest region o f exposed breccia is 1500 m x 500 m ( W a l k e r , 2003). The breccia f o r m s t h i c k units ( m a x i m u m true thickness ~ 110 m ) d i p p i n g to the N E at 30°. The lateral extent and  8  j Mafic to Intermediate  Clastic  • ^  I  Metasedimentary Rock Polymict Volcaniclastic Breccia  O  J Intrusive Rock Lamprophyre  F i g u r e 2.2 S i m p l i f i e d geological map ( m o d i f i e d f r o m Sage, 1995) showing the location o f the occurrences o f p o l y m i c t volcaniclastic breccia and lamprophyre w i t h i n the 2700 M a volcanic cycle o f the M i c h i p i c o t e n Greenstone belt. The numbers on the map correspond to the f o l l o w i n g trench and outcrop locations: 1. 58, 2. 145,3. 5 2 , 4 . 5 1 , 5. 3648, 6. 3647, 7. 3649, 8. B-Z, 9. JR-14, 10. D E - 1 , 11. D E - 2 , 12. D E - 3 , 13. BR-1, 14. E - l , 15. E-2, 16. SE-F (see A p p e n d i x B). U T M coordinates are in N A D 2 7 . 9  Volcaniclastic Breccia  N  A .  A  Lamprophyre -Channel samples  ftt*°. J+m  J• a a a  a  „  Fragment Description: Size: * • sand o A • granule O A • pebble O A • cobble  30-40%  25-30%—  O A Dboulder  40-50% ^  • large clast Angularity: • angular A subroundedSubangular 0 rounded  v  30-40%  .1  5-10%  £>'T-10% i° • . a •  7  .»'»° ° n n f ^  1 5 - 2 0 % \ / ° - . &\  i s  3 n  5 ^  2 1  4M 6M  7 n  9gs  8^  10m  N  B  S '  a B Bl i fijA  45-50%  .-SI  -  Fragment Lithology:  c  .° .  "  "  "  A  • -'p°\tJi:.s.3.;. o f  a  Figure 2.3 Detailed (1:100 scale) maps of trenches based on mapping with measuring tape and Brunton compass. A. Detailed map o f trench B Z indicating lithology, and size, angularity and distribution of the fragments. Symbols for fragment lithology: 1 - intermediate to mafic intrusive rock, 2 - unknown, 3 - felsic metavolcanic, 4 - hornblende-rich, 5 - biotite-rich greenstone, 6 greenstone, 7 - mafic metavolcanic, 8 - greenschist, 9 - gneiss, 10 - actinolite-rich greenstone.  10  F i g u r e 2.3 Detailed (1:100 scale) maps of trenches based on mapping with measuring tape and Brunton compass. B. Detailed map of trench B R - 1 showing lithology, foliation, fractures and veins.  11  in  sg  - O X .  a < D JO  a JO  X)  <  <  ±3  X o x >-,_ca ~ - U CM o (•*•> CN o tN in £ If tN O N -5 < C © O < § 0 A CQ J 3 inP CJ  0  S  u 00 a U T3  . O*-  ca  O  2 < S? o "  0)  ca 6  CQ O O  in 0  '3 > T3 C ca  X <  JO  <  S  tN  — CQ  N O  e*  0 S  s  0  ^  a  o. "ca 3  J3  o a o  03  r  S  u oo ca a <u  t: ca  N CQ  a ca o >  a o  U >n  0  o  X  Q/  in o O o \ —< X 5 N o .. oo a X v o m H Np O 7 r-*-T  H  u U  x <  Al  I o o u 43 a o -o  00  JO Si . « £T -2 oo C3  o <u  00  60 O a  N CQ  C3 ^ IO  ca  ~a ca  00  Loca  3  a  'S ^ a  -  00 P 2 « a <u u a cj ca  _ -o ca -ca "° o .a  a  D O a Tca 3 a 3 Xl <: op E  _  -3 u  Q  a _o  cq ~  S2 S  S I M TJ-  00 a  00 a •3 -a <u CQ  <3\ —i w  •S N 6 u  Q  oo  —  N CQ CO  oa  -o  -o a  fN  S  00 a  Clast  ca -O  P  t  J3  •3 2  O <u T3  00 o a  12  a .2 ca -3 u >b Tca C3 J JO 3 _^  « "2 cS  .s  a s  O OO  c o  < ca  T3 U N  •c CJ  2  CJ  Q CQ a. OS  <i O oSo  <  < 00  oi oo  O  CQ  u. CJ  cl.  cl.  1  ci  < 00  _0J 3  . CQ O  co"  5 •£ co cpa -ow  3 -s  o c'  C« ° E "2  " 00 •£ 5 s  S  S E  CJ  CJ  2 ca  V  < on  Je  0 2  < oo  < 00  < 00  < oo  u  CJ 2  CQ CQ cj (J  6  6  6  2  E  <  OS 00  <L a. oo  Je o *o <  O - 00  Om  CQ  ^  xi  g2 Z  o O o  o a o -g . a. c4  1  £ S <= " j - — -a -a  — c  ° y.sw s  :2,1s-  3 —  —  2  — o CJ  2  Qu 00 L O S < 00  6  u 6  L O S < 00  OS  Je °*  —  ca a.  ao oo  CL.  O uS  ca  <  < 00  °? 6 Je*  < 00  u  O  6  6  0 2 Hi 00  Oi  <  < os  OS  <2  a.  <0 0w 6 0  u wo 3  _- CQ °" " a" o" m  —o  \— E u —  2 2  C3  c E 'j U 00 J  | j o ca 6  13  J. S '3 S o. u D oo ca  c  £ S- " i  s §•»  S oo ca  thickness o f the breccia unit is not w e l l constrained o w i n g to large scale regional f o l d i n g and thrust f a u l t i n g (Arias, 1996). The breccia occurs w i t h i n the 2700 M a volcanic region (Sage, 1994) o f the M i c h i p i c o t e n Greenstone belt ( F i g . 2.2).  I t is intercalated w i t h the diamondiferous lamprophyre, and m i x e d  package o f intermediate to m a f i c intrusive rocks, felsic to intermediate metavolcanic rocks, and intermediate to mafic metavolcanic rocks previously mapped b y Sage (1994; A p p e n d i x C). The breccia appears older than the lamprophyre (see b e l o w ) , and is younger than the metavolcanic and intermediate to mafic intrusive rocks, as it contains fragments o f these rock units.  However,  the breccia is coeval w i t h the metavolcanic and intrusive rocks N E o f trenches E - l and E-2 ( F i g . 2.2).  Contacts w i t h the intermediate to mafic  intrusive rocks, metavolcanic  lamprophyre are sharp and h i g h l y irregular (Fig. 2.4A, B ) .  rocks,  and  I n some areas, the breccia i n f i l l s  fractures along mafic metavolcanic and intermediate to m a f i c intrusive rock contacts ( F i g . 2.4B). Some fragments w i t h i n the breccia, close to these contacts, e x h i b i t j i g s a w - f i t texture. I n some areas, the breccia occurs as t h i n but equant i n shape and prolate inclusions  penetrating  intermediate to mafic intrusive rocks close to the breccia contact ( F i g . 2.4C). I n these areas, the breccia is dominated b y irregular-shaped, intermediate to m a f i c intrusive fragments  which  decrease i n abundance further f r o m the contact. The p o l y m i c t volcaniclastic breccia consists p r i m a r i l y o f angular, pebble-sized, diverse fragment types m a i n l y o f igneous o r i g i n , set i n a greenish-grey, fine-grained m a t r i x ( F i g . 2.2; A p p e n d i x C). The matrix grain-sizes range f r o m < 2 m m to 1 m m . A t least eleven different types o f lithologies are present i n the fragments w h i c h are irregularly distributed throughout the breccia (Table 2.2). The matrix/clast ratio is h i g h l y variable w i t h i n the breccia (Table 2.1), and the breccia occurs both as matrix-supported (Fig. 2.4A, D) and clast-supported ( F i g . 2.4E, F). The population o f clasts is dominated b y locally derived fragments f r o m rocks w i t h w h i c h the breccia is c o m m o n l y intercalated (i.e. mafic and felsic metavolcanic rocks, and intermediate to  14  m a f i c intrusive rocks). Other types o f clasts include fragments o f clast-supported breccia w i t h i n m a t r i x supported breccia (autoclasts?) ( F i g . 2.4A, E ) , fragments o f earlier matrix-supported breccia w i t h < 5 % fragments ( F i g . 2 . 4 G ) , and coated lithic fragments (Fig.2.4H).  O f particular  importance is the presence o f interpreted j u v e n i l e magmatic material, occurring as irregular, r o u n d , and oval shaped, aphanitic fragments ( F i g . 2.41) or as magmatic " r i n d s " up to 3 c m t h i c k o n accessory lithic fragments ( F i g . 2.4J).  These could be rare examples o f primary pyroclastic  textures. Juvenile fragments and rinds can be distinguished f r o m earlier breccia fragments and coatings by the absence o f metavolcanic and/or intermediate to mafic intrusive fragments. M a n y supracrustal and intermediate to m a f i c intrusive fragments are b l o c k y , have curviplanar margins and j i g s a w - f i t texture (Fig. 2 . 4 K ) . boulders o f country rock.  M a t r i x material o f the breccia i n f i l l s fractures i n large  These boulders, i f included i n P V B , can be f o u n d surrounded b y  smaller, m o s t l y irregular fragments o f a similar lithology. O v e r a l l the breccia is massive, unstratified, and p o o r l y sorted according to size w i t h clasts ranging f r o m sand to large boulders (up to 9 m ; F i g . 2.3).  It contains rare p r i m a r y  sedimentary structures that include bedding, crude grading, and structures o f f o l d i n g i n semiconsolidated material (Table 2.1). Often subtle and obvious changes i n clast abundance occur as irregular pods or lenses. B e d d i n g is marked by variation i n clast abundance or variation i n abundance o f felsic metavolcanic fragments (Fig. 2.4L).  The bedding is m e d i u m to very t h i c k (based on I n g r a m ,  1954) and extends laterally up to about 10 m. The beds are tabular to wedge shaped, and have subtle, sharp, and slightly irregular contacts.  The m a j o r i t y o f the beds are massive but rare  subtle grading can be seen. G r a d i n g is m a r k e d b y a subtle concentration o f small boulder sized fragments along bedding planes ( F i g . 2 . 4 M ) , but is not evident i n the distribution o f clasts o f other sizes. The distribution and size o f amygdules i n nearby m a f i c metavolcanic rocks indicate that these beds are overturned and therefore the observed grading is inferred to be n o r m a l .  15  Fig.2.4 continues overleaf  16  Fig.2.4 continues overleaf  17  F i g u r e 2.4 Field photographs o f p o l y m i c t volcaniclastic breccia. A . Irregular, sharp contact o f matrix-supported p o l y m i c t volcaniclastic breccia ( P V B ) w i t h intermediate to m a f i c metavolcanic r o c k ( M V ) w h i c h extends laterally beyond the field o f view. N o t e an irregularly shaped, angular, boulder-sized fragment F o f clast-supported breccia w i t h i n the matrix-supported breccia (outcrop 51). B. Volcaniclastic breccia i n f i l l i n g fractures w i t h i n the m a f i c intrusive rock at the contact between the volcaniclastic breccia and mafic intrusive rock (Trench E-'l). C . T h i n , pebble- to cobble-sized, tabular and oblate shaped bodies o f matrix-supported P V B w i t h i n mafic intrusive rock ( M I ) close to their contact (outcrop 3647). D. Typical matrix-supported p o l y m i c t volcaniclastic breccia (Trench E-2). N o t e the poor sorting and w i d e variation o f fragment types present w i t h i n the breccia. E. Fragment F o f clast-supported breccia (enlarged f r o m A ) is dominated by granule to pebble-sized, angular intermediate to m a f i c metavolcanic fragments. O u t l i n e d are several rounded cored pyroclastic l a p i l l i (outcrop 51). F. Clast-supported p o l y m i c t volcaniclastic breccia dominated b y intermediate to m a f i c intrusive, intermediate to m a f i c volcanic and intermediate to felsic fragments (trench B - Z ) . G. Fragments o f matrix-supported breccia P V B - M S w h i c h contain less than 5 % metavolcanic and/or intermediate to mafic intrusive fragments (outlined by a dashed line) w i t h i n the clast-supported breccia P V B - C S (outcrop 52). H. Hornblende-rich mantle x e n o l i t h M X (white dashed line) is coated b y matrix-supported breccia material P V B - M S (outlined b y a line o f shorter black dashes) w i t h i n clast-supported breccia P V B - C S (outcrop 52). I. Cobble-sized, irregular shaped fragment o f j u v e n i l e magmatic material ( J M ) w i t h i n P V B (trench B - Z ) . J. R i n d o f j u v e n i l e magmatic material J M (dashed outline) cored b y an intermediate to mafic intrusive fragment ( M I ) the P V B (outcrop D E - 1 ) . K. Pebble-sized intermediate to m a f i c intrusive fragment e x h i b i t i n g j i g s a w - f i t texture, i.e. fractured clasts that are slightly scattered but the pieces can still be fitted back together like a j i g - s a w puzzle. L . Tabular shaped beds (dashed outlines) w i t h i n the volcaniclastic breccia m a r k e d b y sharp contacts and variation i n clast abundance. M . A P V B bed e x h i b i t i n g crude grading, w h i c h is m a r k e d by a concentration boulder-sized fragments (dashed outline) at the upper bedding contact. Grading i n the other size fractions o f material is not evident. N . B l o c k o f "softsediment d e f o r m a t i o n " structure (~1 m i n size) occurs as f o l d e d beds marked by variation i n clast content w i t h i n the clast-supported P V B (trench B - Z ) .  18  Structures up to 1 m i n size consist o f f o l d e d , fine-grained laminated and bedded horizons, w h i c h have a "soft-sediment d e f o r m a t i o n " appearance (Fig. 2.4N).  These f o l d e d beds locally exhibit  grading f r o m sand to pebble-sized material. Veins o f chlorite, epidote, iron-oxide, kaolinite, quartz and calcite occur locally w i t h i n the breccias. Structurally, at least t w o foliations are present: a dominant, shallow to moderately N N E d i p p i n g foliation ( S Fig.2.3) and a weaker, shallow to steeply E-SE d i p p i n g f o l i a t i o n 2;  (S4)  w h i c h crenulates S ( A p p e n d i x E; correlated w i t h w o r k o f A r i a s , 1996). Fragments c o m m o n l y 2  are aligned i n the plane o f f o l i a t i o n .  2.3.2  Lamprophyre L a m p r o p h y r e is present o n l y i n the S W , SE, and N W parts o f the property where it is  spatially contiguous w i t h P V B .  L a m p r o p h y r e occurs as narrow d i k e - l i k e structures (Fig. 2 . 5 A )  or i n bodies o f indeterminate m o r p h o l o g y ( F i g . 2.5B) cross-cutting or intercalated w i t h the local country rocks. D i k e w i d t h ranges f r o m approximately 50 c m to 2 m, and locally has offshoots 23 c m t h i c k ( F i g . 2.5C). D i k e contacts vary f r o m sharp ( F i g . 2.5A, D ) and straight to h i g h l y irregular ( F i g . 2.5E, F). Variations i n grain size w i t h i n the dike ( c h i l l margins) and variations i n c o l o u r and mineralogy o f the country rock consistent w i t h h i g h - temperature alteration (baked zones) are not present along the dike margins. The bodies w i t h indeterminate m o r p h o l o g y i n contact w i t h the breccia, are oriented parallel to the S f o l i a t i o n o f the breccia (Fig. 2.5D). 2  I n the field, lamprophyre is distinguished f r o m p o l y m i c t volcaniclastic breccia b y : 1) l o w e r clast content, 2) predominance o f highly-altered, coarse-grained, monominerallic actinolite fragments, 3) rarity o f w a l l rock fragments w h i c h it intrudes, 4) rounded shape o f the m a j o r i t y o f xenoliths, and 5) presence o f weaker fabric.  19  I n one area (outcrop 52) where the lamprophyre intrudes felsic metavolcanic rocks, the contact is u n i q u e l y irregular and accentuated b y the presence o f a h y b r i d contact rock ( F i g . 2.5G). The h y b r i d rock is composed o f bleached oval lenses o f the felsic metavolcanic w a l l rock i n t e r m i x e d w i t h lenses o f lamprophyric material. This contact has the appearance o f m i n g l i n g between the felsic metavolcanic rock and lamprophyre. The lamprophyre dikes are younger than most other map units and cross-cut intermediate to m a f i c intrusive rocks, felsic metavolcanic rocks and P V B . L a m p r o p h y r e w i t h u n k n o w n m o r p h o l o g y predates most o f these units because fragments o f each ( F i g . 2 . 5 H ) are f o u n d w i t h i n it. H o w e v e r , fragments o f lamprophyre have been f o u n d w i t h i n the intermediate to m a f i c intrusive rocks near contacts (Fig. 2.51). The lamprophyre is  fine-grained,  to subangular, cobble-sized fragments.  grey-black, and generally contains 5 - 1 0 % subrounded Eight types o f lithological fragments (Table 2.2) were  i d e n t i f i e d w i t h i n the lamprophyre.  The fragments vary f r o m sand to boulder i n size, and f r o m  rounded  The  to  angular  in  shape.  clast  population  is  dominated  by  actinolite-rich,  m o n o m i n e r a l l i c rocks (Fig. 2.5J), or occasionally b y biotite-rich greenstone and hornblende-rich ultramafic rocks. Some fragments m a y be enveloped by a distinct r i m ( ~ l - 5 c m thick) o f darker lamprophyre enriched i n biotite (Fig. 2.5J). Fragments indeterminate  i n lamprophyre  morphology.  dikes  are different  f r o m those i n the lamprophyre  Firstly, the dikes c o m m o n l y  have b i o t i t e - r i c h haloes  xenoliths whereas the indeterminate bodies do not ( F i g . 2 . 5 K ) .  of  around  Secondly, lamprophyres o f  indeterminate m o r p h o l o g y show positive r e l i e f o f less weathered xenoliths w h i c h are not seen i n dikes ( F i g . 2.5J). Lastly, fragment l i t h o l o g y is less variable i n dikes. The lamprophyre shows a w e a k l y developed spaced S4 f o l i a t i o n , and is locally cross-cut b y quartz and chlorite veins. The lamprophyre groundmass is similar i n appearance to that o f the  20  F i g u r e 2.5. L a m p r o p h y r e field photos. A . L a m p r o p h y r e ( L ) dike cross-cutting intermediate to m a f i c intrusive rock ( M I ) . N o t e field b o o k f o r scale. B. Sharp straight contact between clastsupported volcaniclastic breccia ( P V B ) and l a m p r o p h y r e b o d y w i t h indeterminate m o r p h o l o g y ( L ) . C . N a r r o w off-shoots o f l a m p r o p h y r e d i k e ( L ) cross-cutting felsic metavolcanic r o c k ( F M V ) . D . Sharp, straight contact between m a t r i x - s u p p o r t e d breccia ( P V B ) and l a m p r o p h y r e w i t h indeterminate m o r p h o l o g y ( L ) . Contact o u t l i n e d b y a black and w h i t e line. N o t e pen f o r scale. E. Irregular contact between m a t r i x - s u p p o r t e d breccia ( P V B ) and cross-cutting l a m p r o p h y r e dike ( L ) . Contact o u t l i n e d b y a black and w h i t e line. N o t e field b o o k f o r scale. F. L a m p r o p h y r e dike ( L ) cross-cutting intermediate to m a f i c intrusive r o c k ( M I ) . D i k e is e x h i b i t i n g small scale p i n c h i n g and s w e l l i n g , and contains m o n o m i n e r a l l i c actinolite xenoliths. N o t e the chisel f o r scale. G . L a m p r o p h y r e i n t r u d i n g felsic metavolcanic rock. The contact is irregular and u n i q u e l y accentuated b y the presence o f contact h y b r i d rock. N o t e the pen f o r scale. H. Fragment o f clast-rich breccia ( F ) , outline b y a b l a c k and w h i t e line, w i t h i n l a m p r o p h y r e b o d y w i t h indeterminate m o r p h o l o g y ( L ) . N o t e the field b o o k f o r scale. I . A n g u l a r , triangular shaped l a m p r o p h y r e lense ( L ) , o u t l i n e d b y a b l a c k and w h i t e line, w i t h i n intermediate to m a f i c intrusive r o c k ( M I ) . N o t e the field b o o k f o r scale. J . L a m p r o p h y r e b o d y o f indeterminate m o r p h o l o g y w i t h r o u n d , m o n o m i n e r a l l i c actinolite ( A c t ) and c h l o r i t e - r i c h xenoliths w h i c h are less weathered than the l a m p r o p h y r e . N o t e the field b o o k f o r scale. K. M o n o m i n e r a l l i c actinolite x e n o l i t h s ( A c t ) enveloped b y a d i s t i n c t r i m o f darker r o c k enriched i n biotite w i t h i n the l a m p r o p h y r e dike. L a m p r o p h y r e d i k e is cross-cutting intermediate to m a f i c intrusive r o c k ( M I ) . N o t e the field b o o k f o r scale.  22  breccia matrix. The lack o f S2 f o l i a t i o n , that is pervasive i n the breccias, suggests that the dikes post-date D2 and predate D4.  2.4 Petrography 2.4.1 Polymict Volcaniclastic Breccia The p o l y m i c t volcaniclastic breccia exhibits a fragmental texture i n t h i n section ( F i g . 2 . 6 A ) . T e n types o f fragments identified i n the f i e l d (Table 2.2) were c o n f i r m e d as distinct r o c k types b y optical microscopy. The fragments are contained w i t h i n an inequigranular matrix that consists o f an assemblage o f actinolite, chlorite, albite, ± titanite, ± epidote ± biotite (Table 2.1) typical o f greenschist facies mafic rocks ( Y a r d l e y , 1995). T h e matrix can be subdivided into an assemblage o f coarser (0.2 - 1.5 m m ) grains o f hornblende, biotite and epidote and a finergrained ( < 0 . 1 m m ) groundmass containing a l l o f the above minerals. The m a i n S2 f o l i a t i o n is defined b y the alignment o f fine-grained, acicular actinolite ± chlorite grains that dominate the groundmass (Table 2.1). Coarser grained biotite, epidote, and subhedral to euhedral hornblende pre-date or are synchronous w i t h S2 as they exhibit chlorite pressure shadows and texture w r a p p i n g (Fig. 2.6B, C; Passchier and T r o u w , 1996). T h e rare, subhedral, tabular biotite grains usually have bent cleavage ( F i g . 2 . 6 D ) , fine-grained acicular actinolite g r o w i n g f r o m the grains into the fabric, and inclusion trails o f epidote or titanite almost perpendicular to the f o l i a t i o n . The coarse subhedral to euhedral hornblende grains are n o r m a l l y surrounded b y coronas of, or are partly replaced b y , actinolite ± biotite ± chlorite ± titanite ± albite ± calcite. T h e least-altered hornblende grains frequently show oscillatory ( F i g . 2.6E) and patchy zonation. Groundmass rutile is c o m m o n l y mantled b y titanite. M i n e r a l o g y o f the breccia matrix varies laterally f r o m one outcrop area to another. U s u a l l y the matrix is actinolite-dominated, but chlorite (trench E - l ; Fig. 2.2) and biotite  23  (trenches B Z , JR-14, D E - 3 , E-2, E - l ; Fig.2.1) are also locally predominant. I n trench E - l , chlorite-rich breccia is associated w i t h 1- 3 c m t h i c k quartz veins w h i c h cross-cut the breccia and surrounding intermediate to m a f i c metavolcanic and intrusive rocks. T h e breccia m a t r i x and the fragments w i t h i n the breccia closest to these veins are dominated b y calcite, albite and chlorite, the latter d e f i n i n g the S f o l i a t i o n . T w o metres f r o m the quartz veins the breccia m a t r i x becomes 2  richer i n biotite, w h i c h controls the S2 f o l i a t i o n and forms pseudomorphs the after coarsest ( > 0.1 m m ) hornblende grains, together w i t h chlorite and actinolite. A diffuse contact between the biotite-dominated and the actinolite-dominated breccia m a t r i x was identified through detailed m a p p i n g several metres from the quartz v e i n . Detailed petrography o f the p o l y m i c t volcaniclastic breccia can be f o u n d i n A p p e n d i x D.  2.4.2 Juvenile Magmatic Material Juvenile magmatic material that occurs as discrete fragments and rims o n other clasts i n the P V B is petrographically distinct f r o m the breccia matrix. The j u v e n i l e material is lapilli-sized (2-6.4 m m ) and is elongate and oval i n shape ( F i g . 2 . 6 A ) , possibly as a result o f deformation. The magmatic rinds are up to 2 c m t h i c k and have sharp contacts w i t h the breccia m a t r i x and w i t h the lithic fragments they enclose ( F i g . 2 . 7 A ) . I n general, the j u v e n i l e magmatic material is comparable mineralogically and texturally to the breccia m a t r i x ; c o m p r i s i n g actinolite, titanite, chlorite, and albite (Fig. 2.7B). H o w e v e r , the j u v e n i l e material differs f r o m the breccia m a t r i x as f o l l o w s : (1) contains more abundant > 0.1 m m actinolite grains; (2) less 0.2 - 1.5 m m epidote and fine-grained plagioclase grains, and more fine-grained oligoclase and muscovite (<5 v o l . % ) , (3) more 0.2 - 1.5 m m oscillatory zoned hornblende.  24  Figure 2.6. Photomicrographs o f the P V B . A. Fragmental texture o f the volcaniclastic breccia. Three fragment types are shown by lines w i t h different patterns and noted as J (juvenile magmatic material), M (intermediate to mafic intrusive rock), and F (intermediate to felsic metavolcanic rock). Note that the fragments are preferentially aligned parallel to foliation. The breccia matrix is inequigranular and comprises larger grains o f hornblende, biotite and epidote w i t h i n the fine-grained groundmass. B. Coarser grained epidote wrapped by the S, fabric. C. Coarser (> 0.1 m m ) oscillatory zoned hornblende with chlorite pressure shadows and the S fabric wrapping around the grain. D. S E M photo o f coarser grained (> 0.1 m m ) , pre- to syn-S, biotite exhibiting bent cleavage. E. S E M photo o f coarser grained (> 0.1 m m ) oscillatory zoned hornblende. 2  25  2.4.3 L a m p r o p h y r e The lamprophyre is similar m i n e r a l o g i c a l l y to the m a t r i x o f the volcaniclastic breccia and the j u v e n i l e magmatic material. The inequigranular texture o f the lamprophyre is defined b y 0.1 - 4 m m grains o f hornblende, actinolite, epidote and biotite ( 5 - 1 0 % ) set in a  finer-grained  (<  0.1 m m ) hypidioblastic groundmass (Table 2 . 1 ; Fig. 2.7C). The lamprophyre can be differentiated f r o m the volcaniclastic breccia based on petrography. The lamprophyre contains a l o w e r abundance o f clasts (up to 5%) and fewer l i t h o l o g i c a l clast types. Six types o f clasts were observed i n t h i n sections compared to ten types i n the breccia, corroborating w i t h field observations. U n l i k e the breccia, the lamprophyre does not contain j u v e n i l e magmatic material and oscillatory-zoned hornblende grains are rare. A l s o the lamprophyre may contain m i c r o c l i n e , and a higher proportion o f 0.2 - 1.3 m m biotite grains i n the matrix. A w e a k l y developed S4 f o l i a t i o n is observed i n the lamprophyre, defined by the alignment o f groundmass actinolite, biotite, ± chlorite. Subhedral, tabular and hexagonal-shaped biotite is the most c o m m o n porphyroblast. B i o t i t e grains 0.2-1.3 m m i n size usually have bent cleavage, and contain inclusion trails o f epidote almost perpendicular to the m a i n f o l i a t i o n . M o s t o f the 0.1-4 m m hornblende grains have been pseudomorphed by biotite ± actinolite ± chlorite. W h e r e hornblende grains are preserved, oscillatory zoning is very rare to absent. W i d e mantles o f darker material that often surround xenoliths i n the lamprophyre ( F i g . 2 . 5 K ) are enriched i n biotite, have diffuse contacts w i t h the groundmass, unlike rims o f j u v e n i l e magmatic material, and are interpreted as reaction rims between metastable xenoliths and the magma. I n outcrop 52 (Fig.2.2), where the lamprophyre intrudes felsic to intermediate metavolcanic rock, the resulting h y b r i d r o c k shows structures o f frozen i n t e r m i n g l i n g between the felsic and lamprophyric materials ( F i g . 2.7D). Patches o f darker l a m p r o p h y r i c c o m p o s i t i o n interleave w i t h lighter areas enriched i n quartz and albite. 26  F i g u r e 2.7. Photomicrographs o f the j u v e n i l e magmatic material and lamprophyre. A . A n accessory lithic fragment o f intermediate to m a f i c intrusive rock ( M ) enveloped b y a r i n d o f j u v e n i l e magmatic material (J) w h i c h is contained w i t h i n the breccia matrix ( B M ) . Note the sharp, distinct boundaries between the three rock types. B . S E M photo o f the finer-grained matrix ( = 0.1 m m ) o f the j u v e n i l e magmatic material is dominated by actinolite, chlorite and albite. Hornblende is mantled by actinolite and chlorite. C . Fine-grained ( = 0.1 m m ) matrix o f the lamprophyre d o m i n a n t l y comprises biotite, albite, actinolite, and chlorite, accessory zircon, epidote, apatite, titanite and quartz are also present. D . I n t e r m i n g l i n g o f intermediate to felsic metavolcanic (F) and lamprophyric ( L ) material i n outcrop 5 1 .  2 7  Detailed petrography o f the lamprophyre can be f o u n d i n A p p e n d i x D .  2.5 CHEMICAL COMPOSITION OF MINERALS 2.5.1 Amphiboles O n the basis o f electron microprobe data (Table 2.3; A p p e n d i x G , Table G l ) , the amphiboles f r o m a l l r o c k types are calcic amphiboles ( F i g . 2.8; Leake et al., 1997). There are t w o types o f amphibole, actinolitic amphiboles and hornblende. Hornblende is infrequently f o u n d i n the m a t r i x , and is almost always coarser (>0.1 m m ) and pre- to syn-S2 i n origin. The analysed hornblende occurs as several textural types, the freshest-looking oscillatory zoned hornblende ( m a r k e d O i n Table 2.3), m o t t l e d zoned hornblende ( M ) , and hornblende partly replaced b y fine-grained biotite and actinolite ( A ) . The oscillatory zoned hornblende crystals are probably relict phenocrysts because it is h i g h l y u n l i k e l y that pressure and temperature can oscillate rapidly enough during regional metamorphism to produce classic oscillatory zoning in porphyroblasts ( Y a r d l e y et al, 1991; Shore and Fowler, 1996). Hornblende grains w i t h mottled zoning are interpreted as grains affected b y diffusion d u r i n g metamorphism. The hornblendes show variable contents o f CaO (7.7-12.5 w t % ) , T i 0  2  (0-3.2 w t % ) , K 0 2  (0-1.5 w t % ) and N a 0 (0.2-2.6 w t % ) , l o w C r 0 (<0.15 w t % ) , and are classified as tschermakite, 2  2  3  pargasite, edenite, hastingsite and magnesio-homblende (Fig.2.8; Leake et al., 1997). T h e hornblende compositions f o r all three rock types are similar, w i t h edenite and pargasite as the dominant types ( F i g . 2.9). Hornblendes o f the j u v e n i l e material are less c o m m o n l y pargasitic (Fig. 2.9). Edenitic hornblende is less c o m m o n i n lamprophyres where magnesio-homblende is more abundant (Table 2.3; F i g . 2.9; i n c l u d i n g hornblende chemistry data f r o m Barnett pers. c o m m . o f W a w a lamprophyre).  28  2  o  2  — o ~  2  2  2  — o ~  ;  *  — o  05 2  < = > n  OS  o O  02  O  -  :  6  6  "  CJ  O  - Z 5 o -~ —~ o ~  CQ  CJ  —-  o  fN  f>  2  2  oo  2 2  -  o „  -  —• —  h 8 OO  ~  02  O O  — — o x  CQ O  z: ~ ©  t  \o  02 5  m  °° P! iri  M  O O  r  — r: o CN  o  m  co  ON  O  Q  >n O  Z o —  CN O ™  2  ^  — —  2 = ^oo c—  — O  ^  N  '3  5  00 CQ  P. CQ  CJ  5  o ^  -  — '  ON  O  2  ©  O  2  ^  ^  m rn  — <n  *  « 6  2  r-  o  t £ .5 IS «  "  °  u  O  — \o  2  —  ^  ON  —-  2 02  d r-j  ON  C  OO CO O 0O ^ O  ON  fN  r£  N  6?  oo  . -  6 E  ^ (N T3  N  o o  *n  2  2  o E a •= S  2 2  <N  _ _ o ^  3 5 d —  c  SI  ^ „ o ^  D.  o  o2  o  d S  z < bo 1- <  9,  o o o oo c 2  2  QO cj  S  •2 E°  CQ  29  si  1  & OS 2 b"  c 'S o  s  3  J 3  O  N O u  <  o  S  S  = R  r—»n O~  ^  CN  © 5  CN  oo »  ci O O  „  o  o—  M  r'l  -' 2  o  ^  "i O 6  OO  -  Di O  o  2 2  ei O O  °^ r-- f-o  <=i — oo o\ — o —' o  oo © - °° rN < N QQ  Q  OS  © ™2 © ~  OO  o> m t— — fN o  2 2 ©' d  CJ  <x  o K .  " 1  ON  _,.  ^ rs a 3i o n_j fN _j no "  —  o  — —«  d  > d _2: — oo ^o  CN  ^:  ^  —— o —  —  2 rl S d  IT!  d  oO O  5  -  ^  —  ©  .5  o  CQ  3 2 =  w O O  S  OS  ¥8  °  •?!  § ^ o - fN © ~ £ ©'  Ji N § ?  o o I ^fNN—j^t • O ^ ^ O i2 © QdfN  S E  'I  —n C N r o fN \6 2 o 2 o g o o O— f z < <  <u  ? N 1 O ? E  ^ 2  § s$ 55 ? a ©  E S .2 .5 S -2 2 c 8  a! =S OS  1 1 9 9 9. 2 2 u  CQ  2  ^  30  c  i  A.  Na amphiboles  • 1  • 2 1.5  N a - C a amphiboles  Fe-Mn-Mg-Li amphiboles  EQ -=  1 0.5 z  C a amphiboles  •  1  0.5  1  r  M  B  1.5  W  1  2  2.5  (Ca + Na) in the B-site (a.f.u.)  B.  0.5  0.5 (Na + K.) in the A-site  c. ti  0.5  0.5 (Na + K.) in the A-site  Figure 2.8 A. Classification of amphiboles (after Leake et al., 1997). B. Plot of Na + K. in the A site vs. Ti in the T site for amphiboles with 5.5 to 8 Si formula units to determine the nomenclature for calcic-amphiboles (Deer, Howie, and Zussman, 1997), C. Plot of Na + K in the A site vs. Ti in the T site for amphiboles with 4.5 to 7.5 Si formula units to determine the nomenclature for calcic-amphiboles (Deer, Howie, and Zussman, 1997), Symbols: 1 - Amphibole data collected from this project; 2 - Amphibole data from Barnett pers. Comm. (2002)  31  F i g u r e 2.9 Distribution o f amphibole types w i t h i n A . p o l y m i c t volcaniclastic breccia, B. Juvenile material, and C. Lamprophyre. Symbols: E d - edenite; H a - hastingsite; M - H b l magnesio-homblende; Pa - pargasite; Ts - tschermakite.  32  Fig. 2.10 continues overleaf  33  B.  F i g u r e 2.10 Plots o f compositional zoning f r o m core (1) to r i m (6) in oscillatory-zoned hornblende grains f r o m sample N L - 1 ( A . grain N L - 1 - 2 6 A , B.grain N L - 1 - 9 A ) .  34  Oscillatory zoned hornblende occurs p r i n c i p a l l y i n the P V B and j u v e n i l e material. The grains have a c o m m o n c o r e - t o - r i m compositional pattern s h o w i n g subtle fluctuations i n Si and A1  I V  i n the T site, M g f o r A 1 , F e , F e V I  2 +  3 +  i n the C site, F e  2 +  and Ca i n the B site, and N a i n the A  site ( F i g . 2.10). There is no regular pattern o f compositional variation f r o m core to r i m except for an insignificant decrease i n K a n d N a contents (Fig. 2.10). Oscillatory zoned hornblende does not differ i n composition f r o m all other textural types o f amphiboles, and all structural types o f hornblende are c h e m i c a l l y identical. Hornblende does not change its composition i n contact w i t h biotite pseudomorphs or w i t h biotite o f the matrix/groundmass. A c t i n o l i t e forms mantles on and pseudomorphs after hornblende, and fine-grained ( < 0.1 m m ) matrix and groundmass crystals. It contains up to 2.4 w t % AI2O3 and v a r y i n g FeO (9.8 12.3 w t % ) .  2.5.2. Micas B i o t i t e and muscovite are present i n all the rocks analyzed ( A p p e n d i x G , Table G 2 ) . B i o t i t e is restricted to the P V B and to lamprophyre and never occurs in the j u v e n i l e material, whereas trace amounts ( < 1 v o l . % ) o f muscovite are f o u n d o n l y i n the P V B and j u v e n i l e material. Three textural categories o f biotite grains w i t h i n the P V B and lamprophyre were distinguished: fine (< 0.1 m m ) biotite i n the m a t r i x or groundmass (marked M i n Table 2.4), coarse-grained m i c a ( C ) , and pseudomorphs after hornblende (P). Biotite comprises the m a j o r i t y o f the fine-grained micas i n the P V B and the lamprophyre, and has similar compositions i n both rock types (Fig. 2 . 1 1 ; Table 2.4). However, some o f the m a t r i x biotites w i t h i n the breccia have slightly higher A l i n the Y site, lower M g , and higher N a contents (up to 3.2 w t % N a 2 0 ) thus s h o w i n g a transition to Na-biotite. The o n l y m i c a i n the groundmass o f the j u v e n i l e material is muscovite. Some grains o f muscovite show elevated M g  35  17  16  5  • •  14  M  inetteComr^i  tionalTrend.  13  12 14  FeO • 1 F i g u r e 2.11  T  16  wt%  2 A 3 04 • 5 A6  Plots o f A 1 0 vs T i 0 w t % (A) and A 1 0 , vs F e O w t % (B) o f biotites i n the 2  3  2  2  T  breccia matrix and lamprophyre compared w i t h compositional trends for micas in kimberlite groundmass, lamproites and minettes (after M i t c h e l l , 1995a). Symbols: 1 - coarser (0.1-1.5 m m ) biotite grains in the breccia matrix, 2 - finer grains ( < 0.1 m m ) i n the breccia matrix, 3- biotite i n the breccia matrix pseudomorphing hornblende, 4- coarser (0.1-1.5 m m ) biotite grains in the lamprophyre, 5- finer grains ( < 0.1 m m ) in the lamprophyre m a t r i x , 6- biotite pseudomorphs after hornblende in the lamprophyre. 36  cn CN oo cn ' t  2 c B  cn so  ca  r--  in oo cn  Tj- ©  ©  OS ©  cn © ^  d  ^ ^  CN  SO OO  CQ  d  oo in CQ • so Os 0 0  so  cn In cn oo n os SO in -3- - H cn > CN >n in d Tt d d d OS ~  CN o OS CN 00 CN so CN d m  C  IS 2  so  i  I  X X  oo  CN  in  r~-  t~-  oo cn •n in o d d d 00 d  CN  —"  i  Tt-  in o  CN Os d d d d d o  oo  so CQ  a Br o B o  T3 3 CJ c«  OS  Tt o  « CN oo oo  d ° C°^ N d  %  I  H  B  'S  OS i cn Os i © OS  00  2 . 00 ^  u  CN o so 00  i  o a. B  >n  p CN OS  OS rr p o CN so OS  o  o  _ cn oo m _ o  o oo oo o o m •—i o CN oo O cn d d d OS d  M n 0O r SO so 0O . CN . —-* d i£ d 2 il. d  CQ  8  —  'S ca _u "o  3  OS N so C CN  •  cn o CN so d OS  i  CN CN oo  i  d  -  d  CJ  ,  i  i  cn 00 o CN o o CO © m CN CN i d d d r~ cn  -  ^ oo  l>  o  i<2  m <n OS cn —H <n OS , cn d d d in - < so  — < - — < -  so  so  d  in i CN r~ d OS  00 rr , oo so in CQ OS U oo cn in 1 oo so CQ —< Os  1  ©  CN in OS CN so OS SO m CN p S CN O OS  c 'a  00 X  SO OO , OS CQ in OS OO rr I oo cn so CQ OS  > CJ  X) X  CJ &  ca cj  a.  ej  H c  o x>  O  S3  .  ca  <D d  «  °~ °~N O  u  Qoo  ™ ^ a a -<j. -  37  —  O 3o X H  cj  B  ca  Z  o  (up to 5.1 w t % M g O ) and Fe (6.5 w t % F e O ) , and l o w e r Si trending towards phengite (Table 2.4). B i o t i t e grains > 0.1 m m i n size occur o n l y i n the P V B and l a m p r o p h y r e and do not exhibit any zonation. I n the > 0.1 m m biotite grains, amounts o f all elements except Cr are similar to those i n the matrix/groundmass biotite and biotite pseudomorphs after hornblende f r o m the same r o c k type. W e interpret this as evidence for metamorphic re-equilibration o f all biotite compositions. C h r o m i u m content is always higher (up to 0.4 w t % C r 0 3 ) i n the coarse 2  biotite ( F i g . 2 . 1 1 ; Table 2.4) than i n the matrix/groundmass biotite. The biotite pseudomorphs after hornblende show slightly higher T i 0 2 , l o w e r M g O and occasionally h i g h C r 0 3 (Table 2.4). 2  Some o f these grains have significantly higher FeOiotai contents than the other biotite analyzed.  2.5.3. Other minerals Epidote occurs as coarse or fine grains in the m a t r i x and groundmass o f the P V B , lamprophyre and j u v e n i l e material; we analyzed o n l y epidote grains > 0.1 m m ( A p p e n d i x G, Table G 3 ) . Epidotes o f the three rock types are similar i n c o m p o s i t i o n and m a y be enriched i n Cr 0 2  3  (up to 0.4 w t % ) (Table 2.5). The m a t r i x plagioclase is albite and oligoclase ( A p p e n d i x G , Table G 4 ) . A l b i t e  ( A b 9 8 A n ) is present i n all three rock types, whereas oligoclase ( A b 8 9 A n n ) is restricted to the 2  P V B and the j u v e n i l e material. Oligoclase occurs as patches w i t h i n the anhedral albite grains that appear as c o m p l e x pseudomorphs after oligoclase. These grains are m o r e prevalent w i t h i n the j u v e n i l e material than w i t h i n the breccia. M a t r i x chromite grains (< 0.1 m m ) w i t h i n the P V B (Table 2.5; Table G 5 , A p p e n d i x G ) contain m i n o r M g O (0.2-0.9 w t % ) and F e  3 +  (calculated X F e  3 +  = 0.01), little A 1 0 2  3  (2.7-5.4  w t % ) , and h i g h F e O t a i (39.4-48.4 w t % ) and M n O (1.7-2.7 w t % ) . H i g h content o f Z n O (2-8 To  38  r- oo —i r-~ m oo < N S S -? ^ o. oo. -Sa t~ • no d SO < N °  0 0 C N  d  CS  "a  O ca o  "a  "a  S "a  * -5  "a "a £  N  S  C N  S ^  of u  CO  C N  ^  C N  so  CD  e8  u >  d  o o JQ  0  ^ I "!  r-  cn  H od so  C  S S 2 8; i-: d © £j  d  OS «  so c so  •c  ©  C3  o  S  0 0  cj o  O O < N  Uu  — la0 0  •5t  so  C N  _ ^  «  CB  ca  in  ca g d  ca 2 ^ ca « d  rn  Q  ( N  CL.  a  O  0 0  o  ©  ©  «  a  9  B  ^CB  O  so 0 O C >  cn ca ca ca cn  ~a ~a a  K  Sca ca ca O t-^  a a a  C  C N  oo O S 0 0  ca ca ca so  "a a a ^  OS  u CL,  3  oo OS  Os  in os in so [2 * cn o 5 "5 so © d oo £j  2  Pi o  C N  OS  ~a "a  o ca os d < o in o os o ^ so d d °  0 0  _C3  °  m oo oo o  ca ca ca so od os  o  O S os  c*' -T  1  o  Z <d  O O w  h  OO "  <  M  U  9. 9) ? Q o % o o o o £ s s u z z a o ^ > N t,  39  O  ca ca P  "a -a g  ca ca  ca C N  ca os ca 2 d "a os ~a  3§ 2 S cn 3  n  * * 2  a a  —i  Pi © a  •°  in n  —I  SO  1 CQ  cn os r-  cn cn in OS d cn  <  oo OS  "a a a a  —  C N  C N  o  X5  so ca ca ca — r  d  d < N  -  ca ca  -a -a e  • ~a ~a "a "a u o_, ca ca ca ca os a a ~a Oin od w S  ^ so S so ca O ^ ^cn d ^ . dO ^ so d d £J  U  o  ca ca ca cn  g  f. 2 as  a CJ  "a ^ "a  d  "a ~a ~a ~a  cn  iJ3  3  SO SO  ft- io - oo in cn "! m -5 oo o  in — o  s  H  <  w t % , Table 2.5) f o u n d i n this chromite b y A r m s t r o n g and Barnett (2003) could account f o r the 5 % deficit i n totals i n our chromite analyses. Chromite grains w i t h i n the j u v e n i l e material and lamprophyre are too fine-grained f o r E M P analysis.  2.6 WHOLE ROCK GEOCHEMISTRY The matrix o f the P V B , j u v e n i l e fragments, and lamprophyres have a very restricted range o f c o m p o s i t i o n , w i t h 46-50 w t % S i 0 , 2-5 w t % total alkalies, 9-14 w t % M g O (Table 2.6; A p p e n d i x 2  H ) . Based on the (Na20 + K2O) and S i 0  2  content, the rocks range i n composition f r o m alkaline  to sub-alkaline (Fig. 2 . 1 2 A ) . M o s t samples are basic and all are metaluminous (Fig. 2.12A, E). V a r y i n g K2O contents encompasses a range f r o m l o w - K to shoshonitic series according to the K 0 - S i 0 2 classification o f M i d d l e m o s t (1975), and diverse K2O / Na20 ratios characterize the 2  rocks as ultrapotassic to sodic ( F i g . 2.12B, C). The m a j o r i t y o f element oxides measured f r o m the three rock types are not correlated w i t h Si02 or M g O content ( F i g . 2.13, 2.14). O n l y Ti02, N a 0 and 2  AI2O3 correlate negatively w i t h M g O f o r m i n g c o m b i n e d single trends for all rock  types ( F i g . 2.14). The abundances o f compatible trace elements N i , Cr and Co vary by t w o orders o f magnitude (Table 2.6). M g O correlates strongly w i t h N i ( R = 0.78), and moderately 2  w i t h C r ( R = 0.48) and Co ( R = 0.59); the best positive correlation is observed between N i and 2  2  C r ( R = 0.88). 2  It is uncertain to what extent the b u l k compositions o f the metavolcanic rocks reflect their p r i m a r y magmatic compositions. The l o w m o b i l i t y o f T i i n the W a w a metavolcanic rocks is manifested i n its tight compositional range ( v a r y i n g b y ~0.4 w t % Ti02) determined for the w h o l e r o c k P V B , j u v e n i l e material, and lamprophyre samples. T i and A l are considered to be the least m o b i l e elements i n greenschist facies environments (Pearce and Cann, 1973; R o l l i n s o n , 1993) and are u n l i k e l y to be m o d i f i e d by subsequent alteration and m e t a m o r p h i s m . Large variations i n  40  CA  o E  C3 ca  43  —»  T3  I?  r2  —  < 3 ea r-i  •n >-> JS  CA J* o  e  o G  £  CA c  ,o  > ">  SB  o  T3 43  o ca £ M  § CQ  I  I  sa CQ  'u <~cu ?  r-tN  8 2 X) 2 o  Z  C3  §  •3  rt  cj ca  ca  o+ I I I I  •+3  i  00  * §  o .a £ 3 •a g E 1 2 « ob ca aa ca ca  1  O  1|  K j cd^ z  <  5 3  CA O  fN  O CA  ca Peraluminous  sA U C  -  60-ti  ca ^  •3  |S  —  O  ™  "3 2  -  4) C_  I  1 2 I  I  i  i  CO  o f  i  i  CD d  1  i  rr d  i  i  o  i  p  -I *  -o  J3  C  5 T3 .5  Q  ca  . ca^ E — ca  O  &  •—  oo ca -a  i ^  CJ  42  E  o CJ .s o ©  r4 &  am  -J  ca  CJ  a  oiv  O*M +  «  . i ca E ca 5  -  •  49  oo  r;  o o ca  .22  a  3  I  '  *T3  ft  #  c  ]  ^ •  •  _r ON  ca r~. •S -o 2ao caoo Ec "3  _  *\  *s O  S £ > ca— 2 tg  -  -  O  .S CA  a • .2 Q CA — as  s —< a CA w on . CA  fa >  +  +  +  o  in in 5?  g  +3J  ***  33  X  g" 33  g~ 33  '+  a ca u o > C o  D. Cu 3  ca  o  o (%»<*) ± O *& (  o  un  00  d  l  SO  o  d  ^Cf  o  s  CN  II  (%»«) '0 d !  CN  B >. Cu  o  K  •CO  +  CN  + *-  •  « •  • •  2  6 33  "o x> 5 ca u • u. J2 •» 0 u —  C/3  CJ  «  1ca .3 a cj ca o -H > o 3 u -o o >  S  + m  N  1.1  "ca in  CN  0  _-  6 .2  1 1 |  S  * 'S  CJ u JS >  — 3 Uu CJ 00 CJ C3 CJ  =S £ a CJ 0  'S  ca «j CJ ta '3 > §  'C  i «  2 ? 1 Cu o 'OSX  o  f*-i CN (%»«) O ^ N  o (%»*0  43  —  O  <N  Cu  2o at  *" o  o  s  ax  I *  s  4 +  (%»«) 'OSS  (%»«) 0 " l V  + i  ft*  1£  -*  si  'o DC  s •-L.  (%**) o »N r  (%*») 'O'lV  (%J«) 'O'd  —  o  • +  • • o  o  2  s  o  s  et  +  .1  (%»«) 0«3  (%J<*0 'OU.  44  CJ CJ CJ S-i  -O CJ  +  l#  a  ca  O >  T3 CJ  §  ti o a. Q. 3  §  °  00  (uidd) eg  2 >-, -n c  o s— a.  o  2 * w  gg  CJ  " 2  0  S J=  si  s  9 -H-  2  M  ca ca  1 3 11 a -a 5 u P N (uidd) J 3  0  1  5 m .2 « T 3 CB CB ' C  2  •S  1 I CJ J3  u ~  *- a 5?  CA  -  —1  6ca 't EH  O  oo  S  CO  s 1^  + •++  ca  2  .2  11 M  9  § I (uidd)  03  (uidd) !\|  cu G i. o  a a. e* a  ti 5 45  CN  SO  O  Os  r- o —  m  CN  fN  m m in —  rN »n  ~ o ^ 2 so  OS  r-»  r-»  r-  ^t-  O  —•  os  m  o o  —  oo o  CO —•  m  O  ~-  Os  —  w ©  ~  ©  ^£  OS  —  OO  ©  ©  <i  —  vo —<  ©  m  oo \o  oo —  ©_ ©  T}-  GO m  LT>  CN  vo  —  o _,  U"i  _ ro  fN C N r O C N O  rs  h  ^  m CN  m ©  vo © CN  m  m  O  °  °^  —  os _ ^  m „ <=>  ro  ©  —  o  O o  o —• — ^  fN  ©  m  iTi © sq m —  t vq ©  — © OS  Os  Os  —. — ©  ©  Z  <  U J  O £  O f—  Os in ©  —  — CN  —  ™  © OO ©  —  O  ^  ©  CN  I I  Os m  so in  Os os  !5S \t IN  fN  -  o  CN  -  -  VO © —  © —; ©  —  ©  ^  2  _  vo  °?  CN  §  ^  S £  ^ " 2  — m m CN  ©  Os  v~ = ^ CN  CN © — OS m CN  Os CN  os  oc  "*  M © O  O  m  o> — -  2  O  00  ^  OS  O  o o o  QO  3  p m  O CN ©  CN  oooo© ^  10  in  is**  J ^ f^l J  rN  m ^ fN ©  3  —  Os SO © © "  M  00 -  O  CN © © o^  CN <n i i ;  © CO  r^-  OO CN  o —o :  so —  —  TT  00 CN — OS  00  in vo co CN CN CN — O T T O  o cj z ^  O  46  o  o z um  I  the content o f Na20, K2O, and CaO (up to 3 w t % ) i n the studied samples and the fact that these element oxides do not correlate w i t h most other major oxides, are consistent w i t h the generally m o b i l e behaviour o f these elements i n metamorphic environments (Pearce and Cann, 1973; R o l l i n s o n , 1993). There are f e w systematic differences between compositions o f the P V B , its j u v e n i l e clasts and the lamprophyres. The lamprophyres have the highest K2O and B a O content f o l l o w e d b y that o f the P V B and the j u v e n i l e material (Table 2.6; Fig. 2.15). The K2O and B a O content corresponds w e l l to the h i g h abundance o f biotite in the lamprophyres and the l o w abundance o f biotite i n the j u v e n i l e material. The breccia stands out o w i n g to higher AI2O3 and l o w e r M g O contents than other rock types. A m o n g the breccias, the clast-supported breccia shows the highest AI2O3 and lowest M g O content, w h i c h may be explained by the presence o f more abundant A l - and Si-rich, and M g - p o o r fragments o f felsic volcanic rocks. The whole r o c k compositions o f several types o f large rounded xenoliths n o w completely replaced b y secondary actinolite and hornblende were also analyzed (Table 2.6; A p p e n d i x H ) . Some o f the xenoliths show extremely h i g h amounts o f C r (2300 p p m ) and N i (1500 p p m ) indicative o f an ultramafic a f f i n i t y . Peridotitic predecessors f o r these fragments are c o n f i r m e d the presence o f fresh o l i v i n e in centers o f some large xenoliths i n the W a w a breccias ( D . Francis, Pers. C o m m . ) .  2.7  I N T E R P R E T A T I O N AND DISCUSSION  2.7.1 I g n e o u s p r o t o l i t h s f o r t h e m e t a v o l c a n i c r o c k s The greenschist facies m i n e r a l assemblages (actinolite, chlorite, albite) o f the breccia m a t r i x , j u v e n i l e material and lamprophyre suggest a mafic p r i m a r y magma. M a g m a t i c predecessors f o r the W a w a metavolcanic rocks were inferred f r o m the compositions o f relict p r i m a r y minerals 47  A1 0 2  MgO  3  K O*10 2  F i g u r e 2.15 A M g O - A l 0 - 10 K 0 ( w t . % ) ternary plot f o r w h o l e rock compositions o f the p o l y m i c t volcaniclastic breccia m a t r i x , j u v e n i l e material and lamprophyre. Symbols: 1- clastsupported breccia, 2- matrix-supported breccia, 3 - j u v e n i l e material, and 4 - lamprophyre. 2  3  2  48  and preserved igneous textures using the classification scheme o f W o o l l e y et al., (1996).  The  petrographic and mineralogical criteria should take p r i o r i t y over the classification based on the w h o l e r o c k compositions as these m a y have been m o d i f i e d by m e t a m o r p h i s m , and thus are not useful i n classifying h y b r i d diamondiferous rocks (Rock, 1991; M i t c h e l l , 1995b, W o o l l e y et al., 1996). The coarse grained hornblende is interpreted to represent relict phenocrysts because o f oscillatory z o n i n g ( Y a r d l e y et al., 1 9 9 1 ; Shore and Fowler, 1996) and compositions consistent w i t h a magmatic o r i g i n (Fig. 2.16). The p r i m a r y magmatic composition o f hornblende is most l i k e l y pargasitic, edenitic and rarely hastingsitic, based on analyses o f cores and inner rims o f the crystals w i t h oscillatory zoning. The p r i m a r y hornblende compositions, and the overall mafic character  o f the  metavolcanic  rocks  define  these rocks  as metamorphosed  calc-alkaline  lamprophyre (Rock, 1991; W o o l l e y et al., 1996). The absence o f pseudomorphs after o l i v i n e and l o w content o f T i and alkalies i n relict hornblendes suggest that G r o u p I and I I kimberlites, lamproite or ultramafic lamprophyre are not viable candidates for the magmatic protoliths (Rock, 1991; M i t c h e l l and Bergman, 1 9 9 1 ; M i t c h e l l , 1995a,b). W h o l e r o c k m a j o r element geochemistry o f the W a w a metavolcanic rocks supports the interpretation that they are metamorphosed calc-alkaline lamprophyre. The AI2O3 -TiCh and M g O - S i 0 2 diagrams show that the m a j o r i t y o f the samples plot i n the calc-alkaline field w i t h i n the same range as other k n o w n A r c h e a n lamprophyres, many o f w h i c h have been classified as calc-alkaline (Fig. 2.17). The W a w a calc-alkaline lamprophyres o r i g i n a l l y contained phenocrysts o f hornblende and l i k e l y biotite and clinopyroxene. Other A r c h e a n lamprophyres metamorphosed to greenschist facies have been shown to retain relict igneous amphibole grains (Perring et al, 1989; Currie and W i l l i a m s , 1993; W i l l i a m s , 2002). Compositions o f primary calcic amphiboles i n the W a w a metavolcanic rocks cover the entire compositional range o f this mineral reported f o r calc49  F i g u r e 2.16 A . Plot o f Si in the T site versus A l in the C site o f calcic amphiboles f r o m the breccia matrix, j u v e n i l e material, and lamprophyre (Leake et al., 1997; plot after Leake, 1965). Symbols: 1 - j u v e n i l e material, 2 lamprophyre, 3 - breccia matrix and 4 lamprophyre f r o m Barnett (pers. C o m m . 2002). The solid rectangles show endmember compostions for tschermakite, hastingsite, pargasite, edenite, and actinolite.  50  A.  20  •  15  a < X  / •  5  >>r-^>£  1  6,7  C  3  -t 2  3  TiO, wt%  B.  6 0  X  50  £5 40 \ d' £  .  30  H  20  10  10  15  20  25  30  35  40  MgO wt% + 1 X 2 B 3 « 4 05  X6D7-8  A 9 O10  F i g u r e 2.17 The A 1 , 0 vs T i O , ( A ) and M g O vs SiO, ( B ) plots for whole rock compositions o f the Wawa calc-alkaline lamprophyric rocks. Fields 1 to 8 outline compositional fields for lamprophyres and other p r i m a r y diamondiferous rocks (Scott-Smith, 1995; M i t c h e l l , 1995a; Rock, 1987; 1991) and include 1 - alkaline lamprophyres, 2 - calc-alkaline lamprophyres, 3 ultramafic lamprophyres, 4 - W a w a kimberlites ( K a m i n s k y , 2002), 5 - Group 1 and II kimberlites, 6 - lamproites, 7- olivine lamproites. Symbols: 1 - matrix supported P V B , 2 - clastsupported P V B , 3 - j u v e n i l e material, 4 - lamprophyre, 5 - Archean Shoshonitic lamprophyres ( W y m a n and K e r r i c h , 1993), 6 - Archean U c h i subprovince calc-alkaline lamprophyres ( W y m a n and K e r r i c h , 1989), 7 - Archean Wabigoon and W a w a subprovince calc-alkaline lamprophyres ( W y m a n and K e r r i c h , 1989), 8 - Archean A b i t i b i subprovince calc-alkaline diamondiferous lamprophyres ( W i l l i a m s , 2002); A Y L - Archean Y i l g a r n calc-alkaline lamprophyres (Currie and W i l l i a m s , 1993). 3  51  alkaline lamprophyres ( R o c k , 1991), but N a - r i c h , and A l - p o o r calcic amphiboles (edenites) are also present. The calc-alkaline nature o f the W a w a lamprophyres suggests that they l i k e l y contained phenocrysts o f hornblende, clinopyroxene, and possibly biotite.  Evidence f o r the f o r m e r  presence o f biotite and clinopyroxene phenocrysts i n the W a w a metavolcanic rocks is the C r - r i c h character o f biotite and the fact that epidote replaces f o r m e r coarse phenocrysts.  N o n e o f the  present coarse biotite i n the W a w a metavolcanic rocks plots o n any o f the magmatic trends o u t l i n e d b y M i t c h e l l (1995a) f o r micas i n lamprophyres, kimberlites and lamproites ( F i g . 2.11). This metamorphic biotite m a y have developed after h i g h - C r p r i m a r y mica phenocrysts that are c o m m o n i n mantle magmas ( M i t c h e l l , 1995a), or after clinopyroxene. I t is u n l i k e l y that the coarse C r - r i c h biotite is replacing Cr-poor magmatic hornblende. Moreover, fresh clinopyroxene and biotite are described f r o m A r c h e a n calc-alkaline lamprophyres i n the A b i t i b i greenstone belt 400 k m east o f W a w a ( W y m a n and K e r r i c h , 1993). Compositions o f chromite i n the W a w a metavolcanic rocks (Table 2.5 and W i l l i a m s , 2002) are i n the range typical f o r lamprophyres and dissimilar to those i n kimberlites and lamproites. Calc-alkaline lamprophyres usually contain chromites that are l o w i n M g O and h i g h i n Z n O (up to 7 w t . % ) and M n O (up to 4 w t % ) ( Rock, 1991).  2.7.2 Volcanology of the calc-alkaline lamprophyric rocks A h i g h l y explosive eruption style that produces pyroclastic rocks is not characteristic o f l a m p r o p h y r i c magmas, w h i c h generally intrude as dykes. T h e calc-alkaline lamprophyric breccias have a volcanic o r i g i n as they host rare l a p i l l i - and bomb-sized, j u v e n i l e and cored fragments (Fig. 2.41, 2.4J, 2.6A, 2 . 7 A ) w h i c h have been interpreted t o be pyroclastic. B r e c c i a t i o n can result f r o m several different processes associated w i t h explosive volcanic activity i.e. 52  pyroclastic f l o w , pyroclastic f a l l , pyroclastic surge, f l u v i a l f l o w , grain f l o w , turbidity current, slides and debris avalanches, and debris f l o w s (Table 2.7). Based on the f o l l o w i n g evidence, the P V B is interpreted to represent volcaniclastic g r a v i t y f l o w deposits, specifically debris f l o w s . The volcaniclastic breccia is generally massive and structureless u n l i k e most types o f volcaniclastic deposits (Table 2.7). The f e w sedimentary structures seen here are rare massive and coarse tail normal graded beds (Shultz, 1984; Cas and W r i g h t , 1988; Boggs, 1995). The crude n o r m a l grading may have resulted f r o m particle settling d u r i n g transport i f the matrix viscosity and strength was no longer capable o f supporting large, dense fragments (Shultz, 1984; S m i t h , 1986) or f r o m accretion o f the debris f l o w w h i c h may have had large particles at its front due to kinetic sieving (Vallance, 2000). The breccia units are t h i c k ( m a x i m u m thickness ~ 110 m ) and occur i n discontinuous regions over a 5 x 10 k m area; such large areas occupied by t h i c k volcanogenic units are uncharacteristic o f most pyroclastic deposits, f l u v i a l f l o w s , and grain f l o w s (Table 2.7). Large volumes o f material and long o u t f l o w distances are typical f o r d e b r i s - f l o w deposits that originate on volcanoes ( M c P h i e et al., 1993) bbecause volcanoes provide the necessary components for debris f l o w generation, i.eT abundant loose sediment, steep unstable slopes, water, and a t r i g g e r i n g mechanism (Fisher and Schmincke, 1984; Cas and W r i g h t , 1988; M c P h i e et al., 1993; Vallance, 2000). The clast/matrix ratio varies w i d e l y i n the P V B . The breccia is d o m i n a n t l y matrixsupported w h i c h is typical o f most d e b r i s - f l o w deposits (Stow, 1986; Cas and W r i g h t , 1988). The P V B may be clast-supported, w h i c h has also been documented i n debris f l o w s w i t h as little as 5 % interstitial mud-water f l u i d ( L o w e , 1979, 1982; Fisher and Schmincke, 1984; Cas and W r i g h t , 1988). U n l i k e most pyroclastic deposits, the breccia is p o o r l y sorted i n particle size and particle density (Table 2.7). Fragment sizes range f r o m sand to megablock (up to 9 m i n size). There is 53  CJ  CJ  x> 2 5  2 =2 ta CJ E a. > a  V3  ... 'C CJ•'. cj - ° •3 ii — XI ca ra  90  ca ->,  e—  ,  o| a -w cc u CJ ca  E -B «  U  a E 'S ° E s >, o o E  00  O 13 o  -So."  ™ ty. ^ « °  C T3 11 —  h- u w  .2 +2  +o  £ 5 - P  ^ CJ  j*f # i o  «  <U —  C ' — oi  ^3 '  £ CX O  +  O u m -a  -.ta >.-  £  + o  +s I  X)  X)  + 3 S  CJ  3 j* 3  "°  <  - S E •*  +  ,1 a  •3 « ? o E s CQ 2 o  i! cj P i. t * r c  S E  '3 °  2  o o.  c CJ CJ  5 ^  T3  ~ =a  + ,S =  ja c a  a1  +2  E c  -  T=  E w o  0°3 U2 3£  •o — 2 p ~ « E : M  E  J2  _£3  -o o -r  : 2  a.  E  C3  2  E £  «  E CJ n +, 5 > og E o  LS ca E ..a X J E a. P o U So S *  +73« 2  CJ  o E p  §1  c  <  o S P X) OJ CS » " o j» ca ca  XI  0> t: c u  Eo  XI —  n*  CJ  o -2-3 f S I •sl2-IUar;b >I a  OD £ 1-  (—J  <  x:  LU U  L- "TV.  + .5  t  5 5  O  y S  crt  c  e a  ca 3  CJ  g u. t a § °  >> u- E . n fa — oo " A .5 E a! E -5  .2  P  E E 1-3 2 a  w 3 cca E s .-^o •S =2 S -*  P  P  P  e| a  «  s  - §  cj oo it;  2 E  i  | E o | .§• a E c" u S " 1 P  P  E f  — >  A W A t«  2  P  s o  5  00  5  3  § s «> 54  little evidence o f sorting on the basis o f density. Poor sorting can be attributed to the debris f l o w ' s a b i l i t y to support very large fragments due to its h i g h m a t r i x viscosity, buoyancy effect, dispersive pressure and possible hindered settling ( H a m p t o n , 1979; L o w e , 1979; Fisher and Schmincke, 1984; S m i t h , 1986; M c P h i e et al., 1993). The presence o f accidental megablocks o f country rock rule out most types o f volcaniclastic deposits except debris f l o w s , and debris avalanches and slides (Table 2.7). G o o d preservation o f angular clasts, cored l a p i l l i , j u v e n i l e magmatic material, unbroken phenocrysts, and j i g s a w - f i t textures indicates that the deposits have not been significantly r e w o r k e d in epiclastic f l u v i a l environments (Table 2.7). The preservation o f delicate features is typical o f debris f l o w s because they move b y laminar f l o w and particles are protected by the cohesive m a t r i x strength (Johnson, 1970; Fisher and Schmincke, 1984; Vallance, 2000). M a f i c volcanic fragments w h i c h are extremely prone to mechanical disaggregation and chemical alteration i n turbulent environment are also w e l l preserved i n the P V B . Fragment types w i t h i n the breccia represent a w i d e range o f lithologies (at least eleven different types; Table 2.2) atypical o f pyroclastic deposits (Table 2.7). The presence o f m a n y different types o f fragments is evidence for significant transport ( M c P h i e et al., 1993) w h i c h is possible f o r the P V B as it has been described over 50 k m . M a s s - f l o w deposits are very m o b i l e 2  and have been k n o w n to transport material l o n g distances f r o m site o f f l o w i n i t i a t i o n and as a result h a v i n g the potential to sample diverse lithologies (Fisher and Schmincke, 1984; Cas and W r i g h t , 1988; M c P h i e et al., 1993; Vallance, 2000). Several features observed i n the P V B are explainable b y a mass f l o w o r i g i n , even though these characteristics may not be present i n all debris f l o w s . T h i n irregular tabular bodies o f P V B f o u n d w i t h i n the country rock (Fig. 2.4C) and large boulders i n f i l l e d by breccia matrix c o u l d be sedimentary dikes. T h e y may have been f o r m e d b y forceful injection o f l i q u e f i e d material into fractures o f adjacent rocks. Such injections c o u l d have been triggered by s l u m p i n g or rapid 55  emplacement o f sediment by mass-flow (Boggs, 1995). Breccia inclusions w i t h i n adjoining intermediate to mafic intrusive rocks close to the contacts are interpreted to have been emplaced i n the same fashion as the i n f i l l e d fractures (Fig.2.4B). Folded semi-consolidated material that appears as rare large blocks w i t h i n the breccia (Fig. 2 . 4 N ) c o u l d be an example o f slump structures. T h e y m a y have resulted f r o m soft-sediment deformation due to m o v e m e n t and displacement o f material deposited rapidly i n over-steepened unstable slopes (Potter and Pettijohn, 1977; Boggs, 1995). S l u m p i n g is c o m m o n l y associated w i t h and may lead to debris f l o w s ( S m i t h and Lorenz, 1989; Boggs, 1995). M u l t i p l e mass-flow events f o r m e d the P V B , as indicated b y the presence o f several beds (Boggs, 1995) and fragments o f earlier, different breccias w i t h i n a later breccia (Fig. 2.4A, G and H ) . Similar repetitive processes o f mass-flow deposition are reported for volcaniclastic kimberlites ( F i e l d and Scott Smith, 1999; Graham et al., 1999) that often contain previously f o r m e d "volcaniclastic autoliths". The dominance o f different lithological fragment types i n h i g h l y localized different areas w i t h i n the breccia also supports this conclusion. Such a pattern suggests varied sources for the mass-flow material. The material may have been deposited b y i n d i v i d u a l debris tongues separated spatially or temporally, or b y a single f l o w that sampled many different lithological units and deposited their fragments locally (Vallance, 2000). Due to the fact that both the matrix and pyroclastic components o f the P V B have calcalkaline lamprophyre compositions, indicating a dominance o f volcanic material i n the breccia, the P V B deposits can be further interpreted to be lahars, i.e. debris-flows rich i n volcanic component (Cas and W r i g h t , 1988; Vallance, 2000). The W a w a diamondiferous rocks f o r m e d as one o f the f e w k n o w n lamprophyric volcanoes. Other examples have been described i n N a m i b i a , N e w M e x i c o (Rock, 1991) and Southern A l b e r t a (Kjarsgaard, 1994). The latter occurs as y o u n g (~ 50 M a ) well-preserved  56  scoria-fall and mass-flow deposits p r o x i m a l to the vent, and epiclastic, f l u v i a l l y r e w o r k e d lahar deposits o f minette compositions. Here, the P V B are associated w i t h younger hypabyssal lamprophyric dikes and w i t h lamprophyre bodies o f indeterminate m o r p h o l o g y that c o u l d be either dikes or lava f l o w s . A d d i t i o n a l structural studies are required to establish their true nature more accurately.  2.7.3 Origin of the calc-alkaline lamprophyric magma M i n e r a l and b u l k compositional data have established that these rocks were derived f r o m calc-alkaline lamprophyre dykes and associated volcaniclastic deposits. The calc-alkaline lamprophyres originated as part o f the 2.67 G a subduction-related magmatism i n the M i c h i p i c o t e n greenstone belt. T h e i r contemporaneous emplacement w i t h felsic volcanic rocks is evident f r o m m a g m a m i x i n g structures (Fig. 2.5G) that resulted f r o m lamprophyric magmas i n t r u d i n g into unconsolidated felsic volcanic material. This interpretation o f m a g m a m i x i n g suggests that some o f the felsic volcanic material was still viscous at the time o f lamprophyre emplacement. H o w e v e r , the lamprophyre dikes post-date the W a w a breccia and o n l y record the D4 deformation event. T h e W a w a breccia that post-dates at least some o f the felsic material records both D2 and D4 structures. Based on this evidence there must have been more than one phase o f felsic volcanism. C o e v a l and co-magmatic o r i g i n o f the W a w a breccias w i t h late orogenic alkalic intrusions has been postulated based o n structural, lithologic and geochronological evidence (Stott et al., 2002). Evidence that the diamondiferous lamprophyric magmas originated i n the mantle is p r o v i d e d b y the h i g h amounts o f M g O , N i , Cr, and C o (Table 2.6) i n all samples except f o r the crust contaminated clast-supported breccia. H i g h amounts o f B a i n some o f these N i - , Cr- and C o - r i c h samples reflect the derivation o f m a g m a f r o m l o w degrees o f partial m e l t i n g . A deep  57  mantle source f o r the calc-alkaline lamprophyres is further supported by the presence o f diamonds and mantle-derived ultramafic xenoliths. Calc-alkaline lamprophyres are f o u n d in several Late A r c h e a n greenstone belts o f the Superior province. D i a m o n d i f e r o u s and barren l a m p r o p h y r i c dykes and breccias, very similar to the M i c h i p i c o t e n belt lamprophyres, were described i n the A b i t i b i greenstone belt 400 k m to the east ( W y m a n and K e r r i c h , 1993; W i l l i a m s , 2002). These 2.7 Ga A b i t i b i lamprophyres are more K - r i c h , shoshonitic i n character, and contain phlogopite, o l i v i n e and clinopyroxene phenocrysts ( W y m a n and K e r r i c h , 1993), in contrast to lamprophyres described i n this w o r k . The M i c h i p i c o t e n calc-alkaline lamprophyres are f o u n d i n numerous locations over a large area ( W i l l i a m s , 2002; Kjarsgaard et al., 2003), and not all contain diamonds. These barren lamprophyres o f the M i c h i p i c o t e n and A b i t i b i greenstone belts show no major petrographic contrast to diamondiferous lamprophyres, although the latter have a greater abundance o f chromite and higher w h o l e r o c k M g - n u m b e r s ( W i l l l i a m s , 2002). H i g h e r M g - n u m b e r s i n the calcalkaline lamprophyres ( M g # ' s = 75-85; W i l l i a m s , 2002) than those o f p r i m i t i v e mantle magmas suggest a contamination b y mantle peridotite, w h i c h is typical o f other diamond-bearing volcanic rocks. The A b i t i b i shoshonitic lamprophyres may have originated i n a depleted mantle wedge w h i c h was enriched i n large i o n lithophile elements and light rare earth elements during slab subduction and sediment dehydration ( W y m a n and K e r r i c h , 1993). The l o w T i / Y ratios o f the M i c h i p i c o t e n and A b i t i b i lamprophyric dikes and breccias provide evidence for a garnet-free, s h a l l o w mantle o r i g i n at depths between 30 and 80 k m i n the sub-arc mantle ( W i l l l i a m s , 2002). M a g m a s o f calc-alkaline lamprophyre composition are k n o w n to f o r m in convergent tectonic settings (Rock, 1991), as w e l l as in other active tectonic environments. I n general, lamprophyres are observed i n arcs where the convergent regime is f o l l o w e d b y extensional tectonics ( L u h r et al., 1989). I n the Superior Province, the l a m p r o p h y r i c magma is thought to have been generated by rebound and decompression f o l l o w i n g accretional collision o f t w o 58  allochtonous greenstone terrains at a plate m a r g i n ( W y m a n and K e r r i c h , 1993). A contrasting conclusion is proposed b y Stott et al., ( 2 0 0 2 ) , whereby the f o r m a t i o n o f the M i c h i p i c o t e n diamondiferous lamprophyres occurred i n the regime o f regional crustal shortening during the W a w a n phase o f the Kenoran orogeny.  59  Chapter 3 PHYSICAL AND CHEMICAL CHARACTERISTICS OF THE WAWA DIAMONDS  3.1 ANALYTICAL METHODS E i g h t y diamonds larger than 0.5 m m i n one dimension were selected f o r study f r o m the W a w a d i a m o n d population. These diamonds are amongst the largest w i t h i n the d i a m o n d parcels. H o w e v e r , the m a j o r i t y o f these diamonds have weights < 1 m g and m a x i m u m diameters < 1 m m ( A p p e n d i x K, Table K l ) and are thus considered microdiamonds i n most literature (McCandless et al., 1994). The diamonds were recovered f r o m the p o l y m i c t volcaniclastic breccia trenches ( A p p e n d i x K, Table K l ) described in chapter 2. The physical properties o f the diamonds were examined using a Leica M Z F L I I I Fluorescence Stereomicroscope w i t h reflected light and up to 10X magnification. M o r e detailed study o f surface textures and m o r p h o l o g y was done using a Philips X L - 3 0 scanning electron microscope (Department o f Earth and Ocean Sciences, U n i v e r s i t y o f B r i t i s h C o l u m b i a ) . D i a m o n d colour was determined against an opaque w h i t e background using a reflected light source. N i t r o g e n content and aggregation state f o r 41 diamonds were determined f r o m Fourier T r a n s f o r m Infrared ( F T I R ) spectra obtained using a N i c o l e t 710 F T I R Spectrometer w i t h a N i c Plan I R microscope attachment and l i q u i d nitrogen reservoir (Department o f Earth and Ocean Sciences, U n i v e r s i t y o f B r i t i s h C o l u m b i a ) . A b s o r p t i o n spectra were measured i n transmission mode i n the range o f 4000 to 650 c m " at a resolution o f 8 c m " by averaging the signals o f - 250 1  1  60  scans.  T h e r o u g h stones were m o u n t e d according to the procedure o f Mendelssohn and  M i l l e d g e (1995). T h e diamonds were held o n the edge o f a glass t h i n section slide b y taut double-sided transparent tape, thereby a l l o w i n g the d i a m o n d to be penetrated freely b y the I R beam. Spectra were recorded at the point o f m a x i m u m l i g h t transmission through the sample. O M N I C synthesized software was used to convert the experimental measurements into absorption spectra, f i t a smooth background to the one-phonon region, normalize the baseline, and scale the spectra to a d i a m o n d thickness o f 1 c m . A f t e r conversion to absorption units the spectra were deconvoluted into A , B and D components (e.g. B o y d et al., 1995) using least square techniques, outlined i n detail b y T a y l o r et al. (1990). N i t r o g e n concentrations (atomic p p m ) were calculated using the absorption strength at 1282 cm"' f o r the A-center ( B o y d et a l , 1994b; 16.5±1) and the B-centre ( B o y d et al., 1995; 79±8). T h e calculations were done using A B D F I T and C S V T O A B D software. Detection l i m i t s and errors according to Stachel et al., (1997, 2 0 0 2 ) strongly depend o n the quality o f the crystal face, b u t t y p i c a l l y range between 1020 p p m and 1 0 - 2 0 % o f the concentration, respectively. A d d i t i o n a l uncertainty is introduced b y the heterogeneity o f nitrogen aggregation state w i t h i n the different g r o w t h layers o f d i a m o n d ( T a y l o r et al., 1990). Infra-red absorption spectra were d i f f i c u l t to obtain f o r m a n y o f the opaque and transluscent diamonds, and those w i t h h i g h l y irregular surfaces, especially fine-grained aggregates.  3.2 PHYSICAL CHARACTERISTICS OF DIAMOND 3.2.1 Introduction E x a m i n a t i o n o f the physical characteristics o f diamonds is an important method to classify d i a m o n d populations f o r a specific locality (Harris et al., 1975; Robinson et al., 1989). Establishing the physical characteristics provides a record o f their genesis and post-genetic history. A c c o r d i n g to Robinson (1979) and Robinson et al. (1989), diamonds experience ( i n  61  chronological order), crystallization, plastic deformation, resorption w i t h h i g h temperature etching, crystal breakage, and l o w temperature etching. Some overlap o f the later events may occur. These processes reflect the g r o w t h environment, residence time i n the mantle, transportation to the surface, and residence t i m e i n the host m a g m a f o r a specific d i a m o n d population ( M c C a l l u m et al., 1994; Robinson et a l , 1989; Robinson 1979; Sunagawa, 1984a). The classification scheme used for the study o f 80 W a w a diamonds was based on a combination o f that o f Harris et al. (1975), R o b i n s o n (1979) and Otter (1990) ( A p p e n d i x L, Table L 2 ) . The G Q Property diamonds were characterized b y size, p r i m a r y crystal habit, crystal regularity, b o d y colour, transparency, degree o f resorption, crystal state, surface features and mineral inclusion content ( A p p e n d i x L, Table L 3 ) . The diamonds show variable physical characteristics as shown i n F i g . 3 . 1 .  3.2.1.1 Size Harris et al. (1975) determined that physical characteristics o f diamonds can vary as a function o f size. Thus, size o f a diamonds is important in order to make direct comparisons o f the physical characteristics w i t h i n a population. The W a w a diamonds studied have at least t w o dimensions greater than or equal to 0.5 m m and less than or equal to 1.4 m m . The total w e i g h t f o r the 80 diamonds is 84.939 m g , the average w e i g h t is 1.062 m g , the m a x i m u m w e i g h t is 9.343 m g and the m i n i m u m weight is 0.127 m g . I n d i v i d u a l d i a m o n d dimensions and weights can be f o u n d i n A p p e n d i x L, Table L I .  3.2.1.2 Primary Crystal Habit Crystals are f o r m e d b y the repetition i n three dimensions o f a unit o f structure. The faces o f a crystal depend i n part on the shape o f the unit cell ( K l e i n and H u r l b u t , 1985). I n order to understand the crystal f o r m o f d i a m o n d it is important to be f a m i l i a r w i t h its crystal structure. 62  Figure 3.1 Typical sample of the Wawa colourless and yellow coloured diamond population, displaying a variety of crystal morphologies.  Figure 3.2 Structure of diamond. A . Structural representation of tetrahedral units (Klein and Hurlburt, 1985), B. Posisition of the carbon atoms (small circles) in the crystal arranging a cube (Orlov, 1977).  63  Pure diamond is composed o f carbon. A neutral carbon a t o m has six protons i n the nucleus surrounded by six electrons surrounding its nucleus. Four o f the electrons in carbon are valence electrons w h i c h are available to f o r m bonds w i t h other atoms. I n diamond, every carbon shares all four o f its available electrons w i t h adjacent carbon atoms, f o r m i n g a tetrahedon (Fig. 3.2). The repeating structural unit o f d i a m o n d consists o f eight atoms w h i c h are fundamentally arranged i n a cube ( F i g . 3.2). D i a m o n d is classified ( K l e i n and H u r l b u t , 1985) under the isometric crystal system and the 4 / m b a r 3 2 m symmetry class. I n the isometric system all three crystallographic axes are equal i n length and at right angles to each other. For crystals i n this symmetry class, the 3 crystallographic axes are 4 - f o l d rotation, there are 4 diagonal axes o f 3-fold rotary inversion, there are 6-directions o f 2 - f o l d symmetry, there is a center o f symmetry and 9 m i r r o r planes (Fig. 3.3). The habit o f natural d i a m o n d is a result o f its g r o w t h conditions, such as g r o w t h rate (whether it was fast or s l o w ) , conditions o f temperature and pressure (whether they were constant or fluctuating) and chemistry o f the f l u i d f r o m w h i c h it g r e w (whether f r o m h i g h l y variable or u n i f o r m fluids or melts; Sunagawa, 1984b; K l e i n and H u r l b u t , 1985; Clausing, 1997). G r o w t h habits are the original, p r i m a r y crystal habits. For d i a m o n d , these habits are p r i m a r i l y octahedron and cube ( F i g . 3.3), i n c l u d i n g combinations o f the t w o (cubo-octahedral), m a d e ( t w i n s ; F i g . 3.3), and crystal aggregates (Harris et al, 1975; O r l o v , 1977; Robinson et al., 1989). Dodecahedron w i t h flat faces ( F i g . 3.3) are a rare g r o w t h habit (Seal, 1965; Y a m a o k a et al., 1977; O r l o v , 1977; K a n d a et al., 1977; Machado et a l , 1985; Harris, 1992; B u l a n o v a , 1995). Sunagawa (1984b) describes h o w diamonds are f o r m e d based on the level o f supersaturation between l i q u i d and solid phases w h e n the d i a m o n d crystallizes. Single crystalline habits w i t h flat faces, such as octahedra, g r o w f r o m a silicate melt, layer b y layer by spiral g r o w t h under stable conditions o f l o w carbon saturation. G r o w t h is controlled d o m i n a n t l y 64  001 (Bottom)  C.  Figure 3.3 Primary forms of diamond and their symmetry (modified from Klein and Hurlburt, 1985). A. Octahedron form which is composed of eight equilateral triangles and has the form notation {111} as the triangular shaped faces intersect all three crystallographic axes. B. Cube form which is composed of six square faces at right angles to each other. It has the form {001} whereby each face intersects one of the crystallographic axes and is parallel to the other two. C. Dodecahedron form is composed of twelve rhomb-shaped faces. It has the notation {011} as each of the rhomb-shaped faces intersects two of the crystallographic axes at equidistance and is parallel to the third axes. D. Made form which are octahedral crystals twinned after the spinel law (Harris et al, 1975). Arrows represent the re-entrant twin junctions which are sites for preferential growth (Sunagawa, 1984). 65  by interface kinetics (Sunagawa, 1 9 8 1 ; B u l a n o v a , 1995) rather than e q u i l i b r i u m conditions (Clausing, 1997) and is slow (Sunagawa, 1984 a,b; B u l a n o v a , 1995). S l o w g r o w t h could be attributed to a number o f reasons such as a l i m i t e d volatile supply, a change i n carbon speciation w i t h i n the volatile phase, or a l o w e r surface energy resulting i n less reactive d i a m o n d surface ( B o y d et al, 1994a). Crystal aggregates, the fibrous rims o f coated diamonds, and possibly m a d e crystals ( M c C a l l u m et al., 1994) g r o w m u c h faster w i t h numerous nucleation sites under unstable conditions o f h i g h carbon saturation and represent abnormal g r o w t h (Sunagawa, 1984b; Gurney, 1989). The cube habit also reflects abnormal g r o w t h but at slightly l o w e r supersaturation conditions (Sunagawa, 1984b). G r o w t h o f natural diamonds is often not u n i f o r m . D i a m o n d crystal habits may be m o d i f i e d d u r i n g crystallization due to the presence o f impurities, very fine inclusions, or higher densities o f crystal defects, or changes in the degree o f supersaturation, and the temperature o f crystallization (McCandless et al., 1994; Clausing, 1997).  Octahedron Octahedra are the principal p r i m a r y g r o w t h habit o f d i a m o n d (Harris et al., 1975). This p r i m a r y habit has pointed corners, straight edges and flat faces ( F i g . 3 . 3 A ) . The faces are smooth and even and may have stepped development o f the (111) planes w h i c h appear as stacked triangular lamellae o f successively decreasing size called triangular plates (Harris et al., 1975; O r l o v , 1977). C o m m o n l y the octahedral habit is distorted w h e r e b y the plane-faced g r o w t h habits m a y be elongated, flattened along the b and c crystallographic axes f o r m i n g quadrilaterals, parallelograms and hexagons. D i s t o r t i o n is especially prevalent i n stepped development o f faces and these faces may also exhibit imbricated development ( O r l o v , 1977).  66  Made Octahedral crystals can c o m m o n l y exhibit contact twins or spinel t w i n s according to the spinel law. T w i n n e d crystals that f o l l o w this l a w have a definite composition surface separating the t w o individuals consisting o f t w o p r o m i n e n t (111) faces d i v i d e d b y a t w i n plane to these faces and a 3 - f o l d symmetry t w i n axes (Harris et al., 1975; K l e i n and H u r l b u t , 1985). A b n o r m a l octahedral g r o w t h results i n t w i n n i n g due to preferential g r o w t h along re-entrant comers where dislocations are concentrated and act as preferential g r o w t h sites ( F i g . 3 . 3 D ; K i t a m u r a et al., 1979; Sunagawa, 1984b). T w i n n e d crystals can occur i n a variety o f shapes. The most c o m m o n shape o f t w i n n e d octahedral crystals is flattened t w i n s o f triangular shape termed m a d e ( F i g . 3.3D; O r l o v , 1977).  Cube Cube habit described above and its various combinations w i t h octahedron habits are less c o m m o n p r i m a r y d i a m o n d g r o w t h habits (Harris et al., 1975; Robinson et al., 1989). D i a m o n d crystals o f cubic habit rarely have even { 1 0 0 } faces, more c o m m o n l y their faces are undulatory or concave and indented, as o n skeletal habits ( O r l o v , 1977; Robinson, 1978).  Aggregates Crystal aggregates are described b y Harris et al., (1975) as t w o or more diamonds j o i n e d i n some r a n d o m manner. This means a d i a m o n d can be entirely enclosed w i t h i n another or may be embedded i n the surface o f another, or m a n y stones may be u n c o n f o r m a b l y aggregated together. The aggregates may be o f v a r y i n g degrees o f perfection, size and shape as determined by g r o w t h conditions (Clausing, 1997).  Aggregates are further d i v i d e d into seven varities b y  Sunganawa, (1984b). For the purpose o f this study the simple classification b y M c C a l l u m et al. (1994), outlined i n section 3.2.1.4 and F i g . 3.7, was used. 67  3.2.1.3 Body Colour D i a m o n d can be f o u n d i n m a n y colours. The most c o m m o n are colourless, y e l l o w and b r o w n but d i a m o n d m a y also be green, black, grey, amber, p i n k and purple. N a t u r a l d i a m o n d colour reflects incorporation o f impurities w i t h i n the crystal lattice or interstices m a i n l y during crystal g r o w t h but it m a y also be affected b y post-crystallization processes such as d i f f u s i o n (Robinson, 1978), ductile deformation (Urusovskaya and O r l o v , 1964), and alpha-particle radiation damage (Vance et al., 1973; Otter et al., 1994). A d i a m o n d w i t h no impurities or crystal defects is colourless ( B r u t o n , 1970; Harris et al., 1975). This is because visible light lacks sufficient energy to excite any o f its electrons and therefore no light is absorbed (Davies, 1984). I f impurities or defects are present i n the crystal structure, structural f l a w s can create electron states w h i c h can be affected by the energy in the visible light. I n this case, the energy o f light entering the d i a m o n d equals the amount needed to b u m p an electron to another configuration so parts o f the visible spectrum are absorbed (Davies, 1984).  Yellow Various shades o f y e l l o w coloured diamonds are a consequence o f nitrogen substitution f o r carbon in the d i a m o n d lattice (Harris et al., 1975; Collins, 1982). N i t r o g e n o c c u r r i n g as N 3 centers is responsible f o r the y e l l o w colouration o f T y p e l a diamonds, whereby increasing the concentration o f nitrogen i n this f o r m causes a steady increase in y e l l o w colour (Robinson, 1978). Single substitutional nitrogen causes various intensity o f y e l l o w , or amber colouration o f T y p e I b diamonds depending on the nitrogen concentration (Robinson, 1978; Harris, 1987).  68  Colourless A s mentioned above, colourless diamonds may contain few, i f any impurties, as i n type Ha diamonds but may also result f r o m incorporation o f platelet nitrogen i n type l a diamonds ( B r u t o n , 1970; Harris et al., 1975).  Black The black body o f d i a m o n d is thought to represent a colour resulting d u r i n g crystallization (Robinson et al., 1989) due to microscopic black particles, generation o f lattice dislocations or due to graphite between the g r o w t h layers (Robinson, 1978; Mendelssohn and M i l l e d g e , 1995).  Grey Grey colouration o f d i a m o n d may be a consequence o f microscopic black particles, generation o f lattice dislocations (Robinson, 1978) or o f numerous black graphite-like inclusions ( O r l o v , 1977; K a m i n s k y et al., 2000), and it is believed to be o f primary o r i g i n (Robinson, 1978).  Brown B r o w n coloured diamonds are due to plastic d e f o r m a t i o n (Urosovskaya and O r l o v , 1964; O r l o v , 1977; Robinson, 1979; Robinson et al., 1989; Gurney, 1989) as a result o f stress associated w i t h development o f m a g m a conduits (Robinson et al., 1989). Robinson et al. (1989) ascribes this colour to submicroscopic regions o f graphite localized along glide planes that reflect deformation. Fesq et al.(1975) and M c C a l l u m et al. (1994) also suggest that the b r o w n colour may relate to the presence o f submicroscopic mineral inclusions.  69  3.2.1.4 Degree of Resorption U n m o d i f i e d g r o w t h habits, as discussed above, are rare. M o r e c o m m o n l y the crystals have experienced some f o r m o f dissolution or resorption ( O r l o v , 1977; Robinson et al., 1989). Dissolution is a chemical reaction i n w h i c h a solid material is dispersed as ions in a l i q u i d ( K o t z and Purcell, 1991) and occurs some time after crystallization ( O r l o v , 1977). M o o r e and L a n g (1974) and Seal (1965) p r o v e d through optical and x-topographic investigations o f rounded crystals that dissolution is the process that modifies the primary d i a m o n d crystal habits. T h e y observed that the rounded crystal habit surfaces truncate octahedral and cuboid g r o w t h layers. This also implies that original crystals were m u c h larger and that their present size is the result o f dissolution. The m a j o r i t y o f d i a m o n d resorption is believed to be caused by the host m a g m a (Robinson et al., 1989; Harris, 1992) w i t h i n the graphite stability field (Sunagawa, 1984b; K o z a i and A r i m a , 2003). The host m a g m a acts as a resorbing agent due to its h i g h volatile component (i.e. H2O and CO2 content; Sunagawa, 1984b; Mendelssohn and M i l l e d g e , 1995), w h i c h significantly influences o x i d a t i o n conditions (Harris, 1992). Some resorption c o u l d also be associated w i t h the residence o f the d i a m o n d i n the mantle (Robinson, 1979). V a r y i n g degrees o f dissolution may occur. The degree to w h i c h a d i a m o n d habit is m o d i f i e d by dissolution depends on a number o f factors: temperature (Mendelssohn and M i l l e d g e , 1995), pressure, redox state, activities o f ferric and ferrous iron, and chemical composition o f the host m a g m a , carbon concentration ( K o z a i and A r i m a , 2003) as w e l l as the level at w h i c h it is exposed to the host m a g m a during ascent, and the diamond's original size (Robinson et al., 1989). A c c o r d i n g to the experimental w o r k o f K o z a i and A r i m a (2003) higher degrees o f resorption are expected at higher temperatures and o x i d a t i o n state, and lower CO2 concentration o f the host m a g m a . The first sites to be affected b y absorption are the corners o f the crystal f o l l o w e d b y the edges and then the faces (Sunagawa, 1984b). Dissolution usually occurs u n i f o r m l y i f the  70  d i a m o n d was liberated f r o m its host r o c k d u r i n g the resorption process (Gurney, 1989). M i n o r dissolution leaves the original habit and the structure o f the faces intact. Moderate dissolution results in a complex combination o f a curve-faced and plane-faced intermediate habit. C o m b i n a t i o n habits, whereby some crystal faces are rounded and some preserved, may also develop i f dissolution is not u n i f o r m . N o n - u n i f o r m dissolution can occur i f diamonds in xenoliths are partially exposed d u r i n g the resorption event and are referred by Robinson et al. (1989) as pseudohemimorphic (Otter and Gurney, 1989; Robinson et al., 1989). N o n - u n i f o r m dissolution can also take place i f the p r i m a r y crystal faces were distorted ( M c C a l l u m et al., 1994). H i g h degrees o f dissolution result i n curve-faced, rounded habits w i t h different habits. The type o f crystal habits resulting f r o m dissolution depends on the nature o f the primary crystal, and u p o n the extent and u n i f o r m i t y o f dissolution ( O r l o v , 1977). The curved-faces o f the rounded d i a m o n d habits make it d i f f i c u l t to f o l l o w the rules o f crystallographic classification w h i c h assumes that crystals must have planar surfaces (Raman et al., 1947; Robinson, 1978). For this reason special t e r m i n o l o g y is used w h i c h is specific to the d i a m o n d literature to describe habits o f resorbed d i a m o n d crystals ( O r l o v , 1977). The terms used f o r rounded habits are based on the degree o f curvature o f the crystal face w h i c h were measured ( M o k i e v s k i i and Shafranovskii, 1955; M i t r o f o n o v a , 1956) and by using a photogoniometer ( O r l o v , 1977). M o o r e and L a n g (1974), Harris et al., (1975), and O r l o v (1977) use the m a i n term dodecahedroid or rounded dodecahedron to describe the external m o r p h o l o g y o f the resorped octahedron habit o f diamond. O r l o v (1977) and Harris (1975) define the dodecahedroid as a c u r v e d face crystal similar to a r h o m b i c dodecahedron but w i t h convex, rounded triple faceted faces. I t is the most stable habit for a resorbed d i a m o n d crystal. The m a j o r i t y o f dodecahedroids show a distorted or irregular habit.  71  Robinson (1978) preferred to use the term tetrahexahedroid f o r resorbed d i a m o n d instead o f dodecahedroid because he states that t w e n t y - f o u r rather than t w e l v e like surfaces are usually observed. A classification for resorption was developed based on the percent o f resorption and/or percent o f preservation observed f r o m the d i a m o n d crystals. Tetrahexahedroid is estimated to have lost at least 45 percent o f their original mass (Robinson et al., 1989; Otter and Gurney, 1989). M c C a l l u m et al. (1994) uses a similar classification scheme w h i c h entails six classes defined on the basis o f transitional habits between non-resorbed octahedral (Fig. 3.7), cubo-octahedra or cubes (class 6) and the f u l l y developed tetrahexahedroid (class 1).  3.2.1.5 Surface Features Surface features are a product o f v a r y i n g degrees o f g r o w t h , dissolution, and/or stage etching o f the crystal faces. Surface features f o r m e d during d i a m o n d crystallization reflect the environment o f d i a m o n d g r o w t h . D i s s o l u t i o n and late stage etch features m o d i f y the p r i m a r y d i a m o n d habit subsequent to its f o r m a t i o n (Otter, 1990).  The process o f dissolution reveals the  defects, dislocation outcrops and inhomogeneities o f the internal structure o f crystals and are reflected on the surfaces as resorption features. Each crystal habit displays specific resorption features i n accordance to its particular internal structure. D u r i n g the earliest stages o f dissolution, surface textures f o l l o w the m a i n face structure o f the p r i m a r y , plane-faced crystal. A s dissolution advances and habits w i t h curved faces become more prevalent, the initial surface features are destroyed and new surface textures corresponding to the rounded habits are f o r m e d ( O r l o v , 1977). Dissolution surface textures are f o r m e d at temperatures greater than 950 °C w i t h i n an oxidized environment probably f r o m etching agents such as H2O and CO2 i n melt that became progressively enriched i n o x y g e n w i t h decreasing temperature (Evans and Sauter, 1961; Phaal, 1965; Robinson, 1978; M c C a l l u m et al., 1994). Aggregates are m u c h more susceptible to resorption than single crystals because o f the comparatively rapid o x i d a t i o n at the grain  72  boundaries (Clausing, 1997). Late stage etch features, also k n o w n as corrosion features, are associated w i t h further o x i d a t i o n o f d i a m o n d ( O r l o v , 1977) and are superimposed o n the earlier resorption features (Robinson et al., 1989; M c C a l l u m et al., 1994). There are over forty-one surface textures that have been documented b y Robinson, (1979). O n l y those that were identified w i t h i n the W a w a d i a m o n d population w i l l be described. The surface features f o r the W a w a diamonds are described using the t e r m i n o l o g y o f Robinson (1979) except where otherwise stated i n A p p e n d i x K, Table K 2 .  It is important to recognize the  different types o f surface features pertaining to g r o w t h , resorption, deformation and late etching i n order to formulate the sequence o f events that effected the d i a m o n d p o p u l a t i o n (Robinson et al., 1989).  Features Associated with Crystal Growth Triangular plates are stepped trigonal g r o w t h layers w i t h straight edges that f o r m o n the (111) face w i t h each layer being smaller than that o f the u n d e r l y i n g layer (Robinson, 1979). T h e y f o r m o n dislocations b y spiral g r o w t h (Sunagawa, 1984b). Under conditions o f rapid nucleation, each triangular plate may be separately nucleated (Wentorf, 1965; Robinson, 1979) and are subsequently imbricated (offset f r o m one another). Cubic g r o w t h surfaces on the (110) face have a r o u g h appearance (Sunagawa, 1984b) due the presence o f d r o p - l i k e g r o w t h features ( O r l o v , 1977; Robinson, 1979).  During high growth  rates, nucleation and g r o w t h m a y be initiated at the corners o f cubic crystals resulting i n skeletal g r o w t h (Mendelssohn and M i l l e d g e , 1995).  73  Secondary Features Associated With Oxidation, Etching, and Deformation Shield-Shaped Lamellae Shield shaped laminae ( F i g . 3.9D) are superimposed laminae o f progressive areal extent that occur along edges and corners o f the octahedral face (Robinson, 1979). These textures reflect the internal layering o f the d i a m o n d (Otter, 1990) and m a r k the beginning f o r m a t i o n o f tetrahexahedroid faces.  Trigonal Etch Pits O r l o v (1977) and Sunagawa (1984b) describe etch trigons as triangular pits f o u n d o n almost all octahedral faces and are due to partial resorption o f the (111) face. T h e y state that there are t w o types o f trigons, pointed (P-type) trigons and flat bottomed (F-type) trigons. Pointed trigons have t w o different slopes and appear o n the (111) faces at the earliest stages o f dissolution. T h e y always develop on the outcrop o f dislocation sites ( L a n g , 1964, 1965; Sunagawa et al., 1982, 1984a). T h e y range i n size f r o m 10 - 100 p m . Flat b o t t o m e d etch pits are triangular pits w i t h a flat b o t t o m on the (111) plane. T h e y develop at the same time as pointed trigons but are not associated w i t h dislocation outcrops but probably w i t h point defects like impurities and dislocations just below the surface (Sunagawa, 1984b). T h e y have steeper slopes and their structure is more complex. C o m m o n l y they develop inside one another, f o r m i n g a stepped pattern terminating i n a flat bottom. Trigons c o m m o n l y occur i n groups but sometimes can be f o u n d i n d i v i d u a l l y depending on the location and amount o f dislocations or defects. T h e y can also f o r m i n a linear arrangement i f glide lines near defects are present. D i f f e r e n t t r i g o n morphologies can be observed. Perfect trigons are triangular shaped w i t h three edges closed b y themselves. Trigons can be oriented parallel (positive orientation) or anti-parallel (negative orientation; F i g . 3.9E) to the edges o f the octahedral face (Frank and Puttick, 1959; R o b i n s o n , 1978) depending o n the type o f etchant and the temperature at w h i c h the etching occurs (Phaal, 74  1965; Robinson, 1978). A c c o r d i n g to the experimental w o r k o f Y a m a o k a et al., (1980); Harris, ( 1 9 9 2 ) ; Mendelssohn and M i l l e d g e (1995), f o r all geological temperatures and oxygen partial pressures, trigons predominately have negative orientation.  Hexagonal Etch Pits Hexagonal etch pits are flat bottomed and are usually larger than trigons (Robinson, 1979). T h e y m a y contain trigons ( F i g . 3.9F) w h i c h reflects the c o m b i n e d effects o f t w o echants, one o f w h i c h continues to react after depletion o f the other etchant (Robinson, 1979).  Serrate Laminae Serrate laminae ( F i g . 3.9G) are o n l y f o u n d on resorped octahedrons (McCandless et al., 1994). T h e y are triangular stacked features o f progressively decreasing areal extent (Robinson, 1979; McCandless et al, 1994). T h e y are a product o f exposed internal octahedral g r o w t h layers resulting i n coalescence o f the laterally expanding, flat-bottomed trigons during resorption ( R o b i n s o n , 1979). This surface texture is c o m m o n l y f o u n d on microdiamonds and diamonds recovered f r o m eclogitic xenoliths (Robinson, 1979; McCandless, 1989; Otter, 1990; McCandless et al., 1994).  Tetragonal Etch Pits Tetragonal etch pits ( F i g . 3.9 H ) are f o r m e d o n dislocation outcrops located on (100) faces as a result o f dissolution. They are pits shaped like quadrangular pyramids, w h i c h c o m m o n l y have a stepped structure. The quadrangular pyramids o f different sizes may merge together and b u i l d up on one another resulting i n a complex structure ( O r l o v , 1977). Tetragonal pits can have a positive orientation i f their edges are parallel w i t h the (100) face or a negative orientation i f they are at 45° to the (100) face (Robinson, 1979). 75  Terraces Terraces are concentric layers developed around each 6 - f o l d axial corner o f the tetrahexahedroid (Robinson, 1979). T h e y can only occur on resorbed octahedrons and reflect the internal layering o f the crystal (Robinson, 1979).  Elongate Hillocks H i l l o c k s ( F i g . 3.91) are f o r m e d at the same time as face curvature due to dissolution and therefore are f o u n d o n rounded, tetrehexahedroid diamond crystals and are conditioned b y the internal structure o f the crystal. T h e i r shape depends on the curvature features o f the faces and their position on the faces. Triangular pyramids are the most c o m m o n but they can also f o r m elongated quadrangular pyramids i f they develop at edges or face seams. The pyramidal hillocks are the shape o f a small p y r a m i d w i t h t w o microscopic (111) and (110) faces. W i t h greater dissolution the plane-faced p y r a m i d becomes dropped shaped (ellipsoidal) ( O r l o v , 1977; Robinson, 1978, 1979).  Ruts or Etch Channels Etch channels (Fig. 3.9J) f o r m along planar zones o f weakness (Otter et al., 1994), or cracks expanded b y resorption or etching (Robinson, 1979). These cracks are frequently distorted and can not be related to a particular plane. Some crystals experience only small etch channels w h i c h appear as " n o t c h e s " i n the edges. Other crystals can have a complete system o f deep, intersecting "fissures" develop that d i v i d e the crystal into blocks o f v a r y i n g shapes ( O r l o v , 1977).  76  Inclusion Cavities Inclusion cavities (Fig. 3 . 9 K ) are pits w i t h octahedral sides and indicate previous occupation b y an inclusion. I f an i n c l u s i o n was removed p r i o r to resorption the edges m a y be rounded, otherwise the edges are sharp. These cavities m a y contain trigonal pits and ruts radiating f r o m the cavitity (Robinson, 1979).  Corrosion Sculpture Corrosion sculptures are c o m m o n l y f o u n d on rounded crystals ( O r l o v , 1977; Robinson et al., 1989; M c C a l l u m et al., 1994). T h e corrosion o f the crystal causes f a i r l y deep depressions w i t h elliptical to irregular outlines o n faces sometimes g i v i n g a r o u g h , d u l l , opaque and sometimes even pitted appearance (Robinson, 1979). Striations m a y f o r m i n place o f octahedral edges, octahedral faces m a y show etch pits, and rounded crystals m a y show wedge-shaped rounded hillocks ( O r l o v , 1977). T h e y are a late stage etch feature (Robinson, 1979).  Frosting Frosting is micrometre scale fine trigonal and hexagonal pits ( O r l o v , 1977; Robinson et al., 1989; McCandless et al., 1994) that c o m m o n l y occur due to late stage etching (Robinson, 1979). M c C a l l u m et al. (1994) describe f o u r types o f frosting based on average p i t w i d t h : ( i ) coarse (greater than 100 p m ) , ( i i ) m e d i u m (between 70-30 p m ) , ( i i i ) fine (20-5 p m ) and ( i v ) very fine (less than 5 p m ) .  Shallow Depression Shallow depressions (Fig. 3 . 9 M ) are irregular, curved outlines on the crystal surface that have flat, smooth bottoms. They are similar to corrosion sculpture but are shallower and usually  77  o f greater areal extent (Robinson, 1979). This texture is believed to be either an early or less localized expression o f corrosion (Robinson, 1979).  Irregular Pits E t c h pits ( O r l o v , 1977) or pitted cavities (Robinson, 1979) are usually depressions that are hemispherical to rectangular i n shape and can be a variety o f sizes. T h e y are f o u n d on curvefaced d i a m o n d crystals usually dotted at random but can have assemblages o f pits and even entire faces can be etched ( O r l o v , 1977).  Features Associated with Deformations L a m i n a t i o n lines are parallel linear features that are generally closely spaced or less c o m m o n l y w i d e spread ( M c C a l l u m et al., 1994). The lines are thought to represent slippage along glide planes in the d i a m o n d due to plastic deformation ( W i l l i a m s , 1934; Urusovskaya and O r l o v , 1964; M o k i e v k i i and Shafranovskii, 1955; Harris et al, 1975; Gurney, 1989; Robinson et al., 1989; M c C a l l u m et al, 1994; McCandless et al., 1994). Plastic deformation o f d i a m o n d must occur at temperatures greater than 1300 °C and pressures o f approximately 50 kb (De Vries, 1975; Evans, 1976; Robinson et al. 1989; Gurney, 1989), and must be i n contact largely w i t h solid material (Robinson et al., 1989). These conditions are compatible w i t h those f o u n d i n the mantle and therefore deformation probably occurs as a result o f stress i n aureoles about developing deep-seated magma conduits or i n convecting material ( M e r c i e r , 1979; Robinson et al., 1989). D i a m o n d s w i t h lamination lines were most l i k e l y enclosed i n mantle xenoliths, w h i c h experienced deformation before being incorporated into the ascending host magma ( O r l o v , 1977; Robinson, 1979; McCandless, 1994). L a m i n a t i o n lines are t y p i c a l l y f o u n d on the f o u r - f o l d axes o f tetrahexahedroid habits (Gurney, 1989; M c C a l l u m et al., 1994).  78  3.2.2  Physical characteristics of the Wawa diamonds The W a w a diamonds are h i g h l y variable i n their p r i m a r y g r o w t h habits ( F i g . 3 . 1 ; Fig.  3.4; Fig. 3.5; A p p e n d i x K, Table K 3 ) . T h e y are characterized m a i n l y as octahedral aggregates m a k i n g up 4 4 % o f the population f o l l o w e d b y single octahedral crystals comprising 2 6 % o f the population. The most c o m m o n aggregates are octahedral coarse aggregates, f o l l o w e d b y octahedral coarse and fine aggregates, and fine aggregates. Single cubic and cubic-octahedral crystals and their aggregates, as w e l l as macles are also observed. These habits together make up 2 6 % o f the population but i n d i v i d u a l l y are less than 10%. Forty-eight percent o f the W a w a d i a m o n d population are single crystals, and o n l y 28 diamonds c o u l d be evaluated f o r crystal regularity. The m a j o r i t y o f the W a w a diamonds are distorted to some degree (Fig.3.6; A p p e n d i x L, Table L 3 ) w h i c h is c o m m o n f o r d i a m o n d crystals (Harris et al., 1975) and 1 1 % are nearly equidimensional. The W a w a diamonds were classified b r o a d l y into colourless, b r o w n , grey, black, y e l l o w , and white. Other possible colours o f diamonds such as pink, green, violet and blue are not observed. The W a w a diamonds are colourless ( 5 0 % ) , heterogeneous ( 2 4 % ) , y e l l o w ( 1 1 % ) , black ( 3 % ) , b r o w n ( 1 0 % ) , and grey ( 3 % ) . A l l cuboids i n c l u d i n g the cubic aggregates are y e l l o w i n colour. The m a j o r i t y o f octahedral single crystals and coarse aggregates, as w e l l as a l l macles, are colourless. The heterogeneity i n colour is o n l y present i n aggregates, more c o m m o n l y the heterogeneous and fine grained aggregate varieties. Combinations o f colour f o r these diamonds include black and y e l l o w , black and colourless, y e l l o w and grey, grey and w h i t e , w h i t e and black, w h i t e , and grey and black (see A p p e n d i x K, Table K 3 f o r details). The W a w a d i a m o n d population consists o f 4 8 % transparent crystals, 2 5 % translucent crystals, 1 4 % opaque crystals and 1 4 % c o m b i n a t i o n o f opaque and translucent crystals. T h e transparent crystals occur mostly as colourless and as rare y e l l o w octahedral single crystals, coarse aggregates, and macles. The translucent crystals comprise a l l possible p r i m a r y crystal 79  35.0  N = 66 30.0-  25.0  •  20.0  c u "J —  15.0  10.0  5.0  0.0  Primary Figure 3.4 Histogram showing frequency of occurrence of different crystal forms in the Wawa diamond population. Symbols: C - cubic; C - C A - cubic coarse aggregate; C-O - cubo-octahedral; C-O-CA - cubo-octahedral coarse aggregate; O - octahedral; O - C A - octahedral coarse aggregate; O-FA - octahedral fine aggregate; O-C/FA octahedral heterogeneous aggregate; U - unknown; M - made.  Figure 3.5 Varying primary morphologies of the Wawa diamond population. A . Cube, B. Cube coarse aggregate, C. Cubo-octahedral aggregate, D. Octahedron, E. Octahedral coarse aggregate, F. Made, G . Octahdral fine aggregate, H . Octahedral coarse/fine aggregate.  80  N = 28  Figure 3.6 A pie-diagram s h o w i n g variation i n crystal regularity o f the W a w a diamond population. Symbols: I R - Irregular, E Q - Equidimensional (regular), D - slightly distorted, F Flat, E - Elongate.  Figure 3.7 Classification scheme o f M c C a l l u m et al., (1994) w h i c h describes the degree o f resorption f r o m conversion o f octahedral diamond to a tetrahexahedroid.  81  habits and colours. The opaque crystals are mostly fine grained aggregates w h i c h have some black b o d y colouring. Crystals e x h i b i t i n g the combination o f translucent and opaque are m o s t l y heterogeneous fine and coarse crystal aggregates. The degree o f resorption f o r the W a w a d i a m o n d population was determined using the classification scheme o f M c C a l l u m et al., (1994) (Fig. 3.8; A p p e n d i x K, Table K 3 ) . Some crystals ( 1 4 % ) exhibit n o n - u n i f o r m (pseudohemimorphic) resorption, whereby one part o f the crystal is more strongly resorbed than another. I n such cases both resorption categories were recorded. The W a w a diamonds have generally experienced l o w degrees o f resorption. Over h a l f o f the diamonds f a l l into classes 4 to 6 whereby there are 2 2 % i n class 4, 3 8 % in class 5, and 8 % i n class 6. Some diamonds have experienced extensive resorption but these comprise o n l y 2 1 % (class 1 to 3) o f the population. G r o w t h surface features such as triangular plates ( F i g . 3.9A) and imbricated triangular plates ( F i g . 3.9B) on octahedral crystals, and skeletal corners and edges on cubes ( F i g . 3.9C) were observed on 3 4 % o f the W a w a diamonds. Evidence o f resorption specific to octahedral crystals and octahedral faces on cubicoctahedral crystals is marked b y the presence o f shield-shaped laminae ( 4 9 % ; Fig. 3.9D), trigonal pits ( 3 9 % o f w h i c h 5 2 % have negative orientation ( F i g . 3.9E), 12% have positive orientation, and 3 5 % have u n k n o w n orientation), hexagonal pits ( 1 8 % ) , hexagonal pits containing etch pits ( 2 % ; Fig. 3.9F) and serrate laminae ( 1 6 % ; F i g . 3.9G ). Resorption specifically o f cubic crystals and the cubic face o f cubic-octahedral crystals was identified by presence o f tetragonal pits ( 8 5 % o f w h i c h 6 4 % are o f negative orientation and 3 6 % o f u n k n o w n orientation; Fig. 3.9H). Other surface features specific to h i g h l y resorped crystals (tetrahexedroid crystals) are terraces, and elongate hillocks ( F i g . 3.91) w h i c h are seen on o n l y 4 % and 1 % o f the W a w a diamonds, respectively. The l o w percentage o f these t w o surface features is a reflection o f the l o w degree o f resorption o f the W a w a d i a m o n d population. Late stage 82  40.0 N = 80  30.0  uniform resorption class  Figure 3.8 A histogram showing the degree of resorption of the Wawa diamond population based on the resorption classification scheme of McCallum (1994).  83  84  Figure 3.9 Photomicrographs of typical growth, resorption and oxidation surface textures characterizing the Wawa diamond population. A. Trigonal plates on a cubo-octahedral crystal, B . Imbricated trigonal plates, C. Skeletal growh on a cube, D. Sheild-shaped lamellae, E. Negatively orientated trigonal etch pits, F. Hexagonal etch pit, outlined by a white square, containing two negatively orientated trigons, G . Serrate laminae outlined by white boxes, H . Tetragonal etch pits, I. Elongate hillocks the tetrahexahedroid surface, J. Etch channel, K . Triangular inclusion pit, L . Frosting, M . Shallow depressions.  85  etching features are present on the W a w a diamonds. The most c o m m o n are ruts ( 3 9 % ; Fig. 3.9J) and shallow depressions ( 1 9 % ) . Less c o m m o n etching features observed are frosting ( 9 % ; F i g . 3.9L) and corrosion sculpture ( 8 % ) . D e f o r m a t i o n features such as lamination lines were not observed on the W a w a diamonds. This may be because the m a j o r i t y o f the diamonds do not show high degrees o f resorption w h i c h w o u l d enhance the glide plane dislocations (Robinson, 1979; W i n et al., 2001). The W a w a p o p u l a t i o n contains approximately 4 2 % intact diamonds and 5 8 % diamonds that show evidence o f breakage ( 9 % broken, 5 % fragment, 2 % fraction and 4 2 % breakage). The cleavage and fracture surfaces were studied for evidence o f etching prior to breakage. One t h i r d (3 2 % ) o f breakage surfaces c o u l d not be unambiguously to one or another category, 4 6 % o f breakage surfaces showed no evidence o f etching, and 2 2 % had been broken p r i o r to etching. The relative abundance and colour o f the mineral inclusions present in the W a w a diamonds were recorded ( A p p e n d i x L, Table L 3 ) . M i n e r a l inclusions were identified i n 5 8 % o f the W a w a diamonds. The inclusions were mostly colourless, black n e t w o r k and black discrete i n colour. A f e w orange inclusions were also observed i n one diamond. H a l f o f the W a w a diamonds ( 5 3 % ) are either opaque or translucent m a k i n g it d i f f i c u l t to see inclusions.  3.3 3.3.1  INFRARED ABSORPTION PROPERTIES OF DIAMOND Introduction Fourier T r a n s f o r m Infrared Spectroscopy is a non-destructive method for obtaining  qualitative and quantitative i n f o r m a t i o n about the chemical c o m p o s i t i o n o f diamond, b o n d i n g , and structural impurities w i t h i n the diamond crystal structure ( A p p e n d i x M ) . The infrared absorption for d i a m o n d is w i t h i n the m i d - I R range and is d i v i d e d into one-, t w o - and threep h o n o n regions (Fig. 3.10A; M c N a m a r a , 1994, M c N a m a r a Rutledge and Gleason, 1997). The inherent covalent carbon-carbon bonds o f d i a m o n d are i d e n t i f i e d as spectral peaks i n the t w o 86  p h o n o n region between 1333 and 2666 c m ' ( M c N a m a r a , 1994, M c N a m a r a Rutledge and 1  Gleason, 1997; Fig. 3.1 OA). Spectral absorption peaks outside the t w o - p h o n o n region result f r o m impurities and defects ( F i g . 3.1 OA) w h i c h effect local lattice centrosymmetry (Mendelssohn and M i l l e d g e , 1995). Impurities, such as nitrogen, b o r o n , hydrogen, carbon dioxide, and oxygen (Robinson, 1978; Scarratt, 1992; K a m i n s k y et al., 2000) occur as substitutes w i t h i n the d i a m o n d crystal lattice. These atoms, w i t h the exception o f hydrogen, have similar interatomic b o n d strength and mass, to carbon for w h i c h they are substituting. This study focuses o n substitutional nitrogen impurities and on identification o f the other impurities where present. N i t r o g e n is o f particular importance as it is the second most c o m m o n element i n d i a m o n d (Harris, 1987; M a i n w o o d , 1994).  M o s t diamonds contain nitrogen concentrations  ranging f r o m a f e w atomic p p m to approximately 5000 atomic p p m ( B i b b y , 1982). N i t r o g e n substitution and incorporation into the d i a m o n d crystal sturcture is a kinetic process (Evans and Harris, 1989) w h i c h occurs d u r i n g d i a m o n d g r o w t h and increases w i t h residence time i n the mantle (Evans, 1976, 1992). Once substitution has occurred, nitrogen can migrate through the crystal lattice to f o r m different aggregations (Cartigny et al., 2001). The amount o f nitrogen that enters the diamond structure and the rate o f aggregation depends on the initial nitrogen concentrations in the upper mantle, the temperature(s) i n the upper mantle, and the length o f time the d i a m o n d resided i n the upper mantle (Evans and Q i , 1982; Harris, 1989; Evans and Harris, 1989; T a y l o r et al., 1990; Mendelssohn and M i l l e d g e , 1995; Evans, 1992). Temperature is the most sensitive factor i n the aggregation process ( T a y l o r et al., 1996).  N i t r o g e n aggregation  states are differentiated b y their I R spectra (Evans, 1976; Chrenko et al., 1977; B r o z e l et al., 1978; A l l e n and Evans, 1 9 8 1 ; Evans and Q i , 1982; W o o d s , 1986; Clark and D a v e y , 1984; Mendelssohn and M i l l e d g e , 1995). N i t r o g e n content and aggregation state are important factors because they are useful i n classifying diamonds f o r comparing and f i n g e r p r i n t i n g different 87  88  (V)  c.  J  V -J J (VI)  E .o C  .22 fS <o o o a o  t  B'platelet peak ill at 1370 cm/ U 1  (III)  o  X)  « b  )->  1  (VII)  ^_  (IV)  A  (VIII)  rV 1650  900  900  1650  Wavenumber /cm'  1  F i g u r e 3.10 I R absorption spectra o f d i a m o n d . A . The I R absorption spectrum o f a typical d i a m o n d w h i c h occurs w i t h i n the m i d - I R range. L o c a t i o n o f the one-, t w o - , and three-phonon d i a m o n d regions, w h i c h are specific to the i m p u r i t y , intrinsic d i a m o n d , and hydrogen regions respectively (after M c N a m a r a et al., 1994; M c N a m a r a Rutledge and Gleason, 1997). B. Characteristic absorption spectra in the one-phonon region for the possible nitrogen aggregation states f o u n d in d i a m o n d ( m o d i f i e d f r o m Evans and Q i , 1982 and Taylor et al., 1990). C. I R absorption spectra i n the one-phonon range s h o w i n g the progressive aggregation o f an A - d e f e c t (I) towards the presence o f A-defect, B-, and D-defect, and B ' platelet peak ( I I - I V ) , through to a pure B-defect ( V - V I I I ; Evans, 1992).  89  diamond populations ( K a m i n s k y et al., 2001), and can provide valuable estimates o f mantle residence time and temperatures f o r d i a m o n d (Evans and Harris, 1989; T a y l o r et al., 1990). Diamonds that contain little to no nitrogen probably grew in a nitrogen-free environment, crystallized at relatively l o w temperatures (Evans, 1975; Robinson, 1978), and/or spent m i n i m a l time in the mantle before they were incorporated into an ascending magma.  3.3.1.1  Sequence of Nitrogen Aggregation  The amount and degree o f nitrogen aggregation w i t h i n a d i a m o n d lattice is a reflection o f the mantle nitrogen concentration and temperature i n w h i c h the d i a m o n d grew, and the residence time o f d i a m o n d i n the mantle (Evans and Harris, 1989; T a y l o r et al., 1990; M a i n w o o d , 1994; Mendelssohn and M i l l e d g e , 1995). Experimental studies b y D r y e r et al. (1965) and Chrenko et al. (1977) reveal that nitrogen enters the structure during d i a m o n d g r o w t h i n i t i a l l y as single atom substitutions k n o w n as C-centres ( A l l e n and Evans, 1 9 8 1 ; M a l ' k o v and A s k h a b o v , 1979; Clark and Davey, 1984). C-centres have a characteristic absorption peak i n the one-phonon region at 1130 c m " and a second localized absorption peak at 1344 c m " ( F i g . 3 . 1 0 B ; C l a r k et al., 1992; 1  Evans, 1992).  1  The peak at 1130 cm" is proportional to the single nitrogen concentration present 1  w i t h i n d i a m o n d ( W o o d s et al., 1990b; Clark et al., 1992). N i t r o g e n concentrations i n this state are usually between 50 to 300 p p m (Evans, 1992). The aggregation o f C-centers occurs relatively q u i c k l y o n a geologic timescale ( < 0.5 Ga; T a y l o r et al., 1996), based on activation energies determined by Evans and Q i (1982). Thus diamonds w i t h C-centers are not c o m m o n l y observed i n nature and i f present have experienced a certain degree o f aggregation to A - f o r m , as described b e l o w (Evans and Q i , 1982; W o o d s , 1986; Mendelssohn and M i l l e d g e , 1995). The presence o f C-centres can be attributed to diamonds o f y o u n g age w h i c h were incorporated b y the host m a g m a and/or unusually cool mantle temperatures ( T a y l o r et al., 1996).  Diamonds  w i t h cubic habit more c o m m o n l y have C-centres than octahedrons suggesting different g r o w t h  90  environments. I n general, it may indicate that octahedrons have higher g r o w t h and storage temperatures, older ages, or enhanced aggregation rate due to l o w e r nitrogen activation energy ( T a y l o r et al., 1996). D u r i n g d i a m o n d residence i n the mantle single nitrogen atoms aggregate to f o r m a more stable pair o f adjacent/neighbouring substitutional nitrogen atoms referred to as an A - f o r m or an A-defect (Davies, 1976; T a y l o r et al, 1990; Evans, 1992; M a i n w o o d , 1994). The rate at w h i c h this conversion takes place is controlled by the activation energy f o r nitrogen i n the cubic and octahedral g r o w t h zones ( N a v o n , 1999).  This process is irreversible at mantle temperatures as  the aggregation rate is greater than the disassociation rate f r o m A - f o r m back to C-centres ( B r o z e l et al., 1978; Harris, 1987). A-defects show variable I R absorption i n the one-phonon region, w i t h a m a i n peak at 1282 c m " , a dip at - 1 2 4 2 c m " , and a subsidiary peak at - 1 2 1 5 c m " ( F i g . 1  1  1  3.10B; Mendelssohn and M i l l e d g e , 1995). Extended mantle residence times and higher temperatures (Evans, 1992) result i n the conversion o f t w o A - f o r m nitrogen pairs (Evans and Q i , 1982) into one B - f o r m ( A l l e n and Evans, 1981; Evans, 1992; M a i n w o o d , 1994). A B - f o r m comprises f o u r nitrogen atoms i n a tetrahedral arrangement around a vacancy (Loubser and van W y k , 1981). B-defects have a distinctive I R spectrum that includes a spike at 1332cm" , a plateau between 1310 to 1320 cm" 1  1  and m a x i m u m peak at 1175 c m " w i t h a shoulder at 1100 c m " and 1010 cm" ( F i g . 3 . 1 0 B ; B o y d 1  1  1  et al., 1995). The progressive aggregation o f A-defects to B-defects can also result i n simultaneous f o r m a t i o n o f platelets (Evans and Phaal, 1962; Clark et al., 1992). Platelets are planar defects on the { 1 0 0 } planes (Frank, 1956; Evans and Phaal, 1962; B o y d et al., 1995). is not k n o w n i f platelets are also a product o f A - d e f e c t aggregation, but they are thought to be predominantly interstitial carbon displaced f r o m o r i g i n a l lattice sites to f o r m vacancies d u r i n g the m i g r a t i o n f r o m A - to B-defects (Woods et al., 1990b; Mendelssohn and M i l l e d g e , 1995). Platelets may also contain small amounts o f nitrogen ( M a i n w o o d , 1994), but their exact 91  It  composition and structure has yet to be determined (Evans, 1992; M a i n w o o d , 1994). Platelets are detected i n the I R spectrum b y the presence o f a broad peak, the D-spectrum ( C l a r k and D a v e y , 1984; W o o d s , 1986; B o y d et al., 1995) w h i c h occurs i n the same region as peaks f r o m the A - and B-defects m a k i n g it d i f f i c u l t to distinguish (Fig.3.10B). H o w e v e r , platelets can be readily identified by their characteristic B' peak (Fig.3.10C). The position o f the B' peak can range f r o m 1359 to 1374 c m " ; the higher the wavenumber the smaller the platelet (Sobolev et 1  a l , 1968; Evans and Rainey, 1975; Clarkson et al., 1990; Evans, 1992; Mendelssohn and M i l l e d g e , 1995). This peak is believed to represent stretching o f C-C bonds w i t h i n platelets ( W o o d s , 1986). The strength o f D-spectrum and B ' peaks are proportional to each other and to the strength o f B-defect absorption (Woods, 1986). A d i a m o n d e x h i b i t i n g this relationship is k n o w n as " r e g u l a r " ( W o o d s , 1986). The activation energy o f conversion f r o m an A - f o r m to a B - f o r m is 6.5-7.5 e V (Evans and Q i , 1982; Evans and Harris, 1989). A t mantle temperatures ( > 1000°C), the aggregation process is relatively slow ( D r y e r et al., 1965; Robinson, 1978), therefore the m a j o r i t y o f diamonds undergo o n l y partial conversion ( N a v o n , 1999) indicative o f long mantle residence times ( > 0.5 Gyrs; Richardson et al., 1990; Richardson, 1993; T a y l o r et al., 1996). I f diamonds are stored i n the mantle f o r a greater period o f time, or at increased temperatures, aggregation w i l l continue to advance gradually f o r m i n g pure B-defects (Evans and Q i , 1982; Evans and Harris; 1989) and platelets w i l l concurrently degrade and disappear entirely, along w i t h A-defects ( F i g . 3.10C; B u r t , 1980; Evans, 1992; C l a r k et al., 1992). D i a m o n d s w i t h B' and D-spectrum absorption that is not proportional to the absorption o f the B-defect due to partial or complete platelet degradation are k n o w n as " i r r e g u l a r " ( W o o d s , 1986).  D u r i n g late  stages o f the A-defect aggregation sequence, voidites and dislocation loops begin to f o r m ( W o o d s et al., 1990a; B o y d et al., 1995). Voidites are believed to represent nitrogen defects bounded b y (111) planes (Stephenson, 1978; Evans, 1978; B a r r y , 1986; T a y l o r et a l , 1996) 92  w h i c h nucleate and g r o w m a i n l y at platelet interfaces and dislocations ( W o o d s et al., 1990a). T h e y are believed to be either an aggregation o f the B - f o r m ( W o o d s , 1986; W o o d s et al., 1990a) or a product o f platelet degredation (Burt, 1980; Clark et al., 1992). Transformation o f A to B defects m a y be accompanied b y a m i n o r side reaction p r o d u c i n g N 3 - f o r m s ( T a y l o r et al., 1990). N 3 forms are paramagnetic defects and comprise three neighbouring nitrogen atoms occurring i n a triangle and a vacancy ( T a y l o r et al., 1990). T h e y are not detected b y I R but have a peak i n the visible spectrum at 24 000 c m " (Loubser and 1  W r i g h t , 1973; Davies and Summersgill, 1973; Evans, 1992). A process that decreases nitrogen content o f d i a m o n d by annihilation o f nitrogen defects is annealing at extremely h i g h temperatures (Clark et al., 1992). T h i s process may change the d i a m o n d back to having l o w nitrogen concentration and defects, similar to younger or l o w e r temperature diamonds that have not experienced nitrogen aggregation (Mendelssohn and M i l l e d g e , 1995). The above processes are responsible f o r d i f f e r i n g nitrogen aggregation states i n d i a m o n d populations ( K a m i n s k y et al., 2 0 0 1 ; Davies et al., 2003; A p p l e y a r d et al., 2003) and each g r o w t h layer i n d i a m o n d may show a different nitrogen aggregation state f r o m the previous and subsequent layers ( M i l l e d g e et al., 1989; Mendelsohn and M i l l e d g e , 1995). Layers w i t h little or no nitrogen may be interstratified w i t h layers o f weak to intense nitrogen aggregation ( T a y l o r et al., 1996). This reflects heterogeneity and changing conditions i n the mantle (e.g. W i l d i n g et al., 1994; B u l a n o v a et al., 1999; Deines et al., 1993; Pokhilenko et al., 2003).  3.3.1.2 Classification of Diamonds Using Infrared Spectra Diamonds can be d i v i d e d into t w o m a i n types, Type I and T y p e I I , based on their nitrogen content and aggregation state (Fig. 3 . 1 1 ; Evans and Q i , 1982; Evans, 1992). T y p e I  93  Diamond  Type I  Type II  ( > 10 ppm Nitrogen)  Type la  Type Ib  Type Ha  ( N aggregation)  (Single substitutional N)  (Does not contain Boron)  I Type IaA ( N pair)  (< 10 ppm N)  Type IaAB  Type lib (Contains Boron)  I Type IaB  ( 4 N atoms + a vacancy )  Figure 3.11 Classification of diamond based on the configuration of nitrogen (N) in the diamond lattice and the presence or absence of boron.  Figure 3.12 IR absorption spectra for the different types of Wawa diamonds. A . Atype II, colourless, octahedral aggregate, B . A Type IaA colourless, octahedral diamond. C. A type IaAB colourless, octahedral diamond with platelets and 30% B-defects. D. A type IaAB colourless, octahedral aggregate with platelets and 90% B-defects. Spectra peaks: 1- hydrogen peak, 2- C H stretch, 3- main A-defect peak. 4- subsidiary A-defect peak, 5 - B-defect spike, 6 - B-defect maximum peak, 7 - B-defect shoulder at 1100 cm"', 8 - B-defect shoulder at 1010 cm" , 9 - B ' platelet peak. 1  9 4  d i a m o n d contains nitrogen and includes 9 8 % o f natural diamonds ( D r y e r et al., 1965). T y p e I I d i a m o n d has no infrared-detectable nitrogen ( T a y l o r et al., 1996) and is quite rare (Harris, 1987). T y p e I diamonds are further subdivided into Type l a and type l b depending on the number o f aggregated nitrogen atoms. T y p e l b diamonds are rare, whereby the d i a m o n d has single substitutional nitrogen (C-centres; Harris, 1987). T y p e l b diamonds are y e l l o w , y e l l o w green or orange i n colour (Evans, 1992; Clark et al., 1992; T a y l o r et al., 1996). Cubic diamonds and the fibrous coat on some diamonds are type l b (Dryer, 1965; L a n g , 1974; T a y l o r et al., 1996). T y p e l a diamonds are the most abundant and contain nitrogen as non-paramagnetic lattice defects ( T a y l o r et al., 1990). They t y p i c a l l y contain a total nitrogen content o f 100 - 1000 p p m (Evans, 1992).  Type l a can be further subdivided into: type I a A , i f aggregation is o f the  A - f o r m (Davies, 1976), type I a B , i f aggregation is o f the B - f o r m (Harris, 1987); and type I a A B , i f both A and B f o r m s are present ( B o y d et al, 1995). T y p e I I diamonds are further subdivided into type Ha and type l i b based on their electrical c o n d u c t i v i t y w h i c h is reflected on the basis o f the presence o f substitutional boron. T y p e Ha is non-conducting and therefore does not have boron present. I t is the most c o m m o n o f type I I diamonds. T y p e l i b has boron w h i c h is believed to substitute f o r carbon (Robertson et al., 1934; C o l l i n s and W i l l i a m s , 1971; Robinson, 1978) and is present i n concentrations ranging f r o m 0.02 to 0.26 p p m (Harris, 1987). B o r o n has a characteristic absorption I R peak at 2460 cm"  1  ( C o l l i n s , 1982). I t gives diamond a blue colour (Robinson, 1978) and makes d i a m o n d a semiconductor ( H a r r i s , 1987).  3.3.1.3 Hydrogen Defects Within Diamond H y d r o g e n , w h i c h can be covalently bonded to carbon, is identified i n d i a m o n d b y several distinctive I R spectral peaks in the 3-phonon region ( F i g . 3 . 1 0 A ; 4000-2800 c m " ) . The hydrogen 1  defect or H-defect has a band at 3107 c m " w h i c h can be accompanied b y a weaker band at 1406 1  95  cm" (Runciman and Carter, 1 9 7 1 ; W o o d s and C o l l i n s , 1983). The symmetric and asymmetric 1  stretching vibrations o f the C - H bond have peaks i n the 2750 to 3300 c m " region ( M c N a m a r a 1  Rutledge and Gleason, 1997).  3.3.1.4 Quantitative A nalysis of IR A bsorption Spectra Quantitative measurements o f nitrogen concentration f r o m A - and B- defects can be made f r o m I R spectra in the one-phonon region b y measuring the relative intensity o f the 1282 c m " peak 1  contributed b y the A - , B- and D-defects (Clark and D a v e y , 1984; Evans, 1992). Concentrations are calculated based on the Bouger-Beer-Lambert L a w w h i c h states that absorbance is proportional to the content o f absorbing species ( M c M i l l a n and Hofmeister, 1988) according to:  A(v) = I(v)Ct  (3.1)  where A is the measured absorbance at frequency v; I ( v ) is the molar absorptivity o f the species as a function o f frequency and is obtained experimentally, f r o m measured absorption spectra o f standard samples o f k n o w n concentrations and path length; t is the path length o f the I R beam through the sample, and C is the concentration o f the species. N i t r o g e n concentration i n an A-defect ( N A ) can be calculated on the premise o f equation 3.1: N  ( p p m ) = 1 6 . 5 ± l * p ( 1282cm" )  (3.2)  1  A  A  where 16.5 is the experimental value for 1(1282cm" ) f r o m B o y d et al. (1994b); PA is the 1  absorption coefficient per c m thickness o f d i a m o n d f o r the A spectrum at band 1282 c m "  1  and is  determined b y I R spectral deconvolution (Davies, 1976; W o o d s et al., 1990a; T a y l o r et al., 1996). 96  N i t r o g e n concentration i n a B-defect (NB) can also be calculated on the basis o f equation 3.1: N  ( p p m ) = 7 9 . 4 ± 8 * p ( 1282cm" )  (3.3)  1  B  B  where 79.4 is the experimental value for I(1282cm"') f r o m B o y d et al. (1995); p  B  is the  absorption coefficient per c m thickness o f diamond for the B spectrum at band 1282 cm" and is 1  determined b y I R spectral d e - c o n v o l u t i o n using least square techniques (Davies, 1976; W o o d s et al., 1 9 9 0 a ; T a y l o r e t a l . , 1996). M a n t l e residence t i m e or temperature for a d i a m o n d can be calculated i f one assumes that transformation o f A-defects to B-defects f o l l o w s second order kinetics and the Arrhenius rate l a w (Evans and Harris, 1989; T a y l o r et al., 1990). W e can calculate temperature or time b y c o m b i n i n g these laws. The equation for the second order kinetics is: -dC/dt = k C  (3.4)  2  2  where C = concentration o f the A-defects (atomic p p m ) , t = time (s) and k = the second order 2  rate constant. B y integrating equation 3.4 over time and rearranging the equation to solve for the rate constant gives:  lr k  C  —  ~  2  Co ,  (3.5)  where C = concentration o f the A-defects ( N p p m o f the A - and B-defects ( N = N T  A  + N  B  A  i n atomic p p m ) , C = the total concentration in 0  in atomic p p m ) . The equation f o r the Arrhenius rate  l a w is: k  2  =  A e  [-Ea/ T] R  (  97  3  6  )  where A = the Arrhenius constant, Ea = activation energy for aggregation f r o m A to B - f o r m , T = temperature i n K e l v i n s , and R = gas constant. B y c o m b i n i n g equations 3.5 and 3.6, and s o l v i n g for T , the time-averaged mantle residence temperature T N A can be calculated:  T  N A  (°C) = E a / R l n { A t  M R  / ( l / [ A ] - 1 / [ A ] ) } - 273.15 0  (3.7)  Where: Ea = 7.03 e V or 1.12633x10 J ( T a y l o r et al., 1990) s  R = gas constant, 8.314510 J/K m o i A = Arrhenius constant, 2 . 9 4 1 8 1 x l 0 5 s " ' p p m " ( M c K e n n a , 2001) 1  t-MR = assumed mantle residence time (s) C = concentration o f the A-defects ( N  A  i n atomic p p m ) calculated using equation 3.2  C = the total concentration i n p p m o f the A - and B-defects ( N T = N 0  A  [equation 3.2] +  N s f e q u a t i o n 3.3])  The assumed m a x i m u m possible mantle residence time is determined by subtracting the age o f the d i a m o n d host rock f r o m the age o f the earth. N i t r o g e n i n d i a m o n d cannot aggregate during or after emplacement, because m a g m a ascent and emplacement is very rapid and no significant aggregation can occur at temperatures b e l o w 1050°C (Spera, 1984; T a y l o r et al., 1990).  Equation 3.7 can also be solved f o r IMR. I n this case, temperatures determined f r o m  mineral inclusion geothermobarometry can be used to calculate an estimated average mantle residence time ( T a y l o r et al., 1990). There are several factors that can affect the reliability o f the estimated quantitative thermal history for diamond. The first is the use o f a single I R spectrum on a d i a m o n d heterogeneous i n nitrogen content and aggregation. Thus, values calculated w i l l be an average ( G r i f f i n et al., 1988; 98  T a y l o r et al., 1990). Secondly, d e f o r m a t i o n i n d i a m o n d m a y cause enhanced nitrogen aggregation states and thus m i s l e a d i n g l y higher residence temperatures (Davies, 1984; Evans, 1992). T h i r d l y , diamonds that have experienced advanced stages o f nitrogen aggregation and have degraded platelets m a y no longer f o l l o w the second order l a w o f kinetics (Evans, 1992). F o u r t h l y , accurate rate constants f o r nitrogen aggregation processes still need to be determined ( H u t c h i s o n et al., 1999). Finally, equation 3.7 is not sensitive to extreme d i a m o n d g r o w t h temperatures such as 900°C or 1400°C ( T a y l o r et al,. 1990).  3.3.2  Classification, Nitrogen Content and Aggregation State of the Wawa Diamonds The W a w a d i a m o n d p o p u l a t i o n has variable nitrogen aggregation as shown b y I R  absorption spectra (Fig.3.12). T h e m a j o r i t y o f W a w a diamonds are T y p e I a A B ( 4 9 % ; Fig.3.13), and T y p e Ha ( 3 4 % ) . The remainder are T y p e I a A ( 1 7 % ; Fig.3.13; A p p e n d i x L ) . Hydrogen-defect and CH-stretch peaks are detected i n 6 0 % o f the samples, however most are relatively weak. Table 3.1 summarizes the nitrogen content and aggregation states o f W a w a diamonds. N i t r o g e n contents o f the W a w a diamonds are between 0 - 740 atomic p p m (Fig.3.15A ) , w i t h a mean nitrogen content o f 111 p p m , a median o f 66 p p m , and a mode o f 0 p p m (i.e. b e l o w detection limits). The m a j o r i t y o f W a w a diamonds have l o w nitrogen contents, b e l o w 300 p p m . N i t r o g e n concentrations range f r o m 66-262 p p m f o r Type I a A diamonds and f r o m 19-740 p p m f o r T y p e I a A B diamonds. The W a w a diamonds show variable degrees o f nitrogen aggregation. M o r e than h a l f o f samples show no aggregation ( F i g . 3.13; T y p e H a and T y p e I a A ) , however diamonds w i t h h i g h aggregation states ( > 6 0 % B ) are observed. N i t r o g e n aggregation states show a possible b i m o d a l d i s t r i b u t i o n (Fig.3.15B): the first mode, where the majority o f the samples occur, has < 3 0 % aggregation i n the B - f o r m (mostly T y p e I I and Type I a A diamonds); the second mode has a h i g h aggregation state, w i t h > 6 0 % B (group median 7 9 % B ) . The higher nitrogen aggregation i n the 99  ° 6  C  O _T  g o 2 E -n -a a a u ^ 2 o S t* u, o M 5 i a « o •t3 JS "§  "9  <D  ^  a 5  • <u +5  W  .o < > - 9* 05 U, o gb o ca a r° x 2 = CD  < {3 S u £ ' U  " '—i  • a  n  S cn  0 0  • i S M CD  c  O  c  CD  1  •s « o -c  3  **  1  K  3 <u  s y  <r,  >  B o g  ca  CJ  g  c°  O J2  P o •* C3  •N  "2 * :>  « 2  1= bo 6H  °  OJJ  O  ca  CD I-  1  CD Ui  o S be  •I &01 \> s Q T3  3  m 2:  I  *  ica  1  sI  S 3 ?< 100  u(D) (cm')  A . Plot of platelet peak intensity [I(B') - absorption value of B' peak after subtraction of the 2-phonon tail] divided by total absorption (pT) vs strength of A-defect absorption (uA) divided by total absorption (pT). This plot discriminates between the regular and irregular Wawa diamonds and shows that the majority plot below the regular field. B. Plot of platelet intensity [I(B')] vs strength of the B-defect absorption (pB). This plot is also used to determine regular and irregular diamonds but does not appear as effective as plot A for the Wawa diamonds. C. Plot of platelet intensity (I(B') vs strength of the D-defect absorption (pD). Regular and irregular diamonds should follow the outlined trend. Diamonds that plot below this trend most likely have unreliable p values (Taylor et al., 1990). The plots are from Woods (1986) and are based on the proportionality rules of diamonds that follow the regular aggregation sequence. Fields are based on the slope of the trends with a standard deviation of 20% determined by Woods (1986) which have also been applied by Taylor et al., (1990). The units for I(B') differ by those of Woods (1986) by a factor of ten and are similar to those of Taylor et al., (1990). Error bars represent 20% error from the detection limits and deconvolution method determined by Stachel et al., (2002). F i g u r e 3.14  D  101  0  50  100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 Nt (ppm)  0  10  20  30  40  50  60  70  80  90  100  Nitrogen Aggregation, %B  F i g u r e 3.15 Histograms o f nitrogen content and aggregation for the Wawa diamonds.  102  B - f o r m ( % B ) does not correlate w i t h higher nitrogen content (Table 3 . 1 ; Fig.3.15). T h i s is t y p i c a l for most diamonds around the w o r l d (Stachel and H a r r i s , 1997). O f the T y p e I a A B diamonds, 6 7 % contain platelets, w h i c h show a regular-range o f absorption peaks (1358-1365 c m " ; A p p e n d i x L ) . Three diamonds w i t h l o w aggregation states ( < 1  2 5 % B-defect) do not have platelets developed. One d i a m o n d has 6 3 % B-defect aggregation and does not have a B' peak. M o s t o f the W a w a diamonds ( 6 5 % ) show m u c h l o w e r platelet peak intensities than w o u l d be expected f r o m their p A / p T values ( F i g . 3 . 1 4 A ) and w h i c h coincide w i t h the irregular group o f W o o d s (1986) that have experienced platelet degradation. These diamonds do not correspond to a t y p i c a l aggregation sequence. One d i a m o n d ( G Q E 2 - 2 ) has higher platelet intensity than w o u l d be predicted f r o m its p A / p T value and plots to the right o f the regular d i a m o n d trend ( F i g . 3 . 1 4 A ) . The remainder o f the W a w a diamonds ( 3 5 % ) plot i n the regular f i e l d indicative o f conventional A to B aggregation, thus f o l l o w i n g the relationship I ( B ' ) / p r is proportional to PA/PT-  W a w a T y p e I a A diamonds do not contain platelet peaks nor B-defects,  and have I ( B ' ) = 0 and PA/PT = 1 consistent w i t h the observations o f W o o d s (1986). A plot o f platelet peak intensity as a f u n c t i o n o f absorption coefficient at 1282 c m " o f the 1  B-defect spectrum ( F i g . 3 . 1 4 B ) shows that 8 8 % o f W a w a diamonds plot w i t h i n the linearly correlated f i e l d o f regular diamonds. T h proportion o f regular W a w a diamonds is m u c h l o w e r (35%)  i f based on the correlation o f I ( B ' ) w i t h PA/PT ( F i g . 3 . 1 4 A ) .  diamonds have l o w e r platelet intensities than expected f o r the p  B  These t w o irregular  values w h i c h are consistent  w i t h platelet degradation. The other diamonds recognized as irregular f r o m F i g . 3 . 1 4 A should not have platelet intensities proportional to p , as seen i n F i g . 3.14B, but lower platelet B  intensities based on the observations made b y W o o d s ( 1 9 8 6 ) on diamonds w i t h degraded platelets. N o n - m a t c h i n g estimates for proportions o f regular versus irregular ( 3 5 % i n F i g . 3.14A and 8 8 % in F i g . 3.14B) are c o m m o n , for example the A r g y l e , Ellandale-4, Ellandale-9, and  103  Table 3.1 Characterization of the Wawa diamond population using infrared spectra. Sample GQE1-1 GQE1-2 GQE2-1 GQE2-2 GQE2-3 GQE2-4 GQE3-1 GQE4-5 GQE4-7 GQE4-11 GQE4-14 GQE5-2 GQE5-3 GQE6-1 GQE7-1 GQE8-2 GQE8-4 GQE9-1 GQE10-1 GQE10-2 GQE10-3 GQE10-4 GQE11-1 GQE13-2 GQE13-3 GQE13-4 GQE13-5 GQE14-1 GQE14-2 GQE14-3 GQE14-4 GQE15-1 GQE16-1 GQE16-2 GQE16-3 GQE16-4 GQE17-1 GQE17-2 GQE17-3 GQE17-4 GQE18-1 a  N  A  ^ A (ppm) 211 0 ND 14 ND 63 137 156 ND 214 102 30 124 43 ND ND ND 366 25 0 43 262 n/a ND ND 12 66 49 ND 78 96 ND ND ND 7 196 226 13 70 ND 0  B(ppm)  N  %B  a  63 66 ND 5 ND 19 0 133 ND 38 27 167 41 95 ND ND ND 54 41 145 59 0 n/a ND ND 50 0 0 ND 663 0 ND ND ND 124 82 20 43 0 ND 25  23 100 ND 27 ND 23 0 46 ND 15 21 85 25 69 ND ND ND 13 63 100 58 0 n/a ND ND 80 0 0 ND 90 0 ND ND ND 95 29 8 77 0 ND 100  - nitrogen concentration in A-defects; N  B  a  N ^((ppm) 275 66 ND 19 ND 81 137 289 ND 252 129 197 165 139 ND ND ND 421 66 145 101 262 n/a ND ND 62 66 49 ND 740 96 ND ND ND 132 277 246 55 70 ND 25  3107 cm"' H defect  CH stretch  + + +  + -  -  + + +  c b  Type  IaAB-p IaB* I la IaAB-p I la IaAB laA IaAB-p Ila IaAB-p IaAB IaAB-p IaAB-p IaAB-p Ha Ila Ha IaAB IaAB IaB*-p* IaAB*-p IaA IaA Ila Ila* IaAB-p IaA IaA* Ila IaAB-p IaA Ila Ila Ila IaAB-p IaAB-p IaAB-p IaAB*-p* IaA Ila IaB*-p*  -  C  -  -  -  + +  + + -  -  -  -  +  + +  +  + + -  -  -  -  +  -  +  +  -  -  +  +  + + + -  -  + + * + +  t  * uncertain; p - platelet defect detected  c  + = present; - = absent; * uncertain  d  R = regular; I - irregular; n/a = not available  c  mantle residence temperature (t ) = 1.8 Ga MR  r  R I n/a I n/a R R R n/a R I I I I n/a n/a n/a I I I I R R n/a n/a I R R n/a I R n/a n/a n/a I R R I R n/a I  mantle residence temperature (t ) = 10 M a MR  104  NA  (°C) 1134 n/a n/a 1208 n/a 1164 n/a 1158 n/a 1123 1149 1217 1149 1202 n/a n/a n/a 1107 1215 n/a 1198 n/a n/a n/a n/a 1241 n/a n/a n/a 1193 n/a n/a n/a n/a 1260 1141 1107 1239 n/a n/a n/a  - nitrogen concentration in B-defects; %B - percentage of B-defect; N - total  nitrogen concentration; N D - not detected (i.e. below 10-15 atomic ppm nitrogen present); n/a - not available b  1  "Reg.  f  T (°C) NA  1272 n/a n/a 1362 n/a 1308 n/a 1302 n/a 1259 1291 1373 1290 1355 n/a n/a n/a 1239 1370 n/a 1350 n/a n/a n/a n/a 1402 n/a n/a n/a 1344 n/a n/a n/a n/a 1426 1281 1240 1400 n/a n/a n/a  Copeton diamonds f r o m T a y l o r et al., (1996). However, T a y l o r et al., (1990) do not explain this discrepancy. I t h i n k that the discrepancy between Fig.3.1.4A and B c o u l d be attributed to unexpected increase i n A-defects or A-defects w h i c h have not been able to continue f o l l o w i n g the aggregation sequence. M o s t W a w a diamonds f i t on the linear trend for both regular and irregular diamonds w h e n absorption attributed to platelets is plotted against that o f D-defects ( F i g . 3.14C). The three diamonds that plot b e l o w this trend have lower platelet intensities than expected f o r their po values. H o w e v e r , there is larger uncertainty i n their po values because o f the l o w intensity o f B peaks ( T a y l o r et al., 1990) i n these diamonds. A t present there are no geothermobarometric data or radiogenic isotopic ages f r o m mineral inclusions available for the W a w a diamonds. Thus, mantle residence temperatures were assessed based on k n o w n age constraints for the W a w a diamonds. T w o possible extreme residence times were assumed. The m a x i m u m residence time is 1.8 Ga based on the emplacement age o f the W a w a calc-alkaline lamprophyre (2.67 Ga) and the age o f the earth (4.5 Ga). The m i n i m u m residence time is 10 M a as calculated f o r subduction-related diamonds. This constraint is based on the model o f G r i f f i n et al. (2000) for diamonds f o r m e d i n a cool, subducting slab. L o w temperatures at depth o f diamond stability that a l l o w d i a m o n d to crystallize i n a subduction slab can o n l y be maintained i f subduction is active. Once the subduction stops, the cold slab re-equilibrates w i t h the temperatures o f the surrounding mantle and thus, the diamonds are destroyed. G r i f f i n et al., (2000) estimated that 10 - 30 M a are needed to b r i n g the c o l d slab into thermal e q u i l i b r i u m w i t h the surrounding mantle f o r subduction rates o f 3-8 cm/year. For our constraint on the mantle residence time f o r the W a w a diamonds w e used 10 M a f o r the faster rates o f subduction expected during the A r c h e a n ( H a r t et al., 1970; B u r k e et al., 1976).  105  The temperature distribution f o r both residence times is shown in Fig.3.16. O n l y regular diamonds are plotted. Temperatures corresponding to an age o f 1.8 Ga range f r o m 1108-1262°C and those related to 10 M a range f r o m 1209-1388°C. The temperatures are insensitive to mantle residence time estimates as there is only ~ 150°C difference i n the temperature estimates f o r ~ 2 Ga. Temperatures calculated using both assumed ages are reasonable f o r d i a m o n d f o r m a t i o n and preservation w i t h i n the mantle. H o w e v e r , the m a j o r i t y o f W a w a diamonds show evidence o f platelet degradation and therefore their calculated temperatures may be unreliable as thermal aggregation histories have yet to be determined f o r irregular diamonds (Evans, 1992). The six regular diamonds are part o f the l o w e r temperature ranges w i t h values o f 1108-1164°C and 12401308°C f o r the 1.8 Ga and 10 M a residence times respectively (Fig. 3.17; Table 3.1).  3.4  DISCUSSION  3.4.1  Morphology W a w a diamonds exhibit a diversity o f crystal habits, f r o m octahedral to cubo-octahedral  single crystals to fine and coarse aggregates. The v a r y i n g morphologies represent different or fluctuating environments during d i a m o n d g r o w t h . Aggregates, w h i c h dominate the d i a m o n d population and macles crystallized at numerous nucleation sites under unstable, carbon supersaturated conditions (Harris and Gurney, 1979; Sunagawa, 1984b; Otter et al., 1994; Deines et al., 1993).  The cubic crystals reflect similar g r o w t h conditions as aggregates but have slightly  lower carbon supersaturation (Sunagawa, 1984b) and are rare (Harris, 1992). Single octahedral crystals g r e w s l o w l y under stable g r o w t h conditions o f l o w carbon saturation (Sunagawa, 1984b). The small percentage ( < 5 % ) o f cubo-octahedral diamonds grew under conditions intermediate between those o f octahedral and cubic diamonds (Sunagawa, 1984b). Similar relative abundances o f the p r i m a r y habits w h i c h compose the W a w a d i a m o n d population are f o u n d at other localities w o r l d w i d e . Orapa, Letlhakane and Jwaneng, like W a w a , 106  W a w a d i a m o n d 10 M a residence  1200 T  NA  (°C)  F i g u r e 3.16 Histograms s h o w i n g the distribution o f temperatures recorded by n i t r o g r n aggregation ( T ) for 1.8 Ga and 10 M a mantle residence times. N A  107  CM  O  (  on o  a  o  1—  CJ _ T  "S OS o  22  b  s .a  S3  s- i CU  °  5 U u o  CO  a  2  o  ° S *- o  aj — cj CM  CQ ° CO  9  si?  (uidd) juajuoD IM  w  C cj  o I  U  o  c° CM  4$  DQ  •  3  oo  T J  "1  JS c j — •C C 03 cu ^*  0 CQ S—i  "S 0 3 c« u ° O• SC3D > o — P 2 u s  I  0 0  v  — EQ  -  1 i 5 u o  CJ  1  _r  'C e a  Hi £ 1> U °  •J  ° O CN  I  s  CO  J3  .1 < ? °  •J  S  C  c 1  o 2 ^ ^ .2 b t— "5 o  o o o  «* 1 9 * DC u ci  (Uidd) JU3JUOD M  108  CO  are also dominated b y aggregate crystal habits and contain cubic, cubo-octahedral crystals and macles, (Harris, 1987; Otter et al., 1994; Deines et al., 1993). The m o r p h o l o g y o f diamonds i n the three mines i n Botswana, as w e l l as i n W a w a , is very different f r o m that at other w o r l d w i d e localities w h i c h are c o m m o n l y dominated b y octahedral crystals (Harris, 1992). Cubic crystals dominate a f e w d i a m o n d suites and most c o m m o n l y are completely absent f r o m d i a m o n d populations. I t is therefore u n c o m m o n to have - 5 % cubic and cubo-octahedral d i a m o n d i n a population, as i n W a w a . S i m i l a r l o w percentages ( < 5%) o f cubo-octahedral and cubic crystals have o n l y been observed at pipe D O - 2 7 i n the Slave craton (Davies et al., 1999a) and at Sloan kimberlites, C o l o r a d o / W y o m i n g (Otter et al., 1994). L o w percentages o f cubic crystals ( < 5 % ) have also been documented i n Zaire ( B o y d et al., 1987), h i g h pressure biotite gneisses ( C a r t i g n y et al., 2001), and Guaniamo placer deposits, Venezuela ( K a m i n s k y et al., 2000).  3.4.2  Nitrogen Content and Aggregation State The W a w a diamonds e x h i b i t relatively l o w nitrogen concentrations ( < 300 p p m ) and  variable nitrogen aggregation states ( 0 - 9 5 % nitrogen i n the B - f o r m ) w i t h t w o modes; 1 0 - 3 0 % and 6 0 - 1 0 0 % B (Fig. 3.15).  F e w o f the W a w a diamonds show evidence f o r plastic d e f o r m a t i o n  (i.e. b r o w n colouration and l a m i n a t i o n lines; Evans et al., 1995; Davies et al., 1999b), and therefore the range i n nitrogen aggregation state are thought to represent a range i n the mantle residence time or temperature (Evans and Harris, 1989; T a y l o r et al., 1990) rather than enhanced nitrogen aggregation states i n variously deformed crystals ( G r i f f i n et al., 2000; Davies et al., 2003). The nitrogen contents and aggregation states o f the W a w a diamonds are similar to those o f other studied d i a m o n d suites o f k n o w n sources (peridotitic or eclogitic). The W a w a diamonds plot together w i t h peridotitic and eclogitic diamonds, and are dissimilar to super-deep diamonds ( F i g . 3.18). N i t r o g e n characteristics o f W a w a diamonds are comparable to those o f diamonds 109  10000  1000  _ a  •JaDD  5,  » B  D D  G  B  •a  &  n  a  •  am  & a?  Baa  a  1  a  in  D.  c  a  c B c  T  DT-  ft  T°  a• n  o a  • S °  100  a  a •  o  V  a  J* • o • a  a  10  B.  20  40  •  ° •• •  1  •  3»  •  o  60 % IaB  80  100  10000  1000  ao.  ft o  a.  4*4  c  S o o  100  4 ' ' 4* l ^ l n * 4 4 14 4 4  4 * 4«* 44 *  A  4  4  O *  10  20  40  60 % IaB  80  100  F i g u r e 3.18 Plot o f nitrogen concentration versus % o f nitrogen i n the B - f o r m comparing the W a w a diamonds to diamonds o f mantle o r i g i n w i t h k n o w n paragenesis w o r l d w i d e (Taylor et al., 1990; Deines et al., 1989, 1991, 1993, 1997; Davies et al., 1999a, b; G r i f f i n et al., 2001). S y m b o l s : E- eclogitic diamond, P- peridotitic diamond, W - websteritic diamond, S D - superdeep d i a m o n d , C - W a w a cubic crystals, C - 0 - Wawa cubo-octahedral crystals, O- W a w a octahedral crystals, A - W a w a aggregates. 110  f r o m B i r i m field, Ghana (Stachel and Harris, 1997) and Finsch, South A f r i c a (Deines et al., 1989; F i g . 3.19). I investigated possible correlations o f nitrogen characteristics o f the W a w a diamonds w i t h their other mineralogical characteristics. There was no correlation between colour, resorption or m o r p h o l o g y and nitrogen characteristics (Fig. 3.13). The b i m o d a l distribution o f the diamonds w i t h respect to nitrogen aggregation does not correlate w i t h their other characteristics. The fact that the nitrogen content and aggregation state does not correlate w i t h colour and m o r p h o l o g y is not u n c o m m o n (e.g. Habib, 1998; Deines et al., 1989). Octahedral crystals and aggregates e x h i b i t a range o f nitrogen aggregation states, and thus were classified into most infrared d i a m o n d types (Fig. 3.13B; Table 3.2). Cubo-octahedral crystals ( F i g . 3.13B; Table 3.2) contain p o o r l y aggregated N and b e l o n g to type I a A . The W a w a cubic crystals have higher aggregation states (approaching 100% nitrogen i n the B - f o r m ; Table 3.1) One can compare infrared data o f the W a w a diamonds to analogous data available f r o m diamonds w o r l d w i d e . Cubic and cubo-octahedral diamonds are generally type I a A and thought to be derived f r o m shallow mantle depth. A l t e r n a t i v e l y , they can be y o u n g diamonds that crystallized shortly before magma emplacement or w i t h i n the m a g m a itself ( B o y d et al., 1987; T a y l o r et al., 1990; Deines et al., 1993; Davies et al., 2003). The W a w a cubo-octahedral diamonds resemble other cubo-octahedral diamonds in being T y p e I a A . However, this is not the case f o r W a w a cubic crystals that m a y have had a longer residence time or f o r m e d at higher temperatures than most cubic diamonds.  Ill  40  SO  60  100  Frequency (%) II  •  IaA  IaAB  •  IaB  F i g u r e 3.19 H i s t o g r a m comparing the W a w a diamonds w i t h other diamond suites w o r l d w i d e . Data sources: Ellendale-4, Ellendale-9, Copeton, and Kalimantan (Taylor et al., 1990), K o f f i e f o n t e i n and Jagersfontein (Deines et al., 1991), Guaniamo ( K a m i n s k y et al., 2000), M o m e i k , Theindaw, Phuket ( G r i f f i n et al., 2001), Jwaneng (Deines et al., 1997), Orapa (Deines et al., 1993), B i r i m Field (Stachel and Harris, 1997), Pipe D O - 2 7 (Davies et al., 1999a), Bingara and Wellington (Davies et al., 1999b), Finsch and Premier (Deines et al., 1989).  112  T a b l e 3.2 Comparison o f m o r p h o l o g y , colour, nitrogen type, and resorption category o f the W a w a diamonds. Morphology  Colour  Type  Resorption Category  C  Y  IaA, I a A B  4,5  C-CA  Y  IaA, I a A B , l a B *  4  C-0  C, B R  IaA, I a A B  1,3,6  C-O-CA  H  IaA  4,5  M  C  I a A B , II  O O-FA & O-F/CA O-CA  5  1,3,4, 5 , 6  H, C  I a A B , IaB*, II  l , 2 , 4 * , 5*  C , BR, G Y , Y , H  IaA, I a A B , II  2, 3, 4 , 5 , 6  +  +  +  I a A B , IaA, IaB*, II  +  C , BR, B L  1,4,  +  +  +  +  +  +  +  +  Symbols: for morphology, colour and resorption category are located in Table K2, Appendix K; * = uncertain; H = heterogeneous; = dominant. +  It is apparent f r o m Fig. 3.17 that all o f the W a w a diamonds c o u l d not have f o r m e d at a single temperature as most o f the data does not f o l l o w a single isotherm. It appears that diamonds w i t h similar nitrogen contents show w i d e variations in nitrogen aggregation state. Storage temperatures appear to be greater than 1150°C ( f o r tMR = 1 0 M a ) and 1050°C (for tMR = 1.8 Ga). These temperatures are realistic f o r both estimates o f the residence times in the mantle, and the nitrogen aggregation state thus cannot constrain the age o f d i a m o n d f o r m a t i o n . I f all o f the diamonds f o r m e d simultaneously, a range o f storage temperatures in excess o f 200°C (for tMR = 1.8 Ga) and 350°C (for tMR = 10 M a ) is required to account for their nitrogen aggregation. The fact that most o f the W a w a type I a A B diamonds e x h i b i t platelet degradation suggests annealing under h i g h temperatures ( W o o d s , 1986; T a y l o r et al., 1990). There is no correlation between d i a m o n d m o r p h o l o g y and residence time ( F i g . 3.17). A l l m o r p h o l o g i c a l types appear to have experienced temperatures calculated based on nitrogen aggregation ( T  N A  ) o f 1050°C to ~ 1170°C. The w i d e variation i n nitrogen aggregation and  m o r p h o l o g i c a l types f o r W a w a diamonds suggest that the diamonds f o r m e d under different  113  physical and chemical conditions and hence m a y represent a m i x t u r e o f several diamonds populations. The temperature estimates f o r W a w a diamonds are similar to other analogous estimates o f TNA for d i a m o n d suites w o r l d w i d e (e.g T a y l o r et al., 1990; Deines et al., 1997; Davies et al., 1999a, b; K a m i n s k y et al., 2 0 0 1 ; Westerlund et al., 2003; W h i t e h e a d and Richardson, 2003). The estimated temperatures o f W a w a diamonds (TNA=1 107-1164°C) f o r the 1.8 Ga mantle residence time are similar to those f o r diamonds f r o m Copeton, K a l i m a t a n , pipe D O - 2 7 , Panda, Jwaneng, Guaniamo, Coramandel, and D a l d y n - A l a k i t ( T a y l o r et al., 1990; Davies et al., 1999a; W e s t e r l u n d et al., 2003; W h i t e h e a d and Richardson, 2 0 0 3 ; Deines et al., 1997; K a m i n s k y et al., 2001). The estimated temperatures for W a w a diamonds ( T = 1 2 0 9 - 1 2 6 9 ° C ) at the 10 M a NA  mantle residence time are 100°C higher and similar to those f o r diamonds f r o m A r g y l e , Premier, and Juina ( T a y l o r et a l , 1990; Deines et al., 1997; K a m i n s k y et al., 2001). A l l the above d i a m o n d suites have xenocrystal cratonic origins. M a n y W a w a diamonds ( 3 4 % ; F i g . 3.13) are T y p e I l a , and contain little nitrogen (amounts b e l o w detection l i m i t s ) and thus no nitrogen aggregation. Several hypotheses have been proposed to explain the f o r m a t i o n o f Type I I diamonds. These diamonds m a y have g r o w n in a l o w nitrogen environment (Davies et al., 1999a) or i n an environment where nitrogen m a y not have been present i n a chemical f o r m that can be preferentially incorporated into the d i a m o n d lattice (Deines et al., 1989; Burns et al., 1999; A r a u j o et al., 2003). The nitrogen speciation is dependent on the redox state o f the mantle (Deines et al., 1989). A l t e r n a t i v e l y , T y p e I I diamonds may have been annealed T y p e I diamonds that lost nitrogen to recrystallization and " h e a l i n g " o f defects w i t h i n the.diamond crystal lattice. I n this case, T y p e I I diamonds must have had l o n g mantle residence times at h i g h temperatures ( W a t s o n , 1996; Davies et al., 1999a; K a m i n s k y et al., 2001). C a r t i g n y et al., (2001) propose that the d i a m o n d g r o w t h rate, w h i c h f o l l o w s a second order rate l a w o f kinetics, has a significant influence on the amount o f n i t r o g e n  114  incorporated into the d i a m o n d lattice. Thus, diamonds experiencing slow rates o f g r o w t h w i l l be able to maintain e q u i l i b r i u m C / N ratios w i t h their g r o w t h m e d i u m and should be type I I .  3.4.3  O r i g i n o f the W a w a D i a m o n d s Three potential origins for the W a w a macrodiamonds (0.5- 1 m m in size) need to be  considered, i.e. orogenic, xenocrystal cratonic, and phenocrystal. Orogenic diamonds f o r m e d i n subduction tectonic settings are f o u n d in eclogites, pyroxenites, peridotites and gneisses f r o m ultrahigh-pressure metamorphic terranes (Sobolev and Schatsky, 1990; Cartigny et al., 2001). Orogenic diamonds can be brought to the surface by tectonic u p l i f t like those i n M o r o c c o (Slodkevich, 1983; Pearson et al., 1989; Harris, 1992), T i b e t (Fang and B a i , 1981; Harris, 1992), Kazakstan (Sobolev and Schatsky, 1990), China ( X u et al., 1992), Western N o r w a y (Dobrzhinetskaya et al., 1995), and G e r m a n y (Massonne, 1999; H w e n g et al., 2001) or by magmas sampling the subducting slab l i k e i n N e w South Wales, A u s t r a l i a ( T a y l o r et al., 1990) and French Guiana (Capdevila et al., 1999). These diamonds are characterized by small sizes and c o m m o n graphite pseudomorphs (e.g. De Cortes et al., 1999; C a r t i g n y et al., 2001). Their dominant m o r p h o l o g y is cubic, cubo-octahedra and octahedral single crystals (De Cortes et al., 1999; Cartigny et al., 2001); aggregates are u n c o m m o n . Skeletal and re-entrant crystals can also be present (De Cortes et al., 1999) and are distinctive o f orogenic diamonds. Orogenic diamonds infrequently exhibit surface textures indicative o f dissolution, and never have resorbed faces or experienced n o n - u n i f o r m resorption ( D e Cortes et al., 1999). H i g h nitrogen contents (580-4488 p p m ) and l o w aggregation states ( I b - I a A ; De Cortes et al., 1999; F i n n i e et al., 1994; Dobrzhinetskaya et al., 1995; T a y l o r et al., 1996) are characteristic o f orogenic d i a m o n d populations. These values reflect their short mantle residence times and/or l o w temperatures (De Cortes et al., 1999; Cartigny et al., 2001) that can be as l o w as 885-940° C f o r mantle residence times o f 5 Ga ( D e Cortes et al., 1999). The o n l y suite o f orogenic diamonds  115  w i t h h i g h degrees o f nitrogen aggregation is the one f r o m N e w South Wales, but diamonds there are strongly plastically deformed (Davies et al., 2003). G r i f f i n et al., (2000) and Davies et al., (2003) argue that d i a m o n d deformation resulted i n enhanced nitrogen aggregation states w h i c h are unexpectedly h i g h for l o w temperatures i n the cold subducted slab. Xenocrystal cratonic diamonds are the most c o m m o n i n the w o r l d and are f o u n d i n numerous kimberlites on all continents. The physical and chemical characteristics o f xenocrystic cratonic diamonds are h i g h l y variable and are usually distinct f r o m different parts o f the w o r l d (Harris, 1992; K a m i n s k y et al., 2001). Sizes range f r o m microdiamonds to large crystals (Pattison and L e v i n s o n , 1995). M o p h o l o g i e s m a y be octahedral, cubic, and cubo-octahedral single crystals and aggregates (Gurney, 1989; Harris, 1992). D i a m o n d colours are t y p i c a l l y colourless, y e l l o w and b r o w n but may also be green, grey, black, purple, and p i n k (Gurney, 1989; Harris, 1992). The diamonds show v a r y i n g degrees o f resorption f r o m sharp edges to rounded faces, and a multitude o f different types o f surface textures (Robinson, 1979, 1989; M c C a l l u m et al., 1994). They exhibit a w i d e range i n nitrogen content (0-5000 p p m ; B i b b y , 1982) and aggregation states ( I l a - I a B ; Evans, 1992; Harris, 1992), but are t y p i c a l l y type I a A B ( F i g . 3.19; W i l k s and W i l k s , 1991). X e n o c r y s t a l cratonic diamonds can have similar initial origins to orogenic diamonds. Eclogitic diamonds c o m m o n l y f o u n d b e l o w cratons f o r m e d in the A r c h e a n as a result o f subduction (Helmstaedt and Schulze, 1987). Evidence f o r a subductionrelated o r i g i n for eclogitic diamonds is their light carbon isotopic composition similar to organic carbon, w h i c h is unlike the heavier pristine mantle carbon. This isotopic composition can only be inherited by eclogitic diamonds f r o m oceanic sediments before subduction. The only difference between orogenic diamonds and eclogitic diamonds b e l o w craton is the residence time i n the mantle. Eclogitic diamonds remained i n the mantle for - 2 . 5 - 3 G a ( G r i f f i n et al., 2003) before being entrained to the surface, whereas orogenic diamonds were picked up b y ascending  116  magmas contemporaneously w i t h or shortly after subduction. Based on this difference w e should expect the orogenic diamonds to host less aggregated nitrogen. Phenocrystal diamonds that precipitated f r o m carbon-rich k i m b e r l i t i c magmas are c o m m o n l y small ( < 1 m m ) , euhedral, transparent, sharp octahedrons (Pattison and L e v i n s o n , 1995) or fibrous cubic coats (Gurney, 1989; Pattison and L e v i n s o n , 1995). T h e y t y p i c a l l y show little resorption ( G u r n e y , 1989; Pattison and L e v i n s o n , 1995). D i a m o n d phenocrysts are type I I (Tolansky, 1972), I a A ( T a y l o r et al., 1990; M e y e r et al., 1994; Schrauder et al., 1994) and I b (Schrauder et al., 1994) w i t h respect to nitrogen characteristics. This is consistent w i t h their m i n i m a l residence time in the mantle and/or relatively l o w crystallization temperatures (Pattison and L e v i n s o n , 1995). Crystallization f r o m k i m b e r l i t e m a g m a f o r phenocrystal diamonds is suggested by the presence o f f l u i d inclusions w i t h similar chemical traits to k i m b e r l i t i c magma ( N a v o n et al., 1988; L e u n g et al., 1990; Schrauder and N a v o n , 1994; Schrauder and Koeberl, 1994). Phenocrystal diamonds are f o u n d i n kimberlites f r o m northern A u s t r a l i a ( T a y l o r et al., 1990; Lee et al., 1994), Zaire, Botswana ( N a v o n et al., 1988; Schrauder and N a v o n , 1994; Schrauder and K o e b e r l , 1994), Y a k u t i a , I n d i a (Schrauder et al., 1994), and F u x i a n ( L e u n g et al., 1990). A n orogenic o r i g i n must be considered f o r the W a w a diamonds because they occur i n greenschist facies metamorphic rocks w i t h i n a 2.7 Ga greenstone belt w h i c h m a y have had a higher metamorphic grade and undergone retrograde metamorphism. A phenocrystal o r i g i n must be considered because the W a w a d i a m o n d population is dominated by small sizes o f crystals, w h i c h overall have experienced little resorption. A xenocrystal cratonic o r i g i n , the most c o m m o n f o r diamonds, is also a possibility for W a w a diamonds. Here I argue f r o m evidence based on m o r p h o l o g y , and nitrogen content and aggregation data that the W a w a diamonds are not orogenic or phenocrystal.  117  W a w a diamonds have the f o l l o w i n g characteristics that are incompatible w i t h those o f orogenic diamonds: 1) The predominance o f aggregates; 2) The absence o f skeletal and reentrant diamonds; 3) The presence o f h i g h l y and n o n - u n i f o r m l y resorbed, and etched diamonds; 4) L o w nitrogen contents; 5) The presence o f undeformed diamonds w i t h h i g h l y aggregated nitrogen that f o r m e d at h i g h estimated residence temperatures. W a w a diamonds have the f o l l o w i n g characteristics that are incompatible w i t h those o f phenocrystal diamonds: 1) The presence o f n o n - u n i f o r m l y resorbed and etched diamonds; 2) The l o w proportion o f fibrous cubic diamonds; 3) The presence o f distorted diamonds shapes; 4) The high nitrogen aggregation state ( > 5 0 % B-defects) indicative o f l o n g mantle residence times or high mantle residence temperatures. . W a w a diamonds show a w i d e variation in resorption and some are classified as class 1 and 2 according to M c C a l l u m et al. (1994). 1 1 % o f the W a w a diamonds studied exhibit n o n u n i f o r m resorption w h i c h is a feature o f diamonds that have been partially protected b y mantle xenoliths (Robinson, 1979). The presence o f n o n - u n i f o r m resorbed diamonds w i t h i n the W a w a d i a m o n d population is strong evidence for a xenocrystal o r i g i n .  Further evidence f o r their n o n -  u n i f o r m resorption, is the presence o f ruts (McCandless et al., 1994; Robinson, 1979) on 3 9 % o f the diamonds. The m a j o r i t y o f the W a w a diamonds are not equidimensional (Table L 3 , A p p e n d i x 3). This suggests that g r o w t h o f most diamonds were l i k e l y inhibited b y other neighboring minerals, w h i c h is most l i k e l y to happen i n subsolidus conditions and not i n a melt (Otter e t a l . , 1994) Furthermore, precipitation o f diamond f r o m k i m b e r l i t i c magma proposed b y Pattison and L e v i n s o n (1995) is less l i k e l y than that f r o m the calc-alkaline lamprophyric magmas f o r the f o l l o w i n g reasons. Firstly, the calc-alkaline lamprophyres are poorer in C 0  2  (Rock, 1991) and  therefore u n l i k e l y to be saturated i n C O 2 at depths needed to precipitate diamonds. Secondly, calc-alkaline lamprophyres are generated at shallower depths than kimberlite (Rock, 1 9 9 1 ;  118  M i t c h e l l , 1991) and therefore their C C V r i c h magmatic volatiles are more l i k e l y to have exsolved and escaped. I n f u l l correspondence w i t h this, fibrous coats o f phenocrystal diamonds are absent f r o m k n o w n diamondiferous lamprophyres (MacRae et al., 1998; H a b i b , 1998). Based o n the above evidence a xenocrystal cratonic o r i g i n is suggested f o r the W a w a diamonds.  3.4.4  Tectonic Environment of Diamond Formation D i a m o n d is stable at a h i g h pressure and transforms into graphite at different pressures  depending on the ambient temperature. D i a m o n d is stable at shallower depths i n colder segments o f the mantle. O n l y i n these segments d i a m o n d occurs at the depths (usually <300 k m ) where i t can be p i c k e d up b y ascending mantle magmas. These relatively c o l d mantle terranes exist i n o n l y t w o tectonic settings, under Precambrian cratons ( C l i f f o r d , 1966; Janse, 1989; Helmstaedt and Gurney, 1995), and under subduction zones ( G r i f f i n et al., 2000). Precambrian stable cratons are considered conducive to d i a m o n d f o r m a t i o n because they often contain unusually t h i c k (~ 150-200 k m ) , cool lithospheric roots mapped petrologically and geophysically (Helmstaedt, 1992; Helmstaedt and Gurney, 1995). H o w these t h i c k lithospheric roots that were f o r m e d d u r i n g the A r c h e a n and Proterozoic is still h i g h l y controversial ( H a m i l t o n , 1993; Vlaar et al., 1994; Helmstaedt and Gurney and 1995). T h e greater than average thickness o f the lithosphere results i n convex d o w n w a r d isotherms and a corresponding convex u p w a r d diamond-graphite e q u i l i b r i u m line (Fig. 3.20). Preservation o f these cool, t h i c k lithospheric roots requires that they remain insulated against reheating f r o m mantle plumes, rifts and active tectonic margins and that they stay attached to the craton d u r i n g successive plate m o t i o n ( H o f f m a n , 1990; Helmstaedt and Gurney, 1995). D i a m o n d s f o r m e d in these stable cratonic environments are considered to be o f xenocrystal o r i g i n (section 3.4.3), and were brought to the surface b y magmas generated in the d i a m o n d stability field that rapidly ascend to 119  Crust - 50  . . 900"C 1200"C  ; ; ; ; \ Lithosphere  -100  x  Mantle ...••* \T  -200 250  \  yK  - 150  L  v  s  Root  •s,  / -s/  -  s  Asthenosphere  \/  Simplified model of a diamondiferous lithospheric root (ater Haggerty, 1986; Helmstaedt and Gurney, 1995). F i g u r e 3.20  Thermal structure of a subducting slab (shaded area) showing the low-tempertature region at the top where diamond formation would be most favoured. The downward deflection of isotherms allows the diamond-graphite stability field to occur at shallower depths (after Griffin et al., 2000). F i g u r e 3.21  120  the surface (Helmstaedt and Gurney, 1995). Precambrian cratons are the most c o m m o n d i a m o n d - f o r m i n g environment. Diamonds are also thought to f o r m i n tectonically active margins, crystallizing w i t h i n subducting slabs at relatively shallow depths (~ 100 k m ; G r i f f i n et al., 2000). Subduction o f the . c o l d slab results i n convex d o w n w a r d isotherms and a corresponding convex u p w a r d d i a m o n d graphite stability curve favorable f o r d i a m o n d f o r m a t i o n ( F i g . 3.21). Depression o f isotherms and the potential volume o f material w i t h i n the d i a m o n d stability f i e l d depends on the rate o f subduction; the faster the subduction, the greater the depression o f isotherms and the v o l u m e o f material w i t h i n the d i a m o n d stability field ( G r i f f i n et al,. 2000). D i a m o n d preservation i n this environment is short (10-35 M a depending on the rate o f subduction) because the subducted slab . heats up t o w a r d e q u i l i b r i u m temperature w i t h the surrounding mantle, resulting i n graphitization o f the diamonds ( G r i f f i n et al., 2000). D i a m o n d can be destroyed even more easily i f the geotherm is raised by magmatic a c t i v i t y and an associated mechanism o f advective heat transport ( G r i f f i n et al., 2000). D i a m o n d s f o r m e d and preserved w i t h i n the slab are considered orogenic o r i g i n (section 4.3), and can be brought to the surface either b y obduction or b y a r a p i d l y ascending m a g m a d u r i n g or shortly after ( w i t h i n a f e w tens o f M a ) subduction ( G r i f f i n et al., 2000). The m o d e l proposed b y G r i f f i n et al., (2000) has been quantified to reflect conditions i n m o d e r n subduction settings. The late-Archean tectonic environment was different f r o m m o d e r n day analogues, i.e. the mantle was hotter leading to rapid convection, subduction rates were higher (Hart et al., 1970; B u r k e et al., 1976), and the slabs more buoyant resulting i n relatively shallow angles o f subduction ( A b b o t t and H o f f m a n , 1984; Helmstaedt and Schulze, 1989). A l t h o u g h a t h i c k lithospheric root has been identified b e l o w the Superior craton (Grand, 1987), a stable cratonic environment is u n l i k e l y for the f o r m a t i o n o f the W a w a diamonds. The magmatic and volcaniclastic rocks f r o m w h i c h the diamonds have been recovered are part o f the  121  M i c h i p i c o t e n greenstone belt w h i c h represents an island arc, convergent m a r g i n tectonic setting (Sage, 1994). This active tectonic setting is not conducive to the preservation o f the lithospheric root ( H o f f m a n , 1990) i f one i n fact was present b e l o w the W a w a subprovince tectonic plate at the time o f subduction. Based on the tectonic setting at the time w h e n the W a w a diamonds were emplaced, their f o r m a t i o n should be related to subduction as proposed b y G r i f f i n et al., (2000). H o w e v e r , the studied characteristics o f W a w a diamonds are more t y p i c a l o f those  from  cratonic settings and inconsistent w i t h those o f orogenic diamonds. Further research is required to understand the o r i g i n o f W a w a diamonds. Studies o f mineral inclusion, carbon and nitrogen isotopic compositions o f the diamonds w i l l advance our understanding o f this unusual d i a m o n d suite.  3.4.5  Diamonds in Calc-Alkaline Lamprophyres The presence o f d i a m o n d i n the W a w a calc-alkaline lamprophyres provides some  constraints o n their magmatic o r i g i n . Based o n the presence o f diamonds, I can conclude that f o r m a t i o n o f the host l a m p r o p h y r i c magmas was essentially coeval w i t h subduction and the magmas were produced in a convergent regime. A s discussed previously, diamonds i n a c o l d subducting slab are stable as long as the subduction is active and convert to graphite and disappear - 1 0 M a after subduction ends ( G r i f f i n et al., 2000). Subduction i n the M i c h i p i c o t e n greenstone belt was active between 3.0 and 2.6 (Sage, 1994), so the W a w a magmas must have f o r m e d i n this time interval. The latter constraint fits w e l l w i t h the k n o w n ages o f the W a w a lamprophyres and breccias (2.67 G a ; Stott et al., 2002). Secondly, the presence o f d i a m o n d constrains the depth o f the m a g m a generation. The depression o f the isotherms and the m i n i m u m depth o f the d i a m o n d stability field is dependant pn the rate o f subduction. A t h i g h rates o f subduction (~8 cm/year), d i a m o n d can occur at depths  122  greater than 80-90 k m ( G r i f f i n et al., 2000). A n o t h e r estimate o f the depth f o r the m a g m a generation comes f r o m temperatures assessed b y the nitrogen aggregation (TNA) in the W a w a diamonds. The m i n i m u m TNA for the d i a m o n d suite is between 1100 and 1300°C ( F i g . 3.17) for estimated T.MR= 10 M a . These m i n i m u m temperatures correspond to depths o f ~ 300 k m or greater w i t h i n the fast subducting slab ( G r i f f i n et al., 2000). Thus, the W a w a calc-alkaline magmas m a y have f o r m e d at depths o f 80 to 300 k m . T h i r d l y , the W a w a calc-alkaline lamprophyres must have been emplaced very rapidly to ensure preservation o f diamond w i t h i n the resorbing magma. H i g h m a g m a ascent rates are accepted f o r all m a j o r p r i m a r y diamondiferous magmas, i.e. k i m b e r l i t i c and lamproitic, w h i c h have high volatile contents (Spera, 1984). S i m i l a r h i g h ascent rates are expected i n volatile-rich lamprophyres emplaced explosively. These should have higher d i a m o n d potential than more c o m m o n lamprophyric bodies intruded n o n - v i o l e n t l y as dykes. I n accordance, the younger W a w a lamprophyres are less diamondiferous than the W a w a volcaniclastic breccias even though the latter have been diluted by abundant country r o c k fragments. Pyroclastic deposits not m o d i f i e d and diluted by secondary epiclastic processes should have the most d i a m o n d potential among calc-alkaline lamprophyre rocks.  123  Chapter 4 CONCLUSIONS 1.  T w o types o f Late Archean diamondiferous rocks are recognised i n the W a w a subprovince o f  the Superior craton, metamorphosed p o l y m i c t volcaniclastic breccia and lamprophyre.  2.  The breccia and the lamprophyre are metamorphosed to greenschist facies and consist o f  actinolite, hornblende, chlorite, albite and biotite, w i t h accessory titanite, epidote, and quartz. The o n l y relict magmatic mineral is oscillatory-zoned hornblende.  3.  The overall m a f i c character o f the rocks, preserved igneous textures, composition o f relict  hornblende, and w h o l e - r o c k composition suggest that the magmatic predecessors were calcalkaline lamprophyres.  4.  The p o l y m i c t volcaniclastic breccia was deposited f r o m as debris f l o w s , as suggested by its  large v o l u m e , stratigraphy, w i d e range i n clast lithologies, poor sorting, presence o f delicate structures and large country-rock boulders, and paucity o f sedimentary structures.  5.  M o r p h o l o g i c a l studies revealed that the m a j o r i t y o f the diamonds are colourless, w e a k l y  resorbed, octahedral single crystals and aggregates. A variety o f d i a m o n d colours, as w e l l as cubic and cubo-octaheral single crystals and aggregates were also observed. Infrared spectroscopy determined that the diamonds have nitrogen contents r a n g i n g f r o m 0 to 740 p p m  124  and t w o modes o f nitrogen aggregation at 0 - 3 0 % B and 6 0 - 9 5 % B-centers. The W a w a diamond population exhibits a diversity o f crystal f o r m s and nitrogen aggregation states suggesting the diamonds f o r m e d under v a r y i n g physical and chemical conditions. The m o r p h o l o g y and nitrogen characteristics o f the W a w a diamonds are t y p i c a l o f those f r o m xenocrystal cratonic diamonds and unlike those o f orogenic diamonds f o r m e d i n subduction zones. I t is enigmatic that the W a w a diamonds were emplaced into a subducted-related setting but show characteristics typical o f xenocrystal cratonic diamonds.  125  References A b b o t t , D . H . , H o f f m a n , S.E., 1984. A r c h e a n plate tectonics revisited. 1. 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Schweizerische Mineralogische u n d Petrographische M i t t e i l u n g e n 15, 39-140.  144  Appendix A Location and Trench Maps  145  Figure A l : L o c a t i o n o f the Band-Ores Resources, Pele M o u n t a i n Resources and S p i d e r / K W G properties w i t h respect to the t o w n o f W a w a , O N .  146  -a  r i  c  Q < z  _ Q  3 -fl  z in  fl  is  Cd  cn  in •a aofl a0^ W " i *3 cu  a:  oO  "O * 0  -fl | *>  y E cn c: p — c 1 C(H = c O c  T3O  1  . .  >» o  ri fl  OB cu  —  '3  o f-  Q  §5  bo  *I  u  A  'E_ —  |  .2c  c  CO  Q  a  c2  cn fl °l-i c,_ £  II  A  a —  r-  fl  fl  cu"  O  fl  3  C  EL  Cd  CU  S  O  <U  ft Sb  fl.  A  o u  —  c/a  X) n.  1  SP.a CU — fl  03 •  u  JTJ  E  o XI cu  "3  _CJ  00  S  2 « o - £ g  3 U "O  c a ° -c c 2 3 ,2 CJ CJ Gfl  —  CJ  •a  —  O  CJ  T3 .-  Oa  S S o .. N  m  .  Q ,  u i CCS 3  CJ  i s sa 3 c cj o o  _S  w  73  9  S 2 1  JTJ  >  u  .22  .  —  v  • • • g , ° «  147  .  3,  C  i> "ITS  3 e (N co  ca ccj «  <<<]< o o Q  CU  •  ° I  -=  Q  IDISD <  o « N  I  ^  g  S .2 o = o g -5 A  U. i s  fl  F i g u r e A 3 : Detailed (1:100 scale) trench map o f trench B Z based on tape and brunton mapping s h o w i n g lithology, f o l i a t i o n , fractures and veins. U T M coordinates: 6 6 5 H O E , 5 3 3 4 2 0 0 N ( N A D 27).  148  N  A  0  4  IS  L-2 xSlL-1  X Sample L o c a t i o n 1 1 1 S Foliation  80  2  1—J S Foliation 4  CP  J i —7  ,  •  /  Fracture Shear Sense Fault Volcaniclastic Breccia  F i g u r e A 4 : Detailed (1:100 scale) trench D E - 1 map based on tape and brunton mapping showing lithology, f o l i a t i o n , fractures and veins. U T M Coordinates: 667480E, 5334115N ( N A D 27 ).  149  150  b  151  152  153  o  -a *-»  fN  -9  r3  rc!  5  o  o  5  N  fN  3  OS  30  j  1  5  m m  O f N ^  cl u vo >  CCS  V©  Si s O £ 4£ C ro o - 5 _g  -—i  M C  g C  .2 la  O  CJ  o Er  —  3 b &fl u .22 C  |  JC5  u u —  s8,  c C Q .. oo  3  „  oo cu  C  x>  — o G — „ —  3 S o  a  a  o G cn ft  s ga  § s vi ao ^ •ra ca 2 _  5  ca  tS  c  *•*  ^cS G  U  6 Ja  Q  ag G  • 'G  xci o G  s  G .2 P -G  a  o  3 —  CJ 13 CU  D EH 09  c  ~3  2  3X1X1 3 £ cu O O  O  ca  — cj cu cj  ca  M  'on  ° «  a  o 4i •  •  •—  a cc;  SO  CS  C/5  •  <  w  3 O  O  G g  a •a 3 CJ o 5  ri  a i 3 3 3  — d  5  O  I  CD .2 X .a n.  O Xi ,  ft JS » C3 cj J2 Q.JS :/-. O• o u  3 C  CJ CJ CJ  O  42  cs m o  2  •  T f  i n *o ce  4 CJ  c^  2  cu o ca xj ,  >se c« ^ Q o a •• e 'S » o s -< -G iri cu G O C r2 > 3 C ca BjD to O  •  oO  < < < ]  154  F  o CJ C J  CJ  =  EQ  g  DO  "ej C  „  c3  C3  cd  o w  o «  A O  cO  H  N  *r  Q  -o  41  11-13 U  '5 C3  o  9C  fj  gm  ffl  E  a  CJ  3  CJ  CJ  .9 ^  \B  _2 CJ  '3  1 CO  N  \s  cS P  ccj \CTJ  O  a i .2 Q  3  ••!• U  CO  u  _o  5. A  CO  fN -r O  —  Q  a  O O  ai  1  ro tN rs -r  00o  fN  C  Is  X  oo CQ  fN  fl- fN ea - r  Q  fl  9  .O  CO  03  i  oc ro  8 » f N —<  cl)  v*  Q  fN  *  Q  c  C  ^  o  9-  CU CO 03 J3  03 CO — CU  O.  fl cd  o  I  t3  cd £  r—I  _c CN fl CN fl fl  o  -a  B  . . fN  N  S os .2 > CQ 03  2  1  ro o  u b  o  Q  > \>  CC3 CJ  CJ  o m m rro fN  co (N  5  -tfN  q J»5 oo oo  -fl  <  <u ccd d. ^ cu >n co  o o  - fN  fN m  —  g  sO  *n ro  ^vi  •3- S Q Q M  r,^ K  ri  P  i  >r> f N  fN  Q  22 J.  -  73  IT)  —  O  is oo cu r--  —.  9 w9 « S9^ Q  Q  >0  O  co  •< cy  cd i n i n ro" v t fl O — r o v t  S£  S 155  Q  <N  0  fN fN vT  O  ro CN  r-.  2  fN  Q Q Q Q  8U U & 2  IS00 fN fN  P  < - fl  fa .. oo  fl  — fN  ro  .3 W  f N ro  r= ^ D  oo" in in  fN i  ] 1-1 Q  ^vo rj « cn  r<~\  t>  156  fN  157  158  159  4—>  160  "n*  F i g u r e A 1 6 : Detailed (1:100 scale) trench SE-F map based on tape and brunton mapping s h o w i n g lithology, f o l i a t i o n , fractures and veins. U T M coordinates: 668763E, 5 3 3 5 0 9 6 N ( N A D 27).  161  T3  4=  C <u  _2  a  3  -c  Bo  u u. ora -  d  a  X  d o cu OB  Q d  d  i  o _N cn  c3 «n x  ca  i  PS3 CD3  U  co 3 a>  O  3 £ -3 ° 1 u o o .ti 00 X3l  00 Qi,  CU  X!  -u S 5i 00 N  2m  -  §  5  •cd <on  S 5° f N O c X  3  ro  uu  ^i*  IT)  •I  00^3  o d o %  S 6  oO  00 cu  o 'S O  S3  X! _^  3  O 00 c3  .S  I  -  cu  00  i  °-  ro e  .a -  £  .9  9 0  r—  o  c -  IP  — , fN JD f N Q -3 = HQ -J  4  x c x  a  O  •o u X  c3  C>  o ir> *j d ro cu r o _ ro Uc -  d ,o oc —  o  X u p d or u  cd  g "H o o  cu  3=2 o o  - S 8 >—- G  -a  d  1 5 «  n e  Ii <u  8 g -S oo  d_  "  d  o  i  O >0  ^~ S c <u» -H  <\ 2:1 1§ s B s  162  .©JD "5? cu — T3 00  Appendix B.  Rock and Fragment Sample Data Collection Information  Table B l : Rock sample data collection information UTM _ . Trench/ Sample "Rock Property , Coordinates outcrop Number Unit T  Polished Whole Thin Rock Section Sample  b  "Description  "Thin Section  b  Band-Ore  E-2  KD7231  667730E, 5335830N  pvb  actinolite-rich matrix; volcanclastic breccia-bed 4 and bed 5 (too)  X  Band-Ore  E-2  KD7232-1  667730E, 5335830N  pvb  biotite-rich matrix  X  Band-Ore  E-2  KD7232-2  667730E, 5335830N  pvb  biotite-rich matrix  X  X  Band-Ore  E-l  KD7241  667815E, 5335775N  biotiterich pvb  biotite-rich matrix  X  X  Band-Ore  E-l  KD7245  667815E, 5335775N  biotiterich pvb  biotite and chlorite-rich matrix  X  Band-Ore  DE-1  NL-1  667480E, 5334115N  pvb and jm  actinolite-rich matrix  X  Band-Ore  SE-F  NL-6 000  668763E, 5335096N  pvb  biotite-rich matrix; clastpoor  X  X  Band-Ore  SE-F  NL-6 090  668763E, 5335096N  pvb  biotite-rich matrix; clastpoor  X  X  Band-Ore JR-14-1  NL-8 000  666900E, 5333700N  pvb  biotite-rich matrix; 3035% clast content  X  X  Band-Ore JR-14-1  NL-8 090  666900E, 5333700N  pvb  biotite-rich matrix; 3035% clast content  X  X  Band-Ore JR-14-2  NL-10  666910E, 5333680N  pvb  biotite-rich matrix; 5% clast content  X  X  X  X  X  X  X  X  X  X  Band-Ore  BR-1  NL-12 000  666900E, 5335175N  pvb  15-20% clast content  X  Band-Ore  BR-1  NL-12 090  666900E, 5335175N  pvb  actinolite-rich matrix; 1520% clast content  X  pvb  biotite-rich; clast-rich at contact with clast-poorer breccia  X  X  Band-Ore  BZ  NL-14-A  665110E, 5334200N  Band-Ore  BZ  NL-14-B  665110E, 5334200N  pvb  clast-poorer at contact between clast-rich and clast-poorer pvb  X  X  Band-Ore  DE-3  NL-17  667680E, 53314120N  pvb  biotite-rich matrix  X  X  163  Trench/ Sample „ ™ outcrop Number ^"TT (Nad 27) U  p P r  t  °  p e r t y  „ ,„ Band-Ore  145  . NL-21A  665550E,  Band-Ore  52  NL-25A  £* * * 5333250N  Band-Ore  51  NL-27A  '  Band-Ore  51  NL-27B  665955E - , „ - ' 5333287N  Band-Ore  51  NL-28  X I T  9  °R k Unit _ fragment  D e S C r i  P  "Thin Section  t i o n  b p  °  ° ™ ° Section Sample U s h e d  n  b  W  h  ,  R  C k  coarse hornblende  actino.ite-rich matrix; lapilh  0  665955E  .  0C  actinolite-rich matrix; fragment clast supported fragment within pvb  X  X  actinolite-rich matrix; pvb enclosing clast ,„ supported fragment  X  X  actinolite xeno  X  . lamp  _ ... . mafic dike 2  X  X  lamp  mafic dike 1  X  X  undeterminable , , morphology  pvb  0  0  fragment 533328/N  . Mumms Mountain  xir  ' f . Mumms Mountain  NL-31  P  e  l  \jt  e  P e  Pele . Mumms Mountain  oo  NL-29  663380E, .,.„..' 533722 IN  533722 IN  NL-32  663380E, ' 5337221N  . lamp  X T T  K  Pele . Mountain  Moet  ... , , NL-34  662710E, „ , „ , .' 5337730N  . jm  Band-Ore  3649  NL-35  ^^l?' 53333337N  lamp  Band-Ore  52  NL-36  Band-Ore  52  NL-37  Spider/ KWG Pele Mountain P  e  l  e  Mountain P  e  l  e  . Mountain  ,  c  x„  Mumms w  Moet f  5333250N 665950E „ ' 5333250N  C  l  1  t  a m  P  pvb?  m  X  X  . . . . . biotite-rich matrix  xrr <n NL-50  663380E, „„„„„„,,., 533722 IN  , pvb  ,. . ., . biotite-rich matrix  NL-51  662710E, cim?™ 5337730N  l a m  p  P  164  X  biotite-rich matrix; clastsupported early breccia rich in felsic fragments  . _ pvb?  X T T  X  X  X  662710E, „ „ ™ ' 5337730N  t r  m  X  X  NL-49  a  X  X  clast-poor late breccia  , l  X  X  659955E, 5341810N  X I T  S a n d O T  „, Moet  l  jm in volcanclastic , breccia  J  X  f  ...  Y  d l k e  X  f  v  v  X  „ X  Y  X  X  „ X  X  X  X  e  ^ Trench/ Sample Property „ , outcrop Number _ T  Band-Ore  145  ...  UTM _ ,. . Coordinates (Nad 27) 665550E, 5333069N  Polished "Whole Thin Rock Section Sample  b a  Rock Unit  "Description  "Thin Section X  l a m p  actinolite-rich matrix; soft sed def?clast-rich with sand sized lense within breccia  Band-Ore  BZ  NL-53  665110E, 5334200N  pvb  Pele Mountain  Moet  NL-54  662710E, 5337730N  jm  Band-Ore  E-2  KD3755-1  667730E, 5335830N  pvb  actinolite-rich matrix; pvb-bed 4 and bed 5 " (top)  Band-Ore  E-2  KD3755-2  667730E, 5335830N  pvb  actinolite-rich matrix; pvb-bed 4 and bed 5 (top)  Band-Ore  E-2  KD3757  667730E, 5335830N  pvb  Band-Ore  E-2  KD3758-1  667730E, 5335830N  Band-Ore  E-2  KD3758-2  Band-Ore  E-2  Band-Ore  X  X  X  X  X  2X  X  biotite-rich matrix; pvb bed 3  X  X  pvb  biotite and actinolite-rich matrix; pvb-bed 2 and bed 3 (top)  X  667730E, 5335830N  pvb  biotite and actinolite-rich matrix; pvb-bed 2 and bed 3 (top)  X  KD7229  667730E, 5335830N  pvb  actinolite-rich matrix; pvb-bed 4 and bed 5 (top)  X  E-2  KX>7230  667730E, 5335830N  pvb  actinolite-rich matrix; pvb-bed 4 and bed 5 (top)  X  X  Band-Ore  E-l  KD7236-1  667815E, 5335775N  pvb  biotite and chlorite-rich; contact bewtween pvb and biotite-rich pvb  X  X  Band-Ore  E-2  KD7236-2  667730E, 5335830N  pvb  biotite-rich matrix; contact bewtween volcanclastic breccia and  X  X  Band-Ore  E-l  KD7240  667815 E, 5335775N  biotiterich pvb  biotite-rich matrix  X  X  165  X  X  Trench/ Property outcrop u  l  A  . Sample Number  UTM _ _,. Coordinates (Nad 27)  „ Rock . Unit  c  x  Description F  „ , ^ Band-Ore  , E-l  , KD7242-1  667815 E, „,.__ ' 5335775N  , pvb  chlorite-rich matrix; • J-I breccia dike  „ , ^ Band-Ore  „ „ E-2  „ KD7242-2  667730E,  , pvb  chlorite-rich matrix;  Band-Ore  E-l  KD7243  ^35775N  „ . Band-Ore  ^ , E-l  ,,~-„,, KD7244  667815E, ' 5335775N  Band-Ore  "^E-l  KD7247  f^fl^f' 5335775N  „ , ^ Band-Ore  „ „ E-2  KD7249  667730E, „„ ' 5335830N  Band-Ore  E-2  K.D7250  „ , ^ Band-Ore  ^ • DE-1  ™ . ~ Band-Ore  X  X  pillow basalt  b a s a l t  biotite•, , rich pvb  biotite and chlorite-rich matrix  X  chlorite-rich matrix; contact itact between bioti biotiterich pvb and imi  X  biotite and chlorite-rich matrix  667730 ,„„,„', 5335830N  pvb  biotite-rich matrix  „ NL-2  667480E, 5334115N  pvb and jm  , , mantle around xeno  ^ , DE-1  NL-3  667480E, 5334115N  pvb and • jm  actinolite-rich; mantle , around xeno  , ^ Band-Ore  , DE-1  „ . NL-4  667480E, ,,,, 5334115N  pvb and jm  actinolite-rich matrix; , , mantle around xeno  X  Band-Ore  SE-F  NL-5 000  ' 5335096N  pvb  biotite-rich matrix  X  Band-Ore  SE-F  NL-5 090  „„„„^' 5335096N  pvb  biotite-rich matrix  X  „ , ,A , Band-Ore JR-14-1 NL-7 000  666900E, ' 5333700N  , pvb  biotite-rich matrix; 10 to , 15% clast content  X  •^ ,„ , Band-Ore JR-14-  *„ -, ™« NL-7 090  666900E, 5333700N  , pvb ^  biotite-rich matrix; 10 to , 15% clast content  X  Band-Ore JR-14-1  NL-9  TT  N  m  D A r, Band-Ore  DD r BR-1  xn i r A NL-11A  Band-Ore  BR-1  NL-1 IB  o  T  666900E 5333700N  666900E, 5335175N  5335175N  F  H  matrix ^ bolder in pvb , (may have only sampled around . . , ,, matrix) boulder u n  •  X  X  X  X  X  X  „, X  X  X  X  X  n o w n  X  pvb  actinolite-rich matrix; , ., . . pvb at contact with imi  X  imi  imi at contact with pvb  X  166  X  X  . pvb  r  Polished "Whole Thin Rock _ _ Section Sample  b  Thin „ Section b  a  X  _ . Trench/ Sample Property -. ; outcrop Number  UTM Coordinates (Nad 27)  Rock Unit  "Description  "Thin Section  Band-Ore  BR-1  NL-13 000  666900E, 5335175N  pvb  clast-poor area  X  Band-Ore  BR-1  NL-13 090  666900E, 5335175N  pvb  clast-poor area  X  NL-15 000  665110E, 5334200N  pvb  actinolite-rich matrix; pvb and lense with less clasts (could not find the lense)  X  pvb  actinolite-richmatrix; pvb and lense with less clasts (could not find the lense)  X  biotite-rich matrix; contact pvb/lamp  X  Band-Ore  BZ  Band-Ore  BZ  NL-15 090  665110E, 5334200N  Band-Ore  BZ  „ NL-16  665110E, „,.„... 5334200N  contact  Band-Ore  3647  NL-18  666085E, 5333455N  contact  Band-Ore  145  NL-19  665550E, 5333069N  lamp  Band-Ore  145  NL-20  665550E, 5333069N  fragment  coarse hornblende fragment  X  Band-Ore  145  NL-21B 000  665550E, 5333069N  lamp  matrix (lamp) around fragment  X  Band-Ore  145  NL-21B 090  665550E, 5333069N  lamp  matrix (lamp) around fragment  X  Band-Ore  52  NL-22  665950E, 5333250N  contact  felsic metavolcanic and lamp contact (?)  X  Band-Ore  52  NL-23  665950E, 5333250N  contact  lamp and pvb contact (felsic-rich)  X  Band-Ore  52  NL-24  665950E, 5333250N  contact  imi and pvb (felsic-rich lense)  X  Band-Ore  52  NL-25B  665950E, 5333250N  jm and pvb  actinolite-rich matrix; mantled fragment (cored lapilli)  X  Band-Ore  51  NL-26  665955E, 5333287N  contact  contact between lamp, pvb (2 beds)  i r  Polished "Whole Thin Rock Section Sample  b a  167  lamp contact with coarse  X  X  X  X  Property  Trench / Sample outcrop Number  UTM Coordinates (Nad 27)  "Rock Unit  Thin Section b  "Description  Band-Ore  DE-1  NL-30  667480E, 5334115N  pvb?  X  Band-Ore  DE-1  NL-33  667480E, 5334115N  pvb?  X  Band-Ore  145  NL-38  665550E, 5333069N  lamp  X  666915 E, 5333645N  Diabase Dyke  Band-Ore  GQ-3A NL-39 000  coarse grained mafic CROCK  E-l  NL-40  667815E, 5335775N  fragment bi g "altered" mantle xeno  X  Band-Ore  GQ-3A  NL-42  666915E, 5333645N  Diabase Dyke  outcrop  X  Pele Mountain  Moet  NL-43  662710E, 5337730N  jm  pvb pelletal lapilli  X  Band-Ore  GQ-1  NL-44  666890E, 5333665N  imi  outcrop  X  Spider/ KWG  Sandor  NL-45  659955E, 5341810N  imi  outcrop  X  Band-Ore  GQ-2  NL-46  666914E, 5333657N  imi  outcrop  X  Band-Ore  3647  NL-47  666085E, 5333455N  contact  imi and lamp  X  Band-Ore  3647  NL-48  666085E, 5333455N  lamp  X  Pele Mumms Mountain  NL-55  663380E, 5337221N  pvb matrix around  X  Band-Ore  NL-56  666085E, 5333455N  lamp  biotite-rich matrix  l i s h e d  b  w  h  o  ,  e  Rock Sample  X  Band-Ore  3647  ° Thin Section  b p  X  X  Symbols: pvb - polymict volcaniclastic breccia; jm - juvenile material; lamp - lamprophyre; imi - intermediate to mafic intrusive rock.  a  b  X - type of sample represented  168  •a  3  6b x O  E  x BB-J  OJ  O <*>  g O  so £  O  u< CJ  -5  OJ  cd  CJ  g  M  2  C/5  JS  o  bo  oj  3  01  X  -a cd  T3  •a -c 3 "3 c so  D.  cj fi  OJ  Xl oj  00  c o  co  c c  cd  ^  c  c  eg 2  CJ  o.  cd  •a c  JJ  oo  "3  o  2  a.  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C  t .2 c c 3 O o  «  •2 u s  3  cd  i  2C/5 CJ  O  "° z P  .  o  ca  •. o  &a -  c  •11 00 T3 p -p  x ,=a  o. a. ca  3  X CJ .y  c o CJ  ca  oo  00  E  •s  —  cj  s  -a  CJ  o Pi  P  B  a. .. 0 0 3 O  C  00  ca  B  cJ  o  .22  tex.  —  p CJ ca D. D. C3 O  3  oo  c  ca  -§  z  il 5  p  E  XI oo  T3  ca CJ  E  cj  o  00  c CJ J^ o X o o _CJ  E  CJ  3 o  § -s  ro X  CJ o. ca XI oo  X! oo  in  c/i CJ 'C ca •a c  CJ  ca X)  -a  3  J2  CJ •o c  00 c  -o CJ  3  co  -o c ca oo c _o  PJ  ca ca  p  E <2  ca OO  <~  •a §  O  E  "E. E  CJ  c o  00  o -o  go  3  O  _ca  3  X co  CN ca *—  .ca  o X  00 p  "C  J3  3  o a. P  3  C/3  2? *  -d p  0 0 <<-  O  JS  'CJ 55 OO  00 P  CJ  ro  CJ 00  3  .3  3  t; <H  2: E •a  X 00  -a  ii U O ta 00  pe:  N  3 00  •r  Xj  T3 CJ c  3  T3  o CN  5  E  XI oo  c  o •o CJ  D. D. ca o  rre  =a  p  00 p  XI  <  00  < Er  00 XI  00 CJ  a  E  -a p — x  E  o  a  CN r-  2  CN  Q  o  o x  X  CN  CO  CN r»  CN r—  CN r—  2  u  U.  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CA  o Z  oo a  ca  cx o  z  c  -o c  ca c 3  3  oo c  c CJ  'C O  oo c OS  o -a  -a c  3  3  00 c  3  x  g  E  x  s  I ? | ^3 ° o N  o  CA  O  73  <  o  S  -C O  cj c oo c ca «  S  X CA  oo OJ  c w  3  00  J3 CA  D. ca  ex cx  X CA  3  •a c  00 c  <  00 n _o "cj  00 c  x  <  CA  3  00 c  <  S  s u 00  2  o IS  -3  ca E o  X  co cn  X  •r  1  & CJ  CS CN  CN CN CN r—  2  5  w  w  ro  CN CN r-  Q U  ^  w  T3  CJ  i  X  _  ca E  ^  X  o  2 S tS  Q  Eo  00  2 .c  (N CN C-  Q  CN CN r-  VO CN CN P-  Q  CN (N C--  Q 2  oo  CN CN r—  Q 2 (N  w  w  w  171  w  w  ro ro  ro  ro  ro  oo ro  a\ ro  o  r—  r--  r—  r--  r-  r—  r~  CN  a  <N  CN  CN  CN  CN  CN  CN  2  Q Q Q Q Q U 2 2  —  —  w w w  —  (N  w w w  —  w  Appendix C Photoplates of Country Rock and Fragment Population  172  F i g u r e C l : Photoplates o f A . felsic metavolcanic country rock and B. felsic metavolcanic feldspar crystal t u f f country rock mapped and described b y Sage (1994). B o t h rock types were f o u n d i n contact w i t h the volcaniclastic breccia and lamprophyre.  173  F i g u r e C 2 : Photoplates o f A . massive mafic metavolcanic country rock and B. P i l l o w basalt country rock mapped and described by Sage (1994). B o t h rock types were f o u n d in contact w i t h the volcaniclastic breccia and lamprophyre.  174  F i g u r e C 3 : Photoplates o f A . Coarse grained intermediate to mafic intrusive country rock and B. M e d i u m grained intermediate to mafic hypabyssal - intrusive country rock mapped and described b y Sage (1994). B o t h rock types were f o u n d in contact w i t h the volcaniclastic breccia and lamprophyre.  175  F i g u r e C 4 : Photo plates o f fragments w i t h i n the volcaniclastic breccia and lamprophyre. A . Cobble-sized felsic metavolcanic fragment. B. Clast-supported breccia, dominantely pebble and cobble-sized intermediate to mafic metavolcanic (oulined in black and w h i t e ; basalt) fragments.  176  F i g u r e C 5 : Photo plates o f fragments w i t h i n the volcaniclastic breccia and lamprophyre. A . A megalith ( > 9 m ) o f intermediate to mafic intrusive rock (outline i n black and w h i t e ; trench B Z ) . B. Angular, pebble-sized biotite-rich greenstone fragements (outlined i n black and w h i t e ; trench E - l ) .  177  F i g u r e C 6 : Photo plates o f fragments w i t h i n the volcaniclastic breccia and lamprophyre. A . Cobble-sized fragment o f greenstone (trench E-2). B. Cobble sized fragment o f coarse grained hornblende-rich fragment (trench JR-14-1).  178  F i g u r e C 7 : Photo plates o f fragments w i t h i n the volcaniclastic breccia and lamprophyre. A . Cobble-sized fragment o f gneiss (trench E - l ) . B. C o b b l e - s i z e d fragment o f coarse grained actinolite-rich fragment (outcrop 51). Note that the actinolite crystals are acicular and radiate.  179  F i g u r e C 8 : Photo plates o f fragments w i t h i n the volcaniclastic breccia and lamprophyre. A . Cobble-sized greenschist fragment (trench E-2).  180  Appendix D DETAILED PETROGRAPHY OF THE WAWA METAVOLCANIC DIAMONDIFEROUS ROCKS Petrographic observations were made using transmitted light m i c r o s c o p y o f polished and standard t h i n sections. T h i n section analysis o f the diamondiferous rocks f r o m W a w a was used to characterize the diamondiferous rocks according to their m i n e r a l o g y and microscopic textures. The t h i n section examination was also e m p l o y e d for identification o f possible subtle igneous textures and minerals, w h i c h may have been preserved d u r i n g m e t a m o r p h i s m , to better constrain the p r i m a r y nature o f the magma. This section w i l l outline the t w o diamondiferous rock types distinguished b y f i e l d observations: p o l y m i c t volcanoclastic breccia ( p v b ) and lamprophyre (lamp). B o t h the xenoliths f o u n d w i t h i n these t w o rock types and the surrounding country rock were also petrographically studied and described.  Polymict Volcaniclastic Breccia: Sample Number and Trench Location: Trench  Sample N u m b e r  DE-1 SE-F  NL-1 N L - 5 000, N L - 5 090, N L - 6 000, N L - 6 090  JR-14-1  BZ DE-3  N L - 7 090, N L - 7 000 N L - 1 2 0 0 0 , N L - 1 2 090, N L - 1 3 090, N L - 1 3 000 NL-14B NL-17  Moet  NL-49  The diamondiferous p o l y m i c t volcaniclastic breccia is predominantly m a t r i x supported (Fig.2.6). The m a j o r minerals that comprise the m a t r i x o f the breccia i n decreasing order are actinolite, epidote, titanite, biotite, quartz/feldspar, hornblende, chlorite and calcite. Accessory minerals observed were opaques (pyrite, and u n k n o w n ) , apatite, leucoxene and rutile.  Texture: Fine grained, inequigranular texture ( F i g . D 1 A ) shown by larger grains o f hornblende, actinolite, and occasionally biotite and epidote set i n a finer grained m a t r i x o f actinolite, titanite, epidote, calcite, quartz/feldspar, biotite, chlorite and opaques (Fig. D I B ) . F o l i a t i o n occasionally observed defined by the alignment o f acicular and bladed actinolite grains ( F i g . D 1 C ) . This m a t r i x appears to wrap around certain hornblende, and epidote grains and the fragments (Fig. 2.6 C, D ) .  Mineralogy: 50-75% Actinolite The actinolite grains are colourless to pale green. The grain size ranges f r o m less than 0.1 m m to 0.8 m m i n size. The larger grains are porphyroblasts and poikiloblasts w h i c h  181  are subhedral, columnar, bladed and prismatic i n shape and have serrate grain boundaries. T h e y make up 1 to 1 0 % o f the actinolite population. These actinolite grains m a y have biotite, calcite, chlorite, epidote, opaques and acicular actinolite along cleavage planes, grain boundaries and as inclusions ( F i g . D I N ) most l i k e l y as a replacement o f hornblende grains. There is slight evidence o f deformation where rare c o l u m n a r grains appear k i n k e d . The finer grains less than 0.1 m m i n size and are bladed, d i a m o n d shaped and acicular ( F i g . D I B ) . They make up the m a j o r i t y o f the m a t r i x . I n some t h i n sections the bladed grains were occasionally interleaved w i t h biotite. Where a f o l i a t i o n is observed it is the alignment o f these grains w h i c h define it (Fig.DIC). 1-20% Epidote: The epidote grains are colourless or m o r e c o m m o n l y pale y e l l o w w i t h patchy d i s t r i b u t i o n indicative o f higher Fe content i n these grains. The grains occur as euhedral to anhedral columnar, lamellar and rare hexagonal and d i a m o n d shaped i n d i v i d u a l grains, and granular aggregates. They range f r o m 0.8 m m to less than 0 . 1 m m i n size. The coarser grains have serrate grain boundaries and may occur w i t h biotite ( F i g . D I D ) , chlorite ( F i g . D I E ) and calcite. The grains may s u b - p o i k i l i t i c a l l y enclose acicular actinolite grains. I n some areas the coarser grains appear deformed noted by the bent cleavage ( F i g . D I E ) , undulose extinction and cracked appearance. Pressure shadows o f chlorite and biotite were also observed ( F i g . D 1 F ) . T h i n sections where f o l i a t i o n was noted, the m a t r i x appeared to wrap around the epidote grains (Fig. 2.6B). The finer grains occur i n the m a t r i x w i t h acicular and bladed actinolite, and quartz/feldspar. These finer grains can be d i f f i c u l t to distinguish f r o m titanite 1-20% Titanite Occur as aggregates o f anhedral grains less than 100 microns i n size and anhedral to euhedral, d i a m o n d shaped i n d i v i d u a l grains up to 0.5 m m . Some aggregates are m a n t l i n g rutile. M a y occur w i t h i n actinolite porphyroblasts and chlorite patches. I n some areas appears almost interstitial around the larger grains.  0- 2 0 % B i o t i t e Occurs as anhedral to subhedral tabular, hexagonal cross-sections and irregular crystals, m o s t l y less than 0 . 1 m m i n size but can be up to 0.5 m m . Grains can be partly replaced b y chlorite. Some are s u b - p o i k i l i t i c a l l y enclosing actinolite blades. M a y occur w i t h epidote, contain inclusions o f titanite and occasionally tabular grains are interleaved w i t h chlorite (Fig. D I G ) . Rare grains show evidence o f deformation marked b y bent cleavage ( F i g . 2.6D). 1- 10% Quartz/feldspar Can not distinguish between the t w o minerals under the optical microscope. Occurs w i t h i n matrix. Grains are anhedral w i t h smooth grain boundaries and less than or equal to 100 microns i n size. 0-5 % Plagioclase Grains are anhedral w i t h smooth grain boundaries and less than or equal to 100 microns i n size. Rare anhedral grains up to 0.4 m m i n size exhibit polysynthetic t w i n n i n g .  182  0.5-15% H o r n b l e n d e : H o r n b l e n d e occurs as light b r o w n to green pleochroic crystals w h i c h are subhedral to euhedral, columnar, prismatic, bladed and d i a m o n d i n shape. G r a i n boundaries are serrated. T h e y have occasional simple and lamellar t w i n s ( F i g . D 1 H ) , and m a y exhibit oscillatory ( F i g . 2.6E), normal? (Fig. D 1 I ) and patchy z o n i n g ( F i g . D l J). T h e crystals are up to 1.3 m m i n size and rarely occur as m e d i u m grained aggregates. The grains can be partly altered b y actinolite, biotite, calcite and chlorite along grain boundaries or cleavage planes m a k i n g them d i f f i c u l t to recognize f r o m actinolite porphyroblasts discussed above ( D I M ) or completely pseudomorphed b y these minerals ( F i g . D 1 L ; F i g . D I N ) . The grains pseudomorphed b y decussate textured biotite and fine scaly chlorite are readily distinguished b y distinct amphibole outlines ( F i g . D 1 L ) . T h e y m a y contain inclusions o f carbonate, actinolite, epidote, apatite (hexagonal, l o w interference colours), quartz/feldspar ( l o w order interference colours, anhedral). Possible pressure shadows ( F i g . 2.6C) or t a i l - l i k e structures o f actinolite g r o w i n g into the m a t r i x (Fig. D I O ) were observed. A l s o f o l i a t i o n is occasionally w r a p p i n g around the grains ( F i g . 2.6C). primary?  Possible relict mineral w h i c h c o u l d be  0-15%o M u s c o v i t e M a y be present i n the m a t r i x as acicular grains less than 0 . 1 m m i n size but d i f f i c u l t to distinguish f r o m the acicular actinolite grains. M a n y o f the grains exhibit b i r d ' s eye and parallel extinction. 0- 1 0 % C h l o r i t e M o s t l y o c c u r r i n g as fine scaly patches. The patches are irregular shaped, rounded, elongate and d i a m o n d or columnar shaped. The d i a m o n d and columnar patches have w e l l defined outlines and may be pseudomorphs o f amphibole. A l s o occurs as fine, scaly plates interleaved w i t h biotite ( F i g . D I G ) . 1- 3 % Calcite: Subhedral to anhedral, irregular, rounded and occasional lath-like crystals w i t h irregular grain boundaries. M a j o r i t y o f crystals are on average less than 100 microns to 200 microns i n size but local variations o f larger crystals up to 1.2 m m are observed. O c c u r sometimes as aggregates. Aggregates m a y occur w i t h epidote, chlorite, quartz/feldspar. Some grains appear to be p o i k i l i t i c a l l y enclosing acicular actinolite. 0 - 5 % Opaques Opaques are anhedral, irregular and elongate shape. The grains are less than 0.1 m m to 0.5 m m i n size. Grains are c o m m o n l y altered to leucoxene along the grain boundaries. Some grains appear clustered i n a n e t w o r k pattern w i t h calcite and actinolite ( F i g . D I P ) . Occasional skeletal texture observed w i t h opaque enclosing actinolite or calcite. Rare grains have distinct cubic shape and are probably pyrite. 0-0.5% Leucoxene R e d , o c c u r r i n g as anhedral irregular grains and stringers. The grains are 0 . 5 m m to less than 0 . 1 m m i n size. 0-0.5% R u t i l e  183  A n h e d r a l grains less than 0.1 m m i n size w h i c h are mantled b y titanite.  Fragments: A. Titanite-rich, Quartz-rich, Greenstone: Fragments are irregular and elongate i n shape, rounded to sub angular and 1 m m to 1cm i n size. The minerals that comprise these fragments i n decreasing order are quartz/feldspar, actinolite/muscovite, titanite/epidote, ± biotite, ± chlorite, and ± calcite. The overall texture is fine-grained and equigranular. Possible protoliths include a felsic igneous or sedimentary rock.  B. Actinolite/Muscovite?-rich Greenstone: Fragments are rounded to angular, oval, pseudo-rectangular and irregular shaped, and 2 m m to 1.2 c m i n size. Fragments usually appear grey i n plane polarized light. The minerals that comprise these fragments i n decreasing order are actinolite/muscovite, quartz/feldspar, titanite, ± calcite, ± biotite, and ± chlorite. Some fragments are cross-cut b y calcite veinlets. The overall texture is fine-grained and equigranular. Protolith is u n k n o w n .  C. Metamorphosed Intermediate to Mafic Fine-Grained Igneous (Metavolcanic?) Rock: Fragments are rounded to angular, oval and triangular shaped, and 1 to 8 m m i n size. The minerals that comprise these fragments in decreasing order are plagioclase, quartz/feldspar, titanite/epidote, ± actinolite/muscovite, ± calcite, and ± biotite. The overall texture is finegrained and equigranular w i t h relics o f igneous felty texture. The latter is defined as texture w i t h randomly orientated, microscopically identifiable m i n e r a l laths. Protolith is most l i k e l y a m a f i c volcanic igneous r o c k due to the observed preservation o f fine-grained, relic magmatic texture. 3 0 - 9 0 % o f the rock is replaced by metamorphic minerals o f the greenschist facies.  D. Metamorphosed Intermediate to Mafic Medium-Grained Igneous (Intrusive?) Rock: Fragments are rounded, oval shaped, and range i n size f r o m 3 m m to 8 m m . The minerals that comprise these fragments i n decreasing order are plagioclase, actinolite, and titanite/epidote. The overall texture is m e d i u m grained, equigranular w i t h relics o f igneous felty texture. The p r i m a r y igneous rock c o u l d be hypabyssal or intrusive.  E. Greenstone: Fragments are 1.2 m m to 1.5 c m i n size, irregular, lenticular and elongate shapes w i t h irregular grain boundaries. The minerals that comprise these fragments i n decreasing order are chlorite, titanite/epidote, quartz/feldspar, and ± biotite. The overall texture is fine grained, decussate texture w i t h m i n o r larger crystals. The p r o t o l i t h can not be identified.  F. Quartz/feldspar—rich Greenstone: Fragments range f r o m 4 m m to 1 c m in size, are rounded to angular, irregular, oval and elongate i n shape, and have irregular boundaries. The minerals that comprise these fragments i n decreasing order are quartz/feldspar, ± calcite, ± muscovite/actinolite, titanite/epidote, ± biotite, and ± chlorite. The overall texture is fine grained and equigranular. The protolith f o r these clasts can not be identified; c o u l d be a fine-grained volcanic or sedimentary rock.  G. Metamorphosed Fine- Grained Actinolite-Bearing Igneous Rock:  184  Fragments are rounded to angular, pseudo-oval, and elongate i n shape, and range f r o m 1.7 m m to 3 c m i n size. The rock is n o w converted to an amphibole-bearing greenstone. The minerals that comprise these fragments i n decreasing order are amphibole, actinolite/sericite, titanite/epidote, ± biotite, ± calcite, ± chlorite, and ± quartz/feldspar. The overall texture is fine-grained, and inequigranular w i t h relict fine grained, aphanitic, panidiomorphic igneous texture.  H. Metamorphosed Fine Grained Hornblende-Bearing Igneous Rock: Fragments are rounded, oval, and elongate i n shape, and range f r o m 1 m m to 1 c m in size. The r o c k is n o w converted to a hornblende-bearing greenstone. The minerals that comprise these fragments i n decreasing order are amphibole, ± actinolite/sericite, ± Chlorite, ± epidote, ± titanite, ± calcite, and ± biotite. The overall texture is fine-grained w i t h relict equigranular igneous texture.  I. Biotite-rich Greenstone: Fragments are approximately 1 to 4 m m i n size, subangular to rounded, and have oval and r h o m b i c shapes. The minerals that comprise these fragments i n decreasing order are biotite, chlorite, titanite/epidote, and quartz/feldspar. The overall texture is fine grained and d o m i n a t e d b y the decussate texture o f the biotite.  J. Juvenile Material: Fragments are approximately 1 to 4 m m i n size, angular to subrounded, and have oval and lenticular shapes ( F i g . 2 . 6 A ) . The mineralogy o f these fragments is similar to the breccia m a t r i x however is more abundant i n hornblende and actinolite and less abundant i n quartz/feldspar. The overall texture is fine grained and inequigranular.  Biotized Polymict Volcaniclastic Breccia: Sample Number and Field Location: Trench  Sample  E - l (at contact between A c t and B i - r i c h p v b ) E-l E-2  KD7236 KD7240, KD7241 KD7245  Thin Section Description: The breccia consists o f 55 to 9 5 % m a t r i x and 5 to 4 5 % angular to rounded, 1 m m to 2 c m sized lithic fragments. The breccia is metamorphosed i n the greenschist facies and n o w is an aggregate o f biotite, quartz/feldspar, chlorite, calcite, and, titanite/epidote (Fig. D 1 Q , D 1 R ) . M i n o r actinolite is also present along the contact w i t h the actinolite-rich breccia. Larger grains that may have o r i g i n a l l y been phenocrysts o f amphibole can occasionally be seen. Evidence f o r f o r m e r amphibole is indicated b y biotite pseudomorphs ( F i g . D 1 Q ) w i t h diamond, prismatic and columnar shapes and at the contact w i t h actinolite-rich breccia , relic pale green amphibole is also observed. The m a t r i x o f the r o c k has a fine-grained, inequigranular texture ( F i g . D 1 Q ) .  Mineralogy 1-4%) A l t e r e d amphibole  185  A m p h i b o l e forms columnar, d i a m o n d and prismatic, euhedral crystals, on average 0.3 to 0.8 m m i n size. M o s t crystals are completely pseudomorphed b y r a n d o m l y interlocking, euhedral biotite grains. The pseudomorphs occur w i t h occasional calcite and are c o m m o n l y mantled by chlorite. 10-40% Biotite T a b u l a r and irregular, anhedral to euhedral, r a n d o m l y orientated grains, less than or equal to 100 microns i n size. Some grains contain pleochroic haloes. Grains occasionally occur i n clusters exhibiting decussate texture. Some regions are p a r t l y replaced b y chlorite. 3 0 - 4 5 % Quartz/feldspar Can not distinguish between the t w o minerals i n t h i n section. A n h e d r a l , rounded or irregular grains w h i c h can vary slightly i n size f r o m less than 100 microns up to 500 microns. Grain boundaries are c o m m o n l y interlocking and can be smooth or jagged. Generally sub-poikilitic texture partially enclosing less than 100 m i c r o n acicular crystals o f biotite and chlorite. 5 - 4 0 % Chlorite A n h e d r a l , fine, scaly grains occurring as irregular, isolated patches i n chlorite-poor regions w h i c h become interconnected where chlorite is more abundant. Part o f this chlorite replaces biotite and is occasionally interleaved w i t h biotite. 5 - 2 0 % Calcite A n h e d r a l and intermittently euhedral lath-like crystals w i t h irregular grain boundaries. M a j o r i t y o f crystals are on average 100 to 200 microns i n size but local variations o f larger crystals up to 500 microns are observed. Occur sometimes as aggregates and can be s u b - p o i k i l i t i c a l l y enclosing biotite. 3 - 5 % Titanite/Epidote Can not distinguish between the t w o minerals i n t h i n section. Aggregates o f anhedral grains less than 100 microns i n size. Rare aggregates o f titanite mantle rutile. Some regions contain a second titanite population distinguished b y euhedral, diamond-shaped grains, approximately 200 microns in size. 0-10%  Actinolite A c i c u l a r and bladed, euhedral to euhedral pale green laths ( i n PP), less than 100 microns i n size. O n l y present at the contact w i t h actinolite-rich breccia.  0 . 5 % R u t i l e - Rare anhedral grains mantled b y titanite. 0 . 5 % Opaque? Can be d i f f i c u l t to distinguish f r o m titanite aggregates. A n h e d r a l crystals less than 100 microns i n size. Breccia is cross-cut by quartz, calcite and chlorite veinlets.  186  Fragments: A. Biotite-rich Greenstone: Fragments are variable i n shape (elongate, pseudo-triangular, pseudo-rectangular, oval and irregular i n shape), are subrounded to subangular, and range f r o m 1 to 8 m m i n size. Protolith can not be identified. The overall texture is fine grained and dominated b y the decussate texture o f the biotite 5 0 - 9 0 % B i o t i t e - Tabular and irregular grains, e x h i b i t i n g decussate texture. M o s t l y less than or equal to 0.1 m m in size but can be as large as 1 m m . Grains can be partially altered to chlorite. 0 - 4 5 % Chlorite - Occurs as fine, scaly, anhedral patches and may be partially replacing biotite. 0 - 4 5 % Calcite - A n h e d r a l grains w i t h irregular grain boundaries, mostly less than 0.1 m m to 0.2 m m but can vary locally up to 1mm in size. Grains are present w i t h i n the fragment but also straddling the fragment boundary suggesting calcite crystallized at a later stage, perhaps part o f f l u i d i z a t i o n event f r o m veinlets. Can be f o u n d p o i k i l i t i c a l l y enclosing biotite. 0.5-10% Titanite/Epidote - Can not distinguish between the t w o minerals i n t h i n section. Occurrs as aggregates o f anhedral grains less than 100 microns i n size. 3 % Quartz/Feldspar anhedral, irregular and rounded grains, m o s t l y less than or equal to 0.1 m m but can be up to 0.3 m m i n size. G r a i n boundaries are i n t e r l o c k i n g and can be j a g g e d or smooth. Can be f o u n d s u b - p o i k i l i t i c a l l y enclosing biotite. Fragments are cross-cut by calcite, quartz and chlorite veinlets w h i c h c o u l d attribute to their variation i n mineralogy.  B. Titanite-rich Greenstone: Fragments are subangular to subrounded, pseudo-oval i n shape and approximately 3 m m i n size. Protolith can not be identified. The overall texture is fine-grained and granoblastic. 2 5 - 4 0 % Quartz/Feldspar - A n h e d r a l , smooth, interlocking grains, less than 0.1 m m . 2 5 % - 4 0 % B i o t i t e - Tabular and irregular grains less than 0.1 m m . Can be partly replaced b y chlorite. 5 - 1 5 % Chlorite - Occurs as very small, fine, scaly, patches. 15-20% Titanite/Epidote - Aggregates o f anhedral grains less than 0.1 m m i n size. 3 - 5 % Calcite - A n h e d r a l grains w i t h irregular grain boundaries, ranging f r o m 0.1 to 0.3 m m i n size.  187  C. Greenstone: Fragments are variable i n shape (pseudo-oval, elongate and irregular), are subrounded to subangular w i t h irregular grain boundaries, and range f r o m 1 m m to 1cm i n size. Protolith can not be identified. The overall texture is fine-grained and decussate. A f e w o f the fragments are faintly foliated.  8 0 - 9 0 % Chlorite - Appears like t w o population present; fine, scaly chlorite w i t h first order interference colours and m u c h less c o m m o n tabular grains w i t h anomalous interference colours. 1-10% B i o t i t e - Tabular and irregular grains less than 0.1 m m i n size. Partly altered to chlorite. 1-5%) Quartz/feldspar - A n h e d r a l grains w i t h irregular grain boundaries, 0.1 m m i n size. 1-10% Calcite - A n h e d r a l grains w i t h irregular grain boundaries, 0.1 m m i n size. 0- 3 % Titatite - Less than 0.1 m m , euhedral crystals.  D. Quartz/Feldspar-rich Greenstone: Fragments are spherical, oval and irregular i n shape, are subrounded to rounded, and range f r o m 1 m m to7 m m i n size. The protolith for these clasts can not be identified; c o u l d be a fine-grained volcanic or sedimentary rock. The overall texture is fine-grained, granoblastic, w i t h inequigranular texture 8 0 - 9 0 % Quartz/feldspar - Anhedral grains, less than or equal to 0.1 m m i n size, w i t h i n t e r l o c k i n g j a g g e d or smooth grain boundaries. Can be s u b - p o i k i l i t i c a l l y enclosing biotite. 1- 1 0 % B i o t i t e - Tabular and irregular grains, less than or equal to 0.1 m m i n size. Can be partly replaced b y chlorite. 5 - 1 0 % Calcite - A n h e d r a l grains w i t h irregular grain boundaries, m o s t l y less than or equal to 0.1 m m but can be up to 2 m m in size. 1 % Titanite - Aggregates o f anhedral grains, less than 0.1 m m i n size??  E. Metamorphosed Coarser-grained Amphibole-bearing Igneous Rock: Fragments are rounded, spherical to elongate i n shape, and range f r o m 4 m m to 2 c m i n size. The r o c k is h o w converted to amphibole-bearing greenstone. I t is fine-grained, inequigranular, granoblastic w i t h relic coarser-grained igneous texture.  3 - 1 5 % A m p h i b o l e Porphyroblasts - A m p h i b o l e forms d i a m o n d and prismatic, euhedral crystals, on average 0.3 to 0.8 m m i n size. M o s t crystals are completely pseudomorphed by 188  r a n d o m l y i n t e r l o c k i n g , euhedral biotite grains. The pseudomorphs occur w i t h occasional calcite and are partly altered to chlorite. A t the contact w i t h Phase 2, the amphibole is a relic. The relics are pale green ( i n plane polarized l i g h t ) , euhedral, columnar shaped amphiboles w h i c h range i n size f r o m 0.1 to 0.5 m m . The crystals are partly or completely altered b y calcite and chlorite and are mantled b y decussate textured biotite. 3 5 - 6 0 % B i o t i t e - Tabular and irregular grains less than 0.1 m m i n size w h i c h depict decussate texture. 7-25% Quartz/Feldspar - Aggregates o f anhedral, less than 0.1 m m i n size, rounded and irregular interlocking grains, w i t h or j a g g e d grain boundaries. 6 - 1 6 % Chlorite - Fine, scaly patches. 5-7%  Titanite - Aggregates o f anhedral grains o c c u r r i n g i n sporadically distributed patches.  7 % Calcite - A n h e d r a l grains w i t h irregular grain boundaries. Some areas calcite occurs as aggregates.  F. Metamorphosed Intermediate-mafic igneous rock: Fragments range i n size f r o m 8 m m to 1.5 c m i n size. T h e y are subrounded, elongate and irregular i n shape. Fragments similar to those metamorphosed fine-grained mafic igneous clasts seen i n Phase 3. The rocks are n o w altered to quartz-biotite-calcite-plagioclase greenstone and exhibit fine grained, inequigranular, granoblastic texture w i t h relics o f igneous felty texture. 10-20% Plagioclase - Euhedral crystals occuring as laths w i t h corroded grain boundaries, on average approximately 0.5 m m i n size. Simple t w i n s observed. Felty relic igneous texture is recognized, that is r a n d o m l y orientated lath-like crystals o f w h i c h some properties are microscopically identifiable. Some grains are pseudomorphed by calcite retaining the original lath-like shape. 2 5 - 4 0 % Quartz/feldspar - A n h e d r a l grains, less than 100 microns i n size and s h o w i n g smooth, i n t e r l o c k i n g grain boundaries. 1-5% Chlorite - Occurs as fine, scaly anhedral isolated patches. 10-15% Calcite - A n h e d r a l grains w i t h irregular grain boundaries, vary f r o m less than 0.1 m m to 0.5 m m i n size. 5-15% Titanite - Aggregates o f anhedral, less than 100 m i c r o n grains. 15-20% B i o t i t e - Tabular and irregular grains less than 100 microns i n size. Some grains are p o k i l i t i c a l l y enclosed b y plagioclase laths and quartz/feldspar anhedral grains.  189  Chloritized Polymict Volcaniclastic Breccia: Sample Number and Field Location: Trench  Sample  E - l (breccia i n contact w i t h p i l l o w basalts) E - l (breccia i n contact w i t h intermediate to mafic intrusive r o c k  KD7242-1.KD7242-2 KD7247  Thin Section Description: The breccia consists o f 60 to 8 0 % m a t r i x and 20 to 4 0 % subangular to rounded, 1 m m to 1 c m sized lithic fragments. T h e breccia is metamorphosed i n the greenschist facies and n o w is an aggregate o f chlorite, calcite, quartz/feldspar, titanite/epidote and biotite (Fig. D 1 S ) .  Mineralogy: 5 0 - 6 0 % Chlorite A n h e d r a l , fine, scaly grains occurring as patches w h i c h are interconnected. T h e patches are usually irregular shaped but can also be rounded or elongate. Part o f this chlorite replaces biotite. 1 5 - 2 5 % Calcite A n h e d r a l crystals w i t h irregular grain boundaries. Average size is 300 microns. Occur mostly as aggregates. Appears intergrown w i t h quartz/feldspar, whereby inclusions o f quartz/feldspar are observed w i t h i n calcite and vice versa. 2 0 - 2 5 % Quartz/feldspar Can not distinguish between the t w o minerals under the optical microscope. A n h e d r a l grains less than or equal to 100 microns i n size w i t h i n t e r l o c k i n g , smooth grain boundaries. S u b - p o i k i l i t i c texture partially enclosing less than 100 m i c r o n acicular crystals o f biotite and chlorite. 3 - 5 % Titanite/Epidote Can not distinguish between the t w o minerals under the optical microscope. Appears to have t w o populations o f titanite; occurring both as aggregates o f anhedral grains less than 100 microns i n size and as anhedral to subhedral diamond-shaped and prismatic larger crystals u p to 250 microns i n size. 0 - 3 % Biotite O n l y observed i n sample K D 7 2 4 7 . Occurs as tabular and irregular crystals, up t o 0.25 m m i n size w h i c h show chlorite alteration. B i o t i t e m a y have been present i n sample K D 7 2 4 2 but has n o w been completely chloritized?  Fragments: A . Chlorite-rich Greenstone: Fragment is 1.5 c m i n size, pseudo-oval i n shape w i t h irregular grain boundaries. P r o t o l i t h can not be identified. Texture is fine grained and decussate.  190  8 7 % Chlorite - Appears like t w o p o p u l a t i o n present; fine, scaly chlorite w i t h first order interference colours and m u c h less c o m m o n tabular grains w i t h anomalous interference colours. 10% Quartz/feldspar - A n h e d r a l microporphyroblasts w i t h irregular grain boundaries. Size varies f r o m less than 100 microns to 500 microns. Some larger grains show undulose extinction.  3 % B i o t i t e - Tabular and irregular grains up to 0.2 m m i n size. A l t e r e d to chlorite.  B. Metamorphosed maficfiner-grained(hypabyssal?) igneous rock: Fragments range i n size f r o m 2 m m to 8.5 m m i n size. T h e y are subrounded, elongate i n shape and comprise o f the m a j o r i t y o f the fragments i n t h i n section K D 7 2 4 7 . This sample was taken at contact w i t h mafic intrusive rock w h i c h c o u l d suggest that these fragments are representative o f that rock. The texture is fine grained, granoblastic w i t h relics o f igneous felty texture. 2 3 % Plagioclase - Subhedral crystals occuring as laths w i t h corroded grain boundaries, on average approximately 0.5 m m i n size. Simple twins observed. Felty relic igneous texture is recognized. This texture is defined as randomly orientated lath-like crystals o f w h i c h some properties are microscopically identifiable. 3 0 % Quartz/feldspar - A n h e d r a l grains, less than 100 microns i n size and showing smooth, interlocking grain boundaries. Appears to be i n t e r g r o w n w i t h calcite. 2 2 % Chlorite - Occurs as fine, scaly anhedral interlocking patches and as an alteration product o f biotite. 17% Calcite - A n h e d r a l grains w i t h irregular grain boundaries up to 0.5 m m i n size. Subp o i k i l i t i c a l l y enclosing biotite and quartz. 5 % Titanite - Aggregates o f anhedral, less than 100 m i c r o n grains. Some aggregates appear to be m a n t l i n g and f o r m i n g irregular lines cross-cutting fragments suggesting secondary i n origin. 3 % B i o t i t e - Tabular and irregular grains equal to or less than 100 microns i n size. Partially altered to chlorite.  C. Quartz/feldspar—rich Greenstone: Fragments range f r o m 2 m m to 8 m m in size, are rounded to subangular, variable i n shape (pseudo-oval, pseudo-rectangular, pseudo-triangular and irregular) and have irregular boundaries. H i g h l y variable in mineralogy but stand out f r o m other types o f fragment due to h i g h abundance o f quartz/feldspar. The p r o t o l i t h for these clasts can not be identified; c o u l d be a fine-grained volcanic or sedimentary rock. 5 0 - 9 5 % Quartz/feldspar - A n h e d r a l grains, less than 100 microns i n size. The grain boundaries are smooth and interlocking.  191  5 - 2 5 % Calcite - A n h e d r a l grains w i t h irregular grain boundaries, up to 0 . 5 m m i n size. M o s t l y occur as aggregates. I n t e r g r o w n w i t h quartz/feldspar. 0 - 2 5 % Chlorite - Occurs as fine, scaly patches and tabular grains. N o biotite grains observed i n fragment but tabular grains p r o b a b l y pseudomorphs o f biotite. 0 - 3 % Titanite - Appears to be t w o populations present, occurring as both aggregates o f anhedral grains and anhedral, diamond-shaped crystals. Grains less than or equal to 100 microns i n size. Some fragments are cross-cut b y chlorite veinlet.  D. Metamorphosed fine-grained mafic igneous rock: Fragments range f r o m 2 to 16 m m i n size, and are rounded and spherical i n shape. The p r o t o l i t h for these rocks is l i k e l y to be an aphyric intermediate-mafic volcanic rock. Some relic plagioclase laths discernible o f igneous texture were identified. The sample was taken f r o m breccia dike w h i c h intruded p i l l o w basalts but these igneous fragments do not resemble adjacent basalts. The rock n o w consists p r i m a r i l y o f a greenschist metamorphic mineral assemblage. 3 0 - 3 5 % Quartz/feldspar - A n h e d r a l grains, less than 100 microns i n size w i t h smooth, i n t e r l o c k i n g grain boundaries. Some appear to occur as pseudomorphs o f relic plagioclase laths e x h i b i t i n g symplectic intergrowth o f quartz. 3 0 % Calcite - A n h e d r a l grains w i t h irregular grain boundaries, less than 100 microns i n size. Occur mostly as aggregates. 25%o Chlorite - Occur as fine, scaly anhedral interlocking patches and acicular crystals (possibly pseudomorphs o f biotite). 10-15% Titanite - T w o populations; the m a j o r i t y are aggregates o f anhedral grains less than 100 microns and a f e w subhedral crystals.  192  193  194  195  Figure D I : Photomicrographs o f the p o l y m i c t volcaniclastic breccia (pvb). A . Typical pvb matrix e x h i b i t i n g inequigranular texture, B. Pvb groundmass, C. S p o l i a t i o n defined by the preferred alignment o f acicular actinolite and chlorite grains, D. Large epidote grain g r o w i n g into biotite, E. Large epidote grain interleaved w i t h chlorite, F. Large epidote grain w i t h pressure shadow o f chlorite and biotite, G. Large biotite grain interleaved w i t h chlorite, H . Hornblende grains e x h i b i t i n g simple t w i n n i n g , I. N o r m a l ? zoned hornblende, J. Hornblende partially replaced by biotite, L. B l a d e d hornblende grain pseudomorped by biotite, M . Hornblende grain mantled by actinolite, N. A c t i n o l i t e porphyroblast, O. Hornblende grain mantled by actinolite w i t h the actinolite tail g r o w i n g into the foliated matrix. P. Secondary opaques e x h i b i t i n g a network pattern. Q. M a t r i x o f the biotized pvb e x h i b i t i n g inequigranular texture. Note the pseudomorphed d i a m o n d shaped hornblende grain n o w decussate textured biotite. R. Groundmass o f biotized p v b d o m i n a n t l y composed o f fine-grained biotite. S. C h l o r i t i z e d p v b composed o f chlorite, albite and calcite.  196  Lamprophyre: The diamondiferous lamprophyre comprises o f actinolite, epidote, titanite, biotite, quartz/feldspar, hornblende, chlorite and calcite and accessory opaques (pyrite, and u n k n o w n ) , apatite, leucoxene and rutile. I t is fine grained and exhibits hypidioblastic, equigranular t o inequigranular texture. T h e inequigranular texture ( F i g . D 2 A ) is shown by larger grains, w h i c h comprise up 5 % o f the rock, o f hornblende, actinolite, and occasionally biotite and epidote set i n a finer grained m a t r i x o f actinolite ± titanite ± epidote ±calcite ± quartz/feldspar ± biotite ± chlorite ± opaques ( F i g . 2.6C). W e a k , spaced f o l i a t i o n occasionally observed defined b y the alignment o f acicular and bladed actinolite, and biotite grains (Fig. D 2 0 ) .  Mineralogy: 50-80%  Actinolite The actinolite grains are colourless to pale green. The grain size ranges f r o m less than 0.1 m m to 1.3 m m i n size. T h e larger grains ( m o s t l y 0.1-0.5 m m ) are porphyroblasts and poikiloblasts w h i c h are subhedral, columnar, bladed, hexagonal and prismatic i n shape and have serrate grain boundaries. T h e y make up 1 t o 7 % o f the actinolite population and rarely are not present at a l l except f o r N L - 3 6 where they make-up 15-20% o f the actinolite p o p u l a t i o n . T h e y may be t w i n n e d . These actinolite grains are partly or completely altered to biotite, calcite, chlorite and finer grained, bladed actinolite along cleavage planes and grain boundaries (Fig. D 2 K ) . T h e porphyroblasts m a y occur w i t h epidote, and calcite aggregates or are surrounded b y them. T h e bladed and d i a m o n d shaped actinolite porphyroblasts m a y be pseudomorphs o f hornblende. The finer grains less than 0.1 m m i n size and are bladed, d i a m o n d shaped and acicular. T h e y make up the m a j o r i t y o f the matrix. I n some t h i n sections the bladed grains were occasionally interleaved w i t h or s u b - p o i k i l i t i c a l l y enclosed b y biotite. They may be associated w i t h biotite and calcite. W h e r e a f o l i a t i o n is observed it is the weak alignment o f these grains w h i c h define it. Stringers o f preferentially orientated bladed actinolite and interleaved biotite m a y be observed. T h e finer grains m a y occur i n 0.5 to 2 m m elongate, lamellar, round or oval patches i n w h i c h the actinolite m a y show similar orientation. These patches m a y occur w i t h fine r a n d o m l y orientated fine, scaly chlorite, biotite and/or titanite. Some o f the patches appear like they may be pseudomorphs o f actinolite porphyroblasts.  1-15% Epidote: The epidote grains are colourless or more c o m m o n l y pale y e l l o w w i t h patchy d i s t r i b u t i o n indicative o f higher Fe content i n these grains. T h e grains occur as euhedral to anhedral columnar, lamellar, bladed and rare d i a m o n d shaped i n d i v i d u a l grains, and granular aggregates. T h e y range f r o m 1 m m t o less than 0 . 1 m m i n size. T h e coarser grains have serrate grain boundaries and m a y occur  197  w i t h biotite ( F i g . D 2 N ) , actinolite, quartz/feldspar and interleaved w i t h chlorite. The grains m a y s u b - p o i k i l i t i c a l l y or p o i k i l i t i c a l l y enclose acicular actinolite grains and m a y be s u b - p o k i l i t i c a l l y or p o i k i l i t i c a l l y enclosed by biotite. Inclusions o f leucoxene, calcite and titanite may be f o u n d w i t h i n the larger grains. I n some areas the coarser grains appear deformed noted by the bent cleavage ( F i g . D 2 N ) , and undulose extinction. Rare pressure shadows m a y be observed comprised o f biotite and chlorite. These coarser grains m a y be pseudomorphs after an u n k n o w n mineral. The finer grains occur w i t h acicular and bladed actinolite, titanite, biotite, opaques and quartz/feldspar. I n some cases the fine grained aggregates occur as stringers. These finer grains can be d i f f i c u l t to distinguish f r o m titanite. 1-10% Titanite Occur as aggregates o f anhedral grains less than 0.1 m m i n size and anhedral to euhedral, d i a m o n d shaped i n d i v i d u a l grains. Rare aggregates occur up to 1mm i n size. Some aggregates are m a n t l i n g rutile. M a y occur w i t h i n hornblende pseudomorphs, actinolite porphyroblasts, biotite grains and chlorite patches. Titanite can be d i f f i c u l t to distinguish f r o m epidote.  1-30%  Biotite Occurs as anhedral to subhedral tabular, hexagonal cross-sections and irregular crystals, ranging f r o m 0 . 1 m m to 1.3 m m i n size and may have serrate grain boundaries. Grains can be partly replaced b y or occasionally mantle b y chlorite ( F i g . D 2 B ) . Some are s u b - p o i k i l i t i c a l l y and p o k i l i t i c a l l y enclosing d i a m o n d shaped and bladed amphibole, calcite plates, anhedral epidote grains, smaller biotite laths, and possibly apatite (?). M a y occur w i t h epidote, calcite and epidote contain inclusions o f titanite, calcite, opaques, and epidote and tabular grains m a y be interleaved w i t h chlorite or actinolite. B i o t i t e c o m m o n l y occurs w i t h decussate texture w h i c h most l i k e l y represents amphibole pseudomorphs due to their overall bladed, d i a m o n d and columnar forms. Grains, usually greater than 0.2 m m , may show evidence o f deformation marked by bent cleavage or undulose extinction ( F i g . D 2 C ) . I n some t h i n sections the larger grains appear to have a preferred alignment (lineation?). Rare stringers o f biotite less than 0.1 m m i n size w i t h preferred alignment were observed.  1-15% Quartz/feldspar Can not distinguish between the t w o minerals under the optical microscope. Occurs w i t h i n m a t r i x w h i c h sometimes appears to be interstitial (grain boundaries not defined). Grains are anhedral, less than 0 . 1 m m to 0.8 m m i n size and m a y occur as small aggregates. The grain boundaries o f the aggregates may be smooth, interlocking, and sutured. The anhedral grains may exhibit radial extinction (Fig. D 2 E ) , undulatory extinction and simple t w i n n i n g . The grains m a y be p o i k i l i t i c a l l y enclosing biotite, actinolite, leucoxene, epidote, and calcite. Some grains appear to have a faint lath shape (?). Quartz/feldspar is  198  least present i n N L - 5 1 distinguishing this rock s l i g h t l y f r o m the other lamprophyre t h i n sections. 0 - 5 % plagioclase Grains are anhedral, less than 0.1mm to 0.8 m m i n size. The anhedral grains may exhibit polysynthetic t w i n n i n g (Fig. D 2 D ) and simple t w i n n i n g . The grains m a y be p o i k i l i t i c a l l y enclosing biotite, actinolite, leucoxene, epidote, and calcite. Some grains appear to have a faint lath shape (?). 0-5% microcline Grains are anhedral, less than 0.1mm to 0.8 m m i n size. The anhedral grains exhibit tartan t w i n n i n g ( F i g , D 2 F ) . The grains m a y be p o i k i l i t i c a l l y enclosing biotite, actinolite, leucoxene, epidote, and calcite.  0 - 7 % Hornblende: Hornblende occurs as light b r o w n to olive green pleochroic crystals w h i c h are subhedral to euhedral, columnar, prismatic, bladed, lamellar and d i a m o n d i n shape. G r a i n boundaries are serrated. T h e y m a y exhibit simple t w i n s and rare z o n i n g ( F i g . D 2 G , I ) . The crystals range f r o m 0.1 to 4 m m i n size. The grains can be partly or almost completely altered b y actinolite, biotite, and calcite along grain boundaries or cleavage planes m a k i n g them d i f f i c u l t to recognize f r o m actinolite porphyroblasts discussed above ( F i g . D 2 K ) . Where they have been almost completely replaced their original f o r m can still be determined under the cross polars. The hornblende may be mantled b y actinolite and/ or chlorite (Fig. D 2 H ) . Rare possible pressure shadows comprised o f chlorite were observed ( F i g . D 2 L ) . Some grains maybe pseudomorphed b y decussate textured biotite distinguished b y distinct amphibole outlines ( F i g . D2J). Possible relict mineral w h i c h c o u l d be primary? H o w e v e r , i n one t h i n section appeared to be replacing possibly a t h i r d type o f amphibole 1.4 m m i n size. 0 - 5 % Chlorite M o s t l y o c c u r r i n g interleaved w i t h biotite or as fine scaly patches. The patches are r o u n d and elongate i n shape and may contain biotite, bladed actinolite, titanite, epidote and/or opaques. Occasionally chlorite occurs w i t h epidote w h i c h may represent a pseudomorph o f an u n k n o w n mineral. . 0 - 1 0 % Calcite: Subhedral to anhedral, irregular, rounded and rare lath-like crystals w i t h irregular grain boundaries. M a j o r i t y o f crystals are on average less than 0.1 m m i n size but can be up to 0.4 m m . Occur sometimes as aggregates w h i c h rarely appear as partially m a n t l i n g hornblende. Aggregates may occur w i t h biotite, actinolite, and quartz/feldspar. Some grains appear to be p o i k i l i t i c a l l y enclosed b y actinolite and sometimes p o i k i l i t i c a l l y enclosing actinolite, cubic opaques  199  (pyrite?) and quartz/feldspar. Calcite m a y contain inclusions o f quartz/feldspar, biotite, titanite and apatite (?). 0- 1 % Opaques Opaques are anhedral to euhedral, cubic and rare triangular i n shape. The grains are less than 0.1 m m to 0.8 m m in size. Grains m a y be altered to leucoxene along the grain boundaries. Rare grains appear clustered i n a n e t w o r k pattern w i t h calcite and actinolite. Some grains m a y be p o i k i l i t i c a l l y enclosed b y hornblende, actinolite porphyroblasts, calcite and quartz/feldspar or may occur w i t h i n chlorite patches. Occasional skeletal texture observed w i t h opaque enclosing actinolite or calcite ( F i g . D 2 M ) . Rare grains have distinct cubic shape and are probably pyrite. 1- 2%o FeOxide or Rutile Orange i n colour, anhedral, h i g h relief, upper order interference colours, occurs w i t h biotite and epidote. 0-1%  Leucoxene Red coloured, anhedral, irregular grains. The grains are less than 0 . 1 m m i n size. A n d may occur as inclusions w i t h i n the coarser epidote.  0-0.5%o Rutile A n h e d r a l grains less than 0.1 m m i n size w h i c h are m a n t l e d b y titanite. The lamprophyre rock may be cross-cut b y calcite and quartz/feldspar veinlets.  Fragments: Rare fragments (up to 5%) were observed in t h i n section.  A. Calcite-rich Greenstone: Fragments are angular, rectangular, and up to 8 m m i n size. T h e minerals that comprise these fragments i n decreasing order are calcite, titanite, epidote, actinolite, biotite and opaques. The overall texture is fine-grained and g r a n u l o b l a s t s . P r o t o l i t h is u n k n o w n .  B. Metamorphosed Fine Grained Hornblende-Bearing Igneous Rock: Fragments are rounded, o v a l , and elongate i n shape, and range f r o m 1 m m to 4 m m in size. The rock is n o w converted to a hornblende-bearing greenstone. The minerals that comprise these fragments in decreasing order are amphibole, ± actinolite/sericite, ± C h l o r i t e , ± epidote, ± titanite, ± calcite, and ± biotite. The overall texture is fine-grained w i t h relict equigranular igneous texture.  C. Biotite-rich Greenstone: Fragments are approximately 1 to 8 m m i n size, subrounded, and have an oval shape. The minerals that comprise these fragments i n decreasing order are biotite, chlorite,  200  titanite/epidote, and quartz/feldspar. The overall texture is fine grained and dominated by the decussate texture of the biotite. D. Quartz/feldspar—rich Greenstone: Fragments range from 4 mm to 1 cm in size, are rounded to angular, irregular, oval and elongate in shape, and have irregular boundaries. The minerals that comprise these fragments in decreasing order are quartz/feldspar, ± calcite, ± muscovite/actinolite, titanite/epidote, ± biotite, and ± chlorite. The overall texture is fine grained and equigranular. The protolith for these clasts can not be identified; could be a fine-grained volcanic or sedimentary rock. E. Epidote-rich Greenstone: Fragments are up to 9 mm in size, are subrounded, and oval in shape. The minerals that comprise these fragments in decreasing order are epidote, actinolite, quartz/feldspar, chlorite, titanite, and biotite. The overall texture is fine grained and equigranular. The protolith for these clasts can not be identified. F. Metamorphosed Fine to Grained Actinolite-Bearing Igneous Rock: Fragments are rounded to angular, pseudo-oval, and elongate in shape, and range from 1.7 mm to 3 cm in size. The rock is now converted to an amphibole-bearing greenstone. The minerals that comprise these fragments in decreasing order are amphibole, actinolite/sericite, titanite/epidote, ± biotite, ± calcite, ± chlorite, and ± quartz/feldspar. The overall texture is fine-grained, and inequigranular with relict fine grained, aphanitic, panidiomorphic igneous texture.  201  202  203  Figure D 2 : Microphotographs o f lamprophyre. A . Typical lamprophyre matrix exhibiting inequigranular texture, B. Large biotite grain interleaved w i t h chlorite, C. Large biotite grain w i t h bent cleavage, D. Plagioclase grain e x h i b i t i n g polysynthetic t w i n n i n g . E. Quartz/feldspar crystal w i t h radial extinction, F. M i c r o c l i n e , G. Coarse, normal (?) zoned hornblende, H . Hornblende mantled b y actinolite, I. Hornblende e x h i b i t i n g patchy zonation, J. Hornblende pseudomorphed by decussate textured biotite, K. Larger actinolite grain partly replaced by calcite and biotite, L. Pressure shadow o f chlorite around a hornblende grain, M . Skeletal opaque, N . Epidote intergrown w i t h biotite and e x h i b i t i n g bent cleavage, O. Weak spaced f o l i a t i o n defined by the alignment o f actinolite and coarser biotite grains.  204  Relative Paragenetic Sequence: The t i m i n g o f m i n e r a l f o r m a t i o n relative to the m a i n fabric observed i n the p o l y m i c t volcaniclastic breccia and lamprophyre was examined and is schematically illustrated i n F i g . 1. Hornblende, the coarser grained epidote pseudomorph and occasional biotite appears to be pre- to syn-kinematic based on the presence o f pressure shadows, the actinolite fabric w r a p p i n g around the grains and bending o f cleavage. A l s o hornblende exhibits oscillatory z o n i n g and m a y be partly or completely replaced or pseudomorphed by actinolite, biotite, ± calcite, and ± chlorite. A c i c u l a r actinolite, and some chlorite and biotite are syn-kinematic as their preferred alignment defines the main foliation. Other biotite, chlorite and opaques appear to be post-kinematic as the biotite and chlorite exhibit random orientation, chlorite m a y be partly replacing biotite and the opaques occur i n patches indicating their secondary nature. The t i m i n g o f the quartz/feldspar, m a t r i x titanite/epidote and calcite is u n k n o w n but is mostly l i k e l y syn- to post-kinematic.  Hornblende  Epidote Biotite  .CQacss£j3r.aJn&.....  AMihinjoaalxJx...  DBdDima±Qisins  FaftyafJdbiic".'.'' RarLafiabrJc  Chlorite  decussate..  ....RepladngJaioiite  Calcite Quartz/Feldspar Titanite Secondary patches  Opaques  Syn-Kinematic  Pre-Kinematic  Post-Kinematic  F i g . D 3 : The relative paragenetic sequence o f the volcanic breccia and the lamprophyre based o n the t i m i n g o f the main fabric observed i n t h i n section.  205  Appendix E: Structural Data Table E l : Structural measurements from the detailed 1:100 polymict volcaniclastic breccia trench maps mapped on the Band-Ore Resources GQ Property. Location E-2 E-2 E-2 E-2 E-l E-l E-l E-l E-l E-l E-l E-l E-l E-l E-l E-l BZ BZ BZ BZ BZ BZ BZ BZ BZ  Dip 30 32 60 30 10 25 30 18 46 35 40 30 46 30 10 37 66 45 42 45 33 27 32 45 24  BR-1 BR-1 BR-1 JR-14-1 JR-14-1  25 40  Dip Direction 73 0 10 54 47 67 78 355 112 90 119 80 55 55 260 112 71 109 102 30 35 65 37 17 68 41  Measurement Type S cleavage S cleavage S cleavage S cleavage S cleavage S cleavage S cleavage folded quartz vein S cleavage 2  2  2  4  4  4  4  4  S cleavage S cleavage S cleavage S cleavage S cleavage lineation on S plane 4  4  4  4  4  2  S cleavage contact S cleavage S cleavage S cleavage S cleavage S cleavage S cleavage S cleavage S cleavage 4  4  2  2  2  4  2  2  2  "lithology pvb pvb pvb pvb pvb pvb pvb pvb pvb pvb pvb pvb pvb pvb pvb pvb pvb/lamp lamp pvb pvb pvb pvb pvb pvb pvb  75 30 32  20 19  S cleavage S cleavage S cleavage  imi pvb pvb  44 43  S cleavage S cleavage  pvb pvb  JR-14-2  45  19  S cleavage  JR-14-2  60  45  S cleavage  pvb pvb  DE-1  50 78 84  331 142  S S S S S  DE-1 DE-1 DE-2 DE-2 DE-3 DE-3 DE-3 SE-F  10  227 355 2 21  25 68 32  10 105 28  SE-F  45  5  65 27  2  2  2  2  2  2  2  imi  cleavage cleavage cleavage cleavage cleavage  imi pvb pvb pvb  S cleavage S cleavage  pvb pvb  S cleavage S cleavage S cleavage  pvb pvb pvb  2  4  4  2  2  2  2  4  2  2  "lithology: pvb - polymict volcaniclastic breccia; lamp - lamprophyre; imi - intermediate to mafic intrusive rock.  206  +  B.  F i g u r e E l : Plane to pole stereonets o f A. S cleavage and B. 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Rock Type Polymict Volcaniclastic Breccia NL-11 Sample NL-11 NL-12 Number 4 3 8 "Grain Type  M  M  M  Si0 Ti0  0.42  0.94  0.1  0.13  2.66 36.42 48.39 0.23 2.74 -  3.72  1.03 0.15 5.4  39.46 43.74 0.86 2.72 -  45.66 39.38 0.49 1.71 0.52  2  2  A1 0 2  3  Cr 0 FeO MgO MnO CaO NiO 2  vo 2  3  3  Total  -  -  -  0.4  0.46  0.17  91.72  92.34  94.54  Grain Abbreviations: M - matrix grain (< 0.1 mm). - Blanks are below the minimum detection limit  a  224  oo  om  CN i n  SI 8'  in  so CN  o  so  r--  oo  —  CN  t-  oo  So  ™  ^  .  f5  CJ  SO  00 ©  CN  r  ~  _  ,  o  m  s  oo  o  CN  -C3  C  CN OO  i n r n  m m  00  r-' d  d d  S g 2  CN  i n  —'  3  d  as  so  CN  O  CN  a s m  O  O  O  CN  c  in  N  CN  C  N  so  —  i n  i  CN  o oo  ©  n  CN  i n  •^r  cn cn  CN  os  CN  c n  d  oo  so  CN  —<  —'  TJ-  r n  C—  cn  O  n o. d  i n  cn  N  s o os CN  c n CN  m  CN  ON  t  d  ON CN  B cj  JH 3  o O CD OJ)  CN r~  r-'  00 ©  ©  -  m  ©  so so m so  oo  ©  t-;  as OS  so —'  l  22 — I CN  r-  — OS  OS SO  ^  m  m  © ©  CN 0  '  ©  CN ^  C N C N _ . 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CN '—  ON ON  ,—1 0  sf  — CN  CN OO  0  sf CN d  NO  uo  © o  •  NO  CM  g  ON  £ S  2 P o ®  •c CJ  E —H  C  >  ro  uo -J  N CQ  Z  ^cj «IH "CJ CM  ON ON  uo sf  00  © C ^ . uo  uo CN  r~  sf NO  © NO  ©  00  CO  © ©  CN  ©  00 00  ON  ©  d  ON  CN d  ON  ©  00 CN ©  co NO  NO  CN CO  00  00  ON  d  ©  © NO  CN  — — © zz  sf  NO  00  sf sf CO  —  uo © ro 0  O  sf  ©  ci  *S ^  2  NO  UO  (N CT\  ^  NO  sf  1  0  —  S P. £  ON  3  cu  a. >> H  u o  H  E  o 00  o  H  O O O O o —•  cj  JS J-i  cd  < uZ S 2 u  o cd  S ^ 1  z^  9  eu Cu  I  a, J (-  228  u  O  U  cd CQ  Appendix I Analytical Precision for Geochemical Analyses Calculations for Analytical Precision: A n a l y t i c a l precision was estimated b y calculating the 9 6 % confidence l i m i t or 2 a , sample variance (s ), and relative standard deviation ( R S D ) f o r the representative w h o l e r o c k analyses o f the W a w a metavolcanic rocks (Tables 11-14). Estimates f o r 2 a are g i v e n as the standard error o f the mean, given b y : 2a = 2*a W(N-l) where a is the standard deviation o f the analytical runs and N is the number o f analytical runs. The sample variance is the square o f the standard deviation ( s or a ) . 2  2  Estimates o f precision are given b y the percent relative standard deviation ( % R S D ) w h i c h is given b y : % R S D = 100 * a/|x where a is the standard deviation o f the analytical runs and \i is the mean o f the analytical runs.  229  Table II: Sample standard deviation (<r), variance (cj ), relative standard deviation (RSD) and detection limits for lamprophyre bulk rock geochemistry analyses.  Element  Mean n=9  ST  Avg. a  Si0 (wt%) 2  48.88  3.77  0.42  2.81  2  0.84  0.52  0.06  0.04  Ti0  A1 0  Sum of squares  2a  Avg. %RSD  Range  Detection Limits (ppm)  0.31  22.50  0.42  0.83  46.48-52.24  60  0.00  0.35  0.05  6.13  0.443-1.06  35  Avg. a  2  9.30  6.39  0.71  7.39  0.82  59.11  0.68  7.32  3.26-11.53  120  Fe 0 T  10.12  1.63  0.18  0.52  0.06  4.18  0.18  1.79  8.6-10.99  30  MnO  0.17  0.04  0.00  0.00  0.00  0.00  0.00  2.39  0.151-0.215  30  MgO  14.54  8.34  0.93  11.34  1.26  90.75  0.84  5.97  10.12-19.81  95  CaO  9.28  3.05  0.34  1.98  0.22  15.87  0.35  2.86  7.16-12.22  15  Na 0  1.87  2.38  0.26  0.99  0.11  7.90  0.25  13.75  0.24-3.3  75  K 0  2.14  3.14  0.35  1.39  0.15  11.14  0.30  14.65  0.12-3.77  25  P2O5  0.36  0.21  0.02  0.01  0.00  0.05  0.02  5.86  0.245-0.432  35 100  2  2  3  3  2  2  LOI  2.62  1.98  0.22  0.75  0.08  5.96  0.22  7.97  1.29-4.25  Total  100.12  0.70  0.08  0.07  0.01  0.56  0.07  0.09  99.72-100.4  Cr (ppm)  1042.67  685.42  76.16  76573.25  8508.14  612586.00  69.18  7.41  677-1600  Ni  538.67  439.35  48.82  36014.50  4001.61  2881 16.00  47.44  9.08  293-916  3  Co  52.89  11.63  1.29  23.61  2.62  188.89  1.21  2.03  45-61  10  Ba  585.13  647.44  80.93  67222.11  8402.76  537776.88  64.82  13.44  229-957  17  15  Table 12: Sample standard deviation (cj), variance (a ), relative standard deviation (RSD) and detection limits for matrix-supported polymict volcaniclastic breccia bulk rock geochemistry analyses. 2  Element  Mean n=10  Si0 (wt%) 2  2  Avg. %RSD  Range  Detection Limits (ppm)  2.34  1.61  40.45-54.19  60  0.11  4.48  0.476-1.04  35  1.88  9.36-12.38  120  1.21  3.57  8.63-15.03  30  0.02  4.52  0.13-0.24  30  5.61  9.26-17.80  95  1.44  6.98  6.12-11.85  15  0.92  18.93  0.10-4.60  75  0.63  18.03  0.23-3.50  25  0.11  0.07  12.14  0.15-0.48  35  67.04  1.82  15.80  1.17-9.94  100  0.87  0.21  0.08  99.80-100.74  60379.16  5434124.50  518.03  13.94  516-3207  8331.76  749858.10  192.43  12.11  247-1252  3  146.32  14.63  1316.90  8.06  5.50  36-79  10  48393.34  4839.33  435540.10  146.66  15.93  60-716  17  Sum of squares  2CT  ST  Avg. a  47.50  7.67  0.77  12.35  1.23  111.14  0.85  0.38  0.04  0.03  0.00  0.23  AI2O3  11.45  2.15  0.21  0.78  0.08  7.05  0.59  Fe 0 T  11.32  4.04  0.40  3.29  0.33  29.58  MnO  0.18  0.08  0.01  0.00  0.00  0.01  MgO  12.43  6.97  0.70  7.37  0.74  66.33  1.81  CaO  8.70  6.07  0.61  4.56  0.46  41.74  Na 0 2  1.82  3.44  0.34  1.89  0.19  16.99  K 0 2  1.25  2.26  0.23  0.90  0.09  8.13  P2O5  0.26  0.32  0.03  0.01  0.00  LOI  4.48  7.07  0.71  7.45  0.74  Total  100.25  0.82  0.08  0.10  0.01  Cr (ppm)  1098.50  1531.67  153.17  603791.61  Ni  481.70  583.27  58.33  83317.57  Co  53.90  29.67  2.97  Ba  381.70  608.13  60.81  Ti0  2  3  V  S  T  Avg. a  230  2  15  Table 13: Sample standard deviation (rj), variance (rj ), relative standard deviation (RSD) and detection limits for clast-supported polymict volcaniclastic breccia bulk rock geochemistry analyses. 2  Element  Mean n=5  Sf  Avg. a  S x  Avg. a  2  Sum of squares  2cj  Avg. %RSD  Range  Detection Limits (ppm) 60  Si02 (wt%)  50.96  8.00  1.60  20.80  4.16  83.19  4.56  3.14  47.86-58.96  Ti02  0.84  0.20  0.04  0.01  0.00  0.04  0.10  4.79  0.71-0.94  35  A1203  12.76  2.17  0.43  1.64  0.33  6.55  1.28  3.40  10.59-13.80  120  Fe203T  10.11  2.45  0.49  1.67  0.33  6.70  1.29  4.85  8.79-11.94  30  MnO  0.16  0.05  0.01  0.00  0.00  0.00  0.03  5.79  0.11-0.20  30  MgO  9.68  4.77  0.95  9.32  1.86  37.27  3.05  9.86  5.32-13.90  95  CaO  9.01  2.86  0.57  2.58  0.52  10.31  1.61  6.35  6.38-10.39  15  Na20  2.99  1.32  0.26  0.41  0.08  1.64  0.64  8.86  2.34-3.71  75 25  K.20  1.16  2.26  0.45  1.13  0.23  4.53  1.06  38.87  0.11-2.43  P205  0.21  0.21  0.04  0.01  0.00  0.04  0.10  20.09  0.10-0.32  35  LOI  2.43  2.03  0.41  0.90  0.18  3.61  0.95  16.75  1.44-3.54  100  Total  100.30  0.45  0.09  0.06  0.01  0.24  0.25  0.09  99.90-100.52  Cr (ppm)  620.00  449.00  89.80  68623.50  13724.70  274494.00  261.96  14.48  244-967  Ni  278.60  241.80  48.36  21567.80  4313.56  86271.20  146.86  17.36  72-481  3  Co  44.80  18.40  3.68  145.20  29.04  580.80  12.05  8.21  28-62  10  Ba  352.00  746.00  149.20  120250.50  24050.10  481002.00  346.77  42.39  19-770  17  15  Table 14: Sample standard deviation (cr), variance (a ), relative standard deviation (RSD) and detection limits for juvenile material bulk rock geochemistry analyses. Element  Mean n=4  Sy  Avg. a  Si02 (wt%)  S  2 T  Avg. a  2  Sum of squares  2CT  Avg. %RSD  Range  Detection Limits (ppm)  48.77  3.21  0.80  3.84  0.96  12.07  2.32  1.64412  45.99-50.78  60  Ti02  0.84  0.23  0.06  0.10  0.02  0.05  0.14  6.7078  0.72-1.00  35  A1203  9.71  3.50  0.88  4.20  1.05  12.06  2.32  9.02528  7.74-12.33  120  Fe203T  11.27  2.69  0.67  2.72  0.68  7.64  1.84  5.96817  10.01-13.60  30  MnO  0.21  0.07  0.02  0.01  0.00  0.01  0.05  8.17005  0.18-0.27  30  MgO  14.64  5.65  1.41  9.24  2.31  27.22  3.48  9.65373  11.12-17.78  95  CaO  9.14  1.06  0.26  0.52  0.13  0.98  0.66  2.88912  8.67-9.87  15  Na20  1.56  2.23  0.56  1.87  0.47  5.54  1.57  35.8291  0.34-3.44  75  K20  0.60  1.15  0.29  0.66  0.16  1.39  0.78  48.1125  0.14-1.60  25  P205  0.28  0.11  0.03  0.03  0.01  0.01  0.07  9.74088  0.24-0.35  35  LOI  3.33  0.34  0.09  0.05  0.01  0.14  0.25  2.58094  3.03-3.53  100  Total  100.35  0.25  0.06  0.06  0.01  0.06  0.16  0.06271  100.20-100.51  Cr (ppm)  1089.75  573.31  143.33  79050.10  19762.53  263680.75  342.33  13.1523  757-1376  Ni  541.75  337.75  84.44  31230.37  7807.59  99448.75  210.24  15.5861  326-734  3  Co  57.00  15.01  3.75  45.71  11.43  174.00  8.79  6.58382  50-65  10  Ba  196.25  476.60  119.15  66891.17  16722.79  230734.75  320.23  60.7137  22-609  17  231  15  Appendix J Plot of Compositional Variation in Oscillatory-Zoned Hornblende  232  B.  0.5 0.4 0.3 — sa  0.3,  Core  1  Core  t_  0.1  2  0 5  Core  2  3  4  5  Rim  1  Rim  2  Core  F i g u r e J3 Compositional zoning in amphibole f o r sample N L - 1 - 2 7 A .  235  3  4  5  Rim  236  237  F i g u r e J 6 Compositional z o n i n g i n amphibole for sample N L - 1 - 4 5 A .  238  U M  6X1  °3 E  1  © ©  © ©  CN © ©  © ©  CN © ©  NO ©  CN © ©  CO © ©  (N © ©  © ©  d  ©  ©  ©  ©  ©  ©  ©  ©  ©  ©  ©  ©  CN OO CN  NO s f CN  ON NO  sr  NO CN ON  ON CN  CN r o CN  oo r o  CN OO CN  NO NO S t  CN  OO r o r o  oo oo NO  CO © r o  —'  ©  ©  ©  ©  d  d  ©  ©  ©  ©  uo  UO  r o  sr  s t  uo  r o  d  d  ©  d  d  ©  ©  uo  uo  oo  NO  oo  NO  ©  d  ©  d  d  d  s t  UO ©  © ©  ©  d  d  s f ON CN  NO UO r o  d  d  s t  uo  ©  ©  uo ©  CN © ©  CN ©  O  CN © ©  © ©  © ©  ©  ©  ©  ©  ©  NO  OO CN s t  © © CO  © (N s t  CN CN  ©  ©  d  d  d  00  UO  s f  uo  ©  ©  ©  ©  oo  NO  NO  ©'  ©  d  ©  00  NO  00  ON  NO  NO  uo  ©  ©  ©  ©  ©  ©  ©  ©  ©  d  r-~  o  r^  r^ CN  d  d  —*  r o  CN  uo  NO  uo  r o  s t  s t  d  ©  ©  d  ©  ©  ©  ©  NO  uo  NO  s t  00  uo  NO  ©  NO  ©  d  ©  ©  ©  ©  ©  UO  oo  00  d  ©  ©  NO  ©  d ©  CN  uo  CO  ©  NO  uo  ©  d  I  --o O  CB  "-*«-» uo  o  E  S) •O  CU  rV  £  CB  ca  ca  C3  o-i  Vi  Vi  J3  J3  J3  "&  Vi  w  Vi  0-1  o-i  J3  J3 u  J3  J3 cj  B  pvb  B e  ca  "a  a 12 < " § z u B  CO  "a  Trench  H  O  a  CD U  H  a u  LH  H  cj  B £H  CJ  B  LH  f—  H  x:  XI  CJ CJ u  ca  ca  C3  ca  ca  ca  PL] J3  Vi  w  Vi  Vi  UJ  Vi  J3  J3  J3  J3  J3  J3  CJ  CJ  a H  a  a  LH  "a "a "a ~a "a "a "a ~a "a  CJ  B  CJ  CJ  a  CJ Ui  w  J3 CJ  w J3 CJ  a  CJ u  a  CJ u  O  a CJ U  o  a  CJ  a  LH  LH  u H  H  H  H  H  J3  JD > Q.  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MAIN CRYSTAL FORM (form): C : Cubic O: Octahedral C - O : Cubo-octahedral U: U n k n o w n A : Aggregate - C : Coarse (> 0.1mm) - F : Fine ( < 0.1mm) - C / F : heterogeneous occurring as a combination o f both fine and coarse types o f aggregate T w i n n e d Crystal Forms: M : Contact (macle)  P: Interpenetrant  CRYSTAL REGULARITY (res): Robinson (1979) and Otter (1990) apply crystal regularity to distinguish crystal forms that deviate f r o m their equidimensional or regular f o r m , as a result o f inequalities i n facial development d u r i n g the crystal's g r o w t h . The W a w a diamonds were d i v i d e d into equidimensional, slightly distorted, flat, elongate, and irregular according to R o b i n s o n (1979). Flat crystals have one dimension less than 1/3 o f the other t w o dimensions, elongate crystals have t w o dimensions less than 1/3 o f the other dimension and irregular crystals are o f barely determinate f o r m . Irregular crystals that are flat or elongate were included i n the latter t w o categories. Aggregates and t w i n n e d crystals were not considered f o r this category (Harris et al., 1975; Otter, 1990). E Q : equidimensional (regular) D : slightly distorted F : flat E : Elongate IR: Irregular  COLOUR (col): C : colourless BR: b r o w n G Y : grey  Y : yellow BL: black W : white  TRANSPARENCY (tra): TRP: Transparent OP: Opaque  TRL: Translucent (semi-transparent) U: U n k n o w n  RESORPTION (res): Degree o f resorption documented using M c C a l l u m ' s (1994) classification scheme: 1: Class 1: 1 to 55 % preservation 2: Class 2: 55 to 70 % preservation 3: Class 3: 70 to 80 % preservation 245  4: 5: 6: U:  Class 4: 80 to 90 % preservation Class 5: 90 to 99 % preservation Class 6: 99 to 100 % preservation Unknown  - I f resorption was n o n - u n i f o r m then both resorption categories were recorded.  CRYSTAL STATE (sta): ( K a m i n s k y pers c o m m . , 2002) Crystal state refers to whether the diamond is b r o k e n or not (Otter, 1990). I: Intact B: B r o k e n ( t w o or more faces observed; 1 to 2/3 intact) FG: Fragment (1 face observed; 1/3 to 2/3 intact) FC: Fraction (no faces; 0 to 1/3 intact) BR: Breakage ( i f degree o f breakage u n k n o w n ; m a i n l y f o r aggregates and crystals w i t h imbricated g r o w t h faces)  BREAKAGE SURFACE (B.S.): This category is used to discriminate between breakage surfaces that are a result o f brittle deformation post-dating etching and resorption and those that occurred p r i o r to these t w o processes ( f r o m Robinson, 1979): S: subconchoidal fracture surface  CS: cleavage surface  U: u n k n o w n  SURFACE FEATURES: Growth Features: Octahedral Crystals (octa): TP: triangular plates ITP: imbricated triangular plates Cubic Crystals ( O r l o v , 1977; Afanasiev, 2000): H: H u m m o c k SK: skeletal g r o w t h  Secondary Surface Textures: Octahedral Surfaces (octa): SSL: shield-shaped laminae  HPT: hexagonal etch pits containing trigonal etch pits  TP: trigonal etch pits, w i t h either positive ( + ) , negative (-),or u n k n o w n (u) orientation HP: hexagonal etch pits SL: serrate laminae Cubic Surfaces: TTP: tetragonal etch pits, w i t h either positive ( + ) , negative (-),or u n k n o w n ( u ) orientation Tetrahexahedroidal ( T H H ) Surfaces: T: terraces  EH: elongate h i l l o c k s  D e f o r m a t i o n Features: L L : lamination lines Other Surface Features: R: ruts F: frosting  IC: inclusion cavities  246  C S : corrosion sculpture I P : irregular pit  S D : shallow depressions  E B : degrees o f etching on crystal breakage surfaces; 0-none, 1-moderate, 2-  Preliminary Appraisal of Mineral Inclusions: Abundance: (Harris et al, 1975) N : None F: Few (1-3) M : M a n y (>3)  Colour of inclusions: (Otter, 1990) Transparent inclusions: C : colourless (olivine, opx, coesite)  O : orange (garnet)  Opaque inclusions: B L D : black discrete inclusions (sulphide, spinel, graphite) B L N : black n e t w o r k (graphite) C L : cloudy  247  o  o  o  3 X  D  —'  Q  _j o  Z  o  o  o =j  <  m m a in in  in c o  o  X  X  o x  '55 o _c  5  o  2 tu  cx  c  X  a:  1  Q>  o  0)  X  Q  o  re (A  a Q.  ca  T3 C o u a> CO  o. t=  CO  c  T3 C> t sz CO u O  \— CD  a. •a c re  u 3  3  E _re  '•B re 5 re OJ  sz in u  a. x CO CO  a. o a. o  CL X  X  X  X  CO  a.  1  o O (A  ai  IS CO CO UJ  CO  CO  o  o  cc  cn  CO  o  a: m  cn  m  CO  o  CQ  OS  o n  in  o re o  o re u  '35 >» JZ  a. 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A . Sample G Q E 2 - 1 , B. Sample G Q E 2-3, C. G Q E 4-7, D. Sample G Q E 7 - 1 , E.. Sample G Q E 8-2, F. Sample G Q E 8 - 4 , G. Sample G Q E 1 3 - 2 , H . Sample G Q E 13-3, I. Sample G Q E 1 4 - 2 , J. Sample G Q E 1 6 1, K. Sample G Q E 16-2, L. Sample G Q E 17-4, M . sample G Q E 15-1. Abbreviations: F o r m and colour f r o m Table X , A p p e n d i x X ; N t - total nitrogen content, N D - not detected ( < 15 p p m nitrogen present).  259  Form: O-FA Colour: C/BL Nt = 262.l ppm %B = 0  £1.30  4000  3500  2500  2000  1500  2500  2000  1500  1000  Wavenumbers cm"  w  Main A peak  Subsidiary A peak  i  •e i .oo  50(1  1.10  o  r. Xi  £ 1.00  <  < 0.90 0.80 Form: O  Colour: C  Form: C-O-CA Colour: Y/OR 0.90 Nt = 65.7 ppm %B = 0  0.70 Nt = n/a  %B = n/a  4000 0.60  3500  3000  2500  2000  1500  Wavenumbers cm''  1000  500  0.80 4000  if 3500  3000  1000  500  1000  500]  Wavenumbers era"  1  Form: C-0 Colour: C Nt = 39.8 ppm %B = 0  2500  2000  ]"")  1000  500  Wavenumbers cm"'  4000  3500  2500  2000  1500  Wavenumbers era"  1  F i g u r e L 2 Infrared spectrum o f the Type I a A W a w a diamonds. A . Sample G Q E 3 - 1 , B. Sample G Q E 1 0 - 4 , C. Sample G Q E 11-1, D . Sample G Q E 13-5, E. Sample G Q E 14-4, F. Sample 17-3. A b b r e v i a t i o n s : F o r m and colour f r o m A p p e n d i x K, Table K 2 ; N t - total nitrogen content; % B percentage o f B aggregate; n/a - not able to be calculated.  260  1.90  \  \  1.80  1 |  X  \  8 c 1.70  *  ra  o < 1.60  5 1.80 <  3  Form: C-0 Colour: C 1.50 Nt = 81.5 ppm %B = 23  Form: O-CA Colour: C Nt = 274.5 ppm %B = 23 4000  \  3500  3000  2500 2000 1500 Wavenumbers cm"'  1000  500  4000  3500  3000  2500 2000 1500 Wavenumbers cm"'  1000  500  3500  3000  2500 2000 1500 Wavenumbers cm"'  1000  500|  4000  3500  3000  2500 2000 1500 Wavenumbers cm"'  1000  500  2500 2000 1500 Wavenumbers cm"'  1000  500  <1.I0  4000  nr 1.50 3.0  V  VA  -2.6  3500  ' 1.30  \  Form: O-CA Colour: Y Nt= 129 ppm 2.2 %B = 21 4000  , 1.40  \  ' 2.8;  Form: O-CA Colour: C Nt= 165.0 ppm 1.20 %B = 25  V 3000  2500 2000 1500 Wavenumbers cm"'  1000  500|  4000  3500  3000  Figure L3 continues overleaf  261  1.90  11  5 5  r3  X,  1-70 1.60  1.50 Form: C - O Colour: Br Nt = 420.3 ppm 1.30 % B = 13 4000  3500  3000  2500  2000  1500  1000  500|  Wavenumbers cm"'  2.00 2.70:  \  '-2.60  1.90  Ml  <2.50 3 2.40  4000  3500  3000  V  Form: O 1.60 Colour: O N t = 18.8 ppm %B = 27 1.50;  Form: O - C A Colour: C Nt = 246.1 ppm %B = 8 2500  2000  1500  1000  500  4000  3500  3000  2500  2000  1500  1000  500  Wavenumbers cm"'  Wavenumbers cm"'  F i g u r e L 3 Infared spectrum o f Type I a A B W a w a diamonds w i t h < 5 0 % B-defects. A . Sample G Q E 1 - 1 , B. Sample G Q E 2 - 4 , C. Sample G Q E 4 - 5 , D . Sample G Q E 4 - 1 1 , E. Sample G Q E 4 - 1 4 , F. Sample G Q E 5 - 3 , G. Sample G Q E 9 - 1 , H . Sample G Q E 1 6 - 4 , I. Sample G Q E 1 7 - 1 , J. sample G Q E 2 - 2 . Symbols: f o r f o r m and colour are i n Table K 2 , A p p e n d i x K ; N t - total nitrogen concentration. Spectra peaks: 1- hydrogen peak, 2 - C H stretch, 3- m a i n A - d e f e c t peak. 4 subsidiary A - d e f e c t peak, 5 - B-defect spike, 6 - B-defect m a x i m u m peak, 7 - B-defect shoulder at 1100 cm"', 8 - B-defect shoulder at 1010 cm" , 9 - B ' platelet peak. 1  262  BJ 0.50  -0.25 Form: M Colour: C N t = 197.4 ppm %B = 85  \  0.40  -0.30  \  §0.30 -g -0.35  C  •e  3 «  if  o  < CO  i  4000  3500  3000  2500  2000  N  Form: O - C A Colour: C 0.10 N t = 138.5 ppm %B = 69  MAI \  V  -0.45 j  A  0.20  1500  4000  500  3500  3000  2500  1h  •  1  1.10  M  \  c CS Abs 0.50  \  Vv  0.304000  3500  3000  2500  3  2000  1500  Wavenumbers cm'  A \ \ x  §1.10  a <  \  Form: O Colour: Br Nt = 65.8 ppm %B = 63  500  n  1.30  CJ  r  X  1  k  0.90  •£0.70  1000  1500  Wavenumbers cm'  Wavenumbers cm"'  cl  2000  \ \  \V \ 1  1.00 Form: C - C A Colour: Y Nt = 61.8 ppm 0.90 %B = 80  1000  500  V  3500  0.80  3 |  2500  2000  1500  1000  Wavenumbers cm"'  1  Form: O - C A Colour: C 0.80 | Nt = 740ppm %B = 90 1  0.70  2.00 ! 0.60 ; l .90  0.40  4000  3500  3000  2500  2000  1500  Wavenumbers cm'  VA/  1000  1  500  Form: O - C A Colour: Br N t = 131.7 ppm %B = 95 4000  3500  3000  2500  2000  1500  1000  500)  Wavenumbers cm"'  Figure L4 continues overleaf  263  0.5017 4000  I 3500  3000  I 2500 .  2000  Wavenumbers c m  1500  1000  500  1  F i g u r e L 4 Infared spectrum o f Type I a A B W a w a diamonds w i t h > 5 0 % B-defects. A . Sample G Q E 5 - 2 , B. Sample G Q E 6 - 1 , C. Sample G Q E 1 0 - 1 , D. Sample G Q E 1 3 - 4 , E. Sample G Q E 1 4 3, F. Sample G Q E 1 6 - 3 , G. sample G Q E 1 7 - 2 . Symbols: f o r f o r m and colour are i n Table K 2 , A p p e n d i x K; N t - total nitrogen concentration. Spectra peaks: 1- hydrogen peak, 2 - C H stretch, 3- m a i n A-defect peak. 4 - subsidiary A-defect peak, 5 - B-defect spike, 6 - B-defect m a x i m u m peak, 7 - B-defect shoulder at 1100 cm"', 8 - B-defect shoulder at 1010 cm"', 9 - B ' platelet peak,  264  Table L I Results of Wawa diamond IR spectral deconvolution. Samples u.A cm" u.B cm" uD cm" u,T cm" I (B') cm" Err GQE1-1 12.81 0.79 0.15 13.76 0.75 0.15 GQE2-2 0.83 0.06 0 0.90 0.11 0.80 GQE2-4 0.24 3.80 0.15 4.18 0.00 0.15 8.32 0.00 0.00 8.32 GQE3-1 0.00 0.13 GQE4-11 0.47 0.80 14.26 0.73 12.98 3.50 0.34 GQE4-14 6.19 0.36 6.89 0.00 0.41 GQE4-5 9.44 1.68 0.50 11.62 5.50 0.99 2.11 GQE5-2 1.83 0.57 4.51 5.50 0.17 GQE5-3 0.52 0.62 8.63 0.43 7.49 0.75 GQE6-1 2.62 1.20 0.16 3.98 2.60 0.12 22.21 2.14 GQE9-1 0.68 25.03 0.00 0.89 0.52 0.02 GQE10-1 1.49 2.03 0.00 0.03 GQE10-4 15.88 0.00 0.00 15.88 0.00 0.31 GQE13-4 0.74 0.62 0.00 1.36 0.90 0.36 0.00 0.00 GQE13-5 3.98 3.98 0.00 0.58 4.70 8.35 1.72 14.77 0.42 GQE14-3 23.50 GQE14-4 5.82 0.00 0.00 5.82 0.51 0.00 0.44 1.57 0.00 2.01 GQE16-3 1.35 0.19 GQE16-4 11.86 1.03 0.27 13.16 3.50 0.08 GQE17-1 13.72 0.25 0.22 14.19 1.50 0.25 0.54 GQE17-2 0.76 0.00 1.30 0.75 0.20 GQE17-3 4.23 0.00 0.00 4.23 0.00 0.20 * |xA, uB and uD were deconvoluted using least square techniques (e.g. Boyd et al., 1995). 1  265  

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