UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Stratigraphy, petrography and major element mineral chemistry of the Wadi Qutabah Layered Mafic Complex,… Venturi, Chantal Margot 2013

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
24-ubc_2013_spring_venturi_chantal.pdf [ 16.17MB ]
Metadata
JSON: 24-1.0073644.json
JSON-LD: 24-1.0073644-ld.json
RDF/XML (Pretty): 24-1.0073644-rdf.xml
RDF/JSON: 24-1.0073644-rdf.json
Turtle: 24-1.0073644-turtle.txt
N-Triples: 24-1.0073644-rdf-ntriples.txt
Original Record: 24-1.0073644-source.json
Full Text
24-1.0073644-fulltext.txt
Citation
24-1.0073644.ris

Full Text

Stratigraphy, petrography and major element mineral chemistry of the Wadi Qutabah Layered Mafic Complex, Yemen  by Chantal Margot Venturi HBSc, The University of Toronto, 2001 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE COLLEGE OF GRADUATE STUDIES (Environmental Sciences) THE UNIVERSITY OF BRITISH COLUMBIA (OKANAGAN) March 2013 © Chantal Margot Venturi, 2013  Abstract Little is known about the recently discovered Wadi Qutabah Layered Mafic Intrusion in Yemen. It possesses significant potential for the discovery of economic platinum-group element (PGE) and Ni-Cu-Co mineralization, and is believed to be part of the larger Suwar-Wadi Qutabah Layered Mafic Complex. The intrusion was recently dated as being Neoproterozoic in age (~638.5Ma). The current estimated size of the complex is ~250km2. Mineralization has been identified in the Suwar area which lies ~30km to the southeast of Wadi Qutabah. Anomalous platinum mineralization was identified in stream sediment samples that run off of the Wadi Qutabah intrusion. Little is known about the stratigraphy, mineralization, layering and geochemistry of the rocks from Wadi Qutabah. Drill cores from 14 drill holes were used to study the stratigraphy, petrography and mineral chemistry of the Wadi Qutabah intrusion. Methods employed were drill core logging, petrographic analysis and mineral grain analyses using the Scanning Electron Microscope (SEM/EDS). Rocks from the Wadi Qutabah intrusion are medium to coarse-grained cumulate norites and gabbros with minor anorthosite, pyroxenite, and localized massive sulphide layers. Correlation of the layering was accomplished in a broad scale as a result of modal and phase layering, stratigraphic position and textural variations. Lithological unit codes were created for the purposes of correlation and identification for this study. Each of the units/layers is host to unique textures, mineralogy and stratigraphic position. They correlate across stratigraphy from drill hole to drill hole, but lateral changes in alteration and thickness are common. Significant changes in chemistry occur at the top of unit 5a (augite norite) which occurs in the middle of the section. The reversal in chemistry towards more primitive compositions up stratigraphy, are the result of injection of new hot primitive magma. Comparison of the mineralogy and chemistry of the Wadi Qutabah intrusion with other layered intrusions indicates that the complex is >2km in thickness and that there are prospective areas for PGE mineral exploration. Discriminant analysis of augite composition suggests that the magmas are derived from within plate tholeiites. A composite stratigraphic column yields a section ~500m thick in the area.  ii  Preface The work conducted in this thesis is based on the information and drill core provided by Cantex Mine Development Corporation. They had the drill core shipped from Yemen, and presented me the opportunity to work these rocks. This is a significant opportunity to work on a newly discovered layered mafic intrusion with potential for the discovery of an economic mineral deposit. This could not be passed up.  iii  Table of Contents  Abstract ........................................................................................................................................... ii Preface ........................................................................................................................................... iii Table of Contents ............................................................................................................................iv List of Tables ..................................................................................................................................ix List of Figures .................................................................................................................................xi List of Abbreviations ..................................................................................................................... xx Glossary ........................................................................................................................................xxi Acknowledgements...................................................................................................................... xxv Chapter 1.0 Introduction .................................................................................................................. 1 Chapter 2.0 Geological and Tectonic Setting .................................................................................. 7 2.1 The Arabian Plate ........................................................................................................ 7 2.2 Regional Geology and Tectonic Setting ...................................................................... 7 2.3 Arabian Shield in Yemen ............................................................................................ 9 2.4 Geological Setting of the Wadi Qutabah Intrusion ................................................... 10 Chapter 3.0 Diamond Drill Core ................................................................................................... 15 3.1 Diamond Drill Core: The Samples ............................................................................ 15 3.2 Diamond Drill Core Logging: Procedures ................................................................ 16 3.3 Diamond Drill Core Logging: Summary ................................................................... 17 3.3.1 General Features ...................................................................................... 17 iv  3.3.2 Layering .................................................................................................. 18 3.3.3 Fabric and Structures ............................................................................... 19 3.3.4 Mineralogy .............................................................................................. 19 3.3.5 Veining .................................................................................................... 21 3.3.6 Intrusives and Granite ............................................................................. 21 3.3.7 Alteration ................................................................................................. 22 3.3.8 Rock Quality ........................................................................................... 22 3.3.9 Oxidation ................................................................................................. 22 3.3.10 General Comments ................................................................................ 22 Chapter 4.0 Petrography ................................................................................................................ 25 4.1 Petrography: Sample Selection and Preparation ....................................................... 25 4.2 Petrography: Modal Calculations .............................................................................. 25 4.3 Petrography: General Summary of all Samples ........................................................ 26 Chapter 5.0 Units, Lithology, Petrology and Stratigraphy ............................................................ 35 5.1 Elevation and Dip Corrections .................................................................................. 35 5.2 Units, Petrography, Lithology and Stratigraphy........................................................ 36 5.2.1 Unit: 10b .................................................................................................. 36 5.2.2 Unit: 10a .................................................................................................. 37 5.2.3 Unit: 5c .................................................................................................... 37 5.2.4 Unit: 5a .................................................................................................... 38  v  5.2.5 Unit: 5b .................................................................................................... 39 5.2.6 Unit: 2b .................................................................................................... 39 5.2.7 Unit: 9 ...................................................................................................... 40 5.2.8 Unit: 3 ...................................................................................................... 40 5.2.9 Unit: 12 .................................................................................................... 41 5.2.10 Unit: 8 .................................................................................................... 42 5.2.11 Unit 13a ................................................................................................. 42 5.2.12 Unit: 2a .................................................................................................. 43 5.2.13 Unit: 11a ................................................................................................ 44 5.2.14 Unit: 4 .................................................................................................... 44 5.2.15 Unit: 1a .................................................................................................. 45 5.2.16 Unit: 1ab ................................................................................................ 46 5.2.17 Unit: 7 .................................................................................................... 46 5.2.18 Unit: 6 .................................................................................................... 47 5.3 Correlation ................................................................................................................. 47 Chapter 6.0 Analytical Procedures and Results ............................................................................. 90 6.1 Scanning Electron Microscope (SEM) ...................................................................... 90 6.2 SEM Results .............................................................................................................. 91 6.2.1 Data Trends ............................................................................................. 91 Chapter 7.0 Discussion ................................................................................................................ 114  vi  7.1 SEM ......................................................................................................................... 114 7.2 Comparison to other Layered Mafic Intrusions....................................................... 118 7.3 Tectonic Setting ....................................................................................................... 120 Chapter 8.0 Conclusions .............................................................................................................. 128 Bibliography ................................................................................................................................ 130 Appendices .................................................................................................................................. 135 Appendix A. Petrography of the Wadi Qutabah Samples ............................................. 135 A.1 Petrographic Thin Section Descriptions .................................................. 135 A.1.1 Unit 1a ............................................................................................. 135 A.1.2 Unit 1ab ........................................................................................... 145 A.1.3 Unit 2a ............................................................................................. 156 A.1.4 Unit 2b ............................................................................................. 164 A.1.5 Unit 3 ............................................................................................... 168 A.1.6 Unit 4 ............................................................................................... 171 A.1.7 Unit 5a ............................................................................................. 183 A.1.8 Unit 5b ............................................................................................. 208 A.1.9 Unit 5c ............................................................................................. 212 A.1.10 Unit 6 ............................................................................................. 215 A.1.11 Unit 7 ............................................................................................. 217 A.1.12 Unit 8 ............................................................................................. 223 A.1.13 Unit 9 ............................................................................................. 233 A.1.14 Unit 10a ......................................................................................... 243 A.1.15 Unit 10b ......................................................................................... 248 vii  A.1.16 Unit 11a ......................................................................................... 253 A.1.17 Unit 12 ........................................................................................... 259 A.1.18 Unit 13a ......................................................................................... 274 Appendix B. Logging: Collar Data (all drill holes) ....................................................... 277 Appendix C. Logging: Lithology (all drill holes) ......................................................... 280 Appendix D. Logging: Alteration (all drill holes) ......................................................... 351 Appendix E. Logging: Mineralization (all drill holes) .................................................. 365 Appendix F. Logging: Structure (all drill holes) ........................................................... 382 Appendix G. Logging: Veining (all drill holes) ............................................................ 432 Appendix H. Logging: Sampling (all drill holes) .......................................................... 436  viii  List of Tables Table 3.1.  Drill hole identification numbers, location coordinates (longitude, latitude and UTM), azimuth, dip and hole length. ................................................................ 23  Table 4.1.  Modal % composition of the samples from drill holes H-01 to H-05. Plag=plagioclase, Opx=orthopyroxene, Cpx=augite +/-pigeonite, Hbld=hornblende, Act= actinolite, Bio= biotite, Serp=serpentine, Chl=chlorite, Cal/Carb=calcite, Ser=sericite, Apat=apatite, Qtz=quartz, Rut=rutile, Ilm=ilmenite, Po=pyrrhotite, Cpy=chalcopyrite, Py=pyrite, Gra=graphite, Mag=magnetite, Hem=hematite, Op_Uk=opaque (unknown), Bn_Min=brown mineral (unknown), Gn_Min=green mineral (unknown), Scap=scapolite ......................................................................................................... 29  Table 4.2.  Modal % composition of the samples from drill holes (H-06 to Hp-09). (For mineral code descriptions see Table 4.1) ................................................................. 30  Table 4.3.  Modal % composition of the samples from the western drill holes (Hp-10 to Hp-12) and grab sample YEMWQ1. (For code descriptions see Table 4.1) ........... 31  Table 4.4.  Thin section numbers, rock names and hole IDs from the eastern and western drill holes. ................................................................................................... 32  Table 5.1.  Calculated true thickness for the eastern samples and drill holes: H-01 to H05 for a dip of 25°. ................................................................................................... 50  Table 5.2.  Calculated true thickness for samples and drill holes: H-06 and Hp-07 to Hp09 for a dip of 25°. ................................................................................................... 51  Table 5.3.  Calculated true thickness for samples and drill holes: Hp-10 to Hp-12 for a dip of 25°. ................................................................................................................ 52  Table 5.4.  List of the thin section samples with their assigned lithological unit codes for the eastern and western drill holes. .......................................................................... 53  Table 6.1.  Analyses of plagioclase crystals by SEM/EDS from drill holes H-01 to H-05 from the Wadi Qutabah Layered Mafic Intrusion. Results presented are average weight% of the oxides. ............................................................................... 93  Table 6.2.  Analyses of plagioclase crystals by SEM/EDS from drill holes H-06, Hp-07 to Hp-09 from the Wadi Qutabah Layered Mafic Intrusion. Results presented are average weight% of the oxides. ......................................................... 94  Table 6.3.  Analyses of plagioclase crystals by SEM/EDS from drill holes Hp-10 to Hp12 from the Wadi Qutabah Layered Mafic Intrusion. Results presented are average weight% of the oxides. ............................................................................... 95  ix  Table 6.4.  Analyses of orthopyroxenes by SEM/EDS from the eastern drill holes of the Wadi Qutabah Layered Mafic Intrusion. Results presented are average weight% of the oxides.............................................................................................. 96  Table 6.5.  Analyses of orthopyroxene by SEM/EDS from western drill holes of the Wadi Qutabah Layered Mafic Intrusion. Results presented are average weight% of the oxides.............................................................................................. 97  Table 6.6.  Analyses of pigeonite by SEM/EDS from the Wadi Qutabah Layered Mafic Intrusion. Results presented are average weight% of the oxides. ............................ 98  Table 6.7.  Analyses of augite by SEM/EDS from the eastern drill holes of the Wadi Qutabah Layered Mafic Intrusion. Results presented are average weight% of the oxides. ................................................................................................................ 99  Table 6.8.  Analyses of augite by SEM/EDS from the western drill holes of the Wadi Qutabah Layered Mafic Intrusion. Results presented are average weight% of the oxides. .............................................................................................................. 100  Table 6.9.  Analyses of ilmenite by SEM/EDS from the eastern drill holes of the Wadi Qutabah Layered Mafic Intrusion. Results presented are average weight% of the oxides. .............................................................................................................. 101  Table 6.10. Analyses of ilmenite by SEM/EDS from the western drill holes of the Wadi Qutabah Layered Mafic Intrusion. Results presented are average weight% of the oxides. .............................................................................................................. 102  x  List of Figures Figure 2.1. Terrane map of the Arabian Shield in Saudi Arabia (a) according to (Stoeser & Frost, 2006), with protolith ages given in million years (Ma), ages in parentheses are younger arc assemblages emplaced into older protoliths. (b) Terranes from the Arabian Shield as defined by (Stoeser & Camp, 1985). Figure modified from Stoeser & Frost, (2006) (Fig 1, p.164). ................................ 13 Figure 2.2. Simplified map showing the geology and location of a) the Wadi Qutabah and Suwar intrusions, and b) a map of Yemen with the locations of the Precambrian outcrops and delineation of terranes boundaries. (a) Reproduced from Greenough et al., (2011); (b) map modified from Windley et al., (1996) with additional information from Whitehouse et al., (2001). ............ 14 Figure 3.1. Satellite imagery from Google Earth showing the location of the drill holes from the Wadi Qutabah Intrusion, Yemen (Earth, 2012). ....................................... 24 Figure 4.1. Photomicrographs of thin sections from the Wadi Qutabah Intrusion. Each image represents 5.4mm in width and was taken at 25x magnification under crossed polarized light. a) 829-01 shows cumulus plagioclase and intercumulus ilmenite; b) 793-01 shows cumulus plagioclase with adcumulus growth; c) 842-01 shows cumulus plagioclase with intercumulus augite mantled by hornblende, augite is host to fine grained Fe-Ti oxide exsolution lamellae; d) 876-01 shows cumulus plagioclase and orthopyroxene with intercumulus augite; e) 798-01 shows large intercumulus orthopyroxenes, augite, pigeonite and ilmenite, and orthopyroxene is host to exsolution of augite +/- pigeonite; f) 836-01 cumulus plagioclase and orthopyroxene hosted in a large intercumulus augite in poikilitic texture. P=plagioclase, A=augite, O=orthopyroxene, H=hornblende, Pi=pigeonite, I=ilmenite. ................................................................ 33 Figure 4.2. Backscatter electron image from the scanning electron microscope (SEM) of pentlandite exsolution in pyrrhotite hosted in ilmenite from sample 796-01. Ilm= ilmenite, Po=pyrrhotite, Pent=pentlandite. ..................................................... 34 Figure 5.1. A simplified cross-sectional view of the relationship between a drill hole and the lithologies/stratigraphy, at a dip of 25º. ...................................................... 54 Figure 5.2. Photographs of samples a) 829 and b) 835 from unit 10b. Sample 829 lies stratigraphically higher than 835 and each is from a separate intersection of unit 10b. (Scale is in cm) ......................................................................................... 55 Figure 5.3. Photomicrographs of 829-01 and 835-01 from unit 10b, (width of view 5.4mm, 25x magnification); a) 829-01 under plane polarized light (ppl) showing uralitized cumulate orthopyroxenes with cumulus and intercumulus plagioclase. Plagioclase exhibits irregular to serrated grain boundaries; b) same location as (a) under crossed polarized light (xpl); c) 835-01 under ppl xi  showing uralitized cumulate orthopyroxenes and cumulate plagioclase cut by a thin quartz veinlet; d) same location as (c) under xpl. Grain boundaries between the plagioclase are linear to irregular, and the crystals are locally fractured. Plag=plagioclase, Altd Opx= altered orthopyroxene, Po= pyrrhotite and Qtz= quartz. ...................................................................................... 55 Figure 5.4. Plan view (a) of the eastern drill holes, and b) a vertical section (W-E), looking north of the eastern drill holes (H-01 to H-06) cutting a simplified view of the major lithological layers (unit codes provided). ................................... 56 Figure 5.5. Photographs of samples a) 832 and b) 815 from unit 10a. Sample 832 is from the lower intersection and 815 from the stratigraphically higher intersection of unit 10a. (Scale is in cm) ................................................................. 57 Figure 5.6. Photomicrographs of 815-01(hornblende norite) and 832-01 (orthopyroxene hornblende gabbro) from unit 10a. a) 815-01 under plane polarized light (ppl) showing cumulus plagioclase and orthopyroxene with sharp grain boundaries and minor mantling by hornblende of the pyroxenes; b) same location as (a) under crossed polarized light (xpl) with sharp linear to irregular grain boundaries; c) 832-01 under ppl, showing cumulus plagioclase and orthopyroxenes with hornblende alteration; d) same location as (c) under xpl showing the intensity of the amphibole alteration of the pyroxenes. Grain boundaries between the plagioclases are sharp and irregular. Plag=plagioclase, Opx= orthopyroxene, Hbld= hornblende. All have a field of view of 5.4mm in width. .................................................................. 57 Figure 5.7. Photograph of sample 827 from unit 5c. (Scale is in centimeters.) ......................... 58 Figure 5.8. Photomicrographs of 827-01(augite norite) from unit 5c; a) 827-01 under plane polarized light showing intercumulus orthopyroxene and clinopyroxene hosted in cumulus plagioclase; b) same location as (a) under crossed polarized light. Exsolution of clinopyroxene in the orthopyroxenes is clearly visible, and the partially equilibrated grain boundaries are irregular to linear. Plag=plagioclase, Opx= orthopyroxene, Cpx= clinopyroxene. All have a field of view of 5.4mm in width. .................................................................. 59 Figure 5.9. Photographs of samples a) 851, fine-grained, b) 851, medium-grained, c) 890, d) 884, e) 814, f) 806 contains both fine and medium-grained norite; g) 812, and h) 798 from unit 5a. (Scale is in cm) ......................................................... 61 Figure 5.10. Photomicrographs of 798-01(augite norite), 814-01 (augite norite), FX847937 (hornblende augite norite), 851-02 (augite norite), 884-01 (leuco orthopyroxene gabbro/leuco augite norite) from unit 5a. a) 798-01 under plane polarized light (ppl) showing intercumulus pyroxenes and the relationship of the pyroxenes to plagioclase; b) same location as (a) under crossed polarized light (xpl); Note the presence of kinked plagioclase and exsolution in the pyroxenes, c) same location as (a) & (b) under reflected light (rl) showing ilmenite; d) sample 814-01 under ppl showing intercumulus pyroxenes and cumulus plagioclase; e) same location as (d) xii  under xpl; exsolution in the pyroxenes is a common texture, and the grain contacts show a partially equilibrated texture; f) same location as (d) & (e) under rl with numerous ilmenite crystals; g) FX847937 under ppl showing hornblende alteration of the pyroxenes, h) FX847937 under xpl with exsolution textures in the pyroxenes visible; i) FX847937 under rl with abundant ilmenite and minor pyrrhotite; j) 851-02 under ppl with slightly coarser intercumulus pyroxenes and cumulus plagioclase compared to (a) ; k) 851-02 under xpl is host to exsolution textures in the pyroxenes and partially equilibrated textural geometry; l) 851-02 under rl showing intercumulus ilmenite; m) 884-01 under ppl showing cumulus plagioclase and intercumulus pyroxenes and opaques; n) 884-01 under xpl showing exsolution of augite in orthopyroxene and relationships of mineral grains; o) 884-01 under rl showing intercumulus ilmenite. Plag=plagioclase, Opx= orthopyroxene, Cpx= clinopyroxene, Hbld= hornblende, Ilm=ilmenite, Po=pyrrhotite. All have a field of view of 5.4mm in width..................................... 62 Figure 5.11. Photomicrograph of 798-01 (a) under crossed polars (width of view is 5.4mm) and a selected area outlined in white where the high resolution BSE image; (b) was taken showing fine-grained exsolution of Fe-Ti oxides in the pyroxenes. Ilm=ilmenite, Plag=plagioclase, Aug=augite, Opx=orthopyroxene, Hbld=hornblende, Po=pyrrhotite. ......................................... 64 Figure 5.12. Photomicrographs of FX847934 (orthopyroxene hornblende gabbro) and 806-02 (augite hornblende norite) from unit 5b. a) FX847934 under ppl showing cumulus and intercumulus plagioclase with intercumulus pyroxenes and ilmenite; b) same location as (a) under xpl; c) same location as (a) & (b) under reflected light(rl) showing abundant ilmenite; d) 806-02 (augite norite) under ppl showing cumulus and intercumulus plagioclase with intercumulus pyroxenes; e) same location as (d) under xpl; f) same location as (d) & (e) under rl with numerous pyrrhotite crystals. P=plagioclase, O= orthopyroxene, B= biotite, Ilm = ilmenite, Po= pyrrhotite, ppl= plane polarized light, xpl= crossed polarized light, rl= reflected light. All photos 5.4mm wide. .................................................................. 65 Figure 5.13. Photographs of samples a) 800 and b) 810 from unit 2b. (Scale is in centimeters.) ............................................................................................................. 65 Figure 5.14. Photomicrographs of thin sections 800-01 (leuco hornblende gabbro) and 810-01 (leuco hornblende gabbro) from unit 2b (fields of view 5.4mm wide), a) 800-01 under plane polarized light (ppl), showing pale green hornblende and medium-grained cumulus plagioclase; b) same location as (a) under crossed polars (xpl) were plagioclase is exhibiting a partially equilibrated textural geometry; c) 810-01 taken under ppl showing abundant hornblende and sericite altered plagioclase; d) same location as (c) under xpl, and plagioclase grains exhibiting a partially equilibrated geometry. Plag=plagioclase, Hbld= hornblende, Ilm= ilmenite. .............................................. 66 Figure 5.15. Photographs of samples a) 792, b) 790, mineralized (pyrrhotite), c) 797, and d) 793 from unit 9. (Scale is in centimeters.) ........................................................... 67 xiii  Figure 5.16. Photomicrographs of 792-01 (hornblende augite norite), 797-01 (hornblende augite norite) and 793-01 (leuco hornblende augite norite) from unit 9. a) 792-01 under plane polarized light (ppl) showing cumulus orthopyroxene mantled by hornblende and minor augite, with cumulus and intercumulus plagioclase; b) same location as (a) under crossed polars (xpl); c) 797-01 under ppl showing cumulus orthopyroxene mantled and altered by hornblende, with cumulus plagioclase; d) same location as (c) under xpl, plagioclase showing partially equilibrated textural geometry; e) 793-01 under ppl showing cumulus orthopyroxene and plagioclase; f) same location as (e) under xpl with orthopyroxene mantled and altered by hornblende and large cumulus plagioclase grains. Plag=plagioclase, Hbld= hornblende, Opx= orthopyroxene, Bio=biotite. All photomicrographs 5.4mm wide.................. 68 Figure 5.17. Photograph of sample 795 from unit 3. (Scale in centimeters) ................................ 69 Figure 5.18. Photomicrographs of 795-01 (leuco gabbro/leuco hornblende gabbro) from unit 3. (5.4mm wide) a) under plane polarized light (ppl) showing large anhedral hornblende and cumulus plagioclase; b) same location as (a) under crossed polars (xpl); c) under ppl; d) same location as (c) under xpl showing weak to moderately altered plagioclase. Plag=plagioclase, Hbld= hornblende, Bio=biotite. .......................................................................................... 69 Figure 5.19. Photographs of samples a) 859, b) 845, c) 860, d) 877, e) 796 and f) 880 from unit 12. (Scale in centimeters.) ........................................................................ 70 Figure 5.20. Photomicrographs of thin sections 877-01 (hornblende augite norite) and 859-01 (hornblende gabbro) from unit 12, a) 877-01 under plane polarized light (ppl) showing fine to medium-grained cumulus plagioclase (+/-opx) and intercumulus orthopyroxene and augite with weak hornblende and biotite alteration; b) same location as (a) under crossed polars (xpl) orthopyroxene showing exsolution of augite; c) same location as (a) & (b), under reflected light (rl), showing abundant intercumulus ilmenite; d) 85901 under ppl showing uralitized pyroxenes and cumulus and intercumulus plagioclase; e) same location as (d) under xpl; f) same location as (d) & (e) under rl, showing abundant intercumulus ilmenite. Plag= plagioclase, Ilm=ilmenite. All photos 5.4mm wide. .................................................................... 71 Figure 5.21. Photographs of samples a) 776, b) 778, c) 779 and d) 783 from unit 8. (Scale in cm.) ...................................................................................................................... 72 Figure 5.22. Photomicrographs of thin sections 776-01 (hornblende norite) and 778-01 (hornblende gabbro) from unit 8, (fields of view 5.4mm in wide), a) 776-01 under plane polarized light (ppl) showing cumulus plagioclase and hornblende-altered pyroxene alteromorphs; b) same location as (a) under crossed polars (xpl), plagioclase grain boundaries indicate a partially equilibrated to equilibrated textural geometry; c) 778-01 under ppl showing hornblende and biotite alteration of pyroxenes; d) same location as (c) under xpl. Plag=plagioclase, Hbld=hornblende, Bio=biotite. ................................. 73  xiv  Figure 5.23. Photograph of sample 924, a diabase dyke. Scale in centimeters (cm). .................. 74 Figure 5.24. Photomicrographs of thin section 924-01 from unit 13a (diabase): a) 924-01 under plane polarized light, (fields of view 5.4mm wide) showing altered and zoned plagioclase and augite with euhedral-subhedral to skeletal ilmenite; b) same location as (a) under crossed polars, showing zoned plagioclase and augite; c) same location as (a) & (b), under reflected light showing the various shapes of ilmenite. Plag=plagioclase, Cpx= augite, Ilm=ilmenite............................................................................................................. 74 Figure 5.25. Photographs of samples a) 921, b) 922 and c) 854 from unit 2a. Samples 921 and 922 are from the eastern holes and 854 (coarse-grained) is from the west. Scale in centimeters. ....................................................................................... 75 Figure 5.26. Photomicrographs of 854-01(hornblende gabbro), 921-01(hornblende gabbro) from unit 2a, fields of view 5.4mm wide: a) 854-01 under plane polarized light (ppl) showing coarse-grained cumulus plagioclase and hornblende (possibly altered cumulus orthopyroxene); b) same location as (a) under crossed polars (xpl); c) 921-01 under ppl, showing moderate to strong hornblende and chlorite alteration. Plagioclase is also altered by sericite giving it a dusted appearance; d) same location as (c) under xpl. Plag= plagioclase, Hbld= hornblende, Altd Cpx= altered augite, Chl= chlorite. .................................................................................................................... 75 Figure 5.27. Photographs of samples a) 848 and b) 874 from unit 11a. Sample 874 contains a higher concentration of oxides and sulphides relative to 848. Scale in cm. .............................................................................................................. 76 Figure 5.28. Photomicrographs of 874-01 (leuco orthopyroxene gabbro) and 848-01 (augite norite) from unit 11a; (fields of view 5.4mm in width) a) 874-01 under plane polarized light (ppl) showing poikilitic orthopyroxene oikocrysts and intercumulus augite with cumulus plagioclase; b) same location as (a) under crossed polars (xpl) showing the variation in plagioclase crystal size; c) same location as (a) & (b), under reflected light (rl) showing ilmenite and pyrrhotite as intercumulus phases; d) sample 84801 under ppl, showing small cumulus orthopyroxenes and large intercumulus augite and orthopyroxene with lath shaped plagioclase; e) same location as (d) under xpl showing poikilitic textures; f) same location as (d) & (e) under rl with no opaque phases. Plag=plagioclase, Hbld= hornblende, Opx=orthopyroxene, Cpx=augite, Bio=biotite, Ilm=ilmenite, Po=pyrrhotite. .......................................................................................................... 76 Figure 5.29. Photographs of samples a) 856, b) 804 and c) & d) 866 from unit 4. Samples 856 and 804 are fine and medium-grained gabbros that are mineralized. Sample 866 is medium to coarse-grained and host to pyrrhotite and chalcopyrite mineralization. The scale is in centimeters. ........................................ 77 Figure 5.30. Photomicrographs of 866-01 (hornblende gabbro) ~25% (modal) sulphides from unit 4, a) 866-01 under plane polarized light showing the intercumulus xv  nature of the sulphides; b) same location as (a) under crossed polars, cumulus plagioclase surrounds the intercumulus sulphides that encircle the amphibole altered pyroxenes; c) same location as (a) & (b) under reflected light showing intercumulus pyrrhotite and chalcopyrite. Plag=plagioclase, Hbld= hornblende, Po=pyrrhotite, Cpy= chalcopyrite. All photographs 5.4mm wide. ............................................................................................................ 78 Figure 5.31. Photographs of samples a) 876, b) 840, c) 836 and d) 839 from unit 1a. Scale in cm. .............................................................................................................. 78 Figure 5.32. Photomicrographs of 836-01 (augite norite), 839-01 (hornblende-augite norite) and FX847935 (augite norite) from unit 1a, (fields of view 5.4mm wide), a) 836-01 under plane polarized light (ppl) showing cumulus orthopyroxene and plagioclase and intercumulus augite; b) same location as (a) under crossed polars (xpl); c) 839-01 under ppl showing a large augite oikocryst in a poikilitic texture, hosting plagioclase laths and orthopyroxenes; d) same location as (c) under xpl, a late fracture cuts augite and plagioclase and is host to minor hornblende alteration; e) FX847935 under ppl showing large cumulus plagioclase and orthopyroxene with intercumulus augite, and f) FX847935 at same location as (e) under xpl, note the kinked plagioclase at the bottom right. Plag=plagioclase, Opx=orthopyroxene, Cpx=augite, Hbld=hornblende .............................................. 79 Figure 5.33. Photographs of samples a) 843, b) 909, c) 842 and d) 916 from unit 1ab. This unit shows significant variation in plagioclase content as seen in (a) to (d). Scale is in cm. ................................................................................................... 80 Figure 5.34. Photomicrographs of 843-01 (leuco hornblende gabbro) and 909-01 (hornblende gabbro) from unit 1ab. (fields of view 5.4mm wide) a) 843-01 under plane polarized light (ppl) showing coarse cumulus plagioclase with altered intercumulus augite and cumulus orthopyroxene; b) same location as (a) under crossed polars (xpl) altered pyroxenes in cumulus plagioclase; c) 909-01 under ppl, showing altered cumulus orthopyroxene and intercumulus augite with cumulus plagioclase; d) same location as (c) under xpl. Plag=plagioclase, Opx=orthopyroxene, Cpx=augite, Hbld=hornblende, Altd=altered, Po=pyrrhotite. .................................................................................... 81 Figure 5.35. Photographs of samples a) 906 and b) 908 from units 6 and 7. The top of sample 906 is composed of anorthosite (top row in (a)), and the bottom is pyroxenite. Sample 908 (b) is composed of medium to coarse-grained pyroxenite. The scale is in cm. ................................................................................ 82 Figure 5.36. Photomicrographs of 906-02 (plagioclase bearing pyroxenite) from unit 7. (Fields of view 5.4mm wide) a) 906-02 under plane polarized light (ppl); b) same location as (a) under crossed polars (xpl), abundant intercumulus sulphides (pyrrhotite and minor chalcopyrite). Note the bent or deformed orthopyroxene; c) same location as (a) & (b), under reflected light (rl), showing pyrrhotite mineralization. Opx= orthopyroxene, Po= pyrrhotite. ............. 82  xvi  Figure 5.37. Photomicrographs of 906-01 (anorthosite) from unit 6, (fields of view 5.4mm wide) a) 906-01 under plane polarized light, composed of cumulus plagioclase; b) same location as (a) under crossed polars showing variation in grain size and the partially equilibrated textural geometry. Plag=plagioclase. ..................................................................................................... 83 Figure 5.38. A simplified stratigraphic column created from a compilation of the lithologies of the eastern drill holes (H-01 to H-06) from the Wadi Qutabah Layered Mafic Complex. ......................................................................................... 84 Figure 5.39. A detailed stratigraphic column created from a compilation of the lithologies of the eastern drill holes (H-01 to H-06) from the Wadi Qutabah Layered Mafic Complex. ....................................................................................................... 85 Figure 5.40. A simplified stratigraphic column created from a compilation of the lithologies of the western drill holes (Hp-07 to Hp-12A) from the Wadi Qutabah Layered Mafic Complex............................................................................ 86 Figure 5.41. Detailed stratigraphic column created from a compilation of the lithologies of the western drill holes (Hp-07 to Hp-12A) from the Wadi Qutabah Layered Mafic Complex. ......................................................................................... 87 Figure 5.42. Simplified correlation of the detailed stratigraphic columns from the east and west drill holes of the Wadi Qutabah Layered Mafic Complex........................ 89 Figure 6.1. Variation of SiO2 (avg wt. %) in augite, orthopyroxene and plagioclase versus elevation (m) for the western (a) and eastern (b) samples. The unit codes are displayed, and the horizontal lines (yellow) indicate the top of unit 5a. The dykes/sills (units 12 and 13a) are also included........................................ 103 Figure 6.2. Variation of Al2O3 (avg wt. %) in augite, orthopyroxene and plagioclase versus elevation (m) for the western (a) and eastern (b) samples. The numbers displayed are the unit codes and horizontal lines (yellow) indicate the top of unit 5a. The dykes/sills (unit 12 and 13a) are also included. ................ 104 Figure 6.3. Variation of anorthite content (An%) in plagioclase from the western (a) and eastern (b) samples versus elevation (m). An % of plagioclase mimics the trend exhibited by CaO and Al2O3 for both the east and west samples. An% shows a marked increase above unit 5a (indicated by horizontal yellow lines). The lower An% of plagioclase in unit 12 is consistent with the unit being a sill or dyke. ................................................................................................ 105 Figure 6.4. Variation of FeO (avg wt. %) in augite, orthopyroxene and ilmenite versus elevation (m) from the western (a) and eastern (b) samples. The numbers displayed are the unit codes and the horizontal lines (yellow) indicate the top of unit 5a. The dykes/sills (units 12 and 13a) are also included. ..................... 106 Figure 6.5. Variation of MgO (avg wt. %) in augite and orthopyroxene versus elevation (m) for the western (a) and eastern (b) samples. The numbers displayed are xvii  the unit codes and the horizontal lines (yellow) indicate the top of unit 5a. The dykes/sills (units 12 and 13a) are also included. ............................................ 107 Figure 6.6. Diagrams showing variation in enstatite content (En%) versus elevation (m) in augite and orthopyroxene from the western (a) and eastern (b) samples. Numerical unit codes are displayed and horizontal lines (yellow) indicates the top of unit 5a. The dykes/sills (units 12 and 13a) are also included. En% calculated using cation proportions, where En%=Mg/(Ca+Mg+∑Fe)*100, where ∑Fe= Fe+Mn. .............................................................................................. 108 Figure 6.7. Diagrams showing the variation of TiO2 (avg wt. %) in augite and orthopyroxene versus elevation (m) for the western (a) and eastern (b) samples. The numbers displayed are the unit codes and the horizontal lines (yellow) indicate the top of unit 5a. The dykes/sills (units 12 and 13a) are also included. ......................................................................................................... 109 Figure 6.8. Diagrams showing the variation of TiO2 and FeO (avg wt. %) in ilmenite versus elevation (m) for the western (a) and eastern (b) samples. The numbers displayed are the unit codes and the horizontal lines (yellow) indicate the top of unit 5a. The dykes/sills (units 12 and 13a) are also included. ................................................................................................................. 110 Figure 6.9. Correlation diagrams of a) Al2O3, b) K2O, c) SiO2, and d) FeO vs. CaO/ (CaO+Na2O) in plagioclase. The triangles are for the samples above the unit 5a upper contact (U for upper) and the squares are for samples below the 5a contact (L =lower). E=east and W=west. .............................................................. 111 Figure 6.10. Correlation diagrams of a) Al2O3, b) MnO, c) SiO2, and d) TiO2 vs. MgO/(MgO+FeO) in orthopyroxene. The triangles are for the samples above the unit 5a upper contact (U for upper) and the squares are for samples below the 5a contact (L =lower). E=east and W=west. ........................... 112 Figure 6.11. Correlation diagrams of a) Al2O3, b) MnO, c) TiO2, and d) CaO vs. MgO/(MgO+FeO) in augite. The triangles are for the samples above the unit 5a upper contact (U for upper) and the squares are for samples below the 5a contact (L =lower). E=east and W=west. .............................................................. 113 Figure 7.1. Plot of MAN (meters per 1 unit of anorthite in plagioclase) versus thickness of the intrusion (km). The regression line is indicated on the plot. ....................... 123 Figure 7.2. Stratigraphic sections through the Bushveld (a) (McBirney, 1984) (modified from figure 6-9, p. 193) and the Skaergaard intrusion (b) (McBirney, 1996) (modified from figure 4, p.153), showing stratigraphic positions of similar mineral compositions to the plagioclase, augite and orthopyroxenes from the lower part (red arrows) and the upper part (green arrows) of the Wadi Qutabah Intrusion. ................................................................................................. 125 Figure 7.3. Plot of discriminant functions F1 vs. F2 of augite composition according to (Nisbet & Pearce, 1977) to determine magma types: within plate alkalic xviii  basalts (WPA), volcanic arc basalts (VAB), ocean floor basalts(OFB) and within plate tholeiitic basalts (WPT). Lines are hand drawn by eye according to the divisions created by Nisbet & Pearce, (1977). ............................ 126 Figure 7.4. Ternary diagram TiO2-MnO-Na2O for discrimination of magma type by augite composition (Nisbet & Pearce, 1977). ........................................................ 127  xix  List of Abbreviations The following abbreviations are common in the literature and may appear in the thesis. They are most commonly used here for the purposes of drill core logging, petrographic descriptions, and figure and table descriptions. Act: actinolite Altd: altered Altn: alteration (altn) Amph: amphibole An: anorthosite (lithology code) An%: anorthite % of plagioclase Apat: apatite Aug: augite Avg: average BCON: brecciated contact BFLT: brecciated fault Bio: biotite Ble: bleaching BRX: breccia Carb: carbonate/calcite Chl: chlorite CON: contact Cpx: clinopyroxene Cpy: chalcopyrite Cr or cr: coarse DYK: dyke Epi: epidote Fcarb: iron carbonate alteration FLT/Flt: fault FLZ: fault zone FN or fn: fine FOL/Fol: foliation FRA: fracture FRZ: fracture zone Gab: gabbro GCON: gradational contact Gra: graphite Gran: granite Hbld: hornblende Hem: hematite Ilm: ilmenite Irreg: irregular LC: lost core/ no recovery  LIN/Lin: lineation LIP: large igneous province LMI: layered mafic intrusion M or m: moderate Mag: magnetite Med: medium MLIN: mineral lineation Mus: muscovite NOR: Norite Opx: orthopyroxene Ox: oxidation PAO: Pan-African Orogeny Pent: pentlandite PGE: platinum-group element Pig: pigeonite Plag: plagioclase Po: pyrrhotite ppl: plane polarized light Py: pyrite PYR: pyroxenite Pyrox: pyroxene Qtz: quartz REE: rare earth element Rl: reflected light Rut: rutile S or s: strong SEM: Scanning electron microscope Ser: sericite Serp: serpentine SHR: shear SHZ: shear zone Sil: silica Sulph: sulphide(s) TCA or tca: to the core axis VN or vn: vein VW or vw: very weak W or w or wk: weak Xpl: crossed polarized ligh  xx  Glossary The following terms will be used to describe the rocks in this study. All definitions provided below are with respect to mafic intrusions, since some of these terms also apply to other rock types and geological features of other intrusions, plutons, etc.  Adcumulate: cumulate rock that contains little to no intercumulus material Adcumulate texture: results from the growth of the cumulus crystals through diffusion of material from the main body of magma. This causes a gradual reduction of the pore liquid leading to a cumulate that is lacking in intercumulus phases. The intercumulus phases represent <7% of the rock. The grain boundaries of cumulus minerals are all in contact with one another, which may be attributed to overgrowth of the cumulus grains. Grain boundary recrystallization may also be seen Allotriomorphic/xenomorphic: the rock is comprised primarily of anhedral grains (2005, Lapidus, 2003) Alteromorph: general term used to describe a primary mineral that has undergone alteration or weathering to secondary products of all shapes, sizes and states of preservation (Delvigne, 1998) Anhedral: poorly developed crystal without recognizable crystal faces. Anorthosite: rock containing >90% plagioclase Biotitization: the replacement of pyroxene +/- amphibole by biotite Carbonitization: Alteration of the minerals by carbonate rich minerals Chloritization: the replacement of mafic minerals by chlorite Compaction: reduced pore volume and an increase in packing Cryptic Layering: not visibly obvious) is a systematic variation in the chemical composition of cumulus minerals with stratigraphic height in the layered sequence Cumulate: a rock composed of cumulus and intercumulus minerals that crystallized on the floor, roof and walls of a slowly cooled magma body (in this study, of mafic composition).These rocks are the product of fractional crystallization, in-situ crystallization and to a lesser degree additional processes such as gravitational settling. There are three main types of recognized xxi  cumulates that were originally proposed by Wager et al., (1960): adcumulate, mesocumulate and orthocumulate (McBirney, 2009, Wadsworth, 1985, Wager et al., 1960) Cumulus: Initial crystallizing phases that are typically euhedral to subhedral in habit and generally form the main framework of the rock (Philpotts & Ague, 2009, Wager et al., 1960) Densification: any process or processes that increases the volume of the cumulus phase(s) Equigranular: the grains that make up the rock are all approximately the same size Euhedral (idiomorphic): mineral that is fully developed and is bound by crystal faces Fractional crystallization: the separation of crystals from a melt Gabbro: phaneritic mafic igneous rock composed of 10-90% plagioclase + pyroxenes +/- olivine Graphic: a texture referring to the intergrowth of crystals that create angular wedge shaped forms. This texture may be both macro (graphic) and micro-scale (micrographic). Heteradcumulate: complex adcumulates, whereby the unzoned cumulus crystals are surrounded by unzoned poikilitic crystals that have essentially the same composition Heteradcumulate texture/poikilitic adcumulate: occurs when the cumulus crystals are poikilitically enclosed in large unzoned crystal(s) of another mineral (subclass of adcumulates). It is important to note that the two minerals may have the same composition Hypidiomorphic: the rock is comprised primarily of subhedral grains. Inequigranular: the grains that make up the rock are a variety of sizes Intercumulus: Mineral(s) that crystallized from the trapped or interstitial liquid within the initial cumulate framework. The minerals are typically anhedral and have unusual habits, and are a later crystallization product of the intrusion (2005, Best, 2011, McBirney, 1984) Layer: a stratum of rock of some thickness that has similar internal characteristics Layering: a series of strata, each of some thickness, that are distinguished by their mineral mode, texture and grain size. There are 3 main types of layering recognized in layered intrusions: modal, phase and cryptic layering (McBirney, 1984, Philpotts & Ague, 2009) Lineation (mineral): linear structural feature of a rock. Minerals are elongate or oriented with the long axis parallel to the flow direction or the direction of elongation (shear). The elongate grains may also show a preferred orientation in the plane of foliation. Another type of lineation is where there is a preferred orientation of elongate grains in the plane of two intersecting planar features, and is this called an intersection lineation (McBirney & Nicolas, 1997) xxii  Magmatic Differentiation: process/processes that cause the composition of the magma to change (such as during partial melting, emplacement, fractionation, mixing, contamination/assimilation, etc.) Mesocumulate texture: is an intermediary between orthocumulate and adcumulate, and contains subordinate zoning of the cumulus crystals. The intercumulus phases typically represent 7-25% of the cumulate rock. Many grain boundaries between the cumulus minerals are mutual boundaries Modal Layering: is characterized by a variation in the relative proportion of the constituent minerals Nesophitic: The plagioclase is large and the pyroxenes are interstitial Norite: mafic igneous rocks composed of orthopyroxene and plagioclase +/- clinopyroxene +/olivine Oikocryst: the host phenocryst in a poikilitic texture Ophitic: large pyroxene crystals that enclose smaller plagioclase crystals or laths Orthocumulate: as a cumulate rock composed of essentially one or more cumulus minerals surrounded by a significant percentage of unmodified crystallized intercumulus liquid (material) Orthocumulate texture: is defined as cumulus crystal phases enclosed by poikilitic minerals that nucleate from the intercumulus liquid. The crystals typically show normal zoning. Orthocumulate texture contains between 25-50% postcumulus minerals (analogous to lightly packed sediments) Partition coefficient (D): the distribution of a trace element between a mineral and a melt: D=C min/C liq Platinum group elements (PGEs): Ru (Z: 44), Rh (Z: 45), Pd (Z: 46), Os (Z: 76), Ir (Z: 77), Pt (Z: 78) Phase Layering: is characterized by the appearance or disappearance of minerals in the crystallization sequence developed in modal layers Poikilitic: a host phenocryst contains inclusions of other minerals Postcumulus: involves the crystallization of the intercumulus liquid and may result in the complete crystallization or recrystallization of the intrusion Pseudomorph: one or more minerals replace another but retaining the original crystals shape of the original mineral xxiii  Pyroxenite: Ultramafic rock containing >90% pyroxenes +/- plagioclase+/- hornblende Seritization: the replacement of the plagioclase by sericite Subhedral (subidiomorphic): The crystal form is recognizable but is poorly developed, and is partially bound by well-formed crystal faces Subophitic: Plagioclase crystals/ laths are larger than the pyroxenes and are only partially enclosed Texture: the physical character or appearance of a fully crystallized rock and the arrangement of all of its components. These may include grain size, shape, crystallinity, configuration and the relationship of the components at both the macroscopic and microscopic level (Higgins, 2011) Uralitization: the replacement of pyroxene by amphibole  xxiv  Acknowledgements I would like to thank the staff and employees at Cantex Mine Development Corporation for providing the drill core, the staff at C.F. Mineral Research Ltd for their time, dedication and assistance throughout the logging processes and for the wonderful job in carbon coating the thin sections. Vancouver Petrographics did a great job on the polished thin sections, which were critical to the completion of this study. I offer my gratitude to the faculty and staff of the Earth and Environmental Sciences Department who provided a great deal of support. I thank my committee members for their continued support and insight. I thank Dr. John Greenough who has supported me throughout this process, and whose insight and knowledge was and continues to be invaluable. Special thanks are owed to my family and friends for their continued support. And very special thanks go to my husband for his unwavering support throughout this journey.  xxv  Chapter 1.0 Introduction Layered mafic intrusions or basic intrusions have been the subject of numerous studies over nearly a century. These large, slowly cooled mafic bodies are most often associated with layering, cumulate textures and economically significant platinum-group element (PGE) mineralization. The Bushveld Complex, located in South Africa is the largest known and most well recognized of the large layered mafic intrusions. It is of Precambrian age (2.06Ga) has a thickness of 7-9km and an aerial extent of ~65,000km2 (Eales & Cawthorn, 1996). The Bushveld Complex is also host to the largest known deposits of Cr, V and platinum-group metals (PGMs) in the world (Clarke et al., 2009). Of these, the Bushveld complex is host to ~95% of the known global reserves of platinum group metals (PGMs) (Survey, 2012). Other significant layered intrusions include the Stillwater Complex (Montana), the Noril’sk-Talnakh (Russia), the Great Dyke (Zimbabwe), the Skaergaard Complex (Greenland) and the Lac Des Iles Complex (Ontario), each of which is host to economically significant mineralization. These large mafic intrusions are desirable targets for mineral exploration and a subject of interest for economic geologists. Cantex Mine Development Corporation recently discovered two previously unknown layered mafic intrusions in northwestern Yemen: the Suwar and Wadi Qutabah layered mafic Complexes. There is potential for these intrusions to host economically significant mineralization (Ni, Cu, Co, Pt-Pd). The Suwar Intrusion lies ~30km to the southeast of the Wadi Qutabah Complex, and is currently known to be 32km in length and 8km in width (Corporation, 2012a). The known extent of the Wadi Qutabah intrusion is 23km2, with mineralization being traced for more than 19km in outcrop. Mineralization in the Wadi Qutabah Complex is composed of five known sulphide horizons hosted in noritic to gabbroic rocks. Anomalous platinum mineralization was identified in samples/concentrates from drainages that cut the intrusion. The discovery of anomalous platinum suggests that the Wadi Qutabah Intrusion may be host to an undiscovered platinum deposit (Corporation, 2012). A drill program undertaken in 2007 was completed on the Wadi Qutabah intrusion in hopes of identifying the source of the anomalous platinum. A total of 14 drill holes were completed in 3 areas, for a total of ~1650m of drill core. It is these drill cores from the Wadi Qutabah Layered Mafic Intrusion that are the focus of this study.  1  There is little information available on the Wadi Qutabah and Suwar intrusions. The information on the region is largely a result of mapping, sampling, drilling and geophysics conducted by geologists from Cantex Mine Development Corporation. The gabbroic complex intrudes Precambrian or late Proterozoic amphibolite-facies paragneisses that are exposed in the south, and overlain by flat lying Phanerozoic sedimentary cover and Permian shales. The intrusion is also cut by a Tertiary diabase dyke that runs near north-south. Stratigraphy of the Wadi Qutabah intrusion has been mapped on the large scale. It is broken into 3 distinct sequences based on plagioclase and ferromagnesian mineral content. Each of these sequences is also host to sulphide mineralization which is believed to be conformable to the layering. These sulphide rich layers are recognized in the exposed rock as gossans that reflect surface oxidation. Cantex geologists recognized the more leucocratic nature of the rocks up stratigraphy, suggesting that these rocks are more evolved than those seen at the Suwar intrusion (Corporation, 2012, Plank et al., 2007). The recent study by Greenough et al., (2011) is the only published work on the Suwar and Wadi Qutabah intrusions, and the first dates by U-Pb isotope dilution- thermal ionization mass spectrometry (ID-TIMS) published on any rocks from Yemen. Results of the study returned dates of 638.58±0.51Ma for Wadi Qutabah and 638.46± 0.73Ma for Suwar, which are indistinguishable within analytical error, suggesting that these intrusions are coeval/comagmatic or part of the same intrusion. The geochemical results suggest that the magma source of these rocks is plume related, involved melting of Archean subcontinental lithosphere, and that this region experienced an extensional tectonic regime at the end of the Neoproterozoic (Greenough et al., 2011). Rocks in the Suwar intrusion are olivine rich (Greenough et al., 2011). Olivine cumulates are generally found at the base of large layered mafic intrusions. No olivine was identified in the rocks from the Wadi Qutabah intrusion, which suggests a more evolved magma composition up stratigraphy from which these rocks crystallized. The evidence presented by Greenough et al., (2011) and the more evolved composition of the Wadi Qutabah intrusion compared to the Suwar suggests that they are part of the same intrusion. They will be treated as a single intrusion for the remainder of the text.  2  The discovery of a large layered mafic intrusion of Neoproterozoic age in Yemen has some important implications for the region. The estimated size of the complex is ~250km2, which places the intrusion among the largest layered mafic intrusions discovered to date. In the case of layered mafic intrusions, the bigger the better, since the larger size increases the economic potential of the complex, and makes this a desirable target for mineral exploration (Best, 2011, Greenough et al., 2011). The formation of large layered mafic intrusions requires significant volumes of mafic magma be generated as a result of melting in the upper mantle (Mungall, 2005). The most widely accepted genetic origin of these magmas is from mantle plumes and zones of crustal rifting (Bryan & Ernst, 2007, Mungall, 2005). The large volumes of magma and the tectonic setting suggest a close genetic relationship between layered mafic intrusions and large igneous provinces (LIPs) (Mungall, 2005). A plume origin for the SuwarWadi Qutabah layered complex was proposed by Greenough et al., (2011). Perhaps the SuwarWadi Qutabah Complex is part of a larger system, potentially a new large igneous province. An important factor in the formation of economically significant Ni, Cu, Co, platinumgroup elements (PGEs) mineralization is the high degrees of melting required to generate mafic magmas. The concentrations of compatible elements such as Ni, Cu, Pd and Au increase as sulphide returns or is dissolved in the melt with increasing degrees of partial melting. This leads to the formation of enriched magmas. Economically viable PGE and Ni-Cu-PGE deposits require that processes must operate to concentrate these elements from large volumes of magma into a small volume of rock. The main collectors of these elements are sulphide liquid and chromite (Mungall, 2005). Layered mafic intrusions are also important for the study of magma chambers. Exposures of these deposits offer unique opportunities to study the evolution of magmas, and the processes and mechanisms involved in crystallization, cooling, magma chamber replenishment, assimilation, and late stage processes such as hydrothermal alteration/metasomatism, and metamorphism (Campbell, 1996, Hunter, 1996, Naslund & McBirney, 1996). One of the pivotal publications on layered intrusions is that of Wager & Brown, (1968) entitled “Layered igneous rocks”. In this publication, the authors present a detailed study of the geology, petrography, mineralogy, textures and geochemistry of the Skaergaard Complex in Eastern Greenland. This critical work describes the features of the intrusion, mechanisms of differentiation and suggests possible fractionation trends of the liquid composition as a result of crystallization (Wager & 3  Brown, 1968). Even today, the Skaergaard intrusion is the subject of many geological studies, with a number of questions that still remain unanswered. Cumulate terminology was developed by L.R. Wager, G.M. Brown and W.J. Wadsworth, in their paper entitled “Types of Igneous Cumulates” published in the Journal of Petrology, 1960. The new cumulate terminology was used to describe igneous rocks that formed by crystal accumulation. This was designed to replace the term ‘primary precipitate crystal’ that was in use up to that time. In the literature, cumulate terminology is synonymous with layered mafic intrusions and the description of the rocks which they contain (Hess, 1989, Holness et al., 2007, Hunter, 1996, Irvine, 1982, Wadsworth, 1985, Wager et al., 1960). Formation of cumulate textures and layering are the result of processes occurring in the magma chamber during differentiation. Some of these processes include fractional crystallization, new magma injections, mixing, contamination, changes in the intensive parameters (temperature, pressure, and oxygen fugacity), etc. (Hunter, 1996, Naslund & McBirney, 1996, Robb, 2005). Layering in mafic intrusions consists of sheet like units that are distinctive in their mineralogy, composition and/or textural features (Hess, 1989). Layers vary in thickness, composition, texture, internal structure, shape and/ or form (Irvine, 1982). Layering occurs in a number of different textural and compositional modes, such as in modal layering; which is characterized by a variation in the relative proportion of the constituent minerals. Phase layering is characterized by the appearance or disappearance of minerals in the crystallization sequence developed in modal layers. Cryptic layering (not visibly obvious) is a systematic variation in the chemical composition of cumulus minerals with stratigraphic height in the layered sequence. A rare type called size graded layering shows a smooth and gradual variation in the grain size of cumulate minerals. The regularity of layering may also vary from one location to another, or within the same intrusion. Layering can be rhythmic showing a repetitive sequence of distinctive layers. Rhythmic layering can be microscopic; microrhythmic (on the millimeter-centimeter scale) to macroscopic; macrorhythmic (on the meter scale), or intermittent demonstrating irregular patterns of layering. There are numerous types of layering described in the literature, but the above terms are the most common and widely used (Best, 2011, Hess, 1989, Irvine, 1982, Naslund & McBirney, 1996, Sen, 2001, Wager, 1953).  4  What we know today about large layered intrusions is a result of studies on a small number of large, ore bearing intrusions, which include: the Bushveld Complex (South Africa), the Stillwater Complex (Montana, USA), the Great Dyke (Zimbabwe), Noril’sk-Talnakh (Russia) and the Skaergaard Intrusion (Greenland). All of these with the exception of the Skaergaard are Precambrian in age (Best, 2011). The discovery of a new large layered mafic intrusion of Neoproterozoic age is an opportunity to study a new and younger magma chamber, and to test models for formation, mixing, magma chamber replenishment and mineralization. One of the critical pieces of information necessary in the study of these intrusions is an understanding of the stratigraphy. Even a basic understanding of the size, layering and chemical variation is an opportunity to compare with other intrusions to determine stratigraphic position and make predictions on the location of possible mineralization. Mineralogical, textural and chemical variations occur over stratigraphy as a result of the processes and mechanisms that take place in the magma chamber during the cooling and crystallization of the intrusion. Some trends in mineralogy and chemistry are predictable as a result of fractionation and the crystallization of early crystallizing minerals (e.g. olivine). Some of these include a progressive trend of iron enrichment with stratigraphic height (Veksler, 2009), increasing incompatible element concentrations in the residual liquids, and a general trend towards a more evolved or more felsic composition with stratigraphic height (McBirney, 1996). Knowing stratigraphic position is important in the search for mineral deposits. Economic mineralization is generally found in the stratigraphic centre of large intrusions. There are a few exceptions, where mineralization is found at the base of the intrusion and above the stratigraphic middle, but these are generally sub-economic. There is one significant exception: the Platreef in the Bushveld (Cawthorn, 2005), where the mineralization lies along the floor (at the base) in the northern part of the intrusion (Lee, 1996). The estimated thickness of the Suwar-Wadi Qutabah Complex is a least 400m (Greenough et al., 2011), in which Suwar is considered near the base and Wadi Qutabah lies up stratigraphy, but where, is the question. The full size and extent of the intrusion is unknown, as a result of erosion and sedimentary cover. Therefore, we can only estimate the size and stratigraphic position of these rocks. Understanding the stratigraphy of the intrusion allows for better estimation of stratigraphic position, and proposing areas for mineral exploration. It is also  5  a starting point in our understanding of magma chamber processes and mechanisms that occurred in this intrusion. Currently there is little known of the stratigraphy of the Suwar-Wadi Qutabah Complex. The primary objective of this study is to establish a broad scale stratigraphy of the Wadi Qutabah intrusion and to use this stratigraphy to make inferences about stratigraphic position, economic and tectonic significance and suggest possible target areas for mineral exploration. The 14 drill holes from the 2007 drill program from the Wadi Qutabah mafic intrusion are used for the purposes of correlation, petrographic study and geochemical analysis. Original data and samples were collected during drill core logging; petrographic thin sections were created from selected samples and subsequently studied. The petrographic thin sections were used for major element analyses. The Tescan Mira3 XMU Scanning Electron Microscope (SEM) was used to obtain major element analyses of in-situ mineral grains in petrographic thin sections. Geology, mineralogy, textures, layering, contact relationships, petrographic study, stratigraphic position and geochemistry are employed to create composite stratigraphic sections of the intrusion. Correlation of the layers, stratigraphy and geochemistry are presented over elevation, and comparisons to other famous intrusions are presented to infer stratigraphic position in the rocks from the Wadi Qutabah Complex. The geochemistry of augite is also used to examine the paleotectonic affinity of the magmas from which the intrusion is derived. Results of this study are a starting point for any future work on the Suwar-Wadi Qutabah intrusion, and are beneficial for mineral exploration and may contribute to the discovery of a world class mineral deposit.  6  Chapter 2.0 Geological and Tectonic Setting 2.1 The Arabian Plate Yemen is located on the Arabian Plate, which is one of the youngest and smallest of the tectonic plates. It formed approximately 25-30million years ago as a result of rifting that lead to the separation of Africa and Arabia, and the formation of the Red Sea and the Gulf of Aden (Johnson, 1998, Stern & Johnson, 2010). The plate is bordered by the Eurasian plate to the north, the Indian plate to the east and the African plate to the south and west. The northern border is a convergent boundary, whereas the border with the African plate is a divergent plate boundary, along the Red Sea Rift (Stern & Johnson, 2010). 2.2 Regional Geology and Tectonic Setting The geology of Yemen spans from the Achaean to the Cenozoic (Khanbari & Huchon, 2010). The Precambrian basement of Yemen is an important link in the understanding of the assembly of Gondwana during the Pan-African Orogeny ~870-550Ma (Kroner & Stern, 2004, Whitehouse et al., 2001). The formation of the Arabian-Nubian Shield (ANS) is tied to a supercontinent cycle, and begins with the breakup of Rodinia, and ends with the assembly of east and west Gondwana to form Greater Gondwana. The Juvenile crust of the Arabian-Nubian Shield is believed to have been generated in arc systems that were later accreted to the western margin of Gondwana. Generation and accretion of these arcs and microcontinental terranes occurred from ~870630Ma, (Li et al., 2008, Stern & Johnson, 2010) and from ~660-620 Ma collisional tectonics along the western margin of Gondwana resulted in continental orogenesis. Following orogenesis, the ANS experienced an extensional regime from ~620-540Ma (Stoeser & Frost, 2006). The Arabian-Nubian Shield (ANS) refers to the basement of northeast Africa and western Arabia, and is the northern part of the East African Orogen (EAO) (Abdelsalam & Stern, 1996). The Arabian Shield is located in western Saudi Arabia and Yemen, and is comprised of a series of geologically distinct terranes (Fig. 2.1 and 2.2). These comprise three island arc systems (Asir, Hijaz, Midyan) joined by island-arc-island-arc suture zones to the west, and terranes (Afif, Ad Dawadimi (Al Amrar), Ar Rayn) of continental origin separated by an orogenic belt in the East (Stern & Johnson, 2010, Stoeser & Camp, 1985). The Asir terrane is also referred to as the 7  Asir composite terrane, which contains a number of arc terranes. These include from east to west the Amlah (~720Ma), Tathlith-Malahah (660-700Ma), Al Qarah (715-740Ma), An Nimas (780850Ma), Bidah (>800Ma) and the Jiddah (760-870? Ma) arc terranes. The Paleoproterozoic Afif terrane is also a composite terrane and is composed of 2-3 ensimatic arc terranes and the Khida terrane which is underlain by continental crust. The Afif composite terrane includes the Khida (740-760Ma) in the south, and the Sawdah (670-695), Saqrah (720~740Ma), and the Siham (680-~715Ma) in the north (Stoeser & Frost, 2006). Some of the terrane boundaries are marked by the presence of ophiolite sequences. These range in age from ~690-870Ma (Stern & Johnson, 2010). Accretion of these terranes through collisional tectonics occurred from 715-630Ma, which resulted in the formation of the Arabian Neocraton (Stoeser & Camp, 1985). The accreted arcs resulted in a series of NNE/NE trending terranes (Whitehouse et al., 2001). Magmatism and intracratonic deformation continued and resulted in the formation of large scale left-lateral fault systems. These systems are responsible for the displacement of the northern part of the Shield ~250km to the northwest, and are part of the Pan-African Orogeny (Stoeser & Camp, 1985). Age of the arc assemblages of the Arabian Shield shows a progressive younging of terranes eastward (Fig. 2.1).The oldest of the arc terranes is of Neoproterozoic age (>800Ma) located in the west. It is bordered by younger arc terranes to the east and north, with the youngest of these lying farthest to the east (the Ar Ryan Terrane, 620-700Ma) (Stern & Johnson, 2010, Stoeser & Frost, 2006). The suture zones between these terranes may be significant complex structural features, which locally include ophiolite sequences that represent hundreds of kilometers of displacement. A study of the Nabitah Suture zone in Saudi Arabia revealed that there is significant left lateral displacement with major components of strike-slip movement, which would suggest that there is a component of oblique convergence that played a role in the assembly of the Arabian shield (Quick, 1991). Recognition of these large scale structural features and their direction(s) of movement will be important clues to a more conclusive correlation of the terranes of the Arabian Shield. Some controversy remains about the igneous rocks that date from 850-750Ma in these terranes. It has been suggested that they represent arc volcanism, while others suggest that they formed as a result of continental extension with contributions from underplating plume magmatism, oceanic plateaus, and arcs related to plume activities (Li et al., 2008). 8  2.3 Arabian Shield in Yemen In Yemen, the accreted terranes are from west to east the Asir (continental), Afif? (continental), Abas (continental), Al-Bayda (island arc), Al-Mahfid (continental) and Al-Mukalla (island arc) (Fig. 2.2). Each of these terranes is bordered by a suture zone that is comprised of ductile and brittle deformation (Stoeser & Camp, 1985, Whitehouse et al., 2001). Correlation of the terranes from north to the south is difficult, and hindered by a scarcity of geological and geochronological data. There are also significant changes in the orientation of the terranes and structures from Saudi Arabia in the north to Yemen in the south (Stoeser & Camp, 1985, Windley et al., 1996). Johnson & Stewart, (1996) proposed a correlation of these terranes, but a great deal of uncertainty remains due to the scarcity of data and reliable radiometric dates, as well as the potential for unrecognized faults and structures from the North to the South (Johnson & Stewart, 1996). Additional information is required to verify the correlation with greater certainty (Jackson, 1980). The Precambrian basement of Yemen is sandwiched between a collection of accreted arc terranes (Whitehouse et al., 2001). U-Pb dates of zircons from gneisses of the Al-Mahfid terrane confirmed the presence of Archean crust (~2.95-2.55Ga) and a minor Archean component in the Abas terrane (~2.6Ga)(Whitehouse et al., 1998). The Asir and Afif (composite) terranes of Saudi Arabia have been correlated to the northwestern terranes of Yemen (Fig. 2.2). The Nabitah Suture Zone and orogenic belt is believed to be the boundary between the two terranes. Extensive plutonism and high-grade metamorphism is recognized in the Nabitah orogenic belt (Windley et al., 1996). The Asir terrane, located along the western margin of Yemen, is composed of intercalated greenschist facies volcanics, high grade gneisses and sediments. Two episodes of arc magmatism are recognized in this terrane. The Afif terrane is composed of post-orogenic granites, volcanics and sediments that unconformably overlie the crystalline basement (Stoeser & Camp, 1985). In Yemen, the Afif terrane is recognized as orthogneisses intercalated with arc-type volcanics and intruded by undated post-tectonic intrusions (Windley et al., 1996). The breakup of Gondwana (~180Ma)(Kearey, 2001) led to the formation of large fault systems, and rift basins in the central and interior of Yemen. The orientation of these rift basins appears to reflect acquired Precambrian structural trends (Redfern & Jones, 1995). 9  The accreted terranes in Yemen are overlain by Phanerozoic sedimentary cover. The cover varies in extent and thickness throughout the Arabian plate and the Arabian Shield. There are abundant exposures of the crystalline basement in the western Arabian Peninsula, but few to the east. This is the result of regional uplift of the western margin of the Arabian plate associated with rifting in the Oligocene-Miocene, associated with emplacement of the Afar plume (Menzies et al., 1997). Regional uplift gave rise to the Yemen highlands, which reach 3660m in elevation (Davison et al., 1994), and rifting resulted in the formation of the Red Sea and the Gulf of Aden, and the separation of Africa and Arabia (Stern & Johnson, 2010). In the Oligocene-Miocene, magmatism associated with the Afar plume gave rise to the formation of continental flood basalt volcanism in the region of the African-Arabian triple junction. Volcanism resulted in the deposition of ~350 000km3 of flood basalts and rhyolites (Baker et al., 1998). These subaerial flows in Yemen are known as the Yemen Large Igneous Province or as the Yemen Traps (part of the Yemen volcanic group), and characterize part of the western region of Yemen. The eastern part is characterized by Tertiary deposits of carbonates, shales and sandstone sequences, and thus represents a non-volcanic margin (Khanbari & Huchon, 2010). The western margin of Yemen is characterized by a series of distinct rock types. A simplified list includes the metamorphosed Precambrian basement that is unconformably overlain by Phanerozoic sedimentary cover, which is overlain by the Yemen volcanic group (incl. the Yemen Traps), and intruded by syenitic, granitic and gabbroic bodies (Menzies et al., 2001).  2.4 Geological Setting of the Wadi Qutabah Intrusion The Wadi Qutabah intrusion is located approximately ~70km northwest of Sana’a, along the border of the states of Hajjah and Amran, in Yemen (Fig. 2.2). The intrusion is a layered noritic-gabbroic complex that intrudes late Proterozoic amphibolite-facies paragneisses, and is unconformably overlain by Phanerozoic sedimentary cover. These include the Akbarah shales (lower Permian), the Kuhlan sandstone (lower Jurassic) and the Amran limestone (lower to middle Jurassic) (Plank et al., 2007). The Wadi Qutabah intrusion is located on the western edge of the Afif/Asir terrane (Greenough et al., 2011, Whitehouse et al., 1998, Whitehouse et al., 2001, Windley et al., 1996). These have been interpreted as accreted arc terranes of the Pan-  10  African Orogeny (PAO), related to the assembly of Gondwana (Stoeser & Camp, 1985). The basement of the Afif terrane is believed to be continental in origin (~2.4-1.65Ga) (Whitehouse et al., 1998, Whitehouse et al., 2001). The Wadi Qutabah the intrusion covers an area of 23km2 (current known extents), and the sulphide horizons can be traced for more than 19km in the rugged mountainous terrain (Corporation, 2012). The full extent of the intrusion is currently unknown as a result of sedimentary cover, and the significant geographical area that it underlies. Numerous structural events have affected the intrusion. It is cut by large scale faults that have been identified through surface mapping, the extent of which are not fully determined. The direction and the magnitude of movement along these planes are also uncertain (Plank et al., 2007). A study of aerial photographs, accompanied by field work in the Hajjah district by Heikal, (1989) shows that the structural trends are dominated by faulting, and not folding. The Precambrian rocks in the area have a dominant WNW and NW fracture pattern believed to be related to the Najd fault system (NW-SE wrench faults) of late Proterozoic-Cambrian age (630560Ma possibly to 530Ma) (Heikal, 1989, Kroner & Stern, 2004, Redfern & Jones