GENESIS OF THE BALLYNOE BARITE DEPOSIT,IRELAND,AND OTHER BRITISH STRATABOUND BARI1E DEPOSITS. A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY OF THE UNIVERSITY OF LONDON By JOHN RUSSELL BARRETT Mining Geology Division, Department of Geology, Royal School of Mines, Imperiel College of Science and Technology, The University of London. February 1975 IA curious grey rock' A,B.Wynne 1861 -3- ABSTRACT This thesis describes the geology of a large,stratiform barite deposit located at Ballynoe (near Silvermines) Co.Tipperary,Ireland.The deposithas been investigated from the sedimentological,mineralogical and geochemical aspects in order to determine its probable genesis. The bedded barite is a conformable,mineralised-horizon of Upper Tournaisian age.The barite horizon is associated with a non-sequence at the top of the Muddy Reef Limestone and marks the transition from a quiet water environment to one of dynamic sedimentation.In the footwall succession (Upper Devonian - Lower Tournaisian) a major sedimentary cycle is evident,a cycle which terminates in a non-sequence and is overlain by the barite horizon.Mass extinction of the fauna is associated with the non-sequence. The geometry of the barite orebody correlates with the palaeo-topography of the footwall,the topography acting as an important control over the lateral extent,thickness and nature of the mineralisation.Sedimentary features within the barite horizon suggest that the barite was precipitated in the form of a cryptocrystalline mud.Lithification and diagenesis resulted in extensive stylolitisation,recrystal- lisation and remobilization of the barite. The wallrock geochemistry suggests that the dispersion of anomalous barium is strictly confined to a mineralised- horizon directly overlying the Muddy Reef Limestone.Iron and silicon were associated with the initial emplacement of the barite.Sulphur and oxygen isotope values suggest that contemporaneous slavvater so played a significant role in the precipitation of the barite. The barite was precipitated in a partially restricted marine lagoon (carbonate mudbanks controlling water circul- ation and the Eh and pH conditions),the ore forming solutions probably being chloride-brines debouching from fractures along the Silvermines Fault.The metals in the brines(migrating formation waters) were derived from the Lower Palaeozoic troughs to the north and south of Ballynoe.Some admixing with juvenile waters associated with contemporaneous volcanism probably occurred. ACKNOWLEDGEMENTS This research project was formulated through the insight of Professor G.R.Davis who regarded the Ballynoe barite deposit as a possible 'genetic key' to the mineralisation of the Irish Carboniferous Limestone.The work was also supervised and edited by Professor G.R.Davis whose suggestions and constructive criticism is gratefully acknowledged. The research was supported financially by the Natural Environmental Research Council,an award from the William Selkirk Scholarship fund and a grant from Dresser Minerals. I express my sincere gratitude to these bodies. The field investigations were facilitated through Mr. Ovid Johnson,Jr.,Exploration Manager of Dresser Minerals, whilst sustained assistance in and out of the field was given by Staff geologists,Dr.R.W.Stewart and Mr.R.D.Turner. I offer them my sincere thanks.I am also grateful to Mr.R.B. Harrison,Managing Director,Magcobar (Ireland) Ltd., and to his staff at the Ballynoe Mine. The co-operation received from Dr.W.W.Weber,Vice-Pres- ident of International Mogul Mines Ltd., and Mr.E.Grennan of Basin Exploration is gratefully acknowledged. I express my gratitude to the technical staff of the Department of Geology at Imperial College for their consid- erable assistance,notably to Mr.Tony Thompson of the Applied Geochemistry Research Group and to Mr.B.Foster,Mr.R.Curtis, Miss T.Leslie,Mrs.K.Irving,Mr.N.Wilkinson,Mrs H.Richardson and to the late Mr.Jimmy Gee. I record stimulating discussion with Dr.C.Halls,Dr.P. Garrard,Mr.J.McMoore and with my fellow research students, especially Mr.D.Pearson - many thanks to all. Finally,I should like=to thank my parents for their long continued encouragement and assistance. -6- Note : Units of measurement All units in this work (with minor exception) are in Imperial units.These units are used by Magcobar and Mogul Mines and have been retained to avoid confusion. -7- CONTENTS is Page ABSTRACT 3 ACKNOWLEDGEMENTS 5 CONlhNTS 7 LIST OF FIGURES 12 LIST OF TABLES 15 LIST OF PLATES 16 CHAPTER ONE INTRODUCTION 1-1. Foreward 19 1-2. Location of the barite deposit 19 1-3. Geography 20 1-4. Historical background 21 1-5. The Magcobar operation 23 1-6. The role of barite in drilling fluids 24 1-7. Previous geological work at Ballynoe 26 1-8. The present investigation 30 CHAPTER TWO THE GEOLOGICAL SETTING OF BALLNOE 2-1. Introduction 32 2-2. Regional stratigraphical setting 32 2-3. Regional structural setting 39 2-4. Stratigraphy of the Ballynoc Mine 41 Silurian L .1 Devonian (Old Red Sandstone) 44 Basal Fragmental L7 Lower Dolomite L.7 Muddy Limestone 49 Muddy Reef Limestone 49 Green Argillite 50 Upper Reef Limestone & Dolomite Breccia 55 Chert Horizon 57 Calp Limestone 59 2-5. Structural setting of the Ballynoe barite 59 -8- Page 2-5a. Faulting 59 2-5b, Jointing 63 2-5c. Folding 63 2-5d. Structure of the footwall rocks 66 2-6. Summary 70 CHAPTER THREE THE BARITE HORIZON 3-1. Introduction 72 3-2. Form of the Ballynoe barite orebody 72 3-3. Stratification of the barite horizon 76 3-3a. The basal zone 80 Barite breccia 83 Bedded hematite formation 86 Replacement of the footwall by barite 94 3-3b. The siliceous barite zone 94 3-3c. The stylolitic and spherulitic barite 97 3-3d. Massive grey-black microcrystalline barite 103 3-3e. Massive sulphide 'cap' to ',-„he orebody 109 3-31. Macrocrystalline barite 'cap' to the orebody 111 3-4. Other barite occurrences within the mineralised- 117 horizon 3-5. Summary 119 CHAPTER FOUR THE MINERALOGY OF THE BARITE HORIZON 4-1. Introduction 121 472. Minerals associated with the barite horizon 122 4-3. Descriptive mineralogy 123 4-3a. -Pyrite and marcasite 123 4-3b. Partial trace element content of the pyrite 137 4-3c. Copper mineralisation_ 139 4-3d. Sphalerite and galena 142 4-4. Diagenetic and supergene modification of the 148 barite deposit Page 4-4a. Diagenesis 148 4-4b. Supergene alteration 149 4-4c. Mineral formation as a result of contemporary 151 weathering 4-5. Paragenesis of the barite deposit 154 CHAPTER FIVE GEOCHEMISTRY OF THE BARITE HORIZON 5-1. Introduction 159 5-2. Geochemistry of the wallrocks 159 5-2a. Wallrock dispersion in sub-economic areas of 160 the 'mineralised-horizon' 5-2b, Wallrock dispersion adjacent to the barite ore- 165 1 body 5-3. Element dispersion within the barite orebody 170 5-3a. Silicon 171 5-3b. Strontium 173 5-3c. Aluminium 175 5-3d. Magnesium 175 5-3e. Calcium 177 5-3f. Iron 178 5-3g. Copper 178 5-3h. Lead and zinc 178 5-3i. Other elements 180 5-33. Element dispersion between primary and secondary 180 barite 5-4. Barium content of rocks in the Silvermines region 181 5-5. Sulphur and oxygen isotope geochemistry 183 5-5a. Isotopic data for the Ballynoe barite 185 5-5b. Discussion of results 185 5-6. Summary 188 -10- CHAPTER SIX Eage STRATABOUND BARITE IN THE BRITISH ISLES 6-1 . Introduction 190 6-2. Barite in a sedimentary environment 190 6-2a. Reported occurrences of sedimentary barite 191 Cambrian 191 Devonian 191 Carboniferous 193 Permian 1 96 Triassic 197 Jurassic 198 Cretaceous 198 Eocene 201 6-3. Distribution of Ba in English and Welsh stream 201 sediments Related to mining activity 201 Related to lithologies carrying a high .Ba. background 203 Related to diagenetic barite 204 6-4. The barium anomaly to the NE of Leeds,Yorks. 204 6-4a. Distribution of Ba in stream sediments 206 6-4b. Follow up investigation 206 6-4c. The stratigraphical range of barite mineralisation 213 6-5. Barite 'flatting' deposits 213 6-6. Discussion and conclusions 215 CHAPTER SEVEN DISCUSSION - GENESIS OF THE BALLYNOE BARITE DEPOSIT 7-1. Introduction 21 9 7-2. Geologic environment 220 7-2a. Sedimentary setting 220 7-2b. Fossil topography of the Muddy Reef Limestone 223 7-2e. Sedimentary characteristics of the barite orebody 224 7-2d. Sedimentary characteristics of the sulphide 'cap' 227 7-2e. Summary of the sedimentary features 228 7-3. Deposition of the barite 229 7-4. Nature and source of ore-forming fluid 232 7-5. Genetic model for the Ballynoe barite 236 -11- CHAPTER EIGHT SUMMARY OF CONCLUSIONS Lam 8-1. - Conclusions 239 REFERENCES 242 APPENDIX 253 : Drill Coverage in the Silvermines Area 253 II : The Conolly Contour Method 254 III : The Direct Reading Spectrograph 255 IV The Optical Emission Spectrograph 259 -12- LIST OF FIGURES Page 1.1 Irish production of mined barite 1870 - 1973 25 2.1 Geological map of Ireland 34 2.2 Upper Tournaisian (Waulsortian) facies in Ireland 36 2.3 Stratigraphical column,Silvermines area 43 2,3A Regional geology around Silvermines 43 2,L1. Local geological map of Ballynoe 45 2.5 Devonian - Lower Tournaisian transition sequence 48 2.6 Plot of the diameter of crinoid ossicles in DDH 60-31 2.7 Brecciated zones in the hangingwall rocks 56 2.8 Development of breccia as observed in DDH 88 56 2.9 First and second faulting at Ballynoe 61 2.10 North - south faulting at Ballynoe 62 2.11 The southern limb of the Kilrnastulla valley 64 syncline (Ballynoe section) 2.12 Structure contour plot of the top of the Muddy 67 Reef Limestone 2.13 The footwall 'highs' and 'lows' 69 3.1 The extent of the Silvermines