Kyanite in Kenya—The Mubai and the Musuriamboi Kyanite-Quartz Schists
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FOREWORD Massive easily workable kyanite was first discovered in Kenya in 1942 and pro- duction started in 1944. Six years later Kenya was the world’s chief producer of kyanite. Since then there has been a fall off in production as the more accessible rich ore was worked out, but as a process for the extraction of kyanite from less rich material has been evolved, it may be expected that the production will once again rise. The kyanite now extracted is calcined and converted to mullite before export. Dr. Temperley in this, the first memoir published by the Geological Survey of Kenya, gives a full account of the history of development of the industry and of the kyanite deposits that are either worked or known in various parts of Kenya. He also gives an account of kyanite deposits throughout the world, providing a classification of the various types of deposits, and attempts to solve the problems of the genesis of their rocks. To assist prospectors early chapters of the memoir deal with the properties of kyanite and allied minerals, and the specifications for saleable material. The work entailed in the preparation of the memoir was made possible by means of a grant from the Colonial Development and Welfare Vote. Mr. A. L. Stewart, Metallurgist in the Mines and Geological Department, contri- buted sections on the laboratory investigation of newly discovered deposits. Other colleagues in the department assisted by discussion and in the search for literature. Nairobi, WILLIAM PULFREY, 30th July, 1952. Chief Geologist. CONTENTS PAGE I. Introduction 1 II. Uses and properties of kyanite .. .. .. .. 1 1. Industrial uses and properties . 1 2. Diagnostic properties . .. 2 1H. Specification, preparation for market and tests . 6 IV. Kyanite 1n Kenya—Historical notes, exploitation and production . 11 1. Early records. 11 2. Recentdiscoveries .. .. .. .. .. .. .. .. 12 3. Geological investigations . .. 14 4. Pegging and exploitation . 14 5. Production figures . .. .. .. .. .. 15 V. Kyanite 1n Kenya—The Murka-Loosoito kyanite.belt . .. .. 16 1. Situation and communications . 16 2. Topography and exposures . 16 3. Associated rocks . l6 4. The kyanite-quartz schist, extent, attitude and thickness . 18 5. The kyanite-quartz schist, content of disseminated kyanite . 24 6. Massive kyanite rock; mode of occurrence, associated minerals and alumina content. 27 7. Distribution of massive kyanite rock . 31 8. The origin of kyanite 1n the Murka-Loosoito kyanite belt . 38 VI. Kyanite in Kenya—The Mubai and the Musuriamboi kyanite-quartz schists. 40 1. TheMubaideposit .. .. .. .. .. .. .. .. 40 (1)Fieldwork .. .. .. .. .. .. .. .. 40 (2) Ore-dressing report . 44 2. The Musuriamboi deposit . 45 VII. Kyanite in Kenya—Longalonga-Signal Hill and the“Tulimani-Kyabaluki kyanite belts . 49 1. General . 49 2. The Longalonga-Signal Hill graphitic kyanite be1t- . 50 (1) Situation and extent of belt . 50 (2) Associated rocks . 52 (3) The kyanitic schists . 53 (4) Colluvial and alluvial kyanite . .. 53 (5) Prospecting . S4 3. The Tulimani-Kyabaluki graphitic kyanite.belt . 54 (1) Situation and extent of belt . 54 (2) Associated rocks . 55 (3) The kyanitic schists . ' . 56 (4) Kyanite in quartz veins, pegmatites and other rocks . 56 VIII. Kyanite 1n Kenya~0ccurrences 1n the vicinity of Sultan Hamud . 57 1 General . 57 2. Associated rocks . 59 3. Details of the occurrences . -. 59 IX. Kyanite 111 Kenya——0ccurrences 1n south, central and western Kenya and the Taitahills .. .. .. .. .. .. .. .. .. 52 ii CONTENTS—(Conn!) PAGE X. Modes of occurrence of kyanitemgeneral 1. General Statement ‘ 1 2. Disseminations in polymineralic schists and occurrences in associated quartz veins and pegmatites, and as massive concentrations (1) The staurolite-kyanite subfacies . (2) Exploited polymineralic deposits in the United States . (3) Kyanliutz-bearing quartz veins and pegmatites in polymineralic (4) Massive kyanite concentrations in polymineralic schists . 3. Disseminations in quartzose rocks and associated massive kyanite concentrations and kyanitiferous quartz veins . (1) Exploited deposits'in India . (2) Exploited deposits'in quartzose rocks 1n the United States (3) Deposits in Western Australia, Uganda and Kenya (4) Nyasaland .. (5) Bechuanaland. 4. Occurrences 1n eclogites, steatite, and injection gneisses”and as pseudo- morphs after andalusite. (1) Kyanite"1n eclogite (2) Kyanite in steatite .. (3) Kyanite in injection gneisses . (4) Kyanite after andalusite XI The origin of kyanite . 1. Origin of kyanite disseminated'1n polymineralic schists 2. Origin of kyanite'in quartz veins and pegmatites . 3. Origin of kyanite disseminated and concentrated 1n quartzose rocks . cXII. References APPENDICES No.1. Specification for kyanite purchased by the United States Government for the national stockpile .. 85 No.2. Melting points and'1nversion temperatures of some refractory minerals No.3. World production of kyanite .. .. .. .. .. ' 87 LIST OF ILLUSTRATIONS . The efi‘ect of impurities on the alumina content of kyanite ore Kyanite occurrences in southern Kenya . Murka-Loosoito kyanite belt—Communications . Cross-sections through Murka, Kevas and Loosoito hills Plan of Murka hill . Diagrammatic representation of Murka hill . Kyanite-rock quarries, Murka hill, September, 1951 . Workings of kyanite rock, East Africa Minerals, Ltd. Cross-sections of Loosoito hill . Micrographs showing textural varieties of the kyanite-quartz schist of the Murka- Loosoito kyanite belt . Plan of the Mubai kyanite-quartz schist deposit . Plan of the Musuriamboi kyanite-quartz schist deposit . Micrographs of kyanite-quartz schists from (a) Mubai and (b) Musuriamboi '14. Micrograph of a graphitic kyanite schist from Longalonga - 15. Sketch-map of part of the Longalonga-Signal hill graphitic kyanite belt. 16. Sketch-map of the south-eastern part of the Tulimani-Kyabaluki kyanite belt 17. Sketch-map showing some kyanite occurrences near Sultan Hamud . 18. Diagram to show the equivalence of the kyanite content of schists and kyanite rock to the SiOzz A1203 molecular ratios of clays and loesses . '“KY‘ANITE IN KENYA I—L-INTRODUCI'ION , , Kenya has produced in the last eight years 80,000 tons of kyanite valued at " approximately £570,000. {In 1949, the year of maximum production, kyanite was third in "Value among the mineral prOducts of Kenya, being exceéded only by soda "ash and ' gold. In this memoir the-Murka-L’oosoito kyanite belt, which has yielded the whole kyanite output, is described in considerable detail but chapters are also included giving some information bearing on the potentiality of other kyanite occurrences in the Colony. In order that the Kenya kyanite deposits may be seen in their true relationship to those of other countries a summary review of all the literature on kyanite available in the library of the Mines and Geology Department has been included. Throughout the ‘study the question of the origin of kyanite has been kept in mind and, in the hope that the work might throw some light on this problem, the deposits described have been classified according to the mode of occurrence of the kyanite rather than their economic value. 'In a final chapter on the origin of kyanite the facts that have emerged from this stUdy are summarized, but it has not proved possible to propose any completely satisfactory theory to account for the features of those deposits that have yielded the greatest tonnages of kyanite. The author wishes to thank Dr. J. A. Dunn for a most interesting letter expressing his views on the origin of the Indian kyanite deposits. He is grateful for hospitality kindly afforded to him by Messrs. Kenya Kyanite Ltd. at Murka and by Messrs. East . Africa Minerals Ltd. at Kevas during the several visits he has paid to the, Murka- Loosoito kyanite belt. The author is also indebted to Mr. P. H. Cull of Sultan Hamud for bothghospitality and the provision of guides when he visited the numerous kyanite occurrences discovered by Mr. Cull in that vicinity. The Director and the Game Wardens of the Royal National Parks of Kenya have been most helpful in the facilities placed at the author’s disposal during his work in the Tsavo Park, especially during his exploration of the Longalonga-Signal Hill kyanite belt. II—USES AND PROPERTIES OF KYANITE l. INDUSTRIAL USES AND PROPERTIES (1) Name and Mineral Group The name kyanite or cyanite is derived from the Greek word for blue. Another name for the mineral is disthene, derived from the Greek words for double strength, 'which refers to the fact that the hardness and electrical properties of the mineral vary according to the direction in which tests are made. Kyanite is a memberaof a group of minerals, known in industry as the “sillimanite group”, all of which“ possess important refractory properties. The group includes kyanite, andalusite, sillimanite, dumortierite, topaz and mullite. All are naturally occurring minerals but the mullite used in industry is artificial and produced when any of the other five is heated at temperatures above 1,545" C. Mullite is often referred to in, industry as “artificial sillimanite”, irrespective of the mineral from which it is derived, and the name sillimanite is sometimes applied loosely to any member of the group. The value of all these minerals as refractories depends on the high decomposition temperature (1,810“ C.) of mullite into which they are converted during use. Besides its high decomposition temperature mullite imparts to the products in,which;.it_is formed such highly desirable properties as low thermal expansion with resultant resistance to heat-shock, moderate thermal conductivity, high refractoriness under load even at high temperatures and resistance to chemical corrosion, particularly» by acid slags. A'list of the most refractory minerals with their melting points or decomposition temperatures is given in appendix No. 2. 2 An account of the history of research on, and industrial development of kyanite and sillimanite as refractory minerals up to 1929 is contained in a memoir by Dunn (1929)* on the refractory minerals of Southern India. (2) Industrial Uses A useful account of the sillimanite group of minerals has been given by Riddle and Foster (1949).