NATURAL ENVIRONMENT RESEARCH COUNCIL INSTITUTE OF GEOLOGICAL SCIENCES Report No. 74/14 ASSESSMENT OF BRITISH SANDAND GRAVEL RESOURCES No. 12 The sand and gravel resources of the country around Gerrards Cross, Buckinghamshire Description of parts of 7 : 25 000 resource sheets SU 98, SU 99, TO 08 and TO 09 H. C. Squirrell, BSc, PhD with contributions by C. E. Corser, BSc London: Her Majesty's Stationery Office 1974 The Institute of Geological Sciences was formedby the incorporation of the Geological Surveyof Great Britain and the Museumof Practical Geology with Overseas Geological Surveysand is a constituentbody of the Natural Environment Research Council 0 Crown copyright1974 It is recommended that reference to this report be made in the following form: SQUIRRELL,H. C. 1974. The sand and gravel resources of the country around Gerrards Cross, Buckinghamshire: Description of parts of 1 : 25 000 resource sheets SU 98, SU 99, TQ 08 and TQ 09. Rep. Znst. Geol. Sci., No.74114. 169 pp. ISBN 0 1 1 8807 10 2 ii PREFACE It has become increasingly clear in recent years that an assessment of resources of many minerals should be undertaken. This is the eleventh report of the Mineral Assessment Unit with was set up in May 1968 to undertake such work. It describes the resources of sand and gravel of 143.5 km2 of country shown on the accompanying 1:25 000 resource sheet. This survey is concerned with assessing sand and gravel resources on a regional scale at the indicated level; the deposits are not outlined completely nor their grade established throughout. The work may be regarded as the applicationto large areasof methods used commercially for evaluating reserves on small sites. It may also be regarded as an extension of geological mapping by providing information about the thickness and quality of deposits. The survey was conducted by Dr H. C. Squirrell, assisted by Mr J.A. Gray, Mr A. R. Clayton, Mr P. Robson and Mr C. E. Corser as field officers who supervised the drilling and sampling programme. Mr Corser helped in the preparation of data for this publication. The work is based on a geological survey at 1:lO 560 in 1902-1920 by Mr J.A. Howe, Mr R. L. Sherlock, Mr A. H. Noble and Mr C. N. Bromhead, and revised by Dr Squirrel1 in 1971. Mr J. W. Gardner, CBE (Land Agent) was responsible for negotiating access to land for drilling. The ready cooperation of landowners and tenants in this work is gratefully acknowledged. Financial support for the survey was provided by the Department of the Environment. Kingsley Dunham Director Institute of Geological Sciences Exhibition Road South Kensington London SW7 2DE 1 January 1974 Any enquiries concerning this report may be addressed to Head, Mineral Assessment Unit, Instituteof Geological Sciences, Exhibition Road, LondonSW72DE iii CONTENTS Page INTRODUCTION 1 Aims and Limitations 1 Procedure 2 The Map 3 DESCRIPTION OF THE GERRARDS CROSS AREA 3 General 3 Topography 4 Geology 4 Composition of the Sand and Gravel Deposits 7 Results 9 Notes on Resource Blocks 9 Sand in the Reading Beds 17 List of Quarries 20 REFERENCES 20 APPENDIX A: ASSESSMENTPROCEDURE 21 APPENDIX B: CLASSIFICATION AND DESCRIPTION OF SANDAND GRAVEL 22 APPENDIX C: BOREHOLERECORDS 27 Explanation 27 List of Assessment Boreholes 29 The Records - SU 98 31 TQ 09 99 TQ 08 108 su 99 140 ILLUSTRATIONS Fig. 1. Sketch-map showing the location of the Gerrards Cross area and the position of the resource block boundaries 4 Fig. 2. Particle size distribution for the assessed thicknessof sand and gravel in resource blocks A to I 8 Fig. 3. Example of resource block assessment: statement and calculation 23 Fig. 4. Example of resource block assessment: map of a fictitious block 24 Fig. 5. Diagram to show the descriptive categories used in the classification of sand and gravel 26 Map The sand and gravel resources of the Gerrards Cross area In pocket TABLES Table 1. Classification of mapped deposits 6 Table 2. Summary of statistical results 10 Table 3. Data from assessment boreholes: block A 11 Table 4. Data from assessment boreholes: block B 12 Table 5. Data from assessment boreholes: block C 13 Table 6. Data from assessment boreholes: block D 15 V Page Table 7. Datafrom assessment boreholes: block E 15 Table 8.Data from assessment boreholes: block F 16 Table 9. Datafrom assessment boreholes: block G 16 Table 10. Datafrom assessment boreholes: block H 18 Table 11 Datafrom assessment boreholes: block I 18 Table 12. The thickness and mean grading percentages of Reading Beds sands proved in assessment boreholes 19 Table 13. Classification of gravel,sand and fines 25 vii Summary The geological maps of the Institute of Geological Sciences, pre-existing borehole information, and 143 boreholes drilled for the Mineral Assessment Unit form the basis of the assessment of sand and gravel resources in the Gerrards Cross area, Buckinghamshire. All deposits in the area which might be potentially workable for sand and gravel (mineral) have been investigated geologically and a simple statistical method has been used to estimate the volume. The reliability of the volume estimates is given at the 95 per cent confidence level. The mineral-bearing ground shown on the 1:25 000 map is divided into resource blocks, each ideally containing approximately 10 km2 of sand and gravel. For each block the mineral-bearing area, the mean thickness of overburden and mineral, and the mean grading are given and the geo- morphology and geology of the deposits described. The position of the boreholes and exposures, the geology and topography and the outlines of the blocks are shown on the accompanying map. Detailed borehole data are given. Sommaire Les cartes gdologiques de 1'Institute of Geological Sciences, les renseignements sur des trous de sonde qui existaient ddjja, et 143 trous de sonde, fords pour le Mineral Assessment Unit, constituent la base de 1'4valuation des ressources en sable et en gravier dansla rdgion de Gerrards Cross, Buckinghamshire. Tous les de'p6ts dans la rdgion, qui prdsentent la possibilitd df exploitation pour le sable et le gravier (mineral) ont dtd 4tudids du point de vue gdologique, et on s'est servi d'une mgthocie statistique simple pour en dvaluer le volume. Les 6valuations de volume sont tenues d'6tr-e a 95% exactes. Le terrain mindralisd montrd la carte 1:25 000 est divise/s en blocs de ressources, chacun d'eux avant id6alement environ 10 km2 de sable et de gravier. On donne pour chaque bloc l'dtendue mindralisde, l'epaisseur moyenne de recouvrement et de mindral, et la gradation moyenne, On ddcrit la gdomorphologie et la gdologie des d4p6ts. La situation des trous de sonde et des affleurements, la ge'ologie et la topographie, et la configuration des blocs sont montrds sur la carte. Des donndes ddtailldes des trous de sonde sont donndes. Zusammenfassung Die geologischen Karten von der Institute of Geological Sciences, die vorher existierende information in Bezug auf Bohrlochern, und 143 BohrlGcher, die fur das Mineral Assessment Unit gemacht waren, bilden den Grund fur die Einschatzung der Sand- und Schotter-mittel im Gerrards Cross Gebiet, Buckinghamshire. Man hat im Gebiet alle Ablagerungen, die moglich bearbeitbar fur Sand und Schotter (Mineral) sind, geologisch untersucht, und man hat auch eine einfache statistische Methode .benutzt, urn das Volumen zu schatzen. Man gibt die Zuverlassigkeit der Volumenschatzungen mit 9570 Vertrauens- grenzwerten. Man teilt den mineralhaltigen Grund auf der 1:25 000 Karte in Mittelsblocke, wovon feder idealisch ungefahr 10 km2 von Sand und Schotter einschliesst. Fiir jeden Block gibt man das mineralhaltige Gebiet, die Durchschnittsdicke von Uberlastung und Mineral und die Durchschnittsklassifizierung. Man beschreibt auch die Geomorphologie und Geologie der Ablagerung. Man zeigt die Lage von den Bohrlochern und Aufschliissen, die Geologie und Topographie, auch die Skizzen von den Blocken auf der Regleitkarte. Man gibt ausfuhrliche Bohrlocherdaten. viii The sand andgravel resources of the country around Gerrards Cross, Buckinghamshire Description of parts of 1 : 25 000 resource sheets SU 98, SU 99, TQ 08 and TQ 09 H. C. SQUIRRELL~,BSc, PhD Introduction widely or otherwise inappropriately spaced to permit the mineral bodies to be outlined AIMS AND LIMITATIONS completely or the grade established throughout'. National resources of many of the 'bulk' or (A.non.,1948, p. 15). 'industrial' minerals may seem so large that stocktaking is unnecessary, but the demand for The survey is therefore concerned not with land for all purposes and for minerals is the estimation of reserves (which can only be intensifying. In contrast with other develop- assessed in the light of particular or existing ments of land there may be little or no choice economic considerations), but rather with of area for the workingof minerals and in the resources, which include deposits not currently case of low-price materials such as sand and exploitable but having a foreseeable use. Clearly, gravel transport costs will be an important the social and economic criteria used to decide factor. Whereas the economic benefit of using whether a deposit may be workable at some time land for many other purposes can be assessed, in the future cannot be rigorously defined. A.fter hitherto little has been known of the potential discussion with the industry, the following value, on a regional scale, of any mineral arbitrary physical criteria were adopted for this resources which may be present. A.n important survey: aim of the work is to improve the factual back- a. the deposit should average at least 1 m ground against which planning policies can be (3.3 ft) in thickness. decided(Archer, 1969; Thurrell, 1971). b. the ratio of overburden to sand and gravel should be no more than 3: 1.