'7 >' ( UNIVERSITY OF LONDON IMPERIAL COLLEGE OF SCIENCE AND TECHNOLOGY Royal School Of Mines Department Of Geology Applied Geochemistry Research Group A Thesis Entitled Factors Aff ecting Trace Element Distribution In Stream Sediments In Selected Areas Of Base Metal Mineralization In Lancashire And Cornwall. By Solomon Kwesi Sey Submitted for the degree of Master of Philosophy. March 1981. Dedicated to my daughter, ADWOA ETSIWAA, whose arrival, courage and innocent cheerfulness in adversity, contributed a great deal to the completion of this thesis• ABSTRACT The geochemistry of drainage sediments from two areas in Cornwall and Lancashire with similar base metal mineralization, was studied in order to assess sources of variability in trace element distribution. The Cornwall area was of uniform lithology and there was widespread development of secondary Fe-Mn oxides in drainage channels. The geology of the Lancashire area was more diverse and secondary Fe-Mn oxide development was restricted. Analysis of variance models were used to derive estimates of spatial variability (related to geology), procedural error (sampling and analytical errors) and annual variation. Data obtained by atomic absorption spectrophotometric analysis (AAS) of the Cornwall samples had good precision and indicated that for most elements spatial variability contributed most to total variability, even in this area of uniform geology. Spatial variability for ore-elements reflected the presence of mineralization but for other elements spatial variability was attributed mainly to secondary environmental processes. In general, procedural error accounted for up to 40% of total variability and sampling errors contributed more to this than did laboratory errors • In contrast, data obtained by analyzing the same sample solutions by inductively coupled plasma emission spectrometry (ICP) showed poor precision, with procedural errors exceeding spatial variability for most elements, and laboratory errors exceeding sampling errors. However, the data structure revealed by Principal Component and factor analysis was similar for AAS and ICP data. The Lancashire samples were analyzed by ICP only and the data obtained had similar precision to the Cornwall ICP data. The more complex geology was reflected in increased spatial variability for some elements. Annual variation in sediment trace-element geochemistry was evaluated for the Cornwall area only and found to be unimportant• The influence of secondary Fe-Mn oxides on trace element distribution was confirmed for Zn, Co, Ni and Ag. The possible utility of oxide coatings on the coarse fraction of sediment as a sample medium in geochemical exploration was investigated. Oxide coatings were found to concentrate hydromorphically dispersed elements, such as Ag, whose concentrations are usually low in stream sediments, and to provide useful dispersion trains. ACKNOWLEDGEMNT I am greatly indebted to a number of individuals and organizations for the successful completion of this study. To my supervisors, Professor J. S. Webb and Dr Martin Hale, I am grateful for their patience, understanding and continuous interest in the project. I should like to express my gratitude to Dr R. J. Howarth for his interest throughout the study and for reading through the thesis, to my colleagues for mutually beneficial discussions and use of computer programs, and to the computer centre advisory unit, especially Messrs Roger Hunt and Tony Davison. This thesis was typed with the Draft/Format facility. I should also like to thank the British Council for financial assistance during the course of the study and the Ghana Geological Survey Department for granting me the study leave to pursue it. Finally my thanks go to Nana Aba, Paakow and Maame, for enduring the hardships and family upheavals in the last three years. LIST OF CONTENTS Chapter one -• Introduction 1 1.1 The nature of dispersion halos and trains 3 1.1.1 Background 3 1.1.2 Primary halo 4 1.1.3 Secondary halo 5 1.2 Secondary dispersion and geochemical surveys 5 1.3 Aims of the research 9 Chapter two - Description of the study areas 13 2.1 The Cornwall study area 13 2.1.1 Location 13 2.1.2 Regional setting and geological structure 13 2.1.3 Granite emplacement and mineralization 15 2.1.4 Geology of the study area 16 2.1.5 Field observations 18 2.2 The Lancashire study area 19 2.2.1 Regional setting 19 2.2.2 Mineralization 21 2.2.3 Location and geology of the study area 23 2.2.4 Field observations 26 Chapter three - Analytical techniques 28 3.1 Orientation studies 28 3.1.1 Procedures 28 3.1.2 Nitric Acid 29 3.1.3 Nitric-Perchloric attack method I 29 3.1.4 Nitric-Perchloric attack method II 30 3.1.5 Determinations 31 3.2 Results for fine fraction 31 3.2.1 Loss on ignition 31 3.2.2 Relative efficiency of extraction 33 3.2.3 Analytical precision 35 3.2.4 Anomaly contrast 36 3.2.5 Summary 38 3.3 Results for Fe Mn coatings on coarse fraction 39 3.3.1 Relative efficiency of extraction 40 3.3.2 Analytical precision 41 3.3.3 Anomaly contrast 41 3.3.4 Summary 42 3.4 Partial extraction techniques 43 3.4.1 Sodium dithionite 43 3.4.2 Hydroxyammonium chloride 45 3.4.3 Hydrogen peroxide and hydrochloric acid 47 3.5 Procedures used in this study 50 3.5.1 Experimental 51 3.5.2 Extractibility of selected reagents 53 3.6 Alternative procedures for selected techniques 57 3.7 Other analytical procedures 62 3.8 Summary 62 Chapter four - Analysis of variance on the data 64 4.1 Errors in geochemical data 64 4.1.1 Bias 65 4.1.2 Precision 66 4.1.3 Distribution models 66 4.2 The analysis of variance 67 4.2.1 Normality 67 4.2.2 Homogeneous variance 68 4.2.3 Error independence 69 4.2.4 Zero means 70 4.3 Sampling design 70 4.4 Models for general sampling and laboratory errors 71 4.4.1 Comparisons between sample types and localities 73 4.4.2 Annual variation 75 4.5 Estimated variance components in fine fraction 76 4.5.1 Cornwall study area. AAS results 76 Analytical error 77 Sampling error 77 Spatial variation 77 4.5.2 Cornwall study area. ICP data 78 4.5.3 Lancashire study area. ICP data 79 4.5.4 Variance distribution over sample types and localities 80 4.5.5 Sources of variability in the Cornwall study area 84 4.5.6 Summary 86 4.6 Estimated sampling and laboratory errors in coarse fraction 88 4.6.1 Cornwall study area 88 4.6.2 Lancashire study area 90 4.6.3 Summary 91 4.7 Annual variation 91 4.7.1 Two-way analysis of variance 91 4.7.2 T-Tests 93 (1) Comparisons with standards 94 (2) Comparisons with survey data 94 4.7.3 summary 95 4.8 Discussion 96 4.8.1 Sampling variability 96 4.8.2 Annual variation 98 Chapter five - Geochemical patterns in fine fraction 100 5.1 Statistical distribution patterns 101 5.1.1 Cornwall study area 103 5.1.2 Lancashire study area 106 5.2 Spatial distribution patterns 107 5.2.1 Lancashire study area 107 5.2.1.1 Total and partial correlations 109 5.2.1.2 Principal component and factor analyses 118 A. Principal component analysis 119 B. Factor analysis 120 5.2.1.3 Regression of background factors on ore metals 124 5.2.2 Cornwall study area 125 5.2.2.1 AAS data 125 5.2.2.2 ICP data 129 5.2.2.3 Summary 134 5.2.2.4 Total and partial correlations 135 5.2.2.5 Principal component analysis 140 (1) AAS data 140 (2) ICP data 142 5.2.2.6 Factor analysis 143 5.2.2.7 Regression of backgound factors on ore metals 146 5.3 Patterns in data normalized on Fe + Mn 147 5.4 Summary and discussion 151 Chapter six -- Hydrogeochemical trends 160 6.1 Trends in Newquay waters 161 6.2 Trends in Clitheroe waters 164 6.3 Summary 166 Chapter seven - Geocheraical patterns in oxide coatings 167 7.1 Clitheroe study area 170 7.1.1 Spatial distribution patterns 170 A. Non-normalized data 170 B. Normalized data 171 7.1.2 Total correlations 172 7.1.3 Principal component analysis 173 7.1.4 Factor analysis 174 7.1.5 Summary 175 7.2 Newquay study area 176 7.2.1 Spatial distribution patterns 176 7.2.2 Total correlations 177 7.2.3 Principal component analysis 178 7.2.4 Factor analysis 181 7.3 Silver in oxide coatings 182 7.4 Summary 186 Chapter eight - Nature and formation of Fe-Mn oxides 188 8.1 Structure 189 8.1.1 Primary crystallographic considerations 189 8.1.2 Microscope and electron microprobe studies 193 8.2 Environments and mechanisms of oxide formation 196 8.2.1 Field studies 198 A. Nature, conditions and environments of formation 198 B. Role of organic matter 201 8.2.2 Laboratory studies 202 8.3 Discussion 205 Chapter nine - Discussion 211 9.1 Regional environmental factors 212 9.2 Local environmental factors 214 9.3 Influence of the secondary environment on sediment composition 216 9.4 Application to the study areas 220 Chapter ten - Conclusions and recommendations 223 10.1 Sources of error in drainage data 223 Limitations of the analytical system 223 Sampling variability 223 Secondary processes and annual variation 224 10.2 Results of analytical trials 224 10.3 Dispersion patterns in the study areas 225 Population distribution models 225 10.3.1 Patterns in fine fraction 226 Cornwall study area (Newquay area) 226 Lancashire study area (Clitheroe area) 227 10.3.2 Patterns in oxide coatings on coarse fraction 228 Newquay area 228 Clitheroe area 229 Oxide coatings as a sample medium 229 10.3.3 Patterns in the waters 230 10.4 Assessment of statistical aids 231 10.5 Controls on trace element distribution in sediment 233 10.6 Recommendations 235 Appendix - Details of analytical techniques 237 References 243 LIST OF TABLES Table Page 3.1 Loss on ignition 32 3.2 Results of trial attacks on fine fraction 32 3.3 Relative efficiency