Hazelhoff Roelfzema-BH-1968-Phd-Thesis.Pdf
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A THESIS entitled GEOCHEMICAL DISPERSION OF TIN IN MARINE SEDIMENTS, MOUNT'S BAY, CORNWALL Submitted for the degree of DOCTOR OF PHILOSOPHY in the FACULTY OF SCIENCE IN THE UNIVERSITY OF LONDON By BRUNDT HARM HAZELHOFF ROEEFZEMA Royal School of Mines, April, 1968 Imperial College. ABSTRACT Problems of the geochemical dispersion of tin in the marine sediments are dominantly approached from a sedimentological point of view. Section 1 - The transport of Marazion River was studied with the help of fluorescent tracers. Rainfall and stream velocity were high during the period of observations. All material was transported, but only particles of medium and smaller sizes reached the beaoh. River characteristics did not greatly influence the nature of the transport. Heavy minerals were transported, provided their particle size was equal to or smaller than fine sand. Section 2 - The current pattern in Mounts Bay was studied using bottom drifters. There are two currents in the Bay; the main one is a clockwise current, increasing in strength towards the east. The second current is a smaller clockwise eddy current in the western part of the Bay. No information has been obtained on current velo- city. Transport of heavy minerals in the marine environment was studied by using irradiated tantalite/columbite (sp. gr. 6,95) of minus 200.cesh size. Transport occurred in four directions related to the main tiOn) current, the eddy current, currents induced by the ebbing tide and currents induced by ground swell. A small proportion of the total material only was affected by transport, and overn13 dispersion did not exceed 1 mile during the period of observation. Section 3 - Groups of samples forming traverses have been collected in western Mounts Bay. Grainsize distribution and tin content were studied and indicated a uniform sand body with the maximum tin content confined to the smallest sizes. Interpretation of the data on the Rubey and Rittenhouse application of Stokes law, indicate that the majority of the tin content of the sediments is related to terrestrial sources. In addition, primary minerali- sation is postulated for persistant anomalies south of St. Michaels Mount. Furthermore, there is an additional source of tin in composite grains, whose dispersion is restricted to the eddy current. Discussion is given on the distribution of material and the dispersion of tin in wave action, subsurface samples and fossil beaches. Finally, the copper content of selected surface samples indicate that maxima in tin and copper content coincide. it LIST OF CONTENTS Pap Abstract .. .. D. 0. 4. 40 00 O. 0. i List of Tables .. .. .. .. .. .. pe 00 iv List of Figures .. .. .. .. .. .. .. vi INTRODUCTION . • .. .. .. .. .. .. .. 1 A. GENERAL .. .. • S. 04 .. SO .. .. 1 B. SCOPE OF THE THESIS 00 .. .. .. .. .. 2 C. 111'310,11MGEMENTS .. .. S. SO .. .. 00 2 D. GEolia•L GEOLOGY OF S.W. CORNWALL .. .. .. .. 3 E. GEOLOGICAL ASPECTS OF MOUNTS BAY .. .. .. .. 6 F. CLIMATE AND PREVAILING WINDS .. .. 00 00 00 SECTION 1 TRANSPORT OF MATERIAL BY MARAZION RIVER • • 9 CHAPTER 1 SOURCES uF DEiRITAL TIN S. • • .. .. 10 A. Review of Alluvial Placer Deposits .. O. .. 10 B. Geochemical Dispersion of Tin in Soil Traverses near Rosepeath .. .. .. .. .. .. .. 13 C. Tin Content of Stream Sediments .. • • • • • • 16 CHAPTER 2 TRANSPORT OF FLUORESCENT TRACER BY MARAZION RIVER .. 40 O• •• •• •• •• •• 20 A. Choice of River .. .. .. .. .. .. .. 20 B. Description of Marazion River .. .. .. 21 C. Field and Laboratory Techniques .: .. .. .. 22 1. Choice of tracer 00 .. • • .. .. •• 22 2. Collection and coating of material .. .. 0 0 23 3. Rainfall measurements .. .. .. .. .. 24 4. Stream velocity measurements .. .. .. .. 24 5. Dumping of tracer and sample collection .. .. 25 6. Comparison between natural and coated sand .. 25 7. Counting of fluorescent grains ... .. O. .. 27 D. Presentation and Discussion of Data 40 00 00 28 1. Rolationship between stream velocity and rainfall 28 2. Transport of tracer .. .. .. Le 00 e0 29 3. Representivity of tracers .. .. as 0. •• 37 4. Transport of heavy minerals O. .. .• 00 39 E. Summary of Conclusions .. .. .. 00 • • SS 40 ii Page SECTION 2 TRANSPORT OF MATERIAL IN MOUNTS BAY .. .. 42 CHAPTER 1 CURRENT SYSTEMS IN MOUNTS BAY .. .. 00 43 A. Introduction and Previous Work .. .. .. .. 43 B. Field Techniques .. .. • 0 • • • • • • 0 • 45 1. Selection of release points .. .. .. .. 45 2. Time of release .. .. .. .. 00 00 46 3. Method of dropping .. .. .. .. • 46 4. Recovery of drifters .. .. .. .. .. .. 47 C. Presentation of Results .. 0. .. WO 00 WO 47 D. Discussion .. SO .. .. .. O. .. 0. 56 E. Su :miry of Conclusions .. .. .. .. 00 00 61 CHAPTER 2 MOVEMENT OF MATERIAL IN WESTERN MOUNTS BAY USING RADIOACTIVE TRACERS .. .. .. .. 63 A . Introduction .. .. .. .. O. 00 OM 63 .. B . Previous Work .. .. .. .. .. 0* 00 00 64 C. Choice of Tracer .. .. .. OS .0 00 00 68 D. Preparation of Tracer .. .. • .. .0 O. 00 71 E. Radio-active Background Survey .. •• .. 72 F. Location of Release Point of Radio-active Tracer .. 74 G . Release Technique .. .. .. .. O. 00 60 75 H. Data Collection .. O. • • .. es 00 se 76 I. Presentation and Discussion of Data .. .. .. 77 1. Background radioactivity .. .. 0. 00 so 77 2. Gamma spectrum analysis .. .. 0. 00 .. 78 3. Dispersion of tracer .. .. 00 60 8o 4. Interpretation and conclusions .. 06 G. SO 82 SECTION 3 GEOCHEMISTRY .. .. .. .. .. .. 86 CHAPTER 1 GENERAL CONSIDERATIONS .. .. .. 87 L. Selection and Description of Study Area .. .. .. 87 B. Considerations of Sources of Tin and'Transport of Material .. .. .. .. O. 00 .0 $6 .. ' 89 CHAPTER 2 FIELD AND LABORATORY TECHNIQUES .. .. .. 94 A. Sample Collection .. .. .. .. .. .. .. 94 B. Sample Location .. O. .. O. .. 95 C . Sample Errors .. S. .. .. .. .. OS 95 D . Terminology .. .. .. .. .. .. O. 44 96 E. Mechanical Size Analysis .. .. .. .. 40 0. 96 F . HCl Treatment .. .. .. .. .. .. .. .0 99 iii Page G. Analaysis for Tin .. 0 • • • • • • • • • • • 99 H. Heavy Mineral Separation .. • • • • • a • • • • 100 I. Presentation of Geochemical Data .. • • • • • • 100 la. Grainsize distribution (dry sieving) •• . • 100 lb. Grainsize distribution (elutriation) • • a • 103 2. Tin distribution in surface sediments •• . • 105 CHAPTER 3 DISCUSSION AND INTERPRETATION • • .. .. 113 A . General .. • • 0 • • • • • • • • • • • • 0 113 B. Detailed Discussion on Individual Traverses .. •• 125 Traverse 14 .• a • • • • • • • • • • • • • 126 Traverse 12 • • . • • • • • • • • • •• •• 131 Traverses 15 and78 • • • • • • •• •• 137 Traverses 5 and 6 • • . • • • • • .. •• •• 139 Traverses 11, 10 and 16 .. • • • • •. •• 143 Traverses 17 and 9 • • • • • • • • • • •• •• 147 Traverses 8 and 13 • • • • • • • • •• • •. 150 Traverses 1 and 2 • • • . • • • • •• •• 152 Traverse 19 . • .. • • • • • • • • •• •• 165 Vertical distribution of tin .. • • • • • 0 172 Raised beaches .. .. • 9 • • • • • • 0 • • • 179 Distribution of copper in some selected samples •• 183 Summary and general conclusions • • • • • • 186 iv LIST OF TABLES Table Page 1 Geological time scale in Cornwall (based on Robson, 1944 and Webb, 1947) •• •• 8 1,2 Tin content of red clay and adjacent strata at Marazion Beach .. .. .. • • 4. • • .. 17 1,3 Tin content of stream sediments of some rivers draining into Mounts Bay .. .. .. .. .. 18 114 Convertion of fluorescent grains per gram to number of fluorescent grains per 1000 uncoated grains .. 27 1,5 Stream velocity in ft/sec at 3 successive stations 32 1,6 Comparison between size distribution of selected samples as obtained by fluorescent sand and screening .. 80 00 . 00 00 . 38 2,1 Station 1 .. .. .. .. ee .. .. .. 51 212 Station 2 00 00 00 O. .. • • 51 2,3 Station 3 .. .. .. .. .. .. .. 52 2,4 Station 4 • • . • O. .. • • .. 53 2 5 Station 5 .. .. .. 60 .. .. 51+ 2,6 Relationship between wind direction and force and number of recovered drifters .. .. • • .. 55 2,7 Elements generally used for radio-active tracer experiments .. 00 00 • • •• 00 • • • • 68 2,8 Relation between area of dispersion and total activity 00 00 00 • • • • 00 40 0, 84 3,1 Size fractioning by elutriation, using a water discharge of 5 ml/sec and density of quartz 98 3,2 Representivity test of elutriation .. .. 98 3,3 Correlation coefficient of tin content in different ractions f se • • • • • • • • a. 00 00 106 Table Page 3!4 Comparison of computed relative availability of tin and elutriation .. ., .. .. 110 3,5 Comparison of actual and relative tin content of selected samples from traverse 12 .. .. .. 112 3,6 Average values of absolute and relative tin content of traverses 00 • • O. OS Of C , 118 3,7 Tin distribution of the 150 to 200 mesh fraction in selected samples, using tetrabromethane and clerici .. .. O. • • • • .. 121 3,8 Absolute and relative available tin of traverse 14 129 3,9 Absolute and relative available tin of traverse 12 133 3,10 Absolute and relative available tin of traverses 5 and 6 .. •• • • •• •• ,• • •• 140 3,11 Average, absolute and relative available tin of traverses 11, 10 and 16 O. nn 00 •• 146 3,12 Absolute and relative available tin of traverses 17 and 9 •• •• •• • • •• •• •• •• 148 3,13 Average, absolute and relative available tin of traverses 8 and 13 00 • • 4. n. GO •• 150 3,14 Absolute and relative available tin of traverses 1 and 2 .. OM 04 On 40 .4 •• •• 161 3,15 Absolute and relative available tin of traverse 19 169 3,16 Absolute and relative available tin of tin containing fractions of cores 33 and 34 • • .. 175 3,17 Absolute and relative available tin of core 5 •• 178 3,18 Tin content of raised