Investigation of the South West England Thermal

INVESTIGATION OF THE SOUTH WEST ENGLAND

THERMAL ANOMALY ZONE

Malcolm F. Francis, M.Sc., D.I.C.

June, 1980

A thesis submitted for the degree of Doctor of Philosophy of the University of London.

Geology Department Imperial College London, S.W.7. ii

INVESTIGATION OF THE SOUTH-WEST ENGLAND THERMAL ANOMALY ZONE

The use of specially drilled shallow heat flow boreholes as a reconnaissance technique for potential 'Hot Dry Rock' geothermal resources has been demonstrated. Twenty three boreholes have been drilled in and around

the Cornubian granite batholith. In addition, almost as many boreholes drilled by mining companies and the Institute of Geological Sciences have been taken over for heat flow determinations. Temperature logs have been made and thermal conductivities determined for the majority of these boreholes. Gamma-ray spectrometric determinations of the radiogenic elements, potassium, uranium and thorium have been made on over three hundred representative borehole samples. Anomalously high values of heat flow (120mWm 2) were observed at all sites on or adjacent to the granites, while normal heat flow (around 60mWm 2) was determined at sites remote from the granite. The possibility of enhancement of heat flow through convective circulation at depth, which had earlier been thought to be the case, is virtually ruled out by the uniformly high values over the entire batholith. Using model studies, the observed sharp contrasts of thermal conductivity and heat production, combined with the likely space-form of the batholith, are demonstrated to be the probable cause of the observed thermal anomaly zone. iii

ACKNOWLEDGEMENTS

The research described within this thesis has only been possible by the co-operation and help of a wide range of people. The author would like to express his gratitude to all who gave their assistance, in particular: Mr. J. Wheildon, the project supervisor, for enthusiasm and encouragement throughout this project. He is also thanked for constructive criticism of this manuscript. Dr. A. Thomas-Betts and Mr. J.R.L. Ellis for many hours of stimulating discussion and much practical help. Mr. I. Gollop for invaluable assistance. Mr. S. Ealy and Mr. J. Dare for technical assistance and for preparation and measurement of thermal conductivity material. Mr. A. Sartori, Mr. N. Bassett, Mr. A. Cheyne, Mr. A. Jackson, Mr. J. Robinson, Mr. K. Jason, Mr. L. Zapalowski for their researches into the temperature dependence of thermal conductivity. Dr. A. Batchelor and Mr. M. Waller of the Camborne School of Mines for much enthusiastic assistance. Mr. S. Williams, Mr. F. Priss, Mr. P. Scargill and the staff of Saxton & Co. (Deep Drillers) Ltd, of Camborne, Cornwall. The staff of Boundbar Drilling Ltd. of Malvern, Worcs for the diamond drilling. Numerous members of the Institute of Geological Scien- ces for both advice and practical help. The landowners, tenants and officials who gave permission for drilling. Without their co-operation this project would not have been possible. Dr. C. Bristow, Dr. C. Gronou, Dr. A. Francis, of Eng- lish Clays, Lovering Pochin & Co. Ltd., for help in the reopening of the Gaverigan borehole and for geological advice in the St. Austell area. Mr. J. Christoffersen, manager,Amax Exploration of the iv

UK Inc. and Dr. P. King of Hemerdon mine for access to boreholes and conductivity material. Mr. J. Lewis, chief geologist, South Crofty Mines Ltd for the loan of drill rods at very short notice. Mr. Kerridge and the staff of the University of London Reactor Centre, Silwood Park, Ascot Berks. This research was jointly funded by the Department of Energy, UKAEA(contract No. E/5A/CON/105) and the EEC (contract No. 586-78-1EG UK). The Natural Environment Research Council for my student- ship and the Department of Energy for my final year bursary. Mrs. P.C. Francis for her typing of this thesis. Mrs. Ella Ng Chieng Hin and Mr. D. Knivett for their drafting of thesis diagrams and Ms. Grace Lau for photo- graphy. Mr B. Holt for drafting and reprographics

TABLE OF CONTENTS

Paae

1 Chapter 1 Introduction 16 2 Geology 3 Measurement of Heat Flow: 38 Part I Measurement of Geothermal Gradient 61 Part II Measurement of Thermal Conductivity 97 Part III Calculation of Heat Flow 119 4 Gamma-ray Spectrometry 180 5 Results 212 6 Conclusions

217 Appendix I Heat Flow Plots 264 II Tabulation of Temperature Data 288 III Tabulation of Thermal Conductivity Data 331 IV Tabulation of Heat Production Data 358 V Derivations of Equations used to Calculate Temperature Extrapolations 369 VI Finite Difference Modelling, Equations and Methods used for Models in Chapter 5 377 VII Descriptions of Boreholes of Interest

398 References

408 Borehole Cross-reference Index vi

LIST OF TABLES

Page No. Conversion tables for thermal parameters

120 4.1 Table of heat production constants

122 4.2 Intermediate long lived isotopes of the 238U decay series

140 4.3 Summary table of radiogenic measurements

142 4.4 Average values for the granites of the radiogenic elements.

142 4.5 Average values for the country rocks

158 4.6 Mean and range figures (ppm) for Zr and Ti from the Dartmoor granite (Hawkes and Dangerfield 1978)

170 4.7 Results of shielding experiment.

180 5.1 Average heat flow values

185 5.2 Heat flow in south-west England - summary compilation

199 5.3 Approximate extrapolated temperatures from south-west England heat flow measurements vii

LIST OF FIGURES

Page

4 1.1 Approximate temperature requirements of geothermal fluids for various applications. 6 1.2 Prototype hot dry rock energy system at Fenton Hill in northern New Mexico U.S.A. 7 1.3 Schematic diagram of multiple fracture hot dry rock energy system. 10 1.4 Relationship between heat flow and age of the mountain belt from which the flow is measured. 12 1.5 Geochemical model of continental shield and oceanic lithosphere. 14 1.6 Map of United Kingdom heat flow data. 17 2.1 South-west England simplified geological map. 21 2.2 Simplified Bouguer gravity anomaly map. 23 2.3 Cornubian batholith model. Pseudo- perspective view of a model satisfying the main Bouguer anomaly features based on horizontal polygons at depths 0.1,1,3,9 and 20km. 24 2.4 The disposition of the shot points and recording stations for the south-west Eng- land crustal structure project. 27 2.5 Seismic foci 1889 - 1966. 29 2.6 Laughter Tor, resistivity pseudo section. 32 2.7 Schematic diagram of air system on drilling rig showing modifications from standard. 35 2.8 Schematic diagram to illustrate the vertical misalignment of a percussion borehole. 39 3.1 Borehole resistance thermometer layout. 44 3.2 Electronic depth counter - Sheare wheel. 48 3.3 Relaxation of temperature for Rosemanowas hole D. Temperatures, measured after drilling, versus depth. viii

Page

49 3.4 I.G.S Predannack Down borehole temperature versus depth graph to illustrate heating effect due to curing cement. 51 3.5 Temperature versus depth plot, first log Wheal Jane J. To illustrate disturbance due to water flow. 54 3.6 DDH H19 Hemerdon Mine. A possible example of local heat flow refraction? 56 3.7 Extrapolated surface temperature data as a function of elevation (including Meteoro- logical station data).

57 3.8 Map of extrapolated surface temperature intercepts. 62 3.9 Modified 41mm divided bar apparatus.

64 3.10 Schematic diagram of divided bar apparatus. 72 3.11 'Pill box' thermal conductivity cell. 78 3.12 Thermal conductivity comparison at Troon (Carnmenellis granite). 82 3.13 Granite thermal conductivity histograms. 87 3.14 Line source and thermocouple configurations. 88 3.15 Line source apparatus. 95 3.16 Variation of thermal conductivity with temperature comparison of results. 100 3.17 Diagram to illustrate subroutine structure of program RCHUCK.

102 3.18 Effect of topography on observed temperature gradients. 107 3.19 Carnmenellis heat flow studies step function temperature model used for climate corrections.

109 3.20 Predannack borehole, heat flow versus depth. 111 3.21 Map of mean daily temperature 1940-1970. 112 3.22 Carnmenellis heat flow studies assumed climatic disturbance. 117 3.23 Temperature response to a sudden uplift at the end of the Pliocene era 3million years ago. ix

Page 118 3.24 Step function, model 1 and continuous uplift model 2, considered as likely bounds to a complex, yet more realistic, sequence of tectonic movements. 121 4.1 Diagram to illustrate gamma-ray spectrum of a typical sample as a summation of the spectra of K, U and Th standards. 126 4.2 Theoretical isometric plot to show relationship between Poisson counting statistics and Gaussian distribution due to detector characteristics. 131 4.3 Gamma-ray spectrometer 134 4.4 Flow diagram to illustrate subroutine structure in program gamma. 136 4.5 Subroutine STD. 143 4.6 Carnmenellis granite. 143 4.7 Bodmin Moor granite. 144 4.8 St. Austell granite. 144 4.9 Land's End granite. 145 4.10 Dartmoor granite outcrop. 146 4.11 Radiogenic heat production against distance from centre of granite outcrop. 147 4.12 Heat production versus approximate horizontal distance to granite contact. 148 4.13 Histogram of potassium concentrations.

149 4.14 Histograms of uranium concentrations. 150 4.15 Histograms of thorium concentrations. 151 4.16 Histograms of uranium and thorium concentrations. 153 4.17a Carnmenellis boreholes U concentration versus U/Th ratio. b Bodmin Moor boreholes U concentration versus U/Th ratio. 154 4.18a Land's End and St. Austell boreholes U concentration versus U/Th ratio. b Dartmoor boreholes U concentration versus U/Th ratio. x

Page 155 4.19 Geological sketch map of the Carnmenellis granite showing distribution of the granite types. 157 4.20 Granites of south-west England. 163 4.21 Fractionation models for distribution of radiogenic elements with data from Sierra Nevada batholith. 164 4.22 Reconstruction of the granite roof based on an exponential decay model. 167 4.23 Underground gamma-ray survey.

167 4.24 Porthmeor Cove surface gamma-ray survey: total count. 169 4.25 Sketch of apparatus used in the gamma-ray absorption experiment. 173 4.26 Schematic diagram borehole gamma-ray spectrometer system. 176 4.27 Country rock boreholes, histograms of the concentrations of radiogenic elements. 177 4.28 I.G.S. Wilsey Down borehole; distribution of radiogenic elements and heat generation. 181 5.1 Borehole location map. 182 5.2 Heat flow values corrected for topographs and recent climate only. 183 5.3 Uncorrected heat flow. 184 5.4 Heat flow corrected for palaeoclimate and topography. 189 5.5 Heat flow section across the Carnmenellis granite outcrop. 190 5.6 Heat flow section along the cornubian batholith. 192 5.7 Case 1, crustal temperature profile. 193 5.8 Case 2, crustal temperature profile. 194 5.9 Case 3, crustal temperature profile. 195 5.10 Cases 4 & 5, crustal temperature profiles. 196 5.11 Summary of crustal temperature profiles. Xi

Page

201 5.12 Sketch to illustrate heat flow parallel to a boundary. 202 5.13 Sketch to illustrate heat flow perpendicular to a boundary. 203 5.14 Effect of country rock thermal conductivity. 206 5.15 Effect of country rock thermal conductivity model II 207 5.16 Isometric plot of flow distribution within a finite difference model.

208 5.17 Sketch to illustrate heat flow concentration in a funnel-shaped intrusion of high thermal conductivity.

210 5.18 Heat flow (correction A) versus heat production.

215 6.1 Comparison of heat flow data from south- west England with European data. xii

LIST OF PLATES

Page

59 Plate 1 Divided bar thermal conductivity apparatus

60 Plate 2 New 41mm divided bar apparatus

128 Plate 3 New gamma-ray spectrometer Conversion Tables for Thermal Parameters (one unit of the row parameter equals the table value of the column parameter)

SI CGS Heat Flow mWm-2 ,ucalcm-1s-1 mWm-2 1. 2.39 x 10-2 pcalcm is-1 4.19 x 101 1. -1 Btuft-2hr 3.15 x 103 7.53 x 101

Temperature SI CGS Gradient mKm-1 oC'km-1 mKm 1 1. 1. °Ckm 1 1. 1. -1 °F102ft 1.82 x 101 1.82 x 101

Thermal SI CGS Conductivity Wm-1K-1 mcalcm-2s-loC-1 -1 -1 Wm K 1. 2.39 s mcalcm i -1oC-1 4.18 x 10 1. Btuft-Ihr-loF-1 1.72 4.13

Thermal SI CGS Diffusivity mm2 s-1 cm2 s-1 mm2s-1 1. 1.00 x 10-2 -1 cm2s 1.00 x 102 1. -1 ft2s 2.58 x 101 2.58 x 10-1

Heat Production SI CGS -3 -1 1.114m 10-13calcm-3s J1Wm3 1. 2.39 10-13calcm 3s-1 4.19 x 10-1 1. Btuft-3hr-1 1.03 x 107 2.47 x 107 1. INTRODUCTION

Introduction

The work described in this thesis was carried out over the period October 1976 - January 1980, the project being funded by the European Communities, the Department of Energy and the Natural Environment Research Council. Over one hundred and fifty years earlier, in 1822, Charles Fox had presented the first formally reported Cornish underground temperatures to the Royal Geological Society of Cornwall. Renewed interest and finance stem- med from the possibility of extracting geothermal energy from the Cornubian granite batholith. The aims of this project were to define the extent of the thermal anomaly which had been observed in Cornish mines and to investigate the possible mechanisms. A further aim was to apply the data to determine if high temperatures might be encountered at reasonable depths. The first heat flow studies in Cornwall were carried out in the operating tin mines, Geevor and South Crofty (Tammemagi & Wheildon 1974). Temperature observations, corrected for topography and palaeoclimate, yielded least squares gradients within the granite of close to 40°Ckm-1. These, combined with harmonic mean thermal conductivities which were determined on granite samples collected underground, led to heat flow values 135mWm-2 and 138mWm-2 for Geevor and South Crofty respectively. A significantly lower value of 75mWm-2 was determined for the Wilsey Down borehole situated on the northern flank of Bodmin Moor. A second phase of observations was carried out during 1974 and 1975 using available boreholes drilled by exploration companies and the Institute of Geological Sciences (Tammemagi & Wheildon 1977). High geothermal gradients, of the order of 43°Ckm-1, were observed in four closely 2

spaced boreholes drilled in Lower Devonian Mylor slates on the Wheal Jane property to the east of Redruth. These values, when corrected for the effects of palaeoclimate, yielded heat flows of the order of 125 mWm-2. This site, on the buried eastern extension of the Carnmellis granite, shows good aareement with Geevor and South Crofty. The two remaining sites, which were in Somerset and remote from the granite batholith, yielded heat flows, after correction for palaeoclimate, of 58 mWm-2, confirming the previous impression that the anomalously high heat flow is confined to the batholith. The unusually high heat flow values, such as those observed at Geevor and South Crofty, were interpreted as being due in part to a deepseated convective flow within the granite. Exploration and mining development suggests that much of the mineralization in south-west England occurs in intense belts associated with ridges and 'cusps' in the granite roof, many of which coincide with the 'emanative centres' of mineralization of Dines (1934). Mineralization occurred along fissures and joints forming the plumbing system for the escape of mineralizing fluids. This took place during the intrusion and subsequent cooling of the granite batholith. Both South Crofty and Geevor mines lie on a well-defined mineralized belt, which runs between Land's End and the south of Bodmin Moor, passing across the northern edge of the Carnmellis outcrop. It was considered that a convective upwelling of warm water might occur within the fissure system of the mineralized belt. In order to test whether the high heat flow existed away from the mineralized belt, a special borehole was drilled at Rosemanowas Quarry and reported by the author in 1976. This thesis covers the research undertaken subsequent to that date into the magnitude and distribution of heat flow associated with the Cornubian batholith. A corrected heat flow of 121 mWm-2 was determined for the Rosemanowas borehole CSD-1 (Longdowns). This heat flow 3 agrees well with the previous results and gave the first indication that high heat flows within the batholith were not restricted to the mineralized belt, thereby suggesting for the first time, that convection may not be a necessary contributor to the observed heat flow. oC

180- Evaporation of highly concentrated solutions Refrigeration by ammonia absorption Digestion in paper pulp (Kraft) 170-Heavy water via Hydrogen sulphide process Drying of diatomacious earth

160 - Drying of fish meal Conventional Drying of tomber power production 150-Alumina via Bayer's process E co 140- Drying farm products at high rates Canning of food 130-* Evaporation in sugar refining ro Extraction of salts by evaporation & crystallisation Fresh water by distillation ~ 1120- Most multi-effect evaporation Concentration of saline solution 110H Drying & curing of light aggregate cement slabs

100- Drying of organic materials, seaweeds, grass, vegetables etc. Washing & drying of wool 90 Drying of stock fish Intense de-icing operations 80- Space-heating (buildings & greenhouses)

70- Refrigeration (lower temperature limit)

60-1 Animal husbandry Greenhouses by combined space & hotbed heating

Mushroom growing Balneology Soil warming

30—Swimming pools, biodegradation, fermentations Warm water for year-round mining in cold climates De-icing 20- Hatching of fish. Fish farming Figure 1.1 Approximate temperature requirements of geothermal fluids for various applications. (Lindal 1973) 5

Geothermal Energy

Currently there is a marked growth of interest in geothermal energy, this being, no doubt, stimulated by the oil crisis of 1973. At present, geothermal energy supplies only a tiny fraction of the world's energy needs. Many of the techniques are now available for using geothermal energy, therefore this fraction may be expanded to fulfil a more significant role. The world capacity of geothermal power plant is increasing in an exponential manner, also non-generating applications are growing rapidly. About 90% of the world's consumption of energy is for non-electric purposes. Figure 1.1 shows a number of uses of thermal energy over a temperature range of 20- 200°C. There are several potential uses within the china clay industry which is of regional importance in south- west England. Only by detailed studies can the heat potential of the earth be assessed. With our current understanding one cannot be certain how much of the earth's internal heat could be safely and economically extracted. Such extraction would be analogous to mining, since the geothermal flux would be insufficient to restore the heat within the lifetime of extraction from any given area. Geothermal heat may thus be regarded as a massive reserve but not as a renewable energy source. Areas where the rocks are permeable will most likely contain water. These steam and hot water aquifers form one important form of geothermal reserve. However, in the granite batholith, it is unlikely that suitable aquifers exist at depth. In areas of poor permeability it should be possible to fracture the rocks and induce circulation within an artificial fracture system. This geothermal reserve has become known as the 'Hot Dry Rock' energy source. 6

air cooled heat exchanger

expansion / surge tank

300 - 600 GPM 200 PSI 170°C ground level injection N. .'S'

hole (E E-1) ~~\ 300-600 GPM sedimen--..-'.. S.ts.. 1400 PSI • (GT- 2) volcanics~

precambrian ~'~ } granite 732m Prototype hot dry rock energy system at Fenton Hill in northern New disc shaped Mexico U.S.A. hydraulic ( Smith 1978 ) fracture

Figure 1.2 Prototype hot dry rock energy system at Fenton Hill in northern New Mexico U.S.A.

The oil industry has developed methods of hydraulic stimulation to enhance hydrocarbon recovery from wells. The University of California, at Los Alamos, New Mexico, has done much of the ground work on creating such a system. The Los Alamos group used fluid pressure to create hydraulic fractures. The method involves the isolation of a section of borehole by use of packers. Water is pumped into this section until a circumferential tensile stress develops, sufficient to split the wall of the hole creating a vertical disc-shaped fracture. Pumping is continued until the crack grows to the required size (Smith 1979). Once the fracture has grown, a second borehole may be directionally drilled so as to intersect the fracture and allow water to return to the surface. It is anticipated that thermal stresses would cause extension of the fracture thus increasing the swept area of the system. A relatively small prototype system and flow experiment were demonstrated at a depth of about 2.7 km where rock temperatures of approximately 185°C were encountered.

injection well recovery well

—Heat exchange surfaces

Figure 1.3 Schematic diagram of multiple fracture hot dry rock energy system. 8

If one crack can be developed then it is hoped the boreholes might be progressively extended and refractured to form a series of parallel vertical fractures which will 'harvest' heat from a large volume of rock rather than a planar surface. In south-west England a research group at the Cam- borne School of Mines, under the direction of Dr. A. S. Batchelor, is studying the problem as it relates to the Cornubian granite batholith. Their approach to fracturing is similar to that used at Los Alamos. However, a relatively small unfocussed explosion is used to form a self-propped fracture system at the base of the hole. These fractures are then extended by hydraulic pressure. In this way it is hoped to form multiple fractures rather than a single fracture and thus to expand the reservoir to considerable size. Initial experiments have been carried out in four 300 m boreholes sited at Rosemanowas Quarry on the Carn- mellis granite outcrop. The conclusions from the initial experiments are given as follows (Batchelor 1980). Granite has such a strong fabric that natural joints domin- ate hydraulic stimulation. Circulation can be achieved though excessively high impedances to the flow were encountered. Unfocussed explosive charges combined with hydraulic stimulation were successfully used to improve the flow characteristics. Post-blast geophysical logging demonstrated multiple fractures were formed with a penetration of at least 1 m. In the next stage of development it is hoped to drill two boreholes to a depth of 2 km. At this depth it is expected that the natural stress field will be representative of the stresses at depths of 5000 - 6000 m yet there should be less complications as regard temperature and drilling. For this study these very deep holes, if carefully monitered, should give a better insight into the heat flow than is possible with shallow boreholes. Un- 9

fortunately, with such deep boreholes, it is unlikely that equilibrium measurements will be possible before pumping and other disturbances start. Heat flow measurements will then have to be calculated using transient measurements. 10

World Heat Flow

The heat conducted to the surface of the earth from its interior averages about 60 mWm-2 (Pollack & Chapman 1977). This is relatively small compared to the average solar flux reaching the around which is approximately four orders of magnitude greater. A cold origin is generally favoured in theories of the earth's formation. The currently observed heat flow should be explained in terms of processes that have occurred since accretion, such as adiabatic compression, core formation, tidal interactions and the decay of radioactive elements. The exact mechanisms, deep within the earth, are of little importance to this current thesis as it deals with relatively shallow processes. In the oceans the heat flow decreases with the increasing age of the ocean floor as a consequence of passive cooling and convective interaction with sea water (Richard- son 1975). On continents the mean heat flow in tectonic elements of different ages decreases with increasing age of the tectonic unit to an approximately constant value for the Precambrian Shields and Platforms.

80 age (My)

(y 70

(NJ

a 50

ro v 40

30 200 400 600 800 1000 Figure 1.4 Relationship between heat flow and age of the mountain belt from which the flow is measured, from Polvak & Smirnov (1968). Height of the symbols represents 20— limits; width is conventional (Richardson 1975). 11

Variation of heat flow, about the mean within tectonic units, arises principally from regional variation in crustal radioactivity (Pollack & Chapman 1977). Heat-producing radioactive isotopes of potassium, uranium and thorium are enriched in the rocks of continental crust. Birch et al. (1968) and Roy et al. (1968) divided North America into three heat flow provinces and demonstrated a linear relationship between heat flow Q and the surface radiogenic heat production A.

Q =a +bA (1.1)

Since then, much evidence has been found to confirm this equation and similar relationships have been identified in Australia, Norway, India and other parts of the world. Somewhat paradoxically with increased number of observations the Basin and Range Province, one of the three initially identified provinces, no longer exhibits this simple relationship (Lachenbruch & Sass 1977). Decrease in heat flow with age in the older provinces may be accounted for by the slow erosion of the highly radioactive surface layer and the decay of the radiogenic elements themselves. Information on the constitution of the crust and upper mantle has been derived from the combination of geology and petrology with seismology and gravity. Our understanding of the interior of the earth generally decreases with depth. The crustal temperature distribution is determined principally by the surface heat flux, thermal conductivity and radioactivity distributions. Seismic P wave velocities of 5.8 - 6.4 ms-1 in the upper crust correspond to a 'granitic composition'. The seismic velocities generally increase with depth to yield values of 6.5 - 7.2 ms-1 in the lower crust. At the base of the crust the P wave velocity increases rapidly to about 8.2ms-1 marking the Mohorovicic discontinuity. The thickness of

Shield Ocean Q =44Wm2 Q= 46Wm2

1.26x 106 Wm/ 40.5 x10 6Wm1 4 8km—. 5km Mohorovicic discontinuity 32km 0.25 x 10-6Wm3 Ultrabasic layer Mohorovicic discontinuity 12.6 x 109 Wrri3 95km

Ultrabasic layer T *1500°C

160 km 8.4x1O9Wrri3 Pyrollite II 42 Wm-2 T

T 1530°C 200 km' Pyrollite II 25 Wm2 T

Figure 1.5 Geochemical model of continental shield and oceanic lithosphere (figure 5 of Ringwood 1969) assuming convection maintains a constant temperature at the base of the two lithospheres. Mean conductivity 2.97 Wm'K-1 and adiabatic gradient of 0.3 K krnl have been assumed. 13

crust beneath stable continental regions is usually between 35 - 45 m, with an average close to 40 km. Ringwood (1969) concludes the Moho beneath stable continental regions is not generally caused by an isochemical phase transition between gabbro and eclogite nor between garnet granulite and eclogite. It is therefore necessary to accept the alternative explanation that the M discontinuity is caused by a change in chemical composition. Hurtig and Oelsner (1977) divided Europe into three thermal sub-areas :- 1) The Precambrian platform in the east and north- east, characterized by low heat flows, probably corresponding to a reduced heat production within the crust, and low temperatures occurring down to the upper mantle. 2) Central Europe with relatively high heat flows, a normal or slightly increased radioactive heat production and high temperatures in the lower crust and upper mantle. 3) The boundary region towards the Atlantic Ocean where again low heat flows occur. Superimposed on this large-scale distribution is a thermal fine structure closely related to the tectonic elements of the earth's crust. Hurtig and Oelsner (ibid) proposed an extended heat source beneath central Europe which controls the tectonic processes in the upper crust and the relative movements of of the individual plates. It is hoped that with the im- proved coverage and standardization that is likely to occur due to the European Communities Geothermal Programme, our understanding of the European heat flow on a crustal scale will be considerably enhanced. A compilation of the subsurface temperature, heat flow and geochemical data, relevant to the estimate of the geothermal potential, was compiled by Burley & Edmunds during 1976 and 1977. Many of the reliable heat flow values for the U.K. have been measured by the research group at Oxford University, under Professor E.R. Oxburgh and 14

2 3 4 5 6 Figure 1.6 Map of United Kingdom heat flow data after Burley & Edmunds 1978, Oxburgh et at 1980 and this study. 15

Dr S. W. Richardson. At Imperial College, a group under the direction of Mr. J. Wheildon, has worked extensively on the Cornubian batholith. It is on this programme that this thesis is based. Two belts of relatively high heat flows have been identified, one running NW-SE from Cumbria to the Wash and a second running EW across the south-western part of England (see fig. 1.6). It has been proposed that these two belts of above 60mWm-2 may be due to an increase in radiogenic heat production within the crust (Richardson & Oxburgh 1979). Apart from a few gaps, the regional heat flow coverage in the United Kingdom is almost complete and it is unlikely that further boreholes will substantially change the overall pattern. 16

2. GEOLOGY

The geology of south-west England is dominated by the Cornubian granite batholith intruded into contorted and thrust Palaeozoic rocks. The exposed parts of the batholith comprise six major and several minor masses. The granite was intruded into Devonian and Carboniferous sedimentary and igneous rocks during the latter part of the Hercynian orogeny (270 - 290 My). The sediments were laid down in a geosynclinal environment. The Old Red Sandstone sediments are mainly fluviatile, lacustrine or deltaic. They comprise poorly sorted sandstones and conglomerates interbedded with marls and siltstones. The near-shore marine facies consist of coarse grained sandstones and siltstones in shales and limestones. The deep water sediments comprise shales and limestones. Volcanism associated with the geosynclinal environment gave rise to basic dykes, sills and small bosses which intrude the sediments (Robson 1947). They are generally composed of sodic plagioclase feldspar and pyroxene with chlorite. They commonly form long narrow outcrops generally following the bedding horizons and are often aligned with the margins of the granite bosses. Outcrops close to the granite exhibit metamorphic alteration, the feldspars and pyroxenes commonly being altered to andesine and hornblend"biotite. These basic rocks are generally not a great deal older than the granite. South-west England has been studied by geologists since before 1758, there is now a wealth of information yet also much controversy. The mode of emplacement of the granite batholith has been the subject of much discussion and research by many workers. In the past few years there have been several different interpretations of the Hercynian orogeny based on plate tectonic models

a x) bT SOUTH — WEST ENGLAND SIMPLIFIED GEOLOGICAL MAP LUNDY ISLE ain

EEC CONTRACT NO 586-78-1EGUK

•Z UKAEA CONTRACT NO E/5A/CON/105 T S outh INDEX i Tertiary TERTIARY

-west h Chalk,Greerlsand,Gault CRETACEOUS Lias JURASSIC Yf Keuper Marl f Keuper sst & Bunter sst } TRIASSIC w ed Permian PERMIAN E ds Welcombe formation n Z gl ri4 Bude formation E d3 Crackington formation and d' Crackington & Lower C CARBONIFEROUS . d' Lower Carboniferous d Upper Paton Beds .~'D si c5 Lower Paton Beds

m C7 r Upper Devonian

plifi c' Upper &Middle D. DEVONIAN is e Middle Devonian c1 Lower Devoreian ~,ō c Devonian undifferentiated

ed Co Z Ge Hercynian granite geol CARNMENEL L IS GRANITE o gi Point cal Start Hornblende ,1NI)SEND Schist and (;HAN!It ma Gneiss

p 0 25 50km I

. Lizard series. Gabbro,Gneiss,Serpentine etc, Scale LIZARD PENINSULA

F IGUHL 2.1 National Grid Km East 18

(Nicolas 1972, Floyd 1972, Laurent 1972, Mitchell 1974, McKerrow & Ziegler 1972, Burrett 1972, Burne 1973,Dewey & Burke 1973, Badham & Hall 1975, Bromley 1976). The Hercynian orogeny at the close of the Carboniferous period was characterized by north-south compressive forces which produced an east-west structural trend. Towards the end of the orogeny the granite magma rose from depth to within perhaps a few hundred metres of the surface. The magma itself is likely to have formed due to partial anatexis of crustal material. The mechanism by which this crustal material was heated is still a subject of discussion. Bromley (1976) compares three possible 'thermal engines' which might drive granite production; a) mantle plumes, b) subduction heating and c) radiogenic heating. By studying the normative concentrations of quartz, albite and orthoclase feldspars in granites related to the degree of regional metamorphism, Hall (1972) demonstrated that the Variscan granites of Europe were formed at shallower depth than the Caledonian granites of Great Bri- tain and Ireland. This, Hall argues, would suggest an unusually high geothermal gradient during the latter part of the Hercynian orogeny. If we compare the Cornubian granite with other Variscan granites in Europe we find it has a higher quartz content than the mean. One might therefore suggest the Cornubian batholith was formed at a lower pressure than the majority of the other granites. The strong inverse correlation between confining pressure and normative quartz has also been demonstrated to exist in experimental systems. (Brown 1973). As a magma and less dense than the surrounding rock,the granite was able to rise. The granite magma was either fluid or a crystal mush (Exley & Stone 1964). As the granites solidified, dykes and veins were emplaced. The mineralizing fluids probably eman- ted from the cores of the plutons through pre-granite faults, primary igneous joints and structures created by intrusion. Moore (1975) postulated stress models that indicate that fluid loss from the core is achieved most easily through 19

the flanks of an intrusion. The majority of volatiles would be expected to leave through whichever of the flanks is first to fail. This mechanism, he suggests, provides an explanation for the asymmetrically disposed mineralized belt. During the final stages of cooling the granite gave off active solutions and volatile gases which lead to much of the alteration we currently observe. The larger masses show evidence of multiple intrusion; exposed contacts are sharp but only rarely show evidence of solid intrusion. Contact metamorphism never exceeds that of the hornblende hornfels facies. Permea- tion of granite into the country rock is very limited. Read (1957) described the granites as being 'almost dead when they arrived in their present position'. After granite emplacement south-west England remained a relatively stable area of positive character. Bott & Scott (1964) suggest this could be accounted for by an isostatic mechanism due to the mass deficiency associated with the low density granite. During the period 115-130My there was some apparent Jurasso-Cretaceous activity which gave rise to pitchblende in the Redruth area and the intrusion of the Wolf rock phonolite and Epson Shoal. These two probably contemporaneous lavas are anachronistic in the volcanic history of north-west Europe. During the early Tertiary (50-60My) the Lundy Island granite was emplaced in close association with a basic intrusive centre. Also, at about this time, there was movement along wrench faults which exploited the pattern of cross courses formed during emplacement of the Cornubian batholith (Dearman 1963). Along these wrench fault zones uranium mineralization has been discovered which has yielded uranium-lead ages which mark an event at 60My (Bowie, Ostle, Campbell 1973). This might suggest a remobilization of uranium during the period of faulting. Linton (1955) suggests that a period of deep weathering is indicated during the mid-Tertiary by the granite tors that remain today. 20

During Pleistocene and recent times marine erosion and subsequent uplift produced an uncertain number of raised wave cut platforms.

Si plifi m ed ed B ou guer guer gravit y y

y y anomal . . p a m z.za2n 6T FIGURE 2.2 LAND'S END UKAEA CONTRACTNOE/5A/CON/105 GRANITE EEC CONTRACTNO586-78-1EGUK SIMPLIFIED BOUGUERGRAVITY/ (after I.G.S.1:250000scalemaps) Isogal valuesinmilligals HEAT FLOWCOVERAGE SOUTH —WESTENGLAND

CARNMENELLIS 10 ANOMALY MAP GRANITE ~ 0 20 3 *AO Q 0 'i { 00 1 200" +

TS National Grid KmEast p tF $ ‘c4,+ S 4 /~ r

GRANITE r , ' LUNDY ISLE / \ /

, 10 V PLY OUTH EXMOOR 20 DARTMOOR GRANITE o ~20 Scale • • • 1(Y) ▪ s • • • 1 • Mar( h 197'4) • 22

Geophysics

There is good geophysical and geological evidence to show that the plutons lie on a continuous ridge which extends from Dartmoor to the Scilly Isles and possibly beyond to the rocks of Haig Fras. Bott, Day and Masson- Smith (1958) carried out a regional gravity survey using a Worden gravity meter; further coverage has since been added and marine gravity is now available (Davey 1970). The most striking feature of the Bouguer anomaly map is the belt of large negative gravity anomalies of up to 50mgal amplitude which follows in line with the outcropping granites. These anomalies are attributed to the low density of the granite in relation to the country rocks (Bott & Scott 1964). The granite gives densities of 2.58 - 2.64gcm-3 while the Devonian rocks of south Devon -3 yield densities of 2.61 - 2.86gcm (Bott et al. 1958), whilst the Cornish country rocks locally known as killas give 2.64 - 2.76gcm-3. The Bouguer anomaly map indicates that the granite contacts are steeper on the south side than on the north. This is generally confirmed by the widths of the metamorphic aureoles. Between the granite outcrops the con- cealed granite roof is apparently relatively flat with minor undulations and probably no more than 2-3km beneath the surface. Bott et al. (1958) also suggested a slight westward thinning of the crust, or an increase in mean crustal density, is indicated by the gravity data. From complete gravity coverage Tombs (1977) obtained a model with a thickness of over 20km under Dartmoor and thinning to the west. More detailed gravity surveys have been used to investigate the surface relief of the granite roof beneath the sedimentary cover. These surveys yield evidence of local highs where the granite almost reaches the surface(Beer, Burley & Tombs 1975). Near the granite outcrops, mines and boreholes penetrate granite beneath a

N t7 c M O a I-'• I-+• x (n(DQ • a hi 0 C o rh J N a• O ►f O I-'. aC) N (D O O I-' ti O ~ de En G a a Cr F--H rt H. I-'• a PO En SCILLIES LAND'S END CARNMENELLIS HENSBARROW BODMIN MOOR DARTMOOR O 1-t, o, 1< P a i 4 0 1S:1 ūi rt 0 133 rl- rr1 -4 20km a a to (D N• a cn ru~a rt (D -•~ m1--0 N O • -4 0 O IQ • I-'(D d CORNUBIAN BATHOLITH MODEL ti En (D Pseudo.perspective view of a model satisfying the main Bouguer anomaly features a 0 based on horizontal polygons at depths 0.1. 1. 3. 9 and 20 km. ~ a 9 25km -w W'i7 Hi tD kJ:0'C ri a I-h • m 0.1 01 0 rt rt n c (D (D to 24

9' 8' 7' E' 5' 4'

5 2' 52

25 • 51• 51' • 25 27

C4RTMOJR 28 • 29 • 000MIN MOOR 30 • Alcvvie ■ 31 • MEAARRO CARNMEN 20 2. ELLI5 • ~y L AN)EN 7 oEcZiiC AL MOU, ,SI ~• EN.. IS • '• • 50' 54.• 50' SCILLY ISLES •p • • • „.„0„, 13 34 •0 • • • 35 • L INE 1 • • 7 • 37 • 4 . • 38 LINE 3 3 • • 2 39 • •40 . 49.— 40 • N • SHOT POSITION } CROSS ARRAY STATION -- LINEAR ARRAY STATION — THREE COMPONENT SET • — OTHER STATIONS

SCA;E 25 _ 100

48• 48'

9' 8' 7' 5' S' 4' 3'

Figure 2.4 The disposition of the shot points and recording stations for the south-west England crustal structure project. BOTT et at 1970 25

cover of country rocks. To test the gravity interpretation a number of seismic refraction lines were shot in November 1966 (Bott, Holder, Long & Lucas 1970). Line 1 yielded a crustal thickness of between 23 and 30km, the best estimate being 27km. The granite P wave velocity was estimated at 6.15kms-1. The Moho was clearly defined beneath the line Pn = 8.07kms-1. No sharp floor was detected at the base of the batholith. An interpretation, based on the gravity and seismic evidence, was presented which suggested the granite batholith is approximately 10-12km deep, below which there is a gradational increase in P wave velocity with depth down to the Moho. Tombs (1977) noted that 'the seismic refraction profile of Bott and others was only reversed between Carnmenellis and a point to the west of the Scilly Isles, where his updated gravity model indicates a depth of 10-15km to the base, thereby indicating its diffuseness, it was merely deduced that a base at 12km was consistent with the required velocity distribution'. Bott, Holder, Long & Lucas (1970) support the view that the granite magma was probably formed by selective fusion of the rocks forming the lower part of the crust. They suggested 'the higher velocity in the lower part of the crust could be interpretated as being formed from the residium left after partial fusion and of stoped material from the crust which sunk during emplacement of the batholith'. Such an interpretation is consistent with the gradational velocity distribution observed. 26

Seismicity

England is considered an area of low seismic risk. Few earthquakes occur and those which do are not of 'disa- ster proportions'. Most recorded earthquakes in the U.K. have been along major fault lines in Scotland. Fig. 2.5 (Dollar 1963) with additions, shows the location of most, if not all, of the recorded earthquakes in south-west England. Earthquakes may have been due to the influence of mining operations, though there is no clear relation between the location of mining areas and these earthquakes. It would appear more likely that they occurred along deep fracture systems which control the crustal structure. There is increasing support for crustal faults within geology. The trend of such faults or lineaments are proposed by study of satellite photographs. Unless earthquakes are located accurately it is a worthless exercise trying to assign them to a particular fault, since there are often several likely candidates in any one area. One fear in deep hydraulic fracturing is that water may leak under pressure into an active fault and trigger an earthquake. South-west England does not lie on an active plate margin, though completely aseismic areas are rare. Minor seismic activity is beneficial, since it prevents the build up of massive forces which could lead to a large ground movement. An earthquake artificially triggered however, could lead to claims for damage etc for an event which probably would have occurred in the near future, possibly with greater force.

200 bt SOUTH-WEST ENGLAND n aLUNDY ISLE HEAT FLOW COVERAGE EXMOOR aJ EEC CONTRACT NO 586-78-1EGUK Z

' UKAEA CONTRACT NO E/5A/CON/105 5

as SEISMIC FOCI 1889-1966

utsT Seismic focus with fault strike where known (after Dollar 1963) at h oJ t r a

t 0 Other seismic focus No

All locations very approximate BDDMIN - DAR IMO(P r Km ~• GRANTE ;'~ • • It GR Aa -~

d 0 Gri

l -61 • na io t r- Na 'ARNNW NE L L IS, (RANITF

ST. AUSTELL • - tiepin-to-granite contours -UW) S I . N') — — GRANITE / t'orn /GS gravity mode! 1 iRANI 1 E '~ ~~~ r -r as below;

__,_ 3km _._.—.— 9 km 0 25 50km (1966) Scale depth 18-20 LIZARD PENINSULA or 33 •'00 300 (Awl) 19(30 FIGURE 2.5 National Grid Km East 28

Site Selection

The selection of suitable sites has required geological and geophysical information in order to find the optimum positions. Our initial aim was to measure the surface heat flow over the batholith. A further aim was to indicate whether heat was flowing by pure conduction or if the excess heat flow was due to convective water circulation. It was considered that a line of boreholes across the width of the batholith would yield maximum information. Logistical controls and previous work (Francis 1976) suggested the Carnmenellis outcrop. Five equally spaced boreholes forming a line at right angles to the long axis of the batholith were considered would fulfil these requirements. Once the aims and number of boreholes were set, care was taken in the selection of sites so as not to prejudice these aims. A shallow borehole, when used for geothermal investigations, requires more careful siting than a deeper one. Shallow boreholes are more sensitive to surface effects. Thus sharp topography, later;al variations, un- usual microclimates, man-made disturbances and many other parameters all need to be taken into account. Firstly 1 - 25,000 scale plans were compiled from all available geological information. The granite is criss-crossed by numerous fault zones that range in size from joints between granite blocks to the major cross- 'courses and wrench faults. The major faulting was sket- ched in by interpretation of lineations on air photographs and topographic maps. Some of these lineations followed previously known fault zones. In order to choose a safe course, all major lineations were assumed to be due to faulting, mineralization or alteration and so were to be avoided. Provisional site areas were allocated. These sites were then visited and the landowners' permissions

d bT n ---,Transmitter I- as Example of resistivity

•z site investigation Receiver I

g I

L /P2 iC2 au _mill • • Multi-wire array gh t er T or , I I I I resi 40 50 60 70 80 -80 -7Q -69 -59 -4p -3r0 -20 -1p 19 30 ‚Cl -\)45° I Pr P2 45°~ C21

sti \ i / a.10m 0 0 0 0 0 0 0 0 0

vi 0 0 `0 9.1 5.3 4.9 4.5 4.8 5.1 6.0.. 6.6 ~•'7.2• 7.1 /`!.2 5.30 5.2.' 4.8 t y

pseud a=20m o o ♦ 0 0.... 5.5 4.9 \4.4 4.9 ..5.7 5.3 „•' 4.8 -''S.W ; 6.1 .5.2 4.6

. o a. 30m ° ° °'. .•o '° 4.5 4.4 . ;4.0 3.5 3.8 x/3.9 •• 4.2 4.6 LAUGHTER TOR secti N, / RESISTIVITY PSEUDO-SECTION a. 40m '•• `\ 0 0 / 0 0 3.3 \4,2 3.' 3.3 3.7 Wenner arrays: on P1 P2 C2 \ / 1-.- a -I 2a -I . \a/ o a.50m 10 3.1 Apparent Resistivity 1030m 0 z°n,eves 3 Scale

FIGURE 2.6 30

were sought to continue further. Local parameters were then considered, such as small scale topography, access, likely damage and disturbance due to drilling. Bands of kaolinized granite and deeply weathered granite, are rarely mapped and often form no clear topographic features. During the drilling of CSD-3 (Little Polgear) just such an area was encountered, this lead to the subsequent loss of this borehole due to collapse just below the standpipe. The borehole was later replaced by CSD-7 at Polgear Beacon (Taylor 1977). For the next suite of boreholes, sited on Bodmin Moor, a few simple geophysical surveys were used to test if such zones occurred on or near the borehole sites. The use of resistivity traverses appeared to be the most successful method. In addition to the detection of deep weathering, the depth of unconsolidated material could be estimated. VLF traverses, using a Geonics EM-16 gave a quick reconnaissance of some sites. The EM-16R was also used on a few sites to measure apparent resistivity. Resisti- vity traverses were used on most sites since resistivity is less affected by man-made disturbances and more straight forward to interpret. Surveys over the later diamond drill sites were more extensive as the killas country rock was thought to be less predictable than the granite. On the granite there appeared to be a correlation between low resistivity and poorly consolidated material. Depth soundings were made over the proposed drill location using an expandingWenner array (fig.2I6). These readings were used to estimate the likely depth of the weathered surface zone. Gravity has proved a useful tool in the china clay industry to locate kaolin deposits. Practical reasons lead us to favour resistivity. 31

Drilling

During the course of this work a total of 21 boreholes has been drilled in the granite and some three holes have been drilled in the country rock. In addition, several boreholes have been visited and preserved which were drilled by other agencies. The drilling was undertaken by contract companies. This part of the project constituted the majority of the fieldwork and a large por- tion of the total time available. It is, therefore, perhaps worthwhile to include some details of the methods - used, information about the geology of the sites and what was found during drilling. The boreholes in the granite were drilled by Saxton & Co. (Deep Drillers) Limited of Camborne, Cornwall, using the down hole rotary percussion method. This method is commonly used for the drilling of shot holes for quarry blasting and overburden removal. The first hole drilled on this project, using this method, was sited close to the Rosemanowas Quarry at Long- downs, details are reported by the author (1976). During the drilling of this hole many problems were encountered. Having gained further experience we now have a viable technique of rapidly drilling 100m deep boreholes at reasonable cost. The holes were drilled using Holman Volt- rac 4 mobile surface drilling rigs which are manoeuvrable, one-man operated and designed to cut 85-105mm diameter holes quickly and economically in rock down to a depth of 46 metres. Two compressors were used to provide power in the form of compressed air. Percussive energy is generated by a hammer at the base of the hole. The piston in the hammer strikes the back of the bit, whilst they are being rotated from the surface. The cutting action is like that of a hammer and cold-chisel. This action is well suited to hard brittle rocks such as granite. 32

r Large r feed Rotation motor motor Modification. V separate feed

Holdback feed regulator High pressure feed to drill X3-1 I string only 41 HOIST D4 FpRWARO TUBE X REVERSE CLAMP +OPEN Air Reservoir, CLOSE 200 —240/ Ground level NON RETURN VALVE Removabte ® AI~ LINE joint 0 >HYORAULIC COMPRESSOR ~—~ PUMP (VHPX) Grinding Plastic wheel stand pipe

OIL L°"111 string > DRIVE

NON RETURN VALVE Air Reservoir 700-140psi ii_ I Hammer COMPRESSOR (HPX)

(4") Button bit

Figure 2.7 Schematic diagram of air system on drilling rig showing modifications from standard. 33

Two types of tungsten carbide bit were used, the cross-bit and the button-bit. The cross-bit is suitable for production drilling of many shallow holes as it is easily reground and so can last longer whilst maintaining. an even cut. However, with deeper drilling, they become less economic as they require frequent reorindirg. Grinding takes little time but the round trip from bottom to surface and down again can waste much time. In general, button-bits are regarded as having a shorter overall life than cross-bits. They do, however, have a distinct advantage in that button-bits require less frequent regrind- ing and so there is no need for round trips during the. drilling shift. Starting with a new button-bit it is often unnecessary to regrind during the 100 metres of drilling. This leads to constant drilling rates which reduces the overall drilling time. Occasionally the bit will break up due to the loss of a carbide tip. It is important to ensure that all fragments of carbide are removed from the hole before starting with a new bit, otherwise a series of bit failures may follow. A pair of non-return valves wav used to prevent the hammer from flooding with water during rod changes. One valve,U ear the top of the drill string, traps a column of air pressure. This enables the hammer to continue to flush for a short while, even when disconnected from the air supply. The second valve was fitted directly above the hammer, to prevent a surge back of water and silt when the pressure was suddenly released. Occasionally a non-return valve fails due to a faulty component or some form of blockage. When this happens, the hammer soon fails and fills with fine chippings, thus demonstrating the need for both valves when at a reasonable depth. Compressed air is used to expel the drill cuttings from the borehole; this leads to one of the major problems with percussive drilling. The performance of the hammer 34

deteriorates with increasing volume of water until, finally, there is insufficient pressure drop across the hammer for it to operate. For relatively shallow boreholes, the solution is to increase the air pressure as the drill penetrates deeper. If the water is ejected faster than it can accumulate, the pressure differential across the hammer is kept constant and performance is maintained It is also important to maintain adequate flushing to prevent excessive bit wear. A second problem with the method is the difficulty in maintaining a vertical alignment. Percussive drilling is notorious for deviation. The drill bit has a larger diameter than the hammer or the drill rod to allow air to be exhausted around the outside of the hammer. Thus the drill string cannot use the borehole wall to maintain alignment. In practice deviation may be kept to a minimum by careful alignment of the beam at the start of drilling and for the first few rods. Tight,well-matched drill rods and a rigid beam are required. If the method is to be used for deep holes, additional controls should be employed such as the use of stabilizing reamers. The deviation of the borehole will then largely depend on the, skill of the operator and the rock encountered. Convential wireline diamond drilling was employed in coring country rock boreholes. Drilling technique. was left in the hands of the contractors, Boundbar Drilling Limited of Malvern, Worcs. Emphasis was placed on core recovery and obtaining an open hole rather than speed.- The country rock in Cornwall is relatively easy to drill through but difficult to obtain good core recovery. This is because the rock consists of slates, shales, sandstones and quartz veins, closely interbanded. The shales are soft and are difficult to obtain core from. The quartz veins are very hard and so easily lock in the core barrel causing no further recovery. Due to the care and patience of the drillers core recovery was high, core being recover- 35

• BIT DEFLECTED EITHER BY HARD ZONE 'C'OR BY DRILLING FASTER THAN OPPOSITE

Figure 2.8 Schematic diagram to illustrate the vertical misalignment of a percussion borehole. 36

ed directly after quartz-rich band. Core recovery on Kestle Wartha and Callywith was almost complete. The Merrose Farm borehole frequently encountered quartz veins and so recovery was low over some sections. Core was pulled at lm intervals in these difficult zones. Callywith Farm was drilled using a hybrid rig. The rig started its life as an experimental percussion rig developed by Compair (Holman). In this form it was used to drill Rosemanowas hole 'A' for Camborne School of Mines. This borehole deviated only 3° from the vertical. Dril- ling was, however, slow as many design changes were added and drilling was in short shifts. The rig was bought by Boundbar Drilling Limited who modified it and added the capability of wire line diamond drilling, using tried and tested components from Longyear. The Callywith Farm borehole was the first diamond hole to be drilled using this rig. Again drilling was slow to enable teething troubles to be ironed out; in addition there was a long wait for delivery of drill tubes etc. Nearly complete core recovery was obtained and an accurate dip test found the borehole to be deviating by less than 1° at its base. This type of rig would appear to be most suitable for future geothermal exploration. The rig was mounted on a large Ford special vehicle which had wide wheels and four-wheel drive. When diamond drilling, no additional plant was required. One possible disadvantage is the width of the lorry, making tight lanes and narrow farm gateways a problem. A lighter rig, such as the Voltrac-4 or the tractor mounted Hydreq-Miner, would possibly be more suitable in very difficult terrain. For the relatively shallow percussion boreholes, expensive access roads, compensation etc are not required since disturbance is minimal. On Dartmoor about one hole was drilled per week, only two and a half days being required to drill the one hundred metres. In places, terrain was difficult yet damage, caused by the drilling 37 operation, was minimal. Planning permission to drill within the Dartmoor National Park was eventually granted, after it was assumed that this drilling technique would cause minimal disturbance, little damage and could be completed in a few days. Such stringent requirements could not have been met by other methods. 38

3. HEAT FLOW MEASUREMENTS Part 1 Measurement of the Geothermal Gradient

Temperature Measurement

Temperatures were measured using a thermistor probe suspended on a wire. Depths were measured using a sheave wheel and counter at the top of the borehole (fig. 3.1). Thermistors are semiconductors which have a'large negative coefficient of resistance. They may be used to measure temperature with a precision of - 0.01°C. Ther- mistors, like other semiconductors, have an electrical conductivity approaching that of a metal at high temperatures and nearly an insulator at low temperatures. The depen- dance of conductivity o-, (ohm-1m1) on absolute temperature T in degrees Kelvin, is commonly expressed by :

= A(T) .exp(-E/2kT) . (3.1) in which A(T) is a slowly varying function of temperature, E is an energy term and k is the Boltzmann constant. Several practical equations have been used to convert this expression into a calibration. Over temperature intervals of 1K it is linear to within 0.01K. The expression :

R = exp(A + B/T + C/T2) (3.2) gives a fit to within 0.01K over at least a 15K temperature interval (Morgan 1973), where R = resistance in ohms, T is temperature in K and A,B,C are constants calculated for a given thermistor over a specific range. The effect of pressure on thermistor resistance is negative and very small at about 10-7 bar-1. Over a short period of time and in a limited temperature range thermistors are capable of measuring relative 39

Cable Wheatstone Bridge Bridge volts adjustment Thermistor probe

'O' Ring seals

4 conductor cable gives automatic cable compensation Cable

LA LA, LB Distributed leakage LB — resistance JWIr '0' Ring SA, SB Distributed series seals SA SB resistance

4 rods at 90° forming a cage /

F Type Thermistor - --

BOREHOLE RESISTANCE THERMOMETER LAYOUT

Figure 3.1 Borehole resistance thermometer layout. 40

temperatures at a precision of - 0.0001K. However, the complex calibration curve and the tendency for thermistors to drift, limits their absolute calibration. Thermistor drift is ascribed principally to diffusion of impurity ions resulting from the passage of electric current; other causes may be mechanical shock, thermal shock or disorder- ing of atoms in crystal structure. Measurement of geothermal gradient requires a high precision in relative temperature measurement, whilst the absolute temperature is of no great importance. In this study temperature measurements were obtained at a relative accuracy of ± 0.01K. The thermistors were calibrated in a large temperature controlled water-bath relative to a platinum resistance thermometer (Transfer standard model, WS 104 H-650). Calibration tests were made at frequent intervals to check for thermistor drift. Precautions were taken to minimise this drift, the probe was treated as gen- tly as possible and thermal shock was avoided. The resistance R of the platinum thermometer was measured using a Smith Number 3 Resistance Bridge (by Cropico Ltd.). The platinum resistance thermometer was standardised by the National Physical Laboratory. Using the calibration points supplied by the N.P.L., a calibration table was constructed from the equation,

R = a + bT + cT2 (3.3) (for details see K.Williams 1975). the constants a,b,c were calculated to be

a = 25.49508 b = 0.1016 c = 0.1535.10-4 for the temperature range 0 - 60°C Using the table or a calculator program, calibration points for the thermistor could be obtained to a precision of - 0.01K. 41

Thermistors with high resistance (10,000n) at 18°C. were used so as to minimise the effect of the long connection leads. A four conductor cable system was used to provide automatic compensation for the lead series and shunt resistances. Four different cables and three different. types of thermistor were used in this study, the thermistor's being marketed by ITT. The type 'F' thermistor gave .a rapid response to temperature changes, type 'G' thermistors gave a slower response whilst type 'GT' thermistors the slowest response. Most of the holes reported in this study were measured using type 'F' thermistors. These have the advantage of a very short thermal time constant, 5 seconds in the air, which allows the detection of short period temperature fluctuations. Such fluctuations are often seen as a result of air or water movement. During the course of this study the probes were slightly modified, though essentially the design is the same as that described in detail by Morgan 1973. The thermistor resistances were measured at the surface using a modified Wheatstone bridge circuit described by Williamson 1975. The bridge is capable of resolving temperatures to better than 0.01K. On this type of bridge the amount of compensation required to offset the drift, due to changes in ambient temperature, was set by adjusting a pair of variable resistors. A modified version of the bridge was designed by Mr. K. O'Hara which is self-compen- sating and so required no manual zeroing before each measurement. Checks against standard resistances were used to test for instrument failures and calibration drifts before each log was taken. One type F thermistor (K2F) was used for most boreholes in this study. The thermistor was calibrated near the start of the project (8.11.76) and calibration checks were made during the work. After the last set of boreholes was logged three years later (26.10.79), the thermistor was recalibrated over 51 check points plus 11 at higher temperatures. Over the working range of 42

8-22°C the mean difference between the two calibrations was + 0.007 - 0.001K with a standard deviation of 0.007K. This amount of 'drift' was below the estimated calibration precision of - 0.01K and so was considered acceptable. The rate of drift in calibration would appear to be quite regular since, over the period 22.6.72 to 8.11.76, the drift was 0.007 - 0.002 in the same direction, with a standard deviation of 0.0086K. Temperatures and temperature gradients are therefore measured to a high degree of accuracy and are a negligible source of error. 43

Depth Measurement

The depth of the thermistor was obtained by use of a sheave wheel assembly. The counting wheel rotates once for each 0.305m (1 foot) of cable. The corrections for cable diameter were determined at the Fetcham Mill borehole, Leatherhead. Tape markers were attached to the cables at 15.24m (50 feet) intervals, whilst the cable was hanging in the borehole. The use of markers enabled a constant check to be kept of the counter calibration. An electronic sen- sor unit was designed to mount on the side of the counter (fig. 3.2). The system, which had a resolution of approximately 0.03m, was designed to drive an L.E.D. display. In addition, the pulses may be used to syn :ronise a chart recorder or data acquisition system. Checks were made to test for cable slip on each borehole. The electronic sen- sor had the advantage of accuracy at high speed when the cable was rewound, the mechanical counter being prone to miscount if run too fast up the borehole. Some of the boreholes taken over in this study were inclined. The angle ranges from 45o for certain mineral boreholes to perpendicular. Boreholes deviate for a variety of reasons although some are deviated on purpose. To correct length of borehole to vertical depth, only the inclination need be measured, the azimuth being of little importance. Four methods were used to measure the inclination. The most sophisticated was the use of a gyro system at the Rosemanowas test site. This system is complex and very expensive, so is normally undertaken by a contract company. The inclination is recorded as the position of a short pendulum target on a time lapse film. Azimuth readings are recorded on the same frame by use of a gyro compass. In this way a detailed sequence of dips and directions was used to locate the position of the boreholes to within - 0.6m. This method is more precise than that required for heat flow measurements and the cost for 44

pinch wheel i

route of perspex borehole cable light proof box slotted brass disc

'0' ring seat

rt— t cable to depth indicator 3 photo cells enable direction 50mm of rotation to be determined

Electronic depth counter - Sheave wheel

Figure 3.2 Electronic depth counter - Sheave wheel. 45

shallow borehole would be of a similar order as the drilling cost. A simpler version of this method was used on the Callywith Farm borehole near Bodmin, a Sperry one shot borehole surveying tool being used. A single photograph of a pendulum and magnetic compass card is taken at a preset de- lay after the instrument is set. In non-magnetic rocks. and outside drillrods or casing this method gives an accuracy similar to the gyro method. However, since only one photograph is taken on each run, the method is much slower and so, far fewer measurements are taken. The method is, however, ideally suited for the few measurements required for heat flow boreholes, though the instrument is expensive. The third method used a borehole compass clinometer, manufactured by Pajari Instruments, called the TRO-PARI. The instrument has a clockwork mechanism which locks the instrument once it has been lowered to a known depth. The inclination and azimuth may then be read before resetting the instrument at the next depth. The procedure is slow but sufficiently accurate for heat flow investigations. The fourth method was a rough and ready dip test. The dip test may be done using an acid etch, hydrofluoric acid is commonly used for such tests. This acid is very dangerous and so must be used diluted and with considerable care. A few alternative methods were tested, one involving etching a cross piece of copper-clad board with ferric chloride. The method finally used was a weak solution of calcium sulphate (Plaster of Paris) in water. The solid slowly sediments over a period of about 20 minutes. At the end of this time a remarkably flat surface devoid of a meniscus has formed which sets to form a solid record of the angle of inclination. It was hoped to try a plastic which could be used as a cheap, yet precise, chemical clock. However, when a tropari became available, development in this direction ceased. Since the drill string is a solid steel rod, sharp bends in the hole are less likely than a gradual change, 46 although there may well be exceptions. The deviation between survey points is estimated to follow the arc of a circle of radius r. This radius r is calculated from:

r - dn+1 - dn (3.4) Dn+1 Dn where do is the length of the hole to station n. Dn is the deviation from the vertical measured at station n. The vertical distance z between the two stations is given by:

z _ dn+1 dn (sinDn-1 - sinDn) (3.5) Dn+1 7 Dn

A subroutine was written for the heat flow calculation program RCHUCK which, using the tropari data, was able to calculate the vertical depth of each temperature station, using corrected intermediate distances. When using the subroutine, it is important to input the dip of the borehole at the surface. 47

Temperature disturbances, borehole preservation and errors.

Drilling can cause a disturbance of the temperatures recorded in a borehole. It is generally considered that heat exchange between the drilling fluid and the surrounding rock will affect the temperature field for some considerable time after drilling has ceased. Evans(1975)discussed the effect of drilling in some detail. The method of drilling will alter the length of time required to re- establish equilibrium. Jaeger (1961) carried out detailed studies to investigate the effect of diamond drilling. He concluded that the effect was less than that for rotary drilling. In the particular case studied, he concluded it was unnecessary at any one time to wait more than a day after drilling ceased. On the other hand, Bullard (1939) suggested that one should leave a borehole for forty times the actual time taken to drill. Fig. 3.3 illustrates the relaxation of temperature for Rosemanowas Quarry (Hole D). This 300m borehole was disturbed by drilling for longer than any of the specially drilled granite boreholes. The disturbance might, therefore, be considered as the maximum likely to have occurred. Temperature logs from the remaining percussion boreholes back this conclusion, though fewer logs were run in the period close to drilling. In this study, such considerations were of limited importance, since sufficient time was allowed for all the specially drilled boreholes to attain complete equilibrium. In general, the geothermal gradient is restored fairly quickly but the time to attain equilibrium temperatures takes longer. A further temperature disturbance may be produced as a result of the heating effect due to the curing of cement. This effect may be used to locate the cement grout after injection. Such a survey must be carried out only a short time after cementing. Fig. 3.4 shows the heating effect due to cement in the Predannack borehole. The log was run hours after a black iron pipe had been cemented in place. 48

Temperature difference. AK, relative to final log dated 21 1 79 (129 days after completion) -03 -02 -01 0 0 02 03 04 05 06

19 12 78 19 10 78 30 9 78 20 9 78 18 9.78 rY ■ ~.• x_ Jo - 15978 am. •'~ ~► _- i

7+ 100- Drilling compiled x _ 14.9 78

tres me in

th TEMPERATURE DISTURBANCE Dep 200- CAUSED BY DRILLING Relaxation curves for CSM Rosemanous PBH D

•

300 ti AK (as defined above) -0 3 0 01 02 03 04 05 06 t 1 , ,

Figure 3.3 Relaxation of temperature for Rosemanowas hole D. Temperatures, measured after drilling, versus depth. 49

12 13 14 15 16 17 18 19 20

Temperature °C ---

TEMPERATURE DISTURBANCE CAUSED BY CURING CEMENT

50- IGS Predannack DDH

O x x After break in drilling (3.1.78)

+ + 24 hours after cementings (131.78)

0 0 14 months after completion O. (25.3 79) 100-

s tre me 150- O in th Dep

200- 1°C °

° 250-1

300-

Figure 3.4 I.G.S. Predarnack Down borehole temperature versus depth graph to illustrate heating effect due to curing cement. 50

Boreholes which were considered unstable and likely to collapse were preserved by use of a lining. A cheap and quick-to-insert plastic pipe was used in several cases where no water flow had been detected. This polyorc pipe had an internal diameter of 25.4mm (1 inch) and an external diameter of 32mm (1' inches). The pipe is readily available in 6m lengths which are then glued together with plastic connectors. Each joint takes one minute to bond and it takes a further minute to lower, clean and apply the glue. Thus a 200m hole may be preserved in this way for a rig standing time of about ninety minutes. A more permanent and expensive method was used in the deeper holes and in the cases where water movement along the borehole needed to be sealed. A 32mm (14 inch) blue flash black iron pipe was lowered into the borehole in 6m lengths. Threaded couplings were used to joint the successive lengths. To avoid long delays, the threads were carefully checked, cleaned and greased before coupling. To fill the annular space between the pipe and the borehole wall sufficient liquid cement grout was pumped down the pipe. A separate 'rabbit' was then pumped to the base of the pipe using clear water. A valve was then shut at the top of the hole to hold the pressure during curing. A non-return valve was situated at the base of the pipe to prevent cement re-entering the pipe. The boreholes which were preserved in this way were Predannack and Old Merrose Farm. Although temperature aradients may be measured to a high precision there are many physical effects which may mask the gradients due to the terrestrial heat flow. After drilling,the borehole may allow the flow of water from one fissure or aquifer to the next. Only a small flow of water is required in order to affect severely the temperature gradient and where the flow of water is sufficient, the gradient may disappear completely. An example of water flow is shown in fig 3.5. Even minor water flows may be detected by characteristic short period water tem- 51

TEMPERATURE DISTURBANCE CAUSED BY 'NATER FLOW Wheal Jane DOH J

100

(/') ~ ...... '- ~ E , .~ .c. 200 15. ~ ~ , 1:J "0 u :;:; '- ~ , ~ ~ 300 ,

400

Figure 3. 5 Temperature versus depth plot, first log vlheal Jane J. To illustrate disturbance due to water flow. 52

perature variations observed during logging, in addition to the long term change in gradient. Often superficial flows occur where surface water uses the borehole as a means of reaching the water table. In such cases the borehole may sound highly disturbed as the water cascades down the hole. In south-west England,the few cases where this occurred, the disturbance was only observed a short distance beyond the water table. Only in the case of the Wilsey Down borehole was there any artesian flow, which again seemed to be near the surface. If the water flow between one aquifer and the next is entirely due to the presence of the borehole, then the gradient away from the zone of disturbance will be unaffected. However, if the disturbance existed before drilling, even borehole gradients some distance from the water flow will be affected. The Medlyn Farm borehole on the Carnmenellis granite outcrop is water disturbed down to a depth of 7.7m. Heat flow determinations from the bottom section of the borehole agree well with adjacent values, suggesting the disturbance was initiated at the time of drilling. Such boreholes may be recovered by insertion of a sealed pipe and grouting. This should be done promptly after drilling otherwise a long time will be required for the borehole to attain equilibrium. In the case of the relatively shallow percussion wells the cost of inserting black iron pipes, cement grouting, standing time, etc would not run far short of the drilling cost. With the use of plastic pipes however, this operation would, once again, prove economically viable, since no rig would be required and the grout could be mixed in an open tank by hand and pumped, using a portable petrol driven pump. During the grouting operation on Old Merrose Farm, even after careful checks of the joints etc, the 'rabbit' became stuck part way down the borehole. It was suspected that the rubber seals had failed and allowed water to be pumped past the 'rabbit' after it may have twisted. The 53

rabbit was the last of old stock as an industrial dispute had prevented new stocks being built up. We were, at this stage, left with a borehole full of cement. Since the hole had been drilled so painstakingly in order to obtain good core recovery in difficult ground, it was decided to attempt to recover the situation. Firstly, probings with a heavy metal rod on the wire line were tried. This failed, so 'EQ' drill rods were borrowed from South Crofty Mine. These rods just fitted down the centre of the black iron pipe. On the end was a crude core barrel designed to catch the 'rabbit'. At first all that could be recovered was cement grout, so a homemade tungsten carbide bit was used to drill down to the 'rabbit' through the cement that had leaked past. It then proved possible to recover the 'rabbit' using a core barrel fashioned from a car exhaust tube. Once the 'rabbit' was removed the remaining cement was drilled out using the bit. Such an experience illustrates some of the pitfalls which may occur even in a tried and tested method. After this incident the 'rabbit' was redesigned and has since apparently functioned perfectly well in two>1,000m bore- Old Merrose Fim holes in Northern Ireland. As a consequence the top o hole is still mildly water disturbed over the assumed non- cemented section. The cement top is unknown since the blockage prevented temperature logging shortly after grouting. In some cases drilling did not start at ground level, for example at White Hill Yeo the borehole was drilled (by E.C.L.P.)from a bench within a large china clay works. Also the boreholes at Rosemanowas Quarry were drilled through the quarry floor which is about 20m below the pre- existing ground surface. The effect of a very large quarry would be similar to that of a climatic disturbance: in that the temperature is suddenly changed. However, the magnitude of the change will be quite small.. In addition, climatic changes should start from the pre-existing surface. 54

Temperature °C

10 11 12 13

• • 10 -

20 - Yu 0

30 - °C

-small fault-

,x x

0 TUJ 70- C- a

80 - ō u 1/2m Granite

90- CC x'

100 - 9C 0 obstruction u Temperature loci Hemerdon DDH-H19

Borehole close to vertical boundary between

granite and country rock.

Figure 3.6 DDH H19 Hemerdon Mine. A possible example of local heat flow refraction? 55

Other errors in temperature gradient may occur due to refraction of heat arising from changes in thermal conductivity. An example of possible small scale refraction is given by DDH H19 at Hemerdon Mine (fig.3.6). The extrapolated surface temperature, To, gives an indication of the reliability of an observed gradient. If this is a realistic value, it is likely that the observed gradient is not too strongly disturbed. Fig. 3.7 illustrates the surface intercepts of boreholes in south-west England for which we have temperature data. On the same graph are plotted the 30year temperature averages for the south-west England meteorological stations. The recommended temperature lapse rate for normalizing mean daily temperatures is - 0.6°C per 100m increased elevation (Met Office 1975), the diagonal lines represent this lapse rate. Fig. 3.8 shows the mean surface temperatures at the locations recorded. Since any map of surface temperature would be as complex as the topography, the temperatures have been normalized to sea level. It is of interest to note that borehole data may be used to fill in gaps in the meteorological record. The meteorological stations are situated around the coastline of south-west England and it may well be argued that, as such, they could give a false impression of the local climate due to the moderating effect of warm sea currents. The borehole surface intercepts, Which cover a greater propt.rtion of the area, do agree remarkably well with the meteorological data, in fact, often better than two meteorological stations in the same area. This suggests the local climate of south-west England is fairly consistent. Quite good agreement can also be seen with the recommended lapse rate. The map shows that the average temperature gradually increases towards the south- west. Three boreholes are distinctive in their lower surface temperatures which fall on the same lapse rate. Two of these holes near Wheal Jane mine are on opposite sides of the same valley, whilst the third is close, yet at the

EXTRAPOLATED SURFACE TEMPERATURE DATA AS A FUNCTION OF ELEVATION (including Meteorological Station Data) 400

0 KEY IGS- 2 F1pney Mead • Meteorological Station DM-0+ + Contract borehole ❑ Other Borehole A Mine

LE Lands End CM Carnmenel is SA St Austell BO Bodmm DM Dartmoor + 60-A

480•0

D) O. e

+8D-E bov (a es

tr Wilsey e ❑ Down m 200 +CM-A in CM•D

ion Carloggas

t Ō

a SA-B CNI-C - lev Troon E +LE-A

SA•A 0 + + pcovey Tracey 2 0 +LE•B Gavengan

C49 O \ Neernn East 0 100 Geevor A Hartland Point • • 0 Parbo'a Newton 00.1 Mer-cse F rn Abbot 0 Lizard Cz2, 1, +CD' 14,,s! WorMa Exmouth• Newauay • C urry Prot Forma \ Falmouth • Scilly Isles W •E O •FOweY Ci" ,'ipor, P4 WJ•p❑ ❑ • Plymouth Exeter Au~ Plymouth Hoe Mount • Cannmgton Batten Penzance. SIdmoul •Bode Tc a •Guival • • • tff racombe Starcross Chwenr ••Te'gnmouth 12 0 B 0 90 100 11 p Extrapolated Surface Temperature I C1

Figure 3.7 Extrapolated surface temperature data as a function of elevation (including Meteorological station data)..

200. 300 SOUTH-WEST ENGLAND 110 HEAT FLOW COVERAGE aLUNDY ISLE EXMOOR 0,; EEC CONTRACT NO 586-78-1EGUK 11.6 ' 10.5 UKAEA CONTRACT NO E/5A/CON/105 10.8/ 10 0 II KEY TO BOREHOLES

Contract Sites Other Sites

• Granite oo Granite • Country Rock o Country Rock xla6

10, MAP OF EXTRAPOLATED SURFACE TEMPERATURE BODMIN { ~.~RANITE i,a~ '4e•o DA ANI T O.5 INTERCEPTS. 11 - -arm ,` •' i 1Q 10.5 10.5 I\ 11 •6 , 41$16 • N-- / ' Reduced to sea level using . 1O.s lapse rate of 0.006 °C 0.9 • •••• ~ J Ō 1•° /4/ x /- 10.7 r s // - 10.9 CARNMENEL L IS~~ - CIRANITE. r'' PLYMOUTH ST. AUSTELL 11 Oep1h-to•granite contours LANDS END - GRANITE fro/TICS gravity model GRANITE , i3 below i I km (1091 • • 3krn 11 12/ lkrn 11.4 .4 0 2,5 50km Scare • LIZARD PENINSULA 1•T 11 200 „ UI

FIGURE 3.8 National Grid Km East 58 top of an adjacent hill. It might be suggested that some microclimate exists in this region which has caused a 1°C drop in the mean temperature over a restricted area. p59 PLATE 1 Divided bar thermal conductivity apparatus

p60 PLATE 2 New 41mm divided bar apparatus t~ 61

Part 2 Measurement of Thermal Conductivity

Divided Bar Apparatus

Within a body heat flows from points at higher temperature to points at lower temperature. When heat flows by conduction it does so according to Fourier's Law:

q = K dT (3.6) dz

where q is the heat flow, in direction z, dT/dz is the temperature gradient and K is the thermal conductivity. Thermal conductivity is a physical property of the material through which the heat is flowing. Reliable measurements of thermal conductivity are required in order to compute heat flows from measured thermal gradients. The thermal conductivity of rocks is greater than that of gases but about one hundred times less than that of metals. Thermal conductivities were measured by the divided bar method. The principle of this steady state apparatus was first described by Lees in 1892. The divided bar is a comparative instrument calibrated relative to known thermal conductivities. Essentially the bar consists of a _ disc of unknown thermal conductivity sandwiched between two reference discs of known conductivity. A temperature difference at either end of the 'stack. causes a uniform flow of heat from the hotter end to the cooler. The unknown conductivity is found by measurements of the temperature differences across the sample and reference discs, combined with the sample thickness, (according to equation 3.7) . A full description of the calibration and construct- ion of the 35mm (1 3/8") divided bar may be found in Evans (1975). A new divided bar was built with a diameter of 41mm (1 5/8") to complement the already existing apparatus 62

MODIFIED 41 mm DIVIDED BAR APPARATUS

Top beam

AXial sWivel JOint

Perspex insulator

---+-·OUT ~~~~ ~~------~------~--IN

~------+------~-IN

Outer plastic shell

Perspex insulator

Brass Steel ram 50mm Vertical section

Figure 3.9 Modified 41mrn divided bar apparatus. 63

and to allow the measurement of larger samples. The new bar was designed to minimise the effect of the external environment on the axial flow. Jessop (1970) drew attention to the fact that exchange of heat between the sides of a divided bar and the surrounding air may cause inaccurate measurements. In experiments, Jessop was able to observe differences in thermal conductivity of the order of 15% if the ambient temperature was changed as little as 4°C. Bar behaviour is not simple and it did not prove possible to quantify clearly the effect by mathematical modelling. In most cases the solution is to use relatively thin samples. Coarse-grained rocks require as large a sample as possible, since such rocks may be subject to short circuiting of heat through high conductivity minerals such as quartz. Thick samples have the advantage of a more representative composition and less short circuits. In order to measure thick samples accurately, the new bar was designed to surround the sample with air at the same temperature as the sample. This was achieved by using large water showers. The top shower was warmer than the bottom shower in order to reduce convective effects. With little convection most of the heat loss from the showers should be perpendicular to the faces, thus creating an even temperature gradient between the two plates. The gradient within the bar should be of a similar order leaving only a small temperature difference between the air and the sample, thus significantly reducing lateral heat transfer. The divided bar was enclosed in a perspex box in order to reduce draughts and protect against flying fragments of rock should a sample fragment under compression. The room was air-conditioned to maintain a steady temperature. The divided bar was designed to create a flow of heat predominantly parallel to the axis of the bar. The bar is in two halves, the upper stack and the lower stack. Each stack comprises a thin disc of a polycarbonate plastic 64

AXIAL HEAT FLOW t J J

WATER SHOWER HEAT SOURCE

UPPER STACK [~~~~""""""'--'~~_.....-I

CYLINDRICAL SAMPLE OF UNKNOWN K

LOWER STACK [~-""""-~~~~~~~

Fig 3.10 Schematic Diagram of Divided Bar Apparatus 65

(Lexan) sandwiched between two brass discs which contain thermocouples. The hot and cold showers are fed by Model N.B. thermostatically controlled water-baths by Colora Messtechnik GMBH. The manufacturers specify a temperature constancy of - 0.01°C for these baths. The absolute temperature is not critical, however constancy is required in order for a steady state to be achieved. Minor fluctuations of temperature, due to the short bursts of heating within the baths, are smoothed by Lexan damping plates and also by the large thermal mass of the system. The apparatus was automatically switched on three hours before any measurements were made as the large thermal mass required a long warm-up time to ensure a constant temperature. The stacks are bonded by thin layers of an epoxy adhesive (Araldite AY111 with hardener HY111). This adhesive is slightly flexible so allows limited differential thermal expansion. However, it is difficult to bond poly- carbonates to metal so care has to be taken in the construc- tion of such a bar. A better solution might be to use a thick layer of glue as the reference material and so avoid the weak bond. The thermocouple potentials were measured using a Pontentiometer supplied by Cropico Ltd (Type P10) which has a resolution of 1pV. Measurements were obtained to 0.11V by measuring the deflection of a D.C. null detector which gave a deflection of 50mm per pV. The copper con- stantan thermocouple wire was calibrated relative to a platinum resistance thermometer and found to be linear over the working range, with a sensitivity of 0.024°CiV-1. Thus 0.1pV corresponds to a maximum resolution of ± 0.0024°C. To measure the thermal conductivity of a solid rock, a sample was first machined to form a disc. The faces were then finely lapped on an automatic machine, or by hand, to remove any blade marks and so reduce the contact resistance. 66

A batch of several samples prepared in this way were then saturated with water so as to simulate in-situ conditions. First the discs were loaded into a tough glass jar and evacuated over a period of three hours to achieve a pressure of 130-400Nm-2 (Walsh & Decker 1966). The samples were then flooded with degassed water which was forced into all the pores by atmospheric pressure when the vacuum was slowly released. The thickness of the disc was then measured to an accuracy of ± 0.001mm by taking the average of five micrometer measurements. The likely error on these measurements was considered to be less than 0.02mm, except where discs were poorly prepared. Thy saturated disc was then placed in the divided bar and carefully aligned. A thin film of a mixture, two parts water to one part glycerol, was applied to both faces of the disc to reduce the contact resistance. The disc was then subjected to an axial pressure of 7MNm-2 (-1000psi). The divided bar was then insulated and left to attain equilibrium. After 10-15 minutes, the thermocouple potentials, V1,V2 and V3, across the upper stack, sample and lower stack respectively, were recorded. Five minutes later, they were re-measured. A check was made to see if the potentials had changed significantly, thus testing if the bar had achieved equilibrium. When the sample potential and the sum of the upper and lower stack varied by less than 0.2FV over a five minute period, equilibrium was considered to have been achieved. If not at equilibrium, the potentials were re-recorded at five minute intervals until equilibrium was achieved. The time taken to reach equilibrium varied according to the thickness and thermal properties of the sample. For very thick discs (40mm) the equilibrium time was 90 minutes, whereas for standard discs, this would be reduced to 5-6 minutes. The sample conductivity was then calculated from the equation:

d K S (3.7) S LV2 (V1+V3)Kb where Ks is the sample conductivity Kb is the calibrated bar conductivity ds is the sample thickness L is the apparent bar thickness, i.e. the sum of the thicknesses of the upper and lower Lexan reference discs R is a value which represents the apparent contact resistance between the sample and the stacks.

Fused and crystalline quartz standards were used to calibrate the divided bars. These two standards fall either side of the normal range of rock conductivities. The 35mm (1 3/8") divided bar apparatus was first calibrated in 1972, and a further 124 measurements were reported for the period 9.10.72 to 9.7.74 (Evans 1975). During the course of this work both divided bars have been calibrated several times. Over this period of time a few breakdowns occurred. These fell into two categories; a) failure of a thermocouple and b) an araldite joint failure. After each such breakdown the divided bar's calibration was checked. The absolute values of thermal conductivity of the reference materials were calculated from the following formulae after Ratcliffe (1959). (3.8) Fused quartz conductivity = 1.323 + 0.00193T - 0.0000067T2 Wm-1K-1 (3.9) Crystalline quartz conductivity = (0.145 + 0.000578T)-1 Wm-1K-1 where T represents the mid-point temperature of the bar in behtigrade. 68

A standard method of bar calibration was used as described by Beck (1965). The equation:

LV sKb + RKb (V +V 2) = d (3.10) 1 3 Ks (Jessop 1970)

may be easily derived, where ds is the thickness of a sample, 'L is the summed thickness of the two reference discs, Kb is the apparent reference material conductivity and Ks is the sample conductivity. V1. V2 and V3 are the thermocouple voltages, corresponding to the temperature differences across the upper stack, sample and lower stack respectively and R is a value which represents the apparent contact resistance between the sample and the stacks. A least squares fit of thickness versus LV2/(Vi+V3) gives a slope of Kb/Ks and an intercept RKb. Using absolute values of the standard conductivity, the apparent reference conductivity may be calculated for both ends of the conductivity scale. An average of these two values is assigned as the reference conductivity. The 35mm(1 3/8") divided bar was calibrated in this way by Evans (1975). The bar conductivity was assigned the value of 0.222- .003Wm-1K-1. The calibration has been checked periodically and the total drift over an eight year period has been within one standard deviation of the original measurements. This is despite the occasional rebuilding of the divided bar. The initial calibration and testing of the 43mm(1 5/8") bar was described in detail by P.J. Baker (1978). The apparent bar conductivity was found to be 0.214Wm-IK-1 at 24.4°C being the average of the calibration for fused quartz of 0.214(5)- 0.001Wm-1K-1 and of crystalline quartz of 0.2136- 0.0005Wm-1K-1. This figure of 0.214 is lower than the conductivity of Lexan at a measured conductivity 69 of 0.218, the slight descrepancy probably being accounted for by the thin film of glue bonding the surfaces plus any contact resistance within the bar itself. It is difficult to assess the long term stability of the divided bars since each time a bar is rebuilt it should be treated as a new bar. A divided bar is a comparative measuring instrument thus might yield systematic differences when compared with those of other workers. Interlaboratory checks were reported for the 35mm bar by Evans (1975). Samples of Lexan were measured by the U.S.G.S., Menlo Park, California, Oxford University and the Dominion Observatory Ottawa, Canada. The mean of these values, weighted by the number of measurements, was 0.218Wm-1K-1. This was in agreement with 0.218Wm 1K-1, the mean value of 25 measurements on the 35mm bar. Lexan measurements have been made on both bars, generally twice per working day. The mean of these measurements rarely varied from this value. In this way a constant check has been kept on both bars. A more detailed comparison of 16 rock types was carried out against the apparatus of the Southern Methodist University, Dallas, Texas. From all the tests Evans concluded that the Imperial College divided bar was not introducing any systematic error in relation to other insti- tutes' conductivity measurements. 70

Measurement of Rock Chips

The 'pill box' technique developed by Sass et al.(1971) was used to measure the thermal conductivity of rock chips. This technique was implemented at Imperial College several years before this present study (Morgan 1973). The whole rock conductivity is estimated from the divided bar measurement of a cell containing rock chippings and water. The dimensions of each cell are accurately known, as are the conductivities of the cell materials and the water. The conductivity of the rock chips may then be estimated by modelling the system and calculating the effect of the rock in the system. The method is generally less reliable than disc measurements. However, only rock cuttings were available from the percussion boreholes, which are central to this present study. Two models of the system were used, the Maxwell Spheres model and the Geometric mean model. Before either model can be applied, the thermal conductivity of the water/rock aggregate should be obtained by removing the contribution due to the calculated thermal effects of the cell. In the Geometric mean model , the aggregate conductivity is assumed to be represented by the weighted arithmetic mean of the logarithms of the constituent individual conductivities.

K 62 Kin (3.11) 1 K2 n

For the water rock aggregate this is assumed to be represented by a two component system.

logKa = (1 - 62)logKl + 62logK2 (3.12)

The Maxwell Spheres model uses the mean of the upper and lower bounds given by Maxwell's relation, (Maxwell 1904). This theory describes the thermal conductivity of an aggregate of non-interacting spheres of one conductivity in a 71

matrix of another (Hashim & Strikman 1962, Horai & Simmons 1969 and Evans 1975). -1 1 2)-1 + 6(3K2)-1 (3.13) Klower - K2 + (1-a) (K -K -1 K1 + o (K2-K1)-1 (1-6)(3K 1)-1 (3.14) Kupper

{3.I5} Ka 2 upper + Klower)

The geometric mean model is more commonly used and was adopted in the thesis, since it was generally the closer thermal conductivity in the comparison tests for granites. Porosity can lead to large errors in determination of. rock chip thermal conductivities. The error may be corrected if the porosity can be measured. This is very difficult with rock chips and only an estimate is obtained. Porosity may be determined by a variety of other means, such as borehole density logging or direct measurements within a Kobe porosity meter. Porosity determinations on Cornubian granite samples yielded very low values of--10-4 (A.S. Batchelor 1980). It was considered, therefore, that porosity would only lead to a slight error in determining the thermal conductivity. A further source of error in chip measurements is deformation and wear of the pill-box cell. In order to reduce the contact resistance within the bar, quite high confining pressures (7MNm-2) are used for disc measurements. At such pressures the cell walls may bulge outwards, this leads to an apparent increase in the rock conductivity. The sample becomes thinner than its measured thickness and also the cross section slightly increases. The amount of bulge was determined by careful diameter measurements before and during loading. The pressure at which deformation started was then found and a pressure below this was used for all subsequent measurements. Wear of the cell was corrected for by frequent remeasurements of the cell dimen- 72

sions. It is difficult to maintain a constant standard when measuring chips, as there are many parameters which affect the accuracy.

'PILL BOX' THERMAL CONDUCTIVITY CELL

PLASTIC ~

VERTICAL SECTION

Figure 3.11 'Pill box' thermal conductivity cell. 73

Sampling

The granite gave apparently uniform thermal conductivity with only minor variations. In sampling and processing the thermal conductivity , care was taken to minimise systematic errors. Where possible, measurements were made in a random order of depth so that trends observed in the boreholes would be due to one of the following: geological control, freak statistics or a systematic effect in the sampling. The results obtained show changes, or drifts of conductivity which are apparently due to geological control. An attempt was made to design an automatic computer program to find errors in the data. In statistical sampling for quality control, use is made of confidence limits and the likelihood that these values will be exceeded. When dealing with a mean value which is fluctuating due to geological control, this is not a straightforward process. Deviations from a moving average were tried but found to be unsatisfactory. A method of using Fourier residuals was also investigated. In this method the samples were converted from a depth domain into a distance frequency domain where high frequencies were removed. The data was then converted back to the depth domain. The residuals were then calculated by subtraction of the smoothed values from the original data. In this way samples with a frequency of one would appear prominent. The distributions obtained could then be treated as a standard quality control problem. Those examples exceeding an 'action limit' were first carefully re-examined for typing or obvious reading errors. If no such error was evident the sample was re- measured. There is a danger in this type of quality control that real effects could be lost by selective resampling. On the other hand, if an error is made by accident, it is important that this gross error is not allowed to reach the final stage. It was, therefore, decided not only to search for errors, but also to carry out a system of 74 standard repeats so that a repeat due to a previous error stands out against several standard repeats. As more laboratory time became available and, with two bars running simultaneously, it became standard procedure with the later boreholes to run all chip samples twice. It was gratifying to note that, with the use of careful checking, the number and type of gross errors were almost eliminated. This was achieved by finding the cause of each error and taking steps to reduce the likelihood of a further occurrence. Having reduced the number of gross errors, it is possible to look at the distribution of conductivity in an attempt to find the errors inherent in the method of measurement and the variability of conductivity within the apparently uniform granite. 75

Estimation of Errors

Ratcliffe (1959) estimated the likely error in an individual data point, used to derive the fused quartz relation, to be - 12% at 28°C, although no estimate was given as to the accuracy of the formulae given. The errors quoted for the divided bars were calculated relative to these 'fixed values' for the standard conductivity. For the 35mm divided bar, Evans (1975) estimated the error in calibration to be 2%. This figure was obtained from the variation of inferred crystalline and fused quartz conductivities relative to the Ratcliffe values. Varia- tion in calibration results from variation in the Lexan 'standard' material and composition of the bar. For the initial calibration of the 41mm divided bar the slope of the fused and crystalline quartz reference sets was measured to an uncertainty of less than 1%, the mid-point of the two calibrations being within the standard deviation of each set. Since the 'standard' material is the same for both bars it is reasonable to assume a similar variation with time to that reported by Evans (1975). Bar failures complicate the pattern, since rebuilding the bar leads to a change in resin bond thickness and Lexan thickness. It was, therefore, difficult to assess long term stability. Estimations of errors for disc and chip measurements were considered separately due to the different methods used. From observations of the repeatability of disc samples Evans (1975) estimated that the likely random error inherent in measuring thermal conductivity on the 35mm bar was of the order of 2%. The combination of calibration error and sample measurement error would yield an error of - 4% for the determination of the conductivity of an individual disc of rock of standard character. The estimation of errors in chip cell measurements is far less straightforward. Sass et al. (1971) found 76

that all their determinations fell within about 10% of conventionally measured solid-rock values for a variety of crystalline and sedimentary rocks. A standard deviation of 6% for repeat measurements on non-porous rocks was reported by Evans (1975). To this must be added systematic errors inherent in the method. The 2% error in bar calibration is transformed to a 3% error by the non-linearity of the equations involved. Uncertainty in the conductivity of the water and cell materials leads to a further systematic error, as does the deformation of the cell shape and dimensions due to the loading needed to reduce contact resistances. Wear in the cells, due to abrasion by the rock, necessitated the regular remeasurement of the cell dimensions throughout the course of the project. Evans (1975) evaluated the total error of a single chip cell measurement of a non-porous rock to be - 12%. However, in porous rocks, a further error is included due to the uncertainty of this parameter. Porosity measurements are described in some detail by Morgan (1973) and the calculation of porosity from borehole logs is discussed by Evans (1975). Solid granite has a very low porosity of-- -4 10 (A.S. Batchelor 1980) and so no correction was deemed necessary. Comparative tests between the 35mm and 42mm divided bars show that a significantly better repeatability was obtained by the larger bar; thus the new bar is slightly more accurate than the bar built and described by Evans (1975). This is probably attributable to the larger volume of sample measured and the reduction of lateral heat losses. If the random scatter was of the order 6%, this would have been reduced by the combination of two measurements at the same depth to 4% per depth point. Thus for those boreholes where all the values have been repeated, the 12% error would have been reduced to - 10%, this figure including the calibration error. For a borehole, where 20 depth points were being used to calculate the heat flow, the standard 77

error due to conductivity measurement would be about 7% for chip measurements as compared to 2-3% for disc measurements. There must also have been a certain error inherent in the sampling process, this quantity being much more difficult to assess. In the case of the granite boreholes, variation in conductivity appeared to be relatively minor and so was unlikely to have introduced a large error. In certain areas quartz porphry dykes intrude the granites: these dykes were avoided wherever possible. It is unfortunate that the two granite areas, Troon and Hemer- don Mine, where it was possible to obtain a direct comparison between samples recovered from a percussion borehole and samples recovered from a parallel diamond borehole, were in zones of quartz enrichment. The Holman Test Mine at Troon was the site of inten- sive investigation, initially by Camborne School of Mines and later by A.E.R.E. Harwell. A slim diameter diamond drill hole was drilled by students and staff at Camborne School of Mines. From this borehole 20 sections of core 42mm diameter) at approximately 3m spacing, to the maximum hole depth of 60m were obtained,from each of the eleven sections of core three discs were cut. The remaining nine sections yielded single discs which were measured twice. The mean repeatability was 0.6% for these samples. For the three disc sets the differences in conductivity were on average 2.6% of the mean value of each set. One section of unaltered 'normal' granite at 9.1m was measured in detail. This material was cut to produce 3 sets of core at seven different thicknesses, from 0.5 to 4cm. The purpose of these sets was to test for short circuiting via quartz stringers. It was anticipated that short circuits would be apparent as high values of conductivity in the thinner samples. The average conductivity of the 21 samples was 3.33Wm1K-1 with a standard deviation of - .12. If the samples are combined as a least squares regression of the 78

12- THERMAL CONDUCTIVITY DISC VERSUS CHIP 10- COMPARISON AT TROON

R = mean s = standard deviation

Disc measurements 14 - 60m x=342 s =013

28 30 32 34 36 38 40

currence Single depth disc measurements at 9 1m oc f x =333 s=012 o uency Freq

28 30 32 34 36 38 40 Chip measurements in adjacent borehole using Geometric Mean Model x=325 s=011

28 30 3~2 3~4 3~6 3 8 41 0 4-

using Maxw2II Spheres Model 2- x=313 s=011

0 2~ 8 30 32 3 4 3'6 3-8 4 0 Thermcl Conductivity Wm-1 deg-1

Figure 3.12 Thermal conductivity comparison at Troon (Carnmenellis granite). 79

apparent thermal resistance versus thickness, the slope yields a thermal conductivity of 3.38 - .03Wm-1K-1. The regression shows no indication of short circuits even for the 5mm thickness. The average thermal conductivity from 60 separate discs was 3.39 - 0.13Wm-1K-1. A percussion borehole was drilled within 10m of the diamond drill borehole. 17 chip samples from this borehole were measured using the pill-box method. The average thermal conductivity was 3.13 - .11Wm-1K-1 using the Maxwell spheres model and 3.25 - .11Wm1K-1 using the geometric mean model. The chip measurements yield a Gaussian curve of similar standard deviation to that of disc measurements. The mean is 4% lower than that for all 60 discs and 2% lower than the 21 samples from 9.1m. The disc measurements show a slight positive skew which might be attributed to quartz enrichment. Disc samples with the higher thermal conductivity are slightly discoloured and some contain fine stringers of quartz. Further samples from the quarry area were measured using the line source experiment described later in this chapter. Thermal conductivities may be estimated from their chemical or mineral compositions. This calculation was performed using the Modal Analyses from Exley & Stone (1964). The upper and lower limits of the thermal conductivity of rocks, with negligible porosity, can be estimated if their constituent minerals and the thermal conductivity of these minerals are known. The maximum, that is the parallel computed conductivity, is given by:

100Kp = a1K1 + a2K2 anKn (3.16) where a1,a2,a3 = % of minerals with thermal conductivities K1,K2,K3 The minimum or series conductivity Ks is given by

100 = al + a2 + a3 ....an (3.17) Ks K1 K2 K3 Kn

To estimate the most likely thermal conductivity, two further equations were used (Sibbett et al. 1979, after Powers 1961). In consideration of dispersed particles the Rayleigh-Maxwell dilute dispersion equation was used:

K. K - K = Kc 1+~~-! (3.18) El_2x.1K2Kcc_ +K i xi 2K -K.

where K is the composite conductivity Kc is the continuous phase conductivity Ki are the dispersed phase components xi are the dispersed phase volume fractions For a two component mixture case the Bruggeman equation was used:

2 KB- Km 0 (3.19) xB KB+2Km = EB=1 where B refers to component 1 or 2 of the mixture.

In the case of granite the two feldspars were considered to be a mixed phase, whilst quartz and micas were considered dispersed. The Modal Analysis for a Ghosh type I granite (Chayes 1955) yielded: Maximum conductivity = 4.00 Minimum conductivity = 2.95 Theoretical conductivity = 3.41 This is in close agreement with the disc measurement although there would be expected to be quite a large error in the estimation of thermal conductivity using this method. For instance, if all phases are considered dispersed in just one feldspar, the conductivity is reduced to 3.30 or 3.27, according to the starting feldspar. This mechanism might account for the lower results obtained for the chips since all conductivities are dispersed in a matrix of water. The in-situ experiment yielded - 10% a thermal conductivity of 3.5Wm-1K-1 for the range 20-2000C. One 81

standard deviation of the in-situ measurements overlaps the means of the laboratory methods, except the Maxwell spheres model which lies 10.5% lower than the in-situ result. The comparisons indicate no serious systematic error has occured in the measurement of thermal conductivity since the results from all the different approaches are in reasonable aggreement. This result demonstrates the im- probability of the observed thermal anomaly representing a systematic error in the measurement of thermal conductivity. 82

Granite — Thermal Conductivity Histograms (x = mean s = standard deviation ) DART BODMIN MOOR C4RNMENEL L IS Z BD•A DMA ;: 337 x:323 i Longoowns s: 017 s :012 x,309 s, 034 rill BD•A 1"t , 7:342 S.018 DM B CM•A x : 309 s: 032 x . 337 s:016 —11 `1 BD•C DM•C 3.09 CSD3 3.12 Mlle Polgear s 013 s : 0.28 ;374 5:015 I ce ^1 DMD

en x :3.28

rr s: 0 19 CM-B BD•D P tgear Beacon c: z : 338 3 57 s:017 :LI!: 0.35 Occu 1 Of cy 1 CM-C 8D-E DM-E en L )7: 332 x . 3.28 x.341 u s:023 s:016 s, 017 eq Fr

r-- 1

1— LAND'S END CM-0 Z ST ALISTELL LE •A x.327 SA•A s,012 x , 336 x:314 s: 0 15 s,014

r- LE•B — SA•B CM•E x.336 s ,021 x . 3 38 x.321 Z_ s, 017 s : 0 25

rf 7- 3 4 3 4 3

Thermal Conductivity W m'1 deg -1

Figure 3.13 Granite thermal conductivity histograms. 83

Results

Granite thermal conductivities were uniform over the entire pluton. There was no observed correlation between thermal conductivity and heat production or heat flow. The monumental stone granite (e.g. Longdowns) appeared to have a slightly lower.thermal conductivity than the average. The altered granite of CSD-3, Little Pol- gear, yielded a higher thermal conductivity. Such variations may be accounted for by small changes in quartz content. Thermal conductivity determinations on the country rock boreholes were less straightforward. Most of the country rocks in Cornwall were laid down in the Armorican or Western European Geosyncline at the edge of the 'Old Red Sandstone Continent' during the Devonian period. Rhy- thmic sedimentation is suggested by the finely alternating slates, siltstones and sandstones. Many of the sandstones show graded bedding. The Gramscatho Beds are formed of interbedded greywackes and slates with sporadic limestones, cherts and spilitic lavas. The Mylor Beds comprise slates and siltstones with rare sandstones. The accumulation of these thick geocynclinal flysch-type sediments of south-west Cornwall took place in a rapidly subsiding east-west trough. At the end of Devonian times the region was affected by earth movements to the south, and considerable outpouring of spilitic lava took place. These sediments and lavas have undergone regional and, in some cases, contact metamorphism, in addition to deformation and several phases of folding. As an example of the problem of obtaining an accurate estimate of the thermal conductivity, let us discuss Kestle Wartha, the second of the three specially drilled country rock boreholes. The borehole was sited to the south of the Carnmenellis granite outcrop in Devonian rocks of the 84

Gramscatho Beds. The borehole yielded a good percentage core recovery of a sequence of shales, slates and fine sandstones. Thermal conductivities were determined on 41mm diameter discs. It was found that recoring lead to a bias towards the sandstones. Samples of sandstone were easily recored in these beds whilst shales often proved difficult to recore. Samples were taken at approximately 3m intervals from the core. Conductivity results showed a wide range from 1.02 to 4.57Wm-1K-1. The low values were generally due to shales, whilst the high values were associated with quartz-rich sandstones. If this rock was simply a set of alternating sands and shales it would then be possible to obtain a value for shale and a value for sandstone. The total conductivity could then be obtained by use of a weighted harmonic mean of the constituent parts. The country rock, however, is very mixed, in some cases the shale bands are only a few mm in thickness and sandstones grade in turbidite sequences. Thus continuous variations of grain size and density occur. These sequences vary in thickness from a few mm to about one metre. These variations are thought to be the result of the settling of se- quential influxes of sediments. This type of sediment occurs over much of Cornwall. The amount of sandstone to shale depends upon the original distance to the source of sediment. Heat flow measurements in such sediments become dependent on the method used. For example, the arithmetic mean was 3.06, the geometric mean was 2.89 and the harmonic mean was 2.69. The mean conductivity, as a result of the Bullard method was 2.66Wm 1K-1. The distribution of thermal conductivity is shown on plot 21 (Appendix IV). It would appear that error, due to individual disc measurements, is insignificant in comparison to the errors due to sampling. Only by a large sample set can one obtain a reliable estimate for the thermal conductivity of the country rock. 85

No satisfactory measurements were made on kaolinized granites since such granites fall to pieces during coring, therefore only chip cell measurements can be made. Since kaolin is easily separated from quartz and mica, one can never be certain if the core, which has generally crumbled, is in any way a true representation of the host rock. In addition, kaolin is a clay mineral and so may be expected to swell as it is saturated. Such rocks should be measured in as near in-situ conditions as possible. Measurements on kaolinized granite, eg CSD-3 and RDH- H3, yield high values of thermal conductivity. This leads to a suspicion that some kaolin has been lost, leading to an excess of quartz. On the other hand, kaolin deposits are often associated with a quartz stockwork. The Carlogas and Goon- barrow boreholes have not been converted to heat flow measurements due to their uncertain conductivity. What is required is some form of in-situ determination. This could be undertaken since exposure of kaolinized granite is very extensive in china clay pits.. Such a determination would be possible by, either filling and sealing divided bar cells in the field, or by some form of transient method, such as needle probe determinations. A large probe could be hammered or drilled into the rock since the kaolinized granite is often soft. As with many ideas within the project, lack of time prevented these measurements being obtained. 86

Temperature Dependence of Thermal Conductivity

The decrease of thermal conductivity with increasing temperature was reported by Birch and Clark (1940). The extremely high value of the coefficient of thermal conductivity at room temperature and its sudden drop within the 300-1100K temperature range is a characteristic feature of granites (Peturin & Yurchak 1973). Quartz has a high value of the coefficient of thermal conductivity, and so the characteristic feature may be related to the high percentage of quartz. The relation is very nearly hyperbolic, though in a limited temperature range, may be considered virtually linear. Our initial calculations of temperatures at depth were based on the maximum and minimum coefficients obtained by Birch &Clark (1940) for the Rockport and Westerly granites. Quartz has a high thermal conductivity relative to many other rock forming minerals and so the variation of quartz content between rocks of the same petrological classification may yield a significant difference in thermal properties. It was, therefore, considered unsatisfactory to apply published thermal conductivities of granites from different areas. The line source experiment was used as a method of measuring thermal conductivity in an absolute manner at elevated temperatures with relatively simple and available equipment. It was hoped to investigate the contact problems associated with line sources in rocks. Cylindrical rock samples were heated in an oven to a given temperature and allowed to reach equilibrium. The samples were then heated electrically by an axial nichrome wire, the rise in temperature being sensed by a thermocouple at a small distance from the wire. Thermal conductivity is then calculated by comparison with theoretical models. This research was carried out in association with 87

HEATER WIRE

THERMOCOUPLE WIRE / /6cm

OP 12cm

OFFSET DISTANCE r

WIDTH OF GROOVES ...... 0.55 mm APPROX. DEPTH OF GROOVES 0.60 mm

Figure 3.14 Line source and thermocouple configurations. HEATER CIRCUIT OVEN THERMOCOUPLE CIRCUIT RECORDING PROCESSING

SAMPLE AMPLIFIER D CONVERTER SWITCHING BOX

11 COMPUTER RELAY J LINK SWITCHING MICROPROCESSOR BOX

STEEL BLOCK

I =I

POWER SUPPLY V. O. U .

TAPE ZERO POINT

FIGURE 3.15. LINE SOURCE APPARATUS. 89

A. Cheyne(1978), A. Jackson(1978), J.Robinson(1979) and N.Bassett(1979) who carried out experimental work as student projects, full details of each stage of the work may be found in these references. The development of the A-D circuits and links to the microcomputer was carried out by A Sartori. The line source experiment is an absolute method of thermal conductivity determination similar to the needle probe method. The method yields the conductivity perpendicular to the axis of the core. Granite samples measured were collected from the Holman test mine at Troon on the Carnmenellis granite outcrop and from the Merrivale granite quarry, Dartmoor. For comparison, country rock samples and samples of Norite from South Africa were also run. The granite samples have a large grain size (orthoclase >5mm, quartz 3-5mm) . Quartz has a high thermal conductivity and may give rise to a short circuit of heat and so distort the temperature field. The theory of a line source is based on the assumption that the rock is homogeneous. Any anistropy or grain effects will distort the results. As a precaution the thermocouple was placed in a position so as to avoid large quartz crystals. The eight samples from the Merrivale quarry on Dartmoor were cored at a diameter of 75mm from a single block of granite, all the samples having the same orientation. Thus, variation from one sample to the next, is a function of the problems of measuring a rock of large grain size, rather than differences in rock composition. The cores were cut longitudinally into two halves. A nichrome heater wire and thermocouples were placed in parallel grooves scribed into one half of the core and the two halves were then bonded back together using a hot cure epoxy adhesive. The samples were cured at 180°C then wired up to a pair of switching boxes, one for the heater and a second for the thermocouple leads. A constant voltage was applied to the heater wire by 90 triggering a relay. Temperature readings were taken at 0.lsec intervals for the first 10 seconds and every subsequent 5 seconds up to 100 seconds for 60mm diameter samples and 120 seconds for 75mm diameter samples respectively. A Z-80 microprocessor was used to obtain these readings. Some time was spent building a Nascom-1 microcomputer for this task. To the computer A.Sartori added a timing circuit and an eight bit A-D converter (ADC 0817 N/S). The timing circuit prcvided precise intervals of time to the A-D converter, which samples the voltage output of a Hew- lett-Packard 425 DC microvolt ammeter when triggered by the pulses. The A-D converter interrupted the Z-80 when data was available for storage. Once stored in the microcomputer memory, the data could be stored on magnetic tape via a cassette recorder. In addition a link to the college's CDC Cyber 176 mainframe computer was added, so that the data could be transferred directly for use with computer interpretation and data presentation programs written in Fortran. Further improvements to the measuring circuit have since included the exchange of the 8 bit A-D converter for a 16 bit Analogic MP 6812 Data Acquisition system and the use of a pair of AD 520 K integrated circuit instrumentation amplifiers for two thermocouple input lines. The temperature versus time graphs were interpreted by use of theoretical models of heat flow, derived from the differential heat conduction equation (Carslaw & Jaeger 1959) :

dT = K 02T + A (3.20) dt p c p c where T is temperature K is thermal conductivity p is density c is specific heat capacity 91

A is heat production t is time In the case of a line source, the heater wire is assumed to have negligible radius and negligible heat capacity. The rock was assumed to be isotropic with no heat sources other than the wire. For ease of solution, cylindrical co-ordinates were used with the wire forming the z axis. Three models were used: 1) Logarithmic. For a rock of infinite radius and infinite length the solution of equation (3.20) is: a~ Q e-u T - 4rrK )12 du (3.21)

where r is the radial distance (offset) of the thermocouple from the axis. k is the thermal diffusivity K/pc

r2 u = 4kt (3.22)

If u is small, equation (3.21) may be approximated by:

_ (1nt) + ln (3.23) 4r 2 - y

where Y = 0.5772 Eulers constant. r2/4kt decreases with increasing time so that for small 'r', or large 't', a graph of temperature,T, against the logar- ithm of time, lnEt), should tend towards a straight line with slope, Q/4rrK. This is the expression used for the calculation of thermal conductivity by the needle probe apparatus. However, with samples of finite radius and finite offset r, the experimental results will hold only from the time,t, when r2/4kt becomes small to the time taken for heat to reach the surface of the sample and return again.

In practice, this region may be difficult to define, except when r is very small. 2) Maximum gradient method. Differentiating equation (3.21), with respect to time, gives:

dT dt 4nKt exp [-4,r,t]2 (3.24) which is valid from time 0 to the same maximum as the logarithmic method. dT/dt has a maximum at time t m where:

t r2P c m 4K (3.25) substituting this relation back into equation (3.24) yields:

Q e-1 K 4n dTl (3.26) tm dt t m which is independant of p or c. Thus we have two equations capable of generating a thermal conductivity. The first requires assumed values of /oand c, whilst the second requires measurements of 0 and the maximum gradient itself. It may, therefore, prove possible to use the two routes as an internal check or a method of measuring K and the specific heat capacity c.

Q e-1 dt c (3.27) irr P dT t m For a regular geometry, p is easily measured and varies little. 3) Finite cylinder model. For long periods of time the logarithmic model is not valid, due to the finite sample size. Robinson (1979) obtained the following solution (after Carslaw & Jaeger 1959) for a sample, having radius a, with negligible flow of heat 93

across the boundary.

Q 2kt r2 3 r\ + 2 - 4 - lnCa- T= 2nK a 2 2a

CO (ram) 2 exp(-kam t) Jo (3.28) m=1 (a 1aJ° (a an))

Where am positive roots of J1(aa) = 0 and J n = Bessel function of the first kind of order n. This solution is valid until heat loss at the walls of the cylinder becomes sufficiently large to cause an effect on the temperature field. If the heating current is low, this will not occur for several minutes. During the first stage of this project the use of the DC microvolt ammeter prevented use of the maximum gradient technique. This was due to the slow response of the amplifier which caused an apparent shift in the temperature versus time graph. Recorded temperatures were interpreted according to the logarithmic and finite cylinder models by use of computer programs. The thermal conductivity was plotted as a function of the oven temperature. All the granite samples exhibited a marked decrease in conductivity with increasing temperature. Measurements were obtained from unsaturated samples up to a maximum temperature of 192.6°C. Thermal conductivity determinations were made at 20°C intervals as the temperature was increased, then at 20°C intervals as the temperature decreased. This scheme gave 18 readings at approximately 10°C intervals over the range 20-190°C. Unfortunately the ascending values do not lie on exactly the same trend as the descending values. This change was interpreted as being due to changes in the resin bonding the two halves of the sample. It may also mask any physical or chemical change within the granite over this temperature range, for example the expulsion of the interstitual water. The samples had previously been heated 94

to 180°C during the curing of the clue. Despite experimental problems, a clearly defined relationship emerged from the samples (fig. 3.16), which was not inconsistent with the reciprocal relationship (Birch & Clarke 1940). Two samples of Carnmenellis granite were measured at Los Alamos (Dodson & Sibbet 1979), using a high temperature divided bar apparatus. The results from these two samples agree well with the experimental results within our own laboratory. There can now be little doubt that the thermal conductivity of the Cornubian granite does decrease with increasing temperature, in a similar manner to that observed by Birch & Clarke for other granite rocks. The trend is closer to that of the Rockport granite than the Barre or Westerly granites. The experiment was carried out by physics undergraduate students as part of a geophysics option. During this phase random experimental errors were estimated to be 2.5%. Since this time, further work by A. Sartori and additional students have reduced this to 1.5%. It is intended to make a check against a. Macor reference block in order to detect systematic errors. Macor is a mechanically strong and durable ceramic which can be machined and drilled with conventional machine tools. It has a thermal conductivity of about 1.6Wm-1K-1 and so can be used for comparison of measurements between divided bar, needle-probe, line source and any other conductivity measuring apparatus. it is hoped that the experiment will be continued and further refined to enable the measurement cf saturated samples at in situ pressures and temperatures to be made. The advances of microprocessors has allowed the effective use of transient•methods of measuring thermal conductivity. It is now possible to sample, compute and display several parameters simultaneously. A variety of heater and thermocouple arrays may be used, since the microcomputer may be adapted by changing the software. This will, no doubt, eventually allow in situ determinations to be made 95

FIGURE 3.16 COMPARISON OF THERMAL CONDUCTIVITY RESULTS

3.0

2.0- I-- V -/ OZ w =WESTERLY GRANITE x =BARRE GRANITE =ROCKPORT GRANITE 1.0. 4 a = CARNMENELLIS GRANITE CORNISH GRANITES (BASSETT,1979) CORNISH GRANITE S (ROBINSON ,19791 ---- CORNISH GRANITE • (DODSON 1979) 0 300 250 200 150 100 50 0 TEMPERATURE (°C) 96 with relatively little labour. Use might be made of either the drilling process itself, or by the injection of heat to obtain such results. Several researchers have been working on in-situ methods of thermal conductivity determination (Behrens et al. 1980, Jolivet 1980, Musmann & Kessels 1980). Without the use of a microcomputer, the measurement of many samples, using a line source apparatus, would soon become a very tedious operation and therefore highly prone to human errors. 97

Part 3 Heat Flow Calculation

Methods

Terrestrial heat flow is determined by the combination of the vertical temperature gradient dT/dz with the thermal conductivity K according to:

_ dT (3.29) q ' K dz

an equation derived from Fourier's Law. To calculate heat flow from a borehole, normally several measurements of thermal conductivity and several measurements of temperature are carried out at discrete depths. Two principal methods of heat flow calculation were used in this study. The resistance integral method of Bullard (1939) was the procedure used in most cases. The second method used in this study was the interval method; the average thermal conductivity is combined with the least squares geothermal gradient to yield the heat flow within the interval under consideration. The Bullard method is based on the linear relation:

Tz = To + q fi./Ki (3.30) i 1

Depths z are converted to thermal depths 1JziK. by use of the measured thermal conductivity values K.. The heat flow q is given by the slope of a least squares line of temperature Tz versus the thermal depth. To represents the extrapolated surface temperature and is the zero intercept of the line. The residuals from the least squares line have been termed 'Bullard residuals'. The error in the heat flow evaluation may be taken as the statistical error in fitting the slope. This was the procedure used for the shallow boreholes. Richardson & Oxburgh (1978) suggest that a better estimate of errors would be obtained 98

by combining the standard deviation o-k, for the conductivity of petrographically uniform strata, with the standard deviation a-b, for the gradient measured at 5 or 10m intervals in those strata. The interval method was used to examine variation of heat flow with depth. The heat flow within each interval was calculated by the product of the least squares temperature gradient, with either the arithmetic mean conductivity or the harmonic mean conductivity over the interval. The borehole may be divided into short intervals and a plot of heat flow versus depth obtained. The width of the interval will determine the resolution of the method. Over- lapping intervals were used to obtain a continuous plot. The method was best suited to boreholes where large conductivity changes did not occur over a single interval. The harmonic mean conductivity was generally favoured for the interval method, since combination of thermal resistances, the inverse of thermal conductivity, should be used when calculating series conductivities. Heat flow measurements are based on the assumption that heat transfer is by conduction alone. Over the temperatures encountered and in boreholes free from water disturbances, this is considered to be a valid assumption. As discussed in the previous section on thermal conductivity, the thermal properties of a rock vary with temperature and pressure. However, the variation of thermal conductivity over a temperature change of 10K is small. The thermal conductivity of the rock in-situ in a shallow borehole at a temperature of 11°C would have a marginally higher thermal conductivity than that measured in the laboratory. No correction was applied since the amount required is uncertain yet small. The difference in heat flow at the top and bottom of the specially drilled boreholes due to the radioactivity of the rock within that interval was not considered since it would represent an insignificant fraction of the total heat flow. 99

Heat flow calculations are based on the assumption that heat is flowing under equilibrium conditions and that the measurement represents the vertical heat transfer along the line of the borehole. A computer program RCHUCK was used to calculate the heat flow of individual boreholes. The program, which was originally written before 1968, has been progressively modified over a period of years. During this project the program was completely rewritten and modified so as to yield results in S.I. units with an updated format. The program is divided into several subroutines which may be accessed by means of control cards. The heat flow was calculated, using the Bullard method, in a subroutine called THERMZ. The upper and lower depth limits may be specified on the control card used to call the routine. Thus it was possible to calculate the heat flow over any selected intervals using the Bullard method. A separate subroutine INTERVL was used to calculate the heat flow using the interval method. A modification was made to the program to allow the output of a data file. This data file could be used by a second program, HPLOT, to produce a graphical presentation of the final results. The type of input and output from RCHUCK is set by use of a control card. The input could be either in feet/cgs units or in S.I. units, although once read in, all calculations and presentation of output were in S.I. units. The theory of heat flow is only strictly valid when the horizontal plane z = 0 is held at a constant tempera= ture. In practice, the surface is only rarely a horizontal plane and the temperature is not constant. This gives rise to the need for two types of correction, deviation from the horizontal plane is discussed under the heading topographic correction, whilst corrections for the change of temperature at the earth's surface are considered under the heading of palaeoclimate. The effect of uplift and erosion is dealt with in the last section. 100

MAl N PROGRAM

CJt~TROLS THE SELECTION OF T HE SUBROUTINES control ca rd number IN f( 1 ) 2 I 6 7 8/10 13 ~II \\ ~ RAWOAT THERMZ I NTRVL (ORGLA r- Organizes ~ Bullard llethod 11\ \/ Interval method Palaeoclimate reading of of heat flow I\ of heat flow correction data. calculation calcuLation routine 1 \V RAWTEM TOP(OR _ Reads temper-- ~ \II~ Topl)gra~hic \V,\\/ /\ ature data & 1\ correction' '\ 1\ some comedions / VI I RAW(ON LTsa (ALKa FC08A ~ Reads thermal ~ Least squares Heat flow Error function corrludivity routine calculation routine data. I SORCON Figure 3 ·17 Diagram to L- Sorts cor.ductivif') ~ data if requi red illustrate subroutine structure of program RCHUCK. 101

Topography

Topographic correction is used to correct any variation in the vertical temperature gradient which has occurred due to the influence of the topography. In general, the observed gradients will be greater in valley bottoms than on the tops of hills. Topographic corrections are usually derived from Laplace's equation V2T = 0. Assumptions are made in order to apply such methods: 11 Firstly the subsurface rock is assumed to be isotropicamt from heat sources. Secondly the temperature field is assumed to be at equilibrium and, at great depths, the temperature gradient to be constant. An analytical three dimensional treatment of topography was given by Bullard (1940), after equations derived by Jeffreys (1938), for the correction of gradients in boreholes. This method was considered valid for regions of gentle yet complicated topography and so was used in this study. Several alternative methods are available for sharp, extreme or geometric topography (Lachenbruch 1969). The first stage is the replacement of the irregular surface by a horizontal reference plane at the collar height, temperatures on this imaginary plane varying in proportion to the relative elevation of the actual surface. The apparent differences in mean surface temperature, between the borehole collar and some other point, (x,y in cartesian co-ordinates), may be approximated by combining their difference in elevation (h) with the rate of temperature decrease with elevation in air (g' ie adiabatic lapse rate) .

oT(x,y) = g'h (3.31)

Temperature differences on the plane (AT(x',y')) are Adiabatic lapse rate ISOTHERMS

Effect of Topography on Observed Temperature Gradients

103

calculated from the upward, or downward, extrapolation of the surface temperatures to the reference plane using the observed geothermal gradient (dT/dz).

oT (x' , y') = (g' - dz ) h (3.32)

The problem has now become to find the steady temperature field in a semi-infinite solid z>0 whose surface temperature is given by a continuous function of its position F(x,y). A solution is given by Carslaw and Jaeger (1959). The temperature disturbance at depth z due to the plane is given by: co rm dTz = 2a zF(x',y')dx'dy' (3.33) -CO - O R3

Where R2 = x'2 + y'2 + z'2 i.e. the distance from (O,0,z) to (x',y',O). The equation may be transformed to cylindrical co- ordinates, with the origin at the borehole collar, to give: a 2ir 1 8) r' dA dr dT' = z T (r' , ( 3.34) . z R3 Jo o where r2 = x2 + y2 and R2 = r2 + z2 In program RCHUCK this equation is evaluated by the subroutine TOPCOR. A transparent overlay with equally spaced radii and equally spaced concentric rings was used to obtain a digital model of the topography surrounding the borehole. The equation was evaluated in two stages. The inner integral 2r oT(r',9)d8 was evaluated for each ring by obtaining the ~ average temperature difference dT'r Once the values dT' had been calculated, the second integration was performed for each depth point. 104

co dT' fzdT'rdr (3.35) z 2 0(r + z2)

n dT1a ia dT'z = z (3.36) i=1 ((ia)2 +z2) where a is the increment of radius and Ka is the maximum radius considered. The temperature at depth z was then corrected by the value dT'. The corrected temperatures could then be used to calculate a new heat flow value by either subroutine THERMZ or INTERVL (Bullard or Interval methods). This method of correction was used on all the specially drilled boreholes. A graticule was chosen with 36 radial lines and 30 concentric circles. The graticule was used on a 1:25000 scale map. The closest practical spacing was used, 2.54mm on the map (Morgan 1973), which represents 63.7m on the ground. Since care was taken to site the boreholes on gentle topography, a closer spacing was deemed unnecessary as the currently used grid was considered to be unnecessarily detailed. Thirty concentric circles lead to a maximum radius of just under 2km. Most of the south-west England peninsula is peneplained to a relatively uniform level of 130m and so exerts little influence on the heat flow. The amount of correction produced was small, in the case of the boreholes in granite the correction varied from 0-3%, normally positive, because boreholes were typically located on higher ground to avoid the geological complexi- ties associated with valleys. This could be taken into account in the siting of a very deep hole for expoitation, ie a valley would have a higher geothermal gradient at shallow depth than a hill top. 105

Palaeoclimate

Temperatures at the earth's surface are controlled almost entirely by climatic conditions, by the balance of energy absorbed from the sun and re-radiated into space, terrestrial heat flow having a negligible effect. The effect of climatic changes on thermal gradients was first applied by Lane (1923) and has been studied by Birch (1948) and many others since. It may easily be shown that the shorter the period of fluctuations in surface temperature, the shallower would be the region significantly affected. Thus, annual variations do notpenetrate beyond a few metres, while climatic changes, which have occurred during geologic history, still produce significant pertur- bations at depth, and have to be removed from the measured gradients. Again, the details of the climatic variations, that is the high frequency component of the fluctuations, have little effect on the present gradients. Crain (1967) showed that the critical factors in working out the heat flow corrections were the times of transition between the glacial and interglacial periods and that the assumption of constant temperature during each of the periods does not introduce significant error. The mathematical treatment is based on the solution of the one-dimensional heat diffusion equation:

dT = x d2T (3.37) dt dz2 where T is the temperature, z is the depth, t is time and x the thermal diffusivity of the medium. If the temperature of the surface z = 0 of a semi-infinite solid changes suddenly at t = 0 from a uniform value for the solid, 0°C to T1, the solution of the diffusion equation (Carslaw & Jaeger 1959) is:

T = T1 erfc ( z ) (3.38) (2v/x t) 106

Thus the present temperature disturbances at a depth z, produced by a positive-going (0>T1) temperature change at the surface at time t, before present will be :

AT = Tlerfc ( z ) (3.39) (2v/X t1) and that of a negative-going (T1oC . 0oC) pulse at time t2 before present would be:

OT = -T1erfc (2v'X ) (3.40) t2

Then by Duhamel's superposition theorem, the temperature disturbance at depth z, due to a surface pulse of duration (tl,t2), will be the sum of the above two expressions:

1 - erf (3.41) OT1(z, t) = T erf 2~/X t1 2V/X t 1 2

In program RCHUCK the climatic correction was calculated by subroutine CORGLA. The past climatic changes are treated as a series of step functions. The temperature disturbances, due to these functions at depth z, are superimposed by means of the expression: (3.42) z AT (T, t) =:E: TT. erf -erf i=1 2i-1 2 F2i The temperature at depth z was then corrected by the amount A T(T,t). The corrected temperatures were then used to calculate a new heat flow value. Once a climatic model has been assumed, the magnitude of the correction is dependent on the depth and thermal properties of the rock. In order to obtain a reliable correction, the thermal diffusivity should be known from the surface down to the depth to which the correction is Pleistocene •5— w a a: ok z w U N w w o: w -10-

100 x 103 200x103 300x103 YEARS BP

Holocene w +2_ Carnmenetlis Heat Flow Sites ā v_ Step function temperature model used for z w U Climatic Corrections 'n 0. w w Er 0 1 w 0 I 5x103 10x103 YEARS BP 108 to be applied. The diffusivity is related to the thermal conductivity by the equation:

(3.43) where X is diffusivity K is thermal conductivity io is density c is specific heat capacity In subroutine CORGLA the thermal diffusivity was obtained by dividing the thermal conductivity by c, a conversion factor of 2.26556 x106 was used in this study. The climatic models used were based on climate studies by Lamb (1965) and Fairbridge (1961) fig 3.19. Central England has one of the most detailed climatological records available anywhere in the world. As might be expected, the uncertainties in temperature increase with the age of climatic event concerned. Detailed climatic records start about 1780 a.d., though diaries, ships' logs and other historic information have been used to extend the historical record further. Tree ring measurements and isotope studies of deep sea sediments, stalactites and ice, have all been used to extend the record. The Holocene and Pliestocene ice ages are recorded by varved clays and morphological records. Putting the pattern together is a branch of science in its own right. The amount of detailed work being brought to bear on the problem suggests that, the ability to correct for climate will improve markedly in the next ten years. An alternative approach to the problem is to look at the climatic disturbance in boreholes and derive a function of temperature with time which would cause such a disturbance. Times marking transitions between one climatological period and the next, may be set using geological and historical records, leaving temperature as the unknown variable. A method, derived by Cermak, was used by Evans 109

50 60 70 mWrr,-2 Correct ion A Correction B ~ ~ 70 ,,: "'. ~ --.. x ,~ ''.'-., • •• 100 '---. ~\)( 1 )It lit*

IPRE~ANNACK BOREHOLE I 150

tn ..,Q).... Q) E .5

200=Co Q) C

HEAT FLOW versus DEPTH for:

.-. No palaeoclimate correction _____ peo and LIA correction C>-{) Full palaeoclimate correction 250

Figure 3.20 Predannack borehole, heat flow versus depth. 110

(1975) to approximate the last two climatic steps from a deep borehole at Adare, Ireland. The two steps were: a) Present Climatic Optimum (PCO) 1-70 years BP +0.6°C b) Little Ice Age (LIA) 75-525 years BP - 0.4°C These values were applied to the south-west England data during the course of this study. The model was tested in the Predannack borehole on the Lizard peninsula. The heat flow calculated for this borehole shows a marked decrease near the surface. (fig 3.20) However, after correction for the last two climatic events derived from the Irish data, the upper section of the borehole gave comparable results to the lower section. A method of deconvolving the climate has been developed and tested by J.R.L. Ellis in this department (PhD thesis under preparation). This work has shown that the Cermak method becomes unstable if more than a very few climate steps are modelled. However, good agreement is found between the borehole signature and a model derived from Lamb's data for central England although, apparently, with a 2°C shift, ie south-west England (Lizard) appears to have a milder climate than central England. The map of mean daily temperature (fig. 3.21) shows clearly that this was indeed the case for the period covered by the map (1940-70). Assuming a past climatic model, Eig. 3.22 was constructed. This clearly shows one of the problems associated with shallow boreholes for heat flow measurements. It may be seen on this computer generated model that the correction for a one hundred metre borehole with conductivity 3.33Wm-1K-1 should be approximately 20% and that for a 150metre hole about 15%. The application of this correction has justi- fiably been the subject of controversy. The main point of contention has been that the temperatures are not known accurately enough to provide a valid correction. A further point of contention is whether temperatures within the ground are linked to climate at the surface. The climatic model used is the inverse of an observed borehole signature 111

R.duc.d to M,an Soo l••.1 oe°cnoo mNr.t

Figure 3.21 Map of mean daily temperature 1940-1970. 112

CARNMENELLIS HEAT FLOW SITES ASSUMED CLIMATIC DISTURBANCE

-2-0 -1.0 0 1-0

DEGREES CENTIGRADE

21% CORRECTION

goo 15% CORRECTION

f 200

(I)

cr w 300

F- n_ w 0

400-

Figure 3.22 Carnmenellis heat flow studies assumed climatic disturbance. 113

thus it can be assumed to link in at least one case. The magnitude of the steps obtained are similar to the central England temperatures of Lamb (1965). Applying these temperature steps to the Predannack borehole also illustrates climate coupling with the ground in a second case. It is difficult to observe climatic effects in deep boreholes since the upper part of the borehole must regain equilibrium after the disturbance, due to drilling. A high water table is required otherwise it is difficult to obtain accurate temperatures and rapid downward percolation of ground water would disturb the temperature field. One method of determining whether borehole temperatures are linked to the surface temperature is to extrapolate temperatures back up to the surface. Care is required to ensure the correct conductivity structure is observed. Extrapolated surface temperatures for south-west England boreholes are given in fig. 3.7 . This might be considered as further evidence that the boreholes are linked by some common climate. This has apparently been the case for at least the last thirty years. It is, therefore, no gross assumption to say that this should have been the case for seventy years, whether it was the case over the previous five hundred and twenty five years is less clear. The evidence from Pred- annack borehole however, suggests this was the case. Our main problem arises in obtaining the accuracy and likely error on such observations. To obtain such values statistically would require several boreholes with the data quality of Predannack. The detailed study of climate and its inversion is currently being carried out by J.R.L. Ellis in this department (PhD thesis under preparation). However, it is the last two climatic events that lead to the bulk of the correction and these two events, the Little Ice Age and the Present Climatic Optimum, are clearly docu- mented in historical records. The Present Climatic Optimum is recorded as actual meteorological records, the Little Ice Age started in the sixteenth century, when no detailed 114 records existed, but continued to the nineteenth century by which time detailed records were being kept. The corrections, due to these events, amount to = 70% of the total climatic correction in a 100m granite borehole and, therefore, the procedure is considered to be quite valid. 115

Uplift and Erosion

The effects of past uplifts in south-west England have been the subject of much interest and a certain amount of conjecture. The evidence is based on morphological features which have been interpreted as erosion surfaces. These surfaces are said to mark the end of sub-aerial, marine or arid cycles of erosion. There appears to be no doubt that these surfaces exist, but there is a divergence of opinion about the number and the origin of the features. The preservation of these features is possibly due to the superior hardness of the granite and the rocks of the Lizard. Dating the surfaces is also problematical, upwarped surfaces must clearly postdate major orogenic movements. Despite the strong morphological evidence suggesting a marine origin for the majority of the erosion surfaces, there is a remarkable absence of clearly correlative marine deposits. It is quite likely that such features exist elsewhere in Brit- ain but are not clearly defined. The multiplicity of levels found in Europe has been suggested to represent a wide spread and substantial eustatic shift of sea level in post Alpine time. There are several different methods of modelling uplift. The uplift may be considered as having occurred rapidly, in which case in the model the uplift is assumed to be instantaneous; then the temperature at the earth's surface would change by the adiabatic lapse rate multiplied by the amount of uplift. An alternative view is to consider some form of continuous uplift. Consider the Pliocene-wave-cut-platform at 430ft O.D. (130m). This feature, if it is to be dated as Pliocene, must be at least 3My old. At the present time the common range for the temperature gradients in air is 0.01°C/m - 0.005°C/m. In the extreme case, that is taking the adiabatic rate to be 0.01, there would be a temperature step of + 1.3°C from 3My tow . This can be treated as a

116 sudden change in temperature similar to an evaluated climatic change and the necessary corrections evaluated. Birch (1950) derived a formula which can be applied for the correction of data in the case of continuous uplift under the following assumptions; an initially horizontal plane existed at the earth's surface and the temperature gradient G was uniform in the subsurface up to time t = 0; after this time a continuous uplift has been occurring at a uniform rate at the earth's surface simultaneously with erosion (denudation). The influence of uplift upon the temperature gradient Gc is obtained by differentiating the Tc w.r.t.z

2zG'zu Tc = -bozG'zu = (3.44) Altrkt

-2G'z (3.45) Gc = u

For an uplift at a rate to cause a 131m platform due to a 3My erosion surface ie in areas where we are at present sea level:

G = - 2 x 0.01 x 131 (3.46) c 1/3.142 x 1.5 x 10-6 x 3 x 106x3.156x107

G = 0.124°km 1 For K = 3.33, Qc will be 0.4mWm 2 These calculations show that in south-west England the likely error in neglecting the effect of uplift and erosion may give rise to an inaccuracy of, at the most, 1%. It is, therefore, improbable that the observed thermal anomaly is the result of uplift or erosion. It has not been possible to obtain reliable ages for uplift and erosion and so no correction has been applied. Any recent changes will have been included in the deconvolution of

117

time

re 1. 3° INPUT tu

ra present day e 0 temp CO F 3my

temperature °C 1.3 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1 r r r slope is equivalent to 0.2mWm-2 I

-10km

- 20km I

-30km x I RESPONSE 0w -40km K=3.33Wm 1K-1 r

- 50km

- 60km

- 70km

Figure 3.23. Model 1: temperature response to a sudden uplift at the end of the Pliocene era 3my ago. 118 the last two climatic events.

Model 1

Model 2

older levels Model 2

Model 1 present day

Figure 3.24. Step function, model 1, and continuous uplift, model 2, considered as likely bounds to a complex yet more realistic sequence of tectonic movements. 119

4. GAMMA-RAY SPECTROMETRY

Introduction

Interpretation of the major heat producing elements at depth must rely on sampling restricted to the outcropping and near surface rocks. Experimental and field studies have suggested that uranium is easily leached out of rocks close to the surface, thus surface sampling is likely to produce confusing results (Ball & Basham 1978). In this study the majority of measurements have been made on drill cuttings and core samples from well below the surface weathered zone. Gamma-ray spectrometry was the principal method used to analyse the rock samples for their concentration of radioactive isotopes. The procedures used were set up by Dr H.Y. Tammemagi and P.A. Strachan (Strachan 1973). Initially the spectrometer was housed at the University of London Reactor Centre at Silwood Park, near Ascot. Towards the end of this project a system was set up in the Geophys- ics Department at Imperial College. When radioactive isotopes decay they convert mass into energy involving the production of heat. Currently the major sources of heat within the earth are believed to be 235U, 232 due to the radioactive decay of 238U, Th and 40K. Radioisotopes of relatively short half life, though now ex- tinct, are likely to have played a more important role in the past geological time due to its shorter half life. In order to interpret surface heat flow data, an understanding of the distribution of the major radioactive elements within the crust and upper mantle is required. The amount of heat produced by decay can be calculated from the loss of mass since, except the amount carried away by the neutrino, all energy is converted to heat in the immediate vicinity of the decaying nucleus (Rybach 1973, after Hurley & Fairburn 1953). 120

Until recently the heat production constants of Birch (1954) were used by most heat flow investigators. These constants were revised by Rybach (1973), using the latest available decay schemes, energies and mass differences. In this study the revised constants have been adopted.

Table 4.1

TABLE OF HEAT PRODUCTION CONSTANTS units iuWkg-1

BIRCH (1954) RYBACH (1973)

238U 94.5 92.1 235U 57.2 57.8 U(natural 97.2 95.6 232 Th 26.6 25.7 _3 K(natural 3.59 x 10 3.49 x 10-3 121

K-40

DIAGRAM TO ILLUSTRATE RAY SPECTRUM OF A TYPICAL SAMPLE AS A SUMMATION OF THE SPECTRA OF K, U & Th STANDARDS

Potassium

Uranium Integration Window

Thorium Integration Window K Std — Tr. Si 241 U Std TI -208

Th Std

I 0.260 024 0.30 M

a cc C 0 U

Typical sample

1 0 1.46 1.76 2.0 2.62 30 S ray Energy MeV -->

Figure 4.1 Diagram to illustrate gamma-ray spectrum of a typical sample as a summation of the spectra of K, U and Th standards. 122

Isotopic Abundances and Equilibrium

40K is the only naturally occurring unstable isotope of potassium and has a natural isotopic abundance of 0.0119%(Adams & Gasparini 1970). The electron capture decay of 40K to 40Ar results in a gamma-ray emission with a photon energy of 1.46MeV. The decay series of thorium and uranium are more complex and many more peaks exist. In this study the thorium concentration was deduced from the 2.62MeV peak from the daughter 208T1 whilst the photon used for uranium was the 1.76MeV peak from the daughter 214 Bi of the parent 238U. These peaks are used because of their size and minimum interference (fig. 4.1). In natural uranium 99.28% is 238U and only 0.711% is 235U.. This ratio has only been found to vary in most un- 235 usual circumstances in nature. Since the U series is dominated by the 238U series, it is not usually measured directly in heat production studies, but is inferred from the isotopic ratio. The assumption of radioactive equilibrium within the 238 U and 232Th series and of a constant 40K/K ratio is ful- filled in almost all rock types (Rybach 1973). The abundances of 238U and 232Th and their daughter products must be in equilibrium in order to obtain reliable results. The intermediate long lived members of the decay series have different chemical natures and may be subject to chemical fractionation.

Table 4.2 238 INTERMEDIATE LONG LIVED ISOTOPES OF THE U DECAY SERIES

Approx time to attain Isotope Half life equilibrium with isotope above in decay series

Uranium II 2.47 x 105yr 1 x 106yr 292U

290Th Ionium 8.00 x 104yr 4 x 105yr

288Ra Radium 1.602 x 103yr 1 x 104yr 123

The isotopes listed from the 238U decay series separate the decay chain into two sections. The first section will reattain equilibrium in less than a year. The meas- 214 ured Bi decay occurs in the second section after the long lived intermediate isotopes. However, the second section may take 10 years to reattain equilibrium. The comparatively short half life of all the decay products of 232 Th allows a relatively quick achievement of equilibrium in natural systems. Forty-five years can be considered the maximum time for re-establishing secular radioactive equilibrium (Adams & Gasparini 1970). The Hercynian granite and the surrounding country rocks are considerably older than the maximum time required for equilibrium to be restored for both series. Thus any chemical fractionation which might have occurred during intrusion or deposition will have now re-established equilibrium. Any disequilibrium which might occur would have to be due to a relatively recent mechanism. 234U is leached preferentially to 238U which may lead to a 15% enrichment 34 of 2 U in fresh waters and a corresponding depletion in the host rock or soil. Differential precipitation from water produces an enrichment in 230Th in respect to both U isotopes. The samples used in this study have been collected from below the surface weathering zone. It is, therefore, expected that samples have not suffered serious differential leaching except where close to water bearing fissures. The drilling process might, however, lead to a solution or sorting which could affect the process. A leaching process would lead to a loss of uranium and consequently could give a low result. The crushing action of the drilling might allow loss of radon gas. Measurements in the laboratory (Strachan 1973), were unable to detect any such effect. However, as a precaution, the samples were stored for sufficient time to allow the radon, which has a short life, to reattain equilibrium. A concentration of radio- 124 genic elements could arise from unrepresentative sampling of the drill cuttings, thus great care was taken to obtain a representative sample. 125

Method and Statistics of Gamma-Ray Detection.

Gamma-rays emitted by the sample are detected by a scintillation detector. A gamma-ray (or photon) interacts with the detector to produce an output pulse which is proportional to the energy of the incident photon. There are three main processes by which the photon can interact with the scintillation detector, the photo-electric effect, Compton scattering by electrons in the atoms of the material, and pair production. The scintillations or bursts of light, emitted by the interaction within the crystal, are converted to an electrical pulse and amplified by a photomultiplier tube. These signals are further amplified, scaled and counted in a multichannel analyser. The analyser sorts pulses according to the original energy of the interaction within the crystal. The energy of the individual photons, emitted by a gamma source, have precise energy values fundamental to the chemistry and physics of the decay process. When recorded by the gamma-ray spectrometer, a single energy emission will appear as a near gaussian function, this distribution is a function of the recording instrumentation. The width of the peak may be used to indicate the resolution of the detector. Gamma-ray emissions from the source are random events occurring in a large number of nuclei and can be described by Poisson statistics. The probability Px that x gamma- rays for unit time will be emitted from a given number of identical radionuclides is:

T Px = Nx e (4.1) x! where N is the average gamma emissions for unit time. The counting error is usually expressed as the standard deviation a=)/171-- the probable error is then quoted as p = 0.6745 NAT . At large counts the Poisson distribution approximates to a normal or gaussian distribution.

126

tends to a probability of one that there will be no counts due to this source

,l pul sæ emitted by source = 5 000 1 [ Tota dard deviation .10 .1

Counts =198 Probability of P = 0.028 a given count Poisson counting statistics

11111111111111 14111.111i/C1/ 6---R _ 1IIl i / Cla~usslan distribution ~~~~ ~,:' ;,"/(a function of the / / i 4/ detection system) Individual channe 4'49 /./ ,i/ Ii, ,i, i Mean i;/ ;'1 (=energy of photons III' ; emitted by source) '\ "1tI y ray energy

Theoretical Isometric Plot to show relation between Poisson counting statistics and Gaussian distribution due to detector characteristics. Figure 4.2 127

The isometric plot, (Fig 4.2), is presented to illustrate the relation between the counting statistics and the gaussian distribution due to the detector characteristics. As the total count is increased the standard deviation will increase as VrT. When expressed as a proportion of the count, the standard deviation decreases as the counts increase. However, as the count time is progressively increased, the counting uncertainty does not decrease linearly but rather as a reciprocal function of the counts. This sets a practical limit to the accuracy obtainable by simply increasing the count time. We may also observe from the plot that there is a finite probability that the highest count will not occur at the mean energy value. This gives rise to complications in the automatic picking of peaks of peaks using computer programs. p128 PLATE 3 New gamma-ray spectrometer I R 4 e ft ' uto 111! I 129

Apparatus

In order to obtain effective counting statistics in a practical time from natural samples of relatively low activity, it is necessary to have, high intrinsic efficiency of detector, good stability and minimum noise by all the electronic components and a low background. The detector used was a 76mm x 76mm (3" x 3") thallium- activated sodium iodide crystal, manufactured by Quartz Silice. This detector had a quoted resolution of better than 8% for the half width to peak height of 137Cs. The scintillation detector consists of two sections, the phos- phor, in this case the NaI(Tl) crystal, and the photomultiplier tube which produces an output pulse whose height is proportional to the intensity of the scintillation within the crystal. The photomultiplier tube is surrounded by a cylindrical mu metal shield to minimise the effect of small magnetic fields. These can effect the gain by deflecting the moving electrons within the photo tube. Photomulti- plier tubes suffer from a temperature dependence due to the thermo ionic emissions of electrons at the phcto cathode. This effect was observed as a drift in the gain during a short period of severe temperature changes, observed in the laboratory at Silwood Park. The detector was housed in a 102mm (4") thick lead castle to reduce the background radiation. On the system set up in London this reduced the background level from 387 counts/minute to 5.4 counts/minute.in the energy range 1.36-1.56MeV. This represents a shielding of 98% of the background radiation due to 40K. The samples were crushed twice and packed into perspex containers which overlap the detector to give a maximum geometric advantage. The perspex acts as a beta absorber and so only gamma radiation should enter the crystal. Compton scattering and bremss- trahlung effects are reduced by using a relatively large internal volume lead castle. Crushing was done either 130

using a standard jaw crusher and then a core crusher or by using the drill cuttings directly. The size of the cuttings appeared to have little effect on the accuracy of measurement, though the density of the rock affects the sample weight measured. The containers, when packed as full as possible, contained between 700-1000g of rock. The pulses from the detector are scaled and stored by a multichannel analyser. In this study three systems have been used. Initially measurements were made using an Econ II M.C.A. manufactured by Northern Scientific Ins- truments Inc. When using this analyser the sorted pulses were stored in 255 separate channels, peak picking and integration was achieved interactively with the analyser. The results were recorded on a Teletype output. This procedure at Silwood Park was too inefficient to, process the number of samples being collected during drilling. The system was run at two samples per day on a fulltime basis. One sample was counted for six hours during the day and a second sample counted overnight for twelve hours. An Intertechnique M.C.A. was used as the Econ was unavail- able for full time use. Four hundred channels of data were collected and these were recorded on to paper tape at the end of each run. Loading and labelling the paper tapes on to the computer was initially a long-winded and frustrating experience. In order to minimise the likelihood of errors, due to poor peak picking and uncertain energy calibrations arising from the routine and long term nature of the measurements, a computer program was written to handle the paper tapes recorded for each run. Regular checks were kept on the energy calibration and drift with the aid of this program. The standards were run at regular intervals to ensure a constant standard of measurement. Several problems became apparent with this method of measurement, related to the problems of drift due to the power supply (E.H.T.) and temperature effects in the laboratory. A new system was set up in London using an identical 131

GAMMA RAY SPECTROMETER

Multichannel analyser

2~OO baud IE I A ) Screen Memory c.lssette Inter face controls ... ADC and amp controls EQ& o 0 o o o 0 o 0 EHT 000 from ~ internal ~ power ooaooo o supply

Digital cassette Screen controls Signal recorder lead

roll open lid

lid lifting rings

Twin lead 100mm thick connection lead shield

Overlapping sample container

76x76mm NaI crystal

Photo multiplier wIth mu metal shield

Figure 4.3 Gamma-ray spectrometer. 132 detector linked to a Canberra series 30M.C.A.(fig. 4.3). Once again peak picking and integration could be carried out on the analyser, either directly after measurement or from a magnetic cassette record of the spectrum at some later time. The spectrometer was set up in the thermal conductivity laboratory where the room is temperature-controlled by an air conditioning unit. 133

Interpretation of Gamma Ray Spectra

Peak picking and integration are the first stages in the interpretation, once samples and standards have been recorded. Initially this was achieved manually. During the period when the data was in the form of paper tapes a computer program was written to handle the data. This program is not needed on the London system as the first stage may be achieved interactively with the analyser. Computer packages are available for the interpretation of gamma-ray spectra. A package which would interpret the large number of spectra in the way required could not be found and so the computer program GAMMA was written. Paper tapes were read on to the computer and stored as files on disc. These files were then read by an interactive tape entry program TE. Program TE first requests the number of spectra to be read from disc. For each spectrum the program requests the sample code, run number, time, run time, sample weight and date. The spectrum is then read from disc space, checking as it does so for missing lines, illegal characters, missing channels, and incorrect formats. Such errors generally occur due to problems associated with punching paper tape. If the data passes these checks then, with a heading it is output to a second file in disc space. The file is in a format suitable for permanent storage on magnetic tape via a filing and editing package called UPDATE. The original file may be purged from disc space once all the spectra have been read correctly. The new file, containing several spectra, may be used via an UPDATE routine as the data for program GAMMA. The tape entry stage was separate from GAMMA to prevent data errors interrupting the computation stage. Program GAMMA (fig. 4.4) was written to mimic the peak picking and integration stage, conventionally achieved interactively, on a multichannel analyser.

134

Program GAMMA START

Set A,B Energy calibration

IF -STOP STRING SORT

SAMPLE K STD U STD I Th STDINaC1 B Y88 Find peaks Subroutine STD Find peaks set channels Find peaks,set channels,integrate & set channels integrate & Output results,indicate drift reset,A&B output Output drift

PLOT PEAK GRAPH Microfilm Peak search by Line printer plot of Gaussian smooth graph of spectrum then max search spectrum

Figure 4.4 Flow diagram to illustrate subroutine structure in program GAMMA 135

GAMMA runs independent of interaction using the output from program TE and no other input. Before the program is run, the'approximate energy calibration is set internally. Each spectrum is processed in turn by the appropriate subroutine, according to the type of run. These subroutines direct the routine PEAK where to search for a peak. Peak picking routines of many types were considered, the method developed was chosen for simplicity (and so rapid computation) and reliability with quite noisy data. Peaks appear particularly ragged at low counting rates, therefore, it is difficult to pick a peak from such data. The first stage is to smooth the data within the search window by multiplying by a gaussian peak function. The gaussian operator is used in a manner similar to that of convolution or cross correlation in seismic interpretation. It appears to enhance the positions where a match occurs. A rolling maxima test routine then searches for all peaks within the smoothed window. The largest peak position is returned as the peak position. A zero is returned if no peak is found. The smooth data is only used in the peak search and not in the integration part of the program. Subroutine Y88 searches for the three peaks of the radionuclide yttrium-88 at 0.898, 1.836 and 2.734MeV. Once it has found the first two large peaks it calculates the calibration and searches for the third smaller one using this factor. The Y88 calibration may he used to update the program's internal calibration. Subroutine SAMPLE searches for the 40K peak at 1.46MeV, the uranium peak at 1.76MeV and the thorium peak at 2.62MeV. Once it has found the peaks it sets integration windows sym- metrically about the peaks with widths of 0.26, o.24 and 0.30MeV for the 1.46, 1.76 and 2.62MeV peaks respectively. The counts for each window are output along with the peak positions and inferred drifts. If a peak is not identified, a warning is output and its theoretical position is calcul- 136

ated from a combination of the calibration factor and the known peak positions. Subroutine STD has four routes of calculation :

Fig. 4.5 Subroutine STD

NaC1 K STD U STD Th STD Background

Calculate Find 1.46 peak Find 1.76 peak I Find 2.62 peak peak positions calculate the calculate the calculate the from internal remaining peak remaining peak remaining peak calibration positions from positions from positions from the internal the internal the internal calibration calibration calibration

If no peak found output an error message

Integrate the peaks

Output the appropriate results

return

Other peaks within the standard spectra of uranium and thorium may be used to check the energy calibration.. In this study checks were achieved manually, although an amendment could be made to check automatically in subroutine STD. The program contained options to produce line printer or microfilm graphs of the spectra for visual checking On the new system the same procedure was followed, though performed interactively on the analyser. The spectra are recorded on cassette tape. Three runs were obtained per day, two of six hours and one of twelve hburs. 88Y was also run each day as a part of the careful check which was kept on the rate of drift. At weekends longer runs were used. Once several spectra had been recorded 137 over a period of two weeks, the spectra were replayed and the channel integrations obtained. The use of this system in our London laboratory allowed a marked increase in thro- ughput and also a slight improvement in accuracy. 138

Distribution of Heat-producing Elements

Heat flow, being normally measured in the upper 1% of the crust, can only provide the upper boundary condition, from which crustal temperatures may be modelled. The decay of the radiogenic elements potassium, uranium and thorium results in the production of heat at the rate of -3 0.4 - 5phm in most crustal rocks exposed at the surface (Lachenbruch & Sass 1977). The radiogenic heat production observed in exposed rocks could account for all the surface heat flow, with no mantle contribution, if they were distributed uniformly through the crust. It is for this reason that the distribution of the heat-producing elements within the crust, plays a critical role in understanding the thermal structure of the crust. This distribution has been the subject of considerable study by many researchers. One of the remarkable observations in terrestrial heat flow is a linear relationship between heat flow q and heat production per unit volume of surface rocks Ao.

q = qo + AoD ( 4. 2 ) where D is a constant, with dimensions of length go is the reduced or intercept heat flow This relationship was first described by Birch et al. (1968) and elaborated by Roy et al. (1968). The linear relation has been shown not to apply, (Lachenbruch 1978), in the Basin and Range province where a relation had previously been proposed by Roy et al. (1968). There the variations in hydrothermal and magmatic convection are probably greater by a factor of 3 or 4 than those caused by radioactivity, and heat flux in the lower crust is not uniform; it is probably controlled by the mass flux of intruding magma (Lachenbruch & Sass 1977). Elsewhere, in general, additional results have confirmed the observed relationships. 139

In a gross sense the linear relationship between heat flow and heat production suggests, a simple form for the vertical distribution of crustal heat production beneath granitic rocks (Lachenbruch 1971). There are an infinite number of models which could be applied to fit the observed results. Only an exponential model could take account of differential erosion (Lachenbruch 1968, 1970 & 1971) and still maintain the linear relation. It is for this reason that it is favoured by many workers in the field.

-z/D (4. 3) Az = Ao e

where Az is the radiogenic heat production Ao is the value at the presently exposed surface z=0 D is the slope of the observed linear relation. Field evidence of this decrease is presented by Swan- berg (1972), for the Idaho batholith. Swanberg presents two groups of data from the Idaho batholith. In each he observed the heat production to decrease with increasing depth. The assignment of depth was from observations of metamorphic grades and so is 'tenuous at best' (ibid). He has little doubt, however, that the high level intrusions are enriched in radiogenic elements, relative to deep seated plutons for rock of essentially the same chemical composition. Swanberg concluded that such a distribution was in- compatable with a constant source model and that, although the linear model could not be ruled out, the exponential model would appear to yield a better correlation.

Table 4 . 3 SUMMARY TABLE OF RADIOGENIC MEASUREMENTS

Borehole Uranium Thorium Potassium Heat Production No. of

Code Name plan +/- ppm +/- % +/- NWm 3 +/- Samples CM-A Grillis Farm 12.5 1.9 12.2 2.6 4.9 o.6 4.5 0.5 12 Crf-B Polgear Beacon 10.9 3.3 6.8 0.9 5.1 0.5 3.8 0.9 12 CM-C Medlyn Farm 9.3 3.2 8.9 1.0 4.3 0.4 3.4 0.8 9 CM-D Trevease Farm 12.3 2.0 4.3 0.5 4.1 0.3 3.8 0.5 12 CM-E Trerghan Farm 11.2 4.3 15.6 1.9 5.0 0.4 4.4 1.2 9

BD-A Bray Down 12.9 6.3 20.4 4.8 4.8 0.4 5.2 1.8 13 BD-B Blackhill 8.7 2.0 6.5 0.9 5.1 0.5 3.1 0.5 14 BD-C Pinnockshill 10.3 3.6 7.0 2.8 3.8 1.2 3.5 0.8 14 BD-D Browngelly 15.1 3.0 10.9 1.6 4.7 0.3 5.0 0.8 13 BD-E Great Hammett Farm 9.9 3.3 18.8 2.8 5.2 0.4 4.3 1.0 15

LE-A Newmill 12.6 2.8 17.5 1.2 4.7 0.7 4.9 0.8 11 LE-B Bunker's Hill 13.0 2.4 21.1 2.7 4.7 0.3 5.2 0.7 11

SA-A Tregarden Quarry 7.6 2.1 17.6 3.4 4.7 0.3 3.5 0.6 11 SA-B Colcerrow Farm 12.2 2.0 18.0 2.6 4.5 0.4 4.8 0.7 11

EM-A Winter Tor 16.4 4.5 16.8 4.3 4.1 0.2 5.7 1.3 11 DM-B Blackingstone Quarry 13.5 2.4 15.8 1.7 4.6 0.4 4.9 0.6 11 DM-C Sousson's Wood 13.6 7.2 18.3 2.4 5.0 0.6 5.0 2.0 11 DM-D Laughter Tor 17.6 4.9 15.5 2.7 3.9 0.5 5.9 1.1 11 DM-E Foggintor Quarry 15.1 4.0 8.6 3.1 4.4 0.5 4.9 1.1 11 Table 4.3 continued

Borehole Uranium Thorium Potassium Heat Production No. of

Code Name ppm +/- ppin +/- % +/- NUin 3 +/- Samples CDD-1 Old Merrose Farm 2.6 0.7 13.2 2.7 3.0 0.9 1.9 0.3 17 CDD-2 Nestle Wartha 2.7 0.3 12.6 3.0 2.6 1.1 1.8 0.4 15 CDD-3 Callywith Farm 3.2 0.2 15.4 0.9 3.2 0.4 2.2 0.1 15

Gaverigan (Meadfoot Beds) 3.8 0.4 14.6 0.7 2.6 0.1 2.2 0.2 2 (Granite) 24.7 0.8 9.4 0.9 4.3 0.2 7.4 0.2 3

Wilsey Down (Crackington) 6.0 2.5 11.8 2.1 2.5 0.5 2.6 0.8 3 (Fire Beacon Chert) 7.0 7.8 8.0 4.2 1.8 1.1 2.5 2.1 17 (Upper Delabole Slates) 3.6 0.4 13.6 1.0 3.8 0.4 2.2 0.2 12 (Black Slates) 1.0 (0.1) 2.0 (0.2) 1.2 (.03) 0.5 (0.1) 1

CSD-1 Longdowns 9.1 3.5 12.2 1.4 4.8 0.5 3.6 0.7 (Francis 1976) 142

Granite Results

The initial distributions of radiogenic elements, in the granites and the surrounding country rocks, have arrived by quite different mechanisms and will be discussed as separate groups. All the results are presented in tabular form in appendix IV. The average values for each borehole are presented in table (4.3). The average values for the granites from the 222 samples measured from the specially drilled boreholes were:

Table 4.4 Mean Standard Deviation

Uranium 12.3 4.4 ppm Thorium 13.6 5.8 ppm Potassium 4.6 0.7 Heat Production 4.49 1.25 ,uWm-3

The average granite Th/U ratio was 1.2 The average of 47 samples from the three specially drilled diamond country rock boreholes were:

Table 4. 5 Mean Standard Deviation

Uranium 2.8 0.5 ppm Thorium 13.7 2.6 ppm Potassium 2.9 0.9 % Heat Production 2.0 0.3 pwm-3

The average country rock Th/U ratio was 4.9 In addition to samples from these specially drilled boreholes, a set of 33 samples was measured from the Gayer- igan borehole and several miscellaneous samples were measured. 143

The boreholes each show quite different characteristics with depth. Boreholes are rarely, if ever, deep enough to illustrate statistically the vertical distribution of radiogenic elements. They do, however, give a good surface value for the heat productivity. Average heat productivity for each outcrop are as follows: Land's End 5.1 Carnmenellis 3.9 St. Austell 4.2 Bodmin Moor 4.2 Dartmoor 5.3 The distribution of heat production within the Carn- menellis granite outcrop is of particular interest. The heat production within the outcrop is highest near the granite/country rock contact and decreases towards the centre of the outcrop.

Figure 4.6 Carnmenellis Granite

The Bodmin Moor outcrop exhibits a similar, yet less well- developed pattern. Figure 4.7 Bodmin Moor Granite 144

On the St Austell granite outcrop there are only three heat production boreholes in unaltered granite, yet again a similar pattern appears to exist.

Figure 4.8 St. Austell Granite Gaverigan (value at cor act) 7.4

On the Land's End granite again there are only three points.

Figure 4.9 Land's End Granite

6.5

Here the pattern is not found to be so well-developed as the previous cases, though the value at Geevor mine, on the granite contact, is higher than that observed away from the contact. Finally, the values obtained from the Dart- moor granite are also high near the contact, though they are also high at two sites remote from the contact. They therefore cannot be said to support the hypothesis that 145

heat production within the Cornubian outcrops increases towards the granite/country rock contact.

Figure 4.10 Dartmoor Granite Outcrop

measurements 146

HEAT PRODUCTION vs DISTANCE TO CENTRE OF OUTCROP 7-

Contact 6- Granite Country Rock South Crofty Mine 5- CM-E• •CM-A 4- CM-D• =CSD-I

1- Carnmenellis granite outcrop E I o 0 0 2 I 8 L0 c 6- ad ā •BD-A = 5- •BD-D •BD-E 4- •BD-C 3- •BD-B

1- Bodmin Moor granite outcrop

0 0 2 4 6 8 Distance to centre of outcrop in km --

Figure 4.11 Radiogenic heat production against distance from centre of granite outcrop. 147

DM -D

-DM -A Dartmoor .SLE-B DM-C 1BD-D _ 0 DM—B Soussons LE-A °DM-E SA-B Wood

Bodmin Moor BD-E N\ 4.0 P E SA-A BD-C St Austell Carnmenellis Granite 0 Granite 3.0 .BD-B V 0 L 0

•1-+ 0 = 2.0

HEAT PRODUCTION vs DISTANCE TO GRANITE COUNTRY ROCK CONTACT

0 2 4 6 8km Approximate horizontal distance to granite contact

Figure 4.12 Heat production versus approximate horizontal distance to granite contact.

148

POTASSIUM

CARNMENELLIS BODMIN MOOR DARTMOOR

8 8 -.

4 4

CM.A 8D. A DMA

8 8

4 4

- 1 CM•8 sae DOB r r T r r ~ r

8 8

4 1

CM•C BD.c DM.0

rence r I T

cur 8 Oc 4

CM.D 8D•D DM-D r 1,8r

8 8 cy

en 4 4 u

eq CME BD •E 1 DM. E r r r Fr LAND'S END ST. AUSTELL

16- 4

12. LEA SA- A r P I

8- 8

4- 4

mgocwnS LE• B SA• 8 r i 1 2 4 6 8 10 0 2 4 6 8 10 12 0 2 4 6 8 10 percentage percentage percentage

Figure 4.13 Histogram of potassium concentrations. 14(1

URANIUM

CM.A

2 CM-B n LE. A 4 n

CM-C °I LEB

2 CM- D n -1 SA.A 4

CM-E SA•B

8D-A 1 1 DM. A

4 Z 2 8D-B rr r~ DM •B 4

s ,I BD•C i

2 DM.0 11- BD- D n 4

21 Ī BOE n OM E 1 0 10 20 30 0 10 20 30 ppm ppm

Figure 4.14 Histograms of uranium concentrations. 150

THORIUM

CARNMENELLIS 8 6 BOOMIN MOOR

6 4

4 2 8D-A 2 n

80-B CM-B 6

6 4

BD-C 2 CM-C L 8 rrence 8- 1-6

Occu 6- 4

4- 2 8D- D 2- CM •D 6

4 6 2 4 r 8D- E 2 —8 LAND'S END CM.E -6

14 .4

12 -2 LE•A 10

r Longdowns LEB 0 10 ppm 20 30 0 10 20 30 ppm

Figure 4.15 Histograms of thorium concentrations. THORIUM (continued)

6 Histogram of Thorium concentration for 4 Borehoies CSD.1-t. CSD 21

2 n SA. A

2 SA.B

6 40

2 ĪĪ DM. A

2 DM.B . E

2 20 DM• C

2 I 10

DM E r , r r r 0 10 20 30 10 20 30 ppm ppm 151

Uranium & Thorium Wi::;;;::,; :,::

LE·A

LE·B

SA.A

SA·B

DM·A

DM·B

ppm

Figure 4.16 Histograms of uranium and thorium concentrations. 152

When plotted against the distance to the centre of the batholith, the Carnmenellis results plot along an approximately linear trend, (fig. 4.11). If plotted against distance from the nearest granite/country rock contact, they lie closely along a curve with only minor scatter. This would suggest some mechanism has controlled this distribution and that the observed results are not the result of chance. The Carnmenellis granite outcrop might be described as a well-behaved outcrop, since it is apparently the least altered by kaolinization and has a classic circular outcrop pattern. The results are presented graphically in detail as a series of histograms, one for each borehole (figs. 4.13- 4.16). These histograms also illustrate this apparent concentration of radiogenic elements towards the edge of the outcrops. They also allow a visual assessment of the variance and data reliability. If U is plotted against the U/Th ratio, it is possible to investigate the loss of uranium relative to thorium. In plutonic environments, uranium and thorium, are both in the trivalent state and behave almost like isotopes of the same element. The similar behaviour of uranium and thorium is due to their close correspondence in ionic size, high valence, electronegativity and co-ordination number with respect to oxygen. One might, therefore, expect the uranium/thorium ratio in any one borehole location to be very similar in all samples at the time of crystallization. In oxidizing conditions uranium can be oxidized to the very soluble uranyl form, but thorium has no comparable state under surface or near surface conditions. Evidence for mobilization of uranium is found in the secondary uranium, present as uraninite or pitchblende, along some joint faces, though uranium, contained with zircon or other secondary minerals, is relatively insoluble. If we consider a theoretical rock with a U/Th ratio of 1.0 and an initial uranium concentration of lOppm and we then remove 50% of 153

CARNMENELLIS BOREHOLES

(;• Uranium concentrations

o Prrgea' Bedr r" CM-B versus U/Th ratios

x Mea v r' Fd'.,• CM-

O Treredse? F,pm• C~ 1 D

p Tre'ghdn CME

E a a

BODMIN MOOR BOREHOLES Uranium concentrations versus U/Th ratios

BD•D 0 8D•8

BD•C

C 2 U/Th RATIO

Figure 4.17 •

154

LAND'S END & ST AUSTELL BOREHOLES

Uranium concentrations 25 L EB LEA versus U/Th ratios

E o

a 15 OQA / M 8 +~+ / O

p / o Newmdl LE-A

J 0 O Bunkers Hill LEB

p Tregarden Quarry SA-A

+ Colcerrow Farm SAB

DARTMOOR BOREHOLES

Uranium concentrations o versus U/Th ratios

+ Winter Tor DMA

O Blackrngstone Quarry DM B

x Soussons Wood DM-C

O Laughter Tor DM•D

Foggin Tor DM-E

0 1.0 2.0 3.0 U/Th Ratio

Figure 4.18 155

the uranium, we have a U/Th ratio of 0.5 and a uranium concentration of 5ppm. If all the uranium is removed there is a U/Th ratio of 0.0 and a concentration of zero. If, on the other hand, uranium is added from elsewhere, eg along a joint face or in cracks, then the U/Th ratio will increase but stay on the same U loss line since the thorium concentration has remained constant. Such a line is termed a uranium loss-line. Fig (4.17) shows the U versus U/Th graph for the Carnmenellis borehole samples. There is some scatter as might be expected in geological samples. How- ever, each set of samples plots in a separate area of the graph with relative linear trends which might be interpreted as uranium loss-lines. The results from Trerghan Farm show a particularly well-developed trend, suggesting quite severe loss of uranium in some samples. The results from Polgear Beacon show a cluster around 12ppm uranium and two samples with 4.5ppm uranium, suggesting the cluster is close to the original value, whilst the two low uranium samples have at some time been subjected to oxidizing conditions. A point of particular interest is the increase in the slope of the lines as the boreholes approach the contact, though Medlyn Farm does not exactly follow the trend. This trend might be explained in a variety of ways. Gosh (1934) suggested that the granite within the Carnmenellis outcrop may be subdivided into groups on petrological grounds.

Figure 4.19 Geological sketch map of the Carnmenellis granite showing distribution of the granite types.(after Gosh 1934) 156

The outcrop pattern of type (III) forms a roughly circular region within a ring of type (I). No sharp boundaries have been observed though contacts may be bidden by lack of outcrop. These regions may be the result of fractionation or multiple intrusion. Statistical evidence (Al-Turki & Stone 1978) found little evidence to separate granite types I and II. They did, however, conclude that the differences between the outer and inner granites are both petrographic (Modal) and chemical. Hawkes and Dangerfield (1978) proposed the following broad divisions for the Cornubian granite based on textural grounds

Coarse granite megacrystic types forming over

mesocrystic type 90% of the main plutons

Medium grained non megacrystic restricted lithium micagranite varieties occurrence

Fine granite megacryst-rich types forming less megacryst-poor types than 10% of main plutons

Figure (4.20) shows the distribution of the principal varieties of granite. Megacrystic granites are arbitarily split into two integrated groups by megacryst content; below 10% they are described as poorly megacrystic. Megacrysts are feldspar crystals, principally orthoclase perthites, ranging from 15mm to 170mm in length. Mesocrystic type granites, such as observed on the Carnme- nellis and Bodmin Moor mesocrysts, which are smaller on average than megacrysts, and commonly arranged to give a rock a distinctive linear texture. There is evidence that tOO ~"'I I , 0 6°W

GRANITES Of SOUTH-WEST ENGLAND

PJlli.····..l MtoQa

• Non-m"gA"Y'Ioc Iolhlum-mlCA g'anll.

• MrU"Cly,I'''''''' an" ""'IIAuy,I-II(h lone orllnll~

t-> U, SOkm" ...... J

Seven Stones Kit HIli Hingston Down

I. LAND'S END

~oN 50 St Michael's Mount I km r

0 200 2 0 4 W

Figure 4.20 Granites of south-west England. 158

poorly megacrystic granite grades into mesocrystic granite. Zirconium and titanium, possible indicators of early chemistry are concentrated in the megacrystic granite, relative to the mesocrystic granite (ibid). This is similar to the uranium distribution.

Table 4.6 Mean and Range Figures (ppm) for Zr and Ti from the Dartmoor Granite. (Hawkes &Dangerfield) 1978

Zr Ti Megacrystic 165(56-527) 2899(1400-6400) granite 20 27

Poorly 58(0-320) 1296(90-4200) Megacrystic 38 granite 20

Mesocrystic 30(18-58) 984(527-1600) granite 3 3

The number of samples of each rock analysed are shown below the determinations The U/Th loss line also acts as a warning of uranium loss. In the near surface, down to 10m or more, weathering is probably the main cause of uranium loss. Deeper in the earth loss may be due to the difficulty in sampling chips, metasomatism after intrusion, hydrothermal leaching, deep water circulation or kaolinization. Ball and Basham (1978), in a detailed study, concluded that the most important radioactive constituent of the Cornubian granites was uraninite. They reported that it typically forms individual equant sub-hedral grains, generally associated with pyrite and it occurs as inclusions within the common rock forming minerals, biotite, tourmaline, white micas and feldspars and their grain boundaries. Much less commonly, very small strings of uraninite grains 159 occur along grain boundaries. Uranium also occurs in zircon, monazite and hydrocarbon, but only to a maximum of a few thousands of ppm. Only minor levels (less than 50ppm) are associated with apatite. Dr Ball (ibid) said that the fact that uraninite occurred as inclusions within most of the common rock-forming minerals (except quartz) suggested that it was probably a primary magmatic mineral. However, its origin was probably more complex, since it was commonly associated with pyrite which, one could speculate, may have provided local sites of nucleation for the growth of uraninite. Thorium was found to be located in zircon, monazite and hydrocarbon and as a minor constituent of uraninite. Since thorium is found in zircons the thorium concentration may be linked to the zirconium concentration and thus the U/Th ratio may decrease as a result of increasing thorium concentration due to an increase in the number of zircons towards the edge of the granite. Simpson, Plant & Cope (1977) suggested that the generation of granitic magmas, enriched in uranium, tin and other granophile elements, could occur as a result of partial melting of lower crust and upper mantle, with separation of a highly fractionated differentiate, coupled by a regional enrichment in the underlying crust. The elements with the largest ionic radii tend to exhibit the greatest degree of enrichment on the crust (O'Nions, Hamilton and Evensen 1980). During magmatic differentiation U and Th, as well as K, tend to be successively enriched in progressively more acidic phases. Wood & Fraser (1976) describe the behaviour of trace elements in a crystallizing melt by use of Henry's Law:

a~ = C4 x4 (4.4) 1 1 1 where ai is the activity, Ci is the proportionality constant 160 for the component i in phase j and xi is the concentration. This is only valid for components that are so dispersed that they are surrounded by a uniform environment, and, although such trace components may interact strongly with other components, small changes in concentration of a trace component do not significantly affect the average environment. The activity coefficient therefore, remains constant and the activities of the trace components thus become directly proportional to their concentrations. It should be pointed out that mechanisms to be discussed are, of necessity, a simplification of the much more complicated chemical and physical conditions which exists in the 'real world' and thus the following model should not he expanded beyond its limitations. In general, the rate of diffusion in a melt is much higher than in crystals and, in most cases, either crystals are removed from the system by settling, or diffusion in the crystal is insufficiently rapid to maintain perfect equilibrium. Thus equilibrium occurs at the surface between the solid and liquid phase only. In a mathematical model of fractionation one might envisage a closed system which obeys a few simple rules. During crystallization at any time the liquid phase occupies a volume V and the remaining volume of the magma chamber is occupied by the solid phase. We are assuming no large changes in volume occur. Let Lv be the concentration of a trace element in the liquid phase, when the volume of the liquid is V, and SV be the concentration of the trace element in the solid phase at the same time. Then as crystallization proceeds a small volume, dv, changes phase, the total number of atoms of the trace element must remain constant giving the equation:

dv (4.5) (V - dv) L(V-dv) = VLV -SV

If the trace element obeys Henry's Law and equilibrium only

161

exists at the solid liquid interface, then the following calculation may model these conditions:

SV = C LV (from Henry's Law, C is a constant) (4.6)

substituting for SV in equation (4.5) gives:

dv (4.7) (V - dv) L(V-dv) = V LV - C Lv

Then fōr a small change in volume dv there will be a corresponding small change in concentration dL:

(4.8) where dL = L(V+dv) - LV

rearranging equation (4.7)

dv - CLV dv (4.9) (L(V - dv) - LV )V= L(V-dv)

substituting (Ly_ dv)- LV) by dL

-dLV = (LV - dL)dv - CLVdv

-dLV = (1-C)LVdv + dLdv (4.10)

for dv -► 0 dL -• O

dL = (C - 1) dv LV V

L2 V2 1 dL = (C-1) dv J V JL1 L 1

L2 2 [in L = (C - 1) ln VlV C J V L1 1 V (C-1) ln L2 = ln k7] + ln L1 1 (C-1) 162

(C-1) -(C-1) L2 V2 L1 V1 (4.11)

by substitution of SV = C LV

V = v(C-1) s (1-C) S 2 2 1 1 (4.12)

If crystals are removed by settling, V will be related to depth. For a parallel-sided magma chamber this would be a linear relation and we could write:

(C-i) S Z (1-C) S2 Z 2 1 (4.13) where Z represents the distance to the top of the chamber. In its simplest form the equation will yield larger values of S2 as Z2 decreases (ie if C <1), such a conclusion being merely a statement of fractionation in mathematical terms. It might, however, illustrate why the late fluids have a high concentration of incompatible elements. Of course, at high concentrations, the elements are no longer a 'trace' and so the equation becomes progressively less valid. Both uranium and thorium will have low values of C in the equation since they are incompatible elements. Potassium is also slightly incompatible so would correspond to a value of C below one, though not nearly as low as for uranium and thorium, potassium, however is not a trace element. Swanberg (1972) presented data for the possible vertical distribution of radiogenic elements within the Idaho batholith. Figure (4.21) was constructed using the values he obtained for uranium thorium, potassium and heat production. Superimposed on the results are lines derived from equation (4.13). The heat production line was calculated from three lines for the radiogenic elements combined with their appropriate heat production constants. The result is similar to an exponential distribution, however, the distributions are much steeper near the top of the batholith. A reconstruction of the granite roof, based on an exponential model, is presented for the Carnmenellis and Bodmin

FRACTIONATION MODELS FOR DISTRIBUTION OF RADIOGENIC ELEMENTS WITH DATA FROM THE SIERRA NEVADA BATHOLITH 3 p.p.m. p, p. m. Percentage »Wm I L ....I _. 1 !4 r1 81 T r 1" I I II I i1 I r 2 4 6 8 10 12 14 12 16 201 24 28 32 3161 1 2 3 4 1 2 3 4 '5 6 ;7 K=0.88 Total=3.24%/ 2- 1 2- o. _ • o oo.r i 4- I

6- 6-- .•

8- o 8 -+- Uranium E Thorium Potassium Heat generation (K11-0.2) 10+. (K ~- 0.3) (Kn i O 88) `' 10 t L a 12—o ° 12+

y 1 14- 144- I (K-1) (1-K) I 16-• AI S2--= Z2 . SiZi • o 16-+- i i 1' I! 18 18-* • Curve obtained by combinatiōn Concentration of three previous equations Carnmenellis Granite 0 1 Km l ~ \ L_ Vertical Scale= horizontal Scale

/ / \ / CM-A CM-A CM-C CM-0 CM-F \ N. SOUTHCROFTY MINE //GRILLIS FARM POLGEAR BEACON MEDLYN FARM TREVEASE FARM TRERGHAN FARM \

NORTH \\ SOUTH \ 45 38 34 38 44

Bodmin Moor Granite

\ ..... \ •••.~ \ . \ —..=...... //• / \\ \ / \ / \\ \ // \

/ 80-A 80-B BD-C BD-E \ / BRAYDOWN BLACK HILL PINNOCKSHILL BROWN GELLY GT HAMMETT FARM\ NORTH SOUTH

5?NW's 31 35 50 43 165

Moor outcrops. A value of 7.5km was chosen for the constant D (see equation 4.3). If 16.6km is used, the granite roof would be approximately twice as high. The model illustrates that the horizontal distribution may be related to the vertical distribution within the batholith, since the roof forms a smooth curve (except Bodmin Moor hole D). The model has been criticised by geologists for having too high a roof. This might be evidence for a steeper distribution near the surface. S1 2(1-C) (equation 4.13) may be considered a constant representing the initial concentration and the size of the magma chamber. If the initial concentration is unknown it may be taken to represent any concentration combined with the fluid volume at that time. In addition, it would appear likely that the value of C will change with variations of bulk mineralogy or pressure/temperature conditions. For uranium and thorium one would expect similar values of C. Combining equations for uranium and thorium we may obtain a relation for the U/Th ratio:

U2 = 2(C U-1) U1 21(CTh_1) (4.14) Th2 (CTh-1) Th1 Z (CU-1) Z2 1 (CU-CTh) U = Z2 constant (4.15) Th2

One might, therefore, explain the variation in slope of the Carnmenellis granite by a difference in Cu and CTh. If this is the case, the U/Th loss line may prove to be a sensitive indicator of fractionation within granite magma. This conclusion is, however, dependent on the good behaviour of thorium. The uranium/thorium ratio is much higher in the country rock than in the granite, so large scale assimi- lation would result in an increase in thorium relative to uranium. These points of conjecture may well be solved by a study of other isotopic and petrological investigations. 166

At Porthmeor Cove there is a small outcrop of granite which geologists have, for many years, used as an example in min- iature of the cupolas that form the outcrops of the Cornub- ian batholith. The granite is intruded into the country rock to form a dome-shaped mass with steep sides. The top metre or so is coarse-grained and pegmatic, whilst further into the 'core' of the intrusion, the granite approaches a normal composition. To illustrate the radioactive nature of the granite, a traverse was made with the portable gamma- ray spectrometer. The intrusion shows up clearly as an increase in count rate for all channels. This illustrates the likely pattern over the batholith as a whole (see fig. 4.24). The sharp nature of the contact is well illustrated by a traverse along the Roskear cross-cut in South Crofty mine (Fig. 4.23). The cross-cut starts in granite and con- tinues north to cross the granite/country rock boundary near the end of the drive. The results agree well with uranium determinations on discrete samples (Simpson, Brown, Plant & Ostle 1978). The amount of rock sampled by the portable spectrometer is dependent on the geometry and absorption characteristics of the outcrop measured. 167

SOUTH CROFTY MINE LEVEL 340 - ROSKEAR CROSSCUT N

UNDERGROUND GAMMA-RAY SURVEY Thorium 100

80. c + ~+ so_ f 3- 40- N 300 Uranium 250.

200_ 74 x

c-) 150_

7C0_ Potassium x sooJj x oo x xx/ \x~x\X/ v 500. \X/

xi \ 25 Total Count c \ _❑_❑\ _a p\ 0. 3 0 2 No/ ❑J ❑ U 15 ❑ O

10• Distance in metres 0 20 r 40 60 * 80 t 100 120 140 '60 180 4 Country Rock G ranite Granite l ( vein U .• contact PLAN OF ROSKEAR CROSSCUT N

PORTHMEOR COVE SURFACE (RAY SURVEY >180°geometry 0 at this point TOTAL COUNT 12 000 0 (5minute samples) 0 t O\ / 0 0 \ 0000 1 / I / I 0 i 8 000 1

~~O 1 Cc

0 6 eoe~~ ~

4 Ce0

i 0 Country Rock G,onite Schott I G'anite4 Count, y 000 RocA 168

Shielding Experiment

The following experiment was carried out in order to estimate the absorption characteristics of the Cornubian granite. The absorption of photons by matter has characteristics very different from that of the absorption of charged particles. When a beam of monoergetic parallel photons passes through an absorber, each single photon of the beam either disappears, after giving off all its energy in a single event, or is scattered away from the beam. The number of photons in the beam, therefore, decreases contin- uously as the beam penetrates deeper and deeper into the absorbing medium. If I is the intensity of the beam, defined as:

I = Qhv (4.16) where Q is the number of photons crossing the unit area in the time unit (flux of photons) and by the energy of each photon, then when the beam is passed through a thickness dx of an absorber, the intensity decreases by an amount dI:

dI - -i I dx (4.17) where p is a constant for a given absorbing medium and a given photon energy, called the 'absorption coefficient'. Integrating the above, we obtain:

I = Io exp(-px) (4.18) where Io = Intensity of beam when x = 0 When x is expressed in m and the intensity analogously in mkgs units, p is consequently expressed in m-1. How- ever, it has been found convenient sometimes to express the thickness by multiplying the linear dimension of the absorber by the density; it is therefore expressed in kgm-2. The absorbing properties of a given material can also be expressed in terms of half thickness. The half thickness can be defined as the thickness of a given absorber needed for reducing the intensity of a beam of parallel monoenerg- 169

etic photons to half its initial value.

log z = -pxl log e 2

and = 0.693/x,1

There are three major processes responsible for absorption of gamma-rays in matter. They are the photo electric effect, the Compton effect, and pair production. The total absorption cross-section per atom for removing a photon is the sum of the cross section for each of these three processes. The Compton effect is due to a scattering process between the photon and an atomic electron. The gamma-ray is then not completely absorbed but merely scattered out of the beam. It may still be moving in a forward direction but, of course, with reduced energy. The forward scattered Compton gamma-rays somewhat complicate the calculations of the gamma-ray intensity behind an absorber. A simple experiment was carried out in order to determine the absorption characteristics of the Cornubian granite. Slabs of granite were obtained from the Merri- vale quarry on Dartmoor. The slabs were parallel sided and ranged in thickness from 17.5mm to 140mm. The source, pitchblende, was placed .34m away from a 76mm x 76mm NaI detector. Throughout the next stage of the experiment this distance was kept constant. A slab of Granite was placed between the source and the detector and the spectrum recorded on a multichannel analyser.

Pb shield scattered ray direct rav pitchblende source Na I detector — granite slab

Figure 4.25 Sketch of apparatus used in the gamma-ray absorption experiment. 170

The source was then removed and a background spectrum recorded. This was repeated with slabs of different thicknesses and also with combinations of slabs. Pitchblende yields several uranium peaks which were each identified and their positions recorded so as to keep a check on the detector calibration. Thick shields were measured for 40,000sec onds whilst thin shields were measured for 2,000 seconds. In addition to granite, aluminium and copper plates were also measured giving a sum total of 36 runs. Six energy windows were chosen and the counts per second calculated for each configuration. The counts/second were plotted on a logarithmic scale against granite thickness. Straight lines were obtained for each channel and from the slope of these lines, the thickness of absorber required to halve the number of counts was determined. For the 1.76MeV energy peak this was 60mm. An estimation of the absorption coefficient ,u was obtained from equation (4.20):

1 = 0.693/x1

p= 11.55m-1 for the 1.76MeV energy peak. The mass absorption coefficient was calculated by dividing p by the granite density (2633 ± 2kgm-3)

= 4.4 x 10-3kg-1m2

2 = 4.4 g-1m

This agrees well with a theoretical figure of 4.4g-lm? For the lower energies similar results were obtained. Table 4.7 RESULTS OF SHIELDING EXPERIMENT

Energy of peak .6 1.1 1.25 1.4 1.76

x1 54.7 61.7 68.6 68.9 60.0 P2 12.7 11.2 10.1 10.1 11.5 Pun 4.8 4.3 3.8 3.8 4.4 pm theoretical 7.8 6.0 5.7 5.0 4.4 171

It is apparent that the 1.76MeV results are not affected by the build-up factor, since uranium yields no higher peak large enough to interfere with the 1.76MeV peak. Lower energies show a marked difference between the measured mass absorption coefficient and theoretical value. In each case the build-up factor reduces the experimental absorption coefficient. This effect is particularly marked in the Compton continuum region where x1 was 0.12m, approximately twice that measured for the peaks (0.06m). The conclusion from this experiment was that only .24m of granite are required to reduce the intensity of the 1.76MeV peak by over 90% of its initial value in a linear geometry. It also shows the thickness of the sample used in the laboratory spectrometer does not severely affect the accuracy of the method. A thicker cell, however, would require a correction if the absorption of the sample is not identical to that of the standards. 172

In Situ Measurements

Within this thesis it had been hoped to demonstrate the in-situ determination of the heat producing elements Ih, U and Th. This has not been possible, due to the length of time required to assemble the appropriate apparatus. Once the apparatus was assembled, the sodium iodide crystal was cracked during a test run at the Fetcham Mill borehole near Leatherhead. This accident prevented its use for this project. The apparatus consists of a NUTMAQ 4-channel portable spectrometer, connected to a 102mm x 45mm sodium iodide crystal mounted in a borehole probe containing photomultiplier and a small electronics package. The spectrometer was linked to a chart recorder and the spectrum could be observed, analysed, stored etc., by use of the Canberra series 30M.C.A., described earlier in this chapter. The equipment was to be transported in a Landrover to the borehole site. Additional power was to be obtained using a portable generator, though batteries could be used for all but the chart recorder. Battery chart recorders are, however, available on the open market. The probe performed well in water tank tests. A clear relationship was obtained between water depth and count rate when a pitchblende source was placed over the tank containing the probe. The background of the probe was measured in the lead castle and comparisons made between the efficiency of the probe and the 76mm x 76mm NaI crystal. It was envisaged that it might be possible to estimate the sampling volume by means of backscattering density measurements over particular energy windows, combined with laboratory models, such as the shielding experiment and calibration pits. At Rosemanowas quarry a simple pattern of boreholes was drilled for calibration purposes. In the early stages of this project, in situ determinations of the density and total 6 ray activity were obtained with the aid of the 17

Sheave wheel Electronic Cable drum counter Waterproof Sliprings connector 0

r Digital dep h L display

Electronic package Portable 4channel & r ray spectrometer NUTMAQ

Multichannel spectrometer

be Photo— Canberra series 30 o r multiplier tube p le ho Bore

ite 4 channels recorder Nal (Ti)

Depth Crystal Chart signal recorder

SCHEMATIC DIAGRAM • BOREHOLE Y RAY SPECTROMETER SYSTEM N//

Figure 4.26 Schematic diagram borehole gamma-ray spectrometer system. 174

I.G.S. Engineering Geology Unit, who arranged for the Carr.- menellis boreholes to be logged by S.S.L. Gamma-ray spectrometric logs have been run in the Rosemanowas quarry boreholes by the I.G.S. (Isotope Geol Unit) and Robertson Research Ltd. 175

Country Rock Results

Sediments are often considered to be very low in radiogenic elements. This does not appear to be the case in Cornwall, the average heat productivity for the three country rock boreholes being 2.OpWm-3. This figure was just under half that measured for the granites. The average thorium/uranium ratio was 4.9, much higher than the 1.2 average for the granites. This marked separation of thorium and uranium is probably due to the fact that uranium can be oxidized to the very soluble uranyl form, but thorium has no comparable state under surface or near surface conditions. Under plutonic conditions thorium and uranium, both in the trivalent state, behave almost like isotopes of the same element. Oxidation during weathering forms the major mechanism separating uranium and thorium. Strik- ing evidence of this process is the extremely low thorium/ uranium ratio found in sea water (Koczi 1956). In general, different sediment types will contain different concentrations of radiogenic elements. The amount of uranium in shales will depend upon the degree of leaching that has occurred before sedimentation. Hurley (1956) noted that the thorium/uranium ratios in many shales are known to be related to the distance offshore of the depositional site. Adams and Weaver (1958) suggested three main facies: 1) The low (below 2) thorium/uranium facies 2) The high (above 7) thorium/uranium facies 3) The intermediate(2-7) thorium/uranium facies The ratio for the country rock boreholes was 4.9 which would place these shales and sands in the intermediate group. Intermediate facies represent poor weathering and rapid deposition of rock detritus or mixtures of low and high facies material. This interpretation would be consistent with the geosynclinal environment of very rapid deposition, envisaged by many south-west England geologists. The high thorium/uranium facies occurs due to either the 176

Country Rock Boreholes

r:-t Heat ~Thor,um o PotClSSlum ~ Production 16

12 reo·} Kest'e .~artna &Jrencle

G) 16 '"'c enD·3 Callyw,m Farm Borehole CD ... 12 ~ (J 8 (J 0 4

0- 4 6 0 2 4 6 8 10 12 1·1 16 18 0 2 4 680 2 >- (J C G) :I. 0' IGS WilSey Down Borehole ...CD LL 41

,2 u c c e' D f:: a ~ C . e S· are s'D e von r

024 6 8 10 12 14 16 18 0 2 ~ 6 8 0 2 4 6 ppm per cent 1O-6 Wm-3

Figure 4.27 Country rock boreholes, histograms of the concentrations of radiogenic elements. 177

I. G. S. WILSEY DOWN BOREHOLE DISTRIBUTION OF RADIOGENIC ELEMENTS AND HEAT GENERATION 2 4 6 8 10 12 14 16

Carboniferous 0 Crackington Formation

0 0

+ c

34 0 U. 5PPm • 0

Fire Beacon Chert Formation

(mixture of slate , lsts, cherts etc.)

0 am= - MIEN MEW 0 r1 - 11 J

+xI

+ I X X4{ i Upper Delabole 1+x 0 Slates 11. Pt

41 +1 x I +x 0 I. Black Slates Concentration Heat Production Symbol + Uranium ppm Thorium ippmi X Potassium(%) • (UWm-1) Line .

Figure 4.28 I.G.S. Wilsey Down borehole; distribution Of radiogenic elements and heat generation. 178

concentration of high thorium/uranium resistates, such as monazites in beach sands and placers, or the removal of uranium by thorough weathering and leaching. The low thorium/uranium facies occurs where extraction from the sea or fresh water is the major mechanism for the fixation of uranium in the sediment, for example many black shales and phosphates. The segregation and facies dependence of uranium and thorium will lead to a change in heat productivity from one facies to the next. In the case of the samples measured, there was a correlation between the potassium and thorium content, though this may not be significant in a wider group of sediments. The effect of sediment type on the distribution of heat producing elements is clearly demonstrated by the Wilsey Down determinations (Appendix IV table 24). The two slate sequences show high thorium concentrations ( 13ppm) whilst the cherts and limestones have a significantly lower value. These mechanisms may lead to considerable variations in sediment heat prodictivity. A geosynclinal environment with rapid sedimentation might lead to relatively high sediment heat productivity, whilst a well worked sediment, such as wind blown sands etc., may lead to a low productivity. In this way sedimentary basins may show different characteristics from area to area. A sedimentary basin 5km thick with an average production of 2.0jWm-3 would give 10mWm-2 where as if the production was 0.5pWm-3, it would yield only 2.5mWm-2. Thus an area with a long history of rapid sedimentation from relatively radioactive source rocks would have a higher productivity than one which has a long history of sedimentary reworking. Igneous reworking would, however, increase the crustal productivity, thus zones containing buried granite intrusions would also have a higher productivity. A movement of water during metamorphism will remobilise any uranium that is accessible and lead to 179 a change in the distribution of radiogenic heat productivity. However, in the Gaverigan borehole a contrast of uranium of 3.8ppm can still be seen in the Meadfoot beds to 25ppm in the granite. There is little difference between this value, only a short distance above the granite, and that observed in the Wilsey Down borehole 9km above the granite. In mineral deposits different mechanisms occur but these may be less important to regional heat flow than the much lower concentrations in the bulk of rocks.

180

5 RESULTS INTERPRETATION AND MODELLING

The results of this and earlier investications are illustrated by maps(figs. 5.1 - 5.4)and presented in table (5.2). The column marked 'corr At has been corrected for topography and the following two recent climatic events. Present Climatic Optimum(PCO) 1.70 years PP + 0.6°C Little Ice Age (LIA) 75-525 years BP - 0.4°C The column marked 'corr B' has been corrected for topography and the full palaeoclimatic correction. The effect of palaeoclimate on shallow boreholes has been discussed in Chapter 3. In comparing the results presented here with deep boreholes in areas of study where no climatic correction has been applied, a useful guide may be obtained by using heat flow values corrected for topography and only the last two climatic events. The heat flow versus depth profiles for the Predannack borehole (chapter 3 fig. 3.4) illustrates that this correction should yield a value similar to that obtained from a borehole deeper than 300m. The following figures show the sharp contrast between values measured on or above the Cornubian batholith with those country rock boreholes distant from the batholith. Sites adjacent to the granite are arbitarily defined as sites within the 9km depth contour for the roof of the granite batholith, as obtained from gravity studies (Tombs 1977).

Table 5.1 HEAT FLOW mWm-2 N Uncorr Corr A Corr B st dev st dev st dev

Granite 27 100 12 116 9 123 9 Site Adjacent Granite 10 88 16 96 17 102 17 Country Rock Sites 5 55 10 59 10 65 11 •

3 200 bz SOUTH —WEST ENGLAND

zn LUNDY ISLE HEAT FLOW COVERAGE 4 . EXMOOR IGS,Canningt a. EEC CONTRACT NO 586-78-1EGUK IGS,Honeyrnssd

❑ UKAEA CONTRACT NO E/5A/CON/1O5 IGS, Curry Pool Farm 'S T

KEY TO BOREHOLES Contract Sites Other Sites iog a • Granite o Granite ott . Country Rock o Country Rock aT oT 100_ BOREHOLE LOCATION MAP 2o

~ IGS,Msldon DIGS, Wilsey Down DARTMOOR GRANITE Km A BODMIN uoz i id GRANITE

Gr IGS,BoveyTrace d2u

l O O na io t Na

IGS, Newly CAR!\MENELLIS GRANITE S7 AUSTELL LAND'S END GRANITE GRAN!

Geevor Longdowns,Rosemanowas AA D Mine CM-C CM-0 CM-E 0 25 50 km Scale IGS, Precis LIZARD PENINSULA IGS, KennadrSands_ 300 , March, 7960 National Grid Km East

200- SOUTH—WEST ENGLAND HEAT FLOW COVERAGE EEC CONTRACT NO 586-78-1EGUK UKAEA CONTRACT NO E/5A/CON/105

KEY TO BOREHOLES

Contract Sites Other Sites • Granite o Granite • Country Rock • Country Rock h t r 100 100 HEAT FLOW VALUES No

Corrected for topography and recent 67 BODMIN : I DARTMOO R

Km climate only heat flow in mWrrr 2. ' \ GRANITE i GRANIT /, —_—. N ▪ / id 113 `. ~N,r._--.r ~ / r • • 95 G l

na 4. L --. `, io

t I

Na D ill CAANME ITE l ,o, ; ' ;i •`ao°s__ C3RANlTE o - _ ∎ kV—OUT i ST. AUSTELL Depth-to-granite confnorS LAND'S END — J from /GS gravity model , Q12s GRANITE GRANITE !' --^1 as below __-- / ,. 2 1 km / 3 k r , 112,106 , 106 _._._._ 9 k //i , - 0 25 0km 0 73 Scale r LIZARD PENINSULA 300 March. 1980 200r

National Grid Km East -mojg -42aq pa;oaiiooun E 'S alnbz3

National GridKm FIGURE 100 UK AEACONTRACTNOE/5A/CON/105 LAND'S ENO EEC CONTRACTNO586-78-1EGUK GRANITE 1 / KEY TOBOREHOLES • Contract Sites • HEAT FLOWCOVERAGE r Country Rock Granite SOUTH-WEST ENGLAND i Heat flowinmWm- No correctionsapplied. HEAT 5.3 CARNMENELLIS FLOW VALUES GRANITE Other Sites o o Country Rock 2 Granite . f

LIZARD PENINSULA 200 200 101 95 91 98 105,103,103 ST. AUSTELL National Grid KmEast GRANITE LUNDY ISLE EXMOOR 0 054 Scale 25 as tram IOSwavilyr?)orlel —._.—.— --_ Depth_7o•gran1re contours

below 300 300 -314m

9 Ihm hrn 50km March. 1980 100

68J (50) km March 1'4M 1 50 gravity modei IGS 300 bebw O T I Depth-to•grande conraus from M as N T A R R A 101 G _ // o57 . / 0 Ili 059 /1 , / 112 EXMOOR EXMOOR •

tt~ PLYMOUTH '^ R •- ''s\115 r i' ~ ' /1 / ~ .i ~ J / " d --

rŌ

N ANITE ISLE , R

G N

, -• 6

L 128 aLUNDY

'- GRANITE ‘1

National Grid Km East r —,~ 1 ST. AUSTELL • K 1, .133

i /,, - C

200 4 11P~° S. t11 106 l i . No; Rock 133 i , r r / Granite Country Other Sites o _ - gRANI TF. . 2 CARNMENELLIS 5.4 ,, END HEAT FLOW VALUES HEAT FLOW full palaeoclimate. Heat flow in mWm' Corrected for topography and SOUTH—WEST ENGLAND ENGLAND SOUTH—WEST / Granite Country Rock HEAT FLOW COVERAGE FLOW COVERAGE HEAT • Contract Sites • KEY TO BOREHOLES KEY TO BOREHOLES

I GRANITE EEC CONTRACT NO 586-78 1 EGUK EEC CONTRACT LANDS UKAEA CONTRACT NO E/5A/CON/105 UKAEA CONTRACT 100 FIGURE

eat flowcorr ected forpal aeoclimatea nd H

TABLE 5.2 HEAT FLOW IN SOUTH WEST ENGLAND A. CONTRACT POREHOLFS - SUMMARY COMPILATION No. No. Heat Fl9w Station Name Stn. National Grid Depth Temp. Cond. mi Code Reference (m) Points Points Uncorr. Corr. A Corr. B GRANITE SITES

Grillis Farm CM-A SW 6795 3846 100 20 33 92.2 112.9 119.9 Polgear Beacon CM-B 6927 3663 100 22 23 100.6 121.7 128.6 Medlyn Farm CM-C 7083 3404 100 8 32 98.3 113.6 120.6 Trevease Farm CM-D 7185 3180 100 20 33 91.5 111.9 118.8 Trerghan Farm CME 7353 3033 100 18 32 94.5 112.9 119.7 Bray Down BD-A SX 1907 8177 100 18 31 88.9 113.4 120.2 Blackhill BD-B 1835 7820 100 20 34 97.0 119.0 126.0 Pinnockshill BD-C 1892 7450 100 13 33 102.9 120.7 127.5 Browngelly BD-D 1924 7247 100 21 32 87.1 108.4 115.4 Gt Hammet Farm BD-E 1885 6986 100 20 34 97.7 118.8 125.6 Newmill LE-A SW 4608 3435 100 23 32 102.7 123.8 130.7 Bunker's Hill LE-B 4022 2726 100 23 31 104.5 123.9 130.9 Tregarden Farm SA-A SX 0553 5945 100 20 32 105.8 125.8 132.6 C:olcerrow Farm SA-B 0679 5763 100 20 32 102.8 126.5 133.4 Winter Tor DM-A SX 6117 9156 100 29 34 78.6 107.4 114.2 Blackingstone DM-B 7850 8593 100 31 34 85.5 105.5 112.4 Soussons Wood DM-C 6733 7971 100 27 34 123.4 132.2 139.3 Laughter Tor DM-D 6562 7549 100 31 34 90.0 114.2 121.0 Foggin Tor DM-E 5663 7334 100 31 34 89.0 110.9 118.0 TABLE 5.2 HEFT FLOW IN SOUTH WEST ENGLAND A CONTRACT BOREHOT,FS - SUMMARY COMPILATION continued No. No. Heat Flow Stn. National Grid Depth Temp. Cond. malin Station Nacre Code Reference (m) Points Points Uncorr. Corr. A Corr. B

SITES ADJACENT GRANITE Merrose Farm CDD-1 SW 6559 4351 100 23 23 72.2 79.2 84.1 Kestle Wartha CDD-2 7533 2579 150 47 41 82-2 96.4 102.5 Callywitk Farm CDD-3 SX 0886 6783 150 43 47 91.2 101.1 106.2 Gaverigan GAV SW 9316 5916 325 105 30 97.2 98.1 105.7 TABLE 5.2 HEAT FLOW IN SOUTH WEST ENGLAND B OTHER BOREHOLPS - SUMMARY COMPILATION

No. No. Heat Flow Station Name National Grid Depth Temp. Cond. mN411 Reference (m) Points Points Uncorr. Corr. A Corr. B GRANITE SITES

Geevor SW 3750 3450 403 7 31 128.6 128.6 134.8 Troon 6570 3677 122 36 40 109.1 122.7 129.8 South Crofty 6680 4105 650 7 57 128.9 128.9 137.7 Rosemanowas A 7352 3456 303 99 52 102.8 105.5 113.8 Rosemanowas D 7352 3460 292 97 52 103.4 106.4 114.6 Longdowns 7368 3462 182 51 50 105.2 111.7 118.2 Hemerdon SX 5733 5849 128 42 12 93.3 107.9 114.8 SITES ADJACENT GRANITE

Wheal Jane SW 7840 4380 230 164 49 125.2 125.2 132.9 Newlyn East 8146 5390 103 34 34 90.5 104.6 111.1 Belcwda Beacon 9788 6254 141 20 31 78.1 85.5 91.5 Lanivet SX 0216 6413 86 29 0 79.4 93.1 99.7 Wilsey Down 1797 8890 726 200 42 67.3 67.3 74.5 Meldon 5676 9220 61 17 25 103.7 114.1 120.1 Bovey Tracey 8271 7929 95 35 33 78.7 94.6 100.6 COUNTRY ROCK SITES

Predannack SW 6901 1634 304 100 61 60.4 61.5 68.7 Kennack Sands 7325 1647 152 50 22 68.4 73.1 79.4 Honeymead SS 7990 3930 290 46 15 54.0 54.0 57.4 Currypool Farm ST 2270 3871 182 58 24 52.8 60.7 67.6 Cannington Park 2470 4010 760 234 159 40.1 45.1 50.0 188

The country rock heat flow, corrected for recent climate only (59mWm-2), matches the area-weighted mean for the U.K. (59mWm-2),(Oxburgh et al. 1980). This value is close to the European (64mWm-2) and World (59-64mWm-2) averages for continental regions.(Cermak &Rybach 1979). The granite value 116 (corr A) represents a heat flow excess of 57mWm-2 above the mean for the U.K. and 52mWm-2 above the mean for Europe. The results are very consistent over the entire region, no low values occurring above the granite batholith. Bore- holes close to, yet not above, granite show a slight enhancement. The lines of boreholes across the Carnmenellis and Bodmin Moor outcrops illustrate the heat flow across the granite outcrop (fig. 5.5). A section along the length of the batholith shows that, on the gross scale, each outcrop is similar to the next. From this emerges a fairly constant heat flow for the entire batholith. This is inconsistent with convective circulation of water within the fissure system of the batholith, unless such a system is very deep-seated and of a very large scale. Geochemical studies of the hot springs within the deep mine systems, although not conclusive, did not suggest the need for these springs to be part of a giant water flow system within the granite (Edmunds 1980). They occur at temperatures which may easily be obtained at depths not very much deeper than the deepest mines. It may be that such circulations, within the mineralized belt, are driven by, rather than the cause of, the high observed heat flow. Indeed, such a mechanism may well be an important factor in the mineralization and alteration of the granites. It seems more than likely that the high heat flow is a result of the high radiogenic contribution, coupled with refraction of heat flow due to the high thermal conductivity of the granite. It is unlikely that this is a unique mechanism, indeed the Massif Armorican in Brittany and the Weardale granite in north England, both similar to the Cornubian granite batho-

20km Heat flow section across the Carnmenellis granite outcrop.

Carnmenellis Granite v1'4O- 0129 Land's End Ē 120- 0123 o122 ' ~AA n .,117 _117 n113 Lizard w0 0113 1140 8106 a 0 96

s r Carnmenellis granite outcrop N 80- 0 79 'E 73o 62.Q E 60 —

0 'a- 40-

4- . (0 5 km CU section scale 20-

Grillis Medlyn Farm Far1m 0 Old South Crofty Troon Polgear Longdowns Trevease Trerghan Kestle Wart ha Predannack Kennack Merrose Beacon Rosemanowas A Farm Sands A Rosemanowas 0 B north- west Location south-east

Figure 5.5 ~•41 63 57r'42 Heat flow section along the 100km Q37 Q56 •59 map scale • cornubian batholith Q38•54 Q34 (Section extended to the north east Q60 across southern England to illustrate 460 heat flow contrast.) s. 45 Land's ''625 39 'b53 end 0 0 6 St Austell Q54 6r 4 042 00 ~~ 0 0 Dartmoor 120 1 rre 107 b b67•S- • 0 0co 650v -71j. 100 9'0 11`4 124 10 108 0 129 O A124 67 cv 80 E 0 O O O E 60 _ 0o-. - 8- - -o-o- - - - - cornubian batholith' o 0 0 0 ō O O 40 O .4-- O rv 0 cu O 100 km 20- section scale London 0- 1Carnmenettis granite A Location B south -west north-east Figure 5.6 191 lith, yield relatively high heat flow values (R. Gable 1980 and Bott et al. 1972). The Gaverigan borehole illustrates the mechanism which gives rise to high heat flow values at the sites adjacent to granite. In this borehole Granite was encountered beneath only 293m of country rock. A thin layer of country rock is unlikely to modify the overall pattern and so a high heat flow is measured. Having established the overall pattern of heat flow, it is of interest to look at the deviation from this pattern. The Land's End and St. Austell outcrops show a slightly higher heat flow than those of Carnmenellis and Bodmin Moor. The St. Austell and Land's End granites are nearer to their original roofs than Carnmenellis or Bodmin Moor and so may be higher in bulk radiogenic composition and more dome- shaped. Soussons Wood borehole on Dartmoor yields a high heat flow relative to the other Dartmoor holes. It would be unwise, however, to attach too much weight to this result since the hole is water disturbed down to at least 70m. The Kennack Sands and Kestle Wartha boreholes exhibit higher heat flow than would be expected. These two country rock boreholes may give high results due to problems in as- signing the correct thermal conductivity. On the other hand, they may indicate some hidden feature, though there is no clear indication from the gravity anomaly that such a feature exists. 192

Temperature °C 0 50 100 150 200 250 0

1 CASE 1

2 E -3 N

a. Crustal ~ 4. Temperature Profile

for go_kdT 5 dz

assuming q°_ 124 mWm-2 and k = 3.3 Wm-1K-1

Figure 5.7 Case 1, crustal temperature profile. 193

Temperature °C 0 50 100 150 200 250 0

1 CASE 2

• JO-

Crustal °- 4 - ~ Temperature Profile

for Tz = T,+923+AZ2 k 2k

(Step function heat-production model) assuming 6 q0 .124mWm-2 k. 3.3 Wm-1 K-1 A. 3.86x10-6Wm-3 7

Figure 5.8 Case 2, crustal temperature profile. 194

Temperature °C 0 50 100 150 200 250 0

1 CASE 3

Crustal Temperature Profile for

Tz = To+q0-A0b+A0b2(1. ZIb) k k k 5 - (Exponential function heat - production model) assuming 6 q° .124 mWm-2 k 3-3 Wm--1 K-1 A° .3.86 x10-6Wm3 b = 7.5km 7

Figure 5.9 Case 3, crustal temperature profile. 195

Temperature °C 0 50 100 150 200 250 300 0

1 CASES 4 & 5

Crustal Temperature Profile for

Exponential function heat - production model, and a =627Wm1 5- temperature dependent =1.22Wm 1k-1 thermal conductivity assuming q°=124mWm-2 6- k = 3.3Wm-1K-1 at 24°C A°= 3.86 X10-6 -3 Wm a .184Wm1 b=7.5km f3=2.71Wm-1k- kZ =T + a 7

Figure 5.10 Cases 4 & 5, crustal temperature profiles. 196

Temperature °C 0 50 100 150 200 250 300 0

1 Summary of crustal temperature 2- profiles

• E -3- N t

Case 1. Conduction, no heat-production 6 2. Step function heat- production 3. Exponential function heat-production 4.) Exponential function heat. production 5.» and temperature dependent thermal 7- conductivity. \\ 23 4 1 5

Figure 5.11 Summary of crustal temperature profiles. 197

One Dimensional Depth Extrapolation Models

Temperatures, at depths greater than those sampled, may be estimated by simple mathematical models. Such predictions are required in order that economic estimates and feasibility studies may be carried out to assess south- west England as a possible site for 'Hot Dry Rock' exploi- tation. The main emphasis of this project has been the delin- eation of the region of high heat flow coupled with the search to understand its mechanism. It should be remem- bered that high heat flow does not automatically lead to high underground temperatures. The high heat flow belt may be more accurately described in three dimensions than in one dimension. However, over a limited range of depth and in regions removed from heat refraction, a one dimensional extrapolation may be reasonably valid. The one dimensional modelling has been carried out analytically as a series of steps. The derivations of the equations used are given in Appendix V. Stage 1 Fig. 5.7 illustrates the simplest form of extrapolation, where thermal conductivity and heat flow are constant in depth. 120mWm-2 was considered a likely heat flow for the centre of the Carnmenellis pluton, whilst the thermal conductivity of 3.33Wm-1K-1 represents the arithmetic mean of the Carnmenellis determinations. This simple model yields a standard with which to compare other models. Stage 2 In Chapter 4 models of the distribution of the radiogenic elements were considered. Stage 2 considers the case of constant heat production whilst Stage 3 considers an exponential decrease in the distribution of radiogenic elements with depth. The surface heat production of 3.9yWm-3 represents the mean of 54 samples from the Carnmenellis granite. Stage 4 In Chapter 3 the variation of thermal conductivity as a function of temperature was considered. The recipro- 198

cal relation K = A/T + B was used in the calculation of Stage 4. Two possible lines were considered, one using values for the constants A & B, for the Barre granite and the other for the Westerly granite.(Birch & Clarke 1940). These two relations were thought to represent approximately the likely limits of the relation within granites. As seen from fig. 3.16 Chapter 3, the Cornubian granite follows more closely the Westerly granite trend than the Barre. Stage 5 This combines the consideration of variation in thermal conductivity with a constant heat production. Stage 6 considers variation in thermal conductivity with an exponential decrease of heat productivity with depth. Stages 5 and 6 are the most probable of the models, since they consider all the measured physical parameters. Table 5.3 lists approximate extrapolated temperatures at selected depths based on the Stage 2 equation:

T T + qoz - Aoz z = o (5.1) k0 2k0 where Tz = extrapolated temperature at depth z To = surface temperature = 10°C qo = heat flow, corrected for topography and recent climate only (corr A). z = depth in km kc = surface thermal conductivity 2.50Wm-1K-1 for country rock boreholes 3.33Wm-1K-1 for granite boreholes Ao = surface heat production = 2.0pWm-3 for country rock boreholes = 4.49»Wm-3 for granite boreholes This equation was chosen for consistancy with other researchers (Haenel et al. 1980). Temperature maps based on these figures are presented in Appendix V. The problem of heat flow and heat production within south-west England is a three dimensional one. It is be- TABLE 5.3 APPROXIMATE EXTPAPOLATED TEMPERATURES FROM SOUTH WEST ENGLAND HEAT FLOW MEASUREMENTS

Extrapolated temperatures in degree centigrade Code Borehole Name Heat Flat. K0 0.5km 1.0km .1.51cn 2.0km 2.51m 3.0km 5.0km CM-A Grillis Farm 112.9 3.33 27 43 59 75 91 106 163 CM-B Polgear Beacon 121.7 3.33 28 46 63 80 97 114 176 CM-C Medlyn Farm 113.6 3.33 27 43 60 76 91 106 164 CMD Trevease Farm 111.9 3.33 27 43 59 75 90 105 161 CM-E Trerghan Farm 112.9 3.33 27 43 59 75 91 106 163 BD-A Braydown 113.4 3.33 27 43 60 75 91 106 163 BD-B Blackhill 119.0 3.33 28 45 62 79 95 111 172 BD-C Pinnockshill 120.7 3.33 28 46 63 80 96 113 174 BD-D Browngelly 108.4 3.33 26 42 57 72 87 102 156 BD-E Gt Hammet Farm 118.8 3.33 28 45 62 79 95 111 172

LE-A Newmill 123.8 3.33 28 47 64 82 99 115 179 LE-B Bunker's Hill 123.9 3.33 28 47 64 82 99 116 179 SA-A Tregarden Farm 125.8 3.33 29 47 65 83 100 117 182 SA-B Colcerrow Farm 126.5 3.33 29 47 65 83 101 118 183

DM-A Winter Tor 107.4 3.33 26 42 57 72 86 101 154 DM-B Blackingstone Quarry 105.5 3.33 26 41 56 71 85 99 152 DM-C Soussons Wood 132.2 3.33 30 49 68 87 105 123 192 DMD Laughter Tor 114.2 3.33 27 44 60 76 92 107 165 UI-F Foggin Tor Quarry 110.9 3.33 26 43 58 74 89 104 160 CDD-1 Old Merrose Farm 79.2 2.50 26 41 57 72 87 101 158 CDD-2 I

Extrapolated temperatures in degree centigrade Borehole Name Heat Flow Ko 0.5km 1.0km 1.5km 2.0km 2.5km 3.0km 5.0km

Longdawns 111.7 3.33 27 43 59 74 90 105 161 Rosemanowas-A 105.5 3.33 26 41 56 71 85 99 152 Rosemanowas-D 106.4 3.33 26 41 56 71 86 100 153 Troon 122.7 3.33 28 46 64 81 98 115 177 Hererdon DDH-H23 107.9 3.33 26 42 57 72 87 101 155 White Hill Yeo 139.4 3.33 31 51 71 91 110 130 203

Bovey Tracey 94.6 2.50 29 47 66 84 102 120 189 Meldon 114.1 3.33 27 44 60 76 91 107 165 Newlyn East-1 104.6 2.50 31 51 72 92 112 132 209 Newlyn East-4 101.6 2.50 30 50 70 90 109 128 203 Belowda-1 113.3 3.33 27 43 60 75 91 106 163 Belowda-2 85.5 3.33 23 35 47 59 70 81 133 Predannack Down 61.5 2.50 22 34 46 58 69 80 123 Kennack Sands 73.1 2.50 25 39 53 67 81 94 146 Cannington Park 45.1 2.50 14 28 36 44 53 61 90 Currypool Farm 60.7 2.50 22 34 46 57 68 79 121

Geevor 128.6 3.33 29 48 66 85 102 120 186 South Crafty 128.9 3.33 29 48 67 85 103 120 187

Wheal Jane 125.2 3.33 29 47 65 83 100 117 183 Wilsey Down 67.3 2.50 23 37 49 62 75 87 135 Honeymead 54.0 2.50 21 31 42 52 62 71 108 North Molton 55.3 2.50 21 32 42 53 63 73 111

201 yond the scope of thesis to attempt to model the structures in detail. With the current increase in the use of computers, there has been an apparent shift in scientific method. In geophysics it would appear that the final aim is to fit the observed results into a mathematical framework. This framework can then be used to obtain educated guesses or predictions. Most of the modelling discussed here was not done to build such a mode]. In this instance modelling has been used to investigate mechanisms. For this reason all the modelling is as simple as possible yet is as accurate as the method will allow. Care has been taken to remove mathematical noise which might confuse the mechanism. The first consideration was to determine the effect of the boundary between two rocks of different conductivity. At this stage it became apparent that the boundary conditions play an important role. However, in the simplest form, as shown by Fourier's Law, if the gradient is the same either side of the boundary, then there must be a different parallel heat flow on either side of the boundary.

Fig. 5.12 Sketch to illustrate heat flow parallel to a boundary. o 0 C

dx K B

T dO -21; - KB dx

0+d0°C

A flow of heat at 900 to the boundary will cross the boundary,ea a rod in a vacuum.

202

Fia. 5.13

KA KB

qA qB By conservation of energy

qA = KA d9A dx d8B qB KB dx Sketch to illustrate heat flow perpendicular to a boundary.

The development of computers has allowed the solution of numerical results by finite difference methods. The use of such a method was first described by Mundry (1966) in the solution of the temperature field due to a buried salt dome. A quadratic grid was used. By using an axial- ly symmetrical model, only half the grid points need be calculated. The central line acted as a mirror plane. No heat is permitted to cross the boundary but may be reflected by it. The second vertical boundary was assigned values which represented a fixed undisturbed gradient and in theory should have been at ao . In practice, this boundary was placed at a distance away from the central section where the horizontal heat flow was small. Using this method Model 1 was calculated. It demonstrated the heat flow refraction effect due to a contrast in thermal conductivity, the same effect as that demonstrated by Mundry for salt domes. A serious consequence of this refraction effect is that only boreholes in homogeneous or flat lying media will = 2.5 NWm 3 A Heat flow level in an infinite batholith Heat flow level / / / -1 K 2 -1 Wm I 3.33 75mWm =386 pWm'3 A K= Axial symmetry

8 27 30 2 i i 3.3 30 2.7 2.8 EFFECT OF COUNTRY ROCK THERMAL CONDUCTIVITY ROCK THERMAL EFFECT OF COUNTRY 3 Wrr }~

-25 A

110

-100 -120

- -130

Nea t t ow ow f. E (V Ul E E

Effectof countryr ockth ermalc onductivity. 204 give reliable heat flow results. Boreholes drilled for oil exploration will be particularly suspect, as these holes will normally be carefully sited to intersect oil traps in anticlinal structures and are often close to, or above, salt structures. The size of the effect will depend on the contrast in conductivity and the geometry involved. Simmons (1967) demonstrated that contrasts in heat production give rise to heat flow anomalies. "Temperature satisfies Laplace's equation, so it is possible to use the same techniques to analyse heat flow data for the steady state contrasts in heat production, as are used in the interpretation of gravity and magnetic anomalies" (Simmons ibid) . This theory was applied by Tammemagi & Wheildon (1974) to correct for the effect of the edge of the granite. The size of the gravity anomaly was used to estimate the loss of heat into the country rock. The effect of heat production contrasts can be modelled numerically in a finite difference model, since this is simply a method of solving Poisson's equation in a finite medium. In order to study contrasts in heat production and thermal conductivity in the same model, the two were combined by solution of Pois- son's equation for the flow of heat.

v (KVT) + S = 0 (5.2)

VT2 = -S/K (5.3) (see Appendix VI for details of equation used.)

Using these equations a model was constructed. The model was scaled so that the heat flow, thermal conductivities and heat productions could be input directly in SI units. A scale factor DX was used to represent the grid point spacing in metres. The model represents the steady state heat flow. Surface heat flow was calculated from 205

the formula.

z Tz = To + K - Az2 (5.4) 2K

Surface heat flow q 0

go = T1K + A DX (5.5) DX 2 where A is heat production K is thermal conductivity

The results of this model are presented as a series of surface heat flow profiles, calculated for a set of different country rock thermal conductivities. The refraction effect, due to the contrast in conductivity, causes a temperature trough in which the excess heat, due to high concentrations of radiogenic elements, is retained. Only when the temperature in the granite exceeds that of the country rock will heat flow from the granite to this rock. This will only occur when the ratio of the two heat flows is the same as the ratio of the thermal conductivity values. The important consequence of this phenomenon is, that near the surface, heat flows may suddenly change from one value to the next, according to the thermal conductivity. In general terms the earth will try to keep an even temperature gradient rather than an even heat flow. There is, however, only a finite quantity of heat available, so this limits the degree to which the even gradient is obtained. Unless there is a high contrast between the country rock and the granite, it is unlikely that this refraction effect would cause the high heat flow anomaly observed. However, if combined with relatively high heat production, then an effective mechanism may exist. An inverted funnel- shaped intrusion would enhance the effect, since heat produced within the wide part of the intrusion would tend to channel up the high conductivity region. These refraction o ~• p, '0 o EFFECT OF COUNTRY ROCK THERMAL CONDUCTIVITY CD H MODEL II H Ul . • — tao H 16~ ~t6 Ul Eff —120 20 — — 2-0 e. Heat flow level in an infinite batholith E 0 ect 101(m E 24 2.4 Horizontal Scale 3 28 2.8 0 —100 of 3.33 3.33

c 2.8 28

ou — HO 2.4 2-4

nt 20

r 16 16

y 50

r Axial symmetry ock th COUNTRY ROCK \ GRANITE COUNTRY ROCK er A=446pWm'31 mal A.2.OpWm 3 N A_2OpWrn3 K°333Wm K \ co nd A. 0.9pWm 2 K=2.4 Wm 1K'1 ucti vi t

y 25mWm 2

207

z 0

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tL_

IQI IV / 440 5 - 1' 0 4 4::# (a) — —

Figure 5.16 L) a 206

effects can only work effectively in relatively small intrusions, where the deptl, of the high conductivity region is of a similar order to the width of the intrusion. Ani- sotropy of the country rock would also enhance the effect, if the highest thermal conductivity direction slants upwards towards the granite intrusion. An intrusion will also exhibit a second refraction effect at its base. Model II was constructed to investigate this effect. The temperatures beneath an area of high conductivity are lower than those in the region beneath an area of low conductivity. Thus the lower crustal heat will tend to converge towards the base of the batholith, in this way the contrast in thermal conductivity acts as a lens.

Fig. 5.17 T t rTTrrTTTT r r r I l / Jlll Il\\ \ 1 1 ////1\\\\ TT t ff Sketch to illustrate heat flow concentration in a funnel- shaped intrusion of high thermal conductivity.

All of these mechanisms are likely to be active to a greater or lesser extent in the Cornubian batholith. The constituent parts need to be quantified in order to determine whether they are sufficient to explain the anomaly or whether there is still a hidden mechanism 209

Variation in heat flow may be interpreted as being due to variation in crustal heat production. Richardson and Oxburgh (1979) have correlated heat flow (gomWm-2) with the heat production (A0pWm-3) of rocks sampled in boreholes throughout the U.K. where there are either granites or low grade cleaved rocks:

qō 27 + 16.6 Ao (5.6)

Correlation coefficient = 0.96 The surprising result of this apparently linear relationship is that the same regression would fit qo - Ao observations in both granite and slaty basement. This was interpreted as indicating that both rock types have the same vertical thickness of 16 - 4km. These rocks might then overlie a lower crust of denser rocks depleted in radiogenic elements. Fig. 5.18 illustrates the regression obtained. On the same axes, results from the Cornubian granite batholith have been plotted. At first sight, there is little correlation within the batholith. However, it is of interest to note, that most of the results fall above the regression line whilst the Dartmoor results cluster close to and below the line. (Except Dartmoor-C which is partly water disturbed.) One might interpret this distribution in several ways. The smaller granite outcrops may well be underlain by over 16km of granite or perhaps the buried granite is more radiogenic. This distribution is, however, what would be expected if heat flow refraction is playing a significant role in an area of already high heat productivity. The small outcrops should give higher heat flow, whilst the Dart- moor granite would possibly be too large to show an apprec- iable refraction effect. In the interpretation of heat flow, it is important to note that locally it is the temperature field that seeks 210

G SA-Ax S4-B x o A LE-B E-a BD-Co +CM-B BD-EC OBD-E

CM-C CM-A BD-4 } CM-D }t LongOOwrs+ 'i' CM-E ❑DM-E BD-D'O ❑DM-A DM-B 0

Ga∎eriyarl x

ROokhooe•

HEAT FLOW (corr. A )

versus

HEAT PRODUCTION

Heat Generation 10-6 Wm-3

Figure 5.18 Heat flow (correction A) versus heat production. 211

equilibrium and not the heat flow. However, the degree to which temperature equilibrium is possible is governed by the available heat. 212

6. CONCLUSIONS

The use of relatively shallow boreholes as a means of measuring terrestrial heat flow is a controversial issue. It is apparent that, unless considerable care is taken, misleading results will be obtained. In a very deep borehole it is possible to gain an indication of the reliability of the measurement by comparing heat flow determinations of different units within the same borehole. A second advantage with deep boreholes is the ability to probe beneath the effects of recent climatic changes (though not the ice ages). Thus, there is some advantage in using as deep a borehole as possible to obtain the most reliable results. However, even a deep borehole may give confusing values. Drilling is akin to betting. Is it better to place a large stake on one horse or to spread many small bets on twenty horses? The answer must surely depend upon the particular circumstances. By sup- porting the study of relatively shallow holes it has been possible to make use of several boreholes drilled by the I.G.S. and mining companies. The use of several shallow boreholes has given an insight into the mechanisms giving rise to the thermal anomaly. As development starts, providing sufficient time is available for the deep development boreholes to bP accurately temperature logged, it will be possible to upgrade and improve the results already obtained. It should be possible, with several deep boreholes, to interpret more accurately the role of climatic change. This would not be the case for one deep borehole. Once a deeper development borehole was drilled on the same site, the original exploration hole would be of no further use. One could therefore suggest that the geothermal investigations might be considered in three stages: 1). Measurement in deep boreholes drilled for 213 other purposes, to give the regional heat flow field and to establish the climatic effects. 2). Several 100-150m boreholes to paint in detail and suggest the most economic sites to give establishment of mechanism and physical properties. 3). Detailed modelling then deep extraction trial studies combined with detailed terrestrial heat flow measurements in same holes, to prove geothermal reserves. The depth of drilling will be dependent on many factors, primarily this will be controlled by the availability of finance for experimental work. However, the use to which the geothermal energy is to be put is possibly a more important consideration. Likely temperature depth extrapolations are given in fig. 5.10 Higher geothermal gradients are encountered where the batholith is buried beneath a cover of insulating sediments, such as at Bodmin (Callywith Farm). Perhaps a more important consideration would be where the heat might be used. In this context the main centres of habitation and industry should be considered. Several uses, such as space heating, will be most suited to areas where housing estates and factories are developing. The existence of a geothermal resource should hopefully attract industries hungry for energy to an area where unemployment is currently a problem. Electric power generation would be best suited to positions where the highest underground temperatures exist. One area I would suggest as of particular interest to a pilot study would be St. Austell. This town is the centre of a thriving china clay industry. China clay is mined by use of high pressure water jets. The kaolin is separated by a system of settling tanks and then pressed and dried in massive quantities. A host of possible uses exist for large quantities of hot or even warm water. China clay does amount to one of England's large exports. The monumental stone area on the St. Austell granite 214

outcrop would appear to be a good site for a deep borehole. In this study the two highest heat flows were determined for this region. This area is close to the china clay industry where considerable expertise in pumping and granite geology exists. There are well equipped work- shops and heavy plant close at hand. From the environmental point of view this is an area of mining and quarrying where blasting, drilling and pumping has become a way of life for over a hundred years. In this area a geothermal pilot scheme could have only minimal impact on the environment. Disused stone quarries exist in the area and there is also much land owned by the clay industry. In this area uses could be found for water over a range of temperatures. Should electric power generation prove possible, there is a ready market and a complicated power distribution network exists close to the Garevigan borehole to the north of the granite outcrop. The Carnmellis granite has some practical advantages since it is, so far, the most closely studied outcrop. All the experimental extraction work has so far been carried out on this outcrop. The granite in this region is relatively free from geological complications, though it does not represent the highest gradients. For low temperature uses, such as agriculture etc, the Hot Lode (Fox 1822) and thermal waters, found in the mines, might be investigated more fully, since they occur at relatively shallow depths and might prove economic as a source of heat for greenhouses or fish farms. The consistently high heat flow, observed over the entire granite batholith, can leave little doubt that there is a significant heat flow anomaly in south-west England. Previous studies suggested that the high heat flow, observed within the mines of Cornwall, might be attributed to a convective water flow within the fissure system of the mineralized belt (Tammemagi & Wheildon 1974). The 215

COMPARISON OF HEAT FLOW DATA FROM SOUTH-WEST ENGLAND WITH EUROPEAN DATA

14 s Histogram of South-West England

ion 12 Heat Flow Data (corrected for Topography t

a and Recent Climate only) v 10 BorehoJes in granite 8 Boreholes adjacent to granite

bser 3 Boreholes in country rocks

f o 6

o 4 ber m Nu 20 40 60 80 100 120 140 160

280- Histogram of European Heat Flow Data for Land and Sea Cermāk (1979) 240-

U p200- c0 t) 160- .oO

o 120- L

E 80- 2

40-

T 20 40 601 80 100 120 140 160 Heat Flow (mWm2 )

Figure 6.1 Comparison of heat flow data from south west England with European data. 216 uniformity of the heat flow anomaly, even at sites remote from the mineralized belt, suggest that convective trans- port is not a significant mechanism. High measured concentrations of natural radiogenic elements give rise to a relatively high heat production within the granite. This high heat production, coupled with a measured contrast in thermal conductivity and the likely space form of the batholith, has been demonstrated to be the probable mechanism of the observed thermal anomaly. 217

Appendix I Heat Flow Plots

This appendix contains summary plots of the date and results obtained for each borehole studied. The units are, in most cases, clearly defined.

Heat flow mWm-2(ie10-3Watts per square metre) Heat production...pWm-3(10-6Watts per cubic metre) Temperatures degrees centigrade -1 Thermal gradient Kkm (Kelvin per 1000metres) Thermal conductivities Wm-1K-1(Watts per metre per Kelvin) The corrections for topography and palaeoclimate are expressed as the percentage of the corrected value.

correction - corrected heat flow-heat flow before correctx100 fully corrected heat flow

The national grid reference appears at the top of the right hand column.

Summary Station Name Plot No. 1.1 Grillis Farm 1.2 Polgear Beacon 1.3 Medlyn Farm 1.4 Trevease Farm 1.5 Trerghan Farm 1.6 Bray Down 1.7 Blackhill 1.8 Pinnockshill 1.9 Browngelly 1.10 Gt Hammet Farm 1.11 Newmill 1.12 Bunker's Hill 218

Summary Station Name Plot No. 1.13 Tregarden Farm 1.14 Colcerrow Farm 1.15 Winter Tor 1.16 Blackingstone 1.17 Soussons wood 1.18 Laughter Tor 1.19 Foggin Tor 1.20 Merrose Farm 1.21 Kestle Wartha 1.22 Callywith Farm 1.23 Gaverigan 1.24 Longdowns 1.25 Rosemanowas A 1.26 Rosemanowas B 1.27 Troon 1.28 Hemerdon 1.29 Hemerdon 1.30 White Hill Yeo 1.31 Bovey Tracey 1.32 Meldon 1.33 Newlyn East - 1 1.34 Newlyn East - 4 1.35 Belowda Beacon - 1 1.36 Belowda Beacon - 2 1.37 Lanivet 1.38 Predannack 1.39 Kennack Sands 1.40 Cannington Park 1.41 Currypool Farm ENGLAND FLOW v S.W. P R I L L I S F A R IMPERIAL COLLEGE LONDON TEMP TORE CONDUCTIVITY LITHOLOGY E SW 6796 3846 11 ) D 12 13 2.8 1 3./0 'D3 2'K '3).4 , , , I I , ,

0 MEAN GRADIENT 10 \ 0 0 =27.9 DEG/KM 0 20 \ 0 MEAN CONDUCTIVITY \ 0 \ 0 =3.30 W . /M .OEG . 30 0 HEAT FLOW (UNCORRECTED) -2 t4 ° =92.2 M W.M 40 0 ° HEAT PRODUCTION 0 GRANITE = w 50 0 =4.5 10-6.14 .M-3 o_ ° LLJ w ° ° z fi0 °° CORRECTIONS

0 2.3 70 0 °° CLIMATE 20.8 0 80 El

0 ° CORRECTED 90 ° ° HEAT FLOW 100 ° ā = 1 19 .9 MW.m 2 PLOT 1

._ 0 0 S.W. ENGLAND PERT EL GEOPHYSICS DEPRRTMN1 P IMPERIAL COLLEGE LONDON TEMiP TURE CONDUCT I V I TY LI THOLOGY n ~` (W./M.DEG.K.I 5927 3553 10 11 12 SW i 1 1 3.01 I3.5 14.0

10 \ ME RN GRADIENT \ \ = 29.8 DEG/KM 20 `\ MEAN CONDUCTIVITY =3.38 W./M.DEG. 30 \ HEAT F L OW t UNCORRECTED l \ + + ° ° = 100.6 Mh. M-2 40 + ° -. 0 HEAT PRODUCTION =,r) ° GRANITE 6 -3 1__w 50 -+\ ° =3 . 8 10 •W •M cr CI_ 4\ ° W w t 0 60 ° +\ 0 0 CORRECTIONS Y. 70 +° TOPOGRAPHY 2 .9

ō CLIMATE 18.9 ° 80 ° RRI \I\ECT - I 90 ° ° ° HET FLEA 100 \ :0 ° = 1 28o6MW.M 2 PLOT 2

G-O. ENGLAND HRT FLOW GEOPHYSICS DEPARTMENT `` i- Y E A R v IMPERIAL COLLEGE LONDON TEM(oB3g Ill) RE CONDUCTIVITY L I THOLOGY (W./M.DEG.K.1 S W 11 12 13 14 3.0 3.5 4.0 SW 7083 3404 l I I I , I I I

10 ` o MEAN GRADIENT ° a =29.9 DEG/KM 20 \ a a MEAN CONDUCTIVITY \ 0 =3.29 W./M.DEG. \ in 30 \ + a HEAT FLOW [UNCORRECTED) -2 \ \+ =ō =98.3 MW. M 40 \+ 0 HEAT PRODUCTION 3 0 GRANITE =3.4 ~w 50 10-6 .W.M_ ~~ a a u_, W 4

° 60 °° CORRECTIONS '/. a0 TOPOGRAPHY 1.2 70 +~ ° 0 CLIMATE 17.2 0 80 in 001 :DRRE: TEI 90 0 °° HEAT FL~ A 1 00 a a° - 1 2 0 a 6 M k. rī 2 PLOT 3 f S.W. ENGLRNO HEAT FLOW GEOPHYSICS DEPARTMENT T R - V S H V IMPERIAL COLLEGE LONDON TEMP ERATURE CONDUCTIVITY LITHOLOGY I.CDEG 2.K.3).a SW 7 185 31 80 11 12 13 2.6(~3'/~•DG ti ° MEAN GRADIENT to ` 0 \ 0° :27.9 DEG/KM 20 \ 0 MEAN CONDUCTIVITY \ \ 0 0 =3.28 W./M.DEG. in 30 +\ ° HEAT. FLOW (UNCORRECTED) ° ° = 91.5 M W . M 40 °° HEAT PRODUCTION _0 0 GRANITE H-w 50 ° :3.8 10-6 .N.M-3

w w ° o z so ° ° CORRECTIONS

El0 TOPOGRAPHY 2.1 70 0 0 CLIMATE 20.9 ° 80 °

0 0 CORRECTE

90 ° ° ° HEAT FL3A - 0 100 ° o = 1 18.8 MW. M2 PLOT 4 T n I I fH S.W. ENGLAND HEBT FLOW ~K\ GEOPHYSICS DEPARTMENT -R F \ FRP1 IMPERIAL COLLEGE LONDON TEMpogfTURE CONDUCTIVITY LITHOLOGY SW 7353 3033 11 12 13 3.0 ;J.ppEG23.4 1 3.6 < I I I

MEAN GRADIENT 10 ` a a a =29.2 DEG/KM 20 \ a MEAN CONDUCTIVITY \\ °° =3.24 W./M.DEG.

30 \+ ° ° HEAT FLOW tUNCORRECTEDI \+ ō .794.5 MA. M-2 40 a ° HEAT PRODUCTION ° GRANI T E H w 50 a =4.4 10-6.W.M-3 ( a ,,_, a 'Li, D s0 ō CORRECTIONS a ° TOPOGRAPHY 0.1 70 a a CLIMATE 21.0 a 80 a a ° C3RRE2T`7 90 0 a a ° PT FLOA 100 a a - 1 19.7MA.M 2 PLOT 5 S.W. ENGLAND HEAT FLOW GEOPHYSICS OEPRRTMENT B R ^ I D O A \ IMPERIAL COLLEGE LONDON TEMPERATURE CONDUCT I VI TY L I THOLOGY SX 1907 8177 10 11 12 3(. ./M :9EG .K4 1 3.6 ` , I l I 1 I 1 ` ° ° MEAN GRADIENT 10 ` + o '+ ° 7-26.7 DEG/KM \+ ° 20 \+ 0 MEAN CONDUCTIVITY \\+ °° =3.33 W . /M .DEG . 30 \+ 0 HEAT FL OW( UNCORRECTED 1 M-2 ° ° = 88.9 M W . 40 0 ° HEAT PRODUCTION ° GRANITE -3 50 0 ~ =5.2 10 s.W .M 1_ ~ w w ° so 0 ° CORRECTIONS ° TOPOGRAPHY 4.9 70 0 0 0 CLIMATE 21.1 0 80 0 0 CORRECTE: 90 o 0 HEAT FL E A 100 = 1 20 .2 MW.M 2 PLOT 6 B +` R ~/ G•O. ESI CSND PART FLOW GEOPHYSICS DEPARTMENT It ./ 1~ I IMPERIAL COLLEGE LONDON TEMIP0W.I TIURE CONDUCTIVITY LITHOLOGY SX 1835 7820 10 11 12 2.813 .0 M,.(gG3.4.'3.6 1 1 1 I I \ " 0 + 0 MEAN GRADIENT to ° + ° =28.B DEG/KM + ° 20 `+ ° MEAN CONDUCTIVITY

+\ ō =3.37 W./M.DEG.

30 + 1F ° 0 HEAT E l_ OW I UNCDRRECTED ) ° 2 4-\+ ° =97.0 MW.M 40 ° 0 HEAT PRODUCTION -6 -3 =w So ° ° GRANITE =3.1 10 .N .M c ° Li w ° 60 ° ° CORRECTIONS ° ° TOPOGRAPHY 2.9 70 °° CLIMATE 20.1 ° 80 ° o :O ARE TEH 90 0 H - AT =LDA 100 0 0 0 PI - 126 .0 Mt.M-2 PLOT 7

S.W. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT P I\` 02' S H I L L IMPERIAL COLLEGE LONDON TEMP RR TORE CONDUCTIVITY L I THOLOGY t D G'.~ ~ 1 ./M S X 18927450 10 IF 13 24 :OppEG3K2 1 3.4 I II I I 0 ° MEAN GRADIENT 10 ` + °

+ 0 ° =33.7 DEG/KM 20 " + ° MEAN CONDUCTIVITY \ \ +ō =3.05 W./M.DEG. 30 \ + 0 ° HEAT FLOW ( UNCORRECTED 1 \ 4 =ō 1 02 .9 M W. M 2 40 + 0 ° HEAT PRODUCTION °° GRANITE =w so ++~ =3.5 10-s.W.M-3 Ce + 15 w W + ° C) so + ° ° CORRECTIONS ° TOPOGRAPHY 2.8 70 ° °° CLIMATE 16.5 ° B0 0 90 ° ° 2:RRECTEI 0 ° ° HEAT FLS A 0 100 ° - 127.5 Mk.m 2 PLOT 8 S.W. ENGLAND HERT FLOW GEOPHYSICS DEPARTMENT B IMPERIAL COLLEGE LONDON TEM(oURTURE CONDUCTIVITY LITHOLOGY (W./M. EG.I SX 1924 7247 10 1l 12 3.2 3.4 3.6 3.8 1 1 1 t I

MEAN GRADIENT Io \` 0 0 =25.7 DEG/KM + 0 20 \ + ° MEAN CONDUCTIVITY \ 0 \+ 0 =3.39 W . /M .DEG .

30 \\+ 0 0 HEAT FLOW (UNCORRECTED) -2 °° = 87.1 M W. M 40 0 HEAT PRODUCTION

° GRA N IT E w so ° = 5 .0 10-6. W . M-3 a_ ° W w 0 ° 60 0 CORRECTIONS 0 0 TOPOGRAPHY 2.9 70 0 0 CLIMATE 21.6 0 80 ° 0 0 __, \_, T E ~: 90 °° 0 -EAT FA A 0 l00 ° ° I: 11504M 2 PLOT 9

S.W. ENGLRND HERT FLOW GEOPHYSICS ENT 3 N R M V -V T T FRR' IMPERIRL TEMAMTURE CONDUCTIVITY LITHOLOGY cc cki3. .D G2K.3).4 `)X 1885 6986 10 11 12 13 2.8 0 I 1 1 1 I 1 1 ° ° MEAN GRADIENT 10 \ + ° + ° =30.3 DEG/KM + ° 20 \+ ° MEAN CONDUCTIVITY \~. °° =3.23 W./M.DEG. 30 t+ °° HEAT FLOW (UNCORRECTEOI \+ ° =97 .7 MW.M 2 40 ° ° HEAT PRODUCTION ° GRANITE w 50 0 =4.3 10-6 .W.M-3 x 0 W w ° 60 °° CORRECTIONS ō TOPOGRAPHY 2.9 70 ° ° CLIMATE 19.3 ° 80 ° M 22RRECTEI

90 ° °° --- EAT FL] A 100 ° M ° = 125.6 M W. rī 2

PLOT 10

S .W. ENGLAND HEAT FLOW V GEOPHYSICS DEPARTMENT \E /\ I L L :,RRRY IMPERIAL COLLEGE LONDON TEM(opF TORE CONDUCTIVITY L I THOLOGY (W./M.DEG.K.) SW 1 4 60 0 3 4 3 11 12 13 4 2.5 3.0 3.5 1 1 1 11 1 1 t 0 0 MEAN GRADIENT 10 \` + ° 0 ` *+ 0 =30.5 DEG/KM 20 - 0 MEAN CONDUCTIVITY 4, 0 0 =3.35 W./M.DEG. 30 ++ ° a ° HEAT FLOW I UNCORRECTED I 0 =102.7 M W.M 40 a 0 HEAT PRODUCTION 2u) TE 50 0 © GRAN I =4.9 I0-6 .W.M-3 a_ ° W 11-J C7 D 60 0 CORRECTIONS °° TOPOGRAPHY 2.9 70 ° 0 CLIMATE 18.5 0 80 a m CCRRECTE: 90 a ° HE AT FL DA 0 100 0 = 1 30 . 7 MA.M 2 PLOT 11 IL L S.W. ENGLAND HEBT FLOW GEOPHYSICS DEPARTMENT B,\/ERS FH IMPERIAL COLLEGE LONDON TEM(PERRTURE CONDUCTIVITYW/ L I THOLOGY 31~. )3.8 Sw 14020273 14 3.0 (3 .2M3.D4EG 1! 12I 13

MEAN GRADIENT 10 `+ ° 4\ ° =30.8 DEG/KM +\ ° 20 +" °° MEAN CONDUCTIVITY +\ a =3.40 W./M.DEG. 30 ± ° ° ° HEAT FLOW (UNCO2RRECTED1 4. 4 ° = 104 .5 M W. M 40 ° a HEAT PRODUCTION -6 o ° GRANITE R A N I T E 10 W M-3 = SD =5.2 a_ r ° ~, U-1 ° o 60 ° ° CORRECTIONS ō TOPOGRAPHY 1.5 70 °° CLIMATE 18.6 ° 80 °

0 C :RR-CTE 90 °

in F' HERT FL3/\ ° 100 ° _. 130 .9 MW.M 2 PLOT 12

S.W. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT \ .,PRAY IMPERIAL COLLEGE LONDON TEMIDI TURE CONDUCTIVITY LITHOLOGY SX 2055 0592 11 12 13 14 2.SW./3.0EG.3..6 O \ + a MEAN GRADIENT 10 a a = 33.0 DEG/nM \+ a 20 \+ a MEAN CONDUCTIVITY CD \+ a =3.20 W./M.DEG. 30 HEAT FLOWIUNCORRECTEDI = 105.8 Mii. M 2 40 HEAT PRODUCTION _(JD GRANITE -3 ~ w 50 = 3.5 I 0-6.14 M

W w cl ' 60 a a CORRECT IONS 7. a a TOPOGRAPHY 1.7 70 CLIMATE 18.5

80 a a "- ORRE:TE 90 a O ERT FLO A a] 100 -2 a 132.6m A.M

PLOT 13 S.W.ES CSNDTEPAR GEOPHYSICS DEPARTMENT F--\ P :'f- P R0A FAR -IMPERIAL COLLEGE LONDON TEM(oRQTURE CONDUCTIVITY LITHOLOGY (W./M.DEG.K.) S X 11 12 13 14 3.0 3.5 4.0 2068 0576

to ` + ° ° MEAN GRADIENT \++ 0 ° = 30.7 DEG/KM 20 - ō MEAN CONDUCTIVITY t ° = 3.35 W./M.DEG. 30 ° o HEAT F L OW ( UNCORRECTED I t\+- °~ = 102 .8 MA.M-2 40 ° ° HEAT PRODUCTION a GRANITE X4.8 10- -3 = w so 6 .W .M a_ , ° wW 60 °° CORRECTIONS El TOPOGRAPHY 4.1 70 0 0 CLIMATE 18.8 ° 80 o

°° C]RRESTEI 90 ° ° HI AT FL_A 100 m 0 — 1 3 3 4 Mk .M 2 PLOT 14 S.W. ENGLAND t1EaT FLOW GEOPHYSICS DEPARTMEN1 ~I \TEP TSR IMPERIAL COLLEGE LONDON TEM1ō,~TIURE CONDUCTIVITY LITHOLOGY S X 6 1 1 r7 91 5 (3 9 10 3 .0 3 2 Dt G4

MEAN GRADIENT 10 = 24 .5 DEG/KM

20 + MEAN CONDUCTIVITY +\ +\ =3.2.1 W./M.DEG. 30 NEAT FLOW (UNCORRECTED I = 78.6 Mn.M-2 40 a HEAT PRODUCTION GRANITE SO =5.7 10- .W.M 3 2~ LU u~ O 60 CORRECT IONS TOPOGRAPHY 70 CL_ I MATE

@0 CCiFHELTELL] 90 a a a HET FLOA a 100 a 11402Mh.rī

PLOT 15

B L .--\ T \ G 5 T S.W. ENGLAND HEAT FLOW GEOPHYSICS DEPART MENT 1 I 0 \ 1- IMPERIAL COLLEGE LONDON TEM( F~~ fT~JRE CONDUCTIVITY LITHOLOGY (W./M.DEG.K.~ SX 780 8593 9 10 1 1 3.0 3.5 4.0 I .

MEAN GRADIENT to ` °o +` 0 =27.6 DEG/KM -f\ ° 20 +\ 0 MEAN CONDUCTIVITY 4' °° =3.10 W./M.DEG. • 30 -k °° HEA1 FLOW(UNCORRECTE0) + ~ 0 =85.5 MW.M 2. 40 + ° 0 HEAT PRODUCTION .6 _ ~~ so ° ° GRANITE I TE = 4 .9 10 W M 3 a_ ~- ° UJ w 0 ° 60 0 ° CORRECTIONS 0 TOPOGRAPHY 3.5 70 ° ° ° CLIMATE 20.4 ° 80 0 0 ° :OR=RECTE I 90 ° ° ° HEAT FL]A ° 100 Q = 112.4MW.r12 PLOT 16

S.W. ENGLHNO HEW GEOPHYSICS DEPPIRTMENT 1OPERIPL COLLEGE LONDON

TEMPi oUTURE CONDUCTIVITY L I T H OL O Li W./M.DEG..1 " X '1 3 '7 9 10 11 12 2.5 3.0 3.5 L_

MEAN GRADIENT 10 ."2 DEG/KM

20 MEAN CONDUCTIVITY + 0 73.15 ./M 0 30 0 HEAT FLOW uNcoRRFc -f ED; 0 [9 4 MN. m. 40 [D 0 HE AT PRODUCTION In (r) 50 ID 5 .0 10-6 .k 0 GRANITE u_ F- + \ LLJUJ + \ ILl 60 + \ ID [D CORRECT I ONS + \ 0 TOPOGppPHy 70 ID CL I MATE In 80 ID

ID -■'RECTE- 11 90

[T3 HHUI L....) 100

(Li 3 g PLOT 17 ____ G •O • ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT LP, 73 - TER T IMPERIAL COLLEGE LONDON TEM(DV.Ir1URE CONDUCTIVITY LITHOLOGY 1M.DEG.K.1W./ SX 65627549 9 10 11 2.5 3.0 3.5 i 1 0 +` 0 GRADIENT le \ 0 ` + © = 27 .5 DEG/KM \ + ° 20 \ + 0 MEAN CONDUCTIVITY \+ °o =3.28 W . /M .DEG . 30 vk ° 0 HEAT FLOW (UNCORRECTED 1 + ° © =90.0 MW.M-2 40 0 HEAT PRODUCTION -6 -3 ° ° GRANITE =5.9 10 .N -M m ~ so 0_ , 0 w w 0 D so 0 CORRECTIONS Y. ° TOPOGRAPHY 5.4 70 0 0° CLIMATE 20.2 0 80 0 0 ° C 0 R R E T=I 90 °° 0 '— =RT FL3 A 0 100 0 = 1 2 1° 0 Mk.rī 2

PLOT 18 S.W. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT JDGI `J TOR ORRPY IMPERIAL COLLEGE LONDON TEM( 1 I TURE CONDUCT IVITY LITHOLOGY E SX 5663 7334 9 1 0 11 3.0 3 2 ~ D3 4~ K .31.6 1 1

0 MEAN GRADIENT 10 0 + \ € =26.0 DEG/KM + € 20 + \ 0 MEAN CONDUCTIVITY + \ 0 + \ € =3.42 W./M.DEG. 0 30 +\ +, € HEAT FLOW [UNCORRECTED l 0 € =89.0 MW. M 2 40 0 0 HEAT PRODUCTION 0 - 3 GRANITE = 4 .9 1 0- 6. W M F-- w 50 0 D_ O w 0 O 60 0 0 CORRECTIONS 0 0 TOPOGRAPHY 2.9 70 0 0 CLIMATE 21 .7

80 In 19 r-. 0 11 v R I E L T E 90 € 0 0 H -RT FL: A 0 100 0 -2 0 118.OMA

PLOT 19 V S.W. ENGLAND HEAT FLOW V GEOPHYSICS DEPARTMENT JL ERROSE FRIR IMPERIAL COLLEGE LONDON TEM1PR TURE CONDUCTIVITY LITHOLOGY '/TIEV61 7 SW 65604351 1.1 12 13 14 15 0 1 1

10 MEAN GRADIENT =34.0 DEG/KM 20 MEAN CONDUCTIVITY =2.12 W./M.OEG. 30 HEAT FLOW(UNCORRECTED ~ \+ 0 =72.2 MW. M-2 40 \+ 0 MYLOR HEAT PRODUCTION = U) 4 1-3 50 0 = 1 .9 10-6.W1 C 4 SERIES w W c)= 60 A CORRECTIONS A SLATES TOPOGRAPHY 0.7 70 0 0 AND CLIMATE 13.4 0 0 80 0 SANDSTONE 0 CORRECTEC 90 0 0 HERT FLOA 100 00 + = 84 1 mid.r

PLOT 20

S.W. ENGLAND HEAT FLOW _ GEOPHYSICS DEPARTMENT /cl- STLI- R T A IMPERIAL COLLEGE LONDON TEMTMTpRE CONDUCTIVITY LITHOLOGY IW•/M• K4)DEG• SW 12 13 14 15 16 1 7530 2576

++\ MEAN GRADIENT A 0 t+ =30.9 DEG/KM 25 N++ 0 0 MEAN CONDUCTIVITY 4. ° p -r.2 .66 W . /M .DEG . 0 p ā HEAT FLOW IUNCORRECTEDI 50 0 0 in =82.2 MW. M-2 0 HEAT PRODUCTION ° ° 0 GRAMSCATHO =m w 75 0 1.8 10-6.14 .M-3 ° p BEDS 0 ° SLATES CORRECTIONS 0 AND TOPOGRAPHY loo 0 4.5 ° ° SANDSTONES CLIMATE in 15 .3 0 0 125 0 0~ CORRECTED

0 0 HEAT FLOAT 00 1 150 00 - 1 0 2 . 5 MW •M 2 PLOT 21

I \/ N I T - F V S.W. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT L R IL L 1 11 I Hn P IMPERIAL COLLEGE LONDON TEMPERRTUI RE CONDUCTIVITY LITHOLOG'i I M.QEG.KW ./ 3 l SX 0886 6783 10 11 12 13 14 l5 0 I 1 1 1 I I 11 1

\ \ + 0 0 MEAN GRADIENT + 0 =39.6 DEG/KM 25 ` + 0g \ MEAN CONDUCTIVITY '+ o ° 0 ° =2.31 W./M.DEG. \~++ ° ~ in HEAT FLOW (UNCO2RECTED1 50 ~+ in =91.2 MW.M \+ 0 + 0 DEVONIAN HEAT PRODUCT ION ō =2.2 10 .W.M ° o ,~ 75 SLATES W W in 0 = in 000 AND CORRECTIONS Y. ō ° SANDSTONES TOPOGRAPHY 2.5 100 0 CLIMATE 1 1 .6 in 0 0 °°0 C~RRTE 1 125 ° 0 H=HT F~ A 0 01 + o0 = 106.2MW.rī2 PLOT 22 S.W. LAND HEAT FLOW NT GEOPHYSICS DEPART MENT R E R I 75R\ IMPERIAL COLLEGE LONDON TEMIP(MTURE CONDUCTIVITY LITHOLOGY SW 9316 5916 11 121314151617181920212223 2.0 2 5 ~D3 0~1t~31.5 I, T MEAN GRADIENT

50 =38.4 DEG/KM 0 MEAN CONDUCTIVITY 0 =2.53 W./M.DEG. 100 ° 0 HEAT F LOW (UNCORRECTED 1 0 0 =97.2 MW. M 2 0 HEAT PRODUCTION T.- n 150 ~'' ° ° MERDFOOT L11 =7.3 10-6.W M-3 CC °-W w BEDS o 0 ° 0 CORRECTIONS Y. 200 °° ° ° TOPOGRAPHY 0.9 CLIMATE 7.9 250 AI g CORRECTEI 300 ® 0 HEAT FLOIk o ° GRANITE _ 0 0 ° — 105 .7 MW.M 2 PLOT 23

S.W. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT L H IMPERIAL ITOLLEGE LONDON T MPi f T E. CONDUCTIVITYVI TY L I THOLOGY (W./M.DEG.K.1 3 8 34 [3[3 10 11 12 l 14 15 16 2 S 4 5 I

MERN GR HU I E N1

25 7 3/1 .6 DEG/KM EU NERN CONDUCTIVITY iD4. N ./N .DE . 50 IIE H1 F L Ii k UNCOHNF (:1 FI)1 := 1 05 .0 Ni A Ni 2 7 5 1-1E.f-1- -1 PRODUCT ION

_z . 13 1 0 6 EU Li] R I 1 E 100 CORRECT IONS 1 ()PUGH-1PM' .H 125 CL IMOTE 13 .H

150 1.1:0 -- ECTE[11 HE - 1 FLOk 175 11802- HA.m-2 PLOT 24 S.W. ENGLAND HEHT FLOA GEOPHY SICS l)EPHRIME:NI ~(iSF IMPERIHL COLLEGE LONDON

T E MiPoRt1 TORE CONDUCT IIG V I TY L I THOLOGY 5k 35? 345- 11 12 13 14 15 16 17 18 19 20 0 1 2W 3~4.5E 6 ~~A 9 1 1ERN GRADIENT 31 .7 DEG/KM MEAN CONDUCTIVITY 3.24 W./ M.(.)EG. HE Al FL. OW UNCORRECTED ; = 1 Cie' .8 M

GRANITE

CORRECTIONS

Cl_I MAI E 9.7 o HEBT F LOH 1 1 3 .8 NMrf PLOT 25 S.W. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT ROSEVR\2ARS ' IMPERIAL COLLEGE LONDON TEMPE T.URE CONDUCTIVITY LITHOLOGY t .k~. 9 SW 7352 3460 11 12 13 14 15. ~1~61 17 18 19 20 0 1 ~W3,M.nER A ` ! , 11 /1 1 1 1 1 1 1 1-

~ # MEAN GRADIENT ', = 31 .9 DEG/KM 50 MEAN CONDUCTIVITY =3.24 W . /M .DEG . HEAT FLOW ( UNCORRECTED 1 100 = 103 .4 MW.M-2

150 '~ GRANITE ww 0 CORRECTIONS

200 CLIMATE 9.8

250 C3RRECTEC HEAT FLCA 300 - 114.661. M 2 PLOT 26

S.W. ENGLAND HEBT FLOW T GEOPHYSICS DEPARTMENT P IMPERIAL COLLEGE LONDON TEMIo1RTURE CONDUCTIVITY LITHOLOGY (( pp GG KK ll SA 6570 367H 10 11 12 13 0 1 2W3/ 4~5E 6'7~8 _1_ L I 1 1 1 1 l l I 1 ° \ ° 10 \ + MEAN GRADIENT \+ ° =32.8 DEG/KM ?_O El MEAN CONDUCTIVITY +\ =3.33 N./M.DEG. - 30 + ° + \ ° HER] FI.ONiuNCORR CTEDI + \ lJ _ 2 40 + \ ° = 1 09.1 MA .M + ° +\ ° 50 +\ In +\ ° + \ LJ 60 + °e~ GRANITE ° CORRECTIONS 70 ° ° ° 80 °° CLIMATE 15.9 ° 90 ° LTJ ° CDR :R E 2 1E[D 100 Ln LD ~1 HE ;T FL A 110 [7 [9 L9 1 29 . 8 M nl . ri 2 PLOT 2 7 5.H. ESCSND HEAT FLOW GEOPHYSICS DEPARTMENT [- vl- RDO\ Li D ! ! IMPERIAL COLLEGE LONDON TEMPERATURE CONDUCTIVITY L I THOLOGY IDEG•C.) (W./M.DEG.K.I SX 57335849 10 11 12 13 3.0 3.5 4.0 4.5 1 I I I I / + \ \ + + MEAN GRADIENT ~+ \++ =27.8 DEG/KM ' U N + MEAN CONDUCTIVITY + =3.35 W./M.DEG. + ° HEAT FLOW (UNCORRECTED 1 + o =93.3 M,.M 2

n c O °

S ° PTH TRE 0 GRANITE E ME

D 1 J J 0 0 CORRECTIONS

° CLIMATE 18.7 0

O O CORRECTS ° ° 'ERT FDA

0 1 U N • + = 1 1 48 Mn.M 2 PLOT 28 S .W . ENGLAND HEAT FLOWW H o f n 'O " 3 GEOPHYSICS DEPARTMENT F \ RDH IMPERIAL COLLEGE LONDON TEMA I T IURE CONDUCTIVITY L I THOLOGY lq'/M.QEG.K6 l 10 11 12 13 3 1 I__, 1 1 ( 1 1 `1 \ \ °° MEAN GRADIENT 0 + ° ° =27.7 DEG/KM 25 ` + ° ° MEAN CONDUCTIVITY 0 + 0 1:4.70 W./M.DEG. .+ 0 + 0 HEAT FLOW 1 UNCORRECTED I ++ 0 °° =130.2 M ICI . M 2 50 + ° 0 0 0 L ~ al re 0 ° ALTERED

D 0 GRANITE 75 0 CORRECTIONS o + 00 + 0 CLIMATE 17.8 + 0 ° 100 . 0 0 0 ° LORR=_T.~ ✓ T I /~ °° H _ ^ I F L~ v V V 125 + 0 ° + = 1 58 0 4 MW.rī2 PLOT 29 S.W. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT A H I T 1- 11 I L L I F O IMPERIAL COLLEGE LONDON TEMAMTURE CONDUCTIVITY LITHOLOGY 6 1 SX 5805 5275 10 I I 12 13 3 0 1 1 2'/'~EC~.K 1 l 1 l 1 1 1 l 1 I

\ ~ 0 E to +\ M0 EAN GRADIENT 0 =28.0 DEG/KM 20 ++ 0M EAN CONDUCTIVITY 4 0 =4.02 W./M.0EG. 30 4- 0 + 0 HEAT FLON(ONCORRECTED ) 40 \+, 10 = 1 2 .6 MW. M 2 0 E _ O) 50 E F-- Ill 0 °~ 0 KROL I N I ZED w ul 60 0 ° F 0 CORRECTIONS 7 0 0 GRANITE 0 0 CLIMATE 80 19.6 0 0 90 0 E CORR'CTE 100 00 HEAT FLOA 0 110 = 140.2MW.M 2 PLOT 30 S.W. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT FVEY T IMPERIAL COLLEGE LONDON TEMiPogR.I .: T IURE CONDUCTIVITY L THOLOGY SX 8271 7929 11 12 13 0 1 "2ITV6) 7 1

MEAN GRADIENT 10 OVERBURUFN 7 2. . 9 [IF G / M

\+ ?0 En MEAN CONDUCT IVI 1 \ 4 - ASHT ON 13.16 N./M.0EG. + 30 \ 4- SHALE HE Al F LAN MA.M 40

(r) Li )0 cI-

00 TEIGN CORRECT IONS CHERT 70 In FORMAT ION CLIMATE 21 .8

80 En • In Li -=\)- ELIE. LI 90 FAULT LONE FLE 100 1 DO 5 MM

PLOT 31 S.W. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT 'FLDO\ RRRY IMPERIAL COLLEGE LONDON TEMAU TURE CONDUCTIVITY LITHOLOGY 12•/ 1.QEGG.K.) 7 SX 56769220 10 11 12 13 0 1 1 t

MEAN GRADIENT 10 =33.0 DEG/KM + KERATO- 20 +\ 0 PHYRE MEAN CONDUCTIVITY + \ +\ 0 =3.14 W./M.DEG. 0 30 HEAT FLOW I UNCORRECTED 1 of 2 APL ITE = 1 03 . 7 Mai. M 40

_u) ui 50 2 Deri w MUOSTONES W 0 0 C 60 CORRECT IONS i

TOPOGRAPHY -7 .6 70 CLIMATE 21.2

80 CRRE2T_ 90 HEAT FL3A 100 l 20 a l MW.M 2 PLOT 32

\ L_ Y \ F P 5 1 1 S.W. ENGLAND NERT FLOW GEOPHYSICS DEPARTMENT \ /A \ H 1 IMPERIAL COLLEGE LONDON TEf1F TORE CONDUCTIVITY LITHOLOGY Q (j./M.DEG.K4 1 S W 8 146 5 390 11 12 13 14 I 3 l 1 l { j J I

° ° MEAN GRADIENT 10 \ + ° \+ DEG/KM t ō =30.8 20 + °° MEAN CONDUCTIVITY +\ 4- 0 ō =2.94 W./M.DEG. 30 \+ ° HEAT FLOW 1 UNCORRECTED 1 -2 ° ° =90.5 MW. M • 40 +\ ° ++ \ ° SHALES fem_ ~w 50 + ~ ~~ + 0 AND ō ~ so ° SLATES 0 CORRECTIONS Y. ° ° TOPOGRAPHY U.S 70 + ā CLIMATE 18.0 ° 80 ° ° 7RR LT-1 90 ° ° ° H=AT FLCA IOU ° °° = 1 1 1. 1 MW. M 2 PLOT 33 n S.W. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT El \ F—ST 4 IMPERIAL COLLEGE LONDON TEM(ogATURE CONDUCTIVITY L I THOLOGY EG.K4 1 Ski 8 1 4 1 5 3 8 4 II 12 13 (I 2./M.RI I I 0 lo ` 0 0 MEAN GRADIENT `+ 0 =27.2 DEG/KM 20 \4 0 ° MEAN CONDUCTIVITY t 0 0 =3.03 W./M.DEG. 30 HEAT FLOW (UNCO2RECTE D1 ° + a SHALES 0 =8?_ .4 MW.M 40 AND 0 SLATES 0 0 w 50 Q- icf ° w w D so 0 0 CORRECTIONS 0 0 TOPOGRAPHY 0.6 70 0 CLIMATE 23.0

80 CORRECTEI 90 HEAT FLOi 100 - 10 '7.9 MW.M 2 PLOT 34

•-- .1,4. ENGI AND HEA1 FL Oki GEOPHYSICS OEPARTMhNi AEn N: I MPERIAL COLLEGE i uNDON TEMig0T pRE CONDUCTIVITY LITHOLOGY 5.K 6 1 7 SN ci J T() 9 (i) A 12 13 11 15 16 0 1 (24.31.VG I I I I . 1 1

MEAN GRADIENT 10 =37.1 DEG/KM Li 20 MEAN CONDUCTIVITY =2.65 H./M.OEG. 30 DEVON I AN HEAT FLONtuNcoRREclEni 2 Li 1:98.3 MA.M 40 LI GREY SLPTE LI Li GO LI

[T Li GO */. IL CORRFCTIONS LI 70 Li IlL EL INH1E 1 "7 . /1 L I 80 L LTED 90 FT1 EH 100 ONLY 24H f:1 11--- 1 1. 9 0 m . m

PLOT 35 5.'W. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT ËLADR 0 IMPERIAL COLLEGE LONDON TEMIPDEFATURE CONDUCTIVITY LITHOLOGY Sk 9788 6254 11 12 13 14 15 012 34567

MEAN GRADIENT 31 .3 DEG/KM

25 + MEAN CONDUCTIVITY

O -2.50 N./M.DEG . + 0 0 HEAT FLDWIUNCORRECTED) 0 50 + 0 78 . I MA. M-2 0 ~+ o 0 DEVONIAN 0 0 GREY SLATE 75 0 a MEADFDOT CORRECTIONS 0 0 BEDS a 100 Ll LE_ IMR1F 1~ .5 El 0 0 0

125 0 0 I-17:T EL 0 0 0 2 M 9 1 0 5 MA. M PLOT 36 ENGLRND HEAT FLOW GEOPHYSICS DEPRR1ME1:1 \I I VET Pr'051)1- IMPERIL COLLEGE LONVIN T E M(PDU pRE CONDUCT I VI TY L.. I THOLOGY 5X 02156 1 10 11 12 13 0 1 12 ./3m IEG,5*% ) 7 11 1 1 1 1 1

ED MEHN GFP0 I ENT II) V] ED I . 4 DEG/ FM ED 20 ED MEHN LONDUCIIVllY ED ED H N /N DF . ED 30 ED HE.H1 FL ON UNCORREC1E ED ED -70.4 MN.11 40 ED DEVONIHN w IIfl 50 in SL2 TES Cr in L1J Lit ED El GO In In CORRECTIONS

In 7( CLI MRTE 20.4

80 in In In 90 HE T FLO A 100 ii 99.7 Ni A N PLOT 37 S.W. ENGLAND HEAT FLOk GEOPHYSICS OFPFIRTMEN1 1\\R2 DO A \ IMPERIAL COLLEGE LONDON T E il(PA T pRE CONDUCTIVITY L. THOLOGY (14./M.OEG.K.1 SN 13911111 1 13 11 12 13 14 15 15 17 18 19 20 1_ I

riFPN UPPD I E

in En 2 fl DEG/KM 50 m in ME RN L1JN1111C.1 IVIIY —/M IJF U .

100 HE H1 F I ON ( UNCORRE-LIFH En HU.' NIN.m

En PER IDOTITF (ANNE 211 ONS 200 En [n -10PilUfRW'HI LT.] CI En [Ii 250 En r ED 111- I E El 300 E J PION

68 PLOT 38 S . ENGL AN] HER] I. OW L3f-:-.0P1-1Y5IC S OEPHRT EIENT KF\ DS I MPF R I RI t_f- GE t tINDON

1 E MiPINR.rci T R E CONDUCTIVITY L I THOLOGY IN ./M .DEG 1 —i3c)5 irj4 13 14 15 16 17 2.0 2.5 3.0

ME AN GRAD I ENT

Er] 08 CEO/KM 25 r`l it- MEAN LONI]UL 1 IVIlY

Er] N . /M DE- G

HE-Ri FL ON UNLORRF C1F I) 50 En 7 (3 8 4 M A M En COMPLEX En in SEQUENCE En 75 En GNEISSES En PER IDOT I TE CORRECI I MI5 0. + GABBROS 13 - . () 1 00 TOPOGRAPHY CL Mr-11E 17 .8

Cl 125 C] 'ELTE[) El 0/\

2 150 -_: '79 PLOT 39 ENGLANDSICS FLOW -- \ GEOPHY C I O I N R IMPERIAL COLLEGE LONDON TEMIPUATURE CONDUCTIVITY LITHOLOGY 1 3. /M . EG.K S ) ST 2479 401 1 11 12 I3 14 15 16 17 18 19 20 21 22 2

`"'' MEAN GRADIENT 100 1'=:' - 1 1 .4 DEG/KM c=' PALE GREY "` MEAN CONDUCTIVITY '1 LIMESTONES 200 : ° =3.29 W./M.DEG. c.;_, ri HEAT FLOW (UNCORRECTED) kil DARK GREY =37.6 MW. M 2 11 LIMESTONES 2 c It b a0 ,q.. ° NE w W GRAINED CD °L LIMESTONES CORRECTIONS F. ° NI TH CHERT 500 L ° - ° op CLIMATE 19 ''a ,i,u .8 REEF BEDS 600 01 ° ° AND Id DOLOMITE 'RRE_I -i ev ° LIMESTONES 700 ° H E A T F L 0 A F~ M 2 °0 = 4 7 a 3 Mn. PLOT 40 S .W . ENGLAND HEBT FLOW I;EOPH1•5I[S DEPARTMENT LJ -r IMPERIAL [OLLFOE LONDON TEMPcR R TUP,E CONDUCTIVITY L I THOLOGY (3./M.7EG.1(.I ST 24'7E 4311 11 12 1 3 14 15 16 1' 18 19 20 21 22 L 1 1__1 I I I I l I 1 MEAN GRADIENT 13.8 DEG/KM PALE GREY MEAN CONDUCTIVITY LIMESTONES 3.29 W./M.DEG. .00 HEAT FLOW (UNCORRECTED I

DARK GREY -_:45.B MW. M 2 300 LIMESTONES

u) r_ LLJ

- 400 FINE _LJ :L GRAINED LIMESTONES CORRECT IONS 500 WITH CHERT CLIMATE 21 .6 REEF BEDS 600 AND DOLOMITE LIMESTONES 700 Fi-RT FL W I.M2 57.8 M

PLOT 40 interval 1 S.W. ENGLAND HENT FLOW 13 GEOPHYSICS DEPARTMENT SPNNI\GT:N IMPERIAL COLLEGE LONDON 1EMtDMTURE CONDUCTIVITY L I THOL.OG'Y" 2 t3./M.fIEG.K S I ST 24794011 11 12 13 14 15 16 17 18 19 20 21 22

MEAN GRADIENT 11.5 DEG/KM PALE GREY MEAN CONDUCTIVITY LIMESTONES 3.29 W./M.DEG.

HEAT FLOW ( UNCORRECTED )

DARK GREY = 37.8 MW. M 2 LIMESTONES

0 FINE GRAINED LIMESTONES CORRECTIONS WITH CHERT

CLIMATE 18.0 REEF BEDS AND DOLOMITE LIMESTONES HERT FLD A

46 . 1 Mn . M-2 PLOT 40 interval 2

______•W• ENGLAND HEAT FLOW GEOPHYSICS DEPARI MENT CA\\ I\ 3- T R\ 'RR IMPERIAL COLLEGE LONDON TEMP A~TURE CONDUCTIVITY L I THOLOGY ~r ~7 ~1 r~ 1 3•/M.DIEG.K5 l I 2 4 / 9 4 0 1 1 11 12 13 14 15D16 17 18 1920 20 21 22 2 ( , , , , I , , , , , , I I , , , ►'., •:'•r 111' MEAN GRADIENT 100 = 10 .6 DEG/KM -=' PALE GREY `.. MEAN CONDUCTIVITY p LIMESTONES =3.29 W . /M .DEG . 200 U1y ., HEAT FLOW (UNCORRECTED) • DARK GREY =34.8 M W.M -2 300 ;11 r LIMESTONES

:17i 400 p FINE Lu W .. GRAINED °L;° LIMESTONES CORRECTIONS 500 - WITH CHERT Pf 1...'1't0° CLIMATE 22.5 ° o REEF BEDS 600 IP AND ° DOLOMITE :DAR:TL ' `•y p ° LIMESTONES 700 :: EAT FLEA al

p° — 44.9 Mtl. Mī2 PLOT 40 interval 3 S.N. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT LP\\1N310 PSR IMPERIAL COLLEGE LONDON TEMIPDRifpURE CONDUCTIVITY LITHOLOGY (1•/MIEG•Iy ST 24794011 11 12 13 14 15 16 17 18 19 20 21 22 2

MEAN GRADIENT 100 = 13.0 DEG/KM PALE GREY MEAN CONDUCTIVITY LIMESTONES 200 =3.79 W./M.DEG. HEAT FLOW ( UNCORRECTED I DARK GREY '12.6 MA.M-2 3(l0 LIMESTONES

F INE GRAINED LIMESTONES CORRECTIONS 500 WITH CHERT CLIMATE 198 REEF BEDS 600 RND DOLOMITE ~ DRRF2T - LIMESTONES 700 HEAT FL3A 53 . 1 MN.M 2

PLOT 40 interval 4 S.W. ENGLAND HEAT FLOW GEOPHYSICS DEPARTMENT C U R R Y P C C L F R R v IMPERIAL COLLEGE LONDON TEMMTURE CONDUCTIVITY L I THOLOGY 4 ) 11 13 14 I (W./M.01EG.K ST 2270 3 871

++ MEAN GRADIENT 25 ` =18.7 DEG/KM + ° ° ° MEAN CONDUCTIVITY so ° =2.82 W./M.DEG. o HEAT FLOW( UNCORRECTED) 75 0 = 52 .8 Mw. M-2 0 ° °- SIL TS TONES ° AND ioo o ° SANDSTONES w +l+ ,. o ° CORRECTIONS 125 0 ,

III ° CLIMATE 21.9 iso 13° 15 CORRECTED ° HERT FLOW 200 ° ° 0 = 67.6 MW.M 2 PLOT 41 264

Appendix II Tabulation of Temperature Data

The tabulated temperature data presents the equilibrium or latest temperature data for each of the boreholes studied. Temperatures are in degrees centigrade whilst depths are in metres below ground level. Where the borehole is known to be inclined, this represents the calculated vertical depth and not the length of hole. Temperatures were measured to an accuracy of ± 0.01K. Depths were measured to an accuracy of - 0.03m See chapter 3 for details.

Table Sample Station Name No. Code 1 CSD-02 Trevease Farm CSD-04 Grillis Farm CSD-05 Medlyn Farm 2 CSD-06 Trerghan Farm CSD-07 Polgear Beacon CSD-08 Gt Hammet Farm 3 CSD-09 Browngelly CSD-10 Blackhill CSD-11 Bray Down 4 CSD-12 Pinnockshill CSD-13 Bunker's Hill CSD-14 Newmill 5 CSD-15 Colcerrow Farm CSD-16 Tregarden Farm CSD-17 Blackingstone 6 CSD-18 Winter Tor CSD-19 Soussons Wood 7 CSD-20 Foggin Tor CSD-21 Laughter Tor 8 CDD-01 Merrose Farm 265

Table Sample Station Name No. Code 9 CDD-02 Kestle Wartha CDD-03 Callywith Farm 10 GAV Gaverigan 11 CSD-01 Longdowns 12 ROS-A Rosemanowas A 13 ROS-D Rosemanowas D 14 TROON Troon WHY White Hill Yeo 15 DDH-H23 Hemerdon RDH-H3 Hemerdon 16 BOV Bovey Tracey Lanivet 17 BEL-1 Belowda Beacon - 1 BEL-2 Belowda Beacon - 2 MELD Meldon 18 NEW-1 Newlyn East - 1 NEW-4 Newlyn East - 4 19 PRED Predannack 20 KEN Kennack Sands CUR Currypool Farm 21 CAN Cannington Park

== = =--•=- = _ BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS TREVEASE FARM CSD-02 GRILLIS FARM CSD-04 MEDLYN FARM CSD--05 GRID REFERENCE SW 7185 3180 GRID REFERENCE SW 6796 3846 GRID REFERENCE SW 7083 3404 = I I I I I I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE 'I I DEPTH TEMPERATURE I I METRES DEG C I I METRES DEG C I I METRES DEG C I I I I I I I I 30.63 11.07 I I 30.64 10.91 I I 30.65 11.34 I I 33.69 11.15 I I 33.70 11.00 I I 33.72 11.39 I I 36.76 11.24 I I 36.77 11.08 I I 36.78 11.46 I I 39.82 11.35 I I 39.83 11.15 I I 39.85 11.53 I I 42.88 11.42 I I 42.89 11.23 I I 42.91 11.59 I I 45.94 11.50 I I 45.95 11.31 I I 45.98 11.65 I I 49.00 11.58 I I 49.00 11.39 I I 49.04 11.70 I I 52.07 11.68 I I 52.06 11.48 I I 52.10 11.77 I I 55.13 11.76 I I 55.12 11.55 I I 55.17 11.84 I I 58.19 11.84 I I 58.18 11.64 I I 58.23 11.91 I I 61.25 11.92 I I 61.24 11.72 I I 61.29 12.01 I I 64.31 12.00 I I 64.30 11.85 I I 64.34 12.10 I I 67.37 12.09 I I 67.36 11.92 I I 67.39 12.18 I I 70.43 12.18 I I 70.43 12.00 I I 70.44 12.27 I I 73.49 12.26 I I 73.49 12.09 I I 73.48 12.40 I I 76.55 12.34 I I 76.55 12.16 I I 76.51 12.52 I I 79.61 12.43 I I 79.62 12.26 I I 79.53 12.63 I I 82.66 12.52 I I 82.68 12.33 I I 82.55 12.71 I I 85.72 12.60 I I 85.74 12.42 I I 05.56 12.81 I I 88.78 12.68 I I 88.81 12.50 I I 08.55 12.89 I I 91.84 12.78 I I 91.87 12.58 I I 91.54 12.99 I I 94.89 12.86 I I 94.94 12.67 1 I 94.52 13.08 I I 97.64 12.95 I I 98.00 12.75 I I 97.48 13.16 I I I I I I I _

Table 1. BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS TRERGHAN FARM CSD-06 POLGEAR BEACON CSD-07 GREAT HAMMETT FARM CSE:'-08 GRID REFERENCE SW 7353 3033 GRID REFERENCE SW 6927 3663 GRID REFERENCE SW 1885 6986 I I I I I I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I METRES DEG C I I METRES DEG C I I METRES DEG C I I I I I I I I 30.64 11.56 I I 30.65 9.73 I I 9.26 10.79 I I 33.70 11.65 I I 33.72 10.36 I I 12.35 10.69 I I 36.77 11.73 I I 36.78 10.64 I I 15.44 10.25 I I 39.83 11.78 I I 39.85 10.81 I I 18.52 10.27 I I 42.89 11.87 I I 42.91 10.92 I I 21.61 10.30 1 I 45.95 11.95 I I 45.98 11.01 I I 24.70 10.34 I I 49.00 12.04 I I 49.04 11.09 T I 27.79 10.45 I I 52.06 12.12 I I 52.11 11.19 I I 30.87 10.56 I I 55.12 12.21 I I 55.17 11.29 I I 33.96 10.63 I I 58.18 12.30 I I 58.24 11.37 I I 37.05 10.72 I I 61.24 12.38 I I 61.30 11.47 I I 40.14 10.80 Iln) I 64.29 12.49 I I 64.37 11.57 11 43.22 10.08 I 12 I 67.35 12.56 I I 67.43 11.66 I I 46.31 10.98 I I 70.41 12.65 I I 70.50 11.75 I I 49.40 11.06 I I 73.47 12.73 I I 73.56 11.83 I I 52.48 11.13 I I 76.52 12.86 I I 76.63 11.92 I I 55.57 11.22 I I 79.58 12.92 I I 79.69 12.00 I I 58.66 11.30 I I 82.64 13.03 I I 82.76 12.08 I I 61.75 11.39 I I 85.70 13.10 I I 85.82 12.19 I I 64.83 11.50 1 I 88.75 13.18 I I 88.89 12.27 I I 67.92 11.59 I I 91.51 13.26 I I 91.95 12.36 I I 71.01 11.68 I I I I 95.02 12.43 I I 74.10 11.79 I I 98.09 12.54 I I 77.18 11.90 I I 101.15 12.62 I I 80.27 12.00 I I 103.08 12.68 I I 83.36 12.11 I I I I 06.44 12.18 I I 09.53 12.30 I I 92.62 12.38 I I 95.71 12.48 I 913.79 12.511 I I Table 2.

BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS BROWNGELLY CSD-09 BLACKHILL CSD-10 BRAY DOWN CSD-11 GRID REFERENCE SW 1924 7247 GRID REFERENCE SW 1835 7820 GRID REFERENCE SW 1907 8177 =__ =____ I I I I I I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I METRES DEG C I I METRES DEG C I I METRES DEG C I I I I I I I I 15.40 11.02 I I 9.27 10.17 I I 9.21 9.99 I I 18.48 10.01 I I 12.36 10.06 I I 12.28 9.68 I I 21.56 10.01 I I 15.44 10.10 I I 15.35 9.70 I I 24.64 10.04 I I 18.53 9.97 I I 18.42 9.80 I I 27.72 10.09 I I 21.62 10.00 I I 21.49 9.89 I I 30.80 10.17 I I 24.71 10.03 I I 24.56 9.98 I I 33.88 10.23 I I 27.80 10.06 I I 27.63 10.06 I I 36.96 10.29 I I 30.89 10.24 I I 30.69 10.11 I I 40.04 10.34 I I 33.98 10.35 I I 33.76 10.18 I I 43.12 10.42 I I 37.07 10.46 I I 36.83 10.26 I I 46.20 10.48 I I 40.15 10.54 I I 39.90 10.35 I I 49.28 10.56 I I 43.24 10.62 I I 42.97 10.42 Ill, I 52.36 10.62 I I 46.33 10.71 I I 46.04 10.49 Iao I 55.44 10.69 I I 49.42 10.79 I I 49.11 10.58 I I 58.52 10.77 I I 52.51 10.87 I I 52.18 10.65 I I 61.60 10.85 I I 55.60 10.96 I I 55.25 10.75 I I 64.68 10.93 I I 58.69 11.04 I I 58.32 10.84 I I 67.76 11.02 I I 61.70 11.13 I I 61.39 10.91 I I 70.84 11.10 I I 64.86 11.22 I I 64.46 11.00 I I 73.92 11.17 I I 67.95 11.31 I I 67.53 11.08 I I 77.00 11.25 I I 71.04 11.39 I I 70.60 11.18 I I 80.08 11.33 I I 74.13 11.48 I I 73.67 11.24 I I 83.16 11.41 I I 77.22 11.55 I I 76.74 11.34 I I 86.24 11.49 I I 80.31 11.65 I I 79.81 11.42 I I 89.32 11.58 I I 83.40 11.75 I I 82.88 11.50 I I 92.40 11.65 I I 86.49 11.84 I I 85.95 11.57 I I 95.48 11.74 I I 89.57 11.93 I I 89.02 11.69 I I 98.56 11.81 I I 92.66 12.03 I I 90.52 11.72 I I 101.58 11.93 I I 95.75 12.12 I I I I I I 98.32 12.19 I ______=___ =====a===== _ = I I ===_= _ ======Table 3. ======~=~======BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS PINNOCKSHILL CSD-12 BUNKERS HILL CSD-13 NEWMILL QUARRY CSD-14 GRID REFERENCE SW 1892 7450 GRID REFERENCE SW 1402 0273 GRID REFERENCE SW 1460 0343 ======c======~======I I I I I I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I METRES DEG C I I METRES DEG C I I METRES IIEG C 1 I I I I I I I 9.20 10.31 I I 6.11 10.41 I I 9.17 10.98 I I 12.27 10.29 I I 9.16 11.03 I I 12.23 10.89 I I 15.33 10.27 I I 12.22 10.98 I I 15.29 10.83 I I 18.40 10.23 I I 15!27 11.01 I I 18.35 10.84 I I 21.46 10.24 I I 18.32 11.09 I I 21.40 10.93 I I 24.53 10.24 I I 21.38 11.22 I I 24.46 11.02 r I 27.60 10.26 I I 24.43 11.34 I I 27.52 11.13 I I 30.66 10.27 I I 27.49 11.45 I I 30.58 11.25 I I 33.73 10.30 I I 30.54 11.57 I I 33.64 11.36 r I 36.80 10.33 I I 33.60 11.66 I T 36.69 11.46 I I 39.86 10.42 I I 36.65 11.77 I I 39.75 11.56 I I 42.93 10.46 I I 39.70 11.87 I I 42.81 11.65 I I 46.00 10.51 I I 42.76 11.97 I I 45.87 11. 74 I I 49.06 10.60 I I 45.81 12.07 I I 48.92 11.85 I I 52.13 10.71 I I 48.87 12.17 I I 51.98 11.92 I I 55.20 10.87 I I 51.92 12.26 I I 55.04 12. O~~ r I~ I 58.26 11.03 I I 54.97 12.3°7 I I 58.10 12.13 I I 61.33 11.14 I I 58.03 12.45 I I 61.16 12.22 I I 64.39 11.23 I I 61.08 12.55 I I 64.21 12.31 I I 67.46 11.35 I I 64.14 12.65 I I 67.27 12.40 I I 70.53 11.43 I I 67.19 12.74 I I "70.33 12.49 I I 73.59 11.51 1 I 70.24 12.83 I I 73.39 12.59 I I 76.66 11.59 I I 73.30 12.91 I I 76.44 12.68 I I 79.73 11.68 I I 76.35 13.03 I I 79.50 12.78 I I 82.79 11.79 I I 79.41 13.12 I I 82.56 12.86 I I 85.86 11.90 I I 82.46 13.22 I I 85.62 12.95 I I 88.93 12.06 I I 85.52 13.31 I I 88.68 13.05 I I 91.99 12.17 I I 88.57 13.41 I I 91.73 13.17 I I 95.06 12.27 I I 91.62 13.50 I I 94.79 13.28' I I 97.85 12.36 I I 94.68 1:3.5<) I I 97.85 13.36 I I I I 97.73 13.68 I I 100.91 13.43 I ======I 100.79 13.T7 I I 103.96 13.54 1 I 103.84 13.83 I I 104.82 13.58 I I 105.00 13.88 I I I I I ======Table 4. ======' ======~======BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS COLCERROW FARM CSD-15 TREGARDEN QUARRY CSD-16 BLACKINGSTONE QUARRY CSD-17 GRID REFERENCE SW 2068 0576 GRID REFERENCE SW 2055 0592 GRID REFERENCE SX 7850 8593 ======~======~======;=::~== I I I I I I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I METRES DEG C I I METRES DEG C I I METRES IIEG C I I I I 1 I I I 9.16 11.08 I I 3.06 10.72 I I 12.42 8.71 I I 12.22 10.95 I I 6.11 11.11 I I 15.52 8.82 I I 15.27 10.84 I I 9.17 11.11 I I 18.62 8.94 I I 18.32 10.81 I I 12.23 10.95 I I 21.73 9.07 I I 21.38 10.87 I I 15.28 10.95 I I 24.83 9.17 I I 24.43 10.99 I I 18.34 11.01 I I 27.94 9.26 I I 27.49 11.10 I I 21.40 11.09 I I 31.04 9.35 I I 30.54 11.18 I I 24.45 11.20 I I 34.14 9.43 I I 33.60 11.30 I I 27.51 11.27 I I 37.25 9.52 I I 36.65 11.37 I I 30.57 11.38 I I 40.35 9.60 I I 39.70 11.46 I I 33.62 11.47 I I 43.46 9.68 I I 42.76 11.55 I I 36.68 11.55 I I 46.56 9.76 I I 45.81 11.65 I I 39.74 11.65 I I 49.67 9.84 I I 48.87 11.73 I I 42.79 11.73 I I 52.77 9.92 tv I 51.92 11.82 I I 45.85 11.84 I I 55.87 10.01 I/I-.J I 54.97 11.92 I I 48.90 11.92 I I 58.98 10.08 1° I 58.03 12.01 I I 51.96 12.03 I I 62.08 10.18 I I 61.08 12.11 I I 55.02 12.11 I I 65.19 10.25 I I 64.14 12.20 I I 58.07 12.22 I I 68.29 10.33 I I 67.19 12.29 I I 61.13 12.31 I I 71.39 10.41 I I 70.24 12.39 I I 64.19 12.40 I I 74.50 10.50 I I 73.30 12.48 I I 67.24 12.52 I I 77.60 10.58 I I 76.35 12.58 I I 70.30 12.60 I I 80.71 10.64 I I 79.41 12.68 I I 73.36 12.72 I I 83.81 10.73 I I 82.46 12.77 I I 76.41 12.81 1. I 86.'j)! 10.81 I I 85.52 12.87 I I 79.47 12.91 I I 90.02 10.87 I I 88.57 12.95 I I 82.53 13.02 I I 93.12 11.00 I I 91.62 13.07 I I 85.58 13.13 I I 96.23 11.08 I I 94.68 13.16 I I 88.64 13.21 I I 99.33 11.17 I I 97.61 13.27 I I 91.70 13.34 I I 102.43 11.25 I I I I 94.75 13.39 I I 103.92 11.30 I I ======-=~=~===== I 96.07 13.49 1 I I I ======Table 5. ======BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS WINTER TOR CSD-18 SOUSSONS WOOD CSD-19 GRID REFERENCE SX 6117 9156 GRID REFERENCE SX 6733 7971

I I I I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I METRES DEG C I I METRES DEG C I I I I I I 12.42 8.16 I I 15.52 8.12 I I 15.52 8.24 I I 19.56 8.18 I I 18.62 8.48 I I 21.73 0.29 I I 21.73 8.64 I I 24.83 8.37 I I 24.83 8.73 I I 27.94 8.31 I I 27.94 8.88 I I 31.04 8.3(3 I I 31.04 8.97 I I 34.14 8.34 I I 34.14 9.03 I I 37.25 8.36 I I 37.25 9.10 I I 40.35 8.58 I I 40.35 9.18 I I 43.46 8.64 I I 43.46 9.26 I I 46.56 9.11 I I 46.56 9.32 I I 49.67 9.25 I I 49.67 9.41 I I 52.77 9.45 I I 52.77 9.50 I I 55.87 9.83 I I 55.87 9.58 I I 58.98 9.95 I I 58.98 9.65 I I 62.08 10.10 I I 62.08 9.72 I I 65.19 10.32 I I .65.19 9.80 I I 68.29 10.53 I I 68.29 9.87 I I 71.39 10.60 I I 71.39 9.95 I I 74.50 10.69 I I 74.50 10.02 I I 77.60 10.88 I I 77.60 10.11 I I 80.71 11.01 I I 80.71 10.18 I I 83.81 11.12 I I 83.81 10.25 I I 86.91 11.15 I I 86.91 10.33 I I 90.02 11.26 I I 90.02 10.41 I I 93.12 11.43 I I 93.12 10.49 I I 93.93 11.47 I I 96.23 10.57 I I I I 99.33 10.61 I I I ======BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS FOGGIN TOR QUARRY CSD-20 LAUGHTER TOR CSD-21 GRID REFERENCE SX 5663 7334 GRID REFERENCE SX 6562 7549 ====~======~= I I ======~===== I I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I METRES [lEG C I I METRES DEG C I I I I I I 6.21 9.17 I I 6.21 8.67 I I 9.31 8.82 I I 9.31 8.68 I I 12.42 8.78 I I 12.42 9.23 I I 15.52 8.75 I I 15.52 9.38 I I 18.62 8.76 I I 18.62 9.4-" I 21.73 I 8.81 I I 21.73 9.50 I I 24.83 8.86 I I 24.83 9.49 I I 27.94 9.18 I I 27.94 9.58 I 31.04 I 9.32 I I 31.04 9.60 I I 34.14 9.43 I I 34.14 9.67 I I 37.25 9.52 I I 37.25 9.76 I I 40.35 9.61 I I 40.35 9.86 I I 43.46 9.69 I I 43.46 9.92 I I 46.56 9.78 I I 46.56 10.00 I I 49.67 9.85 I I 49.67 10.11 I I 52.77 9.98 I I 52.77 10.17 I I 55.87 10.04 I I 55.87 10.25 I I 58.98 10.11 J I 58.98 10.35 I I 62.08 10.29 I I 62.08 10.42 I I 65.19 10.29 I I 65.19 10.53 I I 68.29 10.36 I I 68.29 10.58 I I 71.39 10.44 I I 71.39 10.69 I I 74.50 10.51 I I 74.50 10.76 I I 77.60 10.56· I I 77.60 10.85 I I 80.71 10.65 I I 80.71 10.93 I I 83.81 I 10.74 I 83.81 11.02 I I 86.91 I 10.79 I 86.91 11.09 I I 90.02 I 10.82 I 90.02 11.19 I I 93.12 10.99 I I 93.12 11.31 I J 96.23 11.09 I I 96.23 11.40 I I 97010 11.13 I I 98.90 11.47 I I I I I ======Table 7. 273

BOREHOLE TEMPERATURE MEASUREMENTS OLD MERROSE FARM CDD-01 GRID REFERENCE SW 6560 4351 I I I DEPTH TEMPERATURE I I METRES DEG C I I I I 34.14 12.16 I I 37.25 12.28 I I 40.35 12.38 I I 43.46 12.48 I I 46.56 12.59 I I 49.67 12.67 I I 52.77 12.78 I I 55.87 12.91 I I 58.98 13.04 I I 62.08 13.17 I I 65.19 13.32 I I 68.29 13.47 1 I 71.39 13.60 I I 74.50 13.73 I I 77.60 13.87 I I 80.71 14.00 I I 83.81 14.15 I I 86.91 14.30 I I 90.02 14.44 I I 93.12 14.57 I I 96.23 14.67 I I 99.33 14.77 I I 101.16 14.84 I I I

Table 8. 274

BOREHOLE TEMPERATURE MEASUREMENTS KESTLE WARTHA SW 7530 2576 CDD-02 I I I DEPTH TEMPERATURE DEPTH TEMPERATURE DEPTH TEMFERATURE I I METRES DEC C METRES DEG C METRES DEG C I I I I 6.21 : 11.54 55.87 : 12.68 105.54 : 14.18 I I 9.31 : 11.11 58.98 : 12.78 108.64 : 14.30 I I 12.42 : 11.26 62.08 : 12.89 111.75 : 14.40 I I 15.52 : 11.42 65.19 : 12.97 114.85 : 14.50 I I 18.62 : 11.58 68.29 ; 13.05 117.96 : 14.61 I I 21.73 : 11.73 71.39 1 13.16 121.06 1 14.70 I I 24.83 : 11.86 74.50 : 13.23 124.16 : 14.78 I I 27.94 : 11.95 77.60 : 13.33 127.27 : 14.88 I I 31.04 : 12.04 80.71 : 13.44 130.37 : 14.97 I I 34.14 : 12.11 83.81 : 13.53 133.48 1 15.05 I I 37.25 : 12.20 86.91 : 13.66 136.58 : 15.15 I I 40.35 1 12.27 90.02 : 13.74 139.68 1 15.25 I I 43.46 : 12.36 93.12 : 13.83 142.79 : 15.32 I I 46.56 : 12.42 96.23 : 13.91 145.89 : 15.41 I I 49.67 : 12.50 99.33 : 14.04 148.78 : 15.49 I I 52.77 : 12.60 102.43 1 14.11 I I I

BOREHOLE TEMPERATURE MEASUREMENTS CALLYWITH FARM SX 0886 6783 CDD-03 I I I DEPTH TEMPERATURE DEPTH TEMPERATURE DEPTH TEMPERATURE I I METRES DEG C METRES DEC C METRES DEC C I I I I 12.42 : 10.73 58.98 : 11.99 102.43 : 13.63 I I 15.52 : 10.87 62.08 1 12.10 105.54 : 13.72 I I 18.62 : 11.02 65.19 : 12.18 108.64 : 13.92 I I 21.73 : 11.14 68.29 : 12.32 111.75 : 14.07 I I 24.83 : 11.25 71.39 1 12.47 114.85 1 14.20 I I 27.94 : 11.34 74.50 1 12.56 117.96 : 14.31 I I 31.04 1 11.24 77.60 : 12.69 121.06 : 14.44 I I 34.14 : 11.50 80.71 : 12.82 124.16 : 14.56 I I 37.25 : 11.56 83.81 : 12.94 127.27 1 14.66 I I 40.35 : 11.63 86.91 : 13.05 130.37 1 14.76 I I 43.46 1 11.67 90.02 : 13.17 133.48 1 14.88 I I 46.56 : 11.75 93.12 : 13.30 136.58 : 15.03 I I 49.67 : 11.82 96.23 1 13.38 139.68 : 15.13 I I 52.77 : 11.88 99.33 1 13.52 141.39 : 15.22 I I 55.87 : 11.94 I I I

Table 9.

275

BOREHOLE TEMPERATURE MEASUREMENTS GAVERIGAN SW 9316 5916 GAV-01 I I I DEPTH TEMPERATURE DEF'TH TEMPERATURE DEPTH TEMPERATURE I I METRES DEG C METRES DEG C METRES DEG C I I I • I 3.10 : 13.37 111.75 • 14.47 220.39 : 18.70 I I 6.21 . 10.71 114.85 : 14.60 223.49 : 18.83 I • I 9.31 •. 10.67 117.96 • 14.72 226.60 : 18.95 I I 12.42 . 10.99 121.06 : 14.83 229.70 : 19.05 I I 15.52 : 11.14 124.16 : 14.94 232.81 : 19.20 I I 18.62 : 11.28 127.27 • 15.06 235.91 : 19.32 I I 21.73 11.35 130.37 : 15.16 239.01 : 19.42 I • I 24.83 : 11.37 133.48 . 15.29 242.12 • 19.55 I I 27.94 •. 11.55 136.58 • 15.40 245.22 . 19.66 I I 31.04 : 11.67 139.68 : 15.53 248.33 : 19.80 I . I 34.14 • 11.77 142.79 . 15.64 251.43 : 19.93 I I 37.25 • 11.88 145.89 . 15.76 254.53 : 20.05 I • I 40.35 : 11.99 149.00 • 257.64 : 20.17 I • 1.87 I 43.46 : 12.09 152.10 • 16.00 260.74 : 20.29 I • I 46.56 : 12.18 155.20 • 16.14 263.85 : 20.41 I I 49.67 : 12.29 158.:31 16.25 266.95 : 20.53 I . I 52.77 : 12.38 161.41 • 16.38 270.06 : 20.66 I I 55.87 : 12.49 164.52 : 16.51 273.16 : 20.79 I • I 58.98 : 12.60 167.62 . 16.63 276.26 : 20.93 I I 62.08 : 12.76 170.72 : 16.74 279.37 : 21.05 I I 65.19 : 12.82 173.83 : 16.87 282.47 : 21.16 I • I 68.29 • 12.92 176.93 . 17.00 285.53 : 21.28 I I 71.39 : 13.03 180.04 : 17.12 288.68 : 21.42 I . • I 74.50 . 13.12 183.14 . 17.23 291.78 : 21.54 I . I 77.60 . 13.25 186.24 17.34 294.89 : 21.68 I I 80.71 •• 13.35 189.35 • 17.47 297.99 : 21.78 I I 83.81 : 13.45 192.45 • 17.58 301.10 : 21.86 I . I 86.91 . 13.57 195.56 : 17.71 304.20 : 21.96 I I 90.02 : 13.68 198.66 . 17.83 307.30 : 22.05 I I 93.12 • 13.79 201.77 : 17.96 310.41 : 22.15 I I 96.23 : 13.91 204.87 18.06 313.51 : 22.24 I . I 99.33 • 14.02 207.97 : 18.19 316.62 : 22.33 1 I 102.43 : 14.12 211.08 .• 18.34 319.72 : 22.43 I . I 105.54 14.25 214.18 . 18.46 322.82 : 22.52 I • I 108.64 . 14.35 217.29 • 18.57 325.93 : 22.62 I I I

Table 10. ======BOREHOLE TEMPERATURE MEASUREMENTS LONGDOWNS SW 7368 3466 CSD-01 ======~====~== I I I DEPTH TEMPERATURE rfEPTH TEMPERATURE DEPTH TEMPERATURE I I METRES DEG C METRES [lEG C METRES nEG C I I I I 30.65 11.04 82.74 12.77 134.59 • 14.58 I I 33.72 11.15 85.80 12.88 137.62 • 14.68 I I 36.78 11.24 88.86 12.99 140.64 • 14.79 I I 39.85 • ·1.31 91.92 13.09 143.66 • 14.90 I I 42.91 • ! 1. 43 94.98 13.19 146.68 • 15.00 I I 45.98 • 11.53 98.03 13.32 149.69 • 15.11 I I 49.04 11.62 101.09 13.40 152.70 • 15.23 I l~ I 52.10 11.73 104.15 13.52 155.70 • 15.34 I I 55.17 11.83 107.20 13.62 158.71 • 15.42 I I 58.23 11.93 110.26 13.73 161.71 • 15.53 I I 61.30 12.02 113.31 13.84 164.71 • 15.62 I I 64.36 • 12.14 116.36 13.96 167.70 • 15.74 I I 67.42 12.24 119.40 14.04 170.70 • 15.84 I I 70.49 12.33 122.44 • 14.16 173.69 • 15.94 I I 7~3. 55 12.44 125.49 14.27 176.68 • 16.06 I I 76.61 12.55 128.52 14.37 179.67 • 16.16 I I 79.67 12.66 131.56 14.49 182.66 16.21 I I I ======

Table 11.

277

BOREHOLE TEMPERATURE MEASUREMENTS ROSEMNOWAS HOLE A SW 7352 3456 ROS-OA I I I DEPTH TEMPERATURE DEPTH TEMPERATURE DEPTH TEMPERATURE I I METRES DEG C METRES DEG C METRES DEG C I I I I 6.12 :. 11.01 107.03 '. 13.54 204.89 . 16.65 I I 9.17 :. 10.62 110.09 :. 13.65 207.95 : 16.76 I I 12.23 .: 10.55 110.09 .: 13.65 211.01 : 16.84 I I 15.29 :. 10.64 113.15 :. 13.74 214.07 : 16.95 I I 18.35 : 10.76 116.21 : 13.85 217.12 :. 17.04 I I 21.41 '. 10.90 119.26 :. 13.96 2:J.18 .: 17.14 I I 24.46 : 11.03 122.32 :. 14.03 223.24 17.24 I I 27.52 : 11.14 125.38 : 14.13 226.30 : 17.34 I I 30.58 :. 11.21 128.44 :. 14.22 229.36 :. 17.44 I I 33.64 11.33 131.50 : 14.33 232.41 :. 17.54 I I 36.70 : 11.40 134.56 :. 14.41 235.47 :. 17.62 I I 39.75 :. 11.49 137.61 :. 14.50 238.53 :. 17.73 I I 42.81 11.58 140.67 : 14.61 241.59 : 17.82 I I 45.87 :. 11.67 143.73 : 14.71 244.65 : 17.93 I I 48.93 .: 11.77 146.79 : 14.80 247.70 :. 18.03 I I 51.99 .: 11.86 149.85 : 14.89 250.76 . 10.12 I I 55.05 : 11.95 152.90 : 15.01 253.82 :. 18.23 I I 58.10 . 12,05 155.96 :. 15.09 256.88 :. 18.33 I I 61.16 : 12.15 159.02 :. 15.18 259.94 : 18.41 I I 64.22 . 12.23 162.08 . 15.28 262.99 : 18.52 I I 67.28 :. 12.33 165.14 . 15.38 266.05 :. 18.62 I I 70.34 : 12.42 168.19 : 15.47 269.11 : 18.71 I I 73.39 : 12.50 171.25 : 15.57 272.17 : 18.91 I I 76.45 : 12.59 174.31 : 15.67 275.23 : 18.91 I I 79.51 : 12.69 177.37 : 15.77 278.28 :. 19.01 I I 92.57 .4 12.78 180.43 : 15.87 281.34 : 19.11 I I 85.63 : 12.87 183.48 .• 15.96 284.40 :. 19.22 I I 88.68 :. 12.98 186.54 : 16.06 287.46 :. 19.32 I I 91.74 : 13.07 189.60 : 16.16 290.52 :. 19.41 I I 94.80 : 13.17 192.66 : 16.26 293.58 :. 19.5', I I 97.86 : 13.26 195.72 : 16.35 296.63 : 19.60 I I 100.92 :. 13.37 198.77 : 16.45 299.69 19.69 I I 103.97 : 13.45 201.83 .: 16.55 302.75 :. 19.74 I I I

Table 12.

I. 278

BOREHOLE TEMPERATURE MEASUREMENTS ROSEMANOWAS HOLE D SW 7352 3460 ROS-OD

I I I DEPTH TEMPERATURE DEPTH TEMPERATURE DEPTH TEMPERATURE I I METRES DEG C METRES DEG C METRES DEG C I I I I 6.11 ~ 10.92 106.24 : 13.53 201.56 ~ 16.54 I I 9.17 % 11.03 109.26 ~ 13.64 204.51 ~ 16.66 I I 12^22 ~ 10^82 112.27 ~ 13.72 207.45 ~ 16.73 I I 15.28 : 10.68 115.28 ~ 13.82 210^40 : 16.02 I I 13.33 ; 10.73 110.28 : 13.92 213^34 : 16.92 I I 21.39 ~ 10.85 121.29 ~ 14.00 216.28 ~ 17^02 I I 24.44 ~ 10.94 124.29 : 14.09 219.21 ~ 17.11 I I 27.49 : 11^03 127.28 : 14.21 222"15 : 17.19 I I 30^54 : 11.11 130,27 ~ 14.29 225°08 : 17.29 I I 33.58 : 11.22 133.26 : 14.39 228^02 ~ 17.40 I I 36.62 : 11.31 136.25 : 14.50 230^95 ~ 17.50 I I 39.66 ~ 11.41 139.24 : 14.57 233.87 ~ 17.59 I I 42.69 ~ 11.51 142.23 : 14^66 236.80 ~ 17.67 I I 45.72 : 11.60 145.21 : 14.75 239.72 : 17.77 I I 48.76 ~ 11.69 148.20 : 14.85 242.64 ~ 17.87 I I 51.79 : 11.80 151.18 : 14^94 245.56 ~ 17.97 I I 54.82 : 11.89 154.17 : 15.04 248.47 : 18^08 I I 57.85 : 11.98 157,15 : 15.15 251.38 : 18.15 I I 60.88 : 12^09 160^12 ~ 15.24 254.28 ~ 18^25 1 I 63,91 ~ 12.18 163^10 : 15^33 257.18 : 18.34 I I 66.94 ~ 12.28 166^07 : 15.42 260.08 ~ 18^44 I I 69.97 ~ 12.38 169.04 : 15.53 262.97 ~ 18.54 I I 72.99 : 12.47 172.00 ~ 15.61 265.86 ~ 18,64 I I 76.02 : 12.57 174 ^96 ~ 15.72 268.74 ~ 18.71 I 1 79^05 ~ 12.66 177.93 ~ 15^80 271.62 : 18.82 I I 82.07 : 12.76 180,89 : 15.90 274^49 : 18.91 I I 85.10 : 12.86 183.85 : 15.97 277.36 ~ 19,00 I I 88.12 : 12.96 186.80 : 16.08 280.23 : 19.09 I I 91.15 ~ 13,05 189.76 : 16,28 283^09 : 19.19 I I 94.17 : 13.14 192.71 ~ 16.26 285.95 X 19.28 I 1 97.19 : 13.24 195.66 : 16.37 288^81 : 19.34 I I 100°21 : 13.33 198^81 ~ 16.46 291.67 ~ 19.41 I I 103^23 ~ 13.45 I I I

Table 13. 279

BOREHOLE TEMPERATURE MEASUREMENTS TROON DEEP SW 6570 3675 TKN'01 I I I DEPTH TEMPERATURE DEPTH TEMPERATURE DEPTH TEMPERATURE I I METRES DEG C METRES DEG C METRES DEG C I I I I 9.20 : 10°31 45.99 : 10,96 82~79 : 12.31 I I 12.27 : 10.35 49.06 ; 11.09 85.86 : 12.41 I I 15.33 : 10^40 52.13 : 11.19 88.92 : 12,52 I I 18^40 : 10.41 55.19 : 11^30 91.99 : 12.65 I I 21.46 : 10.38 58.26 : 11.48 95.05 : 12.77 I I 24.53 : 10^28 61.33 : 11.61 98.12 : 12.85 I I 27.60 : 10^18 64.39 : 11,71 101.19 : 12.95 I I 30.66 X 10.24 67.46 : 11.82 104.25 : 13.05 I I 33.73 : 10.38 70^52 : 11.92 107.32 : 13.12 I 1 38^80 : 10.53 73.59 : 12^02 110^39 : 13.21 I I 39.86 : 10^71 76.66 : 12.11 113.45 : 13.31 I I 42.93 : 10^85 79^72 : 12.21 116.52 : 13.39 I I I

BOREHOLE TEMPERATURE MEASUREMENTS WHITEHILL YEO SX 5805 6275 ______WHY -01 01 I I I DEPTH TEMPERATURE DEPTH TEMPERATURE DEPTH TEMPERATURE I I METRES DEG C METRES DEG C METRES DEG C I I I I 9.20 : 10,16 45.99 : 11.31 79.72 : 12.23 I I 12.27 : 10^37 49.06 : 11°41 82.79 : 12.32 I I 15.33 : 10.48 52.13 : 11.47 85.96 : 12.39 I I 18.40 : 10.56 55.19 : 11^54 88.92 : 12.47 I I 21.46 : 10^66 58^26 : 11.62 91.99 : 12.60 I I 24.53 ; 10^73 61.33 : 11.70 95.05 : 12.65 I I 27.60 : 10^81 64.39 : 11.77 98^12 : 12,76 I I 30.66 : 10.92 67.46 : 11.86 101.19 : 12.84 I I 33.73 : 10.99 70^52 : 11.94 104.25 : 12.94 I I 36"80 : 11.07 73.59 : 12.03 107^32 : 13.03 I I 39.86 : 11.15 76.66 : 12^13 110.39 : 13.14 I I 42.93 : 11.24 1 I I

Table 14. 280

BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS HEMERDON DDH H23 DDH-23 HEMERDON RDH H3 RDH-03 GRID REFERENCE SX 5733 5849 GRID REFERENCE SX 5733 5849 I II I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I METRES DEG C I I METRES DEG C I I II I I 3.07 12.40 I I 15.33 9.70 I I 6.13 I2.22 I I 18.40 9.91 I I 9.20 9.83 I I 21.46 10.09 I I 12.27 9.85 I r 24.53 10.16 I I 15.33 9.97 I I 27.60 10.21 I I 18.40 10.11 I I 30.66 10.26 I I 21.46 10.32 I I 33.73 10.31 I I 24.53 10.39 I I 36.80 10.38 I I 27.60 10.39 I I 39.86 10.44 1 I 30.66 10.48 I I 42.93 10.50 I I 33.73 10.50 I I 45.99 10.59 I I 36.80 10.58 I I 49.06 10.66 I I 39.86 10.62 I I 52.13 10.71 I I 42.93 10.67 I I 55.19 10.76 I I 45.99 10.75 I I 58.26 10.86 I I 49.06 10.79 I I 61.33 10.94 I I 52.13 10.88 I I 64.39 11.02 I I 55.19 10.91 I I 67.46 11.10 I I 58.26 11.02 I I 70.52 11.18 I I 61.33 11.10 I I 73.59 11.26 I I 64.39 11.18 I I 76.66 11.34 I 1 67.46 11.23 I I 79.72 11.44 I I 70.52 11.32 I I 82.79 11.53 I I 73.59 11.42 II 85.86 11.59 I I 76.66 11.48 I I 88.92 11.68 I I 79.72 11.56 I I 91.99 11.76 I I 82.79 11.67 I I 95.05 11.84 I I 85.86 11.72 I I 98.12 11.97 I I 88.92 11.82 I I 101.19 12.08 I I 91.99 11.90 II 104.25 12.18 I I 95.05 11.99 I I 107.32 12.29 I I 98.12 12.11 I I 110.39 12.37 I I 101.19 12.19 I I 113.45 12.50 I I 104.25 12.29 I I 116.52 12.61 I I 107.32 12.39 I I 119.59 12.71 I I 110.39 12.49 I I 122.65 12.82 I I 113.45 12.59 I I 125.72 12.94 I I 116.52 12.69 I I 128.78 13.03 I I 119.59 12.79 I I 131.85 13.13 I I 122.65 12.90 I I I I 125.72 13.00 I I 127.86 13.07 I I I

Table 15 281

BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS BOVEY TRACEY BOV-01 LANIVET PROSPER 2 PRO-02 GRID REFERENCE SX 8271 7929 GRID REFERENCE SX 0216 6413 I I I I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I METRES DEG C I I METRES DEG C I I I 1 1 I 5.31 10.75 I I 13.28 10.91 I I 7.96 10.93 I I 15.93 10.76 I I 10.62 11.04 I I 18.59 10.o7 I I 13.27 11.13 I I 21.24 10.64 I I 15.93 11.23 I I 23.90 10.63 I I 18.58 11.30 I I 26.55 10.63 1 I 21.24 11.35 I I 29.21 10.71 I I 23.89 11.40 I I 31.87 10.79 I I 26.55 11.47 I I 34.52 10.87 I I 29.20 11,54 I I 37.18 10.94 I I 31.85 11.57 I I 39.83 11.01 I I 34.51 11.64 I I 42.49 11.07 1 I 37.16 11.69 I I 45.14 11.14 1 I 39.82 11.76 I I 47.80 11.21 I I 42.47 11.83 I I 50.45 11.27 I I 45.13 11.90 I I 53.11 11.35 I I 47.78 11.96 I 1 55.77 11.42 I I 50.44 12.01 I I 58.42 11.49 I I 53.09 12.10 I I 61.08 11.t5 I I 55.74 12.21 I I 63.73 11.66 I I 58.40 12.33 I I 66.39 11.74 I I 61.05 12.38 I I 69.04 11.33 I I 63.71 12.42 I I 71.70 11.92 I I 66.36 12.49 I I 74.35 12.02 I I 69.02 12.54 I I 77.01 12.11 I I 71.67 12.60 I I 79.66 12.20 1 I 74.33 12.66 I I 82.32 12.29 I I 76.98 12.73 I I 84.98 12.37 I I 79.64 12.80 I I 86.46 12.34 I I 82.29 12.88 I I I I 84.94 12.95 I I 87.60 13.02 I I 90.25 13.08 I I 92.91 13.11 I I 95.24 13.16 I I I

Table 16.

BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS BELOWDA NI) 1 BEL-01BELOWDA NO 2 DEL-02MELDON QUARRY MEL-01 GRID REFERFNCE SW 9789 6242 GRID REFERENCE SW 9788 6254 GRID REFERENCE SX 5676 9220 I II II I I DEPTH TEMPERATURE II DEPTH TEMPERATURE II DEPTH TEMPERATURE I I MURES DEG C II METRES DEG C I I METRES DEG C I I II II I I 13.63 12.32 II 19.22 12.43 II 12.26 9.76 I I 20.69 12.32 II 25.65 12.05 1 I 15.33 10.03 1 I 27.74 12.68 II 32.08 12.10 1 I 18.39 10.18 I I 34.00 12.95 II 38.51 12.26 II 21.46 10.29 I I 41.06 13.26 11 44.94 12.24 1 I 24.52 10.40 I I 48.91 13.57 II 51.37 12.43 I I 27.59 10.55 I I 55.97 13.86 II 57.79 12.51 I I 30.65 10.69 I ro I 63.02 14.11 I I 64.22 12.55 I I 33.72 10.83 I 70.08 14.36 II 70.65 12.78 I I 36.78 10.95 I I 77.14 14.63 I 1 77.08 13.00 I I 39.85 11.08 I I II 83.51 13.23 II 42.91 11.22 I I 09.94 13.41 I I 45.98 11.32 I (ONLY 24 HRS AFTER DRILLING) I 96.37 13.66 I I 49.04 11.42 1 I 102.80 13.85 I I 52.11 11.51 I I 109.23 14.03 I I 55.17 11.59 I I 115.66 14.20 11 58.24 11.68 I I 122.09 14.33 I I 60.54 11.74 I I 128.51 14.53 I I I I 134.94 14.76 I I 141.37 14.99 I I I

Table 17. 283

BOREHOLE TEMPERATURE MEASUREMENTS BOREHOLE TEMPERATURE MEASUREMENTS NEWLYN EAST 1 NEW-01 NEWLYN EAST 4 NEW-04 GRID REFERENCE SW 8146 5390 GRID REFERENCE SW 8141 5384 I I I I I DEPTH TEMPERATURE I I DEPTH TEMPERATURE I I METRES DEG C I I METRES DEG C I I I I I I 8.60 11.13 I I 10.62 11.04 I I 11.48 11.03 I I 13.27 11.06 I I 14.36 11.03 I I 15.92 11.13 I I 17.24 11.04 I I 18.57 11.20 I I 20.12 11.08 I I 21.22 11.25 I I 23.01 11.12 I I 23.87 11.33 I I 25.90 11,37 I I 26.51 11.37 I I 28.79 11.54 I I 29.16 11.44 I I 31.69 11.56 I I 31.81 11.50 I I 34.59 11.61 I I 34.45 11.56 I I 37.49 11.64 I I 37.10 11.64 I I 40.40 11.68 I I 39,74 11.73 I I 43.31 11.73 I I 42.38 11.80 I I 46.22 11.77 I I 45.03 11.88 I I 49.13 11.88 I I 47.67 11.95 I I 52.05 12.05 I I 50.31 12.02 I I 54.97 12.27 I I 52.95 12.10 I I 57.90 12.37 I I 55.59 12.17 I I 60.82 12.42 I I 58.22 12.23 I I 63.75 12.47 I I 60.86 12.30 I I 66.68 12.63 I I 63.50 12.36 I I 69.62 12.67 I I 66.13 12.45 I I 72.56 12.89 I I 68.77 12.53 I I 75.50 12.90 I I 71.40 12.61 I I 78.44 13.00 I I 74.03 12.66 I I 81.38 13.14 I I 74.40 12.76 I I 84.33 13.22 I I I I 87.28 13.30 I I 90.24 13.37 I I 93.19 13.40 I I 96.15 13.55 I I 99.11 13.61 I I 102.07 13.72 I I 103.11 13.81 I I I

Table 18. 284

BOREHOLE TEMPERATURE MEASUREMENTS F'REDANNACK DOWN SW 6901 1634 PRE-01 I I I DEPTH TEMPERATURE DEPTH TEMPERATURE DEPTH TEMPERATURE I I METRES DEG C METRES DEG C METRES DEG C I I I I 3.06 10.12 107.23 : 13.89 208.34 : 16.63 I I 6.13 : 10.73 110.30 : 13.97 211.40 : 16.72 I I 9.19 : 11.94 113.36 : 14.05 214.46 : 16.80 I I 12.26 : 11.97 116.42 : 14.13 217.53 : 16.88 I I 15.32 : 11.97 119.49 14.21 2^0.59 : 16.97 I I 18.38 : 12.01 12.55 : 14.29 223.65 : 17.06 I I 21.45 12.07 125.61 . 14.36 226.72 : 17.15 I I 24.51 : 12.12 128.68 : 14.44 229.78 : 17.23 I I 27.57 : 12.17 131.74 : 14.52 232.85 : 17,32 I I 30.64 : 12.21 134.81 : 14.60 235.91 : 17.40 I I 33.70 : 12.27 137.87 : 14.68 238.97 : 17.49 I I 36.77 : 12.32 140.93 : 14.77 242.04 : 17.57 I I 39.83 12.38 144.00 14.85 245.10 : 17.66 I I 42.89 : 12.43 147.06 14.92 248.16 : 17.75 I I 45.96 : 12.49 150.12 15.00 251.23 : 17.83 I I 49.02 : 12.55 153.19 : 15.08 254.29 : 17.92 I I 52.08 : 12.61 156.25 : 15.16 257.36 : 18.00 I I 55.15 . 12.67 159.32 : 15.24 260.42 : 18.08 I I 58.21 : 12.73 162.38 : 15.33 263.48 : 18.15 I I 61.28 12.79 165.44 : 15.43 266.55 : 18.24 I I 64.34 : 12.86 168.51 : 15.52 269.61 : 18.32 I I 67.40 : 12.92 171.57 : 15.61 272.67 : 18.41 I I 70.47 : 12.99 174.63 : 15.69 275.74 : 18.48 I I 73.53 13.06 177.70 : 15.77 278.80 : 18,57 I I 76,59 . 13.13 180.76 : 15.85 281.87 : 18.66 I I 79.66 : 13.20 183.83 : 15.93 284.93 : 18.75 I I 82.72 : 13.28 186.89 16.02 287.99 : 18.84 I I 85.79 : 13.36 189.95 : 16.11 291.06 : 18.93 I I 88.85 : 13.43 193.02 : 16.20 294.12 . 19.03 I I 91.91 : 13.51 196.08 : 16.28 297.18 : 19.12 I I 94.98 : 13.53 199.14 : 16.38 300.25 : 19.20 I I 98.04 13.66 202.21 : 16.47 303.31 : 19.28 I I 101.10 : 13.73 205.27 : 16.55 303.92 : 19.35 I I 104.17 : 13.81 I I I

Table 19. 285

BOREHOLE TEMPERATURE MEASUREMENTS KENNACK SANDS SW 7325 1647 KEN-01 I I I DEPTH TEMPERATURE DEPTH TEMPERATURE DEPTH TEMPERATURE I I METRES DEG C METRES DEG C METRES DEG C I I I I 3.08 : 10.18 55.45 . 13.55 107.81 : 15.00 I I 6.16 : 11.06 58.53 : 13.63 110.89 : 15.08 I I 9.24 12.73 61.61 : 13.72 113.97 : 15.18 I I 12.32 12.69 64.69 : 13.81 117.05 : 15.26 I I 15.40 : 12.68 67.77 : 13.91 120.13 : 15.33 I I 18.48 : 12.69 70.85 : 14.02 123.21 : 15.43 I I 21.56 : 12.72 73.93 : 14.12 126.29 : 15.50 I I 24.64 . 12.76 77.01 : 14.2C 129.37 15.62 I I 27.72 . 12.81 80.09 : 14.29 132.45 : 15.73 I I 30.80 12.90 83.17 : 14.38 135.54 : 15.80 I I 33.88 : 12.97 86.25 : 14.46 138.62 : 15.88 I I 36.96 : 13.04 89.33 : 14.55 141.70 : 15.97 I I 40.04 : 13.11 92.41 . 14.62 144.78 : 16.05 I I 43.12 : 13.18 95.49 : 14.70 147.86 : 16.15 I I 46.21 : 13.30 98.57 : 14.76 150.94 . 16.25 I I 49.29 : 13.38 101.65 : 14.84 151.71 : 16.27 I I 52.37 : 13.47 104.73 : 14.91 I I I

BOREHOLE TEMPERATURE MEASUREMENTS CURRYPOOL FARM ST 2270 3871 CUR-01 I I I DEPTH TEMPERATURE DEPTH TEMPERATURE DEPTH TEMPERATURE I I METRES DEG C METRES DEG C METRES DEG C I I I I 9.20 : 11.06 70.52 : 11.71 128.78 . 12.78 I I 12.27 : 11.13 73.59 : 11.76 131.85 : 12.84 I I 15.33 : 10.98 76.66 : 11.81 134.92 : 12.86 I I 18.40 10.90 79.72 : 11.87 137.98 : 12.95 I I 21.46 : 10.89 82.79 11.92 141.05 : 13.02 I I 24.53 : 10.92 85.86 : 11.98 144.12 : 13.08 I I 27.60 : 10.96 88.92 : 12.05 147.18 : 13.14 I I 30.66 : 11.00 91.99 : 12.12 150.25 : 13.20 I I 33.73 : 11.05 95.05 : 12.18 153.31 : 13.26 I I 36.80 : 11.09 98.12 : 12.25 156.38 : 13.32 I I 39.86 : 11.14 101.19 : 12.34 159.45 : 13.38 I I 42.93 : 11.19 104.25 : 12.40 162.51 : 13.43 I I 45.99 : 11.25 107.32 : 12.46 165.58 : 13.49 I I 49.06 . 11.31 110.39 : 12.51 168.65 : 13.55 I I 52.13 : 11.36 113.45 : 12.55 171.71 : 13.62 I I 55.19 11.44 116.52 : 12.59 174.78 . 13.68 I I 58.26 : 11.47 119.59 : 12.67 177.84 : 13.74 I I 61.33 : 11.55 122.65 . 12.69 180.91 : 13.79 I I 64.39 : 11.60 125.72 : 12.74 182.01 : 13.83 I I 67.46 : 11.66 I I I

Table 20. BOREHOLE TEMPERATURE MEASUREMENTS CANNINGTON PARK ST24794 011 CAN-01

I I I DEPTH TEMPERATURE DEPTH TEMPERATURE DEPTH TEMPERATURE I I METRES DEG C METRES DEG C METRES DEG C I I I I 9.31 ~ 10.52 251.41 14.00 493.52 ~ 16.03 I I 12.42 ~ 10,89 254^52 14.04 496^62 : 16.86 1 I 15.52 ~ 11.00 257.62 14.08 499.72 : 16.88 I I 18.62 : 11^10 260.73 14.12 502,83 : 16.92 I I 21.73 ~ 11,14 263.83 14.16 505.93 : 16.96 I I 24.03 ~ 10^87 266.93 14.21 509^03 ~ 16.99 I I 27.93 ~ 11.07 270.04 14.23 512.14 ~ 17.03 I I 31.04 ; 11.16 273.14 14.27 a15^24 : 17.06 I I 34.14 ~ 11.16 276.24 14.30 513.35 ~ 17.09 I I 37.25 ~ 11.16 279.35 14.35 521.45 ~ 17.13 I I 40.35 : 11.17 282.45 14^39 524.55 ~ 17.16 I I 43.45 ~ 11.16 285.56 14.43 527.66 ~ 17^20 I 1 46.56 ~ 11.17 288.66 14.46 530.76 : 17.23 I I 49.66 ~ 11.21 291.76 14.49 533.87 : 17.26 I I 52^77 ~ 11.24 294.87 14.53 536.97 ; 17^30 I I 55.87 ~ 11.20 297.97 14^57 540^07 ~ 17.34 I I 50.97 : 11.29 301.08 14.60 543.13 ~ 17.37 I I 62.08 : 11°34 304.16 14.64 546.28 : 17.41 I 1 65.18 ~ 11.36 307.28 14.68 549^38 ~ 17.43 I I 68.29 ~ 11^40 31O^39 14.73 552,49 : 17.45 I I 71.39 ~ 11.43 313.49 14.76 555.59 ~ 17.51 I I 74.49 : 11.46 316.59 14.79 558.70 ~ 17.55 I I 77.60 ~ 11.52 319.70 14,84 561.80 ~ 17,60 I I 80.70 ~ 11°55 322.80 14.88 564^90 ~ 17.64 1 I 83.80 ~ 11^60 325.91 14.91 568.01 ~ 17.64 I I 86,91 : 11.64 329.01 14.95 571.11 : 17.67 I I 90.01 ~ 11^68 332.11 14.99 574.22 : 17"70 I I 93.12 ~ 11.74 335.22 15.02 577.32 ~ 17.74 I I 96.22 ~ 11.76 338.32 15.05 580^42 ~ 17.78 I I 99.32 : 11.83 341.43 15.09 583.53 ~ 17.82 I I 102.43 ~ 11.89 344.53 15.14 586.63 ~ 17.85 I I 105.53 ~ 11.94 347.63 15.17 589^74 ~ 17.90 I I 108.64 : 11.99 350.74 15.21 592.84 ~ 17.93 I I 111.74 ~ 12.04 353.84 15.25 595.94 ~ 17.96 I I 114.84 ~ 12.09 356.95 15.28 599.05 % 17.99 I I 117^95 ~ 12"14 360.05 15.32 602.15 ~ 18.03 I I 121°05 ~ 12.19 363.15 15.36 605.25 ~ 18.07 I I 124.15 ~ 12.23 386^28 15.40 608"38 ~ 18.10 I I 127.26 ~ 12^20 369.36 15.45 611.46 ~ 18.14 I I 130.36 : 12.32 372.46 15.47 614.57 : 1Q.18 ~ I ~

Table 21. 287

CANNINGTON PARK BOREHOLE TEMPERATURE MEASUREMENTS CONTINUED

I I I 133.47 : 12.37 375.57 : 15.51 617.67 : 18,22 I I 136.57 : 12.41 378.67 ~ 15^54 620 ^77 : 1~.27 I I 139.67 : 12.45 381.78 : 15^58 623.88 ~ 18,28 I I 142.78 : 12^50 384.88 : 15.62 626,98 : 1P.32 I I 145.88 : 12.54 387,98 ~ 15.66 630.09 : 18.35 I 1 148.99 : 12.59 391.09 ~ 15"70 633.19 : 18.37 I I 152.09 : 12.63 394.19 ~ 15.73 636.29 : 18,41 I I 155.19 : 12.68 397.30 : 15.76 639.40 ~ 18,44 I I 158,30 : 1 2^72 400.4C : 15.80 642.50 ~ 18.48 I I 161.40 : 12.76 403.50 : 15.85 645.60 : 18.51 I I 164.51 : 12.80 406.61 X 15.89 648.71 : 18.53 I I 167.61 : 12.85 409^71 : 15.92 651.81 : 18.56 I I 170.71 : 12.89 412.81 : 15.95 654.92 : 18,60 I I 173.82 : 12.95 415.92 : 15.99 658.02 : 18.62 I I 176.92 : 12.99 419^02 : 16.02 661.12 . 18.66 I I 180^02 : 13^04 422.13 : 16.06 664.23 : 18.69 I I 133.13 : 13.08 425.23 : 16^09 667.33 : 18.72 I I 186.23 : 13"13 428.33 2 16.13 670^44 ~ 18.77 I I 10n.34 : 13.13 431.44 : 16.16 673.54 : 18.80 I I 192.44 : 13.22 434.54 : 16.20 676.64 ~ 18.84 I I 195.54 : 13.25 437.65 : 16.23 679.75 : 18.86 I I 198.65 : 13.29 440^75 : 16.27 682.85 : 18.90 I I 201.75 ~ 13.35 443.85 ~ 16^31 685.96 ~ 18~93 I I 204^86 : 13.39 446.96 : 16.34 689.06 : 18.96 I I 207^96 : 13.43 450 ^ 06 : 16.37 692.16 : 19.00 I I 21 1^ 06 2 13,47 453.16 : 16.40 695.27 2 19.03 I I 214^17 2 13.51 456.27 : 16.43 698.37 : 19^05 I I 217.27 : 13.56 459.37 : 16.46 701.47 : 19.09 I I 220°37 2 13.60 462.48 : 16.49 704.58 : 19.12 I I 223.48 ~ 13.64 465.58 : 16.54 707.68 : 19.15 I I 226.58 : 13.68 468.68 2 16.58 710.79 2 19.19 I I 229.69 : 13.72 471.79 2 16.61 713.89 2 19.23 I I 232.79 : 13,77 474.89 2 16.63 716.99 : 19.27 I I 235.89 : 13.79 478^00 : 16.66 720^10 : 19.31 I I 239.00 : 13.85 481.10 : 16.70 723.20 : 19.34 I I 242.10 : 13.89 484.20 : 16.73 726.31 : 19.38 I I 245.21 : 13.92 487.31 : 16.75 729.41 : 19.41 I I 248.31 ~ 13.96 490.41 ~ 16.81 732.51 : 19.43 I I I

Table 21 continued. 288

Appendix III Tabulation of Thermal Conductivity Data

The thermal conductivity data is expressed in Watts per metre per degree (Wm-1K-1). The depth is given as metres along the length of the borehole. In the case of percussion boreholes the depth is only a guide, since there is uncertainty as to the exact depth of the sample measured. Samples were collected over the length of one, approximately 3 metres(10ft), drill rod. The tabulated depth represents the maximum possible depth of the sample. The sample code for percussion boreholes is comprised of, first the borehole code and then the number of the drill rod. The CSD borehole codes are in chronological order of drilling and so do not translate directly into the location code. eg.,

Location code Sample code

CM-A(Grills Farm) CSD-4

CM-B(Polgear Beacon) CSD-7

Details of the measurement and accuracy of these determinations may be found in chapter 3.

Table No. Station Name

1 Grillis Farm 2 Polgear Beacon 3 Medlyn Farm 4 Trevease Farm 5 Trerghan Farm 6 Bray Down 7 Blackhill 8 Pinnockshill 9 Browngelly

289

Table No. Station Name

10 Gt Hammet Farm 11 Newmill 12 Bunker's Hill 13 Tregarden Farm 14 Colcerrow Farm 15 Winter Tor 16 Blackingstone 17 Soussons Wood 18 Laughter Tor 19 Foggin Tor 20 Merrose Farm 21 Kestle Wartha 22 Callywith Farm 23 Gaverigan 24 Longdowns 25 Rosemanowas A 26 Rosemanowas D 27 Troon 28 Hemerdon DDH-H23 29 Hemerdon RDH-H3 30 White Hill Yeo 31 Bovey Tracey 32 Meldon 33 Newlyn East - 1 34 Belowda Beacon - 1 35 Predannack 36 Kennack Sands 37 Cannington Park 38 Currypool Farm 39 Little Polgear 290

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS GRILLIS FARM SW 6795 3846 CSD-04 SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/OEG CSD-04-02 6.1 3.38 CSD-04-03 9.1 3.52 CSD-04-04 12.2 3.02 CSD-04-05 15.2 3.25 CSD-04-06 18.3 3.46 CSD-04-07 •21.3 3.14 CSD-04-08 24.4 3.37 CSD-04-09 27.4 3.28 CSD-04-10 30.5 3.28 CSD-04-11 33.5 3.10 CSD-04-12 36.6 3.29 CSD-04-13 39.6 3.45 CSD-04-14 42.7 3.25 CSD-04-15 45.7 3.46 CSD-04-16 48.8 2.98 CSD-04-17 51.8 3.00 CS0-04-16 54.9 3.32 CSD-04-19 57.9 3.09 CSD-04-20 61.0 3.11 CSD-04-21 64.0 3.64 CSD-04-22 67.1 3.45 CSD-04-23 70.1 3.36 C5D-04-24 73.2 3.43 CS0-04-25 76.2 3.44 CSD-04-26 79.2 3.43 CSD-04-27 82.3 3.40 C5D-04-28 85.3 3.30 CSD-04-29 88.4 3.47 CSD-04-30 91.4 3.23 CSD-04-31 94.5 3.39 CSD-04-32 97.5 3.38 CSD-04-33 100.6 3.25 CSD-04-34 103.6 3.30 ARITHMETIC MEAN = 3.31 STANDARD DEVIATION = .16

Table 1. 291

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS POLGEAR BEACON SW 6927 3663 CSO -07 SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG CSD-07-10 33.5 3.48 CSD-07-11 36.6 2.95 CSD-07-12 39.6 3.20 CSD-07-13 42.7 3.58 CSD-07-14 45.7 3.19 CSD-07-15 48.8 3.32 CSD-07-16 51.8 3.21 CSD-07-17 54.9 3.13 CSD-07-18 57.9 3.51 CSD-07-19 61.0 3.08 CSO-07-20 64.0 3.56 CSD-07-21 67.1 3.93 CSD-07-22 70.1 4.04 CSD-07-23 73.2 4.09 C5D-07-24 76.2 3.99 CSD-07-25 79.2 3.90 CSD-07-26 82.3 3.84 CSD-07-27 85.3 3.48 CSD-07-28 88.4 3.91 CSD-07-29 91.4 4.04 CSD-07-30 94.5 3.77 CSD-07-31 97.5 3.38 CSD-07-32 100.6 3.56 ARITHMETIC MEAN = 3.57 STANDARD DEVIATION = .35

Table 2. 292

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS MEDLYN FARM SW 7083 3404 CSD-05 SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG CSD-05-03 9.1 2.97 CS0-05-04 12.2 3.25 CSD-05-06 18.3 3.08 CSD-05-07 21.3 3.40 CS0-05-08 24.4 4.11 C5D-05-09 27.4 3.38 CSD-05-10 30.5 3.60 CSD-05-11 33.5 3.19 CSD-05-12 36.6 3.13 CSD-05-13 39.6 3.18 CSD-05-14 42.7 3.17 CSD-05-15 45.7 3.38 CSD-05-16 48.8 3.38 CSO-05-17 51.8 3.66 CSD-05-18 51.8 3.33 CSD-05-19 57.9 3.44 CSD-05-20 61.0 3.53 CSD-05-21 64.0 3.50 CSD-05-22 67.1 3.46 CSD-05-23 70.1 3.42 CSD-05-24 73.2 3.28 CSD-05-25 76.2 2.97 CSD-05-26 79.2 3.34 CSD-05-27 82.3 3.22 CSD-05-28 85.3 3.22 C5D-05-29 86.4 3.42 CSD-05-30 91.4 3.22 CSO-05-31 94.5 3.16 CSD-05-32 97.5 2.99 CSD-05-33 100.6 3.21 CSD-05-34 103.6 3.21 ARITHMETI MEAN = 3.32 STANDARD DEVIATION = .23

Table 3. 293

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

TREVEASE FARM SW 7185 3180 CSD-02 SAMPLE CODE DEPTH IN METRES CONDUCTIVITY w/M/OEG CSD-02-02 6.1 3.36 CSD-02-03 9.1 3.36 CSD-02-04 12.2 3.30 CS0-02-05 15.2 3.30 CSD-02-06 18.3 3.20 CSD-02-07 21.3 3.14 CSD-02-08 24.4 3.21 CSD-02-09 27.4 3.16 CSD-02-10 30.5 3.23 CSO-02-11 33.5 3.35 CSD-02-12 36.6 3.25 CSD-02-13 39.6 3.32 CSD-02-14 42.7 3.29 CSD-02-15 45.7 3.22 CSD-02-16 48.8 3.17 CSD-02-17 51.8 3.19 CSD-02-18 54.9 3.30 CSD-02-19 57.9 3.17 CSD-02-20 61.0 3.33 CS0-02-21 64.0 3.28 CSD-02-22 67.1 3.27 CSD-02-23 70.1 3.33 CSD-02-24 73.2 3.52 CS0-02-25 76.2 3.40 CSD-02-26 79.2 3.37 CSD-02-27 82.3 3.43 CSD-02-28 85.3 3.37 CSD-02-29 88.4 3.50 C5D-02-30 91.4 3.37 CSD-02-31 94.5 2.98 CSD-02-32 97.5 3.13 CSD-02-33 100.6 3.03 CSD-02-34 103.6 3.18

ARITHMETIC MEAN = 3.27 STANDARD DEVIATION = .12

Table 4. 294

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS TREGHAN FARM SW 7353 3033 CSD-06 SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/MVDEG CSD-06-03 9.1 2.97 CSD-06-04 12.2 3.00 CSD-06-05 15.2 3.12 CSD-06-06 18.3 3.18 CSD-06-07 21.3 3.24 CSD-06-08 24.4 3.34 CSD-06-09 27.4 3.04 CSD-06-10 30.5 3.30 CSD-05-11 33.5 3.20 CSD-06-12 36.6 3.19 CSD-06-13 39.6 3.04 CSD-06-14 42.7 2.92 CSD-06-15 45.7 3.11 CSD-06-16 48.8 3.45 CSD-06-17 51.8 3.45 CSD-06-18 54.9 3.52 CSD-06-.19 57.9 3.23 CSD-06-20 61.0 3.21 CSD-06-21 64.0 3.42 CSD-06-22 57.1 3.27 CSD-05-23 70.1 3.36 CSD-06-24 73.2 3.26 CSD-06-25 76.2 3.14 CSD-06-26 79.2 3.28 CSD-06-27 82.3 3.25 CSD-06-28 85.3 3.14 CSD-06-29 88.4 3.27 CSD-06-30 91.4 3.66 CSD-06-31 94.5 2.98 CSD-06-32 97.5 3.27 CSD-06-33 100.6 3.06 CSD-06-34 103.6 2.97 ARITHMETIC MEAN = 3.21 STANDARD DEVIATION = .17

Table 5. 295

THERMAL CONDUCTIVITY RESULTS FROM CNIP r£ASUREMENTS

BRAY DOHN SX 1907 8177 CSD-11

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

CSD-11-01 3.0 3.27 CSD-11-02 6.1 3.18 CSD-11-03 9.1 3.17 CSD-11-04 12.2 3.43 CSD-11-05 15.2 3.63 C50-11-06 18.3 3.49 CSO-11-07 21.3 3.68 CSO-11-08 24.4 3.67 CSD-11-09 27.4 3.54 CSD-11-10 30.5 3.51 CSD-11-11 33.5 3.37 CSD-11-12 36.6 3.43 CSD-11-13 39.6 3.32 CSD-11-14 42.7 3.10 CSD-11-15 45.7 3.10 CSO-11-16 48.8 3.22 CS0-11-17 51.8 3.35 C50-11-18 54.9 3.23 C50-11-19 57.9 3.13 C50-11-20 61.0 3.30 C5D-11-21 64.0 3.03 C50-11-22 67.1 3.32 CS0-11-23 70.1 3.41 C50-11-24 73.2 3.41 CSO-11-25 76.2 3.42 CSD-11-26 79.2 3.35 C50-11-27 82.3 3.39 CSD-11-28 85.3 3.64 CSD-11-29 88.4 3.53 C5D-11-30 91.4 3.45 C50-11-31 94.5 3.34

RRITHfETIC KERN = 3.37 STANDARD DEVIATION = .17 i Table 6. • 296

THERMAL CONDUCTIVITY RESULTS FROM CHIP rEASURErENTS

BLACKHILL SX 1835 7820 CSD-10

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

CSD-10-01 3.0 3.34 C5D-10-02 6.1 3.33 CSD-10-03 9.1 3.26 CSD-10-04 12.2 3.80 CSD-10-05 15.2 3.42 CSD-10-06 18.3 3.24 C50-10-07 21.3 3.53 CSD-10-08 24.4 3.53 CSD-10-09 27.4 3.47 CSD-10-10 30.5 3.31 CSD-10-11 33.5 3.24 CSD-10-12 36.6 3.03 CSD-10-13 39.6 3.63 CSD-10-14 42.7 3.27 C50-10-15 45.7 3.28 CSD-10-16 48.8 2.84 CSD-10-17 51.8 3.47 C50-10-18 54.9 3.63 C50-10-19 57.9 3.51 CSO-10-20 61.0 3.46 C50-10-21 64.0 3.55 CSD-10-22 67.1 3.21 CSD-10-23 70.1 3.65 CSD-10-24 73.2 3.50 CSD-10-25 75.2 3.53 CSD-10-26 79.2 3.48 CSD-10-27 82.3 3.56 CSD-10-28 85.3 3.47 CSD-10-29 88.4 3.48 CSD-10-30 91.4 3.31 CSD-10-31 94.5 3.40 C50-10-32 97.5 3.51 CSO-10-33 100.6 3.44 C5D-10-34 103.6 3.47

ARITHrETIC MEAN = 3.42 STANDARD DEVIATION = .18

Table 7. 297

THERMAL CONDLtCTIvITY RESULTS FROM CHIP rERSUREt-ENTS

PINNOCKSHILL SX 1892 7450 CSD-12

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

C5D-12-01 3.0 3.13 CSD-12-02 6.1 2.98 CSD-12-03 9.1 3.14 CSO-12-04 12.2 3.11 CSD-12-05 15.2 3.00 CSD-12-06 18.3 2.96 CSD-12-07 21.3 3.02 CSD-12-08 24.4 3.04 C5D-12-09 27.4 3.10 C50-12-10 30.5 2.91 C5D-12-11 33.5 3.10 CSD-12-12 36.6 3.13 CSD-12-13 39.6 3.12 C5D-12-14 42.7 3.28 CSD-12-15 45.7 3.07 CSD-12-16 48.8 3.02 CSD-12-17 51.8 3.11 C50-12-18 54.9 2.97 CSD-12-19 57.9 3.09 C5D-12-20 61.0 2.92 CSD-12-21 64.0 3.27 CSD-12-22 67.1 3.37 C50-12-23 70.1 3.24 CSO-12-24 73.2 3.15 CSD-12-25 76.2 3.06 CSD-12-26 79.2 2.99 CSD-12-27 82.3 2.98 C50-12-28 85.3 2.86 C5D-12-29 88.4 3.46 CSD-12-30 91.4 3.24 CSD-12-31 94.5 3.01 CSD-12-32 97.5 3.00 CSD-12-33 100.6 3.12

ARITHMETIC MEAN = 3.09 STANDARD DEVIATION = .13

Table 8. 298

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS BRO1NGELLY SX 1924 7247 CSD-09 SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG CSD-09-03 9.1 3.24 csD-09-04 12.2 3.27 CSD-09-05 15.2 3.34 CSD-09-06 18.3 3.22 CSD-09-07 21.3 3.24 CSD-09-08 24.4 3.47 CSD-09-09 27.4 3.75 CSD-09-10 30.5 3.29 CSD-09-11 33.5 3.45 CSD-09-12 36.6 3.48 CSD-09-13 39.6 3.70 CSD-09-14 42.7 3.20 CSD-09-15 45.7 3.17 CSD-09-15 48.8 3.28 C5D-09-17 51.8 3.24 CSD-09-18 54.9 3.45 CSD-09-19 57.9 3.21 CSD-09-20 61.0 3.49 CSD-09-21 64.0 3.30 CSD-09-22 67.1 3.46 CSD-09-23 70.1 3.34 CSD-09-24 73.2 3.43 CS0-09-25 76.2 3.58 CSD-09-28 79.2 3.60 C50-09-27 82.3 3.67 CSD-09-28 85.3 3.70 CSD-09-29 88.4 3.52 CSD-09-30 91.4 3.55 CSD-09-31 94.5 3.56 CSD-09-32 97.5 3.39 CSD-09-33 100.6 3.41 CSD-09-34 103.6 3.25

ARITHMETIC MEAN = 3.41 STANDARD DEVIATION = .17

Table 9. 299

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS GREAT HAMMETT SX 1885 6986 CSD-08 SAMPLE CODE DEPTH !N METRES CONDUCTIVITY W/M/DEG CSD-08-01 3.0 3.22 CSD-08-02 6.1 3.35 CSD-08-03 9.1 3.68 CSD-08-04 12.2 3.39 CSD-08-05 15.2 3.01 CSD-08-06 18.3 3.36 CSD-08-07 21.3 3.60 CSD-08-08 24.4 3.57 cS0-08-09 27.4 3.25 CSD-08-10 30.5 3.27 CSD-08-11 33.5 3.22 CSD-08-12 36.6 3.36 CSD-08-13 39.6 3.39 CSD-08-14 42.7 3.28 C5D-08-15 45.7 3.07 CSD-08-16 48.8 3.30 CSD-08-17 51.8 3.17 C5D-08-18 54.9 3.17 CSO-08-19 57.9 3.09 CSD-08-20 61.0 3.08 CSD-08-21 64.0 3.31 CSD-08-22 67.1 3.32 CSD-08-23 70.1 2.95 CSO-08-24 73.2 3.20 CSD-08-25 76.2 3.33 CSD-08-26 79.2 3.42 CSD-08-27 82.3 3.28 CSD-08-28 85.3 3.16 C5D-06-29 88.4 3.06 CSD-08-30 91.4 3.36 CSD-08-31 94.5 3.36 CSD-08-32 97.5 3.40 CSD-08-33 100.6 3.30 CSD-08-34 103.6 3.17 ARITHMETIC MEAN = 3.28 STANDARD DEVIATION = .16

Table 10. •

300

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

NEWMILL QUARRY SW 4608 3435 CSD-14 SArPLE COPE DEPTH IN METRES CONDUCTIVITY W/M/DEG

CSD-14-01 3.0 3.45 CSD-14-02 6.1 3.36 CSD-14-03 9.1 3.46 CSD-14-04 12.2 3.33 G ;D-14-05 15.2 3.33 CSD-14-06 18.3 3.47 C50-14-07 21.3 3.53 CSD-14-08 24.4 3.30 C5D-14-09 27.4 3.56 C5D-14-10 30.5 3.49 CSD-14-11 33.5 3.36 CSD-14-12 36.6 3.53 CSD-14-13 39.6 3.42 CSD-14-14 42.7 3.59 C50-14-15 45.7 3.14 CSD-14-145 48.8 3.29 CSD-14-17 51.8 3.08 CSD-14-18 54.9 3.20 CSO-14-19 57.9 3.17 CSD-14-20 61.0 3.36 CSD-14-21 64.0 3.34 CSD-14-22 67.1 3.40 CSD-14-23 70.1 3.16 CSD-14-24 73.2 3.30 CSO-14-25 76.2 3.29 CSD-14-26 79.2 3.49 CSD-14-27 82.3 3.54 CSD-14-28 85.3 3.18 CSD-14-29 88.4 3.23 CSD-14-30 91.4 3.44 CSD-14-31 94.5 3.39 CSD-14-32 97.5 3.63 CSD-14-33 100.6 3.42 CSD-14-34 103.6 3.06 ARITHMETIC MEAN = 3.36 STANDARD DEvIATION = .15

Table 11. 301

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS BUNKERS HILL SW 4022 2726 CSD-13 SAMPLE CODE DEPTH IN METRES CONDUCTIvITY W.M,DEG CSD-13-01 3.0 2.98 CSD-13-02 6.1 3.21 CSD-13-03 9.1 3.13 CSD-13-04 12.2 3.18 CSD-13-05 15.2 3.44 CSD-13-06 18.3 3.23 CSD-13-07 21.3 3.68 CSD-13-08 24.4 3.21 CSD-13-09 27.4 3.46 CSO-13-10 30.5 3.22 CSD-13-11 33.5 3.38 CSO-13-12 36.6 3.46 CSD-13-13 39.6 3.14 CSD-13-14 42.7 3.29 CSD-13-15 45.7 3.46 CSD-13-16 48.8 3.13 CSD-13-17 51.8 3.65 CSD-13-18 54.9 3.33 CSD-13-19 57.9 3.29 CSD-13-20 61.0 3.50 CSD-13-21 64.0 3.29 CSD-13-22 67.1 2.74 CSD-13-23 70.1 3.68 CSD-13-24 73.2 3.44 CSD-13-25 76.2 3.59 C5D-13-25 79.2 3.22 CSD-13-27 82.3 3.64 CSD-13-28 85.3 3.47 CSD-13-29 88.4 3.43 CSD-13-30 91.4 3.44 CSD-13-31 94.5 3.50 CSD-13-32 97.5 3.48 CSD-13-33 100.6 3.54 CSD-13-34 103.6 3.60 ARITHMETIC MEAN = 3.36 STANDARD DEVIATION = .21

Table 12. 302

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

TREGARDEN SX 0553 5945 CSD-16 SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

CSD-16-00 3.0 2.97 CSD-16-01 3.0 2.65 CSD-16-02 6.1 3.03 CSO-16-03 9.1 3.33 CSD-16-04 12.2 3.10 C50-16-05 15.2 3.19 CSD-16-06 18.3 3.06 CSD-16-07 21.3 3.20 CSD-16-08 24.4 2.88 CSD-16-09 27.4 3.19 CSD-16-10 30.5 3.16 CSD-16-11 33.5 3.09 C5D-16-12 36.6 3.19 C5D-16-13 39.6 3.20 CSD-I6-14 42.7 3.20 CSD-16-15 45.7 3.28 C5D-16-16 48.8 3.29 CSD-16-17 51.8 3.35 CSD-16-18 54.9 3.23 CSD-16-19 57.9 3.03 C50-16-20 61.0 3.16 C5D-16-21 64.0 3.22 C5D-16-22 67.1 3.07 C5D-16-23 70.1 3.14 CSD-16-24 73.2 3.14 C50-16-25 76.2 3.20 C5D-16-26 79.2 3.00 CSD-16-27 82.3 3.15 C5D-16-28 85.3 3.27 CSD-16-29 88.4 3.07 CSD-16-30 91.4 3.23 CSD-16-31 94.5 3.28 C5D-16-32 97.5 3.05 C50-16-33 100.6 3.39 C50-16-34 103.6 2.94

ARITHMETIC MEAN = 3.14 STANDARD DEVIATION = .14

Table 13. 303

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS COLCERROW FARM SX 0679 5763 CSD-15 SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG CSD-15-01 3.0 3.46 C5D-15-02 6.1 3.15 CSD-I5-03 9.1 3.27 CSD-15-04 12.2 3.65 CS0-15-05 15.2 3.72 C5D-15-06 18.3 3.60 CSD-15-07 21.3 3.54 CSD-15-08 24.4 3.46 CSD-15-09 27.4 3.49 CSD-15-10 30.5 3.72 C50-15-11 33.5 3.27 CSD-15-12 36.6 3.07 CSD-15-13 39.6 3.04 050-15-14 42.7 3.47 CSD-15-15 45.7 3.42 CSD-15-16 48.8 3.39 CSD-15-17 51.8 3.83 CSD-15-18 54.9 4.05 CSD-15-19 57.9 3.50 CSD-15-20 61.0 3.39 CSD-15-21 64.0 3.07 C50-15-22 67.1 3.50 C50-15-23 70.1 3.24 CSD-15-24 73.2 3.49 C50-15-25 76.2 3.09 CS0-15-26 79.2 2.97 CSD-15-27 82.3 3.43 CSD-15-28 85.3 3.11 CSD-15-29 88.4 3.40 CSD-15-30 91.4 3.07 CSD-15-31 94.5 3.26 C5D-15-32 97.5 3.48 CSD-15-33 100.6 3.17 CSD-15-34 103.6 3.22 ARITHMETIC MEAN = 3.39 STANDARD 0EvIATION = .25

Table 14. 304

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS WINTER TOR SX 6117 9156 CS0-18 SAMPLE CODE DEPTH IN METRES CONDUCTIVITY 14/111/DEG CSD-18-01 3.0 3.29 CSD-18-02 6.1 3.20 C50-18-03 9.1 3.25 CSD-18-04 12.2 3.16 CSD-18-05 15.2 3.20 CSD-18-06 18.3 3.24 CSD-18-07 21.3 3.21 CSD-18-08 24.4 3.29 CSD-18-09 27.4 3.12 CSD-18-10 30.5 3.05 CSD-18-11 33.5 3.25 CSD-18-12 36.6 3.33 CSD-18-13 39.6 3.46 CSD-18-14 42.7 3.39 CSD-18-15 45.7 3.20 CSD-18-16 48.8 3.20 CSD-18-17 51.8 3.08 CSD-18-18 54.9 3.17 CSD-18-19 57.9 3.15 CSD-18-20 61.0 3.15 CSD-18-21 64.0 3.13 CSD-18-22 67.1 3.32 CSD-18-23 70.1 3.24 CSD-18-24 73.2 3.26 CSD-18-25 76.2 3.18 CSD-18-26 79.2 3.23 CSD-18-27 62.3 3.14 CS0-18-28 85.3 3.24 CSD-18-29 88.4 3.34 CSD-18-30 91.4 3.04 CSD-18-31 94.5 3.23 CSD-18-32 97.5 3.12 CSD-18-33 100.6 3.65 CSD-18-34 103.6 3.29 ARITHMETIC MEAN = 3.23 STANDARD DEVIATION = .12

Table 15. 305

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

BLACKINGSTONE SX 7850 8593 CSD-17 SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/MVDEG

CSD-17-01 3.0 2.82 CSD-17-02 5.1 2.65 CSD-17-03 9.1 2.74 CSD-17-04 12.2 2.69 CSD-17-05 15.2 3.01 CSD-17-06 18.3 2.91 CSD-17-07 21.3 2.64 CSD-17-08 24.4 2.92 CSD-17-09 27.4 2.83 CSD-17-10 30.5 2.86 CSD-17-11 33.5 3.06 CSD-17-12 36.6 3.08 CSD-17-13 39.6 2.76 CSD-17-14 42.7 3.48 CSD-17-15 45.7 2.69 CSD-17-16 48.8 3.18 CSD-17-17 51.8 2.99 CS0-17-18 54.9 3.19 C50-17-19 57.9 3.32 CSD-17-20 61.0 2.85 CSD-17-21 64.0 3.22 CSD-17-22 67.1 2.93 CSD-17-23 70.1 2.97 CSD-17-24 73.2 3.60 CSD-17-25 76.2 3.67 CSD-17-26 79.2 3.60 C5D-17-27 82.3 2.98 CSD-17-28 85.3 4.02 CS0-17-29 88.4 3.42 CSD-17-30 91.4 3.20 CSD-17-31 94.5 3.12 CSD-17-32 97.5 3.27 CSD-17-33 100.6 3.18 CSD-17-34 103.6 2.87 ARITHMETIC MEAN = 3.09 STANDARD DEVIATION = .32

Table 16. 306

THER'^A;. CONDUCTIVITY RESULTS FROM CHIP t$ASUREW TS S3JS50'S W0CD SX 6733 7971 CSD-19 SA MPLE CODE DEPTh IN METRES CONDUCTIVITY L:/M/DEG CSD-19-01 3.0 2.62 CSD-19-02 6.1 2.80 CSD-19-03 9.1 3.17 CSD-19-04 12.2 3.04 CSD-19-05 15.2 2.90 CSD-19-06 18.3 3.4D CSD-19-07 21.3 2.78 CSD-19-08 24.4 2.82 CSD-19-09 27.4 2.95 CSO-19-10 30.5 2.92 CSD-19-11 33.5 3.08 CSD-19-12 36.6 2.88 C5D-19-13 39.6 3.14 CSD-19-14 42.7 2.91 C50-19-15 45.7 3.48 CSD-19-16 48.8 3.66 CSD-19-17 51.8 3.13 CSO-19-18 54.9 3.14 CSD-19-19 57.9 2.87 CSD-19-20 61.0 3.12 CSD-19-21 64.0 3.25 CSD-19-22 67.1 3.01 CSD-19-23 70.1 3.42 CSD-19-24 73.2 2.95 CSD-19-25 76.2 3.26 C50-19-26 79.2 3.41 CSD-19-27 82.3 3.26 CS0-19-28 85.3 3.77 CSD-19-29 88.4 3.54 CSD-19-30 91.4 3.50 CSD-19-31 94.5 2.84 CSD-19-32 97.5 3.28 CSD-19-33 100.6 3.20 CSD-19-34 103.6 2.73 ARITHMETIC MEAN = 3.12 STANDARD DEVIATION = .28

Table 17. 307

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

LAUGHTER TOR SX 6562 7549 CSD-21

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

CSD-21-01 3.0 3.24 CSD-21-02 6.1 3.12 CSD-21-03 9.1 3.01 C50-21-04 12.2 3.16 CSD-21-05 15.2 2.93 CSD-21-06 18.3 3.30 CSD-21-07 21.3 3.38 CSD-21-08 24.4 3.47 CSD-21-09 27.4 3.46 CSD-21-10 30.5 3.28 CSD-21-11 33.5 3.34 CSO-21-12 36.6 3.92 CSD-21-13 39.6 3.31 CSD-21-14 42.7 3.33 CSD-21-15 45.7 3.36 CSD-21-16 48.8 3.14 CSO-21-17 51.8 3.29 CSD-21-18 54.9 3.67 CSD-21-19 57.9 3.23 CSD-21-20 61.0 3.16 CSD-21 -21 64.0 3.27 CSO-21-22 67.1 3.24 CSD-21-23 70.1 3.23 CSD-21-24 73.2 3.21 CSO-21-25 76.2 3.58 CSD-21-26 79.2 2.99 CSD-21-27 82.3 3.48 CSD-21-28 85.3 3.16 CSD-21-29 88.4 3.22 CSD-21-30 91.4 3.31 CSD-21-31 94.5 3.05 CSD-21-32 97.5 3.40 CSD-21-33 100.6 3.21 CSD-21-34 103.6 3.23 ARITHMETIC MEAN = 3.2g STANDARD DEVIATION = 1

Table 18. 308

THERt1L CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS FOGGIN TOR SX 5663 7334 CSD-20 SAhPLE CODE DEPTH IN METRES CONDUCTIVITY W/r/DEG CSD-20-01 3.0 3.05 CSD-20-02 6.1 3.00 CSD-20-03 9.1 3.27 CSD-20-04 12.2 3.04 CSD-20-05 15.2 3.15 CSD-20-06 18.3 3.27 CSD-20-07 21.3 3.35 CSD-20-08 24.4 3.41 CSD-20-09 27.4 3.63 CSD-20-10 30.5 3.33 CSD-20-11 33.5 3.53 CSD-20-12 36.6 3.38 CSD-20-13 39.6 3.48 CSD-20-14 42.7 3.48 C5D-20-15 45.7 3.48 CSD-20-16 48.8 3.54 CSD-20-17 51.8 3.36 CSD-20-18 54.9 3.31 CSD-20-19 57.9 3.51 CSD-20-20 61.0 3.53 CSD-20-21 64.0 3.69 CSD-20-22 67.1 3.57 CSD-20-23 70.1 3.47 CSD-20-24 73.2 3.50 CSD-20-25 76.2 3.27 CSD-20-26 79.2 3.48 C50-20-27 82.3 3.35 CSD-20-28 85.3 3.68 CSD-20-29 88.4 3.55 CSD-20-30 91.4 3.55 CSD-20-31 94.5 3.43 CS0-20-32 97.5 3.51 CSD-20-33 100.6 3.38 CSD-20-34 103.6 3.44 ARITHMETIC hEAN = 3.41 STANDARD OEv1ATION = .17

Table 19. 309

THERMAL CONDUCTIVITY RESULTS FROM DISC rfASUREMENT';

MERROSE FARM SW 6559 4351 CDD-01

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

MER-034.6 10.5 1.09 MER-056.0 17.1 2.62 MER-069.0 21.0 1.29 MER-071.0 21.6 1.79 MER-082.0 25.0 1.88 MER-095.0 29.0 1.85 MER-098.0 29.9 1.44 MER-120.0 36.6 1.43 MER-136.0 41.5 2.08 MER-161.0 49.1 5.44 MER-225.0 68.6 2.86 MER-225.8 68.8 2.06 MER-235.0 71.6 1.80 MER-250.0 76.2 1.55 MER-253.0 77.1 2.52 MER-267.0 81.4 1.00 MER-283.0 86.3 2.00 MER-292.0 89.0 2.37 MER-293.0 89.3 2.77 MER-297.0 90.5 2.24 MER-307.0 93.6 2.07 MER-311.3 94.9 3.10 MER-319.0 97.2 1.56 MER-323.0 98.5 1.09 MER-327.0 99.7 1.49

ARITHMETIC MEAN = 2.05 STANDARD DEVIATION = .91

Table 20. T-ERr1A, CONDUCTIVITY RESULTS FR3M DISC rEASLRErENTS

KESTLE wARTHA 5W 7533 2579 CDD-02

SAr-LE CODE DEPTH IN r'.ETRES CONDUCTIVITY win/DEG

KSW-037.0 11.3 1.98 KSw-045.0 13.7 1.87 KSW-077.0 23.5 2.90 K5W-091.0 27.7 2.34 KSw-104.0 3I.7 2.71 K5W-116.0 35.4 3.96 KSw-124.0 37.8 4.25 KSw--132.0 40.2 4.02 KSW-138.0 42.1 1.83 KSw-145.0 44.5 3.84 KSW-158.0 48.2 2.52 KSW-168.0 51.2 2.08 KSW-176.0 53.6 1.07 KSW-188.0 57.3 3.92 KSW-199.0 60.7 1.69 KSW-200.0 61.0 2.99 KSw-213.0 64.9 2.80 KSW-220.0 67.1 2.26 KSW-23P.0 71.6 4.47 KSW-2 r6.0 75.0 3.11 KSW-255.0 77.7 4.02 KSW-273.0 83.2 3.29 KSW-285.0 86.9 1.92 KSW-307.0 93.6 4.57 KSW-317.0 96.6 3.48 KSW-327.0 99.7 3.50 KSW-337.0 102.7 2.95 K5W-347.0 105.8 2.63 KSW-357.0 108.8 3.44 KSW-377.0 114.9 3.54 KSW-386.0 117.7 1.02 KSW-405.0 123.5 3.29 KSW-415.0 126.5 1.84 KSW-416.0 126.8 3.47 KSW-425.0 129.5 3.53 KSw-434.0 132.3 3.06 KSW-444.0 135.3 4.13 K5w-456.0 139.0 3.58 KSw-466.O 142.0 3.76 KSw-485.0 147.8 3.92 KSw-496.0 151.2 3.71 ARIT::NETIC NEAN = 3.06 STANDARD DEVIATION = .92

Table 21. 311

THERMAL CONDUCTIVITY RESULTS FROM DISC MEASUREMENTS

CALLYWITH FARM SX 0886 6783 CDD-03

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY w/M/DEG

CAL-0030 9.1 2.51 CAL-0043 12.2 1.90 CAL-0052 15.8 2.74 CAL-00E0 18.3 2.54 CAL-0074 22.4 1.93 CAL-0076 23.0 1.85 CAL-0080 24.4 1.60 CAL-0091 27.6 3.16 CAL -0102 31.0 2.69 CAL-0110 33.4 1.30 CAL-0114 34.8 2.14 CAL-0120 36.6 2.94 CAL-0130 39.6 3.27 CAL -0141 43.0 2.04 CAL-0148 45.0 2.47 CAL-0160 48.8 2.06 CAL-0179 54.5 2.40 CAL-0198 60.4 3.05 CAL-0202 61.6 2.01 CAL-0211 64.2 1.96 CAL-0220 67.1 3.34 CAL-0236 71.9 1.46 CAL-0240 73.2 2.27 CAL-0250 76.2 1.34 CAL-0260 79.2 1.77 CAL-0270 82.4 2.49 CAL-0271 82.5 2.30 CAL-0280 85.3 2.40 CAL-0289 88.2 3.01 CAL-0300 91.4 2.16 CAL-0311 94.7 2.14 CAL-0320 97.5 2.63 CAL-0329 100.3 2.79 CAL-0339 103.2 2.28 CAL-0350 106.7 2.19 CAL-0360 109.7 2.47 CAL-0370 112.8 2.17 CAL-0380 115.8 2.57 CAL-0390 118.9 2.73 CAL -0400 121.9 1.88 CAL-0410 125.0 2.89 CAL -0420 128.0 3.06 CAL-0430 131.1 2.96 CAL-0440 134.1 2.69 CAL-0450 137.2 2.94 CAL-0459 139.9 2.07 CAL -0470 143.3 2.23

ARITHMETIC MEAN = 2.38 STANDARD DEVIATION = .50

Table 22. 3'12

THERM L CONDUCTIVITY RESULTS FROM DISC MEASUREMENTS

GAVERIGAN SW 9316 5916 GAV-01

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

GAV010210 64.0 2.44 GAV010252 76.8 2.08 GAv010287 87.5 2.85 GAV010290 88.4 2.64 GAV010350 106.7 3.39 GAV010357 108.8 2.12 GAV010420 128.0 3.17 GAV010460 140.2 2.83 GAV010472 143.9 2.64 GAVO10575 175.3 2.77 GAV010590 179.8 2.10 GAVD10600 182.9 2.44 GAv010622 189.6 2.53 GAV010650 198.1 2.62 GAV010672 204.8 3.43 GAV010680 207.3 3.01 GAV010707 215.5 2.61 GA"010715 217.9 2.88 GAV010807 246.0 2.12 GAV010815 248.4 2.09 GAV010910 277.4 2.08 GAv010915 278.9 2.03 GAV010957 291.7 2.17 GAV010963 293.5 3.1I GAV010964 293.5 2.18 GAv011005 306.3 3.93 GAV011030 313.9 3.29 GAV011040 317.0 3.71 GAV011076 328.0 3.00 ARITHMETIC MEAN = 2.70 STANDARD DEVIATION = .53

Table 23. 313

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

LONGDOWNS SW 7368 3462 CSD-01

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

CSD-01-01 27.4 2.87 CSD-01-02 36.6 2.86 CS0-01-03 39.6 2.88 CSD-01-04 42.7 3.13 CSD-01-05 45.7 3.06 CS0-01-06 48.8 2.98 CSD-01-07 51.8 2.72 CSD-01-08 54.9 2.94 CSD-01-09 57.9 2.49 CSD-01-10 61.0 3.48 CSD-01-11 64.0 3.34 CSD-01-12 67.1 3.24 CSD-01-13 70.1 3.04 CSD-01-14 73.2 2.73 CSD-01-15 76.2 2.55 CSD-01-16 79.2 2.81 CSD-01-17 82.3 3.05 CSD-01-18 85.3 2.42 CSD-01-19 88.4 3.00 CSD-01-20 91.4 3.89 CSD-01-21 94.5 4.49 CSD-01-22 97.5 3.50 CSD-01-23 100.6 3.25 CSD-01-24 103.6 3.08 CSD-01-25 106.7 3.04 CSD-01-26 109.7 3.23 CSD-01-27 112.8 2.91 CSD-01-28 115.8 3.01 CSD-01-29 118.9 3.30 CSD-01-30 121.9 3.52 CSD-01-31 125.0 2.67 CSD-01-32 128.0 3.13 CSD-01-33 131.1 2.83 CSO-01-34 134.1 2.92 CSD-01-35 137.2 3.23 CSD-01-36 140.2 3.04 CSD-01-37 143.3 3.35 CSD-01-38 146.3 2.97 CSD-01-39 149.4 2.89 CSD-01-40 152.4 3.29 CSD-01-41 155.4 3.02 CSD-01-42 158.5 3.33 CSD-01-43 161.5 2.98 CSD-01--44 164.6 2.91 CSD-01-45 167.6 3.02 CSD-01-46 170.7 3.06 CSD-01-47 173.7 2.82 CSD-01-48 176.8 3.14 CSD-01-49 179.8 3.34 CSD-01-50 182.9 3.31 CSO-01-01 185.9 3.42 ARITHMETIC MEAN = 3.09 STANDARD DEVIATION = .34

Table 24. 314

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

ROSEMANOWaS QUARRY C.S.M. TEST SITE HOLE-

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

R0S-6-001 3.0 3.17 ROS-6-002 6.1 3.25 ROS-6-003 9.1 3.12 ROS-6-004 12.2 3.29 R0S-6-005 15.2 3.25 R05-6-006 18.3 3.32 ROS-6-007 21.3 3.60 ROS-6-008 24.4 3.47 ROS-6-009 27.4 2.63 R05-6-010 30.5 3.32 RO5-6-011 33.5 3.37 ROS-6-012 36.6 3.36 ROS-6-013 39.6 3.36 RO5-6-014 42.7 3.30 ROS-6-015 45.7 3.74 RO5-6-016 48.8 3.31 ROS-6-017 51.8 3.25 RO5-6-018 54.9 3.47 R05-6-019 57.9 3.59 R05-6-020 61.0 3.33 ROS-6-021 64.0 3.53 R05-6-022 67.1 3.37 R05-6-023 70.1 3.36 ROS-6-024 73.2 3.31 R0S-6-025 76.2 3.26 ROS-6-026 79.2 3.33 ROS-6-027 82.3 3.42 RO5-6-028 85.3 3.39 R05-6-029 88.4 3.40 R05-6-030 91.4 3.19 RO5-6-031 94.5 3.13 R05-6-032 97.5 3.17 RO5-6-033 100.6 3.26 R05-6-034 103.6 2.83 RO5-0-035 106.7 3.09 R0S-0-036 109.7 3.13 R05-6-037 112.8 3.23 R05-6-039 118.9 3.20 RO5-0-040 121.9 3.35 ROS-6-041 125.0 3.22 P35-6-042 128.0 3.26 R05-6-044 134.1 3.68 ARITHMETIC MEAN = 3.30 STANDARD DEVIATION = .20

Table 25.

3 L'5

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREPENTS

ROSEMaNOWAS QUARRY C.S.M. TEST SITE HOLE D

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W4M/DEG

ROS-0-141 141.1 3.33 ROS-D-144 143.9 3.27 ROS-D-147 146.9 3.17 ROS-D-150 150.0 3.00 ROS-D-153 153.0 2.99 ROS-D-156 156.1 3.22 R0S-0-159 159.1 2.69 ROS-D-162 I61.8 2.84 ROS-D-283 282.9 3.16 R05-0-298 297.8 3.30

ARITHMETIC DEAN = 3.09 STANDARD DEVIATION = .21

Table 26. 3 L'6

THERMAL CONDUCTIVITY RESULTS FROM DISC MEASUREMENTS

TROON SW 6570 3677 TRN-C6

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

TRN-046-A 14.0 3.34 TRN-046-B 14.0 3.98 TRN-046-C 14.0 3.11 TRN-057-A 17.4 3.48 TRN-057-B 17.4 3.21 TRN-057-C 17.4 3.48 TRN-069-P 21.0 3.28 TRN-069-8 21.0 3.26 TRN-069-C 21.0 3.50 TRN-082-A 25.0 3.29 TRN-082-B 25.0 3.35 TRN-082-C 25.0 3.34 TRN-090-A 27.4 3.26 TRN-090-B 27.4 3.35 TRN-090-C 27.4 3.54 TRN-101-A 30.8 3.61 TRN-101-8 30.8 3.39 TRN-101-C 30.8 3.49 TRN-111-A 33.8 3.38 TRN-111-B 33.8 3.41 TRN-111-C 33.8 3.26 TRN-121-A 36.9 3.34 TRN-121-B 36.9 3.63 TRN-121-C 36.9 3.36 TRN-129-A 39.3 3.30 TRN-129-8 39.3 3.49 TRN-129-C 39.3 3.38 TRN-139-A 42.4 3.60 TRN-139-8 42.4 3.63 TRN-139-C 42.4 3.45 TRN-147-0 44.8 3.76 TRN-154-0 46.9 3.50 TRN-161-0 49.1 3.38 TRN-167-0 50.9 3.45 TRN-172-0 52.4 3.42 TRN-178-0 54.3 3.47 TRN-188-0 57.3 3.60 TRN-194-0 59.1 3.35 TRN-197-0 60.0 2.84 ARITHMETIC MEAN = 3.40 STANDARD DEVIATION = .16

Table 27.

317

THERMAL CONDUCTIVITY RESULTS FROM DISC MEASUREMENTS

HEMERD3N MINE SX 5733 5849 DDHH23

SAMPLE CODE DEPTH IN METRES C3NDUCTIvITY W/M/DEG

DDH-0038 38.0 3.28

ODH-0045 45.0 3.09

DOH-0049 49.0 4.29

DDH-0059 59.0 3.28

DDH-0067 67.0 3.25

DDH-0074 74.0 3.58

DDH-0079 79.0 3.08

DDH-0087 87.0 3.47

DDH-0093 93.0 3.26

DDH-0111 111.0 2.98

DDH-0118 118.0 3.21

DDH-0120 120.0 4.62

ARITHMETIC MEAN = 3.45 STANDARD DEVIATION = .50

Table 28. 318

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

HEMERDON MINE SX 5733 5849 RDH-H3

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

HEM -3-008 6.5 4.98 HEM-3-010 9.5 4.76 NEM-3-012 12.5 4.37 HEM-3-014 14.5 4.83 HEM-3-018 18.5 4.91 HEM-3-021 21.5 5.10 HEM-3-024 23.5 5.54 HEM-3-027 27.5 4.38 HEM-3-030 30.5 5.57 HEM-3-033 33.5 5.82 HEM-3-037 37.5 6.20 HEM-3-040 40.5 5.86 HEM-3-043 43.5 5.60 HEM-3-x]46 46.5 4.37 HEM-3-049 49.5 5.32 HEM-3-052 52.5 4.82 HEM-3-055 55.5 4.70 HEM-3-058 58.5 4.37 HEM-3-061 61.5 3.92 HEM-3-064 64.5 3.46 HEM-3-067 67.5 4.02 HEM-3-070 70.5 5.31 HEM-3-073 73.5 4.25 HEM-3-076 76.5 4.36 HEM-3-078 78.5 4.24 HEM-3-082 83.5 4.66 HEM-3-085 85.5 4.46 HEM-3-091 91.5 4.82 HEM-3-094 94.5 4.52 HEM-3-098 98.5 4.46 HEM-3-101 101.5 4.89 HEM-3-104 104.5 4.22 HEM-3-107 107.5 4.85 HEM-3-110 110.5 5.15 HEM-3-113 113.5 4.27 HEM-3-116 116.5 3.65 HEMP-3-119 119.0 3.95 HEM-3-122 122.0 3.80 HEM-3-125 125.0 4.96 HEM-3-I28 128.0 5.24 ARITHMETIC MEAN = 4.73 STANDARD DEVIATION = .62

Table 29. 319

cR^+F+ C3'+DLCTIvITY RESL'LTS -R2 "EASUPEMENTS

YE? SX SECS 6275 WY1-12

C32E DEPTH IN -E72ES C2r1DLCT1%.ITY W/M/DEG

F"1-12-C4 3.67 .."1-12-17 4.65 .-.": -12-13 3.22 WY/-12-16 3.64

wY1-12-1 `~ 4.49

ARITH`E TIC MEAN = 3.93 STANDARD DEVIATION = .61

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

W►*ITEHILL YEO SX 5805 6275 WY1-14

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

WY1—I4-07 4.93 WY1-14-13 4.43 WY1-14-16 3.87 WY1-14-31 4.38 WY1-14-34 4.02 WY1-14-37 4.36 WY1-14-43 4.50 WY1-14-55 4.16 WY1-14--51 4.13 WYI—I4-88 3.74

ARITHMETIC MEAN = 4.24 STANDARD DEVIATION = .32

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

WHITEHILL YEO SX 5805 6275 WY-15

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

WY1-15-04 4.69 WYI-15-07 2.68 WY1-15-10 4.08 WY1-15-13 3.53 WY1-15-34 4.18 WY1-15-43 3.20

AQITHMETIC MEAN = 3.73 STANDARD DEVIATION = .73

Table 30. 320

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

BOVEY TRACEY SX 8271 7929 BVT-03 SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

BVT102.3- 22.9 4.59 BVT102.6A 25.9 2.72 BVT102.6B 25.9 1.97 BVT102.7- 27.1 2.75 BVT103.3- 32.9 2.56 6VT103.6- 36.0 2.75 BVT104.1- 41.1 3.32 BVT104.4- 43.9 2.45 BVT104.6- 46.0 2.67 BVT105.0- 50.0 2.77 BVT105.2- 52.1 3.32 BVT105.5- 54.9 2.76 BVT105.8- 57.9 4.97 BVT106.1- 61.0 4.14 BVT106.5- 64.9 2.73 BVT106.7- 67.1 5.03 BVT107.1- 71.0 3.05 BVT107.5- 75.0 2.12 BVT107.7- 77.1 4.40 BVT108.2- 82.0 6.96 BVT108.5- 85.0 1.24 BVT108.7- 86.9 2.91 BVT109.0- 89.9 3.66 BVT109.3- 93.0 2.48 BVT109.6- 96.0 3.72 BVT1D9.9- 99.1 2.57 BVT110.3- 103.0 2.95 BVT110.6- 106.1 2.42 BVT110.9A 109.1 3.31 BVT110.9B 109.1 3.44 BVT111.2- 111.9 2.20 BVT111.6- 115.8 5.14 ARITHMETIC MEAN = 3.25 STANDARD DEVIATION = 1.15

Table 31.

321

THERMAL CONDUCTIvITY RESULTS FROM DISC MEASUREMENTS

MELDON OUARRY SX 5676 9220 MEL-01

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

MEL-18 18.0 2.90

MEL-20 20.1 2.95

MEL-22 21.6 3.08

MEL-24 23.5 2.85

MEL-26 25.9 3.00

MEL-28 28.3 3.62

MEL-30 29.6 3.25

MEL-31 30.8 3.31

MEL-32 31.7 3.41

MEL-34 33.8 3.42

MEL-36 36.3 3.44

MEL-38 37.8 3.64

MEL-38 38.4 3.44

MEL-41 41.1 3.38

MEL-43 42.7 3.44

MEL--45 44.5 2.31

ARITHMETIC MEAN = 3.22 STANDARD DEVIATION = .35

Table 32. 322

THERMAL C3NDUST I' I TY RESULTS FP3M DISC NEASL'RErENTS

NEWLYN EAST 5:,J 8146 5390 NE-1

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

NE1-003.0 3.0 3.27 NEI-006.2 6.0 2.28 NE1-009.8 9.0 1.98 NE1-012.0 12.0 2.23 NE1-015.6 15.0 2.33 NE 1-018.6 18.0 3.60 NE 1-021 .9 21.0 3.23 NE1-025.0 25.0 3.65 NEI-028.0 28.0 2.63 NE 1-030.6 30.0 3.65 NE 1-034. 1 34.0 4.08 NE1-036.9 36.0 3.45 NEI-039.7 39.0 2.37 NE 1--043.5 43.0 4.14 NE1-046.6 46.0 3.22 NE1-051.3 51.0 3.22 NE1-053.0 53.0 2.45 NEI-061.6. 61.0 3.10 NE1-067.2 67.0 2.40 NE1-071.1 71.0 3.36 NE 1-074. 1 74.0 3.52 NE1-077.3 77.0 4.21 NE1-080.8 80.0 2.69 NEI-083.2 83.0 2.75 NE1-086.9 86.0 2.78 NE1-096.4 96.0 2.52 NEI-099.6 99.0 3.18 NE1-102.4 102.0 2.61 NE1-105.0 105.0 3.45 NE1-108.5 108.0 2.64 NEI-110.0 110.0 2.77 NE1-114.7 114.0 3.39 NE1-118.5 118.0 2.66 NE1-120.5 120.0 3.14 ARITHMETIC MEAN = 3.03 STANDARD DEVIATION = .58

Table 33. S 323

THERMAL CONDUCTIVITY RESULTS FROM DISC MEASUREMENTS

BELOWDA BEACON SW 9788 6254 BEL-02

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY k/1/DEG

BEL-2- 24 23.5 2.07 BEL-2- 26 25.6 1.99 BEL-2- 31 30.7 3.33 BEL-2- 35 34.5 2.09 BEL-2- 38 38.3 2.27 BEL-2- 42 42.2 3.16 BEL-2- 46 45.8 3.33 BEL-2- 50 49.8 1.85 BEL-2- 55 55.0 2.78 BEL-2- 58 57.5 1.99 BEL-2- 61 61.4 3.84 BEL-2- 65 65.2 3.03 BEL-2- 69 69.0 2.28 BEL-2- 73 72.8 2.17 "BEL-2- 77 76.7 3.64 BEL-2- 81 80.5 4.17 BEL-2- 88 87.9 1.73 BEL-2- 92 92.0 1.90 BEL-2- 96 95.9 2.03 BEL-2-100 99.7 4.91 BEL-2-104 103.8 3.34 BEL-2-107 107.4 1.60 BEL-2-111 111.2 2.78 BEL-2-115 115.3 3.52 BEL-2-120 119.9 6.12 BEL-2-122 122.4 2.29 BEL-2-127 126.6 2.23 BEL-2-130 130.4 2.61 BEL-2-134 134.2 2.35 BEL -2-138 138.0 2.32 ARITHMETIC MEAN = 2.79 STANDARD DEVIATION = 1.02

Table 34. 324

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

PREDANNACK SW 6901 :634 PRE-01

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

PRE-0127- 38.9 2.70 PRE-0137- 41.6 2.29 PRE-0155- 47.4 2.52 PRE-0163- 49.7 2.38 PRE-0171- 52.3 2 69 PRE-0163- 55.9 PRE-01y95- 59.8 PRE-0209- 63.9 2.44 PRE-0219- 66.8 2.61 PRE-0233- 71.0 2.4 PRE-0242- 74.0 01 PRE-0267- 81.4 2.34 PRE-0304- 92.8 2.36 PRE-0316- 96.3 2.13 PRE-0328- 99.9 2.29 PRE-0351- 106.9 2.18 PRE-0363- 110.7 2.45 PRE-0378- 115.2 2.17 -0 119.5 2.49 PRE~ 0403- 123.0 PRE-0416- 126.8 2.46 PRE-0429- 2.24 PRE-0439 - 133.9 2.21 PRE-0451- 137.7 2.54 PRE-0463- 141.2 2.56 PRE-0476- 145.1 2.54 PRE-0489- 149.0 2.58 PRE-0499- 152.2 2.44 PRE-0509- 155.1 2.50 PRE-0525- 160.6 1.84 PRE-0531- 161.8 1.77 PRE-0556- 169.5 1.94 PRE-0573- 174.7 2.43 PRE-0583- 177.9 2.61 PRE--005y94- 181.0 2.54 PRE-0605- 184.6 2.49 PRE-0617- 187.9 2.40 PRE-0630- 191.9 2.35 PR -0641- 195.5 1.94 PRE-..0p655- 199.6 2.54 PRE-0566- 203.1 2.21 5 206.6 2.37 PRE--00690- 210.3 2.42 PRE-0711- 216.9 2.19 PRE-0735- 223.9 1.90 PRE-076p- 231.5 2.40 PRE-0782- 238.4 2.35 -0 2.15 PPE-0832- 253.8 2.28 PRE-0854- 260.2 2.57 PRE-0877- 267.5 2.63 PRE-0902- 274.9 2.20 PRE-0925- 282.1 1.97 PRE-0949- 289.1 2.50 PRE-0990- 301.9 2.43 PRE-1014- 309.1 2.35 PRE-1021- 311.4 2.40 PRE-1066- 324.9 2.22 ARITHMETIC MEAN = 2.36 STANDARD DEVIATION = .22

Table 35. 325

THERMAL CONDUCTIVITY RESULTS FROM DISC MEASUREMENTS

KENNACK SANDS SW 7325 1647 KEN-D1

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY w/M/DEG

KEN-064.0 19.5 2.38 KEN-084.0 25.6 3.01 KEN-113.0 34.4 2.39 KEN-137.0 41.8 2.72 KEN-152.0 46.3 2.20 KEN-169.0 51.5 2.37 KEN-183.0 55.8 2.21 KEN-206.0 62.8 2.11 KEN-220.0 67.1 2.06 KEN-234.0 71.3 3.04 KEN-250.0 76.2 2.44 KEN-270.0 82.3 2.46 KEN-283.0 86.3 2.45 KEN-303.0 92.4 2.72 KEN-327.0 99.7 2.84 KEN-350.0 106.7 2.89 KEN-376.0 114.6 3.05 KEN-392.0 119.5 2.75

KEN-409.0 124.7 1.92 KEN-446.0 135.9 1.89 KEN-466.0 142.0 2.50 KEN-497.0 151.5 2.08

ARITHMETIC MEAN = 2.48 STANDARD DEVIATION = .36

Table 36. 326

THERMAL CONDUCTIVITY RESULTS FROM DISC MEASUREMENTS

CANHINGTOH PARK ST 2470 4010 CAN-01

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY W/M/DEG

CANP010-A 10.0 3.14 CANP015-A 15.0 3.28 CANP019-A 19.0 3.19 CANP025-A 25.0 3.27 CANP029-A 29.0 3.03 CANP035-A 35.0 3.04 CANP040-A 40.0 3.11 CANPO44-A 44.0 3.24 CANP049-A 49.0 3.14 CANP055-A 55.0 3.19 CANP060-A 60.0 3.13 CANP065-A 65.0 3.17 CANP070-A 70.0 3.17 CANP074-A 74.0 3.09 CANP080-A 80.0 3.19 CANP085-A 85.0 3.21 CANP090-A 90.0 3.17 CANP095-A 95.0 3.06 CANP100-A 100.0 3.14 CANP105-A 105.0 3.14 CANP110-A 110.0 3.13 CANP115-A 115.0 3.19 CANP120-A 120.0 3.15 CANP124-A 124.0 3.21 CANP129-A 129.0 3.21 CANP 140-A 140.0 3.18 CANP145-A 145.0 3.31 CANP150-A 150.0 3.28 CANP156-A 156.0 3.20 CANP159-A 159.0 3.17 CANP165-A 165.0 3.17 CANP170-A 170.0 3.24 CANP175-A 175.0 3.72 CANP175-8 175.0 3.21 CANP179-A 179.0 3.22 CANP180-A 160.0 3.21 CANP185-A 185.0 3.23 CANP189-A 189.0 3.21 CANP 195-A 195.0 3.20 CANP200-A 200.0 3.07 CANP202-A 202.0 3.13 CANP205-A 205.0 3.15 CANP208-A 208.0 3.14 CANP210-A 210.0 3.17 CANP215-A 215.0 3.06 CANP220-A 220.0 3.02 CANP225-A 225.0 3.14 CAMP230-A 230.0 3.21 CANP235-A 235.0 3.17 CANP240-A 240.0 3.20 CANP250-A 250.0 3.21 CANP255-A 255.0 3.17 CANP260-A 250.0 3.11 CANP264-A 264.0 3.16

Table 37. 327

UOU rzz aa rrc o gg` 270.0 3.17 N tn 275.0 3.12 aa N oo om Fg

N 285.0 3.18 L z W

a 290.0 3.12 z N m0 to g 296.0

O(Ja rz aa f7 o g 3.11 300.0 3.16 MNl 00ti mrn c fg 305.0 3.19 a r 5

a t' 309.0 3.03 ū mo r= g` l 315.0 ū a N 3.09 fggT 320.0 3.16 t ¢ z aa Nf7 ino 325.0

ū rz 3.06 330.0

a 3.02 ūūūū F1 t' mp

) 335.0 aaa f)

rz 7t g 3.11

M 340.0 D g 3.08 i 345.0 N1

rz tf1 ov 3.06

a 350.0

L r/ U1 g 3.02 JU 354.0 a In 1o o

zz ggg 3.10 360.0 O a torr tno 3.08 3.09

D aa 365.0 z P)

U¢ 370.0 3.02 m zr g 375.0 a N)

f o gg 3.08 ,C .) ) C

a a 380.0 2.99 c C~ mo r e _rz ) ) CI

cU aa CA g 385.0 3.04 390.0 UU t' O) m0 3.07 f )P

395.0 U zz aa 5.63 gg 400.0 Q 0 2.98. i

aaa ~ 406.0

¢ 0 g 3.06 zr .. )

ū Q m 410.0 3.11 . gg - s rnmr)

ūū zz r 415.0 3.11 .i t

419.0

a N 3.11 g 425.0

ūŪ rzz a ~ gg 3.03

a 433.0 3.06 iū 440.0 3.48 aa gg 445.0

c ¢ T 2.99 z o .) 450.0

ū aa T mrn 3.20 zz g 455.0

¢ c T 3.14 I T i 459.0 ¢ c aa W g` 3.24 zr mo i~

465.0 c ¢ r 3.75 Fgg . ~~ 470.0

aa St* r 2.99 zz tno

T 475.0

c ¢ 3.03 .) 480.0 ūū ao TT

rz= mo gg 3.02 485.0 2.96

ūU aa 490.0

tnrn 2.97 ic T 495.0 3.00 r g`

2.99

UU a 0~+ oo 499.0 zr f . 506.0 3.02 a if% lgg 510.0 3.51 OD aa ttl tno z • -+ 515.0 3.02 N z

520.0

U 2.98 z aa ~ mo gg` 525.0 3.46 cU m rr

UU 530.0

a if m 2.87 rg` ta 535.0 2.94 O rr aaa V' p t 540.0 2.94 t( 4OU fc iU 1 545.0 4.38 zs - rfg` 551.0 4.65 U aaa tf l • 1 551.0 UU

zzzr it) tno 2.92

I 555.0 2.92 D F 560.0 aaaa tfl IDrr 3.05 c ¢ tn g` . )ūūū

tf 565.0 3.08 o F l~m 570.0

tno ggcF 3.15 z 576.0

CD 3.50 r .r c aa

¢ ~ 580.0

C mo 3.28 D0' .)U cF

r ttl 585.0 3.33 )

590.0 4.70

Table 37 continued 328 C M

595.0 ~

600.0 m

605.0 t~ )

610.0 C 615.0 M

619.0 Mo 625.0

630.0 o

636.0 cn

639.0 O 646.0 D0 649.0 3N r

655.0 el

660.0 r 664.0 o

670.0 N 675.0 r U'

680.0 m U to L a c o

685.0 m

690.0 t D

695.0 tO

698.0 ri

704.0 ul

710.0 cu

715.0 NN 720.0

725.0 V

730.0 n 1

735.0 Ō~ 740.0

745.0 C UU

750.0 t ~ D

755.0 Ō

760.0 c u

765.0 Nr 770.0

775.0 3 C

779.0 ARITHMETIC MEAN = 3.38 STANDARD DEVIATION = .58

Table 37 continued 329

THERMAL CONDUCTIVITY RESULTS FROM DISC MEASUREMENTS

CURRYPOQL FARM ST 2270 3871 CPF-01

SAMPLE CODE DEPTH IN METRES CONDUCTIVITY WMVDEG

CPF-0029 29.0 3.95 CPF-0034 34.0 3.05 CPF-0035 35.0 4.87 CPF-0042 42.0 3.14 CPF-0059 59.0 2.96 CPF-0072 72.0 3.23 CPF-0077 77.0 3.18 CPF-0081 81.0 2.39 CPF-0085 85.0 1.84 CPF-0094 94.0 3.57 CPF-0102 102.0 2.49 CPF-0105 105.0 4.44 CPF-0121 121.0 3.74 CPF-0127 127.0 3.53 CPF-0143 143.0 2.76 CPF-0144 144.0 2.22 CPF-0150 150.0 2.46 CPF-0156 156.0 2.64 CPF-0159 159.0 2.09 CPF-0176 176.0 2.29 CPF-0160 180.0 2.91 CPF-0184 184.0 4.88 CPF-0195 195.0 3.19 CPF-0199 199.0 2.23 CPF-0205 205.0 2.80

ARITHMETIC MEAN = 3.07 STANDARD DEVIATION = .82

Table 38. 3 fro

THERMAL CONDUCTIVITY RESULTS FROM CHIP MEASUREMENTS

LITTLE POLGEAR BOREHOLE COLLAPSED CSD-03

SAMPLE CODE DEPTH IN METRES CONDUCTIvITY W/M1/DEG

CSD-03-10 30.5 3.54 CSD-03-11 33.5 3.72 CSD-03-12 36.6 3.54 CSD-03-13 39.6 3.64 CSD-03-14 42.7 3.70 CSD-03-15 45.7 3.63 CSD-03-16 48.8 4.02 CSD-03-17 51.8 3.96 CSD-03-18 54.9 3.78 CSD-03-19 57.9 3.64 CSD-03-20 61.0 3.78 CSD-03-21 64.0 3.94 C5D-03-22 67.1 3.76 CSD-03-23 70.1 3.81 CSD-03-25 76.2 3.95 CSD-03-26 79.2 3.83 CSD-03-27 82.3 3.59 CSD-03-28 85.3 3.58 CSD-03-29 88.4 3.75 CSD-03-30 91.4 3.89 C50-03-31 94.5 3.49 CSD-03-32 97.5 3.76 ARITHMETIC MEAN = 3.74 STANDARD DEVIATION = .15

Table 39.

3 3'l

Appendix IV Tabulation of Heat Production Data

The concentration of radiogenic elements are tabulated for each borehole. Heat production was calculated using the following constants (Rybach 1973):

Uranium 95.6 pWkc-1 Thorium 25.7 ,uWkg-1 -1 Potassium 3.49 x 10-3 pWkg

Uranium and thorium concentrations are expressed in parts per million (ppm). Potassium concentration is expressed as a percentage. Heat production is expressed as 10-6Wm-3. The depth interval in metres represents the drill rod over which the sample was collected and so should be treated as a guide only. The value will represent the maximum depth of the sample. For procedural details of the sampling and measurement see chapter 4.

Table No. Station Name

1 Grillis Farm 2 Polgear Beacon 3 Medlyn Farm 4 Trevease Farm 5 Trerghan Farm 6 Bray Down 7 Blackhill 8 Pinnockshill 9 Browngelly 10 Gt Hammet Farm 11 Newmi l l 12 Bunker's Hill 332

Table No. Station Name

13 Treaarden Farm 14 Colcerrow Farm 15 Winter Tor 16 Blackingstone 17 Soussons Wood 18 Laughter Tor 19 Foggin Tor 20 Merrose Farm 21 Kestle Wartha 22 Callywith Farm 23 Gaverigan 24 Wilsey Down Table 1. Heat generation data for Carnmenellis Site A GRILLIS FARM

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm -3 + -

21.3-24.4 CSD-408 12.3 .5 18.8 .9 5.6 .1 5.0 .2 27.4-30.5 CSD-410 12.6 .5 12.2 .7 4.0 .1 4.4 2 36.6-39.6 CSD-413 13.9 .5 12.1 .7 4.3 1 4.8 2 42.7-45.7 CSD-415 12.1 .4 7.2 .5 5.2 1 4.1 1 48.8-51.8 CSD-417 16.0 .5 12.8 .7 4.6 .1 5.4 2 54.9-57.9 CSD-419 15.2 .4 13.2 .6 4.8 .1 5.2 .2 61.0-64.0 CSD-421 10.1 .4 11.2 .6 5.6 .1 3,9 .2 `"' 67.1-70.1 CSD-423 9.2 .4 10.8 .5 5.8 .1 3.6 .1 73.2-76.2 CSD-425 13.4 .5 12.7 .7 4.8 .1 4.8 .2 79.3-82.3 CSD-427 11.6 .4 11.1 .6 4.6 .1 4.2 .2 88.4-91.4 CSD-430 12.1 .4 12.6 .6 4.4 .1 4.4 .2 97.5-100.6 CSD-433 11.8 .4 12.0 .6 4.6 .1 4.3 .2

Mean 12.5 12.2 4.9 4.5 Standard Deviation 1.9 2.6 0.6 0.5 Table 2. Heat generation data for Carnmenellis Site B POLGEAR BEACON

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm -3 + -

27.4-30.5 CSD-710 14.7 .5 8.1 .6 6.0 1 5.0 .2 33.5-36.6 CSD-712 4.3 .3 7.3 .5 5.0 1 2.1 .1 39.6-42.7 CSD-714 12.4 .4 7,5 .5 4.6 .1 4.2 .2 45.7-48.8 CSD-716 13.2 .4 7.9 .6 4.8 1 4.5 .2 51.8-54.9 CSD-718 13.2 .4 7.5 .5 4.7 1 4.4 .2 57.9-61.0 CSD-720 13.4 .4 6.8 .5 4.8 1 4.4 .2 64.0-67.1 CSD-722 4.7 .3 6.8 .5 5.1 1 2.2 .1 70.1-73.2 CSD-724 9.9 .3 5.3 .4 4.5 .1 3.4 .1 76.2-79.3 CSD-726 10.7 .4 6.7 .5 5.3 .1 3.8 .1 82.3-85.3 CSD-728 10.5 .4 6.2 .5 5.0 .1 3.6 .1 88.4-91.4 CSD-730 13.1 .4 5.6 .5 5.7 .1 4.3 .2 94.5-97.5 CSD-732 11.2 ,4 6,2 . 5 5.7 .1 3.9 .1

Mean 10.9 6.8 5.1 3.8 Standard Deviation 3.3 0.9 0.5 0.9 At

Table 3. Heat generation data for Carnmenellis Site C MEDLYN FARM

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm -3 + -

21.3-24.4 CSD-508 13.8 .4 10.6 .6 3.3 .1 4.6 .2 36.6-39.6 CSD-513 9.3 .3 7.4 .5 4.5 .1 3.3 1 42.7-45.7 CSD-515 8.6 .4 9.0 .5 4.2 .1 3.2 1 57.9-61.0 CSD-520 4.3 .3 8.8 .5 4.6 .1 2.1 1 67.1-70.1 CSD-523 7.5 .3 7.5 .5 4.5 .1 2.9 1 73.2-76.2 CSD-525 9.2 .4 9.2 .5 4.5 .1 3.4 .1 79.3-82.3 CSD- 527 6.4 .3 9.7 .5 4.5 .1 2.7 .1 jco 11 u, 85.3-88.4 CSD-529 9.9 .4 8.8 .5 4.2 .1 3.5 .1 94.5-97.5 CSD-532 14.4 .4 9.6 .6 4.3 .1 4.7 .2

Mean 9.3 8.9 4.3 3.4 Standard Deviation 3.2 1.0 0.4 0.8 Table 4. Heat generation data for Carnmenellis Site D TREVEASE FARM

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm-3 + -

21.3-24.4 CSD-208 16.0 .4 4.6 .4 4.4 .1 4.8 .1 27.4-30.5 CSD-210 11.4 .3 3.9 .4 3.9 .1 3.5 .1 39.6-42.7 CSD-214 15.5 .4 4.7 .4 3.8 .1 4.6 .1 42.7-45.7 CSD-215 12.7 .3 4.9 .4 4.6 .1 4.0 .1 51.8-54.9 CSD-218 12.3 .3 3.3 .3 4.2 .1 3.7 .1 57.9-61.0 CSD-220 12.4 .4 4.9 .4 4.0 .1 3.9 .1 i 67.1-70.1 CSD-223 8.? .3 4.0 .4 4.3 .1 2.9 .1 w m 73.2-76.2 CSD-225 10.6 .3 4.7 .4 4.1 .1 3.4 .1 79.3-85.3 CSD-227/228 12.3 .3 4.5 .4 4.1 .1 3.8 .1 88.4-91.4 CSD-230 12.7 .3 3.8 .4 3.7 .1 3.8 .1 94.5-97.5 CSD-232 10.9 .3 3.8 .4 3.9 .1 3.4 .1 100.6-103.6 CSD-234 12.2 .3 4.0 .4 3.7 .1 3.8 .1

Mean 12.3 4.3 4.1 3.8 Standard Deviation 2.0 0.5 0.3 0. 5 Table 5. Heat generation data for Carnmenellis Site E TRERGHAN FARM

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm -3 + -

27.4-30.5 CSD-610 4.7 .4 13.8 .7 4.8 .1 2.6 .2 33.5-36.6 CSD-612 7.0 .4 15.5 .7 5.6 .1 3.4 .2 39.6-42.7 CSD-614 13.1 .5 15.4 .8 5.7 .1 4.9 .2 57.9-61.0 CSD-620 8.7 .4 13.4 .7 5.2 .1 3.6 .2 67.1-70.1 CSD-623 15.9 .5 17.0 .8 4.6 .1 5.7 .2 73.2-76.2 CSD-625 9.2 .4 14.3 .7 4.9 .1 3.8 .2 ro 82.3-85.3 CSD-628 12.7 .5 14.6 .7 4.6 .1 4.7 .2 ' 88.4-91.4 CSD-630 18.2 .7 19.6 1.0 4.6 .2 6.4 .3 97.5-100.6 CSD-633 11.2 .5 16.6 .8 4.8 .1 4.4 .2

Mean 11.2 15.6 5.0 4.4 Standard Deviation 4.3 1.9 0.4 1.2 Table 6. Heat generation data for Bodmin Moor Site A BRAY DOWN

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10"Wm-3 + -

21.3-24.4 CSD-1108 7.2 .5 19.0 .9 4,8 . 1 3.6 .2 27.4-30.5 CSD-1110 8.6 .5 20.2 .9 5.2 .1 4.0 .2 33.5-36.6 CSD-1112 5.6 .4 16.8 Al 4.7 .1 3.0 .2 39.6-42.7 CSD-1114 14.1 .4 9.6 .6 5.0 .1 4.8 .2 45.7-48.8 CSD-1116 9.4 .5 16.5 .8 4.6 .1 3.9 .2 51.8-54.9 CSD-1118 11.6 .6 20.3 .9 4.4 .1 4.8 .2 57.9-61.0 CSD-1120 15.2 .6 24.2 1.1 4.5 .2 6.0 .3 64.0-67.1 CSD-1122 8.0 .5 22.4 1.0 5.5 .1 4.1 .2 70.1-73.2 CSD-1124 17.9 .7 25.0 1.1 4.4 .2 6.8 .3 76.2-79.3 CSD-1126 12.2 .6 24.0 1.0 4.9 .2 5.2 .2 82.3-85.3 CSD-1128 30.3 .9 28.5 1.3 5.3 2 10.2 .3 88.4-91.4 CSD-1130 12.1 .6 21.7 1.0 4.6 .2 5.0 .2 91.4-94.5 CSD-1131 14.9 .6 16.9 .9 4,6 .1 5,4 .2

Mean 12,9 20.4 4.8 5.2 Standard Deviation 6.3 4.8 0.4 1.8 d

Table 7. Heat generation data for Bodmin Moor Site B BLACK HILL

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm -3 + -

21.3-24.4 CSD-1008 8.8 . 3 6.4 .4 4.5 . 1 3.1 . 1 27.4-30.5 CSD-1010 10.2 .3 7.0 .5 4.9 .1 3.5 .1 33.5-36.6 CSD-1012 10.3 3 5.9 .4 5.6 .1 3.6 .1 39.6-42.7 CSD-1014 7.6 3 6.7 . 5 5.5 1 2.9 .1 45.7-48.8 CSD-1016 7.8 3 6.4 . 5 5.1 1 2.9 .1 51.8-54.9 CSD-1018 8.5 3 6.5 .5 5.5 1 3.1 .1 57.9-61.0 CSD-1020 11.3 .4 6.0 . 5 4.3 1 3.7 . 1 64.0-67.1 CSD-1022 5.3 .2 5.0 .4 4.6 . 1 2.1 .1 70.1-73.2 CSD-1024 5.5 3 5.2 .4 5.2 1 2.2 .1 76.2-79.3 CSD-1026 6.0 3 6.2 .5 5.4 1 2.4 1 82.3-85.3 CSD-1028 9.6 3 7.3 .5 5.8 1 3.5 1 88.4-91.4 CSD-1030 10.2 . 3 6.3 . 5 5.0 1 3.5 1 94.5-97.5 CSD-1032 9.9 .4 8.2 .5 5.0 1 3.5 1 100.6-103.6 CSD-1034 10.1 . 3 7.8 . 5 4.8 1 3.6 . 1

Mean 8.7 6.5 5.1 3.1 Standard Deviation 2.0 0.9 0.5 0.5 Table 8. Heat generation data for Bodmin Moor Site C PINNOCK SHILL

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm-3 + -

21.3-24.4 CSD-1208 7.8 .4 9.6 .6 4.0 .1 3.0 1 27.4-30.5 CSD-1210 4.3 .3 12.7 .6 2.7 .1 2.2 1 33.5-36.6 CSD-1212 7.9 .4 10.3 .6 5.8 .1 3.3 1 39.6-42.7 CSD-1214 13.4 .3 3.8 .4 4.6 .1 4 . 1 1 45.7-48.8 CSD-1216 12.8 .4 7.3 .5 2.5 .1 4.0 1 51.8-54.9 CSD-1218 14.1 .4 6.0 .5 4.2 .1 4.4 .1 57.9-61.0 CSD-1220 11.4 .3 5.0 .4 5,0 .1 3.7 .1 64.0-67.1 CSD-1222 16.0 .4 5.9 .5 3.0 .1 4.7 .1 lw0 70.1-73.2 CSD-1224 10.5 .3 4.1 .4 4.4 .1 3.4 .1 76.2-79.3 CSD-1226 6.7 .3 8.1 .5 4.8 .1 2.7 . 1 82.3-85.3 CSD-1228 5.8 .3 10.9 .6 2.3 .1 2.4 .1 88.4-91.4 CSD-1230 14.0 .4 4.6 .4 4.3 .1 4.3 .1 94.5-97.5 CSD-1232 11.7 .3 4.4 .4 4.4 .1 3.7 .1 97.5-100.6 CSD-1233 7.9 .3 5.9 .4 1.8 .1 2.6 .1 Mean 10.3 7.0 3.8 3.5 Standard Deviation 3.6 2.8 1.2 0.8

Table 9. Heat generation data for Bodmin Moor Site D BROWNGELLY

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm +- ppm + - % + - Ax10-6Wm -3 + -

27.4-30.5 CSD-910 14.3 .5 12.0 .6 4.9 1 4.9 .2 33.5-36.6 CSD-912 15.1 .4 8.1 .5 4.6 1 4.9 .2 39.6-42.7 CSD-914 13.6 .4 11.0 .6 4.5 1 4.6 .2 45.7-51.8 CSD-916/917 14.0 .4 11.0 .6 5.0 1 4.8 .2 54.9-57.9 CSD-919 19.0 .5 10.7 .6 4.4 1 6.0 .2 57.9-61.0 CSD-920 15.4 .5 10.4 .6 4.6 1 5.1 .2 ro 64.0-67.1 CSD-922 16.8 .5 10.8 .6 4.4 1 5.4 .2 70.1-73.2 CSD-924 20.4 .6 12.8 .7 4.7 .1 6.5 .2 76.2-79.3 CSD-926 17.1 .5 11.4 .6 4.9 .1 5.6 .2 82.3-85.3 CSD-928 15.2 .5 10.5 .6 4.5 .1 5.0 .2 88.4-91.4 CSD-930 14.8 .4 9.0 .6 4.8 .1 4.8 .2 94.5-97.5 CSD-932 10.1 .4 9.5 .5 5.2 .1 3.7 .1 100.6-103.6 CSD-934 10.0 .4 14.1 .7 5.1 , 1 4.0 .2

Mean 15.1 10.9 4.7 5.0 Standard Deviation 3.0 1.6 0.3 0.8 •

'fable 10. Heat generation data for Bodmin Moor Site E GREAT HAMMETT FARM

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm-3 + -

15.2-18.3 CSD-806 13.1 .6 23.5 1.0 5.9 .2 5.5 .3 21.3-24.4 CSD-808 16.2 .6 23.2 1.0 4.9 .2 6.2 2 27.4-30.5 CSD-810 10.6 .5 18.3 .8 5.3 .1 4.4 2 33.5-36.6 CSD-812 16.0 .7 23.9 1.1 5.1 .2 6.2 3 39.6-42.7 CSD-814 11.8 .6 18.6 .9 5.6 .1 4.8 2 45.7-48.8 CSD-816 10.2 .5 18.7 .8 5.0 .1 4.4 .2 51.8-54.9 CSD-818 9.1 .5 17.8 .8 4.8 .1 4.0 .2 57.9-61.0 CSD-820 11.1 .6 17.9 .9 5.4 :1 4.6 2 64.0-67.1 CSD-822 9.8 .5 19.2 .9 5.2 .1 4.3 .2 70.1-73.2 CSD-824 7.5 .5 16.0 .8 5.0 .1 3.5 .2 76.2-79.3 CSD-826 7.5 .5 17.6 .8 5.1 .1 3.6 .2 82.3-85.3 CSD-828 8.1 .5 17.8 .8 4.8 .1 3.7 .2 88.4-91.4 CSD-830 6.1 .4 15.0 .7 4.8 .1 3.0 .2 94.5-97.5 CSD-832 6.5 .5 18.0 .8 5.7 .1 3.4 .2 100.6-103.6 CSD-834 5.7 .4 15.4 .7 5.2 .1 3.0 .2 Mean 9.9 18.8 5.2 4.3 Standard Deviation 3.3 2.8 0.4 1.0 a

Table 11. Heat Generation Data for Land's End Site B NEWMILL

Depth Interval Sample Uranium Thorium Potassium Heat generation (metres) Number ppm + - ppm + - % + - Ax10- Wm-3 + -

6.1-9.1 CSD-1403 18.5 .5 19.7 .8 5.2 .1 6.6 .2 15.2-18.3 CSD-1406 14.7 .5 19.2 .8 4.5 .1 5.5 .2 24.4-27.4 CSD-1409 13.0 .5 17.6 .8 4.6 .1 5.0 .2 33.5-36.6 CSD-1412 10.2 .4 15.7 .7 5.0 .1 4.1 .2 42.7-45.7 CSD-1415 13.2 .4 17.5 .7 5.0 .1 5.0 .2 51.8-54.9 CSD-1418 10.3 .4 17.2 .7 5.1 .1 4.3 .2 IL) 60.0-64.0 CSD-1421 9.3 .4 16.1 .7 2.6 .1 3.7 .2 70.1-73.2 CSD-1424 13.0 .5 17.3 .7 4.7 .1 4.9 .2 79.3-82.3 CSD-1427 9.7 .4 16.9 .7 4.7 .1 4.1 .2 88.4-91.4 CSD-1430 15.3 .5 17.5 .7 5.6 .1 5.5 .2 97.5-100.6 CSD-1433 11.2 .5 17.6 .8 5.5 .1 4.6 .2

Me an 12.6 17.5 4.7 4.9 Standard Deviation 2.8 1.2 0.7 0.8 a

Table 12. Heat Generation Data for Land's End Site A BUNKER'S HILL

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm-3 + -

6.1- 9.1 CSD-1303 13.6 .5 23.1 .8 4.6 .1 5.5 .2 15.2-18.3 CSD-1306 14.0 .6 24.2 1.0 4.6 .2 5.7 .2 24.4-27.4 CSD-1309 15.6 .6 23.3 1.0 4.6 .2 6.0 .2 33.5-36.6 CSD-1312 14.7 .5 23.7 .9 4.5 .1 5.8 .2 42.7-45.7 CSD-1315 14.8 .5 21.1 .8 4.1 .1 5.6 .2 51.8-54.9 CSD-1318 16.4 .6 22.3 .9 4.4 .2 6.1 .2 60.0-64.0 CSD-1321 10.9 .5 22.7 .9 5.2 .1 4.8 .2 70.1-73.2 CSD-1324 9.8 .4 18.2 .7 4.8 .1 4.2 .2 79.3-82.3 CSD-1327 9.1 .3 17.5 .6 5.0 .1 4.0 .1 88.4-91.4 CSD-1330 11.5 .5 17.4 .8 4.8 .1 4.6 .2 97.5-100.6 CSD-1333 13.0 .5 18.0 .8 5.1 .1 5.0 .2

Mean 13.0 21.1 4.7 5.2 Standard Deviation 2.4 2.7 0.3 0.7 Table 13. Heat Generation Data for St. Austell Site B TREGARDEN QUARRY

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6'. m-3 + -

6.1- 9.1 CSD-1603 8.4 .5 23.9 1.0 4.5 .1 4.2 .2 15.2-18.3 CSD-1606 7.7 .5 21.6 .9 4.6 .1 3.9 .2 24.4-27.4 CSD-1609 9.8 .4 17.7 .7 4.9 .1 4.2 .2 33.5-36.6 CSD-1612 4.4 .4 17.6 .7 5.2 .1 2.8 .2 .1 .2 ,,, 42.7-45.7 CSD-1615 7.8 .4 18.0 .8 5.1 3.7 Il 51.8-54.9 CSD-1618 11.8 .5 18.8 .8 5.1 .1 4.8 .2 fv 60.0-64.0 CSD-1621 8.7 .4 15.9 .6 4.3 .1 3.7 .2 70.1-73.2 CSD-1624 5.4 .4 18.3 .7 5.1 .1 3.1 .2 79.3-82.3 CSD-1627 6.8 .4 15.1 .7 4.5 .1 3.2 .2 88.4-91.4 CSD-1630 6.3 .3 11.2 .5 4.5 .1 2.8 .2 97.5-100.6 CSD-1633 6.8 .4 15.6 .6 4.5 .1 3.2 .2

Mean 7.6 17.6 4.7 3.5 Standard Deviation 2.1 3.4 0.3 0.6 Table 14. heat Generation Data for St. Austell Site A COLCERROW FARM

Depth Interval Sample Uranium. Thorium Potassium Heat Generation (metres) Number ?ppm + - ppm + - % + - AxiO-6Wm-3 + -

6.1- 9.1 CSD-1503 14.2 .5 21.8 .9 4.3 .1 5.5 .2 15.2-18.3 CSD-1506 14.0 .5 17.9 .7 4.2 .1 5.2 .2 24.4-27.4 CSD-1509 13.7 .5 19.9 .9 5.6 .1 5.4 .2 33.5-36.6 CSD-1512 14.7 .5 20.2 .8 4.4 .1 5.5 .2 42.7-45.7 CSD-1515 13.3 .4 20.8 .7 4.4 .1 5.2 .2 51.8-54.9 CSD1518 10.5 .4 17.7 .7 4.1 .1 4.3 .2 60.0-64.0 CSD-1521 10.2 .4 17.9 .7 4.3 .1 4.3 .2 70.1-73.2 CSD-1524 9.3 .4 12.8 .6 4.1 .1 3.6 .2 79.3-82.3 CSD-1527 10.3 .4 15.8 .7 4.5 .1 4.1 .2 88.4-91.4 CSD-1530 11.7 .4 16.4 .7 4.7 .1 4.6 .2 97.5-100.6 CSD-1533 13.9 .4 16.5 .7 4.9 .1 5.1 .2

Mean 12.2 18.0 4.5 4.8 Standard Deviation 2.0 2.6 .4 .7 w

Table 15. Heat Generation Data for Dartmoor Site B WINTER TOR

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm-3 + -

6.1- 9.1 CSD-1803 24.4 .6 16.4 .8 4.3 .1 7.7 .2 15.2-18.3 CSD-1806 16.2 .6 22.8 .9 4.1 .1 6.1 .2 24.4-27.4 CSD-1809 19.5 .6 25.1 .9 4.0 .1 7.1 .2 33.5-36.6 CSD-1812 20.1 .5 15.4 .6 4.5 .1 6.6 .2 42.7-45.7 CSD-1815 12.5 .5 16.1 .7 3.7 .1 4.6 .2 ~ 51.8-54.9 CSD-1818 11.7 .4 15.0 .7 4.2 .1 4.5 .2 60.0-64.0 CSD-1821 13.6 .4 13.7 .6 3.9 .1 4.8 .2 70.1-73.2 CSD-1824 17.1 .4 15.5 .6 3.9 .1 5.3 .2 79.3-82.3 CSD-1827 19.8 .5 20.0 .8 4.0 .1 6.8 .2 88.4-91.4 CSD-1830 8.9 .4 13.0 .6 4.1 .1 3.5 .2 97.5-100.6 CSD-1833 17.3 .4 10.2 .6 4.2 .1 5.5 .2

Mean 16.4 16.8 4.1 5.7 Standard Deviation 4.5 4.3 0.2 1.3 Table 16. Heat Generation Data for Dartmoor Site A BLACKINSTONE QUARRY

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm-3 + -

6.1- 9.1 CSD-1703 11.3 .5 17.7 .8 4.1 .1 4.5 .2 15.2-18.3 CSD-1706 11.7 .5 18.8 .8 4.3 .1 4.7 .2 24.4-27.4 CSD-1709 13.3 .4 15.2 .6 4.9 .1 4.9 .2 33.5-36.6 CSD-1712 12.8 .4 16.8 .7 4.8 .1 4.9 .2 42.7-45.7 CSD-1715 9.6 .4 14.7 .7 5.0 .1 3.9 .2 51.8-54.9 CSD-1718 13.6 .5 16.5 .7 4.4 .1 5.0 .2 ōo 60.0-64.0 CSD-1721 13.4 .4 15.5 .6 4.5 .1 4.9 .2 70.1-73.2 CSD-1724 16.0 .4 16.1 .6 3.8 .1 5.5 .2 79.3-82.3 CSD-1727 14.0 .5 14.3 .7 5.0 .1 5.0 .2 88.4-91.4 CSD-1730 18.3 .4 15.6 .5 4.8 .1 6.2 .2 97.5-100.6 CSD-1733 15.1 .5 12.5 .4 5.0 .1 4.7 .2

Mean 13.5 15.8 4.6 4.9 Standard Deviation 2.4 1.7 0.4 0.6 Table 17. Heat Generation Data for Dartmoor Site C SOUSSON'S WOOD

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm-3 + -

6.1- 9.1 CSD-1903 17.9 .6 19.8 .8 4.7 .1 6.4 .2 15.2-18.3 CSD-1906 12.3 .5 18.0 .8 5.3 .1 4.9 .2 24.4-27.4 CSD-1909 8.6 .4 18.1 .8 4.3 .1 2.2 .2 33.5-36.6 CSD-1912 6.3 .5 24.3 1.0 4.5 .1 3.7 .2 42.7-45.7 CSD-1915 8.4 .4 15.7 .7 5.1 .1 3.7 .2 51.8-54.9 CSD-1918 7.5 .4 16.6 .7 5.0 .1 3.5 .2 60.0-64.0 CSD-1921 13.1 .5 20.4 .8 4.0 .1 5.1 .2 70.1-73.2 CSD-1924 25.1 .6 16.3 .8 6.0 .2 8.1 .2 79.3-82.3 CSD-1927 9.7 .5 17.7 .8 5.5 .1 4.2 .2 88.4-91.4 CSD-1930 28.0 .6 16.7 .8 5.4 .2 8.8 .2 97.5-100.6 CSD-1933 12.5 .5 17.9 .8 4.9 .1 4.9 .2

Mean 13.6 18.3 5.0 5.0 Standard Deviation 7.2 2.4 0.6 2.0 Table 18. Heat Generation Data for Dartmoor Site E LAUGHTER TOR

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number Ppm + - Ppm + - ō + - Ax10-6Wm-3 + -

6.1- 9.1 CSD-2103 15.6 .5 17.5 .8 4.5 .1 5.6 .2 15.2-18.3 CSD-2106 17.8 .5 17.8 .8 4.5 .1 6.2 .2 24.4-27.4 CSD-2109 10.1 .4 17.0 .7 3.8 .1 4.1 .2 33.5-36.6 CSD-2112 12.8 .5 17.4 .8 3.1 .1 4.8 .2 42.7-45.7 CSD-2115 14.1 .5 16.4 .7 4.5 .1 5.2 .2 lG, 51.8-54.9 CSD-2118 15.9 .4 16.1 .6 3.3 .1 5.5 .2 ō 60.0-64.0 CSD-2121 18.6 .5 14.5 .7 3.9 .1 6.1 .2 70.1-73.2 CSD-2124 20.9 .6 16.4 .8 4.0 .1 6.8 .2 79.3-82.3 CSD-2127 17.8 .5 13.1 .7 3.2 .1 5.7 .2 88.4-91.4 CSD-2130 22.0 .5 16.1 .7 3.6 .1 7.1 .2 97.5-100.6 CSD-2133 28.1 .5 8.6 .6 4.1 .1 8.2 .2

Me an 17.6 15.5 3.9 5.9 Standard Deviation 4.9 2.7 .5 1.1 s

Table 19. Heat Generation Data for Dartmoor Site D FOGGIN TOR

Depth Interval Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm-3 + -

6.1- 9.1 CSD-2003 23.1 .6 14.5 .7 3.8 .1 7.2 .2 15.2-18.3 CSD-2006 18.0 .5 13.2 .7 4.6 .1 5.9 .2 24.4-27.4 CSD-2009 9.5 .3 6.5 .4 4.1 .1 3.3 .1 33.5-36.6 CSD-2012 16.6 .3 5.9 .3 3.8 .1 5.0 .1 42.7-45.7 CSD-2015 17.6 .4 5.3 .4 4.1 .1 5.3 .1 51.8-54.9 CSD-2018 14.8 .4 11.9 .6 4.5 .1 5.0 .2 60.0-64.0 CSD-2021 13.3 .3 6.4 .4 4.3 .1 4.2 .1 70.1-73.2 CSD-2024 12.8 .3 7.2 .4 5.1 .1 4.2 .1 79.3-82.3 CSD-2027 17.6 .4 8.2 .5 4.3 .1 5.5 .2 88.4-91.4 CSD-2030 12.9 .3 7.4 .5 5.2 .1 4.3 .1 97.5-100.6 CSD-2033 9.6 .3 8.6 .5 4.6 .1 3.5 .1

Mean 15.1 8.6 4.4 4.9 Standard Deviation 4.0 3.1 0.5 1.1 Table 20. Heat Generation Data for Country Rock Borehole No. 1 OLD MERROSE FARM (CAMBORNE)

Depth Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm-2 + -

10.1 MER-33 2.1 .3 14.2 .7 3.5 .1 1.8 .1 12.2 MER-40 2.2 .3 14.3 .7 3.6 .1 1.9 .1 18.0 MER-59 2.6 .3 13.4 .6 2.8 .1 1.0 .1 24.4 MER-80 2.2 .3 10.8 .5 1.8 .1 1.5 .1 30.5 MER-100 2.4 .3 11.7 .6 1.9 .1 1.6 .1 36.6 MER-120 2.3 .3 13.7 .6 3.5 .1 1.9 .1 42.1 MER-138 2.1 .3 10.9 .5 2.4 .1 1.5 .1 49.7 MER-163 3.8 .3 13.9 .6 3.9 .1 2.3 .1 54.9 MER-180 2.5 .3 11.2 .5 1.9 .1 1.6 .1 61.0 MER-200 1.8 .2 10.0 .4 2.6 .1 1.4 .1 67.1 MER-220 2.8 .3 15.9 .6 4.1 .1 2.2 .1 73.2 MER-240 2.7 .4 18.5 .8 5.1 .1 2.4 .1 79.9 MER-262 2.5 .3 13.8 .6 3.4 .1 1.9 .1 85.6 MER-281 2.9 .3 15.3 .6 4.0 .1 2.2 .1 91.4 MER-300 4.0 .4 17.2 .7 2.3 .1 2.4 .1 97.5 MER-320 1.9 .3 10.9 .5 2.8 .1 1.5 .1 103.6 MER-340 3.9 .2 8.1 .4 2.2 .1 1.8 .1 Mean 2.6 13.2 3.0 1.9 Standard Deviation 0.7 2.7 0.9 0.3 •

Table 21. Heat Generation Data for Country Rock Borehole No. 2 KES T LE WARTHA (HELFORD)

Depth Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + 1 ppm + - % + - Ax10-6Wm` + -

15.2 KES- 50 3.1 .2 15.1 .5 3.4 .1 2.1 .1 22.6 KES- 74 2.6 .3 16.7 .6 4.1 .1 2.2 .1 35.4 KES-116 2.4 .2 9.3 .4 1.4 .1 1.4 .1 45.1 KES-148 3.4 .3 14.9 .6 3.1 .1 2.2 .1 53.6 KES-176 3.2 .3 14.1 .5 2.0 .1 2.0 .1 61.0 KES-200 2.3 .2 14.1 .5 3.4 .1 1.9 .1 69.5 KES-228 2.7 .3 14.3 .5 3.6 .1 2.0 .1 81.4 KES-267 2.8 .3 17.0 .6 4.5 .1 2.3 .1 91.1 KES-299 2.2 .2 8.6 .4 1.5 .1 1.3 .1 101.2 KES-332 2.7 .2 11.6 .5 2.1 .1 1.7 .1 110.9 KES-364 2.8 .2 10.1 .4 1.4 .1 1.5 .1 121.3 KES-398 2.7 .3 15.1 .6 3.9 .1 2.1 .1 130.8 KES-429 2.7 .2 10.2 .4 1.6 .1 1.5 .1 140.8 KES-462 2.5 .2 9.4 .4 1.6 .1 1.4 .1 151.8 KES-498 2.5 .2 8.4 .4 1.5 .1 1.4 .1

Mean 2.7 12.6 2.6 1.8 Standard Deviation 0.3 3.0 1.1 0.4 Table 22. Heat Generation Data for Country Rock Borehole No. 3 CALLYWITH FARM (BODMIN)

Depth Sample Uranium Thorium Potassium Heat Generation (metres) Number ppm + - ppm + - % + - Ax10-6Wm-3 + -

9.1 CALLY- 30 3.1 .3 16.3 .6 2.5 .1 2.1 .1 13.3 CALLY- 60 3.1 .3 17.4 .7 4.1 .1 2.4 .1 27.7 CALLY- 91 3.1 .3 14.7 .6 3.2 .1 2.1 .1 36.6 CALLY-120 3.1 .3 15.2 .6 3.0 .1 2.1 .1 45.6 CALLY-150 2.9 .3 15.4 .6 3.3 .1 2.1 .1 54.5 CALLY-179 2.9 .3 15.0 .6 2.3 .1 2.1 .1 64.2 CALLY-211 2.8 .3 16.1 .6 3.4 .1 2.1 .1 73.2 CALLY-240 3.2 .3 15.5 .6 3.3 .1 2.2 .1 82.5 CALLY-271 3.3 .3 14.7 .6 3.3 .1 2.2 .1 91.4 CALLY-300 3.4 .3 15.0 .6 3.3 .1 2.2 .1 100.6 CALLY-330 3.6 .3 16.9 .6 3.9 .1 2.4 .1 109.7 CALLY-360 3.5 .3 15.2 .6 3.2 .1 2.2 .1 118.9 CALLY-390 3.6 .3 14.5 .6 3.4 .1 2.2 .1 128.0 CALLY-420 3.3 .3 14.9 .5 3.2 .1 2.2 .1 137.2 CALLY-450 3.1 .3 14.4 .6 3.2 .1 2.1 .1

Mean 3.2 15.4 3.2 2.2 Standard Deviation 0.2 0.9 0.4 0.1 •

Table 23. Heat generation data for re-opened borehole at GAVERIGAN

Depth Sample Uranium Thorium Potassium Heat generation (metres) Number ppm + - ppm + - ō + - Ax10- Wm-3 + -

A. Meadfoot Beds (Devonian) 189/206 GAV-620/675 3.4 .3 13.2 .6 2.6 .1 2.0 .1 215/247 GAV-705/810 4.1 .4 15.9 .7 2.6 .1 2.4 .2

B. Granite 313/327 GAV-1028/1073 25.6 .6 8.4 .6 4.5 .1 7.5 .2 317 GAV-1040 24.0 .5 9.4 .5 4.1 .1 7.2 .2 326 GAV-1070 24.4 .4 10.3 .5 4.3 .1 7.4 .2

Granite Mean 24.7 9.4 4.3 7.35 (3 samples only) Standard Deviation .8 .9 .2 .2 Table 24. Heat Generation data for IGS stratigraphic borehole at WILSEY DOWN

Depth Sample Uranium Thorium Potassium Heat Generation-3 (metres) Number ppm + - ppm + - iso + - Ax10-6Wm + -

A. Crackington Formation (Carboniferous) 42.1 WD-138 8.5 .4 13.6 .7 2.3 .1 3.3 .2 55.2 WD-181 6.1 .4 12.3 .7 3.0 .1 2.7 .2 64.6 WD-212 3.5 .3 9.5 .5 2.1 .1 1.7 .1 B. Fire Beacon Chert Formation (Carboniferous) 81.7 WD-268 4.5 .3 11.6 .6 2.7 .1 2.2 .1 92.4 WD-303 4.5 .3 13.0 .6 2.7 .1 2.3 .1 105.2 WD-345 5.8 .3 12.4 .6 3.0 .1 2.6 .1 127.3 WD-417 10.7 .4 12.4 .6 2.7 .1 3.8 .2 197.3 WD-647 7.6 .4 13.1 .7 3.3 .1 3.2 .2 220.6 WD-723 8.3 .2 2.3 .2 0.1 .1 2.3 .1 264.9 WD-869 4.1 .3 11.8 .6 2.8 .1 2.1 .1 271.2 WD-889 34.5 .6 11.6 .7 2.6 .1 9.8 .2 291.4 WD-956 9.2 .3 4.0 .3 0.4 .1 2.7 .1 310.3 WD-1018 4.6 .2 3.8 .3 0.5 .1 1.5 .1 337.1 WD-1106 1.0 .2 2.6 .3 0.1 .1 0.4 .1 357.5 WD-1173 2.3 .3 9.0 .5 2.1 .1 1.4 .1 389.2 WD-1277 0.5 .2 3.9 .3 1.6 .1 0.6 .1 410.9 WD-1348 10.2 .4 8.4 .5 1.5 .1 3.3 .1 42G.1 WD-1398 2.9 .2 7.9 .4 2.7 .1 1.5 .1 436.5 WD-1432 1.3 .1 2.8 .3 0.2 .03 0.5 .1 453.2 WD-1487 6.8 .2 5.2 .3 1.4 .1 2.2 .1 C. Upper Delabole Slates (Devonian) 485.9 WD-1594 3.4 .3 13.3 .6 3.5 .1 2.1 .1 500.5 WD-1642 2.5 .3 13.6 .5 4.2 .1 2.0 .1 520.0 WD-1706 3.5 .4 12.5 .6 3.3 .1 2.1 .1 539.8 WD-1771 3.8 .4 14.3 .7 4.2 .1 2.4 .1 563.9 WD-1850 3.9 .3 12.1 .6 4.0 .1 2.2 .1 579.4 WD-1901 3.6 .3 13.3 .6 4.0 .1 2.2 .1 608.7 WD-1997 3.8 .3 14.2 .6 3.8 .1 2.3 .1 637.6 WD-2092 3.4 .3 13.7 .6 3.5 .1 2.1 .1 652.0 WD-2139 3.5 .3 12.9 .5 3.7 .1 2.1 .1 668.1 WD-2192 3.7 .4 13.6 .7 3.5 .1 2.2 .1 682.8 WD-2240 4.3 .4 16.0 .7 4.5 .1 2.6 .2 702.9 WD-2306 3.9 .4 13.2 .7 3.9 .1 2.3 .2 D. Black Slates (Carboniferous) 719.9 WD-2362 1.0 .1 2.0 .2 1.2 .03 0.5 .1

SUMMARY Mean Std.Dev. Mean Std.Dev. Mean Std.Dev. Mean Std.Dev. A. Crackington 6.0 2.5 11.8 2.1 2.5 .5 2.6 0.8(3) B.Fire Beacon Chert 7.0 7.8 8.0 4.2 1.8 1.1 2.5 2.1(17) C. Upper Delabole Slates 3.6 0.4 13.6 1.0 3.8 0.4 2.2 0.2(12) w S. Black Slates 1.0 - 2.0 - 1.2 - 0.5 - I:11 • 358

Appendix V Derivations of Equations used to Calculate Temperature Extrapolations

All derivations in this section are for a one dimensional interpretation of the temperature field. They have been derived from the assumption that the surface flux has been measured and that extrapolations are to be made down- wards from this value. For this reason, the deeper the extrapolation is taken, the less reliable will be the result. This section is split into stages of increasing complexity, each stage considering an additional parameter.

Stage 1 Linear extrapolation. The simplest form of downward continuation is to consider that heat flux and conductivity remain constant. Thus T. the temperature at any depth z, is given by the equation:

q0 z Tz = -Ko + To (V.1)

where

go = surface heat flux To = temperature at depth z = 0 Ko = thermal conductivity at depth z = 0 This gives a straight line graph with geothermal gradient given by:

dT =o (V.2) dz K 0 Stage 2 Heat flux with heat production constant. By measuring the concentrations of heat producing elements, the surface heat production due to radioactivity may be estimated. If it is assumed this is a constant value then Tz the temperature at any depth z is given by:

359

qoz Aoz2 - T = T + K (v. 3) 0 2K0 where Ao is the measured heat production. This form of extrapolation yields a lower gradient than the linear extrapolation model. General case The heat flux qz at any depth z for any distribution of heat production may be expressed by the equation: z qz = go A(z) dz (V.4)

where A(z) is the function of z describing the vertical distribution of all forms of heat production. At any depth the heat flux is given by:

dT qz Kz dz (V.5)

These equations are fundamental to the continuation method, being derived from the laws of conservation of energy and Fourier's law respectively. Variation of heat production with depth. The linear relation between heat flow and heat production in plutons was first described by Birch et al. (1968) and elaborated by Roy et al. (1968) and Lachenbruch (1968 & 1970). In the areas studied, the measured heat flow q was related to the measured heat production in near surface plutonic rock by the equation:

q = q* +DAo (v.6)

where q* the intercept value, and D the slope, are relatively constant over large geographic provinces. Limited depth penetration has prevented an unambiguous interpretation of these parameters for the Cornubian granite. One model which fits this linear relation is based on heat production decreasing exponentially with depth.

• 360

Stage 3 Heat flow with heat production decreasing exponentially with depth. The following equation was adapted from one quoted by Blackwell (1971). In this instance, however, the surface heat flux qo was used as opposed to the apparent mantle contribution q*: (1 - e-z/D) q z _ A Dz A0 D2 Tz = To + oKz 0Kz + Kz (v.7)

where D is the constant from the expression:

A (z) Ao exp(-z/D) (V.8)

which describes the distribution of heat producing elements. The range of values for D is given as 7.5 - 10km by Lachen- bruch (1970). For results over shallow depths, the error due to this range, was small compared to the total correction. Variation of conductivity with depth. Most measurements of thermal conductivity of rocks have been made in laboratory conditions. It has not yet been proved conclusively how well these data agree with the conductivity values under natural conditions. More reli= able data of mean conductivity would be obtained if an accurate in situ method were available. Relations that govern the dependence of conductivity on temperature should be used with caution. There is al- ways a tendency to apply apparently well-defined relationships with no test on their validity to the case in question. The next step has been taken nevertheless, since ignoring the temperature dependence of conductivity would have been less correct than applying the best estimates presently available. The extrapolations are for one dimension only, so have ignored anistropy of the rocks' thermal conductivity and also the effect of refraction. It is likely that the

361

composition of the granite will vary with depth. A pro- gressive decrease in quartz content would yield a decrease in thermal conductivity and consequently a higher geothermal gradient. If the quartz content decreases, the temperature dependence of thermal conductivity will be less severe.

Stage 4 Thermal conductivity changing as a function of temperature, no heat production. The variation of thermal conductivity is commonly expressed by the equation:

KT = a/T + b (V.9)

where a and b are constants and KT represents the conductivity at temperature T.

Kz , , + b (V.10) z dTz q Z - Kz dz (V.11) t

qz dz = Kz dT (V.12) T 0 T z (a/Tz + b) dT = qz dz (V.13) T 0o

a logTz + bTz - a logTO - bT0 = z az (V.14)

a 1ogTz + bTz = a logTO + bT0 + z qz (V.15)

where Tz = temperature at depth z T. = temperature at depth z = 0 i.e. surface temperature.

It can be seen that, provided a is positive, the temperature will increase faster with depth in this case than in stage 1.

362

Stage 5 Conductivity changing with temperature with constant heat production. Starting with the general equations: 0 (V.4) qz = qo - A(z) dz and z dT (V.5) qz Kz dz dT o K = q - A(z) dz (V.16) z dz o fz Using the relation:

(V.10) Kz = a/Tz + b

for temperature dependence of conductivity where a and b are constants and Tz is measured in Kelvin, dT dzz (a/Tz + b) = qo A(z) dz (V.17)

T - a/T + b) dT = % (q(q0 % A(z)dz)dz (V.18) fT: ~J o .f o z z alog(Z) +bz=zqo +alog(To) +bō-( f f A z) dz dz (V.19) 0 0 The above equation represents the general case i.e. with an unspecified distribution of heat producing elements. For a constant heat production this may be evaluated in the following manner: z a log(Tz) + bTz = a log(To) + bTo + zqo - % Aoz dz (V.20) J o

a log(Tz) + bTz = a log(To) + bTo + zqo - Aoz2 (V.21) 2 363

Stage 6 Conductivity changing with temperature, heat production decreasing exponentially with depth. Starting with the general equation derived in stage 5 (V.19) z z a log(Tz) + bTz = zq -ff o + a log(To) + bTo A(z) dz dz

and using the exponential decay model,

(V.8) A(z) = Ao exp(-z/D) Z z ff A exp(-z/D) dz dz becomes = AoD % (1 - exp(-z/D) ) dz 0 AoDz + Ao D2 exp(-z/D) - Ao D2 which on substitution into the general equation yields:

a log(Tz) + bTz = zC 1 + C2 exp(-z/D) + C3 (V.22) where Cl = qo - AoD C2 = -AoD2 C3 = a log(To) + bTz + AoD2 qo is the surface heat flux Ao is the surface heat production, To is the surface temperature Tz is the temperature at depth z a,b,D are constants. •

SOUTH - WEST ENGLAND 200 HEAT FLOW COVERAGE LUNDY ISLE EXMOOR EEC CONTRACT NO 586-78-1EGUK o21 UKAEA CONTRACT NO E/5A/CON/105

KEY TO BOREHOLES Contract Sites Other Sites

• Granite o Granite

• Country Rock ❑ Country Rock h t r EXTRAPOLATED TEMPERATURES

No 500m DEPTH

Km id

Gr 28• •28 l •26

na 28. tio Na

CARNMENEL L IS PLY OUTH GRANITE

LAND'S END GRANITE 29 27,26,26 • 28 27 (1 25 SC) km .11t'. LIZARD PENINSULA

March WO FIGURE V- 1 National Grid Km East

200 SOUTH -WEST ENGLAND .um LUNDY ISLE HEAT FLOW COVERAGE EXMOOR 28 EEC CONTRACT NO 586-78-1EGUK o31 34 UKAEA CONTRACT NO E/5A/CON/105

KEY TO BOREHOLES Contract Sites Other Sites

• Granite o Granite • Country Rock o Country Rock

EXTRAPOLATED TEMPERATURES 1000m DEPTH

BODMIN GRANITE

4? •

i SGRAUNNITEL 42 CARNMENELLIS PLY OUTH GRANITE

LAND'S END GRANITE 43.41.41 25 50 km

M.1r 1 h 1W1 FIGURE V-2 National Grid Km East 200 SOUTH -WEST ENGLAND LUNDY ISLE HEAT FLOW COVERAGE EXMOOR EEC CONTRACT NO 586-78-1EGUK 052 UKAEA CONTRACT NO E/5A/CON/105

KEY TO BOREHOLES Contract Sites Other Sites

• Granite o Granite . Country Rock o Country Rock h t r EXTRAPOLATED TEMPERATURES 2000m DEPTH No Km

BODMIN id GRANITE Gr t na tIo Na

CARNMENEL L IS PLY OUTH GRANITE

LAND'S END GRANITE 74,71,71 76 25 50 km

March 19,30 FIGURE V-3 National Grid Km East • •

200 300 SOUTH —WEST ENGLAND LUNDY ISLE HEAT FLOW COVERAGE a EXMOOR EEC CONTRACT NO 586-78-1EGUK o71 UKAEA CONTRACT NO E/5A/CON/105 a73

KEY TO BOREHOLES Contract Sites Other Sites

• Granite o Granite • Country Rock o Country Rock h t r EXTRAPOLATED TEMPERATURES L. - 3 000m DEPTH No 087 DARTMOOR GRANITE Km tog BODMIN id GRANITE o120 101W Gr l 0 c , na 0128 tio oa81 ST. AUSTELL

Na 92 GRANITE 132128 0 CARNMENELLIS OUTH GRANITE

LANDS END GRANITE

FIGURE V-4 National Grid Km East •

200 SOUTH — WEST ENGLAND HEAT FLOW COVERAGE EEC CONTRACT NO 586-78-1EGUK UKAEA CONTRACT NO E/5A/CON/105

KEY TO BOREHOLES Contract Sites Other Sites

• Granite o Granite

■ Country Rock o Country Rock h t r EXTRAPOLATED TEMPERATURES ItX 5 000m DEPTH No 165 • o135 _ DARTMOOR GRANITE Km 183 BODMIN d GRANITE o189 Gri l 0 na 202

tio 122 1 • 00 ST. AtJSTELL

Na 1410 v 0 GRANITE 203 CARNMENELLIS OUTH GRANITE 183182

LAND'S END 161,152,153 GRANITE 178 0 25 50 k m 161 i Scale

LIZARD PENINSULA 200 FIGURE V-5 National Grid Km East 369

Appendix VI Finite Difference Modelling, Equations and Methods used for Models described in Chapter 5

The heat flow modelling was carried out by use of the finite difference solution of Poisson's equation in two dimensions:

c2e + d26 + A = 0 (VI.1) dx2 dy2 Time dependence was not included in the models for south-west England since it was considered the region was likely to be close to thermal equilibrium. The finite difference method is based on Taylor's Theorem:

- f(x h) = f(x) - hf' (x) + , h2f" (x) + , h (x) (VI .2 ) 2 3 3 f"

The region was sampled at discrete points on a square grid. Each point has a co-ordinate (i,j) which was represented within the computer as the row and column numbers of a two dimensional array.

+ p O O+ j,increasing Oi-1,j Oi+,j Oi l,j

j+1 --4- -f- -F' +Q + Oi, j+l j+2 —~- -}- -~- -}-

370

For a region of uniform thermal conductivity K and uniform heat production A let 8(i,j) represent the model temperature at co-ordinate point (i,j). Using Taylor's Expansion:

de. +Ax 2 d_20. + 1 Lx 3 d38. e = e. + Ax —~ i1 (VI.3) i +l,j 1j dx 2 6 dx3

2 3 2 d e~1 - 1 Ax3 d e11 e. = e i - Ax IIa + Ax 1VI.4) 1-1,j j dx 2 dx2 6 dx3

Addition of these two equations and ignoring fourth and higher order terms, yields: a2 2 = 2ei.+ j (Ax) dxei;2 (VI.5) ei+1, j + ei-1, j

Similarly in the vertical dimension, d28. e. +e + (62) 2 1 (vI.6) i, j+1 i, j-1 = j dz2

Rearranging the sum of equations (VI.5) and (VI.6) yields:

2 2 e. + e. -2e.. A. +e -2e ae ae _ 1+1,1 -1,i1 11 + 1,1+1 i, -1 ii (VI.7) dx2 dz2 A x2 z2

Substitution of this changes Poisson's equation to the form:

+1, i -26~1 + ,1+1 11, i- -2eii e1 + ei 1, i ei + 2 + K = 0 (VI. 8) Ax 1iz If Lx = Az = 1 unit, we obtain:

8. = ei+1,1 + ei-1,1 + 91,1+1 + e1,1-1 + A (vI.9) tj 4 4K

This equation gives the temperature at point (i,j) in terms of the temperatures of the four closest points. In order to apply this equation we use an iterative solution of the temperature field. 371

Each temperature is calculated from the surrounding points whose temperatures are also unknown, thus the calculation only converges to the correct solution after many iterations. The Gauss-Seidel scheme was used to solve the temperature field. In order to increase the rate of convergence by approximately an order of magnitude, the successive over-relaxation method was applied. Each time a new value of 9ij is calculated from the equation (VI.9), the previous value of 9ij is subtracted from the new one, the difference D is then multiplied by a relaxation factor W and added to the old value to yield the new value of 9ij, expressed in equation form: (VI.10)

+9i, i+1, i +9i-1,1 i+1 +ei, i-1i + p A. = 8. + W `e 9. . 3 ~iJ ~ 4 4K ~ i~ new previous relaxation previous value value factor value

The relaxation factor may have a value between 0 and 2, an estimate of the optimum value for this factor being calculated from the equation,

W = 2 (VI.11) 1 + Where u, the spectral radius of the Jacobi iteration matrix is calculated from p where Dr and D represent 2= Dr/Dr-1, r-1 the average absolute change within the matrix, as a result of consecutive iterations. W was calculated several times at regular stages during iteration in order to maintain the optimum rate of convergence. In the case of the modelling for south-west England, a model symmetric about the penultimate column (j = J-1) was used in the calculation, this being achieved by the use of a mirror plane at the edge of the array. The last column This is simply ac- is calculated using ei-Li - ei+l,.. hieved by introducing an additional column which, after

372

each pass, is made equal to the antepenultimate column. An alternative method is to use the equation: (VI.12 )

+ + w (2e (i-1, 7 ) + 9 (i j+1) 8. = 8 9 (i, 7-1)) 1J i J 4

antepenultimate penultimate last column O 0 0 0 0 0 0

mirror plane O 0• 0• 0 Q 0

0 • • •-• ----.0-----.~------~

O 0• 0 0 O 0 J-2 J J O 0 0 0 0 0 0 Boundary

The top boundary was set with a constant surface temperature for all points. The side boundary was set to be equivalent to the geothermal gradient in an undisturbed region. The model had to be made sufficiently wide so as not to distort the anomaly by imposing boundary conditions.

373

The boundary conditions at the base of the model were calculated in several ways, the simplest method being to use a fixed temperature. This, however severely distorts the model unless it can be moved to a realistic depth beneath the batholith. Two other forms of bottom boundary were tried. In the first, the heat flow on the boundary was allowed to find its own variable level by holding the temperature gradients constant above and below the boundary, i.e. the temperatures on the row immediately below the boundary were taken to be linear continuations of the temperatures on the row above.

DX represents x DX the scaling factor

Boundary 1 J DX t

-2e1,j-ei ei+l,j -1,j temperature--4.-

The second form was the boundary condition finally used, restricting the heat flow across the bottom boundary to a fixed value. At mantle depths this might be represented by q* the reduced heat flow. The boundary between two regions of different thermal properties was calculated according to the following boundary conditions: 374

(1) Heat flow perpendicular to the boundary is continuous. (2) Temperature gradient parallel to the boundary is continuous, i.e. the gradient one side of the boundary, must be equal to the gradient on the other side. N.B. The boundary has no thickness so no heat may flow within it. O 0 0 0 0 0 0 0

O 0 0 0 0 0 0 0

a (1-a) O 0 0---0 0 0 0 0 G. e1 1,j 9b 1 + ,j O 0 0 0 d G 0 0 Boundary between two regions of different thermal properties O 0 0 0 0 0 0 0

The heat flow at point i,j may be resolved into an x vector and a z vector. The heat flow away from i,j in the x direction may be expressed as:

(9. . - 6b) K 1 AlOxa (vi.13) Qij - pxa[ - 4

The heat flow at the boundary b in same direction as:

. . - 6 )K A b 14 Qb = (e110x« 1 + 4 (VI.14) Q - (9b -ei - A2Ax(1-a) +l,i)K2 (VI.15) b - Ax (1-a) 4 375

Subtracting one from the other: (0. - Ob) Kl 9 (eb - 1+1, j ) K2 + (Ala + A2(1-a)) dx (VI.16) 0 ex ac Ax(1-a) 4 K1(1- = ~ 0 (K2 a) + (A a+ A (1-cr.) AX 2 1] B1+1 1 (Kl (1-od + K2ac) j K (1- 1 4 4( vi{ . 17 ) This result may be substituted into equation (VI.13) yield the heat flowing from point (i,j) towards (i+1,j). Heat flowing from Oij towards O is given as follows:

Q.. _ (a 1 - ai ~ - Adx lj 1 ,-1 )K1 (VI.18) Ax 4

This may be repeated for the two flows in the z direction. Point ij occupies no volume (or area) thus heat flowing in and out of the point must be exactly balanced. The four equations obtained therefore, must add up to zero.

2 j±/ 3A1Ax + e 30.. - - ei, 1 - i. j - K1(1-a) Li . - 9i, j- 4 K1(1-a4 +K2 cc

āa + A2Ax2 1Axōc + Oi+l , j K2 AlAx (1-a) _ A = 0 (V I. 19 ) KI(1 -a) 4K1 4K1 , 4K1 This may be rearranged to yield 9ij in terms of the four surrounding temperatures. when a = 1 The equation may be simplified to:

[ Oij = CAl LB i-1, j + Oi, j+l + ai, j-1 + ai+l, j CA2 + CA3(VI. 20 ) where the constants are given by: r CA1 = 15 - CB2 1 -1 CA2 = 2K2 / (K +K ) 2 A1Ax 2 CA3 = (A1+A2) Ax2 / (8 (K1+K2)) + 3.5 4 K 1 CB2 = 2K / (K1+K2) 1 376

Using the same logic, one may obtain the equation for calculating G..1.) near a corner.

i+1,j

Region 1 K1 Al Region 2 K2 A2

+ (VI.21) G. ' CAB1(ei-1,j + ei, j+1 + CAB2(ei+l,j + ei, j-1) CAB3 where

CAB1 = 0.5 / (3.0 - 2K1 /(K1+K2)) CAB2 = 2.0K2 /(K1 +K2) + 1 CABS = (A1+A2)ox / (8(K1+K2)) 3A1ax2 /(4K )

Equation (VI.21) may be manipulated by symmetry to yield each of the four equations required to calculate temperatures at junctions of three or four regions.

Schematic diagram of the four equations used in model II. 377

Appendix VII Description of Boreholes of Interest

This appendix has been added to allow more detailed descriptions of the geology and points of interest within selected boreholes used in this study. This information is in appendix form to allow a smoother flow of information within the body of the thesis.

1. Gaverigan Borehole 2. Predannack Down 3. Kennack Sands 4. Hemerdon Mine 5. Wilsey Down 6. Canningtcn Park 7. Curry Pool Farm 8. Meldon 9. Bovey Tracey 10. Belowda 378

1. Gaverigan Borehole

The Gaverigan borehole is situated close to the Cornish village of Fraddon, about 1km north of the most western part of the St. Austell granite outcrop (Grid ref. SW 1932 0592). This borehole was originally diamond drilled with complete core recovery to a depth of 328m. The borehole had been drilled by English Clays, Lovering & Pochin Co. Ltd. (E.C.L.P.) for china clay expicration. The borehole was reopened for our use by E.C.L.P. under a special Department of Energy contract. The borehole is, in addition to the heat flow point obtained, of particular interest for several other reasons: i) The borehole starts in country rock and at 293m enters unaltered granite. ii) Increasing grades of contact metamorphism are observed with increasing depth within the country rock. iii) The concentration of radiogenic elements for granite just below its contact have been obtained. iv) A sharp change of geothermal gradient is observed at the granite/country rock contact, which graphically illustrates the blanket effect of the poorly conducting country rock. A simplified geological log is illustrated figure VII.1 A mixture of weathered, tourmalinized, kaolinized killas slates were encountered down to a depth of 61m. From this depth to the granite contact at 293m, a series of slates interbedded with calc flinta bands was observed. These rocks exhibited a gradually increasing grade of contact metamorphism towards the granite. The grade of metamorphism is reflected in the degree of recrystallisation, the secondary metamorphic minerals present and the persistence (or lack thereof) of banding and cleavage. Close to the granite the rock is described as a 'hard dark teurmalinised hornfelsed killas with banding still recognisable'. The contact itself is sharp against a fine grained, passing into 379

medium grained. At 321m the granite is hard and fresh with much biotite.

GAVERIGAN Grid reference SW 1932 0592

Metres Figure VII.1 0 Mixture of weathered tourmalinised kaolinised killas slate. 61 Generally steeply-dipping, pyritic slaty killas, extensively sheared with many quartz veins. 155 Steeply-dipping extensively mobilised caic-flinta with actinolite and pyrite. 171 Contorted killas showing extensive mobilisation of caic-flinta and tourmalinisation. 206 Cleavage lost due to tourmalinisation. 265 Re-crystallisation of slate and marked shearing, quartz bands and caic-flinta. Hornfelsed killas actinolite and mica. 293 Hard dark tourmalinised hornfelsed killas. 294 Sharp contact; medium grained porphyritic vesi- cular granite with dark tourmalinised matrix, resorbed potassium feldspars and tourmaline lined vesicles. 303 Medium to fine grained porphyritic granite with feldspars up to 50mm. Large feldspars and matrix slightly kaolinised. 316 Hard porphyritic tourmalinised micaceous granite. 328

N.B. Killas is a local name used to describe a wide range of country rock types within south-west England. The killas within the Gaverigan borehole belongs to the Meadfoot Beds which are of Devonian age. 380

2. Predannack Down

The two Lizard boreholes were diamond drilled for the Petrology unit of the Institute of Geological Sciences. The holes wore completed early in 1978 and were taken over for terrestrial heat flow determinations on completion of drilling. The Predannack Down borehole situated on the Predannack airfield, Goonhilly Downs (grid ref. SW 6901 1634) was drilled to investigate the structure and petrology of the Lizard peridotite. This 326m deep borehole was of particular interest for the following reasons: i) The thermal conductivity of core recovered from the borehole yielded a low yet quite constant value over the length of the borehole. ii) The borehole was lined with a black iron pipe and grouted in place. The temperature log, directly after grouting, illustrated the effect of the exothermic cement reaction. iii) The lack of topographic disturbance, depth and low thermal conductivity made it ideal for demonstration of the effect of past climatic disturbances. iv) The borehole is situated away from the Cornubian batholith and so yields a background level of heat flow. Several contrasting theories have been put forward re- garding the structure and origin of the Lizard peridotite, the Predannack borehole yielded information to help solve the controversy. A simplified geological log is presented in figure VII.2. The borehole was drilled through the concrete base of a demolished Nissen hut and encountered soil, clays and gravel of Quaternary age down to a depth of 6.1m. From this depth to 297m, fairly uniform serpentan- ized peridotite was encountered. Amphibolite, very similar to the hornblende schists of Flett(1946), was found at a depth of 297m. Drilling proceeded through a further 28m of amphibolite to the final depth cf the borehole (325m). 381

The I.G.S. petrologists concluded that, although it is not absolutely certain that this was the base of the peridotite it makes the proposal of Flett (ibid) and Green(1964) that the peridotite is a steep sided Taper or stock-like body, unlikely. The contrasting proposal of Sanders (1954) that the peridotite is a relatively thin sheet now seems more plausible. This conclusion is of importance to mathematical modelling of the temperature field of the Carnmenellis area. 382

I.G.S. PREDANNACK DOWN Grid reference SW 6901 1634

Metres Figure VII.2 0 Quaternary. Soil, clays and gravel 6.1 Age uncertain Reddish brown fine grained partially serpentinised peridotite with white talc/carbonate veins. 15.24 Only a few small fragments of broken serpentinised peridotite recovered. 38.71 Fine grained, reddish brown partially serpentinised schistose peridotite, with talc/carbonate veins. 76.20 Very altered talc ore serpentite with several fine grained basic dykes up to 1.5m in thickness. 92.05 Predominantly medium to fine grained reddish brown partially serpentinised schistose peridotite with 'phenocrysts' up to lcm in length and talc carbonate veins. 172.21 Predominantly medium grained dark grey/green amphi- bole rich serpentinised peridotite with poorly developed schistosity and sporadic phenocrysts up to 3cm in length. 221.28 Medium to fine grained brownish red partially serpentinised schistose peridotite. Phenocrysts sporadic or absent. 297 Complex purplish grey fine grained alteration zone. 298 Medium grained schistose amphibolites with some more mafic layers; fine grained layers, carbonate cemented breccias and one carbonate band 50cros thick (310m)

Logged by Dr. M.T. Styles and Mr. J. Dangerfield. 383

3. Kennack Sands

The Kennack Sands' borehole is situated in the carpark at Kennack Sands on the coast to the east of the Predannack borehole. The borehole was drilled for the I.G.S. to investigate the structure and petrology of the Kennack gneisses, one of the most controversial units of the Lizard complex. For geothermal measurements the borehole was not well placed, being in a steep valley on the coast at the edge of the Lizard plateau. In addition, a fairly wide scatter of thermal conductivity values was obtained. Drilling stopped at a depth of 154m due to an irrepairable breakdown of the drilling rig. A simplified geological log after J. Dangerfield, J.R. Hawkes and M.T. Styles is presented in figure VII.3. There was considerable variation within the gneisses, from essentially basic through to acid, with many interbanded types. 384

I.G.S. KENNACK SANDS Grid reference SW 7325 1647 Metres Figure VII.3 0 Quaternary Yellowish brown sands and gravels with pebbles up to 7cm diameter. 6.10 Age uncertain Deeply weathered basic gneiss 6.20 Purplish-black bastite-serpentine. (No core recovered between 6.63 and 9.32m) 9.91 Basic gneiss 11.43 Bastite-serpentine. 11.84 Basic gneiss 13.03 Massive bastite serpentine with abundant "phenocrysts". 13.77 Medium grained basic gneiss. 14.71 Greenish-black bastite-serpentine with abundant "phenocrysts" up to 6mm diameter. 28.68 Predominantly basic gneiss with acid layers up to 5cm thick. 31.04 Dark greenish-black bastite-serpentine cut by talc and hematite veins. 32.16 Predominantly acid gneiss. 33.10 Reddened bastite-serpentine. 33.43 Acid gneiss. 33.73 Reddened bastite-serpentine. 37.95 Predominantly basic gneiss with acid veins up to 100cm thick. 39.90 Greenish-black bastite-serpentine. 42.67 Acid gneiss. 43.15 Greenish-black bastite-serpentine. 44.55 Acid gneiss in steep contact with serpentine. 45.47 Dark green bastite serpentine with abundant talc veins. 385

I.G.S. KENNACK SANDS continued Metres 45.77 Predominantly basic banded gneiss with acid veins up to a few cros thick. 60.12 Reddened bastite-serpentine. 60.58 Basic gneiss with sporadic thin acid layers. 68.43 Pale greenish-grey serpentine. 68.55 Basic gneiss. 69.16 Greenish-black bastite-serpentine. 70.33 Predominantly basic banded gneiss with acid layers commonly 1-2cms in thickness but rarely up to 50cms 109.60 Dark red bastite-serpentine. 111.44 Predominantly acid gneiss with some layers of banded basic gneiss. 119.61 Dark red bastite-serpentine with sheared gabbro along contacts. 122.07 Banded acid and basic gneisses with some 'epidiorite dykes'. 136.86 Red bastite-serpentine with 'epidiorite dyke' at 137.5m and gabbro vein at 138.3m. 142.32 Predominantly acid and acid and basic banded gneisses. 144.30 REd-green bastite-serpentine. 147.14 Banded acid and basic gneiss. 149.38 Predominantly basic banded gneiss. 152.48 Red bastite-serpentine. 153.06 Basic gneiss. 153.85 Logged by J. Dangerfield, J.R. Hawkes and M.T. Styles. Note The common name 'serpentine' has been used throughout for an ultrabasic rock that is a partially or sometimes completely serpentinised peridotite. Alteration is a partially or sometimes completely serpentinised peridotite. Altera- tion zones usually 2-3cms thick are present at all serpentine/gneiss contacts. 386

4. Hemerdon Mine

Hemerdon Mine is situated south-west of the Dartmoor granite some 3 miles north-east of Plymouth. The mine is sited on a small granite outcrop, thought to be part of a granite ridge, extending southwards from the main Dartmoor outcrop. Wolframite and cassiterite are found along a swarm of quartz veins which form a stockwork. The stockwork granite is extensively kaolinized and, in parts, greisenised. The complex mineralization, extensive kaolinization and multitude of quartz veins have so far prevented an accurate estimation of thermal conductivity. The mine area was being extensively drilled by Amax Exploration U.K. with a view to reopening the previously abandoned mine as a large scale opencast tungsten mine. Eight of the eleven bore holes logged were deeper than 90m. the deepest temperature measurement being from 131m. Due to the poor rock conditions, only lined boreholes survived any length of time. It is unfortunate, in the light of the amount of work put into this site, that the thermal conductivity should be uncertain. With the advance of mining in situ measurements and estimations by normative means may well solve the problem. The temperatures may then, in part, be treated as archive material awaiting further data. The structure of the outcrop is fairly well defined, due to the extensive drilling program, trenching and geophysical surveys undertaken on the site. Our departmental involvement included a detailed gravity survey and modelling which is reported by W.H. Edwards (1978). The gravity over the outcrop is complicated by the strong regional gradient, due to the close proximity of the Dartmoor granite and the associated deep effect of the buried Cornubian batholith, of which the Hemerdon outcrop forms a part. However, when the regional gradient is removed, a negative anomaly does emerge which matches the geological interpretation of the 387

boreholes and thus fills in the areas of scant geological control. The results from these boreholes are plotted as temperature gradients on the residual gravity map (Fic. VTI.4). Boreholes with the index code RDH, were drilled using the reverse flush method of drilling. The rig, a 'Hydreq miner', was converted to use concentric drill tubes. Air at high pressure was forced down the annulus then ejected from the rotary bit and finally forced back up the inner pipe carrying with it drill cuttings and water. The solids and liquid were separated from the air by a cyclone separa- tor, the solids were then separated from the water by means of settling tables. Thermal conductivities were measured on the assay returns from this sampling procedure. For hole RDH H3 the samples were much finer than usually measured on the divided bar and so, until a detailed investigation of the effect of grain size is carried out, these results should be treated with caution. The sampling method ensured almost complete recovery of all the drill cuttings and so may give representative conductivities of this quartz rich rock. 13 disc samples were measured for DDH H23. These discs could not be considered wholly representative of the complete borehole, since sections of core were often either pure quartz or heavily kaolinized, so fell apart.

388

I Hemerdon mine. y -0.7mgals r Locations of , Country Rock boreholes logged; D01-1-H19/ for temperat ure ° - g-,RDDH- H8 ' '

on map of the 1 1 residual gravity. RCH-H6 , I I shaft I I l I I , , 1 1 I f I / , % /' ., 1 r1 , I ,` A 4 , I /../, I , IDDH-H2~ / i✓/I I I ,...... ,...,;1/4 a)23° 1 1 1 /1 I 1 I C I I I I XI ~ i - . I iā • 1 1 1` ‘C a I 1, I ■ I / I ' I ff , RDH-NIB° OOH-H23 .- - ' •' , _1_ %_ Lt-6- -ites-t , 1 , , -- _. 7_ - e, ----/R6H-H4 `, Z 1 .. O 2 ;'`'', GRANITE ~~ 1 ;-0.5 maals -. 0.0 mgals 1, , Country ~~ mine dump -~RDH-H2 - -- ' - Rock N,--,- I , j -" • o ~~ I / I 'DDH-H4 I /fr;; a)18 O ~, ; - " 1 %.- - RDH H3_ "C, - 2 \ ; 4ā)27,/ - -- 1 DDHH3. -r ►I I '20/O 1 I b)35 0.5mgals ,~y ; /+ .'- ~ I +4 Numbers tabetted a 8 b ~ / \ represent temperature

4,- +/ `e gradients in K. km~ Fault - _ - - - - 100 metres / ,__7

-y - / Contour interval 0.2 mgal 389

5. Wilsey Down

Wilsey Down was a deep stratographical borehole drilled by the Institute of Geological Sciences between May and December 1968 (fig. VII.5). It is situated about 6km north of the Bodmin Moor granite outcrop. From the gravity data it is uncertain if Wilsey Down overlies granite. On the batholith model proposed by Tombs(1977) the borehole lies above granite at a depth of over 9km, this being a fairly steeply dipping northern flank of the batholith. The upper part of the borehole is in Carboniferous slates of the Crackington and Fire Beacon chert formations. At 461m it crosses a low angle fault into Upper Delabole slates of Devonian age. Finally, it crosses another low angle fault, at 708m, to re-enter Carboniferous slates and then greenstone down to its final depth at 762m. Heat flow determinations for the Wilsey Down borehole were reported by Tammemagi & Wheildon (1974). Interest was renewed in this borehole since it forms the northern end of an extension to the line of Bod- min Moor boreholes. Sample material was still available, so detailed heat production measurements were carried out as reported in chapter 4. 390

I.G.S. WILSEY DOWN Grid reference SX 1797 8890

Metres Figure VII.5 0 Recent and Pleistocene Head: yellow, stony clay 9.14 Carboniferous Crackington formation: grey slates, siltstones and greywackes, passing down into 76.20 Fire beacon chert formation: dark Grey pyritous slates with thin locally crinoidal limestones; Pyrrhotite common to 850ft (259.08m); several greenstone intrusions between 1080ft and 1459ft 9in (329.18 and 444.93m) 460.55 Low-angle fault Devonian Upper delabole slates: green slates with sporadic thin limestones 690.27 Devonian-Carboniferous Transition group: grey slates with limestones 703.78 Devonian Upper delabole slates: green slates with limy bands 707.06 Low-angle fault Carboniferous Black slates with limy bands at top and silty bands lower down; several greenstone intrusions 739.90 Greenstone 762.43 391

6. Cannington Park

The deep Cannington Park borehole is situated near Bridgewater in Somerset, well away from the Cornubian granite batholith. Cannington Park borehole was drilled to a depth of 1153m by the Institute of Geological Sciences to examine the stratigraphy and lithologies of the Carbonife- rous sequence, to find out what lay beneath the Carbonife- rous limestone and to investigate the large scale structural relationship between rock units. A simplified geological log is presented in figure VII.6. Due to hydrological considerations, only the top 777m were preserved for heat flow investigation. This was the deepest borehole logged during this project and is the deepest temperature logged hole in south-west England at this time. Detailed thermal conductivity measurements were made on 158 disc samples representing the section logged. It was hoped to use this borehole for extensive climatic studies so logging and conductivity were treated with careful attention to detail. Conductivities are well defined down to a depth of 430m. Below this depth, chert and dolomite bands give rise to high thermal conductivities, which cause uncertainty in the precise measurement of heat flow. There is an anomalous zone below 430m which may either be due to water flow or the uncertainty in real value of conductivity. A study was instigated to see if the p-wave velocity was related to the thermal conductivity (J.S. Ekiof 1979). The seismic p-wave velocity was measured for 167 samples. The apparatus consisted of a piezo-electric transmitter and receiver between which was a thermal conductivity disc. The travel time was measured on a simple counter and the velocity calculated. Before the study was started, good velocity agreement was found with samples of uniform composition yet different thickness. The velocity showed no clear relation to the thermal conductivity of the same 392

sample due to the wide scatter of values. It had been hoped to use the Schlumbeger velocity log to estimate the proportion of each rock type, i.e. limestone, chert and dolomite. However, with no clear pattern emerging, this did not prove possible. The Schlumbeger log gave higher velocities than the laboratory results. The velocity log showed no marked contrast below 430m, though the velocity was marginally higher. a 393

I.G.S. CANNINGTON PARK Grid reference ST 2479 4011

Metres Figure VII.6 0 Carboniferous Limestones pale grey oolitic 93 Limestones pale grey dolomitic horizons, substantial fissures. 250 Limestones, finegrained dark grey, abundant fissures. 351 Limestones dark grey fine grained.

Abundant chart horizons pink or red tinted. 556 Limestones (reef beds) medium to pale grey very fine grained, abundant horizons of dolomatised limestone, late Courceyan. 778 Limestone medium to dark. Medium to fine grained with zones rich in chert. Shale and mudstone dark grey with subordinate limestone bands. 1106 Devonian Sandstones; interbedded, argillaceous, occasional limestone. 1153

Geological log after A. Whittaker and R. Scrivener. 394

7. I.G.S. Curry Pool Farm Grid reference ST 2270 3871

The Curry Pool Farm borehole was drilled for the Insti- tute of Geological Sciences to ascertain the age and stratigraphy of the Halseycross Farm Palaeozoic inlier. The borehole formed a part of the investigation of the structural relationships between Devonian and Carboniferous rocks in Somerset.

Metres

0 ? Devonian Siltstones and sandstones, purple and greyish purple, bioturbated and with Chondrites mottles. Strata dip up to 60° and show small scale fractures and listric surfaces in the finer grained siltstones. Some larger-scale fractures are present; minor quartz veining in places. 81.6 Siltstones, dark grey, bioturbated and with some nests of shells. Thin bands of pale grey sandstone here and there and with a striped appearance in places. Fractured and with listric surfaces. 106.6 Sandstones, greyish purple, medium and coarse- grained, quartz veinlets, blocky fracture. Pebbly or conglomeratic in places and becoming a dolomitic, green coloured, pebbly sandstone towards the bottom. 131.4 Siltstones and dolomitic sandstones, dark and pale greenish grey, bioturbated in places and with small-scale fractures. Fossils in places. 154.6 Siltstones, dark grey, with some bands of paler grey and purple sandstone. Faulted near the top. Bioturbated and with a few shells. De- veloping a striped appearance in places and with small scale fractures and listric surfaces. 210.4

Figure VII.7 Geological log of I.G.S. Curry Pool Farm Borehole. 395

8. I.G.S. Meldon Borehole Grid reference SX 5672 9202

Metres

0 River gravels 2 Partly silicified contact altered Keratophyre and Tuff 25.9 Aplite dyke, contact 48° 43.3 Contact altered mudstone with thin Aplite band 46.3 Silty mudstone 54.1 Silicified mudstone 55.8 Contact altered mudstone 56.9 Dolerite with Aplite stringers

Figure VII 8 Sediments belong to the Meldon slate and quartzite formation. (Lower Carboniferous) 396

9. I.G.S. Bovey Tracey G3 Grid reference SX 82707 79292

This was one of four inclined (60°) boreholes drilled by the Institute of Geological Sciences between Bovey Tracey and Hennock to ascertain the cause of coincident geochemical lead anomalies and geophysical anomalies.

Metres

0 Open hole 12.3 Overburden, clayey sand and comminuted rock fragments 21.9 Upper Carboniferous. Crackington Formation Ashton Shale member. Altered dark grey shales. Scattered quartz veins. Some pyritic joint coatings and rare sulphide disseminations. 38.8 Lower Carboniferous. Teign Chert Formation. Dark grey, rarely brown, soft mudstones and tough grey cherts. Mudstone becomes more chertified in depth and cherts commonly become paler grey or cream coloured. Some thin, soft, green tuffaceous bands with associated pink manganiferous cherts. Abundant sulphides as disseminations, lensoid clusters and narrow veinlets. 101.5 Fault zone Fragmented and softened chert and tuff in comminuted shale debris, now largely reduced to clay. Frequent quartz veining and irregular lensoid and vein developments of pyrite. 123.4

Figure VII.9 Bovey Tracey G3 Geological Log by K.E. Beer • 397

10. I.G.S. Belowda No. 1 Grid reference Sw 9789 6242

Metres Figure VII.10

0 Quaternary Soil, subsoil, made ground and head 2.4 Devonian. Meadfoot beds Grey slates with hematised joints and red hematised slates with thermal spotting. Small veins of quartz, quartz-chlorite, quartz-hematite and quartz-tourmaline. 104.6

I.G.S. Belowda No. 2 Grid reference SW 9788 6254

Metres

0 Quaternary Soil, subsoil, made ground and head 2.4 Devonian. Meadfoot beds. Grey, well foliated slates and silty slates, with thermal spotting. Sporadic pale greenish grey sandstones. Red hematization along joints and veins. Veins of quartz, quartz- chlorite, quartz-hematite and quartz tourmaline. 137.9 Hematised fracture zone with much brecciated quartz and slate. 149.2 Grey foliated slates with some hornfelsic horizons. 170.8

Geological logs by B.R. Mountford. 398

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Grillis Farm CM-A CSD-04 SW 6795 3846 1 1 1 1 Polgear Beacon CM-B CSD-07 6927 3663 2 2 2 2 Medlyn Farm CM-C CSD-05 7083 3404 3 1 3 3 Trevease Farm CM-D CSD-O2 7185 3180 4 1 4 4 Trerghan Farm CM-E CSD-O6 7353 3033 5 2 5 5 Bray Down BD-A CSD-11 SX 1907 8177 6 3 6 6 Blackhill BD-B CSD-10 1835 7820 7 3 7 7 Pinnockshill ED-C CSD-12 1892 7450 8 4 8 8 Browngelly BD-D CSD-O9 1924 7247 9 3 9 9 Gt Hammet Farm BD-E CSD-O8 1885 6986 10 2 10 10

Newmill LE-A CSD-14 SW 4608 3435 11 4 11 11 Bunker's Hill LE-13 CSD-13 4022 2726 12 4 12 12

Tregarden Farm SA-A CSD-16 SX 0553 5945 13 5 13 13 Colcerrow Farm SA-B CSD-15 0679 5763 14 5 14 14

Winter Tor DM-A CSD-18 SX 6117 9156 15 6 15 15 Blackingstone DM-B CSD-17 7850 8593 16 5 16 ' 16 Soussons Wood EM-C CSD-19 6733 7971 17 6 17 17 Laughter Tor DM-D CSD-21 6562 7549 18 7 18 18 Foggin Tor DM-E CSD-20 5663 7334 19 7 19 19 BOREHOLE CROSS-REFERENCE INDEX A. CONTRACT BOREHOLES - LOCATION OF DATA WITHIN APPENDICES continued Appendix I II III IV Station Name Stn. Sample National Grid Summary Temperature Conductivity Heat Production Code Code Reference Plots Tabulation Tabulation Tabulation SITES ADJACENT GRANITE

Merrose Farm CDD-1 MER SW 6559 4351 20 8 20 20 Kestle Wartha CDD-2 KES 7533 2579 21 9 21 21 Callywith Farm CDD-3 CALLY SX 0886 6783 22 9 22 22 Gaverigan GAV GAV SW 9316 5916 23 10 23 23

Notes. Gaverigan Borehole also occurs as No. 1 in Appendix VII. Wilsey Down Borehole occurs as No. 5 in Appendix VII and as No. 24 in Appendix IV. Little Polgear, sample code CSD-3, occurs only in Appendix III, as No. 39. BOREHOLE CROSS-REFFRENCE INDEX B. OTHER BOREHOLES - LOCATION OF DATA WITHIN APPENDICES Appendix I II III VII Station Name Sample National Grid Summary Temperature Conductivity Descriptions of Code Reference Plots Tabulation Tabulation Boreholes GRANITE SITES

Troon TROCN SW 6570 3677 27 14 27 - Rosemanowas A ROS-A 7352 3456 25 12 25 - Rosemancwas D ROS-D 7352 3460 26 13 26 - Longdowns CSD-1 7368 3462 24 11 24 - Hemerdon DDH-H23 SX 5733 5849 28 15 28 4 Hemerdon RDH-H3 5733 5849 29 15 29 4 White Hill Yeo WHY 5805 6275 30 14 30 - SITES ADJACENT GRANITE

Newlyn East - 1 NEW-1 SW 8146 5390 33 18 33 - Newlyn East - 4 NEW-4 8141 5384 34 18 - - Belowda Beacon - 1 BEL-1 9789 6242 35 17 34 10 Belowda Beacon - 2 BEL-2 9788 6254 36 17 - 10 Lanivet - SX 0216 6413 37 16 - - Meldon MELD 5676 9220 32 17 32 8 Bovey Tracey BOV 8271 7929 31 16 31 9 COUNTRY ROCK SITES

Predannack PRED SW 6901 1634 38 19 35 2 Kennack Sands KEN 7325 1647 39 20 36 3 Currypool Farm CUR ST 2270 3871 41 20 38 7 Cannington Park CAN 2470 4010 40 21 37 6