A
THESIS
entitled
GEOCHEMICAL RECONNAISSANCE IN RELATION TO
COPPER DEFICIENCY IN LIVESTOCK IN THE
SOUTHERN PENNINES AND DEVON
Submitted for the
degree of
DOCTOR OF PHILOSOPHY
in the
FACULTY OF SCIENCE OF THE UNIVERSITY OF LONDON
by
WILLIAM KENNE2H FLETCHER
Royal School of Mines, Imperial College. April, 1968 ABSTRACT
The results of multi-element stream sediment reconnaissance in south-west England, North Wales and the South Pennines are described and the geochemical patterns related to the incidence of trace element problems in agriculture. Particularly striking correlations are found between anomalous patterns of Mo and the incidence of copper deficiency in cattle in the South Pennines, and between low Co levels and cobalt pine in sheep on Dartmoor.
Detailed studies in the South Pennines have shown that the extensive Mo anomalies delineated by the stream sediment survey correspond to areas in which Mo-rich lower Namurian and Visean shales give rise to molybdeniferous soils. Elsewhere, where the shales are concealed beneath barren drift and on other parent materials, the Mo content of both soils and sediments is normal The distribution of trace elements in soil profiles developed on the anomalous soils is described.
The Mo content of pasture herbage is significantly higher on the anomalous soils than on the control plots, though the contrast between herbage samples is considerably less than between the corresponding topsoils. The relatively low uptake of Mo from the molybdeniferous soils is attributed to its retention by the weathered residues of the parent material and to its fixation, after mobilization, by secondary ferric oxides.
The Mo-Cu-SO status of herbage growing on the Mo-rich soils 4" is within the range associated with molybdenum-induced hypocuprosis in cattle. Complementary studies by I. Thornton and J.S. Webb have shown that 77 per cent of the cattle (excluding those receiving mineral supplements) within the molybdenum stream sediment anomaly are affected by copper deficiency, compared to 37 per cent outside the anomaly,. Furthermore, copper therapy results in a marked improvement in live weight gain by affected animals. These results confirm that the agricultural problem area is considerably more extensive than was suspected prior to the stream sediment reconnaissance.
Similar relationships between the Mo content of rock, soils, sediments and herbage are described in Mo-anomalous catchments detected during stream sediment reconnaissance on the Culm Measures west of Dartmoor, Devon.
The results of the research clearly demonstrate the applicability of sediment surveys to detecting and delineating areas wherein abnormal trace element levels in rocks and soils may give rise to both clinical and sub-clinical problems in agriculture.
ii
CONTENTS
VOLUME I page
.. .. ABSTRACT 00 .9 PO 00 .. O . .. .. •• i
LIST OF TABLITS oil tor se oe to to Ape oke se viii
LI6T OF FIGURES ...... • • • • • • • • O• xiii
CHAPTER 1 INTRODUCTION ...... • 09 • 0 1
(i) REGIONAL GEOCHEMISTRY ...... 2 (ii) ECOLOGICAL APPLICATIONS OF REGIONAL GEOCHEMISTRY 4
(iii) PRESENTATION OF THESIS ...... 10 (iv) ACKNOWLEDGEMENTS ...... • • 11 PART A CHAPTER 2 SAMPLING) ANALYTICAL TECHNIQUES AND DATA HANDLING 13 (i) SEDIMENT SAMPLING AND SAMPLE PREPARATION .. .. 15 (ii) ANALYTICAL TECHNIQUES ...... 16
(a)Spectrographic method .. W. .. .. 17 (b)Colorimetric methods ...... •• 22
A rsenic 00 ...... O. .. 22
Zinc .. 00 60 so 0.. 06 0.1. es 23
(iii) DATA HANDLING 00 0 • .. .. 06 .. 23 CHAPTER REGIONAL GEOCHEMICAL RECONNAISSANCE DEVON AREA 25 (i) DESCRIPTION OF THE AREA .. . • ...... 25 A. LOCATION ...... • • • • • • 25
B. GEOLOGY AND MINERALISATION ...... 25 C. TOPOGRAPHY AND DRAINAGE ...... 28
D. CLIMATE 40 .. .. Of ...... 30 E. SOILS ...... 30
F. AGRICULTURE ...... • • 31
..- (ii) THE REGIONAL GEOCHEMICAL PATTERNS .. .. • • 31 A. PATTERNS RELATED TO THE GRANITE AND THE ASSOCIATED MINERALISATION ...... 32 B. PATTERNS RELATED TO BEDROCK GEOLOGY .. .. 35 C. PATTERNS RELATED TO SECONDARY ENVIRONMENT 38 (iii) CORRELATIONS BETWEEN THE GEOCHEMICAL PATTERNS AND THE INCIDENCE OF AGRICULTURAL DISORDERS .. .. 39 A. COBALT ...... • • • • • • • • • • 39 B. MANGANESE ...... 40
C. COPPER AND MOLYBDENUM ...... O. .. 40
D. ARSENIC AND LEAD ...... 0 .. 41
iii page CHAPTER 4 REGIONAL GEOCHEMICAL RECONNAISSANCE NORTH WALES 42 (i) DESCRIPTION OF THE AREA .. . . • • • • • • 42
A. LOCATION ...... • • 42
B. GEOLOGY AND MINERALISATION ...... 42 C. TOPOGRAPHY AND DRAINAGE ...... 46
D. CLIMATE 00 60 40 66 Oa 0. 40 47
E. SOILS ...... 00 ao 04 00 47
F. AGRICUL=RE 00 .. .. O. .. .. 49
(ii) THE REGIONAL GEOCHEMICAL PATTERNS ...... 50 A. GEOCHEMICAL PATTERNS RELATED TO BEDROCK GEOLOGY AND GLACIAL DEPOSITS ...... 50 B. PATTERNS RELATED TO THE SECONDARY ENVIRONMENT 53 C. GEOCHEMICAL PATTERNS RELATED TO MINERALISATION 56 (a)Cu, Pb and Zn anomalies near Llanwrst 56 (b)Cu-Pb and Pb-Zn anomalies on the Silurian 57 (c)Cu, Pb and Zn anomalies related to mineralisation in the Halkyn-Minera district 58 (iii) CORRELATIONS BETWEEN THE GEOCHEMICAL PATTERNS AND THE INCIDENCE OF AGRICULTURAL DISORDERS 59
A. COBALT.. .. SO ...... O. .. 59
B. MANGANESE .. 00 60 00 .0 .0 66 60
C. COPPER AND MOLYBDENUM ...... 06 60
C. OTHER METALS.. .. 06 O. CHAPTER 5 REGIONAL GEOCHEMICAL RECONNAISSANCE DERBYSHIRE AREA AREA 62 (i) DESCRIPTION OF THE AREA .. • • • • • • .. 62
A. LOCATION 6. .. 66 .. se 00 so 62
B. GEOLOGY 4* *8 .4 ...... 62
C. TOPOGRAPHY AND DRAINAGE ...... 65
D. CLIMATE .. • • ...... 66
E. SOILS .. , • • • • . • • • • .. 68
F. AGRICULTURE .. •• of ...... 68 (ii) THE REGIONAL GEOCHEMICAL PATTERNS ...... 69 A. GEOCHEMICAL PATTERNS RELATED TO BEDROCK GEOLOGY AND GLACIAL DEPOSITS ...... 69 B. GEOCHEMICAL PATTERNS RELATED TO MINERALISATION 72 (iii) CORRELATIONS BETWEEN THE GEOCHEMICAL PATTERNS AND THE INCIDENCE OF AGRICULTURAL DISORDERS .. • • 74
A. COBALT...... 04 *6 .. .. 74
B. MANGANESE ...... 00 .. 74
C. COPPER AND MOLYBDENUM ...... 75
D. OTHER METALS ...... 0 76
CHAPTER 6 CONCLUSIONS.. .. 00 60 SO OS 77 iv
page
PART B
CHAPTER 7 SAMPLING AND ANALYTICAL TECHNIQUES 81
(i) SAMPLING .. •• •• •• •• f• •• •• 81 •• •• •• •• •• 82 (a) Rocks .. • • • (b) Soils .. •• •• •• •• •• •• •• 82 (c) Herbage •• •• •• •• •• 83
(ii) SAMPLE PREPARATION •• •• •• •• •• •• 83 (a)Rocks .. •• •• •• •• •• •• •• 83
(b)Soils .. •• •• •• •• •• •• •• 83
(c)Herbage •• •• •• .• •• •• • • 84
(iii) ANALYSIS .. •• •• •• •• • • •• 85 (a) Molybdenum .. .• .0 •• •• 85 colorimetric determination of molybdenum 85 Ammonium acetate extractable molybdenum in
soils .. •• •• •• •• •• •• 86
(b) Copper O. .0 •0 •• •• •• 88 Copper in herbage •• •• •• •• 88 EDTA-extractable copper in soils •• •• 89 (c) Sulphate •• •• •• •• 90
Soil sulphate .• •• •• •• •• •• 90 Inorganic herbage sulphate •• •• •• 90 (d) Organic carbon •• •• •• •• 90 (e) PH •• •6 00 0. •• •• •• 90 (f) Mechanical analysis of soils .• •• •• 91 Rapid estimation of size analysis using the Bouyoucos hydrometer .. •• 93 Separation of size fractions for trace
element analysis .. .. • • •• 94
CHAPTER 8 DRSCRIPTION OF THE DETAILED STUDY AREA 95
(i) LOCATION .. Ow • .0 00 •• 95 (ii) GEOLOGY .. .. • .. •• •• 95 (a)Pre-Quaternary geology 40 4. •• •• 95 (b)Quaternary geology of 40 04 •• •• 100 (iii) TOPOGRAPHY e6 •• •• 101
(iv) CLIMATE .. 00 .. es Os 06 •• •• 102
(v) SOILS Se 00 •• •• 102
(a) Dominantly residual soils •• •• •• •• 103
(b) Non-residual soils •• •• •• •• 105
Soils derived from drift •• •• •• •• 105
Soils derived from loess •• •• •• •• 105
Alluvial soils • • •• •• •• •• 106
AGRICULTURE .. 04 O. •• •• •• •• 106
page
CHAPTER 9 TRACE ELEMENT CONTENT OF THE BEDROCK (i) TRACE ELEMENT CONTENT OF THE MAJOR ROCK UNITS AND LITHOLOGIES .. 00 06 00 40 De 108 (a)Argillaceous rocks .. 00 00 .. .. 110
(b)Arenaceous rocks O. 00 00 .. .. 114 (c)Limestones .. .0 .. em 00 • • • • 114 (ii) DISTRIBUTION OF TRACE ELEMENTS IN THE LOWER
NAMURIAN AND VISEAN SHALES es 00 00 0. 114 (a)Lateral and vertical distribution of trace elements in the lower Namurian and Visean
shales 00 .. .. 00 0. O. .. 115
M olybdenum .. 00 .. .. •• •• •• 115 Other trace elements ...... 120 (b)Trace element content of the lower Namurian shale facies .. . • • • .. .. •• 122 (iii) DISCUSSION • • 129
CHAPTER 10 REGIONAL DISTRIBUTION OF METAL IN THE OVERBURDEN AND THE RELATIONSHIP BETWEEN THE METAL CONTENT OF THE BEDROCK, STREAM SEDIMENTS AND OVERBURDEN 135
(i) MOLYBDENUM .. .. 00 .. 00 ...... 135 (a)Residual soils .. .. • • .. 00 .. 135
(b) Transported soils .. We 00 00 0. 138 Loess ...... 138
Older Drift ...... 00 .. .. 139 Newer Drift ...... 140 (c)Relationship between the distribution of Mo in the bedrock, stream sediments and overburden 140
(ii) OTHER ELEMENTS .. 00 w0 00 .. 00 00 143 (a)Geochemical patterns in the overburden related to primary syn3enetic dispersion .. .. 144 (b)Geochemical patterns in the overburden related
to mineralisation ea 00 00 .. .. 145 Mineralisation in the lower Namurian shales and Visean shales with limestones .. .. 145 Mineralisation on the margins of the limestone
massif ...... O. .. • • 148 Pb and Zn anomalies on the Bunter Sandstones 148 (c)Relationship between the distribution of trace elements (other than molybdenum) in the bed-
rock, stream sediments and overburden .4 148
CHAPTER 11 METAL DISTRIBUTION IN THE OVERBURDEN 153
(i) METAL DISTRIBUTION IN SOIL PROFILES .. .. 153
vi
page
(a)Residual profiles .. .. of 40 00 154
Farmland OS 410 0. 0. 00 .. .. 154 Moorland ...... • • 163 (b)Transported overburden ...... 168 Soils derived from the Mo-rich Older Drift 168
Alluvial soils ...... 172 (ii) SIZE FRACTION ANALYSIS ...... 177 (a)Distribution of trace element in size fractions ...... 177 (b)Comparison of the metal content of the minus 80-mesh and minus 10-mesh fractions .. .. 182 (iii) DISCUSSION ...... 183 (a)Metal distribution in the overburden .. 183 (b)Factors influencing the mobility and retention of Mo in soils derived from the lower Namurian
shales ...... 00 ...... 186
CHAPTER 12 METAL CONTENT OF THE HERBAGE 191
(i) MOLYBDENUM ...... 00 O. oo 192 (a)Molybdenum uptake by the principal constituents of the herbage ...... 194 (b)Molybdenum content of the herbage in May and
July ...... • • . • DO • • 00 197 (c)Factors affecting molybdenum uptake by pasture
herbage ...... 00 ...... 198 Molybdenum content of the topsoil .. • • 198
toil reaction ...... • • • • 200
Drainage conditions ...... 201 Organic matter ...... O. .. .0 205 Sulphate and phosphate .. .. • . .. 206 (ii) COPPER ...... 207 (a)Copper content of the herbage ...... 208 (b)Factors influencing copper uptake by pasture herbage ...... • • 210 (c)Relationship between EDTA-extractable Cu and herbage uptake ...... • • .. .. 212 (iii) SELENIUM ...... • • ...... 215 (iv) DISCUSSION: ENVIRONMENTAL FACTORS INFLUENCING
METAL UPTAKE BY HERBAGE .. 04 .. • • .. 217
CHAPTER 13 THE MOLYBDENUM-COPPER STATUS OF THE HERBAGE AND THE INCIDENCE OF COPPER DEFICIENCY IN CATTLE 224 (i) THE MOLYBDENUM-COPPER STATUS OF THE HERBAGE IN RELATION TO MOLYBDENUM-INDUCED COPPER DEFICIENCY
IN CATTLE .. .0 00 4. 00 0. 40 00 224
vii
2
(ii) THE INCIDENCE OF COPPER DEFICIENCY IN THE SOUTH PENNINES ...... 229
CHAPTER 14 COMPLEMENTARY GEOCHEMICAL INVESTIGATIONS OVER THE CULM MEASURES WEST OF DARTMOOR, DEVON 235
(i) DESCRIPTION OF THE AREA .. .. 00 .. 235 ..
(ii) THE GEOCHEMICAL PATTERNS ...... 238 (a)Metal content of the stream sediments .. 238 (b)Metal content of the bedrock ...... 242 (c)The distribution of trace elements in the overburden and the relationship between the metal content of rocks, soils and stream
sediments ...... OS .. 01 245 (d)Relationship between the metal content of
the topsoil and herbage ...... 253
CHAPTER 15 THE APPLICABILITY OF GEOCHEMICAL SEDIMENT SURVEYS TO TRACE ELEMENT PROBLEMS IN AGRICULTURE 257
(a)Molybdenum .. .. 00 .. .. O. O0 259
(b)Copper ...... Of e• .. .. 261
(c)Selenium .. .. 6...... 261
(d)Cobalt and Manganese ...... 262 (e)Arsenic, Lead and Zinc .. • • • • • • 264 CHAPTER 16SUMMARY, CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER RESEARCH 266
(i) SUMMARY AND CONCLUSIONS .. me .4 .. .. 266 (a)South Pennine area .. 0* OD SO .. 266
(b)Devon .. .. SO OS Ow 00 .. .. 274 (c)The application of geochemical stream sediment surveys to trace element problems in agriculture .. • • ...... 275
(ii) RECOMMENDATIONS FOR FURTHER RESEARCH .. .. 276
REFERENCES .. 40 • • 04 PO • 278
VOLUME II
Maps depicting the results of the three regional geochemical surveys. viii
LIST OF TABLES
No. Title page
1 Essential trace elements for higher plants, mammals and man .. • • • • • • • • • • • • • • • • 5
2 Regional stream sediment reconnaissance sampling logistics .. e• se e• •• • • • • .. .. 14 3 Spectrographic equipment and conditions . . .. • • 18
4 Wavelengths and useful ranges of concentration .. .. 19 5 Precision of the multi-element spectrographic method at different metal concentrations, based on approxi- mately twenty replicate analyses • • • • 20
6 Precision of the multi-element spectrographic analysis determined by Craven's method ...... 21
7 Stratigraphy of the Devon area ...... • • .. 26
8 pH of streams flowing over major geological units .. 29
9 Range and mean metal content of the minus 80-mesh fraction of drainage sediments from the principal bedrock units, Devon area ...... •• 33
10 Stratigraphy of the North Wales area .. .. • • •• 43
11 pH of streams flowing over major geological units .. 48
12 Range and mean metal content of the minus 80-mesh fraction of drainage sediments from the principal geological units in the North Wales area .. .. • • 51
13 Range and mean metal content of rocks, soils and stream sediment from Denbigh Uplands and Moors .. .. 55
14 Range and mean pH of soil and stream water .. .. 55
15 Stratigraphy of the Derbyshire area .. • • • • • • 63
16 pH of streams flowing over major geological units .. 67
ix
No, Title page
17 Range and mean metal content of the minus 80-mesh fraction of drainage sediments from the principal bedrock units in areas of residual and drift over-
burden, Derbyshire area .. 0. 0. DO •• 70
18 Total and ammonium acetate extractable molybdenum in topsoils compared with the content of the
corresponding herbage ...... 87
19 Instrument settings for the determination of copper using the Perkin Elmer 303 spectrophotometer .. .. 88
20 Comparison of estimates of the sand fraction as determined by the Bouyoucos hydrometer and by
wet-sieving ...... 92
21 Comparison of the size fraction classifications recommended by the International Society for Soil Science and the American Department of Agriculture 93
22 Generalized stratigraphy of the detailed study area, north-east Staffordshire and south-west Derbyshire .. 96
23 Range and mean metal content of the major Carboniferous rock units in the south-west Pennines 109
24 Mean metal content of major Carboniferous rock units from the south-west Pennines compared with mean values in the corresponding units from Co. Limerick, Ireland (after Atkinson, 1967), and with average values for
sedimentary rocks O...... O. 111
25 Lateral and vertical variation of metal content in the lower Namurian and Visean shales of the south-west
Pennines .. 00 00 DO 444. 00 00 116
26 Metal content of composite samples from the lower Namurian and Visean of the Alport Dale borehole,
northern Derbyshire ...... 118
27 Comparison of the principal sedimentary and palaeon- tological features, and their environmental
interpretation, in Sections 1 and 2 .. •• 123
28 Range and mean metal content of shales from contrasting facies in the lower Namurian of north-east Staffordshire 125 No. Title page
29 Range and mean metal content of overburden developed on the principal parent materials, south-west
Pennines .. se • • oo 41. • • o. 136
30 Mean metal content of bedrock, soils and stream sediments
from the south-west Pennines .. •• • • 0. 142
31 Range and mean Cu, Pb and Zn content of residual soils on the lower Namurian and Visean shales, from mineralized
and background areas, north-east Staffordshire .. 40 147
32 Range and mean metal content of soils and stream sediments from moorland and areas of poorly-drained
agricultural soils .. .. 0. 00 •• 151
33 Profile descriptions of residual soils developed on the lower Namurian and Visean shales in north-east
Staffordshire and southern Derbyshire .. .. 155-157
34 Metal content of residual soils developed on the lower Namurian and Visean shales in north-east Staffordshire and southern Derbyshire • • • • .. • • • • 158-159 35 Profile description of a representative peaty gley soil developed on the lower Namurian shales in north-
east Staffordshire O. • • tee 00 4. 164
36 Metal content of a representative profile of a moorland peaty gley derived from the lower Namurian shales in
north-east Staffordshire O. .. .. Oe • • O. 165
37 Range and mean metal content of poorly-drained agricultural and moorland soils developed on the lower
Namurian shales, north-east Staffordshire ...... 167
38 Profile description of a representative local-drift soil overlying Carboniferous Limestone in Derbyshire 170 39 Metal content of a typical local-drift soil on limestone in Derbyshire .. • • .. 00 .4 171
40 Profile descriptions of representative aggraded alluvial terrace deposits on the River Manifold, north-east Staffordshire 00 00 173
41 Metal content of soils developed on aggraded and flood- plain alluvium of streams draining the lower Namurian
and Visean shales in north-east Staffordshire .. O. 174 xi
No. Title page
42 Profile description of a very poorly-drained soil on floodplain alluvium in north-east Staffordshire 176
43 Metal content of size fractions of residual and alluvial soils derived from the lower Namurian shales 178-179
44 Range and mean Mo content of topsoils, pasture grasses and clover from anomalous and background stream sediment
areas .. O. 00 Of 00 00 192
45 Range and mean No content of topsoils, pasture grasses and clovers on soils derived from different parent
materials in the South Pennines ...... 193
46 Range and mean Mo content of topsoils and vegetation from moorland and seepage areas with exceptionally poor drainage .. .. • • .. O...... 196 47 Molybdenum content of pasture herbage on poorly-
and well-drained anomalous soils .. 00 O. 00 202
48 Range and mean Cu content of pasture herbage from
anomalous and background areas .. O...... 207
49 Range and mean Cu content of topsoils and vegetation from moorland and seepage areas with exceptionally poor
drainage .. .. .0 Oa ...... 0. 209
50 Copper content of pasture herbage on poorly- and well-
drained anomalous soils ...... • • 211
51 Selenium and molybdenum content of vegetation from very
poorly-drained seepage areas ...... 216
52 Comparison of molybdenum uptake by herbage and the composition of the topsoils from the anomalous areas
in Co. Limerick and the South Pennines 00 .0 .. 221 53 The molybdenum-copper status of herbage in the South Pennines .. • • • • • • • • • • • • • • • • 226
54 The molybdenum-copper status of pasture herbage in areas
of copper deficiency in cattle ...... 227
55 Blood copper values for cattle grouped according to age, use of mineral supplements and the molybdenum content of
the stream sediments .. 60 .. 231 xii
No. Title page
56 Incidence of copper deficiency in stock grouped according to age, use of mineral supplements and the molybdenum content of the stream sediments .. • • 232
57 Stratigraphy of the Culm Measures at Meldon, Devon .. 237
58 Minor element content of stream sediments on the Culm
Measures west of Dartmoor .. 00 00 • • 240
59 Metal content of the Culm Measures west of Dartmoor, Devon .. • • • • 243
60 Minor element content of the overburden developed on the principal parent materials around Eastcott,
D evon .. OS 00 •• 246
61 Profile description of a representative imperfectly- drained soil developed on the Lower Culm shales near
Eastcott, Devon .. .. • • OS 40 00 • • •• 248
62 Metal content of a representative profile of an imperfectly-drained soil developed on the Lower Culm
shales near Eastcott, Devon 00 • • 0. 04 •• 249
63 Metal content of imperfectly-drained soils on the lower part of the valley slope compared to nearby very poorly-drained soils on the valley floor at
Eastcott 00 .4 .0 0. • • O. .. 252
64 Molybdenum and copper content of herbage growing on anomalous and control plots in April and July 254 LIST OF FIGURES Following No. Title page no.
1 Location of the Regional Stream Sediment Reconnaissance Survey Area .. 10
2 Location and Topography of the Devon-Cornwall
Survey Area ...... •• 25
3 Geology of the Devon-Cornwall Survey Area . . .. . • 26
4 Mining in the Devon-Cornwall Survey Area . . 00 00 27 5 The Incidence of Trace Element Induced Agricultural Disorders in the Devon-Cornwall Survey Area .. •• 39 6 Location and Topography of the North Wales Survey Area ...... • • • • .. 42
7 Geology of the North Wales Survey Area .. .0 .. 43
8 Mineralisation in the North Wales Survey Area .. •• 44 9 The Extent of the Pleistocene Ice-Sheet in North Wales ...... • • .. e0 • • 04 .. • • 45
10 Major Soil Groups of the Western Half of the North
Wales Survey Area O. a. .. 00 • • O. •• 1+9
11 The Relationship between Co and Mn, and As and Fe in drainage sediments from the Denbigh Moors .. • • 55
12 The Incidence of Trace Element Induced Agricultural Disorders in the North Wales Survey Area .. 59 13 Location and Topography of the Derbyshire-Staffordshire Survey Area ...... 62
14 Geology of the Derbyshire-Staffordshire Survey Area .. 63
15 Mineralisation and Smelting in the Derbyshire-
Staffordshire Survey Area .. 00 00 ...... 64
16 The Incidence of Trace Element Induced Agricultural Disorders in the Derbyshire-Staffordshire Area .. 74
17 Soil Texture Diagram .. .. 00 .. .. 93
xiv
Following No. Title page no.
18 Location of the Detailed Study Area in Relation to the Molybdenum Stream Sediment Anomalies in the
South Pennines ...... • • • • • • •• 95
19 Localities Mentioned in the Text and the Topography
of the Detailed Study Area .. •• •• •• •• •• 95
20 Geology of the Detailed Study Area • • •• • • •• 96
21 Superficial Deposits of the Detailed Study Area 97
22 Namurian Palaeogeography •• •• • • •• •• •• 99 23 Distribution of Molybdenum and Vanadium in the Namurian of the Tansley Borehole, Derbyshire 111
24 Location of the Principal Rock Sampling Sections and the Mean Molybdenum Content of the Lower Namurian
Shales 46 • • • • • • • • • • 0. • • •• 116
25 Distribution of Trace Elements in the Lower Namurian
Shales at Edale, North Derbyshire 06 00 •ogo •• 118
26 Distribution of Trace Elements in the Namurian of
the Upper Dove Valley, South-West Derbyshire .. •• 118
27 Variation of Molybdenum with Selenium and Arsenic in
the lower Namurian shales ...... 00 00 • • 120
28 Variation of Molybdenum with Vanadium and Copper in
the lower Namurian shales ...... fa 00 .0 120
29 Distribution of Molybdenum, Selenium and Chromium in Contrasting Shale Facies within the Lower Namurian 123
30 Distribution of Trace Element in Relation to Eh-pH Conditions in the Baltic .. • • • • • • • • 128 31 Relationship between the metal content of the overburden and geology on Traverse 1 (with key to Figs. 31, 32, 33
and 34) 00 04 4. 00 00 .. .4 .0 136
32 Relationship between the metal content of the overburden
and geology on Traverse 2 .. •• • • •• • • 136
33 Relationship between the metal content of the overburden
and geology on Traverse 3 .. •• •• •• 136 Following No. Title page no.
34 Relationship between the metal content of the over- burden and geology on Traverse 4 00 Of .. .. 136
35 Relationship Between Molybdenum content of Topsoils
and Pasture Herbage ...... 199
36 Relationship Between Molybdenum Content of Topsoils and Pasture Herbage Under Various Soil pH Conditions 201 37 Molybdenum Content of Pasture Herbage in Relation to the Iron Content of the Topsoil ...... • • 203
38 Relationship Between Copper Content of Topsoils and Pasture Herbage ...... 212 39 Relationship between Copper Content of Topsoils and Pasture Herbage Under Various Soil pH Conditions Of 212 ko Relationship between EDTA-extractable and total
copper in soils .. .. 00 oe ...... 213
41 Relationship Between the EDTA-extractable Copper Content of Topsoils and Copper Uptake by Pasture
Herbage .. 00 04 *0 00 00 60 00 SO 214
42 Incidence of Bovine Hypocuprosis as Reported Before
the Regional Geochemical Survey ...... 229
43 Geology and Location of the Detailed Study Area on
the Culm Measures west of Dartmoor, Devon ...... 235
44 Localities Mentioned in the Text and Topography of the
Eastcott Area, Devon .. SO ...... 238
45 Geology and Molybdenum Content of Stream Sediments in
the Eastcott Area, Devon ...... 238 46 Distribution of Molybdenum in the Overburden of the
Eastcott Area, Devon .. 00 oe ...... • • 246 xvi
VOLUME II
Maps depicting the results of the three regional geochemical surveys.
PART 1 PART 2 PART 3
Devon-Cornwall North Wales Derby-Staffs
R14 Arsenic R1 Arsenic R27 Arsenic
R15 Chromium R2 Chromium R28 Chromium
R16 Cobalt R3 Cobalt R29 Cobalt
R17 Copper R4 Copper R30 Copper
R18 Ferric Oxide R5 Ferric Oxide R31 Ferric Oxide
R19 Lead R6 Lead R32 Lead
R20 Manganese R7 Manganese R33 Manganese
R21 Molybdenum R8 Molybdenum R34 Molybdenum
P22 Nickel R9 Nickel R35 Nickel
R23 Tin R10 Tin R36 Tin
R24 Titanium R11 Titanium R37 Titanium
R25 Vanadium R12 Vanadium R38 Vanadium
R26 Zinc R13 Zinc R39 Zinc 1
CHAPTER 1. INTRODUCTION
To the layman a good soil supports plants which grow easily and vigorously. Traditionally the soils of some regions are associated with low productivity and unthrifty livestock. In both there is an implicit belief that the quality of the soil influences health of plants and animals.
Agricultural and biochemical sciences are rationali- zing this belief, and, in general, we are increasingly aware of the complex relationships between the health of plants and animals and the chemistry of their environment. FUrthermore, the function of even the minor elements in living organisms is becoming apparent. At the same time, particularly as a result of geochemical prospecting programmes, a rapidly increasing amount of data is accumulating on the trace element composition of rocks, soils, waters, vegetation and stream sediments. Webb
(1964) proposed that geochemical surveys - being used extensively in mineral exploration - could, with little extra effort, be of agricultural and even medical value.
In this thesis the results of multi-element stream sediment reconnaissance surveys in three areas of the U.K. are summarised. Many hitherto unsuspected geochemical patterns - of interest to the geologist, prospector, agricultural advisor and possibly even the epidemiologist - were detected. During 2
follow-up studies the writer investigated the distribution of
Mo in the rocks, soils and herbage of extensive areas of Mo- rich sediments. The relationship between the sediment patterns
and the incidence of molybdenum-induced copper deficiency is
discussed.
(i) REGIONAL GEOCHEMISTRY
The influence of soil parent material on soil compo- sition is fundamental to soil science. Vernadskii, Fersman and Goldschmidt demonstrated, in the 1930s, that this applies not only to the gross physical and chemical constituents, but also to minor element composition. Early research indicated that anomalous concentrations of trace elements in rocks were reflected by anomalous concentrations in soils and plants.
Furthermore, systematic sampling of the latter media could detect concealed mineral deposits.
After the Second World War applied geochemistry found increasing application to mineral exploration in both the USSR and western countries. Techniques of rock, soil, plant and stream sediment sampling and analysis were developed (Hawkes and Webb, 1962).
Today stream sediment analysis is established for a wide range of conditions as an efficient and rapid method of detecting broad metal patterns related to mineral deposits. 3
The technique is founded on the premise that the sediment approximates to a composite sample of the rocks and soils in the catchment area upstream of the sample point. Soluble weathering products may be incorporated with the sediment by precipitation and coprecipitation, or by adsorption and absorption on the clastic particles and organic matter.
Stream-water samples, although homogeneous, are seldom collected since their composition is very subject to seasonal- climatic and other fluctuations. The bulky sample necessary because of the very low trace element concentrations in most natural waters is a further disadvantage.
The principal difficulty is the influence of the local environment on the rock-soil-water-sediment relation- ships. In the early stages of the secondary geochemical cycle the rock weathering and soil-forming processes mobilize and redistribute the elementsi many of which, in their more readily soluble forms, may be utilized by the vegetation and returned to the soil as plant litter, and thence to the stream sediment. The link between the composition of the unweathered rock and the weathering products represented by the stream sediment is therefore very complex. Topography, soil type, hydrology and other environmental factors must all be considered when interpreting the geochemical data.
Despite the complexity of the rock-soil-sediment relationships, sediment mineral reconnaissance in eastern 4
Canada (Hawkes et al, 1956) revealed broadscale, background
variations in the distribution of heavy metals which were
correlated with the major geological units. From this arose
the concept of multi-element sediment surveys reflecting the
trace element composition of the bedrock. Subsequent investi-
gations, first in Zambia (Webb et al, 1964) and then in Sierra
Leone (Nichol et al, 1966A) and elsewhere, confirmed that,
except in extreme circumstances, the composition of the bed- rock was the dominant factor in determin:ng the form of the
geochemical patterns.
(ii) ECOLOGICAL APPLICATIONS OF REGIONAL GEOCHEMISTRY
Advances in agricultural and biochemical sciences
since the 1920s have established that certain elements, in very low concentrations, are essential to healthy plant and animal life. These are the micro-nutrient or so called essential trace elements. Table 1, modified from Schutte (1964), lists the elements known to be essential to higher plant and mammalian life. Other elements, such as selenium and vanadium, may also
be essential. The metallic elements are generally available to the plant from the soil. Disorders resulting from trace element imbalance are described by Schutte (1964) and
Underwood (1962). Certain non-essential elements, notably arsenic and lead, have toxic effects when tolerance levels are exceeded. The close relationship between the mineral balance 5 of the soil, and animal and human health has been emphasised by Voisin (1959).
The sequence of events which will finally control the trace element nutrition of the animal is amazingly complex, and still almost unknown. The interactions between the animal and its geochemical environment are one aspect of the whole ecology.
Table 1
Essential trace elements for higher plants, mammals and man. Modified from Schutte, 1964, p.6,
HIGHER PLANTS MAMMALS AND MAN
iron iron boron chlorine chlorine copper copper cobalt manganese iodine molybdenum manganese zinc molybdenum zinc
Composition of the parent material, the nature of the weathering processes and the chemistry of the resulting soil influence the mobility, distribution and form of the elements according to their chemical properties. Hence their 6 physical and chemical availability to the plant is determined.
Trace element levels in plants differ greatly between species, and fluctuate seasonally-and with the-plants physiological responses to environment. Concentrations in the leaves, stems, roots and other organs vary considerably. The addition of fertilizers or lime and the use of pesticides may drastically change soil chemistry and plant responses.
The trace element intake of domestic livestock is closely related to the composition- of their pasture during the eight months of the grazing seasoiil. Increments of trace elements from the drinking supply are usually slight. Grazing habits and the form of the metallic complexes within the plant are therefore most significant. Additives, supplementary food- stuffs and non-local winter feed all modify the animal's metabolic response to the local geochemical environment.
The links between human health and geology are even more tenuous, especially in the technologically advanced societies. A great variety of foods are consumed from world- wide sources, often after some form of chemical preservation.
Many chemical flavouring and colouring additives 'improve' our meals.
Despite these problems there is an increasing awareness of the role of geology and geochemistry in plant, animal and even human health, and - as part of this role - of the significance of the trace elements. Pioneer 7 studies by Vinogradov and other Soviet scientists led to the concept of 'biogeochemical provinces', defined by Vinogradov
(1963) as •.
regions on the earth's surface that differ from adjacent regions in their contents of certain elements or compounds and thus impress specific biological characteristics on the local flora and fauna. In extreme cases, as a result of deficiency or excess of an element (or elements) certain endemic diseases may exist within a biogeochemical province which affect plants, animals and man.'
Case histories of Soviet research are given by Khobot'ev (1960),
Malyuga (1964) and Vinogradov (1943, 1963).
Major contributions have also been made by western scientists. In domestic livestock toxicity and deficiency diseases have been correlated with the trace element composi- tion of rocks, soils and herbage, especially with regard to Co,
Cu, Mo and Se. Advances particularly relevant to Part B of the thesis have resulted from (i) the collective works of
Clarke (1955), Gimingham (1914), Muir (1936), Ferguson et al
(1943) and recently Le Riche (1959a) on the molybdenum-induced copper deficiency of the 'teart' pastures of Somerset; (ii) investigations of molybdenum toxicity and factors influencing molybdenum uptake by pasture species in the United States, by, for example, Barshad (1951) and Kubota et al (1961); and from (iii) research by Australian and New Zealand scientists on molybdenum deficient pastures and the 8 uptake of molybdenum by legumes (Davies, 1952; Anderson,
1956). A general survey of the many aspects of molybdenum in plant and animal nutrition has been edited by Bear (1956).
Schutte (1959), Warren (1965) and Webb (1964) have all urged the need for co-ordinated geochemical-biochemical investigations and trace element surveys. Webb further proposed that sediment surveys - being used extensively in mineral exploration - could, with little extra effort, yield data of immediate application in many agricultural, epidemio- logical and related investigations. The results of preliminary studies in the U.K. and Ireland (using samples originally collected for prospecting purposes) were encouraging (Webb,
1964).
Thus, on Culm Measure shales in Devon,a reconnai- ssance survey indicated a zone of hitherto unsuspected Mo-rich soils and rocks. Incidences of copper deficiency in livestock are probably related to the high Mo concentrations.
In Ireland, low Co levels in stream sediments in
Co. Wicklow and Co. Carlow reflected not only the outcrop of a granite but coincided with an area of severe incidence of cobalt pine in sheep. Furthermore, anomalous concentrations of Se and Mo were detected in streams in Co. Limerick draining farmland known to be seleniferous, and on which molybdenum- induced copper deficiency was suspected. 9
Subsequent detailed investigations of the geochemistry of Mo and Se in Co. Limerick have been reported (Atkinson, 1967;
Webb and Atkinson, 1965). The enhanced levels of Mo and Se in the sediments defined the outcrop of the metal-rich source shales, and the distribution of molybdeniferous and seleni- ferous soils derived from glacial drift which had been smeared over the shales. Herbage analyses revealed that whereas the total Mo content of soil and herbage were broadly related,
Se-rich herbage developed only on seleniferous soils on the more alkaline, poorly drained, organic-rich sites. This was in agreement with the restricted distribution of selenosia. Since molybdenum-induced copper deficiency was su3pected in the area and the anomalous geochemical patterns extended over 30 square miles or more, the copper status of eight herds was investigated
(Thornton et al, 1966). A highly significant difference was found between the blood copper levels of herds in the zone of maximum Mo concentrations, and the control herds outside the
Mo anomaly. The authors concluded -
'Under conditions where visual symptoms of a deficiency or toxicity are not always apparent and where the problem may be largely at a sub- clinical level, reconnaissance geochemical techniques are seen to present a useful addi- tional aid to the agricultural specialist and advisor.'
In view of these encouraging results, biogeochemical studies were continued as part of an expanded programme of multi- 10 element regional geochemical reconnaissance in the U.K. carried out by the Applied Geochemistry Research Group (hereaf4r abbreviated to 'A.G.R.G.'). The programme was directed by
Professor J.S. Webb and Dr I. Nichol, and the work was supported by a Natural Environment Research Council contract awarded through the Institute of Geological Sciences.
Three field areas (shown in Fig. 1, and hereafter referred to as the 'Devon', 'North Wales' and 'Derbyshire' areas) were selected as including a variety of geological conditions and mineralized zones. Furthermore, trace element induced agricultural disorders had been reported in all three areas. Reconnaissance sampling was undertaken by R.F. Horsnail and the writer in the period April-June, 1965. The writer's subsequent detailed investigations in the molybdeniferous areas of Devon and Derbyshire complemented agricultural studies by I. Thornton, both contributing to the A.G.R.G. programme in
Applied Biogeochemistry supported by a Natural Environment
Research Council Special Research Grant.
(iii) PRESENTATION OF THESIS
Part A introduces the regional geochemical sampling and analytical techniques, and presents the results of multi- element reconnaissance surveys in the three areas. The section is not intended as a definitive description of the geochemical Fig. 1. Location of the Regional Stream Sediment Reconnaissance Survey Areas 11 pattern - even if this were possible - since many aspects are being investigated by the writer's colleagues. Only the principal patterns are examined. Regional geochemical maps, on the scale of 4 miles to the inch, to accompany this section will be found in the folder.
In Part B the distribution of Mo in the rocks, soils and herbage of the molybdeniferous areas in north-east Staffordshire and Derbyshire, and on the Culm Measures west of Dartmoor, is described. The results are related to the incidence of molybdenum- induced copper deficiency. Finally, the application of regional geochemical techniques to agricultural problems is discussed with suggestions for further work.
(iv) ACKNOULEDGEMENTS
The writer wishes to express his gratitude to all members of the A.G.R.G., and in particular to his supervisor, Professor
J.S. Webb, who initiated the project and helped throughout with advice and criticism. Also to Mr I. Thornton for information and discussion of agricultural problems, and Dr I. Nichol for his advice on geochemical techniques. The efforts of the analytical staff are appreciated.
The co-operation of the officers of the Leeds division of the Institute of Geological Sciences, of the Soil Survey of
England and Wales and of the National Agricultural Advisory Service is acknowledged. The writer wishes to thank P. Cazalet of the 12
Geography Department, Bedford College, for discussions and information on pedological problems in north-east Staffordshire.
Also Dr B.K. Holdsworth and Mr N. Train (Department of Geology,
Keele University), Dr P. Morris (Department of Geology, Chelsea
College of Science and Technology), and Dr E.B. Selwood
(Department of Geology, Exeter University) for their advice on local geological conditions.
During the research the writer received a Natural
Environment Research Council grant.
PART A 13
CHAPTER 2. SAMPLING, ANALYTICAL TECHNIQUES AND DATA HANDLING
Geochemical reconnaissance by stream sediment sampling, covering three areas totalling 2500 square miles, vas accomplished during the period April-June 1965 (Table 2).
For nine days during this period samples were collected in south Wales on a project incidental to the main programme.
Excluding samples from south Wales, a total of 2351 sediment samples was collected in 58 sampling days.
Sediment samples were collected following the standard procedures described by Hawkes and Webb (Chapter 14,
1962). All samples were spectrographically analysed for 15 elements and colorimetrically for As and Zn. This yielded more than 35,000 bits of analytical information. Draft regional geochemical maps were ready by August, 1965.
At the same time I. Thornton, after meetings with
N.A.A.S. district officers and local veterinary surgeons, prepared maps showing the distribution of suspected trace element induced agricultural disorders. The descriptions of agricultural practices and trace element problems in each of the three areas are based on data supplied by I. Thornton. 14
Table 2 Regional stream sediment reconnaissance sampling logistics
Reconnaissance area Total mad Devon North Wales Derbyshire Average
Approximate area 800 900 800* 2500 (square miles)
No. of days in 19 field 30 28 77
Sampling days 23 21 14 58 No. of samples 862 903 586 2351
Samples per 0.9 square mile 1.1 1.0 0.7 Samples per sampling day 38 43 42 41
Samples per field day 29 32 31 31
*Excluding area of the main Carboniferous Limestone outcrop (175 sq. miles) 15
(i) SEDIMENT SAMPLING AND SAMPLE PREPARATION
Sediment samples were collected along road traverses from streams with catchments of less than 10 square miles: a final sample density of approximately 1 sample per square mile was achieved. Occasionally,due to inaccessibility, this was not possible. Gaps in the sample plan were filled in later.
Ordnance Survey 22 inch to the mile maps were found most suit- able at this stage.
Duplicate samples of active sediment were taken at
each sample site, wherever possible fine sand and silt being
collected from the middle cr the channel. Collapsed bank
material was avoided. Samples were stored in kraft paper bags holding about 150 gms. of dried sediment. This will usually provide ample -80 mesh material for analysis.
Sample number, the grid reference, whether the bank
was alluvial or colluvial, and the velocity and size of the stream were recorded in duplicate on field data sheets. It was also noted whether the sediment was especially sandy, silty, clayey or enriched in organic matter or coloured by precipi- tated ferric oxides. The geology and any possible sources of contamination were recorded. The pH of the stream waters was rapidly determined using B.D.H. liquid Universal Indicator.
Using one car, a two man sampling team can be expected to collect about 40 samples per day, and one man 30 per day depending on the road and stream density (see also Table 2). 7.6
Samples were dried overnight at 60°C using an electrically heated drying cabinet. It was unnecessary to open the kraft bags. After drying the samples were gently disaggregated in a porcelain mortar and the -80 mesh fraction
(less than 204 microns) sieved off and retained. This frac- tion is suitable for spectrographic analysis without further grinding, and its use - in routine surveys - is standard practice at the A.G.R.G.
Sieved samples were posted to the A.G.R.G. in weekly batches so that analysis was almost concurrent with collection.
(ii) ANALYTICAL TECHNIQUES
In both the spectrographic and colorimetric methods analytical control is obtained by the method of Craven as described by Stanton (Chapter 2, 1966). Members of a stati- stical series - prepared by mixing its high and low components in known ratios - are included in the sample batches. For the spectrographic method one control sample is included on each spectrographic plate. The mean precision at the 95 per cent confidence level is then calculated. Pre:l.sion may also be calculated from the results of series of replicate analyses over the appropriate range of trace element concentrations. (a) Spectrographic method
A rapid semi-quantitative, multi-element technique is
in routine use at the A.G.R.G.. The method has been fully
described by Nichol and Henderson-Hamilton (1965). Ag, Bi, Co,
Cr, Cu, Gal Mn, Mo, Ni, Pb, Sn, Ti, V, Zr and Fe - expressed as
ferric oxide - were all determined in this way.
After ignition at 450°C for three hours the sample is
mixed in a 1:1 ratio with a lithium carbonate - carbon buffer.
The buffer contains, as internal standard, Ge to give 400 ppm in
the final mixture. Sample and buffer are homogenised by shaking
in a Wig-L-Bug for 30 seconds, and are then loaded into a
graphite anode. Equipment, wavelengths and effective ranges
are summarised in Tables 3 and 4 after Nichol and Henderson- Hamilton.
Concentration of the trace elements is determined by
visual comparison against synthetic standards which increase in
concentration logarithmically. Greater precision may be obtained
by comparing the spectral densities using a microphotometer. For
the reconnaissance data precision at the 95 per cent confidence level, calculated either from replicate analyses (Table 5) or by
Cravents method (Table 6), was generally between 30 and 8o per cent. Productivity for the visual method is 26 samples per seven-hour man-day for 15 elements. 18
Table 3
Spectrographic equipment and conditions - after Nichol and Henderson-Hamilton (1965)
Source unit . . Hilger and Watts FS 131 Spectrograph . . Hilger and Watts large quartz E 492
Arc Stand . . Hilger and Watts FS 55 Comparator-microphotometer . Hilger and Watts L 90 Wavelength range . 2800 - 4950 Emulsion . . Ilford N 30
Anode Ringsdorff RW 403 6.15 mm graphite; 2.91 mm diameter crater, 5.0 mm deep crater Cathode . . Ringsdorff RW 403, flat ended Gap . . 3 mm Slit . . 15 ym Arc current . . 12.5 A Collimator . . Internal Step sector . . 1 : 1/4 : 1/16
Exposure . . 20 sec Processing 5 min Kodak D-19b developer at 18'C; 10 sec stop; 10 min fix; wash 19 Table 4
Wavelengths and useful ranges of concentration - modified from Nichol and Henderson-Hamilton (1965)
Wavelength Range of concentration
ppm
Ag 3382.9 0.2 - 1000 Bi 3067.7 5 100 2898.0 loo - 1% Co 3453.5 5 - I% Cr 4254.3 2 500 2843.3 500 1% Cu 3274.0 2 - 200 2961.2 200 - 1% Ga 2943.6 2 - 1% Mn 4034.5 5 - 500 2933.1 500 - 1% Mo 3170:3 2 - 1% Ni 3414.8 5 - 200 3050.8 200 - 1% Pb 2833.1 2 - 100 2873,3 100 - 1% Sn 2840.0 5 - 1% Ti 3377.6 50 - 1% v 3185.4 2 - 1% Zn 3345.0 50 - 1% 20
Table 5 Precision of the multi-element spectrographic method at different metal concentrations, based on approximately twenty replicate analyses.
Element Mean concentration Precisiont (ppm) (± per cent)
8 79 Pb 50 73 Sn 360 78
7 73 Ga 40 30
Bi 17 80 30 32 V 195 47
Mo 45 56 65 48 Cu 220 24
1700 57 Ti 5280 37
25 53 Ni* 210 54 25 56 Co* 100 51
Mn 600 79 65 47 Cr 450 49
Fe203 2.7 60 (9g) 9.8 66 t95 per cent confidence level *Spectral densities compared with microphotometer, all other elements compared visually. 2.1_
Table 6 Precision of multi-element spectrographic analysis determined by Craven's method
Metal Range (ppm) Precision, %t
Co* 14-105 34
Cr 70-400 36
Cu 4o-200 57
Ni* 20-165 31
Sn 5-400 79
Ti 1200-5000 76
V 30-180 8o
tPrecision at the 95 per cent confidence level *Sectral densities compared with the microphotometer; all other elements compared visually 22
Extreme matrices of ferruginous or silica-alumina
composition are known to bias the spectrographic determination
of minor elements (Nichol and Henderson-Hamilton, 1965). In
general, Co, Cu and Ni are enhanced in a siliceous matrix and
Mo and V in a ferruginous matrix. Variation of the silica-
alumina composition of the sediment samples is unknown. Fluc-
tuations of ferruginous composition are minor compared to those
quoted by Nichol and Henderson-Hamilton as producing, in extreme
cases, a twofold variation of trace element composition.
Furthermore, considering the very great range of trace element
concentrations encountered in the stream sediments during the
reconnaissance, matrix effects are unlikely to have any signi-
ficant influence on the geochemical patterns. Samples giving
Ge (internal standard) values of less than 300 ppm or greater
than 600 ppm were reanalysed.
(b) ColorLA tric Mothodo
As and Zn were determined on all samples, and Se,
Sb, U and W on a limited number of selected samples. The
colorimetric methods for As and Zn are briefly described below.
Complete operational instructions and the principles involved for
each of these methods are given by Stanton (1966).
Arsenic iii Arsenicvis reduced to arsenic by potassium iodide and
nascent hydrogen. The nascent hydrogen reacts further with the 23
iii arsenic converting it to arsine. The arsine is swept out of the test-tube by the hydrogen and reacts with mercuric chloride papers giving a yellow to dark brown spot depending on the concentration of the arsenic.
A range of 1-2000 ppm may be covered. The productivity is about 100 samples per man-day.
Zinc
The sample is fused with potassium bisulphate and leached with hydrochloric acid. An aliquot of the leachate is reacted with dithizone in the presence of an acetate buffer
(pH 5.5-6.0). The resulting complex ranges through green and blue to pink with increasing concentrations of zinc.
A range of 5-3500 ppm may be covered. The productivity is 100 samples per man-day.
(iii) DATA HANDLING
The analytical data for each element were arranged into equal logarithmic groups whose mid-points are the spectro-
graphic standards. Frequency distribution plots were then
prepared from the data. Experience at the A.G.R.G. has shown
that geochemical data usually approximate to a lognormal distri-
bution. The geometric mean and other statistical parameters
based on log-transformed data are therefore used. In practice,
histograms are plotted and the geometric mean, standard
deviation and other parameters calculated using a computer 24 program described by Garrett (1966).
For preliminary plotting a drainage base map (scale
1 inch = 1 mile) was prepared on 'permatrace'. Sample numbers and locations, and the analytical results for each element were all plotted on separate 'permatrace' overlays. By combining each overlay with the base map any number of regional geochemical maps can be run off by 'dyeline'.
The initial plotting of the analytical data, though simple, is laborious. To facilitate data handling automatic plotting techniques are being developed at the A.G.R.G. (Nichol et al, 1966B). Using these techniques monochrome and colour- coded geochemical maps of the reconnaissance data have been prepared. 25
CHAPTER 3. REGIONAL GEOCHEMICAL RECONNAISSANCE DEVON AREA
(1) DESCRIPTION OF THE AREA
A. LOCATION
The area, covering approximately 800 square miles, lies entirely within the counties of Cornwall and Devon (Fig. 2).
Okehampton and Launceston are the principal county towns, and the holiday resort of Bude is on the coast. Exeter lies a few miles beyond the eastern boundary.
B. GEOLOGY AND MINERALIZATION
A general description of the geology is given by
Dewey (1948) in the British Geology Memoir for South-West
England. The stratigraphy* is summarised in Table 7, and the geology is shown in Fig. 3.
Structurallyl the area forms part of the southern limb of the Devon synclinorinn; complex folds in the Culm Measures strike approximately east-west. In the Upper Culm the principal
*Since this section was written the Institute of Geological Sciences has revised the nomenclature of the Culm Measures (Khaleelee, pers. comm.). The Lower Culm is reclassified as Dinantian and the boundary with the Devonian modified; the Upper Culm has been subdivided into Namurian and Westphalian. The Westphalian outcrop runs from east to west north of the Permian inlier, and roughly corresponds with the zone of low trace element values in the north (page37).
400 ft. contour Ground over 1400ft. C) Towns — 800 ft. contour Key to rivers 1. R.Exe; 2. R.Taw; 3. R.Torridge; 4. R.Tamar; 5. R.Dart Key to towns Ba. Barnstable; Bo. Bodmin; Bu. Bude; C. Crediton; E. Eater; H. Bolsworthy; L. Launceston; 0. Okehampton; P. Plymouth
Fig. 2. Location and Topography of the Devon-Cornwall Survey Area 26
Table 7
Stratigraphy of the Devon Area (after Dewey, 1948)
System Formation Lithology
( Alluvium Gravels, sands and fine earths Recent ( Peat Peat
Pleistocene Head Unconsolidated stony material
Eocene Bagshot(?) Rolled gravels with granitic gravels sands
Cretaceous Upper sands - often coarse grained Greensand and granitic - and cherty sandstones
Permian Red sandstones and breccias with thin basaltic lava flows
Dartmoor Several varieties of granite - and porphyritic biotite granite Bodmin being the commonest. As, Cu, Granites Pb, Sn and Zn mineralization is associated with the granites.
( Upper Culm* Shales and sandstones Carboniferous ( Lower Culm** Shales with sandstones, cherts limestones and contemporaneous spilitic lavas and basic intrusives
Devonian Upper Devonian Phyllites with sandstones and thin limestones. Contempora- neous spilitic lavas
*Namurian and Westphalian **Dinantian
0 W
files
N
N
-.....ss N 71/ N ++++ .
et,ATedIrap.. k. + +++ + -'+ + + ++ + + _ 4.'011e...... Z%•.., , .f. _,_+ 4+1:4: ++++ + +++:::-I. + 4"ZACIMPATO ++++++++++++ ++ • ++ -+41gpiliak... l'4) 41t + -r -r + 4. + 4. 4.+444÷ .4.+ + + + + _,_÷-4" -4- + + + + + ++ -I- + ++ .44 "- ++ + 4.'- +++ 4- +. 4- 4- -i- I- + + 4- + + + + + + + + -or + ++ + +++ + + + 4°q% //7/ N -4- 4 ++4- 4- + ++ +4- + +4.-*' +.+- + ++++4. +4- + -f+ .4-F, ++ ++ +.' t. + i +++++ +++ -I- + + ++++ -I- ++ ++++ 4- -1-++ + '4 ++ ++ •410,-.14144... z 4- 4- 44 4- + + 4. ' + .14 _,_ + + • ++++ -4- 4- 4. + + +++ +++i- + + 4- +++ ++ -r+ + ++ + 4- /zz/z,/ ,, 4- + 4- No, `1111111M. z/zz/ //// 4- ++++++ + + ++ + + ÷ + -4" •=4"-- + + 4. ++ + +++ + ++++++ ++ ---...... „ N. , •Iib, 4- + -1- + + "++ + + ÷ a ilih. "U. ‘IMINVVINIaii_ •-.... 4- + + + ++ ++ ++ -4- ++++ ++ 4- , 4 4 _i_ '..\ 1=i4a, ....I+.+ +4_ + 4- 4- ++ + , 4-.+4-4-4:4•+++++++4_+++ +.1+4.+4_++4+4-:++++++++++++±.14÷+÷+++ gum. ++++++++ :4 +4..f. +++++:+++ +++4+.+' 4- 4 +4. ++++ ++ . ' + + + + +4- + + +.4- 1-4,4 + 4_ 4- + lit- •-•1•111 + -e- _i_ + 4- - + / +_4_ • + 4..4. 4 + ++_, + _4_ 4, +4_,. + 7> NMI +++ 4- -,-- + '''.1 %._' , . %,i14, ++ + +++ +++++++ + 'i- + -4- +--+_i_ -4. + -T- + + ++ ' + + -I- -T- + -T- + -' _4 1- + re , ', 4_ 4. ,-- + , --,- ' + left. `111: A. + + 4- + 4_ -1- + 4 + + ÷ 4- 4- 4- -r +41 ++ ZZ, 4- 4- 4- -4- 4- 1.14ffh.s. '1101r• ++ 4. .4- -4- 1 4-+++ + 4- +++++4-, + 1- _•. -4-4- ÷ . +++ ++++++ .1. :4' +- ++ i + .4 + • ++ ZZ
Devon an 4- Westphalian l) 1/1111 Tertiary & Cretaceous -4- 4- Granite j (Upper Culm) D 'no n!'un lower N Ncimurian 2% Culm Permian Dolerite
Fig. 3. GEOLOGY OF THE DEVON-CORNWALL SURVEY AREA - lased on information supplied by the I.G.S. 27 lithological units are alternations of shales and sandstones, the thickness of the latter increasing towards the top of the succession. In the soutt Lower Culm shales (with sandstones, cherts, tuffs and beds of limestone) and Devonian phyllites outcrop. Locally basic intrusives and contemporaneous spilitic lavas attain considerable thicknesses.
The Dartmoor and Bodmin granite bosses, intruded into the Devonian and Culm sediments, are the exposed upper levels
of a single granitic batholith. Within the bosses there are
several varieties of granite, the most common being a porphy-
ritic biotite granite. The aureole of thermal metamorphism in the sediments around the granite is between a half and two
miles wide.
The association of mineralization with the granites
is well known. Sn and W veins have been worked in and near the
granite. and Cu, Pb and Zn from lodes in the surrounding
sediments. The reconnaissance area lies a short distance to
the north of the axis of the main east-west metalliferous
zone passing through Tavistock and the Kit Hill and Gunnislake
granite intrusions. Except for a specularite mine on the
eastern flank of Dartmoor, there is no mining activity in the
area today. The locations of the old mines are shown in Fig. 4
(data from Dines, 1956). Fig. 4. 1ITN1NG IN'TH DLVON-CORWALL E;URVEY (flased on Dinos, 1956) 28
Deposits of bedded manganese ores have also been mined, particularly between Okehampton and Launceston and in the Middle Teign valley. The ore is associated with cherts and basic intrusives in the Lower Culm and Devonian.
An outlier of Permian sandstones and breccias, with minor basaltic lava flows, extends west '..hrough Crediton approximately along the axis of the synclinorf_um. No sediment samples were collected from streams draining the outcrops of the Upper Greensand and Eocene in the extreme south-east.
The Pleistocene ice sheets did not extend this far south and there are therefore no till deposits in the area.
Periglacial head deposits are, however, found on the steeper slopes.
C. TOPOGRAPHY AND DRAINAGE
Fig. 2 shows the principal physical features. The alternations of lithologies in the Culm Measures gives rise to moderate slopes and low hills. The transition from Culm to granite is usually marked by a steep scarp, deeply incised by the valleys of fast-flowing streams. Most of Dartmoor is a gently undulating moorland plateau between 1500 and 1700 feet, with isolated tors rising to 2000 feet. East of the River
Hovey, on the north-eastern margin of the granite, the plateau descends to 900 feet and the rough moors give way to farmland. 29
The major catchments are those of the Rivers Taw and
Okement, the Tamar, the Teign and the Yeo (Fig. 2). Only a few short, steep streams flow to the western coast. Over the area as a whole the density of minor tributaries is fairly uniform and road accessibility - with the exceptions of Dartmoor and
Bodmin Moor - is excellent.
Table 8
pH of streams flowing over major geological units
Granite Culm and Permian Devonian
Range 5.0 - 6.6 6.0 - 7.4 6.7 - 8.4 Mean 6.3 6.8 7.2 Number of samples 25 8o 21
Small streams on the Culm have colluvial banks in which the shales are intermittently exposed. The sediment usually consists of small fragments of shale and an adequate sample is not always readily obtained. Valleys on the Permian are similar but,since the sediment is a clean, fine-grained red sand, 30 satisfactory samples are readily collected. On Dartmoor and
Bodmin Moor the streams rise in boggy depressions and flow
down wide boggy valleys. Fine material is very difficult to
collect, the sediment being a quartz-feldspar gravel or
coarse sand. The pH ranges measured in stream waters draining
the major geological units are summarised in Table 8.
D. CLIMATE
Mean annual precipitation for most of the area exceeds
40 inches per year and rises to 80 inches on Dartmoor. Winters
are mild with only about 25 days per year for which a minimum
temperature of 32°F or less is recorded.
E. SOILS
Soils are either residual or developed from local
head deposits. On the Culm Measures only the soils of the
middle Teign valley have been described in detail (Clayden,
1964o). Similar soils can, however, be recognised over a much
larger area (Clayden, 196Lb and pers. comm.). Brown earths are
usually formed on moderate or steep slopes and surface-water
gleys on flatter sites with imperfect drainage.
The soils of Dartmoor (Clayden, 1964a, 1964b) are
developed on several feet of friable, weathered granite.
Blanket peat and peaty gleys cover much of the moor with 31 bogs and peaty ground-water gleys along depressions. Peaty gleyed podzols are found on better drained sites. Soils on the north-east corner of Dartmoor are freely drained, acid brown earths. These soils are traditionally associated with cobalt pine in sheep.
F. AGRICULTURE
Mixed farming predominates with emphasis on dairying and income is based on milk, cereals, beef, sheep, poultry and pigs in that order. Farm units are small, 25 per cent of all holdings being less than 25 acres. A variety of breeds are kept but Friesians are of increasing importance.
Poorly drained soils on the Culm (with high lime and phosphorus requirements) are associated with low productivity and often low standards of farm management. Better yields are obtained from freely drained soils on both the Culm and the
Permian. Upland farms (with Galloway cattle and Scottish
Blackface sheep) on the edge of Dartmoor are least productive.
(ii) THE REGIONAL GEOChTMICAL PATTERNS
The principal geochemical patterns reflect (a) the contrasting geochemistry of the granite and associated mineralization relative to the surrounding sediments; (b) the broad variations in Culm Measure lithologies, and the 32 geochemically distinctive units within the Lower Culm; and
(c) the influence of secondary environment on the distribution of Mn and associated trace elements.
Geometric means and ranges for the trace element content of the stream sediments on the major geological units are summarised in Table 9. Regional geochemical maps to accompany this section will be found in Part 1 of the folder.
A. PATTERNS RELATED TO THE GRANITE AND THE ASSOCIATED MINERALIZATION
Sediments of streams draining the granite are notably impoverished in Co, Cr, Fe, Mn, Ni, Ti and V. In contrast, maximum concentrations of Cr and Ti, and high levels of Ni and
V are associated with streams draining basic igneous rocks
(page 37). This accords with the characteristic geochemistry of basic and acidic igneous rocks.
Massive As, Pb and Sn anomalies characterize the sedi- ments of streams on the granite, and the anomalous zones extend outwards on to the surrounding Culm. Whereas Sn anomalous sediments are widespread on the granite, the Pb-rich sediments are restricted to a small area south of Okehampton. The enhanced concentrations of As are associated with the margins of the granite and a well-defined peripheral zone of Culm.
There are small Pb anomalies on the Culm along the northern Table 9 Range and meant metal content of the minus 80-mesh fraction of drainage sediments from the principal bedrock units, Devon area
.-- , __ Metal content (ppm) Element Granite* Lower Culm* Middle Culm Upper Culm Permian (71)tt (182) (405) (53) (22)
1 Mo <2-5 <2-10 <2-7 <2 <2-2 <2 2 2 <2 <2
Cu 4-150 10-150 8-8o 8-50 10-60 15 45 30 16 20 Pb 30-300 20-6000 15-400 15-100 25-100 45 45 35 3o 35 Sn2 20-4000 <5-2000 <5-200 <5-30 <5-20 215 18 5 4 8 v 10-70 10-200 20-200 30-100 30-150 30 105 90 55 55 Zn 33-190 50-500 45-785 65-190 45-125 8o 190 125 95 75 Ti 800-6000 1500-14,000 l000-6000 1500-5000 1000-4000 1810 396o 3190 260o 1940
Ni 5-30 15-400 10-300 20-40 30-120 8 6o 45 35 4o 2 Co <5-18 8-120 10-100 10-20 7-40 7 25 20 15 16 Mn 100-4000 150-15,000 300-10l000 600-3000 200-2000 400 1700 lo8o 1125 550 Cr 4_70 20-300 30-200 30-150 20-300 20 90 8o 65 55 As2 <5->1000 <5->1000 <5-125 <5-20 <5-40 25 40 9 4 9 Fe 0 1.10-12.00 2.00->30.00 1.70-15.50 , .1.50-6.80 0.95-4.70 2 3 6.03 5.28 (%) 2.73 ), 2.98 2.29 tGeometric mean *High values for AS Cu, Pb, Sn and Zn partly tiNumber of samples in parenthesis reflect contamination' 1Mean calculated with <2ppm = 1 ppm; 2Mean calculated With <5ppm = 3ppm 34 flank of Dartmoor and extensively on the western side of the
Teign valley. Cu and Zn are enriched in sediments on the peripheral zone of Culm but are relatively impoverished on the granite. Bi and U have only been detected in sediments on and close to the granite, and Mo was detected in a few streams on the western side of Dartmoor. Dearman (1965) has reported bismuth and molybdenite at Meldon on the northern border of the granite.
The geochemical patterns are thus, in general terms, in agreement with the established zonal sequence of the metallic ores mentioned on page 27, and the distribution of mine workings shown in Fig. 4. However, the geochemistry of the Culm adjacent to the granite has been complicated by superimposing minerali- zation and thermal metamorphism on syngenetic metal-rich shales.
Many Sn anomalies on the granite can be related to known mineralization and contamination from the abandoned mines shown in Fig. 4, and in all probability most of the remaining anomalies will be traced to small scattered tin workings mentioned, but not recorded in detail by Dines (1956). The sediment patterns, enhanced by contamination, thus reflect the widespread cassiterite mineralization within the granite.
Preliminary follow-up investigations are being made by
I. Nichol, R. Band and other members of the A.G.R.G. 35
Most of the As-Cu-Pb-Zn anomalies on and around the
granite also appear to be related to known deposits and conta-
mination of the streams by mine-waste. Thus the prominent
Pb-Zn anomalies in the upper and middle Teign valleys reflect
mining activity on a north-south lode carrying galena and blende,
and extending for four miles along the western side of the Teign
valley. Less pominent Pb-Zn anomalies, not related to known
mineralization, are being further investigated by the writer's
colleagues. The As-Cu-Zn anomalies on the Lower Culm near
Lydford and west of Launceston may be related to either small
epigenetic deposits - possibly of the lenticular type described
by Dearman and Sharkawi (1962) - or horizons of syngenetically
enriched Culm.
B. PATTERNS RELATED TO BEDROCK GEOLOGY
Geochemical varld.tior3 over the Culm Measures appear
to be related to (i) geochemically distinctive units within the
Lower Culm, particularly basic igneous rocks and horizons of
metal-rich shales, and (ii) widespread changes in the lithology
of the Upper Culm. No prominent geochemical patterns are associated with either the Devonian phyllites or the Permian sandstones.
As, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sn, Ti, V and Zn are
enriched in the sediments of streams draining parts of the
Lower Culm and Devonian. In so far as both of these members 36
of the stratigraphic succession lie dominantly within the east- west mineralized zone,it is difficult to distinguish different aspects of the primary geochemical patterns. Thus As-Cu-Pb-
Sn-Zn anomalies related to mineralization may coincide with sediments enriched in Cr and Ti derived from basic igneous rocks, or in Mo from Mo-rich shales.
A discontinuous zone of Mo-rich sediments can be traced through Launceston, around the northern flank of Dartmoor and into the Teign valley. Anomalous concentrations range from
5-10 ppm Mo (mean 6 ppm) as compared to normal background levels of less than 2 ppm. The western part of the anomaly had also been detected in a previous survey (Webb, 1964). Follow-up studies (reported in Part B of the thesis) west of Dartmoor have related the sediment patterns to the distribution of molybdeniferous shales in the Lower Culm. In view of the association of Mo and Se in Ireland (Chapter 1, page 9 ), selected samples were analysed for Se: the results have been reported by Webb et al (1966k). Concentrations of 0.2-3.8 ppm
Se (mean 1.9 ppm) were associated with the Mo-anomalous sediments, compared to levels of less than 0.2 ppm elsewhere.
Cu, Ni, Pb and V are also slightly enriched in some Lower Culm shales (Chapter 14), and this presumably contributes to the generally enhanced levels of these metals in the sediments.
The coincident Cr-Ti anomalies west of Dartmoor and north of Bodmin appear to reflect the distribution of basic 3? intrusions and spilitic lavas. Sediments of streams draining
catchments in which basic rocks predominate are relatively
enriched in both elements. Similarities between the Cr-Ti and
Ni and V patterns suggest that levels of the last two elements
may also be related to the distribution of basic rocks.
Anomalous Mn-rich sediments on the Lower Culm can be related
to the outcrops of chert beds and also reflect the locations
of the manganese mines shown in Fig. 4. Thus the Mn anomaly
south-west of Lydford, with sediment levels of up to 1 per
cent Mn, can be related to the workings of the old Chillaton
mines. The influence of secondary environment on the distri-
bution of Mn is discussed on page 38. Passing northwards, away from the east-west mineralized
zone and the outcrop of the Lower Culm, the geochemical patterns
appear to reflect broad lithologiaal changes within the Upper
Culm. Thus, As, Co, Cr, Cu, Fe, Mo, Ni, Ti, V and Zn levels
decrease from south to north. Minimum concentrations of these
elements on the Culm are found north of the Permian inlier.
Mo was not detected in the northern area. It is not known whether
the general trend reflects the increased number of arenaceous
units towards the top of the Upper Culm, or indicates a change
in the chemical composition of the interbedded shales.
No distinctive geochemical patterns are associated
with the outcrop of the Permian sandstones. Ti and Mn levels
are somewhat lower and Sn levels slightly higher than on the 38
Culm on either side. The latter may indicate that cassiterite was incorporated in the Permian by erosion of the granite and/ or mineralization in the Culm. Levels of As, Ni and Pb are similar to those on the Culm to the south. Concentrations of the remaining elements are either intermediate or similar to levels on the Culm to the north.
C. PATTERNS RELATED TO SECONDARY ENVIRONMENT
A number of elements are enriched in certain locali- ties in a manner apparently unrelated to either bedrock geology or mineralization. The best example is near Black Torrington, a few miles east of Holswra-thy, in the north of the area. similar features cani however,be recognised on the Culm south of Crediton, in the Teign valley and west of Launceston. In the Black Torrington area Fe and Mn, followed by Co, are notably enriched in the sediments compared to levels elsewhere on the
Upper Culm. Follow-up studies indicated (Horsnail, pers. comm.) that concentrations of these elements were greater in the sediments than in the rocks and soils of the catchment area.
This apparently results from the mobilization and leaching of Fe, Mn and Co from poorly drained soils and their repreci- pitation in the streams. In Devon, Co, Fe, Mn and Ni seem to be most susceptible to the influence of secondary environment.
Similar, although more extensive, patterns were recognised in North Wales (page 53, Chapter 4). 39
(iii) CORRELATIONS BETWEEN THE GEOCHEMICAL PATTERNS AND THE INCIDENCE OF AGRICULTURAL DISORDERS
The distribution of suspected trace element disorders is shown in Fig. 5 based on data compiled during the comple- mentary agricultural reconnaissance by I. Thornton (see also
Webb et al, 1966L).
A. COBALT
Cobalt pine in sheep is traditionally associated with the granite and in particular with the well-stocked farms on the north-eastern margin of the granite. Patterson (1946) reports mean total Co content of pining land as 4 ppm compared to 100 ppm elsewhere. Improved farm management and preventive additives have considerably reduced the incidence of pine. Sporadic cases on the Culm may be a result of depletion of mineral reserves by intensified farming.
The very low levels of Co in the sediments on the granite confirm the absolute deficiency of Co in this part of the area. Over the Culm Co values range from 10-100 ppm with a mean value of approximately 20 ppm. In view of the possibility that Co sediment levels may be somewhat higher than soil values in certain secondary environments (page38), soils on the Culm might well be marginally Co deficient.
0 Cobalt Pine . 0 Swayback • Hypocuprosis Molybdenosis Areas of granitic rock O 0 on which Cobol t Pine occurs Figure. 5. THE- INCIDENCE OF TRACE ELEMENT INDUCED ACRICULlURAL DISORDERS IN THE DEVON—CORNWALL SURVEY AREA. (Dors. comm. I. Thornton) B. MANGANESE
Infertility problems in cattle - attributed in part to manganese deficiency (Wilson, 1965) - are widespread. With the exception of the north-east corner of the Dartmoor granite there is no evidence for any geological control. The main factor is probably overliming which, as the pH rises above
6.0, reduces the availability of soil Mn.
The geochemical data confirm the low Mn status of soils on Dartmoor and suggest that, like Co, the deficiency is absolute. Elsewhere there is no obvious correlation between the incidence of bovine infertility and the geochemical patterns.
C. COPPER AND MOLYBDENUM
A few incidences of swayback and copper pine in sheep have been reported on the Culm near Lydford, and from the northern fringes of Bodmin Moor and Dartmoor. The incidence of copper deficiency cannot be correlated with the distribution of Cu in the sediments. However, in the
Lydford area cases of 'scouring' in cattle and difficulty in rearing lambs occur within the zone of Mo anomalous sedi- ments, suggesting a molybdenum-induced copper deficiency
(Webb, 1964). Similar cases in the Teign valley are also within the zone of molybdeniferous sediments. D. ARSENIC AND LEAD
Poisoning of cattle due to the high As content of pasture herbage has been reported from a small acreage of
!Bastard Red Soil' on Whiddon Down north-east of Dartmoor.
The area is within the zone of highly anomalous stream sediment As levels. The Pb anomaly in the Teign valley is consistent with the traditional belief that chickens cannot be kept in the area due to high lead values in soils and herbage. 42
CHAPTER 4. REGIONAL GEOCHEMICAL RECONNAISSANCE NORTH WALES
(i) DESCRIPTION OF THE AREA
A. LOCATION
The reconnaissance area, covering approximately
850 square miles, is almost wholly within the counties of
Denbighshire and Flintshire but also includes adjoining parts of Caernarvonshire and Cheshire (Fig. 6). The principal towns are Chester, Denbigh and Wrexham and the holiday resorts of
Llandudno, Colwyn Bay and Rhyl.
B. GEOLOGY AND MINERALIZATION
A general description of the geology is given by
Smith and George (1961) in the British Regional Geology Memoir for North Wales. The stratigraphy is summarised in Table 10, and the geology in Fig. 7. The Ordovician outcrop is a complex pile of rhyolites and rhyolitic tuffs with slates above a sequence of slates and sandstones. The volcanic beds represent several episodes of vulcanicity in Lower Bala times which, taken together, consti- tute the Bala Volcanic Series. There are also many igneous intrusions, generally doleritic but occasionally granitic. The
Silurian (represented by the Wenlockian and Ludlovian) consists, at its maximum, of several thousands of feet of shales and mud-
500 500 ft. contour E;; Ground above 1000f1. /771 Ground above 2000ft. 0 5 10 O Towns I Miles Key to rivers 1. R.Dee; 2. R.Clwyd; 3. R.Elwy; 4. R.Conway Key to towns B. Slams* FFestiniog; C. Chester; CB. Colwyn Ray; D. Denbigh; F. Flint L. Llankust; M.Mbld; Rh. Rhyl; Mu. Ruthin; W. Wrexham
Fig. 6. Location and Topography of the North Wales Survey Area 43
Table 10 Stratigraphy of the North Wales area, after Smith and George (1961)
Geological formation Lithology
Recent Blown sands, peats and alluvium Pleistocene Northern Drift Red silty clays largely derived Welsh Drift from the Trias (Northern Drift); grey, stony drifts derived from the local Palaeozoic formations (Welsh Drift); fluvioglacial sands and gravels Trias Bunter Red sandstones and pebble beds (Coal Measures Shales and sandstones with ((Westphalian) coal seams Shales in the north (Holywell) (Millstone Grit Shales) and sandstones in the Carboniferous ((Namurian) south (Cefyn-f-fedw Sandstones) Predominantly limestones with (Carboniferous basement beds comprising (Limestone shales, sandstones and con- ( glomerates
( Mudstones, siltstones and (Ludlovian shales alternating with flags, grits and sandstones Denbighshire Grit Facies, comprising shales and sand- (Wenlockian stones, on the Denbigh ( Uplands: Shale Facies around Silurian ( Llangollen Blue, black and grey grap- ( tolitic shales interbedded with occasional sandy and Valentian ( gritty bands which are most marked in the upper part of the succession Shales and mudstones with grits interbedded with .Ordovician Bala volcanic ashes and lavas; rhyolites, andesites, dole- ritic dykes and granophyres
Ordovician semi Carboniferous Limestone Namurian
Westphalian R14 Trios Recent Intrusive Extrusive igneous rocks igneous rocks
Fig. 7. GEOLOGY OF THE NORTH WALES SURVEY AREA — Rased on 1.0.S. naps 44
stones alternating with flags, sandstones and grits. In contrast
to the Ordovician there is no evidence of volcanic activity.
Minor base metal deposits are known in both the
Ordovician and Silurian (Dewey and Smith, 1922; Archer, 1959).
Thus, west of Llanrwst, galena and sphalerite have been worked
from ore-shoots in the Crafnant Volcanic Series, and until quite
recently from similar deposits at the Trecastell Mine south of
Conway. In the Silurian there is feeble Pb-Cu mineralization
in the Llanfair-Talhaiarn district, and a Pb-Zn lode has been
worked at the Pennant Mine near St. Asaph. The location of
known lodes (from Old Series Geological sheets 74, 78 and 79) is shown in Fig. 8.
Carboniferous limestone outcrops along the western
side of the Vale of Clwyd and in the coastal ridge terminating
in the Great Orme. The outcrop of the limestone east of the
Clwydian Range contains the principal mineral deposits of the area (Schnellmann, 1939, 1959). The orebodies, which consist of galena and sphalerite with minor quantities of chalcopyrite in a calcite gangue, occupy sets of radial dip faults in the limestone and overlying sandstone. The richest orebodies are usually capped by shales. The location of lodes is shown in
Fig. 8, based on the New Series 1-inch Geological sheets 96,
108 and 121. (Pb,Zn) Trecastell
Llanfair Talhaearn • (Cu, Pb,Zn) .1
Carboniferous Limestone
((Cu, Pb,Zn)
L...
0 4 Principal lodes; metal in parenthesis Miles
Fig. B. MINERALIZATION IN THE NORTH WALES SURVEY AREA (based on LG.'S. maps) 45
Eastwards the limestone dips beneath Namurian strata,
which near the coast are argillaceous but become increasingly
arenaceous southwards. Still further east the shales, mudstones
and sandstones of the Westphalian and the red sandstones of the
Trias are generally concealed beneath glacial deposits. Triassic
sandstones and breccias - also covered by glacial deposits -
infill the Vale of Clwyd rift.
The late glacial history of North Wales involved the
meeting of two opposing ice sheets. The path of the Irish Sea
ice, moving south down the Irish Sea, was blocked by North
Wales and the Welsh ice moving radially off the hills. The
Irish Sea ice did however - as shown in Fig. 9, based on data
from Strahan (1886), Embleton (1957), Ball (1960) and Peake
(1961) - penetrate inland particularly along the Vale of Clwyd and on the low ground east of Halkyn Mountain. The till
deposits of the two ice sheets are distinctive. The Northern
Drift is a reddish, silty clay largely derived from Triassic
material, whereas the Welsh till is a grey, stony, silty clay- loam consisting of material derived from Silurian and Carboni- ferous sources. During the contemporaneous retreat stages of the two ice sheets considerable thicknesses of fluvio-glacial sands accumulated in the Vale of Clwyd and in the east. The
Wrexham Delta Terrace was formed at the close of this period.
More recently thick alluvial deposits, interbedded with peat and blown sands, have accumulated in the Dee estuary and the mouth of the Vale of Clwyd. 0 20 Miles N Movement of the Welsh Ice )P. Movement of the Irish Sea Ice A A Limit of the Irish Sea Ice
Ground over 1000 feet
Fig. 9. The Extent of the' Pleistocene Ice-Sheets in North Wales - based on Smith and George ( 1961) 46
C. TOPOGRAPHY AND DRAINAGE
Fig. 6 shows the principal physical features.
Relief is closely controlled by geology. Thus the mountain scenery of Snowdonia, on the complex pile of Ordovician rocks, contrasts with the Silurian hill-blocks of the Denbigh Uplands.
Southwards the Denbigh Uplands increase in altitude from
500-1000 feet to the Denbigh Moors at 1000-1400 feet. Further east the Vale of Clwyd is a distinctive physical feature brought about by periodic downfaulting since Hercynian times. On the eastern side of the Vale, the Clwydian Rangel of Silurian strata, rises steeply and then falls away eastwards over the Carboni- ferous Limestone ridge to the lower hills on the Upper
Carboniferous. Still further east the hills merge with the low-lying Cheshire Plain.
From west to east the principal catchments are those of the Rivers Conway, Clwyd and Dee (Fig. 6). Drainage east of the Clwydian Range is almost exclusively into the Dee, which swinging west through the Pass of Llangollentalso drains the southern margins of the Denbigh Moors. With the exception of the ground underlain by the Carboniferous Limestone, the surface drainage is well developed, and over the area as a whole a density of one sample per square mile was readily maintained.
Generally, weathering and erosion of the Silurian and
Upper Carboniferous rock yield stream sediments consisting of silty-sands with fragments of shale and cobbles of sandstone. In the east, drift and glacial sands contribute to the sediment.
From all these streams satisfactory samples are readily collected.
In contraststhere is often very little fine-grained sediment between the boulders in the fast-flowing streams on the
Ordovician. On the alluvial coastal plain at the mouth of the
Vale of Clwyd there are no streams as such and sediment samples were collected from the largest drainage ditches. The pH ranges measured in stream waters draining the major geological units are summarised in Table 11.
D. CLIMATE
The climate is typically maritime with high humidity, and minimum winter temperatures somewhat higher and summer temperatures a little lower than in the English Midlands (Ball,
1960). Rainfall is lowest along the coast (25 inches per year in the Vale of Clwyd) and in the east, rising to more than
50 inches per year on the Denbigh Moors. In Snowdonia rainfall exceeds 8o inches per year.
E. SOILS
Ball (1960, 1963) has described the soils west of the Clwydian Range. On the Denbigh Uplands freely-drained brown earths (of low base status), derived from the local Silurian drift,predominate. On the Denbigh Moors, with similar parent material, there are peaty gleys and podzolic soils with acid b-8
Table 11 pH of streams flowing over the major geological units
pH Geology No. of and area samples Range Mean
Upper Palaeozoic partly covered by Northern and 34 4.5-9.0 7.5 Welsh Drifts
Triass and Triassic Drift - Vale of Clwyd 49 6.8-9.o 7.5
Silurian - Clwydian Range 45 6.4-7.8 6.8
Silurian - Denbigh Uplands 52 6.3-8.5 6.9
Silurian - Denbigh Moors 41 5.0-7.0 6.5 Ordovician 27 6.2-7.0 6.7 49 hill peat in depressions. West of the Vale of Conway, on the steep rock slopes of the Ordovician, a variety of podzolic and peaty gley soil complexes have been mapped (Fig. 10).
On the coastal fringe and in the Vale of Clwyd many soil series have been recognised associated with a wide variety of parent materials. The predominant types are gleys and imperfectly drained brown earths derived from Northern Drift and alluvium. Characteristically the topsoils are neutral or alkaline and the pH increases down the profile. Freely drained brown earths of high base status are associated with the Carboniferous Limestone.
F. AGRICULTURE
Traditionally dairying, stock rearing and sheep production were associated with the lowland, the semi-upland and the upland (hill) farms respectively (Ball, 1960). Since the Second World War milk production has become the mainstay of most farms, although the traditional enterprises have generally been retained to supplement farm income. Thus,over most of north Denbighshire, farm income is based on dairying supported by stock rearing, sheep, crops and poultry. In the fertile Vale of Clwyd - where dairying has always been important sheep production is increasing, encouraged by a decrease in the percentage of arable land. In Snowdonia, hill sheep farming
(with Welsh Mountain Sheep) predominates.
Brown earths and Gleys Immature soils calcareous soils
Peat, peaty gleys Brown earths Rock dominant with gleying and podzols
Fig. 10. Major Soil Groups of the Western Half of the North Wales Survey Area (modified from Ball-1960-19631 50
(ii) THE REGIONAL GEOCTEMICAL PATTERNS
The principal geochemical patterns are (a) the geral reduction in trace element levels from west to east, (b) varia- tions in the distribution of Fe, Mn and associated trace elements related to the influence of secondary environment, and (c) base metal anomalies reflecting mineralization.
Trace element levels on the major geological units are summarised in Table 12. Since the Upper Carboniferous and Trias in Flintshire and eastern Denbighshire are widely concealed beneath exotic drift (see Fig. 9) and no distinctive geochemical patterns can be related to their suboutcrops, the relevant data have been combined. Regional geochemical maps to accompany this section will be found in Part 2 of the folder.
A. GEOCHEMICAL PATTERNS RELATED TO BEDROCK GEOLOGY AND GLACIAL DEPOSITS
The outstanding regional geochemical feature is the general reduction in trace element levels on passing from the
Lower Palaeozoic in the west to the Upper Palaeozoic and drift deposits in the east. This change is particularly marked along the Vale of Clwyd. Levels of Cr, Ga, Fe,. Ti and V are notably lower (Table 12), and so - with reduced contrast - are levels of Co and Ni. In sediments of streams not draining mineraliza- tion,Cu and Zn values also appear to be reduced. This trend cannot,however,be recognised for Pb. Mn is relatively Table 12 Range and mean metal content of the minus 80-mesh fraction of drainage sediments from the principal geological units in the North Wales area.
Trace element contelt (ppm) Element Ordovician2 Silurian 1 Upper Palaeozoic and Triassic 2 East of the Denbigh Moors Denbigh Uplands Clwydian Hills Vale of Clwyd Clwydian Hills
Mo* <2-40 <2-7 <2-4 <2 <2 <2-15 2 <2 <2 <2 <2 <2 Cul 15-150 15-100 15-400 10-200 10-200 7-400 4o 35 35 25 28 28 Pb 15->l0,000 30-150 10-7000 10-5000 10-8000 30->lol000 80 45 4o 4o 60 18o Sn** <5-150 <5-80 <5-70 <5-20 <5-100 <5-150 10 6 5 <5 <5 ..;i V 30-200 50-200 70-200 20-150 20-180 15-150 1 110 125 135 6o 5o 35 Znl 120-51,750 110-635 90-2090 35-280 25-17,550 40-22,450 385 225 165 130 165 218 Ti ''?06=-8000 1500-7000 2000-7000 700-5000 700-5000 300-5000 45oo 4020 4285 2360 1910 1370
Ni 20-150 [ 30-200 30-100 20-60 10-8o 140-10o 45 6o 45 4 35 3o A, OW* 7-300 10->1000 10-600 <5-30 <5-30 <5-80 40 55 21 12 11 Mt 100-15,000 300-15,000 20-15,000 70-700 70-1500 70-4000 2100 1875 415 200 190 415 Cf 30-150 40-400 40-180 15-100 15-300 10-500 —4— 7o 90 85 55 45 5o Ad** <5-115 <5-90 <5-40 <5 <5-40 <5-20 14 14 <5 <5 ‹.1-5 <5 Ft 2 r 3 1.3-30.0 3.0-13.0 1.4-8.0 0.7-3.3 o:6-8.o 0.5-6.4 .-.. (4) 5.6 5.6 3.5 1.8 1.5 1.6 Numtier of saniges 81 4 1 251 43 98 181 '1 -Geometric mean *1-, can calculated with <2ppm = 1ppm; **Mean calculatl with <5ppm = Abnormally high values partly due to contamination; Areas of acid, peaty moorland soils 52 impoverished only in the Vale of Clwyd, possibly reflecting the immobilization of this element in an alkaline environment
(page 56) In both east and west the geochemical differences between streams draining the various geological units are relatively minor unless influenced by either secondary environ- ment or mineralization. Thus levels of Cr, Ga, Ti and V are similar on both the Ordovician and Silurian despite the obvious geological differences. The striking Mo anomaly, west of
Llanrwst, is exceptional since over the area as a whole Mo is below the detection limit. As in Devon (page 56), the molybdeni- ferous sediments are enriched in Se (Webb et al, 1966c. Se levels range from 0.2-4.0 ppm with a mean of 1.4 ppm compared to background values of less than 0.2 ppm. The enhanced concentrations of both Mo and Se are related to a horizon of black pyritic shales containing 9-60 ppm Mo and 0.2-6.5 ppm Se.
On the Silurian of the Denbigh Uplands and Moors, levels of Cr, Ga, Ti and V show little variation, and Cu and
Pb are enriched in only a few sediments close to mineralization
(page 57). Levels of Co, Fe, Mn, Ni and Zn are fairly uniform over the Uplands but are relatively enriched in sediments on the Moors (page 53). Trace element levels - particularly Cr,
Mn, Ti and V - are somewhat lower on the Silurian of the
Clwydian Range (Table 12). Since these hills are essentially drift free, this may reflect a change in the geochemical compo- sition of the bedrock. 53
In the Vale of Clwyd, Flintshire and eastern Denbighshire
no distinctive patterns can be related to either a single geolo-
gical unit or to the distribution of the various glacial deposits.
As noted on page 47 the readily erodable glacial deposits contri-
bute to the sediments in the east. The absence of distinctive
patterns (other than those related to mineralization) may
therefore be attributed to repeated intermingling and smearing
of the geochemical patterns by the Welsh and Northern ice
sheets.
No coherent regional geochemical patterns were
recognised for Ag, Bi, Mo, Sn and Zr, which over the area as
a whole were below their detection limits.
B. PATTERNS RELATED TO SECONDARY ENVIRONMENT
Geochemical anomalies resulting from the influence of
the secondary environment are characteristically unrelated to
geology. Thus the extensive zone of sediments enriched in As,
Co, Fe and Mn transgresses the major geological boundary between
the Ordovician and the Silurian. The anomalous patterns do,
however,, coincide with the distribution of peaty gleys and
podzolic soils on the Denbigh Moors and in Snowdonia (Fig. 10).
The contrast is most marked between streams draining the Denbigh Moors and the Denbigh Uplands. In both cases the
parent material is drift derived from the Silurian shales and sandstones, but in the latter area the soils are freely drained 5k brown earths. Table 12 shows that the sediments of streams on the moors are relatively enriched in Mn, As, Co, Fe, Ni and Zn, in that order. Furthermore, the sediment levels of Co and Mn, and As and Fe are closely correlated (Fig. 11), possibly reflecting the ability of freshly precipitated Fe and Mn oxides to scavenge certain trace elements (Hawkes and Webb, 1962).
The remaining trace elements show no significant variation between the two areas.
Detailed studies (Nichol et al, 1967) confirmed that the trace element contents of the rocks, soils and sediments of the Upland area are similar. Levels are also similar in the rocks and soils of the moorland, but here the sediments are relatively enriched in Fe, Mn and the associated trace elements
(Table 13). Furthermore, encrustations of Fe and Mn oxides were observed on the banks and sediments of the moorland streams.
It was also found that, although the moorland soils were both more acid and more reducing than the Upland soils, the differences of Eh and pH between the drainage waters of the two areas were relatively slight (Table 14). The authors concluded that the stream sediment patterns are the result of Mn and Fe passing readily into solution and migrating with the circulating ground- waters in the acid, waterlogged soils of the moorland to be precipitated on entering the drainage channel due to increase of pH and Eh. It is believed that the Mn is first precipitated as colloidal hydrated (reducible) Mn01... , and that this then 55 Table 13 Range and mean metal content of rock, soil and stream sediment from Denbigh Uplands and Moors (after Nichol et al, 1967)
Freely-drained Uplands Poorly-drained Moorlands Rock Soil Stream Rock Soil Stream Sediment Sediment Fe(%) 3.1-4.2 1.6-3.3 3.0-4.8 1.5-4.2 1.9-7.7 3.0-15.0 3.5 2.6 3.6 3.2 3.7 8.3 Mn(ppm) 300-600 100-1000 300-500 400-850 40-600 500->l% 475 415 360 540 300 >1% Co(ppm) 16-40 8-13 15-30 5-50 3-16 10-1500 26 10 23 27 7 300 As(ppm) <5 <5 <5 <5-5 3-15 3-90 <5 <5 <5 <5 6 24 Number of 4 7 8 21 8 samples
Table 14 Range and mean pH and Eh of soil and stream water (after Nichol et al, 190)
Soils Stream Water
Upland Moorland Upland Moorland
pH '4.7 -'6.8 2.7 - 4.6 6.6 - 7.2 6.4-7.o 5.8 3.5 6.9 6.6 Eh +0.41 - +0.61 -o.o4 - +0.30 +0.50 - 0.6o 4.o.48-o.6o +0.52 +0.09 +0.55 +0.54 Number of 9 17 4 4 Sites 100 20.000
80 16,000
60 12,000
40 8000
20 4000
+
2 6 10 14 5 0 100 150 200
Fe203 (%) co (pp►) Fig. 11. The Relationship between Co and Mn, and As and Fe in drainage sediments from the Denbigh Moors (Data on minus 80-mesh fraction) 56 ages to inert Mn02. The ratio of reducible to total Mn gives some indication of the magnitude of the leaching process.
The sporadic high Mn values over the area as a whole may therefore indicate locally intensified leaching conditions.
In contrast, the characteristically low Mn values in the Vale of Clwyd may reflect both the low Mn content of the parent materials and soils, and the immobilization of Mn in the alkaline soils.
C. GEOCHEMICAL PATTERNS RELATED TO MINERALIZATION
Striking base metal anomalies, largely related to known mineralization, are superimposed on the low contrast regional geochemical variations already described.. The principal patterns are those for Cu, Pb and Zn (a) on the
Ordovician near Llanrwst, (b) at several localities on the
Silurian, and (c) in the Halkyn - Minera district. The mineral deposits have already been described (page 44).- the locations of known lodes are shown in Fig. 8.
(a) Cu, Pb and Zn Anomalies near Llanrwst
Streams draining the Ordovician west and south-west of Llanrwst are enriched in Cu, Pb and Zn. In the Crafnant
Valley the base metal anomaly is coincident with a zone of
Mo-rich sediments. Most of the anomalous patterns are largely related to known mineralization and contamination from the old mine workings. Follow-up studies (Webb and Nichol, 1967) have 57 related the minor Pb-Zn anomalies in the Crafnant valley to veinlets of galena and sphalerite in the Upper Tuff of the
Crafnant Volcanic Series.
(b) Cu-Pb and Pb-Zn Anomalies on the Silurian
There are three minor base metal anomalies on the
Silurian, one of which cannot be related to either known mineralization or contamination. The most notable anomaly is in the Llanfair-Talhaiarn district where sediments enriched in Pb (up to 7000 ppm) and Cu (up to 400 ppm) can be related to the old workings of a feeble mineralization in the Lower Ludlow
Sandstones. At Bodfari, approximately four miles north-east of
Denbigh, sediment levels of 400 ppm Pb have been traced to a previously unknown smelter site. Soil values of up to 4% Pb were found (Webb and Nichol, 1967). Tributaries of the River
Dee, draining Llantisilio Mountain west of Llangollen, are relatively enriched in Pb and Zn. Follow-up studies (Webb and
Nichol, 1967) have shown that the metals are derived from a small soil anomaly with peak values of 5000 ppm Pb and 700 ppm
Zn. Mineralization has not previously been reported in this area, and there is no evidence of contamination. 58
(c) Cu, Pb and Zn related to mineralization in the Halkyn - Minera district
Sediments of streams draining the Pb-Zn deposits in the limestone of the Halkyn - Minera district are characterised by massive Pb anomalies, variously associated with Cu and Zn.
Surface drainage is almost absent on the limestone and the anomalous streams generally rise on the overlying sandstone, which is also mineralized. Concentrations of Pb are somewhat enhanced in streams, several miles to the east, not directly draining the mineral deposits.
As expected, follow-up studies (Webb and Nichol, 1967) confirmed that most of the anomalies were related to known mineralization, underground drainage from the mines, and mine waste or smelter contamination. The anomaly east of Wrexham was traced to contamination from a disused nitroglycerine factory. Anomalies not explained by known lodes or contamina- tion are being further investigated by the writer's colleagues.
The generally enhanced levels of Pb, several miles east of the limestone and not directly associated with mineralization, may have resulted from smearing of Pb eastwards, by the Welsh ice, from veins exposed at the surface on the
Carboniferous Limestone. 59
(iii) CORRELATIONS BETWEEN THE GEOCHEMICAL PATTERNS AND THE INCIDENCE OF AGRICULTURAL DISORDERS
The distribution of suspected trace element disorders is shown in Fig. 12, based on data compiled during the comple- mentary agricultural reconnaissance by I. Thornton (see also
Webb et al, 1966b).
A. COBALT
Cobalt pine in sheep occurs at clinical and sub- clinical levels on the Ordovician west of the Vale of Conway.
Hughes and Milner (1964) have shown that leached soils on rhyolitic rocks are impoverished in total Co (3 ppm) relative to soils on basic rocks (20 ppm Co). Howevers the density of sheep, although grazing is unrestricted, is greatest on the better quality herbage found on the basic rocks. Cases of acute clinical pine are therefore not very common.
Stream sediment results did not indicate low Co values on the Ordovician. This can be attributed to (i) the hetero- geneous geology of catchments in which both basic and acidic rocks outcrop, and (ii) leaching of Co from the hill soils and precipitation in the streams.
Unthriftiness and suspected cases of cobalt pine in sheep on the alluvium at the mouth of the Vale of Clwyd are associated with very low sediment Co values (range 5-20 ppm, mean 12 ppm), comparable to levels on suspected pining land t..
•
A jv
..--'\ ------\,_ \ 1.— —."— - - N1 r"--- '///1...,,i, .., -9-/-.t••- - //c---- -..-- --N- ,z-J--,---;.--)-,- --7 • < -,r -i;7f _r-K, --- . -..---,,,-,,,-,•,,,,;(7- .„.;-.2-_ ------'-;_l.
-----_-;,:---, --- . ?4- . jr -..N. \i--
71.kt f) '
L ql\
SW y bac I: Cobol': Pine ['d 1 Area in which I irpocuprosis occurs Arco in which Cobalt Pin:: occurF.
Trace el_ n,cni [ff Cr /./,c1r,cjaricsc• clef iciancy in cc..tr.,als Hyp.ocapror.is 0 Area in which Sway!) ac occurs cleficiz!ncy in sk>ci;
tare . :I NC:".1 I/1T, RACE ELE!.11c.:';1 N1'r,1 i) J):1S0E1)1.3 :I N THE NOETil WALES SURVEY A RFAA. (pars. coir' :I . 71“.)11A.011.) 60 in Devon. Furthermore, in these relatively alkaline soils low levels of available Co can be anticipated.
B. MANGANESE
Manganese deficiency has not been related to bovine fertility problems in the area. Manganese deficiency in cereals is,however, reported from the Vale of Clwyd and can be correlated with low sediment Mn levels. The deficiency probably reflects immobilization of Mn in the naturally alkaline soils.
C. COPPER AND MOLYBDENUM
Swayback is found in certain years over most of the area, and is reported to be severest following recent liming and in dry periods. The problem is of major economic signifi- cance on the Denbigh Uplands, where attempts to correlate cases with low levels of available Cu have not been successful (Ball,
1960). Swayback has also been reported west of Llanrwst, on the alluvial soils of the Vale of Clwyd and along the coastal fringe.
Hypocuprosis of cattle is confined to the coastal fringe and the adjacent limestone outcrops.
The regional geochemical Cu pattern cannot be correlated in any way with the incidence of either swayback or hypocuprosis, and since over the area as a whole Mo was undetectedl a molybdenum-induced deficiency is unlikely. The cases of swayback on the Ordovician west of Llanrwst can, 6i however, be correlated with the zone of Mo-rich sediments in the
Crafnant valley.
D. OTIMR METALS
Pb toxicity in livestock and Zn toxicity in cereals have both been reported near old mine workings south of
Prestatyn. Stream sediment levels for both metals are very high. 62
CHAPTER 5. REGIONAL GEOCHEMICAL RECONNAISSANCE DERBYSHIRE AREA
(i) DESCRIPTION OF THE AREA
A. LOCATION
The area, which includes parts of north Staffordshire,
Cheshire and Yorkshire, is within the square formed by the towns of Sheffield, Derby, Stoke-on-Trent and Stockport (Fig. 13). The total area is approximately 950 square miles.
B. GEOLOGY
Edwards and Trotter (1954) have described the geology of the area. The stratigraphy is summarised in Table )5, and the geology is shown in Fig. 14.
Grossly simplified, the structure is that of a dome elongated along a north-south axis and slightly tilted to the east. The outcrop of the Carboniferous Limestone (of Visean age) dominates the centre of the area with successively younger
Namurian and Westphalian strata to the east and west. In the
Namurian an essentially marine shale series (hereafter referred to as the 'Edale Shales') is overlain by the Millstone Grit facies, comprising marine shales and mudstones interbedded with coarse arkosic sandstones and grits. Towards the top of the
Namurian and in the Westphalian the marine phase becomes increas- ingly subordinate to the non-marine phase of the Coal Measure rove4 Towns 400 Contours; height in feet Ground above 1400 ft.
••• 0 4
Miles
Key to rivers 1. R.Derwent; 2. R.Wye; 3. R.Ecclesbourne; 4. R.Dove; 5. R.Manifold; 6. R.Churnet 7. R.Dane
Fig. 13. Location and Topography of the Derbyshire-Staffordshire Survey Area 1 63
Table 15 Stratigraphy of the Derbyshire area after Edwards and Trotter (1954)
Geological formations Lithologies
Recent Peat, alluvium and colluvium Sandy drift largely derived New Drift from the Trias; loess; Pleistocene (Weichsel) solifluction earths; allu- ( Older Drift(s) vial sands and gravels
Permo-Trias Marls, sandstones and 'Pebble Beds'
( Westphalian - Shales and sandstones with ( Coal Measures coal seams ( ( , 'Main Namurian sandstones'- ( ( Millstone Grit facies, ( ( shales alternating with ( ( sandstones and grits ( Namurian ( ( 'Lower Namurian shales'- Carboniferous ( ( dominantly a marine shale ( ( sequence with quartzite ( ( 'Crowstone' facies in ( ( Staffordshire ( Basin facies, marine shales ( Lower with argillaceous lime- Carboniferous stones and, locally, cal- ( - Visean careous sandstones; massif facies, uniform limestones
64 facies. Shales and mudstones are interbedded with fine grained sandstones and coal seams assume importance.
Although feeble mineralization is known in the overlying grits, economic mineral deposits are restricted to the outcrop of the limestone and its immediate extension beneath the Edale
Shales (Varvill, 1959). There are two important mineralized zones running north-west - south-east and separated by almost barren limestone along the Wye Valley (Fig. 15). In the east these zones reappear in the Ashover and Crich limestone inliers.
Lodes carrying galena and sphalerite are found along fault fissures, joints, bedding planes and solution cavities in the limestone. Copper ores have been worked at Ecton on the western edge of the dome, and are also found in the limestone inlier at
Mixon, a few miles to the west.
Permo-Triassic red marls and sandstones unconformably cover the Upper Carboniferous in the south and extreme north-west.
The Bunter Pebble Beds are the most notable formation, and outliers
(for example near Leek) indicate the former widespread Permo-
Triassic cover. There are no younger Mesozoic or Tertiary rocks.
Thick glacial deposits of the Newer Drift (of the
Weichsel Glaciation and equivalent to the Northern Drift in
North Wales) cover the Cheshire Plain but thin out over the
Staffordshire hills (Fig. 14). The drift is a reddish-brown, sandy clay largely derived from the Trias. Jowett and
Charlesworth (1929) traced the eastern boundary of the Newer Cupola • Bole c Mineral veins • smelters smelters
0 5
Miles
Fig. 15. Mineralization and Smelting in the Derbyshire-Staffordshire Survey Area - for sources see text. 65
Drift along the 1250 foot contour on the western side of the north-east Staffordshire hills. To the east there are sporadic relics of older Pennine Glaciations. The loessial deposits on the limestone have been described by Pigott (1962).
C. TOPOGRAPHY AND DRAINAGE
The principal physical features are shown in Fig. 23.
The limestone outcrop forms a well developed undulating plateau, between 900 and 1000 feet, with steep marginal slopes. To the north and east, vales cut in the Edale Shales separate the limestone from the 1200-2000 ft. scarps of the Millstone Grit: the altitude of the scarps decreases southwards until they disappear near Derby. In the west the hills, rising to 1600 feet in north-east Staffordshire, overlook the low undulating Cheshire
Plain. South of the limestone Namurian uplands merge into the Midland lowlands.
Drainage of the principal rivers - the Wye, Derwent,
Dove and Churnet - is south and south-east into the Trent Basin.
Secondary surface drainage is virtually absent on the 175 square miles of the limestone plateau. Elsewhere, particularly in the east, drainagelalthough adequate, is not so well developed as in either Devon or North Wales. Consequently,(Table 2) sample density was somewhat lower than in either of the preceeding areas. 66
Tributary valleys are deeply incised on the alterna-
tions of shales and sandstones, whereas in areas relatively
devoid of hard beds downcutting is less marked and the shales are only intermittently exposed. Alluvial and colluvial banks are about equally developed along the major tributaries, and alluvium is extensive alongside all the principal rivers. A
satisfactory sample can generally be collected except from
catchments in which sandstones predominate and the sediment is a relatively coarse quartz sand. In Staffordshire the readily
erodable New Drift is often exposed in the stream banks and obviously contributes to the sediments. On the Permo-Trias the sediments are generally mixed drift and Permo-Triassic sands. Table 16 summarises the pH of drainage waters on the
major geological units.
D. CLIMATE
Over the area as a whole mean annual rainfall is
between 30 and 40 inches, rising to 50 inches on the hills in north-east Staffordshire and northernDerbyshire. On the wetter, colders exposed uplands, water loss by evaporation is relatively low. Consequently, waterlogged and leached soils are more widespread than in lowland areas. The severity of the climate on the exposed uplands has been a significant factor in retarding their agricultural development. 67
Table 16 pH of streams flowing over the major geological units
pH Geology and No. of soil type samples Range Mean
(i)Dominantly residual soils Triassic sandstones 25 6.5-7.8 7.2
Westphalian shales and 32 4.o-8.o 6.9 sandstones Namurian shales and sand- stones - 'main Namurian 66 6.2 sandstones'
Lower Namurian and Visean shales 31 6.5-8.8 7.4 (ii)Bedrock geology partly concealed by the Newer Drift
Westphalian shales and 5.5-7.4 sandstones 27 7.0 Namurian shales and sand- stones - 'main Namurian 28 4.0-7.0 6:5 sandstones'
Lower Namurian shales 40 6.5-7.5 6.8 68
E. SOILS
The soils of the west Midlands have been described by
Mackney and Burnham (1964), and around Derby by Bridges (1966).
The characteristic soils of the limestone plateau are acid, freely-drained brown earths derived from loessial material
mixed, by cryoturbation, with limestone residues. The loess is believed to have originated on the surrounding gritstone- shale hills. Brown earths, brown earths with gleying and surface-
water gleys are developed on the alternations of shales and sand- stones of the Upper Carboniferous. On the wetter, exposed uplands
podzolic soils are found on freely drained sites, with hill peats,
peaty gleys and peaty gleyed podzols where drainage is impeded.
Surface-water gleys and gleyed brown earths are wide- spread on the sandy Newer Drift. Podzolic soils and acid brown earths are derived from freely-drained Triassic and fluvio-glacial parent materials.
F. AGRICULTURE
Barnes and Jeffery (1964) have classified farming regions in the Dove basin, and Bridges (1966) has described farming around Derby.
Holdings are generally small, particularly on the fringes of industrial areas where smallholdings provide secondary occupations for the workers. Emphasis throughout the area is on dairying variously supported by beef cattle, sheep, cereals, pigs 69 and poultry. Beef cattle and sheep production is most important on the limestone plateau and on the freely-drained Triassic low- lands. In the latter area up to 30 per cent of the land is arable, growing cereals and fodder crops. Minimum stocking densities are found on the north-east Staffordshire hills. This is a region of low productivity and generally poor farm management, and where traditionally all farmland is under permanent pasture.
(ii) THE REGIONAL GEOCHEMICAL PATTERNS
The principal regional geochemical patterns are (a) enhanced levels of As, Mo and associated trace elements related to syngenetic enrichment of the lower Namurian shales, and (b) base metal anomalies reflecting mineralization.
Trace element levels on the major geological units are summarised in Table 17. Areas in which the Newer Drift signifi- cantly modifies the geochemical patterns have been distinguished.
Regional geochemical maps to accompany this section will be found in Part 3 of the folder.
A. GEOCHEMICAL PATTERNS RELATED TO BEDROCK GEOLOGY AND GLACIAL DEPOSITS
Sediments characterised by enhanced levels of Mo delineate extensive areas in north-east Staffordshire and, south of the limestone, in Derbyshire. To the north and east of the limestone the anomaly is intermittent and narrow. The pattern Table 17 Range and meant metal content of the minus 80-mesh fraction of drainage sediments from the princpal bedrock units in areas of residual and drift overburden, Derbyshire area
Trace element content (ppm)
Lower Namurian and Visean Upper Namurian shales Westphalian Triassic Element Shales and sandstones R2 D3 R D R D Mo* <2-50 <2-13 <2-30 <2 <2-16 <2-16 <2-8 7 <2 <2 <2 <2 <2 <2 Cu 20-300 16-85 20-130 20-130 8-300 20-100 16-100 60 40 3o 35 45 45 32 Pb1 8->lo,000 5-4o 16-5000 16-85 20-8500 16-30o 20-85o 150 20 75 30 135 40 108 Sn** <5-40 <5-10 <5-160 <5-20 <5-85 <5-20 <5-400 <5 <5 <5 <5 6 .<5 5 V 20-300 16-160 20-160 20-85 20-160 30-160 10-60 8o 45 45 55 §2 5o 30 Zn1 60-2050 65-290 9-490 40-370 27-910 45-1460 50-2360 400 120 120 150 180 155 175 Ti 400-4000 500-5000 600-4000 600-2000 500-6000 350-4000 600-5000 190o 1515 1600 1330 2400 1740 1500
Ni 20-300 20-160 10-160 30-85 30-500 20-400 10-80 7o 40 35 4o 5o 4o 23 Co** <5-160 10-60 <5-200 10-50 13-85 5-160 <5-40 25 18 15 19 25 18 9 Mn 60-6000 85-4000 20-15000 70-3000 300-4000 100-10,000 85-1600 490 270 290 260 800 450 225 20-160 16-130 15-300 20-300 20-160 20-160 20-300 55 5o 55 45 60 4o 45 As** <5-65 <5-30 <5-30 <5-10 <5-35 <5-30 <5-10 11 <5 <5 (5 <5 <5 <5 Fe203 0.7-7.2 0.6-6.0 0.6-4.4 0.6-3.0 0.6-5.4 0.3-20.0 0.6-7.6 W 2.5 1.6 1.5 1.2 2.5 1.8 1.0 Number of 62 4o 69 34 65 27 27 samples Geometric Dean; *Mean calculated with <2ppm = 1ppm; **Mean calculated with <5ppm = 3ppm 2 Abnormally high values partly reflect contamination; Are.::s of dominantly residual overburden '+Areas in which Newer Drift contributes to the stream sediments (see Fig. 14) Mixed residual and Older Drift overburden on the Trias in South Derbyshire. 71
for As is remarkably similar and to a lesser degree there also appears to be an association of Co, Ni and V, and perhaps Cr,
Fe and Mn, The distribution of the anomalous sediments indicates
that the source of the Mo is predominantly the lower Namurian
shales, and this has been confirmed by the follow-up studies
reported in Chapter 11. In west Staffordshire, despite comparable
trace element levels in the shales, a similar metal association
in the sediments is not apparent. This reflects dilution of the
sediment ipatterns by barren Newer Drift material. Enhanced
levels of Cu and Zn are also generally associated with the
molybdeniferous sediments, but, although Cu is syngenetically
enriched in the shales, these patterns also reflect minerali-
sation (page 72).
The association of Mo, Cu and V - but not As - in
sediments of streams draining Namurian black shale horizons
has previously been reported in Ireland (Webb and Atkinson,
1965). Following Irish experience, selected molybdeniferous
sediments were analysed for Se (Webb et al, 1966a). Se levels
ranged from 0.2-9.0 ppm (mean 2.8 ppm) in Mo-rich sediments
compared to normal background levels of less than 0.2 ppm.
No distinctive geochemical patterns - other than those
related to mineralisation - are recognised on either the Millstone
Grit facies of the Namurian, or on the Westphalian. Levels of Co,
Cr, Fe, Mn, Ni, Ti, V and Zn are somewhat lower on the Westphalian
in the west than in the east. It is not known whether this reflects
(i) a change in bedrock geochemistry, or (ii) the influence of the 72
Newer Drift in the west.
With the exception of Pb and Zn (due to mineralization), trace element levels on the Trias in the south are relatively impoverished. This is most notable for Co, Cr, Fe, Mn and V.
The contrast between trace element levels on the Trias and on the Namurian shales, outcropping immediately to the north, is particularly striking.
No coherent regional geochemical patterns were recognised for Ag, Bi, Sn and Zr, which over the areas as a whole were below their detection limits.
B. GEOCHEI"IICAL PATTERNS RELATED TO MINERALIZATION
Sediments in the east and south-east are characterised by massive Pb anomalies variously associated with Cu and Zn.
In north-east Staffordshire relatively small Cu-Pb-Zn anomalies can be related to both mineralization and syngenetic enrichment of the lower Namurian shales.
Follow-up investigations (Webb and Nichol, 1967) have confirmed that the Pb-Zn anomalies in the east are largely related to known mineral deposits or contamination from mine waste and smelters. Further investigations of unexplained anomalies are in progress at the A.G.R.G., and include the examination and development of criteria for distinguishing significant patterns related to mineralization from non- significant patterns related to other causes. 73
The Pb-Zn anomalies in the south-east can be partially
explained by contamination of the streams rising on the southern
edge of the Wirksworth-Brassington mining district. Many of the anomalies, however, are in streams rising on the Namurian or Trias
several miles to the south. These may reflect either (i) smearing
of the base metal anomalies southwards from veins exposed on the
limestone, by the Pennine Glaciations (this is possibly corrobo-
rated by the writer finding a pebble of galena in a mixed drift-
residual), and/or (ii) mineralisation in the Namurian and Trias.
Green et al (1887) has reported small galena bearing veins in
the Namurian sandstones near Kirk Ireton, and Taylor et al (1967)
have shown that the Pb-Zn anomaly on the Trias partly reflects
the distribution of metal-rich limonitic material in the Triassic
sandstones and conglomerates.
In north-east Staffordshire the generally enhanced
levels of Cu can be attributed to syngenetic enrichment of the lower Namurian shales (Chapter 9). Copper, lead and zinc sul-
phides have, however, been identified in calcite veins exposed
in the streams, and copper ores have been worked at Mixon and
Ecton. There is, therefore, no doubt that both syngenetic and
epigenetic sources contribute to the Cu-rich sediments, whereas
Pb-Zn anomalies are predominantly related to mineralisation.
The Mixon Mine is in a limestone inlier at the southern end
of a north-plunging anticline. The association of Pb-Zn-rich sediments with this anticline could well reflect leakage 74 anomalies - similar to those described by Webb (1959) - from richer mineralization in the generally unexposed limestone core. The most striking anomalies for Pb and Zn, with levels many times background, near Butterton, Mixon and Warslow,are related to contamination from old mine workings.
(iii) CORRELATIONS BETWEEN THE GEOCHEMICAL PATTERNS AND THE INCIDENCE OF AGRICULTURAL DISORDERS
The distribution of suspected trace element disorders is shown in Fig. 16, based on data compiled during the comple- mentary agricultural reconnaissance by I. Thornton (see also
Webb et al, 196%).
A. COBALT
Cobalt deficiency in livestock has not been reported in the area. The relatively low values on the Trias (mean
10 ppm) in the south are comparable with levels on suspected pining land in Devon, and this suggests the possibility of a latent or sub-clinical deficiency.
B. MANGANESE
Mn deficiency has not been associated with bovine fertility problems,although Mn deficiency in cereals and market garden crops has been reported from several parishes in the east.
These cases are believed to reflect immobilization of Mn by over-
• Swayback 0 Hypocuprosis Fig. 16. The Incidence of Trace Element Induced Agricultural Disorders in the Derbyshire-Staffordshire Area (Swayback data - pers. comm. from C.M.Ford to I.Thornton) 75 liming rather than low total Mn soil levels, and cannot be corre- lated with low sediment Mn values.
C. COPPER AND MOLYBDENUM
Swayback in sheep is endemic on the limestone, with the severest incidence in the north. On some swayback farms hypocuprosis in cattle results in copper pine and/or sub- fertility. Severe incidence of hypocuprosis occurs over 10 square miles of Namurian shales around Onecote in north-east
Staffordshire. High levels of Mo are reported in the soils and vegetation of the area, indicating a molybdenum-induced copper deficiency (pers. comm. D.J.C. Jones to I. Thornton).
In the absence of surface drainage, no regional geo- chemical data are available for the limestone. In north-east
Staffordshire the sediment data confirm the high levels of Mo in the soils. The area delineated by the Mo-rich sediments is, however, much more extensive than the reported area of bovine hypocuprosis, suggesting a considerably greater agricultural problem area than hitherto suspected. Furthermore, on the
Namurian shales south of the limestone (where only one case of infertility with hypocupraemia has been reported), the molybdeni- ferous sediments again indicate an extensive potentially suspect area. The results of the writer's detailed studies in these molybdeniferous areas are presented in Part B of this thesis. 76
D. OTHER METALS
Lead poisoning has been recorded in several areas on the limestone in the vicinity of old lead rakes and mine workings.
Shearer et al (1940) have established that high Pb content of herbage is not related to the incidence of swayback in sheep. 7?
CHAPTER 6. CONCLUSIONS
Multi-element stream sediment reconnaissance of three areas in the United Kingdom, totalling some 2500 square miles, has revealed a wide variety of trace element patterns.
Many aspects of these patterns are being further investigated by the A.G.R.G. Nevertheless a number of preliminary conclusions are possible.
(a) Several patterns have disclosed hitherto unsuspected variations in bedrock geochemistry. The most notable are (i) the enrichment of Mo and Se related to shale horizons in the
Lower Culm in Devon and in the Ordovician in North Wales, and
As and Mo - associated with Co, Cu, Ni, Se and V - reflecting metal-rich Namurian shales in Derbyshire, (ii) broadscale geo- chemical variations over the Culm, and (iii) the very striking reduction in trace element levels from west to east in North
Wales, although this feature also reflects the distribution of exotic drift.
(b) The massive base metal anomalies largely reflect known mineral deposits and contamination from mine waste and/or smelters. The outstanding anomalies of this type are (i) As,
Cu, Pb, Sn and Zn related to the granite intrusions and associated mineralization in Devon, (ii) Pb, Cu and Zn on the Ordovician near Llanrwst, (iii) the massive Pb anomalies, variously associated with Cu and Zn, in the drainage east of the Halkyn-Minera mining district, and (iv) the massive
Pb anomalies (with Cu and Zn) east and south-east of the mineralized limestone in Derbyshire. Anomalies not explained
by known mineralization or contamination are being further investigated by the A.G.R.G., although their economic signi- ficance is highly problematic.
(c) Glacial drift, providing it is of local origin, is no serious limitation, although base metal anomalies may be smeared in the direction of ice movement. Thus the anomalies reflecting the Halkyn-Minera mineralization appear to have been smeared eastwards. Thick exotic drift obscures patterns related to bedrock geochemistry. The resulting patterns are still, of course, agriculturally significant.
(d) The distribution of Fe and Mn, variously associated with As, Co, Ni and Zn, in the stream sediment is influenced by secondary environment. These elements are leached from acid-reducing moorland soils and reprecipitated and enriched in the stream channels. Recognition of this phenomena is of obvious importance in interpreting geochemical data (Nichol et al, 1967).
(e) Despite the complexities of rock-soil-sediment and soil-plant-animal trace element relationships the reconnais- sance has been successful in delineating agricultural suspect 79 areas. The correlations between Mo-rich sediments and hypo-
cupraemia in Derbyshire, north-east Staffordshire and Devon,
and very low Co levels and cobalt pine in sheep on Dartmoor
are particularly striking. Low Co levels on the Culm
correspond to suspected pining land, and comparable levels
elsewhere may indicate areas of latent deficiency. Bovine
fertility problems, attributed to Mn deficiency, have been
correlated with low sediment Mn levels on Dartmoor. Res-
tricted cases of As and Pb toxicity in livestock, and Zn
toxicity in cereals correspond to very high sediment
values for these metals.
No correlations are apparent between metal
distribution and incidence of swayback, with the exception
of a limited area in North Wales where the sediments are
enriched in Mo. There is no correlation between Co levels
and incidence of pine on the moorland soils and hetero-
geneous Ordovician geology in North Wales.
(f) Considering the results as a whole, it is apparent
that multi-element geochemical reconnaissance by stream
sediment sampling is an effective and rapid method of
delineating geochemical patterns related to bedrock geology
and mineralization in the U.K. Furthermore the regional
geochemical patterns can often be correlated with the dis-
tribution of clinical and sub-clinical agricultural disorders, 80 and with areas of suspected latent disorders which could
become clinical or sub-clinical if farming practices were changed or intensified. Thus, as first proposed by Webb (1964) and demonstrated in Ireland (Webb and Atkinson, 1965;
Thornton et al, 1966), regional geochemical surveys can
provide information of considerable value to the agricultural specialist and advisor.
PART B 81
CHAPTER 7. S-MPLING AND ANALYTICAL TECHNIQUES,
After a thorough examination of the reconnaissance data it was decided to undertake detailed investigations of areas of molybdenum-induced copper deficiency associated with the Mo anomalies detected in the South Pennines and Devon. Preliminary field studies were made between August and October 1965, and sampling was largely completed between March and July, 1966. During this period compre- hensive collections were made of rocks, soils and herbage from the areas delineated by the Mo-rich sediments and also from adjoining non-anomalous areas. As a part of complementary agricultural investi- gations in the South Pennines, I. Thornton examined the molybdenum- copper status of animals in selected herds.
The procedures employed for rock, soil and herbage sampling and analysis are summarised. In all about 1500 samples were collected, most of which were spectrographically analysed for 15 elements including Mo and Cu. Mo herbage levels were determined colorimetri- cally, and Cu in herbage and EDTA-extractable Cu in soils by atomic absorption.
(i) SAMPLING
Additional stream sediment samples were collected and prepared exactly as described in Chapter 2. Rock, soil and herbage samples were generally collected in large kraft-paper bags and dried overnight at about 60°C using an electrically heated cabinet. 82
(a) Rocks
Exposures in both areas are largely restricted to small stream sections. Representative composite samples were collected from selected sections by chip sampling. Distinctive lithologies were sampled separately. In addition, material was made available by the Institute of Geological Sciences (Leeds Office) from the
Alport borehole in northern Derbyshire.
(b) Soils
Preliminary soil samples were collected at 440 and 880 ft. intervals along traverse lines and grids, the samples being taken at a depth of 12-18 ins. using a 1-in. screw auger. After a thorough examination of the data, plots were selected for a wide range of parent materials and the soil profiles sampled by augering at 6 in. intervals to 30 ins. A composite topsoil sample (0-6 ins.) was obtained by bulking six samples taken over an area of 25 square yards. Finally, on the basis of the soil profile data,representative profiles were examined by pitting and samples collected from each soil horizon.
In all soil profile studies, the site and soil sample were described as fully as possible following the recommendations of
Clarke (1957). Particular attention was given to drainage conditions and the presence of secondary iron-oxide concretions or iron pans.
Soil colour was described by comparison with Munsell Soil Colour
Charts. Field estimates of soil texture were later checked by rapid mechanical analysis with the Bollyoucos hydrometer (Page93). 83
(c) Herbage
Grab samples of pasture grasses were collected from all plots in the South Pennines during the first week in May, and from both areas in the first and second weeks of July. Each sample is the composite of six grab samples cut a few inches above the ground to reduce soil contamination. Samples of white clover were also collected at the beginning of July, and at the same time a rough visual estimate was made of the percentage of clover growing on the plot. Rushes were collected from seepage and low lying poorly- drained sites, and heather and mixed grasses from moorland plots.
(ii) SAMPLE PREPARATION
To avoid contamination all rock and soil samples were siared using nylon bolting cloth sieves. For routine purposes samples were sis'ed to minus 80-mesh which is suitable for spectrographic analysis without further grinding.
(a) Rocks
The chip samples were crushed in a small jaw crusher to minus 80-mesh and coned and quartered to give a 10 g sample. This was then pulverised to minus 80-mesh in a Coor's ceramic ball mill holding six samples. To prevent salting the mills were cleaned between runs with concentrated hydrochloric acid and deionised water.
(b) Soils
For routine purposes soils were gently disaggregated in a porcelain mortar and sieved to minus 80-mesh. Organic soils and 81+ clay-rich samples which harden on drying are difficult to disaggre- gate without vigorous crushing. Soils of this type were therefore stored in sealed Polythene bags until they could be slowly air- dried on covered paper trays at about 45°C.
Standard agricultural practice is to analyse the minus-
2mm fraction. A few samples were accordingly sieved to minus 2ma
(minus 10-mesh) and then ground, in an agate mortar, to minus 80- mesh for analysis. The metal content of the minus 10-mesh and the corresponding unground minus 80-mesh fraction is compared in
Chapter 11.
(c) Herbage
Dried herbage samples were prepared for analysis by grinding to minus 38-mesh in a Christy Norris mill. Samples were not washed before drying and milling and therefore, although cut a few inches above the ground, probably include slight increments of trace elements resulting from soil contamination. Mitchell
(1960) has pointed out that when the metal content of the soil is less than a hundred times the metal content of the plant (dry weight basis) the influence of soil contamination on samples collected as described on page 83 is negligible. Since throughout this study the soil:plant ratios for Mo and Cu are below this level, the herbage results have probably not been significantly increased by soil contamination. 85
(iii) ANALYSIS
All rock and soil samples were spectrographically analysed for Ag, Bi, Co, Cr, Cu, Ga, Mn, Mo, Ni, Pb, Sn, Ti, V, Zr and Fe - expressed as - by the method of Nichol and Henderson-Hamilton Fe203 (1965) described in Chapter 2. Organic-rich peaty soils were weighed before and after ignition at 450°C and the results corrected for ignition loss. Selected samples were colorimetrically analysed for
As, P;;,-.Z. 5c described by Stnton (1966). Available soil Cu, extracted with EDTA, and herbage Cu levels were determined by atomic absorption. The methods of Mo and Cu analysis, along with a number of miscellaneous techniques, are outlined in greater detail below.
Analytical control was maintained either by the method of Craven as described in Chapter 2, or by replicate analysis of selected samples.
(a) Molybdenum
Colorimetric determination of Molybdenum
The Mo content of herbage was determined by a modified dithiol method recently developed at the A.G.R.G. (Stanton and
Hardwick, 1967). The sample is digested in a 4:1 mixture of nitric: perchloric acids, evaporated to dryness and the residue taken up in hydrochloric acid. A suitable aliquot is reacted with dithiol giving a green Mo-dithiol complex. After two minutes the complex is extracted with light petroleum and compared with standards.
Interference by ferric iron is prevented by reduction to ferrous 86 iron with a citric-ascorbic acid solution, which also suppresses interference by tungsten. Interference by copper is suppressed by adding potassium iodide. Precision is better than ± 25% at the
95% confidence level.
Ammonium acetate extractable molybdenum in soils
A wide variety of solvents have been used to assess plant available Mo (Davies, 1956). To investigate the possibility of chemically assessing the available Mo status of soils in the present study, selected topsoil samples were treated with ammonium acetate as recommended by Mitchell (1948, 1966). A 50g (minus 10-mesh) soil sample was shaken for 24 hours with 1 litre of normal ammonium acetate. The extract was then filtered and evaporated to dryness.
Mo was determined colorimetrically with dithiol as described above.
The results are compared with total soil Mo and the Mo content of the corresponding herbage in Table 18 . With one exception, the extractable Mo levels are considerably lower than the herbage content and there is no obvious relationship between the two sets of results. For these soils, therefore, ammonium acetate extractable Mo cannot be considered diagnostic of plant- available Mo. Accordingly, no further extractions were made and available Mo was assessed directly by analysis of the herbage.
87
Table 18 Total and ammonium acetate extractable molybdenum in topsoils compared with the content in the corresponding herbage.
Topsoils (0-6 ins.) Herbage Mo Sample No. Total Mo NH4Ac Ext. (ppm)1 Mo (ppm)2 (ppm)3
2866 15 0.056 2.0 2934 27 0.044 3.o 2961 21 0.340 3.4 2981 <2 0.072 1.2 2998 2 o.o8o 0.6 3013 12 0.172 1.8 3038 3 1.50o 1.o 3485 <2 0.044 2.6
1Data on minus 80-mesh fraction 2Data on minus 10-mesh fraction 30ven dried material
88
(b) Copper
The following procedures have recently been developed
at the A.G.R.G. for the determination of herbage Cu content and EDTA-
extractable soil Cu by atomic absorption. The instrument employed
is a Perkin Elmer 303 spectrophotometer with a hollow cathode
copper lamp. The solutions are sprayed and the absorption measured
at 32478. The instrument settings are summarised in Table 19
Table 19 Instrument settings for the determination of copper using the Perkin Elmer 303 spectrophotometer.
Acetylene cylinder 8psi Auxillary air 30psi Air flow 4.5 divs Fuel flow 4.0divs Slitwidth 4 (= 1 mm slit opening: bandpass 6.5X. U.V. 13.0X Visual)
Wavelength 3247.58
The preliminary procedures are as follows.
Copper in herbage
A 5g sample of the milled herbage is weighed into a platinum dish and ashed overnight at 450°C. The sample is cooled and reweighed to determine the loss on ignition, and the ash digested in a 4:1 89
mixture of nitric and perchloric acids. Hydrofluoric acid is added
and the solution evaporated to dryness. The residue is taken up in
0.5N hydrochloric acid. Standards are also prepared in 0.5N
hydrochloric acid. The solutions are sprayed and compared with the
standards as described above. Precision of the data obtained on the
spectrophotometer is about -1-10;i: at the 95% confidence level.
EDTA-extractable copper in soils
Of the wide range of solvents used to assess the available
Cu status of soils, EDTA (ethylene-diaminetetra-acetic acid) is
usually considered most diagnostic (Mitchell et al, 1957a; Mitchell,
1966). Generally, the quantities of Cu extracted by EDTA from top-
soils and organic-rich soils are considerably greater than by water
or acetic acid. This probably reflects the breakdown of Cu-organic
complexes and the chelation of the Cu ions by EDTA.
The following procedure has been developed at the A.G.R.G. for the determination of EDTA-extractable Cu by atomic absorption.
A 4g sample of minus 10-mesh soil is shaken overnight with 20m1 of 0,05M EDTA (pH 4.8) prepared from di-sodium EDTA. The solution is filtered and sprayed, and compared with standards also prepared in 0.05M EDTA. Precision is about ±5 per cent at the 95 per cent confidence level, and productivity is up to 100 samples per man, per day.
The levels of Cu extracted are compared with herbage levels and the results discussed in Chapter 12. 90
(c) Sulphate
Soil sulphate
The sulphate content of soils was determined by the
method of Scott and Furman (1955) as described by A.G.R.G. Tech.
Comm. No. 33 (1962). The sample is leached with 1M hydrochloric acid, a suitable aliquot taken and sulphate precipitated by adding
barium chloride crystals. The turbidity is compared with standards.
Inorganic herbage sulphate
A method based on that described by Little (1953) was
suggested by Miss G. Lewis of the Central Veterinary Laboratory.
The material is ashed in a muffle furnace and the ash digested
with hydrochloric acid. The sulphate in a suitable aliquot is
titrated with barium chloride using rhodizonic acid as an indicator.
(d) Organic carbon
The method is a modification of that of Schollenberger
(1927) as described by A.G.R.G. Tech. Comm. No. 32 (1962). The
sample is oxidised with clromic acid, and organic carbon estimated
by titration with ferrous ammonium sulphate using diphenylamine as an indicator. Results are somewhat lower than those obtained by
combustion methods.
( e ) EH
Soil pH was determined within a few hours of collection on the fresh material. A 1:2.5 slurry of soil and deionised water 91
was poured into the cap of a glass-calomel electrode on a portable
meter previously calibrated at 4.01 and 9.27 units with buffer
tablets. Two determinations were made for each sample and the mean
taken.
(f) Meobatical analysis of soils
The routine procedure at the A.G.R.G., based on Piper
(1950), has been described by Nicolas (1964). Briefly, the sample
is dispersed with calgon and the amounts of silt and clay estimated
with the Bouyoucos hydrometer. The sample is then remixed and the
sand, silt and clay fractions separated by sedimentation. The
hydrometer settling times quoted by Nicolls are for the International
Society of Soil Science's size classification.
This procedure is not entirely satisfactory because the
hydrometer method was developed for the rapid, approximate estima-
tion of silt and clay fractions and the results are often somewhat
different to those obtained by other methods (Bouyoucos, 1927, 1928,
1934, 1951). The method is not suitable for soils that are difficult
to disperse. The writer found that calgon dispersions of organic-
rich topsoils and of horizons slightly indurated with secondary
ferric oxides were incomplete. Under these conditions the hydro-
meter consistently overestimates the amount of sand, relative to
the values obtained by wet sieving (Table 20) .
92
Table 20 Comparison of estimates of the sand fraction as determined by the Bouyoucos hydrometer and by wet-sieving.
Sand fraction (%)* Sample No. Bouyoucos hydrometer Wet-sieving
3523 48 4o 354o 36 28 3550 44 32 3561 28 21 3578 28 23
*Greater than 0.05 mm to 2.0mm diameter
Furthermorel since the A.G.R.G. method was described by
Nicol's, the International size classification has been widely replaced by the American Department of Agriculture classification.
This increases the range of the silt grade from 0.0O2-0.02mm to
0.002-0.05mm diameter (Table 21). The triangular diagram of soil classification used by the Soil Survey of Great Britain is based on the American system, and this nomenclature has accordingly been used throughout the Thesis (Fig. 17). The following methods of size analysis have been found the most satisfactory - 93
Table 21 Comparison of the size fraction classifications recommended by the International Society for Soil Science and the American Department of Agriculture (after Bouyoucos, 1951)
Sieve size Nominal apperture International American (microns) grades grades -1 10 mesh 2000 20 11 1075 — —Coarse sand 38 520 82 tr 204 7 -- --Sand 125 It 107 --Fine sand 197 53 20 —Silt Silt 2 I] <2 1-- — — Clay Clay
Rapid estimation of size analysis using the Bouyoucos hydrometer
50 or 100g of minus-2mm soil is dispersed in an ultrasonic tank with a 1 per cent calgon solution as described by Nicolls...
The Suspension is transferred to a litre cylinder and made up to 1 litre with deionised water. To ensure a uniform suspension the cylinder is turned end-over-end. If the American classification is being used the percentage of silt+clay is determined with the hydrometer after 40 seconds, and clay after 5 hours. Bouyoucos
(1951) reports that reliable estimates of the clay fraction can be made after only 2 hours, the longer settling time is, however, probably preferable. Using the International size classification, Fig. 17 Soil Texture Diagram 94 readings are taken after 5 minutes and 5 hours. For both systems the readings are corrected by adding 0.3 units for every degree above 19.4°C, and subtracting the same amount for every degree below this temperature.
Separation of size fractions for trace element analysis
A lOg sample of minus-2mm soil..is dispersed with calgon as described. The slurry is wet-sieved through a nylon 197-mesh sieve (mesh aperture 53 microns) into a litre beaker using less than
800 ml of deionised water. To facilitate complete sieving the slurry is gently agitated with the soft rubber bulb of a drnpper. The sand fraction retained in the sieve is dried and weighed, and subdivided into fine and coarse sands, as required, by dry-sieving. The silt+ clay is carefully transferred to a litre cylinder, made up to 1 litre with deionised water, and the clay removed by sedimentation as described by Nicolls.. Sufficient clay for spectrographic analysis is generally obtained after decanting two or three times.
The clay-free silt fraction is dried and weighed, and the percent- ages of sand, silt and clay calculated. All size fractions were prepared for spectrographic analysis by crushing and grinding to minus 80-mesh in an agate mortar. CHAPTER 8. DESCRIPTION OF THE DETAILED STUDY AREA
(i)LOCATION
The area selected for detailed study lies on the south-
western side of the South Pennines, and is centred on the Mo anomalies
covering some 50 square miles east of Leek in north-east Staffordshire and 25 square miles south of the limestone in Derbyshire (Fig.18 ).
The towns and principal villages and the localities mentioned in the
text are shown in Fig. 19. A few samples were also collected further
west in Staffordshire and north of the limestone in Edale.
(ii) GEOLOGY
The stratigraphy is summarised in Table 22 and the geology in Figs. 20 and 2L, both are based on the Geological Survey Old Series
sheets 72 and 81, New Series sheets 98, 110,.123 and 125, and on the
papers mentioned in the text. Particular attention is given to:the deposition of the Namurian shales since, as will be shown in Chapter
9, these are the source of the anomalous Mo levels. Mineralisation and mining have already been described in Chapter 5 (page 64).
(a) Pre-Quaternary Geology
Since the publication of the Geological Survey Memoirs by Hull and Green (1866), Green et al (1877) and Pocock (1906) there have been no comprehensive descriptions of the geology. Various Molybdenum stream sediment anomalies
Detailed study area
N
Carb. 1st. miles
Fig. 18.. Location of the Detailed Study Area in Relation to the Molybdenum Strew SiOdiment Anomalies in the South Pennines
0
.1111 aes Buxton
•' • Land above 1400ft.
,) it clough
, • gno \ \ ..• of • • o o v < --N • )\ lei ••• ‘..J..--• O 1 tV\• c.2,...\ o Haltington -') 6 W. s• C I.\ • C\ \ . I..., *s. I' 1 ,I .. • 1 r C• leek ' s ..--' 4 . —...... ,1 C,''? C..' 1, lr -- • 1 •..../s.,.1 °Q ---‘ - 1.. o nec to •_/ 1 0 •Al•tonefield ) I 0 #).• • G do -\ • P•r wich \ -a Brassington r---6 „.? is,...) 1 0 r • .,' ... a • k .- ( 'boil' . e • \ I k‘41\ I •‘...,a \_.../
err • es - 6" ) OP' • e
WE AVCR • (Nio HILLSti V \ o ulland c); h .Lorne •• -k
Fig. 19. Localities Mentioned in the Text and the! Topography of the Detailed Study Area. 96
Table 22 Generalized stratigraphy of the detailed study area, north-east Staffordshire and south-west Derbyshire (for sources see text)
Geological formation Lithology
Recent Peat, alluvium, colluvium Sandy tills largely derived (Newer Drift from Triassic material: ((Weichsel) and Solifluction earths, aggraded (contemporaneous(?) terraces, and loessial depo- (deposits in sits on the limestone are (unglaciated areas possibly contemporaneous with ( the Newer Drift Pleistocene ( Tills derived from Carboni- 'Older Pennine ferous and Triassic rocks: Drift(s) the latter are red and sandy Sandstones and conglomeratic Trias Bunter 'Pebble Beds' Only the lowest Westphalian (Westphalian is represented in the detailed ((Coal Measures) study area: shales interbedded ( with sandstones and thin coal ( seams
Goniatite Upper zones Carboniferous ( ( Main Namurian sandstones ( R2 interbedded with shales; ( 'upper' Namurian of the text ( R1 (Namurian ( Predominantly marine shale in ((Millstone E2 the detailed study area with Grit) ( El thin quartzite units thickening to the south and west; 'lower' Namurian of the text Basin facies, marine shales Lower with argillaceous limestones Visean Carboniferous and, locally, calcareous sandstones: massif facies uniform limestones 0 1 2 3 4 5
miles
Triassic Sandstones
Westphalian Shales & Sandstones
Upper Namurian Shales & Sandstones
Lower Namurian Sandstones
L.Namurian & Visean Shales
Visean Limestones NMI
Fig. 20. Geology of the detailed study area — for sources see text 97 aspects of Letter and Upper Carboniferous stratigraphy have been discussed by Chalinor (1928, 1929), Hudson and Cotton (1945a), Cope
(1946), and more recently Holdsworth (1963a, 1963b, 1964a, 1964b,
1966), Morris (1966, 1967) and Parkinson and Ludford (1964).
Marine conditions appear to have been fully established during Visean times over the South Pennine region, close to the southern margin of the Carboniferous Central Province (Fig. 22), and to have persisted, without break, until the infilling of the basin at the close of the Namurian. Several contrasting facies can be recognised in the development of the basin. Thus, in the
Visean uniform limestones were deposited on the Derbyshire massif while to the north and west impure limestones and shales accumulated in the basin (Hudson and Cotton, 1945a). The basin facies are now exposed west of the massif limestones in Derbyshire and north-east
Staffordshire (Parkinson and Ludford, 1964). For simplicityiin
Fig. 20 dominantly argillaceous Visean basin sediments have been grouped with the overlying Namurian shales, and the main limestones of the basin and massif margin with the uniform limestones on the massif.
Differential movements between the basin and massif gave rise to a local Namurian-Visean unconformity at the massif margin and resulted in considerably greater thicknesses of Namurian sedi- ments accumulating in the basin than on the massif. At the same time, similar sediments consisting of shales variously interbedded with arenaceous units were being deposited over a much wider area 0 1 2 3 4 5
miles
Limit of the Newer Drift (after Jowett & Charlesworth, 1929; King, 1960) 1
Moorland
Fig. 21. Superficial Deposits of the Detailed Study Area — for sources see text 98 of the Central Province (Trotter, 1951). The Namurian succession is zoned and correlated on the basis of the goniatite faunal bands in the shale horizons (Table 22).
Holdsworth (1963a, 1963b) recognises three major phases of
Namurian sedimentation in north-east Staffordshire. During the first phase (zone El) calcareous intrabasinal turbidities were interbedded with shales deposited under conditions of restricted circulation.
The bottom waters were probably acid and charged with hydrogen sul- phide. In the second phase (zones E2-R1) shales were interbedded with quartzitic turbidites transported from the south and west.
The quartzite units thin to the north-east and are absent in the
Upper Dove valley where, during this period, only shales were deposited. In west Staffordshire, beyond the limits of the detailed study area, the maximum development of the turbidites constitutes the characteristic 'Crowstones' lithology described by Gibson and
Wedd (1905), Pocock et al (1906) and Holdsworth (1964a). Plant debris within the turbidites indicate the proximity of a southern land surface and the influx of the turbidites appears to correspond to periods of reduced salinity and deposition in a relatively acid- oxidising environment. The onset of phase 3 (zones upper R1-R2) was marked by the influx of coarse arkosic sediments from the north.
Grit bands deposited during this phase thin and disappear southwards.
Finally, fluvial sediments covered basin and massif alike and established suitable conditions for the development of the wide- spread paralic environments of the Westphalian. 99
Throughout this study it has been found convenient to distinguish the marine shale sequence in the lower part of the Namurian from the overlying main Namurian sandstones with shales. For simplicity,the lower marine shales and the main sandstones are hereafter referred to as the 'lower' and 'upper' Namurian respectively
(Table 22; Fig.20 ). The boundary between the upper and lower
Namurian is defined by the first major influx of coarse detritus from the north and therefore, over the reconnaissance area as a whole, occurs slightly earlier in the north than in the south. In north- east Staffordshire, the boundary is defined by the onset of phase three sedimentation (see above) during upper R1 times.
In the north-west and along the south-west margin of the detailed eudy area the lower Westphalian (Lower Coal Measures) conformably succeeds the Namurian. The sediments comprise shales alternating with sandstones and associated coal seams, and indicate a continuation of the trend towards terrestial conditions observed in the upper part of the Namurian. The Middle and Upper Coal Measures are not represented, but outcrop to the west in the Potteries.
Triassic red beds, principally the Bunter Pebble Beds characterised by the abundance of well-rounded quartz and quartzite pebbles, outcrop in the south and in a large outlier around Leek.
Pockets of Triassic material on the south of the limestone plateau indicate a former much more extensive cover (Kent, 1957). There are no younger Mesozoic or Tertiary rocks. ' V/V.////////////;,,////////////14//17,!./.;,-.>;,7///V/./Z .//-/WZ/V,r//////V/"//..//ft ////7//77////// /////////7//Vt//////////71/ ://///////////V /V V1/./V///1/ZZVZ /://///////7/
V 1%/.. • 0 E N VINCE I.27;'' • oa- "•••• //// ST. GE RGES z, 77, a 7/Z" ///' LAND •///,'// ;•. if) 7-6, ••‘// • /•4/./, " ////0 • FR :/// ///./• 7,- . IV ////////,zz/ //72/ /// ZZ zyz • .4 ' ( " "././ //z zz z , " T R 0 U G H ///,/,/z/z/zz/zz zz/- %-,' r/ ///,- - //, //// ,z // ..///..,////,z2i2"' .,-- .M.: • ,:- . .. ,._. ////7/,./' ///0/.////, HE ROY NI CO E N T ,5;;//, ././,I /////,;i../,////,0.2" :///1, //flit; ./.,,///,,////// /////j///// ,,,///////// /////%/// -z/z/z/z/z/z/z/z0/ z///1/////; Sea Land
Fig. 22. Namurian Palaeogeography 100
(b) Quaternary Geology
Although ice sheets advanced and retreated over the area several times onlythe Newer Drift deposits of the Irish Sea Ice are widespread. The Older Drift of the penultimate Pennine Glaciation is locally preserved, particularly in the south. The distribution of the various deposits is summarised in Fig.21 based on Jowett and Charlesworth (1929), King (1960), Pigott (1962) and Johnson
(1965).
Small patches of Older Drift are preserved on the north- east Staffordshire hills and the limestone plateau beyond the limits of the Newer Drift (Green et al 1887; Jowett and Charlesworth,
1929). Similar deposits are more widespread south of the limestone where, however, their distribution in detail is largely unknown.
Soil traverses (Figs. 33 and 34, Chapter 10) indicate that the drift is often preserved on the higher ground. The most abundant erratics are local sandstones, limestones, cherts and, in the south, reworked Bunter quartz pebbles.
Near Leek, Jowett and Charlesworth (1929) traced the upper 14mit of the Newer Drift between 1000 and 1250 feet on the western flanks of the north-east Staffordshire hills. King (1960) has continued the boundary southwards. To the west drift cover is generally thickest along the principal valleys and thin or absent on the high ground. The till is characteristically a red-brown sandy clay largely derived, particularly in the west, from Triassic material. The most numerous erratics are local sandstones, Triassic 101
quartz pebbles, and igneous rocks transported from the Lake District
and Scotland.
On the north-east Staffordshire hills and the limestone
plateaus east of the maximum advance of the Irish Sea Ice, there
is abundant evidence of the contemporaneous periglacial climate.
Thus, in the Upper Manifold Valley wide spreads of solifluction
earths, derived from the Namurian shales, have flowed over the
aggraded terraces of the River Manifold and its tributaries. On
the limestone loessial material, possibly derived from the surrounding
Namurian, has been mixed by cryoturbation with limestone residues
(Pigott, 1962).
(iii) TOPOGRAPHY
The north-east Staffordshire hills lie between the
limestone plateau in the east, and the 750 contour from the Weaver
Hills to the Roaches in the west (Fig.19 ). Throughout its length
the western boundary is formed by a series of sandstone edges,
which above a 1000 feet formed a barrier to the advance of the Irish
Sea Ice (Fig.22). The hills to the east include the Millstone Grit
moorlands and the extensive areas underlain by shales around Longnor,
Hartington and Onecote. In the former area the general north-south strike of the rocks is reflected by rocky, upstanding sandstone ridges. Although the shale country is seldom lower than 800 feet and rises to 1600 feet in the west the relief is relatively rounded 102 and subdued. Interbedded sandstones give rise to small local features.
In the south the Namurian shales underlie a rolling upland topography between 60C and 800 feet, and some 200 feet lower
than the upper surface of the limestone plateau. Southwards the uplands merge into the eastern Midland lowlands.
(iv) CLIMATE
The north-east Staffordshire hills, exposed to the pre- vailing west winds, are relatively cold and wet throughout the year.
Mean annual rainfall exceeds 40 inches above 1000 feet and rises to
50 inches on the highest ground. The mean annual temperature at
Buxton is 7.4°C. Since the mean annual loss by evaporation is about 15 inches, roughly 30 inches of rain passes through the soil each year (Mackey and Burnham, 1964). Consequently, gleyed and leached soils are more widespread than over adjoining lowland areas.
On the lower Namurian hills south of the limestone the mean annual rainfall is between 30 and 35 inches and loss by evaporation about
19 inches (Bridges, 1966).
(v) SOILS
The relationship between parent material, soil-type and drainage status summarised below is largely based on the work of
Cazalet (pers. comm.) in north-east Staffordshire. Bridges (1966) has described the soils in the south-east of the area.. 103
Although no soil series map is available for the area as a whole it is possible to anticipate the general nature of the soils from the distribution of their parent materials (Figs. 20 and 21 ).
Dominantly residual soils are developed on the Namurian shales and sandstones beyond the limits of the Newer Drift. Non-residual soils are derived from the Older and New Drifts, loessial material, and from alluvium alongside the principal rivers. Soils on each of these parent materials can be classified according to drainage status, and a sequence of freely-, poorly- and very poorly-drained profiles can be recognised on similar parent materials. It is also possible to distinguish agricultural soils with a plough horizon (Ap) and semi- natural soils under peat.
(a) Dominantly residual soils
On the Namurian, beyond the limits of the Newer Drift, the soils are generally derived from shale and sandstone parent materials mixed by solifluction and colluviation. Furthermore, there has probably been addition of material from the Older Drift and possibly from loess. The soils are therefore not, strictly speaking, residual. Nevertheless the underlying rock formation, if not the immediately underlying stratum, is usually the dominant parent material. Hereafter these soils are referred to as 'residual'.
Agricultural soils underlain by shales, on the wet north- east Staffordshire hills, are characteristically poorly- and very poorly-drained, heavy textured clays and clay loams. As a result of mixing with sandy parent material drainage may be somewhat lok improved and there may be indications of podzolisation. Freely- drained profiles on shales are not widespread. On sandstones, particularly those in the upper Namurian, there is a sequence from ploughed iron podzols on the coarsest textured material, through leached brown earths, to impeded soils with gleying on fine grained parent materials.
Similar trends can be recognised in the semi-natural soils.
Thus, on coarse textured sandstones, humus-iron podzols are developed below a thin organic surface horizon. Whereas on the finer grained parent materials, where drainage is impeded, peat accumulates and a reduced zone is formed. The association of peaty gleyed podzols, peaty surface-water gleys and surface-water gleys is described by
Hackney and Burnham (1964).
Blanket peats have accumulated over the coldest, wettest parts of the area since the Boreal-Atlantic transition of about
6C00 B.C. (Bower, 1960), and are found today on flat and gently sloping sites above 1300 feet where the rainfall normally exceeds
45 inches per year (Fig.21). Valley peats have accumulated in a small depression near Hollinsclough in the Upper Dore Valley.
On the Namurian hills south of the limestone the climate is milder and consequently very poorly-drained soils are less extensive. Deep, poorly-drained soils are derived from shales on gentle slopes, and shallow, relatively freely-drained soils from shales on steep or moderate slopes (Bridges, 1966). The residual soils on the pebbly Trias south of the Namurian are freely-drained sandy loams. 105
Soils derived from the Namurian shales and sandstones are naturally acid and the pH falls to about 5.5 if not maintained at an optimum value of 6.5 by liming. Widespread phosphorus deficiency is alleviated by applying basic slag to shale soils and super-phosphate to soils on sandstones. Dressings are usually required every three years.
(b) Non-residual soils
Soils derived from drift
The most extensive drift soi15. are derived from the red- brown sandy clays of the Newer Drift. Despite the coarse texture of the parent material the soils (loams and clay loams) are normally poorly-drained surface-water gleys. On the higher ground and on the limestone plateau patches of Older Drift give rise to relatively fine textured clays and clay loams. Similar soils are found on the limestone inlier, south of Bradbourne, resting on bright red, very poorly-drained clays. These clays are believed to be limestone residues. Elsewhere in the south the drift includes Triassic material and the soils are similar to those derived from the Newer Drift.
Soils derived from loess
Pigott (1962) has demonstrated that the limestone plateau is covered by silty material possibly blown off the surrounding
Namurian hills under periglacial conditions. The characteristic soils derived from the loess are freely-drained, leached brown earths with acid profiles. Calcareous soils are restricted to 106 limestone colluvium on the lower slopes of the valleys elackney and Burnham, 1964).
Alluvial soils
Broad spreads of alluvium are only developed alongside the principal rivers and their major tributaries (Fig. 19). Two classes of parent materials and soils are recognised: (i) gravels and coarse sands of aggraded terraces giving rise to imperfectly- and poorly-drained loamy soils, and (ii) silty floodplain alluvium with very poorly-drained ground-water gleys. Soils of the former class are only widespread along the Upper Manifold Valley between
Longnor and Hulme End. Elsewhere floodplain alluvium predominates.
(vi) AGRICULTURE
The description of the agriculture is largely based on data collected by I. Thornton during the complementary agricultural survey, and on Bridges (1966), Barnes and Jefferey (1964) and Waud
(1961). The trace element disorders have already been described and related to the reconnaissance geochemical patterns in Chapter 5
(Fig. 16).
Over the area as a whole farm holdings average about 50 acres and farm income is largely based on dairying, variously supported by beef cattle, sheep, pigs, poultry and crops. The importance of these secondary products varies considerably. Thus, on the north-east Staffordshire hills the heavy wet soils are 107 unsuited to ploughing and almost all the farmland is under permanent pasture. The severity of the climate is reflected by a short growing season between the first week in May and the end of September. Heavy rain can be expected throughout this period and the quality of the pasture and hay is therefore poor, consequently stocking rates are relatively lcw and the dairy herds need large quantities of supple- mentary feed. In constrast, on the Namurian hills south of the limestone, the climate is milder and the growing season longer (April to October). Here, although the emphasis is still on dairying, beef cattle contribute significantly to farm income and up to 15 per cent of the land is arable. On the limestone beef production and sheep supplement dairying and some 6 per cent of the land is arable. 108
CHAPTER 9. TRACE ELEMENT CONTENT OF THE BEDROCK
The metal content of the major rock units is described
and the lower Namurian and Visean shales are shown to be the principal
source of the Mo in the anomalous stream sediments. The stratigraphical
and lateral distribution of Mo within the lower Namurian shales is
then discussed and the metal content of contrasting shale facies
compared.
(i) TRACE ELEMENT CONTENT OF THE MAJOR ROCK UNITS AND LITHOI CGIES
Only the lowest part of the Westphalian, comprising shales
and sandstones similar to those in the underlying upper Namurian, is represented in the detailed study area (page 99, Chapter 8). Conse- quently, in presenting the metal content of the principal stratigraphical
and lithological units (Table 23), the data for the Westphalian shales
and sandstones have been combined with those for the corresponding
upper Namurian lithologies. For simplicityl the results for the Visean
and lower Namurian shales have also been combined in Table 232 but are
distinguished in the detailed stratigraphical sections described
later (Tables, 25 and 26).
In Table 24 the results are compared with the metal content
of similar lithologies in the Namurian of Co. Limerick, Ireland
(Atkinson, 1967), and with the average values for sedimentary rocks
from Turekian and Wedephol (1961). The distributions of Ag, Bi and 1 Table 23 Range and mean metal content of the major Carboniferous rock units in the south-west Pennines
_ r-- 7 Rock Unit , Lithology Metal content (ppm) 5•• (No) mo* Cu Se As** V Pb Ga Ti Ni** Co** Mn Cr Fe203 <2 6-50 20- 2- 5-40 1000- 10- 5-60 40- 16- 1.15- Sandstone 130 4.80 Lower Westphalian (9) - - 300 60 6000 130 3000 1 <2 16 50 17 10 2890 35 15 210 40 2.17 and 7 , <2-40 30-85 <0.57 <51 30- 20- 10-30 3000- 16- 1j 175785- 30- 1.25- T.,-Ter Namurian Shale 300 85 6000 200 8500 160 15.00 (11) ' 2 45 <0.5 <5 135 32 18 444o 105 5o 63o 90 4.92L1 , , <2-5 5-50 10- 3- 2-20 1300- ='0-•5-.70 30- 30- 0S2:- ,,anss,one - - 300 40 6000 50 10,000 200 7.6‘.- Lower Namuriam,, 1 (9) <2 17 6o 17 8 3010 35 18 420 65 1.22 and lArgillaceods <2-40 6-160 50- 2-30 2-8- 500- --7-20- -75-47- 0- 10- 0,9- ;l3eun ba.Ein Limestone - - 1000 3000 300 8500 600 2.60 facies (5) 10 35 210 7 3 1000 70 15 2400 45 1.60 <2-50 16-500 0.1- <5- 60- 5-100 6-40 1300- 20- 5-130 30- 20- 1.05- Shale 34.01'x' 451 85o 6000 600 85oo 400 lo.00 (73) 11 110 4.4 17 265 25 19 450o 100 3o 905 100 2.19 Carboniferous Limestone <2 2-3 30-130 2-10 <2 30-600 <5-10 <5 20-600 2-8 0.05- Limestone (5) - - 7.40 <2 2 75 4 <2 55 <5 <5 135 4 0.17 1 Geometric meant (No) Number of samples, except for t5 and tt30 samples *Mean calculated with <2ppm = 1ppm; **Mean calculated with <5ppm = 3ppm 110
Sn, which were only occasionally detected, and of Zr, which showed no significant variations, are not considered further.
(a) Argillaceous rocks
Within the detailed study area only the Visean and lower
Namurian (zones E to R1; page 99, CLapter 8).shales are character- istically enriched in Mo with anomalous values rising to 50 ppm and a mean Mo content of 11 ppm. Sporadic high values were detected in the upper Namurian and Westphalian but most samples of these shales
contained less than 2 ppm Mo. The molybdeniferous shales are also
enriched, compared to the younger shales, in Se (>8x), As (>3x),
Cu (2x) and V (2x), and trace element levels are similar to those associated with 'black-shales' deposited in anaerobic environments
(Table 24). In contrast, the upper Namurian and Westphalian shales are relatively enriched in (2x) and metal values are close to Fe203 those for the average shale. Krumbein and Garrels (1952) have suggested that iron compounds will generally be precipitated in relatively near-shore environments where streams may supply the iron. The enhanced Fe 0 in the shales interbedded with 2 3 values sandstones are therefore consistent with their deposition in a fluvial environment (page 98, Chapter 8).
The distribution of Mo in the Namurian was confirmed by
the analyses of samples from the Tansley borehole on the eastern side of the limestone massif (pers. comm., D. Taylor; Figs.23 and 24),
The Mo content of the shales increases from less than 2 ppm, in the upper part of the borehole, to more than 100 ppm at the base of the
1 Table 24 Mean metal content of major Carboniferous rock units from the south-west Pennines compared with meant values in the corresponding units from Co. Limerick, Ireland (after Atkinson, 1967), and with average values for sedimentary rocks2
Metal content (ppm) Rock type Mo Cu Se As V Pb Ga Ti Ni Co Mn Cr Fe203
Upper Namurian and lower West- phalian sandstones, S.W. <2 16 - 50 17 10 2890 35 15 210 40 2.17 Pennines Lower Namurian sandstones, <2 17 - 60 17 8 3010 35 18 42o 65 1.22 S.W. Pennines Namurian sandstones, Co. <2 12 - 53 11 12 4720 41 18 177 82 5.7 Limerick Average sandstone 0.2 10-40* 0.05 1 20 7 12 1500 2 0.3 385** 35 0.98
Upper Namurian and lower Westphalian shales, S.W. 2 45 <0.5 <5 135 32 18 444o 105 5o 63o 90 4.90 Pennines Namurian siltstones and mudstones, <2 36 0.14 - 95 20 26 6420 58 24 406 124 7.9 Co. Limerick Average shale 2.6 45 0,6 13 130 20 19 4600 68 19 85o 90 4.72
Lower Namurian and Visean shales, 11 lio 4.4 17 265 25 19 4500 100 .70 905 100 2.19 S.W. Pennines Clare Shales, Co. Limerick 27 79 2.9 4-11 365 22 15 2420 54 13-20 340 87 4.5 Average qblack-shale''' 10-300 20-300 - 75-225 50- 20- 70 - 20- 5--50 - 10- 2C00 400 300 500
CarborZ.:erOUS Limestone, S.W. <2 2 - - 75 4 <2 55 <5 <5 135 4 0.17 Pennines Carboniferous Limestone, 'Jo. <2 4 - - 61 4 <2 88 8-lo <5 115 4-7 0.12- Limerick 1.1 Average Limes.one- 0.4 4 o.o8 1 20 9 4 400 20 0.1 1100 11 0.38
1 2 Geometric mean; Data from Turekian and We:lephol (1961) except for *From Krauckepf (1955) and **frc(m Green (1959)
H EPA*
ZONE ro 100 1000
LEGEND
Si= SANDSTONE
1:71 AR01LLACKWS SILTSTONE 2 R AlUDSTONE
LIMESTONE
SASALT
0100
[0W vEtTICAL SCALE
Rl
H
E2 El
D2
Fig. 23. Distribution of Molybdenum and Vanadium in the Namurian of the Tansley Borehole, Derbyshire. Trace element data pers.comm. from D.Taylor; borehole stratigraphy based on Ramsbottom et al (1962) 112
R2 zone. The whole of the underlying lower Namurian is molybdeni-
ferous with a mean Mo content of 54 ppm. The persistence of Mo-rich
shales up into the lower part of the R2 zone, compared to an upper limit in the R1 zone in north-east Staffordshire, is consistent with
the conclusion of Holdaworth (1963b) and other workers that fluvial
conditions were established later over the eastern side of the massif
than elsewhere.
During lower Namurian times sedimentation over the massif appears to have been extremely slow and the succession is condensed
compared to that in the adjoining basin areas (Ramsbottom et al, 1962;
Holdsworth, 1963b). The enhanced Mo values in the shales from the
borehole (mean 54 ppm Mo), compared to the corresponding shales in the basin (mean 11 ppm, Table 23), are compatible with the relatively prolonged extraction of Mo from the water by sorption on the slowly accumulating sediments. The results may, however, partly reflect the contrast between weathered and unweathered material. Hirst and
Dunham (1963) have reported a similar antipathetic variation of Mo content with the rate of sedimentation in the Marl Slate of northern
England.
The lower Namurian shales in the Tansley borehole are also enriched in Co, Cu, Ni and V (As and Se were not determined) compared to values in the upper part of the succession. Cosgrove (1962) found a corresponding increase of e11308 from 0.001% in the upper Namurian shales to 0.002-0.004%; in the lower Namurian. 113
The trace element bedrock patterns are similar to those
in the Namurian of Co. Limerick, where the lower Namurian Clare
Shales are enriched, compared to all other rock units, in Mo and
Se together with Cu and V (Webb and Atkinson, 1965; Atkinson, 1967).
Mean levels of Mo, V and are somewhat higher, and levels of As, Fe203 Co, Cu, Mn, Ni, Ti and Se lower, in the Clare Shales than in the
lower Namurian shales of the present study (Table 24). These
differences presumably reflect variations in the supply of the
elements and/or changes in the environment influencing their con-
centration. The occurrence of comparable bedrock metal patterns
in Namurian sediments deposited some 300 miles apart suggests the
possibility of Mo-rich shale horizons being found over a wide area
of the Carboniferous Central Province (Fig. 22). Curtis (1964)
has reported Mo values rising to 95 ppm in marine Westphalian shales from northern England.
Metal-rich black shales have also been reported in other geological formations in the British Isles. Thus, following up the indications of the reconnaissance stream sediment surveys, hitherto unsuspected Mo- and Se-rich shale horizons have been detected in the Culm Measures of south-west England (page 242, Chapter 14) and in the Ordovician of North Wales (Webb et al, 1966a). Elsewhere enhanced Mo values, variously associated with other trace elements, have been reported in the Marl Slate of Durham (Hirst and Dunham,
1963) and in the Lower Lias shales of southern England (Le Riche,
1959b). 114
(b) Arenaceous rocks
Despite their mineralogical differences, the quartzites
of the lower Namurian and the arkos:'.c sandstones of the upper
Namurian and Westphalian have similar trace element compositions.
The slightly higher content of the arkosic sandstones probably Fe203 reflects their greater proportion of labile minerals, particularly
biotite, which is not found in the quartzites (Holdsw,:rth, 1963a,
1963b). Both groups of arenaceous rocks have higher Co, Ni, V and
Ti values than the average sandstone.
(c) Limestones
The uniform limestones of the massif are impoverished in all elements except V and metal values are very similar to those in the Carboniferous Limestone of Co. Limerick (Atkinson, 1967).
In contrast, the metal content of the thin argillaceous limestones in the V).scan basin facies and lower Namurian is similar to that
1 in the surrounding shales. The enhanced levels of Mc, Co, Cu,
Mn, Ni•t Ti, V and Fe203 are believed to reflect the composition
of the non-carbonate argillaceous fraction. Although molybdeniferous,
the argillaceous limestones are quantitatively insignificant except in the Visean basin facies exposed around Onecote.
(ii) DISTRIBUTION OF TRACE ELEMENTS IN THE LOWER NAMURIAN AND VISEAN SHALES
The distribution of Mo in the lower Namurian shales was investigated by sampling selected outcrops and correlating the 115 sections on the basis of the stratigraphical classification outlined in Chapter 8. Sample locations are shown in Fig. 24. Sampling was severely limited by poor exposure. Thts in the two most complete sections, in the Upper Dove Valley and in Edalef less than a third
of the total estimated thickness of the lower Namurian was actually sampled. Elsewhere samples were collected from scattered exposures.
Consequently, correlation of the stratigraphical variations in metal
content between 7ections ig speculative and the mean zonal metal
values are not necessarily representative (Table 25). In calculating these values the relatively thin H and R1 zones were combined.
Additional information was obtained by analysing material from the
Alport borehole in northern Derbyshire. The stratigraphy of the borehole has been described by Hudson and Cotton (1945b).
(a) Lateral and vertical distribution of trace elements in the lower Namurian
Molybdenum
Molybdeniferous shales were detected in all the sections and in all the zones of the lower Namurian, and also in the Visean basin facies (Tables 25 and 26; Fig. 24). Thus, during lower
Namurian and Visean times, conditions favouring the concentration of Mo in the sediments were widespread around the limestone massif.
The Mo-rich shales in the lower Namurian of the Tansley borehole indicate that similar conditions extended onto the massif (Figs.
23 and 24).
Table 25 Lateral and vertical variation of metal content in the lower Namurian and Visean shales of the south-west Pennines (see also Fig. 24)
Location and zone Metal content (ppm) (Number of samples Mo* Cu Se** As*** V Pb Ga Ti Ni Co Mn Cr Fe 0 in parenthesis) 2 3 ti.) Croker Hill, N. Staffef Basal E <2-30 30-300 - - 130-400 40-100 6-130 2000- 30-200 16-30 600- 50- 1.05E (6) , 6000 850o 130 4.3o 9f` 75 225 55 14 34t)o 60 19 1430 85 1.57. -73i) Rushton nrook, N. Staffs. R1 and H 2-40 20-300 - - 60-600 5-40 8-20 2000- 20-300 5-60 600- 30- 1.05:- 6000 1300 300 3.30 (6) 13 65 180 16 13 3890 70 21 790 75 1.91' E1- grey shale facies <2-2 20-30 - - 60-85 10 10-13 4000- 40 13-30 600- 40 1.20- 5000 1000 1.65 (3) <2 26 75 10 11 464o 40 17 710 40 1.42 (iii) Onecote, N.E. Staffs. R1 and H <2-20 40-400 0.7- .a5-25 200-300 20-40 30 5000- 40-50 13-30 200- 60- 1.70- 2.5 6000 _ 600 16o 2.75 (4) 5 85 1.3 18 245 3o 30 523o 45 24 455 100 2.20. El and E2 10-40 40-300 <0.2- <5-35 eoo-boo Y-6 6-5U 2000- 40-500 ,-6() 50- 40- 1.2 - 34.0 6000 400 300 2. (5) 10 90 3.4 10 410 40 19 482o 115 23 85 110 1.72 Visean (p) 40 85 12.0 30 300 100 13 6000 300 60 600 200 2.65 (1) Grey stab facies in E2 <2-2 16-300 - - 100-400 20-40 13-40 4000- 20-160 20-30 40- 50- o.88- to R1 6000 600 300 1.85 (5) <2 35 220 24 23 5140 60 23 235 100 1.43 (iv) Upper Dove Valley, N.E. Staffs. R1 and H 10-50 60-500 2.5- <5-42 200-600 5-40 8-30 3000- 50-400 20-85 600- 60- 1.50 26.o 6000 4000 200 10.0 (8) 21 185 7.2 28 355 25 23 5140 85 • -45- 1360 loo 3.33 E2 <2-50 30-200 1.5- <5-30 130-600 10-40 10-30 1300- .70-400 20-6o 850- 60 1.4o- 14.o 6000 4000 400 5.4c (8) - 6 115 4.8 14 32o 24 20 4630 125 35 1710 145 2.31 (v) Edale N. Derbys, R1 and H 5-50 60-500 - - 85-300 13-50 13-40 3000- 60-200 30-60 400- 60- 1.25:- 6000 2000 300 3.10 (8) 24 175 23o 27 27 526o 120 45 695 140 2.20 El and E2 <2-30 60-300 - - 160-300 5-40 6-30 2000- 85-200 20-50 850- 50- 1.15- 6000 6000 16o 3.60 (8) lo 115 275 19 17 364o 125 35 287o -. 8o 2.26 (vi) Biggin, S. Derbys. E(?) <2-40 10-300 - - 40-400 5-40 6-40 160o- 30-300 10-85 200- 16- 0.78- 6000 8500 16o 3.4c (6) 8 65 115 15 14 3630 75 26 67o 45 1.69 'All samples are "black shales" unless otherwise indicated; iiGeometric mean *Mean calculated with <2ppm = 1ppm; **Mean calculated with <0.2ppm = 0.1ppm; ***Mean calculated with <5ppm = 3ppm. H rn A '- • 1:. por• • ‘( ) .11/ n c yr ,L,hol e •I
t'sV •••• y (
.1).11_LE SECTION zone. Mc ( pr;m) R II 24 E 10 C'‹
UPPER DOVE / VALLEY SECTION , / -zone No (ppm) or' I,: ER 111 L 21 •->.\ E9 6 \I-1 Sections 1 and 2 ,---y- (pa-ge 122) ,- .2.--/- -• - --.1--- ,1 vC:..\ - - ... .„\.\._-- ONECOTE SECTIONS zone 14 (ppm) RusjiToN Li;Q,01•.:-- _,•?,, -- •-•=-?-?::1:.. f sI•t()-:\T- i Pi II 5 _ 1 _rzc),110-1•10-(spp15:1) E 10 131.001N SECTION 1 \---- zone No (ppil) ‘1E-- E (? ) 8 ci
2/1 Lo cation of the Pri ncipal Lock Sampl ring Sections and the llean 11o:1,\'1)Jk2.nuLl Content of the Lower Namur on hies 117
The principal features of the distribution of Mo are:-
1. In the Edale section the low Mo content of the lower zones
(El and E2), relative to the upper combined zones (H and
R1), reflects Mo values of less than 2 ppm in shale
horizons at the top of El and base of E2 (Table 25;
Fig. 25). Apart, however, from the rather low Mo content
of the micaceous shales (interbedded with thin sandstones)
and the argillaceous limestones, at the top and bottom of
the section respectively, there is no obvious relationship
between Mo content and lithology, At Alport, about four
miles to the north-east of the Edale section, two composite
borehole samples, representing approximately 160 ft. of
shales in the middle of the El zone, are impoverished in
Mo compared to the surrounding shales (Table 26).
The variations of Mo content between the Edale and
Alport sections appears to indicate fairly rapid lateral
changes in either Mo supply and/or environment. The
differences may, however, partly reflect the limitations
of the sampling and the contrast between weathered
samples from Edale and unweathered raterial from Alport.
2. In the Upper Dove valley section (Table 25; Fig. 26),
adjacent to the limestone massif in western Derbyshire,
the mean Mo content of the combined H and R zones is
higher than that of the lowest exposed zone (E2). The
Table 26 Metal content of composite samples from the lower Namurian and Visean of the Alport Dale borehole, northern Derbyshire (Stratigraphy after Hudson and Cotton, 1945b)
Zone Metal content (ppm) (Ft : No) Mo Cu V Pb Ga Ti Ni Co Mn Cr Fe2 03
Hb 6 400 600 3o 3o 4000 300 160 (5o : 6) 20 1300 4.4 Ha 16 4o 200 5 6 3000 3o (46 : 4) 20 3000 30 2.3 Etc (94 : 15) 85 300 400 10 20 3000 160 30 4000 loo 3.3
E2b (6o : 7) 16 6o 300 5 4 85o 85 13 6000 4o 1.o Eta 4o 400 <5 3000 (89 : 5) 5 <2 2 1300 16 50 1.3 Eld 300 6 4 600 4o (54 : 9) 13 100 lo 1300 100 1.4 Elc (62 : 6) <2 30 130 <2 2 850 20 8 85o 30 0.9
Elb 8 30 2 600 16 <5 130o lo 049 (98 : 17) 2 <2
Ela - Elb 13 40 300 16 8 2000 4o 13 600 40 1.5 (391 : 29)
Ela 160 400 13 10 1300 50 10 600 130 1.3 (26 : 2o) 20
Visean P2 10 40 300 5 3 850 40 16 400 5o 1.1 (116 : 6o)
Visean P1 600 5 6 3000 40 <5 30 300 (141 : 36) 30 300 3.1
(Ft : No) (Thickness of zone in feet : number of samples in composite sample) Zone Mo Cu V Ni
1 10 100 10 100 1000 • 10 100 1000 10 100 1000 1
Rya
LEGEND
Hb 7777 Lomposite sample y//1] — Break in section (not to scale)
Ha Silty-shale (with sandstone )
i• • • • I Silty-shale
Etc Shale
Limestone
E2b 0 40ft
Scale Eta
Eid
Eic Eib
Fig. 25. DISTRIBUTION OF TRACE ELEMENTS IN THE LOWER NAMURIAN SHALES AT EDALE, NORTH DERBYSHIRE Zone Mo As Se Cu V Ni
1 10 100 1 10 100 1 10 100 10 100 1000 10 100 1000 10 100 1000
`•••- 1-r' ..a..
Ric
LEGEND Ria.b
Composite sample — Break in section r.„7:0 (not to scale)
Sandstone
H Silty-shale
Shale
Black mudstone
Che rt
Limestone
0 40 ft.
E2 Scale
r Sandstones developed at these horizons to the south-west; Sst Sst marine Rod iolaria comparatively rare.
Fig. 26. DISTRIBUTION OF TRACE ELEMENTS IN THE NAMURIAN OF THE UPPER DOVE VALLEY SOUTH-WEST DERBYSHIRE 119
lower Mo content of the latter zone reflects several shale-
horizons, towards the base of the section, with Mo values
of 2 ppm and less, rather than moderately anomalous values
throughout the whole of the zone. Detailed stratigraphical
studies by Holdsworth (1963a, 1963b, 1966) indicate that
the Mo-impoverished horizons are partly the lateral equi-
valents of sandstone units developed further west and south-
west in Staffordshire.
3. Around Onecote maximuri Mo values are found in the lowest
zones of the Namurian (El and E2) and in the underlying
Visean basin facies shales. Although almost the whole
of the lower Namurian succession in this district appears
to consist of dark blue-grey Mo-rich shales, several
horizons of grey shales with Mo values of 2 ppm and less
are interbedded with the El and E2 sandstone outcrops
shown in Fig. 20. As mentioned above, these sandstones
arc the lateral equivalents of the Mo-impoverished shales
in the Upper Dove valley.
4. Only the dark blue-grey and black shales of the H and
R zones are molybdeniferous in the Rushton Brook section
north-west of Leek. The grey shales interbedded with thin
sandstones in the E zone are characterised by Mo values
of 2 ppm or less. In view of the incomplete exposure,
however, these results may not be representative. At 120
Croker Hill, three miles to the north, basal E2 shales
are molybdeniferous.
Other trace elements
Levels of As, Cu, Se and V are also enhanced in the lower
Namurian shales and many features of their distribution are similar
to those already described for Mo (Table 25). There are, however,
local differences. Thus, (i) in the Onecote section, Se and V -
following Mo - are relatively enriched in the lower zones of the
lower Namurian (El and E2) and in the underlying Visean shales
whereas Cu shows little variation throughout the whole of the section,
and (ii) in Edale, levels of V are similar in both the lower (E) and
upper (H and R1) zones: in contrast, Cu and Mo values are greatest
in the upper part of the succession.
The relationship between Mo and As, Cu, Se and V, in shales
from the Onecote and Upper Dove valley sections, is shown in Figs. 27 and 28. There is no obvious correlation between Mo and As, and Mo and
V in these sections, and levels of As, Cu and V are similar in both
the Mo-rich and the Mo-impoverished shales. A weak tendency for Cu
to follow Mo can, however, be recognised for samples with greater than 2 ppm Mo. Although Se also tends to follow Mo, abnormally high
Se values are found in shales in which Mo is below the detection limit. The results suggest that, although generally similar condi- tions favoured the enrichment of all these elements, either the relative supply and/or the factors influencing the concentration of each element varied.
•Onecote Section + Upper Dove Valley Section
100 —
+ • E Ct. a
E •
1 10-
O
< 2 - • • ++
•• •
<02 1 10 Selenium (ppm)
100 —
E a a E 3
O
<2—
<5 10 100 Arsenic (ppm)
Fig. 27. Variation of Molybdenum with Selenium and Arsenic in the lower Namurian shales
•Onecote Section + Upper Dove Valley Section
100-
++ • +.-r• E a. • a. • + E • ++ ar 10' -0 -0
+ • • is++ <2 -1— •
1 10 100 1000 Vanadium (ppm)
100-
• • + E •• • a. *4 • E
• 4.
0
<2- ▪ + • • •
10 100 1000 Copper (ppm) Fig. 28. Variation of Molybdenum with Vanadium and Copper in the lower Namurian shales 123.
The remaining elements show few systematic stratigraphic or lateral trends. The principal features are:-
1. The content of the shales increases from the Rushton Fe203 Brook section in west, through the Onecote district, to the
Upper Dove valley in the north-east (Table 25). Within each
of these sections the content increases in the upper Fe203 horizons. This trend may possibly reflect the increasing
influence of material derived from the north resulting in
enhanced levels in the upper Namurian and lower West- Fe203 phalian shales (page 110, above).
2. Cr, Ga, Ni and Pb are relatively impoverished in the lower
zone (E) of the Rushton Brook section and in this respect
their distribution follows Mo, Cu and V.
Any conclusions concerning the significance of the observed trends in the distribution of Mo and the other trace elements must necessarily be tentative in view of the relatively few, incom- plete sections sampled. Although conditions favouring the concentra- tion of anomalous Mo values were extensive during the lower Namurian, there appear to have been several relatively brief periods, parti- cularly in the lower zones (El and E2), when shales with Mo values of 2 ppm and less were deposited. Owing to the limitations of the sampling it is difficult to establish whether the No-impoverished shales reflect widespread Iariations of Mo supply and/or environment, or local lateral changes only affecting individual sections. Nevertheless, the low Mo content of the grey shales associated
with sandstones in the Onecote and Rushton Brook sections, and
of shale-horizons at more or less the same stratigraphical level
in the Upper Dove valley, beyond the limits of sandstone develop-
ment, suggests the possibility of relating Mo content of the
shales to broad facies variations.. Consequentlyl the relationship
between the Mo content of contrasting shale facies was investi-
gated in greater detail.
(b) Trace element content of the lower Namurian shale facies
A series of well-exposed shales and turbidites of lower E2 age, outcropping in the stream 490 yds. south of Badgers Croft near
Longnor (grid. ref. SK048633; Fig. 24), was sampled, several chip- samples being taken from each bedrock unit and bulked to give a composite sample. The description and environmental interpretation of the bedrock units, below and in Table 27, is based on the work of Holdsworth (1963a, 1963b).
In the lower part of the exposure (Section 1 of Fig. 29) dark blucfr.grey shales are interbedded with calcareous siltstones.
Holdsworth has suggested, largely on the basis of the data summarised in Table 27, that the shales were deposited under anaerobic condi- tions brought about by restricted circulation in a marine basin.
The bottom waters appear to have been charged with H2S, acidic, and inimical to life. In contrast, the overlying grey shales interbedded with quartzites (Section 2 of Fig. 29) were apparently Table 27 Comparison of the principal sedimentary and palaeontological features, and their environmental interpretation, in Sections 1 and 2, after Holdsworth (1963a, 1963b) (See also Fig. 29 )
Section 1 Section 2
1. Summary of the principal features cf Sections 1 and 2 (i) The Relationship between the argillaceous and arenaceous horizons Silty calcareous hard beds, sometimes laminated, Protoquartzitic sandstones and siltstones monotonously alternating with dark blue-grey and interbedded with grey shale-mudstones. black shale-mudstones. Weak tendency for particle Bedding very regular with sharp contacts size to decrease towards the top of each hard bed. between the base of the sandstones and the Directional sole structures very rare. underlying shales. Decrease of particle size towards the top of the coarse beds. No current bedding. Directional sole structures indicate transport from generally southern points.
(ii) Mineralogy of the hard beds The coarse detrital fraction consists of mineralo- The sands and silts are quartz-rich and gically highly mature quartz-rich silt with trace mineralogically highly mature. Siderite amounts of plagioclase. The carbonate matrix is (FeC0.4) is the dominant carbonate forming dominated by dolomite (CaMg(CO )) and ankerite ironstone bands in the shales and an 3 2 (CaFe(CO )) with lesser amounts of calcite. imparsistent cement in the coarser units. 3 2 There is no calcite or dolomite.
(iii)Palaeontology Autochthonous faunas are scarce and sole- No marine benthonic faunas were found but trails are absent in the shale-mudstones. The the presence of a soft-bodied burrowing hard beds contain an allochthonous fauna of fauna is indicated by the abundance of sole- endothyrid foraminifera and radiolarians. trails. There are large quantities of plant debris in the sandstone units.
2. Environmental interpretation Shales deposited in a marine basin with conditions *Ma episodes of quartz-rich turbidite of restricted circulation. The silty hard beds deposition appears to have occurred during appear to be late-stage differentiates of turbi- periods of reduced salinity and good bottom dity currents and their allochthonous fauna aeration in either a freshwater or brackish suggests a local intrabasinal source for the environment. The abundance of plant debris sediments. The scarcity of an authochthonous in the sandstones suggests the proximity of fauna in the interbedded shales suggests that a heavily vegetated southern land surface. the bottom waters were probably toxic, highly Siderite appears to have accumulated charged with 11,5 and acidic. Carbonates appear directly by precipitation at the sediment/ to have crystallized in abundance only in water interface suggesting that conditions response to slight increases of pH brought were relatively oxidizing and acidic. about by freshening of the bottom during turbidity current inflow. MO ppm Se ppm Cr ppm. •
10 0.3 I 100 10 100 1000
Section 2
LEGEND
QUARTZITE
CALCAREOUS Ela SIMEON( SHALT CALCAREOUS SILTSTONE
SHALE ALUDSTONE
Section HMLE ALUDSMM Mll 11"""440
10 MOOS
" VERTICAL° SCALE
Fig. 29. Distribution of Molybdenum, Selenium and Chromium in Contrasting Shale Facies within the Lower Namurian. Stratigraphy based on Holdsworth (1963a). 124
deposited, under relatively acid-oxidising conditions, in either
a freshwater or brackish environment close to the southern land
surface EFig. 22) and there is abundant evidence of a soft-bodied
burrowing fauna. Over the Carboniferous Central Province as a whole
the marine shales of Section 1 correspond to the 'marine-shale facies',
whereas the grey shales and interbedded quartzites are equivalent to
the =grit-shale facies' described by Trotter (1951).
The distribution of trace elements between the contrasting
facies is summarised in Table28 and Fig. 29. Several trends are
apparent -
1. The shales of Section 1 are enriched, relative to the overlying
grey shales, in As (>3x), Co (2x),. Mn (2x), Mo(>14x) Ni (2x),
Pb (2x) and Se (>12x). This trend is particularly marked for
As, Mo and Se which show considerable enrichment in the shales
of Section 1 and are close to and below their detection limits
in Section 2.
2. In contrast,the shales of Section 2 are enriched, compared to
the molybdeniferous shales, in Cr (3x) and Ga (3x). Levels of
Cu, V and Fe 0 2 3 are similar in the shales of both sections.
3. Although impoverished in trace elements compared to the fine
grained sediments, the metal content of the calcareous siltstones
of Section 1 and the quartzites of Section 2 reflects the trace
element composition of the corresponding shales. Thus the
quartzites contain higher Cr and Ga values than the calcareous Table 28 Range and meant metal content of shales from contrasting facies in the lower Namurian of north-east Staffordshire (see also Table 27z Fig. 29)
Depositional environment/ Metal content (ppm) (after Holdsworth, Lithology (No) Mo* Cu Se As** V Pb Ga Ti Ni Co Mn Cr Fe 0 1963a, 1963b) 2 3 Alternating shales and Quartzitic i<2-5 10- 60- 20- 6-20 3000- 3o- 10- 16o- 6o- 0.76-' („uartzitic sandstones ;sandstones ! 5o 300 40 6000 50 5o 10,00o 200 7.60 deposited under oxidi- (5) i <2 23 105 27 11 3650 45 25 990 100 1.72 sing freshwater or Grey shalesi<2-2 3o- <0.5 <5-5 300- 20- 30-50 3000- 50- 2o- 16o-16o- 1.25- brakish conditions 16o 500 100 (Section 2 of Fig. 29) 850o 600 85 600 400 2.65 (5) 1 <2 8o <0.5 <5 35o 4o 35 6000 220 4o 46o 26o 1.8o Interbedded shales and ;Calcareous <2-13 6-5o 3o- 8-100 2-13 1000- 30- 5-85 100- 20- 0.75- Calcareous siltstones siltstones 300 5000 400 3000 85 2,19 deposited in an anae- i (12) 1 3 14 7o 35 6 2060 65 24 1025 35 1.34 robic marine environ- !Dark blue- i20-50 50- 1.5- <5-75 300- 4o- 10-20 4000- 200- 50- 300- 60- 1.10- ment (Section 1 of }grey shales 130 30.0 500 160 600o 600 160 3000 160 3.60 Fig. 29) I (7) 28 8o 6.o 16 365 85 14 5240 400 75 910 95 1.99 1 Geometric mean; (No) Number of samples in parenthesis *Mean calculated with <2ppm = 1ppm; **Mean calculated with siltstones, whereas the latter are relatively enriched in Mo. The relatively low metal content of the arenaceous units is attributed to the dilution of the argillaceous matrix by large quantities of relatively barren sand and silty quartz-rich detritus. Only Mn is enriched, along with Fe 0 in the sideritic iron- 4. 2 3, stones of Section 2. The enhanced Mo values (mean 28 ppm) in the shales of Section 1, compared to the levels of 2 ppm and less in the grey shales, are consistent with the accumulation of the Mo-rich lower Namurian and Visean shales under stagnant bottom conditions in a 'black- shale' environment. Thcce conditions also appear to have favoured the concentrations of As and Se. In contrast, levels of Cu and V are similar in the shales of Sections 1 and 2. Unlike Mo, therefore, their enrichment in the lower Namurian shales is not confined to shales deposited under anaerobic conditions. These results corroborate the absence of any consistent relationship between the distributions of Mo and Cu, and Mo and V in the Onecote and Upper Dove valley sections (Fig. 28), but do not account for the corresponding lack of correlation between Mo and As, and Mo and Se (Fig. 27). Since the shales of Section 2 probably accumulated under oxidising conditions in relatively close proximity to the southern land surface,their metal content may correspond fairly closely to 127 that of the detrital clays derived from the south. Consequently, the enhanced Cu and V levels in the lower Namurian shales as a whole, compared to the upper Namurian and Westphalian shales (Table %13), possibly reflect enhancLd values in the source area, rather than concentration in a 'black-shale' environment. The considerable enrichment of Mo (>14x) and Se (>12x) in the reduced sediments of Section 1, relative to the values in the shales of Section 2, indicates the action of a powerful concentration mechan- ism in the anaerobic environment. This is discussed further on page 132. Metal distribution in the contrasting facies represented by Sections 1 and 2 can be related to lower Namurian sedimentation over the region as a whole. The grey shales and quartzite units of Section 2 increase in thickness towards their source in the south and west (Holdsworth, 1963a, 1963b). Consequently, their maximum development is to the west of the north-east Staffordshire hills in the area partly covered by the Newer Drift. Here they constitute the distinctive 'Crowstone' lithology described in the Geological Survey Memoirs (Gibson and Wedd, 1905; Pocock et al, 1906; Holdsworth, 1964a). Between episodes of Crowstone deposition in the Rushton Brook and Croker Hill sections, dark blue-grey molyb- deniferous shales accumulated (Fig. 24; Table 25). Within the detailed study area the maximum development of the sandstone units is found to the west and south-west of Onecote, where grey shales interbedded with the sandstones have been shown 128 to be impoverished in Mo (page 119, above; Fig. 20). Over the north- east Staffordshire hills, however, the sandstones are relatively thin and subordinate to the molybdeniferous shales. Although only shales were deposited in the Upper Dove valley area, the Mo-impoverished horizons near the base of the section coincide with the development of sandstones to the west and south-west (Fig. 26). Consequently, the influence of the relatively freshwater and improved aeration associated with the influx of the sandstones appears to have extended beyond the physical limits of turbidity current deposition. Holdsworth (1966) detected a similar influence in the distribution of the radiolarian faunas. The antipathetic relationship between the development of the sandstone units and the Mo content of the shales suggests that Mo-impoverished sediments were being deposited, in relatively close proximity to the southern land surface, at the same time as the accumulation of ho-rich muds in a stagnant marine basin. Manheim (1961) has reported a similar distribution of metal-rich sediments in the Baltic (Fig. 30). North of the limestone massif Mo-impoverished shales were found at slightly different levels in the E zone of the Edale and Alport sections (Tables 25 and 26; Fig. 24). The detailed relationship between these horizons and the Mo-impoverished shales in north-east Staffordshire is not known. Data from the Tansley borehole (pers. comm., D. Taylor) suggests that on the massif, isolated from the action of tu:bidit•* currents in the basin,. 100 e-c- c- c 10 ~ c 0 u "0 Ql ~ ~ a-I +400 Eh(mv) - 200 7-6 , 7S!7-4 \ pH ------, 7-2 7-0 -- 6-8 Sweden S lot" 10 ~ eu level ,------~----~Green I Sands 8. clays I OrgarlC mud --ErosIOn zone----\--Block mUd-I-- -Sand--- Fig. 30. Distribution of Trace Elements in Relation to Eh-pH Conditions in the Baltic - modified from Manheim (1961) 229 a relatively thin succession of Mo-rich shales accumulated without break between the base of the Namurian (El) and the lower part of the R2 zone (Fig. 23). Although the massif formed a submarine 'high' throughout the lower Namurian times (Holdsworth, 1963b), there is no evidence to suggest that this brought about any improve- ment of bottom aeration. Over the region as a whole the influx of coarse detritus from the north, marking the close of a long period of dominantly marine deposition, broughban end to the widespread accumulation of Mo-rich sediments. During the upper Namurian and in the Westphalian the marine phase became increasingly subordinate to fluvial and terrestial conditions. Consequently, the sporadic high Mo valu,:s detected in the upper Namurian and Westphalian shales (Table 23) may indicate the re-establishment of stagnant conditions during relatively brief episodes of marine deposition, or in deltaic environments similar to those described by Dunham (1961). (iii) DISCUSSION During the Namurian the marine-shale facies, described by Trotter (1951), was deposited over wide areas of the Carboniferous Central Province (page , Chapter 8i Fig. 22). Similar sections, with a marine shale sequence below a succession of alternating shales and sandstones, were deposited in Co. Limerick, Ireland, and in the South Pennines. In Staffordshire lower Namurian quartzitic sand- stones and interbedded shales accumulated, under well-aerated bottom 130 conditions, in relatively close proximity to the southern land surface (Holdsworth, 1963a, 1963b). There is no equivalent facies in Co. Limerick. Following the indications of reconnaissance stream sediment surveys detailed geochemical investigations in Co. Limerick (Webb and Atkinson, 1965; Atkinson, 1967) and in the present study area have confirmed that the basal marine shales are enriched in Mo and Se, together with As, Cu and V. This appears to reflect the development of similar anaerobic 'black-shale' environments in both areas. In southern Ireland, however, the Mo-impoverished shale-horizons asso- ciated with the grit-shale facies in Staffordshire are absent. Within the detailed study area the sandstone units in the lower Namurian reflect brief episodes of improved bottom aeration, under freshwater or brackish conditions, in a dominantly marine succession (Holdsworth, 1963a, 1963b). Consequently, the molybdeniferous shales of the South Pennines appear to have accumulated closer to the boundary of a stagnant marine basin than the corresponding deposits in southern Ireland. Although there is no evidence that the metal- rich lower Namurian shales of the South Pennines and southern Ireland were deposited in the same stagnant basin, the coincidence of such remarkably similar metal patterns, in sediments deposited some 300 miles apart, suggests the possibility that Mo-rich shales may be found over a much wider area of the Carboniferous Central Province (Fi. 22). 131 Manheim (1961) has reported the enrichment of trace elements in organic-muds accumulating in the deep troughs of the Baltic (Fig. 30). Levels of Ag, Cu? Mo, U and Zn all show a sharp increase in passing from the near-shore, oxygenated sands and clayey-sands to the reduced muds in the stagnant troughs, and in this respect the distribution of Mo is very similar to that envis- aged in the lower Namurian of north-east Staffordshire. Furthermore, maximum values of Mo (80 ppm) and Cu (250 ppm) are of the same order as in the molybdeniferous shales of the present study. Considerable metal concentration was found to occur where (i) both sediments and bottom waters are stagnant and charged with H2S, and (ii) only the sediments are reduced and the overlying trotters contain considerable dissolved oxygen. Although not apparent in Fig. 30, maximum metal enrichment was found not in the central, most stagnant zones, but in the peripheral transition zone to stagnant conditions. In the lower Namurian shales there is no direct evidence of the relationship between the reduced zone and the sediment-water interface. The distribution of the marine fauna may, however, be significant. Thus Holdsworth (1963b) has suggested that the scarcity of an autochthonous fauna in the lowest zone of the Namurian (El) indicates that the bottom waters were charged with H2S and toxic. Throughout the remainder of the lower Namurian succession a sparse benthonic fauna of thin-shelled lamellibranchs is associated with relatively abundant faunas of free-swimming goniatites and 132 planktonic lamellibranch spat (Ramsbottom et al, 1962; Holdsworth, 1966). Furthermore, Holdsworth (1963a, 1963b) found abundant evidence of a soft-bodied, burrowing fauna in the Mo-impoverished shales associated with sandstone units in north-east Staffordshire. Consequently, although other factors may be involved, the faunal evidence suggests that conditions in the marine basin were most stagnant during El times and that subsequently there was sufficient oxygen at the sediment-water interface to support a limited fauna. Except, however, for periods of improved bottom aeration, when Mo-impoverished shales were deposited, bottom conditions appear to have been inimical to the development of a thriving benthonic fauna. The scarcity or absence of a bottom fauna is characteristic of many other black-shale environments (Dunham, 1961). Despite the extensive literature on metal-rich b-_ -Lck-shales, the mechanism of extraction of Mo from sea-water remains uncertain. Vine (1966) reviewing North American black-shales, Le Riche (1959b) working on the Lower Lias shales of southern England, and Hirst and Dunham (1963) discussing the origin of the metal-rich Marl Slate of Co. Durham, have attributed the concentration of Mo to sorption on organic matter. Korolev (1958), however, has experimentally shown that Mo can be concentrated by coprecipitation with, or sorption on, iron sulphide gels, such as hydrotroilite (FeS.nH2O), which ultimately age to pyrite. This is corroborated by the report of Manheim (1961) that Mo has a strong tendency to follow iron 133 sulphides in the organic-muds accumulating in the Baltic. Se, with a similar ionic radius to S (Se2 1.918 : Se2 1.74R), is readily substituted for S in sulphide lattices and is therefore usually associated with iron sulphides. As also has a tendency to concentrate in pyrite in sedimentary rocks (Goldschmidt, 1954). Either sorption on organic matter and/or association with iron sulphides would reasonably account for the concentration of As, Mo and Se in the lower Namurian shales deposited under stag- nant bottom conditions. Furthermore, both mechanisms are compatible with the somewhat higher Mo values in the condensed shale sequence on the limestone massif compared to the shales in the adjoining basin (page 112 above) . The low values of all three elements,in the grey shales interbedded with sandstones (Table 28), deposited during brief periods of improved bottom aeration in a relatively near-shore environment (Holdsworth, 1963a, 1963b), suggest that the concentrations of As, Mo and Se in the seawater were probably more or less normal. Consequently, the normal weathering of the land surface and the concentration of Mo, As and Se in a black- shale environment is believed to be adequate to account for their enrichment in the lower Namurian shales. A similar suggestion has been made with regard to the origin of the anomalous Mo values in the Marl Slate (Hirst and Dunham, 1963). Le Riche (1959b), however, has suggested that the enhanced Mo values in the Lower Lias of southern England reflect abnormally high concentrations in the seawater. 131+ Cu and V are the only other elements enriched in the molybdenifcrous shales compared to values in the upper Namurian and lower Westphalian shales (Table 23). Both elements appear to have been concentrated independently of Mo and enhanced values are found in the Mo-impoverished shales deposited in a relatively near- shore, oxidising environment (page124, above). The enhanced values in the lower Namurian shales as a whole may therefore reflect higher Cu and V levels in the weathered parent materials, derived from the southern land surface, than in detritus trans- ported from the north during the upper Namurian and Westphalian. Levels of the remaining trace elements are similar in the lower Namurian and in the upper Namurian and Westphalian shales (lable23). Consequently, their concentration does not appear to have been influenced by the conditions which brough about the enrichment of As, Cu, Mot Se and V in the lower Namurian and Visean shales. The enhanced Fe203 values in the upper Namurian and Westphalian shales are consistent with the suggestion of Krumbein and Garrels (1952) that iron compounds are generally precipitated in relatively near-shore environments where streams may supply the iron. 135 CHAPTER 10. REGIONAL DISTRIBUTION OF METAL IN THE OVERBURDEN AND THE RELATIONSHIP BETWEEN THE METAL CONTENT OF THE BEDROCK, STREAM SEDIMENTS AND OVERBURDEN Preliminary soil samples were collected at 440 ft. intervals along regional traverses over the extensive Mo anomalous zones defined by the stream sediment reconnaissance; additional samples were collected on short local traverses as required. In both eases the sample depth was 12-18 ins. The metal content of the overburden developed on the principal bedrock and drift parent materials is summarised in Table 29). (i) MOLYBDENUM (a) Residual Soils The distribution of Mo on the regional traverses (Figs. 31 to 34) and the data in Table 29 clearly indicate that only soils derived from the lower Namurian and Visean shales are characteris- tically molybdeniferous, with values in the residual soils ranging up to 50 ppm Mo and a mean content of 6 ppm. In contrast, mean Mo values of less than 2 ppm are associated with the residual soils developed on the upper Namurian shales and sandstones) and on the Triassic sandstones in the south of the detailed study area. 1 Table 29 Ran e and mean metal content of overburden developed on the principal parent materials, south-west Pennines. Sample depth 12-18 in : data on minus 80-mesh fraction) Soil parent material Metal content (ppm) (No.) Mo* Cu As** V Pb Ga Ti Ni Co** Mn Cr Zn Fe2 03 (a) Residual soils Lower Namurian and <2-50 13-300 <5-220 30-400 10-160 4-30 1000- 5-130 <5-300 16- 30-160 20- 0.55- Visean. _ • shales 6000 >10,000 200 18.00 (68) 6 4o 14 120 30 16 2980 24 9 200 85 6o 2.41 Upper Namurian and <2 5-30 - 20-50 5-30 -30 850- 16-40' <5-30 100- 30-85 - 0.90- Westphalian shales 5000 1000 3.20 (9) <2 14 35 12 11 2600 26 11 320 50 1.65 Upper Namurian and <2-2 10-60 <5-25 30-130 .-200 11-40 1600- 5-40 5-30 30- 30-160 25- 0.70- Westphalian sand- ' 6000 1300 300 4.30, stones (50) <2 23 <5 60 25 18 -,. 3410 25 11 220 70 90 1.72 , Triassic sandstones <2-2 13-130 - 4o-60 40-4000 8-20 1600- 13-30 5-30 300- 30-85 - 1.05- 5000 2000 4.3o (11) <2 24 50 150 12 2560 20 10 600 45 1.47 7E) Transported soils Older drift, largely <2-10 10-60 5-95 40-160 8-1609 2-30 850- 10-160 <5-30 160- 40-300 30- 0.58- derived from lower 4000 1600 320 5.20 Namurian shales (21) 2 28 12 115 35 12 2420 35 12 430 90 115 1.91 Cider drift, largely <2-2 30-50 5-20 40-160 40-160 10-20 2000- 20-30 10-13 100- 30-100 60- 1.40- from Trias 4000 1300 240 3.80 (Ii) <2 45 8 90 6o 19 313o 28 11 255 6o 130 1.95 Loess mi±ed with <2-2 10-60 <5-45t 30-160 10-1300 2-30 850- 20-130 5-30 130- 30-130 65- 0.90- :limestone residues 5000 3000 70 75 9 2830 4o 800t 2.80 (30) <2 26 10 15 770 70 190 1.62 Newer Drift largely <2-3 5-50 - 30-130 5-130 6-30 1300- 8-60 <5-50 4o- 6000 40-16o - 0.70- derived from Trias 2000 5.0 (18) <2 19 70 21 10 2945 35: 15 32o 65 2.22 1 Geometric mean (No.) Number of samples except for 17.8 samples *Mean calculated with <2ppm = 1ppm **Mean calculated with <5ppm = 3 ppm 100 Fe 0 10 2 3 7. 0.1 10,000 1000 Mn 100 10 1,000 100 Co 10 1,000 ) m 100 Ni (pp t 10 Location of the soil traverses shown in Figs 31. 32, 33 L 34 n te n co l 1000 — ta Geological key to Figs 31. 32, 33 & 34 Me MO Pb 10 Tries 1000 Upper Namurian sandstones 100 Cu 10 Upper Namurian shales Sample depth 12-18 riches Data on —80—mesh fraction Lower Namurian 100 sandstones Mo 10 Lower Namurian shales Visean shales Peaty surf ace horizon — —11=1 1,400 11110 --I Carboniferous Limestone f t. Nara O.D. 1000 Me. / All Alluvium 600 14000 16000/1 4000 6000 8000 10000 12000 Fug 31 Relationship between metal content of the overburden and geology on Traverse 1. Data on minus-80—mesh fraction Geology after Holdsworth (1963A ) 100 - Fe 2 01 10000- 1.000 Mn 100 10 100 Co To .45 1000 100 Ni 10 1,000 100 As 10 .45 ) m (pp 10,000 t ten I,000 n Zn 100 co l ta 10 Me Pb Cu Mixon d, s1r.Ct 1,400 m.nersIded ground ft 1- loess Mine(%) 0 D 1.000 - 0, It - I All 1 / / I Fiq 32 Relationship between metal content of the overburden and geology on Traverse 2 Data on minus-BO-mesh fiactton Geology al ter I GS Sheet 81 (1867) and Morris (1966) 0 2000 4000ft 10- Fe203 01 1,000 Mn 1.000 100 — Co 10 1.000 100 E Ni a. 10 WOO _R 100 e Pb 2 ro 1000 100- Cu 10 100 Mo to I —Loess- 1,000 — 1 — Triassic drill — 1 t—Shale driit Alluvium ft OD 600 2000 4000 6000 11000 10000 12000 14000 16 00 el. Fig 33 Relationship between metal content of the overburden and geology on Traverse 3 Data on minus-80—mesh fraction Geology after IC S Sheet 72 118681 10 Fe2O3 of 1000 100 Mn to 101 CO 10 <5 1,000 too Ni 10 10,000 1,000 Pb 100 a) 10 0 100 - a) Cu to 100 Mo 10 42 (.400 - Mono (Pb) ft tpoo A , I-Drift - 1-Drat -I OD -42555Mssmomissae,. too 1 1 1 1 1 1 1 1 1 1 1 T 1 . I I 1 2000 4000 6000 11000 10000 12000 14000 1601:42ft Fig 34 Relationship between metal content of the overburden and geology on Traverse 4 Data on minus-SD-mesh fraction Geology after IG S Sheet 125 (1908) 137 Variations of Mo content within the residual soils on the lower Namurian reflect the composition of the parent material and the redistribution of Mo by pedological processes. Patterns related to the parent material can be attributed to changes in the Mo content of the shales and to the mixing of material from different sources by solifluction and ,:olluviation. Thus,the relatively low Mo content of the residual soils at the western end of Traverse 2 (Fig. 32) is probably due to either (i) dilution of Mo-rich shale parent material by barren colluvium from the sandstone outcrops shown in Fis. 20, or (ii) low Mo values within the shales inter- bedded with the sandstones (page 119, Chapter 9), Similar variations, associated with the outcrops of thin sandstones interbedded with the shaleslcan be recognised elsewhere on the regional traverses. Consequently, the Mo content of anomalous soils developed on shales interbedded with thin sandstones is generally more variable than where soils are residual on shales alone. In the moorland soils developed on the lower Namurian shales of Traverse 1 (Fig. 31) the gleyed mineral horizon, immedi- ately below the strongly acid surface peat, is impoverished in Mo, with values ranging from less than 2 ppm to 10 ppm and a mean of 2 ppm, owing to leaching (page 163, Chapter 11). The influence of pedo- logical processes on the distribution in detail of Mo in the overburden cannot, however, be demonstrated on the regional soil traverses and is therefore described in Chapter 11 dealing with metal dispersion in soil profiles. 138 (b) Transported soils Loess The loessial soils sampled on the west and south margins of the limestone plateau contain 2 ppm Mo or less.. Pigott (1962) has suggested that the loess was blown off the Namurian uplands between the limestone and the eastern limit of the Newer Drift (Figs. 20 and 21). Since it is reasonable to suppose that extensive deposits of wind-borne material, derived from adjoining bedrock sources, would be homogenised during transport, a theoretical Mo value can be estimated for a soil parent material originating on the drift-free north-east Staffordshire hills. Lower Namurian, Mo-rich shales outcrop over about 40 per cent of the.drift-free area, the remainder of which consists of barren, upper Namurian and Westphalian, shales and sandstones. Taking an average Mo content for the lower Namurian shales at 11 ppm and for all other bedrock sources at 1 ppm (Table 23 ), and estimated values of 40 per cent for the proportion of Mo-rich material incorporated into the loess (assuming that the amount of loess derived from any source is broadly related to the area of the source) and 80 per cent for the loessial content of soils on the limestone plateau (Pigott, 1962), the calculated Mo content for loessial soils derived from the Namurian uplands is 4 ppm. This value, based on a very approximate estimate of the proportion of Mo-rich loess, is only slightly higher than the actual Mo content of the loessial soils. 139 Consequently, the differences between the estimated and actual Mo values may not be significant and Mo content cannot be considered a very reliable indicator in discriminating between potential source areas. Nevertheless, the failure to detect any Mo values greater than 2 ppm in the loessial soils suggests that the loess was only partly derived from the drift-free north-east Staffordshire hills. Levels of the remaining trace elements, with less contrast between potential parent materials than Mo (Table 23), are not, however, sufficiently distinctive to indicate an alternative source. Older Drift The Mo content of the Older Drift, patches of which are . preserved on the higher ground of the Namurian uplands south of the limestone plateau (Figs. 33 and 34), varies considerably reflecting .ts origin. Drift: consisting largely of Triassic material and locally concealing Mo-rich lower Namurian shales, as on the middle section of Traverse 3 (Fig. 33), gives rise to distinctive red sandy-clay subsoils with a mean Mo content of less than 2 ppm. in contrast, soils developed on lower Namurian shale-drift are molybdeniferous but are generally difficult to distinguish from residual soils on shales unless erratics have been brought to the surface by ploughing. Consequently, the origin of the molybdeniferous drift- soils is best appreciated south of Bradbourne where drift smeared over the limestone inlier has weathered to Mo-rich loams (Figs. 11+o 20 and 33). Unweathered drift does not appear to have been preserved but the soils contain small shale fragments and occasional igneous erratics (page 169, Chapter 11). The Pennine ice-sheet advanced from the north and the Mo-rich drift was presumably derived from the outcrop of the lower Namurian shales, between one and two miles wide, which separates the inlier from the limestone plateau. Mo-rich drift-soils were not detected over barren bedrock elsewhere on the regional soil traverses and there is no evidence to suggest that similar deposits are extensive in the detailed study area. Smearing of molybdeniferous drift over barren bedrock has also been reported in Co. Limerick (Webb and Atkinson, 1965; Atkinson, 1967). Newer Drift Soils developed on the Newer Drift are widespread over the area underlain by molybdeniferous lower Namurian shales to the west of the north-east Staffordshire hills (Figs. 21 and 32). Their mean Mo content of less than 2 ppm reflects the composition of the non- local upper Namurian, Westphalian and Triassic detritus which is the principal constituent of the drift. (c) Relationship between the distribution of Mo in the bedrock, stream sediments* and overburden Comparison of the regional Mo content of the bedrock, stream sediments and overburden shows that they are generally closely *Regional geochemical sediment maps are included in Part 3 of the folder. related (Table 30). Furthermore, the extensive zones delineated by the anomalous stream sediments correspond to the areas within which molybdeniferous overburden is widespread. Thus on the drift-free hills in north-east Staffordshire the enhanced Mo levels in the lower Namurian shales (mean 11 ppm Mo) are reflected in the abnormally high Mo content of the residual soils (mean 6 ppm Mo) and of the stream sediments (mean 9 ppm Mo). South-east of Leek the boundary of the molybdeniferous zone in the overburden and defined by the stream sediment pattern coincides with the eastern limit of the Newer Drift and with the outcrops of Mo-impoverished sandstones and interbedded shales in the Morridge area (Figs. 20 and 32). Further to the west, over the ground covered by Newer Drift, glacial deposits are thick,3st in the valleys and, being readily eroded, constitute the bulk of the stream sedimen4 . Consequently, the metal Content of the transported overburden and stream sediments is similar and the average Mo value for both is less than 2 ppm. The low Mo values in the stream sediments also partly reflect the relatively thick development of Mo-impoverished sandstones and interbedded shales in this area (page 127, Chapter 9). In contrast, on the Namurian uplands south of the limestone plateau the patches of barren Triassic drift are only locally preserved on the higher ground and the mean Mo contents of the residual over- burden in the valleys (4 ppm Mo) and stream sediments (8 ppm Mo) reflect the primary geochemical pattern. Mo values of 2 ppm or 1 Table 30 Mean metal content of bedrock, soils and stream sediments from the south-west Pennines (soil and sediment data on minus 80-mesh fraction: whole rock analysis) • Parent material and area Media Metal content (;pm) % Co Mn Cr Zn Fe 0 (No) ! Mo Cu, As J Pb Ga Ti Ni 2 3 1 (i) Bunter sandstones S. I Residual soil <2 2t6 - 30 150 112 2560 20 10 600 45 - 1.47 Derbyshire, 1 (11) Sedtro is <2 33 <5 30 100 8 1450 24 10 230 40 165 1.06 (ii) lippr Namurian and Lower, Westphalian, N.E. Staffordshire (a) Sandstones Sandstone <2 16 - 50 17 10 2890 35 15 210 40 - 2.17 (9) Residual soil i <2 23 <5 60 25 18 3410 25 11 220 70 90 1.72 (50) (b) Shales i Shale • 2 45 <5 135 32 18 4440 105 50 630 90 - 4.90 (n) i Residual soil i <2 14 - 35 12 11 2600 26 11 320 50 - 1:65 k (9) (c) Interbedded shales I Sediments ! <2 30 11 55 35 7 1650 35 15 220 60 113 2.00 and sandstones (38) (iii) Lower Namurian and Shale I 11 110 177 265 25 19 4500 100 30 905 100 - 2.19 Visean Shales (73) i (a) Drift-free, N.E. Residual soil. 6 4o 14 120 30 16 2980 24 9 200 85 6o 2.41 Staffordshire hills (68) Sediments 9 70 14 115 40 13 2220 90 30 460 70 330 3.37 (38) (b) Uplands south of Soils 4 35 15 105 45 14 2810 30 13 390 80 110 1.98 limestone plateau; (84) Triassic drift on 8 high ground Sediments 50 10 80 350 10 1960 55 19 535 55 345 2.29 (41) (c) Shales interbedded Soils <2 19 - 70 21 10 2945 35 15 320 65 - 2.22 with quartzites; (18) Drift in principal valleys, N. Sediments <2 39 <5 45 22 9 1515 40 18 275 50 120 1.57 (40) Staffordshire (iv) Limestone Plateau Limestone <2 2 - 75 4 <2 55 <5 <5 135 4 - 0.17 (5) Loessial soil <2 26 10 70 75 9 2830 40 15 770 70 190 1.62 . (30) 1 Geometric mean; (No) No. of samples except t30 samples 143 less are associated with the remaining parent materials and with their weathering products represented by the overburden and the stream sediments. Within the anomalous catchments the Mo content of the overburden is generally more varied than in the associated stream sediments. This reflects the heterogeneous nature of the overburden whereas the stream sediments, by virtue of their origin, represent a more or less composite sample of the weathering products upstream of the sample point. The similarity between the mean Mo content of the residual overburden and stream sediments indicates that Mo largely enters the drainage channel by the erosion of the bank soils. This contrasts with the dispersion of relatively mobile elements, such as Co and Mn, reported on page 148. The factors influencing the mobility of Mo in the overburden are considered in detail in Chapter 11. (ii) OTHER ELITMENTS The principal geochemical patterns of the remaining elements reflect (i) the enhanced metal content of the lower Namurian and Visean shales, (ii) base metal mineralisation, and (iii) the influence of the secondary environment on the primary geochemical pattern. The patterns are summarised below. 11+4 (a) Geochemical patterns in the overburden related to primary syngenetic dispersion Levels of trace elements in the overburden developed on the principal bedrock and drift parent materials are summarised in Table 29 . The only significant pattern directly related to the distribution of trace elements in the bedrock is the enhanced metal content of the overburden-developed from the lower Namurian and Visean shales. As, Cu and V are enriched in residual and Older Drift soils derived from the Mo-rich shales and the general distri- bution of these elements is similar to Mo. The dispersion of Cu and V has, however, been modified by the influence of the secondary environment leading to a reduction in the contrast between over- burden developed on the lower Namurian shales and - on other parent materials (see page 149). The Cu pattern has also been modified by mineralisation (below, page 145). In view of the association between Se and Mo in the lower Namurian shales and anomalous stream sediments,a few selected samples of molybdeniferous subsoils were analysed for Se (Webb et al, 1966a). The samples were collected from 'flush' and low-lying sites with very poorly-drained peaty soils which Irish experience has shown to be favourable to the accumulation and uptake of Se by herbage (Webb and Atkinson, 1965; Atkinson, 1967). .Se values were found to vary between 1.5 and 7.0 ppm with a mean of 4.0 ppm Se compared to normal background levels of less than 0.2 ppm. The Mo content of the anomalous soils was between 8 and 45 ppm with a mean of 20 ppm Mo. The results are of particular interest since, 11+5 together with data from North Wales and south-west England, they provide the first evidence of seleniferous soils in Britain. The relationship between the Se content of the topsoil and herbage is reported in Chapter 12. (b) Geochemical patterns in the overburden related to mineralisation Base metal anomalies in the overburden reflect (i) minerali- sation in the lower Namurian shales and Visean shales with limestoneq, (ii)mineral deposits around the margins of the limestone massif, and (iii)the distribution of metal-rich horizons in the Bunter Pebble Beds. Mineralisation in the lower Namurian shales and Visean shales with limestones Base metal anomalies detected on Traverse 2 (Fig. 32) reflect mineralisation worked from the now disused Mixon Copper Mines near Onecote and the Hays Brook Lead Mine at Warslow. The mineral deposits have been described by Green et al (1887). The mineralisation around Mixon is reflected by Cu, Pb and Zn anomalies in the residual overburden of Traverse 2,which crosses the mineralised zone some two-fifths of a mile south of the mine workings. The extent of the aineralisation, based on the width of the geochemical anomalies, corresponds to the outcrop of the Visean shales and limestones in the core of the north-plunging Morridge Anticline. 146 The metal content of the overburden is compared with background and threshold values* for residual soils on the lower Namurian and Visean shales in Table 31 . The Zn anomaly is both widest and most intense with Zn values up to 20x the calculated threshold value; peak values of Zn (greater than 4000 ppm) and Pb (300 ppm) coincide. In contrast, the Cu anomaly is relatively weak and maximum values of 200 ppm Cu are only slightly above the threshold level. This partially reflects the high threshold Cu content of the shales due to syngenetic enrichment (see Chapter 9). Although not investigated in detaillthe metal content of uncontamin- ated sediments in streams draining the mineralised ground appears to be of the same order as the mean metal content of the overburden (see the Regional Geochemical maps in Part 3 of the folder). Base metal anomalies were also detected in residual overburden on the lower Namurian shales further east on Traverse 2, near the Hays Brook Lead Mine at Warslow. Zn values again show maximum contrast with values between 140 and 2200 ppm Zn. Pb values range from 100 to 700 ppm and Cu from 40 to 300 ppm. The maximum values are probably due to contamination from the mine dumps and the stream draining the mineralised zone is also contaminated. *The data are approximately lognormally distributed and the threshold value was therefore calculated as the mean plus twice the log standard deviation (Hawkes and Webb, 1962). Table 31 Range and mean* Cu, Pb and Zn content of residual soils on the lower Namurian and Visean shales, from mineralized and back- ground areas, north-east Staffordshire (sample depth 12-18 ins. data on minus 80-mesh fraction) Metal Metal content (ppm) Calculated threshold). Background Mineralized ground (PPm) Cu 13 - 300 20 - 200 4o 7o 14o Pb 10 - 160 40 - 300 30 100 70 Zn 20 - 200 50 - 4000 6o 46o 175 No. of samples 68 10 *Geometric mean 'Threshold = background mean + 2 x 13g standard deviation 148 Mineralisation on the mar ins of limestone massif The extensive mineralisation on the southern margin of the limestone massif (Fig. 15) is reflected by a Pb anomaly in the mixed residual-loessial overburden at the northern end of Traverse 4 (Fig. 34). Pb values range from 85 to 6000 ppm; maximum values were detected close to the spoil heaps of the disused Doglow Lead Mine and are probably due to contamination. Pb and Zn anomalies on the Bunter Sandstones Enhanced levels of Pb (200 to 4000 ppm) compared to back- ground levels of less than 100 ppm were detected in three samples of red-brown sandy-loam derived from the Bunter Sandstones at the extreme southern end of Traverse 4 (Fig. 34). Pb values in two reconnaissance stream sediments within the anomalous catchments are 850 and 1000 ppm. The anomalies may reflect either (i) the distri- bution of Pb- and Zn-rich limonitic pseudomorphs after mineralised pebbles in the Bunter Pebble Beds, or (ii) metal-rich limonitic precipitates from circulating groundwaters (Taylor et al, 1967). (c) Relationship between the distribution of trace elements other than molybdenum) in the bedrock, stream sediments and overburden The mobility of Co, Mn and Ni, together with is Fe203 reflected by their very irregular distribution along the regional soil traverses, this being most marked in soils developed on the lower Namurian shales (Figs. 31 to 34). Sporadic enhanced values, apparently unrelated to the bedrock metal patterns, clearly 149 indicate the lateral and vertical redistribution of these elements within the overburden. Comparison of the mean metal content of bedrock and over- burden shows that levels of Co, Cu, Mn, Ni and V are appreciably lower in soils developed on shales than in the parent material (Table 30). This may reflect either (i) the redistribution of these elements within the overburden as a result of the pedolo- gical processes considered in detail in Chapter 11, and/or (ii) leaching from the overburden and their dispersion in the drainage channels. No such trend can be recognised for soils developed on sandstones. Consequently,the contrast for Co, Cu, Mn, Ni and V between shales and sandstones is reduced during weathering. The reduced contrast for Co, Cu, Mn, Ni and V in the overburden on adjoining outcrops of shale and sandstone is con- sistent with the relative susceptibility of shales to chemical weathering. Thus metals concentrated in shales by sorption on clays and organic matter or associated with sulphides are probably more readily mobilized during weathering than the elements bound up in the resistant constituent minerals of sandstones. The apparent immobility of the trace element content of the sandstones may, however, partly reflect the sampling technique employed. In soils derived from sandstones the unground minus 80-mesh fraction retained for analysis may consist of relatively metal-rich material remaining after substantial amounts of barren, coarse sand have been removed. Consequentlyi the relationship between the metal 150 content of the parent material, based on whole rock analysis, and the soils is obscured. In soils derived from shales this effect is negligible since the bulk of the soil consists of minus 80-mesh material (page 177, Chapter 11). Once mobilized in the overburden trace elements may migrate in the circulating groundwaters and eventually enter the drainage channels. Subsequently dispersion may take place in solution or the elements may be concentrated in the sediments by sorption or coprecipitation brought about by changes in the Eh-pH regime. In the present study, sediments of streams draining the lower Namurian shales are enriched in Co, Mn and Ni compared to levels in the overburden. Thus on the north-east Staffordshire hills sediments of catchments in which poorly-drained agricultural soils predominate are enriched in Co (3x), Mn (2x) and Ni (3x), and a similar trend can also be recognised on the lower Namurian shales south of the limestone plateau (Table 30) . In the latter area, however, the contrast between the media is reduced - Co (14x), Mn (lix) and Ni (2x) - as a possible result of the milder climate and the improved drainage conditions. Following experience in North Wales (page 53, Chapter 4; Nichol et all 1967), the enrichment of Mn (26x) and Fe203 (3x) is greatest in streams draining the acid, waterlogged moorland soils of Traverse 1 (Fig. 31; Table 32). This presumably reflects enhanced mobilization and leaching by acid circulating groundwaters followed by precipitation in the drainage channels owing to 151 Table 32 Range and meant metal content of soils and stream sediments from moorland and areas of poorly-drained agricultural soils (soil sapling depth 12-18 ins. data on minus 80-mesh fraction). Moorland Agricultural Land Element Soil Sediment Soil Sediment Co* <5-40 5-130 <5-300 10-50 (ppm) 6 27 9 28 Mn 10-160 40-6000 16->l0,000 loo-4000 (ppm) 30 66o 200 46o Ni 8-85 30-300 5-130 30-160 (ppm) 35 90 24 90 Fe203 0.64-4.70 2.70-9.40 0.55-18.00 1.50-7.20 1.78 5.14 2.41 3.37 (%) • No. of Samples 23 9 68 38 tGeometric mean *Mean calculated with <5 ppm = 3 ppm 152 increased Eli and pH. The absence of a similar trend in streams draining the moorland on the upper Namurian and Westphalian south- west of Buxton probably reflects the dilution of the sediments by barren detritus from the massive sandstone outcrops interbedded with the shales. The secondary environment,thereforel has a considerable influence on the redistribution of Co, Mn and Ni during weathering, with levels in the overburden derived from shales, reduced and levels in the associated stream sediments enhanced. Recognition of this trend is of particular significance to the application of stream sediment surveys to agricultural trace element problems since the metal content of the sediments may have little direct relationship with that of the overburden. 153 CHAPTER 11. METAL DISTRIBUTION IN THE OVERBURDEN The distribution of Mo and other trace elements is described in soil profiles and size fractions of residual and transported overburden derived from the Mo-rich lower Namurian and Visean shales. Metal distribution is related to the influence of pedological and biological processes. (i) METAL DISTRIBUTION IN SOIL PROFIT,FS The regional soil data reported in Chapter 10 clearly indicate that Mo levels consistently higher than the limit of detection (2 ppm) of the routine spectrographic method used are only associated with the overburden derived from the lower Namurian and Visean shales. Preliminary soil profile studies corroborated the regional data and disclosed significant variations of Mo content between the horizons of the molybdeniferous soils. In contrast, on barren parent materials Mo values in the overburden are characteristically 2 ppm and less throughout the profile: the considerable additional effort necessary to determine the actual Mo content was not considered to be warranted. Consequently, detailed investigation of the influence of pedological factors on metal distribution in the overburden was confined to molyb- deniferous soils derived from the lower Namurian and Visean shales. Representative profiles, selected on the basis of the regional soil 154 traverse and preliminary profile data, were examined by pitting and samples collected from each horizon. Sample preparation and analysis have been fully described in Chapter 7. (a) Residual profiles Molybdeniferous residual overburdens derived from the lower Namurian and Visean shalos,is widespread on the north-east Staffordshire hills and on the Namurian uplands south of the limestone plateau (rigs. 31-34; Chapter 10). Poorly-and very poorly-drained soils predominate. Apart from the small area of semi-natural moorland soils preserved on the most exposed part of the north-east Staffordshire hills (Fig. 31) the residium has generally been modified by agricultural management. Metal distribution in profiles on farmland is considered first. Farmland The profiles investigated represent a range of drainage conditions from very poorly-drained (4 and 29), poorly-drained (8 and 37) and imperfectly-drained (28) to well-drained (26). Sample site and profile descriptions are summarised in Table33 and the analytical data are presented in Table 34. Despite differences of metal content similar dispersion patterns can be recognised in several of the profiles. Although variously modified by the local drainage conditions the principal and most general trend is the increase of metal concentration with depth. In this respect metal distribution in Profiles 28 and 29 is particularly interesting. 155 Table 33 Profile descriptions of residual soils developed on the lower Namurian and Visean shales in north-east Staffordshire and southern Derbyshire Profile 29 Location: High Cross Farm, Bradnop, Staffordshire. (grid ref. SK 025555) Relief: gentle slope, SW aspect, below sandstone escarpment at 1150 ft. 0.D.- Land use: permanent pasture. Drainage: very poor, slte frequently waterlogged. Depth (ins): (sample no.) 0-5 Very dark grey* sandy loam with yellowish red mottles (3522) along old root channels; abundant roots; clearly defined boundary to - 5-16 Grey, sandy clay loam with strong brown mottles; few (3523) roots; occasional pieces of sandstone; many mangan- ese concretions; wet; merging boundary to - 16-19 Strong brown, secondary iron oxide indurated clay (3524) loam; mottled grey and with grey clay linings along old root channels; sharp boundary to - 19-30+ Grey clay with sporadic strong brown mottles; pieces (3525) of sandstone; very wet. Profile 4 Location: Upper Brownhill Farm, Warslow, Staffordshire (grid ref. SK 084595) Relief : moderate slope, E aspect at 1025 ft. 0.D. Drainage: very poor. Land use: permanent pasture (cut for hay). Depth (ins. ) : (sample no. 0-9 Very dark greyish brown(clay with traces of ochreous (3527) mottling along old root channels; abundant roots; clearly defined boundary to - 9-14 Light yellowish brown clay with strong brown mottles; (3528) few roots; manganese concretions and occasional shale fragments; merging boundary to - 14-30+ Grey clay with strong brown mottling; sporadic (3529) manganese concretions; numbroun shale and sand- stone fragments. *Munsell Soil Colour 156 Table 33 (continued) Profile 8 Location: New Barns Farm, Hollinsclough, Staffordshire (grid ref. SK073665) Relief: gentle slope, NE aspect at 925 ft. 0.D. Drainage: poor. Land Use: permanent pasture (cut for hay) Depth (ins.): (sample no.) 0-6 Very dark greyish brown clay loam with ochreous mottles (3531) along old root channels; abundant roots; merging boundary to - 6-11 Dark greyish brown clay with ochreous mottles along old (3532) root channels; few roots; occasional pieces of sand- stone and shale; manganese concretions; clearly defined boundary to - 11-17 Light brownish grey clay mottled brownish yellow; (3533) occasional pieces of shale and sandstone; merging boundary to - 17-30+ Dark grey clay mottled brownish yellow and black (3534) speckles of weathering shale; large prismatic structures with grey faces. Profile 37 Location: Biggin, Hulland, Derbyshire (grid ref. SK256488) Relief: moderate slope, ENE aspect at 500 ft. 0.D. Drainage: poor. Land use: permanent pasture. Depth (ins): (sample no.) 0-3 Dark greyish brown sandy clay with ochreous mottles (3544) alorig old root channels; abundant roots; merging boundary to - 3-9 Dark greyish brown and dark brown clay; few roots; (3545) occasional Bunter quartzite pebbles; clearly defined boundary to - 9-25 Yellowish brown and strong brown clay loam; occasional (3546) Bunter quartzite pebbles; Mn concretions towards base; sharp boundary to - 25-30+ Light grey clay mottled reddish yellow; wet; man- (3547) ganese concretions, especially in lower part. 157 Table 33 (continued) Profile 28 Location: New Mixon Hay Farm, Onecote, Staffordshire (grid ref. SK034570) Relief: moderate slope, SW aspect at 1200 ft. 0.D. Drainage: imperfect Land use: permanent pasture (cut for hay and silage) Depth (ins.): (Sample no.) 0-2 Dark greyish brown silty clay with traces of mottling (3516) along old root channels; abundant roots; clearly defined boundary to - - 2-8 Dark brown and very dark brown clay; abundant shale (3517) fragments; clearly defined boundary to - 8-16 Dark yellowish brown clay with small shale fragments; (3518) sharp boundary to - 16-19 Dark grey to brown clay with prominenttstrong brown (3519) mottles; abundant shale fragments; sharp boundary to 19-25 Soft black weathered Visean shales (3520) Hard limestone band in shales. (3521) Profile 26 Location: Mount Pleasant Farm, Upper Elkstone, Staffordshire (grid ref. SK056588) Relief: steep slope, E aspect at 1050 ft. 0.D. Drainage: good Land use: permanent pasture Depth (ins): (Sample no.) 0-2 Very dark greyish brown clay loam with abundant roots; (3560) clearly defined boundary to - 2-6 Very dark greyish brown clay with traces of mottling (3561) along old root channels; few roots; occasional pieces of sandstone; clearly defined boundary to - 6-18 Dark greyish brown clay with numerous shale fragments (3562) 18+ Weathered, steeply dipping, disturbed shales. (3563) Table 34 Metal content of residual soils developed on the lower Namurian and Visean shales in north-east Staffordshire and southern Derbyshire (see also Table 33 ). Sample Depth % % Metal content (ppm)* No. (ins.) pH clay Fe203t Mo Cu EDTA.Cu Pb Ga V Ti Ni Co Mn Cr As Profile 29: very poorly-drained on gentle slope below sandstone escarpment; permanent pasture, 3522 0-5 6.2 14 10.0 10 4o 13.5 loo 6 130 3000 85 20 1600 85 30 3523 5-16 6.5 32 18.5 4o 5o 4.4 3o 20 200 6000 200 50 4000 160 30 3524 16-19 6.4 32 30.0 6o 100 9.5 8 8 300 4000 300 5o 4000 85 65 3525 19-30+ 6.5 4o 9.o 6 85 10.0 16 13 130 3000 130 13 1000 130 5 Profile 4: very poorly-drained on moderate slope_. 3527 0-9 5.6 48 5.o 16 6o 14.8 4o 16 300 5000 4o 8 500 160 5 3528 9-14 5.7 56 5.6 3o 50 6.3 3o 20 300 6000 3o 10 600 16o 45 3529 14-30+ 5.9 52 3.o 5 5o 5.1 8 16 160 5000 3o 8 400 130 5 Profile 8: poorly-drained on gentle slope. 3531 0-6 6.2 36 8.6 20 6o 18.0 130 20 200 6000 30 10 500 130 40 3532 6-11 6.2 54 14.o 3o 130 14.0 130 3o 400 6000 3o lo 300 160 5 3533 11-17 5.8 72 1.7 13 20 10.3 6 6 130 2000 16 5 130 loo 5o 3534 17-30+ 5.2 70 5.2 2) 160 17.0 4o 3o 20o 4000 20 5 50 60 15 (Total iron expressed as Fe 0 2 3 *Total trace element values based on analysis of minus 80-mesh fraction ZDTA-extractable Cu based on analysis of minus 10-mesh fraction Table 34(continued) Sample Depth % % Metal content (ppm)* Mo Cu EDTA.Cu Pb Ga V Ti Ni Co Mn Cr As No. (ins.) pH clay Fe203 • Profile 37: poorly-drained on moderate slope; permanent pasture. 3544 0-3 6.4 28 2.4 lo 40 24.3 5o 5 300 1000 40 10 '3000 200 15 3545 3-9 6.4 53 7.6 30 160 22.0 130 20 400 4000 85 50 4000 400 15 3546 9-25 6.7 40 7.6 4o 300 22.5 4o 20 400 4000 160 50 1000 400 15 3547 25-30+ 6.6 72 8.0 20 130 11.0 10 13 400 4000 4o 10 200 200 30 Profile 28: imperfectly-drained on moderate slope. 3516 0.2 6.6 4o 2.3 6 85 28.3 160 8 300 woo 4o lo 3000 13o 5 3517 2-8 6.6 52 2.8 16 160 26.4 160 6 400 2000 40 20 1300 160 5 3518 8-16 4.9 64 2.4 16 40o 39.3 85 6 600 2000 160 30 1600 300 13 5319 16-19 4.9 64 4.6 6o 600 77.o 13o 16 1300 6000 loo . 16 600 500 35 3520 Shale - - 1.9 30 200 - 60 6 85o 6000 60 13 60o 300 - 3521 Limestone - - 0.6 2 13 - 20 2 300 600 16 5 130 40 - Profile 26: well-drained on steep slope; permanent pasture. 3560 0-2 6.6 32 2.7 4o loo 14.8 300 30 200 5000 5o 5 600 160 25 3561 2-6 6.6 48 1.7 16 4o 14.0 16o 8 130 3000 4o 5 160 5o 15 3562 6-18 6.2 52 1.9 3o 4o 9.3 130 16 200 3000 30 5 200 130 32 3563 Shales - - 0.62 6 10 - 30 13 200 5000 8 5 8 30 - tTotal iron expressed as Fe203 *Total trace element values based on analysis of minus 80-mesh fraction EDTA-extractable Cu based on analysis (...f minus 10-mesh fraction. 1-1 160 Profile 28 Almost the whole of the profile is relatively well-drained and mottling - indicating impeded drainage - was only detected in the lowest horizon which rests directly on weathered Visean shales. The Mo content of the shales is 30 ppm. Regular application of lime to the topsoil is reflected by the contrast between the pH of the upper horizons (pH 6.6) and the subsoil (pH 4.9). Metal content varies from horizon to horizon with levels of all trace elements except Co, Mn, Ni and Pb increasing with depth. Metal values are therefore enhanced in the gleyed horizon at the base of the profile with maximum contrast between this horizon and the top- soil for Mo (10x), As (>7x), Cu (7x), Ti (6x), Cr and V (4x) and Fe* (2x). The gleyed horizon is also metal-rich relative to the underlying shales with appreciably higher levels of Cu (3x), Fe (2ix) and Mo (2x). Compared to the shalest the overburden as a whole is enriched in Cu, Mn and Pb (2x), and impoverished in Ti (2x): mean levels of the remaining elements are similar. The increase of metal content towards the base of the profile is unlikely to reflect elastic dispersion within the over- burden since, (i) the upslope soils are developed on similar parent *Total iron is referred to as 'Fe' throughout the text to avoid confusion with soil ferric oxides: in the tables total iron is expressed as Fe203. tSize fraction analysis shows that the bulk of soils derived from shale parent materials consists of minus 80-mesh material (page below). Consequently, considering the precision of the spectrographic method employed, direct comparison with rock data (whole rock analysis) is acceptable. 161 material and the possibility of dilution of the upper horizons of the profile by barren colluvium is therefore remote, and (ii) although the proportion of clay-size material increases with depth the mechanical eluviation of metal-rich clays is inadequate to account for the magnitude of the contrast between metal values in the top- soil and the gleyed horizon (see also page 181, below). Consequently, the distribution of Mo and associated trace elements in Profile 28 is largely attributed to leaching from the upper horizons, and from upslope soils, followed by fixn.tion on clays or ferric oxides towards the base of the profile. Profile 29 Drainage within the overburden is very poor and the site, which is situated on the gentle slope at the foot of a sandstone ridge, is frequently waterlogged. The strongly mottled subsoil merges into a diffuse zone of semi-indurated secondary ferric oxides deposited immediately above the water-table: manganese oxide con- cretions are also abundant. Below the water-table the predominance of grey colours, and the absence of mottles and concretions, reflects the reduced state of the iron. The profile has an abnormally high Fe content with levels increasing from 10% in the topsoil to more than 30% in the ferruginous zone and then falling to W in the underlying reduced horizon. Metal distribution shows a similar trend. Levels of As, Co, Cu, Mn, Mo, Ni and V increase down the profile with maximum values in the mottled subsoil and/or the ferruginous horizon. Contrast between the 162 ferruginous horizon and the underlying gley, which is impoverished in trace elements, is greatest for As (>13x) and Mo (10x). The accumulation of Fe is attributed to precipitation from circulating groundwaters after leaching from upslope soils. Con- centration of the secondary ferric oxides in the zone immediately above the water-table probably reflects precipitation in the zone most frequently wetted by fluctuations of the groundwater level and leaching within the profile. Bloomfield (1963) has suggested that, once formed, a zone of hydrous ferric oxides would have an ever increasing capacity to adsorb and convert ferrous ions to more ferric oxide. The enhanced Mo levels (60 ppm) in the ferruginous zone probably reflect the outstanding ability of ferric oxides to adsorb dissolved Mo species (Jones, 1957). This is partly borne out by the relatively low Mo content (6 ppm), possibly associated with clay minerals, in the reduced zone. Subsequent size-fraction analysis indicated that whereas Co, Mn and Mo, and possibly Cu and Ni, appear to be associated with the secondary ferric oxides, V is associated with the clay fraction (page 181, below). Consequently the increase of V values with depth in Profile 29 may partly reflect mechanical eluviation of the clays. The influence of pedological processes on metal distri- bution is less clearly defined in the remaining profiles. Except for the increase of Mo, Cu, V and Fe values towards the base of Profile 37 no consistent trends can be recognised. The absence 163 of significant variations of metal content with depth in Profile 26 reflects the relative immaturity of the shallow overburden (depth 18 ins.) developed on a steep slope. The enhanced metal values in the overburden compared to the underlying shales - Mn (25x), Mo (5x), Cr, Cu, Ni and Pb (4x) and Fe (3x) - are probably due to colluviation from upslope metal-rich shale horizons. The enhanced Mo values in the upper horizons of Profile 4 may also reflect collu- viation. Moorland Peaty gleys are developed on the lower Namurian shales on the wettest, most exposed parts of the north-east Staffordshire hills (Figs. 21 and 31). A typical profile is described in Table. 35 and the corresponding analytical data are presented in Table 36; supplementary data based on auger sampling arc summarised in Table 37. Profile 24 is distinguished from the very poorly-drained soils on farmland (Profiles 4 and 29, Tables 33 and 34 ) by the development of a strongly acid peaty surface horizon (pH 3.8). Compared to the underlying mineral soil the peat is impoverished in all trace elements except Cu and Pb which appear to have accumu- lated as a result of fixation by organic matter. Whereas Pb values are abnormally high throughout the peat,Cu is only concentrated at the surface and values decrease with depth. Since EDTA-extractable Cu shows a similar trend, the distribution of Cu within the peat may partly reflect the breakdown and leaching of Cu-organic complexes. 164 Table 35 Profile description of a representative peaty gley soil developed on the lower Namurian shales in north-east Staffordshire Profile 24 Location: Morridge, Staffordshire (grid ref. SKJ38628) Relief: moderate slope, ENE aspect at 1425 ft. 0.D. Drainage: very poor Land use: moorland Depth (ins.): (Sample no.) o-i+ Wet black peat with abundant roots; sharp boundary (3554) to - 1+-7 Brown fibrous peat with few roots; sharp boundary (3555) to - 7-10 Wet black peat; sharp boundary to - (3556) 10-14 Humus stained wet clay with reddish yellow mottles (3557) towards the base; occasional pieces of sandstone; clearly defined boundary to - 14-22 Light grey clay with prominent strong brown mottles; (3558) rootless; wet; abundant pieces of sandstone; clearly defined boundary to - 22-30+ Grey clay without mottling; very wet; abundant (3559) shale and sandstone fragments. Table 36 Metal content of a representative profile of a moorland peaty gley derived from the lower Namurian shales in north-east Staffordshire (see also Table 35) Sample Depth Metal content (ppm)** 0 t Mo Cu EDTA Cu Pb Ga V Ti Ni Co Mn Cr As No. (ins.) pH ign.loss Fe2 3 clay Profile 24: very poorly-drained moorland profile with peaty surface 3554* 0-4 3.8 90.2a 0.2 2 85 21.0 100 2 13 85 10 2 50 5 - 3555* 4-7 3.8 81.1: 0.3 2 26 10.0 120 2 32 1000 8 3 60 26 - 3556* 7-10 3.8 70.0 0.3 2 3 - 90 2 26 600 5 5 120 12 3557 10-14 4.1 48 2.0 2 20 1.4 40 30 160 6000 20 5 85 200 5 3558 14-22 4.3 52 2.5 2 20 30 10 130 4000 10 5 30 200 13 3559 22-30 5.2 48 3.5 5 50 14.8 60 5 200 5000 60 10 200 600 5 tTotal iron expressed as Fe 0 2 3 a *Peaty surface horizons, analytical values corrected for % ignition loss . **Total trace element values based on analysis of minus 80-mesh fraction, EDTA-extractable Cu based on analysis of minus 10-mesh fraction. 166 The results accord with the conclusion of Vinogradov (1959) that, although Cu is fixed by organic matter in the surface horizons of peaty soils, the acid-reaction of the humus favours its removal from the soil. In the horizons beneath the peat, Cr, Cu, Mn, Mo and Ni increase towards the base of the profile with maximum values in the waterlogged clay below the water-table. Since there is no evidence of mechanical eluviation,the variation of metal content is attributed to leaching by acid waters percolating through the peat and the comparatively freely-drained upper horizons of the mineral soil. The unusually low quantities of Cu (1.4 ppm) extracted by EDTA from the humus-stained horizon immediately below the peat shows that almost the whole of its relatively loosely held Cu has been mobilized and leached. Comparison of metal distribution in the peaty gleys and poorly-drained agricultural soils indicates that intense leaching of the overburden in the moorland environment is generally confined to the upper part of the mineral soil within a few inches of the base of the peat (Table 37). Thus the moorland soils sampled just below the peat (12-18 ins.) are relatively impoverished in Mn (26x), Mo (7x), Cu and Ni (3x), and Fe and V (22x), whereas at a slightly greater depth (24-30 ins.) only Mn (10x) and possibly V (2x) are significantly depleted. The increase of the average Mo content of the peaty gleys with depth, from 2 ppm at 12-18 ins. to 7 ppm at 24-30 ins. is particularly striking and contrasts with the usual Table 37 Range and mean metal content of poorly-drained agricultural and moorland soils developed on the lower Namurian shales., north-east Staffordshire Sample Depth Metal content (ppm) Mo Cu V Ni Co Mn (ins) Pb Ga Ti Cr Fe203 (a) Moorland soils (peaty gleys and peaty gley-podzols) 0-6 <2-5 20-80 40-180 5-10 9-100 450-5000 5-20 2-7 15-105 16-100 0.42-1.86 (6)t <3 25 114 7 39 2100 13 4 33 42 1.10 12-18 <2-4 7-30 15-50 <2-20 60-130 300-6000 7-4o <5-20 10-50 17-160 0.36-2.90. ,. (6) <2 22 32 <12 92 3900 24 <8 87 1.88 24-30 <2-15 3o-6o 3o-85 10-3o 60-200 3000- 30-60 10-20 30-60 85-160 2.30-6.20 (5) <7 48 49 18 112 6000 46 15 44 121 4.36 5000 (b) Poorly-drained agricultural soils o-6 4-25 20-160 50-160 5-20 130-4000 2000- 30-160 5-30 130-4000 100- 1.10-8.8o (10) 4000 300 13 67 91 13 197 3100 65 16 1149 171 4.50 12-18 3-30 13-200 20-160 6-20 4o-600 1300- 20-16o <5-40 30-5mo 30-200 1.70-10.50 4000 (lo) 14 59 52 14 203 3000 66 <14 864 168 4.73 24-0 <2-40 20-200 20-60 6-20 100-1000 2000- 30-130 <5-60 30-2000 40-400 1.70-19.0 4000 ( 9) <12 73 37 13 26o 3000 ft <19 460 183 5.03 *Peatl results corrected for ignition loss 'dumber of samples in parenthesis 168 enhanced mobility of Mo associated with alkaline conditions (Jones, 1957; Titley, 1963; Hansuld, 1966). The results (Table 37) also corroborate the data presented in Chapter 10 where it was shown that, compared to the metal content of stream sediments of catchments in which poorly-drained agricultural soils predominate, only Mn is significantly enriched in the sediments of the moorland streams (Table 32). The data in Table37 also show that the peaty moorland topsoils are impoverished, relative to the topsoils (0-6 ins.) of the poorly-drained agricultural soils, in Fe and all trace elements except Pb. (b) Transported overburden Metal distribution is described in (i) soils developed on the Mo-rich Older Drift derived from the lower Namurian shales, and (ii) alluvial soils alongside the principal streams draining catchments in which the lower Namurian and Visean shales outcrop. All the profiles described are situated on farmland. Soils derived from the Mo-rich Older Drift Although drift-soils derived from the lower Namurian shales are probably widespread on the uplands south of the limestone dome, their detailed distribution is largely unknown. Preliminary soil sampling disclosed Mo-rich soils on the limestone inlier south of Bradbourne which have been attributed to the smearing of Mo-rich drift from the lower Namurian shales outcropping between the inlier and the limestone plateau (Fig. 33; page 139, Chapter 10). 169 A typical soil profile is described in Table 38 and the corresponding analytical data are presented in Table 39. The subsoil of Profile 42 is a well-drained, brown clay loam - with small shale framents, pieces of sandstone, limestone and chert and sporadic rounded quartzites and igneous erratics - resting directly on the weathered surface of the limestone. Fissures in the limestone are partly filled by an intimate mixture of the clay loam and a dark red clay which is believed to consist largely of limestone residues similar to those described by Pigott (1962). Unweathered till does not appear to have been preserved. The metal content of the overburden is similar to that of the residual soils developed on the lower Namurian shales and the contrast with the trace element impoverished limestone is particularly striking. Within the overburden metal content increases towards the base of the profile with maximum contrast between the fissure filling and the topsoil for Cr (15x), V (12x), Mo and Ga (8x), Ni and Ti (5x) and Fe (4x). Since (i) the drift parent material would probably have been thoroughly homogenised during transport, and (ii) the increased clay content of the lower part of the profile is inadequate to account for the metal contrast between horizons, the increased values of certain trace elements towards the base of the profile are largely attributed to leaching. Although there is no direct evidencel the abrupt increase of Cr, Ga and V values in the fissure-filling may partly reflect the accumulation of trace elements in the insoluble limestone residues. 170 Table 38 Profile description of a representative local- drift soil overlying Carboniferous Limestone in Derbyshire Profile 42 Location: Horsley Farm, Kniveton, Derbyshire (grid ref. SK200516) Relief: moderate slope of W aspect at 675 ft. 0.D. Dra1nage: good Land use: permanent pasture Depth (ins.): (Sample no.) 0-6 Brown loam with abundant roots; clearly defined (3964) boundary to - 6-19 Brown clay loam; few roots; erratics - local (3965) sandstones, shale fragments and occasional Bunter cjuartzites and igneous rocks; sharp, wavy boundary to •- 19~• Weathered limestone; fissures filled by intimate (3966) mixture of overlying brown clay loam and dark red clay (3968) Limestone Table 39 Metal content of a typical Mo-rich local-drift soil on limestone in Derbyshire (see also Table 38). 0' Metal content (ppm)* pH clay Fe 0 ) Mo Cu EDTA.Cu Pb Ga V Ti Ni Co Mn Cr As Sample Depth 2 3 No. (ins.) Profile 42: well-drained drift-soil derived from the lower Namurian shales; rest-Lag on Carboniferous. Limestone 3964 0-6 5.2 26 0.8 2 20 15.5 20 2 16 600 20 5 130o 13 15 3965 6-19 6.o 38 1.4 5 30 11.3 30 2 60 1300 40 10 1300 16 20 3966 19+ 6.9 52 3.1 16 4o 8.o 6o 16 200 3000 100 10 600 200 5 3968 Limestone 0.5 2 2 2 2 30 50 5 500 5 Total iron expressed as Fe203 *Total trace element values based on analysis of minus-80-mesh.material . MIA-extractable- ..Gu-ased, o n,a mica 1 y StR of minus- -10-m e sh . 172 Alluvial soils `•lithin the zones delineated by the abnormally high Mo content of the stream sediments, alluvium is widespread alongside the River Dove, Manifold, Hamps and Ecclesbourne (Fig. 19), and there are less extensive deposits alongside all but the most minor tributaries. Relatively freely-drained soils developed on aggraded terrace deposits are distinguished from the groundwater gleys on floodplain alluvium. Soils deve3oped on the aggraded terrace deposits Aggraded terrace deposits are particularly extensive along- side the River Manifold and its west bank tributaries between Longnor and Hulme End (Fig. 19). The terrace stands several feet above river level and is being actively eroded. Consequently, it was possible to sample sections of the alluvium exposed in the river bank: these are described in Table 40 and the analytical data are summarised in Table 41. Considering the analytical precision of the routine spectrographic method it is apparent that many of the varia- tions of metal content between the horizons of Profiles 7 and 21 are possibly not significant. Nevertheless, since similar trends can be recognised in both profiles, metal distribution is briefly described. Variations of metal content from horizon to horizon is most marked in Profile 7 in which Fe levels, together with Co, Cu, Mn, Mo, Ni and V, increase towards the base of the relatively freely-drained upper horizons. Furthermore,the well-drained horizons are enriched, 173 Table 40 Profile descriptions of representative aggraded alluvial terrace deposits on the River Manifold, north-east Staffordshire Profile 21 Location: Hulme House Farm, Warslow, Staffordshire (grid ref. SK099605) Relief: flat terrace Drainage: imperfect to poor Land use: permanent pasture (cut for hay) Depth (ins.) (Sample no.) 0-5 Dark greyish brown loam with abundant roots; clearly (3577) defined boundary to - 5-18 Dark greyish brown loam with traces of mottling; few (3578) roots; merging boundary to - 18-27 Dark grey clay mottled brown, sharp boundary to - (3579) 27-63 Dark grey clay loam with very prominent strong brown (3580) mottles; wet; 63+ Coarse alluvial gravels. Profile 7 Location: Hardings Booth, Longnor, Staffordshire (grid ref. SK070645) Relief: flat terrace Drainage: imperfect to poor Land use: permanent pasture (cut for hay) Depth (ins.): (Sample no.) 0-4 Very dark greyish brown loam with ochreous mottles along (3564) old root channels; abundant roots; merging boundary to - 4-16 Dark brown clay loam; no mottling; few roots; sharp (3565) boundary to - 16-38 Dark grey silty clay with prominent strong brown mottles; (3566) large prismatic structures; alluvial pebbles 38+ Gravels Table 41 Metal content of soils developed on aggraded terrace and floodplain alluvium of streams draining the lower Namurian and Visean shales in north-east Staffordshire (see also Table 40 and 42) Sample Depth Metal content (ppm)* No. (ins.) pH clay Fe203t Mo -' Cu EDTA.Cu Pb Ga V Ti Ni Co Mn Cr As Profile 23: aggraded terrace of the River Manifold, imperfectly to poorly-drained. 3577 0.-5 6.6 24 3.8 8 5o 17.o 130 20 130 4000 60 50 1300 100 13 3578 5-18 5.6 43 2.5 lo 4o 15.8 130 lo 130 4000 6o 4o 85o 6o 25 3579 18-27 5.8 24 8.6 16 13o 11.5 160 20 160 5000 100 130 1000 160 15 3580 27-63 5.2 20 11.0 13 50 11.0 60 30 200 6000 130 60 1000 200 13 Profile 7: aggraded terrace of River Manifold, imperfectly to poorly-drained. 3564 0-4 5.4 20 7.6 8 85 17.3 loo 20 160 400o 85 4o moo 200 5 3565 4-16 5.7 34 16.0 20 130 12.3 100 20 300 6000 130 60 1300 200 13 3566 16-38 5.8 44 3.6 13 5o 10.6 6o 13 13o 4000 loo 3o 500 160 :5 Profile 11: floodplain alluvium of the River Hamps, very poorly-drained. 3536 0-3 6.4 3o 7.0 20 300 73.5 160 10 200 3000 160 60 1000 300 35 3537 3-10 6.4 24 5.2 20 400 88.5 160 13 200 3000 160 50 600 200 35 3538 10-20 6.4 4o 2.2 10 200 128.0 100 5 160 1000 130 3o 600 200 15 3539 20-27 6.4 20 4.2 30 300 175.0 100 8 200 3000 160 30 200 1300 35 stream sediment - 3.6, 16 200 - 85 - 160 2000 100 30 400 60 River Hamps Total iron expressed as Fe2 03 *Total trace element values based on analysis of minus 80-mesh fraction EDTA.extractable Cu based on analysis of minus 10-mesh fraction. 175 relative to the underlying poorly-drained clay, in Fe (4x) and Co, Cu, Mn and V (2x). Although drainage conditions also deteriorate towards the base of Profile 21, the contrast in drainage status between horizons is less marked and Fe values increase with depth throughout the profile. There is also a slight increase in Mo, Ni and V with depth. In neither of the profiles does metal distribution reflect textural variations between the horizons. The increased metal content with depth is therefore probably due to leaching. Redistribution of Fe in the lower horizons of both profiles is reflected by the abund- ance of secondary ferric oxide concretions and large ferruginous mottles. Soil developed on floodplain alluvium One groundwater gley (Profile 11) was examined in detail on the floodplain alluvium of the River Hamps at Onecote. The profile is described in Table 42 and the analytical data are presented in Table 41. Apart from the development of a topsoil and the waterlogging of the lower part of the profile there appears to be very little pedological differentiation. Furthermore, except for the decrease in Mn and Fe towards the base of the alluvium, metal content is more or less uniform. Trace element levels in the lowest horizon of the alluvium are very similar to those in the sediments of the River Hamps sampled near the profile pit (Table 41). Thus the abnormal Cu (300 11:1m) -..nd Pb (100 prd) content of the alluvium corresl,onds to the anomalous values in the stream sediment. Cu (200 ppm) and Pb (85 ppm), 176 Table 42 Profile description of very-poorly drained soil on floo.dplain alluvium in north-east Staffordshire Profile 11 Location: Onecote Old Hall, Onecote, Staffordshire (grid ref. SK052550) Relief: flat floodplain terrace Drainage: very poor Land use: permanent pasture Depth (ins.): (Sample no.) 0-3 Very dark grey clay loam with slight ochreous (3536) mottling along old root channels; abundant roots; clearly defined boundary to - 3-10 Very dark grey loam with dark red mottles along (3537) old root channels; merging boundary to - 10-20 Very dark grey loam; wet; merging boundary to - (3538) 20-27 Very dark grey loam with alluvial pebbles; wet (3539) 27+ Gravels 177 and reflects the mineralisation upstream in the Mixon district. (ii) SIZE FRACTION ANALYSIS In order to determine the metal content of the size fractions, selected samples from the profiles described in the preceeding section were subdivided into coarse sand (0.2-2.0mm), fine sand (0.05-0.2mm), silt (0.002-0.05mm) and clay (<0.002mm) fractions by mechanical analysis as described in Chapter 7. To avoid the problems generally associated with the dispersion of organic matter, all the samples were selected from the principal sub- soil horizon immediately below the topsoil. Metal content of the fractions was determined by the multi-element spectrographic method of Nichol and Henderson-HaMilton (1965) described in detail in Chapter 2. (a) Distribution of trace elements in size fractions The metal content of the size fractions was investigated in the Mo-rich subsoils of four residual and two alluvial profiles. The analytical results are summarized in Table 43. The abnormally high contents of Fe and Mn in the sand fractions of samples 3523 and 3545 reflect the abundance of indurated secondary ferric and manganese oxide concretions in these soils (Tables 33 and 34 ). Although concretions are not so abundant in the remaining samples,the irregular distribution of Fe and Mn is probably due to their extensive redistribution within the overburden as a result of gleying processes. Table 43 Metal content of size fractions of residual and alluvial soils derived from the lower Namurian shales Metal content (ppm) % Ti Ni Co Mn Cr Size Fraction* Mo Cu Pb Ga V Fe203t /0a Profile 29 CS 19 200 50 60 <2 20 1800 300 80 >1% 30 38.00 FS 21 50 3o 6o 8 8o 2000 120 4o 6000 100 10.5o Sample 3523 SL 28 12 12 18 2 50 2000 80 <5 3000 50 4.60 CL 32 20 20 30 30 200 6000 400 5 1200 50 5.5o Profile 8 CS 85 60 FS 3 10 50 60 2 1000 10 600 40 9.60 Sample 3533 SL 25 10 20 40 30 120 6000 30 <5 80 40 2.15 CL 72 30 6o 20 4o 400 6000 5o <5 loo 18o 8.2o Profile 37 CS 9 40 50 200 5 200 1000 200 WO >1% 60 10.05 FS 8 40 50 120 2 200 1800 100 120 1% 50 8.60 Sample 3545 SL 30 12 60 180 18 200 6000 100 20 1200 100 5.90 CL 53 4o 18o 100 40 500 8000 120 20 300 200 3.85 CS* = coarse sand (0.2-2.0mm) (Total iron expressed as Fe 0 FS = fine sand (0.05-0.2mm) 2 3 SL = silt (0.002-0.05mm) CL = clay (<0.002mm) Table 43 (continued) Size Fraction Metal content (ppm) , Mo Cu Pb Ga V Ti Ni Co Mn Cr Fe2 03-L Profile 26 CS 10 40 40 200 6 120 1800 40 <5 800 50 3.85 FS 11 6o 5o 180 8 120 2000 40 5 800 4o 2.80 Sample 3561 SL 31 20 50 50 10 200 6000 50 20 1000 60 6.20 CL 48 10 20 50 5 120 1200 30 <5 400 loo 1.6o Profile 21CS 6 6 20 40 4 80 1000 30 40 1800 20 3.25 FS 17 6 30 20 5 4o 1000 4o 3o Soo 30 2.90 Sample 3578 SL 34 10 4o 18 5 60 6000 40 12 1000 50 3.80 CL 43 18 6o 3o 30 200 4000 100 30 1200 100 6.6o Profile 11 CS 9 13 300 130 6 130 2000 130 50 2000 60 5.80 FS 33 30 200 50 • 2 120 1000 120 80 500 120 3.85 Sample 3538 SL 34 20 200 100 20 180 5000 120 30 800 60 5.10 CL 24 40 500 120 30 400 800o 300 loo 1000 18o 9.7o 1 CS* = coarse sand (0.2-2.0mm) Total iron expressed as Fe 0 FS = fine sand (0.05-0.2mm) 2 3 SL = silt (0.002-0.05mm) CL = clay (<0.002mm) 180 Contrast between the metal content of the fractions is most marked in samples 3523 from the very poorly-drained subsoil of Profile 29 (Tables 33 and 34). The coarse sand fraction, con- sisting predominantly of ferric oxide concretions, contains abnormally high values of Mo (200 ppm), Mn (>1%) and Co (80 ppm) compared to the finer fractions. A lesser degree of enrichment of these elements, relative to the silt and clay fractions, is also associated with the enhanced Fe content of the fine sand fraction. Cu and Pb are slightly enriched in the ferruginous sand fractions and Ni in both the sand and the clay, but not in the silt. In contrast, the clay fraction is enriched, relative to the coarse sand fraction, in Ga (>15x), V (10x) and Ti (3x). In the remaining samples the reduced contrast between the Fe content of the fractions is reflected by the relatively uniform distribution of Mo. NeverthelessI the minor variations of Mo correspond to fluctuations of Fe values with maximum No content in the most ferruginous fraction of each sample. Co distribution also tends to follow Fe and/or Mn and conaaquently to be enriched in the coarse sand fraction of several of the samples. This is most marked in sample 3545 with 800 ppm Co and >1% Mn in the coarse sand compared to 20 ppm Co and 300 ppm Mn in the clay grade material. In all samplesl except 3561, levels of Cr, Ga, Ti and V tend to increase with decreasing grain size and these elements are principally associated with the clay fraction. The distribution of Cu, Ni and Pb is less clearly defined. Pb is generally slightly enhanced in the 181 coarse sand fraction whereas Cu and Ni show affinities with both the sand and the clay fractions. Metal distribution in the size fractions is generally con- sistent with their established geochemical affinities in the weathering cycle. Thus Mo is enriched in the ferruginous coarse sand fraction of sample 3523 and the distributions of Mo and Fe are closely related,reflecting the affinity between hydrous ferric oxides and Mo (Jones, 1957). The irregular distribution of Co also appears to reflect its scavenging by ferric or manganese oxides. In the very wide range of oxidising environments - in soils, drainage channels and marine sediments - for which similar processes have been reported Co has generally been found to be accumulated along with the manganese oxides (Vinogradov, 1959; Jay, 1959; Cronan, 1967, Horsnail, 1968; and see also page 53 , Chapter 4). The concentration of Cr, Ga, Ti and V in the clay fraction of even the most ferruginous samples indicates that these elements are principally associated with the clay minerals. Goldschmidt (1954) reports that Ti is usually associated with the clay fraction in soils and Ga, as Ga+3 (0.628); readily s4bstitu6s for A1+3 (0.57R) in clay mineral lattices. The close relationship between Cr and V and the clay fraction is unusual since both elements have a limited mobility within the overburden (Tables:34,36,39 and 41) and would therefore be expected to show some degree of enrichment in the ferruginous fractions (Goldschmidt, 1954; Vinogradov, 1959). It may be, however, that the association of Cr, Ga, Ti and V with 182 the clay fraction is largely inherited from their distribution in the shale parent material. (b) Comparison of the metal content of the minus 80-mesh and minus 10-mesh fractions Following the standard procedure at the A.G.R.G. routine analyses of soil samples have been on the minus 80-mesh fraction. This contrasts with the conventional agricultural practice of analysing the minus 2mm material (minus 10-mesh). For the data in Table 43 the minus 80-mesh fraction corresponds to the fine sand+ silt+clay and the minus 10-mesh fraction is equivalent to the minus 80-mesh material+ the coarse sand fraction (Table 21). Mechanical analysis (Table 1-7 ) shows that for most soils derived from the lower Namurian shales the coarse sand fraction amounts to less than laX of the minus 10-mesh material. Consequently, con- sidering the precision of the analytical method used, the metal content of the minus 80-mesh material is considered to be sufficiently representative of the minus 10-mesh fraction to justify its use for most purposes in these soils. In exceptionally ferruginous soils, however, the coarse sand fraction can amount to more than 10% of the minus 10-mesh fraction, reflecting the abundance of ferric oxide concretions as in samples 3523 and 3545. Furthermore, the concretions are enriched in Mo, Co and Mn and analysis of the minus 80-mesh fraction will tend to under- estimate the values of these elements. Thus for sample 3523 the calculated Mo values for the minus 10-mesh and minus 80-mesh fractions 183 are 58 ppm and 25 ppm respectively. Fortunately, ferruginous samples are easily recognised and if necessary the concretions can usually be disaggregated, without damaging the primary particles, to give a more representative sample. (iii) DISCUSSION (a) Metal distribution in the overburden Although modified by local drainage conditions, the most consistent feature of metal distribution is the increase of metal content towards the base of the overburden (Tables 34,36,39 and 41) Mo, Cu, V and Fe in particular tend to accumulate in the lower horizons of the profiles. Comparison of metal contrast between the topsoil and the horizon of maximum enrichment shows that the trend can only be partly accounted for by translocation of metal-rich clays. Conse- quently, the increased trace element levels in the lower part of the overburden are largely attributed to leaching. This is borne out by the extensive redistribution of Mn and Fe within the overburden and by the scavenging of Mo and Co by the hydrous oxides. The retention of Mo in the overburden is discussed in greater detail below. The enhanced Cr, Ga, Ti and V values in the clays compared to the coarser fractions and the relatively low levels in even the most ferruginous size fractions suggest that in subsoils these elements are largely fixed by sorption on clays (Table 43). Other workers have reported similar distributions of trace elements in English soils developed on a variety of parent materials. 184 Butler (1954) found that maximum concentrations of Fe, Ga, Cr, V, Li, Ni, Co, Zr, Yt, Sr, Ba and Rb occur in the lowest horizons of brown earths and gleyed soils derived from glacial drift and Namurian shales in Lancashire. Investigating metal distribution in brown earths developed on chalky head and loess in southern Englandi Le Riche and Weir (1963) have attributed the increased content of Co, Cr, Cu, Ga, Mn, Ni and Pb with depth, to leaching of the elements associated with the secondary ferric oxides and to translocation of metal-rich clays: Co, Cu, Mn, Pb and V were largely associated with the ferric oxides, Cr and Ni with both the ferric oxides and the clay fructioni and Ga with the clay fraction alone. In contrast, Swaine and Mitchell (1960) found no consistent variation of total trace element content, attributable to pedological processes, in the profiles of a wide variety of Scottish soils. This difference may reflect the nature 'if the parent materials. Thus, most of the Scottish soils were derived from igneous and metamorphic rocks and the trace elements are largely bound up in the lattices of coarse grained ferromagnesian and aluminosilicate minerals. It was found that the proportion of these minerals undergoing weathering was relatively small and consequently only small amounts of trace elements were available for translocation. Exceptionally, however, the profiles of soils developed on ultrabasic rocks contain relatively easily weathered serpentinized olivine crystals and the trace elements bound up in these crystals - Co, Cu, Mn, Mo and Ni - are leached from the topsoils. 185 In contrast, the English soils are largely derived from sedimentary rocks: during previous sedimentary cycles trace elements have accumulated in the shales by sorption on clays and other processes whereas the resistant minerals - principally quartz - have been con- centrated to form sandstones. Compared to the shalesI the sandstones are normally impoverished in trace element (Table 24) and the metal content of the resistant minerals is probably less readily mobilized during weathering. The shales, however, are relatively easily weathered and the trace elements mobilized and transloc-,ted by pedological processes. In soils derived from the lower Namurian shales mobilization is reflected by the extensive redistribution of Fe and Mn as their secondary hydrous oxides and by the accumula- tion of Mo, Cu and V, variously associated with other trace elements, in the lower horizons of the profiles. These results corroborate the soil traverse data reported in Chapter 10. The reduced contrast for Co, Cu, Mn, Ni and V between the overburden derived from shales and sandstones, compared to the relative content of the parent materials (Table 23), apparently reflects their translocation in the overburden derived from the shales. Cu and V tend to accumulate with depth in the overburden whereas Co, Mn and Ni are generally irregularly distributed in the soil profiles. Consequently the reduced values of Co, Mn and Ni in soils, compared to levels in shale parent material and corresponding stream sediments (Tables 30 and 32 ), appear to reflect their migration in circulating groundwaters and accumulation in bank soils and/or precipitation or sorption in the drainage channels (page 150, Chapter 10). 186 (b) Factors influencing the mobility and retention of Mo in soils derived from the lower Namurian shales The mobility of a trace element and its availability to plants are broadly related concepts. Consequently;the factors influencing the mobility and retention of Mo in the soils derived from the lower Namurian shales assume particular significance when considering uptake by herbage (see later, Chapter 12). Before discussing Mo dispersion in the overburden the factors influencing its mobility are briefly reviewed. Unlike most essential trace elements (Table 1), the avail- ability of Mo tends to increase when the pH of the soil is raised (Barshad, 1951; Walsh et al, 1952; Davies, 1956). In both acid and alkaline environments, however, the mobility and availability of Mo can be suppressed by its sorption on hydrous ferril oxides and to a lesser extent clay minerals (Barshad, 1951; Jones, 1956, 1957; Reisenauer et al, 1962; Titley, 1963; Hansuld, 1966). Barshad, Jones and other workers have shown that maximum sorption occurs under acid conditions and have therefore suggested that the -2 1 behaviour of molybdate anions (MoO4 and HMo0 ) in soils is analogous to that of phosphate. In the Mo-rich agricultural soils derived from the lower Namurian shalesl the tendency for Mo to increase with depth indicates some degree of mobility despite the slightly acid reaction of most of the soils (pH range 4.9-6.9). There is, however, considerable evidence that more extensive leaching is prevented by sorption of Mo on hydrous ferric oxides which are particularly abundant in the 187 zone of periodic waterlogging of the poorly-drained soils. Thus in both soil profile and size-fraction studies the distribution of Mo was closely related to that of Fe. Exceptionally, as in sample 3523 with 200 ppm Mo in the coarse sand fraction (Profile 29, Table 43), a combination of gleying processes and scavenging of Mo by the ferric oxides gives rise to ferruginous concretions with an abnormally high Mo content. Other workers have obtained similar results: Atkinson (1967) found that Mo followed the secondary ferric oxides in soils derived from the Mo-rich Clare Shales in Co. Limerick, Ireland. Wells (1956) has demonstrated that Mo sorbed on ferric oxides during the weathering of basalts in New Zealand becomes increasingly fixed and unavailable to herbage as the oxides crystalize. In North American soils retention of Mo has been attributed to scavenging by active ferric oxides formed by alternating period of reduction and oxidation associated with the waterlogging and drying-out of the soils (Robinson and Edgington, 1954). Mo would therefore be expected to be most mobile - other factors being equal - in soils and horizons in which the secondary ferric oxides are either absent or poorly developed. Consequently, mobilization and possibly impoverishment of Mo can be anticipated in zones of reduction and/or strongly acid leaching. This, in fact, appears to be the case, as discussed below. Reduced soils The neutral grey colours and the absence of mottles in 188 the permanently waterlogged horizon at the base of Profile 29 (Tables 33 and 3L}) indicates that iron is largely present in the reduced state: the No content (6 ppm) is low compared with that of the overlying ferruginous zone (60 ppm Mo) and the strongly mottled subsoil (40 ppm Mo). Since the site receives large quanti- ties of percolating groundwater04o distribution probably reflects the inability of ferrous iron in the reduced zone to fix Mo in contrast to the abnormal enrichment of the overlying semi-indurated horizon of secondary ferric oxides. A similar trend may also account for the low Mo content (5 ppm) of the lowest horizon of Profile 4 (Table 34). Mo distribution in the very poorly-drained profiles is therefore consistent with its fixation by ferric oxides in the zone of periodic waterlogging and with relatively increased mobility in the underlying reduced zone. Gleying processes therefore appear to have a considerable influence on the mobility and distribution of No in the overburden. Increased No uptake by herbage has been widely reported on poorly-drained soils compared to that on well- drained soils derived from similar parent materials (Lewis, 1943; Mitchell et al, 1957b; Kubota et al, 1961, 1963). In exceptionally poorly-drained soils, where the groundwater table and the reduced zone is very close to the surface, increased Mo uptake could reflect the increased mobility of Mo in the absence of ferric oxides. Walsh et al (1952) have related enhanced No uptake by herbage on acid, organic-rich soils to the absence of fixing agent in reducing conditions. 189 Leached soils Fe, Mo and associated trace elements are impoverished in the leached mineral horizon just below the strongly acid peat of the moorland soils (Tables 36 and 37). This contrasts with the normal increased mobility of Mo when the pH of a soil is raised but is consistent with mobilization due to the absence of ferric oxides. The accumulation of Mo in the reduced zone of the moorland soils cannot be attributed to fixation by ferric oxides but may reflect either sorption on clays and/or relatively slow migration in the circulating groundwaters under conditions of extremely poor drainage. Wells (1956) also found that leaching and podzolisation allowed No to remain relatively mobile and available to herbage by preventing the ageing and crystalization of hydrous ferric oxides. Ng and Bloomfield (1961, 1962) and Bloomfield (1963) have reported increased mobilization of Mo and Fe under increasingly acid condi- tions during anaerobic fermentation of soils with plant material. This was attributed to either organic matter preventing the sorption of Mo on ferric oxides or to the formation of organic molybdenum compounds. Similar reactions between Mo and the acid humus in the moorland profiles could account for the leaching of Mo. Mo therefore appears to be most mobile where ferric oxides are absent either as a result of reduction in the lowest horizons of the very poorly-drained soils, or due to leaching in the moorland peaty soils. In the periodically waterlogged zone of the gleyed 190 soils and the profiles of the imperfectly and well-drained soils, the mobility - and possibly the availability to herbage - of Mo reflects its fixation by hydrous ferric oxides. The relationship between Mo uptake by herbage and drainage conditions is described in Chapter 12. 191 CHAPTER 12. METAL CONTENT OF HERBAGE The Mo and Cu content of herbage on Mo-rich soils is reported and compared with values for herbage from adjoining areas of normal soils developed on a wide variety of parent materials. Metal uptake is related to the metal content of the topsoil and to those environmental factors which are generally considered most significant in determining the availability of trace elements to plants. The Se content of selected herbage samples is also reported: The principal concern of this thesis is to investigate the applicability of regional stream sediment surveys to the detection of molybdeniferous soils on which high Mo values in herbage can be anticipated and where molybdenum-induced copper deficiency could well be a serious problem. Grasses and white clover constitute the bulk of the pasture herbage and their Mo and Cu content should there- fore largely determine the intake of these elements by grazing animals. Consequently, for the purposes of this study, grab samples of mixed grasses, rather than the sampling in detail of constituent grass species, were considered to be adequate. Samples of mixed grasses were collected in the first week of May (1966) and separate samples of grasses and clover in July. In additionl rushes and grasses were collected from seepage areas and low-lying sites characterised by exceptionally poor drainage, and heather and grasses were collected from moorland. In the case of heather, only the young shoot of the current year's growth were sampled. 192 Sample preparation and analytical techniques have been described in Chapter 7. All the data are reported on a dry-weight basis. The significance of the differences between the mean metal content of groups of samples was assessed with the 't-test' as described by Snedecor (Chapter 4, 1965). (i) MOLYBDENUM The Mo content of pasture herbage is summarised in Table 44 with a more detailed breakdown of the relationship between Mo values in the topsoils and uptake on different parent materials in Table 45 Table 44 Range and mean Mo content of topsoils, pasture grasses and clover from anomalous and background stream sediment areas. Area as defined by Mo content of Mo content (ppm)* the sediments Topsoils Grasses Grasses Clover (0-6 ins) (May) (July) (July) Mo-anomalous soils 4-35 1.0-8.0 1.4-7.0 1.0-30.0 derived from the 16t 3.6 2.8 7.3 lower Namurian (23)tt (22) (23) (17) shales Background soils <2-4 1.4-3.0 0.6-5.0 0.6-8.6 on all other <3 1.9 1.8 3.1 parent materials (12) (8) (12) (12) tArithmetic mean: *Topsoil data based on minus 80-mesh tiNumbor of samples fraction, sample depth 0-6 ins; herbage in parenthesis data on dry-weight basis Table 45 Range and mean Mo content of topsoils, pasture grasses and clovers on soils derived from different parent materials in the South Pennines I Parent material and Mo ______Mo cqntent_(ppm) status pia Topsoil Grasses Gras7ca Clover (0-6 ins) (May) (July) (July) (a)Anomalous soils Residual and local drift 4.9-7.0 4-35 1.0-8.0 1.4-7.0 1.8-30.0 soils derived from the 5.8* 15 3.7 3.1 7.2 lower Namurian shales (14)** (14) (13) (14) (11) Alluvial soils largely 4.6-6.4 <2-35 2.4-7.0 1.4-4.o 1.8-25.0 derived from the lower 5.8 <15 3.5 2.5 7.5 Namurian shales (9) (9) (9) (9) (6) (b)Control soils Upper Namurian sandstones 5.7-6.9 <2-4 1.6-3.0 0.6-2.0 0.6-8.0 6.4 <3 2.1 1.5 2.8 -- (6) (6) (5) (6) (5) Drift consisting largely 5.6-6.1 <2-3 1.6-2.5(5.0)t1.0-8.6 of Triassic material 5.8 <3 - 1.9 4.3 (4) (4) (3) (4) Mixed loessial and 5.8-6.9 <2-3 1.4-1.8 1.0-1.2 1.0-1.6 residual soils on the 6.4 <3 1.5 1.1 <1.5 limestone plateau _ (3) (3) (3) (3) (3) *Arithmetic mean 1Data on minus 80-mesh fraction 4- -Dry weight basis **Number of samples in parenthesis 'Abnormally high value not included in mean 194 The relationship between the Mo-status of the herbage, topsoil values and environmental factors is considered in detail below (part (ii), page 198 ). Before doing so, however, Mo uptake by the principal constituents of the herbage, and the variations of Mo content between samples collected in May and July are briefly described. (a) Molybdenum uptake by the principal constituents of the herbage Although there is no close correlation between the Mo content of grasses and white clover growing on the same soils, the clovers normally contain more Mo than the associated grasses. Thus, on the molybdeniferous soils, the mean Mo contents of grasses and clovers, sampled in July, are 2.8 and 7.3 ppm respectively (Tables 44 and 45). If, however, three clover samples with abnormally high Mo values (14.0, 25.0 and 30.0 ppm) are omitted the latter value becomes 4.1 ppm. On the control soils the difference between the mean Mo content of grasses and clovers is 1.3 ppm (Table 44). Visual esti- mates indicate that the clover usually amounts to between 5 and 20 per cent of the total pasture. Consequently, apart from the few pastures with exceptionally high Mo values in the clover, the content of the herbage as a whole is probably only slightly greater than in the mixed grasses alone. Neverthelessl an abundance of clover could, particularly if the pH of the soil was raised by liming (see below, page 201), appreciably increase the Mo content of the pasture and have an adverse effect on animal health. 195 A similar relationship between the Mo content of grasses and clovers has 1-:en reported in Ireland (Walsh et al, 1952; Fleming, 1965) and on the teart pastures of southern England (Ferguson et al, 1945). Beck (1962), however, found that on Australian pastures the Mo content of the grasses was always higher than in subterranean clover growing in the same area. Variations of 1:o uptake are also apparent between the principal constituents of the vegetation from the seepage areas and on the moorland (Table 46). Thus (i) the mean Mo content of the young shoots of the heather (0..9 and 0.5 ppm in May and July respectively) is less than in the moorland grasses (1.2 ppm in May and 0.7 ppm in July), and (ii) on seepage areas and other exception- ally poorly-drained sites the Mo content of the rushes (mean 3,1 ppm) is slightly higher than in the associated grasses (mean 2.2 ppm). In view of the relatively few samples, however, it is not known whether these differences are significant. Mitchell (1954) has reported a similar relationship between the Mo content of mixed herbage and heather on Scottish moors. Comparison of the data in Tables 44 and 46 shows that the lowest Mo values are associated with the heather and moorland grasses. This may reflect either (i) the low capacity of heather and the constituent species of the grass samples to adsorb Mo, and/or (ii) relatively low levels of available Mo due to either leaching or fixation of Mo in the acid, organic-rich moorland topsoils. The low Mo content of the heather and moorland grasses 196 Table 46 Range and mean Mo content of topsoils and vegetation from moorland and seepage areas with exceptionally poor drainage. Environment and Mo content (ppm) constituent pH herbage • Topsoil Herbage (0-6 ins.) May July (a)Moorland 3.2-3.7 <2-5 0.6-1.8 0.4-1.0 Mixed moor- 3.51 3 1.2 0.7 land grasses (5)T (6) (5) (6) 1 0.4-1.2 0.4-0.6 Heather u " , " It 0.9 0.5 (5) (6) (b)Seepage 1 4.6-6.9 10-40 1.0-5.0 areas i 6.1 19 - 2.2 Mixed grasses (7) , (9) (9) 1.4-5.0 Rushes 11 ►1 U U - 3.1 (8) 1Data on minus 80-mesh fraction; Dry-weight basis *Arithmetic mean; -Number of samples in parenthesis 1 197 is particularly interesting since this vegetation has a higher Cu content than the pasture herbage (page 210, below). Furthermore, the profile studies, reported in Chapter 11, show that, lthough Cu accumulates in the surface horizon of the peat, no such trend can be recognised for Mo. The contrast between the distribution of Mo and Cu in the moorland soils and herbage suggests that low levels of available Mo are likely to be due to leaching. The results also suggest that, with regard to dietary Mo and Cu intake, moor- land grazing could well be 'healthier' than adjoining pastures. (b) Molybdenum content of the herbage in May and July The Mo content of pasture grasses growing on the same soils is generally lower in the July samples than in those collected earlier in the year (Tables 44 and 45 ). On the anomalous pastures the mean Mo content of the grasses falls from 3.6 ppm in May to 2.8 ppm in July and the difference between the means is almost significant for P = 0.100. The same trend can also be recognised in the moorland grasses and heather (Table 46). A similar initial fall in the Mo content of the herbage at the beginning of the growing season has been reported by Havre and Dynna (1961) on molybdeniferous Norwegian pastures. Subse- quently, the Mo content of the pasture usually increases throughout the growing season to give maximum values in the late summer and autumn (Ferguson et al, 1943; Field, 1957; Havre and Dynna, 1961; Fleming, 1965). In north-east Staffcrdshire, preliminary herbage 198 samples, collected from Mo-rich pastures in the October of 1965, have a mean Mo content of 3.1 ppm (range 1.4-5.0 ppm) compared to 3.6 and 2.8 ppm in May and July respectively. Consequently,the increase of Mo values through the summer is probably not very marked. (c) Factors affecting Mo uptake by pasture herbage Mo uptake by pasture herbage is considered in relation to the Mo content of the topsoil, soil reaction, drainage condi- tions, organic matter and to the P and SO4 content of the soils. Similar trends are shown by both the May and July grass samples. Since, however, the latter gave the more consistent results and their Mo uptake can be compared with clovers collected at the same time, the data for the July herbage form the basis of the following descriptions. Molybdenum content of the topsoil Preliminary studies, reported in Chapter 7 (page 86) indicated that there is no obvious correlation between the Mo uptake by herbage and the amount of Mo extracted from the topsoil by neutral ammonium acetate. Consequently, only the relationship between the total Mo content of the topsoil and herbage uptake is described. The data in Tables 44 and 45 clearly indicate that, for samples from anomalous and background stream sediment areas, there is a broad correlation between the Mo content of the topsoils and 199 herbage, with maximum Mo uptake on the anomalous soils derived from the lower Namurian shales. Fig. 35 shows that on the anomalous soils there is a fairly clearly defined tendency for the Mo content of grasses and clovers to increase with increasing topsoil values.. As already mentioned, the Mo content of the clovers is usually higher than in the associated grasses. Comparison of Figs. 35A and 35B indicates that the No content of the clovers is also more varied than in the grasses and that thecontrast between Mo values in grasses and clovers tends to increase with increasing topsoil levels. Except, however, for three clover samples with abnormally high Mo values (14.0, 25.0 and 30.0 ppm), herbage content in the anomalous areas is appreciably lower than in the associated topsoils. On the non-anomalous soils, with a mean Mo content of less than 3 ppm, levels ranging up to 5 and 8.6 ppm are found in grasses and clovers respectively. Consequently,contrast between the herbage on the anomalous and control plots is considerably less than between the corresponding soils. Nevertheless, for the combined data in Table 44 , the difference between the mean Mo content of grasses on anomalous and control soils in July is significant with P<0.025 and in May with P<0.050. Furthermore, although not statistically significant, the increased Mo uptake by clover on the anomalous soils is particularly striking, with values ranging up to 30 ppm compared to 8.6 ppm on the non-anomalous soils. Thus, although the Mo content of the topsoil is the principal factor determining the Mo status of the herbage, a relatively large proportion of the 0 Well-drained anomalous soils Control soils Poorly-drained anomalous soils 100 100 • • 0 • 0 • • ) ) Os • • m 0 m 0 • • o • p • 0 • •0 (p (pp 10 10 0 • • • • . 0 il Mo 0 il Mo • so so +• + ++ Top Top 2 +++++4- + 2 A. B. 06 FO 2 5 10 0.5 FO 2 5 10 30 Mo content of Mixed Grasses (ppm) Mo content of White Clover (ppm) Fig. 35. Relationship Between Molybdenum content of Topsoils and Pasture Herbage (Topsoil data on -80-mesh fraction: Herbage - oven dry weight) 200 total Mo in the anomalous topsoils appears to be in a form =atonable to the herbage. The reduced contrast between herbage values, compared to that between the anomalous and control topsoils, contrasts with the findings of Webb and Atkinson (1965) and Atkinson (1967) that, on the molybdeniferous soils derived from the Clare Shales in Co. Limerick, Mo levels in the herbage are of the same order and even in excess of topsoil values. Since the anomalous Mo values in Co. Limerick and the South Pennines are derived from very similar shale parent materials,it is considered most likely that uptake in the latter area is suppressed by either an environmental factor(s) or reflects differences in the recent geological-pedological histories of the two areas. Relatively depressed uptake has also been reported by Robinson and Edgington (1954) who found, for a North American soil also derived from Mo- rich shales, mean Mo levels in the topsoils and herbage of 31.5 and 1.76 ppm respectively. The low level of available Mo, the lowest of any soil examined, was attributed to the fixation of Mo by active ferric oxides. On the following pages the relationship between Mo uptake and environmental factors is considered in detail. Soil Reaction Unlike most essential trace elements,the availability of Mo normally increases when the pH of the soil is raised (Davies, 1956). Jones (1957) and other workers have demonstrated that this 201 reflects the increased sorption of molybdate anions on ferric oxides, and to a lesser extent on clay minerals, under conditions of increasing acidity. Occasionally, however, abnormally high Mo uptake by herbage is reported from acid, organic-rich soils (Walsh et al, 1953; Mitchell, 1963). A simple pH effect is therefore not always involved. In the present study there is no obvious correlation between Mo uptake by mixed pasture grasses and the pH of the topsoils which varies over the range 4.6-7.0 (Fig. 36). In the case of white clover, however, a broad tendency can be recognised for Mo content to increase with increasing pH values (Fig. 36B). Consequently, on pasture with abundant clover, overliming could increase the Mo content of the herbage and have a deleterious effect on animal health.. The relationship between Mo uptake and soil reaction has usually been established in controlled plot or pot trials. Conse- quently, the failure to detect a correlation between the Mo content of the grasses and topsoil pH values may reflect the influence of the many environmental variables which could not be taken into accpunt.- Alternatively,it may well be that the factor(s) suppressing Mo uptake also inhibits the influence of soil reaction on the availability of MO. Drainage conditions Drainage conditions can influence the mobility and availability of Mo by many interrelated processes. Thus drainage directly influences the leaching of soluble forms of Mo from the topsoil and, indirectly, by modifying Eh and pH reactions within 0 Well-drained anomalots soils Control soils • Poorly-drained anomalous soils 0 7 0 7 o o • ++ 0 • • 0 + + + • .•• ••• 6 040• + 6 o • o + +•+ + + 0 + • • • pH pH 0 • • 0 • • O . • 5 • • 4 4 A I j 1 01 OQ 0-5 1.0 2.0 0.1 02 0%5 1.0 2.0 50 Grasses Mo/Topsoil Mo Clovers Mo/Topsoil Mo Fig. 36. Relationship Between Molybdenum Content of Topsoils and Pasture Herbage Under Various Soil pH Conditions (Topsoil -80-mesh fraction: Herbage - Oven dry weight) 202 the soil, _1:=.7, partly determines the forms of Mo present and its sorption on ferric oxides and clay minerals. Furthermore, changes in Eh and pH, brought about by drainage conditions, may modify the major constituents of the soil, particularly the iron hydroxides, and thereby influence the sites available for Mo retention. Increased Mo uptake by herbage has been associated with poorly drained soils (Lewis, 1943; Mitchell et al, 1957b; Kubota et al, 1961, 1963). Table 47 Molybdenum content of pasture herbage on poorly- and well-drained anomalous soils Molybdenum content (ppm)** Drainage Conditions Topsoil Grasses Grasses Clover (0-6 ins) (May) (July) (July) Poorly- and very 4-25 1.0-6.0 1.4-5.0 1.8-25.0 poorly-drained 13* 3.2 2.8 6.8 soils (14)t (13) (14) (11) Well-drained 4-35 2.4-8.0 1.4-7.0 2.0-30.0 soils 20 4.2 3.0 8.2 (9) (9) (9) (6) *Arithmetic mean: **Soil data on rinus 80-mesh fraction; (Number of samples in herbage data on dry-weight basis. parenthesis The data in Table 47 indicate that levels of available Mo are not appreciably different in poorly- and well-drained soils. The slightly higher Mo levels in both grasses and clovers L.rowin: on 203 the well-drained soils, in contrast to the usual trend, probably reflect the higher Mo content of these soils rather than increased mobility due to improved drainage. Consequently, in view of the relatively few samples, the significance of these results must be doubted. The influence of drainage conditions and the form of the oxides on the mobility of Mo has already been discussed in Chapter 11 (page 180. Briefly, it was shown that Mo appears to be most mobile in the absence of secondary ferric oxides, either under reducing conditions or due to leaching in the moorland environment. On farmland the permanently reduced zone is well- below the depth penetrated by the roots of pasture herbage. Consequently, the availability of Mo may be partly determined by its fixation on secondary ferric oxides. The relationship between the Mo content of the herbage, total Fe - expressed as Fe203 - and soil pH, on poorly- and well- drained soils is shown in Fig. 37. In the case of the mixed grass samples there appears to be, irrespective of drainage conditions, a broad antipathetic relationship between Mo uptake and Fe values in the topsoils. Thus, in grasses growing on soils with more than 5% Fe205' Mo values in the herbage are usually about one-tenth of the total topsoil content, whereas, on a soil containing only 1% Fe203, Mo values in the soil and herbage are more or less the same. A similar, though less clearly defined trend, can be recognised for clovers growing on the molybdeniferous soils (Fig. 37B). These results indicate that, as would be anticipated, Mo retention in 0 Well-drained anomalous soils • Poorly-drained anomalous soils Figures are pB units 10 to 9 9 .41 • 6./ 66.2 • 62 8 otit 8 0 cy 0.5-7 7 7 05.7 •-• 6 6 • it M •1/ O o 064 .3) 5 os.z O 052. 4 4 8 5-5 •52. ps5 'Si 3 o7 o 3 •6. 4 ..1"1 0 7.0 2 °S.? 04 3 2 o .50 5? •5-0 A. 1 , .61? .110• 1 41,51? d 1 012 05 1.0 2:0 0.1 02 05 1.0 2-0 5:0 Grasses Mo/Topsoil Mo White Clover Mo/Topsoil Mo Fig. 37. Molybdenum Content of Pasture Herbage in Relation to the Iron Content of the Topsoil (Topsoil -80-mesh fraction: Herbage - Oven dry weight) 204 the soils by sorption on ferric oxides and its availability to herbage,are inversely related phenomena. The re ration of Mo by ferric oxide concretions in a form unaTailable to herbage, has been reported by Wells(1956) and Robinson and Edgington (1954). In both cases it was found that the availability of Mo decreased as the concretions aged. Although, in the present study, secondary ferric oxide concretions accumulate Mo in the periodically waterlogged horizons of the poorly-drained anoma- lous soils, the bulk of both the poorly- and well-drained soils consists of silt and clay size material (page 177, Chapter 11). Consequently, as suggested by Jones (1957), the antipathetic rela- tionship between Mo uptake and the Fe content of the soils ls probably largely due to the fixation of Mo on the ferric oxides associated with the finer fractions of the soils. Jones (1957), Reisenauer et al (1962) and other workers have shown that the amount of Mo sorbed on ferric oxides decreases as the pH of the soil is raised. No such trend can be recognised in Fig. 37 and Mo therefore appears to be relatively firmly bound to the iron oxides. To complete the description of Mo uptake in relation to draina3e conditionsi the aparently ambiguous results from seepage areas and other, low-lying, sites with exceptionally poor drainage are considered. In these soils the water-table is at, or close to, the surface and the grey colours characteristic of reduced iron predominate throughout the profiles. Consequently, in the absence 205 of ferric oxides, increased uptake of Mo by herbage might be anticipated (page 190, Chapter 11). This does not, however, appear to be the case and Mo levels in both grasses (mean 2.2 ppm) and rushes (mean 3.1 ppm) are similar to values for pasture herbage (Tables/:'} and 46 ). Furthermore,pH (range 4.6-6.9; mean 6.1) and Fe (range 0.8-8.0% Fe203; mean 3.4&) values are not appreci- ably different to those for relatively well-drained soils. While no definite reason can be given for these results, it is evident that fixation of Mo on ferric oxides is not the only factor suiDpressing its availability. It may be relevant that Bloomfield (1963) has suggested that, even in grey gley soils, the bulk of the secondary iron is probably in a ferric form which for some reason does not impart its characteristic colour to the soil. The ca-oacity of ferric iron in this form to absorb trace elements is not:known however. 2EFanic matter On the anomalous farmland organic carbon values in the topsoils (determined by the method of Schollenberger as described in Chapter 7) vary between 2.13 and 4.3M. Over this range there is no obvious correlation between the Mo content of the herbage and the organic carbon values. There is,therefore,no direct evidence of the role of organic matter in the -,.ssimilation of Mo by the herbage. Davies (1956) has suggested that the Mo content of organic matter be in a continual state of circulation through microbial 206 breakdown and both Barshad (1951) and Grigg (1953) have related a part of the readily extractable Mo to the organic matter content of the soils. More recently, Gupta and MacKay (1966) have reported an increase of exchangeable Mo values when the organic matter content increased from 4.0 to 8.9% in podzols. In view of these resultsl it is considered likely that at least a part of the Mo associated with organic matter, through plant growth and the decomposition of plant litter, will be available to the herbage growing on the anomalous pastures. Sulphate and phosphate Stout et al (1951) have shown that Mo uptake by herbage can be increased by the addition of phosphate and that at high phosphate levels added Mo is very rapidly removed. This was tentatively attributed to the displacement of Mo adsorbed on the soil by the phosphate anions. In contrast, sulphate was found to depress Mo uptake, probably due to the competition of the divalent molybdate and sulphate ions for absorption !Bites on the roots. Barshad (1951) has also demonstrated that added phosphate increases Mo uptake and Walsh et al (1952) found that severe Mo disorders in livestock followed heavy dressings of phosphatic fertilizer on Irish pastures. To assess the influence of sulphate and phosphate on molybdenum uptake in the present study, topsoil samples from ano- malous and control plots were analysed as described in Chapter 7. On the anomalous soils sulphate values vary between 400 and 1000 ppm (mean 670 ppm) and between 400 and 800 ppm (mean 650 ppm) on 207 the control plots. The corresponding values for phosphate are 160-1400 ppm (mean 720 ppm) and 500-1000 ppm (mean 720 ppm). Over these ranges there is no obvious correlation between either sulphate or phosphate levels and the Mo content of the herbage. As already mentioned in Chapter 8 (page 7'5) the soils derived from the lower Namurian shales are phosphate deficient and dressings of basic slag are usually required every three years. Apart from any effect of the added phosphate, the slag increases the pH of the soil and may therefore partly account for the increased Mo uptake by clovers on the least acid soils. (ii) COPPER All herbage samples were analysed for Cu and both total and EDTA-extractable Cu were determined on the corresponding top- soils as described in Chapter 7. The results for the pasture herbage are summarised in Table 48. Table 48 Range and mean Cu content of pasture herbage from anomalous and background areas Area as defined by Cu content (ppm) the Mo content of the stream sediments Topsoils Grasses*** Clover Cu.a)TA** May CuT* July .ly Mo-anomalous soils 30-160 6.5-72.0 11.2-23.7 4.2-16.0 5.9-13.3 derived from the 661- 19.5 15.7 8.0 8.5 lower Namurian shales (23)-1`t (21) (22) (23) (16) Background soils in 8-6o 3.6-19.5711.2-22.6 4.8-1o.o 6.4-9.1 all other parent 31 8.0 15.2 7.4 7.8 materials (13) (8) (8) (13) (12) *Total soil Cu determined on minus 80-mesh fraction. **EDTA-extractable soil Cu determined on minus 10-mesh fraction. ***On dry-weight bais. tArithmetic mean ttNumber of samples in parenthesis. ff'Soils on sandstones only. 208 (a) rs?..pper content of the herbage The data in Table 48 clearly indicate that there is no correlation between the Cu content of the herbage and the corres- ponding topsoils. Thus, although the anomalous topsoils contain mean total and EDTA-extractable Cu values of 66 and 19.5 ppm respectively compared to 31 and 8.5 ppm in the control soils, similar herbage values, from 11.2-23.7 ppm in May and 4.2-16.0 ppm in July, are found in the pasture grasses from both areas. Furthermore,Cu values in the clover are also more or less the same on the anomalous and control plots, with levels usually slightly higher than in the associated grasses collected at the same time of the year. A similar relationship between the Cu content of grasses and clovers, growing on soils supplying adequate amounts of Cu, has been reported by Beck (1962) and Mitchell et al (1957a, 1957b). The most spectacular feature of the results is the decline in the Cu content of the pasture grasses from about 15 ppm in May to around 3 ,,:)pm in July. The same trend can also be recognised in the moorland grasses and to a lesser degree in the heather (Table 49). As a result of this trend,the Cu content of pasture herbage falls below the minimum level of 10 ppm recommended for cattle by the Agricultural Research Council (Alderman, 1968). Since pasture grasses collected in the October of the previous year con- tained between 5.8 and 13.2 ppm Cu with a mean of 9,2 ppm, it is considered that the Cu content of the herbage probably remains 209 Table 49 Range and mean Cu content of topsoils and vegetation from moorland and seepage areas with exceptionally poor drainage Cu content (ppm) Environment and constituent pH herbage Toploil Herbage 2 Total Cu EDTA-Cu May July (a) Moorland 3.2-3.7 8-70 1,1-8.0 7.0-20.5 8.3-12.8 Mixed 3.5* 25 4.7 15.8 10.6 grasses (5)t (6) (6) (5) (6) 5.4-20.3 10.2-11.7 Heather II it It tl 11.4 10.6 (5) (5) (b) Seepage 4.6-6.9 13-130 5.5-13.4 areas 6.1 60 - - 8.8 Mixed grasses (7) (7) (9) 3.5-9..3 Rushes II ft II - - 7.1 (7) *Arithmetic mean; 'Number of samples in parenthesis 1Total Cu data on minus 80-mesh fraction 2EDTA-Cu data on minus 10-mesh fraction 3Dry-weight basis 210 fairly constant following the initial fall in values between May and July. similar decrease in the Cu content of pasture grasses has been reported by Field (1957) on fenland in southern England, and by Fleming (1965) on Irish pastures. Apart from the decline in Cu values between May and July, the most interesting feature of the results is the contrast between the Cu status of moorland and pasture vegetation (Tables 48 and 49). In the May samples Cu values are more or less the same in herbage from both environments. In July, however, as a result of the marked decrease in the Cu content of pasture herbage, heather and moorland grasses are the richer source of Cu. EDTA-extractable Cu levels are lower in the peaty moorland soils than in the topsoils on farm- land. Consequently, the enhanced Cu content of the moorland vegeta- tion suggests that the constituent species have a greater capacity to adsorb Cu than the pasture herbage. Alternatively, although collected bt the same time, the moorland and pasture vegetation may be at different stages of maturity. Thomas et al (1945) found that heather was a better source of Cu than lowland grasses grown on the same soil. (b) Factors influencing copper uptake by pasture grasses As already mentionedi the Cu status of grasses and clovers growing on the anomalous and control soils is more or less the same despite the appreciably higher levels of total and EDTA-extractable Cu associated with the anomalous soils (Table 48). This is borne 211 Table 50 Copper content of pasture herbage on poorly- and well-drained anomalous soils Cu content (ppm) Drainage Herbage3 conditions Topsoils (0-6 ins) Total Cul EDTA-Cu2 Grasses Grasses Clover (May) (July) (July) Poorly- and 20-160 6.5-72.0 12.0-16.8 5.1-9.4 6.4-11.8 very poorly- 75* 20.8 14.9 7.3 8.2 drained soils (14)t (12) (13) (14) (11) Well-drained 30-100 14.8-29.3 11.2-23.7 4.2-16.0 5.9-13.3 soils 52 17.8 16.8 9.0 8.9 (9) (9) (9) (9) (6) *Arithmetic mean; 'Number of samples in parenthesis 'Data on minus 80-mesh fraction 2Data on minus 10-mesh fraction 3Dry-weight basis 212 out by the data in Fig. 38 which show that there is no obvious correlation between the Cu content of the herbage and the total Cu values for the corresponding topsoils. The relationship between the Cu status of herbage and the Cu extracted from torsoils by EDTA is considered in d:,t,:d1 below. Environmental factors appear to have no direct influence on Cu uptake by herbage. Thus, in Fig. 39, there is no consistent relationship between the Cu content of grasses and clovers and soil reaction. Mitchell et al (1957a, 1957b) also found that the effect of pH on Cu uptake was slight. With regard to drainage conditions, the same authors have shown that increased uptake is associated with poorly-drained soils. In the present study, however, no such trend can be recognised and higher Cu values are, in fact, associ- ated with herbage growing on well-drained soils, though these .., contain, on average, lower levels of total and EDTA-extractable Cu (Table 50). The difference between the Cu content of herbage from poorly- and well-drained sites is not, however, statistically significant. (c) Relationship between EDTA-extractable Cu and herbage uptake. Mitchell et al (1957a, 1957b) and other workers have recommended the use of EDTA to assess the available Cu status of soils. Unlike ammonium acetate and most other weak extractants commonly employed, EDTA is a chelating agent and will therefore remove at least part of the organically complexed Cu available 8 A. content of Nixed Grasses (ppm) Fig. 38.Relationship Between CopperContentof Topsoils andPasture Herbage 14 10 12 16 8 6 4 2 0 Cu contentoftopsoil (ppm) • + • 0 46 0 0 50 Poorly-drained anomaloussoils Well-drained anomaloussoils • t • (Topsoil dataon -80-mesh fraction: Herbage- ovendry weight) • • 100 • • 0 0 • 150 8 B. content of White Clover (ppm) 16 10 14 12 8- + 2- 4 6 - - 0 + Cu contentoftopsoil (ppm) • • 43) ft 50 Soils onsandstones Alluvial soils • • 100 • • • 0 150 0 • • Well-drained anomalous soils • Alluvial soils Poorly-drained anomalous soils Soils on Sandstones 7 7 0 + • 4 + • • • • • • • A 4- • 0 • • + • • 6 -4- 6 • 0 di • O + • • • + O • PH • • • PH • • • • 0 5 O 5 • 0 • 4 4 A. B. I I 4 7 8 9 10 11 12 4 5 6 7 8 9 10 11 12 Cu content of Mixed Grasses (ppm) Cu content of White Clover (ppm) Fig. 39. Relationship between Copper Content of Topsoils and Pasture Herbage Under Various Soil pH Conditions (Herbage data - oven dry weight) 213 to the herbage. In the present study the amount of Cu extracted by EDTA was determined by atomic absorption as described in Chapter 7. From the data in Table 48 and Fig. 40 it is apparent that there is a broad correlation between the amount of Cu extracted by EDTA and the total Cu content of the soil*. For top- soils on a variety of parent materials about 3:);L of the total Cu is generally extracted whereas from subsoils a lower proportion, usually about 10c.,, is characterieAc. This difference presumably reflects the extraction of the organically complexed Cu associated with the topsoils. Since the Cu content of the extract is broadly related to the total Cu content of the sample,the greatest quanti- ties are extracted from the poorly-drained soils (6.5-72.0 ppm; mean 19.5 ppm) and the least from those derived from sandstones (3.6-19.3 ppm; mean 3.0 ppm). For almost all the soils both the amount ana - roportion of Cu extracted are considerably greater than the values reported by Mitchell et al (1957a) who found that, for Scottish soils containing 4-34 ppm total Cu, EDTA-extracted 0.49-6.79 ppm representing some 5-20 of the total Cu. The enhanced levels of Cu extracted in the present study probably reflects (i) the higher total Cu content of the soils, and *EDM-extractable Cu was determined on minus 10-mesh material whereas total Cu was spectrographically determined on the unground minus 80-mesh fraction. Strictly, therefore, the results are not directly comparable. Since, however, the bulk of the soils consist of minus 80-mesh material (page 177, Chapter 11) the error introduced by doing so is probably not too large. A. Fi g.40.Relationship between E 100 10 1 1 0 Analysis. total Cuonminus-80-mesh; EDTA-ext. Cuonminus-10-mesh. Topsoil Poorly-drained anomaloussoils Well-drained anomaloussoils Total Cu(ppm) (0-bins) 10 • 0 • • + 9 • • EDTA- extractable • A 100 . • 0 A B. EDTA-Cu (ppm) 100 10 1 • and Subsoil Soils onsandstones Alluvial soils total Total Cu(ppm) (12-18ins) 10 copper 0 +o 00 o o 0 ••• a in • • • • A soils • 100 • • • 214 (ii) the relatively long extraction time - overnight - employed at A.G.R.G. The data in Fig. 41 clearly indicate that, in the present study, there is no consistent relationship between the Cu content of the herbage and the amount of Cu extracted by EDTA from the associated topsoil. Furthermore, as previously r.:7'':ioned, (i) Cu levels are similar in herbage growing on both the anomalous and control plots despite the appreciably higher EDTA-Cu associated with the former, and (ii) although the poorly-drained soils contain, on average, the most extractable Cu, higher Cu values are found in herbage growing on well-drained anomalous soils (Table 50 ). Compared to the RDTA-Cu values,the Cu content of both grasses and clovers is fairly constant. Thus clovers contain between 5.9 and 13.3 ppm whereas the corresponding EDTA-Cu values are 3.6-72.0 ppm. On the few soils containing abnormally high levels of extractable Cu there is no evidence of increased uptake by the herbage. Consequentlyl it would appear that either (i) not all the Cu extracted by EDTA is in a form available to the herbage, or (ii) as suggested by Mitchell et al (1957b), there is some physiological mechanism which controls luxury uptake. The results as a whole clearly indicate that, irrespective of the parent material and the total Cu content of the topsoil, up- take by grasses and clovers is fairly uniform. Such variations as do occur cannot be directly related to soil pH or drainage conditions and the influence of these, and other environmental factors, on Cu Well-drained anomalous soils • Alluvial soils 0 Poorly-drained anomalous soils Soils on sandstones 16 • 16 ) m 14 (pp es 12 10 d Grass 0 • • •A 0 • 0 A A ixe o • 09 8 o 8 0 +o • f M + + o • • f • o 6 o 6 • t 0 t n 0 A n te • te n 4 n 4 co co 8 2 8 2 A. 5 10 15 20 5 10 15 20 Topsoil EDTA-extractable Oa (p00 Topsoil EDTA-extractable Cu (ppm) Fig. 41. Relationship Between the EDTA -Extractable Copper Content of Topsoils and Copper Uptake by Pasture Herbage (Topsoil -10-mesh fraction: Herbage - Oven dry weight) 213 uptake is not known. The amount of Cu extracted by EDTA reflects the total Cu content of the soil but cannot be correlated with herbage uptake, which appears to remain more or less the same despite considerable variations in the EDTA-Cu values. Consequently, for these soils, the use of EDTA to assess available Cu status is questionable. (iii) SEI4NIUM In view of the association of Se and Mo in the soils derived from the lower Namurian shalesla preliminary investigation was made, in collaboration with I. Thornton of the Se content of vegetation growing on the anomalous soils. Herbage samples were collected from seepage areas and other low-lying sites with exceptionally poor drainage and organic-rich topsoils, which Irish experience has shown to be favourable to the uptake of Se (Webb and Atkinson, 1965). The results, together with the associated Se top- soil values and the corresponding data for Mot are presented in Table 51. Se values in the topsoils range from 1.7-7,0 ppm with corresponding values in the herbage of <0.2-3.0 ppm. The difference between the So content of the constituentt species is not marked although one sample of rushes (Juncus sps.) contained 3.0 ppm Se compared to 1.0 ppm in the mixed grass sample growing on the same soil. Mo values in the topsoil and herbage, 3-30 ppm and 1.0- 4.4 ppm respectively, are similar to those already reported for pasture herbage. 216 Table 51 Selenium and molybdenum content of vegetation from very poorly-drained seepage areas. Metal content (ppm) .1 Topsoils (0-6 3ns.)1 Vegetation2 Description Se Mo Species Se Mo Dark grey gley 3.7 20 m. ly Holcus - 1.8 mottled silty clay Peaty gley with 6.5 30 Bromus(?) 1.0 4.4 mottling along old Deschampsia 1.0 1.4 root channels; local Carex 1.0 1.0 accumulations of Juncus 0.8 1.2 organic matter Dark grey ‘Jrnwn 7.0 13 Mixed grasses 1.0 3.6 organic alluvial Deschampsia 1.3 1.0 soil Juncus 3.0 • 2.0 Coarse undecomposed 1.7 - Mixed grasses <0.2 1.0 peat Juncus o.8 o.8 Black mud with mottles 2.5 20 Mixed grasses 1.0 1.8 along Juncus 0.7 2.0 _ . 1Data on minus 80-mesh fraction 2Dry-weight basis 217 Apart from the one sample of rushes containing 3.0 ppm Sel values are below the level of 1.5 ppm Se associated with seleniferous vegetation in Co. Limerick (Webb and Atkinson, 1965). Conseguentlyit would appear that, as in Co. Limerick, environ- mental factors generally tend to suppress Se uptake and that only rather restricted environmental conditions favour the growth of toxic herbage. Although no detailed investigation has been made of the factors influencing Se uptake in the South Pennines, there is some evidence that soil reaction may be important. Thus data from Atkinson (1967) show that seleniferous vegetation is restricted to relatively alkaline organic-rich soils (pH 6.6-7.5) and that on topsoils that are similar except for their acidity (pH 4.6-4.8) Se herbage values are less than 0.3 ppm. In the present study the pH of the topsoils in seepage areas varies between 4.6-6.9 (mean 6.1). Consequently the relatively low pH may be one of the factors suppressing Se uptake. (iv) DISCUSSION: ENVIRONMENTAL FACTORS INFLUENCING METAL UPTAK-A BY HERBAGE Detailed follow-up studies have shown that the Mo anomalies delineated by the stream sediment reconnaissance correspond to extensive areas of molybdeniferous soils derived from the lower Namurian shales. Furthermore, her'age analysis indicates that the Mo content of pasture herbage growing on the anomalous soils is significantly enhanced compared to control 218 samples growing on soils derived from other parent materials. Also, despite the enhanced Cu values associated with Mo in the anomalous soils, the Cu status of herbage is more or less the same on both the anomalous and control soils. Although the Mo content of pasture herbage on the anomalous soils is significantly higher than on the control plots, the contrast between herbage values is considerably less than between the corresponding topsoils. Furthermore, apart from the tendency of the Mo content of clovers to increase with increasing pH, soil reaction and drainage conditions appear to have little direct influence on Mo uptake. Profile studies, reported in Chapter 11, indicated that Mo is partly fixed in the soil by sorption on secondary ferric oxides. In relation to herbage up- take it has been shown that on farmland, irrespective of drainage conditions, there is a broad antipathetic relationship between the Mo content of the herbage and the total Fe content of the topsoil. There was, however, no evidence of increased Mo uptake by herbage growing on reduced soils from seepage areas and other sites characterized by exceptionally poor drainage. Davies (1956) has classified the forms of soil Mo under the following heads: (i) 'Unavailable - held within the crystal lattice of primary and secondary minerals (ii) Conditionally available - retained as the MoO4 anion by clay minerals and available to a greater or less degree depending on pH and probably phosphate status 219 (iii) In organic matter (iv) Water-soluble.' Jones (1957) and other workers have shown that Mo freshly sorbed on secondary ferric oxides retains its anion exchange properties. As the ferric oxides age, however, the Mo becomes increasingly fixed in a form unavailable to herbage (Wells, 1956). As previously mentioned? Mo associated with organic matter is probably in a contin- ual state of circulation through microbial breakdown (Davies, 1956). The relatively low contrast between herbage Mo values from the anomalous and control plots compared to that between the corresponding topsoils, and the absence of any general relation- ship between soil reaction and Mo uptake, indicate that the levels of available Mo are relatively low in the anomalous topsoils. Although there is no direct evidence as to the form of available Mo,it is likely that levels of both water-soluble and conditionally available will be limited by fixation on the secondary ferric oxides in the slightly acid soils (see below). Consequently, if microbial breakdown is effective, the Mo associated with decomposing plant litter, which contained several ppm Mo during growth, could ►'--'1 be the principal source. The close relationship between Mo and secondary ferric oxides? and the antipathetic relationship between Mo uptake and the Fe content of the topsoils, indicate that the relatively low levels of available Mo are at least partly due to fixation by ferric oxides, This would be favoured by the slightly acid 220 reaction of the soils. Mo uptake, however, is also low on the reduced soils and other factors must therefore be involved. Total Fe (expressed as Fe 0 ) usually amounts to between 2 and 5% of the 2 3 topsoils with occasional values up to %. Consequently, although there is no doubt about the affinity between Mo and the secondary ferric oxides, it is likely that most of the Mo is still retained in the primary silt and clay fractions of the weathered parent material, which constitutes the bulk of these soils (page 177, Chapter 11). Webb and Atkinson (1965) and Atkinson (1967) found that on soils partly derived from the lower Namurian shales in Co. Limerick, the Mo content of the herbage was the same as and even in excess of topsoil values. Since Mo was concentrated in the shales of both areas in very similar black-shale environments (page 113, Chapter 9) it is considered unlikely that it would be retained in an unavailable form by the weathered residues of the parent material of the one area and not in the other unless either soil forming processes or environmental conditions are appreciably different. The data in Table 52 clearly indicate that, except for SO4 values, the composition of the topsoils is more or less the same in both Co. Limerick and the South Pennines. On the basis of drainage conditions, pH, P and SO4 values, relatively enhanced Mo levels in herbage would be anticipated in the latter area. In Co. Limerick the molybdeniferous soils are predominantly moderately well-drained, Table 52 Comparison of molybdenum uptake by herbage and the composition of the topsoils from the anomalous areas in Co. Limerick and the South Pennines Dominant soil type and Mo content (ppm) To soils Area parent material Fe 0 Organic TopsoilsHerbage pH 2 3 P S0 (0-6 ins) matter% _12 m Moderately well-drained grey-brown podzols derived 3-40 1.2-26.0 4.8-6.2 - - 8o-800 4000- Co. Limerick* from calcareous limestone 10,000 drift smeared over shale 19 11.7 5.4 - 3.1 - outcrop Poorly- and very poorly- 4-35 1.4-7.0 4.9-7.0 1.1-8.8 2.13- . 160-1400 400- South Pennines drained soils; residual 4.30 1000 on lower Namurian shales 16 3.1 5.8 4.3 720 670 *Data from Atkinson (1967) 222 grey-brown podzolic earths derived from calcareous, limestone- drift smeared over the outcrop of the Mo-rich shales (Webb and Atkinson, 1965). Consequently, although the pH of the topsoils is rather lower than in the present study, probably due to leaching, the lower part of the B horizons and the underlying drift are usually alkaline. In contrast, the profiles examined by the writer in the South Pennines were either slightly acid or acid. In view of these differences it is tentatively suggested that, in Co. Limerick, the mixing and grinding of Mo-rich shale material in a limestone drift produced an alkaline rock-flour in which Mo is relatively readily mobilized. Fixation of the Mo on ferric oxides is probably inhibited by the high pH of the subsoils. Large amounts of Mo are therby released from the weathered parent material in a form available for herbage uptake. In the South Pennines, however, Mo appears to be largely retained in ah unavail- able form, probably by the weathered residues of the shale parent material, and any Mo mobilized during weathering and soil formation fixed by sorption on secondary ferric oxides. With regard to Se uptake Irish experience has shown that seleniferous vegetation is restricted to alkaline, organic-rich poorly-drained soils (Webb and Atkinson, 1965). On the ground underlain by the lower Narnurian shales in the South Pennines, organic-rich poorly-drained soils, excluding the acid moorland, are restricted to small seepage areas and low-lying sites along- 223 side streams. Preliminary sampling of herbage growing on these sites failed to detect any evidence of excessive Se uptake, possibly as a result of the rather low pH compared to that associated with Se-rich herbage in Ireland. Consequently, although Se levels in both the lower Namurian shales and in soils derived from the shales are more or less the same as in these media in Co. Limerick, it is considered unlikely that Se will be found to constitute a serious agricultural problem in the South Pennines. 2?1+ CHAPTER 13. THE MOLYBDENUM-COPPER STATUS OF THE HERBAGE AND THE INCIDENCE OF COPPER DEFICIENCY IN CATTLE (i) THE MOLYBDENUM-COPPLR STATUS OF THE HERBAGE IN RELATION TO MOLYBDENUM-INDUCED COPPER DEFICIENCY IN CATTLE Following the recognition of excessive Mo intake as the principal cause of copper deficiency on the teart pastures of southern England (Ferguson et al, 1943) considerable evidence has been forthcoming that Mo interferes with Cu metabolism in cattle (Underwood, 1962). Consequently, copper deficiency may be either 'simple', where the Cu content of the herbage is abnormally low, or 'induced' ('complicated' or 'conditioned') where Cu levels are normal but the Mo content of the herbage is raised. It has also been established that the full limiting effect of Mo on Cu metabo- lism is dependent on there being an adequate amount of inorganic sulphate in the herbage. Many factors are involved and it is therefore not practical to specify precise limits to the Mo-Cu-SO status of herbage asso- 4 ciated with healty cattle or with cases of either simple or induced deficiency. Nevertheless, it is generally accepted that with pasture herbage containing less than 4 ppm Cu, deficiency will occur even if Mo levels are normal (less than 3 ppm), whereas induced deficiency is associated with normal Cu levels, 7 ppm or more, and Mo values in excess of 3 ppm. In the U.K. the Agricultural Research Council has tentatively fixed the Cu requirement of cattle 225 at 10 ppm, below which only a slight conditioning effect from Mo may result in copper deficiency (Alderman, 1968). Comparatively few data are available regarding the effect of inorganic sulphate. Allcroft and Lewis (1956) consider that SO4 values between 0.3 and 1.0% are ample to allow Mo to exert its full limiting effect on Cu storage. The Mo-Cu status of soils and herbage from several well- established areas of copper deficiency is summarised in Table 511-. From the data in Tables 53 and 54- it is apparent that the Mo content of herbage growing on the molybdeniferous soils is at the lower end of the range associated with molybdenum-induced copper deficiency. Although Mo levels are appreciably lower than those associated with induced copper deficiency on the teart pastures in southern England or toxic pastures in Ireland, hypocuprosis has been reported in cattle grazing herbage containing similar Mo (mean 3.24 ppm) and Cu (mean 5.54 ppm) levels in the Valle dis- trict of Norway (Havre et al, 1960). In view of the already raised Mo levels, further increases in Mo uptake resulting from farm management should be avoided. Consideration of the influence of environmental factors suggests that Mo uptake by pasture herbage is most likely to be increased where clover is abundant and the pH of soils is raised by liming or possibly by the application of basic slag. On the other hand, drainage conditions appear to have no direct effect on the Mo status of the herbage. Since the bulk of the total soil Mo appears to be retained in an unavailable form by the weathered residues of the parent material, any significant depletion of Mo reserves by successive cropping will probably only take place over a very long period. Table 53 The molybdenum-copper status of herbage in the South Pennines Metal content herbage (ppm)t Anomalous pasture Normal pasture Moorland Element Grasses Grasses Clovers Grasses Grasses Clovers Grasses Heather (May) (July) (July) (May) (July) (July) (July) (July) 1.0-8.0 1.4-7.0 1.8-30.0 1.4-3.0 0.6-5.0 o.6-8.6 o.4-1.o o.4-o.6 Mo 3.6* 2.8 7.3 1.9 1.8 3.1 0.7 0.5 (22)** (23) (17) (12) (12) (12) (6) (6) 11.2-23.7 4.2-16.0 5.9-13.3 11.2-22.6 4.8-10.0 6.4-9.1 8.3-12.8 10.2-11.7 Cu 15.7 8.o 8.5 15.2 7.4 7.8 1o.6 1o.6 (22) (23) (16) (8) (13) (12) (6) (5) Mean 1:15 Mo:Cu ratio 1:4.3 1:2.8 1:1.5 1:8.1 1:4.2 1:2.5 1:21 1Dry weight basis *Arithmetic mean **Number of samples in parenthesis ?27 Table 54 The molybdenum-copper status of pasture herbage in areas of copper deficiency in cattle. Area and source Mo-Cu status of pasture herbage No cases of copper deficiency were CHavre et al, 1960, found where the pasture herbage con- 1961) tained from 2.15-2.55 ppm Mo and 8.20 ppm Cu: simple copper deficiency occurred where herbage contained 2.26 ppm Mo and 5.55 ppm Cu, and conditioned deficiency with Mo values of 3.24-6.68 ppm and 5.12-7.28 ppm Cu. Inorganic sulphate values were between 0.18 and 0.48% in all herbage samples. Tear-' pastures, Molybdenum-induced copper deficiency is southern En land associated with herbage containing Allcroft and 7.5-13 ppm Cu (mean 10 ppm), 3.6-26 ppm ewis, 1956) Mo (mean 12 ppm) and from 0.30-0.96% inorganic sulphate. Penland, southern Copper deficiency was found to occur on England fenland pastures containing between (Field, 1957) 6.25 and 11.0 ppm Mo and from 9.25- 14.1 ppm Cu: similar cases of defi- ciency were also found on adjoining fields containing 1.3-1.88 ppm Mo and 9.58-17.2 ppm Cu. Consequently, it was suggested that the deficiency was probably not molybdenum-induced. Southern Ireland Herbage was found to give rise to TWalsh et al, 1952) copper deficiency where it contained from 5-25 ppm Mo compared to normal levels of 0.5-2.5 ppm. The Cu content of the herbage was 7 ppm. 228 Following their marked decline between May and July, Cu values over the area as a whole are below the level of 10 ppm recommended by the Agricultural Research Council. Furthermore, as a result of the fall in Cu content, the Mo:Cu ratio is highest and therefore least favourable in July (Table 53). Consequently, induced copper deficiency may be found, a-3 on the teart pastures (Ferguson et al, 1943), to be severest in late summer and autumn. In relation to copper deficiency the status of herbage growing on the control plots, with Cu levels generally less than 10 ppm (mean 7.4 ppm and possibly an unfavourable Mo:Cu ratio, is also suspect. As previously mentioned,the relatively low Mo and high Cu content of moorland vegetation provides a healthier Mo-Cu balance than 1:wland pasture herbage (Table 53). In iiew of the possible limiting effect of low levels of inorganic su:phate on the action of Mo in Cu metabolism, SO4 values were detct.Prmined on samples of pasture grasses collected from the anomalous plo:,s in July. Inorganic sulphate values were found to vary from 0.2.8-1.07%, with a mean of 0.70%, and are therefore well within the range reported by Allcroft and Lewis (1956) as allowing Mo to exert its full effect on Cu storage. Considered as a whole the results show that the Mo-C-I-S0LI. status of ?asture herbage on the anomalous soils is within the range associate(, with molybdenum-induced copper deficiency. This confirms earlier reports which had related the incidence of copper deficiency in the Onecote area to raised Mo levels in soils and herbage (pers. comm., D.J.C. Jones to I. Thornton). Furthermore, taken in conjunc- tion with the extensive Mo anomalies delineated by the stream 229 sediment reconnaissance, the results indicate that the agricultural problem area may well be considerably more extensive than was previously suspected. Complementary investigations by I. Thornton and J.S. Webb into the incidence of copper deficiency have confirmed the agricultural significance of the geochemical patterns. Their findings are summarised below. (ii) THE INCIDENCE OF COPPER DEFICIENCY IN CATTLE IN THE SOUTH PENNINES The incidence of copper deficiency in cattle (bovine hypocuprosis) reported prior to the present study has already been briefly discussed in Chapter 5 and is now shown in Fig. 42. Cases were known to be particularly numerous in the Onecote area, east of Leek, where they had been related to abnormally high Mo value8 in soils and herbage, though the source of the Mo remained unknown (pers. comm., D.J.C. Jones to I. Thornton). On the basis of the stream sediment survey it was tentatively suggested that the problem area could well be considerably more extensive than hitherto suspected in north-east Staffordshire and south of the limestone plateau in Derbyshire where only one case of copper deficiency had previously been reported. The incidence of hypocuprosis was there- fore investigated as a part of a complementary biogeochemical study by I. Thornton and J.S. Webb, who have provided the information for the following summary. A preliminary report of the combined studies has appeared in Webb et al (1968). Molybdenum stream sediment anomaly Reported incidence 0 of hypocuprosis Onecote .?.."" /.1..,...../ N ,.... 1 - ,../' -""..' .., ' ,1 -""- ..." ..,./ ', V / /' , i ,., , '''. /•-• /.. /... .". NI*.N.N..:. Carb.Lst. 0 4 miles Fig. 42. Incidence of Bovine Rypocuprosis as Reported Before the Regional Geochemical Survey — based on Webb et al (1968) 230 On the basis of the stream sediment survey and follow- up studies, the Cu status of selected herds was examined on farms where copper deficiency had not previously been suspected. In all, 26 herds (350 cattle) were examined and blood copper levels determined. 19 of the herds were situated within the Mo anomalies delineated by the sediment survey and the remaining 7 were taken from adjoining background areas. The results are summarised in Table 55 in relation to the blood Cu content; Table 56 shows the number of affected animals, a deficient animal being regarded as one with less than the accepted normal lower limit of 0.O8pg Cu per 100 ml. blood. From the data in Table56it is apparent that the incidence of copper deficiency is much higher in the herds from the anomalous areas than in the controls. The increased deficiency being most marked in young stock (Group II) from the southern area and in adults not receiving mineral supplements (Group III) in north- east Staffordshire. Considering the combined data for each of the age groups from the anomalous areas,the increased incidence of copper deficiency in Groups II and III, compared to the same groups in the control herds, is highly significant (P<0.001). Furthermore, although the comparison is not statistically valid, the difference between the incidence of deficiency for all animals from the anomalous and control areas is particularly striking. Thus on the anomalous farms 64 per cent of all animals are affected compared to 35 per cent in the control herds. Table 55 Blood copper values for cattle grouped accordin; to age, use of mineral supplements and the molybdenum content of the stream sediments +- Mean blood copper values (mg/100 ml) - S.L.F1.* District and Mo (number of animals sampled in parenthesis) content of stream sediment No mineral supplements given Minerals given I II TII IV llmths llmths - abrrs Adult Adult N.E. Staffordshire Anomalous .06881.0044(30) .o3504i.0021(73) .04961,403(43) .o866.10oo24(38) Normal x9172-.0029(4) .0429-x043(27) .0875L,.0025(24) S. Derbyshire Anomalous .03861.0023(41) .056110068(5) .07461.0031(26) Normal - .09511.0028(13) .0801.0056(21) .088 t.0037(5) Combined areas Anomalous .03601..0016(114) .0504-.0031(48) X8221-.0019(64) Normal .08011.0029(45) *Standard error of mean Table 56 Incidence of copper deficiency in stock grouped according to age, use of mineral supplements and the molybdenum content of the stream sediments Percentage of copper deficient stock in different age groups District and Mo (number of animals in parenthesis) content of stream No mineral supplement given Minerals given sediment I II III IV <11mths llmths - 22yrs Adult Adult N.E. Staffordshire Anomalous 40(30) 89(73) 79(45) 18(38) Normal 0(4) 78(27) 12(24, _ S. Derbyshire Anomalous - 80(41) 80(5) 38(26) Normal - 0(13) 43(21) 0(5) Combined areas Anomalous - 86(114) 79(48) 27(64) Normal - 52(40) 27(45) 0(5) • Overall percentage of copper deficient stock excluding animals receiving mineral supplements Anomalous area Normal (control) area Combined areas 77 37 233 From the data in Table 56 it is also apparent that copper deficiency can be reduced by feeding mineral supplements. Thus the incidence is significantly lower (P<0.001) in adult cattle receiving minerals (Group IV) compared to those receiving none (Groups II and III). If animals receiving mineral supplements are omitted the incidence of copper deficiency in the anomalous areas increases to 77 per cent of all animals. Furthermore, although there are often no visible symptoms of the deficiency, preliminary investigations of the effect of Cu injections on affected animals have shown, in many cases, an improvement of live weight gain of over 5 per cent compared to control animals not receiving the treatment. Apart from their economic significancel these results clearly indicate that the agricultural productivity of the area is limited by clinical and sub-clinical hypocuprosis, which is severest within the anomalous zone delineated by the sediment survey. In view of the differences in Mo-Cu status of pasture herbage from anomalous and control plots (Table 53) , it is reasonable to suppose that the almost twofold increase in incidence experienced by herds with the anomalous areas, compared to the controls, reflects the conditioning effect of the raised Mo levels. Consequently, on the basis of the sediment survey, copper deficiency could well be a serious problem over some 50 square miles in north-east Staffordshire and over 25 square miles south of the limestone plateau in Derbyshire. The cause of the limited incidence of copper deficiency in the control herds has not yet been established but may be due to (i) farm 234 management, (ii) areas of molybdeniferous soils too small to be reflected by enhanced Mo levels in stream sediments largely derived from barren material, and (iii) low Cu levels in pasture herbage (mean 7.4 ppm) and an unfavourable Mo:Cu ratio. These results corroborate earlier studies in Co. Limerick, which disclosed a close correspondence between the geochemical patterns and the incidence of bovine hypocuprosis (Thornton et al, 1966), and provide further evidence of the applicability of geochemical techniques to agricultural problems. It is believed that, as first proposed by Webb (1964), sediment surveys, with the advantages of low cost and rapidity, can be a valuable aid in delineating areas wherein trace element imbalances could precipitate clinical or sub- clinical disorders or where latent imbalances could become clinical or sub-clinical if farming practices were changed or intensified. 235 CHAPTER 14. COMPLEMENTARY GEOCHEMICAL INVESTIGATIONS OVER THE CULM MEASURES WEST OF DARTMOOR, DEVON Preliminary investigations of the applicability of regional geochemical sediment surveys to agricultural trace element problems disclosed an hitherto unsuspected pattern of enhanced Mo values on the Culm Measures west of Dartmoor in south-west England (Webb, 1964). The anomalous pattern was subsequently confirmed by the regional reconnaissance reported in Chapter 3 and was shown to be 'part of a discontinuouS zone, characterized by abnormally high Mo values, which could be traced through Launceston, around the northern flanks of Dartmoor and into the Teign Valley. Within the anomalous zone Mo values varied between 5 and 10 ppm with a mean of 6 ppm compared to normal background levels of less than 2 ppm. To complement the detailed studies in north-east Staffordshire and south-w-ast Derbyshire a limited pro- gramme of follow-up studies was initiated across the western half of the anomalous zone (Fig. 4.3. (i) DESCRIPTION OF THE AREA A general account of the ;round covered by the regional reconnaissance has been given in Chapter 3. Before discussing the geochemical patterns the geolcgy of the Culm Measures west of Dartmoor is described in great9r detail. To the west of the Dartmoor Granite the Lower and Upper Treecrare stream .,—s iment transect Tregeore Soil grid 'aunceston Namurian Granite Devonian (Upper Culm) Dinantian Dolerite (Lower Culm) Fig. 43. Geology and Location of the Detailed Study Areas on the Culm Measures west of Dartmoor, Devon. Geology based on information supplied by the I.G.S.. 236 Culm Measures* are repeated in a series of sub-parallel east-west trending outcrops (Fig. ) . The most northerly outcrop of the Lower Culm, on which the Mo anomaly appears to bec*atred, can be traced continuously from an area some eight miles west of Launceston to the northern flank of Dartmoor east of Okehampton. To the sox'. two further zones of Lower Culm can be traced through Milton Abbot and Lydford, and through Marytavy. Dearman and Butcher (1959) have shown that the repetition of the Lower and Upper Culm reflects the disruption and separation, to the north and south, of aA)ile of once connected recumbrent folds. Although there are stratigraphical variations both between the structural units and along the, strike the overall succession remains fairly constant. At Meldon, within the metamorphic aureole of the Dartmoor Granite (Fig. 43), Dearman (1959) has established the succession summarised in Table. 57. The oldest beds exposed are a group of slates and feldspathic siltstones forming a transi- tion series between the Devonian and Lower Culm. The latter comprises two groups of Shales and quartzites separated by the Volcanic Group and succeeded by the Calcareous Group. Within the Calcareous Group, limestones, at the top and bottom of the succession, are separated by cherts and thinly bedded shales. The limestones, *On the regional geochemical maps the Lower and Upper Culm are shown as Dinantian and Namurian respectively in accordance with the Institute of Geological Sciences usage (Table 7 ). Upper Culm of Westphalian age is not present in the follow-up area. 237 Table 57 Stratigraphy of the Culm Measures at Meldon, Devon. Modified from Dearman (1959) Thickness (feet) UPPER Grey,shales, thickly and thinly CULM bedded greenish-grey sandstones MEASURES and grits, which may he current- (Namurian) bedded >1300 Thin black limestones with hard and soft black shales, siliceous mudstones and cherts 18 CALCAREOUS Soft, thinly bedded shales inter- GROUP bedded with thicker chert beds 120 Massive, impure, black limestones with subordinate hard black cherts, siliceous mudstones, and shales 102 240 'LOWER Evenly bedded black shales with CULM UPPER SHALE small lenticles of white quartzite. MEASURES AND QUARTZITE In places beds of quartzite (6- (Dinantian) GROUP 12 in.) with thin shale partings predominate 70 Massive dark-brown tuffs with VOLCANIC thinner tuffs which may show current GROUP and graded bedding. Interbedded with massive buff quartzites and thinly bedded shales similar to those above and below 85-200 LOWER SHALE Similar to Upper Shale and AND QUARTZITE Quartzite Group, variable, with GROUP prominent local development of chiastolite at the base 260 SLATE-WITH- Alternations of dark-brown slates DEVONIAN? LENTICLES and thinly bedded or lenticular GROUP pale-green feldspathic siltstones >390? 238 which are laterally replaced by cherts, have provided the host rock for the lenticular arsenic-copper-iron mineralisation described by Dearman and Sharkawi (1965) and formerly worked in the mines around Bridestowe (Fig. LE 5 ). Bedded manganese deposits are asso- ciated with the cherts. The Upper Culm, which succeeds the Lower Culm with break, comprises a lithologically distinctive series of monotonously alternating grey shales and sandstones. The sharp change from Lower to Upper Culm sedimentation appears to have been brought about by the onset of turbidity current action from the south and west carrying sediment into an area which had previously been deeply submerged and received little detrital material (Prentice, 1962). South-west of Meldon in the Eastcott district, cherts representing the Calcareous Group and Shale-and-Quartzite Groups (Dearman, 1960) form the high ground between Beara and Lee Down on the northern bank of the River Lew (Figs. 44 and 45). Further north a second chert ridge marks the approximate northern limit of the Lower Culm outcrop in this district. Between the main chert ridge and the River Lyd Upper Culm shales and sandstones outcrop on Longham and Fernworthy Down. (ii) THE GEOCHEMICAL PATTERNS (a) Metal content of the stream sediments As a preliminary to the investigation of the trace element content of rock, soils and herbage, stream sediment samples were Fig. 44. Localities Mentioned in the Text and Topography of the Eastcott Area, Devon. Note location of "scouring" disorder in cattle at (A) and difficulty in rearing lambs reported at (B), according to J.C.McKellar, from Webb (1964). Upper CuIm (Namurian) Dolerite & Spilitic Lavas Molybdenum content (ppm) Lower CuIm (Dinantian) F) Granite 0 0 - 3 0 4 - 7 Lower CuIm Cherts CZ Lower CuIm 1 L imestones o >7 Y Mines 0 1 Miles Fig. 45. Geology and the Molybdenum Content of Stream Sediments in the Eastcott Area, Devon. (Data on -80-mesh fraction) 239 collected on detailed transects across the anomalous zone delineated by the reconnaissance survey. The results for the two principal transects, centred on Tregeare and Eastcott (Fig. 43), are summarised in Table 58. The data in Table 58 clearly indicates that the anomalous Mo values, with mean levels of about 5 ppm, are closely associated with the outcrop of the Lower Culm. In contrast,Mo levels of 2 ppm or less are characteristic of streams draining the main Upper Culm outcrop to the north. These findings fully corroborate the distri- bution of Mo reported in Chapter 3. In view of the heterogeneous geology and lack of detailed geological informationlit was not possible to determine Mo values for sediments derived from individual rock units. Nevertheless, in the Eastcott area, where the geology is relatively well-known, it is apparent that the enhanced Mo values are generally found in the streams draining the ground between the main chert ridge and the Upper Culm shales and sandstones of Longham and Fernworthy Down (Fig. 45). Anomalous Mo values were also detected in some, but not all, tributary streams draining ground underlain by the Lower Culm Measures in the Lew and Lyd valleys. In contrast, Mo values of 2 ppm or less are characteristic of sediments derived from the Upper Culm of Longham and Fernworthy Down and from the main Upper Culm outcrop to the north. 240 Table 58 Minor element content of stream sediments on the Culm Measures west of Dartmoor meta' content kppmf\* Location and geology Element Eastcott t Tregeare Mo-anomalous Main Upper Mo-anomalous Main Upper Lower Culm Culm outcrop Lower Culm Culm outcrop Mo** <2-10 <2-5 3-30 <2-2 51' 2 6 <2 Cu 50-160 20-60 40-400 3o-6o 100 40 115 4o V 100-200 100-200 100-300 100-200 150 150 150 140 Pb 40-200 16-85 20-60 16-85 55 33 35 30 Ti 1600-3000 1600-5000 1600-5000 20040-4000 2140 3140 3320 3060 Ni 40-160 40-130 60-200 20-130 go 8o no 7o co 10-60 16-100 16-160 16-50 3o 4o 50 35 Mn 60-10,000 200-850 600-8500 200-600 2290 490 165o 46o Cr 100-130 85-200 85-200 85-160 120 120 120 120 Fe 0 3.10-5.80 2.70-7.60 2.10-9.40 2.40-4.30 2 3 4.3 4.9 5.1 3.2 No. of 8 16 samples 23 30 *Data on minus 80-mesh fraction; **Mean calculated with <2ppm = 1ppm 'Geometric mean 241 Following the recognition of abnormally high Se levels in Mo-rich sediments derived from black shales in Co. Limerick (Webb and Atkinson, 1965; Atkinson, 1967),selected sediment samples were analysed for Se. Values of 0.2-8.0 ppm with a mean of 1.9 ppm were associated with the molybdeniferous sediments compared to normal values of less than 0.2 ppm (Webb et al, 1966a). With regard to the distribution of the remaining elementsl the most significant features are the enhanced levels of Cu and Mn also apparently related to the outcrop of the Lower Culm. Thus in the Fastcott area the mean Mn content of sediments derived from the Lower Culm is 2290 ppm compared to 490 ppm on the Upper Culm outcrop to the north. The corresponding Cu values are 100 and 40 ppm respectively. Similar results were obtained in the Tregeare district with Mn levels of 1650 and 460 ppm and Cu levels of 115 and 40 ppm on the Lower and Upper Culm respectively. Levels of the remaining elements, Co, Cr, Ga, Ni, Pb, Ti and Fe203, are not appreciably different in sediments derived from the different geological units. On the basis of these results metal distribution in other media was investigated, particular attention being given to the Mo and Cu content of rocks, soils and herbage around Eastcott where copper problems in livestock had previously been reported (Webb, 1964). R.F. Horsnail and I. Thornton also independently investigated the distribution of trace elements, notably Co, Cu, Mn and Mo, in this area. 242 (b) Metal content of the bedrock In view of the limited exposure and complex geology, detailed stratigraphical sampling was not possible. Chip samples were collected from stream sections and quarries over a wide area, and the black, sometimes pyritic or cherty, shales exposed in the anomalous catchments near Eastcott were sampled in detail. The results, together with data for rocks collected from the main Upper Culm outcrop by R.F. are compared with the metal content of the molybdeniferous lower Namurian and Visean shales of the South Pennines in Table 59. The results clearly indicate that around Eastcott the source of the anomalous Mo values are Mo-rich shale horizons in the Lower Culm. Mo levels in these shales, ranging up to 30 ppm with a mean of 7 ppm, are only slightly lower than in the South Pennines. In contrast,nearby outcrops of cherts and Upper Culm shales and siltstones, and Upper Culm rocks from the main outcrop to the north contain Mo values of 2 ppm or less. Background Mo values were also detected in Lower Culm shales believed to be older than those exposed in the sections at Eastcott. As in the South Pennines and Co. Limerick, the molybdeni- ferous shales are also enriched in Cu and V with levels approximately twice those associated with barren rock-types. Furthermore, analysis of selected samples showed that the Mo-rich shales contained up to 6.0 ppm Se compared to normal levels of less than 0.2 ppm (Webb et al, 1966a). In contrast, levels of the remaining Table 59 Metal content of the Culm Measures west of Dartmoor, Devon t.ithology and Metal content (ppm)* % Location (No. of samples in Mot Cu V Pb Ga 2i Ni Co Mn . Cr Fe 0 parenthesis) 2 3 'Upper Culm; . . - .. , main outcrop** <2 36 135 16 - 3510 60 18 05- 120 3.7 (21) Upper Culm <2 16-85 85-400 <2-40 10-30 3000-5000 5-30 <5-10 4o0-600 30-50 1.00-1.60 shales and siltstones, <2.: 130 6 16 3940 13 470 40 1.26 bcngham, Down 35 5 (4) Black pyritic <2-30 8-500 30-600 6-160 2-30 600-6000 10-600 <5-60 30-10,000 13-160 0.54-7.60 Lower Culm shales, Fastcott and 7 60 240 24 12 2180 45 9 250 50 1.63 Beara Lower Culm <2-3 13-50 60-400 5-30 5-10 1000-1600 <5-5 90-850 16-30 0.72-0.86 cherts (3) 13-30 <2 35 115 11 7 1370 20 <5 250 20 0.79 Pre-ohert Lower <2 13-30 85-300 5-30 10-20 2000-6000 20-130 <5-30 400-10,000 13-50 1.15-3.00 Culm shales (5) <2 20 155 11 15 3950 40 16 1930 35 1.92 Mo-rich lower Namurian and <2-50 16-500 60-850 5-100 6-40 1300-6000 200-600 5-130 30-8500 20-400 1.05-10.00 Visean shales from the South 11 110 270 27 19 4500 100 30 905 100 2.19 Pennines (73) . *Data on minus 60-mesh fraction: **Data, Horsnail (1968): '.Geometric mean: 114ean calculated with ttMean calculated with <5ppm = 3 ppm <2ppm = 1 ppm 244 elements, Pb excepted, are rather lower in the molybdeniferous shales than in rocks from the main Upper Culm outcrop. In view of the relatively few samples, the variations of metal content between the non-molybdeniferous Lower Culm shales, the cherts and the Upper Culm shales and siltstones of Longham and Fernworthy Down are not necessarily significant. Compared to the Mo-rich lower Namurian and Visean shales of the South Pennine, the anomalous shales in the Lower Culm are relatively impoverished in Mn (4x), Co (3x), and Cr, Ni and Ti (2x). The variations of trace element levels, both within the Culm Measures and between the Mo-rich horizons in the Culm and lower Namurian and Visean shales, presumably reflect differences in the supply of trace element and in environmental conditions determining their concentration during deposition. Although there is no direct evidence of the precise age of the Mo-rich Lower Culm shales, their close association with the cherts, on the southern overturned limb of a recumbrent fold (Dearman, 1960, 1966), suggests that they are probably post-chert and represent a part of the Calcareous Group near the top of the Lower Culm succession. This is to some extent corroborated by the detection of Mo values of 13 and 30 ppm in shales exposed in limestone (Calcareous Group) quarries at Lifton and Lewdown respectively (Fig. 45). On this evidence,the metal-rich shales are probably of upper Visean age and therefore stratigraphically equivalent to the molybdeniferous Visean shales of north-east Staffordshire. 245 The restricted distribution of Mo-rich stream sediments over the Lower Culm outcrop (above, page 239) and the failure to detect enhanced Mo values in the lower part of the Lower Culm and again in the Upper Culmouggests that the period of 'black- shales deposition was relatively brief in south-west England. The upper limit of the period may well coincide with the onset of turbidity current action at the base of the Upper Culm in the area west of Dartmoor. On the northern side of the Devon syncliniorium, where sedimentation was unaffected by turbidity currents until late in the upper Namurian (Prentice, 1962), it is possible that Mo-rich shale horizons will be found to persist into the Upper Carboniferous. (c) The distribution of trace elements in the overburden and the relationship between the metal content of rocks, soils and stream sediments Soil samples were collected from a depth of 12-15 ins. at 88o ft. intervals on the grid shown in Figs. 43 and 46. The soils, which are residual or colluvial, include poorly- and well-drained profiles developed on the Lower Culm shales and on the Upper Culm shales and sandstones, and well-drained soils with organic-rich topsoils on the chert ridge. Very poorly-drained soils are developed on the Lower Culm shales along the valley floor at Eastcott. From the data in Fig.46 and Table 60 it is apparent that the distribution of Mo in the overburden is closely related to bedrock geology. Thus anomalous Mo values, ranging from 4-20 ppm 246 Table 60 Minor element content of the overburden developed on the principal parent materials around Rnstcott, Devon (sample depth 12-15 ins) Metal content (ppm)t Location and parent material Element Lower Culm shales Lower Culm shales Upper Culm N. of the chert Cherts in Eastcott valley Longhorn ridge Down Mo* <2-5 <2-3 4-20 <2-5 <2tt <2 7 <2 . . Cu 40-85 13-16o 4o-400 16-5o 6o 5o 90 35 v 85-160 40-130 100-300 130-300 120 110 170 180 Pb 30-85 20-200 40-160 13-50 55 50 6o 30 Ga 10-16 8-16 10-20 13-20 13 12 14 17 Ti 2000-4000 1600-8000 2000-5000 4000-8500 3180 3680 3720 5060 Ni 20-85 16-50 13-400 8-160 45 27 4o 28 co** 10-20 <5-40 5-40 <5-60 15 7 12 8 Mn 100-1600 100-600 160-85oo 40-2000 55o 285 700 , 415 Cr 40-160 40-130 50-200 100-200 75 6o 130 140 Fe 0 0.95-2.90 0.61-3.90 1.70-5.80 1.90-4.80 %2 3 1.90 1.39 2.81 3.3o No. of samples 11 14 13 16 Mato on minus 80-mesh fraction ''Geometric mean *Mean calculated with **Mean calculated with <2ppm = 1ppm <5ppm - 3 PPm (a)Geology + ++ + ++ + ++++ + + 4- 4- +++ +++++ +++ 4. .+ ++ ++ +4.: +4. + + +++ +t+ +4 +++ + +4.+11111", +++++ + ++++ ++ ++ f t ++ + + + + + + 4. + + ++++ ++ + +ti. 1 +++++ 4. 4. + _Lt.,. t ++++, i. ++ Jt+ ++7-+++++++,7++ +++ 4-4. ++ ' ++++ + + 4. 7 +++++004.4.1 + I.+ + +++ + ++++ + 44+ ,+++, Mo-rich Pre- chert Alluvium Lower Culm Lower Culm shs. Chert Upper Culm (b)Metal content of the overburden \ \ ...... / 11 \ 1 \ .--...... \ ‘ \\ "*. \ \ \ \ N \ \ a/ r-N \ \ I \ \ \ %... \ 1 \ \ \ \ >4 4-7 >7 0 880 1760 feet Fig. 46. Diitribution of Molybdenum in the Overburden of the Eastcott Area, Devon - sample depth 12-15in; data on minus 80-mesh fraction. Note locations of sites (1) and (2) described in Table 63. 247 with a mean of 7 ppm, are associated with the outcrop of the Mo- rich Lower Culm shales in the valley between the main chert ridge and the Upper Culm of Longham Down. A typical anomalous profile is described and the metal content summarised in Tables 61 and 62 respectively. In contrast, Mo values of less than 3 ppm are characteristic of the soils derived from the cherts and from the Upper Culm shales and sandstones. Background Mo values are also associated with soils developed on the Lower Culm shales north of the chert ridge in the Lew Valley. According to Dearman (1960,. 1966), the floor of the valley is underlain by beds equivalent to the Slate-with-Lenticles of Meldon and therefore almost certainly considerably older than the Mo-rich shales exposed near Eastcott. Independent investigations by I. Thornton (pers. comm.) and Horsnail (1968) have shown that the molybdeniferous soils are only extensively developed on the Lower Culm shales in the valley at Eastcott. The Mo content of the bedrock is therefore the principal factor determining the content of the residual overburden and the distribution of the molybdeniferous soils coincides with the anomalous Eastcott catchment area delineated by both the stream sediment reconnaissance and follow-up (Fig. 45). As in the South Pennines the Mo content of associated rocks, soils and sediments is more or less the same and it is therefore probable that the dispersion of Mo is dominantly mechanical. Although cherts and Upper Culm Measures underlie the higher ground within the anomalous catchment, 248 Table 61 Profile description of a representative imperfectly-drained soil developed on the Lower Culm shales near Eastcott,. Devon. Location: Waddlestone Farm, 3 miles south-west of Bridestowe, Devon. (Grid ref. SX482853) Relief: moderate slope, NNW aspect at 64o ft. 0.D. Drainage: imperfect Land use: permanent pasture Depth (ins): (sample no.) 0-2 Weak red,* silt loam with slight rusty mottling; (2820) friable with good crumb structure but liable to poaching; stoneless; roots and earthworms; merging boundary to - 2-7 Dark brown silt loam with good crumb structure; (2821) slight rusty mottling along root channels; abundant roots; small fragments of grey silt- stones and shales; merging boundary to - 7-13 Dark brown silt loam with good crumb structure; (2822) few roots; small fragments of grey siltstones and shales; clearly defined boundary to - 13-25+ Strong brown silt loam with weak crumb structure; (2823) almost rootless; abundant pieces of grey silt- stone. *Munsell Soil Colour Table 62 Metal content of a representative profile of an imperfectly-drained soil developed on the Lower Culm shales near Eastcott, Devon, Sample Depth pH Metal content (ppm)* No. ins. Fe 0 Mo 2 3** Cu Pb Ga V Ti Ni Co Mn Cr 2820 0-2 5.4 4.6 5 85 3o 8 200 4000 16 5 500 13o 2821 2-7 5.1 4.8 6 6o 5o 10 160 5000 16 5 boo 130 2822 7-13 4.8 5.6 5 85 40 30 300 6000 20 5 600 200 2823 13-25+ 5.0 9.8 5 6o 20 30 300 6000 30 5 600 200 *Data on minus 80-mesh material **Total iron expressed as Fe 0 2 3 250 dilution of the sediment anomaly by barren material from these sources appears to be negligible. The distribution of the remaining elements is summarised in Table 60 . The enhanced levels of Cu and Se associated with the Mo-rich shales are reflected in the distribution of these elements in the overburden. Thus Se levels in soils derived from the shales vary between 0.2-4.0 ppm with a mean of 1.5 ppm compared to normal background levels of less than 0.2 ppm (Webb et al, 1966a). Similarly, in the case of Cu the highest mean level, 90 ppm, is associated with the molybdeniferous soils. Levels of Co, Mn and Ni are also enhanced in the low- lying soils in the Eastcott valley compared to levels on the chert ridge to the north and on the Upper Culm to the south. This trend is particularly interesting since rather higher Mn levels were detected in the Upper Culm than in the Mo-rich shales and, although the Upper Culm shales over a wide area appear to contain more Co and Ni than the molybdeniferous shales,this is not apparent in the limited sampling possible in the Eastcott valley. Consequently, the increase of Co, Mn and Ni levels in the soils of the lower slopes of the valley does not appear to reflect the primary geo- chemical patterns. Furthermore, comparison of Tables 58,59 and 60 shows that levels of all three elements are appreciably higher in the stream sediments than in any other media. The same trend was detected independently by Horsnsil (1968) who found that the vory 7ioorly-drained soils on the 251 valley floor and the bank soils of the Enstcott stream were considerably enriched in Co, Mn and Ni with levels comparable to those in the stream sediments. The writer's data do not, however, show any significant increase in these elements in the very poorly- drained soils of the valley floor compared to nearby imperfectly- drained soils on the lower part of the valley slope (Table 63) Mn-oxide concretions in the very poorly-drained soils indicate the mobility and extensive redistribution of this element under gley conditions., On the basis of the results it would appear that, as in the South Pennines (page 149, Chapter 10) and even more markedly in North Wales (page 53 , Chapter 4; Nichol et al, 1967; Horsnail, 1968), the distribution of Co, Mn and Ni is modified by the secondary environment. Around Eastatt,all three elements are apparently leached from the poorly-drained soils on the ridge-crest and tend to migrate downslope in the circulating groundwaters. In the very poorly-drained valley floor soils there is abundant evidence of the mobilization and redistribution of Mn. HorsLail (1968) has shown that as the stream banks are approached the Eh and pH of the soils rise by about 0.2- 0.3 volts and 2-3 units respectively. This change is sufficient to bring about the precipitation of secondary Fe and Mn oxides, together with associated elements such as Co and Ni, in the bank soils and drainage channels. Consequently, the levels of these elements in the sediments often bear little or no direct relation- ship to levels in the associated bedrock or overburden. Cobalt pine in sheep is known to occur on both the chert ridge and Upper Table 63 Metal content of imperfectly-drained soils on the lower part of the valley slope compared to nearby very poorly- drained soils on the valley floor at Eastcott (see also Fig. 46) Drainage Conditions Depth Metal content (ppm)* p (ins) Mo Cu V Pb Ga Ti Ni Co Mn Cr Fe 0 2 3 Imperfectly-drained; 0-6 6 400 300 100 13 3000 6o 16 3000 160 7.0 lower valley slope - 12-18 4 400 200 100 13 3000 130 20 6000 130 9.0 site 1 18-24 4 500 200 50 13 2000 100 16 3000 16o 9.7 Very poorly-drained; 0-6 4 130 130 100 13 2000 40 16 1000 85 4.2 valley floor - site 1 12-18 4 130 160 40 13 2000 85 85 5000 130 3.0 18-24 3 100 16o 4o 16 1600 6o 30 3000 loo 2.8 r---3 Imperfectly-drained; 0-6 100 300 50 20 6000 20 5 600 130 4.9 lower valley slope - 12-18 3 50 200 40 20 5000 20 <5 300 160 3.8 site 2 18-24 3 40 200 20 16 4000 20 5 100 160 2.0 I Very poorly-drained; 0-6 1 3 85 200 50 16 4000 30 5 200 160 2.5 valley floor - site 2 12-18 4 40 130 16 16 3000 30 5 100 130 1.8 18-24 2 50 130 20 13 3000 30 5 130 130 2.0 4 *minus 80-mesh fraction 253 Culm of Longham Down (pers. comm. I. Thornton) but would not be suspected on the basis of stream sediment data unless the influence of the secondary environment on the distribution of Co was appreciated. In the Eastcott areetlevels of the remaining elements (Cr, Gal Pb, Ti and V) show only slight variations in the over- burden derived from the different parent materials and levels in the soils and sediments are more or less the same. Cr levels are rather higher on the Upper Culm and Mo-rich shales than on either the cherts or Lower Culm north of the chert ridge and a similar, though weaker, trend can also be recognised for V. (d) Relationship between the metal content of the 121poil and herbage Pasture grasses were collected from anomalous and control plots at the begining of July. As in the South Pennines,each grass and topsoil sample is the composite of six samples collected over an area of approximately 25 square yards. Earlier in the growing season (April) I. Thornton collected topsoils and herbage samples on a north-south traverse across the anomalous zone.* All these results are summarised in Table 64. The data in Table 64 show a close relationship between the Mo content of the topsoils and herbage. Thus grasses on the anomalous soils derived from the Lower Culm shales on the lower *The plots sampled by I. Thornton do not correspond to those sampled by the writer in July. 254 Table 64 Molybdenum and copper content of herbage growing on anomalous and control plots in April and July (The plots sampled in April by I. Thornton do not correspond to those sampled by the writer in July) Mo status soil Metal content (ppm) (No. of samples in Mo Cu parenthesis) Topsoil* Grasses** Topsoil Grasses In Aprilt Anomalous 3-15 1.8-7.0 55-140 9.5-16.7 (5) 9ff 4.o loo 13.4 Normal- control <2-4 0.8-3.0 40-130 7.4-8.6 (9) <3 1.6 75 11.o II. In July Anomalous 3-6 2.7-4.8 50-400 5.4-9.8 (4) 5 3.6 170 7.6 Normal- control <2-4 1.1-2.2 40-100 4.o-6.6 <3 1.6 (3) 6o 5.1 *Data on minus 80-mesh fraction **Dry weight basis !pers. comm. I. Thornton *'Arithmetic mean 255 slopes of the valley at Eastcott, contain between 2.7-4.8 ppm Mo with a mean of 3.8 ppm. In April it was found that herbage growing on the molybdeniferous soils contained up to 7 ppm Mo with a mean of 4 ppm (pers. comm., I. Thornton). In contrast, herbage on the control plots contained a mean level of 1.6 ppm Mo in both April and July. As in the South Pennines,the contrast between the Mo content of herbage growing on the anomalous and control plots is less than between the corresponding topsoils. This suggests that a relatively large proportion of the total Mo content of the anoma- lous soils is in a form unavailable to the herbage. The soils are generally imperfectly- or well-drained and do not appear to contain any secondary ferric oxide concretions. Consequently, it may well be that Mo is largely retained in an unavailable form by the weathered residues of the parent material. This, however, requires further investigation. Although the total Cu content of the Mo-rich topsoils is notably higher than the corresponding value for the central plots, 170 ppm compared to 60 ppm, Cu uptake by grasses growing on the anomalous soils is not appreciably increased. The mean Cu content of 7.6 ppm for grasses growing in the anomalous plots in July corresponds to a value of 8.0 ppm for herbage on the molybdeniferous soils in the South Pennines. Furthermore, although sampled on different plots in April and July, the marked decline in Cu status of grasses, from about 12 ppm in April to 7 ppm in July, is similar to the trend recognised in the South Pennines. Consequently, Cu uptake appears to be generally independent 256 of the total Cu content of the soil and the variations of Cu uptake between herbage samples growing on different soils are less than the variations relating to seasonal changes. In relation to animal health, the Mo-Cu status of herbage growing on the anomalous and control plots is very similar to that reported in the South Pennines. Thus the mean Mo content of the herbage growing on the anomalous soils, 3.8 ppm in July, is at the lower end of the range associated with molybdenum-induced copper deficiency (Table 54). Cu levels, although more or less normal for herbage growing on soils with adequate supplies of available Cu, fall below the level of 10 ppm recommended for cattle by the Agricultural Research Council (Alderman, 1968). Consequently, the raised Mo values associated with the Mo-rich soils could easily result in a conditioned deficiency in grazing cattle. On the basis of these results it is reasonable to suppose that the copper problems in livestock reported in the Eastcott area are, as first suggested by Webb (1964), a result of molybdenum- induced copper deficiency. Since there is no reason to suppose that conditions differ appreciably over the remainder of the dis- continuous zone of anomalous Mo values detected by the reconnaissance surveyieach of the anomalous catchments is potentially suspect. In view of the complex geology the distribution of molybdeniferous soils within the anomalous catchments is probably best determined by soil traverses. 257 CHAPTER 15. THE APPLICATION OF GEOCHEMICAL SEDIMENT SURVEYS TO TRACE ELEMENT PROBLEMS IN AGRICULTURE Since the Second World Warl the development of applied geochemistry has led to the widespread application of stream sediment surveys to mineral exploration. The technique is founded on the premise that the sediment approximates to a composite sample of the weathering products of the rocks and soils upstream from the sample point. By virtue of their origin, stream sediment samples are representative of much larger areas than either rock or soil samples. The principal difficulties arise from the modifying influences of the secondary environment on the relationship between the metal content of rocks, soils and sediments. Nevertheless, investigations, first in Zambia (Webb et al, 1964) and subsequently in Sierra Leone (Nichol et al, 1966a), showed that, apart from detecting gross geo- chemical anom7tlies related to mineralisation, the metal content of the sediments reflected relatively subtle variations in the geo- chemistry of the country rock. These results confirmed the essential role of be:qrock geology in determining the metal content of the stream sediments. Webb (1964) proposed the application of sediment surveys to detecting and delineating regions wherein agricultural problems could arise from either excess or deficiency of a trace element. Despite the complexity of rock-soil-sediment and soil-herbage- animal interrelationships,preliminary studies in Ireland and south- 258 west England disclosed a promising degree of correlation between the geochemical patterns and the incidence of animal disorders including cobalt pine, m-lybdenum-induced copper deficiency and selenium toxicity (Webb, 1964). The results of subsequent detailed investigations in areas characterized by abnormally high Mo and Se levels in Co. Limerick have been reported by Webb and Atkinson (1965), Atkinson (1967) and Thornton et al,(1966). As part of a continuin A.G.R.G. programme in applied bio- geochemistry, the relationship between the incidence of agricultural trace element disorders and geochemical patterns was further investigated during regional geochemical studies in south-west England, the South Pennines and North Wales. The results, reported in Part A of the Thesis, revealed particularly striking correlations between abnormally high Mo levels and the incidence of copper deficiency in north-east Staffordshire and between low Co levels and cobalt pine in sheep on Dartmoor. Subsequently, the writer investigated the distribution of trace elements, particularly Mo Lnd Cu, in rocks, soils and herb.ge in the South Pennines and on the Culm Measures west of Dartmoor, Devon. As a part of comple- mentary studies I. Thornton and J.S. Webb investigated the incidence of copper deficiency in livestock in the South Pennines. On the basis ref all these studies the application of geochemical sediment surveys can be discussed in relation to many of the agriculturally significant trace elements. 259 (a) Molybdenum In Co. Limerick (Webb and Atkinson, 1965; Atkinson, 1967)• the South Pennines and Devon there -ippears to be a fairly direct relationship between the Mo content of rocks, soils and sediments, and the zones delineated by the Mo-rich sediments correspond to the distribution 'f molybdeniferous residual or drift soils. Further- more, despite variations in Mo uptake by herbage and the relatively low levels of available Mo in the South Pennines and Devon, there is a broad correlation between the Mo content of the sediments and the Mo status of the pasture herbage. Thus, in each of the three study areas, the Mo content of herbage from the anomalous zones falls within the range associated with molybdenum-induced copper deficiency whereas levels in herbage from background areas are normal. Investigations of blood copper levels in cattle in Co. Limerick (Thornton et al, 1966) and the South Pennines (Webb et al, 1968) hove shown that herds within the anomalous zones experience a considerably higher incidence of copper deficiency than the control herds. It is considered particularly significant that in the South Pennines, as a direct result of the reconnaissance sediment survey, (i) the relatively small suspect area around Onecote was extended to include approximately 50 square miles in north-east Staffordshire and 25 square miles south of the limestone plateau in Derbyshire where only one case of copper deficiency had hitherto been reported, and (ii) that in many cases the affected animals showed no visible 260 symptoms of copper deficiency but responded to copper therapy with a marked improvement in live-weight gain. In view of these results,there can be little doubt of the applicability of stream sediment surveys to detecting, under broadly similar conditions, areas of Mo-rich soils wherein enhanced herbage levels may constitute a potential agricultural hazard. Furthermore,it is apparent that the sediment survey is of especial value in delineating areas wherein enhanced Mo levels give rise to sub-clinical copper problems which could well be difficult to diag- nose or define. These conclusions are corroborated by the results cf preliminary studies on the Lias in southern England (Webb and Thornton, 1966; Thornton et al, 1967) and in the Harlech area of North Wal-,s (Thornton and Webb, 1968), which have again shown a close relationship between the distribution of Mo-ri,11 soils and sediments s in regions in which bovine hypocuprosis is known to occur. The relationship between the No content of soils and sediments appears to be straightforward under the conditions encountered in the British Isles. Consequently, it is considered that the principal difficulties with regard to the application of sediment surveys to molybdenum-induced problems are likely to arise fromlariations in Mo uptake by herbage. In this respect further investigation is required (i) to account for the appreci- ably greater proportion of available Mo in the molybdeniferous soils derived from mixed shale-limestone drift in Co. Limerick compared to soils derived from similar shale parent m::terial in the South Pennines 261 and (ii) to determine the effects of environment on the availability of Mo held by different soil fractions. (b) Copper As in the case of Al ,there appears to be a fairly direct relationship between the Cu content of rocks, soils and sediments, although in the South Pennines there is evidence that Cu levels in the upper horizons of soil profiles are somewhat lower than in their shale parent materials (page149, Chapter 10). Abnormally high Cu levels in soils and sediments can be related to mineralisation and mine contamination. Despite variations in the total Cu content of topsoils from 8 ppm to 160 ppm .end corresponding EDTA-extractable Cu values of 3.6 ppm to 72.0 ppm in soils derived from various parent materials in the South Pennines, the Cu content of pasture herbage remains remarkably constant. Furthermore, Cu uptake appears to be largely independent of environmental variables such as pH and drainage conditions. No close relationship can therefore be anticipated between the total Cu content of sediments and the Cu status of herbage except possibly at the extreme limits of the range leading to copper deficiency on the one hand and toxicity on the other. (c) Selenium Stream sediment reconnaissance and subsequent follow-up studies have provided the first evidence of seleniferous soils in England and Wales (Webb et al, 1966a). Preliminary herbage analysis 262 has not, however, detected increased Se levels in herbage growing on the seleniferous soils and it appears that, as in Ireland (Webb and Atkinson, 1965; Atkinson, 1967), potentially toxic herbage is likely to be restricted to areas of poorly-drained organic-rich, alkaline soils. This environment may well occur elsewhere in the U.K. and enhanced Se levels in soils could then constitute an agricultural problem. As first proposed by Webb and demonstrated by Atkinson (1967), combined geochemical-environmental maps could be of considerable value in delineating suspect areas. In view of the low productivity of Se analysis and the close association of Mo and Se in soils and sediments derived from metal-rich black shales, Mo is a useful guide or pathfinder element for Se at the reconnaissance stage. (d) Cobalt and Manganese Although sediment surveys have delineated low Co levels associated with cobalt pine in sheep on the Wicklow Granite in Ireland (Webb, 1964) and low levels of both Co and Mn associated with cobalt pine and bovine infertility problems respectively, on north-east Dartmoor, there is considerable evidence from all three reconnaissance areas that levels of Co and Mn are enhanced in the sediments compared to the associated soils. Follow-up studies in North Wales and Devon (Nichol et al, 1967; Horsnail, 1968) have shown that the enhanced levels in the sediments result from the mobilization and leaching of these elements from poorly-drained 263 soils and their subsequent precipitation in the bank soils and drainage channels. The effect is most marked in moorland areas, where massive Mn anomalies may be developed in the drainage channels, but can also be recognised in areas of poorly-drained agricultural soils. Consequently,the Co and Mn content of the sediments may bear little direct relation to soil content and enhanced sediment values may be associated with the most impoverished soils. If sediment surveys are to be of agricultural value in relation to Co and Mn disorders, the effects of the secondary environment must be fully appreciated. Horsnail (1968) has esta- blished three main criteria whereby areas of leached soils and enhanced sediment values can be recognised: they are (i) the association of Co, Mn and As patterns of high relief, (ii) high values for the ratio of Mn to Cr, Ga, Ti or V, which are relatively uninfluenced by the secondary environment, compared to values on the same parent material elsewhere, and (iii) abnormally large amounts of secondary Fe and Mn oxides can be extracted from the sediments by r..- :gents such as ammonium oxalate. With the application of these criteria, in conjunction with proper orientation studies of soil-sediment relationships prior to stream sediment surveys, it should be possible to distin- guish areas of normal Co and Mn status from those where agricultural problems may arise from either (i) low Co and Mn levels in the bedrock, as on most granites, or (ii) excessive leaching of the elements from soils developed on bedrock with normal Co and Mn 264 values. It should, however, be noted that agricultural problems may also arise, as in the Vale of Clwyd, where normal or marginally low total values are associated with low levels of available Co and Mn due to their immobilization in organic-rich alkaline soils. Total metal analysis of the sediments will not, of course, indicate the low available levels in the soils. (e) Arsenic, Lead and Zinc In Devon and North Wales incidences of Pb and As toxicity in livestock and Zn toxicity in cereals are associated with mine contamination. Pollution of this type,arising from mining or industrial activity, is readily detected by sediment surveys and in each of the affected areas the sediments contain abnormally high metal levels. In view of the considerable public interest in the Pb content of foodstuffs (Lord Douglas, 1967), the epidemiological impli- cations of the massive heavy metal anomalies detected in all three reconnaissance areas require further investigation. The work to date has been largely based on the relationship between the total metal content of soils and sediments. Consequently, considering the complexity of rock-soil-sediment and soil-herbage- animal interrelationships, the correlations between the geochemical patterns and the incidence of animal disorders are surprisingly good. Furthermore, there is no reason to suppose that, with suitable analytical techniques, sediment surveys cannot be extended to cover a wider range of problems arising from trace element imbalance and 265 also possibly from variations of major elements such as N, P and K. Considering the results as a whole it is believed that, as first proposed by Webb (1964), sediment reconnaissance, with the advantages of low cost and rapidity, promises to be a valuable aid in delineating areas wherein trace element imbalances could give rise to clinical or sub-clinical agricultural disorders or where latent imbalances could become clinical or sub-clinical if farming practices were changed or intensified. Furthermore, apart from their value in both mineral exploration and fundamental geology, the regional geochemical patterns may well be relevant to pollution and epidemiological studies. At the same time,geochemical sediment studies, by increasing our data for a generally neglected media, contribute to a better understanding of the geochemical balance of the environment as a whole. 266 CHAPTER 16. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS FOR POTHER RESEARCH (i) SUMMARY AND CONCLUSIONS (4) South Pennine area 1. Geochemical reconnaissance by stream sediment sampling disclosed extensive areas,in north-east Staffordshire and south of the limestone plateau in Derbyshirei characterised by abnormally high Mo values. To the north and east of the limestone, the anomaly is narrow and intermittent. Within the anomalous zone Mo values in the sediments range up to 40 ppm with a mean of 7 ppm compared to background values of less than 2 ppm. The distribution of the anomalous sediments indicates that the source of the enhanced Mo values is associated with the outcrop of the lower Namurian shales. In west Staffordshire, however, where the shales are con- cealed by exotic drift, Mo values are normally less than 2 ppm. A remarkably similar metal pattern can be recognised for As, to a lesser degree for Co, Cu, Ni and V and possibly for Cr, Fe and Mn. Analysis of selected samples showed that the Mo-rich sediments contained Se values up to 9.0 ppm with a mean of 2.8 ppm compared to normal background levels of less than 0.2 ppm. 2. Bedrock analysis confirmed that the lower Namurian and Visean shales? with Mo values up to 50 ppm and a mean content of 11 ppm? are the source of the anomalous sediment patterns. 267 In contrast, Mo levels of 2 ppm or less are characteristic of the Carbonfierous Limestone and of the upper Namurian and Westphalian shales and sandstones. Compared to other bedrock units the molybdeniferous shales are also enriched in As, Cu, Se and V and the trace element assemblage is very similar to that reported by Atkinson (1967) in the Clare Shales of Co. Limerick. The enhanced metal-values are characteristic of shales deposited in an anaerobic 'black- shale' environment. The upper limit of Mo-rich shale deposition in the South Pennines more or less coincides with the onset of coarse detrital sedimentation from the north and appears to have occurred rather earlier in north-east Staffordshire than at Tansley on the eastern side of the limestone massif, Within the lower Namurian succession two facies with con- trasting trace element assemblages can be recognised (i) the Mo-rich 'black-shales' and (ii) the Crowstone facies comprising quartzitic turbidites interbedded with non- molybdeniferous grey shales. The molybdeniferous shales appear to have been deposited in a marine basin under stagnant bottom conditions whereas the Crowstone facies probably represents accumulation in an oxygenated environ- ment relatively close to the southern margin of the Carboniferous Central Province. Detailed sampling of the contraEting facies have shown that the enhanced levels of 268 As, Mo and Se are restricted to the anaerobic sediments where- as Cu and V levels are equally enriched in the shales of both facies. Consequently, the enhanced levels of Cu and V in the lower Namurian and Visean shales as a whole may partly reflect the metal content of detrital material transported from the south. In contrast, enrichment of As, Mo and Se clearly reflects their extraction from seawater under anaerobic conditions. In the case of Mo this was most probably brought about either by sorption on organic matter or by sorption and coprecipitation with iron sulphide gels. 4. The Mo content of the overburden is closely related to geology. Thus mean Mo values of 6 ppm are associated with both residual and transported overburden derived from the Mo-rich shales compared to levels of 2 ppm or less associated with the over- burden developed on other parent materials. As, Cu and V are also enhanced in the molybdeniferous soils. Analysis of selected samples disclosed Se values of up to 7.0 ppm with a mean of 4.0 ppm in Mo-rich soils compared to normal background levels of less than 0.2 ppm. These results provided the first evidence of seleniferous soils in England (Webb et al, 1966a). 5. Base metal anomalies in the overburden can be related to (i) Cu, Pb and Zn mineralisation in the lower Namurian and Visean at Mixon and Warslow, (ii) Pb-Zn mineralisation on the margins of the limestone massif, and (iii) enhanced levels of Pb and Zn associated with limonitic material in the Bunter 269 Pebble Beds in the south-east of the detailed study area (Taylor et al, 1967). 6. On a regional basis the relationship between the Mo content of rocks, soils and sediments appears to be relatively straightforward with similar Mo levels in all three media. In contrast, levels of Co, Mn and Ni are often appreciably higher in the sediments than in the associated soils. This trend, which is most marked on the moorland in north-east Staffordshire but can also be recognised in areas of poorly- drained agricultural soils, is attributed to mobilization and leaching of these elements in the overburden followed by precipitation in the drainage channels as described by Nichol et al (1967) and Horsnail (1968). In soils derived from shales, levels of Cu and V are lower in the overburden than in the parent materials. No such tendency can be recognised on sandstones and the contrast between the Cu and V content of shales and sandstones is thereby reduced during weathering. This difference possibly reflects the greater susceptibility of shales to chemical weathering. 7. The distribution of trace elements in soil profiles was investigated over a range of drainage conditions for residual, local drift and alluvial soils derived from the Mo-rich shales. The most consistent trend is for metal content to increase with depth irrespective of soil-type or drainage conditions. Although most marked for Cu, Mo and V, the 270 increased concentration with depth can be recognised for most elements in at least some profiles. Furthermore, although size fraction analysis indicated that Cr, Ga, Ti and V are closely associated with the clay fraction, the contrast between the metal content of the topsoils and lower horizons is such that, even for these elements, leaching, as well as mechanical eluviation, must be significant in their pedolo- gical redistribution. The extensive redistribution of Fe and Mn in the poorly- and very poorly-drained soils is reflected by the abundance of mottles and concretions of their secondary oxides in the soil profiles. Variations in Mo content from horizon to horizon can often be related to variations in Fe, and Mo tends to accumulate in the ferru- ginous horizons of the poorly-drained soils. Thus the coarse sand fraction of a ferruginous horizon, the bulk of which consisted of secondary ferric oxide concretions, was found to contain 200 ppm Mo. In contrast, relatively low Mo levels are found in the reduced horizons of very poorly-drained soils and in the leached horizons of the moorland soils. On the basis of these results it is suggested that, as demonstrated by Robinson and Edgington (1954) in gley soils from North America, the mobility of Mo in the overburden is to some extent limited by its retention on secondary ferric oxides. 271 8. It has been shown that, although the contrast between the Mo content of herbage is less than between the corresponding topsoils, Mo levels in herbage growing on the anomalous soils are significantly higher than in samples from the control plots. From May to July the mean Mo content of the grasses on the anomalous pastures falls from 3.6 to 2.8 ppm and at the last sampling date the Mo content of white clover is normally higher than the associated grasses. The mean Mo content of white clover growing on the Mo-rich soils in July is 7.3 ppm. Moorland grasses and heather, with mean Mo values of 0.7 and 0.5 ppm respectively, were found to have the lowest Mo content of all herbage samples. 9. Mo uptake by pasture herbage can be broadly related to the total Mo content of the topsoil but does not appear to be influenced directly by drainage conditions, organic matter or by levels of P and SO4. A slight response to soil reaction, with increased Mo uptake as the pH was raised, was detected for white clover but not grasses. In the case of grasses, and to a lesser extent clover, there appears to be a broad antipathetic relationship between Mo uptake and the total Fe content of the topsoils irres- pective of drainage conditions or pH. This relationship is attributed to fixation of Mo by secondary ferric oxides. There is, however, no evidence of increased uptake by grasses growing on reduced soils in seepage areas. In 272 view of these results it was suggested that, although a fraction of the Mo was rendered unavailable to herbage by fixation on ferric oxides, the bulk of the total Mo was probably retained in an unavailable form by the weathered residues of the parent material. The relatively small proportion of available Mo may be (i) in solution, (ii) associated with clay minerals or secondary ferric oxides through anion exchange, and/or (iii) associated with organic matter. 10. The Cu content of the pasture herbage remains remarkably constant despite considerable variations in levels of both total and EDTA-er.tractable Cu. Furthermore, environ- mental factors appear to have no direct influence on Cu uptake. In pasture grasses there is a marked decline in Cu values from about 15 ppm in May to 8 ppm in July. In July the Cu content of white clover is normally more or less the same as in the associated grasses. Throughout most of the growing season moorland grasses and heather, with a mean content of 10.6 ppm, are a better source of Cu than pasture herbage. 11. Preliminary selenium analysis of herbage samples growing on poorly-drained organic-rich soils, which Irish experience had shown to be favourable to Se uptake (Webb and Atkinson, 1965), disclosed no evidence of increased uptake. It is therefore considered unlikely that seleniferous herbage 273 will be found to be widespread over the present study area, although it may well be found in suitable environments else- where in the U.K. 12. In relation to animal disorders, the Mo content of the herbage growing on the molybdeniferous pastures in the South Pennines is at the lower end of the range associated with molybdenum-induced copper deficiency in cattle. Cu levels, although normal for pasture htrbage, are generally below the minimum level of 10 ppm which the Agricultural Research Council has recommended for cattle. Furthermore, inorganic sulphate levels (mean 0.70%) in pasture herbage are adequate to allow Mo to exert its full limiting effect on copper metabolism. In view of these results and the extensive Mo anomalies delineated by the sediment surveys it is considered that molybdenum-induced copper deficiency could well be a more widespread problem than was previously suspected. Copper deficiency is also likely to occur outside the anomalous zones as a result of the inadequate Cu content of the herbage, mean 7 ppm, and unfavourable Mo:Cu ratio from July on. 13. Prior to the A.G.R.G. programme in applied biogeochemistry, cases of copper deficiency were known to occur in the Onecote area of north-east Staffordshire. Investigations, on the basis of the stream sediment surveys and follow-up studies, by I. Thornton and J.S. Webb have shown that the incidence 274 of copper deficiency is much higher in herds from the anomalous areas than in control herds. The incidence of deficiency being most severe in young stock and adult animals not receiving mineral supplements. Furthermore, although in many cases there are no visible symptoms of copper deficiency, preliminary investigations have shown a marked improvement in live weight gain of affected animals following copper therapy. (11..) Devon 14. Complementary investigations over a small area of Culm Measures west of Dartmoor have shown that the discontinuous zone of anomalous Mo values, detected during the stream sediment reconnaissance, reflects the distribution of Mo- rich shale horizons within the Lower Culm. The anomalous shales, containing up to 30 ppm Mo, are also enriched in Cu, Se and V compared to other bedrock units. 15. Soil sampling clearly indicates that the Mo-rich shales, exposed on the lower slopes of the valley near Eastcott, give rise to molybdeniferous residual soils with a mean Mo content of 6 ppm. In contrast, Mo levels of 3 ppm or less are associated with soils developed on older Lower Culm shales, cherts and on Upper Culm shales and sandstones. The distribution of the Mo-rich soils corresponds closely to the anomalous stream sediment pattern. 275 16. Mean Mo values of 3.8 ppm and 1.6 ppm were detected in herbage growing on the anomalous and control plots respectively. Despite considerable variations in the Cu content of the topsoils, herbage levels were fairly constant, around 7 ppm, and the Mo-Cu status of herbage growing on the molybdeniferous soils is within the range associated with molybdenum-induced copper deficiency. In view of these results it is considered likely that, as first suggested by Webb (1964), the copper disorders which have been reported from the zone of abnor- mally high Mo values are molybdenum-induced. ItO The application of geochemical stream sediment surveys to trace element problems in agriculture 17. The results to date suggest that sediment surveys can be of particular value in delineating areas of (i) raised Mo values associated with cases of both clinical and sub- clinical copper deficiency, and (ii) seleniferous soils which could, under suitable environmental conditions, as in Co. Limerick (Webb and Atkinson, 1965; Atkinson, 1967), support potentially toxic herbage. Agriculturally suspect areas arising from low Co and Mn levels may also be detected by sediment surveys provided full account is taken of the influence of the secondary environment on the disper- sion of these elements. No correlation between Cu status of herbage and sediment patterns was detected in the present study but may be found over a wider range of Cu values else- 276 where. In view of the complexity of rock-soil-sediment and soil-herbage-animal trace element relationships, the degree of correlation obtained between the geochemical patterns and the incidence of animal disorders is surpisingly good. 18. Since Webb (1964) proposed the application of sediment surveys to agricultural and health problems, research carried out at the A.G.R.G. has shown that the technique can be a valuable aid in delineating areas in which trace element imbalances may give rise to agricultural problems. Further- more, apart from their value in mineral exploration and geology, the geochemical patterns disclosed by sediment surveys may also be relevant to epidemiological and ecolo- gical studies in both natural and contaminated environments. (ii) RECOMMENDATIONS FOR FURTHER RESEARCH The applicability of sediment surveys to agricultural problems depends on the complexity of the rock-soil-sediment and soil-herbage-animal trace element relationships. Where these relationships are relatively straightforward, as in the case of Mo under conditions in the British Isles, the application of sediment surveys is also relatively direct. For other elements, however, either the soil-sediment, as in the case of Co and Mn, or the soil-herbage relationship, notably for Se, may be compli- cated by environmental factors. Consequently, in order to obtain 277 the maximum benefit from sediment surveys, research is required into the influence of environment on these relationships. Further information will enable a more detailed interpretation of geochemical maps in re1:tion to agricultural problems. 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