A THESIS Entitled the SECONDARY DISPERSION of COPPER in THE

THESIS

entitled

THE SECONDARY DISPERSION OF COPPER IN THE DRAINAGE SYSTEM OF THE KILEMBE MINE AREA, UGANDA.

submitted for the

degree of

DOCTOR OF PHILOSOPHY

in the

FACULTY OF SCIENCE IN THE UNIVERSITY OF LONDON

DIRK RICHARD CLEWS.

Royel School of Mines. Jonuory, 1962. THE UCCITVIRY DISC,T4 OF COPPER IN THE DR n, I N ':GE SYSTEM OF THE KILEMBE MINE AREA, UGANDA. by D.R. CLEWS. .Abstract.

Geochemicel studies have been cerried out over copper- cobalt mineralization in the Kilembe Area, Uganda. The mode of occurrence end dispersion mechenisms of copper were investigated in the soils, ground-waters, surfece waters end active stream sediments. In soils, the copper is mainly concentrated in the clay and silt size fractions, end rather more then half of the metal is associated with secondary iron oxides. Soil creep is active on the steep hill slopes end copper bearing soils enter the drainage vie the stream banks. Metal leeched from the soil by percolating rainwater is transported to the ground-water without apparently being re-precipitated in the lower horizons of the overburden. The solubility of copper in natural waters appears to be related to the pH and bicarbonate-sulphate content of the solutions. Shallow ground-weters ere acidic end contain low concentrations of bicerbonete compared to surface waters, which are neutral or elkaline, end generally contain high bicarbonete concentrations. The ecidity end low bicarbonate concentrations of subsurfece waters ere considered to be mainly due to the high partial pressure of cerbon dioxide in soil air, end ground-waters ere apparently cepable of dissolving larger concentrations of copper then surface waters. The increase in pH end bicarbonste (end the resultant decrease in saturation potential for copper) of surface weters is thought to be caused largely by the loss of cerbon dioxide upon transition from the subsurfece to surface environment. Ground-waters containing copper in excess of the saturation concentrations eppropriate to the surfece environment, precipitate the metal upon emergence into the atmosphere. The copper in stream sediments is concentrated mainly in the clay end silt size fractions. The metel is derived largely from eroded bank soils end, to e lesser extent, by precipitation from weters. Thus, the distribution of copper in the dreinege is controlled by both mechanical end saline dispersion mechanisms. The results of these studies indicate that surfece waters draining mineralization hove negligible drainage treins of ionic copper, but limited dreinege trains of non-ionic copper were observed. However, extensive downdreinege dispersion treins of copper in the sediments were observed, end it is possible to detect the presence of mineralization occurring in the catchment areas of streams by analysing stream sediments for hydrochloric acid soluble metel. CONTENTS Page

Abstract • . • 0 0 0 0 • • 0 • 0 i

Li st of Tebles 0 0 0 a 0 0 • 0 • • 0 • ix List of Figures • • • . • • •• . •.. xiii

INTRODUCTION . • • • • • •• • • 0 • 1

ACKNO7LEDGMENTS • .. . • . •• • • • 0 12

SUMMARY . . . 0 • ...... 13 SECTION I. GEOLOGY AND PHYSICL FEATURES. •• . . • • 21 GENERAL DESCRIPTION.

(i)Location 0 0 0 0 0 0 • 0 0 • 0 • 21 (ii)Topography . • . • • • •• . •• . 22

(iii) Dreinege • • • • • • • • O • 0 • 24

(iv) Climate • • • • • 0 0 • • • 0 P 27

(v) Vegetation end agriculture • • e • • • 28 GEOLOGY

(i) Regional geology • • • • 0 0 • 0 0 31

(e) Rock types . . • •• 0 0 • • 31 (b) Structure .. • •• • . • • 36

(ii) Local geology et Kilembe Mine t 1 4 .. • 38 (a) Geology of mine eree .. • •. . 38 (b) Origin of the Kilembe Series •• • 43

(d) Metamorphism .• a • • • • • • 44 (e) Mineralization end ore—genesis .. • 46 (iii) Geology southwest of Yilembe Mine ... 47 (iv) Geology of the other study cress ... ••. 49

(e) Bukengeme • 0 • • 0 0 • 0 • 49 (b) The ereo between Bukangema end L eke Edward ... • • • 0 • • 54 (c) Asa—Sebwe—Nebiaji Ares •. • •. • 55 ii

Poe

(v) Overburden O 0 • O 0 0 • 0 0 0 0 0 55 SECTION II.

THE SECONDARY DISPERSION OF COPPER O 0 • 0 0 0 59

Introduction O 0 0 O 0 0 59

',. SOILS •.a a 0 0 . • 0 0 • 0 61 (i) Introduction ...... 61 (ii) Distribution of copper in soil profiles ... 62 (iii) Distribution of copper in B horizon soils ... 64 (a)Distribution of copper related to ) 64 mineraliztion 000 0 • 0 (b)Distribution of copper related to geology .00 ...... 66 (iv) Distribution of copper in soil size fractions 71 (v) The distribution of copper in magnetic fractions 73 (vi) The partition of copper between exchangeable lattice-held and secondary iron oxide associated copper ...... 75 (vii) Mode of occurrence and dispersion of copper in soils ... • . . ...

B. TATER ...... 0 0 • 85

(1) INTRODUCTION ... a . 0 0 0 0 0 0 0 85

(2) InITTER" ... 000 000 000 87 (3)GROUND-7PTER ... 0.0 ...... 90 (i)Distribution of copper ...... 91

(ii)Distribution of cobalt 000 000 93 (iii)Distribution of nickel end zinc ... 94

(iv)Distribution of iron ... 000 95 (v)pH ...... 96

(vi)Carbonate and bicarbonate 000 000 100 (vii)Sulphate and chloride ...... 100

(viii)Oxidation-reduction potential (Eh) 000 101

(ix)Conductivity 000 0 0 0 • • • 102

iii

Poge

(x)Temperoture 009 000 BOO 103 (xi)Summary ...... 103 (xii)Anomalous ground-water near the

Brenda tributary 060 000 103 (xiii)Ground-water from deep fissures... 107 (4) SURF "ICS: ',TER .00 ... • . • 109 (i) 'Previous work ...... 109

(ii) The Yvette tributary ... .06

(El) Copper 000 060 112 (b) Cobalt ...... ( c) Zinc ...... 113

(d)Nickel .00 000 114 (e)Iron ...... 114 (f)pH nnd Eh ...... , (g)Specific conductance nnd sod:lumbicarbonote... 115 (h)Chloride End sulphate... 116 (i)Temperature ...... 116 (iii) The Florence tributary ...

(iv) The Yetundu tributary GOO ... 118 (v) Other tributarf.es of the Dungelee River draining mineralized barren rocks 120 (vi) The Dungelee River ... . . 0 124 (vii) The Ise, Sebwe and Nabiaji Rivers ... 127 (viii) Summery of significance of measurements obtained from the surface waters 129 (ix) The Nyamogasani River ...... 129 (5) THE EFFECT OF TIME ON THE ABET 1L CONTENT typ 1-21T7R S'jTPLLS ... 6.0 000 132

(i)Introduction 600 .0. . . 132 (ii)Variations in conductivity rind metal content of surface weter on storage in gloss and polythene ...... 132 (iii)Sulphate End chloride concentrations 136

(iv)Bicarbonate, pH End Eh 000 • 0 • 137 iv Page

(6)SOME THFOR:P,TICn CONSIDERTIONS •O• Co. 138

(7)SUM ,'"RY STD DISCUSSION OF MODE OF OCCURRENCE WD DISPERSION OF COP7ER IN I\TTURU 7P.TER 148

C. I:CTIVT SE7I7ENTS 0.. 090 aoo 164

(i) Introduction, previous and present work *00 164

(o) Introduction ... 000 000 164 (b) Previous work 165

(ii) Distribution of copper in size frections ... 166

( 0 ) Size fractions 167 (b)Total copper content of size fractions 175 (c)The leachable copper content of the cls.y end silt size fractions ... 180 (iii) Mode of occurrence of copper in sediments ... 182

(s) Exchsngenble copper 00O 184 (b) Partition of copper between secondary iron oxides end lattices 000 184 (c) Iron from secondery iron oxides 186

(d) Iron to cooper retios 000 000 186 (e) Partition of cobalt between secondery iron oxides and mineral lattices 187

(f) Discussion •00 ••• 188 (iv) I summery of the regional pattern of metal distribution in streEm sediments ... 193

(v) Geochemice:1 prospecting considerations 000 197

(e) Size fractions 000 000 197

(b) Extractento related to specific forms of copper 000 900 200

(d) Exchangeable copper 000 000 201 (e) Other extrectants ...... 201 (f) The leachable copper content of different size fractions ... 203

(g) Heevy specific grsvity fraction 009 206

(h) Magnetite C 00 ••• 0 0 0 206

(i) Hotel associetions •O• ••• 207

PeE2 D. TIV,NSITION ZONES BETWEEN ENVIRONYIENTS 000 060 208

(i) Introduction 60e 000 208

(ii) Bank soils 000 000 208 (e) Previous work and description 208 (b)Copier distribution in size fractions 211 (c)Distribution of copper in profile 212 (iii) Transition between oxidizing and reducing conditions in soil profiles ... 213 (iv) & seepage zone of impeded drainege 215 (v) Summery end discussion of features observed in transition zones 000 000 216 (e) Freely dr,Dined soils in stream banks 216 (b) The transition zone from ground to surface water 000 000 216 E. DTSPEWTTPTT7p.qSOf COPPEROBSERVED IN SEDW7S OP THE DUNGUJE RIVER THE YVETTE TRIBUTtiRY 221

(i)The Yvette tributary ... peg 000 221 (ii)The Dun ;glee River and tributaries 231 SECTION ITT. THE 111.:.TURL HISTORY OF THE DISPERSION OF COPPER 242 CTTON IV .

P.PPT,ICP.TION 6•• so • •• 0 0 0 • 262 SECTION V.

SUGGESTIONS FOR FLIRT` :R RES:!-;fiRCH 000 000 269 SEOTION VI.

APPENDIX O 00 • • • t 272

1. Sample collection 0•0 ••• 272

(e) Soils • 0 0 O00 O00 272

(i)Profile sampling O0• 272

(ii)Soil sampling • 0 • • 0 • 272 vi Page

(b) Sediments • • . • • • •• • 272 (i)Sediment sampling •• • 272 (ii)Panned concentrates •• . 272 (c) Waters • • • • • • •• • 273

(i) Surface water • • • • 0 0 273

(ii) Ground-water • • • • • 0 273 2. Sample preparation • • • • • • •.. 273 (i) Drying • • • •. • 273

(ii) Dry dispersion a 0 0 • • • 273

(iii)Dry sieving • 0 0 0 • • 273

(iv)Wet sieving • . • ...• ID •

(v) Wet dispersion. • • • 0 0

(vi)Separation of magnetite ...• • • (vii)Magnetic separations •. • 276 (viii) water filtration ... 276

U\11,LYTICA,I, TECHNInUES •• • 0 • • 277 (i) pH • • • • • • •• • •• • 277

(ii) Eh • o • • 0 0 • • • • • • 277

(iii) Conductivity end temperature •• • . • • 278

(iv) Carbonate and bicarbonate • 0 0 0 0 • 278

(v) Chloride 0 • 8 • 0 0 • • • • • • 279 (vi) Copper in soils and sediments •.• •.• 280 (A) Dithizone test •• • •• • 281 (B) Diquinolyl test •• • • • 281

vii

Page, (C)Leachable copper test in soils and sediments ... 000 ••• (D)Hydrochloric acid soluble copper in sediments ... 066 OO41 (E)Exchengeeblc copper test ... 285 (vii) Total cobalt in soils end sediments... 286 (viii) Total nickel in soils and sediments... 287 (ix) Total zinc in soils and sediments ... 288 (x) Total manganese in soils and sediments 289 (xi) Hydrochloric acid soluble manganese in soils end sediments ...... 290

(xii) Total iron in soil end sediments 006 290 (xiii) Hydrochloric acid soluble in soils end sediment 006 000 006 291 (xiv) Solution of secondary iron oxide in soils end determination of the liberated iron, copper end cobalt 000 292 (xv) Total dissolved metals in natural water 293 (xvi) Solvent extraction techniques for ionic cobalt, nickel, zinc and iron in natural waters ...... 293 (xvii) Extraction of ionic copper from water by ion exchange resins ...... 295 (xviii) Sulphate determinations ...... 296 A.Resin—acid salt metal ... 296

B. Visual Thorin method 000 297

(xix) Spectrographic analyses 600 900 299 (xx) Yeasurement of rate of flow of surface water ...... 299 CALCULATION OF SATURATION CONCENTRATIONS

OF COPPER AND IRON •• • 0 • • 0 0 300

••• 304 LIST OF REFERENCES ••• •••

viii

LIST OF TBLES Table Page No4 No, 1 Rainfall at Kilembe and Mubuku ... 28 2 Geological succession of the Ruwenzoris ..• 32

3 Table of Kilembe Series formations 000 37 4 Gradients of five tributaries in the Bukangymy Free See *00 000 51 5 Copper, cobalt, and nickel contents of 'reathered rock types ...... 66 6 Metal content of B horizon soils over various rock types OSO • • • 67 7 Frequency distribution of copper in soils from the Bukangsmy trey 000 00. 68 8 Copper content of soils derived from different rock types in the Kilembe area 69 9 Copper end cobalt content of soils derived from different rock types in the Kilembe nree sile ••• • • • • • • 69 10 Definitions of materiel, mesh and micron size of fictions ... 000 000 71 11 Copper and cobalt content of magnetic fractions of soils 000 SOO 74 12 Partition of copper in stream sediments,

Kilembe ...... 000 76

13 Partition of copper in soils ... • • • 78 14 Partition of cobalt in soils ...... 79 15 Ratios of iron to copper in secondary iron oxides in soils ... 040 • • 0 80 16 pH and conductivity of rainwater at Kilembe

Mine • • • • • • ...... 88 17 Properties of shallow ground—waters from the Kilembe area 000 0Oe 92 18 Contrast between background end anomalous copper and cobalt values in ground—waters,

Kilembe prey 94 19 Composition of ground—water neer the

Brenda tributary, Dungolen Valley ... 104

Table Page Not No! 20 Metal content of soil profile from the Brenda tributary area 105 21 pH of water derived from underground workings et Kilembe Mine ... 108 22 Properties of surface weters from the Yvette tributary • . 111 23 Properties of surface weters from tributaries , flowing into the Dungnlee River 121 24 Properties of surface weters from the Dungolee River ... oes *** 125 25 Properties of surface weters from the Nyamegesoni, Aso, Sebwe ond Nobioji Rivers 128 26 Range of measurements in street-as draining mineralized and barren rocks, End anomaly

threshold OOP 000 000 130 27 Varietions in conductivity, copper, and iron of en enomelous surface water after storage in gloss end polythene containers 134 28 Variation in sulnhote End chloride concentrations upon storage 136 29 Variations in bicarbonate content, pH and Eh upon storsge 000 *00 137 30 Colmleted and observed concentrations of ionic copper in the Yvette tributary water 142 31 Concentrations of ionic copper in ground—weter compered to calculated ionic copper concentrotions 000 143 32 Concentrations of ionic iron in ground— water compared to concentrations calculated from pH and Eh determinations 000 145 33 Calculated End observed concentrations of ionic iron in streem water from the Yvette tributary 000 145 34 Relation between dissolved iron, bicarbonate, pH and Eh in ground—water 147 35 Comparison of the motel contents of ground, transitional and surface weters in the

Yvette rreo 00* • • • 000 157 36 Metal content of weter in drainage from copper mines et Butte, Mont. 000 161 x.

Teble Pege Not No.

37 Copper end cobelt distribution in size frections from the Yvette tributery 168

38 Copper end cobelt distribution in size froctions from the Muchingire and Ketundu tributaries . • . 169

39 Copper end cobelt distribution in size froctions from the Kiteberole streem 170

40 Copper end cobelt distribution in size fractions from the Dungelee River 171

41 Copper end cobalt in size frections from the Brende end Chenjojo tributaries 172

42 Size frection distribution of e soil end sediment samples from the Yvette tributery 173

43 Distribution of copper, end percentage coiner conteined in the different size frections of soil end sediment samples from the

Yvette tributary erect ••• 176

44 Spectrogrephic analyses of streem sediments

from the Kilembe ores • •• •O• 30?

45 Spectrographic analyses of streom sediments

from the Kilembe eree ••• ••• 303

46 Comperison of the totel end cold extrecteble copper content of enomelous snd bockground sediment samples SOO 000 181

47 Pertition of copper in minus 80 sediment size frections 000 000 000 185

48 fverege iron content of different size

frections from soils and sediments • • • 186

49 Pertition of cobelt in sediment size frections 187 50( e ) Copper, cobelt end nickel content of sediments dreining mineralized end berren erees 000 000 195 50(b) Copper, cobelt end nickel content of sediments dreining minerelized end berren arees 196 51 Copper extracted by different solvents from en enomelous end beckground sediment sample 202 52 Copper content of different size frections of streem sediments, Ruwenzori Mounteins, Ugende 004 000 000 203

xi Table Pege Not No. 53 Copper content of sediment size fractions obtained by dry—sieving ... 000 205 54 Distribution of copper end cobelt in size fractions, end the percentage of metal contained in each size frection 211 55 Distribution of total end leachable copper link soil profiles ebove end below the

ter table 4100 000 214 56 The totel end leachable copper content of e seepage zone of impeded dreinege in the enomelous Yvette heedweters 216 57 Copper content of bank soils end grey horizons in the heedweters of the Kiteberole tributery 219 58 Distribution of copper end iron, rotes of flow, end gradients, in the Yvette tributery 223 59 Geology of the Dungelee River eree 4040. 231 60 Distribution of copper end iron in weters, end copper in sediments from the Dungelee River ... 000 0040 233 61 Renge end everege of totel end leachable copper contents of sediments draining snomslous end background cress 234 62 Reproducibility of hydrochloric ocid extrecteble copper enelyses 4040. 285 63 Solvent extractions of copper, cobelt, nickel end zinc from synthetic solutions 294 64 Solvent extraction on duplicate we-ter symples 000 000 295 65 Comperison of solvent extraction end resin extraction for copper 4040. 296

xii LIST OF FIGURES. (bound et end of thesis). Figure No! U Location of Uganda field areas. 2 U Sketch map showing drainage of the Ruwenzori Mountains. 3 U Geology of Ruwenzori Range. 4 Total end leachable copper in soil profiles. 5 Metal content of soil profiles from marginal and sub—economic grade mineralization. 6 Distribution of copper in soil profiles.

7 Total, leachable zinc, copper and nickel anomalies in soils over the Bukangama ridge.

8 Distribution of copper, cobalt, nickel, end zinc in B horizon soils overlying Ore.

9 Distribution of copper, cobalt, nickel, and zinc in B horizon soils overlying marginal grade mineralization.

10 Distribution of copper, cobalt, nickel, and zinc in B horizon soils overlying sub—economic mineralization. 11 ) Distribution of copper end cobalt in size ) 12 ) fractions.

13 Geology of the Bukangama area.

14 Geochemical soil anomalies in the Bukangams area. 15 Geology in the Mubuku—Duberea area. 16 Hydrochloric acid soluble copper geochemical drainage map of the Mubuku—Duberea area.

Figure Not 17 Generel key for Figures 18 to 23. 18 Copper, nickel and zinc content of weters from the Dungelee, Nyamegeseni, Ass, Sebwe; Nebieji Rivers; Yvette end other Dungelee tributeries.

19 Iron content, pH end conductivity of waters from the Dungelee, Nyamageseni, Ass, Sebwe, Nebieji Rivers; Yvette end other Dungel4e tributeries.

20 Bicarbonate content end Eh of weters from the Dungelee, Nyamageseni, Ass, Sebwe, Nabiaji Rivers; Yvette end other Dungelee tributeries.

21 Mangenese end iron content of sediments from the Dungelee, Nysmegeseni, Ase, Sebwe, Nebieji Rivers; Yvette end other Dungeles tributeries.

22 Cobelt, nickel and zinc contents of sediments from the Dungelee, Nyamageseni, Ass, Sebwe, Nebieji Rivers; Yvette end other Dungeles tributaries.

23 Copper content of sediments from the Dungeles, Nyamageseni, Ass, Sebwe, Nebieji Rivers, Yvette end other Dungelee tributaries.

24 Copper values in sediments from the Yvette stream end Dungelee River.

25 Total end leecheble copper in bank soils. 26 -5 27 Section at sulphate activity of 10 showing activities of dissolved copper as functions of pH and total carbonate. 28 Stability field diagram of the aqueous ferric—ferrous system. 29 A Estimation of pH, Eh and iron content of ground—water containing bicarbonate. B Relation of total activity of iron in water, to pH and Eh.

xiv INTRODUCT ION. At the the invitation of the Uganda Geological Survey, Professor J.S. Webb visited the Kilembe area, in 1954. The purpose of the visit was to determine whether the area warranted detailed geochemical research studies. The results of this work were encouraging,. and J.S. Webb established the presence of anomalous copper in soils and stream sediments near sub-outcropping minerElization. As pert of the research programme of the Geochemical Prospecting Research Centre at Imperial College, Messrs. J.D. Jacobson and R.H.C. Holman carried out detailed field studies in the Bukengama area. Jacobson studied the dispersion patterns of copper in the soils overlying mineralization, and Holman studied the distribution of copper in the drainage. The results of Jacobson's investi&ations indicated that sub-outcropping copper mineralization could be detected by analysing the overlying soils for the trace metals copper and cobalt. Holman established that copper mineralization in the catchment areas of tributaries could be detected by analysing stream sediments for copper. He found that abnormally high copper values in the sediments extended downdrainage for approximately 1,000 feet from mineralization, and recommended that samples be collected at 500 foot intervals during reconnaissance prospecting. He developed o "cold extraction" analytical technique which 1. greatly increased enelyticE,1 productivity in the lsborstory, and could nlso be used in the field to detect downdrsinsge dispersions of copper.

R.H.C. Holmen found that sediments from the Kitebsikole tributary contained anomalous copper values which could !1b be related to known minerelizstion. J.S. Webb interested Kilembe Mines Ltd. in the unexplained enomely end, by applying the geochemiccl techniques developed by Jacobson, the CompEny discovered En eres contnining Kilembe type minerclizetion southwest of the BukEngnmr Ridge. Subsequent- ly, the southwestern cues between Kilembe end the Congo Republic were also geochemicelly prospected, f..nd extensive zones of snomtlous soils were delimited. (Figure 16). During the ebove geochemicel exploration programme, the Company personnel found that the dense vegetation surrounding the water courses made it imprncticel to collect sediment samples fit the recomended 500 foot interval. The possibility of extending the limited drainage trains was studied by J.S. Webb End R.E. Stanton (Consultants to Kilembe Mines Ltd.). Loboretory studies of the pertition of copper in the sediments indicated the possibility of improving the dreinege reconneissence technique by fractional enelyses. At J.S. Webb's suggestion, the Company agreed to support v research project to investigr'te in detail the

2. secondary dispersion mechEnisms and mode of occurrence of copper in the surface drainage system. The practical object of this study wEs to improve geochemicvl prospecting methods in the surface dreinnge, and to establish interpretive criterlo. The essentially nrnctical nature of the investigntions is emphasized, but it will also be realised that the interpretntion of these results hEve n direct bearing on estEblishing the mode of occurrence rind dispersion mechnnisms of copper. The secondary dispersion of copper in the zone of weathering is controlled by both mechenicol End chemical processes. The mode of occurrence of the metal depends to e large extent on the neture of these mechanisms, n cleerer understnnding of which will govern the selection of the most efficient geochemicel prospecting technique. The dispersion mechanisms of copper in soils, stream sediments nnd nnturnl waters nre intimately relnted, and therefore the distribution of metal in each environment was studied. The investigations were based cimost entirely on the general principles of geochemionl prospecting for copper, and these principles are outlined below. For clrity, the descriptions ire confined to soil surveys. The basic principles epply ift,ully to sediment and we-ter snmpling, es indicated in the concluding perogrophs.

3. Geochemicel prospecting for copper is concerned essentially with the detection of significant increases in the concentration of copper which may be derived from economic mineralization. In order to appreciate what mey be regarded as o "significant increase", it is essential to determine the range of values occurring in areas fer removed from mineralization, commonly referred to as the regional background. It is sometimes found that mineral deposits occur within c wide zone in which the generl level of values are higher than the regional background range. Aureoles of this type may reflect (o) o widespread impregnation of the country rock during primnry mineraliation, or (b) the aureole may merely reflect the presence of e potentially favourable host rock which may or may not contain economic

mineralization. An example of the latter type of tureole is found at Yilembe (page 69) where the copper concentrations in soils derived from gneiss (10 to 30 ppm) are representative of regional background variations. The fc.vourEble host rock for minerelizttion in the area. is the Kilembe Series rocks which ore overlain by soils containing an average of 100 ppm Cu. When sulphide mineralization is present, the soils contain more than 200 ppm Cu. The Cu values found in the soils derived from non-mineralized Kilembe Series

4. rocks Ere termed local background and the vPlues indicative of mineralization pre termed anomalous. A typical example of en aureole resulting from the impregnation of country rock during 7rimary mineralization is found in the cobalt district of central Idaho (Hawkes, 1952). The regionEl background concentrEtions of cobalt in the soils is 10 ppm, compared to en average local background value of 100 ppm. Economic cobalt mineralization is found only within the zone of locrl background soils. The locEl background values ere important in geochemicel prospecting since they may offer e large target et which to aim during regional rIconnaissance sampling. An important factor in assessing the applicability of geochemicel prospecting techniques is the difference in values, or contrast, between background Find anomelous concentrations related to the sensitivity of the rnelyticel methods. Thus, if background concentrations of total copper (Cu) in soils rre 30 ppm End Pinomalous soils contain 40 ppm Cu, the contrast is almost negligible and the difference of 10 pp-. Cu cannot be detected by the standard anElytical techniques for Cu, which hove a 25 percent mean accuracy, as determined by the method proposed by Craven (1953). If, however, the EnomElous soils contain 90 ppm Cu, the contrast is threefold, and the difference (60 ppm Cu) can be readily and reliably detected by the conventional

5. enelyticel methods.

In order to obtain en increased contrest between background end enomplous values, it is sometimes found expedient to F flelyse c specific size fraction of e semnle. For exemple, the clay-silt size fractions of semples derived from background end cnomelous canoes mey contain 150 end 200 ppm Cu respectively, wherees the plus silt (send) size frEctions may contain 10 and 100 pnm Cu, respectively. Therefore, if only the send fractions were analysed, the contrest would be ten-fold between beckground end anomalous soils compered to e negligible contrest in the cloy-silt size fractions. It is also possible that weathering processes involved in the dispersion of copper from minerelizption may mechanically end/or chemically concentrate the meta in e perticuler type of mcteriel or Et e nerticuler depth (e.g. soil horizon) as opposed to no such concentration in non-mineralized ereos. The contrest between anomalous end background samples will then be increased by enilysing the materiel in which enomclous metal is specifically enriched. In general terms, soils derived from minerelizE.tion will normally contein more copper then soils derived from unminerelized rocks, end the difference in concentrations could elwrys be detected if sufficiently sensitive Enelytical techniques were available.

6. The inadequate sensitivity of current geochemicel analytical methods is reflected in the development of new techniques which distinguish between different forms of copper. The basic principles of these techniques is to extryct from a sample thct port of the copper content derived froma s^ec if 1c source. For example, the copper minerals derived from oxidation of sulphides may differ in chi/Teter from copper minerals derived from other sources. If an analytical technique were developed to extract only the copper derived from sulphides, then the results would be directly in-iicative of sulphide metallization.

The basic principle of these techniques is a chemical attack on the sample which specifically liberates the diagnostic form of copper. For reasons which will be explained more fully in subsequent sections, it is frequently found that copper derived from sulphides is less strongly bonded in the soil than copper derived from silicates.

Analytical techniques have been developed to extract this loosely bonded metal. Thus, progressively more firmly bonded metal is extracted by determining exchangeable copper

(exCu), leachable copper (exCu) and hydrochloric acid soluble copper (HC1-Cu). variation of the technique which extracts a specific form of copper is to determine the copper content of a

7. particular mineral. For example, it may be found thot magnetite, essocieted with minerFlizetion, contains

significantly greeter concentrations of Cu then does

magnetite from other sources.

Another exnmple of association between copper and e

specific mineral, which might be used for prospecting

purposes, is the partition of copper between secondary

iron oxides (Cure) and lattice held copper (Culint). Thus, if it were found that significEnt increases in copper were

nssocieted with the secondt- ry iron oxides derived from oxidized sulphides compered to the copper content of

secondary iron oxides derived from other sources, then c

specific chemical attack, which would liberate only the.

CuFe' would differentiate between enomelous and background simples. atcrnetively, the iron oxides may be separated

from the other minerals by simple hand penning end the

resultant concentrates analysed for Cu.

Cu derived from minerrlizetion may be prcferentielly enriched in minerel constituents which characteristically occur in a particular grain size. In these circumstances a combination of selective size frection and selective

chemical ettock mey obtain the MPXiMUM contrast between enomalous cnd background samples. Thus, it is not unknown for anomalous Cu to be preferentially enriched in specific clay—size minerals.

8. In areas ,,,there the contrast between specific forms of

copper (e.g. Cu, cxCu, Cure, etc) cannot distinguish

between vnomelous and background soils, P third technique

is often used. This technique involves two (or more)

determinations of the concentrations of different forms

of copper and comparison of the ratios between these metals.

Thus, it rag be found that the total Cu content of soils

derived from minerElized areas contain a higher proportion

of exCu, cxCu or HC1—Cu then similar material from non—

mineralized areas. laternttively, the concentrations of

copper and some other associated metal(s) can be determined.

Thus, for instance, the Cu,Co ratios may be divEnobtic of

copper minerrlization when compared to the Cue Co ratios

from non—mineralized areas.

Another indirect technique is the use of pathfinder

elements (7arren and Delcvault, 1953). This technique is generally used in geochemical prospecting for inert metals

such vs gold, but it is possible that the technique may be

utilized in prospecting for copper or for the location of

e favourable host rock for copper mineralization. Thus, if

nickel (Ni) or zinc (Zn) were specificclly associated with

copper ore and these metals occur in negligible concentra—

tion in a non—mineralized area (f- E3 opposed to copper occurring in appreciable concentrations), then differentiatior

between anomalous and background samples can be obtained by

9. onolysing the srmples for Ni. or Zn. Alternotively, if the enolyticel method for Ni were more sensitive and could distinguish between, soy, 1 end 10 ppm Ni (es opposed to, soy, 10 to 40 ppm for Cu), then the presence of copper minerrlizetion could be detected by relatively smell increases in Ni vrlues. Also, if Zn were more mobile then

Cu during primary minerclizotion or upon subsequent weythering of these deposits, then the halo of Zn dispersion would be more extensive Ana, therefore, offer e lorger terget for regional reconnoissfnce prospecting for copper. The ntios of pethfinder metals, which ore essocinted with copper minonlizotion, could also, in certain cases, distinguish between ereos containing copper minerolizetion ond Drees barren of copper. Stream sediments ere essentielly eroded soils from which some meteriol hos been removed by chemical end mechonicol stream action. Metals in solution in notural waters moy be added to sediments by precipitotion or sorption. The principles of prospecting techniques for

copper in sediments are bEsiecaly the some os those

outlined for soils. The saline dispersion of copper in ground end surface waters is essentially chemicolly controlled. The removal

of metal from water by precipitation or sorption effects

10. the distribution of the metal in both soils and sediments.

Two of the principal forms of the total copper content of water ere ionic copper (Cung) which is in true solution, end non-ionic copper (Cusol) which mry occur as soluble complexes, colloidal solutions, suspensions, etc.

The metal content of mitural water is generally in the order of a few parts per billion (ppb) and analytical techniques -re different to those used for sediments and soils, but the basic principles of hydro-geochemicrl prospecting techniques ere the same.

Other than direct analyses for copper and associated metals, hydro-geochemical techniques also utilize indirect measurements such ns pH, Eh, conductivity, sulphate (SO4), chloride (01), bicarbonate (HCO3) etc. These determina- , tions may be regarded ES "pathfinder elements" rnd, for practical purposes, may be applied to hydro:::eochemical

Prospecting for copper in the same manner as pathfinder elements in soils End sediments.

The results of the writer's inv,-stications are presented after a general description of the study areas. Thereafter the natural history of the secondary dispersion of copper in the Trilembe arca is considered. The practical application of the findings to prospecting for copper is

Presented prior to c description of the sampling nnd analytical techniques used for these studies.

11. ACYNOWLEDGMENTS.

The —crk upon which this report is based WES carried out as part cf the orognmme of the Geochemical Prospecting Research Centre at Imperial College.

Sincere apnreciEtion is expressed to Kilembe Mines Ltd. for providing facilities and generous financiEl assistnnce, and to Mr. Pugsley, the General Manager, and Dr. G.R. Davis, the then consulting geologist, who sponsored the reseErch project. The writer worked in close collaboration with Mr. J.S. Smit, the senior explorrtion geologist, and gratefully cknowledges c.11 the help Fnd ccorded to him by Mr. Smit End members of his staff: in particular Messrs. N.M. 7ichaelides rnd M.4. Chcudhry. Indebtedness is clsa. expressed to the chief geologist, Mr. H.H. Bird, for the information on the underground geology of the Mine, rn1 the informatf_—e discussions on the locil geology within the

Yining Le: se. These studies were directed by Professor J.S. Webb, to whom the writer is indebted for nronosing the problem

:- nd his vcluble help cnd advice throughout the work. The help given to the writer by members of the staff at Imperirl College is Elso gratefully acknowledged.

12 SaILIARY

Inproduction.

Copper-cobalt mineralization occurs at Kilembe in the south-eastern foothills of the Ruwenzori Mountains, Uganda. The mineral deposits are being exploited by Kilembe Mines Ltd.

Encouraging results wore obtained in 1954 by Professor J.S. Webb, who appraised the suitability of the area for applied geochemical research studies. J.D. Jacobson (soils) and R.H.C. Holman (stream sediments) subsequently studied the dispersion of copper in the Bukangama rT'ea.

Prospecting techniques and interpretive criteria were established for (a) locating sub-outcropping mineralization by goochemically analysing soil samples for copper (Jacobson) and (b) locating mineralization in the catchment area of minor tributaries by analysing stream sediments for total or leachable copper (Holman). Holman found that anomalous drainage trains of copper extended for approximately 1,000 fact from mineralization, and recommended that sediment samples be collected at 500 foot intervals. Due to the absence of detectable drainage trains in the major rivers, and the dense vegetation surrounding; tributaries, in the extremely rugged foothill areas of the Ruwenzoris, Kilembe Mines' personnel considered that it was impractical to implement Holman's recommendations in regional reconnaissance prospecting.

Subsequent work by Webb (1958), and Webb and Stanton, (1959) indicated that the length of anomalous drainage trains could probably be increased by modifying the sampling and/or the analytical techniques. It was, therefore, decided that the writer should carry out further detailed studios on the distribution of copper in the surface drainage system, and to determine whether it was possible to improve the existing drainage reconnaissance techniques. In order to understand more clearly the dispersion mechanisms of copper, it was found necessary to extend the investigations to soils and ground-waters. In view of the practical nature of the problem, the writer based his investigations almost entirely upon the principles of geochemical prospecting.

Physical and geological features.

The Ruwenzori foothills arc extremely rugged with sharply crested ridges separating narrow and deeply dissected

13. youthful valleys, The valley slopes are steep and commonly exceed 30 degrees.

The elevation of the study areas ranged from 4,000 to 8,000 feet, The climate is sub-tropical. Rainfall is normally about 50 to 60 inches per year and precipitation is spread fairly evenly throughout the year. The foothills are drained by swiftly flowing perennial streams in steep sided gullies, Stream waters below the snow line (13,000 feet) are mainly derived directly from outflowing ground-water. The g2ound-waters are derived in part from molting snow and ice, and in part from the rainwater which percolates through the upper soil horizons. Tho ground-water intake at high altitudes provides a hydrostatic head at lower elevations, and tributaries commonly rise some 700 feet from ridge crests. Shallow ground-waters in the zone of weathering are considered to be derived largely from the rain, and they circulate rapidly before being discharged into the surface drainage system. Deep ground-water is considered to be derived largely from the mel'Ging snow and ice, and it circulates slowly in deep interconnected fiscures, The foothills are generally covered by dense tropical forests and heavy secondary vegetation in deforested areas. Geologically the Ruwenzoris are described as a pre- Cambrian eligmatite complex containing bands of schists, quarttes, amohlbolFGes and other rocks. The favourable host rock for mineralization is an amphibolitic horizon, which generally occurs in the middle of the Kilembe Series rocks. The mineralization is dominantly chalcopyriGe and pyrite with lesser amounts of linnaeite, Soils.

The soil cever is contiw:ous and averages about 6 feet in depth. The soils are essentially residual and are markedly immature. Depths of oxidation are shallow, and erosion is rapid on the steep hill slopes,

Tho intensity of weathering increases and mechanical cohesion decreases towards surface. Mechanical movement of soil down the steep hill slopes occurs mainly in the A horizon and, to a 'lesser extent, in the B horizon. The C horizon is static. Copper, cobalt, nickel and zinc values decrease towards surface due to chemical leaching and mechanical mixing with barren material,

The leachable copper (exCu) content and cxCu:Cu ratios

14 increase towards surface. The cxCu:Cu ratios are a function of depth, remarkably consistent, and are considered to reflect a chemical equilibrium between Cu, cxCu and chemical weathering processes. The acidity of rainwater (pH 5.3) indicates its effectiveness as a leaching agent, and the mechanism by which copper is removed from the soils and transported to the ground-water.

No concentration of copper by mechanical (eluviation) or chemical (precipitation from solution) was observed in any freely drained soil horizon.

The distribution and concentrations of Cu in the -80 mesh B horizon soils reflects sub-outcropping geology. Thus Cu values of greater than 200 ppm indicate possible sulphide mineralization. The Cu content of soils derived from gneissic rocks ranges from 10 to 30 ppm, whereas soils derived from non-mineralized Kilembe Series rocks contain 40 to 200 ppm Cu. The Cu:Co ratios differentiate between soils derived from gneissic rocks, the Middle, Upper and Lower Kilembe Series rocks and the Zn:Co ratios distinguish between footwall and other Kilenbe Series rocks. The Ni:Co ratios derived from mineralization are loss than 2, whereas the ratio is greater than 2 for soils derived from basic dykes.

Size fraction analyses of anomalous and background -80 mesh soils indicate (a) that samples contain a relatively consistent proportion of clay-silt material (60 percent), (b) the Cu content increases with decreasing grain size, (c) the clay-silt fractions contain a relatively consistent percentage of copper (85 percent), and (d) the secondary iron oxide content also increases with decreasing grain size, and the clay-size fractions contain a consistent quantity of secondary iron (29,000 ppm Fe). These features are considered to reflect the essentially chemical nature of the weathering processes and also explains the efficiency of the -80 mesh fractions in geochomical prospecting.

The Cu content of secondary iron oxides derived from oxidized sulphides is 8 times greater than the Cu content of secondary iron oxides derived from other sources. The Cu content of secondary iron oxides is greater than lattice held copper in all soils.

Water.

In order to determine their application to hydro- geochemical prospecting techniques, and also to establish the processes involved in the dispersion and mode of occurrence of copper in the aqueous medium, water samples representative of the following types wore selected for

15. investigation: (a) rainwater, (b) surface water, (c) shallow ground-water and (d) deep ground-water. The following determinations and measurements wore made: total Cu (Cu) and ionic Cu (Cuaq); Co and Coaq; Ni and Niaq; Zn and Znace• Fe and Feaq' HCO3) SO4, Cl; pH; Eh; conductivity; temperature and the volume and rate of flow of surface waters. Some samples were analysed for the full range of properties listed above, whereas other samples were only partially analysed. It is considered that the solubility of Cu and Fe in natural waters is controlled mainly by the pH and Eh of solutions as well as the SO4 and HCO3 concentrations. Theoretical saturation concentrations of Cu (Silman, 1958), and Fe (Hem 1960) in waters have been calculated.

The pH of natural solutions is largely controlled by the partial pressure of CO2. Shallow ground-waters have a low pH and HCO3 content duo to the high partial pressure of CO2 in soil air. However) upon transition to the surface environment, ground-waters lose CO2 and the pH and HCO3 content of solutions increase. The calculated saturation concentrations of Cu and Fe in ground-waters is greatly in excess of the saturation concentrations of surface waters. Upon transition to the surface, dissolved metal in excess of the saturation concentrations appropriate to the surface environment is precipitated from the ground-waters.

In ground-waters, the copper is derived from reactions between (a) percolating rainwater (pH 5.3) and the soils, and (b) ground-water and decomposed rocks and soils. Ground- waters are unsaturated with respect to Cu and Fe due to the lack of available metal and/or the time required for solutions to attain equilibrium. However, total and ionic Cu, Co, Ni and Zn concentrations reflect the presence of mineralization. The dispersion of dissolved metals is controlled by the movement of subsurface solutions and dilution. The saline dispersion of anomalous metals, downridge from mineralization, is in excess of one mile. No relationship between mineralization and any other measurement was observed.

No precipitation of metal from subsurface solutions in any soil horizon was noted, but appreciable amounts of metal

16. are precipitated during transition from the ground to surface environment, and surface waters rapidly attain equilibrium with respect to dissolved metals. Surface waters are generally saturated with respect to copper (±3ppb Cu ae ) and, as equilibrium is rapidly established, only very limited downdrainage dispersion trains from mineralization is found.

The formation of detectable anomalous drainage trains is considered to be dependent on (a) the saturation potential of waters compared to background concentrations, (b) the time required fo.1, solutions to attain equilibrium with the surface environment and the absolute difference between the properties of ground and surface waters, (c) supersaturation, and (d) dilution. Ground and surface waters in the Kilembe area provide examples of all the above mechanisms of Cu distribution and their application to hydrogoochomical prospecting in general is considered.

Non-ionic Cu (Cusol) concentrations in surface waters are considered to reprosonG suspensions of copper salts derived from precipitated ionic Cu. The Cusol is transported mechanically by stream waters, and settling of this material is considered to contribute to the Cu concentrations found in stream sediments. Anomalous downdrainago dispersion trains of Cusol in surface waters wore found to extend for at least a mile rrom mineralization,

Evidence of an independent precipitation of Fe and Cu from natural waters was observed,

Active stream sediments.

Sediments are essentially eroded bank soils, which have been exposed to the mechanical sorting action of flowing waters and the chemical reactions pertaining to the stream environment,

The -80 mesh fractions of stream sedi“ents contain approximately 40 percent clay-silt size material regardless of the distance travelled in the fast flowing mountain streams, or of the parent rock type, (of soils 60 percent clay-silt). The Cu content increases with decreasing grain size and the clay-silt fractions of all sediments contain approximately 85 percent of the total Cu content of the -80 mesh sample (cf. soils 85 percent Cu in the clay-silt fractions). These relative constant proportions of (a) clay-silt fractions, and (b) the Cu content is considered to reflect active chemical weathering in streams, and a balance of equilibrium between weathering processes and the mechanical actions of stream waters. These figures also indicate the reason for the efficiency of the -80 fractions of sediment for geochemical drainage prospecting in the Kilembe area.

Stream sediments derived from mineralized areas contain greater concentrations and proportions of more loosely bonded copper than sediments draining barren areas, and this is considered to reflect the presence of Cu precipitated from anomalous waters.

The secondary iron oxides from anomalous sediments have a higher (6 times) Cu content than iron oxides from background sediments and all sediments contain appreciably more secondary iron oxides than the soils from which they are derived. The increase in secondary iron oxides are mainly derived by precipitation from water and, to lesser extents, by the concentration of the heavier iron minerals by the sorting action of stroar, 1,,ters, and oxidation of Fe minerals in situ. Transition zones.

The transition zones between (a) soils and sediment (stream banks), (b) ground and surface waters (Impeded and free flowing seepage zones)) and (c) oxidizing and reducing conditions insoils, wore investigated.

Stream banks are composed dominantly of A horizon soils moved mechanically down the steep hill slopes by soil creep. Stream secilments arc derived mainly by erosion of the stream banks.

The major transition zone between ground and surface water is a seepage zone of free flowing water (grey horizon) located (1'6 and below the water level along all stream banks. Minor transition zones of impeded drainage are located in the headwaters of tributaries.

The metals which aro precipitated from ground-waters upon transition to the surface environment are (a) accumulated in the zones of impeded seepage, and (b) not accumulated in the zones of free flcwin!7 seepage.

The total copper content of soils permanently inundated by ground-water, (reducing conditions) is not significantly different to the metal content of the overlying freely drained soils (oxidizing, conditions), However, the concentrations and proportions of more loosely bonded copper increases in the zone of reduction and this considered to be duo to minor quantities of Cu removed from ground-waters by sorption on to clays, etc. The dispersion pattern of anomalous copper in the Yvette tributary, and the Dungalea River.

Detailed studies of the metal dispersion patterns in the Dungalea and Yvette water courses indicated that the erosion of anomalous bank soils was the dominant controlling factor in the formation of sedi-lent anomalies. However, it was deduced that from 22 to 36 percent of the Cu contained in anomalous sediments was not derived from bank soils. The major portion of this excess Cu in sediments coincided with zones of (a) a decrease in the Cusol content of surface waters, and (b) of major influx of anomalous ground-water. Also, the concentrations and proportions of more loosely bonded Cu increased in sediments over these zones. precipitation of Cu from (a) anomalous surface waters, and (b) from outflowing anomalous ground-water was fo_onstrated, it was inferred that the excess Cu in the sediments is derived from these sources.

In the Yvette tributary, the presumed zone of major Cu precipitation coincides with a bank soil anomaly and enhances the peak values of the sediment anomaly. However, In the Dungalea River,,the zone of major Cu precipitation occurs a mile downdrainage fro:. mineralization, and thus forms a 'downstreat_ anomaly peak".

Application.

In order to increase the length of anomalous drainage trains in stream sediments, the application of the following techniques wore investigated:-

(a)Size fractions:

The Cu, cxCu, cxCu, Cupe, CuLat concentrations of different size fractions were determined.

(b)Extractants:

The following chemical extraction techniques for a specific form of copper were tested (1) acetate (exCu), (ii) citrate (CuFe ), (iii) phosphoric acid (Cu content of clays), and (iv) various concentrations of HC1 (general solvent).

(c)Minerals:

(1) The. Cu content of magnetite. (ii) The Cu content of panned concentrates.

19. (d) Other Letals (Pathfinder elements): (1) Co, Ni, Zn, En and Fe by wet chemical analysis. (ii) Pb, Sn, Go, Be, Lio, V, Ti, Ag, Zr, Cr, Li, Rb, Ba, Sr. Na20 and K20 by spectrographic analysis. It vas found that the HC1 extraction technique removed a greater proportion of the less firmly bonded copper (diagnostic of zdneralization) and anomalous drainage trains of HC1-Cu extended at least 5 miles downdrainage from mineralization. Other techniques were subject to the same limitations as the cxCu and Cu methods or were not applicable to the Kilembe arca. Sugg;estions for further research. It is suggested that further studies be conducted on:-

(i)The application of geochemical mapping techniques (rocks, soils, sediments and waters) to resolving regional and local geological problems (ii)Rainwater.

(iii)The mechanisms of solution, transport and precipitation of metals and the activity of micro- organisms in (a) profile from deep to shallow ground-waters, (b) tributaries, streams and rivers, and (c) glacial and tropical lake waters. (iv)The practical application to prospecting of:- (a)Shallow around-water sampling in areas covered by alluvium and glacial tillite. (b)The HC1 extraction technique to prospecting for metals other than copper.

Sa:;4, 1ing and analytical methods. Except for the HC1 extraction method, all sampling, sample preparation and analytical techniques were based on standard procedures. The reproducability of analytical results chocked by using a statistical series control method (Craven, 1953), and a '1;25 percent reliability at the 95 percent confidence level was obtained.

20, 1. uEOLOGY AND PHYSICAL FETURE8.

GENERI, DESCRIPTION.

(i) Location. Kilembe Mine is located in the eostern foothills of the Ruwenzori Mountains in Western Uganda (Figure 1U) The mounteins lie astride the 30th degree of east longitude and extend from the equator to 0 degrees 55

minutes north latitude. They are 75 miles long with e maximum width of 32 miles in the centre end narrowing to approximately 25 and 12 miles in the south end north respectively. The total area occupied by the renge is about 1,000 square miles end their longer axis is

directed North 30 degrees Eest. The copper deposits occur along both sides of the Ny&lusegi Valley, latitude Eest 30 degrees 0 minutes 34 seconds end longitude North 0 degrees 12 minutes 15 seconds. Direct rail and air communication exists between Kilembe end Entebbe (capital of Uganda) and the Mine is also linked to the main highway system of Uganda. DetzAled studies of the dispersion of copper in the dreinege system were mode in the Dungelee River end its tributaries, with perticuler emphasis on the south-west slope of the Bukengems Ridge. Regional studies eNtended from the As River in the north to the Dubsrea end Nyomogesani Rivers in the south (Figure 2U.)

21, (ii) Topography. The Ruwenzori Mountains lie within the western branch of the East ifrican Rift Valley System, and consist of a block of pre-Cambrian rocks that have been uplifted several thousand feet by faulting and warping. There are six separate massifs,• permanently snow covered, in the centre of the range. The high points of these massifs vary from 15,163 feet (Weismenn Peak) to 16,794 feet (Margherita Peak). There is a genetic relationship between the boundary scarps of the mountains and those of the rift valleys. The centre of the mountains consists of a domed platform, some 14,000 to 15,000 feet high. Northwards this platform narrows to a single fault-bounded spur, and slopes gradually to an elevation of some 2,200 feet at Kibuku on the Albert rift. To the west the mountains are bounded by steep rugged fault scarps. Southwards and eastwards the plateau falls gradually to the Lake Edward plains and the Lake George depression respectively. Except for a relatively short fault scarp in the Nyamagasoni Valley, the central plateau gradually merges with the Ruwenzori foothills in the Lake George and Lake Edward areas. These foothills are not strictly part of the main mountain range but a south-westerly continuation of the Toro Plateau (elevation approximately

5,00C feet) extending from the Fort Portal area. 22. Mathews (1951) has sugcested three major erosion platforms nt elevotions of 15,000 feet, 8,000 feet and 5,000 to 5, 500 feet. However, McConnel (1959 e) maintains that the summit pinnotion is the only widespread end well-developed surface on the mountoins. The knickpoints in the droinoge, benches and flottened spurs occurring et lower elevotions ore considered to represent local base level pouses during the uplift of the massif, and not complete cycles. McConnel correlates the summit plonotion with the Toro Ploteou which is believed to represent the mid-Tertiary erosion cycle. Thus he concludes thnt the uplift of the Ruwenzori massif has token piece since the Miocene. The uplift ronges from 3,000 feet on the northern ridge to o maximum of 9,000 to 10,000 feet in the central oren. It is of interest to note that the results of n gravity survey carried out by Brown (1956) led him to conclude thet the Ruwenzori moss is in "approximate isostetic equilibrium, provided the concept of regional isostetic compensation is invoked". The present topography of the mountains is typically youthful and chorocterised by deeply incised volleys, with steep ungreded sides. Soil covered slopes of 30 to 40 degrees ore common in the foothills. Evidence of landslides exists along the major volleys ond the upper reaches of tributaries. 23. The effects of glaciation have been reported only above an elevation of 8,000 feet, (iii) Drainage.. Except in the lowest foothills, all the rivers, streams and tributaries in the area flow throughout the year. The major rivers and streams draining the mountains radiate out from the central Ruwenzori massif. These rivers are continuously fed by melting snow r,nd glaciers. Streams and tributaries that rise below the snow line ere fed mainly by underground water. This underground water is considered to be derived from the melting snow and ice and from rainwater entering the underground- water cycle. The Dungalca River rises below the snow line and is a major tributary of the Nyamagasani River. The direction of flow of all rivers, streams and tributaries is controlled by the geology of the underlying rocks. Faillts, fractures, shear zones and bedding ore the major controlling features, Tributaries and the headwaters of streams below the snow line generally rise in seep areas some 700 feet below tie ridge crest. ?roe running water usually appears some 25 to 50 feet below the seep zone. Frequent- ly the water runs underground for distance before

emerging on the surface as an apparent spring. The volume of surface water invariably increases down the drainage channels indicating that ground-water is being

24, added over the entire length.

According to. the Ugende Hydrological Deportment, en increese in volume in the mojor rivers occurs during the period October to December. The mojor rivers ore occesionelly in spate for periods of 6 to 12 hours efter heavy continuous reins in the catchment arer.

During heevy reins of up to one hour's duration, it wee observed that the water soaked through the vegettion matte into the soil, Heavy continuous reins of more then 1 hour resulted in the woter flowing along end through the zone of vegetation matte • into the streams. and tributaries. No evidence o± catestrophic soil erosion was observed. It should be noted that continuous periods of heevy rein are rere below 8000 feet, The influence of the more normal storm-water on the general water table is vary localized end is not reflected in en increase in the rate of flow of streams end tributaries in the immediate vicinity. Consequently, et any perticuler point, the volume of tributery water remains relatively constent thl-oaghout the year. Cate7t2ophic flood alonL the mejor river volleys: hove been mentioned in loco]. African legends. rJ2hese ore undoubtedly due to collapse of dons (the product of landslides end gleciol morrnin) in the upper reaches of the rivers. The only authenticated case of this 25, phenomeno, involving the collopse of E lcndslide deem in 1961, wens reported by N.H. Michnolides (personoI communication) elong o tributnry cf the Duboreo River in the southern portion c: the Ruwenzori Mountains. Fresh rock is impermenble to wotcr except in open fissures. Dimond- drill holes end underground workings indicate that the depth of decomposed rock permeable to underground water is in the order of 50 to 200 feet. Frequently, LI'esh rock is encountered within n few feet of surfnce, but these occurrences hove not been found to hove nny later3L extent of consequence and ore interpreted ups pockets of more weather resisting materiel surrounded, end often bottomed, by ncrniolly decomposed rock. Water-bearing fissures hove been found to depths of hundreds of feet. Die perennial flow from springs within o few hundred feet of the ridge crests indicates the presence of n permanent end continuous supply of underground voter, the direction of flow having o strong component down the .xis of the mojor spurs es well ens towards the valley bottoms (Webb - personal_ comnunicstion). This voter flows in the upper zone of decomposed bedrock os well es in fissures in the unweathered rock. The hydrostatic head behind the grovind-water flow derives from melting snow c, nd ice of the 13,000 foot level. The following stages in strcom folmotion are envisaged. Firstly, active erosion olonr, structursi features forms ever deepening depressions. As soon ens the. 26. erosion level intersects the weter toble, n permanent flow of woter emerges with relotively minor variation in volume. The flow of this woter in the lower reaches of the mountains increases the tempo of erosion and the strerms increase in length by cutting bock along the structure into the highlEnds. The elevation to which octive woter flow in n stream may rise is determined by the elevotion of the woter table, which is, in turn, reloted to the hydrostatic head. The continuation of octive erosion obove the upper limit of water flow olonc the controlling structural fecture is shown by prominent swelo oreos which develop obove the seep oreos of all tributaries. As streams cut deeper into the hinterland, the woter table at lower elevations is gradually lowered causing minor streams and tributories to dry up if the locol rote of erosion cannot keep pace with the descending water toble. This stoge hos, in feet, Elreody been reached in ports of the lower foothills below 4,000 feet, where it has probably been acceleroted by deforestation. Detailed descriptions of the locol droinoge and topography in the study sreos will be given in Section II.

(iv) Climote. The Ruwenzori aren lies within one degree of the equotor. Due to the great variation in altitude, 27. the climatic conditions very from semi-tropiccd around the Jokes, to tropical-hiGhland in the foothillp, perirlment snow line exists at 13,000 feet,

Usnda f4.3 E) whole, there are 4 distnct 2easons, two wet and two dry° The wet sensonr occur during March to and Selotember to October. The dry seasons cover

Jannary to .. eb.zualy. and June to July. aeferanco to the rainfall fig7:.::es f_Table 1)02 19C0 and January to 1961 ot Kilembe ond Mubuku. clearly indicates that these seasons are rathel- poorly defined in the ::::4_Tenzori foothillr3; where the annual precipitation averaEos 6C. fmches. Here the ralative humidity varies from

53 'co 88 percent, Day temperatures ore relatively constant o1 TO decrees F. with a maximum variation of

'3 degrees P„ while at nipht less then 50 degrees ho 7e b,.,:en recorded. (7) ITeretntion ontf',_prricul.tu-re.

1,10thewE7. (1951) cuotes the for.owinE vertical dis-6.zr0uion of 7,cr.es vostation; feet. Elephant graz Yin areas.o Greater 45 inches per ann.= 5ono 7;300 feet. Bracken. :j,0n0 uo r) fpc ,t Forest. 8a 000 - I0,000 feet. Doff:Jo°, - 12;000 feet, Tree heath. ./i-L-JVC, 13-00C feet. Giant lobelia; helicysulT, sonecdo,

28, Rainfall inches! Month/Yenr! Kilembe, Mubuku!

January, 1960 3.35 3.05 February 8.68 4.69 March 5.05 7.25 April 3.12 5.30 May 3.90 6.17 June 2.66 1.55 July 1.70 2.61 August 2.81 5.55 September 7.58 9.18 October 7.02 4.49 November 4.54 5.00 December 1.47

TOTAL FOR i960 000 000 000 51.88 00 0 0 59.47

January, 1961 2.14 1.08 Februory 5.12 6.14' Morch 3.47 4.53 April 6.48 7.27 May 3.78 5.18 June 2.43 5.68

Table 14 Rainfall of Kilembe End Mubuku. (Information supplied by Kilembe Mines Survey Department).

Deforestation for agricultural purposes, as described by Jacobson (1956), has now been stopped. by Government decree. The total remaining forests have been declared reserves and entrance to these nreas is

29 . strictly controlled. The elevotion of the forest reserve boundary varies from 5,000 to 8,000 feet. The indigenous popuiction, the Mekonju, is a Deosont hill tribe. They use primitive methods of cultivation, which entail hoeing of the top 6 inches of the soil. No crop rotation or fertilization is prectised; end lend is allowed to lie follow after losing its fertility. Most of the lend up to the forest boundary, even on the steepest slopes, hos been or is under cultivation. Once abandoned, a neturel gross and brecken vegototion reDiay regenerates, end the denser:atte of roots protects the soil from cetostrophic erosion.

30. GEOLOGY.

The description of the geology is based mainly on the results of mapping by the Uganda Geological Survey, and the 1951-52 British Ruwenzori Expedition (M.cConnel

19 59 a and 19 59 b). The detailed geology of the Kilembe Mine and surrounding areas was provided by the Company's Mines Geological Department, and the geology of the other areas was provided by the Geological. Exploration Deportment, respectively (Bird, 19601 Westell, 1958; Smit, reports and personal. communication); Grimley's Thesis for Ph.D (1958) was consulted. The information obtained from these various sources was supplemented by personal observations made during the course of the field work. (i) Regional geology. t generalized map of the regional geology of the Ruwenzori Mountains is shown in Figure 3U.

(a) Rock types. The Ruwenzori mass is considered to be of pre-Cambrian age. The predominant type is a migmatite series which includes granitic gneiss, syntectonic granites and amphibolites. Belts of mica schist, metamorphosed volconics, massive quartzites and younger, less metamorphosed formations are also found. 31. The succession of the geological formations is summorized in Toble 2:

Formations Series and rock types!

Recent (Volcanic Tuffs (Outwesh Fens

Miocene to Pleistocene Keiso Kisengi Beds Korcgwe - Ankoleon? (Bwambo Pass Series (Lume Calcareous Series (Stenely Volcanic Series (Kilembe Series Ruwenzori Group (Stuhlmenn Pass Series (Freshman Pass Series (Butehu.Series and uncorrelated schists (Toro Quartzites West Nile Group. (Migmetite Series, including (Basement Complex) ( syntectoniegrEnites, ( emphibolite zones and ( Wese Gneiss (Speke Gneiss.

Teble 2: Geological succession after McConnel (1959), of the Ruwenzoris. West Nile Grou. The Migmetite Series is the most widespread group of rocks on the massif. These rocks ore essentially a biotite-oligoclose-gneiss bonded with pegmotitic (microcline) material. These bonds may expand into lenses and sheets of syntectonic granite and orthogneiss. The Luigi Gneiss is a large development of this orthogneiss. Zones of omphibolitic material occur locally 32. in the Series. The Speke Gneiss, according to McConnell is probably grEnitised Wnsn Gneiss thc't hns subsequently been crushed nnd migmctised. The Toro Quartzites, mnssive crystalline eunrtzites, care considered by Devies end Bisset (1947) end McConnel (1959) to be conformably folded with the Migmntite Series. Combe (1944) pieces these rocks in e seperete group. The writer mode e limited number of observations in the quartzite ores: east of Kilembe end els° southwerds to the Congo border along two new rood cuttings. An cppnrent chnnge in the pattern of folding occurs between Kilembe, the quartzite cast of Kilembe End the quertzites further south. It is suggested th[t more deteiled structural mapping in these &rens mny provide additional information on the stretigrophy of the Toro Quartzites.

Ruwenzori Groin. Overlying end folded into the rocks of the Basement Complex rre the Ruwenzori Group. The individuul Series hove not, as yet, been fully correlated and ere, therefore, described seperetely! Stuhlmnnn Pass Series. The mcjor rock type in this series is n biotite-cndElusite-schist with local bends end lenses of ouertzite, marble End trio schist. This series outcrops in e narrow cost-west bond striking ncross the 33, centre of the massif. It is underlain by the Speke Gneiss nnd overlein by the Stonley Volconics. Preshfield Pass Series. This is e similar bend of rocks composed of muscovite and cordierite schist with lenses of cordierite-sillimonite-Bernet-granulites. These rocks ere overlEin by the LuiGi Gneiss end underloin by the Stonley Volconics. They hove been correlated with the

Butehu Series. Butehu Series. A series of muscovite schists outcrop extensively in the south-western eree of the mossif. Isolated synclinol remnents also occur in the southern erec. Stonley Volconic Series. Those rocks ore essentially emphibolites derived from metemorphosed live flows of basaltic type, interstrotified with merbles, ccle-schists L,nd quartzites. It hos been suggested thEt this Series occupies n syncline, overturned to the north end enveloped by the schists of the Stuhlmonn Poss ond Freshfield Poss Series.

Kilembe Series. The Yilembe Series (Bird, 1960) consist of o group of bedded rocks which hove been divided into, throe groups. The upper or hongingwell is essentially on olbite-chlorite rock. The proportions of olbite 34. to chlorite very from o predominance of elbite in the higher levels to e predominrnce of chlorite in the lower levels. The middle or Middling Group is e quortz- felspor-emphibolite rock which hrs gencrclly been severely crushed end folded. All economic metrllizntion occurs in this horizon. The lowest or Footwell. Group is schistose, Pnd gencrolly typified by the presence of biotite. The biotite schist shows increasing :mounts• of grtnitizotion with depth. Type rocks of the Kilembe Series have been traced,

Pructicelly continuously, from the Mine to the Congo border in the south-west. Yrregwe-Ankoleon? Bwombe Pess Series. Talc-schists, quartzites end grits with n besol conglomerEte occur in the northern pert of the massif rnd in the upper Ruimi VElley. The beds dip west c.t 10-20 degrees. Lume Calcareous Series. The rocks ore dark shales with beds of blue limestone bends, bearing no sign of metamorphism. These two_ series hove been provisionally correlated with the Yerrgwe-Ankoleen System, but their stretigrophic

position is still uncertoin. TertieK7 to Pleistocene. The Kfliso-Kisege Beds fill the depression in the

35e rift volley occupied by Lokes George, Edword and Albert. They represent detritus from the uplifted Ruwenzori mass on- 1 volc-mic tuffs from the explosion craters loccted olong the eostern side of the mountains. (b) Structure, McConnel hos stated that, due to its position of the node of the Rift Volley System, the complicated structure of the Ruwenzori Mountains is the cumulative effect of the intimate tectonics of the Pre-Cambrian formutions cnd those connected with the subsequent tectonics. He suggests that the some pattern of forces Feted in this region over the entire period complicoted by changing depth of buriol and granitization. One of the most mErked structural features is the change in strike from 10 to 30 degrees in the northern range to 50 to 70 degrees in the southern rFnges. This change in strike in foot increases to 130 degrees in the south (personal observation). The strike swings in o wide arc col-10ov° to the north cnd centred on the Speke Gneiss. McConnel suggests thFt this hos been caused by forces pushing the southern portion of the mountains against the rigid moss of the Speke Gneiss, cousing tight folding End overturning to the north and some ovorthrusting. This theory is, in part, substantiated by observations of noppe structures in the Butohu Series in the Congo by Hichot ond La Vallee Poussin (1937).

36. No noppe structures hove been mopped in Uganda. Johnson (1952) states thot the Kilembe Series have been subjected to two min structurcl movements. The oldest (Toro) movements ore reflected by strike directions of 10 degrees and the younger (Knrogwe-Ankoleon) movements by strike directions of 70 decrees. Field observotions by the writer in the Kilembe orco (where Johnson mode his observotions) in gencrol confirm these measurements. SouthwErds, however, although the oxis of folding swings to 130 degrees, ors described in the previous porogroph, the writer observed distinct lineation striking between

10 ond 30 decrees. The strike direction of 10 to 30 degrees in the north is reported os bedding, whereos from Kilembe souJ„hwords it commonly occurs os o clenvoge (or frocture) direction cutting ocross the normal bedding ond only rorely hos it the true field chorocteristics of bedding. The writer considers it possible thot the direction of 10 to 30 degrees represents on oxis of regionol folding and thct the 50 to 130 degree direction represents o major dreg around the Speke Gneiss. The rift feulting, the Knrocwe-hnkolenn ond subsequent movements hove considerably modified ond complicated the stracturol pottern. It must be stressed thot this suggestion is 'posed on observotions in extremely limited oreos ond thot very much more detailed work is necesaory

37. before the validity of the interpretation con be ossessed. One further structural fecture of economic significonce observed in the Kilembe Series during the field work is n persistent recionca plunge of 20 to 30 degrees in on ersterly direction along the oxis of folding. The Kilembe Series rocks are generally overfoided to the north, and the subsurface extensions of outcropping minerulizr'tion could follow the dip of the bedding (southwards) and/or the plunge direction (eostwords). (ii) Loccil reolory ot Kilembe Mine. (o) Geology of Mine area. In the post, Kilembe Mine geologists hove described the major rock types as granulites and omphibolites, with minor bonds of colcic rocks, dolerite dykes and ubiquitous pegmrtites (Combe, 1933; Simmons rind

Harwood, 1935). Bird (1960), the present Chief Geologist on the Mine, hos objected to the generrl use of the terms "gronulite" ond "rmphibolite". He points out that it is doubtful whether ony of the Mine rocks con correctly be clossified under the high temperoture "granulite fociea" ond thct, in the post, the term hos been used to describe rocks with c gronoblostic texture. Although rocks which con be strictly defined os omphibolites do occur, the term, as used in the post, includes any rock with

38. prelomincnt mefic minerals.

The stretigrephicrl sequence established by Bird (1960) is given in TEble 3!

Tower Yilembe Series! Footwoll Bf.otite Schists.

Middle Kilenbe Series! Footwell Quertz-felspor-emphibolite Footwell Orebody T iming Quertz-felsper-emphibolite IUddling Chlorite-elbite rock

Hencincwoll orebody. Up_per. Kilembe Series! Hencincwoll chlorite-elbite rock Hencincwell elbite rock.

Table 3! Trble of Irilembe Series formctions. After Bird, 1960.

7ootwoll Biotite Schists. The rock is generally schistose, with biotite, untwinneft ecid plEcioclese, chlorite end sillimenite

es the ruin Concordant rucen on.,4 veinlets of pecmtite rlso cz:rnetiferous zones c.re common. These rocks show increesing rmounts of cronitizotion with depth and oppeor to grade into the underlying 39. Gneiss or crenite.

Middle Kilembe Series. Footwoll ouortz-felsper-emphibolite. westoll (1958) hos described this rock es o fine to medium crrined interlocking, occreLote of voryinu proportions of felspor rnd amphibole with intersttiol gurrtz, biotite, sericite, chlorite, tourmoline, zoisite, epidote, sphene, crlcite, cornet, muscovite ond ore minerrls. The felsper is predominantly untwinned olbite with voryinc amounts of microcline, olicoclese and orthoclose. Thulite is sometimes present. Minute crystals of spene end tourmoline ere essocioted with the sulphides. This rock is usuelly closely essocieted with ore, rnd provides on importont mrrker horizon. In the mine erer it hes been observed thrt week sulphide minerelizetion is cenerolly eccomornied by poor development of this rock type. However, the converse does not Elpply. Footi7r11 This is on economic zone of minerolizetion within the auertz-felspor-rmphibolite. The host rock is essenticilly the some os described ebove, but more crushing- end skrrnificE. tion is present. The rocks ere stronEly bonded in felspers end emphibolites, with sulphides relarcinc the emphiboles. This orebody is pyritic end cobeltiferous, wherens

40.

the Hongingwell orebody is cupriferous.

miallinr ouortz-felsoor-omnhibolite. The rocks ore essentiolly the some ns described above, but the minerolizEtion is sub-economic. This horizon; tocether with the Middling chlorite- olbite rock,,seporotes the Footwell end Hongingwoll orebodies. chlorite-olbite rock. In one of the economic deposits, known os the

Stream deposit, the Foot ond HE.ngincmll orebodies ore separated by weakly mineralized chlorite-olbite rock similor to the HongingwEill type described below.

HonLino/oll orebody. The host rock cpperrs to hove been o colcoraous Greywocke which hos been highly contorted, crushed end subsequently metosomrtired forming colt-silicates such tremolite, ectionolite hornblende, diopside, garnet end enidote. The sulphides tend to repince the mofic silicntes. Tourmeline crd groins of deer quartz ore freouamtly ossociE, ted with the minerolizetion. In some highly contorted orees, the sulphide minerolizotion penetrated the lower zone of the Upper Kilembe Series. Upper Kilembe Serf,es. 1. chlorite-olbite rock.

41. This rock is essentiolly a chlorite—albite rock choirocterized by the abundance of chlorite. In. texture it is either bonded or crenulose. Bonds of epidote ere sometimes present. In locolised orees of higher erode metamorphism, biotite hos been formed in ploce of chlorite: end veinlets end nugen of pingioclose hri-e developed. HonLinFwelL olbite rock.

This is o weekly bonded, medium grained, nibite— chlorite rock, charocterized by the abundance of olbite. guartziitic end biotitic varieties occur. .ATaskjte intrusions. The pecmctites in the Kilembe Series consist of felsper (orthoclase, enorthoclese, olicoclose, olbite.• end microcline) end quartz. Coerce biotite, tourmnline end magnetite frequently occur as occessory minerals. The crystnilizotion of many pegmetites hos been slow end. interrupted, end the general field chorocteristics ore similar to the closkites described by Spurr (1923) from Silver Peck, Nevodn. The intrusions range from smell irregular mosses rind. veins to. large dykes up to 60 feet wide. In general, they conform to the foliation of the host rock; but often they also cut across et o small encl.° without noticeable disturbance of the rdjeccnt rocks. Their concocts with wellrocks are usuo1247 sharp; although tronsitionol zones

42 hove been found. Jacobson (1956) reported the

existence of bonds in the Kilembe Series pocked with coarse crystals of felspar. This feature wus also need_ in drill cores; ond sugEests o stage of gronitizotion. Bird stotes thot the IorEer pegmntites (potoah felspar) ore more prolific in the Middle Kilembe Series. In some cases the pegmotites hove ossimileted the ore, but more frequently they hove sharp contocts. He considers the pegmotites to be post—minerolizotion even though some of the lorEer bodies have hod the effect af locally concentrating or re—distributing the sulphides. Dolerite dykes. Dykes of fine to coorse Eroined dolerite intrude oll the other fomations including the ore and oloskites. Recionolly the gencrf,1 direction of strike is cost—west, but exceptions hove been noted. The dykes ore vertco7 or dip steeply northwords 5nd frequently follow faults rind fractures. The widths vory from o few feet to 200 feet: end the contacts with wollrocks ore olwoys shorp. The dykes ore composed of lobradorite end pyroxene. Interstit'71_ micro—peEmotite in some specimens trio:; reported by 7oylond (1933). Similor to doleritc dykes throuEhout Ugonda, these dykes frequently carry disseminoted iron end copper sulphides.

(b) Although the mineral oss=blor,:e of the

43. rflPri'-)e rorl-- is ijneous (Simons r1,1 Horwood, 19551

Grimley, 1958) their hEbit is sedimentary. Opinions on the origin of the Kilembe Series very, depending an the relative importance individuol investigators give to petrology, metamorphism end metosometism. It is considered probable that these rocks ore sediments derived from the erosion or weathering of a basic igneous complex. Metamorphism end metesomatic processes related to grenitisotion hove resulted in the present suite of rocks. (c)Structure. On the Mine, the Kilembe Series hove been tightly folded end overturned to the north along o general fold exis of 45 degrees. The Series plunges north—east et approximately 20 degrees. Faulting and fracturing are common. According to Bird (personal communication), sheers. ore typified by the formation of chlorite irrespective of the rock type. The original character of the rock is completely destroyed. Results of the most recent underground work indicate that these sheer zones are pre—mineralization and are mojor controlling features in the lateral extent of ore.

(d)Metamorphism. Grimley (1958) did research studies ct Kilembe Mine during 1955 to 1956 to study the wolirock

44. alterations but, owing to the dearth of megascopic evidence in the areas available, the studies were expanded to include the mineraliricn with a view to establishing the origin of the sulphides. Due to circumstances beyond his control, his work unfortunately suffered from a mat'or disadvantage. The detailed stretigraphicol sequence on the Mine was then improperly understood, so that much of his work needs to be re- orientated end re-interpreted in the light of present knowledge. In general, the Kilembe Series appears to hove undergone low-grade metamorphism, es evidenced by chlorite-clbite rocks. In the Middle Kilembe Series, however, Grimley has clearly demonstrated the existence of e high grede metamorphic mineral essemblage. Grimley's work demonstrated two phases of metamorphism, e high- grade phase followed by e low-grade phase. He postulates' the possibility of a retrograde metamorphism to explein the subsequent development of the low-grade mineral assemblage. However, his finel conclusions ore that the low-grade effect was produced by introductions of new material (including soda) resulting in metasomotic replacement of existing high-grade metamorphic minerals. Bird suggests o general low-grade metamorphism end explains the high-grade mineral assemblage, which is strictly confined to the mineralized Middle Kilembe Series, by invoking intense localized metesomotic 45. notion during introduction of the sulphides. (e) Minerelizotion end Ore—Genesis.

Bird (1960) states thot "Underground work on the Mine hos produced sufficient evidence to conclude thot the sulphide minerelizotion occupies the some stretigrrphicol horizons for some thousands of feet" (olonc strike) The terms "Footw&11 ond Hnnringwnll orebodies ere used strictly in the economic sense, i.e. the whole of the upper portion of riddle Kilembe Series is minerelized, but frequently there is c zone of sub—economic minerolizotion in the centre. The minercls of the orebody ore cholcopyriLte pyrite (cubes, octEhedro and mossive), linnEeite, pentlrndite, pyrrhotite, ilmenite, mognetite, sphrlerite end molybdenite. Gold oni silver hove Elso been noted. The cobalt is ossocinted with

octohedrol and mossive pyrite, There is n distinct zoning in metnllizotion, rancinc from cupriferous in the upper zones to coboltiferous in the lower zones. The tenor of the ore rveroced 1.88 percent copper end C.18 percent cobalt for r total of 13,000,OCO tons considered proven in 1957. The bulk of the copper sulphides occurs mainly es blebs, frocturafillings or cs stringers replE'cing mefic minerals. Replacement hos frequently edvenced to

where sbrecci8 ore" consistinE of mossive sulphides

46. with remnonts of gEnrue, hos been formed.

The Middle Kilembe Series has been severely drogfolded End crushed, end the rocks cenerolly show evidence of skornificEtion End ossocieted metosomotic trocesses. Bird (1960) summarizes his conclusions os follows!—

!! .... it is cpriorent thet the controlling fector for economic sulphide minerelizotion wcs dependent on the occurrence of the Middle Kilembe Series, with sufficient folding f- nd frc.cturing to hove stimulated replacement processes. The sulphides ore believed to have been introduced by metesomotic activity, initiated by the younger grz- nites. The economic minerclizotion mcy hove been derived by the concentration of metElliferous disseminations in the country rock, or introduced with grcnitic emcnetions". These conclusions on ore—genesis Ere, in essence, the seine Es those retched by Grimley (1958)

Beceuse of the close Essociction between ore End the Middle Kilembe Series, it hEs been suc,:ested, in the post, that the Yilembe ores ore of syngenetic origin. The consensus of recent opinion is, however, thet the ores ore of hydrothermEl origin.

(iii) Geology south—west of Kilembe Mine.

Ou!cicrop End floEt of rocks of the Kilembe

Series hos been found procticolly continuously from the

47„ Mine to the Conjo border (Smit - personal communicotion).

The dip is southwords 5nd the strike direction swings from 50 degrees ot Yilembe to 130 degrees neor the

Congo border (see poge 36) In sll cones where detailed observotions were mode, the beds ore isoclinolly folded, overturned to the north 5nd plunge of 20 to 30 decrees eostwords. The amplitude of the folds spperrs to wiry;

minimum of c, pproximotely 25 feet wos observed in the

Duborer oreo.

Development of s zone of chloritic schist, typicol of the Kilembe Mine sheer zone m[terisl, hos been noted.

It is thought thrt these may represent thrust pl5nes.

Repetition of Kilembe Series rocks occurs. ?t least

5 cmp'zlibolitic schist zones were recorded over o distance of 3 miles in the Duboreo ores. It is thought thot these occurrences represent repetition of the some beds by folding. The sequence of chloritic HcnginEwoll rocks,

rmphibolitic middling, rocks and biotitic and gorneti- ferous Pootw511 rocks is m&intoined, The south-western

extensions of the biotite schist oppeors to become

increasingly graphitic (Smit person51 communicotion).

Picot ond outcrop of cuortz-felspar-cmphibolite (mineralized 5nd barren) ore frequently found. In

ploces, the Kilembe Series hove been almost completely

Eronitized.

480 Minerolizrtion is ossocioted with the omphibolitic zone End it opPeors to be lenticulnr in hobit. (iv) GeolgLy of the stpki ereos. (0) Bukonrrmo. In order to study the bocci dispersion of copper derived directly from minerolizotion, the virgin

Bukongemo deposits were selected Ens the focol point. (FiEure 13 ). Detoiled studies were conducted within this oreo, wherein the previous work by Webb (1958), Holmon (1956), Jacobson (1956), end Kerbyson (1960, hod been conducted. The locyl ceolocy was re—mopped by Westell (1958). Subsequent to these studies, the exploration stuff et Kilembe Mines hove done o consideroble mount of ceolog!_crl moppinL, ceochemicel somplinc orr' dicmond drillinu. This informttion wos made ovoilcble to the writere Further geolocicol work wos done during the present reseerch studies, when deemed necessmry. The writer's odaitionol work in geologicol observations wos generolly supplementary to previous work, or related to on aspect not previously covered. The prominent feature of this prep is the Bukoncolmo Ridpe some 2 miles long, situoted opproximetely 3 miles west of Tilembe. It is E section of one of the ridges descendinE in o southwesterly direction from the pecks 49, towerds link° George in the rift volley below. At Bukangemc, the elevotion of the ridge crest is 7,300 to 7,000 feet, and the ground drops repidly into the Dungcleo River to the southwest and the Nyclusegi River to the northeast. The difference in elevotion between ridge crest and the Dungelea River varies from 600 feet in the northwest to 1,5CC feet in the southwest, respectively. The avercce grodient of the slopes varies between 16 and 22 degrees, but locally the slopes frequently steepen to 40 ond 50 degrees. The avernge grodient of the Dungaleo River in this oreo is epproximntely 7i degrees (for details see Figure 17). The overage width rnd depth of the river ere 30 feet cnd 18 inches respectively. Apart from run—off during storms, the volume of voter is constrnt cnd increases from approximately 40 cusecs to 45 cusecs over the 2 miles at the bottom of the ridge. The tributaries ore typical of those described in the foothill arec (page 24). 4 common feature is the characteristic changes in grodient thot occur down the length of individual tributnries (Table 4), Probobly related to the pcuses in the uplift of the

Ruwenzori massif.

50. Tributary Gradient in degrees

Upper Lower Reaches! Middle Retches! Reochest

Yvette 15 15 6 26 Kittberole 30 12 22 14 Ketundu 30 14 14 19 GezeGozo 19 14 27 16 William 30 30 19 27

Tnble 4t Gradients of 5 tributaries in the Buknngomt rrea.

A typical example is the Yvette tributory (Tole 4), the overage Gradient of which storts at 15 degrees, then flattens out to 6 degrees over the middle reaches and increoses to 26 degrees in the lower retches. The overage width and depth of the tributaries nre 1-3 feet and 1-6 inches, respectively. The volume of water increoses from on avert-Igo of 0.0C3 cusecs below the herdweter seep areo to 0.05-0.20 cusecs in the lower retches.

As shown in Figure 16, most of the area hos been de—forested and extensively cultivated. On being left follow, the noturol vegetotion of dense elephent grass and brocken rapidly re—establishes itself. The tributaries ore generally heavily overgrown. The rock types cre essentially similar to those

51. found on the Mine. A slight increase in biotite in the hangingwall rocks and e very poor development of the footwall quartz-felspar-amphibolite zone ore the major differences between the two arens (Bird, 1960). Southwest of the ridge, the rocks Generally appear to dip et 30-40 degrees to the southeast, but numerous observations of variable strikes, dips End drag-folding suG,est a more complicated structural pattern. To the east, however, the rocks appear to be relatively regular in dip (approximately 30 degrees S.E) until the mining

nrea is reached. Photogeologicol interpretation, supported by field evidence, indicates e complicated pattern of fracturing or faulting. A prominent direction is N.E-S.W. with vertical or steep dips to the northwest; This direction is the same es the major rift-faulting and locally conforms to the strike of bedding in the Kilembe Series, and of foliation in the Gneiss. Two further prominent

frccture directions ore N.N.W. End few degrees south of east. 4s in Ell areas where ground end aerial observations were made, the drainoe was found to be controlled by the

geology. Thus, the Dungalec River follows the N.N.T. fracture direction to the Ketundu tributary. It then turns almost at right angles to follow the N.E. fracture pattern. The major fault which displaces the Middle

52. Kilembe Series some 2,500 feet southwards also lies in the N.N.W. direction. The line of the tributary drainage between the Gillian and Kntundu tributaries cofqicides with the strike of the bedding of the Kilembe Series, while the Gillian rnd Florence streems follow the N.E. fracture direction. In this area of high relief, the Kilembe Series can be readily delimited by a study of the dry inege pattern of the rir photographs. The foliation in the gneissic rocks is the same as the bedding of the Kilembe Series end this direction coincides with the fracturing. However, in the competent gneissic rocks, the drainage follows the fracturing in preference to the foliation. As the dips of the fractures are verticri or steep to the northwest, the tributaries tend to flow in a general southwest direction. This direction is the surface truce (on the steep hill slopes) of the controlling structure. However, where the ground is underlain by incompetent rocks of the Kilembe Series with c shallow dip towards the southeast, the tributaries follow the bedding end approach the m& in stream in a S.S.17. direction which is the trend of the surface truce of the bedding outcropping on the steep slopes. The renorrl primary mineralization extending from the ridge crest to the Mine has been proven, by diamond drilling end underground development, to be of marginal_ 53. grade, although shoots of ore grade have been found within this zone. Furthermore, three shallow holes have shown that the primary mineralization underlying the southwest slope of the ridge is also sub—economic. Except for grade, however, the mineralization in these areas is the same as on the Mine. (b) The area between Bukangama end Lake Edward. Prom the Katundu tributary southwards, the Dungelea River flows between calluvial banks until it passes into alluvium immediately above the confluence of the Nyer9gasani River (Figure 17). The Dungalea River is occupied by gneissic rocks. The western tributaries of the Dungalea River between the Katundu and Raymond streams drain Kilembe Series rocks and gneiss. Below the Katundui all the eastern tributaries of the Dungalea River drain gneissic rocks only. The average gradient of the river is 4 to. 5 degrees. The gradient in the lower reaches decreases to 2 degrees, and then decreases to 1 degree in the Nyamagasani River to Lake Edward. The flow of water in the Dungelea River increases from 45 to 85 cusecs from the Katundu tributary to the Nyamagasani River. The Nyamegesani River rises from the southern massif of the Ruwenzori Mountains and flows south eastwards until its junction with the Dungalea River (Figure 3U). From this point it swings south to southwest to Lake

54, Edward. From the Dungeles River confluence southwards

the river flows through outwash alluvium and voiconic tuffs. Isolated inliers of Toro quortzites outcrop in the alluvium ores. The flow of water increases from on estimated 400 cusecs ot the Dungoles River junction to approximately 1,000 cusecs in the lower reaches. Yejor tributaries draining the southern portion of the Mountains join the Nyemegasoni River over this distance. (c) Aso-Sebwe-Nabiajj.-Ares. In this nreo the rivers drain Too

quartzites, gneiss and schists. The stratigraphy is not fully understood end the schists could belong to the Basement System or younger pre-Combrion formations. Na knoim minsrelizetion occurs in this area. Sampling was corried out in the lower reoches of the rivers ot approximately the 4,000 foot elevation. 4t this elevation no weter is found in tributaries (refer page 27). The gradients of the Sebwe and Nsbisji Rivers ore opproximotely 2 degrees end the Asa River Eoproximotely 5 degrees. The rotes of flow ore 40,

40 and 20 cusecs, respectively. (v) Overburden. The physical chorocteristics of soils on the Bykongamo Ridge have been described in detail by Jacobson (1956). The profiles ore residual and characteristically immature with generally feeble

55 differentiation of distinct horizons. The soil cover is essentially continuous end varies in depth from 4 to 20 feet, the overage being 6 to 10 feet. Evidence of lend slip on the steep slopes has been noted, but it is

rEre. During the course of the writer's field work, many soil profiles were logged in new road cuttings and pits. This enabled the author to compile c. more comprehensive generalized soil profile then was possible for Jacobson on the limited number of exposures that were available-

to him. The following is e generalized summary of the soil

profiles mapped in the foothill area of the Ruwenzori Mountains between the Aso River and the Congo border:-

Range of Average Hari- thickness thickness Description: zon: Inches Inches:

AO 0 - Rotted vegetation. Al - 12 3 Porous, sondly loam intimately mixed with fibrous organic material. Dark grey to block in colour. Contact gredetionel or sharp with A,.

A 12 - 24 12 (i) Middle Kil.embe Series end 3 basic dykes. Reddish brown cloy loom. (ii) Foot end Hengingwoll Series. Light brown to reddish brown loom.

56 Range of Averoge Hari- thickness thickness Description: Inches! Inches:

iii) Gneissic Rocks. Light brown sandy. _An neorly oll of the pits, the bottom of the /1 horizon is choroctef.ised by the presence of rounded quartz pebbles. These vory in obundonce from 1 to 10 percent by volume, and b-inch to i-inch in. size. Occosionolly, o considernble concentrotion of disorient toted unweathered rock rubble is found in this zone. (Contact with B horizon generally sharply defined by lower limits of quartz pebbles).

B 24 - 96 24 (i) Middle Kilembe Series. Dork red cloy loom sometimes with disorientated rack frogments, accosionol ferruginous ond mongonifer- ous nodules. (ii)Foot and Hongingwall Series. Light to brick red cloy loom sometimes with disorientated rock frogments.

(iii)Foot End Hongingwoli Series. Light to brick red cloy-loam sometimes with disorientated rock frogments. iv) Basic Dykes. Brown red cloy-loom sometimes with rock frogments. (v) Gneissic Rocks. Light brownish sandy loom sometimes with disorientated rock frogments. (Boundary grodationel with C horizon).

573

Range of Averoge Description: Hori- thickness thickness zon: Inches: Inches:

C 96 - The some os for the B horizon. Frequently relic bedding and structure con be observed in the soil, and rock fragments ore orientated. Weathered quartz veinlets and segregations (in situ) were sometimes observed. These rock fragments end qu.ortz ore angular in contrast to the generolly rounded eouivalents which ore found do the B horizon.

58. II. THE STCONDARY DISPERSION OF COPPER.

Introduction.

The secondfry dispersion of cooper is directly relr.ted

to wefthering. The physics zna chemistry of weathering era

complex, but the processes ere essentic- lly equilibrium rerctions thet result in the formation of : new mineral

essemblrge which is 6-triple in the surfece environment

(Reiche, 1950).

An exeminction of the chemicrl F- nd mecheniccl effects

which r'ccomorny rock wecthering, soil profile development, erosion rnd rlso the solution end trfmsport of copper in

the aqueous medium is clerrly necessr- ry to study the

distributio— of copper in the surfece drrdnrge system. In this section the writer will present the results of

the studies on the mode of occurrence en,41

mechrnisms of cop-)or in soils, ground—wfters, surfcce 7'ters, sediments c nd trfnsition zones between the different

environments. The prc.cticl rp-aicetion of the results to prospecting will rlso be considered. The primcry ob;lect of

prospecting is to locrte c grrle of minertlizttion in

sufficient qu.cntities to werrent com-iercirl exploitation. The Lredes end quantities ore in fcct directly relr[ted end lerge tonneces of relatively low `-r de minerrlizf,tion often

constitute ore; wherecs small tonnfzes of high grade minerflizition frequently cannot be mined economicrlly.

59. In these studies no [4.)count is taken of those fetors the ter-as ore, -IcrEinra erode minerrlizetion rml sub-economic Erode minerrlizrtion cre used strictly to inActe the tenor of cop•Der metcdlizetion. Thus, ore is defined cis more then

2.0 percent Cu, =ginfl en ,de is between 1.5 End 2.0 percent, end sub-economic Gr&de is less then 1.5 percent Cu. Unless steted otherwise, ell en -ayses of soil cnd sediment scmples Liven in this thesis refer to the --80 mesh

(B.B.S.) size frr.ction.

60, SOILS.

(i) Introduction.

Streom sediments ore for the most port derived from the soil rid, to o lesser extent, by direct erosion of wecthered bedrock. In order to understrnd more clearly the processes which ore involved in the secondary

dispersion of copper in the droiriTge, it wrs found

necesst- ry to augment with further invest4ctions the

existing informotion on the distribution of copper in the soils. These investigtions supplement rnd extend the work

of Jacobson, Trerbyson fill Webb fnd ore briefly outlined

below. bore ccurrte geologicrl information wfs iruiloble in

1960 then .in 1954, end this enabled the writer to

estcblish more detoiled relfitionship between (o) soil f, nd rock types (SectionI,page5A(b) the copper content of

soils :n:1 tenor of minel-oli c,tion c nd (c) the copper content of soils 11.:1 sub-outcropping geology. Due to the

use of more sensitive fnnlyticul techniques then those used by Jocobson, it wrs caso possible to relEte in greeter

.ftetnil the Cu, Co, Ni fnd Zn content of soils to bedrock

geology. The modes of occurrence end dispersion mechanisms of

copper in soils were investitEted by determining, (u) the

distribution of Cu . /ad exCu in soil profiles, (b) the

61. distribution of Cu in size mrgnetic frctions, (c) the partition of coppor between minerra lottices nnl sconlory iron oxides und (a) exchongeoble cooper. Distribution of cooper in soil profiles.

The soil profiles developed on the Bukrngomr1

Ridge ore chorr.cteristicrlly imEAure. Jacobson (1956) found that copper values decrersel toworls surface end he suggested that the decrease was cuused by o combinotion of chemicrl leochinE end odlition of barren moteriol mechonicrlly movel from upslope. He considered tht the ore minerals in the upper horizons were broken down by chemicol, physicol ond biochemicol reactions. The copper vies considered to be lorEely removed in solution neither Jacobson nor Yerbyson (1960) observed ony enrichment inlicotive of significant precipitfltion in ony porticulEir soil horizon. Jacobson also reported that Cu ond Co ore preferentiolly lezched from the upper soil horizons compared to nickel, end this results in e relative enrichment of nickel with respect to copper end cobalt. The writer determine]. the verticrl profile distribution of Cu end cxCu in the minus 80 mesh size frL'ctions of

soils derived from sub-economic miner;aizotion! the results ore plotted Erophicilly in Figure. Figure 5 shows the vertical distribution of totEl Cu, Co, Ni end Zn in

62e soils derived from sub-economic ,,n1 mr- rEinEll gr'de minerliz-tion respectively.* For comprrntive - larposes, the distribution of Cu in ,profile from unminlized n-L-phibolite is given in Figure 6 . (Ifter Jrcobson, 1956).

The decrese in Cu tow'.ris surface, noted by Jacobson, is clearly demonstrnted in tll profiles. The cxCu content, on the contrary, increases towrrds surface.

Some form of chemical control is iniict, tol by the fact th:t the exCuCu ratios plotted in Figure 4 r Lpv)err- to be

E direct function of depth c.n1 [- re not -:lftel to the Cu content of the soil nor the soil horizon. It is suggested

that chemical werthering which increases in intensity

towards surface, is the controlling factor, and that the consistency of the cxCu! Cu ratio with ..depth reflects an

equilibrium between Cu, cxCu and weathering processes. The cxCu content is a mersure cf the more loosely bonded

metal, and it is probable that it occurs r s sorbed metal on

the direct or indirect products of weathering such as iron

hydroxides (Hem; 1960 c), clays (Corro15 1958), and orgtnic

matter (Jacobson, 1956). Totc:1 Co, Ni and Zn concentrations lecreaso towards

surfcce, also probably as a result of le chin: (Figure 5)

* Jacobson ail. not determine cxCu or Zn, r. nd also -lid c not know the grade of the primry copper mineralization.

63. In the 11 rind B horizons the four metEds behove similnrly, but in the C horizon the fluctutions in indiviauol metol content care more vnrirble. These flucturitions rre considered to reflect irregular distribution of metal in the pc.rent, unwerAhered bedrock (Jocobson, 1956). It will be noted that the erratic distribution of Co in the C horizon of pit(a)(Ficure 5 ) is ossocir, ted with zones of yellow limonite, probably derived '!'om oriEim7,1 pyrite— rich zones (see pege 40). The percentoGe decreese of met€l on pc,ssing from the

C up into the B end horizons is grertest for Cu rqd Co

(which decreF,se by obout the sFme Fmount), End leost for Zn. Thus the proportions of Cu rind Co to Ni rind Zn decrease towrrds gurfcce. (iii) Distribution of canner in B horizon soils. Jr.cobson (1956) recomiended tIKt soil scmnles be

collected from the B horizon, becE, use this horizon is rawnys present, whercrs the upper A horizons hove sometimes been

eroded. Mechrnicrl movement down the steep hill slopes

is greatest in the horizon rnd e riomE,lous soil is rrcpidly. diluted by mixing with br•rren mEterif.1 end chemical leaching.

Relrtively minor soil creep cnd dilution by mixing with

b=en soil occurs in the B horizon, rnd in the Bukongmr creo suboutcronning minerclizEtion could in ell coses be

detected by srmpling the B horizon soils.

64. (a) Distribution of copper related to mineralization. Figure 7 (rfter tTcobson) shows the distribution of Cu, Co, Ni end leichble zinc (cxzn) in the

B horizon of the soils thong r traverse c- cross the Bukc,ngcm& Rid&e. ,Tcobson concluded thE.t the locetion of ,ilomclous soil values corresponds closely to underlying brim ry minerEdizrtion. Even on steep slopes, the B horizon soil cnomJlies show only very slight downslope extensions. Cu, Co, Ni !rld cxZn sire it ., nom lour in soils over minerraizf:tion. A qur., ntitE.tive relationship between tenor of minen- lizrtion rill intensity of soil z. nomEly is indiciited.

Jacobson estblished prospecting techniques F.nd interpretrtive criteria for the locztion of minerlizE.tion of the Kilembe type. His work, however, 71s done on soils which were subsequently proven to be derived from mf.rginr1 grt.de minerclizction. This fact does not detract from the wilidity of his techniques nor of his interpretrtion of dote which hove been repete-lly substEmtirted •luring subsequent prospecting by Kilembe Tines Ltd.

During the course of the =iter's work, selected soil scmples derived from minerrlizction known to be of economic, end sub-economic grEde were onrlysed for Cu, Co,

Ni End Zn. These results c.re suoraementc,ry to Jccobson's work end ore presented in Figures 8; 9 and 10.

65. The data substzntiate Jhcobson's suggestion Ih:t, in the

Bu kangam area, a quantitative relationship exists between the tenor of mineralization and the intensity of soil_

:-, nomaly. Jacobson found that cxZn was anomclous in soils derived from mineralization,Eni the results of the writer's work inlicate that total Zn is also anomalous. It is of interest to note that the Zn. Co ratio (pathfinder elements) is consistently grouter then unity in soils derived from the footwEll rocks.

(b) Distribution of copT)er related to geology.

In order to determine whether the metal content of soils could be related to subsurface geology,

Jacobson EnLllysed both the weathered rock Fnd overlying soils for Cu, Co (nd Ni. The results of his rock Enalyses

,re presented in Table 5,

Rock type! Cu p-orn! Co aim. Ni rnm.

Dolerite 200-250 50 140 anskite 125-175 <50 20 Injection Gneiss 10- 30 <20 Quartzite 40- 75 <50 <20 Gronitite 60-160 <50 20-50 Biotite Schist 150-160 150-200 <50 50 Mineralized amphibolite >200 >50 >50

Table 5 . Copper, cobalt and nickel contents of weathered rock types. After Jacobson (1956).

66. Recent work by Hprden (1961) hos indicated thEt o potassium bisulphate fusion on wecthere.I rock snecimena (es opposed to soils) is generally incomplete end that considertble nroportions of the metFils my not be extracted from the somple. As cll of Jc'cobson's Enrlyses were done by the potassium bisul-phte fusion method, his results should be reviewed in the light of IL- rdenfs findings. Furthermore, due to the incomplete ceologicl information

thEt WE'S then Evriloble, JEcobson's samples are mainly roprosentEtive of footwc11 rocks. The motEl content of the corresponding B horizon soils derived from these rocks ore given in Ttble 6.

Be:4rock! Cu nnm.

Injection gneiss 10- 25 <5C <20 Qubrtzite 40- 60

Granulite 40- 90 <50 <20- 40 Biotite Schist 60 <50 <20 A mphibolite 100-150 <50 <2C- 40 Dolerite 100-150 <50-50 60- 80 Minerolizod omphibolite 150-1500 <50-170 40-100

Cu determined by lithizone, Co .rid Ni by pLper chromoto-- rophy. * No dot. Teble 6 . Copper, cobolt onl nickel contents of B horizon soils over various rock types (-80 mesh). fter irttcobson (1956). 67, 7ebb (1958) End Terbyson (1960) used multimetri trace

Enlyses on srmples collected by J,T.cobson to Aemmstrnte the ('7ppliccbility of these nlethods to EeoloLic-1 mcTDPinE.

During; the course of the 'ITriter's work, the frequency distribution of 4,20 corYpor vnluos wcs exumined to see whether there wns grouping of waues which might reflect the nature of the different bedrocks from which the soils were derived. (TE,ble 7).

Fre- Dom Cu! Frgpuengy. ?pm Cu! Frfaucn2z! TrYrn C11!2 ...U0.=,

10 1449 150 111 290 28 20 65 16C 68 300 - 390 191 30 124 170 31 400 - 490 100 40 94 180 106 50C - 590 44 50 159 190 63 600 - 690 22 60 96 200 62 700 - 790 15 70 52 21C 55 800 - 890 9 80 192 220 23 900 - 990 2 90 164 230 74 ;%1000 51 100 222 240 47 110 86 250 32 120 ."r7 260 27 130 149 270 19 1.40 101 280 61

* Cu determined by Kilcmbe Mines Ltd. by the stEndErd dithizme procedure.

Tnble'7. . Frequency distribution of copper in soils from the Bukringmr, Ere.

68 o No geologically significcnt groupings vre n-)pnrent from the ,lets tl-buletel in Teble 7 , apart from the 10 onm end greeter then 10 ppm vtlues. However, when the coochemicea End geological mops ore superimposed, e relc.tienship between coPper values end geology were observed. (Table 8).

Cu lyom 110npe of vnlues! FOC1C typest

10 Gneiss (nd gronitized footwoll biotite schist.

20 - 100 HongingwnI1 nlbite - chlorite zone. Foetweal biotite schist zone. (Jacobson End 7obb).

100 - 200 Hnngingwoll chlorite - olbite zone. Footwoll quertz - felsoer nmphibolite zone.

200 plus rf.dale Kilembe Series end minernlizotion.

T:b1e 8 . Copper content c soils derived from fliffel-en-

rock types in the Kilembo nrec.

In order to determine whether the Co content or the

Cu! Cc retie in the soils would distinguish between rock

types in more detE il, o selection of representative soil

snmples from type nrer.s were enelysed. (Tnble 9),

Inspection cf the dntF, indicetes thot the Cu. Co ratios differentiate between &11 roc types, except the gneiss

end gronitizel

69, * Cu (pm). Co (opal Cusco Underlying Rock ' Lye- typc. Ronge! Ronge! r[tge! 117tnge! rfTe,

Gneiss. 18 - 30 23 7 - 20 16 1.1. - 1,8 1L.5 Gro, nitisod) Footwoll ) 12 - 23 7 - 20 ) 32 14 C.7 - 5.0 . 8 Schist ) Hongingw11) hlbite/ ) chlorite ) 80 - 125 1CC 30 - 34 2.4 - 3.9 9 zone ) FootwEll ) Biotite ) 92 - 112 101 17 - 31. 27 2.9 - 5.6 4.0 Schist ) Footwo,11 ) Quortz- ) Folsprr ) 112 - 212 151 20 - 29 'Triphib.)lite) 3.7 - 9.0 5,•7 zone ) riadic ) Yilombe ) Series ) 3CC - 1200 900 46 - 114 91 7.0 - 17.0 11,2

* Note! Copper determine' on o 0.2g smple by the diquinoly1 method.

TEkble 9 . Copper end cobolt content of soils .derived from different rock types in the Kilembe oven,

The ratio of Zn!Co is consistently Erecter then unity in soils derived from the foctwnll zone of minerlized I'id le Kilembe Series rocks (Figures 8t 9 Phd10). Holmon: 7erbyson onj Webb -eportel e Ni! Co rr.tio gref ter tlan 02 equal to two in scils derived from dclerites, compare -1 to less then two in soils over

70, minerelized emphibolite. During the course of the writer's work, this cbservetion wos substJnti&ted. (iv) Distribution of co2-Der in soil size fractions. In the followinc sections, size fractions [ire designcited by the B.B.S. mesh sizes. The reletionship between mesh size, type of mteriel fni micron size ere given in Teble 10.

reteriel Mesh size (B.S.S) Microns

Send 20 1.0750 Strid.. 3.6 0.5350 Send 80 0.210C Send 150 0.1040 Serld 200 0.c536 Silt 0.0200 to 0.0020 Cley less then 0.0020

Teble 10. Definitions of m,teriell mesh enJ micron size of fr(7.ctions.

j(cobson lry-sieved semples from pit profiles into• size fractions vcrying from -20 + 36 mesh to -200 mesh• he concluded that ".... in ecch semple the ccp'er content of the vcrious fmctions wris cpproximEtely the some, the exception being that the very fine frections tend to contain slightly mere copper then the course frections", end ".... the pattern of distribution of copper in profile

71. is similor for f-,11 frrctione.

The dry-sieving technique cEnnot seprrote cly- silt size me teriel from the 2CC to silt size si-nl fnctions

(see SecticnI-1_). To effect c complete septicn of the cloy, silt fine sent fnctions, it is noccssry to use

wet dispersion technique bEised on the principles of sedimontticn (Section VT).

In order to esteblish the dot: fled distribution of metal in soils, the wet dispersion meth:;] is:,s used to sept:trte five -20 mesh soil sz-mples into different size fnIcticns, end ech froction wus Enrlysel for Cu end Co.

The sc.m7_,Ies ore ropresent:, tive of soils lerived from minerE,lized 7,-ile-ribe Series rocks (Nes. 1602-6 c nd 1388-9), non--mineralized 711embe Series rocks (No. 123C-8;, br-.rren gneissic roe's odj:-.cont to the Yilembe Series (No. 1596-9), rnd bf.,rren Gneissic rocks fr removed from possible minerclizing influences (No. 1566-76). The results ore presented in Figures 11 and

The proportion of the different size frt ctions in oll soils are generally of the sr-..le crier. The -8C mesh sc'mp]es ccntc.in 52 to 64 percent (c,verzge 60 /Percent) ciry- silt size mrtc,ril.

The Cu end Cc content of the different size fractions increases with decreasing groin size. 77 to 89 percent

(overage 85 percent) of the totl Cu content is concentroted in the size frrotions of the -80 mesh srmples. The -80 mesh fr:_., ctions of smples ore used for iprespectinc r,nd the efficiency of this size frrction is indictel by the consistent ?proportions of cly-silt size moteriul (6o percent), which in turn contcins c relttively consistent proportion (85 percent) cf the totfl Cu content of the sf:.,mrao. The ostz- bli',hment of on equilibrium between wec, thering 'Process - the chr.ricter of soils is suggested by the consistent p:rcportions of cloy-silt size =tericl end the consistent proportions of copper concentryte'l in these size fractions cf soils derived from different rock types, (v) ne_listribution of_copper in mz7.gnetic frt- ctions.

/c3 E first stcce in identifyinc the mode of occurrence copper in the soil , the size -F1':, ctir. between 2CC mesh d silt wcs se/prrted into different nognotic fr:ctions on - Frr.ntz Isodyn- mic Magnetic Soryrotcr, The clEy tn .', silt riz-e fne-GiG,ns could not be used cis they clogged in the mz,chine tnd: for the some refscn,

WrP fir7t removed by The sen:2,cns offectel by this work were () the removl cf the limonitie -Li'cction c t less thy-. .n C,4 amps, rn("L (b) the seporrtion of possible resiJufl hornblende, rctinclite, epidcte, bi.7tite cn1 chlorite from the

n.-J -n-mgaetic miner,:as Fuch cs aurrtz, etc ct on

73. 7mpen,ge of 0.8 (Hess, 1956). Each size froetion woe mocc,sconiclly cm-mined r:nd the seption of the limonitic (less then 0.4 cmps) rnd quE.rtz frnctions (grerter then 0.8 rlips) wi:, s confirmed. The copper end ceblt content of these mc.cnetic fnctions re riven in Trtle 11. The m[gnetfAc wcs not cnJlysed for cobclt because the technique ct- nnot detect cob l.t in the presence of more tlan 25 percent iron (see Appendix).

Semple Ne,2 Sample No.3 S:mple No.4 Frc, ction Am' w:ge Loccil of 4'incmLLpus :haom:lous Icq ckgrouncl m{gnetic soil. soils secr, rr

Cu. Cc Cu ' CO Cu Co npm. ppm: PP171!. ppm ppm. ppm.:

17L'Enetite H:nd— 270 21.0 230 mz- Enet Limonitic fr- ction 0-0.4 1,200 148 230 56 130 120 Mcfic minerrls 0.4-0.8 1,200 60 14C 4C 110 52 Ci=tz frrcticn 0.8 13C <5 50 40 < 5

Table 11. Copper cob; It content 71ignetic frctions of soils.

The Cu content of the mognetite is essentillw the

some for Ell three simples. The copper content of the limonitic end minercl frctins of the nom> lout

74. No. 2 soil is the sr me n.3 there is o mrrkel dr.p in the

quartz fraction. The copper content of samples 3 end 4 decrer'ses with decreasing magnetic susceptibility.

The Co content of all samples decrerses with decreasing mccnetic frnctions.

A distinct tendency for Cu and Co to be associated

with the lirionitic fraction in these soils is indicated by the results.

(vi) Thp partition of copoer between exchanEpable, lattice held and secondary iron oxide associated copper.

Previous work by Webb and Stanton (1959)

(Table 12) indicated that the copper content of secondary iron-oxides (Cope) in stream sediments differen-

tiated between streams draining areas of anomalous and

background soils. The writer's investigations of the copper

content of magnetic fractions of soils is also consistent

with En association between limonite and cop,Jer. It was, therefore, decided to pursue this line of investigation by

determining the partition of copper in soils derived from

anomalous end background areas.

The -80 mesh fractions of soils were separated into

sand, silt and clay sizes an.i each fraction was analysed

separately. The reason for the selection of these size

fractions lies in the fact that all previous work at

Kilembe was done on the -80 mesh samples any. the results

75, Presumed Mode of Occurrence

Incorporated Location of sample Exchangeable in secondary 1 Lattice-held Fe oxides

Cu (ppm)

Anomalous stream

Near mineralization 15 120 135 1100 ft. downstream 12 50 68 1750 ft. downstreamm 5 15 65

Background stream 1 3 26 2 3 30

Presumed partition (per cent)

Anomalous stream

Near mineralization 6 44 50 1100 ft. downstream 9 39 52 1750 ft. downstream' 6 18 76

Background stream 3 10 87 6 9 85

Table 12 . Partition of Cu in stream sediments, Kilembe, Uganda. (After J.S. Webb and R.E. Stanton, 1959, unpublished data).

76. con, therefore, be reloted to previous findings. Also,

the writer's work demonstroted that most of the copper is

concentrated in the clay-silt fractions.

The enelyticel method employed is fully described in

SectionVI, End is e modification of the procedure used by

White (1957) to determine the mode of occurrence of zinc

in soils! the some method tiros ussd by aebb and Stanton to obtain the results mentioned Ebove. Briefly, the total

copper (Cu) end exchongeeble copper (exCu) in the semple is firstly determined, then the secondary iron oxides

&re removed chemically by ri dithion. te extraction

(Aquilere end Jackson, 1953). The Cu content of the residue, which is essumed to be lattice-held (Cu at), is then determined, and the copper held in the iron oxides

(Cu_ ) is obtoined by difference. The results for soils ye derived from different rocks Ere tebuleted in Tables 13 & 14.

These samples were also onolysed for Cope end CoIcit. Any exCo will be included in the Cope figure. The

pertinent observetions ore listed below, End will be discussed in the following subsection (vii).

(0) The secondory iron oxide content of ill samples

increoses with decreasing size fraction. The cloy

size frection of Ell srmples contains e-y2roximotely the some concentretion of secondary iron oxides.

77.

Type and -80 + silt size fraction, som7Dle Derivation! No! Fe in Cu_ Cu)o Lat oxide Cu exCu PPmt PPmt ?Dm! 70M! pnm!'

Anomalous Mineralized 1602-6 amphibolite/ 3,000 130 60 68 2 schist from Yvette Regional Barren Gneiss 1,000 10 5 5 n. background Yotundu 1596-9 Regional BE'rren Gneiss 2,000 10 5 5 n.d background Chanjojo 1566-76

Silt size fraction!

1602-6 15,000 630 250 373 7 1596-9 18,000 7o 20 50 n. d. 1566-76 11,000 50 15 35 n.d.

Cloy size fraction•

1602-6 29,000 800 275 513 12

1596-9 28,000 100 25 75 n,d.

1566-76 30,000 70 25 45

* less than 1.0 ppm exCu.

Table 13 . Partition of copper in soils.

78. Type and -80 + silt size fraction! sample Derivation. No! Co exCo plus CoFe Plpm* CoLet pm!, ppm:

Anomalous Mineralized 40 15 25 1602-6 amphibolite/ schist from Yvette Regional Barren Gneiss 5 5 n.d.* background Metundu 1596-9 Regional Barren Gneiss 5 5 n.d background Chanjojo 1566-76

Silt size fraction.

1602-6 100 50 50 1596-9 15 15 n.d. 1566-76 15 15 n.d.

Cley size fraction:

1602-6 280 100 180 1596-9 35 25 10 1566-76 30 30 n. d.

n.d. . less then 5 ppm Co.

Table 14 . Partition of cobalt in soils.

79.

(b)The different size fractions of soil derived from mineralized rocks contrin 1.1 to 1.5 percent exCu, whereas other soils contEin loss.

(c)The Cu,,e is greeter then the Cu,., in the clay nnd silt size frections of Ell samples, but in the sand

fractions the CuEe is the same es the CuEnt. The proportion of Curc to CuLot in cnch size frection of ell samples is of e similar order.

(d)The Fe!Cu rrtio in secondary iron oxides is given in :able 15.

Fe-Cu ratio in the secondary iron oxide fraction!

Semple! Type! -80 mesh IClny + silt Silt size size size frection- frection 'erection

1602- 6 Anomalous 44 40 57 1596- 9 Regional background 180 360 370 1566-76 Regional background 400 311 666

Teble 15 . Ratios of 1?=:', to Cu in secondary iron oxides in soils. in all size frections of Semple 1602-6 (e)The CoFe (onomolous) is greeter than or equal to CoLot. The cicy size fraction of Sample 1596-9 (regional background) contains more than CoFc. In the CoLot

80. remaining samples n11 the cohrlt is lottice-held.

(vii) Mode of occurrence rnd dispersion of cop2ez• in soils.

This section will denl briefly with the inferred mode of occurrence rnd dispersion mechnnisms of cotrer ns deduced from the evidence rt this stage of the work. n'Tly of the points discussed Till he clucid-ted in subseruent sections where chemic - 1 aspects, such es solubility and precipitation, are considered in more detail.

The mapping of pit profiles has clearly indicated the decrease in mechanical cohesion and an increase of weathering effects towards surface. The essentially residual nature of the B horizon soils is demonstrated by

(a)the observed relationship between soil type and the C horizon which, in turn, reflects bedrock geology, and

(b)the relationship between metal content of soils and bedrock geology. The static nature of the C horizon is indicated by relic bedrock structures and orientated

angular rock fragments which are directly related to the underlying geology. Mechanical movement of material has only occurred in the A and, to a lesser extent, in the B horizons. Eluviation of clays from the A horizons followed by their accumulation in the B horizons is indicated by the fact that the latter is generally more argillaceous. The high Cu content of the finer fractions indicates that this process should result in an increased copper content of the B horizon. However, as no marked increase of Cu in

81, any soil horizon is generally fou.ad, it is inferred that the fine material which is concentrated in the B horizon has

probably been leached of copper. It is, therefore,

concluded that -1luviation is of relatively minor importance

in the dispersion of copper in the soils.

The essentially chemical nature of the weathering

process and its increasing intensity towards surface is indicated by the decrease in metal values and the increase

in ratios of cxCu:Cu, i.e; weathering renders the Cu more soluble, so that it can then be leached by rainwater (see

Section II B) . The consistenf; ratios of cxCu:Cu w ith depth are considered to reflect the chemical nature of the reactions involved, and the establishment of conditions approaching equilibrium between Cu, cxCu and weathering processes. The chemical behaviour (leaching) of Cu, Co, Ni and

Zn in the A and B horizons is generally similar. However, ratios of the metals in the C horizon, compared to the A horizon, indicates inherent differences in the chemical reactions of these metals to weathering processes. It is possible that Cu and Co may be preferentialhy leached in that their weathering products arc more soluble than those of Ni (Rankana and Sahama, 1949; 1ialiuga, 1947). Thus, the Insoluble minerals remain in situ and so produce the effect of relative concentration at surface when compared to copper and cobalt.

Inherent differences between the modes of occurrence

82,, of Cu and Co are indicated by their partition between secondary iron oxides and mineral lattices. Thus, except for the sand fractions, Cu is invariably greater than Fe Cu , w hereas the general trend for Co is for Co to be Lat Lat greater than Co . Fe A variatian in the mode of occurrence and weathering rates of copper and cobalt-bearing minerals is also indicated at Kilembe Mine. The zoning of cobaltiferous pyrite (footwall) to chalcopyrite (hangingwall) and the apparent genetic relationship between cobalt and pyrite have been indicated on page 40 . Pyrite/cobalt concentrates have been stock- piled in outdoor dumps and, even after years of exposure to the elements, no oxidation of consequence of the pyrite has been noted. Inspection of the size fraction data of the -80 mesh samples indicates both the reason for the efficiency of this fraction in geochomical prospecting at Kilembe and the essentially chemical nature of the weathering processes. Thus -80 mesh soil samples derived from anomalous and background areas (a) contain a relatively consistent percentage (60 percent) of clay-silt size material, (b) the copper and iron content from the free, iron oxides increases with decreasing grain size, (c) approximately 85 percent of the total copper is concentrated in the clay-silt size fractions, and (d) the clay size fractions contain a consistent quantity of secondary iron (29,000 ppm Fe).

The order of the Cu : Cu ratios in each size Fo Lat

83. fraction of all soils is approXimite4 the same and is considered to reflect the similarity of the chemical properties of Cu and Fe and their reactions upon weathering

The Fo4Cu ratios in secondary iron aKides clearly Fe differentiate between.solls derived from mineralized rocks whore the ratio is 40 to 57 and non-mineralized rocks for which the ratio is much greater at 180 to 660. The higher Cu content of anomalous soils is considered to be Fe indicative of an original genetic relationship between the two metals.

84. B. VNTER.

(1) Introduction

Tho importance of rain, ground and surface ;ator in the weathering and metal dispersLon cycle has long been recognised. Investigations of the content and dispersion patterns of the constituents of waters have boon the subject of study by water servo departments. In the past these investigations have been mainly connected with water supply for consumption and agricultural purposes. The earlier work in this field dealt mainly with the major constituents affecting supply and potability, This was in part duo to the fact that other constituents were of lessor interest, but mainly due to the fac'J that analytical techniques were insufficiently accurate to d terrain° trace constituents and metals, However, modern analytical procedures capable of detecting a fraction ef a microgram of an element par litre have boon doveloned.

The results of this recent work arc being used to understand more clearly the natural processes involved in weathering and dispersion. The chemica) rrocodures reay also forzi the basis of new pros.aect5:1g techniques in the search for metal deposits,

The solubility of elements in water is a function of many variables. Fundamentally the properties of a solution are dependent on the ,:20120PGICS of tho solute and the solvent, In natural waters, ho7iever, thin relationship

85, between a given solute and the aqueous solvent is considerably nodified by such faoLovs as hydrogen ion

concentration (pH); the oxidation-reduction potential (- 11 ); presence and concentration of other chemical compounds,

ions and gases; ionic dissociation, solubility; chemical reactions; temperature; pressure; micro-organisms;

and the time needed for the solution to attain chemical equilibrium. In general, it may be stated that the

concentration of any 7J.von element in water is controlled by physico-chemicn.l reactions, Water can also car compounds of elements in the form of ionic, molecular or colloidal solutions, A kind of mobile equilibrium exists betwe'n all these forms (Gin7blrg, 1960, In addition to the soluble component, the elements or

their compounds can occur in water as rechanicn1 suspensions; they may also be incorporated in the body structure of micro-organisms that live in the water. Appreciable amounts

of non-ionic metal may be concentrated in micro-organisms (Riley, 1939), The writer conducted relatively detailed investigations

in the Kilembe area specifically concerned with the

dispersion of copper in natural water. although the nature

of the work did not allow for a complete chemical treatment

of the subject, many of the more i:anortant properties that could affect the solubility of copper, as outlined ln previous paragraphs, were deterr Ined. The first object

wa'l to 1 ' ,Dstigate tiye possibility of xelattln6 -)r nter-

86, relating ono or more of the physical measurements such as

pH, Eh, conductivity, etc. to the copper content of waters. If such a relationship were established, it could be of groat practical importance in that these measurements can 13,- made more easily and rapidly than the lengthy techniques needed for trace-metal analyses of water. In addition to measuring the rate of flow of surface water, the following determinations were made on all surface and shallow ground-water samples collected in the Kilembe area; temperature, pH) Eh, conductivity, sulphate, chloride, carbonate, bicarbonate, and the content of ionic copper, cobalt, nickel, zinc and iron; some of these samples were further analysed for total copper, cobalt, nickel, zinc and iron. Some data were also obtained on the pH and conductivity of rainwater, and on pH and ionic copper content of deep fissure water derived from the underground workings in the Kilembe Mine. (2) Rainwater. Rainwater percolating through the soil can materially affect the dispersion of metals therein according to its ability to dissolve their constituents, and transport them to deeper levels where they may be precipitated or remain in solution in the ground-water. The solubility of most elements and the stability of their compounds is extremely sensitive to the pH of the aqueous environment (Hawkes, 1957). In general, the solubility is greater in acid solutions than in alkaline solutions. Copper, cobalt, nickel, zinc and iron are

87. generally soluble in relatively acid solutions. The pH and conductivity of rainwater was measured, and the results are listed in Table 16.

1 Condue- Time of tivity in, Date: Conditions: Samplo: Sampling: RE: microm- I hos per 3 #.;1.1 :

21/1/61 No rain for 39 days. A 1630 to 6.0 63.0 1645 Grass fires. Heavy B 1645 to atmospheric haze; 1705 5.3 31.5 C 1705 to 1715 5.4 30,5

4/2/61 Samplos collected A 6.6 48.0 21/1/61 and stored in glass beaker with B 6.55 36.0 watch glass cover

25/1/61 Occasional light D '-1445 to showers since 21/1/61A 1500 7.3 106.0 Grass fires. Heavy E 1500 to atmospheric haze. 1515 5.4 37,0

3/2/61 Continuously overcast F *1415 to 5.2 14.5 with drizzle and 1430 showers over previous thirty-six hours

Note: The asterisk indicates start of the shower.

Table:16,pH and conductivity of rainwater at Kilombo Mine.

88. The unexpected acidity of the rainwater at Kilembe after the initial precipitation (Table 16) indicates its

potency as a potential leaching agent in weathering processes, particularly in dissolving leachable metals from the zone of weathering and transporting them into the ground-water.

It is of interest to note that the specific conductance readings indicate exceptional concentrations of total dissolved

saltsf The especially high conductance and high pH characteristics of the first few minutes of a shower are undoubtedly related, The nature of the dissolved salts aL. Kilembe was not determined, but the source of the material must be natural, as no artificial contamination of the atmosphere from smelters or industries is found in the area. The heaviest atmospheric haze in this area generally coincides w ith extensive burning of grass and this haze is removed by rain. It is, therefore, considered probable that the grass fires produce large quantities of ash and volatile materials which the rainy/etc: progressively removes from the air

and returns to the ground. It would be of interest to

determine the exact nature of those salts and their influence on the maintenance (or regeneration)of soil fertility, etc. Quantitatively, large tonnages of material

*Footnotes Specific conductance X 0.65 (ed- 0.1) = ppm total dissolved salts (Hem; 1959).

89. are involved.

(3) Ground-waters. Introduction, Ground-waters play an important and integral part in the processes of weathering, by dissolving, transporting and precipitating material in the near- surface environment, Thus, ground-waters dissolve metals in the zone of oxidation and, upon descending to the zone of reduction, some may be precipitated as supergcno sulphides. Downward and lateral migration of ground-waters can also result in precipitation of metals within the soil profile (often in theB1,A1.17,o-1) or in seepage zones. On the other hand, discharge of grouqd-waters into surface drainages can result in more extensive dispersion of the soluble constituents derived from the zone of oxidation. Ten shallow ground-water samples were taken at depths ranging from 0 to 10 feet (Figures140a5).Ninc of these samples are representative of waters derived from mineralized and non-mineralized areas, One sample (No. 2475W) from the Brenda area was intended to be representative of regional background, but was found to bo highly anomalous and will be described separately in sub-section (xII), Attempts to obtain ground-water from within the zone of mineralization were unsuccessful. The water table

"outcrops" in socpage areas and streams, but the depth below surface increases rapidly away from the stream due

90. to tho step hill slopes. The elevation of the spurs separating the tributaries is variable but commonly exceeds 100 foot above the stream beds. The depth of the general water table varies from 0 foot in streams and seeps to an estimated 100 foot below spurs and ridge crests.

(t) Distribution of copper. In order to determine the distribution in ground- water of copper and other variables in relation to mineralization, the samples wore analysed for total and ionic copper as well as the full range of properties detailed on page 87. The samples near the Sobwo River (2542W) and the upper roaches of the Florence tributary (2516W) are removed from the influence of any known mineralization and arc considered to represent regional background concentrations (Table 17). The total copper (Cu) and ionic copper (Cu ag) contents average 7.25 and 4.0 ppb, respectively. Tho three samples from the Yvette headwater area (Nos. 2513W, 2519W and 2520W) are cl.oscst (300 feet; Table 17) to marginal grade mineralization (1.5 to 2.0 percent Cu) and average 60.8 ppb Cu and 31.8 ppb Cu aa, Tho sample (No. 2527W) from above the upper Kitabarole is 1,000 feet downridgo from marginal grade mineralization and contains

37.5 ppb Cu and 25,0 ppb Cuaq. Two samples from the middle reaches of the Kitabarolo tributary (Nos. 2531W and 2530W) drain subeconomic mineralization (less than 1.5 percent Cu) and also in par:;- the water derived from the marginal grade mineralization (3,000 feet). The average of 12.5 ppb Cu Cu Sample Cu aq Cu Sol Co Coaq Cos 1 Zn Zn q Znsol No. ppb ppb ppb ppb ppb ppb pph ppg ppb

2542W 7.0 4.0 3.0 40.5 <0.5 <0.5 15.0 10.0 3.0 2516W 7.5' 4.0 3.5 0.5 <0,5 40,5 11.5 11.0 0,5 2513W 67.5 44.0 23.5 ', 8.5 6,0 2.5 50,0 40.0 10.0 2519W 90.0 32.5 57.5 112.0 6.0 .6',,0 50,0 40.0 0,0 2520W 85.0 19.0 66,0 16.0 10.5 5.5 40.0 20.0 . 0.0 2527W 37.5 25.0 12.5 20.0 12.5 7.5 i0.0 30.0 10.0 2531W 15.0 12.5 2.5 6.5 5.5 1,0 22.0 20,0 2,0 2530W 1000 7.5 2.5 . 3.0 3.0 0 28,0 11.0 17.0 2528W 16.5:, 7.5 9.0 6.0 3.0 3.01 50.0 16.5 33.5

Ni Ni Fe Sample Ni aq Fe aq Fe Sol Nc. ppb ppb ppb ppb ppb ppb

2542W 2.0 1.5 0.5 800 500 300 2516W 3.5 2.0 1 .5 4000 1500 2500 2513W 9.0 6.5 2.5 2500 2500 0 2519W 16.0 11.5 4.5 5000 1700 3300 2520W 17.5 5.0 1265 5300 1300 4000 2527W 9.0 4.5 4.5 8000 4500 3500 2531W 11.0 5.0 6.0 6200 3500 2700 2530W 4;0 2.0 2,0 2800 1160 1640 2528W 20.0' 6.5 13.5 7500 2400 5100

, Sample pH 61- Eh Conduct- NaHCO3 SO4 No. my ivity PPm PPm CQ - - : 9 -1 - C 2542W 6.7 125 78 17.7 sti ) 45

2516W 6.0 140 50 8.2 CQ tO • 2513W 6.2 , 130 101 13.6 tO ‘ a

2519W 6.1 155 100 10.2 C , 1 ) C• -1

2520W 6.0 150 87 20.4- CQ V ) 2527W 6.0 130 95 13.6 9 7 C 4 ) CQ 4 2531W C 5.7 130 67.5 15.0 tr ) 0 •

2530W 5.8 100 39.5 13.6 2528W 5.8 CO 110 41 13.6

For location of sample sites see Figures 14 and 15, Table 17. Properties of shallow ground-waters from the Kilembe area.

92, and 10.0 ppb Cuaq are still anomalous compared to the background samples. Anomalous values wore also detected

In the upper Katundu area (No. 2528W) 5,000 feet downridge from marginal grade mineralization; hero. the ground-water contains 16,5 and 7.5 ppb Cu and Cu respectively. aq These results show contrasts up to about twelve-fold for both Cu and Cu between anomalous and barren ground- aq waters (Table18). Furthermore, downridge saline dispersion of anomalous upper values in ground-water can extend for at least 5,000 foot testifying to the stability of the Cu solutionsi

The copper content of the ground-water decreases with increasing distance from minerilization and the decrease is considered to be caused by dilution.

(ii) Distribution of cobalt. The distribution of total and ionic cobalt is essentially similar to copper (Table 17). Anomalous concentrations of greater than or equal to 3.0 ppb as compared to background values of fass than or equal to

0,5 ppb for both Co and Coaq differentiate between waters derived from naneralized and non-mineralized areas. Saline dispersion of cobalt for 5,000 foot downslopo from mineralization is also demonstrated by the Co and Co aq contents of 6.0 and 3.0 ppb, respectively, in Sample No, 2528W. The regional background concentrations of Co anr2,

Co (both less than or equal to 0.5 ppb) is very low and ; aq in general, contrast between background and anomalous

93. values is greater than the contrast given by copper a.. The comparative figures of contrasts is given in Table 18 assuming background Cu and Cu aq to bo 7.5 and 4.0 ppb respectively and background Co and Co aq to be 0.5 ppb.

Contrast of anomalous values comparod to background Sample No: Type: Cu; Cu. • co Cu 'Cu uoiCo aq: aq: aq: aq:

2542W Background 7.5 4.0 0.5 0.5 & 2516W

2513W Anomalous 67.5 44.0 8.5 6.0 9 11 17 12

2519W do. 90.0 32.5 12.0 6.0 12 1 8 24 12

2520W do. 85.0 19.0 16.0 10.5 11 5 32 21

2527W do. 37.5 25.0 20.0 12.5 5i 6 40 25

2531W do. 15.0 12.5 6.5 5.5 2 3 13 11

2530W do. 10,0 7.5 3.0 3.0 1 2 6 6

2528W do. 16.5 7.5 6.0 3.0 2 12 6

Table 18 . Contrast between background and anomalous Cu and Co values in ground-waters, Kilembe area.

(iii) Distribution of nickel and zinc. In general, the distribution of total and ionic

94 nickel end zinc is also similar to that of copper end again shows e saline dispersion in the ground-we-ter downslope from mineralization (Table 17). The anomaly contrast is lower then for Cu end Co due, no doubt, to the relatively low content of nickel (0.02 percent) and zinc (not determined) in the primary sulphide ore. With one exception (see below), the contrast between anomalous end background velues for Zn range from 2 to 4, whereas for Ni end Ni the and Zneq eq. contrast is 2 to 6. The exception referred to above is Sample No. 2530W, located 300 feet from the middle reaches of the Kiteberole tributary end 400 feet from subeconomic minerelizetion. content of this sample is the same es The Zneq Ni and Niaq the background range. The reason for these low metal velues, undoubtedly, lies in the fact that the grade of primary copper mineralization in this area is approximately 0.5 percent end the essocieted Zn end Ni could, therefore, be expected to be almost negligible. (iv) Distribution of Iron. The contents of 800 ppb Fe end 500 ppb Fe in the regional background water * of the Sebwe ere is of a lower order es compered to all the samples from the Bukangeme area (Table 17). However, the concentrations of iron in the letter, which range from 1,800 to 8,000 ppb Fe and 1,000

to 4,500 ppb Fesq, do not vary sympathetically with distance from mineralization. Footnote: The reasons will be discussed later. 95. (v) pH.

The importance of pH on the solubility of

motals has been mentioned on Pagc 87. The data given in Table 17 show that, apart from tho regional background Sample * (No. 2542W) which has a pH of 6.7, the ground-

water pH ranges between 5.8 and 6.2. No relationship was noted, however, with proximity of mineralization, and hence the pH does not reflect in any direct manner the presence of oxidizing sulphides. The generally acid character of the ground-waters and rainwater (pH 5.3) is indicative of their potency as solvents. The reason for the low pH of ground-water is considered below, The acidity or alkalinity of natural waters depends on the hydrogen ion concentrations. The most Important

source of these ions is the dissoation of H2CO3 (Hem, 1960 b). + H + HCO3 H2CO3 0=-1 _ CO2 + H2O The amount of carbonic acid in water is controlled by the partial pressure of carbon dioxide. Under atmospheric

conditions the partial pressure of carbon dix:ide in the

air is constant and controls the solubility of carbon dioxide in water. However, in shallow ground-waters, particularly those situated in the soil horizons in a humid area, the concentration of carbon dioxide in soil air may be ten to one hundred timos greater than in the

* Footnote: The reasons will bo discussed later. 96. atmosphere (Mohr, 1938). As a result, rainwater moving through the soil will dissolve carbon dioxide; the concentration immediately below the water table will be maintained by the high partial pressure of carbon dioxide in the overlying soil air. Consequently, due to the high partial pressure of carbon dioxide, the equilibrium In the above-mentioned reaction will be shifted to the left, that is towards a lower pH. However, the effective concentration of hydrogen ions retained in solution is controlled by chemical reactions with the constituents of unstable rock-forming minerals leading to the modified reaction:

++ where R :,,,,Jresents such elements as the alkalis, alkaline earths, divalent iron, etc. The high partial pressure of carbon dioxide again causes a shift of equilibrium to the left and a consequent high concentration of hydrogen ions (low pH) and low bicarbonate. However, upon emergence into the atmosphere, the water loses carbon dioxide and the equilibrium is shifted to the right resulting in an increase in pH and bicarbonate content. The importance of the high partial pressure of carbon dioxide in soil air in maintaining the low pH of shallow ground-water is reflected in pH changes that occur upon discharge of ground-waters into the su -face drainage.

This aspect will be dealt with in a subsequent section,

97. but it casts a doubt on the validity of pH (and other) rheasurer.lents obtained from ground-waters that have been exposed to the air before being analysed. Therefore, a description of the method of obtaining ground-water samples and the reliability of the pH measurements is given below. All pits were approximately 30 inches in diameter, and varied in depth from 9 inches to 15 feet 9 inches. The rate of flow of subsurface water seepage into the pits averaged 500 ml per hour, except in Pits 2527W and 2542W w here the rate of flow averaged 7 litres per hour. Each pit was excavated into the zone of seepage, and then

, 11Pwed to stand until the water level remainc-: constant-

This depth 4E:9 nep-iured. The water seeping into a pit immediately after excavation was generally heavily loaded with very fine suspended material which was difficult to remove even by filtration through ultrafine membrane filters. However: if the pit was do-watered and all unconsolidated material removed, the second influx of waer contained negligible amounts of suspended matter. In order to obtain sufficient quantities of clear water, it was found necessary to de-water the pits some 14 to 16 hours before sampling. This do-watering was done in the evenings and the pits wore sampled bet7een 8 and 10 a.m. the following morning. Because of the greater flow of water, Sites 2527W and 2542W could bo sampled about an hour after de-w-:toring.

98. The fact that the water was in contact with the

atmosphere for at least an hour before being analysed undoubtedly affected to sone degree the pH measurements, concentrations of carbon-dioxide, etc. The exact effect of this time lapse cannot be determined, but comparison of the results obtained from Sites 2527W and 2542W to other sites indicates that the effects between one and 16 hours are not significant (Table 17). Reference to the effects of ageing conducted on surface water (see page 132) suggests that the changes which must occur on exposure to the atmosphere probably take place within the first few minutes.

The major change that could be expected would be the loss of carbon dioxide and resultant increase in pH and bicarbonate content. If the pH change were large enough, it could possibly affect the concentrations of dissolved metals, particularly if the pH of hydrolysis wore exceeded ) -and the metals precipitated as relatively insoluble hydroxides and basic salts. Britton (1942) gives the following figures for the pH of hydrolysis: zinc, pH 7.0; cobalt, pH 6.8; nickel, pH 6.7; divalent iron, pH 5.5; and divalent copper, pH 5.3. It is important to note that these figures wore obtained from relatively simple synthetic solutions in a laboratory, and that the actual values can be considerably modified by the complexity of constituents in natural waters. However, theoretical considerations of the solubility

990 of copper and iron in relation to other variables, as

outlined on pages 138-147, suggest that no important changes in metal content of the ground-water occurred before collection, and that the measurements obtained by the writer are sufficiently valid for the pur.?oses of these

studios.

(vi)Carbonate and bicarbonate.

Because of the low pH, no carbonate is found in

the ground-water (Section 'M. Bicarbonate as a direct measurer:ant has very limited

application in location of copper mineralization. However, bicarbonate concentrations are important when considering solution and precipitation of copper and iron (Sim an, 1958;

Hem, 1960 b). The concentration of bicarbonate, expressed as NaHCO3, recorded in the Kilembe samples range from 8.2 to 20.4 ppm (Table 17). For the reasons explained above, these values may be somewhat higher than those actually occurring in the ground--water before exposure to the atmosphere, However,

the distribution of these values shows no apparent relationship to mineralization or the copper content of the

water.

(vii)Sulphate and chloride, The sulphat* content and sulphate:chloride

ratio are important and sometimes diagnos —_c features of water draining oxidizing sulphide deposits (Ginzburg, 1960). At Kilembe, the concentrations of these constituents in

100, the ground-water range from 2.4 to 4.0 ppm S040 and from

0.5 to 1.0 ppm Cl. Neither the content nor the SO4:01 ratio shows any obvious correlation with distance from minerall- zat:ono Having regard to the fairly widespread distribution of sulphides in Kilembe rocks, the observed concentrations of SOA are surprisi-gly low compared to the average abundance of 10-500 ppm SO4 quoted by Ginzburg (1960). While it is possible that the sulphate and chlorVe content are relatively uniform in the Kilembe ground-water, the data are subject to some doubt. Since it was impractical to carry out the determinations at the sample site (see appendix), the samples were analysed in batches at the base laboratory from one to seven days after collection. It is possible, therefore, that the results reflect an equilibrium only obtained during storage and that greater variations might be obtained If analytical techniques for use at the sample site wore employed. Tho effects of storage in general are dealt with more fully in Sub-section(5). (viii) Oxidation - reduction potential (Eh). The Eh of a solution is a measure of the intensity of the oxidizing or reducing conditions In the solution. Increasing positive values of Eh indicate increasing oxidizing conditions (European nomenclature). The pH of a solution generally influences the Eh at which oxidation or reduction reactions can take place, Thus, an increase in the pH of a solution may decrease the Eh at which the oxidation reaction can occur (Gladstone, 1947). Micro- organisms involved in oxidation-reduction equilibria of ions in water, merely accelerate or retard the rate of reaction (Hawkes, 1957). Tho precipitation of ferric iron upon oxidation of ferrous iron could have an important bearing on the distribution of copper. When forric iron is precipitated, the soluble copper may also be removed by affects such as co-precipitation, flocculation and sorption (Hem, 1960). Eh measurements were made in the field in order to determine the possible affect of these reactions and the possibility of the Eh readings differentiating between anomalous and background waters. The Eh ranged from 100 to 155 my and showed no direct relationship to mineralization. Also, when the Eh is related to the pH of the solutions, it Is found that the iron should occur in the ferrous state (Hem and Cropper, 1952) and, consequently, there should be no precipitation of iron likely to influence the copper content of the water.

(ix) Conductivity. The specific conductance of a solution is a function of the total dissolved salts (Hem, 1959). In view of the corrosive power of the acid solutions in the immediate vicinity of oxidizing sulphides, the content of t disso: 3d salts in ground-water draining mineralization could conceivably differ from ground-water in barren areas.

However, at Kilombe, although the conductivity of the

102. ground-water ranges from 395 to 101 micromhos, there is no apparent relationship with proxi ity to mineralization (Table 17). (x)Tor .11perature

The temperature of grounu-water was found to range from 18 to 26 degrees C. No relationship was noted between temperature and any other property of the water. (xi)Summary.

The total and ionic concentrations of copper, cobalt, nickel and zinc in ground-waters reflect the presence of mineralization. There is evidence of saline dispersion of anomalous metal extending downridgo from m s rgintl metallization for distances in excess of 5,000 feet. No direct rcla' _onship between other measurements and the proximity of mineralization was noted. (xii)Anomalous ground-water near the Brenda tributary. Ground-water from a pit located 20 foot from the lower reaches of the Brenda tributary, in the

Dungalca Valley, was analysed (Table 19 ). This pit is some 5 or 6 miles froia tLe Buhangama mineralization, and no mineralization is known to OXAS6 between Bukangama and the lower reaches of the Brenda tributary (Figure 15).

The pit profile is composed of relatively sandy layers alternating with loss aronaccous material, more indicative of alluvium than a normal soil profile,

The water contains anomalous quantities of metal ant: the data obtained from this pit aro tabulated in Table 19.

103r v - Non-Ionic Metal Total Metal Ionic Metal (by (ppb:) (ppb:) difference) (PPID)

Copper 21.5 12.0 9.5 Cobalt 203.0 140.0 62.0 Zinc 900.0 660.0 240.0 Nickel 228.0 92,.0 136.0 Iron 7,700 6,000 1,700

Sulphate 2.4 rig/1.

NaHCO3 not detected m 1. Conductivity 440„0 micromhos per cm3. pH 5.1

Eh 135 my , Temperature 21 degrees C. • ,

Table 19 . Composition of ground-water near the Brenda tributary, Dungaloa Valley (Site 2475W).

No indication of mineralization is given by the metal values either in the soil profile, or in the adjoining stream sediment samples (Figure 16)c However, the copper content of the ground-water is three times greater than regional background, and the cobalt, nickel and zinc values are highly anomalous compared to the Bukangama area. The pH is lower than found elsewhere and the conductivity is abnormally high. 104.. The metal content of the soil profile is given in Table 20.

x Sample Depth Horn. Cu Cu Cu HC1 Co Ni 7.,,.1 Site: Inches: zon Description: ppm: ppm: Per- Cu ppm: ppm: ppm: cent: ppm:

2475W 0 - 4 Al Loam/organic 40 2.6 6,5 20 10 130 40 4 - 13 A3 Sand 30 1.0 3.3 10 15 60 30 13 - 27 A3 Sand/loam 30 1,8 6.0 8 15 50 30 27 - 33 A3 Sand 20 1.6 8.0 6 10 50 30, 33 - 40 A3 Sand/loam 40 2.0 5.0 12 15 50 35 40 - 45 A3 Sand 40 1.3 3.2 7 15 40 201 45 - 55 A3 Sand/loam 50 3.5 7.0 18 12 50 30,',

55 - 56 A3 Sand 50 165 3.0 8 12 50 25 56 - 69 A3 Sand/loam 40 240 5.0 11 12 50 30 Water table 9 - 80 A3 Sand 50 1.9 3.8 20 12 60 40

Table 20. Metal content of soil profile from Site 2475W. (Data refer to -80 mesh fraction).

105. The reason for these abnormal metal contents is not known, It is possible that the explanation may be purely chemical and unrelated to the rectal content of the bedrock

or, alternatively, the results could reflect the presence of mineralization in the vicinity. The lack of corrobora- tory evidence of mineralization in the soil or stream sediments could indicate a very localized source of metals and total dissolved salts. For example, if the material is

alluvium, it is possible that the underlying minerals may have been sulphides derived from a higher elevation in the Dungalea Valley and concentrated locally*. Present-day oxidation of minor sulphides nearby might conceivably account for a ground-water anomaly, unaccompanied by any pronounced anomaly in the soil or surface drainage. Alternatively, a blind sulphide body very recently exposed to oxidizing influences might also account for the phenomenon.

Several explanations are possible, and it would be of interest to determine the reason for this anomalys If the results proved that the ground-wtor anomaly was related to underlying mineralization, it might be possible to develop a practical technique of ground-water analysis for prospecting grou.ld concealed beneath the extensive alluvium of the Rift Valleys.

* Footnote: Sulphides were observed by the writer in river boulders and the panned concentrates of active stream alluvium from the Kabili River (Figure 15). 106, (xiii) Ground•-water from deep fissures.

Several pH measurements on waters discharging from the underground workings at Kilembe Mine were made by Spurr (1961 - personal communication). The writer determined the ionic copper content of 4 representative samples in the pH range 4.6 to 7.8. The combined results are given in Table 21, Bird (personal communication) states that the near surface levels of the mine are now considerably drier than a few years ago and that the present water is derived mainly from deep fissures. Samples 10ED and 13ED to 17ED have a pH range of 7.2 to 7.6, and can be considered as representative of uncontam- inated deep fissure water. No marked change in pH occurs in the water flowing in underground drainages, A very rapid decrease in pH occurs in waters percolating through dumps which are presumably oxidizing. The increased solubility of ionic copper with decrease in pH is demonstrated by these results . It is considered probable that the copper content of samples lED and 3ED is largely derived from oxidizing sulphide minerals exposed by underground workings. The high pH readings from the Mine are exceptional for deposits of this type and is considered to reflect the resistant

nature of the local pyrite and the slow rate of oxidation even when the ore has been opened up by

underground workings.

107, K.M.Ltd. Cu Type: Location: Sample-pH: NO: ppb:

10ED 7.6 UncontaLdnated deep Underground 13ED 7.2 fissure diamond 15ED 7.55 water drill 16ED 7.55 holes

IRDJ 7.8 * 320 Deep fissure water Water flowing in 4ED 7.7 after erlergence into drainage 5ED 7.9 undergrou., d workings. channels, 6ED 7.6 Possibly contaminated 8ED 7.8 by oxidizing 12ED 7,5 sulphides exposed by 1ND 7.8 mining activities.

7ED 7.4 Deep fissure water. Water derived 9ED 3.4-3.5 *10,000 Contamination from shutes, 11ED 6.0 affects not cavings and 14E0 7.2 determined. working faces 17ED 7.55

3ED 7.7 * 300 Deep fissure water Outside 2ND 8.2 in drainage channel underground exposed to surface workings, atmospheric conditions. Possibly contaminated,

2ED 4.6-4,9 *700,000 Water derived from After 3ND 5.8 underground, after percolating percolation through through surface oxidizing surface dumps. dumps. Highly co_lta::inated.

* • Determinations carried out by the writer; other data from Spurr (personal communication).

Table 21 . pH of water derived from underground workings

at Kilembe Mine,

108. It would be of interest to establish the reason for

the low pH of sample No. 9ED and to determine whether

this reading reflects oxidation of a known sulphide deposit.

(4) Surface water.

(1) Previous work at Kilembe,

Holman (1956) analysed selected surface water

samples from the Bukangama area for total heavy metals, using procedures described by Huff (1946). Negative results were obtained using both the mixed colour test

(reported sensitivity 0.01 ppm) and a nonocolour test

(reported sensitivity 0,002 ppm),

Holman also attempted to determine the sulphate content of these waters by means of a barium chloride method developed by Jeffery of the Uganda Geological

Survey (sensitivity 5 ppm), but again obtained negative results. He concluded that no copper dispersion of consequence occurred in surface waters, and assumed that

the ground-water entering the streams contained negligible quantities of coppers The presumed low concentrations of coiner in the subsurface water was considered to be due

either to flow only through the upper soil horizons where any copper was too firmly bonded to be Leached, or to

groat dilution of the ground-water before it entered the streams

Webb (1958), however, noted an increase in the cxCu:Cu

ratio in the upper reaches of the Bulcangama tributaries

109. compared to the lower roaches, and suggested that this was due to copper precipitated from ground-water entering the tributaries,

(ii) The Yvette tributary .

The Yvette tributary rises some 700 foot from the Bukangar.a crest. The upper portion of the tributary is situated Immediately downs lope from marginal grade mineralization (Figure 13), The upper and middle reaches of the tributary flow through Lower Kilenbe Series rocks, which in the lower reaches are granitized,

The distribution of anomalous copper in the surrounding soils is shown in Figure fns A minor tributary (Site 2510W) draining footwall rocks, joins the Yvette appr=imately half--way down, The gradient and rate of flo-; of w ater in the Yvette tributary is shown in Table 22 Figure 17,

The volume of water derived from the minor tributary has been subtracted from the flow of the Yvette tributary so that the figures for the increase in flow downstream indicate the increments derived directly from ground-crater seepage,

Seven water samp)es from the Yvette and one from the minor tribut;try were analysed in detail to determine the

distribution pattern and factors controlling metal dispersion in surf ace water drainin mineralization

(Figures 18, 19 and 20). The character of the water from the minor tributary is essentially similar to that of the Yvette waLers (Table 22),

110, Co Sample Cu Cu aq Cu sol Co aq 1Cosol No: ppb: ppb: ppb: ppb: ppb: ppb:

Upper Yvette 0 ft 2213W 11.0 7.25 3.75 3.5 1.75 1.75 500 ft 2511W 8.0 6.0 2.0 0.5 <0.5 <0.5 1,000 ft 2509W 9.0 6.0 3.0 0.5 <0.5 <0.5 Tributary 2510) 6.0 5.0 1.0 0.5 <0.5 <0.5 1,500 ft 2508W 7.5 6.0 1.5 0.5 <0.5 <0.5 2,000 ft 2507W 10.0 7.0 3.0 0.5 <0.5 <0.5 2,500 ft 2506W 12.5 7.5 5.0 0.5 <0.5 <0.5 3,000 ft 2505W 15.0 7.5 7.5 0.5 <0.5 <0.5

Sample - Zn ,, Ni Ni 1,;, Fe , Fa- , /ID: Ln. aq. Zn Sol Z.I. -a 3o1 '-'-. :act :-J--0.. o.l. ppb ppb ppb ppb ppb ppb PPb PPb ppb

2213W 10.0 6.25 3.75 3.5 1.0 2.5 1600 490 1110 2511W 4.5 3.0 1.5 142 1.0 0.2 1000 400 600 2509W 8.0 6.0 240 210 1.0 1.0 800 340 460 2510W 3.5 3.0 0.5 2.0 1.2 0.8 260 240 20 2508W 7.0' 5.0 2.0 2.0 1.0 1.0 400 300 100 2507V 5.0 4.0 1.0 2.0 1.5 0.5 500 260 240 2506W 6.0 5.5 0.5 1.0 0.5 0.5 440 300 140 2505W 7.0 5.0 2.0 1.0 0.5 0.5 400 300 100

Sample Eh Conduct- NaHCO3 Rate of flow , No: pH: r.-iv: Ivity: ppm: cosecs:

I .

2213W 7.2 70 81 45.2 0.003 2511W 7.3 110 26..5 10.2 0.003 2509W 7.3 140 40.5 21.8 0.003 2510W 7.4 130 30 13.6 0.013 2508W 7.3 135 37 18.0 0.017 2507W 7.4 140 36 17.3 0.077 2506W 7.6 150 ' 52 28.2 0.079 2505W 7.7 155 53 28.6 0.087

Table 22 . Properties of surface waters from the Yvette tributary. The flow of 03013 cusecs in this tributary is relatively

small compared to the 0.094 cusocs of the Yvette itself. For these reasons, any effects engendered by confluence of these two waters are considered negligible and are not considered in the following descriptions. The data are presented in Table 22. They are also depicted graphically in Figures 17 to 20 In order to show more clearly the relationships between the different properties.

(a) Copper. The Cu concentration in the headwater sample is 11.0 ppb (Table 22)3 The content decreases downstream to a value of 7.5 ppb in the middle reaches before increasing steadily to 15.0 ppb in the lowermost sar:ple. A similar

trend is found for both Cuaq and Cus.)1 and in each case the graphical plot shows a trough in the middle reaches of the tributary (Figure 18). This trough corresponds to the peak copper values In the sediments and bank soils (Section II C) the shallowest gradient of the tributary (Figure 17), and

the maximum increase in volume of water, The Cu content of the surface water (11,0 ppb) in the upper reaches of the Yvette tributary is considerably less than that of the adjacent ground-water, which contains an average of 80.8 ppb Cu. This indicates a considerable

loss of copper upon transition from ground to surface water.

The Cuaq content in the ti.ibutary remains relatively constant (6.0 to 7.5 ppb), but the Cusol content ranges

112 from 1.5 to 7.5 ppb.

These observations have a bearing on the dispersion of copper in the drainage systeLl, and will be discussed after describing the distribution of copper in the regional drainage, transition zones and stream sediments. The distribution of other metals and their content in ground and surface water will be given below, but a discussion of the dispersion process will be deferred until later. (b)Cobalt.

The total and Ionic cobalt contents of the Yvette headwater are 3.5 and 1.5 ppb respectively (Table 22). Thereafter, the content decreases downstream to 0.5 ppb Co, and less than 0.5 ppb Coaq. The range of Co values are near the 1.1L,Its of detection of cobalt and, therefore; relatively minor variations at these levels could not be determined.

The average Co in the ground-water derived from the area in the upper roaches of the Yvette is 12.2 ppb, and the adjacent surf ace water contains 3.5 ppb in licating a loss of 8.7 ppb Co.

(c)Zinc.

The Zn and Zn aq contents decrease downstream from 10.0 to 4.5 ppb, and 6,25 to 3.0 ppb, respectively, over the distance of 500 feet which separate the two uppermost samples (Table 22). There,Zter, the concentrations show variations of 5,0 to 8.0 ppb Zn and 4.0 to 6,0 ppb Znaq,

113. which are of 'oho sa:,o order as the variations found in the upper reaches. The average Zn content decreases from 46.7 in the ground-water to 10.0 ppb in the adjoining surface water.

(d) Nickel. NI concentrations decrease downstreaL from 3.75 to

1.5 ppb between the uppermost t-ro sat.iplinG sites (500 feet apart) and then remains constant at 2.0 ppb for the next thousand feet before decreasing to 1.0 ppb over the last ranges between 0,5 and 1.5 ppb, 500 feet (Table 22), Niaq but also shows a general tendency to decrease downdrainage. Ni decreases from 14.2 to 3.75 ppb upon transition from s'round to surface waters. (e' Iron. Fe and Fe pq decreases downdrainage over the first 1,500 foot from 1,600 to 400 ppb and 490 to 300 ppb; respectively (Table 22). Thereafter. both remain relatively constant at 450 - 50 ppb Fe and 280 - 20 ppb Feacj The average 1'o content of the upper :fvette ground-• water is 4,300 ppb compared to 1,600 ppb in the adjacent surface waters. (f) pH and Eh, The pH and Eh increase steadily downdrainage from 7.2 to 7.7 and 70 to 155 mv, respectively (Table 22). No direct relationship is found between these readings and the Cu content. The pH readings arc all appreciably higher

114. than in trio adjacent ground-waters (6.0 to 6,2). The Increase in pH is explained by the reactions involving the loss of carbon dioxide which take place when the ground-water emerges at the surface (page 96). The average Eh of 129 mv is of a siriilar order to that of 1215 my found in ground-waters, but the steady increase downdrainage in the surface water indicates

Increasing oxidizing conditions (page 101). The lower

Eh readings in the surface water compared to ground-water do not indicate that conditions are more oxidizing in the ground-water onviromcnt. The intensity of oxidizing or reducing conditions in a solution is related to the pH

(sec page 101), and the increase in both pH and Eh in surface waters results in an increase in oxidizing conditions compared to the ground-waters. (Figure 28).

(g) Specific conductance and sodium bicarbonate. Conductivity of the ground-water averag,s 96.0 ralcronhos in the upper Yvette area co:.pared to 81,0 micromhos for the adjoining stream water. The difference reflects the loos of total dissolved salts upon transition to surface waters which is also reflected in the decrease in metal values demonstrated above. The average bicarbonate content of the ground-water is 14.7 ppn compared to 45.2 ppm in the adjacent surface water. This increase in bicarbonate is caused by the sa:e reactions responsible for the increase in pH ;page 96).

115 A direct relationship between total dissolved salts

(conductivity) and bicarbonate concentrations is found in the Yvette tributary (Table 22 and Figures 198c20).This is due to the fact that the total dissolved s -A.ts of these waters, and indeed all surface waters, contain between GO and 86 percent bicarbonate.

As the conductivity mainly reflects the content of bicarbonate, which g:!eatly exceeds the contents of dissolved copper and other metals, no relation between ionic metal content and specific conductance could be expected nor indeed is one found in the data for surface waters.

(h' Chloride ond sulvhate,

The chloride concentrations of Sites 2505, 250 and 2213 are 0.75, 0,5 and 0.5 ppm respectively. The sulphate content is constant at 3.2 ppm, except for

7T0:, 2505 and 2213 .17Lich contain 2.4 and 2.6 ppm, respectively.

The concentration of chloride in all surface watel: ranges from 0.5 to 1.5 ppm, while sulphate ranges from

to 3.2 ppm. Yeithev a:c apparently related to mineralization nor to any other prop erty that was determined. Possible reasons for the uniform content of sull7Jlate an:1 chloride have been given on page 101; no further reference is made to those constituents

(1) r7eLPorature.

Temperature of the stream waters was found to

11 6. increase progressively from 15 degrees C. at 8 a.m, to

19 degrees C, at 4 p,m. These temperature variations

are solely related to atmospheric tonneratures,

(1 5i) The Florence tributary.

This tributary In located in background footv;ali gneiss at a higher elevation, and 3:000 feet upridge from known uinc)rallzation, and it was sampled only in the upper

and loner reaches (Fgures)5(14),The rocks in the lower reaches of this tributary arc considered to be gl'anitized

Lover Kileubo Series rocks and are different from the gneissic locks occurring in the headwaters and furGher to the northwest. Tho object of Sample No, 2532W (Table in the upper reaches was to study the effects of transition fro:A ground to surface water; the relevant reglonal background sample is No, 2516W, soc Table 17), In the lower roaches Sample No, 2243W was taken to investigate the dov:nstream dispersion panorne

Cu and Or,aq content of the ground-water is 7,5 and 4.0 ppb, respectively, These va:.ucs decrease slightly to 5,0 ppb Cu and 3,5 ppb Cu.a in the stream headwaters.

Cu in3reasos to 6,5 ppb in the lower roaches, whereas the

Co aq reL.ains relatively constant at 2.5 pcb, indicating an increas in Cusol Thus, although the actual coneentra- tions of cppnor in the upper and lower reaches are loror than those fro:J. the Yvettn tributary, the pattern of d!stribution is similar-

117 Cobalt concentrations are below the limits of detection.

All other LeasureLents, except for the general order of ionic values, are almost identical with those obtained in the Yvette tributary (Table 22)e It nay be conc)uded, therefore, that reactions involved in transition from ground to surface water and the reactions controlling the downdrainage dispersion pattern in the Lower reaches are similar in both tributaries. It will be noted that the middle roaches of the Florence tributary were not sampled and that the above comparisons refer only to the upper and lower reaches of the tributaries.

(iv) The Katundu tributary.

A sot of samples similar to those in the Florence tributary were also taken in the Katundu tributary, The sample site in the headwaters of this tributary is located hangingwall gneiss some 600 feet lower and L,000 feet doweridge from mineralization (Figuresl3&14).The geological conditions are more complicated than the Florence and

Yvette tributaries, in that the lower reaches and the upper northern branch of the tributary are located in hangingwall Kilombe 3cries rocks.

!.!arginai and sub-economic grade mineralization is found in the ground-water catchment area of this tributary,

Tho rate of flow of uater in the upper and lower reaches is 0,004 and 0.15 cusecs respectively. This means that a

118 considerable quantity )f water draining mineralization is added to the stream. The ground-wator near the headwaters contains anomalous copper, cobalt, nickel and zinc val'oes (Sample 2528W, Table 17).

Cu decreases from 16.5 ppb in the ground-water to

5.0 ppb in the headTato:s (Sample 2529W), and then Increases to 9,0 ppb in the lover reaches (Sample 2301W). Cuaq decreases from 7,5 ppb in the ground-water to 2.5 and 240 ppb in the upper and lower reaches, respectively. Non- imic Cu increases downstrear_ from 2,5 to 7,0 ppb, The content of cobalt in the strear, water is beim the of detection, although the ground-water carries 6,0 ppb Co.

The variation in all other measurements upon transition from grolind to surface water and the variations observed in the samples from the upper and lower roaches 13 similar to both the Yvotto and Florence tributaries (Tables 22 h 23), and demonstracs a basic similarity of the reactions involved in the dispersion of copper in the tr*_butaries.

The waters from the upper and lower reaches of the

Yvette tributary contain higher average values of both Cu and Cuaq (13,0 and 7,3 ppb respectively) compared to the Katundu (7,0 and 2,25 ppb) and the Florence (5,7 and

3,0 ppb), The from the upper and lower samples from Cusol each trLbutary average 5,6 ppb (Yvette), 4.7 ppb (Katunclu); and 2,7 ppb (Florence), and thus difforentiato between

119. tributary waters derived from background and anomalous ground-wators.

No other m3asuremont obtained from the surface waters

indicates the anomalous or background nature of tho ground-

water whD.ch discharges into the tributaries. (v) Other tributaries cf the Dungalea River draining : ineralized and barren areas.

Water samples were collected from the lower roaches of 12 other tributaries draining into the Dungalea River (Flgures14,z15).A11 samples were analysed for ionic metal. Four samples of water draining mineralized and unmineralized areas wore also analysed for total metal. The principal

object of this sampling was to determine the influence of major tributaries; such as the ilaud, Kabokonga, Raymond and Brenda, on the Cu content of the Dungalea River water, The tributaries wore also selected to provide a number of samples each of water derived from background and anomalous soil areas. The result-3 of the analyses are presented in Table 23.

The Cu content of most waters range from 2,0 to

3,0 ppb, and this ranee is exceeded only by the Kitabarole

(5.0 ppb), Gazagaza (4.5 ppb) and George (4.5 ppb) tributaries.. The Kitabarole and Gazagaza tributaries drain mineralization, whereas the George tributary drains, as far as is known, barren gneissic rocks.

Tho Cu content of thc lower Kitabarole and Kabekenga tribut.nr. -.tars is 10.0 and 8,5 ppb, respectively; and

120., *Location: Sample Cu Cuaq CuSol Co Coaq Co601 Zn Znaq Znsol No. ppb ppb ppb ppb ppb ppb ppb ppb ppb 0 ‘ LO ../

William 2266W A 3.0 L V 0 11.5 9 LI Muchingira 2279W A 3.0 • 0 V 7.5 • ) Kitabarole 2287W A 10.0 IS 5.0 5.0 0 (0.5. V <0.5 6,0 4.5 1.5 • ) U Katundu 2529W A 5.0 2.5 IS 2.5 <0.5 V 0 <0.5 5.0 3.5 1.5 ) • L Katundu 2301W A 9.0 2.0 7.0 LO <0.5 <0.5 0 6.0 5.5 0.5 •

Gazagaza 2308W A IS

4.5 0 V 4.0 ) • Richard 2318W A 2.5 LO 0 3.0 V . • Kabekenga 2336W A 8.5 0 2.0 6.5 0.65 0 <0.65 6.0 5.0 1.0 100 • Raymond 2339W A 2.5 L9 V 12.0 • Maud 2228W B 3.0 2.5 0.5 <0.5 L <0.5 5.0 V 3.5 1.5. O • U Florence •2532W B 5.0 3.5 1.5 <0.5 00 7.0 NI <0.5 11.5 4.5 L Florence • 2243W B 6.5 2.5 4.0 <0.5 V <0.5 L 6.5 3.0 3.5 O •

Masuli 2356W B 3.0 LO 000 V 6.0 • V Robert 2368W B 2.0 L 5.0 O • •

George 2394W B 4.5 N 8.5. si • Brenda 2443W B 3.0 2.5 0.5 •<0.5 .<0.5 6:0 6.0 0

Ni Ni Fe po Con- TNa Rate Sample Ni Sc)l Fe aq Sol pH Eh duet- HCO3 iInf No. ppb ppb ppb ppb ppb ppb my vity Dgq flow - cusecs 2266W A 1.0 280 7.9 130 70.5 31.3 0.15 2279W A 1.0 600 7.5 140 65.0 34.0 0.10 2287W A 1:[w 1.0 0 800 600' 200 8.2 120 76.5 43.5 0.15 2529W A 1.2 1.0 0.2 1600 1500 10 7.0 105 76.5 44.9 0.004 2301W A 1.5 1.0 0.5 400 36 40 7,4 125 52.5 27.2 0.15 2308W A 0.7 84 7.8 150 140.0 102.1 0.10 2318W A • 0.5 200 7.9 140 130.0 76.2 0.10 2336W A 2.0 1.0 1.0 1400 22 1180 8.0 180 92.0 54.8 1.0 2339W A 3.5 40 7.5 150 58.0 33.025.0. 2228W B 0.5 0.5 0 260 20 60 7.4 100 68.0 40.820.0 2532W B 2.0 1.5 0.5 1400 60 800 7.1 120 47.5 30.6 0.0021 2243W B 2.0 1.0 1.0 1160 36 800 7.4 130 56.0 32.0 0.10 2356W B 0.7 16 7.4 30 94.0 55.5 0.15 2368W B 0.5 2401 7.5 -10 195.01,34.4 0.15 2394W B 1.5 12001 7.2 135 108.0 66.7 0.20] 2443W B 1.2 1.0 0.2 400 3601 40 7.9 105 185.0108.9 1.0 1

A = Draining mineralized areas. B = Draining non-mineralized areas. U = Upper L = Lower. * See Figures 14 and 15. Table 23. Properties of surface waters from tributaries flowing into the Dungalea River.

121. the Cu sol is 5,0 and 6.5 ppb; both these tributaries drain mineralization, The Cu content of the Maud and

Brenda tributaries, which drain barren gneissic areas, is 3.0 ppb, and the Cusol is 0,5 ppb. The waters from the lower reaches of Lost tributaries contain 2,0 to 3,0 ppb Cuaq. This range is exceeded by the Yvette, Kitabarole and Gazagaza tributaries, which are known to drain mineralization, The George tributary draining, as far as is known, barren gneiss also exceeds this range, and should be investigated in

more detail to detormino the source of the metal, AL1 other tributaries draining both mineralized and non-mineral areas contain the same concentrations of Cuaq t In other words, the Cu aq content of the :Later C]:)6S not always provide a reliable criterion for differentiating between tributaries draining anomalous and background areas and,

therefore, has little use in prospecting. The reasons for this will be discussed in Subsection (7), The Cu content of the lower reaches of the Yvette,

Kitabarolo, Katundu and Kabekenga tributaries, which drain mineralization, range from 8,5 to 15.0 ppb., The lower reaches of the 71orence tributary contains 6.5 ppb Cu, possibly on account of the presence of granitized footwall rocks (page 117)- The Maud and Brenda tributaries draining barren rocks, however, on?y contain 3.0 ppb Cu. Thus, mineralization in the catchment area is indicated by a

122.

greater than twofold *_nc-easo in the total Cu content in

waters from the levier reaches of tributaries. The contrast

13 even greater for Cu ,, Thus, if the dubious -,0;_1010 `0_ from the lower reaches of the Florence tributary is omitt e,

concentration for Cusol, as sho\n the 1.Iaud and Frehda

tributaries draining barren roc?,- s, is 0.5 n:)b, while the

tributaries draining minoralization range from 5.0 to 7.5

?Pb, i.e. a greater than or equal to tenfold increase.

The Copq concentrations aro al: below the of detection except for the Gczagaza and Ra:mond

tributaries Llrae_ning mineralization, end contain 0.5

and 2,0 ppb respectively. Co is below its of

detection in all waters, except for the I-abokenga t:'11-)1't'4ry

whiela drains mineralization, and contains 0,35 ppb.

Consequently, although a detectable (i,e, greater

than equal to 0.5 ppb) is indicative of mineralization,

negative values (Lass than 0.5 ppb Co) do not necessarily

that the Jatchment is barren.

With the one exception of water from the Ilaymond

tributary =hick drains m.inorall%ation and contains 3.5

ppb Yi - a'ne for ill is 2 0 p,)b and for aq' is 1 .5 pnb, 1;o relationshin betw'e'l other :_eFsur'ments

and minerail:ation were observed (fable

The results obtal on water sal:n:1_0s from the lowJr

roaches of trJ.butarles in, l_ct_te that the Cu and Cusol

content is ge=ally indicative, where's the Cu contn"lt aq

123 is only rarely indicative, of uineralization in the catchment area. Co and Coaq values of greater than or equal to 0.5 ppb arc infrequently found, and only occur in some of the streams draining mineralization6 All other determinations do not differentiate between barren and Lineralized areas.

(vi) The Dungalea River. Fifteen sa:ples from the Dungalea River were collected over a distance of 42,000 feet from well upstream of the points where it crosses known mineralization down to its junction with the Nyamagasani River. Five samples were analysed for ionic metal. All other samples wore analysed to total and ionic metal(Figures 14 and 15). The object of the samples was to determine the dispersion pattern of copper in the stream waters related to the mineralization which crosses the river, and also to determine to what extent tributary waters influenced the character of the "ain river water. The effects of ground- waters that discharge directly into the river are also considered. The results of this work are presented in Figures 17 to 20 and in Table 24. The volume of water added to the Dungalea River from tributaries south of the Maud and Dungalea confluence is approximately 30 cusocs (Figure 17). The total increase over this distance is approximately 45 cusecs. The river

124. I Sample Loco.- Cu Cu,q Cu Co Coaq Cosol Zn Znaq Znsol No. Lion* lippi; - 610 ppb ppb ,ppb ppb ppb ppb r ppb 2221W 0 3.5 30 0.5 <0.5 <05 <0.5 6.5 6.0 0,5 2237W 3.5 4.0 2.0 2,0 <0.5 <05 .::0,5 6,0 3.5 2.5 2258W 6.0 3.0, <0,5 7.5 2272W 8.0 2.5 <0.5 7.5 2284W 10.0 2,5 <0.5 6.5 2293W 10.7 6.5 2.5 4.0 <0.5 <0;5 <0.5 6.5 5.0 1,5 2312W 13.3 7.0; 25 4.5 <0.5 <0.5 <0.5 5.0 3.5 165 2323W 14.8 260 <0.5 3.5 2345W 17,0 6.0 3.5 2.5 1,5 <0.5 ,.f1.5 6,0 5.0 1.0 2360W 19.0 2.0 <0.5 3,0 2389W 24.5 3.5 2.0 1.5 <0.5 <0.5 <0.5 7.0 5.0 2.0 2406W 27.3 345 265 1.0 <0,5 <0. <0.5 8.0 5.0 3,0 2424W 30.7 3.5 2.5 1.0 <0.5

I pp., 1

CQ CD CD CQ 02 W CQ .0

2221W 0.5 0.5 0 260 60 7.4 90 41.0 .0 20 CO

2257W 1.0 0.5 0.5 260 C 80 V 7.6 110 52.5 40 0 OD ( D CD 0 ) ' 2258V1 065 8.0 90 61.5 .1 C 0 C , •: Q 400 4 ) C CD C 2272W 0,5 7.4 135 63.0 CQ CQ 0 CD D D

2284W 0.5 8.0 75 53.0

tO C) C 45 V) ,4 4 W

2293W 2.0 0.5 1.5 460 120 7.6 115 tr CQ 57,5 U C ) D ) C) ) 000

2312W 1.0 0.5 0.5 360 120 7.6 100 62,0 (0 YD tO t- Y ) CD (1) 2323W 0.5 7.3 140 60.0 II) 5n ,4 F ) C) C CD 2345W 1.5 1.2 0.3 300 140 7.4 40 61.0 CO ,4 u ) PC. CD OD 2360W 0.5 7.2 65 64.0

pr 75 u) r4 ) ) C) W

2389W 1.5 0,5 1,0 580 280 7.9 105 66.5 C CO ) CD CD LO 2406W 1.5 0,2 1.3 58C, 140 7.6 110 73.5 CQ 0 O c

CD 2424W 1.0 0.5 0.5 280 80 7.2

,4 00 CD 130 82.5 . 7J-1 .

2432W 1.0, 0.5 0.5 280 100 7.1 105 78.0 V (0 CD (0

2469W 1.5 1.0r 0.5 600 0 7,6 100 84.5 85

*Upper reaches = 0 feet. Other locations are given in thousands of feet downdrainage. See Figures.141 15 and 17. Table 24. Properties of surface waters from the Dungalea River.

125. thus derives appro.xl:lately one-third of its water directly fro:.: underground sources, The major addition of ground- .;ater occurs between the 1:,aud and Kabekenga strea:..s- where tributaries contribute only approximately 2 cusecs out of

a. total increase of 10 cusocs. From the Kabekenga strecu

to the NyaLagasani River, the tributaries contribute 28 cusecs out of a total increase of 35 cusecs. The Cucci content of the Dungalea waters varies betw3en 2,0 and 3.5 ppb, and is within the range observed in the

liaud and Brenda tributaries draining barren rocks, and

contain 3,0 ppb Cu and 2.E ppb Gunn (Tableg5). On the other 1-1-2r1, Cu concentrations range from 3.0 to 7.0 rpb, the

average being 4.4 ppb, compared to 3,0 ppb from tributaries

draining unmineralizoa areas, The 3 samples located 0 feet

(22M71), 2,500 feet (2312W) and 60 000 feet (23/..5W downsearn from t- he Kitabarole tributary contain values of 6.0, 7.0 and 6-0 ppbGu T Cu content increases from 0,5 ppb (which Sal is the same as for tributaries draining barren reck.$) in

the upper roaches, to a peak of 4,5 ppb below the Gazagaza tributary, Thereafter it decreases to 2.5 ppb at the

Raymond tributcry, after which it decreases gradually and

no difference between Cu and Cuac is observed 5n the lower reaches. The increase in concentration of non-ionic :,etal

coincides with the :,_ajor addition of ground-water and the addition of tributol: waters derived from _mineralizations Thi_s portion of the river also contains anomalous

123 quantities of copper in the sediments (see later). The coincidence of (a) major addition of ground-waters, (b) a decrease in Cusol in the stream water, and (c) peak values in the sediment anomaly, is almost a duplication of conditions in the Yvette tributary. This coincidence has a bearing on the distrilyotion of copper in the sedi.-ients, and will be discussed in Section II E.

The cobalt content in the Dungalea waters is mostly below the limit of detection. However, one value of 1.5 ppb Co is found immediately below (2389W) the Raymond

tributary, and reflects the addition of the 25.0 cusecs of water containing 2.0 ppb Co from the Raymond tributary.

Sample 2469W, located in the lower reaches of the Dungalea

River, contains 0.5 ppb Co, but there is no obvious connection with mineralization. It is suggested that the anomalous nature of the ground-water in the lower Brenda area may possibly accour t for this value (page 103).

None of the other measurements Lade on the Dungalea samples showed any relationship with mineralization

(Table 24).

(vii) The Asa, Sebwo and Nabiaji Rivers.

Three samples from those rivers,rcprosenting regional background, were collected and analysed in detail

(Figures 17-20) .The results are tabulated in Table 25.

The Cu concentrations range from 3.5 to 4.0 ppb, and

the Cu content is a constant 2.5 ppb. The Cu aq sol

127 C!1 Sample Cu Cuaq bel Co Co Co Zn Zn Zn pH Eh aq sol aq Sol No. ppb ppb b • ppb pp ppb ppb ppb ppb ppb my I F 0 I C\ E n 0 1 0

p472W 4.5 3.5 1.0 1,0 8.5 7.5 1

10 <1.0 1.0

7.5 r4 V 0 0 L 2492W 3.5 2.5 1.0

<0.5 LO t'0.5 V 6.0 5.0 1.0 7.1 O 0

N 2489W 3.5 2.5 1.0 X0.5 - 0 10 :0.5 5.5 4.0

1.5 7.0 r--1 0 0 0 2486W 8,5 7,5 1.0 11.5 4.0 11.5 8.0 3.5 6.9 0 V 0 0 2497W 3.5 2.5 1.0 <0,5 <0.5 0 10 410.5 5.5 5.0 6.9 t' e 0 10 0 2215W 4.0 2.5.' 1.5 <0'.5 <0.5 y 10 8.0 5.25 2.75 7.0 0

2218W 3.5 2.5 1.0 <0.5 <0.5 4.0 3.5 0.5 7.3

Rate Sample Ni sn 'NI Fe Fe aq Sol ag Sol , Conduc T1aHC0 flowof No. ppb ppb ppb ppb ppb ppb tivity ppm 3 cusecs CV 0 0

r-1 2472W 0 1.0 1.0 700 460 241 47.0 23.8 400 a 0 2492W 14 LI 1.0 300 140 16* 40.5 18.0 D 0 C e

2489W ' 1.0 0.5 600 220 380 39.0 15.0 4 1 0 3.0 2486W r 1.0 1300 940 360 41,0 12.9 1000 - 4

0 0.5 01 5 100 2497W LO 80 20 34,5 17.0 20 o 0 0,5 <0.5 2215W L 300 215 75 53.0 23.8 40 .0 C

2218W 0,5 <0.5 350 250 100 69.0 38.8 40

* Locat ion

2472W Nyamagasani River above Dungaloa confluence (0 miles) 2492W Nyanagasani River plus 5 miles downstream 2469W Nyamagasani River plus 10 miles downstream 2486W Nyamagasani River plus 19 miles downstream 2497W Asa River 2215W Sobwo River 2218W Nabiaji River

*See Figure 15.

Table 25 . Properties of surface waters from the Nyamagasani Asa, Sebwe and Nabiaji Rivers.

128. concentrations vary from 1.0 to 1.5 ppb,

Co concentrations are loss than 0.5 ppb.

The results of other determinations are listed in Table 25. (viii)Summary of the significance of Leasurer,ente obtained from surface waters.

The range of values in waters draining barren areas in the Dungalea River and its tributaries are, in fact, also representative of regional background variations. Cu sol is the only constituent which consistently show anomalous values in waters draining mineralization; the drainage train may extend for as much as one mile. Cuaq,

Co Coaq, Ni and Yiaci values occasionai3.y7 show abnormally high values in streams draining mineralization (Table 26). No other metal values or determinations differentiate between waters draining mineralized and barren areas.

The range of values observed in the surface waters of the Kilembe area and their significance in prospecting is summarized in Table 26.

(ix)The Nyamazasani River.

Four water samples from the Nyamagasani River collected bet,Jecn a point above its confluence with the

Dungalea River and downstream to Lako Edward were analysed in detail (Figure 3U). The river drains extensive areas

of the southern Ruwenzori Mountaias, and zones of anomalous geocherlical soil values have been delimited within this area (Figure 16). However, very little, if any, evidence

129.

Strear_ draining Anomaly Determina- Threshold Lions: Barren Mineralized Rocks ppb: rocks: ppb ppb

Cu 3.0 - 4.0 5.0 - 15.0 . 4.5 2.0 - 4.0 Cuaq 2.0 - 3.5 7.5 n.d.- 1.5 1.5 - 7.5 2.0 ,„ CuSol Co n.d. n.d.- 3.5 . 0.5

Coaq n.d. n.d.- 2.0 0.5 CoSol n.d. n.d.- 1.75 0.5 Ni n.d.- 2.0 1.0 - 2.0 2.5 Niaq n.d.- 1.5 0.5 - 1.5 2.0 NiSol n.d.- 1.0 0.2 - 1.0 1.5 Zn 3.5 - 11.5 3.5 - 10.0 Unknown *2 Znaq 3.0 - 8.5 3.0 - 7.5 (12.0) Unknown ZnSol 0.5 - 5.0 0.5 - 3.7 Unknown *2 Fe 100 - 1400 260 - 1400 (1600) Unknown *1 Feaq 80 - 1200 240 - 800 (1500) Unknown 2 <10 - 800 600 (1180) FeSol 10 - Unknown.

SO4 ppm 2.4 - 3.2 2.4 - 3.2 Unknown Cl ppm 0.5 - 1.5 0.5 - 1.5 Unknown NaHCO3 ppm 17.0 - 134.4 10.2 - 102.1 Unknown Conductivity) 34.5 - 195.0 26.5 - 140.0 micromhos ) Unknown pH 7.0 - 7.9 7.0 - 8.2 Unknown 1 Eh my - 10 to 150 70 - 150 (180) Unknown.

n.d. Indicates less than 0.5 ppb. * Footnote: The values greater than the upper limit of the observed background range are exceeded once (41) or twice () only, by samples draining minerali- sation, and were not used to establish the anomaly threshold. Table Z6. Range of measurements in streams draining mineralized and barren rocks, and anomaly threshold's' 130. of thIL "Ineralization could be expected so far downdrainage in the Nyamagasani River if the relatively short drainage trains detected In the Dungalea River water are used as criteria. It was, in fact, to test this point that the sampling vas done.

The concentrations of Cu and Cuaq (4.5 and 3.5 ppb) and Co (1.0 ppb) in Sample 2472W located immediately upstream from the confluence with the Dungalea River are weakly anomalous and reflect the presence of the mineralization in the Rube and i\iurusegi Rivers (Table 25,Fig 13). Other determinations carried out on this sample and all data for the next two samples downstream (2492W and 2489W) are within the background ranges established in previous sections. However, the copper, cobalt and nickel concentrations in Sample 2486W, from the lower reaches, are distinctly anomalous. The Cu and Cuaq content is 8.5 and 7.5 ppb respectively, the Co and Coag content Is 11.5 and 7.5 ppb respectively, and the Ni content is 4,0 ppb:

The writer strongly suspects that these results reflect contamination effects from road and bridge repair work which, unbeknown to was in progress some distance upstream at the time of sampling. In view of this, no attempt should be made to evaluate the economic significance of these values until further sampling has been done to chock the possibility of contamination.

131. (5) The effect of time on the metal content of water samples.

(i) Introduction.

Owing the course of work associated with this

research project, a limited number of determinations wore repeated on water samples that had been stored for periods ranging from 4 hours to 5 months. This information should

correctly be given in Section VI as part of the development

of analytical and sampling techniques, but some of these results are used to infer the mode of occurrence and dispersion mechanisms of : et:.ls in water. The results are, therefore, given in this section with special reference to their bearing on the occurrence and dispersion of metals.

(ii) Variations in conductivity and metal content of surface water on storage in glass and polythene containers,

Anomalous surface water samples were collected from the lower reaches of the Yvette tributary. The samples wore stored in pyrex glass and polythene containers. Half the samples were stored without prior treatment, whereas the other half were acidified with 2 ml ,of concentrated

A.R. HC1 per litre to a pH of approxiAately 1.0,

A precipitate of fine brown material commenced separating from the water and settling on the bottom of the containers within minutes of collection. The precipitate in aoldified water samples in polythene containers did not appear to settle as rapidly es in all the other samples,

The precise reason for this could not be established but,

132._ during the course of the studies, it was observed that

polythene is not completely inert chemIce1146 Thus, it

was found that CC1i and C6H6 dissolved polythene. The solubility of polythene in CC14 precluded the use of polythene containers for the solvent extraction technique (Section V4. Further,lore, it was also noted that a

standard solution of 0.5 ppb S02, stored in polythene, deteriorated, and after one week less than 0.1 ppb sulphate was detectable. It is, therefore, suggested that the HC1 in the acidified waters might react with polythene and result in relatively stable suspensions of the precipitate compared to the acidified waters in glass containers. Analyses were carried out periodically using the methods detailed in Section VI. Water samples were removed from the containers by careful decantation, and the precipitate, which had settled on the bottom, was not disturbed. On the first and sixth days, in addition to

the normal analysis, containers were also vigorously shaken to redisperse the precipitate prior to analysis.

The results arc listed in Table 27. The r,aj)r differences occur within the first 4. hours as reflected by t e decrease in specific conductance. Conductivity measurenents after 4 hours remain relatively constant. The specific conductance of surface waters is related to the bicarbonate content (page 115). Thus, the decrease in conductivity indicates lower bicarbonate

133. Cu Cu ConductiViti aq q Cu Cu . ppb ppb ppb ppb Hours Glass Poly- Glass Polythene PolYilcid- Non- the', __ Acid- Non- aeld-Tnon- glass theneuled ac ie-Acid- ge5ii- ified acid if ied acid fled ac id 0 57.0 57.0 8.2- 4 40.5 40. 7.5 6.5 8.0 7.5 10.0 10.0 10.0 9.0 24 38.0 37. 7.5 6.5 8.0 7.0 11.5 10.0 11.0 10.0 * 24 39.0 37. 6.5 6.5 7.0 7.0 12.0 11.5 11.0 11.0 48 38.0 37. 6.5 6.5 7.5 7.0 10.0 10.0 10.0 10.0 72 36.0, 36.3 7.5 6.0 7.5 6.5 10.0 9.0 10.0 8.0 96 39.0 37. 7.0 6.5 7.0 6.5 11.0 10.0 10.0 9.0 120 37.5 36.5' 7.0 7.0 7.0 6.0 9.0 9.0 10.0 8.0 144 39.0 37. 01 6.5 6.0 7.0 6.0 7.5 6.0 10.0 7.5 *144 39.0 37.01 6.5 6.5 6.5 6.0 12.5 11.0 12.0 10.0 I A Pe Fe aq aq Fe Fe ppb ppb ppb ppb Hours Glass Poly- Glass Polythene thene ,1 Acid- Non- Acid- Non- Acid- Non- Acid,- Non- ified acid ified Acid ified acid tried acid

. a - 0 285

1 T) - C 0 4 140 140 140 120 340 340 260 1 3

24 100 •80 80 80 200 180 260 0

* 24 80 80 80 80 520 500 380 01\ 0

1 - h 0 48 100 80 100 80 200 200 200 1 0 72 100 80 80 60 ' 200 160 200 },

1 ) T - C 0 96 100 60 60 60 200 160 180 1

1 - 0 120 80 80 60 40 200 140 200 1 0 144 60 60 60 40 180 140 200 Ni

* 144 80 60 60 40 500 500 400 Co 0

* 5 minute vigorous shake to redisperse precipitate.

Table 27. Variations in conductivity, Cu and Fe of an anomalous surface water after storage in glass and polythene containers.

134. concentrations, i.e. an increase in the partial pressure of CO2 (page 96 ). It is thought that this phenomenon might be related to the activity of micro-organisms which produce CO2. The CO2 thus produced could not readily escape because all containers were stoppered with either screw-caps (polythene ware) or ground glass corks (glassware). The behaviour of iron is distinctly different from copper (Table 27). Thus, after 24 hours the removal of Fe from solution, and the conversion of Feaq to non-ionic Fe is effectively completed, whereas Cu and Cuaq contents generally tend to decrease progressively over the 6 days during which the experiments were conducted. The total Fe and Cu content of the acidified samples stored in polythene is somewhat higher than the equivalent non-acidified samples and the suggested reasons for this feature have been outlined However, the precipitation of both copper and iron in glass and polythene containers Is not significantly affected by the pH of the solution.

The generally slightly lower metal values observed in polythene containers, as compared to glass, is considered to be caused by a film of precipitate that clings to the inside of the container and cannot be removed by manual

agitation. However; bearing in milmitho observed loss of 0.4 ppb sulphate (page 133) from solutions stored in

polythene, it is also possible that part of the metal might be lost by reactions with polythene.

135. (iii) Sulphate and chloride concentrations. Sulphate was determined by the resin method (Section VT). The waters were collected from the sample sites in polythene bottles and passed through the rosin columns during the evening of the day on which they were collected. Water samples wore initially analysed for chloride in batches, at times varying from 1 to 7 days after collection. These samples wore stored in screw-capped polythene bottles and wore analysed for sulphate and chloride by the same methods 5 months after collection. The initial determinations wore made in Uganda, and the final determinations in London. Samples were transported by sea. A representative selection of the results are presented in Table 28:

Sulphate Sulphate Chloride Chloride at after at after 0 months 5 months 0 months 5 months ppm: ppm: ppm ppm:

4.7 3.4 1.25 0.40 2.6 2.5 0.75 0.75 2.4 2.4 1.25 0.75 4.0 4.0 1.25 0.50 4.0 3.7 1.25 0.65 3.6 3,4 0.50 0.35

Table 28. Variation in sulphate and chloride concentrations upon storage.

136 Only slight decreases in the sulphate content in all but two samples are noted, but the chloride content shows a variable decrease towards a possible equilibrium at 0.35 to 0.75 ppL. (iv) Bicarbonate, pH and Eh. These determinations were done in the field with no ti:Je lapse between collection and analyses. The determinations were repeated 5 months later. The water was stored in screw-capped polythene bottles Final determinations were done in London on sea-freighted samples. A representative selection of the results are given in Table 29.

NaHCO3 ppm pH Eh mv On Site: After 5 On Site: After 5 On Site: After 5 months: months: months:

45 40 7.3 6.65 163 90 23 17 7.0 6.4 139 80 65 46 7.8 6.5 128 100 30 21 7.8 6.6 151 90 16 17 5.8 6.4 64 110 17 16 5.8 6.3 46 95

Table 29 . Variation in bicarbonate content, pH and Eh upon storage.

137. These results suggest that the pH and Eh tend to reach an equilibrium of d.3 to 6.6 and 80 to 110 my respectively. The two lower NaHCO3 values remain essentially the same, whereas the higher values tend to decrease on storage.

(6) Some theoretical considerations.

The fundamental chemical nature of the reactions involved in many geologice.1 processes has long been recognised. The application of thermodynamic principles to explain geological processes is, however, a relatively recent development and the specific application to the dispersion and mode of occurrence of copper in the zone of oxidation and secondary enrichment was pioneered by Galirels (1954).

These early applications of thermodynamic principles have subsequently been extended. In particular, the studies relating to the solubility of some copper minerals in natulial aqueous solutions (Silman, 1958) have a bearing on the results obtained by the writer and on results obtained by other workers in the field of hydrogeochemical prospecting. Numerous examples of aqueous dispersion trains and the successful application of hydrogoochemical prospecting techniques to the location of economic mineral deposits can be quoted (e.g. Gin burg, 1960). In certain other case,s, however, waters derived from known oxidizing copper

138c deposits have not displayed an anomalous dispersion pattern in the vicinity of mineraliztion.

Atkinson (1957) used the heavy metal dithizono test on waters derived from known oxidizing copper deposits in Angola, Portuguese lest Africa, and found a constant concentration of 10 ppb during the dry season.

During the rainy season, the concentrations increased up to 100 ppb heavy :etais. Unlike the Kiler;:be area waters, these ionic nintal values do, in fact, indicate the presence of mineralization, because background areas contain less than 10 ppb ionic heavy metal. The relativel*; c,onstant metal content observed by Atkinson in the dry season is indicative of 8020 chemical control which limits the solubility of the heavy metals at this of year.

Hem (1960 c) and Hem and Cropper (1959, applied theluodynaui3 principles to the study of the solubility cf iron Ln aqueous solutions. An interpretation o± the relevant data obtained by the writer on Kilombe area waters, based on Hem and Cropper's conclusions, is both interesting and LLformative,

The following interpretations, which are based on the theoretical findin7,s of [Inman, Hem and Cropper, are essentially qualitative because of the insufficient data available from the writer's Investigations.

Mt,an (1958) studied the solubility of chalcanthite, anthlerite, brochantitc, malachite and tenorie as

139, functions of pH, sulphate and carbonate activity in aqueous solutions. He concluded that the nature of the oxidized copper uinerals existing in solution was controlled by the pH, and the sulphate and carbonate content of the water.

Ho calculated the theoretical saturation concentrations of copper derived fron_ these copper ninerals for variable sulphate, carbonate and pH conditions. Thus, for any particular pH value and sulphate and carbonate concentration, the nature of the stable oxidized copper :Anoral can be detorrined. Then the solubility of this nineral, and hence the theoretical saturation concentration of ionic copper, can be calculated.

Hem and 0i- op.-Der (1959) investigated the inter-relationship in water between dissolved ferrous and ferric iron, pH and Eh. They concluded that the a:Jounts and kinds of dissolved ions or uoleculos containing iron in the ferrous and ferric states arc related to the pH and Eh of the water in which they occur. Quantitative expressions of those relationships wore calculated. The calculations showed that ferric iron solubility is less than 10 ppb at a pH greater than 50. Ferrous iron, in the pH range found in nature, rapidly oxidizes to ferric iron upon exposure to air. It vas found that ferric iron could occur as n_otastable suspensions in natural waters. Hems (1960 a) studied the inter-relations between pH, carbonate, bicarbonate, carbon dioxide and ferrous

140. iron; and the effects of the equilibria on Eh. He concluded that the equilibria between carbon dioxide- bicarbonate-carbonate determine the limits for solubility of iron under reducing conditions. Increasing amounts of ferrous iron can be dissolved with decreasing Eh.

Appreciable quantities of bicarbonate may prevent changes in Eh from affecting the iron content.

All three authors e:iphasised the theoretical nature of their findings and the conplexity of the constituents of natural waters that may considerably modify the reactions involved. In fact, Hor (1960 c & d) also studied the effects of tannic acid on compleximz% ferrous iron as well as some of the chemical relationships between sulphur species amd dissolved ferrous iron. He demonstrated that these processes can result in concentrations of ferrous iron greater than the theoretically calculated values. During the course of a study of the co-precipitation effects in solutions containing ferrous, ferric and cupric ions, Hem

(1960 b) demonstrated that ferric iron can remain in solution as suspended and colloidal -;„] that concentrations greatly in excess of the calculated amounts aro found.

In view of the complexity of natural solutions and

the fact that equilibrium between variables is assumed in these theoretical considerations, the concentrations of metals in natural waters cannot be expected to agree

141. exactly with the calculated concentrations. Therefore

in the following examples, the general order of concentrations of copper and iron are compared rather than specific concentrations . The calculated and observed concentrations of

Cu5.:1,4 the Yvette tributary are Listed in Table 30; and it will be noted that they a7ree closely,

Sample: 2505 2506 2507 2508 2509 2511 2213 2510 Aver- V.4: -, V T W T W W W age:

1 Theoreti:;a1 Cu 4.0 1.2 16,0 13.0 6.7 7.7 aq l'opb* 4.0 6.7 10,0 Observed Cuao ppb 1 7.5 7.5 7.0 6,5 6,0 6.0 7.25 5.0 G.6

'o calculation see Appendix.

Table 30. Theoretical and actual concentrations of ionic

copper in the Y-rette tributary water.

In all other surface waters, the calculated and average concentrations range from 0.4 to 10.0 ppb Cuaq' ppb, T17o observed concentrations range from 2.0.te

and average 2,8 ppb. These figures . .1" in pob Cuaq very close agreement and indicate that the equilibrium arbonato and pH, c ac'

142. assumed by Silman, ar!) in fact rapidly established and maintained in surface waters from the Kilembe area.

The concentrations of Cuaq in ground-waters is given in Table 31.

Calculated Observed Site: pH; NaHCO::, SO Cu Cu PPm: 4 aq aq ppm: ppb: ppb:

2516W 6.0 8.2 4.0 6,400 4.0 2513W 6.2 13.6 3,2 640 44.0 2519.':1 6.1 10,2 3.2 1,600 32.5 2520W 6.0 20.4 4.0 1,60,-) 19.0 2527W 6.0 13.6 3.2 2,0uu 25.0 2531W 5.7 15.0 440 6,40o . 12.5 25301 5.8 13.6 3.2 6,400 7.5 2528W 5.8 13.6 3.2 6,400 7.5 2475W 5.1 :0.1 2.4 640 12.0 2542W 6,7 17,7 2.4 130. 4.0

Table 31 . Concentrations of Cu aq in ground-water compared to calculated Cu concentrations. aq

The concentrations of Cu aq observed in ground-waters is of an entirely different order to the calculated values , except for Sample No. 2542W (see below). If it is assumed that Silman's basic premises are valid for ground-waters,

143. the difference between the calculated and actual values

indicate that ground-waters are unsaturated with respect

to copper.

That Silman's premises are valid for ground-waters is

suggested by a more detailed consideration of conditions

obtaining at Sample Site 2542W, which shows the closest

approach to theoretical equilibrium. This site lies in

the lowest portion of the foothills where the circulation

of ground-water is slower and has travelled farther in contact with the overburden than is the case at higher

elevations (see page 24). The water from this site is,

therefore, more likely to approach chemical equilibrium

with its envirom_ont. This fact suggests that the discrepancies in other ground-water samples can be

accounted for by assuming incompleteness of reactions.

It is of interest to note that the calculated saturation concentrations of Fe related to pH and Eh aq (Hem and Cropper, 1959) indicates a similar situation with respect to Fe, viz the ground-waters are unsaturated and surface waters are saturated with iron. The calculated and observed iron values for ground-water and the Yvette surface water are listed in Tables 32 and 33. respectively.

It will be noted that the observed iron content of ground-water Sample 2542W, which is located in the lower foothills, is closest to the calculated value.

144. Site:- pH: Eh Calculated Observed my: Fe * Fe aq aq ppb: ppb:

2516W 6.0 140 60,000 1,500 2513W 6.2 130 25,000 2,500 2519W 6.1 155 30,000 1,70 2520W 6.0 150 40,03o 1,300 2527W 6.0 130 90,uo0 4,500 2531W 5.7 130 10,000 3,500 2530W 5.8 100 301/43,000 1,160 2528W 5.8 110 2000000 2,400 2475W 5.1 135 1,030,000 plus 6,000 2542W 6.7 125 2,000 500

* For calculations see Appendix.

Table 32. Concentrations of Feaq in ground-water compared to concentrations calculated from pH and Eh determinations.

Sample Site 2505 2506 2507 2508 2509 2511 2213 2510 W W W W W W W , W * * * (Tributarz

Calculated Feaq ppb 20 30 70 500 8 Feaq ppb observed 303 300 260 300 360 400 490 240

* In these sariples iron occurs in predominantly the forric form and concentrations cannot, therefore, theoretically exceed 10 ppb (see page140). Table 33. Calculated and observed concentrations of Feaq in stream water from the Yvette tributary.

145. The calculated saturation concentrations in the Yvette tributary are lower than the observed concentrations. The differences are less than 330 ppb and are probably due to the presence of colloidal ferric iron (Hem, 1960 c) which theoretically should have 'been removed from solution by precipitation. The differences between observed and calculated concentrations of Fe aq of all other surface waters in which iron occurs predominantly in the ferrous form-* are of a similar order to the Yvette. This inequilibrium in ground-waters compared to relative equilibrium in surface waters is substantiated when the ferrous iron concentrations in waters is related to the pH, Eh and bicarbonate content (Hem, 1960 b). The of a solution is calculated from the pH, bicarbonate and ferrous iron content (see Appendix for method). If the calculated figure is within 60 my of the observed figure, Hem considers that equilibrium conditions are indiaateth The relevant figures related to ground-waters is given in Table 34.

* Footnote: The waters from the upper reaches of tributaries contain iron in predominantly the ferrous form, whereas the lower reaches g'nerally contain iron in the ferric form, ice, conditions become more oxidizing downstream. no obvious distribution pattern of ferrous and ferric iron is observed in the major rivers, Slightly less than half of the total number of surface water samples contain iron in predominantly the ferric form„ All ground-waters contain iron in the ferrous form„ 146. Site: Calculated Eh Measured Eh Difference: (my): (my): (m.v):

2516W 260 140 120

2513W 200 130 70 2515W 260 155 105 2519W 240 155 85 2520W 250 150 100 2527W 230 130 100 2531W 280 130 150 2530W 300 100 200 2528W 270 110 160 2475W 390 135 255 2542W 150 125 25

Table 34. Relation between dissolved iron, bicarbonate, pH and Eh in ground-water.

It will be noted that the observed Eh of water from Site 2542W (lower foothill area) is within 25 my of the calculated value, whereas the differences in other ground- waters range from 70 to 255 mv. The difference in surface waters in which iron occurs predominantly in the ferrous form range from 0 to 90 my and average 39 mv.

147 (7) Summary and discussion of mode of occurrence and dispersion of copper in natural water. The solubility of ionic copper in water is controlled by physico-chemical reactions. In ground-water, the copper is derived from reactions between (a) percolating rainwater and soils and (b) ground- water and the rock and soil with which it is in contact. Due to the time factor and/or the availability of soluble copper, ground-waters are generally unsaturated with respect to copper, but in general contain more metal in solution than surface waters. Dispersion of copper in ground-water is controlled by movement of the solutions and dilution.

Appreciable amounts of copper are precipitated during the transition from ground to surface water. Surface waters contain relatively low concentrations of Cuaq. Equilibrium between Cuaq and its environs is rapidly established and very limited downdrainage dispersion trains from mineralization is found. It is of interest to consider in more detail some of the mechanisms of copper solution and precipitation, which could operate in natural waters. The calculated saturation concentrations of water is assumed to be an important controlling factor.

Thus, if a natural water is unsaturated with respect to Cu, it will be capable of dissolving metal. The quantity of Cu which is actually taken into solution will be dependent on the availability of the metal and/or the time

14d. required to establish equilibrium. For example, if within

a background area the Cuaq content of ground-water were

below the saturation concentration, then the water could

dissolve metal when it circulated into a zone containing

more available Cu. Alternatively, if surface waters were

unsaturated with respect to Cu, then metal could be taken

into solution when the water flows over anomalous sediments

or between anomalous banks. The length of detectable down-

drainage dispersion train of Cuaq would be dependent on

the stability of the copper in solution and dilution by barren waters.

Anomalous ground-waters discharging into unsaturated surface waters would precipitate metal in excess of the

surface saturation concentrations and the length of detectable drainage train would be dependent on (a) the difference between background and saturation concentrations;

(b) dilution by background waters, and (c) the stability

of tne copper solutions.

The dispersion trains of Cuaq in surface waters could

also be dependent on the time factor. It is not known how much time is required to establish equilibrium between

Cuaq and the surface environment, but it is conceivable that the time may be related to the difference between

Cuaq concentration of, say, ground and surface waters.

Thus, if ground-wators contained a small excess of Cuaq compared to surface waters only a short time may be required

to establish equilibrium between the water and the factors

149. controlling copper solubility (pH, SO4 and HCO3).

However, if the ground-waters contained a large excess of Cu aq compared to surface waters, equilibrium between Cu and the surface conditions may take longer, aq and this could result in supersaturation with respect to

Cuaq.

The length of drainage train could also be dependent on the volume of anomalous ground-water compared to the volume of background surface water. Thus if a small

volume of weakly anomalous ground-water discharged into a stream containing a large volume of background water, then the dilution factor alone would mask the anomalous character of the ground-water. If, however, a large volume of anomalous ground-water discharged into a stream containing small quantities of background water, then the metal content of the resultant stream waters would be dependent mainly on the ti:le required to establish equilibrium, i.e. the surface waters could retain, for a period of time, some of

the characteristics (pH, SO4, HCO3) of the ground-water,

and this would result in a higher theoretical saturation concentration of metal, and hence a longer drainage train.

The writer suggests that the above mechanisms of

Cu dispersion are responsible, to varying degrees, for the

in waters from the Kilembe observed distribution of Cuaq area. A striking difference between ground and surface

waters is the fact that the former are unsaturated and the

150. latter are saturated with respect to dissolved copper.

The two background subsurface waters, Nos. 2516W and

2542W, both contain 4.0 ppb Cuaq despite the fact that the former sample is considered to have had more time to attain equilibrium with its environs, i.e. the increase in time has apparently merely decreased the calculated saturation concentration of Cu aq (pogo 144. The uniformity of Cuaq content of background ground-waters is considered to

Indicate that the supply of metal is limited to 4.0 ppb.

However, upon circulation into the zone of mineralization, the unsaturated background subsurface waters dissolve appreciable quantities of copper, th;t still remain unsaturated due to lack of time and/or the absence of available copper, The unsaturated solutions appear to be relatively stable as no evidence of Cu precipitation is noted. Therefore, the length of downdrainage dispersion train of Cuaq in ground-waters is thought to be largely controlled by dilution factors.

content of The average observed and calculated Cuaq the surface waters from the Yvette tributary is 6.6 and 7.7 ppb respectively, compared to the average regional values of 2.8 and 3.3 ppb respectively, i.e. the calculated and observed saturation concentrations of the Yvette waters is greater than the average for other waters. It is suggested that the anomalous character of these waters is caused by (a) large volumes of anomalous ground-waters

151. discharging into a stream which contains minor quantities of background surface water and (b) the lack of time needed to establish equilibrim with the surface environment. Thus, the surface water retains some of the characteristics (pH, etc) of the ground-water and precipitation of the excess Cu to background concentrations has not aq yet occurred. Tributary waters derived from background subsurface waters could, in similar circumstances, also have an anomalous saturation potential, but they would remain unsaturated duo to the absence of available copper. The anomalous potential of waters would be dostroyed when ocullibrlum with the surface environment was attained; or masked when diluted by background watcos. It is considered that the phenomenon of supersaturation is demonstrated by a water sample (No. 2504W) collected dowrdrainage from Kilembo Mine in the Nyamwamba River

(Figure 15). This river derives an estimated maximum of

1 to 5 percent of its total volume of water from the mine workings and from water percolating through surface dumps. The water derived from underground contains 300 and 320 ppb

Cuaq, and this water, after percolating through surface dumps, contains 700,000 ppb Cuaq (Table 21). The water Sample No. 2504W, collected 8 miles downstream from the mine; has a pH of 7.4 and a SO4 and NaHCO3 content of 2.4 and 20.E p7m respectively, The calculated saturation concentration of Cuaq is 6,4 ppb. Hov:evo, the observed Cuaq is

152. 760.0 ppb,

The water cannot be classified as a truly natural water; and it is possible that the presence of some other artificial constituent could account for the ciscrepancy between calculated and observed Cuaq content. In this connection, however, it is of importance to note that the Eh (125 niv) and conductivity (94.6 micromhos) as well as the pH, 304, NaHCO3 (sec above) are within the normal range observed in surface waters. It is difficult to envisage an artificial ccnstituont which could specifically increase the quantities of dissolved metal without affecting the other measurements.

It is of interest to note that Hem (1960) also observed that some natural waters arc supersaturated with respect to iron This phenomenon is also observed in the above sample No. 2504W, whore the calculated saturation concentration of iron is 8ppb whereas the observed concentration is 2,800 ppb Feaq.

The non-ionic copper concentrations in water arc considered to represent suspensions of copper salts (simple or complex) derived from precipitated ionic copper. The non-ionic copper is transported ihechanically by the stream water and settling of this material is considered to contribute to the copper concentrations found in stream sediments,

Ionic copper could also be removed from water by

153. co-precipitation effects with iron. -It would be of interest in this connection to dotermine whether it is actually the precipitation of iron which causes the precipitation of copper, or whether a similar solution of coppor containing no iron, would still precipitate the same quantities of copper, 1.e.. is copper actually removed from solution by the iron that is precipitating or are conditions such that a relatively constant proportion of the copper in solution would in any case be removed by precipitation: Are the observed apparent co-precipitation effects with iron purely fortuitous, and do the observations, in fadt, indicate a similarity of chemical reactions of the two elements rather than "scavenging" of copper by iron. In this connection it is of interest to note that Hem (1960 b), who conducted experiments on the co-precipitation effects in synthetic solutions containing ferrous, ferric and upric ions, concluded that (a) absorption of copper by precipitated Ferric ion was more likely than incorporation of 3.-4- pc,r into the crystal lattice; (b) ferric hydroxide colloidal particles are positively charged below a pH of 5.5 and, therefore, absorption effects are negligible; (c) the pH of hydrolysis of cupric ions in the synthetic solutions is 7.3; (d) absorption of copper by negatively charged colloidal ferric hydroxide could,. therefore, only occur between a pH of 5.5 and 7.3, and that absorption on iron hydroxide is relatively minor. compared to absorption

154. on clay particles which contain a natural excess of negative electrostatic charges; (e) the absence of a quantitative relationship between precipitation of ferric hydroxide and copper was experimentally demonstrated by the fact that a tenfold increase of the aLount of iron in solution and, therefore, the amount of iron precipitated resulted in only a twofold increase in the amount of co-precipitatrd copper.

An incidental point of interest, which demonstrates the difference between reactions in synthetic and natural solutions is given by the precipitation of iron. Hem reported that no iron precipitation occurred from solutions below a pH of 445.. The writer observed no marked difference

In the precipitation of iron (and indeed copper) from natural water (pH 7.4) and the sane water acidified to a pH of 1.

The writer's experiments on natural waters also indicated that all the iron had effoOtively precipitated from solution after one day, whereas copper continued to precipitate during the following 6 days. If, as suggested by Hem, precipitated iron colloids were positively charged

In the acidified waters, then absorption cannot account for the loss of copper from solution, and a direct precipitation of copper, unrelated to the precipitation of iron is

Indicated.

In this connection it is of interest to note that

155. Cher and Davidson (1955) observed that "cupric ions have a catalytic effect in oxidation of forroUs iron".

It is possible that the precipitation of iron within 24 hours, regardless of the pH of the solution, reflects this catalytic effect of copper.,

Further confirmation of independent precipitation of Fe and Cu (also Co, Ni and Zn) from natural solutions is given by Sample 2512W which was collected from a depth of one-inch some 20 feet downs lope from the Yvette headwater seepage area (Figure 14), 14c. the ground-water had passed through the seepage area, but had not yet appeared on surface as free-flowing water. The metal content of the adjacent ground (3 samples) and surface waters arc compared to the concentrations observed in

Sample 2512W (Table 35).

Precipitation of Cu, Ni and Zh prior to the precipitation of Co and PG is demonstrated by these results.

It is known that certain types of organic material can accumulate metal. Thus it has been observed that Pb is concentrated in the organic material occurring in soils in conifer areas, whereas Pb is not concentrated in the organic matter of broad-leaved soil areas. (Webb, 1951).

Tho work of Tooms (195) and Jay (1959) also suggests that the organic material found in the seasonal swamp areas of Central Africa is apparently capable of "stripping" Cu and Co from solutions, whereas iron is relatively unaffected by this process.

156... Sample Ground-water 2512W Sample Measurements: ,- Transi- 2213W Range: Average: tional Surface water: water:

Cu (ppb) 67.5 - 90.0 80.8 900 11.0 Co ;ppb! 85 - 1 6.0 12.2 15.0 3.5 Zn (ppb) 40.0 - 50.0 46.7 12.0 10.0 Ni (ppb) 9,0 - 17.5 14.2 4.0 3.5 Fe (ppb) 2,500 - 5,300 4,300 4)000 1,600 HCO3 (ppm) 13.6 - 20.4 14.7 61.9 45.2 Oonductivit:T mierc-lhos 87 - 101 96.0 109.0 81.0 pll 6.0 - 6.2 6.1 7.0 7.2 li"..- (mv) 130 - 155 145,0 0.0 70.0

Table 35 Comparison of the metal contents of ground, transitional and surface waters in the Yvette area.

It is possible that the organic material in the Yvette seepage area is capable of stripping Cu, Ni and Zn, whereas the Co and Fe remain in solution. However, a comparison of the observed and calculated saturation concentrations of Cu and Fe in the transitional water indicates an independent precipitation of individual metals. Thus, the calculated concentrations of copper and iron are 13.0 ppb and 30,000 ppb

157. and the observed concentrations arc 9,0 ppb and 4,000 ppb rospoctivoly. Therefore the water is already saturated with respect to Cu, but is still unsaturated with respect to Fe. However, the adjoining surface water (No. 2213W,

Table 22) is saturated with respect to Fe and contains 490 ppb Fe aq comparod to the calculated saturation concentration of 500 ppb, i.e. during transition from the ground to surface environments, in the Yvette headwater area, the Cu has been precipitated before the Fe.

The above observations confirm the concept that the trace Letal content of precipitated iron hydroxide is not ontirr,ly duo to co-precipitation effects but also reflects the inherent si:'llarity of the chemical properties of iron and the associated rotals. Tho results also suggest that precipitation of dissolved metals from a natural water may be (a) simultaneous, if the critical propfteties controlling solubility ar•e radically and rapidly altered or (b) progressive, if the controlling properties are changed slowly and gradually.

Variations in the rate and extent of change of the properties of a soluti Jr_ have been advanced to explain (a) the presence or absence of ciota] zoning in syngenetic deposits (c .g:, the tL,ace metal content of bog iron), (b) and the development of secondary drainage dispersion trains in sediments and (c) the secondary dispersion haloes in soils surrounding multi-metal deposits. It would be of interest to determine whether other observed secondary metal

5.58. associations, such as for example Din and Co (Jay, 1959) aro predominantly duo to simultaneous precipitation affects rather than 'I scavan3.ing" and sorption of Co from solutions by in

Due to the absence of all the auxiliary measurements, such as pH, Eh. HC05 - etc., it is not possible Cuaq' Cu501' to direct1y relate tho writerfs findings on the dispersion of copper in ground and surface waters to the results obtained by other authors.

The abson3e of an anueous surface or subsurface dispersion train from mineralization can readily be oxplf_ned if the noncept of maximum saturation concentrations

Is Invoked. Thus, if the background concentration of metal in waters is equal to the saturation concentration no more °pricer can be dissolved, irrespective of the availability of total-

If the saturation potential of waters is in excess of backg:_ur.: concentrations then available copper can be diss3lved. In ithese circumstances, if saturation is achieved by the solutions passing through a zone of mineralization, the anomalous values will be of a constant order and the dilution factor by barren waters will have a

aithmetic effect, A typical example of the above dispersion mechanism is provided by Atkinson (1957), AVI20 noted that streams directly draining mineralization contained a relatively cons...ant amount of anomalous metal,

159,

The lose of motal from streaLs, which are not diluted

by barz'en water, has boon reported and an example

provide71 by Huff 0.95,1), The heavy metal content of

77atel,c dischargLng .2rom the U.V.X. .__inc into an a-,tlfical dainge channel, With no dilution or change in pH (8.0) over it's entire length, decreased progressively from 2,000

to 400 ppb over the first 1,8 mil.es and then remained relatively constant at 00 to 60 ppb from 2.4 to 3,5 miles,

It is not possible to determine the precise reason for the high concentrations of heavy metal as other measurements aro lacking, but the *2 :::oval of metallic ions was explained

excl-lano actions possibly accompanied by some removal by bLoLogical actlfity- The writer tentatively suggests t:lat the pragrossi!o- decease in metal over the first 18

miles is related to ineoui:Abrium conditions 3.1 tio surface

envi=ment, ar.e than the constant values over the fina:.

1-7 mi:es Indicati,,e of equilibrium having been

esttAbLI.:311cc,- 7110 in 7_tial high vallcs may be due to eI':her oLpers-Lturatim or tl'o nresenee of some other ccnstituent .,:unction with the pH, controls F0n-, o' etc 7Jhl.ch, in con the solubility o..? the metF-.1s.

Aa examnic disr.,rsion trains of Cu, Zn and Fe

In sul-face water is pi- unided by Huff (1947) from the c opper mines at Butte. The relevant data are listed in Table 36,

160, Distance ppm Streata: below pH: mines (miles) Cu: Zn; Fe:

Silverbow Creek 2 4.5 70 400 80 do. 6 4.8 20 150 30 do. 12 4.8 15 100 11 do. 18 5.0 10 80 2,5 Doer Lodge River 27 5.8 0.5 25 0.8 do. 41 5.8 0.08 10 0.4 Clark Fork River 82 5.8 0.05 3 0.8

Table 36. Metal content of water in drainage from copper niines at Butte, Mont. After Huff, 1947.

It was assumed that the Zn content falls off by a simple factor of dilution and that the Cu behaves similarly until precipitated at a pH of greater than 540 (Table 36). Due to the absence of other relevant measurements, it is not possible to coLment on the validity of these explanations but the observations nlay also be related to saturation concentrations. However, it is of interest to note that the 3 metals react differently in the same environment. If equilibrium concentrations of 0.05to 0.a3 ppm Cu, 0.4 to 0.8 Fe and less than 3.0 ppm Zn are assumed, it will be noted that equilibrium is reached by Fo at 27 miles, Cu at

161. 41 miles and Zn at more than 82 miles downstream from the mines. Thus the 3 metals do not apparently co-precipitate and also the Fo has off,_ctively precipitated prior to the complete precipitation of Cu. These observations are essentially the same as those for the Kilembo area waters upon transition from the ground to surface environment. Seasonal variations in the metal content of waters have been reported by many authors,fer cxamplc Atkinson (1957)

Webb and Idillman (1950). After a heavy rain; Webb and killLan noted a decrease in the heavy-metal content of streams draining an area of lead-zinc mineralization in Nigeria. This was followed by a marked increase in metal content after several days of heavy rainstorms. The initial decrease was considered to be duo to dilution by direct surface run-off and the later increments duo largely to an increase of soluble metals flushed out of the deeper horizons of the soil. Bearing in mind the l'iportance of the high partial pressure of CO2 in soil air in maintaining a low pH in the shallow ground-waters (reactive) compared to the alkaline (inert) deep ground-water at Kilembe, it would be of interest to determine (a) the activity of deep ground-water during the wet and dry season and (b) the seasona2 variation in saturation potential of the surface and ground-waters. It is possible that the flushing out of soluble metals, as suggested by Webb and Killman, may be caused by the increased reactivity of the upper horizons

162. of the elevated ground-water during the rainy season and, as large volumes of this reactive Water are discharging into the streaLIs, the saturation potential could be increased

In the surface environment.

163. C. ACTIVE STREAM SEDIbIENTS.

(i) Introduction, previous and present work.

(a) Introduction.

Almost all the products of weathering in a drainage basin are channelled through the stream and river systems flowing out of the area. The products of weathering are

either soluble or insoluble in natural water. The soluble constituents are dissolved by ground-waters and, unless

the n_aterials are precipitated in an insoluble form, (e.g.

as secondary stable minerals), they may be widely dispersed

in the ground-waters. A portion of the soluble material

enters the surface drainage system and the dispersion

pattern in this medium is determined by reactions involving

physico-chomical equilibria. The insoluble products of

weathering are either stable or unstable with respect to

the varying conditions which exist on surface. Thus the

st:Ible minerals such as resistant primary minerals (e.g.

magnetite) or the stable products of weathering (e.g. clay

minerals and secondary oxides) remain as insoluble material

under natural conditions. The unstable products of

weathering are comprised of minerals that may readily go

into aqu- us solution with changing conditions (e.g..unstable

chemical precipitates frorl aqueous solutions and exchangeable

ions). In surface drainages a form of mobile equilibrium

exists between the different constituents.

164. The total load carried by a streal.: is, therefore, a crude sample of the material in the catchment area of the stream and the chemical composition of the load reflects qualitatively the average chemical ex:position of the rocks in the drainage basin. (b) Previous work.

Holman (1956) investigated the dispersion of copper in sediments from portion of the drainage in the Bukangama area. The results of his Investigations demonstrated that the erosion of anomalous soils in the catchment area of tributaries resulted in detectable drainage trains of Cu and cxCu (Figure 24, after Holman). The drainage trains were found to extend for at least 1,000 feet downdrainage from mineralization. Lo drainage train was found in the Dungalea River

Holman considered that the mechanism of distribution was dominantly mechanical, lo. a mechanical movement of near-surface soil to the stream banks and thence into the stream where stream action merely re-distributed this material,

Webb (1958) studied the distribution of Cu and cxCu in dry-sieved size fractions, ,Ind also noted that the percentage cxCu:Cu of sedi,ents increased upstream in tributaries and related this feature to precipitation of copper from ground-waters.

Webb and Stanton (1559 - personal communication)

165. studied the partition of copper between mineral lattices and secondary iron oxides in sediment samples collected by Holman.

In order to establish the mode of occurrence and dispersion mechanisms of copper, the writer investigated the distribution of copper and cobalt in various size fractions, which were obtained by the wet dispersion method.

The partition of Cu and Co between mineral lattices and secondary iron oxides in sand, silt and clay size fractions was also studied.

The distribution of NI, Zn, Fe and Mn in the -80 mesh fractions of sediments were determined chemically and selected samples were also spr:ctrographically analysed.

The application of the above results to prospecting was investigated and, for the sane reason, the Cu content. of panned concentrates and magnetite was also determined.

These investigations resulted in the development of an analytical technique (hydrochloric acid soluble Cu) which 1,-proved the existing methods of geochemical drainage prospecting in the Kilembo area.

(ii) Distribution of copper in size fractions.

In order to establish the mode of occurrence and dispersion mechanisms of copper in sediments, selected samples were firstly separated into size fractions by the wet dispersion and sedimentation method. It was also necessary to compare the distribution of metal in

166. sedimonts to the distribution in soils in order to determine the affects of the changed environment upon the distribution of copper. Ten sediment samples representing varying conditions with respect to mineralized and non-mineralized areas wore separated into size fractions and the Cu and Co concentrations in each size fraction wore determined. The percentage of Cu and Co in cach size fraction was calculated. The cxCu content of the clay and silt size fractions was also determined. Tho results are presented in Tables 37-41.

In all samples, Co concentrations of loss than 0.5 ppm are reported as "not detected" (n.d).

(a) Size fractions. The size fractions, into which the samples were separated, were chosen purely arbitrarily. However, it is important to consider the nature of the physical changes In composition which occur when a soil enters the drainage system and is subjected to mechanical sorting and weathering in the stream environments. The changes and reactions which arc involved in those processes are in themselves complex, and further complications are introduced by many other factors, such as additions of different material to the stream, changes in gradients, volume of water, etc. This discussion will, therefore, be of a general nature and indicate only the major trends that were observed. Variations in the size distribution of soil and stream sediment particles in the Yvette tributary area aro

167. Size fraction Determination -20 -36 -80 -150 -200 +36 +80 +150 +200 +silt s ilt clay

Anomalous Sample No. 1400 (Headwaters Yvette tributary): Weight percent of size fraction 3 9 17 16 13 19.4 23.6 Cu ppm 110 70 50 50 70 220 250 Percent Cu per size fraction 2.4 4.6 6.2 5.8 6.6 31.2 43.1 cxCu ppm 15.0 40.0 cxCu:Cu (percent) 7 24 Co ppm 90 20 15 15 20 40 100 Percent Co per size fraction 30 7 5 5 7 13 33

Cu observed from an independent determination of the -80 mesh fraction = 125 ppm Cu calculated from size fraction analyses and determinations 136. ppm Co observed from an independent determination of the -80 mesh fraction • 24 ppm Co calculated from size fraction analyses and determinations 33 ppm Weight percent of clay-silt in the -80 mesh fractions 48 Percent Cu contained in clay-silt fraction of -80 79 % mesh sample

Anomalous Sample No. 1313 (Lower reaches Yvette tributary): Weight percent of size fraction 19 31 16 9 3 it 9.9 12.8 Cu ppm 10 10 10 10 90 200 4 400 Percent Cu per size fraction 2.3 3.8 2.0 1.1 3.3 24.4 63.0 cxCu ppm t60.0 125.0 cxCu:Cu (percent) 30 31 Co ppm n.d n.d. n.di n.d. 10 70 100 Percent Co per size fraction 0 0 0 0 5 39 56

Cu observed from an independent determination of the -80 mesh fraction 85 ppm Cu calculated from size fraction analyses and determinations = 81 ppm Co observed from an independent determination of the -80 mesh fraction • 24 ppm Co calculated from size fraction analyses and determinations • 20 ppm Weight percent of clay-silt in the -80 mesh fractions = 46 % Percent Cu contained in clay-silt fraction of -80 nosh sample = 93%

Table 57 . Cu and Co distribution in size fractions from the Yvette tributary. 168.

Size fraction Determination -20 -36 -80 -150 -200 +36 +80 +150 +200 +silt silt clay

Anomalous Sample No. 1270 (Lower reaches Muchin.zira tributary): Weight percent of size fraction 17 23 19 11 6 9.9 13.8 Cu ppm 10 10 10 90 120 270 400 Percent Cu per size fraction 1.6 2.2 1.8 9.4 6.9 25.5 52.6 exCu ppm 30.0 130.0 cxCu:Cu (percent) 11 30 Co ppm n.d. n.d. n.d. 15 20 30 75 Percent Co per size fraction 0 0 0 11 14 22 53

Cu observed from an independent determination of the -80 mesh fraction = 65 ppm Cu calculated from size fraction analyses and determination = 100 ppm Co observed from an Independent determination of the -80 mesh fraction = 28 ppm Co calculated from size fraction analyses and determinations = 16 ppm Weight percent of clay-silt in the -80 mesh fractions . 40 Percent Cu contained in clay-silt fraction of -80 mesh sample = 83%

Anomalous Sample No. 1350 (Headwaters Katundu tributary): Weight percent of size fraction 24.5 29.5 14.5 10 3 9.9 6.8 Cu ppm 10 10 10 10 10 90 150 Percent Cu per 9.0 10.8 5.3 347 1.1 32.7 37.4 size fraction cxCu ppm 7.5 40.0 cxCu:Cu (percent) 8 30 Co ppm n.d. n.d. n.d. n.d. n.d. 40 85 Percent Co per size fraction 0 0 0 0 0 32 68

Cu observed from an independent determination of the -80 mesh fraction = 25 ppm Cu calculated fror_•i size fraction analyses and determinations = 27 ppm Co observed from an independent determination of the -80 mesh fraction = 20 ppm Co calculated from size fraction analyses and determinations = 10 ppm Weight percent of clay-silt in the -80 mesh fractions = 35 % Percent Cu contained in clay-silt fraction of -80 mesh sample = 87 %

Table 38. Cu and Co distribution in size fractions from the Muchin:ira and Katundu tributaries. 169.

Size fraction Determination -20 -36 -80 -130 -200 +36 +80 +150 +200 +silt silt clay

Anomalous Sample No. 1385 (Headwaters minor tributary in the Kitabarole stream): Weight percent of size fraction 13.5 23 17 9.5 7.0 18.4 12.3 Cu ppm 90 80 120 180 200 680 950 Percent Cu per size fraction 3.7 5.7 6.3 5.3 4.3 38.6 36.1 cxCu ppm 60.0 245.0 cxCu:Cu (percent) 11 25 Co ppm 75 35 50 60 100 270 340 Percent Co per size fraction 8 4 5 7 11 29 46

Cu observed from an independent determination of the -80 mesh fraction = 375 ppm Cu calculated from size fraction analyses and determinations = 324 ppm Co observed from an independent determination of the -80 mesh fraction = 94 ppm Co calculated from size fraction analyses and determinations = 120 ppm Weight percent of clay-silt in the -80 mesh fractions = 48 % Percent Cu contained in clay-silt fraction of -80 mesh sample = 82

Anomalous Sample No. 1210 (Lower roaches of Kitabarole stream): Weight percent of size fraction 19.5 17.5 t 17.5 10.5 8.0 15.9 10.8 Cu ppm 40 90 - 120 120 120 340 450 Percent Cu per size fraction 4.6 9.3 12.4 7.4 5.7 31.9 28.7 cxCu ppm 25.0 60.0 cxCu:Cu (percent) 9 17 Co ppm n.d. 10 15 20 35 90 210 Percent Co per size fraction 0 3 4 5 8 26 55

Cu observed from an independent determination of the -80 mesh fraction = 175 ppm Cu calculated from size fraction analyses and determinations = 169 ppm Co observed from an independent determination of the -80 mesh fraction 60 ppm Co -calculated from size fraction analyses and determinations = 46 ppm Weight percent of clay-silt in the -80 mesh fractions = 43 % Percent Cu contained in clay-silt fraction of -80 mesh sample = 90%

Table 39. Cu and Co distribution in size fractions from the Kitabarole stream.

170. Size fraction Determination -20 i -36 -80 -150 -200 +36 1+ 80 +150 +200 +silt silt clay

Background Sample No. 1310 (Dungalea River upstream from Yvette tributary: Weight percent of size fraction 13 25 20 13 5 16.4 7.3 Cu ppm 10 10 10 10 10 90 100 Percent Cu per size fraction 4.4 8.4 6.7 4.4 1.7 49.8 24.6 cxCu ppm 3.0 12.5 cxCu:Cu (percent) 4 12 Co ppm n.d. n.d. n.d. n.d. 15 35 50 Percent Co per size fraction 0 0 0 0 15 35 50

Cu observed from an independent determination of the -80 mesh fraction = 20 ppm Cu calculated from size fraction analyses and determination 29 ppm Co observed from an independent determination of the -80 mesh fraction 14 ppm Co calculated from size fraction analyses and determinations 11 ppm Weight percent of clay-silt in the -80 nosh fractions = 38 Percent Cu contained in clay-silt fraction of -80 mesh sample 85%

Anomalous Sample No. 1147 (Dungalea River downstream from Katundu tributary): Weight percent of sizo fraction 4' 22 29 17 8 7.3 12.4 4.3 Cu ppm 10 20 30 50 90 270 550 Percent Cu per size fraction 2.7 7.2 6.3 4.9 8.1 41.3 29.2 cxCu ppm 50.0 140.0 cxCu:Cu (percent) 17 27 Co ppm n.d. n.d. n.d. n.d. 10 35 75 Percent Co per size fraction 0 0 0 0 8 29 63

Cu observed from an independent determination of the -80 mesh fraction ▪ 60 ppm Cu calculated from size fraction analyses and determinations 80 ppm Co observed from an independent determination of the -80 mesh fraction • 20 ppm Co calculated from size fraction analyses and determinations • 9 PIN.' Weight percent of clay-silt in the--80 mesh fractions 3 4 % Percent Cu contained in clay-silt fraction of -80 mesh sample - 78

Table 40. Cu and Co distribution in size fractions from the Dungalea River. 171. Size fraction

Determination 4 -20 -36 -80 -150 -200 +36 +80 +150 ' +200 silt silt clay

Background Sample No. 1433 (Lower reaches Brenda tributary): Weight percent of size fraction 23 36 13 6 7 10.4 6.1 Cu ppm 10 10 10 10 10 50 60 Percent Cu per size fraction 13.2 20.7 7.5 3.5 4.0 29.9 21.1 cxCu ppm 2.0 7.5 cxCu:Cu (percent) 4 14 Co ppm n.d. n.d. n.d. n.d. n.d. 35 60 Percent Co per size fraction 0 0 0 0 0 36 64

Cu observed from an independent determination of the -80 :osh fraction = 15 ppm Cu calculated from size fraction analyses and determinations = 17 ppm Co observed from an independent determination of the -80 mesh fraction = 22 ppm Co calculated from size fraction analyses and determinations = 8 ppm Weight percent of clay-silt in the -80 mesh fractions = 37 % Percent Cu contained in clay-silt fraction of -80 mesh sample = 78 %

Background Sample No. 1564 (Lower reaches Chanjojo tributary): Weight percent of size fraction 29 34 13 6 4 7.4 7.6 Cu ppm 10 10 10 10 20 90 120 Percent Cu par size fraction 11.7 13.7 5.2 2.0 3.2 26.9 36.8 cxCu ppm 3.5 17.5 cxCu:Cu (percent) 4 15 Co ppm n.d. n.d n.d. n.d. n.d. 40 60 Percent Co per size fraction , 0 0 0 0 0 40 60

Cu observed from an independent determination of the -80 mesh fraction = 35 ppm Cu calculated from size fraction analyses and determinations = 25 ppm Co observed from an independent determination of the -80 mesh fraction = 10 ppm Co calculated from size fraction analyses and determinations = 8 ppm Weight percent of clay-silt in the -80 mesh fractions = 39 % Percent Cu contained in clay-silt fraction of -80 mesh sample = 85 %

Table 41 .. Cu and Co distribution in size fractions from the Brenda and Chanjojo tributaries.

172. summarized in Table 42.

Sample No: 1602-6 1400 1313 Typo of Sample: Soil Sod ire nt Sediment Location: 501 above Upper Lower hoadwatcrs Roaches Roaches Weight percent of -20+36 nosh size 1 3 19 fraction do. -36+80 do. 7 9 31 do. -80+150 do. 10 17 16 do. -150+200 do. 11 16 9 do. -200+silt do. 11.5 13 3 do. silt size 30.4 19.4 9.9 fraction do. clay do. 28.1 23.6 12.8 do. clay and silt In -80 mesh sample 64 48 46

Table42. Size fraction distribution of a soil, and sediment samples from the Yvette tributary.

The soil sample contains increasing proportions of finer material. This trend is also found in the sediment Sample No. 1400, i.e. in the upper reaches of a tributary whore the volume of water is small and the drainage somewhat impeded. Hence the sorting action of flowing water and weathering processes is at a minimum and the sediments

173. display some of the characteristics of a soil. The major difference between these t:osamples is the decrease in the smaller clay and silt size material in the sediment and a corresponding increase in the larger grained sand fractions compared to the soil. A suggestion that a portion of the -200 + silt size material from the headwater sediment has also been removed is indicated by the decrease in quantity of this fraction compared to the silt and 150-200 mesh fractions of the same sample.

The pattern of distribution of the various size fractions inth- two sediment samples from the upper and lower reaches is markedly different in that the quantity of 20 to 80 mesh sand fractions have increased considerably in the lower reaches (Table 42). The -80+150 mesh sand fraction has remained relatively constant in the lower reaches and the proportions of the -150 mesh size fractions have decreased ow- pared to the sample from the upper reaches. These features Indicate that the sorting action of stream waters has removed material finer than 80 mesh resulting in a relative increase in the coarse fractions.

A remarkable characteristic of the sediment samples is the increase in silt and clay-size material compared to the -200 silt size sand fractions. The increase in the amount of fine sized material is considered to be due to active chemical weathering of stream sediments; this subject is further discussed in Section III.

174. The proportion of clay and silt size material in the -80 mesh size fractions of thesetosamples is constant (46-48 percent), and this fact has practical implications which will be considered later.

The distribution of size fractions of all other sedLionts listed in Tables 37 to 41 are essentially similar to the samples from the Yvette tributary described above. The proportion of clay and silt-size material of the -80 mesh size fractions of all sediment samples, which were collected in the Dungalea River and from the upper and lower reaches of tributaries, range from 34 to 48 percent and averages 40 percent corpared to an average of 60 percent for soils (page 72). (b) Total copper content of size fractions. The distribution of copper in the different size fractions of a sedir_ent is governed by a number of factors including the sorting action of stream waters, variation in copper content of soils from which sedi:ents are derived, etc. The distribution of copper is also governed by the dispersion mechanisms of natal which may be either mechanical (as when metal-bearing bank soil is eroded) or chemical, involving the complex reactions which take place during weathering. Descriptions and discussions are, therefore, confined only to the major trends. The distribution of Cu in the various size fractions

175. of the anomalous Yvette soil and sediment samples is listed in Table 43. which also gives the percentage of the total Cu contained in each size fraction.

Sample No: 1602 - 6 1400 1313 Typo of Soil (ano- Sediment (ano- Sediment sample: malous) malous) (anomalous) Location: 50' above Upper reaches Lower reaches headwaters

Cu % Cu Cu % Cu Cu % Cu Size fraction - 20 +36 50 0.01 110 2.4 10 2.3 - 36 +80 60 0.8 70 4.6 10 3.8 - 80+150 130 2.7 50 6.2 10 2.0 -150+200 150 3.4 50 5.8 10 1.1 -200+silt 200 4.8 70 6.6 90 3.3 silt 630 41.1 220 31.2 200 24.4 Clay 800 46.9 250 43.1 400 63.0

Table 43. Distribution of Cu, and percentage Cu contained in the different size fractions of soil and sediment samples from the Yvette tributary aroa.

In general, tho copper content of the sediLents increases with decreasing size fraction, except for the 20 to 80 mesh sand fractions of the headwater sediment sample, which contain more Cu than the medium sand

176. fractions of the same sample. In order to establish the reasons for the increase of Cu in the coarse sand, it is necessary to consider the size-distribution of Cu in the soil and the influence of mechanical sorting by water and chemical weathering in the stream envirohment.

It is found that the sand fractions of 2 representative anomalous soils contain from 50 to 200 ppm Cu (Fiure n).

The copper content of the sand fractions of anomalous soils is considered to be due to the presence of weather resistant copper minerals or concretions and aggregates of copper- bearing iron hydroxides (gossan).

A sililarity of character between the soil and headwater sediLent sample is indicated by the increase in percentage Cu with decreasing size fraction (Table 43). Furthermore, it has already been demonstrated that the physical characteristics of sedLents in the upper reaches of tributaries are si.dilar to the soils from which they are derived, and which have not yet been subjected to extensive alluvial sorting or further weathering. Thus, the sand fractions of headwater sediments can be expected to contain concentrations of Cu similar to the anomalous bank soils from which they were derived. The intensity of weathering increases with decreasing particle-size. Hence the coarser sand fractions of sediments aro more weather resistant than the finer sand fractions, and will retain the characteristics of the soil (e.g. Cu-content) for a longer

1'77 period.

It is unlikely that the Cu content of the sand fractions is due to precipitation of Cu from water, since it is considered that any precipitated copper would be colloidal and would tend to concentrate in the finest fractions of the sediuent. Such precipitated Cu, as did adhere to the coarser grains, would be removed during the course of dispersing the samples in the laboratory prior to separating the different size fractions.

A noticeable trend in th-•twosedinient saLples from the Yvette tributary is the decrease in Cu content of the coarser sand fractions in the lower reaches compared to the headwaters, i.e. the Cu content of the sand fractions decreases during transport in the stream environment. The constant values of 10 ppm Cu in the sands reflect the limitations of the analytical techniques in the low ranges and not, of course, a constant copper content.

The greater values of copper in the clay and silt size material of the sample from the lower reaches compared to the upper reaches of the Yvette tributary is apparently contrary to expectations if related to the fact that the former sample is locato3 closer to anomalous soils than the latter sample (Figure 14). However, this effect is only apparent because the calculated total copper content of the sample from the upper reaches is 136 ppm (observed 125 ppm Cu in the -80 mesh fractions)

178. compared to 81 ppm (observed 85 ppm Cu) in the lower

reaches. Thus, the apparent increase in copper in the clay and silt size fractions of Sample No. 1313 reflects the trend for copper to be concentrated in the finer fractions by weathering and precipitation from water.

It has been demonstrated that the -80 mesh fractions

of sediments and soils contain an average of 40 percent and 60 percent clay-silt material respectively. It is also found that 78 to 93 percent (average 85 percent) of the total copper contained in the -80 mesh fraction of both

soil and sedirdent samples is concentrated in the clay and silt size fractions (Pages- 72, 163-172 ). The relatively consistent proportions of clay-silt and the fairly uniform proportion of the total copper contained in this fraction are considered to reflect dominantly chemical processes of weathering and is discussed in more detail in Section III. Also, because of the relative uniformity of those figures, they can be used to calculate semi-quantitatively the amount of copper which could be expected in the -80 mesh fraction of the sediLents if the copper content of the bank soil, from which the sediments are derived, is known. . The general trends in the distribution of copper in the size fractions of sedinent samples from the upper and lower reaches of the Yvette tributary are found in all other samples listed in Tables 37 to 41 . Thus it is found that the sand fractions of anomalous Sample No. 1385,

179 located in the headwaters of a minor tributary of the

Kitabarole, contain more copper than the equivalent fractions of Sample No. 1210 from the lower roaches. The progressive removal of copper, during transport, from the

sand fractions of other samples and the concentration of metal in the clay-silt fraction is demonstrated by all other samples.

It is of interest to note that the size distribution

of cobalt shows the same general trends as copper (Tables 37

to 41). The fact that the sand fractions of samples located in the upper reaches of tributaries closely resembles the c-Ilffr,Ictions of soils is clearly demonstrated by the cobalt concentrations of these fractions.

(c) The leachable copper (cxCu) content of the clay and silt size fractions. The cxCu content of soils and sediments is considered to be a measure of the more loosely bonded copper contained in the sample. This metal is though,

to mainly represent secondary copper (a) derived from weathering of primary minerals, (b) precipitated from solution, and (c) sorbed on to organic material, clays, etc. Waters derived from oxidizing copper sulphide deposits can be expected to contain more dissolved copper than waters draining barren ground. Therefore, the existing concentrations of cxCu in soils and sediments in the vicinity of oxidizing sulphides can be expected to be further augmented

180. by sorption and precipitation of Cu from solutions. Thus the cxCu concentrations will bo increased, and the presence of mineralization could be indicated by an increase in the ratio of cxCu:Cu compared to samples from a barren area. The use to which this technique is put in prospecting has been indicated in the Introduction, and the distribution of cxCu, and Cu and cxCu:Cu (percent) is listed in Table 46.

Silt size Clay size Sample fraction: fraction: No: Type: Cu ppm: cxCu cxCu: Cu cxCu cxCu:Cu ppm: Cu (20) ppm: ppm: (%)

1400 knomalous 220 15.0 7 250 40.0 24 1313 do. 200 60.0 30 400 125.0 31 1385 do. 680 60.0 11 950 245.0 25 1210 do, 340 25.0 9 450 60.0 17 1270 do. 270 30.0 11 400 130.0 30 1350 do. 90 7.5 8 150 40.0 30 1147 do. 270 50.0 17 550 140.0 27 1310 Background 90 3.0 4 100 12.5 12 1453 do, 50 2.0 4 60 7.5 14 1564 do. 90 3.5 4 120 17.5 15

Table 46. Comparison of the total and cold extractable Cu content of anomalous and background seaimervt samples.

181. The importance of the cxCu values in differentiating between anomalous end background semples (i.e. increasing the contrast) is demonstrated by the figures in Table 46. Thus, if the background value for totel Cu in the silt size fraction is taken es 90 ppm, the contrast for the lowest value (No. 1350) is zero, and for the highest (No. 1385) is 7, whereas the cxCu contrasts for the some semples ere 2 end 15 respectively. Similarly, in the clay size fractions, the Cu contrast for Ssmples 1350 and 1385 is 0 and 8 compared to the exCu contrast of 2 end 14 respectively. It will be recoiled that sediment Semple No. 1350 is located 5,000 feet downridge from mineralization in the headwaters of the Ketundu tributary which drains barren gneissic rocks. However, the edjoining ground-weter (No. 2528W) is anomalous with respect to Cu, end the anomalous cxCu in the sediments is considered to be derived largely by precipitation from the ground-water. (iii) Mode of occurrence of Cu in sediments.

The results of the investigations conducted in the previous sub-section (ii) indicate that Cu is concentrated in the finer fractions, and thet the exCu content gives the greater contrast between anomalous end background sediments. Previous work on Kilembe sediments by Webb end Stanton (1959) (Table 12), and the writer's investigations on the soils indicated thet the secondary iron oxides derived from copper sulphide minerelizetion contain more copper 182 than the secondary iron oxides derived from other sources. Thus, in order to extend the work of Webb and Stanton and to establish the node of occurrence and dispersion mechanisms of copper in sediments, the writer determined the exCu Cu e and CuLat of the -80 mesh sand, silt and clay size fractions of sediments.

The method is fully described in Section II A and is the same as those used for soils (page 77). The same samples selected for studying the size distribution of copper were used for determining the partition of copper between exCu, Cure and CuIat. The results of these investigations are listed in Table 47.

The composition of the stream sediment is largely dependent on the composition of the soil from which it is derived, but the character of sediments is considerably modified by the many complex reactions that take place in streams, These processes nay be classified under the general term of "weathering" and include the removal of material by the mechanical sorting action of water or by leaching, and also the addition of new material by precipitation, or the formation of new secondary minerals by chemical weathering, etc. Due to the lack of information, it is not possible to determine precisely the relative importance of each individual process. The following discussion is necessarily kept as general as possible, and only the major factors and trends are listed for subsequent

183 cons iderat ion.

(a)Exchangeable copper. It was found that 1 to 2 percent of the total copper in anomalous soil occurred as exCu, whereas in background soils exCu was not detected (page 78). Sediments derived from background soils, however, contain no detectable exCu (less than 1.0 ppm). Those figures apply to all size fractions. On the other hand the exCu:Cu ratio of the clay fraction of sedirents derived from anomalous soils ranges from less than 1.0 to 5.0 percent, while in the silt and sand size fractions the ratio ranges from less than 1.0 to 25 percent (Table 47). The high ratios (16.0 to 25.0) found in the sand fractions are suspect because they are associated with very low Cu values at which level a small error would give a considerable change in the ratio.

The trend indicated by these results is that sediments generally contain a higher proportion of exCu than soils, and the reasons for this will be considered below in conjunction with the observed results for the distribution of secondary iron oxides, Cu and Co.

(b)Partition of Cu between CuFe and CuLat. The general trend in all size fractions of yso.o.malous and background soils was for CuFe to be greater than or equal to Cutat (Table 13). Except for the anomalous Yvette Sample No. 1313 (to be discussed later), the

184.

Sample* CuLn.t.-Cu No. Type Fe Cu Fe exC u Fe:Cu exCu:Cu ppm ppm ppm Fe ppm ppm (%)

- 80 silt size fraction: 1100 10,200 60 30 30 n.d. 340 n.d. 1313 A 15,600 40 15 15 10 140 25.0 1385 A 10,000 150 60 90 n.d. 111 n.d. 1210 A 3,000 120 50 66 4 45 3.0 1270 22,000 60 25 25 10 880 16.6 1350 A 2,200 10 5 5 n.d. 440 n.d. 1147 A 4,400 40 20 13 7 338 17.5 1310 B 2,040 10 5 5 n.d • 408 n.d. 1453 B 15,300 10 5 5 n.d 3068 n.d. 1564 B 13,260 10 5 5 n.d. 2652 n.d. Silt size fraction: 1400 A 32,100 220 100 120 n.d. 267 n.d. 1313 'A 50,440 200 100 86 14 580 7.0 1385 A 80,850 680 400 180 n.d. 449 n.d. 1210 A 29,400 340 165 171 4 172 1.2 1270 A 50,440 270 120 136 14 420 5.2 1350 A 13,860 90 50 40 n.d. 277 n.d. 1147 A 20,700 270 125 129 16 160 5.9 1310 B 17,510 90 40 50 n.d. 350 n.d. 1453 B 75;000 50 30 20 n.d. 3,750 n.d. 1564 B 36,800 90 60 30 n.d. 1,226 n.d. Clay size fraction: 1400 A 56,000 250 125 109 12 513 4.8 1313 A 79,200 400 100 284 16 280 4.0 1385 A 100,700 950 550 388 12 259 1.3 1210 A 74,800 450 250 190 10 394 2.2 1270 A 66,950 400 225 155 20 432 5.0 1350 A 37,740 150 85 65 n.d. 580 n.d. 1147 A 53,500 550 350 188 18 284 3.3 1310 B 39;900 100 70 30 n.d. 1,330 n.d. 1453 B 81,600 60 35 25 n.d. 3,284 n.d. 1564 B 58,710 120 80 40 n.d. 1,468 n.d.

n.d. = loss than 1.0 ppm. A = draining mineralizatidn; B = Draining barren rocks. Table 47 . Partition of Cu in -80 sediment size fractions.

186. trend in the clay-size fraction of anomalous and background

sediments is for CuLat to be greater than CuFe. In the silt size fractions, no definite trend is fourid and CuLat content is generally less than or equal to the CuFe. (c)Iron from secondary iron oxides. The iron (Fe) content,associated with secondary iron oxides, increases with decreasing size fraction. The concentration of Fo in sediLents is generally appreciably greater than in the soils (Table 48).

Size Soil Fe m Sediment Fe ... Fraction: Range Average Range ilverage

.- 80 + silt 1,000 - 3,000 2,000 2,000 - 15,600 9,800 silt 11,000 - 18,000 14,700 13,900 - 80,900 41,000 clay 28,000 - 30,000 29,000 37,700 - 100,700 65,000 I

Table 48. Average Fe content of different size fractions fro,1 soils and sediments.

The Fe content of the various size fractions of soils and sediLents does not distinguish between background and anomalous samples (Tables 13 end 47).

(d)Fe:Cu ratios. In the clay-size fraction of anomalous sediments,

186. the Fe: Cu ratio ranges from 284 to 580 and averages 392, whereas the ratio in background sediments range from 1,330 to 3,284 and averages 2027 (Table 47 ). These ratios in the clay size fraction differentiate between anomalous and background sediments. The trend is still apparent in the silt and sand fractions, with the exception of background Sample No. 1310 when the ratio lies within the range for anomalous samples. (e) Partition of Co between Co Fe and CoLat. The clay size fraction of all the selected anomalous sediment samples and the silt fraction of anomalous Samples Nos. 1385, 1313 and 1210 generally contain approximately equal concentrations of Co and Co Fe Lat (Table 49). The clay size fraction of background samples, and the silt and sand

fractions of all other samples, generally contain more CbLat than CoFe.

Size fraction - 80 +silt silt clay ppm ppm ppm Sample Type: Co: Co 1 Co Co: Co Co Co: Co Lat Fe Fe CoLat. Fe No: i 1400 Anomalous 10 10 1 0 . 40 40 0 100 50 50 1313 do 5 51 0 70 40 30 100 40 60 1385 do 55 55 1 0 270 140 130 340 175 165 1210 do 20 10 110 90 55 35 210 100 110 1270 do 20 20 i 0 30 30 0 75 45 35 1350 do 5 5 0 40 40 0 85 35 50 1147 do 10 5 5 35 25 10 75 40 35 1310 Background 5 5 0 35 35 0 50 35 15 1453 do 5 5 0 35 35 0 60 35 25 1564 do 5 5 0 40 40 0 60 35 25

Table 49. Partition of Co in sediment size fractions.

187. (f) Discussion. A conspicuous general trend indicated above is the greater amount of secondary iron oxides in sediments as compared to soils and, in view of the Cu to Fe relationship, it Is necessary to establish the probable source of the metal.

The increase in secondary iron oxide in stream sediment could be duo to the mechanical sorting action of stream

waters by removing the lighter specific gravity minerals with a resultant relative increase in the heavier iron-bearing

minerals. Chemical weathering in the stream environment could conceivably lead to the formation of additional secondary iron oxides from the further decomposition of

partially weathered minerals. Iron oxides could also be added to the sedin,onts by precipitation from waters. The general trend in soils is for CuFe to be greater

than CuLat and, if mechanical concentration of Fe occurred in sediments (i.e. removal of CuLat with clays, etc), then the

CuFe:CuLat ratio in sediments should increase still further. However, in the clay size fraction of sediments, the reverse

trend is found and is greater than CuFe. No consistent CuLat and is found in the silt relationship between CuFe CuLat size fraction of sediments but, in the sand fractions, there

is a general tendency for CuFe to be equal to or greater than CuLat, i.e. the CuLat:Cure ratio for the sand fraction of sediments more closely resembles that of soils than does the ratio in fine fractions. Because the intensity of

108. weathering increases with decreasing grain size, it can be expected that the coarser resistant sand fractions aro more likely to retain the characteristics of the soil from which the sediment is derived. The greater Cu :Cu Fe Lat ratio in soils, as compared to that in the clay and silt fractions of sediments, indicates that the increase in iron oxides observed in sediments cannot be explained by the mechanical removal of CuLat by the sorting action of stream waters, but this factor undoubtedly does influence, in part, the nature of the secondary iron oxides in sediments.

Due to the complexity of the reactions involved, it is difficult to assess the quantitative importance of the formation of secondary iron oxides in situ in sediments.

However, qualitative estImationsof the significance of this process can be made by considering the iron content of the source of material and the relative increase of iron in the different size fractions of sediments. The iron content

(and hence the potential for forming secondary iron oxides on weathering) of the Kilembe Series rocks, which are essentially a basic mineral assemblage, could be expected to be greater than the gneissic rocks which are acidic in character. Thus sediments derived from gneissic soils should contain less secondary iron oxide than sediments derived from soils originating from Kilembe Series rocks.

However, no significant difference in the secondary iron oxide content of those two genetic types is found. Furthermore,

189. as the intensity of weathering increases with decreasing

grain size, a greater relative increase in secondary iron

oxide could be expected in the clay size fractions compared to the coarser fractions. However, the opposite trend is

observed, i.e. the secondary iron oxide of (a) the clay size fraction increases twofold, (b) the silt increases

threefold, and (c) the sand increases almost fivefold (Table 48). It is, therefore, considered probable that, although the

formation of secondary iron oxides by weathering of sediments in situ is in part responsible for the observed increases) it is unlikely to be the major factor.

The precipitation of considerable quantities of dissolved iron and copper from water on transition from the

subsurface to the surface environments has been demonstrated in Section IIB. In the anomalous Yvette area, for example, the ground-water loses 2,000 ppb Fe and 57 ppb Cu on

passing into the surface drainage. The nature of the transition zones are described in detail in Section II D, but briefly they are generally free-flowing zones of seepage in which the precipitated metal does not accumulate, but is flushed into the surface drainage system. It has also been demonstrated experi:aentally that, under laboratory conditions, iron and copper do precipitate from anomalous stream waters. (Section II B). It is considered probable that most of the iron and copper precipitated from water is removed as suspended material and that relatively minor quantities are 190. incorporated in the sediments.

It will also bo recalled that the precipitation of

Cu and Fe from anomalous surface water and on transition from an anomalous ground to surface environment was not

simultaneous. Thus, in the surface waters effective precipitation of all the Fe had occurred after one day,

whereas Cu was still precipitating on the sixth day. Also, in the transitional water most of the Cu had precipitated in the impeded seepage zone prior to the precipitation of Fe. Furthermore, all ground-waters contain a large excess

of Fe compared to the calculated saturation concentrations

for the surface environment, but only anomalous ground-waters contain a significant excess of Cu.

In anomalous and background soils the average ratio of Fe:Cu is 100:2 and 100:0.25 respectively, whereas in sediments it is 100:0.3 and 100:0.05. It is considered probable that the min reason for the difference in Fe:Cu ratios in sediments, compared to soils, is the variation of source of the secondary iron oxides, i.e. the iron oxides are derived in part from eroded soils; in part from the formation of iron oxides in situ and also by direct precipitation from anomalous and background waters, and the Fe:Cu ratios from these varied sources are further modified by mechanical stream action. However, the precise reason for the observed differences in Fe:Cu ratios is of lessor importance than the fact that Fe precipitation from all

191. ground-waters and Cu precipitation from anomalous water

has been established. It is concluded that the increased concentrations of secondary iron oxides in sediments, co:pared to soils, arc derived mainly from this source. Hence, a corollary to this conclusion is that sediments draining mineralization must also derive copper by

precipitation from the anomalous natural water. More detailed considerations of this feature will be given in subsection E, which deals with the distribution of copper in the Yvette tributary and Dungalea River.

The differences in the partition of Cu and Cu Fe Lat between soils and sedi:dents have been described above, and the writer considers that the reasons for the differences are in part due to the source of the secondary iron oxides. Thus, to recapitulate, the three main sources of secondary

iron oxides in sediments are (1) eroded soils; (2) weathering of sediments; and (3) precipitation from anomalous and

background water. Thc partition of Cu between CuFe and

CuLat will depend on all three factors, i.e. if the secondary iron oxides are derived mainly from anomalous

water and anomalous soils, the Cup° will be greater than the CuLat and this mechanism is suggested to explain the large concentrations of Cu Fe in the anomalous sample from the Yvette tributary (No. 1313 - Table 47 ). If, however, the

secondary iron oxides are derived nainly from (i) background soils, (ii) the weathering of non-cupriferous iron

192. minerals, and (iii) the precipitation of iron from background

waters, then the CuLat could be expected to be greater than

the CuFe° Consideration must also bo given to the nature of the CuLat, and this subject is discussed in Section III. Briefly, however, "lattice held copper" can occur in any form other than secondary iron oxide associat,:] copper. Thus, in addition to that which is incorporated in clay minerals, copper may also occur as specific copper minerals

(e.g. malachite) or as a minor constituent of resistant or partially weathered rock-forming minerals. In these circumstances: emphasis on any of these modes of occurrence could result in a high content of CuLat as compared to CuFe. It is of interest to note that the relative concentration of Co Fe and CoLat in sediments, as compared to soils, display the same general trends as does copper. Furthermore, the reactions which affect the mode of occurrence and distribution of copper in sediments appear to affect cobalt in a similar manner, and are indicative of the similarity of properties of the two metals (Table 49).

(iv) i summary of the regional pattern of metal distribution in stream sediments.

In order to determine the regional distribution pattern of metals in the sediments from streams draining a mineralized area, detailed sampling was carried out in the anomalous Yvette tributary and the Dungalea River. The lower reaches of all tributaries draining into this

193.. river were also sampled to study the pattern of metal distribution in sediments draining anomalous and background soils, and also to establish the impact of these sediments upon the distribution of metals in the Dungalea River. The background ksa, Sebwe and Nabiaji Rivers were also sampled in order to determine the metal content of sediments in areas far removed from known mineralization. The results of these studios are presented graphically in Figures 21 to 23 , and the data for copper, cobalt and nickel are summarized in Tables 50 (a) and (b).

The distribution of copper in the Yvette tributary and the Dungalea River is considered in detail in subsection E. The average Cu, cxCu, HC1-Cu, Co and Ni values differentiate between sediments draining mineralized and barren areas, and the values in the Dungalea River downdrainage from mineralization also indicate the presence of sulphides in the catchment area. The cxCu:Cu ratios differentiate between sediments derived from background and anomalous soils in tributaries, but do not indicate that the Dungalea River sediments are in part derived from mineralized areas, whereas the HC1-Cu:Cu ratios do distinguish between the two types of sediment. The anomalous content of exCu and HC1-Cu in sediments is considered to reflect the presence of loosely bonded copier which has been derived from mineralization, and hence both the actual content and the ratios distinguish between anomalous and background

L94. r Cu ppm cxCu pix.1 , Streams draining Range Average Range Average cxQu:Cu (%)

Barren areas. Asa-Sebwe area 20- 30 26 0.3- 0.6 0.5 1.9 Dungalea River tributaries 10- 40 30 0.4- 1.6 0.8 2.7 r Mineralized areas. Yvette tributary 70-350 166 2.3-25.6 8.4 5.0 Dungalea River tributaries 30-150 56 0.6-10.4 2.3 4.0

HC1-Cu ppm Co ppm Ni ppm Streams draining HC1-C Range Average Cu Range Average Runge Average (%) Barren areas. Asa-Sebwe area 5- 7 6 20 5-15 9 20 20 Dungalea River Tributaries 5- 17 8 27 5-15 12 10- 65 30

Mineralized areas, Yvette tributary 29-192 69 41 '15-50 35 40- 60 64 Dungalea River tributaries 11-180 35 63 12-60 24 15-110 50

Table 50 (a). Cu, Co and Ni content of sediments draining mineralized and barren areas.. 195.. Cu ppm cxCu ppm Dungalea River from: Range Average Range Average cxCu:Cu (%)

0 - 6,000 ft* 20-40 30 0.3-0.6 0.4 1.3 - 9,000 ft 20-40 30 0.4-0.7 0.6 2.0 - 16,000 ft 30-50 43 0.6-1.2 1.0 2.3 - 20,000 ft 40-50 47 0:7-1.5 1.1 2.3 - 29,000 ft 30-50 40 0.8-1.6 1.0 2.5 - 42,000 ft 20-50 37 6.5-1.7 0.8 22

, HC1:Cu ppm Co ppm Ni ppm Dungalea River from: Range Average HC(in 1-Cu: Range Average Range Average (51 , 0- 6,000 ft* 7-16 9 30 2-12 8 20-30 23 - 9,000 ft 8-13 11 36 10-15 12 25-30 26 - 16,000 ft 12-24 18 42 10-20 15 25-30 31 - 20,000 ft . 15-32 23 48 15-20 17 30-60 38 - 29,000 ft 10-23' 18 45 10-15 14 25-35 33 - 42,000 ft 7-19 14 38 10-20 13 25-125 33

0 to 9,000 feet - Barren rocks 9,000 to 12,000 feet - Mineralized rocks 12,000 to 42,000 feet - Barren rocks. Table 50 (b). Cu, Co and Ni content of sediments draining mineralized and barren areas.

196. samples. The results of Zn, Fe, HC1-Fe, Mn and HC1-Mn

determinations are plotted in Figures 21 and 22 , and the

distribution and concentrations of those metals in sediments

do not appear to be related to mineralization.

Sediment samples representative of background and anomalous areas were spectrographically analysed for:- Pb: Sn: Ga: Be: iio: V: Ti: kg: Zr:

Cr: Li: Rb: Ba: Sr: Na20: and K20. The results are tabulated in Tables 44W5. No significant relationship between individual metal values and mineralization were noted.

(v) Geoche:ilcal prospecting considerations.

(a) Size fractions.

Holman (1956) and Webb (1958) noted that, by using a -200 instead of a -80 mesh dry-sieved size fraction, the copper values of sediment samples were increased, but no increase in contrast was observed. This is directly due to

the increase in the clay and silt size fractions in which the copper is largely concentrated.

The use of a specific size fraction to increase contrast between background and anomalous values was further studied by the writer by specifically examining the metal content of the size fractions listed in Tables 37 to 41. The soil from which sediments are derived contains copper in all size fractions. Upon exposure to the

19'7. weathering and sorting action of stream waters, the copper

tends to be concentrated in the silt and clay size fractions.

In tributaries draining soils derived from ninerallzed rocks, the affect of weathering and mechanical sorting is limited and the sand fractions contain copper. In the tributaries

draining soils derived from non-mineralized rocks, the sand fractions have a very much lower inherent content of copper which, in most cases, is equivalent to background

concentrations. Thus, in tributaries the copper content

of the sand fraction will differentiate between mineralized

and non-mineralized rocks, and the closer the former sample

Is taken to the source, the greater will be the contrast. The fact that the drainage train in sand fractions is relatively short-lived is shown by the copper content of

the coarser sand fractions in the lower reaches of the anomalous Yvette and Muchingira tributaries which is the same (10 ppm) as for the Katundu tributary which drains background soils. Therefore, in order to differentiate between background and anomalous tributaries of this type,

it would be necessary to analyse the minus 200 plus silt sand size fractions (Tables 37 to 41). The major advantage of analysing sand fractions would be thr greater contrast achieved between background and anomalous values. The major disadvantage would be the very short drainage trains and the fact that sediments in major rivers, due to the dilution factor, do not indicate

198. . rrineralization unless the sample is, actually taken immediately below or over mineralization (e.g. Sample No. 1147 in the Dungaloa River, Table 40 ). The results of

total copper determinations, on size fractions separated by dry-sieving, which substantiate these conclusions, are given in the following subsection.

The very finest fractions of sediments would provide

the longest drainage trains and the length of these would be controlled by the dilution factor only. Precipitation of copper from waters would also increase the Length of the drainage train. The analyses of only the clay and silt size fractions for copper, as compared to the -80 or -200 mesh fractions, would offer no particular advantage, as the contrast is not significantly increased. Any fraction of the sediment that contains a sufficient and relatively constant proportion

of copper-bearing clay-silt fractions would suffice for differentiating between background and anomalous sediments provided the analytical method were sufficiently sensitive.

The dispersion of copper in the -80 mesh fractions from the Dungalca River shows an increase from the average background value of 30 ppm to an average peak value of 47 ppm total copper, i.e. a difference of 17 ppm (Table 50(b) ) . If a finer size fraction were analysed, the absolute values would be increased, but contrast will be decreased (Webb, 1958). However, the absolute difference between

199. background and anomalous Cu content increases. If this

absolute increase is sufficiently large to be detected with greater reliability by the standard geochemical analytical techniques, then the use of the finer size fraction for prospecting purposes would be justified. Theoretically, the length of the drainage train would be

directly dependent on the sensitivity and discrimination of the analytical technique. In the Lilellbe area, the results of the Cu analyses of the different size fractions of sediLents, indicate that longer drainage trains could be detected by analysing only the clay-silt size fractions, as compared to the -80 mesh fraction. The separation of clay-silt size rtaterial from samples entails tedious wet dispersions, and a consequent decrease in analytical productivity. The application of this sample preparation technique to overcome the existing prospecting problem was considered during the studies, but further detailed work was deferred until other less complicated techniques were investigated. (b) Extractants related to specific forms of copper. The principles upon which this technique are based was described in the Introduction, and the significance of the cxCu content of samples has subsequently been discussed. The application of the cxCu analytical technique in prospecting for copper was pioneered by Webb, Holman and Tooms in lifrical and Hawkes in America. The cxCu drainage

200. trains detected at Kilembe are relatively short, however,

and further work was undertaken to see whether other techniques of fractional analysis could be used to obtain a batter extraction of Cu derived from mineralization and thereby increase the length of the drainage trains in this

area.

(c)Iron oxide associated copper. The applicability of Cup° determinations to prospecting is assessed frog the results of the work described in Section II C, (Table 47 ). The ratios of

iron to copper are different for anomalous and background

sediments, but the percentage of CuFe in each individual sample does not clearly distinguish between background and anomalous sediments. The Pe:Cu Fe ratio generally gives a contrast of approximately 6:1 between anomaly and regional

background, but this ratio does not differentiate between weakly anomalous and highly anomalous samples in the Bukangana area.

(d)Exchangeable copper.

The exCu concentrations differentiate between

anomalous and background sediments, but the values are not quantitatively related to distance from mineralization (Table 47).

(e)Other extractants.

Prior to the detailed analyses on which the above conclusions are based, the writer tested the

201. following four solvents on representative sediment samples from Holman's collection:- (;) Dilute hydrochloric acid which is a general solvent as well as specific for certain clay and iron minerals . (B)Normal an.monium acetate specifically for exCu metal. (C)Normal am.aonium citrate for attack of iron oxides. (D)Normal phosphoric acid for attack of clay minerals. The results of "cold extractable" copper by these solvents arc listed in Table 51.

Total ppm Cu extracted by cold reagent Cu Sample Arno- KHSOit.t cx,k HC1 Phos- nium •Ammonium ppm phonic Ace- citrate Acid tate 4

B. Background No. 7 44 1.5 2.0 4.5 2.5 6.5 A. Anomalous No. 9 172 12.5 27.0 9.0 9.0 16.5 Contrast A/B 4 8 13 2 4 2

* Standard test for cxCu.

Table 51 . Copper extracted by different solvents from an anomalous and background sediment sample.

The results for the hydrochloric acid extractions were the most promising, and subsequent development resulted

202 in the present recommended method (Section VI). The reasons for the discouraging results of the other extractants was explained in previous subsections dealing with the exCu,

CuFe and Cu contents of clay fractions of samples and those lines of investigations were not pursued. (f) The leachable copper content of different size fractions. Webb (1958) gave the content of cxCu and Cu in dry-sieved size fractions from background and anomalous sedi3ent samples from the Bukangama area. He found that the contrast between anomalous and background values of total and leachable copper was greatest In the minus 80 plus 200 r:esh size fractions (Table 52).

Weight percent Cu ppm: exCu ppm: Size Fraction: Sample Sample Con- B A tract Contrast back- ano- B A A/B B A A/B ground: malous

- 20 35 27.7 23.0 30 100 3.3 0.2 5 25 - 35 80 26.6 13.8 30 150 5.0 0.4 9 22 - 80 135 9.8 7.8 30 210 7.0 0.-1 16 40 -135 200 4.8 5.0 4'0 260 6.5 0.6 30 50 -200 3.0 2.8 90 500 5.5 2.5 55 22

- 80 45 280 6.2 0.8 28 35

Table 52. Copper content of different size fractions of stream sediments, Ruwenzori Lountains, Uganda, after Webb, 1958.

203. In subsection Cv(e), the writer indicated the reasons

for the contrast in total copper in sand fractions derived

from different rock types exposed to the weathering and sorting processes in streams for different periods of tL:xe. However, the increase in contrast of cxCu in the sand

fractions obtained by Webb suggested a relative concentra-

tion of more loosely bonded copper in the -80 +200 mesh fraction of sedUents derived from anomalous soils. Tho reason for this could si:ply be the location of the sample

sites with respect to the source of the metal. It could

also indicate the presence of some material, such as

)pper bearing concretions of iron, manganese oxides or clays which are more resistant to the weathering processes in streams, but soft enough to be broken down by wet

dispersion methods. Three sediment samples from the Dungalea River and one anomalous tributary were dry-sieved into different size fractions and analysed for Cu and cxCu in order to

investigate in rmore detail the prospecting significance

of the increased cxCu:Cu contrasts in the sand fractions. Two samples were located within the zone of mineralization which crosses the Dungalea, and ono sample was located some 6 ::files downstreaL, from mineralization. It will be recalled

that the major disadvantages of the exCu technique were

the short (1,000 feet) drainage trains in tributaries, and the absence of drainage trains in the Dungalea River.

204. The results of the size fraction analyses ore presented in Teble 53. Size fractions f -10+20 -20+36 -36+80 4-80+150 -150+200 -200 Semple Site cx cx cx cx cx cx Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu

A Anomalous Kiteberole 3.4 130 2.6 150 4.0 150 7.4 150 10.0 180 16.8 190 tributary (Pim) B Dungelea within s zone of 0.4 50 0.4 30 0.4 50 0.4 40 0.6 60 2.6 70 minersli- zetion(ppm) Conti-est A/B 8.5 2.6 6.5 5.0 10.0 3.0 18.5 3.7 16.6 3.0 6.5 2.7 C Dungeles within s zone of 0.4 40 0.4 50 0.4 50 0.6 60 1.6 70 3.0 120 minere1i- zation(ppm) Contrast A/C 8.5 3.2 6.5 3.0 10.0 3.3 12.3.2.5 6.2 2.6 5.6 1.6 D Dungelen 6 miles downstream from 0.4 20 0.4 50 0.6 50 0.4 50 0.4 50 0.8 50 mineralize- tion (ppm) Contrast A/D 8.5 6.5 6.5 3.0 6.6 3.0 18.5 3.0 25.0 3.6 21.0 3.8

Table 53. Copper content of sediment size fractions obtained by dry-sieving.

205. Inspection of the results indicates the same trend reported by Webb, i.e. the contrast between anomalous and

bachground cxCu values is greatest in the medium size sand fractions. However, the absolute cxCu values are not increased sufficiently to eliminate the liliitations of the analytical method below the 2.0 ppm cxCu level, and thus does not overcome the disadvantages of the nonial cxCu

technique.

(g)Heavy specific gravity fraction. Thirty-seven panned concentrate samples wore collected and analysed for total copper to determine whether the Cu content of the high specific gravity minerals of

sediments was indicative of metallization in the catchment areas of streams. These concentrates were examined regascopically and found to consist of a mixture of magnetite (t 48 percent),

limonite (- 30 percent), and quartz (-30 percent) which adhered to the former two minerals. The total copper content of the -80 mesh fraction ranged from 20 to 70 ppm and no significant relationship to mineralization was observed.

(h)Magnetite.

Grimley (1958) reported copper concentrations of 140 to 1100 ppm in finely disseminated magnetite associated with the ore on the hilembe Mine. The writer extracted the magnetite by hand magnet froni panned sediment

206. concentrates. The uagnetite was separated by dry-sieving

into -80 and +80 size fractions. The pulverized sar:ples were analysed for Cu to deteruine the feasibility of applying this :.ethod to prospecting.

Both size fractions of :agnetite from tributaries draining ninerrllization generally contained 100 to 200 ppm

Cu, whereas other tributaries, and the Dungalea River, contained 50 to 70 ppn Cu. (i) 14etal aseDclations.

The prospecting significance of the ratios between

Cu and an associated ,,ctal,(pathfinder Ietals) and the ratios

of pathfinder metals, has been described in the Introduction. The applicability of these techniques in the Kilenbe area were investigated by relating Cu to the other metals listedin Tables 44,45 and Figures 21 clad 22 . The L:etals, other than Cu, were also inter-related, but no practical application to prospecting was found.

207. D. TRANSITION ZCNES BETWEEN ENVIRONMENTS.

(i)Introduction.

In the preceding subsections, the mode of occurrence and dispersion echanism.s of copper in the major environments of soils, waters and sediments were considered as separate entities. Consideration will now be given to the processes that operate on passing from one environment to the other.

(ii)Bank Soils. (a) Previous work and descriptions.

Holman (1956) analysed for Cu and cxCu samples taken towards the bottom of the stream banks. He reported a correspondence between peak Cu values in the bank soils and the soils on neighbouring hill slopes. The ratio of cxCu:Cu in the samples varied from 5 to 10 percent, and appeared to increase upstream. The increase in cxCu:Cu ratios observed in the bank soils from the headwaters of the Yvette tributary were interpreted by Webb (1958) as being indicative of precipitation of Cu from metal bearing ground-waters. Both writers considered that bank soils wore derived from freely drained soils which had moved mechanically down the steep hill slopes. Durir .-; the course of the field work, the writer logged and sampled in detail 35 bank profiles in the

Bukangarea area. These samples were analysed for total Cu and cxCu. The results of 11 representative examples of

208. these profiles are presented in Figures 25 and 26. These results represent conditions in tributaries draining soils from areas upslope (1392-3) and downslope (1356-7) from

:Aneralization, as well as tributaries draining soils derived froL_ mineralized rocks (1321-2, 1316-7, 1273-5, 1213-5 and 1189-91). Four (1303-5, 1252-5, 1225-8, and 1159-63) profiles are from the Dungalea River between the Yvette and Katundu tributaries. The depth of soil varies from 6 to 42 inches, and is generally a sandy loam, which is characteristic of the A horizon. The nature of the profile is remarkably constant.

The A1 and A3 horizons are always present. These are followed by an arenaceous grey coloured horizon at an elevation equal to and below the water level of the stream. In places a stone line, consisting of round quartz pebbles, varying in diameter from one-half to three inches separates the A3 and grey horizons.

It is thought that the pebble zone represents a normal stone lino between the A3 and B horizons, and not an original river-bed boulder horizon, which could be expected to contain country rock as well as quartz. The grey horizon sometimes contains sparse orange mottles (ferric hydroxide) within the first six inches from the bank, but thereafter it is a uniform grey colour. The contact between the grey and overlying horizon was followed into the banks for distances of up to three feet, and it was observed that

209. the grey horizon was always waterlogged.

There is direct contact between stream waters and the bank grey horizon. Ground-waters discharge into the streams through this zone. It is permanently inundated and represents the upper limit of the water table. The material is generally a fine grained sand grading to a sandyellt. The arenaceous nature of this material is considered to reflect the characteristics of the A (sandy) and B (silty) lithological horizons of the soil, accentuated by the fact that a Large portion of the finest material will be removed to the streaLs by the flowing ground-water. Streams are overgrown with heavy vegetation and the banks are remarkably stable. Evidence of bank coll4pse in the tributaries is extremely rare, and was only infrequently noted in the main rivers, but the steep to vertical slopes of the banks indicate very effective bank erosion. The soil enters the streams from the whole face of the bank, and the fact that considerable amounts of material continuously enter the drainage by these means is demonstrated by the cross-section profiles (characteristica concave) found in many tributaries. The material found close to the banks has the general appearance of a soil compared to a typical sandy type of active stream sediment found in the centre of the tributaries. Samples were always collected in the centre of tributaries and rivers to avoid possible contamination from the banks.

210.

(b) Copper distribution in size fractions. Two composite bank samples, including grey horizon material, representing mineralized (No. 1388-9) and non- mineralized (No. 1353-5), were separated into size fractions. The different size fractions were snelysed for Cu, and Co. The results are tabulated in Table 54.

Sample, Size fraction Type, Deter- No, and minat ion: -20 -36' -80 -150 -200 location: +80 +80 +150 +200 silt clay silt

Anomalous. Total Cu ppm 70 120 180 200 200 700 700 No. 1388- Percentage of 9. total Cu 0.4 3.2 5.9 7.7 3.9 32.2 51.2 Headwaters Total Co ppm 10 60 55 55 50 170 240 Kitabarole tributary Percentage of total Co 2 9 9 7 27 37 Percentage of clay and silt in -80 mesh fraction =56

Background Total Cu ppm 10 101 10 20 20 90 130 No. 1353- Percentage 5 of total Cu 1.6 3.4. 2.5 3.6 2.5 29.5 56.3 Headwaters Total Co ppm n.d n.d. n.d 30 40 Kat undu tributary Percentage of total Co 0 0 0 0 0 43 57 Percentage of clay and silt in -80 mesh fraction =57.

Table 54. Distribution of copper and cobalt in size fractions, and the percentage of Anetel contained in each size fraction. 211. The Cu and Co content of the sand fractions and the distribution of metals in the size fractions are essentially the same as for soils (Section IIA). The percentage of clay and silt in the minus 80 mesh fraction is 56 and 58 percent, IlhLch is characteristic of soils (average 60 percent), compared to sediLonts which contain an average of

40 percent. (c) Distribution of copper in profile. The distribution of Cu in bank profiles is relatively constant, but a tendency to increase in depth is observed, cxCu values increase with depth and the percentage ratio of cxCu:Cu is greatest in the grey horizon (Figures 25&26). The profile logging indicates that the freely drained soils above the grey horizon are essentially A horizon material and this observation is substantiated by the fact that the general order of the cxCu:Cu ratio is the same as for A horizons from freely drained soils (Figure 4).

The segregations of ferric hydroxide noted in the grey horizon in bank soils occur only within 6 inches of the bank surfacee. The probable sources of the segregations are (a) ferrous iron contained in soils from the zone of reduction (below the water table) altering to ferric iron when the soil

Is exposed to the oxidizing conditions existing above the permanent water table, and (b) precipitation of ferric iron from ground-waters discharging into the surface environment. The oxidation of ferrous iron, which is contained in

212„ soils from the zone of reduction, does not generally manifest itself by the formation of segregations of ferric

iron, and this is indicated by the rare occurrences noted in the soil profile logging (Section I ). In the stream banks, visible ferric iron segregations were confined to the gray horizon and were found only within the first 6 inches of the bank surface, and this feature indicates a relationship to the proximity of the atmosphere.

It is suggested that the formation of visible segregations of ferric iron hydroxides in the grey horizon is mainly caused by precipitation of iron from ground-waters. It is possible that this feature could be accentuated by oxidation of ferrous iron in the soil during minor fluctuations in the water table, which might result in the grey horizon being alternately exposed to reducing and oxidizing influences. However, the absence of segregations in the freely drained bank soils, which overlie the grey horizon, indicates that this process is probably of negligible Liportance. (iii) Transition between oxidizing and reducing conditions in soil profiles.

Three pits corresponding to the ground-water sample sites 2516W, 2520W and 2542W were sampled in profile and the

-80 mesh soil analysed for Cu and cxCu to determine the distribution of the metal in soils under oxidizing and reducing conditions (Figures 14Jc15)Jhe results are presented In Table 55.

213. cxCu Semple Depth Hori- Description Cu exCu Cu Inches zon ppm ppm (%)

2526 0-24.3 Organic lc= 380 32.0 8.4 2525 48 B Amphibolite Rubble: 700 28.0 4.0 2524 72 C Decomposed schist 250 10.8 4.3 2523 96 C 'Decomposed schist 400 14.0 3.7 2522 120 C Decomposed schist 700 7060 10.0 Water level 2521 132 1 C Decomposed schist 650 95.2 14.7 '

Anomalous amphibolite/schist. Semple Site 2520. Yvette tributary ores.

2516 0- 3 AO Orgenic 120 1.2 1.0 2517 Loam 90 1.5 30 A3 1.7 Water level 2518 39 A Loam 70 2.0 2.9 3 4 Background Gneiss. Semple Site 2516W. Florence tributary area.

2543 0-24 /13 Send 50 0.5 1.0 Walter level Send 2544 48 13 50 0.6 1.2

Background Gneiss. Sample Site 2542W. Sebwe River eree.

Teble 55. Distribution of Cu end cxCu in soil profiles above end below the water table.

214. In all profiles the soil, in contact with the ground- water, contained grey (bleached) material indicating a partially gleyed horizon. The arenaceous or argillaceous char,leter of the A horizon material is indicated by sand and loam respectively in the descriptions. The B horizon in

Site No. 2520W consisted of a heavy rubble zone of weathered

amphibolitic material containing iron and manganese staining. As the C horizon Laterial in this pit is schist, it is

assumed that the amphibolito is derived from the zone of mineralization found upslopo from this site, and the high

metal values found in the A and B horizons reflect

mechanical dispersion downslopc of metal-bearing rock material (Figure 14 ). The slight increase in Cu content In the topmost 3 inches from Pit No. 2516W is probably associated with the characteristic increase noted in the or;anic topsoil by Jacobson (1956).

The Cu content of the soils in contact with ground- water, as compared to the sample immediately above it, are essentially the same. The cxCu and cxCu:Cu ratios in soils increase below the water table, probably due to minor Cu sorption, from ground-waters, on clays and colloids (Carroll, 1958).

(iv) A seepage z)no f impeded drainage.

A sample (Na. 2514) frDm the transiti'm zpne of impeded drainage situated in the headwaters ,f the anomalous Yvette tributary was analysed f r Cu and cxCu (Table 56).

215. Sample Depth Hori- Descrip- Cu cxCu cxCu:Cu No: Inches: zon: tion: ppm; ppm: (percent)

2514 0-9 Glei Clay 2600 640.0 24.6

Table 56 . Cu and cxCu content of a seepage zone of impeded

drainage in the anomalous Yvette headwaters.

The material from this zone is a compact grey (bleached)

clay containing 2,600 ppr.. Cu, 640 ppm cxCu, abundant segrega-

tions of orange coloured ferric hydroxide and sparse segregations of black coloured manganese wad. The sample is representative of the top 9 inches of the seepage zone, and its relationship to other transition zones is discussed be low.

(v) Sunlary and discussion of features observed in transition zones. (a)Freely drained soils in stream banks.

The freely drained soils situated above the grey horizons in stream banks are composed largely of h horizon material and minor amounts of B horizon soil derived from the hill slopes by soil creep. Stream sediments are derived mainly from eroded bank soils.

(b)The transition from ground to surface water.

The major transition zone between grou-ad

216. and surface water is the seepage zone of free flowing water

(grey horizon) located along stream banks. The seepage zones of impeded drainage located in the headwaters of tributaries rarely exceed 250 square yards in area and

only minor quantities of water enter the strears via these

zones compared to the water entering streams via the grey

horizons in banks. Lietal is precipitated from the ground-waters during

transition to the surface environment (Section II B): The ii!etals precipitating from ground-waters accumulate in the

seepage zone of impeded drainage and abundant segregations of ferric hydroxide are found in this zone. However, the grey horizons do not appear to accumulate metal to any significant extent and only sparse segregations of ferric

hydroxide are sometirues observed. The iron hydroxide segregations appear to be related to the proximity of atmosphere rather than a fluctuating water table which produces alternating oxidizing and reducing conditions. The absence of segregations with increasing distance from

surface is manifested in both the profile logging of pits,

which intersected the water table, and the grey horizon of banks, and is considered to reflect the imoortance of the

high partial pressure of ground CO2 (lar/pH) on the solubility of metals in ground-waters (Section II B). The reason for the accumulation of metal in the seepage zones of impeded drainage is considered to reflect

217. the presence of high concentrations of clays, which not only sorb metals, but also prevent the precipitated metals from being flushed out by the water. Those postulates are, in part, substantiated by the high Cu (2600 ppm), and the abundant ferric hydroxide segregations found in the seepage Sample No. 2512W (Table 56). Also the cxCu (640 ppm), and cxCu:Cu ratio (24 percent), is indicative of a high proportion of more loosely bonded metal, i.e. precipitated and/or sorbed copper. The absence of a marked accumulation of metals in the grey horizons of stream banks is indicated by the Cu and cxCu concentrations, and the absence, or presence of only sparse segregations of ferric hydroxide, compared to the seepage zone of impeded drainage. However, minor precipitation of metal is indicated by the slight increase in Cu, cxCu and cxCu:Cu ratios compared to the overlying freely drained bank soils. The absence of significant accumulations of metal is considered to be related to the permeable nature of the grey horizon. Thus, if metals were precipitated within six inches of the bank surface, the precipitate would be flushed out by the free flowing water. Alternatively, the rapid rate of flow of ground-waters through the grey horizon might result in the precipitation of metals only after the water had entcred the stream. It is not possible to decide which of these processes occur, or whether both operate. The

218. slight increases observed in Cu, cxCu End cxCulCu ratios in the grey horizon, compared to the overlying freely drained bank soils, is considered to reflect minor cuantities of copper removed from solution by sorption effects. It is possible that the obsence of accumulated copper in the grey horizon may be due to the obsence of anomalous Cu in the ground—waters. In this connection, it has been demonstrated that the metal content (excluding Fe) of ground— waters draining oxidizing sulphides decreeses with increasing distance from mineralization. However, e down— ridge dispersion of anomalous copper for et least 5,000 feet was proven End, es ell but one sample (Upper Florence) listed in Figures 25 and 26 cre located downridge End within e mile of minerelizetion, it can, therefore, reesonebly be assumed that the ground—waters are anomalous with respect to copper. Further proof that the concentration of Cu in the grey horizon is not dependent on the copper content of ground— waters is provided by the grey horizon materiel from the heed— waters of the Kiteberole tributary (Teble 57).

Sample Sample No. Soil profile Cu ppm East 1379 Al 100 Bank 1380 Grey horizon 150

West 1382 Al 60 Bank 1383 Grey horizon 65

Teble 57. Cu content of bank soils end grey horizons in the heedweters of the Kiteberole tributary.

219. Those samples were collected only 100 feet downslopo from the anomalous ground-water Sample No. 2527W, which contains 37.5 ppb Cu (Table 17 ). It will be noted that the Cu content of the grey horizons (65 and 150 ppm) indicates negligible metal accumulation compared to the ILpeded seepage zone in the Yvette) headwaters (2,600 ppm Cu), which drains anomalous ground-water containing only twice the concentration of copper (80.8 ppb Cu).

220. E. DISPERSION PATTERNS OF COPPER OBSERVED IN SEDIL.ENTS OF THE DUNGALE/, RIVER AND THE YVETTE TRIBUTARY.

In this section, the overall pattern of copper distribution in an anomalous tributary (Yvette) and a major river (Dungalea) will be considered, together with the

dispersion mechanisms responsible for the observed drainage trains. (I) The Yvette tributary.

Recapitulating from previous sections, the Yvette tributary is 3,000 feet long and is fed by ground-waters draining the marginal grade mineralization that occurs within its catchment area (Figures 13&A4).The uppermost two-thirds of the stream flows over footwall rocks of the Kilembe Series, while the lower reaches are underlain by granitized rocks of the same Seriesi The tributary flows in a direction parallel to the surface trace of the bedding. The gradients in the upper reaches average 15 degrees and the rate of flow is 0.003 cusecs. In the middle roaches

the gradient decreases to an average of 6 degrees, and the rate of flow increases to 0.077 cusecs. in the lower reaches, where the water flows over cataracts and waterfalls, the gradient steepens to an average of 26 degrees and the rate of flow increases slightly to 0.00 cusecs. The difference in elevation between upper and lower reaches is 900 feet. The increases in rates of flow represent direct additions of ground-water. The water from the topmost

221. reaches of the Yvette tributary are derived from ground-

waters that pass through a small 250 square yard seepage area

with impeded drainage. Except for the headwaters, ground-water is discharged directly into the tributary through the permeable grey horizon of the bank soil profile.

In the upper reaches, the total copper content of the residual valley-slope soils range from 30 to 250 ppm. Down-

stream the soils derived from the granitized rocks contain an average of 30 ppm Cu. lin isolated geochemical soil anomaly with values ranging from 250 to 490 ppm Cu (with one isolated value of 1,200 ppm copper) crosses the stream at

1,000 to 1,500 feet below the headwaters. Trenching within

the anomaly had disclosed unconsolidated boulders of gossan which were considered to be derived by landslip from the marginal grade mineralization on the ridge crest, (J.S. Smib - personal communication),

Marginal grade mineralization is found on the ridge crest above and within the swale area of the Yvette tributary, and the overlying soils contain up to 5,000 ppm Cu, but the free flowing water in the upper reaches of the tributary does not intersect the soil anomaly. It must be noted that the writer sampled only active stream sediments and, therefore, samples from the swale area anomaly were not collected. The variations in metal content of sedilaents and waters, on passing down the Yvette, are given in Table 58. Inspection of the data show that Cu and cxCu in the sodi:nonts rise to peak values in the middle reaches. In contrast, Cusol is at

222. a minimum over this section.

1 + + Sample Site: 01 (Upper1+500 +1000 +1500 +2000 2500 3000 roaches)!__. ft feet foot foot feet feet

Sediments: Cu ppm 100 130 140 350 270 100 70 cxCu ppm 5i2 8.8 10.4 25.6 12.4 2.8 2.3 cxCu:Cu (%) 5:2 6.7 7.4 7.3 4.6 2.8 3.3

Water: Ionic Cu ppb 7.25 6.0 6.0 6.0 7.0 7.5 7.5 Non-ionic Cu ppb 3.75 2.0 3.0 1.5 3.0 5.0 7.5. Ionic Fe ppb 490 400 360 300 260 300 300 Non-ionic Fe ppb 1110 600 440 100 240 100 100 Rate of fluw cusccs 06003 0.003 0.003 0.017 0.077 0.077 0.087 Increase in rate of flow 0 0 0 0.014 0.060 0 0.010 cusccs

Gradient degree 15 15 15 6 6 26 26

Cu in freely drained soil 20-250 20-250 250-490 250-490 20-250 10 10 (ppm) to to 30 30

Table 58. Distribution of Cu, Fe, rates of flow and gradients in the Yvette tributary.

223. In other words, the peak in the sediment anomaly

coincides with:- (a)the soil anomaly that extends to the banks along the middle reaches, (b)the shallowest gradients along the length of the

tributary,

(c)the decrease in in the surface water, and CuSol (d)the zone of greatest influx of ground-water. Each of these factors might account for the anomaly, viz: (a)erosion of the Cu-rich bank soils,

(b)mechanical settling of Cu-bearing clay and silt size

material derived from the upper reaches and deposited

where the gradients decrease in the middle reaches, (c)precipitation of Cu from surface waters; and

(d)precipitation of Cu from ground-waters entering the stream through the grey horizon. It is probable that all these factors contribute in varying degrees to the concentration of the copper in the sediment anomaly. The relative importance of the individual factors is considered below.

Holman (1958) determined the Cu content of the -80 mesh fraction of both sediment and bank soils collected at 50 foot intervals along the tributary. He reported "the average values ... wore found to be 108 ppm for bank soils and 110 ppm for the sediments". From this Holman concluded that the Zvette anomaly in the sediments was derived almost

224. entirely by erosion of the bank soils. 1, relatively constant proportion of 60 percent clay-silt size material was found in the -80 mesh soils and bank soils from the Bukangama area. The clay-silt fraction of -80 nosh sediments from the upper reaches (48 percent), n:iddle roaches (40 percent* ), and lower reaches (46 percent) of the Yvette tributary averaged 44 percent, compared to an overall average of 40 percent from all sediments (Section IIC). It was also found that approximately 85 percent of the Cu was concentrated in the clay-silt size fractions of soils, bank soils and sediments (Section IIA,Gp.).Bocause of the complexities introduced by weathering, sorting action of streams, different bedrock sources of copper, etc., it is not possible to calculate accurately the precise concentration of copper in the sediments that is derived from the bank soils. However, a semi-quantitative calculation to determine the general order of this Cu can be made. Thus, by simple proportion, it is calculated that the -80 fraction of sediments should contain 73 ppm Cu, if all the metal is derived from the banks. However, the sediments from the total length of the Yvette tributary average 110 ppm Cu, i.e. 36 percent of the copper is probably derived from sources other than eroded bank soils.

* Sample 1318: -20'4.80 33 g; -80+200 40 g; silt 12 g; clay 15 g i.e. -80 mesh sample contains 40 percent clay plus silt.

225. If only the snomely peek is considered in the some manner, it is celculsted that the sediments derived from the soil, which average 350 ppm Cu, should contein 230 ppm Cu. The Cu content of 9 sediment samples from the anomaly peek, collected end analysed by Kilembe Mines Ltd., rsngeci from

220 to 570 ppm Cu and averaged 320 ppm Cu, i.e. 90 ppm Cu,

or 28 percent of the copper is probably derived from sources other than eroded bank soils. However, since the eroded anomalous bank soils would in any event suffer dilution by

mixing with•the relatively Cu-poor sediment derived from the upper reaches, it may be assumed that the fiE'ure of 28 percent is a minimum. The decrease in gredients in the middle reaches of the tributary could result in the settling of Cu-bearing clay and silt size materiel derived from upstream. However, no increase in the percentage clay-silt fractions was observed in the sample from the middle reaches of the tributary compered to the samples from the upper and lower reaches; therefore, the anomaly peek cannot be accounted for by settling of Cu-bearing clay-silt size fractions derived from upstream. Cu precipitated from weters end incorporeted into the sediments could conceivebly account for the observed peek values. It wes found thet the copper content of the surface

226. water decreases in the middle reaches of the tributary, which could reflect precipitation and/or mixing with ground- waters of different Cu content. Also, the major influx of ground-water coincides with the anomaly peak. The tendency for precipitation of copper upon transition from ground to surface water has been established in Section IIB. Thus, both these factors could have a bearing on the distribution of copper in the sedircnts, and are consid6red in more detail.

In order to assess quantitatively the contribution of Cu precipitated in the development of the anomaly peak, it would be necessary to know the metal content of the ground-water feeding into the Yvette along its entire course. Unfortunately, due to the presence of unconsolidated boulders, the pits that were excavated in the middle and lower reaches failed to intersect the water table. However, the location of the Yvette tributary with respect to mineralization and the probable direction of ground-water movement, as indicated by the topography, suggests that all the ground-water feeding into the Yvette is likely to contain anomalous concentrations of copper. Consequently it would seem probable that abnormal amounts of Cu might be precipitated in the sedinent anomaly peak area where ground- water influx is at a maximum. The problem is, however, to what extent does this precipitated metal contribute towards the build-up of values in the anomaly peak area. In this connection, practical experiments carried out on the

227. anomalous Yvette surface water demonstrated that both Fe and Cu were precipitated (page 132). A comparison of the Cu and Fe contents of ground and surface water in the upper reaches of the Yvette tributary also demonstrated that the metals precipitated from the water upon transition from ground to surface (page 109). Further- more the Fe:CuFe ratios of anomalous sediments is 100:0.3 (page 186). Thus, precipitation of Fe and Cu from water has been established and, if the figure of 100:0.3 is assumed for the ratio of precipitated FelCu, then a large concentration of Fe derived by precipitation from waters can be expected to coincide with an increase in Cu which is derived from the same source, i.e. if the anomaly peak was caused by precipitated Fe and Cu from water, the sediments could be expected to contain abnormally high concentrations of Fe compared to the sediments from the upper and lower reaches. The total Fe in the sediment is 65,000 ppm in the upper reaches of the Yvette, 40,000 ppm in the middle reaches and 30,000 ppm in the lower reaches. In other words, there is no increase in total Fe in the middle reaches. It is of interest to calculate semi-quantitatively the amount of Fe that could be associated with the anomaly peak value of 350 ppm Cu, assuming that this value was due solely to precipitation. The calculated results can then be compared to the observed concentrations of metal contained

228 in the sediment in order to qualitatively assess the

importance of precipitation in the formation of the anomaly peak. The total Fe in the sample from the anomaly peak is

40,000 ppm, and the associated Cu, assuming a ratio of

100:0.3 (Fc:Cu), would be 120 ppm i.o. 230 ppm Cu (65

percent) is not associated with iron. It must be noted that the Fe from free iron oxides in a sample must be less than the total Fe. Therefore, the Fe figure assumed for the calculation is in excess of the

true value, and the calculated quantity of associated Cu will also be greater than the true figure. Alternatively, 350 ppm Cu should be associated with 116,000 ppm Fe in the free iron oxides. Thus, qualitatively, these calculations demonstrate that the co-precipitation of copper and iron alone cannot

account for the anomaly peak. However, this does not prove that copper and iron is not precipitated from waters over

the anomaly peak and, in fact, the variations in cxCu:Cu

ratios over the length of the tributary does indicate an increase in precipitation in the middle reaches. The cxCu:Cu ratios from the lower to upper reaches are 3.3, 2.8, 4.6, 7.3,

7.4, 6.7, and 5.2 percent, and these ratios indicate a

regular and progressive increase from the lower reaches to peak values in the middle reaches and then a regular and progressive decrease in the upper reaches. The regularity

229. of the variations do indicate a distinctive trend for increases in the cxCu:Cu ratios over the anomaly peak, however, the order of the anomaly peak ratios are lower than would be expected (see below) if precipitated Cu were assumed to be the major cause of the anomaly peak. In the zone of impeded seepage in the headwaters of the

Yvette tributary where the copper is considered to be mainly derived by precipitation from water, the cxCu:Cu ratio is 24.6 percent (Table 56) and, in the grey horizons of stream banks which are considered to derive minor amounts of Cu from ground-v,ters, the cxCu;Cu ratios are generally greater than 10 percent (Fir:s.25 &26). Thus, it is considered that the cxCu:Cu ratios from the anomaly peak indicate the presence of greater quantities of more loosely bonded copper (i.e. precipitated Cu) than in the lower and upper reaches, but the low order of the ratios suggest that the observed copper values from the anomaly peak cannot be accounted for by assuming copper precipitation from waters to be the major controlling factor.

Thus it may be concluded that the major controlling factor of the formation of the anomaly peak is the anomalous nature of the bank soils, and the differences between calculated and observed copper values indicate that more than 64 percent of the copper in sedinients is derived from the banks. However, copper is also added to the sedir..ents by precipitation from waters, and it is considered probable

230. that copper derived from these sources accentuate the anomaly peak. Hence if no anomalous bank soils existed in the middle reaches of the Yvette tributary, the downstream peak values could still be expected, but they would be of a relatively low order. (ii) The Dungalea River and tributaries. The location of sample sites and the geology of this area aro shown on Figures 17 and 23, and the geology is summarized in tabular form in Table 59.

Distance measured from first sample site in the upper Geology: reaches (feet):

0 - 3,500 Gneiss - 7,500 Granitised Lower Kilembe Series - 9,200 Lower Kilembe Series - 11,000 Middle Kilebbe Serie6 (mineralized) - 12,300 Upper Kilembe Series - 42,000 Gneiss.

Table 59. Geology of the Dungalea River.

All tributaries entering from either bank between 5,000 to 12,000 feet down the Dungalea drain mineralization, which continues into the catchment of the western tributaries for a further 4,800 feet downstream to 16,800

231. foot. These latter tributaries flow over gneiss in their lower reaches. The remaining tributaries drain gneissic rocks only: For the first 27,000 feet, the average gradient of the

Dungalea riverbed is approximately 5 degrees and thereafter. it is 2 degrees (Figure 17 ). Waterfalls and rapids from 5,800 to 8,000 feet and 10,300 to 11,000 feet result in a steepening of the gradient to nearly 10 degrees over these distances. The rate of flow below the Maud tributary (20 cusecs entering at 1,500 feet) is 40 cusecs, and increases steadily to 50 cusocs at the Kabekenga tributary at 16,300 feet; The

Kabekenga (1 cusec) and the Raymond (25 cusecs) tributaries increase the flow in the Dungalea to 75 cusecs.. No other major tributary, except the Brenda (1 cusec), joins the Dungalea before its confluence with the Nyamagasani River.

All the other tributaries each contribute 0.20 cusocs or less; the average being 0.10 cusocs.

The greatest addition of ground-water per unit distance occurs between the Maud and Kabekenga tributaries (1,500 to 16,300 feet), and amounts to 8 cusecs over a distance of about 15,000 feet compared to 2 cusocs contributed by the tributaries over the same section. South of, and including the Kabekenga tributary, ground-water (see Fiy;ure 17) increases the rate of flow by 7 cusecs, while the tributaries contribute 28 cusocs, over a distance of 26,000 feet.

232. The distribution of copper in the Dungalea River is listed in Table 60. The distribution of total copper increases gradually from 30 ppm to a peak of 47 ppm and then decreases to 37 ppm. This peak is of a very much lower order than the Yvette anomaly peak and the Dungalea peak occurs downstream from mineralization.

Distance 0 - 6 - 9 - 16 - 20 - 29 - (feet) 6000 9000 16000 20000 29000 42000

Sediments: Average Cu ppm 30 30 43 47 40 37 Average cxCu ppm 0.4 0.6 1.0 111 1.0 0.8 cxCu:Cu (%) 1.3 2.0 2.3 2.3 2.5 2.2 • Water: Average ionic Cu ppb 2.5 2.75 2.5 2.75 2.25 2.7 Average non-ionic Cu ppb 0.75 * 4.25 2.5 1.25 0.7 Average Ionic Fe ppb 190 235 235 130 370 Average total Fe ppb 260 * 355 270 580 487

* Not determined. Table 60. Distribution of copper and iron in waters, and copper in sediments from the Dungalea River.

The ionic copper content of the water is constant, and ranges from 2.5 to 2.75 ppb. The non-ionic content

233. increases from 0.75 ppb in the upper reaches to a peak of 4.25 ppb between 9,600 and 16,000 foot downstream, and then decreases rapidly to 2.5 ppb over the next 4,000 feet and thereafter it decreases gradually to 0.7 ppb over the next 22,000 feet. The copper content of sediments from tributaries draining mineralization is listed in Table 61, and it will be noted that the sediments from the anomalous peak contain more Cu and cxCu and also higher cxCu:Cu ratios than background sedlents.

Cu ppm: cxCu ppm: `Tributaries draining: Range Average Range Average

Anomalous soils 30 - 150 56 0.6 - 10.4 2.3

Background soils 10 - 40 30 0.4 - 1.6 0.8

Table 61 . Range and average Cu and cxCu contents of sediments draining anomalous and background areas.

The ionic copper content of waters of tributaries draining all areas ranges from 2.0 to 3.0 ppb, and this

234. range is exceeded only by the Kitabarolo (at 10,200 feet), and the Gazagaza (at 12,600 feet) tributaries which contain 5.0 and 4.5 ppb respectively and drain mineralization. The George tributary water entering at 25,400 feet is also anomalous and contains 4.5 pnb ionic copper, although no known mineralization occurs in the catchment area. However, the rate of flow is very low (0.2 cusocs) and this tributary has no discernible affect on the metal content of the Dungalea water downstream from the confluence. The non-ionic copper content of tributary waters draining mineralization ranges from 5.0 to 6.5 and averages 5475 ppb, while the tributary waters draining background areas contain only 0.5 ppb. The distribution of total iron in the Dungalea sediments increases from 23,000 to 46,000 ppm on passing downstream from the upper to the lower reaches. The iron content of sediments from tributaries varies between 30,000 and 65,000 ppm, and does not appear to be related to the presence or absence of mineralization within the catchment area. The ionic iron content of the Duagalea River waters averages 190 ppb over the first 6,000 feet, but increases steadily to 235 ppb at 16,000 feet. Thereafter the content drops to 130 ppb from. 16,000 to 20,000 feet before increasing again to more than 300 ppb in the lower reaches. Ionic iron in tributary waters ranges from 160 to 1,200 ppb and show no relation with mineralization.

235. No ground-waters from the immediate vicinity of the

Dungalea River were analysed, but a study of the ground-

water hydrology indicates that the waters between the

Yvette and Raymond tributaries drain extensive areas of mineralizationd Hence the Cu content of the main volume of ground-water can be expected to be anomalous. Ground-

waters enter the river directly through the permeable grey horizon in the bank-soil.

The soils derived from gneissic rocks generally

contain 30 ppm Cu, while the average values for non- mineralized and mineralized Kilembe Series rocks are 120 and 350 ppri respectively. The geology of the Dungalea catchment is not as simple as the Yvette tributary. Consequently, confluence with

its tributaries and the changing influx of ground-waters

can be expected to result in a complicated pattern of changes in metal distribution down the Dungalea. However, a basic similarity is observed between the sediment anomalies in the Yvette and the Dungalea suggesting a similarity in the fundamental controlling factors. Unlike the Yvette anomaly, the peak of the Dungalea anomaly does not coincide with an anomaly in the adjoining bank soil. However, the peak section of both sediment anomalies have the following characteristics in common:- (a) The anomaly peak is located downdrainage from mineralization (refer to Yvette swale area anomaly).

236. (b)A decrease in content of the surface water is relateaCuSol to the increase in Cu values in sediments. (c)The greatest influx of ground-water, which is derived from a mineralized catchment area, is associated with the peak values.

(d)Both the absolute values of cxCu and the percentage ratios of cxCu:Cu increase over the anomaly peak. (a) The ionic and total iron content of the surface waters decreases over the anomaly peak. In the Yvette tributary, the values tend to remain constant in the lower reaches, whereas in the Dungalea they increase again in the lower reaches. It will be noted that no decrease in gradient is observed coinciding with the anomaly peak in the Dungaloa River, whereas in the Yvette tributary the anomaly peak coincides with a decrease in gradient. However, the decrease in gradient in the Yvette is apparently fortuitous) and not related to the anomaly peak It is of interest to consider semi-quantitatively the iwpact of dilution from barren material on the Cu content of the Dungalea sediments from the headwaters to the Nyamagasani River.

Stream sedir:ents are eroded bank soils and the bank soils are derived from ups lope by mechanical movement of the upper lithological soil horizons. The depth of overburden (residual) is relatively constant in the Dungalea catchment area, and the topography and drainage density is also relatively constant for all rock types. Thus, the

237. amount of material entering the drainage system from various rock typos will be proportional to the surface area of soils derived from the rocks. Therefore, in sediments derived from soils representing mineralized and non-mineralized areas, the dilution factor will be proportional to the surface area of anomalous and background soils. In the Yvette tributary, the metal content of the bank soils were known, and it was considered that one-third of the copper was lost from bank soils upon entering the drainage. It is not possible to repeat the calculation in the Dungalea River, as the detailed distribution of Cu in all bank soils within the catchment area is not known. However, the dilution factor may be obtained because the areas and location of soil anomalies within the catchment area is known (Figure 14 ). The average Cu content of background sedirents is known, and an approximation of the average Cu content of anomalous sediments can be made by averaging the Cu contents of sediment samples collected in the lower reaches of tributaries which drain mineralization: The sediments from tributaries which drain anomalous soils will contain Cu precipitated from waters as well as Cu derived from the bank soils and, therefore, the actual metal content will be somewhat lower than the assumed figure: The surface area of background soils is 10 to 11 times greater than the area of anomalous soils, and the

238. average Cu content of the -80 mesh sediments of

tributaries draining mineralized and barren areas is 30 and 60 ppm respectively. Thus, with a dilution factor of 10 to 1, the resultant Dungalea sediments in

the lower reaches should contain approximately 32 ppm Cu. This figure is exceeded by most samples downdrainage from mineralization and the sedlLents from the lower reaches of the Dungalea River contain an average of 37 ppm Cu. If only the catchment area from the headwaters to 20,000 feet downstream is considered, the dilution factor

is approximately 5 to 1 and the resultant Dungalea sediments should contain 35 ppm Cu. The sediments from 9,000 to 20,000 feet, however, contain an average of 45 ppm Cu, 1.o. approximately 22 percent of the Cu is probably derived from other sources, and the percentage increase is of the same ardor as those from the Yvette tributary (28 and 36 percent) which were calculated from the Cu content of bank soils. It would thus appear that sediments draining mineralization contain between 22 and

36 percent more Cu than could be expected from a purely mechanical dispersion of eroded soils. Furthermore, the increases in cxCu:Cu ratios over the anomaly peaks in both the Yvette and Dungalea suggest that the excess Cu is derived by precipitation from water, and this is, in part, confirmed by the observed associated decreases in Ousol in surface waters over the sediment anomalies and

239. the association of these anomalies with the greatest influx of ground-water draining mineralization. The peak values of sediment anomalies, which are derived fror. mineralization crossing a drainage, are normally displaced slightly downstream. This is due to the dilution factor of barren sedLients derived from upstream and the maximum impact of the anomalous material does not immediately manifest itself in the sediments overlying the mineralization. Lilneralization crosses the Dungalea River between 9,000 and 11,000 feet and all tributaries between 8,000 and 12,000 feet drain mineralization& Comparatively negligible quantities of anomalous sediment are added to the Dungalea River between 12,000 and 16,000 foot► Because of the complexity of factors involved (egg; width of stream, velocity of water flow, quantity of barren material, mixing rate of sediments, etc), it is not possible to determine precisely how far downstream from mineralization the Dungalea River anomaly should occur if it wore derived solely from anomalous bank material. However, the observed peak values in the river are located between 16,500 and 19,500 foot, i.e. one mile downstream from mineralization, and it is difficult to envisage the formation of the anomaly peak so far downdrainage by mechanical stream processes. The improbability of this is substantiated by the semi- quantitative calculations of dilution which indicated

240. that the anomaly peak sedL.ents should contain 35 ppm Cu

Instead of the observed average of 47 ppm Cu.

The addition of ground and surface waters draining mineralization, however, occurs over the total distance between 8,000 and 17,000 feet, and the anomaly peak is

located between 16,500 and 19,500 feeti The location of the anomaly peak, i.e. the source of the copper, is more in keeping with the Dungalea River draining anomalous waters between 8,000 and 17,000 feet than draining anomalous soils between 8j000 and 12,000 feet.

It is, therefore, considered that the Cu content of the Dungalea anomaly peak and downdrainage dispersion train is the result of a saline dispersion of copper in both ground and surface waters, from which copper is precipitated to increase the metal content of the sediments derived from erosion of anomalous soils.

241. III. THE NATURAL HISTORY OF THE DISPERSION OF COPPER.

The primary purpose of the writer's work was to study

the dispersion of copper in the drainage syster. with the specific practical object of 1 .proving geochemical drainage reconnaissance techniques in the Kilembe area. In order to understand more clearly the processes involved in the secondary drainage dispersion of copper, some studies, such as the dispersion of copper in ground-waters and soils, character of rainwater, etc., wore also made. These subsidiary studies are indirectly related to the surface drainage dispersion processes of copper but are, in fact, part of the more comprehensive processes involved in the natural history of secondary dispersion that occur once copper-bearing minerals enter the zone of oxidation. These processes are extremely complex, but the basic controlling factors are the nature of the primary rock minerals and their reaction to weathering processes. This discussion cannot deal exhaustively with the complex factors involved in the dispersion of copper, but an outline of the major controlling factors will be given, and comments will be made on those aspects which have a specific bearing on prospecting problems.

The processes of rock weathering, soil formation and of secondary dispersion of copper in the zone of weathering are essentially physico-chemical in character. The

242. resultant reactions are manifestations of the universal

law of balance or equilibrium. If the chemical properties of substances are disregarded, the establishment of equilibrium is largely dependent on the time factor and the physical nature of the substances. Thus, in a simple two-phase system, two gases will rapidly achieve a balances and progressively increasing periods of time will be required for equilibrium to be attained between gas-liquid; liquid-liquid, liquid-solid, and solid-solid phases. Weathering processes involve a multitude of substances in the gaseous, liquid and solid phases, but probably the most irportant single phase is water, "the universal solvent". This discussion is, therefore, introduced by a brief recapitulation of the salient features of the natural water cycle, and the character of the water. The rainfall in the Bukangarca firea is between 50 and 60 inches par year. Precipitation is spread fairly evenly throughout the year in the form of showers lasting between 30 and 60 minutes, and prolonged periods of drought do not occur. The rainwater contains high concentrations of dissolved salts, and the major volume of water is re:::arkably acid in character (pH 5.3).

The snow line in the Ruwenzori. Mountains is at

13,000 feet, and precipitation above this elevation is mainly in the form of snow. Below the snow line the rainwater percolates through the upper soil horizons to join

243. the ground-water and only very minor amounts enter the streams by direct surface run-off.

All streams and tributaries above the 4,500 foot elevation are perennial. Melting snow and ice from the glaciers food directly into the ma or rivers draining areas higher than 13,000 feet. The water flow in streams and tributaries draining areas below the snow line is maintained by the outflow of ground-waters.

Ground-waters are of two types. Deep fissure water is derived mainly from melting snow and ice in the higher elevations and is considered to flow through deep interconnected fissures, under considerable hydrostatic pressure, to lower elevations& Conditions in the zone through which this water moves are predominantly reducing. The flow is relatively slow, and chemical equilibrium with its environs are probably attained. The pH of this water measured in KiloMbe Mine is 7.2-7.0. This, coupled with the reducing conditions metLioned above, makes it relatively inert chemically, and it does not enter into nor is it much affected by surface oxidation processes. Shallow ground-water in the zone of weathering overlies the deep fissure Ground-water and is mainly derived from the rain. Tho rainwater percolates through the soil horizons and, above 4,500 feet, circulates rapidly in the zone of decomposition before being discharged into the surface drainage. These solutions are highly reactive

244. due to the original low pH of the rainwater and, furthermore, the acidity is maintained in the soil horizons by the high partial pressure of carbon dioxide in soil air. The quantities of Cu that are dissolved by these waters are mainly dependent on (a) the pH, (b) Sulphate content, (c) Carbonate content, (d) the availability of metal, and (e) the tine needed for the solution to attain

theoretical saturation with respect to the metal. The chemical reactions involved in these processes are complex and incompletely understood, but the evidence suggests that shallow ground-waters are unsaturated with respect to

Cu. This could be due to the non-availability of Cu and/or the rapid circulation of waters which do not permit equilibrium to bo attained between the above variables. The availability of metal will be discussed in more detail when rock weathering and soil profile developn_ent are considered. However, ground-waters circulating in areas where copper aLlphldes are oxidizing' contain measurably greater concentrations of Cu than do similar waters in background areas. The dispersion and concentrations of metals in shallow ground-waters downridge from mineralization Is controlled by the movements of water and dilution. No significant precipitation of metal appears to take place in the upper horizons of the ground-water as it moves laterally towards the nearest stream channel. However, the normal precipitation of Cu in the zone of secondary enrichment

245. can be expected from that portion of the ground-water that descends well below the water-table. This water would then become part of the deep fissure water and assume the characteristics appropriate to the deeper environment.

The transition from ground to surface waters is

accompanied by a rapid loss of carbon dioxide with a resultant increase in pH and bicarbonate content. Theoretical

equilibrium conditions between pH, SO4, HCO3 and the aqueous and solid copper phases under atmospheric conditions

permit only a maximum of a few ppb Cuaq to remain in solution in the surface waters. Soluble copper in the ground-water in excess of this concentration is precipitated during the transition into the surface environment. The formation of detectable drainage trains of copper in surface waters and hence the applicability of hydro- geochemical prospecting techniques in locating mineralization Is thought to be controlled by (a) the saturation potential of the surface waters compared to background concentrations,

(b) the time required for solutions to attain equilibrium with the surface environment, and the absolute differences between metal concentrations, pH, etc., of ground and surface waters, (c) supersaturation, and (d) dilution. (a) The saturation potential.

In the Kilembe area, the theoretical saturation potential of surface water is approximately 3 ppb Cuaq, and it Is found that all waters are generally saturated with

246. respect to copper. Upon trensition to the surfece

environment, ground—waters precipitate copper in excess of this concentration and, therefore, no differentietion

is obtained between Cuaq content of surfece waters dreining mineralized end unminerelized rocks. Conditions, however, would be different if the surface

waters in the Yilembe area were unsaturated with respect to copper (3 ppb), end the celculeted ssturetion concentra— tions were, say, 10. ppb Cuaq. In these circumstances, anomelous ground—waters discharging into the surface

drainage would only precipitate copper in excess of 10 ppb, end the length of enomelous drainage trains would be dependent on dilution factors end the stebility of the Cu solutions in the surfece environment. Background subsurface

waters et Kilembe contain only 4 ppb Cuaq end, therefore, upon trensition to the surface environment, would not significantly alter the surface water concentrations of metal. (b) The time fector end the differences between the subsurface end surfece environments. The time required for solutions to attain en equilibrium appropriate to the surface environment is thought to be related to the absolute differences between metal concentrations, pH, etc., of the ground end surface wyters. Thus, if the chemical properties of e ground—water ere similer to the properties of the surface waters, equilibrium will be rapidly established upon trensition from the 247 sub-surface to surface environments. However, if the chemical properties of ground-waters were greatly different to surface waters, the time required to establish equilibrium might be increased, and hence stream waters would retain some of the characteristics of the ground-water. This could result in increased saturation concentrations of copper and thus longer drainage trains of anomalous metal.

(c)Supersaturation.

It is suggested that the ,properties, pH, HCO3 and SO4, of a solution which control the solubility of copper, may more rapidly attain equilibrium with the surface environment than the dissolved metal. In these circumstances, the concentrations of dissolved copper will be in exoess of the calculated saturation concentrations, i.e. indicative of mineralization: (d)Dilution.

In streams, dilution usually has a simple arithmetic effect. However, it is iz portant in hydro-geochemical prospecting to relate the relative volume of outflowing anomalous ground-water to the volume of barren surface water in a streari. Thus, in tributaries, if large volumes of the energent ground-waters contain minor abnormal metal concentrations due to reactions related to the time factor or supersaturation, then the anomalous character could be detected if the volume of background surface water were relatively small. Large volumes of background

248. surface water would effectively mask the presence of small

volumes of weakly anomalous ground-water, and thus no indication of the presence of mineralization would be obtained by sampling rajor rivers. It is of interest to note that ionic iron, cobalt, nickel and zinc also precipitate upon transition from the

ground to the surface environment.

The transition between ground and surface water is of two types. The first are the seepage areas found in the

headwaters of tributaries. These seepage zones rarely

exceed 250 square yards in area and are characterised by

a compact grey clay soil (glei horizon) with abundant ferrous (orange) and sparse manganiferous (black) mottling. Precipitated metal accumulates in these seepages, as

evidenced by the Yvette seepage soil, which contains more

than 0.25 percent Cu. The second type of transition, a partially gleyed horizon, occurs in the zone of seepage (grey horizon) found almost continuously along the entire lengths of all stream banks. This horizon occurs at the level of the stream water. The grey horizon consists of pervious sand or silt through which water can flow freely. Unlike the headwater seepage areas, only minor quantities of precipitated metal accumulates in the grey horizon of the bank soils. This is considered to be due to the fact that the precipitates are either flushed out by the free flowing

249. ground-water, or precipitation from ground-waters occurs immediately after passing through this horizon into the surface drainage. The precipitated copper minerals (i.e. Cusol) could occur as simple or complex compounds of copper and could occur as true solutions, colloidal solutions, or suspensions.

Anomalous concentrations of Cusol are detectable for more than a mile in surface waters draining mineralization in the

Kilembe area. Evidence from the Yvette tributary and the Dungalea

River suggests that the Cusol is mainly derived by precipitation frpn outflowing ground-waters, and the decrease in Cusol concentrations in surface waters, coincides with an increase in the Cu content of the stream sediment. The reactions that result in the transformation of a rock into a soil are predominantly chemical under tropical weathering conditions. The reactions are complex and variable, but the ulti!,.ate result, if the reactions were allowed to proceed to completion, would be the formation of a stable clay mineral assemblage in the soil. The nature of these clay minerals would depend on many factors, including the nature of the original rock minerals, rainfall, temperature, location of soil with respect to the water-table, impeded or free flowing drainage, etc. The physical aspect of this weathering is to reduce the grain size of rock minerals to the ultinate clay size particles.

250. The intensity of weathering decreases and, as a result,

mechanical cohesion increases with depth below surface.

Thus mechanical movement of soil particles by gravity

or water is greatest near surface and decreases with depth. In the Bukangama area, the C horizon of the soil is static and mechanical movement of soil on the steep slopes can occur only in the A and, to a lesser extent, the B horizons. The priAary source of Cu is chalcopyrite which occurs

as blobs, stringers and disseminated grains, Intl: ately

associated with pyrite. The initial solution and subsequent

precipitation of Cu in the zone of secondary enrichment during the procu3ses of weathering is controlled by

oxidation-reduction reactions (Garrel, 1954) involving both pyrite and chalcopyrite& The nature of the resultant re-distribution of Cu in the zone of weathering is dependent

on many factors which are, as yet, incompletely understood.

For the purposes of this discussion, therefore, only the broader generalized aspects of solution and precipitation of Cu will be considered. In the Bukangar area, the gossans which cap

mineralization are essentially limonite with minor quantities of malachite, azurite, tonorite and cuprite (megasconically determined). The B horizon soils derived from the mineralization contain peak values of 0.5 percent

Cu, and the massive earthy gossan of the C horizon contains a maximum of 1.0 percent Cu. The primary sulphides

251. contain approximately 1.5 percent Cu. No evidence of

supergene enrichment was observed to a depth of 20 feet, However, supergeno enrichment, to a limited extent, is

found in the Kilembe 1,Iinc and, therefore, minor enrichment can also be expected in depth in the Bukangama area.

Oxidation depths rarely exceed 60 feet and fresh sulphides

are sometimes found in the C horizon within a few feet of surface. Erosion is rapid.

The decomposition of sulphides containing copper is thought to proceed mainly by oxidation, which in turn

appears to be strongly controlled by the amount of available

sulphur. Chalcopyrite does not contain sufficient sulphur

for its complete oxidation, and an additional source is required for a total conversion to sulphates. This deficiency Is Considered to be supplied by oxidizing pyrite, which

liberates an excess of sulphur. This process is envisaged as resulting in the formation of limonite and oxidized

copper minerals in situ. Relatively small amounts of copper

are removed in solution as indicated by the C horizon values of ± 1.0 percent Cu comnared to the primary sulphide concen-

trations of ± 1.5 percent Cu. The solutions containing copper join the shallow ground-waters. These reactions are thought to occur mainly in the zone of decomposed rock underlying the C horizon. The presence of remnants of oxidizing sulphides in the C horizoL indicates that the final stages of these processes

252,, sometimes occur in the soil horizons and this fact reflects in part the rapid erosion of surface soils and in part the weather resistant properties of the Kilembe pyrite. Subsequent to the oxidation of the sulphides, removal of copper from the soils is indicated by the further progressive decrease in values towards surface in the B and A horizons. This decrease is thought to reflect the addition of , or mixing with, barren material by soil creep in the upper soil horizons, and continuous leaching of Cu during the subsequent mechanical transport downslope

to the streams.

The possibility that eluviation of the clay sized copper-boarIng minerals from the b to the B horizon could account for this near surface decrease can be ruled out, because no evidence of niechanical (or saline) concentration

of Cu is found in the soil profile. It may thus be concluded that the Cu is removed in solution and evidence to suport this hypothesis is provided by the increase towards surface of the cxCu:Cu

ratio. This feature is considered to reflect the increasing

intensity of weathering towards surface, i.e. weathering decreases the firmness of metal-bonding in Cu bearing soil minerals, and subsequent reaction may result in Cu being sorbed onto clays, organic matter, etc. Also, the remarkably constant proportions of loosely bonded copper

253 related to depth is indicative of some form of chemical control related to weathering processes, i.e. an equilibrium between weathering, Cu and cxCu. The acidity of the rainwater indicates its effectiveness as a leaching agent, and it is considered probable that loosely bonded copper in surface soils is dissolved by rainwater and transported to the ground-water. Further evidence of the essentially chemical nature of weathering processes is indicated by the consistency (i.e. an approach to chemical equilibrium) of the following properties of -8C) mesh soils, which have been derived from mineralized and barren rocks (a) The Cu content decreases with decreasing grain size, (b) the percentage of clay-silt size material is relatively consistent (60 percent), (c) the clay-silt fractions contain a relatively consistent proportion of copper (85 percent), and (d) the secondary iron oxide content also decreases with decreasing grain size, and the clay fractions contain a consistent quantity of secondary iron (29,000 ppb). No detailed mineralogical studios to determine the precise mode of occurrence of copper in the soils have been done, but it is of interest to consider in more detail the implication of the results of the partition of copper between lattice and iron-oxide held metal. Secondary copper minerals are generally only stable in contact with copper- rich solutions (Garrels, 1954). However, the shallow

254. depths of oxidation and the rapid rate of erosion in the Bukangama area strongly sug7ests that minor quantities of the secondary copper minerals noted in gossans (page 251) could be expected to occur in the soils. Thus the concentrations of copper reported as "lattice held" would include the copper contained in those minerals. Copper also occurs in association with magnetite. Undoubtedly, copper also occurs in other forms which is not truly "lattice hold". Therefore, the term CuLat strictly refers to any form of Cu which is not associated with secondary iron oxides (excluding exchangeable copper). The copper associated with secondary iron oxides is considered to mainly reflect a Cu:Fe relationship in the primary rock minerals and, to a lesser extent, subsidiary effects such as sorption, etc. Thus the genetic relationship between iron and copper sulphides is thought to be indicated by tho fact that secondary iron oxides in soils derived from mineralization contains more than six titins the concentrations of copper compared to the concentrations observed in soils derived from non-mineralized rocks. Soils enter the streams via the river banks' These bank soils are essentially A horizon material that has been transported mechanically from upslope by soil creep. As mentioned in a previous paragraph, the movement is considered to occur mainly in the uppermost soil horizons. The bank soils arc, therefore, a composite sample representa-

255. tive of the A horizon materiel occurring upslope. The total copper content of soils permanently inundated by ground-water (e.g. river bank grey horizons) is not significantly different to the overlying freely drained soils. The cxCu content, however, increeses slightly and the cxCutCu ratio increases significantly; This is considered to be due to sorption of copper from ground-water solutions on to negatively charged clay particles (Corral, 1958). Sediments ere essentially eroded bank soils. The major physical difference between freely drained soils end sediments is the proportion of clay-silt size materiel. Thus the -80 mesh size fractions of ell soils contain approximately 60 percent cloy-silt, whereas sediments contain approximately 40 percent cloy-silt regardless of the distance travelled in the fest flowing mountain streems or of the parent rock type. It is considered that this feature is related to the active chemical weathering of sediments (Kuenen, 1959) rather than the processes of mechanical diminution of sediments by the ebresive action of stream waters. The reduction in grain- size of sediments undoubtedly does result from the grinding action of boulders during floods, but the periods of flooding are rere end of short duration. Thus ebresion is of minor importance compered to ective chemical weathering of the rapidly eroded, partially weathered, soils from the 256. steep hill slopes. The diminution of stream sediments is, therefore, thought to be mainly controlled by weathering end e balance between the formation of fine meteriel by chemical reactions, end the mechenicol actions of stream waters will be established. This belEnce, or equilibrium, is reflected by the high constent proportions of cloy—silt meteriel in the —80 mesh size fractions of the sediments.

The distribution of metal in the various size frections of sediments is essentially similer to the soils, i.e. ± 85 percent of the Cu is concentrated in clay—silt size frections. 4 semi—quantitative estimation of the Cu content of sediments cen, therefore, be mode if the metal content of the soils from which the sediments ere derived is known. Calculations of the metal content of sediments from the Yvette tributary end the Dungelee River indicete that more Cu (22 to 36 percent) is present then could be accounted for by assuming thet the Cu in the sediments is derived solely from the eroded soil. It is considered thet the excess Cu is derived from woters by precinitetion, end that this process is also related to the secondary iron oxide content of stream sediments. The concentrations of secondary iron oxides in ell sediments is significantly greeter then in the soils, end it is considered thet the increase is due (e) mainly to iron precipiteted from waters, end (b) to e lesser extent to formation of iron oxides in situ by weathering of Fe—beering

257. minerals and the sorting action of stream water which concentrates t1-. reletivaly heavier secondary iron oxides.

The ratio of secondary iron to copper in anomalous soils is 100:2.0, and the ratio of Fe:Cu precipitation from anomalous ground-waters during transition to the surface environment is of a sLailar order. However, the Fe:Cu ratio in anomalous stream sediment is markedly different at 100:003. It is suggested that the difference in ratio is due mainly to the absence of strictly quantitative co- precipitation effects between Fe and Cu and, to a lesser extent, to the different sources of secondary iron oxides in sedirents as outlined above. Furthermore, the ratios will also be dependent on the initial Cu and Fe concentrations in the ground-waters.

The independent precipitation of Cu and Fe from waters has boon demonstrated by (a) the fact that all the Fe had effectively precipitated from an anomalous surface water after one day, whereas Cu continued to precipitate for at least 6 days, (b) the precipitation of Cu prior to Fe in a transitional ground to surface water, and (c) the

absence of quantitative Cu and Fe precipitation observed by

Hem (1960 b) in synthetic solutions containing cupric, ferrous and ferric ions. The importance of the initial

concentrations of Fe and Cu in ground-waters is indicated by the fact that all ground-waters contain an excess of iron compared to the calculated saturation concentrations for the

258. surface environment, whereas only ground-waters draining mineralization 0-.11'3ain similar excess of Cu. Thus, although background sediments also contain more secondary iron oxides than the soils from which they are derived, the ratio of Fe:Cu is 100:0.05, indicating the absence of anomalous Cu concentrations in both the ground-waters and the soils from which the sediments arc derived.

The Cu which is derived from waters by precipitation, occurs as relatively loosely bonded metal. This characteristic of loose bonding of re-precipitated metal, whether it occurs in the soils from which the sediments are derived or whether it actually occurs in the drainage, is the main reason for the offeeflilieness of the cold-extraction anqlytlr,91 tsci_nique used in geochemical drainage roconnaissanc and which specifically measures the concentration of the loosely bonded metal in the sediment. The content of less firmly bonded copper is essentially a function of the saline dispersion of the metal and can be qualitatively related to the amount of metal which is dispersed in the aqueous medium.

i% typical =mole of drainage trains of leachable copper formed by erosion of soils, which contain a high cxCu content, is found in the Rhodesian Copperbelt (Webb and

TOOrtJ, 1958; TOO2S. 1955° Govotte, 1958. Copper is considered to be transported in the ground-waters and deposited in large areas of seepage (seasonal swamps), and

259. subsequent erosion of the seasonal swamp soils is the major reason for the formation of the extensive anomalous drainage trains of cxCu. It is of interest to note that Jay (1959) considers that cobalt drainage anomalies in

Rhodesia are also dominantly of hydromorphic origin. In the foothills of the Ruwenzori Mountains, the zones

of seepage, which are comparable to the seasonal swamp areas of Central Africa, only occur in the headwaters of tributaries and rarely exceed 250 square yards in area. Therefore, erosion of the cxCu rich seepage soils in the

Kilembc area is of relatively minor i.portance in the formation of drainage trains of cxCu in the sediments. The major portion of the copper transported by the ground-waters enters the drainage directly through the permeable grey horizon in stream banks. Thus the nature of the transition zones between ground and surface water, the shallow depth

of oxidation and rapid rates of erosion rosult in the formation of dominantly elastic downdrainage dispersion trains of copper.

The resultant effect of these conditions, on the

dispersion of loosely bonded copper in the sediments, is indicated by the low concentrations and the short drainage

trains of detectable cxCu that are found in the study area.

In stream sedlionts, the presence of low concentrations of loosely bonded copper, which is diagnostic of

mineralization, has, however, boon demonstrated. The

260. development of a more powerful oxtractant, to remove from sediments a greater proportion of relatively less firmly bonded copper than does the cxCu method, is the only modification that was. needed in the Kilembe area to Increase the efficiency of standard geochemical drainage reconnaissance techniques.

261. IV. APPLICATION.

The following characteristic features of sediments were established:- (a)The minus 80 riesh size fractions contain a relatively constant proportion of clay-silt size material. (b)The greater proportion of the total Cu is associated

with the clay-silt size material.

(c)The sand fractions of sediments derived from mineralized rocks contain more Cu than the sand fractions derived from non-mineralized rocks. (d)The tendency is for the Cu originally in the sand

fractions to become concentrated in the clay-silt size fractions.

(e)The anomalous sedlients contain low concentrations of exCu, whereas background sediments contain negligible amounts.

(f)Anomalous sedilents contain higher exCu concentrations and higher cxCu:Cu ratios than background sediments. The Cu content of secondary iron oxides derived from (g) Fe oxidized sulphides is greater than the CuFe of iron

oxides derived from other sources. Most of the above characteristics of sediments differentiate between mineralized and non-mineralized areas, and the results of investigations to determine

their practical applicability has been given in Section IIC.

262. However, drainage trains of anomalOUs metal were found to extend for only 1,000 2,000 feet in tributaries and insignificant trains were found in the larger rivers. According to Webb (1958), the reason for this "lies, no doubt, in the fact that erosion is so active that (a) oxidation and leaching extend only to shallow depths,

(b) the sediment is kept moving at a high rate, and (c) the stream banks are essentially composed of neighbouring valley-slope soil. Anomalous sediments are largely eroded anomalous soils, and only part of the metal has been absorbed from metal bearing surface water. Downstream from mineralization, therefore, the metal content of anomalous sediLent is rapidly diluted as it descends, by incorporation of 'barren' bank material".

The results of the writer's work essentially confirm these conclusions, and also confirms Webb's opinion that longer drainage trains of anomalous metal could be obtained if the relatively small amounts of copper aerived from anomalous soils and waters were specifically extracted. Thus in the Dungalea River, if the upper reaches (6,000 feet) are considered to be representative of background conditions, the minus 80 mesh fraction contains 30 ppm Cu, and 0.4 ppm cxCI (Table 50b). Thereafter, the total and leacnable 'copper increases to a maximum of 47 and 1,.1 ppm respectively, and then decreases slightly in the lower reaches.

263„ The cxCu:Cu ratio also increases in sympathy with the actual increase in Letal. This indicates that the

copper added to the river by mineralization is of a different character to that supplied from background areas. This feature is also demonstrated by the variation in the

cxCu:Cu ratio in the clay and silt size fractions from

anomalous and background sediments (Table 16).

In the extreme case in the Dungalea River, therefore, the increase in Cu from background to peak values is 17 ppm. The cxCu increases by 0.7 ppm, i.e. an approximate 50 percent increase in total metal derived from mineraliza-

tion results in an approximate twofold increase in cxCu.

However, both these increments, which indicate the anomalous nature of the lc:,er Dungalea River sediments, are not

within the accuracy li:Ats of the standard analytical techniques and, therefore, cannot be used for prospecting. Furthermore, the cxCu concentrations are near the lower

limits of detection and an average field La.bonttory couiu not be expected to differentiate between values of less than 1.5 to 2..0 ppm,

An analytical technique that would detect only Cu derived from mineralization would be ideal. In the Dungalea River this would mean 0 ppm Cu for the upper reaches, and values of 0, 13, 17, 10 and 7 ppm Cu going downstream.

However, no practical method of achieving this could be devised by the writer because all extractants also removed

254, portion of the background Cu. The nearest approach to the

ideal extractant fcund to be hydrochloric acid. This extractant specifically removed the major portion of Cu derived from mineralization but, unfortunately, also removed

portion of the Cu contained in background sediments. However the proportion of background Cu is relatively constant, and the technique gives reproducable results in the range

of 1 to 150 ppm. Thus, in the Dungaloa River sediments

the background concentrations from the upper reaches average 9 ppm HC1-Cu (Table 5W. The effective increase in HC1-Cu is, therefore, 2, 9, 14, 9 and 5 ppm, which is the larger proportion of the actual excess amounts of Cu derived

from the mineralization- This is also reflected in the increase in HC1-Cu:Cu ratios (Table 50(b) ).

The exact nature of this copper derived from mineralization was not determined, but the direct constant relationship between the HC1-Cu:Cu and the cxCu:Cu ratios, which

range between 10 and 20, indicates that the copper is more

loosely bonded. In effect, the hydrochloric acid is riA3rely a more effective extractant of leachable copper, and the

analytical technique has greater accuracy in the critical range; therefore, the results are basically comparable to the

drainage reconnaissance techniques used in other areas. It would be of interest to determine whether the HC1-Co, HC1-Ni, etc. content of sediments also reflected the concentrations of more loosely bonded metal in the

265. samples. The HC1-Cu and cxCu contents of s semple ere directly releted, end it is reesoneble to essume that other metels mry reect similarly. If such s relationship were proven, it could be of prEcticel importance in the development of geochemicel dreinege reconneissence tech-

niques (comperable to the cxCu method) for many other metals. The mejor edventege of the HC1 extrection technique for Cu is the increase in length of reliebly detectable

copper dispersion trains, perticulerly in mejor dreinege chennels. This results in cress of economic interest being delimited by relatively widely speced drEinsge sampling. However, once en Free containing enomelous values in tributeries hes been delimited, no perticuler edventege is geined by using HC1 extrection, end the cxCu end totel Cu enslyticel techniques are equelly suitable for locating the source of the minerelizetion. In colleboretion with Professor Webb, the HC1 extrection

procedure wc.s introduced to Kilembe Mines Ltd., end the Compeny leboretory re-Enelysed some 5,000 sediment samples (minus 80 mesh) by this technique. The results confirmed the situation of ell known occurrences of enomelous soils, end elso resulted in the location of previously unsuspected cress of interest (Figures 15 and 16). These figures show only the regionel distribution pattern of HC1-Cu releted to soil enomelies of unknown economic potentiel. As mentioned previously, the detailed 266 distribution within an anomalous area can be established by Cu, cxCu or HC1-Cu Lnalyses. The routine sampling and sample preparation procedures used during the course of this work were the same as

Holman's (1956). The recommended location of sample sites is one duplicate sample every half mile in rivers of more than one mile in length, and ono duplicate sample from the lower reaches of all tributaries less than one mile long. One sample from each pair is analysed for Cu and HC1-Cu in the first instance. Values equal to or greater than 10 ppm HC1-Cu are considered to be indicative of possible mineralization. The second sample of each pair is analysed, therefore, to confirm values of greater than or equal to 10 ppm HC1-Cu. In assessing the significance of values, due consideration must bo given to the size of the stream and catchment area, and also to the phenomenon of downstream anomaly peaks (Section II E). In conclusion, it must be emphasized that the basic object of geochomical drainage reconnaissance sampling is to delimit areas of possible economic interest) The results must bo considered purely qualitatively and standard mineral exploration follow-up techniques must be employed to determine the economic potential. These reconnaissance sampling techniques have been proven to be applicable to a particular type of sulphide mineralization occurring within a particular geological environment. If either or both of

267. these conditions are changed, it is possible that the recommended techniques may have to be considerably modified or indeed entirely altered to suit the changed conditions.

268 V. SUGGESTIONS FOR FURTHER RESEARCH.

1. The geology of the Ruwenzori Mountains and the Kilembe Series are, as yet, incompletely understood.

The results of the research work since 1954 suggests that a detailed study of the trace metal content of rocks, soils, sedir..ents and waters could lead to a clearer understanding of the complex regional and local Kilembe geology (including ore genesis), and the development of geochemical mapping techniques.

2. The unexpected high total dissolved salt content and pH variations of rainwater warrants further studies in order to determine (a) the reasons, and (b) the effects of the precipitated water on weathering processes, soil fertility, etc.

3. The mechanisms of solution, transport and precipitation of metals in natural waters has an important bearing on the interpretation of geochemical data. The practical nature of the writer's investigations precluded a detailed study of the theoretical aspects of the subject. The Kilembe area is ideally suited for studying the processes (a) in profile from deep to shallow ground- waters; (b) tributary, stream and river drainages; and (c) relatively stagnant lakes situated at high elevations near the snow line and in the humid tropical conditions of the low lying rift valleys,

269. Other than a strictly thermodynamic treatment of the subject, it would also be of interest to study the influence of micro-organisms on the distribution of metals in the different environments.

4. It is also suggested that the feasibility of developing the following two new geochemical prospecting techniques be investigated:-

(a)Ground-waters. The saline dispersion from mineralization of anomalous Cu, Co, Ni and Zn in shallow ground-waters

was in excess of 5,000 feet in the Bukangama area. It could be of practical importance to determine

the application of shallow ground-water sampling to the detection of mineralization underlain by the

alluvium of the rift valleys and, if possible, the glacial tillites situated at higher elevations in the Ruwenzori mountains. (b)Sediments,

The economic significance and efficiency of the

cxCu analytical technique in geochemical drainage reconnaissance prospecting for copper deposits, and

the reasons for this, have been outlined in Section II The cxCu concentrations, and the cxCu:Cu ratios

are of considerable importance in interpretation,

and also in evaluating the economic potential of

270. freely drained soil anomalies. Thus, to quote an example, spurious anomalies resulting from the saline transport and subsequent precipitation of copper along fracture zones, in seepage areas, in carbonate rocks, in Fe and Mn-rich B soil

horizons, etc., can frequently be detected by Inspection of the exCu and Cu data. It has been demonstrated that the HC1-Cu

content of a sample is also related to the concentrations of more loosely bonded metal. Therefore, the HC1-Cu and cxCu interpretive criteria

are essentially similar. It is thought that drainage reconnaissance prospecting techniques, and interpretive criteria may be developed for many other metals by us L, the HC1 extraction methode It Is, therefore, suggested that the practical application of this

analytical procedure to prospecting for other metals be investigated.

271. Vl. APPENDIX. SAMPLING AND SAMPLE PREPARATION TECHNIIUES. 1. Sample collection. (a) Soils. (i)Profile sampling. Pits were excavated to weathered bedrock and a six inch wide one inch deep groove was cut down the length of the pit. A groove nine inches wide and six inches deep was cut vertically down the side of stream banks. Samples were taken from the bottom upwards by cutting a regular one inch wide half inch deep channel: with a trowel, and collecting this material in standard kraft paper envelopes. Semple lengths were controlled by the changes in the soil lithology and never contained more then one soil horizon. All sample packets were pre-numbered to avoid duplication.

(ii)Soil sampling. Small pits were excavated to a depth of twenty-four inches. One side, at the bottom of the excavation, was scraped to a depth of half an inch with a trowel and the sample was collected from the freshly exposed, material. The material was stored in pre- numbered kraft paper envelopes. (b) Sediments. (i)Sediment sampling. Sediment samples were collected from the middle of streams and stored in pre-numbered standarl kraft paper envelopes. (ii)Panned concentrates. A standard prospector's pen was filled with sediments collected from the middle of streams. This material was panned, according to standard procedures, in the running water until approximately six ounces of concentrates remained in the pan. The concentrates were stored in pre-numbered standard kraft paper envelopes.

272. (c) Waters. (i)Surface water. Surface waters were collected from the centre of streams. Due to the turbulent nature of the water flow and the shallowness of the streams (eighteen inches) end tributaries (one to six inches), no effort was made to collect water from different depths. Streams were sampled progressively upstream to ovoid contamination. (ii)Ground-water. A detailed description of ground-water sampling techniques has been given In II B (3), 2. Sample preparation. (i)Drying. Samples were sun-dried in the packets.

(ii)Dry dispersion. Each sample was placed in a porcelain mortar end lightly ground with a porcelain pestle. Core was excercised to apply only sufficient pressure to ensure the breakdown of the soil structures and aggregates that resulted from the drying of samples. The actual mineral grains were never pulverized. The mortar and pestle were thoroughly cleaned after the preparation of each sample. This treatment results in o crude dispersion of the soils, and e more efficient separation in sediments which have been partially dispersed by the action of stream waters.

(iii)Dr'r sieving. Sieves are constructed of plastic end silk screening. The required grain. sized material was obtained by hand sieving. When different size fractions from one sample were required, a nest of sieves was used one. Elv.kintz was continued until complete separation was obtained. Sieves were thoroughly cleaned after each operation. Dry sieving does not effect a complete separation of material into size fractions. The finest material, in

273. the form of dust, clings to the coarser fractions. Wet sieving cannot be used to effect e more complete separation, beceuse the finest materiel is lost as suspenstions in the weter. Clay end silt size material cannot be sepereted from each other nor from the finest send fractions (-200 mesh +silt size) by sieving. (iv)Wet sieving. Wet sieving wes used for the seporetion of the send fractions (plus silt) obtained by the wet dispersion method. A nest of stemless steel screens grading from coerse et the top to fine et the bottom were used. The dry send fractions were initially separated by hand shaking. Final end complete separation wos obtained by directing e jet of de-mineralized water on to the materiel in each sieve end washing out the finer fractions to the lower sieves. (v)Wet dispersion. Wet dispersion methods ere used to effect the separation end measure the proportions of clay sine, silt size end sand size materiel. The method used by the writer is described by Piper (1950) end is e modification (Tooms, 1955) of the original method developed by Bouyoucous (1935). Eauipment end Reagents. a. Bouyoucous hydrometer with n stem celibtated to reed grams per litre of solid in suspension. b. An electric stirring unit capable of about 700 revolutions per minute with on efficient peddle. c. A one percent solution of sodium hexemetephosphote (celgon) in metal free water. d. Tell one litre cylinders. Method. e. Weigh 100 grams of minus 20 mesh soil into e 600 ml beeker. b. Add 150 ml of celgon solution end stir for helf en hour. c. Transfer to o one litre cylinder end make up to the one litre mark with deminerelized water. 274,, d. Obtain a uniform suspension by shaking end over end end note the time of commencement of sedimentation. e.Hydrometer end temperature readings are token after five minutes, end the percentege clay end silt size material is calculated after applying the necessary temperature correction (Piper, 1950). f. Hydrometer end temperature reedings ore token after five hours and the percentege clay size materiel is calculated after applying the. necessary temperature corrections.

g. The percentage of silt size materiel is obtained by subtraction. h. Cloy end silt size material is sepereted from the sends by decentetion of the topmost thirty centimetres of suspended material 14.4 minutes efter shaking (20 degrees centigrede). Decants— tion is repeated until no solid matter remains in suspension. i. Clay size meteriol is separated from the combined silt end cloy fractions by decanting the topmost thirty centimetres of suspended material every twenty—four hours (20 degrees centigrede). Decan— tation is repeated until no solid matter remains in suspension. S. Cloy end silt size material is seporoted from the solution by centrifuging. The send fractions ore seporoted by wet sieving. Samples are dried et 90 degrees centigrade and the separate sand fractions weighed. (vi) Separation of magnetite.. Magnetite was seporoted with e hand magnet. Seperetions of the magnetic fraction were repented until no non—magnetic minerals remained. It was found that seven to ten separations were needed to effect this separation. The magnetite was then ground to en impalpable mess with on agate mortar end pestle end the hand magnet seperotion was repeoted to remove material that had adhered to the coarser groins of magnetite in the first seporation.

275. (vii)Magnetic seDarations. A Frantz Isodynomic Magnetic Separator was used to separate into magnetic fractions the —200 +silt size sand obtained by the wet dispersion method. The clay and silt size fractions clogged in the machine and could not be used. Mognetite was first removed 137 hand magnet. The machine was set at thirty degrees forward slope and fifteen degrees side slope. The feed was five cubic centimetres per thirty minutes. Two separations of each fraction were made The separations were effected at settings of 0.4 and 0.8 amps. (viii)Toter filtration. Water samples were filtered at the sample site through acid scrubbed gloss wool. The glass wool was packed into a polythene funnel to a consistency that allowed the water to flow through at a rate of approxi— mately one litre per five to ten minutes. ro visible suspended material could be observed in the water after filtraAon. All filter papers tested in the field were found to contain appreciable quantities of copper. This metal could be removed by repeated acid washings, but the subsequent drying ond ironing of the contorted and creased papers was tedious and decreased productivity. Water first passed through glass wool and subsequ,ntTy through I,hurtmEnsNo. 41 filter paper left no residue on the paper. In order to speed up the rote of filtration, vacuum filtering with a hand pump was tried. However, the partial vFicuum resulted in a visible loss of dissolved gases and, because of the theoretical considerations discussed jn Section II, this technique was not adopted.

276, ANALYTICAL TECHNIQUES. The onalyticol techniques that were used ere ell based on standard procedures with relatively minor modifications. The reproducibility of results were checked by the use of statistical series (Craven, 1953), end Terc. _found to be ± 25 percent et the 95 percent confidence level. The methods ore presented in the form of "operating instructions" end, for further details, the reader is referred to the listed original publications. All work done by the writer to prove the applicability of o porticulor method or, on the develop-aent of a new technique (hydrochloric acid extroctant), will be presented after the description of the method.

(i) pH of waters were measured with the "Analytical Pocket pH Meter", menufectured by Analytical Measurements Ltd. (Richmond). A gloss-calomel electrode wos used.

The instrument was calibrated doily et pH 4.0 end pH 9.2. The probe wos inserted into the water at the sample site end, when the needle remained steady, the pH reading was noted. (ii)Ehs The some instrument used for pH meesuremeno with o platinum-celomel electrode was used. YeasureMents were obtained by inserting the probe into the water et the sample site and noting the reeding when the needle remained steady. Stondordizotion of the meter was achieved by the following procedure (R.E. Stanton, 1960 - personal_ communication)!- 1. Weigh 1.408 g. of potassium ferrocyonide trihydrate. 1.098 g. of potassium ferricyonide. 7.455 g. of potassium chloride. 2. Dissolve in water and dilute to one litre.

277. 3. This solution hos o potential of -0.430 v. at 25 degrees centigrode with respect to the standard hydrogen electrode. 4. With respect to the saturated calomel electrode, the solution gives o potential of +0.175 to +0.200 v. (iii)COrDUCTIYITY TETPERATUR.E. Specific conductance was measured at the somple site using instrument type MC1 (Mark 111) Conductivity Measuring Bridge manufactured by Electronic Switch Tear, London. The temperature of the water was measured and the dial setting odjusted accordingly, before rending the specific conductanoc. The meter was checked by using a 0.00702 TE potassium chloride (0.5232 g. per litre) solution which hos a specific conductance of 1,000 micromhos per cm E. 25 degrees C. (R.E. Stanton - personal communication). (iv)CARBONATE AND BICARBONATE. References Scott, 1950. Procedilres 1.Place 100 ml of filtered water into a 300 ml. white polythene beaker. 2. Add 1. or 2 grope of phenolphthalein solution to the sample. 3' Titrote with 0.01N hydrochloric sold until colourless. 4, Add 1 or 2 drops of screened methyl red solution. 5. Titrate with 0„017 hydrochloric (cold to the first tinge of pink. heogents. 1. 0.01T.hydrochloric acid: Prepare 1Nacid by mixing 40 ml o± concentrated acid (sp. gr. 1.18) with 400 ml of water. Dilute 10 ml of this solution to 1 litre with water. Standardise the 0.O1N solution by using it to titrote 10 ml of 0.O1N sodium carbonate. 278. 2. 0.01N sodium carbonate: Dissolve 530 mg of anhydrous sodium carbonate in water end dilute to one litre with water.

3.Phenollohtholein_solution; Dissolve 50 mg in 100 ml of 50 percent et-.yl-alcohol.

4. Screened indicator solution Dissolve 125 mg of methyl rod end 83 mg of methylene blue in 100 ml of 90 percent alcohol, Calculation. Titration with phenolphtalein as indicator = a ml Titration with screened indicator = b ml Sample volume = v ml. Normality of acid used for titrations = N = .2rif . _x x IJ x 10Q0 nig per litre Na2 CO-)

NeTiCO3 = b x 84 x N x 1000 mg per litre.

1 . The determination should be made immediately the sample has been token. 24 If the water hes e pH value of less than 8.35, there will not he o pink colour with phenolphthalein and carbonate is absent. Proceed at stage 4 to obtain bicarbonate content. (v) CHLORIDE. Referenco British Standards Institute (1960).

Proced=e. 1. Place 20 na of filtered water sample in a test tuba (18 7,c 130 um) calil)rated at 20 ml. 2, Add 1. ml of 0.1N silver nitrate solution and mix.

3. Stand for 10 minutes in the dark end compare- the turbid it with standards against a dark background.

4. Cl (in mg per litre) = lug of matching standard 20

279. Preparation of stenderds.

1. To 11 test tubes (18 x 180 mm calibrated at 20 ml) add respectively C, 5, 10, 20, 30, 40, 50, 100, 150, 200 end 250/ug of chloride. 2. Add 1 ml of 1 percent gelatine solution.

3.Dilute to 20 ml with water. 4. Add 1 ml of 0.1N silver nitrate solution.

5.Mix end stand for ten minutes. Keep in the dark when not in use end avoid direct sunlight at all times. Reagents.

1.0.1N silver nitrete solution: Dissolve L7 g of silver nitrote in water, add 10 ml of nitric acid (sp. gr. 1.42, Ansaer) nnd dilute to 1 litre with water. Store in a darkened bottle. 2.l_percent pelatine solution. Dissolve 1 g in 100 of boiling water.

3. Standard chloride soiution:(5 pg/m1). Dissolve 82.5 mg of sodium chloride in water and dilute to 1 litre. (vi) COPPER IN SOILS AND SEDIMENTS. The writer used, the diquinolyl method for determining total copper because of the greeter productivity. However, previous work hod ell beel. based on modifications of the dithizone method. As these earlier results are frequently quoted, it is adviseble to describe the dithizone method. One further difference between present and post analytical procedures is the solution of the sample. The writer, for convenience in botch operations, used perchloric acid digestion instead of potassium bisulphate fusion. All sempiss were weighed on e torsion balance. The chemicals used ere Anellar grade recgents, end the water mentioned in the tests was first deminerolized by passing distilled water through a mixed anion/cation exchange resin (Biodeminerolit).

280.

All calculations, except where otherwise stated, are based on the following formulae-

m1 of organic phase of sample x /lig of matching standard X ml of organic phase of standard weight of sample in g volume of sample extract in ml aliquot in ml - PPm? (A) DITHIZONE TEST. Reference! Bloom & Crowe, 1953.. Procedure. 1.(a) Potassium bisulphate fusion? Weigh 0.1 g sample into a 16 x 150 mm Pyrex test tube, odd 0.5 g potassium bisulphate, and fuse to a quiet melt.. Add 5 ml N hydrochloric acid, and worm to complete solution of the melt. Add 5 ml deminralized water, end mix well- (b) 60 percent perchloric acid digestion! Weigh a 0.1 g sample in a 16 x 150, mm Pyrex test tube, add 1 ml 60 percent perchloric acid and digest on a sand bath for one hour. The acid should fume slightly and the undissolved matter should be white. Dilute to 10 ml with demineralized water, and mix well. 2.Pipette a 1.0 or 2.0 ml aliquot into a 16 x 150 mm tube, add 5 ml buffer solution and 5 ml 0.001 percent dithizone in benzene. Cork, and shake vigorously for two minutes. (N.B. for aliquots greater than 2 ml, increase volume of buffer proportionately).

3.Compare the tint of the benzene phase with standards prepared similarly from aliquots of standard Cu solution (5 /ug per ml.), containing 0,0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 /Iag Cu. If colour exceeds that of the 5.0 /ug standard, repeat from stage 2 with a smaller aliquot. Reagents. 1- Buffer solution! Dissolve 100 g tri-ammonium citrate (anhydrous) and 200 g hydroxylamine hydrochloride in 700 ml of water. Extract with approximately 50 ml portions of 0.01_ percent dithizone in benzene, until the dithizone remains green. 281. Remove the excess dithizone by extraction with benzene until_ the orgonic phose is colourless. Mike up to 1 litre with water End store in e Pyrex or polythene bottle. 2. Dithizone solution in benzene. (o) 0,,01 percent stock solution! 40 mg dithizone in 400 ml benzene, shake for 20 minutes. (b) Oft001 percent working solutions take 40 ml of 0.01 percent stock end dilute to 400 ml with benaene. 3. Approximate N hydrochloric ocid: Dilute 40 ml concentrated HC? with 400 ml water. 4. Stenderd Cu solution! 0.2 g AR. CuSO4.5H20, add 50 ml. N HC1 End dilute to 500 ml! dilute 5 ml of this solution to 100 ml with water. (1 ml then contains 5 /ug Cu). (B) DIQUINOLYn TEST. Reference! Almond (1955). Procedure. 1. Weigh e 0.1 g somple in a 16 x 150 mm Pyrex test tube, odd 1 ml 60 percent perchloric ocid end digest on o send both for one hour. Dilute to 10 ml with deminerlized water, end mix well. 2.Pipette o 10 ml oliquot in e 18 x 180 mm Pyrex test tube, odd 10 ml buffer solution and 2 ml 0.02 percent diquinolyl in isoemyl alcohol. Cork, end shake vigorously for 90 seconds. 3.Compere the tint of the alcohol phase with stondnrds prepared similarly from aliquots of stondord Cu solutions (1.0 and 10.0 /ug per ml), containing 0, 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 12.0, 14.0, 16.0, 18.0 end 20.0 /ug copper. If the colour excedds the 20.0 /ug stendord, repeat from stoge 2 with a smeller aliquot.

282. Reagents. 1.Perchloric acid; 60 percent. 2.(n) Approximately N hydrochloric acid: Dilute 40 mi concentrated HC1 with 400 ml water. (b) Approximately 2N hydrochloric acid• Dilute 80 ml. concentrated HC1 with 360 ml water. 3. 2-2-diouinolyl, 0.02 percent, Dissolve 0.2 g 2-2-diquinoly1 in one litre of isonmyl alcohol.

4.Buffer solution! Dissolve 400 g of sodium acetate and 100 g of sodium potassium tortrote and 5 g hydroxylemine hydrochloride in one litre of water. Test 10 ml of buffer with 2 ml diquinolyLond, if copper is present, scrub buffer with 0.01 percent dithizone in benzene. 5.Stendard copper solutions: 100 /ug Cu per ml, Dissolve 0.2 g of CuS0.51120 in water, odd 70 ml of HC1 (sp.gr. 1.18) sad dilute with water to 500 ml. (b) 10 /ug Cu per ml, Dilute 10 ml_ (e) to 100 ml with 2N HCI.

(o) 1. /ug Cu per ml, Dilute 10 ml (b) to 100 ml with 2N HC1. (C) LEACHABLE COPPER TEST IT SOIL AND SEDIMENTS. Reference, Holman, 1956. Procedure. 1. Weigh 0.2 g sample in a 18 x 180 mm Pyrex test tube, add 5 ml buffer solution and 2 ml 0.001 percent dithizone in benzene. Cork and shake vigorously for two minutes. 2, Compare the tint of the benzene phase with standards prepared es in total Cu by dithizone (page 280. If the colour exceeds the colour of the 3.0 dug standard, add a further 2 ml 0.001 percent dithizone in benzene and shake for a further two minutes. This operation is repeated until the colour of the benzene phose can be matched with standards between the 0 and /1.g Cu. 3.0 283. Reagents. All reegents ore the same es for total Cu deter— mination by the dithizone in benzene method. (D) HC1—SOLUEL7 COPPER IN SEDIY7NTS. Procedure. 1. Weigh 0.2 g sample in e 18 x- 180 mm Pyrex test tube, add 5 ml 0.5N HC1 and bring to the boil on a sand bath. Continue boiling gently for 15 to 20 minutes. Dilute to 10 ml with 0.5N HCL and mix thoroughly. 2.Pipette a 2.0 mL aliquot in a 18 x 180 mm Pyrex test tube, add 5 ml buffer end 2.0 ml 0.001 percent dithizone in benzene. Cork end shake vigorously for two minutes. 3.Compare the tint of the benzene phase with standards prepared as in tote]. Cu by dithizone (page 281). If the colour exceeds that of the 5.0 dug standard, odd successive 2.0 ml quantities of 0.001 percent dithizone in benzene ond shake for two minutes after each addition until the colour of the benzene phase is less then that of the 5.0 /ttg standard. Reagents. 1.0.511 hydrochloric ecidt Dilute 20 ml concentrate HC1 (sp.gr 1.18) with 420 ml water. 2. Al1 other reagents ore the some as for total Cu determinations by dithizone in benzene. Development work. The extraction procedure for this method was specifically developed for prospecting purposes in the Kilembe area, end modifications may be necessary before it con be applied in other areas. The basic object during the development was, firstly, to find the concentration of acid and the method of extraction which would extrect the major portion of the anomalous copper derived from mineralization as compered to background areas. Thereafter, the method was modified to give maximum reproducibility. The normal practical considerations associated with geochemical analytical techniques, such as productivity end training of personnel, were also considered. 284. Hydrochloric ocid concentrations of 0.1N, 0.5N end 1.0N were used. Extraction techniques ranging from shaking in the "cold" to heeting for verious periods up to thirty minutes were investigated. Variation of sample weight and aliquot size were investigeted. The efficiency of the 0.5N concentration compared to other concentrations was one of degree only. The best reproducibility of results was obtained by heeting for fifteen to twenty minutes. The semple weight end eliquat size wes selected because et these concentrations each 0.1 dug of Cu in the standards represents 1.0 ppm Cu in the sample. The choice of the dithizone insteed of the diquinolyl analytical technique was due to the precticel consideration of productivity. It was found that the finely suspended undigested motericl in the sample caused "off" colours in the diquinolyl test, but did not affect the dithizone test. The time required for this suspension to settle end leave a clear supernatant liquid wes in excess of one end e half hours. The productivity is from 100 to 150 samples per 8-hour-men-day. The reproducobility of the method wes checked by using e statistical series, end o - 25 percent mean accuracy et the 95 percent confidence level was obtained (Craven, 1953). Subsequently e series of check samples ranging from 3 to 153 ppm HC1-Cu were introduced Into routine botch anelyses run by Kilembe Mines Ltd. Each semple was onelysed twenty times. The results of these enelyses ore presented in Table 62. Semple 1 2 3 4 5 6 7 8 9 10 11 12 : — No . Runge 3-4 7-8 10- 16- 15- 21- 23- 27- 44- 62- 72- 127- ppm 15 20 19 26 27 32 46 75 105 180 Wercigc 3 7 12 17 16 23 24 31 45 63 89 153 ppm Table 62. Reproducibility of HC1 Cu analyses.

(E) EXCHNNGEABLE COPPER TEST. The method used wes based on the standard N, NH4Ac method.

285. Procedure. 1. Weigh 0.5 g sample into n 18 x 180 mm Pyre,; test tube, odd 20 ml N NH Ac (pH 7.0). Cork and shake vigorously for 15 minutes.4 Remove liquid phnse by centrifuging end repeat operation. 2.Pipette o 5 ml aliquot end analyse for Cu es in the total copper diquinolyl test. No copper wes found in the supernatant liquid from n second extraction. (vii) TOTAL COBALT IN SOILS AND SEDIMENTS. Reference! Krenck, 1957. Procedure. 1. Weigh 0.1 g sample into El 16 x 1.50 mm Pyrex test tube, add 1 ml 60 percent perchloric ecid nnd digest for one hour. Dilute to 10 ml with water end mix well. 2.Pipette o 2.0 ml aliquot into 10 ml of buffer solution contained in a 16 x 150 mm Pyrex test tube, odd 0.5 ml of 10 percent tri-n-butylnmine solution. Cork and shake vigorously for one minute. 3.Compare the tint of the organic phase with standards similorly prepared from aliquots of stenderd cobalt solution containing 0, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 md 5.0 /ug Co respectively. If the colour exceeds that of the 5.0 /ug standard, dilute with benzene until within the range. Reogents. 1.Perchloric acid; 60 percent. 2.0.5N hydrochloric acid! 20 ml of ecid (sp.gr. 1.18) mixed with 420 ml of water. 3. Buffer solution: Solution A. Dissolve 170 g of sodium acetate (tri-hydrate), 40 g of sodium pyrophoaphete (decohydrote) End 5 g of hydroxylnmine hydrochloride in water, add 140 mL of 6.N hydrochloric acid end dilute to one litre. 286. Solution B. Dissolve 360 g of potassium thiocynnate in water and dilute to one litre. Mix Solution A end Solution B. in the ratio 9:1 es required. 4. 10 percent tri-n-butylsmine solution: Mix together 70 ml of benzene (crystellisoble), 20 ml of normal or iso-amyl alcohol_ and 10 ml of tri-n-butylamine. 5. Stenderd cobalt solution (5 /ug per ml): Dissolve 40.5 g of cobeltous chloride (hexahirdrate) in 20 ml of 0.5N- HCl end dilute to 100 ml with water. Dilute 5 ml of this solution to 100 ml with water. Notes. 1. The buffer solution should be et pH 4.0, snd must not fell below pH 2.0 in the test. 2. The equivalent concentration of patessium pyrophos- ,phete may be used in piece of the sodium snit.

3. The buffer will mask en amount of ferric iron in solution equivalent to 25 percent of Fe in the sample. For economy, smeller quantities of buffer solution may be used, providing that the pH of the final aqueous phase is within the rtnge 2.0-4.0. (viii) TOTAL NICXEL IN SOILS AND SEDIMENTS. Reference: Stanton and Covr.e, 1958. Procedure.

1. Weigh 0.1 g of sieved sample into e 16 x 150 mm Pyrex test tube. 2. Add 1 m1 60 percent perchloric acid end digest for one hour. 3.Dilute to 10 ml with water and mix. 4.Pipette e 2 ml aliquot into 5 ml of buffer solution contained in 16 x 150 mm tube, previously calibrated of 5 ml. 5. Add 1 ml of alpha-furildioxime solution. Cork and shake vigorously for two minutes. 6.Compare with standards. 7.If above the top standnrdt dilute with e known volume: of benzene until within the range. 287. Standards. To 10 test tubes containing 5 ml of buffer solution, edd respectively 0, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 end 4.0 /ug Ni, end 2 ml of N HC1. Add 1 ml of alpha- furildioxime solution end shake vigorously for two minutes. Reagents. 1. Buffer solutions Dissolve 20 g of tri-emmonium citrate in water, odd 130 ml of rimmonie (sp.gr. 0.880) and dilute to 1 litre with water. 2.Perchloric acid! 60 percent. 3.N hydrochloric acids 40 ml of acid + 400 ml of writer. 4. Alpha-furildioxime! 0.3 g dissolved in 90 ml of benzene end 10 ml of ethyl alcohol (absolute). 5.Stendord nickel solution (5 /ug per ml)! Dissolve 50 mg of nickel (metal, powder) in 10 ml of 25 percent nitric acid end dilute to 500 ml with water. Dilute 5 ml of this solution to 100 ml with water. (ix) TOTAL ZINC IN SOILS AND SEDIMENTS. Reference! Bloom end Crowe, 1953. The efficiency of this test on samples containing veriable large concentrations of aluminium is in doubt. Recent work by Stanton (personel communication) heF, indiceted that aluminium con seriously suppress the development of colour. The test hos been used effectively in many arees FS a prospecting method, however. Procedure.

1. Weigh 0.1 g of sample into e 16 x 150 mm Pyrex test tube, add 1 ml 60 percent perchloric acid end digest for one hour. Dilute to 10 ml with water. 2.Pipette e 1.0 eliquot into e 16 x 150 mm Pyrex test tube, odd 5 ml buffer, end 5 ml 0.001 percent dithizone in benzene. Cork end shake vigorously for one minute. 3. Compere the tint of the benzene phase with stenderds similarly prepared from eliquots of stendord Zn solution (5 /ug per ml) containing 0, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 end 3.5 /ug Zn. If the colour exceeds the top standard, repeat from Stage 2 with e smeller Aliquot. 288. Reagents. 1. Buffer solution! Dissolve 500 g sodium acetate (tri-hydrete), 125 g sodium thisulphate and 15 in1 glacial acetic acid in 1500 ml water. Extract with approximately 15 ml portions of 0.01 percent dithizone in benzene until the dithizone remains green. Remove the excess dithizone by extraction with benzene until the organic phose is colourless. Make up to 2 litres with weter. 2. Dithizone solLition in benzene! (a)0.01 percent stock solution! 40 g dithizone in 400 ML benzene; shake for 20 minutes. (b)0.001 percent working solution! take 40 ml of 0.01 percent stock and dilute to 400 ml with benzene. 3. Stenderd zinc solution (5 ug per mL)! Dissolve 50 mg metallic zinc in 5 to 10 ml concentrated HC1 end dilute to 500 ml. Take 5 ml of this solution rind dilute to 100 ml with weter. (x) TOTAL MANGANESE IN SOILS AND SEDIMENTS. Reference! Almond, 1953. Procedure. 1.Weigh 0.1 g of sieved sample into a 16 x 150 mm Pyrex test tube. 2.Mix with 0.5 g of potassium bisulphate end fuse.

3.Leech with 5 ml of 0.5N sulphuric acid. 4.Pipette e eliquot into n 18 x 180 mm test tuba previously calibrated et 5 end 10 ml, and containing 5 ml of acid mixture. 5.Add 0.2 g of potassium periodete and bring to the boil. 6.Boil for 30 seconds, end then heet in e boiling weter bath for 10 minutes. 7.Dilute to 10 ml and compare with standerds.

289.- Standards. To 19 test tubes, each containing 5 ml of acid mixture, add respectively 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 30, 40, 50, 60, 80, 100, 150 and 200 /ug of manganese. Add 0.2 g of potassium periodate and bring to the boil. Continue boiling for 30 seconds, and then heat in a boiling water both for 10 minutes. Keep in the dark when not in use. Reagents. 1.Potassium bisulphate! fused, powder. 2.0.5N sulphuric acid! add 14 ml of sulphuric acid (sp.gr.1.84) to about 500 ml of water and dilute to 1. litre.

3. Acid mixture! Add 125 ml of sulphuric acid (sp.gr. 1.84) to about 500 ml of water, mix well and cool. Add 62.5 ml of nitric acid (sp.gr. 1.42) and 62.5 ml of orthophVic acid (sp.gr. 1.75), mix and dilute to 1 litre with water.

4.Potassium periodate. 5.Standard manganese solution (100 /ug per ml)! Dissolve 203 mg of manganese sulphate crystals in about 100 ml of water, add 100 ml of 0,5N sulphuric acid end dilute to 500 ml with water. 6.Standard manganese solution (5 /ug per ml)! Dilute 5 ml of the 100 /ug per ml solution to 100 ml, with wt‘ter. (xi)HCL SOLUBLE MANGANESE IN SOILS AND SEDIMENTS. 5.0 ml aliquot of the supernatant extract obtained at Stage 1 in the HC1 soluble Cu test (page was pipetted into a 50 ml beaker. 5.0 ml of 0.5N sulphuric acid was added and the mixture evaporated to fuming. The residue was dissolved in 5.0 ml 0.51` sulphuric acid followed by the procedure from step 4 in the total manganese test. (xii)TOTAL IRON IN SOILS AND SEDIMENTS. This method is based on the standard thioglycollic acid analytical technique.

290. Procedure. 1. Weigh 0.1 g of sample into e beaker (30 or 50 m1).

2. Add 0.5 g of concentrated HNO3. If a vigorous reectian occurs, add further small quafi.tities of acid while heating on 6 hot plate until mixture is quiet. 3. Add 5 ml of perchloric acid and heat to fuming. The residue must be pure white. 4.When cold, transfer to a calibrated test tube, diluting to 10 ml with the rinsings from the beaker. 5.Pipette a l_ml aliquot into a test tube (16 x 150 mm) calibrated at 5 and 10 ml, and containing 5 ml reagent solution. 6.Dilute to 10 ml with water and mix.

7.Compare with standards. 8.If above the 200 /ug standard, repeat from 5 with smaller aliquot. Standards. To 12 test tubes, each containing 5 ml of reagent solution, add, respectively, 0, 5, 10, 20, 30, 40, 50, 60, 80,. 100, 150 and 200 /ug of iron! dilute to 10 ml with water and then mix. Keep in the dark when not in use. Reagents. 1. Reagent solution. Dissolve 40 g tartaric acid in approximately 200 ml water, add 50 g (40 ml) thioglycallic acid and 200 ml ammonia, (sp.gr. 0.880) and dilute to 1 litre with water. 2. Standard iron solution. (100 /ug/ml)! Dissolve 432 mg of ferric ammonium sulphate crystals in approximately 50 ml. water, add 5 ml concentrated HC1 (sp.gr. 1.18) and dilute to 500 ml with water. 3.Perchloric acid! 60 percent. (xiii) HC1 SOLUBLE IRON IN SOILS WD SEDIMENT. Pipette 1.0 ml aliquot of the supernatant extract obtained et Stage I in the HC1 soluble Cu test (page 284) into a 16 x 150 mm test tube and proceed as from step 5 in the total iron test. 291. (xiv) SOLUTUN OF SECONDARY IRON OXIDE IN SOILS AND DETERMINATION OF THE LIBERATED Fe, Cu AND Co.

Reference!. Aquilera end Jackson (1953). Procedure. 1. Weigh 1.0 g of sample into as 100 ml Pyrex centrifuge tube. 2. Add 40 ml citrate reagent.

3.Piece on water both and raise temperature to 80 to 90 degrees C. 4. Add dithionete reagent solution.

5.Stir constontly for 5 minutes on water both, and then occasionally for e further 10 minutes.

6. Add 10 ml setureted NeC1, mix end digest for one minute.

7. Centrifuge for 5 minutes at 2,200 revolutions per minute and decent supernatant liquid.

8. Repeat total procedure on the residue, end combine the supernatent liquid with thet derived in 7. 9.Wash residue from 8 once with citrete reagent and combine liquid with 7. Meesure the volume of this liquid. 10.Pipette 10 ml of the supernatant liquid into a 50 ml beaker end eveparete to dryness. add 2 ml concentrated HNO end 1 ml. percent 3, 2 ml concentrated H2SO4 6o perchloric acid end reflux under watch gloss until all the residues ore in solution. Remove watch gloss end fume to dryness. 11.Dissolve residues in 10 ml 0.5N HC1 end determine the iron by the totel iron method. 12.Dry the residues from 9 end determine Cu and Co. Copper and cobalt associated with free iron oxides are calculated by subtraction from the total metal content determined on the original sample. The exCu content of the originel sample is removed with the free iron oxides. Therefore, the exCu value is subtracted from the total Cu of the original sample prior to subtraction of Cu-"Jot.

292. Reagents.

1. Citrate reagents Dissolve 75 g tribesic sodium citrate in 900 ml water. 4dd 0.5M citric acid until the solution is pH 7.3 es measured by e pH meter. Dilute to 1 litre. 2.Dithioncte reagent% For each sample treatment, dissolve 1.0 g Na2S20A in 5 ml we-ter end adjust to pH 7.3 by means of freEhly prepared 10 percent NaOH solution.

3. Setureted NaCi. (xv) TOTAL DISSOLVED MET BLS IN N!'.TURAL

Procedure. 1. One litre of wetter filtered at the sample site is stored in a Pyrex container. 2. Shake vigorously for 5 minutes to redisperse any precipitate end then transfer to a 1 litre Pyrex beaker. Add 2 ml concentrated HoSOn end evaporate to approximately 50 ml under 0 Pyre wFtch gloss. The HoSO4 prevents "tide marks" forming on the sides of the Beaker.

3. Transfer with repeated washings to e 100 ml Pyrex beaker and evaporate to fuming under c Pyrex watch glees. end 1 ml 60 percent 4. Add 2 ml concentrated H2SO4 HC104 end reflux under Pyrex watch glass until all residues are in solution. Remove watch glass end fume to dryness.

5. Pidd 5 ml 0.5N HC1 end reflux under watch glass until ell residues ere in solution.

6. Trosnfer with successive washings of 0.5N HC1 to a test tube end make up to 10 ml with 0.5N HC1. 7.Pipette eliquots from the test tube for determination of Cu, Co, Ni, Zn and Fe by the previously described methods. 8.Do a bleak determination.

(xvi) SOLVENT EXTRACTION TECHNI(UE FOR IONIC Cu, Co, Ni, Zn end Fe IN NATURAL W4TERS. Reference% Aleskovskij, Libine end. Miller (1959). 293. Procedure.

1. Filter 1. litre of water et the sempLe site and transfer to o 2 litre seporating funnel. The pH of the water must be between 3.0 and 9.0. If not, odjust with HCI or NeOH.

2. Add 3 ml 3 percent sodium diethyldithi.3c:_rboratc in water solution, and 15 ml CC14 and shake vigorously for 5 minutes.

3. Allow solvent phase to separate and run it into a 18 x 180 mm Pyrex test tube.

4. Repeat step 3 and combine the solvent phases. Cork the tube. Note: Ionic metals from surface waters in the Kilembe area were removed by two extractions. Ionic metals from ground-waters required up to five extractions. The extroctions were continued until the solvent phase was colourless.

5. Trasnfer organic phase to a 50 ml Pyrex beaker and evaporate to dryness under El Pyrex watch glass.

6. Add 2 ml concentrated H2SO4 end 1 ml 60 percent HC104 end proceed as from step 4 for total dissolved metalg. Experimental determinations carried out on 6. synthetic solution. 8 /ug Cu and Ni, and 4 /ug Zn and 4.8 ug Co were added to 1. litre of water. The solvent phases from one, two end three extroctions were evaporated and analysed. The results are given in Table 63. Number of extractions: Cu Imb: Ni ppb? Co pPb: Zn pub,

One 6.0 7.6 4.8 t;.' Two 8.0 7.2 4.8 4.0 Three 8.0 8.0 4.8 4.0 Blank 0.0 0.0 0.0 0.0. Table 63 . Solvent extractions of Cu, Co, Ni and Zn from synthetic solutions.

One extraction removed ell the cobalt and zinc. Complete extraction of copper required two treatments. Nickel extraction was not constant, but 90 percent of the metal is removed by two extractions, and this was considered sufficient for the actual concentrations occurring in the Kilembe area waters.

294 To test the reproducibility of the method on natural waters from the Kilembe area, 5 duplicate water samples. were treated to 2 extractions each. ¶1 results are presented in Table 64. Sample No! Cu ppb? Co ppb. Ni ppbt Zn ppb! Fe ppb, 1 7.5 0.5 0.5 5.0 30C 6.5 0.5 0.5 4.0 300 2 6.5 0.9 0.5 4.5 280 7.0 0.8 0.5 4.0 300 3 7.5 1.2 1.5 6.0 480 7.0 1.3 2.0 6.5 500 4 2.5 0.5 0.5 6.0 250 2.5 0.5 0.5 4..5 180 5 2.5 0.5 0.5 3.5 200 2.5 0.5 0.5 3.5 300 Table 64 . Solvent extraction on duplicate water samples. The repraducability of determinations was considered satisfactory and this method was used throughout the investigations. (xvii) EXTR1CTION OF IONIC COPPER FROM WATER BY ION =HINGE RESINS. Reference! Rainwater & Thatcher (1960). Prior to the use of the solvent extraction technique, the writer experimented with cation resin. Synthetic solutions containing 1,000 and 4 ppb Cu were passed through 10 ml of resin in a polythene column nine inches long, at a rate of 1 litre per 2 hours. The resin was pre-scrubbed with 2NHC1 until all the iron was removed and then the HC1 was removed from the resin with successive washings with water. The resins were eluted with 1C ml N HC1 by shaking for 5 minutes. The resin containing 1,000 /ug Cu yielded 7.5 to 9.5 /ugCu in each of 4 successive elutions. The resin containing 4 /ug Cu yielded 1.5, 1.35 and 0.2 /ug Cu in 3 successive elutions. Three water samples collected from the Yvette tributary in 1960 were passed through resin columns and eluted once with 10 ml N HC1. The same 3 water samples were analysed by the solvent extraction technique. Five 295. months later, and in 1961, water from the same sites were onolysed in the field by the solvent extrection method. The results ore presented in Table 65.

Cu by solvent Cu by solvent extrection extraction Cu by resin efter on semple Site. 19601 5 months! site, 1961. Lower Yvette 0.9 6.o 7.5 Middle Yvette 0.7 4.5 6.5 Upper Yvette 1.0 5.0 7.25 Table 65. Comparison of solvent extraction end resin extrection for copper. These results indicate the superiority of the solvent extrection technique compared to the resin extraction technique used by the writer. In view of the efficiency of the solvent extraction method, the writer mode no further investications into the improvement of the resin method. (xviii) SULPHATE DETERMIN.ITIONS. A. Resin-acid salt method. Reference! Scott, 1950.

Procedure. 1. Scrub resin four times with acid-salt solution. 2. Remove acid-salt solution from resin by repeated washings with water. 3.Pass 1 litre of neturel filtered water through 10 ml resin et c rate of 1 litre per hour, end leave resin to drein. 4.mix 10 ml acid-salt solution with 10 ml water end wash the resin into e stoppered cylinder with this solution. 5.Shake vigorously for 10 minutes end filter off the solution. 6.Plsce 10 ml of this solution in e test tube (18 x 180 mm) celibreted et 20 end 25 ml.

296. 7. Add 5 ml of acid-salt solution from a polythene wash bottle. 8. ,Aidd 250 mg of barium chloride crystals (dihydrste Analar) using al scoop. 9. Shake for 30 seconds. 10. Compare the turbidity with standards against c &Ark background. Preparation of standards. 1. To 12 test tubes (18 x 180 mm, calibrated st 20 and 25 ml) odd respectively 0, 0.0, 0.1, C.2, 0.3, 0.4, 0.5, C.75, 1.0, 1.25, 1.5 and 2.0 mg of SO4. 2. ;dd 1 ml of gum acacia solution. 3.Dilute to. 20 ml with water. 4. ridd 5 ml of acid-salt solution. 5. Pidd 250 mg of barium chloride crystals (dihydrate). 6.Cork the tubes and shake for about 30 seconds to dissolve crystals. Reagents. 1. acid-salt solutions Dissolve 240 g of sodium chloride in 900 ml of water, add 2C ml of hydrochloric acid (sp.gr. 1.18) and dilute to 1 litre with water. 2. Barium chloride: Dihydrote. 3.Gum acacia solution, Dissolve 10 g in 100 ml of water (boiling) snd filter through a No. 41 Whatmon paper when cold. 4.Standard sulphate solutions Dissolve 907 mg of potassium sulphate in water and dilute to 1 litre to give a solution containing 0.5 mg of SO4 per ml.

5.Resin, De-cidite F.F.

B. Visual Thorin method. Reference; flainwater & Thatcher (1960) Procedure. 1. Rinse the ion exchange column with 20 to 30 ml of the 297. filtered water sample.

2.Foss 25 to 3C ml of filtered water samples through exchange column and collect the effluent.

3.Pipette a volume of effluent containing less than 25 mg sulphate (25.00 ml maximum) into a 15C ml beaker and adjust the volume to approximately 25 ml. The dissolved solids content should not exceed 125 mg far the high-range titration or 50 mg for the low-range.

4. Adjust the pH to between 2.2 and 5.0 with 0.05N NaOH if necessary. 5.:.dd 50 ml. dioxane. 6. Add 1.0 ml thorin indicator.

7. Titrate with BoC1 to the point where the colour changes suddenly from yellow to orange when viewed through a filter. On titrating sulphate concentrations of less than 10 ppm, the end point will appear and then fade on stirring. At the true end point the colour persists for several minutes.

8. Calculations. (a)For concentrations of less than 5.0 mg, prepare a graph by titmting standards with BaC12, 1.00 mi=17 7=0.50 mg sulphate using 0.04 percent thorin x ppm sulphate = 1. 1,000X mg sulphate. density ml sample

(b)When &ICI 1,000 ml 1.00 mg sulphate and 0.1 percent2' thorin indicator is used; 1, 000 ppm sulphate = 1 X ml BnC12. density ml sample Reagents and apparotus. 1. Ion exchange columns, 10 inches long and charged with. approximately 10 ml Of Amberlite IR-120 resin. Resin is regenerated with 30 percent HCl after 3 to 4 posses. 2.Pale blue didymium filter or glass blower's goggles. 3, Titration assembly with a white porcelain base and fluorescent light. 298. 4.0.05N NOOH. Dissolve 1.995 g NoOH in 1 litre of water. 5.Thorin indicator 0.04 percent. Thorin indicator 0.1 percent. 6.1.4 dioxene. 7. BaC1,), 1.00 0.500 mg sul?hate! Dissolve 1.273 g BaC12 in 1 litre of we-ter. BaC12, 1.00 _77_ 1.00 mg sulphetel Dissolve 2.499 g BaC12 in 1 litre of water. (xix) SPECTROGRAPHIC UTALYSES.

The samples were analysed for the writer by the spectrographic laboratory of the GeochemicaL Prospecting Research Centre, London. The ignited sample was crushed end mixed in the ratio 11 1 with carbon, and loaded into a 3.2 x 5.0 x 4.8 mm external diameter crater. The alkalis were arced for 90 seconds end the general metals to completion at 9 amps D.C. The anode layer wes examined. (xx)rEASUREKENT OF ."?..ATE OF FLOW OF SURFACE WATER. The width and overage depth of streams were measured with o tape, and the volume celcULated from these measurements. The velocity was obtained by measuring, to the nearest second, the time taken for a. standard size cork to float a measured distance. The rate of flow was calculated from the velocity and volume. In the upper reaches of tributaries, the rate of flow was obtained by channelling the stream into 1 litre container and measuring the time required to fill the container..

299. CALCULATION OF S,:.TURATION CONCENTRATIONS OF COPPER AID IRON.

*Abbreviated instructions for calculating the saturation concentrations of copper in natural waters, (After Silman, 1958). Refer to Figure 27. Procedure.

1.1rieasurethepRvallle,SO4 andNaliC-00 concentrat ions of the sample.

2. Calculate the NaH(10- 3 concentrations (x mg/litre) as a molarity, x 10- 3 84 3. Assume M-NaHCO-= aH003- 4, In this case = a - CO 2 HCO3 5e With logz-L. and the pH value interpolate log acu .00e::=- 2 6e Cenvert molarity to tug/litre.

Notes. (a)At low concentrations, activity is assumed to be equal to concentration (Silman).

(b)The observed SO4- concentrations in the Kilembe area waters range from 2,4 to 4,0 ppm. :. -5 As (1) a SO4 activity of 10 H = 0.96 mg/litre, _4 and(ii) a SC 4= c.otil;dty of 10 M = 9.6 mg/litre, -5 the sulphate acvity of 10 N was assumed for a calculations * These Instructions were provided by Mr. R.E. Stanton (G.P.R.C.), who also calculated the saturation concentrations of copper, quoted in this thesis, from data provided by the writer. Mr. Stanton's. help gratefully acknowledged.

300- Abbreviated instructions for calculating- (a)the valence of iron, (b)the saturation concentration of ferrous iron, (c)the Eh, in natural waters. After Hem & Cropper, 1959, and Hem, 1960. Refer to Figures 28 end 29. Procedure. 1. Measure the pH and Eh values and the ionic iron and bicarbonate concentrations in the sample. 2. By interpolating the pH and Eh data in Figure 28 determine whether iron occurs in predominantly the ferric or ferrous forms. 3. (a) If iron occurs in the ferric form, the maximum solubility is less than 10 ppb Fe at a pH greater than 5.0. (b) If iron occurs in the ferrous form, Figure 29B Is used to interpolate the calculated theoretical saturation concentrations from the pH and Eh values. 4. The Eh of a solution is determined from Figure 29A by interpolating the pH, ferrous iron and bicarbonate data. Note: (i) If the pH and ferrous iron plot falls to the right of the observed bicarbonate concentration, the solution is supersaturated with respect to iron, and the Eh of the solution cannot be determined. (ii)If the pH and ferrous iron plot falls to the left of the observed bicarbonate concentration, the Eh of the solution can be determined. (iii)If the calculated Eh is within - 60 m.v. of the observed value, the solution is considered to be in equilibrium with respect to pH, Eh, ferrous iron and bicarbonate.

301.

Pb Sn Gs Be Mo V Ti Ag Zr Cr

Anomalous Semple No. 1400 (Heedweters Yvette tributory)!. 8 n.d 10 n.d. n.d. 120 4,000 n.d. 320 90 Anomalous Semple No. 1313 (Lower reaches Yvette tributary)? 15 n.d. 10 n.d. n.d. 120 5,000 n.d. n.d. 160 Anomalous Semple No. 1385 (Headweters of e minor tributary in the Kiteberole stream' 18 n.d. 10 n.d. n.d. 160 6,000 n.d. 600 160 Anomalous Semple Nn. 1210 (Lower reaches of Kiteberole stream) 20 n.d. 15 n.d. n.d. 150 4,000 n.d. 100 180 Anomalous Semple No. 1270 (Lower renches Muchingire tributary); 15 n.d. 15 n.d. n.d. 120 4,000 n.d. 80 130 Anomalous Semple No. 1350 (Hesdweters Ketundu tributary)! 8 n.d. 10 n.d. n.d. 130 8,000 n.d. 1,000 120 Background Semple No. 1310 (Dungelee River upstream from Yvette tributery)T 20 n.d. 8 n.d. n.d. 120 5,000 n.d. n.d. 100 Anomalous Sample No. 11 (Dungelea River downstream from Katundu tributary T 40 n.d. 15 n.d. n.d. 200 8,000 n.d. n.d. 180 Background Semple No. 143 (Lower renches Brenda tribute/7)T 18 n.d. 10 n.d. n.d. 320 10,000 n.d. 1,000 320 Background Semple . 1564 (Lower reaches Chenjojo tributary)! n.d. n.d. 6 n.d. n.d. 160 5,000 n.d. 1,600 180 Limits of detection less than! 8 18 2 10 10 15 100 1 100 10

Table No. 44. Spectrographic analyses of stream sediments from the Kilembe area. 302

Li Rb Bs Sr Ne20(%) Y0(%)

Anomalous Semple No. 1400 (Headwaters Yvette tributary): 15 120 280 80 0.2 1.0 Anomalous Semple No. 1313 (Lower reaches Yvette tributary)! 6o 300 350 80 0.25 >1.6 Anomalous Semple No. 1321 (Headwaters of e minor tributary in the Kiteberole stream): 70 200 320 120 0.5 1.2 Anomalous Sample No. 1210 (Lower reaches Kitebarole stream): 50 300 280 80 0,8 1.6 Anomalous Sample No. 1270 (Lower reaches Muchingire tributory)! 50 600 320 90 0.25 1.6 Anomalous Semple No. 1152 (Headwaters Ketundu tributary)! 40 250 600 200 >1.6 1.6 Background Sample No. 1310 (Dungelea River upstream from Yvette tributary): 15 120 350 140 1.2 1.6 Anomelous Sample No. 11 (Dungelee River downstream from Ketundu tributary): 30 250 400 140 1.5 >1.6 Background Semple No. 1433 (Lower reaches Brenda tributary): 12 120 150 25 0.2 0.9 Background Sample No. 1564 (Lower reaches Chenjojo tributery)t 12 100 350 110 0.8 1.6 Limits of detection less then!

1 100 - 8 3

Teble No. 45. Spectrographic analyses of stream sediments from the Kilembe orea. 303. LIST OF REFERENCES. Aleskovskij, V.B. Concentration end determination of Libine, R.I, micro elements in neturel waters. and In. Geochemicel Prospecting for Ore Miller, tI.D. Deposits in U.S.S.R. 1959. Editor V.I. Kresnikov. Trensleted by University of Alabama, 1959.

Almond, Hy. Rapid field end laboratory method for 1955. the determinetion of copper in soil end rocks. U.S.G.S. Bull. 1036-A. Aquilere, N.H. Iron oxide removel from soils and clays. Jackson, M.L. Soil Sc. Soc. Am. V.17. 1953 Atkinson, D.J. Heavy metal concentrations in streams 1957 in North Angola. Econ. Geol. V. 52. Bird, H.H. Stratigraphical classification of the 1960 Kilembe Series, Kilembe Mines Ltd., Geology Depertment. Memorandum No. 268. Unpublished. Bloom, H. U.S.G.S. open file report. Crowe, H.E. 1953 Boyoucous, G.T. Method for making analysis of the 1935 ultimate natural structure of soils. Soil Sc. V.40. Brown, J.M. Ruwenzori Expedition. A brief 1956 analysis of gravity values. Uganda Geol. Survey Report. British Stenderds, Methods of testing welter used in 1956 Industry. B.S. 2690. Britton, H.T.S. Hydrogen ions. 1942 London, Chspmen & Hell Ltd. Cerrol, P. Role of clay minerals in the 1958 transportation of iron. Geochim. et Cosmochim. V.14. 304. Cher, M. The Kinetics of the oxygenation of ferrous iron in phosphoric acid solution Devidson, N. Am. Chem. Soc. Jour. V.77. 1955

Combe, A.D. The copper deposits of Kilembe, 1933 Ugende Geol. Survey Report. Combe, A.D. Summery of work cerried out by 1944 Combe during 1933. Ugende Geol. Survey Report. Craven, C.A.V. Stetisticel estimation of eccurecy 1953 of essaying. Trens. Inst. Min and Metall. London. Davies, K.A. The Geology end Mineral Deposits of Uganda. Bisset, C.B. Ugende Geol. Survey Bull. 1947 Ra inwater, F. H. Methods of collection of snelysis That cher, L. L. of water semples. 1960. Water Supply Peper 1454.

Gsrrels, Miners1 species es functions of 1954 pH end Eh. cts. Geochim. et Cosmochim. V.5.

Ginzburg, I.I. Principles of Geochemicel Prospecting. 1960 Pf;2gamon Press. Gladstone, Physical Chemistry. 1947 Govett, G.S. Geochemicel Prospecting for copper in 1958 N. Rhodesian Copperbelt. PhD. Thesis. University of London. Grimley, P.H. Kilembe Copper—cobelt deposits, 1958 Ugende. PhD. Thesis. London University.

Harden, G. Geochemicel dispersion patterns 1962 end their reletion to bedrock geology in the Nyewe Free, N. Rhodesia. p14121 Hewkes, H.E. Geochemicel prospecting in the 1952 Blackbird District. Ideho Geol. Soc. Am. Bull. V.63 305 Hewkes, H.E. Principles of Geochemicel Prospecting. 1957 U.S.G.S. Bull. 1000 F. Hem, J.D. Study end interpretation of chemical 1959 characteristics of neturel water. U.S.G.S.. Weter Supply Paper 1473. Hem, J.D. Survey of Ferrous-Ferric Chemical & . Equilibria end Redox Potentials Cropper, W.H. U.S.G.S. Water Supply Paper 1959 1459-A. Hem, JD. Restraints on dissolved ferrous iron, 1960 e. imposed by bicarbonate, redox potential and pH. U.S.G.S. Water Supply Paper 1459-B. Hem, J.D. Co-precipitation effects in solutions 1960 b. containing ferrous, ferric end cupric ions. U.S.G.S. Water Supply Paper 1459-E.

Hem, J.D. Complexes of ferrous iron with 1960 c. tannic acid. U.S.G.S. Water Supply Paper 1459-D. Hem, J.D. Some chemical relationships among 1960 d. Sulphur Species and dissolved ferrous iron. U.S.G.S. Water Supply Paper 1459-C.

Hess, H.H. Notes on operation of the Frantz 1956 Isodynemic Separator. Princetown University. Holman, R.H.C. Geochemicel prospecting studies in the 1956 e. Kilembe area. Uganda Pert I. Dispersion of copper in the drainage system. G.P.R.C., Imperial College, London. Tech. Comm. No. 9. Holman, R.H.C. A method for determining soluble copper 1956 b. in soils end alluvium introducing white spirit es e solvent for dithizone. Trans. Inst. Min. Metall. London. Huff, I.C. Pers. Comm. to Hewkes, 1957. 1947 U.S.G.S. Bull. 1000-P. Huff, I.C. A sensitive field test for heavy metels 1948 in water. Ec. Geol. Vol. 43. 306. Huff, I.C. Pers. Comm. to Hawkes, 1957, 1954 U.S.G.S. Bull. 1000—F. Jacobson, J.D. Geochemicel prospecting studies in the 1956 Kilembe fres. Pert II. Dispersion of copper in the soil. G.P.R.C., Imperial College, Londona Tech. Comm. No: 6. Jay, J.R. Geochemicsl prospecting studies for 1959 cobalt end uranium in N. Rhodesia. Ph.D. Thesis, University of London. Johnson, R.L. Notes on the geology of the Ruwenzoris. 1952 Ugsnds Geol. Survey Report. Kerbyson, D. Application of spectrogrephy to the 1960 study of secondary geochemicsl dispersion patterns related to mineral deposits in Africe and the Far East. Phil). Thesis. University of London. Krancks, S. Some rapid methods of determination of 1957 trace elements in soils end natural waters. M.Sc. Thesis. University of London. Kuenen, Ph.H. Experimental abrasion. 1959 Amer. Jour. Sc. 257 (3).

Maliugo, D.P. On soils end plants es prospecting 1947 indicators for metals (U.S.S.R). Neuk. Inc Ser. Geol. No. 3. Mathews, P.E. Geological traverses on the southern 1951 part of Ruwenzori. Uganda Geol. Survey Report.

McConnell. R.B. Outline of the geology of the 1958 e. Ruwenzori Mountains. Overseas Geological Surveys. McConnell, R.B. The Buganda Group, Uganda, East Africa. 1959 b. Geological Congress, Mexico, 1956. Mohr, E.C.J. The soils of Equatorial Regions. 1938 Piper, C.S. Soil end plant snolysis. 1950 White Inst. Monograph. 307. Renkeme, G. Geochemistry. University of Chicago Press. Scheme, Th.G. 1950 Rai wai-er Mole hcir Sae P 30.S" Reiche, P. 4 survey of weathering processes 1950 end products. New Mexico University Pub. in Geology. G. P.1,730/ Riley. 5.CD L P-10m. V.9. Scott, N.W. Stands/id methods of Chemical 4nslyses. 1950 The Technics]. Press, London, 5th Edition. Silmen, J.F.B. The stabilities of some copper minerals 1958 in aqueous solutions. Ph.D. Thesis. Harvard University.

Simmons, W.C. Petrology of Kilembe Copper Deposits. Uganda Geol. Survey Bull. Herwood, H.F. 1935 Spurr, J.E. The. Ore Msgmss 1923 Vol. 1. Stanton, R.E. Modified field test for the determination of small amounts of Coope, J.A. nickel in soils end rocks. 1958 Trans. Inst. Min. and Metell. London. Tooms, J.S. Geochemicel dispersion related to 1955 mineralization in N. Rhodesia. Ph.D. Thesis, University of London. Werren, Geochemicel prospecting finds widespread epplicetion in British Deleveult, R.E. Columbie. 1953 Min. Eng. V.5. Weylend, E.J. Geol. Survey, Ugende, Annual 1933 Report. Webb, J.S. Heevy metels in neturel waters es e guide to Ore. 4.P. Inst. Min. Metall. Bull No. 518. 1950 Webb, J.S. Observations on Geochemicel Exploration 1958 in Tropics]. Terrains. Geol. Congress, Mexico, 1956.

308.

Westell, R.G. Geology of the Kilembe Mine Area, 1958 Ruwenzori Mountains. M.Sc. Thesis. University of Natal.

White, M.L. The occurrence of zinc in soil. 1957 Economic Geology 52.

309.

3 3 .

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PIT 205/0 PIT 20511E PIT 20 512E PIT 10510

PPM PPM , PPM, PPM awC(.1 20 40 6o So GCVO 60 SO 0x0110 20 40 60 10 G.Lo o 20 40 GxCu 0 Co Cx Co 0 04f. , I Cf4 0 I 5.9 8.7 A 9.2 i - A r ' .--.1...1 - A 4.4 .4.4 I 5.° 5.4 fj z'_ r.__ --. 1 2' -.— 3.6 C 2-7 B 1 2.7 2.7 3' - B - I— • ..1, - .3' _ ,cxcu Cu fj f 2.8 3.1 pn,u1 Cu 2.3 2.1 4' 4' I 4'

Cu 0 400 500 1200 1500 VooPPM CO o 10 6:00 1200 PPM Cu o 400 900 1200 PPM 1. 9 S' - I.6 (0)

1. 6 7' 0.5

Cu 0.4

0.5"

0• 4

0.1 12'

Cu 400,, 400 am 1100 1000 z400 PPM

(d)

FIGURE 4-

METAL LONTENT OF FIGURE METAL CONTENT OF MARGINAL GRADE MINERALIZATION Su8 - ECONOMIC GRADE SOIL PROFILE MINERALIZATION 50IL PROFILE (a) (b) Co Zn. Co, Ni, Zn. - 1 I T T 1 I I I 0 zoo 600 goo 0 (0 0 200 300

A3 L -

2' - .`.03 3.- 3' -

m/y . r J .....• . • - • t Y 6' .-.-g•-•••••••• :t 6' o I I

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• 10' - 1r' -

12' - L 13' -

14'- I F; 1S' - CO AP/ Cu 16' - 16' - Is )7' — o woo lode 30oe .1eoe Soon 6 oee 7coo SeOe 9oao LL I I 181 - Cu potr,

o moo 2000 3000 60 PPM 100 200 300 4.1 SCO 600 L

PIT P6

/- • • • ... -• ... ,.. , 1 - ....-.. / : i ‘...... _. ...- r- .::".... L.

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PIT P7

D/S TRIM/7701V OF C C ,CIPER TA'ar. SOIL PROF,LA-S

After J. D. Jacobson/ 1956. F/GURE Cu, wan, Co NI ANOMALIES ,IN SOILS OVER THE BOKANGAMA RIDGE

Zoo r 100

Chromoogrelphic tfo • ,So method (ea mash) t „ invi too z. loo 1- --\ i•-•\ i N, I %t .1 1 I \ 515 „i \ so I 4 so

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1204

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80o — TOPOGRAPHICAL. AND GEOLOGICAL SECTIONS

t 400 •

After Jacobson (Im)

FIGURE 7

D is I ri,u 11on of Gu, Cot Wand Zn In 3 horizo n 50115. Pia grade Mineralization - PPM

6000

5000

4000

- 3000

- 2 ooe

- 1000

- 90o

_ Soo

Toe

- 600

Soo

- 40o

_300

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FIGURE 8 •

i 5 tr I 0 ,j 0 nci if) I i is

Pa rginai Ore grade blirmralization PPM S000

- 4000

3000

2000

/000

900

Boo

loo

- 600

- 500

_ 400

300

_too

s' /00

• - 70 Zn ..,••••• _ 60

_ 5o

_ 40

•••co - 30

,- /0 rootwall an9trIss,,,11.4

Feet o Z000

F/GURE FIGURE 10 Plstriloution of G,LaiCoi Wicar+d Zn in B horizon soils,

Sub- Economic mineralization

ppm — 30oe

2000

— 1000

—9o0

— 800

— 700

—60o

Soo

—400

—3eo

..... cu —/eo

—90 . / 1 • :/ — So

1 • —7o — 6o •1/4 • •/ —50 *"... —4a •-• ...... —30

—20

—10 IrtancS,nswoll Fool wall 0 Fact co lase 3es. Sample N° /6O2 -6- Sample No 1388-9 Anomalous 5011 Ano,tolous Soil P. P.M. P P.M. 800 - 800 -

700 - 700 Pr

PP Cu 600 - "60 60 0" 60

500 - 50 500" SOZ

cu ti 400 r — -401 4.00" Ic

300 30 ;...4 300 -

200 20 ° _r_F1 200 " -20 it pm co /00 r 10 /00 /0

—J O wa,914 8.0 /0.0 /1.0 1/.5 • 30.4 28.1 % 2.3 ILO 1S.6 I* 3 8.0 /a.s 30.1 7 weight 14—soncl---+14—slit-114--e107—)1 14---sortel so —.Qs Mk— So ...ash

.5ampie Af° /250-8 Local 'Bo'cli5rownd 500 so r— 400 DISTRIBUTION OF Cu Ortol CO co 40 ti SIZji FRAcTIONS o F ANOMALOUS tl 300 30 SOILS. and LOCAL e AC K GROUND li 300 20 (MtPJUS 20 P4 , 314)

100 10

8.0 /4.0 /SO 18.5 J7. 5 „.. yo,.„.1hr 14---- SO"C1----t• I i t e171 1.4"— —80 h )t FIGURE II Sample N° /596 - 9 Sample N° 1566 -76 t! • So ckr- ound Soil ___%Co Background Soil — ti °/,5 Co ti MO - - 70 MO r •e

120 " 60 120 40

PS Cu 100 I I.. so too SO

1124 NN a 40 Ls) $0 I- 40 I en Cu

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DISTRIBUTION OF cu. and Go

IN SIZE FRACTIONS OF BAC-Kt4 k0J1s/D

SOI L5 (MINUS 20 ME"

FIGURER

4- 4- -f- + 4- + + + + +- + + + + + + + ++++++ NEI 5a + + ?

LOWER

+ j •••• - r— K t L.cm3E.- srziroc.:?— r' ? a. mt-pDLr.

,/ ER 1E3

GE0s-OGy Or THE GuKANCAMA AREA Dungoka+ 1 !JPPER K ILE ri SUPOP:01.5 4- ÷ 11- + + + t 7/::=1 ix( / .4,4E15.5 4- + + + t + ileTbc series "t" + + + + + and L_ Groni} Sad roas + + + + + + FIGURE /3 4+ 41+ +++-tt 5c0142:, 1:15:000

2228

% '1. % % % % \ % \ I \ >200 p r ..., cm 1 2237 ,, 4,200 pf ^`CI-1 22.43

/7, 31

• • 1\

• 1210

1' 5' 50q 511 tr ir;) 0 •4‘ yva-e-tar' 5 10 .2213 6'1'5 Xe 0° 1.4° s-5 01 2172 %6X • -.. • . r r \ 5tr r r ss • r , S Much / __•.__ ---- : ,

♦ 3 • 2284 0 2. „ss.

/ ....."-- -,______cr GEOCHEtitCAL SOIL. -147•77.., Sr 230e (ANOMALIES IN THE Gui200 epo.1 Cu 1.0 IC O . Surface. %deter - Sample. Si t¢ 3 7 Ground weier 0 . I sornple site it FIGURE /4 2529 025'28 I Scale:- 1:15,000.....

PPb PP b

12 _ K TOTAL. ZINC • -12. WATE.R - IONIC 2.11.1C • X -it . . • I . • le • -la . • ...... _ . X • _ . 7 ..., -....„ 7. / ' TOTAL, / • 6 .....\ i \ \ • S - , \ / / _ _,A / --- I / • r..., ___ —..... • _ \ ../ \ / ''`.. •X • / \ / 4 - \-- ' / ...X. ----- ...-"' --.._ - \ / 'N.,/ V T11,-- ..... / • -4 1 le. • / —' \ 14‘5'..--. .."--../ k - V ....--- • X It X it

PPb

TOT At. NICKEL • WATER . 1.0,41C MICKLL, X - X 4 . .. . pm • • TovAL Ni 2 • xitx -- • x `sag Zoodtc Ni .., - — -X__ —_------X...... / \ — — K •X - // \ e — — — .... —

PPb -14 14 . . • TOTAL CoTPER • WAT EA 1 \ IONIC CoCop a X 12 - i 1

- le •

• -9 • . 8 --. IC 7 / , - / / • /

- S SC • . I • - 4- Tec••%. Cu ...-..s. / 3 - N IIC • --- ....,... — — — — - .-- x• ------2. - . X - . .04. Cu Set. . _ . - .

FIGURE . . I V ( For k ey refer to F.r 5 23) WICROINHOS PER C M 3 0 * V v F I fl- • 0 0 • ___ _. y

Th ,.. i. • .! i . . „..... 1 .--- - . • . ,

_ , , _ 2 _! _

T I O ONI • TA C L . IR p 1 H R •

ot4 • ON WA _____------x •

1 TER w ATER Th- •

- - - - -

• I

\ ( \------, ------._ , \ •

111 • • • 0. • • • 'It • • • r 1 II l i l l 11 1 . 1 1 1 1 11 1 ( 'I l rl 'i l l i i i l l

ii f e° ::. Le i W if IV f t if I I *Pr i r t r g' '6' ce e g 8 6-' r r $s r v r M/CROMHO$ /PER Clitl„, , "1-: • m V

16 0 — rn v Eh WATER • -,G0 • • . -130 ) .:. • • • - 140 130r — • • • • .. Ile • • is. ., i Us Ile -. - Ile . • I • leo 90 ... - 96 8o -So 70 - 7o Co -Go So -So 46 -40 3o - • -50 Zo

- 7.0 to -lo O -O 10 • . ie

P PA 140 PPM B 'CAR : °HATE WATER --140 13o • -13o 12e .12.0 11 0 m. so • toe • ,-100 90 - 1-90 80 • . -Bo 7e . • -70 Co -60 So • - • -So 4o -.... • • • h4° .341 . • . • --L—. • • • -30 20, ..---'------. • - 2.0 • 'N%•...,...... to • -10 G .- 0 FIGURE 20 (For key racer 4o Fi Q 2 3 ) J

PPM

PPM SS.o•o IRO,* SUWALKI 000 • • -45 Goo • • -40 000

• 000 • • • 54... • -2,Z iloto

• • '-20•.• 2.0 coo -

.17000 ▪ .•. - IRON SIMIMENT 000 IS Soo 000 IS... • • 11 bee II etso _ • • • • • Ooo 90.0 7•.e ▪ oOgo • • • E.•0 too - • • • 3

3000 • • '000 1008

100e _ • MAt4GAI4ESE SEDIMENT -goo 900 _ • • Soo . •

700 •

• • • Soo • •

Soo • -4.o 4.e

Sae

300

- leo Toe HO MANGANESE SEDIMLNT

Geo • - soo Soo • - 400 400 - •

Soo — • • • • loo Zoo • - leo leo . F )(JURE 21 (For- key rafev- 23) PPM ZINC SLDIMLNT • -116 _".. wIt. . ...• • • . • • .. v. . . • • _ eo

_ • • • • • • •• • • . ao • • • • • • • • • • -a. • -2.

MicKii. SEDIMENT • •

• -,• - a. -,o • • . . • • • • . . • • . • • . • . • • • • • • • • • • .... • ...... • • - • . . • • •

COBALT SLIM bill„wr . . • •

• • • • • • • • • • • • . • -

FIGURE22 (For k ey refer F,5.23)

Travarsa in Trcvcr$s ;n DLINGALfA STREAM yVErrE sraram

Ilwirbon +On with IyatteStraeml Out75040 kIJin stream °,554:1r. FJaw

311fo dw are. 140 .fee Mn coo

‹../spar PIM II ; 1 3.. I :1. . : • I • ; \ I I Zoo I ,.—„ i . \ ,A I\ \ ..-i•c*gra..,4, . I \•/\--, i•----: \ \I El! • Total Copper in Bank-Sails (-0.3 mm roctron)

i\ i i\r\,, . /% i ---= • \- I `,'., 1 r.d.,,,..1 .,. ,...,,---" ------./ til s,dir rota/ Coppar in Sseliments /N, V i. 1 (-o.3 MM. fractt0r1) 1 I I 1 1 1 I 1 1 I 2.1_ I I /\ 1 I ae I I \/ I I • t_./ \ '"\,..-''. \ / N ----•/ 1 eack-frevilel Readily-Soli/bid Copper in Bank SoWt I (-0.3 mm. fraction)

I I 1 II 1 1 I 1 I I I 1 I 1 I Ze /1 II I 1 PO I I I I 841Wkisomm• •—•- 1=:: \/ Raseinty-Seluida C.ppdr in Seamants (-0.1 mm. fraction) 1 1 I 1 1 1 1 1 I 1 1 I* 1 1 1 lo 1 1 \ .1 ,-- &slily-Sahli/it Capps,. in Searnsnts ( Unsiaved

Capper Values in Ike Sedi..,e.,ts the yvetta Stream and Dungalea Rarer.

Aftsr .Jo/man, 19.11. FIGURE 24- BANK SOILS Cu and exCAA

r = 20 pps. Cu. jolly a: 10 Mom exCe4 . 0= XexCIA: CIA ••

Middia YVitit Lower yvette LoPier iffurchiattireg - Lower . leotuAdu - • At

'; 4-• ,76 e FIGURE. 25

N 14,

set 4.ro/ Xpurs• A to re/cij I 0) ei A pu it's< ',•..o...9 - Xi.rD "mod q 4ftner .( .:LT

O O .4t) I ® te, •ct 4 X tuevi 1 .1 eon tqc Ap"rs vnt tug ,07N/he p'j WrO/ /Cp. vs- ,A.oaq /96.! 7 /4 6.7

z n rolivsj ,Cpu es ..vro,. r 41' umo-19 -p7 ,y Seas NK BA (,;,.) C)

,„

, n

aa_

T I I 11 i I i 1 T I f f I f i ct 9. A :F4 N A gi A Section at a50: of I 0-5 s P% owins activities of dissolved copper os functions of pH and total coel:ionote. After 5 (mon, 1958

I 1 1 3 4 S 7 8 9 10 I 12 13 14 PH FIGURE 27 2oo

(ori) 3

Soho/ phase

f e+4.

Apeous phrsa.

0 5 6 7 9 PH

Stab;lily - field diagram for aqueous ferric - ferrous Sy stem

Aflcr kletr,4crappar 1959

FIGURE 28

A FIGURE29 o o After Fievn, lq&O o ft-o o .o HCO3 pion, 'cc -4 1 • ______. __ _

- .\\ • _ — • • • 1 i 1 1 Eh El. .. r \ \ ,,,\\ \\ •4v -2v \

/0 00 \ •. 1 it

•,__ • , I 1 boo s ... k I 111 E s i II .- Mk . >... t -0

11WVal -:7)n -4= V n 0 :6 In C to- 0 S. 11111 . - •/-v Iv ov 1 > 111 1 i 0 0.1 .6v :4 40 IR MIA 1/14 WiLIMMIL

1 0.0 1 /0 4 S 6 7 8 9 Pll Il 6 7 4 S 8 9 io Est;n-sot;ort of pH, Eh o‘nd Fe conterd• of ground pH Relation of fotol acttvity of iron, it water to po•Ei, water coektainin• Hc0-3