Geomicrobiological and geochemical investigation of the BCL mine waste tailings dam at Selebi-Phikwe

by

Axel Schippers & Michael Schwartz

Edited by H. Vogel & C. Chilume April 2005

Bundesanstalt für Geowissenschaften und Rohstoffe

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TABLE OF CONTENTS

Page ACKNOWLEDGEMENTS .......................................................................................... 1 1 SUMMARY ................................................................................................................ 1 2 INTRODUCTION ....................................................................................................... 2 3 THE BCL MINE WASTE TAILINGS DAM AT SELEBI-PHIKWE ................................. 3 3.1 Site description ........................................................................................................ 3 3.2 Tailings material ...................................................................................................... 5 3.3 Sampling .................................................................................................................. 5 4 MATERIALS AND METHODS ................................................................................... 9 4.1 Geochemical analysis .............................................................................................. 9 4.2 Geomicrobiological analysis ................................................................................... 9 4.3 Potential micro calorimetric pyrrhotite oxidation rate ............................................ 9 4.4 Pyrrhotite oxidation rate according to the humidity cell test ..................................10 5 RESULTS ..................................................................................................................10 5.1 Geochemical data ....................................................................................................10 5.2 Geomicrobiological data and pyrrhotite oxidation rate ...........................................10 6 DISCUSSION .............................................................................................................14 7 PREDICTION OF AMD FORMATION BASED ON HYDRO-CHEMICAL MODELLING...15 8 CONCLUSIONS .........................................................................................................19 9 RECOMMENDATIONS...............................................................................................20 10 REFERENCES ...........................................................................................................20 APPENDICES ............................................................................................................24 Appendix I: Geomicrobiological data of borehole samples .............................25 Appendix II: Geochemical data of borehole samples 1 .....................................26 Appendix III: Geochemical data of borehole samples 2 .....................................27 Appendix IV: Geochemical data of borehole samples 3 .....................................28 Appendix V: Geochemical data of borehole samples 4 .....................................29 Appendix VI: Geochemical data of borehole samples 5 .....................................30 Appendix VII: Pore size distribution ....................................................................31 Appendix VIII: Humidity cell test data ..................................................................32

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LIST OF FIGURES

Page Figure 1: Deposition of waste material on tailings dam ..................................................... 3 Figure 2: Sketch map of the tailings dam ........................................................................... 4 Figure 3: Acid mine drainage (AMD) from the tailings dump............................................ 4 Figure 4: Water flow sheet of the Selebi-Phikwe tailings dam .......................................... 5 Figure 5: Sampling of recently deposited tailings material................................................. 6 Figure 6: Weathered tailings material on tailings dam surface ........................................... 6 Figure 7: DGS drilling rig in operation on the tailings dump in November 2003 .............. 7 Figure 8: Removal of a drill core......................................................................................... 7 Figure 9: Sample recovery from a drill core........................................................................ 8 Figure 10: Surface sampling with steel sample rings .......................................................... 8 Figure 11: Depth profiles of pH, humidity, Stotal and total reduced inorganic sulphur ....... 12 Figure 12: Depth profiles of microorganisms and potential pyrrhotite oxidation rate........ 13 Figure 13: Annual net infiltration and annual seepage 15 years post closure ..................... 18 Figure 14: Calculated pore water residence time ............................................................... 18 Figure 15: Simulated acidity of seepage water ................................................................... 19 LIST OF TABLES Table 1: Mean values and standard deviation of geochemical parameters. ....................... 11 Table 2: Mean values and standard deviation of microbiological parameters ................... 11 Table 3: Physical parameters used for the oxidation simulation ........................................ 16 Table 4: Soil-hydraulic parameters and vegetation information ......................................... 16

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Acknowledgements The authors express their sincere thanks to all the institutions and individuals who contributed to the project, in particular to T. Machacha (DGS Director), H. Vogel (BGR Project Manager), and M. Hagger (BCL Manager Safety, Security, Health & Environment). In addition, we extend many thanks to the DGS Drilling Section and to K. Keipeile for their dedicated sampling. The samples were analysed by BGR staff in Hannover, Germany. U. Siewers and H. Lorenz performed the ICP-MS analyses, the XRF analyses were carried out by J. Lodziak, F. Korte and D. Rammlmair, and H. Wehner did the Corg and Stotal analyses. M. Böttcher (Max Planck Institute for Marine Microbiology, Bremen, Germany) analyzed Ssulphide. W. Sand and his team (University of Hamburg, Germany) conducted micro calorimetric measurements. BC Research (Vancouver, Canada) accomplished the humidity-cell testing. 1. Summary The mine waste tailings dam at Selebi-Phikwe was investigated to assess the potential for acid mine drainage (AMD) with a view to develop a remediation strategy for mine closure. Presently, the mine is planned to close in the year 2014. The dam, which is approximately 40 m high, covers an area of about 1 km2. Water covers the central part of the dam, but the periphery is dry. It was in the dry periphery that the DGS Drilling Section percussion drilled three holes through the unsaturated zone down to the saturated zone at about 25 m depth. From these boreholes, we collected sixty-five solid samples at 1-m intervals. All samples went through geomicrobiological and geochemical analyses. Brown precipitates of iron (hydro) oxides were discernible throughout the entire unsaturated zone in which the paste pH was in the range of 3 to 4. The tailings had sulphur concentrations in the range of 2 to 8 % by weight (average 4 %). Total sulphur consisted mainly of reduced inorganic sulphur. Pyrrhotite was the main metal sulphide; pyrite, and nickel and copper sulphides occurred in minor amounts. Metal sulphide oxidizing bacteria of the type Acidithiobacillus ferrooxidans were present in large numbers throughout the entire unsaturated zone. The mean value according to the most-probable-number method was 3 x 106 cells g-1 dw. Mean numbers of living Bacteria (CARD-FISH) and total microorganisms (SybrGreen direct counts) were 1 x 107 cells g-1 dw and 8 x 107 cells g-1 dw respectively. The average potential pyrrhotite oxidation rate measured by microcalorimetry was 1.9 x 10-9 molpyrrhotite m-2 s-1 related to the pyrrhotite surface. The proportion of biological to chemical pyrrhotite oxidation was found to be fifty-fifty. The potential average pyrrhotite oxidation rate for the assumed 0.1 m thickness of the oxidation zone within the 25-m thick unsaturated zone was 3.4 x 10-5 mol m-2 s-1 (94 kg FeS m-2 year-1) related to the dam surface. According to this rate, all pyrrhotite in the tailings dam would be oxidized within 80 years (Schippers et al., 2005). In addition, we established hydro-chemical models with computer codes for water-balance, sulphide oxidation rate, and hydro-chemical equilibrium calculations. The oxidation of pyrrhotite proceeds at a much faster rate than the oxidation of pyrite. The PYROX code used for kinetic calculations can consider these differences by applying different oxide-coating diffusion coefficients (D2) for pyrrhotite and pyrite.

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Humidity-cell testing is widely used to predict the post-mining composition of drainage water in humid climates. However, the semi-arid climate at Selebi-Phikwe only allows for a minimal water flux within the dam. Under such conditions, humidity-cell testing is likely to overestimate the seepage-water pH. This is clear from the hydro-chemical equilibrium calculations for the post-mining period at Selebi-Phikwe, which predicted a seepage-water pH about one unit lower than the pH at the end of the 26-weeks humidity-cell testing period. If an oxygen barrier were to be installed below the evaporation zone than the acidity of seepage water would be reduced by about half a pH unit. A 0.5 m thick clay layer that is covered by >1.5 m of tailings material represents the optimal design for a wet barrier. All three computer codes used for water-balance calculations (HELP3, UNSAT-H and HYDRUS-1D) predict an average water saturation of >85 % for such a layer, which diminishes the diffusion of oxygen into the pile and the production of SO4

2- and H+. The alternative design for a dry barrier consists of a 1 m thick vegetated silt layer on top of the tailings. However, such a barrier does not significantly influence the diffusion of oxygen although it reduces the net infiltration of water to less than 12 mm per year (Schwartz et al. 2005). 2. Introduction The aim of this study was to understand, quantify, and predict the generation of acid mine drainage (AMD) in the mine tailings dam at Selebi-Phikwe. AMD is a strongly acidic solution containing large amounts of heavy metals and sulphate that threaten groundwater quality. AMD is generated by chemical and biological oxidation of pyrite, pyrrhotite, and other metal sulphides in mine tailings dumps that store material from sulphide ore processing (Johnson et al., 2000; Jambor et al., 2003; Schippers, 2004; Höglund & Herbert, 2004). The pyrite oxidation rate depends on temperature, pH, humidity and the availability of oxygen in the tailings, which is controlled mainly by diffusion. In addition, the oxidation rate strongly depends on the abundance of acidophilic Fe(II)- and metal sulphide oxidizing microorganisms, which accelerate the kinetics of pyrite oxidation 30 to 300 fold (Nordstrom & Southam, 1997; Nordstrom & Alpers, 1999). The important role of acidophilic Fe(II) oxidizing microorganisms (such as Acidithiobacillus ferrooxidans) for the generation of AMD is called to attention by geomicrobiological and geochemical studies of mine tailings containing pyrite and pyrrhotite (Silver 1991; Blowes et al., 1995; 1998; Elberling et al., 2000; Schippers et al., 2000; Dold & Fontboté, 2001). Only a few studies included the measurement of pyrite or pyrrhotite oxidation rates (Elberling & Nicholson, 1996; Elberling et al., 2000; Elberling & Damgaard, 2001). Due to pyrrhotite oxidation, sulphuric acid is formed according to equation 1 (Seal & Hammarstrom, 2003): Fe1-xS + (2-x/2) O2 + x H2O ----> (1-x) Fe2+ + SO4

2- + 2x H+ (1)

Based on the mineralogical composition, x ranges between 0 and 0.125 Fe(II) may be further oxidized to Fe(III)hydroxide according to equation 2: Fe2+ + 0.25 O2 + 2.5 H2O ----> Fe(OH)3 + 2H+ (2)

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The kinetics of chemical pyrrhotite oxidation, which is critical for AMD generation, have been studied in the laboratory and reaction rates up to 3.5 x 10-8 mol m-2 s-1 at pH 2.75 were determined (Janzen et al., 2000). The chemical pyrrhotite oxidation rate was found to be about 20 to 100 times those measured for pyrite (Belzile et al., 2004). To our best knowledge, biological pyrrhotite oxidation rates have not been determined. 3. The BCL mine waste tailings dam at Selebi-Phikwe 3.1 Site description The climate in Selebi-Phikwe is semi-arid with an average annual temperature of 21°C. The tailings dam, which is approximately 40 m high, stores waste from 32 years of processing nickel, copper, zinc, and cobalt sulphide ore. The final height shall be 50 m in the year 2014. Mafic rocks that metamorphosed under amphibolite-facies conditions (Baldock et al., 1976) host the ore. Approximately 204 t of dry solids are deposited per hour on the tailings dam from the ore processing plant (concentrator) (Fig. 1). At the end of 2003, the dam covered an area of about 1 km2 (Fig. 2). Currently, the surface of the central part is covered by water but the periphery of the dam surface is dry.

Figure 1: Deposition of waste material on the tailings dam (Background: ore processing plant)

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Figure 2: Sketch map of the tailings dam

Figure 3: Acid mine drainage (AMD) from the tailings dump

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The mine waste tailings dam at Selebi-Phikwe generates large amounts of AMD, which is collected in a drainage ditch surrounding the dam (Fig. 3). To prevent contamination of surface water, AMD is purified in a plant by adding limestone to increase the pH and to precipitate metals (Fig. 4).

Stream Number 1 2 3 4 5 6 7Flow (m3/d) 8193 - 6300 1200 2400 2400 0

NB: Currenly the water in the seepage sump is pumped to the clear water dam. The Seepage Treatment Plant (STP) has been sized for a maximum of 100m3/hr. Seepage is estimated at 50m3/hr and the STP has an extra 50m3/hr for dealing with water from the emergency catchment dam. Pipe 2 usually has no flow. Pipe 7 has no flow when all flow goes back to Concentrator.

Tailings Dam

Concentrator

Clear Water Dam

Seepage Sump

Tailings

Seepage Treatment Plant

Evaporation

Evaporation

6

5

4

2

3

31

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Figure 4: Water flow sheet of the Selebi-Phikwe tailings dam 3.2 Tailings material Tailings material from the ore processing plant consists of approximately 35 % solid material. The average grain size is about 0.1 mm in diameter. The solid material contains about 12.5 % metal sulphides, and hornblende and feldspar as major gangue minerals. Pyrrhotite makes up 88 % by volume of the sulphide fraction. The remainder is pyrite (6 %), pentlandite (4 %), and chalcopyrite (2 %). Recently deposited fresh tailings material was grey (Fig. 5), whereas brown precipitates of iron (hydro) oxides due to pyrrhotite oxidation were visible in material deposited several month before (Fig. 6). 3.3 Sampling We sampled within the dry periphery of the dam surface (Fig. 2), where we took sixty-five samples at 1-m intervals from three drilled holes (Fig. 7-9). The holes extended down to the saturated zone at about 25 m depth. To analyse pore size distribution an additional 24 surface samples were taken using 100 cm3 steel sample rings (Fig. 10).

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Figure 5: Sampling of recently deposited tailings material

Figure 6: Weathered tailings material on tailings dam surface

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Figure 7: DGS drilling rig in operation on the tailings dam in November 2003

Figure 8: Removal of a drill core

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Figure 9: Sample recovery from a drill core

Figure 10: Surface sampling with steel sample rings

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4. Materials and methods 4.1 Geochemical analysis The paste pH was measured with an electrode after shaking 5 g samples in 12.5 mL 1 M KCl for one hour. Humidity was determined as weight difference after drying. The elemental composition of the solid material was determined by XRF analysis. Organic carbon (Corg) and the total amount of sulphur (Stotal) were measured with a LECO CS 200 instrument after acid removal of carbonates. Total reduced inorganic sulphur (TRIS) was determined as chromium reducible sulphur following the procedure described by Fossing & Jørgensen (1989). Samples were freeze dried and homogenized in an agate mortar. The powder was distilled for two hours in acidic Cr(II) chloride solution and the hydrogen sulphide that evolved was precipitated quantitatively as ZnS in a Zn acetate trap. The sulphide concentration was determined according to the methylen blue method by spectrophotometry (Cline, 1969). All photometric measurements were done in duplicate. Results agreed within ± 5 %. A pore water press was employed to obtain pore water, which was then analyzed for elemental composition by inductively coupled plasma optical emission spectroscopy (ICP-OES). 4.2 Geomicrobiological analysis The total number of microorganisms (including living and dead cells) was determined under a fluorescence microscope according to Weinbauer et al. (1998) by counting cells stained by SybrGreen. The number of living bacteria was determined by catalyzed reporter deposition - fluorescence in situ hybridization (CARD-FISH) (Pernthaler et al. 2002). The number of metal sulphide oxidizing bacteria of the type Acidithiobacillus ferrooxidans was quantified by the “most probable number technique” (MPN) (McCrady, 1915; de Man, 1983) using a medium for enrichment of acidophilic Fe(II) oxidizers (Leathen et al., 1951). 4.3 Potential micro calorimetric pyrrhotite oxidation rate Because the reaction rate correlates with the heat output, the potential pyrrhotite oxidation rate was determined by microcalorimetry at 25 °C and at atmospheric oxygen partial pressure (Schippers et al., 1995; Rohwerder et al., 1998; Elberling et al., 2000). A Thermal Activity Monitor Thermostat type 2277 (Thermometric; Järfälla, Sweden) equipped with 20 mL Ampoule Micro Calorimetric Units (type 2230-000) was used to measure the heat output (µW) due to the exothermal pyrrhotite oxidation in 10 g sample each. The heat output caused only by chemical pyrrhotite oxidation was measured in a second run after inactivating microorganisms at 65°C for 6 hours. The difference between the values of the two measurements per sample is the heat output due to biological pyrrhotite oxidation in µW. A complete oxidation of FeS to Fe(III) and sulphate produces a reaction energy ∆fH0 of - 940 kJ mol-1. Using this value, the molecular mass of FeS of 0.088 kg mol-1, the measured heat output “a” (µW) and the sample weight “w” (g), the combined pyrrhotite oxidation rate “r” was calculated according to the following equation: r (µg kg-1 s-1) = - 0.94-1 (mmol kJ-1) 0.088 (kg mol-1) a (µW) w-1 (g-1)

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The rate was converted to µmol m-3 s-1 using an estimated tailings density of 1700 kg m-3. Since the micro calorimetric measurements were done at atmospheric and not at in situ oxygen partial pressure, the obtained value is considered a potential pyrrhotite oxidation rate. 4.4 Pyrrhotite oxidation rate according to the humidity cell test A 26-weeks humidity-cell test was carried out on 1 kg of a selected sample (B/H1, 9-10 m depth) according to the MEND procedure (http://www.nrcan.gc.ca/mms/canmet-mtb/mmsl-lmsm/mend/default_e.htm). The pyrrhotite oxidation rate was calculated from the sulphate release and compared to the potential micro calorimetric pyrrhotite oxidation rate. 5. Results Brown precipitates of iron (hydro) oxides due to pyrrhotite oxidation were found throughout the entire unsaturated zone. The analysis of polished sections of 25 samples from core 1 showed that the average surface area of grains is approximately 1 m2/g and the fraction of oxidized pyrrhotite varies between 5 and 50 % (average 20 %), not showing any correlation with depth. The oxidation products are goethite and sulphate minerals. 5.1 Geochemical data Throughout the entire depth profile, the pH was in the acidic range with values around 3 to 4 (Fig. 11). The humidity mainly fluctuated between 5 and 20 wt-%. The average total reduced inorganic sulphur concentration (TRIS) was 4.6 wt-% in one drill hole (B-H1), and 4.3 wt-% in another (B-H2). The average ratio between TRIS and Stotal was identical for both holes (0.86 : 1). For mean values and standard deviations of these and other geochemical parameters, see Table 1. Organic carbon (0.05 %) played only a minor role in the tailings dam. The amounts of Fe, Ca, and Mg were high. Pore water was obtained from one sample from 10 m depth from one borehole only (B-H1) and the following concentrations were measured (mg/L): Al 8.24, Ba <0.10, Ca 526, Cd <0.01, Co 0.33, Cr <0.10, Cu <0.10, Fe 1516, K 393, Li 1.09, Mg 472, Mn 44.8, Na 469, Ni 68.1, Pb <0.10, Sr 2.10, Zn 4.04. The high values for Al, Fe, and Zn are typical for AMD. 5.2 Gemicrobiological data and pyrrhotite oxidation rate We detected large numbers of total microorganisms, living Bacteria, and Acidithiobacillus ferrooxidans-like bacteria throughout the entire depth profile (Fig. 12; for mean values and standard deviations of the microbiological parameters see Table 2). The numbers of total microorganisms and of living bacteria did not show any trend with depth. The numbers of Acidithiobacillus ferrooxidans-like bacteria were significantly lower at the tailings surface than in deeper layers, but we could not observe a depth trend. One eight of the number of total microorganisms were detected to be living bacteria. Out of these, about one third was Acidithiobacillus ferrooxidans-like bacteria.

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The high numbers of metal sulphide oxidizing bacteria were consistent with high potential pyrrhotite oxidation rates of up to 1 mmol m-3 s-1 for all depths. The proportion of biological to chemical pyrrhotite oxidation was fifty-fifty. Related to the pyrrhotite surface, a mean potential pyrrhotite oxidation rate of 1.9 x 109 molpyrrhotite m-2 s-1 was determined, considering that all TRIS was sulphur in pyrrhotite for which the formula FeS was used for calculations. The oxidation rate determined at the end of the 26-weeks humidity-cell testing was 2 x 10-10 molpyrrhotite m-2s-1.

Mean value Standard deviation Analyzed samples

Humidity 12 % 4 % 65

pH 3.8 0.7 65

Corg 0.05 % 0.02 % 64

Stotal 4.4 % 1.8 % 64

TRIS 3.8 % 1.8 % 42

Fe2O3 (total Fe) 19.9 % 3.4 % 65

MgO (total Mg) 7.5 % 1.0 % 65

CaO (total Ca) 6.0 % 0.6 % 65

Table 1: Mean values and standard deviation of geochemical parameters. Standard deviations are related to the amount of analyzed samples.

Mean value

Standard deviation

Analyzed samples

Potential pyrrhotite oxidation rate at 25 °C at atmospheric oxygen pressure related to the pyrrhotite surface

1.9 x 109

molpyrrhotite m-2 s-1

1.3 x 109

molpyrrhotite m-2 s-1

41

Proportion of biological pyrrhotite oxidation 52 % 32 % 41

Total number of microorganisms 8 x 107

cells g-1 dw 1 x 108

cells g-1 dw 24

Number of living Bacteria 1 x 107

cells g-1 dw 2 x 107

cells g-1 dw 24

Number of Acidithiobacillus ferrooxidans-like bacteria

3 x 106

cells g-1 dw 5 x 106

cells g-1 dw 41

Table 2: Mean values and standard deviation of microbiological parameters.

Standard deviations are related to the amount of analyzed samples.

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0 5 10 15 20 25

0

5

10

15

20

25

30

Humidity (wt-%)

Core 1Core 2Core 3

Dep

th (m

)

2 3 4 5 6 7

0

5

10

15

20

25

30

paste pH

Core 1Core 2Core 3

Dep

th (m

)

1 2 3 4 5 6 7 8 9

0

5

10

15

20

25

30

S total (wt-%)

Core 1Core 2Core 3

Dep

th (m

)

0 2 4 6 8 10

0

5

10

15

20

25

30

TRIS (wt-%)

Core 1Core 2

Dep

th (m

)

Figure 11: Depth profiles of pH, humidity, Stotal and total reduced inorganic sulphur (TRIS) for different cores from the tailings dam Selebi-Phikwe.

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105 106 107 108 109

0

5

10

15

20

25

30

Total microorganisms (N/g)

Core 1

Dep

th (m

)

105 106 107 108 109

0

5

10

15

20

25

30

Living Bacteria (N/g)

Core 1

Dep

th (m

)

10 1001000 104 105 106 107 108

0

5

10

15

20

25

30

Acidithiobacillus ferrooxidans- like bacteria (N/g)

Core 1Core 2

Dep

th (m

)

0 200 400 600 800 1000

0

5

10

15

20

25

30

Potential pyrrhotite oxidation rate(µmol/m3 s at 25°C)

Core 1Core 2

Dep

th (m

)

Figure 12: Depth profiles of numbers of total microorganisms, living Bacteria, metal sulphide oxidizing Acidithiobacillus ferrooxidans-like bacteria, and

potential pyrrhotite oxidation rate.

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6. Discussion The geochemical and geomicrobial data for the Selebi-Phikwe tailings dam showed clearly that pyrrhotite is oxidized at high rates, both chemically and biologically, in the unsaturated zone. A high proportion of pyrrhotite oxidizes within the first years of deposition. Metal sulphide oxidizing bacteria, such as Acidithiobacillus ferrooxidans-like bacteria, are present in large numbers of 3 x 106 cells g-1 dw in the entire unsaturated zone of the tailings dam and generate AMD. Other species of the living Bacteria (1 x 107 cells g-1 dw), which we did not determine, may also contribute to the overall metal sulphide oxidation activity. To our surprise, the abundance of microorganisms did not decrease with depth in the unsaturated zone unlike found in other pyrite containing tailings (Silver, 1991; Elberling et al., 2000). Numbers of Acidithiobacillus ferrooxidans-like bacteria, determined by the most-probable-number cultivation technique, were significantly higher in the Selebi-Phikwe tailings dam than in other tailings (Silver, 1991; Blowes et al., 1995; Blowes et al., 1998; Elberling et al., 2000; Schippers et al., 2000). The mean potential pyrrhotite oxidation rate for the Selebi-Phikwe tailings dump of 1.9 x 109

molpyrrhotite m-2 s-1 is in the range of 3.5 x 10-8 to 6 x 10-10 mol m-2 s-1 as worked out for laboratory pyrrhotite oxidation (Janzen et al., 2000). The rates determined in this study are potential rates, because the micro calorimetric measurements were done at atmospheric and not at the in situ oxygen level in the tailings dam, which varies with depth. Consequently, the oxidation rate determined at the end of the 26-weeks humidity-cell testing is considerably lower: 2 x 10-10 molpyrrhotite m-2s-1 (1 kg sample - MEND procedure). The in situ pyrrhotite oxidation rate in the tailings is limited by oxygen diffusion, which also determines the thickness of the oxidation zone at the top of the tailings. For other tailings, depletion of molecular oxygen was measured within the top 0.2 to 0.6 m, which strongly depended on the sulphide content and the humidity of the tailings material (Elberling & Nicholson, 1996; Blowes et al., 1998; Elberling et al., 2000; Blowes et al., 2001). Because of the high oxygen consumption due to the high pyrrhotite oxidation rate, we assumed a thickness of the oxidation zone of only 0.1 m for the Selebi-Phikwe tailings dam. In this case, the average potential pyrrhotite oxidation rate would be 3.4 x 10-5 mol m-2 s-1 dam surface (94 kg FeS m-2 year-1). This rate is about 10 times higher than the maximum pyrrhotite oxidation rate determined (as in situ O2 consumption rate) for a pyrrhotite-rich tailings pond in the Sudbury area in Ontario, Canada (Elberling & Nicholson, 1996), and about 30 times higher than a previously measured pyrite oxidation rate in an arctic tailings impoundment in northern Canada (Elberling et al., 2000). The latter study showed that in situ O2 consumption rates and micro calorimetrically determined rates are almost identical. The different rates determined for different tailings may be due to differences in molecular oxygen diffusion, temperature, metal sulphide reactivity, and abundance of metal sulphide oxidizing bacteria. Water content mainly controls the diffusion of molecular oxygen. Consequently, pyrite oxidation rates at different sampling sites at an arctic tailings impoundment varied by a factor of 100 depending on water content (Elberling et al., 2000). Temperature differences explained variations in pyrite oxidation rates by a factor of 2 given a temperature shift from 10 to 20°C (Elberling et al., 2000). The reactivity of different metal sulphides varies over a wide range (Nicholson & Scharer, 1994; Elberling et al., 1994; Janzen et al., 2000; Belzile et al., 2004; Jerz & Rimstidt, 2004). The chemical pyrrhotite oxidation

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rate was found to be approximately 20 to 100 times those measured for pyrite (Belzile et al., 2004). Metal sulphide oxidizing bacteria such as Acidithiobacillus ferrooxidans have shown to increase the chemical pyrite oxidation rate by a factor of 30 to 300 (Nordstrom & Southam, 1997; Nordstrom & Alpers, 1999). However, according to the micro calorimetrically determined potential average oxidation rate of pyrrhotite of 94 kg FeS m-2 year-1, annual sulphate production is approximately 100 kg per m-2 dam surface per year. This translates into an annual sulphate production of 100,000 t for the Selebi-Phikwe tailings dam. Based on the mean TRIS value, we calculated a total sulphate formation potential of 8 x 106 t. Assuming a constant pyrrhotite oxidation rate over time, all pyrrhotite would be oxidized within 80 years. The results of humidity-cell testing correspond to an annual sulphate production of 66 kg SO4

2- per m2 dam surface. This estimate is based on the assumption that only the uppermost 1.25 m of the rising tailings dam are oxidized each year (the thickness of the impoundment increases at an average rate of 1.25 m per year). From the observed mineralogical composition of the tailings material, an annual sulphate production of 56 kg SO4

2- per m2 is to be expected; again assuming that only the top 1.25 m of the impoundment becomes oxidized each year. In summary, the calorimetric data would lead to a gross overestimation of sulphate production if applied to the total top 1.25 m of the tailings, while the humidity-cell testing produced an oxidation rate that is quite close to that derived from the mineralogical data. According to all these rates, all pyrrhotite would be oxidized within 80 to 140 years. 7. Prediction of AMD formation based on hydro-chemical modelling We used the HELP3 programme to simulate daily weather data for 1 to 50-years periods. Three models for the water balance of the tailings dams were compared, using three computer codes, namely HELP3 (Version 3.07; Schroeder et al., 1994), UNSAT-H (Version 3.01; Fayer, 2000), and HYDRUS-1D (Version 2.02; Simunek et al., 1998). We based all simulations on the unsaturated hydraulic conductivity calculated with the Brooks & Corey (1964) formulae, and a unit vertical hydraulic gradient as lower boundary condition. The kinetics of sulphide oxidation was calculated with the PYROX programme (Wunderly & Blowes, 1997). The geochemical equilibrium calculations were performed with PHREEQCI2.8 (Parkhurst & Appelo, 1999) using the integrated database file “phreeqc.dat” and additional thermodynamic properties for clinozoisite calculated with the SUPCRT92 programme (Johnson et al., 1992). The results of the various calculations were integrated into synoptic hydro-chemical models. Except for the PYROX programme, the software used for the modelling is public domain. The PYROX code is based on the shrinking core-oxidation model (Davis & Ritchie, 1986). This model assumes that sulphide oxidation is limited by the supply of oxygen through the pore space of the sulphide particles, followed by oxygen diffusion into a moving reaction front within the particles (Wunderly et al., 1995); see Table 3 for the physical parameters used for the oxidation simulation and Table 4 for the soil-hydraulic parameters used for calculating water balances for the Selebi-Phikwe mine tailings dam.

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Moisture content (vol/vol) 0.08 Pore space O2 diffusion coefficient D1 (m2/s) Determined from moisture contentOxide coating O2 diffusion coefficient D2 (m2/s) 2.0e-13 Fe sulphide mineral Pyrrhotite Sulphide particle radius (m) 0.0001 Normalized starting position of the unreacted core 0.9 Porosity (vol/vol) 0.457 Tailings bulk density (kg/L) 1.7 Weight % sulphur 4.4 Depth (m) 50 Oxidation time steps (years) 0.01 Number of nodes 201

Table 3: Physical parameters used for the oxidation simulation

HELP3 UNSAT-H

HYDRUS-1D Class

3 Class 9 Class

26 Class 3

Class 9 Class 26

Saturated water content (vol/vol) 0.457 0.501 0.445 0.457 0.501 0.445 Residual water content (vol) 0.02 0.048 0.083 0.02 0.048 0.083 Saturated hydraulic conductivity (cm/s)

0.0031 0.00019 1.90E-6 0.0031 0.00019 1.90E-6

Brooks-Corey parameter 0.4105 0.2611 0.123 Air entry head (cm) 3.031 27.808 95.487 Pore-connectivity parameter l 2 2 2 2 2 2 Moisture at 0.33 bar capillary pressure (vol/vol)

0.083 0.284 0.393

Moisture at 15 bar capillary pressure (vol/vol)

0.033 0.135 0.277

Evaporative depth (cm) 150 150 150 Fraction of vegetated area 0.25 Maximum leaf area index 1 1 Maximum rooting depth (cm) 50 Growing season (Julian day) 302-92 302-92

Table 4: Soil-hydraulic parameters of HELP3 Default Soil Class 3 (fine sand), Class 9 (silt) and Class 26 (clay) and vegetation information for the Class 9 cover, used for calculating

water balances of the Selebi-Phikwe mine tailings dam. Together with the tailings discharge, the dam receives 3 m3 water per m2 dam surface in a year (written communication by BCL staff in 2003). As mentioned above, the central part of the dump is under water. The size of the pool varies between 0.1 and 0.3 km2. Most of the seepage water collected at the bottom of the dam is recycled and used in the flotation plant. The seepage water had a pH in the range of 1.7 - 2.4 (average 2.2) between April and October 2003 (written communication by BCL staff in 2003). The pH of the humidity-cell water during 26 weeks of testing fluctuated between 2.3 and 2.8, the final pH was 2.7. After mining operation cease in 2014, dewatering of the dam will start.

17

Based on an average annual precipitation of 450 mm, the three computer codes used predicted that it will take about 10 years before a quasi-steady state is reached, i.e. before the average annual surface flux will more or less equal the average bottom flux (Fig. 13). There is little difference between infiltration rates predicted by the three computer codes (134-146 mm per year). The residence time of pore water at steady-state conditions is difficult to estimate because the various computer codes obviously predict water contents (0.14 - 0.158 vol/vol) that are higher than empirical values. Using an average moisture content of 0.08 vol/vol (as determined for the Matchless mine site in Namibia), the calculated residence time is in the range of 27 to 30 years (Fig. 14). Note that the residence time is defined by the relationship: Residence time (a) = water storage in the system (mm)/net infiltration (mm/a). The acidity of the seepage water will increase to pH values in the range of 1.1 - 1.4 after a lapse time approximately equivalent to the residence time. Twenty-five years later (residence time plus 25 years), we may expect a decrease in acidity to pH values in the range of 1.6 - 2.1 (Fig. 15). These estimates take into consideration the published alkaline-earth metal concentrations of mine water with a pH in the range of 1 - 3 (Plumlee et al., 1999). According to this data, it can be assumed that the minimum concentration of acidity-buffering components corresponds to the composition of the humidity-cell water at the end of the testing period (76 mg/L Al, 136 mg/L Ca, 0.4 mg/L K, 12 mg/L Mg, 3 mg/L Na and 24 mg/L Si). The maximum concentration of these elements should be no more than 30 times these values. Furthermore, it is assumed that the partial oxygen pressure is 10-40 bars and the saturation index of goethite is less than 1.8 (typical values of drainage samples at Matchless mine in Namibia). Pyrrhotite is supposed to have an average composition of Fe0.85S, corresponding to the composition of pyrrhotite formed in equilibrium with pyrite at 600°C that is at amphibolite-facies conditions (Toulmin & Barton, 1964). The parameters for the pyrrhotite oxidation rate (Table 3) correspond to a sulphate production of 56 kg SO4

2- per m2 dam surface in the first year after mine closure, in agreement with the mineralogical data. If an oxygen barrier is installed below the evaporation zone than the acidity of seepage water can be reduced by about half a pH unit. A 0.5 m thick clay layer (HELP3 Soil Class 26), covered by >1.5 m tailings, represents the optimal design for a wet barrier. All three computer codes used predict an average water saturation of >85 % for this layer. The purpose of the wet barrier is to diminish the diffusion of oxygen into the pile and production of SO4

2- and H+. The alternative cover scenario is a dry barrier on top of the tailings (HELP3 Default Soil Class 9). The main purpose of such a silt layer is to impede the percolation of water and thus lateral drainage at the bottom of the dam. For a 1 m thick vegetated cover, HELP3 simulates an average net infiltration of 11 mm per year, and 32 mm/year surface runoff (assuming a 3 % slope, 400 m long). Very little annual net infiltration (<1 mm) and runoff (<1 mm) is predicted by both UNSAT-H and HYDRUS-1D. The average residence time of pore water in the tailings is more than 100 years. Flow velocity in the vadose zone below the tailings is minimized and the reaction time for neutralization processes is maximized. The addition of SO4

2- and H+ to the

18

groundwater is less than expected in the “no-cover” scenario but probably more than in the “wet-barrier” scenario.

Figure 13: Annual net infiltration and annual seepage at Selebi-Phikwe 15 years post mine closure (HELP3 code); also shown is the moisture storage (vol/vol) at the beginning of each year. The synthetic weather data were generated with HELP3 based on meteorological records from Francistown. The tailings are assumed to have the soil-hydraulic properties of the HELP3 Default Soil Class 3 (Table 4).

HYDRUS1D�

HELP3�

UNSAT-H�

0� 10� 20� 30� 40� 50� 60�

Moisture calculated� Moisture=0.08 vol/vol�

Figure 14: Calculated pore water residence time at Selebi-Phikwe at quasi-steady state conditions, derived from the net infiltration rate and moisture storage. The residence time referring to theoretical moisture storage of 0.08 vol/vol is shown for comparison. The tailings

19

are assumed to have the soil-hydraulic properties of the HELP3 Default Soil Class 3 (Table 4).

Figure 15: Simulated acidity of seepage water of the Selebi-Phikwe tailings dam during 50 years following mine closure. The residence time of pore water in the central portion of the dam, where it is 50 m high, is assumed 27 years. Dispersivity is assumed to be 0.1 m. See text for further explanation. 8. Conclusions The chemical composition of the seepage water (acid mine drainage) at the Selebi-Phikwe mine waste tailings dam depends mainly on the metal sulphide oxidation rates and the buffering capacity of the alumino-silicates and carbonates in the tailings. The oxidation of pyrrhotite at Selebi-Phikwe proceeds at a much faster rate than the oxidation of pyrite at the Matchless mine waste tailings near Windhoek, Namibia (Schwartz et al., 2005); this in spite of the fact that both tailings are located in semi-arid areas and though both feature similar grain size and specific surface area. This is in agreement with published kinetic studies on pyrrhotite and pyrite oxidation. The PYROX code considers these differences by applying an oxide-coating O2 diffusion coefficient (D2) for pyrrhotite that is greater than D2 for pyrite. The length of time of AMD production is critical for the evaluation of potential remediation measures after mine closure. According to the rate measurements of this study, the time needed for the complete oxidation of pyrrhotite at Selebi-Phikwe is between 80 and 140 years (constant rates assumed). This length of time coincidences with findings made elsewhere. For tailings impoundments with low to moderate sulphide contents and shallow water-table positions, the duration of sulphide oxidation can be relatively brief, with peak oxidation occurring during the first 20 to 30 years. In sulphide-rich tailings with a deep water table, sulphide oxidation is predicted to continue for centuries in the absence of remedial actions (Blowes et al., 2003). It is problematic to predict the future development of the AMD chemistry from the results of the analyses of seepage water collected at the bottom of the Selebi-Phikwe tailings dam. Humidity-cell testing has been used to predict the composition of drainage water in humid climates (see, for example, Morin & Hutt, 1997; Bennett et al., 2000). However, the semi-arid climate at Selebi-Phikwe allows for only minimal water flux within the dam. Under such conditions, humidity-cell testing is likely to overestimate the seepage-water pH. This is clear

20

from hydro-chemical equilibrium calculations carried out with the PHREEQCI2.8 software, which predict a minimum pH that is about one unit lower than the pH at the end of the 26-weeks humidity-cell testing period. The choice of the transport model (HELP3, UNSAT-H or HYDRUS-1D) and the choice of the sulphide oxidation model (based either on mineralogical composition or on humidity-cell testing) have only little influence on these pH estimates. 9. Recommendations To reduce AMD formation during mining operations in Selebi-Phikwe, pyrrhotite and other metal sulphides ought to be stored separately. Separation could either be achieved through gravimetric or magnetic separation. To prevent oxidation, the separated sulphidic waste should be deposited either under a dry or under a water cover. To reduce AMD formation and to improve seepage water quality after mine closure, we recommend the installation of a barrier. A 0.5 m thick clay layer covered by >1.5 m tailings material represents the optimal design for a wet barrier. All three computer codes used for water-balance calculations (HELP3, UNSAT-H, HYDRUS-1D) predicted an average water saturation of > 85 % for such a layer, which diminishes the diffusion of oxygen into the pile and the production of sulphate anions (SO4

2-) and hydrogen cations (H+). The alternative cover design would be a dry barrier. The dry barrier should be in the form of a 1 m thick vegetated silt layer on top of the tailings. This would impede water percolation and thus lateral drainage at the bottom of the dam. However, such a barrier would not significantly influence the diffusion of oxygen though it was to reduce the net infiltration of water to less than 12 mm per year (Schwartz et al. 2005). 10. References Baldock, J., Hepworth, J. & B. Marengwa (1976): Gold, base metals, and diamonds in Botswana. Economic Geology 71: 139-156. Belzile, N., Chen, Y.-W., Cai, M.-F. & Y. Li (2004): A review on pyrrhotite oxidation. J. Geochem. Explor. 84: 65-76. Bennett, J., Comarmond, M. J. Jeffery (2000): Comparison of sulfidic oxidation rates measured in the laboratory and the field. Proc. 5th International Conference on Acid Rock Drainage, pp. 171-180, Society for Mining, Metallurgy, and Exploration, Littleton, U.S.A. Blowes, D., Al, T., Lortie, L., Gould, W. & J. Jambor (1995): Microbiological, chemical, and mineralogical characterization of the Kidd Creek mine tailings impoundment, Timmins area, Ontario. Geomicrobiological Journal 13: 13-31. Blowes, D., Jambor, J., Hanton-Fong, C., Lortie, L. & W. Gould (1998): Geochemical, mineralogical and microbiological characterization of a sulphide-bearing carbonate-rich gold-mine tailings impoundment, Joutel, Québec. Applied Geochemistry 13: 687-705. Blowes, D., Reardon, E., Jambor, J. & J. Cherry (2001): The formation and potential importance of cemented layers in inactive sulphide mine tailings. Geochimica et Cosmochimica Acta 55: 965-978.

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Blowes, D., Ptacek, C. & J. Jurjovec (2003): Mill tailings: hydrogeology and geochemistry. In: Environmental aspects of mine wastes. Short course series, Vol. 31. Mineralogical Association of Canada, Vancouver, BC, Canada, Chapter 5, pp. 95-116. Brooks, R. & A. Corey (1964): Hydraulic properties of porous media. Colorado State University Hydrology Paper 3: 1-27. Cline, J. (1969): Spectrophotometric determination of hydrogen sulphide in natural waters. Limnology and Oceanography 14: 454-458. Davis, G. & A. Ritchie (1986): A model of oxidation in pyritic mine wastes: part 1 equations and approximate solution. Applied Mathematical Modelling 10: 314-322. De Man, J. (1983): MPN tables, corrected. European J of Appl Biotechnology 17: 301-305. Dold, B. & L. Fontboté (2001): Element cycling and secondary mineralogy in porphyry copper tailings as a function of climate, primary mineralogy, and mineral processing. Journal of Geochemical Exploration 74: 3-55. Elberling, B. & R. Nicholson (1996): Field determination of sulphide oxidation rates in mine tailings. Water Resources Research 32: 1773-1784. Elberling, B. & L. Damgaard (2001): Microscale measurements of oxygen diffusion and consumption in subaqueous sulphide tailings. Geochimica et Cosmochimica Acta 65: 1897-1905. Elberling, B., Nicholson, R., Reardon, E. & P. Tibble (1994): Evaluation of sulphide oxidation rates: a laboratory study comparing oxygen fluxes and rates of oxidation product release. Canadian Geotechnical Journal 31: 375-383. Elberling, B., Schippers, A. & W. Sand (2000): Bacterial and chemical oxidation of pyritic mine tailings at low temperatures. Journal of Contaminant Hydrology 41: 225-238. Fayer, M. (2000): UNSAT-H version 3.0: unsaturated soil water and heat flow model - theory, user manual, and examples. U.S. Dept of Energy, Oak Bridge, Various paginations. Fossing H. & B. Jørgensen (1989): Measurement of bacterial sulphate reduction in sediments: evaluation of a single-step chromium reduction method. Biogeochemistry 8: 205-222. Höglund, L. & R. Herbert (Eds.)(2004): MiMi - Performance assessment main report. MiMi print, Lulea, Sweden. Jambor, J., Blowes, D. & A. Ritchie (2003): Environmental aspects of mine wastes. Short course series, Vol. 31. Mineralogical Association of Canada, Vancouver, BC, Canada. Janzen, M., Nicholson, R. & J. Scharer (2000): Pyrrhotite reaction kinetics: reaction rates for oxidation by oxygen, ferric iron, and for nonoxidative dissolution. Geochimica et Cosmochimica Acta 64: 1511-1522. Jerz, J. & J. Rimstidt (2004): Pyrite oxidation in moist air. Geochimica et Cosmochimica Acta 68: 701-714.

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Johnson, R., Blowes, D., Robertson, W. & J. Jambor (2000): The hydrogeochemistry of the Nickel Rim mine tailings impoundment, Sudbury, Ontario. Journal of Contaminant Hydrology 41: 49-80. Johnson, J., Oelkers, E. & H. Helgeson (1992): SUPCRT92: a software package for calculating the standard molal thermodynamic properties of minerals, gases, aqueous species, and reactions from 1 to 5000 bar and 0 to 1000° C. Computers and Geosciences 18: 899-947. Leathen, W., McIntyre, L. & S. Braley (1951): A medium for the study of the bacterial oxidation of ferrous iron. Science 114: 280. McCrady, M. (1915): The numerical interpretation of fermentation-tube results. Journal of Infectious Diseases 17: 183-212. Morin, K. & N. Hutt (1997): Comparisons of AMD predictions with historical records. Proceedings of the Workshop on Acid Mine Drainage, 15-18 July 1997, Darwin, Australia, Australian Centre for Minesite Rehabilitation Research: 33-44. Nicholson, R. & J. Scharer (1994): Laboratory studies of pyrrhotite oxidation kinetics. In: Alpers, C. & D. Blowes (Eds.): Environmental geochemistry of sulphide oxidation. American Chemical Society, Washington, U.S.A., pp. 14-30. Nordstrom, D. & G. Southam (1997): Geomicrobiology of sulphide mineral oxidation. In: Banfield, J. & K. Nealson (Eds.): Geomicrobiology: Interactions between microbes and minerals, Reviews in Mineralogy, Vol. 35, Mineralogical Society of America, pp. 361-390. Nordstrom, D. & C. Alpers (1999): Geochemistry of acid mine waters. In: Plumlee, G. & M. Logsdon (Eds.): The environmental geochemistry of mineral deposits. Reviews in economic geology, Volume 6A, Littleton, Colorado, Society of Economic Geologists, Inc., pp. 133-160. Parkhurst, D. & C. Appelo, (1999): User's guide to PHREEQC (Version 2) - a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations. U.S. Geological Survey, Denver, 312 p. Pernthaler, A., Pernthaler, J. & R. Amann (2002): Fluorescence in situ hybridization and catalyzed reporter deposition for the identification of marine bacteria. Applied and Environmental Microbiology 68: 3094-3101. Plumlee, G., Smith, K., Montour, M., Ficklin, W. & E. Moiser (1999): Geologic controls on the composition of natural waters and mine waters draining diverse mineral-deposit types. Reviews in Economic Geology 6A: 373-432. Rohwerder, T., Schippers, A. & W. Sand (1998): Determination of reaction energy values for biological pyrite oxidation by calorimetry. Thermochimica Acta 309: 79-85. Schippers, A. (2004): Biogeochmistry of metal sulphide oxidation in mining environments, sediments and soils. In: Amend, J., Edwards, K. & T. Lyons (Eds.): Sulphur biogeochemistry - Past and present. Special Paper 379, Geological Society of America, Boulder, Colorado, pp. 49-62. Schippers, A., Hallmann, R., Wentzien, S. & W. Sand (1995): Microbial diversity in uranium mine waste heaps. Applied and Environmental Microbiology 61: 2930-2935.

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Schippers, A., Jozsa, P.-G., Sand, W., Kovacs, Z. & M. Jelea (2000): Microbiological pyrite oxidation in a mine tailings heap and its relevance to the death of vegetation. Geomicrobiology Journal 17: 151-162. Schippers, A., Kock., D., Schwartz., M., Böttcher, M., Vogel, H. & M. Hagger (2005): Geomicrobiological and geochemical investigation of a pyrrhotite containing mine waste tailings dam near Selebi-Phikwe in Botswana. J. Geochem. Explor. (in press). Schroeder, P., Dozier, T., Zappi, P., McEnroe, B., Sjostrom, J. & R. Peyton (1994): The hydrologic evaluation of landfill performance (HELP) model - engineering documentation for version 3. Risk Reduction Engineering Laboratory Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, U.S.A., 116 p. Schwartz, M., Schippers, A. & L. Hahn (2005): Numerical models of the sulphidic tailings dumps at Matchless (Namibia) and Selebi-Phikwe (Botswana). Environ. Geol. (in press). Seal, R. II & J. Hammarstrom (2003): Geoenvironmental models of mineral deposits: examples from massive sulphide and gold deposits. In: Environmental aspects of mine wastes. Short course series, Vol. 31. Mineralogical Assoc. of Canada, Vancouver, Chap 2, pp. 11-.50. Silver (1991): Distribution of iron-oxidizing bacteria in the Nordic uranium tailings deposit, Elliot Lake, Ontario, Canada. Applied and Environmental Microbiology 53: 846-852. Simunek, J., Sejna, M. & M. van Genuchten (1998): The HYDRUS-1D software package for simulating the one-dimensional movement of water, heat, and multiple solutes in variably-saturated media. U.S. Salinity Laboratory, Agricultural Research Service, U.S. Dept of Agriculture, Riverside, 178 p. Toulmin III, P. & P. Barton Jr., (1964): A thermodynamic study of pyrite and pyrrhotite. Geochimica et Cosmochimica Acta 28: 641–671. Weinbauer, M., Beckmann, C. & M. Höfle (1998): Utility of green fluorescent nucleic acid dyes and aluminium oxide membrane filters for rapid epifluorescence enumeration of soil and sediment bacteria. Applied and Environmental Microbiolog 64: 5000-5003. Wunderly, M. & D. Blowes (1997): PYROX Version 1.1 user's manual. Institute for Groundwater Research, University of Waterloo, Canada, 8 p. Wunderly, M., Blowes, D., Frind, E., Ptacek, C. & T. Al (1995): A multicomponent reactive transport model incorporating kinetically controlled pyrite oxidation. Proceedings of Sudbury '95, Conf. on Mining and the Environment, Sudbury, Canada, 28 May-1 June, pp. 989-998.

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APPENDICES

25

Appendix I: Geomicrobiological data of borehole samples

Sample Sample Upper Lower Water Fe(II)-oxidizing

bacteria Total bacteria Living bacteria Total heat outputChemical heat

outputBiological heat

outputnumber borehole depth depth content pH (MPN) (SybrGreen) (CARD-FISH) (calorimetry) (calorimetry)

(m) (m) (%) (N/ g dw) (N/ g dw) (N/ g dw) (µW/ g dw) (µW/ g dw) (%)B1 B/H1 0 0.05 6.86 4.84 1.6E+03 3.0E+07 1.1E+06 63 56 11B2 B/H1 0 1 8.50 6.41 1.6E+02 2.3E+07 4.0E+05 29 3 89B3 B/H1 1 2 4.60 3.98 4.1E+02 7.8E+06 0.0E+00 219 52 76B4 B/H1 2 3 4.70 3.73 1.1E+04 2.0E+07 4.8E+06 146 137 7B5 B/H1 3 4 9.26 3.50 1.2E+07 8.1E+07 1.7E+07 166 152 8B6 B/H1 4 5 8.51 3.78 1.2E+05 2.2E+07 3.4E+06 267 146 45B7 B/H1 5 6 13.39 3.91 1.2E+04 1.4E+07 6.7E+05 202 125 38B8 B/H1 6 7 10.13 3.43 3.3E+05 3.6E+07 8.8E+06 122 104 15B9 B/H1 7 8 9.72 3.89 2.8E+05 6.7E+06 5.7E+05 293 98 67B10 B/H1 8 9 13.37 2.97 1.3E+07 1.3E+08 3.0E+07 315 28 91B11 B/H1 9 10 15.87 3.18 1.3E+07 8.3E+07 3.8E+07 87 14 84B12 B/H1 10 11 17.93 3.52 5.4E+06 3.9E+07 3.5E+07 305 158 48B13 B/H1 11 12 14.85 3.25 1.3E+07 4.9E+08 5.2E+07 210 198 5B14 B/H1 12 13 14.83 3.80 1.8E+05 7.2E+06 2.8E+06 90 4 96B15 B/H1 13 14 16.66 2.74 1.3E+07 5.6E+08 9.5E+07 64 29 54B16 B/H1 14 15 7.40 3.76 4.3E+05 4.8E+06 1.3E+06 nd nd ndB17 B/H1 16 17 7.41 3.60 1.6E+05 3.4E+07 7.6E+06 331 4 99B18 B/H1 17 18 10.86 2.78 2.8E+05 1.6E+08 3.4E+06 207 177 15B19 B/H1 18 19 7.36 3.67 1.6E+03 5.8E+06 7.7E+06 321 122 62B20 B/H1 19 20 10.03 3.77 4.9E+06 1.2E+08 3.8E+06 551 115 79B21 B/H1 20 21 11.04 3.58 1.2E+07 1.0E+07 3.1E+06 246 216 12B22 B/H1 21 22 10.50 3.73 2.7E+05 3.7E+07 2.3E+06 337 44 87B23 B/H1 22 23 17.34 3.56 3.0E+06 7.4E+07 7.7E+06 162 134 17B24 B/H1 26 27 15.29 4.10 2.9E+05 3.9E+07 3.5E+06 155 120 23B25 B/H2 0 1 5.78 4.07 nd nd nd 27 15 46B26 B/H2 1 2 5.47 3.49 9.4E+01 nd nd 11 2 80B27 B/H2 2 3 8.81 3.79 4.9E+06 nd nd 21 15 30B28 B/H2 3 4 20.28 4.04 1.4E+06 nd nd 332 136 59B29 B/H2 4 5 11.13 3.55 1.2E+06 nd nd 99 40 59B30 B/H2 5 6 15.75 4.12 1.8E+06 nd nd 28 36 0B31 B/H2 7 8 19.72 5.18 1.3E+06 nd nd 47 21 55B32 B/H2 8 9 17.00 3.67 1.3E+07 nd nd 80 41 49B33 B/H2 14 15 17.18 3.83 1.3E+06 nd nd 91 24 74B34 B/H2 15 16 15.32 3.65 1.3E+07 nd nd 172 107 38B35 B/H2 17 18 12.43 2.54 5.1E+06 nd nd 376 116 69B36 B/H2 18 19 10.92 3.61 8.2E+05 nd nd 36 4 88B37 B/H2 20 21 9.52 3.99 1.7E+06 nd nd 98 57 41B38 B/H2 21 22 12.86 2.87 1.1E+05 nd nd 255 156 39B39 Surface 0 0.05 9.44 4.75 4.4E+01 nd nd 9 5 41B40 Surface 0 0.05 7.59 5.22 4.4E+01 nd nd 508 388 24B41 B/H2 0.02 0.07 6.66 4.12 1.2E+05 nd nd 319 21 93B42 B/H2 24 25 14.94 3.67 1.3E+06 nd nd 280 41 85B43 B/H2 25 26 17.27 4.16 3.0E+04 nd nd 185 5 97B44 B/H3 0 1 2.24 4.01 nd nd nd nd nd ndB45 B/H3 1 2 8.63 5.31 nd nd nd nd nd ndB46 B/H3 2 3 9.72 3.33 nd nd nd nd nd ndB47 B/H3 3 4 12.08 3.29 nd nd nd nd nd ndB48 B/H3 4 5 14.04 3.83 nd nd nd nd nd ndB49 B/H3 5 6 16.78 5.02 nd nd nd nd nd ndB50 B/H3 6 7 12.18 3.59 nd nd nd nd nd ndB51 B/H3 7 8 13.64 3.91 nd nd nd nd nd ndB52 B/H3 8 9 19.17 3.10 nd nd nd nd nd ndB53 B/H3 9 10 22.12 4.86 nd nd nd nd nd ndB54 B/H3 10 11 19.53 4.74 nd nd nd nd nd ndB55 B/H3 11 12 15.78 3.69 nd nd nd nd nd ndB56 B/H3 12 13 14.64 3.79 nd nd nd nd nd ndB57 B/H3 13 14 11.24 3.52 nd nd nd nd nd ndB58 B/H3 14 15 11.89 2.93 nd nd nd nd nd ndB59 B/H3 15 16 10.56 3.26 nd nd nd nd nd ndB60 B/H3 16 17 10.22 3.08 nd nd nd nd nd ndB61 B/H3 17 18 10.44 2.99 nd nd nd nd nd ndB62 B/H3 18 19 9.53 3.18 nd nd nd nd nd ndB63 B/H3 19 20 9.29 3.16 nd nd nd nd nd ndB64 B/H3 20 21 8.11 3.34 nd nd nd nd nd ndB65 B/H3 21 22 12.76 3.23 nd nd nd nd nd ndB66 B/H3 22 23 14.67 3.71 nd nd nd nd nd nd

nd = not determined

26

Appendix II: Geochemical data of borehole samples 1

Sample Organic Totalnumber carbon sulfur TRIS* SiO2_SI TiO2_SI Al2O3_SI Fe2O3_SI MnO_SI MgO_SI CaO_SI Na2O_SI K2O_SI

(%) (%) (%) % % % % % % % % %B1 0.06 2.01 2.53 47.97 0.399 14.15 15.5 0.142 8.44 6.408 1.76 1.134B2 0.03 5.50 4.85 43.34 0.341 12.62 22.85 0.139 7.59 5.94 1.67 0.884B3 0.03 7.62 5.80 37.18 0.284 10.82 27.39 0.125 6.74 5.254 1.39 0.706B4 0.04 8.46 7.21 38.42 0.305 11.1 28.82 0.128 6.69 5.322 1.42 0.743B5 0.06 4.91 2.38 43.32 0.353 12.45 21.11 0.129 7.21 5.909 1.66 0.814B6 0.05 4.37 4.15 44.69 0.353 13.15 19.59 0.132 7.93 6.319 1.71 0.882B7 0.06 3.19 2.96 45.78 0.383 13.76 17.26 0.135 8.42 6.575 1.72 0.986B8 0.03 3.47 2.55 45.37 0.372 13.14 18.42 0.13 7.61 6.13 1.66 0.814B9 0.04 4.27 3.74 46.3 0.383 13.4 18.77 0.129 7.59 6.207 1.74 0.825

B10 0.05 2.10 0.97 45.68 0.367 13.64 16.53 0.136 8.48 6.772 1.69 0.654B11 0.04 1.64 0.90 46.22 0.356 14.37 14.74 0.135 9.13 6.923 1.65 0.811B12 0.05 2.47 1.89 45.27 0.34 13.93 16.75 0.141 8.93 6.906 1.64 0.726B13 0.08 3.37 2.18 43.56 0.317 12.63 18.91 0.136 8.21 6.359 1.49 0.648B14 0.05 3.37 3.93 45.19 0.357 13.6 18.41 0.141 8.38 6.345 1.67 0.855B15 0.06 3.60 1.70 43.62 0.338 12.89 19.36 0.127 7.2 6.042 1.75 0.743B16 0.07 4.45 4.09 44.11 0.333 13.21 20.4 0.138 8.05 6.258 1.67 0.846B17 0.04 5.50 4.53 43 0.346 12.76 22.27 0.129 7.54 5.927 1.7 0.834B18 0.05 5.44 4.84 41.41 0.343 11.68 21.46 0.11 5.98 5.215 1.59 0.714B19 0.04 7.94 8.41 40.68 0.341 11.63 26.9 0.113 6.15 5.084 1.57 0.794B20 0.05 5.29 4.42 44.04 0.356 12.23 20.93 0.121 6.48 5.488 1.63 0.747B21 0.05 4.62 6.25 46.22 0.396 12.88 19.47 0.12 6.65 5.497 1.8 0.93B22 0.04 6.79 5.69 38.57 0.335 10.98 24.99 0.105 5.44 4.837 1.66 0.676B23 0.03 4.76 4.36 46.81 0.386 12.66 19.52 0.113 6.15 5.566 1.94 0.832B24 0.06 8.67 7.54 43.47 0.354 11.36 26.57 0.103 5.47 4.728 1.67 0.813B25 0.16 5.75 4.79 42.37 0.332 12.66 23.26 0.14 7.71 6.079 1.59 0.786B26 0.05 6.38 5.90 40.77 0.308 11.66 23.66 0.121 6.32 5.176 1.58 0.841B27 0.03 4.40 4.40 44.49 0.348 12.8 20.7 0.132 7.33 5.735 1.68 0.964B28 0.06 1.97 2.59 47.84 0.4 14.22 14.9 0.14 8.13 6.712 1.81 0.931B29 0.04 3.69 3.65 44.75 0.363 13.19 18.76 0.133 7.59 6.102 1.7 0.891B30 0.05 3.17 2.81 46.52 0.373 13.83 17.14 0.137 8.32 6.639 1.71 0.863B31 0.09 1.96 1.21 46.93 0.402 14.31 15.06 0.148 8.89 6.888 1.66 1.041B32 0.06 1.84 0.87 47.39 0.405 14.2 15.03 0.137 8.58 6.712 1.73 0.907B33 0.07 2.79 2.15 45.54 0.361 13.84 17.34 0.144 8.62 6.574 1.63 0.844B34 0.04 3.49 2.42 45.3 0.363 13.43 18.32 0.13 7.81 6.289 1.78 0.937B35 0.07 4.23 2.75 42.68 0.348 12.4 19.81 0.13 7.21 5.999 1.63 0.77B36 0.02 3.56 3.11 45.7 0.371 13.71 18.16 0.14 8.06 6.336 1.73 0.93B37 0.04 4.15 3.31 45.63 0.379 13.4 19.12 0.125 7.06 5.825 1.84 0.964B38 0.05 3.75 3.27 44.65 0.379 12.47 18.15 0.114 6.45 5.576 1.77 0.854B39 0.04 3.61 3.56 49.13 0.373 13.72 17.27 0.133 7.2 6.095 1.95 0.993B40 0.04 13.10 12.44 31.26 0.3 9.62 38.55 0.129 6.63 5.205 1.08 0.426B41 0.04 3.18 1.95 45.8 0.341 13.22 17.74 0.143 8.11 6.419 1.77 0.917B42 0.04 4.33 3.60 46.29 0.379 12.84 18.76 0.121 6.78 5.766 1.86 0.954B43 0.05 6.14 5.51 44.48 0.378 12.58 21.93 0.114 6.47 5.429 1.89 0.982B44 0.04 6.22 nd 41.45 0.316 12.28 24.31 0.129 7.41 5.829 1.61 0.874B45 0.04 4.50 nd 44.39 0.34 12.92 20.7 0.138 7.7 5.986 1.73 0.995B46 0.04 3.60 nd 45.54 0.354 13.16 19.05 0.132 7.68 6.022 1.76 0.989B47 0.04 3.10 nd 45.69 0.369 13.42 17.87 0.133 7.78 6.137 1.76 1.029B48 0.05 3.99 nd 45.44 0.389 13.22 17.73 0.136 8.14 6.274 1.76 1.008B49 0.06 3.38 nd 46.15 0.373 13.63 17.69 0.137 8.26 6.535 1.79 1.003B50 0.04 8.15 nd 39.65 0.336 11.49 25.96 0.115 6.68 5.326 1.55 0.828B51 0.05 6.89 nd 41.95 0.361 12.13 24.05 0.128 7.23 5.763 1.6 0.862B52 0.04 1.78 nd 46.6 0.387 14.1 14.66 0.132 9.11 7.028 1.76 0.864B53 0.07 1.76 nd 45.92 0.42 14.47 14.68 0.149 9.42 7.117 1.7 1.048B54 0.05 2.19 nd 46.03 0.37 14.12 16.49 0.144 9.37 6.698 1.69 1.018B55 0.06 3.18 nd 45.68 0.344 13.36 18.12 0.134 8.51 6.321 1.59 0.946B56 0.16 3.34 nd 45.33 0.351 13.52 17.91 0.136 8.6 6.584 1.63 0.87B57 0.05 4.14 nd 45.06 0.344 13.07 19.34 0.129 7.68 6.169 1.77 0.891B58 0.05 3.05 nd 44.77 0.343 13.11 18.21 0.138 8.07 6.315 1.74 0.878B59 0.04 3.04 nd 45.78 0.353 13.37 17.91 0.137 8.06 6.337 1.8 0.937B60 0.07 3.63 nd 44.86 0.353 13.25 18.91 0.135 7.78 6.171 1.86 0.934B61 nd nd nd 44.28 0.354 12.49 20.14 0.122 7.07 5.824 1.79 0.883B62 0.05 6.39 nd 40.79 0.339 11.34 23.72 0.108 5.94 5.023 1.68 0.882B63 0.04 5.37 nd 42.74 0.347 12.2 21.46 0.116 6.55 5.553 1.76 0.85B64 0.04 6.81 nd 42.55 0.358 11.84 24.45 0.116 6.4 5.264 1.72 0.891B65 0.04 6.20 nd 42.87 0.36 12.07 22.54 0.116 6.49 5.402 1.74 0.874B66 0.05 8.16 nd 42.17 0.359 11.51 25.72 0.111 6.08 5.151 1.7 0.861

*TRIS = Total Reduced Inorganic Sulphur

27

Appendix III: Geochemical data of borehole samples 2

Sample number P2O5_SI (SO3)_SI (Cl)_SI (F)_SI LOI_SI Sum_RF

% % % % % %B1 0.066 0.21 0.007 <0.05 3.22 99.43B2 0.056 0.2 0.006 <0.05 3.71 99.4B3 0.043 0.2 0.004 <0.05 9.16 99.28B4 0.044 0.16 0.004 0.07 6.07 99.29B5 0.059 0.26 0.003 0.14 6.03 99.47B6 0.057 0.21 0.004 0.15 4.17 99.34B7 0.057 0.37 0.004 0.09 3.8 99.34B8 0.057 0.22 0.005 0.09 5.43 99.44B9 0.061 0.2 0.003 <0.05 3.79 99.42

B10 0.054 0.3 0.005 0.1 5.14 99.54B11 0.05 0.33 0.006 0.07 4.73 99.51B12 0.057 0.29 0.005 0.05 4.44 99.48B13 0.054 0.3 0.005 0.12 6.8 99.53B14 0.057 0.24 0.003 0.11 4.12 99.47B15 0.052 0.27 0.004 0.07 7.06 99.52B16 0.049 0.18 0.007 0.07 4.01 99.33B17 0.057 0.22 0.004 0.06 4.45 99.29B18 0.058 0.28 0.006 0.06 10.36 99.26B19 0.062 0.16 0.004 0.07 5.7 99.26B20 0.068 0.19 0.003 <0.05 7.02 99.32B21 0.068 0.24 0.005 <0.05 5.02 99.3B22 0.057 0.25 0.003 0.06 11.13 99.1B23 0.072 0.29 0.006 0.15 4.88 99.37B24 0.064 0.13 0.004 0.1 4.32 99.17B25 0.057 0.17 0.008 <0.05 4.1 99.3B26 0.047 0.21 0.007 <0.05 8.6 99.35B27 0.055 0.21 0.008 0.1 4.88 99.43B28 0.065 0.46 0.008 <0.05 3.77 99.43B29 0.058 0.42 0.007 0.07 5.26 99.3B30 0.062 0.29 0.006 0.1 3.33 99.32B31 0.062 0.55 0.007 <0.05 3.45 99.42B32 0.067 0.38 0.006 <0.05 3.85 99.43B33 0.057 0.34 0.004 0.08 4.03 99.41B34 0.059 0.32 0.012 <0.05 4.72 99.49B35 0.056 0.45 0.006 0.09 7.85 99.43B36 0.061 0.31 0.008 <0.05 3.81 99.34B37 0.057 0.29 0.008 <0.05 4.61 99.34B38 0.066 0.42 0.005 <0.05 8.45 99.38B39 0.079 0.21 0.007 0.11 2.23 99.49B40 0.051 0.15 0.006 <0.05 5.67 99.06B41 0.068 0.16 0.004 0.11 4.79 99.59B42 0.071 0.16 0.004 <0.05 5.35 99.36B43 0.067 0.14 0.002 <0.05 4.86 99.36B44 0.049 0.13 0.004 0.06 4.94 99.39B45 0.056 0.15 0.006 <0.05 4.29 99.39B46 0.061 0.14 0.003 <0.05 4.57 99.48B47 0.061 0.18 0.004 0.05 5.05 99.53B48 0.069 0.23 0.002 <0.05 4.12 98.57B49 0.063 0.29 0.003 0.08 3.34 99.34B50 0.055 0.16 <0.002 <0.05 6.33 98.49B51 0.059 0.15 0.004 <0.05 4.47 98.75B52 0.057 0.34 0.004 0.07 4.51 99.62B53 0.067 0.43 0.004 0.1 3.87 99.4B54 0.055 0.23 0.003 0.06 3.27 99.54B55 0.055 0.2 0.003 0.07 4.22 99.56B56 0.055 0.19 0.003 <0.05 4.3 99.49B57 0.053 0.21 <0.002 <0.05 4.72 99.45B58 0.054 0.24 0.006 0.14 5.56 99.57B59 0.054 0.2 0.005 <0.05 4.52 99.51B60 0.056 0.29 0.006 <0.05 4.87 99.48B61 0.058 0.25 0.002 <0.05 6.22 99.54B62 0.053 0.16 0.003 <0.05 9.15 99.15B63 0.056 0.2 0.003 <0.05 7.45 99.32B64 0.063 0.15 0.003 0.09 5.43 99.33B65 0.06 0.17 0.002 <0.05 6.57 99.26B66 0.067 0.17 0.004 <0.05 5.41 99.23

28

Appendix IV: Geochemical data of borehole samples 3

Sample number (As)_SI Ba_SI Bi_SI Ce_SI Co_SI Cr_SI Cs_SI Cu_SI Ga_SI Hf_SI La_SI

mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kgB1 6 186 13 <20 67 278 6 829 15 <5 <20B2 5 143 8 69 93 261 6 519 13 <5 <20B3 5 116 10 40 126 251 <5 536 10 7 <20B4 <2 117 4 37 130 247 7 539 13 <5 <20B5 6 147 8 <20 90 248 <5 474 14 <5 <20B6 <2 143 9 <20 119 269 7 1077 12 <5 <20B7 5 156 13 <20 97 284 6 836 17 <5 <20B8 5 165 5 <20 72 261 <5 399 12 <5 <20B9 <2 163 <3 <20 74 260 6 442 15 <5 <20B10 3 136 <3 <20 48 255 <5 496 13 <5 146B11 90 135 4 <20 55 285 6 257 12 <5 <20B12 <2 117 7 <20 72 277 <5 286 14 <5 20B13 6 114 <3 <20 73 308 6 276 12 <5 <20B14 5 140 <3 <20 75 287 <5 265 13 <5 <20B15 <2 149 <3 <20 59 264 <5 363 13 <5 <20B16 3 138 4 <20 103 267 <5 705 12 <5 <20B17 10 145 <3 <20 119 255 <5 585 11 <5 <20B18 5 136 <3 <20 134 216 <5 622 11 <5 <20B19 8 150 <3 <20 132 214 <5 496 10 <5 <20B20 5 147 <3 23 118 233 <5 524 16 <5 <20B21 2 176 <3 <20 114 210 8 919 11 <5 <20B22 3 126 8 <20 171 192 7 991 10 <5 <20B23 23 166 6 <20 99 187 <5 785 10 <5 <20B24 8 164 <3 <20 147 186 <5 1015 11 <5 <20B25 <2 130 <3 <20 104 259 <5 731 13 <5 <20B26 12 151 <3 <20 92 236 <5 452 10 <5 <20B27 4 165 <3 <20 81 234 <5 374 13 <5 <20B28 9 174 <3 22 61 283 <5 510 15 <5 <20B29 15 156 9 <20 97 248 7 924 14 <5 <20B30 2 148 6 <20 93 284 <5 868 13 <5 <20B31 3 170 5 <20 74 309 <5 448 16 6 <20B32 5 164 7 20 69 276 <5 484 16 <5 <20B33 5 144 <3 <20 73 326 <5 316 15 <5 <20B34 3 155 <3 <20 58 260 <5 309 12 <5 <20B35 4 145 <3 <20 82 258 <5 577 13 5 <20B36 3 159 <3 <20 86 293 <5 425 13 <5 <20B37 3 173 <3 <20 102 239 <5 415 13 <5 <20B38 5 168 <3 <20 88 229 <5 494 13 <5 <20B39 3 187 <3 <20 58 272 <5 160 15 <5 <20B40 8 68 12 <20 161 292 <5 538 4 <5 <20B41 2 138 6 <20 60 275 6 182 15 5 <20B42 <2 158 9 <20 102 209 <5 1165 12 8 <20B43 <2 159 10 <20 116 194 <5 709 14 <5 <20B44 <2 127 7 <20 102 252 <5 653 10 <5 <20B45 <2 151 6 23 93 252 6 807 12 <5 <20B46 <2 158 8 <20 65 242 6 445 13 <5 <20B47 <2 165 7 <20 77 255 6 423 10 <5 <20B48 2 158 <3 42 223 273 <5 4599 11 <5 <20B49 <2 148 9 <20 107 274 6 1249 14 8 <20B50 <2 133 5 32 287 230 <5 3681 11 <5 <20B51 11 143 4 <20 229 253 <5 3037 12 5 <20B52 2 146 7 <20 43 271 7 270 14 <5 <20B53 3 164 5 28 95 305 6 883 13 <5 <20B54 <2 148 <3 31 61 282 6 254 10 <5 <20B55 <2 140 <3 <20 59 296 <5 309 12 8 <20B56 <2 137 6 <20 70 289 6 340 12 <5 <20B57 <2 148 11 22 81 248 <5 465 12 <5 229B58 <2 137 6 <20 58 276 7 680 12 <5 <20B59 <2 147 7 29 82 273 <5 555 14 <5 <20B60 11 150 8 22 81 259 <5 649 12 6 <20B61 <2 146 5 <20 70 257 <5 511 12 <5 <20B62 <2 139 11 26 151 231 6 773 14 <5 <20B63 4 135 9 <20 144 236 6 769 12 <5 <20B64 7 140 4 <20 126 225 <5 667 13 7 <20B65 5 143 5 <20 139 207 6 818 10 <5 <20B66 <2 147 5 <20 134 199 7 900 11 8 <20

29

Appendix V: Geochemical data of borehole samples 4

Sample number Mo_SI Nb_SI Nd_SI Ni_SI Pb_SI Pr_SI Rb_SI Sb_SI Sc_SI Sm_SI Sn_SI

mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kgB1 12 4 <50 1189 9 <50 46 <5 15 <50 9B2 <2 3 <50 1827 10 <50 41 <5 14 <50 6B3 <2 3 <50 2651 5 <50 32 <5 12 <50 6B4 <2 3 <50 2809 14 <50 31 <5 12 <50 6B5 <2 3 <50 1632 6 <50 33 <5 12 <50 11B6 <2 <2 <50 2205 11 <50 36 <5 14 <50 4B7 12 4 <50 1970 9 <50 39 <5 15 <50 9B8 <2 2 <50 1518 9 <50 33 <5 12 <50 6B9 <2 5 <50 1453 16 <50 25 <5 13 <50 6B10 6 3 <50 704 <4 <50 34 <5 13 <50 7B11 8 3 <50 1013 <4 <50 32 <5 14 <50 4B12 5 3 <50 1293 9 <50 27 <5 14 <50 5B13 3 4 <50 1107 7 <50 25 <5 15 <50 7B14 <2 2 <50 1509 <4 <50 37 <5 14 <50 6B15 <2 2 <50 851 10 <50 34 <5 13 <50 5B16 <2 3 <50 1942 13 <50 29 <5 14 <50 10B17 3 3 <50 2404 6 <50 30 <5 13 <50 6B18 <2 3 <50 2386 10 <50 22 <5 11 <50 5B19 <2 3 <50 2603 <4 <50 29 5 11 <50 9B20 <2 3 <50 1886 8 <50 28 <5 13 <50 10B21 <2 3 <50 1790 6 <50 31 <5 12 <50 7B22 <2 2 <50 3471 8 <50 23 <5 11 <50 6B23 3 5 <50 1638 12 <50 32 <5 12 <50 8B24 <2 4 <50 3036 21 <50 29 <5 11 <50 10B25 <2 4 <50 2119 8 <50 28 <5 12 <50 7B26 <2 2 <50 1795 6 <50 28 <5 12 <50 6B27 <2 6 <50 1570 7 <50 38 <5 14 <50 9B28 8 6 <50 1022 6 <50 31 <5 14 <50 8B29 <2 2 <50 1952 5 <50 32 <5 12 <50 7B30 <2 3 <50 1810 13 <50 34 <5 13 <50 6B31 11 2 <50 1227 11 <50 39 <5 14 <50 9B32 11 2 <50 1080 12 <50 36 <5 13 <50 9B33 <2 4 <50 1288 8 <50 30 <5 14 <50 7B34 <2 3 <50 1036 10 <50 33 <5 13 <50 10B35 <2 4 <50 1197 6 <50 27 <5 13 <50 7B36 <2 5 <50 1640 11 <50 30 <5 14 <50 6B37 <2 3 <50 1815 17 <50 37 <5 13 <50 5B38 3 3 <50 1524 19 <50 36 <5 12 <50 7B39 <2 6 <50 1036 14 <50 30 <5 14 <50 12B40 <2 <2 <50 3857 <4 <50 13 <5 11 <50 8B41 4 3 <50 983 14 <50 38 <5 13 <50 9B42 <2 4 <50 1800 18 <50 45 <5 12 <50 3B43 <2 <2 <50 2287 9 <50 48 <5 14 <50 8B44 <2 3 <50 2104 6 <50 37 5 11 <50 7B45 4 2 <50 1678 16 <50 44 <5 13 <50 3B46 <2 3 <50 1356 13 <50 48 <5 12 <50 6B47 4 2 <50 1296 13 <50 46 <5 14 <50 8B48 3 <2 <50 4407 10 <50 44 <5 15 <50 6B49 5 <2 <50 2042 16 <50 47 <5 14 <50 10B50 <2 3 <50 5704 13 <50 38 <5 11 <50 7B51 <2 <2 <50 4308 8 <50 37 <5 13 <50 6B52 13 5 <50 699 19 <50 47 <5 14 <50 7B53 11 5 <50 1781 13 <50 49 <5 14 <50 7B54 9 2 <50 1100 8 <50 44 <5 14 <50 8B55 4 <2 <50 1113 10 <50 41 <5 14 <50 5B56 3 2 <50 1231 15 <50 40 <5 14 <50 9B57 3 <2 <50 1352 7 <50 45 <5 12 <50 6B58 7 <2 <50 939 15 <50 42 <5 14 <50 11B59 6 3 <50 1294 17 <50 43 <5 16 <50 10B60 <2 3 <50 1237 5 <50 47 <5 15 <50 8B61 6 2 <50 1168 7 <50 48 <5 14 <50 9B62 <2 2 <50 3488 12 <50 44 <5 12 <50 4B63 <2 <2 <50 2541 6 <50 41 <5 12 <50 5B64 <2 <2 <50 2622 7 <50 38 <5 12 <50 14B65 <2 <2 <50 2851 6 <50 41 <5 12 <50 6B66 <2 2 <50 2790 15 <50 44 <5 13 <50 12

30

Appendix VI: Geochemical data of borehole samples 5

Sample number Sr_SI Ta_SI Th_SI U_SI V_SI W_SI Y_SI Zn_SI Zr_SI

mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kgB1 82 <5 <5 4 110 <5 5 118 71B2 71 <5 <5 4 119 <5 6 120 81B3 59 <5 <5 6 120 <5 5 113 74B4 64 <5 <5 <3 125 <5 7 108 71B5 75 <5 <5 <3 132 <5 <3 109 82B6 78 <5 <5 3 106 <5 8 104 84B7 77 <5 <5 6 111 <5 3 116 73B8 79 <5 <5 <3 113 <5 <3 104 80B9 85 <5 <5 <3 111 6 3 105 83

B10 79 <5 <5 3 115 <5 <3 116 69B11 76 <5 <5 <3 104 <5 <3 116 60B12 79 <5 <5 5 108 <5 <3 121 70B13 63 <5 <5 9 111 <5 <3 106 61B14 77 <5 <5 3 106 <5 <3 108 69B15 78 6 <5 4 116 <5 3 103 67B16 74 <5 <5 8 103 <5 <3 121 67B17 68 <5 <5 4 108 <5 <3 114 78B18 70 <5 <5 <3 92 <5 <3 92 76B19 74 <5 <5 7 118 6 <3 105 76B20 70 <5 <5 4 106 <5 <3 113 91B21 77 <5 <5 4 111 6 <3 112 81B22 66 <5 <5 <3 92 <5 <3 104 77B23 79 <5 <5 9 108 7 <3 116 109B24 74 <5 <5 8 102 <5 <3 106 78B25 69 <5 <5 8 125 6 <3 123 73B26 61 <5 <5 <3 110 <5 <3 101 76B27 71 <5 <5 3 122 <5 <3 109 78B28 81 <5 <5 9 117 <5 <3 108 76B29 77 <5 <5 7 115 <5 <3 112 77B30 80 <5 <5 8 110 <5 <3 116 78B31 84 <5 <5 11 105 <5 <3 117 67B32 85 <5 <5 3 118 <5 <3 113 72B33 74 <5 <5 6 116 <5 <3 120 64B34 79 <5 <5 3 96 <5 <3 112 71B35 74 <5 <5 <3 122 <5 <3 108 70B36 78 <5 <5 <3 105 11 <3 119 78B37 80 <5 <5 12 99 <5 <3 108 76B38 73 <5 <5 8 99 <5 <3 98 81B39 85 <5 <5 6 109 7 <3 104 98B40 46 <5 <5 9 127 6 <3 105 84B41 79 <5 <5 8 98 <5 9 104 85B42 81 <5 <5 3 92 <5 7 112 95B43 79 <5 <5 <3 92 <5 14 110 91B44 68 <5 <5 7 127 <5 9 106 73B45 82 <5 <5 3 126 <5 11 116 81B46 80 <5 <5 8 120 <5 7 116 83B47 80 <5 <5 3 111 <5 9 110 76B48 83 <5 <5 8 104 <5 13 126 84B49 85 <5 <5 <3 103 <5 9 116 84B50 71 <5 <5 <3 111 <5 7 121 73B51 75 <5 <5 4 110 <5 5 118 74B52 90 <5 <5 <3 108 6 7 112 69B53 84 <5 <5 4 102 <5 9 125 53B54 76 <5 <5 <3 117 <5 3 118 61B55 74 11 <5 5 105 <5 4 112 67B56 77 <5 <5 <3 112 <5 <3 113 63B57 79 <5 <5 5 122 <5 7 115 74B58 76 <5 <5 3 109 <5 12 113 70B59 80 <5 <5 <3 124 <5 12 124 76B60 81 <5 <5 <3 127 <5 10 118 76B61 78 <5 <5 5 94 <5 9 98 83B62 68 <5 <5 4 106 <5 9 97 83B63 79 <5 <5 5 114 6 11 114 88B64 72 <5 <5 4 113 <5 12 116 77B65 74 <5 <5 4 94 <5 8 117 84B66 69 <5 <5 <3 106 <5 7 111 89

31

Appendix VII: Pore size distribution

Equivalent Fine porespore diameter 10 µm 3 µm 1 µm 0.2 µm

LabNo Depth 29.5 kpa 98.3 kpa 295 kpa 885 kpa(cm) (%) (%) (%) (%)

M4114 5 11.48 9.13 7.02 6.42M4115 200 3.86 3.58 3.36 2.82M4116 5 14.81 11.31 7.95 7.41M4117 5 22.19 17.33 13.31 11.33M4118 5 8.34 6.24 5.41 4.81M4119 5 7.47 5.79 4.58 4.26M4120 5 5.71 4.28 3.44 2.73M4121 5 7.18 6.31 5.59 5.00M4122 5 5.70 4.95 17.47 4.21M4123 5 5.48 4.77 3.78 3.58M4124 33 10.40 9.06 7.02 7.01M4125 33 9.64 7.92 5.90 5.52M4126 33 7.80 6.96 5.83 5.18M4127 5 13.59 12.72 11.57 10.82M4128 5 4.22 3.09 2.10 1.76M4129 5 5.95 5.21 4.17 3.82M4130 5 16.03 9.50 7.17 5.74M4131 5 29.51 27.70 23.63 18.56M4132 5 29.90 26.66 19.83 15.13M4133 5 19.84 16.87 13.85 10.63M4134 5 15.87 12.36 9.47 6.50M4135 5 12.50 9.01 6.91 5.27M4136 5 6.70 4.31 3.25 2.80M4137 5 6.29 4.73 3.86 2.97

Medium pores

Pore size distribution determined for steel cylinder surface samples using fractionated dewatering at different pressures

32

Appendix VIII: Humidity cell test data (1 kg sample B/H1, 9-10 m depth)

Cycles Date Vol. Input Vol. Output pH EC Sulphate Acidity to pH 4.5 Acidity to pH 8.3 (ml) (ml) (umhos/cm) (mg/L) (mgCaCO3/L) (mgCaCO3/L)

1 05-Mar-04 750 360 2.75 49002 12-Mar-04 500 555 2.76 4300 4760 1696 30803 19-Mar-04 500 475 2.56 33604 26-Mar-04 500 425 2.55 2690 1830 784 14645 02-Apr-04 500 435 2.69 26906 09-Apr-04 500 395 2.70 2870 2500 855 15107 16-Apr-04 500 507 2.79 26408 23-Apr-04 500 440 2.72 1787 1370 634 16429 30-Apr-04 500 405 2.26 187610 07-May-04 500 410 2.42 2300 1460 650 100011 14-May-04 500 365 2.52 232012 21-May-04 500 435 2.52 1890 1255 490 70013 28-May-04 500 300 2.65 195314 04-Jun-04 500 390 2.71 1919 1400 596 94815 11-Jun-04 500 410 2.49 156416 18-Jun-04 500 395 2.65 1715 1235 422 71617 25-Jun-04 500 425 2.62 164718 02-Jul-04 500 445 2.68 1505 1105 418 65819 09-Jul-04 500 425 2.80 153520 16-Jul-04 500 360 2.69 1577 1025 356 61221 24-Jul-04 500 430 2.76 168722 31-Jul-04 500 460 2.64 1559 1080 420 63023 07-Aug-04 500 500 2.84 155124 14-Aug-04 500 435 2.46 1564 1290 410 57025 21-Aug-04 500 530 2.73 145426 28-Aug-04 500 475 2.70 1254 1250 350 520