TECHNICAL ARTICLE

Acid Mine Drainage at the Abandoned KettaraMine (Morocco): 1. Environmental Characterization

Rachid Hakkou Æ Mostafa Benzaazoua ÆBruno Bussiere

Received: 12 January 2008 / Accepted: 18 March 2008 / Published online: 29 May 2008

� Springer-Verlag 2008

Abstract The Kettara site (Morocco) is an abandoned

pyrrhotite ore mine in a semi-arid environment. The site

contains more than 3 million tons of mine waste that have

been deposited on the surface without concern for envi-

ronmental issues. Tailings were stockpiled in a dyke and

pond and in piles, over an area of about 16 ha, and have

generated acid mine drainage (AMD) for more than

24 years. The mine waste and secondary precipitates from

this mine were characterized using geochemical and min-

eralogical techniques. The Kettara wastes contain 1.6–

14.5 wt% sulfur, mainly sulfide minerals (e.g., pyrrhotite,

pyrite, chalcopyrite, galena, and sphalerite). The main

gangue minerals were goethite, quartz, chlorite-serpentine,

talc, muscovite, and albite. Carbonates occur at very low

quantities (less than 1 wt%). The most abundant heavy

metals were Cu, Zn, Cr, Pb, Co, As, Cd, and Ni. Acid–base

accounting static test results showed that all the samples

have low values of acid-neutralizing potential (NP) (0–

9 kg CaCO3/t). The mine waste has high acid-producing

potential (AP) (51–453 kg CaCO3/t). Abundant secondary

mineralogy is present, consisting mainly of halotrichite,

goethite, jarosite-hydroanion, hydroniumjarosite, starkey-

ite, gypsum, alunite, copiapite, butterite, and coquimbite.

Hardpans, which can prevent water infiltration to fresh

tailings beneath and thereby lessen the rate of sulfide

reactivity, were observed during sampling of the fine tail-

ings. Mineralogical analysis indicated that the cementitious

phase of the hardpan is mainly goethite. The alteration

observed in the tailings pond does not extend more than

5–15 cm.

Keywords Acid mine drainage � Kettara mine site �Mine waste � Morocco � Sulfides

Introduction

Mining has been, and remains, a fundamental part of the

Moroccan economy. Acid mine drainage (AMD) is a

major environmental problem facing the Moroccan as well

as the international mining and mineral industries. The

leachate from such sites (rich in sulfate, iron, and soluble

heavy metals) has the potential to contaminate the ground

water as well as the local watercourses. The oxidation of

sulfide minerals within mine wastes and workings may

continue to release metals into the surrounding environ-

ment for decades to millennia (Nordstrom and Alpers

1999; Pyatt and Grattan 2001). Description of the chem-

ical reactions by which AMD is produced from pyrite and

other iron sulfide minerals can be found in Evangelou

(1995), Kleinmann et al. (1981), Lovell (1983), Rose and

Cravotta (1998), and Singer and Stumm (1970). There are

relatively few environmental studies on Moroccan mine

sites, and no national program exists for the restoration of

these sites.

The rehabilitation strategy for closing a mine and the

costs of reclaiming such a site depend strongly on the acid

generating potential of the wastes. Different predictive

methods can be used to evaluate the short and long-term

acid generating potential of mine wastes; among these, one

R. Hakkou (&)

Equipe de Chimie des Materiaux et de l’Environnement,

Faculte des Sciences et Techniques, Univ Cadi Ayyad,

BP 549/40000, Marrakech, Morocco

e-mail: rhakkou@fstg-marrakech.ac.ma; hakou@yahoo.com

M. Benzaazoua � B. Bussiere

Univ du Quebec en Abitibi Temiscamingue,

445 Boul de l’Universite, Rouyn-Noranda,

QC, Canada J9X 5E4

123

Mine Water Environ (2008) 27:145–159

DOI 10.1007/s10230-008-0036-6

can mention static and kinetic tests, and mathematical

predictions (Aubertin et al. 2002; Benzaazoua et al. 2001;

Bussiere et al. 2002; Molson et al. 2005; Morin and Hutt

1997; Ritcey 1989; SRK 1989).

Secondary minerals, typically formed during weath-

ering of mine waste storage areas when the concentration

of soluble constituents exceeds the corresponding solu-

bility product, are also important. These secondary

minerals can precipitate from weathering solutions or

form on the surface of other minerals in response to a

number of processes, including oxidation, dilution, mix-

ing, evaporation, and neutralization. Crucial factors

governing precipitation of minerals are pH, Eh, degree of

oxidation, moisture content, and solution composition

(Nordstrom 1982). The most common secondary mineral

compositions are hydrous iron oxide and hydrated iron

sulfate (Alpers et al. 1994; Nordstrom and Alpers 1999).

Precipitation and dissolution cycles of soluble secondary

minerals may be responsible for seasonal variations in

effluent quality (elemental concentrations and acidity)

(Alpers et al. 1994; Bayless and Olyphant 1993; Blowes

and Jambor 1990; Kwong et al. 1993; Lin and Herbert

1997; Lin 1997). Precipitation of sulfate minerals may

help remove metals from the water, but subsequent dis-

solution can increase concentrations of dissolved metals

(Cravotta 1994; Nordstrom and Alpers 1999). In addition,

in countries where water is not very abundant, the high

concentrations of sulfate may be critically detrimental to

water resources (Pulles 2003). Thus, it is necessary to

understand the composition of secondary minerals in the

mine-waste environment to ensure accurate prediction of

effluent quality and implementation of appropriate recla-

mation strategies.

At the abandoned Kettara mine, which is located in a

semi-arid climate, mine wastes have been weathering for

more than 24 years. Initial-field work at the Kettara mine

was carried out in the summer of 2003 to characterize the

waste disposal areas and to evaluate its environment

effects. The goal of the research was to determine the

potential for the release of acidic drainage and dissolved

metals from the Kettara mine tailings. Based on the min-

eralogy and total chemical composition, the mineralogy of

the fresh (unoxidized) and oxidized tailings was estimated.

The samples were also characterized for their main phys-

ical characteristics and their acid generation potential using

static tests. Then the secondary minerals were identified

and characterized.

The companion paper (Hakkou et al. 2008) presents the

geochemical behavior of Kettara’s mine tailings. Humidity

cells and mini-alteration cell tests were performed to

determine the rate of acid generation and metal release of

tailings samples taken from the Kettara mine site.

Description of the Kettara Mine Site

The abandoned Kettara pyrrhotite ore mine, exploited by

SYPEK corporation, is located approximately 35 km

northwest of the town of Marrakech in the core of the

central Jebilet mountains (Fig. 1). The mining village of

Kettara and infrastructures are located downstream from

the tailings pond area. According to the latest statistics

(2004), the population of Kettara is approximately 2,000.

The climate is classified as semi-arid with a mean annual

rainfall of approximately 250 mm. Rainfall can occur over

short periods and with high intensity. Annual potential

evaporation typically exceeds 2500 mm. Average monthly

temperatures in the area range from 12�C in January to

29�C in July (ONEM 1997).

The Kettara sulfide deposit is a typical example of

metamorphosed deposits hosted by Visean volcano-sedi-

mentary formations. The mineralized body consists of

major and minor lenses of massive pyrrhotite, with small

amounts of sphalerite, galena, chalcopyrite, pyrite, arse-

nopyrite and glaucodot. The structure resulted from an

intra-Westphalian tectono-metamorphic phase of the

Hercynian orogeny (Hibti et al. 1999).

From 1964 to 1981, the mine produced more than

5.2 million tons (Mt) of pyrrhotite concentrate containing

an average of 29% sulfide. The Kettara pyrrhotite was used

by the Maroc Chimie 1 Company (OCP group), located in

Safi, to produce sulfuric acid. Even though the ore reserves

were still high, the mine was closed in June 1982, due to

difficulties encountered during the production of the pyr-

rhotite concentrate and its use in the roasting unit of Maroc

Chimie 1. Also, the mining infrastructure and equipment

had been corroded by the production of AMD at the site.

Pyrrhotite was extracted from the ore by gravimetric

separation (jigs). This ore enrichment process generated a

wide range of particle size fractions in the tailings (jigs refuse

materials). The tailings can be divided into two broad classes

of material: coarse tailings (fine gravel) were deposited on

the 15 m high dyke and 1 m high-tailings piles; fine tailings

(silt) were deposited in the tailings pond. During mining,

more than 3 Mt of mine wastes, containing more than 0.4 Mt

of coarse tailings, were stockpiled in pond, dykes, and piles

over an area of about 16 ha. The mine wastes were deposited

without concern for environmental issues. During the mining

operations and after plant closure, the tailings that were

deposited in the surface tailings impoundment were sub-

jected to weathering processes. The surface of the oxidized

tailings are colored rust-orange (Fig. 2) and the water and

soil are polluted. Ground water sampled from wells at the

mine had high concentrations of SO4 (1,300 mg/L); the

metal content of the soil exceeded European standards (El

Khalil et al. 2007).

146 Mine Water Environ (2008) 27:145–159

123

During dry periods, secondary minerals can be observed

in streams and on exposed tailings. During a significant

rainfall event, the dissolution of these precipitates causes

concentrations of SO42- and Al in streamwater to increase

significantly, to values as high as 45 and 4.2 g/L, respec-

tively (Hakkou et al. 2006).

Materials and Methods

Tailings

Tailings samples from the field site were analyzed

in the laboratory to determine the mineralogy, chemical

Marrakech

Youssoufia

El Kalâa

Benguerir

Chemaïa

Chichaoua

Amizmiz

A NN T O URG

JE

B L E TIAT

LANTI

C

OC

EAN

Essaouira

R.P

. 7

R.P.10

R.P.2

4

R.S

.507

Paleozoïque

Eocene (phosphate)

Rabat

Safi

Marocco

Marrakech

Spain

Ocean

Atla

ntic

0 25 50 75Km

Oued

Tensift

Recette VI

vers

Cas

abla

nca

Safi

Mine site

Sidi Bou Othmane

(OCP)

Kettara

Fig. 1 Location and simplified

geological map of the study area

Fig. 2 Photographs indicating

some of the locations where

serious AMD has occurred, or

still occurring, at the Kettara

mine site

Mine Water Environ (2008) 27:145–159 147

123

composition, physical properties, and acid generation

potential. Sampling locations are indicated on Fig. 3.

As shown in Fig. 4, two trenches were excavated in the

tailings pond to a depth of 80 and 85 cm. In each trench,

significant variation in coloration was observed. The

unoxidized tailings are dark brown, whereas the oxidized

are dominantly orange-yellow. The tailings contained an

oxidation zone at a depth of 5–15 cm below the surface.

Samples were collected during Summer 2003 from the

surface and at various depths in each trench (Fig. 4).

Samples R1–R4 were collected at different depths in the

first trench. The sample of fresh fine tailings (R1) was

taken at 80 cm. Samples R2 and R3 were taken at 27 and

15 cm, respectively, and correspond to unaltered and oxi-

dized fine tailings. Sample R4 was collected at the surface

of the tailings pond in the oxidized zone. Samples R5–R8

were taken in the second trench. R5 and R6 correspond to

unoxidized tailings. They were collected at 85 and 15 cm,

respectively. R7 was collected in the oxidized zone (5 cm),

and R8 is a sample taken at the surface.

An exploratory trench, 1.10 m deep, was also excavated

in the main dyke. The oxidized zone was thicker in these

coarse tailings than those observed in the fine tailings

(more than 75 cm) (Fig. 4). Samples S1–S7 were collected

from the top to bottom at equal intervals of 20 cm. S1–S5

correspond to unaltered coarse tailings and S6 and S7,

collected at the surface (0 cm), correspond to oxidized

coarse tailings.

Samples K1, K3 and K2, K4 were taken from two

tailings piles (see Fig. 3) and correspond respectively to

unaltered collected at the surface and oxidized coarse

tailings collected at 50 cm depth.

Sampling of Secondary Minerals and Precipitates

Secondary weathering products sampled for this study

include precipitates (powder and hardpan crusts) and

efflorescent salts. In order to verify the chemical compo-

sition and mineralogy of the secondary minerals at the

Kettara mine site, various representative samples were

collected of secondary precipitates formed in the tailings

dam and pond (Fig. 3), based on the color of the material.

The presence of these minerals in significant quantities are

the mineralogical expression of the AMD process (acidi-

fication/neutralization, oxidation, dilution, evaporation,…).

Samples D1–D5 correspond to precipitates formed in the

tailings pond. D6 corresponds to a white precipitate formed

near the dyke and the tailings piles. D5 and D6 are the most

frequently found secondary minerals at the Kettara site. D7

was taken in an ocherous tailings pile and D8 corresponds

to a secondary phase formed in the main dyke.

Analytical Methods

The chemical composition (Al, As, B, Ba, Be, Bi, Ca, Cd,

Co, Cr, Cu, Fe, Mg, Mn, Na, Ni, Pb, S, Se, Zn, and SO4) of

the different tailings was analyzed with a Perkin Elmer

Optima 3100 RL ICP AES following a total HNO3/Br2/HF/

HCl digestion. Dilute HCl was used to extract sulfates, and

the solution obtained was analyzed by ICP AES. Si and K

were analyzed at the SGS Canada Inc. laboratory in Rouyn-

Noranda.

The sample’s particle size distribution was determined

using a Malvern Mastersizer laser particle size analyzer. The

specific gravity (Gs) was measured with a Micromeritics

Fig. 3 Samples locations of

tailings and secondary minerals

148 Mine Water Environ (2008) 27:145–159

123

Accupyc 1330 helium gas pycnometer. The specific surface

area (Ss) was determined by measuring the BET of the

powders using a Micrometrics Gemini III 2375 apparatus.

The initial tailings mineralogy was determined by a

combination of X-ray diffraction spectroscopy (XRD)

and SEM analysis. XRD analyses were carried out using

a Bruker AXS D8 Advance diffractometer equipped with

a scintillation detector and Co Ka radiation. The data

were collected in 5–70� by steps of 0.005� and a count

time of 0.5 s per step. Access to the JCPDS database

allowed qualitative analysis of the mineralogy (e.g.,

phase determination); the Rietveld method was used for

quantitative analyses of known phases. Compositional

phases were quantified within 0.5% error. A scanning

electron microscope (SEM) equipped with a microanal-

ysis system (Energy Dispersive Spectroscopy) was also

used to study polished sections of tailings samples. The

SEM is a pressure vacuum Hitachi S 3500 N equipped

with backscattered and secondary electron detectors

and a Link Isis microanalysis system from Oxford

Instruments.

The static test most commonly used to predict the acid

generating potential is acid–base accounting (ABA). ABA

measures the balance between the acid-producing potential

(AP) and neutralizing potential (NP) of a sample. The NP

was determined using the modified static test proposed by

Lawrence and Wang (1997) for each different tailings

sample. The NP analyses were run in duplicate, and results

were expressed in kg CaCO3/t. AP, also expressed in kg

CaCO3/t, was calculated by using the sulfide sulfur portion,

obtained by subtracting the sulfate sulfur from the total

sulfur. The net neutralization potential (NNP) was calcu-

lated by subtracting the AP value from the NP value. It is

usually recognized that values of NNP \ -20 kg CaCO3/t

indicate an acid-producing material, whereas materials

with NNP [ 20 kg CaCO3/t are considered to be acid

consuming. Hence, an uncertainty zone for this technique

exists between 20 [ NNP [ -20 kg CaCO3/t (Miller et al.

1991; SRK 1989).

Another useful tool to evaluate the AMD production

potential from static tests results is the NP to AP ratio.

Typically, the material is considered non acid-generating if

NP/AP [ 2.5, uncertain if 2.5 [ NP/AP [ 1, and acid

generating if NP/AP \ 1 (Adam et al. 1997).

Results and Discussion

Physical Properties

Table 1 summarizes the main physical parameters (grain

size distribution parameters, Gs, Ss) of the fine and coarse

tailings studied. Figure 5 presents the grain size distribu-

tions of the different samples.

In term of grain size analysis (Fig. 5), the fine tailings

(R1–R8) were statistically indistinguishable. The tailings

are typical of fine tailings from a hard rock mine (Aubertin

et al. 2002; Bussiere et al. 2006; Vick 1983), with D10

(grain size at 10% passing) ranging from 0.37 to 2.09 lm

and D80 between 12 and 150 lm. The mean particle sizes

(D50) range from 7.69 to 65.39 lm. The specific gravities

(Gs) are between 2.43 and 3.32 (see Table 1) and are

indicative of the mineralogy (Greater Gs values indicate a

greater proportion of sulfide minerals) while the specific

surface area reflects the particle size distribution and the

presence of some phyllosilicate minerals well known for

their high specific surface. The fine grain size of the tail-

ings leads to a large ratio of surface area to mass,

significantly increasing the potential for exposure and

oxidation of sulfide minerals.

Figure 5 shows that samples S1–S7 have coarser texture

than samples R1–R8 and can be classified as a fine gravel.

The D80 was estimated to be between 10.5 and 13 mm and

to have less than 1% particles smaller than 80 lm. The Gs

values for all coarse tailings samples varied between 2.82

and 3.15.

The alteration process has been more intense in the

tailings dyke than the tailings pond. Indeed, in the coarse

tailings, extensive oxidation was observed through the

upper 75 cm (see Fig. 4). Due to their large particle size,

coarse tailings facilitate the access of oxygen and increase

oxidation of sulfides (e.g., Lefebvre et al. 2001). In con-

trast, the alteration in the tailings pond does not extend

more than 15 cm in depth from the surface. This may have

Fig. 4 Trench’s sampling on

Kettara fine and coarse tailings

Mine Water Environ (2008) 27:145–159 149

123

resulted from the hardpan layer formed at the surface of

tailings pond.

Chemical Analysis

Results from the chemical analysis of the fine and coarse

tailings are given in Table 2. Elements with very low

concentrations (such as Ba, B, Ti, and P) or below detec-

tion limits for the ICP analysis are not presented. As shown

in this table, the chemical composition varies with depth.

The important constituent determining the reactivity of the

fine and coarse tailings is the S, ranging from 1.6 to

14.5 wt%. However, part of the analyzed S is present as

sulfate, especially in the oxidized tailings samples R4 and

R8. The coarse tailings samples collected from the dyke

(S1–S7) contain less sulfur than the fine tailings (1.6–

3.7 wt%). Iron, which could be associated with pyrrhotite

and pyrite or with secondary oxide and sulfate minerals, is

present in relatively high quantities (17.4–40.7 wt%). The

mean molar ration of Fe/Ssulfide (8.5) exceeds the one

expected for pyrite or pyrrhotite. This confirms that a

significant proportion of the iron is associated with sec-

ondary minerals. Coarse tailings in piles (K1–K4) and in

dyke (S1–S7) have a similar chemical composition.

Variations with depth of Fe and SO42- concentrations in

tailings solid samples from the tailings pond and dyke are

shown in Fig. 6. The two profiles taken in the tailings pond

show a gradual decrease in sulfate concentration with

depth. However, contrary to what was observed for the fine

tailings, sulfate concentration in the dyke (made of coarse

tailings) varied little with depth. There was also no sig-

nificant difference between SO4 concentrations in the

oxidized and unoxidized zones, as the sulfates produced

by the oxidation of sulfides are evacuated progressively

since, in coarse tailings, water flow is much greater than

in the tailings pond. As an example, the saturated

hydraulic conductivity determined for S1 is relatively high

(1.7 9 10-2 cm/s).

The Fe concentrations vary little with depth in the dyke;

the values of samples taken in the oxidized zone are

slightly higher than those from the unoxidized zone. The

Fe concentrations vary more with depth in the tailings pond

and the values are higher in the interface between the

oxidized and unoxidized zones.

The tailings are also characterized by a significant pro-

portion of silicon and aluminum; the silicon (6–20 wt%)

and aluminum (1.1–7.8 wt%) contents indicate the pres-

ence of phyllosilicate gangue. Magnesium (1.6–5.2 wt%)

exceeds calcium (0.3–1.8 wt%), sodium (0.1–0.5 wt%),

and potassium (0.2–1.2 wt%). Table 2 shows the content of

some trace elements in the different tailings and coarse

tailings materials.

Table 1 Physical properties of the fine and coarse tailings studied

R1 R2 R3 R4 R5 R6 R7 R8 S1 S2 S3 S4 S5 S6 S7

Gs (specific gravity) 2.948 2.790 2.875 2.437 3.328 2.945 2.803 2.601 2.891 2.963 2.852 2.846 2.820 3.00 2.974

Specific surface area (m2/g) 6.345 19.613 20.829 3.759 3.223 6.559 ND ND – – – – – – –

D80 (% under 80) (mm) 0.013 0.020 0.130 0.076 0.095 0.0145 0.150 0.062 14 14 13 16 10.5 17 13

D10 (mm) 0.0011 0.0007 0.00037 0.0004 0.0021 0.00092 0.0005 0.0005 3.5 3.5 2.5 1.6 1.6 5.7 1.5

D50 (mm) 0.0057 0.0081 0.0096 0.0097 0.0351 0.0060 0.0149 0.153 9.8 8.5 7.9 9.5 5.8 12 5.6

D90 (mm) 0.0168 0.0396 0.1516 0.2433 0.1302 0.0207 0.2076 0.0874 14 15 13.3 17 11 22 14

ND not determined

0

20

40

60

80

100

0.01 0.1 1 10 100 1000

Grain size (µm)

Acc

umul

ated

vol

ume

(%)

R1R2R3R4R5R6R7R8

A

0

20

40

60

80

100

0.01 0.1 1 10 100

Grain size (mm)

Per

cent

pas

sant

(%

)

S1

S2

S3

S4

S5

S6

S7

B

Fig. 5 Size distribution for Kettara mine wastes

150 Mine Water Environ (2008) 27:145–159

123

Ta

ble

2C

hem

ical

com

po

siti

on

of

the

tail

ing

san

dco

arse

tail

ing

sst

ud

ied

Sam

ple

Tai

lin

gs

po

nd

(fin

eta

ilin

gs)

Dy

ke

(co

arse

tail

ing

s)T

aili

ng

sp

iles

(co

arse

tail

ing

s)

Tre

nch

1T

ren

ch2

Tre

nch

1T

ren

ch2

R1

R2

R3

R4

R5

R6

R7

R8

S1

S2

S3

S4

S5

S6

S7

K1

K2

K3

K4

Dep

th(c

m)

80

27

15

08

51

55

01

10

90

70

50

30

10

05

00

50

0

Maj

or

elem

ents

(wt%

)

Sto

tal

3.5

2.9

4.9

9.5

14

.55

.64

.11

0.0

3.2

2.8

2.5

1.6

2.3

2.1

3.7

3.6

4.1

5.6

1.1

Ssu

lfide

2.4

0.8

2.8

3.0

13

.64

.01

.53

.52

.52

.10

.80

.71

.21

.53

.40

.80

.71

.8N

D

SS

O4

1.1

2.1

2.1

6.5

0.9

1.6

2.6

6.5

0.7

0.7

1.7

0.9

1.1

0.7

0.3

2.8

3.4

3.8

ND

Ca

0.4

0.7

0.5

0.5

0.4

0.5

0.7

0.5

0.9

0.5

1.8

0.7

0.8

0.6

0.3

0.6

0.9

1.3

1.2

Si

15

.01

5.0

10

.06

.01

0.0

13

.01

2.0

7.0

20

.01

9.0

18

.01

9.0

19

.02

0.0

17

.01

9.6

18

.51

4.6

17

.0

Mg

5.1

4.1

1.6

2.2

2.2

5.2

2.5

2.1

3.6

4.2

3.1

2.7

3.0

3.4

3.0

3.0

2.9

4.3

3.5

Na

0.4

0.4

0.4

0.4

0.4

0.4

0.5

0.4

0.3

0.3

0.4

0.3

0.3

0.3

0.3

0.1

0.1

0.2

0.2

K1

.20

.40

.20

.20

.20

.50

.30

.20

.70

.40

.50

.40

.60

.30

.40

.50

.60

.30

.3

Fe

19

.32

6.8

39

.62

8.0

40

.72

2.1

34

.13

1.4

17

.41

7.9

17

.82

0.1

18

.81

8.9

22

.01

8.3

19

.31

9.2

19

.9

Al

7.8

3.2

1.1

2.3

3.1

6.3

1.6

1.6

6.6

7.0

6.0

5.2

5.8

6.1

6.0

5.6

5.4

5.0

5.1

Tra

ces

elem

ents

(pp

m)

Cu

1,9

30

1,8

90

1,3

80

2,6

00

4,2

00

3,0

00

1,0

00

1,7

20

1,2

40

1,2

20

2,6

60

1,5

50

2,2

40

1,1

10

1,7

80

1,2

18

1,3

20

1,8

91

1,3

68

Zn

43

01

30

33

02

00

43

09

01

30

34

04

70

33

05

00

43

02

40

30

04

60

41

05

15

60

35

97

Pb

90

80

10

04

06

00

01

00

70

10

30

30

50

80

40

72

18

21

81

13

1

As

00

00

18

02

03

04

01

20

00

70

20

20

44

06

93

25

59

63

Cd

50

60

90

60

90

60

80

70

30

30

30

30

30

30

30

25

.52

1

Co

60

40

30

70

23

08

02

06

07

05

04

03

03

05

05

03

52

20

11

16

2

Cr

27

02

70

35

02

70

37

02

80

31

02

90

27

03

30

25

03

20

24

02

60

25

07

36

88

28

4

Mn

1,2

10

48

02

90

75

07

70

1,1

30

36

07

50

1,0

90

1,1

30

96

07

90

89

09

30

99

09

12

90

21

,25

11

,15

5

Ni

30

10

01

02

03

00

10

70

90

60

70

50

60

40

27

18

.52

52

8

ND

no

td

eter

min

ed

Mine Water Environ (2008) 27:145–159 151

123

XRD Analysis

Relative abundance of minerals present in the Kettara mine

wastes as determined by X-ray diffraction were determined

using a Rietveld refinement method on a full XRD profile

(see Table 3). For all of the materials, the main minerals

found by the XRD analysis were goethite (FeO(OH)) (3.49–

72 wt%), quartz (6–43.5 wt%), chlorite–serpentine (Mg,

Al)6(Si, Al)4O10(OH)8) (6–48.5 wt%), talc (Mg3Si4O10

(OH)2) (7–16 wt%), and muscovite (KAl2.20(Si3Al)0.975O10

((OH)1.72O0.28) (0.8–8 wt%). Albite (NaAlSi3O8) is also

present in some samples. The carbonate content in the

various samples varied from practically 0 to a maximum of

1 wt%. The principal carbonate was identified as calcite. The

dominant mineralogy (quartz, silicates, aluminosilicates,

and goethite) is in agreement with the Si, Al, K, Mg, Na, and

Fe concentrations (see Table 2).

The X-ray diffraction data indicate that the main sulfide

minerals were pyrrhotite and pyrite. In the tailings, the

pyrrhotite and pyrite contents are almost identical and

reached a high value in R5, which aligns with the high

Ssulfide content in this sample (see Table 2). The pyrrhotite

and pyrite are accompanied by small amounts of chalco-

pyrite and traces amounts of galena and sphalerite.

Table 3 Relative abundance of investigated phases as determined by X-ray diffraction

Pyrrhotite Pyrite Chalcopyrite Sphalerite Quartz Chlorite Talc Muscovite Albite Goethite Magnetite Calcite Gypsum Jarosite

R1 Tr Tr Tr Tr M TA M F Tr M Tr Tr Tr Tr

R2 F F Tr Tr F F M Tr Tr TA Tr Tr F Tr

R3 Tr Tr Tr Tr F Tr M F Tr TA Tr Tr F Tr

R4 Tr Tr Tr Tr M F F F F A Tr Tr F M

R5 F F Tr Tr M M F Tr Tr A Tr Tr Tr Tr

R6 F F Tr Tr M A M F Tr M Tr Tr Tr Tr

R7 Tr Tr Tr Tr F F M Tr Tr TA Tr Tr F Tr

R8 F F Tr Tr M F M F F A Tr Tr F Tr

S1 F F Tr Tr A A M Tr Tr F Tr Tr Tr Tr

S2 F F Tr Tr A A M Tr Tr F F Tr Tr Tr

S3 Tr Tr Tr Tr A A M Tr Tr F Tr Tr F Tr

S4 Tr Tr Tr Tr A M M Tr Tr M Tr Tr Tr Tr

S5 Tr Tr Tr Tr A M M Tr Tr M F Tr F Tr

S6 Tr Tr Tr Tr A A M Tr Tr F Tr Tr Tr Tr

S7 F F Tr Tr A A M Tr Tr M F Tr Tr Tr

K1 Tr Tr Tr Tr A A F F Tr M Tr Tr Tr Tr

K2 Tr Tr Tr Tr A A F F Tr M F Tr Tr Tr

K3 F F Tr Tr M A F F Tr M Tr Tr F Tr

K4 Tr Tr Tr Tr A A F F F M Tr Tr F Tr

TA highly abundant ([50%), A abundant (30–50%), M medium (10–30%), F low (2–10%), Tr trace (\2%)

Fine tailings pond, Trench 2

Unoxidized Zone

0

20

40

60

80

100

120

Dep

th, c

m

Dyke made of coarse tailings

Oxidized Zone

Unoxidized Zone

FeSO4

Fine tailings pond,Trench 1

0

10

20

30

40

50

60

70

80

90

0wt. %

Dep

th, c

m

0

10

20

30

40

50

60

70

80

90

Dep

th, c

m

Unoxidized Zone

Oxidized Zone

20 40 60 0wt. %

20 40 60 0wt. %

10 20 30Fig. 6 Variation with depth of

iron and sulphate concentrations

in tailings solid samples from

tailings pond and dyke

152 Mine Water Environ (2008) 27:145–159

123

The amounts of jarosite (K, H3O)Fe3(SO4)2(OH)6) in

the oxidized fine tailings collected in the surface (R4 and

R8) are significant (1.4 and 1.22 wt%, respectively)

Jarosite was not detected in the coarse tailings (S1–S7 and

K1–K4). Due to their larger particle size, water migrates

rapidly through the tailings dyke, which reduces the

possibility of jarosite precipitation. High gypsum

(CaSO4�2H2O) levels were also detected in the oxidized

fine tailings, R4 and R8 (see Table 4). Figure 7 shows that

the pyrite and pyrrhotite concentrations increase with

depth in the fine tailings samples, while gypsum and

jarosite concentrations decrease with depth. These spatial

relations result because the secondary minerals (gypsum

and jarosite) are products of pyrite and pyrrhotite oxidation

and neutralization. Quantitative estimates of mineral

weight percentages are provided in Fig. 3.

The oxidation in the tailings is also indicated by the

high concentration (0–68 wt%) of iron oxyhydroxide,

represented by goethite. Figure 8 shows that goethite

abundance usually decreases with depth. At the surface of

the tailings pond and dyke, sulfides were replaced by

secondary iron solid phases.

SEM Analysis

The mineralogical alteration of primary minerals in contact

with AMD was demonstrated by SEM analysis. Figure 9a

shows the SEM micrographs of a pyrite particle that has

been altered to secondary minerals (jarosite). Pyrite can

also be coated by goethite and iron oxyhydroxide (FeO-

OH), as shown in Fig. 9b. The SEM micrograph in Fig. 9c

shows chlorite and quartz grains covered by iron sulfate,

probably jarosite or copiapite. Figure 9d shows a thin layer

of an iron oxide in direct contact with altered mixed pyr-

ite–chalcopyrite phase in the coarse tailings, S1. Figure 9d

also shows secondary gypsum in direct contact with pyrite

and a mixed pyrite–chalcopyrite phase. The precipitation

of weathering products onto tailings surfaces could influ-

ence their chemical and dissolution properties.

Fluoroapatite (Ca5(PO4)3F) and ilmenite (TiO2) were

identified by SEM analysis, as were other minerals, mostly

in trace amounts, such as: smectite (Na, Ca0.5)0.3(Al,

Mg)2(Si4O10)(OH)2,nH2O, monazite (Ce, La, Nd)PO4,

arsenopyrite (FeAsS), and barite (BaSO4). Traces of Bi,

Se, and Zr were also detetected.

Results of XRD and SEM performed on Kettara samples

combined with the chemical analysis show that:

• Mg is not associated with carbonates but rather with

silicate minerals (chlorite and talc)

• Al is bonded with the chlorite, muscovite, and albite

• Si is associated with quartz, chlorite, muscovite, albite,

and talc Ta

ble

4A

cid

-bas

eac

cou

nti

ng

fro

mth

eta

ilin

gs

and

coar

seta

ilin

gs

R1

R2

R3

R4

R5

R6

R7

R8

S1

S2

S3

S4

S5

S6

S7

K1

K2

K3

K4

AP

(kg

CaC

O3/t

)1

10

91

15

42

96

45

31

75

12

93

11

10

18

77

95

17

36

71

14

11

31

28

16

6–

NP

(kg

CaC

O3/t

)N

DN

DN

DN

DN

DN

DN

DN

DN

DN

DN

DN

DN

DN

DN

DN

D9

4.3

5

NN

P(k

gC

aCO

3/t

)-

11

0-

91

-1

54

-2

96

-4

53

-1

75

-1

29

-3

11

-7

7.8

-6

5.5

-2

6.3

-2

2.5

-3

7.8

-4

6.1

-1

04

.8-

78

.5-

10

1.9

-1

13

.7–

NP

/AP

00

00

00

00

00

00

00

00

.10

.04

0.0

4–

ND

no

td

etec

ted

by

the

met

ho

du

sed

Mine Water Environ (2008) 27:145–159 153

123

• Na is related to albite

• K is associated with muscovite

• Ca is present as gypsum and/or calcite

• In the fresh tailings, the sulfides have been partly

altered to secondary minerals (jarosite, gypsum, copia-

pite, and goethite); primary minerals, such as chlorite

and quartz grains, are covered by iron sulfate.

Acid–Base Accounting

Table 4 summarizes the modified ABA static test results.

The AP was corrected by first deducting the initial sulfate

content in each sample. All of the samples had negligible

NP, except for samples K2, K3, and K4 that had low NP

values: 9, 4.3, and 5, respectively. The AP was high, with

values between 51 and 453 kg CaCO3/t, which corresponds

to negative NNP values ranging from -453 to -22.5 kg

CaCO3/t. Using the criteria of Miller et al. (1991) or the NP

to AP ratio criteria of Adam et al. (1997), all of the Kettara

mine wastes are potentially acid-generating. Nevertheless,

the fine tailings have higher sulfur contents and acid-gen-

erating potential (average value of NNP = -215 kg

CaCO3/t) than the coarse tailings (average value of

NNP = -62.4 kg CaCO3/t).

Secondary Minerals

At the Kettara mine site, several secondary minerals have

been observed at the surface. These minerals occur as

extremely fine-grained particles (D1, D2, D3, D7, and D8),

or as a continuous precipitate layer known as hardpan (D4).

Other precipitates occur in other forms such as ‘‘blooms’’

or efflorescent salts (D5 and D6). The presence of these

minerals in large quantities shows that AMD generation is

very active at Kettara. Elements released by oxidation and

dissolution of primary minerals may be incorporated into

secondary minerals by co-precipitation, adsorption, or ion

exchange.

The chemical analysis and mineralogy determined by

XRD of samples D1 to D8 are presented in Table 5.

Analysis of the white precipitate (D1) formed in the tail-

ings pond indicated the presence of chlorite and quartz, and

various secondary minerals: halotrichite (FeAl2(SO4)4

22H2O), goethite (FeO(OH), jarosite-hydronian (K, H3O)

Fe3(SO4)2(OH)6), starkeyite (MgSO4 4H2O), gypsum, and

Fine tailings pond, Trench 2

Unoxidized Zone

0

20

40

60

80

100

120

Dep

th, c

m

Dyke made of coarse tailings

Unoxidized Zone

Oxidized Zone

xPyrite Gypsum Jarosite

Fine tailings pond,Trench 1

0

10

20

30

40

50

60

70

80

90

0

wt. %

Dep

th, c

m

0

10

20

30

40

50

60

70

80

90

Dep

th, c

m

Unoxidized Zone

Oxidized Zone

5 10 15 0

wt. %

2 4 6 0

wt. %

2 4 6

Pyrrhotite

Fig. 7 Variation with the depth

of pyrite, pyrrhotite, gypse and

jarosite concentrations in

tailings solid samples from

tailings pond and dyke

0

20

40

60

80

100

120

0

wt. %

Dyke made

of coarse

Oxidized Zone

Unoxidized Zone

Fine tailings pond,

Trench 1

0

20

40

60

80

100

0

wt. %

Oxidized Zone

Unoxidized Zone

Fine tailings pond,

Trench 2

Unoxidized Zone

Dep

th, c

m

0

20

40

60

80

100

Dep

th, c

m

Dep

th, c

m

25 50 75 0

wt. %

4020 60 80 5 10 15

Fig. 8 Variation with depth of

goethite concentrations in

tailings solid samples from

tailings pond and dyke

154 Mine Water Environ (2008) 27:145–159

123

alunite (KAl3(SO4)2(OH)6). The low K content in the

jarosite is probably due to hydronium substitution. In

the other white precipitate (D6) collected near the dyke

and the tailings piles, halotrichite and starkeyite were

present as secondary minerals. Heulandite (Ca3.6K0.8Al8,

8Si27O72�26.1H2O) was also detected by XRD. However,

the MEB analysis and chemical analysis could not con-

firm the presence of this phase. Interpretation of the

X-ray diffraction pattern in this particular case was diffi-

cult because of the chemical complexity of the samples and

the high degree of alteration of the sulfide and silicate

phases. In addition, the complex structure of the sulfate

phases yielded numerous peaks that were difficult to

interpret.

The white precipitates (sample D6) also contained:

Cu (1.3 wt%), Zn (0.08 wt%), Co (750 ppm), and Mn

(1,090 ppm). These metals are probably sequestered in the

secondary minerals through co-precipitation and adsorp-

tion. Given the relative low solubility of jarosite, this

will likely retain these elements more effectively in the

solid phase than soluble sulfate secondary minerals (e.g.,

copiapite) (Dutrizac 1984; Norton et al. 1991).

In the lemon-yellow colored sample (D2), the same

mineral phases were observed as was found in the white

precipitate. According to the chemical analysis, this sample

contained a considerable amount of unaltered iron sulfides.

In the greenish deposits (D3), the XRD analysis

showed the presence of only one mineral phase: copiapite

Fig. 9 SEM micrographs of

a pyrite grain in tailings

containing interstitial jarosite

and surrounded by and siderite,

b pyrite coated by goethite and

oxyhydroxide, c Quartz and

Chlorite surrounded by iron

sulfate, d Gypsum and iron

oxyhydroxide formed on the

surface of pyrite and

chalcopyrite in the coarse

tailings

Mine Water Environ (2008) 27:145–159 155

123

(Fe0.65Fe4(SO4)6(OH)2(H2O)20). This agrees with chemical

analysis concentration of Fe and SO4 (see Table 5). The

presence of this mineral at acid generating mine sites has

been noted by several authors (e.g., Bayless and Olyphant

1993; Cravotta 1994; Jambor 1994; Lin 1997; Zodrow

1980). Copiapite is a relatively soluble sulfate secondary

mineral that is as an indicator of extremely acidic

conditions.

The yellow-orange sample (D4) was collected from a

hardpan layer formed at the surface of the Kettara tailings

pond. Mineralogical analysis indicated that the cementing

materials of the hardpan are primarily composed of sec-

ondary goethite. XRD analysis also revealed the presence

of elementary sulfur, which is an intermediate phase of

pyrrhotite or pyrite oxidation (Belzile et al. 2004). Ele-

mentary sulfur can be also formed under low oxidation

conditions (Flan and Lukazewki 1970). The main heavy

metals associated with this phase were Cr (140 ppm) and

Cu (2,090 ppm).

Previous studies of inactive mine-tailings impoundments

have reported similar hardpans composed of Fe(III)

cementing minerals (Blowes and Jambor 1990; Blowes et al.

1991; Coggans et al. 1999; Courtin- Nomade et al. 2003;

Giere et al. 2003; Johnson et al. 2000; McGregor and Blowes

2002; Tasse et al. 1997). Hardpan layers attenuate metal ions

by adsorption and co-precipitation processes (Blowes et al.

Table 5 Chemical composition and Mineralogical analysis of the secondary precipitates

Identification D1 D2 D3 D4 D5 D6 D7 D8

Color White Lemon-yellow Green Yellow–

orange

Yellow &

green

White Ochre Light gray

Major elements wt%

Stotal 13.7 13.1 13.8 15.9 14.2 13.9 12.7 10.5

Ssulfide 0.6 5.0 0.0 14.6 0.8 0.6 3.9 4.3

SSO413.1 8.1 13.6 1.3 13.4 13.3 8.8 6.2

Ca 0.1 0.2 0.1 0.3 0.1 0.1 0.1 0.7

Si 1.1 5.3 0.5 5.8 1.1 1.0 2.6 19.9

Mg 3.4 2.3 0.6 1.0 0.7 3.8 0.5 0.7

Na 0.1 0.2 0.1 0.3 0.1 0.1 0.2 0.2

K 0.1 0.2 0.1 0.1 0.0 0.0 0.1 0.2

Al 4.7 3.1 0.9 1.5 0.6 3.9 0.4 1.0

Fe 5.7 20.2 21.2 43.9 27.1 5.5 41.9 6.4

Minor and trace elements ppm

Ba 10 30 0 60 0 0 0 100

Zn 810 540 170 150 290 800 200 100

Cu 5,500 3,940 3,150 2,090 4,250 13,000 3,000 700

Pb 10 60 20 80 30 0 100 100

As 0 40 0 50 0 0 50 230

B 180 560 260 750 320 140 940 50

Cd 0 10 10 10 10 0 10 0

Co 350 230 170 50 350 710 230 30

Cr 100 120 60 140 60 40 70 80

Mn 860 670 190 430 240 1,090 140 200

sNi 70 60 20 50 20 70 20 30

Minerals determined

by XRD

Chlorite Chlorite Copiapite Goethite Copiapite Halotrichite Copiapite Sulfur

Gypsum Gypsum Sulfur Hydronium

jarosite

Starkeyite Hydronium

jarosite

Quartz

Goethite Goethite Quartz Butterite Heulandite Hematite Coquimbite

Jarosite-

hydronian

Jarosite-

hydronian

Chlorite

Alunite Alunite Talc

Halotrichite Halotrichite

Starkeyite Starkeyite

Quartz Quartz

156 Mine Water Environ (2008) 27:145–159

123

1991), and can also serve as a barrier to oxygen diffusion and

water infiltration into the tailings, limiting (at least tempo-

rarily) pyrite and pyrrhotite oxidation. This agreems with

observations made at the Kettara mine site, where depths of

the oxidation front in the tailings pond do not exceed 15 cm

where the hardpan layer is present.

The yellow and green precipitate formed under the

hardpan layer (D5) is mainly copiapite, hydroniumjarosite

((H3O)Fe3(SO4)2(OH)6), and butterite (Fe(OH)SO4�2H2O).

The yellow and green colors are respectively characteristic

of jarosite and copiapite. The expansion generated by the

formation of these secondary phases has raised the top

cemented layers in the tailings pond (D5).

The secondary minerals hydroniumjarosite, hematite,

and copiapite predominated in the precipitate (D7),

collected from an ochreous tailings pile (see Fig. 6). Sig-

nificant quantities of Cu (3,000 ppm) were also present.

The gray precipitate (D8) formed in the coarse tailings

at the main dyke is primarily quartz. The secondary min-

erals identified by XRD are coquimbite (Fe3(SO4)3�9H2O)

and native sulfur. The chemical analysis showed higher

arsenic concentrations (230 ppm).

Conclusions

At the Kettara mine site in Morocco, an abandoned pyr-

rhotite ore mine located in a semi-arid climatic zone, more

than 3 million tons of mine wastes (fine and coarse tailings)

were deposited at the surface without concern for environ-

mental issues. These tailings contain 1.2–14.5 wt% sulfur.

Twenty four years after mine closure, pyrite and pyrrhotite

still remain at significant concentrations; pyrrhotite content

ranges between 0 and 2.1 wt% and pyrite content ranges

between 0.56 and 2.6 wt%. Significant concentrations of

Cu are present in the solid samples (1,100–4,200 ppm

(mg/kg)), with lesser amounts of Zn (130–460 ppm), Cr

(68–370 ppm), Pb (0–182 ppm), Co (20–230 ppm), As

(0–440 ppm), Cd (1–90 ppm), and Ni (0–90 ppm). These

results show that AMD generation will continue for decades

or centuries if no remedial actions are taken.

Acid–base accounting static test results showed that all

of the samples have very low (4.3–9 kg CaCO3/t) to nil NP.

The mine wastes are considered highly acid-generating,

with an AP estimated to range from 51 to 453 kg CaCO3/t.

These results are in agreement with the S contents and the

XRD analysis, which shows the presence of many sulfide

minerals and the absence of neutralizing minerals.

Several types of secondary minerals have formed at the

site. The main phases detected were: halotrichite, goethite,

jarosite–hydronian, hydroniumjarosite, starkeyite, gypsum,

alunite, copiapite, butterite, coquimbite, and native sulfur.

Goethite, jarosite, halotrichite, and copiapite were the most

frequently found minerals in the studied paragenesis. The

main alteration products from the oxidation of sulfide

minerals in the oxidized zone of the coarse tailings were

coquimbite and native sulfur. Relatively high concentration

of heavy metals were associated with the secondary min-

erals: Cu concentrations ranged up to 1.3%, Zn 0.08%, Co

750 ppm, and As 230 ppm. These secondary minerals

represent a volumetrically minor constituent within the

mine site, but their impact can be very significant. Soluble

sulfates, formed in a semi-arid environment by evapora-

tion, can store metals and acidity during the dry periods

and then dissolve during the wet season. The metal

pollutants and the sulfate are then released by runoff

and recharge during storm events, increasing water

contamination.

In the main dyke, extensive oxidation of the coarse

tailings occurs in the upper 75 cm, whereas alteration in

the fine-grained tailings pond does not extend 15 cm

beneath the surface. Due to their large particle size, the

coarse tailings in the dyke may facilitate access of oxygen,

increasing sulfide oxidation. Despite the larger surface area

of the fine tailings, which can increase oxidation rates, the

coarse tailings seem to be more environmentally reactive

and, hence, more significant sources of pollution than the

fine tailings at the Kettara mine.

Rehabilitation of the Kettara mine site is necessary to

limit further environmental impact. One scenario would be

to build a store-and-release capillary barrier cover on the

Kettara mine wastes. This would limit the percolation of

water to the reactive mine wastes, hence reducing AMD

production (see Aubertin et al. 2006; Khire et al. 2000 for

more details). Another option would be to use alkaline

waste rock generated at a nearby phosphate quarry as an

amendment, to neutralize acidity generated by the tailings.

The neutralization products likely would consist of goethite

and other secondary minerals. If a hard pan layer could be

formed by these secondary minerals, percolation of water

and oxygen and oxidation at depth may be reduced.

Acknowledgments The authors thank the Agence Universitaire de

la Francophonie (AUF), the Canada Research Chairs on the Resto-

ration of Abandoned Mine Sites and Integrated Management of

Sulphidic Mine Waste using Fill Technology, and the Unite de

Recherche et de Service en Technologie Minerale (UQAT), for their

financial and technical support.

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