Tailings dams and rock dumps from mining operations often contain hazardous waste that can pollute the environment if released. There are over 3,500 tailings dams worldwide. Tailings dams are susceptible to failures, which have released millions of cubic meters of toxic slurries. Major documented failures include releases in China (2006), USA (2000), Spain (1998), Guyana (1995), and Italy (1985), resulting in loss of life and extensive environmental damage. Upstream construction is most prone to failure, with a 5% failure rate.

1. Topic 4: Mine wastes
From a series of 5 lectures on
Metals, minerals, mining and (some of) its problems
prepared for London Mining Network
by
Mark Muller
mmuller.earthsci@gmail.com
24 April 2009

2. Outline of Topic 4:
• Types of mine waste: mine waters, tailings, sulphidic wastes
• Rock dumps
• Focus on tailings dams
Tailings dam construction methods
Water balance in tailings dams
Tailings dam failure, with case studies
• Thickened paste disposal
• In-pit disposal
• Riverine tailings disposal
Case study on riverine tailings disposal
• Submarine tailings disposal
Case study on submarine tailings disposal
• Focus on radioactive wastes of uranium ores
Radioactive minerals, radioactive decay products and health risks
Release of radioactive minerals into the environment by oxidation
Impact of release of radioactive minerals

3. Mineral extraction: from mining to metal
Mining
Mineral
concentrate
METAL EXTRACTION
Metal
Figure from Spitz and Trudinger, 2009.

4. Mines wastes:
Mine wastes are problematic because they contain hazardous substances that
can be (or are) released into the environment around the mine – heavy
metals, metalloids, radioactive elements, acids, process chemicals –
and therefore require treatment, secure disposal, and monitoring.
Wastes are not only produced during mining, but also at mineral
processing plants and smelter sites and include effluents, sludges,
leached ore residues, slags, furnace dusts, filter cakes and smelting
residues.
Mine wastes may be in the form of: solid waste, water waste, or gaseous
waste.
Environmental contamination and pollution as a result of improper mining,
smelting and waste disposal practices has occurred, and still occur,
around the world (Lottermoser, 2007).

5. Mine wastes:
Open-pit mining Produces waste rock:
Underground mining either barren host rock (referred to as “spoils” in coal
mining),
or “ore” that is too low-grade, overburden soils and sands.
Mineral processing Produces processed solid wastes that includes tailings and
Hydrometallurgy sludges with different physical and chemical properties.
Tailings can be used as mining back-fill, but are generally
contained on surface.
Also produces mill-water and other processing waste-water
also produced, as well as atmospheric emissions.

6. Sulphidic mine wastes:
Sulphide wastes are the biggest problem on mines because of
potential for generating acid mine waters. Pyrite is the major
concern.
Sulphide minerals occur abundantly in many types of deposits
- Metallic ore (Cu, Pb, Zn, Au, Ni, U, Fe)
- Phosphate ores
- Coal seams
- Oil shales
- Mineral sands
Sulphide minerals may be exposed (just about) everywhere in mines
- Tailings dams
- Waste rock dumps and coal spoil (overburden) heaps
- Heap leach piles
- Run-of-mine and low-grade ore stockpiles
- Waste repository embankments
- Open-pit floors and faces
- Underground workings
- Haulroads and road cuts

7. Acid mine waters:
“Acid mine drainage” (AMD) refers to a particular process whereby low pH
mine water is formed from the oxidation of sulphide minerals. It
provides one of the most significant hydrological impacts of mining.
AMD is particularly prevalent in both metallic mineral and coal mines.
Some authors refer to “Acid rock drainage” (ARD), “acid sulphate waters”
(ASW); and also “acidic ground water” (AG) when referring to impacted
ground-water specifically.

8. Waste-rock disposal – rock dumps:
“Waste-rock” is rock emerging from the mine that will not be processed
further. It is either “ore” that is below the cut-off grade, or is simply
the barren host-rock to the mineral deposit.
Rock dumps contain an wide variety of different rocks and minerals that
is site specific, depending on the nature of the ore deposit and the
host-rock. If sulphide minerals are present in any of the rocks, there
is the potential for acid mine drainage.
Generally rock dumps are not sealed at their base, and the risk of
acid water incursion into the surface drainage system or subsurface
aquifers is very high.
Rock dumps are also highly porous to water flow, and therefore
increases significantly the risk of AMD production.

9. Top-down storage: waste
rock is dumped over an
Rock dumps
advancing face.
Bottom-up storage:
waste rock is
dumped in a series
of piles, and later
spread out and
flattened, to be
covered by the next
layer of dumping.
Trucks (the size of houses) dump 200-ton loads of waste rock from an open pit mine in
Nevada. A composite storage approach is used here: top-down dumping is following after
an earlier phase of bottom-up dumping.
http://science.nationalgeographic.com/science/enlarge/dumping-waste-rock.html

10. Waste-rock disposal – rock dumps:
Typically a “plume” of contaminated water (either acidic or not) and
precipitated waste products is developed below and around a rock
dump.
Figure from Lottermoser, 2007, reproduced from Jurjovec et al., 2002.
DUMP
SURFACE
Potential for lateral migration
of contaminated or acidic
water within subsurface
aquifers
Schematic cross-section of a sulphide waste dump showing a plume of acid water seeping
into the ground. Also shown is how various subsurface minerals (at this particular site) help
to buffer, or neutralise, the acid. The initial highly acidic pH value of 1, directly below the
dump, is buffered back to a neutral pH value of 7 at some depth below the dump.

11. Tailings disposal:
Tailings are (generally) stored in engineered structures or impoundments,
called “tailings storage facilities” or “tailings dams”. It is estimated
that there are at least 3,500 tailings dams worldwide (Davies and
Martin, 2000).
Tailings dams should be constructed to:
- Contain waste materials indefinitely, and provide long term stability
against erosion and mass movement.
- Achieve negligible seepage of tailings liquids into ground and surface
waters to prevent contamination of these waters.
- Prevent failure of dam structures.
The overriding issue with tailings dams is getting the liquid out of
them, safely, both during mining and afterwards.

12. Tailings disposal:
In an alternative disposal approach (that is often highly criticised), no
impoundment is used at all, and tailings are pumped directly into rivers
(riverine tailings disposal), lakes (lacustrine disposal) or into the
ocean and onto the seafloor at some water (submarine tailings
disposal – STD).

13. Tailings composition:
Tailings consist of a liquid and solid component: generally about 20 – 40
weight percent solids (Robertson, 1994). The composition of both is
highly site-specific, depending on the ore and gangue minerals and
the nature of the water (fresh or saline) and processing chemicals used.
Tailings waters may be alkaline (cyanide used in processing), acidic
(sulphuric acid used in processing) or saline (saline water used in
processing). They are a complex cocktail of residues of the processing
chemicals. The waters are highly chemically reactive.
GRAIN SIZES OF SOLIDS
Tailings solids. Solids are very fine
grained.
Figure from Lottermoser, 2007.

14. Tailings disposal methods
Different disposal methods
are used at different mines,
sometimes in combination,
depending on local
circumstances and
constraints.
Factors may include:
Composition of tailings
Climate
Local land use
Local topography
Costs
Environmental impacts
Safety concerns
TSF = “Tailings storage facility”
(i.e., tailings dam)
Figure from Spitz and Trudinger, 2009.

15. Tailings disposal on surface – tailings dam styles or configurations
Topographic conditions around the
mine generally dictate the
configuration of the tailings dams.
Additional storage capacity can be
obtained by filling depressions or
valleys in the topography.
3 configurations of tailings dams used
- Paddock (or ring-dyke): 4 dam walls
needed
- Hill-side: 3 dam walls needed
- Cross-valley: 1 or 2 dam walls
needed.
Figure from Spitz and Trudinger, 2009.

16. Tailings dams – construction:
Tailings dams hold up to several hundred million cubic meters of water
saturated tailings – they can be very, very large structures.
The fundamental constructed elements of a tailings dam are:
- Dam walls (dykes) to contain the tailings. These are normally constructed
using waste rock and material available at the dam site. The maximum
wall height is reported currently to be about 100 m.
- Impermeable liners at the base of the dam to prevent leakage of fluids.
Linings may consist of geomembranes (polyethylene or PVC), or clay
layers, or a combination of the two.
- Drainage ditches around the periphery of the tailings dam to collect
seepage.
- Under-drains to facilitate drainage and consolidation of the tailings in the
dam. (Not all tailings dams have under-drains installed). Without under-
drains, tailings dams can only dry-out by evaporation and seepage, which
generally takes a long time (years after mining has ceased).

17. Tailings dams – construction
Tailings dam at Chatree
Gold Mine (Thailand)
shortly after
commissioning, showing
under-drains installed
in a herring-bone
pattern. Under-drains
significantly improve
water drainage from the
tailings dam, thereby
reducing water saturation
of tailings sediments and
improving geotechnical
strength and safety of the
dam.
Figure from Spitz and Trudinger, 2009.
Best practice tailings dam construction will consist of:
(i) drains beneath the dam walls,
(ii) double liners under the dam, with a leak detection system between layers,
(iii) under-drains at the base of the tailings and a liquid recovery system.

18. Tailings dams – construction
Mature, but active,
tailings dams located
south of Johannesburg,
South Africa. These
dams are receiving the
final tailings products of
the reprocessing of
numerous old mine-
dumps spread around
Johannesburg. The
mines were closed in
the 1960s.
http://www.panoramio.com/photo/2399572

19. Tailings dams – construction
Dam walls are built up successively, from a Solid tailings become segregated in
“starter dyke”, during the mine lifetime. Three the tailings dam, based on their
methods of successive build-up are commonly grain-size and distance from the
used. discharge point.
Surface
UPSTREAM
METHOD
Liner
DOWNSTREAM
METHOD
Fine-grained Coarse-grained
CENTRELINE sediments settle sediments settle
METHOD further from the closest to the
discharge point, discharge point,
and are and are
significantly less significantly more
In the “upstream” method, note how much thinner the dams permeable permeable – they
walls are, and how much less construction material is (porous). drain more easily.
used. Also note that new embankment material overlies
These sediments These sediments
earlier tailings deposits, which may not have adequate
have lower shear have higher shear
strength to support the weight of the embankment, strength. strength.
especially if water saturation levels in the tailings suddenly
increase, or in the face of earthquake-induced tailings
liquefaction.
Figures from Lottermoser, 2007.

20. Tailings dams – water balance
Tailings dams remain wet during their entire operational life, and only start drying out
after decommissioning.
Contamination-plumes below tailings dams are normally much reduced compared to
rock-dumps, due to the low porosity of tailings materials and the low permeability
of the liner at the base of the tailings dams.
Water extracted for re-use High potential for sulphide oxidation and
from decant pond Precipitation of salts at acid development in area immediately
edge of decant pool above saturated zone
Beach UNSATURATED
Hill-side
ZONE
SATURATED ZONE Drainage
ditch
Liner
Water exchange below the Dam-wall may be saturated at its
tailings dam depends on base, particularly if the decant
permeability of the liner pond is too close to it – saturation
weakens the strength of the wall
Figure modified from Spitz and Trudinger, 2009.

21. Tailings dams – failure:
More than 50% of tailings dams worldwide are built using the upstream
method, although it is well recognised that this construction method
produces a structure which is highly susceptible to erosion and failure
(Lottermoser, 2007) – less construction material is used, and the dam
walls are thinner. Statistically, every 20th upstream tailings dam that
is built, fails (a 5% failure rate), and there have been about 100
documented significant upstream tailings dam failures (Davies and
Martin, 2000).
Lottermoser (2007) catalogues 26 tailings dam failures that have
occurred within the last twenty years, and 13 within the last 10
years.
There are at least 138 known significant tailings dam failures to date. (
http://www.wise-uranium.org/mdaf.html; Spitz and Trudinger, 2009;
UNEP, 2001)
Most failures, whatever the construction method, have occurred in humid,
temperate regions. There have been very few failures in semi-arid and
arid regions.

22. Tailings dams – failures 1909 to 2000, per decade
Contemporary
failure rate of
tailings dams is
much higher than
water supply dams.
Average failure
rate for 1998 to
2008 was 1.3
failures per year.
Low numbers of failures recorded in early
years due to: (i) lower numbers of tailings
dams and (ii) less complete records of
failure from these years.
Figure from Spitz and Trudinger, 2009 (Based on data from UNEP, 2001).

23. Tailings dams and rock dumps - selected list of major failures
Date Location Incident Release Impact
Tailings dam failure during wall 17 people missing. Cyanide release to
2006 April 30 Miliang, China raise ? local river
3
950 000 m coal waste Contamination of 120 km of rivers and
2000 October 11 Inez, USA Tailings dam failure slurry streams. Fish kills
Grasberg, Irian Jaya Waste rock dump failure after Unknown quantity heavy 4 people killed. Contamination of
2000 May 4 (West Papua) heavy rain metal bearing wastes streams
2,616 ha farmland and river basins
flooded with tailings. 40 km of stream
3
Los Frailes, Collapse of dam due to foundation 4.5 million m of acid, contaminated with acid, metals and
1998 April 25 Aznalcóllar, Spain failure pyrite rich tailings metalloids
3
4.2 million m cyanide 80 km of local river declared
1995 August 19 Omai, Guyana Tailings dam failure bearing tailings environmental disaster zone
Merriespruit, South 17 people killed. Extensive damage to
3
1994 February 22 Africa Dam wall breach after heavy rain 600 000 m town
Olympic Dam, South Leakage of uranium tailings dam
3
1994 February 14 Australia into acquifer 5 million m ?
Ok Tedi, Papua New Collapse of waste rock dump and 170 Mt waste rock and 4
1989 August 22 Guinea tailings dam Mt tailings Flow into local river
Failure of fluorite tailings dam due
3
1985 July 19 Stava, Italy to inadequate decant construction 200 000 m 269 people killed. Two villages buried
Embankment failure of platinum
Bafokeng, Impala, tailings dam due to excessive 15 people killed. Tailings flow 45 km
3
1974 November 11 South Africa seepage 3 million m downstream
Failure of coal refuse dam after 150 people killed. 1,500 homes
3
1972 February 26 Buffalo Creek, USA heavy rain 500 000 m destroyed
Tailings move into underground
1970 September 25 Mufulira, Zambia workings 1 Mt 89 miners killed
Aberfan, Great Liquefaction of coal refuse dam
1966 October 21 Britain after heavy rain ? 144 people killed
Liquefaction of 2 tailings dams 250 people killed. Tailings traveled 12
1965 March 28 El Cobre, Chile during earthquake 2 Mt km downstream, destroyed El Cobre
List selectively extracted from Lottermoser, 2007, with further information added from http://www.wise-uranium.org/mdaf.html

24. Tailings dam failure – Stava, Italy, 19 July 1985
When a tailings dam breach occurs, some or all of the tailings migrate out of the impoundment and
flow downstream. Obstructions in the path of the flow are either swamped or carried downstream.
A disastrous dam failure and flow of tailings occurred in 1985 at Prestavel mine in Stava, Italy.
The dam breached as a result of heavy rains which caused overtopping. The flow travelled down
the valley through the town of Stava, killing 268 and destroying 62 buildings and 8 bridges.
Stava before the breach. Stava covered by tailings as they
www.wise-uranium.org/mdafst.html travel through the valley.
www.wise-uranium.org/mdafst.html From TAILSAFE, 2004.

25. Tailings dam failure – Los Frailes, Aznalcóllar, Spain, 25 April 1998
A tailings dam failed at Los Frailes mine in Aznalcóllar, Spain in 1998. The failure is thought to
have occurred as a result of the marl foundations of the dam being eroded by the acid seepage
from the tailings that passed through the embankment walls. The weakness in the foundations
combined with the minimal length of beach (i.e., ponded water was encroaching the embankment)
caused high stress in the foundations, thus resulting in the failure of the embankment material.
In total, 4.6 million cubic meters of toxic tailings and effluent poured into the Río Agrio and
Río Guadiamar Rivers. Note: marl is a clayey limestone and it dissolves in acid.
Aerial photo of breached
embankment.
www.tailings.info
From TAILSAFE, 2004.

26. Tailings dam failure – Mufulira, Zambia, 25 September 1970
On the 25th September 1970 an underground breach of No. 3 tailings dam occurred at the Mufulira
Mine in Zambia. As the night shift crew were on duty, the tailings dam above them collapsed
causing nearly 1 million tons of tailings to fill the mine workings, killing 89 miners. A sinkhole
opened on the surface allowing surface water to continue to pour into the workings.
Two years prior to the disaster, sink holes opened up within the No.3 tailings pond due to roof
collapse underground, and a surface depression developed in the impoundment. There were also
two cases of minor mud ingress into the mine a few months before the main failure. Management
were reluctant to accept and investigate the potential impact of future sink holes. Finally, a sink
hole opened connecting the underground workings and the tailings in the impoundment.
Aerial photo of the sinkhole in No. 3 dam. Sinkhole in No. 3 dam and processing plant.
From www.tailings.info and TAILSAFE, 2004.

27. Tailings dams – failure – causes:
Poor choice of site, poor dam design, poor dam construction, or poor
management
Liquefaction of tailings and dam: Liquefaction describes the change in
behaviour, from “solid” to liquid, of a liquid-saturated sedimentary unit in
response to increased pore-fluid pressures (pores are the spaces
between particles) – the solid particles literally loose contact with each
other and the unit loses its physical cohesiveness. High pore-fluid
pressures are induced by ground motions resulting from earthquakes
(e.g., Veta de Agua, Chile, 3 March 1985), mine blasting, or nearby
motion and vibrations of heavy equipment.
Rapid increase in dam wall height: If an upstream dam is raised and the
dam filled too quickly, very high internal pore pressures are produced in
the tailings and dam walls, decreasing the dam stability and leading to
dam failure (e.g., Tyrone, USA, 13 October 1980).

28. Tailings dams – failure – causes:
Foundation failure: If the base below the dam is too weak to support the
weight of the dam, movement along a failure plane will occur (e.g., Los
Frailes, Spain, 25 April 1998).
Excessive water levels: Dam failure can occur if the top of the saturated
zone in the tailings dam rises too high. Flood inflow, high rainfall, rapid
melting of snow, and improper water management may cause
excessive water levels. If “over-topping” of the embankment occurs,
breaching, erosion, and complete failure of the dam walls are possible
(e.g., Baia Mare, Romania, 30 January 2000). It is important to keep
decant pond as small as possible and as far as possible from the
containing embankments.
Excessive seepage: Seepage within or beneath the dam causes erosion
along the seepage flow path. Excessive seepage may result in failure
of the embankment (e.g., Zlevoto, Yugoslavia, 1 March 1976).

29. Tailings dams – failure – consequences:
Release of huge volumes of tailings, that may enter underground
workings, towns and villages or spill into waterways and travel
downstream, polluting streams for considerable distances and covering
large surface areas with thick, metal-rich mud, and causing significant
environmental damage to impacted ecosystems.
Significant loss of life.

30. Thickened discharge and paste disposal
Thickened tailings
AIR-PHOTO PLAN VIEW
are discharged
from central “riser”
and a series of
outer risers to
create a set of
cone shaped
impoundments.
The “risers” are
moved up
incrementally as
the layers of
tailings material
build up.
Figure is greatly
vertically
exaggerated:
the slope of 1 – 3°
“beaches” is
only 1 to 3°
Figure from Spitz and Trudinger, 2009.

31. Thickened discharge disposal – advantages and disadvantages:
See e.g., Williams and Seddon, 1999; Brzezinski, 2001.
Advantages over conventional tailings disposal are that:
(i) The disposal site covers a much smaller surface area,
(ii) tailings are not segregated into coarse and fine components, which
improves the geotechnical properties of the pile,
(iii) water consumption is significantly reduced,
(iv) process chemicals are recovered with the water, rather than left with the
tailings,
(v) contaminated water drainage into the subsurface and surface water
systems is reduced,
(vi) The resulting cone shaped deposit provides an attractive landform (say
the miners!), more amenable to rehabilitation.
Disadvantages of the method include:
(i) The operations are subject to dust generation,
(ii) failure due to liquefaction is not ruled out entirely during the period
required to dry the paste (McMahon et al., 1996).

32. In-pit waste disposal:
Tailings may be pumped into mined-out open pits (as well underground mine workings)
for final disposal.
Backfilling an open-pit eliminates the formation of an open-pit lake.
Any backfill material placed below the water table will form part of the subsurface
acquifer. The extent to which the water level inside the open pit equilibrates with
the regional water table will depend on whether or not the open pit is lined with clay
or other impermeable layer.
Water-waste reactions may lead to the mobilisation of contaminants into ground waters.
Backfilled open-pit showing
return of the water table to
pre-mining levels.
Sulphidic tailings with high
acid generating potential are Water
placed at a depth below the saturated
final level of the water table
(to limit oxygen supply to the
sulphides and hence
minimise the risk of acid
water development).
Figure from Lottermoser, 2007.

33. Riverine tailings disposal:
Riverine tailings disposal is currently used in more than a few modern
mining projects, e.g., the copper mines at:
- Grasberg-Ertsberg, Indonesia
- Porgera, Papua New Guinea
- Ok Tedi, Papua New Guinea
- Bougainville (closed), Papua New Guinea
Riverine disposal is “preferred” in these areas because earthquakes,
land-slides and very-high rainfall makes the construction of tailings
dams geotechnically “impossible”.
Miners argue that high natural sediment loads in rivers, generated by the
high rainfall, is able to dilute the mine tailings discharges. (Nonsense –
tailings volumes are huge compared to the natural sediment load).
Tailings can be neutralised before disposal into the river systems (but they
are not always).
Historically riverine tailings disposal from mines was commonly practiced.

34. Riverine tailings disposal – impacts:
The solids and liquids of tailings are transported down rivers for
considerable distances: tens to hundreds to thousands of
kilometers.
Sulphide minerals in discharged tailings generally oxidise in oxygenated
river waters, creating the potential for acidification of waters.
Problems include:
- Significantly increased sedimentation and turbidity in the river
system, and associated flooding of lowlands.
- Contamination of the stream and floodplain sediments with metals,
and associated impact on aquatic ecosystems.
- Diebacks of rainforests and mangrove swamps.

35. Riverine tailings disposal – case study – Ok Tedi, Papua New Guinea:
Ok Tedi open-pit mine is located at 1,600 m elevation in the Star Mountains,
in a high rainfall, mudslide and earthquake prone region.
The mine produces a copper-gold-silver concentrate for export, accounting
for a significant proportion (about 16%) of PNG’s total annual export
income (Enright, 1994; Murray et al., 2000).
In 1976, the state of Papua New Guinea authorized BHP, Australia’s biggest
mining corporation, to prepare a development plan for the mine. Four
years later, the government committed to a partnership in Ok Tedi Mining
Limited with a 20 percent shareholding. The other shareholders were
BHP (the major shareholder), Amoco Minerals, and a consortium of
German companies (World Resources Institute report
http://archive.wri.org/page.cfm?id=1860&z=?, and references therein)
Mine construction was authorised in August 1981, with production scheduled
to begin May 1984. The Environmental Impact Assessment was only
completed in June 1982, a year after construction started, at which
time the decision not to mine was no longer an option (Townsend and
Townsend, 2004).

36. Riverine tailings disposal – case study – Ok Tedi, Papua New Guinea:
A tailings dam was constructed initially, but was swept away by a
landslide just before production started in 1984. At that time, the
PNG government controversially granted permission to the mine’s main
shareholder and operator (BHP) to utilise riverine tailings disposal.
Riverine disposal is thus allowed under, and is in compliance with,
PNG laws and regulations. (Which does not necessarily make it
environmentally or socially desirable though).
Since 1986, tailings have been discharged, and waste rock dumps
have been left to erode, into the headwaters of the Ok Tedi and Fly
river systems, which subsequently drain, via the Strickland River and
estuary, into the Gulf of Papua, over a total distance of over 1,000 km
(Hettler et al., 1997).

37. Riverine tailings disposal – case study – Ok Tedi, Papua New Guinea
The volume of tailings generated and deposited into the Ok Tedi and Fly rivers is enormous.
The discharge rate amounts to about 160,000 tons of waste per day. About 1,400 million
tons of waste is estimated to have been released into the tropical river system during the
period 1984 – 2007.
Ok Tedi gold and copper mine (Papua New Guinea)
5 June 1990 26 May 2004
Image source: “One Planet, Many People: Atlas of our Changing Environment”, UNEP, 2005.

38. Riverine tailings disposal – case study – Ok Tedi, Papua New Guinea:
Impacts on the environment include:
- Increased river turbidity. The small grain size (<100 μm diameter) and
large quantity of waste has increased the sediment load to the middle
Fly River by 5 – 10 times the normal load, impacting on aquatic life.
- Increased sedimentation. The wastes are deposited everywhere along
the river, all the way down to the Gulf of Papua, but particularly on the
floodplains of the middle and lower Fly River. Large areas of tropical
lowland rainforests and mangroves have also been covered with a thin
veneer of waste.
- Metal contamination of sediments. Deposited sediments are
enriched in copper and gold, and contamination moves into the river
waters themselves, with high potential toxicity to fish populations and
communities living along the rivers.

39. Riverine tailings disposal – case study – Ok Tedi, Papua New Guinea:
Social impacts:
By 1989, river communities were struggling to produce enough food,
and a social impact study in 1991 showed that environmental
degradation was causing severe hardships to peoples living
downstream from the mine.
“This chronic build-up of waste has had a devastating effect on the 50,000 people who live in the
120 villages along the two rivers and depend on them for subsistence fishing and other river-
based resources. Before the mine, taro and bananas were commonly grown in village
gardens and riverside sago palms often provided the mainstay of local diets. But since the
early 1990s, the build-up of sediment in the rivers and subsequent flooding of forests have
dramatically altered the local environment. Fish stocks have fallen by 70–90 percent,
animals have migrated, and about 1,300 square kilometers of vegetation have died or
become blighted, forcing villagers to hunt and fish over larger distances (BHP report 1999:
9; Higgins 2002: 2). Copper concentrations in the water are about 30 times background
levels, though the river still meets World Health Organization drinking water standards (BHP
report 1999: 8–9)”. (World Resources Institute report: http://archive.wri.org/page.cfm?
id=1860&z=?)
A 2001 study showed that even if mining were to stop [then], the sheer
volume of tailings already in the river, and continued erosion from the
waste rock dumps adjacent to the mine, would see the problems grow
worse over the next forty years.

40. Riverine tailings disposal – case study – Ok Tedi, Papua New
Guinea:
“High-value” out of court compensation settlements have been made by
BHP in favour of local communities affected by the mine (MAC report
http://www.minesandcommunities.org/article.php?a=622 and World
Resources Institute report http://archive.wri.org/page.cfm?id=1860&z=?).
In August 1999, BHP announced that it regarded the mine as being
incompatible with its environmental values.
In February 2002, BHP withdrew from the mine. Their 52 percent
equity share was transferred to an offshore trust, set up on behalf of
the Papua New Guinea people. The PNG government gave BHP
Billiton legal indemnity from responsibility for future mine-related
damage to the Ok Tedi ecosystem (although the legality of this deal
may still be challenged in the country’s courts).
The mine is still currently operating, and although a limited dredging
operation has been introduced, mine waste disposal into local rivers
continues. Operations are scheduled to end in 2010.

41. Submarine tailings disposal
Coagulants and flocculants
used to bind particles together
to form a thicker mixture to
prevent wide dissemination of The euphotic layer is defined as
the tailings-plume underwater the depth reached by only 1% of
photosynthetically active light
(High density
polyethylene)
Greater
than 50 m
water
depth
Seafloor
De-aeration and mixing with
seawater to increase density Plume of lighter Final resting place
of slurry tailings material of tailings on the
sea-floor
Figure from Spitz and Trudinger, 2009.

42. Submarine tailings disposal (STD):
STD is used in coastal settings where the earthquakes, land-slides and
very-high rainfall (as for riverine disposal) make construction of tailings
impoundments geotechnically unfeasible.
The aims of STD are:
- to place the tailings into a deep marine environment which
has minimal oxygen concentrations – thereby avoiding sulphide
oxidation and acid generation.
- to prevent tailings from entering the shallow, biologically
productive, oxygenated zone.
Tailings are discharged at water depths of greater than 50 m, create a
plume of material in the vicinity of the discharge point, and
subsequently settle on the sea-floor.
STD has a very damaging impact on seafloor ecosystems. There is
high potential for metal uptake by fish and bottom dwelling organisms.

43. Submarine tailings disposal – case study – Black Angel, Greenland
Open adits in the
footwall below the
massive sulphide
orebody.
Cable-car
entrances
to mine
The “angel” is a
contorted pelite bed
(metamorphosed
mudstone), and not the
orebody itself.
View of the 700 m cliff face that overlooks Affarlikassaa Fjord at
Black Angel Mine.
Figure from Lottermoser, 2007.

44. Submarine tailings disposal – case study – Black Angel, Greenland:
Black Angel lead-zinc underground mine is located on the west coat of
Greenland, about 500 km north of the Arctic Circle. The orebody was
mined between 1973 and 1991, with a total production of 11 million tons
of ore, consisting of sulphide minerals sphalerite and galena (and
pyrite) (Asmund et al., 1994).
The mine is located at the top of a 700 m cliff face above the junction of the
4-km-long Affarlikassaa Fjord and the 8-km-long Qaumarujuk Fjord.
Waste rock was allowed to accumulate at the base of the cliff in a 0.4
million ton rock-dump at the shoreline of the Affarlikassaa Fjord.
Mined ore was transported by cable-car across the fjord to an industrial
area for processing using conventional selective flotation.
Tailings were discharged directly into Affarlikassaa Fjord. The total
amount of tailings discharged was about 8 million tons, containing
elevated arsenic, cadmium, copper, lead, and zinc values (Poling and
Ellis, 1995).

45. Submarine tailings disposal – case study – Black Angel, Greenland:
While tests prior to mining indicated elevated metal concentrations in
seaweed and mussels due to the natural exposure of the orebodies to
weathering and erosion, problems relating to the tailings disposal
quickly emerged.
Within a year of starting STD, distinctly elevated lead and zinc values
were found in waters and biota of the entire fjord system.
Extensive investigation at this stage indicated that (Poling and Ellis,
1995):
(i) The assumption that all the metals in the tailings would be present
only in insoluble sulphide minerals was incorrect – the tailings in fact
contained minerals that could be dissolved in sea-water.
(ii) The assumption that the discharged tailings would be permanently
protected [from oxidation] by stagnant bottom waters in the fjord was
incorrect – the disposal site in fact did not have a permanently layered
water column, and complete mixing of the fjord waters [including
the oxygenated upper layers] took place during winter.

46. Submarine tailings disposal – case study – Black Angel, Greenland:
Changes made subsequently to the processing and discharge methods:
(i) Minerals processing changes reduced the lead content in the tailings
from 0.4% Pb in 1973 to 0.18% Pb in 1989.
(ii) Increasing the density of the tailings, by addition of seawater and
coagulation and flocculation chemicals, helped reduce the extent of
dispersion of metals away from the submarine deposition site (Asmund
et al., 1994).
These changes reduced, but did not eliminate, the elevated metal levels.
The tailings discharge resulted in the metal enrichment of water,
suspended particulate matter, sediment and biota in the Affarlikassaa
and Qaumarujuk fjords up to 70 km away from the tailings outfall
(Loring and Asmund, 1989; Elberling et al., 2002).
While analyses of seals and fish species largely revealed no metal
contamination during mining, deep sea prawns and capelins, as well
as the livers of certain fish species and sea-birds contained lead
concentrations above the safe consumption limit (Asmund et al.,
1994).

47. Submarine tailings disposal – case study – Black Angel, Greenland:
Since mine closure in 1991, metal concentrations declined in fjord waters,
as well as in animal and plant life (Asmund et al., 1994), but dispersion
and release of metals from the tailings still continues (Elberling et al.,
2002).
In hindsight:
“detailed mineralogic, leaching, and oceanographic studies, which
are now conventional at proposed new mines, would have
produced more detailed information on which to base the decision
whether submarine tailings disposal (STD) was appropriate at this
particular site” (Poling and Ellis, 1995).

48. Black Angel Mine, Greenland:
The case is not yet closed.....
Press Release 28/05/2008:
“A&R [Angus & Ross] (AIM: AGU.L), a zinc/lead mining company focused on re-opening the
Black Angel Mine in Western Greenland, is pleased to announce that its wholly owned
subsidiary, Black Angel Mining A/S, has been awarded a 30 year licence to mine zinc, lead
and silver ore from the Black Angel Mine.” (http://www.angusandross.com/AR-NEW/news/PR-28-05-
08-Mining-license.htm)
“Pillar mining will require strategically placed backfill.
The pillar mining plan with the use of backfill [shown
right] has been developed by Golders of Vancouver”
“Phase One is expected to last for 4 years, during
which time 1.3 million tonnes [of ore] is expected to
be mined.”
http://www.angusandross.com/AR-NEW/pages/proj-black-angel-
phase1.htm
A&R are currently refurbishing the mine for “Phase One” which will
“concentrate on the development of infrastructure and extraction of the
pillars from the old mine” and also the “production of 'dry concentrate'
in the mine” (http://www.angusandross.com/AR-NEW/pages/proj-black-angel-phase1.htm)

49. Black Angel Mine, Greenland:
Production of “dry concentrate”.....
“Processing of the mined ore was to take place in a mill in Europe according to the Bankable
Feasibility Study (BFS). This possibility still exists, but the fall in metal prices since the
completion of the BFS makes it less attractive than before. In this context our technical
team is working on a solution to produce concentrate on site. The nature of the ore makes
is suitable for 'dry concentration' e.g. by gravity concentration or optical ore sorting. Such
concentrate could be shipped directly to a smelter thus significantly reducing shipping
costs. (http://www.angusandross.com/AR-NEW/pages/proj-black-angel-phase1.htm)
Press release 19/02/2009:
“US specialist Wardrop Engineering, a Tetra Tech Company ("Wardrop"), and Canadian based
SGS Minerals Services UK Limited ("SGS"), have been selected as the main nominated
contractors for the development of the Black Angel Mine mineral processing and waste
handling plant..... to be installed inside the Black Angel Mine”.
“This will consist of a primary and secondary crushing circuit, pre-concentration by optical ore
sorting, with milling and fine grinding feeding a conventional froth flotation plant. Premium
grade Zinc (59-61% Zn) and Lead concentrates (69-71% Pb) will be produced. These will
be shipped to the logistics hub at Maarmorilik for bonded product storage as part of the
recently announced off-take agreement with Swiss metal trader MRI Trading AG”.
(http://www.angusandross.com/AR-NEW/news/PR-19-02-09-tech-app-of-contractors.htm )
And of the fate of the large volumes of tailings that will be produced
by milling and “conventional” froth flotation.... Not a word.

50. Worldwide uranium mining and waste production:
There are probably more than 500 million tons of uranium tailings
located around the world (Waggitt, 1994). Uranium mine tailings are
defined as “low-level” radioactive wastes, and their long term
containment is a great environmental concern.
World’s ten largest uranium mines in 1997.
(From Hockley et al., 2000, using data from Uranium Institute).

51. Radioactive wastes of uranium ores:
The mineral processing of hard-rock uranium ores proceeds along the same
route as typically used for sulphide or gold bearing ores. Either
sulphuric acid or ammonium carbonate (alkali) leaches are used to
dissolve the uranium-bearing oxide minerals from the mined ore rocks.
The “pregnant” uranium-bearing leach solution is subsequently chemically
processed to extract the uranium and produce yellowcake.
Vat leaching. The ore processing may include crushing and grinding of ore
rock followed by vat leaching – which will generate waste waters (both
mill-water and process-water) and large volumes of tailings.
Heap leaching. Alternatively, low-grade uranium ore may be processed in
leach heaps, generating waste that consists largely of process-waters,
with little or no tailings.
Waste rock dumps, old leach heaps and tailings dams are all potential
areas where dissolved uranium can be mobilised into surface and
subsurface water systems.

52. Radioactive wastes of uranium ores:
While uranium oxide minerals form the basis of uranium ores (primarily
uraninite, UO2), sulphide minerals are also ubiquitous in uranium
orebodies. Particularly where pyrite and marcasite (FeS2) are present
and exposed by mining, acid mine drainage may develop in
workings and mine wastes. More detail on AMD follows in Topic 5.
Thorium occurs together with uranium in uranium ore deposits.
The mining of placer and mineral sand deposits for gold, diamond,
sapphire, ruby, titanium (in ilmenite and rutile) and tin (in cassiterite)
also accumulates gangue minerals that contain radioactive
uranium and thorium (e.g., the minerals monazite, xenotime, zircon,
tantalite, columbite). If accumulations of such gangue-mineral wastes
are allowed to weather and break down, both uranium and thorium
may enter surface and subsurface waters.
Phosphate mining for both fertilisers and Rare Earth Elements (contained
in the mineral monazite) may also generate uranium-bearing waste
products.

53. Uranium radioactive decay series
Uranium-238 (92 protons, 146 Series starts with
radioactive isotope
neutrons) accounts for 99.28%
of the Earth’s uranium.
Critical U-238 decay products:
Radium-226
Radon-222 (gas)
Series ends with
stable lead isotope
Uranium-235 (92 protons, 143
neutrons) accounts for 0.71% of
the Earth’s uranium. Its decay
products are therefore
negligible.
Low abundances and
very short half-lives
with respect to radium
(Ra) and radon gas (Rn)
Thorium-232 (90 protons, 142 isotopes generated by
neutrons) is the most abundant uranium-238 decay –
radioactive thorium isotope. therefore negligible
with respect to the
impact of U-238.
Table from Lottermoser, 2007, and references therein.

54. Impacts of uranium and thorium radioactive decay:
All three types of radiation (alpha, beta and gamma) from all parent and
daughter radionuclides are extremely damaging to living organisms:
(i) living cells and tissue are directly damaged, and (ii) water molecules
in the organisms are damaged, releasing free radicals and chemicals
that are toxic.
Alpha particles are not deeply penetrating, and when external to the body,
are stopped by the outer layer of skin. They are particularly damaging
to internal organs when ingested or inhaled.
Radium-226 (Ra-226). Is particularly of concern for several reasons:
(i) With a half life of 1,622 years it persists in uranium mine wastes.
(ii) Compared to uranium and thorium, Ra-226 is more easily liberated from
minerals in uranium orebodies during natural weathering and mineral
processing. It is also more soluble in water and therefore more mobile
in the environment.
(iii) Ra-226 behaves biologically similarly to calcium (Ca) and forms
compounds that can be taken up by humans, plants and animals.
(iv) Ra-226 has a high radiotoxicity and accumulates in bones.
(v) It decays to a further problematic radioactive element – radon-222 gas.

55. Impacts of uranium and thorium radioactive decay:
Radon-222 (Rn-222). Radon is a colourless, tasteless and odourless
gas, that is the most abundant isotope of radon. Although Rn-222
has a short half-life (3.8 days) and decays quickly, it occurs in
abundance and is constantly replenished due to the abundance of
its very long-lived “parent” U-238.
Rn-222 is of concern for several reasons:
(i) It is constantly replenished by U-238.
(ii) It is soluble in water and therefore mobile within the environment.
(iii) When Rn-222 is inhaled by humans its decay products are solid and
become lodged in the lungs, and are themselves highly radiotoxic –
polonium-218, lead-214, and bismuth-214 – emitting α, β and γ
radiation and inducing lung cancer. Radioactive lead-210, near the
end of the decay series, has a half-life of 22.5 years, so will remain
resident in lungs for most of a person’s lifetime, emitting β radiation
and generating further radioactive “progeny”.

56. Radioactive wastes of uranium ores:
While the hydrometallurgical processing of uranium ore is very selective and
efficient in extracting uranium, not all of the uranium is extracted, and
tailings will always contain small amounts of uranium. Moreover,
most of the undesired (from an extractive point of view) and undesirable
(environmentally) daughter radionuclides from the U-238 decay
series end up in the tailings.
As a result of the selective extraction, only 15% of the initial radioactivity of
the orebody is transferred to the uranium yellowcake concentrate, while
75% of the radioactivity remains with the tailings (Landa, 1999;
OECD, 1999; Abdelouas et al., 1999).
Unlike acids which can (in principle) be neutralised, and free cyanide and
cyanide complexes which can (in principle) be destroyed or will degrade
naturally with time, radioactivity and radioactive elements cannot be
destroyed. All one can hope to achieve in dealing with radioactive
mining wastes is to immobilise the radioactive minerals, prevent
dissolution of uranium and thorium from them, and isolate them from the
environment safely and permanently (which is not easily achieved).

57. Oxidation and dissolution of uranium wastes
Atmospheric Rock dumps at Sherwood
oxygen (O2) Water (H2O) Uranium Mine,
Washington State, USA,
before reclamation. The
mine operated from 1976
Uraninite (UO2) + to 1985. Subsequent
reclamation work
sulphuric acid (H2SO4)
completed in June 2000.
Photo August 1985.
Uranyl sulphate
(UO2SO4)
dissolved in
water
http://ecorestoration.montana
.edu/mineland/histories/miner
als/sherwood/default.htm#
2 UO2 + 2 H2SO4 + O2 2 UO2SO4 + 2 H2O
Uraninite Sulphuric acid Oxygen Uranyl sulphate Water
(solid) (dissolved) (gas) (dissolved) (liquid)
Note: the sulphuric acid is generated by oxidation of coexisting sulphide minerals (acid mine drainage).

58. Oxidation and dissolution of uranium wastes:
Uraninite (UO2) in uranium ores can be broken down by the process of
oxidation when exposed at the surface in rock dumps or tailings dams.
The resulting oxidised uranium compounds are highly soluble in water, highly
mobile and easily dispersed in surface or subsurface drainage
systems for significant distances away from the mine site.
Uranium oxidation-dissolution can occur in both acidic and alkaline waters,
given the presence of an oxidising agent (atmospheric oxygen) to trigger
the process.
Acid conditions particularly favour the dissolution of uranium. As sulphide
minerals are also ubiquitous in uranium orebodies, acid conditions are
very commonly generated through sulphide oxidation (see Topic 5).
Oxidised uranium mineral forms that are found dissolved in water, or
precipitated as salts adjacent to surface water, are highly toxic and
include uranyl sulphate UO2SO4 (yellowcake!) and uranium sulphate
U(SO4)2 (under acidic conditions) and uranyl carbonate complexes
UO2(CO3)n (under alkaline conditions).