MINING MARKET CYCLES AND TAILINGS DAM INCIDENTS
Michael Davies1 and Todd Martin2
Vice-President, AMEC Earth & Environmental
2
Principal, AMEC Earth & Environmental
Vancouver, British Columbia
1
ABSTRACT
Tailings dam incidents, namely physical failures
and major operational upsets, have been
described in literature for over 30 years. These
accounts typically address the contributing
physical attributes and/or design/operational
deficiencies that led in whole, or in part, to the
recorded incident. One aspect of tailings dam
stewardship not typically noted let alone evaluated
in terms of contribution to incidents of record are
the prevailing economic conditions during a key
period of dam design, construction and/or
operation. An evaluation of the temporal trends in
tailings dam incidents relative to the cyclical nature
of the economic realities of the mining industry is
examined. Although clearly no perfect correlation
exists, there appears some validity to the
hypothesis that the frequency of tailings dam
incidents can be expected to increase some
relatively short period after a cyclical “boom” in the
mining industry.
INTRODUCTION
The Mining Industry is driven by cyclical global
economic conditions. The demand for the
commodities produced by the industry, though
certainly having trends that for individual metal and
non-metal commodities can differ from overall
global industry trends, is an excellent barometer of
global economic health. The end to the most
recent high in the economic cycle hit the
commodity prices for most mined materials
severely. Though there have been exceptions such
as gold, most commodities are, in mid 2009,
trading at levels at or below the beginning of the
most recent boom. This most recent boom cycle
started gathering some modest signs of life in 2003
through 2005 but took off in early 2006 to what
eventually became many unprecedented highs in
commodity prices.
Though this most recent 2006-2008 boom was
exceptional in terms of its height and the rapid and
severe nature of its contraction, it is far from the
first such cycle the mining industry has seen.
Using data from indicator commodities such as
copper and gold, a comparison of tailings dam
incidents with mining cycles over the past few
cycles (up to about 30 years) is explored. Both the
nature and frequency of tailings dam incidents is
noted in the comparison. Incident records are from
both published and less available sources. From
the comparisons made, trends appear that should
reinforce high prioritization within the Mining
Industry for enhanced tailings dam stewardship in
the near future. The paper includes some
anecdotes from projects completed in this most
recent boom to illustrate some of the reasons why
the trends noted may exist. Further, the paper will
provide some thoughts on how to prevent this
trend reappearing during the inevitable next cycle
in the Mining Industry.
TAILINGS DAM INCIDENT RECORDS
Though no single comprehensive public database
of mine tailings dam incidents exists, there are
numerous sources of information including:
•
•
•
•
•
•
USCOLD (1994)
UNEP (1996)
U.S. EPA (1997)
Vick (1997)
Davies et al. (2000)
WISE (wise-uranium.org).
In addition, through incident review assignments
and other similar sources the authors have been
able to augment the published information with
approximately 20 additional incidents beyond the
published accounts. In total, from December 1968
through to August 2009, there were 143 tailings
dam incidents that were available to evaluate in
terms of their trends. These 143 events occurred
over the nearly 42 years of record used in the
database.
Figure 1 presents a summary of the incidents from
all available sources over the nearly 42 years.
Figure 1 depicts the total number of “incidents”
(defined as physical failure of some or all of a
given tailings dam and/or a significant operational
issue leading to disruption of the associated mining
operation for a period of greater than one month)
and plots these incidents on a per two year basis.
The data used to develop Figure 1 are considered
more thorough post approximately 1992 as since
that time, it is more difficult to have incidents that
go unreported. The two year basis was selected to
provide a better sampling of the information and
due to how it “worked” with trends presented later
in this paper. In each case, the date provided is the
end of the given two year period for which the data
is provided. For the last data point, which is August
2009, the period of record is only 20 months
versus 24 for all other periods noted.
Number of incidents (per preceding 2-year period)
20
18
16
?
16
14
12
12
12
12
10
8
9
9
7
6
0
1970
7
6
6
5
4
2
9
8
4
4
4
4
3
3
2
1975
1980
1985
1990
1995
2000
2005
2010
Year
Figure 1 - Tailings Dam Failure Incidents – 1968 to 2009
From Figure 1, which makes no attempt to
regionalize or discretize the data by failure mode
for the purposes of this paper, “peaks and valleys”
in the temporal distribution of failure events
certainly appear to exist with several cycles of
increased incident frequency apparent, raising the
question as to the drivers behind these cycles.
MINING MARKET CONDITIONS
The global mining market constitutes a diverse
number of commodities mined and marketed
across all regions of the world. The historic global
market conditions and trends for each of these
commodities are individually complex and worthy
of extensive evaluation in their own right (which
they do, and will continue to receive). Perhaps the
most predictable aspect of these conditions is their
unpredictability. For example, while there are no
shortage of supposedly prescient “experts” now
assuring the industry they had the dramatic Q3-Q4
2008 fall in mined commodity prices “fully
predicted and accounted for”, the reality is this
most recent decline was seemingly just as
surprising to an industry that has experienced
these cycles many times before as all the other
declines have been over the decades. To quote
George Bernard Shaw, “We learn from history that
we learn nothing from history.”
While the 2005-2008 rally in most mined
commodity prices may have been unprecedented
in terms of the market capitalization values
reached by mining companies, and the commodity
prices realized, in many ways it was simply just
another cycle in a cyclical industry that very much
mirrors the global economic situation.
To mirror the industry, copper is an excellent
bellwether commodity. In many ways, it is the
engine that powers the mining industry and its
“health” dictates global mining (and overall
economic) conditions like no other commodity.
Figure 2 shows the price of copper, in period
pricing, from January 1968 to present. In addition
to copper, and to have another comparative
commodity for evaluative purposes, gold was
selected as an additional commodity of interest for
this paper. Though in terms of commodity tonnage
gold is far from the second most prevalent mined
material, there are an abundance of gold mines
and gold mine tailings dams that have contributed
a significant portion of the tailings dam incident
record; in fact providing more dam failures than
any other single commodity. Figure 2 therefore
also provides the historic gold price from January
1968 to present, and it is apparent that the cycles
in both copper and gold prices are largely similar.
As such, for the purposes of this paper, copper
price is taken as a proxy for mining commodity
cycles.
An alternative means of plotting commodity price is
in terms of the inflation-adjusted value. This in
effect “normalizes” the commodity price over time,
and, as illustrated in Figure 3 for copper, provides
a means of amplifying the price cycles. The
inflation-adjusted copper price plotted in Figure 3 is
based on an average annual inflation rate (for the
United States) of 4.1% from 1946 through 2008.
1000
Prices not adjusted for inflation.
3.6
800
3.2
700
2.8
600
2.4
500
2
400
1.6
300
1.2
200
0.8
100
0.4
0
1968
0
1972
1976
1980
1984
1988
1992
1996
2000
2004
2008
Year
Figure 2 - Copper & Gold Price – 1968 to 2009
4.5
4
Copper price ($US/lb): unadjusted
Copper price ($US/lb): inflation-adjusted
Copper price from LME data. Inflation-adjusted price
based on average annual inflation rate of 4.1% (1946
through 2008).
Copper price ($US/lb)
3.5
3
2.5
2
1.5
1
0.5
0
1968
1972
1976
1980
1984
1988
1992
1996
2000
2004
Year
Figure 3 - Copper Price (inflation-adjusted) - 1968 to 2009
2008
Copper Price ($US/lb)
Gold Price ($US/oz)
900
4
Gold price ($US/oz)
Copper price ($US/lb)
TAILINGS DAM INCIDENTS
MINING ECONOMIC CYCLES
AND
Whenever data involving two or more variables is
compared, the questions of relevancy and
causation must be raised, for correlation alone
cannot in isolation infer a causal relationship.
There is no question in the thesis of this paper
there are lots of “darts” that can be thrown at any
relationship derived between commodity prices for
copper and gold and tailings dam incidents, given
the many variables contributing to the latter. As an
example of one such objection, commodity prices
are a reflection on overall economic activity and
when more mines are operating, the likelihood of
incidents will be higher even if the rate of incident
per operating mine remains the same. Another
legitimate objection would the reliability of the
incidents database, given the increased likelihood
of such incidents being reported, and documented,
in recent years than would have been the case
decades ago. However, the concept that there may
be a relationship of some manner between the
booms in the mining cycle and the damage to the
overall mining industry created by tailings dam
incidents seemed worthy of examination.
In evaluating the tailings dam incident database, a
database that includes 143 incidents, a few trends
were apparent:
•
•
•
over the nearly 42 years of record, the
143 incidents leads to an average rate of
incidents of about 6 to 7 per any average
two year period.
there were very distinct variations to any
average trend with a range of between 2
and 16 incidents per any two year period
(starting January 1968 and every two
years afterwards)
there were sub-trends or two-year
windows outside of ones starting in
January that included one two-year period
(September 1980 to August 1982,
inclusive) with 17 incidents.
From Figure 1, five periods of peak incident
frequency (the starting date for a higher than
average period of tailings dam incidents) can be
identified. The fifth period includes the present
which is not a complete record. It may be that the
present time constitutes a lead up period versus a
peak depending upon whether the trends of the
previous four peaks sustain through to 2010-2011
as will be discussed later herein.
Table 1 provides a summary of the two-year
periods from 1968 to present where higher than
average tailings dam incidents were recorded.
Table 1 – Tailings Dam Incidents – Periods of
Higher than Average Occurrence
Start of Two
Year Period
of Increased
Tailings Dam
Incidents
January 1976
January 1984
Peak of
Copper Price
Peak of Gold
Price
January 1974
September
1980
January 1974
September
1980
December
1987
March 1990
June 1989
February 1998
September
1995
January 1996
Q1-Q2 2009
(?)
February 2008
February 2008
Table 2 provides a summary of the peaks of the
gold and copper prices over the past 42 years.
Ironically, there have essentially been five peaks in
each of these, in comparison to the peak periods in
tailings dam incidents noted in Table 1.
Table 2 – Periods of Peak Copper and Gold
Prices Compared to Periods of Peak Tailings
Dam Incidents
Start of Two-Year
Period
January 1976
January 1984
March 1990
February 1998
Early to Mid 2009 (?)
Number of Tailings
Dam Incidents
8
12
16
12
>12
Using the first four peak periods, the time lag
between the peak of the copper price and the start
of the next two-year period of increased frequency
of tailings dam incidents was:
•
•
•
•
24 months
39 months
9 months
28 months
The average lag from peak of copper price to
period of increased frequency of tailings dam
incidents from these four event windows is
25 months. For the gold price peak data, the
corresponding time lags from peak price to
increased incidence frequency for the first four
incidents peaks were:
24 months
39 months
27 months
25 months
The average lag in the gold peak price to start of
increased incidence period was 29 months.
For the most recent boom there is insufficient
information to know if a peak in incidents has
occurred or there is a ramping up of activity
towards one.
From the available information, there appears to
be a lag of between 2 and 2.5 years from the end
of a mining boom to the start of a two-year period
Looking at the data in some more depth, the
two-year incident window could not be improved
upon much though the number may be a range of
between 18 and 36 months post peak price versus
a set period as implied by the simplistic average
used above. It is undoubtedly the case that the lag
is driven by many factors, including for example
the duration of the upswing in terms of commodity
prices, as a longer such period would likely result
in more projects being developed.
Tailings dam incidents/preceding 2-year period
18
4.40
Tailings dam incidents
Inflation-adjusted copper price
16
4.00
14
3.60
12
3.20
10
2.80
8
2.40
6
2.00
4
1.60
2
1.20
0
1965
1970
1975
1980
1985
1990
1995
2000
2005
Year
Figure 4 – Adjusted copper price and tailings dam incidents
2010
0.80
2015
Inflation-adjusted copper price ($US/lb)
•
•
•
•
of increased frequency of tailings dam incidents.
This is illustrated in Figure 4, which plots both the
tailings dam incidents (per two year period), and
the inflation-adjusted copper price. While the time
lag between the peak in the adjusted copper price
and the peak of the tailings dam incidents varies
for each cycle, it is very clear that each commodity
price cycle peak, as represented by the copper
price, can be correlated to a subsequent peak in
the number of tailings dam incidents.
ANECDOTES
BOOM
FROM
THE
RECENT
There is a common discussion question amongst
long-term designers of tailings dams during mining
booms – who is doing all that extra work? The
reputable design houses and their senior
resources are typically fully-occupied during
average economic conditions and can quickly
become stretched during peak periods. When a
prolonged peak of an unprecedented nature
occurs as did recently between 2005 and 2008, it
is difficult indeed to imagine where all that
additional capacity came into the industry in terms
of design, operating and regulatory experience.
The complexity of a tailings dam, in comparison to
many engineered structures including conventional
water retention dams, cannot be overstated. These
structures are never at steady-state conditions
during operations and are often constructed over
decades where the initial portion of the dam may
include design criteria and construction practices
long out of date.
However, what really does occur during boom
times that could represent the causal link between
the trends noted in this paper? One window into a
portion of the reasoning is offered through a few
select anecdotes from the recent boom.
1. Following the OMS Manual?
At one mine, the Operating, Maintenance and
Surveillance (OMS) Manual for the tailings area
included a stipulation that the tailings dam and
impoundment be visually inspected daily or
whenever “was convenient” (the latter portion was
handwritten, word for word, in the OMS manual).
Apparently the daily requirement for this dam and
impoundment, which was more than five km from
the main operations, was onerous so a somewhat
lesser frequency was adopted. When the long
overdue viewing did take place it was discovered
that the tailings line had cracked at a valve on the
crest of the dam, eroding a significant portion of
the earthfill and allowing tailings to find their way
into a stream bed for about two km downstream.
During the incident review, it was determined that
the “job” of the daily (or “convenient”) was formerly
done by someone who had left the mine for
another opportunity and they were awaiting some
new hire to fill the position but were having
problems getting someone. That problem had
gone on for 14 months – clearly the period
between inspections as well – so instead of daily,
“convenient” turned out to be about every
400 days. The owners of the mine were
“impressed” with how much damage a cracked line
could do when left alone for about 400 days.
2. Interesting Design
At one mine, space was at a premium. There
simply was very little room for all of the
infrastructure
and
the
desired
tailings
impoundment directly adjacent to the mill.
However, an enterprising designer came up with a
solution by simply (seemingly) ignoring upstream
failure modes. The rock shell was impressive and
steep getting to more than 40 m in height at about
1.5H:1V. The dam was being constructed in an
upstream manner with tailings and supernatant
“supporting” the rock shell (this was the part the
designer did not seem to include in their
assessment). When the tailings in the
impoundment simply could not take the loading of
the rock shell any longer, and it is incredible failure
did not occur prior to the rockfill reaching 40 m in
height above the tailings, it failed into the tailings
beach effectively shutting the mine down for a
prolonged period of repair. A post-incident review
confirmed no consideration of the upstream
support requirement of the beach to the rock shell
had ever been considered by the designers who,
by their own admission, had “only started”
designing tailings dams.
3. Drainage, Drainage, Drainage!
A review of a proposed tailings dam included a
very insightful view to an interesting approach to
dam design. Beached hydraulic tailings tend to
create quite a high level of anisotropy in terms of
their hydraulic conductivities (the horizontal value
tends to be many times the vertical value –
typically in the order of two orders of magnitude
greater). As such, basal drains can have some
impact for the first number of metres of a tailings
impoundment but at some point, the influence of
basal drains on the beached tailings becomes
quite negligible. This was apparently lost on the
design for this particular facility that was to be up
to 150 m in height behind a fully drained and
competent rock shell. There were no fewer than
300 separate drains in the basin design, totalling
more than 20 km in length, consisting of very
expensive and totally unnecessary pipe that some
supplier was very anxious to provide to the mine.
Not all design errors lead to failures – some are
simply huge added expenses based upon nothing
more than a lack of experience.
4. We Have a Permit!
The current regulatory climate around the world
can only be termed “challenging” by those who
work in the mining industry. There are a series of
permits required with nearly every one offering a
unique opportunity to create a design problem by
getting caught up with the myopic drive to obtain
the permit – fast, and at any cost. Getting a new
tailings facility permitted can be one of the greatest
of those challenges. However, meeting that
challenge via a design for a facility that is either
economically, technically, and/or operationally
infeasible, but that expedites the granting of a
permit, is not the answer.
On one particular project, the use of paste tailings
technology was nominated as the panacea for the
project. Some small bench scale laboratory testing
showed that if the paste was thick enough (low
water content) and had sufficient cement and other
agents added, a 30 mm high pile could be
repeatedly created at about a 10% slope. From
this, it was extrapolated that such a result could be
recreated at full field scale! Moreover, no bleed
water emanated from the uniform hardening slope
so no dam of any sort (starter or otherwise) would
ever be required. Designs and extensive
documentation with stunning three-dimensional
pictures were developed showing uniform 10%
slopes up to 50 metres in height without any need
for anything more than the 5% by weight cement
addition plus many other useful additives. No other
works, particularly earthworks, would be required.
The regulators were enthusiastic over the concept
and a permit was obtained “much quicker than we
thought” for the no dam, no seepage and no
worries uniform sloped tailings pile. Mission
accomplished!
However, in the course of a subsequent review,
once having convinced the owner that there may
be a flaw, a somewhat larger scale trial was
commissioned whereby it was shown that the
laboratory slope could not be maintained over a
few metres, let alone 500 metre long beaches. It
was also eye-opening for the owner to see the
calculation of how much money per tonne these
tailings needed in terms of the paste additives
(including the cement). However, the worst news
(at that time it seemed) was the need for
earthworks, which would mean a totally different
impact situation and essentially restart the
permitting process. While no other facility had ever
been designed or constructed in any form similar
to the conceptualized facility, none of the owner,
the regulator, or the designer let that lack of
precedent impede the single-minded task of
getting this project its permit by writing promissory
notes that physical reality, and project economics,
could not honour.
REASONS FOR THE TRENDS?
Taking the trends in peak incident events relative
to periods of commodity price peaks as valid
indicators of a causal relationship, and then using
the above and many, many similar anecdotes from
the recent and previous booms, perhaps some
“whys?” begin to emerge. The authors suggest the
following are only a handful from a wide
assortment of “whys?” but ones that would
seemingly be avoidable with some better judgment
from the key parties involved. In other words, it
should not be inevitable that more tailings dam
failure incidents are recorded just because there is
commensurately more activity brought about by
more robust commodity prices.
Some potential reasons for the trends that have
been readily observable from the past few boom
cycles include:
•
•
•
•
•
•
•
Permit haste:
o use
of
fashionable
but
projectinappropriate tailings technologies
o unprecedented design/operation to satisfy
non-realistic regulatory or third party
stakeholders preference
o defaulting to flooding for potential ARD
despite dam safety risks
o acceptance of sites that are pleasing to
regulators but not to geotechnical reality
o over-taxed regulatory capacity.
Fast tracking of investigation, design and
construction to take advantage of the price
cycle
Inadequate appreciation of capital and
operating costs associated with designs based
more on rapid permit procurement than
technical and economic realities
Rapid
cost
escalation
during
project
construction due to boom times, necessitating
cost cutting
Inexperienced (but overconfident) designers
Experienced (but overly-subscribed) designers
Lack of independent, third party review
•
•
•
•
•
Rapid turnover of key mine management and
operating personnel as new opportunities
abound during the boom times
Disconnect between design expectations and
operational realities
Development of long-known deposits that have
been left undeveloped for good reasons
Pressures to cut costs for once mines
constructed on the basis of rising commodity
prices are forced to operate with the reality of
lower commodity prices
“Cookie cutter” designs having attributes well
and good in, for example, South Africa, but
being used for a project in a high rainfall, high
seismic environment.
The list above is far from exhaustive. However,
there is not a single item in that list that would
qualify as a justification for the postulated
relationship between commodity price booms and
tailings dam incidents, and as such merely points
to a lack of discipline in sticking with
well-established design and stewardship practices.
A lack of discipline brought about by the need to
make hay while that economic sun shines, even
when it leads to another case history in the
growing catalogue of tailings dam incidents, is
understandable but is not acceptable.
SUMMARY THOUGHTS
The evaluation of tailings dam incidents versus the
price of commonly mined commodities is
admittedly not a scientific endeavour, per se, and
certainly was not given extensive rigor in terms of
statistical evaluation, assessment of other
underlying causes in the data trends, etc.
However, there appears to be some correlation
between a mining boom cycle and an increased
number of tailings dam incidents approximately 24
to 36 months after the end of the boom, in the
manner of a hangover after a good party. Another
way to look at it, as most booms are several years
in length, the increased number of incidents
appears to occur within four or five years of there
being more market capital and, commensurately,
more project construction following ore definition,
engineering, permitting and construction. The lag
appears somewhat more quickly than a typical
timeframe to get a mine from concept to operation
but there are perhaps many projects just waiting
the improved financial condition to finally be
constructed, or restarted etc. The correlation may
also imply that facilities that are constructed or
restarted during a boom are seemingly more
susceptible to having failure incident early on in
their initial or restarted operating period.
Is there really a correlation between tailings dam
incidents and mining cycle booms? If the trends
suggested by the data over the booms of the
period since 1968 provide some guide to the
future, the implications to the mining industry in
2009, on the heels of an extraordinary boom, are
clear and perhaps daunting. The recent boom that
ended so abruptly in 2008 was unprecedented in
terms of copper price. The apparent building up of
tailings dam incidents of the past year or so may
only be background level activity to a peak in
incidents coming in the next 12 to 30 months.
Such a pessimistic viewpoint is perhaps an unlikely
version of the future that unfolds. There are very
sound guidance documents, corporate standards
and increased awareness in design houses to
avoid the failures of past periods. Major mining
companies in particular have for over a decade
now been implanting increasingly stringent
controls, and applying consistently improved
stewardship practices (e.g. the Mining Association
of Canada guidelines) pertaining to tailings
management facilities. At the same time, some of
the anecdotes offered in this paper lead one to a
perhaps tempered optimism and a more of a “wait
and see” approach. What is clear, the exercise of
evaluating the incident database in a few years
time will be very illustrative in light of the trends
suggested by the data presented in this paper.
Perhaps the trends of the past 40ish years will not
be repeated; for the mining industry this is most
certainly the desired outcome.
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st
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