CORRECTED-Brazil dam collapse reignites debate over storing mining waste

(Corrects paragraph 20 to Porgera mine "once considered", not
is "working on", mixing tailings with coarse waste rock and mud
to create a product that can be stored on the surface in dumps,
and adds current technology. Corrects paragraph 21 to "a
different" wet and dry disposal technology to make clear that
Teck Resources does not use the same system as considered at
Porgera.)
* Disposing of ore waste big global safety, environmental
issue
* Alternative engineering known as "dry stack" often put
forward
* Cost, climate can make alternatives costly, unviable

By James Regan and Susan Taylor
SYDNEY/TORONTO, Nov 20 (Reuters) - A deadly mud slide at an
iron ore mine in Brazil has reignited calls for safer ways to
dispose of millions of tonnes of ore waste held back by man-made
dams.
The disaster at the Samarco iron ore mine is only the latest
in a series involving tailings - waste in mining parlance - that
have devastated the environment, and in the case of Samarco,
killed at least 11 people and left another 12 missing.
Tailings are typically a mud-like material and their storage
and handling has become a major safety and environmental issue,
since they can be toxic and may need to be kept isolated.
The Nov. 5 disaster has been termed an "environmental
catastrophe" by Brazil after sending waste across two states and
liability could fall on Samarco's joint owners Vale VALE5.SA
and BHP Billiton BHP.AX BLT.L .
BHP Billiton's chief executive said the miner was reviewing
all of its dam facilities and that the companies involved in
Samarco would set up an inquiry with submissions from a wide
range of experts, including on the history of tailing dams.
"That is why we will be entirely open with the findings of
this report to hope that regulators and companies around the
world benefit from that learning, so that something like this
never happens again," Andrew Mackenzie told an analysts call.
In Brazil, at least, the industry could face tougher rules
after a congressman said a proposal for a new mining code would
include stricter regulations for tailings dams and could make
dry processing obligatory. urn:newsml:reuters.com:*:nL1N13516V
Alternative engineering known as "dry stack" is often put
forward as a way to mitigate disasters such as Samarco.
The process removes water from spent ore using vacuum or
pressure filters, allowing tailings to be stacked and better
controlled.
Advocates say it can also curb waste seepage into
groundwater that risks extending environmental liability for an
operator long after a mine has run its course.
But partly due to cost it is rarely employed, meaning that
thousands of wet tailing dams have been built with more planned.
There are 839 tailings dams in the United States alone and
some 3,500 worldwide, according to the U.S Army Corps of
Engineers and the United Nations.

DRY STACKING ECLIPSED
A tailings dam rupture at the Mount Polley copper mine in
British Columbia, Canada, 15 months ago led experts to recommend
that mines in the province use the best available technology,
including dry stacking.
"Mount Polley started this big cry for dry stack, which is
an entirely different form of tailings deposition but it often
doesn't work for any number of reasons," said Lindsay Newland
Bowker, a policy advisor and consultant on mine tailings waste.
Toronto-listed Seabridge Gold SEA.TO this year rejected
dry stacking for a new mine in British Columbia, concluding it
wasn't feasible in wet, mountainous regions.
Even so, some are using the technology.
The Greens Creek gold mine in Alaska was among the first to
use it. The La Coipa mine in Chile's Atacama Desert and Hudbay
Minerals' HBM.TO proposed Rosemont copper mine in the U.S
state of Arizona also plan to employ dry stacking.
A drying process at Australia's Karara iron ore mine leaves
a chemically inert material that is stacked on a patch of
outback desert before being returned to the soil.
"Where we are seeing dry stack technology being more
embraced is in areas where water is scarce," said Dirk Van Zyl,
professor of mining engineering at the University of British
Colombia.

"COMES DOWN TO ECONOMICS"
The Porgera mine in Papua New Guinea, which is jointly owned
by Barrick Gold Corp ABX.TO and China's Zijin Mining Group
601899.SS 2899.HK , once considered mixing tailings with
coarse waste rock and mud to create a product that can be stored
on the surface in dumps. This was never implemented and instead
a plant at the mine removes coarser content from tailings, which
is then mixed with cement and pumped underground. The finer
tailings mix is then discharged in a river.
A different wet and dry disposal technology is already being
used by Canada's Teck Resources Ltd TCKb.TO at its Elkview
coal mine, while the Silvertip lead mine in British Columbia
will use a combination of dry and underground storage.
John Werring senior science and policy advisor with the
David Suzuki Foundation, a Canadian environmental group, said
more mines might use dry stacking if governments stopped
approving conventional tailings dams and pushed companies to
come up with alternatives.
"But it always comes down to economics," Werring added.
Nonetheless, failure to contain mine waste can be costly.
During construction of Papua New Guinea's OK Tedi copper
mine the tailings dam failed and waste was directly discharged
into the creeks running into two rivers, destroying thousands of
hectares of forest and inundating villages and vegetable
patches.
In 1996, then-owner BHP Billiton agreed to a $400-million
out-of-court settlement for the land holders near the mine and
five years later divested its majority interest.

(Editing by Ed Davies)