Posts Tagged ‘Tailings’

bruce lake

Read today the news that the Brucejack Mine have been given an environmental assessment certificate by the British Columbia Ministry of the Environment.   The regulators say construction can begin once they are sure that discharges from water treatment plants will not harm the Unuk River.  Some of the tailings will go back underground; some will go to Brucejack Lake which is apparently “fishless.”  Most of the waste rock will go to the lake.

I read the following in the June 2014 Feasibility Study and Technical Report Update for Pretium Resource Inc. by Tetra Tech.

Approximately 3.5 Mt of waste rock and 8.7 Mt of tailings are anticipated to be deposited in Brucejack Lake over the projected 18-year mine life. Stringent discharge criteria (based on the Metal Mining Effluent Regulations (MMER)) state that the total suspended solids (TSS) concentrations in the outflow at Brucejack Creek must be less than 15 mg/L.

The tailings deposition system has been developed to minimize the concentration of fine suspended solids in the outflow to Brucejack Creek by discharging near the bottom of the lake (at 80 m depth) and under the accumulations of tailings solids.

On the other hand, waste rock with a wide range of particle sizes is to be deposited in the lake by surface dumping from causeways raising the possibility that fine granular material will be introduced to the surface layer of the lake and to the outflow.

Hydrodynamic modelling of Brucejack Lake was carried out by Lorax (2013) to examine the likelihood of the migration of tailings solids into lake surface waters. The results indicated that the potential for elevated TSS levels in surface waters was unlikely if the minimum particle diameter was greater than or equal to 5 µm.

However, it will be necessary to control the TSS concentrations at the outlet of Brucejack Lake to meet the MMER regulations. The current design basis for control of suspended solids includes the following:

  •  install one or more lines of turbidity curtains at the outlet of the lake to contain suspended solids
  • install a flow monitoring weir across Brucejack Creek downstream from the lake outlet to facilitate monitoring.

An allowance for site investigation and design of the outflow monitoring weir has been included in the capital cost estimate. As a contingency to the use of turbidity curtains, an outlet control structure was designed to allow storage and release of lake water in a controlled manner.

Review of the storage capacity versus lake level elevation for the outlet control structure indicates that flow from the lake could be stopped for a period ranging from several days (e.g. during freshet) to several tens of days (e.g. during the summer and early fall) depending upon runoff conditions in the lake catchment area.

If you have an idle weekend, you can spend plenty of time reading additional documents at this link.   For me it is off to the MET opera, the Tales of Hoffman, so I will say no more than this seems good news:  a BC mine advancing with a rational tailings and waste rock disposal system.  Good for them.  I hope they succeed.

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Here are links to a few of many publications and presentations for the USACE of the topic of risk assessment of dams and levees.  Katrina forced them to think hard and deep.  This is a snapshot of the work.

Risk-Informed Approach to Flood-Induced Dam and Levee Failures

Risk Management Guidelines, Prioritization, and Process

USACE Levee Safety Program

The questions that arise are: Should the mining industry adopt similar criteria, methods, and results?  Should the Canadian Dam Association be leading the way on this?  How will we be able to justify a significantly different approach?

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The snow blanketed us today as the Denver Society of Mining Engineers convention begun.  Yet it is warm enough to walk through the snow in shirt sleeves.  Typical Denver in winter/spring. Yesterday I attended the short course on Seismic Engineering for Tailings Dams.  It was well-attended and featured magnificent speakers who brought us up-to-date with current practice in predicting earthquakes and analyzing their impact on mine tailings dams.   Of course there was discussion of predicting the maximum credible earthquake, which Jonathan Bray says we are doing it wrong.  Contact me if you want the details. (more…)

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Today I took the ferry across the bay from Puerto Santa Maria to Cadiz.  Took a bike and rode around the city sea-wall and around the old city center.  It is a great ride around the sea-wall.  It reminds one of the age of some engineering works. For here we have fortifications that have been four hundred years in the making.  I saw forts and castles built three hundred years ago to defend the city from the French, the Brits, and the Dutch, who attacked at different times. (more…)

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This picture and the others in this posting were taken by me at Knotsberry Farm in California.
A great place to visit and enjoy a terrifying ride along the raging river of insanity.

If you seek a thorough and intelligent analysis of dealing with uranium mill sites (and particularly the tailings facility) take a look at the following–it is an amazingly comprehensive document–and should be required reading for all involved in mine management, regardless of whether the mine is uranium, copper, gold, or something else. (more…)

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A simple cover for a tailings facility may be no more than a layer of compacted tailings overlain by soil in which vegetation can grow. If control of infiltration is not required, this cover may be cost effective.   If the climate of the site is good, the layer of soil thick, and the vegetation abundant, you may have an evapotranspirative cover that limits infiltration. (more…)

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Foto: Peter Öhman

The translation above the pictures reads:

It doesn’t matter that it is Sweden’s most modern mine, built according to environmental laws, which the Government says is the world’s strongest. In addition, Northlands mine outside Pajala is a financial flop, it is now also an ecological disaster.
One million cubic metres of water with toxic heavy metals such as nickel, cadmium, lead, copper, and more flows straight out of the wrecked mine dam to Muonioälven and later the Torne River, which is classified as a national river.

At this link you will find four photos that appear to show the breach of the perimeter embankment or dike and spillage of tailings into the surrounding countryside.  Above is one of them.

The reports make little mention of the causes of failure.  Although the four pictures appear to show more than one breach.  A posting on Facebook dates the failure as 19 July 2014.

Please comment if you know more.

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