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Mining facts

Mining’s Future in a Green Economy

Michael Goehring, CEO, Mining Association of BC discusses mining’s important role in the green economy.

credit: Mining Association of British Columbia

“BC is a hotbed of innovation, so our industry is working closely with BC’ tech sector so we can conserve more, waste less, and reduce our environmental footprint.”

“The minerals and metals that BC produces – copper, silver, gold, steel-making coal, aluminum, molybdenum – they are all essential to a low-carbon future. An electric vehicle takes four times as much copper as a traditional internal combustion vehicle. You can’t make solar panels without silver. And you can’t transmit power from solar panels without copper. Our mineral sand metals are essential to a low carbon future.”

“We now know, in BC, our steel-making coal – which is critical to renewable energy infrastructure – wind mills, for example, has half the GHG emissions intensity as our competitors in Australia. BC’s Copper has about 40-50% less GHG emissions than copper from Chile. Our industry has been reducing its GHGs for several decades. The real driver is our clean energy, driven out of our hydroelectric assets.”

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Mining facts

Mining and Mineral Processing at the Mount Polley mine

In the Mount Polley Mine, run-of-mine ore from the open pits and underground is hauled to the crusher.  The crusher has three stages of crushing involving five crushers, twenty conveyors and four sets of screens.  Ore is dumped by the surface mining fleet into the feed pocket of the primary gyratory crusher, and is then crushed in three stages to produce a product at finer than 16 mm for the grinding circuit. Periodically, the crusher also used for the production of aggregates used in tailings construction and other tasks.

The grinding circuit consists of two parallel rod mill/ball mill circuits and a pebble mill circuit. Crusher product is first split between two rod mills where water is added to form slurries.  The rod mill discharge is pumped to the primary hydrocyclones that classify the particles by size.  The larger particles flow to feed the ball mills while the fine particles report to two flash flotation cells. The ball mills are in “closed circuit”, meaning that the discharge is pumped to the classifying units (primary hydrocyclones) and the particles will not pass to the next grinding stage until they are fine enough to feed through the flash flotation cells.  The underflow from the flash flotation cells is pumped to the secondary hydrocyclones, the flash flotation product can report directly to the concentrate circuit or to regrind for further upgrading.

The coarse particles classified by the secondary hydrocyclones reports to three pebble mills for further size reduction. The pebble mills are in “closed circuit” with the secondary hydrocyclones and product that is sized at 65% finer than 200-mesh is fed to the flotation circuit. Pebbles obtained from the triple deck screen in the crusher are used as grinding media in the pebble mills.

The flotation circuit separates the valuable minerals from the rest of the crushed rocks. With the addition of reagents, the valuable minerals, mostly in the form of sulphide minerals chalcopyrite and bornite, are separated by flotation and are collected and upgraded to produce a concentrate. Initial separation is completed in a rougher/scavenger circuit, where the remaining minerals are discarded as tailings (which flow by gravity to the Tailings Storage Facility).  Rougher concentrate is reground in a regrind mill and further upgraded in a cleaner circuit to produce the final concentrate product. Cleaner tailings are recycled to the scavenger circuit.

The concentrate from the flotation circuit is dewatered in two stages: the thickener settles particles and decants water so that the settled particles form a sludge by sedimentation and have a reduced water content of roughly 25%-30%; pressure filtration further reduces water content to approximately 8%. The water removed is utilized as process water. The filtered concentrate is stored in the load-out building and loaded onto 40-tonne trucks for shipping. Tailings materials generated by mill operations are piped via gravity to the TSF.

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Mining facts

How does Mount Polley decide to process?

Gold and Copper

The broken rock in the open pit is segregated into ore and waste based on the assay of rock cuttings sourced from the blasthole production drills.

This assay analysis determines the sulphide copper percentage and gold grams per tonne for material within the vicinity of each blasthole. 

The forecasted metal prices and metallurgical recovery is used to calculate copper equivalent percentage.

A forecast of mining and treatment costs establishes the mining cutoff grade and hence the material to be trucked to the plant for processing.

The plant uses three stage crushing, and conventional rod and ball mills with a flotation and dewatering circuit to produce a copper /gold concentrate.

When the mine is up-and-running, it mine moves 80,000-90,000 tonnes of material per day, the mill has a capacity to process 17,800 to 22,000 tonnes per day (tpd) of ore depending on hardness. Mount Polley concentrates are trucked to facilities at the Port of Vancouver and then shipped to overseas smelters.

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Community Mining facts

Who works at Mount Polley?

At Mount Polley, we look for individuals to join our workforce who display a variety of skills and training levels.

We have a training department that will train workers from other industries.

Our key goal is to source workers locally. The furthest away workers are usually recruited from is Quesnel or Williams Lake. Several of Mount Polley’s staff are from Big Lake, Horsefly, and Likely, and live near the mine.

Staffing Numbers at Mount Polley

When Mount Polley is in full operation, we have as many as 370 staff working on rotation at the mine, most often in four crews.

Shifts are typically a 12-hour day shift and 12-hour night shift; four crews; seven days on, seven days off.

Additionally, we have about 50 support staff including administrators, supervisors, warehouse workers, engineers, geologists, assayers, technical personnel, and human resource staff.

Mount Polley mine
Mount Polley mine – Creative Commons license CC0
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Mining facts

Likely Area Mining History

The area around Likely has a long and fascinating history of placer mining. Placer mining refers to mining materials (mostly gold) deposited in ancient stream beds that are still largely unconsolidated (i.e. relatively loose materials).

Some of the earliest gold discoveries in the area were made in 1859, one in the Horsefly River, and one in the Dancing Bill Gulch. The latter became known as the China Pit and then the Bullion Pit, and is located just downstream of Likely on the west side of the Quesnel River. The Bullion Pit is now a local historic site with a public walking trail.

Quesnel Forks information sign at the entrance to the historic townsite

Placer gold was also discovered near the mouth of Keithley Creek on the Cariboo River about 12 km upstream from Quesnel Forks in July 1860. Other significant discoveries were subsequently made just 4 km south of Likely on Cedar Creek, and in Quesnel River itself.

In 1897, the Golden River Canal Co. decided to build a dam across the Quesnel River at the outlet from Quesnel Lake in order to block the river and be able to work the gravels from the bottom of the river. The tent town that developed on the site was known as ‘Quesnel Dam’. In 1920, the dam was dynamited and the remnants of the dam can be seen just north of the Likely Bridge in Likely. After the removal of the dam, the residents decided to rename the town ‘Likely’ after a local prospector, John Likely.

Drone image of the Bullion Pit near Likely, BC

The Bullion Pit ulimately became a very significant gold producer in the area. BC Minfile report number 093A 025 states that “In 1897, the Consolidated Hydraulic Mining Company commenced full scale operations and between 1898 and 1902, the company processed 5,912,700 cubic metres of mixed materials, recovering 1,402,316 grams of gold at a recoverable grade of 0.132 grams per tonne gold… Estimations indicate that a total of 200 million tonnes of material were removed by hydraulic methods and 5.463 million grams (175,644 ounces) of gold were produced.” Indications are that much of this material was discharged directly into the Quesnel River.

Polley Lake Outlet Structure: water works for placer mining — early 1900s. Courtesy of BC Archives.

The shortage of water in the early 1900s led the operators of the Bullion Pit to construct a number of water control and diversion works on local streams and lakes to gather water for the hydraulic operations at the pit. Photos from the BC archives, including ones featured in the TV program “Gold Trails and Ghost Towns – The Bullion Pit episode”, document weirs and diversion ditches built on Polley Lake and Hazeltine Creek and other creeks in the area.

To learn more about Likely’s mining history, visit the Cedar City Museum and Info Center located in the Cedar Point Provincial Park in Likely, BC.

This Facebook page gives regular updates on the areas in BC that were part of the mine’s early gold mining history.

Historic building in Quesnel Forks

Many placer mines continue to operate in the area around Likely, including near Quesnel Forks. Quesnel Forks is a restored ghost town located 12 km outside of Likely with a rich mining history and is also worth a visit. It is situated at the point where Cariboo River meets the Quesnel River, and features a beautiful campground and a number of restored and partially restored old buildings.

Historic building in Quesnel Forks. Courtesy of Mount Polley
Historic building in Quesnel Forks overlooking Quesnel River. Part of the history of the Mount Polley site and surrounding area.
View of Quesnel River at confluence with Cariboo River from Quesnel Forks historic townsite
View of Quensel River from Quesnel Forks historic townsite.
Cedar City Museum and information centre in Cedar Point Provincial Park in Likely, BC on Quesnel Lake.
Historic mining equipment on display in Cedar Point Provincial Park in Likely, BC
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Mining facts

Is Mount Polley Dumping Waste into Quesnel Lake?

There has been recent speculation about whether or not Mount Polley is dumping waste into Quesnel Lake. In short, the answer is no. Current treatment of water at Mount Polley, including the dilution zone at depth in Quesnel Lake, ensures water released into Quesnel Lake is in line with BC and Canadian water quality standards. Mount Polley discharges only treated mine site water that meets strict Environmental Management Act (EMA) permit guidelines.

All mine site water is collected and is treated by a Veolia ACTIFLO™ water treatment plant before it is released into Quesnel Lake. (see veoliawatertech.com for more information on their treatment systems and how they work.) The water going into the WTP (influent) is monitored on an ongoing basis (measurements of turbidity every 15 seconds) and the treated water leaving the plant (effluent) is sampled regularly for analysis. The lake water quality is also routinely monitored and sampled regularly as part of the mine’s Comprehensive Environmental Monitoring Plan.

The following are facts that explore, in more detail, the discharge from Mount Polley into Quesnel Lake. We hope this information provides factual clarity about Mount Polley’s approved activities.

Is Mount Polley’s discharge having negative effects on Quesnel Lake?

There are no indications in the monitoring data that the Mount Polley discharge is having any negative effects on Quesnel Lake water quality. If you are interested in looking at some of the water quality data that has been collected on surface water in the area around the Mount Polley Mine, the results are available through the BC Government Surface Water Monitoring Sites Interactive Map

Is the water in Quesnel Lake contaminated? Is it safe to drink?

At this time, there are no indications of contamination of Quesnel Lake water from the Mount Polley spill. The mine, and the Ministry of Environment and Environment Canada, continue to monitor Quesnel Lake. With the exception of natural causes, the lake does not exceed environmental guidelines for any of the constituents of concern that are found in the Mount Polley tailings.

As early as August 12, 2014, BC’s Interior Health Authority (IHA) rescinded all water use restrictions from Quesnel Lake (including for “drinking water, personal use, fishing, swimming and recreational purposes”), except for the immediate impact zone where Hazeltine Creek entered Quesnel Lake. The IHA notice also stated that “Interior Health has no reason to believe that this water was ever exposed to unsafe levels of contaminants from the mine breach. As a result, flushing and testing of individual water supply systems is not considered necessary.”

All water use restrictions were fully rescinded July 13, 2015. (Note: IHA always advises that surface water be treated for pathogens prior to use/consumption.)

How much is the mine discharging into Quesnel Lake?

The Environmental Management Act permit annual average authorized discharge rate is 29,000 cubic meters per day. The actual discharge rate depends upon the rainfall experienced at site which varies from year to year. In 2019, the annual average discharge rate has been 14,883 cubic meters per day, significantly less than the mine’s permit allows.

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Mining facts

Tailings – What are they and what is in the Mount Polley tailings?

First, what are tailings?

Tailings are essentially crushed rock, and are the leftover material after the minerals containing the “elements of interest” have been removed. At Mount Polley the elements of interest are copper, gold and silver. The minerals containing the copper, gold and silver are released by crushing and grinding the mined rock down to sand and silt sized particles.

At Mount Polley, a process known as flotation is then used to separate the important copper-bearing minerals from the rest of the crushed ground rock. The remaining crushed rock is considered waste (gangue) and is what makes up the tailings. No cyanide is used at Mount Polley.

Read more about Tailings on the Mining Association of BC’s website here.

What is the in the Mount Polley tailings?
At Mount Polley, the valuable elements are copper, gold and silver and they are found most commonly in the sulphide minerals, chalcopyrite and bornite. The leftover minerals found in the waste are piped as a slurry with water to the tailings storage facility. [ref: Community Updates 2017 Issue 3; 2016 Apr Issue 2]

The rocks that are mined at Mount Polley are around 200 million years old and represent ancient volcanic rocks and magma that intruded into these rocks. The intrusive rocks host the copper, gold and silver mineralization.

Let’s talk rocks!
The rocks which host most of the ore are made up primarily of the minerals orthoclase (potassium feldspar), albite (sodium plagioclase), magnetite (iron oxide), Ca-plagioclase (calcium plagioclase), diopside (pyroxene), garnet, biotite (mica), epidote and calcite (calcium carbonate). These minerals are all common rock-forming minerals, and represent 90% of what ends up in the Mount Polley tailings pond.

Of the other 10 percent, most are also common minerals, with a minor amount of sulphide minerals, including a little bit of chalcopyrite (0.17%) that didn’t get captured in the mill and a small amount of pyrite (0.04%).

What is unusual about Mount Polley is that, when compared to many other copper deposits (and the reason why these tailings are considered by geochemists to be chemically quite benign) there is very little pyrite (iron sulphide) and a fair amount of calcite (calcium carbonate) in the tailings.

Due to this, Mount Polley’s tailings do not generate “acid rock drainage”. This is the process that happens when sulphide minerals, especially pyrite, are exposed to the atmosphere and react to form sulphuric acid, which then can leach metals out of tailings and lead to metal mobility and potential contamination.

Mount Polley’s tailings do not have this “acid rock drainage” problem, as there is very little pyrite, and calcite acts as a neutralizing agent if any of the minor amounts of sulphide in the tailings breaks down. The vast majority of the rest of the minerals in Mount Polley’s tailings does not react easily with air or water, and are very similar to natural sand.