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Publication of the Geotechnical Institute of TU BerlinIssue no. 58, Berlin 2011, pp. 163-180Presentation on the 7th Hans Lorenz Symposium on 06/10/2011

Special foundation engineering elsewhere:

Passive Vertical Drains for one of the largest Copper Mines in the World

Dipl.-Ing. Holger Itzeck

BAUER Resources Canada Ltd., Edmonton, Canada

Dipl.-Ing. Verena Schreiner

BAUER Resources Canada Ltd., Edmonton, Canada

1 Summary

In the vicinity of Kamloops in the Canadian province of British Columbia, the mining company TECK

Resources Limited operates one of the largest copper ore mines in the world. During operations for

extending the life of the mine, problems pertaining to the stability of the mine slopes were

encountered. For the "Big Bear Pushback", special measures were required to ensure the stability of

the pit walls. BAUER was commissioned to drill 27 passive drainage wells, viz. "Passive Vertical

Drains". For this purpose, bores with a diameter of 1,200 mm were drilled down to a depth of around

115 m and subsequently filled with a filter material specially made for this purpose. The objective was

to drain water from the landslide-prone slopes and to discharge it into a deeper, water-conducting

layer. The holes drilled are amongst the deepest holes ever drilled using the kelly-drilling method and

could be drilled with the equipment available on site only after some adjustment were made by using a

little trick. This presentation deals with the basic concepts of slope stabilization and the special

challenges of such types of boreholes. Furthermore, the authors attempt to offer an insight into mining

in Canada.

2 H. Itzeck, V. Schreiner

2 Copper mining in Canada

After iron and aluminium, copper is one of the most widely used metals and constitutes an important

economic factor for producers and consumers. Copper is primarily used in the electrical industry, in

communication technology and in construction.

Fig. 1: World copper production 2010 [16]

Although in some countries, a remarkably large amount of copper is obtained from recycling

processes – around 45 % in Germany – worldwide around 15.9 million tonnes (2010) of copper are

extracted and processed in mining operations. Chile is by far the largest producer of copper ore,

followed by the Peru, China and a number of other countries, which contribute quite a considerable

amount to the world production. Copper ore is thus a frequently occurring material worldwide (see

Fig. 1). Over the years, Canada's ranking in this list has varied depending on the source. In any case,

with an annual production of 525,000 tonnes, Canada is one of the 10 largest producers of copper in

the world.

After a slump caused by the financial crisis of 2008, copper prices once again reached new heights

owing to the boom in the demand for raw materials worldwide at the end of 2010 (Fig. 2) and has only

been going down slightly since. Copper mining has thus once again become a lucrative option.

Indonesia872 US

1,110 China1,190

Peru1,250

Chile5,420

Australia870

Zambia690

Russia703

Canada525

Other countries 3,270

in thousand metric tons

15,900

Passive Vertical Drains for one of the largest Copper Mines in the World 3

Fig. 2: Copper prices in the last 5 years [7]

3 Economic considerations in open pit mining

3.1 Strip Ratio

The "Strip ratio", i.e. the mass ratio of the extracted ore to the mass of the waste rock be removed and

displaced in order to extract the ore, plays an important role in determining the economic viability of

an open-pit mining operation. The general angle of the slope and the installation and execution of

berms are the determining factors (see [3]). Figure 3 shows an example of the effect of the strip ratio –

in this case, for a coal mine – on the economics of a mining operation. Depending on the value of the

extracted material, the rates – of coal in British Columbia and iron ore in Quebec to uranium ore in

Saskatchewan – vary significantly from 1:3 to 1:100 (see 6th HLS). For economic reasons, the

objective was to optimize the construction of the mining slopes in such a manner that while ensuring

the stability, a steepest possible slope can be created and a favourable strip ratio can be achieved.

Cop

per P

rice

USD

/to


Fig. 3: Impact of Strip ratio on profitability (as per [3])

The biggest cost factor for an open pit mine are generally the vehicle fleet and the facilities for

processing and treating the extracted material. Therefore, uniform utilization of the equipment and

facilities has high priority. Continuous operation is an important prerequisite for the economic use of

the multimillion dollar vehicles, crushing plants and ore treatment facilities.

Fig. 4: Mining operation: Constant strip ratio (as per [3])

Any unnecessary interim storage or additionally needed movement of enormous masses of mining

waste or ore has significant economic consequences. Also, supply contracts with buyers on the world

market are very often long term and based mostly on continuous supply. Fig. 4 shows a simplified

mining plan and Fig. 5 the corresponding production rate and transport vehicle utilization for the

intended uniform mining operation. Needless to say, such plans are liable to change depending on

fluctuations in demand in the markets, discontinuities in deposits or other influences, all of which

Steps

Stripping

Ore Mining

Milling

Directs

Indirects

Product Cost

Shipping

$/ton

3.20

4.50

12.00

4.20

3.80

Strip ratio

12

Cost

4.50

12.00

4.20

3.80

38.40

Strip ratio Cost

19

4.50

12.00

4.20

3.80

60.80

62.90 85.30

38.10 38.10

Average Sales Price: 122.00 US$ 101.00 123.40

789

10987

123456

Mineral ResourceWaste Rock


cannot be accurately predicted at the beginning of operations. This especially includes factors arising

from geological or hydrogeological conditions for the operation of an open pit mine.

Fig. 5: Uniform utilized capacity for a constant stripping ratio

4 Slope Stability

A number of calculation models are used to determine the stability of a slope. These are based almost

exclusively on 2D and 3D observations and comparisons of active, pushing forces and passive,

holding forces along theoretically given slip surfaces which follow circular paths or spirals. The

resulting values are set in relation with each other and a safety factor is determined. When using this

procedure it is clear to all parties involved that the in-situ conditions cannot be reproduced 100 % by a

model. Many factors such as rock stresses, cracks and crevices, groundwater fluctuations,

accumulation of surface water and other climatic influences are difficult to estimate, but have a

significant impact on the slope stability. In addition, the use of heavy equipment and the often very

intensive use of explosives in daily mining operations can lead to slope failure. In British Columbia,

there are additional considerations pertaining to earthquake events.

Mio to/year

years


Fig. 6: Effect of water pressure on movement of the slope (Smreka iron mine) [9]

In practice, therefore, slopes formed on this basis are generally monitored through continuous geodetic

measurements at least. In the Highland Valley mine, around 500(!) measuring points are continuously

monitored. Complex evaluation systems can immediately help detect unusual movements. The number

of measuring points might initially seem excessive, but is to be considered appropriate in light of the

scale of open pit mining operations. Because of the diameter and depth of the pits, the accuracy and

reliability of the measurement data obtained during on-going mining operation are not always

completely unambiguous and reliable from the beginning. Owing to a continuous reduction in

potential sources of error, however, this monitoring has meanwhile become the basis for control

activities in the field of slopes (see [11]). These results are complemented by further measures and

facilities for observing processes in slope-areas that are several hundred meters high. Extensometers

are used to check for cracks and crevices, while piezometers are used to monitor the groundwater

situation.

There is a good reason as to why water pressure monitoring has come to assume special significance.

According to experts, an astonishingly high number of mine-slope failures can be attributed to the

effects of water. Figure 6 shows how an increase in pore water pressure can quickly lead to slope

movements that are difficult to control. In approximately 40 % of the cases evaluated by the Mandzic

[9] method, water-related risks play a decisive role in the failure of slopes. Conversely, a reduction in

water level or water pressure in a slope can improve safety to a significant extent. This is also what the

engineers in charge of the Highland Valley Mine do in order to stabilize the east-side side mine slope.

P

Pore pressure Travel speed[cm/day] 0.0

0.10.2 0.30.40.50.6

0.01.02.04.06.0

10.0> 10.0

ru = u/γ


5 The Highland Valley Copper Mine

5.1 Type of copper deposit

Copper deposits in the Highland Valley Copper mine are of the porphyry type. Porphyry deposits

typically possess low quantities of copper, ranging from 0.4 to 1.0%, but owing to their large volume,

they are the major sources of copper in the world. These deposits usually also contain small amounts

of other metals such as molybdenum, gold or silver. In the Highland Valley Copper Mine, in addition

to copper, molybdenum is also extracted and treated.

The estimated copper ore deposit in the Highland Valley mine (as of December 2011, [10]) is 673

million tonnes, with an average copper content of 0.2 % and a molybdenum component of 0.008 %.

These estimations are not final; they are regularly updated on the basis of results from exploration

works.

5.2 History

The history of the Highland Valley Copper mine dates back to 1962, with the start of the mining

operations in the Bethlehem Copper Mine. Until 1982, copper was extracted from three open pit mines

there. The Lornex ore deposit was discovered in 1963 and in 1970, stripping of the overburden in

order to reach the ore deposit was started. In 1972, the Lornex ore was smelted for the first time in the

copper processing plant. Copper ore deposits in the valley were detected in 1964 and stripping of the

waste rock began in 1982. The Highmont Operating Corporation commenced copper mining

operations in 1979, and operations continued until the mine was closed down in October 1984. In

January 1989, the copper processing facilities of Highmont Mill were added to Lornex Mill's existing

operations. In 1986, the Lornex Mining Corporation and Cominco Ltd. came together to form the

Highland Valley Copper partnership; in 1988, the Highmont Operation Corporation joined the

partnership. [4] Today, the Lornex and the Valley open pits are still in operation. With a depth of 800

m and a diameter of around 3 km, the "Valley Pit" (see Fig. 7) is the largest open-pit mine in Canada

and one of the largest open-pit mines in the world.


Fig. 7: Valley Pit, 2010

5.3 Production numbers

In 2010, a total of 42,488 thousand tonnes of copper ore with an average copper content of 0.27% was

extracted from the Valley and Lornex pits. At a recovery rate of 86.3%, approx. 98.5 thousand tonnes

of copper was produced and marketed. In addition to copper, 3,130 tonnes of molybdenum was

extracted. [15]

Despite the relatively low grades of copper and the temporary reduction in extracted volumes owing to

stability problems with the mining slopes, good returns could be obtained because of the high price of

copper.

5.4 Copper ore extraction

Copper ore is extracted by means of the so-called 'truck and shovel' method. After the ore body is

uncovered underneath the overburden, it is loosened by blasting; the crushed rock is loaded by means

of electric shovel excavators onto haul trucks that can transport up to 250 tonnes of ore in a single

load. The trucks transport the ore to one of the semi-mobile crushers, which crushes the rock into

small pieces with a maximum particle size of 165 mm, and the crushed ore is transported to the

processing plant over a 2 km long conveyor belt system.

5.5 Copper ore processing

The pre-crushed copper ore is transported from the crusher to the processing plant, where it is

pulverized to a particle size approximately equal to that of fine sand. The pulverized ore is transported

to the flotation tank. Copper and molybdenum are separated from the rock matrix here. In another

flotation process, the copper concentrate is separated from the molybdenum concentrate. The


concentrates are filtered, dried and then prepared for shipping. The tailings are transported through

pipes to the tailings pond of the mine.

6 Expansion of the Valley Pit

In 2007, a "Mine Life Extension" was announced by Teck. The mine life was to be extended from

2013 (originally) to 2019, during which a further 247 million tonnes of copper ore are expected to be

extracted. This goal was to be realised through expansion of the Valley open-pit. In order to be able to

begin mining in 2009, a substantial additional investment in equipment was necessary. [14]

Fig. 8: Slope failure in the Valley Pit in June 2009

During the expansion of the Valley Pit, the eastern slope slid in June 2009 (see Fig. 8). During the

expansion of the open-pit mine, a basin of glacial and fluvial deposits – the so-called Highland Valley

– surrounding the ore body was increasingly exposed (see Fig. 9). Around 200 m of water-bearing

sediments were present above a layer of lacustrine clay (layer 10B). Due to the water problem

mentioned in Section 4, the stability of the slope decreased with the progress in excavation, ultimately

leading to slope failure.

Failure of the Valley Pit East slope

Ultimate Pit 2009

End of 2001

Upper AquifersMain AquiferBethsaida FanBasal Aquifer

10A10B10C

LEGEND:


Fig. 9: Cross-section of the Valley Pit and the neighbouring Highland Valley

Subsequently, a number of immediate measures were taken. First, copper mining in the critical areas

was stopped so as to not further endanger the slope stability. To reduce the load on the slope, removal

of the overburden on the eastern periphery of the Valley Pit was commenced. A part of the removed

material was moved to the foot of the slope to give further support. For a long-term restoration of

slope stability, however, additional measures were necessary.

Fig. 10: Eastern slope of the Valley Pit before and after the dewatering program

A major part of load reduction on the eastern slope was achieved through a dewatering program

involving a system of dewatering wells [5]. In addition to a number of conventional drainage wells

from which groundwater is to be pumped, a large number of passive dewatering wells (Passive

Vertical Drains) were constructed (see. [15] ). Figure 10 provides an overview of the complete

program for depressurization of the eastern slope.


7 Passive Vertical Drains as part of the dewatering program

BAUER Resources Canada Ltd. was commissioned to drill 27 passive vertical drains. These PVD

wells should collect water from the upper layers and discharge it into the so called basal aquifer, a

deep aquifer (schematic diagram see Figure 11).

Fig. 11: Principle of a Passive Vertical Drain

7.1 Technical description

The specified diameter of the wells was 1.2 m. The final depth is between 80 and 115 m below ground

level. The target was to drill each well at least 15 m into the "basal aquifer". The wells were drilled

into the soil of the Highland Valley from two levels, 1070 and 1055 m above sea level. The following

geological formations were encountered while drilling: The top 40-55 meters of drilling is in zone

10A, a silt with fine sand and traces of organic material, clearly noticeable by its dark colour. Beneath

it is a layer of lacustrine clay (10 B), partially silty, with an approximate thickness of 15 m. Below the

clay is a 20 m thick layer of silty sand (10C). The basal-aquifer, sandy gravel with a quite varying

composition was expected to be found at around 75-90 m below surface. The wells had to be driven

sufficiently deep into this layer to make sure the water from the upper aquifer could be discharged.

The depth of this aquifer varies considerably, in some areas it was not encountered until 100 m drilling

depth. This was the reason for the new record depth for the BG36 in kelly drilling mode to be achieved

in the course of the project.

Each borehole was supported by a double walled casing down to a depth of 30 m. At greater depths,

the borehole stability was ensured using a slurry fluid consisting of water and polymers (see section

7.2.2).


Fig. 12: Principle of the drilling procedure

7.2 Scope of work and challenges

7.2.1 Drilling depth

The deepest of the holes drilled was 114.5 m below top of the casing, i.e. about 113 m below ground

level – one of the deepest holes ever drilled with a BAUER BG using the kelly drilling method.

7.2.1.1 Kelly bars

Basically, there are two types of kelly bars; the friction kelly and the lockable kelly. Both are

telescopic, the difference being that in a lockable kelly, the individual segments are force-fitted

together by means of a sophisticated system consisting of lock bars, drive keys, grooves and locking

pockets (see Fig. 13). Thus, the entire crowd force of the machine, around 35 tonnes in case of the

BG 36, can be activated as pressure for the drilling tool. As against that, in the case of the friction

kelly, there is only the dead weight of the kelly bar (here around 16 tons) and the weight of the drilling

tool. The power transmission between the individual segments, takes place, as the name suggests, only

through friction. Thereby, the crowd force can hardly be transferred onto the drilling tool. In simple

words, you can imagine such a type of kelly bar as an upside down car antenna of an older design. In

hard, dense soils it is difficult to achieve a good drilling progress using the friction kelly. However,

these kelly bars are easier for the rig operator to handle as they don’t have to be locked/unlocked


which, especially for longer bars, requires attention and experience. Friction kellys have a lower dead

weight and - at the same maximum drilling depth - a slightly shorter overall length. This is important

if the operating limits of the drilling rigs are reached, and the available mast length and the maximum

capacity of the main winch become critical factors.

Fig. 13: Structure of a lockable kelly bar [1]

For the Highland Valley Copper Project, an 85 m long friction kelly as well as a 40 m and a 72 m

lockable kelly were used. Always, for the first 40 m, the short kelly bar was used. Thus, the tool could

be lifted over the casing (which was sticking out more than 5 m above ground level at times, without

any difficulty. Particularly in the10B layer, which mainly consists of very stiff clay, no significant

drilling rate could be achieved using the friction kelly. The performance in the basal aquifer, which is

made of relatively densely packed and gravelly sand, was not satisfactory too. Therefore, for greater

depths than 40 m, the 72 m lockable kelly was used. To reach the required depths of up to 115 m, kelly

extensions had to be used after having reached the maximum depths of the kelly bars. It turned out that

the drilling rate achieved using the 72 m lockable kelly in combination with an extension was better

than the drilling rate achieved using the 85 m friction kelly. More on this in the following section.

7.2.1.2 Drilling with kelly extensions

Drilling with kelly extensions is a quite complex process. If, however, drilling depths are above the

maximum range of the kelly bar that is available for the provided BAUER BG rig, the use of kelly

extensions is rather unavoidable. Fully extended, the longest lockable kelly bars for a BG 36 have a

length of 72 m and were thus short by more than 40 m to reach the final depth of 115 m. In such cases,


the mentioned kelly extensions are used. They are steel bars that can be attached to the kelly bar stub

at the end of the bar using a conventional kelly stub-kelly box connection. For the Highland Valley

Copper Project, BAUER Resources Canada provided three kelly extensions of 13.5 m length each.

With these extensions, an additional drilling depth of 40 m was possible. Drilling with kelly

extensions significantly slows down the drilling process especially using all three of the extensions. In

order to empty the drilling bucket, first, every single kelly extension must be secured on top of the

casing, separated from kelly bar and set aside with the help of a crane. Now, the drilling tool can be

lifted with the kelly bar, opened and emptied. Then, the entire process takes place in the reverse order

and it takes some time until the tool reaches the bottom of borehole again. Drilling PVDs with a depth

of more than 72 m resulted in a significant decrease in the drilling rate, depending on the number of

kelly extensions used. Kelly extensions are not used very often because they are difficult to handle and

because the drilling progress slows down significantly.

Fig. 14: Drilling with kelly extensions at the Highland Valley Copper Mine

7.2.2 Borehole stability

Due to the great depth and large diameter, a fully cased borehole (using recoverable casing) had to be

ruled out. In terms of procedure and cost, lost casing was also out of question. Moreover, this would

not have served the actual purpose of the wells. The finally drilled, partially cased bores require, in

first place, sufficient hydrostatic pressure that has to be higher than in the surrounding soil at all times

during the drilling process. Furthermore, suitable fluid additives were needed, which would:


maintain the stability of borehole walls

avoid slough

prevent the swelling of the clay-layer 10B

prevent the clay particles from the 10B layer from getting suspended in the supporting slurry

fluid

Bentonite, which is usually used for stabilising boreholes or diaphragm wall panels, was not applicable

in this case. On the one hand, the danger with the use of a clay suspension would be that it would

possibly impair the groundwater in the water bearing layers from entering the wells. On the other

hand, a resulting thick filter cake of clay particles could clog the pores of the basal aquifer and could

likewise negatively affect the functioning of the wells. Finally, products from the series of polymers or

methyl cellulose, which were available in the North-American market and were meanwhile being

widely used in drilling technology, were used. With the addition of this substance, the swelling of the

clay layer was inhibited and excessive loading of the supporting slurry fluid was prevented.

Theoretically, relatively thin but solid filter cakes are formed, which can later be completely flushed

back by water entering the drain. The sometimes fanciful product names such as Poly-Plus 2000 (clay

inhibition) or Platinum Pac UL (filter cake reduction) do not really help here. Perhaps, the dosages are

important, which are around 2 l/m3 for the former product and 4 kg/ m3 for the latter product. In the

further course of the work, the dosages were further reduced because the sedimentation in the bores

and the loading of the drilling fluid with clay particles was less than as expected in the preparation

phase of the work. In Germany, such fluid additives are available in the Viscopol product line, for

instance, and are used in similar dosages in the construction of drinking-water wells.

7.2.3 Ongoing mining operation

During the execution of the project, we had to constantly ensure that our activities would in no way

disturb the copper ore mining in the valley pit.

7.2.3.1 Health and Safety

Occupational Health and Safety is of utmost importance for mining companies. Every mine has a

specific safety policy. The Highland Valley Copper Mine has strict safety rules for its own employees.

These, however, also apply to all other companies that work for TECK as contractors on the mine site.

All their employees must first participate in a safety training before they are allowed to work at the

mine. There, they are trained in all important points regarding the topic occupational health and safety.

In particular, conduct in emergency situations and communication channels play an important role.

While this instruction programme at Logan Lake only lasted a few hours, it may also extend over

several days for other mines (Red Dog Zinc Mine, Diavik Diamond Mine). One of the important


points of these instructions is the special traffic rules at mining sites (see 7.2.3.2). The mandatory

personal protective equipment (PPE) at the mine site comprises safety shoes, safety glasses, high

visibility vests and hardhats. An according to the German standards slight violation of safety rules,

such as standing in the working area without wearing personal protective equipment, is punished

severely. Misconduct may result relatively quickly in the errant employee being immediately laid off

or even the company being excluded from other orders. All these safety trainings and measures taken

lead to a positive result. The number of the accidents and downtime there differ considerably from the

numbers in Germany, as we know from the various divisions of specialist foundation works in

Germany.

7.2.3.2 Mine transport

In mining trucks, the operator's cab usually is located on the left hand side of the vehicle. Due to the

huge size of the truck, the vision of the operator is very limited, especially on the right hand side of the

vehicle. Therefore, from safety point of view, at the most of the mining sites with truck and shovel

operation, there is left-hand traffic. The general operations at the mining site must, in every respect,

follow this direction of traffic.

Fig. 15: Blind spot of a mining truck [6]

The "blind spots" of the trucks remain a risk (see Fig.15). Therefore, before passing a mining truck,

the driver must always be addressed per radio and his/her approval must be taken. Since, due to their

enormous weight, fully loaded haul trucks move very slowly on their way from the excavator to the

crusher, passing manoeuvres are sometimes necessary, but should be performed with extreme caution.


Fig. 16: Traffic at the mine site

7.2.3.3 Transport

For the project, the drilling rig with all the accessories was transported to the 1070 and 1055 berms of

the valley pit. A heavy transporter for the base machine and in total 11 truckloads were brought to and

unloaded in the Valley Pit in close co-operation with mine safety. Every single transport vehicle was

to be accompanied with an escort vehicle and before entering into the mine, an announcement was to

be made over radio so that the mine truck traffic in the valley pit would be prepared.

Fig.17: Heavy transporter coming out from the valley pit


8 Conclusion

The work was completed by BAUER Resources Canada Ltd. within budget and ahead of schedule.

The client was more than satisfied with the performance. One of the reasons was certainly that a

competitor had previously completely failed at the same task. A positive approach to the topic

"drilling with kelly extensions", originally for the reasons described unpopular with all parties

involved, has certainly contributed to the success. Especially with this work process, significantly

higher performance could be achieved than it was initially estimated in terms of costing and

scheduling. Key success factors once again turned out to be good, experienced and highly-motivated

employees.


9 Literature and Internet

[1] BAUER Maschinen GmbH (2009): Product catalogue kelly bars Schrobenhausen, March

2009

[2] Girard Jami; McHugh Ed (2000): Detecting Problems with Mine Slope Stability. 31 st

Annual Institute on Mining Health, Safety and Research, Roanoke, VA., August 2000.

[3] Hartman, Howard et al. (1992): SME Mining Engineering Handbook. Society of Mining

Engineering, ISBN 0873351002, April 1992.

[4] Highland Valley Copper Partnership (1999): Mining History of the Highland Valley.

http://www.venturekamloops.com/SiteCM/U/D/99B842C0BACECDF0.pdf

[5] Hill, L. (2009): Teck sees lower output after Highland Valley pit wall movement. Mining

Weekly Online, 25.06.2009.

[6] http://www.cdc.gov/niosh/mining/topics/electrical/pwsselection.htm (27/07/2011)

[7] http://www.infomine.com/investment/metal-prices/copper/5-year/ (23/09/2013)

[8] http://www.teck.com (27/07/2011)

[9] Mandzic, E.H. (1992): Mine Water Risk in Open Pit Slope Stability. Mine Water and the

Environment, Vol. 11, No. 4, December 1992.

[10] Ministry of Energy, Mines and Natural Gas (2013): Exploration and Mining in British

Columbia, 2012. Victoria, BC, January 2013.

[11] Newcomon, Warren; Murray, Colin; Skwydiak, Loyd (2003): Monitoring Pit Wall

Deformations in Real Time at Highland Valley Copper. BGS publications, 2003

[12] Sjoeberg, Jonny (1996): Large Scale Slope Stability in Open Pit Mining: A Review.

Lulea University of Technology, ISSN 0349-3571, 1992.

[13] Summit Environmental Consultants Ltd. (2002): Environmental Impact Assessment of

Basal Aquifer Dewatering Project. Report Prepared for Highland Valley Copper,

February 2002.

[14] Teck (2007): Teck Cominco announces Highland Valley mine life extension to 2019.

External News Release Teck Resources Ltd., 12.02.2007.

[15] Teck (2011): Teck reports unaudited results for 2010. External News Release Teck

Resources Ltd., 08.02.2011.

http://www.cdc.gov/niosh/mining/topics/electrical/pwsselection.htm


[16] United States Geological Survey (USGS) (2012): Mineral Commodity Summaries 2012,

p. 49.

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