May 12 – Centinela

Today, we closed our Chilean Research Trip with a tour of Centinela Mine.  The property is 70% owned by Antofagasta Minerals, the only private Chilean mining company, and 30% by Marubeni Corporation.  Like most mines in the Calama region, Centinela produces copper as its primary product.  We began our trip with an introduction to the property and a safety briefing.  The site consists of four active pits, primary crushing and grinding, separate oxide and sulphide processing lines (which produce 29 ktpd and 89 ktpd respectively) and a thickened tailings storage facility.

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After receiving our PPE, we began our tour with a visit to Esperanza, Centinela’s sulphide pit.  Esperanza moves 420,000 tpd to send 100,000 tpd to the mill and 20,000 tpd to a stockpile.  The pit is currently 450 m deep and when finished, with be 2 km in diameter and 650 m deep.  In addition to Esperanza, the site has three pits producting oxide ore (Central and Northeast Tesoro and Mirador) that move 150,000 tpd to send 30,000 tpd to a leach pad.  To facilitate this, the site has an impressive fleet of equipment: eighty trucks, five cable shovels, two hydraulic shovels, six front end loaders and sixteen drills.

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The current mine plan will develop eight pits within an area spanning 40 km distance.  To manage the challenges of material transport, Centinela plans to heap leach oxides near their farthest pits and transport pregnant solution by pipeline to the SXEW plant.  By the time operations is ready to mine sulphides, another flotation plant will be built closer to the pits.  Currently, ore from Esperanza is crushed at the pit and transported via a 3.5 km conveyor from the primary crusher to the ore stockpile.

Out next stop was to the plant, were we were excited to find the Mill Manager was a former UBC graduate.  Francisco Melo worked on his Masters of Applied Science in 2005 and helped explain to us Centinela’s sulphide processing line.  We began at the control room, which has stations to control the primary crusher, grinding circuit, pebble crushers and flotation circuit.  After that, we were able to view the entire mill from a viewpoint behind the control room.  The mill processes 110 to 114 thousand tpd with a head grade typically between 0.48 to 0.50% copper and 0.25 g/t gold.  After identifying that their SAG mill was at capacity and that their two ball mills were underutilized, Centinela saw the opportunity to increase throughput by adding a secondary and tertiary crushing plant. The plant can crush up to 20ktpd of material fed from the main stockpile. This is crushed to a P80 of 9mm and fed straight into the ball mills, bypassing the SAG.

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Once reduced to a P80 of 180 microns, the ore is sent to flotation.  Like its neighbour, Sierra Gorda, Centinela uses seawater for its flotation process.  Fifty to sixty thousand cubic meters of saline water is transported by a 145 km pipeline from the coast.  Processing with sea water adds challenges to the mill.  Instead of depressing pyrite with lime, as with freshwater flotation, sodium methyl bisulphate is used to increase the pH because of the buffering caused by seawater.  Additionally, the mill has to take extra precautions to mitigate corrosion, such as using liners and using special paint.

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The plants two rougher lines recover 94% copper and sends the product to a regrind to reduce the P80 to 40 microns.  The ore then goes to a two stage cleaner line which uses conventional and then column flotation.  The ultimate recovery is 87% copper to produce a concentrate with a 24% copper grade.  The final product also contains gold at 6 to 8 ppm and molybdenum at 0.5%.

Like every operation, Centinela manages operating challenges.  Specific to the mill is the management of high pyrite grades and the need to meet and improve throughput demands.  Because Centinela is located in the driest desert in the world, water is a definite concern.  The mine aims to achieve to 67% solids in its tailings storage facility and does so by using three thickeners and two paste thickeners.  Centinela operates at a USD 1.80 per pound production cost and is targeting USD 1.30 per pound by using economies of scale and adapting innovate technologies.  This includes a thermal solar plant to heat SXEW process water and the use of seawater in its sulphide circuit.  In the future, Centinela plans to add a separate molybdenum circuit to improve the recognized value of its products.

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The mine is an impressive example of innovation and technology and it was great to visit and learn from their mining and milling expertise.  Material movement from several small pits is very similar to mining diamonds from several small pipes located over a large areas and it was interesting to see different solutions to moving ore across a large site.  Because of our location in British Columbia, we are familiar with sulphide flotation, however, the ability to see a plant in open air was a great opportunity to appreciate the scale of the operation and the separate circuits involved.  Antofagasta Minerals was a great host and we are grateful for the tour!

– Grace Ma

May 11 – Sierra Gorda

On Wednesday morning we awoke to the sweet sounds of our alarm clocks in order to catch our 7:00am bus out to the Sierra Gorda mine, the second to last tour of our trip.

Sporting a 0.39% copper head grade, Sierra Gorda is a relatively new operation having commissioned the mill in late 2014. Due to this, the class was treated to the finest facilities that we’ve experienced so far on the trip. Every aspect of this 110,000 tonne per day operation reflected state of the art design considerations.

The tour began, as per usual, with a safety & introduction presentation, after which we were served breakfast sandwiches and coffee (to the delight of everyone). As we ate breakfast and chatted with the office staff, small groups were rotated through the sleekest, most modern control room that we had ever seen. Even the mill rats (myself included) were impressed! Various operators explained to us their respective unit operations and happily fielded any questions we had. The guide had to drag each group out to ensure that the others would get a chance to see it.

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Once everyone had rotated through the control room and breakfast was done, we loaded onto a pit bus and headed out to the lookout point of Sierra Gorda’s primary pit. Another advantage of a new operation is that the pit is not too deep, especially compared to Chuquicamata. The shallow pit allowed us to see five of the six Bucyrus-Eerie shovels loading the 53 Komatsu 930E trucks at any given time and actually wrap our heads around the production that was taking place. There was a blast scheduled for 1:00pm that the pit shifter invited us to stay and watch but unfortunately there was an issue with moving the drill off the pattern and the blast was delayed. We thanked the shifter for answering our questions and hopped back on the bus for the final leg of the tour.

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Sierra Gorda has a very unique milling process; instead of conventional crushing and primary grinding with a SAG mill, the operation utilizes a three-stage crushing circuit. The tertiary step consists of four parallel high-pressure grinding rolls. HPGR technology is a relatively new approach to comminution. It typically has an energy savings of 10 – 15% over the conventional approach, as well as several other operational benefits downstream. So why isn’t it more common across other operations? The mining industry is typically reluctant to embrace novel technologies, given the large capital expense necessary to build concentrator facilities. This conservative nature results in the selection of methods that have been proven time and time again (regardless of how old they might be).
The image below shows an outside view of the HPGR’S.

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Following the secondary crushing (4×1250 Metso cone crushers) and tertiary HPGR step, the banana-screen undersize is fed to three gearless-drive ball mills. The closed ball mill circuit reduces material to a float feed P80 of 160 microns.

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Bulk flotation follows, recovering a copper and molybdenum concentrate. Selective floatation then separates the copper and moly, ultimately producing two concentrates. Currently, overall plant recovery of copper is around 75% with intentions of improving that to ~85% in the future. Sierra Gorda has one of the highest moly head grades in the world: 15% for the first five years of the mine life. This compares to other copper-primary operations averaging closer to ~0.04%. Special considerations have been taken in designing the moly circuit. It can handle the large production that comes with the astronomical head grade at the start of mine life and can then be easily retrofitted to accommodate the much lower head grade from year 5 onward.

Click here for a simplified animation of the entire Sierra Gorda Milling process:

http://www.sgscm.cl/proceso_productivo_eng.html

It’s also important to note that being in the middle of a desert, there isn’t an abundant amount of water readily available for use in the process. Sierra Gorda has gotten around this by constructing a 143 km pipeline to the coast to obtain used cooling water from a coastal power plant. The 42-inch pipe feeds ~2,000 liters per minute over the distance and elevation gain of ~1,700 m with the help of three pump houses.

Sierra Gorda serves as an example of the potential of HPGR technology. In our world of falling head grades and ever-rising costs, it takes innovations and a willingness to step away from the status quo to maintain and increase global metal production.

The class thanks all of the staff at Sierra Gorda for organizing such a well-run tour. None of us had ever seen a circuit fully committed to HPGR technology resulting in an exciting and truly engaging experience. Tomorrow holds the final mine tour of our trip, Minera Centinela.

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– Jim Mackay

May 10 – Chuquicamata Mine

Today we visited Codelco’s Chuquicamata mine, the largest open-pit operation in the world. 460,000 tonnes per day of material is moved with 160,000 of that being ore sent to the mill.

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The day began with Codelco graciously providing us with transport from our hotel in Calama to the mine site. As we boarded the coach bus all personal protective equipment was provided, again highlighting Codelco’s regard for safety as witnessed at Andina.

The first part of our tour consisted of visiting the mine’s processing plant. Accompanied by the Mill Superintendent, we viewed the sites dewatering facilities, considered to be one of the best in the world in terms of water reuse. Chuquicamata draws water from 4 naturally occurring springs on site as well as transporting water from the Andes Codillera. The milling process uses 2 cubic meters of water per tonne of ore milled, with 75% (1.5 cubic meters) being recycled. Being situated in an arid climate, this is one of many factors that allows for Chuquicamata to remain competitive with other operations. The picture below shows one of the nine 350-ft diameter thickeners that are utilized on site.

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After this, we visited the chuquicamata copper concentrator. The operation has a combined throughput of 160,000 tpd. Initially the mill was constructed for a 40,000 tpd operation during the early life of the mine. However, as the copper markets evolved and the deposit further explored, an extension of the mine life as well as an increase in throughout became feasible. As a result, a secondary plant was constructed to accommodate the additional tonnage.

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The mineralization at Chuquicamata is primarily sulfide copper. Sulphide ore is processed in the concentrator. The mill feed is supplemented with sulphide ore conveyed from Coldelco’s nearby Radomiro Tomic mine. Radomiro Tomic is primarily a heap leaching operation which processes oxide copper material. As a cost saving measure, Radomiro Tomic does not have its own sulphide processing plant but instead conveys sulphides to Chuquicamata.

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The mill employs two 32-ft SAG mills feeding a complex arrangement of rod and ball mills. A final grind size of 219 microns is achieved before the slurry is passed on to flotation.

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The mill head grade for sulfide processing is approximately 0.8% Cu and also contains significant amounts of molybdenum making two separate concentrates viable. The final copper concentrate is smelted and then refined prior to shipment, both processes are carried out on-site and were part of the next stop of our tour.

The concentrator contains a separate circuit for recovery of copper from the on-site smelter slag. Slag can contain between 8 and 10% Cu and is sent to its own process line containing a SAG mill two ball mills, and floatation circuit.

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Codelco operates three refineries to produce its final copper product from its smelting processes. The refinery at Chuquicamata refines product from not only its own operations, but as well as the El Teniente and Altonorte smelters to ensure it remains at capacity.

Fortunately during our tour, scheduled maintenance was being carried out in many areas of the refinery allowing for us to get an unprecedented up-close look at the plant.

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The refinery upgrades anodes produced from smelting to 99.9% Cu from 99.6%. Each anode is placed in tanks and copper is deposited on both sides of a steel cathode as electrolysis is carried out over an 18 day residence time to produce the final copper product. As an interesting note, our tour guide mentioned that Canadian made machinery is used in the process to split the copper sheets from the steel cathodes. The byproducts from refining is collected to produce a gold, lead and antimony bar for sale. According to the numbers provided during our tour, this refinery produces approximately 2.5 million lbs of copper each year!

The image below shows a copper anode (the product of the smelter) before refining (99.6% Cu).

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The image below shows a copper cathode (the product of the refinery) which grades at 99.9% Cu.

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To finish off the tour before departing, we viewed the open-pit from a lookout point where we could grasp the scale of this giant mine. A fleet of 82 haul trucks passed us by as we took photos and thanked our tour guides for their hospitality, without it this amazing tour would not have been possible.

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– Maher Chaudhary

May 9 – Spence Mine (BHP)

We left San Pedro monday morning and traveled west to the Spence copper cathode project. Spence is located 60 km to the east of the city of Calama and is owned by BHP Billiton. The mine began production in 2007 and processes both sulphide and oxide ore, grading at 1.4% Cu, via heap leach.

Once we arrived at the mine we were treated to lunch in the cafeteria and a tour of the camp facilities. The camp included a full gymnasium, workout room, movie theatre and entertainment space. Workers are on a 7/7 rotation and appeared very comfortable in this world-class facility.

Open pit mining is conducted at a rate of 200,000 – 250,000 tpd of material moved. The mining fleet consists of four P&H 4100 shovels and forty CAT 793C trucks. Additionally the site has six CAT 994 loaders and a Bucket Wheel excavator to service the leach pads. Oxide ore is leached on one pad with sulphuric acid while sulphide ore is bio-leached with bacteria on a separate pad.  Everyday approximately 60,000 t of ore (at a 4:1 stripping ratio) is placed on/removed from the leach pads, which are leached in a continuous fashion.

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Next we visited Spence’s truck shop which we all agreed was the cleanest shop any of us had visited. Also of interest was the fact that every type of oil/lubricant/hydraulic fluid that was needed to work on the trucks was available to each bay through a series of pressurized lines.

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Spence currently performs 5 blasts a week at a bench height of 15 m. Two pits are currently being mined and they will eventually merge into a single pit. Blasts are limited to less than 900,000 t due to the community of Sierra Gorda being located 50 km to the south of the mine. The mine is actively trying to reduce the number of blasts per week to 4 in order to minimize the total amount of ground vibration felt collectively from all mines in the region. The mine life is currently until 2025 however plans are to build a flotation plant in the next five years. At this time they will be through the deposit’s oxide cap and into the sulphide zone which makes up the bulk of the deposit. This flotation plant will extend the mine’s life an additional 50 years. The final pit is estimated to 1 km x 1 km and 850 m deep.

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Finally we visited Spence’s electrowinning facility. Here the pregnant solution is processed into copper cathodes. Spence produces roughly 200,000 t per year of copper cathodes. Production costs are roughly $1.6 per pound of copper produced. The picture below shows Spence’s automated electrowinning plant.

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The employees at Spence were great hosts to their Canadian copper cousins. They were very proud of their mine and, as we have found all over this country, they were very proud of the mining culture in general in Chile. Our tour ended up being much more detailed than originally planned and as such it ran quite over time, however they graciously offered us dinner. After dinner we loaded back on our bus and headed for Calama. We checked into our hotel Los Domos de Calama and settled into bed, off to Chuquicamata tomorrow.

– Davis Kelly

May 7 & 8 – San Pedro de Atacama

May 7  – San Pedro de Atacama Tours: Day 1

Today was the first day of activities in San Pedro de Atacama. The group departed at 7am to the “Lagunas Altiplanicas” located South of San Pedro at an altitude of 4,220 meters above sea level. This lake is part of the Flamingos National Reserve and is a very special location as it is administered by the Socaire Indigenous community. The lake is in a protected park and environmental conditions are kept pristine as it is a nesting area for the Andian Coot. This type of bird does not migrate and spends its entire life in the same geographical location.

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After the laguna, we continued our expedition to the Atacama Salt Flats (Salar de Atacama). The salt flats are located at 2,305 meters above sea level and are a Flamenco sanctuary. Brine shrimp is the main source of food for the flamencos which is abundant in the shallow waters of the Salar. The salt flats cover approximately 3,000 km2 in a subsiding sedimentary basin. This area was once part of the ocean but due to tectonic movements, it became isolated by a series of mountain ranges including the Andes Mountains. Also, the Atacama Salt Flats contain the world’s largest concentration of lithium which is recovered from the brine at various small operations in Northern Chile.

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After the Lagunas Altiplanicas we returned to the hostel for a two-hour break before leaving for our last tour of the day. In this tour we visited a natural salt cave, hiked to a sand dune and finally watched the sunset at the Valle de la Luna (Valley of the Moon). The photo below shows some of the mining grads climbing though the caves with surrounding allite salt walls.

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Next we went hiking through some picturesque terrain where we were able to capture some stunning images of the desert landscape.

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At last, we ended our evening at the Valle de la Luna. What began as a cloudy sunset, ended as an amazing display of colours that were reflected through the clouds above us and the mountains.

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May 8  – San Pedro de Atacama Tours: Day 2

Today was the last day of activities in San Pedro and began with an early start at 5am from the hostel. Our destination was the Geysers del Tatio (Geysers of Tatio), which is located at an altitude of 4,320 meters above sea level. Due to the high altitude, the ambient temperature is generally below zero in the morning and this allows the formation of visible steam clouds emanating from the geysers.

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After arriving, we explored the geyser field with our tour guide and later went to the hot springs for a swim. Only a small group of brave students dared to swim into the lukewarm waters of the hot spring with outside temperatures below 0 degrees.

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On our way back to the hotel we stopped at the town of Machuca. This small town has 12 families that dedicate their lives to agriculture, farming, and cheese production. We spent close to 40 minutes exploring the town and tasting their cuisine, which included barbecued llama and cheese empanadas.

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During our last day in San Pedro, we visited the Laguna del Cejar (Cejar Lagoon). This is located in the Flamingo National Reserve and consists of 3 small ponds that are considered sinkhole lakes. The lake water has salt concentrations that range from 5% to 28% salt. This high concentration of salt creates a floating effect, similar to the Dead Sea in Israel. The temperature of the water is close to 16 degrees Celsius, a perfect temperature for any Canadian.

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To conclude our evening, our tour company organized a get together with the mining group. We drank the traditional pisco sour and ate snacks while watching the sunset at the lagoon.

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May 6 – Finning Plant Tours

Today marked the end of our stay at Hostal Provindencia in Santiago. We left at 3am to catch an early flight towards the North of Chile, Antofagasta.  Once landed, we embarked on a 45 minute bus ride to the largest Caterpillar distributor in the world, Finning. We made our first stop at the facility, Sucursal Antofagasta, where used Caterpillar equipment from the many open-pit mines is brought for component overhauls. The primary maintenance activities included overhauls of engines, drive shafts and other major components of CAT equipment.

 

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From here we moved to Finning´s second facility in Antofagasta, where the location was designated for equipment assembly. We had the opportunity to see the haul truck bay, where the largest mining haul trucks in the world, Caterpillar 797F´s, are built. Finning was very generous in providing us lunch at their cafeteria and a picture of the grads on a Caterpillar 797F.

 

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After our visit at the Finning facility, we traveled through the Atacama Desert, one of the most arid places in the world, where the average rainfall is 15 mm per year. We drove through several mining operations along the way, which will be visited next week. After a long 4-hour bus ride, we reached our destination at San Pedro de Atacama. Over the next couple days we plan on exploring the high-altitude lagoons, nearby geothermal geysers and the valley of the moon. More updates are soon to follow.

– Eric Yang

May 5 – Andina Mine

Today we left at 5am to visit the Andina Mine, located 80km northeast of Santiago at an elevation of 3500-4200m above sea level. Andina is a combined open-pit and block caving operation. We toured the open pit which sees a total of 230,000 tonnes of material per day moved with a fleet of 30 trucks. The pit has a 2:1 strip ratio and an average head grade of 0.7% Cu. This is considered as Codelco’s smallest operation.

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In order to get this tour we were required to do extensive medical tests which included a blood test, electrocardiogram and chest x-ray. The Andina division of Codelco has impressively strict safety regulations to ensure everyone is fit to visit high altitudes. Luckily nobody was severely affected by the altitude and we managed to get through the tour without any fainting.

For the first part of the visit we traveled to La Mirador to meet with the general foreman and get some views over the open-pit mine. Three loaders and two shovels are currently operating on multiple pit phases including a pushback of a 600 meter high wall.

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Due to the high risks of avalanches and steep terrain, the Andina mill is located underground. Haul trucks feed two primary crushers on the surface which convey material to an ore bin underground. Large underground chambers house the SAG, grinding, and flotation circuits. Copper concentrate is produced and is piped down to the bottom of the mountain pass in slurry form. It is then dewatered and trucked to the Ventanas smelter on the coast. The biggest challenge of having the mill located underground is the complex ventilation system that is required to deal with dust.

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Part of the unique history of Andina is how the tailings management plans have changed over the years. Initially the tailings dam was located near the open pit operation for ease of tailings disposal. At one point in the 1990’s, Andina nearly suffered a breach of the tailings dam when central Chile was undergoing heavy rain during an El niño event. After that event, Codelco moved the tailings dam to a valley that is approximately 45km west of the mine. This location provides significantly more space for tailings disposal and also moves the dam away from the Santiago-area water shed and any glacial discharge. When we arrived in Santiago on May 2nd, we were able to get some aerial photos of the tailings dam before the plane landed.

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