In winter 2010 the Queen’s University 4th year mining engineering class went to Chile for their field trip. The Mantoverde mine was visited by the group on February 17th. This wiki provides a detailed overview of the Mantoverde mine. Topics covered in the paper are the background of the mine, the geography, the orebody, the mining methods used, the mines equipment and the processing techniques. The Mantoverde mine is an open pit mine that produces copper from an oxide ore. The main extraction process used is leaching. The mine was designed to produce a yearly production of 42 000 tonnes of high purity (99.99% Cu) metallic copper. Currently the mine produces 60 000 tonnes per year of copper cathodes.
The Mantoverde mine is found in the northern region of Chile. It is owned and operated by Anglo American and is 100% employed by Chileans. The Mantoverde mine produces copper cathodes through electrowinning. The mine currently has 3 operating open pits mining oxide ore and another pit being developed for mining starting 2010. The four pits are Mantoverde Norte, Mantoverde Sur, Manto Ruso and Kuroki. Figure 1 shows a satellite image with the highlighted pits. The copper is extracted though heap leaching as well as ROM dump leaching. The life of mining the oxide ore will run until 2014. After 2014 the mine will then begin mining sulphide ore. The Mantoverde mine runs under a SHEQ management system, which is based on Safety, Health, Environment and Quality. The system follows 3 principles; culture, learning and standards to achieve zero harm.
The deposit was first developed in 1906 by the Societé des Mines et Usines de Cuivre. High grades were mined near surface and then sent to overseas and local smelters for processing. From 1948 to 1950 Anaconda Mining exercised purchase options on the deposit. Then in 1964 until 1968 Down Santa Rosa S.A. purchased the deposit and had a development and extraction program. Then in 1972 ENAMI (National Mining Corporation) bought the deposit. In 1976 Compañía Minera Mantoverde S. A. purchased the deposit and performed metallurgical tests and a feasibility study to determine if the mine could be developed to a large scale. In 1988 to 1992 Anglo American purchased the deposit under the subsidiary Minera de Mantos Blancos S.A. Industrial development begins in 1995 on the Mantoverde deposit. Finally in 2000 Anglo American acquired 99.97% of Minera de Mantos Blancos S.A.
Mantoverde Awards and Achievements
Mantoverde has received numerous awards for its outstanding safety and sustainable operations. In 2009, Mantoverde was the recipient of the John T. Ryan Safety Trophy for the safety performance in 2008. Mantoverde was also awarded the Coresemin Award for the safety performance in 2008 and also awarded the Sernageomin Category B at the national level for 2008. Mantoverde was given the distinction in 2009 of the Asociacion Latinoamericana de Seguridad e Higiene en el Trabajo, ALASEHT, for excellence in sustainable safety results. An achievement that Mantoverde was proud to accomplish was on June 23, 2009 which was marked as one year, over 2 million man-hours, without a lost time incident.
Mantoverde is a mine in northern Chile. It is in region III, the Atacama Region, located in the Chañaral Province in the Los Pozolos district.
The Mantoverde mine is in the Chilean Coastal Cordillera. The closest towns to the mine are Chañaral and Diego de Almagro which are about 50 to 60 km to the northern west and east. Copiapo is located 100 km to the south and Antofasgasta is 400 km to the north. The mine is also located at 900m above sea level.
The climate in the Atacama Region can be broken down into mainly 3 desert climates. The coastal desert climate, on the pacific coast, has frequent cloud cover. The middle region of Chile has a transitional desert climate. Towards the Andes incurs a cold mountain desert climate and finally a high altitude tundra climate. There is very little rain in the winter time and no rain in the summer time. The summers are very hot and dry (28° C) and the winters can get mild (11°C).
The region consists of the following individual deposits; Manto Verde, Manto Ruso, Manto Monstruo and Monte Cristo. The deposit is a copper oxide orebody.
The primary mineral extracted is copper at the Mantoverde mine. The region is also known to have some silver and gold within the orebody. The main copper minerals within the orebody are brochantite, chrysocolla, malachite and atacamite.
The deposit lies along the north – south direction in the Mantoverde cross fault. The deposit is shallow and thus is mined by open pit mining. The pre-feasibility and feasibility study for the orebody has shown the global reserves at 83 million of high grade copper ore at 0.82% Cu and 21 million tons of marginal ore at 0.45% Cu. The current total measured and indicated reserves have stayed relatively close to the initial values in recent years, as seen below in Table 1.
Table 1. Global reserves as reported on an annual basis
The method used at the Mantoverde mine is open pit mining. The Mantoverde operation includes the open pit mines, crushing plants and processing facilities on site. There are approximately 800 employees at the Mantoverde mine, of which roughly half are contractors.
Mantoverde mine has four open pits that are along the orebody that stretches approximately 7.8 km in length. A design plan view can be seen in Figure 3. One difficulty with the mining operation is that the mantoverde pits are beside another company and the open pit on the ore zone shares a wall. The neighbouring mine is a smaller gold silver operation. This adds some difficulty to the wall design as well as coordinating the blasting for the mine.
Figure 3. Mantoverde design plan view
The bench height is 20m, the road width is 30m, and the ramp inclination is at a maximum of 10%. The mines roads are all left hand side drive and all vehicles, large haul and small personal vehicles share the same driving laws in the mine, including all posted signs and speed limits. The overall pit wall slope is 56° but the mine is currently undergoing modifications to some walls which will be at a slope of 61°. The mine does not have any ground control problems, as well as the walls and benches are kept very clean with scaling and dozers. This supports the excellent health and safety record of the mine.The water used at the mine comes from two sources. Since the climate is a desert region water was initially all transported from the town of Copiapo. Recently the mine was able to drill wells and now pumps 3800 cubic meters per day. The mine still does transport water from Copiapo as the wells only provide approximately 50% of the water needed for running the mine. The drilling and processing alone uses 1600 cubic meters per day.
The mine was initially designed to have a life of 16 years. The initial project was planned to have an extraction of 5.4 Mt/year of copper mineral ore then process to produce 42 000 t/year of electrolysis produced high purity copper cathodes (99.99% Cu). The mine currently moves about 92 000 tonnes per day of which 30 000 tonnes go to be processed. The cut off grade for the mine is 0.18% copper. Anything below 0.18% Cu is sent to the dump, while between 0.18% and 0.38% Cu is sent to be processed at the dump leach, and anything above 0.38% is sent to be processed at the heap leach pile.
The mining cost per tonne at the Mantoverde mine is approximately $1.12 which is quite low, and that is including the leasing costs. With the good wall stability and the close locations of the dump sites and ore processing areas with downhill loaded driving the costs are able to be kept down.
Mantoverde is an open pit mine that uses trucks and front loaders / wheel dozers to move the ore. The ore gets moved to the crusher, to the low grade stock pile or waste dump. The mine also has drills and a variety of auxiliary equipment. The availability of the equipment is very good. There is not a lot of down time for the equipment. The maintenance shop spends roughly 65% of the time on preventative maintenance, and the other 35% of the time on breakdowns. The average mean time to repair, MTTR, is only about 5 hours, and the MTBF is about 45 hours. The most common maintenance issue for the mine is the hydraulics on the loaders and drills.
The mine has two sizes of front end loaders. There are 3 CAT 994 F loaders with a 22.3 cubic yard bucket capable of moving approximately 30 000 tonnes per day, and also 3 CAT 992 G loaders with a 14.4 cubic yard bucket capable of moving 15 000 tonnes per day. Figure 4 shows the loading of some trucks. The loaders have an availability of around 84%.
The mine uses trucks for hauling the ore to the crusher or dump sites. There are 9 CAT 785C trucks which are 150 ton used to move waste and 8 CAT 777D trucks which are 90 ton for moving ore. The haul trucks have an availability of about 90%. On Average the trucks must haul 2200m to reach the primary crusher
The mine has 4 Ingersoll Rand DM 50 drills that drill 7 7/8 inch hole size.
The mine has 3 CAT D10T bulldozers, 2 CAT 834G wheeldozers, 2 CAT 773E water trucks and 1 CAT 16H motorgrader. The average availability for the auxiliary equipment is 87%.
There is a multiple stage process to produce the high purity copper cathodes from the initial ore removed from the mine. The main process used to extract and collect the copper is leaching. There two lines of production that the ore can go through. The low grade ore goes to the dump leach and the high grade ore to the heap leach. The cut off grade for the heap leach is 0.38% and the cut off grade for the dump leach is 0.18%. Additionally recovery for heap leaching is 85% and 90% for dump leach. The mine currently produces 60 000 tonnes per year of high purity copper cathodes.
The benches are drilled and loaded with explosives that have a powder factor around 160g / t. The ore is then hauled and dumped into the primary crusher. The primary crusher is a gyratory crusher with a x95 passing size of 5 inches. The crushed material is then transported via conveyor belt to the secondary crusher.
The secondary stage utilizes a cone crusher with a apron screening system. Due to the large percentage of clays present in the geology a vibrating screen is not feasible. Using conveyors the material is then passed to the tertiary crusher. The tertiary crusher is a closed circuit with a passing size of 11mm. At this point the material is treated with sulfuric acid to facilitate the reaction that takes place in the heap leaching stage. The tertiary stage is the most fickle as CaCO3 levels need to be monitored consistently making blending control critical.
Following this the material is placed into the heap leach pile which ranges in height from 2.8m to 6.5m. After proper placement 12 g / L sulfuric acid is used to produce a soltuion containing 2.5g/L Cu. This fluid is then collected and sent for electrowinning. It is worth noting that to acheive maximum recovery the material must be left in place for 120 days.
The solvent extraction selectively removes the copper and leaves behind the remaining ions in the aqueous solution. The electrowinning process uses electrolysis to produce the high purity (99.99% Cu) copper cathodes.
Each copper cathode weights approximately 75 kg and once cooled are ready for transportation and sale on the market.
Figure 5. Heap leaching process at Mantoverde
The heap leach solvent extraction electrowinning process was originally selected to have 15 000 tonnes per day processing rate in the pre-feasibility / feasibility study. This would then produce 42 000 tonnes per year of high purity copper cathodes. Currently the mine processes 25 000 tonnes per day and produces an output of 60 000 tonnes per year of the copper cathodes.
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