Linking pit and valley - Global news

Mining in an area where the processing plant is much higher in altitude than the pit presents a number of challenges for even the most accomplished mining teams. At Minera Media Luna’s El Limón gold mine in Mexico the processing plant is located on a steep ridge about 400m higher than the open pit. This means that 1 000 metric tons of gold ore per hour have to be transported over a distance of 1.3km up a very steep incline.

El Limón-Guajes is located about 180km south-west of Mexico City in the state of Guerrero, Mexico. Minera Media Luna (MML), the company that operates the pit, is a subsidiary of Canadian based Torex Gold Resources. The ore mined at the two pits of El Limón and Guajes is processed in one central processing plant. During the planning phase, one of the issues that had to be addressed was the transport of the material from the pit into the valley and up the steep ridge. Along with the costs, operational safety and the impact on the environment had to be taken into account.

In March 2013, MML decided to use an innovative means of transport known as RopeCon. The system covered the vertical rise of 400m and the length of 1.3km with just one tower structure before unloading the material onto a stockpile.

Construction of the RopeCon started in early 2014. Doppelmayr, the Austrian-Swiss company that manufactures the system, assembled it in just six months – accident-free and on schedule. The RopeCon took up operation as planned in March 2016. It now connects the pit with the processing plant.

RopeCon relies on a flat belt with corrugated side walls to transport materials of all kinds. The belt performs a haulage function and is driven by, and guided around, a drum at both ends. To account for the great vertical rise and consequently the steep incline between the El Limón pit and the valley, the belt has been fitted with cleats to prevent the material from slipping. Axles are mounted on the belt at regular intervals to support it. They have plastic running wheels attached to their ends. These wheels run on track ropes with fixed anchoring and guide the belt. The track ropes run over tower structures so that this conveyor system is lifted off the ground, leaving only a minimal footprint.

The system features three track rope pairs in total, with the bottom pair supporting the empty belt and the pair in the middle carrying the loaded belt. An inspection vehicle travelling on the third track rope pair at the top serves to provide easy and safe access to any point along the line. Almost all moving parts are attached to the belt and therefore pass through the stations at regular intervals. Service and maintenance works can thus be performed at one central point.

The El Limón RopeCon system generates about 1MW of green energy from braking actions, which contributes to a reduction of the overall operating costs. This, and the fact that no fossil fuel (diesel) is required to operate the system is one of the significant differences between RopeCon and trucks, the other means of transport under consideration for the transport of the ore.

Apart from the positive effects on operating costs, resulting from straightforward maintenance and regenerative operation due to downhill transport, the avoidance of dust and noise emissions is another argument which strongly supports the use of the RopeCon. The automatic transport system will also help to enhance operational safety and its controls can be integrated into the central control system of the mine.

The decision to use the RopeCon to transport the crushed ore from the pit to the stockpile in the valley also means that the access road to the pit does not have to be upgraded for truck transport. Access can now be narrower and steeper and can follow a different route. The footprint of the roads can thus be reduced. The RopeCon system as such operates off-ground and does not touch the ground between the loading station and the track rope anchoring point in the valley except with one tower structure. With a height of 44m, this tower achieves the discharge height required for the stockpile. The span between the loading station and the tower structure is 1 200m. The conveying angle comes up to 32 degrees.

Viewed over the entire life of the mine of an estimated 10 years, the RopeCon system will transport close to 1 000 metric tons of ore per hour from the crusher to the stockpile, from where the material will then be taken to the processing plant.

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