Truckless Mining Skip Conveying – An Approach to optimise Cost and Energy Efficiency in Hard Rock Mines
A newly developed mining method allows ore and overburden in hard rock mines to be transported more efficiently and with significantly lower environmental impact. It involves an integrated conveying and processing system to avoid heavy truck transportation in inverted cone-shaped opencast mines.
Opencast mines for copper, iron ore and other materials including gold frequently take the shape of an inverted cone, with the ore and overburden mined by blasting and then transported away by truck/shovel operations.
Mine trucks weighing between 106 and 260 tonnes and carrying payloads from 136 to as much as 400 tonnes transport the materials from the bottom of the pit via unpaved roads and slowly rising, winding tracks to the dumping area outside the mine pit or to the crusher station several hundred meters above at the top of the mine. The ore is reduced in a crusher station, and in larger mining operations is then transported away via overland conveyors at a rate of 10,000 tonnes per hour and more.
Thyssenkrupp Fördertechnik – a supplier of mining, crushing, processing and materials handling systems – is developing and has patented a mining method that allows ore and overburden in hard rock mines to be transported more efficiently and with significantly lower environmental impact. It involves an integrated conveying and processing system to avoid heavy truck transportation in inverted cone-shaped opencast mines.
A rope-driven conveyor system transports complete truckloads of material in skips travelling on tracks inclined at up to 75 degrees by the shortest route to the crusher station at the mine head. Like a freight elevator, as one loaded skip moves upward, an emptied skip moves in parallel downward to the bottom of the mine. The two skips are connected via a rope system, pulleys, and a traction sheave drive system at the top of the mine such that the dead weight of the skips is fully balanced at all times and no unnecessary lifting power needs to be expended.
The major advantages of the new system are highlighted through a concrete example and may give operators food for thought when planning or redesigning mines in the future.
Typical Opencast Mining Operations
Fig. 1 shows a typical opencast mine for copper and gold ore with its steep banks and winding roads. The photo shows one of the world’s biggest copper/gold mines in Indonesia. It extracts and processes around 220,000 tonnes of copper/gold ore per day in truck/shovel operation. Looking at the photograph closely it can be seen that heavy-load trucks or mine trucks are moving up and out of the mine in a train-like formation on ramped roads, travelling at average speeds of around 15 to 20 kilometres per hour.
The line of trucks works its way upwards on largely unpaved winding roads with gradients of up to 9 percent until it reaches the top of the mine. The trucks carry ore from the bottom of the mine to the crushing station at the top, as well as overburden to dumping areas outside the mine.