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Are we entering the last age of the open cut mine? Is the end of open pit mining near? Speaking to a number of sources, the answer is clearly no, but as grades decrease and deposits become deeper, the increase of underground mining will continue apace as older open cut mines are worked out and new, deeper deposits are discovered.
Underground mining will soon count for a much larger proportion of total mining. According to a Rio Tinto seminar in 2010, in 2009 underground operations accounted for 26 per cent of all copper production, however Rio forecast that by 2025 underground operations would account for 40 per cent of global copper production.
This included major copper producers such as Chile and Australia, where massive open cut pits are the norm. But this is not to say open cut mining has been uneconomical. Surface mining has been, for some time, the most economical form of mining in Australia.
Underground contract mining specialist Pybar’s group business development manager David Noort told Australian Mining “open cut mines have been, economically, the most viable, which has been due to relatively near surface expressions”.
With wide open spaces and often remote locations, it has been the more cost effective form of mining, but globally it has already started coming to an end, with Noort explaining that “many of these higher grade expressions close to the surface have already been discovered, so we are left chasing ore down”.
Speaking to Sandvik Mining and Construction’s underground mining specialist Malcolm Campbell, he told Australian Mining that “globally many surface mines are getting to the end of their economic life, where they are now removing too much waste rock to be considered economical”.
However, Campbell did clarify that in the case of iron ore mines, particularly in Western Australia, surface mining will remain de rigueur; many operations will keep going that way due to many of the deposits being closer to the surface, although they may approach it differently, with operators such as Fortescue Metals Group using surface miners instead of the traditional excavator and truck model.
Previously speaking to Barminco CEO Peter Stokes on the issue of underground mining, he stated “we are seeing a great trend towards underground contracting, and the fact that our techniques are getting better is only helping this”.
Technologically, underground mining is also looking more prospective for equipment manufacturers.
Speaking to Rio Tinto’s Australian general manager for geotechnical engineering and cave management, Andre van As, he told Australian Mining that as Rio Tinto develops its block caving expertise in Australia will be looking to unique technologies to do it in more efficient ways.
Rio Tinto has been one of the major developers of the block caving methods, implementing it at its former Northparkes mine and the Argyle Diamond mine, with van As stating that “block caving is a very attractive mass mining method”.
Whilst block caving methods have been around since the 19th century, the technique has been coming along in leaps and bounds, particularly in South America, with van As stating that “the Chileans have been doing it for much longer [than we have in] Australia, most of Codelco’s copper mines (such as the massive Chiquicamata) are block caving operations, and [one of the world’s largest mines] Freeport Grasberg in Indonesia is also doing it”.
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