Mining methods yesterday and tomorrow

Mining methods change when new technology arrives. Sometimes an apparently small change can have a profound impact. For example, the availability of remote-controlled LHDs in the 1990s enabled narrow sublevel stopes to be accessed along strike, instead of via drawpoint crosscuts. This not only saved development but made a lot of additional mineralization economic to mine. Remote operation was not a new idea; it evolved from developments with Cavo loaders in the early 1960s.

The term “trackless mining” first appeared in the mid-1950s. The first mine to use diesel dump trucks underground was Noranda’s Gaspe copper, in 1959, where trucks were loaded from orepasses and later by short-boom electric rope shovels. The first mines designed specifically for LHDs, like Lake Dufault in 1964, used underground workshops to assemble machines lowered via a shaft. By this time, Mt Isa Mines in Queensland was using Wagner St5 and ST1.5 LHDs, Cat 922B front-end loaders, Atlas T4G autoloaders, and various Eimco rail boggers. But only a handful of mines worldwide were experimenting with diesel mechanization, and most still relied on rope scrapers and rail haulage.

The first permits to use diesels underground in Western Australia were issued to Mt Charlotte mine in 1964, but union opposition delayed their introduction. Inco apparently tested an LHD during 1966 at Frood, then introduced 14 units at Creighton by mid-1969. Back in Australia, New Broken Hill Consolidated began to mechanise with ST5 LHDs in 1967, loading through chutes into rail trucks. An ST4A was installed at Pamour Porcupine Mines (Canada) in 1967, where it replaced 25 production haulage employees achieving a twelve-month payback, and elsewhere the improvement was just as dramatic, with Inco, for example, reporting a 300% increase in productivity (from 75 to 225 tpms)!

What about the successor to the LHD? A Canadian programme in the early 1980s used gathering-arm loaders in drawpoints, with semi-mobile Eagle crushers and flexible conveyors feeding an orepass. This system failed due to poor stope fragmentation and, more important, a lack of mobility. Should something similar be tried again and, if so, how would we build the equipment to take advantage of thirty years of technological improvements?

The big change is just around the corner. Three major manufacturers are serious about continuous cutting of hard rock, which is likely to revolutionize mining methods, both underground and open pit. The last big change in open pits was the application of hydraulic excavators and shovels which, like haul trucks, got bigger and bigger. Continuous excavation and flexible conveyors will allow surgical selection of valuable mineral in a way that can only be seen today in soft-rock and coal mines. There will always be applications for drill and blast, particularly in massive orebodies, but many supposedly massive orebodies are actually quite variable on a scale of a few metres. If we halve the amount of sub-grade material finding its way into the ore stream, we will cut processing costs dramatically and halve the size of our tailings dams. That is something to wish for.