This blasted and boring business
Metal demand is rising, ore grades are falling and hard rock mining productivity has plateaued. The industry has to change. The biggest suppliers already have their plans in place. It will be interesting to see how the smaller players respond.
There have been major productivity jumps before. Dynamite was patented in 1867 by Alfred Nobel and the pneumatic drill in 1871. The combination made drilling and blasting the technique of choice for underground hard rock mining to this day. Add jumbo drills and the front-end loader and you have the backbone of today’s mine.
Blasting is the most energy-efficient way to break large quantities of rock. Unfortunately, drilling and blasting introduces a cycle into mining that is remarkably inefficient. The mine has to be evacuated before a blast. The drill-blast-clean-support-load-haul cycle means ore is moving from the face for only a small fraction of the workday. Incremental improvements in each part of the cycle can shorten shifts incrementally, but won’t allow whole new cycles to be added to the day.
There are at least two ways around the problem. Big equipment manufacturers have been adapting the tunnel boring machine for hard rock mining. Others are exploring ways to telescope the drill-blast-haul cycle.
Boring machines worked well in soft materials. Salt, coal and potash mines have converted almost completely to mechanized rock cutting. Gold, diamonds, copper, silver, nickel and zinc are usually found in igneous or metamorphic rock, which is relatively hard (>150 MPa compressive strength). The forces required to break the rock, the wear of the tools caused by the rock’s abrasiveness and the tight working conditions have held back adoption.
Nonetheless, boring machines appear to offer many advantages. Less over- and under-cutting than with blasting means less waste, less chance of weakening the surrounding rock, less need for shotcrete, bolting, and backfill, and less risk for workers. The relatively small and uniform chips produced may improve milling and eliminate the need for primary crushing, although they may increase unwanted oxidation. Ventilation requirements should be lower. Improved cutting designs and harder carbides are available. Both Caterpillar and Atlas Copco’s progeny, Uniroc, are now marketing boring machines for hard rock mining.
Continuous rock cutting machines still have problems. The term “continuous” itself is a misnomer because even in soft rock they are rarely continuously cutting. Delays occur while roof support is installed and often while waiting for cars to return from their discharge point for reloading. These are the same problems plaguing the drill and blast method. The machines are also complex and capital intensive. The large size, high weight, and long setup time work against the boring machines as a flexible mining tool. They don’t turn corners well, and are not likely to work well in small mines or mines with complex geometries.
They are also single-supplier solutions, potentially leaving miners tied to one large supplier and leaving little room for smaller competitors.
The alternative approach is to telescope the drill-blast-haul cycle. Continuous mucking and transport can speed up the drill-blast cycle. Automated bolting and portable shelters would enable bolting to happen at the same time as drilling.
Furthermore, drill and blast is easily adapted to irregular orebodies.
This alternative line of development may be more suitable for small and complex mines. In addition, telescoping the drill-blast-haul cycle opens up opportunities for mid-level mining equipment suppliers to develop and supply new equipment and services.