Indeed, some people would say that miners have so far only scratched the surface of what’s available to them in the Earth’s crust. That’s true in the sense that the mineral industry explores and mines within only a small proportion of the depth range over which common ore minerals are stable and subject to natural concentration. Most of its activities take place within a kilometre or two of the Earth’s surface, though there are a few so called ultradeep mines working at depths as great as four kilometres. Drilling for oil and gas quite often goes to depths of five kilometres of more: beyond that, high temperatures and pressures, and sealing of the rocks, usually cause a sharp fall off in prospectivity.

The development of sophisticated mechanical shovels, very large haul trucks, and flexible conveyor belt systems have meant that since the middle of the last century more and more mining has been done in open pits. This trend has been encouraged by breakthroughs in explosives technology, giving efficient fragmentation of harder rocks and ores, and in rock mechanics, giving better ways of modelling and improving the stability of open pit faces.

There have also been real and convincing advances in the environmental rehabilitation and stabilization of exhausted open pits and their waste products. All of these considerations are built into modern mine plans.

Further contrasts feed the perception that oil and, to a lesser extent, gas resources are finite whereas mineral and metal resources are almost infinite. One is the relative ease with which miners can increase recovery from a given resource by extracting a higher proportion of the ore.

Open pits are generally favoured compared to underground operations – although as the orebody goes deeper, underground mining is often the only economic solution, notwithstanding the challenges. Some underground operations involve partial extraction of the ore, leaving behind a percentage as pillars to support the roof. These pillars can often be extracted in the next phase of mining. In coal mining, the seam is fully extracted and the roof allowed to collapse, relieving the build-up of stresses.