The Mining cycle

The following is an excerpt from the ninth edition of Mining Explained, published by The Northern Miner.

The miner’s job is to break ore and rock and get it from underground to surface.

The first step in the mining cycle is to drill holes in the rock and ore. These holes are loaded with explosives which are detonated to break the rock. In modern-day mining, electric-hydraulic drill jumbos drill the pattern of short holes required to break the rock or round and advance the development heading. A drift round or breast round will normally advance the drift face about 3-4 metres (10-13 ft.).

Older, pneumatic jumbos and hand-held jack-leg drills and stopers are still used for certain specialized drilling jobs and in stopes where the work space is confined.

Large-diameter (10-to-15-cm) blasthole drills, and 2-boom, small-diameter (5-to-10-cm) longhole drills are in common use for production in stopes.

Loading and blasting

Once the holes have been drilled, a blasting crew loads the holes with explosives. Nitroglycerine dynamites and ammonium-nitrate blasting agents are the common types of explosive. A mixture of fertilizer (ammonium nitrate) and fuel oil called anfo (an acronym for ammonium nitrate and fuel oil) is commonly used in mining. It is set off or initiated by a high-explosive blasting cap or primer. Machines for loading explosives range from small portable anfo loaders to specially designed mobile vehicles with large hoppers for transporting and loading bulk explosives pneumatically.

Holes are loaded so that each charge is fired in a designed sequence. This is important in order to obtain the desired break.

Large blasts or charges are usually set off electrically from surface once all underground workers are out of the mine, usually at the end of a work shift. The timing not only ensures safety; it also allows the dust and fumes caused by a blast to be dissipated by the ventilation system before the next shift goes underground.

Mucking

Once the ore or rock has been broken by explosives, it is called “muck,” and the pile of broken ore is called the “muck pile.” The ore must be loaded into trucks or rail cars and transported to an ore pass for further transfer to surface. The loading procedure is called “mucking.” A variety of loaders and haulers is available to mining companies.

The load-haul-dump (LHD) machine is perhaps the most common mucking machine. These rubber-tired machines range in size from small, compact units with buckets that can handle 0.4 cubic metre (14 cubic ft.) of muck to much larger units equipped with 6-cubic-metre (212-cubic-ft.) buckets or greater. LHDs can be powered by electric motors or by diesel engines. In mines where haulage distances are great, LHDs are used to load haulage trucks or rail cars, which then haul the ore (or rock) to surface via a ramp, or to an ore pass — a vertical working down which the ore can be dumped like laundry or garbage down a chute. From the ore pass, the ore either goes to an underground crusher or is hoisted to surface.

Continuous mucking machines lift the muck from the floor directly to a conveyor belt, which then loads it into a truck or on to another conveyor. High-speed electric trolley trucks can also be used to bring the material to surface. Conveyor belts, too, are finding more applications in underground mines (for transporting ore to an ore pass or crusher). Such large-volume mucking systems are usually restricted to mines that use bulk-mining methods in the range of thousands of tonnes per day.