Maurice Jones explores the potential of drill-and-blast efficiency over traditional drilling techniques
A dilemma facing government authorities and underground mining companies, mainly in ‘developing’ countries, is whether to mechanise and automate production blasthole drilling, or to retain traditional drilling only with pneumatic ‘air-leg’ drills.
The first has the potential for greatly increased drill-and-blast efficiency but eliminates jobs, while the second retains labour-intensive work but carries greater risks for safety, ore dilution with waste, and lost mineral due to accurate drilling pattern execution.
Whatever the wider economic and political implications it is clear that a wide range of efficient production drilling methods are now available and being used successfully. This is particularly so in mines situated in ‘developed’ regions such as Australia and North America where the drive for more efficient ore extraction is continuous.
Selection of an appropriate and efficient means of production drilling largely depends on the size and shape of the ore body, the means of access, and how easily the ore fragments for drawing off as in caving.
As in opencast mining, if possible management usually tries to reduce the number of holes to be drilled by increasing their diameter, and so improving the ‘powder factor’. Underground the scenario is rarely so simple but the main objective is the same. Fairly recent developments that have improved production drilling efficiency include faster hydraulic drills, use of bits of larger diameter in longer holes, and computer control, particularly of drill patterns, to maximise accuracy. Where circumstances allow, downhole (DTH-ITH) drilling can aid accuracy in drilling larger diameter holes.
For some ore bodies, such as stratified deposits, the same type of face-drilling jumbos can be used for production as well as development, but for large ore bodies and narrow veins, dedicated rigs are usually required.
In 2010, Sandvik became the sole distributor for Canadian-made Cubex drills, which employ ITH (downhole) methods underground as, it claims, global leader in such rigs design and manufacture. Downhole drilling can be used for longer and larger diameter holes. The rigs are available on crawler-track or tyred, articulated carriers. Sandvik Mining has just announced that it is to acquire Cubex.
Sandvik’s own range of top-hammer drills are intended for holes up to 54m long. There are six standard models in the DL series, a low-profile rig, and two for narrow vein production drilling.
Atlas Copco’s mainstay of production drilling is the Simba, which is now available with the same RCS computerised rig control systems and E-series rigid rectangular booms as the manufacturer’s jumbos and other rigs, both aiding accuracy as well as productivity. Improved boom capacity enables the RHS 35 rod-handling system to be installed, with stability further improved by four ‘stingers’. Recent developments at Russia’s expanded Norilsk nickel mining complex resulted in an order for 15 Simba rigs.
Modern mines and contractors
A feature of many modern mines is the use of contractors, not only for shaft construction and development drives but also sometimes for production drilling, particularly longhole.
This is common in Australia (eg, Barminco and Pybar and Canada. Boart Longyear’s services are available worldwide, and Bergteamet of Sweden is also a leader in this activity.
Contractors operate their own fleets of drill-rigs or lease them.