The commodity price squeeze is pushing both asset owners and service providers to do things smarter. In 2016, innovation, efficiency and productivity will remain key mining trends; the challenge lies in finding ways to increase productivity while reducing costs.
In drill and blast, one effective strategy for achieving this is to optimise existing drill rigs to enhance blasthole drilling capabilities, rather than commissioning additional larger, more costly equipment.
The purpose of drilling blastholes is to facilitate the efficient distribution of explosive energy within the rock mass, where the same chemical energy will deliver more useful work than if it was piled up on the surface. The optimum depths and diameters of the blastholes to be drilled in any drill and blast project depend on the type and depth of the rock being broken, the type of explosives being used to break it and the objectives of the blast. Ground conditions can vary significantly in a single project so the ability to tailor the drilling accordingly is the ideal approach to optimise the blast – and herein lies the challenge.
Drill rig challenges
In the competitive environment that is mining, it is common for drill manufacturers to compete in ‘classes’. Each supplier will offer a drill suited to certain diameters or hole depths: smaller, less costly drills for the small, shallow holes and larger and more expensive drills for the large, deep holes. Neither typically have the capabilities to drill holes in the other’s class.
Big drills are more expensive to purchase, operate and maintain, but big drills drill larger diameter holes, and this is where they deliver their cost benefits. The geometry of blasting is generally a squared relationship – if the diameter of the drill bit is doubled, the number of holes needed will be reduced by a factor of four. Less holes means drill patterns can be drilled quicker and less explosives accessories are required so the cost of achieving the end result – blasted material – is cheaper than if the same amount of work had been done with smaller drills.
For the end user, this presents challenges if a mine has varying blast requirements and/or where reducing dilution and ore loss are key objectives.
It means the blast will be designed around the capabilities of the drill available rather than designed to maximise the explosive energy. It can result in a sub-optimum blast to the detriment of subsequent mining activities and project costs.
Alternatively, it means acquiring an additional drill and more cost.
Overcoming rig challenges
Where there is a problem, there is innovation. Solutions–focused drill and blast teams are finding ways to overcome rig challenges by optimising smaller rigs to drill larger hole sizes, effectively enabling them to perform in a higher drill class but without the additional operational costs associated with running a larger piece of equipment.
These optimised rigs use multiple bit diameters and can perform angled drilling to suit varying ground types, final wall designs and bench heights. By drilling a wide variety of blasthole sizes, the team can get the most efficient work out of the explosives and therefore deliver the best downstream benefits to the mine such as better rock fragmentation to improve dig rates and crusher throughput, optimal muckpile profiles and better final wall stability.
The ability to use optimised smaller drills in a greater number of situations delivers a number of value-adds to a drill and blast operation and indeed to the mining project as a whole:
- Better overall flexibility: Small rigs have the capability to perform a number of roles from production drilling to drilling contours, trims, batters, presplits and toe. They can be used for depressurisation drilling, installing collar pipes and can operate in tighter spaces.
- Reduced operating and capital costs: Smaller rigs are generally less costly to acquire, maintain and run. But more may be required if production requirements are high.
- Ability to achieve more consistent fragmentation: If dilution and ore loss are a concern, designing a blast with smaller holes closer together results in better explosives distribution and will therefore produce more consistent fragmentation and less oversize than designing larger holes further apart. This improves the fill factors for digging buckets and haul trucks and means, in general, smaller digging equipment can be used for excavation. An optimised small rig can provide the flexibility to drill small and larger holes as the project requires.
Case study: Rig optimisation delivers at Greenbushes lithium mine
Prior to 2013, drilling production techniques at Talison Lithium’s Greenbushes mine had traditionally used GD5000 top hole hammer drills to drill 115mm to 127mm blast holes on 5m to 10m benches. However, Talison had a requirement for deeper and more accurate 30m pre-splits to provide a continuous split line between each berm, which the GD5000s struggled to perform at the accuracy required. The client also wanted larger hole sizes in the bulk waste zones to reduce drill and blast costs, and was considering the use of reverse circulation (RC) drilling to improve the site’s grade control process.
ADB developed and implemented a customised production technique to meet the client’s objectives by acquiring an Atlas Copco D65 drill – set up with RC but also capable of being easily changed over to drill conventional blast holes. The drill can comfortably drill up to 165mm diameter holes and its down hole hammer can provide accurate pre-split holes to the required depth of 30m. With the RC set up, the D65 is also able to fulfil the grade control requirements. The rig can perform all the functions required with no extra cost to the client for an additional machine.
The value of this professional service has seen production targets consistently met, waste blasting costs reduced and an exceptional safety record to date with no lost time to injury since ADB commenced on site in 2011.