Accurate drilling is a cornerstone of cost-effective ore production

By Simon Walker, European Editor

Production drilling encompasses a wide range of technologies, each of which has a critical role within the complete system. Drill rigs, rods and bits have to be selected to perform in the best possible combination for a given set of orebody-geometry conditions, with other significant factors that govern the choice of system including the rock hardness, the need for more or less fragmentation, and the technical capabilities (and cost) of the workforce employed.

As with most of the technology used in modern ore production, production drilling systems have become increasingly sophisticated over time. The hand-held stopers and jacklegs that were common worldwide in the 1960s and 1970s gave way to the first generations of jumbos and production rigs, and these in turn formed the foundation for increasing levels of automation. In countries where high labor costs have become a crucial component of overall production costs, or where the commodity being produced lies within a highly competitive market, the emphasis has been on the individual miner being able to do more with less physical input. Conversely, in situations where labor costs are lower or where the orebody geometry simply cannot accept complex mechanization, the skills of the miner remain key to achieving cost-effective ore production. An analogy lies in today’s agriculture, with a place for both the high-tech tractor and the simple plow within the wider framework of current practice.

Personal safety has also been a major factor in the drive for greater mechanization. Today’s rigs reduce the miner’s exposure to dust and noise, as well as the risk from rockfall; the degree to which these can be achieved depends on the level of automation or remote control included in the operating package. There is, of course, a trade-off involved between the degree to which a machine can be automated and its cost, with the competency of the operator another significant input to the equation. On a personal level, I can recall a visit to the Kilo-Moto gold mines in what was then Zaire (now the DRC) in the early 1980s, and seeing a brand-new, unused stoping rig lying abandoned in a shed on surface. No one had the skills to use it, and the company had no money to maintain either it, or the vast pile of scrap jackleg drills that lay alongside.

This article looks at some of the systems available for underground production drilling, with the emphasis on the higher-tech end of the market. As with other drilling systems, this is dominated by a very few, internationally orientated equipment producers, although on a regional level there are other companies that offer highly competitive products that have often been designed specifically with local conditions in mind.

Hydraulics Make an Impact
If the 1980s and 1990s were marked by big advances in hydraulic drilling, with oil replacing compressed air to transmit the driving force, water power seems to be making inroads as an up-and-coming technology, at least for some applications. One of the first water-power installations, at the Northam platinum mine in South Africa, was commissioned in the late 1980s, based on the principle that the water head generated by deep shafts could be put to good use in production drilling.

By the late 1990s Sulzer, one of the leaders in the development of water-powered drilling, had more than 1,300 units in use within South African mining, with a simpler, lightweight machine then entering production. The success of the concept drew other manufacturers to the market, including South Africa’s Novatek, which now claims to be the country’s principal supplier.

In a paper presented to the SAIMM’s 2008 conference on narrow vein and reef mining, Novatek’s Managing Director Julian Wills stated a strongly positive case for wider consideration of water power as a viable competitor to both pneumatic and electric drilling systems. Using the power output in relation to a drill’s mass as a benchmark, he demonstrated water-powered drills can produce significantly higher ratios than either direct electric or compressed-air powered drills; to be fair, he did not include hydraulic oil-based systems in his comparison, since these drills are more often used on carriers in larger-scale operations than were being discussed at that particular meeting.

Claims for the benefits of water power for drills, made by Novatek, include greater drilling speed over pneumatic machines, more efficient use of energy, better visibility for the operator and lower noise levels. Specifically, the company claims that capital costs for a hydropowered system can be up to 60% less than that of an equivalent pneumatic system, while operating costs can be up to 40% less.

Water-power developments have by no means been confined to South Africa. Perhaps the best-known international supplier, the Swedish company Wassara, has transferred the concept to much heavier drilling machines than those used in earlier applications. Examples the company cites of the use of its machines include installations in Chile, Austria and Canada.

In Chile, Codelco uses a modified Tamrock Solo rig equipped with a Wassara hammer and bit for drilling 115-m-long, 149-mm-diameter upward holes for orebody preconditioning, presumably at El Teniente. The application at WBH’s Mittersill scheelite mine in Austria involves both up- and down-production drilling, while in Canada, Barrick’s Williams gold mine in the Hemlo camp in Ontario uses a Wassara hammer and bit to drill 30-m-long downward blast holes, using a Cubex Aries rig.

Wassara claims its system’s advantages center on its ability to drill long, straight holes which, it says, translates into a higher ore yield per meter drilled. It also states its technology gives a markedly improved work environment, with less drill dust and no oil mist.

In August, Wassara introduced an updated version of its W80 hammer, the W80 N2, which has a heavier piston, increased striking velocity and slightly reduced frequency than its predecessor. This, the company says, increases the hammer’s output power significantly and can give improved drilling performance in very hard formations.

A recent entrant into the water-powered drilling market, British-based Peterstow Aquapower, has taken a somewhat different approach to the technology. One of the constraints imposed by systems up to now, according to Peterstow, is the amount of water needed to power drills; the company quotes a figure of around 5 mt of water for every tonne of ore drilled off.

The company has developed a closed-loop water hydraulic system that operates as a self-contained unit, with the pressurized water that powers the rock drill being re- tained within the system. Results from trials undertaken in underground mines have indicated water consumption 60% lower than that achieved by conventional water-power installations, at around 2 mt per tonne of ore. In this case, the water is pressurized using a mobile electric pump unit, a concept that has been used by others but not, apparently, in a closed-loop configuration.

The stimulus for this development, and of others that focus on water power, is as a means of getting away from the infrastructural straitjacket imposed by compressed air. Even with good maintenance, compressed air pipeline systems are notoriously leaky, meaning expensive energy input on surface is often just blown away without any value created. Water-power systems, while needing very clean water to work effectively, seem to offer one way of cutting energy bills while improving working conditions.

Rigs that Do the Job
It is no secret two main manufacturers dominate the world market for production-drilling rigs: Atlas Copco and Sandvik. Both companies have a comprehensive range of machines that cover different drilling requirements, and can handle the complete spectrum of production layouts and processes. The following paragraphs provide just a sample overview of each of the companies’ ranges.

Atlas Copco markets its production drilling rigs under the Simba banner. With 11 models in its top-hammer series and a further five designed for in-the-hole (ITH) drilling, the company can provide hole diameter coverage from 51 to 178 mm (2–7 in).

Last year, the company introduced the Simba S7 D as a replacement for its 1257 model, aimed at production drilling in small- and medium-sized drifts. The machine has been designed for applications such as long-hole and production drilling, and drilling for cable-bolt holes. Rod-handling is fully mechanized, with a carousel capable of holding up to 10 rods that give a 20-m hole-depth capability.

Among recent applications reported by Atlas Copco, Norilsk Nickel is using Simba L6C and M7C rigs to handle its production-drilling needs at its Severny-Gluboky operation on Russia’s Kola Peninsula. The mine operates both long-hole and sub-level caving stopes, with hole lengths of up to 30 m in some cases.

Sandvik’s production-drill range runs to eight standard-height models, plus one low-profile unit for tight-headroom applications. Hole diameters from 51 to 127 mm are matched by hole-length capabilities of up to 54 m using hydraulic drills, or 60 m in the case of the Wassara hammer-equipped DL520-W.

Sandvik claims this machine represents state-of-the-art technology in underground mining. Used for DTH production drilling, its features include uphole fan automation, automatic hammer and drill-bit change-out, remote-controlled drilling and boom movement, and a sophisticated on-board system for programming, monitoring and diagnostics. Using the Wassara system helps reduce capital and operating costs, the company claims, as well as improving the quality of drilling.

U.S.-based and ASX-listed Boart Longyear notes narrow-vein and other underground mining applications always present unique limitations and restrictions when it comes to mechanized drilling, which is why it designed its StopeMaster and StopeMate drills for good access, mobility, flexibility and productivity. The StopeMate is a lightweight, pneumatic production drill that can handle drilling depths of 12–15 m yet can be be broken down into six manageable pieces to gain access to captive areas, the company says. It has hydraulically driven wheels that provide skid-steer maneuverability in tight spots.

The larger StopeMaster is geared toward bulk-mining applications, delivering a drill depth of 20–35 m in 64- to 106-mm holes. Equipped with an HD 155 hydraulic rock drill, it features 360° rotation, up to 1.5 m side-shift and can work in drift heights as low as 2.4 m. This versatility allows precision drilling in both parallel and straight applications, the company says, while giving accurate operator control in drop-raise, cable-bolting, and fan-, ring- and parallel-drilling applications. The StopeMaster can also be configured with a self-propelled diesel option, with four-wheel independent drive that can be disengaged for towing.

Canadian company Cubex offers a six-model range of production drills within its Constellation series, of which the Aquarius and Aquarius-B are equipped for Wassara water-power technology. How- ever, its most recent innovation has been its Scorpion rig, designed specifically for freeze-hole drilling at Cameco’s high-grade McArthur River uranium mine in northern Saskatchewan.

Freeze-hole drilling is an essential part of the production process at McArthur River, with the Cubex rigs that had been used in the past capable of drilling down-holes, but not the up-holes needed as well. Cameco’s need for a more flexible machine led Cubex to design the Scorpion, which can drill both up- and down-holes, and uses Wassara hammers. According to Cubex, the reports that this system has proved to be five times more efficient than the diamond drilling method used before for the up-holes, machine set-up is much quicker, and more holes can be drilled per set-up without having to move the rig repeatedly.

Cubex also recently reported on the successful implementation of its PT-50 pipe-handling system for ITH production drill rigs, designed specifically for Agnico-Eagle’s Goldex operation in Québec. The challenge came with the need to handle up to 38 m (125 ft) of 5-in.-diameter pipe, which was obviously far more than a standard carousel could hold, without the need for manual handling.

Since 2007, the mine has been drilling up to 200,000 m per year of 6½-in. holes up to 130 m long, Cubex reports, with all of the drill rods being handled by its PT-50 system. Only one operator is needed for both the drill and the handler, with a resultant improvement in personal safety and working conditions.

At the Sharp End
Production drilling is not just about the rigs, of course, with hammers and bits equally critical components within the whole package. At the bauma 2010 trade show in Germany, U.S.-based Rockmore International introduced a new top-of-the-range hammer to its existing ROK series: the ROK 875. Designed for mining, blast-hole, construction and quarry applications, the hammer features a new design that reduces the number of hammer components, Rockmore says, thereby reducing the number of component wear points, cutting costs and simplifying service. The ROK 875 is a 203-mm (8-in.)-diameter hammer that accepts 215–254 mm (8-1/2–10 in.) industry-standard drill bits.

Sandvik introduced its most recent bit developments at MinExpo in late 2008. Its RT300/GT60 bits feature a new super-grade of cemented-carbide and a new universal face design, making the buttons stronger and more wear resistant, the company claims. The new bits are matched to top-hammer rigs capable of drilling 92–152 mm (3-5/8–6 in.)-diameter holes up to 33 m (110 ft) long. Both spherical and ballistic carbide button profiles are available, with Sandvik reporting significantly better productivity and bit life compared to previous designs.

Atlas Copco introduced the latest member of its Secoroc COP Gold hammer family a year ago with the launch of the COP 44 Gold. This is designed for blast-holes from 110 to 130 mm (4-3/8–5-1/8 in.) diameter. The company claims its Gold range hammers are maintenance-free and have a 10%–15% longer service life than competitive models, as well as being able to be rebuilt up to three times to restore their original performance.

High productivity and hole accuracy are just two of the criteria on which today’s production drills and consumables are judged by the industry. Greater levels of automation, with or without remote operation, have proved to be a major advantage in some applications, although it has to be remembered that not every underground mine has an ore resource that can benefit from cutting-edge technology.

Energy usage is coming increasingly into the spotlight across the whole mining spectrum, and production drilling is no exception. The advances made in water-power are just one example of how suppliers and mining companies alike have been working together to develop more energy-efficient drilling systems. Drill holes may be ephemeral, but remain critical to the whole ore-production process.