While the world’s major mines focus on bulk extraction, narrow-vein deposits demand a different approach—and different equipment. E&MJ looks at some of the possibilities.
By Simon Walker, European Editor
Go back a hundred years—150 certainly—and most of the world’s mineral production came from narrow-vein deposits. Processing technology had not yet matured sufficiently to be able to handle bulk materials, flotation had still to be adopted for sulphide treatment and the introduction of the industrial-scale cyanidation processes that are today taken for granted as the prime precious-metals recovery route was still in the future. Mines had traditionally operated in a narrow-vein environment, even if veins ran en echelon, simply because the technology of the day would not allow anything more extensive. And, of course, waste-rock handling was minimized as mining was highly selective, keeping profitless dilution at rock-bottom.
The discovery of massive sulphide deposits, and gold plays such as the AJ near Juneau in Alaska—where block caving was invented—changed all that, with new stoping methods being developed to extract them. Throughout the 20th century the focus tightened increasingly on higher-tonnage, lower-grade deposits as economies of scale in mining and processing broadened the viability range for orebodies. Add to that the realization that the epithermal vein systems that had been worked in the past were merely a near-surface expression of larger bulk resources below, and it is easy to see why the emphasis shifted away from narrow-vein opportunities.
Nonetheless, smaller mines worldwide continued to run on a more selective basis, with the major manufacturers keeping them supplied with equipment that was suitable for their constricted mine infrastructure. Looking back to the late 1980s, Tamrock, Secoma, Atlas Copco and several other suppliers all had drill rigs that were designed specifically for small-scale development; Tamrock’s MiniMatic and Secoma’s Quasar were two examples of single-boom jumbos targeted at the small-mine market.
In addition, the introduction of rubber-tired jumbos to replace hand-held development drifters forced a re-think in terms of mucking technology. Tires and rails do not really mix in development headings, so small-capacity LHDs supplanted rail-mounted Eimco loaders and wagons.
The shift from pneumatic to hydraulic drilling also brought changes to the narrow-vein mining market, in that compressed-air ranges became less important within the mine infrastructure. Conversely, having more diesel-powered equipment in the close confines of a vein-mining system brought new ventilation challenges, while few narrow-vein mines today rely solely on shaft access; diesel vehicles need ramp access, as well as underground service facilities.
The high gold price in recent years has led to a resurgence in interest in small, limited-resource deposits that can be mined profitably using narrow-vein techniques. Lake Shore Gold’s Bell Creek mine, near Timmins, Ontario (Reviewed in the February edition of E&MJ, pp.28–34), is one such, with a tightly constrained ore zone that demands both small development equipment and close sub-level spacing for longhole stope drilling. A 2-yd3 LHD takes broken rock from the development ends and stopes to the transfer point on the main ramp, from where it is handled by larger loaders and mine trucks. And, even though the orebody appears to widen as it gets deeper, it is unlikely to warrant the use of much larger-scale equipment—apart from ramp haulage—for the foreseeable future.
Production Rigs for Tight Spaces
According to the company’s global product manager, John Nielson, Boart Longyear’s StopeMaster and StopeMate rigs are ideal for the tight and narrow spaces typically seen in underground mining operations. As a result, the company is seeing the demand for these rigs increase as operations move underground. Each is specifically designed for underground applications, Nielson added, allowing for better access, mobility, flexibility and productivity in tight spaces.
Boart Longyear notes that safety is one of its key concerns, with the StopeMaster and StopeMate rigs having been developed with heavy-duty hydraulic hoses to protect the driller from hose rupture, and guarding for protection from moving parts. Removing the operator from the immediate drilling area, the rigs can be controlled remotely from up to 25 m away. They also come equipped with emergency stop circuits to cut the power to the drill in the event of an incident.
Both the StopeMaster and the StopeMate are equipped with a pneumatic top-hammer production drill that features 360° rotation for greater flexibility, together with a rotating/pivoting traverse. This configuration ensures precision drilling in both parallel and straight applications, and accurate operator control in drop-raise, cable-bolting, fan-drilling, ring-drilling and parallel-drilling applications, the company says.
Both rigs are skid-steer, mounted on four solid-tired wheels, with a four-wheel independent drive and braking system. With 30% gradeability, they can be used in quite steep applications. In use, both can also be operated in a minimum back height of 2.44 m (96 in.), while the StopeMate is small enough to fit through a 1.27 x 1.9-m (50 x 75-in.) opening.
Designed for bulk mining, the StopeMaster is capable of drilling 64- to 106-mm holes measuring up to 35 m deep while the smaller, more compact StopeMate can fit into a lift cage and drill 51- to 76-mm diameter holes at depths of 12–15 m. Both drills are offered in standard and HX versions. The StopeMate HX features an added hydraulic positioner, and the StopeMaster HX features the same positioner as well as a self-propelled diesel option. The self-propelled version can disengage gears in order to facilitate towing where required.
Compact Machines for Narrow and Low Stopes
In January, Sandvik Mining announced an order for 83 machines for Royal Bafokeng Platinum’s new Styldrift mine in South Africa. Scheduled for delivery during 2014, the equipment consists mainly of low-profile DD210-L drill rigs, LH208 LHDs, and the mechanized low-profile roofbolter, the DS210L-M. The company notes that the development contractor is also using DD210L drill rigs for this stage of the project.
The DD210L is a single-boom jumbo designed to work in stopes as low as 1.6 m. Despite having a carrier height of just 1.3 m, it is easy to operate and maintain as well as having a large boom coverage, Sandvik says. An HLX5 hydraulic drill handles hole sizes from 43 to 64 mm (111⁄16–2½ in.)
Meanwhile, the Sandvik DD210-V is a compact narrow-vein single-boom electro-hydraulic drill rig designed for drilling in sections as narrow as 3.2 m (10 ft. 6 in.). It can be used for development, bolting and/or production drilling. Just 1.2 m wide and 1.85 m high with the canopy down for transport, it has a multi-purpose boom that give up to 27 m2 of face coverage. A double rotation device allows the operator to position the drill feed vertically on both sides and close to the side walls.
For production drilling in small drifts, Sandvik offers its DL210 rig. Compact and flexible, this is suitable for various drilling applications, the company notes, being capable of drilling 51- to 64-mm (2- to 2½-in.) holes up to 20 m long. Its sister machine, the DL230, extends this range to 23 m (75 ft), being equipped with a boom that can drill parallel up- or down-holes and has a cable remote-control system for greater operator safety.
When it comes to loading out from narrow spaces, Sandvik’s smallest diesel-engined LHD is the 0.7-yd3-capacity (1-mt-payload) LH201. Powered by 33 kW (45 hp) Deutz engine, the machine has hydrostatic four-wheel drive. Its 3.65 mt operating weight means it is simpler to take underground than larger machines, while its length (4.6 m) and width (1.1 m) allow access to very narrow stopes and drifts.
Also suitable for narrow-vein applications, the slightly larger LH203 has the best payload-to-own weight ratio in its class, Sandvik claims. With bucket options of between 2 and 2.3 yd3, and up to 3.5 mt payload, the machine’s unique bucket-filling system means that it has an excellent bucket fill factor, Sandvik adds, while its low weight helps increase tire life and cut fuel consumption.
Transferring Demolition Technology
The Swedish manufacturer of compact demolition equipment, Brokk, recently introduced its new model 100 as the successor to one of its most widely used machines. Although designed for use in construction demolition where access space is restricted, the machine can also be adapted for use in narrow-vein mining underground, the company said.
Weighing just 990 kg (2,200 lb) and capable of fitting through a 780-mm (31-in.)-wide opening, the Brokk 100 has a boom that can be equipped with a range of accessories. While its standard tool in demolition mode is a hydraulic breaker, such as Atlas Copco’s 55-kg SB152, it can also carry a rock drill or a bucket for mucking out headings. The maximum weight attachment is 150 kg (330 lb), according to Brokk—light in terms of other drilling or mucking systems, but still effective in situations where narrow headings are needed to minimize dilution. There is also the potential for using a breaker, not only for scaling, but also for selective mining, especially where high-grade ore is held in very narrow zones.
Brokk notes that although the 100 has good reach and power, it folds into a surprisingly compact package, and can be transported in a small truck or trailer. It is also small enough to fit into most mine cages, with only a power supply needed for it to be put to work. Brokk’s range now encompasses eight models, all of which are crawler-mounted, have a three-section articulated boom and are remote controlled for operator safety.
The German company, Hermann Paus Maschinenfabrik, reports that it can provide individual solutions developed specifically for the demands of mining, with its PFL series of LHDs having been used successfully in operations worldwide for many years. The range includes small LHDs for narrow-vein operations, which are also designed for use at high altitudes.
The smaller and narrower the gallery, the smaller a machine needs to be in order to stay maneuverable, Paus said, although there still has to be enough room for components and, of course, the operator. The company added that it takes a lot of experience to address these challenges without making too many compromises. Since there are standards to follow (which may be different for different markets), such as safety and a minimum space for the operator, or exhaust gases that require after-treatment and produce additional heat, this becomes even more complicated.
However, with its PFL 8, Paus copes with all of these issues. With a 1.5-mt payload using a 0.8-m3 bucket, the PFL 8 is one of the smallest underground loaders worldwide, although it is built strong enough to withstand tough conditions with poor roadway conditions. Paus points out that even though it is small in size, its 40-kW Deutz diesel engine gives enough power to perform properly, with a maximum tramming speed of 11 km/h.
Paus is going to launch an electric-powered LHD for narrow-vein mining at the bauma 2013 trade fair in April—the PFL 12e. The company’s general manager, Franz-Josef Paus, pointed out to E&MJ that electric LHDs will become increasingly common in narrow-vein operations, since they offer a number of advantages over diesel engines. Ventilation requirements is one factor, with electric LHDs being a real alternative where the tramming distance is less than 200 m. In addition, he said, maintenance costs are up to 20% lower than for diesel-powered LHDs, with electric LHDs being more cost-efficient in life-cycle terms than their diesel counterparts.
The 40-kW, hydrostatic-drive PFL 12e is equipped with a 120-m-capacity cable drum. With a 1.2-m3 bucket capacity, its payload is 2 mt, while it has a maximum tram speed of 12 km/h.
Paus states that both of these machines are maneuverable and compact, but with good operator comfort. All the controls are arranged clearly and are within close reach of the operator’s seat. Control is via two joysticks: one for the driving direction and gear shifting, and the other for the boom hydraulics. Both air- and water-cooled Tier 3-complaint engines are available, as are different bucket types, including a side-dump bucket, with optional quick-coupling hydraulics that allow various attachments to be interchanged in minutes.
Canadian-designed Drills and LHDs
Within its product range, Ontario-based Mining Technologies International (MTI) supplies development and production jumbos, LHDs and mine trucks that are suitable for use in narrow-vein operations.
The company’s eight-model LHD range includes four diesel-engined machines that have capacities of less than 2.5 yd3 (1.9 m3), equivalent to payloads of between 700 kg and 3.6 mt. The LT-70 is the smallest, with a 0.5-yd3 bucket and a hydrostatic powertrain. MTI claims that the operator cab fitted to the LT-70 is the largest in this class of machine, while the long wheelbase gives better stability in rough underfoot conditions.
The company’s other small LHDs include the LT-210, LT-270 and LT-350, which carry 1–1.25-yd3, 1.5-yd3 and 2.5-yd3 buckets respectively, with payloads of 2 mt, 2.7 mt and 3.6 mt. All of these feature a mechanical powertrain.
In terms of longer-distance haulage, MTI also has an eight-model mine truck portfolio, of which the DT-704 and DT-1604 would be best equipped for working in constrained areas. The DT-704 has a 6.3-mt payload in a 3.3-m3 (4.3-yd3) body, while the larger DT-1604 carries 14.5 mt and has an 8-m3 (10.5-yd3) body. The company can also supply low-profile and ejector-type dump bodies for use in restricted-height applications. All of its mine trucks are four-wheel-drive, with an all-mechanical powertrain and load-sensing hydraulics.
Turning to drills, MTI’s Vein Runner II single-boom hydraulic rig is designed for drilling vertical, horizontal and angled holes in underground production headings. Equipped with a single hydraulic percussion drifter, it can be used to drill headings up to 5.5 x 5.1 m in size (18 ft by 16 ft 9 in.). Both Cummins and Deutz engines are available for moving the rig, which has a 107-m (250 ft)-capacity cable reel for the drilling power supply.
With an overall length of 10.7 m (35 ft 3 in.), the Vein Runner has an inside turning radius of 3.1 m (10 ft). Two boom options are available, giving different face-coverage possibilities, as well as three different feed lengths. The company uses Montabert hydraulic drifters on its machines.
E&MJ asked Atlas Copco’s product manager for face-drilling equipment, Peter Bray, for his views on some aspects of equipment that is suitable for narrow-vein applications. “Narrow-vein mining can be divided into two main areas,” vertical/close to vertical and horizontal/close to horizontal ore deposits,” he responded. “Both areas require equipment models that can physically operate in the drive sizes.
“To meet this need for small size equipment, Atlas Copco has a range of face drilling, long-hole drilling, bolting and loading and haulage equipment suitable for both types of orebody,” Bray said. “For the vertical type, some of the key machines are the Boomer T1 D face drill and Scooptram ST2 G loader, while for horizontal-type ore bodies, key machines include the Boomer M1 L, Scooptram ST7 LP loader and Minetruck MT2010 LP truck.”
The company launched the Boomer T1 D in 2010 as a replacement for the Boomer 104, which had been in production since the 1990s. Key features upgraded on the T1 D included a stronger frame with a lower center of gravity, a more powerful engine, an improved boom-suspension system to reduce stress on the machine, a more ergonomic operator’s cab and improved serviceability.
The single boom is designed to carry Atlas Copco’s COP 1638, COP 1838 or COP 2238 hydraulic rock drills, with a hydraulically controlled drilling system that incorporates the company’s Rotation Pressure Controlled Feed (RPCF) anti-jamming function. The on-board compressor supplies 11.7 liter/s (25 cfm) at 7 bar (100 psi).
The Boomer M1 L, meanwhile, also carries either the COP 1638 or COP 1838 drills, but can operate in a minimum tramming height of 2.2 m (7 ft 3 in.). The machine uses the same compressor as the Boomer T1 D, with both rigs using hydrostatic steering and transmission systems.
Asked how the technologies used have developed—given that narrow-vein operations are often run by companies with less-extensive capital budgets—Bray noted that recent developments have focused on increasing productivity through the mechanization of equipment functions, and on improving the ruggedness of machines to meet the often challenging conditions encountered in narrow-vein mines. “What is important to remember, is that the capital cost of equipment is only one aspect of the total cost of ownership for a machine. Mines often forget to look beyond the purchase price, and may overlook equipment alternatives that could greatly benefit their operation,” he said.
Looking ahead, Bray suggested that technologies transferred from tunneling, such as electronic drill plans coupled with semi/full automation, have great potential to improve efficiencies and reduce wastage in narrow-vein mining. These systems can help reduce overbreak, the drill meters needed and the amount of explosives required, give improved fragmentation that simplifies loading and haulage, and generally cut drilling and mucking costs, he said.
Where loading and hauling is concerned, there is great potential to make use of intelligent vehicle-operating systems that can cut fuel and tire consumption and increase productivity, with automation, object detection and steering assistance being just some of the areas that could benefit narrow vein and other mining operations, he added.