Edge Drilling director, John Argiropoulos, recently took delivery of a Boart Longyear LS250 MiniSonic rig that is suited to a variety of soft ground, shallow drilling projects including environmental, tunneling, water management, grade control, leach pads, and tailings dams.

The rig delivers faster penetration for nearly undisturbed samples using little or no fluids, said John, and its casing system makes it ideal for a variety of applications including mining, environmental, and infrastructure projects.

The rig provides extremely accurate sampling for unconsolidated formations which makes it suited to mining, but it also eliminates the risk of cross contamination making it ideal for environmental and geotechnical work. It can also precisely drill straight holes at varying angles which ticks the box for infrastructure projects.

“We've already got five months of work lined up with the rig," John told Australasian Drilling.

The idea of acquiring a sonic rig first came to John during a visit to Christchurch in New Zealand where he saw the rigs undertaking post-earthquake recovery sampling work.

“I've been looking at getting into this type of drilling from the first time I saw it,” he said.

“After the earthquake in Christchurch, I saw massive advantages with sonic rigs in drilling overburden and getting near on 100 percent recovery sampling. The rigs were drilling every house in carports or garages and were looking for signs of liquefaction.”

Liquefaction is where the strength and stiffness of soil is reduced by earthquake shaking. If liquefaction was found following testing in Christchurch, the dwelling would be demolished.

“They had conventional rigs at the start including standard diamond drilling, but they weren't getting any core recovery, being glacial fill," John said. "However, the sonic rigs collected everything from pebbles and cobbles, to rock, clay, silt and sand. They were very impressive.”

With work increasing, John eventually took the plunge and invested in a sonic rig.

“We're getting much busier,” he said. “In the space of 12 months, we've gone from two rigs at the start of last year to seven rigs now. We've expanded quite a lot.”

John said work began to resurge since 2016. A big push by Main Roads WA (Western Australia) for testing bridges across the state is creating work from the rollout of the government's METRONET program and is expected to generate more construction activity and geotechnical work in the near future. The METRONET program is one of the largest single investments in public transport that Perth has seen and will involve about 72 km of new passenger rail and up to 18 new stations.

With enhanced capabilities thanks to the new rigs, John is upbeat in his outlook for the business. However, like most contractors, he is feeling the pain of skill shortages. John said he is managing the issue through in-house training.

"I'm a firm believer of training in-house as the best way forward because we can train personnel according to our standards, expectations, policies, and procedures.”

Originally published in Australasian Drilling Magazine, February/March 2020

Greenstone and sedimentary formations like mudstone and conglomerate, while variable, are typically low in Moh’s hardness. Moving into the actual ore zone, the formation consists of various types of rock such as feldspar, muscovite schist, and fragmental biotite, introducing abrasiveness related to the rock’s quartz content.

The challenge in softer abrasive formations is to pick a diamond drilling bit tough enough to get good life without sacrificing penetration rate.

Adding in the drive for productivity creates an additional challenge. The driller cannot simply pick the toughest bit available; life needs to be increased while still maximizing penetration rate or tripping out rods to change bits impacts overall productivity.

Using patented technology, the new Longyear Bits have diamonds that are chemically bonded to the matrix creating a more versatile, faster penetrating, and a longer-lived bit. All drillers from the newly promoted to the seasoned veteran find the color-coded Longyear Diamond Bits considerably more effective in obtaining higher productivity. For each hardness rating on Mohs hardness scale, Boart Longyear has created a recommended color. The complete line of Longyear Diamond Bits includes a Red, Orange, Yellow, Green, Blue, and Purple Bit.

Originally, Alpha series 08 and 09 were chosen in Stage3 to get a good combination of life and penetration rate. These bits, while achieving acceptable penetration rates, fell significantly short on life at 43m, the average over three months. In looking at the Longyear Bit series cross reference chart, Alpha series 08 and 09 would be replaced by the Longyear Green bit. Given the low hardness of the formation, the Longyear Blue bit was also selected to determine the best solution. In stark contrast, to the Alpha series bits, the penetration rate and bit life both increased. Using a combination of the Longyear Blue and Green bits, driller’s averaged 109 meters per bit and increased penetration rate. When drilling softer formations at site, the drillers used the Blue bit and found this bit to be incomparable when looking at the production rates and bit life. The two formulas combined yielded a 60% improvement in life and an 8% increase in productivity.

Boart Longyear Canada East Coring Supervisor, Jeremy Dykstra said, “In the beginning, we struggled to meet our production targets due to slower penetration rates and poor bit life. Once we started to trial the new Longyear Diamond Bits, the performance improvement was noticed immediately with all crews at site. Smoother cutting of the formations and longer bit life helped push us towards the successful and safe production shifts we aimed to have both for our client and our business.”

Established in 1890, Boart Longyear is the world’s leading provider of drilling services, drilling equipment and performance tooling for mining and drilling companies.

The Global Drilling Services division operates for a diverse mining customer base spanning a wide range of commodities, including copper, gold, nickel, zinc, uranium, and other metals and minerals. The Global Products division designs, manufactures and sells drilling equipment, performance tooling, down-hole instrumentation and parts and services.

Ready to take the Longyear Bit challenge? Contact your Boart Longyear representative today to order trial bits and download this blank bit log sheet to keep track of bit performance so you can compare the productivity and speed of both your current diamond bits and Longyear Bits.

Using patented technology, the new Longyear bits have diamonds that are chemically bonded to the matrix creating a more versatile, faster penetrating, and a longer-lived bit. The new Longyear bits retain the smooth drilling characteristics drillers prefer, resulting in more core in the box on every shift for every crew. Available in 16mm more open, express geometry for even higher cutting speeds as well as 16mm Stage and 25mm Stage 3 configurations.

“Just some feedback… the other night I witnessed a bit cutting 24 inches a min … by far the fastest cutting bit Boart Longyear has made…” Boart Longyear Site Supervisor, Western Territory.

On the surface, the Laverton district is a flat, hot, dry environment with scattered acacia trees only interrupted by dry, salt lake beds, and gypsum sand dunes. The high concentration of salt results in a very saline aquifer. While the high salinity is hard on equipment it does not factor heavily into bit selection and drilling performance.

Underground, the formation is a mesothermal, meaning deep extending, gold deposit typical in Western Australia, composed of greenstone, a rock type common to gold deposits globally, basalts, magnetite shales and banded iron formations (BIF). 

Within this host rock, the gold is typically contained within intrusive dykes of quartz porphyry near the shear and fracture networks which supported gold-bearing hydrothermal flow. The greenstone, shale and even basalts are only of medium hardness and have the potential to be cut quite quickly, while the sections of BIF, quartz and fracture zones force slower penetration rates. The ideal bit would be versatile; free-cutting enough to easily handle the occasional BIF and quartz but tough enough to penetrate the greenstones quickly.

The underground portion of the mine is decline accessed and extends 900m below the original open pit. Due to its “nuggety” deposit, diamond drilling tends to underestimate grade, so the mine has adopted new techniques of grade control. RC drilling has been introduced underground to produce larger sample volumes, which match well with the bulk mining techniques being used. Considering that RC drilling is typically half the cost-per-meter and three times faster, and the industry-wide initiatives to drive down all in sustaining costs, a lot of scrutiny is paid to the productivity of remaining diamond drilling.

After optimizing drilling parameters, the incumbent product’s (Hayden 9AA and KS5) average performance, maxed out at 180 meters/bit life and 22 centimeters/min of penetration rate over the three months of monitoring. While solid performance, a new solution was needed to continue improving productivity.

The first step was to introduce the new Longyear Green Bit in a Stage 3 25mm configuration. The Longyear Green formula (Prototype P520) was selected to drill like the competitor’s 9AA formula with Stage configuration to maximize life. Comparing performance in the three-month period after adoption, penetration rate increased to 26 centimeters/minute and bit life nearly doubled, increasing to 356 meters/bit. The ease of use and consistency across shifts was appreciated by the crews and helped produce the measurable gain. These improvements combined to noticeably increase core in the box by 6%. The Boart Longyear drill crews correctly observed that such long life was not driving a significant increase in productivity as reduced tripping time has less impact than improved penetration, so the decision was made to trial even more free-cutting formulas.

The next bit trialed was the Longyear Yellow (Prototype P575) again in the Stage 3 25mm configuration to line up against the competitor’s KS5 and even 12-14. The penetration rate jumped to an average of 35 centimeters per minute and life held at an impressive 300 meters per bit. Since the bits were still achieving much better life, Boart Longyear Drilling Services moved one more step up to the Longyear Red bit (Prototype P566). Since the goal was to maximize penetration rate, the Longyear Red bits were produced in the 16mm express configuration with a more open area for enhanced penetration.

The Longyear Red bits achieved an astonishing 60 centimeters per meter penetration rate and still lasted 120 meters. With the goal of maximizing productivity, the drill crews decided to use one Longyear Red at the top of the hole and finish it with a Longyear Yellow in 25mm Stage 3. The results speak for themselves. After 3 months of measurement, this two-bit strategy averaged 283 meters/bit, still a 60% improvement over the competition and 34 centimeters per minute, a full doubling of penetration rate. The combined result put 23% more core in the box.

Express Geometry

With the competitiveness of today’s market, everyone is looking to cut faster, especially underground. To support higher penetration rates, we have combined the new Longyear formulas with a new, more open express geometry. Tapered intermediate waterways improving flushing and prevent accumulation of debris. Designed for fast cutting in competent ground, the new express geometry is available in our 16mm crown heights to maintain bit life at higher cutting speeds.

After the promising initial results, trials were started using the new Longyear bits on all Boart Longyear Drilling Services sites in Australia and select sites globally. Now, all sites in Australia have converted to great effect on productivity. Over the next six months, the new Longyear bits in the Longyear line will be launched, moving from prototype to full production. Longyear bits are now stocked in Australia and available to order.

Near the coastlines of Northeastern Newfoundland sits the Ming Mine, operated by Rambler Metals and Mining. Rambler was in need of an important ventilation raise to install 400,000 cfm ventilation exhaust fans for their ventilation system up to the surface. 

Rambler first started out on the project utilizing two different surface drills but were unsuccessful. Then they contemplated using an Alimak raise climber or mining a conventional raise using stoper drills.

However, both of these alternatives were unattractive due to their time and costs.

Rambler then discussed the situation with Brian Winsor, Boart Longyear long hole driller, who proposed using a Boart Longyear Stopemaster to complete the complicated drop raise.

Brian drilled his first hole but did not break through. Undeterred, Brian approximated the location of that hole using the deviation distance and offset his second drill hole which ultimately did break through. Brian drilled the remaining holes using a pattern based on the initial breakthrough hole. The drilling went smoothly and as per the plan Brian created, based on the initial breakthrough hole.

Brian blasted the raise, squaring up the face and bringing up the cut to breakthrough to the surface. He blasted the remaining drill holes to the full design of the ventilation raise.

No damage was sustained to any of the high-voltage power lines and surface installations which were in close proximity to the surface collar location and the blasting was completed without delays to the underground mining.

Brian was able to complete this project to Rambler’s satisfaction using drilling intuition, critical thought, and hard work. He was able to, as Dan Kirkey, Division Manager, Drilling Services and Production Drilling Services, commented “Drill the raise by “feel” rather than by engineered drawings making this especially impactful showing his skill as a driller.” Brian has recieved a Bravo! award and client recognition for his success. Congratulations!

Learn more about Boart Longyear's Production Drilling Services

Drill Crews Experience a 300% Increase in bit life

At a nickel mine in Manitoba, Canada, Boart Longyear Drilling Services field tested the new Stage 3 25mm diamond coring bit in a multi-site deployment. Drill crews experienced bit life gains of up to 300% over their previous standard 12mm crown.

Boart Longyear Drilling Services has employed 12mm bits for more than three years at a nickel mine in Manitoba, Canada. The ground conditions are demanding due to the variability in the formation, not only from one part of the mine to the other, but even within a single hole. Formations in Manitoba are typically hard abrasive quartz mixed with medium hard and coarse ground.

Until recently, the 12mm 08ABR formula had proven to be the best bit in use at the mine with an average bit life of 37.5 meters.

Extending Bit Life in Hard, Abrasive Ground Conditions

With the proven performance of the 12mm crown, the drilling crews were unsure about trying the new 25mm Stage 3. Boart Longyear field engineers knew that upgrading to the Stage 3 would provide a significant performance increase. Engineers delivered the bits to the drill crews in the 08ABR formula.

Bit Life is More Than Three Times as Effective

After putting the bits to the test, the drill crews were stunned by the 25mm Stage 3 results. The average bit life of the Stage 3 was 120 meters—more than three times the life of the 12mm crown.

As more Stage 3 bits are deployed in the field, the results continues to prove what drillers and mine operators are saying: “Boart Longyear has delivered another industry first.”

Heap leach pads are large piles of rock waste from a mine operation that receive further processing through a leaching solution to remove the mineral ore from the rock. The leaching solution is applied via an irrigation or sprinkler system to the top of the heap leach pad. The solution penetrates the heap leach pad and separates the mineral ore from the rocks. At the bottom of the heap leach pad is an impermeable liner that is angled to allow the solution to be collected in a reservoir and then be sent for further processing.

Using one of their sonic rigs, the LS600, Boart Longyear can collect highly representative samples and achieve excellent sample recovery. Leach pads are made up mostly of unconsolidated material and the LS600 has proven effective in these conditions by producing 100 percent accurate in-situ core samples. The rig is also used to install wells in the heap leach pad.

Boart Longyear was contracted to sample and install solution wells for the largest gold heap leach pad in the USA, located in Northwest Nevada. The heap leach pad is over 400 feet tall. To achieve that height the mine operation built up the heap leach pad via 50 foot lifts.

When constructing each level, the haulers unavoidably crush and compress the previous top layer of the pad while adding material to the top of the pile. This creates a dense layer that causes a dam effect and does not allow the leaching solution to penetrate through the heap leach pad properly. The heap leach pad can then develop dry pockets where no leaching activity takes place — lowering the efficiency and return on investment.

Boart Longyear was hired to detect dry zones in the leach pad and to reactivate the zones via solution enhancement wells. First the Boart Longyear team drilled test holes to determine the depths of the dry zones and the specific lithological (physical characteristics of the ground) information.

These boreholes were 107 meters (350 ft) deep and were 15 to 23 meters (50 to 75 ft) above the heap leach pad liner. A continuous core sample was obtained by using the LS600 sonic rig. This allowed the Boart Longyear team to determine moisture concentration at accurate depths and to identify exposed ore.

Once depths of ore and moisture levels of the dry zones were indicated, Boart Longyear installed solution enhancement wells using an 11.5-centimeter (4.5 in) flush threaded well casing. The casings allowed the borehole to stay intact as an upper and lower k-packer were installed at specific depths. A 100-foot injection screen was placed between the k-packers to direct the leaching solution into targeted dry zones.

This process was repeated on an eight-week cycle with four weeks of solution and four weeks of rest. Once the cycle was completed, the k-packers and screen were moved to a new depth. The well would receive the solution at three heights, spanning 100 feet each time — bottom, middle, and top.

Over a three-year period, the team, using the LS600 sonic rig, drilled 55 gravity flow solution wells to alleviate the fine unprocessed gold from the heap leach pad. This resulted in 6,100 ounces of gold that equated to $8 million ($1,300 per ounce average). The project paid for itself within the first 70 days and the client received a 400 percent internal rate of return (IRR).

Northern Star Resources Limited awarded Boart Longyear Drilling Services the directional drilling job to develop a paste fill hole at Paulsens gold mine, located in northern Western Australia.

The paste fill hole acts as a delivery system and allows for a paste-like mixture of cement and mine tailings to backfill the underground zones where mining and excavations occurred. This provides additional ground support and pillar recovery, which optimizes further mining of adjacent stopes.

The paste fill hole needed to be drilled to a 310-millimeter (12.25 in) diameter to allow it to be internally lined down its entire length with a 203.2-millimeter (8 in) diameter casing. Because of the unusual requirement for a larger hole, a regular mineral exploration drill rig could not be used.

The traditional method of drilling this type of hole would be to first drill a pilot hole with diamond drills, then enlarge the hole using rotary drilling methods on a second — and potentially even a third — pass. This method could take as many as 45 to 50 shifts to complete the drill.

An additional challenge for the driller was making sure the hole would intersect within the 5-meter (16.4 ft) diameter target in the underground development zone. This created the need for concise and accurate surveying over the duration of the directional drilling. Meaning Boart Longyear would have to work with a third-party specialist, Surtron Technologies, to deliver the paste fill hole on target.

Because of the large hole requirements, Boart Longyear elected to use a water-well-style drill rig with the ability to accommodate large-diameter casing and a deeper drilling capability via a powerful 130,000-pound pullback.

An additional booster compressor was also provided as the entire hole was drilled using conventional DTH hammers. The booster compressor was essential to keep the DTH hammer efficient and to lift and clear the cuttings from the hole.

The Boart Longyear crew set up the rig and was operational within one week after arriving on the jobsite. As drilling commenced, the hole was collared and cased with a 470-millimeter (18½ in) diameter drill bit for the top 6 meters (19.6 ft) before reducing to a 381-millimeter (15 in) diameter. This was progressed to a depth of 56 meters (183.7 ft) before the hole was once again cased. The bottom hole assembly was then reduced to the final diameter of 310 millimeters (12.25 in), and drilling recommenced.

As the hole progressed, multi-shot surveys were regularly undertaken by Surtron Technologies and Boart Longyear adjusted drilling parameters as needed to ensure the hole trajectory remained on target.

“It is great that Northern Star Resources Limited and Boart Longyear can come together on a well-planned and executed program to an outcome using a technique that is unique, but also safe and accurate,” says Bernie Sostak, general manager of business development and technical services at Northern Star Resources Limited. “Both teams are to be commended on a high quality technical success story.”

Actual drilling operations required a total of 39 12-hour shifts to reach the target depth of 656 meters (2,152 ft). Most importantly, the hole successfully intersected its required target at only 2 meters (6.56 ft) from center. The average drilling was 22.6 meters (74.14 ft) per shift, and the single best shift produced 90 meters (295.28 ft) between the depths of 428 and 518 meters (1,404.2 to 1,699.5 ft).

Regular rod pulls were conducted for drill bit inspection/replacement, as well as surveying of the hole. As ground formations became harder, Boart Longyear pulled the rods to switch out drill bits and DTH hammers to provide an optimized combination for the drilling conditions.

“This was one of the most successful surface paste fill delivery holes I have been associated with, and considering it was drilled in one pass, this saved not only time, but, as we all know, money,” added Sostak. “The hole was drilled 656 meters (2,152 ft) from surface and intersected within 2.1 meters (6.9 ft) of target, which was very impressive.”

With the use of a water-well-style rig, Boart Longyear was able to achieve a one-pass shot in 39 shifts, helping the owner to realize approximately $5 million in future gold value per mining level for this particular pillar extraction.

Mountain Regional Water Special Service District is a large government water supplier which serves nearly 5,000 customers in the western region of Summit County, near Park City, Utah. The District covers roughly a 25 square mile territory and has an elevation gain of over 3,000 feet. “Serving customers in this area can be a real trial, not only because of the energy challenges with servicing such a diverse geography, but also the difficulties finding groundwater at high elevations, and in a steep mountainous environment. All groundwater sources in this territory are based on deep bedrock aquifers, with many obstacles. And most of the District’s 15 or so wells produce 200 gallons per minute or less.” says Mountain Regional Water District’s Doug Evans.

In 2015, the District decided to expand its well production and targeted an aquifer that would be highly productive. The Bison Bluff well was proposed to be a 1,000 foot deep well, with a completed depth of 700 feet and fitted with a 16 inch diameter steel louvered casing.

The District outlined several criteria that needed to be met to make this a succcessful project. First, the drilling to be performed near Park City was situated within a residential neighborhood. This would require critical noise control, as well as lighting and difficult access considerations. Secondly, the project needed to be completed in the winter, before the Christmas holiday season, when water demands were at a minimum.  The timing was important because an existing production well near the project would be precluded from operation during the drilling. This all meant that the project would need to be drilled around the clock and would also be under the microscope of the local home owner’s association and Summit County officials.

Local County ordinances identified noise prohibitions as well as criterion for measuring noise levels when it is anticipated the requirements in the ordinance might be exceeded. The stated noise threshold required that the noise levels not exceed 65 dBA.

Before the project began, noise monitoring was conducted to measure and document the existing ambient conditions adjacent to the project site. The results of the ambient noise levels indicated existing dBA levels between 60.3dBA and 69.3dBA which meant that essentially no recordable increase to the ambient dBA levels could be added by drilling activities. Boart Longyear proactively prepared and delivered a detailed report of the study to both the District and the County.

As a result, a Boart Longyear LR175 electric/hydraulic rotary drill with a quiet genset operating the electric motor and a self-contained electric mud system was utilized in place of the typical diesel/hydraulic rotary drill. This greatly reduced the typical operating noise level.

Sound attenuation curtains were also constructed on three sides of the project site and air dump mufflers were installed on the drilling rig, to further reduce noise output. In addition, since the drill site could create intermittent noise that could have exceeded the 65dBA threshold, Boart Longyear instituted additional mitigation measures.

• Shift changes were scheduled for 7:00 am and 7:00 pm.
• Truck deliveries were restricted to daytime hours.
• Back-up alarms were disconnected and spotters were used.
• Noise from banging, hitting of down hole tools, hand tools, and other equipment was monitored and reduced to “as absolutely necessary” situations and was restricted to daytime only.

Using the same methodology used for identifying the existing ambient noise levels, the maximum noise level generated by the Boart Longyear drilling operations was recorded at the same three locations. One additional site (SML 4) was added in order to evaluate how much of the noise energy traveled above the sound attenuation walls and potentially impacted the residences on the bluff overlooking the project site. The average measured and calculated noise levels were well below the threshold.

The project was completed successfully with no disruption to the local community and there was no recordable down-time or violations to the strict noise ordinance.

According to Doug Evans, Chief Technical Officer at Mountain Regional Water, “District management and staff could not say enough about the professionalism and technical expertise exhibited by the Boart Logyear team. The District was included in all phases of the drilling project, from initial safety planning to completion and cleanup. The Boart Longyear team met the challenges head on, and worked with the District on a community education plan, and even went door to door with District personnel as we handed out literature and educated the community, not only on the needs of the project, but how all of their concerns would be mitigated. Boart Longyear also utilized state of the art equipment in this project to minimize drill time and to lessen any impacts. Utilizing their LR175 electric drilling rig, which had an extremely large impact on noise, the entire site was also protected by sound walls, and lighting at night was minimized by using many small shop lights on the site instead of large construction flood lights. The site also abutted up against a very popular community walking trail and the area was kept very safe, clean, and neat.”

Dual-tube flooded reverse circulation method develops water wells
Boart Longyear has multi-year contracts with the largest iron ore mining operations in the Pilbara region of northern Western Australia (WA) to undertake water well drilling at active and future mine sites.

The fleet of Boart Longyear dual-tube flooded reverse circulation (DTFR) water-well drill rigs have the ability to accommodate casing diameters of up to 28-inches, attain deep drill targets via a powerful 130,000-pound pullback and are mounted on a highly mobile platform. The rigs use a closed circulation mud system with a proprietary mud tank. By installing dewatering wells via DTFR, it is possible to control high producing aquifers during drilling that are problematic for conventional mud or conventional air drilling.

The DTFR method is distinguished from other drilling methods by the way the drill cuttings are returned to the surface through the drill string, whereas with conventional mud or air operations the cuttings are returned up the annulus. 

1. Cutting return is quicker than a conventional mud method. Cuttings don’t co-mingle with the annulus, as with conventional drilling systems, eliminating contamination and reducing annular washouts or hole enlargement. Cutting return via the drill string means that mud loss will not stop drilling operations as long as the drill bit remains submerged. Circulation is almost never lost and drilling mud can be replaced during drilling without the need to stop.
   
   
2. The mud system is a closed loop. Utilizing a special mud tank and drill cutting exchange, DTFR greatly reduces the drilling footprint compared to conventional mud drilling operations. Formation water is not an issue during drilling with almost zero discharge during drilling operations — making water management a non-issue.
   
   
3. DTFR mud circulates in the annulus under ambient pressure conditions reducing development time. The residual mud is easily removed from the annulus wall during development. In addition to faster and more complete mud removal, the amount of discharge water managed at the surface is lessened due to the reduction in development time.

The Boart Longyear DTFR drilling method was used to work in active mine sites in the Pilbara region — where there is a high volume of water discharged during drilling — without hindering active mining operations.

Historically, conventional air drilling or dual rotary drilling was used to set large diameter water supply, dewatering and injection wells. While these methods have the potential to drill quickly, maintaining circulation and hole integrity can be a challenge in fractured and friable ground conditions.  As a result of circulation loss or collapsing, boreholes are often completed at shallower depths.

Drilling a large diameter hole with either conventional air or dual rotary air, can also produce a tremendous amount of discharge water. This is an issue because many drill locations cannot release water to the environment due to water quality issues. So, the water is contained in giant sumps dug parallel to the drill rig. Often these pits fill quickly during drilling and operations must be stopped to allow for draining. With DTFR the need for large sumps is eliminated because water is not discharged during drilling. This is a tremendous advantage working in-pit where water management issues can interrupt mining operations.

Over the period of a year, Boart Longyear drilled 2300 meters for a large mine operator in the Pilbara region with hole diameters of 17.5 and 20 inches. The completed wells reached depths of 250 meters and were cased with 10- to 12-inch production strings.

For the development of one ex-pit dewatering well in particular, the DTFR reached a depth of 144 meters with less than 1 percent of deviation during drilling.

Geology encountered included, banded iron, thick sequences of friable mineralized ore, and shale inter-bedded with hard chert bands. These changing ground conditions were easily handled by the DTFR and drilling did not stop at any point due to loss of circulation. Prior to the use of the DTFR in the Pilbara region, there was speculation that a tri-cone drill bit, which is typically used on all types of mud drilling, would not be able to handle the hard rocks associated with iron ore deposits. These concerns were quickly alleviated with DTFR, which helped persuade other large iron ore producers to sign multi-year contracts with Boart Longyear.

Waste rock dumps are often placed adjacent to mine pit areas, and as mining expands more room is needed for the waste rock. Certain physical and chemical characteristics of the waste rock dumps are often needed to better understand the geotechnical and geochemical behavior of the large dumps and to evaluate potential mineral value. Sonic drilling enables the collection of highly representative samples and excellent sample recovery. This method of drilling has been used for the re-exploration of dumps, tailings and heap leach pads.

Waste rock dumps consist of mainly unconsolidated material – and it’s often difficult to know how deep they are or what types of material they contain – which can lead to challenges in drilling. Sonic technology provides a solution by being able to produce 100 percent accurate in-situ core samples through varied ground conditions.

Boart Longyear Drilling Services took on the challenge of drilling core samples from the unconsolidated waste rock dump at Kennecott Utah Copper’s Bingham Canyon Mine. The intent of the drilling was to define the contents of the waste rock dump. The waste rock dump consisted of rock blast material ranging in size from 254 to 304.8 millimeters (10 to 12 in) in diameter and was made up mainly of porphyry deposits (granite-like rocks).

With a targeted depth of 213.36 meters (700 ft), the main goal was to provide a detailed continuous sample of the waste rock dump material and confirm bedrock depth. Boart Longyear also needed to install piezometers (water level monitors) and lysimeters (moisture content monitors). Geotechnical samples would also need to be taken every 6.096 meters (20 ft) to confirm stability and moisture content for the first 60.96 meters (200 ft).

Sonic drilling is the perfect method for drilling in unconsolidated material, such as the waste rock dump at the Bingham Canyon Mine, because of its sample recovery rate, straight cased borehole and the flexibility to offer geotechnical sampling via the split spoon sampler.

As drilling commenced, Boart Longyear took on the task one step at a time by tackling the depths in stages. For the first 106.68 meters (350 ft), they drilled a 228.6 millimeter (9 in) borehole while tripping the drill string every 6.096 meters (20 ft) to pull a split spoon geotechnical sample for the first 60.96 meters (200 ft).

For the second stage, the team drilled to 152.4 meters (500 ft) using a 203.2 millimeter (8 in) bit with casing. Moving deeper to 228.6 meters (750 ft), they used a 177.8-millimeter (7 in) bit with casing for the third stage. Surpassing their targeted drill depth of 213.36 meters (700 ft), the drillers still had not reached the bedrock formation.

Needing to find the true depth of the waste rock dump, Boart Longyear felt like the rig still had the capability and pullback to go deeper. Easing forward they drilled to 264.261 meters (867 ft) using a 152.4-millimeter (6 in) bit with casing. The last stage couldn’t be drilled with casing as they needed to move to a 101.6-millimeter (4 in) borehole. Leaving only the bit for the final push to 274.32 meters (900 ft) – and setting a new Boart Longyear record for sonic drilling – they reached a 28 percent greater depth than initially targeted.

It took 16 shifts of 12 hours (192 hours) to accomplish the new record depth for sonic drilling. Boart Longyear lost two of those shifts (24 hours) to rain. Another key accomplishment was the entire depth was reached through dry drilling and achieved 100 percent in-situ core samples at less than 1 percent hole deviation.