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42 eXPloSiVeS & blaSting

• ANFO (ammonium nitrate fuel oil): is a widely used bulk industrial explosive mixture. It consists of a low-density (porous) ammonium nitrate prill and fuel oil. ANFO is chosen typically when low cost and ease of use are the primary considerations over water resistance, oxygen balance, high detonation and performance.

• Bulk emulsion: consists of the same chemistry as ANFO but differs in physical form. Bulk emulsions provide greater water resistance and were developed to allow safer and more efficient use in bulk loading systems. Bulk loading saves time, saves labour and improves explosives performance.

• Blends (heavy ANFO): are a mixture of ANFO and emulsion. The ratio can span 1% emulsion to 99% emulsion. The main benefits of blends are to increase the energy density of explosives in the borehole to enhance fragmentation, provide more water resistance than ANFO and reduce the overall project cost by permitting expanded drill patterns.

• Water gels: contain a substantial amount of water and are less sensitive than nitroglycerin dynamites. Water gels are available in two basic forms, packaged or bulk, making it possible to accommodate a wide variety of blasting requirements. They are not, however, in wide use currently.

• Dynamite: is a cartridge explosive used only in conventional, non-bulk, loading applications. Dynamite is wrapped in paper shells or plastic film/tubes. Although still in use for specific purposes, other explosive products have widely replaced the use of dynamite.

• Packaged explosives: Packaged explosives include traditional dynamite, packaged ANFO, emulsion and water gel explosives.

Types of explosives

The bulk explosives most widely used in today’s surface mining industry are ammonium nitrate

(AN)-based. Falling under this umbrella are emulsions and ammonium nitrate fuel oil, better known as ANFO. ANFO was the first of the two to see commer-cial use, primarily due to its simplicity and cost-effectiveness. However, its lack of water resistance led to the develop-ment of emulsions.

ANFO is a simple mix of porous AN prill and an organic fuel oil such as diesel, while emulsion is a viscous water-resistant blasting agent that must be sensitised by reducing its density. This is done by creating airspaces in the emulsion by using: physical mixing, with a density-reducing agent; or chemical gassing to create small gas bubbles.

The application of these two forms of AN-based explosive is rarely exclusive.

Blends of AN prill and emulsion (sometimes called heavy ANFO) are very common in today’s blasting operations and blends can contain from 1% emulsion to 99% emulsion.

The main benefits of blends are to increase the energy density of ANFO in the borehole to enhance fragmentation, provide more water resistance and reduce the overall project cost by permitting expanded drill patterns.

Blends with up to 50% emulsion are delivered as ‘dry’ products, which are augured; blends with 60%-plus emulsion are pumped. Blends containing 30-50% emulsion provide fair water resistance and, due to the large per cent age of ANFO, generally do not require the use of density-reducing agents.

Pumped blends with 70% or greater emulsion content are considered to give excellent water resistance with the ability to displace water when loaded from the bottom of the hole upwards, and they do require the use of physical or chemical density-reducing agents.

Although still in use for specific purposes, other explosive products have widely replaced the use of dynamite,

which was invented by the Swedish chemist and engineer, Alfred Nobel (Dyno Nobel’s namesake). Dynamite is a cartridge explosive used only in con ventional, non-bulk, loading applications. It comes wrapped in paper shells or plastic film or tubes and is therefore considered a ‘packaged explosive’. Water gels contain a substantial amount of water and are less sensitive than nitroglycerin-based dynamites. They are available in two basic forms, packaged or bulk, making it possible to accommodate a variety of blasting requirements.

eXPloSiVeS SelectionKey factors to be considered when selecting the type of explosives include: • the type of rock that needs to be

blasted; • diameters of the blastholes; • bench height, burden and spacing;• detonation velocity of the explosives;• fragmentation requirements for

loading, hauling and crushing;• height of the water table on-site; • supply and storage logistics; and• final result required.

forward chargeCarly Leonida asked four key companies about current blasting practices and technologies in the surface mining market

“Blast modelling

pro grammes have

become a significant

tool in helping design

engineers to achieve

accurate simulation

and analysis of different detonation

designs”

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The primary consideration in selecting the correct product is the explosive’s water resistance. However, once this consideration is satisfied, there are various other site-specific considerations that lead to the right choice of explosive:• Heave versus fragmentation: emulsion’s high-density yields a higher velocity of detonation (VOD), which gives greater fragmentation, while ANFO gives a large gas volume, creating more displacement of the muck pile. Higher VODs of emulsion blends are also found to achieve better floor control in tough geological conditions.• Environmental concerns: the high density of emulsion blends yields a higher explosive weight per borehole than ANFO; this can be a concern for operations needing to minimise blast induced vibration.• Primer use/availability: detonator-sensitive emulsion cartridges are weak primers for emulsion explosives, while they are sufficient for initiating ANFO. Cast boosters are generally preferred.• Loading times: many operations choose to use only pumped emulsion blends regardless of the presence of water in order to remove the operational delay caused by changing from one product to another and the evaluation/decision-making process associated with the change.• Bench access: ‘dry’ products must be augured or poured into the hole. This

requires the bulk truck to be able to arrive close to the hole, or bags to be carried to the hole. On the other hand, pumped emulsion blends are delivered through a long product hose which can be carried to various holes while the truck maintains the same position.

All of these considerations are, of course, weighed against the respective economic and operational benefits of each type of explosive; emulsions typically cost more than ANFO.

Storage anD tranSPortProper storage and transportation are constant considerations when dealing with explosives. Rob Bush, technical

representative at Austin Powder, explains: “Today’s use of AN-based explosives has helped the industry to improve safety in both the transportation and storage of explosives. AN prill is not an explosive until mixed with an organic fuel, while emulsion is not an explosive until mixed with greater than 50% AN prill or a density-reducing agent.

“The equipment to realise these blending processes in the field are readily available on the market which allows for the storage and transportation of blasting agents rather than explosives.”

This practice in turn allows for safer storage and transportation of blasting agents in large quantities due to their lack of sensitivity. This improves

A typical complex hard­rock blast, designed using BME’s BlastMap software

Far left: loading a blasthole from the MPU, Isaac Plains coal mine

Left: priming a blast hole, Isaac Plains coal mine, Bowen Basin, Queensland

“Blast fragment­ation can hugely affect a mine’s profit ability”

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44 EXPLOSIVES & BLASTING

operational efficiency by reducing both the number and size of explosives magazines needed on a mine site, as well as the number of deliveries from the explosives provider required to match consumption.

There have also been efforts in explosives manufacturing to improve traceability of explosives and explosives accessories so that they can be tracked on a piece-by-piece basis from the moment they are produced until they are used on the mine site. “Traceability is continually improving and the ability to be able to accomplish piece-by-piece tracking is already required in some regulatory environments,” adds Bush.

There are strict regional requirements in relation to the storage and transporta-tion of explosives. These are detailed and stringent to ensure safety. For example, all vehicles transporting explosives should be well maintained and have all necessary safety equipment such as fire extinguishers. They must also display adequate warning signs and placards.

Most explosives companies are highly supportive of these regulations and work hard to ensure their compliance.

Tony Rorke, director of blasting technology at African explosives and services provider BME, comments: “Currently, most countries have stringent legislation regarding the storage and transport of explosives, and explosives companies are in full support of this. BME is looking at unique methods of identifying and recording product unit identifications for easy tracing.”

Lance Tinney, SVP, HSE and business excellence at Dyno Nobel, agrees: “Safety is our core value and number-one priority. We ensure that our operators and blasters are fully trained and certified to best-practice standards. We operate a fleet that meets or exceeds applicable regulations and we monitor our fleet through high-tech fleet-tracking satellites.”

SoftwareBlast fragmentation can hugely affect a mine’s profitability, so it is important to plan blast patterns and parameters correctly and ensure maximum efficiency. Every mine site has different geological conditions, and the ability to model and adjust blast designs based on these factors can give sites a distinct advantage in reacting to changing conditions, or better yet, proactively adjusting to them.

Blast modelling programmes have become a significant tool in helping design engineers to achieve this through accurate simulation and analysis of different blast designs. Equally important is the ability to measure what happens during blasts in order to deal with

application issues and to get a better understanding of the rock response.

“This enables changes to design parameters prior to implementation in the field, and software reporting functions allow for accurate information to be passed on to the shot firer,” explains Stephen Timbrell, blasting specialist at Action Drill & Blast.

One example of this is in the case of blast modelling for final wall stability and pre-split designs. “Using advanced pre-split design wizards coupled with blast energy analysis programs, explosives engineers are able to adjust pre-split charging configurations based on rock conditions, as well as minimise blast-induced vibrations in the final wall,” says Bush. “This in turn leads to accomplishing designed stripping ratios, or even improving upon the design to accomplish more favourable stripping ratios. This is especially valuable in thin-veined deposits where stripping ratios tend to be very high.”

Blast energy modelling also allows for blast optimisation by giving the ability to maximise the efficiency of the explosives used and therefore minimise the quantity needed to achieve the desired fragmentation.

“The advent of blast modelling software can be very much attributed to the advent of electronic detonators. Precise control over blast timing has allowed for more precise analysis of what actually goes on in a blast,” adds Bush.

Austin Powder uses software developed in-house for blast design and analysis. “Our most advanced software includes 3-D surface mine modelling to allow Austin technical personnel to assist customers in mine planning, and to allow for importing GPS blasthole surveys that can be placed onto real terrain data,” says Bush.

Action Drill & Blast uses 2D Bench and Geovia’s Surpac packages for modelling. Blasting expert, Laurie Pratt, explains: “2D Bench provides a cost-effective solution for blast design, analysis and tie-in plans for shot firers. It is also used for

Below left: loading the

mobile processing unit

at the Middlemount

coal mine.

Below right: rotary drills,

blast hole drilling,

Fortescues Cloudbreak

project, in Pilbara, Western

Australia

Right: AXXIS – BME’s digital

initiation system. Above: prepar­

ing for an AXXIS electronic

detonator blast

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46 eXPloSiVeS & blaSting

basic mine planning. Surpac provides additional benefits such as 3-D modelling and allows blast designs to be created using topographic information and pit designs.”

Dyno Nobel uses several different software tools for blast modelling:• HSBM is a 3-D numerical modelling

software package that uses a combination of discrete and continuous numerical techniques to model detonation, dynamic wave propagation, rock fragmentation and muck-pile formation.

• FAS-Blast uses an empirical model to allow input of bench conditions and provides initial design parameters for

a shot. It also has a fragmentation pre-diction tool and vibration prediction based on prior results.

• ViewShot is an advanced timing design program that allows created designs to be used to programme electronic detonators on the blast.

• Electronic Shot Report compiles data from previous blasts such as geology, pattern info, product usage, seismograph readings and timing (among others) to allow document-ation of blasting results. Web access to information allows ease of access to assist with designing future shots.

“These tools allow multiple scenarios to be examined and can assist in picking the correct products and timing to be used for a set of conditions. Advanced blasting software supplements local knowledge about blasting conditions by using actual data to calculate blast designs that are specific to local conditions,” says Jeff Averett, blasting software manager at Dyno Nobel.

BME has developed BlastMapIII, a blast design tool that also uses measured data to help with variance analysis. “All our clients have access to BlastMapIII. We use the most modern monitoring equipment and analysis software available in the market to measure blast results,” says Rorke.

As well as modelling blasts and fragmentation, software programs can help ensure the correct amount and type of explosive is delivered to each drill-hole.

“The drill-hole and rock-recognition information from the software in the blasthole drills can be fed into the blast design program,” explains Timbrell.

“The type/amount of explosive for each hole is calculated by the design program and can be sent directly to the GPS-ena-bled mobile processing unit (MPU). As the MPU positions over each hole, it is auto matically loaded as per the design.

DetonatorSMost detonators can be classified into three types: non-electric detonators, electric detonators and electronic delay detonators (see box).

Non-electric detonators have the advantage of being more cost-effective and readily available from numerous suppliers and are widely recognised as being easier to use in the field. The main disadvantages of some non-electric detonators are: the timing imprecision or scatter that can occur, which is not desirable for vibration-con-trolled blasting; and the limited range of detonator timing delays available on the market, which reduces design flexibility. However, this is not the case with all non-electric detonators.

Electronic detonators have the advantage of high-precision timing, which is ideal for vibration-controlled blasting and achieving improved fragmentation on a site-specific basis. When modifications are required to blast designs, electronic detonators eliminate concerns relating to detonator scatter. Electronic systems with two-way

• Non-electric detonators: these utilise shock tube (plastic tube) in which the inside walls are covered with a reactive material. This material can carry a shockwave strong enough to initiate a pyrotechnic detonator. Pyrotechnic delay detonators offer millisecond timing accuracy and are easy to use. These non-electric systems are economical and can be used in all mining applications.

• Electric detonators: electric initiation systems use an electrical power source to initiate detonators. Delay powders inside the detonators control the detonator firing times. These were introduced in the 1940s. The primary benefit is that the blaster can confirm that the initiation voltage will reach all detonators in the circuit. The primary limitation is that some detonators can be susceptible to initiation by stray current, static electricity, or direct electric current.

• Electronic detonators: electronic initiation systems are the most recent development in blasting initiation technology. Each electronic detonator contains an integrated circuit chip and a capacitor to control the initiation time and provide voltage to fire the bridge-ware. Although more costly than electric and non-elec-tric detonators, the key advantage with electronic detonators is very precise and accurate timing. Near-absolute timing allows for significant improvement in blasting results of fragmentation, vibration control and air blast control.

Detonator types

Blasting sequence at

Anglo American’s

Kolomela iron­ore mine

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eXPloSiVeS & blaSting

communication can identify detonator misfires before initiation.

William Codd, of Action Drill & Blast, says: “From our experience, the main disadvantages of electronic detonators are the relatively high cost and additional training requirements required for shot firers, plus the potential for incorrect data entry and no visual check other than the display on the program-ming unit.”

“Mines that have a focus on their overall efficiencies, including blasting prefer using the much more accurate electronic delay detonators,” says Rorke. “The overall financial benefits in improved productivity far outweigh the price premium of the electronic detonator systems.”

Indeed, the surface mining industry is gradually transitioning to the complete use of electronic detonators, as the added value in terms of safety and security, timing precision, and opera-tional flexibility is found by an increasing number of users to overcome their added cost.

“Electronic detonators have opened

new doors for the blasting industry. The ability to do advanced analysis of blast energy has increased dramatically due to the confidence and precision given by electronic detonators. They are becoming more economical every day thanks to their steadily growing customer base. This, in turn, is providing increasing opportunities for blasting engineers to learn how to harness blast energy more efficiently to better accomplish various goals, depending on their site-specific challenges,” states Bush.

Electronic detonators also offer safety mechanisms. For example, they cannot be initiated without their accompanying blast equipment; they can be electroni-cally verified for proper programming and connection before leaving the blast area; and they are generally not susceptible to initiation from stray currents.

“Their precision allows for blast optimis ation in many forms, such as vibration minimisation, improved fragmentation, and improved control of the muck-pile profile,” says Bush.

Most electronic detonator systems allow for re-programming of a detonator right up to the moment of firing the blast. They also provide ample flexibility in blast design, as fixed-delay detonator inventories do not have to be consid-ered, and trunk line or legwire lengths for surface connections are not necessary. This flexibility provides much simplified inventory management, from an operational perspective.

Remote (wireless) firing systems are becoming increasingly popular as they allow the blast to be initiated from a safe distance and offer the ability to fire multiple blasts from one position.

The primary markets for these systems are in mining operations that have very large evacuation radii around the blast area, or restricted line-of-sight access to the blast area from the firing position.

Bush says: “Geographically, it is helpful

if the site is not mountainous and if open pits are not small with very steep walls. However, most sites that elect to use a wireless system are able to find ways to at least partially overcome such obstacles.”

He goes on to explain that a good example of an ideal application for a wireless firing system is one of Austin’s clients whose operation has over 30 separate open pits. Between nine and 12 pits are active at any one time, and there is a maximum driving distance of 20km between pits.

“The site is very remote, and the blast area evacuation distance is 2km. The mine loads and fires up to six separate blasts per day, usually in distinct pits. The quantity of lead-in-line required to reach each blast, coupled with the time it would take to manually walk the line out, made lead-in-line use not feasible,” Bush says.

“Therefore, the initiation method being used was safety fuse, which comes with various inherent risks – the principal being the inability to abort a blast after the safety fuse has been lit. A remote system was implemented which has greatly increased both the safety and efficiency of the operation.”

trenDS outlooKWhile many industry experts regard the introduction of emulsions and emulsion blends, the implementation of blast

The benefits of going electronicElectronic detonators allow for better communication with the detonator while in the borehole to ensure it is active. Some of the improvements observed from the use of electronic initiation systems include: • Lower vibration levels• Higher cast percentages• Pattern expansion• Improved fragmentation• Higher frequencies• Greater safety through encrypted firing signal

Left: a BME emulsion truck charging small­diameter blastholes with HEF 100

“Most electronic initiation systems allow for re­program­ming of a detonator right up to the moment of firing the blast”

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48 EXPLOSIVES & BLASTING

modelling and software packages, and the advent of electronic detonators as key developments which have changed the face of mine blasting over the past 20 years, we must continue to look forward; which trends or technologies could be the next game changer?

“I believe there is still a lot of potential development work in electronics where the computational power of each detonator can provide useful information to the blasting engineer during and after each blast,” says Rorke. “Measurement techniques and improved blast modelling pro-grammes will help to further improve blasting. BME is also busy with R&D in emulsion technology to further improve our ability to utilise used engine oil in our stable emulsion explosives.”

Bush agrees, stating that the continuing trend of the blasting industry to move towards electronic initiation systems will fuel technological advances in blast analysis equipment and software. “This will lead to a deeper understanding of blast energy and how to best utilise it,” he says. “The resulting improvement in blast design could have a very significant effect on the efficiency of blasting operations in the mining industry.”

Improving safety will always be a key trend. Looking at ways to reduce the number of personnel exposed to the risks of blasting will continue to influence development of blasting technologies.

Pratt lists explosives automation, and the development of MPU trucks and equipment using GPS guidance and remote operation as a few areas that could contribute to greater safety.

Since mining operations are becoming more challenging, and remaining mineral deposits are deeper, lower-grade and harder to find, blasting technologies also need to become more efficient and effective at extracting the ore.

Dyno Nobel has developed a proprietary technology called Differential Energy. This enables the explosive engineer to selectively target areas of the powder column in wet or dry boreholes with different amounts of explosive energy.

“Explosive energy is more effectively used to best match changing rock

properties in the borehole, that is, putting the right energy in the right place,” explains Larry Mirabelli, bulk products and delivery system manager at Dyno Nobel. “In a recent trial using Differential Energy, a large gold mine reduced its overall powder factor by 18%, realised an 8% increase in shovel productivity in both waste and ore, and experienced no reduction in crusher throughput of ore. Additionally, they dramatically reduced visible nitrous oxide fumes in even the wettest areas of the pit.”

outSourcing blaStingAs such a high degree of specialist knowledge and skill is required to complete blasting operations safely and efficiently, it is common for mining companies to employ specialist contractors to handle their blasting needs throughout the life-of-mine.

Many explosives and technology providers offer additional services in order to cater to this market. “It is quite common for mining companies to request service beyond just delivery of explosives, and in many cases, it is the expectation,” says Bush.

For example, technical support provided for customer blasting operations can range from scheduled and one-off visits by blasting specialists, to permanent on-site mining engineers who provide daily technical support. Most explosives companies also provide a full blasting service that consists of the provision of crews/equipment to carry out all blast loading operations, magazine and inventory management, and administrative requirements.

“Along with the use of specialist blasting companies that provide both technical and operational service, comes a broad resource of knowledge that is at the customer’s fingertips,” says Bush. “It is true that mine personnel who are

on-site daily know their operations best. But when challenges arise, having access to a broad range of experience across various mine types, environments and countries can prove invaluable when coupled with the knowledge of local personnel.”

Rorke reports similar findings: “Often mining companies use BME to supply the blasting service and, in some cases, pay us on a ‘rock-on-ground’ basis. This type of service appears to be in increasing demand because of the shortage of skilled blasting people and their very high cost.”

He continues: “BME and some of our competitors invest substantially in blasting technology and related services, which our clients have access to. This is a big benefit to mines as their primary focus is on mining and not the science behind blasting.”

The provision of blasting services on remote mine sites generally requires a dedicated on-site crew. This, in turn, requires that the mine is of a size to justify this cost. If the mine is not in a remote area, it can often be serviced by a centralised magazine location and size is not such a restriction.

“We find that operations/companies of all sizes can have needs for technical service. Larger operations are in cont inual search of even minute improvements that have big impacts when dealing with economies of scale,” says Bush. “But smaller operations can often face environmental issues such as vibration control that can threaten to significantly reduce their reserves or even may threaten to shut the operation down.”

“Blasting is a specialist skill area and the blasting process occurs at the start of the mining cycle, so getting it right is essential,” says Codd. “Action Drill & Blast understands the mine-to-mill optimisation process and our systems, processes and skilled personnel ensure we are able to provide what our clients need [in order] to carry out their digging, crushing and processing operations efficiently and cost-effectively.

“We find that most in-house operations have limited technical ability related to blasting and often need additional resources to achieve the same results as a specialist blasting company.”

Dyno Nobel has gone one step further and established a dedicated division, DynoConsult, which provides technical expertise to its blasting customers. “Because our consultants have a breadth of industry experience across different commodities, mining methods and challenges, they can, in collaboration

Above and above right:

blasting preparation and

activity with a Dyno Nobel

team

BME supplies explosives and

blasting services to the African

mining, quarrying and

construction industries

“Looking at ways to

reduce the number of personnel

exposed to the risks of

blasting will continue to

influence develop­ment of blasting

tech­nologies”

49EXPLOSIVES & BLASTING

November 2013www. .com

Operating in one of the most competitive markets in the world, an Indonesian explosives manufacturer serving the mining industry recently switched to using a low-grade AN bulk explosive for its blasting programme as part of a cost-reduction initiative.

Immediately following the change, the company experienced significant crystallisation with its emulsifier, which led to poor blast performance, and it switched back to the competitive emulsifier it had been using previously. However, the company still experienced crystallisation issues and inconsistent blast performance, partially due to a reaction between the competitive emulsifier and the sodium naphthalene sulphonate crystal modifier/anti-caking agent used.

The explosives manufacturer also supplies material to customers who drill up to 500 holes in their blast patterns and depend on the explosive to offer a maximum seven-day sleep-time.

It was imperative the company offered a dependable product. Chemical expert Clariant was tasked with developing a new,

custom-designed emulsifier that eliminates large crystal formations and improves blast consistency when using low-grade AN bulk explosives.

As Clariant’s technicians worked through emulsifier trials with the customer, they discovered that the commonly used ‘feel’ testing procedure (involving rubbing the emulsion between the fingers) to determine the amount of crystallisation was too subjective to give accurate, repeatable results, especially as the act of rubbing the emulsion itself can cause crystal formation. To overcome this, the technicians developed a more quantifiable testing procedure that was able to determine the amount of crystallisation.

Sodium naphthalene sulphonate is commonly used by manufac-turers of low-grade ammonium nitrate as a crystal modifier/anticaking agent. Clariant discovered that the quantities of materials added to this agent varied widely, even within the same product.

Clariant also tested varying percentages of diesel fuel oil and recycled oil, as well as a variety of its own Arkomon emulsifiers as part of the research programme. In head-to-head testing against competitive products, three, one-week trials were conducted to test the performance of different Arkomon emulsifier formulations against the customer’s current emulsifier.

Five Arkomon formulations passed the quantitative crystallisation tests, showing only negligible to moderate crystal formations after nearly a month. By contrast, the competitive emulsifier failed the quantitative tests, exhibiting moderate crystallisation within five days and heavy crystallisation after nearly a month.

Clariant’s Arkomon XP 1014 formula was chosen as the best-performing emulsifier and was adopted by the customer.

Case study: Clariant custom­developed emulsifiers

with our customers, develop technical solutions to ensure their operations are performing optimally,” says David Gribble, manager at Dyno Consult.

“By adopting a holistic approach to projects, DynoConsult can deliver sustainable benefits including cost-sav-ings and productivity gains. With an emphasis on sustainable results – not just recommendations – the DynoConsult team works in close partnership with our customers from the scoping stage through to implementation and ensuring the benefits are locked in,” he adds.

“The provision of blasting services on remote mine sites generally requires a dedicated on­site crew”

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