Diesel use in copper mining and impact on emissions
According to the Australian Renewable Energy Agency (ARENA) the Australian mining sector accounts for around 10 percent of Australia’s energy use, with around 41 percent of energy supplied by diesel and 33 percent natural gas.1 This equates to diesel consumption at approximately 5 billion litres of diesel per annum.
Azadi et al. (2020) notes that Chile which hosts the world’s largest copper operations in a setting of declining grades has seen an increase in fuel consumption of 130 percent alongside electricity consumption that increased by 32 percent per unit of mined copper from 2001 to 2017.2
Diesel powered equipment has been the mainstay of copper mining operations for a number of years. This is due to widespread technology, hardware, fuel availability, service choice and capability. Diesel powered units offer known performance, power density and flexibility. These advantages are coupled with proven asset longevity.
The International Council on Mining and Metals (ICMM) note that large mining mobile equipment currently makes up around 30-50 percent (and up to 80 percent) of the Scope 1 emissions at a mine.3 In this context the on-going use of diesel is counter intuitive to the copper industry’s goal to achieve a zero emission objective, and it is essential to explore alternatives to existing models of operation.
The significant energy use and asset deployment across the industry offer the potential for operators to explore and drive economies of scale for new technologies to address emission and environmental impact with an objective to deliver a positive impact to operating costs.
However, the pathway to reduce and ultimately eliminate diesel use is complex, site specific and depends on a range of short- and long-term decision factors related to the selection of mobile capital equipment. This includes navigating the choice between electrification or adoption of alternate fuels such as hydrogen or biofuels.
On one hand an operator can deploy short term initiatives that could achieve a reduction in the use of diesel. This could include initiatives to optimise existing operating practice or deploy equipment modifications. Understanding fleet and fuel consumption dynamics can progress a range of available and “off the shelf” innovations that can provide broader efficiency and production benefits.
Ultimately to achieve more significant decarbonisation objectives, decisions are required to progress activity that could replace diesel use altogether. This could include a movement toward electrification or the adoption of hybrid systems such as trolley assist, battery storage technologies or hydrogen fuel cells. A suite of activities is occurring across the industry at an increasingly rapid pace, and there is an observed increased level of collaboration across a range of initiatives and demonstrations.
Case Study: Innovation for Cleaner, Safer Vehicles (ICSV)
Case study: “Clean” diesel oils and biofuels
A number of mining companies have announced initiatives to reduce their Scope 1 emissions through the pathway of electrification and have announced plans to shift to renewable energy for process power for future projects. Broadly speaking these commitments generally take the form of three tiers: the use of grid-connected renewable energy, electrification of light vehicles and auxiliary equipment, and electrification of heavy haulage.
Due to considerable investment and development in the commercial sector, the deployment of light vehicle battery-electric vehicles is now increasing in both open cut and underground applications. For example, in 2018 BHP introduced battery electric vehicles trials at their Olympic Dam and Broadmeadow sites.4
Beyond light vehicles, a shift is also occurring toward the electrification of specialised and heavy haulage equipment. Glencore has commenced use of battery-electric loaders in underground operations, where reduced diesel emissions has resulted in immediate safety and efficiency benefits.5 Newmont Goldcorp has committed to an all-electric fleet at their Borden site in Ontario, Canada, featuring electrified heavy haulage in addition to a full-fleet of battery-electric light vehicles.6
Adapting electrification technologies to the mine haulage environment centres on two key operational challenges. The first is duty cycle. Unlike commercial and personal vehicles, mine equipment must operate nearly continuously, and downtime is undesirable. The second is the rugged environment of the mine site, which imposes stringent durability and safety requirements.
The first challenge is a question of advancements to battery technology and fast-charge technologies, which have now progressed to a point of viability. The second is a challenge for mining OEMs under active development.
Electric vehicle advantages for mine haulage
When combined with a renewable electricity source, the electrification of mine haulage presents the opportunity to eliminate what is likely the single largest source of carbon emissions from a modern copper mine. There are three key short-term practical advantages to battery-electric vehicle (BEV) adoption.
The first is improved energy efficiency providing direct operational cost benefits, especially in an environment of rising diesel fuel prices. In addition to improved energy efficiency, advancements in regenerative braking technologies allow energy to be captured when the vehicle slows or goes downhill, improving overall energy efficiency. Generally, the electricity cost for a battery-electric vehicle is around one third that of the equivalent diesel fuel.7
Another is the reduction of diesel particulate matter (DPM) and combustion by-product gases that include sulphur dioxide, carbon monoxide and fine particulate emissions that arise from diesel engine use. Reducing these emissions is especially beneficial in underground operations, where fumes and particulates present inhalation safety risks and impose increased mine ventilation requirements.
A report led by the University of Adelaide in Australia and Universidad de Concepcion in Chile show that electrifying underground mines can lead to significant energy and economic benefits. Equipment electrification can result in energy and operating cost savings of 70 percent related to ventilation and cooling.8
Furthermore, BEVs have significantly reduced supply and logistics trains. By eliminating the need to bring quantities of diesel fuel on site, a significant amount of secondary vehicle transportation can be eliminated. BEVs are (typically) mechanically much simpler than diesel-electric vehicles offering the opportunity for a reduction in spare part inventory, usage efficiencies, and simplified maintenance.
Challenges to adoption
The technical challenges related to BEV adoption vary with the specific circumstances of each site but fall under a few broad themes. Two critical ones, which determine the viability of BEVs overall, are:
Battery energy density, and
In roles where BEVs are appropriate, there are some secondary concerns that will need to be addressed:
OEM adoption, and
Revamped logistics, training, emergency response, occupational health and safety (OH&S).
Battery energy density
The primary technological factor limiting the adoption of electric vehicles in mining and beyond is the energy density of battery technology. For mobile applications, the space is dominated by lithium-ion batteries. Many other battery technologies exist, such as redox flow and molten salt, that present desirable properties for stationary energy storage, but the power-to-weight ratio makes lithium-ion the clear choice and current market leader for vehicles and other mobile equipment.
Lithium battery technology development has tripled the effective energy density from 2010 to 2020, and prices per kWh have fallen by almost an order of magnitude in the same time. However, a present peak energy density of 300 Wh/kg is still merely 2 percent of the mass energy density of diesel fuel (50:1 factor, ~12,400 Wh/kg). While this is not a valid direct comparison, it does convey the higher mass that needs to be dedicated to batteries versus a diesel fuel tank, alongside more frequent recharging required. In the past, this presented a barrier to the adoption of BEVs, but current numbers are now sufficient. Further improvements are expected (as of 2022, 400 Wh/kg batteries are being claimed by several manufacturers),9 but extrapolating these trends further is challenging. Exotic chemistries, such as lithium-oxygen, potentially promise order-of-magnitude improvements in energy density, but this is still an area of active research.
Current mine haulage demonstration vehicles do not use the highest energy-density chemistry available, instead focusing on technologies like lithium ferrophosphate (LFP) that offer superior cost/energy trade-offs.10 The batteries themselves should be considered a Horizon 1 technology, in that the Technology Readiness Level (TRL) of the batteries alone is high. Adoption to mine haulage vehicles are Horizon 2, as a technology that is under development and demonstration but not yet complete.
Technology improvements are likely given the broad level of worldwide investment into consumer EVs, but battery energy economic efficiencies are difficult to predict with high certainty.
Charging and charging speed
The barriers related to battery energy density lead to another obstacle: the need for frequent charging. Charging is much slower than refuelling. The high energy density of diesel fuel is again an advantage here, as power transfer is the energy density multiplied by the flow rate. Advances in high voltage charging technologies among consumer applications such as the Tesla Supercharger, have addressed these barriers somewhat, but the resulting duty cycle (the time the truck is available for work versus time spent recharging) is still not acceptable in an operational context. Two main technologies exist for solving this: in situ charging systems and battery swap.
In situ charging is an extension of existing electric trolley systems, where diesel-electric trucks attach to a tram-style charging line during certain parts of their operation. The trolley system takes over from the onboard diesel engine, reducing fuel consumption and engine wear during that segment of road.
In situ charging extends these systems. While trolley charging only provides enough energy to operate the vehicle while it is connected, in situ charging operates at higher voltages and currents to recharge the batteries while the truck is in operation. This allows the truck to rely on batteries while operating away from the charging network. In principle, these systems allow the battery to be charged during productive work, allowing a nearly 100 percent operational duty cycle. Because of the central role these systems will play in mine operations, current development (especially through the Charge-On Challenge) aims to use improved design and robotics to reduce the current mechanical and operational limitations of trolley systems (operational complexity, increased operator workload, and risk of damage during engagement/disengagement).
A competing technology under consideration is battery-swap systems. Rather than charging the battery in place, the battery pack is removed and replaced with a full pack, before being charged at a slower rate. Battery swap is quicker than a charging operation but adds additional mechanical complexity, something especially undesirable in a harsh mine environment.
Finally, some prototype systems incorporate a secondary hydrogen fuel cell system in addition to the primary battery-electric powertrain. This allows for backup charging and fast refuelling in circumstances where battery charging is not feasible. However, a fuel cell brings increased complexity. Hydrogen would be especially complex to manage in an underground mine system due to leakage, flammability, and ventilation issues.
Together, these two factors related to energy storage and power delivery determine the ability of the BEVs to be effective in a mine haulage application. Since approximately 2020, there is broad consensus that this threshold has passed with evidence that BEV prototypes are now emerging on mine sites.
While BEVs are now reaching viability from an economic and technology standpoint, there is still significant R&D work required to develop specific vehicles. Some of this is supported by mining companies (the Charge On Challenge is a good example here), but this R&D cost still primarily falls with the OEMs. This incentive-alignment could slow adoption if not efficiently addressed in a coordinated manner.
Logistics, hazard, and risk
While electric vehicles in general have a smaller logistical footprint than diesel vehicles, broadscale adoption will require a significant rework of the current diesel garage and spare parts supply chain. BEVs require specialised, usually OEM-specific training for technicians and personnel.
In addition, lithium batteries and high voltage supplies present novel safety, emergency response, and firefighting challenges, which require adaptation of existing procedures and training. This presents an additional cost during the early phases of adoption.
Opportunities for upstream copper production
With over 52,000 off-road haul trucks in operation distributed at surface mines across the globe11 most mining operations do not yet benefit from significant amounts of electrified equipment, and it is likely that such technology is not yet in countries with the largest fleet portfolios. This may present a substantial opportunity for the future of mining electrification, as the market is still relatively nascent and ripe for investment. Considerable challenges remain when it comes to weaning the industry off diesel and replacing fleets with BEVs, particularly in surface mining where assets are long-life and BEV technology remains at the prototype and demonstration stage.
Alongside technological challenges the transition to electrification will impact power demands to sites and will rely on access to renewable energy sources which are not always readily available.
Mining firms will need to take a long-term view to balance how they advance sustainability goals, employee safety, and their own viability in an increasingly competitive marketplace. For those who do adopt earlier electrification, the overall benefits may significantly outstrip initial costs.
There are a range of BEV demonstrations in development that include:
Anglo-American / Williams Advanced Engineering – BEV with hydrogen backup12
Fortescue Future Industries / Williams Advanced Engineering - BEV13
Kuhn Schweitz Elektro Dumper - BEV14
Xiangtan Electric Manufacturing Co. Ltd.15
Caterpillar / BHP – Collaboration announced16
Case Study: Charge On Innovation Challenge
Case Study: Electric Mine Consortium
When produced from a renewable energy source, the use of hydrogen does not emit greenhouse gases. As the world seeks clean, flexible, and safe fuels to reduce carbon emissions and mitigate the impacts of climate change, hydrogen is gaining attention and shaping up to play a significant role in a clean energy future.
It is the flexible and wide-reaching application of hydrogen that is gaining attention as a significant opportunity to contribute to decarbonisation efforts. Applications include energy intensive industries and hard to abate sectors. According to IEA (2022) hydrogen is mostly used in the refining and chemical sectors and accounts for 6 percent of natural gas use and 2 percent of coal consumption.17 Recognised emerging applications for hydrogen include transport and mobility including vehicle fleets and shipping, large-scale and residential power generation, grid stabilisation and resilience, energy for heating and industrial processes, blending into gas networks and as a molecular feedstock for sustainable chemicals and materials that may be further utilised and traded.
In 2021 the World Energy Council conducted a comparative assessment of hydrogen demand scenarios and concluded that hydrogen industries could reach up to 25 percent of global energy consumption by 2050.18
Hydrogen when produced from renewable sources is currently enjoying significant momentum, with announced policies and projects around the world expanding rapidly. According to the Hydrogen Council announced hydrogen projects grew from 228 to 359 in the first six months of 2021 alone and more than 30 governments across the world have announced net zero policy commitments with an estimated US$76b allocated to advance hydrogen strategies and projects.19
It is no surprise that the variety hydrogen use cases across the low carbon economy foretells how hydrogen is also being investigated for a range of applications including upstream mining.
Hydrogen colours – what do they mean?
Hydrogen is a colourless, odourless, tasteless, non-toxic and highly combustible gas and is the most abundant element in the universe. Hydrogen does not typically exist by itself in nature, but rather as a component in chemical compounds such as water, fossil fuels and biomass. It can be produced as either a gas or liquid and can be used across a variety of applications. Hydrogen has current application in industry including refining oil and producing ammonia for fertiliser.
Methods to produce hydrogen are not new, and the most common methods include steam methane reforming (SMR), gasification or electrolysis of water. Hydrogen is often assigned a colour to designate the method of production, mainly differentiating the feed source and energy source. While there is there is no universal naming convention, a summary of generally accepted hydrogen colours and description is shown in Table 4 below.
Table 4: A summary of the ‘colours’ of hydrogen and related production process20
|Description of Production Process
|• Electrolysis of water using a renewable power source •Zero carbon emissions
|• Production process is the same as brown or grey hydrogen • Carbon emissions are captured
|• Produced from methane or natural gas inputs through steam methane reforming • Material carbon emissions are released during production
|• Produced from coal inputs through gasification • Material carbon emissions released during production
|• Produced when natural gas is broken down via methane pyrolysis. The process is driven by heat produced with electricity, rather than through the combustion of fossil fuels. • Carbon is produced in a solid form mitigating requirement for carbon capture and storage (CCS) • Where the electricity driving the pyrolysis is from a renewable source the process is zero carbon, or even carbon negative if the feedstock is bio-methane rather than natural gas.
|• Produced by electrolysis using nuclear power.
|• Produced by electrolysis using grid electricity.
|• Naturally occurring hydrogen found in underground geological settings. • Hydrogen is potentially sourced though fracking.
How is hydrogen stored and transported?
When hydrogen is produced from a renewable energy source or process, it can be an enabler to store, move and use renewable energy in different ways and at a time when it is needed.
However, hydrogen is a gas that at ambient temperature and atmospheric pressure has an inherently low volumetric energy density (kWh/m3). This presents a challenge to store adequate supplies for large scale industrial use. Due to this challenge, hydrogen is often stored in other forms that include:
Compression: Gaseous hydrogen is compressed and stored at higher pressures to increase the volumetric energy density.
Liquefaction: Hydrogen is both pressurised and cooled to -253°C so that it is in a liquid state.
Chemical: Hydrogen can be stored in other compounds such as, but not limited to, ammonia and metal hydrides.21
Although theoretically hydrogen can be transported by any type of vehicle, including truck, trail or ships, the application across a range of transport types has not reached wide spread commercial acceptance. The readiness and application to various transport modes is dependent on a range of factors including:
target distance; and
safety and regulatory considerations.
For large quantities of hydrogen, it can be blended into existing gas lines. Dedicated pipelines can also be used to transport a pressurised gas, and this is under consideration in a range of large-scale emerging projects.
Developments and trends
Green hydrogen production uses renewable electricity such as wind or solar power to drive the electrolysis of water to form hydrogen and oxygen. This reaction occurs in an “electrolyser”, which consists of a positive electrode (anode) and negative electrode (cathode) separated by an electrolyte or a membrane. When electrical potential is applied across the electrodes, hydrogen is formed at the cathode and oxygen at the anode, with the hydrogen collected for use. Two types of electrolyser systems are most common, being alkaline and PEM (Polymer Electrolyte Membrane) technologies, with solid oxide electrolysis also emerging.
While significant potential is recognised, green hydrogen production is yet to enjoy wide scale commercial adoption due to its comparatively high costs, efficiency losses, and challenges related to handling. The process of electrolysis is both energy and capital intensive. The past decade however has seen significant reduction in capital costs. Capital has fallen around 75 percent in the past 4 years, driven mainly by market demand for larger systems and innovation in system design and manufacturing. Capital costs are forecast to drop by a further 30-50 percent in the next decade, as low-cost renewable energy supply, pilot projects and demand offtake growth are realised.22
The International Renewable Energy Agency (IRENA) forecast that hydrogen technology improvements, learning rate, electrolyser size and cost will follow a similar trajectory to that seen in renewable generation sectors with outcomes dependent on future energy scenarios.23
As noted by CSIRO (2018) and shown in Figure 16 below, hydrogen must be both affordable and sustainable if it is to diversify and supersede traditional energy sources and applications.
The multitude of potential use cases for hydrogen and the extent to which they can overlap and intersect presents both a challenge and an opportunity. The evolution of segments of the industry is not mutually exclusive but rather will be accelerated by nuanced and multi-faced points of adoption and turning points as the industry matures. In the context of emerging and complex production and offtake scenarios, the identified potential for a range of opportunities including that for mining operations shows clear promise but is largely not yet at commercial scale. The technical challenges and timelines for adoption will likely be addressed through a combination of integrated technology development programs, open innovation models and structural support.
Case Study: OZ Minerals Hydrogen Hypothesis
Opportunities for hydrogen in upstream copper production
Theoretically there exists a range of opportunities for green hydrogen in upstream copper production. For example, hydrogen could be used at a remote site as a way to store renewable energy and to generate and stabilise electricity. It could be used as a clean fuel or as a feedstock for a secondary process to produce other powerfuels, chemicals and green commodities.
Hydrogen as a fuel could be used to power vehicles and specialised equipment. It could also present opportunity for downstream processes and metallurgical applications.
The introduction of hydrogen into underground mining is likely to face some safety and regulatory challenges. However, there are open cut applications that are showing promise in the medium term including:
Hydrogen fuel cell application to mining vehicles and trucks.
The application of a production, generation, storage and power generation cycle to complement or replace battery and diesel hybrid systems in remote power service.
Longer term grid firming for intermittent and dispatchable renewable systems
There is evidence of several large mining companies that have made commitments to lower emissions including zero emissions goals including FMG, BHP, Rio Tinto, and Anglo American. All recognise that diesel consumption is a major source of emissions in the mining industry and are exploring ways to mitigate use. More recently a number of these miners are involved in various hydrogen projects, with some forming consortia to tackle specific technical application. An example of this is the Green Hydrogen Consortium. This group is comprised of BHP, Fortescue, Anglo American and Hatch who have come together with a broad scope to accelerate the application of hydrogen. The consortium’s members share progress and lessons learnt in an open environment and have committed to collaborate to address specific challenges.
Open cut copper operations place a high value on the mine planning flexibility provided by haul truck fleets and mobile excavators. This flexibility can allow for changes to the mine plan to optimise grade of material being extracted or change to the location of waste disposal at short notice.
A shift away from diesel vehicles can introduce constraints on the ability to quickly adapt. For example, conveyor dominated systems require years of forward planning, and similarly, overhead trolley assist systems cannot be moved to new mining areas at short notice without incurring significant cost.
As the industry looks to hydrogen, it is recognised that hydrogen haul trucks could offer the potential for both fast refuelling and flexible operations, when compared to alternatives.
In the long term, there is increasing confidence that the economic gap associated with alternate heavy-duty vehicles is closing and likely to bring increased choice to the industry.
Case Study: Hydrogen trucking developments
A comparison of battery electric vehicles versus hydrogen
Not surprisingly there is an increased level of debate regarding hydrogen and electrification when future mining equipment technology options are considered. Diesel fuel is currently the lifeblood of material movement in mining, supplying energy for light and heavy haulage across the material movement chain. The question of how diesel will be replaced in this role is a central one. Currently, there are essentially two central candidate power sources for electric haulage trucks: pure battery-electric vehicles (BEVs) and hydrogen fuel cell systems typically with a small onboard battery as an energy buffer.
Commitment to one system or another demands a significant investment of resources, not only in vehicles themselves, but in ongoing OEM R&D and at-site implementation development, workforce training, management systems, spare parts, ancillary equipment, and charging/fuelling infrastructure. The ultimate outcome of this technology race will have significant impact for OEMs and producers, especially given that many of these investment decisions will have to be made years in advance and while the outcome is still unclear.
The basic trade-off between the two technologies is one of performance versus simplicity. Hydrogen fuel cells are able to take advantage of the significantly higher energy density of hydrogen for storage and transfer. The basic energy density of hydrogen is immense: 120 MJ/kg equal to 33,300 kWh/kg which does not take into account the mass of the heavy pressure vessels needed to contain the gas, nor the fuel cell itself. The weights of these systems vary, but practical compressed- hydrogen systems have been known to have an effective energy density of 550-600 Wh/kg.24 While more modest, this still outperforms the energy density of typical lithium-ion battery technologies (120-220 Wh/kg) by a factor of three or more.25 This allows hydrogen vehicles to devote less onboard volume and mass to fuel and more carry more useful payload over a longer range. Hydrogen can be pumped much more rapidly than batteries can be charged, since no chemical reaction has to take place. Together, this means that hydrogen vehicles could theoretically spend more time on-shift and carry a greater proportion of load on each vehicle, leading to improved productivity and output.
The penalty for hydrogen systems is complexity. Lithium-ion batteries are heavy, but comparatively simple devices, while hydrogen vehicles have to store hydrogen in pressure vessels before circulating it to the fuel cell (FC), which in turn may be connected to a smaller battery for short-term bursts of power. Efforts have turned to super capacitors (SC) that are being used for short bursts of power, and hybrid FC+battery+SC control systems.
The resultant complexity means that hydrogen vehicles are expected to cost more in initial Capital Expenditure (CAPEX). Fuel cells also require dedicated fuelling infrastructure to transfer hydrogen, which in turn imposes additional cost. The additional step of converting electricity to stored hydrogen and back into electricity introduces inefficiencies, meaning that hydrogen vehicles consume more energy per kilometre, than equivalent BEVs.
To understand how this may play out, it is helpful to compare how things have unfolded in two areas where zero-emission vehicles are more developed than mine haulage: personal vehicles and long-haul road transport.
In personal vehicles, battery-electric vehicles are the clear current technological winner. After attempts to commercialise both types of vehicles in the early 2010s, battery-electric vehicles pulled ahead due to the declining cost of lithium batteries and a simpler roll-out of charging infrastructure. While hydrogen vehicles remain under development and more hydrogen fuelling stations are gradually being built, BEVs currently dominate the market. This is attributable to more mature technology, lower initial unit cost, and much more widely deployed charging infrastructure.
Long-distance road haulage is both more demanding and more sensitive to underlying efficiencies than personal transport. Here the outcome is less clear, with both BEVs and hydrogen vehicles being trialled in 2022.26, 27 As in potential mining haulage applications, vehicle duty cycle and fuelling times are crucial, which has led to a greater push for hydrogen trucking. However, at this time, hydrogen trucks are still restricted by fuelling infrastructure, which limits available routes.
When it comes to mine design, this restriction may actually be less important. This is because mining engineers have both the burden and freedom of choosing and installing their own infrastructure as part of the process of mine design.
In the short term, this may still bias operators toward electric vehicles, as modern mines will have at least some degree of electrical infrastructure, while hydrogen fuelling is more novel. In many cases, clever systems design can compensate for technology limitations.
One key example of this is in truck size: while classical diesel-electric design has trended towards larger and larger ultra-class trucks in the name of efficiency, current battery-electric vehicles are not yet able to provide drop-in replacements in this heavy haulage role. An electric ultra-class haul truck may not have the onboard energy storage to exit a very large pit in a single charging cycle, for instance, requiring either charging or trolley infrastructure to be built along the access road at additional cost.
Smaller trucks, however, may be able to make the trip without stopping. Initially, this may seem like a reduction in efficiency. However, the lower operating costs of electric vehicles, combined with reduced energy consumption from intelligent scheduling, and the ability to more precisely dispatch smaller loads to where they are needed, can actually improve overall system cost effectiveness and efficiency. As with all zero-emissions technologies, this is not necessarily a search for a simple swap-out of existing systems. Rather, mine site material movement designers should understand the interdependencies, so that systems are both cleaner and more profitable.
In the longer term, it is still unclear whether or not electric or hydrogen will be the ultimate power source of choice for mine haulage. It is likely from current technology trends that the performance of both system types will improve significantly, with lithium battery technologies increasing in energy density and hydrogen systems becoming cheaper and more mature. In the short-term, battery-electric vehicles have dominated adjacent transport spaces, but the driving factors behind the commercial space (a relative indifference to small performance differences and a need to rely on existing infrastructure or new publicly funded infrastructure) are not as relevant to a mining context. Ultimately, both technologies may prove viable, with the choice of a given system being context or site dependent.