Tag Archives: Shaft sinking

South32 making engineering and design headway at Hermosa project

A stellar set of annual financial results has provided the ideal backdrop for South32 to update shareholders on its rapidly progressing Hermosa project in Arizona, USA.

Released late last month, the company’s 2022 financial year results showed off record earnings of $2.6 billion, record free cash flow from operations of $2.6 billion and record return on invested capital of 30.1%.

With group copper-equivalent production expected to increase by 14% in the next financial year, South32 looked to be well leveraged to in-demand metal markets at the right time.

The company has progressively been repositioning its portfolio toward metals critical for a low-carbon future, having already established a pipeline of high-quality development options. One of these high-quality development options is Hermosa.

Hermosa, which the company acquired outright back in 2018 as part of a takeover of Arizona Mining, is key to the company’s critical metals pursuit, having exposure to base and battery metals that are expected to grow in demand – both domestically in the US and internationally.

It is being designed as South32’s first ‘next generation mine’, according to Hermosa President, Pat Risner, with a series of technical reports highlighting its use of automation and technology to minimise its impact on the environment and target a carbon-neutral mining scenario in support of the group’s goal of achieving net zero operational greenhouse gas emissions by 2050.

These same reports also highlighted the potential to develop a sustainable, low-cost operation producing zinc, lead and silver from the Taylor deposit, with the bonus of possible battery-grade manganese output for rapidly growing domestic markets from the Clark deposit.

In the latest results, the company said it was devoting $290 million of growth capital expenditure in the 2023 financial year to progressing Hermosa as it invests in infrastructure to support critical path dewatering and progress study work for the Taylor Deposit. This is ahead of a planned final investment decision expected in mid-2023, which should coincide with the feasibility study.

South32 is devoting $290 million of growth capital expenditure in the 2023 financial year to progress Hermosa

Some $110 million of this was assigned to construction of a second water treatment plant (WTP2) to support orebody dewatering at the asset, alongside dewatering wells, piping systems and dewatering power infrastructure.

An additional $95 million was slated for engineering and initial construction ahead of shaft sinking at the operation, plus work to support power infrastructure and road construction.

The remaining amount was expected to support work across the broader Hermosa project, including Clark study costs and the Taylor feasibility study.

All signs from these results are that the company is laying the groundwork to develop this project ahead of that mid-2023 deadline.

In another sign of progress, South32 recently signed a “limited notice to proceed” for shaft engineering and design at Hermosa with contractor Redpath, Risner confirmed, adding that the award represented a positive step forward for the project.

“We look forward to continuing our engagement with local communities and all of our stakeholders as we make further progress with the project,” he said.

Redpath will no doubt be evaluating the technical studies that have been signed off to this point and informing future reports.

The PFS design for Taylor is a dual shaft mine which prioritises early access to higher grade mineralisation, supporting zinc-equivalent average grades of approximately 12% in the first five years of the mine plan. The proposed mining method, longhole open stoping, is similar to that used at Cannington, in Australia, and maximises productivity and enables a single stage ramp-up to the miner’s preferred development scenario of up to 4.3 Mt/y.

Yet, the Clark deposit opportunity – which has become even more tantalising with the US Government invoking the Defense Production Act and supporting the production of critical metals including manganese – could see the plan change.

The company says it may accelerate the prefeasibility study for the Clark deposit, which is spatially linked to the Taylor deposit. A scoping study has previously confirmed the potential for a separate, integrated underground mining operation producing battery-grade manganese, as well as zinc and silver from the deposit.

South32 previously said Clark has the potential to underpin a second development stage at Hermosa, with future studies to consider the opportunity to integrate its development with Taylor, potentially unlocking further operating and capital efficiencies.

With a PFS selection study expected later this year, investors and interested parties will soon know the role Clark could play in the wider Hermosa project.

What is easy to gauge already is that Hermosa is progressing on a track that many other development projects in in-demand sectors have gone down.

Woodsmith Shaft Boring Roadheaders about to re-start cutting process

One of the most-watched shaft sinking projects in the sector right now is located in the UK, with the Woodsmith project in north Yorkshire having been on the radar for a number of reasons.

First off, it is a project that has changed hands recently.

Originally guided by Sirius Minerals, the 10 Mt/y project was acquired by Anglo American in 2020, a transaction that came with a fresh look at the whole project execution phase.

The change in ownership and re-assessment of plans drawn up by Sirius – a much smaller company guided by different investor pressures and operating procedures – led to Anglo American relieving DMC Mining, the lead shaft sinking contractor, of its duties.

Another reason for watching the project is the planned use of Shaft Boring Roadheader (SBR) technology from Herrenknecht.

After debuting at the Jansen potash project in Saskatchewan, Canada, where it excavated two 8-11 m diameter blind shafts down to circa-1,000-m-depth with the help of DMC as the contractor, SBR 2.0 – the second generation of the technology – was put to the test in Belarus at the Slavkaliy-owned Nezhinsky potash project. It ended up breaking shaft sinking records under the guidance of contractor Redpath Deilmann on a project to sink two 8-m diameter shafts (one to 750-m depth and one to 697-m depth).

Herrenknecht, with its experience in mechanised tunnelling, developed the SBR for the mechanised sinking of blind shafts in soft-to-medium rock. Based on the proven technology of the Herrenknecht Vertical Shaft Sinking Machine, the SBR offers improved safety performance compared with conventional shaft sinking methods while also achieving higher advance rates, according to the company.

The SBR is a 60-m tall, suspended shaft sinking machine, with 12 work decks and two service platforms. A telescopic, boom-mounted cutting head is used to precisely excavate rock via a partial-face cutting method. The cutting head works in a cycle, starting each cut from shaft centre to shaft wall, repeating until a layer of material is removed. Excavation proceeds in 1-m increments, followed by SBR lowering sequences.

The SBR was chosen for Woodsmith by Sirius over the conventional drill and blasting method due to its advantages in improving safety and schedule. This methodology, Sirius said, would allow the company to satisfy several operational objectives, moving away from the use of explosives and providing a safer, more predictable work method. Instead of a linear process, the SBR allows work to be completed concurrently as the shaft is sunk, as well as minimising damage to exposed host rock, and further improving safety while minimising downtime. Work decks above the cutting head allow workers to install shaft lining and tubbing as excavation continues, while a pneumatic mucking system removes waste rock.

The third generation of technology – which builds on the first two deployments with, among other things, the addition of two retractable robotic probes to test and grout the ground ahead for safer excavation and an additional control cabin on surface for more remote operation – is due to sink production and service shafts with 6.75-m diameters to depths of 1,594 m and 1,565 m, respectively, at Woodsmith based on the Sirius plan.

These SBRs are being supported by four triple sheaved winches from SMS SIEMAG and conveyors from Herrenknecht-owned H + E Logistik GmbH, among other support equipment.

Work on the service shaft commenced in 2021 with former Anglo American Chief Executive, Mark Cutifani, confirming in July of that year that the “first cut” with the SBR had taken place in the service shaft.

This progress was made while the company was still completing a detailed technical review on Woodsmith to ensure the technical and commercial integrity of the full scope of its design. This review has a particular focus on the sinking of the two main shafts, the development of the underground mining area, and the changes required to accommodate both increased production capacity and the more efficient and scalable mining method of using only continuous miners, Anglo American said.

Since the first cut was made in July 2021, however, Anglo American and Redpath Deilmann – which is now leading the sinking project as shaft sinking contractor – have been reviewing the existing plans for sinking with the SBRs, carrying out minor hardware changes on the machines and ensuring all staff have the appropriate training to facilitate the completion of the shaft sinking process. The Redpath Group is also involved in the drill-and-blast-based sinking for the materials transport system (MTS) shaft.

Various shaft sinking rates have been mooted in the past at Woodsmith, and Anglo American is currently working to develop the optimal solution for the facility based on technical standards.

The sinking at Woodsmith represents a different challenge to the two previous SBR projects conducted to this point.

For starters, there is no ground freezing expected to take place at Woodsmith – unlike what happened in Canada and Belarus. This process, while time consuming and only used to freeze unstable water-bearing strata around the shaft, can create more rock uniformity to aide consistent cutting rates.

There is also the MTS level to consider at Woodsmith, with plans to carry out lateral development work around the 360-m-level to join up the production shaft with this level where polyhalite ore will be transported along a 37-km tunnel to Wilton near the port. This means vertical cutting and loading may be halted while the MTS level connection is established.

All these factors, along with the performance of previous SBR work, will be incorporated into the engineering work Anglo American is carrying out at Woodsmith, but, in terms of the SBR, signs are that work on the service shaft could recommence shortly, with plans to start sinking in the production shaft by the end of the year.

Cementation, Sandvik and Micon achieve flexible raisebore-based sinking at Solvay Chemicals #5 shaft

Cementation Americas has announced the completion of the full faced raisebored raise at Solvay Chemicals #5 shaft in Green River, Wyoming, USA.

The project required the company to complete a 22 ft (6.7 m) diameter shaft, complete with concrete liner, from surface to a depth of 1,506 ft (459 m).

Concrete liner thickness increased as the depth of the shaft increased, so the initial concept was to complete a pilot slash raise with a raisebore drill and then slash from the top down to achieve the differing diameters to accommodate concrete liner thickness, the company explained. Cementation instead proposed a full face raisebored shaft solution with variable diameters for each section.

“We worked closely with Sandvik to design, engineer and manufacture a reaming head that could be diminished in diameter rather than manufacturing different diameters of outside wings,” Cementation said. “Final design allowed for five diameter options; maximum of 26.67 ft (8.1 m), down to 24.48 ft, in increments of 6.6 in (168 mm). The 26.67 ft. diameter reamer consisted of 12 individual sections, 46 cutters and weighed 136,000 lbs (61,689 kg).”

Following completion of 68 ft deep collar excavation and lining, Cementation’s Strata 950 Raise Drill was set up over the collar and a 16 in diameter pilot hole was drilled with Micon’s rotary vertical drilling system (RVDS). When the completed pilot hole was surveyed, the total deviation from vertical was found to be less than 4 in over entire length of pilot hole, according to the company.

Based on the pilot hole survey, it was determined that the first leg of the shaft would be reamed to 26.13-ft diameter for 588 ft of shaft, followed by 25.02-ft diameter for the next 285 ft of shaft and 24.47-ft diameter for the final 535 ft of shaft to surface.

Reaming of the shaft was completed on April 24 and the Cementation shaft crews are now in the process of completing the shaft lining.

This raise was one of the largest ever pulled in the Americas and was completed without incident, the company noted.

Its success was the result of a collaborative effort by all parties involved by providing the best technical solution for the Solvay Chemicals #5 Shaft, which is part of the company’s trona operations in Green River.

Pictured is the Solvay reaming head at the Sandvik workshop in Sudbury, Ontario, Canada

Master Drilling talks up MTB 2.0 as it progresses work on Shaft Boring System

Master Drilling Group’s annual results presentation provided a few eye-opening updates on the company’s mechanised mine development fronts, with Director, Koos Jordaan, highlighting a potential first deployment of the company’s Shaft Boring System (SBS) at Royal Bafokeng Platinum’s Styldrift mine in South Africa.

A raiseboring specialist that has diversified into other complementary areas over the last decade, Master Drilling has consistently devoted capital towards its technology developments.

During the 2021 annual results presentation, Jordaan confirmed that the company had started tunnelling work on an exploration decline at Anglo American Platinum’s Mogalakwena PGM mine in South Africa, using its Mobile Tunnel Borer (MTB), as well as highlighted the ongoing development of a next-generation design that would cater to the industry need to safely and quickly establish twin declines for mine access.

The MTB is a modular horizontal cutting machine equipped with full-face cutter head with disc cutters adapted from traditional tunnel boring machines. Unlike these traditional machines, it is designed to work both on inclines and declines, with the ability to navigate around corners and construct 5.5-m diameter decline access tunnels.

Having initially been tested in a quarry in Italy in soft rock, it then made the trip back to South Africa to carry out a 1.4 km project at Northam Platinum’s Eland platinum group metals operation in South Africa, in harder rock. This project was terminated in March 2020 due to the COVID-19 pandemic. Last year, however, the company announced it had signed an agreement with Anglo American Platinum to deploy the MTB at Mogalakwena as part of a turnkey contract to sink an exploration decline.

On the development of MTB 2.0, Jordaan said: “We are already working on the second-gen MTB being confident that the concept provides competitive value versus the past as well as other current developments.”

He said the company envisioned future projects using two MTBs simultaneously to establish traditional twin declines for access to underground mines for fast access from “A-to-B” and a quick turnaround to steady-state mining operations.

The company is also carrying out early-stage work with Element Six and the De Beers Group on cut and break technology which, when applied in tandem with the use of the MTB, could enable even more continuous cutting applications.

Element Six, as a company, was established to harness the unique properties of synthetic diamond (polycrystalline diamond or PCD) and tungsten carbide to deliver supermaterials that improve the efficiency, performance and reliability of industrial tools and technology. One of the obvious applications was in hard-rock cutting where OEMs have trialled PCD materials.

Jordaan said the company could leverage cut and break technology with MTBs to create flat floors and breakaways, allowing the circular MTB to continue cutting the face without stoppages.

Looking at vertical developments, Jordaan also provided an update on the SBS.

This machine was initially billed as a blind shaft boring system able to sink 4.5-m diameter shafts in hard-rock down to 1,500 m depth.

Last year, Jordaan said it planned on introducing a “smaller scope system” as part of its introduction to the industry, adding that it had signed a letter of intent with a prospective South Africa project that could see a machine start sinking activities in the first half of 2022.

In the most recent update, he said the letter of intent was with Royal Bafokeng Platinum’s Styldrift mine.

“We are now building the SBS and working towards hopefully converting the letter of intent from RB Platinum to a contract award; we already engaged with them in investigation and readiness work should approval be granted,” he said.

The first SBS being built is a 4.1-m-diameter scope machine with a capability of sinking shafts up to 1,500 m depth, according to Jordaan, who explained that this “smaller shaft scope” was part of a plan to lower the machine’s implementation cost.

“But we are already engaged with opportunities regarding a larger scope of service,” he clarified. “The cost benefit of this method drastically increases as the scope increases versus conventional sinking.”

Aside from the MTB and SBS projects, Jordaan said the company was working on the LP100 development project for its raiseboring division. This is a highly mobile and high-capacity articulated wheel carrier to carry out up and down slots, as well as smaller raiseboring holes, remotely, he explained. At the same time as this the company is looking at developing electric track carriers for its raisebores that, when applied, would come with a much lower carbon footprint.

This came on top of plans for a new box hole boring machine, two new core drilling rigs – one for underground and one for surface – and an experimental rock cutter machine it is working on with African Rainbow Minerals in South Africa.

Anglo American signals design changes at Woodsmith polyhalite project

Anglo American has outlined plans to change elements of the design at its Woodsmith polyhalite project in the UK, which will have a bearing on both the sinking of the two main shafts and development of the underground mining area at the project.

The company has been running a detailed technical review on Woodsmith since mid-2020 to ensure the technical and commercial integrity of the full scope of its design. This followed the acquisition of the asset as part of a takeover of Sirius Minerals earlier that year.

“Now largely complete, the review has confirmed the findings of Anglo American’s due diligence that a number of elements of the project’s design would benefit from modification to bring it up to Anglo American’s safety and operating integrity standards and to optimise the value of the asset for the long term,” the company said.

Anglo is also making a change to the leadership at Woodsmith following its integration into Anglo American and ahead of the full project execution phase. Tom McCulley, who has led the development of the Quellaveco copper project in Peru, will take over from Chris Fraser as CEO of Crop Nutrients. This will see Fraser step aside and take on a strategic projects role for Anglo.

“The Woodsmith team is further developing the engineering to optimise the configuration of the project, recognising the multi-decade life of the mine,” Anglo said.

Particular attention is on the aspects identified at the outset of Anglo American’s ownership – namely, the sinking of the two main shafts, the development of the underground mining area, and the changes required to accommodate both increased production capacity and the more efficient and scalable mining method of using only continuous miners, it said.

The sinking of the two main shafts is due to be carried out using Herrenknecht’s Shaft Boring Roadheader (SBR) technology. DMC Mining, a company familiar with the technology thanks to its work sinking shafts at Jansen in Saskatchewan, Canada, was previously tasked with sinking the production and service shaft, each around 1,500 m deep, and two smaller shafts associated with the materials transport system, each approximately 350 m deep. Its contract was ended in 2020.

These improvements will, the company said, require the installation of additional ventilation earlier in the development of the underground mining area.

“Anglo American expects that these changes to the design of the mine infrastructure – which will result in a different, enhanced configuration and therefore a different construction and production ramp-up schedule – will ensure that its exacting standards are met and the full commercial value of the asset is realised,” the company said.

Mark Cutifani, Chief Executive of Anglo American, said: “We are very happy with the high quality and exciting potential of Woodsmith, with the scale and quality of the polyhalite orebody pointing to a quartile one operating cost position and strong margins. This is a very long-life asset and we are going to take the necessary time to get every aspect of the design right to match our long-term vision and value aspirations.

“We have said from the outset that we expect to make improvements and that we will execute certain elements of the construction differently and with a more conservative schedule. We expect to have completed our design engineering, capital budget and schedule at the end of 2022, with a fully optimised value case that recognises the upside potential we see in Woodsmith, and we will then submit the full project to the board.”

In the meantime, construction of the major critical path elements of the project, principally the two main shafts and the mineral transport tunnel, is progressing, with approximately $700 million of capital expected to be invested in 2022, Anglo said.

The plan at Woodsmith under previous owners Sirius was to extract polyhalite via two mine shafts and transport this outside of the National Park to Teesside on a conveyer belt system in an underground tunnel. It would then be granulated at a materials handling facility, with the majority being exported to overseas markets. The company was previously aiming to achieve first product from the mine by the end of 2021, ramping up to an initial production capacity of 10 Mt/y and then full production of 20 Mt/y.

The changes to McCulley’s and Fraser’s roles are effective January 1, 2022. Anglo American has appointed Adolfo Heeren as CEO of Anglo American in Peru, effective from the same date. Heeren will work together with McCulley during the first half of 2022 to ensure a smooth transition from the construction and commissioning phase of Quellaveco into operations, expecting first copper production in mid-2022.

RUC Cementation Mining to carry out shaft work on Western Areas’ Cosmos nickel op

RUC Cementation Mining Contractors is set to carry out the shaft infrastructure design, construction and equipping for the Cosmos nickel operations in Western Australia after signing a contract with mine owner, Western Areas Ltd.

This contract represents the culmination of an engagement that has been ongoing for some six months, not including the excavation works which RUC is completing, having recently successfully holed the top leg of the shaft, RUC said.

“Furthermore, this cements a long-term relationship between both companies that spans over 15 years,” it added.

In Western Areas’ 2021 financial year (to June 30, 2021), capital investment at Cosmos totalled A$84 million ($63 million) for the year as the Odysseus mine construction activity increased, including full mobilisation of the underground mining contractor with over 3 km of underground decline and capital development being completed.

Odysseus mine development reached first ore earlier this month, with the raisebore back reaming having worked through 630 m of development at a diameter of 5.7 m, completing Leg 1 of the shaft hoisting and intake air system.

At the time, Western Areas Managing Director, Dan Lougher, said: “It is an exciting milestone to reach first ore and we now look forward to continuing ore production and construction activities, while also advancing offtake tenders for new nickel sulphide supply into the class 1 nickel market.

“The raisebore breakthrough (pictured) is also a key achievement that further de-risks project delivery and allows completion of the shaft sub-brace concrete works, as well as remaining surface civil works, associated with the shaft. Importantly, the work was completed without a safety incident, for which credit must be given to the site management team and RUC, the raise bore contractor.”

Byrnecut assigned to Wira shaft sinking at OZ Minerals’ Prominent Hill operation

OZ Minerals, in its latest quarterly results, has confirmed that Byrnecut Group will sink the Wira shaft at its Prominent Hill copper-gold operation in South Australia.

Byrnecut has extensive experience of shaft sinking in the Asia-Pacific region, according to OZ. It is also the underground mining contractor at its Prominent Hill and Carrapateena mines, which, the miner says, will assist in the integration of activities as it continues to increase production rates from Prominent Hill.

Back in August, the OZ Minerals Board approved construction of a hoisting shaft at Prominent Hill, paving the way for a mine life extension and throughput expansion.

Coming with a pre-production capital expenditure of A$600 million ($449 million), the Wira Shaft expansion project will see the underground production rate increase to 6 Mt/y from 2025. At this point, the average annual copper and gold production is expected to be circa-54,000 t and circa-108,000 oz, respectively, some 23% more than expected in the current trucking operation.

Back then, OZ said sinking of the shaft was expected to commence in the March quarter of 2022. Mining and installation of underground and surface infrastructure was scheduled for completion along with commissioning of the Wira shaft at the end of 2024, with nameplate capacity expected in the first half of 2025.

In an update last week, OZ said the shaft collar construction site works had commenced and were due for completion in January 2022.

“The award of the shaft sink contract followed after a lengthy period of Early Contractor Involvement working through various contractors’ proposals and then selecting the best for project outcome with reduced risk and an effective delivery period at an economic cost,” it said. “The designs for the shaft sinking equipment are progressing well. Orders have been placed on the mill runs for the headframe steel with delivery scheduled for December 2021.”

The shaft design comprises a 1,329-m-deep, concrete-lined shaft with a diameter of 7.5 m. Construction of the shaft will be via conventional strip and line method, with the sinking period approximately two years.

The shaft mine expansion also enables generational province potential with further mine life extensions possible as 67 Mt of resource remains outside the shaft expansion mine plan, OZ Minerals says. Further, an exploration program has also identified that mineralisation remains open at depth beyond the current resource boundary, potentially accessible via the shaft.

Prominent Hill produced 17,565 t of copper and 41,245 oz of gold in the September quarter.

UMS gearing up for shaft sinking work at Karowe Underground

With a team comprising some of the most experienced professionals in shaft sinking, United Mining Services (UMS) says it is gearing up for the pre-sinking of two shafts for the Karowe Underground Mine Expansion Project (UGP) in Botswana.

Following the completion of the feasibility study for the Karowe UGP, UMS was appointed by Lucara Botswana Pty Ltd and JDS Energy & Mining Inc in October 2019 to engineer and design the shaft sinking of the production shaft (8.5 m in diameter), and the ventilation shaft (6 m diameter), both reaching a depth of approximately 750 m below surface.

Fully commissioned in 2012, Karowe is an open-pit diamond mine with operations until 2026. The UGP will extend Karowe’s mine life to at least 2040. At the end of 2020, Karowe’s total probable reserve stood at 53.9 Mt containing 7.4 Mct including stockpiles.

According to Lucara, the Karowe mine remains one of the best producing mines of high quality plus-10.8 ct diamonds, having yielded five of the 10 largest diamonds in recorded history. It is also the only mine to have recovered three diamonds greater than 1,000 ct.

Dr Pieter Louw, Group Executive Project Services at UMS and UMS’ Project Manager, says the company’s wealth of knowledge and expertise in shaft sinking played a key role in securing the contract, and that the company is bringing in the heavyweights in the industry for the project.

Louw, himself, has a long history in underground mining and shaft sinking, having worked for major players in the mining and engineering sectors. He was involved in the De Beers Venetia Underground Project feasibility study, as well as a number of other feasibility projects for mines that are now in development or have already started production.

Louw explains that the two shafts at Karowe will be blind sunk using conventional drill and blast techniques. The production and ventilation shafts will both have equipment installed to pre-sink to a shaft depth of 100 m, if required, to accommodate the main sink shaft equipment. The pre-sink phase also allows the sinking process to commence as soon as possible while the main sink infrastructure is being fabricated and installed.

The new underground mine’s production shaft will have an A-frame type headgear, which will hoist 21-t payload skips, and will have a single drum auxiliary winder for people movement, and a man/material winder with counterweight and a big cage to service the underground.

UMS has refurbished four winders, which will be going to the mine for shaft sinking, including two stage winders and two Kibble winders. The company also purchased and refurbished Scotch derrick winder cranes for the pre-sink.

Louw says that UMS is in the process of mobilising up to 170 people to site for the pre-sink, which is expected to commence at the end of August and will take between eight and 12 months to achieve changeover ready for the start of the main sink. The main sink will take another two years after that, ready for mine development to commence in 2024, and full underground operations in 2026.

To make sinking safer, Louw says that UMS has adopted different sinking methodologies and equipment to be used at Karowe.

“In the past, we used to sink with cactus grabs which needed people in the bottom,” Louw said. “We are now using vertical shaft muckers and are buying state-of-the-art jumbo drill rigs to drill at the bottom. We’re doing inline work as opposed to concurrent work with people working at the bottom.”

He adds that, as part of its safety management plan, UMS has established a training centre on site at Karowe that facilitates inductions and training of local operators on the various equipment. The company is constructing a mock-up training tower on the surface to train operators on vertical shaft muckers and will have a similar training simulator for excavator operators.

Louw says UMS is fully established in Botswana and has partnered with Botswana Investment and Trade Centre to ensure that the project work permits run smoothly. Furthermore, the UMS design engineers are registered with the Botswana certification boards and can sign off all engineering designs and drawings for the project.

OZ Minerals Board gives go ahead for shaft expansion at Prominent Hill

The OZ Minerals Board has approved construction of a hoisting shaft at the Prominent Hill copper-gold mine in South Australia, paving the way for a mine life extension and throughput expansion.

Prominent Hill mine began operation in 2009 as an open pit and is now an underground mine producing 4.5 Mt/y, moving to 4.5-5 Mt/y from 2022 via a trucking operation.

Coming with a pre-production capital expenditure of A$600 million ($436 million), the Wira Shaft expansion project will see the underground production rate increase to 6 Mt/y from 2025. At this point, the average annual copper and gold production is expected to be circa-54,000 t and circa-108,000 oz, respectively, some 23% more than expected in the current trucking operation.

The study leverages close to 100 Mt of mineral resources outside the previous Prominent Hill ore reserves of 38 Mt of underground material.

Sinking of the shaft is expected to commence in the March quarter of 2022. Mining and installation of underground and surface infrastructure is scheduled for completion along with commissioning of the Wira shaft at the end of 2024, with nameplate capacity expected in the first half of 2025.

The shaft design comprises a 1,329-m-deep, concrete-lined shaft with a diameter of 7.5 m. Construction of the shaft will be via conventional strip and line method, with the sinking period approximately two years.

The shaft mine expansion also enables generational province potential with further mine life extensions possible as 67 Mt of resource remains outside the shaft expansion mine plan, OZ Minerals says. Further, an exploration program has also identified that mineralisation remains open at depth beyond the current resource boundary, potentially accessible via the shaft.

Announcing the expansion today, OZ Minerals Chief Executive Officer, Andrew Cole, said: “We are thrilled to see a long and productive future for Prominent Hill with the Wira shaft mine expansion enabling access to areas previously thought uneconomic and opening up potential new prospects.

“Prominent Hill is a quality orebody and remains open at depth. The reliable performance of the operation and its consistent resource to reserve conversion rate were all influential in the decision.”

For the first time, the company has used a carbon price in determining the project valuation, a practice it plans to adopt in other OZ Minerals projects going forward, Cole said.

The company plans to reduce its underground loading fleet to eight vehicles, from nine after the shaft expansion, with its trucking fleet going from circa-14 to five, post-shaft.

Scope 1 emissions intensity per tonne of concentrate are also expected to drop from 0.47 t CO2-e/t to 0.28 t CO2-e/t after the shaft installation.

The pre-production capital of A$600 million, which was an increase on the A$450 million outlined in the November 2020 expansion study, enables transformation of the site in line with the strategic aspirations of OZ Minerals, it said.

Provisions have been included in site capital projections to support this transformation, including progressing underground fleet electrification, upgrading some of the existing infrastructure, remote operation capability and automation.

The company expanded on this: “A battery-powered mining fleet is part of the future vision as OZ Minerals moves towards its zero-carbon emission aspiration. For this study, diesel trucks were assumed. However, installation of enabling infrastructure is included in the Prominent Hill Expansion case to minimise future disruptions when the switch to an electric fleet occurs. This, implemented as part of the asset’s site-wide electrification aspiration, would contribute to a further reduction in Scope 1 emissions.”

A pilot study is also being undertaken to review a low-energy dry grinding option. The Prominent Hill Expansion Study is not directly connected to, nor dependent on this ongoing work, however, the work presents potential future cost reduction and other opportunities, OZ Minerals said.

UMS to start pre-sinking work at Lucara’s Karowe Underground Expansion project

Lucara Diamond Corp’s Karowe Underground Expansion project (UGP) in Botswana is moving ahead with mobilisation of shaft sinking teams commencing late in June, and pre-sinking activities scheduled in the September quarter.

The Karowe UGP, which is expected to extend the operation’s mine life to 2040, is in a fully-financed position, with the latest schedule expected to see underground production hit full production by the end of 2026.

The 2019 feasibility study for the project envisaged life of mine production of 7.8 Mct, a payback period of 2.8 years and an after-tax NPV (5% discount) of $718 million; all from $514 million in pre-production capital.

COVID-19 delays have pushed the project off the original schedule – both in terms of timeline and cost – but the company says it is now making headway towards a 2026 start to underground production.

Lucara said no “material variances” between the 2019 feasibility study and the current execution plan have resulted, despite the delays.

“Rather, during this period in 2020 and 2021, all critical path items were addressed and a concerted effort was placed on detailed design, engineering and procurement which have helped to significantly de-risk the project,” it said.

Out of the total capital budget, the company has spent $51.4 million on project execution activities through 2020 until the end of June 2021, including shaft and geotechnical engineering, procurement of long lead time and essential shaft sinking items, surface infrastructure and construction activities, bulk power supply power line engineering and procurement.

Mobilisation of the shaft pre-sink team has commenced with shaft pre-sinking on track to commence in the middle of the current quarter.

Detailed engineering and design of the underground infrastructure and layouts will commence this quarter and are expected to be competed in the September quarter of 2022, with no major changes from the 2019 study plan anticipated.

Underground mine development is scheduled to commence in the second half of 2024 with underground production ramp up starting in 2026. Full production is scheduled for the end of 2026.

At the same time, open-pit mining operations have been adjusted to limit the risk of production shortfalls during the ramp up of the underground mine operations commencing in the first half of 2026. The open-pit mine is expected to terminate in mid-2026, Lucara said.

Access to the underground mine will be via two vertical shafts, the production and ventilation shafts. The shafts will be concrete lined with the production shaft acting as the main air intake and the ventilation shaft as the exhaust.

The number of shaft stations and nominal elevations remain the same as the feasibility study, with the planned depth of the production shaft still at around 767 m. The final planned depth of the ventilation shaft has, however, increased marginally to 733 m, from 716 m.

A 7,200 t/d shaft operation using long hole shrinkage (LHS) mining will provide an additional 13 years of mine life to the Karowe operation after a five-year construction period. The 767-m-deep production shaft will be equipped with two 21 t skips for production hoisting and a service cage for man and material movement through the mine. This shaft will also serve as the main fresh air intake to the mine.

The pre-sink construction contract and shaft sinking equipment procurement were awarded to UMS Botswana and UMS South Africa, respectively. METS International Ltd, a subsidiary of UMS, was awarded the shaft engineering contract.

The company explained: “Detailed design and engineering work on the production and ventilation shafts is now 90% complete, and has resulted in the following changes to the 2019 feasibility study: i) production shaft diameter has increased from 8 m to 8.5 m, ii) ventilation shaft permanent headframe, hoists and internal conveyances have been removed, iii) parallel pre-sinking of both shafts, iv) ventilation fans and coolers to be located on surface, v) in-shaft grouting of water strikes changed from grout curtain installation from surface, vi) planned development of an additional sublevel to assist in drilling of drawbells, and vii) removal of 670L de-watering galleries.”

Increased schedule time related to shaft sinking has been a result of the increased production shaft diameter, time allowances for in-shaft grouting during sinking operations planned at known water strike horizons, holing through all shaft stations between shafts and additional ground support for underground stations/level breakouts, the company said.

UMS is in the process of mobilising crews to Karowe to initiate pre-sink works. Pre-sinking of the two shafts will run in parallel and start with mobile cranes and then transition to Scott Derrick cranes with the final depth of pre-sink at around 40 m below surface.

With the exception of an additional sublevel (340L) to assist with drill and blast of drawbells, the design, layout and infrastructure of the underground mine all remain aligned with the 2019 feasibility study, the company noted.

Temporary power for shaft sinking is required until such time as the upgrade bulk power supply infrastructure is commissioned in the December quarter of 2022. A three-phased ramp up of the generator capacity is planned to support the increasing power requirements related to the shaft sinking activities.

A power supply and services contract for the temporary generators has been signed with Aggreko International Projects Ltd. Mobilisation has been initiated with the generator pad established. Commissioning of Phase 1 is scheduled during the September quarter to support the start of pre-sink activities.

The Karowe UGP is targeting the substantial resources remaining below the economic extents of the open pit in the South Lobe.

The LHS method is planned to systematically drill and blast the entire lobe on a vertical retreat basis. In LHS, a significant proportion of the blasted muck is left in the stope during blasting and stoping to stabilise the host rock with only the swell extracted during the drill and blast phase. Mucking will take place from draw points from the 310L extraction level. Once the column is fully blasted, the stope will be drawn empty by mucking the draw points.

The bottom-up approach of the LHS mining method takes advantage of the higher value EM/PK(S) kimberlite unit at depth in the South Lobe at Karowe, and balances high initial capital costs with low operating costs while de-risking the project with respect to the geotechnical and hydrogeological aspects of the host rocks, according to Lucara.

A revised project cost and schedule has been developed that captures the detailed engineering and design work through 2020 until May 2021, incorporating all changes, improvements, and COVID-19 related delays. Overall capital expenditures, including contingency, have increased marginally by some 4%, to $534 million, driven by the increase to the production shaft diameter and additional mine development.

The schedule to 75% of full production has increased by 1.3 years, driven mainly by COVID-19-related delays to commence the shaft pre-sinking and additional planned time for shaft station break-outs and ground support, Lucara added.

During 2020, Lucara negotiated and signed a self-build agreement with the Botswana Power Corp (BPC) for the construction of two substations and a 29-km-long 132 kV transmission line from BPC’s newly established Letlhakane substation to the Karowe mine. The planned route follows an existing regional 400 kV line and then runs parallel to the existing 11 kV transmission line currently supplying bulk power to the Karowe mine.

The new power infrastructure will provide the required power for the current open pit, processing plant and the underground mine expansion. Commissioning of and handover to BPC is scheduled for the December quarter of 2022. Construction of substations is scheduled to commence this quarter and power line construction in the March quarter of 2022, the company said.

JDS Energy & Mining Inc is the engineering procurement and construction manager for the execution of the Karowe UGP and is currently building up the on-site project team in conjunction with Lucara’s owners team and working in close cooperation with the Karowe Diamond Mine operations team.