Tag Archives: diamonds

TOMRA Mining to demonstrate Final Recovery diamond sorter at Electra Mining 2022

TOMRA Mining will showcase its sensor-based sorting solutions at the Electra Mining 2022 exhibition, in Johannesburg, South Africa, in September, showcasing, for the first time, live demonstrations of its COM XRT 300 /FR Final Recovery sorter for diamond operations.

Representatives from its Sales and Field Service teams will also present TOMRA’s offering of advanced digital products and services, such as the TOMRA Insight cloud-based platform and its latest generation TOMRA ACT PC-based system, as well as its portfolio of sorting solutions for the diamonds, metals and industrial minerals industry at the show, which runs from September 5-9.

Corné de Jager, Diamond Segment Manager TOMRA Mining, said: “The Electra Mining Show is the perfect platform for us to showcase TOMRA’s advanced mining solutions. This important exhibition attracts a wide audience – from operators and metallurgists – interested in smart solutions that are simple to operate and maintain, to decision makers who need to be up to date with the latest value-adding technologies. At the event we will have the opportunity to meet them face-to-face and discuss their requirements, giving them a taste or TOMRA’s collaborative approach, product expertise and after-sales support.”

TOMRA will demonstrate the Final Recovery sorter with fine kimberlitic or alluvial ore together with diamond powdered tracers in a Final Recovery and Sort House application. Visitors will be able to experience first-hand the sorter’s capability to produce an ultra-high diamond-by-weight concentrate with an exceptionally low yield by using TOMRA’s proprietary ultra-high-resolution sensor, advanced new image processing and high-precision ejector valve system, the company says. The sorter offers 100% diamond detection within the specified size fraction and > 99% guaranteed diamond recovery with appropriate feed material preparation.

“We are very excited to demonstrate the TOMRA COM XRT 300 /FR sorter,” de Jager says. “It completes our unique partnered diamond recovery ecosystem, which covers the entire process. We are now able to offer our customers a full XRT solution to sort +2-100 mm particles: +4-100 mm particles with our bulk concentration sorters, and +2-32 mm particles with the COM XRT 300 /FR in its Final Recovery, Sort House or small-capacity exploration applications. The sorter offers higher efficiency, better grade, simplified security requirements with fewer sorting stages and a smaller footprint. It reduces complexity and operational costs, and unlocks the potential for previously deemed non-profitable projects and marginal deposits to be economically viable. ”

The COM XRT 300 /FR sorter can also add value to existing kimberlitic and alluvial operations that use conventional bulk-concentration methods like rotary pans, dense medium separation or X-ray luminescence, if installed in a Final Recovery and/or Sort House function after these existing processes. With a contained capital expense, operations can benefit from a quick, simple and significant revenue gain, TOMRA says.

The TOMRA team at the exhibition will explain the full benefits of its complete partnered diamond recovery ecosystem consisting of XRT technology covering the entire process – from Bulk Concentration to Final Recovery and Sort House applications – as well as its advanced digital products and services. These include the newly refreshed TOMRA ACT PC-based system interface and TOMRA Insight cloud-based subscription solution.

TOMRA Mining has 190 sorter installations operating around the world, of which more than 60 are in Africa. It offers installation opportunities in Africa in the metals industry, for example in applications such as lithium, chromite, platinum, manganese and gold.

WEC Projects devises sewage treatment plant plan for Mothae diamond mine

WEC Projects, a South Africa-based EPC contractor specialising in water and wastewater treatment solutions, says it will soon complete the installation of a new WEC Model B packaged sewage  treatment plant at the Mothae diamond mine in Lesotho.

The mine is 70% owned by Lucapa Diamond Company and 30% by the Government of Lesotho.

Rudolf de Koning, Sales Representative at WEC Projects, says: “The mine lacked a sustainable sewage solution. Producing 60 cu.m of domestic raw sewage per day, Mothae utilised honeysuckers – sewage trucks – to dispose of the sewage at the nearest disposal facility, almost 130 km away. This was obviously a very costly method of sewage disposal. WEC proposed the installation of its Model B conventional activated sludge treatment plant with a daily capacity of 80 cu.m, which allows for future upgrading and expansions of the mine operations.”

The R3.2 million ($194,817) installation is a combined activated sludge and clarification treatment plant. Its modular design simplifies the logistics involved in transporting to the site and simplifies assembly as well as ensures a smaller overall footprint, according to WEC Projects. The Mothae installation also integrates a Wastemaster that includes screening, de-gritting and oil removal to cope with fats and oils present in the sewage which could adversely affect the aerobic process in the plant’s reactor. The Wastemaster removes the oils, fats and non-biodegradable material upstream from the treatment process. The plant will treat the mine’s grey and black water piped to the current septic system.

“Besides the high fat and oil levels, another factor which could affect the treatment plant’s effectiveness was the high altitude of the site which results in low, fluctuating temperatures,” de Koning explains. “The biological population growth occurs optimally at around 19°C and above. In order to ensure the proper ambient temperature is maintained, the plant will be assembled within a larger enclosed facility.”

In addition to making the mine more environmentally compatible through the effective treatment of its domestic sewage, the plant also reduces the costs of transporting waste to the nearest disposal facility, it says. Another consideration is that water availability reduces considerably in the area during the winter. The new plant can help the mine reduce its water consumption.

Thato Tsephe, Project Foreman at Mothae, says: “We worked closely with WEC Projects on-site to develop a sustainable solution. WEC Projects had previously installed a sewage treatment plant at the neighbouring Letseng Mine and it was that facility that encouraged us to approach them. What is critical for us, what is critical for us is to complete the civil works and installation and commissioning of the plant during the winter season with the harsh climate posing many challenges.”

Concor to construct new pollution control dam at Venetia Underground Project

Leading South Africa-based, black-owned contractor Concor is engaging on a 17-month project to construct a new pollution control dam at De Beers’ Venetia diamond mine, South Africa’s largest diamond producer.

The well-advanced Venetia Underground Project (VUP) will extend the mine’s life span to at least 2045, and the new dam – Pollution Control Dam 3 (PCD3) – is the main containment facility in its Storm Water Management Project (SWMP). The SWMP is a key part of the mine expansion, ensuring compliance with the Government Notice R704 on the protection of water resources, preventing the possibility of flooding and ensuring the safety of people working in the new underground mine.

Concor Operations Executive, Christo Schoeman, explains that PCD3 will cover some 27 ha to the west of the mine and will be constructed to a maximum height of 13 m. This will equip the facility to hold over 1 million cu.m of water. The water will emanate from upstream catchments including runoff from the adjacent coarse residue deposit and fine residue deposit, as well as potential overflow from the other upstream water containment facility. It will also contain water that has been pumped out the of mine’s open-cast pits and the VUP underground workings.

“Zero harm to our employees and the environment whilst executing our projects remains our principle objective,” Schoeman says. “In order to prioritise these endeavours and ensure that construction work does not impinge on the mining operation itself, among the first tasks required will be to secure the works by installing a new security fence, and upgrading the existing access road to our temporary site facilities which will ensure optimised access to our site and help streamline our workflow.”

As part of the bulk earthworks operations, the topsoil over the dam area will be stockpiled during the excavation operations, to be used later for slope protection and to ensure the regrowth of flora once construction is completed.

“In line with environmental requirements and legislation, the excavated structure will be lined with am HDPE geomembrane to prevent any seepage into the groundwater system,” he says. “A specialised service provider will supply and install the lining.”

Concor’s scope of work includes the construction of a pump station and dam spillways, as well as the installation of a 2.5 km return water pipeline to the mine’s processing plant. This will allow significant volumes of water to be efficiently recycled and re-used in processing, it says.

Schoeman highlights that the project contains a strong local procurement, employment and skills development component. He notes that Concor has always been committed to local enterprise and skills development initiatives in the areas where it undertakes projects.

“We are working closely with our client to source general workers and suppliers locally, who we will, where necessary, upskill with training, supervision and mentoring,” he says. “Certain aspects of the project can be subcontracted to these local enterprises, following the systematic process of identification and engagement.”

Concor supervises the work of subcontractors closely as part of its enterprise development commitments, he notes. Combined with dedicated mentoring, this ensures not only a quality outcome in each deliverable, but also higher levels of sustainability amongst subcontractors once the project is complete.

African Star appoints new mining contractor at Oena diamond mine

Southstone Minerals Ltd’s 43% owned subsidiary, African Star Minerals, has entered into a contract mining and diamond recovery agreement with Oryx Mining for the Oena diamond mine, in South Africa.

Oryx, at its own cost and expense, will provide and maintain all the plant and equipment as required to perform the mining services, Southstone says.

The diamonds produced by Oryx will be sold via a designated tender facility in South Africa and 80% of the gross income of net diamond sales, less commission, will be paid to Oryx for the duration of the 36-month agreement, the company explained. For any individual stones recovered with a gross selling price, less commission, of greater that ZAR10 million ($664,529) Oryx will be paid 70% of the gross income.

Oryx specialises in the processing of alluvial diamond deposits in South Africa and the operation is currently targeting to operate 24 h/d, six days a week with total headfeed capacity of 200 t/h. Equipment and road building is ongoing, and it is expected production will commence in May 2022.

The contract award follows the conclusion of mining by another contractor, Bluedust 7 Propriety Ltd.

Oena consists of an 8,800-ha mining right located along the Orange River in a well-established alluvial diamond-mining province that produces high quality and large sized diamonds.

TOMRA continues to build ore sorting Insight across mining space

Some 18 months after launching TOMRA Insight to mining customers, the cloud-based data platform is making inroads across the North American mining sector, Harold Cline and Jordan Rutledge told IM on the side lines of the MINEXCHANGE 2022 SME Annual Conference & Expo in Salt Lake City recently.

TOMRA rolled out the subscription-based service to mining back in late 2020, with one of the early adopters being the Black chrome mine in South Africa, one of two mining projects that form the basis of the Sail Group’s plans for long-term sustainable chrome production.

TOMRA Insight, the company says, enables sorting machine users to improve operational efficiencies through a service that turns these machines into connected devices for the generation of valuable process data.

Cline and Rutledge, both TOMRA Sorting Area Sales Managers for North America, said numerous customers were now taking advantage of TOMRA Insight across the region, with many more interested in leveraging the continuous data streams coming off a web-based portal stored securely in the cloud.

TOMRA’s Harold Cline & Jordan Rutledge

“This is seeing mine managers able to tap into how operations are performing today, while tracking that against performance over the last day, week, month, quarter, etc,” Cline told IM. “With the help of our support network, these operations are able to achieve more consistent performance.”

With more customers signing up to TOMRA Insight and more data being generated, the pair were confident future iterations of the platform would be able to offer machine-learning algorithms that helped, for example, predict failures or highlight potential areas for operational improvements.

At the show, the pair were also highlighting the ongoing demand for TOMRA’s Final Recovery sorter, the COM XRT 300/FR, which, since launch, has been successfully deployed at the Letšeng diamond mine in Lesotho, owned by Gem Diamonds. The solution has gone on to be rolled out at other operations.

The introduction of the COM XRT 300/FR, TOMRA became the first company in the industry able to supply a full diamond recovery solution using XRT technology from 2-100 mm, with the unit delivering concentration factors of up to one million with limited stages and guaranteeing more than 99% diamond recovery, according to the company.

Outside of diamonds and sorter analytics, Cline was keen to talk up demand from the gold sector for the company’s sorters.

One of the key differentiators of its offering to the yellow metal space is the ability to scan the material with a multi-channel laser sensor. In an ore sorting setup that involves both XRT and LASER sensor-based machines, the TOMRA solution can remove particles containing sulphide minerals using XRT and subsequently leverage laser sensors to remove particles containing quartz and calcite.

TOMRA says its segregated option can potentially improve recoveries in quartz-associated gold applications thanks to a laser chute-based machine that analyses rocks from both sides. Other belt-based laser machines can only analyse a maximum of 40% of the rock’s surface, according to TOMRA.

“In the gold scenario, we are using XRT to sense and sort with sulphide minerals as a proxy,” Cline said. “At the same time, our laser scanner allows further separation capabilities through identification of minerals such as quartz and calcite.”

Vista Gold, which is developing the Mt Todd project in Australia, anticipates that this combined solution could eliminate approximately 10% of the run-of-mine feed to the grinding circuit, allowing the company to decrease the grind size and thereby increase recovery of the contained gold.

The COM XRT 300/FR offers a full diamond recovery solution

Cline added: “In North America, we have three projects in the gold space we’re working on at the moment that appreciate our unit’s ability to analyse the whole of the particle through our chute mechanism, as opposed to conveyor-based systems that can only analyse one angle of the particle.”

While TOMRA offers multiple sensors on its units through its modular platform, Rutledge said the company continues to have discussions on combining its solutions with other bulk sorting suppliers to further improve the process, naming prompt gamma neutron activation analysis (PGNAA) technology as one specific area of interest.

“We very often refer clients on to other companies when our solution may not match their brief,” she said. “At the same time, we have done some flowsheet work to include our solution with others currently on the market and believe it is only a matter of time before a combination of the two comes into a flowsheet.”

Weba Chute Systems solves choking problem at Botswana diamond mine

Weba Chute Systems has come to the rescue of a large Botswana diamond producer suffering from continuous chute maintenance with a customised solution that came with a 12-month guarantee.

This primary crusher discharge chute had been a headache for the company, with the crunch coming when, after considerable capital expenditure, the new conventional chute needed maintenance just six weeks after installation.

Hilton Buys, Regional Manager at Weba Chute Systems, said: “This could not continue and the mine needed a long-term solution which is why we believe they came to us for a proposal. Senior experts from our company visited the site to take a careful look at the conditions the chute needed to deal with, and we took our conclusions back to our design office.”

Among the challenges were large lump sizes in the ore stream, contributing to build-up of material in the chute and regular choking, Buys said. Also, while Botswana’s dry season is long, the rain that does fall causes considerable problems to the flow dynamics. The kimberlite on the mine – depending on which part of the pit it comes from – can become very sticky in wet weather, according to the company.

“We therefore had to pay particular attention to flow angles, and the design had to effectively accommodate both wet and dry conditions,” Buys said. The concept design – which included quick-release lips on dead boxes – was approved by the mine and the final design, manufacture and successful installation was conducted.

Adding to the complexity was that the feed end of the primary crusher was some 8 m below ground level, while the crusher itself stood about 10 m tall. The chute had to be positioned below the rock box, which stores the material from the crusher discharge, channelling the stream into the Weba chute at a transfer height of 9 m to the conveyor belt.

“The conventional chute also created excessive dust through uncontrolled rock velocity over this considerable transfer height,” Buys said. “By contrast, our chute’s controlled flow meant that the mine did not even have to apply its dust suppression system.”

After installation, Weba Chute Systems gave the customer a 12-month guarantee on this chute, as it does with all its new chutes. This guarantee, which comes with regular inspection reports, assures the customer that the performance will meet their expectations.

“These inspections allow us to monitor wear, so we can advise the customer on what action is required so that they can schedule maintenance and avoid unexpected downtime,” Buys said.

Installed in 2017, the chute is still operating with little maintenance, having been delivered at a highly competitive price compared to the one it replaced.

“Designing a long-lasting chute is not just about creating a box with some reinforcing where you think there will be wear,” Buys said. “It is an endeavour that must be scientific, based on in-depth analysis of material and flow conditions.”

Buys highlighted the importance of asking a range of technical questions about the specific application so the design answers those needs. The latest software and modelling tools are then applied by the Weba Chute Systems team to guide the most effective design.

WEC Projects looks to nature for Lucara Karowe sewage treatment plant

WEC Projects has secured a R3 million ($187,460) contract to supply a new sewage treatment plant for the expansion of Lucara Diamond’s Karowe diamond mine in Botswana.

The mine, near the village of Letlhakane in the eastern Kalahari Basin region of Botswana, is planning to cease open-pit activities by 2026 after which it will continue mining underground, extending its operational life to around 2040. More than 1,000 m above sea level, the mine operates in a region where temperatures average 35°C and water is scarce; so much so that the Government of Botswana has legislated mandatory water saving requirements for industry.

WEC Projects installed the original treatment plant in 2012 and will integrate the new system into the existing facility, increasing throughput from 100 cu.m/d to 150 cu.m/d to meet the requirements of an increase in the number of staff at the mine. While the treatment plant itself is a fairly standard installation, the mine requested a variation to the original project scope – a man-made natural reed bed wetland system that will provide a “polishing” phase to the treatment process, using natural organisms and filtration processes to further clean the wastewater, WEC Projects said.

Wayne Taljaard, Managing Director of WEC Projects, said: “This is a particularly unique feature for a mine as usually such reed bed wetlands are built for much larger installations such as municipal sewage treatment. The government’s mandate for water conservation has forced companies in Botswana to apply creative thinking to overcome the challenge of operating in an arid country.”

The main sewage treatment facility will consist of a WEC Projects Model A treatment plant, an extended aeration system using conventional activated sludge to process the sewage. The wastewater passes through a mechanical screen which removes solids and is then treated by a biological reactor which integrates anoxic, aerobic and clarification zones.

After treatment, the water will enter the reed bed wetland area where it will percolate through the reed bed allowing microorganisms to breakdown contaminants such as sulphur, heavy metals and chlorine. The water produced by this process, while not for human consumption, will be reused by the mine for applications such as irrigation and dust suppression, according to the company.

To create the wetland, a shallow dam will be built, its bottom to be filled with gravel and reeds planted. The water from the treatment plant will feed into the wetland area where nature will be left to take its course.

Taljaard added: “The reed bed solution offers a number of advantages for the mine as the effluent will be relatively odourless and is flexible enough to cope with fluctuations in input. It also requires little maintenance once it is up and running and will ensure that the mine remains within the constructs of the law.”

ALROSA looks to reclaim Aikhal tailings pit as part of 650 ha land restoration project

ALROSA plans to reclaim the tailings pit of processing plant No. 8 at its Aikhal Division by 2029 in a project worth over RUB2.5 billion ($34.3 million) that will seek to restore 650 ha of land and have it planted with pine forests, the diamond miner says.

The tailings pit is located 1.2 km southwest of the village of Aikhal (pictured) in the Sokhsolookh River valley in Yakutia, Russia. The decision to reclaim the facility followed the completion of mining at the Komsomolsky open pit and the closure of processing plant No. 8 at the end of 2020.

During the plant’s operations, tailings were stored in the tailings pit as a liquid slurry. In terms of environmental danger, the slurry belongs to the lowest hazard waste category (virtually non-hazardous waste or category 5 under the Russian Federal Law on Industrial and Consumer Waste), ALROSA says. The tailings pit was a key hydrotechnical facility ensuring water recirculation at the processing plant: after the slurry settled in the pit, clarified water was fed back into the plant to be re-used in processing diamond ore, the company explained.

The reclamation project will be implemented in two stages.

The first stage will include draining the pit and restoring a part of the original course of the Sokhsolookh River back to its natural state.

Later on, from 2025 to 2029, the tailings facility will be dismantled, and work will be carried out to improve the land, dig drainage ditches, install waterproofing, lay fertile soil and landscape the area. To achieve this, 160,000 Scots Pine seeds have been sown in 2021 in a disused sand and gravel open pit not far from the Aikhal village. This conifer is not native to this area and does not grow locally on its own.

Once all the work is complete, the land beneath the tailings pit will be restored to its original condition and, as mentioned, over 650 ha of replanted area will be handed over to local authorities.

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.

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.