Tag Archives: heap leach

Kışladağ and Weir Minerals on the HPGR-backed gold recovery trail

The story that led to the installation of a Weir Minerals Enduron® high pressure grinding roll (HPGR) at Eldorado Gold’s Kışladağ heap leach operation in Turkey is a fascinating read, as well as a great example of the benefits of using such technology.

Back in March 2018, Eldorado announced it would suspend mining to evaluate processing options for the operation. This decision followed extensive laboratory tests that indicated gold recoveries would continue to trend downwards around the base of the open pit where mining was underway.

This suspension, plus further engineering and test work, led to the company advancing the potential development of a mill project. The transition away from its heap leaching roots to a possible mill and carbon-in-leach (CIL) process would have added significant capital costs and shortened the mine life significantly.

Before making this significant capital decision, Eldorado paused to take time to undertake the necessary technical work and sought the technical collaboration of Weir Minerals on a solution.

“It was a very challenging period,” George Burns, President & CEO of Eldorado Gold Corporation, told IM. “Kışladağ is a cornerstone asset in our portfolio. It required collaboration with our geologists, metallurgists, site teams and technology providers, including Weir, working together on a solution.”

(Credit: Eldorado Gold)

In late 2018, results showed increased recoveries from an extended leach cycle. Following a deeper understanding of the geometallurgical drivers of the sulphide component of the deposit, improved heap leach recoveries were realised by optimising the metallurgical conditions. With these improved recoveries confirmed, the heap leach plan was revised in early 2019. Eldorado announced plans to resume mining, crushing, stacking and heap leaching at Kışladağ, and suspended plans to build the processing plant.

The decision came following metallurgical test work on the material placed on the heap leach pad in 2018. Gold recovery had increasingly exceeded expectations throughout the year, providing a new, positive heap leaching outlook beyond the near term. At the same time, Eldorado worked with Weir Minerals on the potential use of an HPGR at the operation.

HPGR creates a finer particle size, which helps to liberate the gold particles, resulting in increased recoveries.

An improved understanding of the leaching process on its low-grade ore and the potential of this cost-effective grinding addition provided it with the confidence to continue heap leaching beyond the short-term time horizon previously envisaged.

“Our collaboration with Weir on this effort is an excellent example of how Eldorado collaborates with technology leaders and seeks out solutions,” Burns said. “We believe this is a strength of the company’s core business values. We are agile and flexible ‒ a good example in both business and operations to find innovative, technical solutions and demonstrate prudent capital discipline. Ultimately, the solution was the best technical and economic decision for Eldorado.”

Testing, testing, testing

“The relationship between Weir Minerals’ and Kışladağ goes back to 2013,” Bjorn Dierx, Global Product Manager Enduron HPGR, told IM.

The OEM had been provided with samples on several occasions to investigate different flowsheet possibilities.

“The benefits of HPGR in heap leaching recovery were known by the site’s crew,” he said.

Enduron technology was tested at the quaternary crushing stage before heap leaching, in the quaternary crushing stage before ball milling and at the tertiary crushing directly before heap leaching.

All the time, the mine operator, Tuprag, Eldorado Gold’s subsidiary in Turkey, was evaluating the impact on gold recovery.

Although HPGR in closed circuit with screening was also tested, most of the test campaigns were focused on a configuration with so-called ‘Partial Product Recycling’ (PPR), according to Serhat Onol, Weir Minerals Senior Process Engineer.

“This system includes splitter plates underneath the rolls which ‘cut’ a proportion of the product discharge and reverts this back to the HPGR head feed,” he explained. “This recycle stream can be adjusted online to adapt the product grind towards the downstream requirements.”

PPR is not an option for every application but for Tuprag – due to the feed and desired product size – all specifications showed it was the best route.

“The hybrid solution with screening serves to increase the flexibility and to control the circulating load to the HPGR,” Onol said.

With capacity rates of around 4,200 t/h at Kışladağ, the screening area requirement was reasonably high, he explained.

“The hybrid solution uses screening only for the recirculating stream: the centre product of the HPGR reports to downstream leaching, whereas the rest is recirculated,” he said. This not only removes the fines re-entering the HPGR and, thus, reduces the circulating load, but also avoids the over-grinding of fines before leaching.

The PPR option, itself, is a very flexible operation, with the adjustable discharge splitter plates providing the best circuit flexibility in terms of throughput and product size, according to Onol.

(Credit: Eldorado Gold)

Great expectations

With the main driver of the HPGR installation being an improved gold recovery scenario, leading to an increased heap leach life, the pressure has been on Weir Minerals to come up with the goods.

The final flowsheet, which includes a 2.4 m diameter by 2.2 m long Enduron HPGR with the capacity to process 4,200 t/h, is much simpler than the existing circuit, according to Dierx, with less equipment to maintain, control and monitor.

“A single Enduron HPGR will replace all of the five existing tertiary crushers of which liners would have an average lifetime of circa-one month with a crusher availability of 85%,” he said. “The HPGR tyres have a wear life close to 18 months, with the HPGR achieving a high asset availability of more than 95%.

“Additionally, as a result of the HPGR combined with the hybrid PPR system, the existing four tertiary screens are also being decommissioned.”

Not only has the HPGR alleviated the use of this equipment, it is also set to boost that bottom line gold recovery.

“During testing, it was determined that the circuit configuration and HPGR operating conditions, such as pressure, have a direct influence on the gold recovery,” Dierx said. “The current expectation is that the average recovery increase after the commissioning of the Enduron solution will be approximately 4%.”

This could bring gold recovery to approximately 56%, as was declared in a 2020 press release from Eldorado that highlighted a 15-year mine life at Kışladağ with an average annual production of 160,000 oz.

In action

One of the largest brownfield HPGRs Weir Minerals has ever installed has just processed its first material at Kışladağ, which is testament to the hurdles both the Weir Minerals and Tuprag teams overcame during the height of the COVID-19 pandemic.

“Despite the challenges we faced during the pandemic, we were able to fully install the machine, including pre-commissioning, in only 22 weeks,” Dierx said.

(Credit: Eldorado Gold)

This was achieved by minimising the amount of work carried out on site via pre-site testing and modular HPGR assembly.

“As the available footprint in existing sites is limited, the unique Enduron design (length:diameter ratio) not only improves the grinding efficiency but also allows for easier implementation with less civil requirements,” Dierx said.

The machine has the potential to be digitally connected to the Weir Synertrex® IoT platform where operators can benefit from direct access to maintenance specialists, who will be monitoring performance and provide necessary operating guidance.

And the Weir Minerals team is confident more Enduron HPGR installations will follow the one at Kışladağ.

“We are very proud of the product’s recognition by our customers as the Enduron HPGR has been selected for all major greenfield HPGR projects in the hard-rock space,” Dierx said. “Despite all the key Enduron differentiators, it is not only merely about the product but particularly the wider experience across Weir Minerals in both the upstream and downstream processes via our wide product portfolio.

“Particularly in these brownfield applications, the system is not operating in a vacuum and every process change influences how the overall circuit works. This requires tacit knowledge, which Weir Minerals holds across their global teams.”

Eldorado’s Burns concluded: “We are pleased to implement a solution that increases gold recovery and supports a 15-year mine life at Kışladağ, allowing Eldorado to continue to provide employment and economic opportunity in the region, as well as provide a solid foundation for future growth.

“Kışladağ has been the cornerstone asset of Eldorado for over a decade, producing over 3 Moz of gold and generating significant value for all stakeholders during that period. This project is a testament to our exceptional team and technology partners working together to execute in challenging circumstances during the pandemic.”

Vermeer Terrain Leveler surface miner delivers results in Chile

In 2017, a prominent non-metallic mine in Iquique, Chile, began using precision surface mining methods. The mine had a goal of taking a broader approach and evaluating the benefits of precision surface mining from pit to heap leach. Results have been measured and compared with traditional drill and blast methods, and after almost 3 Mt of material cut, the benefits are sound and clear. The mining operation has reported positive results in the areas of material separation, better access in areas that were off limits before, more consistent particle sizes and gains in the heap leaching process.

César Leite, Vermeer Regional Manager for Chile and Specialty Excavation, said that surface mining operations throughout the region have put precision surface mining machines, like the Vermeer T1655 Commander® 3 Terrain Leveler® surface excavation machine (SEM), to work and been happy with the results. “We’ve helped many surface mining operations in the region deploy precision surface mining methods that help address many challenges associated with traditional methods,” he explained.

Safety

Safety while working with explosives used for drilling and blasting has been a major focus area for the mines in Chile. “It is not just the nature of the traditional process that makes it risky, but the number of people involved,” Leite said. “With the precision surface mining process, workers have a controlled way of extracting material, and the process does not have a single step where high levels of energy are stored and released.”

Precision work

Precision surface mining has also helped dilution issues because of the way the Terrain Leveler SEM cuts material in layers. With a modulable cutting depth, miners can be highly selective in the way they recover the mining ore with minimum presence – if any – of sterile material. Geological mapping of the pit can result in less dilution. It can help improve efficiencies through the whole process from loading and hauling of rich and concentrated mineral ore to a heap leaching process with a high level of mineral recovery.

Exclusion areas

The amount of energies stored and released by blasting can cause significant ground vibration, which is why many mines have areas that are off limits to traditional methods. Selective surface mining has provided a unique solution for some Chilean mines, by exploiting these massive areas otherwise prohibited. Using surface mining machines has opened about 80,000 sq.m of new areas in Chile near roads, warehouses, medium voltage lines and other areas previously unavailable.

A Vermeer T1655 Commander 3 Terrain Leveler surface excavation machine (SEM) on a job site in Chile

Particle size

In non-metallic surface mining operations, the effectiveness of the leaching process can be affected by the direct particle size output of the blasting stage. “In normal conditions, blasting is simply not able to control or guarantee a consistent particle size,” Leite explained. “Inconsistent particle sizing can result in poor recovery during heap leaching stages. With selective surface mining, there is a high level of consistency in particle sizes, which can result in better mineral recovery in latter heap leaching stages. On top of that, avoiding big chunks of rocks – very common in blasting – increases the efficiency of the hauling process as more material is transported in a given spatial volume.”

Around 95% of the material cut with the Terrain Leveler SEM produced particle sizes below 25.4 cm.

Heap leaching process

As with every mining activity, there are details that will provide a clear insight into any improvements introduced in previous stages. In some of the non-metallic mining operations, heap leaching is the key process that will clearly show the benefit of a given innovation. The heap leaching process happens slowly, so – although the insight is clear – it takes time to realise the benefit of any given change in the previous stages. The required time for a heap to deliver all the mineral recovered may vary depending on heap dimensions, particle size consistency, leach solution and some other factors. On average, 12 months seems to be a very common time frame for a heap to deliver its benefits. Naturally, the shorter the period, the better to recover the same amount of mineral, but if there’s even more mineral recovered, then it is simply a remarkable result. This is precisely what was observed in Chile: more mineral recovered in less time.

The results of mineral recovery at heaps created exclusively by selective surface mining with the Vermeer Terrain Leveler SEM showed 12% more mineral recovery than heaps with traditional mining. This mineral recovery rate was achieved in a period 33% shorter than using traditional mining methods.

Thiess set to operate and maintain two mining fleets at Austral’s Anthill copper project

Thiess says it has been selected as preferred mining services contractor for Austral Resources’ Anthill copper project, near Mount Isa in Queensland, Australia.

Austral has notified Thiess of its intention to enter exclusive negotiations to finalise the terms of a three-year mining services contract. Under the scope of works, Thiess will operate and maintain two mining fleets, undertaking mining services to support Austral’s copper production requirements.

Thiess CEO and Executive Chairman, Michael Wright, said: “Thiess has a long history operating in the Mount Isa region dating back to the early 1960s, and we’re very pleased to be back. With our selection as preferred contractor, Austral Resources has recognised our team’s specialist mining capability and our flexible approach to meet the needs of their mine.

“This project is very important to Thiess as we continue to diversify our business across commodities, mining regions and services. We are positioned well to support Austral Resources and the local community, with the right equipment, technical capability and operations team.”

The Anthill project is around 80 km northwest of Mount Isa and will extend copper production from the existing Lady Annie Operations.

Austral says CSA Global completed an updated mining study in April 2021 on Anthill resulting in a JORC 2012 compliant ore reserve of 5.1 Mt grading 0.94% Cu containing 47,700 t of copper. This study outlined that ore will be mined from two pits over a 40-month period. Total recovered copper from the heap leach process will be 40,400 t over a 44-month period.

Fortuna pours first gold at Lindero heap leach mine

Fortuna Silver Mines has reported the first gold pour from its Lindero mine, in the Province of Salta, Argentina.

The pour took place on October 20, 2020, producing 728 oz of gold.

It follows on from the starting of irrigation and leaching of ore placed on the heap leach pad, reported in early September.

Jorge A Ganoza, President, CEO and Director of Fortuna, said: “The first gold pour at Lindero, our third mine in the Americas, is a significant achievement for the company as we advance the mine’s ramp-up phase towards commercial production in the first (March) quarter of 2021. Lindero is a mine with reserves for a projected life of 13 years and is a pillar in Fortuna’s asset portfolio.”

Ganoza continued: “I want to take this opportunity to commend our Salta-based team’s commitment and hard work in achieving this milestone, especially in the context where COVID-19 related restrictions continue to pose multiple limitations.

“If conditions permit, we look forward to hosting an on-site inauguration ceremony of Argentina’s newest gold mine with provincial and federal authorities early next year.”

Equinox pours first gold at Castle Mountain mine

A month after declaring construction of the Phase 1 operation at its Castle Mountain gold mine was complete, Equinox Gold has poured first gold from the heap leach asset in California, USA.

“Pouring first gold at Castle Mountain, our newest producing mine in the Americas and our second operating mine in California (on top of Mesquite), launches what will be a long-life flagship asset for the company,” Christian Milau, CEO of Equinox Gold, said.

“I’d like to thank our employees, consultants, San Bernardino County and the State of California for their support and efforts as we brought the Castle Mountain Mine to production on time, on budget and with no lost-time injuries, all while managing through the COVID-19 pandemic.”

Equinox commenced construction of the Phase 1 mine on October 30, 2019.

It commenced pre-production mining in early June and, as of September 17, had stacked more than 1.4 Mt of ore on the leach pad.

The heap leach operation is expected to process around 12,700 t/d of ore, with Phase 1 expected to produce, on average, 45,000 oz/y of gold. The company is completing a feasibility study for the potential Phase 2 expansion, which is expected to average 200,000 oz/y of gold. This feasibility study is targeted for completion by the end of the year.

US DFC investment paves way for Piauí nickel-cobalt production, TechMet says

The US International Development Finance Corp (DFC) has made a $25 million investment into TechMet Ltd, a private investment company with a portfolio of projects that produce, process and recycle metals tied to the production of electric vehicles (EVs), renewable energy systems and energy storage.

The funds will be used to bring into initial commercial production one of TechMet’s core investments, Brazilian Nickel Plc, which will be a low-cost nickel-cobalt producer in Piaui, in north-eastern Brazil, it said.

Piauí is a nickel laterite heap leaching project that has a combined measured and indicated JORC compliant resource of 72 Mt at 1% Ni and 0.05% Co. Brazilian Nickel has previously completed a large-scale demonstration of the heap leaching, purification and recovery of nickel and cobalt from the Piauí ore (pictured).

The DFC investment, part of TechMet’s Round 2 equity raising, follows on the heels of US President, Donald Trump, signing an Executive Order and declaring a National Emergency to expand the domestic mining industry, support mining jobs, alleviate unnecessary permitting delays, and reduce the US’ dependence on China for critical minerals.

Nickel and cobalt are two key ingredients in the production of lithium-ion batteries that power EVs and provide renewable energy storage. As battery technologies transform the global mobility and energy landscape, the demand growth for these metals is expected to accelerate.

TechMet said: “While China has built a position of overwhelming supply chain dominance, the United States’ continued reliance on imports for the supply of critical metals represents a significant threat to the long-term competitiveness of American industry. TechMet, aligned with US interests, is committed to developing an independent supply of these critical metals.”

Brian Menell, Chairman and CEO of TechMet, said: “We are very pleased to have secured this funding and support from DFC, which enables Brazilian Nickel Plc to begin the commercial production of nickel and cobalt products used in the production of EV batteries. Having this level of US support is a great endorsement of TechMet’s team and strategy.”

Adam Boehler, CEO of the US International Development Finance Corp, a US Government agency, said: “This important financing will support economic growth in one of Brazil’s most underdeveloped areas. Investments in critical materials for advanced technology support development and advance US foreign policy.”

TechMet has been operational for three years and its core investments include:

  • Brazilian Nickel Plc;
  • Li-Cycle – lithium-ion battery recycling with a producing plant in Canada and a plant under construction in Rochester, New York;
  • US Vanadium – vanadium specialty chemicals production in Arkansas (USA); and
  • Tinco – one of the largest tin and tungsten mines in Rwanda.

TechMet also has an interest in a producing Rare Earths metals project and is developing TechMet Ventures to invest in new opportunities across the supply chain, it says.

GBM, Round Oak celebrate first gold doré at White Dam

GBM Resources and Round Oak Minerals’ White Dam gold-copper heap leach asset in South Australia, has poured its first gold doré bar.

The achievement follows the completion of the sulphidisation-acidification-recycling-thickening (SART) plant build back in July, which earned GBM its 50% stake in the asset. GBM says the SART plant, and associated copper concentrate production, continues to ramp-up broadly in-line with expectations, while identified optimisation opportunities are expected to drive further expanded production and reduced costs.

White Dam, around 50 km southwest of Broken Hill, is a heap leach operation that, since 2010, has produced about 175,000 oz of gold from heap leaching of 7.5 Mt of ore at 0.94 g/t Au (which was mined from two open pits).

The JV owners say evaluation of the estimated remaining resources of 4.6 Mt grading 0.7 g/t Au for 101,900 oz of gold has commenced to determine the viability of the extraction and leaching of this material.

Peter Rohner, Managing Director and CEO, said: “I would like to thank the Round Oak site team for their ongoing efforts in optimising the SART plant operation. While recent rain has resulted in some minor delays, the additional water is set to drive increased heap leach irrigation and thus higher gold and copper production in the near term.

“We are now working to finalise shipping of the first copper concentrates once the concentrate drying process is completed. The SART plant is meeting its design objectives of removing copper and increasing the recovery of the cyanide solution back into the circuit to increase gold recoveries, which together enhance the overall economics of the White Dam operation.”

Fortuna keeps Lindero on track for first gold pour in early October

Fortuna Silver Mines says it has started the irrigation and leaching of ore placed on the heap leach pad at the Lindero gold project, in Salta Province, Argentina.

This is ahead of the first gold pour, expected in early October.

Jorge A Ganoza, President, CEO and Director, said: “In spite of all the restrictions and challenges brought by the COVID-19 pandemic, we are managing to successfully advance Lindero in a safe and secure manner for our personnel and neighbours.

“With the start of irrigation, we achieved one more key milestone in the pre-production phase as we prepare for what follows, the first gold pour at our third producing mine.”

Back in July, Fortuna said it had completed the primary and secondary crushing circuits at Lindero and it had started stacking ore on the heap leach pad.

The night shift operations at the primary and secondary crushing circuits began in mid-August and, at month’s end, daily throughput peaked at 17,400 t/d or 93% of design capacity of 18,750 t/d, Fortuna said.

This has seen 277,000 tonnes of ore averaging 0.87 g/t Au, containing an estimated 7,750 oz of gold, placed on the leach pad as of August 31.

Meanwhile, irrigation and leaching of ore on the leach pad commenced on September 1. The company also noted that pre-commissioning of the ADR (adsorption, desorption and regeneration) plant was 80% complete.

GBM earns 50% stake in White Dam through SART plant delivery

Having completed the construction of the SART plant at the White Dam gold-copper heap leach asset in South Australia, GBM Resources has earned a 50% stake in the joint venture operation.

The execution of the joint venture between GBM and Round Oak Minerals, signed on December 18, 2019, was conditional on the completion of the sulphidisation, acidification, recycling and thickening (SART) plant at White Dam.

The SART plant construction was completed broadly as planned, with only slight COVID-19 related delays to delivery times of some key equipment, GBM noted. Staged commissioning activities commenced over the past three weeks as circuits in the plant were progressively completed.

The circuit has also now been continuously operated, with reagent additions and first copper sulphide concentrate having been produced, according to GBM. The gold leaching circuit and SART plant are targeted to reach steady-state operations during the current quarter.

Key contractors contributing to the design and construction of the SART plant include Core Metallurgy (metallurgical test work and process design), ammjohncm (civil and electrical design), Environmental Construction (civil construction) and DKM Electrical (electrical).

GBM also expects to complete a JORC 2012 compliant mineral resource estimate for White Dam shortly, which is expected to identify additional production potential of the existing heap leach operation moving forward, it said.

Peter Rohner, Managing Director and CEO, said: “I would like to thank the Round Oak team, both for their efficiency in finalising the joint venture documentation and, in particular, the efforts of their team on site in constructing the SART plant. I would also like to thank the other contractors involved in completing the construction work in a safe and timely manner.

“We are now working to finalise commissioning and look forward to shipping the first copper concentrates and recovering additional gold bullion in the current quarter.

“The SART plant project at White Dam is not only expected to generate cashflow for GBM, but also to extend the life of the operation and deliver an improved outcome for ultimate project closure by removing copper from the existing heaps.”

White Dam is around 50 km southwest of Broken Hill. It is a heap leach operation that, since 2010, has produced about 175,000 oz of gold from heap leaching of 7.5 Mt of ore at 0.94 g/t Au (which was mined from two open pits).

Fortuna starts stacking at Lindero heap leach gold mine

Fortuna Silver Mines has completed the primary and secondary crushing circuits at the Lindero gold project, in Salta Province, Argentina, with the company starting to stack ore on the heap leach pad.

As of the end of June, the overall project is now 97% complete, with the first gold pour expected at the end of the September quarter, Fortuna said.

Jorge A Ganoza, President, CEO and Director of Fortuna, said: “The successful commissioning of the primary and secondary crushing circuits and the start of stacking ore on the heap leach pad are key and much awaited milestones at Lindero. Our project team is delivering on schedule and budget according to the revised plan, despite the challenges and limitations of carrying on construction activities under COVID-19 related constraints.

“The next upcoming milestone is the start of heap irrigation which is scheduled for the end of August.”

The ramp-up phase of the primary and secondary crushing circuits will involve an increase in production until nominal rates of 18,750 t/d are achieved, the company said. Fortuna expects to achieve nominal rate production in the December quarter of 2020, inclusive of the tertiary high pressure grinding roll system and agglomeration plant.

Ore for the commissioning and initial ramp-up of the crushing circuit and stacking on the heap leach pad is being sourced from the medium-grade coarse ore stockpile inventory of around 1 Mt averaging 0.55 g/t Au.

During the period from July to December, an estimated 1.7-1.9 Mt of ore is scheduled to be placed on the leach pad with an average gold grade of 1-1.1 g/t, the company said. The estimated stripping ratio during this period is 0.68-0.75.

Final construction activities related to the process ponds, ADR (adsorption, desorption and regeneration) and SART (sulphidisation, acidification, recycling and thickening) plants continues with electrical and piping installations progressing according to plan, Fortuna said. The process pond and ADR plant electric rooms have been energised, with pre-commissioning of the solution handling system commencing on July 11 with the barren pond pumping equipment.

Lindero has been designed as an 18,750 t/d owner-operated open-pit mine with a pit life of 13 years based on current mineral reserves.