Tag Archives: sulphides

Rio Tinto’s Nuton ready to leverage its leaching R&D legacy

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More than a few companies and technology providers claim to have solved the primary copper sulphide leaching conundrum, but only one has close to 30 years of R&D and the Rio Tinto name behind it.

Rio, through its Nuton venture, is the latest to table a solution to treat primary copper sulphides such as chalcopyrite, having introduced the company to the sector earlier this year in an attempt at growing the miner’s copper business.

At its centre is a portfolio of proprietary copper leach related technologies and capability that, Nuton says, offer the potential to economically unlock known low-grade copper sulphide resources, copper bearing waste and tailings, and achieve higher copper recoveries on oxide and transitional material. This allows for a significantly increased copper production outcome, according to the company.

One of the key differentiators of Nuton is the potential to deliver leading environmental performance, including more efficient water usage, lower carbon emissions and the ability to reclaim mine sites by reprocessing mine waste, it claims.

Column test work at Rio Tinto’s R&D centre in Bundoora, Melbourne

Adam Burley, Rio Tinto’s Nuton venture lead, said at the core of Nuton is an elevated temperature bioleaching process that can, in the right thermochemical conditions, deliver “peak” copper recovery from primary sulphides such as chalcopyrite.

“Taking advantage of naturally-occurring processes, we have nurtured a culture of microorganisms that establish and thrive in those optimised conditions,” he told IM. “The elevated temperatures are generated by the work of the bacteria; under the base case, we don’t need to heat the heap from external sources, which can often be financially and environmentally costly.”

This leaching core is enhanced by a range of “additives” and expertise that can, for example, deal with high precipitation and cold weather climates.

Having assembled and extensively tested this portfolio, Nuton and Burley are confident enough to state expectations of delivering greater than 80% copper recoveries from chalcopyrite ore with its process.

“This is, from our understanding, some way above the next best leaching technologies available,” Burley said.

The testing behind such numbers is extensive, dating back to 1994 when the company carried out its pilot heap leach operation and developed its initial predictive modelling capabilities at the Kennecott copper mine in Utah, USA.

“Since that time, we’ve conducted hundreds of column tests across tens of orebodies,” Burley said. “We have run columns at a range of scales – a metre high to 10 metres high – and a range of diameters – from tens of centimetres to 5-metre diameter cribs. Some of those range from tens of kilograms to 300 tonnes – large scale with a lot of instrumentation.”

Combining this body of work with a 70,000 t leaching trial the company carried out at Kennecott from 2012 to 2014, Nuton has been able to calibrate its computational fluid dynamic models to accurately predict a range of inputs and outputs for leaching suitability.

“We are left in a position today where we have a high degree of confidence in being able to evaluate the suitability of different ore types and Nuton’s leach response fairly quickly,” Burley said.

This has led to the company going out to market, partnering with companies that own deposits that pass the Nuton thresholds.

The company has signed deals with Lion Copper and Gold Corp, and Arizona Sonoran Copper Company to test out the technology on Lion’s copper assets in Mason Valley, Nevada, and Arizona Sonoran’s Cactus Mine and Parks/Salyer projects, in Arizona.

It has also more recently agreed a pact with McEwen Copper on the Los Azules project in Argentina.

These assets, agreements and potential leaching applications are all different – covering former operating mines and greenfield assets; earn-ins, exclusivity periods and equity stakes; and oxides and sulphides.

“We recognise that due to the high variability of copper deposits and mine waste that one size doesn’t fit all,” Burley said. “A single technology solution is unlikely to perform well at every site.

“Our approach is to work with our partners to understand site-specific characteristics, such as the mineralogy of the available ore and waste, designing a tailored approach by selecting the most applicable technology configuration from within the Nuton portfolio.”

And, according to Burley, these current and future agreements could see Nuton operate the equipment and plant associated with the Nuton process.

“In many cases, we envisage supporting our partners with an end-to-end process, including engineering, build out and operating the gear,” he said.

The test site at Kennecott being prepared and lined ready for the rock to be leached

While the sulphide copper recovery numbers are likely to take the headlines, Burley was able to point out several key differentiators from other leaching solutions targeting minerals such as chalcopyrite.

“Those recovery numbers are a step change, as opposed to an incremental improvement,” he said. “That gives us a lot more optionality in terms of the cutoff grade of the material we can process economically.”

And, with that higher resource utilisation, comes less waste and an overall higher process efficiency, meaning, under certain conditions, Nuton can compete with a pre-existing processing route such as a concentrator, Burley says.

“In some cases, in a greenfield setting, we could see a better economic and environmental outcome than a concentrator, particularly given no tailings or smelting is required, and you could have a finished product produced in country.”

He continued: “Our focus on ESG and our ability to process waste due to that low cutoff grade is one of the key differentiators that opens a whole set of use cases in the legacy mine domain too. Being able to restore and reclaim mine sites by reprocessing waste is very attractive.”

The eventual aim, according to Burley, is to deliver carbon-neutral copper from the Nuton process, yet Rio estimates it can already deliver 0.4 tonnes of CO2 equivalent for Scope 1 and 2 emissions per tonne of Nuton copper produced, compared with a global average of 5.2 tonnes of CO2 equivalent as per standard, conventional primary copper production.

Away from the technical elements, the “partnership” business model Nuton uses also stands out.

Nuton testing up and running at Kennecott (from previously mentioned trials)

“The approach is to work with our partners and assess the value case at specific sites, agreeing a commercial framework that works for everyone,” Burley said. “We are quite open minded as to what that might look like – it could be ownership and equity participation to royalty and licensing type arrangements.

“So, there is the financial strength Rio brings, as well as the deep technical expertise.”

These elements are clearly beneficial to any of Rio’s fellow mining companies that have projects with copper sulphides or those that will be transitioning to sulphide processing in the future, yet a lot of the progress made with these technologies was tied to the development of Rio’s own project, La Granja.

“In that case, part of the resource contains high arsenic and arsenic-related mineralogy,” Burley said of La Granja. “That was the trigger really for a concerted effort to look at an alternative to a concentrate and processing route. We made quite a number of Nuton breakthroughs in our study of that deposit.”

La Granja has been in Rio’s portfolio since winning the right to develop it in 2005, but is not currently in the development pipeline.

Asked if other assets within the company’s portfolio are potential Nuton candidates, Burley answered: “The potential exists to deploy Nuton within the Rio Tinto copper portfolio. We are currently evaluating a number of internal deployment options across our assets and joint ventures, but we also recognise the full value potential of Nuton – environmental and social, as well as financial – lies outside of the Rio Tinto portfolio.

“To capture the full size of prize that Nuton offers, we need to go out to market, which is what we have been doing pretty aggressively throughout the year and will continue to do going forward.”

TOMRA continues to build ore sorting Insight across mining space

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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.”

Hycroft Mining continues evaluation of novel sulphide heap oxidation/leach process

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After testing out a “novel” oxidation and leaching process at the Hycroft Mine in Nevada, USA, Hycroft Mining Holding Corp is making plans to go back to a conventional oxide leaching setup in 2021.

The company produced 27,392 oz of gold and 178,836 oz of silver in 2020, an almost three-fold increase over 2019. It hit these numbers while operating at a pre-commercial scale using the novel process, which oxidises sulphides ahead of leaching.

It is now planning for run-of-mine production of 45,000-55,000 oz of gold and 400,000-450,000 oz of silver in 2021 using conventional cyanide heap leach.

It is anticipated that mining in the first four months of 2021 will be performed using the existing Hycroft fleet and a rental fleet, moving approximately 1.5 Mt/mth of ore and waste. For the remainder of the year, Hycroft intends to mine some 500,000 t of oxide and transitional ore and waste per month with a more cost-effective mining fleet.

Diane R Garrett, President & Chief Executive Officer, reflected on the results: “2020 was an important year for Hycroft as the company continued to focus on the restart of the Hycroft Mine. Throughout the year, we advanced work on the proprietary two-stage sulphide heap oxidation and leach process and made several important findings that will need to be addressed prior to our implementing the novel technology on a commercial scale.

“In 2021, we expect to mine predominantly oxide and transition material, which are more economic when treated using a conventional run-of-mine heap leaching method, which gives us the opportunity to continue to refine the operating parameters and flowsheet for the new heap leach pad and novel process. While the company continued to make significant progress in better understanding this proprietary process and its application on a commercial scale, the past year also presented some operational challenges, including learning to navigate in a newly emerged COVID-19 world.”

In the last few months, Hycroft says it has worked alongside consultants to identify and investigate opportunities for improvements in operating parameters for the two-stage sulphide heap oxidisation and leach process. The result of the work to date has identified several items that were not considered or included in the original plan and design but are critical to the success of this process. These findings include:

  • Adding a forced air injection system for the leach pad which is a key component of the oxidation process;
  • Developing a system for segregating solution flows to and from the heap leach pad to avoid co-mingling of solutions among heap lifts and ore processing stages that negatively impact recoveries and conditions on the leach pads;
  • Identifying that the finer crushed material requires agglomeration in order to achieve optimal permeability and gold/silver recoveries;
  • Understanding that higher soda ash, caustic soda, and cyanide consumption will be required which Hycroft experienced throughout the 2020 pre-commercial test pad programs and recently confirmed through the review of the test work;
  • Determining that some transitional ores are more economically attractive when processed as direct leach, run-of-mine material; and
  • Concluding that additional variability metallurgical and mineralogy studies will be required to better understand each of the geometallurgical domains in the orebody. While there was some variability work completed in the past, the recent test work has revealed that additional variability test work and compositing is necessary to fully understand the geometallurgy of each domain, and that additional sampling, including sampling below the water table where the predominance of the sulphide resources exist, is required given the complexity and variability of the large orebody.

The additional variability test work will also include detailed mineralogy studies as it is important to understand the role other minerals may play in the overall oxidation process and to enhance Hycroft’s ability to measure oxidation rates accurately and consistently, it said.

The team at Hycroft has developed an approximate $10 million program for drilling and additional metallurgical and mineralogical studies in 2021. This program of work has been approved by the Board of Directors of Hycroft and can be funded from existing cash and Hycroft’s current operating plans.

Hycroft expects to mine and stockpile at least 300,000 tons (272,155 t) of sulphide ore in 2021 that, once sufficient additional work on the novel process has been completed, will be available for testing to further refine operating parameters and measure its performance for large scale application of the oxidation heap leach.

Garrett added: “2021 is a foundational year designed to advance the work necessary in preparation for larger-scale sulphide operations. The team is working diligently to optimise current and future heap leach mine plans and to evaluate all opportunities for more profitable mine plans in the near and medium term. This work involves taking a ‘ground up’ approach working from the orebody out. The company’s prior plan was developed using a $1,200/oz gold price pit shell which leaves profitable ore behind in the current gold and silver price environment. By running pit shells at recent gold and silver prices, we have identified additional areas of oxide mineralisation that can generate cash flows over the next several years and we have already begun to identify areas of higher-grade mineralisation that will become important for mine sequencing and further improving cash flows prior to accessing sulphide material.”

As the company considers life-of-mine development and planning for the Hycroft deposit, particularly in the current gold and silver price environment, Hycroft says it is prudent to evaluate proven processing technologies for treating some ore types that may be more profitable than only using the two-stage sulphide heap oxidation and leaching process.

Potential opportunities being examined by the company in 2021 include: developing an understanding of the grade range distribution of the sulphide material; completing on-going work on the higher-grade areas of Hycroft; and following up on historical high-grade intercepts.

In order to capitalise on these potential opportunities, which take advantage of the current commodity price environment, Hycroft believes that it should also evaluate the benefits of a multi-process operation. Long-term operating scenarios may include conventional run-of-mine cyanide heap leaching for the oxide and transitional material, sulphide heap oxidation and leaching using the novel process, and an appropriately sized milling and flotation plant for processing the higher-grade ranges of sulphide material.

“The company believes that the plan it has put in place for 2021 will provide the new team the time to fully consider and evaluate these opportunities and make any necessary changes to improve the leach pads, process plants and process flowsheet, maintain and develop its workforce, and advance the project, in order to further enhance the value of the project,” it said. “As the test work advances and alternative processes are considered, the company expects to perform technical studies and trade-off evaluations which may result in an updated feasibility study.”

Atalaya Mining evaluating Lain Tech’s E-LIX System for copper cathode production

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Atalaya Mining has commenced the execution of a feasibility study to evaluate the economic viability of producing cathodes from complex sulphide ores prevalent in the Iberian Pyrite Belt through the application of a new extraction process called the E-LIX System.

The production of cathodes has the potential to generate cost savings by reducing charges associated with concentrate transportation, treatment and refining, and penalty elements, while also reducing carbon emissions, the company said.

E-LIX System is a newly developed electrochemical extraction process developed and owned by Lain Technologies Ltd, led by Dr Eva Lain, who holds a PhD in Electrochemistry research from the University of Cambridge.

Through the application of singular catalysts and physico-chemical conditions, E-LIX System is able to achieve high metal recoveries under low residence times, by accomplishing rapid reaction rates while overcoming classic surface passivation issues that have typically impaired metal recovery from complex sulphide ores, Atalaya said. E-LIX System is considered to be a more environmentally-friendly process than existing technologies; it generates zero emissions and does not consume water or acid, and runs under mild operating conditions (atmospheric pressure and room temperature).

Patented in 2014 by Lain Tech, the E-LIX System has been developed in collaboration with Atalaya from an initial concept in the laboratory to a fully operational pilot plant located at Proyecto Riotinto, in Spain.

The pilot plant with a capacity of 5 t/d has been running for the past nine months, with only mandatory stoppage owing to COVID-19 restrictions. Leach rates of up to 250 kg/h have been achieved processing copper concentrates, zinc concentrates and blends of different types of sulphides, according to the company. The pilot plant also contains a solvent extraction and electrowinning (SX-EW) section and has successfully produced high purity copper cathodes as a proof of concept.

Excellent leach results with recovery rates well over 90% have been attained, the company said. Fast kinetics for copper and zinc have also been successfully achieved overcoming the well-known passivation problem of leaching primary sulphides.

The pilot plant has demonstrated that the E-LIX System effectively treats the impurity levels typically associated with the complex sulphides present in the pyrite belt that runs through the south of Portugal and Spain and prevalent at Proyecto Riotinto.

During the past five years, Atalaya has provided financial assistance to Lain Tech to develop the E-LIX System and has now reached an agreement with Lain Tech to use its patents, on an exclusive licence basis within the Iberian pyrite belt in Spain and Portugal.

Under the terms of the licence agreement and based on the encouraging operating results at the pilot plant, the company has commissioned a feasibility study to evaluate the construction of an industrial scale plant for the production of a minimum of 10,000 t/y of copper cathode metal. The study at a cost of around €1 million ($1.2 million) will be funded by Atalaya and is expected to be finalised in 2021. The agreement also provides for a profit sharing arrangement between Atalaya and Lain Tech.

“The feasibility study will be based on the results obtained from the pilot plant and aims to confirm the scalability of the E-LIX System and the capital and operating costs of the industrial plant,” Atalaya said. “Should the industrial plant be built, it will be funded and constructed by Atalaya with Lain Tech designing, operating and managing the E-LIX System.”

Atalaya believes that the use of the E-LIX System could potentially be applicable to the large amount of complex sulphide ore inventory present throughout the Iberian pyrite belt, including Atalaya’s mining properties such as Proyecto Riotinto and Proyecto Masa Valverde, it said.

Atalaya CEO, Alberto Lavandeira, said: “We are fortunate to have been given this unique opportunity to work with Dr Eva Lain in the development of the E-LIX System. I believe this system has the potential to play an important role in the economic treatment of many complex orebodies worldwide. We look forward to updating the market on the results of the feasibility study.”

Corvus Gold weighs heap leach, BIOX route at Mother Lode project

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Corvus Gold has announced the results of a preliminary economic assessment (PEA) for its Mother Lode project (MLP) in southwest Nevada, USA.

The study outlines a project able to produce 170,980 oz/y of gold and 79,600 oz/y of silver through a combination of heap leaching and biological oxidation (BIOX).

Based off measured and indicated resources of 1.55 Moz of gold and 1.51 Moz of silver, and inferred resources of 170,000 oz of gold and 400,000 oz of silver, the study estimated an operation with an eight-year mine life and an initial price tag of $406 million. Using a $1,500/oz gold price, the payback period was estimated at 2.7 years.

Jeffrey Pontius, President and CEO of Corvus, said: “The results from our initial PEA study of the Mother Lode standalone project are encouraging. The potential projected annual gold production of over 200,000 oz/y during the first three years is significant, especially as a new project, which could provide an increase to the Corvus Gold future production profile. The PEA demonstrates the preliminary potential for the project, on its own, to produce significant free cash flow and after-tax NPV.

“Corvus now has a number of strategic alternatives available to it to drive shareholder value. Given the recent interest in the Bullfrog Gold District from multiple producing companies with adjacent land packages, Corvus’ compelling and accretive projects and its commanding land position with what we believe is demonstrated high exploration potential, has positioned the company to deliver increased shareholder value.”

The Mother Lode project is modelled as a large, open pit, with a biological oxidation mill to treat the higher-grade sulphide mineralisation and a heap leach pad for treatment of oxide mineralisation. The mining plan uses standard mining practices and has a production scale that is currently being used by many operating mines, the company said.

The new PEA study, which assumes a standalone project, also includes a number of other changes to the previously assumed concept for the combined Mother Lode-North Bullfrog project configuration, which enhance the project. This includes:

  • Employing BIOX to treat the MLP sulphide mineralisation would increase gold recovery by 11%. Metallurgical testing of a stirred BIOX process on the MLP whole sulphide mineralisation from Mother Lode demonstrated gold recoveries of 91-92% as compared with the previous testing on MLP flotation concentrate;
  • Eliminating the need for the concentrator, oxygen plant and autoclave components of the previous plant concept simplified the plant conceptual design and would reduce the process plant capital cost;
  • Ongoing work expanding Mother Lode resources in the CIZ area and the main Zone with ongoing work at improving the open-pit mining and development plans will enhance project economics; and
  • New experimental work on conducting the BIOX process in a heap is being tested as follow-up on past successful studies and could substantially cut operation and capital costs with the elimination of the mill circuit.

The PEA only includes drill results completed up until September 2020. In addition, Corvus will continue follow-up mineral resource expansion work and new discovery drilling on priority targets at both the North Bullfrog and Mother Lode properties through 2021, it said.

Full speed ahead for Wiluna Mining sulphide gold project

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Wiluna Mining’s board has approved the staged development of its sulphide project at the Wiluna gold operation in Western Australia, enlisting GR Engineering Services to build the 750,000 t/y concentrator required to process the ore.

The development will see the company transition from its current production profile of producing 62,000 oz/y from mining free milling ore through the current 2.1 Mt/y carbon-in-leach processing facility, initially producing 100,000-120,000 oz/y of gold and gold in concentrate.

This will be implemented using the current, recently refurbished crushing circuit, the previously expanded mill circuit and a new 750,000 t/y concentrator by October 2021, the company said. This forms Stage 1 of the project. Wiluna then intends to increase production of gold and gold in concentrate by, at a minimum, doubling the mining rate and the concentrator to produce circa-250,000 oz/y by the end of 2023/early 2024. This is Stage 2.

Of the A$81 million ($58 million) capital cost estimate of the sulphide project, of which around A$20 million has already been committed, the concentrator is expected to cost A$26 million, pre-production underground mine activities/infrastructure development is estimated at A$37 million, drilling comes in at A$9 million and the feasibility study had a A$2 million price tag. A 10% contingency of A$7 million was also calculated.

Wiluna said Murray Engineering has been contracted to supply and maintain mine fleet for current production associated development and stoping, while Byrnecut Contractors have been engaged to provide equipment and personnel for existing development rehabilitation and new development for resource-reserve drill out programs and production from new mine areas.

To complement the current equipment and development work, the first development crew from Byrnecut is expected to be mobilised in the December quarter with further development crews to be mobilised during June 2021 to maintain the required work program, the company said.

GR Engineering has been appointed as the engineering, procurement and construction contractor by Wiluna for Stage 1 works relating to the concentrator development, the engineering firm said, adding that it expects to commence work in early December with commissioning scheduled for October 2021.