Tag Archives: Steinert

Northern Minerals lays the groundwork for Steinert XRT ore sorter installation

Comminution of minerals, Energy minerals, High tech minerals, Mine operation news, Mineral processing, Mineral project development, Mining equipment, , , , , , , , , , , , , , , ,

Northern Minerals is set to commission a Steinert sensor-based ore sorter for use at its Browns Range rare earth pilot plant, in northern Western Australia, after gaining the relevant regulatory approvals for installation of the machine.

The ore sorting equipment concentrates ore prior to the beneficiation circuit by selecting ore and rejecting waste based on X-ray Transmission. This has the potential to double the feed grade and reduce production costs, according to the company.

Both the Western Australian Office of the Environmental Protection Agency and the Department of Water and Environmental Regulation have now cleared the installation and commissioning, with construction commenced on the structural and mechanical equipment (pictured). Commissioning is scheduled for mid-2021.

The total capital investment for the procurement, installation and commissioning of the ore sorter is budgeted at A$5.9 million ($4.3 million), Northern Minerals said.

Previous trials of ore sorting technology at Browns Range, announced in October 2018, identified the potential to double the mill feed grade. This would lead to an increased production rate of heavy rare earth carbonate and a potential lowering of overall operating costs.

Once the ore sorting system is commissioned, Northern Minerals plans to run additional test work at pilot plant scale on all ore types to establish baseline data on feed grade improvements, it said. This work will also help evaluate material flow-through benefits of ore sorting on overall processing efficiencies, feeding into any future commercial, large-scale project feasibility studies at Browns Range.

Northern Minerals says it is also evaluating the economics of further downstream processing options for Browns Range ore.

To date, Browns Range has produced a mixed heavy rare earth carbonate for small-scale export to offtake partners. The options being assessed would take a further step along the supply chain to produce separated heavy rare earth oxides.

The company announced in August 2019 it had commenced a scoping study with US-based K-Technologies Inc to investigate a separation technology on intermediate mixed rare earths materials produced at Browns Range. K-Tech’s technology is focused on continuous ion exchange, continuous ion-chromatography and related advanced separation methodologies.

The study continues to progress well, with positive test results being achieved at K-Tech’s facilities in Florida albeit slower than planned because of constraints associated with COVID-19, Northern Minerals said. However, the company expects to see separated dysprosium and terbium oxides from the study before the end of this year.

Separately to collaborating with K-Tech, Northern Minerals is pursuing studies into traditional solvent extraction to produce oxides from the mixed heavy rare earth material produced at Browns Range.

Northern Minerals CEO, Mark Tory, said: “With approvals in place for the ore sorter and installation now under way, we will be in a strong position to thoroughly evaluate the flow-through benefits of that technology at a pilot plant scale.

“The results will provide a valuable input into future feasibility studies to assess the commercial viability of a large-scale heavy rare earths mining and processing operation at Browns Range.

“In addition to our investment in ore sorting to improve the mill feed grade, we are also committed to assessing opportunities to further unlock value at Browns Range through downstream processing to oxide products, which opens up a wider field of offtake and future project financing opportunities.”

Northern Minerals started producing rare earth carbonate through the Browns Range pilot plant in October 2018 as part of a three-year pilot assessment of economic and temporarily technical feasibility of a larger scale development at Browns Range.

Steinert to bolster sorting system test capacity in Pulheim

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Steinert is to introduce additional sorting lines for mining and waste recycling at its new test and development centre in Pulheim, Germany, the company says.

The new lines are being installed in an effort to better achieve the company’s aspiration of “test before you buy”, allowing it to “respond with ever more accuracy to the sorting aims of extraction, purity and profitability for each sorting task”, Steinert said.

Steinert’s sorting solutions are used throughout the mining industry as a way of pre-concentrating material ahead of milling.

The metal sorting line of the new test and development centre will official go into operation on September 22. This milestone will be marked with a virtual event held on that day.

By opening the new building, the company is trebling its testing capacity, allowing it to be more flexible in responding to customer demands, it said.

“The processing sequence deployed in the sorting systems is the same as that used in a real industrial plant,” Peter Funke, CEO of the Steinert Group, said. “We are delighted that even more customers can try out our technology, from magnetic separators to sensor-based sorting systems, such as X-ray transmission, X-ray fluorescence and near-infrared (NIR),”

The research and development team is also moving to the same building in Pulheim, seven kilometres away from STEINERT’s headquarters in Cologne, allowing customers to derive even more benefits from the latest developments, the company said.

CEEC Medal recipients recognised for pushing lower footprint mineral processing

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Two standout research and field work contributions that have the potential to improve environmental, social and governance (ESG) performance across industry have been awarded the highly respected CEEC Medal for 2020.

Attracting a record 23 high-quality nominations from across the globe, the shortlisted Operations and Technical Research papers showcased exciting site improvements and innovative ideas for future technologies, according to the Coalition for Energy Efficient Comminution (CEEC).

Now in its ninth year, the CEEC Medal recognises the best published papers that raise awareness of comminution research findings, alternative comminution strategies and installed outcomes.

CEEC Director and Medal Evaluation Committee Chair, Dr Zeljka Pokrajcic, said this year’s nominations reflected industry trends to install renewables, consider embodied energy and emissions, and the continued embracing of technologies such as pre-concentration and coarse flotation.

“It’s rewarding to see how industry leaders and experts are collaborating to forge improvements that make good business sense and proactively improve efficiency,” Dr Pokrajcic said.

The 2020 recipients are:

Operations

Peter Lind and Kevin Murray of Newmont and Alan Boylston and Isaias Arce of Metso Outotec, (formerly Metso), for their paper titled, ‘Reducing Energy and Water Consumption through Alternative Comminution Circuits’. This was presented at the 7th SAG Conference in Vancouver, Canada, in 2019.

Technical Research

Dr Grant Ballantyne (pictured), for his paper titled, ‘Quantifying the Additional Energy Consumed by Ancillary Equipment and Embodied in Grinding Media in Comminution Circuits’. This was also presented at the 7th SAG Conference in Vancouver.

Dr Pokrajcic said the winning Operations paper from Newmont/Metso Outotec documents a successful miner/vendor collaboration on how to assess the comminution circuit options in a low energy and water environment.

The paper considers a typical case of a low grade, bulk tonnage copper-gold orebody in an arid climate (Chile, South America) with significant energy costs. It brings together important solutions – including energy-efficient comminution, ancillary equipment, preconcentration and flotation – and presents compelling economic comparisons.

CEEC CEO, Alison Keogh, said of the paper: “This global knowledge sharing offers real value for decision-making across the globe. The paper’s practical, systematic technology approach, which incorporates all-important financial analysis, has the potential to accelerate industry’s progress to deliver lower footprint minerals.”

The paper’s co-authors, Lind and Boylston, explained that the work was the result of collaboration between many innovative thinkers, with ideas and approaches built over many years.

“We wanted to make a difference, to bring technologies together to show that you can save energy, save water and save money as well. This was a group effort, not only by our extended teams at Newmont and Metso Outotec, but also involving Steinert and Scantech in working through how to apply technologies,” they said.

The CEEC Medal Evaluation Committee praised the winning Technical Research paper from Dr Ballantyne as being “an impressive approach to capturing and quantifying energy consumption of ancillary equipment and energy used to manufacture and transport grinding media”.

The paper shares insights on embodied energy using data collected from sites and presents results on the CEEC Energy Curves.

“The research presents a broader approach that considers the impacts of not just energy used in particle breakage but also embodied energy in the manufacture and transport of grinding media, and energy used in the operation of ancillary equipment such as conveyors and pumps,” Dr Pokrajcic said.

“Bringing this spotlight to embodied energy has strategic value. Many companies are including investigation of supply chain in their procurement decisions.”

Dr Ballantyne, previously a Senior Research Fellow at the Julius Kruttschnitt Mineral Research Centre (JKMRC), and now with Ausenco, noted that his work started in 2012, building on earlier concepts shared by industry at a CEEC workshop in Australia. These concepts were developed further following industry input at the 2015 SAG Conference in Canada.

“I also acknowledge the inspiration and collaboration of Chris Greet (Magotteaux), Evert Lessing (formerly Weir, now Metso Outotec), Malcolm Powell (formerly The University of Queensland) and Greg Lane (Ausenco) for contributing expert input and data to the work,” Dr Ballantyne said.

“New research ideas and collaboration with industry are key to industry innovation,” he said. “Support and mentoring from these suppliers as well as experts from Ausenco and The University of Queensland ensured these new ideas could be published for industry to progress thinking.”

In addition to the two CEEC Medals awarded in 2020, three publications received High Commendations.

High Commendations – Operations

Ben Adair, Luke Keeney, and Michael Scott from CRC ORE, and David King from Minera San Cristóbal operations, for their paper titled ‘Gangue rejection in practice – the implementation of Grade Engineering® at the Minera San Cristóbal Site’. This was presented at Physical Separation 2019, in Cornwall, United Kingdom.

This paper shares the prediction and outcomes of a Grade Engineering pilot at Sumitomo’s Minera San Cristóbal operations in Bolivia. The work identifies ore amenability and levers to optimise up-front rejection of gangue before processing.

Keogh said: “This approach highlights the scale of the opportunity for mining leaders to invest in unlocking hidden value for shareholders through productivity step-change while significantly reducing impact on the environment.”

High Commendations – Operations (continued)

Malcolm Powell, Ceren Bozbay, Sarma Kanchibotla, Benjamin Bonfils, Anand Musunuri, Vladimir Jokovic, Marko Hilden, Jace Young and Emrah Yalcin, for their article titled ‘Advanced Mine-to-Mill Used to Unlock SABC Capacity at the Barrick Cortez Mine’. This was presented at the 7th SAG Conference in Vancouver.

This work was a collaboration between three organisations: JKMRC at The University of Queensland’s Sustainable Minerals Institute, Barrick’s Cortez mine and JK Tech. It shares an advanced mine-to-mill approach that unlocks improved SABC production capacity at Barrick’s Cortez mine in Nevada, USA.

Dr Pokrajcic said the article was an excellent review of the dynamic between SAG and ball mills, illustrating how mine-to-mill, with the consideration of blast movement as well as fragmentation, and operation-wide optimisation could empower sites to identify and sustain long-term improvements.

“It highlights the opportunity of operationalising cooperative ore blend control to balance energy use across the milling circuit, reducing specific energy consumption while benefitting from increased production,” she said.

High Commendation – Technical Research

Paul Shelley and Ignacio Molina (Molycop) and Dimitrios Patsikatheodorou (Westgold Resources), for their paper titled ‘SAG mill optimisation insights by measuring inside the mill’. This was presented at the Procemin-Geomet Conference in Santiago, Chile, in 2019.

In a first for industry, this innovative approach aims to collect data from sensors inside the grinding balls within grinding mills, CEEC said. It brings potential application for high frequency measurement of temperature and impacts inside the mill.

Dr Pokrajcic said: “If this early work can be successfully commercialised and scaled up, it could bring new insights that link to operational and energy efficiency improvements.”

Keogh said nominations for the 2021 CEEC Medal were now open, and she encouraged the submission of relevant, ground-breaking articles from online events and industry presentations.

“Because of disruptions to physical events, we have extended the closing date for submissions to October 30, 2021.”

Details of the application process for the 2021 CEEC Medal can be found here.

Novo Resources to take Steinert ore sorter into the field

Comminution of minerals, Mineral exploration, Mineral processing, Mineral project development, Mining equipment, Precious metals, , , , , , , ,

Novo Resources says it is in advanced discussions with Steinert Australia to procure a 1 m wide KSS 100F LIXT fine mechanical sorting unit, to be deployed at its wholly-owned Purdy’s Reward and Comet Well JV gold projects, in Western Australia, during the 2020 field season.

The sorter will be manufactured by Steinert in Germany with an expected 18-week delivery time to Australia, Novo said.

Approvals are being prepared for field testing of up to 10,000 t of material from Purdy’s Reward, Comet Well, and 47K, respectively (total up to 30,000 t). Novo also plans to utilize this sorter to test field exploration samples delivered from its other projects including Egina, it said.

Field test work will be designed to better understand gold grades, the extent and location of mineralised conglomerate units, evaluate mechanical sorter gold recovery at production throughput rates and of various sorted size fractions, and provide critical input concerning operational costs, the company explained.

The company has previously carried out ore sorting test work in the lab on samples from its Reward and Comet Well JV gold projects.

Rob Humphryson, Novo’s CEO and a Director, said: “We have achieved outstanding laboratory level mechanical sorting test results utilising both Steinert and TOMRA sorters. It is now time to field test productivity and performance. This Steinert unit will be equipped with technology that is capable of testing material from all our coarse gold projects.”

Humphryson said the decision to initially deploy a Steinert unit into the field was more a reflection of “local, non-technical factors” than any distinct differentiation of capabilities between the two suppliers’ sorters.

He added: “Should field testing of mechanical sorting prove successful, it is likely that the final utilisation of this technology will involve a hybrid solution involving equipment from both suppliers. In light of this, we intend to maintain a close working relationship with both suppliers.”

Steinert ore sorting tech picks up the Beaton’s Creek gold fine print

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Novo Resources says initial laboratory-scale tests using Steinert mechanical ore sorting technology indicates an upgrade of gold into significantly reduced mass is achievable at the Beaton’s Creek project in Western Australia.

The mechanical sorting tests carried out in Australia on the Beaton’s Creek bulk sample showed that nuggety gold occurring in Beaton’s Creek conglomerates is finer grained (generally sub 1 mm) than gold at Novo’s Egina and Karratha projects (generally over 1 mm), the company said. The company is also considering using ore sorting at these two projects.

Test work was conducted on a 2.8 t split of crushed (-50 mm) and screened Beaton’s Creek bulk sample material, with analyses conducted as part of this sorting test work generating a calculated head grade of 5.72 g/t Au for the bulk sample. The vast majority of gold reported to mechanically sorted concentrates in each of the three size fractions tested, with 90.2% of gold recovered in 54.5% of the mass of the +18/-50 mm fraction; 68.8% of gold recovered in 42.4% of the mass of the +6/-18 mm fraction; and 95.5% of gold recovered in 20.3% of the mass of the +2.3/-6 mm fraction.

Material finer than 2.3 mm, comprising 17% of the total mass of the bulk sample, was not tested due to excessive dust issues, the company said. “Novo believes such material is treatable by means of gravity concentration,” it added.

“Test results are considered indicative, and Novo and Steinert see additional opportunity to optimise sorting conditions and parameters that may result in further efficiencies,” the company said. “Nevertheless, these tests indicate robust potential for upgrading nuggety conglomerate gold mineralisation, and perhaps, a broader spectrum of gold mineralisation types.”

A second 2.8 t split of the same bulk sample material has been delivered to TOMRA Sorting’s mechanical sorting test facility in Castle Hill, New South Wales, where it will soon undergo similar testing using various TOMRA mechanical sorters, the company said.

Rob Humphryson, CEO and Director of Novo Resources, said: “We are highly encouraged by these initial results. We are already fully confident about the outcome of Egina mechanical sorting test work, which demonstrated excellent recoveries into very small concentrates. Our Beaton’s Creek test work is more investigative in nature owing to the finer gold grain size, so to achieve such levels of upgrade in first phase testing is remarkable.”

He added: “Test work is being developed and supervised by Novo staff specialising in mining engineering, metallurgical processing, and importantly, our geology team. This means those people engaged in exploration are fully aware of the profound impact that mechanical sorting potentially imparts on the economic viability of our prospects. Mechanical sorting test work is likely to become an integral part of future exploration and economic modelling as we hopefully progress each of our projects towards production should the economic viability and technical feasibility of the project be established.”

Novo heralds ore sorting developments as it lines up Steinert and TOMRA trials

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Novo Resources Corp says it is planning mechanical sorting test work on multi-tonne samples of gold-bearing conglomerate from its Beatons Creek project (pictured) and gold-bearing gravels from its Egina project, both in Australia, with Steinert Global and TOMRA.

Mechanical sorting of small particles of gold is seen as a potentially important breakthrough for Novo and its various nuggety gold projects throughout its large land holdings across the Pilbara, the company said.

An approximate 5 t sample of Beatons Creek gold-bearing conglomerate and an a similar sized sample of Egina gold-bearing gravel have been shipped to Perth for sorting trials at Steinert Global’s test facility in December. Conglomerate from Beatons Creek is being crushed and screened, and gravel from Egina is being screened in preparation for test work.

Once mechanical sorting tests have been completed at Steinert Global, bulk test material will be shipped to TOMRA’s test facility in Sydney for testing during the March quarter of 2020, Novo said.

Novo, earlier this month, said recent tests of Steinert mechanical sorting equipment had demonstrated recovery of fine gold nuggets as small as 0.4 mm, which was a significant step toward a potentially cost-effective “dry and chemical free” means of gold recovery.

The test work is designed to assess the veracity of recent advances in scanning and sorting capabilities of both companies, while determining – on Egina material, at least – the gold recovery capabilities of this technology as a means of primary separation; the applicability of mechanical sorting as a tool to support field exploration activities; and which model of mechanical sorter is preferred for deployment for field trials.

“Owing to recent rapid advancements in mechanical sorting technology, Novo has conceptualised a potentially viable alternative ‘dry’ processing pathway for Beatons Creek,” it said.

While testing is required to better assess sorter manufacturer claims that fine gold particles can be detected and sorted, according to Novo, the company said it sees considerable merit in this ‘dry’ processing model for the following reasons:

  • Potential to significantly reduce capital and operating costs compared to conventional ‘wet’ processing schemes;
  • Potential to reduce construction timeframe compared to conventional ‘wet’ processing;
  • ‘Dry’ processing schemes might be amenable to modular design suited to cost-effective mobilisation and relocation;
  • Negates or minimises use of water and chemicals; and
  • ‘Dry’ processing could help unlock Novo’s other assets in the East Pilbara region.

Successful mechanical sorter trials of Beatons Creek material are anticipated to lead to a larger metallurgical test work program to fully assess means of crushing, screening and sorting to be incorporated to a process flowsheet, the company said, adding that it foresees using proven technologies given there is a spectrum of commercially available equipment for dry crushing, grinding and screening.

Rob Humphryson, CEO and director of Novo Resources Corp, said: “The pace of development of mechanical sorting technology continues to astound us. We are fortunate that our nuggety gold deposits appear to lend themselves to ‘dry’ processing pathways involving mechanical sorters, technology that may generate favourable economic and environmental outcomes.

“Considering we can readily access outcropping gold mineralisation on all of our properties, we have a unique opportunity to quickly collect bulk samples for testing mechanical sorting technology on a meaningful scale.”

Snow Lake, DRA and Steinert investigate ore sorting at lithium project

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Snow Lake Resources is the latest company to eye up ore sorting to reduce costs and increase productivity, with the exploration company asking DRA Global to come up with an effective strategy for its Thompson Brothers lithium project, in Manitoba, Canada.

Brent Hilscher of DRA will be in charge of this ore sorting project, examining the best laser or X-ray method to help separate out waste material from the spodumene pegmatite at Thompson Brothers, thereby increasing the overall grade of the final product at a low cost per tonne.

Snow Lake has collected 120 scoping samples from the company’s drill core library as part of this test work, with these samples to be sent to Steinert in Kentucky, USA, for analysis.

The company also created four bench test “bulk samples” from the existing core library, which will be used as trial material at Steinert on a full-scale ore-sorting machine once DRA Global concludes the appropriate algorithm for sorting, it said.

As part of the ore-sorting strategy, the company says it will need a higher degree of understanding of the mineral assemblage of the spodumene pegmatites at its project.

The company has, so far, collected nine core samples from the company’s core library and left them with the Saskatchewan Research Council (SRC) in Saskatoon, Canada. These samples will go through QEM-SCAN petrography analysis at SRC, providing DRA with a report on the mineral assemblage of the pegmatite.

From the nine samples, the company will select three samples for microprobe analysis of the various mineral phase.

Snow Lake said: “These studies will give the company an understanding of the mineral chemistry of the feldspar phases. This will help support the X-ray sorting works, as there may be a chemical element that the X-ray sorter can focus on to eliminate the feldspars from the spodumene pegmatite feed.”

As part of a bulk sample program for 2020, the company will also provide samples to SRC to conduct acid–base accounting testing to help assess the acid-producing and acid-neutralising potential of rocks prior to large-scale excavations at the project.

Snow Lake is expecting to publish a maiden indicated resource on the Thompson Brothers project in the near term, given that the company, its consultants and external laboratories have all the data in hand for the study.

Northern Minerals backs XRT ore sorting pilot plant plan with Steinert order

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Northern Minerals has capped off its ore sorting project enhancement initiatives at the Browns Range rare earths project, in northern Western Australia, with the selection of a Steinert ore sorter for use at its pilot plant.

The selected machine is in stock in Perth and a deposit has been paid in order to secure it and avoid any lead time lags or delays, the company said.

Nexus Bonum, which previously completed the feasibility study for the x-ray transmission ore sorter system at the pilot plant, has been engaged to undertake the front-end engineering and design work required for the inclusion of the sorter into the pilot plant beneficiation circuit.

The company said: “As previously announced, the findings from initial test work and studies indicate that the inclusion of ore sorting at Browns Range has the potential to double the mill feed grade potentially leading to an increased production rate of heavy rare earth carbonate and a potential lowering of operating costs.”

The company is currently working with stakeholders and regulators on obtaining the approvals required for the installation of the ore sorter at Browns Range and is aiming to have the system installed and commissioned by mid-2020, subject to receiving these approvals in a timely manner.

Northern Minerals’ Managing Director and CEO, George Bauk, said: “Following the recent capital raising, we have moved quickly to progress this critical piece of equipment that has the potential to be a game changer for the project.

“Higher grades going into the plant would result in higher production rates and lower operating costs, a double win in terms of proving the economics of the Browns Range project.”

Northern Minerals commenced production of heavy rare earth carbonate at the Browns Range pilot plant back in October. This followed plant commissioning in June.

The project is designed to assist the company in evaluating the economic and technical feasibility of mining at Browns Range and will provide the opportunity to gain production experience and surety of supply for its offtake partner. This could see the company become the first significant producer of dysprosium outside of China.

Saturn Metals makes ore sorting ‘breakthrough’ at Apollo Hill gold project

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Saturn Metals is heralding the first pass results of a laser ore sorting test at its Apollo Hill gold project, near Leonora in the Western Australia goldfields, saying there is potential for using this type of mineral processing upgrade on a future mining operation.

Testing using a STEINERT Fines KSS L machine showed mineralised quartz can be efficiently separated from non-mineralised host basalt, according to the company, with the first sorting test achieving a 1.5x upgrade to the grade of a sample, taking material from 0.78 g/t Au to 1.2 g/t Au. Alongside this was a strong gold recovery of up to 91.9% with only two ore sorting passes.

Other notable results from this test work included a 28% volume reduction, which was achieved through the effective ejecting of a significant portion of waste rock and marginal material and, importantly, only 0.55% of the gold in sample was lost to fines in preparation for ore sorting (crushing and wet screening to +10 mm ore sorting size). “This low figure is considered a positive result as loss of metal to fines can otherwise render ore sorting ineffective,” the company said.

Saturn explained: “Ore sorting, particularly with strong recovery results as seen in the test conducted at Apollo Hill, can result in a more efficient mineral processing solution being developed for mining projects, with smaller tonnages of higher-grade material being beneficiated for mineral processing. This can potentially reduce the size and cost of mineral processing circuits, or increase gold milling capacity, and, in turn, positively impact overall project economics.”

Successful ore sorting treatment of selective higher-grade material from Apollo Hill could also lead to truck and toll treatment options for the deposit, according to the company.

Following these initial results, the company is planning further test work to refine and improve the application of ore sorting technology at Apollo Hill, it said.

Saturn Managing Director, Ian Bamborough, said the results were a “very important breakthrough” for project, which currently contains an indicated and inferred mineral resource of 20.7 Mt grading 1 g/t Au for 685,000 oz of gold.

“Positive ore sorting results have the potential to deliver a step change in the feed grade of material delivered into any mineral processing circuit,” he said. “Subject to further positive results, we may have the potential to significantly improve options for the economic development of Apollo Hill.”

Two Mile Hill underground mine concept a step closer following ore sorting trials

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The stage two ore sorting campaign on drill core from Middle Island Resources’ Two Mile Hill tonalite gold deposit in Western Australia has confirmed the technology’s potential to improve gold grades and cut waste processing.

Two Mile Hill, part of the wider Sandstone gold project, comprises a “ubiquitously gold mineralised, tonalite (granite) plug or stock”. At surface, the deposit measures some 250 m in length, 80-90 m width and extends to at least 700 m depth. It is some 4km north of the company’s 600,000 tonne per year Sandstone processing plant.

Middle Island has been looking for ways to improve the economics of mining the deposit through the use of ore sorting technology. This followed recognition that more than 96% of the gold at Two Mile hill was hosted by quartz veins within the tonalite. The deposit hosts 391,000 ounces of gold inferred resources grading 1.35 grams per tonne, according to a 2004 JORC study.

Stage one trials, using X-ray and optical sensors, indicated sorting could deliver a 185-257% increase in feed grade, with gold recoveries in excess of 93%. Up to 64% of the sorter feed material could be rejected, delivering significant economic benefits.

While stage one focused on the concept of selective underground mining with open stoping – therefore, using diamond core intervals with a higher head grade – the latest trials envisaged sub-level caving and took into account core that was representative of the entire sample.

A series of four primary (fresh) composites and a single transitional (partially oxidised) composite comprising intervals of half HQ and half PQ diamond core from hole MSDD261 were selected for crushing prior to ore sorting.

The results from stage two trials, which involved initial sighter and scoping tests at both Steinert in Perth and TOMRA in Sydney before moving onto the latter’s commercial scale sorting equipment and a combination of colour and X-ray sensors, were “broadly in line with the earlier scoping trials”, Middle Island said.

Sorting of the primary composites (A, B and C) resulted in upgrades to the sorted concentrate in the range of 155-213%, with the majority of gold selected by way of colour differentiation. Sorting recoveries for primary composites ranged from 67-93%, while sorting yields (percentage of feed reporting to product) ranged from 39-51%.

Middle Island said: “Recoveries and yields are variable, and somewhat lower than demonstrated in the preliminary work, in part due to the higher proportion of fines generates by crushing the larger diameter core and in part by weaker oxidation and associated iron-staining in material comprising Primary Composite A.”

These results are a precursor to an updated resource estimate for the upper half of the 0.9-1.5 million ounce exploration target at Two Mile Hill and an underground mining study.

The company thinks further work is needed to ascertain the factors that give rise to the variance in recoveries between the samples, with stage three ore sorting testwork likely focusing on these aspects and anticipated enhancements using TOMRA’s recently commissioned, commercial-scale, laser sorting unit.