Tag Archives: Vista Gold

TOMRA continues to build ore sorting Insight across mining space

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

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

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

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

TOMRA’s Harold Cline & Jordan Rutledge

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

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

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

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

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

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

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

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

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

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

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

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

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

Vista Gold sorts Mt Todd ore processing issues with TOMRA’s XRT technology

Vista Gold has turned to TOMRA Sorting Mining’s ore sorting technology to reignite the Mt Todd gold project, in the Northern Territory of Australia.

Mt Todd, which was acquired in 2006, hosts one of the country’s biggest undeveloped gold resources. A recently completed prefeasibility study outlined a 50,000 t/d operation producing 413,400 oz/y of gold over the 13-year mine life at Mt Todd, with average all-in sustaining costs of $746/oz.

Mt Todd briefly operated in the 1990s, but is known for having hard ore that can prove tricky when finding an efficient processing route.

Fred Earnest (pictured below), President and CEO of Vista Gold, said: “We had a desire to find a way to only be spending money to process the rock that had gold in it. We started looking for ways that we could get rid of the non-mineralised host rock prior to the grinding circuit.”

The company looked at different technologies to address the issues at Mt Todd and contacted TOMRA to find out about its sensor-based sorting technology, Earnest said.

TOMRA invited the Vista Gold team to visit its testing facility in Germany with a sample from the project to see first-hand what could be achieved, TOMRA said.

The test was an eye opener for Fred Earnest, according to the technology company: “In every evaluation of new technology, we have ‘aha moments’. For us it was the day we were at the facility in Germany watching our rock be sorted on a production-scale machine. When we saw how fast it was happening, when we saw the product sorted and rejected, and when we were able to pick it up and look at it – we realised that this was not just a dream, this was real technology being applied at a production rate to our rock.

“All of a sudden, we realised that this was technology that would work for us at Mt Todd and that we needed to evaluate more seriously.”

Following extensive testing, Vista Gold has integrated TOMRA’s two-stage sorting solution in its planned flowsheet at Mt Todd: the system sorts 20 t/h, using X-ray Transmission (XRT) technology to remove particles containing sulphide minerals and subsequently lasers to remove particles containing quartz and calcite.

The benefits of TOMRA’s solution to the Mt Todd project are two-fold, according to the company.
On the one hand, operating costs have been reduced: “We’re getting rid of material and we’re not spending money grinding rock that has no value,” Earnest explains. On the other hand, gold recovery has improved: “We’ve been able to make design changes in the plant. Because we’re processing less material, we’re now able to do a finer size. With finer grind, our gold recovery has gone up. This has resulted in improvements of grade by 10%. Our feed grade to the mill has gone up from 0.84 g/t to now 0.91g/t.”

What’s more, the savings in operating costs have paid for the improvements to the plant, according to TOMRA.

Earnest said: “We’ve been able to achieve all of this on a capital-neutral basis. We’ve been able to incorporate the equipment for the sorting to add fine grinding equipment, all with the money that we’ve saved from the ball mills.

“And, so ore sorting has opened up a whole new window of opportunity for us with the Mt Todd project. We’re very excited about what this technology means to the mining industry and specifically to our projects in the future. And we look forward to seeing this technology grow and become even more efficient and of greater value to us.”

TOMRA says it worked closely with Vista Gold’s team to identify the best solution for the Mt Todd project – from testing rock from the mine at its facility in Germany, to analysing the situation at the project and advising on how its sensor-based sorting technology could fit in its operation to deliver the best results.

Earnest added: “We have been thoroughly impressed with the team at TOMRA. We’ve done a number of tests with them, we’ve worked with them closely. The people at the [testing] facility in Germany have been very accommodating. We’ve been able to be there on the floor, watching the test, looking at the results, asking questions. It’s helped us immensely to have this open exchange with the team at TOMRA and we look forward to a very long relationship with them.”

Vista Gold Mt Todd PFS points towards use of ore sorting, fine grinding

Following extensive metallurgic test work carried out over the past year, Vista Gold looks like it has settled on a flowsheet for its Mt Todd gold project in the Northern Territory of Australia that includes ore sorting and the selection of the FLSmidth VXP mill as the preferred fine-grinding mill.

The company detailed this in an updated prefeasibility study (PFS) for the project, which factored in the results of metallurgical optimisation test work, a redesign of the fine grinding circuit, construction and ramp-up schedule changes and a comprehensive review of all aspects of the project.

The process improvements resulted in improved projected gold recovery and increased estimated gold production at Mt Todd, Vista Gold said.

According to the PFS, a 50,000 t/d operation at Mt Todd could see the operation produce 413,400 oz/y of gold over the 13-year mine life at average all-in sustaining costs of $746/oz.

The estimated initial capital requirement came in at $826 million, with the project offering an after-tax net present value (5% discount) of $823 million at a $1,350/oz gold price and a $0.70=A$1.00 exchange rate.

In the company’s metallurgy, processing and infrastructure section, it detailed the processing side of Mt Todd, saying that recent metallurgic test programs had confirmed the efficiency of ore sorting across a broad range of head grades and the natural concentration of gold in the screen undersize material prior to sorting. The company carried out such test work at TOMRA Sorting Solutions in Germany, where two-stage (X-ray Transmission and laser) sorting tests were completed using production-sized and commercially available equipment.

It also said such test work had confirmed the efficiency of fine grinding and improved gold leach recoveries at an 80% passing grind size of 40 microns, in addition to the selection of the FLSmidth VXP mill as the preferred fine-grinding mill.

The company previously sent samples to Core Metallurgy Pty to obtain fine grinding data simulating grinding in the horizontal IsaMill and to the FLSmidth Minerals Testing and Research Center to obtain data simulating grinding in the vertical VXP Mill.

HPGR and ore sorting stack up for Vista Gold’s Mt Todd gold project

Toronto and New York-listed Vista Gold reports recent high pressure grinding roll (HPGR) crusher and ore sorting tests on high-grade samples at its Mt Todd gold project, in the Northern Territory of Australia, have confirmed previous test results.

The company has also announced plans to complete fine grinding and leaching tests in the March quarter and to follow these results with updated prefeasibility study (PFS) economics in the June quarter.

Vista said additional HPGR and ore sorting tests were completed on two, 2.5 t samples from Mt Todd’s Batman deposit containing 1.39 g/t and 1.70 g/t gold, respectively. This testing programme confirmed two important results:

  • HPGR crushing, followed by screening, results in increased concentration of gold in the fine fraction, and;
  • The small amount of gold lost in the rejected material is proportionally lower when sorting higher-grade material.

As with previous tests, the samples were HPGR crushed at the facilities of ThyssenKrupp Industries in Germany and screened at 16 mm. The coarse fraction (+16 mm) was sent to the facilities of Tomra Sorting Solutions in Germany, where two-stage (X-ray Transmission and laser) sorting tests were completed using production-sized and commercially available equipment. The following table summarises the results of the testing programme for each of the samples and compares these results to previous bulk tests on low-grade samples:


(g Au/t)

Sorter Feed (+16mm) Sorter Product Sorter Reject Gold Loss (%)
Fraction of Total Sample (%) Grade

(g Au/t)

Fraction of Total Sample (%) Grade

(g Au/t)

Fraction of Total Sample (%) Grade

(g Au/t)

1.39 17.8% 0.731 9.4% 1.238 8.4% 0.158 1.0%
1.70 18.6% 0.737 10.3% 1.239 8.3% 0.110 0.7%
Previous Results
0.63 17.5% 0.533 10.5% 0.817 7.0% 0.103 1.1%
0.34 17.8% 0.255 11.0% 0.365 6.8% 0.075 1.5%
0.67 18.7% 0.619 11.3% 0.901 7.4% 0.192 2.0%

Frederick Earnest, President and Chief Executive Officer, said the tests confirmed the benefit of ore sorting for Mt Todd and demonstrated lower gold losses with higher grade crusher feed.

“We attribute these results to the favourable characteristics of the Batman deposit. Simply stated, the gold-containing sulphide minerals and quartz/calcite veining are more easily broken into small particles than the non-mineralised host rock,” he said. “Where this breakage does not result in clean separation from the host rock in the first pass of HPGR crushing, the gold-bearing minerals are easily identified and separated in the ore sorting circuit.”

The results complement Vista’s previously announced fine grinding and leaching test results, Earnest said, adding that he expects them to support additional improvements in the economics of the Mt Todd gold project when the PFS is published later this year.

The crushed and sorted samples have been transported to the facilities of Resource Development Inc, where sample preparation has been completed for assaying and additional fine grinding, leaching and tailings characterisation tests.

Samples are being sent to Core Metallurgy Pty to obtain additional fine grinding data simulating grinding in the horizontal IsaMill and to the FLSmidth Minerals Testing and Research Center to obtain data simulating grinding in the vertical VPX Mill.

“Both tests will target a final product size of 38-45 microns and will generate a sufficient volume of material for subsequent leach tests,” the company said, adding the fine grinding and leach tests were expected to be completed in the March quarter, with final results expected in the following quarter.

The company has completed additional tailings characterisation tests and concluded that no material design changes are required to proceed to the economic analysis using a final grind size of 38-45 microns.