Tag Archives: pyrite

Heritage eyes up Mount Morgan riches, rehabilitation

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A partnership between GreenGold Engineering and Heritage Minerals Pty Ltd has plans to return the Mount Morgan gold mine in Queensland, Australia, to some of its former glory by creating a mean and green way to extract gold from its ample tailings deposits.

The cooperation allows Heritage Minerals to develop the project in a proactive program to maximise the best chance of project success, the company says. Heritage admits it has a big task on its hands, facing doubters that have witnessed a string of false starts at Mount Morgan.

The story behind Mount Morgan dates to 1882 when a syndicate was created to open a gold mine at Ironstone Mountain, 39 km south of Rockhampton.

Ironstone Mountain, later renamed Mount Morgan, was originally operated as an open-pit gold mine at the top of the mountain, before being converted to an underground copper and gold mine.

In 1935, it transitioned back to an open-pit operation and continued until the mine closed in 1980. After this, Peko Wallsend Ltd ran a tailings treatment operation from 1982 until 1991, recovering gold from 27 Mt of tailings.

Mount Morgan pioneered many metallurgical processes to cope with the unique properties of the ore over this time. From chlorine leaching in the early days to various flotation and smelting furnace techniques for the copper/gold ore, the Mount Morgan tailings stockpiles have a rich and varied history.

At different stages over the life of the mine, copper was either a bonus or a nuisance. When copper grades were high, copper was a financial benefit; when the copper grade was low, the metal increased the operating cost associated with gold recovery.

This more than century of mining and processing came with consequences.

The pyrite remaining in the mine and tailings dumps is acid-forming and has generated a significant environmental legacy which remains today. This legacy has become the responsibility of the State of Queensland (1993) and is managed by the Department of Natural Resources and Mining’s (DNRM) Abandoned Mines Division.

Despite these environmental liabilities, five companies have come back to Mount Morgan since Peko Wallsend stopped operations in the early-1990s, encouraged by higher yellow metal prices and improved processing options for the refractory ore.

“We’re the sixth company to have a shot at reprocessing the tailings, with none of the companies before us getting past the feasibility study stage into financing,” Peter Mellor, Corporate Secretary at Heritage Minerals, told IM.

All of them were unsuccessful primarily because of the presence of nuisance copper and the high cyanide consumption that comes with removing this, according to Mellor.

The most recent company to try its luck at Mount Morgan is a case in point.

ASX-listed Carbine Resources developed a process flowsheet to remove part of the troublesome copper by acid leaching the tailings and producing copper sulphate. Additional revenue from the production of pyrite concentrate supplemented gold sales.

It was the production of premium quality (50% sulphur) unroasted iron pyrite concentrate that enabled the commencement of the reduction of acid-forming material at Mount Morgan, Carbine said.

Despite coming up with a 1.1 Mt/y blueprint that, in the expanded case, could operate for 20 years and produce 23,000 oz/y of gold, 2,700 t/y of copper sulphate and 200,000 t/y of pyrite concentrate, the plan ultimately fell down on the projected economic returns, negatively impacted by excessive royalty liabilities.

A February 2018 update came with a revised operating model at Mount Morgan showing all-in sustaining costs (AISC) of A$862/oz ($621/oz), A$313/oz higher than the company’s December 2016 feasibility study.

“The increase is due primarily to higher cyanide consumption and lower by-products credits due to a lower pyrite price and the loss of copper sulphate premium associated with a change in the copper products produced,” Carbine explained.

Fresh approach

To be fair to Mellor and the Heritage team, they are not looking to repackage the same project blueprint in a markedly better gold price environment as other companies have been known to attempt. Instead, they are setting up the project and the town of Mount Morgan for a brighter and sustainable future.

After gaining rights to the project from Norton Gold Fields following Carbine’s exit, one of the first things Heritage did was appoint GreenGold to carry out the definitive feasibility study.

Equipped with its ReCYN resin-based technology that has been shown on other projects to reduce cyanide consumption by up to 50% through capturing free cyanide from plant tailings and recycling it back into the leach circuit, the selection was an obvious choice.

The company could potentially detoxify the tailings stream and clean up the water discharge at Mount Morgan. This would be a boon for the DNRM, which currently treats the water from the open pit and tailings deposits before being released into the local creek due to the low pH levels caused by the acid-forming pyrite.

“Our process plant will use this water, treat it and send it out as clean water down the creek,” Mellor explained.

This is one of several changes the company is implementing to make the project viable.

“For example, Carbine were previously looking to float off the nuisance copper at the start, which came with the associated capital costs of building a flotation plant,” Mellor said. “Yet, the copper really represented a low amount of revenue (2,700 t of copper sulphate in the studies) overall.”

The ReCYN resin plant can deal with the higher cyanide consumption needed to treat the copper at the back end of the flowsheet. This will allow the company to focus on the gold – which represents 90% of revenue – that can be processed by a technically-simple carbon in leach plant.

Malcolm Patterson, MD of Heritage Minerals, and Peter Papa, Technical Director of Heritage Minerals, observe the task ahead at Mount Morgan

The open pit is partially filled with previously processed tailings, with Mellor saying the reprocessing of 10 Mt of tailings (averaging 1.1 g/ Au) can help complete the rehabilitation process.

“We have come up with a really neat environmental rehabilitation scenario where we fill the existing open pit up, and cap it all off nicely so the surface water cannot penetrate,” he said.

Set to build a 2 Mt/y plant to re-process this material, Heritage is only looking five years out from first production, although there is potential for this processing quantity to be doubled.

Even with this near-term gaze, the definitive feasibility study (DFS) anticipates a one-year payback and an upfront capital expenditure bill of A$74 million (compared with Carbine’s last A$96 million estimate).

“There is more potential than this,” Mellor says of the feasibility study, highlighting several areas of interest within proximity of the existing open pit. “Yet, we wanted to get the economic, environmental and social aspects ticked off first before laying out any longer-term plans.”

The company has been very thorough in coming up with this five-year plan.

Already blessed with an extensive JORC resource database from previous Mount Morgan tailings reprocessing protagonists, the company continued to drill for tonnage and bulk density definition of the tailings resource; the latter with a Dando percussion drill rig capable of punching 1 m cores down to 30 m depth.

With a board decision on the DFS expected before the end of the year, Heritage could soon enter the financing stage, followed (hopefully) by construction.

If all goes to plan, operations – a simplified earthmoving and processing method – could begin in 2022.

“Mount Morgan is definitely not the easiest site, but it is the most prestigious in terms of history and challenges,” Mellor says.

Heritage and GreenGold will soon be judged by the financing community on whether they are up to such a challenge.

Orica turns wireless blasting dream into a reality at Europe’s deepest mine

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In Europe’s first demonstration of wireless blasting, Orica has enabled First Quantum Minerals’ (FQM) Pyhäsalmi underground mine in Finland to recover ore it previously thought inaccessible.

Orica’s WebGen™ 100, the first truly wireless rock blasting system, has been used in trials at the zinc-copper-pyrite mine since September 2018, with FQM, to date, carrying out five blasts.

Since the invention of the safety fuse by William Bickford in 1831, there has been three revolutions in blast initiation methods – electric detonators (1930s), shock tube (1980s) and electronics (~2000s). Every new initiation method development has increased the safety, precision and possibilities of initiating blasts.

The new Safety Integrity Level 3 certified WebGen system could end up being the fourth revolution in this line-up, Orica believes.

Still in its infancy with, as of August, more than 250 blasts fired using wireless initiation, the WebGen technology has already led to the development of several new mining techniques such as Temporary Rib Pillar (TRP), Temporary Uppers Retreat Pillar, Reverse Throw Retreat, Longitudinal Transverse Retreat and Pre-Loaded Retreat that would not be viable or possible without wireless blasting technology.

WebGen comprises the following components:

  • WebGen primer and accessories – including the high explosive Pentex™ W booster, i-kon™ plugin electronic detonator, the Disposable Receiver (DRX) and the encoder controller;
  • Transmission system – including transmitter, antenna and transmitter controller; and
  • Code Management Computer (CMC) – including the unique global blast and arm codes.

The system achieves wireless blasting through very low frequency magnetic induction (MI) signals communicated to the in-hole primer, with the special site-specific group ID, arm and firing codes embedded in the MI signals. The system eliminates the lead wires of conventional initiation systems, thereby also eliminating the ‘hook-up’ process at the blastholes.

The operation works as follows: The i-kon plugin detonator plugs into the DRX, energising the device and initiating a self-test. After passing the self-test, the device can be encoded with the blast code and the delay timing. The booster is attached after encoding the device. At this stage the WebGen primer is ready to be placed into the blasthole.

The transmitter controller – a magnetic induction system connected to an antenna – sends the arming signal to the transmitter. Once the arming process is successful the firing window is presented to the blaster.

The CMC is the data hub of the system and supplies the identification and firing codes as well as the mine specific codes. Orica explained: “It culminates in the ready to fire file for transmission.”

Game changer

With the elimination of lead wires, it is possible to pre-charge a full stope (eg sub-level caving mining method) and fire every ring when required without sending personnel back to the dangerous brow area to connect lead lines, Orica says. “Misfires related to damaged wires are eliminated and primers can be fired regardless of any dislocations of blasthole and/or charge.”

The Ernest Henry mine, in north-eastern Australia, engaged Orica in 2016 to perform a demonstration of sub-level caving using WebGen. The mine wanted to reduce the time spent by personnel at the brow of the cave. With the use of WebGen they were successful in pre-loading the stope production rings and eliminating the need to return to the brow for hooking up.

At Newmont Goldcorp’s Musselwhite mine, productivity and ore recovery were the main drivers for looking into wireless blasting. Together with Orica, Musselwhite developed the TRP mining method where a temporary pillar is used to withhold backfill while the second mass blast (i-kon electronic detonators) of the stope is mucked out.

Orica explained: “Once the stope is mucked out, the TRP is fired remotely and the ore can be recovered.”

With this method the mine established a 93% reduction in dilution, increase in mucking of 27% and a two-week saving in time per stope, the company said.

FQM – Pyhäsalmi

In March 2018, a team of Orica Technical Services Engineers commenced preparations and planning for the first wireless demonstration in Europe with the FQM Pyhäsalmi mine, in Finland, the deepest mine in the continent.

At the time, the mine was scheduled to close in September 2019; most of the stopes had been mined out and the remaining stopes and pillars were becoming increasingly challenging to mine. Orica said: “Pyhäsalmi had developed a system to mine the stranded pillars, but this was incurring considerable time and costs. Pyhäsalmi mine acknowledged that WebGen 100 could be a solution for the problems in retrieving remaining ore in difficult areas.”

As a first stop, the Orica team of blasting specialists had to assess if the WebGen system would successfully function in Pyhäsalmi mine. “Before firing the WebGen shot it was important to investigate if the system would work in the mine and what the maximum signal reach would be for both the quad loop and cable loop antenna,” the company said.

Signal strength testing provides positive confirmation of coded signals being received through the mine and also validates if there are any parts of the mine where the system has a reduced range.

A smaller antenna and a larger antenna were tested.

Pyhäsalmi experiences occasional sulphur dust explosions and, therefore, personnel are not allowed to be underground while blasting, Orica said. As a result, blasting takes place at the end of the shift after the shift explosives supervisor checks everyone has vacated the mine.

Initial signal testing with the smaller antenna validated the system was working with a range of at least 200 m. Further signal testing was performed using the larger antenna.

It was validated the system could send and receive signals from the production level to the furthest stope, which was 450 m away, Orica said.

After assessing the MI signal test results, it was decided it would be more convenient to use the smaller antenna.

In September 2018, the EMEA WebGen team returned to Pyhäsalmi mine for the first wireless blast in Europe. The final three rings of stope 18b10-11 on Level 1,175 were selected for the demonstration blast.

On September 4, 2018, at 22:00, the first wireless blast in Europe was fired without any issue.

Since the introduction of wireless blasting, Pyhäsalmi mine has fired a total of five blasts in challenging areas.

For one of the wireless blasts, a stope would not be accessible after the first blast, but, as the stope could be pre-loaded with wireless detonators, the mine could blast and produce 4,000 t of extra ore that otherwise would have been sterilised.

Katja Sahala, Mine Planning Engineer, FQM Pyhäsalmi mine, said she saw the WebGen wireless system as helping operations in several applications such as when ore needs to be left behind to support pillars, or where there is weak rock, or fill and selective mining is required.

She said: “In uphole charging, you need to work close or even below an open face during drilling and blasting. If it’s possible to drill and charge an entire stope before the first hole is fired, then safety will surely be improved.”

Orica said wireless blasting is a new and exciting technology that eliminates the use of cumbersome and complex wiring hook-ups while having the accuracy of an electronic detonator. It has already enabled safer work methods and mining techniques that increase recovery, productivity and efficiency, according to the company.

It concluded: “Many technical and regulatory challenges will be faced by wireless blasting, but it is a fundamental step in the automation of the explosives charging and blasting process. With the first WebGen blasts at FQM Pyhäsalmi mine, wireless blasting is no longer a dream in Europe, but a reality.”