Tag Archives: Hemi

Weir to supply Enduron HPGR for De Grey Mining’s Hemi gold project

Comminution of minerals, Mineral processing, Mining equipment, Precious metals, , , , , , , ,

Weir has been awarded the contract to supply a large ø2.4m x 2.25 m Enduron® HPGR (high-pressure grinding rolls) for De Grey Mining’s flagship Hemi gold project in the Pilbara of Western Australia.

Hemi has a mineral estimate of 10.5 Moz and at full capacity, the processing plant will have a nameplate throughput of 10 Mt/y.

Peter Holmes, Project Director of De Grey Mining, said: “De Grey Mining is pleased to partner with Weir on one of its key long lead items for its Hemi Gold Project and appreciates Weir having a local service facility to provide the required support to our site and the region.”

Bjorn Dierx, Global Product Manager for Enduron HPGRs, said: “Our partnership with De Grey Mining further expands our footprint in sustainable comminution. Our proven track record of developing highly engineered solutions for the industry, together with our capability to partner with our customers to bring projects to life, ensures that De Grey Mining will be in good hands to achieve its productivity, sustainability and project execution targets.

“The Hemi gold project will benefit from Weir’s state-of-the-art Enduron HPGR technology, which delivers operational flexibility, grinding efficiency and equipment availability. Importantly, Enduron HPGRs also provide significant improvements versus traditional tumbling mill technology with energy savings of up to 40% and in turn, a lower carbon footprint. This will be the fifth, similar-sized Enduron HPGR in the Pilbara region alone, which is a testament to its credibility in high capacity, hard-rock grinding.”

Weir recently opened its Port Hedland Service Centre, strategically located to support its customers in the Pilbara region in Western Australia. The centre features facilities for Enduron® HPGR servicing, including tyre roller assembly, and will allow De Grey Mining to benefit from product training in close proximity to the mine site.

Kristen Walsh, Regional Managing Director of Weir’s Minerals Division, said: “This win further underscores Weir’s commitment to making mining more sustainable and demonstrates the substantial opportunity that can be made to CO2 emissions reduction when choosing an energy-efficient technology in a large greenfield project.”

Wood tradeoff study puts HPGR, POx processing ahead at De Grey’s Mallina gold project

Comminution of minerals, Environmental, Mineral processing, Mineral project development, Mining equipment, Mining services, Precious metals, Sustainable mining, , , , , , ,

Prefeasibility process engineer Wood Australia has completed a comprehensive nine-month trade-off study into the preferred process flowsheet design for De Grey Mining’s Mallina gold project, selecting a process flowsheet that incorporates high pressure grinding roll (HPGR) and pressure oxidation (POx) technology.

The project, which includes the Hemi Deposit, is in the Pilbara region of Western Australia.

In late 2019, De Grey made a large scale, high value, near surface gold discovery at Hemi – an intrusion-hosted form of gold mineralisation new to the Pilbara region that, the company says, shows a scale of mineralisation not previously encountered in the Mallina Basin. The company currently has 6.9 Moz of measured and indicated resources declared at the project, with plans to turn this into an open-pit mining operation down the line.

The findings have come out ahead of the full PFS, which is due for announcement in the September quarter of this year.

The trade-off study has confirmed that Hemi mineralisation has excellent recovery and is amenable to HPGR and POx processing technologies, the company said. The process route chosen has demonstrated advantages relative to other processing technologies including:

  • Proven and accepted technology for the scale of operation and style of mineralisation;
  • Lower capital and operating costs;
  • Higher gold recovery between 93% and 95% depending on average feed grades;
  • Circa-20% lower energy consumption;
  • Circa-25% lower reagent (lime) consumption;
  • Circa-25% lower CO2 emissions;
  • No heat addition required to sustain – or cooling to control – the POx process; and
  • Robust and proven equipment.

The flowsheet selections have the benefit of lower carbon emissions through lower energy requirements and lower greenhouse gas emissions as a result of improved neutralisation and consequent lower lime consumption, De Grey added.
“Further studies are in progress as part of the PFS on the carbon intensity and greenhouse gas emissions for the Mallina Gold Project development,” it said.

The currently envisaged flowsheet at Hemi sees ore crushed and ground in the comminution circuit before being fed to the flotation circuit. Any gravity recoverable gold will be recovered prior to flotation with the use of, for example, a Knelson or Falcon concentrator. Test work has shown gravity recoverable gold is present in the Hemi and regional mineralisation, and the extent of gravity-recoverable gold will continue to be assessed through test work.

The flotation circuit will process gold bearing sulphides in Hemi ore producing a “low mass pull” gold-rich sulphide concentrate. The POx circuit is designed to receive the gold-rich sulphide concentrate from the flotation circuit. The POx circuit will have a throughput of 8% (800,000 t/y) of the throughput of the comminution circuit.

The POx circuit will convert the sulphide concentrate to a gold bearing residue amenable to standard carbon in leach (CIL) processing. The underflow from flotation is also amenable to standard CIL processing. Both streams will enter the CIL circuit followed by electrowinning to produce gold bars on site. This has numerous benefits for the POx circuit including lower capital and operating costs compared with projects that require whole of ore treatment through POx.

Tailings from the CIL circuit will be pumped to a tailing storage facility.

Hemi mineralisation has two significant and attractive mineralogical characteristics that lead to the overall expected metallurgical recovery of between 93% and 95% at expected mined grades, namely:

  • The majority of gold at Hemi can be floated into a low mass pull concentrate that recovers very high levels of sulphides and gold ahead of oxidation; and
  • The flotation tail contains gold that can be successfully recovered using standard CIL processing.

The crushing circuit will include a primary gyratory crusher, a secondary cone crusher and. The secondary cone crusher will operate in closed circuit with a sizing screen while the HPGR will operate in closed circuit with wet sizing screens to produce a nominal less than 7 mm mill feed. The grinding circuit will consist of two ball mills with conventional pinion drives each with their own classification circuit.

The oxidation circuit throughput for Hemi is proposed to be 800,000 t/y, or 8% of the proposed comminution circuit throughput of 10 Mt/y. The oxidation circuit will treat the gold-bearing sulphide concentrate generated by the flotation circuit. The POx circuit will consist of flotation concentrate thickening and storage, POx utilising autoclave technology and neutralisation in association with the flotation tail prior to co-leaching in a CIL circuit.

The oxidation circuit will be designed to have sufficient storage capacity prior to the autoclave to allow for maintenance shutdowns without the need for a mill shutdown. This decouples the comminution and oxidation circuits ensuring that each circuit does not impact on the availability of the other.