American Rare Earths Ltd (ASX:ARR)’s recent metallurgical tests have paved the way for a potentially low-cost mining and processing operation using conventional technology.
Metallurgical work at the Halleck Creek Rare Earth Elements Project in Albany County, Wyoming, USA, conducted by Wood Australia, shows that Halleck Creek has favourable characteristics on several counts:
- Low ore strength: the ore can be liberated easily, with the ore strength ranking in the lowest 14th percentile of more than 1,300 deposits globally. This requires minimal energy use.
- Ore abrasiveness is below average.
- The ore will require less coarse grinding at the processing plant, meaning another level of energy expenditure and the opportunity to increase capacity.
- These factors will make possible a simplified flow sheet reflecting lower capital cost outlays.
Managing director Chris Gibbs said that one of the major costs in any processing plant was within the crushing and grinding circuit.
“These test results indicate there could be significant energy savings due to the ore softness. Simply put, the easier the ore is to crush and grind, the lower our operating costs will be.
"It will also enable higher throughput rates and efficiencies as the comminution circuit is so often the limiting factor for plant capacity. And, apart from energy savings, the less abrasive ore will lead to reduced wear and tear.”
About the test work
Under the guidance of Wood Australia, Nagrom Laboratories concluded the Feed Characterisation/Comminution module of the test-work program.
This included SMC Testing Pty Ltd (SMC) which produces data used for the sizing of SAG mills and was originally designed to support Mine-to-Mill studies.
The SMC test work results indicate low ore competency which would translate to low specific energy consumption in a SAG mill.
Compared to SMCs global database of more than 1,300 deposits, Halleck Creek was rated in the 14th percentile for ore competency. The Bond abrasion index test returned a value of 0.24, which is below the average of Wood Australia’s database.
The Bond ball mill work index test result of 15.6 kWh/t is close to average hardness relative to Wood’s database.
The combination of values suggests that Halleck Creek ore should be suitable for processing in a SAG-ball mill configuration without the need for pebble crushing and could also be processed in a single-stage SAG mill.
Other modes of grinding, such as high-pressure grinding mills and vertical roller mills may also be considered down the track when sufficient sample mass is available for testing.
Supply chain player
The work being done at Halleck, as well as its operations at the La Paz REE project in Arizona, is designed to position ARR as a key player in the North American supply chain for the renewable future.
ARR has welcomed US Government policy that now supports the revival of the American rare earths industry which will see it decrease dependence on Chinese supply.
What’s next
Test work is now underway on additional steps in the process flow sheet, including magnetic separation testing being done at Nagrom Laboratories in Perth, Western Australia.
ARR will then transition to flotation testing of WHIMS magnetics at Auralia Metallurgy, to assess the potential for further upgrading.
Following that, testing will start on the leach process using Watts & Fisher’s proprietary leach technology. ARR will continue to provide updates on metallurgical testing as results come to hand.
The company feels that combined with mineralogy test results announced earlier this month, the economic and technical benefits from these new test results could be significant.
Previously ARR advised that mineralogy tests have shown that rare earths host mineral at Halleck Creek can easily be liberated, while the host mineral Allanite contains approximately 90% of total rare earths present.
ARR noted that Halleck Creek has the potential to be a key strategic project with the US, helping to bring supply of critical rare earths onshore.