Alice Queen says German ore sorting technology could be ideal for material from Horn Island gold project

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By Imelda Cotton - 
Alice Queen ASX AQX Tomra bulk ore sorter Horn Island gold

Ore sorter test work resulted in a “significant” uplift in gold grades from Horn Island samples.


Advanced gold explorer Alice Queen (ASX: AQX) has confirmed material from its Horn Island gold project in Queensland’s Torres Strait could benefit from German low-cost, low-energy processing technology.

Samples of drill core and historic mine waste dump material from the project site were the subject of a pilot-scale test program in February to test the amenability of the material to specialised techniques developed by Germany’s Tomra Ore Sorter Solutions Pty Ltd.

Tomra used its proprietary XRT sorter system to sort two bulk samples of mineralised vein material from barren granite host rock.

The samples included a 2-tonne diamond drill core composite sample from Horn Island’s resource area and a 5t sample of legacy low-grade stockpiled material from the historic 1980s gold mining operation.

High-volume feed rates of 48t per hour and 79tph were applied to return high gold recoveries of 94% and 93%, respectively.

A significant uplift of gold assay grades was returned for the drill core samples, achieving up 392% increase with a significant mass reduction of up to 88%.

Waste dump material recorded a 463% increase in grade and a reduction mass of 89%.

Grade increases

Alice Queen managing director Andrew Buxton said the test program demonstrated the XRT sorting system’s ability to achieve grade increases, low mass pull to the concentrate stream, and high-volume throughputs.

“By reducing the mass of ore reporting to the capital and energy-intensive grinding and leaching circuits, we believe the project’s economics will be significantly enhanced,” he said.

“The results [overall] indicate positive amenability to the Tomra XRT sorting technology and will be integrated into metallurgical testing for our ongoing scoping study.”

Electrical x-ray system

Tomra’s proprietary XRT sorter employs a broadband electrical x-ray system which is applied to the material to be sorted while it is moving along a conveyor belt.

The system sits below the belt and produces a digital image of the material using two different energy bands.

X-ray attenuation through the material is different within the two bands and depends on the material thickness and atomic density, which allows for the identification and separation of sulphide-containing material from barren waste, which is then rejected.