The verdict is positive on the Tomra ore sorter at the Cariboo gold project in British Columbia, says owner Osisko Development. Using an x-ray transmission (XRT) sensor, the equipment does improve the grade.
A 2,200-kg ore sample was first screened to remove fine particles <10 mm so that it would compare to the medium grade mineralized material typically found around high grade veins and replacements of the deposit. The grade of the remaining 1,800 kg was passed through the sorter, and the grade increased.
The tests proved that 50% of the waste rock can be removed from the ore after initial crushing using the XRT sorter for less than C$2 per tonne. That means almost 50% less material that needs further grinding and flotation. The lesser mill throughput will save an estimated 30% in capital costs, 25% in processing costs, and 7% of overall operating costs. Process water and power consumption in the mill will also be cut by as much as 50%.
Less rock and water going through the mill also means fewer tailings. Osisko estimates that only 13% of all extracted ore will need storing at the existing QR mill facility as filtered tailings.
Osisko says that ore grading higher than 4.0 g/t gold will go directly to flotation and lower grades will be passed through the sorting process before further treatment. Gold recovery from flotation of the higher grade ore is 98.3%.
Further testing of the ore sorting technology is planned.
(This article first appeared in the Canadian Mining Journal)