Extensive metallurgical testwork has been carried out on the Watershed deposit. Mineralogical investigations of the ore have been made from both bulk samples and metallurgical drill core from 11 HQ/PQ holes drilled specifically for this purpose.
The metallurgical bulk samples were targeted to be representative of the ore resource by taking samples across the whole deposit to ensure that the scheelite mineralisation was amenable to the proposed metallurgical flowsheets.
More than one hundred tonnes of material were mined from two adits and a single surface location. A total of 11 HQ/PQ drill core samples were drilled into the deposit to obtain spatially representative samples for metallurgical viability testing.
A characteristic of scheelite ores is that scheelite grinds preferentially to other minerals and over grinding must be prevented in order to maximise mineral recovery. The flowsheet has been developed to meet these objectives.
Based on recent ore-sorting, gravity separation and flotation testwork Sedgman and Vital have developed a process flowsheet which includes:
- Two stage crushing to -80mm;
- X-Ray Transmission (XRT) ore sorting at three sizes -80+40mm, -40+20mm, and -20+10mm;
- Rod mill grinding of -10mm and XRT accept material to -600 microns;
- Gravity Separation Circuit incorporating Spirals and Screening;
- Ball mill grinding to 100% -125 microns, and
- Three stage flotation circuit:
- sulphide flotation
- scheelite flotation, and
- modified Petrov Process heated scheelite flotation.
Average plant recovery is projected to be around 73.6% WO3, with a tungsten product grade in excess of 65% WO3, and very low levels of arsenic
Opportunities to increase the metallurgical recovery have been identified, and with further test work recoveries could be increased up to around 77% WO3 by simplifying the process flowsheet including the removal of the sulphide flotation stage.