Resumen de Northern's dysprosium hopes with Brown
Over 74,000 metres of drilling underpins the current total mineral resource at the Browns Range project which is estimated at 6.48 m tonnes at 0.74% TREO containing 4,000 tonnes dysprosium within 47,997 tonnes TREO using a cut-off grade of 0.15% TREO ( Table 1 ). At the Wolverine deposit the total mineral resource is estimated at 4.46 m tonnes at 0.86% TREO containing 3,300 tonnes dysprosium within 38,269 tonnes TREO using a cut-off grade of 0.15% TREO. Of the total mineral resource, 66% is classified as indicated resource, with the remainder in the inferred resource category.
The proposed mining fleet will transport the run-of-mine ore to the run-of-mine pad where the ore will be stockpiled and blended to the desired grade before transferring to the crushing circuit which consists of a primary jaw crusher, followed by a 750kW 4.8 metres diameter x 2.4 metres SAG mill and then a 1700kW 4.2 metres diameter x 6.2 metres ball mill that grinds the ore down to a size of 80% passing 63 metres.The ground ore is fed to a wet high gradient magnetic separator (WHGMS) that produces two products, a magnetic concentrate rich in xenotime and iron oxide, and a non-magnetic stream containing largely silica and mica which is rejected as tailings. The magnetic concentrate is then fed to a flotation circuit where selective reagents are used to collect the xenotime material in the froth and reject unwanted gangue material in the tailings. The flotation tailings are combined with the WHGMS circuit tailings and thickened before being comingled with the hydrometallurgical tails and pumped to the tailing storage facility. The 20% TREO flotation concentrate is thickened, filtered and stored in bunkers prior to being fed into the hydrometallurgical plant.
The 20% TREO mineral concentrate is reclaimed from bunkers with a bobcat, fed into a live bottom bin and screw conveyed into a dryer. The dry concentrate is fed into an acid mixer and then the kiln. The sulphation bake is performed at 275-300 [superscript]o C which cracks the xenotime mineral and the rare earths are readily leached in water. Following the water leach step, the leach residue is washed, filtered and separated from the pregnant leach solution (PLS). The PLS undergoes a series of purification steps where the pH of the solution is steadily increased with lime and magnesia to reject impurities such as phosphate, iron, aluminium, thorium and uranium. The purification residue is separated from the PLS by thickening and filtering, and the PLS is passed through an ion exchange column to remove any residual uranium. The purification residue is repulped and mixed with the repulped water leach residue before being comingled with the beneficiation tailings and pumped to the TSF. Following purification and ion exchange, the PLS is contacted with oxalic acid which selectively precipitates the rare earths. The mixed RE oxalate is thickened, filtered and washed before being calcined to a high purity, mixed RE oxide ( Figure 8 ).
