Metallurgical Test Work
Metallurgical test work has been completed by SGS in Lakefield, Ontario and by Base Metallurgical Laboratories in Kamloops, British Columbia. The test programs have covered samples from the Marathon, Leprechaun, and Berry deposits and included chemical head analysis, comminution, metallurgical (gold recovery) and tailing detoxification testing. Test work examined two flowsheets. In the simpler flowsheet, to be used in a first phase of operations, the feed material is finely ground, coarse gold recovered by gravity concentration and intensively leached, and the gravity tailings separately leached. For the later phase of operations, the processing rate is increased, the grinding circuit is allowed to produce a coarser product, gravity concentration continues to be used, froth flotation is used to recover the bulk of the remaining gold with the concentrate finely ground and intensively leached, then further leached with the flotation tailings. The level of gold recovery from each flowsheet has been determined for samples ranging in gold feed grade from less than 0.5 g/t to greater than 5 g/t and grade-extraction recovery relationships developed for both flowsheets and the individual deposits.
Ore characterization included chemical head analysis on material from several geographical zones representing each of the Marathon, Berry and Leprechaun deposits. Samples were subjected to comminution testing, including SAG mill comminution (SMC) testing, Bond rod mill work index (RWi), ball mill work index (BWi), and abrasion index (Ai) tests. The comminution tests showed that all material behaved similarly and a suitable grinding circuit has been designed.
The gravity concentration process was applied to all of the samples tested to determine the expected level of coarse gold recovery. Additionally, the industry-standard Extended Gravity Recovery Gold (E-GRG) test was applied to nine composite samples from the three deposits to define equipment requirements and expected recovery levels which were in the range of 40 to 50% of feed gold. Intensive leach tests on gravity concentrate samples indicated 96% gold extraction or higher in a single pass with subsequent treatment increasing extraction from gravity concentrate to greater than 99%.
Gravity tailings from all samples were subjected to leach testing. Analysis of the data from the gravity recovery and leach tests led to development of gold feed grade-extraction relationships for the three different deposits. As an example, the relationship indicates that at a feed grade of 2 g/t, and processing approximately equal mixture of material from the three deposits, gold extraction is expected to be 94.0%. This is reduced to 93.0% recovery when allowance is made for soluble and other losses.
The Phase 2 circuit includes gravity concentration and leaching, flotation and intensive treatment of the flotation concentrate, and leaching of the flotation tailings. All of these were studied in detail and gold grade-extraction relationships were developed for this flowsheet. As an example, the relationship indicates that at a feed grade of 2 g/t gold extraction will be 96.7% which is reduced to 95.7% recovery after allowance for soluble losses.
Testwork also covered development of design data for tailings detoxification circuit, sizing data for tanks, pumps, thickeners and other equipment as needed for the detailed design of the process plant.