Trace Mineral Searches (TMS) for gold were conducted on the high grade composites of both clusters using QEMSCAN to determine liberation and association characteristics of the gold particles within the samples and to ascertain if differences between the two samples existed. Results showed that in the South Cluster samples, a higher percentage of the gold was present in inclusions with other minerals compared with that of the North Cluster samples. Inclusions are when the gold particle is surrounded by the other minerals. This could reduce or eliminate contact between a leach solution and the gold particle, possibly inhibiting leach performance. These minerals would more likely be recoverable to a flotation concentrate. Finer grinding or increased leach times may be required to leach such gold particles, a process which will be further investigated with the Phase 2 work.
Composites from the North Cluster have a higher combined percentage of gold particles that were liberated or associated with sulfide minerals when compared to the South Cluster. They would likely have a higher specific gravity and therefore may respond better to gravity separation.
A Bond ball mill work index test was also conducted on the Master Composite. Those tests are performed to assess the energy, and therefore costs, that would be required to grind the samples. The result was a Bond ball work index of 13.8 kW-hr/tonne; this would characterize the composite as moderately soft.
Summary of Phase 1 Metallurgical Testing
Master Composite Results
On the Master Composite, a series of Knelson gravity concentrations with hand panning of the gravity concentrate were conducted with cyanide leach extractions of the gravity tailings. These were completed at four primary grind sizes: 130, 105, 79 and 56 microns at K80 (80% passing). The best combined gravity and cyanide leaching (48 hours leach) recovery obtained was about 89% at the 79 microns K80; 23% of which was by gravity separation. A grind target of 75 microns K80 was chosen for subsequent testing of the individual composites. A rougher flotation test on the Master Composite conducted at a primary grind sizing of 130 microns K80, recovered 89% of the feed gold to a rougher concentrate containing about 11% of the mass.
South Cluster Results
A series of gravity concentrations with cyanide leaches of the tailings were conducted on the individual composites from the North and South Clusters at primary grind sizing targeting 75 microns, 80% passing, with 1,000 ppm sodium cyanide ("NaCN") concentration in the leaching and 48 hour leach duration.
The South Cluster samples showed a gravity recovery of between 12 and 25% and combined recovery of approximately 79% to 84% feed gold. These samples were subsequently improved to approximately 90% by grinding the samples finer (50 microns, 80% passing), with most of the gain coming from improved gravity separation. Diagnostic leaching of leach tailings also showed potential improvement of overall recovery from the Southern Cluster samples by increasing leach intensity or duration.
Of about half the unrecovered gold from the South Cluster tests, approximately 9% of feed gold was found to be in sulfide minerals and non-recoverable through direct leaching at the current primary grind sizing. A number of cyanidation tests were therefore conducted on the South Cluster composites with attempts to improve recovery. The best combined recoveries were achieved with 96 hour leach durations and with reducing primary grind targets to 50 microns, 80% passing. This test showed improved gravity recovery, as well as improved overall recovery with about 91% to 92% percent of feed gold being recovered. Under these conditions, cyanide consumptions remained relatively low at 0.4 kg/tonne feed.
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