The 2017 Savannah North mineralogical and metallurgical testwork programs, undertaken under the supervision of a metallurgical consultant, are now complete and the results have been reviewed by an independent metallurgical consultancy. The programs were primarily focused on determining the expected metallurgical performance of treating Savannah North ore through the existing Savannah plant to deliver an optimum bulk nickel/copper/cobalt concentrate product for sale.
Savannah North mineralisation is broadly similar to Savannah ore, i.e. pyrrhotite-dominant sulphides with sub-ordinate pentlandite and chalcopyrite. QEMSCANTM mineralogical testwork shows that approximately 85% of the elemental nickel occurs as pentlandite, with around 7% of the nickel occurring as non-sulphide. Laser ablation ICP-MS confirms that the remainder of the nickel is present as solid solution in pyrrhotite. Approximately 60% to 75% of the pentlandite occurs in a liberated form, with the less liberated pentlandite mainly locked with pyrrhotite (occurring as fine inclusions, thin or thick flames). The P80 of pentlandite varies between 59µm and 78µm across the sample set. Chalcopyrite has a P80 of about 80µm and about 75% is classified as ‘liberated’; the less liberated chalcopyrite is mainly locked with pyrrhotite and less frequently with pentlandite. Cobalt occurs within the pendlandite, with no discrete cobalt minerals observed in the QEMSCANTM study.
QEMSCANTM mineralogical testwork completed on bulk composites and individual variability samples from Savannah North has shown that Savannah North ore, whilst mineralogically similar to Savannah ore, has a higher pyrrhotite:pentlandite ratio than Savannah. Nickel in solid solution with pyrrhotite in the Savannah North Upper Zone (SNUZ) and Savannah North Lower Zone (SNLZ) composites accounts for 16-17% of the overall nickel content, compared to 12% in the Savannah reference composite. The implication of this difference in nickel deportment, is that nickel recovery from SNLZ and SNUZ may be 3-5% lower than for Savannah ore at an equivalent concentrate grade.
Comminution testwork returned Bond Work Indices ranging from 9.5 to 12.5 (“medium”). SAG mill comminution (SMC) testing showed the Savannah North mineralisation to be “very soft” to “soft”. The softer comminution parameters will provide some scope to either maintain mill throughput while producing a finer grind P80 or alternatively maintain the existing grind P80 at a slightly higher mill throughput.
Flotation testwork on Savannah North material for the Updated FS is now complete. A total of 46 rougher-scavenger flotation tests and 19 cleaner tests were conducted. The final product specifications are a function of mineralogy, plant configuration and performance, customer requirements and offtake terms. Historically, the optimum product from Savannah was a bulk concentrate averaging 7.5% nickel grade at a recovery of 85-87% depending on the mill head grade. Laboratory scale flotation testwork has shown that Savannah North samples achieve a slightly lower recovery (typically 3-5% lower) compared to a Savannah reference sample, which is reflective of the higher pyrrhotite:pentlandite ratio. The flotation testwork indicates average recoveries of ~84% for SNLZ and ~82% for SNUZ into a bulk Ni-Cu-Co concentrate targeting an 8% nickel in concentrate grade.
The flotation testwork indicates that recoveries for Cu and Co from Savannah North are expected to be higher than historically achieved from Savannah. Forecast recoveries for SNUZ are 99% for Cu and 92% for Co, and SNLZ are 99% for Cu and 95% for Co.