The Updated FS assumes no change to the existing Savannah processing plant configuration or capacity. The nominal throughput capacity of the Savannah plant is approximately 1.0Mtpa. Between February and May 2016, prior to going into care and maintenance, the Savannah plant was operating between 120tph and 140tph, averaging approximately 130tph (85,000t per month, or over 1Mtpa).
For the Updated FS, plant throughput ranges between 90tph and 130tph, averaging approximately 120tph at full production (approximately 78,000t per month). On an annual basis, life-of-mine mill throughput averages 0.94Mtpa, up from 0.82Mtpa in the February 2017 FS, and peaks at 0.95Mtpa. A three-month ramp-up to steady-state production (~65,000tpm) is assumed in the Updated FS and full production is achieved after 12 months, as Savannah North material becomes available.
Life-of-mine nickel head grade for the Updated FS averages 1.42% Ni, with monthly averages varying from 1.0% Ni to 1.7% Ni. Lower nickel grades are processed in the first year of production, associated with the remnant Ore Reserves at Savannah. The annual milling profile and ore sources are shown in Figure 3.
For the Updated FS, the Company is targeting production of a bulk Ni-Cu-Co concentrate with a concentrate grade of 8% Ni. Processing recoveries at the target concentrate grade will vary with each ore type. Over the mine life, recoveries average 83% Ni, 98% Cu and 92% Co, based on historical plant performance for Savannah ore and the 2017 metallurgical testwork results on Savannah North samples.
Savannah Processing Plant
Metal in concentrate production is forecast to average 10,800t Ni, 6,100t Cu and 800t Co per year with 90,200t Ni, 50,700t Cu and 6,700t Co in concentrate produced over life of mine. Annual metal in concentrate production is shown in Figure 4.
The Savannah North concentrate is low in impurities and has attractive Fe:MgO and Ni:Fe ratios, making it an ideal blending feed for nickel concentrate smelters. Typical concentrate specifications, based on analysis of concentrates from the 2017 metallurgical testwork program, are shown in Table 5.
The existing processing plant and accommodation camp are sufficient for the proposed future operations under the Updated FS.
Infrastructure required for a re-start of operations remains on site and is being maintained by care and maintenance crews. Major fixed plant and mobile equipment is either ready to be recommissioned or can be at short notice, with refurbishments costed in the financial model. Underground decline and pumping systems have been maintained and operated so that minimal rehabilitation will be required to recommence underground operations.
The Company has received pricing estimates from two independent engineering firms for refurbishment of the Savannah processing plant, paste fill plant and Wyndham concentrate storage shed. Due to the age of some components, the Company considers it prudent to bring forward some aspects of the process plant refurbishment prior to recommissioning, in order to mitigate unplanned maintenance. This refurbishment has resulted in an increase in pre-production capital costs, as discussed below.
Other major infrastructure works required on re-start of operations for the Updated FS are unchanged from the February 2017 FS, and include: Savannah North decline access development, Savannah North Fresh Air Rise and tailings storage facility wall lift.
The Updated FS includes provision for solar power. A proposal for solar power has been provided by the incumbent third-party power provider, utilising a 4MW system generating approximately 10% of the life-of-mine power requirement. Modelling assumes the Company will own the solar power infrastructure. Annual savings on power costs of approximately $2M are estimated, compared with 100% diesel power.