100% of cyanide usage is required to be purchased in the ‘Base Case Optimised Plan’ run, with only the shortfall after ReCYN™ recovery in the ‘ ReCYN™ Optimised Plan’ run. 85% of consumed cyanide was assumed to be recovered of the portion consumed by copper (first bullet point in the above list) and free cyanide in CIL tail (third bullet point). This recovery cost was modelled as US$1,050/T Cyanide recovered. Copper Modelling The cost of copper recovery used was US$1,037 per copper tonnes recovered. 97% of recovered tonnes was assumed to be payable to model sales expenses, and a market price of US$6,061/t based on US$2.75/lb. Detox cost modelling The ‘Base Case Optimised Plan’ detoxification variable rate based on cyanide-soluble copper content in the CIL Feed was scaled down in the ReCYN™ modelling runs. In cases where the ore block or parcel of ore had a cyanide-soluble copper ppm of >=50ppm, 20% of this ‘Base Case Optimised Plan’ detox rate was applied in ReCYN™ optimisation. If less than 50ppm, no variable detox costs were applied in ReCYN™ optimisation. Capex A capex cost of US$5M for the addition of the equipment needed for the ReCYN™ process, incurred in 2018, was used in ReCYN™ runs. This does not include a royalty to Greengold that may be applicable to other projects. The ReCYN™ process was assumed to be available for all 2018 feed, despite the capex being incurred in the same year. 3.3.3 3.3.4 3.3.5 3.4.1 Mining Physical Adjustments and Limits Only Measured and Indicated material for Purnama and Barani sites were included, with the addition of Inferred only for the newer sites, Ramba Joring and Tor Uluala. Processing Physical Adjustments and Limits ‘Base Case Optimised Plan’ gold and silver recovery (before silver uplift due to ReCYN™) were derived from the various block-by-block recovery fields, used currently by PTAR in their resource models. With the increase in intensity at the CIL tail, PTAR identified the potential for a 1g/t reduction in silver in the tails. This equates to an uplift in recovery equivalent to: 3.4.2 Given for combinations of grades and recoveries (particularly lower grades), this calculation would produce an adjusted recovery over 100%. A three-tier approach was implemented to practically model this with sensible outcomes. This caps maximum uplift to ensure recovery does not exceed 85%, where original recovery was lower than this: • If the original Silver recovery in the resource model was greater than 85%, ReCYN™ Silver recovery is unchanged • If calculated ReCYN™ Silver recovery after uplift would exceed 85%, the recovery after uplift used is capped at 85% • Otherwise calculated uplift recovery as above is used. Post ReCYN™ Process Silver recovery (0-1%) = Original Silver recovery (0-1%) + 1 ÷ Silver Feed Grade 3.4 P HYSICALS M ODELLING AND C ONSTRAINTS
ReCYN™ Case Study – Martabe Operations
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