The contingency cost in the PFS is based on the total direct and/or indirect costs and are included to account for unanticipated costs within the scope of the estimate. The contingency percentage allowances vary and are individually assessed based on the accuracy of the quantity measurement, type and scope of work, and price information for the capital cost estimate.
The PFS estimate is based on the cost of new equipment supported by budget quotes from vendors which do not reflect discounts for negotiated prices, bulk purchasing, or used equipment purchases where appropriate, any of which could lead to reductions in actual capital costs relative to the prices used in the capital estimate.
The PFS mine plan provides for the excavation of 127.1 million tonnes of ore and 468.9 million tonnes of waste for a combined total of 596.0 million tonnes of material at a life of mine stripping ratio of 3.69:1. Mining will be conducted with conventional open pit mining techniques over a 16 year mine life in two pits, the Toroparu Pit which will be mined in 13 phases, and the nearby South-East Pit (1.2 km to southeast of Toroparu), which will be mined in four phases.
Mining operations are planned to commence during the second year of construction of the Project in the center of the Toroparu pit, with mining of saprolite Au Ore to support pre-production of gold in saprolite Au Ore processing. The following year mining will be expanded to include mining and stockpiling of fresh rock ore to support the start-up of fresh rock Au/Cu Ore processing in the first year of production. Total mining during the 2 pre-production years is estimated at 15.2 million tonnes at a stripping ratio of 1.05:1. From this point, the mine plan calls for 14 years of mining out of a total 16 year production life. The first five years of mining will continue in the center of the Toroparu Pit at a rate of 40 million tonnes per year, utilizing small scale mining equipment fleet based on 50 tonne capacity haul trucks at a stripping ratio of 3.29:1. Mined fresh rock Au/Cu Ore will be processed in the concentrate circuit and fresh rock Au Ore will be stockpiled for later feed into the expanded cyanide leach circuit beginning in year 4 (Phase 3). Ore loading operations will be accomplished with a fleet of hydraulic excavators (to enhance ore selectivity) and shovels, with operational flexibility provided by a wheel loader.
In the 6th year of the mine plan the annual mining rate is expected to be ramped up to an average of 50 million tonnes and the main truck fleet will be switched over to 133 tonne capacity haul trucks to support the expanded processing capacity. In year 13, the annual mining rate will reduce to 21 million tonnes. In year 14, open pit operations will be completed for the mineral reserves defined in the PFS mine plan. The processing plant will continue operating for another two years processing from low grade ore stockpiles.
Comprehensive metallurgical programs were conducted at Inspectorate Exploration & Mining Services Ltd. of Richmond, British Columbia in 2012 on saprolite Au Ore; and at SGS Canada Inc. of Lakefield, Ontario in 2012 that tested recovery and reagent consumptions separately for the two fresh rock ore types identified as Au/Cu Ore and Au Ore. The results prompted a redesign of the PEA processing circuit to enable the separate treatment of both fresh rock ore types.
Saprolite Au Ore, part of the Au Ore type, consists of 80-85% fines (less than 75 micron) and therefore only 15-20% coarser fraction will require grinding. All saprolite Au Ore will be ground in a small ball mill and then treated in a cyanide leach circuit. Recovered gold will be further refined into gold dore on site. All fresh rock ore will be processed through crushing and grinding to a P80 150 micron (100 Mesh) with gravity concentration included. All fresh rock Au Ore will be treated in a cyanide leach circuit. Cyanide leach tailings will be subjected to cyanide detoxification using Air/SO2 technology to reduce cyanide concentrations to Guyana and World Bank environmental standards. Fresh Au/Cu Ore will be sent to a rougher flotation circuit for copper and gold recovery. Tailings from the rougher float circuit will be discharged, and the rougher concentrate will be reground to P80 38 microns and processed through a cleaner circuit to produce a final concentrate that is shipped to an offshore smelter. First cleaner-scavenger flotation tailings will be further processed in the cyanide leach process. Cu/Au Ore concentrate analyses have been discussed with and preliminarily accepted by European and Asian based smelters.
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