Mining capital requirements for initial contractor mobilisation, establishment of the contractor, and site clearing is estimated to be $13.7 million. As the Esaase deposit is a green field site which starts with the mining of a ridge of approximately 100 metre high hills, there is very little pre-stripping to be done. A clearing and topsoil stripping cost has been included in the capital in the sum of $6.9 million. Most of the pre-strip material will be used for initial tailings dam wall construction.
Under the supervision of Lycopodium in Australia four extensive phases of test work were completed for the Esaase Gold project up to an including the Esaase PFS that was published in 2011. Based on a review of the phase I - IV test work, a phase V test work programme was initiated by DRA in the last quarter of 2012 and completed in Q1 2013. By doing additional test work on composite samples made up of the left over material from the phase III and IV test work, an optimal plant configuration was developed (Figure 2).
To view Figure 2, visit the following link: http://media3.marketwire.com/docs/Process_Flow_Sheet.jpg
The plant is a conventional crushing, milling, gravity recovery followed by flotation, with the flotation concentrate being reground and then leached in a standard CIL circuit using AARL elution technology. The flotation tails are low enough in grade to be discarded.
ROM ore will be treated in an open circuit primary crushing system consisting of ROM bin and gyratory crusher. Product from the primary crusher will be conveyed to a secondary cone crusher. Secondary crusher product will be routed onto a 10,000t mill feed stockpile. Material will be withdrawn from the stockpile using belt feeders that feed directly onto the mill feed conveyor.
The ball milling circuit is designed to a feed rate of 635t/h dry solids. The mill will operate in closed circuit with a cluster of hydrocyclones. The ball mill will be a 13MW dual motor configuration producing a p80 grind of 75 micrometre. The cyclone overflow will be gravity fed to a flotation circuit. The cyclone underflow will be sent to a primary gravity concentration circuit, with the tails being recycled to the mill feed.
The primary gravity concentrator circuit will include two independent Knelson XD-48 concentrators with capacity to each treat 400t/h. The gravity concentrate will report to a high intensity batch dissolution reactor. The pregnant solution from the intensive dissolution reactor will be pumped to the electrowinning cell feed tank.
The flotation circuit will comprise of a single bank of seven 130m3 forced air rougher flotation cells in series. The flotation tailings will be pumped to flotation tailings storage facility while the flotation concentrate will be fed to de-sliming cyclones on a regrind circuit. The cyclone overflow will be routed to a pre-leach thickener while cyclone underflow will be treated in a Vertimill to achieve a P80 of 20 micrometre. Regrind mill product will be pumped to a secondary gravity concentration unit; the concentrate will be routed along with concentrate from the primary gravity concentrator to the intensive dissolution reactor. Pre-leach thickener underflow will be pumped to the CIL circuit.
The CIL circuit will consist of seven 330m3 tanks in series. Slurry will flow from one CIL tank to another via Kemix inter-tank pumping screens and launders. CIL tailings will be screened for carbon and pumped to the cyanide and arsenic detoxification circuits. Detoxification will be achieved by the SO2/Air process in two detox tanks. Copper Sulphate will be added to catalyse the reaction. The detox circuit will be operated to achieve a cyanide concentration in the final tailings stream of less than 50ppm CNWAD. Chloride addition in a third tank will be used to facilitate the precipitation of the arsenic, present in the tailings stream. The arsenic concentration, in solution, will be reduced to less than 0.1ppm As.
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