Tank leach laboratory test work carried out on samples from ENK PLC’s Acoje Nickel Project by the Beijing General Research Institute of Mining and Metallurgy in China has shown superior recoveries and economics from tank leaching as opposed to heap leaching. Recoveries of nickel and cobalt over a three stage leaching circuit averaged 92% and 97% respectively over a 22 hour leach period.
Based on the average diluted grades of the Acoje mining inventory, an implied cash cost of US$2.93 per pound of nickel produced, net of by products, was calculated. Assuming a nickel price of US$7 per pound (US$15,430/ tonne) and 80% payability, a notional refining charge of US$1.40 needs to be added for a total cash cost to nickel metal of US$4.33 per pound.
Sulphuric acid will be one of the major consumables utilized, representing 62% of the total operating costs. The company has therefore taken a conservative view on the cost of sulphur of US$170/tonne. This is a 270% increase over the cost of sulphur used in the prefeasibility study (PFS), and demonstrates the robustness of the tank leaching process in a high sulphur price environment.
All other operating costs associated with tank leaching were determined through the escalation of applicable PFS costs in line with current market conditions or obtaining updated cost estimates from equipment vendors and service providers. The company anticipates that the capital costs required for tank leaching will be equivalent or less than those for heap leaching and will require significantly lower working capital as a result of reduced ground works and the ability to commence production more rapidly.
The company will now only take the tank leaching option forward into the Bankable Feasibility Study (BFS) due for completion at the end of the second quarter of 2012.
Infill drilling of the resource at Acoje is complete and drilling at the Zambales Chromite tenement is about 25% complete. Both resource updates will be incorporated into the BFS.
ENK’s managing director Robert Gregory says, “Not only does tank leaching offer superior economics, it is an inherently less risky option compared to heap leaching in a high rainfall environment. Tank leaching also lends itself to a staged construction approach offering a reduction in initial capital costs and its associated financing. It is for these reasons that we have elected to utilize tank leaching for the BFS.”