Nevsun Resources Ltd. (TSX:NSU) (NYSE MKT:NSU) is pleased to announce commissioning of the new copper flotation plant is progressing well with continued production of saleable copper concentrate and commercial production expected before the end of year.
The initial plant commissioning commenced in June 2013 and first produced a precious metals concentrate from pyrite sands ore, which was followed by the production of lower grade copper-gold-silver concentrate in August 2013. Since mid-August 2013 there has been a steady improvement in plant stability. The plant has been operated at lower than design throughputs during this commissioning phase as the Company cautiously advances the project. The commissioning with pyrite sands caused some premature wear to part of the plant including cyclone feed pump internals, piping and valves, particularly in the flotation circuit, however once the feed transitioned to planned supergene ore, both corrosion and abrasion effects significantly declined. Minor plant design modifications and rectification of these worn components has been systematic in approach and thus far successful. Steel piping in certain sections evidencing high wear is being replaced with high density polyethylene piping, various critical steel pumps with stainless steel equivalents, and high wear sections to be reinforced with ceramics and chrome, rubber linings or epoxy.
Two notable issues requiring extra attention involved the flotation conditioning tank and the rougher flotation dart valves. For the conditioning tank, whose main function is to alleviate surge to the rougher flotation cells while properly conditioning the ore slurry with reagents, the tank bottom suffered significant corrosion from the abrasive pyrite sands. Temporary tank repairs will be complete by early November 2013. In 2014 a new section of the tank will be installed and the tank will be lined with epoxy. The plant is able to continue operating with a conditioning tank by-pass but throughput is a somewhat reduced.
The second issue involved damage to the rougher flotation dart valve shafts due to siltation in the tanks from the high density pyrite sands. Most of these bent shafts have been straightened, with the option to replace some in the future with more robust shafts. All conditions noted above will be monitored. The cost of these fixes has not been significant in relation to the investment with capital for copper flotation plant completion still well below budget. Copper concentrate continues to be produced in sufficient quantities with two additional shipments planned for November 2013 following the two shipments already completed in October 2013.
Copper recovery improvements are expected to grow to over 80% and these levels are anticipated once the design target grind size of the ore is achieved, expected after the conditioning tank and dart valves are fully operational thus allowing the regrind mills to function at full capacity. Likewise, the introduction of non-acidic process water for flushing, spray water and hosing purposes as well as chromium coated grinding media to reduce grinding media consumption are assisting in further achieving this goal. Two of the regrind mills are currently operating while the remaining two will be commissioned when throughput increases.
The entire front end of the plant, consisting of crushing and grinding circuit, as well as the back end of the plant, which includes tailings thickening and discharge, is the same as used during the gold phase and accordingly no commissioning was required.