Global tonnes of ore over the existing reserve and assumed recoveries of 70 % for copper to copper concentrate and 80 % for zinc to zinc concentrate .
Several million tonnes of additional high-grade resource in the original pit design could also potentially be brought back into the mine life . The company expects to assess investment in an additional cut-back to access this resource in late 2019 . Approval will depend on performance in delivering the cost targets and increased mining rates for the extension announced recently .
Brief history
The USD250-million Bisha Mine was constructed on time and under budget from 2008 to 2010 . Processing oxide ore , the mine produced low-cost gold-silver doré until mid-2013 . Through a USD110-million copper expansion project , also delivered on time and under budget , throughput expanded to 2.4 million tonnes per annum ( Mtpa ) supergene ore and the product switched to copper concentrate .
Commissioning of the zinc expansion plant commenced in June 2016 and commercial production was declared in October 2016 . The plant cost about USD77-million to construct , compared to a budget of USD100-million .
The Bisha main deposit is located within the Bisha mining license , and the Harena satellite deposit lies in a separate mining license located six kilometers south , connected by a flat unsealed road . Bisha Main and Harena currently constitute 100 % of the mineral reserves for Bisha . The Bisha VMS District remains underexplored and holds strong potential for expanding mineral resources and reserves for the Bisha mill . The State of Eritrea has a 40 % interest in the Bisha Mine through Enamco , 30 % of which it bought from Nevsun prior to initial construction . As a result , Enamco contributed 33 % of the initial build capital and , as a partner with Nevsun , has been
Nevsun Resources
Bisha is a large , high-grade volcanogenic massive sulphide ( VMS ) deposit located 150km west of Asmara , Eritrea , East Africa . The Bisha Mine benefits from high-grade base metal reserves , strong support from the Government of Eritrea , and an advantageous location with good local road and port infrastructure .
integral to the success of the Bisha Mine . Bisha is mined using conventional drill and blast opencast mining techniques to remove waste and deliver ore to the run-of-mine ( ROM ) stockpile . Mined ore is reclaimed from the ROM stockpile and fed to the conventional single-stage crushing , semi-autogenous grinding ( SAG ), and then ball mill comminution circuit . The copper and zinc flotation plants are both conventional circuits with rougher , cleaner , and IsaMill regrind . Copper and zinc concentrates are thickened , dewatered , and stockpiled prior to land transport to the Port of Massawa for shipment to world markets . Tailings are pumped and placed in the lined tailings management facility ( TMF ) at site .
Power is currently provided to the Bisha plant by a fleet of dedicated diesel generators managed by Aggreko . Nevsun recently signed a long-term power agreement with Aggreko to supply the mine with a combination of diesel and solar power . Water is sourced from pit dewatering , the tailings pond , and from local well fields .
Export infrastructure
Concentrate is being exported using a proven system with industry-leading environmental controls . At present , concentrate is loaded from the mine site stockpiles into custom-sealed shipping containers and transported to the Port of Massawa by truck . The sealed containers of approximately 35t each , including the weight of the container , are stockpiled in Massawa at the container port facilities awaiting bulk ship arrivals . The Rotainer crane system then discharges the containers through a tipping 360-degree rotation into the hold of the bulk vessels , and the empty containers are returned to Bisha for reloading . The bulk vessels deliver the concentrate to smelters worldwide , typically in 11 000-tonne parcels .
The Bisha Main deposit is a high-grade VMS deposit . It is configured in three distinct layered zones : a 35m-thick surface gold-silver oxide zone ( mined out in mid-2013 ) immediately overlying a copper-enriched supergene zone , which itself overlies a primary sulphide zone containing both zinc and copper . b