The mineral deposits at Neves-Corvo are classified as volcano-sedimentary massive sulphide (VMS). They typically occur as lenses of polymetallic (Cu, Zn, Sn, Pb) massive sulphides that formed at or near the seafloor in submarine volcanic environments. They formed from accumulations of the focussed discharges of hot metal-enriched fluids associated with seafloor hydrothermal convection, typically in tectonic areas of active submarine volcanism, including rift spreading centres and island arc subduction zones. The massive sulphide lenses are commonly underlain by sulphide-silicate stockwork vein systems, although the stockwork systems may extend into the hanging-wall strata above the massive sulphide lenses. The immediate host rocks can be either volcanic or sedimentary. The deposits are overlain by a repetition of volcano-sedimentary and flysch units.

VMS deposits readily accommodate strain during regional deformation because of the ductile nature of massive sulphide bodies, and can therefore display much higher degrees of recrystallisation and remobilisation than the surrounding volcanic and sedimentary strata. The tectonic remobilisation may result in duplication of the stratigraphy further localising the sulphide mineralisation.

Six massive sulphide mineralised zones have been defined within the Neves-Corvo Mining Area and comprise Neves, Corvo, Graça, Zambujal, Lombador and Monte Branco. The Semblana massive sulphide zone is located within the Semblan ........

Neves-Corvo has been developed as an underground operation and exploits a number of polymetallic sulphide orebodies. The mine currently hoists approximately 3.5Mt of ore per year via a 5m diameter shaft from the 700m level (underground elevations relate to a datum of 1,000m below sea level with the mine surface elevation at approximately 220mASL, or 1,220m above datum). Ore from the deeper levels is transported to the 700m level via an incline conveyor from the 550 level. Principle access to the mine is via a ramp from surface and the numerous internal ramps serving the various mining areas. Mining methods have been dictated by geology and geotechnical considerations and at the present time, drift and fill as well as bench and fill mining methods are utilised with the fill comprising predominantly paste fill.

Drift-and-fill was the original mining method selected for Neves-Corvo. Although the method has relatively low productivity rates and high unit costs, it was chosen because it is highly flexible and can achieve high recovery rates in high grade orebodies with complex and flat dipping geometry. The initial copper reserves at Neves-Corvo, largely in the Graça and Upper Corvo orebodies, averaged in excess of 8.0%Cu and it was important to select a method that extracted all of this high grade mineralisation.

Drift-and-fill stopes at Neves-Corvo are normally accessed from a footwall ramp with footwall access drives driven along the orebody strike at 20m ........

- subscription is required.

The process plants use conventional flowsheets consisting of crushing, grinding and flotation and the company is a significant producer of both copper and zinc concentrates. Operations are split between two processing plants, namely the Copper Plant and the Zinc Plant.

Copper Plant:
The installed capacity of the Copper Plant is 2.5Mtpa. To achieve this throughput the plant is manned continuously using a five-shift rotating roster. The operation starts at the coarse ore stockpiles, through pre-screening, crushing, grinding, flotation, filtration to concentrate storage and despatch and includes utilities and tailings management.

From the primary grinding circuit the slurry passes through two aerator conditioners (2 Dorr-Oliver 38m3 cells) to the flotation circuit, 62 cells of 17m3 and 12 of 38m3, all Dorr Oliver.

Concentrate from the first bank of rougher #1 (3 cells of 17m3) feeds the first cleaner, but can optionally go to the regrinding. The remai ........