The Stratoni polymetallic ore consists of stratabound replacement mineralisation hosted within marble horizons and may be termed a distal skarn. The mineralisation was emplaced by hydrothermal fluids driven by a granodioritic intrusive which was intruded some 30 million years ago. The mineralised zone is often referred to as the Stratoni-Piavitsa belt, and the total sulphide content of this belt prior to mining has been estimated at 25Mt. The deposits consist of massive sulphide carbonate and aplite replacement, restricted to two Marble horizons, interlayed with biotite gneiss and schist. The model therefore requires two components; marble horizons that have been thickened and structurally prepared by thrusting and folding prior to the introduction of mineralising fluids and; a structural architecture which has allowed the channelling of fluids from a magmatic source to the chemically reactive marbles. Exploration uses these two elements as a guide to identifying potential new ore zones.

The massive sulphide mineralisation has a relatively simple mineralogy, and the most abundant ore minerals are pyrite, sphalerite, galena, arsenopyrite and chalcopyrite. The dominant exploited minerals historically have been sphalerite, pyrite and galena; the ore is often abbreviated to BPG from the old notation blende, pitch, galena. The ore is also gold bearing, mostly associated with the arsenical pyrite and arsenopyrite. Quartz, calcite and minor rhodochrosite form the gangue minerals.

The mineralisation is hosted either in the marble or replacing aplite as irregular and sub-parallel layers of sphalerite, pyrite and galena. These lenses occur from footwall to hanging-wall, varying from few centimetres to tens of metres. Galena is seen as the most deformed mineral, commonly re-crystallised into coarse grains. Galena also exhibits curved cleavage and elongated and foliated grains. Zonation of the sulphides is not clear.

The Mavres Petres orebody is some 500 metres in strike length, between 100 and 340 metres in dip extent. The true width is on average 25 metres. The strike of the orebody is close to east west and the dip is 30° to the south.

The Mavres Petres orebody shows an average gold grade of around 4 to 6 g/t Au. Its presence is strongly associated with the arsenical pyrite and arsenopyrite, which appears to be a different stage of mineralisation within the matrix of hydrothermal breccias or in veins cutting the Pb-Zn sulphides. The gold mineralisation is not coincident with the massive sulphide mineralisation. The gold is completely refractory and not considered to be of any economic value.

Mining is a combination of transverse and longitudinal drift-and fill methods with rock breaking by conventional drill and blast. The stoped area is then tight filled with cemented tailings from surface. Previous mining has generated considerable experience with the ground conditions and the rock mass’ physical and geotechnical characteristics. Support varies based on size and ground conditions. Some areas are supported with backpacked steel sets while others are supported with rock bolts and shotcrete.

The crushing facility has spare capacity and is capable of crushing up to 750,000 dmt per annum and as a consequence is currently only operating for approximately one third of the available time. Maximum crushing capacity is 170 dmt/hr, but normal operating capacity is 120 dmt/hr.

The ore is received from the mine in trucks and dumped onto an ore storage area. Ore is reclaimed from the storage area by FEL and dumped into a hopper feeding the crushing plant.

The ore is dry crushed in three stages of crushing using a primary jaw crusher, a standard Symons secondary crusher and two shorthead Symons tertiary crushers. The standard Symons crusher operates in open circuit with a vibrating screen while the shorthead Symons crushers operate in closed circuit with two other vibrating screens. The crushed ore is conveyed to the fine ore bin.

Ore is automatically fed at a controlled tonnage from the fine ore bin and subsequently wet ground to a nominal 80% minus 212 microns in a conventional rod mill/ball mill circuit. The rod mill operates in open circuit while the ball mill operates in closed circuit with a 500 mm cyclone.

Lead, silver and zinc recoveries of 91.5%, 80% and 91.5%, respectively, are achieved. The grade of the bulk lead/silver concentrate is typically 70.5% Pb with approximately 1,600 g/t Ag; the zinc concentrate contains 50% Zn.

The flotation scheme is operated in the differential mode. Lead is floated first and the zinc minerals are subsequently recovered from the lead circuit tailing.

The cyclone overflow passes to a conditioner and then to the lead roughing and scavenging flotation cells. The lead scavenger concentrate returns to the lead conditioner or to the feed cyclone. The lead rougher concentrate is cleaned in three stages to produce a final lead cleaner concentrate.

Standard reagents and pH control are used in the flotation circuit to achieve the production of the two concentrates.

The initial reagents are added to the rod mill and further additions are staged through the circuit.

The zinc circuit configuration of conditionin ........