The sulphide ore comprises both undeformed massive sulphides and deformed sulphide ore with the latter characterised by brecciation, mylonitisation, folding and shearing.    The most abundant ore minerals are pyrite, sphalerite, galena, arsenopyrite and chalcopyrite.    Similar chemistry and fine zoning of sphalerite in both deformed and undeformed ore suggest that they come from the same system and were deposited after the onset of regional metamorphism.    In addition copper-lead- zinc– silver bulk ore chemistry and together with lead silver relations, irrespective of deformation, indicate similarity to recognised skarn – replacement type deposits (Kalogeropoulos, Kilias and Bitzios, 1989).

The Olympias mineralisation is a massive stratabound polymetallic replacement deposit hosted in the marble-gneiss contact of the Kerdilia Formation.    The deposit comprises pyrite, arsenopyrite, sphalerite, galena, tetrahedrite-tenantite, boulangerite and chalcopyrite with secondary cerussite, chalcocite and covellite.  Manganese oxides represent alteration of rhodochrosite.  Gangue minerals include quartz, calcite, rhodochrosite, feldspar, kaolinite, chlorite, ankerite and graphite. The ore minerals are mainly massive in form. Kaolinisation is the main type of alteration associated with the deposit.    Hydrothermal brecciation is common and chloritisation and silicification of host rocks immediately around the mineralised section is frequently observed.   

The mineralisation occurs within two orebodies.   The West orebody is approximately 250 m wide and plunges 1,500 m to the southwest.  It has been intersected from surface to a depth of 500 m and is open down plunge.  Its width varies between 5 m to 15 m, with dips averaging 30° to 35° east.  The East orebody lies some 150 m east of the West orebody, has an anticlinal structure, exhibiting axial thickening, with steeper dips toward the peripheries.  It dips an average 25° to 30° to the southeast.   Its width averages 75 m and its average thickness is 7 m.  The mineralisation has been traced for 600 m down plunge.

The ore zones at the Olympias Project are variable in ore geometry and ground conditions. The ore contacts are well defined and are often irregular on the footwall.  The high grades associated with these types of ore dictate that a selective mining method will be used. The mining method will be conventional transverse and longitudinal Drift & Fill. A double lift Drift & Fill method (Mini Bench & Fill) in wide orebody areas has been considered but is only applicable to approximately 15% of the reserve and only in very good, stable geotechnical hangingwall conditions. As a result, the mineral reserves have been computed based solely on the conventional Drift & Fill method.  A conventional drill and blast and load-haul-dump (LHD) method of mining will be employed in both production and development. The method is flexible allowing headings to change direction with changing ore geometry.

An existing ramp has been driven in the footwall from surface at +50 m down to -230 m level. This ramp will be enlarged and resupported to allow access and ventilation. This existing ramp will form the West Ramp from the -110 m junction (with the new Olympias Decline) and will eventually be extended to the base of the orebody at -630 m level. A new Olympias Decline of 1,300 m will be developed from surface in the area north west of the concentrator to intersect the existing ramp at -110 m where a new East Ramp will commence to access the East ore body. This decline is necessary primarily for ventilation purposes but also provides an ore/waste truck haulage route directly to the process plant on surface in the initial years. Access crosscuts to intersect the orebody will be driven from the main West and East ramps.

The mining method is expected to be longitudinal or transverse Drift & Fill depending on orebody geometry.  If the distance between the hanging wall and the footwall is very variable from narrow to wide, then a mixed method of longitudinal and transverse would be adapted to suit the conditions.
   
Generally, for footwall to hanging wall thickness of 10 m or less, the stope will be developed for longitudinal drift & fill mining. This involves developing on the footwall contact avoiding exposing poor hanging wall ground conditions.    After completion of the footwall drift, depending on the orebody width and ground conditions, the ore on the hanging wall side will be either stripped on the retreat, or the drift will be filled and a second drift on the hanging wall side started.

For a thickness greater than 10 m, the transverse drift & fill method is preferable driven along the centre of the orebody from which transverse drifts are mined to the hanging wall and footwall on the retreat from the ends of the orebody. This method of mining from footwall to hanging wall has the advantage of offering increased hanging wall stability by reducing the area of exposure at any one time.  Where primary and secondary mining is scheduled, productivity is also increased as a single stoping level will have many more available faces than with the longitudinal method.

Ore is removed from the stopes after blasting using load haul dump machines.  It is tipped into the orepass system alongside the main ramp or in the lower areas directly into the dump trucks. A loading bay is developed if logistically necessary.  The stoped area is then filled.

The Olympias Project is being developed in phases.    Initially the Olympias Project will utilise the rehabilitated existing concentrator plant at Olympias to treat reclaimed existing tailings for 3 to 4 years and will then be supplied by ore mined underground for a further 4 years.  A new concentrator is scheduled to be built on a brownfield area at the Stratoni mine site ready for year 9 of the operation to accommodate increased ore production 850,000 dtpa which will be delivered by trucks through a decline tunnel linking the Olympias mine to the new concentrator.

In both phases, the concentrates produced from run of mine ore will be:
• lead/silver concentrate
• zinc concentrate
• gold bearing pyrite / arsenopyrite concentrate  

The metal concentrates will either be trucked to Hellas Gold’s Stratoni port facilities for bulk sea freight shipment or stuffed into containers and transported to Thessaloniki for export.  

Once the stored tailings have been exhausted, the flotation circuit will be slightly modified so that it can produce the three concentrates: lead/silver concentrate; zinc concentrate and the gold bearing pyrite / arsenopyrite concentrate.   Ore will be directed from the underground mine to the crushing plant producing a crushed product with a nominal sizing of 80% passing 12 mm and thence to the grinding mills where the solids will be milled to give a sizing in the region of 80% passing 180 microns.  The crushed ore will be transferred to the fine ore bin ahead of the rod mill and the secondary ball mill.  The overflow from the hydro-cyclones classifier will be directed to the flotation circuit.  The flotation section will produce three concentrates, firstly lead/silver, secondly zinc and thirdly the refractory auriferous arsenical pyrite concentrate.  

Separation of the minerals into the three concentrates is achieved through a combination of pH control and conventional reagents for the depression and activation of the various mineral species as appropriate.  The plant is being refurbished with mechanical flotation cells with a capacity of 3 m³ units for roughing and scavenging and 1.5 m³ for cleaning.  The concentrates will be directed to their respective thickeners and filters, conveyed to storage ready for despatch to market.

The tailings from the concentrator will be separated into course and fine fractions, the fine fraction, which is about 20% of the total and water treatment plant sludge, will be filtered by a new filter press installed during the plant rehabilitation programme and the fine fraction transported as filter cake to Stratoni for disposal on the existing TMF.  In the first years of operation before mining has been established, the course fraction of the residue from the tailings phase will be used by local contractors as aggregate.

As the Olympias Project develops, a new concentrator plant will be constructed.  This will be located at the Stratoni site close to the old Mavres Petres works and will be supplied by trucks through the newly excavated decline from the Olympias mine.  The new concentrator is scheduled to come on line six to seven years after the resumption of operations at the Olympias mine.

The mill will be rated to process 850,000 tpa of ore. The ore will be primary crushed on surface before being conveyed to the plant. The concentrator will be of conventional design and will comprise the following unit operations:

• Ore will be transferred from the mine by truck via the 8.5 kilometre Stratoni Decline to the brownfield Stratoni mine site.  Primary crushing will be carried out at the new plant area. The ore will be stored on a crushed ore stockpile from where an ore reclaim system and SAG mill feed conveyor will feed the SAG mill;
• A single SAG mill running in combination with two ball mills.   A pebble crushing facility is provided for breaking down SAG mill discharge oversize material.    The SAG and ball mills discharges are classified in a cluster of hydro-cyclones with the overflow proceeding to the flotation stage and the undersize making up ball mill feed;
• The flotation section is operated in the differential mode.    The lead/silver concentrate is floated first, the zinc concentrate second and the refractory gold bearing pyrite concentrate third.  The separation of the feed into the three concentrates is achieved with a combination of pH control and reagent addition.  The respective rougher concentrates are upgraded to the final product grade by cleaning stages.  Provision will be made for the storage, mixing and distribution of milk of lime and reagents;
• The three concentrates will be thickened and filtered.  In the case of the lead/silver and zinc concentrates, these will be transferred to the storage and loading facility at the port in Stratoni.  The gold bearing pyrite concentrate will be sold (or transferred to the gold plant storage shed ahead of the drying plant at the flash smelting furnace complex);
• The design of the process plant will incorporate features to provide for worker health and safety.