Olympias is a gold-rich polymetallic sulphide replacement-style deposit formed within strongly deformed metamorphic rocks of the Paleozoic Kerdylia Formation of the Serbo-Macedonian Massif. The orebodies are hosted by marble interlayered within a sequence of biotite-gneiss, amphibolite and orthogneiss. The deposit consists of multiple stratabound orebodies that overall plunge shallowly to the southeast for over 1.8 km, subparallel to the orientation of fold hinges and a locally developed intersection lineation.

The Olympias deposit massive sulphide lenses are grouped into three major spatial domains: East Zone, West Zone and Flats Zone. Two smaller sub-zones, the Remnants and North zones, are considered as part of the West Zone for the purpose of resource estimation. The East Zone ore lenses occur dominantly in the footwall to the steeply northeast-dipping East fault, hosted by marble at or below the contact with overlying gneiss.

The ore lenses dip shallow to moderately to the northeast with individual thicknesses ranging up to 10 m and widths up to 130 m. The West Zone ore bodies occur along and adjacent to the Kassandra fault and have a steep (~ 60°) northeast dips that shallow at depth approaching the Flats zone. The West Zone has an east-west strike extent of ~ 1.2 km, with individual lenses up to 25 m thick with a down dip extent up to 200 m. The Flats Zone extends eastward from the West Zone and dips shallowly to the northeast; however locally lenses of the Flats Zone extend westward into the footwall of the Kassandra fault, below the West Zone. The Flats Zone has an east-west strike extent of over 1 km. Individual ore lenses are up to 15 m thick, although more commonly range from 3 to 10m thick, and are tens of metres to up to 100 m wide.

Sulphide minerals in the Olympias deposit occur in massive and mineralogically banded lenses dominated by variable amounts of coarse-grained sphalerite, galena, pyrite, arsenopyrite, chalcopyrite and boulangerite. Ag and Au occur primarily in solid solution within their respective host minerals; Ag in galena and Au in both arsenopyrite and pyrite.

Mine nomenclature classifies the mineralization into eight ore types. Ore types 1 to 3 are base metal and pyrite dominant, ore types 6 and 7 are arsenopyrite-rich and silica bearing, ore type 8 is manganese rich and ore types 4 and 5 consist of sub-economic pyritic wall rock alteration. Ore types 1, 2 and 3 are gradational and reflect end-members of galena-sphalerite dominant (ore type 1) to pyrite dominant (ore type 2) to transitional mixed galena-sphalerite-pyrite (ore type 3). Arsenopyrite is common in all three ore types but is not the dominant sulphide. These three ore types typically occur as massive to banded sulphide zones with medium to coarse grained sphalerite-galena-pyrite-arsenopyrite and calcite gangue. Ore types 1 to 3 are dominant in the Flats Zone. Ore type 7 is arsenopyrite-rich and has the highest gold content. The mineralization is typically siliceous with massive to banded sulphide dominated by blocky to acicular arsenopyrite with lesser pyrite, galena and sphalerite. Ore type 7 is locally gradational to ore type 3, and banded zones commonly comprise intergrown ore types 1 to 3 and 7. Ore type 7 is dominant in the East Zone. Ore type 6 is a paragenetically younger quartz-rich sulphide assemblage that locally overprints the early replacement massive sulphide ore horizons. Ore type 6 can vary from banded siliceous zones to extensive intervals of grey siliceous matrix breccia that contains angular altered wallrock fragments. These quartz-rich sulphide bodies consist of interlocking, euhedral and growth-zoned quartz accompanied by interstitial arsenopyrite and boulangerite with subordinate pyrite, galena and sphalerite. The breccia matrix consists of dark gray chalcedonic quartz containing disseminated, euhedral pyrite, fibrous boulangerite and bladed arsenopyrite. In places ore type 6 grades into ore type 7, and commonly these quartz-rich ore types are surrounded by lower grade quartz-rhodochrosite alteration of the marble (ore type 8).

The Olympias mine is a 100% underground (UG) mining operation extracting ore from three zones: East, West and Flats and two sub-zones: Remnants, and North. Mining is currently at a rate of 360 ktpa. There is a production increase planned to take place between 2019 and 2023 to a steady-state value of 650 ktpa.

The mining methods planned for future operations at Olympias mine are DAF (the current method) and TLHOS. DAF is envisaged to be used in all mining areas (East, West, Flats, Remnants, and North), whereas TLHOS is projected for use in the Flats.

Ground support is a combination of shotcrete, split sets and swellex bolts of varying lengths. All mined out areas are backfilled either with paste fill or cemented aggregate fill.

Mining at Olympias will be a combination of drift and fill (DAF) and transverse longhole open stoping (TLHOS). TLHOS will be confined to areas of the Flats where geometry and ground conditions support the use of the higher productive method. The remainder of the mine will use DAF.

TLHOS will be excavated 10 m wide and 30 m high maximum. The maximum length varies depending on the height and average rock quality. Blind uppers will be used for drill and blast with no top accesses.

DAF mining utilizes the overhand mining method. Stopes are accessed on the foot wall side from the main ramp starting at the bottom of each 20 m high stoping block. Each lift is mined 5 m high, with each panel limited to 5 m wide. There are two methods of DAF stoping, longitudinal and multi-pass.

Longitudinal is utilized where the stopes are less than 10 m wide. A single pass is mined down the length of the stope and any remaining ore is slashed off the HW on retreat. The stope is then filled prior to taking down the back in the access for the next lift.

Multi-pass is utilized where the stopes are greater than 10 m wide. Mining starts by cross cutting the ore body from footwall to HW. Then a single drift is developed in the ore to the extents of the stope in both directions along the footwall. Transverse cuts are then made from footwall to HW at multiple locations such that multiple working faces are established. After each cut is made it is backfilled, and then a new cut is mined beside the previous one. Once the lift is completely mined out, the back of the access is taken down to start the next lift.

All stopes are filled with backfill after excavation. Currently a combination of cemented aggregate fill (CAF) and paste fill is used. The paste fill system has been designed to produce 42 m3/hr of paste, which will meet all future backfill requirements at 650 ktpa production with 70% utilization. CAF is delivered to stopes by truck and pushed into place with loaders. Paste is delivered with positive
displacement pumps via drill holes and pipes.

There are two declines currently in use, one accessing the West Zone down to the Flats and one accessing the East Zone down to the Flats. There are multiple cross-over drifts between the two declines. Both declines are currently being extended into the Flats and to the bottom of the mine.

Both ore and waste are hauled to surface utilizing 40 tonne haul trucks on the existing and expanding declines. This will continue to be the case after the production increase to a steady-state value of 650 ktpa.

There is currently 23 large pieces of mobile mining equipment on site: four jumbos, two bolters, five trucks, six loaders, four transmixers and two shotcrete sprayers. To achieve the production increase to 650 ktpa, funding has been allocated to increase this fleet number to 33. The increase will consist of one jumbo, two bolters, two longhole drills, two trucks, and three loaders.

The crushing plant is operated 350 days per year, 16 hours per day at a crushing rate of 125 t/h. The crushing product size is 100% passing 13 mm and 80% passing 10 mm.

A 600 mm x 800 mm inclined static grizzly is fitted to the primary crusher feed hopper for protection from oversize rocks. The oversize rocks are periodically broken to less than 600 mm with a mobile rock breaker. The primary crusher feed hopper is equipped with dust suppression spray.

The primary crusher is fed by a vibrating grizzly feeder that scalps the rocks greater than 75 mm ahead of crushing. The undersize material is directed onto the crusher discharge conveyor. Grizzly feeder oversize feeds a jaw crusher (Sandvik CJ411) at closed side setting (CSS) of 75 mm.

The jaw crusher product (100% passing 180 mm and 80% passing 90 mm) reports to the crusher discharge conveyor and is delivered, along with the fines from the vibrating grizzly feeder, to the primary crushed coarse ore stockpile feed conveyor. The coarse ore stockpile feed conveyor discharges onto the coarse ore stockpile with a live capacity of 79 tonnes.

Primary crushed ore is withdrawn from the coarse ore stockpile by a vibrating feeder and transported to the secondary crusher feed screen conveyor. A metal detector is installed on the secondary crusher feed screen conveyor to ensure all tramp metal is removed.

The primary crushed ore then reports to a double-deck scalping screen with 50 mm aperture for the top deck and 20 mm aperture for the bottom deck. The oversize material from both decks is directed to the secondary crusher (Sandvik CH430 with CSS at 28 mm) whilst the screen undersize and the secondary crusher product are deposited onto the secondary crusher discharge conveyor, which in turn discharges onto the tertiary crusher feed screen conveyor.

Ore on the secondary crusher discharge conveyor transfers onto the tertiary crusher feed screen conveyor, and then to the tertiary product screen.

The tertiary crusher feed hopper is fitted with a belt feeder. The tertiary crusher (Sandvik CH430 at CSS of 13 mm) is a short head cone crusher that operates in closed circuit with the product screen. The crusher discharges directly onto the tertiary crusher discharge conveyor, which in turn discharges onto the secondary crusher discharge conveyor (thus operating in closed circuit with the product screen).

The final crusher product after screening has a P80 of 10 mm and is deposited onto the tertiary screen undersize conveyor, which in turn discharges onto the fine ore bin feed conveyor. The fine ore bin feed conveyor transfers the final crusher product to the fine ore bin (FOB). The crushing rate is monitored by a weightometer located on the fine ore bin feed conveyor. The FOB has a live
capacity of 1,155 tonnes to provide 21.8 hours of mill feed.

Mill feed is withdrawn from the FOB via five variable speed belt feeders. A weightometer indicates the instantaneous and totalized mill feed tonnage for control of belt feeder speed. Mill feed from the FOB is transported to the grinding circuit by the ball mill feed conveyor.

The grinding circuit consists of a single-stage overflow ball mill that operates in closed circuit with hydro-cyclones to produce a ground product slurry with P80 of 120 µm and with a flash flotation cell for recovery of galena from the cyclone underflow.

Mill feed enters the grinding circuit through the mill feed chute, where process water is added. The ball mill is 3.65 m diameter by 4.00 m long effective grinding length and powered by a 900 kW variable speed drive. Normal operation requires 700 kW power draw. The ball mill is fitted with a trommel screen. Trommel screen undersize slurry reports to the cyclone feed hopper.

Reagents are added to the cyclone feed hopper for depression of sphalerite, arsenopyrite and pyrite.

Cyclone overflow flows by gravity to the trash screen feed box. A single horizontal vibrating trash screen (0.8 mm x 12 mm slotted aperture) removes trash from the flotation feed. Oversize trash gravitates directly to a trash bin. Screen undersize gravitates to the lead rougher flotation conditioning tank.

Cyclone underflow gravitates to the underflow distribution box where the flow is split. Up to 100% of cyclone underflow stream can be directed to the flash flotation circuit to recover fast-floating galena. Dilution water and flotation reagents are added. Concentrate flows by gravity to the flash flotation concentrate transfer pump before being pumped to the inline stream analyzer (ISA) for analysis and then regrinding. The flash flotation coarse tailings flows by gravity to the ball mill for further grinding. The fine tailings from the top outlet flows to the cyclone feed hopper or to a surge tank and then to conditioning tank ahead of lead rougher flotation

The current process plant is currently able to treat 400,000 tonnes per annum at 53 t/h. A few key
features are as follows.
- Three-stage crushing
- Single-stage ball milling in closed circuit with hydrocyclones
- Nearly all hydrocyclones underflow is fed to flash flotation.
- Lead flotation consists of rougher, scavenger, regrinding, three stages of cleaning
- Zinc flotation consists of rougher, scavenger, regrinding, three stages of cleaning
- Gold-Pyrite flotation utilizes rougher, scavenger, and single stage of cleaning
- Concentrate thickening, filtration, and packaging
- Tailings thickening and filtration
- Tailings paste backfill
- Reagent mixing, storage and distribution
- Water and air services