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.

Olympias is an example of a polymetallic carbonate replacement deposit, however it is somewhat unusual due to the high Au content of the deposit (cf. Siron et al. 2019). Key characteristics of this class of deposit include carbonate host rocks, massive sulphide mineralization, spatial and temporalrelationship with magmatism and zoned metal distribution (Megaw, 1998). Geochronological and paragenetic relationships described by Siron et al. (2016, 2018) confirm that Olympias was coeval with late Oligocene (~ 25-22 Ma) magmatism in the region although the source intrusion has not been identified. Nonetheless, carbon and oxygen isotopic data support a magmatic fluid source (Siron et al. 2019), and the zonation towards Mn-rich alteration in the upper levels of the deposit (North Zone) are consistent with shallow, distal portions of a magmatically derived carbonate replacement system.

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 East, West, Flats, and Remnants zones. In 2022, mining will concentrate on the West, East and the beginning of the Flats zones with a small proportion from the Remnants area. Mining is currently at a rate of 430 ktpa ROM ore. There is a planned production increase culminating in a steady-state rate of 650 ktpa by 2025. In order to achieve the planned higher production, the Company is taking steps to improve equipment availability / utilization and worker productivity. There are also further capital requirements to allow the process plant to treat 650,000 tpa.

Mining at Olympias will be a combination of drift and fill (“DAF”) and another method may be introduced: longhole open stoping (“LHOS”). LHOS will be confined to areas where geometry and ground conditions support the use of this more productive method. LHOS excavations will be limited to maximum dimensions of 10 m wide and 30 m high. 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 to minimize ore development requirements. 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 with consideration given to 6m high and 6 m wide stopes.

Ground support is a combination of shotcrete, mesh, split sets and swellex bolts of varying lengths. All mined out areas are backfilled either with paste fill, cemented aggregate fill (“CAF”) or rockfill. 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 can be 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 Zone and one accessing the East Zone down to the Flats Zone. There are multiple cross-over drifts between the two declines. Both declines are currently being extended into the Flats Zone 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 are currently 21 large pieces of mobile mining equipment on site: three jumbos, three bolters, four trucks, four loaders, two transmixers and three shotcrete sprayers. To achieve the production increase to 650 ktpa, funding has been allocated to increase this fleet number to 32. The increase will consist of two jumbos, one bolters, three trucks, and five loaders.

The ventilation system consists of a single exhaust raise with fan. Air intake is via the two declines, the shaft and the old workings. Two means of egress are provided by the two declines and old shaft. Current flow is 265 m3/s; this will increase to 420 m3/s for the 650 ktpa production rate.

Currently packaged explosives are being used for all blasting. There are no active magazines on site and explosives are brought to site daily by the supplier. The use of bulk explosives is being investigated as an opportunity. The construction of a new underground magazine is planned for 2023. Steady-state full production explosives consumption is estimated at 35 tonnes per month.

As an operating mine, infrastructure is well developed with existing process water, compressed air, electrical distribution, and dewatering systems. For the 650 ktpa expansion, a new main substation, main dewatering facilities, underground workshop, grout delivery line and other ancillary facilities are required. Some of these items are beneficial for the current project and the construction of these facilities is currently in progress.

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.

A regrind circuit provides size reduction of the rougher, scavenger, flash flotation and cleaner scavenger concentrates to improve mineral liberation and clean particle surfaces.

The Olympias lead-zinc-gold-silver process plant, commissioned in late 2017, is capable of processing 475 ktpa of ore. The process facility consists of comminution, flotation and filtering to produce three saleable concentrates: lead / silver (lead), zinc and arsenopyrite / pyrite gold (gold). All concentrates are sold to worldwide markets. Tailings are used for underground backfill via the on-surface paste plant. Any tailings not used for underground mine backfill are filtered and trucked from the Olympias processing facility to the Kokkinolakkas tailings management facility (“TMF”) over public roads. The expansion project involves upgrading of the existing Olympias process plant to handle a mine feed rate of 650 ktpa of ore, and upgrades to the port facilities at Stratoni. Studies are currently underway to extract more value from the gold concentrate that is currently being sold to traders and smelters around the world. If a viable extraction method is developed, then construction ........