On March 29, Eldorado Gold Corporation (Eldorado) and its subsidiary Hellas Gold published a new technical report for the Skouries Project located in Halkidiki Peninsula in northern Greece. The information and data were prepared in accordance with NI 43-101 Standards of Disclosure for Mineral Projects. Eldorado is an international gold mining company based in Vancouver, British Columbia. Hellas Gold was acquired as part of the acquisition of European Goldfields Limited (EGL) completed in February 2012. The Skouries Project is an advance stage project with development work on process facilities and infrastructure started, but it remains on care and maintenance awaiting approval of several permits necessary to complete the development plans.
The Skouries Project is a gold-copper porphyry deposit to be mined using a combination of conventional open pit and underground mining techniques. The mineral process facilities will produce doré and a gold-copper concentrate. The previous technical report on the Skouries Project was filed by EGL in July 2011. The new report updates the mineral resource and mineral reserve estimate and reflects updates to the open pit and underground mining production schedules, tailings and water management designs reflecting industry best practice, and updates the operating and capital cost estimates reflecting the changes to the scope of the project.
The open pit optimisation was carried out using Hexagon Mining MineSight mine planning software. The Skouries open pit is constrained by the existing EIS boundary on surface and the underground mining crown pillar, which limits the pit depth to 420 masl. In addition to the physical boundary constraints, the open pit design and overall size is also affected by a requirement to provide construction materials for the integrated waste management facility (IWMF). The mineral reserves for the open pit deposit has been evaluated at a $9.47/t NSR cutoff grade. The proven and probable mineral reserves are 59.5 Mt with an average grade of 0.56 g/t Au and 0.40% Cu.
The underground contribution to mineral reserves has been evaluated at a diluted NSR cut-off of $33.33/t, incorporating 5% unplanned diluting material by weight that is assumed to carry no metal value, and assuming an overall mining recovery of 95%. The mineral reserves for the underground deposit has been estimated to be 98.2 Mt with an average grade of 0.84 g/t Au and 0.55% Cu.
The Skouries Project is designed as a two phase mining operation. Phase 1 consists of a combined open pit and underground mine, operating over 10 years. Phase 2 consists of mining from the underground mine for a further 13 years. The total life of mine (LOM) is 23 years. Open pit mining will be by conventional truck-shovel operation. Based on the modelled rock types, approximately 17% of the mined material is amenable to free digging, this material will not require blasting. Direct feed ore from the open pit will be hauled to the Skouries processing plant by the owner operated fleet of 90 t trucks. During Phase 1 a portion of oxide ores will be hauled to the oxide ore stockpile (OOS) where it is planned to be re-handled during the Phase 2 of the Project. Waste material will be hauled to a transfer point adjacent to the OOS by the 90 t trucks where it will be re-handled by a fleet of smaller contractor trucks and placed in one of the material management structures within the IWMF.
There is no separate waste rock dump, all waste material will be utilised for construction of structures within the IWMF. The number of haulage units was determined by calculating cycle times in RPMGlobal Talpac using annual haul cycle profiles from Hexagon MineSight. Haul simulations were carried out based on the designated 90 t haul trucks and the smaller 60 t, 40 t and 15 t contractor trucks.
The Skouries orebody that extends below the bottom of the open pit is amenable to a bulk underground mining methods and has been evaluated under several different design approaches since the late 1990s including block caving, SLC and SLOS. SLOS has been confirmed as the most appropriate underground mining method for the Project and was incorporated into the EIS/JMD approval in 2011. Standard stope dimensions of 65 m high x 30 m long x 15 m wide in porphyry, and 65 m high x 20 m long x 15 m wide for primary stope design in schist can be realised. Production stopes will be backfilled with cemented paste fill. The stoping methodology is the same for both Phase 1 and Phase 2. Two test stopes have been planned to provide proof of concept for the 60 m high x 15 m wide x 30 m long basic stoping units in both porphyry and potassic schist rock types. All levels in both phases have similar designs. Peripheral development ring-drives will provide access to all sides of the orebody. Ore drives for stope extraction will traverse the orebody on 15 m centres, developed incrementally to meet the production schedule and mining sequence. Both ramps are planned to be used to haul ore, with the orebody divided into East and West in order to maintain a stope extraction sequence from the centre out.
The material handling strategy for Phase 1 is based on truck haulage of ROM ore directly to surface from the loading bays via a dual ramp system. The blasted production ore from the stopes will be loaded into haul trucks by LHDs at remuck/loading points off the production level U-drives. Ore is then hauled by trucks to the surface and will be crushed on surface by the same crusher that processes the open pit ore. The maximum rate at which material can be moved to surface is constrained by the number of haulage trucks that can use the ramps simultaneously with other equipment that also use the ramps. This volume of material must also account for development activities generated from the Phase 2, which must begin in Year 4. The Phase 2 materials handling will involve shaft hoisting of ore to surface. Shaft hoisting is critical to enable a ramp up to the maximum production of 6.4 Mt/y from the Phase 1 production of 2.5 Mt/y. During Phase 2, all stope ore and possibly some development ore will be hoisted to surface via the shaft. Development waste will continue to be trucked to surface via the dual ramp system, but these quantities are expected to be minimal. The use of ore and waste passes within the underground mine is not planned and no provision is made to hoist waste rock to surface.
In order to hoist the ore to the surface ROM ore will have to be crushed underground. The materials handling will include ROM and fine ore bins and underground crushing. The blasted production ore from the stopes will be loaded into haul trucks by LHDs at remuck/loading points off the production level U-drives. Ore is then hauled by trucks to one of two ROM bin dump pockets accessed from the 50 Level or directly to one of two crusher dump pocket on the -10 Level. The coarse ore bin dump pockets are each equipped with a grizzly and rock breaker, the crusher tipping points are equipped with a stationary rock breaker. The production hoist will be a multi-rope friction hoist and has been rated to have 25% excess hoisting capacity in line with all other fixed underground mine plant. The hoist will be operated in fully automated mode apart from maintenance or emergencies.
The primary grinding circuit is designed to reduce the feed ore with a particle size of 80% passing 150 mm to a product with a particle size 80% passing 120 μm. The size reduction is achieved by a two-stage wet grinding circuit comprising a SAG mill driven by variable speed motors, a ball mill (with a fixed speed motor) and a pebble crushing circuit. A gravity concentration circuit is integrated in the primary grinding circuit. The flotation is carried out in six stages: rougher, 1st cleaning, cleaner scavenger, 2nd cleaning, 3rd cleaning, additional cleaning, in order to produce a clean copper/gold concentrate. The rougher flotation circuit is comprised of a bank of ten 160 m3 cylindrical tank cells. The 1st cleaning flotation circuit is comprised of the first cleaner conditioning tank, of 50 m3 net capacity, and four 50 m3 flotation cells. The cleaner scavenger flotation circuit is comprised of six 50 m3 cells. The 2nd cleaning flotation circuit is comprised of five 10 m3 cells. The 3rd cleaning flotation circuit is comprised of four 10 m3 cells.
The additional cleaning flotation circuit is comprised of four 100 m3 cells. The gold gravity concentration circuit is comprised of centrifugal FLSmidth Knelson gravity concentrators. The principle of operation of the gravity concentrators is based on the difference between specific gravities of gold and other accompanying minerals, through which separation is accomplished. This circuit is comprised of three stages.
