The Ada Tepe deposit is a prime example of a high-level epithermal gold-silver deposit, formed during the Neogene within the Southern Rhodope tectonic zone.

The Ada Tepe deposit is a low-sulphidation adularia-sericite gold-silver epithermal deposit located within Palaeocene sedimentary rocks overlying the north-eastern end of the Kessebir core complex.

The gold precipitates predominantly in the veins. The Ada Tepe deposit shows a multiphase history of formation with several brecciation and vein emplacement events resulting in complex overprinting infill stages and crosscutting relationships between the veins.

Two major styles of mineralisation are apparent at Ada Tepe:
• Initial stage of mineralisation hosted by a massive, shallow-dipping (15° north) siliceous body forming the hangingwall to the detachment and defining the contact between the core complex and overlying sedimentary rocks. This mineralisation is termed the “Wall Zone” by local geologists and displays multiple stages of veining and brecciation.

• Second phase of mineralisation represented by steep dipping veins that exhibit textures indicative of formation within an epithermal environment. These veins have a predominant east-west strike, crosscut the shallow-dipping siliceous Wall Zone mineralisation, and extend upwards into the sedimentary breccia unit above the Wall Zone. This phase of mineralisation has been locally termed the “Upper Zone”.

The initial stage Wall Zone mineralisation is interpreted to be associated with early silica flooding and relatively low gold grades. However, regions of the Wall Zone through which well-developed Upper Zone vein mineralisation passes are typically thicker, more intensely brecciated and contain epithermal vein and hydraulic breccia infill textures and associated high gold grades that are not present in regions where Upper Zone vein mineralisation is absent. These thick strongly continuous regions of high-grade Wall Zone mineralisation generally thin and diminish in grade away from and between regions of well-developed Upper Zone vein mineralisation.

Typical epithermal textures present at the Ada Tepe deposit include the following:
• Crustiform and colloform banding
• Chalcedonic banding
• Bladed silica replacement textures after carbonate
• Compositionally zoned crystals
• Hydraulic breccia textures
• Late-stage carbonate veins.

The textural style and grade of mineralisation at Ada Tepe, high grades in association with open-space fill textures, such as bladed silica replacement after carbonate (i.e. evidence of boiling), hydrothermal breccias and also the presence of sinter material, suggests proximity to the paleo surface and a lowsulphidation nature of mineralisation.

The Ada Tepe mine is approximately 600 metres long (north-south), and up to 300-350 metres wide (east-west). The wall zone is up to 30 metres thick. The thickness of the Upper Zone vein mineralization is very variable, from less than one metre thick, to more than 30 metres thick. The Wall Zone exhibits very good continuity. The Upper Zone vein system exhibits less continuity than the Wall Zone, necessitating a higher drilling density that has been applied during the delineation of the Ada Tepe mine.

The mining methods used at the Ada Tepe pit are conventional excavator and truck methods. Drilling and blasting of ore and waste is conducted over bench heights of 5 m and explosives are delivered to the hole by the drill and blast contractor. Hydraulic excavators are used to achieve good selectivity in conjunction with good blasting practice and mine to a 2.5 m flitch height. Ore and waste are generally loaded to 40-tonne capacity off-highway haul trucks to a ROM stockpile or to the IMWF.

All the production fleet is principally sourced from Caterpillar. In addition to the main equipment units there are graders and water trucks as well as various support and service equipment in use. Mining operations are conducted in two 8.0-hour shifts per day. The mining production rate is about 3 Mtpa total material.

Pit Design
The selected economic pit shell was used to drive the pit design work. The pit design was checked against the Whittle shells to ensure they match reasonably well. The design difference is minimal with less than 3% loss in ore and less than 1% change in total tonnage. This is considered reasonable considering the requirement for ramps and other practical mining considerations.

The ultimate and phase pits were designed following the slope geotechnical criteria and selected pit shell. Four phased pushbacks were used for the LOM plan. All pits were designed on a 5 m mining height. The ultimate pit was designed with 15 m bench heights and 7.5 m berm widths following the slope design guidelines. The interim northern pit walls in the initial three pushbacks were designed with 10 m bench heights.

Road and ramp parameters have been designed for Caterpillar (“CAT”) 770G rigid trucks and CAT 745C articulated dump trucks which are currently used on site.

Pit design parameters:
Haulage width - 20 m
Max in-pit ramp gradient - 10%
Minimum mining width - 25m
Pushback width - 150m

The pit is approximately 350 m in width and 580 m in length at its widest points and 125 m in depth.

The mining operation is planned to be carried out via three intermediate and a final fourth pushback (Phases 1 to 4). Mining of the pushbacks is developed towards the north, reaching the final design limit in the south, east and west for each of Phases 1 to 3. The final pit is up to 115 m deep and has a width at surface of more than 350 m. The elevation of the deepest bench in the fourth pushback is 340 mRL and the maximum elevation of the pit benches is 455 mRL.

The pushbacks are designed with 20 m-wide ramps to allow more space at the bottom of the pit. The pit ramp exits the pit at the southwest edge.

Ore is processed by crushing the mined ore in the primary jaw crushing circuit, grinding in a semi-autogenous grinding (“SAG”) milling circuit followed by a further secondary grind in a vertimill circuit.

• Primary crushing of ROM ores to a design P80 size of 110 mm with subsequent crushed ore storage in the Coarse Ore Bin with 24 hours live capacity. The crusher is designed to operate for 12 hours per day at 80% utilisation for a throughput rate of 263 dry tph.

• The grinding and flotation circuits are designed to operate for 8,000 hours per annum, which is equivalent to 91.3% overall utilisation. Due to the quite different comminution characteristics of the two mined ore types, varying proportions of each during the LOM and a capital cost reduction exercise completed during April 2013, a variable range of grinding circuit throughputs was adopted for the final design. Depending upon the proportion of the harder Wall material, the design grinding circuit throughput ranges from 105 tph (~99% Upper Oxide) to 90 tph (~36% Wall) and varies for every month of operation over the eight-year mine life.

• Crushed ore is reclaimed to a single-stage Metso SAG milling circuit equipped with pebble crushing (SAC). The SAG mill is a 6.71 m (22’) diameter by 3.96 m (14’) EGL unit equipped with a 3,000 kW (6.6 kV) variable speed drive (“MVVVF”) motor. The SAG mill is designed to operate within a ball charge envelope of 6% to 15% and reduce the 110 mm F80 material to a P80 size of 125 µm in closed circuit with the Primary Classification bank of six 400 mm hydrocyclones (four operating).

• SAG mill discharge is screened and washed via a trunnion mounted trommel to produce a feed stream to the pebble crushing circuit. The pebble crusher is a Sandvik CH320 hydroset type cone crusher designed to reduce 30% of the SAG mill feed throughput to a P80 size of 13 mm for recycle to the SAG mill via the feed conveyor system.

• SAG milling circuit cyclone overflow reports to a vibrating trash screen where the undersize is directed to the Primary Regrind Classification system, a bank of twelve 250-mm diameter hydrocyclones (nine operating). The system cyclone overflow, at a design P80 size of 30 µm, is directed to the Rougher flotation circuit. The underflow stream is gravity transferred to two Metso vertimill 1250WB regrind mills (932 kW installed each) operating in parallel and with mill discharge streams recycled to the classification feed system in closed circuit.

• Primary regrind circuit cyclone overflow is transferred to the rougher flotation circuit comprised of a conditioning tank, four rougher SFRs operating in series and flotation tails and concentrate pumping systems.

The Ada Tepe process plant and associated service facilities handles ROM ore from the mine and produces a gold-bearing concentrate for shipment to a smelter. The process encompasses crushing and grinding of the ROM ore, followed by froth flotation to produce a gold-bearing concentrate. Tailings is thickened to a sufficient density to enable deposition in the IMWF.

The Ada Tepe processing facility was designed to recover very fine free gold and silver from oxide host rock by flotation to a high-grade concentrate for off-site precious metals refining. Two main ore types are present within the orebody (i.e. Upper Oxide and Wall), where the latter represents a much lower proportion of mill feed tonnes but at considerably higher precious metals grades.

The key project and ore-specific criteria for the plant design are:
• Treatment of a maximum of 0.85 Mtpa of ore for each year of operation.
• Operation of the crushing plant on a 12 hours per day basis; mill ........