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.

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 ........