The Perama Hill gold deposit is a stratabound, sediment hosted deposit of Eocene to Oligocene age, located at the eastern edge of the Maronia Graben at the contact point with a north northeast trending eastern graben fault. The Perama Hill deposit is described as an initial high sulphidation epithermal system overprinted by typical low sulphidation banded quartz chalcedony, barite, pyrite stockwork veins, and veinlets. Two key controlling factors on the mineralization are the porosity and rock competency contrasts between the volcanic sandstone and underlying andesite package.

The deposit extends 750 m in a north-south direction and up to 300 m in an east-west direction and the thickness varies from 15 m to 20 m at the flanks and up to 125 m at the centre. The gold mineralization has been fed into the system by structurally controlled feeders inside andesitic volcanic breccia and disseminated into overlying porous sandstone units. The central part of the deposit is mushroom-shaped. Eighty percent of the gold is hosted by sandstones and the rest is associated with andesitic volcanic breccia and conglomerates.

Mineralogical studies from the Perama Hill gold deposit indicate that gold mineralization is very uniform throughout the deposit and the gold grain size is small, generally less than 2 µm.

Gold mineralization occurred during the latest stage of silicification and gold bearing siliceous fluids were introduced after structural preparation by hydraulic fracturing and veining of the same hardened silicified rock. Gold is identified in the sulphide mineralization in association with very fine pyrite containing sub-micronic gold and gold silver telluride. Enargite and stannite group minerals (Cu, As, Sb sulphides) were also introduced in this event. Galena and sphalerite are also present in the sulphide ore but do not appear to correlate with gold.

The gold occurs as micron size particles in association with quartz, clay and hematite.

Mineralization in the sandstones accounts for more than 80% of the oxide deposit. Hydrothermal fluids, which travelled upwards through structurally controlled conduits in the andesite breccia were able to disseminate and travel laterally through a finely developed network of fracture systems developed in the porous sandstones.

Mineralization in the volcanic breccia unit is confined to the sulphide facies in the central part and the oxidized uplifted panel in the northern part of Perama Hill. Due to less supergene leaching in these less porous, quartz-free and strongly clay altered rocks, metals like Cu and Pb can be identified in outcrop in association with clay and strongly developed limonite minerals. Heterogeneity of the rock, allowing fluid circulation at the contact between clasts and matrix under hydraulic pressure, was a favourable factor.

The Perama Hill project has an orebody that is amenable to conventional open pit mining. The rate of production is 1.2 Mt of ore per year and an additional 350,000 tonnes of waste and low-grade material.

Using fracture spacing and hardness models a matrix of the two was made to identify the degree of blasting or ripping that will be required. The material is generally soft and fractured. Although a large percentage of the material is expected to be ripped and/or excavated without any need for ripping, a conservative 100% drilling and blasting mining method was selected for equipment requirements and costing. Light and medium blasting will be employed for most of the material with an average powder factor of 0.12 kg/t, hard blasting, which is a fraction of about 1% of the total material would use a powder factor of 0.20 kg/t.

The selected excavating equipment will be two Caterpillar 385C hydraulic backhoes each with 5.5 m³ bucket capacity loading into a fleet of six Mercedes Actros 4150 8x4 dump trucks each with a payload of 33 tonnes.

The Perama Hill process plant will be designed to treat 1,250,000 t/a of conventional oxide ore cap containing gold and silver bearing ore at a treatment rate of 3,400 tonnes per calendar day at an overall plant availability of 90%. The processing facilities include three stage crushing, followed by a single stage ball mill with a classification step to produce 80% passing 75 µm product size.

Milled ore will be thickened in a high rate thickener prior to pre-aeration and gold/silver dissolution in the CIL circuit. Hydrated lime will be added in the milling circuit. Precious metal dissolution will be by cyanide. Oxygen will be injected into the pre-aeration tank and leaching tanks to enhance the leach kinetics. The CIL circuit will consist of six tanks with a total retention time of 20 hours.

The CIL tailings will be detoxified to remove any remaining cyanide by the INCO SO2 Process. The Environmental Terms of Reference (ETR) requires a CNWAD of < 10 mg/L. Studies ........