The Banket Series in the mine lease areas form prominent, arcuate ridges extending southwards from Tarkwa, westwards through Iduapriem and northwards through Teberebie to Mantraim. The ridge segments are supported by a massive lithological unit known as the Footwall Quartzite, which is a strongly-bedded rock of blue-grey colour exhibiting a sub-parallel haematitic/black sand banding and which locally forms the basal stratigraphic unit to the Banket Reef Zone (BRZ).

The BRZ comprises a sequence of individual beds of quartz pebble conglomerates (Banket beds), breccia conglomerates, metasandstones (also called quartzites and grits). All known gold mineralisation within the Banket Formation is associated with the conglomerates and is found within the matrix that binds the pebbles together. Gold content is presumably a function of the size and amount (packing) of quartz pebbles present within a conglomeratic unit- more pebbles present suggest more gold.

Gold mineralisation is hosted by conglomeratic sedimentary packages referred to as zones or reefs and is considered to be of primary palaeoplacer origin. There are four recognized reefs, namely A, B, C and D and which are equivalent to the Tarkwaian Sub-Basal, Basal (or Main), Middle (or West) and Breccia Reefs respectively. The B and C reefs are oligomictic, and consist of well sorted conglomerates and have been mined underground in some areas for over a century. The A and D reefs have a lower gold tenor and are polymictic containing both well rounded and angular fragments. The gold is fine-grained, free and not associated with sulphides. The main ancillary mineral is magnetite.

At Iduapriem, the entire Tarkwaian Group has been folded into a broad syncline, locally referred to as the Tarkwa Syncline. The reefs are stratigraphically located within the Banket Formation and are the locus of the mine towards the southern closure of the Tarkwa Syncline. With the gold mineralisation being stratabound, the characteristics of the mineralisation are defined by the reefs. The Tarkwa Syncline covers the eastern portion of the lease (Blocks 1-8), with the Ajopa deposit located in the north-western lease on the western limb of the Ajopa anticline.

For blocks 1 to 8, the pits are numbered sequentially from east to west across both limbs of the Tarkwa Syncline. These limbs, which outcrop and express themselves as topographic ridges, trend NE on the easterly limb and NNE on the westerly limb. The closure of the syncline results in an east-west cuspate shape to the reefs at the southern limits of the Banket formation. Reef dips are variable and reflect the structural complexity of the basin. The eastern limb of syncline dips steeply 70-80 degrees towards the west, however this changes to the south where the dips become steeper, eventually becoming overturned and southerly dipping at the southern margin of the basin in the vicinity of blocks 1 and 2. Moving westwards to block 3, the dips again dip into the syncline and flattening to approximately 50 degrees by Block 3 east. At Blocks 7 and 8, which are the dominant constituents of the Ore Reserve, the reefs dip 35 to 30 degrees to the west. Reef packages vary in thickness, with those in Blocks 7 and 8 being between 3 and 10m thick, but in the vicinity of Block 1 reefs thin, onlap and thicken due to thrusting.

At Ajopa, where the reefs are expressed as a topographic ridge striking NE-SW, dips are generally 50 to 60 degrees to the west. All four reefs are present, however the B and C reefs are more dominant and thicknesses vary between 3m and 8m.

Faulting is common and major faults are believed to be contemporaneous with the folding. Within the Tarkwa Syncline, faults form bounding structures to the blocks and separate the individual pits from each other.

Iduapriem is an open pit mine which makes use of contract miners. It uses conventional drill and blast, with truck and excavator load and haul.

The Iduapriem Mine started operating in June 1992. The original plant, designed to treat about 2.4Mtpa of ore, has undergone several expansions. The most recent expansion work was completed and commissioned in 2009 which incorporated a new 800tph 2-stage crushing plant, a second ball mill at the CIL plant together with a 24 meter diameter thickener, a second Knelson concentrator, and an upgrade of the oxygen plant capacity from 4.0 to 8.0 tonnes per day. The main objective of the expansion project was to increase plant throughput to 4.3Mtpa.

A gravity circuit comprising of 2 XD48 centrifugal (Knelson) concentrators and an In-line Leach Reactor (ILR – Series 1000) recovers free gold (gravity gold) by processing the dense particles from the cyclone underflow slurry. Each circuit has 1 Knelson and part of the cyclone underflow is bled to feed the Knelson.

The concentrator operates in batch mode. Once the preset time has elapsed, the unit goes through a flush cycle ........