The Geita Greenstone Belt (GGB) hosts several world-class shear-hosted Archaean lode gold deposits and forms the northern portion of the regional Sukumaland Greenstone Belt, itself one of several belts that comprise the Lake Victoria Goldfields. Other gold mines hosted in the Lake Victoria Goldfields include Golden Pride, Bulyanhulu, Tulawaka, Buzwagi and North Mara.

The east-west oriented GGB is 60km in length, up to 15km wide. The Geita terrain is comprised of upper- to mid-Nyanzian greenschist facies units, made up of clastic sediments, black shales, banded iron formation (BIF) and volcaniclastics. These have been intruded by a variety of felsic to mafic intrusive bodies, dykes and sills. Regional north-northeasterly structures hosting Proterozoic gabbro dykes are also prominent geological features in the area.

North-west trending deformation corridors divide the GGB into three distinct sub-terrains, namely the Nyamulilima Terrain in the west (hosting the Star and Comet, Ridge 8 and Roberts deposits), the Central Terrain in the central part (hosting the Nyankanga, Geita Hill, Lone Cone and Chipaka deposits) and the Kukuluma Terrain to the north-east (hosting the Matandani, Kukuluma and Area 3 West deposits).

Geita’s gold mineralisation is preferentially hosted in BIF, cherts and ironstones that have been affected by both ductile and brittle deformation associated with shear zones. The shears exploit fold axial planes as well as the contacts between the supracrustal and intrusive rocks.

The GGB has been through a protracted history of deformation, which resulted in a large-scale synformal configuration in the Central Terrain, with west-northwest trending limbs connected by a north-east trending hinge zone. The deposits of the Central Terrain are mainly located within the relatively low-strain hinge zone. The Nyankanga deposit is hosted in a BIF-dominated supracrustal package that is extensively intruded by, and locally form a roof-pendant within the dioritic Nyankanga Intrusive Complex. At Geita Hill, dioritic rocks are present as sills and dykes intruded into a supracrustal sequence that has been subject to extensive polyphase folding.

To the west, the Nyamulilima Terrain comprises a semi-circular structure surrounding intrusive centers, which internally encompasses structural systems of variable scale that locally control gold mineralisation. At Star and Comet, a folded sedimentary package of BIF intercalated with clastic and tuffaceous meta-sediments is intruded by a tonalitic complex.

The Kukuluma Terrain trends west-northwesterly, with sub-vertical limbs being dominant over compressed, multiphase folded zones. The three major deposits in the area (Kukuluma, Matandani and Area 3) are located along a 5km long east southeast mineralisation trend. The geology of the deposits is dominated by volcano-sedimentary rocks that are polydeformed and intruded by syn- to latefolding diorite bodies. Host rocks for mineralisation are fine-grained iron-rich clastic sediments, cherts, BIF and tuffaceous rocks, with local intercalated carbonaceous shales.

Gold mineralisation at Nyankanga occurs within a northeast-trending and northwest-dipping anastomosing shear system, typically along the lowermost shears, with higher grade mineralisation mainly proximal to the basal contact of BIF packages. Mineralisation is associated with chlorite-carbonate-silica alteration and pyrite-dominant sulphide in the damage zones surrounding the shear surfaces as veins, veinlets, local breccias and sulphide replacement of magnetite layers. At Geita Hill, mineralisation at the deposit scale is controlled by a narrow NE-trending and NW-dipping shear zone that exploits the axial surfaces of F3 folds. The bulk of the ore is also carried by damage zones adjacent to the main shear.

At Star and Comet, a major mineralised shear zone runs NNW-SSE through the deposit where it is localised along the contact of BIF and tonalite. An envelope of mostly brittle deformation up to 10m thick affecting both lithologies occurs either side of the shear zone and controls distribution of mineralisation. Most of the gold mineralisation is hosted in pyrrhotite patches associated with strong silicification together with carbonate alteration.

Within the Kukuluma Terrain, steeply dipping ductile/brittle gold-fertile shear zones are developed along, or close to, the edges of an elongate diorite body, hosted in iron-rich host rocks and locally exploiting axial surfaces of tight folds. Gold mineralisation in the Kukuluma terrain is strongly associated with pyrrhotite, pyrite and arsenopyrite concentrations, accompanied by strong carbonate and silica alteration of host rocks. Gold is present in gold minerals and sulphides, dominantly in arsenopyrite.

Mining at Geita is by both open pit and underground methods. The open pit mining is currently undertaken by conventional truck-and- shovel open pit mining method on one active pit (Nyankanga). The open pit mining is conducted using Geita owned, operated and maintained fleet. A contractor provides drilling and blasting services. Underground mining commenced at Star and Comet in 2016 and subsequently at Nyankanga in 2017 using the services of an underground mining contractor. Ore is hauled from the Star and Comet operation to the central ROM pad by the Geita surface mining fleet.

The Geita process plant was designed and constructed by Lycopodium, a process engineering company based in Perth, Western Australia. The plant, which was commissioned in June 2000, had a conventional gold ore processing flow sheet with a design throughput capacity of 4 million tonnes per annum. In December 2002 a secondary crushing plant, two additional leach tanks and the cyclone classification circuit were upgraded, resulting in the throughput capacity of the plant being raised to 6 million tonnes per annum for a predominantly soft blend (and around 5 million tonnes per annum for a harder blend). In 2011, a tertiary crushing plant was constructed to improve mill feed stability.

The process plant includes:
- Primary, secondary and tertiary crushing plants - Semi-autogenous grinding (SAG) mill and ball mill
- SAG mill scats recycle line - (Scats/pebble crusher was decommissioned)
- G-max Cyclones
- High rate thickener
- Pre-oxidation in the first 2 tanks followed by a ten stage carbon-in-leach (CIL) process
- Gold recovery circuit (Elution, Electrowinning and Smelting)
- Gravity concentration section within the milling and classification circuit, where the gravity gold is recovered using Knelson concentrators and an intensive cyanidation process.

The majority of the ore from the pit is dumped onto the run-of-mine (ROM) stockpile, and then fed into the gyratory crusher by a front end loader. The plant design is such that all ore passes through this crusher. The crusher feed rate is higher than the plant design rate which is currently targeted at around 640 tonnes per hour, and there is a buffer stockpile with a total capacity of around 100,000 tonnes. Reasonable stock of critical crusher spares is always maintained to ensure minimum delays in the crushing operation.

The ore is crushed in a three stage crushing circuit and the crushed product is deposited on the fine ore stockpile. A conveyor belt transfers the ore form the fine ore stockpile directly into the SAG Mill feed.

The SAG mill is 9.14m in diameter, and 5.5m long. The underflow from the primary cyclones passes into the, 6.71m in diameter and 9.6m in length, Ball Mill. This mill operates in closed circuit with the cyclones. Two 48 inch Knelson Concentrators are used for gravity gold recovery.

The concentrate from the gravity circuit (Knelson concentrators) enters a closed circuit Acacia Reactor from where the solution is pumped to the gold room where it is passed through a dedicated electro winning cell.

The overflow material from the cyclones passes through linear screens, before entering the 25m diameter high rate de-watering thickener. The overflow from the thickener flows into a settling dam, which has provision to overflow into the emergency pond, in case the settling pond is full.

The underflow from the thickener first enters a series of two pre oxidation tanks in CIL circuit, and then it flows into the first leach (CIL) tank where the first stage Sodium Cyanide is added. Second stage addition is done into Tank #6 to maintain a more consistent free cyanide profile in solution at lower terminal values. Cyanide addition is controlled automatically using a TAC 1000 control unit. There are ten 2240m3 leach tanks in total. All ten CIL tanks have activated carbon which is moved counter currently to the slurry flow. The vessels are all mechanically agitated, and have air agitation as a backup. The air also acts as a backup for the oxygen system. The overflow from the final leach tank passes through safety screen to recover any escaped carbon, and then into a 40m3 tailings tank from where it is pumped to the tailings dam.

WAD cyanide to the Tailings Storage Facility (TSF) is controlled with automatic addition of dilution water using a TAC1000 cyanide controller to the tailings tank. During periods of low dilution water or spikes in free cyanide, an automatic peroxide addition system has been added to the control system.

The loaded carbon is transferred into an acid wash column. Dilute hydrochloric acid solution is added in a batch process before the carbon is transferred into the elution column. Here it is stripped of the gold using a hot dilute caustic solution. Strip water is pumped from the strip solution tank, and heated in a heat exchanger in counter flow with the eluate outflow, as well as by two 2.25MW diesel-fired heaters in series.

The eluate solution passes through the eluate filters and is stored in a stainless steel eluate storage tank. The eluate is then transferred into the gold room where it is pumped through the electro-winning cells. The cathodes are removed from solution and washed, together with the underflow (sludge) from the electro-winning tanks.

The sludge is de-watered in a filter press, and the filter cake fed into one of four calcine ovens. From the ovens, the gold is then finally smelted in a diesel fired furnace and poured into bullion bars. The induction furnace slag is crushed and fed back into the SAG mill feed. Gold is sent to Rand Refinery in South Africa, usually via Dar-es-Salaam.

The barren carbon is regenerated in the diesel fired rotary kiln.