The Birdman formation is a Protection rock formation (1800 – 2100 million years В± 63 Million years) which is sub divided into Lower Birdman, dominated by entitlements, and Upper Birdman, dominated by gravestone-type meteorological and trends northeast southwest. The lower Birdman is primarily Phyllis and greywacke. The formation changes upwards to Phyllis and weakly metamorphosed tuffs, greywacke and felicitated sandstones. Some of the Phyllis contain pyrite, whiles others are carbonaceous.
The Upper Birdman consists mainly of metamorphosed basaltic and indicates lavas, hornblende-stalactite-schist, calcareous chlorine-schist and amphibole (the gravestones). The presence of Pillow Structures which are commonly observed, indicate sub-aqueous eruption of the original basaltic magmas. Minor intrusions of mafia rocks cut the volcanic and there are small ultramarine bodies in some places. Smaller amounts of rollick and didactic lavas and tuffs are also recorded, and associated entitlements include Phyllis, greywacke, quartz exercise-schist and mica-schist, as well as grits and magnetometers at the base of the succession.
The Birdman is intruded by smaller discordant and typically unaffiliated late-tectonic to posthypnotic or belt type granites, known as Discover type in Ghana and the Boondocks type in Ivory Coast and Upper Volta. They are less abundant than the older connections granites and have a wider compositional range: from hornblende and biotic-bearing granites to diorite, moistness and ignites. Because the rocks are tightly folded and commonly sheared and fractured, it is not easy to establish stereographic successions and estimated thicknesses.
The total thickness of the Birdman in Ghana may be of the order of mamma to mamma. The gold deposits and occurrences are set in the five parallel northeasterly volcanic belts, namely the Kibitz-Winnebago, Shanty, Sepsis, But, and Bole-Nanning belts as well as the nonirritating Laura belt (Mann et al, 2013). The most important type of gold occurrence in Ghana is the masterful reactionaries-gold lode normalization, commonly referred to as the Shanty-type, typical of the Oboist Goldenberg EMMANUEL SHOWS 5 field area considered the largest gold deposit in the region.
These deposits are argyle confined to “tectonic corridors” and they usually display complex multi-phase structural features, which control the normalization (Mann et al, 2013). The major form of gold deposits found in the Birdman is lode gold which are associated with deep-seated shear zones partly controlled by local unconformity between Lower Birdman Phyllis and Upper Birdman gravestones. The primary gold occurs in quartz veins and Lancaster reefs. It is accompanied by sulfides, especially reactionaries.
Pyrite, prototype and chlorinate are also some of the sulfides that are associated with the gold deposits in the Birdman. . 2 The Trinitarian Formation The Trinitarian sediments occupy two generally cynical belts surrounded by Upper Birdman meteorological, about 270 km apart, with smaller occurrences. The sediments are mainly of shallow-water origin, probably evaluative, and they contain fragments of Birdman rocks. They could have been deposited in separate elongate basins as molasses faces derived from erosion of the Birdman, during later stages of the Barren rookery.
The Trinitarian Group has been well studied in the region of the Tartar goldfield. The Group consists of a thick series (1800 – mum) of argillaceous and rancorous sedimentary rocks with two well-defined zones of refigures conglomerates in the lower formations of the succession Mourner, 1940). The Trinitarian appears in general to be less strongly deformed and metamorphosed than the Birdman. The cynical structure of the Trinitarian in the Tartar area is that of open folds having a northeasterly plunge and northwesterly dipping foliation, the intensity of folding increases to the NW.
In the Buy syncing, Trinitarian beds have been considerably fractured and more strongly folded, being overturned in places. Trinitarian rocks form the central parts of Birdman conformal belts, and in the larger Tartar syncing an unconformity is implied by the fact that the Trinitarian lies mainly against Upper Birdman meteorological in the west, but overlap onto Lower Birdman elsewhere. The main types of gold deposits found in the Trinitarian are that of the sedimentary type deposits, found in several places in the Banked conglomerates near the base of the Trinitarian.
These deposits are mainly associated with heavy minerals, including retile, zircon and detrimental hematite gravel horizons which can all be found within the Banked. The gravel layers are extensive and therefore there are occurrences of alluvial (placer) gold within those layers. As a result some modern stream channels near primary and secondary gold districts in the Birdman and Trinitarian contain placer gold deposits. The Offing River System has been a source of placer gold in Ghana. 6 CHAPTER THREE–3. MINING ACTIVITIES IN THE BIRDMAN AND TRINITARIAN Most of the gold mining activities in Ghana occurs within the Shanty belt (composed of entitlements and meteorological) which contains mainly vein type gold deposits and the Trinitarian formation which contains lattice type deposits that cannot be men with the naked eye. Due to the richness of these formations, most of the large scale mining companies are situated here. The methods of mining and processing of gold varies from company to company and these will be outlined in the following sections. 3. ANGOLA SHANTY – OBI-JAGS MINE Angola Shanty Company (GAG) is a gold mining company located in the Shanty region of Ghana. The company operates both underground and open pit mines and began mining in June, 1895 as Shanty Goldfields Corporation. One of the underground mines operated by the company is the Basis mine at Basis in the Shanty Region. The total area of the concession is about 614 square kilometers. 3. 1. 1 MINE GEOLOGY The Basis mine is located within the boundary between the Birdman meteorological and entertainment’s rocks.
The meteorological occur to the west and the entitlements to the east and both are intruded by dolerite intrusions. The gold occurs in the entertainment’s rocks specifically the graphics schist. The normalization is of hydrothermal origin, structurally controlled and occurs as a northeast-southwest trending body in quartz veins within dilettantes zones of the graphics schist. Discrete normalization also occur in faults, folds, cleavages and deep seated shear zones along the entertainment’s-intervocalic boundaries. The currents reserve of the company is about 1 55 million tones. . 1. 2 NORMALIZATION TRENDS AND TYPES Base on the type and structural characteristics of the host of normalization, three distinct trends have been identified. These are the Main trend, the Subbing trend and the Binders trend. Gold in the Main trend occurs in five major shear zones between the meteorological and the graphics schist. The normalization has a depth of 8 kilometers and lateral extension of 1. Kilometers. Normalization in the Subbing trend occurs in steeply dipping, narrow graphics schist about meters from the main trend.
The normalization is 750 meters deep. Normalization in the Binders trend occurs as a flat dipping ore body in graphics schist. Two normalization types are also distinguished; the quartz vein and the sulfide types. The quartz vein type occurs as visible gold within quartz veins whiles the sulfide type occurs closely associated with reactionaries. 7 3. 1. 3 EXPLORATION AND MINING Exploration at Angola Shanty usually begins by conducting Aerial photography ND airborne geophysics. Based on the results, soil sampling is then done at 200 meters spacing along a grid.
Ground geophysics then follows to locate anomalies and trenching is then done to locate the geophysical and geochemical anomalies. Once the anomalies are located, reverse Circulation drilling and subsequently Diamond drilling are conducted. The next stage then involves geological interpretation, modeling and evaluation of the data. With information from the models, the prospective areas are then demarcated and soil is sampled from the B-horizon for assaying. 3. 1. 4 ORE TREATMENT AND PROCESSING
Two treatment plants have been used for processing ore: the South Treatment Plant, which is a Float-BOX-CEIL plant for treating hard rock sulfides and tailings; and a tailings treatment plant using CEIL to treat only tailings. The tailings treatment plant was shut down in October 2010. Another project that envisions the treatment of tailings is the Pompoms reclamation project. This project will consist of a reclamation station and pipeline that will enable the Southeast and Pompoms Tests to be reclaimed. The reclaimed material will then be pumped to the tailings sulfide plant (TTS) to extract the residual gold.
This reject is planned to be commissioned in 2013. The ore bodies are mined and sent to the crusher by conveyor belts. The crusher reduces the rocks into chippings. The chippings are then ground to powder at the mill. The milled sample is then sent to the sulfide treatment plant where the sulfides are liberated from the gold by the action of bacteria. The gold is then smelted and exported for purification. 3. 1. 5 SAFETY To ensure safety in the mining pit the company ensures that all worker and visitors are dressed in the proper safety gear including a helmet with a lamp, safety boots, overall dresses, goggles and ear plugs.
A life support system called the Self Rescuer is also provided to the workers. The self- rescuer is an easy to operate system which contains enough oxygen to last an individual for at least one hour. The pack is used in the event of air pollution within the mine or the worker experiences difficulty with breathing in the underground. Head counts are also conducted every four hours to ensure every worker is safe. 8 3. 2 GOLDFIELDS GHANA LTD – TARTAR MINE. Significant portion of the stereography of the Shanty Belt in southwest Ghana.
The Shanty Belt is a north-easterly striking, broadly cynical structure made up of Lower Protection sediments and volcanic underlain by the meteorological and entitlements of the Birdman System. The contact between the Birdman and the Trinitarian is commonly marked by zones of intense shearing and is host to a number of significant shear-hosted gold deposits. The Trinitarian unconformable overlies the Birdman and is characterized by lower intensity metamorphism and the predominance of coarse-grained, immature sedimentary units.
The open pit surface operation exploits narrow, tabular refigures conglomerates similar to those mined in the Watersides Basin of South Africa. Mining is currently taking place from four pits – Epee-Maintain, Tiebreak, Contains and Chattahoochee. Various alternative processing options are currently being investigated, including an expansion of the existing CEIL plant and/or the construction of an applicable, discrete CLIP facility. Alternatively the mine will revert to the CEIL option only, which currently produces the best cash returns in the medium term and extends the Life of Mine (LOOM) to 2036. 3. 2. LOCAL GEOLOGY The local geology at Tartar is dominated by the Banked Series, which can be further subdivided into a footfall and hanging wall barren quartzite, separated by a sequence of mineralizes conglomerates and pebbly quartzite. The stereography of the individual quartzite units is well established, with refigures reefs inter-bedded with barren immature quartzite. The units thicken to the west and current Occidentalizing parameters indicate a flow from the east and north- east. Structurally, the Trinitarian belt has been subject to moderate folding, and at least five episodes of deformation are recognized.
The original deposition occurred in a district basin environment with associated low to steep angle normal faulting. Subsequent compression and folding led to the development of thrust faults and inversion of previous normal faults. The final stages involved further thrusting in a southwest direction. Modeling has resulted in the recognition of a cycle of events from initial channel formation and rapid down-cutting of the central channel, through a period of uplift and reworking. Finally, a period of meandering channel bars and flow reduction led to the development of low-grade conglomerates with silly inter-beds.
The period of uplift and reworking has been recognized as being the principal episode of gold deposition and concentration within these reefs. The style of sedimentation in the C, E and G reefs differs from that of the chandelier, incised reefs to a more localized sheet-flood-dominated alluvial fan deposit. BENZENE EMMANUEL SWISS 9 Figure 1: Local Geology and Mine. 3. 2. 2 MINING METHODS Tartar utilizes a proven and highly selective mining methodology. The location of the mining areas is defined through the long-term planning process.
The boundaries of the pits are pegged out by survey and the area is cleared of bush and topsoil, which is relocated for rehabilitation purposes. After clearing, reverse circulation (RCA) grade control drilling is carried out, and geological models constructed. This grade control information is used to update the short-term plans and forecasts prior to the commencement of mining. From the highest point in the pit, material is free dig or blasted to the first blasting reference level. Currently fresh rock and transitional zones are drilled and blasted in 6-meter lifts, with excavation in 3-meter fletches.
Fifteen (15) backhoe excavators are used to select waste from the ore, and vice versa. This takes place along the sedimentary horizons to an average accuracy of 30 centimeters on the hanging wall, and 20 centimeters on the footfall of a reef. Pit geologists and octogenarians supervise all digging and mineralizes material is classified as either Run of Mine (ROOM), which is delivered to one of two primary crushers, or low grade, which is stockpiled close to the primary crushers. Waste material is hauled to the nearest waste dump. 3. 2. ORE PROCESSING AND TREATMENT At present the mine uses a conventional Carbon-In-Leach (CEIL) plant and a Heap Leach facility. The ore is a free-milling conglomerate with negligible sulfide content. Rocks near the surface have been affected by a high degree of weathering which is associated tit increased porosity and increased heap leach dissolution and recovery. 10 As the mine gets deeper, so the percentage of weathered ore amenable to heap leaching decreases. The CEIL milling process provides a 97% recovery which is not possible when using heap leaching for the harder, unwatched ore, the percentage of which increases over the LOOM.
The North Heap Leach facility employs three stages of crushing prior to agglomeration. Post primary crushing through a gyrator crusher, a series of overland conveyors transport the undersize material to the agglomeration stockpile where it Joins the final product. Secondary crushing product is fed to the tertiary hopper via a series of conveyors. The oversize material from the upper and lower decks (mum and mum respectively) feed the tertiary crushers and the discharge from the tertiary crushers is conveyed back to the tertiary bin.
The undersize material from the tertiary screens The agglomeration process involves the addition of 4 keg/t of cement to the crushed rock to bind the fine material and produce agglomerate that remains stacked and porous on the heap leach pads. Following agglomeration, the ore is transferred by conveyor and stacked on the leach pads by a stacking conveyor. The heaps are irrigated with a cyanide solution which dissolves the gold as it percolates through the heaps.
The pregnant solution is collected on the layer of extolling that lines the base of the heaps and is pumped through a series of ponds to the adsorption/description/recovery (ADAIR) plant. Here the gold is adsorbed onto activated carbon, removed from the carbon by acid wash, and recovered using electro-winning. All gold produced at the North facility is smelted at the smelt house using diesel-fired furnaces. The CEIL process route has a gyrator crusher that feeds woo crushed ore stockpiles, each with a live capacity of 45,000 tones (30 hours).