Prestea Sankofa Gold Limited was incorporated in 1994 with a United Kingdom based Company name Samax Limited owning 50.4 percent, Ghana National Petroleum Corporation (GNPC) owning 39.6 percent and the Government of Ghana with the remaining 10.0percent. Samax Limited, which traded on the Canadian stock exchange, was taken over by Ashanti Goldfields Company (AGC) in September 1998. AGC had little interest in the Prestea project because it did not fit into her corporate portfolio released the 50.4 percent share it owned to GNPC, with the Government of Ghana approval in November 2000.
The Company is now essentially a Ghanaian gold mining company extracting gold mainly from old tailings and waste ore dumped as a result of 100 years mining activity in the Prestea Gold belt.
Location and Accessibility
The Prestea Sankofa Gold Limited (PSGL) operation is located at Prestea, within the Wassa West District in the Western Region of Ghana, a second class tarred road 148 kilometres from Takoradi and about 135 kilometres from Kumasi through Obuasi accesses the town, it is also about 56km by road and 29km by rail north west of Tarkwa the district capital.
The climate within the Prestea area is tropical with high temperature and humidity. The main seasons are dry (November to February) and rainy (March to October) seasons. The peak rainy months fall between June and July the peak dry months are January and February.
The mean annual rainfall peaks at 1500 mm as the area lies within the high rainfall belt of Ghana. The mean annual temperature is 27.5oC with a variation of +3oC. Annual relative humidity ranges from 65% in December and January to 81% in June and July.
The South-western equatorial climatic seasons are influenced by the moist, southwest monsoon winds from the South Atlantic Ocean and the dry dust-laden north east trade winds (Harmattan) which blow over the Sahara desert from the northern sub tropical high pressure zone. The wind direction is predominantly in the SW/NE quadrant with winds rarely originating from the easterly direction.
Mining is on contract, and based on a mining plan. Currently most equipment (such as excavator and trucks) are hired and used for mining under the control of the Exploration & Mining Manager. The material excavated is hauled to the Run-of-Mine (ROM) Stockpile at the Processing plant.
The ore mined is treated at the Processing Plant, which is made up of the Feed Preparation, Milling, Leaching and Adsorption, Elution and Electro-winning, and Smelting sections. A picture of the Prestea Sankofa Gold Limited Cyanide Leach Plant is shown on Plate 1.
The process consists of feeding oxide / rocks onto a grizzly feeder by front-end-loader, to feed through a jaw and cone crushers and / or Tailings onto the tipping bin. This is followed by ball milling to 80% passing 75 microns (µm). The constituents are interlinked by conveyor belting. The pH of the resultant slurry of fine solids is adjusted to 10+ by the addition of lime before addition of cyanide to leach the contained gold. The gold thus is absorbed onto activated carbon by the Carbon-In-Leach process (CIL).
Plate 1: Prestea Sankofa Gold Limited Cyanide Leach Plant
The activated carbon is removed from the CIL circuit when laden with gold, and this gold is then stripped from the carbon in an Elution plant by hydrometallurgical means with dilute solutions of cyanide and caustic soda, after pre-treatment of the carbon with dilute hydrochloric acid. The gold is electrowon from the carbon elution liquor onto steel wool cathodes, which are then calcined and the gold subsequently smelted to bullion. The diluted acid and a bleed from the elution are the only effluents from this section which are discharged to the CIL circuit, where the high pH neutralises the acid and the residual cyanide is re-utilised in the leach process.
The tailings from the CIL process, containing residual cyanide levels of 50 – 80 parts per million (ppm) are pumped to the tailings impoundment. By filtering, solids are retained and the water recovered is returned to the plant, thus closing the water circuit and precluding the need to discharge effluent streams to the environment. Residual cyanide contained in the tailings dam breaks down relatively quickly to no hazardous products.
The only emissions to air are dust in the feed (stockpile area) and crushing area and negligible fumes from the calcining and smelting furnaces that operate ±3 hours on a weekly basis.
Dust suppression is provided at all points of generation in the plant.
All wet processing areas in the plant are provided with concrete bunded spillage areas to allow recovery of spillage.
The average monthly reagents usages are as follows:
Sodium Cyanide 1.2 kg / t 30,000 kg / month
Lime 1.5 kg / t 37,500 kg / month
Caustic Soda 3,000 kg / month
Hydrochloric Acid 2,400 kg / month
Process Residue Disposal (Tailings Dam)
The tailings dam is located in the Subri valley (1km from the processing plant), with the dam embankment on the western side of the Subri stream, as shown on Plate 2. The dam is that of an upstream design. Tailings are spigotted (by means of 5cm diameter pipes) from the crest of the embankments, with discharging points relocated around the perimeter of the dam on two weekly bases. This results in a decant pond forming away from the walls, leaving beaches of solids, which consequently provide delay time to allow high free cyanide decay levels, as well as strengthening the geotechnical stability of the dam. The dam is constructed from chemically stable quartz clay earth that was locally available.
Plate 2: Prestea Sankofa Gold Limited Tailings Storage Facility (Dam)
The design is in accordance with sound structural and hydraulic engineering principles. It was designed to achieve the following:
- Provide a permanent storage site for tailing solids.
- To have a capacity sufficient to contain the volume of tailings anticipated over the life of the mine, with staged increases in capacity.
- An emergency spillway is provided to pass the runoff from extreme rainfall event, and prevent overtopping of the embankment.
Records indicate that, the maximum rainfall event appears to be on a 30-year cycle, with a maximum wet season monthly rainfall of about 530 mm.
- Tailings are deposited by sub aerial deposition to maximise consolidation and decay of degradable contaminants, and minimise seepage.
- Tailings water is recycled and used as process water.
A 100 KVA diesel powered generator is used to run a 55 kW motor-pump arrangement for the recycling of water to the processing plant.
Supporting Facilities at PSGL
Other facilities within the PSGL plant area include an administration block, a laboratory, a workshop, a reagent shed, an oxygen plant, a clinic, a chop kitchen and an Accra office.
The administration block, located on an elevated ground, houses the offices of the Managing Director, Finance Manager, Processing Manager, Environmental & Technical Services Manager and the Receptionist on one wing of the Building. Geology, Procurement and Administrative staff, Corporate & Human Resources Manager and Security, have also been provided offices in the other wing of the same block.
The laboratory currently serves mainly as a place where ore and solution samples are prepared before submission to SGS Laboratory at Tarkwa for analysis. A room is provided in the laboratory for storage of various chemicals that are used in the laboratory work. Another room is also provided in the laboratory for the analysis of physical parameters of all the environmental water samples taken in the mine.
This is a building in which electrical, mechanical, welding and carpentry repair works are performed and an office complex provided for the Engineering management.
This is a shed with wire mesh fencing to accommodate mainly sodium cyanide and lime prior to their usage in the leaching process.
The oxygen plant is accommodated under a shed, which has been fenced around with metal mesh. It is located within the plant area to generate and supply oxygen to supplement that from the atmosphere during leaching of gold, this now houses high pressure compressors.
The clinic is a room adjacent to the laboratory and it is located within the plant area. A Senior Nursing Officer, who treats minor cases reported to him and administers first aid. Serious cases and emergencies are referred to the Government Hospital at Prestea.
The chop kitchen is located at a short distance away from the plant area. Workers of the company are provided one hot meal a day in this facility. The meal service is contracted out.
The company has an office in Accra, located at No. 15 Watson Avenue Loop at Adabraka. The office has essentially four (4) rooms and serves as the office of the Company’s legal officer who heads the Accra Office, an office secretary and two (2) office assistants. The office serves as a liaison between the operations at Prestea and the Government Departments in Accra as well as seeing to the international arrangements of the company.
Particulars of Prestea Sankofa Gold Limited
|Name of Company||Prestea Sankofa Gold Limited|
|Site Office Location||Prestea – W/R|
|Postal Address||Post Office Box 127, Prestea – W/R
Post Office Box KIA 9098 – Accra Office – G/R
|Head Office Location||Prestea – W/R|
|Postal Address||Post office Box 127, Prestea – W/R|
|Telephone (s)||030 272 2266 / 0302732256|
|Major Equity Holders||Ghana National Petroleum Corporation (GNPC )|
|Ownership Structure||1. Ghana National Petroleum Corporation (GNPC)
2. Government of Ghana (GoG)
|Major Equity Holder’s Address||Petroleum House Harbour RD, Tema PMB, Tema|
|Preference Share and Debenture Holders||1. Ghana National Petroleum Corporation (GNPC)
2. Government of Ghana (GoG)
|Directors||YAW KYEI – BOARD CHAIRMAN
NANA OGYEAHOHO YAW GYEBI II
BARBARA OTENG-GYASI (HON)
BENJAMIN K. ACOLATSE
|General Managing Director||JUSTICE MAXWELL ACQUAH|
|Accra Office contact Address||131B Dzorwulu Crescent,
|Mining Method||Tailings Treatment|