Obuasi

Overview

Obuasi is located in the Ashanti region of southern Ghana, approximately 80km south of Kumasi. It is primarily an underground mine operating at depths of up to 1,500m with a continuous history of mining dating back to the 1890s. 

Although no open-pit mining has taken place at Obuasi since 2005, three pits still contain a Mineral Resource. Underground mining operations have produced 313,000 ounces of gold in 2011.

Location

Obuasi is located in the Ashanti Region of Ghana, some 320km northwest of the capital Accra. 

The Obuasi Gold Project is located within the Obuasi Mining District. Access to the properties is via paved roads from Accra. Travel time from Accra to Obuasi is approximately four to five hours depending on traffic in Accra. The Edikan mine (Perseus Mining Ltd.) is situated 45km south of the Obuasi mine. 

The mine is situated in a largely forested region at an elevation of 280m above sea level and the mining concession covers an area of 47,500 ha. 

The surrounding land is occupied by subsistence farming and eighty communities are located within a 30km radius of the mine.

Geology & Mineralization

Southwest Ghana hosts one of the world’s most significant Proterozoic gold belts. The Birimian Supergroup rocks are volcanic rocks that are separated by intervening Tarkwaian sedimentary basins and rocks.

The mine is located within the Obuasi concession area in south-western Ghana along the northeast striking Ashanti volcanic belt.

At Obuasi gold mineralization occurs within a shear zone along what is known as the Obuasi Trend. Mineralization occurs in complex series of steeply dipping orebodies of variable thickness and extent. The gold bearing system extends laterally over 8 km and persists to depths of at least 1,500 m.

From a metallurgical point of view there are three main ore types: gold-quartz veins; gold sulfides (in arsenopyrites); and oxidized ore. The gold quartz veins contain free milling gold, whiles the sulphide rich refractory ore is disseminated as alteration haloes around the gold vein lodes. Gold mineralization is associated with pervasive silica, carbonate and sulphide hydrothermal alteration.

As of December 2011, mine ore reserves stood at 41.23 million tonnes at 7.07 g/t gold for 9.37 million ounces gold; and another 2.71 million tonnes at 13.08 g/t gold for 1.14 million ounces ore reserves below infrastructure.

Mining & Operation

Obuasi is converting from the current transverse and longitudinal open stoping mining method to the longitudinal retreat mining method. This conversion will take place in the mining blocks where it is suitable to do so. The major advantage of this method is that there should be up to 50% reduction in waste development; reduced capital expenditure and additional reef drive exposure.

Although no open-pit mining has taken place at Obuasi since 2005, three pits still contain a Mineral Resource.

Processing

Two treatment plants have been used for processing ore: the South Treatment Plant, which is a Float-BIOX-CIL plant for treating hard rock sulphides and tailings; and a tailings treatment plant using CIL to treat only tailings. The tailings treatment plant was shut down in October 2010. 

Another project that envisions the treatment of tailings is the Pompora reclamation project. This project will consist of a reclamation station and pipeline that will enable the Kokoteasua and Pompora TSFs to be reclaimed. The reclaimed material will then be pumped to the tailings sulphide plant (TSP) to extract the residual gold. This project is planned to be commissioned in 2013.

Environment & Community

The implementation of the recommendations of the 2009 Social Study report on Obuasi communities continues to receive attention.

The mine site continued to engage with surrounding communities including the Artisanal Miners Association. There was an increase in the number of communities covered under the stakeholder engagement plan from 48 in 2009 to 58 in 2010.

On legacy issues, farms impacted by mining activities have been assessed and some compensation paid. Grievances have been investigated and documented, and proactive engagement through regular meetings with communities has been instituted.

Regarding economic development, three projects are being piloted at Obuasi to create employment opportunities for the communities, namely a piggery, aqua culture and a garment factory.

AngloGold Ashant's staffing needs in the community and social development spheres have been expanded and training is being provided to environment and community staff. Implementation of management standards to prevent or avoid the creation of additional legacy issues has commenced.

The occasional chemical treatment of process water for discharge in positive water balance situations to streams and rivers has been curtailed and rehabilitation of mined-out pits has commenced at Adubriem and Sansu. The road to Sansu village is being resurfaced by the company.

The mine continued to fund and operate its Malaria Control Programme, which has successfully reduced the incidence of malaria in the community, of more than 250,000 people, by more than 75%. The programme is a world benchmark and has been selected by the United Nation's Global Fund with AngloGold Ashanti as the principal recipient to expand the Obuasi model to 40 districts around Ghana. Funding of $130m will be provided over five years at which time the Obuasi programme will be included in the Global Fund programme. The programme awaits government tax exemption on the Global Fund donor funds, which should be forthcoming in 2011.

In addition, Obuasi continues its support of the municipality on waste and hygiene management, education, HIV/Aids awareness and treatment.

The mine underwent its ISO 14001 surveillance audit in November after successfully completing a certification audit in December 2009.