Siguiri

Overview

Siguiri gold mine is located in the Siguiri district of northeast Guinea. The mining concession consists of four blocks totaling 1,495 square kilometers. Anglogold Ashanti holds 85% interest in the property while the country’s government holds the balance of interest.

Alluvial mining was carried out by Societe Aurifere de Guinea in the 1988-1992 period. Subsequently, Ashanti acquired the mineral property - it commenced hard rock mining activities in 1998.

Nowadays Siguiri is a conventional multi-pit oxide gold mining operation. All ore and waste is mined by a mining contractor in a conventional open pit mining operation. Processing of the ore is done by a CIP plant.

In 2011, the mine produced 249,000 ounces of gold.

Location

Siguiri gold mine is situated in the Siguiri District of northeast Guinea, Africa. It is about 850 km from the capital city of Conakry and close to the town of Siguiri on the banks of the Niger River. Siguiri , a former French fort, boasts a population of 30,000 people. It is renowned for its goldsmiths.

Guinea is a country of 10 million people located in West Africa on the shores of the Atlantic Ocean. The country’s population is predominantly Muslim. Its economy is based on agriculture and mining – the country is the world’s largest producer of bauxite. Alluvial gold mining was carried out since the 13^th century, and the renowned British gold coin ‘guinea’ is a testament to that.

Siguiri mine is located in a savannah region.

Geology & Mineralization

The gold mineralization at Siguiri occurs in Paleoproterozoic Birimian rocks consisting of turbidites and lesser volcaniclastic sequences situated in a large zone of shearing  that forms part of the northerly trending, continental scale shear zone system that transects the West African Craton .

There are two types of oxide mineralization in the Siguiri basin: eluvial or alluvial hosted laterite mineralization and primary quartz vein and associated shear hosted mineralization. The laterite mineralization occurs as alluvial lateritic gravel adjacent to and immediately above the in-situ vein related mineralization. The primary vein related mineralization is hosted in metasediments and areas of economic gold mineralization are formed where these veins are spaced closely together. 

The main vein related mineralization at Siguiri is structurally controlled and associated with a major, east-northeast trending and steep south dipping sheeted quartz vein sets that generally occur in the coarser, brittle siltstones and sandstones lithologies.

A deep oxidation (weathering) profile is developed in the region, varying between 50m to 150m. The mineralized saprolite provides the primary oxide feedstock for the CIP plant.

The main focus of drilling in 2011 was to continue exploring for potential extensions of the mineralization around the current pit areas, as well as to investigate new reconnaissance targets. 

As of December 2011, mineral reserves were estimated at 107.9 Mt at 0.67 g/t gold for 2.31 Moz gold.

Mining & Operation

The mine is a conventional open pit operation. Mining is done by a contractor. All ore and waste is mined via conventional open pit mining methods. Due to the weathering profile of the mineralized and associated waste zones, extensive areas can be freely dug by hydraulic excavators, with light padlock blasting operations conducted where required. 

The primary material movement fleet is a combination of 160 tonne and 100 tonne hydraulic excavators loading 85 tonne carrying capacity trucks. The mining fleet comprises all the requisite auxiliary equipment (dozers, graders, water carts, etc) for haul and pit access road construction, maintenance and rehabilitation work. 

Ore is hauled directly to the primary crusher or to run-of-mine stockpiles adjacent to the primary crusher. Crushed ore from the primary crusher is delivered by conveyor to the treatment facilities for processing. In case of conveyor failure, ore can be hauled to original stockpile and crushing facilities and fed by front end loaders as part of the ore processing operation.

Processing

Ore is processed using the heap leach method. The heap leach facility currently has a design capacity of 8 mtpa. The facility includes the heap leach pad area, ore crushing, agglomeration and stacking system, solution ponds and gold extraction plant. 

Ore is crushed and mixed with a cement binder to agglomerate the material, which aids percolation and ph-control and gives stability to the stacked ore. The material is then stacked in 10 metre lifts on large plastic sheeted pads. Currently, ore is stacked in two 10 metre lifts, with third lift stacking planned for the near future. The stack is then sprayed with a dilute cyanide solution which percolates the material and leaches the gold during its passage. The plastic sheeting prevents the cyanide solution from contaminating the ground and allows the gold-bearing solution to be gravitated to collection ponds. The solution is then either re-sprayed back onto heaps or pumped to the gold recovery section of the plants. Activated carbon is then added to adsorb the gold from solution. This is then eluted and the gold electro-won onto cathodes. The cathodes are smelted to produce doré bars.

Environment & Community

Current estimated liabilities total $35.7 million of which half is scheduled for rehabilitation and the other half for decommissioning.

Siguiri continued its engagement with stakeholders to assure adoption of strategies to achieve common goals..

Mine closure planning remained high on the agenda, resulting in a closure gap analysis being carried out and measures put in place to close the identified shortfalls.

Siguiri was certified to be in full compliance with the International Cyanide Management Code in March 2010. Certification is valid for three years. A successful ISO 14001 surveillance audit was conducted during the year.