41% IAMGOLD, 41% AngloGold Ashanti, Government of Mali 18%
The Sadiola Gold Mine is located in southwest Mali, West Africa near the Senegal Mali border, approximately 70 kilometres south of the town of Kayes, the regional capital. Kayes has a population of roughly 127,000 people and is located 510 kilometres northwest of the Mali capital Bamako.
The Republic of Mali is a landlocked nation bordering Algeria on the north, Niger on the east, Burkina Faso and the Côte d'Ivoire on the south, Guinea on the southwest and Senegal and Mauritania on the west. The country is just over 1,240,000 km² with an estimated population of almost 12,000,000.
The Sadiola mining permit covers an area of 302 km² in a remote part of Mali with little infrastructure. The minesite is accessed by a regional gravel road to Kayes. There is an airstrip at the Sadiola Gold Mine capable of handling light chartered aircraft. Kayes is serviced by rail, road and air from Bamako and from Dakar, the capital of Senegal. Bamako has an international airport with daily flights to many West African and European destinations. Dakar is a major port of entry to West Africa by sea and air and the primary supply route for imported goods coming to the minesite.
The Sadiola mine is a joint venture operation with AngloGold Ashanti and accounts for roughly 10% of IAMGOLD’s production. The existing plant was not built for hard rock processing and because the mine is nearing the end of its supply of oxide ore, or soft rock, an expansion is necessary. Though depleting, mining of the oxides is expected to continue until 2018.
The Sadiola deposit is located within the Malian portion of the Kenieba–Kedougou window, a major Palaeoproterozoic inlier along the northeast margin of the Kenema–Man shield. The Birimian components of the window can be interpreted as a collage of at least two N-S trending terranes. To the west, an older (+/- 2.2 Ga) volcano-sedimentary succession intruded by major calc-alkaline batholiths belongs to the Saboussire Formation. It is separated from the dominantly sedimentary Kofi Formation by the major north to northeast trending Senegalo-Malian Shear Zone. The Kofi Formation is significantly younger and intruded by calc-alkaline batholiths dated at 2.0 – 2.05 Ga. Metamorphic grade attains greenschist facies, with amphibolite grades developed locally near major intrusions. The Senegalo-Malian Shear Zone hosts several significant gold deposits along its splays including Sadiola, Yatela, Loulo and Yalea.
The Sadiola deposit is located in the north central section of the window and is hosted by sediments of the Kofi Formation, which have been intruded by numerous felsic intrusives. The sediments consist of fine-grained greywacke, probably distal turbidites, and impure carbonates with minor tuffs and acid volcanics.
The deposit occurs along the 010º striking Sadiola Fracture Zone (“SFZ”), which is interpreted as a brittle-ductile splay off the Senegalo-Mali Shear Zone at a sinistral releasing bend. The SFZ follows the steeply west dipping contact between greywacke to the west and impure carbonate to the east. The SFZ and its wallrock are intruded by discontinuous diorite dykes, which may contain a weak mineral foliation and rarely intense ductile deformation. Quartz-feldspar-porphyry (QFP) dykes intrude younger, 020º striking and steeply west dipping faults and preserve more brittle deformational features.
Pervasive gold mineralisation ranging in grade from 2 g/t to 20 g/t occurs along the SFZ over a strike length of approximately 2,500 metres and remains open to the north and south. The location and geometry of high grade mineralisation appears to be controlled by the confluence of the SFZ with the 020º striking splays, resulting in steeply to vertically plunging zones within the plan of the SFZ.
Gold mineralisation occurs in all of the four major rock types (marble, greywacke, diorite and quartz-feldspar porphyry), and is spatially associated with a complex alteration pattern. Alteration assemblages identified to date include calcsilicate, potassic, chlorite–calcite and carbonate and point to a mesothermal origin for gold mineralisation. Gold is associated with both arsenic and antimony dominated sulphide assemblages including arsenopyrite, pyrrhotite, pyrite, stibnite and gudmundite. Primary gold is extremely fine grained, dominantly less than 15 microns, with rare grains approaching 50 microns.
The Sadiola deposit has been intensely weathered to depths of up to 220 metres. The operation has mainly exploited soft oxide ore since startup with the current known oxide reserves expected to be mined out by 2016. A significant mineral resource of hard sulphide ore occurs below the final Sadiola pit design and is currently the target of an expansion project pending final approvals.
The Sadiola Gold Mine is operated by AngloGold Ashanti.
Mining is carried out using conventional open pit techniques with a carbon-in-pulp processing plant. There are currently five open pits. The main pit oxide resource recently completed mining however mining is currently occurring in the satellite orebodies FE3 and FE4 southeast of the main pit.
The pit slopes have been engineered to industry standards of stability for the range of lithologies present at Sadiola, following risk management principles. Grade control is effected by drilling 10 metre long vertical holes on a 10 metre by 5 metre grid. Ore is transported to the ore stockpile located one kilometre from the pit and waste is disposed of in dumps adjacent to the pit.
Approximately 90% of ore is stockpiled before processing. The ore stockpiling facility is located between the pit and the process plant and its purpose is twofold. Primarily, the area allows stockpiles of ore with differing oxide and sulphide mineralogy, gold grades, hardness, viscosity levels to be laid down separately. Ore is reclaimed from the stockpiles and fed into the process plant on a blended basis contributing to the efficiency of the process plant and maximising gold recovery. The second function of the stockpile is to provide a reserve of ore to sustain feed when pit operations are affected by external factors such as heavy rains.
The Sadiola Gold Mine processing plant consists of two identical parallel circuits, collectively capable of treating approximately 5.3 million tonnes of saprolite ores per year. This twin-stream design allows for a degree of flexibility in plant operation and maintance in the event of equipment failure, important in this case as local infrastructure and maintenance support for heavy industry is virtually non existent.
Most of the ore is delivered from the pit to a stockpile/reclaim area, adjacent to the processing plant site. The ore blend is reclaimed from the stockpile and fed to two parallel mineral sizers, a type of crusher designed to handle the softer ores that are found at the Sadiola Gold Mine. The ore passes to surge bins located ahead of the two SAG mills. A single regrind mill is incorporated, serving both circuits, to further grind the coarse fraction contained in the output from the SAG mills.
The discharge from the mills is fed to cyclones, the overflow from which goes to the leach circuit where the pulp is subject to cyanide leaching while the underflow goes to the regrind mills. Following leaching, the pulp is fed to CIP adsorption tanks where the gold is absorbed onto activated carbon. This ‘‘loaded’’ carbon is stripped of its gold and the gold bearing solution is pumped to storage tanks. The stripped carbon is regenerated in an oil fired kiln and then reused. After leaching, the barren slurry after removal of the gold is pumped to the tailings dam 3 kilometres southeast of the process plant for final disposal. The gold is recovered from the solution by electroplating onto stainless steel wool cathodes. The cathodes are washed and the gold bearing sludge dried and placed in an induction furnace for smelting to produce gold bullion.
In 2002, the Sadiola plant was modified to increase the recovery on the sulphidic saprolite ore from approximately 65% to 75%. In 2008 a gravity circuit was commissioned to treat a portion of the cyclone underflow in the grinding circuit. The circuit has allowed for improved recovery on high grade oxide ores from the satellite pits that contain a significant coarser “nuggety” gold fraction.
An expansion at Sadiola is one opportunity that we are considering as a potential organic growth opportunity. This would enable the mining of the harder sulphide materials beneath the soon to be depleted oxides and has the potential to increase production by up to 3 million ounces and extend the mine life by up to 10 years.
To facilitate that expansion we are in discussions with our partner, AngloGold Ashanti.This is an attractive opportunity because of our familiarity with the asset, the regional geology, and regulatory process for mining in Mali and our long history of profitable mining in the region without interruption due to political change or civil unrest. We will, however, continue to base our investment decisions only when satisfied that our investment choices will generate attractive economic returns.