95% IAMGOLD, 5% Government of Suriname
The Rosebel gold mine is located in the mineral rich Brokopondo district in north eastern Suriname, South America. Suriname is a former Dutch colony situated in northern South America bordering the Atlantic Ocean between French Guiana and Guyana.
The Rosebel property lies approximately 85 kilometres south of the capital city of Paramaribo. The mining concession covers 170 square kilometres, with the Suriname River to the east, the Saramacca River to the west and the Brokopondo reserve to the south. The country covers an area of approximately 163,270 square kilometres with a population of around 500,000.
The property is accessible via paved and all weather gravel roads from Paramaribo, a drive of about 110 kilometres. There is a small airstrip located onsite approximately 2 kilometres from the mill operations. Suriname’s Zanderij International Airport is approximately 60 kilometres by road north of Rosebel. Electrical energy is purchased directly from the Surinamese government and from a parastatal energy company. Rosebel’s power is sourced from the nearby Afobaka hydroelectric generating station and from a diesel generation plant.
The economy of Suriname is dominated by the natural resources sector, in particular the bauxite industry. Additional natural resources include oil, gold, iron ore and forestry. The economy draws less than 10% of its income from the export of agricultural products including bananas, rice, timber, citrus fruits, shrimp and fish.
The Rosebel gold mine began commercial production in 2004 and as at the end of 2015 had produced 4.1 million ounces of gold.
The Rosebel concession lies within the Paleoproterozoic Guiana Shield. The Suriname portion of the shield is characterized by discrete corridors of low grade metamorphic rocks (greenstone belts), separated by large granite gneiss terranes.
The local greenstone belt stratigraphy comprises a basal mafic to felsic volcanic package (Paramaka Formation) and two overlying volcano-sedimentary sequences (Armina and Rosebel Formations). The Armina Formation includes intermediate to mafic volcanics and volcaniclastics, trubidite and minor conglomerate whereas the unconformably overlying Rosebel Formation is mainly comprised of coarser grained sandstone and conglomerate with subordinate mudstone. The entire sequence has been deformed by east-southeast to east-west striking folds and faults. A large tonalitic pluton occurs in the southern part of the property (Brinks Granite). Metamorphism is greenschist to lower amphibolites facies.
The Rosebel property contains eight orogenic gold deposits distributed along three major structures. The northern mineralized trend has a strike length of 12 kilometres and hosts the Pay Caro, East Pay Caro, Koolhoven and J-Zone deposits. The southern mineralized trend has a strike length of 15 kilometres and hosts the Mayo, Royal Hill and Roma deposits. The Rosebel deposit occurs at the eastern extremity of the central mineralized trend.
Primary gold mineralization occurs in several different styles on the property but is typically associated with multiple generations of quartz, quartz-carbonate and quartz-carbonate-tourmaline veining. Vein arrays are thought to have developed preferentially along pre-existing structural heterogeneities such as lithological contacts, fold closures and sub-vertical shear cooridors during major deformation phases. For example, gold mineralization at the Rosebel deposit is associated with north dipping quartz and quartz carbonate vein sets localised along shear corridors developed at contacts between sandstone and siltstone units of the Rosebel Formation. Low grade gold mineralization is widely dispersed in sericitic alteration halos surrounding these structures. Diamond drilling has intersected economic gold mineralization to a vertical depth of 200 metres below surface and the continuity of the mineralization can be traced for over two kilometres along strike. The deposit, like most others on the property, remains open on strike and at depth.
Gold mainly occurs in its native form as free grains, often precipitated close to vein selvages or as intergrowths in pyrite crystals within veins and adjacent country rocks. Mineralized quartz veins range from a few centimetres up to 4 metres in thickness and are typically associated with a wall-rock alteration assemblage comprising sericite, chlorite, carbonate, tourmaline, pyrite, pyrrhotite and plagioclase. Alteration halos range from 0.25 metres around individual veins to over 20 metres around major vein sets.
Mining at Rosebel has been carried out at eight open pits to date: Royal Hill, Pay Caro, East Pay Caro, Koolhaven, Rosebel, Roma, J-Zone and Mayo. Mining is by conventional open pit methods, using excavators and trucks. Material is designated as soft rock, transition or hard rock with the latter two types requiring blasting.
Mining progresses according to a planning schedule based on a three- month forecast. The mining sequence includes drilling, blasting and hauling for both ore and waste rock.
Mill processing unit operations include a gyratory crusher and coarse ore stockpile with feeders, a grinding circuit, a gravity recovery circuit, a leaching circuit, a carbon-in-leach (CIL) circuit, a carbon stripping circuit and a refinery as shown in the mill flow sheet.
Hard and transition rock is reduced in size through a primary crusher then stacked over two apron feeders for delivery to the mill grinding. Soft rock is fed by excavators through two apron feeders in parallel to the primary crusher, reporting to the grinding circuit on the same conveyor as the hard and transition rock. Ore is ground to 80% -75 microns to liberate the gold for leaching (pulp). Within the grinding circuit, a portion of the cyclone underflow reports to the gravity circuit where screens, cones and a Knelson concentrator are used to separate gravity recoverable gold (GRG). Gravity gold is then further concentrated on a Deister table, dried and refined in the induction furnace at 1,250oC.
The pulp from the cyclone overflow is thickened and then fed to leach tanks where 70% of the feed gold is leached to be recovered by activated carbon in the CIL process. Pulp leaving the CIL circuit reports to the tailing pond with trace levels of gold. The loaded carbon from the CIL process is recovered by screening and sent to the stripping circuit where gold is stripped from carbon and put into solution. The solution reports to an electro-winning process where the gold is plated onto cathodes by electrolysis, the gold sludge is washed from the cathodes, dried and finally refined in the induction furnace.
Depending on the gold mineralogy, the rock type, the ore grade, and the processing rate, recovery at Rosebel is typically in the low to mid 90% range.
The Company expects mining activity in 2016 to be comparable to 2015. Operational enhancements continue as the Company explores further opportunities to improve performance, manage grades and reduce unit production costs. As soft rock milled continues to decline, increasing mill capacity for the processing of hard rock is a main priority. A number of cost-free initiatives such as changing grinding media size and the configuration of mill liners, along with the low-cost installation of secondary crusher, are being implemented in an effort to aid the transition of soft rock to hard rock. Attributable production in 2016 is expected to be in the range of 285,000 to 295,000 ounces.
Exploration in the JV areas within the vicinity of Rosebel mine continues to remain a priority. Finding a mineable resource of softer rock will allow the mine to continue to maintain high throughput levels and to take advantage of a negotiated price for power that is lower than the rate currently paid for processing ore from the existing concession.
A revised life-of-mine plan for Rosebel, completed in December 2015, demonstrates a mine life of 6.6 years and average attributable gold production of 316,000 ounces per year.