The Saramacca Gold Deposit – A New Orogenic Gold Discovery in the Guiana Shield
Craig MacDougall, IAMGOLD
The Saramacca gold deposit is located in the Republic of Suriname, South America, 100 kilometres southwest of the capital city of Paramaribo and 25 kilometres southwest of IAMGOLD’s Rosebel Gold Mine. The deposit occurs within the Marowijne Greenstone Belt of the Paleoproterozoic Guiana Shield, largely constrained between 2.26-2.08Ga. The Guiana Shield is regionally extensive, extending from the Amazon River in Brazil to the Orinoco River in Venezuela, covering an area of more than 900,000 km2. Fundamental to exploration, the Guiana Shield has undergone prolonged chemical weathering, reflecting a humid, tropical paleo-climate that may have started as far back as the Cretaceous period. The chemical weathering has produced a well-preserved, laterite/saprolite profile, which locally extends up to 100 metres in depth from surface.
The Marowijne Greenstone Belt is divided into the Paramaka and Armina Formations, dominated by volcanic basalts and a mixed metasedimentary, greywacke–mudstone sequence, respectively. These are in turn overlain unconformably by the Rosebel Formation, comprising quartz-rich arenites interlayered with polymictic conglomerates. The Saramacca gold deposit is hosted by metabasalts of the Paramaka Formation. Younging from southwest to northeast, the main units of the Paramaka Formation are a lower massive basalt successively overlain by a thin, amygdular basalt unit and a thick unit of pillowed basalt. Rocks have been metamorphosed to greenschist facies and have developed an assemblage of actinolite-chlorite-epidote-plagioclase.
Mineralization is principally hosted within a series of north-northwest trending, brittle-ductile, sub-vertical fault zones ranging between two to forty metres in width and currently defined over a strike length of 2.2 kilometres. Several sub-parallel structures have been identified in the hanging wall, which to date lack the continuity of the primary fault structures, but are also mineralized. The primary structures are localized along or near the contact between massive and pillowed basalt units, and strong, penetrative shear fabrics are observable in drill core in proximity to the faults. Various kinematic indicators suggest that the northeast block moved up relative to the southwest block.
Mineralization is open at depth in primary or fresh rock, and extends to the surface through thick, soft saprolite and laterite surficial layers. Mineralization is associated with hydrothermal dolomite occurring as veins and breccias carrying pyrite, minor arsenopyrite and locally visible gold. The dolomite breccias are characterized by repeated “crack n’seal” and “dilational infill” textures. Veins are often folded and boudinaged.
IAMGOLD declared an initial NI 43-101 compliant resource estimate for the Saramacca deposit (effective August 28, 2017) comprising 14.4 million tonnes of indicated resources grading 2.2 g/t Au for 1.0 million contained ounces, and 13.6 million tonnes of inferred resources grading 1.18 g/t Au for 518,000 contained ounces (see news release dated September 5, 2017). Exploration drilling is ongoing to further expand the resources of the Saramacca deposit.
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