Shear-zone related gold mineralisation in silicified meta-sediments: The Paleoproterozoic Overman deposit (Guiana Shield, Suriname)

The Overman deposit, located near the well-endowed Rosebel gold-mining district in Suriname, is hosted by the Paleoproterozoic Marowijne Greenstone Belt in the north-eastern Guiana Shield. Gold enrichment is centred in a lensoid interval of pervasively silicified rock within a sequence of strongly deformed, predominantly phyllitic meta-sediments of the Armina Formation, considered to be turbiditic in origin. The auriferous silica-body is closely associated with a significant unit of carbonaceous phyllites. The entire sequence experienced greenschist-facies metamorphism with peak temperatures around 500 °C and a polyphase deformation history, comprising an initial phase of tight folding followed by an episode of brittle-ductile shearing. Field relationships and microtextural evidence point to a protracted period of sulphide mineralisation during major shearing, which post-dated peak metamorphism and the silicification event. Arsenic enrichment accompanied the ore forming stage. Zircon U-Pb dating of host sediment and a crosscutting rhyolitic dyke, in combination with the chronological framework of regional geologic events, indicates that gold mineralisation occurred late in a 2.08–2.03 Ga interval, i.e. towards the end of the D2 stage of the Trans-Amazonian orogenetic cycle. The Overman anomaly is part of a larger sediment-hosted orogenic gold corridor, which coincides with a crustal-scale shear zone, marking the location of Paleoproterozoic oblique collision between crustal blocks. Comparable post-collisional geodynamic conditions were likely instrumental for the emplacement of orogenic gold in metasediments elsewhere in the Marowijne Greenstone Belt. Conspicuous similarities with the major Paleoproterozoic gold deposits hosted by shear zones in turbidites in the Ashanti belt of Ghana are indicative of common genetic controls.

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