The Storø greenstone belt in Godthåbsfjord, southern West Greenland consists of juxtaposed rock units of different age and origin, and hosts gold mineralisation that is associated with arsenopyrite along a contact between lithological units and along the axial plane of a large fold core. The age and origin of the gold is debatable, but in this paper, we present new arsenopyrite Re-Os and zircon U-Pb data to constrain the age of the Storø gold deposit. A 2.71±0.05Ga arsenopyrite isochron and 2.707±0.008Ga highly radiogenic arsenopyrite from a mineralisation along a rock contact, together with a 2.64±0.02Ga arsenopyrite isochron along the axial plane of the fold core indicate a two-stage mineralisation process. While the 2.707±0.008Ga highly radiogenic arsenopyrite provides firm support for an early mineralisation event, a mixing origin cannot yet be excluded for the 2.71±0.05Ga isochron. The 2.64±0.02Ga isochron is in perfect agreement with recent U-Pb zircon data (Nutman et al., 2007. Precambrian Research 159, 19-32) and these data are best explained by orogenic mineralisation during amphibolite facies metamorphism along structural weak planes. The initial 187Os/ 188Os value of 0.56±0.16 for the 2.64±0.02Ga isochron indicates a crustal source for the metals, whereas the initial 187Os/ 188Os=-0.1±0.6 for the 2.71±0.05Ga isochron remains unconstrained. Re-Os data are best explained by relatively short crustal residence times of less than 0.1Ga, wherein the Os, and associated metals, were extracted from the mantle at a time younger than 2.8Ga, and in which the 2.64±0.02Ga stage formed by mobilisation of an earlier mineralisation. Detrital zircon constraints imply volcanism and sediment deposition for parts of the belt at ≤2.84Ga and that these units were tectonically juxtaposed to ∼3.05Ga rocks within the belt. The units that were deposited ≤2.84Ga record metamorphic zircon U-Pb ages of ∼2.63Ga, but evidence for 2.72Ga metamorphism, which is ubiquitous in adjacent terranes, is lacking.
- Programområde 4: Mineralske råstoffer