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The Sm-Nd technique has been successfully used to date scheelites from lode gold and tungsten deposits in the Archean Midlands greenstone belt, Zimbabwe. Two phases of mineralization have been established which correlate with Late Archean and Early Proterozoic magmatic events in the region. The gold deposits are mainly structurally controlled and are spatially associated with high strain zones and internal synvolcanic to late-tectonic tonalite plutons. Most gold-bearing structures can be categorized into one of two preferred orientations: parallel to acutely oblique with the main S1 fabric, or crosscutting S1 at a high angle and striking parallel to locally developed D2 structures or fabrics. Sm-Nd dating of scheelite demonstrates that these two structural populations are characterized by discrete phases of gold mineralization. The main S1-parallel gold deposition, dated at 2.66 ± 0.05 Ga, correlates with the Late Archean trondhjemite-tonalite-granodiorite event in Zimbabwe. The S1 discordant phase has yielded an age of 2.41 ± 0.07 Ga, broadly corresponding to the timing of emplacement of the Great Dyke and reactivation of the Late Archean high-strain zones. Sr isotope data provide important constraints on the evolution of the hydrothermal fluids. |
