LATE ARCHEAN AND EARLY PROTEROZOIC GOLD-TUNGSTEN MINERALIZATION IN THE ZIMBABWE ARCHEAN CRATON - RB-SR AND SM-ND ISOTOPE CONSTRAINTS

The Sm-Nd technique has been successfully used to date scheelites from lode gold and tungsten deposits in the Archean Midlands greenstone be lt, 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 a re spatially associated,vith high strain zones and internal synvolcani c to late-tectonic tonalite plutons, Most gold-bearing structures can be categorized into one of two preferred orientations: parallel to acu tely oblique with the main S1 fabric, or crosscutting S1 at a high ang le and striking parallel to locally developed D2 structures or fabrics , Sm-Nd dating of scheelite demonstrates that these two structural pop ulations are characterized by discrete phases of gold mineralization. The main S1-parallel gold deposition, dated at 2.66 +/- 0.05 Ga, corre lates with the Late Archean trondhjemite-tonalite-granodiorite event i n Zimbabwe. The S1 discordant phase has yielded an age of 2.41 +/- 0.0 7 Ga, broadly corresponding to the timing of emplacement of the Great Dyke and reactivation of the Late Archean high-strain zones. Sr isotop e data provide important constraints on the evolution of the hydrother mal fluids.