Age constraints on host rocks for gold mineralisation in the Ashanti Belt, Ghana

The Ashanti Belt region, Ghana possesses one of the richest gold endowments of the West African Craton, hosting several multi-million ounce deposits. One of these deposits is Wassa along with the Benso satellite deposits, located in the southern section of the Belt. Wassa is hosted in a series of interlayered mafic flows and volcaniclastic beds with greywackes, detrital magnetite units, mafic intusives and plagioclase rich porphyritic intrusive rocks; while the Benso is hosted within a mafic intrusive complex and sheared mafic volcanic flows. The ages of the Wassa porphyry host rock and the Benso G-zone sample were determined using U-Pb SHRIMP dating methods, respective dating of 2192.7 +/- 4.6 Ma and 2159.5 +/- 7.5 Ma. These intrusions are considerably older than the previously reported gold hosted intrusions from that region (ca. 2103 Ma, Oberthur et al. 1998). As a result, this new data confirms the presence of older stratigraphy in the southern Ashanti Belt. These results, in combination with recent structural studies that interpret the Wassa mineralisation to be of pre-Eburnean origin strongly support the possibility of significant gold mineralisation occurring during the Eoeburnean orogeny ca. 2190-2140 Ma and brings a new understanding of gold mineral systems in the Ashanti Belt.