REPLY TO COMMENTS BY J.H.W. WARD ON THE PAPER "CRATONIC EXTENSION AND ARCHAEAN GOLD MINERALISATION IN THE SHEBA-FAIRVIEW MINE, BARBERTON GREENSTONE BELT, SOUTH AFRICA" BY P.H.G.M. DIRKS, E.G. CHARLESWORTH AND M.R. MUNYAI (SAJG, 112, 291-316, 2009)

Abstract

[Extract] We would like to thank Ian ward for his comments, and we agree that many of the mineralised structures are indeed complex. Mineralised shears commonly display several episodes of deformation usually including an early ductile stage overprinted by several stages of brittle-ductile deformation including extensional, strike-slip and compressional events. We note that this complexity is not commonly recognised, described or discussed in any sort of detail when interpreting the kinematics of mineralised shear zones. Instead most studies concentrate on more obvious ductile structures (e.g. Anhaeusser, 1976), noting the presence of later overprinting faults and shears, but generally interpreting them as post-mineralisation (e.g. de Ronde and de Wit 1994). In this context it is commonly observed that mineralisation occurs in close association with accretionary thrusts. However, it is not the thrusts that control mineralisation, but rather later overprints or stages of reactivation that potentially developed during a different, and unrelated tectonic stage, of the greenstone belt. The thusts may be good receptacles trapping mineralising fluids passing by, but they do not necessarily exert a primary control.