Bedding-parallel shear,thrusting and quartz vein formation in witwatersrand quartzites

Evidence is presented which clearly demonstrates the presence of thrust faults in the gold-bearing sedimentary rocks of the Witwatersrand Supergroup. A package of these rocks subjected to shear strain allowed overlying beds on the northern margin of the Witwatersrand Basin to move outwards in a N-NW direction. Movement took place on ductile shear zones which were parallel to the bedding and often reveal excellent examples of ramp and duplex structures. It has also been established that syntectonic foliation planes were utilized as planes of shear in certain circumstances. Quantitative estimates of strain for the pile, which are of necessity minimum values, give γ ≈ 1. Fluids, from which vein quartz formed, played a critical role in the shear plane movement and may have relieved a portion of the overburden load during deformation.