Abstract We have developed a quantitative model of void and vein development in fault zones based on observations of fault roughness and the contact characteristics of rough, directionally anisotropic fractal surfaces. This model includes progressive dilation of the fault during slip events and the elastic deformation of the surfaces normal to the fault plane (closure) as new void space develops. The model predicts vein geometries that are qualitatively similar to those observed in fault-controlled mineral deposits. The statistics of the vein system are described and strategies for sampling of such structures by drilling are developed. The results have significant implications for evaluation of ore reserves and evaluating the fluid transport properties of faults.