Numerical modelling of gold transport and deposition

Abstract

A pair of mathemat .cal model? are preje. id : >r .. ir lating the hydraulic transport and depc it.on of go . in fluvial systems such as existed durL.g the formation of Witwatersrand reefs. The first model describe transverse distribution of suspended p rtic oxer plain areas adjacent to channels whii th* eccr : describes the longitudinal distribution within i channel. These models enable the distr ibut ion patte-r gold deposits to be related deterministically channel geometry and the hydraulic 1: • : ing during reef formation. The gold now present in the reefs v. , * ransported mainly in suspension. This is confirmed by showing that the hydraulic conditions required to mobilize the largest quartz particles in a typica- reel samp.e are easily capable of suspending typical gold particles. Deposition patterns of gold are therefore closely related to the distribution of gold particles in suspension, which car be described iy the diffusion analogy. The transverse movement of suspended particles from a channel over an adjacent inundated plain is described by a --vo-dimensi x-nal elliptic partial differential equation which accounts for transport by diffusion and convection in the vertical ind transverse directions. This equation is solved in finite difference form for steady, longitudinally uniform flow conditions. The transverse model is verified by comparing predicted and measured distributions c ‘ fine sand deposits in a laboratory flume with a compound section. The model is applied to hypothetical situations to determine which factors have the greatest influence on the extent and variation of plain deposits. Several gold distributions