Refining gold to highest degree always require two step purification. It is virtually impossible to refine gold to 99.99% and better quality in a single step when your starting material is less then 95% purity, regardless what different manufacturers are claiming. In real life most of the time gold from low grade feed material will be refined to 98% - 99.5%, depending on composition.
For high purity refining Wohlwill process is used as a second step. With feed material over 98% this protocol is capable to provide 99999 purity.