Parting is a process by which gold is purified to a commercially-tradeable standard, typically ≥99.5%.  Removal of silver is of particular interest since the two metals often co-purify. The standard procedure is based on the Miller process. The separation is achieved by passing chlorine gas into a molten alloy. The technique is practiced on a large scale (e.g. 500 kg).  The principle of the method exploits the nobility of gold, such that at high temperatures, gold does not react with chlorine, but virtually all contaminating metals do.  Thus, at c. 500 °C, as the chlorine gas is passed through molten mixture (again, mainly gold), a low-density slag forms on top, which can be decanted from the liquid gold. Silver chloride and other precious metals can be recovered from this slag.  The slag layer is often diluted with a flux like borax to facilitate the separation.  
Alternative methods exist for parting gold.  Silver can be dissolved selectively by boiling the mixture with 30% nitric acid, a process sometimes called inquartation. Affination is a largely obsolete process of removing silver from gold using concentrated sulfuric acid.  Electrolysis using the Wohlwill process is yet another approach.