Roasting of Gold or Precious Metal Samples

Roasting is a technique used to handle difficult gold or precious metal samples. Minerals decomposed in this way include sulphides, arsenides, antimonides and tellurides. A successful roasting can render samples amenable to standard flux mixes. Weigh 50 grams of a sample into a shallow dish and place it into an open furnace at 100 0C. Raise the temperature slowly to 600’C with careful stirring. When no fumes are seen, raise the temperature to 700’C for 20 minutes. The S, As, Sb, and Te are lost as volatile species. Their elimination simplifies the fluxing and prevents the formation of speiss or matte deposits. Care must be taken not to fuse galena because Ag is lost during this roasting process.