Gold can be concentrated and recovered by applying different methods and the final product has variable quality. In this way, it is necessary to have a better marketable product so that the incomes can be improved. Then, we have two smelt and cast the gold into bars called bullion or Dore. The name bullion is restricted to the precious metals, refined or unrefined, in bars or ingots that contain small contaminants. For many years, the term bullion made reference to coins and the name base-bullion is for pig-lead or copper bottoms obtained in smelting operations of lead and copper concentrates. The last product is characterized for containing small amounts of gold and silver. The treatment of these products depends on the metallurgical extractive process of lead and copper.
It has been shown that concentrates obtained by gravity devices and cathodes can be smelted directly most the time. Silver-gold concentrates can be smelted too. Under this consideration, a concentrate must contain at least 20 oz/t of gold. Obviously, if the higher grades are better and 50 oz/t is a good average value. It is important to mention that a silver-gold concentrate obtained by flotation has a high silver content. For example a concentrate assaying 1400 oz/t Ag and 8 oz/t Au can be smelted directly.The smelting process involves several operations, retorting, smelting and refining.
Gold Bullion just extracted from mold