Gold Bar

Gold Bars are most commonly made by smelting Gold Ore.

Source
Gold Bars can be smelted at a forge by a miner with at least 155 mining skill. Smelting consumes one Gold Ore per bar.

Alchemists can also transmute Iron Bars into Gold Bars using their Philosopher's Stone and the Transmute: Iron to Gold transmutation. The transmute requires an alchemy skill of 225.

Gold Bar as a Quest Objective

 * This quest is how miners learn to Smelt Dark Iron.
 * This quest is how miners learn to Smelt Dark Iron.