The anodes are placed into a bath of hydrochloric acid and an electric current is passed through it, which causes the gold to dissolve and then deposit on a cathode at purity of 99.99%. If there is demand in the market for a higher purity gold, then the 99.5% pure gold from the chlorine refining process is cast into anodes to be used in the electrolytic refining process, also known as the Wohlwill process. The silver chloride is then reduced to metallic silver and is then refined by electrolysis. The key output of the chlorine refining process is silver chloride, which enters a silver leaching process to remove the base metals. This process produces gold to a purity of 99.5%, which is usually cast directly into odd weight 400oz bars used in the wholesale markets. This involves bubbling chlorine gas through the molten dore metal in which the silver (and most other metals) react with the chlorine to form silver chloride as a slag on top. The dore bar first goes through a chlorine refining process, also known as the Miller process. The dore bar then becomes the property of the refiner. Miners will then either sell this pure gold and silver for cash, or request a loco swap. The miner then receives an outturn, which is a statement indicating the weight of the dore bar, the percentage of gold and silver in the bar, and from these two, a calculated amount of pure gold and silver. A sample is taken from this melted dore and assayed to determine the exact amount of gold and silver present. The composition of dore can vary significantly between mines, but generally the gold dore bars the Perth Mint processes are composed of between 70-80% gold and 10-15% silver.ĭore bars are first weighed and melted to ensure the metal is homogenous, that is, that there are no pockets of high or low purity within the bar. Gold mines process ore using various techniques to produce an alloy composed primarily of gold and silver, which is called a dore bar. Please note that this is highly simplified and does not detail the many sub-processes involved within each key process, the chemical inputs involved in each process, as well how the waste outputs from each process are handled. The diagram below gives an overview of the key processes involved in the refining of gold and silver. For investors purchasing gold & silver securely.
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