The mining of precious metals has taken place throughout the history of mankind. However, the methods of mining gold and silver for refining into coins and bars have varied across the centuries as technology has advanced. In this guide we will discuss how gold and silver are mined today.
Although different countries may undertake varying mining methods, those described within this article will work as a good guide to the mining of precious metals in the 21st century.
It is impossible to say for certain when the first mining of gold took place, however, there is evidence that the oldest gold mine could be traced back to the USA, to around the 3rd or 4th millennium BC.
To reach the gold buried deep underground, miners will dig shafts into the ground. When underground, gold usually mixes with another mineral known as quartz, in a vein which has often split into the surrounding rocks. These rocks are then loosened and removed by explosives and picks and the loose sediment is then often filtered using water jets. Up to three tons of rock can sometimes be required to produce just an ounce of gold.
After the rocks containing gold are removed from the mine, they are then ground into dust using a crusher. In the past, gold was separated from this dust using a process involving mercury. However, this process was stopped due to the extremely poisonous nature of mercury and a more efficient process was developed which involves using cyanide: cyanidation.
Cyanidation involves the use of dilated sodium cyanide to separate gold from the ore. When this is added to the rock dust, it dissolves the gold so it can then be separated from the cyanide solution. This gold, called ‘crude bullion’, is then cast into moulds and refined into pure material.
The mining of silver is said to have first taken place in Mexico during the 16th century. The method used to mine silver at this time, was known as the ‘patio process’ and involved mixing silver ore, salt, copper sulphide, and water. Mercury was then added to this solution to extract the silver. This method was found to be highly inefficient and was soon replaced by the ‘Von Patera Process’.
The Von Patera Process involved ore being heated alongside salt and rock, which produced a silver chloride. This silver chloride was then filtered out using sodium hyposulfite. This method is said to have inspired more modern methods of mining silver.
Today, the processes of sourcing silver are similar to gold. Blasting operations are the first step to extracting the silver from the earth. Once the silver has been blasted and exposed, the raw silver ore is collected and then transported to special refineries where the extraction process then takes place.
Silver is rarely found on its own, and the metal that silver is found with determines which extraction method is used. For example, in order to recover silver from zinc-ores, the ore is heated until molten, and as the zinc cools, silver forms on its surface. The silver and zinc are distilled so the zinc becomes separated from the silver.
To extract silver from copper, an electrolytic refining process is used. The ore is placed into an electrolytic cell and electricity is conducted through the solution; the silver accumulates as paste as the copper is deposited.
Once extracted, silver ore is then crushed down into smaller pieces and refined using chemical processes, filtered, melted and made into bullion bars.
Mining has attracted much scholarly, scientific and engineering interest over hundreds of years. It is central to obtaining both gold and silver for the bullion coins and bars we know so well, as well as for use in jewellery and technology. The mining of precious metals will no doubt continue, as societies across the globe still seek silver and gold and the precious qualities and appeal that these metals hold.
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