Gold ores

By Shristi Ghosh

What is your chosen metal, and why?

I chose Gold as it will be interesting to see how a commonplace metal (used in jewellery) is extracted and how it comes to be used in everyday life, the process, and how it is found.

Where in the world is gold mined?

Gold can be found mainly in Africa and occasionally in Asia, however the largest gold mine in the world is where an asteroid landed; the Witwatersrant basin in South Africa. Virtually all discovered gold is discovered to have been deposited there by asteroids and meteorites, the Witwatersrant basin being one of many in the continent. Witwatersrant basin alone has produced 40,000 metric tons of Gold from just one asteroid.

How is it dug up from the ground?

It is mined using several different methods, two of which are listed below.

Placer mining

  • This is where tunneling may damage the gold, so as a replacement they use water or derdging to bring it up to ground level.

Panning

  • Sand and/or gravel is dug up in steel pans and separated manually from gold, by filling with water and shaken. Since gold is much denser than rock, it will immedately sink to the bottom of the pans.

Hard rock mining

  • This invloves digging up gold incased in rock rather than fragments in loose sediments, to be extracted later. This is the most common method of mining gold, and is the method we will study.



How is the metal is extracted from its ore?

To first separate the gold from other metals in the ore, such as silver, the gold may added to nitric acid, which will dissolve most base metals, but will leave gold intact. Gold is then treated with cyanide salts (if in fine particles), followed by recovering it from the solution.