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    {\displaystyle \mathrm {Au} +\mathrm {O} _{2}\neq }
  
  
    
      
        
          A
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            3
          
        
        
          
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                  C
                
              
            
          
        
      
    
    {\displaystyle \mathrm {Au} +\mathrm {O} _{3}{\overset {\underset {t<100^{\circ }{\text{C}}}{}}{\neq }}}
  Some free halogens react with gold.
In 2007 China (with 276 tonnes) overtook South Africa as the worlds largest gold producer, the first time since 1905 that South Africa had not been the largest.In 2020, China was the worlds leading gold-mining country, followed in order by Russia, Australia, the United States, Canada, and Ghana. In South America, the controversial project Pascua Lama aims at exploitation of rich fields in the high mountains of Atacama Desert, at the border between Chile and Argentina. It has been estimated that up to one-quarter of the yearly global gold production originates from artisanal or small scale mining.The city of Johannesburg located in South Africa was founded as a result of the Witwatersrand Gold Rush which resulted in the discovery of some of the largest natural gold deposits in recorded history. The gold fields are confined to the northern and north-western edges of the Witwatersrand basin, which is a 5–7 km (3.1–4.3 mi) thick layer of archean rocks located, in most places, deep under the Free State, Gauteng and surrounding provinces. These Witwatersrand rocks are exposed at the surface on the Witwatersrand, in and around Johannesburg, but also in isolated patches to the south-east and south-west of Johannesburg, as well as in an arc around the Vredefort Dome which lies close to the center of the Witwatersrand basin.