Question

Where did all the gold on earth come from?

Answer 1

Hint: The process of extracting various elements from the core of earth is known as metallurgy. Any element can be present in two states known as native state or combined state.
Native elements- these are low reactive elements which are not attacked by atmospheric oxygen, air or moisture, carbon dioxide or other gases in the atmosphere. For example gold, silver, platinum, mercury, palladium, antimony, bismuth etc.

Complete answer:
 A large number of elements are present at the center of earth in its lithosphere layer. During the evolution of earth formation all the different elements get deposited into the center of earth. Movement of these elements causes migration of all the other unique elements of the earth into the core of it which include gold, platinum, silver etc. These metals get concentrated into the core of earth in their native form. Due to higher density of gold element $\left( {19,300kg{m^{ - 3}}} \right)$ large proportion of gold gets deposited at the bottom of the ocean. Some natural activities are also responsible for deposition of gold like volcanos, earthquakes etc.
Gold remained undetected until George Harrison of South Africa discovered it and after that mining of gold continues worldwide.
As we know that gold is an example of native element which means that it is a less reactive element which is not attacked by atmospheric oxygen, air or moisture, carbon dioxide or other gases in the atmosphere.
In order to extract all the gold metal present in the core of earth we have to perform various types of metallurgical reactions followed by purification treatment to get pure form of gold metal.

Note:
In the early days of gold mining South Africa was the major source of it but now China is the largest gold producer in the world.
Gold and silver are extracted by the process of hydrometallurgy in which ores of an element are first dissolved in a particular chemical reagent and then precipitate the element by treating it with a more electropositive element.
 Gold $\left( {Au} \right)$ and silver $\left( {Ag} \right)$ are first treated with cyanide ions $\left( {C{N^ - }} \right)$ to form their respective soluble complexes.
$4A{u_{\left( s \right)}} + 8C{N^ - }_{\left( {aq} \right)} + 2{H_2}{O_{\left( l \right)}} + {O_2} \to 4{\left[ {Au{{(CN)}_2}} \right]^ - } + 4O{H^ - }_{\left( {aq} \right)}$
$4A{g_{\left( s \right)}} + 8C{N^ - }_{\left( {aq} \right)} + 2{H_2}{O_{\left( l \right)}} + {O_2} \to 4{\left[ {Ag{{(CN)}_2}} \right]^ - } + 4O{H^ - }_{\left( {aq} \right)}$
Now these metals are recovered by treating them with more electropositive elements like zinc.
$2{\left[ {Au{{(CN)}_2}} \right]_{\left( {aq} \right)}}^ - + Z{n_{\left( s \right)}} \to 2A{u_{\left( s \right)}} + {\left[ {Zn{{(CN)}_4}} \right]^{ - 2}}_{\left( {aq} \right)}$
$2{\left[ {Ag{{(CN)}_2}} \right]_{\left( {aq} \right)}}^ - + Z{n_{\left( s \right)}} \to 2A{g_{\left( s \right)}} + {\left[ {Zn{{(CN)}_4}} \right]^{ - 2}}_{\left( {aq} \right)}$
Atomic number of gold is $79$ and the atomic mass is $196.96gmo{l^{ - 1}}$.