...Dipping up some gravel and some water with a trough. Washing the gravel for gold with circular movement and throwing the contents back to the stream so that grains of gold dust remain on the trough bottom. This is how gold was mined yesterday.
...Grasping the rock with a huge machine, crushing, grinding, and filtering it and recovering grains of gold. This is how gold is mined today.
The demand for gold is growing because it serves as a material for microelectronics, aerospace industry, medicine, etc. What is to be done? Should we dig our planet over? To mine one gram of gold, it is necessary to extract tons of gold-bearing rock.
Perhaps it is high time to transfer to a microlevel. Plants extract microelements, including gold, from the ground. Research proved that alfalfa is a champion in extracting gold. Nanoparticles of gold were found in the plant's roots. Chances are that an alfalfa field will replace a gold-mining plant in the course of time.

...Cultivating a field, scattering it with alfalfa seeds, harvesting the crop, separating gold nanoparticles… And what shall we do next? 
 

Information source: SciTecLibrary.com.