Following are details on how a gold medal is made for the Rio 2016 Olympics:
First, a mold is designed at the Brazilian Mint. The core of each medal is cast in recycled silver from melted down mirrors and X-ray plates. Gold plating makes up 1.2% of each medal.

Solid gold has not been used since the 1912 games. Finally, the medals are embossed, buffered, and varnished. View video here.

It takes the team of 80 people two days to craft a single medal. They will be producing 5,130 in total.

It’s a sense of great satisfaction that our work will be worn on the chests of athletes who have given everything to win.
Nelson Neto Carneiro, Brazilian Mint Worker.