Mardani beat Brazilian Guilherme Felix 16-11 in the men’s over-80kg event.
The Iranian representative then beat Asian champion Smaiyl Duisebay from Kazakhstan 13-7.
Mardani also defeated Croatian Vedran Golec 8-4.
He lost to Russian Vladislav Larin 15-12 in the semi-final and claimed a bronze medal.
The competition is the last event before next month's World Taekwondo Finals in Fujairah, the United Arab Emirates.
Top competitors are awarded ranking points towards the World Taekwondo world ranking which could help them quality for the 2020 Olympic Games in Tokyo.