His assistant, Mohammad Esmail Qassemi, was also hanged early Wednesday, state-run Iranian Students News Agency said.
Iran detained Mr Mazloumin, 58, in July for hoarding 2 tonnes of gold coins.
"With these abhorrent executions the Iranian authorities have flagrantly violated worldwide law and once again displayed their shameless disregard for the right to life".
Philip Luther, Middle East research and advocacy director at the human rights organisation, said: "With these abhorrent executions the Iranian authorities have flagrantly violated global law and once again displayed their shameless disregard for the right to life".
His network's transactions were reportedly in the hundreds of millions of dollars.
The currency's fall came as the United States in May withdrew from the 2015 nuclear deal between Tehran and world powers, and in August started reimposing economic sanctions that had been lifted in exchange for curbs on Iran's nuclear activities.
Fearing for the economy, many Iranians rushed to secure their savings by buying foreign exchange and precious metals, the AFP news agency reported.
In the wake of the latest round of U.S. sanctions on Iran, the rial has fallen about 70% against the USA dollar.
There have been widespread reports this year of dealers and middlemen manipulating the markets by hoarding dollars and coins in order to push up prices.
In August, Iran's Supreme Leader approved a request by the Head of Judiciary to set up special courts to deal with crimes involving financial corruption. Since that time, at least seven people received death sentences.
A second co-defendant, Hamid Bagheri-Dermani, was also accused of corruption and sentenced to death at the original trial.
At least seven death sentences have been delivered by the courts since the crackdown, with numerous trials being broadcast live on national TV.
A second phase of sanctions targeting Iran's energy sector officially started on November 5.