Six persons had waylaid the van carrying the staff of a jewellery shop in the city, while they were taking the gold and five kg of silver bars from their factory in Bharathi Nagar to the store on September 14.
They were allegedly assaulted and the valuables looted at gun point, police said.
There were four persons, including the driver in the van, but they could not put up any resistance as the gang members, who had concealed their face by wearing helmets, threatened to shoot them to death, police said.
Based on his confession, Saravanakanth, Hariharan, Raja and Benjamin were arrested, police said, adding they have been remanded to custody.
The stolen gold and silvers bars were recovered, police added. Police are on the lookout for another person identified as Santhosh.