The incident of the 7 December occurred as a train with 13 waggons was crossing the bridge on its way to Buenos Aires.
The 300m steel truss bridge, a key link for the transport of sugar produced locally, crosses the Colorado River north of Pichanan town in Salta province.
According to the state-owned Belgrano Cargas y Logistica, which operates the freight network, 11 waggons were left stranded on the collapsed structure.
The train driver escaped without injury and managed to uncouple the locomotive immediately after the collapse.
The causes of the incident are under investigation.