Highway police say they found more than 200 large pieces of meteorites hidden under the seats of a truck which they had stopped in a random check.
Three Argentines and a Paraguayan were arrested.
The province of Chaco is world famous for meteorites, which are protected under Argentine law.
Chaco contains an area known as "Campo del Cielo", or the "Field of Heaven".
It spreads out over an area of 1,300 sq km (500 sq miles) and is littered with meteorites which fell around 4,000 years ago.
The largest, named El Chaco, was discovered with a metal detector in 1967 and weighs 37 tonnes.
El Chaco is the second-biggest meteorite ever found - and it too aroused avarice among speculators and collectors.
In 1990, an Argentine highway police officer foiled a plot to steal it for sale to a private US collector.
Police in Argentina have arrested four men who appear to have been trying to steal more than a tonne of meteorites in the northern province of Chaco.