Work is expected to start immediately on both packages.
The first package is to design and build three 400-bed temporary construction camps for workers on the Carmichael railroad. That contract is valued at about $40 million.
The second package is an initial $1.4 million early contractor services contract to scope the bulk earthworks needed along the primary freight rail alignment.
A contract for construction works hinges on successful completion of that ECS.
Adani Mining CEO Lucas Dow called the $40 million-plus contract with Decmil a win for regional Queensland.
"This contract means more jobs and economic activity for Rockhampton and regional Queensland," he said.
"The Decmil team will move in to our Rockhampton office along with Martinus, our track laying contractor.
"This announcement brings the total value of contracts awarded for the Carmichael project to date to more than $500 million.
"The operations of the rail camps will be based in Collinsville, earthworks and civil works are coming from Townsville and Rockhampton, fuel supply is from Townsville, telecommunications is from Mackay, and many other regional businesses across regional Queensland are also getting involved."
Dow said the accommodation camps for the rail construction crews would have air-conditioned rooms, dining messes, gyms and recreation areas.
"They will also comply with the high standards of environmental regulation that have been set for our project," he said.
"Our rail construction crews will live in these camps while they build our 200km long railway line that will link the Carmichael mine with the existing rail network."
Decmil shares closed 1c higher at 91c, valuing the contractor at $217 million.