A CIVIL engineering company has scored a hat-trick of Territory projects.

Macmahon has been awarded the $120 million contract to dig a massive exploration tunnel at the Territory's only uranium mine.

The announcement follows the company winning two other major jobs - the $104 million Marine Supply Base and a share of preparing the ground at Blaydin Point for the Ichthys LNG plant.

Macmahon, which built the Tiger Brennan Drive extension, will have to take on hundreds of additional workers for the three projects.

Work on the Ranger 3 Deeps decline is to start next month.

Energy Resources of Australia made it clear that Macmahon won the job because it has a good reputation in the Territory.

"This furthers Macmahon's long history of delivering key infrastructure projects," its chief executive Rob Atkinson said.

The exploration decline will determine whether underground mining is viable at Ranger.

It will go down to an estimated resource of 34,000 tonnes of uranium oxide, one of the biggest new uranium discoveries in the world.

ERA is also investing in a $40 million three-year drilling program to look for other uranium oxide deposits at the Ranger site near Jabiru, 220km east of Darwin.

The miner is also conducting a major water management study, and seems to have forged a better working relationship with the Gundjeihmi Aboriginal Corporation, which represents the Mirarr traditional owners.

Macmahon will excavate a box cut and install a portal access tunnel at Ranger 3 Deeps.

Work will then start on constructing the 2.2km decline down to 400-500m.

The decline will be used to carry out a drilling program.

ERA has set aside an additional $55 million to study the results and decide whether an underground mine is viable.

NT Resources Minister Kon Vatskalis welcomed the massive investment.

He said digging the decline would create 50 jobs.

Mr Vatskalis said a "rigorous consultation and environmental assessment process" would be carried out following any application for an underground mine.