The funds are on top of the $120 million already committed to build the exploration decline.

Construction began earlier this month for completion in early 2014.

The PFS funds were included in ERA's $500 million capital raising completed last year.

The study will include 16,000m of drilling in addition to the 35,000m already approved as part of the decline project, with all results to be incorporated into the PFS.

The deposit already has a resource of 34,000 tonnes of uranium oxide.

The extension of the decline and the installation of a ventilation shaft will be evaluated.

ERA chief executive Rob Atkinson said the approval was an important step in determining the viability of the Ranger 3 Deeps project.

"We will continue discussions with the Mirarr through their representatives, the Gundjeihmi Aboriginal Corporation, as well as with the Commonwealth government and Northern Territory government, in relation to this project and the outcomes of the study," he said.

A decision into the underground development is expected to be made in late 2014.

The Ranger open pit mine produced 612t uranium oxide in the March quarter.

Shares in ERA, which are 68%-owned by Rio Tinto, gained 1.5c to $1.22.