It follows the company being granted a mining licence for its Bayan Khundii gold project, about 16km away, in August.
The Altan Nar licence is also valid for 30 years with an option to extend for up to 70 years.
The project, which has an indicated 317,700 ounces of gold and an inferred 185,700oz, is expected to add to the mine life at Bayan Khundii, where a bankable feasibility study is underway.
President and CEO Peter Akerley said Altan Nar's resources were recoverable through the planned Bayan Khundii plant.
A "compelling base case" announced in October envisaged Bayan Khundii producing an average annual 61,000oz of gold per year at a head grade of 3.73g/t over seven years, followed by a three-year openpit operation at Altan Nar producing an average annual 48,000oz at 3.46g/t gold.
Initial capex was put at US$40 million for Bayan Khundii in its prefeasibility study and at an incremental $2 million for Altan Nar in its updated preliminary economic assessment.
The post-tax IRR was put at 42% and 92% respectively.
Akerley said Altan Nar also showed "exceptional exploration potential", citing recent drilling results including 7m at 45g/t.
An exploration programme is expected to start in the second quarter.
The company has said it's targeting first production at Bayan Khundii in late 2021.
Erdene shares hit a one-year high of C32c in February, double December's low of 16c.
They closed down 6.8% yesterday to 20.5c to capitalise it at $39.3 million (US$28.7 million).