Geological workers have discovered a large gold mine in northwest China's Xinjiang Uygur autonomous region, officials said on Tuesday.

With gold reserves of at least 53 tons, the mine in Xinyuan county in the Ili Valley is expected to have an economic value of 20 billion yuan ($3.2 billion), said Zeng Xiaogang, head of the region's geology and mineral resources bureau.

Covering a length of 3 km and depths of 60 to 300 meters, the mine also holds 31,200 tons of copper, said Zeng.

He said the bureau, in cooperation with the Meisheng Group based in Hainan province, took five years to find the mine, finally confirming its location on May 13.

The group has invested nearly 150 million yuan in the project, which will be put into operation by the end of 2015. Its annual gold production capacity is expected to reach three tons, or 1 billion yuan of production value every year, according to Zeng.

It is the second large gold mine discovered in the Ili Valley following one with gold reserves of 50 tons found in 1988.

According to the bureau, the mine is the largest such resource found in the area of Xinjiang's western Tianshan Mountains. The zone is within the Narat-Hongliu River metallogenic belt, together with gold mines in Uzbekistan, Kyrgyzstan and Kazakhstan, indicating further ores are likely to be found in the belt.