Zambia’s statistics office expects to show that the country’s  $20.7 billion economy is 20 percent larger than previously thought, according to a Bloomberg report.

With the expansion of the country’s mining industry, Africa’s biggest copper producer has “completely” changed structurally since 1994, the current base year used for calculating the size of the economy, said John Kalumbi, director at the Central Statistics Office.

The mining industry was in disarray 1994, Kalumbi said. “In the last three or four years the mining sector has changed in terms of structure and contribution. There are other sectors that have come on board in the last 10 years or so, and these have also completely changed the structure of the economy.”

Zambia began selling copper mines to private investors in the 1990s, reversing a nationalization program in the 1970s. The country has benefited from growing private investment in mining, as well as increased investment in agriculture, with GDP growing by 7.3 percent last year, according to the World Bank, the report said.

The Central Statistical Office will re-base the country’s GDP numbers once it has assessed the results of an economic census in October, which will form the base of the exercise, Kalumbi said.

“It will be in the range of 20 percent higher,” Kalumbi said.

Zambia produced 818,000 metric tons of copper in 2012, and this will grow to 1.1 million tons by 2015, Yamfwa Mukanga, then minister of mines, said in April.

The Southern African country rebased its currency, the kwacha, at the beginning of 2013, removing three zeros.