(Bloomberg) — Zambia’s tax agency plans to conduct audits on mining companies in the country running back six years after uncovering 76.5 billion kwacha ($7.9 billion) of underpayment by a “prominent” miner.

The Zambia Revenue Authority may extend the period of the audit should it find a pattern of “consistent, systematic, premeditated” tax evasion, it said in a statement.

“We are announcing the preliminary assessment of 76.5 billion kwacha issued to a prominent mining company for misclassifying consumables and spare parts at importation for the last five years,” the tax authority said, without identifying the company. “The said items were declared as mining machinery, which attract customs duty at zero percent, when in fact not.”

Zambia is Africa’s second-biggest copper producer. (Written by Taonga Clifford Mitimingi)