(Adds detail on duty, executive comments, updates stock price)
TORONTO/LONDON, March 21 (Reuters) - Canada's First Quantum Minerals said on Wednesday that it disputes a 76.5 billion Zambian kwacha ($8.07 billion) bill by Zambia's tax agency for unpaid duties on imports to its Sentinel mine between January 2012 and December 2017.
Zambia has reduced "significant" tax assessments against it in the past, First Quantum said on a conference call. But the company would not speculate on any outcome of a review of the government's claim, which could take up to six months.
The bill comprises $150 million for higher import duties, $2.1 billion in penalties and $5.7 billion in interest, said First Quantum, which owns two copper mines in Zambia and has a market value of $9.5 billion.
The company's preliminary review of documents, which it said are submitted to authorities before any goods are allowed for import, showed errors in the application of both higher and lower duties than appropriate, Chief Executive Philip Pascall said on a conference call with analysts.
"We have in the past seen assessments that were significant and then the settlement might be reduced considerably," Pascall said. "In this context, it's not prudent for us try and speculate."
Zambia's tax agency said that a 25-percent duty rate should apply to $540 million in mining equipment the company imported, rather than rates up to 15 percent which were applied, First Quantum said.
First Quantum shares dipped 0.2 percent on the Toronto Stock Exchange to C$17.97 on Wednesday. The stock dropped 12.4 percent on Tuesday before trading in its shares was halted. ($1 = 9.4810 Zambian kwachas) (Reporting by Susan Taylor in TORONTO and Zandi Shabalala in LONDON; Editing by Tom Brown)