Petra, which mines diamonds in South Africa and Tanzania, said revenue for the quarter to Sept 30 was $82 million.
Production fell 10% year on year to 974,346 carats due to the ongoing closure of the Williamson mine in Tanzania, which Petra shuttered in April. Its reopening is contingent on stronger diamond prices and market conditions, Petra said.
The miner kept production guidance for the full-year 2021 suspended.
"While the mines are generally operating at planned levels, there remain risks to production relating to the impact of the stringent COVID-19 measures in place," Petra said.
Although diamond prices have improved since March, they are still down around 10% compared with pre-COVID-19 levels, the company said.
The economic fallout of the pandemic has dealt a heavy blow to the diamond industry which relies on consumer demand for luxury jewellery.
Petra last week announced a debt restructuring agreement including a debt-for-equity swap which would leave noteholders with a combined 91% of the shares and dilute existing shareholders to just 9%.
(Reporting by Helen Reid; editing by Jason Neely, Kirsten Donovan)