"Illegal panners invaded the mine and took part in unlawful explosive blasting," the private company said.
"Tragically, nine panners lost their lives."
Metallon, which is suing the government over a separate matter, said none were employees of Metallon and its workers who were involved in keeping the mine on care and maintenance had been accounted for.
It suspended underground mining at Mazowe in July 2018, announcing plans for a US$110 million expansion and modernisation to increase annual production to 93,000 ounces.
It said the mine, about 50km from Harare, was one of the oldest in Zimbabwe.
The company said an investigation into the fatalities was ongoing and it expressed condolences to the bereaved.
Meanwhile, it has been forced to put its other mines on care and maintenance, Metallon said earlier this month, "because of the unsustainable costs of running them without proper compensation for its proceeds from the government of Zimbabwe".
It said it would sue the government for $132 million for failing to pay for gold, including interest.
It was also suing the Zimbabwe Ministry of Mines and Mining Development for the unlawful withholding of a mining lease that was approved by the Zimbabwean Mining Affairs Board earlier this year, Metallon said.
