The West Africa-focused company had been aiming for first gold in June.
Thor said yesterday mining was underway and the remaining work was focused primarily on the gold room, elution and electrowinning circuit, power connection, instrumentation and control installations.
"Once again, I would like to thank the entire team, which has done an excellent job amidst the difficult circumstances of the global pandemic to reach this key step in the development of the Segilola gold project as we gear up towards production," president and CEO Segun Lawson said.
"We continue to work towards, and look forward to, first gold pour before the end of the month."
Thor said production guidance for 2021 remained at 40,000 ounces, in a presentation last month.
Segilola's openpit is expected to average 85,000oz in years one to five, with a reserve of 518,000oz grading 4.02g/t.
Thor also owns the Central Houndé project in Burkina Faso after recently acquiring Barrick Gold's stake and has 70% of the Douta gold project in Senegal.
Its shares debuted on London's AIM a month ago.
Its Toronto-listed shares (TSX: THX) rose from about C20c a year ago to 44.5c in May.
They closed up 3% yesterday to 34c, capitalising it at $212 million (US$166 million).