The company maintained it was on schedule for its first pour in June, at what it bills as the country's first gold mine.
Thor said it had boosted the reserve estimate by 28% and improved Segilola's life-of-mine plan which would have "a materially positive effect on the project economics".
The reserve now stands at 517,800 ounces at 4.02g/t gold, which Thor said represented a 28% increase on the reserve used in the 2019 definitive feasibility study.
The process plant design capacity was increased by 14% to 715,000 tonnes per annum, which along with other optimisations such as a larger pit design, "resulted in a significant increase in project value for our shareholders at a competitive forecast all-in sustaining cost of US$685/oz," president and CEO Segun Lawson said.
This was slightly higher than the $662/oz AISC forecast in the 2019 study.
However, the base case NPV5 was now $311 million and the IRR 85%, compared with $138 million and 50%, respectively.
The new forecast used a base case $1,600/oz gold price, compared with the previous $1,200/oz.
Gold is currently above $1,700/oz on the spot market.
"The increased production capacity and mine plan are being implemented within the company's existing project funding," Lawson said.
Nigeria also extended the tax holiday for miners from three to five years in October, in a bid to boost the sector amid dwindling oil and gas revenue.
Thor's 2019 study had put Segilola's initial LOM production from the openpit at 393,000oz or about 80,000oz annually over five years.
Thor now expects Segilola to produce 502,000oz between June this year and 2027-28.
The company is also investigating the project's underground potential, which a preliminary economic assessment in 2019 said could add a further 33,000oz per annum at a development capital cost of $13 million.
Elsewhere, Thor has exploration interests in Senegal and a joint venture with Barrick Gold in Burkina Faso.
Thor shares (TSXV: THX) have ranged between C13.5-32c over the past year.
They closed up 4.75% yesterday to 22c, capitalising it at $136.7 million (US$108.6 million).