Thor, which is already listed in Toronto's TSX Venture Exchange (TSX-V), will use the proceeds of the new listing mainly to fund its Segilola Gold Project in Nigeria. The company also has two gold projects in Senegal and Burkina Faso.

"AIM is the front runner but we are not closing any doors," Chief Executive Segun Lawson told Reuters, adding London was preferred because it had large pool of investors and an appetite for resource firms with projects in Nigeria.

But he said other options involved listing in Australia or Johannesburg, or upgrading to the main board in Toronto.

Thor wanted to raise $30 million to $35 million via a listing at the start of the fourth quarter, Lawson said.

Nigeria has introduced tax breaks for miners to encourage investment in its bid diversify the economy away from oil.

"The current government is actively encouraging exploration in the mining sector," Lawson said, adding Thor's Segilola project was expected to start production in 12 to 15 months after the planned listing.

Incentives included a tax holiday for the first three to five years of production for miners, the opportunity to recoup capital expenditure and free foreign currency transfers through the Central Bank of Nigeria, Lawson said.

(Reporting by Zandi Shabalala; Editing by Edmund Blair)