Block 14 is currently planned as an openpit project, but Orca said recent drill results showed high-grade mineralisation far below the forecast pit level.

Orca said one intercept between 354.6 and 372m in Gulat Sufar South's east zone was 17.4m at 7.92g/t Au.

A different drill hole outside the resource between 400m and 411m returned 3.68g/t  over 11m.

Orca is working on a feasibility for Block 14 which is expected in the June quarter next year.

Orca CEO Rick Clark said underground mining was now on the table.

"The intercept in the high-grade shoot is not only impressive in grade but is also significant in width," he said.

"Ongoing drilling will further test this and other high grade structures at depth towards a review of underground options at both GSS and Wadi Doum."

GSS is currently planned as a two-pit operation, split between the main zone and larger east zone.

Toronto investors were not impressed by the idea.

Orca's share price fell 3% on opening to C$0.62 per share (US$0.49) after the announcement.