Initial ground works at the Komana West deposit have also been completed, with mining there underway.

The aim of the exploration drill campaign is to convert the 2.2 million ounces resource base to reserves and extend Yanfolila's mine life.

Four rigs are on site and will drill over 50,000m across six existing deposits, all close to the Yanfolila processing plant.

Hummingbird expects to extend the current mine life past 10 years by targeting the known resources and also expects to improve the grade delivered to the process plant at certain stages of the mine plan.

"This could result in higher annual production levels and therefore improve projected annual free cash flow," it said.

At Komana East, below the Yanfolila openpit mine, DRA Projects carried out an underground study of the ex-pit mineral resources, which added 113,000 ounces of producible gold to the existing mine plan.

The study calculated a mining breakeven cut-off grade of 1.7g/t and the resources beneath the current pit were considered as economic using mining stope optimiser software.

Five mine design options were identified and tested, with the best option resulting in an IRR of 43% with over 113,000oz produced at a grade of 3.45g/t. It also had the option to improve the IRR by relocating the portal position to the base of the pit.

Under the option, a total 1.3 million tonnes of ore will be mined, with the highest levels of production planned for the second and third years of the four-year schedule.

Hummingbird said only current resources were used for the study, meaning any new resources delineated this year along strike or down dip would add and further improve the planned underground production.

Yanfolila reached commercial production during the March quarter, with the company hoping to produce 105,000-115,000oz of gold in 2018..

Shares in Hummingbird were up 2.79% Monday morning to 31.35p (US41.28c).