The dual-listed company has lifted its Vetleegte coal resource to 629.3 million gross tones in-situ.

The gross in-situ estimate was made as the explorer noted that Waterberg coal typically occurs interlaminated with shale that for the most part cannot be mined separately from the coal.

The resource upgrade was based on a 29 diamond drillhole program covering 3340m, and Firestone said each hole intersected coal.

More drilling is planned to advance the resource to a measured status.

Meanwhile, Firestone used widely-spaced percussion drilling at its South African Olieboomsfontein property, also part of the Waterberg project.

The company said it intersected considerable thicknesses of coal with six preferred coal zones close to the surface.

Firestone chief executive officer Garth Higgo said the company aimed to turn the Waterberg project into an open pit coal operation with a low strip ratio.

The company aims to produce enough thermal coal to support a power station which consumes 15 million tonnes per annum and to export semi-soft coking coal.

The Waterberg project is part of a joint venture with Sekoko Resources subsidiary Sekoko Coal.

Shares in the junior closed up 20.6% to 4.1c on Friday.