The second ball mill will allow the company to increase plant throughput capacity to 1.4 million tonnes per annum of blended ore and 1.24Mtps of only fresh ore from the current 1.24Mtpa blended and 1Mtpa fresh.
It decided on a secondary milling circuit over a tertiary crushing circuit, as the latter would have substantially higher costs and complexity of operation and a trade-off study determined the former would result in incremental gold recovery and increased revenue.
Hummingbird expects the second mill to cost around US$13 million and to be operational in the September 2019 quarter.
CEO Dan Betts said the new mill and initial drilling results showed the company's confidence in increasing Yanfolila's reserves.
He added the second mill would provide greater flexibility and 24% more throughput when operating on 100% fresh ore.
The company was also pleased with the first drilling results.
Highlights intersects of the drilling results at Komana West deposit included 11.45m at 8.69g/t from 69m depth; 25.75m at 2.95g/t from 117m depth; 8.05m at 4.98 g/t from 72.4m depth; and 8.1m at 5.52 g/t from 84.9m depth.
From the Guirin West deposit, the best intersections were 16m at 3.11g/t from 38m depth; 4m at 8.12g/t from 13m depth 9m at 2.06g/t from 27m depth; and 13m at 1.91 g/t from 16m depth.
Through the drilling programme started in July, Hummingbird is targeting the conversion of Yanfolila's 2.2 million-ounce resource base to reserves and also some new reserves not defined as resources.
The company's shares were up 0.37% Wednesday after the news to 27.3p (US36c).