Hummingbird Resources has decided to add a second ball mill to its Yanfolila mine in Mali, only nine months since the operation started producing gold.

The addition of a second ball mill at Yanfolila is in place of the tertiary crusher the company initially thought would be suitable for later life as the operation transitioned to 100% fresh ore.

The mill is due to be operational in the September quarter of next year and is expected to set the company back some $13 million.

The Yanfolila crushing circuit is currently a two-stage operation incorporating both primary and secondary crushing circuits designed to treat a blend of oxide and harder ores. The ore is non-
refractory and the process plant design uses gravity and carbon-in-leach for the processing and recovery of the gold which averages 92.5% over the life of mine.

The original definitive feasibility study plan was to add a tertiary crushing circuit in order to allow the plant to process 100% hard fresh ore later in the mine life.

“However, the annual throughput was expected to decrease from 1.24 Mt/y to 1 Mt/y, when operating with 100% fresh ore which led to the life of mine average production dropping to 107,000 oz/y from 130,000 oz/y in the first full year of commercial production,” Hummingbird said.

On top of this, a review of the scope for a tertiary crushing circuit indicated higher costs and complexity of operation, leading the company to carry out a tradeoff study between the secondary ball mill and tertiary crusher.

The conclusion was the addition of a secondary ball mill could maintain the current 1.24 Mt/y capacity when processing 100% fresh ore and, when blended with 25% oxides, throughput rose to 1.4 Mt/y.

Hummingbird concluded: “The incremental gold recovered, and increased revenue associated with installing a secondary milling circuit outweighs the higher operating costs and incremental capital costs associated with the same.”

The addition of a second mill also provides the company with some flexibility should issues arise with the primary mill, supplied by Outotec.

Project management and engineering firm SENET will carry out the installation of the mill as part of an EPCM contract. SENET was the EPCM contractor for the Yanfolila mine build, which was delivered on time and budget.

Hummingbird expects to pour some 105,000-115,000 oz of gold this year.