Metals Exploration plc said that cynanide contamination has temporarily halted ore processing and production for six weeks at its Runruno gold mine in the Philippines.
TUNNELS
The company first thought that the contamination originated in water upstream of the mine from illegal mining activity.
However, after draining and cleaning the BIOX circuit and inoculting new bacteria, contamination remained as the new bacteria were unable to recover fully.
“Unfortunately, the BIOX bacteria has been unable to cope with the levels of cyanide in the BIOX feed,” added Metals.
“Accordingly, new and additional monitoring protocols will be introduced to minimise the impact of this contamination, both now and in the future, which are expected to resolve the issue.”
A second source comes from ore feed, from stages five to six small-scale mining tunnels, where illegal mining has resulted in residual cyanide contamination of ore delivered to the run-of-mine (ROM) pad.
Metals said that removal of all illegal ball mills last year had resulted in the use of cyanide to process ore within the illegal miners’ tunnels.
The company’s “ongoing policing and security efforts” have limited the reopening of illegal tunnels, thus limiting cyanide contamination.
As mining at Runruno progresses through stages five and six, Metals has found an “extensive network of illegal miners’ tunnels” but will be able to manage the “isolated” cyanide issue.
“Testing of ROM pad ore is currently underway to ringfence the remaining contaminated ore to prevent a repeat of damage to the BIOX circuit bacteria,” said the company.
The source of water contamination is also resolved and the water feed will undergo regular tests.
GUIDANCE
Production levels are due to return to planned levels within the next two weeks, while full-year guidance is likely to be towards the lower end of the forecast range of 70,000 – 75,000 ounces.
Chief executive officer Darren Bowden added: “We are disappointed that we have had to temporarily defer ore processing operations at Runruno due to the contamination impacting the BIOX circuit.
“However, we are pleased to have found the causes as to why this contamination has taken place, and are implementing additional monitoring processes to minimise the impact at present, as well as in the future.”