At the same time, it updated its mineral resource estimates for the complex to 3.9 million ounces of gold and 22.6 million ounces of silver measured and indicated and an additional inferred resource of 4.2 million ounces and 15 million ounces, respectively. 

Gran Colombia executive co-chairman Serafino Iacono called the change to its mining approach “prudent” as it switches from its previously outlined large-scale, low-grade open-pit operation to smaller-scale, higher-grade underground mining.

“We have already commenced some high level scoping analysis for future mining operations and over the next six months we will be preparing a preliminary economic assessment targeting higher grade material with the intention of developing an expanded underground mining operation at Marmato with a minimum 12-year mine life and life-of-mine gold production of more than 1.5 million ounces,” he said. 

Marmato’s deep mineralisation remains open along strike and at depth. The miner said its exploration for the coming year includes substantial additional drilling as it works to expand its understanding of the deposit’s potential.

Gran Colombia’s NRE was prepared by SRK Consulting US and it carries an effective date of June 16.