Sierra Studying Expansion at Cusi Silver Mine

A 3D model shows the mineralized ore bodies at the Cusi mine in Mexico.
Sierra Metals has reported the results of a preliminary economic assessment (PEA) of a major expansion of production at its Cusi silver mine in Chihuahua state, Mexico. The PEA supports expansion from a current mine operating rate of 650 metric tons per day (mt/d) to 1,200 mt/d by the first quarter of 2019 and 2,700 mt/d by mid-2021. Silver production would total 30 million ounces (oz) over a mine life of nine years based on existing mineral resources.

Life-of-mine capital costs of the expansion program are estimated at $104 million. Sierra Metals is pursuing ongoing exploration programs and expects to continue to grow the mineral resources at the Cusi mine. Mechanized bench-and-fill mining will be introduced to achieve sustainable mine production of 2,700 mt/d. Improved productivity will be accompanied by improved safety, as the requirement for man-time spent in stopes will be significantly reduced. Head-grades are expected to reduce from the current 201 g/mt silver to 161 g/mt at 1,200 mt/d and 145 g/mt at 2,700 mt/d.

Cusi mine production is processed at Sierra Metals’ Mal Paso plant, approximately 44 km from the mine. The plant is based on a conventional crushing-milling- flotation circuit that produces commercial quality lead/silver and zinc concentrates. Mineral is delivered from the Cusi mine to the plant in 20-mt trucks.

In line with proposed increases in mine output, processing capacity at Mal Paso will be increased to 1,200 mt/d in 2019, and a new plant with a capacity of 1,500 mt/d is proposed for construction at Cusihuariachi to come online mid-2021, bringing total capacity to 2,700 mt/d. The proposed plant at Cusihuariachi is significantly closer to the Cusi mine than the Mal Paso plant, and the shorter haul distance is expected to translate into an operational savings of $4/mt.

The Cusi property is located 135 km southwest of Chihuahua. Epithermal mineralization has been mined in the area since its discovery in the early 1800s.

Eight mineralized zones are recognized at the property. The zones are up to 10 m across and include silicified faults, veins and breccias. Veins typically range between 0.5 and 2 m wide, dip steeply, extend 100 to 200 m along strike, and extend up to 400 m depth.

As featured in Womp 2018 Vol 07 -