The company processed 602,087 tonnes during the quarter from its three operations, including the Cusi silver mines in Mexico, a 32% increase from the same quarter in 2017.

Sierra CEO Igor Gonzales chalked up record throughout at Yauricocha and Bolivar to successful operational improvement programmes.

Copper production for the June quarter jumped 62% year-on-year to 8.6 million pounds (3,901t), gold production was up 38% to 1,814 ounces, silver output rose 12% to 700,000oz, zinc production jumped 11% to 20.3Mlb, while lead output dropped 16% to 7.1Mlb.

Sierra attributed the increase in metal output to higher ore throughput, higher copper and gold head grades, and higher copper, lead and gold recoveries.

"A strong increase in tonnage at Cusi was noted in the second (June) quarter, and the company is reaping the rewards of a successful turnaround programme and the refocusing of the mine's production to the Santa Rosa de Lima zone, which boasts higher grades and increased widths," Gonzales said.

Sierra expected to continue to realise the benefits of the Cusi programmes over the rest of the year.

The company also expects to complete final infrastructure for the Yauricocha tunnel early in the September quarter to allow more capacity to handle larger volumes of waste and ore. It is also sinking the mine's shaft to the 1,270 level this year to access more reserves and resources.

At Bolivar, the company expects production to increase further in the second half of 2018 to around 3,500t per day by the end of the year.

"Installation of an additional mill in the second half of this year will help grind size optionality and improve recoveries at the plant," Gonzales said.