The company has released significant resource updates for both operations and a preliminary economic assessment on expanding Yauricocha from 3,780tpd to 5,500tpd.

At Cusi, measured and indicated resources increased 18% in tonnage to 5.3 million tonnes for 37 million ounces silver-equivalent, and inferred rose 200% to 4.8Mt for 28.8Moz Ag-eq.

"This updated mineral resource estimate is the foundation of our upcoming preliminary economic assessment update that will help us to determine the most capital efficient expansion scope for the Cusi mine, in a similar way that we have evaluated the Yauricocha mine in Peru and Bolivar mine in Mexico," CEO Luis Marchese said.

Sierra had announced a positive PEA on doubling Bolivar's output to 10,000tpd in October.

At Yauricocha, Sierra said the PEA's starting point of 3,780tpd represented the expected upcoming expansion from the current 3,150tpd to 3,600tpd plus a 5% overallotment allowance, pending a permit expected in early 2021.

Marchese said the PEA determined a further expansion to 5,500tpd was the optimum production level based on its current, expanded mineral resource base.

Sierra reported a 26% tonnage increase in the measured and indicated resources to 15.9Mt and a 79% increase in inferred resource tonnage to 11.6Mt, which Marchese said was "the highest resource in the mine's history" since acquiring it in 2011 with an indicated resource of 5Mt and having since mined 9.1Mt of ore.

The PEA put the life-of-mine and sustaining capital cost at US$268.5 million and the after-tax NPV8 at $333 million.

Over 12 years, Yauricocha was expected to produce 419 million pounds of copper, 13.7Moz of silver, 43,000oz of gold, 541Mlb of zinc and 167Mlb of lead.

"The company plans to continue with its disciplined approach of profitable growth and now plans to proceed with the next step of the completion of a prefeasibility study to further de-risk the plan and determine the best path forward," Marchese said.

Sierra Metals had reported a 350% year-on-year jump in headline earnings earlier this month, as record production from Bolivar and Cusi coincided with higher metals prices, helping offset lower sales and increased treatment and refining charges at Yauricocha.

Sierra shares (TSX: SMT) reached a 12-month high of C$3.67 this week.

They closed down 0.3% to $3.38 to capitalise it at $550 million (US$420 million).