"The economics in this PEA confirms the rationale for approving this project in April of this year, which is proceeding on a fast track basis," CEO Luis Marchese said.

The updated PEA put the after-tax NPV8 at US$361 million compared with $283 million in a 2020 PEA.

"The incremental benefit includes iron ore production and increasing production to 10,000 tonnes per day from 5,000tpd is now estimated to have an after-tax NPV8 of $78.2 million, an IRR of 69% versus an NPV of $57.4 million and an IRR of 27.9% previously reported," Sierra said.

The update estimated a 14-year mine producing 551 million pounds of copper, 150,000 ounces of gold, 12.9 million ounces of silver and 5.7Mt of 62% iron concentrate.

Sierra had last week reduced its 2021 production guidance and raised its costs outlook for its three mines due to COVID-19 and operational challenges.

It's now expecting to produce 67-69 million pounds copper-equivalent at Yauricocha in Peru, 31-33Mlb Cu-eq at Bolivar and 1.27-1.4Moz silver-equivalent at Cusi in Mexico - or a total 110-115Mlb Cu-eq, down from 130-141Mlb Cu-eq.

It revised 2021 capex up from $78 million to $100 million due to constructing the iron ore processing plant at Bolivar.

The company was continuing to consider "all options" as part of a strategic review and expected to provide a detailed report on progress in the coming weeks. 

Sierra had cash and equivalents of $76.1 million and $17.2 million net debt at June 30.

Its shares (TSX: SMT) are trading near the middle of a one-year span and closed down 4.4% to C$3.01 yesterday, valuing it about $492 million (US$390 million).