The strike by members of the Union of the Mine and Metallurgical Workers of Minera Corona resulted in the company suspending all mining and milling activities on Tuesday March 19th.

The Ministry of Labour was informed upon the company receiving notification by the union of its intent to strike. The ministry said the strike could not proceed and deemed it illegal under current legislation once it began.

"Management believes that this strike action will not materially affect the company's annual production guidance or mine budget," said president and CEO Igor Gonzales.

Yauricocha produced 157.2 million pounds of zinc equivalent in 2018 at an all-in sustaining cost of US$0.73 per pound by processing an average of 3,162 tonnes per day. The company aims to increase throughout to 3,600tpd in 2020 and possibly on to 5,500tpd in 2021.

It produces a lead concentrate, copper concentrate and combined lead-zinc-copper concentrate.

Sierra's shares (TSX:SMT) were down about 2% in early trading at C$2.13 valuing the company at $355 million. Its share price has fallen 12% so far this year.