At 3am (Chihuahua time) on April 15, a group of armed intruders entered the mine, locked the staff in a sea container, and made off with around 80 tonnes of zinc and lead concentrates valued by the company at US$120,000.
No security guards or employees were harmed during the incident and are being counselled and supported, the company said this morning.
In November, a group of armed bandits entered the mine late at night, again locked them in the shipping container, and stole some 90t of concentrates, then valued at $90,000.
After the first incident the company upgraded security, including upgrading physical barriers on the access road and the police and Mexican Army offered to provide enhanced security in and around Plomosas.
Further security measures will now be considered.
The first theft meant the company deferred some $90,000 of upgrades.
ConsZinc commenced mining at Plomosas in September 2018 and achieved commercial zinc production later this year, but while it calls the operation "one of the world's highest grade, low cost zinc mines", rich but historically underexplored project has been troubled.
Most recently, it has been a victim of logistics and operational issues, including a shortage of spare parts that meant its mining fleet were often out of action, and December quarter production was just 60% of target.
Diesel and key reagents have also been hard to source.
December quarter sales were 377t of zinc and 112t of lead, and there some 98t of concentrate stockpiled at the mine in January.
While the mining has been troubled, the orebody is considered extremely robust and much of the ore mined has come from outside the resource envelope.
The company started the year with A$317,000 in cash, but recently raised $1.55 million via a 2.5c placement to fund due diligence on a planned move into Western Australian lithium, nickel, and rare earth assets.
The company's shares last traded at 2.9c, valuing it at $10.5 million.