It said a contractor was pinned by a rockfall from the drill face on March 7, treated quickly by the site emergency response team and transported to Zacatecas Hospital, where he passed away.
"It is with great sadness that I report such a tragic loss," president and CEO Darren Pylot said.
"Our immediate priority is to support his family and colleagues through this difficult time.
"The safety and well-being of our employees and contractors remains our top priority."
Capstone said no other employees or contractors were injured and there was no ongoing safety risk.
Operations were immediately suspended but had since restarted in the mill and mining was expected to resume yesterday.
The company said an investigation into the cause of the accident was ongoing and the necessary authorities had been notified.
Capstone had last reported a fatality at Cozamin in March 2018.
The company, which expects to become debt free this year, updated Cozamin's reserves by 31% in January which is set to extend the mine life to 2031.
Its other mine is the Pinto Valley copper operation in Arizona.
Its shares (TSX: CS) have ranged from C33c-$4.18 over the past year and closed yesterday at $3.74 to capitalise it at $1.5 billion (US$1.2 billion).
