A security guard has died in a ruby heist during which thieves stole a stash of gems from miner Mustang Resources.

The rubies, which totalled about 19,000 carats , were stolen from the Montepuez Ruby Project mine in Mozambique in a “grab-and-run” heist from a small safe by a group of thieves who are still on the run.

“Tragically, during the incident one of Mustang’s security guards guards on site died,” the company reported this morning.

“His family is being notified.”

It was not immediately clear how the security guard died. Mustang has been contacted for comment.

Mustang (ASX:MUS) had been preparing to sell the rubies at upcoming auctions in Mauritius from October 27.

“None  of the larger safes containing a limited number of higher-value rubies were broken into,” Mustang told investors today.

Most rubies are moved from the site to offshore safe houses, the company said.

“Minimal quantities are left at the mine site at any given time.

“Mustang believes the break is of a “grab-and-run” nature and highly opportunistic, taking place when the mine was closed in the very early hours of the morning.

“Mustang’s board of directors and management extend their deepest sympathies to [the security guard’s] family at this very sad time and offer them the company’s full support.”

Despite the theft Mustang would have more than 300,000 carats to sell at the auctions, the company reported.