For the third time this year, gold miners in Mexico have come under attack, highlighting the perils of mining in the country.

McEwen Mining Inc. became the latest victim, when armed robbers looted about $8.4-million (U.S.) worth of gold this week from the Canadian miner's refinery in the Mexican state of Sinaloa.

The Toronto-based company said none of its employees were seriously injured, nor were its facilities damaged, when the approximately 900 kilograms of gold ore was stolen. The ore is expected to contain 7,000 ounces of gold, but it is unclear how the thieves will process the rocks.

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The robbery comes about a month after four of Goldcorp Inc.'s Mexican employees went missing after leaving the company's Los Filos mine. Three of the four have since been found dead, the Canadian company said. A Reuters report said the bodies were found in a mass grave and showed signs of torture. The fourth employee was released with minor injuries.

The kidnappings took place in Guerrero, a southern Mexican state where 43 students were seized en route to a protest last year and are presumed murdered.

Torex Gold Resources Inc., another Canadian miner, also faced security problems in Guerrero. In February, a dozen residents on a highway near Torex's construction site were abducted, four of which were affiliated with the company's gold project.

The residents were later released. The company is hoping the area will get permanent security presence from federal or state authorities.

Many Canadian companies are operating and exploring for precious metals in resource-rich Mexico. Those include Agnico Eagle Mines Ltd., Scorpio Mining Corp., Timmins Gold Corp., First Majestic Silver Corp. and Alamos Gold Inc.

Agnico said the Mexican government has been responsive to the mining industry's concerns about security.

"We are hopeful that this ongoing dialogue will result in better conditions for the industry as a whole," said Tim Haldane, Agnico's senior vice-president of U.S. and Latin American operations. "Fortunately, in the communities where we operate we have not observed any recent new security challenges."

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Danger in the mining industry extends beyond Mexico. Colombian rebels kidnapped a Canadian mining executive in 2013 over a fight over mineral rights. The Canadian company eventually pulled out of Colombia and the executive was freed.

Goldcorp said it has strict travel protocols in place in Mexico and that its operations have not been affected.

McEwen Mining also said its operations were not affected, though it said its insurance policy will not cover the entire loss.

The incidents come as the price of gold hovers around $1,200 an ounce and companies are under pressure to cut costs to deal with the lower bullion value.