MEXICO CITY, Aug 19 (Reuters) - Shares in Mexican miner Grupo Mexico fell more than 2 percent on Tuesday, a day after Mexico's environmental authority said it would file a criminal complaint against the company for a toxic spill at its Buenavista mine in northern Mexico.
The federal attorney general's office for environmental protection (Profepa) said in a statement on Monday night it would bring charges against Buena Vista del Cobre, the Grupo Mexico subsidiary that operates the copper mine.
Profepa said the spill, which was detected on the morning of Aug. 6, pumped 40,000 cubic meters of toxic mining acid into the Bacanuchi river in northern Sonora state.
The agency said the fine for the spill could reach up to 40 million Mexican pesos, or about $3 million.
Grupo Mexico shares were down about 2.5 percent to 46.30 pesos in mid-morning trading.
Traders attributed the share price drop to the charges being announced.
"Everyone knew about the spill, but now we know about the size of the fine," said Gerardo Roman, head of stock trading at Actinver brokerage in Mexico City. "It's not so much the economic impact; it's that people don't look kindly on them contaminating."
Grupo Mexico did not immediately respond to a request for comment. (Reporting by Gabriel Stargardter; Editing by Paul Simao)