Santa Rosa De Cajacay, Peru --

It began with a loud pop like a tire bursting. A toxic cocktail of copper concentrate laced with a periodic-table's mix of volatile compounds then shot skyward.

The pipeline that carries slurry at high pressure from Peru's most productive mine 188 miles to its desert coast had sprung a leak at a pumping station in this village of poor farmers. It was 9:15 a.m.

Abraham Balabarca , who was building a house nearby, ran to the station with others to try and halt the flow. But the door was chained and bolted. The security guard had no key. By the time someone pried open the lock with a crowbar, the town was shrouded in a toxic  cloud .

In the next days, about 350 villagers would be treated for headaches , respiratory tract bleeding, nausea and vomiting, according to the mayor's office. At least 69 were children.

Silence on slurry

Three weeks after the leak spilled 45 tons of slurry into the town of Cajacay, spreading toxic dust that left 42 people hospitalized for up to 11 days, the copper mine's owner, mining complex Antamina, has said little about the accident, and has been silent about the slurry's chemistry.

Environmental protection has traditionally been lax in Peru, where mining has been the engine of a decade of average 7 percent annual growth that has made the Andean nation a darling of investors. But an antimining backlash has been growing in the country. In the past three months, eight Peruvian civilians have been killed in antimining protests that have dominated the country's political agenda, prompting the resignation of two prime ministers.

Most Cajacay villagers are subsistence farmers who grow lima beans and raise sheep. About two in five children in the highlands region suffer from malnutrition and anemia. The town has no running water or sewage system.

People treated at the San Pablo hospital said they requested but were denied results of their blood tests or any other documentation that would attest to their hospitalization, which Antamina paid. Hospital director Raul Guisse refused to discuss the cases with the Associated Press .

Maximum fine

Antamina is the world's third-largest zinc and eighth-largest copper mine, according to Xstrata, which along with BHP Billiton, the world's largest mining company, holds a 33.75 percent stake. Environment Minister Manuel Pulgar had demanded the company be made to pay the maximum fine permitted under law, or $13.7 million, for negligence.

His deputy, Mariano Castro , said his agency's investigation is not over. He declined to say whether more serious sanctions could be ordered. A 2009 law permits egregious violators to be suspended or even shut down.

Antamina has not yet explained what caused the leak or why it took two hours to halt the slurry flow. Company officials did not respond to repeated telephone and e-mailed requests for comment, and refused to talk to reporters at the town meeting.

In the highlands town of Espinar, farmers have mounted protests saying contaminated runoff from a copper mine owned by Xstrata is killing their llamas, sheep and vicunas - an allegation the company denies.

Espinar Mayor Oscar Mollohuanca was jailed for 15 days after a protest in which police fired on demonstrators and at least two people died.

"In this country it's the mining companies who govern," he said. "At their service they have the president, the police and the bullets."