Cleanup under way at Los Frailes mine

A tailings dam failure at the Los Frailes mine, about 30 km northwest of Sevilla, Spain, has flooded a large area of farmland, and Spanish authorities are considering pressing charges.

The mine, owned by Boliden (BOL-T) and operated since February 1997 by Boliden’s Spanish unit, Boliden Apirsa, was shut down shortly after the spill and has not resumed production. The discharge from the breach in the tailings dam, now stopped, flowed into a nearby watercourse and into flat lands along the banks of the Guadiamar River.

A 50-metre section of the dyke failed on April 25, releasing about 4 million cubic metres of wastewater and another 1 million cubic metres of solids. The wastewater is moderately acidic, with a pH (measure of hydrogen ion concentration) of about 3, and contains dissolved zinc, copper, lead, iron, and sulphate ions. Ores from volcanic-hosted massive sulphides like Los Frailes may also contain trace levels of mercury and cadmium, which could be in the wastewater.

Boliden could not confirm the amount of actual metal content in the wastewater, so it was not possible to determine whether the metals were present at toxic levels. Greenpeace statements describe the discharge as “a huge tide of poisonous waste,” but Juantxo Lopez de Uralde, a Greenpeace spokesman on site, says the organization has no figures on the metallic content of the wastewater or sludges. He says the organization would be sampling river sediments at a later date, to determine their heavy metal content.

The solid material is made up of silicates and unrecovered sulphides, mainly pyrite. Press reports of an “oily black material” in areas affected by the spill probably arose from misidentification of the fine-grained sulphides in the solids. Boliden staff estimate that most of the solid material settled in the area immediately downstream from the breach, and that about 95% has been transported no more than 10 km from the dam.

The discharge from the tailings pond was stopped on April 26, by which time most of the wastewater had already flowed through the breach and into the Rio Agrio watershed. The Rio Agrio (Spanish for “Sour River”) flows over pyritic bedrock and so has a natural pH near 4 (about the same as very acidic rain). A dilution ratio of 10 volumes of river water to one of effluent at a pH of 3 would bring the pH back to natural levels.

Boliden says aerial photography shows that 20 sq. km of land had been flooded. A local agricultural association, which accused Boliden of negligence, estimated 100 sq. km had been flooded, then revised its estimate to 60 sq. km, then down to 50 sq. km. The group placed damage figures around $14 million, while Greenpeace suggested the figure might be $20 million, with a further $95 million over the next two years.

The area downstream, where the Agrio joins the Guadiamar River, is a major agricultural area, producing tomatoes, rice, wheat, oilseeds and cotton.

There are also orange and olive groves. Television coverage carried pictures of dead fish along river banks.

The company said there had been inspections by outside consultants and regulators in 1996 and 1997, and that the most recent in-house inspection took place on April 14. None of these inspections had shown any signs of instability in the dam.

In a normal inspection routine, staff would have measured the water levels in monitoring wells in and around the dyke to see whether water pressure was building up on one side of the earthwork. They would also have inspected the well casings for any deflection that would indicate the earthwork was shifting.

The principal concern during the flood was that wastewater would reach the Donana National Park, 55 km south of Los Frailes on the Guadiamar River.

Donana, a United Nations biosphere reserve and World Heritage Site, is Spain’s largest single wetland and an important wildlife sanctuary.

An emergency dyke-building program diverted the flood away from the wetland and into the larger Guadalquivir River, which flows into the Gulf of Cadiz.

Municipal governments along the Guadiamar issued warnings against drinking well water, fearing that contaminated runoff might already have reached the water table. By presstime, there had still been no figures released on the chemical composition of the surface or ground waters.

Los Frailes’ shutdown forced Boliden to declare a force majeure on its smelter contracts, which are principally with European and Japanese smelters. Enirisorse in Italy takes about 40,000 tonnes, and Norzink in Norway about 20,000 tonnes of zinc concentrate yearly from Los Frailes, which produces 125,000 tonnes of zinc — probably about 250,000 tonnes of concentrate — annually.

Spain’s attorney general, Jesus Cardenal, instructed provincial officials in Sevilla to keep his office informed on developments and said he would use “all legal means available” to determine the cause of the incident. The involvement of the attorney general implies that charges are being considered.

The local authorities have engaged consultants to inspect the dam failure.

Boliden has also hired consultants for its own investigation, including some who are sampling river waters downstream from the spill.

Boliden Aspira received its environmental permits for Los Frailes after satisfying certain conditions, including expansion of a water treatment plant and modifications to the tailings dam to control seepage. The expanded water treatment plant was deemed necessary owing to unusual climatic conditions in southern Spain in recent years, including both a drought and severe flooding, which disrupted operations at a nearby mine.

Los Frailes is in the Iberian pyrite belt, a 230-km-long belt known for its massive sulphide deposits and historic mines. The belt contains many other base metal mines, including the Neves Corvo, Rio Tinto and Tharsis.

Last year, Boliden moved its head office to Toronto from Sweden (where most of its operations are situated), after parent company Trelleborg AB sold its 51% stake in the company through a public offering on the Toronto Stock Exchange. Early this year, Boliden acquired control of Westmin Resources, a Canadian-based company with domestic and foreign projects.