Thousands of gallons of a highly toxic solution used at the Freeport McMoRan copper mine in Morenci were blocked from pouring into the San Francisco River in Clifton at midafternoon Thursday.

A small army of FMI workers descended on Clifton with earth-moving equipment and dump trucks to create dams in Chase Creek to keep the slow but steadily moving dark-green solution from reaching the confluence of the creek and river. The confluence is near the Circle K convenience store. Arizona Department of Environmental Quality spokesman Mark Shaffer said Friday morning that three investigators are in Clifton to inspect the spill and cleanup. In some places, the solution appeared to ooze down the creek rather than flow. The solution had a strong, foul odor. An unofficial source told Clifton Town Manager Ray Pini that an estimated 43,000 gallons of the solution spilled into the creek.

FMI personnel and firemen worked feverishly to spread a large load of dirt dumped into the creek bed about 100 yards from the river around 2:30 p.m. It was as far as the solution flowed.

Freeport McMoRan Morenci copper mine workers and Morenci firefighters spread dirt dumped into Chase Creek to create a dam to stop a toxic solution from running into the San Francisco River. Photo by Walter Mares

More equipment was brought in to shore up the dam and create another dam about 100 yards farther up the creek.

Pini said he was told by another unofficial source that “someone opened the wrong valve” somewhere in the mine, allowing the sulfuric acid electrolyte solution to run into the creek. The solution is used in FMI’s solvent extraction/electrowinning plant to extract copper from low-grade ore.

The valve to which Pini referred may be the control mechanism to a pipe through which Chase Creek water is routed around the mine and returned to the creek bed on the outskirts of Clifton.

The creek has been dry for several weeks. Clifton Volunteer Fire Chief Peter Ortega said, “Thank God it hasn’t been raining.” Ortega said he was puzzled that the Morenci Volunteer Fire Department was called before Clifton’s Department was notified of the spill.

One witness said she saw green water in the creek around noon. It is not known when FMI was alerted about the spill, but Greenlee County Sheriff Steve Tucker said he felt FMI’s response was “very quick.”

FMI spokesman Richard Peterson, who was contacted around 4 p.m., said he could not yet comment on the incident.

No known injuries or property damage was sustained. Clifton Police and Greenlee County Sheriff officers were at the scene to control the heavy flow of equipment and regular traffic.