The county Board of Supervisors has approved a conditional-use permit for the 13-acre site near the mine, above.

A.E. Araiza / Arizona Daily Star 2011

The parent company of Asarco Mission Mine is looking to make another major investment at the site near Green Valley.

The Kotmatsu America Corp. wants to build a roughly 13-acre equipment-testing facility close to the open-pit copper mine. No dollar figure for the project was given.

In filings with Pima County, company officials said the site will be used by its research and development division to test new machinery.

The company was operating a similar facility nearby at the Twin Buttes Mine in Green Valley, but a change in that mine’s ownership is forcing Kotmatsu/Asarco to relocate. (Freeport-McMoRan bought the long-closed Twin Buttes Mine site, near Sahuarita, for $200 million in 2010.)

References to a planned 63,000-foot “truck shop facility” suggest Kotmatsu/Asarco will be testing the next generation of the massive mining trucks used to haul ore.

Last week, the Pima County Board of Supervisors approved a conditional use permit for the site, the first in a series of approvals needed to move forward on the project.

A representative of the mine told the board the new facility would trigger the hiring of more engineers and bring other high-paying jobs to the site.

About 660 Mission Mine employees earn an average take-home pay of more than $62,000 per year, plus benefits, the company says.

A spokesman for Asarco, Tom Aldrich, did not return calls seeking additional details on the proposal filed with the county.

A public hearing on the proposed facility was lightly attended, mostly by nearby property owners, said Tom Drzazgowski, the deputy chief zoning inspector for Pima County.

No one at the hearing was in direct opposition at the time, Drzazgowski said.

Many residents focused on questions about hours of operation, potential air pollution and dust control, traffic on Mission Road, potential impacts on water quality and light pollution as well as impacts on a nearby scenic corridor, he said.

Many of those issues will be answered when Asarco files detailed engineering reports and architectural renderings with the county as part of its request for a building permit.

However, mine officials already have said the facility will operate primarily between 6 a.m. and 7 p.m. during the week, unlike the round-the-clock operations of the Mission Mine.

The company could break ground on the equipment testing facility as early as next year.

Earlier this month, Tucson-based Asarco finished the expansion of the south mill at the Mission Mine. The $60 million project adds 9,000 tons per day of crushing and milling capacity.

Since 2010, Asarco has invested an average of $120 million per year in its mining and processing units in the United States.