About 12 years ago or so, I had the opportunity to visit the PD copper refining facility in El Paso, TX. The surprise was seeing their narrow-gauge railroad on the premises. I'm guessing it was about 2' gauge with Plymouth-looking gas locomotives and small hopper-like cars for transporting electrodes around. It was very much an active industrial line within the plant though I did not see any moving trains the day of my visit.
There was also an impresssive water tank on the premises holding half million to a million gallons of water for fire-fighting contingencies.