* Key mines halted in world's top copper producer
* Outage may pressure struggling President Pinera
* Power blackout hits most populated regions of Chile
* Energy restored in at least one area of capital
* Collahuasi unaffected
By Moises Avila (Recasts, adds lights coming on in Santiago, El Teniente)
SANTIAGO, Sept 24 (Reuters) - A massive power blackout paralyzed crucial copper mines in Chile on Saturday and darkened vast swaths of the country including the capital Santiago before energy started to be restored, officials said.
The outage acutely exposed the fragility of the energy grid in the world's top copper producer, which was devastated by a powerful earthquake in 2010.
Critics have blamed Chilean President Sebastian Pinera for under-investment in infrastructure and his popularity ratings have dropped since taking office last year. Prior to the power failure, he has already struggling with massive protests by university students demanding deep educational reforms.
Engineers scrambling to restore power were able to get the lights turned on in at least some districts of Santiago and at the sprawling El Teniente copper mine of state-owned Codelco, officials and Reuters witnesses said.
Chilean Energy Minister Rodrigo Alvarez said the cause of the failure was unknown but that computers that help run the energy grid had also malfunctioned.
"This affects the fourth and seventh region, or much of the country's most populous area," he said on state TV. Those regions include about 10 million people in the center of the country.
Angloamerican (AAL.L) said operations at its Los Bronces mine was halted by the blackout and state-run Codelco said its Andina division was also paralyzed.
Authorities said the Collahuasi and Chuquicamata mines in the far north of Chile were not affected and that the power outage did not extend to them. (Reporting by Moises Avila; editing by Todd Eastham)