SANTIAGO, Feb 26 (Reuters) - Chile's power grid and

major copper mines slowly came back online on Wednesday morning

after a major outage hit the world's top producer of the metal,

with power firms working to restore the system to full

operation, authorities said.

The power outage, caused by a transmission line failure in

northern Chile, struck mid-afternoon on Tuesday, plunging most

of the country into darkness and knocking out electricity to

major mines, buffeting global metal markets.

In an early morning report on Wednesday, Chile's National

Electricity Coordinator (CEN) said that more than 90% of

residential consumption had been restored, though there were

reports of intermittent power in some cities.

"Both the incident and its impact are a cause for worry,"

Interior Minister Carolina Toha told a press conference, noting

that a number of safety nets failed and other power stations

failed repeatedly when trying to come back online.

The failure was attributed to energy distributor ISA

Interchile, a subsidiary of Colombia's ISA, which is owned by

state oil company Ecopetrol.

Local media said that ISA Interchile issued a statement

blaming the outage on an "unwanted operation of protection

systems", adding that it would investigate the cause.

Toha said that an official state of emergency and curfew in

place since 10 p.m. on Tuesday had been lifted. She said that

about 220,000 users remained without power, mostly in the north,

down from 8 million homes affected by the outage at its peak.

Major copper mines also started to come back online on

Wednesday.

Anglo American said its Los Bronces and El Soldado

mines, as well as its Chagres smelter, in central Chile were

restoring operations on Wednesday morning.

Chile's Codelco, the world's largest copper producer, said

that operations at all its divisions were gradually coming back

online. Antofagasta ( ANFGF ) also said its operations had resumed.

Other mining companies had yet to provide an update on the

status of their operations. Santiago's subway service announced

that it would resume services on most of its lines and stations.