UPDATE 1-New Caledonia allows conditional restart of Vale nickel mine
* Vale nickel plant at Goro closed early May after acid leak
* Spill sparked violent protests causing more than $20 mln in damage
* Goro nickel plant has troubled history with spills, protests
* World nickel prices up strongly this year on supply concerns (Adds quotes, detail on statement)
By Cecile Lefort
SYDNEY, June 2 (Reuters) - New Caledonia authorities said on Monday they have authorised a conditional restart of Brazil-based Vale's nickel operations, which were suspended more than three weeks ago after acid-tainted effluent spilled into a river.
The leak sparked violent riots by young Melanesians that caused more than $20 million in damage to buildings, equipment and vehicles and left three policemen with gunshot wounds.
Police remained on alert as protesters maintained a presence near the plant.
"The situation is calm and some (protesters) are still camping near the plant," said a local government spokeswoman. Continuación...