Kazakh workers start copper mine sit-in
* Workers at Kazakhmys mine refuse to return to surface
* Some 80 miners protesting, source says
* Security tightened at mine; 2011 oil strike turned violent
By Mariya Gordeyeva
ALMATY, May 5 (Reuters) - Copper miners in Kazakhstan went on strike on Saturday, staying inside a mine owned by Kazakhmys to demand higher wages from their employer in a move likely to unnerve authorities in the Central Asian state just months after deadly oil town riots.
Some 80 miners at the Annensky mine in central Kazakhstan refused to return to the surface after a shift that began on Friday, a company official told Reuters by telephone, requesting anonymity.
Kazakhmys, the world's 11th-largest copper producer, which trades on the London Stock Exchange and is in the FTSE 100 index , said in a statement that work at the mine had been disrupted but that the miners had not made any official demands.
The company said it understood that the strikers were seeking a wage increase for workers carrying out basic tasks at the mine such as drilling.
Authorities in Kazakhstan, a former Soviet republic of 16.7 million people, are especially wary of labour unrest in single-industry towns after a months-long dispute by sacked oil workers last year erupted into the country's worst violence in decades.
At least 14 people were killed in clashes in December when police used live rounds against protesters in the remote oil town of Zhanaozen. The unrest posed the most serious challenge to President Nursultan Nazarbayev in his more than 20-year rule.
The company source said security had been tightened around the copper mine's explosives warehouses.
Kazakhmys said it had brought in officials from the nearby town of Satpayev to participate in discussions and urged workers to open negotiations.
It said it had increased salaries across the entire group, including miners' salaries, by an average of 20 percent in 2010. Since February 2011, it had offered performance-related bonuses of up to 15 percent, it said.
The company source said the average monthly salary for Kazakhmys miners was around 240,000 tenge ($1,622), nearly three times the national average.
Annensky is one of six underground mines operated by Kazakhmys near the city of Zhezkazgan, an area of central Kazakhstan that contributes about 70 percent of the company's mined ore. It also operates one open-pit mine nearby. (Writing by Robin Paxton; Editing by Robin Pomeroy)