About 4,200 workers at Freeport McMoran Copper & Gold Inc's Indonesian mine, mainly contractors and nonunion staff, have returned to work, allowing some mining to resume, but around 8,000 remain on strike, the firm's spokesman said on Monday.

Spokesman Ramdani Sirait declined to comment on the impact on production and shipments after around half the workforce returned from the strike at the world's third-largest copper mine, which has limited mining, milling and concentrate shipping activities.

Freeport has a total workforce of about 23,000, thousands of whom began a one-month strike at the Grasberg mine on Sept. 15.

Up till Sunday, around 4,200 workers have returned to the highlands. Mobilising materials from the open pit mine and underground mining have started operating as well as plant activities, Sirait said in a text message to Reuters.

Union officials met in the capital Jakarta to keep up pressure on Indonesia's parliament following a deadlock in tripartite talks involving the government. Workers have threatened to extend the strike beyond one month.

The Freeport union wants higher pay and says other Freeport workers around the world get paid 10 times as much. Workers have demanded a pay rise to between $17.5 and $43 per hour, from a current $1.5 to $3 an hour rate.

We refuse to continue mediation as we're deeply disappointed with the management stance that doesn't want to change the value that we asked for, union official Juli Parorrongan told Reuters on Monday.

The strike may also have been spurred by record prices for gold , given that Grasberg also has the world's biggest gold reserves, though prices have dived almost 20 percent since hitting a peak on Sept. 6.

The stoppage has stirred concerns over a broader push by workers for a greater share of profits in Southeast Asia's biggest economy. Pilots and supermarket staff have also recently gone on strike.

The copper market extended losses on Monday on fears of global recession following Greek default. Three-month copper on the London Metal Exchange fell 0.7 percent to $7,307.75 a tonne by 0352 GMT after tumbling to its lowest since Aug. 25, 2010, in the previous session.

Based on the mine's daily production target, the strike has potentially cut output of 230,000 tonnes of copper ore per day, a government official had previously said.