The miners demand better redundancy payouts, a union official said.
The South African-listed miner held off expansion of the Sadiola mine and suspended excavation at Yatela last year, citing higher operational costs and lower gold prices.
Gold prices have fallen from a record 1,920.30 US dollars an ounce in 2011 to about 1,275.90 US dollars, prompting mining firms to consider suspending or halting projects.
Alfouseyni Toure, Secretary General for the civil engineering, mines and energy labour confederation Synacome, said by midday on Monday, 70 percent and 95 percent of workers had downed tools at Sadiola and Yatela respectively.
Another union representative said about 2,000 people in total are employed at both mines. According to AngloGold's website, it employs about 783 people in Sadiola and 407 in Yatela.
"The company told us that because of the crisis and the fall of gold prices, they are forced to lay off workers, which we accepted. What we are demanding, is a redundancy package for the laid-off workers," Toure told Reuters in Bamako.
"In the package, we asked for 36 months of salary plus 1 million CFA francs for medical care for every laid-off worker, but the company has remained deaf to this demand, that is why we have embarked on a strike," he said.
Toure said AngloGold had offered to pay each employee seven days' worth of salary for every year worked.
AngloGold, which jointly operates both mines with Toronto-listed IamGold, was not immediately available for comment.