By LUIS ANDRES HENAOSANTIAGO, Chile (AP) â¿¿ Chilean state-owned mining company Codelco has resumed shipments of copper after a port strike blocked exports in the world's top copper producing nation, the company's CEO said on Monday. Port workers returned to work after reaching a deal to end three weeks of strikes that halted shipments of copper, fruit and wood pulp in the export-dependent nation. The strikes caused serious concerns because Chile produces a third of the world's copper and its solid economy is built around mineral exports. "We retook normal shipments of our production, of all refined (copper) on Saturday," Chief Executive Officer Thomas Keller told foreign correspondents. "It will take us about 30 days to reach a normal level." About 60,000 metric tons of Codelco's copper was stuck at port and the company lost more than $500 million since the strike began. Copper alone accounts for roughly a third of government revenue, and the state has a policy of shoring up national reserves during periods of high prices. Mining also offers many of Chile's poor their best chance at a middle-class life, especially in the rural and rugged desert areas in the north, where most mines are located. Labor unions at Codelco and private mining companies plan to announce a national strike for Tuesday. Keller said the stoppage might have a "marginal" effect, but he doesn't expect increased labor unrest ahead of November's presidential elections to affect copper output. Chile will remain a competitive leader against metals-producing countries like neighboring Peru, despite energy shortages, dwindling ore grades and high costs, Keller said. "The best way to predict production at a long term is the efforts made in exploitation," he said. "And Chile continues to be the country that by far attracts the most resources for exploitation." Chile's energy-intensive mining industry is clamoring for more power. Some analysts say the power-strapped Andean country must triple its capacity in just 15 years, despite having no domestic oil or natural gas. Chile imports 97 percent of its fossil fuels and depends largely on hydropower for electricity, creating a crisis when a drought drains reservoirs or a far-away dispute affect fuel imports.