By LUIS ANDRES HENAOSANTIAGO, Chile (AP) â¿¿ Just how to define a glacier is at the heart of a Chilean congressional battle that could determine the future of mining in the world's largest copper-producing country. The revival of legislation to ban mining in glacial areas is spawning debate among miners, farmers and environmentalists about how to protect both vital water supplies and Chile's mining industry. If the bill passes, mining experts fear it could shutter multibillion-dollar mining projects and slow investment. The key will be in the fine print of whether the final bill defines glaciers as including frozen areas around them, too, and whether the protections would apply retroactively to mines already operating next to glaciers. "If it passes as a law with tough conditions, it could harm not only the operation of current projects but also future projects," said Juan Carlos Guajardo, head of the Chilean mining think tank CESCO. "Depending on the conditions, the scenarios would make mining activity very difficult in high mountain areas." Environmentalists point to the crucial role played by glaciers in protecting Chile's water as reason enough to implement the wider definition. A glacier is snow that has compacted into ice and that survives the warm summer months. Glaciers are important because they act as natural dams, storing water for use throughout the year after the winter snow has melted. Even small glaciers can hold gigantic amounts of water that become critical during warm months and especially in long dry spells. Argentina, across the Andes mountains from Chile, adopted a law in 2010 that broadly defines glaciers â¿¿ theoretically protecting not only the icy masses most people think of, but also "rock glaciers" and frozen groundwater on mountaintops where glaciers have melted away from the surface. The Argentine National Glacier Institute, which had a heavy hand in drafting Argentina's law, pushed the definition because it's believed most glacial water actually comes from such reserves.