Chile will invest 875 million U.S. dollars to transform the world\'s largest opencast copper mine into a subterraneous one, state-owned mining giant Codelco said Wednesday. The project will allow for the exploitation of a part of the existing reserves, which have been calculated at about 1.7 billion tons of copper and molybdenum, more than 60 percent of the total volume exploited in the last 90 years, it said in an on-line statement. The expected output of the subterraneous mine will be similar to the El Teniente mine in central Chile, which is considered the largest mine in the world. The subterraneous operation is the only workable solution after the opencast mine lost profits a few years ago, mostly due to an increase in transportation costs. Codelco accounts for almost 9 percent of the world\'s entire copper production, and expects its 2011 output to reach 1.7 million tons. Copper is Chile\'s main export product.