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Principal forms in which copper ores are found include native copper, porphyry copper, massive deposits, and mixed ores. Native copper is simply the metal found unadulterated in nature. Occasionally copper is still found in its native form, but more frequently it is mixed with other minerals, some of which may have value themselves. The amount of copper in an ore can vary from 0.4 percent to more than 12 percent. Porphyry copper deposits, in which the copper materials are more or less uniformly scattered throughout the rock, account for the greatest tonnage of metal in the producing areas of the ...(100 of 4534 words)