High zinc prices, as well as high by-product metal prices, encouraged an increase in mine supply in 2007. They also lead to an increase in exploration activity, both greenfield and in the vicinity of existing operations. Moreover, they made it economic to mine low-grade ores, and allowed companies to reduce the cut-off grades that they employ when calculating their mines' reserves. We have collected production and reserve figures from 56 mines for which firm figures are available (in some cases they are mid-year numbers). This sample excludes mines that did not operate continuously in both 2006 and 2007, and specifically ignores Antamina and Golden Grove because head grades at these mines typically fluctuate as operations shift between copper-rich and zinc-rich ores
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