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U.S. Regions
Most zinc worldwide is mined as sphalerite, replacing smithsonite (calamine), a zinc carbonate that occurred closer to the surface and is now depleted. The vicinity of Joplin, Missouri, contains the largest known deposits of sphalerite worldwide. However, in 2007, Alaska mined 83 percent of U.S. production, with other production from mines in Idaho, Missouri, Montana, New York, Tennessee and Washington. Total U.S. production was 769 thousand tons, an increase of 10 percent over the prior year. Total production for year 2007 was valued at $2.6 billion.
Largest U.S. Mines 2007
Red Dog mine was owned by Native Alaskans and operated by Teck Cominco of Canada. Greens Creek mine on Admiralty Island in Tongass National Forest was operated by a subsidiary of Kennecott Minerals of Salt Lake City. Lucky Friday mine near Coeur d'Alene, Idaho, was operated by Hecla Mining. Balmat No. 4 in upstate New York was operated by a subsidiary of Hudbay Minerals of Canada. Coy, Immel and Young mine in Tennessee was operated by Glencore of Switzerland. Pend Oreille mine in northeast Washington was operated by a subsidiary of Teck Cominco of Canada.
Worldwide
Leading national producers of zinc outside the United States in 2007 were China, Australia and Peru. Leading industrial companies recovering sphalerite worldwide were Xstrata of Switzerland (8 percent), Teck Cominco of Canada (5.8 percent), Glencore of Switzerland (5.1 percent), Zinifex of Australia (4.8 percent) and Hindustan Zinc of Udaipur, India (4.7 percent). Global production is measured as "zinc concentrate," a semi-refined product after sphalerite is milled, heated to isolate sulphur and electrolyzed to collect zinc on a cathode. Global production in 2007 was 11.1 million metric tons.
Hydrothermal Source
By 1920, sphalerite formation was described as hydrothermal crystallization on the walls of fissures in sediments associated with sulphur-bearing igneous rocks. Crystals are clear to slightly yellow in pure zinc sulfide, but sphalerite can contain impurities that darken the color. The darkest sphalerite is as much as 20 percent lead and is nicknamed "Black Jack." Other sphalerite crystals can be bluish, purple and reddish.
Bacterial Source
Redox reactions are a reduction of the amount of oxygen atoms attached to a molecule. Before Earth's atmosphere was oxidated in the Proterozoic period (about 2 billion years ago), anaerobic bacteria metabolized oxygen from metal sulfates and created less soluble sulfides. By 2000, the role of anaerobic bacteria in the redox formation of iron sulfides was widely accepted and prompted experiments where sphalerite was similarly precipitated by bacteria. Consequently, bacteria are now suggested as a source for the zinc sulfide sphalerite and for other metal sulfides found with it.