Carlin district in Nevada. Homestake was the longest continually operating mine in United States history. The Homestake mine ceased production at the end of 2001. Reasons included low gold prices, poor ore quality, and high costs. Conversion to use for scientific research The Barrick Gold corporation (which had merged with the Homestake Mining Company in mid-2001) agreed in early 2002 to keep dewatering the mine while owners were negotiating with the National Science Foundation over the mine as a potential site for a new deep underground laboratory (DUSEL). But progress was slow and maintaining the pumps and ventilation was costing $250,000 per month. The owners switched the equipment off on June 10, 2003 and closed the mine completely. The Homestake Mine was selected in 2007 by NSF for the Deep Underground Science and Engineering Laboratory (DUSEL). In June 2009, researchers at University of California Berkeley announced that Homestake would be reopened for scientific research on neutrinos and dark matter particles using DUSEL and Large Underground Xenon experiment. Research into enhanced geothermal systems is being prepared in the mine. Geology The gold at Homestake is almost exclusively confined to the Homestake Formation, an Early Proterozoic layer with iron carbonate and iron silicate. The original 20–30 m thick Homestake Formation, has been deformed and metamorphosed, resulting in upper greenschist facies of siderite-phyllite, and lower amphibolite facies of grunerite schists. The iron may have been deposited by volcanic exhalation, perhaps in the presence of microorganisms as a banded iron formation. Gold ore mineralization is most intense in the Main Ledge, at the surface, and the 9 Ledge, at the 3200 level (feet below the Incline Shaft, at 1594 m above sea level). See also Colorado Mineral Belt, regarding the Henderson Mine Volcanogenic massive sulfide ore deposit (VMS), the base-metal rich equivalent to Homestake References Further reading External links Homestake mine visitors center website Sanford Underground Laboratory at Homestake Homestake DUSEL Black Hills Geology photo album, mostly of the mine area, by geologist James St. John Black Hills Gold mines in the United States Buildings and structures in Lawrence County, South Dakota Surface mines in the United States Underground mines in the United States Former mines in the United States Mines in South Dakota Tourist attractions in Lawrence County, South Dakota Stamp mills 2002 disestablishments in South Dakota