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• • iii iiiiiiiiiiiii iii <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Deparlmem ul Nalu rul Resources <br />1313 Sherman SI ,Room ?1 S <br />Denver, Colorarlu 8U?U3 <br />Phone: ~3U31 866-35fi7 <br />FAX: (1031 83_'81 U6 <br />DATE: October 28, 1996 <br />TO: Berhan Keffelew <br />FROM: Jim Pendleton / ~ ~' '~/~~- <br />RE: Cripple Creek & Victo old Company <br />"Miscellaneous cedures and Other Items <br />Related To Operations and Construction" <br />(Permit No: M-80-244) <br />II~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Roy Romer <br />Governor <br />dames 5. Lochhead <br />Eeecmive Director <br />Michael B. Lang <br />Division Dueclor <br />I have reviewed Mr. Hardaway's letter bearing the above "Reference". I offer the following <br />comments for your consideration. <br />111 Biologically-Assisted Cyanide Destruction <br />As John states, biologically-assisted cyanide destruction has been successfully applied <br />by Homestake Mining at the Leeds project. Terry Mutter, along with many cohorts, <br />spent years working on the process and its related environmental impacts and <br />benefits. A similar proposal was bench tested for possible application at the <br />Summitville mine clean up site. The process proved very effective at reducing cyanide <br />in the columns. Interestingly, sulphide minerals were precipitated within the test <br />columns. A concern developed relating to whether these sulphide minerals might <br />represent contaminant sources if the pile were to reacidify for any reason. Because <br />the Summitville pile proved to have been effectively detoxified by test flushing the <br />process was never applied and the additional investigations never completed. One of <br />the considerations leading to the decision to forego bio-detoxification of the <br />Summitville heap leach pile involved the relatively high cost of the procedure. <br />In any case, CC&VG will have to perform bench scale tests before any "trial basis" <br />applications were attempted on a field scale. When CC&VG believes the time is <br />appropriate it should submit an appropriate amendment application, including <br />specification of appropriate bench scale and field scale testing protocols. CC&VG will <br />also have to provide an appropriate cost evaluation to allow appropriate adjustment <br />of its surety for the permit. <br />