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iii iuiiiiiniu iii <br />BATTLE MOUNTAIN GOLD COMPANY <br />ANDRE J. DOUCHANE <br />GENERAL MANAGER <br />NORiII AMERICAN OPERATONS <br />April 1, 1992 <br />i <br />_., <br />BYRE MOUNWN <br />GOLD COMPANY <br />Mr. James C. Stevens ~ ~ ~, ~- ~ ~ ~ ~ <br />Geohydrologist <br />Colorado Mined Land Reclamation aP13 ~ 19y~ <br />Division <br />1313 Sherman St. f~l11eG ~anU <br />Denver, CO 80203-2273 Reclamation nl...l 1,, <br />Re: Permit M88-112 Technical Revision Kp_~' <br />Dear Mr. Stevens: <br />Thank you for your time to meet with Matt Lewis to discuss <br />the tailings detoxification system (AVR) at the San Iluis mine. <br />As you arp aware, cyanide concentrations in the tailings pond <br />are greater than originally anticipated at the time tine permit <br />application was approved. In general, BMR beleives the higher <br />concentrations are attributed to differences in ore <br />characteristics. Additionally, there are some indications that <br />natural cyanide degradation in the tailings pond may not be as <br />significant as previously predicted during winter cornditions. <br />The original ore test program is still valid for the bulk of <br />the ore, with the exception of a potential increase in copper <br />contained in the ore. To immediately respond to this <br />situation, BMR has requested approval to utilize zi>r~c ferrous <br />sulfate as a detoxification reagent. The sulfate will be added <br />to the slurry line prior to the AVR system in either d solution <br />or dry state form. The initial application strength will <br />provide excess free cyanide detoxification capacity 8or use in <br />the pond. The sulfate concentration will then be reduced to <br />the level necessary to detoxify the fresh tailings slurry to be <br />placed in the tailing facility. We expect the complete system <br />to be detoxified of free cyanide in approximately 14 days. The <br />collection pond below the main embankment will be detoxified <br />immediately upon CMLRD approval by directly adding the sulfate <br />to the lined conveyance ditch which carries flow from the drain <br />blanket to the collection pond. <br />The sulfate addition will reduce the concentrations of <br />free cyanide in the pond. A substantial reductign in WAD <br />cyanide levels will require potentially longer term treatment, <br />which BMR is currently evaluating. BMR believes that the <br />5670 GREENWOOD PLAZA BLVD. SUITE 106 ENGLEWOOD, CO 80111 (303) 7216744 FAX (303) 72t~813 <br />