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1 <br />BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT <br />CMLRD ADEQUACY LETTER RESPONSES <br />Page 1 of 28 <br />EXHIBIT D, MINING PLAN <br />' 1. On page D-]4, reference to a "dilute cyanide solution" is made in <br />discussing the carbon-in-]each method of ore processing. What is the <br />expected concentration of cyanide in this process solution? <br />RESPONSE: The expected concentration of cyanide in the carbon-in-leach process <br />solution is 0.5 to 0.75 lbs per ton of ore. The solutions are <br />expected to have total cyanide levels of approximately 175 ppm and <br />free cyanide levels of approximately 60 ppm. As described on page <br />D-16, these solutions are contained in sealed tanks only. <br />Additionally, the mill design includes internal curbing and a <br />' solution collection system to further ensure containment within the <br />mill in the unlikely event of a tank leak (see response to question <br />5). <br />1 2. On page D-16, reference is made to use of sulfuric acid in treating <br />the tailings scurry prior to disposal. An equilibrium diagram is <br />provided to indicate that 70% of the cyanide will be volatilized at <br />' pH 9. What is the expected concentration of free cyanide in the <br />treated slurry solution? <br />' RESPONSE: Laboratory test methods currently available do not allow for an <br />accurate and consistent determination of free cyanide. free cyanide <br />is unstable at the pH of the slurry and difficult to measure and the <br />test method is subject to interference from other elements. Total <br />' and weak acid dissociable cyanide tests provide a more reliable <br />indication of cyanide present in a solution. BMR performed laboratory <br />testing to evaluate total, weak acid dissociable and free cyanide <br />' present in the slurry solution. The data shows total cyanide values <br />of 4.4 ppm and weak acid dissociable cyanide values of 3.8 ppm. The <br />data also indicated free cyanide values of 52.0 ppm, weld in excess <br />' of the total and weak acid dissociable values and, therefore, <br />physically impossible. In this case, web that thi <br />he testin a more reliable to al and weak <br />acid dissociable cyanide es s indicate that actual fhee c anid <br />levels in the tailings slurry are below 4.4 ppm. e a oh~atory est <br />~a is inc u e as Attachmen an wi e a ed to Appendix F of <br />the permit amendment application. Humidity cell testing is ongoing, <br />' however, preliminary test results as well as test results from the <br />approved permit indicate that the San Luis ore is not acidic. <br />t <br /> <br /> <br />