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Mr. Peter Hays, DRMS <br /> January 14,2015 <br /> (c) The contact person for this event is: <br /> Tim Haynes <br /> 19302 County Road 3, <br /> Parshall, CO 80468 <br /> Phone: 720-942-3518 <br /> timothy haynes(afmi.com <br /> (d) No monitoring or analyses were performed for this situation since process water and/or <br /> material was not released off-site and did not impact waters of the United States. <br /> (e) Following an in-depth investigation conducted by tailing engineering, operations, <br /> management and the environmental department, Henderson has concluded that <br /> operational factors and flows were the primary contributor to this incident. Henderson <br /> Operations is currently realizing an overall decrease in the ore concentration of <br /> molybdenum disulfide feed from the mine. To counteract this decrease, increased <br /> throughput has become a necessity to meet operational targets. With regard to the <br /> actual cause of this issue, Henderson staff believes that varied cyclone operation, <br /> supplemental water and designed concentrate thickener overflows are collective factors <br /> contributing to this event. <br /> Prior to increased throughput efforts, it was typical to run four primary mills with three <br /> cyclones operating on each mill's cyclone bank. Three cyclone operation provides a finer <br /> grind, but slows throughput due to increased circulation of material through the primary <br /> mill circuits prior to the milled slurry continuing on to rougher flotation, the next step in the <br /> process. To increase throughput, a two-cyclone configuration is used, which will move <br /> ore through the primary milling circuit more quickly, but the coarser grind, when <br /> introduced to the rougher flotation circuit can create "sanding" issues (sanding - milled <br /> material settling out of slurry solution quickly and effectively stopping the flotation <br /> process. In extreme cases, it completely overpowers a rougher cell, which then must be <br /> manually excavated). To combat sanding issues in the rougher circuit, supplemental <br /> water must be added to ensure that the overall percent of solids in the slurry solution <br /> stays sufficiently low. This is where we believe excess flow volumes is coming from. <br /> When a rougher cell is in jeopardy of sanding, supplemental water is added to the <br /> rougher cell (either from recycled thickener overflow when available, or from incoming <br /> mill water), which in turn increases the overall flow volume out of the tailing line. <br /> To manage this issue, Henderson went through a step test with our mills, which involved <br /> starting with all of the primary mills running with three cyclones per mill in operation. <br /> Over the course of a run weekend (Friday Jan 9th— Monday Jan 12th), operations brought <br /> one mill down to two cyclones, watched the flow and pressure curves, then brought a <br /> second mill down to two cyclones. This was done while closely monitoring the TDL flow <br /> and pressures. At present, we have been able to meet production demands, while <br /> running two mills with three cyclones and two mills with two cyclones. Henderson's <br /> operations and tailing engineering group will continue to monitor these trends, while <br /> minimizing excess water input to the circuit, where possible. <br /> Additional engineering controls being contemplated at this point include surge protection <br /> measures, which at present may include a surge overflow conduit from the thickener <br /> overflow tank inside of the mill, or a high-level surge spillway which automatically diverts <br /> surge flow from the mill into the Emergency Cut Out line at the tailing distribution box <br /> (diversionary structure where mill tailing flow is either diverted to the TDL or the <br /> Emergency Cut Out line). If necessity dictates that an engineering control be put in <br /> Page 2 <br />