2011-09-27_REVISION - M1990057 (10)

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MILL DESIGN AND CAPACITY The mill is a classic concentration plant design incorporating crushing, grinding, classification, flotation and filtration circuits that is primarily comprised of vintage equipment. Tailings from the operation report to the tailings pond. Process water is reclaimed for reuse in the process. Originally the mill was designed to process 125 ton/day of Pb -Zn sulfide ore using conventional flotation technology. Later the mill was reconfigured to recover metals exclusively using gravity and magnetic separation. The gravity and magnetic concentration circuits, comprised of jigs, tables and a wet magnetic separator, has since been removed, and the mill process again uses a conventional flotation circuit technology. The mill will process gold, silver, lead, zinc, copper sulfide ore hosted in quartz monzonite. The mill produces a single (bulk) gold, silver, lead, zinc, copper concentrate. The plant is anticipated to operate at the rate of 8 ton/hr ore throughput using three -8 hour shifts per day for a 20 -shift cycle with the 21 shift reserved for maintenance. With additional downtime and operational delays, this mill in the current configuration will operate at 160 tons /day or 56,000 ton/year. The RoM ore ( -1/2 ") from the Cross mine in Nederland, Colorado is delivered to the mill by truck. The mill will contract with local trucking contractors for the hauling of the ore from the Cross mine to the mill. The material will be hauled in conventional over - the -road (OTR) highway truck - trailer units, complying with county, state and federal Interstate highway hauling requirements. Similarly, the mill loads the concentrates on contracted haul trucks for transportation to the smelter. Existing Crushing Circuit Material will be dumped directly from the OTR trucks into a 35 ton capacity coarse ore bin prior to feeding the crusher circuit. Upstream of the crusher is a vibratory screen designed to screen out 3/8" minus material bypassing the crushing circuit. The crushing circuit is composed of a 9 "x15" jaw crusher, which discharges directly into a roll crusher (16" x10" face). RoM ore will report to the vibratory screen where approximately 25% of the mass will report to the jaw crusher as oversize and 75% to the ball mill feed conveyor. The jaw crusher will be set to a closed side setting of approximately 0.5 ". The product from the jaw crusher will report directly to the secondary roll crusher. Product from the roll crusher will join the screen undersize to be conveyed to the ball mill feed bin. The ball mill feed bin has a maximum capacity of 120 tons. Dust control will be managed in the crushing plant by use of an exhaust air system which will draw air down through the crusher away from the crusher operator. Pollutants from the screening, primary, secondary crushing, material transport and fine ore storage operations are limited to fugitive pm. Negative pressure ventilation, direct venting to the cartridge dust collector, controls the flow of fugitive pm during the screening and crushing operations. The proposed unit is estimated to operate at 3500 -4500 ft/min (fpm) of air flow. The dust collector is rated at 2500 cfm. The unit handles 28.2 tons /year crushed ore fugitive pm and an additional 0.4 ton/year reagent fugitive pm for a combined 165 lb /day at a 99.8% published efficiency. The captured .dust will be collected in drums and returned to the material flow at the grinding mill. M1990 -057 September 27, 2011