2021-12-07_REVISION - M2012032 (25)

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Blasting is not expected to impact surface structures. Little to no vibrations would be felt at the surface from underground blasting due to the size of the blasts and the distance to the surface. OSMI calculated the Peak Particle Velocity(PPV) for a variety of blasting scenarios. The closest OSMI would mine to the surface would be 50 feet. The PPV at that distance would be 17-20 mm/s,which is the lower limit that a drywall structure could be damaged. There are no structures planned that would be located above the areas where blasting will be taking place. Typical blasting scenarios would be more than 200 feet from the surface,would be barely detectible, and would only last for a one to two seconds. 3.6 Ore Handling Ore is delivered directly to the underground mill.No ore will be stored on the surface. The mill will process approximately 120,000 tons of ore per year. Details of the mill process are discussed in in Section 4 of this Exhibit D. Mill certification documentation was provided to DRMS as part of TR-15. Concentrate will be packed in super sacs and transported to the surface through the mill tunnel via skid steer equipped with forklift or forklift and hauled off site for direct sale using highway trucks. 4 MILL OPERATIONS The general process flow of the mill is described below. More detailed descriptions of the mill operations may be found in TR-15. The Revenue Mill is designed as an underground mill with a 540 ton per day of ore capacity. The Mill area excavations (four tunnels that constitute the mill complex)include: 1) The mine car unloading tunnel and coarse ore bin with slusher; 2) The crushing gallery with conveyor leading to the mill tunnel(fine ore bin incline), 3) The mill tunnel,which contains two flotation circuits (lead and zinc) and leads to the filter building at the outside edge of the mill tunnel; and 4) The decline tunnel,which provides equipment access to the crushing gallery from the mill tunnel. The original mill was designed by CH2MHi11 in Denver, Colorado based on ore samples and production targets for the mine and mill. Tunnel excavation began in March of 2013. Installation of mill concrete flooring, crushers, screens,ball mill,flotation cells,water handling systems,filter presses,control room, reagent storage, and electrical room equipment occurred in April of 2014. Barr Engineering of Minneapolis, Minnesota redesigned the mill in 2017 under OSMI direction. Mill upgrades were necessary to improve ore recovery. TR09 permitted replacing the previous single stage jaw crusher followed by a cone crusher with two-stage jaw crushers and a rod mill to prevent clogging with fines. The original cyclone circuit was inadequately sized to achieve the correct operating pressure given the expected tonnages;the screens that were approved under TR-09 are not reliant on operating pressure. Changes in the flotation system were also needed based on two years of successive metallurgical testing, which proved that changes in reaction time and reagents will improve metal recovery from the ore. As permitted in TR-09,the mill filter building was expanded to house a compressor room and reagent room as well as a small roof structure over the transformers near the mill entrance. A simplified flow diagram that outlines the milling process is found in Figure 1. A detailed flow diagram of the milling process is found in drawings that were submitted to DRMS as part of TR-15. Revenue Mine Amendment 02 D-8 December 2021