On a general scale, the hydrothermal system and subsequent mineralization developed at Midas is currently interpreted as a low sulfidation, epithermal precious-metal vein system, as part of a larger magmatic system at depth. The Midas Mine is the largest known Au-Ag epithermal deposit along the Northern Nevada Rift (“NNR”) and is located, located in the mining district of Midas, also known as the Gold Circle district. The Midas deposit consists of a series of complex steeply dipping, quartz-calcite-adularia precious metal veins hosted by volcanic and volcanoclastic rocks and locally contains mineral grades greater than (>) ten ounces per ton (opt) of gold. Gold mineralization occurs as electrum and is intimately associated with selenide and sulfide minerals. It belongs to a suite of middle Miocene low-sulfidation epithermal gold and silver mineralizing systems associated with magmatism and faulting along the NNR (Leavitt et al., 2004). The mineralization model at Midas is a shallow, low-sulfidation, vertically- and laterally-zoned, epithermal gold-silver system. Rocks in the Midas district are primarily ash flow, air-fall and lithic tuffs, felsic plugs, volcanoclastic sediments and gabbroic sills and dikes. Gold and silver mineralization at Midas is hosted in several north-west striking veins. The veins are divided into four principle groups based on their location and orientation. The two groups hosting mineral resources are the Main Veins which dip easterly and are pre ........

Longitudinal sublevel (longhole) stoping has historically been the primary mining method for the five narrow Main Veins at Midas as well as the East Veins, including 905, 9052, and 805. From the portal, there are three major haulages that access these veins through eight different spirals. Generally, upper and lower sections of the same spiral connect only through ventilation/escape raises. All mineralized material produced is hauled out of the portal in trucks to a temporary stockpile where it is loaded onto a surface haul truck and delivered to the on-site mill.

Mine development is controlled by geological conditions in the area. For the sublevel stoping method, sill development is driven at a nominal seven feet wide by twelve feet high to accommodate the size of longhole drills and two-cubic yard (yd3) loaders. Where the vein thickness is wider than six feet, the sill width is increased to capture the entire vein. Sills are typically driven 600 feet north and south from the spiral cross cut. Once sills are developed, stoping begins. Stopes are drilled with a longhole drill from the floor of one level to the back of the one below, then remote mucked from the bottom level, and finally backfilled from the top level.

Typically, the mineralized material is divided into stope blocks of about four levels for development, or 200 feet vertically. Stoping begins by creating a cemented backfill barrier pillar at the bottom level of the mineralized material bloc ........

Mineralized material from the Midas Project is processed in the Midas Mill. Material from each project is segregated through the crushing circuit. The mill has two 500-ton fine ore bins located between the secondary crusher and the ball mill, and one bin is dedicated to each mine. Head samples are taken on each reclaim conveyor at regular intervals, and tonnage measured by a belt scale prior to comingling the mineralization streams.

Underground mineralized material is hauled from the Midas mine portal to the run of mine (ROM) pad where it is placed on short term ROM mineralized material stockpiles. Typical mineralized material classifications are: low grade (less than [<] 0.3 opt gold or < 6 opt silver; high grade (0.3 to 0.5 opt gold or 6 to 20 opt silver); and ultra-high grade (> 0.5 opt gold or > 20 opt silver). Underground mineralized material is hand-picked on the pad for scrap wire mesh and rock bolts before being fed to the crusher.

Mineralized material is crushed in two stages through a 30-inch by 40-inch primary jaw crusher and 53 inch secondary cone crusher. Both jaw and secondary crusher products are fed to a six feet by 20 feet Nordberg double deck vibrating screen fitted with two-inch top deck and one-half inch bottom deck screen panels to produce a 95% passing three-eighths inch product. A continuous self-cleaning belt magnet and a metal detector are used to remove tramp metal from the crusher screen feed and to protect the cone crusher from damage. Screen undersize is conveyed to one of two 500-ton fine mineralized material bins.

Crushed and screened material is transported from the fine material bins by individual belt feeders into the 10.5 feet by 15 feet rubber lined Nordberg ball mill. The ball mill is charged with a blend of three-inch and two-inch grinding balls to maintain an operating power draw of 800 horse power (HP). Mill discharge pulp is pumped to a nest of four ten-inch Krebs cyclones (three duty, one standby) for classification. Cyclone overflow, at 85% passing 200 mesh, reports to the trash screen. Cyclone underflow reports to a two millimeter (mm) aperture scalping screen, with the screen undersize being distributed by three-way splitter to the ball mill, verti-mill, and gravity circuit. Lead nitrate solution is added to the ball mill feed chute to enhance silver leach kinetics.

A split of the screened cyclone underflow reports to the 250 HP verti-mill for open circuit grinding with the verti-mill discharge overflowing back to the primary ball mill discharge pump box. The verti-mill is charged with one inch grinding balls.

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