The origin of the wide variety of mineralization occurrences at Hangar Flats, West End, and Yellow Pine deposits is enigmatic and past workers have attributed the District metal endowment to deep seated intrusives and associated deep high temperature and high pressure processes as well as shallower lower temperature, lower pressure hydrothermal processes within an epithermal environment. However, there is no single deposit model applicable to the deposits within the District that have been discovered to date.

Mineralization occurs in numerous locations throughout the District in medium- to coarse grained, felsic to intermediate intrusive host rocks and typically occurs as disseminated replacement mineralization within structurally prepared dilatant zones or adjacent to district and regional-scale fault zones. Mineralization also occurs associated with sheeted veins, stockworks, endoskarns, and complex polymictic breccias. In the metamorphosed sedimentary rocks, mineralization occurs associated with dense fracture zones in structurally prepared sites and as stratiform manto-style replacements in reactive carbonate and calcareous siltite and schist units, as well as in cross-cutting breccia veins and dikes.

Field observations, petrographic studies, metallurgical studies, and process mineralogy studies indicate that there were likely multiple stages of mineralization, possibly separated by extended time periods. Early higher temperature, precious metal-rich mineralization with a potential magmatic fluid source was overprinted by younger, lower temperature Au and Sb-Ag mineralization; this was again overprinted by later epithermal mineralization involving meteoric water input into the hydrothermal system with a distinctly different style and geochemical signature.

The gold mineralization at the Hangar Flats and Yellow Pine deposits occurs in intrusive rocks associated with the Atlanta Lobe of the Idaho Batholith. Strong mineralization is localized along an overall north to south striking fault zone and also along northeast striking splay faults and dilatational fault jogs. Dilatant zones have generally provided conduits for movement of mineralizing hydrothermal fluids. Multiple episodes of fracturing have allowed multiple episodes of hydrothermal mineralization.

The gold mineralization at the West End Deposit occurs in metasedimentary rocks intruded by the Idaho Batholith and also within the intrusive rocks. The metasediments occur as pendants and xenoliths within the intrusive rocks. Strong mineralization is localized along a northeast striking fault zone and splay faults that strike northeast and east. Pull-apart fracturing along dilatant northeast fault jogs and splays provided conduits for movement of mineralizing hydrothermal fluids. Multiple episodes of fracturing allowed multiple episodes of hydrothermal mineralization.

Intrusive hosted precious metals mineralization typically occurs in structurally prepared zones in association with very fine-grained disseminated arsenical pyrite (FeS2) and to a lesser extent arsenopyrite (FeAsS). Base metal sulfides are uncommon. Arsenical pyrite is the primary host for gold mineralization, and gold only rarely occurs as discrete particles and, if so, typically only in rare sub-micron size particles, but the vast majority of the gold instead occurs in solid solution within the pyrite crystal lattice. Arsenopyrite is the only other significant gold-bearing sulfide mineral in the intrusive hosted deposits. Base metals (except for arsenic, antimony, and tungsten) are rare and occur at very low concentrations, at or below typical crustal abundance levels. Various oxidized products of the weathering of the primary sulfides are found in the intrusives, including goethite, hematite, jarosite, and scorodite and host precious metal mineralization in the oxidized portions of the deposits.

Antimony mineralization occurs primarily associated with the mineral stibnite (Sb2S3). Other antimony-bearing phases include miargyrite (AgSbS2), gudmundite (FeSbS), chalcostibite (CuSbS2), tetrahedrite [(Cu, Fe)12Sb4S13], and owyheeite [(Pb)10(Ag)3-8(Sb)11-16(S)28]. There is a weak, but persistent association of volumetrically small, typically <0.25%, base metal mineralization associated with the antimony mineralization and includes rare occurrences of chalcopyrite (CuFeS2), galena (PbS), sphalerite (ZnS) and molybdenite (MoS2). Zones of high grade, silver-rich mineralization locally occur with antimony and are related to the presence of pyrargyrite (Ag3SbS3), hessite (Ag2Te) and acanthite (Ag2S).

Tungsten mineralization is typically and essentially exclusively associated with the mineral scheelite (CaWO4). Observations suggest tungsten occurs late in the paragenesis, but precedes the stibnite mineralization since stibnite has been found in numerous past studies cementing veins and brecciated scheelite fragments.

Although mercury mineralization is rare in the area of the three main deposits and in the west side of the district, studies of the mineral occurrences to the east in the Cinnabar district, where mercury was historically produced, indicate the primary mercury-bearing minerals are cinnabar (HgS) and coloradoite (HgTe) and to a lesser extent tiemannite (HgSe) and amalgam (HgAg).

Metasediment-hosted mineralization has a similar sulfide suite and geochemistry, but with higher carbonate content in the gangue and a much more diverse suite of late stage minerals. As in the intrusive-hosted mineralization, gold is associated with very fine-grained arsenical pyrite and is tied up in the pyrite lattice. Rarely, submicron sized native gold occurs as inclusions and along fractures, and may be disseminated in highly fractured zones and may produce locally high grades and a minor nugget effect. Metallurgical test work completed by Midas Gold to date suggests around 20% of the gold in the West End metasediment-hosted mineralization may be particulate in nature, but extremely fine-grained.

Mining at the Stibnite Gold Project would be accomplished using conventional open pit hard rock mining methods. Mining is planned to deliver 8.05 Mst of ore to the crusher per year (22,050 st/d), with stockpiling by ore type (low antimony sulfide, high antimony sulfide and oxide).

The mine plan developed for the Project incorporates the mining of three primary mineral deposits – Yellow Pine, Hangar Flats, and West End – and re-mining and re-processing of the Historic Tailings.

The Historic Tailings are situated within the footprint of the proposed Main WRSF, and would be re-mined and reprocessed during the first four years of the mine schedule to provide adequate terrain for the WRSF. As the tailings material is currently at a size of 97% passing #40 mesh, it is not anticipated to overwhelm the process plant through the additional throughput. The tailings are currently overlain with 5,752 kst of neutralized spent heap leach ore (commonly referred to as the SODA) that must be removed before the Historic Tailings can be mined. The SODA material is planned to be used in the construction of the TSF starter dam during pre production.

The Stibnite Gold Project process plant has been designed to process both sulfide and oxide mineralized material from three deposits (Hangar Flats, Yellow Pine, and West End) as well as Historic Tailings from former milling operations. The design of the processing facility was developed based on the laboratory testing, to treat an average of 22,046 st/d, 365 days per year for a total of 8.05 million tons per year.

ROM material would be crushed and milled, then flotation and hydrometallurgical operations would be used to recover antimony as a stibnite flotation concentrate (with some silver and minor gold), doré bars containing gold and silver, and small quantities of elemental mercury, collected in flasks, to prevent its potential release into the environment. Historic Tailings would be introduced into the ball mill during the first 3 - 4 years of operation.

The processing plant consists of a primary crusher, SAG mill, ball mill, two sequential flotation circuits, a POX circuit, CIP circuit, CIL circuit, and a conventional adsorption desorption-recovery (ADR) plant. The designed process plant processes sulfide material to produce up to two mineral concentrate products: (1) when there is sufficient antimony grade to warrant, an antimony sulfide (stibnite)\ concentrate that would to be filtered, trucked off-site and sold; and, (2) for all material processed, an auriferous sulfide concentrate that would be oxidized onsite via POX, then processed via agitated leach, carbon stripping and refining to produce a gold- and silver-rich doré.

The process plant was designed to process 22,046 st/d through crushing, milling/grinding, flotation and tailings processing operations. Zones in both Yellow Pine (YP) and Hangar Flats (HF) contain sufficient antimony to warrant processing for antimony recovery. The antimony would be recovered as stibnite flotation concentrate and would be shipped off-site for further processing.

Run-of-mine (ROM) material would be crushed and milled, then flotation would be used to recover antimony as a stibnite flotation concentrate (with some silver and minor gold) when there is sufficient antimony to justify it. For all sulfide ore, an auriferous bulk sulfide flotation concentrate would be produced and oxidized in an autoclave. The autoclave residue and flotation tailings would be processed through conventional cyanidation and, doré bars produced containing gold and silver. Historic Tailings would be introduced into the ball mill during the first 3 - 4 years of operation. Tailings from the operation would be deposited in a geomembrane lined TSF. The process operations include the following components:

- Crushing Circuit – ROM material would be dumped onto a grizzly screen and into the crusher dump hopper feeding a jaw crusher operating at an average utilization of 75% yielding an instantaneous designthroughput of 1,225 short tons per hour (st/h).

- Grinding Circuit – The grinding circuit incorporates a single semi-autogenous (SAG) mill, single ball mill design with an average utilization of 92%, yielding an instantaneous design-throughput of 998.5 st/h. When Historic Tailings are processed during early years of the operation, the slurry from the plant would also flow to the cyclone feed pump box. Cyclone underflow flows by gravity to the ball mill; cyclone overflow, at 33% solids with a target size of 80% passing (P80) 75 microns, would be screened to remove tramp oversize and flow through a feed sample system and on to the antimony or gold rougher flotation circuit, depending on the antimony concentration of the material.

- Flotation Circuit (Antimony and Gold) – The flotation circuit consists of up to two sequential flotation stages to produce two different concentrates; the first stage of the circuit was designed to produce an antimony concentrate when the antimony grade is high \ enough, or bypassed if not, and the second stage was designed to produce a gold-rich concentrate.

- Pressure Oxidation Circuit – Two concentrate surge tanks would be pumped to the autoclave feed tank, which would feed the autoclave. The autoclave is designed to provide one hour of retention time at 428 degrees Fahrenheit to oxidize the sulfides and liberate the precious metals. Autoclave discharge would be processed through flash vessels and gas discharge is processed through a scrubber. Slurry discharge from the flash vessels would be processed through the basic ferric sulfate (BFS) re-leach tanks to stabilize the solids prior to cyanide leaching.

- Oxygen Plant – An oxygen plant producing 670 st/d of gas at 95 percent oxygen and a gauge pressure (psig) of 570 is planned. The oxygen would be from a vendor-owned oxygen plant located near the autoclave building providing the autoclave with an “over the fence” supply.

- Oxidized Concentrate Processing – Post-POX, the concentrate stream would be conditioned with lime and leached for 24 hours and discharged to a six stage pump-cell carbon-in-pulp (CIP) circuit for precious metal recovery from this high grade stream. The CIP tailings would be discharged to the flotation tailings leach circuit for extended retention time and to minimize reagent costs for the tailings leach system.

- Oxide Carbon-in-Leach and Tailings Detoxification – A (CIL) circuit was included in the design of the process plant to recover gold from non-refractory material in the flotation tailings, and in oxide material from the West End deposits that would be processed during oxidation circuit scheduled maintenance periods.

- Carbon Handling – Loaded carbon from the CIP circuit would be processed through a conventional carbon handling circuit.

- Gold Room – Precious metals would be recovered from the strip solution by electrowinning.

- Tailings – Tailings would be pumped from the process plant to the TSF In a HDPE-lined carbon steel pipe.

- Process Control Systems - The process plant design includes an integrated process control system.