Geological mapping and sampling in the Windy Gulch Segment of the Dawson Project led to the realization that all the rocks hosting the gold mineralization could be better characterized as aluminum-rich (peraluminous) intrusions that not only host the gold but were also the direct sources of the gold mineralization (Keith et al., 2016). As such, the peraluminous intrusions comprise a portion of a staged intrusive sequence. Each stage is associated with a specific magmato-hydrothermal greisen-like hydrothermalite rock that is variously biased for a specific metal suite ranging from copper dominated to gold dominated. When compared to the literature, the gold deposits at Dawson can be broadly described as “intrusion related gold deposits” as in the recent summary of the problem by Pertzel (2013), which is a reconstitution of the phenomena as anticipated by Spurr (1906). The development of the peraluminous portion of the model was discussed by Keith and Swan (1985), Swan and Keith (1986) and at a symposium on the subject chaired by MagmaChem in Denver (Swan and Keith, 1987).

Gold and base metal mineralization occur within an east-northeast trending, south-southwest-dipping fault in amphibolite-grade, Proterozoic-age metamorphic rocks. Strike-length of the entire mapped horizon is about 3.4 mi, of which about the eastern 1.6 mi, which is gold prospective, occurs within the Property.

East of the Windy Point Segment, mineralization is dominated by iron and copper sulphides with minor gold. The mineralized zone is apparently terminated on the east by the Front Range Reverse Thrust Fault, which juxtaposes Proterozoic rocks over Mesozoic rocks; it is terminated on the west by the Marsh Gulch Fault. The mineralized horizon is quite recognizable on the surface as a gossan, with limonite and hematite-stained siliceous rock from about 2 inches to about 10 ft wide and local malachite-azurite fracture-fill.

The mineralized host rock is predominantly a quartz-biotite gneissic aplite with variable amounts of iron-rich garnet and other silicates with local zones enriched in sulphides; it lies stratigraphically above the quartz-biotite-feldspar gneiss (Pbu/Pmu). The horizon has an average thickness of about 9.1 m, with gold occurring predominantly at several stratigraphic positions below the sulphide-bearing zones, but also at the base of the sulphide unit itself. The mineralized parts of the horizon are relatively discrete and range from approximately an inch to 49 ft in true thickness, with a sharp drop-off in metal values away from the contacts (Wilson, 1982).

The sulphide-rich zones are typically 10 to 50 modal percent base-metal sulphides in a fragmental chloritebiotite matrix with local quartz- or anthophyllite-rich zones. Typical gangue mineralogy includes quartz, biotite, phlogopite, garnet, magnetite, amphiboles, sillimanite, cordierite, anthophyllite, gahnite, staurolite, sericite, talc, hematite, limonite, and calcite. Sulphides include pyrite and chalcopyrite with lesser amounts of pyrrhotite, sphalerite, and galena plus rare gold, molybdenite, and bismuth sulphosalts. Later-stage talc and serpentine fill fractures in both the sulphide and auriferous zones.

Historical mineralogical and metallurgical studies of core by US Borax found that native gold occurs as flakes up to 1.4 mm in size. A hole wedge-drilled from GC40 by Uranerz in 1990 (GC40-W2) intersected visible gold particles up to 3 mm in size. Uranerz also had 26 core samples from the Dawson Segment mineralogically analyzed and found gold flakes up to 0.24 mm in size. The gold is typically associated with sillimanite, sericite, or biotite; it inhabits cracks in quartz and garnet, and along grain boundaries, between quartz and sillimanite, sericite, or biotite. Gold can be associated with carbonate and/or siliceous veinlets and rarely occurs as inclusions in pyrite or chalcopyrite (Mettler, 1991). Probing of selected polished sections from drill hole GC05 showed that gold occurs freely as blebs within biotite. Various workers have noted the “nuggety” nature of the gold mineralization. During metallurgical and flotation studies, most gold was found to liberate during processing, with a smaller percentage of gold grains attached to silicate or sulphide gangue (Ganderup and Woods, 1986).

Several mining methods could be applied to this deposit, including “Alimak mining,” shrinkage stoping, and longhole sublevel stoping. The various advantages and disadvantages of each method were considered and longhole sublevel stoping was selected for preliminary mine design.

For the Dawson deposit, the portal will be at elevation 6,500 ft. The base of the known mineralization is at about 5,400 ft, a vertical distance of 1,100 ft.

The terrain at Windy Gulch is steep and small, crawler-type drills are proposed. Excavation could be carried out using a relatively small excavator (25 to 45 ton). Articulated, six-wheel-drive haul trucks (20 to 35 ton) are appropriate for the steep, rough terrain. Any pit haul roads that are needed would be kept outside the cut as much as possible.

The small open pit could be profitable, however, with the assumptions made and the required infrastructure necessary to excavate the pit, the economic value does not justify including the Windy Gulch indicated and inferred resources in the economic assessment.

The proposed process plant at Dawson project site near the town of Cañon City, in Fremont County, Colorado will be based on an annual plant throughput rate of 120,728 tn (109,500 t) of Run-of-Mine (ROM) ore from the mine based on a 365 days per year operation. Daily nominal throughput rate will be 330.8 tn (300 t).

ROM ore from the open pit will be delivered by 20-ton ore trucks and dumped directly into a coarse ore dump hopper equipped with a grizzly on top and a vibrating grizzly feeder at bottom. The apron feeder will reclaim ore and feed it to a primary jaw crusher which will be set to produce a nominal 3-inch crushed product. The crushed ore will be removed by scissor conveyors to a vibratory screen which will be equipped with 2-inch top and 5/8-inch bottom opening screen panels. The nominal -5/8-inch screen undersize will fall by gravity into a 300-ton live capacity fine ore bin underneath the screen. The fine ore bin will provide approximately 20-hour surge capacity ahead of the grinding circuit. The +5/8-inch screen oversize on the other hand will feed a secondary cone crusher which will be set to deliver a -5/8-inch product. The cone crusher product will join the jaw crusher discharge on the crushed ore conveyor for transfer to the vibratory screen operating in closed circuit. A magnet placed over the crushed ore conveyor will help to remove tramp iron from the stream and a metal detector placed on the vibratory screen feed conveyor will help remove tramp iron ahead of the cone crusher. Dust is controlled by the use of a wet scrubber with the discharge slurry returning to the mill as recycle. The crusher will be scheduled to operate 16 hours per day or as required by the ore delivery and grinding circuit demands.

The fine ore, reclaimed by a belt conveyor/feeder from the fine ore bin, will feed the grinding ball mill. The grinding circuit will consist of a single ball mill operating in closed circuit with a hydrocyclone for classification. The grinding circuit is designed to treat fresh feed with an 80% passing size of 0.47 inches (12,000 µm) to produce a finished product with a target primary grind 80% passing size of 200 mesh (74 µm). The cyclone overflow will proceed to flotation while the cyclone underflow will gravitate to the ball mill for further size reduction.

A portion equivalent to approximately 70% of fresh mill feed tonnage will be diverted from the cyclone feed to the gravity circuit for the recovery of free gold. Major process equipment in this circuit will consist of a safety screen, a centrifugal gravity concentrator (CGC), and a shaking table. Gravity gold concentrate from the shaking table will be collected and may be processed on site to doré and separate marketing, or mixed with the flotation concentrate depending on its grade.

Cyclone overflow from the grinding circuit gravitates to rougher/scavenger flotation bank of cells for bulk flotation concentrate recovery. A sulphide mineral collecting agent (PAX, potassium amyl xanthate) and a frother (MIBC, methyl isobutyl carbinol) are added ahead and during flotation for the promotion and collection of its precious metal and sulphide mineral content. Small addition of a secondary collector specific for the promotion of gold such as a dithiophosphate may be used. The rougher and scavenger flotation circuits produce their respective concentrates, which are then combined and reground ahead of cleaner flotation to produce a marketable grade final concentrate. Conventional trough style flotation cells providing 40 minutes of rougher/scavenger flotation residence time and 38 minutes of cleaner flotation residence time will be employed. The regrind mill will operate in closed circuit with a hydrocyclone to produce a target 80% passing regrind size of 400 mesh (37 µm).

Regrind cyclone overflow will gravitate to a bank of three-stage cleaner flotation cells operating in counter-current configuration. Third cleaner concentrate will head to dewatering, while the cleaner tailings will join the rougher/scavenger flotation tailings for dewatering for dry-stack tailings disposal.

The rougher/scavenger flotation circuit will produce approximately 75% to 80% of the plant feed mass, while the cleaner flotation circuit tailings stream will account for approximately 15% to 20% of the plant feed mass. The final concentrate product will account for the remaining 5% to 10% of the plant feed mass depending on mill feed and optimized concentrate grades targeted.

The final cleaner flotation concentrate will first be thickened in a concentrate thickener to approximately 60% solids density. A flocculant will be used to aid in settling. Thickener underflow will be sent to a filter feed stock tank ahead of concentrate filtering. Concentrate filter cake at a target moisture content of 10% will be packaged into 2-ton bulk bags for shipment to markets. Filtrate water will be sent to the concentrate thickener, while the overflow from the thickener will be sent to process water tank as make up recycle water. It is estimated that approximately 5% to 10% of plant feed by weight or 1.6 to 3.3 tons per day will be recovered into the flotation concentrate.