Deposit Types
The Gold Rock Property is a Carlin-type gold deposit (CTGD) and features sediment-hosted, disseminated gold deposited within Mississippian limestone and siltstone units, namely the Joana Limestone and, to a lesser extent, the overlying Chainman Shale and underlying Pilot Shale. CTGDs in northern Nevada are divided into a series of trends. The Gold Rock Property lies on the south eastern end of the Battle Mountain-Eureka Trend. Several authors propose that the trends for CTGDs in northern Nevada reflect structural lineaments in the basement (e.g. Cline et al., 2005; Muntean et al., 2011). The Battle Mountain Eureka trend corresponds to a boundary between two portions of crust which have different Gravity and Magnetic signatures (Grauch et al., 1995, 1998; Tosdal, 1999).

Carlin-type gold deposits in northern Nevada represent the second highest concentration of Au in the world and around 6% of global annual Au production (Muntean et al. 2011).

Geometry of Mineralization
The primary feeder structure at Gold Rock is postulated to be a steeply dipping reverse fault reactivated with extensional dip-slip, known as the EZ Junior Fault (Carden, 1988). The EZ Junior Fault is adjacent to and sub-parallel with the western limb of the EZ Junior Anticline in the area of the EZ Junior open pit. When these fluids intercepted rock with the favorable geochemistry and porosity (Joana Limestone and Chainman Shale), the fluids reacted with the rocks causing first the formation of solution breccias and then more violent hydrothermal breccias as the reactions progressed. Gold would have precipitated as part of this fluid-rock reaction. It is likely that the complex faulting and folding on the property provided fluid pathways and traps which accentuated the mineralization in specific areas.

Figure 7.12 illustrates the cross-sectional geometry of mineralization of the Gold Rock Deposit as interpreted from drilling with respect to the typical geology. At the apex of the EZ Junior Anticline, the mineralization is largely restricted to Joana Limestone and the base of the overlying Chainman Shale. In both the east and west limbs, mineralization extends downward, largely in the Joana Limestone.

Mineralization was exposed at the pre-mining surface of the EZ Junior open pit. Along strike (6,000 ft [1,830 m] south-southwest and 1,000 ft [305 m] north-northeast of the EZ Junior Pit), the mineralized lower Chainman Shale and upper Joana Limestone are covered by 300 to 500 ft (90 to 150 m) of poorly exposed Chainman Shale. Mining at EZ Junior extracted a small portion of the near surface resource. Historical drill intercepts indicate that significant mineralization still exists below the EZ Junior open pit and along strike to the north and south.

Additionally, historical drilling at Meridian Flats, nearly a mile south of the EZ Junior open pit, intersected significant mineralization within the same faulted anticline geometry, as shown in Figures 7.10 and 7.12. In general, the trace of the EZ Junior Anticline hinge zone is fairly horizontal and oriented at about N14oE along the length of the Gold Rock resource area. Locally, the EZ Junior Anticline can display slight plunges in and around cross faults. However, the depth from surface to the top of the EZ Junior Anticline appears to be more affected by elevation changes on either side of the cross faults due to some vertical movement along the faults than by plunge of the anticline. This also likely can be said for the main trend of the known EZ Junior mineralization as it appears to be spatially related to the anticline hinge zone and the contact between the Joana and the Chainman formations.

The Gold Rock Project is composed of a single project with three mining areas: the previously developed North Pit area in the Northern portion of the project; the Center Pit area in the central portion of the project south of the North pit; and the South Pit area located south of the Center pit area.

Pit shells were determined for the Gold Rock Deposit using a whittle economic pit optimization described below. Based on these initial open pit optimization results, a pit shell was selected to design the phased pits that make up the three mining areas for this PEA.

Standard mining technology has been utilized to create an open pit for each of the three mining areas. The South Pit has approximate dimensions of 1,030 feet (315 m) south to north by 430 feet (130 m) east to west and a maximum depth of 225 feet (70 m) below current ground level. The South Pit is composed of a single mining phase. The North Pit has approximate dimensions of 5,120 feet (1,560 m) south to north by 1,590 feet (485 m) east to west and a maximum depth of 620 feet below current ground level. The North Pit is composed of four mining phases with the first phase being a standalone starter pit. The Center Pit has approximate dimensions of 1,950 feet south to north by 1,490 feet east to west and a maximum depth of 690 feet (190 m) below current ground level. The Center Pit is composed of two mining phases the first phase being a standalone starter pit. All the pit shells were selected from the whittle open pit economic optimization discussed below and were used to guide the design of the three mining areas.

A mine contractor will be used for the mining activities including site preparation, haul road construction and maintenance, mineralized zones and waste drilling and blasting, excavation and haulage of mineralized material and waste, management of waste dumps, oversize breakage, and pad stacking. The mine contractor will provide all the required open pit mining and haulage equipment.

Mine Design
The ultimate pit limits selected for the three mining areas for the Gold Rock Project were selected based on Whittle open pit economic optimizations. The three mining areas will be developed using seven distinct phases designed to approximate an optimal extraction sequence. The phased pit designs are based on slope design parameters and benching configurations provided by Fiore, as reviewed for reasonableness by BOYD in the context of this PEA. Topographic files were also provided by Fiore. A mine production schedule was prepared by BOYD using Maptek’s Chronos scheduling software.

Mining Dilution
The mineral resource block model was provided to BOYD by APEX and included a diluted gold grade using a fixed block size of 10 feet by 10 feet by 10 feet (3 m by 3 m by 3 m) which is considered the smallest selective mining unit (SMU) for the project. Mining will be completed using a 20-foot-high (6 m high) bench. Based on this selected SMU size, and recognizing that the zones are gradational defined by cut-off grade boundaries, no additional waste dilution other than internal included waste was deemed appropriate for this PEA mine plan.

Whittle Pit Optimization
In order to design the various required phased designs for the Gold Rock Project, BOYD completed a new open pit optimization to determine the optimal economic open pit configuration for the overall project. To accomplish this task, BOYD used the Whittle open pit economic optimization software. This software uses the industry standard Lerchs-Grossmann algorithm to determine an optimal pit shape using various economic, geotechnical, and metallurgical parameters. A Whittle optimization was completed on the resource model and a final conceptual pit shell was determined. These open pit shells were then used for PEA-level detailed phased open pit designs and production scheduling.

Initial PEA level operating costs were calculated and used to provide the economic basis for the various Whittle open pit economic optimization runs that were completed. All runs included indicated, and inferred resources as defined under NI 43-101 requirements.

Whittle open pit economic optimizations were completed on the Gold Rock mineral resource model using the economic parameters in Table 16.2 as well as the geotechnical parameters presented in Table 16.1. The initial Whittle runs used only the overall inter-ramp slope. Results from these runs were examined and the overall slope was flattened to reflect the inclusion of ramps into the design. The addition of ramps to the Whittle results decreased the overall pit slope from 52 degrees to 47 degrees.

Design Criteria
Single benching of 20-foot production benches was determined to be feasible in all geologic units. Catch or safety benches with a width of 30.8-feet (9.4 m) are used in all designed phases. These safety benches are applied on every third bench (60-feet vertically). Ore and waste mining is planned on the full 20-foot (6 m) production benches. Two-way haul roads, 100 feet (30 m) wide at a 10% grade, were designed in most cases where higher traffic may require extra width for safe and efficient passing of trucks. To maximize ore recovery at depth, the final benches of each pit floor were designed with single-lane access (50-foot width). Safety berms were designed in accordance with the recommendations provided by BOYD. Minimum mining widths of 100 feet (30 m) were applied to each phase design.

Phased Pit Designs
The Whittle pit shells described above were used to construct individual pit phases at each of the three mining areas. The phases were designed to provide high-value early phases as well as balancing waste stripping over the entire life of each pit. All the phased designs used the same geotechnical and design criteria described above.

Comminution
The crushing circuit planned includes primary, secondary and tertiary crushers. The primary and secondary crushers would operate in open circuit, while the tertiary crusher would operate in closed circuit. During standard operation, the crushing circuit is designed to produce 6,000 tpd of feed to the grinding circuit at a particle size of P80 3/8 inch. However, the crushing circuit has the capacity to crush up to 10,000 stpd to P80 5/8 inch. The extra capacity of the crushing circuit will provide the flexibility to reduce the particle size of the feed to vat leaching circuits for ore types that provide improved gold cyanide leach extractions at finer particle sizes.

The recirculating vat leach circuit has therefore been designed to allow for a higher percentage fine material to report to the recirculating vat leach system if warranted. The crushing circuit as preliminarily designed includes:

- standard 36” X 50” jaw crusher
- heavy duty 51” X 24” horizontal vibrating grizzly feeder
- 400 hp secondary cone crusher
- 300 hp tertiary cone crusher
- All required transfer conveyors and inter-stage screens for the primary and secondary crushers.
- Tramp metal removal system.

The rod mill is designed to operate in open circuit to produce up to 6,000 stpd at P8 065 mesh. At this grind, it is expected that 1,200 tpd will report to the slimes vat leach circuit and 4,800 tpd will report to the sand vat leach circuit. Absent Bond work index testing, based on typical feed for the Gold Rock Project, a nominal 12 ft x 20 ft rod mill requiring +/- 950 hp is expected to be required.

Crushing
The low-grade crushing circuit is planned to utilize an open circuit horizontal shaft impact crusher (HSI) capable of producing a particle size of P80 3 inch at up to 6,000 stpd. While abrasivity and other parameters will need to be verified by further testing, given the nature of the feed material, consisting primarily of Joana limestone and shale and Chainman shale, both of which have only moderate unconfined compressive strength, are highly friable, and are only moderately abrasive, in BOYD’s opinion HSI crushing is likely to be the most cost effective solution in this instance. Impact crushing has the significant benefit, when suitably applied, of producing greater reduction ratio in a single pass and generating a broader distribution of product particle size which is expected to benefit subsequent belt agglomeration with dewatered vat tailings and cement prior to heap stacking. Though HSI is not commonly used in the metals mining industry, this method is widely used for aggregate production in material types similar in nature to the projected feed at Gold Rock.

Summary
For the higher-grade fraction of process feed (> 0.015 opt Au), static sand vat leaching for coarser material (28 mesh X 150 mesh) and recirculating vat leaching for P80 -150 mesh material is planned. A general description of this process is outlined below and is shown graphically on the process flowsheet in Figure 17.1. Key process elements include:

- Crushing through primary, secondary, and tertiary crushing stages,
- Open circuit grinding by rod milling to P80 28 mesh
- Separation by particle size by cycloning at 28 mesh X 150 mesh reporting to cyclone underflow, and nominal – 150 mesh to cyclone overflow
- Leaching of sand fraction in static sand vats with seven days retention time
- Loading gold on carbon from sand vat preg-solution through staged carbon columns
- Leaching of slimes fraction in continuously recirculated vats with two days retention time
- Processing slimes through carbon in pulp circuit to load gold from ........