The Livengood deposit is hosted by rocks of the Livengood Terrane, an east–west belt, approximately 150 mi (240 km) long, consisting of tectonically interleaved assemblages, which include: i) the Amy Creek assemblage, a sequence of latest Proterozoic and/or early Paleozoic basalt, mudstone, chert, dolomite, and limestone; ii) a Cambrian ophiolite sequence of mafic and ultramafic sea floor rocks thrust over the Amy Creek Assemblage, in turn overthrust by; iii) a sequence of Devonian clastic sedimentary, volcanic, and volcaniclastic rocks (Athey et al., 2004).

Gold mineralization is associated with disseminated arsenopyrite and pyrite in volcanic, sedimentary and intrusive rocks, and in quartz veins cutting the more competent lithologies, primarily volcanic rocks, sandstones, and to a lesser degree, ultramafic rocks. Mineralization appears to be contiguous over a map area approximately 2.5 km2; a 0.1 g/mt grade shell averages 920 ft (280 m) thick and drilling has not closed off the deposit at depth. The stronger zones of mineralization are associated with areas of more abundant dikes. South of the Lillian Fault individual mineralized envelopes are tabular and follow stratigraphic units, particularly the Devonian volcanics, or lie in envelopes that dip up to 45° to the south, mimicking the structural architecture and attitude of the diking. On the north side of the Lillian fault, mineralization is similar in style and orientation and hosted primarily in steeply dipping Upper Sediments. Three principal stages of alteration are currently recognized; in order from oldest to youngest, these are characterized by biotite, albite, and sericite. Arsenopyrite and pyrite were introduced primarily during the albite and sericite stages. Gold correlates strongly with arsenic and occurs primarily within and on the margins of arsenopyrite and pyrite grains. Carbonate was introduced with and subsequent to these stages. Dating of the sericite alteration (Athey, Layer, and Drake, 2004) indicates that mineralization and alteration were contemporaneous with the emplacement of the dikes.

Interpretations of the occurrence of massive stibnite veins (MSV) was interpreted using Leapfrog software. MSV host high concentrations of the element antimony (Sb). Sb is known to have an inverse relationship to Au metallurgical recoveries. Fifty-four individual occurrences of MSV have been identified within a corridor of Sb mineralization within the Livengood deposit.

The Livengood deposit will be mined using conventional open pit mining methods consisting of drilling, blasting, loading, and hauling with large-scale mining equipment. Vegetation, topsoil, and overburden will be stripped and stockpiled for future reclamation use. The ore and waste rock will be drilled and blasted with 32.8 ft (10 m) high benches and loaded into haul trucks with a fleet of diesel-powered hydraulic excavators and front-end wheel loaders.

During the preproduction phase of the Project, a total of 89 Mt (81 Mmt) of waste rock has been estimated to be required for the construction of certain infrastructure such as the tailings management facility (TMF) starter dike, mine haul roads, site access roads, and platforms for the processing facilities and other buildings. It has been assumed that all waste rock types will be acceptable as construction material except for overburden.

A starter pit, also referred to as Phase 1, was designed on the eastern side of the open pit, which targets the waste rock requirements and minimizes the amount of ore that would have to be stockpiled during preproduction. A trade-off study was carried out early in the Project, which evaluated a starter pit on the west side of the open pit. The western starter pit targeted an area that would expose ore quicker but was not used in the PFS due to the longer haul distances relative to the eastern starter pit. The Phase 1 starter pit contains 5.6 Mt (5.1 Mmt) of overburden, 91.4 Mt (82.9 Mmt) of waste rock and 5.4 Mt (4.9 Mmt) of ore. The bottom of the starter pit is at the 385 m elevation, and the total depth of the starter pit is 328 ft (100 m).

The phase designs were guided by the lower revenue factor pit shells from the pit optimization analysis. A total of five phases have been designed in addition to the starter pit. To ensure the phases can be mined safely and efficiently with the selected fleet of mining equipment, a minimum width of 400 ft (122 m) has been considered between each phase. Narrower widths down to 130 ft (40 m) have been allowed for short segments. For all phases, the haul ramp exits have been located on the northside of the pit to avoid haul road construction requirements on the south side, which would negatively impact the visual effects of the Project.

Phase 2 targets an area on the east side of the pit with a very low strip ratio of 0.3 to 1. The bottom of Phase 2 is at the 305 m elevation, and the total depth of Phase 2 is 540 ft (165 m). Phase 3 targets a high grade area on the west side of the pit with an average grade of 0.75 g/mt. The stripping ratio is relatively low at 0.9 to 1.0. The bottom of Phase 3 is at the 210 m elevation, and the total depth of Phase 3 is 920 ft (280 m). Both Phase 2 and Phase 3 will be mined at the same time to separate the equipment fleet, which will allow for higher productivities. Phase 4 is an expansion of Phase 2. The bottom of Phase 4 is at the 245 m elevation, and the total depth of Phase 4 is 820 feet (250 m). Phase 5 mines the pit to its final limits on the east side and Phase 6 mines the pit to its final limits on the west side. Since the Phase 5 ramp cuts off access to the remaining benches above the 350 m elevation, a ramp has been included in the northwest corner of the pit in Phase 6 to access this material.

Primary Crushing
The primary crushing system is a single stage open circuit (60 × 89) gyratory crusher (1,000 hp, 746 kW). The crusher selection is based upon a feed (F80) size of 31.5 in (800 mm) and a product (P80) of 5.4 in (138 mm), with an expected utilization of 65% at 65,000 t/d (59,000 mt/d). The live capacity of the feed and discharge hoppers to the gyratory crusher are designed for slightly over two truckloads, assuming a nominal payload of 320 t (291 mt). The gyratory crusher’s instantaneous throughput is 4,167 t/h (3,780 mt/h) and the system is equipped with a sacrificial conveyor.

Crushed Ore Stockpile
The crushed ore storage pile is designed for a live capacity corresponding to approximately 12 hours of crushing or 34,946 t (31,703 mt). The total capacity of the storage pile (live + dead) is 113,961 t (103,384 mt). The coarse ore stockpile is covered by a dome.

Secondary Crushing (Pre-Crushing)
Ore reclaim from the stockpile is fed from a reclaim tunnel. The reclaim tunnel is equipped with three apron feeders that feed a secondary cone crusher installed in an open circuit. Two screens 12 ft × 27 ft (3.7 m × 8.2 m) receive the gyratory crusher product, which directs oversize material to a cone crusher (1,250 hp, 932 kW) that crushes the oversize to a P80 of 1.65 in (42 mm). The screen undersize and secondary crusher product is subsequently fed to the SAG mill. The secondary crusher is equipped with a by-pass chute to maintain high plant availability.

Grinding and Pebble Crushing
A SAG mill / ball mill, in a SABC configuration has been selected (Figure 13-5) for the Livengood Gold Project; this configuration provides increased efficiency for competent to medium hard ores. In a SABC circuit, the SAG mill operates in closed circuit with a pebble crusher. The SAG mill is equipped with pebble ports, which evacuate the hard, critical size pebbles that are then conveyed to the pebble crusher, before being returned to the SAG mill. The ball mill operates in closed circuit with hydrocyclones. The required SAG mill power is estimated at 4.7 kWh/t (5.2 kWh/mt), while the required ball mill power is estimated at 4.9 kWh/t (5.4 kWh/mt), for a combined total of 9.6 kWh/t (10.6 kWh/mt) at the pinion, excluding the pebble crusher and secondary crusher power.

The grinding circuit product used to design the mill power is 250 µm (P80). The total power required to grind from primary crusher to final ball mill product is 10.2 kWh/t (11.3 kWh/mt). Note that all estimated power values cited are based on the motor output. The grinding circuit is based on one grinding line, which is comprised of a SAG mill (D×L: 36 ft × 20 ft,) with installed power of 20,115 hp (15,000 kW) and a ball mill (26 ft × 40.5 ft) with installed power of 20,115 hp, (15,000 kW).

The product from the SAG mill will fall onto a classification screen. The oversize from the scalping screen will be conveyed to a single cone (pebble) crusher (1,250 hp (932 kW)), the product of which is returned to the SAG mill. A scalping screen undersize product of 2,800 µm (P80) is discharged into the cyclone feed pumpbox, from which the slurry is pumped to two hydrocyclone clusters. The cyclone underflow is fed to the ball mill. The product is discharged into the gravity feed pumpbox which feeds the gravity circuit. The overflow of the gravity feed pumpbox is returned to the cyclone feed pumpbox along with the tails of the gravity circuit. The feed to the gravity circuit (93,600 t/d (84,910 mt/d)) goes to a distributor that feeds eight gravity screens (four per line), each of which feeds its own gravity concentrator (127 in). The gravity screen oversize and gravity concentrator tails are returned to the cyclone feed pumpbox. The gravity concentrate,
amounting to approximately 0.05 wt% mass pull, is sent to the intensive cyanidation (ILR) system.

Pebble lime will be added continuously at the ball mill to maintain ball mill discharge pH above 9.0 to promote sodium cyanide leaching downstream and limit the amount of conditioning required prior to CIL.

The Livengood process facilities will consist of a comminution circuit (one SAG and one ball mill) followed by a gravity concentration circuit. The tailings from the gravity concentration circuit will be fed to a CIL circuit. Gold will be recovered by an adsorption, desorption and recovery (ADR) circuit, where the final product will be doré. Process tailings will be thickened, treated to detoxify cyanide, and discharged to the tailings management facility (TMF). The gravity gold will be intensively leached from the gravity concentrate.

Gravity and Intensive Leaching
The Livengood gold ore contains significant amounts of free gold, which responds well to gravity concentration. The gravity circuit consists of two parallel lines composed of four Knelson concentrators each fed by a portion of the ball mill discharge. Based on testwork and simulations conducted by FLSmidth, the design gold recovery of the gravity circuit is estimated to be 30% for an average feed blend. A b ........