The mineral deposits along the Carlin Trend form a suite of deposits known as Carlin-type. Carlin deposits comprise stratabound disseminated gold mineralization hosted by Silurian-Devonian carbonate rocks that have been metamorphosed to varying extents. The deposits are hydrothermal in origin and are usually structurally controlled.

The mineralization of Gold Quarry is generally bounded on the northwest by the northeast-striking Chukar-Alunite Fault zone, and on the southeast by the north–northeast-striking Deep Sulfide Feeder Fault zone. Mineralization is preferentially located in the hanging wall of the Chukar-Alunite Fault Zone and in the footwall of the Good Hope Fault. Gold mineralization is disseminated, with higher gold grades concentrated adjacent to structures.

Ten geologically distinctive mineral zones have been defined, referred to as Quarry Main, Deep West, Deep Sulfide Feeder, Chukar North, Chukar South, Good Hope, Mac, Magpie, Southwest, and Wedge.

Six major lithologic units are recognized in the Gold Quarry deposit from surface mapping and drill hole logging: Tertiary Carlin, Devonian Slaven, Devonian Rodeo Creek, Devonian Popovich, Silurian Roberts Mountains, and Ordovician Hanson Creek Formations.

The four main gold-hosting lithologies are:

• Silty limestone sections of the Roberts Mountains Formation;

• The upper 90 metres of the Popovich Formation consisting of silty limestone and calcarenite;

• Siltstone, siliceous mudstone, and cherty siltstone of the Rodeo Creek Formation; and

• About 60 metres of upper-plate sedimentary rocks of the Marys Mountain sequence that consists of limy mudstone and siltstone. Detailed surface mapping and drill hole interpretation indicates that there are four dominant fault sets at Gold Quarry. These include (from youngest to oldest): north striking basin-bounding, normal faults (Grey, and Tuff Faults), northeast-striking normal faults (Chukar, Alunite, Bad Attitude, and Deep Sulfide Feeder Faults), northwest-striking Good Hope reverse Fault, and low-angle Roberts Mountains thrust.

Oxide gold ore consists of minute particles of finely-disseminated native gold within the host rock. Oxidization of portions of the deposit may have occurred as a result of late hydrothermal acidleaching and supergene leaching of the original refractory material. Oxide material is subdivided into oxide carbonate (OC) and oxide siliceous (OS) styles, based on the presence of carbonates. Refractory mineralization is subdivided into silica sulfide refractory (SSR), carbon sulfide refractory (CSR), and unoxidized carbonate (UC). Refractory conditions of each type are due to a combination of silica ± pyrite encapsulation of gold ± the presence of naturally activated organic carbon ± the presence of carbonate. These represent the unoxidized portions of the Gold Quarry deposit. Mineralization is associated with As, Sb and Hg.

Sulfidation, decalcification, and dolomitization of the Popovich and Roberts Mountains limestones and silicification of the Rodeo Creek siliciclastic rocks are the dominant alteration types associated with mineralization. Barite and clay-altered intrusive rocks have been noted in association with the Alunite and Good Hope Faults.

The Chukar Footwall Underground mine workings are collared in the southwest corner of the Gold Quarry Pit; three portals are being driven into the walls of the open pit mine. Ore is mined using longhole-stope and cut-and-fill methods.

Chukar – located in the Gold Quarry pit. Mining started in 2002 and was completed in 2019.
[Carlin Technical Report 2020. P.57]

The Mill 5 facility uses a combination of flotation and cyanide leaching to recover gold. The basic steps are as follows:

• Crushing and grinding where ore is ground to the appropriate particle size, usually about 65% -200 mesh;
• Conditioning with a mixture of chemicals to provide for air bubble attachment to pyrite, arsenian pyrite, and arsenopyrite particles while minimizing bubble attachment to gangue minerals such as silica or calcite;
• Froth flotation where the pyrite, arsenian pyrite, and arsenopyrite are floated into a concentrate by sparging air into the conditioned slurry;
• Concentrate is thickened and filtered so that it can be further processed through a separate oxidizing facility such as the Mill 6 roaster or the Sage autoclave;
• Residual gangue or flotation tailings contain sufficient residual gold to warrant CIL processing;
• CIL processing involves leaching of the slurry with cyanide to dissolve the gold and then adsorb the gold o ........