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.

Gold deposits of the Leeville underground Complex are hosted by lower Paleozoic carbonates of the Devonian Rodeo Creek Formation (Drc), Devonian Popovich Formation (Dp), and Siluro-Devonian Roberts Mountains Formations (SDrm), and a series of highly altered, undifferentiated dikes cross cutting stratigraphy.

Gold mineralization is controlled by a combination of lithology and structure. Intrusive rocks occur as dikes and sills, and locally host mineralization. Lithologic hosts include Rodeo Creek, Popovich, and Roberts Mountains Formations that vary between sub-horizontal to moderately folded. Mineralized material consists of 60 – 90% quartz, 5 - 20% kaolinite, 1 - 17% carbonate, and 3 – 7% pyrite. Gold mineralization in the Leeville complex is wholly refractory.

The Carlin Complex has three major operating underground mines including Goldstrike underground, Leeville and the Portal Mines (including Pete Bajo and Exodus/Northwest Exodus). All mines utilize drift and fill and/or long-hole stoping and are accessed by shaft or portals.

The mining method primarily used on the West Leeville orebody is longhole stoping with typical stopes of dimension 30.5 metres (100 ft) long, 9.1 metres (30 ft) wide and 18.3 metres (60 ft) high. The mining methods employed at the Turf orebody are longhole stoping and underhand cut and fill, depending on what geotechnical constraints allow. Stope geometries for the Turf orebody follow the same constraints as the West Leeville orebody. In the cut and fill areas of the Turf orebody, 4.6 to 5.2 metres (15 to 17 ft) wide primary and secondary drifts will be cut in four 4.6 to 6.1 metres (15 to 20 ft) high lifts, designated A-D.

The Four Corners orebody is designed to be mined with the same methods as those being used on the Turf orebody, but a geotechnical evaluation is being performed to determine mining method improvement. The maximum stope dimensions for the Four Corners orebody have been set at 30.5 metres (100 ft) long, 6.1 metres (20 ft) wide, and 24.4 metres (80 ft) high. In Four Corners orebody cut and fill areas, only 20-ft wide primary drifts will be cut in 4.6 to 6.1 metres (15 to 20 ft) high lifts, A-D.

The Leeville Complex utilizes three forms of backfill:
• Cemented Rock Fill (CRF);
• Uncemented run of mine waste; and
• Paste fill.

Primary stopes mined prior to 2018 were backfilled with CRF, and secondary stopes with uncemented run of mine waste, dependent on future mining plans.

Leeville now uses a surface paste plant and underground reticulated paste fill system. The paste consists of different ratios of crushed aggregate, processing tails and cement slurry. Paste is used to fill the majority of the stope and CRF, as well as for the jamming and capping of backfilled areas. Uncemented run of mine waste will continue to be utilized for secondary stopes and drifts in which future mining is not planned directly adjacent.

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 ........