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.

Lithologic units include the typical Carlin lower plate stratigraphy of the Ordovician Hanson Creek Formation (Ohc), Silurian/Devonian Roberts Mountains Formation (SDrm), Devonian Popovich Formation (Dp), Devonian Rodeo Creek Formation (Drc), and upper plate Ordovician Vinini Formation (Ov). The Devonian Popovich Formation consists of sub-units Upper Mud (DpUM), Soft Sediment Deformation (DpSSD), Planar (DpPL), and Wispy (DpWS). A series of igneous dikes intrude the sediments and have been identified as lamprophyres, biotite-feldspar porphyries, and granodiorite. These units are uncomformably overlain by the upper plate Ordovician Vinini Formation.

Mineralization, primarily hosted in the Devonian Popovich Formation (Dp), is bound on the west by the Castle Reef Fault (CRF) and restricted to the east by the Eastern Dike Swarm (EDS). This structurally controlled system follows near vertical structural fabrics and crosses stratigraphic boundaries. The highest gold values are located adjacent to, or within, the steeply dipping Big Green Dike (BGD), Castle Reef Intrusive (CRI), and Eastern Dike Swarm (EDS). These intrusive filled structures appear to be the main conduits for Exodus gold mineralization. Sediment hosted mineralization appears to have no correlation with a specific alteration type. Mineralization also occurs on the footwall side of the CRF in the lower Silurian/Devonian Roberts Mountains Formation and upper Ordovician Hanson Creek Formation.

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 primary mining method at Exodus and Northwest Exodus is long-hole open stoping with some drift and fill mining planned in areas with less vertical extent.

Northwest Exodus is mined with longhole open stoping using a primary and secondary pass sequence similar to Exodus. Results of the geotechnical analysis completed for Northwest Exodus have been used to develop design criteria for the mine. Because poor ground conditions at Northwest Exodus are expected to be encountered, the production levels are spaced at 19.8 metres (65 ft) intervals, with single lift stopes being mined. Primary stopes at Northwest Exodus are designed at widths of 6.1 metres (20 ft) and secondary stopes are designed 12.2 metres (40 ft) wide. Stopes and stope development are backfilled with either CRF or unconsolidated waste rock.

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 ........