The Fort Knox deposit is hosted entirely within the Fort Knox Pluton, and Au-Bi-Te mineralization is strongly structurally controlled. Drilling has identified mineralization to the -535 ft level. Gold occurs within and along margins of pegmatite veins, quartz veins and veinlets, within shear zones, and along fractures within the granite.

Vein-types and associated alteration styles found at Fort Knox (Bakke et al., 1998) are:

(1) Pegmatite veins and veinlets: range in thickness from micro-scale to 8 cm. Composed of clear to gray quartz, large K-spar megacrysts, and micaceous clots. Potassic alteration halos, rarely exceeding 1 cm thick, consist of an assemblage of variable amounts of secondary biotite and K-spar overgrowths on primary K-spar within the granite matrix.

(2) Pegmatite veins similar to (1) above with alteration envelopes consisting of a variably developed phyllic (sericite-pyrite) assemblage.

(3) Stockwork quartz veins and veinlets: range in thickness from micro-scale to 15 cm. These veins possess thin albitic alteration halos.

(4) Quartz veins and veinlets similar to (3) above with phyllic alteration envelopes that range in thickness from 0.5 to 3 cm.

(5) Low temperature fracture coatings and chalcedonic veins and breccia composed of zeolite-calcite-clay-chalcedony. Pervasive throughout the deposit in the form of fracture coatings and breccia zones. Argillic alteration halos as much as 7 m in width are developed adjacent to the larger chalcedonic breccia zones.

Mining at Fort Knox is by conventional truck-shovel open pit methods with loading and hauling rates of up to 92 Mt/a. Material moved consists of ore and waste mined from the pit plus ore and waste rehandling. Higher grade ore is processed in a CIP mill, typically at a rate of approximately 13.2 Mt/a. Up to 30 Mt/a of lower grade run-of-mine (i.e., uncrushed) ore is processed at a heap leach facility.

Fort Knox operates two ore processing lines: a mill operation consisting of crushing, grinding, agitated cyanide leaching, and a carbon-in-pulp (CIP) circuit; and a run-of mine valley-fill cyanide heap leaching operation where gold is recovered using two parallel carbon-in-column (CIC) circuits. Gold is recovered from solution by electrowinning and poured into doré bars at the in the mill refinery.

Higher grade ore from the Fort Knox mine is processed in the CIP mill, which is located near the Fort Knox open pit. The mill processes ore 24 hours per day, 365 days per year at a nominal capacity of 36,287 t/d (40,000 stpd) of fresh feed. The mill includes of a primary crusher, a conventional semi-autogenous mill and 2 ball mills operating in closed circuit with hydrocyclones to control grind size, gravity concentrators to recover coarse gold, cyanide tank leaching, recovery of gold on activated carbon in the CIP circuit, and a carbon elution and carbon regeneration circuit.