Jerritt Canyon is a Carlin-type gold deposit, which are hydrothermal in origin and they are usually structurally controlled. Current models attribute the genesis of Carlin-type gold deposits to:

• Epizonal plutons that contributed heat and possibly fluids and metals;
• Meteoric fluid circulation resulting from crustal extension and widespread magmatism;
• Metamorphic fluids, possibly with a magmatic contribution, from deep or mid crustal levels;
• Upper crustal orogenic-gold processes within an extensional tectonic regime.

Jerritt Canyon is hosted by silty carbonate or carbonaceous siliciclastic rocks originally deposited as shelf sedimentary rocks during the Paleozoic age. The Paleozoic host rocks have been imbricated, faulted, and folded through several orogenic events in the Paleozoic and Mesozoic.

In general terms, the intersection of structures with favourable host rocks is the primary control and the form of mineralization ranges from apparently stratabound to fault hosted where the faults can be either highly discordant to bedding or bedding parallel. Deposits at Jerritt Canyon are mostly stratabound or fault hosted. Gold occurs as very fine, micron-size, particles in pyrite and arsenian pyrite. Other sulphides are orpiment, realgar, and stibnite. Alteration include carbonatization, decalcification, and silicification (jasperoid).

The Jerritt Canyon Gold District is located in the Great Basin, north and northeast of the Carlin Trend of gold deposits.

The regional thrust fault is referred to as the Roberts Mountain Thrust. A foredeep basin formed to the east in front of the thrust belt resulting in deposition of Early Mississippian synorogenic and Pennsylvanian post-orogenic sedimentary rocks including conglomerate, siltstone, and limestone (Antler Overlap Sequence). Northeast Nevada was further subject to compressional tectonism in the Pennsylvanian through to the Permian Humboldt and the Early Triassic Sonoma Orogenies.

Carlin-type gold mineralization is preferentially hosted by Ordovician to Devonian shallow shelf-slope carbonate shale sequence. These rocks are commonly referred to as “Lower Plate” rocks owing to their position in the footwall of the regional Roberts Mountain Thrust. The deep water siliciclastic dominant rocks forming the hanging wall of the Roberts Mountain Thrust are commonly referred to as “Upper Plate” rocks. This sequence of less reactive and less permeable upper plate rocks, acting as an aquitard over variable to highly permeable lower plate rocks, is regarded as a primary control on the deposition of Carlin-type gold mineralization. The Carlin-type gold deposits in northeastern Nevada formed in the Middle to Late Eocene during the period 42 to 36 Ma. Deposition is regarded as part of a magmatichydrothermal event related to regional extension utilizing reactivated, variably oriented preEocene structures.

The occurrence and distribution of gold mineralization at Jerritt Canyon is controlled both by lithology and structure. Gold mineralization at Jerritt Canyon is hosted by Hanson Creek Formation units I to III and the lower part of the Roberts Mountains Formation. The Saval discontinuity, being the contact between the Hanson Creek and the Roberts Mountain Formations, is interpreted as a primary control on gold mineralization at Jerritt Canyon. Gold mineralization is hosted by or spatially associated with high angle westnorthwest and north-northeast trending structures. Much of the more continuous gold mineralization occurs within the favourable stratigraphic intervals along the limbs or hinge zones of large anticlinal folds, and at the intersection of the two sets of high angle structures. The mineralized zones form along well-defined structural and mineralization trends as stratigraphically controlled tabular pods that are locally stacked upon one another resulting from the presence of more than one favourable stratigraphic unit and/or local thrust and/or high-angled fault intersection controls. The deposits are Carlin-type, sediment-hosted gold mineralization within carbonaceous sediments. The gold occurs as very fine-grained micronsized particles as grain boundaries or inclusions in pyrite, and as free grains in carbonaceous-rich and fine-grained, calcareous, clastic sedimentary rocks.

Alteration in the Jerritt Canyon district includes silicification, dolomitization, remobilization, and reconstitution of organic carbon, decalcification, argillization, and pyritization (typically containing elevated arsenic). The rocks also exhibit hypogene and supergene oxidation and bleaching. The most important alteration types relative to gold deposition are silicification, remobilization, and reconstitution of organic carbon, pyritization, and decalcification.

Jerritt Canyon has been in operation since 1981. Between 1981 and 1999, mining was by open pit methods. Underground operations began in 1993 with the opening of the SSX and Smith mines. The Smith and SSX underground mines are currently operational using mining contractors. The Saval 4 mine and the West Mahala zone contained within the SSX mine are owner operated.

The cut and fill stoping method is used for production from the Smith and SSX mines, including the West Mahala zone. Minimum mining openings are 15 ft by 15 ft and widths of up to 25 ft where justified by the ore width. Stopes are mined using an underhand method in a top down sequence.

The Saval 4 mine uses the sublevel longhole mining method, with primary stope mine openings of 20 ft wide by 15 ft high and typical stope dimensions of 20 ft wide by 75 ft high and 80 ft long. Stopes are mined bottom up using primary-secondary sequencing.

Ore is hauled to surface stockpiles using mine haul trucks for grade control and contractor haulage to the mill feed stockpile.

The Smith, SSX, West Mahala, and Saval 4 underground mines are all accessed by way of surface portals and 15 ft by 15 ft declines typically grading 12% to 15%. Underground lateral development including level accesses and stope accesses is generally designed to be 15 ft by 15 ft. Cut and fill stope are mined in up to five lifts with access drift gradients varying from +15% to -15%. All aspects of the mining cycle are fully mechanized with excavations created using conventional drill, blast, muck, and support techniques.

Backfilling of production voids is completed using a cement consolidated rock fill, which is produced by crushing and screening mine waste. Cement content varies from 5% to 7% for adjacent and undercut mining, with the majority of fill placed with 7% cement content. Cemented rock fill is mixed at batch plants located near the portal of each mine and hauled underground by mine haul trucks. In cut and fill mines, cemented rock fill is loaded into cut and fill stopes using loaders and pushed tight to the back using a dozer or loader. At Saval 4 mine, the haul truck dumps cemented rock fill directly into the stope and loaders push the fill into the stope after the fill reaches the level.

ROM ore is crushed to minus six inches with a 36 in. by 42 in., 200 hp jaw crusher.

Crushed ore from the primary crushing circuit is fed to the propane-fired dryer via 100 st surge bin and a 48 in. by 20 in. apron feeder. The Heyl and Patterson dryer is 14 ft by 60 ft, driven by a 350 hp variable speed motor. Rotation speed is two to four revolutions per minute. The dryer shell contains 300 lifters (i.e., flights). The feed end of the dryer is equipped with a Hauck special open fired Starjet Sj750 Ratiomatic burner. Feed rate to the dryer is controlled to maintain ore discharge moisture less than one percent. The discharge air from the dryer goes through two pulse-jet type bag houses, each containing 810 bags. Gas discharge from the bag houses is fed to a 56 ft, dual bed wet scrubber to remove remaining particles and mercury. Each bed contains 15 ft of Tri-Mer packing.

Dried ore from the dryer is conveyed to the secondary crushing vibrating screen, this is a 5 ft
by 12 ft double-deck screen with 20 mm top deck screen panels and seven millimetre bottom deck screen panels. The screen oversize is fed to the 4.25 ft standard Omnicone crusher. The minus seven millimetre screen undersize by-passes the secondary crusher and is transported by screw conveyor and a standard conveyor belt to the high angle conveyor belt that joins the material on the fines conveyor belt from the crushing circuit. The fine material is transported to the fine ore bin (FOB). Approximately 30% of the material discharging from the dryer discharge is minus seven millimetre.

Ore from the secondary crusher is conveyed to the 100 st tertiary crusher feed bin. The bin has two discharge points that each feed a 6 ft x 16 ft double-deck vibrating screen. The top deck of the screens has three quarter inch openings and the bottom decks have one quarter inch openings. Oversize from each screen is fed to a 4.25 ft short head Omnicone crusher. The minus one quarter inch material by-passes the tertiary crushers and reports to fines conveyor that transports the material to a high angle conveyor that discharges to the FOB. The FOB is 2000 st. The material stored in the FOB feeds the grinding circuit.

The fine crushing circuit is served by a north and a south baghouse. The fine material collected in the north baghouse is pneumatically conveyed to the roaster feed bin (RFB) by a puker system. The south baghouse has a FL Smidth Fuller-Kinyon pump to move fine material collected in the baghouse to the RFB.

Ore from the FOB is conveyed to the 14.5 ft x 18.5ft ball mill. The grinding circuit was designed to reduce the ore from 100% passing (P100) one quarter inch ore to P100 35 mesh (i.e., 500 µm). The ball mill is driven by a 2,750 hp synchronous motor. The mixed ball charge is approximately 40% by volume. The makeup ball sizes are 2.5 in., 2.0 in., and 1.5 in. Ore passes through the discharge grates to an air slide and then to a bucket product elevator that transfers the ground material to an Osepa air classifier. The classifier oversizereports back to the ball mill for further size reduction. The circulating load is approximately 300%.

The fines from the classifier oversize go to separator cyclones. They remove approximately 88% of the fines from the air stream. The collected fines are deposited into the product bucket elevator feed air slide. The air stream, with the remaining 12% entrained fines, reports to the 700 hp, 131,000 actual cubic feet per minute (acfm) separator fan. The majority of this stream is fed back into the air classifier through the separator fan, while 25% to 33% of the stream is bled into the classifier baghouse.

The classifier baghouse uses the 125 hp classifier baghouse fan to pull 44,800 acfm air through the bag filters. The captured dust is transported via an air slide and the 60 hp product bucket elevator to the RFB.

The processing facilities at Jerritt Canyon are designed to operate at a rate of 4,500 stpd with an operating availability of 90% and are permitted to operate at 6,000 stpd. The facilities include:
• Primary crushing
• Ore drying
• Secondary crushing
• Tertiary crushing
• Dry grinding
• Roasting
• Thickening
• Carbon-in-leach (CIL)
• Carbon stripping
• Carbon reactivation
• Electrowinning
• Electrowinning sludge refining
• Oxygen plant
• Cooling pond
• Water evaporation pond
• Tailings Impoundment.

ROASTER
The roaster feed bucket elevator lifts the mixture of ore and pulverized coal approximately 135 ft and discharges into the roaster feed air slide. A disengaging bin receives the air slide discharge and funnels this material into the fluidized feed distributor. The roaster system is comprised of two identical, side by side roaster trains, each train is permitted for 125 dry ........