The South Arturo Mine is located in the northern end of the Carlin Trend, a 60 km long northnorthwest alignment of sedimentary rock-hosted gold deposits. These deposits are generally known as Carlin-type deposits named after the Carlin deposit. Characteristically, the gold mineralization in Carlin-type gold deposits is dispersed, micron-sized, and found commonly on the rims of pyrite grains in predominately carbonate-bearing host rocks. Decalcification, silicification, and dolomitization are the most dominant alteration features. Generally, there is negligible base metal content, low silver to gold ratios, and a geochemical enrichment in arsenic, antimony, and mercury.

The South Arturo gold-silver deposits can be divided into five mineralized areas. These areas are the South Arturo, West Button Hill, Southwest Dee pit, Deep North, and Hinge. The majority of these deposits are classified as “Meikle Type” breccia-hosted Carlin-type deposits. A complex set of breccias occur at the upper contact of the Bootstrap limestone. These breccias can be generalized into four basic types: silicified heterolithic breccias, silica-sulphide breccia, dolomite breccia, and cavity-fill breccia. The oldest breccias are the silicified heterolithic breccias and the dolomite breccias which have been crosscut and replaced by mineralized silica-sulphide breccias. The youngest breccias are the post mineral cavity-fill breccias.

The northern extent of South Arturo mineralization lies approximately 60 m southeast of the Dee pit and under 180 m of waste rock. An overall north-south orientation to mineralization is inferred from the grade thickness contours, which define an area 520 m in a north-south direction by 100 m to 115 m wide in an east-west direction. The mineralization and Tertiary contact dip 15° to 20° to the south. Drilling has shown that rocks are oxidized to a depth of up to 600 m. Paleozoic rocks host the mineralization mainly in multi-stage, multi-lithic breccias with gold values ranging from 0.2 g/t Au to more than 35 g/t Au with an average grade of approximately 2.0 g/t Au. These breccias are commonly formed by karsting or dissolution of carbonate rock and subsequent collapse and cavity fill. In general, decalcification is followed by weak to strong silicification with local argillization. Silver to gold ratios are generally 1:1 at grades of greater than 2.06 g/t Au but increase to 5:1 at lower gold grade values.

Dee Deep North is a north-northeast trending pod of mineralization that plunges slightly north and is approximately 180 m long, 45 m wide, and 45 m thick. The majority of high-grade refractory mineralization is in silica-sulphide breccia within a flat to west-dipping silicified, multilithic breccia body above the Bootstrap limestone between 1,494 MASL and 1,554 MASL. The principal controls are the north-northeast trending high angle EB fault and southwest dipping low angle structures.

The Southwest Dee pit mineralization is along the north-northeast trending, west dipping Dee Fault Zone. The mineralization is carbonaceous, partially oxidized, variably silicified mudstone/ siltstone breccia approximately 100 m in a north-south strike length, 30 m wide, and 45 m in thickness. The mineralization sits between 1,494 MASL and 1,554 MASL, with a small portion exposed along the southwest high wall at the bottom of the Dee pit.

The West Button Hill mineralization trends north-northeast for over 600 m in strike length, in pods that vary up to 120 m wide and 15 m thick. The majority of high-grade refractory mineralization is in the lower Rodeo Creek Formation and multi-lithic breccias above the Bootstrap limestone. The principal controls are the north-northeast and north-south trending high angle structures and favorable host rocks.

The Hinge zone is a north-south striking zone that lies between the Arturo zone to the south west and West Button Hill to the northeast and is due east relative to the existing Dee pit. It is approximately 425 m long and up to approximately 90 m wide, lying between elevations of 1,450 MASL and 1,600 MASL at depths from 100 m to 270 m below surface. Mineralization is hosted in the lower portion of the Rodeo Creek Formation and silicified breccias of the Basal Rodeo Creek and Popovich Upper Muds units.

El Nino is a high-grade underground deposit situated down plunge of the Phase 2 pit, where mining was concluded in 2017. Underground drift and fill mining is successfully extracting mineralization below the Phase 2 Pit.

El Nino underground is accessed via a portal located at 1,536 m (5,040 ft) elevation above mean sea level ("amsl") within the South Arturo Phase 2 pit. Two portals were connected via a looped decline to access the ore deposit. The current mine depth for reserves extends down to 1,477 m (4,845 ft) amsl elevation and exploration potential exists down dip to the east and down plunge to the north.

Dimensions of the major access development drifts are 16-feet wide x 17-feet high. Major access drift gradients do not exceed +/-15%.

Underhand drift and fill mining is the preferred mining method at El Niño. Attack ramps and production drift dimensions are 15-feet x 15-feet. Attack ramps are driven from the main development to the mineralization boundary. Attack ramps may have a gradient of +/-15%, however, production drifts are preferred level. Once completed, a drift is backfilled with cemented rock fill (CRF) allowing the adjacent drift to be excavated. This process of drifting and backfilling is repeated until all economic mineralization has been mined in a 15-foot thick vertical horizon. Sample drilling the ribs helps define the boundaries. Where the remining mineralization does not justify the excavation of another drift the ribs may be slabbed to recover the mineralization before backfilling.

To initiate the next drift and fill horizon either a new attack ramp is driven, or the sill of the previous attack ramp is mined to reach the next drift and fill level elevation. Drifts under or alongside fill require less ground support than drifts entirely surrounded by rock. Drifts under fill can be widened to widths up to 20-feet.

The ground conditions at El Niño are typical of the northern Nevada extensional tectonic environment. Joint spacing varies from a few inches to a foot or more. Primary ground support includes 6-gauge 3-inch x 3-inch wire mesh, and 8-foot expandable rock bolts installed on a 4-foot x 4-foot pattern. Intersections are supplemented with 12-foot heavy duty expandable bolts installed on a 6-foot x 6-foot pattern. Development excavations have one or two coats of shotcrete applied at 2-inches thick per coat. Shotcrete is applied to production excavations as needed.

Cemented rock fill (CRF) is mixed on the surface and hauled underground in the same trucks used to haul broken rock to the surface. A truck will dump its load of CRF in the drift being filled and a load haul dump (LHD) or dozer fitted with a “Jammer” attachment will push the CRF tight to the back and ribs eliminating all void spaces. Mining alongside fill can occur as early as seven days following its placement and usually less than 28 days to mine underneath.

All mining at the El Niño Mine is conducted by a qualified underground mining contractor.

Ore from South Arturo is being processed via one of three possible routes: ROM heap leaching (possible in the future if economics warrant), milling and CIL, or roasting and CIL. The heap leach ore is segregated for possible processing in the future. Currently, production at the South Arturo project comes from El Niño underground mine. Underground reserves are refractory and are processed at the Goldstrike roaster as they are mined. Ore that requires milling is transported to a pre-determined stockpile location for transportation to Nevada Gold's Goldstrike facilities for processing, located approximately five kilometers from the South Arturo Mine. Refractory ore is also transported to the Goldstrike facilities. The roaster pre-oxidizes ore that contains refractory carbonaceous and sulfidic material so it can be effectively processed in a traditional CIL circuit. Goldstrike includes roaster and autoclave processing facilities. Sub-grade or incremental material may be placed in stockpiles or on a selected portion of the overburden storage areas for possible future processing. Oxide mill ore is minimal and could be transported by truck to the Cortez operation for processing, which is located approximately 118 kilometers (73 miles) from the South Arturo Mine. The Cortez Mill could process the oxide mill grade South Arturo ore on a campaign basis. The flowsheet includes crushing, semi-autogenous grinding (SAG), ball milling, grind thickening, carbon-in-column (CIC) circuit for the grind thickener overflow solution, CIL circuit, tailings countercurrent decantation (CCD) wash thickener circuit, carbon stripping and reactivation circuits, and a refinery to produce gold doré. CIL mill recovery is dependent on cyanide solubility and silica content. The Goldstrike roaster processes consists of primary and secondary crushing, two parallel dry grinding circuits, two parallel dual stage fluidized bed roasters, off-gas handling, mercury recovery systems, a slurry neutralization circuit, a carbon-inleach (CIL) circuit with carbon stripping, cyanide detoxification circuit, and electrowinning for gold recovery. The Goldstrike autoclave circuit processes consists of primary crushing, two parallel semi-autogenous grinding (SAG) Mill-Ball Mill grinding circuits with pebble crushing, five parallel autoclaves capable of acid pressure oxidation (POX) and three of which are capable of alkaline POX with carbon-in-leach (CIL) gold recovery, electrowinning for gold recovery, and a refinery producing doré bullion from both autoclave and roaster circuits. Goldstrike autoclave RIL to CIL conversion project Goldstrike implemented a novel thiosulfate leaching process following pressure oxidation for problematic preg-robbing sulphide ores with gold recovery by resin adsorption. The conversion from POX-CIL to POX-CaTS-RIL was commissioned in 2014 to advance gold production and provide an alternative to roasting of double refractory material. The implementation of non-cyanide solution chemistry provides a process alternative to mitigate “pregrobbing” (losses of gold in solution) caused by organic carbon in autoclaved slurry. Following the exhaustion of these stockpiled problematic ores, the plant is being converted back to a more conventional POX with carbon-in-leach (CIL) gold recovery to treat amenable ores facilitated by the joint venture. In March 2023, the conversion of the Goldstrike autoclave to a conventional carbon-in-leach process was completion.

- subscription is required.