The Carlin Complex is operated as a joint venture (JV) through Nevada Gold Mines (NGM) which was formed in 2019. Barrick is the JV operator and owns 61.5%, with Newmont owning the remaining 38.5% JV interest.
Background: On March 10, 2019, Barrick entered into an implementation agreement with Newmont to create a joint venture combining the companies’ respective mining operations, assets, Reserves and talent in Nevada, USA. This included Barrick’s Cortez, Goldstrike, Turquoise Ridge and Goldrush properties and Newmont’s Carlin, Twin Creeks, Phoenix, Long Canyon and Lone Tree properties. On July 1, 2019, the transaction closed, establishing NGM and Barrick began consolidating the operating results, cash flows and net assets of NGM from that date forward.
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Summary:
The Carlin Trend is an approximately 64 km long, NW-trending alignment of predominantly carbonate-hosted gold deposits. Paleozoic tectonothermal events of the western United States shaped the geology of the Carlin Trend, principally characterized by broad amplitude, NW-trending, northerly-plunging anticlines within autochthonous carbonate assemblage rocks that are now preserved in uplifted tectonic windows. From north to south these tectonic windows include Bootstrap, Lynn, Carlin, Maggie Creek, and Rain. All Carlin Trend gold deposits discovered to date occur either within or proximal to these tectonic windows.
Deposit Type
The mineral deposits along the Carlin Trend form a suite of deposits known as Carlin type deposits and includes the archetype Carlin deposit that was discovered in 1961.
Carlin mineral systems are a unique class of epigenetic ore deposits with enigmatic origins. They are unique due to the size and scale of deposits that formed exclusively within NE Nevada during the middle-Eocene period (42-35 Ma), establishing this area as a world-class gold complex. Carlin mineral systems are enigmatic due to their unknown, distal source of gold, as well as deposit characteristics and hydrothermal conditions that culminate to being atypical of most documented mineral systems.
The leading hypothesis for the genesis of Carlin-type deposits is a magmatic-hydrothermal origin (Muntean et al., 2011).
Mineralization
The Carlin Complex can be divided into 6 main geologic zones or windows which host the active and prospective mining areas. These mining areas are extracted via open pit methods, underground methods or both. The geologic zones are distinguished by geologic controls which are described later.
Gold mineralization was emplaced approximately 39 Ma ago in response to slab rollback induced extension and asthenospheric upwelling, which generated voluminous magmatism simultaneously with mineralization. Eocene intrusions within the Carlin Trend are presumed to exist at depth beneath the district, with discrete felsic dikes intruding various deposits. Muntean et al., 2011 and references therein propose that the source of gold is magmatic-hydrothermal related to this event.
The culmination of structural preparation through the complex evolution of Nevada generated intensely altered rocks and localized dissolution-collapse breccia that focused along favorable structural intersections. This resulted in discrete, prolate zones of hyper-focused fluid-rock interaction that typically hosts the highest gold grades. Where fluid-rock interaction was lower, or adjacent to the discrete, high-grade zones, are laterally extensive, oblate mineralization that is dominantly stratabound, albeit at relatively lower grades.
Gold is transported by bisulfide complexes that are destabilized during high fluid-rock reaction facilitated by available ferrous iron. Sulfidation occurs at the interaction with reactive ferrous iron destabilizing the sulfur from solution and is the principal mechanism for gold precipitation. Gold is structurally bound to the crystal lattice of the resultant hydrothermal pyrite, which is commonly arsenian and/or trace element enriched. Hydrothermal pyrite forms a rim on pre-ore pyrite. Muntean et al. (2011) postulated that gold traveled in its ionic form (Au1+), resulting in a highly efficient scavenging of gold from solution due to the strong affinity to the negatively charged surface of hydrothermal pyrite. This may explain the extraordinary size and tenor of gold deposits along the Carlin Trend.
South Arturo
South Arturo is located in far north of the Carlin Trend that forms three structurally discrete ore bodies; the west, east and north.
South Arturo is a regionally distal Carfin-type deposit characterized by prolate mineralization geometries that are dominantly structurally controlled. Stratabound mineralization is apparent but far less continuous than similar deposits on the Carlin Trend. This likely reflects relatively lower hydrothermal fluid-rock interaction coupled with less favorable host rocks where planar faulting and fold features were the most permeable traps. Thus, mineralization orientations are highly variable due to the locally complex structural controls.
Mineralization is primarily hosted within the shelf-facies Rodeo Creek Formation. Discontinuous zones of mineralization occur within the allochthonous sequence of Vinini Formation but are minor. The platform-facies Bootstrap limestone is not a major host to mineralization but plays an important chemical and rheological competency contrast focusing fluid flow along its contact with Rodeo Creek Formation.
Goldstrike
The Goldstrike deposit, is the largest gold deposit on the Carlin Trend divided into three sub-deposits; Goldstrike OP, Goldstrike UG, and the Ren Project.
Mineralization is dominantly hosted within the Popovich, and lesser so within the Rodeo Creek and Roberts Mountain formations. Geometrically complex breccia development occurs in variably orientated structures, which concentrate the highest-grade mineralization. Jurassic dike swarms of varying compositions also utilize these structures and may also be a significant host to mineralization, particularly within the Goldstrike Open Pit. Consequently, disconcordant mineralization can be hosted within less favorable units such as the Bootstrap limestone.
Mineralization is dominantly refractory in Goldstrike UG and the Ren Project. Significant oxide material is present in Goldstrike OP, with gold associated with secondary oxides. Weathering alteration extends up to 200 m in depth resulting in oxide mineralization, which overlies the refractory sulphides.
Goldstar
Mineralization is preferentially hosted in the Wispy sub-unit of the Popovich Formation and in breccia along upper Roberts Mountain sub-unit contacts. The highestgrade gold mineralization is hosted within the Tuscarora anticline axial plane extending into the overturn east limb. This zone of the Roberts Mountain Formation is significantly jointed and intensely sicilfied at the contact with the Popovich Formation. Localized mineralization also concentrates at the structural intersection of the Wispy sub-unit with high-angle structures that are variably infilled with pre-mineral, undifferentiated dikes.
Exodus
Mineralization is preferentially hosted in Popovich, Rodeo Creek and Roberts Mountains units, with locally discrete zones of mineralization associated with pre-mineral dikes of various composition and orientations. Both deposits exhibit strong structural controls on mineralization with emphasis on the high-angle Castle Reef Fault.
Greater Leeville area
Deposits of the Greater Leeville area include Leeville (West Leeville, Turf, Four Corners orebodys), Fallon, Pete Bajo and Rita K. Leeville, Pete Bajo, Rita K and Fallon.
Gold mineralization is hosted within Popovich, Rodeo Creek, and Roberts Mountains formations, and associated with a series of variably orientated, discordant undifferentiated dikes that are intensely argillized. Local Phase II thrust-propagated folding structurally controls the highest-grade zones of mineralization within the anticline axial planes, disseminating outwards as stratabound mineralization in favorable sub-units. Subsequent high-angle normal faulting offsets the fold-thrust package and provide feeder-style transport for the hydrothermal fluid event often hosting mineralization associated with dikes.
The Gold Quarry
Gold mineralization is principally hosted within Rodeo Creek, Popovich and Roberts Mountain formations. High-grade mineralization is structurally controlled along complex intersections.
Highest grade mineralization is typically observed along major fluid conduits and regional scale fold hinges, concentrating higher grades along their structural intersection.