Archimedes Project is 100% owned by i-80 Gold Corp. through its wholly owned subsidiary Ruby Hill Mining Company LLC, the direct owner of the project, while Golden Hill Mining Corporation, another i-80 subsidiary, holds adjacent assets unrelated to Archimedes.
- subscription is required.
Summary:
East Archimedes, West Archimedes, 426, Ruby Deeps, 007, 008, Hilltop and Blackjack are located on the
eastern side of the near north-trending Holly Fault.
The 426 zone is spatially associated with the NE-trending 426 fault zone and north of the Blanchard fault zone. The 007 zone is spatially associated with the NNE-trending NS Fault, also lying north of the Blanchard fault zone. The 008 zone lies between the 426 and NS faults, north of the Blanchard fault zone, along the hinge of an anticline formed above and intrusive lens.
Structure within the Ruby Deeps deposit area is a continuation at depth of faulting related to the Archimedes deposit to the east and the Mineral Point deposit to the west. The Ruby Deeps deposit is bounded to the east by the Graveyard Flats fault and the west by the Holly fault. The Blanchard fault zone transects the center portion of the deposit but does not appear to offset mineralization.
The Hilltop Fault has similar orientation to the Blanchard fault. It trends WNW just south of the Archimedes pit, from the Holly Fault towards the Graveyard Flat intrusion. It is undetermined whether the Hilltop fault transects the Ruby Deeps deposit or defines its southern boundary. Several drillholes have intersected CRD mineralization at various elevations along the Hilltop fault.
Mineralization
The mineralization at Ruby Hill is characterized by intrusion-related distal-disseminated, carbonate replacement, and skarn deposits that have been overprinted by younger Carlin-type gold mineralization.
Polymetallic Carbonate Replacement Deposits
The carbonate replacement mineralization is similar to other polymetallic (Pb-Zn-Ag ± Au) deposits found worldwide that are spatially associated with Cretaceous age intrusive units. The carbonate replacement mineralization consists of massive to semi-massive pyrite, galena, sphalerite, and other sulfides typically with sharp boundaries into barren marble. Locally, mineralization is oxidized into gossanous bodies. Fluids are sourced from intrusions, with metals in bisulfide complexes at temperatures of 250°-500°C, with the depositional mechanism typically being a pH change that results in rapid deposition of metals.
Skarn Deposits
The skarn deposits at Ruby Hill are consistent with zinc skarns throughout the Cordillera. The Blackjack deposit is located along the margin of the Cretaceous Graveyard Flats stock. However, drilling by i-80 Gold suggests this is a faulted contact. At Blackjack, sphalerite is found disseminated and semi-massive to massive in garnet-pyroxene altered carbonates. In the eastern Hilltop area zinc skarn is contained within carbonates altered to marble and wollastonite and appears to be located more distal to the Graveyard Flats stock. Both zones typically show evidence of brecciation associated with mineralization. Zinc skarns typically form distal to their source intrusions at temperatures of 350-450°C with mineralization subsequent to metamorphism.
Carlin-Type Gold Deposits
Gold and silver mineralization within the Ruby Hill deposits is predominantly attributed to a Carlin-type overprint interpreted to temporally coincide with the onset of extensional tectonics and Eocene-Oligocene magmatism. The structural setting, alteration mineralogy, and mineralization characteristics of the Ruby Hill gold deposits are consistent with Carlin-type deposits as defined in Radtke and Hofstra and Cline
At East and West Archimedes, gold-rich mineralization is associated with jasperoid and moderately to strongly decarbonatized limestone. Gold occurs in the oxidized ores as discrete grains less than 3 microns in diameter. Mineralization is controlled by structure and lithology. Second order control to mineralization within West Archimedes is focused by steeply dipping, N-trending normal faults. Within East Archimedes, second order control to mineralization is by the N-trending Graveyard fault and East Archimedes fault.
East Archimedes mineralization is a NW-trending, roughly tubular shaped mineralized body, approximately 1,350 ft in height, 800 ft in thick, and 1,900 ft wide. The upper portion flattens and flares out to the west and connects to West Archimedes. Mineralization extends from surface to approximately 1,400 ft below surface and the main host rocks include Ogll and Og2 of the Goodwin Formation.
The West Archimedes zone is NW-trending, roughly cigar shaped, 1,700 ft long, 200 ft thick, and varies from 400 ft to 1,200 ft wide. Mineralization extends from surface to approximately 150 ft below surface and the main host rock is Og2 of the Goodwin Formation.
Mineralization at 426 is NE-trending, roughly rod-shaped, 1,300 ft long, 250 ft thick, and 250 ft wide. Mineralization is variably oxidized. Oxidation correlates strongly with proximity to fault structures and secondarily with elevation. The top of mineralization commences approximately 800 ft below surface with the main host rocks being the Og1 (oxide-rich) and Ogll (sulfide-rich) units of the Goodwin Formation.
Mineralization at Ruby Deeps is N-S trending, tabular zone comprised of stacked mineralized bodies developed within favorable lithological horizons. The overall zone is 2,200 ft long, 900 ft thick, and 800 ft wide. Mineralization is locally oxide at higher elevations and predominantly sulfide-bearing at lower elevations. The top of mineralization is approximately 1,200 ft below surface with the main host rock being the Windfall Formation.
Alteration
Within the East and West Archimedes deposits the three main alteration types are observed along with skarn and propylitic assemblages proximal to the intrusive units.
Silicic alteration is spatially associated with the Blanchard Fault zone, and subsequent intersecting N- to NE-trending faults (Holly, 150, 194, Armpit, 426, and Graveyard Flats). Decarbonatization with breccia textures are observed in carbonaceous sedimentary units. Argillic alteration is logged extensively along the Blanchard fault zone and at the intersections of the Blanchard fault zone with the N- to NE-trending faults.