Summary:
The mineral deposits along the Carlin Trend form a suite of deposits known as Carlin type deposits.
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 Gold Quarry deposit contains both Mineral Resources and Mineral Reserves and is currently in operation as the Gold Quarry OP. This deposit was historically mined as the Chukar underground in conjunction with open pit operations.
Gold mineralization is principally hosted within Rodeo Creek, Popovich and Roberts Mountain formations. High-grade mineralization is structurally controlled along complex intersections of Phase II thrust-propagated folds with upright Phase III folds, forming discrete, prolate geometries. The deposit is bound to the west by the NE-trending Chukar-Alunite fault zone, to the east by the NEtrending Deep Sulfide Feeder fault zone, and to the north, the Good Hope fault, all host variable degrees of mineralization.
Gold Quarry exhibits an east verging fold and thrust architecture which has been overprinted by extensional faults and brecciation/de-calcification associated with hydrothermal fluid flow. Dominant extensional features include the Chukar-Alunite fault zone and the deep sulphide feeder, which have served as major fluid conduits to gold mineralization.
Locally, gold mineralization exploits preferential sub-units of the Rodeo Creek and Popovich formations, particularly where they have been thickened by early compressional events. Highest grade mineralization is typically observed along major fluid conduits and regional scale fold hinges, concentrating higher grades along their structural intersection.
Ten geologically distinctive mineral zones have been defined, referred to as Quarry Main, Deep West, Deep Sulfide Feeder, Chukar North, Chukar South, Good Hope, Mac, Magpie, Southwest, and Wedge.
Six major lithologic units are recognized in the Gold Quarry deposit from surface mapping and drill hole logging: Tertiary Carlin, Devonian Slaven, Devonian Rodeo Creek, Devonian Popovich, Silurian Roberts Mountains, and Ordovician Hanson Creek Formations.
The four main gold-hosting lithologies are:
• Silty limestone sections of the Roberts Mountains Formation;
• The upper 90 metres of the Popovich Formation consisting of silty limestone and calcarenite;
• Siltstone, siliceous mudstone, and cherty siltstone of the Rodeo Creek Formation; and
• About 60 metres of upper-plate sedimentary rocks of the Marys Mountain sequence that consists of limy mudstone and siltstone.
Detailed surface mapping and drill hole interpretation indicates that there are four dominant fault sets at Gold Quarry. These include (from youngest to oldest): north striking basin-bounding, normal faults (Grey, and Tuff Faults), northeast-striking normal faults (Chukar, Alunite, Bad Attitude, and Deep Sulfide Feeder Faults), northwest-striking Good Hope reverse Fault, and low-angle Roberts Mountains thrust.
Oxide gold ore consists of minute particles of finely-disseminated native gold within the host rock. Oxidization of portions of the deposit may have occurred as a result of late hydrothermal acidleaching and supergene leaching of the original refractory material. Oxide material is subdivided into oxide carbonate (OC) and oxide siliceous (OS) styles, based on the presence of carbonates. Refractory mineralization is subdivided into silica sulfide refractory (SSR), carbon sulfide refractory (CSR), and unoxidized carbonate (UC). Refractory conditions of each type are due to a combination of silica ± pyrite encapsulation of gold ± the presence of naturally activated organic carbon ± the presence of carbonate. These represent the unoxidized portions of the Gold Quarry deposit. Mineralization is associated with As, Sb and Hg.
Sulfidation, decalcification, and dolomitization of the Popovich and Roberts Mountains limestones and silicification of the Rodeo Creek siliciclastic rocks are the dominant alteration types associated with mineralization. Barite and clay-altered intrusive rocks have been noted in association with the Alunite and Good Hope Faults.
The dimensions and orientations of the modelled mineralized domains for Gold Quarry deposit:
Length - 490 – 1,490 m
Width - 360 – 1,160 m
True Thickness - 40 – 200 m
Approximate Strike Direction - NNE.