Equinox, through its indirect wholly owned subsidiary NewCastle Gold Ltd., has 100% of the right, title, and beneficial interest in and to Castle Mountain Venture which owns the Castle Mountain Mine.
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Summary:
Castle Mountain is classified as a low-sulfidation epithermal gold deposit (Scott et al., 2018), a sub-type of the epithermal class of gold and silver deposits (Sillitoe and Hedenquist, 2003).
Mineralization
Structure and associated rock porosity-permeability characteristics are the first-order control on the distribution of gold. Flow-dome breccia margins, phreatic diatremes, fault cataclasite and fractures focused provided conduits for hydrothermal fluids and contain the highest gold grades. Unfractured coherent flow-dome facies, clay altered volcaniclastic facies, and clay altered phreatomagmatic diatremes with low or variable permeability are weakly mineralized due to lower fluid interaction. Lower permeability units that are mineralized have been cut by structures such faults, fractures, or phreatic diatremes that promoted hydrothermal fluid interactions.
Gold is focused along structures and margins of facies contacts. It is believed that sub-vertical structures acted as pathways for magma and are responsible for the emplacement of the felsic volcanic package. These same structures also acted as conduits for gold-bearing hydrothermal fluids. Intersections of the steep structures with more permeable volcanic rocks created an environment for enhanced gold precipitation from hydrothermal fluids, possibly due to processes of boiling and interaction with meteoric water.
Lithologic controls are dependent on the host rock texture. Tuff beds, auto-breccias, and hydrothermal breccias have permeable fragmental textures. Brittle rhyolite flows and intrusive equivalent rocks exhibit intense fracturing and are characterized by cooling joints, vesicular zones, spherulitic vugs, and flow foliations. Gold occurs within secondary silica in all these features. Major fault and fracture systems and intersections of fracture systems provided structural controls for mineralization. In the deposit area, north-northeast-striking, mineralized fracture zones are exposed in outcrop.
The morphology of mineralization follows two patterns. Firstly, gold is enriched along steep to vertical brecciated contacts of flow-domes and phreatomagmatic diatremes. Secondly, gold occurs in broad tabular zones that correlates with the general orientation bedding. The lateral extent of the mineralized bodies centered around fault zones are dictated by the intensity and extent of fracturing and faulting, in addition to the paleo-porosity of the host rocks.
Some faults and fracture zones are not gold-bearing since the structural regimes through the Project were active both pre- and post-mineralization. Gold seems to have precipitated during a single phase within a larger and longer-lived structural and hydrothermal event.
Silicification is commonly associated with gold occurring as pervasive silica flooding and quartz veining. Quartz veins can be vitric and “gel-like” or opaque white-gray opal. Vitric quartz veins typically occur in clusters as sheeted veins or stockwork in zones ranging from 3 to 35 ft (1 to 10 m) wide. Amorphous quartz occurs as discontinuous irregular veins and as open space filling quartz. The strongest silica alteration associated with gold is found along brecciated coherent rhyolite margins; this results in mosaic breccias where angular rhyolite clasts are within a hydrothermal-related silica matrix.
Gold on the Project occurs in oxidized fractures, faults, discontinuous veins, and breccia matrix. Gold mineralization correlates best with the deep red, red-brown and brown iron oxide that can range in color from pink to red-brown. The iron oxide intensity and appearance are commonly controlled by the volcanic facies occurring as discontinuous, fracture-controlled textures in coherent rhyolite facies, as matrix replacement in rhyolite breccias, wispy selvages and clast haloes in volcaniclastic rocks, and pervasive or matrix selective in diatremes. These iron oxide textures can be cut by fracture and vein filling iron oxide that ranges in color from brown-tan to red.
Visible gold is rarely observed in hand specimen and core. In petrographic samples collected near JSLA, visible gold is associated with iron oxide and silica and proximal to illite and adularia alteration (Cline, 2016). Gold deportment studies from Oro Belle by Chudy and Lane (2020) indicate that mineralization is roughly 79% native gold, 17% electrum and 4% silver minerals by frequency of grain count. Quartz may be intergrown with iron oxides/hydroxides, most commonly as hematite, which have formed as oxidation products of former sulfide minerals. There is a low abundance of sulfides observed on the Project. The most common sulfide mineral is pyrite, and varies from nil to 1%, which occurs within clasts and matrix.