Mineralization and Alteration

Mineralized Zones
Marc, AV, JW and NK Zones

  • The Marc, AV, JW and NK Zones are found at the core of the Bitter Creek Antiform
  • The gold-silver ore bodies are crudely tabular with sulphide-rich stockwork vein systems
  • Main ore bearing sulphide is pyrite, with gold occurring in its native form , electrum, petzite, and Au-tellurides and locked within sulphosalts
  • Ore zones are generally marked by pyrrhotite and sphalerite halos
  • Pyrite veins typically carry gold grades ranging from 3 g/t to greater than 100 g/t

Gold-silver mineralization in the Marc, AV, JW, and NK Zones is characterized by irregular sulphide-rich stockwork vein systems. The ore bodies, are formed into crudely tabular, northwesterly trending and moderately to steeply southwesterly dipping zones within the Hillside Porphyry, volcano-sedimentary contact zones, and in intrusive breccias. The main gold bearing sulphide mineral is pyrite; however, pyrrhotite can be locally important. Stockwork vein systems are developed primarily in strongly sericite altered Hillside Porphyry; but, also in rafts of sedimentary and volcaniclastic rocks associated with the emplacement of the Hillside unit.

Course Grained Pyrite Veins
Course Grained Pyrite Veins
Pyrite Microveins
Pyrite Microveins
Breccia Matrix Pipe
Breccia Matrix Pipe

The stockwork vein systems are composed of:

  • Pyrite microveins
  • Coarse grained pyrite veins
  • Irregular coarse grained pyrite masses
  • Breccia matrix pyrite

Vein widths vary for 0.1 cm to approximately 80cm and carry gold grades ranging from 3 g/t to greater than 100 g/t. Gold found in the zones occurs as blebs native gold, electrum, petzite and a variety of gold tellurides and sulphosalts. These gold-bearing blebs, which are typically 0.5-15 microns in size occur along pyrite crystal cracks that are found within quartz and calcite infill in pyrite veins. Gold minerals are also found as inclusions within pyrite crystals. Pyrite veins in the deposit typically carry gold grades ranging from ~3 g/t to greater than 100 g/t. These systems are surrounded by a widespread envelope of disseminated pyrite, pyrrhotite and sphalerite alteration.
Alteration Zones of the Hillside and Goldslide Porphyry

  • Alteration is overlapping and gradational
  • Alteration assemblages on the property range from actinolite dominant to quartz stockwork molybdenum copper
  • Alteration weakens in intensity laterally to the southwest

Generally, the hornblende phenocrysts in Hillside Porphyry alter to chlorite, black-brown tourmaline, calcite and sericite. Whitish beige sericite dominates the assemblage and is due to the alteration of plagioclase. Unaltered Hillside Porphyry is black/grey in colour and becomes white, light grey, or pink when altered. Alteration zones in the Hillside and Goldslide Porphyry are anywhere from 5m to >200m thick, and have been identified by analysing mineral assemblages found in veins. Alteration zones range from the highest, actinolite dominant alteration to the lowest, quartz stockwork molybdenum copper, alteration intensity corresponds with decreasing elevation. Alteration at Red Mountain weakens in intensity laterally to the southwest. Alteration effects a range of units and transects stratigraphy, weakening in intensity laterally to the southwest of the property.

 

Alteration Thickness Veins Mineralogy of pervasive alteration
Actinolite dominant alteration >150 m Chlorite + Pyrite + Actinolite + Calcite Green to grey K-feldspar + actinolite + chlorite + titanite + albite + pyrite ± pyrrhotite
Tourmaline stockwork 100-300 m Tourmaline + Pyrite + Chlorite + Pyrrhotite Grey K-feldspar + chlorite + titanite + pyrite + tourmaline + pyrrhotite
Pyrrhotite dominant alteration 100-200 m Pyrrhotite + Pyrite ± chalcopyrite ± chlorite ± calcite ± quartz ± sphalerite ± galena Grey to brown-grey K-feldspar + sericite + pyrrhotite + pyrite + chlorite ± tourmaline
Auriferous pyrite + pyrrhotite stockwork 10-50 m Pyrite ± pyrrhotite ± quartz ± chlorite Intense grey sericite + pyrite; mantled by disseminated and veinlet sphalerite + pyrrhotite + pyrite
Pyrite-dominant alteration 100-200 m Pyrite ± calcite ± quartz ± chlorite Cream to tan sericite, pyrite ± calcite ± chlorite ± tourmaline
Gypsum Stockwork <5-100 m Gypsum + pyrite + calcite ± quartz Pale grey sericite + pyrite ± quartz ± K-feldspar
Quartz Stockwork, molybdenum-copper >200 m Quartz + pyrite ± chlorite ± epidote ± magnetite ± molybdenite ± chalcopyrite Green to grey sericite + quartz + pyrite + chlorite + K-feldspar ± epidote ± tourmaline ± magnetite ± hematite
(Rhys et al, 1995, and Thompson, 1994)

Ore and Alteration Formation

  • Alteration and mineralization at Red Mountain were due to influence from hydrothermal systems
  • Development occurred over the following steps:
    • Pre-ore tourmaline alteration
    • Pre/Early-ore stockwork vein development
    • Syn-ore fracture controlled alteration and mineralization
    • Late/Post-ore fracture controlled mineralization/alteration
  • Textures and structures developed during these stages are directly related to ore bodies.

Before the formation of the ore deposits, the rocks at Red Mountain underwent a pervasive brown and black tourmaline alteration. This was followed up with pervasive and fracture-controlled alteration and stockwork vein system development, just before and in the early stages of ore development. During this pre/early-ore stage tight to very weakly dilatant fractures formed, and pyrite micro-veinlets formed. Alteration from this stage is either pervasively chlorite-rich or sericite rich, both of which had abundant disseminated Fe-sulphides. The alteration that is syngenetic with the ore formation is fracture-controlled. Coarse-grained ore-related pyrite crystals precipitated, in reopened pyrite microveinlets. Coarse grained pyrite veins and clots are commonly enclosed by bleached alteration envelopes and haloes. Some wide coarse-grained Au-bearing pyrrhotite veins are found proximal to the ore zones, and have similar textures to syn-ore coarse grained pyrite veins. Post ore formation alteration was fracture controlled with less pervasive alteration and mineralization. Sphalerite rich veins, dissemination and replacement, which overlap with ore, are common on the periphery of the ore body and form a sphalerite halo. Quartz-calcite ± sulphide extension veins also formed at this time.

Deposit Model

Deposit Model

Red Mountain Mineralized Zone Model

Red Mountain Mineralized Zone Model

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