Summary:
The Valentine Lake property hosts a structurally controlled, mesothermal gold deposit associated with Salinic aged crustal shortening and deformation. Gold mineralization is developed within QTP vein sets associated with brittle-ductile deformation of granitoid rocks of the Neoproterozoic Valentine Lake Intrusive Complex in contact with the Silurian Rogerson Lake Conglomerate. This contact is formed by the Valentine Lake Shear Zone, a major crustal-scale, NE-SW lithotectonic boundary.
Mineralization
A schematic model of the QTP-Au vein sets and their geometrical relationship with mafic dykes include:
• Set 1 QTP-Au veins occur as uniformly shallow southwest dipping, en-echelon arrays orientated at high angle to the regional penetrative S1 foliation and cleavage fracture.
• Lesser Set 2 QTP-Au veins are steeply northwest dipping to subvertical, parallel the regional S1 shear fabric, and commonly developed at contacts with mafic dykes or as localized zones of intense stockwork veining.
• Rare Set 3 QTP-Au veins are steeply dipping with a NW-SE orientation orthogonal to the strike of the S1 foliation (Kruse, 2020).
• At the Berry deposit, a fourth vein set has been identified with a very low angle dip to the NNE (Kruse and Bartsch, 2021). Each vein set is mineralized, with a strong dominance in frequency of occurrence and gold content exhibited by Set 1.
The Set 1 extensional and Set 2 shear-parallel QTP-Au veins are up to 1.5 m thick and have been traced in trenched outcrop exposures for over 280 m of continuous strike length; however, the observed strike length of individual veins is typically in the range of meters to tens of centimeters
The visible gold in QTP veining occurs as grains, ranging in size from <0.1 mm and up to 1-2 mm, hosted by quartz, tourmaline masses, within and along the margins of pyrite, or associated with minor tellurides. Highest gold grades are commonly associated with large (1-3 cm), euhedral and occasionally subhedral pyrite in QTP veining. In weathered surfaces, the gold is observed in limonite patches derived from weathering of the pyrite (Barbour, 1999). Other sporadically observed sulphides, in decreasing order of abundance, include chalcopyrite, pyrrhotite, sphalerite and galena. These minerals form minor components to the overall mineralization.
Marathon Deposit
The Marathon deposit is located 6 km northeast of the Leprechaun deposit and consists dominantly of shallow, southwestdipping en-echelon stacked QTP gold veins that intrude dominantly quartz-porphyry and lesser aphanitic quartz-porphyry and mafic dykes of the VLIC. The gold-bearing QTP veining occurs up to 250 m to the northwest of the VLSZ.
The Main Zone of gold-bearing QTP veining forms a northeast-trending sub-vertical mineralized corridor of intense QTP gold veining that ranges between 50 to 200 m in width, occurs over a strike length of more than 1.5 km, and has been observed in outcrop and drill-observed to a downhole depth of 1,000 m. The Main Zone contains a lenticular series of shallow, SW-dipping, gold-bearing QTP veining and is open at depth. At present, the peripheries of the Marathon deposit mineralized zone are relatively poorly defined, with a preliminarily observed outward gradational decrease in quartz vein density northwest and southeast from the central, dense vein zone.
Leprechaun Deposit
The Leprechaun deposit consists of QTP gold-bearing extensional and lesser shear parallel veins that intrude the variably sheared and fractured trondhjemite, as well as sheared mafic dykes of the VLIC.
Mineralization at Leprechaun occurs over a strike length of greater than 900 m and has been identified at surface in outcrop in drilling at depths of up to 400 m. The Leprechaun deposit differs from the Marathon deposit in the relatively tight concentration of mineralization in Main Zone type configurations of en-echelon stacked QTP-Au vein sets. These Main Zones range from 30 to 120 m wide, dip to the northwest, and are located proximal to the VLSZ contact within the VLIC trondhjemite. In the characteristic fashion, the dominant en-echelon stacked, southwest-dipping extensional QTPAu (Set 1) veins occur at high angle to the penetrative regional L1 stretching lineation, while the lesser shear parallel QTP-Au veins strike subparallel to slightly oblique to the VLSZ (Dunsworth, 2011; Dunsworth et al. 2017; Lincoln et al., 2018a, 2018b). Set 1 extensional QTP-Au veins at Leprechaun appear to have a moderately steeper SW dip than at Marathon (Kruse and Bartsch, 2021).
The QTP-Au mineralization at Leprechaun has been modelled in three zones from west to east: Hanging Wall Zone, Main Zone and Footwall Zone (Lincoln et al., 2018. The Main Zone is open at depth and is constrained to the southeast by the VLSZ with a gradational transition to the Hanging Wall to the northwest. A highgrade central core exists within the Main Zone, bounded by mafic dykes to the northwest and the Rogerson Lake Conglomerate to the southeast, forming a lenticular body of dense QTP veining open at depth.
The Hanging Wall Zone occurs transitionally west of the Main Zone and consists of a series of variably shallow to moderately dipping, stacked en-echelon extensional QTP tension gashes with minor steeper-dipping QTP veins that extend up to 350 m northwest into the hanging wall. The vein density and concentration of vein arrays increases toward the east, proximal to the Main Zone, and remains open to the northwest.
The Footwall Zone is a minor component of the Leprechaun deposit and comprises localized extensional QTP veins that extend into the structurally underlying Rogerson Lake Conglomerate. Toward the southern part of the deposit, the Main Zone appears to peel slightly further away from the fault contact which spatially coincides with a marked increase in the volume of wide, discontinuous mafic dykes observed near the contact in this area. The gold-bearing mineralizing fluids appear to have localized flooding along the mafic dyke contacts and regular breaching and brecciation within.
Berry Zone
The Berry deposit is located approximately 3 km northeast of the Leprechaun deposit and 2 km southwest of the Marathon deposit and spans a strike length of 1.5 km. This recently discovered area consists of dominantly shallowly southwestdipping, en-echelon, extensional QTP veining hosted in quartz-eye porphyry and lesser mafic dykes and aphanitic quartz porphyry. The mineralized corridors are generally 20 to 60 m wide and have been traced to depths of over 350 m. In localized zones, mineralization penetrates across the VLSZ and is found up to 20 m into the Rogerson Lake Conglomerate. Mineralization at the Berry deposit is found in tight QTP vein set packages bounded to the southeast by the VLSZ and the NW by a series of mafic dykes oriented sub-parallel to the shear zone. This style and configuration of mineralization is reminiscent of the tightly concentrated mineralized QTP vein set packages of the Leprechaun deposit.
The dominant vein orientation in the Berry deposit was found to be the extensional Set 1 veining dipping shallowly to the southwest, like that found in Leprechaun and Marathon deposits. In addition to the three vein sets found in Leprechaun and Marathon, Kruse (2020) documented a fourth orientation of mineralized veining at Berry which dips shallowly to the NNE. This QTP-Au vein set, referred to as “Set 3” of the four vein sets, is unique to Berry and appears to have a moderate (yet secondary) association with gold mineralization.