An investigation of the geology, geochemistry and timing of gold mineralization at the viking gold deposit, White Bay, Newfoundland

Minnett, Matthew (2012) An investigation of the geology, geochemistry and timing of gold mineralization at the viking gold deposit, White Bay, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Silurian-Devonian orogenic gold deposits in Newfoundland are typically situated proximal to major regional scale structural lineaments. Such deposits are formed in accretionary settings, late in the orogenic process with nearby intrusions of similar age, by low-salinity, H₂O-CO₂ ± CH₄ fluids at temperatures ranging from 250-350°C. The White Bay area of western Newfoundland contains at least 3 styles of mineralization including structurally controlled orogenic gold- base-metal mineralization (Type 1), stratabound galena mineralization (Type 2), and minor fluorite and molybdenite occurrences (Type 3). These deposits are proximal to the Doucer's Valley fault system, an interpreted Taconic thrust surface which offsets Carboniferous strata. This fault system may have been episodically active for ca. 150 m.y. providing conduits for mineralizing hydrothermal fluids on a regional scale. -- The Viking gold property, located 10 kilometers south of the community of Pollards Point, contains Type 1 orogenic-style gold mineralization west of the Doucer's Valley fault system in the Humber Zone. High-grade mineralization consists of coarse (50 to > 140 micron) blebby gold and argentiferous electrum hosted both within quartz veinlets and as inclusions in the sulfide assemblage (pyrite, galena, sphalerite, and chalcopyrite) of these veinlets. Lithogeochemistry and previous U-Pb geochronology demonstrate that the hosts to this mineralization/alteration are ca. 1030 Ma, Grenvillian A-type anorogenic granitoids, ca. 615 Ma continental tholeiitic dykes and inclined sheets of the Long Range dyke swarm and calc-alkaline lamprophyric dykes of unknown affiliation. ⁴⁰Ar-³⁹Ar thermochronology on late-syn-kinematic biotite porphyroblasts constrains the age of the last peak (ca. 250° C) metamorphism to the latest Silurian at ca. 419 Ma. Hydrothermal sericite from the alteration assemblage yields plateau and pseudoplateau ages ranging from 409 ± 12 Ma to 377 ± 1.5 Ma. Fluid inclusion assemblages have homogenization temperatures that range from 240-320°C and are low salinity. Sulfur isotope results indicate that δ³⁴S values are heavier than sulfur from magmatic origins and Pb model ages suggest that Pb was scavenged from multiple sources. These observations collectively suggest that the Viking gold mineralization represents a unique silver-bearing, granite-hosted, orogenic gold deposit in the Humber Zone formed in the Lower Devonian after orogenic collapse, from auriferous fluids fluxed along the Doucer's Valley fault system.

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