Genesis of gold-silver mineralization in epithermal quartz veins along the Magaguadavic Fault zone in the Pokiok plutonic suite southwestern New Brunswick

Abstract

The regional-scale Magaguadavic Fault that hosts the gold and silver and minor base-metal mineralization at the Pokiok property, located approximately 45 km west of Fredericton in southwest New Brunswick. The Magaguadavic fault is a subvertical, north-south regional structure that extends approximately 65 km across the Pokiok Batholith. At the Pokiok property this fault locally marks the boundary between fine- to medium-grained, pink biotite granite and minor muscovite-biotite of the Hawkshaw and muscovite-biotite Allandale granites. At the Pokiok property base(Cu, Pb, etc.)- and precious (Au-Ag) metal-bearing mineralization is associated with extensive quartz veining within an envelope of pyrite-sericite-chlorite alteration. Float samples containing native Au in comb-quartz veins was during their trenching and drilling program conducted in 2012 but assays from drill core were disappointing. During the present investigation re-analysis of rejects material using Au-Fire Assay –Metallix Screen-500g and Aqua Regia ICP-MS techniques and yielded higher Ag and Au (up to 3460 ppb) grades than previously reported. The study of drill core, polished thin sections, and polished slabs of samples collected from the six drill cores through the altered and mineralized zone failed to identify Au. Quartz vein textures such as (fine comb, crustiform, colloform, infill breccias) and mineral associations (chalcedonic quartz, adularia, pyrite, sphalerite, arsenopyrite, Ag-sulphides, calcite, chlorite, fluorite, sericite) is characteristic of low-sulphidation epithermal systems. The 40Ar/39Ar geochronology of muscovite in the mineralized zone yielded an age of mineralization of 389 Ma, which is at least 13 My younger than the age of the host intrusion. This indicates that the heat from the granitic intrusions was not responsible for the convection of the meteoric fluids which transported the mineralization, but rather a deeper magmatic source of heat beneath the Hawkshaw and Allandale granites or seismic pumping is the cause.