Resolving the Relative Timing of Au Enrichment in Volcanogenic Massive Sulfide Deposits Using Scanning Electron Microscopy-Mineral Liberation Analyzer: Empirical Evidence from the Ming Deposit, Newfoundland, Canada

Abstract

The metamorphosed Cambro-Ordovician Ming volcanogenic massive sulfide deposit in northern Newfoundland, Canada, is locally overlain by a unit consisting of mafic to intermediate medium-to coarse-grained volcaniclastic breccia with up to 10 vol % sulfide clasts. Analysis via mineral liberation analyzer of two sulfide clasts, completed using scanning electron microscope observations, allowed the identification of a number of microscopic and submicroscopic electrum grains. These electrum grains occur in three types of textural settings: (1) free electrum grains with tellurides within gangue minerals, (2) inclusions of electrum with tellurides in pyrrhotite grains, and (3) free electrum grains with base metals and tellurides interstitial between base metals and along cataclastic fractures in pyrite. These three textural settings are similar to those in the underlying massive sulfide orebodies that represent very likely sources to the sulfide clasts. The polylithic nature and angularity of the volcaniclastic fragments in the breccia suggest a postmineralization gravity-controlled debris flow proximal to its source. The mineral assemblage and textures of electrum in the sulfide clasts implies evidence in support of syngenetic and predeformation Au introduction in the volcanogenic massive sulfide deposit, and argues against an orogenic overprint as the cause for Au enrichment. † Corresponding

The Development of Microscopic Imaging Technology and its Application in Micro- and Nanotechnology

“…It has a significant impact on geology ( Chen et al, 1980 ). JL Pilote studied the relative enrichment time of gold in volcanic massive sulfide deposits using scanning electron microscope mineral liberation analysis (SEM-MLA) in 2016, contributing to the research of deposit formation ( Pilote et al, 2016 ). In the biomedical field, in addition to the traditional structure observation research direction, SEM has been applied in some research directions, which is emerging.…”

Dissolution-reprecipitation vs. solid-state diffusion in electrum: Examples from metamorphosed Au-bearing, volcanogenic massive sulfide (VMS) deposits

“…The deposit is hosted in the upper part of the Rambler Rhyolite Formation (Figure 1), which is a folded, dome-shaped, sequence of quartz-phyric rhyodacite, quartz-bearing intermediate to felsic tuff and tuff breccia formed during the Cambrian-Ordovician (ca. 487 Ma, Skulski et al, 2010;Pilote et al, 2016). Upper greenschist to lower amphibolite facies metamorphism affected most of Rambler Rhyolite Formation, including four phases of regional deformation (Hibbard, 1983;Castonguay et al, 2009).…”

“…There are five massive sulfide orebodies hosted within variously hydrothermally altered volcaniclastic rocks, which are the 1807, 1806, Ming North, Ming South and Lower Footwall zones. The ore mineralogy in the 1807 zone consists of (1) pyrite, chalcopyrite, sphalerite, pyrrhotite, arsenopyrite, and galena, (2) uncommon tellurides, selenides, and sulfo-animonides, (3) sulfosalts (tennantite-tetrahedrite), (4) precious metals (electrum, Ag-sulfosalts, and minor silver), and (5) oxides (magnetite, ilmentite, chromite) (Brueckner et al, 2016;Pilote et al, 2016). Precious metal (Au-Ag) emplacement is syngenetic (Brueckner et al, 2014).…”