Mineralogy and mineral chemistry of the metamorphosed and precious metal-bearing Ming deposit, Canada

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

“…At Ming, the close mineralogical association of the Ag-rich electrum core with arsenopyrite, chalcopyrite, pyrrhotite, and sphalerite suggests that Au was transported by bisulfide complexes at a temperature < 300℃, in reduced fluids, whereas the association of Ag-rich electrum rim with galena and chalcopyrite suggests that Ag was transported by chloride complexes (Seward, 1973;Huston et al, 1992;Williams-Jones et al, 2009;Brueckner et al, 2016). The silver-rich electrum core suggests a low pH solution, because silver chloride complexes are far more soluble than the bisulfide complexes at low pH, indicating Ag is more mobile than Au (Mann, This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.…”

“…http://www.minsocam.org/ 1984; Wilson, 1984;Gammons and Barnes, 1989). The formation of electrum grains along fractures in recrystallized pyrite or arsenopyrite has been interpreted to be of syngenetic origin between 260℃ to 300℃ at Ming, whereas the regional Silurian-Devonian deformation indicates a peak metamorphic temperature of 500℃ (Brueckner et al, 2016). At elevated temperature, silver likely tends to be dissolved via reaction (1), leading to the increase in Au content to form the Au-rich zone with a gradational contact with the electrum core (Gammons and Williams-Jones, 1995;Migdisov et al, 1999).…”

“…DOI: https://doi.org/10.2138/am-2021-7674. http://www.minsocam.org/ because both have common gold mineralization characteristics: (1) occurrence of zoned electrum, (2) an overlap of VMS and epithermal (Ag, As, Sb, Hg) mineralization with interpreted magmatic contributions (e.g., Bi, Te), (3) complex ore mineralogy with abundant sulfides and sulfosalts, (4) association with andesite-dacite-rhyodacite-rhyolite rocks, and (5) metamorphism and deformation overprints resulting in remobilization of gold (Mercier-Langevin et al, 2011;Mercier-Langevin et al, 2013;Brueckner et al, 2014;Brueckner et al, 2016). Here, we present in situ textural and chemical composition results of electrum from the Boliden and Ming deposits, to investigate compositional zoning characteristics in electrum grains and to constrain the mechanisms responsible for chemical zoning in electrum.…”

“…2.26 wt% Cu, 1.13 g/t Au, 6.78 g/t Ag, and 0.32 wt% Zn) located in the northern central part of the Baie Verte Peninsula of Newfoundland (Canada, Pilote and Piercey, 2013;Brueckner et al, 2016). 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.…”

“…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).…”