MINERALOGY OF RARE OCCURRENCES OF PRECIOUS-METAL-ENRICHED MASSIVE SULFIDE IN THE VOISEY'S BAY Ni-Cu-Co OVOID DEPOSIT, LABRADOR, CANADA

Abstract

The Voisey's Bay Ovoid Ni-Cu-Co magmatic sulfide deposit, Labrador, is generally poor in precious metals (Pt, Pd, Ag, Au), but unusual occurrences with elevated levels (Pt + Pd > 0.5 ppm) are present. We present a quantitative description of the precious-metal mineralogy of four such occurrences within massive sulfides. The four samples, all from near the center of the Ovoid, were examined by SEM-based Mineral Liberation Analysis for characterization of precious-metal minerals. Distributions of precious metals among the major sulfide minerals were estimated using mass-balance calculations based on bulk assays of the samples and the proportions and compositions of the minerals. The results indicate that the majority of precious metals are present as discrete mineral phases including sperrylite, froodite, michenerite, Au-Ag alloy, volynskite, stützite and acanthite, whereas minor to moderate amounts of Pt, Pd, Ag and Au are found in solid solution in pyrrhotite, pentlandite, chalcopyrite and galena. The precious-metal minerals are normally associated with pentlandite, galena, chalcopyrite, pyrrhotite and magnetite, and rarely with breithauptite (NiSb), altaite (PbTe), other precious-metal minerals and native bismuth. With the exception of sperrylite, which is coarse grained and liberated easily by electric pulse disaggregation, the precious-metal minerals are most commonly found as fine inclusions in pentlandite and galena, and less so as larger attachments. The associations are consistent with previously reported precious-metal mineral data from a hornblende gabbro dyke of the Southeast Extension Zone at Voisey's Bay, demonstrating similar modes of crystallization, which are likely related to crystallization of a highly differentiated sulfide magma in both areas. Processing of Pt from sperrylite and perhaps Pd from froodite could be achieved in ores with a mineralogy similar to the samples described here by grinding, and gravity or flotation methods, but the Au-Ag alloy, volynskite and stützite would likely be too fine to recover as discrete grains for Ag and Au concentration. Instead, the Ag and Au could be recovered as a by-product of Ni-Cu-Co processing of the pentlandite and chalcopyrite, which are the major hosts of the Ag and Au minerals. SoMMAiReLe gisement Ovoid de sulfures magmatiques de Ni-Cu-Co à Voisey's Bay, au Labrador, est généralement appauvri en métaux précieux (Pt, Pd, Ag, Au), mais il y a néanmoins des indices inhabituels ayant des teneurs élevées (Pt + Pd > 0.5 ppm). Nous présentons une description quantitative des minéraux porteurs de ces métaux précieux dans quatre de ces indices au sein des amas de sulfures massifs. Les quatre échantillons, prélevés près du centre du gisement Ovoid, ont été examinés avec un microscope électronique à balayage et une analyse des minéraux libérés afin de caractériser les minéraux porteurs des métaux précieux. Nous avons évalué la distribution des métaux précieux parmi les sulfures importants en effectuant des calculs des bilans de masse fondés sur les résultats...

MLA-SEM Characterization of Sulphide Weathering, Erosion, and Transport at the Voisey’s Bay Orthomagmatic Ni-Cu-Co Sulphide Mineralization, Labrador, Canada

“…As shown by the BSE images, the coarse reject sulphides contained a variety of precious and base metal sulphide inclusions. Precious metal (PM) concentrations at Voisey's Bay are typically low compared to other orthomagmatic sulphide deposits, but [21] report discrete PM minerals (e.g., sperrylite, michenerite, Au-Ag, acanthite) in pentlandite, chalcopyrite and pyrrhotite from the Ovoid deposits. Huminicki et al [22] found that Pd was a solid solution component of pentlandite.…”

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

“…Notes: x = texture observed, -= texture not observed presence or underestimating the amount of microscale precious metal grains due to grain size), and at a much higher resolution compared to common petrographic or exploratory SEM methods (Sylvester, 2012). Although, the application of MLA is often focused in applied mineralogy and metallurgical processes (Fandrich et al, 2007;Ford et al, 2011;Kelvin et al, 2011), heavy mineral provenance in sediments and sedimentary rocks (Lowe et al, 2011;Tsikouras et al, 2011), and till and stream-sediment prospecting (Wilton and Winter, 2012), it can be a strategic tool when used with basic geologic, stratigraphic, mineralogical, and alteration observations to solve genetic problems in the study of metallic mineral deposits.…”

Distribution of Sb minerals in the Cu and Zn flotation of Rockliden massive sulphide ore in north-central Sweden

“…Complex trace mineralogy is reported, for example, for uranium (U), silver (Ag), rare earth element (REE) and platinum group element (PGE) ores (e.g. Bowell et al, 2011;Chetty et al, 2009;Grammatikopoulos et al, 2013;Kelvin et al, 2011;Rohde et al, 2014). In such cases a large number of mineral grains, and thus a large number of samples, are measured by automated mineralogy tools (Chetty et al, 2009).…”