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TitrePrecious metal enrichment processes in volcanogenic massive sulphide deposits - a summary of key features, with an emphasis on TGI-4 research contributions
TéléchargerTéléchargement (publication entière)
AuteurMercier-Langevin, P; Hannington, M D; Dubé, B; Piercey, S J; Peter, J M; Pehrsson, S J
SourceTargeted Geoscience Initiative 4: Contributions to the understanding of volcanogenic massive sulphide deposit genesis and exploration methods development; par Peter, J M (éd.); Mercier-Langevin, P (éd.); Commission géologique du Canada, Dossier public 7853, 2015 p. 117-130, https://doi.org/10.4095/296548
Année2015
ÉditeurRessources naturelles Canada
Documentdossier public
Lang.anglais
DOIhttps://doi.org/10.4095/296548
Mediaen ligne; numérique
Référence reliéeCette publication est contenue dans Peter, J M; Mercier-Langevin, P; (2015). Targeted Geoscience Initiative 4: Contributions to the understanding of volcanogenic massive sulphide deposit genesis and exploration methods development, Commission géologique du Canada, Dossier public 7853
Formatspdf
ProvinceNunavut; Territoires du Nord-Ouest; Nouveau-Brunswick; Manitoba; Québec; Terre-Neuve-et-Labrador
SNRC75I; 75J; 75K; 75L; 75M; 75N; 75O; 75P; 76; 85I; 85J; 85O; 85P; 86A; 86B; 86G; 86H; 86I/01; 86I/02; 86I/03; 86I/04; 86I/05; 86I/06; 86I/07; 86I/08; 86I/09; 86I/10; 86I/11; 86I/14; 86I/15; 86I/16; 86P/01; 86P/02; 86P/07; 86P/08; 86P/09; 86P/16; 21O/01; 21O/02; 21O/03; 21O/06; 21O/07; 21O/08; 21O/09; 21O/10; 21O/11; 21P/04; 21P/05; 21P/12; 63K/16; 32G/09; 32G/10; 32G/15; 32G/16; 12A/10; 12H/16
Lat/Long OENS-116.0000 -104.0000 68.0000 62.0000
Lat/Long OENS -66.5000 -65.7500 47.7500 47.1333
Lat/Long OENS-102.0000 -98.0000 56.0000 54.0000
Lat/Long OENS -75.0000 -74.0000 50.0000 49.5000
Lat/Long OENS -56.5833 -56.5833 48.6667 48.5000
Lat/Long OENS -56.0217 -56.0217 49.9317 49.8658
SujetsArchéen; gîtes volcanogènes; gîtes sulfureux; altération; métamorphisme; assemblages de minéraux; minéralisation; directives d'exploration; roches volcaniques; gisements minéraux; or; argent; métaux précieux; géologie économique; Précambrien
Illustrationsschematic diagrams; cross-sections; flow charts
ProgrammeÉtude des gîtes de sulfures massifs volcaniques, Initiative géoscientifique ciblée (IGC-4)
LiensCanadian Database of Geochemical Surveys, downloadable files
LiensBanque de données de levés géochimiques du Canada, fichiers téléchargeables
Diffusé2015 06 11
Résumé(disponible en anglais seulement)
Volcanogenic massive sulphide deposits contain precious metals (Au, Ag) that can be present in high to low grades and total amounts; depending on tonnage and/or precious metal grade, such deposits can represent desirable exploration targets. Globally, deposits with >3.46 g/t Au are considered "auriferous", those with >-31 t of contained Au are "anomalous", and those with both large tonnage (>-31 t Au) and high gold grade (>3.46 g/t Au) are considered "Au-rich". There are still no clear statistical criteria to determine thresholds that would define "anomalous" Ag grades and/or total amount of Ag in volcanogenic massive sulphide deposits, as grades vary widely depending on the nature of the host succession. Two general requisites may explain anomalous primary precious metal budgets in volcanogenic massive sulphide deposits: 1) inherently Au- and/or Ag-enriched source rocks and fluids due to a specific geodynamic setting or heritage and/or to magmatic input, and 2) efficient transport (favourable ligands) and precipitation (e.g. boiling/phase separation, zone refining). These two requisites, which are of different scales, may or may not be mutually exclusive. Late or "secondary" Au- and/or Ag-enrichment in volcanogenic massive sulphide deposits can be due to the superposition of mineralizing systems of a different style (e.g. epithermal, intrusion-related, orogenic, etc.). Weathering processes (e.g. supergene enrichment) on the seafloor or on land can also significantly modify the distributions of precious metals in a volcanogenic massive sulphide deposit.
Volcanogenic massive sulphide deposits in volcanic belts that formed in pericratonic settings or on older crust basement in the early stages of rifting are commonly slightly better endowed in precious metals than those formed in belts or settings with no or limited basement influence. Gold-rich and auriferous VMS are preferentially associated with calc-alkaline or transitional magmatic successions, with andesite-dacite-rhyodacite- rhyolite magmatic suites and with thick (10s to 100s of m) felsic volcanic packages. Evidence for a magmatic input and of deposition in response to boiling/phase separation include the presence of complex mineral assemblages comprising sulphosalts, sulphides, native elements, and anomalous trace element signatures (e.g. enrichment in the "epithermal suite" of elements Au-As-Sb-Ag-Hg and/or in felsic magmaassociated elements Bi-W-Te-In-Sn). A laterally extensive sericitic (phyllic) }siliceous alteration halo, a zone of intense aluminous (argillic to advanced argillic-style) alteration, and heterogeneous Au and Ag distributions and mineralogical residence sites within or near the sulphide bodies are also indicators of a possible magmatic contribution of Au, Ag, and other metals, such as Te and Bi, or metal deposition due to boiling in VMS systems.
GEOSCAN ID296548