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TitreA review of analytical methods for regional geochemical survey (RGS) programs in the Canadian Cordillera
AuteurLett, R; Rukhlov, A S
SourceIndicator minerals in till and stream sediments of the Canadian Cordillera; par Ferbey, T (éd.); Plouffe, A (éd.); Hickin, A S (éd.); Geological Association of Canada, Special Paper vol. 50, 2017 p. 53-108
Année2017
Séries alt.Mineralogical Association of Canada, Topics in Mineral Sciences 47
ÉditeurAssociation géologique du Canada
ÉditeurAssociation minéralogique du Canada
Documentpublication en série
Lang.anglais
Mediapapier
Référence reliéeCette publication est contenue dans Ferbey, T; Plouffe, A; Hickin, A S; (2017). Indicator minerals in till and stream sediments of the Canadian Cordillera, Geological Association of Canada, Special Paper vol. 50
ProvinceColombie-Britannique; Yukon
SNRC82; 83; 84; 85; 92; 93; 94; 95; 96; 102; 103; 104; 105; 106; 107; 114; 115; 116; 117
Lat/Long OENS-141.0000 -113.5000 70.0000 48.0000
Sujetsgisements minéraux; prospection minière; techniques de prospection; exploration de dépôts glaciaires; levés géochimiques; sediments; dépôts glaciaires; tills; dépôts fluviaux; dépôts lacustres; eaux de surface; géochimie des eaux lacustres; géochimie de l'eau de cours d'eau; eau souterraine; dépôts organiques; échantillons de minéraux lourds; végétation; méthodes d'échantillonage; méthodes analytiques; preparation d'échantillons; analyses colorimétriques; analyses des éléments en trace; analyses par activation neutronique; analyses spectroscopiques; analyse par spectromètre de masse; etudes isotopiques; analyses des éléments majeurs; géochimie des éléments en trace; analyses granulométriques; fractionation; lithologie des galets; analyses des minéraux lourds; microscopie électronique à balayage; origine; historique; Canadian Cordillère; Contrôle de la qualité; géologie économique; géologie des dépôts meubles/géomorphologie; géochimie; Phanérozoïque; Cénozoïque; Quaternaire
Illustrationslocation maps; tables; flow diagrams; bar graphs
ProgrammeSystèmes porphyriques, Initiative géoscientifique ciblée (IGC-5)
Résumé(disponible en anglais seulement)
Commonly sampled media for regional geochemical survey (RGS) programs in Canada are stream and lake sediments and waters, and till deposits. During the last 60 years in the Canadian Cordillera of British Columbia and Yukon, surveys have advanced by sampling more diverse media such as moss mat sediment, stream heavy mineral concentrates, vegetation, and using increasingly sophisticated analytical methods. In the 1950s, stream-sediment samples collected by mining companies as part of regional geochemical surveys were typically analyzed for a small number of elements by colorimetric techniques. Later Canadian government-managed regional geochemical surveys used other sample types (e.g., lake sediment and water), initially to locate strategic metals (e.g., uranium) and later to detect other metals. For these surveys sample densities range from one sample per 5-10 km2 for till and vegetation to one sample per 10-15 km2 for stream and lacustrine sediments. Samples from these surveys were analyzed for a greater number of elements by a combination of colorimetric, fluorimetric and acid digestion-atomic absorption techniques. A greater appreciation of Cordilleran glacial geology and ice-flow patterns led to till geochemistry being successfully used to detect new sources of bedrock mineralization concealed beneath locally transported surficial cover. At the same time as new sample media were being applied to regional geochemical surveys, new analytical methods were being developed, such as instrumental neutron activation (INAA), aqua regia digestion followed by multi-element analysis by inductively coupled plasma emission spectroscopy (ICP-ES) and, later, mass spectroscopy (ICP-MS). Over time, the development of systematic quality control schemes for sampling and sample analysis and new standard reference materials by the Geological Survey of Canada improved the reliability of regional survey geochemical data. Routinely sampled as part of regional geochemical survey (RGS) programs in the Canadian Cordillera are stream and lacustrine sediments and waters, vegetation, and till deposits.
Since 2000, heavy mineral (e.g., >SG 3.2) concentrates recovered from the <2 mm grain-size fraction have been prepared from many stream-sediment and till samples collected in British Columbia. After microscopic examination, these concentrates are analyzed by methods such as scanning electron microscopy (SEM) combined with Energy Dispersive X-ray Spectroscopy (EDS) to identify and count gold, platinum, sulphide, oxide, and silicate grains. Different deposit types contributing to the mineral suite in a sample can be distinguished from different indicator mineral assemblages such as diamond indicator minerals, magmatic/metamorphosed massive sulphide indicator minerals or porphyry Cu indicator minerals. Other micro-analytical methods such as in situ high-precision isotope analysis and laser ablation followed by ICP-MS can also be applied to better identify mineralized source rocks of heavy mineral concentrates. Combining heavy mineral studies with the results of sediment and till sample geochemistry has added a new dimension to applying regional survey data to explore for new mineral resources in the Cordillera.
GEOSCAN ID308170