RGS Methodology
The British Columbia Ministry of Energy, Mines and Petroleum Resources has been involved in reconnaissance-scale stream sediment and water surveys since 1976. This joint federal-provincial initiative was originally referred to as the Uranium Reconnaissance Program (URP). In 1978 the program was renamed the Regional Geochemical Survey (RGS) and in 1987 the Province began to independently administer surveys conducted in British Columbia. As part of Canada's National Geochemical Reconnaissance (NGR) program, the RGS program continues to maintain sample collection, preparation and analytical standards established by the Geological Survey of Canada.
Reconnaissance-scale drainage sediment and water surveys in British Columbia are typically conducted during the summer months. Regions surveyed are based on NTS 1:250 000 map sheets and often evaluate areas in excess of 10,000 square kilometres. Samples are systematically collected at a average density of one sample site every 13 square kilometres. Field duplicate samples are routinely collected in each analytical block of twenty samples.
On average, targeted primary and secondary drainage basins have catchment areas of less than 10 square kilometres. A small number of samples have been collected from streams with basin areas that are less than one square kilometre or greater than 25 square kilometres. In general, the remaining unsurveyed areas represent broad valley floors which are characterized by meandering river channels or swamps that do not provide appropriate stream sediment material. Some stream networks bounded by surveyed drainages may have been intentionally excluded from sampling to maintain the intended sample density of the survey. Designed to provide cost effective regional geochemical data, the RGS program does not define the geochemistry of every first or second order stream within a map area.
Sediment samples weigh approximately 1 to 2 kilograms and are obtained from the active (subject to annual flooding) stream channel and placed in kraft paper bags. Samples are composed of fine-grained material mixed with varying amounts of coarse sand, gravel and organic matter. Contaminated or poor-quality sample sites are avoided by choosing an alternate stream or by sampling a minimum of 60 metres upstream from the source of contamination. Clean surface water samples are collected in 250 millilitre bottles. Standard field observations regarding sample media, sample site and local terrain were also recorded.
At a field camp, sediment samples are air dried at a temperature range of 30°C to less than 50°C. Material finer than 1 millimetre is recovered by sieving each dried sample through a -18 mesh (<1 millimetre) ASTM screen. Field-dried sediment samples are shipped to a sample preparation laboratory for final sample preparation. The -80 mesh (<177 microns) fraction is obtained by dry sieving. Control reference material and analytical duplicate samples are inserted into each analytical block of twenty sediment samples. Any remaining -80 mesh sediment and a representative sample of +80 to -18 mesh fraction is archived for future analyses. Quality control reference standards are also inserted into each analytical block of twenty water samples.
Antimony was determined by aqua regia digestion - hydride generation atomic absorption spectroscopy. A 0.5-gram sample was placed in a test tube with 3 millilitres of concentrated nitric acid and 9 millilitres of hydrochloric acid. The mixture was allowed to stand overnight at room temperature prior to being heated to 90°C for 90 minutes. The mixture was cooled and a 1-millilitre aliquot was diluted to 10 millilitre with 1.8M hydrochloric acid. The solution was analyzed for antimony by hydride generation atomic absorption spectroscopy as described by Aslin (1976).
Arsenic, bismuth and selenium were determined by aqua regia digestion - hydride generation atomic absorption spectroscopy. A 1-gram sample was digested with 3 millilitres of concentrated nitric acid for 30 minutes at 90°C. Concentrated hydrochloric acid (1 mL) was added and the digestion was continued at 90°C for an additional 90 minutes. A 1-millilitre aliquot was diluted to 10 millilitres with 1.5M hydrochloric acid in a clean test tube. The diluted sample solution was added to a sodium borohydride solution and the hydride vapour passed through a heated quartz tube in the light path of an atomic absorption spectrometer.
Barium was determined using energy-dispersive X-Ray fluorescence. A 5-gram sample is placed in a 10 millilitre plastic vial. The sample is exposed to a radioactive source and the intensities of X-rays emitted are measured. The amount of barium is measured by comparison to standards. Corrections are made for inter-element interference.
Chromium was determined on a 0.25-gram sample heated with a mixture of 2-millilitres of nitric acid, 2-millilitres of perchloric acid and 5-millilitres of hydrofluoric acid at 90 to 100°C until the solution is reduced to dryness. The residue was dissolved in 10-millilitres of 10 percent hydrochloric acid and analyzed for chromium by atomic absorption spectrometry using a nitrous oxide-acetylene flame and background corrections.
Cadmium, cobalt, copper, iron, lead, manganese, nickel, silver and zinc were determined by aqua regia digestion - flame atomic absorption spectroscopy. A 1-gram sample was reacted with 3 millilitres of concentrated nitric acid for 30 minutes at 90°C. Concentrated hydrochloric acid (1 mL) was added and the digestion was continued at 90°C for an additional 90 minutes. The sample solution was then diluted to 20 millilitres with metal-free water and mixed. The solution was analyzed for metals by atomic absorption spectroscopy using an air-acetylene flame. Background corrections were made for lead, nickel, cobalt and silver.
Fluorine was determined by specific ion electrode as described in Ficklin (1970). A 0.25-gram sample was sintered with a 1-gram flux consisting of 2 parts by weight of sodium carbonate and 1 part by weight of potassium nitrate. The residue was then leached with water and the sodium carbonate was neutralized with 10 millilitres 10 percent citric acid. The resulting solution was diluted to 100 millilitres with water to a pH of 5.5 to 6.5. Fluoride was measured using a fluoride ion electrode and a reference electrode.
Gold was determined by mixing a 10-gram sample with a flux composed mainly of lead oxide. The proportions of the flux components are adjusted depending on the nature of the sample. Silver is added to help collect the gold. The samples are fused at 1066°C until a clear melt is obtained. The resultant lead button containing the precious metals is then separated from the slag. Heating in a cuppelation furnace separates the lead from the noble metals. The precious metal beads that remain are irradiated in a neutron flux for 1 hour, cooled for 4 hours and counted by gamma ray spectrometry. Calibrations are carried out using standard and blank beads. Depending on the amount of sample available, lesser weights were sometimes used (minimum 5 grams). This resulted in a variable detection limit of 1 ppb gold for a 10-gram sample and 2 ppb for a 5-gram sample.
Molybdenum and vanadium were determined by aqua regia digestion - atomic absorption spectroscopy using a nitrous oxide acetylene flame. A 0.5-gram sample was reacted with 1.5 millilitres of concentrated nitric acid at 90°C for 30 minutes. Concentrated hydrochloric acid (0.5 mL) was added and the digestion continued for an additional 90 minutes. After cooling, 8 millilitre of 1250 ppm aluminium solution was added and the sample solution diluted to 10 millilitre before determination of molybdenum and vanadium by atomic absorption spectroscopy.
Mercury was determined by aqua regia digestion - flameless atomic absorption spectrometry. A 0.5-gram sample was reacted with 20 millilitres of concentrated nitric acid and 1 millilitre concentrated hydrochloric acid in a test tube for 10 minutes at room temperature and then for 2 hours in a 90°C water bath. After digestion, the sample was cooled and diluted to 100 millilitres with metal-free water. The mercury present was reduced to the elemental state by the addition of 10 millilitres of 10% weight per volume stannous sulphate in sulphuric acid. The mercury vapor was flushed by a stream of air into an absorption cell mounted in the light path of an atomic absorption spectrometer. Measurements were made at 253.7 nanometres. This method is described in detail by Jonasson et al. (1973).
Tin was determined on a 200-milligram sample heated with amonium iodide. The sublimed tin iodide was dissolved in acid and the tin determined by atomic absorption spectrometry.
Tungsten was determined using a 0.2-gram sample fused with 1-gram potassium bisulphate in a rimless test tube at 575°C for 15 minutes in a furnace. The cooled melt is leached with 10 millilitres concentrated hydrochloric acid in a water bath heated to 85°C. After the soluble material has completely dissolved, the insoluble material is allowed to settle and an aliquot of 5 millilitres was transferred to another test tube. Five millilitres of 20% stannous chloride solution is added to the sample aliquot, mixed and heated for 10 minutes at 85°C in a hot water bath. A 1-millilitre aliquot of dithiol solution (1% dithiol in iso-amyl acetate) is added to the test solution and the solution is heated for 4-6 hours at 80-85°C in a hot water bath. The solution is then removed from the hot water bath, cooled and 2.5 millilitres of kerosene is added to dissolve the globule. The colour intensity of the kerosene solution is measured at 630 nanometres using a spectrophotometer. This method is described by Quin and Brooks (1972).
Uranium was determined using a neutron activation method with delayed neutron counting. A detailed description of the method is provided by Boulanger et al. (1975). A 1-gram sample was weighed into a 7-dram polyethylene vial, capped and sealed. The irradiation was provided by the Atomic Energy of Canada's Slowpoke II reactor. Calibration was carried out once a day as a minimum, using natural materials of known uranium concentration.
Loss on ignition was determined using a 0.5-gram sample. The sample was weighed into a 30 millilitre beaker, placed in a cold muffle-furnace and heated to 500°C over a period of 2 to 3 hours. The sample was allowed to cool at room temperature for 4 hours before weighing.
Instrumental Neutron Activation Analysis (INAA)
Sediment samples are analyzed for antimony, arsenic, barium, bromine, cerium, cesium, chromium, cobalt, gold, hafnium, iron, lanthanum, lutetium, molybdenum, nickel, rubidium, samarium, scandium, sodium, tantalum, terbium, thorium, tungsten, uranium, ytterbium and zirconium using thermal (Activation Labs, Ancaster, Ont.) or epi-thermal (Becquerel Laboratories, Mississauga, Ont.) instrumental neutron activation analysis (INAA). Instrumental neutron activation analysis involves irradiating the sediment samples, which range from 5 to 40 grams (average 20-grams), for 30 minutes with neutrons (flux density of 7x1011 neutrons/cm2/second). After approximately 1 week, the gamma-ray emissions for the elements are measured using a gamma-ray spectrometer with a high resolution, coaxial germanium detector. Counting time is approximately 15 minutes per sample.
RGS Stream Water Analysis
pH of waters was measured by a combination glass-reference electrode and a Fisher Accumet pH meter using an aliquot of sample in a clean dry beaker.
Sulphate in waters was determined by a turbidimetric method. A 20-millilitre aliquot of the sample was mixed with barium chloride and an isopropyl alcohol - hydrochloric acid - sodium chloride reagent. The turbidity of the resulting barium sulphate suspension was measured with a spectrophotometer at 420 nanometres.
The determination of fluoride in waters involved mixing an aliquot of the sample with an equal volume of total ionic strength adjustment buffer (TISAB II solution). The fluoride was measured using a Corning 101 meter with an Orion fluoride electrode.
Uranium in waters was determined by laser-induced fluorescence analysis. A 5-millilitre sample was spiked with 0.5-millilitres of fluran solution for 24 hours and irradiated by a laser to induce fluorescence. Uranium was determined with a Scintrex UA-3 uranium analyzer.
References
Aslin, G.E.M. (1976): The Determination of Arsenic and Antimony in Geological Materials by Flameless Atomic Absorption Spectrophotometry; Journal of Geochemical Exploration, Volume 6, pages 321-330.
Ficklin, H.E. (1970): A Rapid Method for the Determination of Fluorine in Rocks and Soils, Using an Ion Selective Electrode; U.S. Geological Survey, Paper 700C, pages 186-188.
Jonasson, I.R., Lynch, J.J. and Trip, L.J. (1973): Field and Laboratory Methods Used by the Geological Survey of Canada in Geochemical Surveys: No. 12, Mercury in Ores, Rocks, Soils, Sediments and Water; Geological Survey of Canada, Paper 73-21.
Boulanger, A., Evans, D.J.R. and Raby, B.F. (1975): Uranium Analysis by Neutron Activation Delayed Neutron Counting: Proceedings of the 7th Annual Symposium of Canadian Mineral Analysts. Thunder Bay, Ontario, Sept. 22-23, 1975.
Quin,B.F. and Brooks, R.R.(1972): The rapid determination of tungsten in soils, stream sediments, rocks and vegetation; Anal. Chim. Acta. 58, pages 301-309.
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