PCT. 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). In brief, a 1 gram sample is weighed into a 7 dram polyethylene vial, capped and sealed. The irradiation is provided by the Slowpoke reactor with an operating flux of 10** 12 neutrons/sq cm/sec. The samples are pneumatically transferred from an automatic loader to the reactor, where each sample is irradiated for 60 seconds. After irradiation, the sample is again transferred pneumatically to the counting facility where after a 10 second delay the sample is counted for 60 seconds with six BF 3 detector tubes embedded in paraffin. Following counting, the samples are automatically ejected into a shielded storage container. Calibration is carried out twice a day as a minimum, using natural materials of known uranium concentration. Detection limit = 0.5 ppm. ▇▇▇▇▇▇▇▇ was determined as described by ▇▇▇▇▇ (1976). A 500 mg sample is placed in a test tube; 3 mL concentrated HNO3 and 9 mL concentrated HCl are added and the mixture is allowed to stand overnight at room temperature. The mixture is heated slowly to 90 ° C and maintained at this temperature for at least 90 minutes. The solution is cooled and diluted to 10 mL with 1 . 8 M HCl. The antimony in an aliquot of this dilute solution is then determined by hydride evolution - atomic absorption spectrometry. Detection limit = 0.2 ppm. ▇▇▇▇▇▇▇▇ was determined as described by ▇▇▇▇▇▇▇ (1970). A 250 mg sample is sintered with 1 g of a flux consisting of two parts by weight sodium carbonate and one part by weight potassium nitrate. The residue is then leached with water. The sodium carbonate is neutralized with 10 mL 10% (w/v) citric acid and the resulting solution is diluted to 100 mL with water. The pH of the resulting solution should be from 5 . 5 to 6 . 5 . The fluoride content of the test solution is then measured using a f luoride ion electrode. Standard solutions contain sodium carbonate and citric acid in the same quantities as the sample solution. Detection limit = 20 ppm. Gold was usually determined on a 10 g sediment sample; depending on the amount of sample available, lesser weights were sometimes used. This resulted in a variable detection limit: 2 ppb for a 5 g sample, 1 ppb for a 10 g sample... The sample was fused to produce a lead button, collecting any gold in the sample, which was cupelled in a muffle furnace to produce a silver (dore) bead. The silver beads were irradiated in a neutron flux for one hour, cooled for four hours, and counted by gamma ray spectrometry. Calibration was carried out using standard and blank beads. ▇▇▇▇▇▇▇▇ was determined as follows: A 0 . 2 g sample of stream sediment was fused with 1 g K2S2O7 in a rimless test tube at 575 ° C for 15 minutes in a furnace. The cooled melt was then leached with 10 m L concentrated HCl in a water bath heated to 85° C. After the soluble material had completely dissolved, the insoluble material was allowed to settle and an aliquot of 5 m L was transferred to another test tube. 5 mL of 20% SnCl2 solution were then added to the sample aliquot, mixed and heated for 10 minutes at 85 ° C in a hot water bath. A 1 mL aliquot of dithiol solution (1% dithiol in iso- amyl acetate) was added to the test solution and the test solution was then heated for 4 to 6 hours at 80 - 85 ° C in a hot water bath. The test solution was then removed from the hot water bath, cooled and
Appears in 2 contracts
Sources: Canada – Yukon Mineral Development Agreement, Canada – Yukon Mineral Development Agreement
PCT. 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). In brief, a 1 gram sample is weighed into a 7 dram polyethylene vial, capped and sealed. The irradiation is provided by the Slowpoke reactor with an operating flux of 10** 12 neutrons/sq cm/sec. The samples are pneumatically transferred from an automatic loader to the reactor, where each sample is irradiated for 60 seconds. After irradiation, the sample is again transferred pneumatically to the counting facility where after a 10 second delay the sample is counted for 60 seconds with six BF 3 detector tubes embedded in paraffin. Following counting, the samples are automatically ejected into a shielded storage container. Calibration is carried out twice a day as a minimum, using natural materials of known uranium concentration. Detection limit = 0.5 ppm. ▇▇▇▇▇▇▇▇ Antimony was determined as described by ▇▇▇▇▇ (1976). A 500 mg sample is placed in a test tube; 3 mL concentrated HNO3 and 9 mL concentrated HCl are added and the mixture is allowed to stand overnight at room temperature. The mixture is heated slowly to 90 ° C and maintained at this temperature for at least 90 minutes. The solution is cooled and diluted to 10 mL m L with 1 . 8 M HCl▇▇ ▇. The antimony in an aliquot of this dilute solution is then determined by hydride evolution - atomic absorption spectrometry. Detection limit = 0.2 ppm. ▇▇▇▇▇▇▇▇ Fluorine was determined as described by ▇▇▇▇▇▇▇ (1970). A 250 mg sample is sintered with 1 g of a flux consisting of two parts by weight sodium carbonate and one part by weight potassium nitrate. The residue is then leached with water. The sodium carbonate is neutralized with 10 mL 10% (w/v) citric acid and the resulting solution is diluted to 100 mL with water. The pH of the resulting solution should be from 5 . 5 to 6 . 5 . The fluoride content of the test solution is then measured using a f luoride ion electrode. Standard solutions contain sodium carbonate and citric acid in the same quantities as the sample solution. Detection limit = 20 ppm. Gold was usually determined on a 10 g sediment sample; depending on the amount of sample available, lesser weights were sometimes used. This resulted in a variable detection limit: 2 ppb for a 5 g sample, 1 ppb for a 10 g sample... sample . The sample was fused to produce a lead button, collecting any gold in the sample, which was cupelled in a muffle furnace to produce a silver (dore) bead. The silver beads were irradiated in a neutron flux for one hour, cooled for four hours, and counted by gamma ray spectrometry. Calibration was carried out using standard and blank beads. ▇▇▇▇▇▇▇▇ Tungsten was determined as follows: A 0 . 2 g sample of stream sediment was fused with 1 g K2S2O7 in a rimless test tube at 575 ° C for 15 minutes in a furnace. The cooled melt was then leached with 10 m L concentrated HCl in a water bath heated to 85° C. After the soluble material had completely dissolved, the insoluble material was allowed to settle and an aliquot of 5 m L was transferred to another test tube. 5 mL of 20% SnCl2 solution were then added to the sample aliquot, mixed and heated for 10 minutes at 85 ° C in a hot water bath. A 1 mL aliquot of dithiol solution (1% dithiol in iso- amyl acetate) was added to the test solution and the test solution was then heated for 4 to 6 hours at 80 - to 85 ° C in a hot water bath. The test solution was then removed from the hot water bath, cooled andand 2.5 mL of kerosene added to dissolve the globule. The colour intensity of the kerosene solution was measured at 630 nm using a spectrophotometer. The method is described by Quin and ▇▇▇▇▇▇ (1972). Detection limit = 2 ppm. Tin was determined as follows: A 200 mg sample was heated with NH4 I; the sublimed SnI4 was dissolved in acid and the tin determined by atomic absorption spectrometry. Detection limit = 1 ppm Barium was determined as follows: A 0.25 g sample was heated with 5 mL concentrated HClO4 were added and heated to l ight fumes; 5 mL of water were added and the solution was transferred to a calibrated test tube and diluted to 25 mL with water. Barium was determined by spectroscopy. Detection limit = 40 ppm. Fluoride in stream and lake water samples was determined using a fluoride electrode. Prior to measurement an aliquot of the sample was mixed with an equal volume of TISAB II buffer solution (total ionic strength adjustment buffer). The TISAB II buffer solution is prepared as follows: to 50 m L metal- free water add 57 mL glacial acetic acid, 58 gm NaCl and 4 gm CDTA (cyclohexylene dinitrilo tetraacetic acid). Stir to dissolve and cool to room temperature. Using a pH meter, adjust the pH between 5.0 and 5.5 by slowly adding 5 M Na OH solution. Cool and dilute to one litre in a volumetric flask. Detection limit = 20 ppb. Hydrogen ion activity (pH) was measured with a combination glass-calomel electrode and a pH meter. Uranium in waters was determined by a laser-induced fluorometric method using a Scintrex UA-3 uranium analyser. A complexing agent, known commercially as fluran and composed of sodium pyrophosphate and sodium monophosphate ( Hall, 1979 ) is added to produce the uranyl pyrophosate species which fluoresces when exposed to the laser. Since organic matter in the sample can cause unpredictable behaviour, a standard addition method was used. Further, there have been instances at the GSC where the reaction of uranium with fluran is either delayed or sluggish; for this reason an arbitrary 24 hour time delay between the addition of the f luran and the actual reading was incorporated into this method. In practice 500 µL of fluran solution were added to a 5 mL sample and allowed to stand for 24 hours. At the end of this period fluorescence readings were made with the addition of 0.0, 0 . 2 and 0.4 ppb U. For high samples the additions were 0.0, 2.0 and 4.0 (20 µ L aliquots of either 55 or 550 ppb U were used). All readings were taken against a sample blank. Detection limit = .05 ppb. Table 1 provides a summary of analytical data and methods. The following discussion reviews the format used to present the Au geochemical data and outlines some important points to consider when interpreting this data. This discussion is included in recognition of the special geochemical behaviour and mode of occurrence of Au in nature and the resultant difficulties in obtaining and analyzing samples which reflect the actual concentration level at a given site. To correctly interpret Au geochemical data from regional stream sediment or lake sediment surveys requires an appreciation of the unique chemical and physical characteristics of Au and its mobility in the surficial environment. Key properties of Au that distinguish its geochemical behaviour from most other elements include (▇▇▇▇▇▇, 1982):
(1) Au occurs most commonly in the native form which is chemically and physically resistant. A high proportion of the metal is dispersed in micron- sized particulate form. Gold's high specific gravity results in heterogeneous distribution, especially in stream sediment and clastic-rich (low LOI) lake sediment environments. Au distribution appears to be more homogeneous in organic-rich fluviatile and lake sediment environments.
(2) Gold typically occurs at low concentrations in the ppb range. Whereas gold concentrations of only a few ppm may represent economic deposits, background levels encountered from stream and centre-lake sediments seldom exceed 10 ppb, and commonly are near the detection limit of 1 ppb. These factors result in a particle sparsity effect wherein very low concentrations of Au are heterogeneously enriched in the surficial environment. Hence, a major problem facing the geochemist is to obtain a representative sample. In general, the lower the actual concentration of Au the larger the sample size, or the smaller the grain size required to reduce uncertainty over whether subsample analytical values truly represent actual values. Conversely, as actual Au concentrations increase or grain size decreases, the number of Au particles to be shared in random subsamples increases and the variability of results decreases (▇▇▇▇▇▇▇ et al., 1969; ▇▇▇▇▇▇, 1982). The limited amount of material collected during the rapid, reconnaissance- style regional surveys and the need to analyze for a broad spectrum of elements, precludes the use of a significantly large sample weight for the Au analyses. Therefore, to the extent that sample representivity can be increased, sample grain size is reduced by sieving and ball milling of all samples. The following control methods are currently employed to evaluate and monitor the sampling and analytical variability which are inherent in the analysis of Au in geochemical mediums:
(1) For each block of twenty samples:
(a) random insertion of a standard reference sample to control analytical accuracy and long-term precision;
(b) collection of a field duplicate (two samples from one site) to control sampling variance;
(c) analysis of a second subsample (blind duplicate) from one sample to control short-term precision.
(2) For both stream sediments and lake sediments, routine repeat analyses on a second subsample are performed for all samples having values that are statistically above approximately the 90th percentile of total data set. This applies only to gold analyses by f ire assay preconcentration followed by neutron activation. Such routine repeat analyses are not performed for INA analyses of archived samples.
(3) For lake sediments only, a routine repeat analysis on a second subsample is performed on those samples with LOI values below 10%, indicating a large clastic component. On-going studies suggest that the Au distribution in these samples is more likely to be variable than in samples with a higher LOI content. Again, routine repeat analyses are performed only when the fire assay preconcentration/neutron activation method is used. Au data presentation, statistical treatment and the value map format are different than for other elements. Au data listed in the open file may include initial analytical results, values determined from repeat analyses, together with sample weights and corresponding detection limits for all analyzed samples. The gold, statistical parameters and regional symbol trend plots are determined using the following data population selection criteria:
(1) Only the first analytical value is utilized.
(2) Au values determined from sample weights less than 10 g are excluded, except where determined by instrumental neutron activation analyses.
(3) Au values less than the detection limit (<1 ppb) for 10 g samples are set to
Appears in 1 contract
Sources: Canada – Newfoundland Mineral Development Agreement (1984 1989)
PCT. 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). In brief, a 1 gram sample is weighed into a 7 dram polyethylene vial, capped and sealed. The irradiation is provided by the Slowpoke reactor with an operating flux of 10** 12 neutrons/sq cm/sec. The samples are pneumatically transferred from an automatic loader to the reactor, where each sample is irradiated for 60 seconds. After irradiation, the sample is again transferred pneumatically to the counting facility where after a 10 second delay the sample is counted for 60 seconds with six BF 3 detector tubes embedded in paraffin. Following counting, the samples are automatically ejected into a shielded storage container. Calibration is carried out twice a day as a minimum, using natural materials of known uranium concentration. Detection limit = 0.5 ppm. ▇▇▇▇▇▇▇▇ was determined as described by ▇▇▇▇▇ (1976). A 500 mg sample is placed in a test tube; 3 mL concentrated HNO3 and 9 mL concentrated HCl are added and the mixture is allowed to stand overnight at room temperature. The mixture is heated slowly to 90 ° C and maintained at this temperature for at least 90 minutes. The solution is cooled and diluted to 10 mL m L with 1 . 8 M HCl▇▇ ▇. The antimony in an aliquot of this dilute solution is then determined by hydride evolution - atomic absorption spectrometry. Detection limit = 0.2 ppm. ▇▇▇▇▇▇▇▇ was determined as described by ▇▇▇▇▇▇▇ (1970). A 250 mg sample is sintered with 1 g of a flux consisting of two parts by weight sodium carbonate and one part by weight potassium nitrate. The residue is then leached with water. The sodium carbonate is neutralized with 10 mL 10% (w/v) citric acid and the resulting solution is diluted to 100 mL with water. The pH of the resulting solution should be from 5 . 5 to 6 . 5 . The fluoride content of the test solution is then measured using a f luoride ion electrode. Standard solutions contain sodium carbonate and citric acid in the same quantities as the sample solution. Detection limit = 20 ppm. Gold was usually determined on a 10 g sediment sample; depending on the amount of sample available, lesser weights were sometimes used. This resulted in a variable detection limit: 2 ppb for a 5 g sample, 1 ppb for a 10 g sample... The sample was fused to produce a lead button, collecting any gold in the sample, which was cupelled in a muffle furnace to produce a silver (dore) bead. The silver beads were irradiated in a neutron flux for one hour, cooled for four hours, and counted by gamma ray spectrometry. Calibration was carried out using standard and blank beads. ▇▇▇▇▇▇▇▇ was determined as follows: A 0 . 2 g sample of stream sediment was fused with 1 g K2S2O7 in a rimless test tube at 575 ° C for 15 minutes in a furnace. The cooled melt was then leached with 10 m L concentrated HCl in a water bath heated to 85° C. After the soluble material had completely dissolved, the insoluble material was allowed to settle and an aliquot of 5 m L was transferred to another test tube. 5 mL of 20% SnCl2 solution were then added to the sample aliquot, mixed and heated for 10 minutes at 85 ° C in a hot water bath. A 1 mL aliquot of dithiol solution (1% dithiol in iso- amyl acetate) was added to the test solution and the test solution was then heated for 4 to 6 hours at 80 - to 85 ° C in a hot water bath. The test solution was then removed from the hot water bath, cooled andand 2.5 mL of kerosene added to dissolve the globule. The colour intensity of the kerosene solution was measured at 630 nm using a spectrophotometer. The method is described by ▇▇▇▇ and ▇▇▇▇▇▇ (1972). Detection limit = 2 ppm. Tin was determined as follows: A 200 mg sample was heated with NH4 I; the sublimed SnI4 was dissolved in acid and the tin determined by atomic absorption spectrometry. Detection limit = 1 ppm ▇▇▇▇▇▇ was determined as follows: A 0.25 g sample was heated with 5 mL concentrated HClO4 were added and heated to l ight fumes; 5 mL of water were added and the solution was transferred to a calibrated test tube and diluted to 25 mL with water. Barium was determined by spectroscopy. Detection limit = 40 ppm. Fluoride in stream and lake water samples was determined using a fluoride electrode. Prior to measurement an aliquot of the sample was mixed with an equal volume of TISAB II buffer solution (total ionic strength adjustment buffer). The TISAB II buffer solution is prepared as follows: to 50 m L metal- free water add 57 mL glacial acetic acid, 58 gm NaCl and 4 gm CDTA (cyclohexylene dinitrilo tetraacetic acid). Stir to dissolve and cool to room temperature. Using a pH meter, adjust the pH between 5.0 and 5.5 by slowly adding 5 M Na OH solution. Cool and dilute to one litre in a volumetric flask. Detection limit = 20 ppb. Hydrogen ion activity (pH) was measured with a combination glass-calomel electrode and a pH meter. Uranium in waters was determined by a laser-induced fluorometric method using a Scintrex UA-3 uranium analyser. A complexing agent, known commercially as fluran and composed of sodium pyrophosphate and sodium monophosphate ( Hall, 1979 ) is added to produce the uranyl pyrophosate species which fluoresces when exposed to the laser. Since organic matter in the sample can cause unpredictable behaviour, a standard addition method was used. Further, there have been instances at the GSC where the reaction of uranium with fluran is either delayed or sluggish; for this reason an arbitrary 24 hour time delay between the addition of the f luran and the actual reading was incorporated into this method. In practice 500 µL of fluran solution were added to a 5 mL sample and allowed to stand for 24 hours. At the end of this period fluorescence readings were made with the addition of 0.0, 0 . 2 and 0.4 ppb U. For high samples the additions were 0.0, 2.0 and 4.0 (20 µ L aliquots of either 55 or 550 ppb U were used). All readings were taken against a sample blank. Detection limit = .05 ppb. Table 1 provides a summary of analytical data and methods. The following discussion reviews the format used to present the Au geochemical data and outlines some important points to consider when interpreting this data. This discussion is included in recognition of the special geochemical behaviour and mode of occurrence of Au in nature and the resultant difficulties in obtaining and analyzing samples which reflect the actual concentration level at a given site. To correctly interpret Au geochemical data from regional stream sediment or lake sediment surveys requires an appreciation of the unique chemical and physical characteristics of Au and its mobility in the surficial environment. Key properties of Au that distinguish its geochemical behaviour from most other elements include (▇▇▇▇▇▇, 1982):
(1) Au occurs most commonly in the native form which is chemically and physically resistant. A high proportion of the metal is dispersed in micron- sized particulate form. Gold's high specific gravity results in heterogeneous distribution, especially in stream sediment and clastic-rich (low LOI) lake sediment environments. Au distribution appears to be more homogeneous in organic-rich fluviatile and lake sediment environments.
(2) Gold typically occurs at low concentrations in the ppb range. Whereas gold concentrations of only a few ppm may represent economic deposits, background levels encountered from stream and centre-lake sediments seldom exceed 10 ppb, and commonly are near the detection limit of 1 ppb. These factors result in a particle sparsity effect wherein very low concentrations of Au are heterogeneously enriched in the surficial environment. Hence, a major problem facing the geochemist is to obtain a representative sample. In general, the lower the actual concentration of Au the larger the sample size, or the smaller the grain size required to reduce uncertainty over whether subsample analytical values truly represent actual values. Conversely, as actual Au concentrations increase or grain size decreases, the number of Au particles to be shared in random subsamples increases and the variability of results decreases (▇▇▇▇▇▇▇ et al., 1969; ▇▇▇▇▇▇, 1982). The limited amount of material collected during the rapid, reconnaissance- style regional surveys and the need to analyze for a broad spectrum of elements, precludes the use of a significantly large sample weight for the Au analyses. Therefore, to the extent that sample representivity can be increased, sample grain size is reduced by sieving and ball milling of all samples. The following control methods are currently employed to evaluate and monitor the sampling and analytical variability which are inherent in the analysis of Au in geochemical mediums:
(1) For each block of twenty samples:
(a) random insertion of a standard reference sample to control analytical accuracy and long-term precision;
(b) collection of a field duplicate (two samples from one site) to control sampling variance;
(c) analysis of a second subsample (blind duplicate) from one sample to control short-term precision.
(2) For both stream sediments and lake sediments, routine repeat analyses on a second subsample are performed for all samples having values that are statistically above approximately the 90th percentile of total data set. This applies only to gold analyses by f ire assay preconcentration followed by neutron activation. Such routine repeat analyses are not performed for INA analyses of archived samples.
(3) For lake sediments only, a routine repeat analysis on a second subsample is performed on those samples with LOI values below 10%, indicating a large clastic component. On-going studies suggest that the Au distribution in these samples is more likely to be variable than in samples with a higher LOI content. Again, routine repeat analyses are performed only when the fire assay preconcentration/neutron activation method is used. Au data presentation, statistical treatment and the value map format are different than for other elements. Au data l isted in the open f i le may include initial analytical results, values determined from repeat analyses, together with sample weights and corresponding detection limits for all analyzed samples. The gold, statistical parameters and regional symbol trend plots are determined using the following data population selection criteria:
(1) Only the first analytical value is utilized.
(2) Au values determined from sample weights less than 10 g are excluded, except where determined by instrumental neutron activation analyses.
(3) Au values less than the detection limit (<1 ppb) for 10 g samples are set to
Appears in 1 contract
Sources: Mineral Development Agreement