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In this study, results by direct portable XRF (‘pXRF’) on unsieved till samples were compared with those by established laboratory methods (aqua regia or fusion ICP-MS and ICP-ES) on the In general, the performance of pXRF in the four test areas was very good where concentrations of elements of interest (indicator or pathfinder elements) were substantially above detection limits by this technique (in the low ppm range for many elements). The following elements, shown to be useful indicator elements (important constituents of the ore/commodity) or pathfinder elements (those associated with the commodity elements) by the established methodology, showed similar patterns by pXRF on the unsieved material: Zn, Cu, Pb, and As at Halfmile Lake; W, Mo, Cu, Zn, Pb, and As at the Sisson deposit; Zn, Pb, and Fe at Pine Point; and Ca, Sr, Cr, and Ni at Triple B. Pathfinder elements whose concentrations were too low for determination by pXRF include: Ag and Sb at Halfmile Lake; Ag and Cd at Sisson; Cd, S, and Se at Pine Point; and Co, Mg, P, U, and Th at Triple B. The high background for Bi by pXRF, equivalent to c . 50 ppm, and its noisy signal precluded its use at Halfmile Lake and Sisson. Elements which tended to show poor precision (three analyses each sample) by pXRF in some samples due to sample heterogeneity include Sn, V, and W. Mercury was erroneously reported for the majority of samples in the low ppm range by pXRF whereas its concentration in fact was in the low ppb range. Several Pb-, Zn- ( c . 1% Pb, Zn) and Fe-rich (up to 16% Fe) samples demonstrated spectral interferences by: Pb on As, Th and Se; Zn on Cu; and Fe on Co. Results for six till samples analysed in Ziploc® and Whirl-Pak® bags showed that Ziploc® absorbs fewer low-energy photons and hence is preferable for determining light elements such as Si, K and Ca. Supplementary material: Four data-sets are available at http://www.geolsoc.org.uk/SUP18897

Metallurgical pretreatment of As-bearing ores involves oxidation of sulphides (most often As-bearing pyrite, arsenopyrite or enargite) resulting in complex oxidized As-bearing products. We have evaluated roasting pretreatment of arsenic-bearing ores in a broad context and related this to the specific operations at the Giant mine, Yellowknife, NWT, Canada, which roasted arsenopyrite (FeAsS)-rich gold ore concentrates during 50 years of operations. A large portion of the As was collected and stored in underground vaults as As 2 O 3 dust; however, some of the As was also released with tailings which contain concentrations between 1000 to 5000 ppm. Powder X-ray diffraction (XRD) and sequential extractions have been completed on samples of mill products and various ages of tailings at the Giant mine. These data along with petrographic and synchrotron μXRD and μX-ray absorption near-edge spectroscopy (μXANES) indicate that the largely oxidized roaster products (calcine) and electrostatic precipitator (ESP) dust host most of the As in the tailings with a lesser component of sulphide arsenic. The fine-grained nature of these oxidized products has led to hydraulic sorting within the tailings impounds and dispersal to downstream creek and lake sediments.

This paper describes a project sponsored by the Canadian Mining Industry Research Organisation (CAMIRO) to evaluate the strengths and weaknesses of portable XRF for use in mineral exploration and mining and to develop best-practice protocols in the analysis of rocks, soils, sediments and drill-core. Phase I focussed on the analysis of pulp control reference materials (CRMs) to determine the figures of merit, principally accuracy and precision, of the technique before introducing the confounding parameters associated with in-situ analysis such as heterogeneity, particle size and moisture. Five instruments (three handheld and two portable benchtop) from three manufacturers were used to carry out replicate analyses (n = 10) of a diverse suite of 41 CRMs, from barren granites, through soils and sediments, to ores. Standard factory calibration, in mining and soil modes, was used. The performance of the instruments was evaluated using x-y plots of results versus established element concentrations for the CRMs and the values of goodness of fit (r 2 ), slope and intercept documented for both full and restricted concentration ranges. For many elements, the performance across the instruments varied markedly, as did the ability to correct for spectral interferences. Numerous interferences were encountered, particularly from the rare-earth elements (REEs) on transition elements, but also for well-known interference pairs such as Pb on As, Zn on Au, U on Mo, and Th on Bi. In general, major elements with the exception of the light element Mg were well determined, as were Mn and Ti. Sensitivity was inadequate for Cl and P; however, S could be measured with acceptable precision to c. 0.05% S. Performance for the trace elements was categorized as follows: very good for As, Cu, Nb, Pb, Rb, Sr, and Y (r 2 >0.9 for more than 1 instrument); good for Ba, Mo, Sn, Zn and Zr (r 2 >0.9 for 1 instrument); moderate for Cr, Sb, Se, Th and U (r 2 = 0.6–0.8); poor for Ag, Cd, Co, Ni and V; and very poor for Au, Bi, Cs, Hf, Hg, Pd, Sc, Ta, Te and W. Of the REEs determined (La, Ce, Nd, Sm, using the standard calibration by the manufacturer, i.e. not REE-specific), only La showed adequate sensitivity and precision (3–5% RSD), however, only at concentrations approaching c. 1000 ppm (50–100% RSD at La Slopes of the best-fit lines, where r 2 ≥0.6, ranged from 0.5 to 5.0, indicating that calibration is required by the user for both the soil and mining modes. The precision, shown by 10 replicate readings, was excellent and usually better than 10% RSD except where close to detection limit or where major interferences were present. The beam time study showed that, in most situations, 60 s was a good compromise between productivity and precision but also highlighted cases of significant drift and a lack of improvement in precision with longer beam time. A study of the thin-film sample cover used for cups demonstrated that 4.0-µm Prolene® is superior to the same thickness of Mylar® in both transmittance (especially for Mg, Al, Si) and contamination properties.

Chronic exposure to high concentrations of arsenic (As) in windblown and vehicle-raised dust from tailings sites in Nova Scotia poses a potential health risk to recreational users of these areas and to nearby residents. The exposure may involve inhalation of dust, as well as oral ingestion of particles. It is important to understand the mineralogy and morphology of As-bearing dust particles in order to evaluate the risk posed by near-surface particulates in As-bearing tailings fields, as this will influence the stability and toxicity of As in the wastes. Optical mineralogy, scanning electron microscopy, electron microprobe, X-ray diffraction, synchrotron-based micro-X-ray diffraction (μXRD) and micro-X-ray absorption near edge structure (μXANES), and sequential leach extractions were applied to tailings samples from three sites in eastern Nova Scotia. Arsenic occurs naturally in these gold deposits mainly in arsenopyrite (FeAsS). In the near-surface material of the tailings fields, sulphide minerals have almost completely oxidized to secondary minerals such as scorodite (FeAsO 4 •2H 2 O) and Ca-Fe arsenates. Iron oxyhydroxides contain variable amounts of As 2 O 5 from trace to 30 wt.% and CaO up to 8 wt.%. The presence of multiple As-hosting solid phases, including relatively soluble Ca-Fe arsenates and Fe oxyhydroxides with adsorbed As has important implications for human health risk assessment and remediation design.

An objective of the North American Soil Geochemical Landscapes Project is to provide relevant data concerning bioaccessible concentrations of elements in soil to government and other institutions undertaking environmental studies. A protocol was developed that employs a 1-g soil sample agitated overnight with 40 mL of reverse-osmosis de-ionized water for 20 h, and determination of 63 elements following three steps of centrifugation by inductively coupled plasma–atomic emission spectrometry and inductively coupled plasma–mass spectrometry the following day. Statistical summaries are presented for those 48 elements (Ag, Al, As, B, Ba, Be, Br, Ca, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Ho, I, K, La, Li, Lu, Mg, Mn, Mo, Na, Nb, Nd, Ni, P, Pb, Pr, Rb, Re, S, Sb, Si, Sm, Sn, Sr, Tb, Ti, Tl, Tm, U, V, W, Y, Yb, Zn, Zr, and pH) for which

The application of a sequential extraction scheme provides information on the phase association of elements in a sample, such phases being described, for example, as ‘exchangeable/adsorbed’, ‘amorphous Fe/Al oxides’ and ‘soluble organics’. It is therefore critical to maintain the chemistry of a sample from the time of collection to its analysis and during its preparation for analysis. This paper focuses on the redistribution of elements, amongst five operationally defined phases, that occurs on air-drying of the sample; the effect of subsequent storage of the sample is not addressed. Two lake sediment cores (‘Green Lake’, 31 cm, and ‘Gravel Pit Lake’, 19 cm) were sampled at 1-cm intervals and divided into two sets immediately prior to sequential leach analysis of the ‘wet’ sample. The other set was air-dried prior to sequential leach analysis. Most of the 39 elements determined in the Green Lake sediment showed, on drying, a redistribution to more labile forms. For example, increases in Fe concentration in the oxide phases were observed with a concomitant decrease in the crystalline forms of Fe reporting to the final aqua regia digestion. These changes are generally small in magnitude (

Understanding the solid-phase speciation of arsenic in soils and sediments is important in evaluations of the potential mobility of arsenic and of its bio-availability in the environment. This is especially true in mine-infl uenced environments, where arsenic commonly is present at concentrations two and three orders of magnitude above quality criteria for soils and sediments. Arsenicbearing particulates dispersed through hydraulic transport or aerosol emissions can represent a persistent source of contamination in sediments and soils adjacent to past mining and metallurgical operations. The stability and mobility of arsenic associated with these phases depend on the chemical form and oxidation state of the arsenic and the interaction with post-depositional geochemical conditions. The Giant mine in Yellowknife, Northwest Territories, roasted arsenic-bearing gold ore from 1949 to 1999. The roasting process decomposed arsenic-bearing sulfi des (pyrite and arsenopyrite) to produce a calcine containing fi ne (generally

The final step in a sequential extraction procedure for Hg in geological samples usually involves a strong acid attack such as aqua regia. It is assumed that the Hg component measured in this step represents HgS (cinnabar), the common and highly insoluble form of Hg in nature. This paper describes the optimization of an HNO 3 -based dissolution of all non-sulphide forms of Hg while minimizing the solubilization of HgS. Previous work indicated that 12M (75% v/v) HNO 3 would fulfil that objective but its application in this work to samples containing very fine-grained HgS showed that this concentration was too strong as it partially dissolved HgS. Thus, HgS control samples were used to study the effect of HNO 3 concentration, duration of extraction and sample-to-volume ratio on the chemical breakdown of HgS. The recommended procedure to separate HgS from other forms of Hg is a two-hour extraction of 1 g of sample in 20 ml of 40% HNO 3 with constant agitation followed by a 10-ml rinse with 40% HNO 3 . This then ensures that all the cinnabar, fine- and coarse-grained, reports to the subsequent aqua regia step.

Mercury and Sb in soils (humus, B horizon, C horizon) and environmental biomonitors (moss and epiphytic lichen) were examined near two past-producing Hg mines located in British Columbia, Canada: Pinchi Lake and Bralorne Takla mines. Sequential extraction analyses and scanning electron microscopy were used to determine the chemical associations of Hg and Sb and the mineralogical forms of Hg in soils. Mercury and Sb in the C horizon are derived mostly from natural sources because their concentrations are controlled by the bedrock geology, glacial transport, and sediment types. Distribution of Sb in the B horizon is similar to that of the C horizon suggesting a common geogenic source. Mercury in the B horizon at Pinchi Lake mine could be derived in part from anthropogenic sources, because (1) only at that site, and not at any other sites of cinnabar occurrences in bedrock, is there a labile Hg enrichment in the B compared to the C horizon, and (2) there is a weak correlation between non-labile Hg concentrations in the B horizon and distance from the mine which occurs independently of the natural concentrations of the C horizon. Mercury and Sb concentrations in humus near Pinchi Lake mine (

Abundances of 35 elements and ions were determined by inductively coupled plasma mass spectrometry, inductively coupled plasma atomic emission spectroscopy, and ion chromatography, in samples of snowpack obtained using ultraclean procedures, along three 50-km radial transects emanating from the Horne base metal smelter in Rouyn-Noranda, Quebec. This was done to constrain: what is emitted; regional background concentrations of elements in snow; the rate of anthropogenic deposition on the surrounding landscape; how far emissions are transported; and what processes control their deposition. The approach used is at least as effective as methods based on isotopic ratios but has the added advantage of providing direct constraint on a large suite of elements, and of being independent of changes in the isotopic composition of emissions. Reproducibility of the method was determined using field duplicates and blanks. This accounts for snow heterogeneity, analytical precision, reagent quality, and sample handling and was determined to be ±20%. Concentrations of Cu, Pb, and Zn near the smelter are 525, 353, and 149 μg/Lmeltwater, respectively, and drop to 2.1, 3.5, and 3.1 μg/L by 45 km distance. The level of enrichment of these elements, relative to upper crustal abundances, similarly drops from about 10,000 to 100 from proximal through to distal sites, forming an “enrichment gradient.” This is the result of a binary mix of smelter emissions and regional background concentrations. Elements that display a significant gradient must therefore be emitted by the smelter. This method shows that Cu, Ag, In, Sb, Pb, As, Tl, Mo, Zn, Cd, Co, Be, Ni, Na, Ba, Fe, Cr, V, Ti, Y, Al, U, Ce, Li, S, La, and Sr are deposited on the landscape by the smelter. For many elements, the slope of this binary mixing line is still non-zero at a distance of 50 km, indicating that the impact of the smelter is still detectable, and that regional background levels have not yet been reached. Data from more distant sites are used to estimate regional background concentrations to be 1.1, 1.7, and 1.6 μg/Lmeltwater for Cu, Pb, and Zn, respectively. We quantify the partitioning of elements between the dissolved phase (meltwater) and the solid phase (particulates) in melted snow. It varies with distance from the smelter but is element specific. Representative end-members are: Tl, Cu, Pb, Zn, and Sb with 78, 68, 67, 55, and 20% in the dissolved phase near the smelter, respectively, vs. 4, 60, 73, 80, 58% at distances greater than 35 km. This is due to changes in mineralogy and particle size. The significance of this is, that for those elements with high variation such as Tl and Sb, only the total load (meltwater + particulate) can reliably reflect atmospheric deposition. For those elements that vary little such as Cu and Pb, measurement of just the dissolved load (meltwater) can be used as an adequate proxy for the total deposition. Observed patterns of deposition suggest that inside 15 km radius, it occurs by wet+dry mechanisms whereas beyond 15 km wet deposition dominates. Emissions transported beyond 15 km are therefore available for long-range transport during dry weather and likely have an atmospheric residence time similar to that of water vapour. A well fitting mathematical model supports this interpretation. Using modelled background concentrations, the model can account for only 49, 15, 23, and 9% of reported emissions of Cu, Pb, Zn, and Cd within 50 km of the smelter, respectively. Using lower (minimal) background concentrations based on observations at more distant sites, these numbers increase to 78, 19, and 43%, respectively (Cd excluded), and can be considered maximums. The rest of the emissions are therefore transported further distances during dry weather.

A surface and subsurface investigation of pH, oxidation–reduction potential (ORP) and spontaneous potential (SP) was carried out over sulphide-hosted gold mineralization in an area of thick and extensive glacially derived overburden. Protocols were developed to measure ORP and pH in clay slurries, peat and groundwater to test for the presence of redox and pH phenomena that were predicted to occur over mineralization. ORP protocols focused on removing memory effects caused by probe history and storage and on obtaining a reproducible measure of the ORP over mineralization relative to background areas. The results confirm the presence of distinct reduced ‘columns’ in clay and interstitial groundwater overlying sulphide mineralization that are in fact reduced ‘curtains’ that follow the trace of mineralization. These are accompanied by high pH within the reduced column, with minor lows on the flanks, and elevated H 2 S and CO 2 in shallow groundwater over mineralization. Whereas the H 2 S appears to have its source in bedrock mineralization, the CO 2 is likely a secondary near-surface phenomenon related to oxidation of metals in the reduced column, which produces acid and concomitant dissolution of carbonate in the clays. Wide groundwater temperature anomalies are spatially associated with mineralization. High ORP in shallow peat above mineralization may be evidence of an ‘oxidized cap’ over the reduced column. A minor SP response in surface peat was noted but is small in comparison to the redox field voltage . The presence of reduced columns and other features are consistent with a previously published redox-gradient transport model.

An investigation of surface and subsurface redox and electrical field conditions was carried out over a volcanogenic massive sulphide (VMS) deposit in thick glacial clay and sand terrain of the Abitibi clay belt of northeastern Ontario. Thirty-seven boreholes were drilled to 9 m depth on two lines crossing the strike of mineralization and were completed in either sand or clay. An additional three were drilled 30 to 50 m and completed in bedrock. Monitoring wells were installed in all holes and groundwater was later sampled. A variety of oxidation–reduction potential (ORP) and spontaneous potential (SP) techniques were used, the methodologies for which were introduced earlier and are further developed here. The best definition of redox conditions was obtained by ORP measurement of clay and sand slurries from split-spoon samples collected and analysed during the drilling programme. Related techniques included groundwater ORP and down-hole platinum-SP (PtSP) testing, the latter measuring total potential field, which is the sum of the electrical and electrochemical components of voltage. Although the performance of the methods differed, the results consistently show chemically reduced areas (reduced ‘columns’) in the phreatic zone above mineralization with overlying acidic ‘caps’ in the vadose zone. Other features noted over mineralization include carbonate remobilization, partial extraction metal anomalies in shallow soils, CO 2 enrichment in groundwater, and elevated groundwater temperature. These varied features are related and provide evidence for upward transport of reduced species from mineralization. They agree well with phenomena predicted in a previously published redox-gradient transport model. SP was measured, both down-hole and on surface, and shows a weakly negative electrical field response over mineralization. This response is small in comparison to the redox response and is interpreted to occur because, in addition to being oxidizable, the sulphide is also conductive and SP currents within it produce a small electrical field. It is postulated that oxidizable but non-conductive features such as sphalerite, would also produce a reduced column but without an electrical field, whereas, conductive, non-oxidizable features such as graphite would produce an electrical field but with little or no redox response.

It has become increasingly common for geologists to drill through 100 m or more of cover in search for buried mineral deposits. Geochemistry is one tool applied to this search, using a variety of approaches, including selective leaching of soils to extract the mobile component of elements, and the measurement of inorganic and organic gases. This paper provides an overview of some of the work carried out by the project Deep-Penetrating Geochemistry, sponsored by the Canadian Mining Industry Research Organization (CAMIRO), and supported by 26 Canadian and international companies and by the Ontario Geological Survey and the Canadian Geological Survey. The objective was to provide the mining industry with information relating to processes that may form anomalies at surface over buried deposits and to provide comparative data on methods used to detect these anomalies. Phase I of the project considered the theoretical and experimental framework for the movement of material from deeply buried deposits to the surface; much of this information has come from research on the containment of buried nuclear waste. In arid or semi-arid terrain, with a thick vadose zone, advective transport, which is the mass transfer of groundwater or air along with their dissolved or gaseous constituents, is the only known viable means of moving elements to the surface; diffusion of ions in water or gases in air is orders of magnitude slower. Examples of advective transport are pumping of mineralized groundwater to the surface during seismic activity and the extraction of air plus gas by barometric pumping. Both mechanisms require fractured rock and the interpretation of the derived anomalies requires consideration of neotectonic structures. In wetter climates, where water lies close to the surface, a variety of mechanisms have been proposed for creating anomalies at the surface. Diffusion-based models again suffer from slow rates of migration. Electrochemical models show a cathodic zone at the top of a buried sulphide conductor. Cations are attracted to the cathode, rather than to the surface, yet metals that most commonly migrate as cations are found to form anomalies at the surface. Phase II of the CAMIRO study involved field studies at ten test sites. The test sites included buried porphyry deposits in northern Chile, a gold–copper deposit in the Carlin district of Nevada, and volcanogenic massive sulphide bodies covered by glacial sediments in the Abitibi greenstone belt of Ontario. In all cases anomalies were found in soils above buried mineralization. It is suggested that anomaly formation is an episodic and cyclic process, in which batches of metal in water-soluble form are introduced and the metal is then progressively incorporated with time into the secondary minerals of soil. Selective leaches have been developed to dissolve specific phases in the soil to detect these anomalies. We have compared the results for five selective leaches that are available from commercial laboratories: deionized water, ammonium acetate, hydroxylamine hydrochloride, Enzyme Leach and Mobile Metal Ion (MMI) plus one non-selective decomposition, aqua regia. In addition, the Institute of Geophysical and Geochemical Exploration laboratory in China has supplied data for four sequential selective leaches: water-extractable, adsorbed, organic-bound and iron- and manganese-bound. The weakest leaches dissolve mainly the most recently introduced metals that remain in water-soluble form. Other leaches dissolve specific secondary minerals, such as carbonates, or iron and manganese oxides, which contain the introduced metals. The usefulness of leaches that dissolve secondary minerals depends on the ratio of introduced (exogenic) metal that the minerals contain relative to that of endogenic origin derived from the primary minerals of soils. Our results indicate that this ratio is variable from site to site, so that there is no universal ‘best’ leach for dissolving secondary minerals in exploration surveys. For the test sites in Chile and Nevada, anomalies may have formed incrementally over a period of a million years or more, which permitted metals of exogenic origin to become incorporated into many secondary minerals. For these sites, some anomalies can be detected by aqua regia, although the anomaly/background contrast is less than for selective leaches. For the test sites in Ontario, only a few thousand years have elapsed since glacial sediments were deposited to conceal mineralization. Over this short period, metal of exogenic origin has been incorporated into only the most labile of secondary minerals and it is the leaches that dissolve these labile minerals that can successfully identify anomalies. At the two sites where the most detailed studies have been carried out, the Spence deposit in Chile and Cross Lake near Timmins, we have found that the optimum sampling depth in soils is critical to detecting anomalies.

Twenty-six international geological certified reference materials (CRM) and two in-house soil control samples were gathered and submitted ‘blind’ in duplicate to five commercial geochemical laboratories for the determination of Au and the platinum group elements (PGEs). The methods employed comprise: Pb fire assay (PbFA) combined with inductively coupled plasma mass spectrometry (ICP-MS); NiS fire assay combined with ICP-MS or instrumental neutron activation analysis (INAA); and aqua regia ICP-MS, with and without prior roasting of the sample at 600 o C. The CRMs vary widely in their matrix and PGE concentrations, ranging from a background soil (e.g. GPt-1), sediment (e.g. GPt-2, JSd-2), and rock (e.g. WGB-1, CHR-Bkg) to altered rocks (e.g. WPR-1) and ore material (e.g. GPt-6, SARM-7b, WMS-1). The results of this ‘round-robin’ are provided and discussed in this paper. Results for Au showed the greatest variation across the laboratories, with one evidently encountering significant and spurious contamination. Comparison of the two fire assay techniques for Au, Pt and Pd was difficult as the number of data points was low and the variance within each technique across laboratories was too high. In general, PbFA-based methods for Au, Pt and Pd produced more accurate and precise results than those by NiS fusion and the data support PbFA detection limits for a 5–10 g sample of 1, 0.1 and 0.5 ppb for Au, Pt and Pd, respectively. A PbFA dataset for Rh demonstrated that this element is not recovered efficiently using an Ag inquart. Measurement of Rh by INAA rather than ICP-MS following NiS fusion facilitates detection below 1 ppb to c. 0.1–0.2 ppb. NiS/ICP-MS results for Ru, Os and Ir support detection limits of 1–2, 2–3 and 0.1 ppb, respectively; mean precision for these elements is in the range 10–15% RSD. Recovery of Os was very low by one laboratory, probably caused by its volatilization as OsO 4 during final digestion in the NiS procedure. As expected, recovery of the analytes by aqua regia was low and highly variable across the different matrices for Pt, Ru, Os and Ir but that for Au and Pd was often >80%; prior roasting of the samples had mixed effects.

Sediment cores were collected from 20 lakes from the Muskoka region of Ontario, Canada, to study vertical changes in trace metal concentrations with depth and the distribution of metals amongst humic material, amorphous and crystalline Fe and Mn oxides, insoluble organics/sulphides, and silicates. Based on their total concentrations, trace elements displayed different degrees of affinity for the organic fraction (represented by organic C) and the mineral fraction (represented by Al). Certain elements (Hg, As, Sb, Pb, Cd, and Zn) displayed a positive correlation with organic C, a negative correlation with Al, and enrichment in surface sediments (with enrichment factors ranging from 2 to 24). Detailed speciation studies revealed that these elements were associated mainly with humic material and to a lesser extent with oxides in surface sediments. Other elements (Al, Cr, Co, Fe, and Mn) displayed a negative correlation with organic C, a positive correlation with Al, and no consistent enrichment in their total concentration at the surface. The speciation study revealed that metals of the latter group were mainly associated with the silicate fraction in both surface and deep sediments. This study shows that relative affinities for organic and mineral fractions play an important role in the distribution of trace metals during burial and diagenesis, and hence in the shape of their vertical profiles.

The objective of the work carried out was to recommend protocols for the collection, filtration (0.45 microm) and preservation of surface water samples for the subsequent determination of total 'dissolved' Hg. Cold vapour (CV) ICP-MS was employed to determine Hg; samples were acidified to a strength of 4 mol l(-1) HCl and 1% NaBH4 was used as the reducing agent in-line. Four types of 125 ml bottles were studied (Teflon, fluorinated ethene propene copolymer, FEP; high density polyethylene, HDPE; polyethylene terephthalate copolyester, PET; polypropylene, PP), together with three cleaning methods (EPA Methods 1631, 1638 and a rinse with reverse osmosis deionised water, 'MilliQ'). The transmission properties of the four materials were also studied to evaluate the potential for contamination from atmospheric Hg0. Results of this bottle study (n = 195), all below the detection limit of 0.5 ng l(-1), indicate that the bottles of choice, from an economic and time-saving perspective, are HDPE and PP, the latter being preferable if the sample is to be stored in a contaminated atmosphere. The bottles would be used on a once-only basis, negating the need for labourious and costly cleaning on repeat use. A simple rinse with MilliQ water would suffice prior to use. Twelve 0.45 microm filter systems (mostly Millipore and Gelman) were studied for (a) their potential Hg contamination properties and (b) their retention of Hg, possibly in colloidal form, during filtration. Ottawa River water, spiked at 50 ng l(-1) Hg, was used as a control sample. Again blank values were all negative, indicating contamination was not a concern but different recoveries of Hg were obtained across the different systems. The optimum systems to use, in that they provided maximum recovery (ca 80%) of Hg, are the Millipore Sterivex capsule and the Millipore Millex disc, both based on the hydrophilic Durapore membrane. The lowest recoveries (23-36%) were found with the Gelman AquaPrep systems and the Millipore HN nylon filter. Four control samples, Ottawa, Rideau and Gatineau Rivers, and a MilliQ blank, were used to study three preservation approaches, in the media: 0.5% BrCl, 2% HCl and 0.04% K2Cr2O7 in 1% HNO3. Mercury was stable for 28 days in a medium of 0.5% BrCl in all four samples but the other two media showed a loss of up to ca 20% Hg over this time frame, the loss being sample and time dependent. This may be a species transformation which is not detected by CV-ICP-MS from an HCl medium but this requires further investigation. Mercury was stable over the 28 days in the spiked blank MilliQ sample for all three preservation media.

Sodium hexametaphosphate, Na 6 (PO 3 ) 6 , is often used as a dispersant in wet grain size separation procedures to obtain the clay-sized (6 (PO 3 ) 6 dispersant during the clay-sized separation. Consequently, the concentrations of labile or weakly bound forms of elements reported in a sequential extraction scheme could be reduced because of a loss to the Na 6 (PO 3 ) 6 dispersant.

A detailed investigation of the mineralogy of As in the tailings of the Rabbit Lake uranium ore processing facility was conducted. The milling/ore extraction process was sampled at three different locations to obtain information about when, where and under what condition secondary As phases form. These samples were compared with four samples of varying As content from the Rabbit Lake in-pit tailings management facility (TMF). Up to 20% As in the tailings are present in primary minerals that reach the tailings directly because they are not dissolved during the uranium extraction. The remaining 80% constitute As that was dissolved during ore extraction and then re-precipitated before being discharged into the tailings pond. It was not possible to conclusively identify any individual re-precipitated (secondary) As minerals in the Rabbit Lake TMF. Indirect evidence from sequential extraction analyses suggests the presence of an amorphous Ca-As phase and a possible, but unlikely, minor amount of an amorphous Fe-As phase. However, the close association between hydrous ferric oxide (HFO) and As could be clearly demonstrated. HFO was identified to be 2-line ferrihydrite and its XRD pattern geometry indicates a substantial amount of adsorbed As. This is in good agreement with SEM, TEM and sequential extraction analyses that all showed the close association of HFO and As.

Ground and surface waters collected from two undisturbed Zn–Pb massive sulphide deposits (the Halfmile Lake and Restigouche deposits) and active mines in the Bathurst Mining Camp (BMC), NB, Canada were analysed for the rare earth elements (REE). REE contents are highly variable in waters of the BMC, with higher contents typical of waters with higher Fe and lower pH. There are significant differences between ground- and surface waters and between groundwaters from different deposits. The REE contents of surface waters are broadly similar within and between deposit areas, although there are spatial variations reflecting differences in pH and redox conditions. Surface waters are characterised by strong negative Ce anomalies ([Ce/Ce*]NASC as low as 0.08), produced by oxidation of Ce3+ to Ce4+ and preferential removal of Ce4+ from solution upon leaving the shallow groundwater environment. Groundwaters and seeps typically lack significant Ce anomalies reflecting generally more reducing conditions in the subsurface environment and indicating that Ce oxidation is a rapid process in the surface waters. Deeper groundwaters at the Halfmile Lake deposit are characterised by REE patterns that are similar to the host lithologies, whereas most groundwaters at the Restigouche deposit have LREE-depleted patterns compared to NASC. Halfmile Lake deposit groundwaters have generally lower pH values, whereas Restigouche deposit groundwaters show greater heavy REE-complexation by carbonate ions. Shallow waters at the Halfmile Lake and Stratmat Main Zone deposits have unusual patterns which reflect either the adsorption of light REE onto colloids and fracture-zone minerals and/or precipitation of REE–phosphate minerals. Middle REE-enrichment is typical for ground- and surface waters and is highest for neutral pH waters. The labile portion of stream sediments are generally more middle REE-enriched than total sediment and surface waters indicating that the REE are removed from solution by adsorption to Fe- and Mn-oxyhydroxides in the order middle REE≥light REE>heavy REE.

The coral reef that circles Ambitle Island, Papua New Guinea, is exposed to the discharge of a hot, mineralized hydrothermal fluid. The hydrothermal fluids have a pH of {approximately}6 and are slightly reducing and rich in As. Seven individual vents discharge an estimated 1500 g of As per day into an area of approximately 50 x 100 m that has an average depth of 6 m. Despite the amount of As released into the bay, corals, clams, and fish do not show a response to the elevated values. The authors analyzed hydrothermal precipitates for their chemical and mineralogical composition in order to determine As sinks. Two mechanisms efficiently control and buffer the As concentration: (1) dilution by seawater and (2) incorporation in and adsorption on Fe(III) oxyhydroxides that precipitate when the hydrothermal fluids mix with ambient seawater. Fe(III) oxyhydroxides contain up to 76,000 ppm As, by an order of magnitude the highest As values found in a natural marine environment. Following adsorption, As is successfully retained in the Fe(III) oxyhydroxide deposits because oxidizing conditions prevail and high As activity allows for the formation of discrete As minerals, such as claudetite, arsenic oxide, and scorodite.

Previous research on mercury (Hg) in lakes and rivers has identified pH, alkalinity, and organic carbon levels as the major environmental variables which predict Hg concentrations in fish and invertebrates. However, the factors that regulate accumulation in wetland systems and aquatic plants in particular have yet to be identified. Total Hg in sediments, water, and four species of aquatic macrophytes [yellow pond lily (Nuphar variegatum), eurasian water milfoil (Myriophyllum spicatum), common waterweed (Elodea canadensis), and curly leaf pondweed (Potamogeton crispus)] were measured in twenty-three wetlands along the St. Lawrence River. The total Hg concentration in N. variegatum ranged from 6.4 to 36.5 ng/g and remained fairly constant in relation to measured environmental variables (pH = 7.6 to 8.4; alkalinity = 1,217 to 3,128 eq/L Ca; DOC = 3 to 12 mg/L; organic content of the sediment = 0.9 to 49%). As well, water Hg (3 to 19 ng/L), and sediment Hg concentrations (15 to 882 μg/kg) showed no relationships with Nuphar Hg. Because the plant concentrations were lower than the sediment concentrations, it appears that Nuphar is an excluder of Hg. In contrast, Hg concentrations of the submerged species were significantly higher with the highest concentrations found in Myriophyllum (63 to 240 ng/g) followed by Elodea (58 to 225 ng/g) and Potamogeton (80 to 85 ng/g), and these species were often found to be Hg accumulators in the wetlands. However, as with Nuphar, no correlations were observed with environmental concentrations of Hg and the chemical variables measured. None of these macrophyte species appear to be good biomonitors of sediment Hg contamination.

Two selective extraction schemes, that commonly known as Tessier's and that used by the Geological Survey of Canada (GSC), are compared. The nominal phases identified include: adsorbed/exchangeable/carbonate, ‘AEC’; amorphous Fe oxyhydroxides (including Mn oxides), ‘amFeox’; organics and sulphides, ‘org/sul’; and residual (silicates and more resistant minerals). Three standard reference soil samples, SRMs 2709, 2710 and 2711, were analysed in triplicate for the elements Ca, Cd, Cu, Fe, Mn, Ni, P, Pb, Ti, V and Zn. Results by both methods agree extremely well for Ca, Mn and Cd, and for Ni and V in SRMs 2709 and 2711. For other elements, there is a strong tendency for a higher percentage to be dissolved earlier in the GSC scheme (in the AEC, amFeox and org/sul phases). Consistently more Fe reports to the amFeox and org/sul phases by the GSC method, otherwise present in the residual phase by the Tessier scheme. Results for P do not compare well, with a much greater proportion of the element being extracted in the amFeox phase by the GSC procedure. Very little P appears to be labile by the Tessier protocol. This paper suggests that more research is needed into the nature of phases purportedly extracted by selective leaches.

The objective of this study was to formulate a protocol for the collection and preservation of natural water samples (lakes and streams) to be analysed for the inorganic species As(III) and As(V). The analytical technique employed was HPLC-ICP-MS, using a proprietary anion exchange resin (ANX-1606-AS from Cetac) as the basis for separation of the two species. Initial experiments carried out at room temperature, where de-ionised water and Ottawa River water samples were spiked at low (0.5-20) µg l –1 concentrations of As(III) and As(V), demonstrated that As(V) is actually reduced to As(III) within a few days. This reduction is matrix and concentration dependent and was confirmed by independent analysis using HGAAS with hydride generation at pH 4.5 and

A non-linear prediction model for the Cd content of durum wheat grain has been developed based on the 0.1 M Na4P2O7-extractable Cd and organic carbon in the

Extraction of soils by leaching 20 g in 50 ml of unbuffered 1 M NH4NO3 for 2 h has become the standard German protocol (DIN 19730) to estimate mobile and potentially hazardous forms of trace elements. This protocol was examined using soil controls of chernozem and podzol character collected in the Canadian Prairies and Ontario. It was found that this procedure was not robust with respect to change in sample weight per unit volume of reagent or to contact time. A 3- to 15-fold increase in Cd extracted was produced by decreasing sample weight from 10 g to 1 g in 50 ml of reagent. This change in extractable-Cd was more pronounced with increasing pH of the soil, ranging from 5.2 to 8.1 amongst the control samples. Leach period was less significant in determining results but longer time (1–3 h) generally produced lower extractable-Cd, suggesting readsorption. Lack of stability of Cd in this reagent was further demonstrated by spiking experiments where Cd was added at the beginning of the leach. Recoveries of Cd at 50 and 200 ppb were below 20% for soils of pH 6.1 and 6.9. Such severe adsorption of Cd was not encountered with another unbuffered reagent, 1 M NH4Cl, operating at a similar initial pH of 5. Cadmium levels extracted from soils by NH4Cl and 0.1 M Na4P2O7 were comparable and could be used to predict uptake in durum wheat on the Canadian Prairies, whereas data by the 1 M NH4NO3 leach were generally near the detection limit of 0.1 ppb (ng g−1) Cd. Readsorption of Cd and lack of equilibrium in the 1 M NH4NO3 extraction could lead to underestimation of plant-available Cd in neutral and alkaline soils.

Analysis of soil and sediment samples, using selective extraction methods to distinguish different phases, is of particular interest in exploration geochemistry to locate deeply buried mineral deposits. There are various mechanisms of binding labile elements in the secondary environment, including physical and chemical sorption, precipitation, chelation and complexation. Phases present in soils and sediments which are likely to scavenge `free' elements include amorphous Mn and Fe oxides, the humic and fulvic components of humus, and clays. This paper reviews these forms of trace elements and the methods in current use to quantify them. Examples of precision data, both for control and survey samples, are given with respect to trace elements dissolved from the `soluble organic' component of humus, Mn oxides and amorphous Fe oxides. The high sensitivity of inductively coupled plasma mass spectrometry (ICP–MS) is required to measure accurately and precisely a large suite of trace elements, especially where only small fractions of elements are dissolved by such leaches as the commercially available Enzyme and MMI (Mobile Metal Ion) extractions. The relative standard deviations (RSD) obtained for 33 elements (e.g. Ag, Cd, In, I) in the standard reference sample (SRM), TILL-2, are in the range 0.5–8% for the hydroxylamine hydrochloride (NH2OH·HCl) leach designed to extract hydrous Fe and Mn oxides. The corresponding RSDs for elements in the reactive Mn oxide phase extracted by the Enzyme leach are in the range 3–19% except for some trace elements at levels close to detection limit (e.g. Cd, Bi). The RSDs obtained for field duplicates are inferior to those for analytical replicates (i.e. sample splits), probably a reflection of different concentrations of the host phase. In one soil survey, the Fe extracted by a 0.25 M NH2OH·HCl leach ranged conservatively from 0.2 to 1.7% whereas the Mn extracted by the Enzyme leach varied extensively, from 0.3 to >999 ppm. In contrast, precision, at 1–7% RSD, for field duplicates was found to be comparable with that for both analytical duplicates and the SRM, LKSD-4, for elements associated with the humic and fulvic component of humus samples sieved to

Recently, occurrences of elevated arsenic concentrations in bedrock groundwaters used for individual and municipal water supplies have been recognised along the mainland coast of southern British Columbia, Canada. An area on Bowen Island (Queen Charlotte Heights community) was chosen to investigate the source(s) of arsenic, geochemical processes controlling its aqueous uptake, the role of geology and structure in the formation of these waters, and the use of hydrogeochemical survey methods for detecting arsenious groundwater regions. Pyrite- arsenopyrite-Cu mineralisation in the Queen Charlotte Heights area is present as veins associated with NE-trending fault zones and as disseminations in marginal breccia and stockwork zones of a ryhodacite porphyry stock. Near surface mineralisation was later altered by supergene events to form minor pyrite- arsenopyrite in a matrix of limonite and clay. Geochemical factors that control the concentration and mobility of arsenic in these groundwaters include: (a) anion exchange of arsenic from clay minerals during cation divalent/univalent exchange processes (water softening) which leads to waters of high pH and high anion exchange capacities; (b) desorption of arsenic from Fe and Al oxyhydroxide minerals during pronounced shifts in pH from acid to alkaline conditions brought on by the water softening process; and (c) stepwise oxidation of arsenopyrite mineralisation to form arsenious sulphate-bearing groundwaters. The inconsistent behaviour of the As3+ and As5+ ions during the complex waterrock interaction processes described above, precludes the use of detailed chemical analyses to predict relative abundances of the more toxic As3+ species. For a full appreciation of the toxic impact of groundwaters containing total arsenic concentrations that are above regulatory guidelines an arsenic speciation analysis is required.

Analytical data are reported for As, Bi, Sb, Se and Te in fifty five geological reference materials (RM). The method used is based on hydride generation inductively coupled plasma-mass spectrometry (HG-ICP-MS) following digestion of the samples in the mixed acid attack of HF-HClO4-HNO3-HCl. Analytes were separated from potential interferences by coprecipitation with La(OH)3. This scheme results in method detections limits of: 1 ng g−1 for Bi and Te; 6 ng g−1 for Sb and Se; and 10 ng g−1 for As. The average relative standard deviation (RSD) for three 0.5 g subsamples of each RM analysed by this method are: 3.7% for As in the range 0.35-187 μg g−1; 5.6% for Sb in the range 0.03-22 μg g−1; 6.8% for Bi in the range 0.002-48 μg g−1; 7.2% for Se in the range 6-3610 ng g−1; and 9.0% for Te in the range 2-445 ng g−1. Les resultats de dosage de As, Bi, Se et Te dans cinquante-cinq materiaux geologiques de reference sont donnes ici. La methode utilisee est basee sur l'analyse par spectrometrie de masse couplee a un plasma entretenu inductivement associee a un generateur d'hydrure (HG-ICP-MS), ceci apres que les echantillons aient ete mis en solution par‘action du melange dacide HF-HClO4-HNO3-HCl. Les elements a analyser ont ete separes des interferences potentielles par coprecipitation avec La(OH)3. Cette procedure permet d'obtenir des limites de detection, pour cette methode, de 1 ng g−1 pour le Bi et le Te, 6 ng g−1 pour Sb et Se et 10 ng g–1 pour As. Les deviations standard relatives moyennes (RSD) pour trois prises de 0.5 g chacune par materiau de reference analyse sont : 3.7% pour As pour des concentrations entre 0.35 et 187 μg g−1, 5.6% pour Sb pour des concentrations entre 0.03 et 22 μg g−1, 6.8% pour Bi pour des concentrations entre 0.002-48 μg g−1, 7.2% pour Se pour des concentrations entre 6 et 3610 ng g−1 et 9% pour Te dans une gamme de concentration de 2-445 ng g−1.

This study compares the performance of hydride generation quartz tube atomic absorption spectrometry (HG-QTAAS) and inductively coupled plasma mass spectrometry (HG-ICP-MS) in the determination of Bi, Se and Te in 38 geological reference materials (GRMs). Samples are decomposed in aqua regia and analytes separated from potential liquid-phase interferents (e.g., Cu, Ni, Co) by coprecipitation with La(OH) 3 . Method detection limits using HG-QTAAS are 10 ng g −1 for all three elements and are improved using the more sensitive HG-ICP-MS, to 1 ng g −1 for Bi and Te, and 6 ng g −1 for Se. Results for Bi by both techniques compare well, with typical relative standard deviations (RSD) of 3–4% for the triplicate digestions and analyses of the GRMs. For the most part, results are also in agreement for Se but diverge for those samples where As is present in excess over Se by about 150-fold. In these cases, mutual interference by As suppresses the Se signal in measurement by HG-QTAAS. Mutual interferences in HG-QTAAS are worse for the element of lowest natural abundance, Te. In the presence of As at 300-fold excess, recovery of the Te signal is only 50%. In the drainage sediment GSD-6 which contains As at 13.6 μg g −1 , the value for Te by HG-QTAAS is as low as 68 ng g −1 compared to that by HG-ICP-MS of 157 ng g −1 and a proposed literature value of 140 ± 40 ng g −1 . An excess of 120-fold of Se IV also reduces the Te signal by 50%, but this is of less concern given the relative levels of As and Se in geological materials and can be negated in any case by preferential reduction to the non-reactive Se 0 with a small amount of KI. The only mutual interference warranting attention in determination of these elements by HG-ICP-MS is that of As V on Te where an excess of As of 5000-fold can suppress the Te signal by 35%. This can be negated by reduction to the non-interfering As III by addition of KI (to a concentration of 0.005%) prior to analysis. Thus, HG-ICP-MS is clearly the preferred method for the determination of Te, with precision typically at 5–7% RSD at levels of Te above 10 ng g −1 . Analysis of a subset of 16 GRMs using the mixed-acid attack, HFHClO 4 HNO 3 HCl, demonstrates that while aqua regia can be expected to result in full recovery for Bi, it provides incomplete digestion for some sample matrices for Se and, to a greater extent, for Te.

Samples of humus and B-and C-horizon till collected from the north and east margins of the Sudbury Basin were analyzed for about 30 trace elements. The data consist of two sets of analyses, one being a conventional “near total” analysis following an aqua regia digestion, the other being a “partia” analysis from a selective leach designed to extract the metals bound to the soluble organic fraction of humus and to the amorphous Fe and Mn oxides of B- and C-horizon till. Statistical processing, using both standard approaches and some newly developed methods of spatial analysis, were applied to evaluate spatial geochemical patterns and their relationship to geological factors such as proximity to known mineral occurrences. In particular, the information content of the partial analyses was evaluated to determine whether the partial analyses reveal interpretable patterns not detected in the “near total” analyses. From a visual appraisal of dotplots of Ni and Cu in till, it is difficult to determine whether the partial data add anything not already seen in the “total” data. However, when residuals obtained by removing that part of the partial variation explained by the “total” variation are mapped, distinctive patterns are produced. These patterns are enhanced by applying an adaptive filtering technique using a spatial U-statistic. Multielement groups (“total” data, 30 elements in till) determined by principal components analysis show that the first two components are due to Ni-Co-Cr-Cu-Zn and Pd-Au-Pt-Sb associations. A multifractal area-concentration model fitted to component scores allows multielement anomalies to be mapped. The first component is shown to be spatially associated with Ni-Cu deposits, the second with Au and Ni-Cu-Au deposits. Analysis of variance, with “total”, partial and residual data taken in turn as the dependent (“response”) variable, shows that both Ni and Cu in till are significantly “explained” by geological factors (underlying rock type, proximity to contacts and to mineralization). Neither the “total” nor the partial analyses on their own show significant associations with these geological factors for either element in C-horizon till. This demonstrates the value of selective leach analyses, where they are carried out in addition to the “total” analyses, for this dataset. A multivariate analysis of variance shows that if all three surfical media (humus, B- and C-horizon till) are used, the selective extraction data are not so advantageous, although still adding some predictive capability, because additional “explanatory” information comes from multimedia rather than multiphase sources.

This paper reports the evaluation of a new cold vapour atomic absorption spectrometer applied to the direct determination of Hg in geological materials. The AMA-254 is based on thermal decomposition of the sample and collection of the evolved Hg vapour on a gold amalgamator. A suite of 33 reference materials, including rocks, soils, sediments and coal, was analysed in duplicate, using sample masses ranging from ca. 30 to 300 mg. Agreement with recommended values was good for all but one sample, TILL-1, where this method produced high results of 145 µg kg - 1 Hg compared to a proposed value of 92 µg kg - 1 obtained by HCl–HNO 3 digestion. Precision, over the range of Hg in these samples of 4 to 6250 µg kg - 1 , was shown to be 10% (±5% RSD). Cycle time was 5 min per sample.

A new method to determine Bi, Sb, Se and Te, at concentrations as low as their natural concentration ranges in geological samples, has been developed based on continuous flow hydride generation inductively coupled plasma mass spectrometry. Samples are dissolved by digestion in either aqua regia or HF–HClO 4 –HNO 3 –HCl acid mixtures and analytes separated from potential interferences ( e.g. , Cu, Ni and Co) by coprecipitation with La(OH) 3 . Addition of a small amount of KI and ascorbic acid, to a concentration of 0.005% in the final analysis medium of 4 m HCl, negates the most serious mutual interference of As V on Te. Analysis is carried out in two batches, the first for Se alone, and the second for the other three elements in the presence of KI. The method was applied to 18 stream sediment and rock standard reference materials from the People's Republic of China (GSD and GSR series). Precision is typically in the range 3–8% relative standard deviation, the higher values usually being associated with concentrations in the very low µg kg -1 range. Detection limits were achieved of 1 µg kg -1 for Bi and Te, and 6 µg kg -1 for Sb and Se. Bismuth was completely extracted from all samples by both digestions but some matrices required the more comprehensive decomposition of HF–HClO 4 –HNO 3 –HCl for full recovery of Te, Se and, to a lesser degree, Sb.

Hard rock groundwater (145) samples collected from private drinking water wells in the environs of Oslo and Bergen were analysed for their radon and fluoride contents. A further 62 elements were determined by inductively coupled plasma mass spectrometry (ICP-MS). For 59 elements, more than 50% of all concentration values were above the detection limit. Characteristic differences between the Oslo- and Bergen-dataset can be shown to be related to host rock lithology. Variation in element contents generally spans 2–6 orders of magnitude. Concentrations of several elements (e.g. Ba, F, Fe, Mn, Na, Rn) exceed current drinking water action levels in a significant number of cases. High levels of other parameters such as Be, Mo, Th and U, which could have an impact on health, were observed. There are no Norwegian action levels currently defined for these elements. The economic and toxicological impacts of these findings require urgent assessment.

Pb isotope ratios obtained from fine-grained fractions ( In this study, Pb isotopic measurements, and selective leaching of 6 near-surface till samples down-ice from the Chisel Lake (Manitoba) and Manitouwadge (Ontario) VMS deposits were carried out in order to determine the location and nature of the Pb within till. Elemental abundances from selective leachates for all 6 samples display similar patterns and show that chalcophile elements (Cu, Ni, Pb and Zn), derived predominantly from the underlying VMS deposits, occur as (i) adsorbed/exchangeable metals; (ii) associated with oxyhydrous Fe and Mn; (iii) crystalline Fe oxides, and/or (iv) silicate. Despite the relative proximity of some of the till samples to the VMS deposits, only a very small component of the chalcophile elements is present as sulfide. This result is consistent with those from studies of weathered (oxidized) tills, which show that labile minerals such as sulfides have been completely destroyed and their chemical constituents reprecipitated or scavenged locally by clay-sized phyllosilicates and secondary oxides/hydroxides. Pb isotopic ratios for selective leachates from till samples with VMS-like (anomalous) signatures are similar to those from ore (galena) within the proximal VMS deposits. This indicates that the Pb is of a secondary nature and was probably scavenged and deposited after destruction of original sulfide minerals during till formation. The lack of a predominant sulfide-held Pb component within the selective leachates supports this interpretation. In contrast, Pb isotopic ratios for the same selective leachates from “background” samples are significantly higher and show that the Pb is not derived from proximal VMS deposits but from a more radiogenic source. Till samples were also leached using 2.5 M HCl (ldconventional” leaching). The Pb isotope ratios from the conventional leachates are similar to those obtained from the selective leachates, and show a large difference in Pb isotopic ratios between anomalous and background samples. We propose, therefore, that the conventional leaching rather than selective leaching or complete dissolution of a particular grain-size fraction be adopted for mineral exploration purposes using glacial sediments. The results from this study support the effective use of Pb isotope ratios from near-surface till as an exploration tool despite the weathered nature of the latter. We feel that this represents a more cost-effective technique over traditional geochemical prospecting methods, if used in conjunction with Pb abundance data.

The almost universally accepted operational definition for dissolved constituents is based on processing whole-water samples through a 0.45-μm membrane filter. Results from field and laboratory experiments indicate that a number of factors associated with filtration, other than just pore size (e.g., diameter, manufacturer, volume of sample processed, amount of suspended sediment in the sample), can produce substantial variations in the ‘dissolved’ concentrations of such elements as Fe, Al, Cu, Zn, Pb, Co, and Mi. These variations result from the inclusion/exclusion of colloidally-associated trace elements. Thus, ‘dissolved’ concentrations quantitated by analyzing filtrates generated by processing whole-water through similar pore-sized membrane filters may not be equal/comparable. As such, simple filtration through a 0.45-μm membrane filter may no longer represent an acceptable operational definition for dissolved chemical constituents. This conclusion may have important implications for environmental studies and regulatory agencies.

The effectiveness of the 0.1 M Na 4 P 2 O 7 (sodium pyrophosphate) leach commonly used in soil science to extract humic and fulvic acid components was studied for application to humus samples collected in exploration geochemistry programs. This digestion is viewed as an alternative to the stronger aqua regia attack, to preferentially dissolve those elements bound to or scavenged by humic and fulvic complexes present in soils. Study of the contact time of 1 g of humus in 100 ml of 0.1 M Na 4 P 2 O 7 solution for 30 samples revealed that the conventional 16-h duration could be decreased to 1 h (with constant agitation) without significantly lessening the amount of Co, Cu, Fe, Ni. Pb or Zn extracted. In fact, the amount of Ni apparently extracted increased, reflecting readsorption of Ni onto the substrate in the longer procedure. About 10–20% more element, including organic carbon, was extracted by a second 1-h treatment with fresh Na 4 P 2 O 7 solution but Mn behaved differently in that a greater proportion was dissolved, about 30% more than by the first leach. This pattern was further shown by another group of 125 humus samples to which two 3-h Na 4 P 2 O 7 leaches were applied. The greater amount of Mn extracted in the second leach (30 vs. 10–20% for the other elements) is probably due to dispersion of Mn-containing colloidal particles rather than to organic dissolution. At 1 g subsampling, results for two in-house humus control samples and the international standard reference lake sediment, LKSD-4, demonstrated relative standard deviations in the range 2–7% when element concentrations were a decade above instrumental detection limits. Similar precision was shown by replicate samples of 37 humus samples sieved to Detection limits in the order of 1 ppm for these elements in the original sample by atomic absorption spectrometry are improved by one to two orders of magnitude by flow injection inductively coupled plasma mass spectrometry. The latter technique requires dilution of the leachate by about 20-fold to obviate severe drift due to salt build-up on the sampling orifice, even with the use of flow injection.

A sequential extraction scheme for application to soils, tills and surficial sediments is described that elucidates the form in which an element is held and provides information as to its provenance. The phases selected for extraction have been categorised as: adsorbed/exchangeable/carbonate (using CH3COONa as extradant); amorphous Fe oxyhydroxide (0.25 M NH2OH-HCl); crystalline Fe oxide (l M NH2OH-HCl); sulphides and organics (KClO3/HCl); and residual, mainly silicates (HF-HClO4-HNO3-HCl). Particular attention has been paid to the specificity of the reagent used for extraction of the amorphous Fe oxyhydroxide phase, well recognised for its scavenging properties of trace metals in the surficial environment. Atomic absorption spectrometry (AAS) was the main analytical technique employed to determine the elements Zn, Cu, Pb, Ni, Co, Mn and Fe. Inductively coupled plasma emission spectrometry (ICP-ES) and ICP mass spectrometry were used to extend this element suite. Results from standard reference materials, TILL 1–4 and LKSD-4, indicate long term relative standard deviations (RSD) for Zn, Cu, Pb, Ni, Co, Mn and Fe extracted from the five phases of 5–12%, at concentrations a decade above detection limits. Comparison of results for the TILL series with those obtained by direct digestion in HF-HClO4-HNO3-HCl shows that losses of element through the various manipulations of sequential extraction are minimal (< 10%). Replicate analyses of 1-g subsamples of soil, till and humus show excellent precision, at 3–10% RSD. A second extraction with fresh solution in each of the first three leaches was examined. An additional recovery of 35–40% for the CH3COONa extraction, 20–25% for 0.25 M NH2OH · HCl, and 15–20% for the 1 M NH2OH · HCl reagent was seen for Zn, Cu, Pb. Ni and Co. Manganese behaves differently: a less consistent pattern between the two leaches is shown by the 221 samples tested; and the second application generally dissolves proportionately less than is the case for the other elements. Omission of this second step could lead to erroneous interpretation of the results. The relatively high concentration of HCl, at 0.25 M, used in the extraction of the amorphous Fe oxyhydroxide phase leads to significant dissolution of sphalerite and galena. Less than 1 % of these sulphides is dissolved if the acid strength is reduced to 0.05 M. However, at either HCl concentration, this attack was shown to dissolve a considerable amount of “soluble” organic component. As much as 15000 ppm C was dissolved from the SRM LKSD-4 by this leach, an amount equal to 63% of that extracted by 0.1 M sodium pyrophosphate which is designed to dissolve metals bound to humate and fulvate components of soil.

Field and laboratory experiments indicate that a number of factors associated with filtration other than just pore size (e.g., diameter, manufacturer, volume of sample processed, amount of suspended sediment in the sample) can produce significant variations in the “dissolved” concentrations of such elements as Fe, Al, Cu, Zn, Pb, Co, and Ni. The bulk of these variations result from the inclusion/exclusion of colloidally associated trace elements in the filtrate, although dilution and sorption/desorption from filters also may be factors. Thus, dissolved trace element concentrations quantitated by analyzing filtrates generated by processing whole water through similar pore-sized filters may not be equal or comparable. As such, simple filtration of unspecified volumes of natural water through unspecified 0.45-μm membrane filters may no longer represent an acceptable operational definition for a number of dissolved chemical constituents.

The effect of 4 different 0.45 μm pore size filter membrane systems on the ‘dissolved’ concentration of 28 elements in 5 natural water samples of varying matrix is reported. In 3 of the 5 waters, consistently higher concentrations of most elements (minor and trace) are obtained using Nucleopore 47 mm filter and the cellulose acetate/nitrate 47 mm filter than those measured using the 142 mm cellulose nitrate MFS filter or the Gelman capsule 47 mm filter. These distinct and coherent patterns in elemental behaviour disappear for the other 2 samples, an organic-rich peat water of high suspended load and a mineralised sample high in Si and Ca. Thus the nature and degree of filtration artifacts is matrix-dependent. These trends are evident in both data sets produced by 2 independent laboratories using different instrumentation, techniques and calibrating procedures. The average relative standard deviation in elemental concentration across the 4 filter types is in the range 9–21%. The presence of such filtration artifacts must be considered in projects where, for example, seasonal variability of water composition is under examination, data from various sources are being merged or hydrogeochemical surveys are being conducted.

Phase selective extractions are employed in the chemical analysis of geological materials to identify the forms in which the element is present and hence to elucidate the mechanisms by which the element has been transported and eventually accumulated in such media. Quantitation of Au bound to the “soluble organic” phase of a humus or lake sediment sample would indicate hydromorphic or chemical dispersion as distinct from mechanical dispersion suggested by Au in an inorganic or metallic form. The majority of analyses carried out for Au in exploration geochemistry are based upon instrumental neutron activation or Pb fire assay for total Au and aqua regia leaching for “near total” Au. Selective leaching of metals scavenged in the surficial environment by the humate and fulvate components of organic material has been successfully carried out for elements such as Zn, Cu, Pb, Co and Ni using alkaline sodium pyrophosphate (Na4P3O7) solution. This paper describes the problems encountered in application of this extraction in batch mode to humus, soil and sediment samples for Au. The concentration of “organically” bound Au in a lake sediment control (Red Lake) is shown to be largely dependent upon the sample weight:leach volume ratio. This concentration is determined to be 128 ppb Au (46% of total Au) at 0.5 g subsampling and 59 ppb Au at 3 g subsampling, both leached with 100 ml of 0.1 M Na4P2O7 solution. Thus, the larger the sample taken per unit volume, the lower the proportional amount of gold apparently extracted. Recovery of AuCl3 spike added at the 83 ppb level to 3 g of Red Lake is less than 20%; “lost” Au is shown to be present in the sample residue. Similar low recoveries of 12–21% were obtained for four humus samples and slightly higher values of 23–25% were found in application of this leach to a gabbro control, WGB-1. Readsorption of Au in six soil samples was also observed in application of the NH2OH · HCl leach, specific for dissolution of amorphous Fe oxyhydroxides. Thus selective leaching for Au is severely hampered by the difficulty of maintaining Au in solution in the presence of the sample substrate. Separation of the competing kinetics of dissolution and readsorption would more appropriately be addressed by use of a flow-through system rather than batch extraction.

Concentrations of Pt have been determined in seepage waters, organic soil horizons and trees in and upslope from a seepage site on the dunite core of the platiniferous Tulameen ultramafic complex. The concentrations of Pt (together with Sb, Cr, Ni, Br, Co, As and Cu) are enhanced twenty-fold in the organic seepage soils compared to Pt concentration in both the LFH horizons of the upslope soils and Pt concentrations found in the ash of twigs and bark of trees growing on the seep. The seepage waters contain 0.4 to 0.8 ng/L Pt. The study provides evidence that weathering under temperate conditions can release Pt from platinum group minerals and that the released Pt can then be transported, either in solution or a colloidal form, to seepage sites where it is accumulated by organic matter. Organic-rich soils from seepage sites might therefore provide suitable sampling media for geochemical surveys for Pt.

The method to analyse rocks, soils, sediments and humus samples for Au, Pt and Pd at low ppb (ng g−1) levels by Pb fire assay and nebulization ICP-MS is described. This simple and cost effective method is capable of achieving practical detection limits of 2, 0.1 and 0.5 ppb for Au, Pt and Pd, respectively, representing significant improvement over conventional methods for Pt and Pd. Detection capability for Au and Pd would be further enhanced by the purification of flux reagents and dedication of assay equipment (furnaces, crucibles) to the processing of low-level samples only. Replicate results are given for six new geological reference materials intended for monitoring accuracy and precision of analysis for Au and platinum-group elements present at both low and high concentration ranges. Precision at low ppb concentrations is dominated by homogeneity of the element in a particular sample rather than by the variability inherent in the method itself. For example, an average relative standard deviation (RSD) for Pt at the 5-ppb level is ±9% in the diabase, TDB-1, but climbs to ±42% in the gabbro, WGB-1, at equivalent Pt concentration. Pd is also more heterogeneously distributed in the gabbro but typically the RSD for Pd at concentrations of 20–1300 ppb is in the range ±3–10%. The nugget effect for Au is evident, with RSD's in the range ±11–55%, independent of concentration level or nearness to detection limit. Evidence of excellent precision at analyte levels between 1 and 20 ppb is seen in replicate analyses of 16 sediment and humus samples taken in recent surveys. This methodology will facilitate studies of the mobility of Au, Pt and Pd in the surficial environment and improve our understanding of their behaviour, knowledge hitherto impeded by inadequate analytical capabilities.

From 1933 to 1964 gold was extracted by underground mining at the northeast shore of Jack of Clubs Lake. At present, tailings and waste rock 4.5 m thick covers approximately 25 hectares of land adjacent to the lake. Arsenic concentrations (>2,000 μg.g‐1) were found in the tailing materials. Two simultaneous processes are controlling the elevated As concentrations in the lake sediments (up to 1,104 μg.g‐1), deposition of suspended particles enriched with As and subsequent diagenetic cycling of sedimentary As. Arsenic concentrations (as high as 556 μg.L‐1) in water samples adjacent to the tailings indicate mobilization of As. However, dissolved As is readily scavenged or coprecipitated with iron hydroxides. The greatest proportion of As in the sediment cores is associated with iron oxides and sulphides. Under oxic conditions the high concentrations of Fe in the tailings is actually beneficial and very effective at limiting the migration of undesirable elements.

This study describes and evaluates the results of a round-robin wherein 22 lake water samples were submitted to eight private sector laboratories for application of their inductively coupled plasma emission spectrometry (ICP-ES) or mass spectrometry (ICP-MS) analytical packages. An objective of the project was to gain an appreciation for the quality of water analyses amongst production-oriented laboratories, and hence to use this information to assist in the design of sample collection and analytical programs in support of hydrogeochemical surveys. The 22 samples were in fact 11 duplicate pairs in order to provide data to facilitate an estimation of precision both within a laboratory and across laboratories; precision control charts were employed to this end. The accuracy observed for each element was more difficult to quantify, but was assessed by the degree of convergence of results using these independent analytical methods and techniques. The samples were spiked with varying amounts of Ba, Be, Cd, Co, Cu, Cr, Mn, Mo, Ni, Pb, V and Zn in order to raise their concentrations to levels above the detection capability of both techniques. The best estimate of precision (defined as twice the relative standard deviation) observed across the laboratories is: 10% for Mg, Mn, Na and Sr, 15% for Ba, Be, Ca, Cd, Co, Mo and V; 20% for As (ICP-MS only), Cu and Pb; 25% for Cr and K (ICP-ES only); 30% for A1 and Sb (ICP-MS only); 35% for Zn; and 60% for Fe. Good precision was not necessarily a guide to good accuracy and the range in mean values for duplicates across laboratories was particularly wide for A1, B, Ca, Fe, K, Na and Zn. Most of the data from one laboratory had to be excluded from assessment of both precision and accuracy as their values deviated greatly from the average. A bias in absolute values between the two techniques was shown for A1 only, ICP-MS yielding the lower results. Superior reproducibility was observed in the MS data for A1, Cr, Ni and Zn. The higher detection power of ICP-MS allowed the measurement of additional elements, namely As, Ce, Cs, I, La, Rb, Sb, Ti and U, to lower limits of 0.01 ppb.

A method has been designed to determine Au in rocks, soils and sediments based upon the use of a field portable anodic stripping voltammeter, the PDV-2000 ® . Sample pretreatment comprises decomposition with hot aqua regia, extraction of Au from potential interferents (e.g., Hg, Ag) with ethyl acetate and redissolution into a final electrolytic solution of 1% HCl-2% HNO 3 . In order to negate the interference from small amounts of Cu in the analysis step, Cu is added in excess to Au at a level of 1 mg 1 −1 for calibration at 5–100 μg 1 −1 of Au and at 10 mg 1 −1 for calibration at 100–1000 μg 1 −1 of Au. Using a sample weight of 10 g for digestion and a 120-s plating period, a detection limit of 10 ng g −1 for Au is obtained. Application of the method to standard reference ores, rocks and soils containing Au in the range 40–1330 ng g −1 indicates that an average precision of ±8% RSD (relative standard deviation) is obtained for the combined extraction and analytical procedure. Comparison of results with those by the well-established technique of graphite furnace atomic absorption spectrometry demonstrates the good accuracy of the anodic stripping voltammetry (ASV) measurement. Application of the method to the analysis of cyanide leaches is shown to be partially successful following oxidation of Au to the III valency state; results by ASV for one solution containing 100 mg 1 −1 Au are low by 50%.

Inductively coupled plasma mass spectrometry (ICP-MS) has had a profound effect in the discipline of geoanalysis since its commercial availability in 1983. In particular, the ability to determine precious metals, rare earth elements (REEs) and refractory elements such as Hf, Ta and W at their natural levels in geological materials has dramatically improved through the application of this highly sensitive, multielement technique. Its capability to measure individual isotopes has been directed mainly towards the Re-Os chronometer pair in ore genesis studies, and to a lesser extent to the quantitation of Pb isotope ratios. The impact of ICP-MS to date in exploration geochemistry is reviewed in this paper, together with a description of the instrumentation, the principles of the technique and the procedures suitable for its optimal use. As with every analytical technique, ICP-MS suffers from interferences; although the degree of spectral interference is lower than in ICP atomic emission spectrometry (ICP-AES), the opposite is true in the case of matrix-induced effects. Its intolerance towards solutions containing high concentrations of dissolved solids (>0.2%) has fostered research into modes of sample introduction other than conventional nebulisation. Applications of alternate means of introduction based upon electrothermal vaporisation, laser ablation, slurry nebulisation and flow injection are discussed here. Waters are an ideal medium for analysis by ICP-MS, though there are as yet only a few studies examining the potential use of this sample type in geochemistry. As happened in the 1980s with the complementary technique of ICP-AES, the 1990s will see the establishment of ICP-MS as a rugged, efficient analytical tool in production-oriented laboratories together with continuing research into design improvements and new applications.

A field portable anodic stripping voltammeter, the PDV-2000®, is evaluated for application to the analysis of the sulphide-selective leach, KClO3HCl and waters. The accuracy and precision obtained in the determination of Zn, Cd, Pb and Cu are assessed by application to international standard reference samples and by concurrent atomic absorption spectrometric analysis. Accuracy for Zn in the presence of potential interferences, Cu and Ni, is ensured by the addition of 500 mg 1−1 Ga and calibration by standard additions; in this manner, concentrations up to 20-fold excess of Cu and 30-fold excess of Ni are tolerated. Using a 60-s plating period, the detection limits in a 10-ml solution are ∼ 0.8 μg 1−1 for Zn and Cu, and ∼ 0.2 μg 1−1 for Cd and Pb. Relative standard deviation at the 10 μg 1−1 level is typically ±4% for Zn and Cu and ±2% for Cd and Pb.

The concentration and distribution of Au and the platinum group elements (PGEs) Pd, Pt and Rh were studied in two arctic shrub species, Labrador tea and dwarf birch, growing in the vicinity of PGE bearing NiCu mineralisation at Ferguson and Townsend Lakes, NWT. Abundance of these elements in ashed vegetation from the gossan was several orders of magnitude above background with values ranging up to 4014 ppb Pd, 275 ppb Pt, 223 ppb Rh and 387 ppb Au. Enrichment of the elements in a direction down-ice from the gossan varied depending on the element; however distances were generally less than 450 m. There were concentration differences between tissue types for Pd, with generally higher levels in twigs; however the concentration of Pt, Rh and Au were similar between tissues. This study demonstrates the applicability of a recently developed analytical method to determine Au, Pt and Pd in ashed vegetation samples, weighing only 0.3 to 1 g, to detection limits of 0.5–1 ppb. The sample is ashed at 870°C, digested in HF-aqua regia, the analytes separated by co-precipitation on Te and re-dissolved in a solution ideal for analysis by inductively coupled plasma mass spectroscopy (ICP-MS). Precision obtained is dominated by the homogeneity of each 0.3–1 g sub-sample, Pt showing the greatest degree of heterogeneity as demonstrated by duplicated analysis of 10 Labrador tea samples. Results given for Rh are tentative as synthetic standard evaporates show some volatilisation losses upon ashing at 870°C; however the spatial pattern for Rh in both species at Ferguson Lake demonstrated patterns similar to the other elements.

Two approaches to the analysis of vegetation for Au have been taken and their results compared. One method is most suited to the direct determination of Au in the dry form of the sample while the other, comprising simultaneous analysis for Pt and Pd, requires wet chemical digestion of the ashed sample. The widely employed procedure based upon instrumental neutron activation ana- lysis (INAA) of a dried 8-g pellet is evaluated with respect to analysis by inductively coupled plasma mass spectrometry (ICP-MS) following ashing at 875 °C and dissolution in HF-aqua regia. Samples were collected from an area of known Pd-Pt-Au mineralization at Ferguson Lake, Northwest Territories, Canada and comprise twig and leaf tissue of Labrador tea (Ledum palustre ssp. decumbens) and dwarf birch (Betula glandulosa). The two sets of data for 149 samples were statistically tested for bias, specifically to determine whether Au was lost on ashing at the high temperat- ure of 875°C. This was found not to be the case; indeed, a slight rotational bias was evident above 1 ppb Au (dry Weight) indicating higher results by 1CP-MS. This was probably due to differences in calibration strategies in the two analytical techniques and implies that one method should be employed consistently throughout a survey area. The larger control data showed superior precision by the ICP-MS method, suggested to be a reflection of the larger sampling weight and five-fold lower detection limit of 0.02 ppb Au. Both methods delineated the zone of mineralization well.

Results are presented of the determination of Zr, Nb, Hf and Ta in 74 standard reference materials by inductively coupled plasma mass spectrometry (ICP-MS). Samples are decomposed by fusion with lithium metaborate and the analytes are separated prior to analysis by precipitation of their cupferrates. Calibration is made using synthetic solutions and internal standardization with Ru (for Zr and Nb) and Re (for Hf and Ta). Accuracy is assessed by comparison with recommended values and precision is evaluated by replicate analyses of five SRMs.