Heather E. Jamieson

A re-evaluation of the olivine-spinel geothermometer

The Irvine olivine-spinel geothermometer, as formulated by Jackson (1969), appears to yield magmatic temperatures when applied to plutonic rocks such as the Stillwater Complex but Evans and Wright (1972) have demonstrated that it gives temperatures in excess of 2,000 ° C when applied to volcanic assemblages. A re-evaluation of the geothermometer has shown that more realistic temperatures can be obtained for volcanic rocks by using a different free energy value of FeCr2O4 in the formulation. The revised geothermometer gives temperatures in the range 1,100–1,300 ° C for samples from Kilauea and 500–800 ° C for basic plutonic rocks from layered intrusions, indicating that Mg and Fe2+ have re-equilibrated at subsolidus temperatures in these intrusions as suggested by Irvine (1965). This theory was tested by heating uncrushed natural samples from layered intrusions to magmatic temperatures for periods ranging from two days to four weeks. The result was a marked increase in the Mg/Fe2+ ratio in the spinels and a decrease in the Mg/Fe2+ ratio in the olivines, confirming that considerable subsolidus re-equilibration had taken place in the unheated samples.

Effects of Soil Composition and Mineralogy on the Bioaccessibility of Arsenic from Tailings and Soil in Gold Mine Districts of Nova Scotia

Bioaccessibility tests and mineralogical analyses were performed on arsenic-contaminated tailings and soils from gold mine districts of Nova Scotia, Canada, to examine the links between soil composition, mineralogy, and arsenic bioaccessibility. Arsenic bioaccessibility ranges from 0.1% to 49%. A weak correlation was observed between total and bioaccessible arsenic concentrations, and the arsenic bioaccessibility was not correlated with other elements. Bulk X-ray absorption near-edge structure analysis shows arsenic in these near-surface samples is mainly in the pentavalent form, indicating that most of the arsenopyrite (As(1-)) originally present in the tailings and soils has been oxidized during weathering reactions. Detailed mineralogical analyses of individual samples have identified up to seven arsenic species, the relative proportions of which appear to affect arsenic bioaccessibility. The highest arsenic bioaccessibility (up to 49%) is associated with the presence of calcium-iron arsenate. Samples containing arsenic predominantly as arsenopyrite or scorodite have the lowest bioaccessibility (<1%). Other arsenic species identified (predominantly amorphous iron arsenates and arsenic-bearing iron(oxy)hydroxides) are associated with intermediate bioaccessibility (1 to 10%). The presence of a more soluble arsenic phase, even at low concentrations, results in increased arsenic bioaccessibility from the mixed arsenic phases associated with tailings and mine-impacted soils.

The impact of tailings dam spills and clean-up operations on sediment and water quality in river systems: the Rı́os Agrio–Guadiamar, Aznalcóllar, Spain

The Aznalcollar tailings dam at Boliden Apirsas Aznalcollar/Los Frailes Ag–Cu–Pb–Zn mine 45 km west of Seville, Spain, was breached on 25 April 1998, flooding approximately 4600 hectares of land along the Rios Agrio and Guadiamar with approximately 5.5 million m3 of acidic water and 1.3×106 m3 of heavy metal-bearing tailings. Most of the deposited tailings and approximately 4.7×106 m3 of contaminated soils were removed to the Aznalcollar open pit during clean-up work undertaken immediately after the spill until January 1999. Detailed geomorphological and geochemical surveys of the post-clean-up channel, floodplain and valley floor, and sediment and water sampling, were carried out in January and May 1999 at 6 reaches representative of the types of river channel and floodplain environments in the Rio Guadiamar catchment affected by the spill. The collected data show that the clean-up operations removed enough spill-deposited sediment to achieve pre-spill metal (Ag, As, Cd, Cu, Pb, Sb, Tl, Zn) concentrations in surface sediment. These concentrations, however, are still elevated above pre-mining concentrations, and emphasise that mining continues to contaminate the Agrio-Guadiamar river system. Dilution by relatively uncontaminated sediment appears to reduce metal concentrations downstream but increases in metal and As concentrations occur downstream, presumably as a result of factors such as sewage and agriculture. River water samples collected in May 1999 have significantly greater dissolved concentrations of metals and As than those from January 1999, probably due to greater sulphide oxidation from residual tailings with concomitant release of metals in the warmer early summer months. These concentrations are reduced downstream, probably by a combination of dilution and removal of metals by mineral precipitation. Single chemical extractions (de-ionised water, CaCl2 0.01 mol l−1, CH3COONH4 1 M, CH3COONa 1 M and ammonium oxalate 0.2 M) on alluvial samples from reaches 1 and 6, the tailings, pre-spill alluvium and marl have shown that the order of sediment-borne contaminant mobility is generally Zn>Cd>Cu>Pb>As. Pb and As are relatively immobile except possibly under reducing conditions. Much of the highly contaminated sediment remaining in the floodplain and channel still contains a large proportion of tailings-related sulphide minerals which are potentially reactive and may continue to release contaminants to the Agrio–Guadiamar river system. Our work emphasises the need for pre-mining geomorphological and geochemical data, and an assessment of potential contributions of contaminants to river systems from other, non-mining sources.

Application of Synchrotron Microprobe Methods to Solid-Phase Speciation of Metals and Metalloids in House Dust

Determination of the source and form of metals in house dust is important to those working to understand human and particularly childhood exposure to metals in residential environments. We report the development of a synchrotron microprobe technique for characterization of multiple metal hosts in house dust. We have applied X-ray fluorescence for chemical characterization and X-ray diffraction for crystal structure identification using microfocused synchrotron X-rays at a less than 10 μm spot size. The technique has been evaluated by application to archived house dust samples containing elevated concentrations of Pb, Zn, and Ba in bedroom dust, and Pb and As in living room dust. The technique was also applied to a sample of soil from the corresponding garden to identify linkages between indoor and outdoor sources of metals. Paint pigments including white lead (hydrocerussite) and lithopone (wurtzite and barite) are the primary source of Pb, Zn, and Ba in bedroom dust, probably related to renovation activity in the home at the time of sampling. The much lower Pb content in the living room dust shows a relationship to the exterior soil and no specific evidence of Pb and Zn from the bedroom paint pigments. The technique was also successful at confirming the presence of chromated copper arsenate treated wood as a source of As in the living room dust. The results of the study have confirmed the utility of this approach in identifying specific metal forms within the dust.

Mineralogical characterization of arsenic in gold mine tailings from three sites in Nova Scotia

ABSTRACT 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 (FeAsO4•2H2O) and Ca-Fe arsenates. Iron oxyhydroxides contain variable amounts of As2O5 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.

The effect of ore roasting on arsenic oxidation state and solid phase speciation in gold mine tailings

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 As2O3 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.

Identification and Characterization of Arsenic and Metal Compounds in Contaminated Soil, Mine Tailings, and House Dust Using Synchrotron-Based Microanalysis

ABSTRACT A comprehensive understanding of the risk associated with metal-rich soils and other materials includes identification of the solid phases hosting the metals. Synchrotron microanalysis provides a powerful diagnostic tool to characterize metal-bearing particles in mine tailings, soils, lake sediments, windblown dust, and household dust. A near simultaneous combination of X-ray fluorescence, diffraction, and absorption experiments using a microfocused beam can provide information on elemental concentrations, crystal structure, and oxidation state of individual particles. This approach can distinguish multiple metal-hosting minerals and industrial compounds in a single sample. Our objective is to provide examples of the application of this technique to a range of materials representing potential risk to human or ecosystem health. These examples include arsenic-contaminated materials and metal-rich household dust. We have identified grains of scorodite and other arsenate minerals in mine tailings and associated airborne dust, arsenic trioxide in organic soils near an ore roaster, metallurgical products dispersed to the environment, and various metal-rich particles in household dust. A comparison of chemical analysis of individual particles using electron microprobe analysis and synchrotron-based X-ray fluorescence analysis is provided.

Optimizing experimental design, overcoming challenges, and gaining valuable information from the Sb K-edge XANES region

Abstract There are many challenges associated with collecting, processing, and interpreting high-energy XAS data. The most significant of these are broad spectra, minimal separation of edge positions, and high background owing to the Compton tail. Studies of the Sb system are a particular challenge owing to its complex bonding character and formation of mixed oxidation-state minerals. Furthermore, in environmental samples such as stream sediment containing mine waste, different Sb phases may coexist. Ways to overcome these challenges and achieve accurate and useful information are presented. Our investigations used Sb K-edge X-ray absorption near-edge spectroscopy (XANES) to elucidate Sb geochemical behavior. Several Sb mineral spectra are presented, including Sb sulfosalts, and contrasted based on the different hosting and coordination environments around the Sb atom in the crystal structure. These comparisons lead to the recognition of how the different hosting and coordination environments are manifested in the shape of the Sb mineral spectra. In fact from the shape of the spectra, the occupation of the Sb atom in a single or in multiple crystallographic sites, regardless of whether multiple phases are present in the sample, is discernible. Furthermore, we demonstrate that quantitative information can be derived from the XANES region using linear combination fitting of the derivative spectra, rather than the energy spectra. Particularly useful to the advancement of Sb research is the demonstration that a significant amount of information can be gained from the Sb K-edge XANES region.

Organic matter control on the distribution of arsenic in lake sediments impacted by ~ 65 years of gold ore processing in subarctic Canada

Climate change is profoundly affecting seasonality, biological productivity, and hydrology in high northern latitudes. In sensitive subarctic environments exploitation of mineral resources led to contamination and it is not known how cumulative effects of resource extraction and climate warming will impact ecosystems. Gold mines near Yellowknife, Northwest Territories, subarctic Canada, operated from 1938 to 2004 and released >20,000t of arsenic trioxide (As2O3) to the environment through stack emissions. This release resulted in elevated arsenic concentrations in lake surface waters and sediments relative to Canadian drinking water standards and guidelines for the protection of aquatic life. A meta-analytical approach is used to better understand controls on As distribution in lake sediments within a 30-km radius of historic mineral processing activities. Arsenic concentrations in the near-surface sediments range from 5mg·kg-1 to over 10,000mg·kg-1 (median 81mg·kg-1; n=105). Distance and direction from the historic roaster stack are significantly (p<0.05) related to sedimentary As concentration, with highest As concentrations in sediments within 11km and lakes located downwind. Synchrotron-based μXRF and μXRD confirm the persistence of As2O3 in near surface sediments of two lakes. Labile organic matter (S1) is significantly (p<0.05) related to As and S concentrations in sediments and this relationship is greatest in lakes within 11km from the mine. These relations are interpreted to reflect labile organic matter acting as a substrate for microbial growth and mediation of authigenic precipitation of As-sulphides in lakes close to the historic mine where As concentrations are highest. Continued climate warming is expected to lead to increased biological productivity and changes in organic geochemistry of lake sediments that are likely to play an important role in the mobility and fate of As in aquatic ecosystems.

Geochemistry of lakes across ecozones in the Northwest Territories and implications for the distribution of arsenic in the Yellowknife region. Part 1.

We obtained near total element geochemistry on 211 near-surface sediment samples from lakes along a transect across the Western Interior Platform to the central portion of the Slave Geological Province with a focus near the City of Yellowknife, Northwest Territories, to document regional concentrations of arsenic (As) and other elements in lake sediments. Concentrations of major and trace elements, including elements of potential human and ecological concern (As, Cd, Cr, Cu, Pb, Zn), were extracted from sediments using a modified aqua regia digestion. Concentrations of As exceed Canadian federal guidelines for the protection of aquatic life in most of the lakes sampled in the Slave Geological Province. Seventy one percent (n=149) of all sediment samples contain As concentrations higher than the Canadian Council of Ministers of the Environment (CCME) Interim Freshwater Sediment Quality Guideline of 5.9 mg/kg and 54% (n=114) of the samples contain As concentrations that exceed the CCME Probable Effect Level of 17 mg/kg. Sediments with the highest As concentrations are from lakes near the City of Yellowknife and likely reflect a combination of contamination associated with past industrial activity and geogenic input from mineralized bedrock and derived surficial materials (median As concentration 107.9 mg/kg, range 6.30->10,000+, n=95). Arsenic concentrations in lake sediments sampled elsewhere in the central Northwest Territories are lower (Ingraham Trail, median As concentration 10.6 mg/kg, range 1.9-101.6, n=27; Tibbitt to Contwoyto Winter Road, median As concentration 7.9 mg/kg, 0.3-101.4, n=52; Western Interior Platform, median As concentration 1.1 mg/kg, 0.1-7.1, n=37). Based on our data and a review of existing literature, background As concentration in lake sediments appear to ~25 mg/kg for the Yellowknife region, and lower for other regions in the central NWT. Other elements (Cr, Cu, Pb, Zn) are below sediment quality guidelines in the majority of lake sediments sampled.