RESUMO
Reactive transport models have proven abilities to simulate the quantity and quality of drainage from mine waste rock. Tracer experiments indicate the presence of fast and slow flow regimes in many heterogeneous waste-rock piles. Although multidomain models have been developed specifically for systems with such distinctive hydrodynamics, there have been limited applications of multidomain reactive transport models to simulate composite drainage chemistries from waste-rock piles to date. This work evaluated the ability of dual-domain multicomponent reactive transport models (DDMRTMs) to reproduce breakthrough curves of conservative (chloride) and reactive (molybdenum) solutes observed at a well-characterized experimental waste-rock pile at the Antamina Mine, Peru. We found that the DDMRTM simulations quantitatively matched eight-year-long records of conservative transport through the waste-rock pile when parameterized mainly with field-measured properties obtained from the site and limited calibration. The DDMRTM model also provided a reasonable match to field observations of the reactive solute. The limited calibrated parameters are physically realistic, corroborating the ability of these multidomain models to reproduce the complex reactive-transport processes governing polluted rock drainage from large-scale waste-rock piles.
Assuntos
Mineração , Modelos Teóricos , PeruRESUMO
The stable isotope composition of molybdenum (Mo) and zinc (Zn) in mine wastes at the Antamina Copper-Zn-Mo mine, Peru, was characterized to investigate whether isotopic variation of these elements indicated metal attenuation processes in mine drainage. Waste rock and ore minerals were analyzed to identify the isotopic composition of Mo and Zn sources, namely molybdenites (MoS2) and sphalerites (ZnS). Molybdenum and Zn stable isotope ratios are reported relative to the NIST-SRM-3134 and PCIGR-1 Zn standards, respectively. δ(98)Mo among molybdenites ranged from -0.6 to +0.6 (n=9) while sphalerites showed no δ(66)Zn variations (0.11±0.01, 2 SD, n=5). Mine drainage samples from field waste rock weathering experiments were also analyzed to examine the extent of isotopic variability in the dissolved phase. Variations spanned 2.2 in δ(98)Mo (-0.1 to +2.1) and 0.7 in δ(66)Zn (-0.4 to +0.3) in mine drainage over a wide pH range (pH2.2-8.6). Lighter δ(66)Zn signatures were observed in alkaline pH conditions, which was consistent with Zn adsorption and/or hydrozincite (Zn5(OH)6(CO3)2) formation. However, in acidic mine drainage Zn isotopic compositions reflected the value of sphalerites. In addition, molybdenum isotope compositions in mine drainage were shifted towards heavier values (0.89±1.25, 2 SD, n=16), with some overlap, in comparison to molybdenites and waste rock (0.13±0.82, 2 SD, n=9). The cause of heavy Mo isotopic signatures in mine drainage was more difficult to resolve due to isotopic heterogeneity among ore minerals and a variety of possible overlapping processes including dissolution, adsorption and secondary mineral precipitation. This study shows that variation in metal isotope ratios are promising indicators of metal attenuation. Future characterization of isotopic fractionation associated to key environmental reactions will improve the power of Mo and Zn isotope ratios to track the fate of these elements in mine drainage.
RESUMO
The isotopic double-spike method allows for the determination of stable isotope ratios by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) with accuracy and precision in the range of â¼0.02 amu(-1), but its adoption has been hindered by the perceived difficulties in double-spike calibration and implementation. To facilitate the implementation of the double-spike approach, an explanation of the calibration and validation of a (97)Mo-(100)Mo double-spike protocol is given in more detail than has been presented elsewhere. The long-term external standard reproducibility is 0.05 on δ(98/95)Mo measurements of standards. δ(98/95)Mo values for seawater and U.S. Geological Survey (USGS) reference materials SDO-1 and BCR-2 measured in this study are 2.13 ± 0.04 (2 SD, n = 3), 0.79 ± 0.05 (2 SD, n = 11), and -0.04 ± 0.10 (2 SD, n = 3) relative to the NIST-SRM-3134. The double-spike method corrects for laboratory and instrumental fractionation which are not accounted for using other mass bias correction methods. Spike/sample molar ratios between 0.4 and 0.8 provide accurate isotope measurements; outside of this range, isotope measurements are inaccurate but corrections are possible when standards and samples are spiked at a similar ratio.
RESUMO
The extraction of bitumen from the Alberta oil sands using in-situ technologies is expanding at a rapid rate; however, investigations into the environmental impacts of oil sands development have focused on surface mining in the Athabasca region. We measured polycyclic aromatic hydrocarbons (PAH) in soils, spruce needles, and lake sediment cores in the Cold Lake oil sands region to provide a historical and spatial perspective on PAH contamination related to in-situ extraction activities. A pronounced increase in PAH concentrations was recorded in one of two study lakes (Hilda Lake) corresponding to the onset of commercial bitumen production in ~1985. Distance from extraction rigs was not an important predictor of PAH concentrations in soils, although two samples located near installations were elevated in alkyl PAHs. Evidence of localized PAH contamination in Hilda Lake and two soil samples suggests that continued environmental monitoring is justified to assess PAH contamination as development intensifies.
