『Abstract
　Desert mine tailings may accumulate toxic metals in the near surface centimeters because of low water through-flux rates. Along with other constraints, metal toxicity precludes natural plant colonization even over decadal time scales. Since unconsolidated particles can be subjected to transport by wind and water erosion, potentially resulting in direct human and ecosystem exposure, there is a need to know how the lability and form of metals change in the tailings weathering environment. A combination of chemical extractions, X-ray diffraction, micro-X-ray fluorescence spectroscopy, and micro-Raman spectroscopy were employed to study Pb and Zn contamination in surficial arid mine tailings from the Arizona Klondyke State Superfund Site. Initial site characterization indicated a wide range in pH (2.5-8.0) in the surficial tailings pile. Ligand-promoted (DTPA) extractions, used to assess plant-available metal pools, showed decreasing available Zn and Mn with progressive tailings acidification. Aluminum shows the inverse trend, and Pb and Fe show more complex pH dependence. Since the tailings derive from a common source and parent mineralogy, it is presumed that variations in pH and “bio-available” metal concentrations result from associated variation in particle-scale geochemistry. Four sub-samples, ranging in pH from 2.6 to 5.4, were subjected to further characterization to elucidate micro-scale controls on metal mobility. With acidification, total Pb (ranging from 5 to 13 g kg^-1) and labile fractions decreased with decreasing pH. Zinc was found to be primarily associated with the secondary Mn phases manjiroite and chalcophanite. The results that progressive tailings acidification diminishes the overall lability of the total Pb and Zn pools.』

1. Introduction
2. Site description
3. Materials and methods
　3.1. Field-scale variation in DTPA extractable metals
　3.2. Bulk physical, mineralogical and chemical characterizations
　　3.2.1. Particle size separation and analysis
　　3.2.2. Particle digestion and total elemental analysis
　　3.2.3. Bulk and clay mineral composition
　　3.2.4. Aqueous extraction
　　3.2.5. Sequential chemical extraction
　　3.2.6. X-ray absorption spectroscopy
　3.3. Grain phase identification and elemental associations
　　3.3.1. Preparation of thin sections
　　3.3.2. X-ray fluorescence spectroscopy
　　3.3.3. Micro-Raman spectroscopy
4. Results
　4.1. Tailings physical-chemical properties
　4.2. Bulk and clay mineralogy
　4.3. Single and sequential extractions
　4.4. X-ray diffraction of bulk residues
　4.5. X-ray absorption spectroscopy of bulk residues
　4.6. Particle-scale elemental mapping and identification
5. Discussion
　5.1. Role of parent mineral weathering
　5.2. Consequences for contaminant metal lability
6. Conclusions
Acknowledgements
References