Selenium Distributions in Kanawha Formation Rocks from Boone County, West Virginia WEST VIRGINIA MINE DRAINAGE TASK FORCE SYMPOSIUM April 22-23, 2008 Dr. Dorothy Vesper West Virginia University Department of Geology & Geography WV WRI Hydrogeology Research Center DOE-NETL Research Fellow Hydrogeology Research Center WV Water Research Institute
Selenium distribution and mode of occurrence in the Kanawha Formation, southern West Virginia, USA Vesper DJ, M Roy and CL Rhoads (2008) International Journal of Coal Geology73: 237-249.
Se in rock core Overall Purpose • Better understand the chemistry of Se in coals and related strata • Help predict where Se is most likely to be found Two topics • Distribution in rock cores - stratigraphy • Mode of occurrence in rocks 2004 – 1 core, mostly mode of occurrence
Location of cores WVGES
Selenium by coal bed WVGES, 2002(coals only) Stratigraphy Coal Se (ppm dry wt) Pittsburgh Kittanning Coalburg & Winifrede
Distribution in rock core Bull Creek Mine (Coal River watershed) 5 rock cores • Coal, shale, mudstone, sandstone, carbolith • Kanawha Formation (Coalburg – Winifrede coal beds)
Distribution in rock core 287 Samples • 191 had Se > 0.2 mg/kg • Max 11.9 mg/kg in a mudstone Sample prep by Research Environmental & Industrial Consultants • Lithology described • Ground/composited to <60 mesh by lithology • Total digestion using nitric acid and hydrogen peroxide (EPA Method 3050B) • Analysis for total Se using Graphite Furnace Atomic Absorption Spectroscopy (GFAA) (EPA Method 270.2)
2004 Bull Creek Mine Coalburg Coalburg (upper line) Winifrede (lower line) Winifrede Bull Creek Coal River 1 km Lick Creek
Distribution in rock core How is the Se distributed? • Stratigraphy • Rock type • Formation • Location relative to coal bed • Other chemical parameters • Sulfur (S) • Total organic carbon (TOC)
Distribution in rock core Do Se concentrations change with rock type?
Distribution in rock core Do Se concentrations change by core?
Distribution in rock core For non-coal units – distance to the coal matters • Proximate distance – shortest distance from bed to coal • 0 distance = adjacent to coal • Trends agree with Mullenex (2005) for a similar section in WV
Distribution in rock core What is the relationship between Se & sulfur? All data (R2 = 0.21) Coal only Shale Agrees with Coleman et al. (1993), Mullenex (2005), Neuzil et al. (2005) – FOR THIS REGION. Only Mullenex looked at multiple rock types
Distribution in rock core What is the relationship between Se & total organic carbon (TOC)? All data Coal Mudstone &Shale (only core 2)
Multivariate analysis Principle component analysis (PCA) • Multivariate • Looks for commonalities between variables • Identifies “factors” which are groups of variables
PCA Results • PC1– Sulfur, acidic, non-carbonate, strongly related to sulfur concentration • PC2 –Carbonate, some acid, limited S • Se loads onto both the sulfur and non-sulfur PCs • Similar results obtained for PCA of coals in WV, based on WVGES database(2003) 169 samples; acidity and neutralization potential as calcium carbonate equivalent tons per 1000 tons
PCA Results Map Se and S concentrations for each sample against PC1 and PC2 scores for each sample PC1 Scores (Sulfur-rich) R2 = 0.87 R2 = 0.36 PC2 Scores (more neutral) R2 = 0.36 R2 = 0.01 Scores provide the weighting of that sample on that principle component Selenium Sulfur
PCA Results Mudstone, shale, sandstone Neutral. potential more controlling Carboliths Coal Sulfur more controlling
Conclusions of rock core study • Distribution of total Se: • Se highest in coals; rocks adjacent to coals • Not all units close to coal are high in Se; but the layers that are high in Se are typically found with two feet of the coals • Se probably present in more than 1 mode • No strong correlations with S, TOC • Extraction data indicates both organic & sulfide • PCA analysis shows no single trend for Se • Sulfide more important for coals & organic-bound for shales (?)
Possible Interpretation • Why these patterns in the rock record? • Steps to preservation: • Changing source through time • Immobile – during/after rock formation • (Se less mobile at low pH)
Possible Interpretation • Depositional environment for Kanawha Formation • Domed swamp • (Rain water fed, • Typically acidic, • Low in nutrients) Planar swamp (Ground water fed, neutral pH) Modified from USGS Circular 1143 (2003), Coal—A Complex Natural Resource
Possible Interpretation • Why these patterns in the rock record? • 1. Less S-associated Se • Deposition in domed peat swamp, more oxidizing • Less total S in system (no source vs. loss) • Se reduction vs. S reduction
Possible Interpretation • 2. Possible redistribution after deposition • Se conc. above & below coal have similar trends • From compaction or later fluids
A final thought Depositional environments
Selected References Cecil, CB, RW Stanton, SG Neuzil, FT Dulong, LF Ruppert and BS Pierce (1985). "Paleoclimate controls on the late Paleozoic sedimentation and peat formation in the central Appalachian Basin (U.S.A.)." International Journal of Coal Geology5: 195-230. Coleman, L, LJ Bragg and RB Finkelman (1993). "Distribution and mode of occurrence of selenium in US coals." Environmental Geochemistry and Health15(4): 215-227. Mullennex R (2005) Stratigraphic Distribution of Selenium in Upper Kanawha-Lower Allegheny Formation Strata at a Location in Southern West Virginia. The 23rd Annual Intern Pitt Coal Conf Neuzil, SG, FT Dulong and CB Cecil (2005). Spatial trends in ash yield, sulfur, selenium, and other selected trace element concentrations in coal beds of the Appalachian Plateau Region, U.S.A. (preliminary report). Reston, VA, U.S. Geological Survey. USGS (2005). Coal—A Complex Natural Resource, An overview of factors affecting coal quality and use in the United States with a contribution on coal quality and public health. Circular 1143. WVGES (2003) Trace Elements in West Virginia Coals. Selenium. Online graphs and data Acknowledgements U.S. Department of Interior Office of Surface Mining (OSM) West Virginia Water Research Institute REIC (Tim Keeney) Decota Consulting Pritchard Mining Questions?