A Geochemical and Geospatial Investigation of Heavy Metals in the Marcellus Shale

Tracy L. Bank¹, Lauren A. Fortson¹, Brett P. Yatzor¹, and Thomas R. Malizia^2
1University at Buffalo, Buffalo, NY, [email protected], [email protected], [email protected],
²Chevron U.S.A. Inc., Moon Township, PA [email protected]

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and scanning electron microscopy (SEM) were used to determine the chemical and physical associations of uranium and other heavy metals with the mineralogy and organic matter of the Marcellus and Utica Shales. Samples analyzed include both core and outcrop samples. The total organic carbon (TOC) content varied between 0.06 wt% and 14.0 wt%. Uranium concentrations ranged from 4.0 ppm to 67.8 ppm. ToF-SIMS analyses identified two dominant forms of uranium in core and outcrop samples: a charged uranium species (U⁺) and uraninite (UO₂). The charged uranium species was found in all shale samples and uraninite was identified in all samples with a concentration of uranium exceeding 5 ppm. Detailed Region of Interest (ROI) analyses were used to correlate the mass spectra of uranium with other mass signals present in the shale. These data indicate that both forms of uranium are strongly correlated to inorganic material that is present in all core and outcrop samples. SEM-EDS analyses confirmed the presence of uraninite and also identified brannerite ((U, Ca)(Ti, Fe)₂O₆) in one core sample. Uraninite grains were <1 μm in size and brannerite grains were 5-10 μm in size. No spectroscopic evidence of a chemical or spatial association between uranium and organic carbon was detected despite a strong geochemical correlation of uranium and TOC values (R² = 0.65).

AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012