EVIDENCE OF RARE EARTH ELEMENT ENRICHMENT IN SEDIMENTARY ROCKS FROM PENNSYLVANIA

Sedimentary rocks that comprise the overburden and underclay near coal seams in central Pennsylvania have been investigated as sources of rare earth and critical elements. More than 400 surface exposures and drill core samples were studied and more are being added to the data set regularly. A rigorous statistical analysis of the sample set was completed and a comparison with standard reference materials was performed. Data indicate that the rocks in this study are enriched in total rare earth elements compared to both the NASC and PAAS. Pearson correlation studies indicate that the light rare earth elements are likely concentrated in phosphate minerals and the heavy rare earth elements are correlated with iron-bearing mineral phases. A correlation of total rare earth elements with Ti/Al in stratigraphically collected samples indicates that in some sample locations high total REE contents occur in samples where depositional rates were highest. These data support the hypothesis that REE are physically weathered into the sedimentary rocks and that chemical erosion was minimal. In other sample locations, geochemical and mineralogical evidence supports aqueous remobilization of REE and critical elements. In these cases, minor deposits of adsorbed REE, similar to the ion adsorbed REE deposits of China, may have formed.