Occurrence and Significance of Metals in Solid Bitumens: An Organic Geochemical Approach

Abstract

First-series transition element concns. (Co, Cr, Cu, Fe, Mn, Ni, V, Zn) are examd. in 27 solid bitumens from the US, Canada, Mexico, and Spain. Results are compared with org. geochem. parameters for whole bitumen and extractable org. matter, and the origin of metals in solid bitumens is discussed. In general, Co, Cr, and Cu are present in concns. <100 ppm; Mn, Ni, and Zn are 10-1000 ppm; and Fe and V at levels >1000 ppm. Solid bitumens having geol. and geog. similarities also have similar metal distributions. This is the case regardless of differential solubilities for bitumens within a single basin (e.g., Uinta Basin). Of the elements examd., V and Ni have the strongest org. affinities for the bitumens in this sample set, although such affinities are apparent for all elements in 14 of the samples. V and Ni are dispersed proportionately in the sol. and insol. portions. 13C NMR aromaticity values (fa) in the sample set are controlled predominantly by maturity level (rather than source influence). Whereas, the V/(V + Ni) ratio and the V concn. do not correlate with fa in the sample set, Ni concn. increases with increasing fa. These metal-fa relationships are probably due to the occurrence of V and Ni in host complexes of different stabilities. The chem. compn. of sedimentary org. matter is controlled by original source influences and the effects of maturation, migration, and post-migration alteration. Data presented here provide support for source-control and maturity effects (particularly for Ni) on the compn. of solid bitumens. Implications of future technol. developments, including online liq. chromatog.-inductively coupled plasma-mass spectrometry and liq. chromatog.-mass spectrometry, are noted.