GEOCHEMISTRY AND MINERALOGY IN SOILS FROM A N/S TRANS-ALASKA TRANSECT

Geochemical variations along soil transects have been used to 1) delineate the natural range in elemental variation relative to bedrock, surficial deposits, and areas of mineralization, and 2) identify variations arising from ecosystem and anthropogenic factors. The objective of this study is to explore regional geochemical variations in soils along a transect that followed the Richardson, Elliott, and Dalton highways of Alaska from the Beaufort Sea to Prince William Sound (70^oN to 61^oN latitude). This is the first regional-scale geochemical soils transect in Alaska. The major, minor, and trace-element chemistry of the mineral soil horizons (A, B/C) was analyzed by ICP-MS following either a four-acid or sinter digestion. Quantitative bulk soil mineralogy was determined by powder X-ray diffraction analysis. Relative to quartz, the carbonate minerals (calcium carbonate and dolomite) are consistently elevated in soils of the coastal plain and the dolomite/quartz ratio is consistently elevated in soils of the southern Alaska Range and Copper River Basin. The plagioclase/quartz and the K-feldspar/quartz ratios are elevated through the southern Alaska Range and Copper River Basin and K-feldspar/quartz is elevated in the vicinity of the alkaline granites of the Ray Mountains. The latitudinal variations in major elements mirror those of the primary mineralogy: Ca and Mg, and K and Na vary with variations in the carbonate and feldspar mineralogy, respectively. Only Ca, S, P, Hg, Mo, and Cd are enriched in the A horizon, relative to the deeper horizon. Strontium concentrations are enriched throughout the southern Alaska Range and Copper River Basin – a geochemical signature which is identifiable in fish otoliths from this area– and there is a muted but discernible rise in Cr, Ni, Cu through the mafic igneous rocks of the southern Alaska Range. The U, Th, Nb, and total rare earth element (REE) concentrations are greatest near the alkaline granites of the Ray Mountains. In summary, geochemical variations along the transect predominantly reflect variations in the parent material, as opposed to ecosystem or anthropogenic factors.