ABSTRACT

Sediments were sampled over 130 mi of the Buffalo River in northern Arkansas. Aqua regia extracts of the minus 95 mesh fraction of the sediments were analyzed by atomic absorption for Na, K, Mg, Ca, Zn, Cd, Cu, Pb, Fe, Co, Cr, Ni, and Mn. Zirconium was determined by X-ray fluorescence. There was a general decrease downstream in Fe, Cu, Cr, Ni, Mn, Pb, K, and Na as the drainage area increased in carbonate rock and decreased in shale. The elements Mg, Ca, Zn, and Cd increased in sediments downstream.

The sediments are mainly quartz and chert grains. These grains are apparently coated with hydrous iron oxide which acts as a sorbent for most of the metals and is a dominant transport mechanism for acid extractable Co, Cr, Ni, Cu, Mn, and K. Other acid extractable metals, particularly Mg, Ca, Zn, Cd, and Pb are mostly in clastic grains. Cadmium to zinc ratios in the sediments and in ore minerals of the area are similar.

The ore metals of the drainage area are Zn, Pb, and Cu. The acid extractable amounts of these metals in the sediments rise and fall with the extractable amounts of Ca plus Mg in the sediments, indicative of the favorite host rock, dolomite. Tributaries are sites of rapid rise and fall of metal values within a few miles from background to anomalously high values and return to background.