Stream sediment geochemical investigations in Arkansas - comparisons of manganese, zinc and lead-zinc districts with an unmineralized area

Aqua regia extracts of the minus 95-mesh fraction of bottom stream sediments from four areas in the State of Arkansas, U.S.A., all with contrasting mineralogy and/or lithology, were analyzed for Fe, Mn, Co, Ni, Cu, Zn, and Ba. Each of these elements increased uniformly with Mn content in Area I, a Mn district, whereas in the other areas only some of the elements followed this pattern. Background metal values of the stream sediments are similar for the manganese area and two other areas, all three of which have appreciable amounts of black shale outcrops. A fourth area containing little shale and mineralized in Zn is characterized by uniformly low background metal values, except for Zn. The largest anomalous values for Co, Cu, Ni and Ba are associated with the area enriched in Mn (Area I). Apparently Mn coatings on clasts and clasts of Mn ore are enriched in Co, Cu, Ni, and Ba and are responsible for these anomalous values. These high values, rather than base metal/Mn ratios, are the best geochemical indicators in stream sediments for this type of strata-bound Mn mineralization.