GEOCHEMICAL MAPPING EMPLOYING ACTIVE AND OVERBANK STREAM SEDIMENT, LAKE SEDIMENT AND LAKE WATER IN 2 AREAS OF NEWFOUNDLAND

Geochemical data from samples of active and overbank stream sediment in one area and from lake sediment and lake water in another are compared and evaluated. Samples of both types of stream sediment were collected from drainage basins 2-10 km(2) in area in a glaciated landscape and the <63 mu m fractions were analyzed for 38 elements. In general, trace element distribution patterns are similar in the two media and reflect the chemistry of the underlying bedrock. Absolute concentrations are higher for most elements in the overbank sediment. For elements having concentrations near the analytical detection limit, such as Au, Mo and Pb, the overbank sediment provides more reliable data in those parts of the area with low background levels. In this area, suitable overbank material is more widespread and available for sampling than is active sediment. In some drainages, stream-sediment data are clearly contaminated by past mining activity but overbank data appear unaffected. Lake water was collected from another area where a lake sediment survey had been conducted eleven years earlier. The <180 mu m fraction of sediment was analyzed for 29 elements and the water for about 50 elements. Due to the contrasting nature of these two sample media, element distribution patterns are less similar than in the case of the two types of stream sediment. Nonetheless, elements which are hydromorphically dispersed and which are partitioned consistently between water and sediment (such as F, U, As, and rare earths) do demonstrate a strong spatial correlation. As analytical detection limits for water continue to improve, the versatility of this medium in geochemical mapping will increasingly complement more conventional sampling media as well as providing an alternate medium in areas where sediment is unavailable.