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 i n one area and from lake sediment and lake water in another are compar ed and evaluated. Samples of both types of stream sediment were collec ted from drainage basins 2-10 km(2) in area in a glaciated landscape a nd the <63 mu m fractions were analyzed for 38 elements. In general, t race element distribution patterns are similar in the two media and re flect the chemistry of the underlying bedrock. Absolute concentrations are higher for most elements in the overbank sediment. For elements h aving 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 o verbank 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 unaffect ed. Lake water was collected from another area where a lake sediment s urvey had been conducted eleven years earlier. The <180 mu m fraction of sediment was analyzed for 29 elements and the water for about 50 el ements. Due to the contrasting nature of these two sample media, eleme nt distribution patterns are less similar than in the case of the two types of stream sediment. Nonetheless, elements which are hydromorphic ally dispersed and which are partitioned consistently between water an d sediment (such as F, U, As, and rare earths) do demonstrate a strong spatial correlation. As analytical detection limits for water continu e to improve, the versatility of this medium in geochemical mapping wi ll increasingly complement more conventional sampling media as well as providing an alternate medium in areas where sediment is unavailable.