Collaborative Research: Analysis of the Transport and Storage of Contaminated Sediments in the Rio Pilcomayo Basin, Bolivia: A Geochemical-Geomorphic Approach

皮尔科马约河位于玻利维亚的Cerro Rico de Potosi贵金属多金属锡矿上。波托西矿藏的开采是西班牙人于1545年开始的，一直持续到现在。我们以前的研究表明，过去450年来采矿和制粉废物向环境的排放导致皮尔科马约河谷上游的水和沉积物受到广泛污染。这项调查的主要目的是确定铅同位素能否有效地用于大型河流系统，以量化采矿作业产生的污染碎片的十年尺度、运输和储存情况。为完成项目目标，将完成以下几项任务：(1)根据铅的地理分布和铅同位素特征，查明里约热内卢皮尔科马约盆地上游的铅源，并确定其特征。这一步骤将包括收集和分析Cerro Rico的矿石样品，Cerro Rico是分水岭下的主要基岩单元，支流盆地内的矿化带，以及主要支流内的河床沉积物；(2)支流盆地的冲积地层学和地貌将被记录下来，并与里约河皮尔科马约河现有的地貌地层学数据相联系，以(A)加深我们对里约河沿岸历史地貌事件的时间、规模和性质的了解，(B)深入了解从支流流入里约河皮尔科马约河的沉积物的时间和规模(据信这两条支流都对受污染沉积物的下游运动产生了影响)；(3)选定金属和铅同位素比率的空间变化将记录在案，它们垂直于流动、下游和受年龄限制的冲积矿床。将重点分析从受污染的洪水沉积组成的冲积阶地中提取的1.5-2米长的岩芯；以及(4)将使用沉积物混合模型来量化来自每个划定的铅源的冲积沉积中铅的相对比例。

0207439Miller The Rio Pilcomayo heads on the Cerro Rico de Potosi precious metal-polymetallic tin deposits of Bolivia. Mining of the Potosi deposits was initiated by the Spanish in 1545 and has continued without interruption to the present. Our previous studies have demonstrated that the release of mining and milling wastes to the environment during the past 450 years has resulted in extensive contamination of water and sediments of the upper Pilcomayo valley. The primary objective of this investigation is to determine if Pb isotopes can be effectively used in a large river system to quantify the decadal scale transport and storage of contaminated debris from mining operations. Inherent in the study is an analysis of the linkages between geomorphic processes and the long-term dispersal of contaminated materials.To accomplish the project objectives several tasks will be completed: (1) Pb sources within the upper reaches of Rio Pilcomayo basin will be identified and characterized in terms of their geographical distribution and Pb isotopic signatures. This step will involve the collection and analysis of ore samples from Cerro Rico, the major bedrock units that underlie the watershed, mineralized zones within tributary basins, and channel bed sediments within major tributaries; (2) the alluvial stratigraphy and geomorphology of the tributary basins will be documented and linked to the existing geomorphic-stratigraphic data on the Rio Pilcomayo to (a) refine our understanding of the timing, magnitude, and nature of historic geomorphic events that have occurred along the Rio Pilcomayo, and (b) gain insights into the timing and magnitude of sediment influx to the Rio Pilcomayo from tributaries (both of which are believed to have had an impact on the downstream movement of contaminated sediment); (3) spatial variations in the total concentration of selected metals and Pb isotopic ratios will be documented perpendicular to flow, downstream, and vertically within age-constrained alluvial deposits. Emphasis will be placed on the analysis of 1.5-2 m long cores extracted from contaminated alluvial terraces composed of vertically accreted flood deposits; and (4) sediment mixing models will be used to quantify the relative proportion of Pb in alluvial deposits that is derived from each of the delineated Pb sources.