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

0207439Miller Rio Pilcomayo 号驶向玻利维亚的 Cerro Rico de Potosi 贵金属多金属锡矿床。 波托西矿床的开采由西班牙人于 1545 年开始，一直不间断地持续至今。 我们之前的研究表明，过去 450 年来向环境中排放的采矿和铣削废物已导致皮尔科马约河谷上游的水和沉积物受到广泛污染。 本次调查的主要目的是确定铅同位素是否可以在大型河流系统中有效使用，以量化采矿作业中受污染碎片的十年尺度运输和储存。 该研究的本质是分析地貌过程与污染物质长期扩散之间的联系。为了实现项目目标，将完成几项任务：（1）将识别里奥皮尔科马约盆地上游的铅源，并根据其地理分布和铅同位素特征来表征。 这一步骤将涉及收集和分析来自塞罗里科（Cerro Rico）的矿石样品，这是流域下方的主要基岩单元、支流盆地内的矿化带以及主要支流内的河床沉积物； (2) 将记录支流盆地的冲积地层和地貌，并将其与皮尔科马约河现有的地貌地层数据联系起来，以 (a) 完善我们对皮尔科马约河沿线发生的历史地貌事件的时间、规模和性质的理解，以及 (b) 深入了解皮尔科马约河支流沉积物流入的时间和规模（据信这两者都产生了影响）受污染沉积物向下游的移动）； (3) 将记录垂直于水流、下游和年龄受限冲积矿床内垂直方向的选定金属总浓度和铅同位素比的空间变化。 重点将放在分析从受污染的冲积阶地提取的 1.5-2 m 长的岩心，这些冲积阶地由垂直积聚的洪水沉积物组成； (4) 沉积物混合模型将用于量化来自每个划定铅源的冲积矿床中铅的相对比例。

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.