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

[0207507] lechler里约热内卢Pilcomayo矿区位于玻利维亚的Cerro Rico de Potosi贵金属多金属锡矿床。波托西矿床的开采始于1545年，并一直持续到现在。我们之前的研究表明，在过去的450年里，采矿和碾磨废料释放到环境中，导致了上皮科马约山谷的水和沉积物的广泛污染。本研究的主要目的是确定铅同位素是否可以有效地用于大型河流系统，以量化采矿作业中污染碎片的年代际运输和储存。这项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。为实现项目目标，将完成以下几项工作：(1)对里约热内卢Pilcomayo盆地上游Pb源的地理分布和Pb同位素特征进行识别和表征。这一步骤将包括收集和分析来自塞罗里科、分水岭下面的主要基岩单元、支流盆地内的矿化带和主要支流内的河床沉积物的矿石样本；(2)支流盆地的冲积地层学和地貌将被记录下来，并与里约热内卢Pilcomayo的现有地貌地层数据联系起来，以：(a)完善我们对里约热内卢Pilcomayo沿线发生的历史地貌事件的时间、规模和性质的理解；(b)深入了解沉积物从支流流入里约热内卢Pilcomayo的时间和规模（这两个因素都被认为对受污染沉积物的下游运动产生了影响）；(3)特定金属总浓度和Pb同位素比值的空间变化将在垂直流向、下游和垂直方向上记录。重点分析了由垂直堆积的洪水沉积物组成的受污染冲积阶地中提取的1.5-2 m长的岩心；(4)沉积物混合模型将用于量化每个已圈定的铅源所衍生的冲积矿床中铅的相对比例。

0207507Lechler 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.