Bonotto Daniel Marcos, Vergotti Marcelo
Departamento de Petrologia e Metalogenia, Universidade Estadual Paulista (UNESP), Câmpus de Rio Claro, Av. 24-A No.1515, C.P. 178, CEP 13506-900 Rio Claro, São Paulo, Brasil.
Fundação Universidade Federal de Rondônia (UNIR), Av. Presidente Dutra No. 2965, CEP 78900-500 Porto Velho, Rondônia, Brasil.
Appl Radiat Isot. 2015 May;99:5-19. doi: 10.1016/j.apradiso.2015.02.002. Epub 2015 Feb 7.
Gold exploration has been intensive in Brazilian Amazon over the last 40 years, where the use of mercury as an amalgam has caused abnormal Hg concentrations in water bodies. Special attention has been directed to Madeira River due to fact it is a major tributary of Amazon River and that since 1986, gold exploration has been officially permitted along a 350km sector of the river. The (21)(0)Pb method has been used to date sediments taken from nine lakes situated in Madeira River basin, Rondônia State, and to verify where anthropogenic Hg might exist due to gold exploitation in Madeira River. Activity profiles of excess (21)(0)Pb determined in the sediment cores provided a means to evaluate the sedimentation rates using a Constant Flux: Constant Sedimentation (CF:CS) and Constant Rate of Supply (CRS) of unsupported/excess (21)(0)Pb models. A significant relationship was found between the CF:CS sedimentation rates and the mean values of the CRS sedimentation rates (Pearson correlation coefficient r=0.59). Chemical data were also determined in the sediments for identifying possible relationships with Hg occurring in the area. Significant values were found in statistical correlation tests realized among the Hg, major oxides and Total Organic Carbon (TOC) content in the sediments. The TOC increased in the sediment cores accompanied by a loss on ignition (LOI) increment, whereas silica decreased following a specific surface area raising associated to the TOC increase. The CRS model always provided ages within the permitted range of the (21)(0)Pb-method in the studied lakes, whereas the CF:CS model predicted two values above 140 years.
在过去40年里，巴西亚马逊地区的黄金勘探活动十分密集，在该地区，汞作为汞齐的使用导致水体中汞浓度异常。马德拉河受到了特别关注，因为它是亚马逊河的一条主要支流，并且自1986年以来，已正式允许在该河350公里的河段进行黄金勘探。（21）（0）Pb法已被用于测定从朗多尼亚州马德拉河流域的九个湖泊采集的沉积物的年代，并验证由于马德拉河的黄金开采，人为汞可能存在的位置。在沉积物岩心中测定的过量（21）（0）Pb的活度剖面提供了一种使用无支撑/过量（21）（0）Pb模型的恒定通量：恒定沉积（CF:CS）和恒定供应速率（CRS）来评估沉积速率的方法。发现CF:CS沉积速率与CRS沉积速率的平均值之间存在显著关系（皮尔逊相关系数r = 0.59）。还测定了沉积物中的化学数据，以确定与该地区汞含量可能存在的关系。在沉积物中的汞、主要氧化物和总有机碳（TOC）含量之间进行的统计相关性测试中发现了显著值。沉积物岩心中的TOC增加，同时伴有烧失量（LOI）增加，而二氧化硅则随着与TOC增加相关的比表面积增加而减少。CRS模型在研究湖泊中始终提供在（21）（0）Pb法允许范围内的年龄，而CF:CS模型预测了两个超过140年的值。
