Geochemistry of suspended matter in the Amazon river waters

Abstract

The duplicate samples of the Amazon River suspended matter (SM) collected during Cruise 9th of R/V Professor Shtokman were studied using modern analytical techniques. Waters of the Amazon basin are subdivided into three main types differing in SM content and chemical composition: white (turbid yellow waters of the Amazon River and Madeira tributary), clear (transparent waters of the large Xingu, Tapajós, Trombetas, and Tocantins tributaries) and black (waters with strong coffer color, high content of dissolved organics, and elevated acidity, Riu Negro). The specific features of SM from different parts of the river basin have been established. The contents and relationships of major and trace elements in SM vary within wide ranges, but in general the bulk composition of SM is close to the average composition of river SM and clay rocks, except for some samples from clear waters. The SM of the white and clear waters (blackwater samples unfortunately have not been preserved) are variably enriched in Hg. Literature data indicate that artisanal gold mining with the use of Hg (amalgamation method) has been carried out for many years in the Amazon Basin, i.e., SM enrichment in Hg is related to the anthropogenic factor. At the same time, significant (up to two orders of magnitude) enrichment of SM of the clear water Xingu and Tokantins rivers, the Amazon tributaries, in Sn, Zn, Pb, and to lesser extent, in Cu, Cd, Ag, and some other metals give grounds to suggest ore mineralization in these regions.