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Fig. 4.9 a
Longitudinal (downstream) changes in Pb concentrations within channel bed sediments
of the Rio Pilcomayo from 2000 to 2004.
b
Comparison of
206
Pb/
207
Pb ratios measured in channel
bed sediments sampled in 2000 (
blue circles
) and 2002 (
red squares
). In 2000,
206
Pb/
207
Pb ratios
decreased downstream indicating that the relative contribution of Pb from mining operations at
Cerro Rico declined as the result of mixing as 'clean' sediment from tributaries was introduced to
the channel during runoff events. In 2002, precipitation and runoff events were limited. As a result,
Pb ratios were generally indistinguishable from the Cerro Rico type ore deposits, suggesting that
nearly all of the Pb was derived from mining operations (from Miller et al.
2007
)
and
206
Pb/
208
Pb ratios similar to what they informally referred to as Porco type ores,
whereas in 2002 samples collected from along the same reach exhibited a signature
comparable to Cerro Rico type ores (Fig.
4.9
b). Thus, they were not only able to
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