Abstract
We investigated Cr isotope fractionation during soil formation from
Precambrian ultramafic rocks. A soil profile was logged in an active
open-cast chromite mine (Sukinda Valley, India). In addition, mine and
river waters, as well as seawater were collected to trace the Cr-isotope
signal into the sea. The aim of the study is to recognize Cr isotope
fractionation processes within the mining-area and the impact of the
mine runoff on the δ53Cr of the nearby river. The weathering profile
shows a distinct upward trend to more negative δ53Cr values. While
the well preserved rocks at the base closely reflect mantle inventory
(-0.124±0.101‰ 1), the δ53Cr from the more weathered upper part of
the profile is as low as -1.28±0.022‰. These data are consistent with
the findings of Crowe et al. (in press). They demonstrated that Cr(III)
becomes oxidised during rock weathering, which leads to an isotopic
fractionation, where Cr(VI) lost to runoff is enriched in the heavier
53Cr. At the same time, the residual Cr(III) pools become enriched in
the lighter 52Cr. Waters collected within the chromite mine have δ53Cr
values corresponding to the unweathered host rock. Before reaching
the mine, river waters have δ53Cr values as heavy as +1.33±0.05‰.
Where the drainage water merges with the river water, a slightly
positively fractionated δ53Cr value (0.03±0.019‰) reflects a mixed
isotope signal. With increasing distance from the mine, river water
δ53Cr again becomes increasingly positively fractionated, indicating
redox processes within the river.
1Schoenberg et al. (2008), Chem. Geol.
2Crowe et al. (in press), EPSL
Precambrian ultramafic rocks. A soil profile was logged in an active
open-cast chromite mine (Sukinda Valley, India). In addition, mine and
river waters, as well as seawater were collected to trace the Cr-isotope
signal into the sea. The aim of the study is to recognize Cr isotope
fractionation processes within the mining-area and the impact of the
mine runoff on the δ53Cr of the nearby river. The weathering profile
shows a distinct upward trend to more negative δ53Cr values. While
the well preserved rocks at the base closely reflect mantle inventory
(-0.124±0.101‰ 1), the δ53Cr from the more weathered upper part of
the profile is as low as -1.28±0.022‰. These data are consistent with
the findings of Crowe et al. (in press). They demonstrated that Cr(III)
becomes oxidised during rock weathering, which leads to an isotopic
fractionation, where Cr(VI) lost to runoff is enriched in the heavier
53Cr. At the same time, the residual Cr(III) pools become enriched in
the lighter 52Cr. Waters collected within the chromite mine have δ53Cr
values corresponding to the unweathered host rock. Before reaching
the mine, river waters have δ53Cr values as heavy as +1.33±0.05‰.
Where the drainage water merges with the river water, a slightly
positively fractionated δ53Cr value (0.03±0.019‰) reflects a mixed
isotope signal. With increasing distance from the mine, river water
δ53Cr again becomes increasingly positively fractionated, indicating
redox processes within the river.
1Schoenberg et al. (2008), Chem. Geol.
2Crowe et al. (in press), EPSL
| Original language | English |
|---|---|
| Publication date | 2013 |
| Publication status | Published - 2013 |
| Event | VII Congreso Uruguayo de Geología - Montevideo, Uruguay Duration: 13 Nov 2013 → 15 Nov 2013 |
Conference
| Conference | VII Congreso Uruguayo de Geología |
|---|---|
| Country/Territory | Uruguay |
| City | Montevideo |
| Period | 13/11/2013 → 15/11/2013 |