The chemical composition and extraction behaviour of Ranger RP1 sediments

2001

Internal Report 356
leGras C & Boyden J
Supervising Scientist Division
Department of the Environment, Water, Heritage and the Arts

About the report

Ranger Retention Pond 1 (RP1) was excavated as part of mine construction in 1980. Its primary purpose is as a sediment trap, to prevent erosion products from mine rock used in tailings dam construction, and other purposes, leading to unacceptable increases in the suspended load of Coonjimba Creek, and ultimately Magela Creek.

There have been recent observations of increased uranium concentration in RP1 water, and the discovery of elevated uranium concentration in RP1 sediments. These are presumed to primarily constitute alluvium transported from the catchment. Hence the chemical contents of the sediments, at least to 10cm depth, are probably mostly catchment derived, and only weakly related to chemical processes in the pond itself. An exception to this is the formation of sulfidic mineralisation, which is probably caused by in-situ reduction of sulphate by sulphate-reducing bacteria.