Processes of formation and distribution of Pb-, Zn-, Cd-, and Cu-bearing minerals in the Tyne Basin, northeast England: Implications for metal-contaminated river systems

Historic mining has produced widespread Pb, Zn, Cd, and Cu contamination in the fluvial deposits of the Tyne River Basin, northeast England. Detailed mineralogical analysis of contemporary overbank river sediment, mining-age alluvium, and mine-waste tips and of suspended solids in river waters has defined a general weathering reaction paragenesis of pb-, Zn-, Cd-, and Cu-bearing minerals: sulfides --> carbonate, silicate, phosphate, and sulfate weathering products --> iron and manganese oxyhydroxides. Textural and chemical evidence suggests that the sulfides alter to carbonates in high pH/pCO(2), limestone-dominated source terrains. These minerals and other contaminant metal-rich minerals such as silicates and manganese oxyhydroxides decline and disappear downstream in lower pH shale/sandstone-dominated environments. The concomitant decrease in total Pb, Zn, Cd, and Cu sediment contents in the Tyne and possibly other metal contaminated rivers may be related to these essentially chemical weathering and dispersion processes. These are augmented by physical, hydrodynamic processes that to a large extent effect dilution by premining Quaternary sediment and by uncontaminated sediment from tributaries.