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. This study investigates the mineralogical processes involved in the formation and distribution of these metals by analyzing contemporary overbank river sediment, mining-age alluvium, mine-waste tips, and suspended solids in river waters. Detailed mineralogical analysis reveals a general weathering reaction paragenesis involving Pb-, Zn-, Cd-, and Cu-bearing minerals which includes sulfide carbonates, silicates, phosphates, and sulfate weathering products, along with iron and manganese oxyhydroxides. Textural and chemical evidence indicates a transformation of sulfides into carbonates in limestone-dominated source terrains with high pH/pCO2 conditions. In contrast, the study finds that these minerals, along with other metal-rich contaminants, diminish downstream in environments dominated by shales and sandstones due to lower pH conditions. The concurrent decrease in total Pb, Zn, Cd, and Cu sediment contents suggests that these chemical weathering and dispersion processes are integral to understanding the contamination mechanisms in the Tyne and possibly other metal-contaminated rivers. Furthermore, physical hydrodynamic processes contribute significantly to the dilution effects by pre-mining Quaternary sediments and uncontaminated sediments from tributaries.