Dynamics of arsenic in the mining sites of Pine Creek Geosyncline, Northern Australia

The transportation and fixation of arsenic (As) in soil and sediments fromfivemine sites within the Pine Creek Geosyncline, Northern Territory, were examined based onmeasurements of operationally-defined fractions ofAs in soils, sediment and evaporates.Arsenic was mainly retained in sediments in the form iron arsenate (Fe–As). In wetland systems, As was retained as Fe–As together with calcium arsenate (Ca–As) fromalkaline groundwater and organic-bound As from detrital material. In retention ponds As was retained as Fe–As, Ca–As and residualAs (Res-As) up to 1700mg/kg. Sediment traps can retainAs fromalkaline and acidic source seepages. The retention of Res-As and other mineral particulates during erosional or controlled process water discharges was associated with high Fe–As and organic-bound As in sediment. Arsenicwas retained as Fe–As, Ca–As and residual As in 100 year old tailings atMillarʹs Battery, Union Reefs mine nearby McKinlay River and the small copper mine lease MLN 95 adjacent Copperfield Creek nearby Pine Creek. Natural geo-mobilisation of As was observed in upstream sediments at Copperfield Creek (5–8 mg/kg), Mt. Bundey Creek (10–12 mg/kg), upstream Ryanʹs Creek (10–12 mg/kg) and downstream East branch Ryanʹs Creek (7 mg/kg). Erosion of As-containing mineralisation was observed in the McKinlay River upstream and downstream (23–26 mg/kg) and upstream Ryanʹs Creek boundary of the Goodall mine leaseMLN 1049 (24–40 mg/kg). Overall, As was mainly retained in sediments in the form Fe–As. The concentration data for As were used to propose mechanisms of As dispersion and retention occurring at the various mine sites that can be utilised for future mine water management design to minimise As dispersion.