ALBERT

Description: Direct observations made during underground hydrogeochemical surveys of abandoned lead-zinc mines has highlighted the precipitation of secondary zinc minerals within abandoned lead-zinc mine workings in the north Pennines. Chemical analysis of mine waters has shown that molar concentrations of sulphate exceed those of zinc by two or three orders of magnitude, although they are released in equimolar proportions following the weathering of sphalerite. The excess of sulphate over zinc indicates that there must be significant sinks for zinc within the mine workings. Secondary zinc mineral sinks (principally hydrozincite and smithsonite) are the most likely explanation for the deficit in molar zinc concentrations and these minerals have been identified underground. In addition to the secondary zinc minerals, secondary calcite and aragonite from the workings have also been shown to provide sinks for zinc (by coprecipitation and solid-solution incorporation of zinc in these minerals). Calculation of the molar quantities of zinc and sulphate involved showed that as little as 5% of the zinc, weathered daily from the mineral deposits within the workings, is found to leave the mine dissolved in the mine water. However, this is sufficient to adversely impact the ecology of the receiving waters of the River Nent, which currently receives five circumneutral zinc-rich mine water discharges and drainage from a disused aqueduct.