School of Earth Sciences - Theses

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End date: 2001 × Subject: water quality × Start date: 2001 ×

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    Acid mine drainage at Rosebery Pb-Zn mine, Tasmania
    Hale, Cindy Therese ( 2001)
    Rosebery underground base metal (Pb, Zn, Cu, Fe, Ag, Au) sulphide mine in Tasmania, Australia has been in production for over 100 years. It is a massive sulphide deposit hosted in a fractured rock aquifer. It produces an average of 60L/sec of acidic waste water contaminated with Pb, Zn, Cu, Fe, Mn, Mg and sulphate. The study objectives were to firstly determine the water sources and flow pathways within the mine. Secondly, by chemical analysis and extensive pH and electrical conductivity testing, to determine the deterioration of water quality over time, within acid generating areas. Time was measured from the closing down of a production area (or the end of work) to sampling time. The oldest area measured ceased production thirty years ago. Testing of the objectives involved chemical sampling, stable isotope analysis, water flow measurements, pH, temperature and electrical conductivity measurements, and extensive mapping of underground levels. The results confirmed the sources of water recharge, which included rainfall, a fault - bound creek, and high pressure sealed water bearing faults intersected by underground workings and drilling. Water flow pathways within the mine include extensive secondary permeability as a result of workings, fallen abandoned zones acting as water conduits; an extensive fault in the south linking the creek to underground workings, and fractures and surface workings channelling rainfall. Results also indicated a strong seasonal pattern to groundwater recharge at the southern end of the mine, due to an extensive, and previously undocumented fault system. The seasonal variation in rainfall correlated with discharge underground and to the total mine dewatering rates. Water quality was assessed as a function of pH and electrical conductivity. There was a strong correlation found between water quality deterioration and time. In sulphide zones, AMD generation occurred within two years. This relationship is an easily applied tool for the prediction of water quality deterioration in any other producing base metal mine.