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Nabarlek Pit decommissioning migration of sulphate, nitrate and radium ions in groundwater - preliminary modelling



Nabarlek Pit decommissioning migration of sulphate, nitrate and radium ions in groundwater - preliminary modelling


Appleyard, S.


E-Publications; E-Books; PublicationNT; Report ; 41/1984




Made available via the Publications (Legal Deposit) Act 2004 (NT).





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Dept. of Transport and Works

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Report ; 41/1984

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Technical Report WRD84041 Viewed at 14:07:09 on 29/07/2010 Page 4 of 34. I I I I I I I I I I I I I I I I I I I I I 2. HYDROGEOLOGICAL SETTING OF THE NABARLEK PIT Mineralisation at Nabarlek is hosted within a sequence of Proterozoic micaceous and chloritic schists (the Nourlangie Schist) adjacent to a large differentiated dolerite sill (the Oenpelli Dolerite) (Anthony, 1975). The transmissivity of rock near the pit lies in the range 0.1 to 10 m3 /day/m, whereas schistose rock SOOm to the south east of the pit has a transmissivity in excess of 100 m3 /day/m. Recent geological evidence (Noakes, Q.H.L., ores. corom 1984) suggests that the low transmissivities close to the pit are due to the presence of a well developed chlorite alteration halo that encircled the original orebody. The approximate boundary of this low transmissivity zone is shown in a schematic cross section (Fig 2.1). The main aquifer in the area between Cooper Creek and the Nabarlek pit consists of fracture zones within schistose rocks. Most water is found in partially weathered schist (10 to 20m thickness) and this is overlain by a 10m thick confining layer of clay (Fig 2.1). If the pit water level is raised to RL 70m, groundwater outflow will possibly occur at a rate of 35 m3 /day (AGC, 1984) and pore \'later velocities are expected to be in the range 0.02 - 0.6 m/day. The great range in estimated pore W'ater velocities is due to the fact that the extent to which a hydraulic connection bet,veen the chlorite halo and surrounding rock exists is not known. Geophysical and pump testing work will be carried out by AEC to try to resolve this problem. SA2/11 :TJ

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