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ItemPetrogenesis of the Melba Flats Ni-Cu-PGE Deposit in Western Tasmania: Insights from a Geochemical and Geochronological InvestigationPhua, Marcus ( 2016)Since its discovery in 1893, the Melba Flats Ni-Cu-PGE deposit has produced 10,000 tons of Ni and Cu at an average grade of 9.7% and 4.7% respectively. It is a magmatic sulphide deposit located 8 km north-east of the township of Zeehan, along the eastern margin of the Dundas Trough in Western Tasmania. The deposit is associated with a suite of bifurcating mafic intrusions hosting magmatic Ni-Cu-PGE sulphides intruded into a sequence of volcaniclastic lithic greywackes, which are correlated to the Crimson Creek Formation. U-Pb detrital zircon geochronology was utilized to show that the Melba Flats sediments have a maximum depositional age of c. 582 Ma. The Melba Flats mafic intrusions were formed by primitive magmas with 13 to 16 wt% MgO and a sub-alkaline tholeiitic affinity. 40*Ar/39Ar hornblende geochronology was employed to establish that the mafic intrusions were emplaced at c. 568 Ma, along an attenuated continental margin characterized by a transitional rift setting, analogous to the early Paleogene break-up margin of East Greenland. Melba Flats Ni-Cu-PGE sulphides are characterized by massive-to-semi-massive sulphides that possess high Ni, Cu and PGE tenors and mantle-like δ34S values and S/Se ratios and disseminated sulphides that have low Ni, Cu and PGE tenors, along with crustal δ34S values and S/Se ratios. Geochemical data indicates that the massive-to-semi-massive sulphides were formed at depth before being transported to their current sites, whilst the disseminated sulphides were formed during transport as the primitive magma interacted with the S-bearing crustal rocks.
ItemAcid mine drainage at Rosebery Pb-Zn mine, TasmaniaHale, 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.