Bachelor of Science (Honours)
School of Earth & Environmental Sciences
Knight, Daniel, The Geochemistry, Distribution and Mobility of Metals About an Abandoned Cu-Pb-Zn Mine at Mount Bulga, Orange, NSW: Implications for Acid Rock Drainage, Bachelor of Science (Honours), School of Earth & Environmental Sciences, University of Wollongong, 2014.
Mining activities at the abandoned Mount Bulga Cu-Pb-Zn-Ag deposit resulted in large amounts of previously buried sulfides being brought to the surface causing the potential of acid mine drainage to be a problem or concern. The pH values measured in the surface soils range from strongly acidic to neutral (3.6-7.9) but averaging mildly acidic (5.2). The distribution of metals in the soils show a distinct zonation between the different geological units clearly defining fault contacts between these units. The XRF analysis using the portable XRF was compared to a laboratory XRF instrument and most metals correlated well except for vanadium, barium and thorium. The highest concentrations of metals were detected about the old mine sites and slag heap as well as related to exposed regions of the shear zone. The mobility of the metals Cu, Pb, Ni and Cr were determined with the order of mobility based on the percentage of total metal concentration mobile as Cu>Pb≈Ni>Cr. Zn was below the limit of detection for the dilutions used. Metal mobility and mineral associations were discovered for Pb and Cu with these metals more mobile with the increase in quartz and less mobile with the increase in actinolite, hornblende, vermiculite and cordierite. Total Cr and Ni concentrations had associations with minerals also with the increase in Ni and Cr concentrations with the increase of hornblende, vermiculite, cordierite, actinolite and a decrease with quartz. Profile analysis demonstrated chromium and nickel associated with parent material or immobile phases at depth, while copper may be a result of dispersion although remaining mostly in the surface soil. Soil particle size analysis determined the surface soils at Mount Bulga to be mainly silt loam with some minor occurrences of sandy loam and silt. The highest average sand content was in the soils overlying the Mullions Range, while the highest average clay content was related to soils of the Anson Formation. Profile samples were predominantly silt loams and profile MBP2 demonstrated a decrease in sand and increase in silt and clay with depth, although one point had the opposite trend. Mineralogy investigations of soils overlying the different geological units determined different mineral associations between the soils. The soil overlying the Byng Volcanics contained tremolite, hornblende, cordierite, actinolite and quartz as the major mineral phases. The soil overlying the Mullions Range Volcanics contained quartz as the major mineral phase with common trace amounts of mixed-layer illite-smectite and chlorite. The soil overlying the Anson Formation contained quartz, chlorite and muscovite as the major mineral phases with common trace amounts of mixed-layer illite-smectite, kaolinite, gypsum and biotite. Profile MBP2 determined a change of mineralogy with depth in both the sand and silt/clay fractions with quartz suddenly dropping to trace amounts at 115 cm depth while vermiculite, cordierite, actinolite, tremolite and hornblende increased from this depth down. Mineralogy investigations identifying proportions of clay minerals in the soils along with total organic carbon content estimated the cation exchange capacity of the soils to be fairly low, though this increased with depth. There is ongoing remediation of the mine site and limestone drains have been placed along the path of drainage. These show virtually no signs of iron precipitation and water in the creeks also show no sign of iron precipitation. A localised map surrounding the mine site appears to show a slight downhill migration from the mine site.