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1996 - 19972

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    Rehabilitation of unoxidised pyritic waste rock and tailings at Martha Hill Gold Mine, N.Z. : a thesis presented in partial fulfilment of the requirements for the degree of Master of Horticultural Science in Soil Science at Massey University
    (Massey University, 1996) Mason, Kathy Anne
    At the Martha Gold and Silver Mine in Waihi, New Zealand, land disturbed by mining operations is required to be revegetated. Areas include pit walls above the natural water level, the slopes of the dam impounding the tailings and the tailings surface. The research work reported in this thesis is concerned with revegetation of acid generating material situated on the pit walls, and tailings revegetation. Hydroseeding with grass species onto pit slopes comprising unoxidised pyritic rock material proved to be unsuccessful because of acid generation which caused the pH to drop as low as 2.2 on the slope surface. Where calcite veins were present the pH was maintained at higher levels. It was found that a mixed species of hydroseeded grass grew successfully where the pH was 6.0 or above. Clover began to show signs of stress when the pH dropped to 4.5 and when the pH fell as low as 3.6, all grass died. Boreholes at a diameter of 100 mm were drilled to a depth of 500 mm into the slope surface of pyritic rock material to provide planting holes for native species at 1.5 m intervals. Toetoe, manuka, kanuka, flax and akeake all had acceptable survival rates over a ten month period. Coprosma kirkii was not successful and is not recommended for further plantings. Topsoil placed in the boreholes was found to have a beneficial effect on the overall plant survival rate, more so than the addition of lime or fertiliser. Although survival rates for native plants were acceptable over a ten month period, the objective of providing a vegetation cover that would improve the visual appearance of the slope was not achieved with 1.5 m spacings between plants. In contrast to the unoxidised pit slope material, tailings were found to have few limitations to plant growth. In 1992, two separate tailings trials were established to investigate the use of native plants as an alternative land use to pasture and the use of compost as an amendment for pasture production and native plant growth. Within the first six months following sowing, pasture dry matter yields from tailings plots with a 50 mm layer of compost applied to the surface were not significantly different from yields from tailings plots without a compost amendment although clover production was visually greater on compost plots. For subsequent cuts, compost-amended plots gave significantly higher pasture dry matter yields than nil-compost plots. Yield differences after the first six months were considered to be due to the improved P status on compost-amended plots. Yields off nil-compost plots in the first year of the 1992 trial averaged 11,000 kg DM/ha, compared to 9,000 kg DM/ha obtained from an earlier trial on an older tailings deposit (Union Hill). Yields off the compost-amended plots in the 1992 trial averaged 14,000 kg DM/ha, significantly higher than topsoil-amended plots in the Union Hill trial which yielded between 6,000 and 7,000 kg DM/ha in the first year. Yield differences between treatments of the two separate trials may have been due to differences in P status or rainfall. The survival rate for the native plants in the tailings trial (flax, cabbage tree, kanuka and Pittosporum tenufolium) was 100%. The addition of compost caused significantly higher growth rates in the first six months but beyond six months no significant differences were observed. A rehabilitation predictive model was developed for tailings rehabilitation which investigated costs and returns over a fourteen year period based on five different rehabilitation scenarios. The scenarios included the use of clay covers, resurfacing with compost in the event of a topsoil shortage, and a comparison between pasture and native plant land uses. It was found that if a clay cap was required on the tailings surface, large quantities of material would be required. Relatively high costs were found to be associated with the need for a clay cap and compost. Rehabilitation with native plant species was found to be more expensive than rehabilitation to pasture, and if treatment of surface water derived from the tailings surface was required, there would be significant added costs. Maintenance costs for natives were also found to be high and where pasture provides some revenue, further trials are required to determine whether revenue from natives timber species is possible.
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    An assessment of the revegetation potential of base-metal tailings from the Tui Mine, Te Aroha, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1997) Morrell, William John; Morrell, William John
    The overall objective of this study was to investigate the revegetation potential of abandoned base-metal (Cu-Pb-Zn) tailings at the Tui mine site near Te Aroha, New Zealand. An estimated 100,000 m3 of sulphide-rich tailings are the legacy of a once prosperous mining venture conducted at the site between 1967 and 1974 by the now defunct Norpac Mining Ltd. The oxidation of remnant sulphides, which constitute as much as 15% of the tailings by weight, has prevented plants from colonising the tailings for more than 20 years and resulted in the formation of Acid Mine Drainage (AMD) which continues to degrade ground and stream waters in the vicinity of the dam. This study focused on characterising the physical and chemical properties of the tailings in terms of their plant growth potential using a variety of techniques including; Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDS), Flame Atomic Absorption Spectrometry (FAAS), X-ray diffraction (XRD) as well as field based observations and standard laboratory analyses. A long term incubation experiment (carried out over a 1 1/2 year period) and two plant growth trials were also conducted to investigate the ability of liming materials and/or organic waste to ameliorate the tailings in order to provide a suitable growing medium for plants. The research indicated that, whilst the tailings do not exhibit any major physical limitations to plant growth, chemically the tailings are an extremely hostile plant growth medium. The surface tailings exhibited variable but generally very low pH (2.76 - 3.85) and high concentrations of potentially phytotoxic elements including As (254 mg/kg), Cu (26-991 mg/kg), Pb (1503-27416 mg/kg) and Zn (123-2333 mg/kg). The high availability of these and other metals, including Al and Fe. under the acidic conditions prevailing in the tailings, were identified as the primary factors currently inhibiting plant growth. The distribution of heavy metals, sulphate and total sulphur with depth indicated that the surface tailings (0-200 mm) have been extensively weathered since their deposition and contain relatively low concentrations of most heavy metals compared to subsurface tailings. An assessment of the Acid Generating Potential (AGP) of the tailings, using both static and kinetic tests, similarly indicated that the surface tailings have a comparatively low ability to generate acidity by sulphide oxidation. The application of lime at a rate of about 50 Mg CaCO3/ha is calculated to theoretically prevent the surface tailings from reacidifying. Below 200 mm depth, however, the AGP is appreciably higher (>140 Mg CaCO3/ha) and concentrations of both total and labile (0.1M HCl extractable) Cu, Fe and Zn were found to increase substantially, reflecting an increase in the abundance of chalcopyrite (CuFeS2), pyrite (FeS2) and sphalerite (ZnS) and sulphates with depth. The presence of high concentrations of acid-generating sulphide minerals (primarily pyrite) at shallow depths has important implications in that revegetation of the tailings should be based on techniques that minimise the exposure of the largely unweathered, sulphide-rich, subsurface tailings. The results obtained from the plant growth trials indicated that, on tailings treatments sown with metal-tolerant varieties of Festuca rubra or Agrostis capillaris, satisfactory cover was achieved upon the addition of lime at a rate of 16.5 Mg/ha or composted sewage sludge at rates >220 Mg/ha. These metal-tolerant plants were found to out yield their non-metal-tolerant counterparts on the limed treatments by as much as 4 and 10 times, respectively. Although vegetation was successfully established on Tui tailings treated with lime, dry matter yields were relatively low compared to treatments receiving high rates of sludge. The growth of all plant taxa was found to significantly decrease where very high rates of lime (112 Mg/ha) were added due to pH-induced nutrient deficiencies. Results obtained from both the plant growth trials and the lime incubation experiment indicated that the application of low rates of lime and/or sludge (8.25 and 110 Mg/ha respectively) were ineffective at creating a suitable plant growth medium and, in fact, exacerbated growing conditions within a few weeks of application by increasing the availability of labile (0.1M HCl extractable) metals. The findings of this study indicated that the use of amendments may provide a relatively inexpensive way of facilitating the establishment of plants on the tailings at the Tui mine site. It is envisaged that, at the very least, a vegetative cover will improve the aesthetic appearance of the site and at best reduce AMD by creating an oxygen-depleting, organic-rich cover which may ultimately facilitate the establishment of native species from the adjacent forest.