Kidston Gold Mine Research Articles

MINErosion 3: Using measurements on a tilting flume-rainfall simulator facility to predict erosion rates from post-mining landscapes in Central Queensland, Australia.

Open-cut coal mining in Queensland results in the formation of extensive saline overburden spoil-piles with steep slopes at the angle of repose (approximately 75% or 37o). These spoil-piles are generally found in multiple rows, several kilometers in length and heights of up to 50 or 60 m above the original landscape. They are highly dispersive and erodible. Legislation demands that these spoil piles be rehabilitated to minimize on-site and off-site discharges of sediment and salt into the surrounding environment. To achieve this, the steep slopes must be reduced, stabilized against erosion, covered with topsoil and re-vegetated. Key design criteria (slope gradient, slope length and vegetation cover) are required for the construction of post-mining landscapes that will result in acceptable erosion rates.A novel user-friendly hillslope computer model MINErosion 3.4 was developed that can accurately predict potential erosion rates from field scale hillslopes using parameters measured with a 3m laboratory tilting flume-rainfall simulator or using routinely measured soil physical and chemical properties. This model links MINErosion 2 with a novel consolidation and above ground vegetation cover factors, to the RUSLE and MUSLE equations to predict the mean annual and storm event erosion rates. The RUSLE-based prediction of the mean annual erosion rates allow minesites to derive the key design criteria of slope length, slope gradient and vegetation cover that would lead to acceptable erosion rates. The MUSLE-based prediction of storm event erosion rates will be useful as input into risk analysis of potential damage from erosion.MINErosion 3.4 was validated against erosion measured on 20 m field erosion plots established on post-mining landscapes at the Oakey Creek and Curragh coalmines, as well as on 120 and 70 m erosion plots on postmining landscapes at Kidston Gold Mine.

Geochemical characteristics of rehabilitated tailings and associated seepages at Kidston gold mine, Queensland, Australia

This study investigated an uncapped tailings storage facility in a semi-arid subtropical climate, with the aim of understanding the hydro-geochemical processes controlling the seepage water quality and the dispersion/attenuation of metals and metalloids within the tailings and through a constructed wetland. While direct re-vegetation helped to stabilize the surface of tailings, development of an oxidation front in the tailings resulted in high sulphate and arsenic concentrations in the seepage. The findings of this study will assist maximizing the efficiency of any future passive treatment system on site and provide useful information for similar tailings closure strategies elsewhere.

Evaluation of pyritic mine tailings as a plant growth substrate

At the Kidston gold mine, Australia, the direct establishment of vegetation on tailings was considered as an alternative to the use of a waste rock cover. The tailings acid/base account was used to predict plant growth limitation by acidity, and thus methods capable of identifying tailings that would acidify to pH 4.5 or lower were sought. Total S was found to be poorly correlated with acid-generating sulfide, and total C was poorly correlated with acid-neutralizing carbonate, precluding the use of readily determined total S and C as predictors of net acid generation. Therefore, the selected approach used assessment of sulfide content as a predictor of acid generation, and carbonate content as a measure of the acid-neutralizing capacity available at pH 5 and above. Using this approach, the majority of tailings (67%) were found to be non-acid generating. However, areas of potentially acid-generating tailings were randomly distributed across the dam, and could only be located by intensive sampling. The limitations imposed by the large sample numbers, and costly analysis of sulfide and carbonate, make it impractical to identify and ameliorate acid-generating areas prior to vegetation establishment. However, as only a small proportion of the tailings will acidify, a strategy of re-treating acid areas following oxidation is suggested. The findings of the present study will assist in the selection of appropriate methods for the prediction of net acid generation, particularly where more conservative measurements are required to allow vegetation to be established directly in tailings.

Object-based classification of semi-arid vegetation to support mine rehabilitation and monitoring

Mining activities result in significantly modified landscapes that require rehabilitation to mitigate the negative environmental impacts and restore ecological function. The aim of this study was to develop a remote sensing method suitable for monitoring the vegetation cover at mine rehabilitation sites. We used object-based image analysis (OBIA) methods and high-spatial resolution SPOT-5 imagery to identify discrete land-cover patterns that occur at fine spatial scales. These patterns relate to spatial processes that are important drivers of successful restoration of mine sites. SPOT-5 imagery of the Kidston Gold mine tailing dam in semi-arid tropical north Queensland was acquired in July 2005, comprising four 10-m spectral bands and a 2.5-m panchromatic (PAN) band. The classification scheme used in this study was adapted to the spatial scale of SPOT-5 imagery from mine closure criteria cover requirements, according to a mine rehabilitation plan. Four land-cover classes were identified: tree cover, dense grass, sparse grass, and bare ground. First, textural layers (contrast, dissimilarity, and homogeneity) were derived for each vegetation class except for bare ground from the PAN and multispectral bands. Of all textural layer combinations, homogeneity and contrast in the PAN band were identified using a Z-test as the most useful for differentiating between multiple land-cover classes. Next, an optimal segmentation scale parameter of 15 was identified using an analysis of spatial autocorrelation. Finally, the SPOT-5 image bands, derived textural layers, and normalized difference vegetation index (NDVI) were used in an OBIA fuzzy membership classification approach to map vegetation land-cover classes. The classification results were assessed with the traditional error matrix approach and the object-based accuracy assessment method. The overall classification accuracy using the error matrix was 92.5% and 81% using the object-based method. The relatively high-classification accuracy demonstrates the potential of SPOT-5 imagery for monitoring mine rehabilitation. The complete spatial coverage associated with remote sensing data at fine spatial scales has the potential to complement field-based approaches commonly used in rehabilitation monitoring. Furthermore, SPOT-5 data along with OBIA can characterize vegetation spatial patterns at spatial scales appropriate for monitoring rehabilitated landscapes, providing an important tool for landscape function analysis.

English

The rehabilitation of potentially acid forming waste rock is site specific, being a function, among other factors, of the rock types, the dumping and storage method employed, and the climatic setting. The store/release cover developed to manage acid rock drainage from mineralized waste rock piles at Kidston Gold Mines' open pit operations in the semi-arid, seasonal, sub-tropical climate of North Queensland, Australia, has been monitored for nine years. The paper describes the philosophy behind the store/release cover design and its adaptation over time to suit Kidston's conditions. The results of monitoring of a number of covers over the nine years since the first cover was constructed are presented, together with data on seepage flows and water quality emanating from the piles, and estimates are made of the overall water balance of the rock piles. The Kidston story is a valuable case study of a successful approach to remediating an identified source of acid rock drainage in a semi-arid climate, which has actively engaged all Stakeholders.

A field study conducted at Kidston Gold Mine, to evaluate the impact of arsenic and zinc from mine tailing to grazing cattle

The grazing trial at Kidston Gold Mine, North Queensland, was aimed specifically to assess the uptake of metals from the tailing and the potential for unacceptable contamination of saleable meat. Further aims included estimating metal dose rates and identifying potential exposure pathways including plant uptake of heavy metals, mine tailings adhered to plants and direct ingestion of mine tailing. It was found that of the 11 metals analysed (As, Zn, Co, Cd, Cr, Sn, Pb, Sb, Hg, Se and Ni) in the animal's liver, muscle and blood during the 8-month trial period, only accumulation of arsenic and zinc occurred. A risk assessment including these two metals was conducted to determine the potential for chronic metal toxicity and long-term contamination, using the estimates of metal dose rate. It was concluded that no toxicity or long-term contamination in cattle was likely at this site. Management procedures were therefore not required at this site; however, the results highlight percent ground cover and standing dry matter (DM) as important factors in decreasing metal exposure from direct ingestion of tailings and dust adhered to plants.

The Evolution of Wall Control Programs at Kidston Gold Mines

Concerns with crest losses have seen changes to a number of design and operating parameters to retain the integrity of the wall and the berms of the Kidston Gold Mines’ Eldridge Pit. Until trials began in 1999 most final wall designs utilised large diameter blastholes up to the presplit row to achieve the wall angle. The berm crests were being lost, wall support requirements were increasing and affecting mining schedules and several fault areas were putting pit access at risk. Standard designs had been determined during the early mining years and while periodic modifications had been made there was a need for major blast pattern revision. This paper traces the development of wall control blasting programs over the years, relating designs to the geology and the evidence in the walls with the theories of the day and includes the recent trials that were conducted in what is a most unforgiving geology. Trials and improvements to ensure the walls were safe were conducted even as the mine neared its economic li...

Engineering Closure of an Open Pit Gold Operation in a Semi-Arid Climate

Along with material characteristics and geometry, the climate in which a mine is located can have a dramatic effect on the appropriate options for rehabilitation. The paper outlines the setting, mining, milling and waste disposal at Kidston Gold Mine's open pit operations in the semi-arid climate of North Queensland, Australia, before focusing on the engineering aspects of the rehabilitation of Kidston. The mine took a holistic and proactive approach to rehabilitation, and was prepared to demonstrate a number of innovative approaches, which are described in the paper. Engineering issues that had to be addressed included the geotechnical stability and deformation of waste rock dumps, including a 240 m high in-pit dump: the construction and performance monitoring of a “store and release” cover over potentially acid forming mineralised waste rock; erosion from the side slopes of the waste rock dumps; the in-pit co-disposal of waste rock and thickened tailings; the geotechnical stability of the tailings dam wall; the potential for erosion of bare tailings; the water balance of the tailings dam; direct revegetation of the tailings; and the pit hydrology. The rehabilitation of the mine represents an important benchmark in mine site rehabilitation best practice, from which lessons applicable worldwide can be shared.

English

An investigation of litter decomposition was undertaken at the Kidston Gold Mine in north Queensland, Australia with the aim of assessing the status of nutrient cycling capacity on a directly-revegetated tailings dam. Weight losses from leaf litter contained in litterbags placed in a 5-year old revegetated section of the dam were not significantly different from losses observed at two unmined reference sites over the 18 month study period, representing a rapid improvement in nutrient cycling capacity in the reconstructed ecosystem. However, fitted decay curves for each site predicted a slower decay constant and a longer litter half-life on the dam, which indicated that full pre-mining capability had not yet been achieved. Weight loss in the reconstructed system was most constrained by the low build-up of microbial biomass within the surface soil, which is expected to take at least 10 years to achieve pre-mining levels. In contrast, weight losses in the unmined sites appeared more related to the abundance of invertebrate fauna rather than microbial content. The results presented here of a developing system suggest that the importance of different factors affecting decomposition will reflect those that are most limiting over the course of ecosystem recovery. Additional

Engineering properties of gold tailings

ABSTRACT A comprehensive laboratory testing program has been conducted to establish the engineering properties of gold tailings from Kidston Gold Mines in North Queensland, Australia. The engineering properties of the tailings have been categorised into textural, hydraulic, and mechanical properties. The textural properties include the particle size distribution and the specific gravity. The hydraulic properties include the water characteristic curve, and the saturated and unsaturated hydraulic conductivity. Various models that describe the tailings water characteristic curve and hydraulic conductivity function have been presented. The mechanical properties include the bulk modulus, Poisson's ratio, the friction angle, the dilation angle, and the unsaturated shear strength parameters. The engineering properties of the tailings are vital to the management of the tailings both during the mine's operation, and long after its de-commissioning.

3-Dimensional effects on slope stability of high waste rock dumps

ABSTRACT A knowledge of angle of repose and stability of waste rock dump slopes is of vital importance at all mine sites. Conventional slope stability analyses model slopes in plane strain. In reality, slopes advance in a curvilinear pattern in plan and hence produce slope faces that are either convex or concave in plan. The three—dimensional shape of the waste rock dump is similar to that of a solid body of revolution, which may be modelled using a two-dimensional grid and a radial coordinate system. A 250 m high in-pit waste rock dump at Kidston Gold Mines Limited, North Queensland, Australia was modelled using this technique. The analysis showed that adopting a non-linear Mohr-Columb envelope resulted in a more deeply—seated failure plane than would occur using a linear envelope. A slope with a concave advancing face in plan was stable at an angle at least 2° steeper than an identical slope advancing in a straight line in plan. On the other hand, a convex advancing slope was only just stable at an angle of 0.5° flatter than an identical slope advancing in a straight line. Formerly; Ph.D. Candidate at the University of Queensland, Brisbane, Australia.

Grade control strategies and reconcilation procedures at Kidston Gold Mine, North Queensland : D. L. Collet, in: Managing risk. Proc. 4th open pit conference, Perth, 1994, (AIMM), 1994, pp 75–85

Grade control strategies and reconcilation procedures at Kidston Gold Mine, North Queensland : D. L. Collet, in: Managing risk. Proc. 4th open pit conference, Perth, 1994, (AIMM), 1994, pp 75–85

Commuter Mining and the Kidston Gold Mine: Goodbye to Mining Towns?

Commuter Mining and the Kidston Gold Mine: Goodbye to Mining Towns?

SAG mill operations at Kidston Gold Mines

The purpose of this paper is to outline the design, specification, and operation of the 8.5-m-diam (28-ft-diam) SAG mill commissioned at Kidston Gold Mines during January 1985. Amenability of Kidston ore to SAG milling, coupled with substantial cost advantages, led to the specification of this mill, equipped with variable speed drive to overcome the large variation in ore hardness. Operation of the mill is effected via a number of automatic control loops. Problems experienced with automatic control plus other electrical and mechanical failures have led to design changes and the formulation of future operating strategies.