1.

CHAPTER 1

INTRODUCTION

Rehabilitation of mined land and the treatment of waste materials from mineral processing have become essential considerations for mining companies. The emphasis in recent times on rehabilitation is a reflection of modern attitudes toward the environment and a recognition of the need to protect the land resource.

There is a greater awareness by mining companies, the community and the Government that safe, economic, and environmentally acceptable means of mine waste rehabilitation are required in an endeavour to reduce stream turbidity and pollution, minimize dust problems and return areas disturbed by mining to ecologically stable communities.

In an era when mineral extraction is competing with other interests such as agriculture, forestry and urban development, and when the ever watchful eye of the environmentally minded is focused on the industry, the rapid rehabiliation of mined and waste disposal areas and the assurance of long term stability is essential.

The majority of rehabilitation programmes are aimed at establishing a vegetative cover. There are many possible adverse chemical and physical conditions which are inhibitory to successful vegetative establishment. Mine sites and hence mining residues are very site specific with respect to their rehabilitation potential. The mineralogy, mining and processing method and treatment of waste materials will determine the physical and chemical characteristics of the material to be rehabilitated. The identification of the physical and chemical limitations to rehabilitation and the amelioration required has therefore become an essential prerequisite to the commencement of rehabilitation programmes.

The aim of this study is to investigate the tailing disposal system of the New England Antimony Mines N.L. Company at Hillgrove, located 30 kilometres east of Armidale in New South Wales, to define the problems involved and to investigate the physical and chemical parameters of the tailings, with respect to the establishment of vegetation. This study results from an approach by the mining company to the Soil Conservation Service of New South Wales in 1976, to assist in the design of a tailings disposal system and provide recommendations for subsequent rehabilitation. 2.

This thesis describes the mine environment, the milling and processing operations, and the design of the tailings disposal system, together with the investigations and experiments conducted on the tailings. Prior to the commencement of the investigations and experiments a literature review was undertaken to ascertain the current knowledge on mine rehabilitation. 3.

CHAPTER 2

REVIEW OF LITERATURE

2.1 INTRODUCTION

Revegetation of mining areas was carried out as early as 1815 when the Earl of Dudley made plantings on limestone workings at Dudley Castle and Wrens Nest in England (Whyte and Sisam, 1949).

In South Africa, attempts were made in 1911 to control the dust nuisance arising from tailings dams. The general procedure was to spray the surface of the tailings with a sludge of black soil (James, 1964).

In the United States, early rehabilitation work was undertaken by individual mining companies. However, it has not been until relatively recent times that a concerted and co-ordinated approach to rehabilitation has been adopted. The programmes have been initiated primarily as a result of public demand, individual company concern and conscience, and legislation. Kenahan and Flint (1971) have reviewed much of the work carried out by the United States Department of Mines, which pioneered work in the fields of secondary metals recovery and waste reclamation.

Much of the early work was centred on the identification of natural colonizing vegetative species found on existing mined areas and waste sites. Brierley (1956) undertook such a study of 40 pit heaps in the Nottingham, Derbyshire and Yorkshire coalfields in an attempt to discover what factors led to the establishment of vegetation on such heaps, and the species of plants involved. Similiar studies have been carried out by Hall (1957) and Mitchell (1959).

For all but the most hostile environments, natural revegetationfAlrill occur in the long term (Black and Truidinger, 1976). However, to achieve an effective cover which will reduce the erosion hazard and increase the stability and aesthetic appearance of mined sites and tailings areas the adoption of a sound programme to :establishh-vegetatiOn is-parumount. Natural recolonization will follow as a result of the improved physical and chemical conditions produced by the introduced species (James, 1966). Revegetation is universally recognised as an indispensable means of reclaiming strip mined land. Limstrom (1964) states that forestation is 4. recognised, as the most widely applicable type of vegetation, however, this would not necessarily be the case in the Australian environment.

Massing (1974) cites a good example of co-ordinated development following lignite mining in the lower Rhine area of Germany. Of the 2 2,500 km which have been mined in the area since last century a total 2 2 cif 154 km have been restored; of this total 91 km have so far been 2 recultivated, approximately 45 km for forestry, approximately 34 km2 for agriculture and approximately 12 km2 for highways, housing and 2 recreational use. One of the Great Lakes covers 20 km and attracts over 20,000 visitors from the metropolitan areas of Cologne, Bonn and Dusseldorf at weekends.

Erosion and leaching of waste dumps have caused considerable environ- mental pollution. Anderson et at. (1973) found a reduction in food supply and direct toxic effects from uranium mill waste on the biota. Verschuer (1976) stresses the need to incorporate the principles of landscape design into mining areas as rehabilitation success can be greatly enhanced.

Dean et at. (1969) state that the principle requirements of plants which are used for vegetative stabilization are the ability of the plants to renew themselves and provide a suitable habitat for the encroachment of native plant species. Chenick (1960) states that plants should have the following properties to be successful rehabilitation species:-

1. Low growing - either bushy or mat forming. 2. Ability to develop quickly. 3. Herbaceous or perennial. 4. Frost resistant. 5. Heat resistant with an ability to withstand full exposure to the sun, on account of exposed habitats. 6. Easily propagated by seed or cuttings. 7. Production of abundant viable seed. 8. Ability to grow on an acid medium, but this is not universally essential.

The establishment of an effective, self-perpetuating community of vegetation, which will afford maximum protection and stability whilst being aesthetically appealing, is the long term aim of the majority of rehabilit- ation programmes. Dean and Havens (1971) concur with the aim of estab- lishing a self-perpetuating plant cover, but state that if this 5. cannot be achieved directly the vegetative stabilization should foster entrapment and germination of native plant seeds that will i be self- regenerating without the need for irrigation or special care. Permanence of vegetative cover could be achieved advantageously by selecting species adapted to growth, spread and reproduction (James, 1966).

2.2 TYPES OF MINE WASTE

The type of mine waste has a major influence on the type of rehabilita- tion programme adopted and on the subsequent success of the programme. The general rehabilitation potential can be judged on the basis of climate, soil and vegetative site components, but each site will also have its own particular micro-climate in terms of specific physiographic, biotic and hydraulic components (Farmer et at., 1974).

There is a great diversity of mining operations which produce specific waste materials of variable physical and chemical conditions. No attempts will be made here to discuss all of these, but the majority of operations will fall into one of the following broad categories.

2.2.1 Open cut Operations

There are many scars on the Earths surface, especially in coal mining areas throughout Britain, Europe, the United States and Australia, which bear witness to the ravages of this process. The many forms of open cut mining are discussed by Gunnet (1975). He stresses the need to choose the best method for each particular case so as to ensure the selection of mining procedure that will provide maximum return on investment, desired production tonnages and effective land reclamation.

Three broad categories of open cut mining can be recognised. Firstly, those operations which result in long term excavations and associated spoil dumps and/or benches. The surface mining for iron ore, copper and bauxite are examples of this type. The mining for bauxite in the Darling Range of Western Australia results in large excavated pits being left on the hillsides. Prior to the removal of the bauxite bearing material all topsoil.is removed. After the removal of the bauxite material, an infertile and densely compacted kaolin clay layer is left. Successful rehabilitation of these pits has been achieved by deep ripping, replacement of topsoil, contouring and planting of PhytophthoAa cinnamoni fungus resistant tree varieties (Anon, 1974a). 6.

The second category is the open cut operations which allow for pro- gressive back filling of spoils. Strip mining for coal in the United States is a good example. Strip mining is the systematic process of simultaneously removing overburden and extracting the coal. This mining method facilitates the rehabilitation of the site in such a manner so as to enable use of the surface for the production of agricultural or forest products. This is the most popular surface method of coal mining (Otte and Boehlje, 1975).

Thirdly, there are open cut operations in which all material is the resource and no backfilling is possible. Many of the silica sand operations on the coastal areas of Australia are examples of this type. However, in some instances a limited amount of overburden is present and is replaced.

There has been considerable research into the rehabilitation of open cut mined areas, although much of the published literature refers specifically to the coal industry (Schessler and Droege, 1965; Wilson, 1957; Limstrom, 1960; Sherman, 1960; Gibbons, 1961; Aldon, 1965; Ashby and Baker, 1968; Bengston et a.1., 1973; Higgins, 1973; Farmer et at., 1974; Packer, 1974; Selner, 1975; Vogel, 1975; Yamamoto, 1975; Glover, 1976; Hayes et at., 1976; Coaldrake and Russell, 1978; Depuit and Coenburg, 1979; Schafer, 1979; Lyle and Evans, 1979; Majer, 1980). This work will not be reviewed in detail, however, specific examples will be referred to.

2.2.2 Underground Operations

Material won from underground mining operations is brought to the surface for the extraction of the minerals contained in the ore bearing rock, or as in the case of coal, for grading and possible washing prior to sale.

Quantities of rock are sometimes also brought to the surface during underground mining operations. In such cases, adequate rock dumps or disposal sites are necessary and will require rehabilitating. 7.

Ore bearing rock is usually put through a milling and processing plant to extract the minerals. These operations produce the tailings which usually possess varying degrees of physical and chemical limitations for plant growth.

2.2.3 Treatment or Processing Wastes: These are usually described as tailings, slimes, slurry, chitter or mullock depending on the mineral being won and the form of the waste material.

Tailings are, by definition, fine particle residues of milling operations. The industry refers to tailings as either sands or slimes. These terms are purely descriptive and bear no relation to other systems of sizing employed by agriculturalists or soil scientists (Down and Stocks, 1977a). The major waste disposal problem in the fluorspar industry in Great Britain is the 200,000 tonnes of solid material dis- carded annually as an aqueous slurry of low solids content. Dewatering to improve stability, chemical stabilization, thermal drying and calcina- tion have been proposed, however, they do not provide economically viable alternatives to the present system of pumping into tailings dams (Johnson, 1976).

Tailings can be deposited in two different forms. Firstly as a slurry and secondly, hydrocycloned into the differing size fractions which are usually referred to as sands and slimes. Tailings may be dis- charged on land, into a watercourse or placed underground. Land based disposal almost invariably involves the disposal into constructed ponding structures or dumps. Down and Stocks (1977b) divide tailings dams into three categories, the valley dams, lagoon and valley side dams; and describe the various methods of construction and the advantage of each type. Klohn and McManus (1971) and Klohn and Maartman (1972) discuss the construction of tailings dams by cycloning and spigotting. Con- struction techniques are also discussed by Laird (1972), Windolph (1972), Down and Stocks (1976 and 1977b).

Holz (1962) outlines three main reasons for the growing interest in the stabilization of tailings dams. These are:-

1. The desire to eliminate the dust problem arising from wind- borne fines from slimes dams. 2. To prevent pollution of water courses with mine sand and slimes washed into them during rain storms. 8.

3. To change the generally unsightly appearances of tailings dams.

Mine dumps are a familiar landmark around mining areas the world over. The dumps may be composed of unwanted rock fragments-but-zrore commonly refer to the dumps of waste material or tailings following the processing or extraction of minerals. It is with the latter form of dumps that most investigations have been conducted, as these dumps usually have significant physical and chemical problems which make them extremely hostile environments for vegetative establishment.

James (1966) states that surface residues from gold mining on the Witwatcrstra-nd in South Africa exceed a surface area of 10,000 ha. In this area he described two distinctly different types of dumps which principally resulted from different methods of tailings disposal. Firstly, sand dumps which are heaps of ground rock from which the gold has been recovered. These dumps may reach heights of up to 80 m and cover areas as large as 50 ha per dump. Secondly, slime dams which are composed of more finely ground material which is suspended in water to form slimes and then pumped through pipes to the area where it is to be stored. The retaining wall is constructed of dried slimes, rock, overburden or other waste material. These dumps frequently reach heights of 80 m and cover up to 100 ha per dump.

Harris and Leigh (1976) described the dump at the Zinc Corporation at Broken Hill in New South Wales to be not unlike those described by James (1966). The Broken Hill dump comprised 12 million tonnes of residue and was 650 m long, 300 m wide and 35 m high.

Thr, stability of tailings structures has always been of some concern. Down and Stocks (1977a) cite the case of the collapse of ten out of fourteen tailings dams in Chile in 1965 following an earthquake. The flowing tailings killed 250 people following the collapse. Blume (1972) discusses the probability of earthquakes and resultant ground motion while Smith (1972) discusses the factors and lessons gained from tailings disposal. Further comments on the stability of such structures are given by Donaldson (1960).

The Mufulira mine disaster of 1970 in Zambia when a surface tailing dam collapsed and flooded underground workings with the loss of 89 lives and the rehabilitation of the mine to productive capacity is outlined by 9.

Neller et at. (1973). Ayerst (1978) cites the failure of the shale dump in Aberfan in South Wales in 1966 where the centre of the tip turned to a slurry which broke out, flooding the village and killing 144 people including 116 children in the school. The stability of deep surface coal spoil dumps in Australia has been investigated by a team of C.S.I.R.O. workers headed by Mallett (1981).

Although not basically considered sand dumps, as described by James (1966), the residue sands resulting from the extraction of minerals during metaliferous sand mining provides similar harsh environments for rehabilitation. In Australia, during the mining process in which sand is passed through the extraction plant, only .25 to 1.5% of the sand volume is removed from the site (Newey and Lewis, 1976). This volume contains the rutile and zircon materials. Sand mining along the Australian coastline is involved with a very delicate environment and as a result considerable tension exists between mining companies, Government Departments and conservation bodies. The reclamation of sand mined areas in Australia and in overseas countries is well docu- mented (Barr, 1965; Barr and Atkinson, 1970; Clark, 1975; Quilty and Reid, 1975; Thatcher and Westman, 1975; Brookes, 1976; McRae, 1979).

Underground disposal of tailings is relatively widely practiced in underground mining operations to back-fill excavated areas, however, Down and Stocks (1977a) suggest that only 5% of produced tailings can be disposed of in this way. Tailings from the Mount Isa mines in Queensland are deslimed in a two stage cycloning operation, and the coarse fraction mixed with Portland cement and pumped underground to backfill mined areas (Hunter and Whiteman, 1974; Down and Stocks, 1977a).

A team of researchers from C.S.I.R.O. used iron sulphide tailings containing 40-70% pyrrhotite as a cementing agent for underground filling (Anon., 1977). The researchers believe that it is technically and practically feasible to percolate the tailings into mines already filled with rock wastes. This process would result in mined out areas being filled, thereby allowing the removal of the remaining ore bearing rock which previously had to be left for mine support to ensure safety during mining operations (Anon., 1977). 10.

Down and Stocks (1977a) cite a number of examples of marine, river and lake disposal of tailings. These forms of tailings disposal are mainly restricted to mining areas close to water bodies, and even then increased environmental legislation will reduce this form of disposal in the future. The piping of 70,000 tonnes of tailings per day to marine disposal points by the Atlas Consolidated Mining and Development Corporation in the Philippine Islands is an example of this method of tailings disposal (Anon., 1972). The disposal of 80,000-90,000 tonnes of tailings per day into the sea by the Bougainville copper mine in Papua New Guinea, is a further example of marine tailing disposal (Hartley, 1976). Marine disposal of tailings will receive greater attention as the prospects for ocean mining and hence ocean disposal of residues becomes necessary.

The economic utilization of tailings and mine wastes has received increased attention in recent years. Considerable work has been done in this field by the United States Bureau of Mines. The use of tailings in the construction of foamed building blocks, glass, dense calcium building blocks, thermal insulation; prozolons for concrete work and stabilizing agents has been noted by Down and Stocks (1976). Mullock from the copper mines at Cobar in New South Wales has been used for road construction following crushing (P.Walker, personal communication).

Red mud from the Kaiser Aluminium and Chemical Corporation in Louisiana in the United States is being used for land fill and following dewatering for the production of agricultural crops. Prior to this the red mud was being pumped into the Mississippi River (Anon., 1975 ). Tailings from the New England Antimony mine have been used as a orozolon in brick manufacture.

2.3 DEFINITION OF PROBLEMS

One of the most significant aspects of mine reclamation is that it is site specific, however, a review of the literature suggests that similiar problems are common to many sites. 11.

Although many of the problems experienced may be similar, it would be unwise to apply a technique from one area to another. Hunter and Whiteman (1974) attribute this to three factors:-

1. A variation in geology between and even within mining areas. This will give a different chemical composition and physical character to the wastes.

2. Different extraction and treatment processes.

3. Climate. Mining areas are located throughout the world in differing climatic regimes. In Australia they are more closely related to hot dry climates while the mining areas of Europe are favoured by a temperate climate.

2.3.1 Physical

A lot of attention has been given to chemical factors in mine rehabilitation with both nutrient deficiencies and chemical toxicities being cited in the literature as problems. The physical characteristics of mine wastes are also very important considerations for rehabilitation. For example, Brierly (19156) concluded that the ability of plants to become established depended upon mechanical rather than chemical factors following a study of 40 pit heaps in Great Britain.

Physical limitations to vegetative stabilization of mining wastes include low permeability, poor aeration, low water retention, surface crusting, sand blasting of plants and instability of the wastes. The physical properties which affect plant growth are primarily related to their particle size distribution. Fine materials are very susceptible to erosion, low permeability and aeration and surface crusting, while coarse materials are commonly limited by low water holding capacities.

2.3.1.1 Particle Size Distribution

The physical characteristics of the tailings are controlled by the crushing or milling process. The distribution of particle sizes varies markedly between mines and ores. However, generally tailings are composed of small and uniform particles, mainly in the sand and silt categories. The low amounts of aggregating material;- clay particles, organic matter and its various breakdown products derived from microbial decomposition, means that the material has a poorly developed unstable structure and is prone to erosion (Burton et at., 1978). 12.

Down and Stocks (1977a) investigated particle sizes of tailings from a wide range of mines, including copper in the United States and British Columbia, limestone in the United States, gold in South Africa, Iron orein Germany and Canada,lead and zinc in the United States and molybdenum in British Columbia. They found that it was common for around 50% of tailings to pass through a 0.2 mm sieve. Johnson ( 1976) found that 52% of oven dried tailings consisted of fine sand (0.2,-0.02 mm) in fluorspar tailings in Britain, while Craze (1977) found the greatest particle size fraction represented in tailings dumps at the Captains Flat mine in New South Wales was the coarse sand (2.0-0.2 mm). Approxim- ately 62%of the nickel refinery wastes from Yabulu in North Queensland were coarse sand (2.0-0.2 mm) size fractions (Bell and Evans, 1980).

Schessler and Droege (1965) found that fine earth particles, with a diameter of 2 mm or less, comprised between 17 and 57% of the materials in spoil banks on strip mined land throughout the United States. They found that trees would establish with as little as 20% fine earth. Spoils with low amounts of fine earth are less likely to he affected by frost heave (Schessler and Droege, 1965). Working with coal spoils in Wyoming, U.S.A., Jacoby (1968) found that the extremely coarse bouldery surfaces were broken down as a result of weathering and this created an improved environment for plant establishment.

As mentioned above, poorly developed and unstable tailings have structures, however, in such materials the porosity is not favourable for satisfactory root penetration and development, water infiltration and percolation rates may show limited aeration (Martinick, 1976). Water penetration is frequently slow on tailings waste because of their compacted state. This slow infiltration rate could be a drawback when the material requires leaching to remove excess soluble salts or toxic substances (Hunter and Whiteman, 1974).

James (1966) also found permeability to be low on slime dams in the Witwaterstrand and it was therefore considered neither practical nor desirable to flood the tops of slime dumps with water since pro- longed flooding compacted the material and produced conditions unfavour- able for plant growth. This is in conflict with the practice" offlooding thetcolis of dumps to reduce wind erosion and resultant dust. 13.

Verma and Thames (1975) found that reclaimed overburden from coal mining in Arizona, U.S.A., had no structure and therefore tended to puddle and form surface crust. Surface crusting and low infiltration rates were limiting factors to vegetative establishment on spoils in the Black Mesa area of Arizona (Schuman et at., 1976).

When tailings are not separated by hydrocycloning into the differing size fractions and are simply pumped to the disposal site, the different rates of sedimentation give rise to different particle size distributions. Coarse fractions separate from suspension quickly and as such aid the consolidation and stabilization of the perimeters of the dump due to their lower plasticity. Despite the general fractionation during sedimentation, the ratio of coarse to fine particles is subject to great variation with no clearly defined pattern in either the vertical or horizontal plane (Johnson, 1976). Hunter and Whiteman (1974) found similar particle size distributions during revegetation trials at the Mount Isa mine in Queensland. This distribution produced a variation in bulk density from -3 1.20 to 1.75 g am both in the vertical and horizontal planes.

2.3.1.2 Bulk Density

Due to the characteristics of tailings, porosity, aeration, water infiltration and percolation are frequently unsatisfactory for plant growth. Surface crusting, compaction and high bulk density are inhibiting to root penetration and growth (Williamson and Johnson, 1981).

The particle size distribution in combination with the repeated wetting and drying cycles experienced on tailings dumps leads to high bulk densities. High bulk densities are not only likely to depend on particle size distribution but also on particle shape and interparticle forces (Mullins and Panayiotopoulos, 1980). The amount of organic matter and other stabilizing agents can also affect the bulk density of materials. With a great range of mine wastes, especially the fine tailings, organic matter content is usually low and in such materials the shape and arrangement of particles would have a major influence on the degree of packing. 14. -3 Shetron and Duffek (1970) recorded bulk densities as high 1.54 g cm on iron mine tailings in Michigan, U.S.A. but found in general that bulk densities and percent water by weight at field capacity were comparable to soils of similar particle size developed under natural forested -3 conditions. Ogram and Fraser (1978) found bulk densities of 1.6-2.9 g cm to be limiting to plant growth in high sulphide tailings from the Hudson Bay Mining and Smelting operations at Flin Fon, Manitoba, Canada. Ruschena et a/. (1974) recorded bulk densities as high as 7.5 g am-3 on metal mining wastes at Mount isa, Queensland. Bulk density by itself is of little value for assessing the rootability of material because of the high values arising from the varied and often high particle density of the minerals present in the spoil. Bulk density gives no information on pore size and it is therefore limited in its ability to predict the suitability of a material for plant growth.

Craze (1976) found during studies to determine the optimum density of topsoil layers to be used in the rehabilitation of the Captains Flat mine wastes in New South Wales, that roots quickly penetrated the upper loose layers and in treatments with bulk densities less than -3 -3 1.5 g cm . In the 1.5 g am layer growth was retarded while in -3 layers with a bulk densities greater than 1.5 g cm it was entirely impeded. Elliot et at. (1980) recorded bulk densities in coal over- -3 burden in the Hunter Valley in New South Wales of 1.3-1.6 g am but concluded that the stone fragments in the material may have influenced the readings and vegetative establishment may not be as difficult as the higher bulk densities would indicate.

Penetrometers are generally used to provide an index of mechanical resistance. Taylor and Burnett (1964) state that it is soil strength as measured by a penetrometer and no other physical factor, that controls the growth of roots through soils. Soil strengths of 2500-3000 kPa were enough to prevent root penetration. However, because of variations in probe design, heterogeneity of resistance in mine wastes, and because of differences between roots and metal probes in their mode of penetration, penetrometer resistance lacks general utility as a predictor of root growth (Greacen et at., 1969). Penetrometers should therefore be regarded as comparative guides to forces that roots experience in penetrating a medium (Russell and Goss, 1974). 15.

2.3.1.3 Temperature

Most spoil material has dark coloured surfaces which warm rapidly during the day and cool rapidly at night throughout the growing season and when combined with their very low water availability due to their particle size and distribution, stress is placed on the vegetation (Shetron and Duffek, 1970; Bennett, 1973; Martinick, 1976). Temperatures as high as 70°C have been measured on dark coloured shaly spoil bank surfaces in the United States and when combined with high winds excessive moisture losses from such surfaces result (Schessler and Droege, 1965). Bradshaw and Chadwick (1980) state that temperatures of 60°C have been recorded on colliery waste in the United States. Temperatures of this magnitude can have a devastating effect on vegetative cover. Under such conditions sparsely growing plants transpire so rapidly that they cannot maintain their water content and die. The temperature is highest at the soil surface and plants may also die directly from the heat at this point. This is known as head girdling (Bradshaw and Chadwick, 1980).

2.3.1.4 Erosion

Because of the physical characteristics of mine wastes, and in particular, tailings, soil erosion is an inevitable problem. Due to the harshness of the majority of wastes, vegetative establishment is usually slow, predisposing such surfaces to both wind and water erosion. Bell and Evans (1980) found that the nickel refinery wastes at Yabulu in North Queensland become non coherent on drying and were extremely susceptible to wind erosion. Bradshaw and Chadwick (1980) state that a lot of mine wastes are dumped by dragline or conveyor and have steep 0 sides with a natural angle of rest, of about 30 . In such cases, water erosion is usually a major problem.

Shetron and Duffek (1970), Bennett (1973), Verma and Thames (1975), Martinick (1976), Shirts and Bilbery (1976), Bennett et at. (1976), Johnson (1976), Ogram and Fraser (1978) and Schuman et at. (1980) all found erosion either resulting from wind or water or both, a significant problem to be overcome in rehabilitation programmes. 16.

Among the studies made to reduce erosion on the surface of tailing dumps and to improve the aesthetic quality of such areas are those by Dunn (1971), Murray (1973) and Murray and Moffett (1977). Gilley et U.Q. (1976) studied the run off and erosion characteristics of surface mined sites in Western North Dakota, U.S.A., using simulated rainfall on pre- mined and mined sites. Applications of straw reduced soil loss by 84% on the spoil and 93% on the topsoil sites while run off averaged 60% and 70% of rainfall applied on the respective topsoil and spoil treatments. Glover (1976) found uncontrolled erosion from haulage ways to be a major source of sediment during strip mining for coal in west Virginia, U.S.A. This was controlled by the construction of sediment traps, rock rip rap, ditches and culvert structures together with the grading of the wall which had been left following mining. The surface Mining and Reclamation Act of 1971 limits the highwall to a maximum of 10 m.

Following a number of pilot plant evaluations of soil loss from disturbed sites, Kirkpatric and Seith (1975) concluded that the Universal Soil Loss Equation could not accurately predict sediment yield on slopes greater than 1:5. Such slopes are commonplace in mining wastes, thereby emphasizing the need for greater research on erosion and sediment yield from such areas.

Reduction in the length of slopes, terracing or staircase grading help to reduce susceptibility to erosion and facilitate later establish-

ment of vegetation (Kay et at., 1977).

R. Nunn (personal communication) during studies on bauxite mined land in the Darling Range of Western Australia, found varying sediment yields from treatments of native and improved pasture, tree cover and of bitumen, and straw mulch. As a result of the study the tree planting programme has been combined with a cover of understory grasses and legumes to reduce erosion and turbidity of water. This is especially important as the bauxite mining areas in the Darling range are located in the catchment area to Perths water supply.

Bengston et at. (1973) found that pine trees alone did not produce cover fast enough to retard gully erosion, which was quite rapid and severe on the steeper slopes on coal mine spoil areas in north eastern Alabama. The establishment of a grass cover followed by tree planting in the following year was the preferred treatment. 17.

In a study of derelict mine lands at Tuena in New South Wales, Sewell (1978) found that wherever the soil was disturbed for mining operations an erosion hazard developed. Corrective measures involved construction of earthworks and the establishment of a dense cover of vegetation.

Brenner et at. (1975) believed that to meet the objectives of environmental protection and rehabilitation consistent with necessary extraction of coal, the reclamation practices utilized on strip mining spoils should provide adequate sediment and erosion control, food and cover for wildlife and/or agricultural production and aesthetics, utilizing a reasonable cost/benefit ratio.

The construction of sediment ponds is a necessary function in strip mining activities in most states in the United States of America. Reed (1975), Nawrocki and Kathuria (1975) and Connell (1975) evaluated the effectiveness of these structures. Using water quality models the latter authors found that turbidity was the least predictable of all the parameters used. Settling in sediment ponds proved ineffective in controlling turbidity at a surface mine at Centralia in the State of Washington, U.S.A. Dispersed clay particles repelled each other resulting in continued turbidity. Turbidity was overcome by automatically monitoring the levels of turbidity and adding the required amount of chemical to flocculate the clay (McCarthy, 1973).

Changes in spoil dump shape and the concentration of spoil on solid excavated benches reduced the problems of spoil slides and resultant erosion, sediment yield and stream pollution on coal mine spoils in western United States (Williams, 1973). Schuman et at. (1976) found spoil shape, batter slope and length of slope were all critical in the rate of water erosion on metaliferous mine wastes in western United States.

Wind blasting causes scouring and cutting of the foliage and may result in exposing of root systems of some plants and the complete or partial burial of other plants. The fine textured surfaces of tailings dumps are predisposed to wind erosion and hence, sand blasting, especially when they are in a dry state. Well designed windbreaks of fast growing trees planted around the perimeter of a dump and on progressive benches or levels as the dump rises, will strike the problem at its source (Quilty, 1975). Dwyer (1981) found wind blown material from acid coal washery wastes in the Hunter Valley to be unacceptable, while Green (1981) found dust produced from gold mine tailings at Cobar to be a problem. 18.

Ogram and Fraser (1978) found sand blasting to be a significant cause of poor vegetative establishment on high sulphide tailings at the Hudson Bay Mining and Smelting plant in Flin Flon, Manitoba, Canada. They found that, of the treatments tested, only incorporated straw proved successful in reducing surface erosion.

Sand blasting was a problem encountered by James (1966) on the Witwaterstrand gold fields. He found that a system of low wind breaks constructed out of stems of reeds(Ph) agm4te4 COmmun,bS)afforded excellent protection of seedlings until they became established. Wind erosion and subsequent dust movement can be controlled by moistening of the surface with water, spraying with fuel oil, sealed with a chemical mulch or bitumen (Quilty, 1975). Harris and Leigh (1976) state that the only reasonably effective method so far devised for the suppression of wind erosion and dust on the top of "live" dumps is to keep all of the top surface wet with freshly placed materials. Chenick (1963), discusses the various types of windbreaks used in tailings areas in South Africa.

Dust pollution is a significant problem encountered in most mining areas especially when the mines and waste disposal sites are located adjacent to townships such as is the case in Broken Hill in New South Wales. The dust problems encountered at Broken Hill not only caused unpleasantness for the inhabitants (Harris and Leigh, 1976) but the metals contained in the dust posed a problem for vegetation and stock which grazed the plants upon which the dust settled (Bradshaw and Chadwick, 1980). Junor (1978) found wind erosion of coal ash dams produced a significant dust nuisance at Port Kembla in New South Wales. The sites were successfully stabilized with vegetation following deep ripping and the spreading of 25-75 cm of topsoil.

Because of the necessity to achieve a quick and effective cover of vegetation on spoils and tailings areas for both reduction of soil erosion and sediment yield, and for aesthetic reasons, there has been considerable use made of artificial stabilizing agents which both protect the surface as well as provide a favourable environment for plant establishment.

Jacoby (1968) compared the effectiveness for soil protection and plant establishment of straw mulch, jute netting, snow fence and a combination of these treatments. All treatments gave considerable 19. advantages, evaluated accordingnto their ability to influence seedling density. A combination of straw mulch and jute gave the highest seedling density. The uses of jute netting, bitumen emulsion and bitumen emulsion and straw are discussed by Clothier and Condon (1968) and Nebauer and Good (1971). Adams (1966) studied the effects of mulches of straw, gravel and djmethyl ammonium chloride on run-off, erosion and soil moisture depletion. Mulches of straw and gravel proved the most effective.

Straw incorporation, organic emulsions and snow fences were tried as methods of dust control.(Ogram and Fraser, 1978). Black plastic was laid on the surface to eliminate wind erosion and retain moisture as were jute mesh ground covers. Of the methods used to reduce surface erosion by wind and water,only incorporated straw proved successful. Schuman et at. (1980) found that direct seeding into standing cereal stubble has advantages over the use of crimped straw or hay residue as a mulch for wind and water erosion control on mined land. Standing stubble in addition to remaining longer than the straw resulted in less temperature fluctuations at shallow soil depths and produced a 25% greater cumulative water infiltrations

Surface modification techniques such as contour furrows, benches, pitting, dozer basins, gauges and other methods of increasing surface roughness can be used to reduce wind and water erosion and retain moisture for on site plant use (Hodder, 19731 Schuman et at., 1976).

Chemical stabilization offers an alternative to vegetative cover. Harris and Leigh (1976) discuss the use of waste oil as a surface stabilizer against wind erosion at Broken Hill. Kremmel (1976) discusses the types, uses, advantages and disadvantages of various types of chemical stabilizers. He states that vinyl styrene butadiene, and vinyl acrylic latexes;, polyvinyl acetate, polymer, wax and rubber emulsions and various petroleum derivatives are among the more common base products.

Binding agents function in two distinct ways; some form a crust or film to physically hold the surface intact against erosion, while others contain components which impart a hydroscopic property to the 20. binding agent, allowing it to absorb moisture from the atmosphere to keep the surface continually moist. Dean Qt at. (1969) and Havens and Dean (1969) also report examples of chemical stabilization.

The United Steas Bureau of Mines has pioneered chemical stabiliza- tion and identified various compounds of use for mine waste rehabilitation. Amongst the most successful materials are petroleum-based products, resin emulsions, lignosulphonateS, bitumen-based materials and organic polymers (Shirts and Bilbery, 1976). Ross (1977) and Rostler and Kunkel (1964) report that chemical soil stabilizers have been used extensively for controlling dust and wind erosion in the arid regions of the United States, but information on their success in humid regions is limited.

2.3.2. Chemical

There are abundant examples cited in the literature of the many chemical limitations to effective rehabilitation. Nutrient deficiencies, toxic levels of elements in the waste material, extremes of pH, salinity and the effects of mine drainage containing toxic substances are among the most significant. These aspects will be reviewed, however, part- icular attention will be given to the elements arsenic and antimony as it is possible that these two substances could be found in toxic concentra- tions at the Hillgrove-mine site.

Working with high sulphide tailings at Flin Fon, Manitbba, Canada, Ogram and Fraser (1978) found the most serious growth limiting factors to be acid generation, nutrient deficiency, extreme microclimate, salt formation, lack of organic matter and low cation exchange. As a result of the magnitude of the problems encountered the project was cancelled until "advances in the state of the art warrant". Butterfield and Tueller (1980) found acidity and low nitrogen availability to be the main Limiting factors to plant growth in acid mine wastes from a sulphur mine in north eastern California, U.S.A. Working with pulverised fuel ash, Cope (1962) described phosphorus and nitrogen as low. Smith and Bradshaw (1970) showed that fertilizer, especially the slow release forms, was necessary for satisfactory growth on acidic lead/zinc mine spoils in Wales. They concluded that growth in metaliferous wastes was restricted chiefly by toxicities and lack of nutrients and not by physical factors. This is not necessarily so, as can be seen from the previous discussions on the physical aspects of mine wastes. 21.

2.3.2.1 Nutrient Deficiencies

Nutrient deficiencies, particularly nitrogen and phosphorus have been reported on numerous types of mine wastes throughout the world by

Cope (1962), Chenick (1963), Barnheisel and Massey (1969), Davies et at. (1971), Dean and Havens (1971), Parsons (1975), Johnson (1976), Down ana Stocks (1976 and 1977b), Reynolds et at. (1978), Ogram and Fraser

(1978), Bell and Evans (1980), Elliott 2.t at. (1980), Bradshaw and Chadwick (1980), Elliott and Hannan (1980), and Dwyer (1981).

James (1966) found that South African dumps contained no organic matter, there was no microflora other than bacteria that oxidized iron and sulphur, and no nitrogen was detectable by chemical analysis. Nitrogen, phosphorus and to a lesser extent, potassium calcium and magnesium levels are invariably inadequate. Hunter and Whiteman (1975b) working with tailings at Mount Isa in Queensland obtained responses to phosphorus applications far in excess of those normal for arable soils. Bell and Evans (1980) found that the phosphorus deficiency in the nickel refinery wastes at Yabulu was so severe that no growth of any of the nine tested pasture species occurred without fertilizer. Maximum yield of Rhodes grass (Cynodon dactyton) was achieved with an application of 400 -1 kg ha of phosphorus fertilizer.

Working with coal mine spoils in Poland, Aldag and Stryzyszcz (1980) achieved increased tree growth with nitrogen fertilizers. Studies were also made on mineral nitrogen forms in phyllosilicate. material and the mine spoil was found to contain up to 40% total carbon and up to 0.7% total nitrogen.

Murray (1973) following investigations of metaliferous and coal mine wastes found that apart for situations where trace elements occur in phytotoxic concentrations supplies of the essential micro-nutrients is usually not limiting. However, Parsons (1975) found manganese deficiencies limiting to plant growth on red sand tailings from an alum- inium refinery at Gladston in Queensland. Boron deficiency in fly ash was also noted by Parsons while Bennett (1973), Armiger and Jones (1973) noted magnesium deficiencies on strip mine spoils in Appalachia in the United States. Boron deficiency limited plant growth on copper mine tailings at Bougainville in Papua New Guinea, (Hartley, 1976) while Elliot and Hannan (1980) found boron and molybdenum to be deficient in coal overburden material in the Hunter Valley. 22.

Bingham and Garber (1960) in the United States, studied the solubility and availability of micro nutrients in relation to phosphorus fertiliza- tion. They found that regardless of source, excess phosphorus resulted in acute copper deficiency and in the case of acid soils reduced uptake of boron and zinc usually followed excess phosphorus fertilization. Excessive phosphorus . . fertilization of acid soils resulted in increased manganese and molybdenum uptake, whereas in alkaline soils excessive phosphorus, reduced the availability of molybdenum.

Nutrient deficiencies are not always a limiting factor to plant growth. Jacoby (1968) found that mine spoils from open cut coal mining in Wyoming, U.S.A., were quite fertile. Verma and Thames (1975) working with coal mine spoils in the states of Arizona, Colorado and Utah, U.S.A. found that recontoured material following mining had higher total values of nitrogen, phosphorus •.F and potassium than the soils in the natural watershed.

Shetron and Duffek (1970) working with iron mine tailings in Michigan, U.S.A. found a relationship between texture and availability of nutrients. The infertile nature of the tailings necessitated the applica- -1 tion of an average of 125 kg ha of fertilizer as premixed ammonium nitrate, triple superphosphate and muriate of potash. All trial plots had significantly more phosphorus than nitrogen and potassium in the upper several centimeters of tailings. It was concluded that this was due to the slow leaching properties of the phosphate fertilizers compared to nitrogen and potassium which are both susceptible to leaching.

Davidson and Jefferies (1966) conducted experiments on the nutrition of plants growing on coal mine heaps in Britain. A number of typical pit heap species were grown from seed in different spoils at 17 0C in a growth cabinet. Different nutrient solutions were applied and after five weeks the plants were harvested, dried and weighed. All spoils were severely deficient in phosphorus and nitrogen. Experiments on seedling establishment showed that nutrient treatments had no effect on establish- ment but had an enormous effect on subsequent growth. Similar germination results have been achieved by Hunter and Whiteman (1974) on tailings at Mount Isa in Queensland and Harris and Leigh (1976) on tailings from a lead/zinc mine at Broken Hill in New South Wales. The latter authors found that root and shoot growth following establishment reflected the physical characteristics and nutritional status of the medium. 23.

Leaf disorders and discolourations consistent with nitrogen, phos- phorus and potassium deficiencies were found by Green (1981) during vegetative trials on metaliferous mine spoil at Cobar in New South Wales. The susceptibility of nutrients to leaching indicates the importance of including nitrogen fixing legumes in seed mixtures even though they can prove difficult to establish especially in arid conditions(Bradshaw and Chadwick, 1980).

Because of the inherent poor fertility of the majority of mine wastes, amelioration by the addition of organic and/or inorganic fertilizer to supply both essential macro and micro nutrients is paramount if success- ful vegetative establishment is to be achieved. In Great Britain,400-800 -1 kg ha of a high phosphate, complete (N.P.K.) fertilizer has been recommended as a primary treatment to rectify nutrient deficiencies on metaliferous and coal mine spoils by Bradshaw and Chadwick (1980).

Shetron and Duffeck (1970) studied the potential for vegetative growth on infertile iron mine tailings in Michigan, U.S.A. and found that at least three applications of ammonium nitrate, triple superphosphate and potassium chloride at 23, 76, 76 kg ha -1 were required for successful establishment of grass/legume and pure grass swards respectively. Fitter and Bradshaw (1974) concluded that fertilization increases root growth and penetration of plants on metaliferous and coal mine spoils and that there is a linear response by the roots to fertilizer up to high appli- -1 cations (1,000 kg ha ).

Maintenance applications of fertilizer, and lime when required is essential if vegetative establishment is to be maintained on the very harsh environments encounted on most mine spoils. In South Africa the recommended maintenance fertilzer treatments for gold mine tailings -1 -1 -1 is 60 kg ha of nitrogen, 20 kg ha of phosphorus and 30 kg ha of potassium, to be applied annually to sand dumps, biennially to the perimeter of slimes dams and every third year to slime dam surfaces (Chamber of Mines, 1979). Bradshaw and Chadwick (1980) recommended -1 annual applications of 25 kg ha of N.P.K. for at least six years while Dawn.and Stocks (1977b) advocate a post establishment application of 75 -1 kg ha of nitrogen, to overcome the considerable losses which occur in early 24. vegetative establishment. Whilst these authors have provided general recommendations, it should be remembered that mine waste rehabilitation is very site specific and the initial and maintenance fertilizer require- ments will change from site to site, depending primarily on the chemical and physical characteristics of the spoil and climatic conditions of the area.

2.3.2.2 pH and Phytotoxicity

In terms of chemical composition, mine tailings often contain phytotoxic levels of heavy metal ions, residual quantities of process reagents, chemical complexes formed during processing and a high level of dissolved solids (Bell, 1975).

Extremes of pH are known to adversely affect plant growth. Little growth occurs at pH values less than 4.0 due to aluminium and manganese toxicity, or greater than about 9.0 due to trace element immobilization (Bell and Whiteman, 1975). In addition to aluminium and manganese toxicity at very low pH levels, calcium deficiency may also be responsible for poor plant growth (Chapman, 1966).

Mine spoil material is usually unweathered and leached and may contain substantial amounts of trace elements which will be released into the rooting environment with subsequent weathering (Massey and Barnhisel, 1972). Butterfield and Tueller (1980) found that low pH of spoil material was the most important factor which hindered vegetative establishment on acid mine spoils from an open pit sulphur mine in north eastern California, U.S.A.

At high levels of soil acidity large quantities of heavy metals are made soluble, and are thus available for plant uptake. Of special significance are the high concentrations of aluminium, iron and manganese (Massey, 1972; Berg and Vogel, 1973; Rorison, 1973). In general, the soluble metal concentrations are inversely proportional to pH (Struthers, 1964; Massey, 1972; Massey and Barnhisel, 1972; Berg and Vogel, 1973). Massey (1972) established quantitative relationships between soil pH and the log of the concentrations in acid strip mine spoils in western United Slates. 25.

Oxidation of pyrite and a subsequent rise in acidity has been reported by numerous people. Grube et at. (1972) reported that the sandstone overburden from strip coal mining in north west Virginia, U.S.A., produced problems of acidity as a result of pyrite oxidation. James (1966) found that the slimes as deposited on the Witwaterstrand gold fields in South Africa were alkaline in reaction. When deposited however, the oxidation of pyrite, often accelerated by bacteria, caused a gradual accumulation of acidity in the surface layers. Jacoby (1968), Vogel (1975),Von Demfange and Warner (1975), Down (1975) have all found low pH levels and acidity, caused by pyrite oxidation e limiting factor to plant growth.

In a study of weathered sulphide tailings in north eastern New Brunswick, Boorman and Watson (1976) found that oxidation of pyrites occured down to 50 cm depth on mine spoils. Craze (1977) found that pyrite oxidation was the main cause of acidity at the Captains Flat Mine in New South Wales. The low pH levels (2.8-2.9) were greatly influenced by the accelerated oxidation of pyrite by the ThjAacitews bacteria, in particular Th.thic-oxidan2s, Th. ,6etAo-oxidan and Th.denitAiicaivs.

Barnheisel and Massey (1969) found the extreme acidity in Eastern Kentucky coal fields to be associated with toxic levels of iron, manganese, copper and zinc, They recommended that the acid producing layers should be buried within the spoil bank or that large amounts of limestone should be added to neutralize the acids.

Schessler and Droege (1965) describe a classification system of spoils developed by the Central States Forest Equipment Station in the United States, based on pH valves:

1. Toxic wastes were those with a pH of 4.0 or less. 2. Marginal - 51% to 75% of the bank surface has a pH of 4.0-6.9. 3. Calcareous - 50% or more of the bank surface has a pH of 7.0 or more.

4. Mixed - less than 50% of the bank surface is toxic acid or calcareous. 26.

Sodium was found to be present at levels sufficient to cause physio- logical disorders and growth depression at the Drayton and Maitland Main mine sites in the Hunter Valley in New South Wales (Elliott and Hannan, 1980). They concluded that drainage of revegetated sites should therefore he designed to minimize the accumulation of sodium at the base of slopes, in bank channels and in drainage lines.

Bradshaw and Chadwick (1980), state that in general, metal concentra- tions above 0.1% prove phytotoxic, though this depends on the metallic species, release characteristics and the nature of the accessory minerals. Metals including arsenic, cadmium, antimony and silver may be present in mine wastes at concentrations above the normal range for agricultural soils (Swaine, 1955).

Lime is commonly used to raise pH levels on acid tailings and lower the concentration of heavy metals. Most heavy metals become unavailable in alkaline conditions (2razey. 1977).

Large quantities of lime are usually required to raise the pH level. -1 Craze (1977) found that 55 t ha of lime was required to raise the pH of the top 9 cm of tailings at Captains Flat to pH7. Nielson and Peterson -1 (1972) found an application of 160t ha of lime on coal mine wastes in Utah U.S.A., sufficient to maintain the pH level above 7 for more than 6 months. Vogel (1975) achieved good initial results with lime addition on coal mine spoils in the United States but he reports that the effective- -1 ness of the original application of 34t ha was reduced after three years.

James and Mrost. (1965), removed acidity from gold-tailings .on the Witwaterstrand. in South Africa by leaching. Liming was first used, but pH values remained low even after the addition of lime in quantities that had been considered sufficient to neutralize the acid present. The downward movement of the acidity was encouraged by an extremely fine spray of water at a rate matching the infiltration rate.

Chemical tests on sulphide tailings at Flin Flon, Manitoba, Canada, revealed very poor cation exchange capacity, high conductivity and pH levels of the older oxidised tailings of between 3.0 and 4.0. Water leaching proved ineffective (Ogram and Fraser, 1978). 27.

The problem of high pH values or alkalinity is little reported compared to low pH levels and as such would appear to be less of a problem in mine waste reclamation. However, fly ash may have pH values ranging from 7 to 10 (Davies, 1964). Potentially toxic levels of boron have been found in fly ash (Cope, 1964; Holliday et at., 1958).

The majority of mining residues are extremely low in organic matter .rld similarly low in soil microflora. The pH of the medium has a direct effect on soil microflora. Blake (1967) states that the optimum pH for the growth of most bacteria, algae and protozoa is about 7.0 and with few exceptions these organisms do not grow below pH 4.0 or above pH 9.0. Exceptions include species of Thiobacittuz, Acctobactut and the nitrogen fixing bacterium Be.ifeitinckia which can multiply and grow at a pH of 2.5-3.5.

Golomzik et Ca.(1974a,b)andKaravaiko et at. (1974) working in the Ural mountain mineral province in Russia, demonstrated that the thionic bacteria oxidised the sulphide ores under low concentration conditions of oxygen, mineral nitrogen, phosphorus, low temperatures and uneven and limiting moisture contents. Karavaiko et at. (1974) further found that the distribution of thionic bacteria was regulated by the pH of the environment and the finenessof . the ores, and that various natural mutants of the bacteria seem to be resistant and active only under those conditions to which they adapted in the deposits.

High concentrations of heavy metals in plant litter inhibit the activity of decomposers. They retard mineralization, cellulose and starch decomposition and enzyme activity, (Tyler, 1974, 1975, 1976) and result in smaller microbial populations (Jordan and Lechevalier, 1975).

Williams et at. (1977) studied the decomposition of vegetation growing on metal mine wastes contaminated with high concentrations of lead and zinc. High concentrations of lead and to a lesser extent zinc accumulated in metal tolerant grasses. A greater accumulation of litter, less humus formation, reduced soil urease and smaller microbial and microfaunal populations were evidence of the effects of heavy metals on the soil microflora and subsequently on organic matter breakdown and nutrient recycling. 28.

Contamination of vegetation growing on fluorspar mine tailings in Britain was found by Johnson (1976), when harvested material from trials exhibited concentrations of heavy metals and fluoride. The uptake of copper and zinc by the roots of metal-tolerant AgicaSt ,66-tenu-i4 plants, with accumulation of metals in the cell wall fraction, has been reported by Bradshaw et at. (1965) and Turner (1970). High concentrations of lead and zinc were found in the A. tenui.4 plants growing on mine wastes, especially in root tissues (Williams et at., 1977). The products of plant material decomposition may themselves complex with or partially solubilize heavy metals (Bloomfield et at., 1976).

Deselm and Shanks (1973) studied the accumulation and cycling of organic matter and chemical constituents during early vegetational succession on a radioactive waste disposal area in Oak Ridge in the Tennessee Valley, U.S.A. They found that cesium-137 and strontium-90 were the main radioactive materials taken up by the plants. Wallace et ca. (1977) conducted glass house trials and studied the effect of cadmium on plant growth. They found significant reductions in growth at low cadmium concentrations and interrelationships with micro nutrients such as iron, zinc, manganese and copper. Synthetic chelating agents were found to increase the uptake of cadmium with further decreased yields.

The selection of metal tolerant species of vegetation has been investigated in an endeavour to successfully rehabilitate toxic wastes. Smith and Bradshaw (1970 , 1972) have reported considerable success in the selection of metal tolerant strains of plants, especially Aymotirs and Fez-taut species for the revegetation of mine residues in Britain, which contained high concentrations of lead, copper and zinc. Gadgil (1969) also studied the heavy metal tolerance of AgA04ti,6 and FeAtuca as well as Anthwta►thum species on similar spoil sites and found that inorganic and organic additives had no direct ameliorative effects which could be related to degree of tolerance. Johnson (1976) found whilst investigating metal tolerance in vegetation growing on fluorspar tailings in Britain that red Fescue(Feztuca AubAa)and Vernal sandwort(Minuattia VeAna)usually dominated calcareous sites while common bent grass(A. tenuiA) usually dominated acidic and metal contaminated sites.

2.3.2.3 Antimony

Information on antimony and its environmental effects are not well documented. A bibliographic search by computer of six world data banks revealed very little information. Published information on antimony is mainly confined to its use in the medical field, and its presence in food

stuffs. 29.

Vinogradov (1959) reports that the antimony content of rocks is -5 very small, in the order of 10 %. Bowen (1966) found the concentrations of antimony, range from 0.05 ppm in standstone rocks to 1.5 ppm in shales, with igneous and limestone rocks containing 0.2 ppm.

Antimony is enriched in sulphide minerals and during oxidation enters into sediments and soils (Vinogradov, 1959). Concentrations of antimony are usually associated with high arsenic concentrations in sulphide ores and have been used as path finders for gold (Hawkes and Webb, 1962). Concentrations of 50 ppm of antimony derived from stibnite have been reported to extend over several kilometres of sandstone and sands in Rhodesia (Wild, 1974a). As a result, gold mine spoil materials commonly contain hundreds of ppm of antimony and may be as high as 50,000 ppm in isolated dumps (Wild, 1974b; Hill and Nothard, 1973).

Little is known of the global cycling of antimony (Peterson,e.t at., 1981) However, Klein et at. (1975) calculate that weathering and mobilization 3 contributes 5 x 10 tonnes antimony per year to the environment. Seasonal fluctuations of antimony in the air have been measured and found to be especially high in winter months (Peirson and Cawse, 1979). It is, however, present in substantial concentrations in precipitates from hot springs, boreholes and geothermal waters in which it plays an important role in co-precipitation reactions of antimony sulphide (Sabadell and Axtmann, 1975). Concentrations of up to 12.6 ppm antimony have been found in Bamboo leaves which were growing near a geothermal area (Nakahara et at., 1977).

OToole et at. ( 1971) found antimony contamination of soils and plants by stack dust and smelter fumes from a gold mining and refinery site at Yellow Knife, N.W. Territories. Up to 280 ppm antimony was recorded near the stack while grass contained up to 15.4 ppm, exceeding the background levels in adjacent uncontaminated areas by one to three order of magnitude. Antimony contamination of surface soils by fallout has been reported near a copper smelter (Crecelius et at., 1974). Sdils contained up to 20 ppm and plants 14 ppm. This contrasted with background values of 3-5 ppm for soil and 3-4 ppm for plants (Lim, 1979). Pulverised fuel ash was found to have 4-5 ppm antimony and this increased with decreasing particle size (Coles et at., 1979). 30.

Sewerage sludge in the United States was found to have antimony concentrations ranging from 2.6-44.4 ppm (Furr et at., 1976) and 4.3- 15.9 ppm (Nadkarni and Morrison, 1973). Values of 15-19 ppm were reported by Wiseman and Bedri (1975) in Britain.

Very little is known about the details of mobilization and absorption of antimony in soils. Soluble antimony probably occurs as antimonate although complexes with humates are also possible (Valente, 1978). Antimonates are probably absorbed by the same minerals which bind phos- phate and arsenate (Peterson et at., 1981).

Little is known of the accumulation, metabolism and toxicity effects of antimony in plants. Gough and Shacklette (1976) omitted antimony from a major review of elements and their toxicity effects in plants, animals and man. However, antimony at 4 and 20 ppm in a solution culture was found to be toxic to cabbage plants grown under water culture conditions. Toxicity was characterised by the appearance of a purple colour on the leaf veins and mid rib of the outer leaves (Hara et at.,. 1977). Palladin and Cohnstamn (1914) found that respiration of etiolated shoot tips of vetch was stimulated by 1% of antimony tartrate while the respiration of germinating peas was decreased by the same concentration.

Fredrick (1941) reported on the toxicity of antimony in animals and humans and found, in general, antimony to be more toxic than lead. It is therefore, surprising that it is not listed in the "Clean Waters Act" of N.S.W. and an acceptable concentration level stated. Hara et at. (1977) state that the chemical properties of antimony are analogous to those of lead.

2.3.2.4 Arsenic

Considerable literature is available on arsenic and its toxicity effects in soils. Arsenic concentration in igneous rocks average 2-3 ppm but shales, clays and phosphate rocks generally have much higher concentra- tions (Levander, 1977). Vinogradov (1959) states that arsenic is carried down by precipitates of iron hydroxides and sulphides during the formation of sedimentary rocks and can be precipitated from the atmosphere. 31.

Arsenic can be emitted into the atmosphere from high temperature sources such asvapour from coal fired power generation plants, burning of vegetation and volcanism. (Peterson et at., 1981). Estimates of 8 -1 industrial and fossil fuel emissions are high, 780 x 10 g arsenic yr 8 -1 compared with mining, 460 x 10 g arsenic yr and continental and 8 -1 volcanic dust fluxes, 28 x 10 g arsenic yr (Mackenzie et at., 1979).

In a reducing sedimentary environment, arsenate is reduced to arsenite and methylated to methylarsonic acid or dimethylarsenic acid. These compounds may be further methylated or reduced to trimethylarsine or dimethylarsine and lost to the atmosphere (Wood, 1974). Mackenzie et at. (1979) calculated that 210 x 10 8 g arsenic are vaporited annually from the land surface by these processes.

High concentrations of arsenic have been found in geothermal areas (Lancaster et at., 1971; Reay, 1972; Fowler, 1977). The soils and ground water of these areas contains such high concentrations of arsenic that the health of stock is affected (Grimmett, 1939; Grimmett and MacIntosh, 1939).

The presence of arsenic in lead, zinc and copper ores and in most pyrites, leads to the pollution of the environment in the vicinity of smelters, treating such ores (Crecelius et at., 1974; Ragaini et at., 1977). Gold ores also contain significant levels of arsenic, mainly as arsenopyrite, giving rise to pollution near gold mines and refinery operations (OTool et at., 1971; Rosehart and Lee, 1973; Jervis and Tiefenbach, 1979).

Arsenic concentrations in tailings as high as 300-5000 ppm have been found during gold mining in Rhodesia (Wild, 1974a). The arsenic was usually associated with antimony in sulphide ores. Arsenic mine dumps and smelter slag heaps containing high concentrations of arsenic and other metals in the United Kingdom have been studied by Porter and Peterson (1975, 1977a, b) and in Rhodesia by Hill and Nothard (1973), Wild (1974b). The spoils in the United Kingdom had a pH of 2-4 and in Rhodesia of 8-9. The United Kingdom spoils have a higher arsenic toxicity level due to their low pH. 32.

Hutchinson and Kuja (1979) grew Dewhampisia ce4pito4a on spoils containing 5,200 ppm arsenic at a pH of 1.8-2.0 and found that the plants contained 3,200 ppm arsenic. The same species grown on a spoils dump with a pH of 6.9-7.0 and a arsenic concentration of 72,000 ppm contained only 300 ppm. Porter and Peterson (1975) found arsenic concentrations of 1p00-3p00 ppm in mature A. tenct4:4 leaves harvested from mine sites throughout the United Kingdom. Mine spoils in Rhodesia containing high levels of arsenic are mainly devoid of vegeta- tion (Wild and Wiltshire, 1971a, b).

Arsenic concentrations in coal from the United States, Australia and the United Kingdom range from around 0.5-93 ppm, with coal from the United States containing the highest concentrations (Lim, 1979). Arsenic exists largely as arsenopyrite in coal (Duck and Himus, 1952; Swaine,1975).

Concentrations of arsenic of up to 2,000 ppm were recorded in top- soil adjacent to a lead smelter (Temple et at., 1971). Soils derived from quartzite containing a number of mineral veins near Brisbane contained 100-200 ppm arsenic and produced reduced growth and toxicity symptoms in banana leaves (Fergus, 1955). Affected leaves contained up to 2 ppm arsenic.

Regardless of the form in which the arsenical is applied, it is eventually oxidized and metabolized to arsenate (Woolson, 1973). The form of arsenic in the soil is important. Machlis (1941) reports that pentavalent arsenic is less toxic than trivalent arsenic, hence 10 ppm of sodium arsenite is lethal to a tomato plant but the same plant can withstand over three times the concentration of sodium arsenate.

Insoluble or fixed arsenic may become available to plants (Rosenfels and Crafts, 1939). For example, lead arsenate was found to be very insoluble. However, insolubility was roughly proportional to the percent- age of soluble salts in the soil, with acid salts and those which hydrolize with an alkaline reaction increasing lead arsenate solubility the most (Stewart and Smith, 1922).

Arsenic toxicity is greatest in lighter textured soils (Gill, 1936; Rosenfels and Crafts, 1939; Machlis, 1941; Vincent, 1944). Soils low in organic matter are also more susceptible to arsenic toxicity (Vincent, 1944). 33.

Contamination can result from the use of arsenic based herbicides and insectofungicides, especially in the orchard industry (Gill, 1936; Vincent, 1944; Johnson and Hiltbald, 1969; Woolson et at., 1971a). In studies of orchard soils, levels of arsenic up to 2,500 ppm were found to be phyto- toxic to plants (Woolson et at., 1971b). However, the degree of toxicity depended on pH, form of arsenic present, and the concentration of phosphate iron, aluminium and the organic matter content (Jones and Hatch, 1937; Rosenfels and Crafts, 1939; Kardos et at., 1941). Phytotoxicity is also dependent upon the sensitivity of the plant (Deuel arid Swoboda, 1972a; Woolson, 1973).

Sodium arsenate has been widely used as a weed killer and soil sterilizer, while arsenic acid has been used extensively as a cotton desiccant (Woo, 1965; Steevans et at., 1972; Levander, 1977).

The reduction of toxicity by the addition of phosphorus has been reported by Rumberg et at. (1960), Bishop and Chisholm (1962), Benson (19531, Hurd-Karrer (1936); and Woolson et at. (1973). Arsenate but not arsenite uptake is affected by phosphorus (Clements and Munson, 1947). Arsenate is chemically similar to phosphorus and hence competes for the same sites in soils or transport systems (Dean and Rubins, 1947). Hurd-Karrer (1939) found that arsenic injury is a function of the available phosphate concen- tration with the protective arsenic phosphorus ratio in nutrient solutions being near 1:5.

Batjer and Benson (1958) found that zinc-iron chelates were helpful in overcoming arsenic toxicity of peach trees, while Overlay (1950) found additions of dry manure and wheat straw were effective.

Plant survival on arsenical mine spoils has been proven to be due to the evolution of tolerance to arsenic (Rocovich and West, 1975; Porter and Peterson, 1975). In the United Kigdom, AgA04t4:4 plants were specific to arsenate tolerance on arsenic toxic mine spoils (Porter and Peterson, 1977a). No conclusive evidence on a mechanism of arsenic tolerance has been found (Peterson et at., 1981). However, it may be possible that mycor- rhizal association with arsenic and plants reported by Benson et at. (1980) can ameliorate arsenite toxicity by increasing phosphate supply or inhibiting arsenate uptake into the plant (Peterson et at., 1981). 34.

Rosehart and Lee (1973) reviewed arsenic and its removal from gold extraction plant effluents. Chemical precipitation, sorption processes such as ion exchange and activated carbon absorption and reverse osmosis are the main methods of arsenic removal. Chemical precipitation proved effective and arsenic together with other heavy metals were removed when the pH was raised above 10. The removal of arsenic was success- fully achieved using 0.5 m Nact or a mixture of _NaCL and Na0H.. Activated carbon was less effective in removing arsenic than other methods but loaded arsenic was easily removed by pH adjustment. Whilst effective, the high cost of reverse osmosis, considering the volumes involved is prohibitive.

2.3.2.5 Salinity

High levels of salinity are often associated with heavy metal con- centrations in mine wastes. Craze (1977) reports that the formation of sulphates of iron, copper, lead and zinc caused high salinity levels at Captains Flat mine in New South Wales. Saturated extracts of slimes and solids had electrical conductivities of 31 m • acm and. 62mS:cm, respect- ively with soluble sodium and potassium contributing 28 and 16 pm and 57 and 33 ppm respectively.

In mine wastes which contain sulphides such as pyrite and carbohatet of calcium and magnesium, salinity may be a problem. When the pyrite oxidises to give sulphuric acid, it is neutralised by the carbonate to give calcium and magnesium sulphates. These sulphates are soluble and in arid climates may accumulate and cause salinity in surface layers of the waste dump as moisture evaporates. The critical level for normal plants is when the conductivity of the soil solution reaches 8 mScm-1 (Bradshaw and Chadwick, 1980). Rhodes grass(Cktak4A gayana)is one of the most salt tolerant grasses being able to tolerate an electrical con- -1 ductivity of 8m S (cm without a yield reduction, while sub tropic/t1 legumes such as siratro can only tolerate an E.C. of 3.3niSam before yields decrease (Bell and Evans, 1980). -1 Electrical conductivity readings as high as 63m.Scm have been found in some Colarado mine wastes by Nielson and Peterson (1972) but even at such high salinity levels they felt that the osmotic effects of high salinity were not as detrimental to plant growth as the toxicity effects of heavy metals. 35.

Bell and Evans (1980) found that the electrical conductivity of nickel refinery wastes at Yabulu in North Queensland was sufficiently high to restrict growth of all but the very tolerant vegetative species. 1 Leaching, effectively reduced the salt levels from 6.4 m cm to an accept- -1 able level for plant growth of 0.72 m S cm. .

Leaching with ionized water was found to be successful for the removal of excess soluble salts from bauxite refining products of fly ash, red sand and various mixtures of ash, sand and red mud (Parsons, 1975). -1 Electrical conductivity levels of saturated extracts of less than 0.4 mScm were readily achieved by leaching and as such the reduction of salinity by field irrigation was considered practicable.

At Mount Isa mines in Queensland, where evaporation greatly exceeds rainfall throughout the year, high surface salt concentrations cause major problems for plant establishment (Farrell, 1977). Leaching of mine 1 wastes at Mount Isa to a conductivity level of a32.TIS m produced good vegetative growth (Hunter and Whiteman, 1975b).

The use of gypsum in replacing sodium in sodic soils is well proven (Davidson and Quirk, 1961; Bridge and Tunny, 1973). Doering and Willis (1975) used highly soluble calcium nitrate in laboratory tests to reclaim sodic strip mine spoil material. By using water with a sufficiently high electrolyte content, the hydraulic conductivity of the spoil material was sufficiently high to permit the replacement of sodium on exchange sites by divalent cations. Although effective, the process could not be recommended on a large field scale because of the extreme cost.

2.3.2.6 Mine Drainage

Mine drainage, especially when it contains heavy metals, is a significant problem to be overcome in mine waste rehabilitation. Polluted water can have deleterious effects on the biological activity of rivers and streams and on crops when irrigation is used.

Schmidt and Conn (1971) have summarized the main mine drainage problems and have divided them into two categories. Firstly, acid mine drainage which is characterised by acidic pH, high metal content, high dissolved solids and lack of organic matter. Secondly, the tailings pond discharges which are characterised by an alkaline to neutral pH, high suspended solids, significant organic content and mill reagents and possible high levels of sulphur salts together with significant levels of heavy metals. 36.

Studies throughout the world on eliminating acidic seepages from sulphide containing rocks have attempted one of the following techniques:

1. Exclude water from contacting the ore by covering rocks with vegetation soil or spraying with a sealing compound.

2. Exclude air from contacting the water and sulphide material, for example by using an atmosphere of nitrogen.

3. By adding a bactericide to kill the sulphide oxidizing bacteria.

4. Reduce the acidity of mine drainage water by the addition of chemicals.

Mine drainage pollution of Captains Flat in New South Wales, degraded the biology of the Molonglo River and reduced the usefulness of the stream (Anon., 1974b). The main sources of pollution were identified as erosion and leaching of the waste dumps, mine water flowing from the main spring and river bed sediments derived from erosion and collapse of mine waste dumps. The oxidation of the complex ore of pyrite, chalcopyrite, sphalerite and galena produced sulphuric acid as well as soluble copper and zinc sulphates and insoluble lead sulphate. All products except for the lead sulphate were readily leached and flowed with the mine drainage into the Molonglo River. Remedial measures devised included the reshaping of the dumps and the diversion of run-off water; covering the reshaped dumps with consecutive layers of clay, rock and soil; and revegetating the reshaped and covered area (Craze, 1977).

Wittman and Forstner (1976a,1977) studied the problems cf a high heavy metal content in mine drainage at the Witwatersfrand gold fields, the Rustenberg Platinum mining area and the Klerksderp West Wits and Evander gold fields in South Africa. At the former site they found that the mine drainage occurred from not only the mine itself but from the waste rock dumps and tailings areas. The latter two sources contained sulphides and/or sulphate salts, and exhibited very low pH values. The highest measured contents of dissolved manganese, iron, cobalt, nickel, copper and zinc exceeded the normal surface water values by a factor greater than 1,000. Enrichment of dissolved chromium, cadmium, and lead were not widespread-but respective values were still alarmingly high. 37.

Mine drainage from tailings in the Rustenberg platinum area in South Africa revealed low levels of metallic and non-metallic ions. However, water from the hydro metallurgical process used in the refining of platinum ores contained appreciable amounts of heavy metals.(Wittman and Forstner, 1976a, b, 1977).

Mine drainage from the I

Chapman (1981) found that the most common method of treating mine drainage is to neutralize the effluent with lime, limestone or soda ash. The increased pH causes the heavy metals to precipitate as hydroxides and carbonates. The treatment of drainage from rock dumps and tailings dams has to be continued long after mining has ceased due to continued leaching.. One measure under consideration is the planned construction of dumps by locating them on areas of basic rocks which would promote neutralization of acids and absorption of metal ions.

Houston and Warren (1976) stressed the need to locate tailings disposal areas at the Mount Gunson uranium mining area in South Australia away from streams and water courses so that drainage and inadvertent spillage would not cause pollution. 38.

The writer has observed that acid mine drainage from the Brukunga pyrite mine in South Australia resulted in major stream pollution and caused damage to vines that were irrigated with the polluted water. At Brukunga a two stage process was investigated in which caustic mud was added to mine water in the first stage and lime to the second stage (J.Lackey,personal communication). This produced seepage water with low heavy metal concentrations and a pH increase from 2.6 to 10. After successfully neutralizing the contained seepage, it was planned to replace neutralization with evaporation pans as it was found acid mine drainage evaporated at a slightly faster rate than water. The main disadvantage of both treatments is that they do not treat the source of the problem, namely the acid producing ore.

The treatment of acid mine drainage containing iron as outlined by Burke and Cudmore (1972) involves the following stages:

1. Neutralization, which raises the pH to an acceptable level before discharge. This creates the oxidation of ferrous to ferric iron.

2. Aeration, which allows removal of carbon dioxide from reagents.

3. Clarification, wherby the solids are removed by settling in large ponds and the clear water discharged.

2.4 VEGETATIVE ESTABLISHMENT

Vegetative stabilization, usually has advantages over physical and chemical methods in terms of economy, efficiency, aesthetic value and long term productivity of the area. A vegetative cover which is permanent, self sustaining and maintenance free is the optimum in most rehabilitation projects. To achieve a self sustaining vegetative cover, amendments and/or specialised establishment techniques are usually required.

The re-establishment of natural plant communities on areas which have been totally disturbed, as occurs with surface mining, is a slow process (Dressler and Sowards, 1975). Mitchell (1959) studied soil structure, fertility and vegetation on tin mine tailings in Malaya and found that after 20 years, natural fertility had only risen to one fifth or less of adjacent unmined areas. 39.

Errington (1975) has shown that the lack of adequate seed dispersal may be an important factor in the slow natural regeneration of large scale disturbances. The consistent negative relationship between slope, steepness and volunteer vegetation is probably due to instability of the seedbed on steep slopes on mine spoils (May et a., 1971; Errington, 1975).

Shetron and Duffek (1970) studied the potential of vegetative growth on infertile iron mine tailings. In controlled areas the growth of all grass and legume species was poor with plants stagnating at a height of 6 cm and covering only 20-25% of the surface area. They concluded that results reflected the very low levels of necessary plant nutrients combined with a pH of 7.8 to 8.1. Adequate fertilizer applications produced a dense sward in one year. Working with tailings banks in Canada, Mackenzie (1964) considered pH and nutrition to be important. Vogel (1975) working with strip coal mine spoils in Kentucky, United States, found that although the survival of trees was not significantly reduced by herbaceous cover during the first three years, height growth was. The effect of grass cover compared to grass plus legume on tree growth was marginal during the first three years, however significant tree growth occurred in the fourth year, on the tree, grass plus legume treatment. This increased growth was attributed to the increased nitrogen status.

Fisser and Ries (1975) stress the desirability of conducting detailed resource studies prior to mining. They conclude that the only logical rehabilitation procedure for establishment of a stable biological system appeared to be one which will attain a native short mixed grass cover. This type is considered to be most successful because:

1. A mixed species grassland provides for a continuing grazing resource.

2. Native species are genetically and climatically adapted to normal environmental fluctuations such as seasonal and periodic droughts and seasonal temperature fluctuations. 3. A mixture of native species provides a self maintaining ecologic- ally stable growth cover resistant to grazing pressure, low water and nutrient availability.

4. Native species propagules are already present in the area in the form of seeds, root stocks and rhizomes which may be used to achieve an "advanced" successional stage which will be important in stabilizing soil against wind and water erosion as well as allowing grazing productivity at the earliest possible time. 40.

This approach would surely depend on site and climatic conditions.

Although the use of native species is usually highly desirable, the collection of native seed is difficult, and subsequent germination can be very poor. Variations in seed set as affected beseasonal conditions, seed dormancy and low viability of harvested seed are common problems (Quilty, 1975).

2.4.1 Amendments

Many ameliorative treatments, too numerous to discuss in detail have been used in the reclamation of mining residues. The majority of these, aim at ameliorating the wastes to create a better physical or chemical environment to achieve increased vegetative establishment and reduced erosion and siltation. They vary from the very complex chemical treat- ments to various additives of fertilizer, limestone and rock phosphate to mulching materials such as pulp fibre, straw, woodchips, burlap, sawdust and effluent products. A number of amendments used for erosion control have previously been mentioned in section 2.3.1.4.

Unfavourable textures can be improved by the incorporation of organic materials such as straw, wood by products, broiler litter, sewerage sludge or animal manures. Many of these organic residues provide essential nutrients, particularly nitrogen, in slow release form. They also benefit rehabilitation by complexing heavy metals.(Williamson and Johnson, 1981).

Cyprus pine(CaLitk.i4 CauMettaA.Wsawdust appeared to have a suppresive effect on germination and growth during acid mine rehabilitation trials at Cobar in N.S.W. (Green, 1981). However, at Broken Hill in N.S.W., sand-sawdust mixtures proved successful for establishing tree seedlings prior to planting on tailings areas (Quilty, 1975). The sawdust, derived from coastal timbers, carried spores of mychorrhizal fungus which enhanced the breakdown of humus and the release of plant nutrients. Sawdust Increased the water holding capacity of iron mine tailings in Britain, but complete plant mortality resulted due to a lack of adequate plant nutrients (Shetron and Duffek, 1970). The authors found, however, that sawdust and fertilizer gave good establishment of alfalfa and clover. Whilst sawdust was beneficial in improving the water holding character- istics of the tailings, the mechanical operation of discing it into the surface destroyed the fine texture surface layers which acted as water and nutrient reservoirs. 41.

Bennett et at. (1961) tested rapid and slow setting asphalt emulsions in the United States to evaluate their effect on grass establishment. The rapid setting emulsions have the best moisture conservation and thus seedling establishment. Soil temperatures, to a depth of 20 cm were increased by both types of emulsions. Collis - George et at. (1963) achieved similar results during studies on bituminous mulches near Sydney in N.S.W. They found that the overall effect of bitumen was to raise the temperature and that at application rates greater than 4.5 litres per square meter the emergence and establishment of plants was restricted. Nebauer and Good (1971) and Jaabuck and Muzzell (1971) found bitumen emulsion and straw very effective methods of establishing vegetation especially on embankments.

Straw or organic plant residue of some form is the most widely used material for mulching to enhance vegetative establishment. Besides creating a more favourable environment for vegetative establishment by increasing moisture retention and temperature, it aids in the protection of the surface from rainfall erosion. The incorporation of residues from cereal crops was used to improve soil structure at the Cyprus Pine Copper mine in Arizona (Ludeke, 1973). -1 Straw mulch applied at a rate of 4 t ha proved successful in establishing vegetation on uranium mine tailings in New Mexico (Reynolds et at., 1978). Ogram and Fraser (1978) found straw to be superior to jute mesh for vegetative establishment on high sulphide tailings at Flin Flon, Manitoba, Canada, as the latter material whilst initially effective.was soon rendered useless by blowing tailings. However, Jacoby (1968) found a combination of straw mulch and jute mesh gave the highest seedling -1 density. Straw mulch applied at a rate of 4 t ha proved successful in establishing vegetation on uranium mine tailings in New Mexico (Reynolds et at., 1978).

Schuman Qt at. (1976) found that direct seeding into standing cereal stubble grown on both metaliferous and coal mine wastes in western United States has many advantages over straw residue spread on the surface. Standing stubble, in addition to remaining longer resulted in less tempera- ture flucuations at shallow depths and produced a 25% greater cumulative water infiltration. 42.

A number of materials and techniques have been tried at an experi- mental stage to study their potential to enhance vegetative establishment on denuded sites such as mine wastes. For example, the effect of a white styrofoam granule mulch on the growth of sweet clover was studied in glass house trials by Asford and Reed (1962). The styrofoam signifi- cantly increased dry matter yield and uptake of phosphorus. The styrofoam also gave a greater dry matter per unit water yield than bare soil surface plots. The treatment of coal mine water in the United States with calcium carbonate produced a precipitate known as "yellow boy". This substance contains traces of minerals including phosphorus and is useful as a soil conditioner and fertilizer (Goddard, 1970). Injection of a peat-wood cellulose slurry mixed with fertilizer and limestone has proved successful in establishing trees on mine waste dumps in the United States (Sheldon and Bradshaw, 1976). The use of supplemental root transplanting techniques and paper tubes for plant establishment has proven successful in the research stage (Hodder, 1973).

Gray (1976) during studies into the rehabilitation of the Maslins Beach sand mine in South Australia found that cellulose mulch at the rate -1 of 1,000 kg ha was useful. A reduction in the rate can be made if bonding agents are used, however a 15% reduction in germination can be expected. Gray (1976) also reports on the use of enzyme ingredients which have the main aim of increasing surface root penetrability.

Green (1981) used grass cuttings, sawdust and slag as mulches during rehabilitation experiments on acid mine tailings at Cobar in N.S.W. The grass mulch proved the most successful and had the added advantage of introducing other species of vegetation. After two years, visual estimates of vegetative coverage was grass mulch 80%, slag mulch 70% and sawdust mulch 40%. Granulated sedge peat proved greatly superior to sand or soil for decreasing the toxicity of chromate wastes to Lotium pevtene, iron sulphate also decreased toxicity at a chromate smelter in Britain (Gemmeli, 1972).

Techniques of hydromulching and hydroseeding are detailed by Gray, (1976) and Jaaback and Muzzell (1971). Hydroseeding is a specialised method of applying seed and fertilizer and other substances such as 43. chemical stabilizers to surfaces. The materials are mixed in a tank and sprayed under pressure through a nozzle which can be directed at the required surface. The term hydromulching refers to the same machine when it is used to spray a mulch, for example, wood pulp. Such techniques are especially useful for revegetating inaccessible and long steep-batter slopes (Connally and Brook, 1983).

Henry et at. (1981) found hydroseeding and hydromulching to be the most favoured vegetative establishment techniques on surface mined land in Kentucky. However, it was noted that a comparison of these techniques with other methods of vegetative establishment revealed no significant differences in stands after three seasons in either eastern or western Kentucky. The most important benefit of the hydroseeder is the establish- ment of a favoured micro environment for germination and early establishment, and its ability to seed and mulch in normally inaccessible areas, especially in steep and high slopes. When using the hydroseeder care must be taken to ensure adequate legume establishment, since these species are very sensitive to the hydroseeding process (Roberts, et at., 1982). This is predom- inantly due to the inability of the machine to handle inoculated legume seed as the inoculant usually detaches itself from the seed during the mixing process. Kay et at. (1977) carried out experiments on the effect of presoaking of seeds and seed damage in the use of hydroseeders in an attempt to increase plant establishment.

Synthetic plastic emulsions such as acrylic and styrene butadiene proved successful as binders to hold soil, seed, fertilizer and mulches such as straw and wood fibre in place and achieved increased vegetative establishment on denuded sites in the United States (Fowler and Maddock, 1974). Brown et at. (1979), also obtained very good vegetative establish- ment when an acrylic emulsion was applied to wood fibre mulch during hydroseeding. Cost savings were produced with no decrease in vegetative establishment when acrylic emulsion was used in conjunction with wood fibre mulch as apposed to the mulch by itself at a higher application rate. 44_

The term topsoil is generally used to apply to the A horizon of the soil profile and in particular the Al horizon. It is this material which is usually organically coloured and forms the upper most layer of the soil. Topsoil is universally regarded as having advantages over subsoil or mine spoil material for vegetative establishment. Compared to the latter, it is usually better structured chemically more fertile and its physical properties provide for a better soil-water-plant relation- ship (Watkins, 1981).

The benefits of topsoil for mine waste rehabilitation have been recognised by many governments throughout the world. For example, in N.S.W the topdressing of coal mine overburden is a condition attached to the Right to Mine. Conditions pertaining to topsoiling are also incorporated into a mining lease when granted for metaliferous mining within N.S.W. In the United States, environmental protection performance standards enacted as part of the Federal Surface Mining Control and Reclamation Act of 1977 - Public Law 95 -87, requires that the A and B horizons of a natural soil be segregated and replaced when prime farm land is disturbed by surface mining for coal. However, it is possible to use alternative material to the B horizon provided that it can be shown that it is both texturally and chemically suitable and to be equal or more favourable for plant growth than the B horizon (McSweeney et at., 1981).

The depth of topsoil on a great number of mining sites is very limited. For example, in soil profiles developed from the Permian Age sediments in the Hunter Valley in N.S.W the topsoil is generally very limited and may be only 2 cm thick (Bradshaw and Chadwick, 1980). Invariably lower horizon material is striped and incorporated during the removal operation. Elliott and Veness (1981) working in the Hunter Valley of N.S.W developed a key for the recognition of suitable material which can be mixed with topsoil to provide suitable topdressing material for the rehabilitation of coal mine overburden. The key is based on the recognition and interpretation of the following soil characteristics, structure, coherence, mottling, microstructure, ped strength, texture, gravel and sand content, pH and soil colour. The key has proved very useful in the identification of suitable subsoil or B horizon material. 45. Miyamoto a at. (1975) working with coal overburden in north western New Mexico and Schuman and Taylor (1978) in studies on coal overburden in Wyoming in the United States found that by studying biomass production, material other than that from the Al horizon can be suitable as a plant growth medium. There are conflicting views on the suitability of different textured material for topdressing. For example, Junor (1968, 1978) in studies on coal ash rehabilitation and denuded earthen embankments indicated that topdressing material of any texture could be used in revegetation. However, Schafer (1979) found following studies on coal mine wastes that materials with textures coarser than sandy loam were less desirable for use in strip mine reclamation than medium textured material.

The inclusion of undesirable subsoil material will have adverse effects. A high clay content usually predisposes the material to surface sealing and available moisture limitations for revegetation. Poorly structured material with a high bulk density may give rise, to mechanical impedance and aeration problems for plant growth. It is therefore apparent that the selection and subsequent treatment of the topsoil material is of paramount importance and it should not be merely assumed that the material on the surface layer of the soil is the most desirable. Pre mining investigations are therefore essential. The characterization of soil material by visual appraisal and analytical methods is necessary to ascertain its desirability and to ensure that during the mining operation provision can be made fdr the separation of different soil layers and adequate stock piling of the desired material.

In a study of the rehabilitation potentials and limitations of surface mined land in the Northern Great Plains in Montana and Wyoming in the U.S.A.,. Packer (1974) concluded that the productivity and stability characteristics of surface soil materials was one of the three major environmental factors influencing the potential for rehabilitating surface mined land. The others being the suitability of native plant species for plant cover re-establishment and, the amount and distribution of ,recipitation. A similar study was undertaken, by Houston and Warren (1976) at the Mount Gunston Uranium Mine site in South Australia.

The stockpiling of topsoil for long periods is not recommended because the resulting compaction and oxidation of organic matter will effect soil structure (Russell, 1961). The loss of structure and fertility will reduce the water and nutrient status of the material (Bradshaw and 46.

Chadwick, 198Q). Quilty et at. (1978) suggest that grass seed viability will be improved by storage of topsoil in large heaps, however, Elliott (1981) states that as the relative humidity of the soil atmosphere rarely falls below 98% and grass seeds are best stored at relative humidities of 15-20% stock piling would be expected to reduce green seed viability.

Stockpiling of topsoil, as used in coal mine rehabilitation in the United States has been studied by Miller and Cameron (1976), Reeves et at. (1979) and Singleton and Williams (1979) to determine its effect on the physical, chemical and biological parameters. They found that the major changes occurring in stockpiled topsoil are the reductions in soil fungi, mycorrhizae and other micro-organisms. Davidson (1976) states that mycorrhizae play a particulary important role in the phosphorus nutrition and water uptake of plants.

The depth of topsoil to be used in mine rehabilitation will be influenced by the quantity and quality of the material available and the chemical and physical properties of the mine waste material. Top- soiling, whilst necessary in the majority of cases is a costly operation, and therefore the choice of the optimum depth to be applied requires strong consideration and investigation. Gillham and Davies (1972) concluded that an optimum depth of topsoil on fuel ash lagoons at Besthorpe in Nottinghamshire, England was 8 cm and there was nO benefit to be gained by mixing the fuel ash and soil together. Hodgson et at. (1963) made similar observations following a study of crop performance as a result of various soil depths on pulverised fuel ash in England.

Schuman et at. (1980) found that during studies on coal mine wastes in the United States that infiltration was greatly increased with a covering of topsoil. Cumulative infiltration was greatest with a 40 cm topsoil depth. They found that soil water storage was inversely related to topsoil thickness because the wastes had a greater water holding capacity than the topsoil. No added benefits were derived with the addition of a further 20 cm of topsoil. Power et at. (1976) found that 6 cm topsoil coer reduced run-off by 47% and hence greatly increased infiltration on sodic strip mine spoils. When the spoil was not covered by topsoil, the cumulative intake of water was only 44% of that where 6 cm of topsoil was 47. placed over the same spoil. Studies by Bauer et at. (1978) and Gilley et at. (1976) found that on sodic strip mine spoils in the United States the maximum topsoil depth required for adequate infiltration and water storage was 76 cm while Barth (1980) found water infiltration on similar wastes increased with increasing soil thickness with a maximum being reached with 40 cm of topsoil.

Mechanical roughening or cultivation of sodic mine spoil at a number of sites in western north Dakota before topsoiling did not greatly increase infiltration Gilley et at., 1976). This meant that moisture was limited to the 15 cm of topsoil. Total water storage and hence water availability was reduced. The deep ripping of bauxite mine pits in the Darling Range in Western Australia was found necessary prior to topsoiling to ensure an adequate depth of root for trees. Without ripping, the tree roots could not penetrate the compacted layers and the trees were felled by the strong winds (R Nunn, personal communication). McGinnies and Nicholas (1980) found that a major portion of the plant root system on coal mine spoils in Colarado U.S.A were limited to the topsoil. Barth (1980) concluded that the restricted root development was due to the physical and chemical characteristics of the spoil. The concentration of the plant roots in the top layers encourages the plants to be shallow rooted and susceptible to drought (Bradshaw and Chadwick, 1988).

Power et at. (1981) in a study of topsoil depth and the mixing of A and B horizon material on coal mined land in north Dakota, U.S.A found that the highest yields of most crops occurred where 20 to 60 cm of top- soil was used. The response for 20 cm of topsoil was similar to that when 60 cm was used, thereby indicating little benefit for the more costly increased depth. When the topsoil and subsoil material was mixed, yields were variable but did not achieve the same maximum yields of those species grown in topsoil. Barth (1980) achieved similar results to Power et at. (1981) during a study of topsoil depth of 0 to 150 cm on 14 active coal mines in the Northern Great Plains of U.S.A. Biomass generally increased as topsoil thickness increased from 0 to 70 cm. However, minimal increased responses were achieved between 70 and 150 cm.

Topsoil can be a ready source of seed and rhizome material. Beauchamp et at. (1975) during a study on six coal strip mined sites in Wyoming, U.S.A found that although sufficient viable seed existed in the top 5 cm 48. of each site to provide potential revegetation, the germination of primary succession species was poor, thus necessitating the seeding or transplanting of desired species. Hodder (1977), made similar observations and noted that the type and quality of vegetation would be altered because most of the seedlings were those found in pioneer stages of secondary succession. Howard and Samuel (1979) reported that topsoil stripped and immediately respread is a good source of useful plants for revegetation, due to the transfer of roots and rhizome material. The topdressing operation may also result in the introduction of weeds or undesirable native species which are not suitable pioneer species (Doyle, 1976). Farmer et at. (1974) found that 47% of the total yield from a topsoiled plot on coal mine spoils in south eastern Montana U.S.A was in desirable grass species, the rest was in weeds.

Cornally and Brook (1983) found during rehabilitation studies at the Clarence coal colliery that by using ample topsoil (at least 20 em) over areas to be rehabilitated a pralific growth of understory shrubs and ground covers occurred naturally. They state that where ever possible, areas of undisturbed vegetation should be retained through- out the site as these act as seed sources, sight and noise screens.

It is apparent from the literature, that, although sewerage sludge and liquid effluent can posses problems of excess heavy metals, excessive salts, p athogens and an objectionable odoux,there are considerable benefits of both a physical and chemical nature to be gained from using such products on mine wastes, especially the poorly structured and inert fine tailings. The infiltration rates, hydraulic conductivity and water holding capacity values are usually increased while the bulk density values are decreased (Stewart and Webber, 1976). The improvement in soil structure is mainly attributed to the increase in the total organic matter of the soil (Anon, 1981).

Menzies (1973) following studies on waste management reports that nitrogen is the most important plant food element in sludge. On a dry weight basis the total nitrogen in sludge will range from 1-6% while phosphorus will be from 1-2%. He concluded that sewage sludge was a slow release organic fertilizer valued mainly as a soil conditioner. Whilst nitrogen is possible the most highly prized constituent of 49. sewage sludge it can be in excess. Field trials with sludge from the Bolivar effluent plant at Adelaide in South Australia showed that yields were reduced not by heavy metal toxicitybrut by a rapid release of nitrate nitrogen into the soil (Anon, 1981).

The composition of sewage sludges and effluents will depend on the waste treatment process, treatment plant operation practices and the source of the sewage. Therefore, depending on the physical characteristics and chemical constituents sewage wastes can have both beneficial and adverse effects. Heavy metal toxicity is potentially one of the greatest hazards (Menzies, 1973; Anon., 1976; Bennett et a-e.,1976; Dowdy et at., 1976; Martin et at., 1976). In addition to the dangers of heavy metal toxicities, excess salts in sewage can pose a problem. Salts such as ferric chloride, alum and lime are added to flocculate and settle solids during waste water treatment and considerable quantities remain in the treated effluent. An application of 225 metric tonnes per hectare of digested sludge from a treatment plant in Washington, D.C., increased -1 the electrical conductivity of a silt loam soil from 0.4 m S cm to -1 5.5 m S cm (Dowdy et at., 1976).

The effectiveness of sewage sludge on vegetative yield on mine wastes has been variable. Increased yields have been reported by Giordano et at. (1975), King and Morris (1972) and Lutrick (1974), while yield reductions -1 have been reported when sludge application was greater than 45-90 t ha (Lunt, 1959; Merz, 1959; Kelling et at., 1977). Pietz et at. (1982) found grain yields of corn (Zea mao L.) were significantly reduced by sludge application on calcareous strip mine spoil near Chicago in the United States. Spoil factors which affected the yields included, shallow rooting depth, soluble salts, moisture stress, and element interactions in plant tissue, sludge and spoil.

Restoration of acidic mine spoils with sewerage sludge was achieved by Stuckey et at. (1980). Sludge increased the pH of the spoils from 3.0 5.5 at the end of the first growing season. This enabled the establish- ment of an 85% vegetative cover_ after three growing seasons. Reed canary grass (PhataA.6 aAundinacea), switch grass (Panic.um A•agatUM), and orchard grass (Dactyt.iz gtomeitata) were the three most successful species established. 50.

Fuller et at. (1982) found that the application of sewage sludge to the surface of red mud (Bauxite residue) to be an inexpensive, effective ameliorative method for establishing a plant cover of alkaline tolerant grasses without costly chemical neutralization or fertilizer additions. The use of sewage sludge to successfully reclaim strip mine spoils in the United States has been reported by Kardos et at. (1979) and Sutton and Vimmerstedt (1974).

Sopper and Kardos (1972) conducted trials on strip mined spoils in the United States to evaluate the effects of sewage effluent and liquid digested sludge on planted tree and grass species. No vegetation survived on the untreated boxes while 3 cm of effluent plus 3 cm of sludge per week produced the best overall survival for trees and a 6 cm per week application .of both products produced the best germination and growth of grasses.

Stuckey et at. (1980) found during research at the Southern Illinois University, U.S.A that acid mine spoils with an initial pH of 3.0, an application of sludge increased the mean pH to 4.4-5.5 at the end of the first growing season. The data indicated that a 65 and 80% cover at the end of the first growing season was achieved when the pH was 5.1 and 5.5 respectively. In general, plants that established where the pH was greater than 5.5 accumulated lower quantities of metals than plants grown in spoils with a mean pH of less than 5.5. The latter findings on metal content are supported by the findings of Rorison (1973) and Massing (19741 who found that metal solubility was inversley proportional to pH.

Sewage sludge and liquid effluent have been used successfully to achieve increased vegetative growth on mine wastes at Broken Hill, N.S.W. The liquid effluent was applied by drip irrigation. The detergents in the effluent water dissolved the petroleum products used to control wind erosion and thereby achieved maximum penetration of effluent and hence plant response, whilst still achieving maximum protection against wind erosion (J,Spangler, personal communication). 51.

Berry and Marx (1980) following studies at the Forestry Sciences Laboratory, Athens, Georgia, report on the significance of various soil amendments to borrow pit rehabilitation with pine and grass species. They found that mean seedling volume was 28 times greater, and grass biomass five times greater on the sewage sludge plots than on non sludge plots. Generally, soil amended with sludge contained more nitrogen, phosphorus, organic matter and had a higher cation exchange capacity.

Hortenstine and Rothwell (1972) found that composted town refuse improved the physical and chemical properties of the sand tailings from phosphate mining. Plant growth yields were small but were greatest with compost plus nitrogen, phosphorus and potassium fertilizer additions. 2.4.2 Irrigation

Failures of artificial revegetation and slowness of natural revege- tation of mine spoils are often attributed to lack of available water for plant growth (May et at., 1971; Errington, 1975). The use of suppliment- ary irrigation in one or more forms can therefore be an advantage for vegetative establishment. The physical characteristics of the greater number of mine wastes, especially the fine tailings is such that water availability and infiltration is often poor. The problem of poor water holding capacity of tailings is accentuated in areas which have a naturally occurring dry climate. Many of the mining areas in Australia experience very low annual rainfalls. Water drawn from underground mines and/or from the treatment circuit is suitable for irrigation use, provided it does not contain toxic minerals or higher concentrations of salts (Quilty, 1975).

Working with coal mine spoils in New Mexico, Aldon (1965) conducted trials on native species established with the use of both sprinkler and drip irrigation. Sprinkler irrigation supported 24 Atizati zaccton seedlings per square metre with a twice weekly application of 14 cm for a one month period. Drip irrigation trials were conducted on flowering saltbush and western wheat grass(AgA0WOn Withii)with each species being planted alternatively at each drip emitter. Drip irrigation significantly improved the survival, height, diameter and size index of both species.

The primary advantage of drip irrigation is the conservation and efficient use of water. For mine waste vegetation drip irrigation offers the added advantages of reduced hazards of surface run-off and erosion, increased plant responses and hence quicker slope stabilization. The 52. deeper wetting patterns of drip irrigation help to reduce the problems of excess salts and other phytotoxins by leaching them from the root zone (Bengson, 1977). The application of liquid fertilizer at set concentrations to individual plants is an added advantage of drip irri- gation (Quilty, 1975; Bengson, 1977).

Bengson (1977) describes the use of many and varied drip irrigation systems used to successfully vegetate mine wastes of an open pit copper mine in the Phoenix Desert Shrub environmental zone in southern Arizona. Such systems proved very successful for vegetating steep and difficult slopes and were particularly well suited to arid environments. Bach (1972) used drip irrigation to successfully establish tree growth on mine tailings in Tuscon, Arizona. Drip irrigation was used to leach toxic mats from tin root zone. The drip system also.allowed :the application cf liquid ihrti- lizer and achieved reductions in surface erosion.

Application of sewage effluent through drip emitters proved success- ful on a tailings dump at the Zinc Corporation at Broken Hill in N.S.W. Harris and Leigh (1976) report that luxuriant growth was achieved with the effluent, but the application of fertilizer plus fresh water proved disappointing. The reason for the difference is believed to be that the detergents in the effluent water dissolved the petroleum products used on the dump to control wind erosion. The drip emitter was both successful in applying the necessary quantity of effluent, whilst maximum protection against wind erosion was achieved (J. Spangler, personal communication). Burst dripper lines resulted in considerable surface erosion on the Zinc Corporation dumps, but these problems were overcome by using improved quality products.

Irrigation of colonizing plants particularly during germination and early establishment, greatly enhances their growth. A 50% increase in native tree and shrub establishment at the Clarence Colliery in the Blue Mountains area of New South Wales was achieved by using irrigation (Lee, 1983).

Ruschena et a1. (1974) found supplimentary irrigation was necessary to establish a good vegetative cover on trial plots of tailings at Mount Isa in Queensland, whilst spray irrigation successfully established a crop of cereal rye on red mud alumina tailings at the Kwinanan alumina refinery (Anon., 1975). 53.

CHAPTER 3

HILLGROVE MINE ENVIRONMENT

3.1 LOCATION AND CLIMATE

Hillgrove is situated 30 km east of Armidale on the New England Plateau in N.S.W, latitude 30°34, longitude 151°56 and is 990 m A.S.L (Figure 3.1). The area experiences a temperate climate and is typical of much of the Northern Tablelands of N.S.W, which has a summer dominant and reliable rainfall pattern (Lovett, 1972). There are no detailed climatic records for Hillgrove, however the climate is similar to that of Armidale (Table 3.1).

Table 3.1 Monthly Mean Temperatures, Total Rainfall and Potential Evapotranspiration, Armidale N.S.W. (After: Duncan, 1980). Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Avge

Maximum temperature (°C)

27.1 26.4 24.1 20.4 16.4 13.0 12.3 14.1 17.8 21.5 24.7 26.5 20.4

Minimum temperature (°C) 13.7 13.3 11.3 7.6 4.0 1.6 1.0 1.3 3.9 7.3 10.2 12.5 7.3

o Mean temperature ( C) 20.4 19.9 17.7 14.0 10.2 7.3 6.6 7.7 10.9 14.4 17.5 19.5 13.9

Rainfall (mm) 99 71 57 47 37 59 54 39 53 60 73 87

Potential evapotranspiration (mm) 142 120 107 75 55 39 39 50 71 92 131 150

3.2 GEOLOGY AND MINERALIZATION

The Hillgrove area is contained in the Nambucca Block which is an irregular fault bounded block composed largely of low grade metasediments of Permian age. Granite intrusions of Permian to Early Triassic age have been emplaced throughout the block but are of limited aerial extent (Suppel, 1974). Within the area of the study are found the Hillgrove 53a

FIGURE 3 . 1: Locality Map.

a. The Armidale Area in New South Wales.

1.50000

44LARMIDALE .:•. .... ■-, N. to DO(rig° IllQ' --;. ..F ct / LD .? HILLGROVE :,.w : /r,:: 4 URALLA

b. Location of Hillgrove in relation to Armidale 54_ adamellite to the north and east and the Bakers Creek diorite to the south (McClatchie and Griffin, 1979). The metasediments consist of Schist, quartzite, slate and metamorphosed greywacke. The metasedimentary material has been subjected to strong vertical shearing resulting in the development of tensional fractures which strike northwest - southeast. These fractures provide favourable sites for dyke and lode emplacements (Langley, 1974). A large number of dykes, of microgranite, microdiorite, aplite, felsite, and porphyry occur within the metasediments (Suppel, 1974). Biotite and nepheline dyke rocks also occur and are particularly evident in the Swamp Creek gorge.(Langley, 1974).

Harrison (1953) divided the Hillgrove mineralization into three phases:

1. Scheelite and quartz. 2. Gold and quartz with pyrite and arsenopyrite. 3. Stibnite and calcite.

The antimony ore bodies are mostly confined to the sediments and occur as predominantly north easterly striking fissure veins 60 cm or less in width. (McClatchie and Griffin, 1970). Pyrite and arsenopyrite concentrations in the wall rock associated with the stibnite (antimony sulphide) veins are generally low, with 0.75% for both substances usually being present (J. Magnuson, personal communication).

3.3 MINING HISTORY AND USES OF ANTIMONY

The first documented discovery of minerals was in 1877 when the Havershed brothers and Thomas discovered antimony near the Hopetown reefs (Andrews, 1900). The Campbell brothers discovered antimony on the Metz side of the gorge at about the same time (Carne, 1912). The first dis- covery of gold was made by Aron Smith in the number 2 shaft of the Isabella line of reef, now known as the North Garibaldi shaft (Andrews, 1900).

Andrews (1900) outlines the production of gold and antimony of a . number of mines up to 1900, while McClatchie and Griffin (1970), give the antimony production figures for a number of mines from 1882-1958 and Green (1956) gives an outline of the complete history of the Hillgrove goldfields. 55.

After the Eleanora and Garibaldi shafts had been worked for some time the main attention of miners was directed towards gold production. A rise in demand for antimony in 1882 saw increased prospecting. By 1886, however, antimony had fallen in value to such an extent that pros- pecting again turned towards gold. The discovery of the Big Reef, Middle and Little Reefs by G Smith created a minor goldrush and during the period from 1877-1900 there was a considerable increase in the production of gold from the Hillgrove field.

The dramatic production of gold in the late 1800s culminated with 21,764 ozs being purchased in 1889, but by 1903 production had fallen to 7,332 ozs. The decline can be attributed to water problems in the mines and the lack of finance (Green, 1956).

In the years 1905-1907 there was yet another boom in the value and consequently the production of antimony (Green, 1956). The Hillgrove mining history began with antimony and again today antimony is one of only two products produced on a comwerical basis. The other is gold which has seen increased attention in recent times due to more favourable gold prices.

The Hillgrove field has been the greatest stibnite producer in the State, as well as ranking as one of the chief gold producers. Production of antimony from this field has amounted to at least 14,700 tonnes and gold production to 15,000 kg (Suppel, 1974).

The mining of stibnite ore and the production of antimony is, today, only carried out on a commercial scale by one company in the Hillgrove area, the New England Antimony Mines N.L. (N.E.A.M.) (Plate 3.1). The location of the N.E.A.M. operations and the general layout of the Hillgrove mining field are shown in Appendix 1.

Whilst it is only used in small quantities in the majority of its applications, antimony is an essential ingredient in a wide range of products. One of its main uses has been in lead batteries, but the intro- duction of maintenance free batteries in recent years has seen a dramatic downturn in its use for this purpose. 55a

(a) Tailings dams A and B.

(b) Location of tailings dam C at time of excavation. Plate 3.1: The N.E.A.M. milling and processing operations. 56. As an oxide antimony is used in flame proofing of textiles and plastics, as a bullet alloy and tracer compound, in ceramic glazes, medicines, dyes, pigments, mordants pewter and fireworks. As a sulphide it is used as a friction compound in non-corrosive premiers and as an ingredient of eyeshadows. As a metal it is used in cable sheathing, solder type metal, optical glass and electronics. 3.4 N.E.A.M. OPERATIONS

The company has worked a number of mines including the Eleanora Freehold and the Smiths, the latter mine from the Smiths and Waterfall adits (Appendix 1). More recently, the Garibaldi South Mine has been brought into production again. The majority of mines are located in the Bakers Creek gorge. The milling of the stibnite ore is carried out at the processing plant located on the plateau between the Hillgrove township and the gorge (Plate 3.1). The flow diagram (Figure 3.2) depicts the milling and processing operations in which antimony sulphide is extracted using a sulphide floatation process.

Research and investigation on rehabilitation at the mine began in 1976 with initial work being completed during 1978. At this time, the operation involved the milling of up to 150 tonnes of ore per day with a daily water usage of approximately 455,000 litres (M.Binns, personal communication). The head grade of the ore was approximately 4% antimony, 0.3% arsenic, 0.3% lead and 9 per tonne gold. The final antimony concentrate produced was 65% antimony, 0.5% combined lead and arsenic and approximately 25% sulphur, with the remainder being predominantly silica. A combined arsenopyrite and gold product was collected at the mill for later processing for gold extraction.

The tailings from the floatation process were pumped as a slurry to a tailings dam and hydrocycloned into two size fractions (Plate 3.2). The water was decanted from the surface.

During the sulphide floatation process the following chemicals were added and, as such, could be possible contaminants of tailings:

1. Methyle I.S.O. Butyle Carbonal (MIBC) is a water soluble petroleum derivative which is used to enhance the frothing action in the floatation process of extracting the stibnite. FIGURE 3 . 2 : Flow Diagram of N.E.A.M. Milling and Processing Operations as at 1978

Ore trucked from mines To sands dam Auto J. Cyclone sampler Flotation I:3 conditioner Hydrocyclone To bank of Coarse flotation cells ore bin

To slimes dam < IV

Antimony Flotation Ball Jaw Apron concentrate concentrate mill crusher / feeder Thickener Table/ / 1 Antimony EMU ISM Drum tabling SEMI Mill Exhaust Belt filter Table/ rejects gases 2 weigher / Auto sampler Dust Oil fired Concentrate cyclone rotary dryer /A. V Gyro cone crusher concentrate V Fine Table ore 3 storage Solids to bin thickener Gold Bagging tabling machine Four Tails double y Tails spirals Cone concentrator Drummed Bagged low - grade antimony Drummed gold concentrate concentrate gold concentrate 56b.

Plate 3.2: Hydrocycloning of antimony tailings into the sand and slime fractions. 57.

2. Lead nitrate is used as an activator agent and attaches to the stibnite which enables effective extraction of the antimony.

3. Sodium ethyl xanthate (S.E.X.) is used as a collector agent and, as such, becomes attached to the stibnite and brings it to the surface with the frothing action of the process.

The M.I.B.C. is a volatile substance and should therefore, not be a contaminant. The lead nitrate is added in such small quantities that it is unlikely to be present in toxic amounts. This is born out in the chemical analyses repotted in Section 5.3. It is most likely that the lead precipitates as lead sulphate due to the sulphate in the tailing water. S.E.X. hydrolyses and the amounts used are so small that its pollution effects are negligable (M,Binns, personal communication).

The initial tailings disposal dump was located between the process- ing plant and the Eleanora Dam (Dam A Plate 3.1). Its capacity had been exceeded by early 1976, resulting in considerable run-off during wet periods which flooded parts of the mill. Erosion and batter collapse have resulted in considerable quantities of tailings being deposited into the Eleanora Dam.

The problems requiring attention at that time were therefore:

1. The location of a new tailings disposal dump, combined with a structural and hydrological design of the area.

2. The adoption of a vegetative programme to achieve effective rehabilitation of the existing and proposed tailings areas.

Increasing gold prices and a drop in the head grade of antimony in a number of the mines saw a change in mine policy. Firstly in 1981, they designed and installed a thio-urea leaching plant (Figure 3.3) and upgraded the remaining processing equipment (Figure 3.4). Secondly, in May 1983 they commissioned a plant to treat tailings from previous operations (Figure 3.5).

Gold recovery on the gravity tables (Figure 3.2) was only 35%. -1 The gravity gold concentrate contained 2,000-4000 g tonne gold, 20% arsenic and 15% antimony. To improve the recovery of gold i the antimony concentrate from the floatation process was passed through the thio--ture-a leaching plant and the gold extracted by a filter press containing activated FIGURE 3 . 3 : Flow Diagram of N.E.A.M.Thiourea Leaching of Gold in Antimony Concentrate Operations

PREGNANT PREGNANT SOLUTION WASH LIQUOR LIQUOR MAKE UP WATER TANK TANK TANK TANK SHRIVER FILTER PRESS Wash water to lime pit

Antimony FILTER CAKE concentrate Carbon gold l■ —,110-1--- From 1 \ concentrate Thickener (Figure 3.4) ACTIVATED CARBON FILTER PRESS

ANTIMONY CONCENTRATE BARREN r LEACH TO DRYER AND SOLUTION TANK BAGGER TANK FIGURE 3 . 4 Flow Diagram of N.E.A.M. Milling and Processing Operations as at 1982

Ore trucked from mines

Coarse ore bin

Jaw Apron\1 crusher feeder -E- Vibrating Belt fvscreen cyclone OIS weigher /S D Auto 42) — o/s .0 0 Low grade 1.) C=3 sampler • • - 42) CL gold cons. —> Gyro cone Fine Reichert Table Head Gravity gold crusher ore MD L cons. Cons. 3 storage Discharge concentrate bin Trommel 12mm V Tails Tails Tails Ball Mill Feed mill scats Gold Concentrate Upgrading

Thickener Grinding Classifying Section Gravity Concentration Section

Cons To Thiourea Leaching Stibnite flotation 1.■..■•••311111.0 Table Head Plant ( Figure 3 . 3 ) Condi- denver cells 1 tioner y Tails tank V Tails Table HeadV 2 t Tails Antimony Flotation Section Antimony Concentrate Cleaning

To Tailings Retreatment Plant (Figure 3 . 5 ) FIGURE 3 . 5 : Flow Diagram of N. E .A.M . Tailings Retreatment Operations

TAILS DAM MILL SITE

LOADER ---31 TRUCK STOCKPILE ----> LOADER 25 T.P.H.

Grizzly .( Scrubber j Trammel aperture 10 mm 15 Tonne el 0 hopper Trash (i r) Belt feeder

Static screen Mass flow instrumentation 300,u ( Nuclear density gauge and magnetic flow meter )

Cyclone Reagents Reagents Scavenger Antimony cells Rougher cells scavenger cells i---- Conditioner Slimes tank •It To Tailings dam -""--,...... ----" "4-\..../..

To storage Reagents for later regrind Water

1st stage 2nd stage VF---- cleaner cells cleaner cells Conditioner tank T To concentrating 0 )/1. table N9 3 KEY lo To mill feed Sample ( Regrind ) Tailings T V Concentrate . . C E Sands 1.0 3.0 Alternative storage L J 111. for later regrind Thickener To Tailings dam 25 56

Gold - Arsenopyrite cons 7. to Thiourea Leaching Plant ( Figure 3 . 3 ) 58. -1 carbon. This process produced 6,000 g tonne gold. During the thio- urea process, sulphuric acid, ferric sulphate, thio-urea and hydrogen peroxide are added. The sulphuric acid is neutralized with limestone during the process while the ferric sulphate precipitates out and the do-urea breaks down to sulphur. The hydrogen peroxide is used to adjust the redox potential of the solution. Because of the limited quantities of these substances used, contamination of the tailings would not pose a problem.

The new plant (figures 3.4 and 3.5) produces a 68% antimony concen- trate and an arsenic/gold concentrate which contains 25% arsenic, 250 g tonne -1gold and less than 5% antimony. Tailings from the new plant contain -1 0.1% antimony, less than 0.05% arsenic and less than 0.5% g tonne gold. This compares favourably with the tailings produced from the original milling and processing plant (Figure 3.2) which contained 0.3% antimony, 0.35% arsenic -1 and 3.5 g tonne gold.

In addition to, or, in place of the M.I.B.C., lead nitrate and S.E.X. which were added in the existing plant a number of different collectors and frothing agents, such as sodium secondary butyl xanthate, potassium amyl xanthate, Orfom c, 8,000 - a sulphur based collector and Aerofroath 65 a poly propylene glycol ether are now used. These substances are used in such small amounts that they will not contaminate the tailings.

The retreatment of existing tailings it was necessary to:

1. Locate a suitable tailings disposal dump and carry out the necessary hydrological and structural designs, 2. Integrate the additional tailings dumps with existing plant and tailing disposal systems.

3 . 5 VEGETATION SURVEY

The native vegetation of the surrounding undisturbed area is dry sclerophyll forest with a cover of native perennial grasses and low shrubs and bushes. A survey of the existing tailings dump and immediate surroundings at the N.E.A.M. mill revealed the following species:

Low shrubs - Cazinia. gain. que6 4:Ct.

Cool season perennial grasses - DanthonZx Dan thonil Aacemoza, 59.

Danthon-ia taen-i4, D.&hetachne 4c.imea, D.ichetachne ininata, Poa 4.iebanana, Warm season perennial grasses - Cynodon dactyton, Themeda austAatiA, Bothltiochtoa 4p.

Vegetative establishment had only occurred on the lower slope areas on relatively stable slopes. Rock debris on the batters appeared to act as seed ledges in enabling germination and establishment to take place. No colonization of vegetation was seen on any freshly deposited tailings less than two years old. While on older areas of deposited tailings vege- tation was very sparse.

The following native tree species were found in the Hillgrove area but were not noted growing on recently deposited tailings (up to two years old) areas, however all species were noted growing on older tailings areas:

Red stringbark (Et olyp.tws manoithyncha) , White box (E. cabeivS) , New England black butt (E. anditemii), Die hard stringbark (E. camelton.ii), Cabbage gum (E. amptiAotia) , Brittle gum (E. michaet.iana), Hillgrove gum (E. cypettocaApa).

A number of smaller perennial shrubs were found but were not identified. 3.6 PREVIOUS VEGETATIVE ESTABLISHMENT TRIALS

To date, Gibbs (1976) and Cornally (1977) have conducted vegetation trials on the sand or coarser fraction of the tailings from the N.E.A.M. process.,ng plant. Gibbs (1976) conducted fertilizer/species interaction trials using eight species of grass, one species of clover and one legume. The perform- ance of couch grass (Cynodon dactyton), Rhodes grass (Chtoit.iis gayana), cOcksfoot (DactyA gomeAata ), kikuyu (Penn.i.setum aande4Vnum), paspalum (Pavatum ditatatum), perennial rye grass (Lotium pexenne), phalaris (Phatalc.iz dqUatiCa), and tall fescue (Refstuca mundinacea) were monitored following -1 the application of 0, 250, 500 and 1,000 kg ha of Grower 11 (11:34:11) -1 fertilizer. Gibbs found no significant response at 0 and 250 kg ha 60. -1 of fertilizer between species but at 500 and 1,000 kg ha growth of kikuyu and couch grass was significantly higher than other species. -1 At 1,000 kg ha kikuyu performed poorly and couch grass became the only species to grow significantly better than the rest. Both lucerne and white clover failed to germinate. Gibbs suggested that the topsoil- ing of the dumps to a depth of several centimetres prior to attempts to -1 vegetate may be a more viable alternative than applying 1,000 kg ha of Grower 11 fertilizer. No explanation was given for this difference in performance.

Cornally (1977) conducted trials to determine toxicity and nutrient deficiencies. A factorial trial using the following rates of nitrogen, sulphur and potassium was conducted: 0, 40, 80, 120 kg ha -1 , 0, 60 kg ha-1 -1 and 0, 75, 150 kg ha respectively. A second trial to determine magnesium deficiencies was also conducted. Magnesium was applied at -1 0, 15, 30 and 60 kg ha and a basal dressing of nitrogen, sulphur and -1 potassium applied at the rates of 80, 60 and 100 kg ha . Phosphorus was not applied in any of the treatments as chemical analysis had detected 640 ppm of combined arsenic and phosphorus. The question of phosphorus analyses and availability is discussed in section 5.3.

Japanese Millet(ECUYIOChtea utiti/S) was used as an indicator species on both trials. Germination was good but plants failed to develop beyond past 5-8 cm in height and then died. Examination of roots revealed clubbing. Cornally concluded that the failure of the plants to obtain significant growth was due to arsenic toxicity. He also pointed to the possibility of water stress and the very low field capacity of the material. 61.

CHAPTER 4

HYDROLOGICAL AND STRUCTURAL DESIGN

4 .1 INTRODUCTION

An important component of a successful mining, milling and processing operation is the design of a sound tailing disposal system (Houston and Warren, 1976).). No matter how well or faithfully a project is carried out, if the planning, and design of the system is not appropriate, the result will be at best unsatisfactory and at worst a practical disaster (Verschuer, 1976).

The mountainous terrain of the Hillgrove area, and in particular the location of the milling and processing plant on the edge of the Bakers Creek gorge, restricted tailings disposal to either surface storage or underground placement. The disposal of tailings into underground mine workings involves a desliming operation, with only the coarse fractions being suitable for underground disposal (Williams, 1975). At Mount Isa mines in Queensland the coarse fractions are mixed with cement and pumped underground, while the finer fractions or slimes are stored on the surface (Hunter and Whiteman, 1974).

Underground disposal of tailings by the method outlined by Hunter and Whiteman (1974) precludes the reprocessing of tailings. At many mines throughout the world, technological advances in equipment and metallurgical processes has made the reprocessing of tailings an economic proposition. The writer, during an inspection of mining operations at Broken Hill in 1976, found that the triple M mining company was operating economically by reprocessing tailings.

Because of the possibility of reprocessing tailings, N.E.A.M. chose the surface storage method of disposal. The design of the tailings dis- posal system (Section 4.3) has been carried out in two stages. The aim of the first stage in 1976 was to locate a new tailings dam, as the cap- acity of the existing structure had been surpassed. This had resulted in pollution of the Eleanora water storage dam by erosion of the tailings and the flooding of the milling and processing plant by surface runoff (Plate 3.1). The second stage involved the siting of a new tailings dam because of the commissioning in 1983 of a tailings retreatment plant. 62.

4 .2 TAILINGS DISPOSAL SITE SELECTION CONSIDERATIONS

Site investigations for tailings disposal should include; considera- tions of topography, hydrogeologic environment, availability of appropriate construction materials, hydrology, seismic conditions and climatic factors such as the amount and seasonal distribution of precipitation, and the velocity and direction of winds. A comprehensive investigation of these factors will afford the maximum protection of the environment from pollu- tion by leachates, water and wind erosion and catastrophic failure caused by floods or seismic events (Williams, 1975).

In considering the topography, care should be taken to appraise geomorphic features such as old landslide areas and fault lines, which could indicate possible failure sites for tailings structures. A study of the topography will also reveal the most appropriate location for roads and pipe lines. These items should be located, if possible on sites that will cause the least disturbance to the soil surface. This will avoid excessive damage by erosion, which if severe, could cause considerable environmental pollution.

The general geological character of a potential site should be one of the primary considerations (Williams, 1975). Unconsolidated materials should be mapped and their grain size distribution, permeability and other engineering properties determined, so that possible settlement, leakage and other failure problems can be anticipated and taken into consideration in the design of the disposal system. Klohn (1972) discusses the hydro- geologic investigations required to be undertaken at a possible disposal site.

The permeability of the underlying geologic material is very important, as seepage from highly permeable material could result in pollution of ground waters. Williams et at. (1973) have shown that ions such as lead, zinc and cadmium from tailings can enter and travel with ground water, under certain hydrogeologic conditions. Hughes and Cartwright (1972) point out that, while low permeability materials are the safest environment for waste disposal sites, the low permeability of the underlying material could lead to a saturation of the wastes. In such cases, where the surface of the waste is higher than its surroundings, water could escape around the margins of the wastes through seepage. This could cause pollution and/or instability of the dump. Williams et a1. (1973) describe methods of using mill tailings to minimize leakage from tailings dams. 63.

Blume (1972) discusses the probability of earthquakes and resultant ground motion, and delineates zones that are prone to earthquakes of specific intensities on a worldwide basis. Where tailings dams are to be constructed in areas prone to seismic activity, Williams (1975) states that in addition to intensity, other earthquake phenomena such as antici- pated . epicentral distance, focal depth amplitude, period of particle motion, and peak ground acceleration should be investigated. This informa- -ion enables the likelihood of ground motions at a specific site to be predicted. From a knowledge of the geology of the site, the tailings dam can be designed accordingly.

The climatic conditons of an area are of particular significance as they affect the vegetative rehabilitation dEwaste sites. Wind velocity and direction affect not only revegetation due to wind blasting, but they also determine the amount of dust which can be generated from waste sites. Dust is an important consideration where waste sites are located near towns, such as in Broken Hill in N.S.W. The affects of dust and sand blasting have been previously described in Section 2.3.1.2.

In addition to geological investigations, it is important to investi- gate the engineering properties of the soil material if it is to be used for tailings dam wall construction. In many cases, tailings dam walls are constructed from a combination of the coarse tailings, waste rock and soil.

The calculation of runoff for a site is important as it provides an indication of the amount of water which may enter the tailings area. Williams (1975) states that, if possible, all runoff onto or through a site should be eliminated. This of course is not always possible or practicable.

4.3 N.E.A.M. TAILINGS DISPOSAL SYSTEM

The design of the tailings disposal systems has been carried out in conjunction with N.E.A.M. staff. The detailed site testing and engineering design of the tailings structure were carried out by the mining company. However, the planning and design of the runoff and erosion control works, together with much of the onsite planning of the stability of the existing and proposed tailings structures has been carried out by the writer. 64.

The design of the runoff and erosion control structures have been based on the formula and techniques are described in the Soil Conservation Service of N.S.W. Design Manual for Soil Conservation Works (Soil Conservation Service, 1982). 4.3.1 Stage 1, 1976 – 1982 With the capacity of the existing tailings area having being reached (Dam A in Plate 3.1), a new tailings disposal site had to be found. The site chosen was in a valley to the south of the processing plant and immediately downstream of the Eleanora water storage dam.

The overall plan for runoff, erosion control and tailings disposal is depicted in Figure 4.1. The works programme consisted of:

1. Construction of dams and diversion banks to divert runoff water away from the milling and processing plant and tailings areas.

2. Extention of the spillway of the Eleanora dam to divert over- flow water to an alternate watercourse.

3. Siting of the proposed tailing structure (Dam B in Plate 3.1).

4. Construction of two dams below the new tailings structure. The first was for the collection of seepage, the second for the treatment of excess water which may be toxic. Treatment would be carried out prior to the release of the excess water into Bakers Creek.

5. Installation of a pumping system to facilitate the recirculation of seepage water from the tailings dam to the Eleanora water storage dam.

The construction of the new tailings dam should be carried out in accordance with recognised construction and engineering techniques, as discussed by Klohn and Marrtam (1972), Laird (1972) and Down and Stocks (1976). The works programme created a closed system in which treatment of both waste liquids and solids could be manipulated. Cross sections of the new tailings dam, depicted in figure 4.1 are contained in Appendix 2.

4.3.1.1 Rehabilitation of Tailings Structures

Recommendations for the rehabilitation of the existing tailings area and the proposed new tailings dam were prepared by the writer.

To ensure the structural stability of this dump the following procedures were recommended: M L A 353 a)

GARBAL D srm4 SHAFT 40,9 ,

50irn X m

E LE AMOR A

M P L 1427

DAM

EXISTING GARIBALDI NTH SHAFT TAILINGS

DAM 160 P.L.L. 350

N 144

ECSTiNG M. L.A 20 LAM 150

/52

P L L 3827 PL.L. 416

Figure 4. 1 : Stage 1. Hydrological ---fl Structural Design Programme for CRUSHER

WORgSMOP Water Diversion Tailings Disposi I DRAIN

ate R M.L.A. 439 TANKS 65.

1. Reduction of batter grades from the present 1:1.5 to 1:2.5 and the use of graded rock to ensure a reduction in surface erosion and provide seed ledges.

2. Removal of sufficient quantities of tailings to reduce flooding of the processing plant during wet conditions.

3. The shaping of the dump to facilitate good drainage of the dump surface and surrounding areas.

4. The establishment of a self perpetuating cover of vegetation. Recommendation were to be provided following the results of investigations and experiments with the tailings.

The rehabilitation recommendations for the new tailings dam included:

1. Batter grades and treatment should be consistent with those for the rehabilitation of the original dump.

2. The dumping of tailings and subsequent rehabilitation should be carried out in progressive stages, to ensure that a limited area of tailings is exposed to erosion at any one time and a reduction in pollution potential is achieved.

3. The establishment of a vegetative cover by the same methods adopted for the original dump. 4.3.2 Stage 2, Post 1982

With the commissioning of the tailings retreatment plant for reasons which have been previously outlined in Chapter 3, it was necessary to locate a suitable site for tailings disposal, as tailings from the two previous storage sites were to be recycled. A site was found to the east of the existing facilities (Dam C in Plate 3.1).

The plan for runoff, erosion control and tailings disposal is depicted in Figure 4.2. This system is based on the same design criteria as the plan depicted in Figure 4.1, in that a closed system has been created.

Provision has been made for two settling dams to be included in the seepage water collection and recirculation system. These dams will allow for the removal of solids which have been pumped from the seepage storage dam or deposited from the diversionary banks. IN L. 655

P L L 350

M L 1427

F RA 14M

f L 219 ;

T T TA ,,S AM

ALL GATT [NS 2S AVE RAG( WY101 aoc K MON G

1■11 P L 919 Figure 4 . 2 , Stage 2. Hydrological Structural Design Programme for Water Diversion Tailings Disposal. 66.

The tailings dam should be constructed on sound engineering designs with established techniques as was required for tailings dam B (Plate 3.1). The structure is to be constructed in three stages.

Years of Construction Capacity in tonnes

3 390,000 6 690,000 8 863,000

Rehabilitation recommendations are consistent with those previously discussed for tailings areas A and B in Plate 3.1. Cross sections of the tailings dam in Figure 4.2 are contained in Appendix 3.