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By Smith IEM

Some samples from arc-type volcanic suites collected in northern New Zealand and southeastern Papua New Guinea show rare earth element (REE) and Y abundances which are enriched relative to the those typical of their respective associations. This enrichment appears to be the result of an alteration process which selectively mobilises the REE and re-precipitates them as REE-bearing minerals in veins and interstitial patches. The alteration is on a micron scale and is not detected in routine petrographic examination. The spectre of REE mobility in young apparently fresh rocks is important to igneous geochemists who use REE abundances to constrain petrogenetic models and may also be important because it indicates the operation of a natural REE enrichment process which could operate in the formation of economic REE deposits.

Jan 1, 1990

By Prohaska G, Jackson F, Jack B

To learn more about the fundamental roof behaviour in South African coal mines, accurate underground measurements of roof deflection were conducted in bord and pillar panels during development and pillar extraction. To conduct these measurements a survey levelling technique was adapted. The overall system reading accuracy was established as being within 0,4 mm on a 15 m sighting distance. The underground sites were modelled and, for a roadway development, similar symmetrical curvatures were calculated by a linear elastic model, as were measured underground. In a pillar extraction panel, a significant amount of bed separation was measured and the roof underwent an a-symmetric movement due to the close presence of the mined out area at one side of the roadway.

Jan 1, 1992

Lake Kopiago is located some 71km northwest of Tari in the Southern Highlands Province and lies on the northern edge of the Papuan Fold Belt. The area is underlain by middle Miocene carbonate and fine grained clastic sediments intruded by late Miocene hornblende gabbros.Two mineral deposits occur to the south of Lake Kopiago. These are the Bisamu gold prospect and the Wunaki zinc-lead gossan.The Bisamu deposit consists of a calcic skarn assemblage which is geochemically anomalous in gold, silver, copper, zinc, cobalt, bismuth and tellurium. The prograde mineral assemblage includes garnet, clino-pyroxene and epidote whereas the retrograde assemblage includes epidote, quartz, actinolite and chlorite. Pyrrhotite is the dominant sulphide with minor pyrite and marcasite and trace chalcopyrite and sphalerite. Minor magnetite is also present. The Bisamu skarn shows many of the features typical of gold-skarn type mineral-isation.

Jan 1, 1994

The Electricity Commission of New South Wales is the largest single user of coal in the State, burning some 8.5 million tonnes during 1972-73. This coal is converted in power stations into electrical energy which is then distributed throughout the State and supplies the electricity requirements of 99% of users in New South Wales. Barring any major change in energy consumption growth, or change in the current mode of power generation, the consumption of coal by the Commission is estimated to have a doubling period of from 10 to 14 years. Coal is used to generate up to 87% of the electrical energy sold, the balance being obtained from hydro gen- eration, mainly in the Snowy Mountains, and, to a much smaller extent, from diesel generation at Broken Hill. A very large proportion of this coal is consumed in pulverised fuel boilers in the Commission's power stations, located mainly on the various coalfields of New South Wales. Coal supplies are drawn from a large number of mines, some owned or controlled by the Commission, others being owned by public companies. The coals used, originate from at least ten different seams located in the northern, western and southern coalfields of New South Wales, and therefore have a wide variety of properties and characteristics. To ensure an adequate fuel supply well into the future, the Commission is continuously engaged in coal prospecting in various areas. Bore data is used in assessing coal reserves and is also the basis of economic studies for their possible future exploitation. The numerous coal cores obtained during drilling operations are carefully tested and analysed in order to assess their suitability for power generation purposes, and to provide data for the design and operation of boiler plant using these coals. In existing power stations coal deliveries are systematically sampled and tested for quality control, for pay- ment of purchases based upon certain quality parameters and to check for any possible plant operating or main- tenance problems that might arise from the use of the particular coals. Almost all the properties of coal that may be necessary in the Commission's work are obtained using standard testing procedures carried out by the Commission's chemists, in laboratories located at the various power stations or at its Central Laboratories in Pyrmont. Where specialised analysis or testing is required, this is ordinarily undertaken on a commercial basis by outside bodies, expert in the particular field. The significance of the various properties of the coal for use in p.f. boilers is outlined and related to their proper application to boiler plant design and to plant operation.

Jan 1, 1975

Ok Tedi Mining Limited commenced construction in mid-1981 of facilities and infrastructure to mine and process gold ore at Mt Fubilan in Papua ew Guinea. Production ofgold began more or less on schedule in mid-1984 although design capacity is yet to be achieved. Due to geotechnical problems, two important items of infrastructure, hydropower and permanent tailings disposal, are not yet in place. Current low metal prices make it likely that copper facilities will be postponed.The deposit compriscs a leached gold capping overlying copper sulphide porphyry mineralisation containing significant gold and molybdenum. Mining is by open pit methods. The soft leached capping gold ore is ripped and dozed, loaded by hydraulic shovel and trucked to a dump pocket. After passing a large semi-autogenous mill of nominal capacity of I, I00 tonnes per hour, the ore is treated by the carbon-inpulp process, with a gravity circuit to recover coarse gold. The final product is 12 kg dore bullion bars.At present, all tailings are detoxified with hydrogen peroxide; after cycloning, the coarse fraction is stored, and the slime fraction discharged into the river system; expected environmental impact is acceptable. Investigations for a suitable dam site for a permanent tailings system are still underway.Peak 'I. hour power demand for Stage I is 17 MW, presently supplied by a diesel alternator power station and a 2 MW mini hydropower plant.Initial access to the base camp at Tabubil was only by air. Eventually a road was pushed through 134 km from the river port at Kiunga (where port facilities have been constructed) and a further 23 km to Mt Fubilan.Roads are constructed of compacted gravel and crushed limestone generally underlain by geofabric. Eight major steel bridges were built.The town of Tabubil has been established, including housing, airport, shops, offices, schools and all facilities.Environmental studies have been extensive and a detailed monitoring program is maintained. Ok Tedi Mining Limited is making considerable efforts to train Papua New Guineans and to foster local business.

Jan 1, 1985

By D Morris

This presentation discusses a water filtration technology termed Fabric Media that is somewhat novel to the Australian market place and reports several recent mining industry installations. Like many novel household cleaning products, the Fabric Media technology applies the science of active washable micro fibres as the means of capturing contaminant solid particles. The simple Fabric Media water filtration product offers several attractive attributes when compared to the more traditional media bed filtration processes such as sand filters, and barrier filters such as micro membranes. A micro fibre based filtration media enables both superior adsorption for the contaminant and wash ability. Stronger adsorption capture enables a much higher flux and greater solids loading density for the filtration task, meaning that lower cost and smaller footprint equipment is available. For Fabric Media water filters, a textile weave is selected that minimises the flow backpressure for a given particle size separation. Thus for an equivalent filtration performance this provides a much lower operating energy requirement, generally between 50 and 80 per cent less than for a sand filter. A Fabric Media is not abrasive to itself or to the filter tank. The filtration performance remains constant and predictable. The equipment life is much longer and the asset value of the new filtration equipment should maintain throughout the project life. Fibres are extremely mechanically robust and chemically inert. Fabric Media survives repetitive exposure to a rapid mechanical washing event providing high wash efficiency with minimum equipment off-line time for the backwash. Dislodging captured contaminants by a high-speed mechanical agitation enables a minimum off-line time during backwash events. The vigorous backwash destroys adhering flocculant and eliminates the formation of mud balls, which can permanently foul sand filters. The mechanical agitation wash of the Fabric Media water filter ensures complete removal of grease and biofilm, which can adhere and block a membrane surface. In comparison to sand filters and micro filtration membranes, the Fabric Media product is applicable to a significantly wider range of solids concentrations without permanent damage. The technology is very forgiving to excursion in plant control and is therefore considered a very operator-friendly concept.

Jan 1, 2006

Location & Permit Status Three major Mesozoic Tertiary basins exist along the continental shelf area of southeastern Australia, known as the Bass Strait area. They are the Gippsland (east of the longitude of Melbourne) Otway (west of Melbourne) and the Bass (underlying central Bass Strait between Victoria and Tasmania). The total area, both onshore and offshore, is approximately 100,000 square miles. In March 1960, the Broken Hill Pty. Co. Ltd. acquired exploration title to the continental shelf areas of the Gippsland, Bass and Otway basins from the States of Victoria and Tasmania. The title to that part of the Otway Basin in South Australian waters was granted in July, 1961. Other exploration permits, being 8 miles wide in Gippsland, held by Woodside :E.) Oil Co. N.L., and 15 miles wide along the southwest coast of Victoria, held by Mobil-BP-Interstate Oil (Frome-Broken Hill Co. Pty. Ltd.), were in existence prior to granting the B.H.P. title. Subsequently, Shell, B.H.P., Esso and Magellan have been granted title to the remaining areas of the continental shelf in the basins under discussion. In three separate agreeme negotiated between 1964 and-1966, Esso obtained farm-in rights to B.H.P.'s Gippsland, Bass and Ott' Permits.

Jan 1, 1970

By D Schwab, R M. Tosdal

The Quesnell-Stikine arcs, in the Canadian Cordillera, are host to Triassic and Early Jurassic alkalic porphyry Cu-Au and calc-alkalic porphyry Cu-(Mo-Au) deposits formed outboard of ancestralNorth America in island-arc tectonic settings (McMillan, 1991). The majority of the alkalic porphyry Cu-Au deposits are products of a discrete magmatic event at the end of the Triassic, with a second and smaller event in the Early Jurassic (Mortensen, Ghosh and Ferri, 1995). Of the Triassic complexes, the Galore Creek alkalic intrusive suite is one of the largest and most silica-undersaturated intrusive complexes, and host to the most significant undeveloped alkalic porphyry Cu-Au resource in North America (Lang, Stanley and Thompson, 1995). Because of the common presence of feldspathoidal-bearing rocks in the complex (Enns et al, 1995), Galore Creek likely represents an end member example of the alkalic porphyry Cu-Au class. The Galore Creek alkalic Cu-Au-Ag porphyry district, located in NW British Columbia (Canada), contains 12 mineralised prospects (Enns et al, 1995; Micko et al, 2007; Schwab et al, in press) with a total measured and indicated resources of 785.7 Mt at 0.52 per cent Cu, 0.29 g/t Au and 4.87 g/t Ag (NovaGold Resources Inc, February, 2008). The Central Zone is the largest and best delineated. Other economically important mineralised centres include the South-West, Bountiful, West Fork and Junction deposits. The South-West Zone, the focus of this contribution, is a Cu-Au-Ag breccia-centred deposit with a measured and indicated resource of 69 Mt grading 0.42 per cent Cu, 0.69 g/t Au, 2.67 g/t Ag. Hosted in brecciated intrusive rocks, the South-West Zone is distinctly younger than the Central Zone and most of the other mineralised centres (Enns et al, 1995; Schwab et al, in press). The South-West Zone therefore preserves the late stages of hydrothermal evolution at Galore Creek. An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation.

Jan 1, 2008

By F A. Roddick, C Swaminathan

As remaining gold deposits tend to become more refractory, some form of oxidative pre-treatment involving hydro or pyrometallurgy is necessary to maintain high metal recoveries. These pre-treatments include pressure oxidation, bio-leaching or roasting. In the past, the primary criterion for selection of oxidative pre-treatment relied mainly on the extent of gold recovery and relative economics. In this study, a different approach has been adopted, ie the quantitative determination of environmental performance of the oxidative pre-treatment processes bio-leaching, roasting and pressure oxidation to assess which had the least impact on the environment. By establishing the environmental performance of processes, waste minimisation can be addressed early in process selection. Using mass balances, the environmental theme method was applied to determine the performance, on the basis of gold treated, of the oxidative pre-treatment processes of selected plants. No clear trend was observed in the overall impacts of each of seven plants, with all but one of the environmental evaluation indices being of the same order of magnitude; this was probably due to masking effects arising from the large variations in feed composition, tonnage, and gold levels. Within each type of pre-oxidation plant however, certain trends were detectable. For instance, irrespective of plant size, ore composition or mineralogy, for the bio-leaching and pressure oxidation units, the general order of environmental impact from greatest to least was sequentially toxicity, acidification potential, depletion of resources, solid waste generation and greenhouse enhancement. For the roasters the acidification potential was the most significant. Determination of the environmental performance of the oxidative pre-treatment of a hypothetical ore in a plant of fixed tonnage was undertaken to remove the possible masking effects of variables associated with feeds of different mineralogy, gold tenor and tonnage. The bio-leaching process gave a marginally better performance than pressure oxidation, the roasting process the worst, although there was not a great difference between them. The decreasing order of contribution to the environmental index was acidification potential, toxicity, resource depletion, solid waste generation and greenhouse enhancement for bio-leaching and pressure oxidation; whereas it was acidification potential, solid waste generation, toxicity, resource depletion and greenhouse enhancement for roasting. Since the major contributor to the environmental index was the acidification potential, the environmental performance of treatment processes for the acidic effluents was calculated. After neutralisation of the net acid resulting from bio-oxidation and pressure oxidation, and the application of various scrubbing and product formation processes for the sulphur dioxide from the roasting process, it was shown that pressure oxidation gave a marginally better performance than bio-leaching, ahead of roasting. This study demonstrated the potential for the development of a predictive tool which could be used in determining the environmental performance, and thus the selection, optimisation, and improvement of pre-oxidation processes for least impact on the environment. These would allow operation of these processes within defined environmental performance limits and decisions regarding the desirability of processing various parts of a heterogeneous orebody to be made on environmental grounds.

Jan 1, 2000

By Darby H. P, Vincent R. J

Sydney's Eastern Suburbs Railway from Central to Bondi Junction required the construc- tion of 10.4 km of single-track tunnel and five underground stations. Much of this work took place beneath the commercial centre of Australia's largest city. This paper discusses the general precautions taken and the specific design solutions made for such problems as support of a 15-storey building with foundations several metres above the excavation to ensure negligible differential settlement, excavation immediately below running tunnels, underpinning of multi-storey buildings, tunnelling under massive masonry retaining walls and demolition and rebuilding of part-completed structures.

Jan 1, 1981

Samples of the feed, underflow and overflow mediums from dense medium cyclones operating at low separation densities in eight commercial coal washeries were sized and analysed, to obtain comparative cyclone classification performance curves for the magnetite, shale and coal components in the circulating medium. The resulting component classification curves indicated that the dense medium cyclones hydraulically classify the magnetite and the shale to the underflow with a Stokesian size and density relationship at these low medium densities, ie the shale curve was shifted parallel to and appropriately coarser than the magnetite curve because of the lower density of the shale. However the lower density coal reverse classified to the overflow (ie away from the cyclone wall) with a similar Stokesian relationship. By correcting the magnetite and shale classification curves for the bypass inefficiency to underflow, and similarly correcting the coal classification curves for the bypass inefficiency to overflow, the corrected classification curves for the magnetite, shale and coal were reasonably parallel (considering that the coal has a range of densities). Using a value of five for the density of the magnetite, the displacement of the shale and coal curves corresponded to densities of 2.27 and 1.38 respectively for one circuit, although the data was not as good for the other circuits. This reverse classification mechanism was confirmed in a 140 mm diameter laboratory dense medium cyclone circuit using low density (1.20 - 1.30 RD) tracers, sized from 0.25 to 2 mm. These classification performance curves were corrected for bypass ineffiency (as above). The corrected curves were parallel and displaced according to tracer density, even though the lowest density tracers were reverse classified to the overflow. The data indicate that the rates of classification of all particles could be described by the same Stokesian relationship, regardless of the direction of travel, except for a narrow band at the partition density. Particles heavier than the partition density classified to the underflow, particles lighter than the partition density reverse classified to the overflow and particles identical to the partition density were not classified at all. Consequently it should be possible to simulate partition in dense medium cyclones, operating under free settling low density conditions, with a simple cyclone classification model, provided the partition density can be accurately calculated from, or correlated with the cyclone feed, underflow or overflow pulp densities. The tracer partition performance in the laboratory cyclone was an inverse function of the tracer particle size, as proposed by King and Juckes (1984) for medium/coal ratio in low density medium systems. Their sized coal data was parallel, with lower partition values due to a higher energy cyclone. Partition data with similarly sized tracers (Scott, 1988) showed a parallel shift to higher partition values due to the separate effects of higher viscosity medium and a larger diameter lower energy Cyclone.

Jan 1, 1993

By OÆBrien D, Priddle D

In order to avoid costly moisture penalties on coal shipments and to minimise rail freight costs, screen bowl centrifuges were selected and installed in the Mount Thorley Coal Preparation Plant for dewatering fine coal product. The Mount Thorley fine coal circuit consists of desliming the -0.5 mm (ww) fine coal in two stages of classifying cyclones prior to recovery by froth flotation. Provision has been made to bypass the flotation circuit with the classified flotation feed reporting directly to product and the centrifuge dewatering circuit has been designed to handle either flotation feed or flotation product. Major mechanical failures of the gearboxes and the ceramic tiling occurred early in the operation life of the machines which led to design changes being made to achieve satisfactory operation. This paper discusses the operating experience at Mount Thorley with respect to both mechanical and metallurgical performance of the screen bowl centrifuges since their installation in 1985.

Jan 1, 1989

By Roberts C

The satisfactory testing and characterisation of mineralisation amenable to heap leaching, is of prime importance to successful operation of a project. This paper outlines a methodology for assessing material suitability. A general model is used for classing material types for suitability for treatment and for economic analysis. The four levels of these are overburden, oxide, transitional and unoxidised materials. During exploration, reverse circulation (RC) drilling can be used effectively to define these zones by a combination of logging, analysis and provision of cuttings for column leach and bottle roll trials. RC cuttings can he used effectively for column leach trials, when calibrated against conventional processing-sized samples, obtained from surface. Tbis allows metallurgical testing to depth and definition of transitional ore types and the base of oxidation, accurately and economically with an acceptable density of samples. The accurate prediction of base of oxidation and variations in recovery with depth and ore types can be used to develop 'economic' pit designs with zones of variable recovery. Petrological studies of leaching results and examination of mineralisation types carried out on concentrates, provide information on gold distribution and physical and chemical constraints. The examination of concentrates can be particularly useful for types of mineralisation when overall gold content is frequently at or below one pan per million. Explanation of anomalous recovery of gold grains in dense goethite and solution-robbing by carbonaceous material can be identified by use of petrological and scanning electron microscope. An understanding of the role of the host rock in leaching characteristics can also he provided by petrology where siliceous or clayey materials can require significantly different treatment.

Jan 1, 1994

By W J. Bruckard, M J. Vaisey

Ashton Mining Ltd (Ashton) and Lynas Corporation Ltd (Lynas) have established a joint venture partnership to develop and process rare earth oxides (REOÆs) from the Mt Weld deposit in Western Australia. The deposit is located in a deeply weathered volcanic carbonatite structure that contains approximately two million tonnes of rare earth oxides at an average grade of 20 per cent REO. As part of the 1999/2000 feasibility study currently being undertaken by Ashton and Lynas, an extensive laboratory beneficiation test program was undertaken by CSIRO Minerals on diamond drill core samples from the Mt Weld orebody. The aim was to develop a flowsheet, based primarily on flotation that could be confirmed at pilot plant scale. The target concentrate grade was 52 per cent REO with a REO recovery of at least 35 per cent. Two main ore types, nominated as CZ (limonitic siltstone) and LI (nodular limonitic ironstone) were identified for separate laboratory evaluation. The lower grade LI-type ore overlies the higher grade and more extensive CZ-type ore. The majority of the work was conducted on the CZ ore; only limited testing of the LI ore was undertaken. The latter contains a clay component that will present difficulties in processing due to its poor filtering and settling characteristics. Two processing options for treatment of CZ ore were presented for pilot plant consideration. One (Option 1) includes gravity concentration prior to flotation while the other (Option 2) includes finer grinding and four stages of open circuit cleaning. The benefits of each scheme are discussed in detail. Neither has been fully optimised and the definitive flowsheet is most likely to be a hybrid of the two schemes, incorporating the best features of each. Typical metallurgical results from each scheme were final concentrate grades of 49 per cent REO, 10-16 per cent Fe2O3 and 3.2-4.8 per cent CaO. REO recoveries were above 35 per cent in both cases. Features of the processes developed by CSIRO were the inclusion of a gravity concentration stage prior to flotation, a modified flotation reagent scheme, a change in the method of feed preparation, and incorporation of magnetic separation to upgrade final flotation concentrates. Metallurgical results obtained from flotation tests on LI ore were much poorer than those obtained for CZ ore. The best rougher/scavenger result, with the limited amount of testing so far completed, was an REO grade of 32 per cent with a recovery of 28 per cent. Further work is needed to develop a viable processing route for this ore type.

Jan 1, 2000

By Gray J, Krouse HR, Changkakoti A, Kwak TAP

The Dachang tin field with more than one hundred million tonnes of ore at 1% tin and 3% Zn is one of the largest tin fields in the world. It comprises five carbonate replacement tin deposits, of which the Changpo deposit containing about 80 million tonnes of ore at about 1% tin is the largest deposit. The deposit, hosted by middle Devonian limestone, argillaceous limestone and black shale, is genetically related to the Longxianggei granite.The oxygen, hydrogen and carbon isotope data of minerals, rocks and fluids suggest a magmatic fluid which evolved during the crystallization of the Longxianggei granite. Mass balance calculations show that the depletions observed in 180 and 13C values of calcites from the ore bodies to the country rocks were due to continous isotopic exchange reactions between the magmatic fluid and the marine limestones at different W/R ratios and between 300 and 600¦C.

Jan 1, 1990

This paper examines the various stages of development and design work which were necessary to develop the cemented rock fill system for copper mining at Mount Isa. The reason for a cemented sand fill development program together with details of the test work undertaken are briefly outlined. The testwork associated with the selection of a suitable local rock to supple- ment the cemented hydraulic fill is discussed, as is the method for underground placement and mixing of the graded rock with the cemented hydraulic fill. The design features of the final system which incorporates a graded rock handling system and a cemented hydraulic fill reticula- tion system is outlined.

Jan 1, 1973

By D M. Aranha, A R. Cabral

Theories on the origin of the Itabira iron formation (itabirite) in Quadrilßtero Ferrffero (QF), as elsewhere in the world, are restricted by the apparent lack of adjoining volcanic units, severe syndeformational metamorphism and deep weathering. Besides the three types of iron formations at QF (siliceous, dolomitic and amphibolitic; Dorr, 1969) we include a fourth type initially described as ocherous, goethitic, limonitic or even yellow iron formation. Considering its high magnetite content, it has been described as yellow magnetite itabirite (Pires, 1979). It was reported as formed by the alteration of the dolomitic itabirite (Dorr, 1969) although the anomalous Al2O3 contents are high for normal weathered itabirite. The yellowish magnetitic itabirite occurs at the bottom of the Itabira Iron formation, along the contact with the Batatal schists, and at the top units of the Itabira, within the Gandarela Formation. Within the magnetitic itabirite at the Tamanduß iron ore mine there are metric zones, concordant to the bedding of pillow-like structures, exhibiting a porous core, surrounded by an intermediate, more granular zone with numerous, minute rounded cavities grading to an external, fine-grained zone with much less minute cavities. In the external portions of some pillows a breadcrust type structure, derived by quenching with the water can be observed. In some other zones, such as the Barreiro hill, an outer, vesicular, whitish yellow, 5 - 10 mm thick, band grades to an aphanitic, isotropic band. The vesicles are slightly flattened against the band surfaces. The existence of fragmental layers showing flowage and fragment alignment, kaolinitic laminas and vesicles filled with kaolinite at Barreiro Hill and Capitpo do Mato Mine represent mesoscopic structures, indicators of a possible volcanic origin. Chemical compositions of the magnetitic itabirite from a wide area in QF revealed a relatively high Al2O3 content, consistent with a volcanic origin.

Jan 1, 2005

By Mandzic E. H

The Dome Mine of Timmins Mining company is located in South Porcupine, N.W. Ontario. The orebody being mined partially lies in the No. 3 shaft pillar. Stability analysis has been carried out to establish the influence of nearby mining on ground movement in the shaft vicinity. Mathematical modelling of shaft displacement has been done for stope layout at depths from 180-210 m and distances of 10-50 m from the shaft. Analysis indicated that ground displacement around the shaft is below 1 mm/m and one third less for cut and fill than in the case of open stope mining. The result of the investigation was later confirmed by cut and fill mining of this orebody.

Jan 1, 1986

Opinions vary widely within the community on what are legitimate environmental social respon- sibilities. The extreme conservationists see the responsibility as the total preservation of the natural environment achieved by opposition to all forms of industrial development that would disturb it. The `growth-at-any-price men' consider it more important to stimulate economic growth, develop new industries, and maximize profit letting the environment take care of itself: within this wide spectrum of concern are the middle-of- the-road men, part of the vast majority, fully aware of the need to compromise to achieve a satisfactory economic growth rate whilst pre- serving to the greatest extent practicable the con- ditions upon which we depend for a balanced self-perpetuating existence. Environmental change is not new. It is the inevitable accompaniment of human activity. Plato wrote in the 5th Century B.C.* of the devastating changes wrought by man and his animals on the ancient world of the Mediter- ranean. Down through the ages rural development to *The Dialogues of Plato: `What are now her moun- tains were lofty, soil-clad hills; her so-called shingle plains of the present day were full of rich soil; and her mountains were heavily afforested-a fact of which there are still visible traces. There are moun- tains in Attica which can now keep nothing but bees, but which were clothed, not so very long ago, with fine trees producing timber suitable for roofing the largest buildings; and roofs hewn from the timber are still in existence. There were also many lofty cultivated trees, while the country produced bound- less pasture for cattle. The annual rainfall was not lost, as it is at present, through being allowed to flow over the denuded surface into the sea, but was received by the country, in all its abundance, into her bosom, where she stored it in her impervious potter's earth and so was able to discharge the drain- age of the heights into the hollows in the form of perennial springs and rivers throughout the land.' provide the necessities of life for expanding populations has required the destruction of vast areas of forest. Industrial activities over the last 200 years have discharged enormous quantities of solid wastes, liquid and gaseous effluents that were environmental pollutants of the worst kind. Urbanization has drawn people, their machines, and industries into vast concentrations aggregat- ing the environmentally bad effects of each to the extent that there is evidence that through thermal pollution these large urban industrial complexes nrp nffPrtina raainnnl rlimnta.c

Jan 1, 1978

By Stewart R

Potential acid rock drainage from the destruction of metalliferous sulph-ides is recognised as a critical factor in the design and economics of any mining venture. While this realisation is relatively new, mining companies have embraced the issue with the aim of scientifically quantifying the magnit-ude of the problem, specific to indiv-idual properties.Coinciding with the development of the open pit mine at Porgera, a comprehensive assessment of the potent-ial for the formation of acid rock drainage was initiated in 1991. Detail-ed study of the mineralogical charact-eristics of all rock types, along with extensive test work to determine the maximum potential of rocks to generate and consume acid (known as acid base accounting or ABA), has been conducted. Correlating this with the known and interpreted geology of the open pit has indicated a strong relationship between rock type, sulphur content and the acid base character. This relationship is used daily as a simple, cost effective means for classification and management of the variety of material types produced from the minincx operation.

Jan 1, 1994