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This paper will present a series of examples drawn for a number of Australian and international mining companies showing their recent attempts at optimisation of capital. The results will be compared, contrasted and discussed in the light of six factors that are considered crucial to any analysis of this subject. The factors are: ò the market availability of capital ò the corporate strategy and performance ò the capital structure appropriate to the corporate positioning within the industry ò the parties to the optimisation equation ò the measurement of success of optimisation The factors above are not mutually exclusive and are generally interdependent so their order above is of little consequence. Other papers presented at this conference will dwell in more depth on all these factors, therefore this paper shall focus only on the key elements of each factor. By way of summary this paper will also address the issue of the longevity of optimisation - is it temporary or long term.

Jan 1, 1991

By Morrison R

Optimisation has two distinct applications in the concentrator ò the first is in the area of the flowsheet and the operating parameters of the various unit operations ò the second is associated with the higher levels of process control. The Plant Metallurgist is faced with a library of complex theories relating to optimisation. The practical reality of optimisation lies in a combination of steady state simulation to ensure that the process route will permit maximum productivity and an appropriate process control system which will permit achievement of the production and quality objectives.

Jan 1, 1991

In March 1990, Heritage Mining conducted a 2000 line km high resolution aeromagnetic survey of all its prospects in the Coromandel Peninsula. One of the areas covered was the Onemana Peninsula, situated about 5 km north of Whangamata. Details of location and geology are given by Robson and Stevens (this volume).   The detailed helicopter-borne magnetic and radiometric survey over the Onemana area consisted of 163 line kmÆs of flying, and was carried out in order to assist in the definition of hydrothermal alteration and pre- or post- mineralisation structures. The line spacing chosen was 100 m, flown east-west, with a mean sensor terrain clearance of 80 m. Tie lines were flown north-south every kilometre for levelling purposes. The sensor was a Geoinstruments G-813 proton precession magnetometer in a towed bird, with data recorded using a Geoinstruments G-2000 acquisition system.   The Onemana alteration system is at the northern end of a major north-north east trending structural corridor defined by regional aeromagnetic surveys performed by AMOCO in 1980 (Rabone, 1991). T his structure hosts a number of other extinct hydrothermal systems including Karangahake and Golden Cross. In the Onemana contour plot the predominant north-northeast structures form the boundaries of a large area of subdued magnetism in the southern part of the surveyed area that is caused by intense hydrothermal alteration. This area is about 3.5 km long by 1 km or more wide and contains outcropping sinters and hydrothermal eruption breccias, as described in Robson and Stevens. A number of other structures transect this alteration zone, with strike directions ranging from northwest to north. A northwest feature notably truncates the zone to the south, while the northern end seems to be simi1arly bounded; however as data coverage ends at the coast, this feature is less conclusive.    Two distinctive types of strongly magnetic rock were discernible the contoured data. The strong negative magnetic anomalies the north and west are caused by fresh negatively magnetised rhyolites. This was confirmed by ground follow-up work that showed the rocks to be fresh biotite rhyolites with high magnetic susceptibilities.

Jan 1, 1991

The Porgera Joint Venture commenced production during September 1990. A small tonnage underground mine extracts high grade gold ore using small scale stopes. Conventional drill and blast methods are used for development and production mining. Ground support is effected with Splitset anchors, grouted rebar bolts and grouted cable bolts. Splitsets and grouted rebar can be installed by mechanised means. Vertical crater retreat, slot and massfire, and modified VCR stoping tech- niques are used at Porgera. Stopes are backfilled with a relatively strong cemented rockf ill. Future stope sequences require recovery of pillars beside and under filled stopes.

Jan 1, 1991

Mt Waruwari, host to the Porgera underground gold mine in the Highlands of Papua New Guinea (PNG), is a prominent ridge of sediments and dioritic intrusives rising approximately 600m above the surrounding valley floor. Consequently, mining occurs in a low stress environment where structural and material considerations are foremost in the design of ground support and reinforcement. Three major rock types are encountered in the underground mine. These are locally referred to as "black sediments" (slightly indurated mudstones and clayey siltstones), "altered sediments" (derived from black sediments by thermal metamorphism), and "intrusives" of dioritic composition. The rocks are moderately to highly fractured, the black sediments being generally weak and occasionally sheared while the altered sediments and intrusives are quite strong but often brittle. Mining takes place from a series of stopes extracted by either slot and mass blast or a modified vertical crater retreat method (VCR), which are backfilled with a cemented rock fill. Ground support and reinforcement has been relatively conserv- ative to date and generally relies on pattern reinforcement of all development with cement grouted "rebar" bolts and mesh, extending to pattern cable bolting with occasional mesh in stope backs. In addition there has been considerable reinforcement of stope hangingwalls in some cases. A programme of broad scale structural mapping, monitoring with extensometers, material property testing, and stress analysis has been devised to allow optimum design of ground support and reinforcement in the future. Considerable work remains to ,omplete this task.

Jan 1, 1991

By Tran T, Young D

During the processing of gold, effluents that are discharged into the tailing dams contain free cyanide, metal cyanide complexes of zinc, copper, iron, etc and their oxidised products such as ammonia, cyanate and thiocyanate. A knowledge of how different cyanides behave in the solution is vital to metallurgists working in the area of cyanide waste treatment. Although the free cyanide ion is not stable in aqueous solutions and is expected to degrade in a natural environment by atmospheric oxidation, the metal cyanide complexes, especially of iron, are very stable. The CHEMIX program from the THERMODATA package, developed by the CSIRO Division of Mineral Products, was used to evaluate various copper-cyanide and iron-cyanide systems. The simulation of these systems show how the free cyanide and cyanide complexes behave at different conditions of solution composition and acidity (pH).

Jan 1, 1991

Subsidence prediction methods can be divided into two basic types: empirical and analytical. Empirical methods are based largely on a combination of experience, intuition and observations from a large number of observed subsidence data. They are simple in their application, but they are not based on any principle of mechanics. Analytical methods are based on equivalent material modelling principles, where the ground surrounding the extraction is mathematically represented by idealised materials that deform according to the principles of continuum mechanics. Wide applicability and improved understanding are the principal advantages claimed for this approach. In NSW, significant progress has been achieved in the area of subsidence prediction during the last ten years. Empirical prediction curves are available in NSW for predicting the ground movement in the Southern and Newcastle Coalfields. A' comparison of subsidence values predicted from these curves with the actual monitored values indicates that the curves are adequate for use in conjunction with the existing damage assessment methods. Future research for improving the existing empirical prediction curves can only be justified if it is cost effective. There are several numerical models currently in use in NSW for predicting subsidence. The models do not appear to be superior in their ability to predict subsidence when compared with the empirical curves. the performance of these models will no doubt improve along with advances in defining strata properties and failure mechanisms.

Jan 1, 1991

By Campbell J

After eighteen months of discussions with employees and their trade unions, multiskilling was introduced at the Hellyer concentrator in early 1989, coinciding with the plant commissioning. Multiskilling was introduced with the Hellyer Skills Acquisition Program together with intensive training and performance assessment. Design innovations have helped to improve productivity. There have been some difficult times with personnel tending to return to the old and traditional ways of operating. In general, these have been overcome to ensure the success of multiskilling at Hellyer. The main factors making multiskilling effective have been continual training and assessment, and a competent team of shift supervisors. This has improved work standards towards the high level expected from a multiskilled approach without compromising safety standards.

Jan 1, 1991

By Whitham M

Prior to exploitation, the feasibility of mining and recovering ore can usually be determined to a satisfactory level of uncertainty by the consideration of conceptual scenarios, using a range of reasonable parameter values. Such values are selected on experience, knowledge of other mining operations, and the characteristics of the particular deposit being considered. Having established such feasibility, it is usually considerably more demanding to determine what the optimum set of parameters might be. Yet many decisions taken at the feasibility stage represent commitments extending at least into the medium term.

Jan 1, 1991

The Golden Cross Mine will be the first underground gold mine in New Zealand to operate since 1952. The development plans, along with the conditions and circumstances presently found in the now ongoing mine development, will be discussed as well as a brief review of planned stoping activity and stoping results to date.

Jan 1, 1991

By Avraamides J, Ritchie I. M

Gold Tellurides are important sources of gold at Kalgoorlie, Western Australia, Cripple Creek, Colorado and Vatukoula, Fiji. Unlike free gold, the tellurides of gold are rather refractory and the usual treatment practice has been to oxidize the tellurides, either chemically or by roasting prior to cyanidation of the liberated free gold. There is a large measure of disagree- ment as to the actual cause of the refractory nature of gold tellurides. In order to investigate the leaching chemistry of gold telluride, a study was undertaken on the thermodynamics and kinetics of its dissolution using electrochemical methods. From this study suitable direct leaching condi- tions are suggested. In acidic chloride solutions gold telluride can be leached using iron(III) as the oxidant. At lower acid concentrations the reaction is controlled by the formation of a passivating film of H2TeO3. In alkaline solutions containing cyanide the rate of gold telluride dissolution increases with increasing pH and strength of oxidant. However, this can result in excessive consumption of cyanide in the presence of stronger oxidants.

Jan 1, 1991

By Kilgour I

The installation of a final cleaning column at Ok Tedi Mining Limited was carried out to increase final concentrate grade in order to reduce concentrate handling, shipping and treatment charges and to reduce penalty payments. To fast-track the project a decision was made to install a full-size column on one of the two parallel circuits, designed on information readily available and utilising the experience of mill staff and an engineering consultant, rather than delay installation while a pilot scale program was conducted. A 3.66 m diameter by 12.8 m high column was installed to produce 40 t/h of final concentrate from a combination of rougher concentrate and recleaner concentrate. The column design and sparger system were by Cominco Engineering Services Limited.

Jan 1, 1991

By Silver EA

The Finisterre Range on the north coast of Papua New Guinea is the uplifted forearc riagio.n. of a modern arc-continent collision. The core of the range is composed of the P- nisterre Volcanics, an Oligocene''-arc terrane. The southern flank of the range consists of a clastic sedimentary sequence which is an uplifted accretionary wedge and collision complex. This clastic sequence can be subdivided into three distinct units. To the south of aiid structurally below the Finisterre Valcanics are the Mebu beds, an Oligocene- $arly Miocene sequence of volcanolithic turbidites. The Erap Structural Complex is south of, and structurally below the Mebu 43eds. , It consists of three subunits; the 3rly Pliocene micaceous turbidites of the Sukurum unit, contemporaneous pillow basalts AF{ the Basalt unit, and Late Pliocene to Pleistocene volcanolithic turbidites of the -Nariawang unit. The Quaternary Leron Formation, a fluvial to shallow marine 'clastic unit, is the southernmdst. and structurally lowest unit of the clastic -sequence The Finisterre Range is dominated by a fold-and-thrust belt with most thrusts "dipping steeply N. Melange fabric _ is developed in the vicinity of major thrusts. "ffle thrust belt strikes NW, oblique to the regional convergence direction, but no strike-slip motion is observed along NW striking faults.

Jan 1, 1991

By D Vickers, N C. Fowke

The reduction of geological risk for planning of high production longwall faces is essential. Geological and geophysical techniques applied at Huntly West Mine before 1989 were unable to reduce the geological risk to an acceptable level. The success of a trial long-hole directional drilling programme at Huntly West Mine (Fowke et al, 1989) has encouraged the Coal Corporation of New Zealand to use the technology long-term, for seam definition. Initial drilling in 1989 completed a total of 3543 metres, with the longest borehole length being 369 metres (limited by number of rods available). A major re-interpretation of seam structure resulted from the drilling, which was able to fill in seam details between surface exploration boreholes. The undulating thick seam conditions at the mine require a refinement of drilling strategies used overseas. Long-hole directional drilling also displays potential for inseam gas drainage. Gas flows of the order of 1000 L/min were initially indicated in individual boreholes. Other gas parameters of the seam have been studied by Beamish et al (1991), and highlight the significance of the natural gas resource in the Huntly Coalfield.   The continued development of drilling technology will be of major benefit sustainable development, particularly in policy.

Jan 1, 1991

This paper reviews the current techniques employed in the prediction of subsidence and how they have been applied to partial extraction systems. The method using influence functions to describe the shape of the profile is investigated in detail and has been adopted to model the subsidence over workings in Huntly. It is compared with the profile methods developed in the United Kingdom and found to predict the subsidence profile more accurately than these methods.

Jan 1, 1991

By Churchill M

One of the significant changes which has occurred in the flotation sector of the minerals industry, over the last two decades, has been the successful development of the very large flotation machine. The last twenty years has seen the volume of the individual cell, available to the industry, increase by a factor of ten. Today, new mills, and existing mill modernization plans, can consider individual cell volumes as large as 85 m3 with the certainty that the metallurgical performance capability of the large machine is inherently as efficient as the smaller machine. The large flotation cell offers benefits to the user such as reduced floor space, lower total power, process control simplification, and reduced maintenance. However, the flotation machine size selection process, based on overall installation economics, must include such factors as process tonnage, flotation kinetics characteristics, and metallurgical performance objectives. This paper discusses the flotation machine size and circuit arrangement selection based on both metallurgical performance and economic considerations. A computer based flotation kinetic analysis technique, which has proven valuable in quantifying the metallurgical response of flotation circuits having different cell sizes and number, is utilized to illustrate the selection of cell size and arrangement best suited to a client's Requirement.

Jan 1, 1991

By Higuchi K

For the mechanisation or automation of mining, recognition of the shape of mined cavities is basic information. A three dimensional shape measuring system, developed and tested, includes an ultrasonic range finder which is attached to the tip of a serial link manipulator. The range finder can be moved to any position and direction in the operational space of the manipulator. The position of a point on the surface of the object is obtained from the position of the range finder, the direction of the beam of the ultrasonic waves and the measuring distance of the range finder.To avoid collision between the sensor and the object, the manipulator is controlled to trace the surface of the object For the tracing control, another ultrasonic range finder is employed. The test results show that the developed system has high performance.

Jan 1, 1991

By Qi P. H

Gold dissolution can be achieved with a number of complexing ligands, all with varying degrees of stability. Processes based on the use of halogens have been known for many years. Beside providing the necessary complex- ing role, the halogens under the appropriate conditions are very effective oxidants for gold. Of the halogens, the gold iodide complexes are the most stable in aqueous solution. Iodine can establish the desired oxidation poten- tial for oxidizing gold, and unlike chlorine and bromine, the oxidizing potential of iodine is mild enough to avoid the oxidation of impurity constituents like metal sulfides. A series of experiments to investigate the fundamental electrochemistry of gold in different halide solutions was performed. Cyclic voltammograms of gold in the presence of 10-2 M chloride, bromide and iodide, respectively show that for a given potential the rate of oxidation is much faster in iodide solution than in either chloride or bromide. An overlay of linear sweep voltammograms for the anodic oxidation of gold in iodide and the cathodic reduction of iodine species on gold provides an effective method for examining the dissolution of gold in iodideftodine solution. The dissolution rates obtained from both electrochemical and actual leaching results are compared. Optimum leaching conditions are analyzed in terms of the iodide/iodine concentrations. Conceptual processes for the recovery of gold and iodide and the regeneration of iodine are discussed.

Jan 1, 1991

By Smith P

The past 20 years have seen the replacement of hydraulic control of longwall mining systems by the neater. smaller and better controlled electronic units.Early problems of moisture and other effects on reliability were overcome to see electronically controlled supports chosen for Corrimal Colliery ten years ago. Lessons from Corrimal and elsewhere, with following improvements and sophistication led to wider use as exemplified by Meco and other electronically controlled supports used in more recent installations in New South Wales, Queensland, USA and Czechoslovakia of the total of over 80 electronically controlled support installations worldwide in the past decade. Present work is toward a fully "integrated face" of British Coal by 1993, incorporating the Meco automatic face straightening system already due for practical use in the UK later this year. However the manless face still appears to be some way off although the present minimum crews and close monitoring, including early warning, are promising stages.

Jan 1, 1991

The results expected from a longwall face can best be estimated from the ideal production rate, determined by the capacity of the equipment and the conditions in which it is installed, the effective operating hours, and the utilisation.The effective operating hours are determined by a number of scheduling factors which include the proportion of manned time to calendar time, the effective shift factor (effective time to manned time) and the move times.Analysis of the results achieved on the last 121 completed longwall panels in Australia (1984 onwards) shows a significant trend between 'actual tonnes/manned hour' and 'ideal production rate' (the measure of the capacity of the installation).Using 1982 'state of the art' longwall equipment, (the average in use in the seven year period), it should be possible to produce around 2.7M tonne/year ROM from a mine with one longwall. Few mines are achieving this.A review of production scheduling factors and general natural hazards affecting some mines suggests three things.1. Whilst some increase in average effective hours has followed the CIT decision, further improvement is possible at many installations.2. Many mines subject to general natural hazards, such as high gas make and high general stress, have found effective solutions and achieve the same utilisation as the overall average.3. A small number of faces within such mines have been severely affected, some less so. The most severe effects of natural hazards appear to be very site specific. This emphasises the need for detailed investigation of the causes, and development of means of predicting their presence. Only then can either satisfactory technical solutions be found to overcome the problems or prior decisions be chosen not to mine badly affected panels.

Jan 1, 1991