Search Documents

By P J. Fairfield

This paper reflects on the author’s experience working in site-based technical and management roles over a 29 year period, and the past 12 years in internal and external consulting roles. It discusses the author’s experiences and observations of operations management, and the significant value of the technical specialist’s role in providing management with information on what to base tactical decisions, which may or may not be part of a defined strategy.The landscape of mine management changes with the cyclical nature of commodity prices driving operating and capital prudence, as operations change their focus from expansion and growth to staying in the game. The role of the mine manager and management team in navigating through these changing times, attitudes and stages of the project life can influence the success or otherwise of many projects.Technical knowledge is one of the key drivers in realising or destroying the value of a project or operation. As managers focus on people management, management systems and processes, recognising and understanding value in underlying technical knowledge, and getting back to the fundamentals/basics, can be overlooked. In reaction to the fluctuating commodity cycle, managers implement changes through optimisation, fast tracking or parallel streaming, expansion projects and changes in the application of technology. These responses occur against the background of changes in the appetite for risk, acceptance of project uncertainty and changes in personnel which result in a loss of knowledge and experience – often at critical times.This paper shares the author’s experiences and lessons learnt in dealing with and observing these issues. The author questions whether we really understand our projects and are valuing the most important asset, our people and, in particular, the technical specialist and their experience and knowledge.CITATION:Fairfield, P J, 2016. Staying in the game – the importance of engineering-based decisions, in Proceedings International Mine Management Conference, pp 67-74 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jun 22, 2016

By T X. Le, H T. Tran, K Zaw, T Manaka

"An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation. The Truong Son fold-thrust belt (TSFTB) is a prominent tectonic component of mainland Indochina that occurs as a north-west–south-east-trending tectonic entity that extends from north-eastern Laos, straddles the Laos-Vietnam border area and is submerged under the sea basin in east central Vietnam. The TSFTB hosts numerous regional-scale gold and polymetallic base metal deposits, and the mineralisation occurs along the strike of the belt; however, the potential of many of these deposits are inadequately evaluated. The ore mineralisation is hosted by different rock assemblages, including highly metamorphosed Late Proterozoic metasedimentary rocks and Palaeozoic sedimentary and/or volcanic packages, which were intruded by several phases of magma and underwent a number of tectonic events. Several ore-forming styles – including porphyry, Carlin-type and sediment-hosted orogenic Au – were formed during at least two phases of regional thermotectonism that have been identified in the TSFTB. However, all of the major gold deposits/mineralisations are closely related to region-wide structural breaks and many of them are controlled by large-scale, high-strain zones. The fold-thrust structures in the TSFTB therefore play important roles for regional gold mineralisation and metallogeny.CITATION:Tran, H T, Zaw, K, Le, T X and Manaka, T, 2015. Structural controls on gold mineralisation in the south-eastern Truong Son fold-thrust belt and its significance in regional metallogeny, in Proceedings PACRIM 2015 Congress, pp 521–530 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Mar 18, 2015

By N Weerasekara, M Bird, M Yahyaei, M M. Hilden, M S. Powell, J Franke, P Toor

The combination of new tools with a more rigorous approach to understanding the interaction of mill liners with overall mill performance and economics, forms the basis of an integrated approach to liner management. Based on accurate liner wear measurements, some (limited) physical mill inspections and surveys, accurate calibration of the mill load and analysis of process data, a whole new approach to liner selection, relining intervals and mill control is proposed. Collection and analysis of this information in operating mills illustrates the mill performance improvement which can be attained through this careful measurement and modelling approach.A more holistic approach to liner management is proposed, including a broadening of the current work to cover the potential benefits of improved relining technologies and predictive liner wear modelling. CITATION:Powell, M S, Hilden, M M, Weerasekara, N, Yahyaei, M, Toor, P, Franke, J and Bird, M, 2012. A more holistic view of mill liner management, in Proceedings 11th AusIMM Mill OperatorsÆ Conference, pp 95-104 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 29, 2012

Anglo Coal Australia (ACA) takes a proactive position with regards to attracting and retaining employees at a graduate level. Currently, ACA has graduates in its program across all disciplines: Mining Engineering, Mechanical Engineering, Electrical Engineering, Commercial, Occupational Health and Safety, Environmental Engineering, Human Resources, Safety Engineering and Processing Engineering. The current program is three years in duration and involves two (generally) equal periods at different ACA mine sites or Brisbane Corporate Office. ACA takes an active role in promoting its status at the university level by maintaining a scholarship program. Six undergraduate scholarships are offered each year across all disciplines. Associated Vacation Employment is offered to each scholarship holder during the period of his or her university study. This commitment to education is regarded highly by future graduates. ACAÆs active role in sponsoring student bodies is also known and appreciated amongst the university population. ACAÆs graduate program has been a successful training program for future leaders of the coal mining industry. The company is committed to making the program more suited to the needs of the graduates across all disciplines and as a result the program is not stagnant but is constantly changing and evolving. Recently the æGraduate PassportÆ has been drafted with an aim to keep each graduateÆs needs in relation to experience and training firmly in focus for the duration of the three-year program. Appropriate training for each graduateÆs position is supported by the company; for instance, support through funding and time for a commercial graduateÆs CPA qualifications is provided.

Jan 1, 2005

By May J. R

Exploration, including research, has fuelled the enormous expansion of the Australian mineral industry in the last three decades. Analysis of success and failure in exploration and research has therefore potentially powerful lessons and messages which may be used to influence the future shape and direction of the mineral industry. Research has been an integral part of organised corporate mineral exploration since its beginnings in Australia in the 1930s. In corporations, the activity generally called project generation or new project development is the main expression of exploration research but mostly it goes unidentified and poorly documented except perhaps when a successful discovery is made and reported on. The competitive nature of exploration means that extended and detailed analysis of corporate exploration research across the industry is impossible to achieve.

Jan 1, 1992

By M Watkinson

Tube bundle monitoring systems have come a long way from their first introduction to coal mining in the late 1960s/1970s. Early developments in the United Kingdom (UK) commenced with single gas analysers (carbon monoxide) and quickly moved towards introducing oxygen analysers and methane analysers for improved analysis, in particular the calculation of air-free results. Recommendations were made in the early days as to how and where to run tubes and on the matching of sample pump and purge pump pressures. Current Australian installations are commonly based on a four-gas multianalyser, infrared for carbon monoxide, carbon dioxide and methane, and paramagnetic for oxygen. These systems are controlled with programmable logic controllers (PLC), with component monitoring as an integral part of the software. This paper discusses the development of tube bundle systems from the 1960s to the current date and looks at the advantages and disadvantages of the installations, along with making operational recommendations to be considered with the siting of the analyser building, running of tubes and maintenance of the system.CITATION:Watkinson, M, 2015. Developments in tube bundle gas monitoring, in Proceedings The Australian Mine Ventilation Conference, pp 259–266 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 31, 2015

Recovery of gold by smelting zinc dust concentrate has been carried on at Lake View and Star, Ltd., since July, 1930, when the Merrill-Crowe precipitation plant was first put into operation.Part I describes the development of current gold-room practice, commencing with the clean-up of the MerrillCrowe plant, a procedure that has not materially changed since its inception, and then shows how modifications to straight roasting and smelting became necessary, following a gradual increase in the copper content of the ore treated by the mill.Present smelting practice converts most of the copper into a mixed copper-lead matte, thE sulphur being supplied by the addition of flotation concentrates containing about 35% sulphur as pyrite. The process yields gold bullion of a sufficiently high grade to send to the Royal Mint, but until 1943, suffered from the disadvantage of giving matte and slag by-products high in gold and silver, that were not recovered directly but had to be sent to a smelter.Part Il gives details, of experimental work cnrried out since 1943 which led .to a process for the satisfactory and economic recovery of not only the gold and silver, but also the copper from these, hitherto, troublesome by-products. Nevertheless, incidence of matte in a smelt has always been considered undesirable, and it is hoped that eventually it will be obviated by removing most of the copper from the zinc slime before smelting.Part III indicates the methods by which this might be achieved, and outlines the experimental work that has been done up to the present.

Jan 1, 1948

The green field site is one that has no history of mining and as such it presents the designer with a blank canvas, on which any number of drill and blasting options can be drafted. No matter which mining method is selected all technology and experience will need to be acquired from outside sources, applied quickly and produce the right results. North Limited, in joint venture with the Sumitomo Group (20 per cent), have developed AustraliaÆs first block cave mine at Northparkes in New South Wales, Australia. This innovative and large scale mining project was taken from a green field site in November 1993 to a fully commissioned block cave mine in December 1997. NorthparkesÆ Endeavour 26 mine is now producing at a rate of 3.9Mt per annum from a 27Mt ore block. Prior to 1993 no history of mining activity existed at Northparkes. The rock had never been blasted and many questions were raised about how it would behave. While it was clear that the Endeavour 26 (E26) orebody contained geotechnical properties appropriate to block caving, the blasting methods required to establish a block cave mine had never been used in Australia and no designs were available. The joint venture partners had no prior experience with block caving and it was immediately apparent that this blasting technology would have to be acquired from foreign sources and applied to the unique local conditions. Conceptual designs for the block cave drill and blast were first drafted in 1994, first issued for drilling in December 1995 and first blasted in January 1996. 470 km of drill metres and four million tonnes of rock were blasted to complete the undercutting project by September 1997. This paper will provide those developing new drill and blast projects with an inside view of how one small technical team solved many design challenges to successfully construct AustraliaÆs first block cave mine under strict quality controls and ambitious time constraints.

Jan 1, 1998

By D Hunter

A production information management system (PIMS) was recently implemented at Queensland NickelÆs Yabulu Refinery. Although a strong business case was developed to justify the significant investment in PIMS some potential beneficiaries remained sceptical of the anticipated benefits. The decision to install PIMS was justified as the on-line availability of continuous production data enabled the optimisation of some crucial operations resulting in significant cost savings, improved throughput and final product quality. Furthermore the rapid access to extended historical data has allowed the cause of repeated failure of equipment to be determined. The investment is expected to pay for itself within two years and has already contributed towards significant savings. This paper focuses on some of the diverse production improvements gained and compares the anticipated benefits in the business case to those achieved. A brief outline of the phased implementation of the OSIsoft PI data historian and complementary client software at Yabulu is included, along with details of the lessons learned.

Jan 1, 2003

By K H. Esbensen

Optimisation of a real-time at-line monitoring system for control of industrial granule coating quality is presented. The system is based on a fluorescence imaging system, because fluorescence originates in the interiors of enzyme granules but is significantly quenched by a polymer coating (which is needed due to environmental precautions). We have developed an image analytical system for direct prediction of coating quality, which is based on application of the Angle Measure Technique (AMT) for image complexity characterisation; AMT is briefly described. The first part of the presentation addresses pixel sampling strategies within a digital industrial image, inherent in application of AMT, in which the unfolded image is regarded as a one-dimensional object in analogy with 1D process sampling in Theory of Sampling (TOS). The effects of random, stratified and systematic pixel selections in the unfolded image are evaluated. Also factors such as the fraction of image pixels and the effects of specific unfolding strategies (there are three principal strategies, termed æchopÆ, æsnakeÆ and æspiralÆ respectively) are investigated. It turns out that unsuspected artifacts are sometimes produced, related to the specifics of the unfolding procedure, which interferes with a straightforward 1D TOS process sampling analogy. These artifacts have a wider interest û among others, for 2D sampling û and therefore receive special attention in this presentation. The optimal pixel selection strategy for the AMT algorithm is found to be systematic or stratified sampling (not surprising according to TOS) of 500+ initiating points, but need to be unfolded in the novel spiral- or snake-wise fashions in order to effectively counteract these artifacts. This also has a general impact on various suggested standard schemes for 2D grid-sampling, among others, from the geoscience realms. The second part of the presentation is directed towards optimal image analytical sampling of a continuous series of fluorescent images (imaging of conveyor belts of æinfinite lengthÆ), ie optimisation of process image sampling. The minimum number of images needed to uphold a sufficiently good on-line estimate of the quality control (QC) parameter in question is found to correspond to the relatively high sampling rate of 15 - 20 per cent, which can be shown to be related to an intrinsic very high measurement error level (25 per cent) of a mandated analytical reference method.

Jan 1, 2005

By J Seccatore, T Marin, M Cardu, G De Tomi, F Galvão, A Rezende, E Melo

Small-scale mining operations are characterised by a large variety of equipment availability and a high level of operational flexibility. Mine planning is usually scarce or absent in small quarries in Brazil, and mine management generally focuses on daily operations. As a result, analysis of the effects of unit operations, such as blasting, over the whole mining process is often neglected. The goal of the following project was to study the effect of production blasting on loading and hauling times, secondary breaking times and primary crushing times at the Experimental Mine of the Research Center for Responsible Mining of the University of São Paulo, Brazil. The operations analysed included blasts that performed:under the average operational standard, defined in this paper as Case 1according to quarry standards, defined in this paper as Case 2.In order to establish the effects of blasting on the downstream process, three key performance indictors were used:The time taken to load the truck, when there is the need for material selection. Due to the fact that we do not have an operational baseline, the increase in time cannot be established, meaning that we must content ourselves with comparing the mean time in each scenario.The average time used for secondary breaking machinery.The time required for the primary crusher to fully process the load of a single truck. The results obtained indicate correlations between the coarseness of the blasted material and these operational times. Solutions are suggested and evaluated for the improvement of the small-scale mining process.CITATION:Marin, T, Melo, E, Seccatore, J, Cardu, M, Galvão, F, Rezende, A, Bettencourt, J and De Tomi, G, 2015. The effect of drilling and blasting performance on fragmentation in a quarry and time for loading, secondary breakage and crushing, in Proceedings 11th International Symposium on Rock Fragmentation by Blasting, pp 355–362 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 24, 2015

In this paper a quantitative deterministic risk modelling approach (Quadrim) is introduced. The mathematical framework and equations for quantifying uncertainty within and aggregating across value chain nodes from error propagation techniques is proposed and discussed. A case study and worked examples, based on a hypothetical mine are then presented. This illustrates how uncertainty from the mining and economic value chains can be handled in a typical net cash flow calculation, and how this can be translated to a risk model. It is then illustrated that current valuation techniques do not just result in an information gap for decision makers. Traditional approaches such as discounted cash flow (DCF) analysis and truck and shovel productivity analysis, which do not take into account uncertainty in input values, can result in potential bias in estimates such as net present value (NPV) or equipment hours

Sep 26, 2011

Permeability and fluid pathways in fracture-controlled hydrothermal systems are governed by a dynamic competition between permeability-creation processes and permeability-destruction processes. Permeability evolution is coupled with the evolution of fluid pressure and stress states. Key permeability-creation processes are micro-scale to macroscopic fracture growth, and the generation of damage zones during co-seismic slip on faults or aseismic creep on faults and shear zones. The competing permeability-destruction processes include crack-healing and sealing, compaction and pore cementation. High rates of permeability destruction in hydrothermal systems require ongoing permeability enhancement to sustain high fluid fluxes and ore genesis.   In aseismic regimes, competition between permeability-creation processes and permeability-destruction processes can lead to continuous flow in deep level hydrothermal systems. However, in seismogenic regimes, rapid co-seismic permeability-enhancement is followed by progressive permeability-destruction in the intervening interseismic periods, and leads to episodic flow. The results of high pressure experiments are used to illustrate how pore fluid factors and stress states are dynamically coupled with permeability evolution in hydrothermal regimes. Particularly in the seismogenic mid- to upper crust, large changes in permeability during the seismic cycle govern relative rates of change of fluid pressure around active faults and shear zones. Rapid, post-seismic recovery of pore fluid pressures, relative to rates of shear stress recovery, leads to growth of hydrofracture networks prior to successive fault rupture events.   Pre-rupture hydrofracture networks do not develop where post-rupture fluid pressure recovery is modest relative shear stress recovery. At elevated temperatures, low rates of pore fluid pressure recovery relative to shear stress recovery promote ductile shear failure and grain-scale permeability enhancement within shear zones prior to rupture events.   The influence of pore fluid pressure cycling, shear stress cycling, and deformation processes in controlling the evolution of permeability, flow localisation, and flow anisotropy at the deposit scale are illustrated for mesothermal and epithermal lode gold systems.

Jan 1, 2005

During 2009 the technical services staff at Barrick Gold Corporation's Australian Business Unit conducted a review of their five underground mines that utilise pastefill as the backfill component for these operations. Of the five mines reviewed three use dry tailings and two use wet tailings plants. The primary aim for these reviews was to determine whether pastefill was the right option to be used, and if not, what where the alternatives. The reviews undertaken focus on several areas including, paste plant operation, reticulation and barricade techniques, the geotechnical requirements for pastefill in regards to the current mining methods, the consideration of alternative methods, capital and operating cost histories compared to initial estimates, and a cost benefit analysis of pastefill against other mining methods. The main benefits from the use of pastefill is increasing the extraction of the resource, reducing or eliminating the need to leave pillars. In some mines the use of pastefill is geotechnically driven, to manage high stress environments or mining induced seismicity. A third benefit of using pastefill in some circumstances is that it reduces dilution, however it is considered that this is not a valid argument for most of the mines reviewed. At two mines no alternative to pastefill was determined, whilst differing extraction and filling strategies were potentially identified at the other three mines. The reviews developed cost benefit curves for those sites that had alternative mining methods to assist in determining whether pastefill is the right option to use for any particular stope. At the grades typically mined in each operation, pastefill was the preferred option to use. In all mines, pastefill was determined to be the best option at this time.

Nov 25, 2010

By T Dawson, B Haskins

Fatigue is it the newest buzz word or is fatigue a real phenomenon that is creating safety and organisational risk for you? There is no debate that fatigue is natural, and it affects us all, just like gravity; however, there has been much debate on the severity of its impact in the workplace. For many years the impact was not measurable, hidden out of sight and, quite frankly, written off as the infamous ‘operator error’. Over the last several years, advancements in technology have provided safety and health professionals, sleep scientists, fatigue experts and organisations with the ability to monitor and detect fatigue events in real time, as well as predict and monitor increased risk for fatigue events. Caterpillar Safety Services has assembled an extensive and exceptional set of technologies that will provide the best methods and data to measure the impact of fatigue. This paper will discuss fatigue in the workplace and review the technologies and data sets available, which will allow the reader to determine whether this risk is real or rubbish.CITATION:Haskins, B and Dawson, T, 2017. Fatigue risk in your operations – real or rubbish? It actually depends , in Proceedings 13th AusIMM Underground Operators’ Conference 2017, pp 137–142 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 16, 2017

By G Harbort

Traditional engineering design for flotation circuits use the “Rule of Thumb” approach. Typically this uses a nominated maximum head grade for design. A scale-up factor is applied to laboratory flotation tests for residence time. This scale-up factor is usually based on a designers experience at other flotation sites and may or may not be relevant to the circuit being designed, or the flotation equipment being used. A small number of locked cycle tests are assumed to represent the ore body and the results of these are often used for financial analysis, independent of changes in mine plan throughput and mineralogy.The engineering “Rule of Thumb” approach is only strictly accurate where there is very little variability in throughput, head grade and mineralogy. It may provide accurate design for mature established operations where a brownfield expansion is being considered but is unlikely to provide accurate design for a new, greenfield site.The use of geometallurgical modeling with floatability component simulation provides a design methodology with significantly less associated risk. The use of geological data for optimisation of operating plants has become a significant part of the modern process mindset. The underlying principle is to use spatial metallurgical information to drive production planning, mine planning, blast design, blending strategies and plant set-up. At a design stage the process designer can use geometallurgical information to evaluate bottle necks and potential design flaws and propose the best investment strategy for the project benefit.This paper details the geometallurgical characterisation of the Andash deposit and methodology used to review the project’s detail design and projected production.

Aug 8, 2011

By B Lumsden

During periods of high metal prices and strong metal demand tailings retreatment can be economic. Most tailings retreatment operations are technically challenging, low margin operations, because the easily recovered mineral has already been removed, therefore, process improvements can potentially yield large economic benefits. The Hellyer tailings dam was owned by Intec Ltd and contained 10.9 million tonnes grading 2.8 per cent zinc, 3.0 per cent lead, 88 g/t of silver, 0.16 per cent copper and 2.6 g/t gold. In November 2006 the Polymetals Group, as operator, restarted the Hellyer plant to retreat these tailings. Within a few months the operation had stabilised and Polymetals was meeting budgeted targets of throughput, metal recovery and concentrate quality. Polymetals and Intec then investigated methods that would improve the metallurgical result for this difficult to treat tailings. Since the tailings are fine-grained with 80 per cent <45 ¦m, magnetic aggregation of the paramagnetic sphalerite was evaluated. Magnetic aggregation of an oxidised tailings feed has not been tested before, nor had the technology been available when Hellyer ore was originally processed. Extensive statistical test work showed magnetic aggregation of the sphalerite fines in the zinc cleaner circuit increased total zinc recovery. The increase in the mean zinc recovery with magnetic conditioning was 3.63 per cent, at a statistical level of confidence of 97.8 per cent, and at the same mean zinc concentrate grade.

Jan 1, 2009

By Kato T, Eguchi M, Seino T, Itagaki K, Kimura T, Muto T, Shimizu T, Kobayashi T

Behaviour of minor elements in the dust collecting system connected with fluidized bed roaster for zinc concentrate was investigated by use of the bench scale experimental appara- tus. The dust collecting system was consisting of two dust chambers, hot electrostatic precip- itator, washing tower, mist electrostatic pre- cipitator, drying tower, absorption towers and potassium permanganate solution towers. Some volatile elements such as lead, cadmium and arsenic tend to concentrate in the fine calcine obtained in hot electrostatic precipitator especially in the case of the roasting with insufficient air supply. Special attention was paid to behaviour of mercury. In the roasting tests for plain zinc concentrate, it was considered that most mercury volatilizes at first as elemental vapour in the roaster, but with decrease in temperature of gas around a half of mercury forms compound, and both elemen- tal and compound forms of mercury were found in the gas stream. Elemental mercury is of course difficult to be trapped in the dust collecting system. To promote the compound formations, some additives for concentrate, such as selenium and halogens were effective, especially selenium of a few times equivalent to form HgSe repre- sented complete conversion of mercury from elemental to compound. To clarify the behaviour and removal mech- anism of mercury, various small scale laboratory tests were also carried out. It was confirmed that mercury sulfate formation is possible if temperature and flow rate are adjusted adequate- ly for gas stream consisting of 02-SO2-N2. To trap elemental mercury, various substances were tested, and excellent results were obtained with selenium. Satisfactory results were obtained with a selenium disc heated at 100 to 200¦C in a mercury containing gas stream. Also, applica- bility of scrubbing method with SeO2 solution was investigated, and the solution containing a few hundred ppm SeO2, 0.01 per cent additive and 6 per cent H2SO4 proved to be satisfactory.

Jan 1, 1980

By M Sebbag, T Taimre

Barrick Gold Corporation is proceeding with development of the Buzwagi Mine in the Lake Victoria Greenstone Belt District of Tanzania. The Buzwagi orebody occurs in the Nzega Shear zone within the Greenstone Belt and is hosted in a K-Feldspar rich granite in contact with mafic volcanic. The orebody presents 2.6 M ounces in 41 Mt of reserves, at 2.0 g/t. Over the ten year mine life, total material movement will be 261 Mt. The feasibility study was completed in 2006 and presented several technical challenges. Two principle challenges are grade control and the impact of dilution on the economic viability of the project. The principle challenges for grade control will be quality control and quality assurance in the sampling of the massive coarse grained granite, which comprises 70 per cent of the deposit. The principle challenge with dilution will be with the selective mining of the narrower mineralised zones contained within the mafic volcanics. This paper will focus on the mine planning methodology which has been applied including selective mine unit (SMU) and dilution estimation, net smelter revenue (NSR) calculation and the effects of cut-off grades to the project economics and mine schedule.

Jan 1, 2007

NEARLY all problems in mining engineering involve the transport and distribution of materials from place to place, and in general the most economically managed mines and plants are those in which the transport of materials has been carried out most efficiently. Of all these transport problems, the hoisting of ore out of the mine and the distribution of same to the various treatment works is perhaps one of the most important. It is proposed in the present paper to traverse the conditions,affecting the location, scale of operations, and design of the main shaft and head gear at the Mount Morgan mine; afterwards describing the designs and workings of the shaft house, winding engine, and transport from the shaft house to the treatment works.LOCATIONWhen the copper-gold ore was developed sufficiently to determine approximately the boundaries of the ore-body, it was found that the existing vertical shafts would be wholly inadequate to deal with the increased quantity of ore required to be handled. It was proposed, therefore, to construct a new shaft, and to handle in this...

Jan 1, 1911