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By T Honeyands

At present we are witnessing large investments in the iron ore industry, fuelled by demand from Asia. At the same time, there is a changing landscape in pricing of iron ores, with the recent demise of the benchmark system and the evolution of market based index pricing systems. From a customer perspective, it is the behaviour of iron ores in downstream processing that gives them their value; their impact on the sintering or pelletising process and subsequently blast furnace ironmaking. It is therefore important to consider this value when developing projects, making mine planning/cut-off grade decisions, and in setting quality price differentials.This paper describes the use of the Marx value in use (VIU) model to quantify the downstream value of iron ores. The Marx model consists of heat and mass balance modules for sintering, pelletising and a rigorous two-stage heat and mass balance model of blast furnace ironmaking. Mass balance and cost models are applied for steelmaking, casting and rolling. The use of a heat and mass balance allows accurate comparison of the impact of raw material properties on blast furnace operation. The impact of minor elements, such as alumina, silica and phosphorus, and metallurgical properties on ironmaking is described, and examples given for the relative value of haematite, Marra Mamba, and channel iron deposit (CID) ores.

Jul 11, 2011

By A Jewbali, R Perry, R Inglis, L Allen

"The use of conditional simulation to characterise mine plan uncertainty is increasing for the assessment of risk in mining projects. While the development of grade uncertainty profiles is relatively straightforward and can be validated using standard geostatistical techniques, the addition of geological uncertainty to evaluate total risk remains problematic. Some of the problems associated with geological uncertainty methods include the clustering of data in favourable geologic units, difficulty in training image definition and the inability to address change of support issues for categorical variables. Despite these obstacles, the importance of geological uncertainty as a contributor to total uncertainty has prompted Newmont to explore and evaluate the use of various techniques (and combinations of techniques) on different deposit types.Two orogenic deposits of different geological complexity were selected for the study: Subika, a shear zone-hosted deposit, and Merian, a deposit containing gold mineralisation associated with quartz vein zones and stockwork within which are found higher-grade quartz breccia zones. Newmont trialled various categorical simulation approaches to determine the applicability of these methods for each deposit type and the effect of parameter choice on the width of the uncertainty interval. Some of the techniques that were trialled include multiple point statistics methods, sequential indicator simulation using local probabilities as well as variations of these methodologies.The goals of this study included: gaining an understanding of which techniques may work best in which deposit types gaining an understanding of the intricacies of each method gaining an understanding of the effect that each method has on total uncertainty analysis.This paper presents a comparison of the various techniques and makes recommendations for their use in uncertainty analysis.CITATION:Jewbali, A, Perry, R, Allen, L and Inglis, R, 2014. Applicability of categorical simulation methods for assessment of mine plan risk, in Proceedings Orebody Modelling and Strategic Mine Planning Symposium 2014, pp 85–98 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Nov 24, 2014

By C Slaughter, J C. Tien

Commonly held ideas about effective training have long emphasised the importance of realism. Realistic training builds better experience among the trainees and a better perspective on the training material, making training more effective. While great strides have been made in this realm for mine safety and mine rescue training there are still areas that can be improved. One possible area is the expanded use of a mine fire simulation program where the migration of gases and smoke can be realistically displayed in an emergency, and outcomes varied as different conditions are being simulated. The use of mine fire simulation software potentially allows for the creation of more realistic scenarios in that smoke advance rates can be measured and recreated in evacuation scenarios, or that gas readings in mine rescue training can be dynamically and realistically changed to show the effect that time has on the fire scenario.CITATION:Slaughter, C and Tien, J C, 2015. The potential use of mine fire simulation software as an enhancement for mine safety and mine rescue training, in Proceedings The Australian Mine Ventilation Conference, pp 285–290 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 31, 2015

A major high grade zinc deposit, Dugald River has fine-grained and complex mineral associations which provide considerable metallurgical challenges for both mineral dressers and downstream processors. A long history of metallurgical testing focusing on mineralogy and flotation concentrate production has shown that while separate lead and zinc concentrates can be produced at saleable grades, high levels of iron, and particularly manganese, are likely to place constraints on the marketing of zinc concentrate produced from deeper zones where coincidentally lode development is at its maximum. Testwork has focused on characterising the flotation response of ore types ranging from banded and stringer sulphides to brecciated ores in a variety of sulphide matrices. A high level of variability with lower than expected metal recoveries has been indicated across some of the higher grade brecciated ores. However, the dominant slatey breccia has generally provided the best results. Heavy media preconcentration testwork has been moderately encouraging and at this stage, although value adding downstream of concentrate production on-site is not seen as an economic option processing developments are being monitored on a broad front. Providing satisfactory means can be developed for handling manganese during downstream processing of the concentrate, it is not difficult to see a world-class operation emerging from the resource in the medium-term Future.

Jan 1, 1993

By Liu X

The solubility of cobalt oxide in iron silicate slags has been measured at 1573 K by equilibration of silica and alumina saturated slags with liquid Co-Au-Fe alloys, and by equilibration of silica unsaturated slag with solid Co-Fe alloys, at oxygen pressures of either 10-9 or 10-10 atm (1 atm = 1.013 x 105 Pa). The activity coefficient of cobalt oxide has been calculated and compared with previous studies.

Jan 1, 1991

By Hindmarsh G

The colliery is owned by the BHP Collieries Proprietary Ltd., the principal shareholders being the Broken Hill Pty. Company Ltd. and Hebburn Limited.It is situated due west of Newcastle and 6 south-east of Cessnock, N.S.W., and is conneeted by 36 miles of railway to the port of Neweastle. Of this mileage, 3 miles are owned by the Company, 3 by Hebburn Limited, 9 by the South Maitland Railways Ltd., and 21miles by the Government Railways.The seam worked is known as the Main Greta Seam of the Greta Coal Measures and is on the southern slope of the Lochinvar anticline.At the shaft, the seam is 1190 ft. below the surface, and the section of the coal measures is:-Upper or Main Seam, . 24 ft. 0 in.Conglomerate and shale 70 ft. 0 in.'Middle Seam 8 in.Conglomerate 25 ft. 0 in,Bottom Seam 1 ft. 2 in.These lie between two marine measures, and are the lower coal series of the permo-carboniferous period.Only the upper seam is workable in this area, the lower seams being too thin for eompetitive working. The section of the workable seam at the shafts is as shown on Fig. 1.Unfortunately, only the lower 12 ft. 5 in. of the seam is saleable.

Jan 1, 1935

By Jaracz K

At the operation of mine winders in deep shafts considerable oscillations of winding ropes may occur due to elasticity of both wind-ing and balance ropes. The amplitudes of longitudinal oscillations may reach + lm at relatively low frequencies, ranging from 0.5 to 2 c/s. These oscillations may be dangereus for the rope and produce several hazards to the winding installation as a whole. They may cause conside-rable instant accelerations on the pulley and dangerous tensions in ro-pe wires. The excessive acceleration may cause the uncontrolled rope slip on the pulley. Several methods of limitation of these accelera-tions were developed, some of them have been already in control system: of electric drive of the winder. The most simple ones are: a/ limita-tion of the rate of change of acceleration and retardation of the win-der /so called "jerk"/ and b/ the proper selection of regulators of the winder control system to get the optimal control. The trouble in solv-ing the problem of rope oscillations is that the dynamic system of the winder is a nonstationaryone owing to changing distance of conveyance from the pulley. Besides, the system is described by the equations with distributed parameters. The brief discussion of the theory and its practical aspects are enclosed as well.

Jan 1, 1985

By Kissell F. N, Volkwein J. C

The U.S. Department of Interior's Bureau of Mines has the opportunity to visit many U.S. mines, including some that claim 2 to 5 times the national average of 334 raw tonnes/unit shift (tps) from a continuous miner section. In a project to assess the reasons for this high production, the Bureau conducted two studies. The first study focused on the 25 highest producing continuous miner sections. What stood out during the visits-was the quality of the labor-management relations. In each of the mines there was a positive labor/management relationship based on mutual trust and a sense that the employees were the company's most valuable resource. Discussions with labor revealed a universally positive attitude toward the company. Interviews with the mine superintendents invariably ranked the quality and attitude of workers as more important than anything else. Also during the mine visits of the 25- mine study, no engineering factors obviously stood out. Time at the face was greater than average, most were in coal over 1.52 m and the roof was generally good. Also, none of the 25 mines had to contend with high methane levels. Because this study found that a high percentage of mines were in seams less than 1.52 m thick, the second study examined thin seam mines only.

Jan 1, 1988

By J Li, A McFarlane, J Yu, L L. Kuhar, R Meakin, N Chapman

"Column leach tests are used frequently to predict recoveries and reagent consumption for nickel laterite heap leaches. These column leaches often run for more than 100 days and therefore require long-term monitoring and data analysis to achieve the desired information. To minimise the cost and time required to obtain relevant information for nickel laterite heap leaching, we have developed a small-scale hydrogeometallurgical laboratory test to serve as a proxy to column, and by inference, heap leaching. In excess of 50 leach tests were conducted using four different small-scale proxy and column leach tests to compare predicted nickel recoveries, acid consumption and leach kinetics and to determine whether insight into potential scale-up effects can be obtained. The most promising proxy test was identified and we achieved a statistically significant recovery and acid consumption correlations between this test and the column leach tests. The accuracy of the small-scale tests was confirmed by column tests run on new laterite ores. This geometallurgical proxy could be of use for the population of block models and process selection during the mine planning phase or for optimisation and control during processing.CITATION:Li, J, Kuhar, L L, Meakin, R, Chapman, N, McFarlane, A and Yu, J, 2016. A Geometallurgical Proxy for Nickel Laterite Heap Leaching, in Proceedings The Third AusIMM International Geometallurgy Conference (GeoMet) 2016, pp 335–340 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Jun 15, 2016

By D Johansson, A Nordqvist, D Mihaylov, N Petropoulos, M Wimmer

The flowability of the caved rock masses in the sublevel caving (SLC) mining method is of great importance. During the blasting process of a SLC-ring, the caved rock mass in front of the ring is compacted. As a result of this compaction, the mechanical properties of the fractured rock masses change, for example void ratio, angle of internal friction and structure of the compacted material. The changed mechanical properties of caved rock mass and recent blasted material can influence the mobility of the material, which could result in blockage of the flow path of the material. The identification of the involved mechanisms in this process can be done after a series of tests in different scales. However, there is no available equipment for dynamic measurements during blasting, ie velocity and displacement of the burden and in the caved masses. This study focuses on the development and laboratory evaluation of a measuring system that can be installed in a borehole. The first trial was carried out in a pillar, where two blastholes had been drilled (9.5 m) parallel with the drift and two measuring holes (16.5 m) were perpendicular to the drift. Two measuring systems were installed in the measuring holes. Some preliminary tests were carried out to find suitable initiation procedures for the emulsion explosive. Applicability and robustness of the developed measuring system were also evaluated. In addition to these tests, an expandable cement mixture was developed to firmly anchor the measuring systems in the boreholes. The measuring system consists of an anchor, armoured cable in a pulling tube and a protective case. The anchor is equipped with uniaxial and triaxial accelerometers. A potentiometric measuring system for displacement up to 2 m is installed at the end of the pulling tube and connected to an extendable spiral cable. All sensors are connected to a data acquisition system (DAS). Both measuring systems have their own DAS to acquire data in case of failure of one of the systems. The measuring system was tested in laboratory conditions with impact velocity up to 10 m/s. It was proven to be functional and gave reliable results.CITATION:Petropoulos, N, Mihaylov, D, Johansson, D, Wimmer, M and Nordqvist, A, 2015. Design of equipment for dynamic burden measurements, in Proceedings 11th International Symposium on Rock Fragmentation by Blasting, pp 493–500 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 24, 2015

By D Kentwell

IGO Ltd’s (IGO) Nova Operation (Nova) is 160 km east-north-east of the town of Norseman in Western Australia (WA). Discovered by Sirius Resources NL (Sirius) in 2012 and acquired by IGO in 2015, the Nova-Bollinger Deposit (Nova-Bollinger) occurs within the Fraser Zone of the AlbanyFraser Orogen. Nova-Bollinger is a complex nickel-copper-cobalt (Ni-Cu-Co) magmatic intrusive sulfide deposit, which is characterised by high-grade folded and undulating breccia lodes that host the bulk of the payable metals. Significant sulfide mineralisation is also found in several magmatic intrusive styles including net-textured, disseminated and blebby styles. A smaller but material volume of sulfides has also been remobilised into the deposit’s footwall rocks as ‘stringer’ bands in metasediments, or as discrete massive sulfide lenses. When interpolating Mineral Resource estimate (MRE) block grades in the presence of locally varying grade connectivity trends, such as folds or undulations, the sample search neighbourhood, which is used to identify the composites subset that is used for each block estimate, should be oriented to match the local trends. In theory, the most robust method of estimation where locally varying angles (LVAs) are applied to search neighbourhoods, are techniques where the composites and the blocks to be estimated are transformed to an unfolded coordinate system (UCS). However, UCS methods can be tedious to implement and require subjective decisions to be made that cannot always be fully defended. An alternative LVA method commonly used in the industry is dynamic anisotropy (DA), which is much simpler to implement and is often assumed (but not that often demonstrated) to result in similar results to UCS-style estimation. In 2018, Nova’s Mine Geology team (MGT) estimated the grades and density of the Nova-Bollinger MRE using the UCS approach. For the 2020 MRE update, Nova’s MGT tested and compared the USC grade interpolation method with the DA approach. As applied to the Nova-Bollinger’s 2020 MRE, the comparison, advantages and disadvantages of the two estimation methods are the subject of this paper

Mar 22, 2022

By M Haest, O Dominguez, D Mittrup

Technological innovations and emerging analytical capabilities are transforming the way drill samples are analysed, with real-time mineralogical analysis made possible. In addition, new business/technical requirements are challenging long standing processes to incorporate more sources of information during planning in order to improve compliance to plan during mining and processing. Unfortunately, the new sources of information that are added do not always have adequate protocols in place to ensure quality data is collected.Spectral data covering the visible – near – short wave – midwave – longwave range are routinely collected by the Geoscience and Exploration department at BHP Billiton Iron Ore for accurate mineralogical identification. These data are used for geological interpretations (logging and modelling) and prediction of physical variables (metallurgical and geotechnical properties).This paper introduces how sampling and quality assurance / quality control concepts have been applied in the spectral data process. The described routine for sampling, data collection/management and reconciliation has been developed to track system precision and accurately and consistently ensure the data is of high quality before it is used across the mining chain.CITATION:Mittrup, D, Dominguez, O and Haest, M, 2017. A new approach to implement quality assurance and quality control to technological innovations – quality of spectral data capture and processes in the minerals industry, in Proceedings Eighth World Conference on Sampling and Blending , pp 265–270 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2017

By J Naser, M Tuck

This paper reports a computational study using computational fluid dynamics (CFD) in a mine ventilation system. Ambient air is injected to a rectangular mine drive through a circular duct. Moisture evaporates from shaft wall depending on flow properties of air in the drive-duct system. The physical process involves simultaneous momentum, heat and mass transfer. A species transport equation is employed to account for the moisture concentration in air. The momentum equation is solved using standard k- model, while energy and species transport equations are solved using standard expressions for moisture evaporation rate and heat flux from the drive wall. The aim of this paper is to investigate effectiveness of CFD simulation in relation to mine ventilation in a drive where a significant mass transfer phenomenon occurs. Results from simulation are compared with existing data from a site in Victoria.

Jan 1, 2005

By D Stepanenko, G Stovpchenko, L Lisova, D Togobitskaya, L Medovar

Classical electroslag remelting of consumable electrodes is a drop-by-drop melt feeding through a slag layer into a renewing molten metal bath, slowly solidifying into a homogeneous, dense, defectfree ingot in a copper water-cooled mould. The new look at the additive nature of the electroslag remelting (ESR) process in a protective atmosphere allowed us to formulate the principles of a comprehensive thermodynamic-based model that can predict dynamic changes in slag and metal composition at certain ingot remelting. The model considers drastically different slag-to-metal mass ratios at the beginning and end of remelting and predicts gas, slag and metal composition in a chain of thermodynamic subsystems. Despite consisting of calcium fluoride and stable oxides, the ESR slag can oxidise main and active elements from steel and alloys (primarily aluminium, titanium and silicon) due to chemical reactions between slag and metal. ESR is not an electrochemical process in its nature. However, slags are ionic melts and deviation in their composition causes a change in their properties, affecting both operation mode and ingot quality. Another important understanding derived from the modern metallurgy technological route is that the ability to refine metal from impurities is not a priority for the ESR because consumable electrode has already passed all stages of refining and deep degassing at ladle treatment that changes ESR slags engineering principles. The critical importance became slag’s ability to generate process heat and keep the melting composition in the metal bath unchanged (except for non-metallic inclusions assimilation). Slag engineering for ESR required a compromise between chemical inertness to a metal composition and desired physical properties deriving from technological reasons. The Directed Chemical Bonds Concept (DCBC) in a multicomponent oxide system was used to build predictive models of electric conductivity and the melting temperature of fluoride-oxide slag based on their chemical composition. Both models help to design a customised composition of effective slags for steel and alloy groups or individual grades, and they are significant steps in the development of a comprehensive model of electroslag remelting.

Aug 21, 2024

By S Maritsa, D Simbi, E K. Chiwandika, S M. Masuka

The steel industry is facing challenges on a global scale that include depletion of resources, huge energy consumption, and the emission of CO2. The demand for iron products is increasing due to the increased infrastructural development. Zimbabwe produced cast iron from scrap metals. However, there is currently a shortage of scrap, and yet Zimbabwe is rich in limonite ores that are currently being underutilised. The possibility of using limonite ore as a sustainable feed for pig iron production was investigated by preparing some limonite ore carbon composite pellets. The results showed that the addition of coal to the limonite ore and calcium carbonate mix to form the composite pellets resulted in a decrease in the drop number as well as the dry compressive strength of the composite pellets. This research aims to improve the physical properties of the green pellets by the careful addition of hydroxyethyl cellulose as a binder that was found to improve the physical properties of the green pellet. This is important for materials handling during the production process of the composite pellets. Results showed that the drop number was substantially improved by the addition of 0.4 wt per cent hydroxyethyl cellulose while the dry compression strength improved from 2.5 kg/pelIet to around 23 kg/pellet irrespective of the amount of binder added. The binder improved the physical strength of the iron-carbon composite pellets enough to allow for large-scale production of the pellets that can be an alternative and sustainable feed for cast iron production. However more results on the indurated compression strength and other properties such as the reduction degradation index, swelling index, and the reducibility test are required.

Jun 19, 2024

By D Cliff

Despite advances in technology, the Australian underground coal mining industry continues to have incidents involving spontaneous combustion. Managing these incidents relies heavily on understanding the state of the event as it develops and controls are applied. Gas analysis plays a major role in aiding this interpretation. This interpretation is based upon laboratory testing of coal samples under conditions very different to those found in an underground coal mine. This paper will explore the links between laboratory data and actual events. It will highlight the difficulties of using laboratory data. It will outline the relevance of laboratory data and how it can be usefully applied to manage spontaneous combustion events as well as in establishing relevant trigger action response plans to facilitate early detection and control of such events. The paper will identify some of the factors that need to be applied when adapting laboratory data to apply to the underground coal mine. It will outline the need for comprehensive knowledge of the local conditions and gas concentrations to be expected at all locations in an underground coal mine. Further, it will demonstrate the need for mine environment monitoring to go beyond simply measuring gas concentrations but also to include reliable atmospheric pressure, temperature and air velocity monitoring.CITATION:Cliff, D, 2013. Gas analysis - Linking the laboratory with reality, in Proceedings The Australian Mine Ventilation Conference , pp 277-282 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 1, 2013

By T J. M Harvey

This paper gives an overview of the ASHRAE LibHuAirProp, CoolProp and REFPROP software packages. These packages were predominantly developed for heating, refrigerating and air conditioning engineers and the refrigeration and steam power industries, although CoolProp and REFPROP also cover combustible gases. The main aim of this paper is to highlight the existence capabilities and status of the different packages and where they can be used. The paper gives typical examples of the use of these software packages, specifically as Excel add-ins, and provides a comparison of results of typical mine psychometric and gas drainage calculations using the packages and more traditional ventilation and gas drainage calculation methods. The paper also introduces a hybrid method that improves accuracy compared to traditional methods. In typical mine situations, the use of software packages is probably not required; however, with the increasing accuracy of instruments, potential greenhouse emission costs and the sale of mine gas, more accurate measurements and calculations can potentially save (or make) significant sums of money.CITATION:Harvey, T J M, 2015. The use of psychometric, thermodynamic and transport property software in mine ventilation and gas drainage calculations, in Proceedings The Australian Mine Ventilation Conference, pp 201–210 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 31, 2015

By G D. Price

The Golden Blocks Goldfield is located in the Slaty Creek area,North West Nelson, about 20 km west of Collingwood. Alluvial gold was discovered in Slaty Creek in 1861. Gold was mined from quartz veins up to 1.5 m thick at nine mines from the 1890s until the closure of the Aorangi Mine in 1911. Total production from the Golden Blocks Goldfield is estimated at 46 000 ounces of gold. The Aorangi Mine was the largest mine, with a recorded production of 27 978 ounces of gold at an average grade of 36 g/t. Quartz veins containing gold and sparse sulphide mineralisation occur in a slightly metamorphosed, complexly deformed over-turned sequence of Lower Ordovician sandstones and shales. Primary gold mineralisation is associated with intensely deformed zones that occur near or at carbonaceous shale and sandstone contacts. Some eighty-five percent of all gold production (39 000 ounces) came from four mines confined to the stratigraphically lowest, most widespread shale unit. The quartz veins exhibit textures consistent with a hydraulic fracturing mode of vein formation with fissure infill vein types predominating over replacement textures. Stylolites of carbonaceous material and recrystallization features within the veins suggest multiple phases of deformation. The lack of wall rock alteration, and low primary fluid inclusion temperatures of 200¦ - 265¦ indicate that the ore fluids were associated with a low temperature epithermal system. A model consistent with similar mineralisation styles observed in Ordovician sediments from Pacific Rim occurrences is presented. The high grades (up to 100 g/t) mined from the upper levels of several mines suggests supergene enrichment processes associated with the Upper Cretaceous weathering surface. The Golden Blocks Goldfield has had no modern exploration. The most recent exploration was undertaken in the early 1980s. There are known acid intrusives in the area, with potential for the application of new models of intrusive-related gold mineralisation.

Jan 1, 2004

By T Roesch, M Neurohr, S Stratton

"Dwindling commodity prices are forcing today’s mining operations to increase output. Sometimes the solution is to upgrade the existing infrastructure; however, in most cases it has to be achieved with the same or reduced workforce and with the same equipment capacity through improved process efficiency and higher uptime.Measure, Manage and Improveis the mantra for this years’ Mill Operators’ Conference and while this in most cases relates to the above process efficiency, Siemens has set its focus on the availability and uptime aspect since unscheduled downtime is one of the biggest threats to any grinding operation. Pinion misalignments, resonance, unbalance and bearing and gear meshing faults in geared trains, as well as long-term changes in the condition of the mechanical components or structures and auxiliary systems in gearless systems are the main reasons for unscheduled downtimes in today’s mill drive trains. Our paper outlines the efforts that have gone into adapting conventional condition monitoring methods in conventional, pinion driven mill drive trains as well as gearless systems to capture the gradual deterioration of wearing parts or structural changes in the drive train not only on fixed speed application but also on variable speed applications with multiple operating points. The paper further explores the use of condition monitoring systems as a tool to assess spare thermal motor capacity to potentially push equipment beyond its nameplate rating, along with the process that was followed to correlate measured frequency spectra and envelopes to ambient and load data to understand the kinematics of the drive train.Citation:Neurohr, M, Stratton, S and Roesch, T, 2016. Advancements in Condition Monitoring on Mill Drive Trains for Proactive Maintenance and Early Fault Detection Purposes, in Proceedings 13th AusIMM Mill Operators’ Conference 2016, pp 263–272 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Oct 10, 2016

Sample preparation for gold samples, where the distribution and size of gold particles is often irregular, usually demands that a relatively large sample weight is taken to produce a representative sample for analysis. Traditional sample preparation of gold samples incorporated multiple stages of coarse particle size reduction followed by subdivision of the sample prior to final fine pulverising. This technique developed because of the limited equipment options available to laboratories. As a result significant errors are introduced and the final sample size being pulverised is a small fraction of the original sample weight. Three significant developments have occurred in the last 25 years to significantly improve sample preparation of gold samples: 1.  large capacity fine pulverising,2.  fine jaw crushing, and3.  whole sample coarse pulverising. In the mid-1980s an Australian manufacturer developed large capacity pulverising bowls which had the ability to reduce samples with a mass of 1.5 - 3.5 kg to a nominal 0.075 mm product in approximately three to five minutes. Laboratories were able to produce a large homogeneous pulverised sample which significantly reduced the error in sampling. However, exploration and mine samples are usually 7 to 10 kg and the sample requires a subdivision stage following crushing to produce the 3.5 kg for the pulverising step, thus introducing potential for significant error. The development of fine jaw crushing allowed particle size reduction to -2 mm which reduced the subdivision error of the bulk sample prior to fine pulverising. Subdivision of the crushed sample at -2 mm still results in potential sampling errors, where the gold particles are not sufficiently liberated to be representatively sampled. Clearly the best option would be to reduce the particle size small enough to ensure a representative sample prior to final pulverising. Continuous mills offer a partial solution but are relatively slow and subject the sample to differential pulverising prior to subdivision. Clearly this does not provide the best solution for routine laboratory applications where high volumes of samples are to be processed. The recent development of a large capacity coarse pulverising system allows samples of up to 10 kg to be reduced to -0.25 mm prior to subdivision, and fine pulverised to -0.075 mm. Laboratories now have the necessary equipment to perform reliable large capacity sample preparation of gold samples. The exact choice of a sample preparation scheme may still depend on particular ore types but the need for multiple crushing and subdivision stages is redundant.

Jan 1, 2008