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By Carlini G, Ibba R

The KSS Lead Plant (Kivcet - SNAMPROGETTI - SAMIM) of Por tovesme, owned by Nuova Samim (the sector-head Company for non ferrous metals and derivatives owned by ENI), has been operating since february 1987. This plant is based on the Soviet Kivcet licence and testwork carried out on the pilot plant of VNIITSVETMET in Ust Kameno gorsk fed by the Nuova Samim's concentrates. The plant is com pletely automatized using the most advanced technologies and it is operated by nineteen people on shift work, including all ancillary units and lead decopperizing-casting. The expected performance of the plant has been confirmed and improves day by day in relation of the operating experience, thanks to the new conceptual design of the furnace. Due to the remarkable flexi bility of the process, the integration of the lead plant with the other plants of the metallurgical complex of Portovesme rro-#4 (Electrolytic Zinc Plant, Sulphuric Acid Plant, Imperial Smel ting) has shown all the economic advantages. The lead content in the ambient air, detected by the monitors, either in the working area and on the ground outside the complex, is widely Pb W" below the stricter new limits recommanded by the E.E.C. (Economic European Community) rules and by the Italian law. The whole process is carried out in equipment completely closed and under suction and it does not require manual operations with exposure to the lead. The production cost is much lower than that performed by the traditional technology. This advantage permits wide margin to consider investment to replace the traditional technology.

Jan 1, 1989

By R Zhang, J Xu, X Lv, C Bai, S Zhang

This paper studies the grinding behaviour of vanadium-titanium magnetite concentrate in a ball mill. The grinding kinetics, surface morphology, lattice distortion, wettability and moisture capacity were analysed. Grinding kinetics equation was established based on population balances model with the size distribution data from a laser diffraction technique. The SEM photos of the ground concentrate showed that the surface gets rough with increasing grind time. Agglomeration of fine particles was enhanced when the grinding time reached 30 minutes. X-ray diffraction results showed that a loss in crystalline occurred with increasing the grinding time. The peaks of the X-ray diffraction patterns are significantly broadened with increasing grinding time. Wettability, characterised by contact angle between the material and water, improved due to the fact that the surface roughness increased with increasing grinding time. Moisture capacity of concentrate ascends abruptly in the first three minutes and then changed slowly with increasing grinding time. The water transfer coefficient in the particles increased rapidly in the first six minutes and then decreased quickly until grinding time reached 12 minutes.CITATION:Zhang, R, Lv, X, Bai, C, Xu, J and Zhang, S, 2013. Wet grinding of ?vanadium-titanium magnetite concentrate in a ball mill, in Proceedings Iron Ore 2013 , pp 511-518 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 12, 2013

By D Henderson, M Germain

The beneficiation of iron ore deposits to yield haematite and magnetite concentrates for steel making processes typically require the use of one or a combination of wet processing techniques based on gravity, magnetic or froth flotation processes. With the need for more cost-effective technologies with a lower water demand, a re-examination of dry processing techniques has been initiated. For example, a dry processing capability may offer an advantage where suitable quality and quantity of process water hinders the development of a particular resource. This paper describes recent laboratory test work for the production of high grade concentrates using dry electrostatic techniques for -300 ¦m haematite and magnetite ores and compares them with magnetic separation techniques.

Jan 1, 2009

By J Pan

In this paper, the technology of producing fluxed pellets by using hydrated lime as binder instead of bentonite was carried out. The properties of the two types green balls (0.8 per cent bentonite and 2.0 per cent hydrated lime) were as follows: drop numbers of 4.8 - 5.0 times/0.5 m, compressive strength of 19.7 - 24.2 N/pellet and thermal shock temperature of 280° - 385°, respectively, under the same conditions of 1.5 per cent coke, 1.45 basicity and balling at 8.5 per cent moisture for 13 min in disc pelletiser. Comparing with bentonite as binder, the compressive strength of fired pellets with hydrated lime is elevated by 13.8 per cent and climbs up to 3113 N/pellet under the following conditions: preheating at 1050°C for ten minutes and fi ring at 1300°C for 15 min. In the mean time, the hydrated lime also improves the metallurgical performance of fired pellets. The reduction index was enhanced from 68.6 - 70.6 per cent, RDI+3.15+ increased from 90.1 to 98.8 per cent and reduction swelling index dropped from 22.4 - 7.4 per cent, respectively. The mineral compositions and microstructure of fi red pellets shows that the fired pellets containing 2.0 per cent possess more calcium ferrite and magnesium ferrite and compact microstructure, leading to the higher compressive strength.

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 A N. Kusnanto, D Sims, L Henim, S Crispin, J Hertrijana

The high sulfidation Purnama Au-Ag deposit located on the Indonesian island of Sumatra entered production in mid-2012 following a two-year program of construction and development. Discovered in 1997 following a regional stream sediment geochemical sampling program by the Normandy Anglo Asia joint venture, it is the first and largest deposit in G-Resource’s Martabe Project to enter production and is the centrepiece of a series of six deposits totalling 8.1 Moz Au and 73.8 Moz Ag in Mineral Resources (G-Resources, 2013a).In 2011 investigation into the controls of high-grade mineralisation in isolated parts of the deposit identified a potentially significant mineralisation style which had not been previously recognised or accommodated in the resource model. An extensive investigation of core and logging data followed to confirm the distribution of the somewhat unusual mineralisation style – a sedimentary-like cavity infill of very high-grade auriferous pyrite within the steep hydrothermal breccia feeders to the system. With the bulk of mineralisation located within the adjacent volcanic sequence and sandy-matrix phreatomagmatic breccia surrounding the feeders, the lack of constraint for high-grade intersections in the hydrothermal breccia zones had potential to significantly impact the mine plan in the lower sections of the planned pit through overestimation of local gold grade. Combined with new data emerging from grade control drilling and infill resource drilling in the pit, a program of reinterpretation of the deposit was initiated to update the geological and alteration framework underpinning the resource model. The result has improved the economics of the project and added metal to the Ore Reserve for Purnama.CITATION:Sims, D, Henim, L, Hertrijana, J, Kusnanto, A N and Crispin, S, 2014. Remodelling the Purnama deposit – an interpretation case study from G-Resources Martabe Project, Indonesia, in Proceedings Ninth International Mining Geology Conference 2014 , pp 229–236 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 18, 2014

By D van der Spuy, T Kewe, K Keet, N Moffatt, A P. Paine

The Blue Cube Mineral Quantifier Inline (MQi) instrument uses reflective light spectroscopy and advanced chemometrics to measure mineral or elemental grade in a slurry line. The instrument takes scans continuously and sends data to the DCS or PLC control system.Controlling the concentrate grades on a flotation circuit using low-frequency measurements can be difficult or impossible, especially on a circuit that has fast process dynamics. The ability to rapidly measure changes in grade makes it possible to continuously manipulate the flotation circuit operating parameters such as level, airflow and reagent addition set points to optimise plant performance throughout changing conditions.At Barrick’s Porgera mine in Papua New Guinea the flotation circuit feeds sulfide concentrate slurry to a pressure oxidation circuit. In order to maximise gold recovery in the flotation plant and increase performance in the pressure oxidation process, there is a stringent requirement to maintain a stable and optimum sulfur grade. The gold recovery is directly affected by the sulfur grade as most of the gold at Porgera is submicroscopic and associated with the sulfides (disseminated?pyrite).Porgera considered various points in the flotation circuit for installing Blue Cube analysers. This was part of a plant upgrade to improve process control. Due to budget constraints it was decided to initially only install one Blue Cube analyser on the final concentrate stream of the flotation circuit measuring sulfur, sulfides, gold and particle size. The accuracy of the calibration results were very good for all these properties. The sulfur measurement was used in an advanced control system to optimise and stabilise the grade. The paper presents comparisons between mineral grades determined using analytical laboratory analyses and the online Blue Cube data measurements, as well as benefits achieved by measuring grade online. An analysis of the plant data before and after installation of the Blue Cube and the advanced process control upgrade indicate that the flotation recovery increased by 1.98 per cent.CITATION:Kewe, T, Moffatt, N, Strobos, P, van der Spuy, D, Paine, A P and Keet, K, 2014. Evaluation of the Blue Cube MQi slurry analyser for application in an advanced control system for the optimisation of a gold sulfide flotation circuit, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 357–362 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By J Player, G Sweby, S Webber, E Jones

Seismic systems are a tool for the monitoring and forecasting the rock mass response to excavation. Common issues encountered at mine site audits and reviews are: how to design an effective seismic system, implementation of the design, interpretation of seismic source results and understanding the reliability of the seismic source. These issues are often a function of several items including: • Experience of site personnel in undertaking seismic system design. • Personnel not envisioning multiple phases of system expansion to understand system robustness issues. • System design/expansion occurring in response to damaging seismic activity rather than planned expansion of a system • The mine access development is often localised in comparison to the total orebody being mined hence, planning sensors in longholes in advance of development rather than in short holes close to development will improve the three-dimensional aspect of the network. • Limited site processing of the seismic event data, hence engineers do not see the uncertainty associated with event location, size, source and system layout. Mine site users require a framework to appreciate the challenges and limitations in locating large events. For example, event locations are given as precise measurements (to the nearest centimetre) whereas the volume of deformation resulting in the event often has dimensions of tens of metres or more (as defined by the source radius). A stronger awareness of the uncertainty of rock mass yield within large seismic sources will assist site users in the interpretation of rock mass damage. The encountered design and implementation errors are reviewed and discussed with a practical set of rules presented to provide a robust seismic system that provides consistent results and increases the user’s understanding of uncertainty in source location and size. The authors’ experience across multiple mine sites, seismic systems and damaging seismic events over a 30 year period has been summarised into practical rules for site personnel of all experience levels.

Nov 29, 2022

By B Walker, A Robertson, C Wels, S Fortin

A background characterisation study was carried out in the Sangre de Cristo mountains, New Mexico, to: quantify naturally occurring contaminant loads from mineralised areas; define site-specific background concentrations; and to determine key factors controlling spatial and temporal variations in contaminant concentrations. The study included a comprehensive sampling and testing program (paste pH/EC, ABA, leach extraction tests) of soil/bedrock from mineralised areas (including erosional scars), and a ground water and surface water quality monitoring program in selected mineralised watersheds. Results demonstrate that high concentrations of contaminants occur naturally in ground and surface water draining the mineralised area of the Red River basin. The erosional scars were found to represent the major source of acid rock drainage (ARD) (~66 per cent) in this area due to: high rates of weathering and erosion, which continually exposes sulfide-bearing outcrops; and high rates of run-off as a result of high elevation and lack of vegetation. The scar material is generally very acidic (paste pH ranges from 8.5 to 1.5; average = 3.6) with highly elevated concentrations of sulfate and leachable metals. The composition and concentration of leachable metals vary significantly, not only between scars but also within a given scar. While all streams draining the various scar watersheds are highly acidic, each has a characteristic æfingerprintÆ of sulfate and metal concentrations. Most of the run-off from the scars infiltrates into alluvial debris flow aprons and reaches the Red River via groundwater flow.

Jan 1, 2003

By A K. Bhatnagar, S Saha, P Dixit, A K. Mukherjee, P Patra

TATA Steel’s R&D Division at Jamshedpur has developed a slime beneficiation process to recover iron values from iron ore slime. This process recovers iron ore concentrate containing 2.2 per cent alumina from a feed containing 7–10 per cent alumina. The reject generated from beneficiation of iron ore slime is treated as waste as the iron content in the reject is below 45 per cent. Effective utilisation of this waste is required for making the iron ore slime beneficiation process a zero-waste technology. In this connection several studies were made towards utilisation of slime waste. One of these studies revealed that slime waste can be used as a soil conditioner. Slime waste contains particles of size less than 10 micron and when these particles are mixed with soil in definite proportions, the porosity and the permeability of the mixture goes down. As a result, the water holding capacity (WHC) improves. This concept was evaluated through a series of tests at greenhouse level to optimise the soil to slime ratio. Finally, a pilot scale field trial was carried out over a period of three months using paddy rice as the crop. Three separate plots with compositions of: soil + organic matter comprising Farmyard Manure (FYM), (ii) soil and slime waste (2:1) + organic matter (FYM), and (iii) soil and slime waste (2:1) + organic matter (FYM) + Nitrogen, Phosphorus and Potassium (NPK) fertiliser were used for the pilot trial. The results showed a 20 per cent increase in the productivity of paddy rice for plot (ii) as compared to plot (i). This was due to the beneficial effect of slime waste in the soil. The addition of inorganic fertiliser such as NPK in the ratio of (4:2:1) further enhanced the productivity of paddy rice.

Sep 18, 2023

Upon subduction, water is liberated from the sediments and the porous struc- ture of the oceanic crust and from de- hydration of minerals for redistribution and chemical reaction. A survey of pro- cesses which are likely to occur along the subducting plate reveals that water may well be basic in subduction induced gas generation, magma formation and ore deposition. In analogy to the industrial water gas process, reaction of water with car- bonaceous matter, in subducted sediments is likely to yield substantial volumes of hydrogen and carbon dioxide. While water and carbon dioxide appear to play a determining role in the development of differentiated magmas, hydrogen will react with metal sulfides and sulfur to form hydrogen sulfide which is essential in sulfide ore depo- sition. A survey of possible metal extrac- tion chemistry along subduction suggests a stepwise solubilization of metals from sediments and oceanic crust, and a poten tial accumulation of dissolved metals in zones of characteristic composition. The metal spectrum in ore deposits at near surface appears to reflect the com- position of the solution in the respec- tive subduction zone. A tendency for preferential solubi- lization of copper at subductidn level, from among the transition metals, an in- creasing generation of hydrogen sulfide in the sane direction and partition effects as well as sulfide precipitation characteristics lead to enrichment in copper and to its selective deposition in the direction towards the trench as observed in S. Latin America. A postscript deals with the formation of native copper.

Jan 1, 1986

By Erickson M. E, Smith C. K, Carswell J. T

Thirteen holes totalling 3200m were surveyed using a downhole time domain Geonics EM37 system at the 830 metre level within the CSA Mine, Cobar, New South Wales, in order to search for blind, electrically conductive sulphides at some distance from exploration drillholes. A significant off-hole conductor was detected in only one drillhole.Geophysical modelling and interpretation of the survey results indicated that this off-hole conductor was caused by a sulphide lens 30 metres from the drillhole at a hole depth of 220 metres.

Jan 1, 1990

Our modern cities are almost incapable of sustaining themselves without subsurface infrastructure, which is not identifiable at first glance. This very soon becomes evident when the chaotic conditions prevailing in some cases in the multi-million cities on the African, Asian and South American continents are taken into consideration. This does not simply apply to the hopelessly congested streets in the downtown areas. If anything, it is shown here too that a subsurface infrastructure represents an important prerequisite for public health right up to banishing the danger of disease. Even during the 1990s, this has been clearly underlined through examples of cholera and plague epidemics in parts of Central and South America as well as on the Indian subcontinent. The overriding significance of an inner urban subsurface infrastructure in order to create decent conditions in the major built-up areas was once again emphasised not all that long ago at the United Nations HABITAT-II Conference in Istanbul, Turkey, in June 1996. More than 15 000 delegates from all over the world mulled over and discussed the prerequisites for humane living conditions in human settlements taking the varying climatic, topographical and cultural marginal conditions in different regions of the globe into account. Apart from the built-up areas themselves, the utilisation of underground space is experiencing high and ever increasing significance in less densely populated regions. Attractive and fast transport links between industrial centres call for high- performance transport arteries for the economic, speedy and unhampered carriage of people and goods. Important impulses for the economic power of a region or nation are provided by transport development and links. As a consequence, tunnels for roads and railways are being built or planned to a great degree for crossing mountain ranges, rivers and straits.

Jan 1, 1999

By B Morey, J Gordon, P Mackenzie

Mount Tom Price Mine is peerless amongst Rio Tinto iron ore resources around the world. It has provided Hamersley Iron with premium quality, high lump yield haematite ore over the last four decades. The Brockman type bedded ore, containing bands of haematite and shale of varying thicknesses has been traditionally bulk mined to either high-grade or low-grade based on alumina cut-off grades. As open pit mining has progressed deeper into the orebody approaching the keels of the megastructure, increased structural complexity, chemical and physical variations in the ore, unfavourable ore presentation and reduced blending options have become an issue for grade control and may have serious impacts on product stockpiles. The grade blocks and boundaries must be accurately defined according to geological contacts and where identified, selective mining may be applied. Therefore in-pit geological mapping is the definite and ultimate guide to achieve target grades and grade predictions. Under this scenario, it is absolutely vital that the mine geology team ensures this geological knowledge is passed onto the related departments including mining crews as well as to the short- and long-term planners.

Jan 1, 2002

By T Sua, B Wright

"BHP Billiton West Australian Iron Ore (WAIO) conducts an extensive geometallurgy program for its iron ore deposits in the Pilbara with the focus on determining the lump yield (the mass percentage of >6.3 mm rocks) and the lump and fines grade for iron ore products. The geometallurgy program provides accurate information to design engineers and technical marketing teams on the performance of different iron ore mineralogies for future deposits. Additionally geometallurgy results are being used to guide short-term production planning with their introduction into short-term geology models and grade control models. The data that underpins this knowledge is from dedicated geometallurgical programs, drilled using PQ (~83 mm) holes. These holes are crushed by intervals that are based on geological definition which provides an indicative lump yield and lump and fines grade. The lump is then subjected to standard dropping and tumbling test stages to produce a simulated lump and fines product. In the past, quality assurance, quality control holes were drilled using HQ (~64 mm) holes for geochemistry purposes. These holes were crushed to provide an indicative lump yield and lump and fines grade and then 100 per cent is sent for assay (with no dropping and tumbling). Utilising data from HQ holes can significantly increase the indicative geometallurgical data available. This paper compares the geometallurgical results from both PQ and HQ holes from a range of bedded iron deposits (Brockman and Marra Mamba). The PQ and HQ data are compared by orebody, stratigraphy and depth to exclude factors that are expected to influence geometallurgical results.CITATION:Wright, B, Sua, T, Robertson, B and Van Dijken, B, 2016. Comparison of Diamond Drill Size on Iron Ore Geometallurgical Results, in Proceedings The Third AusIMM International Geometallurgy Conference (GeoMet) 2016, pp 161–166 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Jun 15, 2016

By J Finlay, P Betts, D Milton, H Williams

The aim of this paper is to present an innovative method to help delineate potential target volumes for haematite-goethite mineralisation as opposed to more magnetic ores. This is achieved through interpretation and modelling (2.5D and 3D inversions) of ground magnetics and gravity surveys over the Koolanooka South prospect in Western Australia. The targets are assumed to be dense and weakly magnetic and hosted within banded iron formation (BIF) horizons. Geophysical interpretation (2D map) was performed using a variety of processed magnetic and gravity images (Betts et al, 2007) to determine the distribution of lithologies, to understand the structural architecture and to map out any anomalous areas of excess density (possibly indicating goethite alteration). The created geological map is used to build geological cross-sections (geometrically consistent) that were modelled (in 2.5 D) against both potential field datasets. The crosssections are consequently used as the framework to build a 3D geological model. The model defines 3D volumes of rocks including several BIF horizons. The distribution of densities and magnetic susceptibilities of the BIFs is inverted within the GOCAD«-VPmg environment to reduce the misfit between the response of the model and the observed gravity and magnetics. By combining the results of both petrophysical property distribution it is possible to map out (using classical GIS type queries in 3D) volumes of higher density and lower magnetic susceptibility.

Jan 1, 2009

The Porgera gold deposit in the Papua New Guinea highlands contains about 387 tonnes of gold. The results of its exploration show the benefits of persistence and commitment to this difficult deposit. The mineralization consists of a complex intermix of auriferous and argentiferous sulphides, gold tellurides and free gold as disseminations, veins, stockworks and breccia matrix. Its deposition was structurally contolled within a system of mafic diorite intrusions and adjacent sediments. Two styles of alteration accompany the mineralization. Gold grades vary erratically throughout the deposit. Over a period of 22 years nine phases of exploration have been undertaken by six companies or consortia of companies. Surface rock chip sampling, geological mapping followed by scout and systematic grid diamond drilling have been the most successful exploration tools. Exhaustive metallurgical process investigations and economic evaluations of mining options have been invaluable in guiding the exploration towards defining the ore body. Impetus was given to the project during times of flagging enthusiasm by several important discoveries and a breakthrough in the metallurgical processing approach. The discovery of high grade ore deep in Zone VII in 1984 turned this marginal deposit into a potentially very large gold mine.

Jan 1, 1987

By M Sandy, A Vakili, J Albrecht

Although rock strength anisotropy is a well-known phenomenon in rock mechanics, its impact on geotechnical design is often ignored. No widely accepted guideline currently exists for its characterisation. Anisotropy can significantly control the failure mechanism and progression of damage into the rock mass, particularly in high-stress conditions. As such, it can play a key role in the stability of underground excavations and subsequent geotechnical design.This paper introduces the concept of anisotropy at both intact and rock mass scales. It then presents guidelines for measuring anisotropy and assigning rock mass strength properties. An improved unified constitutive model (IUCM), which can account for more complex failure mechanisms, is then briefly described. This IUCM is used to better understand the typical responses of anisotropic rocks to underground mining and to develop an improved damage classification scheme for these conditions.The application of conventional design methods in anisotropic conditions is shown to lead to significant errors. Two case histories are then presented, illustrating how the proposed methodology can improve the reliability and accuracy of the geotechnical analysis when compared with conventional design methods.CITATION:Vakili, A, Albrecht, J and Sandy, M, 2014. Rock strength anisotropy and its importance in underground geotechnical design, in Proceedings AusRock 2014: Third Australasian Ground Control in Mining Conference , pp 167–180 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 5, 2014

By Ring R. J, Waters D. J, Vautier F. E, Fulton E. J

Laboratory leach tests have been carried out by the Australian Atomic Energy Commission to compare the effectiveness of Caro's acid (permonosulphuric acid) as an alternative oxidant to pyrolusite in the leaching of uranium ores. Results demonstrated that Caro's acid reduced acid consumption in leaching and the lime required for neutralisation of tailings liquor. The uranium extraction was unaffected by choice of oxidant.Following this study, Interox Chemicals Pty Ltd arranged a plant trial using Caro's acid at the Nabarlek uranium mill of Queensland Mines Ltd. The trial confirmed that significant savings in acid and lime usage can be achieved under plant conditions.Plant operations also demonstrated that Caro's acid has a number of significant operating advantages over pyrolusite.Queensland Mines Ltd have recently decided to convert their leaching process from pyrolusite to Caro's acid. The new system is expected to be fully operational by mid 1983.

Jan 1, 1983

By J D. Lubben

Hibbing Taconite is a Lake Superior-type granular magnetite taconite deposit occurring within the Biwabik Iron Formation along Minnesota’s central Mesabi Iron Range. The deposit is situated on the northern margin of the Proterozoic Animikie Basin. The deposit strikes northeast, dips gently southeast, and occupies 10 km of strike length. Mining focuses on 50 m of granular cherty and laminated slaty taconite within the Lower Cherty member.Ores generally consist of a quartz, magnetite, siderite, ankerite, minnesotaite, stilpnomelane, and haematite mineral assemblage. Processing is optimised by exploiting the physical and chemical variations that exist between three major ore types. Taconite ore averages 20 per cent magnetic iron (MagFe), 27 per cent weight recovery (WtRec) and produces a final concentrate with 4.5 per cent silica (SiO2). Since 1976, production has totalled approximately 237 million long tons (Mlt) of pellets (8 Mlt per year rated capacity).Ore processing uses a simple fl ow sheet of autogenous grinding (<0.044 mm) followed by two phases of wet magnetic separation, fi ltering, limestone/bentonite addition, balling, and firing to create pellets averaging 66 per cent total iron. A Liberation Index (LIS) is used as a primary guide for ore grading and metallurgical control. Grind requirements, magnetite liberation and silica grade are closely monitored to ensure plant optimisation and product quality.A recent program of benefi ciation of low-grade ores by in-pit crushing and dry magnetic cobbing has demonstrated that low-grade ores (<17 per cent MagFe, <25 per cent WtRec) can achieve a signifi cant metallurgical upgrade (up to 25 per cent MagFe and 40 per cent WtRec). This operation recovers 60 per cent of the total crushed volume, and has a calculated effi ciency factor (magnetic iron recovery) of 79 per cent. This paper discusses the benefi ts of this upgrading and its effects on ore blending and processing.

Jul 11, 2011