Magnetite mining method

Abstract

A method of mining magnetite iron ore, and apparatus when used for the method, comprising: assessing a two-dimensional grain size distribution of magnetite mined from an ore body; measuring a three-dimensional grain size distribution of the mined magnetite; determining a relationship between the two-dimensional and three-dimensional grain size distributions; and using said relationship to classify the ore body into regions based on three-dimensional grain size inferred from assessing two-dimensional grain size distribution of magnetite of each region. An additional method of mining magnetite iron ore comprising mining ore from an ore body and separating the mined ore into magnetite and gangue via a leaching process, where the two-dimensional grain size of the magnetite may be assessed after removing the gangue.

Description

MAGNETITE MINING METHODTECHNICAL FIELD

[0001] The present invention relates to a method and apparatus for mining magnetite and more specifically, but not exclusively, to a method and apparatus for mining magnetite with improved cost effectiveness and / or energy efficiency.BACKGROUND

[0002] Iron ore is one of Australia’s most significant exports. Broadly speaking, iron ores are rocks and minerals from which metallic iron can be economically extracted. The iron itself is usually found in the mineral forms of magnetite, hematite and goethite.

[0003] Australian miners have concentrated their efforts on the Pilbara region for many years, with over 95% of the mined ore from this region being hematite. These existing operations in the Pilbara have deterred Australian miners from investing more in magnetite mines, which typically need more investment to produce a saleable, high grade product compared with hematite mining.

[0004] With declining deposits of high grade hematite in Australia, there has been a renewed interest in magnetite deposits, due at least in part to the emerging "green steel" sector. While not reliant on coal, green steel requires a significant supply of high grade ore. Given that magnetite concentrate grades are generally in excess of 66% iron by weight, it is particularly attractive to the green steel industry. However, there exists a problem in that processing magnetite ore into a high grade concentrate is typically high cost as it requires a lot of energy and water.

[0005] Magnetite deposits typically comprise of mineral material that requires liberation from surrounding gangue. Grinding is a commonly used liberation technique, with the degree of grinding being a function of, amongst other things, grain size of the magnetite. For example, a typical magnetite deposit may comprise material of varied grain size which requires fine grinding that is admixed with material of very fine grain size which requires extremely fine grinding for liberation. With this in mind, it is known to explore unmined portions of an ore body by deep drilling (i.e. diamond drilling and reverse circulation drilling). Diamond drilling is used to obtain a rock sample that is then subjected to a grinding operation to liberate the magnetite particles which are then sized. However, these methods do not provide magnetite grain size data prior to the grinding step, and thus the "natural" (i.e. in-situ) grain size of the magnetite is not attainable.

[0006] Other existing methods that may be used to classify the ore body including 3D tomography are expensive and time-consuming, while also being limited in grain size characterisation since they cannot separate joined grains and create a bias towards coarseness.

[0007] Within this context, there is a need for a method of mining magnetite with improved cost effectiveness and / or energy efficiency, or to at least provide the public with a useful choice. The present invention was conceived with these shortcomings in mind.SUMMARY

[0008] In a first aspect, the invention provides a method of mining magnetite iron ore, comprising: assessing a two-dimensional grain size distribution of magnetite from an ore body; measuring a three-dimensional grain size distribution of the magnetite; determining a relationship between the two-dimensional and the three-dimensional grain size distributions; and using said relationship to classify the ore body into regions based on three-dimensional grain size inferred from assessing two-dimensional grain size distribution of magnetite of each region.

[0009] Assessing the two-dimensional grain size may comprise acquiring an image of a thin section of the ore body with a scanner. Assessing the two-dimensional grain size may comprise mounting mined ore from the ore body or processed concentrate within an epoxy substrate for scanning with the scanner. Assessing the two-dimensional grain size may comprise analysing the acquired image with image processing algorithms. Assessing the two-dimensional grain size may comprise mapping the acquired image into areas of magnetite and gangue.

[0010] In some embodiments, measuring the three-dimensional grain size comprises separating the ore into magnetite particles and gangue. Measuring the three-dimensional grain size may comprise liberating magnetite without crushing or otherwise comminuting the ore. Measuring the three-dimensional grain size may comprise separating magnetite particles from gangue via a leaching process. Measuring the three-dimensional grain size may comprise digesting the gangue in a chemical solution. Measuring the three-dimensional grain size may comprise sorting the liberated magnetite particles according to size. Measuring the three- dimensional grain size may comprise sizing the magnetite particles by laser.

[0011] Classifying the ore body may comprise segmenting the ore body into regions abundant in coarse-grained magnetite. Segmenting the ore body may comprise domaining the ore body into regions abundant in coarse-grained magnetite. Classifying the ore body may comprise segmenting the ore body into regions abundant in fine-grained magnetite. Segmenting the ore body may comprise segmenting the ore body into regions abundant in fine-grained magnetite. Classifying the ore body may comprise extracting a sample of ore from an unminedregion of the ore body such that a two-dimensional grain size distribution of magnetite within that region represents a natural grain size distribution of magnetite within that region.

[0012] In some embodiments, the method may comprise the additional step of: mining ore from the ore body. The step of mining ore may comprise extracting ore from the ore body via diamond drilling. The step of mining ore may comprise downhole mining of ore from an underground portion of the ore body.

[0013] The method may comprise the additional step of: processing mined ore in a downstream processing plant to produce upgraded magnetite material. The step of processing the mined ore may comprise selecting ore from a respective region of the ore body based on the inferred three-dimensional grain size of that region to optimise feed to equipment within the processing plant. The step of processing the mined ore may comprise blending feed stock from different regions of the ore body to provide a feed mixture of known average grain size.

[0014] In a second aspect, there is provided an apparatus when used for mining magnetite iron ore, comprising: a device for extracting ore from an ore body; a scanner configured to assess a two-dimensional grain size distribution of magnetite within defined regions of the ore body; and a processing plant configured to produce upgraded magnetite material; wherein a feed to the processing plant is optimised based on three-dimensional grain size inferred from a two- dimensional grain size distribution of magnetite within the respective regions.

[0015] The scanner may be configured to acquire magnified images of mined ore showing a grain structure thereof.

[0016] In some embodiments, the apparatus may further comprise a separator configured to liberate magnetite particles from gangue. The separator may be configured to liberate the magnetite particles via a leaching process.

[0017] The apparatus may further comprise a sizer configured to measure a three- dimensional grain size distribution of the magnetite particles. The sizer may comprise a laser diffraction unit.

[0018] Preferably, a three-dimensional grain size distribution of magnetite particles within a respective one of the regions may be correlated with the two-dimensional grain size distribution of that region to calibrate the scanner such that a three-dimensional grain size distribution of magnetite within successive regions can be inferred from the two-dimensional grain size distribution thereof.

[0019] In some embodiments, the processing plant may be a wet processing plant.

[0020] In a third aspect, the invention provides a method of mining magnetite iron ore, comprising: mining ore from an ore body; and separating the mined ore into magnetite and gangue via a leaching process.

[0021] Separating the mined ore may comprise liberating magnetite particles from the gangue without crushing or otherwise comminuting the mined ore. Separating the mined ore may comprise digesting the gangue in a chemical solution.

[0022] In a fourth aspect, the invention provides an apparatus when used for mining magnetite iron ore, comprising: a separator for liberating magnetite particles from mined ore, wherein the separator is configured to provide a magnetite concentrate via a leaching process; and a processing plant downstream of the separator for producing an upgraded magnetite product from the magnetite concentrate.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:Figure 1 is a flowsheet illustrating a magnetite processing apparatus in accordance with an embodiment of the invention;Figure 2 is a schematic representation of an ore body classified into regions according to grain size;Figure 3 is a flowsheet illustrating a method of mining magnetite in accordance with an embodiment of the invention;Figure 4 is a flowsheet illustrating a magnetite processing apparatus in accordance with an embodiment of the invention; andFigure 5 is a flowsheet illustrating a magnetite processing apparatus in accordance with an embodiment of the invention.DETAILED DESCRIPTION

[0024] In the following detailed description, reference is made to accompanying drawings which form a part of the detailed description. It will be readily understood that the aspects of thepresent disclosure, as generally described herein and illustrated in the drawings may be arranged, substituted, combined, separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure.

[0025] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, a limited number of the example methods and materials are described herein.

[0026] The embodiments of the invention shown in Figures 1 to 5 are described herein in the context of a method of mining magnetite iron ore with improved cost effectiveness, and an apparatus for carrying out the method. The invention also extends to a method of producing a magnetite concentrate product, and to an apparatus for carrying out the method.

[0027] With reference to Figure 1 , there is shown an apparatus 10 for mining magnetite from an ore body 16.

[0028] The apparatus 10 includes a device or machine 12, for example a drill, for extracting or otherwise mining ore material 14 from an ore body 16. The ore body 16 may be a banded iron formation or Bl F. It is to be understood that the ore may be mined by any suitable mining method and equipment. For example, the material 14 may be mined by drilling and blasting ore and transporting the mined ore from the pit by trucks and / or conveyors. Alternatively, the ore material 14 may be mined by surface miners moving over a pit floor and then transporting the mined ore from the pit by trucks and / or conveyors. Alternatively, the material 14 may be sourced from an existing stockpile or reserve of material sourced from a known region of the ore body 16. The equipment may be a powered machine, hand-held equipment and / or any suitable combination. Preferably, the mining machine 12 is configured to extract ore from a coarse reserve of the ore body 16. For example, the ore material 14 may be extracted by diamond drilling or reverse circulation drilling.

[0029] A scanner 18 is provided downstream of the mining machine 12. The scanner 18 is configured to assess a two-dimensional grain size distribution (GSD) of the magnetite within the mined material 14. For example, the scanner 18 may comprise a microscope or other form of image capturing device for imaging a flat section sampled from the mined material 14. The flat section may comprise a portion of the mined material 14 that has been mounted or otherwise set within a substrate such as epoxy resin. For example, the material may be subjected to a gentle de-agglomeration process (preferably with non-metal or plastic tools so as to avoid static and / orre-agglomeration) prior to being set in epoxy billets that are cut into vertical slices which, in turn, are then set on flat thin sections and polished to about 30 micron. The applicant has determined that cutting of vertical slices and subsequent setting on the flat thin allows more grain sizes to be captured, by substantially obviating a tendency of the particles to settle during the setting process which may result in some particles sitting below the surface of the thin section. An acquired image 20 may then be assessed via an image processing device 22. The image processing device 22 may be part of the scanner 18 or provided as a separate piece of equipment that is in communication with the scanner 18. The image processing device 22 may comprise software that uses pattern recognition algorithms to segment the image 20 into regions of magnetite 24 and gangue 26. The pattern recognition algorithms may comprise a match filter and / or involve artificial intelligence based on trained images of target regions of magnetite. Segmentation of the image 20 may result in an area calculation that can be used to determine the GSD of the sample.

[0030] The apparatus 10 also includes a separator 28. The separator 28 is configured to separate the mined material 14 into magnetite 24 and waste material or gangue 26. Preferably, the separator 28 is a chemical separator or bath that operates on a leaching process. In this manner, the magnetite material 24 may be liberated from the gangue 26 without the need for crushing or otherwise comminuting the ore material 14. The leaching process may be conducted on all of the material 14 mined from the ore body 16 or only on the portion of the mined material 14 that was assessed by the scanner 18. The leaching process includes feeding the mined material 14 into a chemical digest. A chemical solution or solvent used for the digest may be selected from a group that comprises any one of several suitable chemicals, including, by way of non-limiting example, hydrochloric acid, nitric acid, sodium hydroxide (caustic soda) and / or combinations of similar chemicals. It is desirable to select an appropriate solvent that achieves a strong liberation of the magnetite 24 without the solvent attacking or otherwise affecting the magnetite particles themselves. In the illustrated embodiment, the separator 28 is provided downstream of the scanner 18. However, it is also contemplated that in other embodiments, the scanner 18 may be provided downstream of the separator 28, and used to perform a two- dimensional grain size assessment on magnetite particles that have already been liberated from the gangue phases.

[0031] The liberated magnetite particles 24 are then assessed by a sizer 30. The sizer 30 is configured to measure a three-dimensional grain size distribution (GSD) of the magnetite particles 24. For example, the sizer 30 may be a laser sizer that operates on laser diffraction to directly measure a size of the magnetite particles across three dimensions. Advantageously, if the sizer 30 is used on magnetite material 24 that has been separated via the leaching process, the measured three-dimensional grain size represents the "natural" grain size of the magnetite 24within a portion or region of the ore body 16 from which the mined material 14 was sourced. In other embodiments, the sizer 30 may be a visual or image based sizer such as a camera or other form of image acquisition device. For example, the sizer 30 and the scanner 18 may be one and the same device. It is contemplated that a screen 29 may be used in combination with the sizer 30. The screen 29, may, for example, be a sieve or a series of sieves that is used to perform a sorting or "rough" sizing of the separated material, with only undersize material being sent onward to the sizer for "fine" sizing. For example, the screen 29 may be a dry sieve that is used to separate the magnetic particles at +212 micron and -212 micron (to be sized with sizer 30). In this way, the total throughput and particle size band / range to the sizer 30 is reduced, enabling calibration / performance of the sizer 30 to be optimised. Prior to assessment by the sizer 30, it is preferable that the liberated magnetite particles 24 are subjected to a de-magnetisation and deagglomeration treatment to avoid agglomeration of the magnetite particles 24 prior to sizing. For example, an ultrasonic bath or similar may be used to de agglomerate and remove any residual digest residue prior to sizing, with a Davis Tube producing DTR mags which are then dried and de-magnetised with a coil. The applicant has found that oven drying the DTR mags prior to demagnetising at a temperature of about 105 degrees Celsius produces optimal results. Further, it is understood that in order to avoid re-magnetisation and to reduce the impact of static force during the sizing assessment, contact with metal and plastic articles / equipment should be avoided. For example, it is preferable that the samples are packed in in glass containers or paper bags. Trials by the applicant have determined that such treatment substantially obviates an inherent bias to coarseness when assessing the magnetite due to an attraction between the magnetite digest and agglomeration.

[0032] The apparatus 10 also includes a processing plant 32. The processing plant 32 may be an ore processing facility or OPF that comprises equipment that is used to upgrade or otherwise work the magnetite ore 24 into a sellable "high grade" concentrate product 34. For example, ore 14 from low grade iron ore resources can be upgraded using wet processing equipment that includes, comminution equipment such as mills and crushers (for example HPGRs, jaw crushers, cone crushers and the like) and separation equipment (for example a series of screens, magnetic-based separators and / or gravity / density-based separators). Such wet processing can be used to separate waste material from the valuable magnetite mineral 24. Notably, however, the yield of product from the processing plant 32 is dependent upon the physical characteristics and liberation characteristics of the feed ores. Ore that is of a fine or small grain size is more difficult to break down to a desired product size, and requires additional energy and water resources when compared to ore that is of a coarse or larger grain size.

[0033] Turning now to Figure 2, which illustrates an example of a block model 36 of an ore deposit, including ore body 16. The model 36 is used to characterise the ore body 16. In the model 36, the ore body 16 is segmented into a number of discrete regions or domains 38. The regions 38 may be substantial, for example, the regions may be tens or hundreds of meters in length, width and depth. Accordingly, it is understood that the regions 38 may contain significant tonnages of ore. For example, the regions 38 may contain several thousand tonnes of ore or even several million tonnes. In particular, the ore body 16 is segmented into regions 38 based on the average natural or in-situ three-dimensional grain size of the magnetite within said regions 38. For example, the body 16 may be segmented into regions 38a of "coarse grain" with an abundance of magnetite 24 having a grain size that is above a predetermined threshold and regions 38b of "fine grain" which is largely depleted of magnetite 24 having a grain size above the predetermined threshold. It is also contemplated that the regions 38 may, alternatively, be classified based on the abundance or scarcity of magnetite 24 that is below a predetermined threshold, or a combination of the classification methods hitherto described.

[0034] It is envisaged that each region 38 will be analysed by assessing a three-dimensional grain size distribution of samples 14 of ore taken from a series of drilled holes within each region 38 in order to determine whether the ore within that region 38 is (a) "coarse grain" or (b) "fine grain" on a mass average basis. The cut offs between "coarse" and "fine" grades are dependent on a range of factors and may vary from mine to mine and in different sections of mines. When the assessment and determination of grain size within each region 38 is completed, the block model 36 of the ore body 16 is coded with the geo-metallurgical domains corresponding to the natural or in situ magnetite grain size. The model 36 may locate the drilled samples on a map of the ore body 16. Regions 38a of "coarse grain" and regions 38b of "fine grain" are marked on the map, with marked boundaries separating different regions. The boundaries may also be selected with regard to other factors, such as geological factors including ease of equipment access to said regions 38, weathering and oxidation and hardness of surrounding or intermediate rock. It is also contemplated that other mechanisms may be used in combination with grain size to domain the regions 38. Such mechanisms may include, for example, segmentation based on chemistry and other natural characteristics of the ore body. The regions 38 define blocks of the ore body 16 to be subsequently mined. The regions 38 may then subsequently be mined by, for example blasting using explosives, with mined ore material 14 then transported to the processing plant 32 by conveyor or truck.

[0035] The block model 36 is used to guide feed stock blending to the processing plant 32, in order to optimise the target grind size, in particular to minimise energy and water usage to magnetite mass recovery. For example, ore 14 mined from regions 38a of "coarse grain" may bemixed with ore 14 mined from regions 38b of "fine grain" in order to provide a targeted, consistent feed to the processing plant 32. A consistent feed may, for example, reduce the reliance on feedback loops associated with comminution equipment where fine grain material requires several passes through regrind mills in order to be reduced to the desired target particle size. This reduction in regrinding may lead to significant energy and water savings, while also minimising a potential bottleneck in the associated equipment workflow of the processing plant 32.

[0036] Notably, while the block model 36 is domained or otherwise segmented into regions 38 based on the three-dimensional grain size of the magnetite, it is not necessary to directly measure the three-dimensional grain size of each region with sizer 30. Rather, the three- dimensional grain size can be predicted from an assessment of the two-dimensional grain size of a sample of material 14 taken from each region. Specifically, as described above, the scanner 18 is used to analyse a sample 14 taken from one of these regions 38, in order to assess the two- dimensional grain size distribution of the magnetite 24 thereof. The sizer 30 is then used to analyse the sample 14 to measure the three-dimensional grain size distribution of the magnetite particles 24. Data relating to the three-dimensional grain size distribution of the material 14 from the sizer 30 is then compared or otherwise correlated with the two-dimensional grain size distribution obtained via the scanner 18 to determine a relationship therebetween.

[0037] In this way, it is understood that the sizer 30 provides a calibration of the scanner 18. Put differently, the sizer 30 may be considered to provide a stereological correction of two- dimensional grain size using three-dimensional data study. What is meant by this is that further operations performed subsequently by the scanner 18 (for example assessments of two- dimensional grain size distributions of ore material 14 that has been sourced from other regions of the ore body 16) can then be adjusted or otherwise weighted based on this calibration. A result being that an assessed two-dimensional grain size distribution of ore material 14 from a region of the ore body 16 can be used to infer the natural or in-situ three-dimensional grain size of magnetite from that region without the need to physically measure or otherwise conduct sizing with the sizer 30. Compared to existing methods of assessing or measuring three-dimensional grain size of ore bodies in-situ (such as, for example, 3D tomography), the described method is far more cost- effective, providing a 2D based imaging system that is used to predict or otherwise correlate the 3D population of magnetite within the ore body. In addition to being cost effective, the results provide a more reliable and accurate estimate of the natural grain-size - due, at least in part, to the obviation of any comminution of the ore material 14 prior to the assessment with the scanner 18 and / or an inability of existing methods to separate joined grains leading to a coarseness bias. The results of the 2D analysis may remain perpetually available for ongoing assessment, suchthat the algorithms that are used to determine the relationship between the 2D and 3D grain size may be tuned and / or improved over time.

[0038] A method of mining magnetite iron ore using the apparatus 10 will now be described with reference to Figure 3.

[0039] In an initial step 110, ore material 14 is extracted from the ore body 16 using mining or any other suitable machinery 12. During this step, the ore material 14 may, for example, be extracted down-hole from an ore body 16 by way of diamond drilling.

[0040] At least a sample of the mined ore material 14 is then transported, for example via conveyor or otherwise, towards the scanner 18. In an assessment step 120, a two-dimensional grain size distribution of the magnetite within the mined ore 14 is obtained. It is contemplated that the assessment step 120 comprises a step 122 of mounting a sample portion of the mined material 14 or a sample of processed concentrate in a substrate. An image of the thin section may then be acquired in an image acquisition step 124. The assessment step 120 may further comprise an analysis step 126 whereby the acquired image 20 is analysed with the image processing device 22. A mapping step 128 may follow in which the image processing device 22 uses image processing algorithms to map or otherwise segment the acquired image 20 into areas of magnetite 24 and gangue 26, with the relative areas of magnetite 24 and gangue 26 representing the two-dimensional grain size distribution.

[0041] In a measuring step 130, the at least a sample of the mined ore material 14 is then measured using the sizer 30, in order to measure the three-dimensional grain size distribution of the magnetite 24. This measuring step 130 may include a separation step 132, in which the magnetite particles 24 of the ore 14 are separated from at least the gangue. The separation step 132 may also result in the magnetite particles 24 being separated from the substrate should the measuring step 130 be conducted on the same sample of material 14 that was assessed by the scanner 18. Preferably, the separation step 132 involves liberating the magnetite 24 from the gangue via a chemical leaching process 134. The leaching step / process 134 involves feeding the ore material 14 into a digest of chemical solution. The chemical solution may comprise, by way of non-limiting example, hydrochloric acid and / or nitric acid and / or sodium hydroxide (caustic soda). The leaching process aims to liberate at least 95% of the magnetite particles 24 from the surrounding gangue 26, without attacking or otherwise damaging the magnetite particles 24. Once the magnetite particles 24 have been liberated, the particles may be sorted according to size in a sorting step 136. The sorting step 136 involves a "rough" sizing of the particles by screen or screens 29, which reduces volume and variation in particle size of a magnetite stream that is then assessed by a downstream sizer 30. Undersize particles from the screen or screens 29 arethen forwarded to the sizer 30 for "fine" sizing. The three-dimensional grain size distribution of the particles 24 is then acquired in a sizing step 138. The sizing step 138 may utilize the use of a laser diffraction unit or other forms of sizer 30. It is also contemplated that the separation step 132 may occur prior to the acquisition step 124, such that the image 20 acquired by scanner 18 is a two-dimensional image of separated "natural" grain magnetite.

[0042] Following the measuring step 130, results thereof are compared with the results of the assessment step 120 in a correlation step 140. During the correlation step 140, the two- dimensional and three-dimensional grain size distributions of the ore material 14 are compared, in order to determine a relationship between the results. For example, mathematical algorithms may be used to develop a ratio or equation that is then used to calculate a calibration factor or similar that can be used to estimate a three-dimensional grain size from a two dimensional grain size distribution of subsequent feeds of ore material 14.

[0043] In a classification step 150, a block model 36 of the ore body 16 is developed, in which the body 16 is domained or otherwise segmented into distinct regions 38 based on the three- dimensional grain size thereof. For example, the classification step may include domaining the ore body 16 into discrete regions 38a that are abundant in coarse-grained magnetite and regions 38b that are depleted of coarse grained magnetite. The regions 38 may be transient or fluid regions. That is, the boundaries of the regions 38 may change during the life of the mine with subsequent sampling / classifying of the ore material. During this classification step 150, the relationship or correlation between the two-dimensional and three-dimensional grain size distributions of an initial region 38 of the ore body 16 calculated during the correlation step 140 is used to infer the three-dimensional grain size of other regions 38 of the ore body from the two- dimensional grain size distribution alone - obviating the need to carry out the measuring step 130 when mining ore 14 from these other regions 38. That is, classification step 150 may include repeating steps 1 10 and 120 for other, unmined regions of the ore body, and then inferring or otherwise predicting the natural grain size of magnetite within these regions from the two- dimensional grain size distribution thereof.

[0044] Once the block model 36 has been developed, a processing step 160 may follow. The processing step 160 includes a selection step 162 in which the block model is used to determine or otherwise select the feed of ore material to the ore processing plant 32. That is, ore may be sourced from selected regions 38 of the ore body 16 based on the model, in order to ensure a feed of material of a consistent (estimated) average grain size to the equipment of the processing plant 32. For example, ore material selected from regions of "coarse" and "fine" grain size may be blended together to form a mixture of material having a desired, chosen, average grain size. An upgrade step 164 follows, in which the feed of material into the processing plant 32 isconcentrated into a high grade magnetite concentrate product 34. The upgrade step 164 may include, for example, comminuting the ore via a series of crushing and grinding steps, and filtering or otherwise separating the magnetite mineral via wet separating.

[0045] Another embodiment of the invention, in the form of apparatus 210, will now be described with reference to Figure 4.

[0046] The apparatus 210 is similar to the apparatus 10 described previously, with the exception that the flow sheet does not necessarily require the scanner 18 and sizer 30. For ease of reference, similar reference numerals will be used to describe analogous components.

[0047] The apparatus 210 is designed to produce a magnetite concentrate product 234 while obviating the need to grind or otherwise comminute the mined ore. As previously discussed, comminution of mined ore is both energy and resource intensive, and therefore the ability to produce a magnetite product 234 without requiring comminution steps represents both a commercially and environmentally attractive prospect. The magnetite product 234 may be a "cons grade" magnetite product.

[0048] As shown in the Figure, the apparatus 210 includes a mining machine 212, for example a drill, for extracting ore material 214 from an ore body 216. It is to be understood that the ore may be mined or otherwise extracted / sourced by any suitable method and equipment. The mined ore 214 is then transported to a separator 228 by way of conveying equipment, trucks or other means. It is noted that the mined ore 214 need not be transported directly after extraction, and may, for example, be stockpiled prior to transport.

[0049] The separator 228 is a non-comminutive separator. What is meant by this is that the separator 228 does not perform any form of physical breaking, grinding or other comminution action onto the ore material 214. In this way, magnetite 224 within the ore 214 may be liberated from surrounding gangue without the need for energy intensive machines such as crushers and grinders. Rather, it is contemplated that the separator 228 is a chemical separator, utilising a chemical digest to break down the gangue phases 226 and separate the magnetite particles 224 therefrom. The separator 228 shall provide a similar level of liberation as more conventional comminution based separation techniques - for example, achieving up to 95% liberation of the magnetite.

[0050] The separated magnetite 224 may then be processed via a processing plant 232. The processing plant 232 may be a wet processing plant that provides an upgrade circuit for concentrating the magnetite 224 into a "high grade" magnetite product 234. It is understood that the term "high grade" may refer to the % iron / magnetite mass concentration of the product 234.Notably, the processing plant 232 may constitute a portion of an existing processing plant 232 used for more conventional processing of magnetite ore - for example an upgrade circuit thereof.

[0051] A method of mining magnetite iron ore using the apparatus 210 will now be described with reference to Figure 5.

[0052] In an initial step 310, ore material 214 is mined from the ore body 216 using mining machinery 212. During this step, the ore material 214 may, for example, be stockpiled before being transported to the separator 228.

[0053] In a separation step 332, magnetite particles 224 are liberated from surrounding gangue phases 226 via a non-comminutive process. Specifically, the separation step 332 may involve a leaching step / process 334 that includes feeding the mined material 214 into a chemical bath that contains a chemical solution. The chemical bath may utilize solvents, such as, for example, hydrochloric acid and / or nitric acid and / or sodium hydroxide (caustic soda).

[0054] The separated magnetite material 224 may then, optionally, be fed through the processing plant 232 in an upgrading step 364. During the upgrade step 364, the magnetite 224 may be fed through an upgrade circuit comprising, for example, wet separators such as screens, desliming apparatus and similar in order to further concentrate the magnetite in order to produce a high grade magnetite concentrate product 234.EXAMPLE

[0055] Trials by the applicant have demonstrated the following flowsheet to be particularly suitable for calibrating or otherwise correcting stereoscopic bias in grain size data derived from 2D imagery of a magnetite BIF (banded iron formation).• Procuring a sample of mined magnetite - for example from a coarse reserve (-3.35 mm).• Liberating of the magnetite from the gangue phases of the BIF via a leach process.• Sorting the leached magnetite product by size.• Subjecting the sorted product to a de-magnetisation and de agglomeration procedure.• Sizing the leached grains by laser to produce a first (measured) data set “Data Set A”• Optional - sizing the leached grains by 3D tomography to produce a second (measured) data set “Data Set B”• Producing a thin section by setting the sized grains in resin and cutting into vertical slices.• Acquiring or otherwise assessing 2D magnetite grain size of the leached grains (“Data Set C”) by imaging a thin section formed by setting the grains in resin and cutting into vertical slices.• Obtaining a correlation between the 2D grain size data (Data set C) and the measured 3D grain size data (Data Sets A and B).

[0056] Applying the correlation to 2D grain size data (Data Set D) acquired from imagery of further thin sections of the Magnetite BIF to infer a 3D grain size thereof. Summarily, embodiments of the present invention provide a cost effective and / or energy efficient method for mining magnetite ore from an ore body. For example, some forms of the present invention provide an alternative chemical leach based separation technique that is not reliant on conventional energy intensive comminution methods. In addition, some forms of the present invention provide an image-based method of characterising regions of an ore body according to "natural" or three- dimensional grain size. Compared to existing methods of assessing or measuring three- dimensional grain size of ore bodies in-situ (such as, for example, 3D tomography), the described method is far more cost-effective, providing a fast 2D based imaging system that is used to predict or otherwise correlate the 3D population of magnetite within the ore body.

[0057] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavor to which this specification relates.

[0058] Throughout this specification and the claims which follow, unless the context requires otherwise, the word ‘comprise’, and variations such as ‘comprises’ and ‘comprising’, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.LEGEND

Claims

CLAIMS1 . A method of mining magnetite iron ore, comprising: assessing a two-dimensional grain size distribution of magnetite from an ore body; measuring a three-dimensional grain size distribution of the magnetite; determining a relationship between the two-dimensional and three-dimensional grain size distributions; and using said relationship to classify the ore body into regions based on three-dimensional grain size inferred from assessing two-dimensional grain size distribution of magnetite of each region.

2. The method of claim 1 , wherein assessing the two-dimensional grain size comprises acquiring an image of a thin section of the ore body with a scanner.

3. The method of claim 2, wherein assessing the two-dimensional grain size comprises mounting mined ore from the ore body within an epoxy substrate for scanning with the scanner.

4. The method of claim 2 or claim 3, wherein assessing the two-dimensional grain size comprises analysing the acquired image with image processing algorithms.

5. The method of any one of claims 2 to 4, wherein assessing the two-dimensional grain size comprises mapping the acquired image into areas of magnetite and gangue.

6. The method of any one of claims 1 to 5, wherein measuring the three-dimensional grain size comprises separating the ore into magnetite particles and gangue.

7. The method of any one of claims 1 to 6, wherein measuring the three-dimensional grain size comprises liberating magnetite without crushing or otherwise comminuting the ore.

8. The method of any one of claims 1 to 7, wherein measuring the three-dimensional grain size comprises separating magnetite particles from gangue via a leaching process.

9. The method of claim 8, wherein measuring the three-dimensional grain size comprises digesting the gangue in a chemical solution.

10. The method of any one of claims 1 to 9, wherein measuring the three-dimensional grain size comprises sizing the magnetite particles by laser.1 1. The method of any one of claims 1 to 10, wherein the step of classifying the ore body comprises segmenting the ore body into regions abundant in coarse-grained magnetite.

12. The method of claim 11 , wherein the step of segmenting the ore body comprises domaining the ore body into regions abundant in coarse-grained magnetite.

13. The method of any one of claims 1 to 12, wherein the step of classifying the ore body comprises extracting a sample of ore from an unmined region of the ore body such that a two- dimensional grain size distribution of magnetite within that region represents a natural grain size distribution of magnetite within that region.

14. The method of any one of claims 1 to 13, comprising the additional step of: mining the ore from the ore body.

15. The method of claim 14, wherein the step of mining ore comprises extracting ore from the ore body via diamond drilling.

16. The method of any one of claims 1 to 15, comprising the additional step of: processing mined ore in a downstream processing plant to produce upgraded magnetite material.

17. The method of claim 16, wherein the step of processing the mined ore comprises selecting ore from a respective region of the ore body based on the inferred three-dimensional grain size of that region to optimise feed to equipment within the processing plant.

18. The method of claim 16 or claim 17, wherein the step of processing the mined ore comprises blending feed stock from different regions of the ore body to provide a feed mixture of desired average grain size.

19. An apparatus when used for mining magnetite iron ore, comprising: a device for extracting ore from an ore body; a scanner configured to assess a two-dimensional grain size distribution of magnetite within defined regions of the ore body; and a processing plant configured to produce upgraded magnetite material;wherein a feed to the processing plant is optimised based on three-dimensional grain size inferred from a two-dimensional grain size distribution of magnetite within the respective regions.

20. The apparatus of claim 19, wherein the scanner is configured to acquire images of mined ore showing a grain structure thereof.

21. The apparatus of claim 19 or claim 20, further comprising a separator configured to liberate magnetite particles from gangue.

22. The apparatus of claim 21 , wherein the separator is configured to liberate the magnetite particles via a leaching process.

23. The apparatus of any one of claims 19 to 22, further comprising a sizer configured to measure a three-dimensional grain size distribution of the magnetite particles.

24. The apparatus of claim 23, wherein the sizer comprises a laser diffraction unit.

25. The apparatus of any one of claims 19 to 24, wherein the three-dimensional grain size distribution of magnetite particles within a respective one of the regions is correlated with the two- dimensional grain size distribution of that region to calibrate the scanner such that a three- dimensional grain size distribution of magnetite within successive regions can be inferred from the two-dimensional grain size distribution thereof.

26. The magnetite iron ore processing apparatus of any one of claims 19 to 25, wherein the processing plant is a wet processing plant.

27. A method of mining magnetite iron ore, comprising: mining ore from an ore body; and separating the mined ore into magnetite and gangue via a leaching process.

28. The method of claim 27, wherein separating the mined ore comprises liberating magnetite particles from the gangue without crushing or otherwise comminuting the mined ore.

29. The method of claim 27 or 28, wherein separating the mined ore comprises digesting the gangue in a chemical solution.

30. An apparatus when used for mining magnetite iron ore, comprising: a separator for liberating magnetite particles from mined ore, wherein the separator is configured to provide a magnetite concentrate via a leaching process; and a processing plant downstream of the separator for producing an upgraded magnetite product from the magnetite concentrate.

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