TECHNICAL FIELD

The invention relates to processing mined material in underground mines to recover valuable metals from material.

The invention relates particularly, although by no means exclusively, to processing mined material from a block cave mine to recover valuable metals from material.

The invention relates to processing mined material from other underground mines, such as a sub-level cave mine to recover valuable metals from material.

BACKGROUND ART

An increasingly important issue for the mining industry is to maximize the “economic value” of mined material that is taken from a mine to a downstream mineral processing plant and is processed in the minerals processing plant to recover a valuable metal(s) from the material.

This is of increasing importance due to the gradual decline of plant feed grades across a broad range of commodity types. Traditionally, lower feed grades have been compensated for by mining and processing larger volumes of material. This has led to higher up front capital costs and longer lead-times from discovery and development to operating mines. While operating costs do decline with increasing scale, the law of diminishing returns applies. Increases in the volume of material processed beyond a certain point do not necessarily lead to a quantifiable reduction in the per tonne processing cost.

Ultimately, this leads to lower economic value being generated per tonne of mined material and therefore less viable mines when compared to historic mineral resources.

The issue is relevant to other underground mines, such as sub-level cave mines.

In the case of block cave mines, typically all of the material that is discharged from the multiple draw points of a mine is transported from an extraction level of the mine to the surface, typically via an underground primary crushing circuit.

Typically, all of the extracted material is processed in a mineral processing plant at the mine.

The invention provides an opportunity to selectively direct extracted material from all, or a subset, of the draw points on an extraction level to:

(a) a minerals processing plant for processing material through the plant, for example via a short-term operating stockpile, often called a Coarse Ore Stockpile (COS), or (b) a holding stockpile for future processing of the material (could be the following week, the following month or end of life), or

(b) a waste stockpile for storing the material as a waste material for assessment at a later point in time.

The above comments are not intended to be an admission of the common general knowledge in Australia or elsewhere.

SUMMARY OF THE DISCLOSURE

In the context of a block cave mine, noting that the invention extends to other types of underground mines, the invention selectively processes mined material from all, or a subset, of the draw points in the mine based on grade of material at the draw points. This makes it possible to intentionally manipulate the grade of material that is transported to the surface in any given period of time. This provides an opportunity, for example, to (a) process the highest grade mined material in the minerals processing plant for a period of time or (b) stockpile a lower grade material for later processing in the minerals processing plant for a period of time or (c) remove waste altogether from the feed to the minerals processing plant for a period of time. This ultimately can result in an opportunity for continuous maximisation of the “economic value” of material that is processed by the minerals processing plant in any given period of time. The extent to which grade manipulation may be useful will depend on factors at any given period of time, for example, the production capacity of a minerals processing plant.

The term “economic value” is understood herein to be a broad term.

There is a number of possible measures of economic value.

One measure is the value of metals in a mined material from a mine at the point in time that the material is discharged from a draw point or at any other suitable time.

Another measure is the value of metals that are ultimately recovered from a mined material in a mineral processing plant of a mine.

Typically, the economic value of a mined material is also assessed against the capital and operating costs of a mine.

There may be other measures depending on the industrial context.

The economic value of a given mined material may be different at different times in the life of a mine and at the same time in different mines.

In broad terms, the invention is a method of underground mining, including but not limited to block cave mining, a material that can selectively deliver material based on the economic value of the material to a minerals processing plant. Generally, it is comprised of the following steps:

(a) predicting or measuring directly or indirectly the grade of a valuable metal, such as gold or copper, in the material from one or more extraction points, and

(b) selecting a processing option for the material from the extraction points based on an “economic value” of the material, with the economic value being calculated having regard to a range of factors including the grade of the valuable metal in the material, with the processing options comprising (i) a minerals processing plant for processing the material to recover the valuable metal and at least one of (ii) a holding stockpile for future processing of the material in the minerals processing plant and (iii) a waste stockpile for storing the material as a waste material, and

(c) transferring the material to the selected processing option.

In the context of block cave mines, the invention is a method of block cave mining a material that comprises the steps of:

(a) predicting or measuring directly or indirectly the grade of a valuable metal, such as gold or copper, in the material moving downwardly to or being discharged from at least some of the draw points of the block cave mine, and

(b) selecting a processing option for the material from the draw points based on an “economic value” of the material, with the economic value being calculated having regard to a range of factors including the grade of the valuable metal in the material, with the processing options comprising (i) a minerals processing plant for processing the material to recover the valuable metal and at least one of (ii) a holding stockpile for future processing of the material in the minerals processing plant and (iii) a waste stockpile for storing the material as a waste material, and

(c) transferring the material to the selected processing option.

The invention, as described in the preceding paragraph in relation to block cave mining, assesses the grade of the valuable metal in the material moving to or being discharged from draw points and selects processing options for the material from the draw points having regard to the “economic value” of the material.

In some situations, step (b) may comprise selecting draw points that have the highest- grade material and transferring the material to the mineral processing plant. In other situations, step (b) may comprise selecting draw points that have the lowest- grade material and transferring the material to the waste stockpile. When the selected processing option is processing in the minerals processing plant, the method may comprise processing the material in the plant and recovering the valuable metal from the material.

The term “grade” is understood herein to mean the concentration of a metal in a material.

The invention extends to situations in which the grade of the valuable metal is measured directly or measured indirectly in step (a).

For example, direct measurement can be via chemical assays of samples periodically collected from extraction points such as draw points in the block cave mine.

Another example of direct measurement is scanning material presented at a face of a draw point with equipment capable of measuring the grade of certain, or all of, the elements in the rock at the face. One example of this is the use of x-ray fluorescence (XRF) systems mounted in the buckets of loading equipment capable of continuously measuring the grade of certain elements in all of the material mined from extraction points such as draw points in the block cave mine.

A further example of direct measurement is the use of belt-based grade sensors, like, but not limited to, Magnetic Resonance (MR) and Prompt Gamma Neutron Activation Analysis (PGNAA) sensors, on the crusher feed and or discharge belts. Readings from these sensors may be linked back to individual extraction points such as draw points in the block cave mine via loader identifiers, material dump timing and dispatch data on loader operating areas.

For example, indirect measurement can be via measuring concentrations of contaminants or penalty elements, such as phosphorus in the case of iron ore, and calculating grade via a correlation between contaminant concentration and grade.

In this context, the terms “contaminant” and “penalty element” are understood herein to mean an element or compound in a material that does not have value and in certain concentrations result in a reduction in the “economic value” of the material being mined and processed.

By way of further example, indirect measurement can be via the direct measurement of the concentration of another valuable metal, where there is a correlation between the two valuable metals. One example is gold. A prediction of gold grade can be made in some cases from measurements of concentrations of other valuable metals, such as copper, in an ore body.

The valuable metal may be a precious metal, such as gold. The valuable metal may be a base metal, such as copper and molybdenum.

The valuable metal may be more than one metal.

The applicant is concerned particularly with gold, copper and molybdenum.

The invention extends to any suitable options for predicting grade of the valuable metal at extraction points such as draw points of the block cave mine.

The invention extends to any suitable options for directly or indirectly measuring grade of the valuable metal moving to or being discharged from extraction points such as draw points of the block cave mine.

By way of example, grade of the valuable metal may be measured at extraction points such as draw points of the block cave mine by taking samples periodically and then chemically assaying the samples for the valuable metal, such as gold, copper, molybdenum, etc.

Another option is sensors on fixed or mobile mining machinery at extraction points such as draw points of the block cave mine. The mobile mining machinery may include any one or more of loaders, mobile draw point feeders, and vehicles, such as haul trucks, for transporting the material from extraction points such as draw points. The fixed mining machinery may be a tipple, crusher feed and discharge hoppers and collection belts and conveyors.

MineSense is one company that has sensor technology that is an example of sensor technology in embodiments of the invention. MineSense technology may include high-speed x-ray fluorescence (XRF) sensors installed on mobile mining machinery, such as shovels and loaders, that scan the material. Software processes the primary sensed data using machine learning algorithms developed for that ore body. This information is combined - in real-time - to provide grade and material classification data. The data is then digitally provided directly to FMS software to direct vehicles that are loaded with the material to a required location having regarded to the sensed grade data, with no operator intervention required. Alternatively, such decisions can be made by an operator seeing the grade data. In this situation, the sensor technology is not tied into the FMS software and re-direction will be done via a machinery, such as a shovel, operator talking with a haul truck driver when a change of destination is required.

Another option is measuring the grade of the valuable metal in the material downstream of extraction points such as draw points, for example on conveyors for transporting crushed material, and linking the measured grade to specific extraction points. Step (a) of the method may include measuring the grade of the valuable metal in the material being discharged from at least some of the extraction points such as draw points of the block cave mine, typically all extraction points, at any suitable frequency needed for making decisions about processing options in real-time.

The measurement frequency may be determined based on a range of factors including downstream system constraints, measured grade variability of extracted material, and system sorting limitations, i.e., ore body heterogeneity and the mechanical ability of the system to sort material.

The method may include building a database of grade distribution versus time for all extraction points such as draw points on the extraction level.

Step (a) may include collating sensor-based grade measurements from extraction points such as draw points of the block cave mine across the extraction level into a single understandable grade of “value” model.

Step (b) may include processing the grade or a “value” model based on grade across the mine system and determining theoretical groupings of individual extraction points such as draw points of the block cave mine into grade or “value” categories.

Step (b) may include considering total system constraints, including individual system constraints in the mining, material transfer and the minerals processing plant systems of the mine, and the selection of appropriate draw points to maximise instantaneous system wide “economic value”.

Step (b) typically includes considering other fundamental aspects of mining, such as predetermined rules on even draw across the extraction level on a daily basis for a mine. Lack of proper regard for the fundamentals may lead to an overall reduction in the future economic potential of the system and should be avoided whenever possible.

The selection of the processing option in step (b) may also take into account the availability of the minerals processing plant, such as the production capacity of the plant during a given period of time.

By way of example of taking into account plant availability, if there is a period of time in which the mine is outproducing the minerals processing plant, higher economic value draw points will be selected for extraction to maximise economic value from the plant and selectively transported to a Coarse Ore Stockpile (COS) and held in the stockpile and then processed in the plant to recover the valuable metal. The number of draw points selected for this time period typically needs to be flexible and able to maximise the economic value from the minerals processing plant for the plant production rate. This flexibility may mean not complying with predetermined rules, such as even draw across the extraction level, for this time period, after this time period, another selection of draw points may then be mined and transported to the surface for storage in other stockpiles to return the mining operation to the predetermined rules, such as even draw. These stockpiles may then be drawn into the plant when needed.

The processing options may be any suitable options.

As noted above, by way of example, the processing options may include transferring mined material to any one or more of: i. a minerals processing plant for processing material through the plant, for example via a short-term operating stockpile, i.e., a Coarse Ore Stockpile (COS), to recover the valuable metal, or ii. a holding stockpile for future processing material (could be the following week, the following month or end of mine life) in the minerals processing plant, or iii. a waste stockpile to be stored as a waste material and not, in the foreseeable future, to be processed in the minerals processing plant.

By way of example, the processing options may include the following options in the case of a block cave mine.

1. _ Processing option 1

Transferring the material from a 1 ^st group of draw points for a 1 ^st period of time to a minerals processing plant (optionally, via a crusher and optionally via a Coarse Ore Stockpile (COS)) and recovering the valuable metal from the material, where the selection of the 1 ^st group of draw points is based on the average grade of the valuable metal exceeding a threshold grade that provides economic value.

The time period may be any suitable time period.

Optionally, changing the draw points in the 1 ^st group over time having regard to factors, such as (for example) average grade of the valuable metal at the draw points (e.g., the average grade may drop below the threshold) and an objective of maintaining an even pull of material from the block cave to avoid damage to the block cave, noting that this may not be possible for the whole time period that the material is transferred from the selected draw points.

Optionally, the amount of the material in the 1 ^st group of selected draw points is selected to match a processing rate (i.e., the capacity) of the minerals processing plant in a processing window, noting that the invention extends to options where this is not the case. The term “processing window” is understood herein to mean a standard production planning time period for the mine.

The threshold value may change with time. Typically, the threshold value is linked to the sale price of the valuable metal and takes into account metal recovery in the mineral processing plant and mining and processing costs.

2. _ Processing option 2

Transferring the material from a 2 ^nd group of draw points for a 2 ^nd period of time to a stockpile (optionally, via a crusher), where the selection of the 2 ^nd group of draw points is based on the average grade of the valuable metal being equal to or below the threshold grade that provides economic value.

The time period may be any suitable time period.

Optionally, changing the draw points in the 2 ^nd group over time having regard to factors, such as (for example) average grade of the valuable metal at the draw points (e.g., the average grade may change) and an objective of maintaining an even pull of material from the block cave to avoid damage to the block cave.

Optionally, recovering the valuable metal from the stockpiled material at a later point in time if the economic value warrants recovery.

Optionally, not recovering the valuable metal from the stockpiled material.

The threshold value may change with time. Typically, the threshold value is linked to the sale price of the valuable metal and takes into account metal recovery in the mineral processing plant and mining and processing costs.

The above processing options are examples of a number of possible processing options.

The invention makes it possible to discard “non-economic” material before the minerals processing plant.

The invention also makes it possible to maximise grade throughput of a minerals processing plant of a mine by selectively transferring higher grade material to the minerals processing plant of the mine.

This may be important where the mining rate is greater than the mineral processing plant production rate.

For example, the invention provides an opportunity to maximise revenue during a planned or unplanned shutdown when the processing capacity of a minerals processing plant is reduced. For example, the invention makes it possible to supply an amount of a higher-grade material to the minerals processing plant that matches the capacity of the minerals processing plant during the planned or unplanned shutdown when there is reduced capacity in the plant and to stockpile a lower grade material for processing at a later time (or not at all) when there is a higher capacity in the plant.

For example, the invention provides an opportunity to right-size a minerals processing plant to the amount of mined material that is economically valuable to process in the minerals processing plant in a period of time.

For example, if a decision is made to increase the amount of mined material per year produced in an existing mine, the invention provides an opportunity to use the existing minerals processing plant and not increase the capacity of the plant.

In this scenario, the invention makes it possible to calculate a minimum threshold grade of mined material to be processed in the minerals processing plant to match the current capacity of the plant. This will mean that material below the threshold grade is stockpiled and processed through the minerals processing plant at a later time, for example when there is an unscheduled interruption to mining in the mine and it is necessary to draw down stockpiled material to be supplied to the minerals processing plant.

The invention is applicable to situations in which the mine includes material that is not economic to process in the mineral processing plant at a given point in time.

The “non-economic” material can be stockpiled and processed later if the economics change.

The invention works particularly well, but not only, when the grade of the valuable metal varies across draw points, noting that the grade from a given draw point may vary over time.

The material may be transferred from draw points to an underground crusher, for example via LHDs or any other suitable vehicle.

The crushed material may be transferred from the underground crusher by a conveyor to the stockpile of the minerals processing plant.

In another embodiment, the material may be transferred from draw points to an above-ground crusher or to the stockpile or to the minerals processing plant via vehicles. In this embodiment, it is not necessary to push all of the material through the underground crusher. The vehicles may be loaders, such as LHDs, or other vehicles. The vehicles may be electric, diesel, etc. The vehicles may be manned or autonomous.

The invention also provides a block cave mine that comprises: (a) a plurality of draw points for discharging a material into an extraction level of the mine;

(b) a system for predicting or measuring the grade of a valuable metal in the material moving downwardly to or being discharged from the draw points,

(c) a processor for processing grade data from the draw points and making decisions about processing options, with the decisions being based on an “economic value” of the material that is calculated having regard to a range of factors including the grade of the valuable metal in the material, with the processing options comprising a minerals processing plant for processing the material to recover the valuable metal and at least one of a holding stockpile for future processing of the material in the minerals processing plant and a waste stockpile for storing the material as a waste material,; and

(d) extraction equipment for moving the material from the draw points to selected locations in accordance with the processor’s decisions, and

(e) a minerals processing plant for recovering the valuable metal from the material that is transferred to the plant.

The system for predicting or measuring the grade of the valuable metal may be any suitable system.

The extraction equipment may include mobile mining machinery, such as loaders, mobile draw point feeders, and vehicles, such as haul trucks, for transporting the material from the draw points.

The above description of the invention focuses on block cave mining.

The invention is applicable to underground mining generally.

By way of example, the invention extends to sub-level cave mining.

The invention provides more broadly, a method of underground mining a material that comprises the steps of:

(a) predicting or measuring the grade of a valuable metal in the material being mined at multiple locations of a mine at a point in time,

(b) selecting a processing option for the material from each location based on the “economic value” of the material, with the economic value being calculated having regard to a range of factors including the grade of the valuable metal in the material, with the processing options comprising a minerals processing plant for processing the material to recover the valuable metal and at least one of a holding stockpile for future processing of the material in the minerals processing plant and a waste stockpile for storing the material as a waste material, and (c) transferring the material to the selected processing option.

The invention also provides in broad terms an underground mine that includes:

(a) a plurality of locations for extracting material in the mine;

(b) a system for predicting or measuring the grade of a valuable metal in the material at the locations,

(c) a processor for processing grade data from the locations and making decisions about processing options, with the decisions being based on the “economic value” of the material that is calculated having regard to a range of factors including the grade of the valuable metal in the material, with the processing options comprising a minerals processing plant for processing the material and at least one of a holding stockpile for future processing of the material in the minerals processing plant and a waste stockpile for storing the material as a waste material,;

(d) extraction equipment for moving the material from the locations to selected locations in accordance with the processor’s decisions; and

(e) a minerals processing plant in one of the locations for recovering the valuable metal from the material that is transferred to the plant.

The mine may be any suitable underground mine.

The mine may be a block cave mine.

The mine may be a sub-level cave mine.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described further below by way of example only with reference to the accompanying Figure which is an extraction level plan view which shows the average gold grade sampled at the draw points of a block cave at the Cadia mine of the applicant at a point in time.

DESCRIPTION OF EMBODIMENT

As noted above, an increasingly important issue for the mining industry is to maximize the “economic value” of mined material that is taken from a mine to a downstream mineral processing plant and is processed in the minerals processing plant to recover a valuable metal(s) from the material.

As is also noted above, in the context of a block cave mine, the invention selectively processes mined material from all, or a subset, of the draw points in a block cave mine. This makes it possible to intentionally manipulate the grade of material that is transported to the surface in any given period of time. This provides an opportunity, for example, to (a) process the highest grade mined material in the minerals processing plant for a period of time or (b) stockpile a lower grade material for later processing in the minerals processing plant for a period of time or (c) remove waste altogether from the feed to the minerals processing plant for a period of time. This ultimately can result in an opportunity for continuous maximisation of the “economic value” of material that is processed by the minerals processing plant in any given period of time. The extent to which grade manipulation may be useful will depend on factors at any given period of time, for example, the production capacity of a minerals processing plant.

The following description is in the context of a block cave mine for recovering gold and copper from a hard rock ore body.

The following description does not include a detailed description of the configuration of a block cave mine. The details of block cave mine construction are well-known to a skilled person. The description focusses on the extraction level of a block cave mine.

The invention is not confined to gold and copper recovery from a block cave and extends generally to recovering any valuable metal from a hard rock ore body below ground by any suitable underground mining method, such as a sub-level cave mine.

A typical block cave mine includes a plurality of draw points for discharging a material into an extraction level of the mine. Typically, a mine plan for the mine selects the draw points from which material is extracted from draw points for downstream crushing and mineral processing the crushed material to recover valuable metal from the material. Typically, the selection is based on a range of factors, including maintaining an even pull of material from the mine. This is an important consideration. Typically, material is extracted from only a comparatively small percentage of the draw points in the mine at a point in time, with the selected draw points varying over time. Typically, mine operators will try to draw from as many draw points in a mine in a day as possible, with an overall objective of even pull across the mine, typically via every draw point being drawn every day or every other day. It is noted that mine operation practices can vary depending on the particular circumstances of mines.

The invention is described broadly in the context of a block cave mine as a method of mining a material that comprises the steps of:

(a) predicting or measuring the grade of gold (or copper) in the material moving downwardly to or being discharged from at least some of the draw points of the block cave mine, and (b) selecting a processing option for the material from each draw point based on an “economic value” of the material, with the economic value being calculated having regard to a range of factors including the gold grade of the material, and

(c) transferring the material to the selected processing option.

The processing options may include, by way of example, transferring mined material to any one or more of: i. a minerals processing plant for processing material through the plant, for example via a short-term operating stockpile, i.e., a Coarse Ore Stockpile (COS), to recover the valuable metal, or ii. a holding stockpile for future processing material (could be the following week, the following month or end of mine life) in the minerals processing plant, or iii. a waste stockpile to be stored as a waste material and not, in the foreseeable future, to be processed in the minerals processing plant.

The extent to which grade manipulation may be useful will depend on factors at a given period of time, for example, the production capacity of a minerals processing plant.

The invention is also described broadly in the context of block cave mining as a block cave mine that includes:

(a) a plurality of draw points for discharging a material into an extraction level of the mine;

(b) a system for predicting or measuring the grade of a valuable metal in the material moving downwardly to or being discharged from the draw points,

(c) a processor for processing grade data from the draw points and making decisions about processing options (such as those described in items i-iii above), with the decisions being based on an “economic value” of the material that is calculated having regard to a range of factors including the grade of the valuable metal;

(d) extraction equipment for moving the material from the draw points to selected locations in accordance with the processor decisions, and

(e) a minerals processing plant for recovering the valuable metal from the material that is transferred to the plant.

The grade prediction or measuring system may be any suitable system.

For example, the grade measurement system may be a Prompt Gamma Neutron Activation Analysis (PGNAA) system.

The extraction equipment may be any suitable extraction equipment. For example, the material may be transferred from draw points by vehicles to an underground crusher, crushed in the crusher, and then transported via a conveyor to a stockpile or a mineral processing plant at the surface.

In another option, the material may be transferred from draw points by vehicles to an above-ground crusher or to a stockpile and from the crusher to the minerals processing plant. The vehicles may be loaders, such as LHDs, or other vehicles.

In both options, the vehicles may be electric, diesel, etc, and the vehicles may be manned or autonomous.

The Figure illustrates an embodiment of the invention in the context of the Cadia mine of the applicant.

The Figure is an extraction level plan view of a block cave at the Cadia mine of the applicant.

The Figure shows the average gold grade sampled at the 256 draw points of the block cave at a point in time, noting that gold grade is an indicator of economic value in this instance.

The plan view is divided into rectangular sections, each section indicating a draw point and the draw area of that draw point at the extraction level.

Each draw point section is shaded in accordance with the legend that forms part of the Figure to indicate the grade of gold in material at the draw point.

The grade at each draw point is an average of the gold grades of the last 5 samples at the draw point, as determined by chemical analysis of the samples.

By way of example, there are shaded areas that indicate a gold concentration in a range of 0.001-0.3 g/t of material, there are other shaded areas that indicate a gold concentration in a range of 0.9- 1.2 g/t of material, and there are other shaded areas that indicate a gold concentration in a range of 1.5-1.8 g/t of material. There are other grade concentrations in the legend.

It is clear from the Figure that there is a substantial variation in gold grade across the draw points.

The experience of the applicant is that there is also a variation in grade at a given draw point over time.

Therefore, this block cave is a good example of an opportunity to selectively remove material from draw points having regard to economic value considerations and other factors such as availability of a minerals processing plant, including the production capacity of the plant. For example, there is a material difference in economic value operating the applicant’s Cadia block cave mine to extract higher grade material from draw points that are shaded to indicate a gold concentration in a range of 1.5- 1.8 g/t of material for a 1 ^st time period compared to extracting lower grade material from draw points that are shaded to indicate a gold concentration in a range of 0.001-0.3 g/t of material for the same time period.

The economic value of the material at the draw points can be calculated from the gold grades at the draw points or by other measures of economic value and taking into account recovery in a mineral processing plant and operating and other costs.

Therefore, there is an opportunity to extract material from those draw points that have a gold grade above a threshold grade that will provide an acceptable economic value for the mine, noting that this threshold grade may change over time depending on changes in gold price, recovery in a mineral processing plant, and operating and other costs.

The applicant has found in a technology assessment at the applicant’s Cadia block cave mine that grade sensors on extraction equipment in the mine can provide accurate grade information that can be transferred and processed to facilitate mine planners’ making decisions on the selection of draw points from which material is extracted.

By way of example, in one but not the only embodiment of the invention, after considering grade data derived from grade sensors measuring grade of material being extracted from draw points and other information such as the capacity of the mineral processing plant in a processing window and an objective of maintaining an even pull from the mine and establishing a threshold grade that provides a minimum acceptable economic value of metal recovered from the mine, the mine planners decide that the mine should be operated as follows over a time period X + Y +Z in this embodiment:

Period X, say 6 hours - material that is above the threshold grade is moved from a 1 ^st group of selected draw points to an underground primary crusher, the crushed material is moved to the surface and stockpiled in a Coarse Ore Stockpile (COS) of the minerals processing plant, and stockpiled material is moved from the COS through the minerals processing plant to recover gold and copper from the material.

Next Period Y, say 3 hours - material that is below the threshold grade is moved from a 2 ^nd group of selected draw points to an underground primary crusher, the crushed material is moved to the surface and stockpiled in a “waste” stockpile, with the term “waste” being a relative term and based on a determination of economic value that may change over time. Next Period Z, say 5 hours - material that is above the threshold grade is moved from a 2 ^nd group of selected draw points to an underground primary crusher, the crushed material is moved to the surface and stockpiled in the COS of the minerals processing plant, and stockpiled material is moved from the COS through a minerals processing plant to recover gold and copper from the material.

It is noted that the draw points in the groups of draw points may be different or there may be some overlap of the draw points across the groups.

It can be appreciated that the above assessment process is repeated for each successive nominated time period.

It can be appreciated that, for example, the mine planners may change any one or more than one of the selected draw points, the threshold grade, and the time period X, Y, and Z having regard to relevant factors at that time.

The embodiment is relevant in a situation where the capacity of a mineral processing plant of a mine is lower than the mined material production rate of the mine for the time period X, Y, and Z. In this situation, it makes sense to selectively process mined material from the mine so that (a) the amount of mined material that is transferred to the mineral processing plant to match the processing capacity of the minerals processing plant has a grade that is above the above-mentioned threshold grade and (b) the remainder of the mined material, which has a lower grade, is transferred to a stockpile, to be processed at a later time when there is increased capacity of the mineral processing plant.

Assessment - selective processing grade measurements

A grade sensor, using Prompt Gamma Neutron Activation Analysis (PGNAA), located on the main conveyor to the surface of the applicant’ s Cadia block cave mine was used to make an assessment of whether grade sensors at this location underground can provide accurate information to facilitate selective processing of mined material.

The PGNAA system, namely a Geoscan system from Scantech, measures copper, sulphur, and a range of gangue elements accurately.

A comparison of the daily plant balanced (OneView) mine actual grade (determined by chemical assays) and the Geoscan measured copper grade was made.

The Geoscan data and the mine actual copper grades showed good agreement, providing confidence that copper grade could be measured with reasonable accuracy via these sensors. The assessment showed that a PGNAA system’s measurement of copper grade could be used as a source of grade information to allow decisions to be made reliably so that material could be selectively processed through a minerals processing plant at the mine, diverted to a stockpile to be processed later, or to a waste stockpile.

The installation and use of a PGNAA system on the main conveyor is an indication that grade sensors measuring grade of material is an option for accurate grade measurement.

The assessment also indicates that PGNAA system sensors located at other locations underground, for example at draw points, can provide accurate grade measurements at these locations to facilitate selective processing decisions to be made.

Assessment - selective processing viability economically

A desk-top analysis was carried out to assess the viability of selective processing in accordance with an embodiment of the invention as a processing option at the applicant’s Cadia block cave mine during a mill motor replacement in the minerals processing plant at the mine, which resulted in a 30-40% loss of capacity of the minerals processing plant at the mine for a period of several months.

The capacity loss meant that the production rate from the mine, which did not change during this period, exceeded the capacity of the minerals processing plant and it was necessary to stockpile 30-40% of the mined material.

Monthly PCBC data by draw points for a 4 months period was used for the analysis.

The analysis considered a reduction in the amount of material that could be processed in the mill circuit of the minerals processing plant and then through the plant as a consequence of the loss of milling capacity due to the mill motor replacement, resulting in a need to stockpile a substantial amount of material during the course of the mill motor replacement and process that material through the minerals processing plant at a later time after the mill motor replacement was completed.

The analysis considered whether selective processing mined material in accordance with an embodiment of the invention could have provided a material increase in economic value produced by the mine in this period compared to the economic value of material processed through the mineral processing plant in the same period in accordance with a standard non-selective processing practice used at the mine, i.e., without considering the grade of material from draw points. The data provided quantification of planned tonnes to be extracted, $/tonne value, gold grade in g/t, and copper grade in % for individual draw points across all active areas of the block caves in the mine. Totals were assessed.

Selective processing in accordance with an embodiment of the invention included ranking draw points by $/tonne value, with material with the lowest $/tonne value being selected for stockpiling and material of higher value being selected as mill feed of the minerals processing plant, via a Coarse Ore Stockpile (COS).

The applicant calculated that there would have been a 25% lift in the gold grade of material processed in the minerals processing plant with selective processing in accordance with an embodiment of the invention relative to the gold grade of material processed through the minerals processing plant that was supplied to the plant via the above-mentioned standard non-selective processing practice in use at the mine.

It was also calculated that material selected to be transferred to the minerals processing plant in accordance with an embodiment of the selective processing invention and then processed through the minerals processing plant had double the economic value of the remainder of the material selected to be stockpiled for processing through the plant later in accordance with an embodiment of the invention, driven primarily by the differential in gold grades.

The lift in gold grade to the minerals processing plant over the course of the time period was calculated to be equivalent to milling a significant additional amount of material in the standard non-selective processing practice during the trial period.

Outcome of selective processing analysis

The projected increase in gold and copper grade to the minerals processing plant, along with the corresponding lift in recovery in the minerals processing plant, was calculated to result in material additional amounts of gold and copper and revenue compared to the standard no-selective processing option.

The assessment found that there would be no tangible increase in operating costs, when compared to the no-selective processing practice.

It follows from the above that the invention is a viable option.

Many modifications may be made to the above-described embodiment of a mine and a mining method without departing from the spirit and scope of the invention. By way of example, whilst the above embodiment is described in the context of the Cadia mine of the applicant, the invention extends generally to block cave mines and the invention also extends to other underground mines.

By way of example, whilst the above embodiment relied on the use of a PGNAA grade sensor, the invention is not confined to this type of grade sensor.