Ore reserves and grade control can be managed dynamically to satisfy both mineral processing and management requirements by shipping a balanced mill feed grade and adjusting mine-planning to economic factors. To attain this goal, mine engineers need to develop and use flexible mining methods to withstand sudden changes of grades, metal prices or recoveries that cause fluctuations of cashflow and profits. To accomplish this, computerized ore reserves have been used extensively at the Mobrun mine, owned 70% by Au drey Resources, and 30% by Minnova Inc. Mobrun is 30 km north of Rouyn-Noranda, Que. Mobrun Mine Discovered in 1956, the Mobrun main deposit is a massive sulphide lens steeply dipping north, near surface, cut by a 1-m-thick dyke parallel to its east-west strike. It averages 240 m in strike length, 200 m in depth and 15 m in thickness.
Production started in an open pit in the last quarter of 1986. Underground operations began in the second half of 1987. Operating costs have fluctuated between $25 and $45 per tonne and the Net Smelter Return (nsr) between $30 and $60 depending on planned stages of mining and development: open pit or underground. Production in 1988 reached 311,538 tonnes at a rate of 1,000 tonnes per day. Today’s reserve stands at 6 million tonnes of 0.71% copper, 3.37% zinc, 5.5 g silver and 2.52 g gold per tonnne plus an extra 3.2 million tonnes at similar grades in probable reserves (class II) from new lenses recently discovered less then 200 m south-east of the actual mine. Metal Zoning
The Mobrun deposit has a high density of 4.5 and well defined internal metal zoning because of its volcanogenic origin. The metal zoning is made of a copper-rich footwall, a zinc- rich hangingwall and fringes, and an intermediate gold-rich pyrite zone. Silver is more or less evenly spread in the orebody. Pyrite accounts for 90% of the mass. The sulphide lenses have very sharp vertical contacts, but the economic ore reserves within them rely on metal zoning. The different metal zones extend into each other. More than one metal may be present in relatively high grade in some places. These metal zones reflect the temperature gradient of hot spring water carrying mineral salts (sulphides) emerging from a vent on the sea floor. These vents formed a massive sulphide mound as the contact with sea water made the temperature drop and forced the sulphides to crystalize. The sulphides are spread around the hydrothermal vent according to their degree of solubility (chalcopyrite greater than pyrite/gold greater than sphalerite) and the environment: topography, sea water current, and so on. The flat tabular body resulting from this was later tilted and put in a vertical position structurally. NSR and Grades
Knowing that some areas were sub- economic, selective mining had to be used. In 1986, it appeared interesting to “keep the door open” in case metal prices increased or metal recoveries at the mill improved. In order to find and modify the ore reserve outline, the NSR was calculated in Canadian dollars for each sample, each block or polygon, each stope and the whole mine. This provided a way to design the stopes and review the mining sequence down to every single blast based on an updated NSR. To keep things straight, it must be understood that the NSR is an economic factor based on grades and smelter contracts, metal prices, metal recovery, and the like. Grades are estimated from samples taken in diamond drill holes and mine workings: face, channel, muck, draw points, and so on.
The quality of the grade estimation is a function of the quality of sampling and of the estimation method used. The NSR used to design the mine is mostly dependent on forecasted metal prices which may be highly speculative. Smelting costs are fixed by contract. That is to say that in an ideal situation where ore-sampling, grade estimation, as well as production costs cannot be improved, the NSR can still fluctuate and make the operation more or less profitable. In a gold mine where there may be only one metal, the process of designing the mine is more straightforward but could also be done using economic factors instead of grades. It is a standard practice in polymetallic mines to convert grades into one metal grade equivalent, let’s say gold or copper. A cut-off grade is then determined for that metal and used for all mine-planning. The problem with this simple method is that once the transformation is done, people tend to forget that the conversion is based on fluctuating metal prices and recoveries and that the dollar is the true common denominator for any grade conversion. It also ignores the cost of smelting and refining and cannot conveniently be compared with operating costs. For example, one stope could have the same grade equivalency in raw metal value (say 4% copper) than another that contains zinc or gold instead of copper and end up with a totally different profit margin because of the difference in smelting cost. The NSR is definitely a better selection tool.
In the case of the Mobrun mine, the relationship between copper and gold is also important. With gold being recovered with copper, there exists a necessity for a minimum copper feed grade at the mill to attain minimal efficiency of gold recovery. For example, if the mill received no copper, gold would not be recovered. Ideally, copper grade should be regular and made as high as possible. Updating the NSR
There was some difficulty for management to accept the use of the NSR for mine-planning. For example, the contours of the NSR value, drawn on sections used for stope design, varied depending on irregular updates of the economic factor used to calculate the NSR. To solve that problem, the NSR on sections is updated once a year, based on the economic factors forecasted by management or as required by consensus. A full set of sensitivity tables with associated graphs are produced with the yearly set of sections to help understand the fluctuation of the NSR based on metal prices, monetary rate of exchange, metal recoveries at the mill, ore grades, grinding (i.e., grade of concentrate), and so on. Another important problem was to determine what production figure was right when the geology department disagreed with the engineering department or the mill.
Management was inclined to distrust the estimates of the geological department in the beginning as the other sources of information (from the mill and engineering) are traditionally more reliable. As it turned out, the ore reserves and grade control procedure were generally very accurate with average errors less than 10% on a quarterly basis. In fact, the ore reserve and grade control system showed that the biggest shortcomings came from the ton management system, which could not be accurate within a 10% margin of error on a monthly basis because of the long- hole/open-stope mining method. It also showed where the production plan failed to be followed. But the credit for this must go to using geostatistics and proper programming tools to manage the mineral inventory rather than using the NSR, which gives the sensation of navigating on a small boat in the middle of a storm when metal prices swing like they did in 1988. Mine Design and Ore Reserves
The technique developed boils down to dynamically modifying the ore reserves based on economic factors. As development in the mine advances, the less flexible it becomes. The limit to using selective mining is this: to blast or not to blast a block of ore that has been fully developed and drilled for production or to leave broken muck in stopes or stock piles. Using the NSR to design the mine requires not only a minimum effort from all mine staff but also, for the sake of efficiency, the use of a computer. This also permits the use of the best ore reserve estimation techniques.
The geology department’s staff at Mobrun was already familiar with the software package of Geostat System International Inc. (gsii). The package provs the option of buying modules for any of the ore reserve estima tion methods, including the commonly used polygonal cross-section method. They also supply all the software tools, support, training and services required to build a complete ore reserve and mine model. The mine currently uses the geostatistic method of estimation for all grade estimations. It has proven very accurate, even more so than estimations from the mill according to the smelter payback on adjusted grades of concentrates.
The NSR calculation is totally independent of which estimation method is used but is more conveniently used with a block model. A simple and easy-to-understand geostatistical model was created for grade estimation. The orebody was subdivided into 15,000 blocks, each measuring 9 m high, 5 m long and 2 m thick and weighing 400 tonnes, which is equivalent to 40% of a day’s production at Mobrun. The size of individual blocks was chosen to match section spacing and bench height in the open pit so that all the massive sulphide lens could fit into one block model. A diamond drilling pattern was set accordingly, to obtain the best grade estimate possible on a 10×10-m-square grid approximately. Grade Control
One very important aspect of all calculating ore reserves is the calculation of tonnages and weighted average grades. The BlkCad or SectCad programs of the GSII package are used to do that part of the work. A common misconception is that these programs are insufficiently powerful or have some other shortcomings. They indeed can be at fault, but it is their misuse that is the principal cause of problems in general. First the grade estimation cannot be better than the sample on which it is based and a proper definition by the mine geologist of how they have to be used by any computer programs. Geological Interpretation
The tonnage of each ore block is accurately calculated based on proper geological interpretation only. Good basic geological work is the key to successfully using these computer packages. One needs to understand what one is doing. Mine management should supervise closely the use of these systems and should not stay under the impression that they do mysterious things. Good old rules of thumb can still be used in most cases to supervise the computer work. It is all too easy for unfamiliar or incompetent staff to blame the computer system. The computer will not defend itself nor complain. On the other hand, it should be understood that inexperienced staff need training and support. Some of today’s micro- computers have more power under their hoods than old mainframes.
A clear distinction must be made between geological and mineable reserves. Geological reserves may be well drilled and defined, while mineable reserves may change with fluctuations in metals prices. Mine-planning is based on the best possible information available, but it has to be reviewed. At Mobrun, the mine geologist worked alone with a single trained technician to handle all the workload, including field work except for the help of an extra technician during underground definition drilling. Apart from working in the open pit and underground, the mine technician was trained to calculate ore reserves and to update and draw all the plans and sections of the mine with the computer.
The system is organized so that every month all the drill logs and samples from all sources are entered into the computer. He also digitizes all mine survey of drifts and raises, mine- planning and blast outlines used as reference for grade control. The geologist may change some basic factors in the model but, generally, does not have to. On a Compact 386/20 micro- computer, the entire ore reserve calculation of the mine and all plans and sections can be updated in 16 hours, overnight, after all new information has been entered in the computer.
It takes only one or two day’s work to complete the month-end update and report. The longest part of the work is to enter the data and do the geological interpretation revisions. That is generaly done using a spreadsheet (Symphony from Lotus) and AutoCad. The way the system works is fast and produces information of high quality. But the sudden change of economic factor may give a hard time to the engineering department. For example, a service raise was developed in waste in 1986 at Mobrun. It is now in ore because of improved economic factors. Another advantage of using the computer in geology has been to double-check the surveyor’s and the engineer’s calculations much more easily and accurately. Mine Planning
Mine planning is still a human task. To computerize it will require expert systems. But it is already possible to customize some of the mine design task by using parametric stope design with an AutoCad system, for example. For flexible mining methods, it appears that vertical crater retreat (VCR) and bulk mining are solutions that reduce the risk by minimizing useless developments. Large-volume operations imply lower cost which, in turn, implies increasing the reserve because of the lower cut-off grade.
The mining industry is on a fast track. It needs to improve its use of new technologies in the office as well as it did with mechanization in the past 20 years. This will change the ratio of capital investment over operating costs in offices and require computer-skilled staff. But there has been a real breakthrough in the smaller mines that previously did not have access to computers. Similar rules to the ones used for the mechanization of mining operations should be applied to office work. For example, it is necessary to train office staff to use computers. Pierre-Jean Lafleur is chief geologist at the Mobrun mine. STEPS TO COMPUTERIZED ORE RESERVE CALCULATIONS
* Find a computer and software package with which you’re comfortable that can draw sections and calculate reserves. It should be simple. The more sophisticated ones can be difficult to learn and they might perform unnecessary tasks. And they usually cost more. On the other hand, the program should be able to run automatically on its own for updates and handle some of the more sophisticated tasks you might want to do in the future. Micro-computer based systems definitely help control costs and are sufficient for the vast majority of mine-site installations. Stick to one supplier for all your needs to avoid compatibility problems. Contract out the work and training you cannot handle in-house. Get a service contract for all your equipment and software.
* Get or make a diamond drill hole computer log program — the simpler the better. All companies and projects may have different formats of logs. Start computerizing the most vital information, for example: hole location, deviation and samples with main geological contacts. Concentrate on elements of economic geology unless the goal of the work is pure exploration.
* Software like DBase III (database), Lotus 1,2,3 (spreadsheet), WordPerfect (word processing) or AutoCad are highly recommended because they are industry standards. All good programs have functions to convert and modify data format. Get familiar with those very important functions and the ones to interchange data. Data computerization is the most time- consuming and important step of any computer modelling. It should not be left in the hands of unqualified or untrained staff without support.
* Do your basic statistical study of sampling results. Find the high- grade sample value cut-off for erratic values if need be; otherwise, these values could cause an overestimation of grades in ore reserves. Check if their is more than one mode of distribution for mineralization from your histogr ams and find out what geological features control each of them and where these features are encountered. Also, control the quality of sample analysis, especially for gold or any mineral substance with low grades measured in parts per million, grams or parts per billion. More important than anything else, check the variances on the grades of the minerals you are studying. The higher the variance, the less accurate should your ore reserve grade estimation be. Good geological interpretation is the most important aspect of ore reserves estimation. Statistics can help you do it and are almost always neglected.
* Both geological interpretation and mine planning compose the geometrical base for ore reserve calculations. There exist computer programs to help build geological models and mine plans, but these tasks still rely a lot on human brainpower. Computer systems generally lack the capacity to look at all the fine details. Expert systems are being developed, but often reality deviates or will deviate from the projected plans these systems or we, humans, can produce. So don’t get lost in details.
* Finally, the definition of an ore reserve calculation can be stated in the following way: using the most appropriate method to combine sampling results and a physical model to estimate the tonnes and grades of an orebody to be mined profitably, given specific economic factors. There exist a variety of methods to calculate reserves: polygons, sections, inverse square distance and kriging. They have all been computerized. Some are more accurate than others. The most powerful method, kriging, offers the best results for grade estimation but needs information of the best quality and skilled people to use it. Any method can be misused and misunderstood.
The biggest shortcoming right use. The biggest shortcoming right now is the lack of trained and skilled people to use it. The technology itself will only get better and cheaper.
Ore reserves and grade control can be managed dynamically to satisfy both mineral processing and management requirements by shipping a balanced mill feed grade and adjusting mine-planning to economic factors. To attain this goal, mine engineers need to develop and use flexible mining methods to withstand sudden changes of grades, metal prices or recoveries that cause fluctuations of cashflow and profits. To accomplish this, computerized ore reserves have been used extensively at the Mobrun mine, owned 70% by Au drey Resources, and 30% by Minnova Inc. Mobrun is 30 km north of Rouyn-Noranda, Que. Mobrun Mine Discovered in 1956, the Mobrun main deposit is a massive sulphide lens steeply dipping north, near surface, cut by a 1-m-thick dyke parallel to its east-west strike. It averages 240 m in strike length, 200 m in depth and 15 m in thickness.
Production started in an open pit in the last quarter of 1986. Underground operations began in the second half of 1987. Operating costs have fluctuated between $25 and $45 per tonne and the Net Smelter Return (nsr) between $30 and $60 depending on planned stages of mining and development: open pit or underground. Production in 1988 reached 311,538 tonnes at a rate of 1,000 tonnes per day. Today’s reserve stands at 6 million tonnes of 0.71% copper, 3.37% zinc, 5.5 g silver and 2.52 g gold per tonnne plus an extra 3.2 million tonnes at similar grades in probable reserves (class II) from new lenses recently discovered less then 200 m south-east of the actual mine. Metal Zoning
The Mobrun deposit has a high density of 4.5 and well defined internal metal zoning because of its volcanogenic origin. The metal zoning is made of a copper-rich footwall, a zinc- rich hangingwall and fringes, and an intermediate gold-rich pyrite zone. Silver is more or less evenly spread in the orebody. Pyrite accounts for 90% of the mass. The sulphide lenses have very sharp vertical contacts, but the economic ore reserves within them rely on metal zoning. The different metal zones extend into each other. More than one metal may be present in relatively high grade in some places. These metal zones reflect the temperature gradient of hot spring water carrying mineral salts (sulphides) emerging from a vent on the sea floor. These vents formed a massive sulphide mound as the contact with sea water made the temperature drop and forced the sulphides to crystalize. The sulphides are spread around the hydrothermal vent according to their degree of solubility (chalcopyrite greater than pyrite/gold greater than sphalerite) and the environment: topography, sea water current, and so on. The flat tabular body resulting from this was later tilted and put in a vertical position structurally. NSR and Grades
Knowing that some areas were sub- economic, selective mining had to be used. In 1986, it appeared interesting to “keep the door open” in case metal prices increased or metal recoveries at the mill improved. In order to find and modify the ore reserve outline, the NSR was calculated in Canadian dollars for each sample, each block or polygon, each stope and the whole mine. This provided a way to design the stopes and review the mining sequence down to every single blast based on an updated NSR. To keep things straight, it must be understood that the NSR is an economic factor based on grades and smelter contracts, metal prices, metal recovery, and the like. Grades are estimated from samples taken in diamond drill holes and mine workings: face, channel, muck, draw points, and so on.
The quality of the grade estimation is a function of the quality of sampling and of the estimation method used. The NSR used to design the mine is mostly dependent on forecasted metal prices which may be highly speculative. Smelting costs are fixed by contract. That is to say that in an ideal situation where ore-sampling, grade estimation, as well as production costs cannot be improved, the NSR can still fluctuate and make the operation more or less profitable. In a gold mine where there may be only one metal, the process of designing the mine is more straightforward but could also be done using economic factors instead of grades. It is a standard practice in polymetallic mines to convert grades into one metal grade equivalent, let’s say gold or copper. A cut-off grade is then determined for that metal and used for all mine-planning. The problem with this simple method is that once the transformation is done, people tend to forget that the conversion is based on fluctuating metal prices and recoveries and that the dollar is the true common denominator for any grade conversion. It also ignores the cost of smelting and refining and cannot conveniently be compared with operating costs. For example, one stope could have the same grade equivalency in raw metal value (say 4% copper) than another that contains zinc or gold instead of copper and end up with a totally different profit margin because of the difference in smelting cost. The NSR is definitely a better selection tool.
In the case of the Mobrun mine, the relationship between copper and gold is also important. With gold being recovered with copper, there exists a necessity for a minimum copper feed grade at the mill to attain minimal efficiency of gold recovery. For example, if the mill received no copper, gold would not be recovered. Ideally, copper grade should be regular and made as high as possible. Updating the NSR
There was some difficulty for management to accept the use of the NSR for mine-planning. For example, the contours of the NSR value, drawn on sections used for stope design, varied depending on irregular updates of the economic factor used to calculate the NSR. To solve that problem, the NSR on sections is updated once a year, based on the economic factors forecasted by management or as required by consensus. A full set of sensitivity tables with associated graphs are produced with the yearly set of sections to help understand the fluctuation of the NSR based on metal prices, monetary rate of exchange, metal recoveries at the mill, ore grades, grinding (i.e., grade of concentrate), and so on. Another important problem was to determine what production figure was right when the geology department disagreed with the engineering department or the mill.
Management was inclined to distrust the estimates of the geological department in the beginning as the other sources of information (from the mill and engineering) are traditionally more reliable. As it turned out, the ore reserves and grade control procedure were generally very accurate with average errors less than 10% on a quarterly basis. In fact, the ore reserve and grade control system showed that the biggest shortcomings came from the ton management system, which could not be accurate within a 10% margin of error on a monthly basis because of the long- hole/open-stope mining method. It also showed where the production plan failed to be followed. But the credit for this must go to using geostatistics and proper programming tools to manage the mineral inventory rather than using the NSR, which gives the sensation of navigating on a small boat in the middle of a storm when metal prices swing like they did in 1988. Mine Design and Ore Reserves
The technique developed boils down to dynamically modifying the ore reserves based on economic factors. As development in the mine advances, the less flexible it becomes. The limit to using selective mining is this: to blast or not to blast a block of ore that has been fully developed and drilled for production or to leave broken muck in stopes or stock piles. Using the NSR to design the mine requires not only a minimum effort from all mine staff but also, for the sake of efficiency, the use of a computer. This also permits the use of the best ore reserve estimation techniques.
The geology department’s staff at Mobrun was already familiar with the software package of Geostat System International Inc. (gsii). The package provs the option of buying modules for any of the ore reserve estima tion methods, including the commonly used polygonal cross-section method. They also supply all the software tools, support, training and services required to build a complete ore reserve and mine model. The mine currently uses the geostatistic method of estimation for all grade estimations. It has proven very accurate, even more so than estimations from the mill according to the smelter payback on adjusted grades of concentrates.
The NSR calculation is totally independent of which estimation method is used but is more conveniently used with a block model. A simple and easy-to-understand geostatistical model was created for grade estimation. The orebody was subdivided into 15,000 blocks, each measuring 9 m high, 5 m long and 2 m thick and weighing 400 tonnes, which is equivalent to 40% of a day’s production at Mobrun. The size of individual blocks was chosen to match section spacing and bench height in the open pit so that all the massive sulphide lens could fit into one block model. A diamond drilling pattern was set accordingly, to obtain the best grade estimate possible on a 10×10-m-square grid approximately. Grade Control
One very important aspect of all calculating ore reserves is the calculation of tonnages and weighted average grades. The BlkCad or SectCad programs of the GSII package are used to do that part of the work. A common misconception is that these programs are insufficiently powerful or have some other shortcomings. They indeed can be at fault, but it is their misuse that is the principal cause of problems in general. First the grade estimation cannot be better than the sample on which it is based and a proper definition by the mine geologist of how they have to be used by any computer programs. Geological Interpretation
The tonnage of each ore block is accurately calculated based on proper geological interpretation only. Good basic geological work is the key to successfully using these computer packages. One needs to understand what one is doing. Mine management should supervise closely the use of these systems and should not stay under the impression that they do mysterious things. Good old rules of thumb can still be used in most cases to supervise the computer work. It is all too easy for unfamiliar or incompetent staff to blame the computer system. The computer will not defend itself nor complain. On the other hand, it should be understood that inexperienced staff need training and support. Some of today’s micro- computers have more power under their hoods than old mainframes.
A clear distinction must be made between geological and mineable reserves. Geological reserves may be well drilled and defined, while mineable reserves may change with fluctuations in metals prices. Mine-planning is based on the best possible information available, but it has to be reviewed. At Mobrun, the mine geologist worked alone with a single trained technician to handle all the workload, including field work except for the help of an extra technician during underground definition drilling. Apart from working in the open pit and underground, the mine technician was trained to calculate ore reserves and to update and draw all the plans and sections of the mine with the computer.
The system is organized so that every month all the drill logs and samples from all sources are entered into the computer. He also digitizes all mine survey of drifts and raises, mine- planning and blast outlines used as reference for grade control. The geologist may change some basic factors in the model but, generally, does not have to. On a Compact 386/20 micro- computer, the entire ore reserve calculation of the mine and all plans and sections can be updated in 16 hours, overnight, after all new information has been entered in the computer.
It takes only one or two day’s work to complete the month-end update and report. The longest part of the work is to enter the data and do the geological interpretation revisions. That is generaly done using a spreadsheet (Symphony from Lotus) and AutoCad. The way the system works is fast and produces information of high quality. But the sudden change of economic factor may give a hard time to the engineering department. For example, a service raise was developed in waste in 1986 at Mobrun. It is now in ore because of improved economic factors. Another advantage of using the computer in geology has been to double-check the surveyor’s and the engineer’s calculations much more easily and accurately. Mine Planning
Mine planning is still a human task. To computerize it will require expert systems. But it is already possible to customize some of the mine design task by using parametric stope design with an AutoCad system, for example. For flexible mining methods, it appears that vertical crater retreat (VCR) and bulk mining are solutions that reduce the risk by minimizing useless developments. Large-volume operations imply lower cost which, in turn, implies increasing the reserve because of the lower cut-off grade.
The mining industry is on a fast track. It needs to improve its use of new technologies in the office as well as it did with mechanization in the past 20 years. This will change the ratio of capital investment over operating costs in offices and require computer-skilled staff. But there has been a real breakthrough in the smaller mines that previously did not have access to computers. Similar rules to the ones used for the mechanization of mining operations should be applied to office work. For example, it is necessary to train office staff to use computers. Pierre-Jean Lafleur is chief geologist at the Mobrun mine. STEPS TO COMPUTERIZED ORE RESERVE CALCULATIONS
* Find a computer and software package with which you’re comfortable that can draw sections and calculate reserves. It should be simple. The more sophisticated ones can be difficult to learn and they might perform unnecessary tasks. And they usually cost more. On the other hand, the program should be able to run automatically on its own for updates and handle some of the more sophisticated tasks you might want to do in the future. Micro-computer based systems definitely help control costs and are sufficient for the vast majority of mine-site installations. Stick to one supplier for all your needs to avoid compatibility problems. Contract out the work and training you cannot handle in-house. Get a service contract for all your equipment and software.
* Get or make a diamond drill hole computer log program — the simpler the better. All companies and projects may have different formats of logs. Start computerizing the most vital information, for example: hole location, deviation and samples with main geological contacts. Concentrate on elements of economic geology unless the goal of the work is pure exploration.
* Software like DBase III (database), Lotus 1,2,3 (spreadsheet), WordPerfect (word processing) or AutoCad are highly recommended because they are industry standards. All good programs have functions to convert and modify data format. Get familiar with those very important functions and the ones to interchange data. Data computerization is the most time- consuming and important step of any computer modelling. It should not be left in the hands of unqualified or untrained staff without support.
* Do your basic statistical study of sampling results. Find the high- grade sample value cut-off for erratic values if need be; otherwise, these values could cause an overestimation of grades in ore reserves. Check if their is more than one mode of distribution for mineralization from your histogr ams and find out what geological features control each of them and where these features are encountered. Also, control the quality of sample analysis, especially for gold or any mineral substance with low grades measured in parts per million, grams or parts per billion. More important than anything else, check the variances on the grades of the minerals you are studying. The higher the variance, the less accurate should your ore reserve grade estimation be. Good geological interpretation is the most important aspect of ore reserves estimation. Statistics can help you do it and are almost always neglected.
* Both geological interpretation and mine planning compose the geometrical base for ore reserve calculations. There exist computer programs to help build geological models and mine plans, but these tasks still rely a lot on human brainpower. Computer systems generally lack the capacity to look at all the fine details. Expert systems are being developed, but often reality deviates or will deviate from the projected plans these systems or we, humans, can produce. So don’t get lost in details.
* Finally, the definition of an ore reserve calculation can be stated in the following way: using the most appropriate method to combine sampling results and a physical model to estimate the tonnes and grades of an orebody to be mined profitably, given specific economic factors. There exist a variety of methods to calculate reserves: polygons, sections, inverse square distance and kriging. They have all been computerized. Some are more accurate than others. The most powerful method, kriging, offers the best results for grade estimation but needs information of the best quality and skilled people to use it. Any method can be misused and misunderstood.
The biggest shortcoming right use. The biggest shortcoming right now is the lack of trained and skilled people to use it. The technology itself will only get better and cheaper.
Be the first to comment on "STATISTICAL GEOLOGY (November 01, 1988)"