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Only small errors in the inputs are required to cause a large portion of an ore reserves estimate to have negative value, due to the preponderance of marginal-value material in many ore reserves estimates that rely on the use of a break-even cut-off grade. In some cases, rounding errors alone can result in a significant percentage of an ore reserve having negative value. An ore reserves estimate containing negative-value tonnages can still legitimately be called an ore reserve under the definition of the JORC Code (2012) if it is still economic as a whole, but negatively geared ore reserves will put a company at greater financial risk should commodity prices fall. The most common errors leading to negatively geared ore reserves include the assumption of a fixed processing recovery down to an inappropriate low grade, ignoring real laboratory or operational data, using median or modal values rather than mean values for parameters informing the analysis of the cut-off grade, cost errors, cost omissions, such as ignoring sustaining capital, and deliberate aggressiveness by companies to increase the ore reserve size without new discoveries. The ore reserves estimate should ideally be based on a cut-off grade that maximises the value objective of an organisation, such as net present value, but if a break-even cut-off grade must be used, it is essential that the cut-off grade calculation is undertaken using the best available data, preferably based on actual operation or suitably modified laboratory data, and a full set of cost data, including all contributory costs., Only small errors in the inputs are required to cause a large portion of an ore reserves estimate to have negative value, due to the preponderance of marginal-value material in many ore reserves estimates that rely on the use of a break-even cut-off grade. In some cases, rounding errors alone can result in a significant percentage of an ore reserve having negative value. An ore reserves estimate containing negative-value tonnages can still legitimately be called an ore reserve under the definition of the JORC Code (2012) if it is still economic as a whole, but negatively geared ore reserves will put a company at greater financial risk should commodity prices fall. The most common errors leading to negatively geared ore reserves include the assumption of a fixed processing recovery down to an inappropriate low grade, ignoring real laboratory or operational data, using median or modal values rather than mean values for parameters informing the analysis of the cut-off grade, cost errors, cost omissions, such as ignoring sustaining capital, and deliberate aggressiveness by companies to increase the ore reserve size without new discoveries. The ore reserves estimate should ideally be based on a cut-off grade that maximises the value objective of an organisation, such as net present value, but if a break-even cut-off grade must be used, it is essential that the cut-off grade calculation is undertaken using the best available data, preferably based on actual operation or suitably modified laboratory data, and a full set of cost data, including all contributory costs.

A review of life-of-asset work at the Rosebery Zn-Pb-Cu-Ag-Au mine in Tasmania included a proposal to increase production from 800 000 to 1 200 000 tpa, and questions were raised concerning whether the proposal would actually add value, the sustainability of the production rate and whether it was the best identifiable value-adding configuration. A multiple scenario analysis study using the hill of value approach was conducted to model how various cut-off grade values against mill throughput and associated capital expenditure would affect the potential value of the operation. The use of net smelter return for the whole mine analysis was considered to potentially introduce a large amount of variability to the model as the ore types were thought to have different processing costs and the underground lenses different mining costs. An alternative constant cut-off value measure, mine variable value, was suggested for all ore block values irrespective of lens location. This allowed for the variable factors associated with final metal concentrate production to be removed from the ore value, including the haulage distance from ore source to run-of-mine, the amount of reagents required in the mill and the power required for crushing, grinding and tailings handling. Preliminary results indicated that increased values would be gained by increasing cut-off grade or increasing mill throughput rate. The validity of the result was tested using alternative price scenarios, which did not significantly change the value-adding strategies. Realisation of the value increases depends on achieving higher sustainable development and backfilling rates and overcoming recognised ventilation constraints., A review of life-of-asset work at the Rosebery Zn-Pb-Cu-Ag-Au mine in Tasmania included a proposal to increase production from 800 000 to 1 200 000 tpa, and questions were raised concerning whether the proposal would actually add value, the sustainability of the production rate and whether it was the best identifiable value-adding configuration. A multiple scenario analysis study using the hill of value approach was conducted to model how various cut-off grade values against mill throughput and associated capital expenditure would affect the potential value of the operation. The use of net smelter return for the whole mine analysis was considered to potentially introduce a large amount of variability to the model as the ore types were thought to have different processing costs and the underground lenses different mining costs. An alternative constant cut-off value measure, mine variable value, was suggested for all ore block values irrespective of lens location. This allowed for the variable factors associated with final metal concentrate production to be removed from the ore value, including the haulage distance from ore source to run-of-mine, the amount of reagents required in the mill and the power required for crushing, grinding and tailings handling. Preliminary results indicated that increased values would be gained by increasing cut-off grade or increasing mill throughput rate. The validity of the result was tested using alternative price scenarios, which did not significantly change the value-adding strategies. Realisation of the value increases depends on achieving higher sustainable development and backfilling rates and overcoming recognised ventilation constraints.

Detailed examination of waste blasting practices at Sons of Gwalia showed that excessive front row burdens can cause poor fragmentation, excessive breakback (uneven faces), tight digging, toe, uneven floor and higher ground vibration. A relatively simple field technique is presented for ensuring correct front row burdens., Detailed examination of waste blasting practices at Sons of Gwalia showed that excessive front row burdens can cause poor fragmentation, excessive breakback (uneven faces), tight digging, toe, uneven floor and higher ground vibration. A relatively simple field technique is presented for ensuring correct front row burdens.

SIROFRAG is a computer-based imaging system, developed by CSIRO, ICI Explosives and BHP Australia Coal, that quantifies the post-blast rock fragment size distribution in a muckpile in a mine environment. It is based on active stereo image analysis and uses a light stripe to illuminate a muckpile and a pair of video cameras to determine the 3D nature of the scanned objects. The imaging system is based on a novel prototype scanning projector that allows images to be captured in full daylight. Microsoft Windows software controls the projector and interprets the captured images to provide a size distribution of exposed rock fragments., SIROFRAG is a computer-based imaging system, developed by CSIRO, ICI Explosives and BHP Australia Coal, that quantifies the post-blast rock fragment size distribution in a muckpile in a mine environment. It is based on active stereo image analysis and uses a light stripe to illuminate a muckpile and a pair of video cameras to determine the 3D nature of the scanned objects. The imaging system is based on a novel prototype scanning projector that allows images to be captured in full daylight. Microsoft Windows software controls the projector and interprets the captured images to provide a size distribution of exposed rock fragments.

The underground copper mine, opened in 2000, was developed beneath existing operations in Queensland at a cost of Aus, The underground copper mine, opened in 2000, was developed beneath existing operations in Queensland at a cost of Aus

This paper discusses the effects on mine production rate of changing the number of stopes by altering the cut-off grade or the stope size. It suggests situations in which it may be beneficial to decrease the size of the stope, despite the resulting increase in operating cost per tonne and decrease in average production rate per stope. For the orebody investigated, the eight-year sustainable steady-state production rate can be increased by 20% if stope size is reduced from a 40 x 40 m to 34 x 34 m plan., This paper discusses the effects on mine production rate of changing the number of stopes by altering the cut-off grade or the stope size. It suggests situations in which it may be beneficial to decrease the size of the stope, despite the resulting increase in operating cost per tonne and decrease in average production rate per stope. For the orebody investigated, the eight-year sustainable steady-state production rate can be increased by 20% if stope size is reduced from a 40 x 40 m to 34 x 34 m plan.

This article argues that the way the base and precious metals mining industry uses break-even grades is not consistent with the stated objectives of the mining company, and therefore if not plainly wrong, is at least deeply flawed and subject to so many soures of error that value is almost guaranteed to be destroyed. It is a major contributor to the underlying problems with the financial returns of the mining industry. The case study in this article shows that an error of just 0.1 g/t in the break-even cutoff grade of a large-scale open pit gold mine can result in 50-60% of the ore reserve having zero value. It is more common than not that mines have ore reserves with this scale of error. While the current process commonly used to estimate an ore reserve is deeply flawed, the resulting declared ore reserve is not necessarily invalid. The JORC code only requires that the ore reserve is shown to be 'economically mineable' and does not say anything about having to exclude substantial amounts that are negative in value. It is implied in the JORC code that the ore reserves quoted are what will be mined and processed by the mining company., This article argues that the way the base and precious metals mining industry uses break-even grades is not consistent with the stated objectives of the mining company, and therefore if not plainly wrong, is at least deeply flawed and subject to so many soures of error that value is almost guaranteed to be destroyed. It is a major contributor to the underlying problems with the financial returns of the mining industry. The case study in this article shows that an error of just 0.1 g/t in the break-even cutoff grade of a large-scale open pit gold mine can result in 50-60% of the ore reserve having zero value. It is more common than not that mines have ore reserves with this scale of error. While the current process commonly used to estimate an ore reserve is deeply flawed, the resulting declared ore reserve is not necessarily invalid. The JORC code only requires that the ore reserve is shown to be 'economically mineable' and does not say anything about having to exclude substantial amounts that are negative in value. It is implied in the JORC code that the ore reserves quoted are what will be mined and processed by the mining company.