A probabilistic approach to the value chain of underground iron ore mining: From deposit to product
MetadataShow full item record
Mining activities will eventually deplete any deposit. In a sustainability perspective, the deposit should therefore be utilised optimally during production. A prerequisite to achieve this is the deliberate and consistent utilisation of the variations in the deposit. In an ideal world everything is certain. In the real world nothing is certain. In the real world everything is more or less probable. Therefore, the question asked is how an underground iron ore mining company like Rana Gruber AS can benefit from knowing and exploiting the uncertainty and variability of decisive ore parameters. The perspective is the value chain from in-situ ore to product, whereas the focus is on deposit characterisation and production. In order to answer this question the existing database with geodata from the Kvannevann Iron Ore is reviewed and estimation techniques based on kriging and geostatistical simulation algorithms (Turning Band) are implemented to identify and assess the ore deposit uncertainties and variations and associated risks. Emphasise is on total iron in the ore (FeTot), total iron in the ore originating from magnetite (FeMagn), manganese oxide (MnO) and joint parameters. Due to insufficient number of assays of MnO, a geochemical MnO-signature is developed using cluster analysis. This geochemical signature is applied as input in the kriging with inequalities procedure. This procedure is based on soft data (lithologies) and a conditional expectation of the MnO level in the different lithologies. A cut-off based on both hematite and magnetite is estimated. A process analysis is performed to visualise the working processes, related inputs, outputs and controlling-, supporting- and risk elements. The process analysis is based on the IDEF process modelling methodology. Given the identified deposit uncertainties and variations, systems to evaluate potential mining stope performance are developed and implemented for one of the mining stopes. To test the possibility to decrease the ore-related uncertainty, a method for collection of drill cuttings has been developed and tested. The correlation between magnetic susceptibility and FeMagn and the correlation between ore density and FeTot are both investigated. The results show that an illustrative and useful overview can be won by using the IDEF-based process modelling methodology. A non-linear relationship between density and FeTot is established and it is shown that the density can be used as a FeTot indicator. This relationship is also used in the reserve and resource estimation. As expected a positive correlation between FeMagn and magnetic susceptibility measured on cores could be established. However, the deviation from other reported relationships is considerable. The importance of magnetite is emphasised and quantified by the cut-off estimation. The cluster analysis reveals that the MnO levels in the different lithologies are significantly different. This result is implemented into the kriging with inequalities procedure and immediate effects can be observed. The development of the geodata collector and the collection of drill cuttings show that it is possible to obtain precise analysis of collected drill cutting material. Although high- and low assay values have been correlated with geological observation in the mine, the accuracy has been difficult to assess. The estimation and the simulation of the ore properties illustrate and quantify the uncertainties and variations in the ore deposit well. The structural analysis performed prior to the estimation and the simulation reveals anisotropies for all ore decisive parameters. The quantification of ore variations provides a useful input into the a-priori assessment of stope performance. It is also shown that the probability that a SMU is above or below some cut-off value can be assessed using the simulation results and the systems developed in standard software. It is concluded that the process analysis approach offers valuable input to gain an overview of the mining value chain. It is also an approach that constitutes an important step in the identification and assessment of IT-requirements, bottlenecks, input- and output requirements and role- and skill requirements along the value chain. However, the process analysis approach requires sufficient organisational resources, which also is the case regarding the implementation of the grade- and stability issues that are presented. Further it is concluded that the ore variations can be utilised to some extent by using standard software. The ore in question is a Neoproterozoic (600 to 700 Ma) metasedimentary magnetite-hematite ore deposited under shallow marine conditions. Primary precipitate was probably ferric hydroxide. Applied methods have been chosen to handle the uncertainty along the value chain of Rana Gruber AS. Every aspect of these methods may therefore not be directly applicable to other mining operations. However, the general aspects have a broad area of use.