Diego Machado Marques

The effect of accumulation in 2D estimates in phosphatic ore

The geological modeling of stratiform deposits can become very complex, often making use of geological envelopes of small thickness and requiring the use of subblocks (based on Cartesian coordinates) to produce a coherent block model. However, geological events after the formation of the deposit (folds, faults, etc.) can change the direction of spatial continuity of certain attributes, with the mixing of samples belonging to different formation eras (in the case of stratiform deposits) in the same elevation. This study presents a solution for deposits with stratigraphic grades combined with samples of different origins. The solution is a two-dimensional estimate obtained by accumulating the thicknesses of P 2 O 5 in a phosphate deposit (as compared to traditional statistical analysis in three dimensions).

A comprovação da relação volume x variância na homogeneização da sílica em minério de ferro

Combinacoes de minerio provenientes de diferentes frentes de lavra e pilhas de homogeneizacao sao, comumente, empregadas para reduzir a variabilidade dos teores nas plantas de beneficiamento. A metodologia proposta, nesse trabalho, visa a quantificar a variabilidade das diversas etapas em um sistema de homogeneizacao. O parâmetro quimico avaliado e silica (SiO2) de minerio de ferro, na faixa granulometrica inferior a 0,15 mm. Este e um contaminante erratico, nesse tipo de deposito. Os resultados mostram a variância esperada para os diversos tamanhos de pilhas. Fica demonstrado que a variância, reduz com o aumento da massa da pilha.

Aperfeiçoamento da estratégia de homogeneização em pilhas chevron utilizando simulação geoestatística

Blending and homogenization piles are usually employed for reducing grade fluctuation from the ore feeding a processing plant. These piles are characterized by their form, size (length and height), construction lay-out and number of layers. Various methods are found for blending piles design and most fail to incorporate the in situ grade variability intrinsic of a mineral deposit. The methodology suggested in this study is able to quantify the variability of the homogenization system using multiple equally probable realizations derived from a geostatistical simulation for the grade block model. The variable tested was silica (SiO 2 ) in a grannulometry below 0,15mm (SI3), an erratic contaminant in iron deposits. The results demonstrated a reduction exceeding 90% in the original variability (in situ compared to grades feeding the processing plant) of the system in favorable conditions. Finally, the reduction in the uncertainty in the head grades feeding the processing plant, leads to cost savings and lower economical risks.

Reconciliação dos resultados do planejamento de pilhas de homogeneização auxiliada por simulação geoestatística dos teores de minério

Mineral processing in order to ensure high ore recovery at the final product depends on many factors, among them, the low variability in the head grades feeding the plant. For this, homogenization piles have been an effective tool for significantly diminishing variability. This study tests the efficiency of geostatistical simulations to predict in situ grade variability and how this variability is transposed to the ore, forming blending piles. Traditionally, the methods used in designing these systems are not capable of properly incorporating the uncertainty associated with the estimated value. Ordinary kriging, for example, results in best local estimates, but with a smooth global variance. Conversely, geostatistical simulations provide equiprobable scenarios for the grades of a given deposit. These scenarios honor the sample values, their histogram and spatial distribution. They also provide a set of possible values for each block which forms each homogenization pile. Finally, it is possible to predict the in situ grade variability, given the real grades. The results were compared against the real (reference) mined grades through reconciliation. Results demonstrated that the methodology is accurate and precise enough to be applied in blending piles design.

Plurigaussian Simulations Used to Analyze the Uncertainty in Resources Estimation from a Lateritic Nickel Deposit

Mining industry increasingly uses simulations to predict fluctuations in ore grades. However, in some cases grade fluctuations analysis is not enough for risk assessment, as in some cases ore recovery at the processing plant depends on the rock type rather than the grades. Lateritic nickel weathering profiles are highly complex in its composition. The dataset used in this study is divided into five geological domains, which present in many locations changes in the sequence or lenses of different material trapped inside a major geological domain. It is common the absence of certain domains at some borehole intercepts. The use of a deterministic or interpreted model for defining the orebody contacts in this dataset is unsatisfactory. Instead to use deterministic models to define this orebody, based only in the interpretation of the drill holes (which does not take into account the uncertainty of lithological domains in areas with no information), this paper presents plurigaussian simulation as an alternative to generate equally probable scenarios from the orebody. Combining these realizations it is possible to map the uncertainty in the volumes and contacts. The simulation results showed good reproduction of the conditioning data, both laterally and vertically. Thus, the result of each simulation is also a possible geological model, presenting the spatial variability of the phenomenon, without the smoothing shown by other techniques. One advantage in using plurigaussian simulation for lateritic nickel profiles is the reduction of working time in a very complex geological model, using the simulations to mimic the reality and producing a set of different equally probable scenarios allowing to access the uncertainty in defining the geological domains.

The Use of Geostatistical Simulation to Optimize the Homogenization and Blending Strategies

Homogenization piles are largely used in the mining industry for variability reduction in the head grades feeding the processing plants. Various methods are found for homogenization piles design and most fail to incorporate the in situ grade variability intrinsic of a mineral deposit. The methodology proposed combines longitudinal piles and geostatistical simulation to emulate the in situ and the pile reclaimed grade variability. Variability reduction in large piles is based on the volume-variance relationship, i.e. the larger is the support the smaller is the variability. Based on a pre-defined mining sequence to select the blocks that will form each pile for each simulated block model, the statistical fluctuation of the grades derived from real piles can be simulated. These piles are characterized by their form, size (length and height) and number of layers. Using this methodology, one can evaluate within a certain time period the expected grade variability for various pile size and also the internal grade variability when a given pile is reclaimed. Results from a case study at two large iron mines operated by Vale proved the adequacy and functionality of the method. It is demonstrated the rate of variability decrease as the pile size increases and the internal grade variability to a given pile size, with different numbers of layers.