عنوان مقاله [English]
In this study the optimized size for block modeling and the role of block size in reserve estimation were investigated. For this purpose, the deposits with different genesis were considered as case studies in order to investigate the effect of different variability in block size optimization. For this plan, the data of Surk iron ore and Esfordi phosphate deposits were used. The database was built using borehole data and the composite samples were prepared with length of 2 m. The data was converted to normal distribution using normal score transformation. Variography was used for investigate ore continuity and variability and the suitable variograms and anisotropy ellipsoids were obtained. Totally 256 block models were made for Surk and Esfordi deposits and the kriging efficiency was calculated in different block size. Due to proposed large block sizes in comparison to operational models and their incoherency to real anisotropy ratios, the method was ignored. In the next approach, the Gaussian Conditional Simulation method was used for different block size investigation. In each simulation, 20 realizations were produced and the variance between realizations was calculated. The less variance is the more similarity of realizations, which is the criterion for choosing the optimal block sizes. By this method the block dimension of 7.5*7.5*7.5 and 10*7.5*10 were calculated for Surk and for Esfordi deposits, respectively. The calculated block sizes were in good agreement with operational conditions and the anisotropy ratios. Therefore the obtained block sizes were used in reserve estimation of the deposits. The estimated reserves were 9.84 Mt for Surk in cut off grade 20% of iron and 11.93 Mt for Esfordi deposit on the basis of 5% cut off grade of phosphorus.