Mineral processing efficiency depends on various factors and one of them is quality fluctuations feeding the processing plant. Coal quality can fluctuate beyond an admissible range, implying recovery decrease for the mineral of interest Grades feeding the processing plant depend on the geological domain which is mined and on the mining schedule. Therefore, it is necessary to keep quality variability under control. Blending piles is an efficient alternative to reduce quality fluctuations. The main factors influencing blending efficiency are the pile size or its mass, and the number of layers used to pile up. Large piles are more efficient to reduce variability; however, there are economical and operational limits associated with them. This study investigates a methodology to analyze the ideal pile size to reach an acceptable variability given the in situ quality fluctuations. Geostatistical simulations provide the means to assess quality variability using an optimized mining schedule. Block quality values are used to simulate any given pile throughout the mine life. The methodology was illustrated using a case study to control coal ash content at a mine supplying ROM coal to a power plant. (C) 2010 Published by Elsevier B.V.