Circuit of one processing plant was studied in order to adjust the mass balance. The granulometric composition of the streams that belong to grinding and classifying processes was analyzed, while the chemical content was determined only at the streams related to separation process. Three connection matrixes are considered in this paper, one corresponding to the size fraction equations, the second corresponding to the chemical content measurements and the third, the solid flow rate balance. The technique used consisted of filtering all the data by a weighted least-squares procedure. Then running the output data in a custom designed feature of the computer program MATLAB. The raw data was then corrected and the different missing assays calculated and presented here.