Characterization of Metal Grades in a Stockpile of an Iron Mine (Case Study- Choghart Iron Mine, Iran)

In any mining operation due to the cut-o grade (economic criteria), materials are classi ed into ore and waste. The material with grade equal to or higher than the cut-o grade is considered as ore and the material with grade less than the cut-o grade is transported as waste to waste dumps. However, because of an increasing metal demand, depletion of in situ ore reserves is occurring and so there is a reduction of cut-o grades for many metals, and the mentioned waste dumps are considered as valuable ore reserves named stockpiles. In this paper, multivariate geostatistics was used to estimate the iron grades of two stockpiles following the sequential piling procedures from the main source -the ore deposit -to the piling eld. One stockpile is characterized by phosphorous concentration ((P %) > 0.6 %), while the other by iron concentration ((Fe %)< 50%). Since economic and physical constraints made sampling physically and economically problematic, the grade distribution and variability were estimated on the basis of primary blast-hole data from the main ore body and the mine's long-term planning policy. A geostatistical model was applied to the excavated part of the iron deposit and by reconstructing ore selection, the haulage and the piling method. Results were validated through spatial variability of iron and phosphorous concentrations by comparing grade variability (Fe and P) with mining and piling units. A comparison of the grade variability has shown that with the same variogram models (with a larger range and smaller variance), the spatial variability of stockpiles have followed the variability of the selected part of the ore body. This point can be used to predict the grade variability of stockpiles from the origin source and the methodology allows characterizing the iron grades within stockpiles without any extra sampling.