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Session:

Mining 3

Abstract No.:

O-042

Title:

Combined use of lithological and grade simulations for risk analysis in iron ore, Vale-Brazil

Author(s):

D G Roldao, Vale (BR)
D T Ribeiro, Vale (BR)
E Cunha, Vale (BR)
R Noronha, Vale (BR)
A Madsen, Vale (BR)
L Masetti, Vale (BR)

Abstract:

The majority of economic feasibility studies of mineral projects use discrete geologic block models and grade estimation. Those discrete block models do not allow risk analysis of the project. There is a smoothing of grade variability, and lithological dilution in each block is not considered. The uncertainty of geologic block model can be evaluated by geostatistical simulation methods. The main objective of this project is to evaluate the impact of lithological and grade simulation in the economic studies of a world class iron ore deposit. An iron ore deposit from Carajás Province (Brazil) composed of low grade (jaspelite) and high grade ore (hematite) was selected as a case study. The hematite body is 9 km long, 3 km wide, and 300 m deep, with as average grade of 66% iron. The uncertainty of the lithological contacts among hematite and waste/low grade rocks is as important as the ore grade variability. For this study, drillhole database (hard data) and section interpretation (soft data) was used, in order to improve the lithological conditioning. Different geostatistical simulations were combined to generate equiprobable realizations for lithologies (SL) which are derived of superimposed different geological events; supergene and sedimentary/volcanic rocks. Two types of supergene events were simulated; the thickness of canga duricrust (2D TB simulation, SC) and the transition of the weathering zone (3D SIS simulation, SS). The levels of Banded Iron Formation and volcanic rock were simulated generating the primary rock facies (3D SIS simulation, SV), independently of supergene simulations. SL=(SCSV)((SVSS)\SC). The grade variables were simulated in cascade, one grade simulation for each lithology simulation. The results of the simulations were compared with the official reserve calculated with discrete block model in order to measure the risk of the project and the impact of waste dilutions in the quality of the product.