Abstract
In the earth sciences modeling, a great deal of uncertainty is associated with interpretation of subsurface data. Drilling borehole is one of the best tools for subsurface exploration and data gathering. Uncertainty of ore reserve modeling can be reduced by intelligent design of complementary drillings between the primary boreholes. This paper introduces a new method for determination of number, as well as directional and dimensional properties of such additional drillings based on ore value and objective functions, by applying an interval threshold concept. The proposed method is verified in Choghart iron deposit, central Iran. After calculations of descriptive statistical parameters, followed by geostatistical stages such as variography, anisotropy modeling, and kriging estimation of Fe (iron) and P (phosphorus) variables are performed. Thresholds commonly separate data sets into two classes by a sharp boundary and assigning samples to these indicators involve uncertainty. Instead of point threshold, an interval threshold with fuzzy membership function was implemented. Interval threshold is applied to determine indicators by considering Fe and P grades of kriging (soft) outputs. On the basis of one threshold for Fe and two thresholds for P, six classes of combination indicators of Fe and P were generated. Indicator-weighted average (IWA) and class membership degrees (CMD) for each block (sample) were measured by interval thresholds. Fe and P preference functions were defined for modeling of positive, neutral, and negative values (behaviors) in different ranges of grades. Ore value function is defined as a function of CMD, preference degrees, and weight factors for Fe and P grades. Finally, multiplicative equation of the ore value function and kriging variance is computed as objective function. Given large amounts of the objective function, four vertical and a single-directional drilling along with approximate length, priority of locations, azimuth, and dip angles of drillings are the final output of this method.
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