A Practical Application of Inverse Distance Weighting Method to Identify Cobalt Anomaly Distribution in Laterite Deposit (Case study in Block R, Wasile Subdistrict, East Halmahera)

Selection of a suitable interpolation method for predicting ore grade at un-sampled location is a key factor to map the anomaly distribution and resources estimation. Objective of this study is to apply and to assess the performance of the inverse distance weighting (IDW) with manipulating exponent of one to five to identify cobalt grade distribution and potential resources in laterite deposit. In this study the ArcGIS 10.2 with Geostatistical Analyst Extensions was used in exploratory data analysis. To choose the value of power with the best performance were used statistic parameter of the root mean square error (RMSE) value which was obtained from cross-validation procedure. The method with the smallest RMSE value was chosen as the best performance. Result reveal that IDW power of 1 performed best for cobalt grade while IDW power of 2 procedures gave the best result when applied to limonite thickness. Cobalt distribution with grade separation of 0.1% reveal that the areas with cobalt grade > 0.1%, as an anomaly area, distributed to the north and narrowed in the southern part of the study area. Resource estimation indicated 15,956,776 ton of limonite ore with average grade of 0.12% Co or equivalent to 16,576.53 ton of Cobalt.