1. Ahmad, W. (2001). Chemistry, mineralogy and formation of Ni laterites (pp. 41–54). Sorowako: PT. INCO Indonesia.
2. Brand, N. W., Butt, C. R. M., & Elias, M. (1998). Nickel laterites: Classification and features. Australian Geology and Geophysics, 17(4), 83–88.
3. Darijanto, T. (1999). The influence of morphology to the formation and distribution of laterite nickel deposits. In Proceedings of 8th Indonesian association of mining experts (pp. 1–18). Bandung, Indonesia.
4. Dowd, P. A. (1992). Geostatistical ore reserves estimation: A case study in a disseminated nickel deposit. Geological Society of London Special Publications, 63, 243–255.
5. Emery, X. (2006). Two ordinary kriging approaches to predicting block grade distributions. Mathematical Geology, 38(7), 801–819.