Comparison of Ordinary Kriging and Multiple Indicator Kriging Estimates of Asuadai Deposit at Adansi Gold Ghana Limited

Abstract

Adansi Gold Ghana Ltd has taken over from the then Resolute Amansie Ltd and has three main historical deposits: Nkran, Adubia, Abore, and a new deposit, Asuadai. The company now wants to evaluate the resources at Asuadai which is about 7.5 km from Nkran deposit where Ordinary Kriging (OK) method had been used for estimation. Results of the estimation showed a consistent underestimation of tonnage and grade. Linear estimation models such as OK often produce good estimates but may encounter problems estimating recoverable reserves in cases where the distribution of samples is highly skewed. Multiple Indicator Kriging (MIK) is one of the popular non-linear methods that can handle skewed distribution such as that for gold grades, and addresses some of the deficiencies of the linear methods. This paper compares the estimation results obtained by using MIK and OK for the Asuadai deposit and establishes that MIK presents a better estimate than the OK, and recommends that MIK be used to estimate the gold resources of the Asuadai deposit and other deposits with similar geological settings. Keywords: Indicator Kriging, Ordinary Kriging, Variography, Gold, Outlier