Testing the Exactitude of Estimation Methods in the Presence of Outliers: An accounting for Robust Kriging

The estimation of gold reserves and resources has been of interest to mining engineers and geologists for ages. The existence of outlier values shows the potential worth of the deposits and is not a result of human or technical error. The presence of these high values causes a pseudo dramatic increase in the variance estimation of the economic value when applying conventional methods such as kriging. Conventional approaches such as replacing the upper limit (capping), log-normal and median-indicator kriging have resolved some of the problems associated with estimation techniques but do, however, still pose numerous drawbacks. The Zarshuran Gold Deposit is one of the proposed gold deposits in Iran that offers a great opportunity for the use of estimation procedures. Robust kriging is a method that is able to reduce the allocated pseudo kriging weights of the blocks surrounded with high value data, and correct them in a manner that not only enhances the accuracy of the estimation but also reduces the estimation variance to a reasonable level. In this method, the estimation can be implemented in the presence of outliers and does not need to eliminate, reduce or transfer the data to another space (normalization). In this paper an attempt was made to estimate the amount of gold in ore using the robust kriging method compared with the capping high value method. Results showed that the robust kriging method has a high efficiency and is able to run estimations accurately and with high precision due to the high value reduction.