The mysterious case of the missing half-ton of gold

Abstract

A milling circuit in the concentrator processing ore at one of the gold mines managed by Johannesburg Consolidated Investments had apparently been losing a substantial part of the gold input to it for several months. At the time of investigation, the gold unaccounted for totalled nearly half a ton, worth some $5 million. A specially adapted distributed lag model was fitted to measurements made of the input and output, and far from confirming the apparent loss of gold, indicated that the plant's output balanced its input. The apparent contradiction between the total input and output and the more detailed accounting of the distributed lag model (which included variable time lags explicitly) gave rise to a closer investigation of the circuit which led to an explanation of the apparent discrepancies, and the actual location of a large amount of gold.